BE894964A - PHOTOGRAPHIC PRODUCTS COMPRISING SENSITIZED EMULSIONS CONSISTING OF TABULAR GRAINS - Google Patents

Description

       

  Photographic products comprising sensitized emulsions

  
and made up of tabular grains.

  
The present invention relates to photographic products with at least one silver halide emulsion layer, comprising tabular silver halide grains and a dispersing medium.

  
at. Speed, granularity and awareness

  
Silver halide photography uses radiation-sensitive emulsions, which include a dispersing medium, usually gelatin, into which microcrystals (referred to as grains) of silver halides are incorporated. sensitive to radiation. During the photographic exposure, latent image centers are formed by absorption of only a small number of quanta of radiation which make a whole grain selectively developable. It is this property that precisely gives silver halide photography its exceptional speed, compared to many other imaging means.

  
Continuous research continued for more than a century has improved the sensitivity of emulsions to silver halides. Various types of chemical sensitization have thus been developed, for example by means of noble metals such as gold, by means of chalcogens such as sulfur and / or selenium and by reduction sensitization. These sensitizations, used alone or in combination, make it possible to improve the sensitivity of the emulsions to silver halides. When the chemical sensitization is pushed beyond an optimal level, relatively small gains in speed are obtained, which are further accompanied by a sharp drop in image discrimination (maximum density minus minimum density). This decrease results from an increase in the haze (minimum density).

   Optimal chemical sensitization therefore consists in finding the best compromise between speed, image discrimination and minimum density, for a determined photographic application.

  
In general, when "the silver halide emulsions are chemically sensitized, the sensitivity extension that is obtained beyond the spectral region of natural sensitivity is quite negligible. To sensitize the silver halide emulsions over the entire visible spectrum and even beyond, spectral sensitizers are used which are methine dyes. The sensitivity of the emulsion is extended from the region of natural sensitivity as a function of the concentration of spectral sensitizer dye and this up to to reach an optimum beyond which in general this sensitivity then decreases rapidly (conf. Mees, Theory of the Photographic Process, Macmillan, 1942, pp. 1067-1069).

  
In the range of dimensions of the silver halide grains of common photographic products, the maximum speed that can be achieved for optimal sensitization increases linearly with increasing grain size. We can consider that the number of quanta that a grain must absorb to become developable is independent of its size. However, the density that a given number of grains forms during development is directly related to the size of these grains. If the objective is to produce a maximum density of 2 for example, less is needed

  
  <EMI ID = 1.1>

  
you. In total, less radiation was necessary to make a smaller number of grains developable.

  
Unfortunately, the density produced is concentrated on a smaller number of sites and the point variations in density are greater. The one who examines the image draws a perception which is called the grain

  
of the image. The objective measurement of these same variations constitutes granularity. Although the quantitative granularity measurements could have been made in different ways, the most common measurement is that known as RMS (root mean square) granularity which can be defined as the deviation-

  
  <EMI ID = 2.1>

  
Once the maximum acceptable granularity has been determined for a given emulsion, the maximum speed that can be obtained with this emulsion is also determined.

  
From the above, it is understood that the problem is not generally to achieve maximum speed in the absolute sense, but rather to reach maximum speed with optimal awareness, while obtaining the granularity required for the case practice considered. The real improvements, as regards the sensitivity of the emulsions, are those which make it possible to improve the speed without sacrificing the granularity, or to decrease the granularity without sacrificing the speed, or which make it possible to improve both the speed and the granularity.

   The usual vocabulary of technology has summarized this definition of the improvement of the sensitivity in the expression: improvement of the relation speed / granularity of an emulsion Figure 1 schematically represents a graph of the variation of speed as a function of granularity for five silver halide emulsions 1, 2, 3, 4 and 5 of the same composition which each differ in grain size, while also being sensitized, coated and treated identically. The emulsions have respectively a maximum speed and a different granularity, but there exists between these emulsions a predictable linear relationship, as the line shows

  
A representing the variation of the speed as a function of

  
granularity. All emulsions whose representative points can be aligned on line A have the same speed / granularity relationship. Emulsions including

  
the sensitivity is really improved, have a representative point located above the line A. For example,

  
emulsions 6 and 7 whose representative point is located on the speed / granularity curve B have a better speed / granularity relationship than that of any of emulsions 1 to 5. Emulsion 6 has a speed greater than that of l emulsion 1, but its granularity

  
is not stronger. The speed of emulsion 6 is identical to that of emulsion 2, but with a granularity

  
very inferior. The emulsion 7 has a speed greater than that of the emulsion 2, but its granularity is less than that of the emulsion 3 which, itself, has a speed less than that of the emulsion 7. The emulsion

  
8, the representative point of which is located below line A has the worst speed / granularity relationship in FIG. 1. The emulsion 8 indeed has

  
the highest photographic speed of all the emulsions represented, but this speed can only be achieved at the cost of a disproportionate increase

  
granularity.

  
Given the importance of the speed / granularity relationship in photography, significant efforts have been made to be able to determine this relationship in all cases quantitatively. Compare with

  
  <EMI ID = 3.1> which differ in only one characteristic, for example the size of the silver halide grains, is normally an easy problem. We have often compared the

  
  <EMI ID = 4.1>

  
5 the characteristic curves are similar. However,

  
quantitative comparisons of relationships between speed and scale of photographic products have not generally been carried out since such comparisons have a subjective character which becomes more pronounced

  
  <EMI ID = 5.1>

  
different. In addition, quick relationship comparisons

  
granularity

  
deity /,. between photographic products forming silver images, for example, products for black and white photography, and products which form

  
  <EMI ID = 6.1>

  
sensitivity. Indeed, the substances responsible for the formation of density and therefore responsible for the granularity, are of very different origin and nature. Regarding the granularity measures in the

  
analogue and color image formation systems, see: "Understanding Graininess and

  
  <EMI ID = 7.1>

  
available from the Eastman Kodak Company, Rochester New York 14650; Zwick, "Quantitative Studies of Factors Affecting Granularity", Photographic Science and Engineering, Vol. 9, N [deg.] 3, May-June 1965; Ericson and Marchant, "RMS Granularity of Monodisperse Photographic Emulsions", Photographic Science and Engineering, Vol. 16, N [deg.] 4, July-August 1972, pp. 253-257; and Trabka "A Random-Sphere Model Dye Clouds", Photography Science and Engineering

  
Flight. 21, N [deg.] 4, July-August 1977, pp. 183-192.

  
Silver halide emulsions comprising halides other than silver bromoiodides are of limited use for photographic products which must exhibit sensitivity for shooting. U.S. Patent 3,320,069 describes a silver bromoiodide emulsion with an iodide content between 1 and
10% by mole and which has a very exceptional speed / granularity relationship for the formation of silver images (i.e. black and white images). Unless otherwise indicated, all the halide percentages are given in relation to the silver present in the emulsion, the grain or the part of grain considered. For example, a grain of silver bromoiodide containing 40% by mole of iodide comprises 60% by mole of bromide. The emulsion is sensitized to sulfur, selenium or tellurium.

   The emulsion is applied in a layer on a support at a rate of 33 to

  
110 mg of silver per square decimeter, then it is exposed in an intensity scale sensitometer and treated with

  
  <EMI ID = 8.1>

  
p-aminophenol and hydroquinone sulfate) for 5 minutes. Under these conditions, the emulsion provides a logarithm of rapidity from 280 to 400.0 on the other hand, the index calculated by subtracting the value of the granularity from the logarithm of rapidity, is between 180 and 220. Preferably, the or in combination with the sensitizer belonging to the sulfur group and the silver halides are precipitated in the presence of thiocyanate. However, if desired, this thiocyanate can be added to the silver halide at any time before washing. The use of thiocyanate during precipitation and sensitization of silver halides is described in US Patents 2,221,805, 2,222,264 'and 2,642,361. Emulsions in the United States Patent

  
  <EMI ID = 9.1>

  
dity / granu / exceptional for color photography, although granularity values for dye images are not available.

  
In a small number of cases, it was investigated which were the highest photographic speeds that could be achieved at higher levels of granularity than those usually used. In "The

  
Speed

  
Relationship Between / and Grain Size ", The Journal of Photography Science, vol. 17, 1969, pp. 116-125, Farnell reports on work concerning speed in blue

  
  <EMI ID = 10.1>

  
diameter of 0.8 (m), Farnell observes that the speed no longer increases when the grain size increases, as one would normally expect if one retains the hypothesis that the number of quanta absorbed necessary to obtain a developable grain is independent of the size of this grain; in fact, a decrease in speed as the grain size increases is indicated. Farnell attributes the decrease in sensitivity of large grains to the fact that their diameter is large compared to the average diffusion distance of electrons formed by photochemical means, and necessary to produce the latent image sites, which is limited. More light quanta must be absorbed by a large grain than by a small one in order to form a latent image site.

  
Another author, Tani, in "Factors Influencing Photography Sensitivity", Journal Soc. Photogr. Sci. Technol. Japan, vol. 43, N [deg.] 6, 1980 pp. 335-346, formula

  
the same conclusions as Farnell and continue the discussion concerning the reduction in sensitivity of large silver halide grains by relating it to other causes linked to the presence of dyes used for spectral sensitization. According to Tani, the sensitivity of a spectrally sensitized emulsion also depends (1) on the relative quantum yield of spectral sensitization,

  
(2) desensitization due to dyes and (3) absorption of light caused by dyes. Tani observes that the parameter (1) is very close to unity and is therefore not likely in practice to be further improved. Tani also indicates that the absorption of light by grains covered by dye molecules is proportional to the volume of the grain when the grain is exposed to blue light and proportional to

  
the grain surface when the grain is exposed to light from the blue minus. Thus, the importance of the increase in sensitivity in the blue minus is generally lower than the increase in sensitivity in the blue when the grain size of the emulsion increases. If one tries to increase the absorption of light simply by increasing the quantity of dye covering the grain, this does not necessarily lead to an increase in sensitivity because of the desensitization caused by the dye as and when the quantity of the latter increases. The desensitization is attributed more to a less good formation of the latent image than to a decrease in the formation of the electrons generated by photochemical way. Tani suggests that one possibility, to improve the relationship

  
  <EMI ID = 11.1>

  
size, would be to prepare heart and shell emulsions in order to avoid desensitization. (The internal doping of silver halide grains in order to allow the use of quantities of dyes which would otherwise cause a desensitizing effect, is described in US Patent 3,979,213).

  
b. Sharpness

  
Granularity, because of its relationship to speed, is often a point on which the discussion regarding image quality focuses; however, the issue of image clarity can be considered independently. Some factors that influence image clarity, such as lateral scattering caused by image forming products during processing, are related to image forming products and processing more than the silver halide grains themselves. However, since they scatter light, the silver halide grains also have a direct influence on the sharpness at the time of the photographic exposure. We know for example, that with silver halide grains whose diameter is between 0.2 and 0.6 m m, the diffusion of visible light is maximum.

  
The decrease in sharpness of an image caused by light scattering generally increases as the thickness of the silver halide emulsion layer increases. The explanation of this phenomenon illustrated by the diagram in fig. 2, is as follows. If a light photon 1 is deflected at a point 2 by a grain of silver halide at an angle 0 measured with respect to the direction of its original path and if this photon is then absorbed by a second grain of halide money, at point 3,

  
  <EMI ID = 12.1>

  
the photon recording of the photon undergoes a lateral displacement 2x. So we understand that bigger

  
  <EMI ID = 13.1>

  
of silver in a photographic product, the greater the risk of a reduction in image clarity by scattering of light. Of course, Figure 2 is a block diagram showing the phenomenon in a very simple case; in practice, a photon undergoing the reflection of several grains successively before being actually absorbed, it is necessary to use statistical methods to predict what may be its final point of absorption.

  
In the case of products for color photography, containing at least three layers of superimposed silver halide emulsion, the risk of loss of image clarity is increased since the silver halide grains are distributed over the minus three layer thicknesses. In certain cases, the displacement resulting from this thickness is further increased by the presence of additional elements, i.e., substances which contribute to increasing the thickness of the emulsion layers themselves, for example when dye image-forming substances are incorporated into the emulsion layers, that is, additional layers interposed between the silver halide emulsion layers, which also contribute to increasing the deviation due to the thickness;

   such additional layers are, for example, the separate layers adjacent to the emulsion layers containing the substances for consuming the oxidized developer or the dye image-forming substances. In addition, in color photography products, there are at least three superimposed elements each containing at least one layer of silver halide emulsion. This characteristic constitutes an important cause of loss of image clarity by scattering of light. Since the diffusion phenomena caused by the different layers of superimposed emulsions being added to each other, the emulsion layers furthest from the exposure source can exhibit particularly significant decreases in sharpness.

  
U.S. Patent 3,402,046 describes a means for obtaining clear, crisp images in the green-sensitive emulsion layer of a product for color photography. In such a product, the green-sensitive emulsion layer is placed under the blue-sensitive emulsion layer and this respective arrangement of the two layers is responsible for a loss of sharpness in the green-sensitive layer. According to US Patent 3,402,046, it is proposed to reduce the scattering of light by using, in the upper emulsion layer sensitive to blue, grains of halides

  
  <EMI ID = 14.1>

  
for the grain diameter resulting in maximum diffusion.

  
vs. Separation of velocities in blue and minus

  
blue

  
The natural sensitivity of the silver bromide and silver bromoiodide emulsions in the blue part of the

  
spectrum is sufficient to allow these emulsions to record blue light without the aid of spectral sensitization in blue. When these emulsions are used to record exposures to green and / or red light (blue minus), they are spectrally sensitized

  
Consequently. Regarding black photography

  
and white and monochromatic (chromogenic) photography,

  
orthochromatic or panchromatic awareness which

  
the result is advantageous.

  
With regard to color photography, advantage is taken advantage of the natural sensitivity of silver bromide and silver bromoiodide for emulsions

  
used to record blue light. However, when these silver halides are used in the emulsion layers intended to record the light of the green and red parts of the spectrum, the natural sensitivity in blue becomes a drawback. Indeed, in these emulsion layers, the

  
  <EMI ID = 15.1>

  
or with blue light and red light, will alter the hue of the color image that we are trying to reproduce.

  
In the design of products for color photography using silver bromide or silver bromoiodide emulsions, the question of color alteration can be analyzed in two different ways. The first way is to consider the difference between the speed in the blue of the emulsion layers recording

  
the green or the red and the respective rapidities in the green or the red of these same emulsion layers. The second way to approach the problem is to consider the difference between the speed in blue of each emulsion layer recording blue and the speed in blue of the corresponding emulsion layers recording green or red. In general, to obtain a product intended for color photography, capable of recording exactly color images by exposure to daylight (i.e. at 55000K), it is necessary to provide a difference of approximately 1.0 log E between the speed in blue of each emulsion layer recording blue and the speed in blue of the corresponding emulsion layers recording green or red.

   It is known that such speed differences cannot be achieved with silver bromide or silver bromoiodide emulsions, unless they are used in combination with one or more known means for reducing the color alteration. . And even in this case, we are not always able to obtain a product in which the velocities are separated by a difference of one

  
  <EMI ID = 16.1>

  
speed could be obtained, a further increase in the separation between the speeds in blue and the blue minus will correlatively obtain a decrease in the recording of blue by the layers to record the blue minus.

  
By far the most common way to reduce the effects of exposure to blue emulsion layers

  
silver bromide and silver bromoiodide spectrally sensitized for red and green, i.e.

  
in fact to decrease their speed in the blue, consists

  
to have emulsion layers behind a yellow wire layer, that is to say a blue absorbing layer.

  
Yellow filter dyes or yellow colloidal silver are generally used interchangeably for this purpose. In a typical multi-layer product for color photography, all of the emulsion layers are made of bromide or silver bromoiodide. The emulsion layers intended to record the green and the red, are placed behind a yellow filter, while the layer

  
  <EMI ID = 17.1>

  
very blue light are arranged in front of the filter layer.

  
Such an arrangement has a number of drawbacks which are well known. pi the exposure to blue light of the emulsion layers recording green and red is reduced to a tolerable level, the use of the yellow filter imposes an order in the arrangement of the layers which is not ideal. The emulsion layers recording green and red receive light which has already passed through both the blue sensitive emulsion layer and the yellow filter. This light has undergone a certain diffusion and, consequently, the sharpness of the image is affected.

   Since the emulsion layer recording blue provides by far the recording which contributes the least to the visual impression, the fact that this layer is arranged so as to be closest to the source of exposure does not constitute for image clarity a factor as favorable as that which could be obtained by placing in the same place the emulsion layers sensitive to red or green. In addition, the yellow filter is itself imperfect and in fact absorbs a small part of the green light in the spectrum, which results in a loss of speed in the green. The substance used to constitute the yellow filter, in particular if this substance is yellow colloidal silver, increases the cost of the products and makes it necessary to replace treatment solutions more frequently, in particular the solutions

  
bleaching and bleaching-fixing.

  
Separating in a photographic product the emulsion layer (s) sensitive to blue and the emulsion layers sensitive to red or green by inserting a yellow filter, has the additional disadvantage of causing a reduction in the speed of the layer d emulsion sensitive to blue. This is due to the fact that the yellow filter layer absorbs the blue light which passes through the blue-sensitive emulsion layer (s), while in the absence of the yellow filter layer, this blue light would be reflected

  
and would enhance exposure. One way to increase the speed is to move the yellow filter layer so that it is not placed immediately under the blue-sensitive emulsion layer. Such a means is described in English patent 1,560,963; However, this patent recognizes that the improvement of the speed in the blue is effectively obtained, but at the cost of an imbalance in the reproduction of the colors in the emulsion layers sensitized to the green and to the red which are arranged on the filter layer. yellow.

  
Various ways have been suggested to eliminate the use of yellow filters; each proposed solution has its own drawbacks. US Patent 2,344,084 proposes to have a layer of silver chloride or silver chlorobromide spectrally sensitized for green or red in the position closest to the source of exposure, being given that the natural sensitivity of these silver halides in blue

  
is negligible. Since the natural sensitivity of silver bromide in blue is high, it is not used in the emulsion layer closest to the source of exposure, but forms an underlying emulsion layer intended to record the blue light.

  
According to the patents of the United States of America 2 388 859 and 2 456 954, it is proposed to eliminate the contamination due to blue light in the emulsion layers recording

  
green and red by giving these layers a sensitivity 50 times and 10 times lower respectively than that of the emulsion layer recording blue. On these emulsion layers, there is the yellow filter layer, so as to adjust the sensitivities of the emulsion layers recording blue, green and red for the blue, green and red lights respectively and to increase the separation of the velocities in the blue and the blue minus of the emulsion layers recording the blue minus.

  
This means allows the emulsion layers to be applied in any order, but its disadvantage is that it requires the presence of a yellow filter; it also has other drawbacks. In order to obtain, without the use of a yellow filter, differences in sensitivity between the layers recording the blue and the blue minus, according to the teachings of the patents of the United States of America 2 388 859 and 2 456 954, grains are used. silver bromide or larger silver bromide in the blue recording emulsion layer.

   But if we try to obtain the desired differences in sensitivity, only by playing on the differences in grain size, we are led to use emulsion layers sensitive to blue with excessive grain and / or layers of emulsion recording the blue minus whose grain size is too small and which are

  
therefore relatively slow. To remedy this difficulty, it is known that the proportion of iodide in the grains of the layer registering blue can be increased; this way you can increase the sensitivity in blue without increasing the grain size. But then again, if the goal is to get layers

  
an emulsion recording the blue minus, which have / photographic speed exceeding a very average level, obtaining a layer of emulsion recording the blue, whose speed would be at least ten times greater, is not pos- sible while maintaining an acceptable grain level, even

  
increasing the percentage of iodide in the emulsion layer recording the blue.

  
Yellow filters, although they are used to decrease the proportion of blue light reaching the underlying emulsion layers, do not in any way eliminate the transmission of blue light. Thus, even in the case where yellow filters are used, one can hope for further improvements by better separation of the sensitivities in the blue and the blue minus of the bromide emulsion and silver bromoiodide layers intended to record. the blue minus of the spectrum.

  
As indicated in US Patent 2,344,084, silver chloride and chlorobromide can be used in layers recording the blue minus of a product for color photography without requiring protection a yellow filter; however, it should be understood that these emulsions also absorb blue radiation, even if this absorption is less than that of other emulsions. In certain applications, this absorption of the blue part of the spectrum (often designated by the term "absorption tail") by emulsions containing silver chloride can constitute a drawback, even if it does not exceed a low level. For example, if for a shooting, it is desired to use with adequate speed, a photographic product comprising an emulsion layer

  
with silver chloride, by exposing to radiation not belonging to the blue part of the spectrum, that is to say a green, red or infrared radiation and if then the photographic product is treated in the presence of blue light, the emulsion layers may have a natural sensitivity in the blue sufficient for this treatment to

  
a

  
light causes in the background / increased density or haze. The blue sensitivity of a chloride-containing emulsion represents a small part of the sensitivity to radiation used during exposure; but the duration of the exposure to light during the treatment is considerably longer and as a result, a decrease in the sensitivity in blue of the silver chloride and chlorobromide emulsions compared to their sensitivity in another region of the spectrum. can also be beneficial.

  
d. Tabular silver halide grains Different grain patterns, regular and irregular, have been observed in photographic silver halide emulsions. Regular grains are often cubic or octahedral in shape. The grain edges can be rounded due to ripening effects and, in the presence of strong ripening agents such as ammonia., The grains can even be spherical or have the form of thick, almost spherical tablets, as is described for example in the patent of the United States of America

  
3,894,871 and by Zelikman and Levi in "Making and Coating Photography Emulsions", Focal Press, 1964, pp. 221-223. Stick-shaped or tabular-shaped grains have frequently been observed in varying proportions associated with grains of other shapes, especially when pAg
(ie the negative logarithm of the silver ion concentration) of the emulsions was modified during precipitation, as is the case, for example, in single-jet precipitation processes.

  
Tabular silver bromide grains have been the subject of numerous studies, but the grains thus studied were often large grains without photographic utility. What, in the present description, is understood to be a tabular grain is a grain delimited by two parallel or practically parallel crystalline faces which each have a significantly larger surface than any other face of the crystal constituting the grain. The shape index, i.e. the ratio of the diameter to the thickness of a tabular grain, is therefore clearly greater than 1: 1.

  
Tabular-grain silver bromide emulsions of high shape index have been described by De Cugnac and Chateau in "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science and Photographic Industries Vol. 33, N [deg.] 2 (1962), pp. 121-125.

  
From 1937 until around the 1950s, the Eastman Kodak Company sold a film for radiography called "Duplitized" and whose reference was "No Screen X-ray

  
Code 5133 ". This product included on each side of a film support a sulfur-sensitized silver bromide emulsion. Since the emulsions were intended for direct exposure to X-rays, they were not spectrally sensitized. were tabular and had an average shape index of 5 to 7: 1 and these tabular grains represented more than 50% of the projected surface, while the non-tabular grains represented more than 25% of the projected surface. several times, we find that in the emulsion where the shape index is the most

  
  <EMI ID = 18.1>

  
7: 1. Other reproductions of these emulsions have provided

  
thicker, smaller-diameter beans that have a lower average shape index.

  
None of the tabular grain emulsions of silver bromoiodide described in the prior art actually have a high average shape index. The question of tabular grains of silver bromoiodide is discussed

  
by Duffin, Photographie Emulsion Chemistry, Focal Press, 1966, pp. 66-72 and by Trivelli and Smith, in "The Effect of Silver Iodide Upon The Structure of Bromo-Iodide Precipitation Series", in The Photography Journal, Vol. LXXX,

  
July 1940, pp. 285-288. According to Trivelli and Smith, a marked decrease in grain size and shape index is observed as iodide is introduced.

  
Gutoff, in "Nucleation and Growth Rates During the Precipitation of Silver Halide Photography Emulsions", Photography Sciences and Engineering Vol. 14, N [deg.] 4, JulyAugust 1970, pp. 248-257, describes the preparation of bromide and silver bromoiodide emulsions by a single jet process using a continuous precipitation apparatus.

  
Methods for preparing emulsions consisting mainly of silver halides in the form of tabular grains have recently been described in publications. U.S. Patent 4,063,951 describes the formation of limited tabular silver halide crystals

  
  <EMI ID = 19.1>

  
U.S. Patent 4,067,739 describes the preparation of silver halide emulsions consisting of

  
  <EMI ID = 20.1>

  
: Crystals are formed by first preparing seeds for the crystalline sowing which is then grown by Ostwald naturation in the presence of a silver halide solvent and the growth of the grains is completed without renucléa: ion or Ostwald maturation by controlling the pBr (legislative logarithm of the bromide ion concentration). United States patents 4,150,994, 4,184,877 and 4,184,878, as well as English patent 1,570,581 and German patent application publications 2,905,655 and 2,921,077 relate to grain formation. octahedral twinned silver halides of octahedral form from seed seed crystals with an iodide content of at least <EMI ID = 21.1>

  
, 'increase in covering power and it is indicated that the emulsions obtained are useful for black and white and color street shooting films. According to United States patent 4,063,951, the upper limit of the shape index of these tabular grains is 7: 1;

  
but, according to the very low shape indices obtained in the examples (2: 1), this upper limit of 7: 1 appears to be overestimated. It is clear, as shown in the reproduction

  
examples and review of published photomicrographs.

  
that the grain shape indices obtained according to the above references are also less than 7: 1. The

  
Japanese patent application 142,329, published on November 6, 1980, apparently incorporates the same elements as those of the patent

  
from the United States of America 4,150,994, although not limited to the use of crystal seed seeds of silver iodide.

  
The subject of the present invention is a photographic product with at least one layer of silver halide emulsion comprising tabular silver halide grains and a dispersion medium. These photographic products make it possible to obtain an improved sharpness with at the same time

  
time a better separation of the velocities between the

  
regions of the spectrum where the silver halide grains

  
have a natural sensitivity and the regions of the spectrum in which these grains have been spectrally sensitized. A remarkable increase in speed is also obtained when these grains are sensitized in the region of the spectrum.

  
where they have their natural sensitivity. According to a mode

  
of preferred embodiment, these products also have a better speed / granularity relationship.

  
The photographic products according to the invention are characterized in that the tabular grains of silver halides which they contain are chemically sensitized

  
and spectrally and have a thickness of less than 0.5 µm,

  
  <EMI ID = 22.1>

  
greater than 8: 1 and represent at least 50% of the total projected area of the silver halide grains.

  
The shape index is the ratio of the grain diameter

  
0 on the grain thickness and the grain diameter is the diameter of the circle whose surface is equal to the projected surface of the grain.

  
The present invention provides significant advantages over the prior art. Sharpness of photographic images can be improved

  
by means of the photographic products of the present invention, in particular if grains of large average diameter are used. When they are sensitized spectrally outside the part of the spectrum where they have their natural sensitivity, the emulsions used according to the present invention exhibit a clear separation between the sensitivity in the blue region of the spectrum where they have their natural sensitivity and the sensitivity in the spectral awareness region.

   The silver bromide and silver bromoiodide sensitized emulsions for blue minus used according to the present invention are much less sensitive to blue light than to blue minus light and do not require any filter protection to obtain recordings. blue minus when exposed with neutral light, for example with daylight to

  
  <EMI ID = 23.1>

  
and in particular the silver bromide and silver bromide emulsions have an improved speed / granularity relationship, compared with that of known tabular grain emulsions and by comparison with the best speed / granularity relationships obtained so far. general with silver halide emulsions of the same composition. With the silver bromide and silver bromoiodide emulsions of the present invention, very large increases in speed can still be achieved.

  
blue by comparison with the natural sensitivity in blue, provided that spectral sensitizers are used for blue.

  
The emulsions according to the present invention are also useful for producing radiographic products carrying a layer on each face of a support transparent to radiation, and in which the exposure of each layer is controlled through the support. If one compares radiographic products comprising emulsions according to the invention with similar radiographic products but produced with conventional emulsions, it is found that this parasitic exposure through the support can be reduced thanks to the use of emulsions according to invention and with lower silver titles.

  
Photographic products according to the invention in the form of elements for image transfer photography make it possible to obtain better photographic speed as a function of a given silver grade (the silver grade is the quantity of halide of silver per unit area of layer), faster access to the visible transferred image and better contrast of the transferred image for a shorter development time.

  
Figures 1, 5 and 6 are graphs showing variations in speed as a function of granularity.

  
Figures 2 and 4 are diagrams relating to light scattering phenomena and, Figure 3 is a photomicrograph of an emulsion consisting of tabular grains having a high shape index.

  
at. Tabular emulsions and preparation of these emulsions According to the present invention, the term "high shape index" has the following meaning: it applies to silver halide grains the thickness of which is less than 0.5%. 65533; m (less than 0.3 dans m in certain preferred embodiments) and whose diameter is at least

  
  <EMI ID = 24.1>

  
at 8: 1 and they represent at least 50% of the total projected area of the silver halide grains.

  
The preferred silver halide tabular grains according to the present invention are those whose thickness is

  
  <EMI ID = 25.1>

  
medium is greater than 12: 1 and preferably 20: 1. Preferably, the silver halide grains which have the characteristics of diameter and thickness indicated above represent at least 70% and preferably at least
90% of the total projected surface of the silver halide grains.

  
The thinner the tabular grains representing a given percentage of the projected surface, the higher the average shape index of the emulsion. In general, the thickness

  
  <EMI ID = 26.1>

  
in photographic films by image transfer, it may be desirable to use thicker tabular grains

  
  <EMI ID = 27.1>

  
use average grain thicknesses up to 0.5 à m when recording blue light. However, to obtain high shape indices without excessively increasing the grain diameter, it is considered that normally the average thickness of the tabular grains according to

  
  <EMI ID = 28.1>

  
Slowly demonstrated by methods well known in the art. As indicated, the expression "index ie shape" designates the ratio of the diameter of the grain to the thickness of this grain. The term "diameter" itself is defined: as the diameter of a circle having an area equal to the projected area of the grain as it appears on a photomicrograph or on an electron micrograph of the sample d 'emulsion. From the shadows cast by an electron microscopy image of an emulsion, it is possible to determine the thickness and diameter of each grain and to identify those of the tabular grains whose

  
  <EMI ID = 29.1>

  
data, the shape index of each of these tabular grains can be calculated and the shape indices of all the tabular grains of the sample whose thickness is less

  
  <EMI ID = 30.1>

  
which is the average shape index. According to this definition, the average shape index is the average of the shape indices of each grain. In practice, it is generally easier to obtain an average thickness and an average diameter of the tabular grains having a thickness of less

  
  <EMI ID = 31.1>

  
the ratio of these two means. Whatever the evaluation method chosen, and taking into account the tolerances of the particle size measurements, the values obtained for the average shape index do not differ significantly.

  
One can add up the projected surfaces of the tabular grains of silver halides which satisfy the conditions of thickness and diameter then separately, one can add up the surfaces of the other grains of silver halides of the photomicrography; from these two respective sums, one can obtain the percentage of the total projected surface occupied by the tabular grains of silver halides whose thickness and diameter satisfy the conditions expressed above.

  
For the above assessments, a reference tabular grain was chosen; this grain has a thickness of less

  
  <EMI ID = 32.1>

  
thin tabular grains of thicker tabular grains with inferior photographic characteristics

  
  <EMI ID = 33.1>

  
reference given that for smaller diameters, it is not always possible to distinguish the grains which are tabular from those which are not.

  
The term "projected area" is used in the same sense as the terms "projective area" or "projection area", commonly used in the art (see for example James & Higgins, Fundamentals of Photography Theory, Morgan & Morgan New-York , p. 15) FIG. 3 represents a typical photomicrography of an emulsion according to the present invention which has been chosen to illustrate the various grains which may be present. The grain 101 constitutes an example of a tabular grain whose thickness and diameter meet the conditions expressed above. It is clear that the vast majority of the grains present on the photograph in FIG. 1 are tabular grains whose thickness and diameter meet these conditions. The average shape index of these grains is
18: 1.

   But, in this photomicrography, we also note the presence of a small number of grains whose thickness and diameter do not meet the above conditions. Grain 103, for example, is an example of grain that <EMI ID = 34.1>

  
Grain 105 is an example of a fine grain that does not meet the requirements for the diameter. The grain 107 is a thick tabular grain which fulfills the condition concerning the diameter, but does not fulfill the condition concerning the thickness. Depending on the conditions of the emulsion preparation, which will be examined in more detail below, secondary populations of non-tabular grains, fine grains or thick tabular grains may be present alongside the grains having the desired characteristics. It is also possible that other non-tabular grains, for example in the form of sticks, are

  
  <EMI ID = 35.1> also present. We generally seek to obtain a maximum of tabular grains satisfying the relative conditions

  
thickness and diameter; however, the presence of these secondary grain populations does not leave an emulsion outside the scope of the present invention from the moment when this emulsion has a high shape index as defined above.

  
A preferred embodiment of the present invention, which achieves many of the benefits observed, is the use of high form index silver bromoiodide emulsions. Such emulsions are not mentioned in the prior art. They can be prepared as follows. A dispersion medium is introduced into a reactor which is conventional for the precipitation of silver halides, equipped with an appropriate stirring device. In general, the dispersion medium thus initially introduced into the reactor represents at least about 10% and preferably from 20 to 80% of the total mass

  
dispersion medium which will be present in the silver bromoiodide emulsion at the end of the precipitation. The dispersion medium can be removed from the reactor by ultrafiltra-

  
  <EMI ID = 36.1>

  
according to the indications of the Belgian patent 886,645 and the French patent 2,471,620; however, the volume of dispersion medium present at the start in the reactor can be equal to or even slightly greater than the volume of the silver bromoiodide emulsion which will be in the reactor at the end of the precipitation of the grains. Preferably, the dispersion medium introduced at the start consists of water or of a dispersion of peptizer in water possibly containing-

  
ripening agents and / or

  
  <EMI ID = 37.1>

  
metal, described in more detail below. When a peptizing agent is present at the start, its concentration represents at least 10% and preferably at least 20% of the total peptizing agent present at the end of the precipitation of silver bromoiodide. An additional quantity of the dispersion medium is added to the reactor with the silver salt and the halides and optionally by means of a separate jet. Usually, the proportion of dispersing medium is adjusted, in particular in order to increase the proportion of peptizing agent, once the addition of the salts is complete.

  
A small part, generally less than 10% by mass of the bromide used to form grains of silver bromoiodide, is present at the start in the reactor to adjust the concentration of bromide ions at the beginning of the precipitation of silver bromoiodide. In addition, at the start of precipitation, the dispersion medium contained in

  
the reactor should in principle not contain iodide ions; in fact, the presence of iodide ions before the introduction of silver salt and bromide promotes the formation of thick grains which are not tabular. When in

  
the present description, it is indicated that the reactor does not in principle contain iodide ions, this means, with regard to the ingredients present in the reactor, that if the iodide ions are present in the reactor, their concentration relative to the bromide ions is insufficient to cause precipitation of a distinct phase of silver iodide. This is why, in practice, it is preferred to maintain the iodide concentration in the reactor below 0.5 mol% relative to the total amount of halides present in the reactor before the introduction of the silver salt. If the pBr of the dispersion medium is initially too high, the tabular grains of silver bromoiodide produced will be comparatively thick and therefore have a low shape index. So we watch

  
maintaining the initial pBr of the reactor at a value equal to or less than 1.6 and preferably less than 1.5. On the other hand, if the pBr is too low, this promotes the formation of silver bromoiodide grains which are not tabular; this is why it is necessary to maintain the pBr equal to or greater than 0.6 and preferably greater than 1.1. Recall that pBr is the negative logarithm of the concen-

  
  <EMI ID = 38.1>

  
are respectively defined in the same way for the concentrations of hydrogen, chloride, iodide and silver ions.

  
During precipitation the silver salts, bromide and iodide are added to the reactor according to well known techniques. In general, a solution of a soluble silver salt, for example a solution of silver nitrate, is introduced into the reactor, together with solutions of bromide and iodide. Bromide and iodide are also introduced in the form of an aqueous solution of one or more ammonium or alkali metal salts, for example sodium or potassium, or alkaline earth metal salts, for example magnesium or calcium. The silver salt, at least initially, is introduced into the reactor by a separate jet from that of the iodide. The iodide and bromide can be added to the reactor separately or as a mixture.

  
When a silver salt is introduced into the reactor, the nucleation phase of the grain formation process is started. We form a population of germs capable of constituting precipitation sites for arom bromide.

  
  <EMI ID = 39.1>

  
silver salt, bromide and iodide salt continues to be added.

  
  <EMI ID = 40.1>

  
existing germs constitutes the growth phase of grain formation. The shape index of the tabular grains formed according to the present invention is less influenced by the concentration of iodide and bromide during the growth phase than during the nucleation phase. This is why during the growth phase, it is possible to increase the latitude for fixing the pBr so as to have, during the introduction of the salts un.pBr of between approximately 0.6 and 2.2 and preferably between 0 , 8 and 1.6. This latter interval is particularly preferred when the rate of germ formation continues appreciably during the introduction of the salts, as is the case in the preparation of emulsions with high polydispersity. If the pBr rises

  
above 2.2 during the growth of the tabular grains, this leads to the formation of thicker grains, but there is in many cases a tolerance which makes it possible to still obtain shape indices greater than 8: 1.

  
A variant for the introduction of silver salts,

  
to introduce bromide and iodide

  
at the start or in the growth phase, in the form of fine grains of silver halides suspended in a dispersion medium. The diameter of the grains is such that their maturation of Ostwald on larger seeds is possible as soon as they are introduced into the reactor, if such seeds are present. The maximum useful grain diameter depends on the specific conditions prevailing in the reactor, for example the temperature and the presence of a solubilizing or maturing agent. It is thus possible to introduce grains of silver bromide, of silver iodide and / or of silver bromide; since bromide and / or iodide preferentially precipitates over chloride, it is also possible to use grains of silver chlorobromide and silver chlorobromoiodide; these silver halide grains are preferably very small, that is to say

  
  <EMI ID = 41.1>

  
Subject to the conditions relating to pBr set out above, the concentration and the flow rate of the jets of bromide silver salts and of iodide can be produced in suitable conventional forms. The silver salts and the halides are preferably introduced at a concentration of between 0.1 and 5 moles per liter, although wider intervals can be envisaged ranging from 0.01 mole per liter to saturation. The preferred precipitation techniques are those which allow the shortest precipitation times to be obtained by increasing the quantities of silver salts and halide introduced during precipitation. This increase can be obtained

  
by increasing either the flow rate or the concentration of the salt jets. We prefer to increase the flow rate of the jets, but

  
by keeping it below a threshold from which the formation of new germs would be favored, that is to say from which there would be a renenucleation according to the indications given to the patents of the United States of America 3,672,900, 3,650,757, 4,242,445, as well as the publication of the German patent application 2,107,118, the European patent application 80102242 and by Wey in Photographie Science

  
  <EMI ID = 42.1>

  
In the growth stage, relatively monodispersed populations of tabular grains of silver halide can be obtained. Emulsions with coefficients of variation of less than about 30% can be prepared. Remember that the coefficient of variation is the standard deviation of the grain diameter multiplied by one hundred and divided by the average grain diameter. If deliberately promoting renucleation during the growth phase, it is of course possible to form polydispersed emulsions whose coefficient of variation is significantly higher.

  
The concentration of iodide in the silver bromoiodide emulsions according to the present invention can be controlled by acting on the introduction of iodide. Any conventional iodide concentration can be used. Even very low concentrations, for example as low as 0.5 mole percent, may be known to be advantageous. Preferably, the emulsions according to the invention contain approximately at least 0.1 mol% of iodide. Iodide

  
  <EMI ID = 43.1> limit of solubility of silver iodide in silver bromide at the grain formation temperature. Thus, for precipitation temperatures of 90 [deg.] C, the concentration of silver iodide can reach 40 mol% in the tabular grains of silver bromoiodide. In practice, the precipitation temperature can be lowered almost to room temperature, i.e. up to 30 [deg.] C, but in general, it is preferred to carry out precipitation at

  
  <EMI ID = 44.1>

  
in photographic applications, the maximum iodide concentration is limited to about 20% and preferably does not exceed about 15%.

  
The respective amounts of iodide and bromide introduced into the reactor during precipitation can be maintained in a fixed ratio, so as to obtain tabular grains of silver bromoiodide whose iodide concentration has a uniform profile, but it is possible to do vary this profile to obtain various photographic effects. Special advantages can be obtained by increasing the proportion of iodide in an annular or peripheral region of the silver bromoiodide grains with a high shape index; this means that in these regions of the tabular grain, the iodide concentration is higher than it is in the center of the grain.

   The iodide concentration in the center of the grain can be between 0 and 5 mol% and, at least in a peripheral annular region, the iodide concentration can go up to the solubility limit of silver iodide in silver bromide; preferably the iodide concentration can reach up to
20% by mole, and optimally up to approximately 15% by mole. In this annular region.

  
A variant consists in stopping the addition of iodide from the addition of bromide and iodide before stopping the addition of silver salt, so that the excess of halides reacts with the salt of silver. As a result, a shell of silver bromide is formed on the tabular grains of silver bromoiodide. It is therefore clear that the tabular grains of silver bromoiodide according to the invention can have uniform or variable iodide concentration profiles and that this variation can be controlled if desired to favor a higher iodide concentration either at

  
  <EMI ID = 45.1>

  
silver bromoiodide laires. or on this surface.

  
The preparation of silver tabular grain bromoiodide emulsions of high shape index has been described with reference to a process providing emulsions which are neutral or non-ammoniacal; but the present invention is not limited to this particular process. Another method is an improvement on that described in US patent 4,150,994, as well as in the publications of German applications 2,985,655 and 2,921,077. In a preferred form, the concentration of silver iodide is lowered in the reactor below 0.05 mole per liter and the maximum diameter of the silver iodide grains initially

  
  <EMI ID = 46.1>

  
Tabular-grain silver bromide emulsions of high form index without iodide can be prepared by the method described in detail above modified

  
do not use iodide.

  
High bromide tabular grain silver bromide emulsions can also be prepared according to a method based on the indications given by De Cugnac and Chateau in the publication cited above.

  
High shape index silver bromide emulsions consisting of square and rectangular grains can be prepared by a method of using cubic shaped seed grains with an indentation

  
  <EMI ID = 47.1>

  
seed grains between 5.0 and 8.0, the emulsion is matured in the absence of a complexing agent of the silver ion other than the halides, so as to form tabular grains of bromide silver with an average shape index of at least 8: 1. The examples below provide other methods of preparing bromide emulsions.

  
silver with tabular grains of high form index without iodide.

  
Some of the advantages of the present invention, notably the sharpness and the advantages relating to radiographic applications and image transfer processes, are independent of the halide composition of tabular grain emulsions with a high shape index.

  
The variety of emulsions which can be used according to the invention can be illustrated by the fact that tabular grains of silver chloride can be prepared, the interior of which contains practically neither silver iodide nor silver bromide. To this end, a process is implemented

  
double-jet precipitation method according to which chloride and a silver salt are introduced at the same time into a reactor containing a dispersion medium in the presence of ammonia. During the introduction of the chloride, the pAg in the dispersion medium is maintained between 6.5 and 10 and the pH between 8 and

  
10. At high temperatures, the presence of ammonia tends to cause the formation of thick grains. This is why the

  
  <EMI ID = 48.1>

  
silver chloride emulsions with tabular grains of high shape index.

  
It is also possible to prepare tabular grains containing at least 50 mol% of chloride and, of which two opposite crystalline faces are in crystalline planes.

  
  <EMI ID = 49.1>

  
preferred embodiment being parallel to a crystallographic vector <211> in the plane of one of the main faces. Such tabular grain emulsions can be prepared by reacting aqueous solutions of silver salt and halides containing chloride in the presence of an amount of an aminoazaindene in an amount suitable for modifying the crystalline form and a peptizing agent containing a thioether bridge.

  
It is also possible to prepare tabular grain emulsions in which the grains contain chloride and bromide at least in one annular region of the grain and preferably throughout the grain. The regions of the tabular grains containing silver, chloride and bromide are formed by maintaining the molar ratio of chloride to bromide between 1.6: 1 and 260: 1 and maintaining the total concentration of halide ions in the reactor between 0.10 and 0.90 N during the introduction of the silver salt, chloride and bromide and optionally iodide, into the reactor. The molar ratio of silver bromide to silver chloride in the tabular grains is between 1:99 and 2.3.

  
The tabular grain emulsions according to the present invention can have very high shape indices. These shape indices can be increased by increasing the grain diameter. One can thus obtain advantages as regards sharpness, but the maximum diameter of the grains is generally limited by considerations of granularity for a given photographic application. Shape indices can be increased by decreasing the average grain thickness. When the silver title is kept constant, the reduction in the thickness of the tabular grains generally leads to an improvement in the granularity in direct proportion to the increase in the shape index. As a result, the maximum average shape index of the tabular grain emulsions according to the invention depends on the maximum average diameter acceptable for the photo-

  
of

  
  <EMI ID = 50.1>

  
can get. The maximum shape indices that we have observed are variable depending on the precipitation techniques used. The highest form indices that

  
observed are 500: 1 for the tabular grains which still have grain diameters useful from a photographic point of view; these grains were obtained by Ostwald ripening of silver bromoiodide grains; indices of 100: 1, 200: 1 or more have been obtained with techniques

  
double jet precipitation. The presence of iodide generally leads to a reduction in the maximum average shape indices that can be obtained, but it is also possible to prepare emulsions with tabular grains of silver bromoiodide whose shape indices reach 100: 1, and even
200: 1 or more. Tabular silver chloride grains may be prepared, possibly containing bromide and / or iodide, the shape indices of which reach

  
50: 1 or even 100: 1.

  
Modifiers may be present during precipitation of the tabular grains, either initially in the reactor, or added along with one or more of the salts, according to conventional methods. These modifiers can be compounds of copper, thallium, lead, bismuth, cadmium, zinc, medium chalcogen (i.e. sulfur, selenium and

  
tellurium), gold and noble metals of group VIII, according to the indications given to the patents of the United States of America 1 195 432, 1 951 933, 2 448 060, 2 628 167,

  
2,950,972, 3,488,709, 3,737,313, 3,772,031, 4,269,927 and in the journal Research Disclosure, volume 134, June 1975 publication 13452. The journal Research Disclosure and the title that preceded it, Product Licensing Index , are published by Industrial Opportunities Limited; Homewell, Havant; Hampshire, P09; 1EF; United Kingdom. Tabular grain emulsions can be sensitized by reduction inside the grains during precipitation, as described by Moisar et al; Journal of Photographie Science, Volume 25, 1977 pages 19 to 27.

  
The silver salts and the halides can be added to the reactor by means of surface or sub-surface supply tubes, by gravity feed or by means of devices which allow the rate of addition to be regulated. as well as the pH, pBr and / or pAg of the contents of the reactor, according to the indications given to the patents of the United States of America 3 821 002 and 3 031 304 and by Claes in Photographische Korrespondenz, volume 102, n [deg .], 10, 1967, page 162. To obtain a rapid distribution of the reactants in the reactor, it is possible to use specially adapted mixing devices such as those described in the patents of the United States of America 2 996 287, 3 342 605, 3,415,650,

  
3,785,777, 4,147,551 and 4,171,224, to British patent application 2,022,431A, to German patent applications

  
2,555,364 and 2,556,885 and in Research Disclosure, volume
166, February 1978, publication 16662.

  
To precipitate tabular grain emulsions,

  
a dispersing medium is initially present in the reactor. Advantageously, the dispersing medium is formed of an aqueous suspension of peptizer. The concentration of peptizer can be between 0.2 and about 10% by mass relative to the total mass of the constituents of the emulsion in the reactor. It is common to keep the peptizer concentration in the reactor below around 6%

  
of the total mass, before and during the formation of the silver halide, and later to adjust the vehicle concentration of the emulsion to higher values (the term vehicle including the binder and the peptizer), by additional vehicle additions to achieve optimal sleeping characteristics. The emulsion initially formed can contain approximately from 5 to 50 g of peptizer per mole of silver halide, preferably approximately from 10 to

  
30 g per mole of silver halide. An additional vehicle can be added later to bring the concentration up to 1000 g / mole of silver halide. Advantageously, in the finished emulsion, there are more than 50 g of vehicle per mole of silver halide. Once coated and dried in a photographic product, the vehicle forms approximately
30 to 70% by mass of the emulsion layer.

  
Vehicles can be chosen from the substances usually used in silver halide emulsions for this purpose. The preferred peptizers are hydrophilic colloids which can be used alone or in combination with hydrophobic substances. Suitable hydrophilic vehicles include substances such as proteins, protein derivatives, derivatives

  
cellulose, for example cellulose esters, gelatin, for example gelatin treated with an alkaline agent (skin or bone gelatin) or gelatin treated with an acid agent (pigskin gelatin), derivatives gelatin, for example acetylated gelatin and phthalylated gelatin. These and other vehicles are described in Research Disclosure vol. December 176, 1978, publication 17643, section IX.

  
Vehicles in particular hydrophilic colloids, as well as useful hydrophobic substances combined with them can be used not only in the emulsion layers of the photographic product elements of the invention, but also in other layers, such as overlays , interlayers and layers placed below the emulsion layers.

  
The preparation of the silver halide emulsions according to the invention can comprise a step of maturation of the grains and the preferred way consists in carrying out the naturation of the grains in the reactor during at least the formation of the silver halide grains. Solvents of known silver halides are used to promote naturation, such as for example an excess of bromide ion in the reactor. It is known for example that the solution of

  
  <EMI ID = 51.1> maturation. Other ripening agents can also be used, which can be fully incorporated into the

  
dispersing medium in the reactor before the addition of silver salt and halide, or which can be introduced into the reactor at the same time as one or more of the silver salts, halides or peptizer. According to another mode

  
In one embodiment, the curing agent can be introduced independently during the addition of the halide and the silver salt. Although ammonia is a known ripening agent, it is not a preferred ripening medium.

  
for the emulsions according to the invention whose speed / granularity relationship is the highest. Preferably, the emulsions according to the invention are not ammoniacal, or are neutral.

  
Advantageous ripening agents are those which contain sulfur. Thiocyanates can be used in the form of alkali metal salts, usually sodium and

  
potassium, and ammonium thiocyanates. Conventional amounts of thiocyanate can be used, but the preferred concentrations are generally between about

  
0.1 and 20 g of thiocyanate per mole of silver halide. The use of thiocyanate as a ripening agent is described in US Patents 2,222,264,

  
2,448,534 and 3,320,069. Thioethers such as those described in US Patents 3,271,157, 3,574,628 and 3,737,313 can also be used conventionally.

  
The tabular grain emulsions with a high shape index are preferably washed to remove the soluble salts, by known techniques such as decantation, filtration and / or by jelling and filtration, like this

  
is described in Research Disclosure, Vol. 176, December 1978; publication 17643, section II. It is particularly advantageous according to the present invention to complete the maturation of the tabular grains by washing after the end of precipitation, to avoid increasing their thickness, reducing their shape index and / or excessive increase in their diameter. Emulsions with or without a sensitizer can be dried and stored before use.

  
Once the tabular grain emulsions of high shape index have been formed, they can be surrounded by a shell to obtain a core and shell emulsion, by methods well known in the photographic art.

  
Any photographically useful silver salt may be used for the formation of a shell on the tabular grain emulsions of high shape index prepared by the present process. Techniques for forming silver salt hulls are described in US Patents 3,367,778, 3,206,313, 3,317,322 and 4,150,994. Conventional hull formation techniques do not promote the formation of tabular grains with a high shape index, the average shape index of the emulsion decreases with

  
as the hull grows. If the conditions in the reactor are favorable for the formation of tabular grains during the precipitation of the hull, the growth of the hull occurs preferentially

  
on the outer edges of the grains so that the shape index does not decrease. Tabular grain emulsions with a high shape index and having a core and a shell are particularly useful for forming internal latent images, and can be used to obtain products with a negative or positive-direct effect.

  
The methods of preparing tabular grains described above make it possible to obtain emulsions in which the tabular grains meeting the criteria of thickness and diameter necessary to obtain a high shape index, represent at least 50% of the total surface projected of the total silver halide grain population; but additional benefits can be obtained by increasing the proportion of tabular grains. It is advantageous that at least 70% (and optimally, at least
90%) of the total projected area is represented by

  
tabular silver halide grains meeting the thickness and diameter criteria. Although the presence

  
small amounts of non-tabular grains is fully compatible with most photographic applications, the proportion of tabular grains can be increased to obtain the full benefits of tabular grains. Larger, tabular silver halide grains can be mechanically separated from smaller, non-tabular grains in a mixed grain population using conventional separation means, such as a centrifuge or hydrocyclone. Separation by hydrocyclone is illustrated in US Patent 3,326,641.

  
b. Sensitization

  
The tabular-grain silver halide emulsions of high form index, according to the present invention, are chemically sensitized. They can be chemically sensitized with active gelatin, as indicated by T.H. James, The Theory of the Photographic Process 4th Ed., Macmillan, 1977, pp. 67-76; chemical sensitization can also be carried out with sensitizers

  
sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhodium, rhenium,

  
or with phosphorus or with combinations of these different sensitizers and a pAg of, for example, between 5 and 10 and a pH of between 5 and 8, and at a temperature of

  
  <EMI ID = 52.1>

  
Research Disclosure, Vol. 120 - April 1974 - $ 12008, Research Disclosure, Vol. 134 - June 1975 - $ 13452,

  
to patents of the United States of America 1,623,499, 1,673,522, 2,399,083, 2,642,361, 3,297,447, 3,297,446; English Patent 1,315,755; to United States of America patents

  
3,772,031, 3,761,267, 3,857,711, 3,565,633, 3,901,714 and 3,904,415 and English patent 1,396,696; chemical sensitization is optionally carried out in the presence of thiocyanates, as described in patent of the United States of America 2,642,361, in the presence of compounds containing sulfur such as those described in the patents of United States of America 2 521,926, 3,021,215 and 4,054,457. Emulsions can be chemically sensitized in the presence of chemical sensitization modifiers, i.e. compounds known for their ability to suppress haze and

  
to increase the speed under these conditions; such compounds are for example aza.indènes, azapyridazines, azapyrimides, benzothiazolium salts and sensitizers having one or more heterocyclic rings. Examples of modifiers are given in U.S. Patents 2,131,038, 3,411,914, 3,554,757,

  
3,565,631, 3,901,714 as well as Canadian patent 778,723 and by Duffin in Photographie Emulsion Chemistry, Focal Press
(1966), New York, pp. 138-143. In addition to the various chemical sensitizations defined above, or as an alternative to these sensitizations, the emulsions can also be sensitized by reduction, for example with hydrogen, as described in the United States patents. 'America 3 891 446 and 3 984 249, or by subjecting them to conditions bringing together a low pAg, for example less than 5 etr / pu a high pH, for example greater than

  
8 or by means of various reducing agents such as stannous chloride, thiourea dioxide, polyamines

  
and borane amines, as described in the patents

  
from the United States of America 2,983,609, 2,518,698, 2,739,060,

  
2,743,182, 2,743,183, 3,026,203, 3,361,564, as well as in Research Disclosure, Vol. August 136, 1975, $ 13654. Surface chemical sensitization or chemical sensitization can be carried out in an area immediately below the surface, as described in U.S. Patents 3,917,485 and 3,966,476.

  
In addition to chemical sensitization, the high form index tabular grain emulsions of the present invention are also spectrally sensitized. With the tabular grain emulsions of high shape index according to the invention and with other emulsions also mentioned in the present description, provision is made to use spectral sensitizing dyes which exhibit maximum absorption in blue and minus blue, that is to say in the red and in the green of the visible spectrum. In addition, for certain specific uses, spectral sensitizing dyes can be used which improve the spectral response in the region of the spectrum situated beyond the visible part. One can for example use spectral sensitizers absorbing in the infrared region.

  
Silver halide emulsions can be spectrally sensitized with dyes belonging

  
to various classes, including cyanines, merocyanines, cyanines and complex merocyanines (tri-, tetra-,

  
or polynuclear), oxonols, hemioxonols, styryl, merostyryl dyes and streptocyanines.

  
Spectral sensitizing dyes of the cyanine type comprise two heterocyclic rings of basic character linked by a methine bond; these heterocyclic nuclei are derived for example from quinolinium nuclei,

  
  <EMI ID = 53.1>

  
oxazolium, cxazolinium, thiazolinium, thiazolium, selenazolium, selenazolinium, imidazolium, imidazolinium, benzoxazolium, benzothiazolium, benzosélénazolium, benzimidazolium, naphtoxazolium, naphtothiazolium, naphtoselenazoliumazaphiniumaziazide

  
The spectral sensitizing dyes of the merocyanine type comprise, linked by a methine bond, a nucleus of basic character of the type found in the formula of cyanines and an acid nucleus derived for example from barbituric acid, acid 2 -thiobarbiturate, rhodanine, hydantoline, 2-thiohydantolne, 4-thiohydantolne, 2-pyrazoline-5-one, 2-isoxazoline-5-one, indan-1,3-dione, cyclohexane -1,3-dione, 1,3-dioxane4,6-dione, pyrazolin-3,5-dione, pentane-2,4-dione, alkylsulfonyl acetonitrile, malononitrile, isoquinolin-4- one and chroman-2,4-dione.

  
One or more spectral sensitizing dyes can be used. Dyes are known with sensitization maxima for wavelengths distributed over the entire extent of the visible spectrum and providing spectral sensitivity curves of very different shapes. The choice and relative proportions of dyes depends on the region of the spectrum to which the grains are to be sensitized and

  
of the shape of the spectral sensitivity curve that we want to obtain. Dyes with partially overlapping spectral sensitivity curves often provide, when used in combination, a curve such that the sensitivity at each wavelength in the overlap region is approximately the sum of the sensitivities of each dyes. Thus, it is possible to use combinations of dyes having different maxima, in order to obtain a spectral sensitivity curve having a maximum situated between the sensitization maxima of each of the dyes.

  
Certain combinations of spectral sensitizing dyes produce an oversensitizing effect, that is to say provide in a region of the spectrum, a spectral sensitization greater than that resulting from the use of one of the dyes alone at any concentration,

  
or resulting from the addition of the effects of dyes. Oversensitization can be achieved with selected combinations of spectral sensitizing dyes and other additives such as stabilizers, anti-stars, development accelerators or inhibitors, coating aids, optical brightening agents and

  
anti-static drugs. Mechanisms to explain

  
oversensitization and compounds to achieve it, are described by Gilman in "Review of the Mechanisms of Supersensitization", 'Photography Science

  
and Engineering, Vol. 18, 1974, pp. 418-430.

  
Spectral sensitizing dyes can also exert other actions on emulsions. These dyes can also play the role of anti-veil, stabilizers, development accelerators or inhibitors, halogen acceptors or electron acceptors, as described in the United States patents. America 2,131,038 and 3,930,860.

  
For the spectral sensitization of grains of non-tabular silver halides or of weak shape index, the conventional amounts of dyes can be used. To take full advantage of the advantages offered by the present invention, it is preferable to adsorb an optimal quantity of sensitizing dyes on the surface of the tabular grains of high shape index. By optimum quantity is meant the quantity sufficient to reach at least 60% of the maximum photographic speed which it is possible to achieve with these grains under the conditions provided for the exposure. The amount of dye to be used depends on the nature of the dye or the combination of dyes chosen, or on the size and shape index of the grains. It is known in the photographic technique that one can obtain an optimal spectral sensitization with

  
organic dyes when these dyes are used in an amount which makes it possible to produce a monolayer on approximately 25% or more of the total available surface of the silver halide grain with surface sensitivity, as described for example by West in "The Adsorption of Sensitizing Dyes in Photographic <EMI ID = 54.1>

  
by Spence et al. in "Desensitization of Sensitizing Dyes", Journal of Physical and Colloid Chemistry, vol. 56 n [deg.] 6,

  
June 1948, pp. 1090-1103; and by Gilman et al. in U.S. Patent 3,979,213. Optimal amounts and concentrations of dyes can be determined by the methods indicated by Mees, in Theory of

  
the Photography Process pp. 1067-1069, already cited.

  
In order to record the exposure to blue light in the emulsion layers, it is generally sufficient to use the natural sensitivity in the blue of bromide or silver bromoiodide; but according to a specific aspect of the present invention, appreciable advantages can be obtained by using spectral sensitizers, even with sensitizers whose main absorption is located in the region of the spectrum where these emulsions have their natural sensitivity. For example, the present invention particularly relates to obtaining specific advantages linked to the use of spectral sensitizing dyes for

  
blue. Even when the emulsions of the present invention consist of grains having a high form index of bromide and silver bromoiodide, significant increases in speed can be achieved by using spectral blue dyes. When it is intended to exhibit the emulsions of the present invention in the region of their natural sensitivity, gains in sensitivity can be obtained by increasing the thickness of the tabular grains. For example, it is advantageous to increase the thickness of the grains in the case of photographic products for image transfer. According to a preferred embodiment of the invention, the emulsions consist of silver bromide and silver bromoiodide sensitized for blue, the

  
  <EMI ID = 55.1>

  
greater than 8: 1, preferably greater than 12: 1 and these grains represent at least 50% of the total projected surface of the silver halide grains present in the emulsion; this percentage is preferably equal to 70% and, according to an optimal embodiment, at least 90%.

  
To sensitize spectrally in blue the emulsions of silver bromide and bromoiodide with tabular grains of high shape index, it is possible to choose dyes from all known classes of spectral sensitizing dyes. The spectral sensitizers for blue, which are preferred, belong to the class of polymethine dyes such as cyanines, merocyanines, hemicyanins, hemioxonols, merostyryls. In general, it is possible to choose spectral sensitizers for blue, useful in these classes of dyes according to the absorption characteristics, that is to say according to

  
the tint. It was established however with the characteristics

  
structure of correlations which can serve as a guide for an advantageous selection of blue sensitizers. In principle, the shorter the methine chain, the shorter the wavelength of the maximum sensitization. The nuclei also have an influence on absorption. The addition of cycles attached to the nucleus tends to favor absorption towards the longer wavelengths. The substituents can also modify the absorption characteristics. In the formulas which are given below and

  
unless otherwise specified, the alkyl groups contain from 1 to 20 carbon atoms and preferably from 1 to 8 carbon atoms. The aryl groups contain from 6 to 15 carbon atoms and are preferably phenyl or naphthyl groups.

  
The spectral sensitizers for blue belonging to the class of cyanines are preferably monomethine cyanines; however, useful cyanines can be chosen from those represented by formula I below:

  

  <EMI ID = 56.1>


  
  <EMI ID = 57.1>

  
each feel the elements to complete a cyclic radical deriving from basic nitrogen heterocyclic compounds such

  
that oxazoline, oxazole, benzoxazole, naphthoxazoles,

  
  <EMI ID = 58.1>

  
and naphth / 1,2-d7oxazole), thiazoline, thiazole, benzothiazole, naphthothiazoles (e.g. naphtho-

  
  <EMI ID = 59.1>

  
nuclei can carry one or more substituents such as hydroxy, halo (for example, fluoro, chloro, bromo, and iodo), alkyl or substituted alkyl (for example, methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl, octadecyl, 2-hydroxyethyl, 3-sulfopropyl, carboxymethyl, 2-cyanoethyl and trifluoromethyl), aryl or substituted aryl
(for example, phenyl, 1-naphthyl, 2-naphthyl, 4-sulfophenyl, 3-carboxyphenyl and 4-biphenyl), aralkyl (for example, benzyl and phenethyl), alkoxy (for example, methoxy, ethoxy and isopropoxy), aryloxy (for example, phenoxy 'and 1-naphthoxy), alkylthio (for example, methylthio and ethylthio), arylthio
(for example, phenylthio, p-tolylthio, 2-naphthylthio), methylenedioxy, cyano, 2-thienyl, styryl, amino, substituted amino (for example, aniline, dimethylamino, diethylamino and morpholino),

   acyl such as carboxy (e.g. acetyl, benzoyl) and sulfo;

  
  <EMI ID = 60.1>

  
represent alkyl, aryl, alkenyl or aralkyl groups, with or without substituents (for example, carboxymethyl, 2-hydroxyethyl, 3-sulfopropyl, 3-sulfobutyl, 4-sulfobutyl, 4-sulfophenyl, 2-methoxyethyl, 2-sulfatoethyl, 3 -thiosulfatopropyl, 2-phosphonoethyl, chlorophenyl and bromophenyl);

  
  <EMI ID = 61.1>

  
R 4 and R 5 represent hydrogen or an aryl group of 1 to 4 carbon atoms;

  
  <EMI ID = 62.1>

  
are not equal to 1 at the same time;

  
is 0 or 1, but when m is 1, [pound] and [pound]

  
  <EMI ID = 63.1>

  
imidazoline, oxazoline, thiazoline or selenazoline;

  
A is an anionic group;

  
B is a cationic group and

  
  <EMI ID = 64.1>

  
together represent the atoms to complete an alkylene bridge.

  
Some examples of cyanine sensitizing dyes in blue are given in Table I.

  
  <EMI ID = 65.1>

  
1. 3,3'-diethylthiacyanine bromide

  

  <EMI ID = 66.1>


  
  <EMI ID = 67.1>

  

  <EMI ID = 68.1>


  
  <EMI ID = 69.1>

  
cyanine
  <EMI ID = 70.1>
 4. Triethylamine salt of anhydro hydroxide

  
  <EMI ID = 71.1>

  
thiacvanine.

  

  <EMI ID = 72.1>


  
  <EMI ID = 73.1>

  
carbocyanine.

  

  <EMI ID = 74.1>


  
  <EMI ID = 75.1>

  
zolocyanine.

  

  <EMI ID = 76.1>
 

  
  <EMI ID = 77.1>

  
benzothiazolinium.

  

  <EMI ID = 78.1>


  
8. Sodium salt of anhydro hydroxide-5.5'-

  
  <EMI ID = 79.1>

  

  <EMI ID = 80.1>


  
The preferred merocyanines useful as sensitizers

  
  <EMI ID = 81.1>

  
times useful merocyanines can be chosen from the dyes defined by formula 2.

  

  <EMI ID = 82.1>
 

  
or :

  
  <EMI ID = 83.1>

  
Formula 1 above;

  
R4 and R5 represent hydrogen, an alkyl group of 1 to 4 carbon atoms or an aryl group (for example, phenyl or naphthyl);

  
G <1> represents an alkyl or substituted alkyl group, an aryl or substituted aryl group, an aralkyl group, an alkoxy group, an aryloxy group, a hydroxy group, an amino or substituted amino group; for example, the groups indicated for formula 1;

  
G2 can represent any of the groups

  
  <EMI ID = 84.1>

  
acidic rings such as those derived from 2,4oxazolidione (for example, 3-ethyl-2,4-oxazolidindione), from 2,4-thiazolidindione (for example, 3-methyl-2,4thiazolidindione), 2-thio-2,4-oxazolidindione (for example 3-phenyl-2-thio-2,4-oxazolidindione), rhodanine, such as 3-ethylrhodanine, 3-phenylrhodanine, 3- ( 3-di-methylaminopropyl) rhodanine and 3-carboxymethylrhodanine, hydantoline (for example, 1,3-diethylhydan-

  
  <EMI ID = 85.1>

  
hydantoin), 2-pyrazolin-5-one, such as 3-methyl1-phenyl-2-pyrazolin-5-one, 3-methyl-1- (4-carboxybutyl) 2-pyrazolin-5-one, and 3-methyl-2- (4-sulfophenyl) -2-pyrazolin-5-one, 2-isoxa2olin-5-one (for example, 3-phenyl-2-isoxazolin-5-one), 3,5-pyrazolidindione
(e.g. 1,2-diethyl-3,5-pyrazolidindione and

  
  <EMI ID = 86.1> of 1,3-dioxane-4,6-dione, 1,3-cyclohexanedione, barbituric acid, (for example, 1-ethylbarbituric acid and acid 1, 3-diethylbarbituric) and 2-thiobarbituric acid (for example, 1,3-diethyl-2-thiobarbituric acid and 1,3-bis (2-methoxyethyl) -2-thiobarbituric acid);

  
r and n can each be equal to 0 or 1, but when n is equal to 1, in general either Z represents only imidazoline, oxazoline, selenazoline, thiazoline, imidazoline, oxazole or the benzoxazole, i.e. G <1> and G2 do not represent a cyclic system. Some examples of merocyanine dyes useful as blue spectral sensitizers are given in Table II.

TABLE II

  
1. 5- (3-ethyl-2-benzoxazolinylidene) -3-

  
phenylrhodanine ..

  

  <EMI ID = 87.1>


  
  <EMI ID = 88.1>

  

  <EMI ID = 89.1>


  
3. Potassium salt of 4- (3-ethyl-2-benzothiazol-

  
  <EMI ID = 90.1>

  
5-one.

  

  <EMI ID = 91.1>
 

  
4. 3-carboxymethyl-5- (5-chloro-3-ethyl-2-

  
benzothiazolinylidene) rhodanin

  

  <EMI ID = 92.1>


  
  <EMI ID = 93.1>

  

  <EMI ID = 94.1>


  
Hemicyanin dyes useful as blue sensitizers include those represented by Formula 3.

  

  <EMI ID = 95.1>
 

  
or

  
  <EMI ID = 96.1>

  
formula 2; G <3> and G 4 may be the same or different and may represent alkyl, substituted alkyl, aryl, substituted aryl or aralkyl as for the substituents of the rings in formula 1, or G <3> and G 4 together represent the atoms to complete a ring system derived from a cyclic secondary amine, such as pyrrolidine, 3-pyrroline, piperidine, piperazine (for example, 4-methyl-piperazine and 4-phenylpiperazine), morpholine,

  
  <EMI ID = 97.1>

  
represent the elements to complete a carbocyclic alkylene bridge;

  
n is 0 or 1; and

  
A and k have the same definition as in formula 1.

  
Some examples of hemicyanin dyes useful as blue sensitizers are given in Table III.

TABLE III

  
  <EMI ID = 98.1>

  

  <EMI ID = 99.1>


  
  <EMI ID = 100.1>

  

  <EMI ID = 101.1>


  
  <EMI ID = 102.1>

  

  <EMI ID = 103.1>
 

  
Useful hemioxonol dyes sensitizers in blue include those represented by Formula 4.

  

  <EMI ID = 104.1>


  
or :

  
G <1> and G <2> have the same meaning as in formula 2;

  
  <EMI ID = 105.1>

  
in formula 3, and

  
  <EMI ID = 106.1>

  
sants in blue are given in Table IV.

TABLE IV

  
  <EMI ID = 107.1>

  
diethyl-2-thiobarbituric.

  

  <EMI ID = 108.1>
 

  
  <EMI ID = 109.1>

  

  <EMI ID = 110.1>


  
  <EMI ID = 111.1>

  

  <EMI ID = 112.1>


  
Blue sensitizing merostyryl dyes include those represented by Formula 5.

  

  <EMI ID = 113.1>


  
or :

  
  <EMI ID = 114.1>

  
formula 4.

  
Some examples of sensitive merostyryl dyes

  
  <EMI ID = 115.1>

TABLE V

  
  <EMI ID = 116.1>

  
2-pentanone.

  

  <EMI ID = 117.1>


  
  <EMI ID = 118.1>

  

  <EMI ID = 119.1>


  
  <EMI ID = 120.1>

  

  <EMI ID = 121.1>
 

  
Spectral sensitization can be carried out at any stage of the preparation of the emulsion which has been recognized to be useful for this purpose. Usually, spectral sensitization is carried out after the end of chemical sensitization. However, spectral sensitization can be carried out, either at the same time as chemical sensitization, or entirely before chemical sensitization, and even

  
it can be started before the precipitation of the silver halide grains, according to the indications given to the patents of the United States of America 3 628 960 and 4 225 666. The patent of the United States of America 4 225 666 specifically provides for introducing the spectral sensitizing dye into the emulsion in stages, so that part of this dye is present before the chemical sensitization, while another part is introduced after

  
chemical awareness. Unlike what is shown in US Patent 4,225,666, it is possible according to the present invention to add the spectral sensitizer after 80% of the silver halide has been precipitated. Sensitization can be improved by adjusting the pAg, including through cyclic variations, during chemical sensitization and / or spectral sensitization. A specific example of pAg adjustment is given in Research Disclosure, volume 181, May 1979 publication 18155.

  
Silver bromoiodide emulsions with tabular grains of high shape index, chemically and spectrally sensitized, have a better speed / granularity relationship than those obtained so far

  
with conventional emulsions of the same composition in silver halide. It is well known that it is silver bromoiodide emulsions which provide the best speed / granularity relationships. This is why these emulsions are used for products intended for shooting. Silver bromoiodide emulsions with tabular grains of high in-dice shape, when they are optimally spectrally and chemically sensitized, moreover exhibit an improved speed / granularity relationship compared to the best speed / granularity relationships obtained up to 'now.

   More generally, when exposed in a region where they are spectrally sensitized, these emulsions exhibit improved speed / granularity relationships, compared with those of conventional emulsions with a similar halide composition. These improvements in the speed / granularity relationship are particularly remarkable for the silver bromide and bromoiodide emulsions according to the invention which are spectrally sensitized in green and / or red and exposed to radiation from this part of the spectrum. In the part of the spectrum corresponding to the natural sensitivity ((for example, in the blue part of the spectrum), it is also possible, by using spectral sensitizing dyes for blue, with the emulsions according to the invention, to improve the

  
  <EMI ID = 122.1>

  
obtained with conventional emulsions, that is to say with low shape index, tabular or not, and sensitized in the same way and consisting of grains whose individual volumes are comparable.

  
According to an advantageous embodiment, the spectral sensitizers are incorporated into the emulsions of the invention before chemical sensitization. Similar results have also been obtained in some cases by introducing other adsorbable substances, such as curing modifiers into the emulsions before chemical sensitization.

  
Independently of the prior incorporation of a.sorbable substances, it is advantageous to use thiocyanates during chemical sensitization at concentrations of between approximately 0.002 and 2 mol% relative to silver, as described in the patent of United States of America 2,642,361 previously cited. Other curing agents can be used during chemical sensitization.

  
A third means which can be used alone or in combination with only one or two of the means indicated above, consists in adjusting the silver concentration and / or

  
  <EMI ID = 123.1>

  
during chemical sensitization. Soluble silver salts can be introduced, such as silver acetate, silver trifluoroacetate and silver nitrate, as well

  
only salts which can precipitate on the surface of the grains, such as silver thiocyanate, silver phosphate,

  
silver carbonate, etc. Fine silver halide grains (i.e. bromide, iodide and / or silver chloride) can be introduced capable of undergoing

  
Ostwald maturation on the surfaces of the tabular grains For example, a Lippmann emulsion can be introduced during chemical sensitization. Chemical sensitization of spectrally sensitized high index tabular grain emulsion can be carried out at one or more sites distinct from the tabular grains. It is believed that the preferential adsorption of spectral sensitizing dyes on the crystallographic surfaces forming the main faces of the tabular grains allows chemical sensitization to occur selectively on surfaces of these grains, other than crystallographic.

  
Advantageous chemical sensitizations to obtain the best speed / granularity relationships are awareness of gold and sulfur, awareness

  
with gold and selenium, and awareness of gold, sulfur and selenium. In an advantageous embodiment of the invention, the tabular-grain silver bromide and bromoiodide emulsions with high shape index contain a chalcogen, such as sulfur and / or selenium, which may not be detectable , and gold that is detectable. Emulsions also usually contain detectable amounts of thiocyanate, although the concentration of thiocyanate in the final emulsion can be greatly reduced by known washing techniques.

   In the various embodiments indicated above, the surface of the tabular grains of silver bromide or bromoiodide can comprise another silver salt such as a silver thiocyanate, or another different silver halide ( e.g. silver chloride or silver bromide) although this other silver salt may be present in undetectable amounts.

  
Although it is not necessary to obtain all their advantages, the emulsions defined according to the invention are preferably sensitized chemically and spectrally in an optimal manner, in accordance with current manufacturing practices. This means that their speed represents at least 60% of the maximum of the logarithm of the speed that can be expected from the grains in the spectral region of sensitization and under the intended conditions of use and treatment. The logarithm of speed is defined as 100 (1-log E), where E is measured in lux. second at a density of 0.1 above the veil.

   Once the silver halide grains of a product have been characterized, it is possible to estimate, from other analyzes carried out on the product and from the evaluation of its performance, whether a layer d The emulsion of this product was sensitized chemically and spectrally in an optimal way, by comparison with other comparable commercial products. To obtain the advantages of clarity presented by the products according to the invention, it does not matter that the silver halide emulsions have been sensitized chemically or spectrally in an effective or ineffective manner.

  
vs. Formation of silver images.

  
Once tabular grain emulsions of high shape index have been produced by the precipitation processes, washed and sensitized as described above, the preparation can be completed by incorporating additives conventional photographic images, and they can be used in photographic applications requiring the production of a silver image, for example conventional black and white photography.

  
The photographic products according to the invention intended to form silver images can be tanned sufficiently to avoid having to use additional tanning agents during processing. This makes it possible to increase the covering power, in comparison with photographic products tanned and treated in a similar manner, but containing emulsions with non-tabular grains. In particular, it is possible to tan the tabular grain emulsion layers of high shape index and the other hydrophilic colloid layers of a black and white photographic product sufficiently to reduce the swelling of the layers to less than 200%. The percentage of swelling (a) is determined by incubating the photo-

  
  <EMI ID = 124.1>

  
50%, (b) by measuring the thickness of the layer, (c) by immersing the photographic product in distilled water

  
  <EMI ID = 125.1>

  
layer thickness. It is particularly preferable to tan the photographic products intended to form silver images since the addition of tanning agents in the processing solutions is not necessary, but the emulsions used according to the present invention can be subjected to tanning. of different strength commonly used. It is also specifically planned to incorporate the tanning agents in the processing solutions, as described for example in Research Disclosure vol. 184, August 1979,

  
  <EMI ID = 126.1>

  
processing of radiographic products.

  
Usually useful tanning agents, or pre-tanning agents, are described in Research Disclosure, Volume 176, December 1978, item 17643, Section X.

  
One can prevent the instability which increases the minimum density in the layers of emulsion of the negative type that is to say the haze, or which increases the minimum density or decreases the maximum density in the layers of positive emulsion- direct, incorporating stabilizing agents, anti-stars, agents inhibiting the effects of mechanical stresses, agents stabilizing the latent image and similar additives in the emulsion and the adjacent layers before coating, as described in Research Disclosure , volume 176, December 1978, item 17643, Section VI. Most anti-stars effective in emulsions can also be used in developers, and can be classified into a few general categories, as proposed by C.E.K.

   Mees, in The Theory of the Photography Process, 2nd edition, MacMillan, 1954, pages 677 to 680.

  
When tanning agents of the aldehyde type are used, it is possible to protect emulsion layers with conventional anti-stars.

  
In addition to sensitizers, tanning agents, anti-stars and stabilizers, various other conventional photographic additives can be added. The choice of additives depends on the exact nature of the photographic application and is within the reach of the technician. Various useful additives are described in Research Disclosure, volume 176, December 1978, publication 17643. Optical brightening agents can be introduced, as described in publication 17643 in paragraph V. They can be used in the emulsion layers or in the separate layers of the photographic products according to the invention, of the absorbent and diffusing substances, described in paragraph VIII.

  
Coating adjuvants described in paragraph XI, and plasticizers and lubricants described in paragraph XII can be added. Antistatic layers described in paragraph XIII can be added. Methods of introducing the additives are described in paragraph XIV. Matting agents described in paragraph XVI can be incorporated. It is possible, if desired, to incorporate developers and development modifiers described in paragraphs XX and XXI. When the photographic products according to the invention are to be used for radiography applications, the emulsion

  
and the other layers of the radiographic product can take any of the forms described in Research Disclosure publication 18431, cited above. Emulsion layers described here as well as the other conventional silver halide emulsion layers, interlayers, overlays and substratum. If the product according to the invention contains them, can be applied and dried as described. in Research Disclosure, Volume 176, December 1978, publication 17643, paragraph XV.

  
According to a common practice in the art, provision is made to mix the tabular grain emulsions with a high shape index of the present invention either with another such as those described above, or with a conventional emulsion, to obtain characteristics. specific. For example, it is known to mix emulsions to adjust the characteristic curve of a photographic product for a specific purpose. The mixture can be used to increase or decrease the maximum densities obtained by exposure and treatment, to decrease or increase the minimum density, and to adjust the shape of the characteristic curve between the foot and the shoulder.

   The emulsions used according to the invention can be mixed with conventional silver halide emulsions such as those described in Research Disclosure volume 176, December 1979, publication 17643, paragraph I, particularly in paragraph F of paragraph I.

  
When a relatively fine grain silver chloride emulsion is mixed with the emulsions of the present invention, or when this silver chloride emulsion is introduced into an adjacent layer, an additional increase in contrast and / or sensitivity, that is to say that the relationship between speed and granularity of the emulsion is improved, as described in US Patents 3,140,179 and 3,152,907.

  
In the simplest form, the photographic products according to the invention are formed from a single layer of emulsion containing an emulsion of silver halides with flat grains of high shape index and a photographic support. Of course, they can comprise more than one layer of silver halide emulsion as well as an overlay, a substratum and interlayers. Instead of mixing the emulsions as indicated above, one can

  
in general to obtain the same result by applying the emulsions to be mixed in the form of distinct layers. The application of separate layers to obtain the latitude of exposure is well known in the art and has been described by Zelikman and Levi, "Making and Coating Photographic Emulsions", Focal Press, 1964, pages 234-238 and the United States Patent. United States of America 3,662,228 and British patent

  
923 045. It is also well known that the photographic speed can be increased when rapid emulsions and slow emulsions are applied in separate layers,

  
instead of mixing them. Usually, the fast emulsion layer is applied closer to the source of exposure radiation than the slow emulsion layer. This means can be extended to at least three superimposed layers of emulsion. Such layer arrangements are provided in the production of the products according to the invention.

  
The layers of the photographic products can be applied on various supports. Typical photographic supports include polymer films, wood fiber, for example paper, metal plates and sheets, glass and ceramic supports, provided with a

  
or several substrates to improve the adhesive, antistatic, dimensional, abrasive, antihalo, hardness and friction characteristics, and / or the other surface properties of the support. These supports are well known in the art. See for example Research Disclosure volume 176, December 1978, publication 17643, Section XVII.

  
The emulsion layer or layers are generally applied in the form of continuous layers on supports having opposite planar main surfaces, but this is not always the case. The emulsion layers can be applied as segments of laterally spaced layers on the surface of a flat support. When the emulsion layer or layers are segmented, a microcell support is preferably used. Such supports are described in PCT patent application W080 / 01614 published on August 7, 1980 and in

  
corresponding Belgian patent 881 513 as well as the United States of America patent 4,307,165. The width of the microcells

  
  <EMI ID = 127.1>

  
ordinary black and white photography applications, especially when the photographic image needs to be enlarged.

  
The photographic products according to the invention can be exhibited photographically in any usual manner. See in particular Research Disclosure publication
17643, cited above, paragraph XVIII. The present invention is particularly advantageous when the photographic exposure is carried out with electromagnetic radiation belonging to the region of the spectrum in which the included spectral sensitizers have absorption maxima. When photographic products are intended to record blue, green, red or infrared exposures, spectral sensitizers absorbing in the blue, green, red or infrared parts of the spectrum are present.

   For the formation of black and white images, it is advantageous that the photographic products are sensitized orthochromatically or panchromatically, in order to extend the sensitivity throughout the visible spectrum. The radiant energy used for the exposure can be non-coherent or coherent, that is to say in phase, for example produced by lasers.

   Within the useful response limits determined by conventional sensitometric techniques, photographic exposures under conditions of ambient temperature and / or pressure, high or reduced, low or high intensity exposures, continuous or intermittent exposures can be used , exposure times ranging from about one minute to relatively short durations of the order of a millisecond or microsecond, solarization exposures, as described by TH James, The Theory of the Photographic Process, 4th edition, MacMillan, 1977, Chapters 4, 6, 17, 18 and 23.

  
After exposure, the photosensitive silver halide contained in photographic products can be treated in a conventional manner to form a visible image, by bringing this silver halide into contact with an aqueous alkaline medium in the presence of a contained developer. in the middle or

  
in the product.

  
Once the silver image has formed in the photographic product, it is common practice to fix the undeveloped silver halide. The high form index tabular grain emulsions of the invention are particularly advantageous in that they allow fixing to be carried out more quickly, which makes it possible to obtain more curved treatment times.

  
d. Dye imaging

  
The photographic products and techniques described above for producing silver images can be readily adapted to the production of color images, through the use of colorants. Probably the simplest way to obtain a projectable color image is to incorporate a conventional dye into the support of a photographic product, and to form a silver image as described above. In the areas where the silver image is formed, the product can no longer transmit light, and in the remaining areas, the light is transmitted with a color corresponding to the color of the support. One can easily form a colored image this way. The same results can also be obtained by using in conjunction with a product containing a transparent support, a layer or a separate product containing a color filter.

  
Dye images can be formed in silver halide photographic products by selective destruction or formation of dye. Developers containing dye image formers can be used such as the couplers described in Research Disclosure, volume 176, December 1978, publication 17643, section XIX, paragraph D. The developer contains a chromogenic developer (for example an aromatic primary amine ) which is capable in its oxidized form of reacting with the coupler to form the dye.

  
One can also, in a conventional manner, incorporate

  
dye-forming couplers in photographic products. They can be incorporated in various quantities to obtain different photographic results. For example, it is possible to limit the concentration of coupler relative to the silver content to values lower than those normally used in emulsion layers of intermediate sensitivity or of high sensitivity.

  
In general, colorless non-diffusible dye-forming couplers are chosen which are capable of forming primary subtractive colors, that is to say yellow, magenta and blue-green. Dye-forming couplers having different reaction rates in separate layers or in a single layer can be used to achieve the desired results in specific photographic applications.

  
Dye-forming couplers can liberate at the time of coupling photographic effect groups, such as inhibitors or development accelerators, bleaching accelerators, developers, silver halide solvents, tone modifiers, tanning agents, veiling agents, anti-stars, competing couplers, chemical or spectral sensitizers and desensitizers. Couplers releasing a development inhibitor (DIR) are well known in the art. Dye-forming couplers and non-dye-forming compounds are also known which, by coupling, release various photographic effect groups. It is also possible to use DIR compounds which do not form a dye by reaction with oxidized chromogenic developers.

   It is also possible to use DIR compounds which cut through oxidation. Relatively light-insensitive silver halide emulsions such as Lipmann emulsions,

  
as interlayers, and overlays, to prevent or control the migration of development inhibitor groups.

  
In photographic products, color chromogenic couplers such as those used can be incorporated.

  
to form full face masks for negative color images, and / or competing couplers. Photographic products may further contain conventional stabilizers for the dye image. All that has just been described is described in Research Disclosure, volume 176, December 1978, publication 17643, Section VII.

  
Dye images can be formed or enhanced by methods which involve combining with a color image-reducing reducing agent, an oxidizing agent under

  
  <EMI ID = 128.1>

  
a peroxide.

  
Color images can be produced in the photographic products according to the invention by selective destruction of dyes or dye precursors, for example by bleaching processes for silver dyes.

  
To form color images in silver halide photographic products, the developed silver is usually removed by bleaching. The bleaching can be improved by incorporating a bleaching accelerator or a bleaching accelerator precursor into the treatment solution or into a layer of the product. In some cases, the amount of silver formed by development is small compared to the amount of dye produced, particularly in processes including enhancement of the dye image, as described above, and bleaching can be suppressed money with no significant visual effect. In other applications, the silver image is kept and a dye image is produced to increase or supplement the density provided by the silver image.

   When it is desired to enhance the silver image with a dye, it is usually preferred to form a neutral dye or a combination of dyes which together produce a neutral image.

  
e. Partial grain development

  
It is known that certain photo-detectors have, for the detection of energy quanta, a higher efficiency than that of silver halide products. The study of the fundamental properties of silver halides shows

  
that this is due in large part to the binary nature of the functioning of the silver halide grains rather than to a low sensitivity to quanta. Comments on this can be found in "Multilevel Grains and the Ideal Photography Detector" by Shaw, Photography Sc. & Engineer. Flight. 16, N [deg.] 3, May / June 1972, pages 192-200.

  
The functioning of silver halide grains is called binary (or "all or nothing"), because,

  
once a latent image center is formed on a grain, this grain becomes fully developable. In general, the development is independent of the quantity of light received by the grain, above a threshold which corresponds to the quantity necessary for the formation of the latent image.

  
The silver halide grain produces exactly the same result, whether it has absorbed many photons and whether several latent image centers have been formed, or whether it has absorbed only the minimum number of photons and one only latent image center has been formed.

  
Upon exposure to light, latent image centers are formed in and on the high shape index grains according to the invention. Some grains may have only a latent image center, others have many and others have none.

  
However, the number of latent image centers formed is a function of the amount of light received at the time of exposure. The tabular grains have a large diameter and their speed / granularity relationship can be high, particularly in the case of silver bromoiodide sensitized chemically and spectrally optimally; under these conditions, the speed of these tabular grains can be relatively high. Since the number of latent image centers present in or on each grain is a direct function of the quantity of light received during the exposure, the conditions are met for high quantum detection efficiency.

  
According to a preferred mode, each latent image center is developed so as to increase its size without fully developing the silver halide grains. This can be achieved by interrupting the development of the silver halides, well before the usual limit for optimal development in an ordinary application. Another technique is to use a DIR coupler and a chromogenic developer. The inhibitor released during coupling

  
can be used to prevent the complete development of silver halides. The preferred way of implementing this technique is to use an auto-inhibitory developer.

  
Such a developer triggers the development of silver halides, but stops development by itself before the grains have been fully developed. Preferred developers are auto-inhibitor developers containing para-phenylene diamines, such as those described by Neuberger et al in "Anomalous Concentration Effect: An inverse Relationship Between the Rate of Development and

  
  <EMI ID = 129.1>

  
Photographic Science and Engineering, Vol. 19, N [deg.] 6, Nov.-Dec. 1975, pp. 327-332. By interrupting development or by developing in the presence of DIR couplers, it is possible to completely prevent the development of grains whose development induction period is longer than that of adjacent developable grains. However, the auto-inhibiting developer has the advantage that the development of a silver halide grain is prevented only after the development of that grain has started.

  
Strengthening the development of latent image centers leads to the formation of metallic silver centers. The size and number of these metal centers are proportional to the degree of exposure of each grain. Since the preferred auto-inhibitory developers contain chromogenic developers, the oxidized developer which forms can react with a dye-forming coupler to give a dye image. However, only a limited part of the silver halide is developed and the quantity of dye thus formed is therefore also limited.

   To remedy this limitation, without affecting the proportionality between the dye density and the degree of exposure, it is possible to use a redox reaction catalyzed by silver operating with a peroxide or a complex of a transition metal, and a chromogenic reducer, for example a chromogenic developer, as described in the patents of the United States of America 3,748,138, 3,826,652, 3,862,842.3 989,526,

  
3,765,891, 3,674,490, 3,822,129, 3,834,907.3 902,905,

  
3,847,905, 3,847,619, 3,904,413 and in Research Disclosure vol. 116, item 11160 and vol. 148, items 14836, 14846 and
14847. According to the indications provided in these publications, where the silver halide grains form surface latent image centers, the centers themselves can provide sufficient silver to catalyze a reaction

  
strengthening the dye image. Therefore, strengthening the latent image by development is not essential, although it is a preferred variant.

  
According to the preferred embodiment, all visible silver remaining in the photographic product after having formed the dye image therein is removed by bleaching, in the usual manner.

  
The photographic image obtained is a dye image whose point dye density is proportional to the amount of light received during the exposure. As a result, the quantum detection efficiency of the photographic product is high. High photographic speeds can easily be obtained, although the oxidation reactions described above can contribute to increasing the granularity.

  
The granularity can be reduced by using a microcellular support such as that described in PCT application WO 80/01614, already cited. The feeling of granularity is given not only by the size of the individual dye particles constituting the image, but also by the random nature of their arrangements. By applying the emulsion in the form of a network of microcells formed on the support, and by spreading the dye formed in each micro-cell so as to distribute it uniformly, the feeling of granularity is reduced.

  
Although the question of partial grain development has been raised with reference to image formation

  
of dyes, what has been indicated also applies to the formation of silver images. By developing to form a visible silver image, the granularity can be decreased by stopping development before the grains containing the latent image sites have been fully developed. Since more metallic silver centers can be produced by partial development of the grains than by complete development, the feeling of granularity for a given density is reduced.

  
Likewise, a decrease in granularity can also be obtained by forming dye images with incorporated couplers whose concentration is limited so as to be less than the usual value which is based on the stoichiometric reaction with the silver halides. Although the silver titers in the photographic product must initially be stronger to allow the partial development of the grains and the obtaining of maximum densities comparable to those resulting from a complete development, the silver halide which is not developed can be removed by fixing and recovered; silver consumption is therefore not increased.

  
With the technique of partial silver development and by using photographic products with microcellular support, it is possible to reduce the granularity of the silver image as described above for the dye images. For example, if a silver halide emulsion according to the invention is used to fill the network of microcells with a support and is then exposed and partially developed, metallic silver centers are produced,

  
in proportion to the quanta of radiation received during the exhibition and the latent image sites formed. The covering power of metallic silver centers is low in comparison with what one would obtain by complete development, but one can increase this covering power by fixing the silver halide which has not been developed, by rehalogenating the silver formed in the microcells and then carrying out the physical development of this silver on a uniform layer of germs of physical development contained in the micro-cells. Since silver obtained by physical development on fine germs can provide a much higher density than silver obtained by chemical development, a much higher maximum density is easily obtained.

   In addition, the silver formed by physical development provides a uniform density in each microcell. This makes it possible to reduce the granularity, since the random arrangement of the money is replaced by the regular arrangement of the network of micro-cells.

  
f. Sensitivity as a function of the region of the spectrum When the tabular grain emulsions according to the invention are sensitized optimally in accordance

  
to the indications given above in a determined region of the spectrum, and that the sensitivity of the emulsion in this region of the spectrum is compared with its sensitivity in

  
a region where the emulsion is supposed to have a natural sensitivity due to its halide composition, we

  
observed a greater difference in sensitivity than those generally observed with conventional emulsions. In

  
color photography, the poor separation of the sensitivities of bromide and silver bromoiodide in blue, green or red has long been a drawback.

  
The advantages resulting from the differences in spectral sensitivity presented by the silver bromide or silver bromoiodide emulsions according to the invention are illustrated in the case of products for color photography. The differences in increased spectral sensitivity presented by the emulsions according to the invention are not limited to the case of bromoiodide or silver bromide or to emulsions for color photography. These differences can also be observed in the case of products with a single emulsion layer. In addition, these benefits can be obtained in

  
the case of various applications made with emulsions having any halide composition recognized useful in photography. For example, silver chloride and chlorobromide are known to have a natural sensitivity in blue, weak enough to allow them to register green and red in products for color photography, without protection from light blue, but in other applications there is an advantage in increasing the difference in sensitivity between the different regions of the spectrum.

   In particular, if a silver chloride emulsion with tabular grains of high shape index is sensitized to infrared, and exposed in the region of spectral sensitivity, it can then be treated with light with less increase in the minimum density as a result of the low sensitivity of the emulsions according to the invention in the regions of the spectrum where there has been no spectral sensitization.

  
g. Color photography

  
The present invention can be used to obtain color images. In general, any product for color photography of the conventional type containing at least one layer of silver halide emulsion, can be improved simply by adding to this layer of emulsion
(or by replacing it with), a layer of emulsion with tabular grains of high shape index, in accordance with the present invention. The present invention thus finds application in color photography, either by additive or subtractive three-color synthesis.

  
With regard to the formation of color images by additive synthesis, an application of the invention consists in using the networks of elementary filters, blue, green and red in combination with a photographic product in accordance with the present invention and capable of providing a silver image. Through this network of additive primary filters, a photographic product is photographically exposed comprising a panchromatic sensitized layer and consisting of an emulsion according to the present invention, that is to say with tabular grains of high shape index. After processing and developing a silver image, examining this silver image through the network of filters allows us to observe a color image. The best way to use these images is to examine them by projection.

   Thus, both the photographic product and the filter network have the same transparent support in common.

  
By applying the invention to the product for color photography by subtractive synthesis of dyes, other particular advantages can be obtained. This type of photographic product includes a support and in general a set of three superimposed layers of silver halide emulsions for separately recording blue, green and red, providing dye images respectively yellow, magenta and blue- green. The present invention applies to any photographic product of this type and therefore relates to any photographic product of this type comprising at least one layer of tabular silver halide grain emulsion of high shape index. However, additional advantages are obtained when using tabular grain emulsions of index

  
high form consisting of bromide and silver bromoiodide. Consequently, the following description relates more particularly to certain embodiments in which emulsions of bromide and bromoiodide of silver are used, but if desired, silver halides with shape index may be used instead. high of any composition. Unless expressly indicated, the products for color photography have the characteristics of the photographic products described above.

  
According to a preferred embodiment, an emulsion of silver bromide or bromoiodide with tabular grains of high shape index, sensitized for the blue minus, in accordance with the indications given above, forms at least one of the layers intended recording green light or red light in a set of three emulsion layers for recording blue, green and red of a product for color photography; in addition, this tabular grain emulsion is arranged to receive, during the exposure of the photographic product to a neutral light at 5500 [deg.] K, blue light in addition to the light that the emulsion is intended to record. The relation between the blue light and the light of the blue minus that the layer receives, can be expressed

  
  <EMI ID = 130.1>

  
  <EMI ID = 131.1>

  
log AND representing the logarithm of the exposure to green light or red light depending on what the tabular grain emulsion records and

  
log EB representing the log of the blue light exposure that these tabular grains also receive. (In each case, E is expressed in lx.s unless otherwise indicated).

  
In practice, according to the present invention, a value of

  
  <EMI ID = 132.1>

  
still to obtain an acceptable reproduction of a poly-chrome subject. This is a surprising fact if we consider the high proportion of grains of the emulsion according to the invention.

  
a

  
  <EMI ID = 133.1>

  
emulsion of comparable silver halides, but not tabular or made up of grains whose index of form is lower, the color rendering is more disturbed and is unacceptable in general. It is known in the art that aberrations in the color rendering from sensitized emulsions in green and in red can be reduced by using grains of smaller average diameter. However, these results are obtained at the cost of limiting the maximum photographic speed that can thus be obtained. With the emulsions of the present invention, it is not only possible to obtain an advantageous separation of the speeds in the blue and in the blue minus, but in addition, this advantage can be retained without any limitation as regards the maximum speeds that can be get in the blue minus.

  
According to a specific and preferred embodiment, a product according to the invention comprises a series of three emulsions recording blue, green and red, at least those recording blue minus are conformal bromide or silver bromoiodide emulsions to the present invention. The emulsion layer recording the blue of this series of three emulsions can also advantageously be an emulsion with tabular grains of high shape index according to

  
the present invention. According to a preferred embodiment, the tabular grains present in each of the emulsion layers of this series of three elements have a

  
  <EMI ID = 134.1>

  
Still further a preferred form of the present invention, the products for color photography have an ISO sensitivity index at least equal to 180.

  
The products for color photography according to the present invention do not need a yellow filtering layer placed between the exposure source and the emulsion layers sensitive to green and / or red to protect these layers from exposure to blue light. However, such a yellow filter layer may be present and in this case, its density may be reduced to a value lower than that of any other yellow filter layer which has been used until now to protect the sensitive emulsion layers. green and red in photographic products intended to be exposed to daylight. According to a preferred embodiment, there are no emulsion layers registering blue between the emulsion layers registering green and / or red and the radiation source used for the exposure.

   This is why, in practice, the photographic product does not contain any substances absorbing blue between the layers of emulsion sensitive to green and sensitive to red and the incident radiation from the exposure.

  
Although only one of the green or red bromide or silver bromoiodide emulsion layers should consist of tabular grains of high shape index, the color photography product contains minus three separate emulsions to record blue, green and red respectively. The other emulsions, that is to say the emulsions other than those consisting of grains with a high shape index, can be conventional emulsions of any shape. Different types of conventional emulsions are described in Research Disclosure, publication 17643 cited above, $ I. According to a preferred embodiment of the present invention, all the emulsion layers contain grains of bromide or silver bromoiodide .

   In particular, at least one emulsion layer recording green and at least one emulsion layer recording red consist of tabular grains with a high shape index, in accordance with the present invention. If the product includes more than one emulsion layer to record green and / or red, the preferred embodiment is that at least the fastest emulsion layer

  
  <EMI ID = 135.1>

  
high, as indicated above. Of course, all the emulsion layers registering blue, the

  
green and red of a photographic product can advantageously consist of tabular grains such as those described above, although this is not necessary for the implementation of the present invention.

  
The present invention applies perfectly to products for color photography as described above in which the speed and the contrast of the emulsion layers recording blue, green and red can be very variable. Since the emulsion layers

  
silver bromide or bromoiodide with tabular grains of high shape index, spectrally sensitized in green or red, have a relatively low speed in blue, it is possible to arrange these emulsion layers recording green and / or red at any place in a product for color photography, without taking into account the remaining emulsion layers and without taking the usual precautions to prevent the exposure of these emulsion layers to blue light.

  
The present invention applies in particular to products for color photography intended for the reproduction of colors by exposure to light from

  
day. Photographic products of this type are characterized in that they provide recordings of blue, green and red exposures, the contrasts of which are more or less harmonized and the speed of which presents limited variations when exposed to a source of

  
  <EMI ID = 136.1> harmonized "means that the contrast of the blue, green and red records differ by less than 20% and preferably by less than 10% compared to the value of the contrast of the recording in blue. The variations limited

  
speed of recording in blue, green and

  
red can be expressed as a variation

  
At log E which is less than 0.3 log E. The variation in speed is the greatest of the differences between the speed of green or red recording and the speed of blue recording.

  
The measurements of contrast and logarithm of rapidity necessary for establishing these relationships can be determined in a photographic product according to the invention by exposing this photographic product to a temperature

  
  <EMI ID = 137.1>

  
but not selective (neutral density), for example a carbon control object, then by treating the photo-

  
  <EMI ID = 138.1>

  
corresponding to those of the use for which it is intended. The densities in blue, green and red are measured by transmitting blue light at a wavelength of
435.8 nm, green light at a wavelength of
546.1 nm and red light at a wavelength of
643.8 nm, as described in the American standard PH2.1-1952 published by the American National Standards Institute
(ANSI), 1430 Broadway, New York, N.Y. 10018; the characteristic curves in blue, green and red of the photographic product are thus obtained. If the photographic product has a reflective support rather than a transparent support, density measurements are carried out by reflection. From the characteristic blue, green and red curves, speed and contrast can be determined by well-known methods.

   The particular techniques for measuring speed and contrast are of no specific interest from the moment when each of the blue, green and red records is the subject of identical measurements in order to allow comparisons. Many standard sensitometric measurement techniques for color photographic products for different applications have been published by ANSI. These are for example the American Standard PH2.21-1979, PH2.47-1979 and PH2 .27-1979

  
The products for color photography according to the present invention allow the reproduction of colors when exposed to daylight and they provide particular advantages compared to conventional products having these characteristics. In the photographic products according to the invention, the speed in the blue of the tabular bromide or silver bromoiodide emulsion layers and spectrally sensitized in the green and

  
red is limited and this limited speed can be used to separate the speed in blue of the emulsion layer recording blue and the speed in blue of emulsion layers recording blue minus. Depending on the application considered, the use of tabular grains in the emulsion layers recording green and red may in itself provide sufficient separation of the responses in blue from the emulsion layers recording blue and blue minus.

  
For some applications, it may be desirable to further increase the separation between the speed in blue of layers recording blue and layers recording blue minus; for this, use is made of conventional separation techniques which thus add to the separation possibilities obtained using the tabular grains with a high shape index according to the present invention. For example, in a photographic product, the fastest green emulsion layer can be placed in the closest position to the radiation source and the emulsion layer is

  
the fastest blue in the position farthest from the source of exposure; in this case, the separation of the velocities in the blue of the emulsions recording the blue and the green, although being equal to 1.0 log E when these emulsions are applied in separate layers and exposed separately, can be effectively reduced by the layering; indeed, the emulsion layer registering the green receives all the blue light during the exposure, but this layer registering the green and the other layers which are above can absorb

  
or reflect some of the blue light before it reaches the blue-recording emulsion layer. In

  
in such a case, increasing the proportion of iodide in the blue-recording emulsion layer may help to increase the separation of the velocities in the blue from the blue-recording layers and the blue minus which is already obtained by using the tabular grains. When an emulsion layer recording blue is placed closer to the radiation source used for exposure than the emulsion layer recording blue minus, a yellow filter layer of limited density can be used.

  
emulsion layers recording blue and blue minus to increase the separation between blue and blue minus. However, it is never necessary to use any of these conventional techniques for separating velocities so that they are used in the prior art to obtain a difference of 1 log E or something similar for the separation of speed in blue. However, this remains possible if one wishes an exceptional separation of the velocities in the blue and in the blue minus, for a determined application.

  
Thus, the present invention achieves the objectives which, in color photography, condition the exact reproduction of colors in balanced lighting conditions, while allowing a wider choice in the production of the photographic product, compared to previous possibilities.

  
Products for color photography are often described so as to highlight the various elements of color forming layers which compose them. Most often, these products contain three of these superimposed elements each containing at least one layer of silver halide emulsion capable of recording an exposure corresponding to a separate third

  
of the spectrum and at the same time produce the complementary primary subtractive dye image. In this way, the elements recording blue, green and red respectively provide yellow, magenta and cyan dye images. The dye-forming substances need not be in the dye-forming elements; they can be supplied entirely from the processing solutions. When the dye-forming substances are incorporated into the photographic products, they can be placed in an emulsion layer or in a layer intended to collect an oxidized developer or an oxidized electron transfer agent coming from an emulsion layer adjacent to the same dye-forming element.

  
In order to prevent the migration of oxidized developers or oxidized electron transfer agents between two dye-forming elements and thus avoid the resulting color alteration, it is common practice to use substances which react with these oxidation products. Such substances can be incorporated into the emulsion layers themselves, as indicated in the patent of the United States of America

  
2,937,086, and / or in interlayers between each dye-forming element, as described in US Patent 2,336,327.

  
Each color forming element may contain only one layer, but most often it contains 2, 3 or more, having different photographic speeds. When the order of the layers does not make it possible to have this set of emulsion layers of different speeds in a single element, it is common to produce a photographic product with several (usually 2 or 3) elements recording blue, green and / or red.

  
According to the present invention, at least one emulsion layer recording green or red containing tabular grains of bromide or silver bromoiodide according to the invention, is arranged in the photographic product so as to receive a higher proportion blue light during the exposure. This higher proportion of blue light reaching the tabular grain emulsion layer of high shape index is the consequence of a lower absorption of blue light by the superimposed yellow filter or is simply the result of the elimination of this yellow filter. The higher proportion of blue light reaching the tabular emulsion layer may also result from a new arrangement of the dye-forming element which is closer to the source of exposure.

   For example, elements recording red and green and containing tabular grain emulsions of high shape index recording green and red, may be arranged closer to the source of exposure relative to the element recording the blue.

  
Products for color photography according to

  
the present invention may have any form compatible with the conditions defined above. Any of the six structures presented in "Spectral Studies of the Photography Process" (table 27-a, p. 211), Focal ress, New York, can be used. In order to provide a simple example, it is possible during the preparation of a conventional silver halide product for color photography, to add to it one or more layers of tabular grain emulsion of high shape index.

  
sensitized to the blue minus and arranged to receive the exposure before the other emulsion layers. However, in most cases, it is preferable to replace one or more layers of conventional emulsions recording the blue minus with corresponding layers made up of tabular grains with a high shape index, possibly by modifying the order of the layers.

  
To illustrate the invention, a number of preferred structures are shown below.

  
Structure I
  <EMI ID = 139.1>
 Structure II

  

  <EMI ID = 140.1>


  
Structure III

  

  <EMI ID = 141.1>


  
Structure IV
  <EMI ID = 142.1>
 Structure V

  

  <EMI ID = 143.1>


  
Structure VI
  <EMI ID = 144.1>
 Structure VII

  

  <EMI ID = 145.1>


  
Structure VIII
  <EMI ID = 146.1>
 Structure IX

  

  <EMI ID = 147.1>


  
  <EMI ID = 148.1>

  
recording blue, green and red of any conventional type.

  
  <EMI ID = 149.1>

  
sion contain tabular grains with a high shape index.

  
F, in prefix, means that the layer has a higher speed than that of at least one other element which, in the structure registers light in the same part of the spectrum.

  
  <EMI ID = 150.1>

  
slower, that is to say has a lower speed than that of at least one other element of the structure recording light in the same part of the spectrum.

  
I, denotes an interlayer containing a substance to react with the oxidation products, but practically without a yellow filter.

  
Each fast or slow element may have a different photographic speed than that of another element of the structure which records light in the same third of the spectrum, due to its arrangement in the structure, its inherent properties or the association of these two factors.

  
In structures 1 to IX, the place of the support has not been shown. In general, the support is the most distant from the source of exposure, that is to say that in the diagrams it would be under the emulsion layers. If the support is colorless and transmits non-scattered light, that is to say if it is transparent, it can be placed between the exposure source and the layers. Of a

  
more generally, the support may be disposed between the source of exposure and any color forming layer recording radiation for which the support is transparent.

  
In structure I, we see that there is no yellow filter. However, in accordance with practice, in products which contain a yellow filter, the blue-forming color forming element is arranged closest to the source of exposure. In its simplest form, each element of this product consists of a single layer of silver halide emulsion. In the variants, each color forming element may contain 2 or 3 or more different layers of silver halide emulsion.

   In the case of sets of 3 layers of emulsion, we compare the layers which in each element have the strongest speed, we preferably harmonize the contrasts and in this case, the photographic speeds of the layers recording the green and the red differ from the speed of the blue recording layer by a difference of less than 0.3 log E. When, in each element, there are 2 or 3 layers of emulsion of different speed or more, there are also preferably 2 or 3 sets of three or more emulsion layers

  
  <EMI ID = 151.1>

  
whose speed presents this relationship.

  
yellow filter below the blue recording element increases the photographic speed of this element.

  
The absence of a yellow filter in the interlayers is not absolutely necessary in the case of structure I. It is possible to have between the elements recording the blue and the green a yellow filter, at the rate of a quantity lower than the normal normal , without departing from the scope of the present invention. In addition, the interlayer separating the elements recording the green and the red can likewise also contain a yellow filter at a rate of a quantity which can go up to that used in a conventional manner.

   When using such quantities of yellow filter, it is not necessary to limit the composition of the element recording the red to the tabular grains of bromide and silver bromoiodide, as indicated above, but any conventional form of grain can be used compatible with the required considerations of contrast and speed.

  
We will not return to the common aspects of structures II to IX. The explanations which follow relate only to the aspects specific to each of the structures. In structure II, blue, green and red are each recorded by two distinct elements at the

  
instead of incorporating the slow and fast emulsion layers recording blue, red or green respectively in the same elements. It is only necessary that the emulsion layers of the fastest elements consist of tabular grains of silver bromide or silver bromoiodide according to the invention. The slower elements registering green and red, because of their slower speed, and the presence of the layer registering the faster blue which is above, benefit from appropriate protection against exposure to blue light, without the need to use a yellow filter.

   The use of bromide or silver bromoiodide emulsions with tabular grains of high shape index in the emulsion layers of low speed elements registering green and red is not excluded. If one places the fastest element recording red on the slowest element recording green, one can increase the speed according to the indications of the patent of the United States of America 4,184,876 as well as to the publications German application 2 704 797, 2 622 923, 2 622 924 and 2 704 826.

  
  <EMI ID = 152.1>

  
following references:

  
The element recording blue is furthest from the source of exposure. As a result, the green recording element is closest to the exposure source and the red recording element is closer to the exposure source than in the conventional case. This arrangement is very advantageous for obtaining images

  
in very sharp colors with excellent color quality. Since the element recording green, which contributes the most to the visual impression of the color image, being the closest to the source of exposure, it can provide an image of great clarity, since it does not there is no interposed layer to diffuse the light. The element recording the red, which comes second for the contribution to the visual impression of a color image, receives a light which

  
passed through only the element registering the green and which consequently was not diffused by an element registering the blue. Of course, the element registering the blue undergoes, by comparison with the structure I, a loss of sharpness, but this drawback is not significant with regard to the advantages resulting from the arrangement of the elements registering the green and the red, because the the contribution of the blue recording element to the visual impression of the color image is by far the least important.

  
Structure IV derives from structure III; it includes distinct, fast and slow elements for registering red, made up of tabular grain emulsions with a high shape index.

  
The structure V differs from the structure IV by the presence of an additional element recording the blue, placed on the elements of low speed recording

  
green, red and blue. The fastest blue recorder includes a tabular-grain silver bromide or bromoiodide emulsion of high shape index. In this case, the fastest blue recording element helps absorb the blue light and therefore

  
to attenuate the transmission of blue light on the elements recording green and red of lower speed. A structural modification consists in not using emulsion with tabular grains of high shape index in the elements registering green and red, of slower speed.

  
Structure VI differs from structure IV in the presence of a tabular grain element recording blue, between the elements recording green and red and the source of exposure. As indicated above, the tabular grain element registering the blue may consist of one or more tabular grain layers registering the blue and when there are thus several layers of emulsion registering the blue, their speed may be different. To counterbalance the effects of the less favorable position occupied by the element registering the red, structure VI provides a second rapid element registering the red which is placed between the tabular grain element registering the blue and the source of exposure.

   Because of its favorable arrangement, this second rapid element registering the red is faster than the first rapid element registering the red, this insofar as these two elements consist of identical emulsions. Of course, this first and second rapid elements recording the red can be made up of identical or different emulsions, the relative speeds of which can be adjusted by known techniques. Instead of using two rapid elements recording red, the second rapid element recording red can be replaced by a second rapid element recording green.

  
Structure VII is identical to structure VI, except that it provides both a second rapid element recording red and a second rapid element recording green arranged between the exposure source and the tabular grain element recording blue . Structures VIII and IX are of the classic type where an interlayer with a yellow filter is placed under the layer recording the blue. However, in these structures, a silver halide emulsion with tabular grains of high shape index is used in the emulsion layers closest to the source of exposure. These tabular grain emulsions can be sensitized to register red light or to register green light, or can be sensitized in pairs to register red and green lights respectively.

  
Many other interesting structures are also

  
  <EMI ID = 153.1>

  
only examples. In each of these structures, the position of the elements registering green and red can be exchanged: the position of the fastest elements registering red and green can be exchanged in the different structures and / or it can be the same for the slowest elements registering green and red.

  
In general, for color photography, the emulsions are arranged so as to form a set of superimposed layers containing substances forming dyes incorporated, for example couplers, but this is not essential.

  
Three chromogenic components each containing a silver halide emulsion recording light corresponding to a third of the spectrum and a coupler forming the complementary primary subtractive dye, can be arranged together in a single layer of a product for color photography. Examples of such products are given in U.S. Patents 2,698,794 and 2,843,489.

  
It is thanks to the relatively large separation between the sensitivities in the blue and the blue minus of the elements recording the green and the red and made up of emulsions of bromide or silver bromoiodide with tabular grains, that one can decrease the quantity of yellow filter or even eliminate these yellow filters and / or - arrange the layers according to new structures. To measure

  
the relative response of the elements registering green and red to blue light in a product for color photography, one technique consists in exposing a sample of such a product through a density scale with neutral light, it is that is to say with a

  
  <EMI ID = 154.1>

  
process the sample. A second sample is then exposed in the same way, but by inserting a Wratten 98 filter which transmits light only between 400 and
490 nm; the product is then treated in the same way as above. Using the transmission densities in blue, green and red, determined according to the American standard PH2.1-1952 mentioned above, three characteristic curves can be plotted for each sample. The differences A and A ′ between the speed in the blue of the element (s) recording the blue and the speed in the blue respectively of the element (s) recording the green and the red, can be determined from the following relationships:

  

  <EMI ID = 155.1>


  
in which :

  
BW98 is the speed in blue of the element recording the blue exposed through a Wratten 98 filter;

  
  <EMI ID = 156.1>

  
registering the red, exposed through the Wratten 98 filter;

  
BN is the speed in the blue of the element registering blue, exposed to neutral light;

  
VN is the speed in the green of the element registering the green exposed to neutral light and;

  
  <EMI ID = 157.1>

  
recording red, exposed to neutral light.

  
In the present description, it is accepted that the densities in blue, green and red are due only to the elements recording respectively blue, green and red, which amounts to neglecting the parasitic spectral absorptions of the dyes yellow, magenta and Blue green. In fact, the importance of these parasitic absorptions is rarely sufficient to exert a practical effect on the results obtained in the applications mentioned.

  
The elements recording the blue of the products for color photography according to the invention exhibit, in the absence of any yellow filter, a speed in the blue which is at least equal to six times, preferably at least eight times, and according to the optimal embodiment at least ten times, the speed in the blue of the elements recording the green and / or the red consisting of emulsions with tabular grains of high shape index conforming to the above indications.

   By way of comparison, an example is given below showing that, in a conventional product for color photography, in the absence of a yellow filter, the speed in the blue of the element recording the blue is less than four times
(0.55 log E) the speed in the blue of the elements registering green by comparison with the factor 10 (0.95 log E) indicated above for a comparable product according to the invention. This comparison illustrates the advantage with regard to the decrease in speed in the blue of the elements registering the green, when emulsions of bromide or bromoiodide of silver consist of tabular grains with high shape index.

  
The separation between the sensitivities in blue and in the blue minus of a product for color photography according to the invention can be measured in another way. This other measure is to compare the speed in

  
the green of an element recording green, or the speed in red of an element recording red, with the speed in blue of these same elements. The exposure and treatment techniques described above are still used, with the difference that instead of exposure to neutral light, exposure to blue minus is used by inserting a Wratten 9 filter which transmits light only beyond 490 nm. We thus determine the different

  
  <EMI ID = 158.1>

  

  <EMI ID = 159.1>
 

  
  <EMI ID = 160.1>

  
registering the red exposed through the Wratten 9 filter.

  
As before, the parasitic spectral absorption produced by the dyes, which is rarely significant, is neglected.

  
Elements recording red and green and containing tabular bromide or silver bromoiodide emulsions according to the above indications have velocities in blue and in the region of the spectrum where they are spectrally sensitized which are at least in a ratio 10 (1.0 log E) and preferably at least in a ratio 20 (1.3 log E). This expresses the difference between

  
the rapidities in the blue and the rapidities in the blue minus. An example is given below in which the velocities are in a ratio greater than 20 (1.35 log E), while in a conventional product for comparable color photography and not containing a yellow filter, the velocities are in a ratio of less than 10 (0.95 log E).

  
If we compare the relations A and B and the relations C and D for the same product, the results are not identical, even if the elements recording the green and the red are identical, except as regards the length of wave of their spectral awareness. Indeed, in most cases, the element recording the red receives a light which has already passed through the element recording the green. However, if you prepare a second identical product

  
on the first, but in which we have exchanged the position of the elements recording the green and the red, we note that the element recording the red of the second product presents

  
for relations B and D practically identical values <EMI ID = 161.1>

  
elements recording the green of the first product. In other words, the choice of spectral sensitization in green as opposed to spectral sensitization in red has no determining effect on the quantitative values obtained with the above relationships. This is why it is customary not to distinguish speed in green and in red when compared to speed in blue, but to designate them generically under the name of speed in blue minus.

  
h. Diffusion at wide angles

  
The emulsions with tabular grains of high index of form according to the invention are advantageous, because, compared to non-tabular emulsifiers or of index of lower form, they make it possible to reduce the scattering of light at large angles. As already indicated above in the comments relating to FIG. 2, it is well known that the sharpness of the image decreases when the thickness of one or more layers of halide emulsions d increases. 'silver. However, Figure 2 also shows that the lateral component of the diffusion

  
(x and 2x) increases directly with increasing angle
0. As long as the angle 0 remains small, the lateral displacement resulting from the scattering remains low and the sharpness of the image remains good.

  
The characteristic advantages that can be obtained

  
as regards sharpness, by using the tabular grains of high shape index according to the invention, result from the reduction of the diffusion at large angles. We can give a quantitative demonstration of this. According to what is shown in FIG. 4, a sample of emulsion 1, in accordance with the present description.

  
  <EMI ID = 162.1>

  
1.08 g of silver per square meter. Preferably, the emulsion and its support are immersed in a liquid (not shown in the figure) having an appropriate refractive index to reduce the effects of Fresnel reflection on the surface of the support and the emulsion. The emulsion layer is exposed in a direction perpendicular to the plane of the support a &#65533; by means of a collimated light source 5. From the source, the light follows a path materialized by the dotted line 7, forming an optical axis, which meets the emulsion at point A. The light which passes through the support and the emulsion can be detected at a constant distance of the emulsion on a hemispherical detection surface 9.

   At a point B which is at the intersection of the extension of the optical path and the detection surface, a maximum of light intensity is detected.

  
An arbitrary point C is chosen on the detection surface. The dotted line connecting A and C forms an angle &#65533; with the emulsion layer. By moving point C on the detection surface, you can vary the angle 0 from 0 to 90 [deg.]. By measuring the intensity of scattered light as a function of &#65533;, it is possible, because of the symmetry of the scattering of light around the optical axis 7, to determine the cumulative light distribution as a function of &#65533;65533;. For this distribution, see DePalma and Gasper, "Determining the Optical Properties of Photographic Emulsions by the Monte Carlo Method", Photography Science and Engineering, Vol. 16, N [deg.] 3, May-June 1971, pp. 181-191.

  
After determining the cumulative light distribution based on &#65533; for values from 0 to 90 [deg.] in the case of emulsion 1 according to the invention, the same process is repeated in the case of a conventional emulsion consisting of grains whose average volume is the same and applied with the same silver title on another part of the support 3. We compare the cumulative light distributions

  
  <EMI ID = 163.1>

  
for values of 0 up to 70 [deg.] and in some

  
7 <EMI ID = 164.1>

  
that the amount of scattered light is lower with the emulsions according to the invention. In Figure 4, the angle

  
  <EMI ID = 165.1>

  
  <EMI ID = 166.1>

  
with tabular grains of high shape index according to the invention, have less diffusion at large angles. Since the wide-angle scattering contributes significantly to reducing the sharpness of the image, the emulsions according to the invention make it possible in each case to increase this sharpness.

  
In the present description, the term "capture angle" designates the value of the angle 6 for which half of the light which reaches the detection surface is contained in a surface subtended by a cone formed by the rotation of the AC line around the polar axis of

  
  <EMI ID = 167.1>

  
the detection surface is in the remaining part of the surface.

  
The following theoretical considerations

  
about the decrease in wide angle scattering, cannot limit the present invention.

  
It is assumed that the main faces of a flat crystal, with a high shape index, as well as the orientation of the grains in the layer are responsible for the improvements.

  
sharpness. It has been observed that the tabular grains present in the silver halide emulsion layers are approximately aligned in parallel with the flat surface of the support on which the layer is applied. Thus, the light, whose direction is perpendicular to the photographic product, has an incidence also perpendicular to one of the main faces of the crystals. The small thickness of the tabular grains, as well as their orientation in the layer, allows the emulsions according to the invention to be applied in thinner layers than conventional emulsions, which also contributes to improving the sharpness. However, the emulsion layers of a product according to the invention see their sharpness improved, even when their thickness is comparable to that of conventional emulsion layers.

  
According to a specific embodiment of the invention which is also preferred, the emulsion layers consist of tabular grains of high shape index whose

  
  <EMI ID = 168.1>

  
still 2 &#65533; m. By increasing the average grain diameter, you can achieve both better speed and better sharpness. Although the maximum average grain diameters may vary according to the tolerable granularity in a given application, the maximum average diameters of grains with a high form index of emulsions according to

  
  <EMI ID = 169.1>

  
In addition to the sharpness advantages indicated above for the average diameters mentioned, one can

  
with emulsions with tabular grains of high shape index avoid a certain number of drawbacks from which conventional emulsions consisting of grains having an average diameter of this order suffer. First of all, it is difficult to prepare conventional non-tabular emulsions which

  
  <EMI ID = 170.1>

  
as noted by Farnell in the publication cited above, a decrease in the speed characteristics is observed when the mean grain diameter is greater

  
  <EMI ID = 171.1>

  
grains of large average diameter, a larger volume of silver is present in each of the grains, in comparison with tabular grains of comparable diameter. Therefore, unless you realize conventional emulsion layers with a higher silver titer, which constitutes an undeniable practical disadvantage; the granularity obtained with a conventional emulsion consisting of grains of large average diameter is greater than that obtained with emulsions according to the invention consisting of grains of which

  
  <EMI ID = 172.1>

  
large coarse grains are used with or without an increase in the silver titer, this leads to the preparation of thicker layers to take account of the large thicknesses of these large diameter grains. On the contrary, the thickness of the tabular grain layers can remain very small even when the diameters exceed the values indicated to obtain the advantages as regards sharpness.

  
These advantages of sharpness which can be obtained with tabular grains result in part from the shape of the grains independently of their average diameter and this is why these grains make it possible to improve the sharpness by comparison

  
with conventional non-tabular grains.

  
Although it is possible to decrease the diffusion

  
at wide angles with monolayers of emulsion with tabular grains of high shape index according to the invention, this

  
does not necessarily mean that wide-angle scattering is reduced in the layers of a product for color photography.

  
layers for color photography, the tabular grain emulsions of high shape index according to the invention can indeed cause an alteration of the sharpness

  
underlying layers.

  
In structure I, we see that the emulsion layer recording the blue is the closest

  
of the radiation source used for the exposure, then

  
that the underlying emulsion layer recording the green consists of an emulsion with tabular grains according to the invention. This emulsion layer registering green

  
is itself above the emulsion layer registering red. If the blue emulsion layer contains grains with an average diameter included

  
  <EMI ID = 173.1>

  
many non-tabular emulsions, we will observe a maximum diffusion of light passing through this layer before reaching the emulsion layers registering green and red. Unfortunately if the light

  
has already been broadcast before reaching the emulsion layer

  
tabular grains with a high shape index forming the layer registering green, the tabular grains can diffuse more than a conventional emulsion

  
which crosses them to reach the layer registering the red. Consequently, the choice of emulsions and the arrangement of the layers entail in this particular case a significant degradation of the sharpness of the emulsion layer registering the red, degradation which is - more important than that which would be observed if this product did not include emulsion according to the invention.

  
In order to obtain the best advantages of the present invention with regard to sharpness, in an emulsion layer which is located under a tabular grain layer of high shape index according to the invention, it is desirable that this tabular grain layer is arranged so that it receives practically non-scattered light. In other words, in the photographic products according to

  
the present invention, improvements in sharpness are obtained in the emulsion layers arranged under the tabular grain emulsion layers only if these tabular grain emulsion layers are not themselves disposed under a layer whose turbidity causes diffusion light. For example, if a layer of emulsion recording green, consisting of grains with a high shape index, according to the invention is arranged

  
on an emulsion layer recording red and under a Lippmann emulsion layer and / or an emulsion layer

  
&#65533;

  
recording blue with tabular grains having a high shape index according to the invention, the sharpness of the layer registering red will be improved by the presence of the emulsion layers with tabular grains which are located above. If the capture angle of the layer or layers on the emulsion layer recording the green which includes tabular grains of high shape index

  
is less than about 10 [deg.], an improvement in the sharpness of the layer registering red can be obtained. It is of course unimportant that the recording layer

  
the red is itself a layer with tabular grains of high shape index according to the invention, at least as regards the effects of the layers lying above on the sharpness of the layer registering the red.

  
In a product for color photography containing several color forming elements arranged one above the other, it is preferable that at least the emulsion layer intended to be closest to the radiation source used for the exposure , or consists of an emulsion with tabular grains of high shape index, in order to take advantage of the advantages provided by this invention as regards image clarity. According to a particularly preferred embodiment of the present invention, each emulsion layer which is arranged so as to be closest to a radiation source with respect to another emulsion layer, consists of an emulsion with tabular grains with a high form index.

   The layering arrangements II to IX described above constitute examples of products for color photography which, according to the present invention, make it possible to obtain a significant improvement in the sharpness of the underlying emulsion layers.

  
Color photography products have been used to illustrate the benefits that tabular grain emulsions with high form index provide. <EMI ID = 174.1>

  
to get regarding sharpness; but we can also improve the sharpness of multi-layer products for black and white photography, that is to say products forming silver images. In a common way, we separate the emulsions forming black and white images into fast layers and slow layers. If the tabular grain emulsions according to the present invention are used in the layers closest to the sources of exposure, the sharpness of the underlying emulsion layers is improved.

  
The following examples illustrate the invention. Examples illustrating the relationship between speed and granularity.

  
According to the indications given below, a series of silver bromoiodide emulsions with different shape indices are prepared. In each of the following examples, the contents of the reactor are vigorously stirred during the entire time in which the silver salts and the halides are introduced. Percentages are expressed by mass

  
unless otherwise indicated. The term M expresses the molar concentration. All solutions are aqueous unless otherwise indicated. The description of the physical characteristics of the emulsions is presented in Table IV below, after the description of the procedure for preparing the emulsion n [deg.] 7.

  
A. Preparation and sensitization of emulsions

  
Emulsion 1 (Example)

  
By the double jet technique and with stirring, 2.2 M solutions of potassium bromide and 2.0 M silver nitrate to 5.5 liters of a 1.5% solution of gelatin at 80 [deg.] C, containing 0.17 M potassium bromide; in doing so, we maintain the pBr at a value

  
0.8 (0.56% of the total amount of money used is consumed). The addition of the bromide solution is stopped

  
and the addition of the silver nitrate solution is continued for 3 min (5.52% of the total amount of silver used is consumed). The solutions of silver bromide and nitrate are then added together, maintaining the pBr at 1.0, in 13 min and by the accelerated flow technique, the flows being multiplied by 2.2, between the start and the end of precipitation (34.8% of the total amount of money used is consumed). The addition of the bromide solution is stopped and the addition of the silver nitrate solution is continued for 1.7 min (which consumes 6.44% of the total amount of silver used). The silver solution and a 1.8 M solution of potassium bromide containing in addition 0.24 M are added by double jet.

  
potassium iodide; we carry out this addition in

  
15.5 minutes with accelerated flow rates, the flow rates being multiplied by 1.6 between the start and the end of the precipitation, maintaining the pBr at 1.6; 45.9% of the total amount of silver used is thus consumed. The addition of the two solutions is stopped and digestion is carried out for 5 min using 1.5 g of sodium thiocyanate per mole of silver. By double jet and with equal flow rates, a 0.18 M solution of potassium iodide and the silver nitrate solution are then added until a pBr of 2.9 is obtained which consumes 6.8% of the amount of total money used. In total, about 11 moles of silver were used.

  
The emulsion is cooled to 30 [deg.] C and washed by coagulation according to the technique described in United States patent N [deg.] 2,614,929. The emulsion being at

  
  <EMI ID = 175.1>

  
after 20 min, the pAg is adjusted to 8.4. To this emulsion, 3.5 mg per mole of sodium thiosulfate pentahydrate and 1.5 mg / mole of silver of potassium tetrachloroaurate are added. The pAg is adjusted to 8.1 and the emulsion is heated <EMI ID = 176.1>

  
tion of potassium bromide.

  
Emulsion 2 (Example)

  
  <EMI ID = 177.1>

  
with a pH of 5.9 and containing 0.17 M of potassium bromide, 2.1 M of potassium bromide and 2.0 M of silver nitrate are added with a double jet and with stirring; this addition is carried out in two minutes while maintaining the pBr at 0.8 which consumes 0.53% of the total amount of silver used. The addition of the bromide solution is stopped by continuing the addition of the silver nitrate solution for 4.6 minutes (8.6% of the total silver solution used is consumed). In 13.3 minutes, the bromide and silver nitrate solutions are then added at the same time with accelerated flow rates (the flow rates are multiplied by 2.5 between the start and the end of the addition), maintaining the pBr at 1.2, which consumes 43.6% of the amount of silver used. The addition of the bromide solution is stopped

  
and the addition of the silver nitrate solution is continued for one minute, which consumes 4.7% of the amount of silver used.

  
In 13.3 minutes and by double jet with accelerated flows (the flows are multiplied by 1.5 between the start and

  
at the end of the precipitation), a 2.0 M potassium bromide solution containing 0.30 M is added.

  
potassium iodide and the silver nitrate solution, keeping the pBr at 1.7, which consumes 35.9% of the total amount of silver used. To this emulsion is added 1.5 g per mole of silver of sodium thiocyanate

  
and thus the mixture is kept for 25 min. By double jet and with constant and equal flows, we add in

  
5 minutes a 0.35 M solution of potassium iodide and the silver nitrate solution until a pBr of 3.0 is reached, which consumes approximately 6.6% of the total amount of silver used. A total of about 11 moles of silver were thus consumed.

  
Then a solution of 350 g of phthalylated gelatin in 1.2 liters of water is added, the emulsion is cooled to

  
  <EMI ID = 178.1>

  
optimally chemically and spectrally sensitizes this emulsion in a manner analogous to that described for emulsion 1.

  
Emulsion 3 (Example)

  
By double jet and with stirring, a solution containing 1.2 M of potassium bromide and a solution containing 1.2 M of silver nitrate containing 30.0 liters of a 0.8% gelatin solution is added. 75 [deg.] C containing 0.10 M potassium bromide; this addition is carried out in 5 min while maintaining the pBr at 1.0 (2.1% of the total amount of silver used is consumed). 5 liters of a solution containing 17.6% of phthalylated gelatin are then added and the emulsion is left to stand for 1 min. The quantity of silver nitrate solution necessary to obtain a pBr of 1.35 is then added to the emulsion, which consumes 5.24% of the total quantity of silver used. By double jet and with accelerated flow rates (the flow rates being multiplied by two, between the beginning and the end of the operation), a 1.06 M solution of potassium bromide is added containing

  
nitrate

  
0.14 M potassium iodide and the solution / silver, keeping the pBr at 1.35 (which consumes 92.7% of the total amount of silver used). A total of about 20 moles of silver were thus used.

  
The emulsion is cooled to 35 [deg.] C, washed by coagulation and it is sensitized optimally, spectrally and chemically as described for emulsion 1.

  
Emulsion 4 (Example)

  
  <EMI ID = 179.1>

  
0.17 M of potassium bromide at 55 [deg.] C and at pH 5.6, a solution of 1.8 M of potassium bromide and 2.0 M of nitrate is added by double jet and with stirring. silver ;

  
each of the two solutions is added in one minute maintaining equal and constant flow rates and a pBr of 0.8, which consumes 0.7% of the amount of silver used. In

  
7 min and keeping the pBr at 0.8, then adding in

  
bromide

  
at the same time the solution of the silver nitrate solution and a 0.26 M solution of potassium iodide, with equal and constant flow rates, which consumes 4.8% of the amount of silver used. This triple-jet addition is then continued for an additional period of

  
37 min while maintaining the pBr at 0.8 with accelerated flow rates
(multiplied by 4, between the start and the end of the operation), which consumes 94.5% of the total amount of money used <A total of around 5 moles of silver was used.

  
  <EMI ID = 180.1>

  
of water containing 200 g of phthalylated gelatin, it is washed by coagulation. The emulsion is then sensitized optimally, spectrally and chemically, in a manner similar to that described for emulsion 1.

  
Emulsion 5 (Witness)

  
This emulsion is precipitated according to the technique described in the United States of America patent 4,184,877.

  
To a 5% solution of gelatin in 17.5 1 of water at

  
  <EMI ID = 181.1>

  
and 4.7 M silver nitrate; the addition is carried out in 3 minutes by double jet with constant flow rates and

  
  <EMI ID = 182.1>

  
22% of the money used to prepare the sprouts. The flow rate of the two solutions is then adjusted so as to consume in approximately 15 minutes approximately 78% of the total amount of silver used for the preparation of the sprouts. The addition of the ammonium iodide solution is then stopped while continuing the addition of the nitrate solution

  
  <EMI ID = 183.1> as a seeding emulsion for the continuation of the precipitation described below. The average diameter of germs

  
  <EMI ID = 184.1>

  
15 liters of a 5% gelatin solution containing 4.1 moles of the pre-silver iodide emulsion are heated to 65 ° C.

  
  <EMI ID = 185.1>

  
equal and constant flows, a solution is added in 7.1 min.

  
a solution

  
4.7 M ammonium bromide and / 4.7 M silver nitrate, maintaining the pBr at 4.7 which consumes 40.2% of the total amount of silver used for precipitation on the germs. The addition of the ammonium bromide solution alone is continued until a pBr of approximately 0.9 is obtained and the jet of ammonium bromide is then stopped. 2.7 liters of an 11.7M ammonium hydroxide solution are then added and the mixture is left to stand for 10 minutes. The pH is adjusted to 5.0 with

  
sulfuric acid and the addition by double jet of the ammonium bromide and silver nitrate solutions is continued for 14 minutes while maintaining the pBr at approximately 0.9 and with a flow rate consuming 56.8% of the total amount of money used. The pBr is then adjusted to 3.3 and cooled

  
  <EMI ID = 186.1>

  
silver.

  
A solution containing 900 g of phthalylated gelatin is added and the emulsion is washed by coagulation.

  
Adjust the pAg of the emulsion to 8.8 and add

  
4.2 mg per mole of silver sodium thiosulfate pentahydrate and 0.6 mg per mole of silver of potassium tetrachloroaurate. The emulsion is then heated for

  
16 minutes at 80 [deg.] C, cooled to 40 [deg.] C, then add a spectral sensitizer for green, sodium salt

  
anhydro-5-chloro-9-ethyl-5'-phenyl-3'- hydroxide
(3-sulfobutyl) -3- (3-sulfopropyl) -oxacarbocyanine. The emulsion is left to stand for 10 min. The chemical and spectral sensitization is optimal taking into account the sensitizers used.

  
Emulsion 6 (Witness)

  
This emulsion is of the type described in US Patent 3,320,069.

  
42.0 liters of a solution brought to a temperature

  
  <EMI ID = 187.1>

  
double jet, with stirring and maintaining equal and constant flow rates, a 1.32 M solution of potassium bromide further containing 0.11 M potassium iodide and a 1.43 M solution of silver nitrate. This addition is carried out approximately in 40 minutes. Rush consumes
21 moles of silver. The emulsion is cooled to 35 [deg.] C and washed by coagulation according to the technique described in US Patent 2,614,925.

  
The emulson's pAg is adjusted to 8.1 and then 5.0 mg per mol of silver of sodium thiosulfate pentahydrate and 2.0 mg / mol of silver of potassium tetrachloroaurate are added. The emulsion is then heated to 65 [deg.] C; we

  
  <EMI ID = 188.1>

  
a spectral sensitizer for the green which is the sodium salt of anhydro-5-chloro-9-ethyl-5'- hydroxide

  
  <EMI ID = 189.1>

  
the emulsion is left to stand for 10 min. Chemical sensitization and spectral sensitization are optimal for the sensitizers used.

  
Emulsion 7 (Witness)

  
This emulsion is of the type described in US Patent 3,320,069.

  
A 42.0 liters of a solution brought to a temperature of 68 [deg.] C and containing 1.25% of phthalylated gelatin, 0.050 M of potassium bromide, 0.012 M of potassium iodide and 0.051 M of thiocyanate of potassium, we add by double jet, stirring and maintaining equal and constant flow rates a 1.37 M solution of bromide

  
"&#65533;

  
potassium containing 0.053 M potassium iodide and a 1.43 M solution of silver nitrate. This addition is carried out approximately in 40 minutes. The precipitation consumes 21 moles of silver. The emulsion is cooled to 35 [deg.] C and washed by coagulation in the same way as emulsion 6.

  
The pAg of the emulsion is adjusted to 8.8 and added to it
10 mg / mole silver sodium thiosulfate pentahydrate

  
and 2.0 mg / mole silver of potassium tetrachloroaurate.

  
The emulsion is then heated to 55 [deg.] C, then cooled.

  
  <EMI ID = 190.1>

  
finally the emulsion is left to stand for 10 min. Chemical sensitization and spectral sensitization are optimal for the sensitizers used.

  

  <EMI ID = 191.1>


  

  <EMI ID = 192.1>


  

  <EMI ID = 193.1>
 

  
Emulsions 1 to 4 are emulsions with tabular grains of high shape index within the limits defined according to the invention. Grains whose diameter is

  
  <EMI ID = 194.1>

  
mean diameter of the tabular grains in this example and the following examples except where it is expressly noted that they were excluded but the number of these tabular grains of small diameter was insufficient to affect the results significantly.

  
To obtain a representative shape index for the grains of the control emulsion, we compare their average diameter with their average thickness. The projected area of a few tabular grains fulfilling the conditions of

  
  <EMI ID = 195.1>

  
by visual examination that these grains, if any, form a small population compared to the total population of grains of the control emulsion.

  
B. Speed / granularity relationship of single-layer photographic products with incorporated coupler

  
The chemically and spectrally sensitized emulsions (emulsions 1 to 7) are applied separately in a layer to each time form a product with a single magenta layer on a cellulose triacetate film support. Each product includes a silver halide emulsion

  
  <EMI ID = 196.1>

  
previously added a dispersion in a solvent of a magenta image-forming coupler, 1- (2,4-dimethyl-6-

  
  <EMI ID = 197.1>

  
pyrazolone, at a rate of 0.75 g of coupler per square meter, 3.2 g per mole of silver 5-sec-octadecyl-hydroquinone potassium sulfonate and 3.6 g per mole of silver of an anti-

  
  <EMI ID = 198.1>

  
then apply an overcoat comprising 0.88 g of gelatin per square meter, and a tanning agent, bis- (vinylsulfonylmethyl) - <EMI ID = 199.1>

  
ether at a rate of 1.75% relative to the total mass of gelatin.

  
With a tungsten source of 3000 * K with a power of 600 W, each product is exposed for 1 / 100th s by inserting a density scale, from 0 to 3.0 and by inserting a Wratten N filter [deg.] 9 and a neutral filter with a density of 1.26. The product is treated at 37.7 ° C. according to a method of the type described in British Journal of Photography Annual, 1979, p. 204-206. The development times are varied so as to obtain the haze densities of 0.10. The relative sensitivity in the green and the rms granularity are determined for each of the photographic products
(the rms granularity is measured by the technique described by H.C. Schmitt, Jr. and J.H. Altman, Applied Optics, 9,

  
pp. 871-874, April 1970).

  
The speed / granularity relationships of these layers are represented by representing in accordance with FIG. 5 the variation of the logarithm of the speed in the green as a function of the granularity rms x 10. FIG. 5 shows that the silver bromoiodide emulsions with a high shape index which have been optimally sensitized chemically and spectrally, exhibit a much better speed / granularity relationship than that of silver bromoiodide emulsions whose shape index is lower.

  
It should be noted that this experiment, carried out on layers of single-layer products in which all the silver halide emulsions have the same silver content and have a silver / current coupler ratio, constitutes the best way of illustrating the speed relationship. / granularity of a silver halide emulsion without introducing a disturbing interaction.

  
C. Improving the Speed / Granularity Relationship in

  
a multi-layer product with incorporated coupler

  
A product with incorporated couplers for color photography is prepared by applying the following layers in order on a triacetate film support. <EMI ID = 200.1>

  
cellulose:

  
Layer 1 Slow or slow blue-green layer

  
comprising a red bromoiodide emulsion sensitized to red, gelatin, a blue-green image-forming coupler, a colored coupler and a DIR coupler.

  
Layer 2: Fast blue-green layer comprising a silver bromoiodide emulsion sensitized in red faster than that of layer 1, gelatin, a blue-green image-forming coupler, a colored coupler and a releasing coupler a development inhibitor (DIR coupler).

  
Layer 3: Interlayer comprising gelatin and a

  
agent against the yellow veil, 2,5-di-secdodécylhydroquinone.

  
Layer 4: Slow magenta layer comprising an emulsion of

  
silver bromoiodide sensitized to green
(1.48 g of silver and 1.21 g of gelatin per square meter) 0.88 g per square meter of a magenta-forming coupler, the 1- (2,4,6-tri-

  
  <EMI ID = 201.1>

  
benzamido7-5-pyrazolone, 0.10 g per square meter of a colored coupler, 1- (2,4,6-trichlorophenyl) -3- / a- (3-tert-butyl-4-hydroxyphenoxy) tetradecanamido- 2-chloroanilino7-4- (3,4dimethoxy) -phenylazo-5-pyrazolone, 0.02 g per

  
  <EMI ID = 202.1>

  
lone and 0.09 g per square meter of potassium 5-sec-octadecylhydroquinone-2-sulfonate
(agent against yellow veil).

  
Layer 5: Fast magenta layer comprising an emulsion

  
faster green-sensitized silver bromoiodide (1.23 g silver and 0.88 g gelatin per square meter), 0.12 g per square meter of a magenta coupler, 1- (2.4 , 6-

  
  <EMI ID = 203.1>

  
tamido) -benzamido7-5-pyrazolone, 0.03 g per square meter of colored coupler (1- (2,4,6-

  
  <EMI ID = 204.1>

  
0.05 g per square meter of potassium 5-sec-octadecylhydroquinone-2-sulfonate.

  
Layer 6: Interlayer comprising gelatin and a

  
agent preventing yellow veil.

  
Layer 7: Yellow filter layer comprising yellow colloldal silver and gelatin.

  
Layer 8: Slow yellow layer comprising an emulsion of

  
silver bromoiodide sensitized in blue, a coupler forming yellow dye and an agent to prevent yellow veil, potassium 5-secoctadecylhydroquinone-2-sulfonate. Layer 9: Rapid yellow layer comprising an emulsion of

  
faster bromoiodide silver sensitized in blue, a yellow-forming coupler and an agent preventing yellow veil.

  
Layer 10: UV absorbing layer comprising

  
gelatin and a compound for absorbing UV radiation, 3- (di-n-hexylamino) allylidenemalononitrile.

  
Layer 11: Protective overcoat comprising gelatin

  
and bis-vinylsulfonylethyl ether.

  
  <EMI ID = 205.1>

  
In each image-forming layer, the silver halide emulsions consist of polydispersed grains, with a low shape index of the type described in United States patent 3,320,069. All the emulsions are sensitized so optimal with sulfur and gold in the presence of thiocyanate and spectrally sensitized to the appropriate regions of the visible spectrum. The emulsion used in the fast magenta layer is an emulsion of silver bromoiodide with 12% iodide by mole,

  
  <EMI ID = 206.1>

  
is weak (about 3: 1); this emulsion was prepared in a similar manner to emulsion n [deg.] 6 described above.

  
We are preparing a second product for photography

  
in the same color, except that in the fast magenta layer, instead of the emulsion

  
low shape index, an emulsion of silver bromoiodide at 8.4% by mole of iodide consisting of tabular grains. The grains of this emulsion have an average size of about

  
  <EMI ID = 207.1>

  
an average shape index greater than 20: 1 and their projected area measured according to the indications given above represents more than 75% of the total projected area. Emulsions with a high and low shape index receive the same optimal, spectral and chemical sensitization, according to the present invention.

  
Each photographic product is exposed for 1 / 50th of a sec. in the light of a tungsten source of

  
  <EMI ID = 208.1>

  
color densities from 0 to 3.0 (with a neutral density of 0.60 moreover). Then treat for 3 1/4 minutes in

  
a color developer of the type described in British Journal of Photography Annual, 1979 p. 204-206. The sensitometric results are presented in Table VII below.

  

  <EMI ID = 209.1>


  

  <EMI ID = 210.1>


  

  <EMI ID = 211.1>
 

  
The results presented in Table VII show that the tabular grains of the present invention make it possible to obtain an increase in sensitivity in the green with at the same time a very small increase in granularity.

  
D. Relation speed / granularity of the products for the

  
Black and white photography.

  
To illustrate the advantages of the invention with regard to black and white photography, five products are prepared from the chemically sensitized and spectrally prepared emulsions above (emulsions

  
  <EMI ID = 212.1>

  
on a polyethylene terephthalate film support. Each product comprises a silver halide emulsion at a rate per square meter, of 3.21 g of silver and 4.16 g of gelatin to which 3.6 g of 4-hydroxy-6-methyl- have been added before. 1,3,3a-7-tetraazaindene (anti-veil) per mole of silver. On each emulsion, an overlay is applied comprising 0.88 g of gelatin per square meter and a tanning agent, bis- (vinyl) sulfomethyl) -ether at a rate of 1.75% relative to the total mass of gelatin.

  
Each photographic product is exposed 1 / 100th of a second to a 30000K tungsten light source with a power of 600 watts and through a scale of

  
  <EMI ID = 213.1>

  
and with N-methyl-p-aminophenol sulfate (developer Kodak DK50), for 5 min in the case of emulsions with a low form index and for 3 and a half minutes for those with a high form index, so as to obtain comparable corrected curves. The measures of speed and of granularity are plotted on the graph of FIG. 6 with on the abscissa the granularity rms multiplied by ten and on the ordinate the logarithm of the speed in the green. The speed / granularity relationships of control emulsions 5, 6

  
and 7 are lower than those of emulsions 1 and 4 according to the present invention.

  
Example concerning emulsions with tabular grains doped with a noble metal from Group VIII of the periodic table.

EMULSION A

  
  <EMI ID = 214.1>

  
described in US Patent 3,320,069, an emulsion of silver bromoiodide (1% by mole) is prepared

  
  <EMI ID = 215.1>

  
and a low form index (less than 3: 1); the formation of silver halide crystals is carried out in the presence of 0.12 mg of ammonium hexachlororhodate (III) per mole of silver. The emulsion is then sensitized at 60 [deg.] C for 23 min with 4.4 mg of sodium thiosulfate pentahydrate per mole of silver, 1.75 mg of potassium tetrachloroaurate per mole of silver and 250 mg of 4 -hydroxy-6-methyl-

  
  <EMI ID = 216.1>

  
chemical sensitization, the emulsion is spectrally sensitized with 87 mg per mole of silver of anhydro5,6-dichloro-1,3'-diethyl-3- (3-sulfopropyl) benzimidazoloxacarbocyanine hydroxide.

  
This silver bromoiodide emulsion with an index of

  
weak form is then applied in a layer at a rate of

  
1.75 g of silver and 4.84 g of gelatin per square meter on

  
a layer of titanium dioxide and gelatin (10: 1) itself applied to a paper support. The emulsion contains 4.65 g of 4-hydroxy-6-methyl-1,3,3a-7-tetraazaindene per mole of silver. An overcoat comprising 0.85 g of gelatin per square meter is then applied to this emulsion layer.

EMULSION B

  
By double jet, 2.34 M solution of

  
potassium bromide and 2.0 M silver nitrate at 4.5 liters of a 1.5% aqueous gelatin solution at 55 [deg.] C additionally containing 0.17 M potassium bromide. This addition

  
is carried out in 2 minutes while maintaining the pBr at 0.8, which consumes 1.6% of the total amount of silver used. The jet of the bromide solution is stopped and the addition of silver nitrate is continued for approximately 11 min at a rate such that 8.5% of the total amount of silver used is consumed and until a pBr 1.1; 8 min after the start of the addition, 0.1 mg of ammonium hexachlororhodate is added per mole of silver (relative to the final mass of silver) to the reactor.

  
When the pBr reaches a value of 1.1, we add

  
by the double jet technique the silver nitrate solution and a 2.14 M solution of potassium bromide which is also 0.022 M in potassium iodide; this addition is carried out approximately in 22 min by maintaining the pBr at 1.1 and by accelerating the flow rates so that they are multiplied by 4.3 between the start and the end of the operation; 77.9% of the total amount of silver used is thus consumed. A 2.0 M solution of silver nitrate is added to the emulsion until a pBr of 1.7 is obtained, which consumes 12.0% of the total amount of money used. We used a total of

  
  <EMI ID = 217.1>

  
a solution of 200 g of phthalylated gelatin in 1.0 l of water is added to it and the emulsion is washed by coagulation.

  
There was thus obtained an emulsion of silver bromoiodide at 1% by mole of iodide consisting of tabular grains with an average diameter of 1.5 μm and an average thickness of

  
  <EMI ID = 218.1>

  
average shape of 19: 1 and these grains represent 90% of the projected area of all the grains.

  
This tabular grain emulsion is then chemically sensitized for 10 minutes at 65 [deg.] C with 5 mg per mole of silver sodium thiosulfate pentahydrate and 5 mg per mole of silver of potassium tetrachloroaurate, so as to obtain a optimal finish. The emulsion is then sensitized spectrally with 150 mg per mole of silver of anhydro-5,6-dichloro-1,3'-diethyl-3- hydroxide.
(3-sulfopropyl) benzimidazoloxacarbocyanine. This tabular grain emulsion (emulsion B) is applied in the form of a layer, in the same way as emulsion A.

  
Exposure and treatment

  
The two layers described above are exposed

  
  <EMI ID = 219.1>

  
Grier, using a density scale from 0 to 3.0 and a filter with a neutral density of 0.85.

  
After exposure, the two layers are developed in a black and white developer with hydroquinone and 1-phenyl-3-pyrazolidone, then they are fixed, washed and examined by densitometry. The results obtained are presented in Table VIII below.

  

  <EMI ID = 220.1>


  

  <EMI ID = 221.1>
 

  
The results of Table VIII show that the tabular grain emulsions of silver bromoiodide doped with rhodium, whose title in silver is lower, have, compared to the control, a maximum maximum density of 0.23 and a greater rapidity of 109 units of relative speed (0.32 log E). The contrast of the two products is practically equivalent.

  
Examples illustrating the increased separation of velocities between regions of spectral sensitization and regions of natural sensitivity.

  
Four products for color photography are hereinafter designated under the name of structures 1 to 4; except for the structural characteristics expressly identified below, the structure of these elements is the same.

  

  <EMI ID = 222.1>
 

  
SC is an overlay of gelatin;

  
  <EMI ID = 223.1>

  
colloidal yellow serving as a yellow filter and the other abbreviations are identical to those already indicated for

  
  <EMI ID = 224.1>

  
blue (B), green (V) and red (R), the code of which does not include the letter T, consist of silver bromoiodide emulsions with low shape index, prepared according to United States patent United States of America 3,320,069 (the corresponding layers in the different structures have the same iodide content, unless otherwise specified.

  
The rapid emulsion with tabular grains sensitized in green (identified with the letter T in the diagrams above) is prepared as follows.

  
2.25 1 of a 1.5% by mass aqueous solution of bone gelatin containing potassium bromide (0.17 M,

  
  <EMI ID = 225.1>

  
simultaneously by double jet in two minutes and at constant flow rate, aqueous solutions of potassium bromide
(2.19 M, solution B-1) and silver nitrate (2.0 M, solution C-1) (0.61% of the silver nitrate was thus consumed).

  
After two minutes, the introduction is stopped

  
of solution B-1, but the introduction of solution C-1 is continued until a pBr of 1.00 to 80 [deg.] C is reached (2.44% of the silver nitrate has thus been consumed ). We add

  
0.4 1 of a phthalylated gelatin solution at 20% by mass containing 0.10 M of KBr (solution D), at pBr 1.0 and 80 [deg.] C.

  
By double jet, solutions B-1 and C-1 are then added in 24 minutes to the reactor using accelerated flow rates (multiplied by 4.0 between the start and the end

  
of the preparation). 44% of the total amount of silver nitrate was thus consumed. After 24 minutes, the jet of solution B-1 is stopped and the addition is continued

  
  <EMI ID = 226.1>

  
By double jet, the solution C-1 and a solution B-2 of potassium bromide are then added to the reactor.
(2.17 M) and potassium iodide (0.03 M); this addition is carried out in 12 minutes with accelerated flow rates
(multiplied by 1.37 between the beginning and the end of the precipitation) by consuming 50.4% of the total silver nitrate.

  
A double jet then adds aqueous solutions of potassium iodide (0.36 M, solution B-3) and silver nitrate (2.0 M, solution C-3). We realize this

  
  <EMI ID = 227.1>

  
pBr of 2.16, which consumes 2.59% of the total silver nitrate.

  
A total of 6.57 moles of silver nitrate were used to prepare this emulsion.

  
The emulsion is cooled to 35 [deg.] C, it is mixed with 0.30 liter of an aqueous solution of phthalylated gelatin

  
(13.3% by mass of gelatin) and washed twice by coagulation.

  
The fastest green sensitive emulsion layer contains tabular silver bromoiodide grains including

  
  <EMI ID = 228.1>

  
In 90% of the projected area of the total grains and according to the technique described above, an average shape index of about 45: 1 is measured for the grains of this population. The fastest green and red sensitive layers

  
  <EMI ID = 229.1>

  
whereas the faster green and red sensitive tabular emulsion layers of structures III and IV contain 1.5 and 1.2 mol% iodide respectively.

  
The fastest green-sensitive tabular grain emulsion is then spectrally and chemically sensitized optimally by the addition of 350 mg per mole of silver in the sodium salt of 5-chlorohydroxide.

  
  <EMI ID = 230.1> carbocyanine, 101 mg / mol of silver of the sodium salt of anhydro-11-ethyl-1,1'-bis (3-sulfopropyl) -naphth- hydroxide

  
  <EMI ID = 231.1>

  
sodium cyanate, 6 mg / mole silver sodium thiosulfate pentahydrate and 3 mg / mole silver potassium tetrachloroaurate.

  
The fastest red-sensitive tabular grain emulsion is prepared and sensitized optically

  
  <EMI ID = 232.1>

  
with tabular silver chlorobromide sensitized for green described immediately above, with the only difference that is used as spectral sensitizers
144 mg per mole of silver anhydro hydroxide 5,6-dichlo-

  
  <EMI ID = 233.1>

  
anhydro-5,5'-dichloro-3,9-diethyl-3 '- (3-sulfobutyl) thiacarbocyanine hydroxide.

  
Further details regarding structures I to IV can be found in the United States patent

  
4,184,876.

  
The structures I to IV are subjected to an identical neutral exposure by means of a source of 2850 [deg.] K with a power of 600 watts by inserting a filter for daylight 5 and a density scale from 0 to 4 with ranges of 0.20. We expose other samples of structures I to IV as mentioned above, but intercalating

  
in addition a Wratten 98 filter so as to obtain the results of exposure to blue. Other exhibits are exposed

  
  <EMI ID = 234.1>

  
by additionally inserting a Wratten 9 filter, so as to obtain the results of exposure to the blue minus. All samples are treated in the same way by the C-41 color negative processing method described in British Journal of Photography Annual, 1979, p. 204. The curves obtained for the different samples are compared after harmonization of the minimum density levels, that is to say by superimposing the parts of curves corresponding to the minimum densities. The results are collated in Table IX.

  

  <EMI ID = 235.1>


  

  <EMI ID = 236.1>
 

  
  <EMI ID = 237.1>

  
the blue of the chromogenic element recording blue and the logarithm of the rapidity in blue of the chromogenic element recording green; this difference is expressed

  
  <EMI ID = 238.1>

  
tee in the blue of the chromogenic element recording the blue and the logarithm of the speed in the blue of the chromogenic element recording the red; this difference is expressed by equation B indicated above;

  
  <EMI ID = 239.1>

  
is the difference between the logarithm of the rapidity in the green of the chromogenic element recording the green and the logarithm of the rapidity in the blue of the element recording the green; this difference is expressed

  
  <EMI ID = 240.1>

  
dity in the red of the element recording the red and the logarithm of the speed in the blue of the chromogenic element recording the red, expressed by the equation D ci-

  
  <EMI ID = 241.1>

  
The comparison of structures I and III shows that the separation of velocities is better with the structure

  
III which is produced with tabular grains in accordance with the present invention. In structure III, the separation of the velocities does not reach the value of structure I, but structure III does not use a yellow filter and consequently it does not entail the drawbacks already mentioned with regard to the use of these filters. Structure IV uses

  
a yellow filter in a larger quantity than that required for the photographic products in accordance with the present invention, but it is found that in this structure IV a separation of the velocities greater than that of the structure III could be obtained if it was desired even with densities small yellow filter.

  
We prepare a monochrome product by applying on

  
a film support the composition of the emulsion layer

  
tabular grain sensitized for the fastest green described above, then applying a protective gelatin overlay to this layer. The separation between the speed in blue and the speed in blue minus of this product is determined by means of the exposure and treatment techniques already described. The quantitative expression

  
of this separation is given by equation (C):

  
  <EMI ID = 242.1>

  
results show that an appropriate separation of the velocities in the blue and the blue minus can be carried out in accordance with the invention when a tabular emulsion layer with a high shape index recording the blue minus is arranged so as to be the layer closer to the source of exposure and without benefiting from the protection of an overcoat absorbing blue light.

  
Examples of improving image clarity in multi-layer photographic products containing tabular grain emulsions.

  
The following three examples show how image clarity is improved using emulsions

  
with tabular grains of high shape index. In these examples, the control products are produced with silver bromoiodide emulsions with low shape index of the type of those described in US Pat. No. 3,320,069. These emulsions with low shape index are designated in the following under the name of conventional emulsions and their physical characteristics are presented in Table X below.

  

  <EMI ID = 243.1>


  

  <EMI ID = 244.1>
 

  
Four silver bromoiodide emulsions with tabular grains (high shape index) are prepared by techniques similar to those described above in the example relating to the improvement of the speed / granularity relationship. The physical characteristics of these emulsions are presented in Table XI.

  

  <EMI ID = 245.1>


  

  <EMI ID = 246.1>
 

  
The silver bromoiodide emulsions described above C1 to C6 and T1 to T4 are used to prepare a series of multilayer products. Variations are noted in the results table. Although these emulsions are chemically and spectrally sensitized, such sensitization is not essential to obtain the results observed with regard to sharpness.

  
Basic structure A

  

  <EMI ID = 247.1>
 

EXPOSURE AND TREATMENT

  
The samples are exposed and developed as before. Sharpness measurements are made by determining the modulation transfer functions. This process is known and described for example in Journal of Applied Photography Engineering, 6 (1): 1-8, 1980.

  
We obtain the modulation transfer functions

  
in red light by exposure of the products to several layers for 1 / 15th of a second (60% modulation) through a Wratten 29 filter and a neutral filter with a density of 0.7. The modulation transfer functions for green light are obtained in the same way, but using a Wratten 99 filter.

  
  <EMI ID = 248.1>

  
by means of process C-41 for color negative product, described in British Journal of Photography Annual, 1979; p. 204. After the processing, from the modulation transfer curves, acutance measurements are carried out by cascade modulation transfer (CMT), at the magnification used for the 16 mm wide film.

RESULTS

  
The composition of the control samples and of the samples in accordance with the invention, as well as the cut-off values for the exposures in red and in green are presented in Table XII.

  

  <EMI ID = 249.1>


  

  <EMI ID = 250.1>
 

  
Surprisingly, the results in Table XII show that the use of tabular grain emulsions in layers of a multi-layer product for color photography can lead to a decrease in sharpness. If we consider the acutance in the red, we note that the sample 2 containing two layers with tabular grains is less clear (-1.0 CMT sharpness) than the control 1 which includes only conventional emulsions. Similarly, sample 3 with four tabular grain layers is less clear (-1.3 CMT unit) than sample 4 which contains only three tabular grain layers and is also less clear (-0.4 CMT unit) as sample 5 which contains two tabular grain layers.

   However, samples 6 and 7 show that with an appropriate arrangement of tabular grain emulsions (it is noted that the CMT height in the red of sample 6 is 1.3 units greater than that of sample 4) in the layers closest to the radiation source used for the exposure, very significant improvements are obtained compared to the control samples comprising only conventional emulsions. As shown in the table above, the CMT height in the green of sample 6 is 6.3 CMT units higher than that of sample 1 and the CMT height in the green of sample 7 is greater than 6.6 units than that in sample 1.

  
Structure

  

  <EMI ID = 251.1>


  
The structural products were exhibited. and we treat them

  
  <EMI ID = 252.1>

  

  <EMI ID = 253.1>


  

  <EMI ID = 254.1>
 

  
The data in Table XIII show that the sharpness is improved when the tabular grain emulsions are arranged in the layers closest to the radiation source used for exposure; sharpness is changed

  
unfavorably when the tabular grain emulsions are arranged in intermediate layers themselves placed under light-scattering layers.

  
Structure C

  

  <EMI ID = 255.1>


  
Two monochrome products are prepared by applying compositions for fast and slow magenta layers to a support.

TABLE XIV

  

  <EMI ID = 256.1>


  
The sharpness of the monochrome products is then measured according to the technique described above and the following results are obtained:

TABLE XV

  

  <EMI ID = 257.1>
 

  
Example showing the reduction of light scattering at a wide angle by the use of tabular grains

  
The quantitative detection method of angular light scattering described above is used with reference to FIG. 4 to specifically illustrate the reduction in wide angle scattering which the tabular grain emulsions with shape index allow to obtain. high according to the invention, by comparison with an emulsion with non-tabular grains of the same average volume. The emulsions according to the invention essentially consist of a dispersion medium and tabular grains whose diameter

  
  <EMI ID = 258.1>

  
average shape index of 23.5: 1. Tabular grains represent more than 90% of the total projected grain surface

  
  <EMI ID = 259.1>

  
of the same volume, i.e. equivalent spheres, mean that the two emulsions have approximately the same grain diameter). For both emulsions, the total transmittance is 90% when immersed in a liquid with an appropriate refractive index. Each emulsion is applied to a transparent support at the rate of 1.08 g of silver per square meter.

  
As shown in the table below, the percentage of total transmitted light received

  
over the entire detection surface subtended by an angle &#65533; with a value of 84 [deg.], is lower with tabular grain emulsions of high shape index than with the control emulsion whose average grain volume is

  
of capture

  
  <EMI ID = 260.1>

  
for both emulsions is less than about 6 [deg.]. Consequently, neither of these two emulsions can be considered as having diffusing characteristics resulting in real turbidity. When the angle est is 70 [deg.], The emulsion according to the invention has a wide angle light scattering which is only half that of the witness.

TABLE XVI

  
  <EMI ID = 261.1>

  

  <EMI ID = 262.1>


  
Example illustrating the spectral sensitization in blue of the tabular grain emulsion A

  
A tabular silver bromoiodide emulsion containing 3% of iodide by mole is prepared as follows:

  
To 3.0 liters of a 1.5% gelatin solution,

  
  <EMI ID = 263.1>

  
yes, we add by double jet and with stirring, a solution

  
  <EMI ID = 264.1>

  
  <EMI ID = 265.1>

  
  <EMI ID = 266.1>

  
the total amount of money used. The addition of the bromide solution is stopped and the addition is continued

  
silver nitrate solution for 1.8 min until reaching a pBr of 1.3 which consumes 4.3% of the silver used. The silver nitrate solution and a 6% gelatin solution containing 4.0 M potassium bromide and 0.12 M potassium iodide are then added simultaneously; this addition is carried out in 24.5 min with accelerated flow rates (by multiplying the flow rate by 2.0 between the start and the end of the operation) and maintaining the pBr at 1.3, which consumes 87.1% total money used. The addition of the bromide solution is stopped and the addition of the silver nitrate solution is continued for 1.6 min with a flow rate consuming 3.8% of the total silver used and until reaching a pBr of 2.7.

  
The emulsion is then cooled to 35 [deg.] C, 279 g of phthalylated gelatin dissolved in 1 liter of distilled water are added to it and washed by coagulation. There was thus obtained an emulsion of silver bromoiodide at 3 mol%

  
  <EMI ID = 267.1>

  
  <EMI ID = 268.1>

  
a shape index 10: 1. These tabular grains represent more than 85% of the projected surface of the total of the silver halide grains present in the emulsion layer.

  
The emulsion is sensitized chemically with sodium thiocyanate, sodium thiosulfate and potassium tetrachloroaurate.

  
  <EMI ID = 269.1>

  
A sample of this chemically sensitized emulsion is applied to a cellulose triacetate film support. The emulsion layer obtained comprises the tabular emulsion of silver bromoiodide at a rate per square meter of 1.8 g of silver and 2.9 g of gelatin to which a coupler forming the magenta dye, the

  
  <EMI ID = 270.1>

  
sulfohydroquinone (1.69 g / mole of silver) and 4-hydroxy6-methyl-1,3,3a, 7-tetraazaindene (3.62 g / mole of silver). LAYER N [deg.] 2

  
A second sample of the tabular emulsion of silver bromoiodide is spectrally sensitized to blue by the addition of 3 x 10 -4 mole per mole of silver of the triethylamine salt of 5,6-anhydro hydroxide dimethoxy -5-

  
  <EMI ID = 271.1>

  
As before, this spectrally sensitized emulsion is then applied in a layer, with the same magenta dye-forming coupler as in layer 1. Each product is exposed for 1 / 25th of a second through a density scale from 0 to 3.0, using a source of

  
  <EMI ID = 272.1>

  
milk for 3 min in a color developer of the type described in British Journal of Photocraphy Annual, 1979

  
p. 204-206.

  
Product n [deg.] 2 has a photographic speed 0.42 log E higher than that of product 1, which shows the contribution of sensitization in blue to the increase in speed.

  
Sensitization of a silver chloride emulsion with grains of high shape index.

  
A silver chloride emulsion with tabular grains of high shape index is prepared as follows:

  
2.0 l of a solution containing 0.63% of a copolymer of 3-thiapentyl methacrylate, acrylic acid and 2-methacryloyloxyethyl-1sulfonic acid in the form of sodium salts are introduced into a reactor. 0.35% adenine. The solution is also - 0.5 M in calcium chloride and 0.0125 M in sodium bromide. The pH is adjusted to 2.6, at a temperature of 55 [deg.] C. Then added to the reactor by double jet at constant flow rates, a 2.0 M solution of calcium chloride and a 2.0 M solution of silver nitrate; this addition is carried out in 1 min which consumes 1.2% of the total silver nitrate used. The addition of the solutions is continued for 15 min with accelerated flow rates, by multiplying the flow rates by 2.33 between the start and the end of the operation; 28.9% of the total amount of silver nitrate used is thus consumed.

   The pCl is maintained throughout the preparation at the value read in the reactor 1 min after the start of the addition. The addition of the solutions is continued for a further 26 minutes at a constant flow rate, consuming 70% of the total silver nitrate used. A 0.2 M sodium hydroxide solution is slowly added during the first third of the precipitation to maintain the pH at 2.6 to 55 [deg.] C. In total, 2.6 moles of silver were precipitated.

  
The tabular grains of this emulsion have an average diameter of 4.0 to 4.5 µm and an average thickness of

  
  <EMI ID = 273.1>

  
about an average shape index of 15: 1 and representing at least 80% of the total projected surface of the grains. These tabular grains are apparently dodecahedral, which suggests the presence of {110} and {111} edges.

  
This tabular grain silver chloride emulsion is separated into four parts. Part A is neither chemically nor spectrally sensitized and is applied to a polyester film support at a rate of 1.07 g of silver from 4.3 g of gelatin per square meter.

  
Part B is sensitized as follows: 1.0 mg per mole of silver of gold sulfide is added thereto, then it is maintained for 5 min at 65 [deg.] C. The emulsion is spectrally sensitized

  
  <EMI ID = 274.1>

  
silver sodium salt of anhydro-5-chloro9-ethyl-5'-phenyl-3,3'-di (3-sulfopropyl) oxacarbocyanine hydroxide, then apply the emulsion as a layer A. The chemical and spectral sensitizations are optimal for the sensitizers used.

  
Parts C and D are sensitized in an optimal manner. To part C, 0.75 mmol / mole of silver of anhydro-5-chloro-9-ethyl-5'-phenyl-3,3 is added. '-bis-
(3-sulfopropyl) oxacarbocyanine as sodium salt

  
  <EMI ID = 275.1>

  
add a solution at 3.0 mol% of sodium bromide relative to the total of halides, then heat

  
  <EMI ID = 276.1>

  
silver mole of sodium thiosulfate pentahydrate, 1600 mg / silver mole of sodium thiocyanate, 5 mg per silver mole of potassium tetrachloroaurate and heated

  
  <EMI ID = 277.1>

  
Part D is sensitized like part C, except that 10 mg / mol of silver of sodium thiosulfate pentahydrate is used.

  
Each layer is exposed for 1 / 50th of a second

  
  <EMI ID = 278.1>

  
power of 600 W then treated for 8 min at 20 [deg.] C in a surface developer with N-methyl-p-aminophenol sulfate and ascorbic acid. The sensitometric results are presented in the table below.

  

  <EMI ID = 279.1>


  

  <EMI ID = 280.1>


  

  <EMI ID = 281.1>
 

  
Table XVII shows the higher speed of the emulsions sensitized optimally in accordance with the invention.

  
Emulsion consisting of tabular grains with internal latent image

  
To 5.0 liters of a 0.9% solution of gelatin at 80 [deg.] C and whose pBr is adjusted to 1.3 with sodium bromide which contains 2.44 x 10'4 mole of germs seeding

  
  <EMI ID = 282.1>

  
double jet a 1.25 M solution of silver nitrate and a 1.25 M solution of sodium bromide; this addition is carried out in 1 min with a flow rate consuming 0.1% of the total silver nitrate used in this precipitation. While maintaining the pBr at 1.3, the sodium bromide and silver nitrate solutions are added for 10.9 min with accelerated flow rates (the flow rates are multiplied by 29.4 between the start and the end of the 'operation) which consumes 17.2% of the. total silver nitrate used. Maintaining the pBr at 1.3, add a 5.0 M solution of sodium bromide and 5.0 M silver nitrate by double jet in 13.9 min and with accelerated flow rates (the flow rates being multiplied by 2 , 2 between the start and the end of the operation) and 68.8% of the total silver nitrate used is consumed.

   The pBr is then adjusted to 2.8 by adding a 5.0 M silver nitrate solution over 4 min, which consumes 11.0% of the total silver nitrate used. The emulsion is cooled to 35 [deg.] C and the

  
  <EMI ID = 283.1>

  
total used). In total, about 4 moles of silver nitrate were used to precipitate these grains.

  
The tabular grains of the bromoiodide emulsion

  
  <EMI ID = 284.1>

  
about 31: 1.

  
This emulsion is chemically sensitized in the following manner. At 35 [deg.] C, its pH is adjusted to 4.0 and its pAg to 6.0. Then added, per mole of silver, 3.0 mg of sodium thiosulfate pentahydrate and 3.0 mg of tetra-

  
  <EMI ID = 285.1>

  
0.4% gelatin containing 0.20 mole silver of the tabular grain silver bromoiodide emulsion described

  
  <EMI ID = 286.1>

  
pBr at 1.6. Maintaining the pBr at this value, a 2.5 M solution of sodium bromide and a solution are added.

  
2.5 M silver nitrate; this addition is carried out by double jet in 28 min with accelerated flow rates (the flow rates being multiplied by 6.6 between the start and the end of the operation); thus consuming 78.7% of the total amount

  
of silver nitrate involved in this precipitation. The silver nitrate solution is then added at a constant rate for 9.5 min until a pBr of 3.0 is obtained, which consumes 21.3% of the total silver nitrate used. In total, about 0.8 moles of silver nitrate were used in this precipitation.

  
Cool the emulsion to 35 [deg.] C, add 30 g

  
phthalylated gelatin and washed twice by coagulation.

  
A silver bromoiodide emulsion with tabular grains was obtained having internal sensitivity; the

  
  <EMI ID = 287.1>

  
40: 1 ron. Tabular grains represent at least
85% of the total projected surface of the silver halide grains.

  
This emulsion is then sensitized spectrally by adding 502 mg / mole of silver to the sodium salt of 5-chloro-9-ethyl-5'-phenyl-3 'anhydro hydroxide - (3sulfobutyl) -3- ( 3-sulfopropyl) -oxacarbocyanine and 144 mg

  
per mole of silver of the sodium salt of anhydroxide <EMI ID = 288.1>

  
cyanine. In addition, a 3.0% molar iodide solution based on the total amount of silver halides is added to this spectrally sensitized solution.

  
This tabular emulsion with internal sensitivity is applied to a polyester film support at the rate of 2.15 g of silver and 10.4 g of gelatin per square meter. It is exposed for 1 / 100th of a second through a continuous density scale from 0 to 4.0, by inserting a Wratten 12 filter and using a tungs light source.

  
  <EMI ID = 289.1>

  
aminophenol and hydroquinone additionally containing potassium iodide. The internal negative image exhibits good discrimination with a minimum density of 0.20 and a maximum density of 1.36.

  
Example

  
A. Preparation of silver bromide emulsions

  
Emulsion 1

  
A solution of 1.15 is added to 8.0 liters of a 1.5% by mass, well-stirred bone gelatin solution containing 0.14 M of potassium bromide. M potassium bromide and a 1.0 M solution of silver nitrate. This precipitation is carried out in 2 minutes at pBr 0.85 and at 60 [deg.] C and 2.3% of the total silver is consumed. A 2.0 M solution of silver nitrate is then added at a constant rate and approximately in 5 minutes, until a pBr of 1.2 to 60 [deg.] C is reached; 5.7% of the total money used is thus consumed. By double jet and with accelerated flow rates (multiplied by 5.6 between the beginning and the end of the precipitation), a 2.3 M solution of potassium bromide and a 2.0 M solution of silver nitrate are added.

   This addition is carried out in 25.6 min at 60 [deg.] C by adjusting the pBr to 1.2 and 49.4% of the total silver used is consumed. At constant flow, a 2.0 M silver nitrate solution is added; this addition is carried out in 5.4 min at 60 [deg.] C until a pAg of 8.25 is reached, consuming 7.7% of the total silver used. By double jet, and at constant flow rates, a solution is added

  
2.3 M potassium bromide and a 2.0 M solution of silver nitrate. This addition is carried out in 49.4 min and at 60 [deg.] C

  
by setting the pAg to 8.25 which consumes 34.9% of the total money used. In total, about 11.3 moles of silver were consumed for the preparation of this emulsion.

  
  <EMI ID = 290.1>

  
and 2.2 liters of a 15.3% by weight phthalylated gelatin solution are added thereto. The emulsion is washed by coagulation according to the method described in US Patent 2,614,929. Then, 1.9 liters of a 13.5% by weight bone gelatin solution are added and adjusts the pH to 5.5 and the pAg to 8.2 to 40 [deg.] C.

  
The tabular silver bromide grains obtained have an average diameter of 1.67 μm, an average thickness of

  
  <EMI ID = 291.1>

  
projected. The average form index is 16.7: 1.

  
Emulsion 2

  
To 6.0 liters of a well-stirred aqueous solution of bone gelatin at 1.5% by mass, containing 0.14 M of potassium bromide, a 1.15 M KBr solution and a solution are added by double jet. 1.0 M silver nitrate; this addition is carried out in 2 min at constant flow while maintaining a

  
  <EMI ID = 292.1>

  
used. After 0.5 min at pBr 0.85 to 65 [deg.] C, a 2.0 M solution of silver nitrate is added in approximately

  
7.5 min until reaching a pBr of 1.23 to 65 [deg.] C, which consumes 6.0% of the total silver used. 2.3 M solutions of potassium bromide and 2.0 M silver nitrate are added by adjusting the pBr to 1.23 at 65 [deg.] C; this addition is carried out in 25.5 min by double jet with accelerated flow rates (multiplied by 5.6 between the start and the end of the addition), which consumes 29.8% of the total money used. A 2.0 M solution of silver nitrate at constant flow rate is added over approximately 6.5 min until a pAg of 8.15 to 65 [deg.] C is reached, which consumes 6.4% of the total money used. Then, a 2.3 M solution of potassium bromide and a 2.0 M solution of silver nitrate are added; this addition is carried out in 70.8 min by double jet with constant flow rates pAg 8.15 and at 65 [deg.] C, consuming 56.2% of the total silver used.

  
About 10 moles of silver were used to prepare this emulsion.

  
After precipitation of the emulsion it is cooled

  
at 40 [deg.] C and added 1.65 liters of phthalylated gelatin
(15.3% by mass solution), then washed twice by coagulation according to the method described in US Patent 2,614,929. 1.55 liters of bone gelatin are then added ( 13.3% by mass solution) and adjust

  
the pH at 6.5 and the pAg at 8.3 at 40 [deg.] C.

  
The tabular silver bromide grains obtained have

  
  <EMI ID = 293.1>

  
occupy more than 95% of the projected surface.

  
Emulsion 3

  
To 8.0 liters of an aqueous solution of bone gelatin
(1.5% by mass) well stirred containing 0.14 M potassium bromide, a 1.15 M solution of KBr and a 1.0 M solution of AgNO 3 are added; this addition is carried out in 2 min by double jet and with constant flow rates, maintaining the pBr at 0.85 at 60 [deg.] C, which consumes 3.6% of the total silver used. A 2.0 M solution of AgN03 is then added at constant flow rate over 5 min until a pBr of 1.2 is reached.

  
at 60 [deg.] C which consumes 8.8% of the total money used. By double jet and with accelerated flow rates (multiplied by 5.6 between the start and the end of the addition), a 2.3 M solution of KBr and a 2.0 M solution of AgNO 3 are added; this addition is carried out in 25.5 min while maintaining the pBr at 1.2 at
60 [deg.] C, which consumes 75.2% of the total money used.

  
Then added in 5.73 min a 2.0 M solution of AgN03 at constant flow rate until reaching a pAg of 7.8 to 60 [deg.] C, which consumes 12.4% of the total silver used .

  
A total of about 7.4 moles of silver was used to prepare this emulsion.

  
After precipitation, the emulsion is cooled to 40 [deg.] C and 1.4 liters of phthalylated gelatin (solution at
15.3% by mass). The emulsion is washed by coagulation according to the method described in US Patent 2,614,919, then 1.3 liters of a gelatin solution of bone are added.
13.5% by mass and the pH is adjusted to 5.5 and the pAg to 8.2 at
40 [deg.] C.

  
The tabular silver bromide grains obtained have

  
  <EMI ID = 294.1>

  
more than 95% of the projected surface.

  
Emulsion 4

  
4.5 liters of a well-stirred aqueous solution of bone gelatin (0.75% by mass), containing 0.14 M KBr,

  
a 0.39 M solution of KBr and a 0.10 M solution of AgN03 are added: this addition is carried out in 8 min with constant flow rates while maintaining the pBr at 0.85 at 55 [deg.] C, which consumes 3.4% of the total money used. The emulsion is maintained for 0.5 min at pBr 0.85 and at 55 [deg.] C, after which a 2.0 M AgN03 solution is added to it in 18 min and at constant flow rate until a pBr of 1.23 to 55 [deg.] C, which consumes
15.4% of the total money used. By double jet and with accelerated flow rates (multiplied by 5.6 between the beginning and the end of the addition), a KBr 2.3 M solution and a 2.0 M AgN03 solution are added in 27 minutes while maintaining the pBr at 1.23 to 55 [deg.] C, which consumes 64.1% of the total money used.

   A 2.0 M solution of AgNO 3 is then added at constant flow rate over approximately 8 minutes until a pAg of 8.0 to 55 [deg.] C is reached, which consumes 17.1% of the total silver used.

  
About 4.7 moles of silver were used to prepare this emulsion.

  
  <EMI ID = 295.1>

  
0.85 liters of phthalylated gelatin (solution to
15.3% by mass) and washed twice by coagulation according to the process described in the patent of the United States of America

  
2,614,929. 0.8 liters of a 13.3% by mass bone gelatin solution are then added and the pH is adjusted to 5.5 and

  
  <EMI ID = 296.1>

  
average form of 26.1: 1 and they occupy more than 95% of the total projected area.

  
Emulsion 5

  
To 6.0 liters of a well-stirred aqueous solution of bone gelatin at 1.5% by mass, containing 0.14 M KBr, a solution is added by double jet at constant rates.

  
1.15 M KBr and 1.10 M solution of AgN03; this addition is carried out in 16 min while maintaining the pBr at 0.85 to 55 [deg.] C, which consumes 3.4% of the total silver used. Then a double solution of 2.3 M solution is added. KBr and a 2.0 M solution of AgN03; this addition is carried out in approximately 25 min, with accelerated flow rates (multiplied by 5.0 between the start and the end), maintaining the pBr at 0.85 to 55 [deg.] C, which consumes 64.4% total money used.

  
A 2.0 M solution of silver nitrate is added at a constant flow rate, over approximately 15 minutes, until the pAg reaches 8.0 to 55 [deg.] C, which consumes 32.2% of the total money used.

  
A total of 4.66 moles of silver was used to prepare this emulsion.

  
  <EMI ID = 297.1>

  
and 0.85 liters of a solution of phthalylated gelatin at 15.3% by mass are added thereto, then it is washed by coagulation according to the method of US Patent 2,614,929.

  
0.8 liter of bone gelatin solution is then added

  
at 13.3% by mass and the pH is adjusted to 5.5 and the pAg to 8.1 at
40 [deg.] C.

  
The tabular silver bromide grains obtained have

  
  <EMI ID = 298.1>

  
95% of the total projected area.

  
Emulsion A (control)

  
To 2.2 liters of an aqueous solution of phthalylated gelatin 4.54% by mass, well stirred, at pH 5.6, the following is added:

  
  <EMI ID = 299.1>

  
AgN03; this addition is carried out while maintaining the temperature at 70 [deg.] C and the pAg at 8.3. The halide and nitrate solutions are added in stages, according to the process described in German patent application 2 107 118; the addition is carried out in seven stages of 4 min, increasing the flow rates according to the progression X, (no acceleration of the flow rates), 2.3 X; 4 X; 6.3 X; 9 X; 12.3 X and 16 X ml / min, between the start and the end of the addition.

  
About 7.0 moles of silver were used to prepare this emulsion.

  
After precipitation, add 0.4 liters of a

  
  <EMI ID = 300.1>

  
and the emulsion is washed twice by coagulation, according to the method of US patent 2,614,929. 2.0 liters of an aqueous solution of bone gelatin 10.5% are then added. mass and the pH is adjusted to 5.5 and the pAg

  
at 8.5 to 40 [deg.] C.

  
Emulsion B (control)

  
To 2.0 liters of an aqueous solution containing 1.25% by mass of gelatin of bone and 3.75% by mass of phthalylated gelatin, 558 g (0.6 mol) of emulsion A are added and stirred at pH 5.8.

  
A 3.5 M solution is then added by double jet.

  
KBr and 3.5 M AgN03 solution; this addition is carried out at 70 [deg.] C, maintaining the pAg at 8.3. The halide and nitrate solutions are added in stages, according to the process described in German patent application 2 107 118; the addition is carried out in seven stages of 4 min by increasing the flow rates according to the progression X; 1.2 X; 1.5 X; 1.8 X; 2.0 X; 2.4 X and 2.7 X ml / min between the start and the end of the addition.

  
About 6.4 moles of silver were used in addition to the seed grains to prepare this emulsion.

  
After the precipitation, 0.65 liters of an aqueous solution of phthalylated gelatin at 10% by mass are added at 40 ° C. and the emulsion is washed twice by coagulation according to the method of patent 2,614,929. then add 2.0 liters of an aqueous solution of bone gelatin at 10.5% by mass

  
  <EMI ID = 301.1>

  
Emulsion C (control)

  
A 2.0 liters of an aqueous solution containing 2.8%

  
by mass of bone gelatin and 2.2% by mass of phthalylated gelatin, 1169 g (1.3 mole) of emulsion B are added and the mixture is stirred at pH 5.7.

  
A 3.5 M solution of

  
  <EMI ID = 302.1>

  
genide and nitrate are added in stages according to the method of German patent application 2 107 118; the addition is carried out in twelve steps of 4 min by increasing the flow rates according to the progression X; 1.2 X; 1.3 X; 1.5 X; 1.6 X; 1.8 X; 1.9 X; 2.1 X; 2.3 X; 2.5 X; 2.7 X and 2.9 X ml / min between the start and the end.

  
5.7 moles of silver were used in addition to the seed grains to prepare this emulsion.

  
After precipitation, 406 deg C. is added 0.96 liter of an aqueous solution of phthalylated gelatin 10% by mass and the emulsion is washed twice by coagulation according to the method described in the patent of the United States. from America 2,614,929. 2.0 liters of an aqueous solution of bone gelatin at 10.5% by mass are then added and the pH is adjusted to 5.5 and the pAg to 8.5 to 40 [ deg.] C.

  
Emulsion D (control)

  
1.3 liters of aqueous gelatin solution
(5.07% by mass) 1395 g (1.4 mol) of emulsion C are added and the mixture is stirred at pH 5.3. Then added by double jet, keeping the pAg at 8.3 at 70 [deg.] C, a 3.5 M solution of KBr and a 3.5 solution of AgNO3. The halide and nitrate solutions are added for 60 min with accelerated flow rates
(multiplied by 1.86 between the beginning and the end), which consumes 89% of the total money used. The halide and nitrate solutions are then added at a constant rate for 5 min, which consumes 11% of the total silver used.

  
About 2.1 moles of silver were used in addition to the seed grains to prepare this emulsion.

  
After precipitation, 0.70 liter of an aqueous solution of phthalylated gelatin (10% by mass) is added to
40 [deg.] C and the emulsion is washed twice by coagulation according to the method of the patent of the United States of America 2,614,929.

  
1.0 liter of an aqueous solution of bone gelatin (10.5% by mass) is then added and the pH is adjusted to 5.5 and the pAg to 8.5 to 40 [deg.] C.

  
The physical characteristics of the tabular grain emulsions and of the control emulsions are collated in Table XVIII.

  

  <EMI ID = 303.1>


  

  <EMI ID = 304.1>


  

  <EMI ID = 305.1>
 

  
B. Awareness of emulsions

  
The AgBr emulsions with tabular grains and the AgBr control emulsions with octahedral grains are sensitized optimally, chemically, then spectrally in the green according to what is specified in Table XIX below.

  
The values are expressed in mg of sensitizer per mole of silver.

  

  <EMI ID = 306.1>


  

  <EMI ID = 307.1>


  

  <EMI ID = 308.1>
 

  
C. Emulsion layers

  
The tabular grain emulsions and the control emulsions are applied in a single layer on a cellulose triacetate support, at a rate per square meter of 1.07 g of silver.

  
and 2.15 g of gelatin. The layers also contain a solvent dispersion of a magenta image-forming coupler,

  
  <EMI ID = 309.1>

  
anti-veil, 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene

  
(sodium salt), at a rate of 3.6 g / mol of silver and 3.5 g / mol of silver of potassium 5-sec-octadecylhydroquinone-2-sulfonate.

  
Apply an overlay of gelatin (0.51 g / m <2>) and

  
tanned with 1% bis (vinylsulfonylmethylether) by

  
compared to total gelatin.

  
D. Comparison of the speed / granularity relationships

  
Using a tungsten light source from

  
  <EMI ID = 310.1>

  
layers for 1 / 100th s through a set consisting of a density scale from 0 to 3.0, a Wratten filter

  
N [deg.] 9 and a neutral filter with a density of 1.2. We treat with different durations, staggered between 1.5 min and

  
6 min at 37.7 [deg.] C in a developer of the type described in British Journal of Photography Annual, 1979, page 204, (chromogenic developer), so as to obtain harmonized haze levels.

  
Relative speed and granularity measurements are made independently at 0.25 density units above the web. The variation of the logarithm of the speed in the green, as a function of the granularity rms X 10 <3> is represented in figure 7. The logarithm of the speed is equal to 100 (1-log E), where E represents the exposure in lx.s to. a density of 0.25 above the veil. It is found that the tabular grain emulsions of silver bromide have a better speed / granularity relationship than that of the non-tabular control emulsions.

  
E. Separation of speed in blue and speed

  
in the blue minus

  
The emulations with tabular grains N [deg.] 1, 3, 4 and 5 are compared with the emulsions with non-tabular grains A, B and D, with regard to the separation of the velocities in blue and in blue minus. The emulsions are sensitized chemically and spectrally, in an optimal manner. They are applied in layers and exposed for 1 / 100th s in the blue region of the spectrum using a tungsten light source of 5500 [deg.] K with a power of 600 watts and a set consisting of a scale of densities from 0 to 3.0 and a Wratten N filter [deg.] 36 + 38 A. The exposure in the blue minus is carried out in the same way but with a Wratten N filter [deg.] 9 in place of the filter Wratten N [deg.] 36 + 38 A.

  
The chemical and spectral sensitizations were made as described above.

  
The samples are then processed the same

  
so that for the test relating to the evaluation of speed / granularity.

  
Relative speed values are measured

  
at 0.25 density unit above the veil. The sensitometric results are collated in Table XX.

  

  <EMI ID = 311.1>


  

  <EMI ID = 312.1>
 

  
The results of Table XX show that in the case of AgBr emulsions with tabular grains, the separation of the speed in blue and the speed in blue minus is better. Tabular grain AgBr emulsions of high shape index which have been optimally sensitized in the blue minus therefore exhibit a separation of sensitivity in blue and blue minus, better than that of non-tabular grain AgBr emulsions which have been optimally sensitized.

  
Examples illustrating the properties of silver bromoiodides with a uniform iodide distribution

  
A. Preparation of emulsions

  
Emulsion 1

  
To 30.0 liters of an aqueous solution of bone gelatin at 0.8% by mass and containing 0.10 M of KBr, well stirred, a solution is added by double jet and at constant flow rates

  
  <EMI ID = 313.1>

  
total used. 2.4 liters of a solution are then added.
20% by mass of phthalylated gelatin in the reactor and the mixture is stirred for 1 min at 75 [deg.] C. The silver nitrate solution is then added at a constant rate for approximately 5 min.

  
  <EMI ID = 314.1>

  
total money used. A double jet then adds a 1.06 M KBr aqueous solution additionally containing 0.14 M

  
  <EMI ID = 315.1>

  
tion with accelerated flow rates, multiplied by 2.4 between the start and the end of the addition, at pBr 1.36 and at 75 [deg.] C, in

  
50 min until the silver nitrate solution is used up, which consumes 92.8% of the total silver used.

  
A total of about 20 moles of silver were used to prepare this emulsion.

  
After precipitation, the emulsion is cooled to 35 [deg.] C, 350 g of phthalylated gelatin is added to it, the mixture is stirred and washed three times by coagulation according to the method described in US Patent 2,614 929. Then we add

  
2.0 liters of 12.3% w / w gelatin solution

  
  <EMI ID = 316.1>

  
more than 85% of the total projected surface of the silver bromoiodide grains present in the emulsion.

  
Emulsion 2

  
To 7.5 liters of a 0.8% by mass solution of well-stirred bone gelatin, further containing 0.10 M of KBr, a 1.20 M solution of KBr is added by double jet and 1.20 M AgN03; this addition is carried out at constant flow rate in 5 min at a

  
  <EMI ID = 317.1>

  
used. An aqueous solution of phthalylated gelatin is added
(0.7 liter, 17.1% by mass) then the emulsion is stirred for 1 min at 65 [deg.] C. A 1.20 M solution of silver nitrate at 65 [deg.] C is then added until a pBr of 1.36 is reached, which consumes 4.1% of the total silver used.

  
By double jet, a 1.06 M KBr solution also containing 0.14 M KI and a 1.20 M solution of AgN03 is then added.

  
This addition is carried out with accelerated flow rates multiplied by two between the start and the end of the addition, in 52 min at pBr 1.36 and 65 [deg.] C which consumes 93.5% of the total money used .

  
A total of about 5.0 moles of silver was used to prepare this emulsion.

  
After precipitation, the emulsion is cooled to 35 [deg.] C, the pH is adjusted to 3.7 and washed according to the method of US Patent 2,614,929. Then added

  
0.5 liters of a 17.6% phthalylated gelatin solution; then, after having stirred for 5 min, the emulsion is again cooled to 35 [deg.] C (pH 4.1) and washed by the same process as above. 0.7 liters of an aqueous solution are added <EMI ID = 318.1>

  
of bone gelatin at 11.4% by mass, then the pH is adjusted to 5.5 and the pAg to 8.3 to 40 [deg.] C.

  
The tabular grains of silver bromoiodide obtained

  
  <EMI ID = 319.1>

  
average of 0.11 m, an average shape index of 20: 1; they occupy more than 85% of the total projected area of

  
silver bromoiodide grains present in the emulsion.

  
Emulsion 3

  
To 7.5 liters of a well stirred solution of bone gelatin at 0.8% by mass, containing 0.10 M KBr, is added

  
1.20 M KBr solution and 1.20 M AgN03 solution; this addition is carried out by double jet with constant flow rates, in 5 min at pBr 1.0 and at 55 [deg.] C, which consumes 2.40% of the total silver used.

  
After adding 0.7 liters of an aqueous solution

  
of phthalylated gelatin at 17.1%, and stirred for 1 min at 55 [deg.] C, a 1.20 M solution of AgN03 is added at constant flow rates until a pBr of 1.36 is reached, which consumes 4 , 1% of the total money used. By double jet and with accelerated flow rates (multiplied by two between the start and the end of the addition), a 1.06 M KBr solution containing 0.6 M KI and a 1.20 solution are added in 52 min. M of AgN03; this addition is carried out at pBr 1.36 and 55 [deg.] C, which consumes
93.5% of the total money used.

  
About 5.0 moles of silver were used to prepare this emulsion.

  
After precipitation, the emulsion is cooled to 35 [deg.] C, the pH is adjusted to 3.7 and washed according to the method described in US Patent 2,614,929. 0.5 is added. liter of a phthalylated gelatin solution at 17.6% by mass and

  
after having stirred for 5 min, it is again cooled to

  
35 [deg.] C (pH 4.1) and washed as above. 0.7 liter of an aqueous solution of bone gelatin is then added.

  
at 11.4% by mass, the pH is adjusted to 5.5 and the pAg to 8.3 at
40 [deg.] C.

  
The silver bromoiodide emulsion obtained (88:12) comprises tabular grains with an average diameter of

  
  <EMI ID = 320.1>

  
average shape of 15.5: 1; these tabular grains occupy more than 85% of the total projected surface of the silver bromoiodide grains present in the emulsion.

  
Emulsion 4

  
7.5 liters of a well-stirred 0.8% w / w gelatin solution containing 0.10 M KBr are added

  
1.20 M KBr solution and 1.20 M solution

  
of AgN03. This addition is carried out by double jet and

  
with constant flow rates in 2.5 min at pBr 1.0 and at 55 [deg.] C,

  
which consumes 2.40% of the total amount of money used.

  
0.7 liters of an aqueous solution of phthalylated gelatin at 17.1% by mass are added, and the mixture is stirred for 1 min at 55 [deg.] C, then a 1.20 M solution of silver nitrate is added. at constant flow, until the pBr reaches 1.36, which consumes 4.1% of the total silver used.

  
A halide solution containing 1.06 M is added

  
of KBr and 0.14 M of KI and a solution containing 1.20 M of AgN03. This addition is carried out by double jet with accelerated flow rates multiplied by two between the start and the

  
end of the addition, in 52 min at pBr 1.36 and at 55 [deg.] C, which consumes 93.5% of the total silver used.

  
In total, about 5.0 moles of silver were used to prepare this emulsion.

  
After precipitation, the emulsion is cooled to 35 [deg.] C, the pH is adjusted to 3.7 and washed according to the method described in US Patent 2,614,929.

  
0.5 liters of a phthalylated gelatin solution at 17.6% by mass and the emulsion is redispersed at pH 6.0 and at 40 [deg.] C.

  
After having stirred for 5 min, the emulsion is again cooled to 35 [deg.] C (pH 4.1) and washed as above. 0.7 liters of an aqueous gelatin solution of bone are added

  
to 11.4% by mass and the pH is adjusted to 5.5 and the pAg to 8.3 to 40 [deg.] C.

  
The emulsion obtained comprises tabular grains

  
silver bromoiodide (88:12) with an average diameter

  
  <EMI ID = 321.1>

  
10: 1 average shape. These tabular grains occupy more than
55% of the total projected surface of the silver bromoiodide grains present in the emulsion.

  
Emulsion A (control)

  
9 liters of an aqueous solution of phthalylated gelatin at 1.7% by mass, containing 0.045 M KBr, 0.01 M KI and 0.11 M sodium thiocyanate are introduced into a reactor and stirred. The temperature is adjusted to 60 [deg.] C. A 1.46 M KBr solution containing 0.147 M KI and a 1.57 M solution of AgN03 is added by double jet; this addition is carried out in 40 min at 60 [deg.] C and with constant flow rates, which consumes 4.0 moles of silver. About 1 min before the end of the addition, the halide jet is stopped. After precipitation, the emulsion is cooled to 33 [deg.] C and washed twice according to the method described in the patent of the United States of America

  
2,614,929. 680 ml of a gelatin solution are then added.

  
  <EMI ID = 322.1>

  
Emulsion B (control)

  
The procedure is identical to that used to prepare emulsion A, except that the temperature is lowered to 50 [deg.] C and the total duration of addition is lowered to 20 min.

  
Emulsion C (control)

  
The procedure is identical to that used to prepare emulsion A, except that the temperature is lowered.

  
  <EMI ID = 323.1>

  
Emulsion D (control)

  
The procedure is identical to that used to prepare emulsion A, except that the temperature is raised to 75 [deg.] C. The total duration of the addition is 40 min.

  
The physical characteristics of the tabular grain emulsions and of the control emulsions are collated in Table XXI.

  

  <EMI ID = 324.1>


  

  <EMI ID = 325.1>


  

  <EMI ID = 326.1>
 

  
B. Formation of color images

  
Silver bromoiodide tabular grain emulsions and control emulsions are chemically sensitized.

  
  <EMI ID = 327.1>

  
provided in Table XXII. Tabular grain emulsions are spectrally sensitized to pAg 9.95 at

  
  <EMI ID = 328.1>

  
Control emulsions are spectrally sensitized after chemical sensitization and without adjusting the pAg. All values for the amount of sensitizer are expressed in mg / mole of silver.

  

  <EMI ID = 329.1>


  

  <EMI ID = 330.1>


  

  <EMI ID = 331.1>
 

  
The differences that appear in the sensitization, in Table XXII, are necessary to obtain the optimal sensitization in each of the emulsions. If the control emulsions had been sensitized chemically and spectrally in a manner identical to that of the emulsions

  
with tabular grains, their relative performances would not be optimal.

  
To show the results of identical sensitization of the control emulsions and of the tabular grain emulsions, samples of emulsion 2 and of emulsion C, hereinafter called emulsion 2x and emulsion Cx, are chemically and spectrally sensitized with in an identical manner as follows: Each emulsion is spectrally sensitized with 900 mg of dye A per mole of silver, at pAg 9.95 at 40 [deg.] C; the pAg is adjusted to 8.2 to 40 [deg.] C, then chemically sensitized for 20 min at 65 [deg.] C, 4.0 mg of potassium tetrachloroaurate per mole of silver, 12.0 mg of sodium thiosulfate pentahydrate per mole of silver and 100 mg

  
sodium thiocyanate per mole of silver.

  
Tabular grain emulsions and controls are applied separately to a cellulose triacetate film support to obtain two products with a single magenta layer, at a rate of 1.07 g of silver per square meter and 2.15 g of gelatin. per square meter. The products also contain a dispersion, in a solvent, of a coupler forming

  
  <EMI ID = 332.1>

  
(3-n-pentadecylphenoxy) -butyramido7-5-pyrazolone at a rate of 0.75 g per square meter, an anti-veil, the sodium salt of 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene at 3.6 g per mole of silver and a parasitic coloring inhibiting agent, potassium 5-sec-octadecylhydroquinone-2-sulfonate, at 3.5 g per mole of silver. The layers are covered with a layer of gelatin (0.51 g / m <2>) and is tanned with bis (vinylsulfonylmethyl) ether (1.5% relative to the total mass of gelatin).

  
  <EMI ID = 333.1>

  
1.5 min and 6 min to obtain concordant haze levels, using a color developer of the type described in The British Journal of Photography Annual, 1979, pages 204 to 206.

  
The granularity and the relative speed are independently measured, for a density of 0.25 above the veil. Figure 8 gives the logarithm of the speed in the green as a function of the RMS granularity multiplied by 10. As can be seen, the silver bromoiodide emulsions with tabular grains have a higher speed / granularity relationship than that of the control emulsions.

  
We must particularly compare the speed / granularity relationship of the 2x and Cx emulsions given in Figure 8. By sensitizing the 2x and Cx emulsions, chemically and spectrally, in an identical manner (unlike the optimal chemical and spectral sensitizations obtained individually in the case emulsions 2 and C), a speed / granularity relationship even greater than that of emulsion Cx (control) is obtained for the 2x emulsion (tabular grains). This is particularly surprising since the 2x and Cx emulsions have average grain volumes

  
  <EMI ID = 334.1>

  
vement.

  
The relative separations between the rapidities in the blue minus and the blue of the emulsions according to the invention and control are compared. For this, the sensitized and coated emulsions, as indicated above, are exposed to the blue region of the spectrum for 1 / 100th of a second to a tungsten light source of 600 W and 3000 [deg.] K behind a density scale of 0 to 3.0 (density ranges 0.15), a Wratten N filter [deg.] 36 + 38A and a neutral filter of density 1.0. The exposure to blue minus takes place in the same way with, however, the use of different filters
(Wratten filter n [deg.] 9 and neutral filter of density 1.8). The products are treated with a chromogenic developer of the type described in The British Journal of Photography Annual, 1979,

  
  <EMI ID = 335.1>

  
variable durations (1.5 min to 6 min). Curves giving the speed as a function of the veil are obtained and the relative velocities are recorded in blue and the blue minus, for a density of 0.2 above the veil. Table XXIII gives the sensitometric results.

TABLE XXIII

  

  <EMI ID = 336.1>


  
* 30 units of relative speed = 0.30 Log E

  
** A (speed) = speed in the minus blue minus

  
speed in the blue.

  
As shown in Table XXIII, silver bromoiodide emulsions with tabular grains show a separation between the velocities in the blue minus and the

  
blue and blue clearly superior to that of the control emulsions having the same halide composition. These results show that optimally sensitized tabular grain AgBr I emulsions of high shape index generally exhibit increased sensitivity in

  
spectrum region considered, relative to that of emulsion

  
  <EMI ID = 337.1>

  
optimal. If the iodide content decreases, a much greater separation between the velocities in

  
blue minus and blue, as has already been shown in previous examples.

  
We compare the sharpness of emulsions 1, 2 and 3 and

  
that of the control emulsions A, B, C and D. The sensitization, coating and treatment of these emulsions are those indicated above. The modulation transfer functions for an exposure in the green are obtained by exposing

  
  <EMI ID = 338.1>

  
second, at a modulation of 60% using a Wratten n [deg.] 99 filter. After processing, the accutance rates by cascade modulation transfer (CMT) are determined from the modulation transfer curves at magnification used for a 16 mm wide film.

  
The CMT acutance for the exposure in the green of the emulsions according to the invention is between 98.6 and 93.5:
that of the control emulsions is between 93.1 and 97.6. The values of the accutance CMT in the green of emulsions 2 and C, which have practically similar volumes per grain, are given in Table XXIV.

TABLE XXIV

  

  <EMI ID = 339.1>
 

  
C. Formation of argentic images

  
The pH of the control emulsions is adjusted to 6.2 and the pAg

  
at 8.2, at 40 [deg.] C. They are sensitized under the conditions indicated in Table XXV. They are sensitized chemically in an optimal way by the addition of tetrachloroaurate

  
potassium and sodium thiosulfate pentahydrate and

  
the emulsions are maintained at the temperature and for the duration indicated in Table XXV. &#65533; A spectral sensitization takes place by adding sodium salt of anhydroxide

  
  <EMI ID = 340.1>

  
pyl) oxacarbocyanine (dye A) and anhydro3-ethyl-9-methyl-3 '- (3-sulfobutyl) thiocarbocyanine hydroxide (dye B) in amounts indicated in Table XXV.

  
The emulsions with tabular grains are spectrally sensitized by adding dyes A and B to pAg 9.95 to

  
  <EMI ID = 341.1>

  
spectral sation by addition of sodium thiocyanate, sodium thiosulfate pentahydrate and potassium tetrachloroaurate, the temperature and duration conditions being given in Table XXV.

  

  <EMI ID = 342.1>


  

  <EMI ID = 343.1>


  

  <EMI ID = 344.1>
 

  
The emulsions are applied to a film support at the rate of 4.3 g of silver per square meter and 7.53 g of gelatin per square meter. All the layers are tanned with mucochloric acid (1.0% by mass relative to gelatin). Each layer is coated with a layer of gelatin
(0.89 g / m <2>).

  
The method for obtaining modulation transfer functions is described in Journal of Applied Photographic Engineering, 6 (1): 1-8, 1980.

  
The modulation transfer functions are obtained by

  
  <EMI ID = 345.1>

  
60% using a 1.2 density neutral filter. It is treated, for 6 min, at 20 [deg.] C, in a developer with N-methyl-p-aminophenol sulfate and hydroquinone (Developer Kodak D-76). After processing, the accutance rates by cascade modulation transfer (CMT) at the magnification used for a 35 mm wide film are determined from the modulation transfer curves (see table XXV).

  
The results given in Table XXV clearly show that better clarity is obtained with a black and white product containing a tabular grain emulsion.

  
To compare the speed / granularity relationships of analog images, separate samples of the layers described above are exposed for 1 / 100th of a second to a 600 W tungsten light source and

  
  <EMI ID = 346.1>

  
4.0. The samples are treated for 4 min, 6 min and 8 min,

  
at 20 [deg.] C in a developer with N-methyl-p-aminophenol sulfate and hydroquinone (Developer Kodak D-76). The relative velocities are measured for a density of 0.30 above the veil and the semispecular granularity rms is determined.

  
(in the green) for a density of 0.6 above the veil.

  
Figure 9 gives the logarithm of the speed as a function of the semispecular granularity rms (X10) for 6 min of development. The speed / granularity relationships of <EMI ID = 347.1>

  
lower than those of control AgBr I emulsions. With development times of 4 min and 8 min, similar results are obtained. In cases where the contrasts do not

  
are inconsistent, tabular grain emulsions have higher contrasts. This shows that the emulsions

  
Tabular grains with higher contrast have a greater granularity than would be obtained if the contrasts of the emulsions were consistent. So although Figure 9 shows that tabular grain emulsions are <EMI ID = 348.1>

  
where tabular grain emulsions present higher contrasts than those of control emulsions, all the superiority of their speed / granularity relationship cannot be demonstrated.

  
Example of an emulsion with a shape index of 175: 1

  
In this example, an emulsion of silver bromoiodide with tabular grains of high shape index is used. The

  
  <EMI ID = 349.1>

  
about 175: 1. These grains represent more than 95% of the total projected surface of the silver bromoiodide grains present.

  
The emulsion is chemically and spectrally sensitized

  
  <EMI ID = 350.1>

  
sodium cyanate (150 mg per mole of silver), triethylamine salt of anhydro-5,5-dichioro-3,3'-bis- hydroxide
(3-sulfopropyl) thiacyanine (850 mg per mole of silver), sodium thiosulfate pentahydrate (1.50 mg per mole of silver) and potassium tetrachloroaurate (0.75 mg per mole of silver).

  
A coupler is associated with the emulsion thus sensitized.

  
  <EMI ID = 351.1>

  
amido) -acetanilide (0.91 g per square meter), 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene (3.7 g per square meter), and

  
  <EMI ID = 352.1>

  
(3.4 g per mole of silver). The emulsion is coated on a polyester support at a rate of 1.35 g of silver per square meter and 2.58 g of gelatin per square meter. We apply

  
on the emulsion an overlay of gelatin (0.54 g / m <2>) containing bis (vinyl-sulfonylmethyl) ether (1.0% of total gelatin mass).

  
The dry product is exposed for 1 / 100th of a second,

  
to a tungsten light source of 500 W and 5500 [deg.] K, behind a graduated density scale associated with a neutral filter of density 1.0 and a Wratten 2B filter. The product is treated for 4.5 min at 37.8 [deg.] C in a chromogenic developer of the type described in The British Journal of Photography Annual 1979, pages 204 to 206. The product has a minimum density of 0.13, a maximum density of 1.45 and a contrast of 0.56.

CLAIMS

  
1. Photographic product with at least one emulsion layer comprising tabular grains of silver halides and a dispersion medium, characterized in that at least 50% of the total projected surface of the grains of silver halides consists of tabular grains chemically and spectrally sensitized, of which

  
  <EMI ID = 353.1>

  
by 8: 1, the shape index being the ratio of the diameter to the thickness of the grain and the diameter of the grain being the diameter of a circle whose surface is equal to the projected surface of the grain.


    

Claims (51)

1 to 20, characterized in that the grains are chemically sensitized in the presence of at least part of the amount of the dye used for spectral sensitization. 1 to 12, characterized in that the tabular silver halum grains are chemically sensitized in the presence of a ripening agent. 1 to 11, characterized in that the tabular grains  <EMI ID = 355.1> a noble metal, a chalcogen, a reduction sensitizer or a combination of these sensitizers. 2. Product according to claim 1, characterized in what the tabular grains which represent at least 50% of the total projected surface has a thickness <EMI ID = 354.1> 3. Product according to one of claims 1 or 2, characterized in that the emulsion consists of grains silver bromide. 4. Product according to one of claims 1 or 2, characterized in that the emulsion consists of silver bromoiodide grains. 5. Product according to one of claims 1 to 4, characterized in that the tabular grains of the emulsion have an average shape index of at least 12: 1. 6. Product according to one of claims 1 to 4, characterized in that the tabular grains of the emulsion have an average shape index of at least 20: 1. 7. Product according to one of claims 1 to 6, characterized in that the tabular grains of the emulsion layer represent at least 70% of the total projected surface of the silver halide grains. 8. Product according to one of claims 1 to 6, characterized in that the tabular grains of the emulsion layer represent at least 90% of the total projected surface of the silver halide grains. 8: 1 and occupy at least 50% of the total projected area of the silver halide grains. 8, characterized in that the silver halide grains comprise up to 40% by mole of iodide. 9. Product according to one of claims 1, 2 and 4 to 10. Product according to one of claims 1 to 9, characterized in that the internal part of the silver halide grains is doped with a compound modifying the sensitivity. 11. Product according to claim 10, characterized in that the internal part of the grains is doped with a noble metal from group VIII of the periodic table. 12: 1, represent at least 70% of the total projected surface of the silver bromoiodide grains present in the same emulsion layer, and are chemically sensitized on the surface with gold and at least one sulfur and selenium, - the product is practically free of yellow filter substance between the incident exposure radiation and the emulsion layers recording the green and the red of the set of three layers. 12: 1 and which occupy at least 70% of the total projected surface of the bromide or silver bromoiodide grains of this layer and at least one of the tabular grain emulsion layers of bromide or silver bromoiodide is placed to receive, during exposure of the photographic product to a color temperature  <EMI ID = 363.1> that the layer is intended to record, 0 log E for said emulsion layer being less than 0.6, where A log E = log ET - log EB log AND being the logarithm of the exposure to red or green light that said emulsion layer is intended to record, and  <EMI ID = 364.1> blue light from said emulsion layer. 12. Product according to any one of the claims 13. Product according to any one of the claims 14. Product according to claim 13, characterized in that the ripening agent contains sulfur. 15. Product according to one of claims 1 to 13, characterized in that the grains of the emulsion are sensitized optimally, chemically and spectrally, up to 60% of the maximum of the logarithm of the speed that can be obtained with these grains in the region of spectral sensitization. 16. Product according to claim 4, characterized in what the silver bromoiodide grains comprise from 0.1 to 20% by mole of iodide and in.  <EMI ID = 356.1> an average aspect ratio of at least 12: 1, occupy at least 70% of the total projected area of the silver halide grains. 17. Product according to one of claims 1 to 16, characterized in that a blue sensitizer is adsorbed on the surface of the tabular grains of bromide or silver bromoiodide. 18. Product according to one of claims 1 to 17, characterized in that the blue sensitizer is chosen from the class consisting of the dyes cyanine, merocyanine, hemioxonol, merostyryl, hemicyanin. 19. Product according to one of claims 1 to 18, characterized by the following points: - the tabular grains of the emulsion are grains of silver bromoiodide containing up to 40% by mole of iodide, the thickness of which is less than 0.3 μm, the <EMI ID = 357.1 > at least 12: 1 and occupy at least 50% of the total projected area of the silver bromoiodide grains; these grains are sensitized optimally, chemically with gold in combination with at least one sulfur or selenium sensitizer, in the presence of a thiocyanate as maturation agent, and spectrally with a spectral sensitizer having a peak of absorption in the blue minus of the spectrum. 20. Photographic product conforming to any of the Claims 1 to 19, characterized in that the tabular grains have an average shape index of between 20: 1 and 100: 1. 21. Product according to any one of the claims 22. Photographic product conforming to any one of the Claims 1 to 21, characterized in that an additional silver halide is present on the surface of the silver bromoiodide grains in an amount sufficient to increase the sensitivity. 23. Product according to one of claims 11 to 21, characterized in that the tabular grains contain rhodium in an amount causing an increase in contrast. 24. Product according to one of claims 1 to 23 comprising a first layer of silver halide emulsion arranged to receive light which is transmitted without diffusion and a second layer arranged to receive light transmitted through this layer, characterized in that at least this first layer contains tabular grains of chemically and spectrally sensitized silver halides, the thickness of which  <EMI ID = 358.1> the average shape index greater than 8: 1 and which occupy at least 50% of the total projected surface of the silver halide grains. 25. Product according to claim 24, characterized in what tabular silver halide grains have  <EMI ID = 359.1> 26. Product according to one of claims 1 to 25, for black and white photography, characterized in that the tabular grains of silver bromoiodide are optimally sensitized chemically and spectrally, orthochromatically or pantachromatically. 27. Product according to claim 26, for black and white photography, characterized in that the emulsion layer comprising the tabular grains is arranged to receive during the exposure a light not diffused or practically not diffused by a layer arranged above. 28. Product according to claim 26, for black and white photography, characterized in that the emulsion layer containing the tabular grains of silver halides is the outermost layer of the photographic product. 29. Product conforms to one of claims 26 to 28, characterized in that the emulsion layer containing the tabular grains is arranged so as to receive the incident light during the exposure within the limits of a capture angle less than 10 [deg.]. 30 to 35, characterized in that the tabular grains of silver halides are chemically sensitized at the surface with a gold sensitizer and at least one sulfur or selenium sensitizer. 30. Product according to one of claims 1 to 25, for color photography, comprising emulsion layers for separately recording blue, green and red; the emulsion layers recording green and red respectively containing spectral sensitizing dyes for green and for red, characterized in that at least one of the emulsion layers recording green and red contains tabular grains of chemically and spectrally sensitized silver halides of lesser thickness  <EMI ID = 360.1> of the total projected area of the silver halide grains. 31. Product according to claim 30, characterized in that one of the emulsion layers containing the tabular silver halide grains is placed to receive the exposure radiation before the other emulsion layers of the product. 32. Product according to claim 30, characterized in that one of the emulsion layers containing the tabular grains of silver bromoiodide is placed to receive light transmitted without diffusion, and is situated above at least one other emulsion layer of the photographic product. 33. Product according to one of claims 30 to 32, characterized in that the blue recording emulsion layer comprises tabular grains of chemically and spectrally sensitized silver halides of which  <EMI ID = 361.1> 34. Product according to one of claims 30 to 33, characterized in that at least one of the emulsion layers recording red and green comprises grains of bromide or silver bromoiodide. 35. Product according to claim 34, characterized in what grains of bromide or silver bromoiodide optimal are chemically and spectrally optimal sensitized 36. Product according to any one of the claims 37. Product according to one of claims 30 to 36, characterized in that it comprises tabular grains of silver bromoiodide sensitized chemically in an optimal manner in the presence of a ripening agent containing sulfur. 38. Product according to claim 37, characterized in that the ripening agent is a thiocyanate. 39. Product according to one of claims 30 to 38, characterized in that at least one of the emulsion layers registering green or red contains tabular bromide or silver bromoiodide grains chemically or spectrally sensitized, having <EMI ID = 362.1> 40. Product according to claim 39, characterized in that the product contains a quantity of yellow filter less than the usual quantity or is free of yellow filter substance, between the radiation of incident exposure and at least one of the emulsion layers containing tabular grains. 41. Product according to claims 39 or 40, characterized in that at least one of the layers containing the tabular grains of silver bromide or bromoiodide is placed to receive the exposure radiation before the blue-recording emulsion layer. 42. Product according to claims 39 or 40, characterized  <EMI ID = 365.1> Silver bromide or bromide broth is placed to receive exposure radiation before all other layers of silver halide emulsion in the photographic product. 43. Product according to one of claims 39 to 42, characterized in that the tabular grains of bromide or silver bromoiodide are present in the emulsion layer registering green and / or the emulsion layer registering red. 44. Product according to claims 30 to 43, formed of a support and elements of dye-forming layers separately recording blue, green and red, chosen so that after exposure of the product  <EMI ID = 366.1> spectrally non-selective density scale / treatment the product presents, compared to its contrast and its speed in blue, variations in contrast in green and in red less than 20% and variations in speed in green and in red less than 0.3 log E, these variations in contrast and speed being determined by measuring the blue, green and red densities in accordance with the American standard PH2.1.1952, each dye-forming element comprising at least one emulsion layer consisting of a dispersion medium and of silver halide grains, the silver halide grains of at least one set of three emulsion layers separately recording blue, green and red being placed to receive exposure radiation before any other layer  <EMI ID = 367.1> characterized by the following points: - the silver bromoiodide grains in the layers recording the green and the red of said set of three <EMI ID = 368.1> 45. Product according to claim 44, characterized in that the dye-forming elements recording the green and the red of a set of three elements exhibit a speed in the blue minus greater than at least ten times their speed in the blue. 46. Product according to claim 44, characterized in that that the elements of dye-forming layers recording the green and the red of a set of three elements exhibit a speed in the blue minus at least twenty times greater than their speed in the blue. 47. Product according to claim 44, characterized in that the speed in blue of recording the blue provided by the product is at least six times greater than the speed in blue of recording the blue minus provided by the product. 48. Product according to claim 47, characterized in that the speed in blue of recording the blue provided by the product is at least eight times greater than the speed in blue of recording the blue minus provided by the product. 49. Product according to one of claims 44 to 48, characterized in that the dye forming layer elements recording blue, green and red separately contain couplers forming dyes yellow, magenta and blue-green respectively. 50. Product according to one of claims 44 to 49, characterized in that the emulsion layer recording elements the blue of a set of three / contains a higher mole percentage of iodide than the emulsion layers recording green and red of this set of three elements. 51. Product according to one of claims 44 to 50, characterized in that one of the emulsion layers of a set of three elements is arranged to receive practically all the radiation sent to the product to expose it.