US3403025A - Desensitization of silver halides to visible radiation with thiuram disulfides - Google Patents

Description

United States Patent 3,403,025 DESENSITIZATION OF SILVER HALIDES TO VISIBLE RADIATION WITH THIU- RAM DISULFIDES William W. Rees and William H. Russell, Rochester, N .Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Aug. 25, 1965, Ser. No. 482,632 20 Claims. (Cl. 96-101) ABSTRACT OF THE DISCLOSURE The photographic sensitivity of silver halides to visible radiation with a combination of a thiuram disulfide silver halide desensitizer and a piazine is disclosed. X-ray sensitive materials employing such silver halides exhibit improved room-light handling characteristics.

This invention relates to reducing the sensitivity of silver halides to visible radiation and compositions which are useful for this purpose. In one of its aspects, this invention relates to photographic silver halide emulsions and elements which can be used in radiography. In another of its aspects, this invention relates to X-ray sensitive photographic elements which have materially reduced sensitivity to visible radiation.

It is known that photographic'silver halides, particularly those employed in photographic silver halide emulsions designed for use in radiography, can be substantially desensitized to visible radiation without substantially affecting their sensitivity to X-rays. For example, US. Patent 3,184,313, issued May 18, 1965, discloses the use of thiuram disulfides to reduce the sensitivity of photographic silver halide emulsions to visible radiation. The thiuram disulfide silver halide desensitizers have the advantage of only slightly lowering the sensitivity of X-ray sensitive elements to X-rays while materially reducing their sensitivity to visible radiation. X-ray sensitive elements containing these thiuram disulfides can be easily handled under ordinary safelight conditions while dry. However, X-ray sensitive elements containing thiuram disulfides are not completely protected against visible radiation while wet, i.e., during processing. It is evident that it would be desirable to protect X-ray sensitive elements against the adverse effects of visible light during all stages of handling, i.e., in both dry and wet stages.

Accordingly, it is an object of this invention to provide a composition which materially reduces the sensitivity of silver halides to visible radiation.

It is another object of this invention to provide X-ray sensitive elements which are stabilized against the effects of visible radiation during both dry and wet handling of the element.

It is another object of this invention to provide a photographic silver halide emulsion which is desensitized to visible radiation without any substantial reduction in sensitivity to X-rays.

It is a further object of this invention to provide an X-ray sensitive photographic element which combines good X-ray speed stability during storage with good stability against the effects of visible radiation during both dry and wet handling.

It is another object of this invention to provide a combination of desensitizing materials which will materially reduce the sensitivity of silver halides to visible radiation without adversely affecting sensitivity to X-rays.

It is another object of this invention to provide photographic silver halide emulsions and elements which contain a combination of a thiuram disulfide and a piazine which combination materially reduces the photographic sensitivity of photographic silver halides to visible radiation without adversely affecting their sensitivity to X-rays.

Other objects of this invention will be apparent from an examination of the specification and claims which follow.

In accordance with this invention it has been found that a combination comprising a thiuram disulfide and a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically will materially reduce the sensitivity of photographic silver halides to visible radiation without any substantial adverse effect on X-ray sensitivity.

In one embodiment of this invention, the aforementioned combination is employed to desensitize a photographic silver halide emulsion to visible radiation. Another embodiment of this invention relates to a photographic element comprising a support and a photographic silver halide layer desensitized to visible radiation with a combination of a thiuram disulfide silver halide desensitizer and a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

A significant feature of this invention is that the thiuram disulfide silver halide desensitizer and the piazine must be used in combination to protect X-ray sensitive materials from the adverse effects of visible radiation during all stages of handling, i.e., in the dry and wet stages, and also to stabilize the X-ray speed of the element during storage. Thus, as shown in the following working examples, the thiuram disulfides are effective to stabilize the speed and fog of a silver halide emulsion during dry handling but they do not give good X-ray speed stability during storage. Conversely, the piazine imparts good wet stability but gives very poor incubation speed stability.

The disulfide compounds employed in the pnactice of this invention are thiuram disulfide silver halide desensitizers. Typical thiuram disulfide silver halide desensitizers are disclosed in US. Patent 3,184,313, issued May 18, 1965. These compounds are characterized by marked desensitizing action toward silver halide emulsions insofar as their sensitivity to visible radiation is concerned (particularly in the blue region of the spectrum) while retaining substantially the sensitivity of the emulsions to X-rays. The concentration of thiuram disulfide silver halide desensitizer employed is subject to wide variation depending upon the particular silver halide used, the amount of gelatin or other colloidal binder and other variables. In general, quite useful results can be obtained at concentrations as low as 2 mg. per mole of silver halide, while concentrations as high as mg. per mole of silver halide can be used without adversely affecting the X-ray sensitivity too seriously. The preferred range of thiuram disulfide employed in the practice of this invention is in the range of about 20 to about 30 mg. of thiuram disulfide per mole of silver halide. As already indicated, silver halide desensitizers are employed in combination with the piazines described herein. While the concentration of the thiuram disulfide and the piazine in the combination can be widely varied, it is prefer-red that the major component of the combination be thiuram disulfide, useful results being obtained with combinations in which the weight ratio of thiuram disulfide to piazine is in the range of about 2:1 to about 20: 1, preferably about 2:1 to about 10:1. Typical thiuram disulfide desensitizers which can be employed in the practice of this invention include those represented by the following general formula:

wherein R and R each represents an alkyl group, such as methyl, ethyl, propyl, butyl isobutyl, etc. (e.g., an alkyl group containing from 1 to 4 carbon atoms), an aryl group, such as phenyl, tolyl, etc., or together R and R represent the atoms necessary to complete an azine ring, such as morpholine, piperidine, etc., or, alternatively, a pyrrolidine ring, for example. The thiuram disulfide compounds are characterized in that the nitrogen atoms thereof are tertiary nitrogen atoms. Typical compounds included by the above general formula are, for example, the following:

The piazines employed in the practice of this invention are heterocyclic compounds having two nitrogen atoms in the para position. The pi azines contain a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically and can be in the free or quaternized form. Where reference is made in the specification and claims to a piazine containing a pyrazine ring to which two 6membere-d carbocyclic rings are fused symmetrically, it is intended to include the compound in its free or quaternized form. As shown in the formulas which follow, the pyrazine ring in the piazine is fused to two symmetrical carbocyclic rings which can be unsubstituted, as in phenazine, or substituted by a variety of substituents including one or more other carbocyclic rings, for example, one or two fused aromatic rings as in naphtho-phenazine and naphthazine. Examples of substituents which can be present to form the resulting substituted phenazines or napthazines include amino, hydroxy, methyl amino, ethyl amino, meth yl, ethyl, dodecyl, carboxyethyl, sulfopropyl, sulfobutyl, phenyl, benzyl, acetyl, and the like. It is obvious that the nature of the substituents on the two 6-membered fused rings in the piazine is subject to wide variation. However, it can be seen that these piazines are characterized by a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

Piazines having up to about 24 carbon atoms, preferably 12 to 20 carbon atoms, give particularly advantageous results in the practice of this invention. Piazines which are particularly useful in the practice of this invention can be represented by the following formulas:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of 0 to 2.

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6- membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of (l to 2 and z is an integer of 0 to l. The piazines containing other rings which are fused to the 6-rnembered carbocyclic rings which are in turn fused to the pyrazine ring can also be represented by the formula:

where each of a, b, c and d is an integer of 0 to 1 and each Z represents the non-metallic atoms necessary to form a 6-membered carbocyclic ring,

where Z, a, b, c and d are as defined above, R is alkyl, hydroxyalkyl or aryl, z is an integer of O to 1 and X is an anion such as halogen, chlorate, sulfate, methyl sulfate, p-toluene sulfonate and the like.

Like the thiuram disulfides, the concentration of piazine employed in the practice of this invention is subject to wide variation. In general, however, quite useful results can be obtained with concentrations in the range of about 1 to about 50, preferably about 2 to about 10 mg. per mole of silver halide. As previously indicated, it is preferred that the desensitizing combination contain a minor portion of the piazine in comparison to the thiuram disulfide. Typical piazines which can be employed in the practice of this invention include the following:

phenazine 2-hydroxyphenazine 2,3-diaminophenazine 3-amino-2-hydroxyphenazine 3,6-diaminophenazine 3-amino-7-dimethylaminophenazine 2-methy1-3-amino-7-dimethylaminophenazine naphtho-phenazine naphthazine phenanthrophenazinc 2,3-dihydroxyphenazine 2-acetamino-3-acetoxyphenazine 1,3-diamino-5-methy|1phenazinium chloride 1,3-diamino-S-phenylphenazinium chloride 3,7-diamino-5-phenylphenazinium chloride 2,8-dimethyl-3,7-diamino-5-phenylphenazinium chloride H30 CH3 3-amino-7-phenylamino-5-phenylphenazinium chloride 2,3,7,8-phenylamino-5-phenylphenazinium chloride 1,3-diamino-5-ethylphenazinium chloride 7 1,3-diamino--p-hydroxyethylphenazinium chloride oi- \le@/ -NH3 OH 1,3-diamino-5-benzylphenazinium chloride 2 K l 01- wii The desensitizing combination of this invention can be used to materially reduce the sensitivity to visible radiation of any of the dilterent types of photographic silver halides. For example, silver halides such as silver chlo ride, silver bromide, silver chlorobromide, and the like can be employed in practicing this invention although iodide containing photographic silver halide emulsions are especially useful. Such emulsions include silver bromoiodide, silver chloroiodide, silver chlorobromide and the like. Photographic silver halide emulsions which form the latent image predominantly Within the silver halide grain can be usefully employed in the practice of this invention. Such internal latent image emulsions are described in Davey and Knott U.S. Patent 2,592,250 issued Apr. 8, 1952.

The photographic silver halides desensitized according to the practice of this invention can be dispersed in any of the conventional hydrophilic water permeable binding materials, particularly those employed in the preparation of photographic silver halide emulsions and elements, as exemplified by gelatin, colloidal albumin, cellulose derivatives, synthetic resins such as polyvinyl coumpounds, acrylamide polymers and the like as well as mixtures of these materials. Such binding materials are generally employed in coating photographic silver halides on supports. However, photographic silver halides which are coated in the absence of such binding materials, for example, those coated by vacuum deposition, can be readily desensitized according to the practice of this invention.

The photographic silver halides employed in the practice of this invention can be coated on a wide variety of supports in preparing photographic elements. The silver halides can be coated on one or both sides of the support, which is preferably transparent and flexible. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film, and related films or resinous materials as well as glass, paper, metal and the like. Supports such as paper which are coated with a-olefin polymers, particularly polymers of a-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene-butene copolymers and the like, can also be employed.

In order to decrease still further the sensitivity of the silver halide emulsions of our invention to visible radiation, a small amount of a light-absorbing organic dye can be employed either in the emulsion or in an overcoating layer. Since the silver halide emulsions of our invention may retain some sensitivity in the blue region of the spectrum, it has been found that many azo dyes, such as tartrazine, can be usefully employed. Other visible radiation absorbing dyes which can be employed in such arrangements are 2-(2-methoxy styryl) quinoline hydrochloride, the condensation product of two molecular proportions of quinaldine methosulfate and one molecular proportion of 4,4-diphenyl dialdehyde pyridine, 4,4- methenyl bis (1 naphthyl-3-methylpyrazoline-5 etc. Other light-absorbing dyes are described in Dostes and Pfafi U.S. application Ser. No. 83,709, filed Ian. 19, 1961. The amount of light-absorbing dye used to reduce the sensitivity of our photographic elements can vary as de scribed in said U.S. application Ser. No. 83,709. Instead of using a dyed silver halide emulsion layer or a dyed overcoating layer to protect further the radiographic sensitive layer, it is possible to use a light-absorbing silver halide emulsion layer which has very low sensitivity to visible radiation. Lippmann-type emulsions can conveniently be employed for this purpose. Silver iodide-containing emulsion layers are also useful for this purpose.

The photographic silver halide emulsions described herein can be chemically sensitized with compounds of the sulfur group, noble metal salts such as gold salts, reduction sensitized with reducing agents, and combinations of these. Furthermore, emulsion layers and other layers present in photographic elements made according to this invention can be hardened with any suitable hard ener such as aldehyde hardeners, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxystarch, oxy plant gums, and the like.

The photographic silver halide emulsions can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, stabilizers or antifoggants, particularly the water soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in U.S. Patent 2,829,404, the substituted triazaindolizines as disclosed in U.S. Patents 2,444,605 and 2,444,607, speed increasing materials, plasticizers and the like. Sensitizers which give particularly good results in photographic compositions are the alkylene oxide polymers which can be employed alone or in combination with other materials, such as quaternary ammonium salts, as disclosed in U.S. Patent 2,886,437 or with mercury compounds and nitrogen containing compounds, as disclosed in U.S. Patent 2,751,299.

This invention can be further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLE 1 As already indicated, the thiuram disulfides or piazines alone, will not combine good X-ray speed stability during storage with protection against visible radiation during both wet and dry handling. To illustrate, an ordinary coarse-grained silver bromoiodide emulsion of the type normally used in radiography, which is chemically sensitized to its optimum speed, is divided into three portions. One portion of emulsion is untreated and serves as a control. Another portion, A, is treated with 22.5 mg. of bis(dimethylthiocarbamyl) disulfide per mole of silver halide. The remaining portion, B, is treated with 20 mg. of 1,3-diamino5-methylphenazinium chloride per mole of silver halide.

Each of the three portions of emulsion is coated on an ordinary cellulose acetate film support and the coatings are dried. The coatings are then divided into five samples, each of which is tested in the following manner:

Test l.--Exposure to kv. X-rays. Processed for 6 minutes in an ordinary MQ developer, i.e., a developer containing hydroquinone and N-methyl-p-aminophenol sulfate, such as Kodak Developer D-19b to which is added a small concentration of alkali to increase the pH to about 11.0. After development, the samples are fixed, washed and dried in the usual manner. The speeds of the samples are measured at a density of 0.85 above fog, the

initial control speed being taken as 100 in each case.

Test 2.A low-intensity light exposure of 60 seconds in an intensity scale sensitometer to a 500-watt bulb of the type normally used in radiography, but having a greater sensitivity than the emulsion described in Example 1, is prepared and divided into eight portions. These portions of emulsionare then treated as described below:

modulated with a 2.27 neutral density filter. Processed as 5 described in Test 1.

Test 3.-The samples are incubated for 2 weeks at Portion Treatment 120 F., 50% relative humidity before exposure and I N further t eatment. Control. processing as describedinTest 2. II 20 mg. 1,3-diamino methylphenazinium Test 4.Dry safelight test. This test consists of exchloride per mole of silver halide. posure of the dry element to a safelight containing a 25- III 30.6 mg. of bis(morpholinothiocarbamyl) diwatt bulb modulated by a Morlite Filter I-11814 (desulfide per mole of silver halide. scribed hereinafter) for 16 minutes at a distance of two IV 30.6 mg. of bis(morpholinothiocarbamyl) difeet from the film plane. Processing is as described in ulfide per mole of silver plus 2.0 mg. of Test 1. 1,3 diamino-5-methylphenaziniun1 chloride Test 5.--Wet safelight test. This test consists of exper mole of silver halide. posure of the element while immersed in Kodak De- V 30.6 mg. of bis(morpholinothiocarbamyl) diveloper D-19b to a safelight containing a -watt bulb sulfide per mole of silver halide plus 4.0 mg. modulated by a Morlite Filter I-11814 for three minutes of 1,3-diamino-S-methylphenazinium chloin a white tray at a distance of two feet from the film 20 ride per mole of silver halide. plane. After development the samples are fixed, washed VI 30.6 mg. of bis(morpholinothiocarbamyl) di and dried in the usual manner. sulfide per mole of silver halide plus 2.0 mg.

Test 1 Test 2 Test 3 Test 4, Test 5, Portion gross gross Speed Fog Speed Fog Speed Fog density density Control 100 0.07 100 0.14 166 0.10 2.70 1. 54 A 07 0. 04 2. 4 0. 14 4. s 0. 14 0. 14 0. 39 B 76 0. 02 4. 4 0. 14 18.0 0. 14 0. 15 0. 10

1 Base density=0.l3.

EXAMPLE 2 of 1,3-diamino-S-ethylphenazinium chlo- 'de per mole of silver halide. The combination of thiuram disulfides and piazlnes n described herein impart to photographic silver halide ele VII of bls(morpt.lolmothl.ocarbamyl) sulfide per mole of silver halide plus 4.0 mg. ments and emulsions good X-ray speed stability upon of 13 diamino 5 eth l henazinium hloride storage and protection against visible radiation during er of Sn erh y c both wet and dry handling. To illustrate, several addi- P e v a 1 tional coatings similar to Portion A described in Ex- 40 VIII 30.6 mg. of bis(morpholinothiocarbamyl) diample l are prepared. One portion remains unchanged to sulfide per mole of silver halide plus 8.0 mg. serve as a control. Three other portions are treated with of l,3-diamino-S-ethylphenazinium chloride the varying concentrations of the piazines identified per mole of silver halide. below. The coatings are exposed and processed as described in Tests 1-5 listed in Example 1 to give the fol- Samples of each of the above emulsions are coated on lowing results: an ordinary cellulose acetate film support and the coatings 1 rd Testl Test2 Test?! Test 4, Test 5, Addenda (mg'lmo e-sflver ha 1 9) Speed Fog Speed Fog Speed Fog de iii i ti 1 d ii ifiy 1 00111101 100 .02 100 .12 182 .12 0.14 0. 40 22.02%:l'fififfiiifliil?Tit???i if i 102 .02 00 .12 101 .12 0.14 0. 22 iiifi 107 .02 95 .12 191 .12 0.14 0.17

1 Base density=0.l3.

Similar results are obtained when bis(dimethylthioexposed and processed as described in Tests 1-5 of Excarbamyl disulfide is replaced in the above procedure ample 1. The following results are obtained: with bis(diisobutylthiocarbamyl) disulfide, bis(l-piperidylthiocarbonyl) disulfide, bis(diethylthiocarbamyl) dl- Portion igl g g g. T st 5, sulfide, bis(N-methyl-N-phenylthiocarbamyl) disulfide p p 9 i l 55%; x and bis(diphenylthiocarbamyl) disulfide. Other piaz nes m0 135 4 00 1 10 such as phenazine, 2-hydroxyphenazine, 2,3-d1am1no 65 H 82 me phenazine, 3-amino-2-hydroxyphenazine, 3,6-d1am1no- 3i -g g-g 3%: gphenazine, l,3-diamino-5-phenylphenazinium chloride, 410 51s 0114 0:15 3,7-diamino-S-phenylphenazinium chloride, 2,8-dimethylg1 g-g g}: g-fg 3,7-diamino-S-phenylphenazinium chloride, 3-amino-7- 94 515 51s 9114 0:10 phenylamino-S-phenylphenazinium chloride and 2,3,7,8- 70 lBase dmsity=o 13 phenylamino-5-phenylphenaz1n1um chloride can also be employed 1n the above procedure to obtain similar results. It can be seen from the above results that the combinations of this invention give the desired safeli ht rotection EXAMPLE 3 g P 1 both Wet and y, ompanied by excellent incubation An ordinary coarse-gram silver bromo1od1de emulsion 7 stability and an X-ray sensitivity.

Kodak Developer D19b has the following composi tion:

Grams N-methyl-p-aminophenol sulfate 2.2 Hydroquinone 8.8 Sodium sulfate anhydrous 72.0 Sodium carbonate crystalline 130.0 Potassium bromide 4.0

Water to make 1 liter.

For use in the present invention, this developer is found most effective when the pH is raised slightly to 11.0 by the addition of additional alkali.

The Morlite 1-11814 Safelight Filter transmits visible radiation principally between about 540 and 700 m with maximum transmission at from about 580 to 700 (density of about 0.1 in this range).

Thus, by the practice of this invention there is provided a means for reducing the sensitivity of silver halides to visible radiation without deleteriously affecting their sensitivity to X-rays. This invention makes it possible to protect X-ray sensitive elements from the adverse effects of visible radiation in all stages of processing, i.e., in both the dry and wet stages.

Although the invention has been described in con siderable detail with reference to certain preferred embodiments thereof it will be understood that variations and modifications can be eifected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic silver halide emulsion desensitized to visible radiation with a thiuram disulfide silver halide desensitizer and a piazine containing a pyrazine ring to which two 6-mernbered carbocyclic rings are fused symmetrically.

2. A photographic silver halide emulsion desensitized to visible radiation with a thiuram disulfide silver halide desensitizer and a piazine having up to 24 carbon atoms and containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

3. A photographic silver halide emulsion desensitized to visible radiation with a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having up to 24 carbon atoms and containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically, the concentration of said thiuram disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

4. A photographic silver halide emulsion desensitized to visible radiation with a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-merr1- bered carbocyclic ring and each n is an integer of to 2, the concentration of said thiuram disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said thiuram disulfide to said piazine being in the range of about 2: 1 to about 20: 1.

5. A photographic silver halide emulsion desensitized to visible radiation with a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of 0 to 2 and z is an integer of 0 to 1, the concentration of said thiuram disulfide being in the range of about 2 to about mg. per mole of silver halide and the weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

6. A photographic silver halide emulsion desensitized to visible radiation with bis(dimethy1thiocarbamyl)disulfide and 1,3-diarnino-5-methyl phenazinium chloride, the concentration of said disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20: l.

7. A photographic silver halide emulsion desensitized to visible radiation with bis(morpholinothio carbarnyl) disulfide and 1,3-diamino-5-methyl phenazinium chloride, the concentration of said disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20: 1.

8. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with a thiuram disulfide silver halide desensitizer and a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

9. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with a thiuram disulfide silver halide desensitizer and a piazine having up to 24 carbon atoms and containing a pyrazine ring to which two 6-rnembered carbocyclic rings are fused symmetrically.

10. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with a thiuram disulfide silver halide desensitizer and a piazine having up to 24 carbon atoms and containing a pyrazine ring to which two G-membered carbocyclic rings are fused symmetrically, the concentration of said thiuram disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

11. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of 0 to 2, the concentration of said thiuram disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and Ithe weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

12. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroxy, hydocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring, R is alkyl, hydroxyalkyl or aryl, X is an anion, each n is an integer of 0 to 2 and z is an integer of 0 to 1, the concentration of said thiuram disulfide being in the range of about 2 to about 75 mg.

13 per mole of silver halide and the Weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

13. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with -bis(dimethylthio carbamyl) disulfide and l,3-diamino-5-rnethyl phenazinium chloride, the concentration of said disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20:1.

14. A photographic element comprising a support and a photographic silver halide emulsion layer desensitized to visible radiation with bis(morpholinothio carbamyl) disulfide and 1,3-diamino-5-methyl phenazinium chloride, the concentration of said disulfide being in the range of about 2 to about 75 mg. per mole of silver halide and the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20: 1.

15. A photographic silver halide desensitizing combination comprising a thiuram disulfide silver halide desensitizer and a piazine containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically.

16. A photographic silver halide desensitizing combination comprising a thiuram disulfide silver halide desensitizer and a piazine having up to 24 carbon atoms and containing a pyrazine ring to which two 6-membered carbocyclic rings are fused symmetrically, the weight ratio of said thiuram disulfide to said piazine being in the range of about 5:1 to about 10:1.

17. A photographic silver halide desensitizing combination comprising a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroxy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring and each n is an integer of 0 to 2, the weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

18. A photographic silver halide desensitizing combination comprising a tetraalkyl thiuram disulfide silver halide desensitizer and a piazine having the formula:

where each of R and R is amino, hydroXy, hydrocarbyl amino, alkyl, aryl, acyloxy, acylamino or a fused 6-membered carbocyclic ring, -R is alkyl, hydroxyalkyl or aryl, X is an anion, each m is an integer of 0 to 2 and z is an integer of 0 to 1, the weight ratio of said thiuram disulfide to said piazine being in the range of about 2:1 to about 20:1.

19. A photographic silver halide desensitizing combination comprising bis(dimethylthio carbamyl) disulfide and 1,3-diamino-5-methyl phenazinium chloride, the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20:1.

20. A photographic silver halide desensitizing combination comprising bis (morpholinothio carbamyl) disulfide and 1,3-diamino-5-methyl phenazinium chloride, the weight ratio of said disulfide to said phenazinium chloride being in the range of about 2:1 to about 20:1.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. R. EVERETT, Assistant Examiner.