JPS6336487B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-developable photosensitive material that has good storage stability and is free from background stains. To obtain a photographic image using a general silver halide photographic light-sensitive material, it is developed and fixed after exposure, or in the case of a color light-sensitive material, after image exposure, it is processed into an oxidized form of a developing agent. An azomethine dye image or an indoaniline dye image can be obtained by developing with an aromatic primary amine developing agent in the presence of a coupler that reacts with the dye to form a dye, bleaching, and fixing. Such processing steps often require additional processing steps due to practical needs, eg, to halt the progress of development or to increase the stability of the image during storage. On the other hand, with the recent popularization of simplified or rapid processing, a method of incorporating a developing agent in a stable form as a precursor into a photosensitive material and developing it with an alkaline activator solution has become available. U.S. Patent No. 3295978, U.S. Patent No. 3342599
No. 3719492, specifications and JP-A-1983-
It is described in Publication No. 79035, etc. The above method can simplify the composition of the treatment liquid, making it easier to manage the treatment liquid, and is also useful for improving waste liquid treatment.There are also high expectations for faster processing due to the simplified treatment. Therefore, it is attracting attention. In addition to the above method, a dry processing method for photographic materials has also been proposed, and is disclosed in US Pat. No. 3,457,075.
The dry silver process described in the specification is a typical example. In the dry silver process, a photothermographic material containing a small amount of silver halide, a silver salt oxidizing agent, and a reducing agent as essential components is used. The composition of the photosensitive material consists of a small amount of silver halide and an organic silver salt that is stable to light, and when this is heated to 80°C or higher after image exposure, the organic silver salt oxidizing agent and reducing agent in the photosensitive layer are removed. causes an oxidation-reduction reaction due to the catalytic action of the exposed silver halide present in the vicinity, producing silver and blackening the exposed area to form an image. In this process, it is not necessary to perform a stabilization treatment on the silver halide in the unexposed areas. On the other hand, color photothermographic materials containing couplers are also known, such as U.S. Pat. No. 3,531,286
No. 3761270, No. 3764328, No. 3764328, No. 3761270, No. 3764328, No.
No. 4021240, No. 4124387, etc., propose color photothermographic materials containing a coupler and a reducing agent in which the oxidized form of the reducing agent can react with the coupler to form a dye. There is. Furthermore, JP-A-46-4728, JP-A No. 48-28221,
and Japanese Patent Publication No. 49-25498 also describe heat-developable photosensitive materials using a photosensitive complex of silver and dye instead of silver halide as a photocatalyst. Reducing agents used in these known photothermographic materials include (1) di- or polyhydroxybenzenes and their monoethers, (2) substituted or unsubstituted aminophenols, and (3) p-phenylene. Diamines (4) Substituted or unsubstituted mono- or bisnaphthols and di- or polyhydroxynaphthalenes (5) Reducing sugars (6) 3-pyrazolidones, pyrazolines and pyrazolones (7) Ascorbic acid and its derivatives ( 8) Substituted phenols, substituted or unsubstituted bis, tris and tetrakisphenols (9) Hydroxylamines (10) Reductones (11) Hydrazides (12) 1 and 3 described in JP-A-47-10282 - Indans, etc. are known. Among the above reducing agents, when heat development is performed using a bisphenol derivative as a reducing agent for a monochrome photothermographic material and silver behenate as an organic silver salt, the type of substituent of the reducing agent In many cases, this may cause significant thermal fog or severely hinder development. In addition, regarding heat-developable photosensitive materials for color, the reducing agents reported in the above-mentioned patent materials include p-phenylenediamine derivatives, as well as aminophenols and p- Although there are sulfonamide phenols and the like, p-phenylenediamine derivatives have excellent developability, but have poor storage stability and cause significant coloring to the background. Furthermore, aminophenols and p-sulfonamide phenols both have excellent storage stability, but are inferior in color development. Therefore, the first object of the present invention is to provide a heat-developable photosensitive material with excellent preservability and image quality, and the second object of the present invention is to provide a photothermographic material with excellent preservability, image quality, and developability. An object of the present invention is to provide a color heat-developable photosensitive material containing a coloring agent. According to the present invention, a thermal developable material having, on a support, (a) a layer containing an organic silver salt, (b) a layer containing a photocatalyst, and (c) a layer containing a reducing agent represented by the following general formula. By using a photosensitive material, the above objective can be achieved. general formula [In the formula, R ¹ and R ² represent an alkyl group having 1 to 30 carbon atoms which may have a substituent, and R ¹ and R ²
may be ring-closed to form a heterocycle. ^R3 , ^R4 ,
R ⁵ and R ⁶ represent a hydrogen atom, a halogen atom, an alkoxy group, an acylamino group, an arylsulfonylamino group, an alkylsulfonylamino group, or an alkyl group having 1 to 30 carbon atoms which may have a substituent, R ¹ and R ³ and R ² and R ⁵ may each be closed to form a heterocycle. M represents an alkali metal, ammonia, a nitrogen-containing organic base, or a compound containing a quaternary nitrogen atom. ] The nitrogen-containing organic base in the above general formula is an organic compound containing a basic nitrogen atom capable of forming a salt with an inorganic acid, and particularly important organic bases include amine compounds. Chain amine compounds include primary amines, secondary amines, and tertiary amines.
Examples of cyclic amine compounds include typical heterocyclic organic bases such as well-known pyridine, quinoline, piperidine, and imizodal. In addition, compounds such as hydroxylamine, hydrazine, and amidine are also useful as chain amines. In addition, as the salt of the nitrogen-containing organic base, inorganic acid salts of the organic base (eg, hydrochloride, sulfate, nitrate, etc.) as described above are preferably used. On the other hand, examples of the compound containing quaternary nitrogen in the above general formula include salts or hydroxides of nitrogen compounds having a tetravalent covalent bond. Next, preferred specific examples of the reducing agent represented by the above general formula are shown below. The reducing agent used in the present invention can be prepared by known methods such as Houben-Weyl, Methoden der
It can be synthesized according to the method described in Organischen Chemie, Band Synthesis Example Synthesis of Exemplified Compound 1. 6.60 g of 4-amino-N,N diethylaniline,
Cool 50 ml of chloroform with ice-sodium chloride,
While stirring, 1.55 g of chlorosulfonic acid was added over 40 minutes. After the dropwise addition, chloroform was distilled off under reduced pressure, and the residue was dissolved in water. The aqueous solution was made alkaline with sodium carbonate, and the precipitated oil was removed with ethyl acetate. The aqueous solution was dried under reduced pressure, and the residue was extracted with methanol. By distilling off methanol under reduced pressure, 6.4 g of a slightly gray solid was obtained. mp245℃ (decomposition) The following reducing agent was obtained by the same method.

[Table] The amount of the reducing agent used in the present invention varies depending on the organic silver salt, photocatalyst, coupler, color toning agent, other additives, etc., but it ranges from 0.1 mol to 10 mol per mol of the organic silver salt. A suitable amount is mole, preferably 0.2 mole to 3 mole, and two or more kinds may be used in combination, or they may be used in combination with a known reducing agent. The reducing agent used in the present invention may be added to the same layer as the organic silver salt and the photocatalyst, or may be added to a separate layer, and the method of addition is not limited, but when a hydrophobic binder is used, the binder solution is It can be added by dissolving it in a solvent that is miscible with the binder solvent that does not insolubilize the binder inside, but if it is only soluble in a solvent that is immiscible with the solvent of the binder solution, it can be added after dissolving and dispersing. It may be added by dispersing it in a solid state without using a solvent. Even if a suitable solvent does not exist, it may be added in a dispersed manner in a solid state. When using a hydrophilic binder, it may be dissolved in a hydrophilic solvent and added, or dissolved in a water-immiscible solvent and dispersed and added by a method known in the art. Moreover, when a suitable solvent is not present, it may be added in a dispersed state in a solid state. Next, the organic silver salts used in the present invention include those that react with a reducing agent to form a silver image when heated to 80°C or higher in the presence of silver halide, such as silver behenate, stearin, etc. Silver salts of aliphatic carboxylic acids such as silver acids, silver aromatic carboxylates such as silver benzoate and silver phthalate, silver sulfonates such as silver benzenesulfonate and silver diphenylaminesulfonate, p-toluenesulfinic acid Silver, silver sulfinate such as silver benzenesulfinate, silver phenyl phosphate, silver organic phosphate such as silver 1-naphthyl phosphate, silver benzotriazole, silver 5-nitrobenzimidazole, silver carbazole, silver phthalazinone, silver saccharin, phthalimide silver salts of organic compounds having imino groups such as silver tetrazole, silver pyrrolidone, silver imidazole, silver salts of thione compounds described in U.S. Pat. No. 3,785,830 and silver 2-mercaptobenzothiazole, etc. Examples include silver salts of organic compounds having mercapto or thione groups. When using silver halide or a photosensitive silver dye complex as a photocatalyst, these organic silver salts include long-chain aliphatic carboxylic acid silver salts having 15 or more carbon atoms, because they are relatively stable to light. For example, silver stearate, silver behenate, etc. are preferred. Regarding the preparation method of the above-mentioned organic silver salt, please refer to the specifications of U.S. Pat. No. 3,457,075, U.S. Pat.
It is described in publications such as No. 94619, No. 49-93310, and No. 49-13224. The optimum particle size of the organic silver salt is 0.01 to 10 microns, preferably 0.1 to 5 microns. Photocatalysts used in the present invention include silver halides and photosensitive complexes of silver and dyes, and photosensitive silver halides include commonly known silver chloride, silver bromide, and silver iodide. , silver chlorobromide, silver iodobromide, silver chloroiodobromide or mixtures thereof can be used. These silver halides are used in an amount of 0.001 mol to 0.5 mol, preferably 0.01 mol to 0.1 mol, per mol of organic silver salt. The above-mentioned method for producing silver halide involves treating a solution or dispersion of an organic silver salt or a sheet material containing this organic silver salt with a photosensitive silver halide forming component to remove a portion of the organic silver salt. It is formed by converting it into a photosensitive silver halide. According to US Pat. No. 3,457,075, it is stated that the photosensitive silver halide formed as described above is in sufficient contact with an organic silver salt and can provide a good heat-developable photosensitive material. ing. The photosensitive silver halide forming components will be specifically described below. (a) Inorganic halides, for example halides represented by MXn (where M represents H, NH ₄ or a metal atom,
X represents chlorine, bromine, or iodine; n represents 1 when M is H or NH ₄ ; when M is a metal atom, it represents its valence. Almost all metals on the periodic table of elements, including lithium, sodium, and potassium, can be used as metal atoms. ) (b) Halogen-containing metal complexes, such as K ₂ ptCl ₆ , K ₂ ptBr ₆ , HAuCl ₄ ,
(NH ₄ ) ₂ IrCl ₆ , (NH ₄ ) ₂ RuCl ₆ , (NH ₄ ) ₃ RhCl ₆
and so on. (c) Onium halides For example, quaternary ammonium halides such as trimethylphenylammonium bromide, cetylethyldimethylammonium bromide, trimethylbenzylammonium bromide, quaternary phosphonium halides such as tetraethylphosphonium bromide, and trimethylsulfonium iodide. There are tertiary sulfonium halides such as (d) Halogenated hydrocarbons Examples include iodoform, bromoform, carbon tetrabromide, and 2-bromo-3-methylpropane. (e) N-halogen compound, for example, a compound represented by the following formula,

[expression] or

[Formula] or -SO ₂ NX- group (where X is Cl or
N-halide () with Br). (In the above general formulas () and (), X is
Cl, Br, I, and Z represent an atomic group necessary to form a 5- to 7-membered ring, and this 5- to 7-membered ring may be further fused with another ring. A represents an arbonyl group or a sulfonyl group, and R ₁ and R ₂ represent a hydrogen atom, an alkyl group, an aryl group, or an alkoxy group. ) Specific examples include N-chlorosuccinimide, N-bromphthalimide, N-bromoacetamide, N-bromooxazolinone,
N-chlorophthalazone, N-bromo-N-methylbenzenesulfamide, 1,3-dibromo-
Examples include 4,4-dimethylhydantoin and trichloroisocyanuric acid. In addition, N-halogen compounds of benzotriazole having substituents are also effective. Also included are N-halogen compounds such as benzimidazoles. (f) Other halogen-containing compounds, such as triphenylmethyl chloride, 2-bromobutyric acid, 2-bromoethanol, benzophenone dichloride, and triphenyl bromide. The silver halide forming components exemplified above can be used in combination of two or more, and the amount used is as follows:
The amount ranges from 0.001 mol to 0.5 mol, preferably from 0.01 mol to 0.3 mol, per mol of organic silver salt. If the amount used is less than this, the sensitivity will decrease, and if it is more than this, discoloration will occur due to light, resulting in coloring of the image background. Apart from forming photosensitive silver halide by the method using photosensitive silver halide forming components as described above, photosensitive silver halide is prepared by any known method, and this is further mixed with an organic silver salt and a reducing agent. There is also a method of mixing with a redox composition containing a coupler if necessary. However, U.S. Pat.
According to the specification of No. 3457057, in the heat-developable photosensitive material prepared in this way, there is insufficient contact between the photosensitive silver halide and the organic silver salt, and satisfactory sensitivity cannot be obtained. is proposed. One example is a method in which silver halide prepared in polyvinyl butyral is mixed with an organic silver salt (U.S. Pat. Nos. 3,706,565, 3,706,564, and U.S. Pat.
3713833, etc.), a method of mixing in the presence of a surfactant (U.S. Pat. No. 3,761,273, JP-A-50-32926, and JP-A-50-32928), enzymatic decomposition of silver halide emulsions. There is a method in which silver halide is then mixed with an organic silver salt (British Patent No. 1354186) and a method in which silver halide is prepared almost simultaneously with the production of an organic silver salt (Japanese Patent Application Laid-open No. 17216/1983). This method has been reported and can also be applied to the heat-developable photosensitive material of the present invention. Furthermore, as mentioned above, a photosensitive complex of silver and a dye can be used instead of silver halide as a photocatalyst, and a metal diazosulfonate described in U.S. Pat. No. 3,152,904 can be used as a photocatalyst. Salts, sulfinates can also be used as photocatalysts. Although photoconductive substances such as zinc oxide and silica oxide may also be used, it is most preferable to use silver halide as the photocatalyst when a highly sensitive heat-developable photosensitive material is required. In either method, after adding the silver halide forming component or silver halide, if necessary, a sulfur-containing compound such as thiosulfate, a metal such as gold, palladium, iridium, lithium, tin, or chromium, or a reducing agent, or at room temperature or at a suitable temperature (preferably 30°C to 100°C) in the presence of a mixture of these compounds.
By leaving it to mature for 30 minutes to 2 days, it is possible to increase sensitivity and reduce thermal fog. Similarly, after forming silver halide, the silver halide or the mixture of silver halide and organic silver salt is precipitated by centrifugation or the like, and then redispersed in a binder containing the remaining components. Photographic properties can be improved by coexisting heavy metal salts such as thiosulfates, tetrazaindenes, benztriazoles, mercapto or thione compounds, iodides, iridium salts, and rhodium salts during redispersion. Silver halide as a photocatalyst is disclosed in, for example, US Pat. No. 1,623,499;
Chemical sensitization can be carried out by known methods such as that described in U.S. Patent No. 2,399,083.
Stabilization can also be carried out by methods such as those disclosed in 2728663 and 2839405. Further, optical sensitization can be carried out using ordinary optical sensitizing dyes, but particularly effective sensitizing dyes for the heat-developable photosensitive material of the present invention include the rhodanine nucleus described in U.S. Pat. No. 3,761,279. There are merocyanine dyes having a thiohydantoin nucleus or a 2-thio-2,4-oxazolidinedione nucleus. The amount of these dyes added is from 10 ^-4 mol to 1 mol per mol of silver halide or silver halide forming component. Furthermore, even when silver halide is not used, JP-A-48-28221 and JP-A-49-91214
The sensitizing dyes described in each publication can be used. In this case, preheat (70℃~120℃) before exposure.
It is even more effective to give As the coupler used in the present invention, couplers commonly used in silver halide color light-sensitive materials can be used. For example, yellow dye-forming couplers include benzoylacetanilide couplers, pivaloylacetanilide couplers, and 2-equivalent couplers in which the carbon atom at the coupling position of these is substituted with a substituent that can be separated during coupling (so-called split-off group). There is a yellow dye-forming coupler etc. US Patent No. 3265506
No. 2875057, No. 3408194, No. 3408194, No.
No. 3447928, No. 3277155, No. 3415652, No. 3664841, each specification and patent 1977-29432
No. 48-66834, No. 50-28834, No. 49-
It is described in No. 10736, No. 50-132926, No. 49-122335, and Japanese Patent Publication No. 49-13576. Examples of magenta dye-forming couplers include 5-pyrazolone type couplers, pyrazolotriazole type couplers,
There are pyrazolinobenzimidazole type couplers and their two-equivalent magenta dye-forming couplers, etc., and are disclosed in U.S. Patent Nos. 2,600,788, 3,062,653 and
No. 3127269, No. 3311476, No. 3419391, No. 3519429, No. 3558319, No. 3684514,
No. 3888680, each specification and JP-A-49-29639
No. 49-111631 and other publications.
Examples of cyan dye-forming couplers include phenolic couplers, naphthol couplers, pyrazoquinazolone couplers, and their two-equivalent cyan dye-forming couplers, which are disclosed in U.S. Pat.
No. 2423730, No. 2474293, No. 2801171, No. 2895826, No. 3476563, No. 3737316,
Specifications of No. 3758308, No. 3839044, and JP-A-47-37425, No. 50-10135, No. 50-25228
No. 50-112038, No. 50-117422, No. 50-
It is described in various publications such as No. 130441. In addition to these couplers, the black dye-forming couplers described in German Patent Application No. 2644915 and others are also useful in the present invention. Various conventionally known methods can be applied to the heat-developable photosensitive material of the present invention in order to prevent thermal fog. For example, JP-A-49-10724,
No. 49-97613, No. 49-90118, No. 49-125016
No. 49-130720, No. 48-106724, No. 49-
No. 121631, No. 49-29463, No. 49-131827, No. 49-131827, No. 49-29463, No. 49-131827, No.
It is described in Publications No. 49-128767, No. 50-187, and No. 50-299. The heat-developable photosensitive material of the present invention preferably contains a compound effective for preventing photodiscoloration after image formation. Examples of such photochromic inhibitors include US Pat. No. 3,839,041 and US Pat.
Compounds described in each specification of No. 3700457, No. 3707377, and No. 3893859 or methods described in Specification of No. 3617289 or JP-A-50-54329 can be used. Furthermore, it is preferable to use a toning agent alone or in combination in the heat-developable photosensitive material of the present invention, which accelerates development and darkens the image. The heat-developable photosensitive material of the present invention can be provided with auxiliary layers such as an antistatic layer, an antihalation layer, an undercoat layer, and a protective layer. Each component used in the invention is dispersed in at least one colloid used as a binder. These binders may be either hydrophilic or hydrophobic. Examples of the binder include gelatin, gelatin derivatives, cellulose derivatives, dextran, gum arabic, as well as dimensionally stable latex-like vinyl compounds and synthetic polymers. Among these synthetic polymers, polyvinylpyrrolidone, a copolymer of vinyl chloride and vinyl acetate, polyvinyl butyral, polyvinyl acetate, ethyl cellulose, polymethyl methacrylate, cellulose acetate butyrate, gelatin, polyvinyl alcohol, and the like are particularly preferred.
Two or more of these binders may be used in combination, but the amount of binder should be determined based on the weight ratio of the organic silver salt.
The ratio is 10:1 to 1:10, preferably 4:1 to 1:4. The organic silver salt, photocatalyst, and reducing agent used in the present invention may each constitute a photosensitive material as separate layers by using a binder as described above, or may be combined, for example, with the organic silver salt and reducing agent. may be formed as the same layer, or the above three components may be formed as the same layer. Further, as a support for the heat-developable photosensitive material of the present invention, commonly used plastic films, sheets, paper, metallic glass, etc. are used, and the photosensitive composition is coated onto this. The amount of organic silver salt and silver halide in terms of silver amount is preferably 0.2 g to 3 g per 1 m ² of support.
It is applied in an amount ranging from 0.3g to 2g. Next, a method for preparing the photothermographic material of the present invention will be specifically described. First, an organic silver salt is produced by reacting an organic silver salt-forming component with a silver ion supplying agent such as silver nitrate in the manner described above. After washing the organic silver salt thus prepared with water or alcohol, it is dispersed in an emulsion binder. For dispersion, a ball mill, a homomixer, a homogenizer, a grind mill, a V-type mixer, a colloid mill, or a dyno mill tube can be used. A silver halide forming component is added to the silver salt polymer dispersion thus prepared to convert a portion of the organic silver salt into silver halide. As mentioned above, the silver halide may be prepared in advance and added, or the silver halide may be prepared simultaneously with the organic silver salt. Next, various additives such as a sensitizing dye, a reducing agent, and a toning agent are sequentially added as a solution. Once all the additives have been added, the coating solution has been prepared. Coating onto the support may be performed by dipping, air knife, curtain coating, hopper coating, or the like. Coating of auxiliary layers other than the photosensitive layer can also be done by the same method. The heat-developable photosensitive material produced in this way is heated to 80°C to 180°C, preferably 100°C, after image exposure (if necessary, it may be preheated to 80°C to 140°C before exposure).
Developing can be done simply by heating from ℃ to 150℃. The heating time depends on the temperature, but ranges from 0.1 seconds to 60 seconds. The present invention will be described below with reference to Examples, but the present invention is not limited thereto. Example 1 6.8g of behenic acid in 60ml of ethanol at about 60℃
Heat and dissolve in 20ml of 1N caustic soda solution while stirring.
When added, insoluble matter appears. Add 240 ml of water and heat to make a homogeneous solution, then add 200 ml of 0.1N silver nitrate aqueous solution dropwise over about 10 minutes while keeping the internal temperature at about 65°C. The obtained insoluble matter is centrifuged, thoroughly washed with water and ethanol, and thoroughly dried to obtain silver behenate. 10g polyvinyl butyral and 1g behenic acid.
The entire amount of silver behenate obtained as described above was dissolved in 120 ml of methyl ethyl ketone and dispersed in a ball mill for about 15 hours. 4.6 ml of a 3% ammonium bromide methanol solution and a 4.5% methanol solution of ammonium iodide were added to the resulting dispersion.
Stir at ℃ for 1 hour and 30 minutes to convert a portion of silver behenate to silver halide. The following components were sequentially added at 25° C. at 10 minute intervals to the silver salt polymer dispersion thus obtained to prepare a coating solution. (1) Sensitizing dye (merocyanine dye of the following formula) 0.05wt% methanol solution 1ml (2) Color toning agent (phthalazinone) 2.5g (3) Antifoggant (mercury acetate) 5% methanol solution 5ml (4) Reducing agent Exemplary compound of the present invention (2) 5.8g Apply the coating solution onto polyethylene terephthalate film size-pressed on both sides with polyvinyl alcohol at a silver content of 0.4 per ^square meter.
g, and heat-developable photosensitive material (A-
1) was created. Separately, for comparison, a comparative heat-developable photosensitive material (R-1) was prepared by using the following comparative reducing agent-1 in the same molar amount in place of the exemplified compound (2) of the present invention. Comparative reducing agent-1 The heat-developable photosensitive material (A-
1, R-1) was exposed to tungsten light through an optical wedge (exposure amount: 10 ⁴ lux seconds), and then exposed at 120°C for 10
Table 1 shows the results of developing by heating for a second.

[Table] It is clear that the sample (A-1) using the reducing agent according to the present invention provides images with less fog and higher density. Similar results were obtained when a xenon light source, a fluorescent light source, a mercury lamp, a CRT light source, a laser light source, etc. were used instead of the tungsten light source. Example 2 Example 1 except that no toning agent and reducing agent were added.
A polymer dispersion coating solution of silver salt prepared in the same manner as above was coated on a polyethylene terephthalate film size-pressed on both sides with polyvinyl alcohol.
The lower layer of the heat-developable photosensitive material was prepared by applying the silver in an amount of 0.4 g per m ² . A solution having the following composition was applied thereon at 26.4 ml per 1 m ² to prepare a heat-developable photosensitive material. Polyvinylbutyral phthalazinone 2,4-dibromo-α-naphthol Reducing agent Acetone:Toluene = 2:1 solution 6 g 1.7 g 1.1 g 7 × 10 ^-3 mol 100 ml (The above reducing agents are listed in Table 2. ) The resulting heat-developable photosensitive material is imagewise exposed to tungsten light through an optical wedge (exposure amount: 10 ^{x 4} lux seconds).
After that, development was performed at 100°C for 10 seconds and at 120°C for 10 seconds, and the results are shown in Table 2. The concentrations in the table indicate the absorbance of light transmitted through a red filter.

[Table] Comparative reducing agents - (2) Comparative reducing agent-(3) As is clear from Table 2, although the photosensitive materials using comparative reducing agents (2) and (3) can be developed at lower temperatures, the difference between the maximum density and the fog density is high due to the high fog density. Compared to the reduced wedge image obtained, the reducing agent of the present invention provides the same maximum density as the comparative reducing agent without increasing thermal fog up to higher temperatures. Instead of 2,4-dibromo-α-naphthol as a coupler, 1-phenyl-3-methyl-2-
Similar results were obtained using pyrazolin-5-one or α-benzoylacetanilide. Example 3 The heat-developable photosensitive material used in Example 2 was exposed to sunlight for 5 hours without being developed, and the storage stability of the background was tested. Table 3 shows the results. The concentrations in the table are expressed as absorbance against light transmitted through a blue filter.

[Table] As is clear from Table 3, the heat-developable photosensitive material using the reducing agent according to the present invention is stable against light without any special stabilization treatment, and after the photosensitive material is developed, it is naturally stable. It has been proven that there is little coloring when left alone.

Claims (1)

[Claims] 1. On a support, an organic silver-containing layer, a photocatalyst-containing layer,
and a photothermographic material having a ring agent-containing layer, wherein a compound represented by the following general formula is used as the reducing agent. general formula [In the formula, R ¹ and R ² represent an alkyl group having 1 to 30 carbon atoms which may have a substituent, and R ¹ and R ²
may be ring-closed to form a heterocycle. ^R3 , ^R4 ,
R ⁵ and R ⁶ are a hydrogen atom, a halogen atom, an alkoxy group, an acylamino group, an arylsulfonylamino group, an alkylsulfonylamino group, or an alkyl group having 1 to 30 carbon atoms which may have a substituent. and R ¹ and R ³ and R ² and R ⁵ may each be closed to form a heterocycle. M is an alkali metal, ammonia, a nitrogen-containing organic base, or a quaternary
Represents a compound containing a class nitrogen atom. ]