JPS6115418B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a silver halide emulsion for direct positive photography containing a novel dimethine cyanine dye as an organic desensitizer. Specifically, by incorporating a new dimethine cyanine dye containing a 2-(nitro-substituted phenyl)-indole nucleus, it has good sensitivity and density, and is suitable for direct positive photography without dye color stains remaining after processing. This invention relates to silver halide emulsions. It is well known that positive images can be directly obtained using certain silver halide photographic materials without intervening a negative medium, but generally only those with extremely low sensitivity can be obtained. Among this type of direct positive silver halide photographic light-sensitive materials, one that has relatively high sensitivity uses a silver halide photographic emulsion that has been given an appropriate fog in advance, and a process in which the fog is destroyed by exposure. A so-called solarization-type direct positive silver halide photographic light-sensitive material is known, which directly obtains a positive image using solarization, but even this is insufficient in terms of sensitivity, and there is a need for photographic light-sensitive materials with even higher sensitivity. The current situation is that this is required. To increase the sensitivity of this type of photosensitive material, various additives such as solarization promoters, spectral sensitizers, and organic desensitizers to effectively destroy fog have been applied to silver halide photographic emulsions. Although there are known methods to
Even if good sensitivity is obtained, there are disadvantages in that the fog density decreases markedly, or the formed fog is not destroyed by exposure and becomes a fog. For example, dimethylene cyanine dyes containing a 2-phenylindole nucleus or a 2-pyridylindole nucleus are useful as organic desensitizers in direct positive photographic silver halide emulsions and have been shown to have high positive sensitivity, as described in US Pat. No. 3582343,
It is described in the specifications of the same No. 3501312, the same No. 3505070, the same No. 35985596, etc. However, even with the above-mentioned organic desensitizers, there are drawbacks such as insufficient positive sensitivity, a decrease in maximum density, or color staining of the dye remaining after processing, resulting in a high minimum density that is not useful as a photograph. Ta. A first object of the present invention is to provide a direct positive silver halide photographic light-sensitive material having good sensitivity and maximum density, and low minimum density. The second object of the present invention is to contain a novel dimethine cyanine dye as an organic reducing agent.
The object of the present invention is to provide a direct positive photographic silver halide emulsion that provides high sensitivity and maximum density, and low minimum density. A third object of the present invention is to provide a dimethine cyanine dye containing a novel 2-(nitro-substituted phenyl)-indole nucleus, thereby producing a dimethine cyanine dye containing a 2-phenylindole nucleus or a 2-pyridylindole nucleus. It is an object of the present invention to provide a silver halide photographic light-sensitive material for direct positive use, which can optically sensitize a silver halide emulsion layer to provide extremely high sensitivity compared to cyanine dyes, and can prevent color staining after processing. . The above object of the present invention and other objects described below are to contain at least one type of silver halide imparted with fog and a compound represented by the following general formula [] (hereinafter referred to as the compound of the present invention). This was achieved by a direct positive photographic silver halide emulsion characterized by: General formula [] Each symbol in the formula represents the following meaning. R ₁ : Hydrogen atom or nitro group, R ₂ : Lower alkyl group or allyl group, R ₃ : Lower alkyl group, allyl group or phenyl group, Z: imidazo[4,5-b]quinoxaline nucleus, pyrrolo[2,3] -b] Atom group necessary to form a pyridine nucleus, or a benzothiazole nucleus, benzoselenazole nucleus, benzoxazole nucleus, or indole nucleus each substituted with at least one nitro group, X: anion. m and n: 1 or 2. However, when the compound forms an internal salt, n represents 1. The most important structural feature of the compound of the present invention is that it has a phenyl group substituted with a nitro group at the 2-position of the indole nucleus, as clearly shown in the general formula []. When the nitro group is substituted at the para position, one of the objects of the present invention, which is to leave no color stain after processing, can be most effectively achieved. In addition, in the general formula [], R ₁ represents a hydrogen atom or a nitro group, but the nitro group shows a higher effect, and this nitro group is particularly effective when substituted at the 5-position of the indole nucleus. bring about favorable results. As the other substituent of this indole nucleus, namely R ₂ , among those mentioned above, a methyl group or an ethyl group is useful. As mentioned above, the compound of the present invention is characterized by a 2-(nitrophenol)indole nucleus, and is effective in achieving the object of the present invention regardless of the ring nucleus formed by Z.
Particularly high effects are observed when the following rings are formed among the above. In other words, the imidazo[4,5-b]quinoxaline nucleus is 1,3-
Examples include diethyl substituted product, 6-chloro-1,3-diallyl substituted product, and 6-chloro-1,3-diphenyl substituted product. The pyrrolo[2,3-b]pyridine nucleus is 3,3-dimethyl or 3,3-diethyl substituted product, and the benzothiazole nucleus is 5-
Mononitro substituted products such as nitrobenzothiazole or 5-chloro-6-nitrobenzothiazole, mononitro substituted products such as 5-nitrobenzoselenazole as the selenazole nucleus, mononitro substituted products such as 6-nitrobenzoxazole as the benzoxazole nucleus , the indole nucleus is 3H-nitroindole nucleus, especially 3,3'-dimethyl-5-
Examples include nitro-3H-indole and 3,3'-diethyl-5-nitro-3H-indole. The anion represented by It may be appropriately selected from among ion, paratoluenesulfonate, thiocyanate, sulfamate, methylsulfate, perchlorate, and the like. Of the above, para-toluene sulfonate, methyl sulfate or perchlorate are particularly useful. Next, specific examples of compounds exhibiting particularly excellent effects among the compounds represented by the above general formula [] will be shown. The numbers shown to the right of the compound are the wavelengths of maximum absorption of the compound in methanol. These compounds can be synthesized in the same manner as conventionally used photographic sensitizing dyes. An example is shown below. Synthesis Example 1 Synthesis of Exemplified Compound (A-7) In 10 ml of complex acid anhydride, 0.65 g of 1-methyl-2-(4-nitrophenyl)-3-formyl-5-nitroindole and 1,2,3,3- 0.61 g of tetramethylpyrrolo[2.3-b]pyridium iodide was heated and refluxed for about 3 minutes. The reaction mixture was cooled on ice, about 10 ml of ethyl complex acid was added, and the crystals were collected by filtration, washed with a mixture of ethyl complex acid and ethanol, and the obtained crystals were recrystallized from methanol to give a reddish-orange compound of 0.56
g (yield 46%) was obtained. The resulting compound is mp222
It was ~223℃. Synthesis Example 2 Synthesis of Exemplified Compound (A-4) 0.28 g of 1-methyl-2-(4-nitrophenyl)-3-formylindole in 8 ml of complex acid anhydride
and 6-chloro-2-methyl-1,3-diphenylimidazo[4,5-b]quinoxalinium-p
-Heat 0.55g of toluene sulfonate, approx.
Refluxed for minutes. The reaction mixture was ice-cooled, 10 ml of ethyl acetate was added thereto, and the separated oil layer was stirred, resulting in orange crystallization. The crystals were collected by filtration, washed with a mixture of ether and ethanol, and recrystallized from methanol to obtain 0.64 g (yield: 80%) of an orange compound.
It was mp304°. The following reference examples show 1-methyl-2-(4-nitrophenyl)-3-formylindole and 1-methyl-2-(4-nitrophenyl)-3-formylindole used to synthesize the compounds of the present invention.
A method for producing methyl-2-(4-nitrophenyl)-3-formyl-5-nitroindole intermediate will be described. Reference Example 1 Synthesis example of 1-methyl-2-(4-nitrophenyl)indole Mix 27 g of 4-nitroacetonephenone-methylphenylhydrazone and 200 g of polyphosphoric acid, and heat at 80°C.
heated for 30 minutes. After cooling the reaction mixture,
The mixture was poured into ice water, the product was extracted with ether, the ether layer was washed with water, and then evaporated. When the residue was recrystallized from dimethylformamide, mp.173-174
15 g (yield 59%) of the purified target product was obtained. The elemental analysis values of this target product are as follows.

[Table] Reference example 2 1-methyl-2-(4-nitrophenyl)-3-
Synthesis example of formyl indole: 5 phosphorus oxychloride in 40 ml of dimethylformamide
ml of 1-methyl-2-
(4-nitrophenyl)indole 12.6g at 40℃
A small amount was added while keeping the amount below. 45 more mixture
The reaction mixture was kept at 1 hour at °C, poured into 300 ml of water, neutralized by adding about 80 ml of 2.5N caustic soda water, and boiled for 5 minutes. The generated solid was collected by filtration, thoroughly washed with water, dried, and recrystallized from dimethyl formamide to obtain the desired product, pm.155.
11.7 g (yield 84%) of yellowish brown crystals at ~160°C were obtained.
The elemental analysis values of this target product are as follows.

[Table] Reference example 3 1-methyl-2-(4-nitrophenyl)-5-
Synthesis example of nitroindole 12.6 g of 1-methyl-2-(4-nitrophenyl)indole was dissolved in 70 ml of concentrated sulfuric acid, and on the other hand, a solution was prepared by dissolving 4.3 g of sodium nitrate in 60 ml of concentrated sulfuric acid. 0-5℃ in indole solution
was added while maintaining the temperature. After further stirring for 1 hour, the mixture was poured into ice water 1, and the precipitated solid was collected by filtration, thoroughly washed with water, and dried. When this was recrystallized and purified from dimethylformamide, the mp.218℃
9 g (yield: 60%) of yellow needle-like crystals, which was the desired product, were obtained. The elemental analysis values of this target product are as follows.

[Table] Reference example 4 1-methyl-2-(4-nitrophenyl)-3-
Synthesis example of formyl-5-nitroindole 6 ml of phosphorus oxychloride was added to 100 ml of dimethylformamide at 10°C or lower, and 1-methyl-2-(4-nitrophenyl)- synthesized according to Reference Example (3) was added thereto. 9.9 g of 5-nitroindole was added in small portions at below 40°C. Furthermore, this mixture was heated to 50℃,
Stirred for 2 hours. This reaction mixture was poured into 1.5 liters of water, neutralized with 2.5N caustic soda water, and then
Heated at 80°C for 10 minutes. After cooling, the solid matter was collected by filtration, thoroughly washed with water, dried, and purified by recrystallization from dimethylformamide to obtain 63 g (yield: 58%) of the desired yellow needle crystals having a temperature of 242°C. The elemental analysis values of this target product are as follows.

[Table] The direct positive photographic silver halide emulsion of the present invention is produced by incorporating the compound of the present invention, which is an organic desensitizer, into silver halide which has been dispersed in a suitable dispersion medium and has been previously fogged. A direct positive photographic silver halide light-sensitive material is obtained and coated on a support. The silver halide photosensitive material generally has other auxiliary layers such as a subbing layer, an antihalation layer, a protective layer, etc. Depending on the purpose of the photosensitive material, silver halide emulsions and intermediate layers may be added. , a filter layer is provided. The compounds of the present invention can be dissolved in a suitable single solvent such as water, methanol, acetone, fluorinated alcohol, dimethylformamide, dimethyl sulfoxide, etc., or a mixture thereof.
It can be added to silver halide photographic emulsions. Furthermore, the dye of the present invention can be added at any time during the manufacturing process of the photographic emulsion (for example, during mixing, physical ripening, fogging, immersion in a dye solution before coating and before exposure, etc.). , preferably added after fogging. The amount of the compound of the present invention added varies depending on various factors such as the above-mentioned addition time, silver halide composition, emulsion preparation method, and desired sensitivity, but is generally 0.005 to 5 g, preferably 0.2 g per mole of silver halide.
It is desirable to use it in the range of g to 2 g. Furthermore, the compound of the present invention can be added not only to the emulsion layer but also to a layer adjacent to the emulsion layer, such as a protective layer, an intermediate layer, or an antihalation layer, and can be incorporated into the emulsion layer by diffusion of the dye. Any suitable method may be employed to impart fog to the silver halide used in the present invention. fogging, for example by uniform exposure to light over the entire surface, or chemically using suitable reducing agents or compounds of metals that are more electrically positive than silver as described in British Patent No. 723019. can be granted. In order to obtain a direct positive image with high sensitivity, it is preferable to use the method described in US Pat. No. 3,501,307, etc., in which fogging is caused by a combination of a reducing agent and a gold compound. Also, special public service 11563-11563
A method in which a compound of a metal that is electrically more positive than silver and at least one compound of a thiosulfate, a thiodianate, or a hydrocyanic acid salt is combined with the above-mentioned combination, and a reducing agent is further added to the above-mentioned combination. It is also possible to add fog. Typical reducing agents useful for imparting such fog include, for example, formalin, hydrazine, foliamine (e.g., triethylenetetramine, tetraethylenepentamine, etc.), thiourea oxide, tetra(hydroxymethyl)
Phosphonium chloride, boron compounds (e.g. aminephorane, sodium borohydride, etc.),
Contains stannous chloride, tin ()chlorad, etc. Typical useful metal compounds that are more electrically positive than silver include soluble salts of gold, rhodium, platinum, palladium, iridium, etc., such as potassium chloroaurate, chloroauric acid, palladium ammonium chloride, Included are sodium iridium and the like. The fogging of the direct positive silver halide emulsions used in the present invention can be varied over a wide range. The degree of fogging depends on the silver halide composition of the silver halide emulsion used, as is well known to those skilled in the art.
It is related to the particle size, etc., the type and concentration of the fogging agent used, the PH of the emulsion at the time of fogging, pAg, temperature, time, etc. The fogged silver halide grains used in the direct positive silver halide emulsion of the present invention include chloride, silver chlorobromide, silver chloroiodobromide, silver bromide, silver iodobromide emulsions, etc. These emulsions can be prepared by various methods, such as a method of incorporating a soluble Group 8 metal salt, a method of preparing an ammonia emulsion, a method of preparing a monodisperse emulsion, a method of preparing a heterodisperse emulsion, a method of preparing a regular grain emulsion, a method of preparing a covered grain emulsion, and a method of preparing a regular grain emulsion. ) Various methods can be applied, such as an emulsion preparation method or an internal latent image type emulsion preparation method. The grain size of the silver halide may be arbitrarily selected depending on the purpose, use, etc. of the photosensitive material. The direct positive photographic silver halide agents of the present invention include solar recess promoters such as soluble halogen salts such as potassium iodide and potassium bromide, selenium compounds, halogen-free photoactive compounds, and optical sensitizers such as dimethine trimethine cyanine. Dyes, halogen-substituted hydroxyphthalein dyes, phenazine dyes, benzothiazole, cyanine dyes containing benzoselenazole nuclei, cyanine dyes containing naphthoxazole nuclei, triphenylmethane dyes,
Cyanine dyes containing an indolenine nucleus, cyanine dyes containing a 2-hyridine-rotanine nucleus, cyanine dyes containing a thiazole nucleus, asymmetric cyanine, quinoline, meso-substituted cyanine dyes, cyanine dyes containing a rhodanine nucleus, cyanine containing a benzimidazole nucleus dye, polymethine dye with three nuclei,
It is possible to further sensitize with a dye selected from merocyanine dyes and the like. Furthermore, organic desensitizers similar to the compounds of the present invention (also called electron-accepting compounds because they are substances that capture free electrons generated in silver halide grains) such as bis-(1-alkyl-2- Phenylindole-3) trimethine cyanine dye, cyanine dye containing aromatic substituted indole nucleus, imidazoquinoxaline dye, asymmetric cyanine dye containing carbazole nucleus, trimethine cyanine dye containing 2-aromatic substituted indole nucleus, 2.3. Cyanine dyes containing a 3-trialkyl-3H-nitroindole nucleus, cyanine dyes containing a complex-fused pyrimidinedione nucleus, 2-isoxazoline-5
- quaternized merocyanine dyes with a 2-hylazolin-5-one nucleus or a complex fused hyrimidine nucleus, a 2-allylimino (or alkylimino)-4-allyl (or alkyl)-3-thiazoline nucleus; Cyanine dyes containing 3-arylamino or 3-lower fatty acid amide-substituted 2-pyrazolin-5-ones, merocyanine quaternary ammonium salt dyes, pyrylium, thiapyrylium, selenapyrylium salt dyes, nitro-substituted 2-arylindole nuclei a cyanine dye containing a hyrol nucleus bonded at the 2-position carbon atom, a cyanine dye containing a hyrol nucleus bonded at the 2-position carbon atom, a cyanine dye containing a 4-pyrazole nucleus, a polymethine dye containing an imidazole nucleus, Dimethine cyanine dye containing a 2-phenyl substituted indole nucleus, trimethine cyanine dye consisting of two indole nuclei, cyanine dye containing a 1-cyanoalkyl-arylindole nucleus,
Cyanine and merocyanine dyes with desensitizing groups such as two nuclear nitro groups, 1-alkyl-2
- Cyanine dyes containing phenyl-substituted indole nuclei, cyanine dyes containing 1-alkoxy-2-arylindole nuclei, cyanine dyes containing imidazo[4,5-b]quinoxaline nuclei, dyes containing cyclohebutanetriene rings, indole nuclei containing dimethine cyanine dye, pyrazolo[1,5-a] cyanine dye containing benzimitasole nucleus, pyrazolo[5,1-b] cyanine dye containing quinazolone nucleus, pyrrolo[2,3-b] cyanine dye containing pyridine nucleus. cyanine dyes containing dimethine cyanine dyes, cyanine dyes containing pyrrole nuclei, dyes containing pyrrolo[2.1-b]thiazole nuclei, cyanine dyes containing indole or indolenine nuclei containing benzoyl or phenylsulfonyl substituents, and many others. It is also possible to further sensitize with dyes selected from dyes. Other photographic additives can also be added to the direct positive silver halide emulsion used in the present invention. In other words, as a stabilizer, for example,
-16035, gopolymer compounds described in Japanese Patent Publication No. 49-12651, Japanese Patent Publication Nos. 50-85330 and 51-
Particularly preferred are compounds described in No. 34712, etc., and adducts of acidic sulfites and aldehydro compounds.
Or triazoles, azaindenes, quaternary
benzothiazolium compounds, mercapto compounds,
Alternatively, water-soluble inorganic salts such as cadmium, cobalt, nickel, manganese, thallium, gold, and zinc may be included. As the hardening agent, for example, aldehydes such as formalin, glyoxal, and mucochloric acid, s-triazines, epoxies, aziridines, and vinylsulfonic acid are preferably used. In addition, examples of coating aids include saponin,
Sodium polyalkylene sulfonate, lauryl or oleyl monoether of polyethylene glycol, amylated alkyl taurine, JP-A-Sho
Fluorine compounds selected from those described in No. 49-10722 and No. 49-46733 are preferably used, and as sensitizers, for example, polyalkylene oxides and derivatives thereof are preferably used. Furthermore, it is also possible, for example, to contain color couplers.
In addition, a whitening agent, an ultraviolet absorber, a preservative, a matting agent, an antistatic agent, etc. can also be contained as necessary. The direct positive photographic silver halide emulsion of the present invention is grafted with protective colloids such as natural substances such as gelatin and gelatin derivatives, as well as polyvinyl alcohol, polyvinyl acrylate, polyvinylpyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, and ethylene oxide. Hydrophilic polymers such as poly(N-hydroxyalkyl)β-alanine derivatives can be included.
Furthermore, a dispersion polymerized vinyl compound may be included as an emulsion binder. For example, special public relations
Polymer latex of unsaturated ethylenically monomer emulsion-polymerized in the presence of an activator as described in No. 32344, polymer latte obtained by grafting a polymer compound having a hydroxyl group with an unsaturated ethylenically monomer using a ceric salt. It is preferable to include Tx and the like from the viewpoint of improving the physical properties of the film. The direct positive photographic silver halide emulsion of the present invention includes:
It is possible to protect and contain the developer, or to protect and contain higher fatty acids such as stearyl acetoglyceride to improve film properties. The direct positive photographic silver halide emulsion thus obtained can be applied to any suitable photographic support, such as glass, film, cellulose acetate, cellulose acetate butyrate, cellulose nitrate, polyester, polyamide, polystyrene, etc., paper, paralyte, etc. It is coated onto a support such as coated paper, polyolefin coated paper, for example polyethylene or polypropylene coated paper. and,
For example, polyolefin coated paper can be made to have good emulsion adhesion by electron impact treatment or the like. The direct positive photographic silver halide emulsion of the present invention is applied to various uses. For example, various photosensitive materials for printing such as duplication, reproduction, and offset mastering, X-rays,
Various types of special photographic light-sensitive materials such as flash photography and electron beam photography, as well as for general copying, microcopying, direct positive color, quick stabilized, diffusion transfer, color diffusion transfer, one-bath development and fixing, etc. Used in direct positive silver halide photographic materials. These photosensitive materials can be processed with various developers depending on the purpose. For example, it can be processed with a general black and white developer (for example, a phenidone-hydroquinone developer, a metol-hydroquinone developer, a hydroquinone developer, a tanning developer, etc.), a color developer (for example, a phenylenediamine developer), or the like. After development, normal fixing processing can be performed. The present invention will be specifically illustrated below with reference to Examples. Example 1 While vigorously stirring an aqueous gelatin solution with pH=2.0
At a temperature of 65°C, a potassium bromide and potassium iodide aqueous solution and a silver nitrate aqueous solution were simultaneously added over a period of about 45 minutes to form a particle containing 25 mol% silver iodide and an average particle size of about 0.25μ. Make a silver iodide emulsion.
After neutralizing this emulsion, it is cooled and desalted according to a conventional method.
Finish by adding gelatin. This emulsion has a pH of
6.5, adjust PAg to 8.0, add 6.0 mg of tetraethylenepentamine per mole of silver halide and ripen at 65°C for 30 minutes, then add 3.0 mg of chloroauric acid per mole of silver halide at 65°C. at 60
Aged for a minute, causing fog. To the capped emulsion, 600 milligrams of the compound of the present invention and a comparative sample were added per mole of silver halide as shown in Table 1, saponin was added as a coating aid, and formalin was added as a hardening agent, pH = 6.5, pAg. =8.5
Each emulsion was applied to a polyester film at an amount of 3.0 grams of silver per square meter and dried. The sample thus obtained was exposed to light using a sensitometry light wedge, and developed with the following developer for 30 seconds at 35°C. Developer composition Anhydrous sodium sulfite 60 g Hydroquinone 20 g 1-phenyl-1,3-hirazolone 0.8 g Potassium hydroxide 15 g 5-methyl-benztriazole 0.04 g Potassium bromide 3 g Glutaraldehyde 4 g Glacial acetic acid 13 g With water 1. After that, it was fixed with an acidic hardening fixer, washed with water, and dried. The total processing time was 90 seconds. For practical purposes, positive sensitivity is calculated from the reciprocal of the exposure amount required to destroy fog up to a density of 0.2 with white exposure.
The sensitivity of each sample containing the comparative compound was set as 100, and the sensitivity was expressed as relative sensitivity. Note that the color contamination density is a value measured using a color filter with a color tensitometer (manufactured by Konishiroku Photo Industry Co., Ltd.). Comparative compounds used for comparison are shown below.

[Table] As is clear from the results in the above table, the samples using the compounds of the present invention have high sensitivity and have very little color staining after processing. Example 2 An aqueous solution of silver nitrate was added to an aqueous gelatin solution at a temperature of 40°C with vigorous stirring, and after 1 minute, an aqueous solution of potassium bromide and potassium iodide containing aqueous ammonia was added, followed by aging for 5 minutes. By doing so, it contains 1.5% silver iodide and the average grain size is approximately
Make a 0.3μ silver iodide gelatin emulsion. This emulsion is neutralized, cooled, desalted in a conventional manner, and finished by adding gelatin. This emulsion has a pH of 6.0 and a pAg of 8.5.
0.7 milligrams of thiourea oxide per mole of silver halide was added, and the mixture was aged at 50°C for 60 minutes, followed by addition of 3.0 milligrams of sodium thiosulfate and 3.0 milligrams of chloroauric acid per mole of silver halide. Aged at 60℃ for 45 minutes to produce fog. To the fogged emulsion were added 600 milligrams of the compounds of the present invention and comparative compounds per mole of silver halide as shown in Table 2, saponin as a coating aid and formalin as a hardening agent, pH = 6.8.
The pAg was adjusted to 8.5, and each emulsion was coated on a polyester film at an amount of 3.0 g of silver per square meter and dried. The thus obtained sample was treated in the same manner as in Example 1, and the results are shown in Table 2. In addition, compounds used for comparison are shown below. In the table, the relative sensitivity is expressed with the sensitivity of 1 as 100.

[Table] As is clear from the above results, it can be seen that the compounds using the compounds of the present invention have high sensitivity and have very little color staining after processing. Preferred embodiments of the present invention are shown below. (1) A direct positive photographic silver halide emulsion as claimed in the claims, wherein R ₁ is a nitro group. (2) The direct positive photographic silver halide emulsion according to the above (1), wherein the compound represented by the general formula [] is a compound represented by the following formula. or (3) Claims in which silver halide grains are fogged with a reducing agent and a gold compound;
The direct positive photographic silver halide emulsion described in (1) or (2).

Claims (1)

[Scope of Claims] 1. A direct positive photographic silver halide emulsion characterized by containing fogged silver halide and at least one compound represented by the following general formula []. General formula [] [In the formula, R ₁ is a hydrogen atom or a nitro group, R ₂ is a lower alkyl group or an allyl group, R ₃ is a lower alkyl group, an allyl group, or a phenyl group, Z is an imidazo[4,5-b]quinoxaline nucleus, pyrrolo [2・3
-b]pyridine nucleus, or at least one each
a benzothiazole nucleus substituted with two nitro groups,
In the atomic group necessary to form a benzoselenazole nucleus, benzoxazole nucleus or indole nucleus, X represents an anion, and m and n each represent 1 or 2. However, when the compound forms an inner salt, n represents 1. ]