JP2005208288A - Method for manufacturing organic silver salt dispersion, organic silver salt dispersion and heat developable photosensitive material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silver salt photothermographic dry imaging material having low fog and excellent in productivity. <P>SOLUTION: In a method for manufacturing an organic silver salt dispersion by mixing an aqueous solution or suspension of an alkali metal salt of an aliphatic carboxylic acid with silver nitrate, when the aqueous solution or suspension of the alkali metal salt of the aliphatic carboxylic acid is prepared using a dispersion medium, a part or all of an aqueous solution of an alkali metal salt is added to the dispersion medium as primary addition before adding the aliphatic carboxylic acid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an organic silver salt dispersion in which an aqueous solution or suspension of an alkali metal salt of an aliphatic carboxylic acid and silver nitrate are mixed, an organic silver salt dispersion obtained by the production method, and the organic silver salt dispersion The present invention relates to a photothermographic material containing

  Conventionally, in the fields of printing plate making and medical treatment, waste liquids resulting from wet processing of image forming materials have been a problem in terms of workability. In recent years, reduction of processing waste liquids has been strongly desired from the viewpoint of environmental conservation and space saving. It is rare. Therefore, there has been a need for a technique relating to photothermographic materials for photographic technology that can be efficiently exposed by a laser image setter or a laser imager and can form a clear black image with high resolution.

  As a technique for this purpose, as a photothermographic material (hereinafter also referred to as a photosensitive material) for forming a photographic image using a thermal development processing method, for example, the above-mentioned D.I. The method described in “Dry Silver Photographic Materials” by Morgan (Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991) and the like is well known.

  By the way, the thermosensitive material is basically prepared by adding an aliphatic carboxylic acid in water or an alkali metal salt, and then adding silver nitrate to replace the alkali soap with silver soap (see, for example, Patent Documents 1, 2, and 3). reference). In addition, alcohol may be added to enhance the concentration effect and uniformity.

However, there is no detailed description for preparing alkali soaps, and aliphatic carboxylic acids are difficult to dissolve even at temperatures above the melting point, making it difficult to prepare uniform alkali soaps in a short time (improvement of productivity). Was requested). Further, when the non-uniform alkali soap is replaced with a silver soap, there is a problem that a uniform silver soap cannot be obtained and the heat-sensitive material is highly fogged.
US Pat. No. 3,152,904 US Pat. No. 3,457,075 JP 2000-7683 A

  Accordingly, an object of the present invention is to provide a silver salt photothermographic dry imaging material having low fog and excellent productivity.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
In a method for producing an organic silver salt dispersion in which an aqueous solution or suspension of an alkali metal salt of an aliphatic carboxylic acid and silver nitrate are mixed, the aqueous solution or suspension of the alkali metal salt of an aliphatic carboxylic acid is dispersed using a dispersion medium. A method for producing an organic silver salt dispersion comprising preparing one part or the whole of an aqueous solution of an alkali metal salt as a primary addition before adding the aliphatic carboxylic acid as a primary addition.

(Claim 2)
The method for producing an organic silver salt dispersion according to claim 1, wherein the alkali metal salt in the aqueous solution of the alkali metal salt is potassium hydroxide.

(Claim 3)
The method for producing an organic silver salt dispersion according to claim 1 or 2, wherein the dispersion medium is water.

(Claim 4)
The amount of the primary addition at the time of adding the aqueous solution of the alkali metal salt is set to 60 mol% or more based on the number of moles of the aliphatic carboxylic acid. The manufacturing method of organic silver salt dispersion of description.

(Claim 5)
An organic silver salt dispersion obtained from the method for producing an organic silver salt dispersion according to any one of claims 1 to 4.

(Claim 6)
A photothermographic material comprising a photosensitive layer containing the organic silver salt dispersion according to claim 5, photosensitive silver halide grains, a reducing agent and a binder on a support.

  The silver salt photothermographic dry imaging material according to the present invention has low fog and an excellent productivity effect.

  Hereinafter, the present invention will be described in more detail.

  In the photothermographic material of the invention, an organic silver salt dispersion is prepared by mixing an aqueous solution or suspension of an alkali metal salt of an aliphatic carboxylic acid (hereinafter also referred to as an organic acid) and silver nitrate. In that case, the alkali metal salt is added first before the addition of the aliphatic carboxylic acid. This is to increase the solubility of the aliphatic carboxylic acid by placing an aqueous solution of an alkali metal salt in the ground. The addition method may be either batch addition or divided addition.

  As the alkali metal salt preferably used in the present invention, potassium hydroxide is most suitable. The solubility can be further increased by using potassium hydroxide. Although the solubility can be increased by using alcohol, it is not suitable for production cost.

  Furthermore, the invention of claim 3 of the present invention is characterized in that the primary addition amount (the initial addition amount in divided additions, the total amount in batch addition) is 60 mol% or more with respect to the number of moles of the aliphatic carboxylic acid. And Preferably it is 80 mol% or more, More preferably, it is 90 mol% or more. By these preparation methods, the aliphatic carboxylic acid can be dissolved more quickly, and a uniform alkali soap can be prepared in a short time.

  Examples of suitable organic silver salts of the present invention are described in Research Disclosure Nos. 17029 and 29963, including: : Silver salt of aliphatic carboxylic acid (eg, silver salt of gallic acid, oxalic acid, behenic acid, arachidic acid, stearic acid, palmitic acid, lauric acid, etc.); silver carboxyalkylthiourate (eg, 1- (3 -Carboxypropyl) thiouric acid, silver salts such as 1- (3-carboxypropyl) -3,3-dimethylthiouric acid); silver complex of polymer reaction product of aldehyde and hydroxy-substituted aromatic carboxylic acid (for example, aldehydes) (Formaldehyde, acetaldehyde, butyraldehyde, etc.), hydroxy-substituted aromatic carboxylic acids (eg silver complexes of polymer reaction products with salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, 5,5-thiodisalicylic acid) A silver salt or complex of thiones (eg, 3- (2-carboxyethyl) -4-hydroxyme Silver salt or complex of ru-4-thiazoline-2-thione); imidazole, pyrazole, urazole, 1,2,4-thiazole and 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole and A complex or salt of nitrogen acid and silver selected from benzotriazole; silver salt such as saccharin and 5-chlorosalicylaldoxime; silver arachidate and silver stearate. In the present invention, silver behenate, silver arachidate, and silver stearate are particularly preferable.

  The organic silver salt can be obtained by mixing a water-soluble silver compound and a compound that forms a complex with silver, and a normal mixing method, a back mixing method, a simultaneous mixing method, or the like is preferably used. It is also possible to use a controlled double jet method as described in JP-A-9-127643.

  Specifically, an alkali metal salt (for example, sodium hydroxide, potassium hydroxide, etc.) is added to an organic acid to prepare an organic acid alkali metal salt soap (for example, sodium behenate, sodium stearate, sodium arachidate). Then, silver nitrate is added to the soap to prepare organic silver salt crystals. Alcohol may be added to increase the solubility of the organic acid when forming the organic acid alkali metal salt soap.

  In the present invention, the crystal of the organic silver salt may or may not be desalted after formation. However, when desalting is performed, the salt is removed by washing with a method known in the art such as a flotation separation method or a centrifugal separation method. Can be salted.

  The organic silver salt crystals of the present invention can be subjected to a drying step for removing water before the dispersion step. There is no particular limitation on the drying apparatus applied in the present invention, and any apparatus can be used. Examples of the drying apparatus used in the present invention include a vacuum dryer, a freeze dryer, a hot air heating type box dryer, an airflow dryer, a spray dryer, a fluidized bed dryer, etc. An airflow dryer is preferably used in the present invention. In the present invention, the drying may be performed twice or more from the viewpoints of productivity and prevention of overdrying.

  The organic silver salt of the present invention is preferably dispersed and pulverized (mainly dispersed) with a media disperser or a high-pressure homogenizer after predispersing the organic silver salt particles and the dispersing binder together with a surfactant as required. For the preliminary dispersion, a general stirrer such as an anchor type or a propeller type, a high-speed rotating centrifugal radiation type stirrer (dissolver), or a high-speed rotating shear type stirrer (homomixer) can be used.

  In the present invention, the photosensitive silver halide may be mixed in any step such as during preparation of the organic silver salt or during dispersion of the organic silver salt or immediately before coating. However, it is necessary to perform sufficient mixing using an appropriate stirring member.

  The photothermographic material of the present invention contains a reducing agent. Examples of suitable reducing agents include those described in U.S. Pat. Nos. 3,589,903 and 4,021,249 or British Patent 1,486,148 and JP-A-51-51933. -36110, 50-116023, 52-84727 or JP-B-51-35727, for example, 2,2'-dihydroxy-1,1'-binaphthyl, 6, Bisnaphthols described in US Pat. No. 3,672,904 such as 6′-dibromo-2,2′-dihydroxy-1,1′-binaphthyl, and further, for example, 4-benzenesulfonamidophenol, Such as 2-benzenesulfonamidophenol, 2,6-dichloro-4-benzenesulfonamidophenol, 4-benzenesulfonamidonaphthol, etc. It can be used sulfonamidophenols or sulfonamidonaphthols, such as described in national patent 3,801,321. Particularly preferred reducing agents are bisphenol compounds (particularly hindered phenols linked by a branched alkylene chain).

  Preferred typical specific examples are shown below, but the present invention is not limited thereto.

The amount of the reducing agent including a compound represented by the embodiment preferably 1 × per silver mole 10 ^- 2 to 10 moles, particularly preferably 1 × 10 ^-2 to 1.5 mol.

  In the present invention, the reducing agent (silver ion reducing agent) and a compound which is a bisphenol derivative represented by the following general formula (A ′) can be used in combination. By using the bisphenol compound represented by the general formula (A ') in combination with a reducing agent having another different chemical structure, performance deterioration due to fog generation during storage of the photothermographic material of the present invention and after heat development It is possible to unexpectedly suppress color tone deterioration and the like during storage of silver images.

In the bisphenol compound represented by the general formula (A ′), Z represents a —S— group or a —C (R ³³ ) (R ³³ ′) — group, and R ³³ and R ³³ ′ are each a hydrogen atom or a substituted group. Represents a group. Examples of the substituent represented by R ³³ and R ³³ ′ include an alkyl group (for example, methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, sec-butyl, t-butyl, cyclohexyl, 1-methyl). -Each group such as cyclohexyl), an alkenyl group (for example, each group such as vinyl, propenyl, butenyl, pentenyl, isohexenyl, cyclohexenyl, butenylidene, isopentylidene, etc.), an alkynyl group (each group such as ethynyl, propynylidene), In addition to aryl groups (eg, phenyl, naphthyl, etc.), heterocyclic groups (eg, furyl, thienyl, pyridyl, tetrahydrofuranyl, etc.), halogen atoms, hydroxyl, alkoxy, aryloxy, acyloxy, sulfonyl Oxy, nitro, amino, acylami , Sulfonylamino, sulfonyl, carboxy, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, sulfamoyl, cyano, each group sulfo and the like. R ³³ and R ³³ ′ are preferably a hydrogen atom or an alkyl group.

R ³¹ , R ³² , R ³¹ ′ and R ³² ′ each represent a substituent, and examples of the substituent include the same groups as the substituents represented by R ³³ and R ³ 3 ′. R ³¹ , R ³² , R ³¹ ′, and R ³² ′ are preferably an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, and the like, and an alkyl group is more preferable. Examples of the substituent on the alkyl group include the same groups as the substituents represented by R ³³ and R ³³ ′. R ³¹ , R ³² , R ³¹ ′ and R ³² ′ are more preferably tertiary alkyl groups such as t-butyl, t-amyl, t-octyl and 1-methylcyclohexyl.

X ³¹ and X ³¹ ′ each represent a hydrogen atom or a substituent, and examples of the substituent include the same groups as the substituents represented by R ³³ and R ³³ ′.

  Specific examples of the bisphenol compound represented by the general formula (A ′) are shown below, but are not limited thereto.

  As a method for adding the compound represented by the general formula (A ′), these layers may be dispersed in water or dissolved in an organic solvent to be contained in a photosensitive layer coating solution or an adjacent layer coating solution. Can be contained. As the organic solvent, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, and aromatics such as toluene and xylene can be arbitrarily selected.

The amount of the compound represented by the general formula (A ′) is suitably in the range of 1 × 10 ⁻² to 10 mol, preferably 8 × 10 ^{−2 to} 1.5 mol, per mol of silver.

  The photothermographic material of the present invention preferably contains an antifoggant. Mercury ions are known as the most effective antifoggants. The use of a mercury compound as an antifoggant in a photothermographic material is disclosed, for example, in US Pat. No. 3,589,903. However, the use of mercury compounds is environmentally undesirable.

  Examples of non-mercury antifoggants include antifoggants as disclosed in US Pat. Nos. 4,546,075, 4,452,885 and JP-A-59-57234. Agents are preferred.

  Particularly preferred non-mercury antifoggants are compounds such as those disclosed in US Pat. Nos. 3,874,946 and 4,756,999, —C (X1) (X2) (X3) (Wherein X1 and X2 each represent a halogen atom, and X3 represents a hydrogen atom or a halogen atom). As examples of suitable antifoggants, compounds described in paragraph numbers [0030] to [0036] of JP-A-9-288328 are preferably used. Another preferred antifoggant is a compound described in paragraph numbers [0062] to [0063] of JP-A-9-90550. Still other suitable antifoggants are disclosed in US Pat. No. 5,028,523 and European Patent Nos. 600,587, 605,981, 631,176, etc. A compound or the like can be used.

  To the photothermographic material of the invention, it is preferable to add a color tone for the purpose of improving the silver tone after development. The toning agent has a function of making the resulting silver image dark, particularly black, by participating in the redox reaction between the organic silver salt and the reducing agent. Examples of suitable toning agents for use in the present invention are disclosed in Research Disclosure No. 17029 and include:

  Imides (eg, phthalimide); cyclic imides, pyrazolin-5-ones, and quinazolinones (eg, succinimide, 3-phenyl-2-pyrazolin-5-one, 1-phenylurazole, quinazoline, and 2,4- Thiazolidinedione); naphthalimides (eg, N-hydroxy-1,8-naphthalimide); cobalt complexes (eg, hexamine trifluoroacetate of cobalt), mercaptans (eg, 3-mercapto-1,2,4-triazole) N- (aminomethyl) aryl dicarboximides (eg, N- (dimethylaminomethyl) phthalimide); combinations of blocked pyrazoles, isothiuronium derivatives and certain photobleaching agents (eg, N, N'-F A combination of Samethylene (1-carbamoyl-3,5-dimethylpyrazole), 1,8- (3,6-dioxaoctane) bis (isothiuronium trifluoroacetate), and 2- (tribromomethylsulfonyl) benzothiazole ); Merocyanine dyes (e.g. 3-ethyl-5-((3-ethyl-2-benzothiazolinylidene (benzothiazolinylidene))-1-methylethylidene) -2-thio-2,4-oxazolidine Dione); phthalazinone, phthalazinone derivatives or metal salts of these derivatives (eg, 4- (1-naphthyl) phthalazinone, 6-chlorophthalazinone, 5,7-dimethyloxyphthalazinone, and 2,3-dihydro-1 , 4-phthalazinedione); a combination of phthalazinone and a sulfinic acid derivative (for example, 6- Lorophthalazinone + sodium benzenesulfinate or 8-methylphthalazinone + sodium p-trisulfonate); phthalazine + phthalic acid combination; phthalazine (including adducts of phthalazine) and maleic anhydride, and phthalic acid, 2,3 A combination with at least one compound selected from naphthalenedicarboxylic acid or o-phenylene acid derivatives and anhydrides thereof (eg phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid and tetrachlorophthalic anhydride); quinazoline Diones, benzoxazines, naphthoxazine derivatives; benzoxazine-2,4-diones (eg, 1,3-benzoxazine-2,4-dione); pyrimidines and asymmetric-triazines (eg, 2,4- Dihydroxypyrimidine) and tetraaza A pentalene derivative (for example, 3,6-dimercapto-1,4-diphenyl-1H, 4H-2,3a, 5,6a-tetraazapentalene). Preferable colorant is phthalazone or phthalazine.

  Examples of the photothermographic material of the invention include those disclosed in JP-A Nos. 63-159841, 60-140335, 63-231437, 63-259651, 63-304242 and 63-15245. Each publication, U.S. Pat. Nos. 4,639,414, 4,740,455, 4,741,966, 4,751,175, 4,835,096 Sensitizing dyes can be used.

  Useful sensitizing dyes used in the present invention are described or cited in, for example, Research Disclosure No. 17643IV-A (December 1978, p.23), 18431 (August 1979, p.437). It is described in the literature. In particular, a sensitizing dye having a spectral sensitivity suitable for the spectral characteristics of various scanner light sources can be advantageously selected. For example, compounds are preferably used as described in JP-A Nos. 9-34078, 9-54409, and 9-80679.

Sensitizing dyes may be used alone, or two or more kinds of sensitizing dyes may be used in combination. When the sensitizing dye is used alone or in combination, the total amount is 1 × 10 ^{−6 to} 5 × 10 ⁻³ mol, preferably 1 × 10 ^{−5 to} 2.5 × 10, per mol of silver halide. ^-3 mol, more preferably 4 x 10 ^-5 to 1 x 10 ^-3 mol in the silver halide emulsion. When two or more sensitizing dyes are used in combination, they can be contained in the silver halide emulsion in an arbitrary ratio.

  A combination of sensitizing dyes is often used for the purpose of supersensitization. Along with the sensitizing dye, the emulsion itself may contain a dye having no spectral sensitizing action or a substance that does not substantially absorb visible light and exhibits supersensitization.

  In the present invention, a mercapto compound, a disulfide compound, and a thione compound can be contained in order to control (suppress or promote) development, to improve spectral sensitization efficiency, and to improve storage stability before and after development. When a mercapto compound is used in the present invention, it may have any structure, but those represented by Ar-SM and Ar-SS-Ar are preferred. In the formula, M is a hydrogen atom or an alkali metal atom, Ar is an aromatic ring or condensed aromatic ring having one or more nitrogen, sulfur, oxygen, selenium or tellurium atoms. Preferably, the heteroaromatic ring is benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotelrazole, imidazole, oxazole, pyrazole, triazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine , Pyrazine, pyridine, purine, quinoline or quinazolinone. This heteroaromatic ring has, for example, a halogen atom (for example, Br, Cl), a hydroxyl group, an amino group, a carboxy group, an alkyl group (for example, one or more carbon atoms, preferably 1 to 4 carbon atoms) And an alkoxy group (for example, one having one or more carbon atoms, preferably one having 1 to 4 carbon atoms). Mercapto-substituted heteroaromatic compounds include 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, 2-mercapto-5-methylbenzothiazole, 3-mercapto-1,2,4-triazole, 2 -Mercaptoquinoline, 8-mercaptopurine, 2,3,5,6-tetrachloro-4-pyridinethiol, 4-hydroxy-2-mercaptopyrimidine, 2-mercapto-4-phenyloxazole, and the like. It is not limited.

  In the present invention, it is preferable to contain a matting agent on the photosensitive layer side, and it is preferable to dispose the matting agent on the surface of the photothermographic material in order to prevent damage to the image after heat development. It is preferable to contain 0.5-30% by mass ratio with respect to the total binder on the photosensitive layer side.

  Further, when a non-photosensitive layer is provided on the opposite side of the photosensitive layer with the support interposed, it is preferable that at least one layer on the non-photosensitive layer side contains a matting agent, and the photothermographic material is not slippery and prevents fingerprint adhesion. Therefore, it is preferable to dispose a matting agent on the surface of the photothermographic material, and the matting agent should be contained in a mass ratio of 0.5 to 40% with respect to all binders on the layer opposite to the photosensitive layer side. Is preferred.

  The material of the matting agent used in the present invention may be either organic or inorganic. Examples of inorganic substances include silica described in Swiss Patent No. 330,158 and the like, glass powder described in French Patent No. 1,296,995, and British Patent No. 1,173,181. Alkaline earth metals or carbonates such as cadmium and zinc described in the book can be used as the matting agent. Examples of organic substances include starch described in US Pat. No. 2,322,037 and the like, starch derivatives described in Belgian Patent 625,451 and British Patent 981,198, and the like. No. 44-3643, polyvinyl alcohol described in Swiss Patent No. 330,158, etc., polystyrene or polymethacrylate described in US Pat. No. 3,079,257, etc., polyacrylonitrile described in US Pat. An organic matting agent such as polycarbonate described in Japanese Patent No. 3,022,169 can be used.

  The shape of the matting agent may be either a regular shape or an irregular shape, but is preferably a regular shape, and a spherical shape is preferably used. The size of the matting agent is represented by a diameter when the volume of the matting agent is converted into a sphere. The particle size of the matting agent indicates the diameter converted into a spherical shape. The matting agent used in the present invention preferably has an average particle size of 0.5 to 10 μm, more preferably 1.0 to 8.0 μm. The coefficient of variation of the particle size distribution is preferably 50% or less, more preferably 40% or less, and particularly preferably 30% or less. Here, the variation coefficient of the particle size distribution is a value represented by the following equation.

(Standard deviation of particle size) / (Average value of particle size) × 100
The matting agent can be contained in any constituent layer, but is preferably a constituent layer other than the photosensitive layer, and more preferably the outermost layer as viewed from the support.

  The method for adding the matting agent may be a method in which the matting agent is dispersed and applied in advance, or a method in which the matting agent is sprayed after the coating solution is applied and before the drying is completed may be used. When a plurality of types of matting agents are added, both methods may be used in combination.

  In the present invention, a conductive compound such as a metal oxide and / or a conductive polymer can be included in the constituent layers in order to improve the chargeability. These may be contained in any layer, but are preferably contained in the undercoat layer, the backing layer, the layer between the photosensitive layer and the undercoat, and the like. In the present invention, the conductive compounds described in US Pat. No. 5,244,773, columns 14 to 20 are preferably used.

  Various additives may be added to any of the photosensitive layer, the non-photosensitive layer, and other constituent layers. In addition to those described above, for example, surfactants, antioxidants, stabilizers, plasticizers, ultraviolet absorbers, coating aids and the like may be used in the photothermographic material of the invention. As these additives and other additives, compounds described in Research Disclosure No. 17029 (June 1978, p. 9-15) can be preferably used.

  Binders suitable for the photothermographic material of the present invention are transparent or translucent and generally colorless, and include natural polymers, synthetic polymers and copolymers, and other film-forming media such as gelatin, gum arabic, polyvinyl alcohol, hydroxy Ethyl cellulose, cellulose acetate, cellulose acetate butyrate, polyvinyl pyrrolidone, casein, starch, polyacrylic acid, polymethyl methacrylate, polymethacrylic acid, polyvinyl chloride, copoly (styrene-maleic anhydride), copoly (styrene-acrylonitrile), copoly (Styrene-butadiene), polyvinyl acetals, such as polyvinyl formal, polyvinyl butyral, polyesters, polyurethanes, phenoxy resins, polyvinylidene chloride, polyepoxy S, polycarbonates, polyvinyl acetates, cellulose esters, there is a polyamide or the like, or a non-hydrophilic or hydrophobic. However, among these binders, water-insoluble polymers such as cellulose acetate, cellulose acetate butyrate, and polyvinyl butyral are particularly preferable, and polyvinyl butyral is particularly preferable.

  Further, in order to protect the surface of the photothermographic material or prevent scratches, a non-photosensitive layer can be provided outside the photosensitive layer. The binder used for these non-photosensitive layers may be the same as or different from the binder used for the photosensitive layer.

In the present invention, the binder amount of the photosensitive layer is preferably 1.5 to 10 g / m ² in order to increase the speed of heat development. More preferably, it is 1.7-8 g / m < ² >. If it is less than 1.5 g / m ² , the density of the unexposed area is significantly increased and may not be used.

  The support used in the photothermographic material of the present invention is transparent and is a plastic film (for example, polyethylene terephthalate, polycarbonate, polyimide, nylon, cellulose triacetate, polyethylene naphthalate) in order to prevent deformation of the image after development processing. Is preferred.

  Among them, preferable examples of the support include polyethylene terephthalate (hereinafter abbreviated as PET) and a plastic (hereinafter abbreviated as SPS) support including a styrene polymer having a syndiotactic structure. The thickness of the support is about 50 to 300 μm, preferably 70 to 180 μm. A heat-treated plastic support can also be used. Examples of the plastic to be used include the plastics described above. The heat treatment of the support is a temperature higher than the glass transition point of the support by 30 ° C. or more, preferably 35 ° C. or more after the formation of these supports and before the photosensitive layer is applied. Preferably, heating is performed at a temperature that is 40 ° C. or higher.

  PET is composed of polyethylene terephthalate as a component of polyester. However, in addition to polyethylene terephthalate, terephthalic acid, naphthalene-2,6-dicarboxylic acid, isophthalic acid, butylene dicarboxylic acid, 5-sodium sulfoisophthalic acid, It may be a polyester in which a modified polyester component such as adipic acid or the like and ethylene glycol, propylene glycol, butanediol, cyclohexanedimethanol or the like as a glycol component is contained in an amount of 10 mol% or less of the total polyester.

  Unlike ordinary polystyrene (atactic polystyrene), SPS is a sterically regular polystyrene. The regular stereoregular structure part of SPS is called a racemo chain, and it is preferable that there are more regular parts such as 2-chain, 3-chain, 5-chain or more, and the racemo chain is 85% or more in 2 chains. It is preferable that it is 75% or more in 3 chains, 50% or more in 5 chains, and 30% or more in more chains. The polymerization of SPS can be carried out according to the method described in JP-A-3-131833.

  Known methods can be used for the film forming method and the undercoating method for the support used in the photothermographic material of the present invention, and preferably paragraph numbers [0030] to [0070] of JP-A-9-50094. Using the method described in.

  The photothermographic material of the present invention forms a photographic image by heat development processing and suppresses a reducible silver source (organic silver salt), a photosensitive silver halide, a reducing agent, and, if necessary, the color tone of silver. The photothermographic material preferably contains a toning agent to be dispersed in a normal (organic) binder matrix.

  The photothermographic material of the present invention is stable at room temperature, but is developed by heating to a high temperature (for example, 80 to 140 ° C.) after exposure. By heating, silver is generated through an oxidation-reduction reaction between an organic silver salt (functioning as an oxidizing agent) and a reducing agent. This redox reaction is promoted by the catalytic action of the latent image generated in the silver halide upon exposure. The silver produced by the reaction of the organic silver salt in the exposed areas provides a black image that contrasts with the unexposed areas and forms an image. This reaction process proceeds without supplying a treatment liquid such as water from the outside.

  The photothermographic material of the present invention has at least one photosensitive layer on a support. Although only the photosensitive layer may be formed on the support, it is preferable to form at least one non-photosensitive layer on the photosensitive layer. In order to control the amount of light passing through the photosensitive layer or the wavelength distribution, a filter layer may be formed on the same side as or opposite to the photosensitive layer, or a dye or pigment may be contained in the photosensitive layer. As the dye, a compound described in JP-A-8-201959 is preferable. The photosensitive layer may be a plurality of layers, or a high-sensitivity layer and a low-sensitivity layer may be provided for adjusting the gradation, and these may be combined. Various additives may be added to any of the photosensitive layer, the non-photosensitive layer, and other forming layers. As described above, for example, surfactants, antioxidants, stabilizers, plasticizers, ultraviolet absorbers, coating aids and the like may be used in the photothermographic material of the invention. The non-photosensitive layer preferably contains the binder and matting agent, and may further contain a polysiloxane compound, a slipping agent such as wax or liquid paraffin.

A preferable total silver amount of the photothermographic material is 0.5 to 1.5 g / m ² .

  Details of the photothermographic material are as described above, for example, U.S. Pat. Nos. 3,152,904, 3,457,075, and D.I. Morgan, “Dry Silver Photographic Materials” (Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991) and the like. Among them, the present invention is characterized in that an image is formed by thermally developing a photothermographic material at 80 to 140 ° C. and fixing is not performed. Therefore, the silver halide and the organic silver salt remaining in the unexposed portion remain as they are in the photothermographic material without being removed.

  In the present invention, it is preferable that the optical transmission density of the photothermographic material containing a support at 400 nm after heat development is 0.2 or less. A more preferable value of the optical transmission density is 0.02 or more and 0.2 or less. If it is less than 0.02, the sensitivity is so low that it cannot be used.

  Examples of the solvent used in the present invention include ketones such as acetone, isophorone, ethyl amyl ketone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of alcohols include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, diacetone alcohol, cyclohexanol, and benzyl alcohol. Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and hexylene glycol. Examples of ether alcohols include ethylene glycol monomethyl ether and diethylene glycol monoethyl ether. Examples of ethers include ethyl ether, dioxane, isopropyl ether and the like. Examples of the esters include ethyl acetate, butyl acetate, amyl acetate, isopropyl acetate and the like. Examples of hydrocarbons include n-pentane, n-hexane, n-heptane, cyclohexane, benzene, toluene, xylene and the like. Examples of chlorides include methyl chloride, methylene chloride, chloroform, dichlorobenzene and the like. Examples of amines include monomethylamine, dimethylamine, triethanolamine, ethylenediamine, and triethylamine. Other examples include water, formamide, dimethylformamide, nitromethane, pyridine, toluidine, tetrahydrofuran, and acetic acid.

  However, it is not limited to these. These solvents can be used alone or in combination of several kinds.

  The content of the solvent in the photothermographic material can be adjusted by changing conditions such as temperature conditions in the drying step after the coating step. The content of the solvent can be measured by a method using gas chromatography.

The total amount of the solvent contained in the photothermographic material of the present invention is preferably 5 to 1000 mg / m ² , preferably 10 to 300 mg / m ² . When the content is within the above range, a photothermographic material having a low fog density and a high sensitivity can be obtained.

  In the present invention, exposure is preferably performed by laser scanning exposure. It is particularly preferable to use a laser scanning exposure machine in which the angle formed between the exposure surface of the photothermographic material and the scanning laser beam is not substantially perpendicular.

  Here, “substantially not perpendicular” means that the angle closest to the vertical during laser scanning is preferably 55 degrees or more and 88 degrees or less, more preferably 60 degrees or more and 86 degrees or less, and still more preferably. Means 70 degrees or more and 82 degrees or less.

  The beam spot diameter on the exposed surface of the photothermographic material when the laser beam is scanned onto the photothermographic material is preferably 200 μm or less, more preferably 100 μm or less. This is preferable in that a smaller spot diameter can reduce the angle of deviation of the laser incident angle from the vertical. The lower limit of the beam spot diameter is 10 μm. By performing such laser scanning exposure, it is possible to reduce image quality deterioration related to reflected light such as generation of interference fringe-like unevenness.

  In addition, the exposure used in the present invention is preferably performed using a laser scanning exposure machine that emits scanning laser light that is a vertical multi. Compared with a single longitudinal mode scanning laser beam, image quality degradation such as generation of interference fringe-like unevenness is reduced. In order to make a vertical multiplex, methods such as using return light or applying high-frequency superposition by multiplexing are preferable. The vertical multi means that the exposure wavelength is not single, and the distribution of the exposure wavelength is usually 5 nm or more, preferably 10 nm or more. The upper limit of the exposure wavelength distribution is not particularly limited, but is usually about 60 nm.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the embodiment of this invention is not limited to these.

Example 1
《Preparation of underdrawn support》
8 W / m ^{2 on} both surfaces of a commercially available biaxially stretched heat-fixed thickness of 175 μm and an optical density of 0.170 (measured with a Densitometer PDA-65 manufactured by Konica Corporation) blue-colored with the following blue dye.・ A corona discharge treatment was applied for one minute, and the following undercoat coating solution a-1 was applied on one surface to a dry film thickness of 0.8 μm and dried to form an undercoat layer A-1, and on the other side The undercoat coating solution b-1 shown below was applied to the surface so as to have a dry film thickness of 0.8 μm and dried to form an undercoat layer B-1.

<Undercoat coating liquid a-1>
Copolymer latex liquid of butyl acrylate (30% by mass) / t-butyl acrylate (20% by mass) / styrene (25% by mass) / 2-hydroxyethyl acrylate (25% by mass) (solid content 30%) 270 g
(C-1) 0.6g
Hexamethylene-1,6-bis (ethylene urea) 0.8g
Finish to 1L with water <Undercoating liquid b-1>
270 g of copolymer latex liquid (30% solid content) of butyl acrylate (40 mass%) / styrene (20 mass%) / glycidyl acrylate (40 mass%)
(C-1) 0.6g
Hexamethylene-1,6-bis (ethylene urea) 0.8g
Finish to 1L with water.

Subsequently, a corona discharge of 8 W / m ² · min is applied to the upper surfaces of the undercoat layer A-1 and the undercoat layer B-1, and the following undercoat upper layer coating solution a is applied on the undercoat layer A-1. -2 as an undercoat upper layer A-2 so that the dry film thickness is 0.1 μm, and the following undercoat upper layer coating solution b-2 is formed on the undercoat layer B-1 so that the dry film thickness is 0.4 μm. Was coated as an undercoat upper layer B-2 having an antistatic function.

<Undercoating upper layer coating solution a-2>
Mass to become gelatin 0.4g / m ² (C-1) 0.2g
(C-2) 0.2g
(C-3) 0.1 g
Silica particles (average particle size 3μm) 0.1g
Finish to 1L with water <Undercoating upper layer coating solution b-2>
Sb-doped SnO ₂ (SNS10M; manufactured by Ishihara Sangyo Co., Ltd.) 60 g
80 g of latex liquid (solid content 20%) containing (C-4) as a component
Ammonium sulfate 0.5g
(C-5) 12g
Polyethylene glycol (weight average molecular weight 600) 6g
Finish to 1L with water.

<< Preparation of backcoat layer coating solution >>
While stirring 830 g of methyl ethyl ketone (MEK), 84.2 g of cellulose acetate butyrate (Eastman Chemical, CAB381-20) and 4.5 g of a polyester resin (Bostic, VitelPE2200B) were added and dissolved. Next, 0.30 g of infrared dye 1 was added to the dissolved liquid, and 4.5 g of F surfactant (Asahi Glass Co., Surflon KH40) dissolved in 43.2 g of methanol and F surfactant (large 2.3 g of Nippon Ink Co., Ltd. (MegaFag F120K) was added and stirred well until dissolved. Next, oleyl oleate was added at 2 and 5 g. Finally, 75 g of silica (WR Grace, Syloid 64X6000) dispersed in methyl ethyl ketone at a concentration of 1% by mass with a dissolver type homogenizer was added and stirred to prepare a backcoat layer coating solution.

<< Preparation of backcoat layer protective layer coating liquid >>
Cellulose acetate butyrate (10% methyl ethyl ketone solution) 15 g
Monodispersed 15% monodispersed silica (average particle size: 8 μm, surface treatment with 1% by mass of aluminum based on the total mass of silica) 0.030 g
C ₈ F ₁₇ (CH ₂ CH ₂ O) ₁₂ C ₈ F ₁₇ 0.05 g
C ₉ F ₁₇ —C ₆ H ₄ —SO ₃ Na 0.01 g
Stearic acid 0.1g
Oleyl oleate 0.1g
α-Alumina (Mohs hardness 9) 0.1g
The backcoat layer coating solution and the backcoat layer protective layer coating solution prepared in this way were extruded with a coater at an application rate of 50 m / min so that the dry film thickness was 3.5 μm. The undercoating upper layer B-2 was applied. The drying was performed for 5 minutes using a drying air having a drying temperature of 100 ° C. and a dew point temperature of 10 ° C.

<< Preparation of photosensitive silver halide emulsion A >>
A1
Phenylcarbamoyl gelatin 88.3g
Compound (1) (10% methanol solution) 10 ml
Potassium bromide 0.32g
Finish to 5429 ml with water B1
0.67 mol / L silver nitrate aqueous solution 2635 ml
C1
Potassium bromide 51.55g
Potassium iodide 1.47g
Finish to 660ml with water D1
Potassium bromide 154.9g
4.41 g of potassium iodide
0.0093 g of iridium chloride
0.0081 g potassium ferrocyanide
Finish up to 1980ml with water E1
0.4 mol / L potassium bromide aqueous solution The following silver potential control amount F1
56% acetic acid aqueous solution 16.0 ml
G1
Anhydrous sodium carbonate 1.72 g
Compound finished to 151 ml with water (1):
_{HO (CH 2 CH 2 O)} n- [CH (CH 3) CH 2 O] 17 - (CH 2 CH 2 O) mH
m + n = 5-7
Using the mixing stirrer disclosed in Japanese Patent Publication Nos. 58-58288 and 58-58289, the solution (A1) was mixed with 1/4 of the solution (B1) and the total amount of the solution (C1) at 45 ° C., pAg8. While controlling at 09, the addition was performed in 4 minutes and 45 seconds by the simultaneous mixing method, and nucleation was performed. During this time, pAg was appropriately prepared using an aqueous solution (E1).

  After the elapse of 7 minutes, the remainder of the solution (B1) and the total amount of the solution (D1) were added over 14 minutes and 15 seconds by a simultaneous mixing method while controlling the temperature at 45 ° C. and pAg 8.09. During mixing, the pH of the reaction solution was 5.6.

  After stirring for 5 minutes, the temperature was lowered to 40 ° C., the whole amount of the solution (F1) was added, and the silver halide emulsion was precipitated. The supernatant was removed leaving 2000 ml of the sedimented portion, 10 L of water was added, and after stirring, the silver halide was precipitated again. The remaining portion of 1500 ml was left, the supernatant was removed, 10 L of water was further added, and after stirring, the silver halide was precipitated. After leaving 1500 ml of the sedimented portion and removing the supernatant, the solution (G1) was added, the temperature was raised to 60 ° C., and the mixture was further stirred for 120 minutes. Finally, the pH was adjusted to 5.8, and water was added to 1161 g per mol of silver.

  The emulsion was cubic silver iodobromide grains having an average grain size of 0.06 μm, a grain size variation coefficient of 12%, and a [100] face ratio of 92%.

<< Preparation of powdered aliphatic carboxylic acid silver salt >>
<Preparation of powdered aliphatic carboxylic acid silver salt 1>
1000 g of stearic acid was dissolved at 85 ° C. in 18880 ml of pure water. Next, 2620 ml of a 1.5 mol / L NaOH aqueous solution was added to obtain a sodium aliphatic carboxylate solution. When the pH was stabilized, 306 ml of 6% nitric acid was added, and then cooled to 55 ° C. and maintained at 55 ° C., 205 g of the above photosensitive silver halide emulsion A and pure water 1344 were added and stirred for 5 minutes. did.

  Next, 3151 ml of 1 mol / L silver nitrate solution was added over 2 minutes and stirred for 10 minutes. Thereafter, the solution was sent to a centrifuge, and deionized water was added, and washing with deionized water was continued until the conductivity of the drainage reached 30 μS / cm. After completion of washing with water, centrifugal dehydration was performed to remove excess water, and then drying was performed with a hot air circulating dryer at 40 ° C. until there was no mass loss, whereby powdered aliphatic carboxylic acid silver salt 1 was obtained.

<Preparation of powdered aliphatic carboxylic acid silver salt 2>
To 18880 ml of pure water, 2620 ml of a 1.5 mol / L NaOH aqueous solution was added, the temperature was raised to 85 ° C., and when the temperature was stabilized, 1000 g of stearic acid was dissolved to obtain an aliphatic sodium carboxylate solution. When the pH was stabilized, 306 ml of 6% nitric acid was added, and then cooled to 55 ° C. and maintained at 55 ° C., 205 g of the above photosensitive silver halide emulsion A and pure water 1344 were added and stirred for 5 minutes. did. Next, 3151 ml of 1 mol / L silver nitrate solution was added over 2 minutes and stirred for 10 minutes. Thereafter, the solution was sent to a centrifuge, and deionized water was added, and washing with deionized water was continued until the conductivity of the drainage reached 30 μS / cm. After completion of washing with water, centrifugal dehydration was carried out to remove excess moisture, and then drying was performed with a hot air circulating dryer at 40 ° C. until there was no mass loss, whereby powdered aliphatic carboxylic acid silver salt 2 was obtained.

<Preparation of powdered aliphatic carboxylic acid silver salt 3>
First, 786 ml of a 1.5 mol / L KOH aqueous solution was added to 18880 ml of pure water, and the temperature was raised to 85 ° C. When the temperature was stabilized, 1000 g of stearic acid was dissolved. Next, 1834 ml of the remaining 1.5 mol / L KOH aqueous solution was added as a secondary addition to obtain an aliphatic potassium carboxylate solution. When the pH was stabilized, 306 ml of 6% nitric acid was added, and then cooled to 55 ° C. and maintained at 55 ° C., 205 g of the above photosensitive silver halide emulsion A and pure water 1344 were added and stirred for 5 minutes. did. Next, 3151 ml of 1 mol / L silver nitrate solution was added over 2 minutes and stirred for 10 minutes. Thereafter, the solution was fed to a centrifuge, and deionized water was added, and washing with deionized water was continued until the drainage conductivity reached 30 μS / cm. After completion of washing with water, centrifugal dehydration was performed to remove excess water, and then drying was performed with a hot air circulating drier at 40 ° C. until mass loss disappeared, whereby powdered aliphatic carboxylic acid silver salt 3 was obtained.

<Preparation of powdered aliphatic carboxylic acid silver salt 4>
Powdered aliphatic carboxylic acid silver salt 4 was obtained in the same manner as powdered aliphatic carboxylic acid silver salt 3, except that the primary addition of the 1.5 mol / L KOH aqueous solution was 1834 ml and the second addition was 786 ml.

<Preparation of powdered aliphatic carboxylic acid silver salt 5>
Powdered aliphatic carboxylic acid silver salt 5 was obtained in the same manner as powdered aliphatic carboxylic acid silver salt 3, except that the primary addition of the 1.5 mol / L KOH aqueous solution was changed to 2358 ml and the second addition was changed to 262 ml.

<Preparation of powdered aliphatic carboxylic acid silver salt 6>
To 18880 ml of pure water, 2620 ml of a 1.5 mol / L KOH aqueous solution was added, the temperature was raised to 85 ° C., and when the temperature was stabilized, 1000 g of stearic acid was dissolved to obtain an aliphatic potassium carboxylate solution. When the pH was stabilized, 306 ml of 6% nitric acid was added, and then cooled to 55 ° C. and maintained at 55 ° C., 205 g of the above photosensitive silver halide emulsion A and 1344 g of pure water were added and stirred for 5 minutes. did. Next, 3151 ml of 1 mol / L silver nitrate solution was added over 2 minutes and stirred for 10 minutes. Thereafter, the solution was sent to a centrifuge, and deionized water was added, and washing with deionized water was continued until the conductivity of the drainage reached 30 μS / cm. After completion of washing with water, centrifugal dehydration was performed to remove excess moisture, and then drying was performed with a hot air circulating dryer until the mass was not lost at 40 ° C., whereby powdered aliphatic carboxylate silver salt 6 was obtained.

[Evaluation of complete dissolution of alkali soap]
As comparative dissolution evaluation of alkaline soap, the time from the addition of all of the aliphatic carboxylic acid and alkali metal salt to the pH stabilization time was compared as complete dissolution. The shorter the time until the pH stabilization time is, the better the productivity is. The evaluation results are shown in Table 1.

  From Table 1, it can be seen that the alkaline soap of the present invention is effective for productivity.

Example 2
<< Preparation of Preliminary Dispersions A to F >>
Preliminary dispersions were prepared using powdered aliphatic carboxylic acid silver salts 1 to 6 used in Example 1.

  14.57 g of polyvinyl butyral powder (Sekisui Chemical Co., Ltd., ESREC BL-5) was dissolved in 1457 g of methyl ethyl ketone, and the resulting powdered aliphatic silver carboxylate was stirred with a dissolver DISPERMAT CA-40M manufactured by VMA-GETZMANN. Preliminary dispersion A was prepared by gradually adding 1,250 g of salt and mixing well.

  Preliminary dispersions B to F were prepared in exactly the same manner except that powdered aliphatic carboxylic acid silver salts 2 to 6 were used.

<< Preparation of photosensitive dispersed emulsions A to F >>
Media type disperser DISPERMAT SL- filled with 80% of the internal volume of 0.5 mm diameter zirconia beads (Torayserum manufactured by Toray) so that the residence time in the mill is 1.5 minutes using a pump. Photosensitive dispersion emulsion A was prepared by supplying to C12EX type (VMA-GETZMANN) and dispersing at a mill peripheral speed of 8 m / s.

  Photosensitive dispersion emulsions B to F were prepared in the same manner except that the preliminary dispersions B to F were used.

(Preparation of stabilizer solution)
1.0 g of Stabilizer 1 and 0.31 g of potassium acetate were dissolved in 4.97 g of methanol to prepare a stabilizer solution.

(Preparation of infrared sensitizing dye solution)
19.2 mg of infrared sensitizing dye 1, 1.488 g 2-chloro-benzoic acid, 2.7779 g stabilizer 2 and 365 mg 5-methyl-2-mercaptobenzimidazole in 31.3 ml MEK in the dark And an infrared sensitizing dye solution was prepared.
(Preparation of supersensitizer solution)
50.1 mg of supersensitizer 1 was dissolved in 8.8 g of methanol to prepare a supersensitizer solution.

(Preparation of additive solution a)
27.98 g of the reducing agent (A-8), 1.54 g of 4-methylphthalic acid, and 0.48 g of infrared dye 2 were dissolved in 110 g of MEK to obtain an additive solution a.

(Preparation of additive liquid b)
3.56 g of antifoggant 2 and 3.43 g of phthalazine were dissolved in 40.9 g of MEK to obtain additive solution b.

<< Preparation of photosensitive layer coating solutions A to F >>
50 g of photosensitive dispersion emulsion A and 15.11 g of MEK were kept at 21 ° C. with stirring, 390 μl of antifoggant 1 (10% methanol solution) was added, and the mixture was stirred for 1 hour. Further, 494 μl of calcium bromide (10% methanol solution) was added and stirred for 20 minutes. Subsequently, 167 mg of a stabilizer solution was added and stirred for 10 minutes, and then 2.622 g of an infrared sensitizing dye solution was added and stirred for 1 hour. Thereafter, the temperature was lowered to 13 ° C. and further stirred for 25 minutes. While keeping the temperature at 13 ° C., 0.70 g of a supersensitizer solution was added and stirred for 5 minutes, and then 13.31 g of polyvinyl butyral (S-LEK BL-5 manufactured by Sekisui Chemical Co., Ltd.) was added and stirred for 30 minutes. Thereafter, 1.084 g of tetrachlorophthalic acid (9.4 mass% MEK solution) was added and stirred for 15 minutes. Further, while continuing stirring, 12.43 g of additive liquid a, 1.6 ml of Desmodur N3300 / Mobey aliphatic isocyanate (10% MEK solution), and 4.37 g of additive liquid b were sequentially added and stirred for photosensitivity. A layer coating solution A was obtained.
Photosensitive layer coating solutions B to E were obtained in the same manner except that the photosensitive dispersion emulsions B to F were used.

(Preparation of matting agent dispersion)
Cellulose acetate butyrate (Eastman Chemical Co., 7.5 g CAB171-15) was dissolved in 42.5 g of MEK, and 5 g of calcium carbonate (Speciality Minerals, Super-Pflex 200) was added thereto, and a dissolver type homogenizer was used. A matting agent dispersion was prepared by dispersing at 8000 rpm for 30 minutes.

<Preparation of surface protective layer coating solution>
While stirring MEK865g, cellulose acetate butyrate (Eastman Chemica, CAB171-15) 96g, polymethylmethacrylic acid (Rohm & Haas, Paraloid A-21) 4.5g, vinyl sulfone compound (HD-1) 1. 5 g, 1.0 g of benzotriazole, and 1.0 g of F-based surfactant (Asahi Glass Co., Surflon KH40) were added and dissolved. Next, 30 g of the above matting agent dispersion was added and stirred to prepare a surface protective layer coating solution.

<Preparation of thermosensitive material>
(Photosensitive layer side coating)
The photosensitive layer coating solution A and the surface protective layer coating solution were simultaneously applied in multiple layers using a known extrusion coater. The coating was carried out so that the photosensitive layer had a coated silver amount of 1.7 g / m ² and the surface protective layer had a dry film thickness of 2.5 μm. Thereafter, drying was performed for 10 minutes using a drying air having a drying temperature of 75 ° C. and a dew point temperature of 10 ° C., to prepare a photosensitive material 101.
Photosensitive materials 201 to 601 were produced in the same manner except that the photosensitive layer coating solutions B to F were used.

[Exposure, development, evaluation]
From the photosensitive layer side of the photothermographic material produced as described above, exposure by laser scanning was given by an exposure machine using a semiconductor laser having a longitudinal multimode wavelength of 800 nm to 820 nm as a light source by high frequency superposition. At this time, an image was formed by setting the angle of the exposure surface of the photothermographic material and the exposure laser beam to 75 degrees.

  Thereafter, the film was subjected to heat development at 110 ° C. for 15 seconds using an automatic developing machine having a heat drum so that the surface protective layer of the photothermographic material was in contact with the drum surface. At that time, exposure and development were performed in a room adjusted to 23 ° C. and 50% RH. The obtained image was measured with a densitometer, and the fog density (unexposed area density, Dmin) was determined. Table 2 shows the photographic performance (fogging evaluation).

  As is apparent from Table 2, it can be seen that the photosensitive material of the present invention is very effective from the viewpoint of photographic performance (fogging).

Claims (6)

In a method for producing an organic silver salt dispersion in which an aqueous solution or suspension of an alkali metal salt of an aliphatic carboxylic acid and silver nitrate are mixed, the aqueous solution or suspension of the alkali metal salt of an aliphatic carboxylic acid is dispersed using a dispersion medium. A method for producing an organic silver salt dispersion comprising preparing one part or the whole of an aqueous solution of an alkali metal salt as a primary addition before adding the aliphatic carboxylic acid as a primary addition. The method for producing an organic silver salt dispersion according to claim 1, wherein the alkali metal salt in the aqueous solution of the alkali metal salt is potassium hydroxide. The method for producing an organic silver salt dispersion according to claim 1 or 2, wherein the dispersion medium is water. The amount of the primary addition at the time of adding the aqueous solution of the alkali metal salt is set to 60 mol% or more based on the number of moles of the aliphatic carboxylic acid. The manufacturing method of organic silver salt dispersion of description. An organic silver salt dispersion obtained from the method for producing an organic silver salt dispersion according to any one of claims 1 to 4. A photothermographic material comprising a photosensitive layer containing the organic silver salt dispersion according to claim 5, photosensitive silver halide grains, a reducing agent and a binder on a support.