JP4420831B2 - Photothermographic material - Google Patents

Description

The present invention relates to a heat-developable photosensitive material that has a sufficiently strong adhesive force between a photosensitive layer and a support and does not peel off during development or storage.

Since silver halide photosensitive materials have excellent photographic characteristics such as high resolution and high definition, they have been used in the field of image formation as a wide range and high quality materials. However, in addition to the complexity of the development process and the fixing process, when the development process is wet, waste liquid is generated, which is a problem in terms of environment and workability. Therefore, in recent years, a photothermographic material in which the development process is performed by dry heat treatment has been developed and put into practical use.

A heat-developable photosensitive material generally comprises a photosensitive layer made of a composition obtained by dispersing a fatty acid silver salt, an organic reducing agent, photosensitive silver halide, etc. in a binder resin, and a support. For example, Patent Document 1 discloses a photothermographic material having a photosensitive layer containing a silver halide that is catalytically contacted with an organic silver salt, a reducing agent, and organic silver ions.

Examples of the binder resin for forming the photosensitive layer include polyvinyl butyral, polymethyl methacrylate, cellulose acetate, polyvinyl acetate, cellulose acetate propionate, and cellulose acetate butyrate. Of these, polyvinyl butyral is preferably used. However, the photosensitive layer using a polyvinyl butyral resin as a binder resin and a support made of PET or the like have low adhesion, and there is a problem that peeling may occur during development or storage.

Japanese Patent Publication No.43-4924

In view of the above problems, an object of the present invention is to provide a heat-developable photosensitive material in which the adhesive force between a photosensitive layer and a support is sufficiently strong and peeling does not occur during development and storage.

The present invention relates to a polyvinyl acetal resin (hereinafter also referred to as a low polymerization degree resin) having a residual acetyl group amount of 25 mol% or less, a residual hydroxyl group content of 17 to 35 mol% and a polymerization degree of 200 to 600, and a residual acetyl group. A photosensitive layer having a binder resin as a mixed resin with a polyvinyl acetal resin (hereinafter also referred to as a high polymerization degree resin) having an amount of 25 mol% or less, a residual hydroxyl group content of 17 to 35 mol% and a polymerization degree of 900 to 3000; A heat-developable photosensitive material.

As a result of intensive studies, the present inventors have obtained a photosensitive layer having sufficient strength by using a mixed resin of a low polymerization degree resin and a high polymerization degree resin as a binder resin for the photosensitive layer. The present invention has been found to be able to maintain the coating properties when forming the film, and at the same time, improve the adhesion between the photosensitive layer and the support, and dramatically improve the storage stability of the heat-developable photosensitive material. It came to complete.

The low polymerization degree resin is used for the purpose of increasing the adhesive force between the photosensitive layer and the support. The lower polymerization degree resin has a lower limit of 200 and an upper limit of 600. If it is less than 200, sufficient coatability cannot be obtained even when used in combination with a high polymerization degree resin, or the strength of the resulting photosensitive layer is poor. If it exceeds 600, a sufficient adhesive improvement effect cannot be obtained. A preferred lower limit is 300 and a preferred upper limit is 500.

The high polymerization degree resin is used for the purpose of increasing the strength of the photosensitive layer and maintaining the coatability. The high polymerization degree resin has a lower limit of 900 and an upper limit of 3000. If it is less than 900, the coatability and the strength of the photosensitive layer are poor, and if it exceeds 3000, the coatability and dispersibility are poor. The preferred lower limit is 1000 and the preferred upper limit is 1500.

The weight blending ratio of the low polymerization degree resin and the high polymerization degree resin is preferably 6: 4 to 9: 1 . If the blending ratio is outside this range, sufficient adhesion between the photosensitive layer and the support cannot be obtained, or the strength of the photosensitive layer cannot be obtained.

As for the said polyvinyl acetal resin, the upper limit with the preferable amount of residual acetyl groups is 25 mol%. When the residual acetyl group amount exceeds 25 mol%, the resulting heat-developable photosensitive materials may be blocked or the resulting image may not be clear. A more preferred upper limit is 15 mol%.

The polyvinyl acetal resin has a preferred lower limit of the residual hydroxyl group content of 17 mol% and a preferred upper limit of 35 mol%. When it is less than 17 mol%, the dispersibility of the silver salt is poor when used as a binder resin, and the sensitivity may be lowered. If it exceeds 35 mol%, the photosensitive layer of the photothermographic material obtained has high moisture permeability, fogging may occur, storage stability may be deteriorated, and image density may be lowered.

The polyvinyl acetal resin has a preferable lower limit of the degree of acetalization of 40 mol% and a preferable upper limit of 78 mol%. If it is less than 40 mol%, it may be insoluble in an organic solvent and cannot be used as a binder resin for the photosensitive layer of the heat-developable photosensitive material. If it exceeds 78 mol%, the amount of residual hydroxyl group decreases and the polyvinyl acetal resin The toughness of the coating may be impaired and the strength of the coating film may be reduced.
In this specification, the method for calculating the degree of acetalization is a method of counting two acetalized hydroxyl groups since the acetal group of the polyvinyl acetal resin is acetalized from two hydroxyl groups. Is used to calculate the mole percent of the degree of acetalization.

As said polyvinyl acetal resin, as a functional group in a side chain, a functional group represented by the following formula (1), a functional group represented by the following formula (2), a functional group represented by the following formula (3), From the functional group represented by the following formula (4), the functional group represented by the following formula (5), the functional group represented by the following formula (6), a tertiary amine group, and a quaternary ammonium base. A modified polyvinyl acetal resin having at least one functional group selected from the group consisting of By having such a hydrophilic functional group in the side chain, the dispersibility of the organic silver salt can be improved.

In the formula, M represents H, Li, Na, or K, and R represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

Examples of the tertiary amine group include trimethylamine, triethylamine, triethanolamine, tripropylamine, tributylamine, and the like. Moreover, when R is an alkyl group, a C1-C10 thing is preferable, for example, a methyl group, an ethyl group, isopropyl group, a butyl group, t-butyl group, a cyclohexyl group etc. are mentioned.

The preferable lower limit of the functional group amount in the modified polyvinyl acetal resin is 0.1 mol%, and the preferable upper limit is 5 mol%. If the amount is less than 0.1 mol%, a sufficient effect of improving the dispersibility of the organic silver salt may not be obtained. If the amount exceeds 5 mol%, the solubility in an organic solvent may be lowered.

As the polyvinyl acetal resin, a modified polyvinyl acetal resin having an α-olefin unit in the main chain is also suitable. Although it does not specifically limit as said alpha-olefin unit, For example, what originates in a C1-C20 linear or cyclic alkyl group is suitable. If it is in the said range, you may contain both the branch and the linear site | part, and the cyclic | annular site | part. When the number of carbon atoms of the α-olefin unit exceeds 20, the solvent solubility of the modified polyvinyl alcohol resin used as a raw material is lowered, so that the acetalization reaction does not proceed sufficiently and a modified polyvinyl acetal resin cannot be obtained. In some cases, the resulting modified polyvinyl acetal resin has low solvent solubility and cannot be used as a binder resin for the photosensitive layer of the heat-developable photosensitive material. More preferably, it is derived from a linear or cyclic alkyl group having 1 to 10 carbon atoms, and more preferably it is derived from a linear alkyl group having 2 to 6 carbon atoms. Specifically, for example, units derived from methylene, ethylene, propylene, isopropylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, cyclohexylethylene, cyclohexylpropylene and the like are preferable.

The minimum with preferable content of the said alpha olefin unit in the principal chain of the said modified polyvinyl acetal resin is 1 mol%, and a preferable upper limit is 20 mol%. If it is less than 1 mol%, a sufficient moisture permeability reduction effect cannot be obtained. If it exceeds 20 mol%, the solvent solubility of the modified polyvinyl alcohol resin used as a raw material is lowered, so that the acetalization reaction does not proceed sufficiently and a modified polyvinyl acetal resin cannot be obtained. Since the solvent solubility of the acetal resin is low, it cannot be used as a binder resin for the photosensitive layer of the photothermographic material. A more preferred upper limit is 10 mol%.

As for the said polyvinyl acetal resin, the upper limit with the preferable amount of residual halides is 100 ppm. If it exceeds 100 ppm, it becomes a light-sensitive silver halide product, lowers the storage stability of the coating solution, and may cause a decrease in storage stability of the heat-developable photosensitive material, fogging, and the like. As a method for reducing the amount of residual halide to 100 ppm or less, for example, a non-halogen type catalyst is selected as a catalyst used for acetalization. When a halogen type catalyst is used, a mixed solution of water and water / alcohol For example, a method of purifying by a washing operation such as, and removing to a specified amount or less. A more preferred upper limit is 50 ppm.

The polyvinyl acetal resin can be synthesized by an acetalization reaction between polyvinyl alcohol having a saponification degree of 75 mol% or more and various aldehydes. The polyvinyl acetal resin is generally synthesized by reacting polyvinyl alcohol with various aldehydes using an acid catalyst in an aqueous solution, an alcohol solution, a water / alcohol mixed solution, a dimethyl sulfoxide (DMSO) solution, or the like. Can also be synthesized by adding an acid catalyst and an aldehyde to an alcohol solution of polyvinyl acetate or modified polyvinyl acetate.

As the aldehyde, any aldehyde that can be acetalized, such as formaldehyde, acetaldehyde, butyraldehyde, propylaldehyde, and the like may be used, but acetaldehyde and butyraldehyde are preferably used alone or in combination. Moreover, it is preferable that the ratio of the part acetalized by the acetaldehyde in the part acetalized of the polyvinyl acetal resin is 30% or more. When the portion acetalized with acetaldehyde is less than 30%, the glass transition point of the obtained polyvinyl acetal resin is 80 ° C. or less, the nucleation of the photosensitive silver salt proceeds excessively, and the dispersibility of the silver salt is sufficient. In some cases, the resolution and sharpness of the image cannot be sufficiently obtained. More preferably, it is 50% or more. In addition, by using a polyvinyl acetal resin with an acetoacetal moiety, the dispersibility of the silver salt is improved, the heat melting property, the cooling curability, etc. are sharpened, and the silver salt nucleus growth can be accurately controlled. As a result, the sharpness of the image and the gradation portion is improved.

The acid catalyst is not particularly limited, and either an organic acid or an inorganic acid can be used. Examples thereof include acetic acid, paratoluenesulfonic acid, nitric acid, sulfuric acid, and hydrochloric acid. Moreover, as an alkali used when stopping the said synthetic reaction, sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate etc. are mentioned, for example.

In the acetalization reaction between polyvinyl alcohol and aldehyde, an antioxidant is usually added to the reaction system or resin system to prevent oxidation of the aldehyde or to improve oxidation resistance and heat resistance of the resulting resin. However, in the synthesis of the polyvinyl acetal resin, a hindered phenol-based, bisphenol-based, phosphoric acid-based antioxidant that is usually used as an antioxidant is not used. When such an antioxidant is used, the antioxidant remains in the polyvinyl acetal resin, causing a decrease in pot life of the coating solution, a decrease in storage stability of the heat-developable photosensitive material, and so on. The sharpness of the gradation part may be impaired.

In addition, as a method for obtaining a modified polyvinyl acetal resin having the functional group in the side chain, for example, a modified polyvinyl alcohol resin obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester and a monomer having the functional group is used. Examples of the raw material include a method of acetalizing this; a method of introducing a functional group using a hydroxyl group bonded to the main chain of polyvinyl alcohol resin or polyvinyl acetal resin, and the like.
Examples of the monomer having a functional group include acrylic acid, maleic acid, itaconic acid, and the like.

The method for obtaining a modified polyvinyl acetal resin having an α-olefin unit in the main chain is, for example, a modified polyvinyl alcohol resin obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester and an α-olefin. And a method of acetalizing this.

The mixed resin is preferably obtained by acetalizing polyvinyl alcohol having a polymerization degree of 200 to 600 and polyvinyl alcohol having a polymerization degree of 900 to 3000.
The mixed resin obtained by using such a method is partially intermolecularly cross-linked by aldehyde, so the solubility of the entire resin in the solvent, transparency and dispersibility of the compound are improved, and fogging occurs. Can be suppressed and the coating property can be improved.

In the mixed resin, a preferable lower limit of the weight average molecular weight / number average molecular weight (Mw / Mn) is 3.5. If it is less than 3.5, the thixotropy is lowered and the viscosity is increased at the time of coating, so that the productivity of the photothermographic material of the invention may be deteriorated. The molecular weight distribution Mw / Mn can be measured by using gel permeation chromatography (GPC) or the like using THF or the like as a solvent, standard polystyrene or the like as a calibration sample.

The heat-developable photosensitive material of the present invention is formed by a photosensitive layer using a mixed resin of the polyvinyl acetal resin as a binder resin and a support.

The photosensitive layer comprises a mixed resin of the polyvinyl acetal resin as a binder resin, an organic silver salt, an organic reducing agent, an organic solvent, and a small amount of photosensitive silver halide or silver halide forming component as required; other additives It is formed by coating the dispersion liquid containing the composition on the support surface.

The organic silver salt is a colorless or white silver salt that is relatively stable to light, and reacts with an organic reducing agent to produce silver when heated to 80 ° C. or higher in the presence of a photosensitive silver halide. If it is a thing, it will not specifically limit, For example, the silver salt of the organic compound which has a mercapto group, a thione group, or a carboxyl group, benzotriazole silver, etc. are mentioned. Specifically, a silver salt of a compound having a mercapto group or a thione group, a silver salt of 3-mercapto-4-phenyl1,2,4-triazole, a silver salt of 2-mercapto-benzimidazole, 2-mercapto-5 -Silver salt of aminothioazole, silver salt of 1-phenyl-5-mercaptotetrathiazole, silver salt of 2-mercaptobenzothiazole, silver salt of thioglycolic acid, silver salt of dithiocarboxylic acid such as silver salt of dithioacetic acid Silver salt of thioamide, silver salt of thiopyridine, silver salt of dithiohydroxybenzol, silver salt of mercaptotriazine, silver salt of mercaptooxadiazole, silver salt of aliphatic carboxylic acid; silver caprate, silver laurate, silver myristate, palmitic acid Silver, silver stearate, silver behenate, silver maleate, silver fumarate, silver tartrate, silver furoate, silver linoleate Silver oleate, silver hydroxystearate, silver adipate, silver sebacate, silver succinate, silver acetate, silver butyrate, silver camphorate, etc., aromatic carboxylic acid silver, thione carboxylic acid silver, aliphatic carboxylic acid having thioether group Acid silver, silver salt of tetrazaindene, silver S-2-aminophenylthiosulfate, metal-containing amino alcohol, organic acid metal chelate and the like.

Of the organic acid silver salts, a silver salt of an aliphatic carboxylic acid is preferable, and silver behenate is more preferable. The organic acid silver salt has a preferable lower limit of the particle diameter of 0.01 μm and a preferable upper limit of 10 μm, a more preferable lower limit of 0.1 μm, and a more preferable upper limit of 5 μm.

In some cases, photosensitive silver halide is brought into catalytic contact with the organic acid silver salt. In this case, for example, a silver halide forming component is allowed to act on a pre-prepared solution or dispersion of an organic silver salt, or a heat-developable photosensitive material containing the organic silver salt, thereby partially halogenating the organic silver. The method etc. which form in silver are mentioned.

The photosensitive silver halide forming component is not particularly limited as long as it acts on an organic silver salt to form silver halide. The photosensitive silver halide is 0.0005 based on 100 parts by weight of the organic silver salt. It is preferable to use -0.2 weight part, More preferably, it is 0.01-0.2 weight part.

In the dispersion, the ratio of the polyvinyl acetal resin is preferably 10 parts by weight, preferably 1000 parts by weight, and more preferably 20 parts by weight, and more preferably 500 parts by weight with respect to 100 parts by weight of the organic silver salt. Parts by weight.

The reducing agent is not particularly limited and is appropriately selected depending on the organic silver salt used together. For example, substituted phenols, bisphenols, naphthols, bisnaphthols, polyhydroxybenzenes, dihydroxynaphthalenes or polyhydroxynaphthalene. , Hydroquinone monoethers, ascorbic acid or derivatives thereof, reducing sugars, aromatic amino compounds, hydroxyamines, hydrazines and the like. Among these, a photodegradable reducing agent is preferably used, but a thermally decomposable reducing agent is also used. Furthermore, a compound that promotes photolysis can be used in combination, and a coating agent for inhibiting the reaction between silver halide and the reducing agent can be used in combination.

As said organic solvent, the thing which melt | dissolves polyvinyl acetal resin and has little water content is used suitably. Of these, ketones and esters are preferable, and diethyl ketone, methyl ethyl ketone, ethyl acetate, and the like are more preferable. In addition, when ethanol, normal propyl alcohol, isopropyl alcohol or the like is used as the solvent, it is preferable to use a dehydrated one.

When forming a black image with silver, the dispersion liquid may contain a toning agent as an additive. Moreover, when forming a color image, you may contain a color coupler, a leuco dye, etc. Furthermore, you may contain conventionally well-known additives, such as a sensitizer, as needed.

As a method for producing the photothermographic material of the present invention, for example, a low polymerization resin and a high polymerization resin are mixed to form a mixed resin, and then an organic silver salt, an organic reducing agent, and an organic solvent are dispersed with a ball mill. Further, if necessary, a silver halide, a silver halide forming component, and various additives are added and dispersed with a ball mill to prepare a dispersion.
Next, the dispersion is applied onto the support so that the organic silver salt has a prescribed amount, and the solvent is evaporated. In addition, the organic silver salt and the organic reducing agent may be combined into a polyvinyl acetal resin and formed in a single layer on a support, or the organic silver salt and the organic reducing agent may be separately added to the polyvinyl acetal resin. You may mix | blend with acetal resin and form these on a support body in 2 layers separately.

In addition, the photothermographic material of the present invention may be prepared by mixing a low polymerization resin and a high polymerization resin as described above to produce a mixed resin. A mixed resin may be prepared by acetalizing a mixture of alcohol and an aldehyde.
By producing the photothermographic material of the present invention using such a method, intermolecular crosslinking with aldehyde is partially performed, so that the solubility of the entire resin in the solvent, transparency, and dispersion of the compound The coating property can be improved, the occurrence of fogging can be suppressed, and the coating property can be improved.

Examples of the support include polyethylene terephthalate, polycarbonate, polyethylene, polyvinyl acetal, cellulose ester, cellulose triacetate, nitrocellulose, polyethylene naphthalate and other plastic films, glass, paper, and metal plates such as aluminum plates.

As the amount of silver coated on the support, a preferable lower limit per 1 m ² of the support is 0.1 g, and a preferable upper limit is 5 g. If it is less than 0.1 g, the image density may be low, and if it exceeds 5 g, no improvement in image density is observed. A more preferable lower limit is 0.3 g, and a more preferable upper limit is 3 g.

According to the present invention, it is possible to provide a heat-developable photosensitive material in which the adhesive force between the photosensitive layer and the support is sufficiently strong and peeling does not occur during development and storage.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Synthesis of Resin A)
100 g of polyvinyl alcohol having a polymerization degree of 500 and a saponification degree of 98% was dissolved by heating in 700 g of distilled water, and kept at 20 ° C., and 25 g of 35% hydrochloric acid was added thereto.
4 g was added. Next, it was cooled to 10 ° C. and 60 g of butyraldehyde was added. After the resin was precipitated, the mixture was kept for 30 minutes, and then 100 g of hydrochloric acid was added, and the temperature was raised to 40 ° C. and kept for 6 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 8. The solution was held at 50 ° C. for 5 hours and then cooled. At this time, the pH of the solution was 8.
Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The polyvinyl butyral resin thus obtained had a residual acetyl group content of 1.7 mol% and a residual hydroxyl group content of 23 mol%.

(Synthesis of Resin B)
After heating and dissolving 132 g of polyvinyl alcohol having a polymerization degree of 400 and a saponification degree of 98% in 1600 g of distilled water, the temperature was kept at 20 ° C., 100 g of 35% hydrochloric acid was added thereto, and 30 g of acetaldehyde was further added. Next, it was cooled to 12 ° C. and 35 g of butyraldehyde was added. After the resin was precipitated, it was kept for 30 minutes, and then heated to 45 ° C. and kept for 4 hours. After completion of the reaction, the solution was washed with distilled water, and sodium bicarbonate was added to the vinyl acetal resin dispersion after washing to adjust the pH of the solution to 8. The solution was held at 70 ° C. for 5 hours and then cooled. The pH of the solution at this time was 8.
The solution was washed again with 100 times the amount of distilled water relative to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The polyvinyl acetal resin thus obtained has a residual acetyl group amount of 1.5 mol%, a residual hydroxyl group amount of 25 mol%, and an acetoacetalization degree of 39 mol% (the ratio in the total acetalized portion is 53.1%). ), Butyral degree was 34.5 mol%.

(Synthesis of Resin C)
Using polyvinyl alcohol having a polymerization degree of 1000 and a saponification degree of 98%, a polyvinyl butyral resin having a residual acetyl group of 1.6 mol% and a residual hydroxyl group amount of 21 mol% was obtained in the same manner as in the resin A.

(Synthesis of Resin D)
Polyvinyl alcohol having a polymerization degree of 1200 and a saponification degree of 96 mol% was used, and the residual acetyl group amount was 3.5 mol%, the residual hydroxyl group amount was 29 mol%, and the acetoacetalization degree was 38 mol% (total acetalization) in the same manner as the resin B. The proportion in the part was 56.3), and a polyvinyl acetal resin having a butyralization degree of 29.5 mol% was obtained.

(Synthesis of Resin E)
132 g of itaconic acid-modified polyvinyl alcohol having a polymerization degree of 1400 and a saponification degree of 97% was dissolved in 1600 g of distilled water by heating and kept at 20 ° C. To this was added 110 g of 35% hydrochloric acid, and then cooled to 12 ° C. 85 g of butyraldehyde was added. After the resin was precipitated, it was held for 30 minutes, and then heated to 30 ° C. and held for 7 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the modified polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 8. The solution was kept at 60 ° C. for 5 hours and then cooled. At this time, the pH of the solution was 8.
Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The thus obtained itaconic acid-modified polyvinyl butyral resin had a residual acetyl group amount of 1.5 mol%, a residual hydroxyl group amount of 21 mol%, and a butyralization degree of 28.5 mol%.

(Synthesis of Resin F)
80 g of polyvinyl alcohol having a polymerization degree of 300 and 98% saponification and 20 g of polyvinyl alcohol having a polymerization degree of 1600 and 98% saponification were dissolved in 700 g of distilled water by heating and kept at 20 ° C., and 35% Hydrochloric acid 29g was added, and butyraldehyde 14g was further added. Next, it was cooled to 12 ° C. and 64 g of butyraldehyde was added. After the resin was precipitated, the mixture was kept for 30 minutes, and then 108 g of hydrochloric acid was added and the temperature was raised to 30 ° C. and kept for 10 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 7. The solution was held at 50 ° C. for 10 hours and then cooled. At this time, the pH of the solution was 6.7.
Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The polyvinyl butyral resin thus obtained had a residual hydroxyl group content of 21 mol% and a residual acetyl group content of 1.5 mol%. Moreover, as a result of measuring molecular weight distribution by GPC using PLgel 5μ (guard column + 100,000Å + 500Å) manufactured by Polymer Labo as a column and THF as a mobile phase, Mw / Mn = 4.5.

(Synthesis of Resin G)
90 g of polyvinyl alcohol having a polymerization degree of 300 and 98% saponification, and 10 g of polyvinyl alcohol having a polymerization degree of 2600 and 98% saponification were dissolved in 1500 g of distilled water by heating and maintained at 20 ° C., and 35% Hydrochloric acid 100 g was added, and acetaldehyde 30 g was further added. Next, it was cooled to 12 ° C. and 40 g of butyraldehyde was added. After the resin was deposited, it was held for 30 minutes, and then heated to 60 ° C. and kept for 4 hours. After completion of the reaction, the reaction mixture was washed with distilled water, and sodium bicarbonate was added to the polyvinyl acetal resin dispersion after washing to adjust the pH of the solution to 8. The solution was held at 70 ° C. for 5 hours and then cooled. The pH of the solution at this time was 8.
Next, the solution was washed again with 100 times the amount of distilled water relative to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The polyvinyl acetal resin thus obtained had a residual hydroxyl group content of 25 mol%, a residual acetyl group content of 1.5 mol%, an acetoacetalization degree of 38.5 mol%, and a butyralization degree of 35 mol%. It was. Moreover, as a result of measuring molecular weight distribution by GPC using PLgel 5μ (guard column + 100,000Å + 500Å) manufactured by Polymer Labo as a column and THF as a mobile phase, Mw / Mn = 6.5.

(Synthesis of resin H)
80 g of itaconic acid-modified polyvinyl alcohol having a polymerization degree of 350 and a saponification degree of 97% and 20 g of itaconic acid-modified polyvinyl alcohol having a polymerization degree of 1500 and a saponification degree of 97% are dissolved by heating in 1500 g of distilled water, and then heated to 20 ° C. This was added with 100 g of 35% hydrochloric acid, then cooled to 12 ° C. and 70 g of butyraldehyde was added. After the resin was precipitated, it was held for 30 minutes, and then heated to 30 ° C. and held for 7 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the modified polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 8. The solution was kept at 60 ° C. for 5 hours and then cooled. At this time, the pH of the solution was 8. Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The thus obtained itaconic acid-modified polyvinyl butyral resin had a residual hydroxyl group content of 22 mol%, a residual acetyl group content of 1.5 mol%, and a butyralization degree of 74.5 mol%. Moreover, as a result of measuring molecular weight distribution by GPC using PLgel 5μ (guard column + 100,000Å + 500Å) manufactured by Polymer Labo as a column and THF as a mobile phase, Mw / Mn = 4.5.

(Synthesis of Resin I)
150 g of α-ethylene modified polyvinyl alcohol having a polymerization degree of 350 and 93% saponification, and 20 g of α-ethylene modified polyvinyl alcohol having a polymerization degree of 1500 and 93% saponification degree.
After dissolving by heating in 0 g of distilled water, the temperature was kept at 20 ° C., 100 g of 35% hydrochloric acid was added thereto, then cooled to 5 ° C., and 70 g of butyraldehyde was added. After the resin was precipitated, it was held for 30 minutes, and then heated to 30 ° C. and held for 7 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the modified polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 8. The solution was kept at 60 ° C. for 5 hours and then cooled. At this time, the pH of the solution was 8.
Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The α-ethylene-modified polyvinyl butyral resin thus obtained had a residual hydroxyl group content of 21 mol%, a residual acetyl group content of 1.5 mol%, and a butyralization degree of 70.5 mol%. Moreover, as a result of measuring molecular weight distribution by GPC using PLgel 5μ (guard column + 100,000Å + 500Å) manufactured by Polymer Labo as a column and THF as a mobile phase, Mw / Mn = 4.5.

(Synthesis of Resin J)
100 g of polyvinyl alcohol having a polymerization degree of 500 and a saponification degree of 98% was dissolved by heating in 700 g of distilled water, and kept at 20 ° C., 29 g of 35% hydrochloric acid was added thereto, and 14 g of butyraldehyde was further added. Next, it was cooled to 12 ° C. and 64 g of butyraldehyde was added. After the resin was precipitated, the mixture was kept for 30 minutes, and then 108 g of hydrochloric acid was added and the temperature was raised to 30 ° C. and kept for 10 hours. After completion of the reaction, the solution was washed with distilled water, and sodium hydroxide was added to the polyvinyl butyral resin dispersion after washing to adjust the pH of the solution to 7. The solution was held at 50 ° C. for 10 hours and then cooled. At this time, the pH of the solution was 6.7.
Next, the solution was washed with 100 times the amount of distilled water with respect to the solid content, and the solution was kept at 50 ° C. for 5 hours, then washed with 10 times the amount of distilled water, and dehydrated and dried. The polyvinyl butyral resin thus obtained had a residual hydroxyl group content of 21 mol% and a residual acetyl group content of 1.5 mol%. In addition, as a result of measuring molecular weight distribution by GPC using PLgel 5μ (guard column + 100,000Å + 500Å) manufactured by Polymer Labo as a column and THF as a mobile phase, Mw / Mn = 3.1.

(Examples 1-9 and Comparative Examples 1-4)
A mixed resin obtained by mixing the obtained resins A to E with the blending ratio shown in Table 1 and the obtained resins F to J as binder resins, 5 g of silver behenate and 40 g of diethyl ketone were added to each 5 g. The mixture was mixed with a ball mill for 24 hours, 0.2 g of N-lauryl-1-hydroxy-2-naphthamide was further added, and the mixture was pulverized again with a ball mill to obtain a coating solution.
The obtained coating solution was applied on a polyester substrate so that the thickness after drying was 10 μm and dried. On this coated surface, a solution composed of 0.5 g of N, N-dimethyl-p-phenylenediamine sulfate, 2 g of polyvinylpyrrolidone and 30 mL of methanol is applied and dried so that the thickness after drying is 1 μm. A photothermographic material was obtained.

<Evaluation>
The following evaluation was performed about the obtained coating solution and a heat developable photosensitive material. The results are shown in Tables 1 and 2.

(1) Evaluation of coating properties The coating properties when coating the obtained coating solution on a support were evaluated according to the following evaluation criteria.
(Double-circle): It was easy to apply and the coating film of uniform thickness was obtained, and also dispersion of silver behenate was good.
◯: Easy to apply and a uniform thickness coating film was obtained.
X: It was hard to apply and the coating film of uniform thickness was not obtained.

(2) Evaluation of coating properties The coating properties were evaluated by measuring the surface roughness of the coated surface after drying of the obtained photothermographic material. The surface roughness was determined by calculating the average roughness (Ra) using a surface roughness meter in accordance with JIS B 0601. The average roughness is preferably small, and is preferably 0.3 μm or less.

(3) Image evaluation The obtained heat-developable photosensitive material was exposed for 0.3 seconds at a distance of 20 cm with 250 watts of high-pressure mercury through a gradation pattern film, and then heated for 5 seconds using a 120 ° C hot plate. A good cyan pattern image was obtained.
The obtained image was exposed to white light, and the image change was evaluated according to the following evaluation criteria.
○: Almost no change in pattern contrast.
X: Some coating unevenness was confirmed, and the density of the image was seen.

(4) Evaluation of Adhesive Strength The obtained heat-developable photosensitive material was subjected to a cross-cut tape peeling test using a method based on JIS D 0202 (1988) “General Rules for Coating Films of Automobile Parts”. That is, using a cellophane tape (“CT24”, manufactured by Nichiban Co., Ltd.), it was peeled after closely contacting the heat-developable photosensitive material with the belly of the finger. Evaluation was represented by the number of squares peeled out of 100 squares.

As shown in Table 1 and Table 2, in Examples 1 to 9, the heat developable photosensitive material having a coating layer with a good coating property, a uniform film thickness, and a photosensitive layer having a small average roughness. Was able to be produced. Further, the obtained heat-developable photosensitive material had good images and was excellent in adhesion between the photosensitive layer and the support.
On the other hand, in Comparative Examples 1-4, the coating property of the coating solution was poor, and a photosensitive layer having a uniform film thickness and a small average roughness could not be produced. Further, the obtained heat-developable photosensitive material was found to have deteriorated images which are considered to be caused by the non-uniformity of the film thickness, and the adhesion between the photosensitive layer and the support was low.

According to the present invention, it is possible to provide a photothermographic material in which the adhesive force between the photosensitive layer and the support is sufficiently strong and peeling does not occur during development or storage.

Claims (6)

A polyvinyl acetal resin having a residual acetyl group content of 25 mol% or less, a residual hydroxyl group content of 17 to 35 mol% and a polymerization degree of 200 to 600, a residual acetyl group content of 25 mol% or less, and a residual hydroxyl group content of 17 to 35 A heat-developable photosensitive material comprising a photosensitive layer having a mixed resin with a polyvinyl acetal resin having a mol% and a polymerization degree of 900 to 3000 as a binder resin. A polyvinyl acetal resin having a residual acetyl group content of 25 mol% or less, a residual hydroxyl group content of 17 to 35 mol% and a polymerization degree of 200 to 600, a residual acetyl group content of 25 mol% or less, and a residual hydroxyl group content of 17 to 35 2. The heat-developable photosensitive material according to claim 1 , wherein a weight blending ratio with respect to a polyvinyl acetal resin having a mol% and a polymerization degree of 900 to 3000 is 6: 4 to 9: 1 .
The polyvinyl acetal resin has a functional group represented by the following formula (1), a functional group represented by the following formula (2), a functional group represented by the following formula (3), and the following formula (4) in the side chain. A functional group represented by the following formula (5), a functional group represented by the following formula (6), a tertiary amine group, and a quaternary ammonium base. 3. The photothermographic material according to claim 1, wherein the photothermographic material is a modified polyvinyl acetal resin containing 0.1 to 5 mol% of at least one functional group.

In the formula, M represents H, Li, Na or K, and R represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. The heat of claim 1, 2, or 3, wherein the mixed resin is obtained by acetalizing polyvinyl alcohol having a polymerization degree of 200 to 600 and polyvinyl alcohol having a polymerization degree of 900 to 3000. Developable photosensitive material. 5. The photothermographic material according to claim 1, wherein the mixed resin has a weight average molecular weight / number average molecular weight (Mw / Mn) of 3.5 or more. 6. The photothermographic material according to claim 1, wherein the polyvinyl acetal resin is a modified polyvinyl acetal resin containing 1 to 20 mol% of an α-olefin unit in the main chain.