JP2006267209A - Silver salt photothermographic dry imaging material and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silver salt photothermographic dry imaging material having high sensitivity, low fogging and high maximum density and excellent in silver tone, and an image forming method. <P>SOLUTION: The silver salt photothermographic dry imaging material has, on a support, a photosensitive layer containing an organic silver salt, photosensitive silver halide grains, a reducing agent and a binder, wherein an ultraviolet absorber is contained in the photosensitive layer, the photosensitive silver halide grains contain 5-100 mol% silver iodide, and the silver salt photothermographic dry imaging material is exposed with laser light having peak intensity at a wavelength of 200-350 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a silver salt photothermographic dry imaging material (hereinafter also referred to as a photothermographic material or a photothermographic material) and an image forming method using the photothermographic material.

  In recent years, there has been a strong demand for a photosensitive material free from a developing solution waste in terms of environmental protection and workability in the medical and printing fields. For example, U.S. Pat. Nos. 3,152,904 and 3,487,075 and 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. Since these photosensitive materials are usually developed at a temperature of 80 ° C. or higher, they are called photothermographic materials.

  The photothermographic material has a much larger number of kinds and added amounts of built-in chemical substances than the conventional photosensitive material processed by liquid processing, and accordingly, the film thickness of the photosensitive layer and the non-photosensitive layer is increased. It tends to increase. As a result, the coating process or the drying process at the time of manufacturing the light-sensitive material requires a lot of time and has the disadvantage that the productivity is lowered.

  On the other hand, for the purpose of reducing the size of the apparatus and increasing the definition of the image, a laser beam having an emission peak at 350 to 450 nm is applied to a photothermographic material having a silver iodide content of 5 to 100 mol% in the photosensitive silver halide. A technique for forming an image using a generated light source is disclosed (see Patent Document 1).

However, further downsizing of the apparatus and higher definition of the image are demanded, and the above technique is insufficient for solving these problems.
JP 2003-91053 A (Claims)

  The present invention has been made in view of the above circumstances, and provides a silver salt photothermographic dry imaging material and an image forming method that have high sensitivity, low fog, high maximum density and excellent silver tone even when the apparatus is downsized. The purpose is to do.

  The above object of the present invention has been achieved by the following constitutions.

(Claim 1)
In a silver salt photothermographic dry imaging material having a photosensitive layer containing an organic silver salt, photosensitive silver halide grains, a reducing agent and a binder on a support, the photosensitive layer contains an ultraviolet absorber, and A silver salt photothermographic dry imaging material, wherein the photosensitive silver halide grains contain 5 to 100 mol% of silver iodide.

(Claim 2)
In a silver salt photothermographic dry imaging material having a photosensitive layer containing an organic silver salt, photosensitive silver halide grains, a reducing agent and a binder on a support, the photosensitive layer contains an ultraviolet absorber, and The photosensitive silver halide grains contain silver iodide in a proportion of 5 to 100 mol%, and the silver salt photothermographic dry imaging material is exposed with a laser beam having a peak intensity at a wavelength of 200 nm to 350 nm. Silver salt photothermographic dry imaging material.

(Claim 3)
An image forming method comprising exposing the silver salt photothermographic dry imaging material according to claim 1 with a laser beam having a peak intensity at a wavelength of 200 to 350 nm.

  According to the present invention, a silver salt photothermographic dry imaging material and an image forming method having high sensitivity, low fog, high maximum density and excellent silver tone can be provided.

  Details of the present invention will be described below. First, components of the present invention will be described sequentially.

(UV absorber)
In the present invention, an ultraviolet absorber is used. The ultraviolet absorber referred to here is a compound having spectral absorption characteristics in the ultraviolet region (200 to 400 nm). Among them, a compound having a maximum absorption wavelength at 230 to 350 nm is preferable, and a compound having a maximum absorption wavelength at 250 to 330 nm is more preferable. As such an ultraviolet absorber, a benzotriazole type, benzophenone type, cinnamic acid type, aminobutadiene type, or thiazolidone type is preferably used. Specific examples of the compound include compounds UV-1 to UV-29 described in paragraphs “0036” to “0040” of JP-A No. 11-295846, and paragraphs “0059” to “0086” of JP-A No. 11-44930. Described compounds 1-1 to 1-9, 2-1 to 2-17, 3-1 to 3-11, 4-1 to 4-7, 5-1 to 5-3, 6-1 to 6-7 7-1 to 7-32 and the like. Although the specific example of the ultraviolet absorber used by this invention is given to the following, this invention is not limited to these.

The said ultraviolet absorber may be used independently and may use 2 or more types together. The addition amount is usually 1 mg to 1 g / m ² , and more preferably 10 mg to 0.5 g / m ² .

(Organic silver salt)
The organic silver salt according to the present invention is a non-photosensitive organic silver salt that can function as a supply source for supplying silver ions for forming a silver image in the photosensitive layer of the photothermographic material. That is, this organic silver salt is a heat development process heated to 80 ° C. or higher in the presence of photosensitive silver halide grains (photocatalyst) having a latent image formed on light exposure on the grain surface and a reducing agent. Is a silver salt that functions as a silver ion supply source and can supply silver ions and contribute to silver image formation.

  As such non-photosensitive organic silver salts, silver salts of organic compounds having various chemical structures are conventionally known. For example, paragraphs “0048” to “0049” of JP-A-10-62899, European Patents Application Publication No. 803,764A1, page 18, line 24 to page 19, line 37, European Patent Application Publication No. 962,812A1, JP-A-11-349591, JP-A-2000-7683, JP-A-2000-72711, JP-A-2002-23301. No., 2002-23303, 2002-49119, 196446, European Patent Application Publication No. 1246001A1, European Patent Application Publication No. 12587775A1, JP-A No. 2003-140290, JP-A No. 2003-195445, No. 2003-295378 2003-295379, 2003-295380, 20 No. 3-295381, it is described in JP 2003-270755 and the like.

  In combination with or without using various organic silver salts disclosed in the above-mentioned patent publications, etc., silver salts of aliphatic carboxylic acids, especially those having 10 to 30 carbon atoms, preferably 15 to 28 carbon atoms. A silver salt of a chain aliphatic carboxylic acid can be used. The molecular weight of the aliphatic carboxylic acid for producing the silver salt is preferably 200 to 500, more preferably 250 to 400. Preferred examples of the aliphatic carboxylic acid silver salt include silver behenate, silver arachidate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate, and a mixture thereof. Including.

  In the present invention, among these aliphatic silver carboxylates, the fatty acid having a silver behenate content of preferably 50 mol% or more, more preferably 80 to 99.9 mol%, still more preferably 90 to 99.9 mol%. It is preferable to use silver.

  Prior to the preparation of the aliphatic carboxylic acid silver salt, it is necessary to prepare an alkali metal salt of an aliphatic carboxylic acid. Examples of the types of alkali metal salts that can be used in this case include sodium hydroxide. Potassium hydroxide and lithium hydroxide. Among these, it is preferable to use one kind of alkali metal salt such as potassium hydroxide, but it is also preferable to use sodium hydroxide and potassium hydroxide in combination. The combined ratio is preferably such that the molar ratio of Na: K of the above-mentioned hydroxide is in the range of 10:90 to 75:25. When used in the above range when reacted with an aliphatic carboxylic acid to form an alkali metal salt of an aliphatic carboxylic acid, the viscosity of the reaction solution can be controlled to a good state.

  In addition, when preparing an aliphatic carboxylate silver salt in the presence of silver halide grains having an average particle size of 0.050 μm or less, the alkali metal salt of the alkali metal salt has a higher potassium ratio. It is preferable because dissolution of silver particles and Ostwald ripening are prevented. Moreover, the size of fatty acid silver salt particle | grains can be made small, so that the ratio of potassium salt is high. A preferable ratio of the potassium salt is 50 to 100 mol% based on the total alkali metal salt used in the step of producing the aliphatic silver carboxylate. The concentration of the alkali metal salt is preferably 0.1 to 0.3 mol / 1,000 ml.

  Examples of organic silver other than the above include organic silver salts having a core / shell structure (Japanese Patent Laid-Open No. 2002-23303), silver salts of polyvalent carboxylic acids (EP1246001, Japanese Patent Laid-Open No. 2004-061948), and polymer silver salts (Japanese Patent Laid-Open No. 2000-292811, JP-A 2003-295378 to 2003-29581) can also be used.

  The shape of the aliphatic carboxylic acid silver salt that can be used is not particularly limited, and may be any of a needle shape, a rod shape, a flat plate shape, and a scale shape. In the present invention, scale-like aliphatic carboxylic acid silver salts and short needle-shaped or rectangular parallelepiped-shaped aliphatic carboxylic acid silver salts having a major axis / minor axis length ratio of 5 or less are preferably used. In this specification, the scaly organic silver salt is defined as follows.

  The organic silver salt is observed with an electron microscope, the shape of the organic silver salt particle is approximated to a rectangular parallelepiped, and the sides of the rectangular parallelepiped are defined as a, b, and c from the shortest side (even though c is the same as b) When it is good), the shorter numerical value a, b is used to calculate x as follows.

x = b / a
Thus, x is calculated | required about about 200 particle | grains, and when it is set as the average value x (average), what satisfy | fills the relationship of x (average)> = 1.5 is made into a scaly shape. Preferably, 30 ≧ x (average) ≧ 1.5, more preferably 20 ≧ x (average) ≧ 2.0. Incidentally, the needle shape is 1 ≦ x (average) <1.5.

  In the scaly particles, a can be regarded as the thickness of a tabular particle having a main plane with b and c as sides. The average of a is preferably 0.01 to 0.23 μm, and more preferably 0.1 to 0.20 μm. The average of c / b is preferably 1 to 6, more preferably 1.05 to 4, still more preferably 1.1 to 3, and particularly preferably 1.1 to 2.

  The particle size distribution of the organic silver salt is preferably monodispersed. Monodispersion is preferably 100% or less, more preferably 80% or less, and even more preferably 50% of the value obtained by dividing the standard deviation of the lengths of the short and long axes by the short and long axes. It is as follows. The shape of the organic silver salt can be determined from a transmission electron microscope image of the organic silver salt dispersion. As another method for measuring monodispersity, there is a method for obtaining the standard deviation of the volume weighted average diameter of the organic silver salt, and the percentage (variation coefficient) of the value divided by the volume weighted average diameter is preferably 100% or less, more Preferably it is 80% or less, More preferably, it is 50% or less. As a measuring method, for example, the particle diameter (volume weighted average diameter) obtained by irradiating an organic silver salt dispersed in a liquid with laser light and obtaining an autocorrelation function with respect to the time variation of the “fluctuation” of the scattered light. Can be obtained from

  Known methods and the like can be applied to the production of the organic silver salt and the dispersion method thereof. For example, Japanese Patent Application Laid-Open No. 10-62899, European Patent Application Publication No. 803,763A1, European Patent Application Publication No. 962,812A1, Japanese Patent Application Laid-Open No. 2001-167022, No. 2000-7683, No. 2000-72711, 2001-163889, 2001-163890, 2001-1663827, 2001-33907, 2001-188313, 2001-83651, 2002-6442, 2002-31870, 2003 Reference can be made to 280135.

  A photosensitive silver salt such as photosensitive silver halide grains can coexist when the organic silver salt is dispersed. However, when silver halide grains are allowed to coexist at the time of dispersion of the organic silver salt, fog is increased and sensitivity is remarkably lowered. Therefore, it is more preferable that silver halide grains are not substantially contained at the time of dispersion. In the present invention, the amount of silver halide grains in the aqueous dispersion to be dispersed is preferably 1 mol% or less, more preferably 0.1 mol% or less with respect to 1 mol of the organic silver salt in the liquid. More preferably, the active addition of silver halide grains is not performed.

  In the present invention, a photosensitive material can be produced by mixing an organic silver salt aqueous dispersion and a photosensitive silver halide particle dispersion, but the mixing ratio of the organic silver salt and the photosensitive silver salt can be selected according to the purpose. However, the ratio of the photosensitive silver halide grains to the organic silver salt is preferably in the range of 1 to 30 mol%, more preferably 2 to 20 mol%, particularly preferably 3 to 15 mol%. Mixing two or more kinds of organic silver salt dispersions and two or more kinds of silver halide grain dispersions when mixing is a method preferably used for adjusting photographic characteristics.

The organic silver salt of the present invention can be used in a desired amount, but the silver amount is preferably 0.1 to 5 g / m ² , more preferably 0.3 to 3 g / m ² , still more preferably 0.5 to ² g / m ² . m ² .

(Photosensitive silver halide grains)
The photosensitive silver halide grains according to the present invention (hereinafter also referred to as photosensitive silver halide or simply silver halide) can inherently absorb light as an intrinsic property of silver halide crystals, or artificially. In the silver halide crystal when visible light or infrared light can be absorbed by a physicochemical method, and light in any region within the light wavelength range from the ultraviolet light region to the infrared light region is absorbed. And / or silver halide crystal grains that have been processed and produced so that physicochemical changes can occur on the crystal surface.

  The silver halide grains themselves can be prepared as a silver halide grain emulsion (also referred to as a silver halide emulsion) using a known method. That is, any of acid method, neutral method, ammonia method, etc. may be used, and as a method of reacting soluble silver salt and soluble halogen salt, any one of one-side mixing method, simultaneous mixing method, combination thereof, etc. may be used. Of these methods, the so-called controlled double jet method in which silver halide grains are prepared while controlling the formation conditions is preferred.

  Usually, silver halide seed grains are divided into two stages: grain nucleation and grain growth, and these may be performed continuously at once, or the formation of nuclei (seed grains) and grain growth are separated. It is also possible to do this. The controlled double jet method in which the particle formation is controlled by controlling the pAg, pH, etc., which are particle formation conditions, is preferable because the particle shape and size can be controlled. For example, when performing a method in which nucleation and grain growth are separated, first, an aqueous silver salt solution and an aqueous halide solution are uniformly and rapidly mixed in an aqueous gelatin solution to produce nuclei (seed particles) (nucleation process). Thereafter, silver halide grains are prepared by a grain growth process in which grains are grown while supplying an aqueous silver salt solution and an aqueous halide solution under controlled pAg, pH, and the like. After the formation of grains, a desired silver halide emulsion can be obtained by removing unnecessary salts and the like by a desalting step by a known desalting method such as a noodle method, a flocculation method, an ultrafiltration method, or an electrodialysis method. .

  The particle size distribution of the silver halide grains of the present invention is preferably monodispersed. The monodispersion mentioned here means that the coefficient of variation of the particle diameter obtained by the following formula is 30% or less. Preferably it is 20% or less, More preferably, it is 15% or less.

Coefficient of variation of particle size% = (standard deviation of particle size / average value of particle size) × 100
Examples of the shape of the silver halide grains include cubes, octahedrons, tetrahedron grains, tabular grains, spherical grains, rod-like grains, and potato-like grains. Among these, cubic, octahedral, 14 Planar and tabular silver halide grains are preferred.

  The average aspect ratio in the case of using tabular silver halide grains is preferably 1.5 to 100, more preferably 2 to 50. These are described in US Pat. Nos. 5,264,337, 5,314,798, and 5,320,958, and the desired tabular grains can be easily obtained. Further, grains having rounded corners of silver halide grains can be preferably used.

  There is no particular limitation on the crystal habit on the outer surface of the silver halide grain, but when using a sensitizing dye having crystal habit (plane) selectivity in the adsorption reaction of the sensitizing dye on the surface of the silver halide grain. It is preferable to use silver halide grains having a relatively high proportion of crystal habits adapted to the selectivity. For example, when using a sensitizing dye that is selectively adsorbed on the crystal face of the Miller index [100], the proportion of the [100] face on the outer surface of the silver halide grain is preferably high, and this ratio is 50 % Or more, more preferably 70% or more, and particularly preferably 80% or more. The ratio of the Miller index [100] plane is a T.K. based on the adsorption dependency of the [111] plane and the [100] plane in the adsorption of the sensitizing dye. Tani: J.M. Imaging Sci. 29, 165 (1985).

  The silver halide grains used in the present invention are preferably prepared using low molecular weight gelatin having an average molecular weight of 50,000 or less at the time of forming the grains, and particularly preferably used at the time of nucleation of silver halide grains.

  The low molecular weight gelatin preferably has an average molecular weight of 50,000 or less, more preferably 2,000 to 40,000, and particularly preferably 5,000 to 25,000. The average molecular weight of gelatin can be measured by gel filtration chromatography. Low molecular weight gelatin can be decomposed by adding gelatin-degrading enzyme to a commonly used gelatin aqueous solution with an average molecular weight of about 100,000, hydrolyzing by adding acid or alkali, and heating under atmospheric pressure or pressure. Can be obtained by thermal decomposition, decomposition by ultrasonic irradiation, or a combination of these methods.

  The concentration of the dispersion medium at the time of nucleation is preferably 5% by mass or less, and more preferably 0.05 to 3.0% by mass.

  As the silver halide grains, it is preferable to use a compound represented by the following general formula when the grains are formed.

YO (CH ₂ CH ₂ O) _m [CH (CH ₃ ) CH ₂ O] _p (CH ₂ CH ₂ O) _n Y
In the formula, Y represents a hydrogen atom, —SO ₃ M, or —CO—B—COOM, and M represents a hydrogen atom, an alkali metal atom, an ammonium group, or an ammonium group substituted with an alkyl group having 5 or less carbon atoms. B represents a chain or cyclic group that forms an organic dibasic acid. m and n each represents 0 to 50, and p represents 1 to 100.

  The above-mentioned spot type polyethylene oxide compound comprises a step of producing a gelatin aqueous solution, a step of adding a water-soluble halide and a water-soluble silver salt to a gelatin solution, and an emulsion on a support. It has been preferably used as an antifoaming agent for significant foaming in the case of stirring or moving the emulsion raw material, such as a coating step, and the technology used as the antifoaming agent is, for example, JP-A-44-9497. It is described in. The polyethylene oxide compound also functions as an antifoaming agent during nucleation.

  The compound represented by the above general formula is preferably used at 1% by mass or less, more preferably 0.01 to 0.1% by mass with respect to silver.

  The polyethylene oxide compound only needs to be present at the time of nucleation, and is preferably added in advance to the dispersion medium before nucleation, but it may be added during nucleation or a silver salt used at the time of nucleation. You may add and use for aqueous solution or halide aqueous solution. Preferably, it is used by adding 0.01 to 2.0% by mass to the halide aqueous solution or both aqueous solutions. The compound of the above general formula is preferably present for a time of at least 50% of the nucleation step, more preferably 70% or more. The compound of the above general formula may be added as a powder or dissolved in a solvent such as methanol.

  The temperature at the time of nucleation is usually 5 to 60 ° C., preferably 15 to 50 ° C. Even if the temperature is constant, the temperature rising pattern (for example, the temperature at the start of nucleation is 25 ° C. It is preferable to control the temperature within the above temperature range even when the temperature is gradually raised and the temperature at the end of nucleation is 40 ° C.) and vice versa.

The concentration of the aqueous silver salt solution and aqueous halide solution used for nucleation is preferably 3.5 mol / L or less, and more preferably used in a low concentration range of 0.01 to 2.5 mol / L. The addition rate of silver ions during nucleation is preferably 1.5 × 10 ^{−3 to} 3.0 × 10 ⁻¹ mol / min, more preferably 3.0 × 10 ^{−3 to} 8.0, per liter of the reaction solution. × 10 ^-2 mol / min.

  The pH at the time of nucleation can usually be set in a range of 1.7 to 10, but it is preferably pH 2 to 6 because the particle size distribution of nuclei to be formed is broadened at the pH on the alkali side. Moreover, pBr at the time of nucleation is usually 0.05 to 3.0, preferably 1.0 to 2.5, more preferably 1.5 to 2.0.

  The average grain size of the silver halide grains is usually 10 to 50 nm, preferably 10 to 40 nm, and more preferably 10 to 35 nm. If the average grain size of the silver halide grains is smaller than 10 nm, the image density decreases, or the light irradiation image storage stability (the image obtained by heat development is used for diagnosis in a bright room or stored in a bright room) Storage stability) may be deteriorated. On the other hand, if it exceeds 50 nm, the image density may decrease.

  The average grain diameter referred to here is the length of the edge of the silver halide grains when the silver halide grains contained in the silver halide grain emulsion are cubic or octahedral so-called normal crystals. To tell. Further, when the silver halide grain is a tabular grain, it means the diameter when converted into a circular image having the same area as the projected area of the main surface. In addition, in the case of non-normal crystals, for example, in the case of spherical particles, rod-shaped particles, etc., the diameter when considering a sphere equivalent to the volume of the silver halide grains is calculated as the particle size. The measurement is performed using an electron micrograph, and the average particle diameter is obtained by averaging the measured values of the particle diameters of 300 particles.

  In the present invention, the gradation of the image density can be adjusted by using silver halide grains having an average particle diameter of 55 to 100 nm and silver halide grains having an average particle diameter of 10 to 50 nm in combination. In addition, the image density can be improved, and the decrease in image density over time can be improved (smaller). The ratio (mass ratio) of silver halide grains having an average particle diameter of 10 to 50 nm and silver halide grains having an average particle diameter of 55 to 100 nm is preferably 95: 5 to 50:50, more preferably 90. : 10-60: 40.

  As described above, when two types of silver halide grain emulsions having an average particle diameter are used, the two types of silver halide emulsions may be mixed and contained in the photosensitive layer. In order to adjust the gradation, it is also preferred that the photosensitive layer is composed of two or more layers, and each layer contains the silver halide grain emulsions having the two average grain sizes separately.

(Silver halide grains having a silver iodide content of 5 to 100 mol%)
As the silver halide grains according to the present invention, silver halide grains having a silver iodide content of 5 to 100 mol% are used. More preferably, it is 40-100 mol%, More preferably, it is 70-100 mol%, Most preferably, it is 90-100 mol%. If the silver iodide content is within this range, the intragranular halogen composition distribution may be uniform, changed stepwise, or continuously changed. Further, silver halide grains having a core / shell structure having a high silver iodide content inside and / or on the surface can also be preferably used. A preferable core / shell structure is a 2- to 5-fold structure, more preferably a 2- to 4-fold structure.

  As a method for introducing silver iodide into the silver halide grains, a method of adding an alkali iodide aqueous solution during grain formation, fine grain silver iodide, fine grain silver iodobromide, fine grain silver iodochloride, fine grain silver iodochlorobromide Among them, a method of adding at least one kind of fine particles, a method of using an iodide ion releasing agent described in JP-A-5-323487 and JP-A-6-11780 are preferable.

  The silver halide grain according to the present invention preferably exhibits direct transition absorption derived from the silver iodide crystal structure at a wavelength of 350 to 440 nm. Whether or not silver halide has light absorption of direct transition can be easily distinguished by the fact that exciton absorption due to direct transition is observed in the vicinity of 400 to 430 nm.

(Heat conversion internal latent image type silver halide grains)
The photosensitive silver halide grains are preferably silver halide grains whose surface sensitivity is lowered by converting from a surface latent image type to an internal latent image type by heat development. That is, in the exposure before heat development, a latent image that can function as a catalyst for a development reaction (reduction reaction of silver ions by a silver ion reducing agent) is formed on the surface of the silver halide grains, and the exposure after the heat development process has passed. Then, since many latent images are formed inside the surface of the silver halide grains, the silver halide grains are characterized in that the formation of latent images on the surface is suppressed. Heretofore, it has not been known to use silver halide grains having a latent image forming function greatly changed before and after the heat development processing in the photothermographic material.

  In general, when photosensitive silver halide grains are exposed, the silver halide grains themselves or spectral sensitizing dyes adsorbed on the surface of the photosensitive silver halide grains are photoexcited to freely move electrons. Although generated, these electrons are competitively trapped (captured) by an electron trap (photosensitive center) existing on the surface of the silver halide grain or an electron trap inside the grain. Therefore, when there are more chemical sensitization centers (chemical sensitization nuclei) and dopants effective as electron traps on the surface than inside the silver halide grains and there are an appropriate number, latent images are formed on the surface preferentially and developed. It becomes possible. Conversely, if there are more chemical sensitization centers (chemical sensitization nuclei) and dopants effective as electron traps on the inside than the surface of the silver halide grains and there is an appropriate number, a latent image is preferentially formed inside. Surface development becomes difficult. In other words, in the former case, the surface sensitivity is higher than in the interior, and in the latter case, it can be said that the surface sensitivity is lower than in the interior (TH James Edition: The Theory of the Photographic Process, 4th edition, McCillan). Publishing Co., Ltd. 1977, edited by the Japan Photographic Society: Revised Basics of Photographic Engineering (Silver Salt Photography), Corona, 1998, etc.).

  In the photosensitive silver halide grain according to the present invention, it is preferable in terms of sensitivity and image storage stability to contain a dopant functioning as an electron trapping dopant at least during exposure after heat development. . In addition, a dopant that functions as a hole trap at the time of exposure for image formation before heat development, changes in the heat development process, and can function as an electron trap after heat development. Particularly preferred.

  The electron trapping dopant used here is an element or compound other than silver and halogen constituting silver halide grains, and the dopant itself has a property of trapping (capturing) free electrons, or the dopant is halogen. This refers to a material in which a site such as an electron trapping lattice defect is generated by being contained in a silver halide grain. For example, metal ions other than silver or salts or complexes thereof, chalcogens (oxygen group elements) such as sulfur, selenium and tellurium, or inorganic or organic compounds containing nitrogen atoms, or metal complexes thereof, rare earth ions or complexes thereof, etc. Is mentioned.

  Examples of metal ions or salts or complexes thereof include lead ions, bismuth ions, gold ions, etc., or lead bromide, lead nitrate, lead carbonate, lead sulfate, bismuth nitrate, bismuth chloride, bismuth trichloride, bismuth carbonate, sodium bismuthate Chloroauric acid, lead acetate, lead stearate, bismuth acetate and the like.

  As the compound containing chalcogen such as sulfur, selenium, and tellurium, various chalcogen-releasing compounds generally known as chalcogen sensitizers in the photographic industry can be used. Moreover, as an organic substance containing chalcogen or nitrogen, a heterocyclic compound is preferable. For example, imidazole, pyrazole, pyridine, pyrimidine, pyrazine, pyridazine, triazole, triazine, indole, indazole, purine, thiadiazole, oxadiazole, quinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole , Thiazole, oxazole, benzimidazole, benzoxazole, benzothiazole, indolenine, tetrazaindene, preferably imidazole, pyridine, pyrimidine, pyrazine, pyridazine, triazole, triazine, thiadiazole, oxadiazole, quinoline, phthalazine, naphthyridine , Quinoxaline, quinazoline, cinnoline, tetrazole, thiazole, ox Tetrazole, benzimidazole, benzoxazole, benzothiazole, tetraazaindene.

  The heterocyclic compound may have a substituent, and the substituent is preferably an alkyl group, an alkenyl group, an aryl group, an alkoxy group, an aryloxy group, an acyloxy group, an acyl group, or an alkoxycarbonyl group. Aryloxycarbonyl group, acyloxy group, acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, sulfonyl group, ureido group, phosphoric acid amide group, halogen atom, cyano group, Sulfo group, carboxyl group, nitro group and heterocyclic group, more preferably alkyl group, aryl group, alkoxy group, aryloxy group, acyl group, acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamido. Group, sulfamoyl group, carbamoyl group, ureido group, phosphoric acid amide group, halogen atom, cyano group, nitro group, heterocyclic group, more preferably alkyl group, aryl group, alkoxy group, aryloxy group, acyl group, An acylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, a halogen atom, a cyano group, a nitro group, and a heterocyclic group.

  The silver halide grains include transition metal ions belonging to groups 6 to 11 of the periodic table so that they function as electron trapping dopants as described above or as hole trapping dopants. May be included by chemically adjusting the oxidation state of the metal with a ligand (ligand) or the like. As the transition metal, W, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, and Pt are preferable.

  As for the various dopants described above, one kind may be used, or two or more kinds of the same kind or different kinds of compounds or complexes may be used in combination. However, at least one kind needs to function as an electron trapping dopant at the time of exposure after thermal development. These dopants may be introduced into the silver halide grains in any chemical form.

  In the present invention, an embodiment in which any one of Ir or Cu complex or salt is used alone is not preferable.

The preferable content of the dopant is preferably in the range of 1 × 10 ⁻⁹ to 1 × 10 mol and more preferably in the range of 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ mol with ^respect to 1 mol of silver. Furthermore, 1 * 10 ^{< -6} > ^-1 * 10 ^<-2> mol is preferable. However, since the optimum amount depends on the kind of dopant, the grain size and shape of the silver halide grains, and other environmental conditions, it is preferable to examine optimization of the dopant addition conditions according to these conditions.

  As the transition metal complex or complex ion, those represented by the following general formula are preferable.

General formula [ML ₆ ] ^m
In the formula, M represents a transition metal selected from Group 6 to 11 elements in the periodic table, L represents a ligand, and m represents 0,-, 2-, 3-, or 4-. Specific examples of the ligand represented by L include halogen ion (fluorine ion, chlorine ion, bromine ion, iodine ion), cyanide, cyanate, thiocyanate, selenocyanate, tellurocyanate, azide, and aco. A ligand, nitrosyl, thionitrosyl and the like can be mentioned, and ako, nitrosyl, thionitrosyl and the like are preferable. When an acoligand is present, it preferably occupies one or two of the ligands. L may be the same or different.

  The compounds providing these metal ions or complex ions are preferably added at the time of silver halide grain formation and incorporated into the silver halide grains. Preparation of silver halide grains, that is, nucleation, growth, physical ripening In addition, it may be added at any stage before or after chemical sensitization, but it is particularly preferable to add it at the stage of nucleation, growth and physical ripening, and more preferably at the stage of nucleation and growth. Most preferably, it is added at a later stage or immediately after nucleation. In addition, it may be divided and added several times, and can be uniformly contained in the silver halide grains. For example, JP-A-63-29603, JP-A-2-306236, As described in JP-A-3-167545, JP-A-4-76534, JP-A-6-110146, JP-A-5-273683, etc., the particles may be included with a distribution.

  These metal compounds can be added by dissolving in water or an appropriate organic solvent (alcohols, ethers, glycols, ketones, esters, amides). For example, an aqueous solution of metal compound powder or metal A method in which an aqueous solution in which a compound, NaCl, and KCl are dissolved together is added to a water-soluble silver salt solution or a water-soluble halide solution during particle formation, or when the silver salt solution and the halide solution are mixed at the same time. Add as a third aqueous solution and prepare silver halide grains by the method of simultaneous mixing of three liquids, add a required amount of an aqueous solution of a metal compound to the reaction vessel during grain formation, or prepare in advance at the time of silver halide preparation There is a method of adding and dissolving another silver halide grain doped with metal ions or complex ions. In particular, a method of adding an aqueous solution of a metal compound powder or an aqueous solution in which a metal compound and NaCl, KCl are dissolved together is added to the water-soluble halide solution. When added to the particle surface, a required amount of an aqueous solution of a metal compound can be charged into the reaction vessel immediately after the formation of the particle, during or after physical ripening, or at the time of chemical ripening.

  In addition, a nonmetallic dopant can also be introduce | transduced inside a silver halide by the method similar to said metallic dopant.

  In the photothermographic material of the present invention, whether or not the above dopant has an electron trapping property can be evaluated by a method generally used in the photographic industry as follows. That is, a silver halide emulsion comprising silver halide grains doped with the above-mentioned dopant or a decomposition product thereof in silver halide grains is subjected to photoconductivity measurement using a microwave photoconductivity measurement method or the like, and the halogenation does not contain a dopant. It can be evaluated by measuring the degree of decrease in photoconduction based on a silver grain emulsion. Alternatively, it can be performed by a comparative experiment of the internal sensitivity and surface sensitivity of the silver halide grains.

  Alternatively, after making the photothermographic material, the method for evaluating the effect of the electron trapping dopant according to the present invention is, for example, heating the photothermographic material under the same conditions as normal practical heat development conditions before exposure. Then, for a certain period of time (for example, 30 seconds), white light or light in a specific spectral sensitization region (when spectral sensitization is performed on laser light in a specific wavelength region, For example, when spectral sensitization is applied to infrared light, infrared light, light in a photosensitive region unique to silver halide grains, for example, blue light when sensitized to blue light) is optical It is obtained on the basis of a characteristic curve (sensitometry curve) obtained by exposing through a wedge or performing exposure by changing the illuminance of the surface of the photosensitive material of the laser light stepwise, and further by heat development under the same heat development conditions as described above. Sensitivity to the electron trapping dopant It can be evaluated by comparing the sensitivity of the photothermographic materials using silver halide grain emulsion which does not contain. That is, it can be confirmed by confirming that the sensitivity of the former sample containing the silver halide grain emulsion containing the dopant according to the present invention is lower than the sensitivity of the latter sample not containing the dopant.

  The photothermographic material is usually exposed after being exposed for a certain period of time by white light or light in a specific spectral sensitization region through an optical wedge or by changing the photothermographic material surface illuminance of laser light stepwise. With respect to the sensitivity (S1) obtained based on the characteristic curve obtained when thermal development is performed under the practical thermal development conditions, heating is performed under the same conditions as the thermal development conditions before exposure, and then the same as the exposure described above. The sensitivity (S2) obtained on the basis of a characteristic curve obtained by exposure under exposure conditions and thermal development under the same development conditions as the thermal development is 1/10 or less, preferably 1/20 as a relative ratio (S2 / S1). Hereinafter, in the case of a photothermographic material in which a silver halide grain emulsion is further chemically sensitized, the sensitivity is preferably 1/50 or less. Furthermore, it is most preferable that the surface sensitivity after heat development is substantially zero in both cases where chemical sensitization is not performed and when chemical sensitization is performed.

  Here, normal heat development conditions are used when a silver salt photothermographic material is thermally developed using a commercially available laser imager in a medical institution such as a hospital to obtain an image suitable for diagnostic use. It refers to conditions that are in an appropriate range for conditions such as temperature, development time, and environmental humidity.

  The silver halide grains may be added to the photosensitive layer by any method. For example, it is possible to prepare silver halide grains, particularly heat-converted internal latent image type silver halide grains in advance, and add them to a solution for preparing aliphatic carboxylic acid silver salt grains. The particle preparation step and the aliphatic carboxylic acid silver salt particle preparation step can be handled separately, which is preferable in terms of production control. In addition, it is more preferable to prepare silver halide grains and aliphatic silver carboxylate grains separately and add them to the photosensitive layer preparation liquid immediately before the coating step.

  Separately prepared photosensitive silver halide grains are subjected to desalting by using a known desalting method such as a noodle method, a flocculation method, an ultrafiltration method or an electrodialysis method. However, it can be used without desalting.

  The silver halide grains according to the present invention are used in an amount of 0.001 to 0.7 mol, preferably 0.03 to 0.5 mol, per mol of the aliphatic carboxylic acid silver salt.

(Chemical sensitization)
The photosensitive silver halide grains can be chemically sensitized. For example, by using a noble metal compound that releases a chalcogen such as sulfur, selenium or tellurium or a noble metal ion such as gold ion by the method described in JP-A Nos. 2001-249428 and 2001-249426, Chemical sensitization centers (chemical sensitization nuclei) capable of capturing electrons or holes generated by photoexcitation of photosensitive silver halide grains or spectral sensitizing dyes on the grains can be provided. In particular, chemical sensitization with an organic sensitizer containing a chalcogen atom is preferred.

  These organic sensitizers containing chalcogen atoms are preferably compounds having groups capable of adsorbing to silver halide and unstable chalcogen atom sites.

  These organic sensitizers are disclosed in JP-A-60-150046, JP-A-4-109240, JP-A-11-218874, JP-A-11-218875, JP-A-11-218876, JP-A-11-194447, etc. Sensitizers having various structures can be used, and among them, the chalcogen atom must be at least one compound having a structure in which a carbon atom or a phosphorus atom is bonded to a double bond. preferable. In particular, a thiourea derivative having a heterocyclic group and a triphenylphosphine sulfide derivative are preferred.

  As a method for performing chemical sensitization, techniques according to various chemical sensitization techniques commonly used in the production of conventional silver halide light-sensitive materials for wet processing can be used (edited by TH James: The Theory of the Photographic Process, 4th edition, McCillan Publishing Co., Ltd., edited by the Japan Photographic Society: Basics of Photographic Engineering (Silver Salt Photography), Corona, 1979, etc.). In particular, when the silver halide grain emulsion is previously chemically sensitized and then mixed with non-photosensitive organic silver salt grains, it can be chemically sensitized by a conventional method.

The amount of the chalcogen compound used as the organic sensitizer varies depending on the chalcogen compound used, silver halide grains, reaction environment for chemical sensitization, and the like, but it is 10 ⁻⁸ to 10 ⁻² per mole of silver halide. Moles are preferred, more preferably 10 ⁻⁷ to 10 ⁻³ moles. There are no particular restrictions on the environmental conditions for chemical sensitization, but in the presence of a compound capable of eliminating or reducing the size of silver chalcogenide or silver nuclei on the photosensitive silver halide grains. In particular, it may be preferable to perform chalcogen sensitization using an organic sensitizer containing a chalcogen atom in the presence of an oxidizing agent capable of oxidizing silver nuclei. The sensitizing conditions in this case are preferably 6 to 11 as pAg, more preferably 7 to 10, pH is preferably 4 to 10, more preferably 5 to 8, and the temperature is increased at 30 ° C. or less. It is preferable to give a feeling.

  Further, chemical sensitization using these organic sensitizers is preferably performed in the presence of a heteroatom-containing compound having adsorptivity to spectral sensitizing dyes or silver halide grains. By performing chemical sensitization in the presence of a compound having an adsorptivity to silver halide, dispersion of the chemical sensitization central core can be prevented, and high sensitivity and low fog can be achieved. Although the spectral sensitizing dye will be described later, preferred examples of the heteroatom-containing compound having an adsorptivity to silver halide include nitrogen-containing heterocyclic compounds described in JP-A-3-24537. Examples of the heterocyclic ring in the nitrogen-containing heterocyclic compound include pyrazole, pyrimidine, 1,2,4-triazole, 1,2,3-triazole, 1,3,4-thiadiazole, 1,2,3-thiadiazole, 1, Each ring such as 2,4-thiadiazole, 1,2,5-thiadiazole, 1,2,3,4-tetrazole, pyridazine, 1,2,3-triazine, a ring in which 2 to 3 of these rings are bonded, For example, triazolotriazole, diazaindene, triazaindene, pentazaindene ring and the like can be mentioned. A heterocyclic ring in which a monocyclic heterocyclic ring and an aromatic ring are condensed, for example, phthalazine, benzimidazole, indazole, benzothiazole ring and the like can also be applied.

  Among these, an azaindene ring is preferable, and an azaindene compound having a hydroxyl group as a substituent, for example, hydroxytriazaindene, hydroxytetrazaindene, hydroxypentazaindene compound and the like are more preferable.

  The heterocyclic ring may have a substituent other than the hydroxyl group. Examples of the substituent include (substituted) alkyl groups, alkylthio groups, amino groups, hydroxyamino groups, alkylamino groups, dialkylamino groups, arylamino groups, carboxyl groups, alkoxycarbonyl groups, halogen atoms, cyano groups, and the like. May be.

The amount of the heterocyclic compound added varies over a wide range depending on the size and composition of the silver halide grains, other conditions, etc., but the approximate amount is from 10 ⁻⁶ to 10 ⁻⁶ per mole of silver halide. The range is 1 mol, and preferably in the range of 10 ⁻⁴ to 10 ⁻¹ mol.

  The photosensitive silver halide can be subjected to noble metal sensitization using a compound that releases noble metal ions such as gold ions. For example, a chloroaurate or an organic gold compound can be used as a gold sensitizer. The gold sensitization technique disclosed in JP-A-11-194447 is useful as a reference.

  In addition to the above sensitization methods, reduction sensitization methods and the like can also be used. Examples of reduction sensitization shell-like compounds include ascorbic acid, thiourea dioxide, stannous chloride, hydrazine derivatives, and borane compounds. A silane compound, a polyamine compound, or the like can be used. Further, reduction sensitization can be performed by ripening the emulsion while maintaining the pH at 7 or higher or the pAg at 8.3 or lower.

  The silver halide grains subjected to chemical sensitization may be those formed in the presence of an aliphatic carboxylic acid silver salt, those formed in the absence of the organic silver salt, or a mixture of both. It may be done.

  When the surface of the photosensitive silver halide grain is chemically sensitized, it is necessary that the chemical sensitization effect substantially disappears after the thermal development process. Here, the effect of chemical sensitization substantially disappears when the sensitivity of the photothermographic material obtained by the chemical sensitization technique is 1. Say to decrease to 1 times or less. In order to eliminate the chemical sensitization effect in the thermal development process, an oxidant capable of destroying the chemical sensitization center (chemical sensitization nucleus) by an oxidation reaction at the time of thermal development, such as a halogen radical releasing compound described later, etc. It is necessary to contain an appropriate amount in the emulsion layer and / or the non-photosensitive layer of the photothermographic material. The content of the oxidizing agent is preferably adjusted in consideration of the oxidizing power of the oxidizing agent, the reduction range of the chemical sensitization effect, and the like.

(Spectral sensitization)
The photosensitive silver halide of the present invention is preferably subjected to spectral sensitization by adsorbing a spectral sensitizing dye. As the spectral sensitizing dye, dyes such as cyanine, merocyanine, complex cyanine, complex merocyanine, holopolar cyanine, styryl, hemicyanine, oxonol, hemioxonol and the like can be used. For example, JP-A-63-159841, JP-A-60-140335, JP-A-63-231437, JP-A-63-259651, JP-A-63-304242, JP-A-63-15245, U.S. Pat. The sensitizing dyes described in US Pat. Nos. 4,740,455, 4,741,966, 4,751,175, and 4,835,096 can be used.

  Useful sensitizing dyes used in the present invention are described in, for example, Research Disclosure (hereinafter abbreviated as RD) 17643IV-A (December 1978, page 23), RD18431X (August 1978, page 437). It is described in the document described or cited. In particular, it is preferable to use a sensitizing dye having a spectral sensitivity suitable for the spectral characteristics of various laser imagers and scanner light sources. For example, compounds described in JP-A Nos. 9-34078, 9-54409, and 9-80679 are preferably used.

  Useful cyanine dyes are cyanine dyes having basic nuclei such as thiazoline nucleus, oxazoline nucleus, pyrroline nucleus, pyridine nucleus, oxazole nucleus, thiazole nucleus, selenazole nucleus and imidazole nucleus. Useful merocyanine dyes are preferably acidic nuclei such as thiohydantoin nucleus, rhodanine nucleus, oxazolidinedione nucleus, thiazolinedione nucleus, barbituric acid nucleus, thiazolinone nucleus, malononitrile nucleus and pyrazolone nucleus in addition to the above basic nucleus. Including.

  In the present invention, a sensitizing dye having spectral sensitivity particularly in the infrared can also be used. Examples of infrared spectral sensitizing dyes preferably used include infrared spectral sensitizing dyes disclosed in U.S. Pat. Nos. 4,536,473, 4,515,888, and 4,959,294. It is done.

  In the photothermographic material used in the heat development method of the present invention, the sensitizing dye represented by the general formula (1) and the general formula (2) described in U.S. Published Patent Application No. 20,040,224,266. It is preferable to select and contain at least one of sensitizing dyes represented by general formula (5), and at least from the sensitizing dye represented by general formula (5) and the sensitizing dye represented by general formula (6). It is more preferable to select and contain one kind. It is particularly preferable to use a sensitizing dye represented by the general formula (5) and a sensitizing dye represented by the general formula (6) in order to improve the exposure wavelength dependency during exposure.

  The above-described infrared sensitizing dyes are described in, for example, F. F. Hammer: The Chemistry of Heterocyclic Compounds, Vol. 18, The Cyanine Dies and Related Compounds, published by A. Weissberger ed. It can be easily synthesized by the method described.

  These infrared sensitizing dyes may be added at any time after the preparation of the silver halide. For example, it is added to a solvent or dispersed in the form of fine particles, so-called silver halide grains or silver halides in a solid dispersion state. It can be added to a light-sensitive emulsion containing grains / silver aliphatic carboxylate grains. Similarly to the heteroatom-containing compound having adsorptivity to the silver halide grains, chemical sensitization can be performed after adding and adsorbing to the silver halide grains prior to chemical sensitization. Thus, dispersion of the chemical sensitization central core can be prevented, and high sensitivity and low fog can be achieved.

  The above spectral sensitizing dyes may be used alone, but as described above, it is preferable to use a combination of a plurality of types of spectral sensitizing dyes. Often used for purposes such as supersensitization and expansion or adjustment of the photosensitive wavelength region.

  The emulsion containing the photosensitive silver halide and aliphatic carboxylic acid silver salt used in the photothermographic material of the present invention substantially absorbs a dye having no spectral sensitizing action or visible light itself together with a sensitizing dye. A substance that does not exhibit a supersensitization effect may be included in the emulsion, whereby the silver halide grains may be supersensitized.

  Useful sensitizing dyes, combinations of dyes exhibiting supersensitization, and substances exhibiting supersensitization are described in RD17643 (issued in December, 1978), page 23, Section J, or Japanese Patent Publication No. 9-25500, 43-4933, JP-A-59-19032, JP-A-59-192242, JP-A-5-341432, and the like. Examples of supersensitizers include heteroaromatic mercapto represented by the following. A compound or a mercapto derivative compound is preferred.

Ar-SM
In the formula, M is a hydrogen atom or an alkali metal atom, and Ar is an aromatic ring or condensed aromatic ring having one or more nitrogen, sulfur, oxygen, selenium or tellurium atoms.

  Preferably, heteroaromatic benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotelrazole, imidazole, oxazole, pyrazole, triazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine , Purine, quinoline, quinazoline and the like. However, other heteroaromatic rings are also included.

  In addition, a mercapto derivative compound which substantially forms the above mercapto compound when contained in a dispersion of an aliphatic carboxylic acid silver salt or a silver halide grain emulsion is also included. In particular, mercapto derivative compounds represented below are preferred examples.

Ar-SS-Ar
Ar in the formula has the same meaning as in the case of the mercapto compound represented above.

  The heteroaromatic ring is, for example, a halogen atom (chlorine, bromine, iodine), a hydroxyl group, an amino group, a carboxyl group, an alkyl group (preferably having 1 to 4 carbon atoms) and an alkoxy group (preferably 1). Can have a substituent selected from the group consisting of ˜4 carbon atoms).

  In addition to the supersensitizer, a macrocyclic compound having a heteroatom disclosed in JP-A No. 2001-330918 can also be used.

  These supersensitizers are preferably used in a photosensitive layer containing an organic silver salt and silver halide grains in an amount of 0.001 to 1.0 mole per mole of silver. Particularly preferred is an amount of 0.01 to 0.5 mole per mole of silver.

  In the present invention, it is preferable that spectral sensitization is performed by adsorbing a spectral sensitizing dye on the surface of photosensitive silver halide grains, and that the spectral sensitization effect substantially disappears after the thermal development process. . Here, the spectral sensitization effect substantially disappears when the sensitivity of the photothermographic material obtained with a sensitizing dye, supersensitizer, etc. is not subjected to spectral sensitization after the thermal development process. It is said to decrease to 1.1 times or less.

  In order to eliminate the spectral sensitizing effect in the thermal development process, a spectral sensitizing dye that is easily detached from the silver halide grains by heat is used during thermal development, or / and the spectral sensitizing dye is oxidized by an oxidation reaction. It is necessary to contain an appropriate amount of an oxidizing agent that can be destroyed, such as the above-mentioned halogen radical releasing compound, in the emulsion layer and / or the non-photosensitive layer of the photothermographic material. The content of the oxidizing agent is preferably adjusted in consideration of the oxidizing power of the oxidizing agent, the reduction range of the spectral sensitization effect, and the like.

(Reducing agent)
The reducing agent is capable of reducing silver ions in the photosensitive layer and is also called a developer.

  In the present invention, it is preferable that at least one silver ion reducing agent is a compound represented by the following general formula (RD1) alone or in combination with a reducing agent having another different chemical structure.

In the formula, X ₁ represents a chalcogen atom or CHR ₁ , and R ₁ represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an aryl group or a heterocyclic group. R ₂ represents an alkyl group and may be the same or different. R ₃ represents a hydrogen atom or a group that can be substituted on a benzene ring. R ₄ represents a group that can be substituted on the benzene ring, and m and n each represents an integer of 0 to 2.

Among the compounds represented by the general formula (RD1), it is particularly preferable to use a highly active reducing agent (hereinafter referred to as a compound of RD1a) in which at least one of R ₂ is a secondary or tertiary alkyl group. It is more preferable in that a heat-developable photographic material having a high concentration and excellent in light irradiation image storage stability can be obtained.

  In order to obtain a desirable color tone, it is preferable to use a compound of (RD1a) and a compound of the following general formula (RD2).

In the formula, X ₂ represents a chalcogen atom or CHR ₅ , and R ₅ represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an aryl group or a heterocyclic group. R ₆ represents an alkyl group, which may be the same or different, but is not a secondary or tertiary alkyl group. R ₇ represents a hydrogen atom or a group that can be substituted on a benzene ring. R ₈ represents a group substitutable on the benzene ring, and m and n each represents an integer of 0 to 2.

  The combined ratio of both reducing agents is preferably [mass of compound of (RD1a)]: [mass of compound of (RD2)] is 5:95 to 45:55, more preferably 10:90 to 40. : 60.

  Hereinafter, the compounds represented by the general formulas (RD1) and (RD2) will be described in detail.

In the general formula (RD1), X ₁ represents a chalcogen atom or CHR ₁ . The chalcogen atom is sulfur, selenium or tellurium, preferably a sulfur atom. R ₁ in CHR ₁ represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an aryl group or a heterocyclic group. The halogen atom is a fluorine, chlorine, bromine atom or the like, and the alkyl group is preferably a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. Specific examples include methyl, ethyl, propyl, butyl, hexyl, heptyl. Alkenyl groups include vinyl, allyl, butenyl, hexenyl, hexadienyl, ethenyl-2-propenyl, 3-butenyl, 1-methyl-3-propenyl, 3-pentenyl, 1-methyl-3-butenyl, etc .; aryl groups As phenyl, naphthyl group; and heterocyclic groups as thienyl, furyl, imidazolyl, pyrazolyl, pyrrolyl and the like.

  These groups may further have a substituent, specifically, halogen atoms (fluorine, chlorine, bromine, etc.), alkyl groups (methyl, ethyl, propyl, butyl, pentyl, i-pentyl, 2- Ethylhexyl, octyl, decyl, etc.), cycloalkyl groups (cyclohexyl, cycloheptyl, etc.), alkenyl groups (ethenyl, 2-propenyl, 3-butenyl, 1-methyl-3-propenyl, 3-pentenyl, 1-methyl-3- Butenyl, etc.), cycloalkenyl groups (1-cycloalkenyl, 2-cycloalkenyl groups, etc.), alkynyl groups (ethynyl, 1-propynyl, etc.), alkoxy groups (methoxy, ethoxy, propoxy, etc.), alkylcarbonyloxy groups (acetyloxy) Etc.), alkylthio group (methylthio, trifluoromethylthio, etc.), acyl group (aceto , Benzoyl, etc.), carboxyl group, alkylcarbonylamino group (acetylamino etc.), ureido group (methylaminocarbonylamino etc.), alkylsulfonylamino group (methanesulfonylamino etc.), alkylsulfonyl group (methanesulfonyl, trifluoromethanesulfonyl) ), Carbamoyl group (carbamoyl, N, N-dimethylcarbamoyl, N-morpholinocarbonyl, etc.), sulfamoyl group (sulfamoyl, N, N-dimethylsulfamoyl, morpholinosulfamoyl etc.), trifluoromethyl group, hydroxyl group Nitro group, cyano group, alkylsulfonamide group (methanesulfonamide, butanesulfonamide, etc.), alkylamino group (amino, N, N-dimethylamino, N, N-diethylamino, etc.), sulfo group Phosphono group, sulfite group, sulfino group, alkylsulfonylaminocarbonyl group (methanesulfonylaminocarbonyl, ethanesulfonylaminocarbonyl, etc.), alkylcarbonylaminosulfonyl group (acetamidosulfonyl, methoxyacetamidosulfonyl, etc.), alkynylaminocarbonyl group (acetamidocarbonyl) , Methoxyacetamidocarbonyl, etc.), alkylsulfinylaminocarbonyl groups (methanesulfinylaminocarbonyl, ethanesulfinylaminocarbonyl, etc.) and the like. Moreover, when there are two or more substituents, they may be the same or different. Particularly preferred substituents are alkyl groups.

R ₂ represents an alkyl group, which may be the same or different, but at least one is preferably a secondary or tertiary alkyl group. The alkyl group is preferably a substituted or unsubstituted one having 1 to 20 carbon atoms, specifically, methyl, ethyl, propyl, i-propyl, butyl, i-butyl, t-butyl, t-pentyl, t-octyl. , Cyclohexyl, cyclopentyl, 1-methylcyclohexyl, 1-methylcyclopropyl and the like. Although the substituent of the alkyl group is not particularly limited, for example, aryl group, hydroxyl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, acylamino group, sulfonamido group, sulfonyl group, phosphoryl group, acyl group, carbamoyl group, An ester group, a halogen atom, etc. are mentioned. Or it may form a saturated ring with (R ₄₎ n and (R ₄₎ m. R ₂ is preferably a secondary or tertiary alkyl group, and preferably has 2 to 20 carbon atoms. A tertiary alkyl group is more preferable, t-butyl, t-pentyl, and 1-methylcyclohexyl group are more preferable, and a t-butyl group is most preferable.

R ₃ represents a hydrogen atom or a group that can be substituted on a benzene ring. Examples of the group that can be substituted on the benzene ring include halogen atoms such as fluorine, chlorine, bromine, alkyl groups, aryl groups, cycloalkyl groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, amino groups, acyl groups, acyloxy groups, Examples include acylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, sulfonyl group, alkylsulfonyl group, sulfinyl group, cyano group, and heterocyclic group. R ₃ is preferably methyl, ethyl, i-propyl, t-butyl, cyclohexyl, 1-methylcyclohexyl, 2-hydroxyethyl group or the like. More preferred are methyl and 2-hydroxyethyl groups.

These groups may further have a substituent, and the substituents mentioned in the above R ₁ can be used as the substituent. R ₃ is preferably a C 1-20 alkyl group having a hydroxyl group or a precursor group thereof, and more preferably a C 1-5 alkyl group. Most preferred is a 2-hydroxyethyl group.

In the most preferred combination of R ₂ and R ₃ , R ₂ is a tertiary alkyl group (t-butyl, 1-methylcyclohexyl, etc.), and R ₃ is a primary alkyl group having a hydroxyl group or a precursor group thereof ( 2-hydroxyethyl and the like). A plurality of R ₂ and R ₃ may be the same or different.

R ₄ represents a hydrogen atom or a group capable of substituting on the benzene ring, specifically, an alkyl group having 1 to 25 carbon atoms (methyl, ethyl, propyl, i-propyl, t-butyl, pentyl, hexyl, decyl, Octadecyl etc.), halogenated alkyl group (trifluoromethyl, perfluorooctyl etc.), cycloalkyl group (cyclohexyl, cyclopentyl etc.), alkynyl group (propargyl etc.), glycidyl group, acrylate group, methacrylate group, aryl group (phenyl, Naphthyl, etc.), heterocyclic groups (pyridyl, thiazolyl, oxazolyl, imidazolyl, furyl, pyrrolyl, pyrazinyl, pyrimidinyl, pyridazinyl, selenazolyl, sriphoranyl, piperidinyl, pyrazolyl, tetrazolyl, etc.), halogen atoms (chlorine, bromine, iodine, fluorine), Alkoxy (Methoxy, ethoxy, propyloxy, pentyloxy, cyclopentyloxy, hexyloxy, cyclohexyloxy, etc.), aryloxy groups (phenoxy, etc.), alkoxycarbonyl groups (methyloxycarbonyl, ethyloxycarbonyl, butyloxycarbonyl, etc.), aryloxy Carbonyl group (phenyloxycarbonyl, etc.), sulfonamide group (methanesulfonamide, ethanesulfonamide, butanesulfonamide, hexanesulfonamide group, cyclohexanesulfonamide, benzenesulfonamide, etc.), sulfamoyl group (aminosulfonyl, methylaminosulfonyl, Dimethylaminosulfonyl, butylaminosulfonyl, hexylaminosulfonyl, cyclohexylaminosulfonyl, phenylaminosulfo Nyl, 2-pyridylaminosulfonyl, etc.), urethane groups (methylureido, ethylureido, pentylureido, cyclohexylureido, phenylureido, 2-pyridylureido, etc.), acyl groups (acetyl, propionyl, butanoyl, hexanoyl, cyclohexanoyl, benzoyl) , Pyridinoyl etc.), carbamoyl group (aminocarbonyl, methylaminocarbonyl, dimethylaminocarbonyl, propylaminocarbonyl, pentylaminocarbonyl group, cyclohexylaminocarbonyl, phenylaminocarbonyl, 2-pyridylaminocarbonyl), amide group (acetamide, propionamide, Butanamide, hexaneamide, benzamide, etc.), sulfonyl group (methylsulfonyl, ethylsulfonyl, butylsulfonyl, Cyclohexylsulfonyl, phenylsulfonyl, 2-pyridylsulfonyl, etc.), amino group (amino, ethylamino, dimethylamino, butylamino, cyclopentylamino, anilino, 2-pyridylamino, etc.), cyano group, nitro group, sulfo group, carboxyl group , Hydroxyl group, oxamoyl group and the like. These groups may be further substituted with these groups. n and m represent an integer of 0 to 2, and most preferably n and m are 0.

R ₄ may form a saturated ring with R ₂ and R ₃ . R ₄ is preferably a hydrogen atom, a halogen atom or an alkyl group, more preferably a hydrogen atom. A plurality of R ₄ may be the same or different.

In General Formula (RD2), R ₅ is the same group as R ₁ , R ₇ is the same group as R _3, and R ₈ is the same group as R ₄ . R ₆ represents an alkyl group, which may be the same or different, but is not a secondary or tertiary alkyl group. The alkyl group is preferably a substituted or unsubstituted one having 1 to 20 carbon atoms, and specific examples include methyl, ethyl, propyl, butyl, hexyl, octyl and the like. Although the substituent of the alkyl group is not particularly limited, for example, aryl group, hydroxyl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, acylamino group, sulfonamido group, sulfonyl group, phosphoryl group, acyl group, carbamoyl group, An ester group, a halogen atom, etc. are mentioned.

R ₆ may form a saturated ring with (R ₈ ) n and (R ₈ ) m. R ₆ is preferably a methyl group. Among the compounds represented by the general formula (RD-2), compounds preferably used are compounds satisfying the general formula (S) and general formula (T) described in European Patent No. 1,278,101. Specifically, the compounds of (1-24), (1-28) to (1-54), and (1-56) to (1-75) described on pages 21 to 28 of the same publication can be mentioned.

  Specific examples of the compounds represented by general formula (RD1) and general formula (RD2) are shown below, but the present invention is not limited to these.

  These bisphenol compounds represented by the general formula (RD1) and general formula (RD2) can be easily synthesized by a conventionally known method.

  Examples of the reducing agent that can be used in the present invention further include, for example, the specifications of US Pat. Nos. 3,770,448, 3,773,512, and 3,593,863, RD17029 and 29963. And reducing agents described in JP-A-11-119372 and JP-A-2002-62616.

The amount of the reducing agent including the compound represented by the general formula (RD1) is preferably 1 × 10 ⁻² to 10 mol, particularly preferably 1 × 10 ^{−2 to} 1.5 mol, per mol of silver. It is.

(Image tone)
Next, the color tone of an image obtained by thermally developing a photothermographic material will be described.

  With regard to the color tone of an output image for medical diagnosis such as a conventional X-ray photographic film, it is said that a cool tone image tone is easier for a reader to obtain a more accurate diagnosis observation result. Here, the cool image tone means a pure black tone or a bluish black tone of a black image. On the other hand, the warm image tone is said to be a warm black tone with a black image, but in order to allow a more precise quantitative discussion, the International Lighting Commission (CIE) ), Based on the recommended expression.

The terms “more cold” and “more warm” regarding the color tone can be expressed by the hue angle hab at the minimum density D _min and the optical density D = 1.0. That is, the hue angle hab is expressed by the following equation using the color coordinates a ^* and b ^* of the L ^* a ^* b ^* color space, which is a color space having a perceptually uniform rate recommended by the CIE in 1976. Ask.

hab = tan-1 (b ^* / a ^* )
As a result of examination by the expression method based on the hue angle, the hue of the photothermographic material of the present invention after development is preferably such that the range of the hue angle hab is 180 degrees <hab <270 degrees, and more preferably 200 degrees < It has been found that hab <270 degrees, most preferably 220 degrees <hab <260 degrees. This is disclosed in Japanese Patent Application Laid-Open No. 2002-6463.

Conventionally, the CIE 1976 (L ^* u ^* v ^* ) color space or the (L ^* a ^* b ^* ) color space near the optical density of 1.0 is specified as u ^* , v ^* or a ^* , b ^* . It is known that a diagnostic image having a favorable color tone can be obtained by adjusting the numerical value, and is described in, for example, Japanese Patent Application Laid-Open No. 2000-29164.

However, as a result of further intensive studies on the photothermographic material of the present invention, the horizontal axis is u ^* or a ^* and the vertical axis in the CIE 1976 (L ^* u ^* v ^* ) color space or (L ^* a ^* b ^* ) color space. When plotting u ^* , v ^*, or a ^* , b ^* at various photographic densities on a graph with v ^* or b ^* as a linear regression line, the linear regression line is defined within a specific range. As a result, it has been found that it has a diagnostic performance equivalent to or higher than that of conventional wet silver salt photosensitive materials. A preferable range of conditions is described below.

1. The CIE 1976 (L ^* u ^* v ^* ) color space is measured by measuring the optical densities of 0.5, 1.0, 1.5 and the lowest optical density of the silver image obtained after heat development processing of the photothermographic material. of the horizontal axis u ^*, the vertical axis v ^* to the 2-dimensional coordinates to, the u ^* at each optical density, v ^* was placed create determine coefficients of a linear regression line was (multiple determination) R2 is 0.998 It is preferably ˜1.000. Furthermore, it is preferable that the v ^* value of the intersection with the vertical axis of the linear regression line is −5 to 5 and the slope (v ^* / u ^* ) is 0.7 to 2.5.

2. Also, the optical density of the photothermographic material is measured at 0.5, 1.0, 1.5 and the lowest optical density, and the horizontal axis of the CIE 1976 (L ^* a ^* b ^* ) color space is represented by a ^* , The coefficient of determination (multiple determination) R2 of the linear regression line created by arranging a ^* and b ^* at the respective optical densities on the two-dimensional coordinates with the vertical axis b ^* is 0.998 to 1.000. Is preferred. Furthermore, it is preferable that the b ^* value of the intersection with the vertical axis of the linear regression line is −5 to 5 and the slope (b ^* / a ^* ) is 0.7 to 2.5.

An example of a method for creating the above-described linear regression line, that is, a method for measuring u ^* , v ^*, a ^* , and b ^{* in} the CIE 1976 color space will be described next.

A four-stage wedge sample including an unexposed portion and optical densities of 0.5, 1.0, and 1.5 is prepared using a heat development apparatus. Each wedge density portion thus created is measured with a spectrocolorimeter (Minolta Co., Ltd .: CM-3600d, etc.) to calculate u ^* , v ^* or a ^* , b ^* . The measurement conditions at that time are F7 light source as the light source, the viewing angle is 10 degrees, and the measurement is performed in the transmission measurement mode. Plot u ^* , v ^* or a ^* , b ^* measured on a graph with u ^* or a ^{* on} the horizontal axis and v ^* or b ^{* on the} vertical axis to obtain a linear regression line, and the coefficient of determination (multiple determination) Find R2, intercept and slope.

  Next, a specific method for obtaining a linear regression line having the above characteristics will be described.

  In the present invention, adjustment of the addition amount of a compound or the like directly or indirectly involved in the development reaction process of a reducing agent (developer), silver halide grains, aliphatic silver carboxylate and the following toning agent, etc. Thus, the developed silver shape can be optimized to obtain a preferable color tone. For example, when the developed silver shape is dendritic, it becomes a bluish direction, and when it is a filament shape, it becomes a yellowish direction. That is, it can be adjusted in consideration of the tendency of the developed silver shape.

  Conventionally, phthalazinone or phthalazine and phthalic acids and phthalic anhydrides are generally used as toning agents. Examples of suitable toning agents are disclosed in RD17029, U.S. Pat. Nos. 4,123,282, 3,994,732, 3,846,136, 4,021,249, and the like.

  In the present invention, rapid processing is performed using a compact laser imager with a short cooling section length. However, there is a problem that the silver tone is greatly deviated from the neutral preferable tone as compared with the normal processing. In order to solve these problems, the above-mentioned conventional color-adjusting agents are insufficient, and compounds (such as leuco dyes and coupler compounds) that form a dye image by developing an imagewise color during heat development. )Is required. As these compounds, there are compounds that form a dye image that develops a color upon thermal development and has a maximum absorption wavelength of 360 to 450 nm, or compounds that develop a color upon thermal development and form a dye image that has a maximum absorption wavelength of 600 to 700 nm. Although it is preferable, the case of containing both compounds is particularly preferable for obtaining a good silver tone. As these compounds, it is preferable to use couplers disclosed in JP-A-11-288057, European Patent 1,134,611A2, etc., or leuco dyes described in detail below.

(Leuco dye)
The photothermographic material of the present invention can also be adjusted in color tone using a leuco dye as described above. The leuco dye is preferably a colorless or slightly colored compound that is oxidized to a colored form when heated at a temperature of about 80 to 200 ° C. for about 0.5 to 30 seconds. Any leuco dye that oxidizes to form a pigment can be used. Compounds that are pH sensitive and can be oxidized to a colored state are useful.

  Representative leuco dyes suitable for use in the present invention are not particularly limited, for example, biphenol leuco dyes, phenol leuco dyes, indoaniline leuco dyes, acrylated azine leuco dyes, phenoxazine leuco dyes, phenodiazine leuco dyes and phenothiazines. And leuco dyes. Also useful are U.S. Pat. Nos. 3,445,234, 3,846,136, 3,994,732, 4,021,249, 4,021,250, 4 No. 4,022,617, No. 4,123,282, No. 4,368,247, No. 4,461,681, No. 50-36110, No. 59-206831, No. 5-204087. No. 11-231460, JP-A Nos. 2002-169249, 2002-236334, and the like.

  In order to adjust to a predetermined color tone, it is preferable to use leuco dyes of various colors singly or in combination. Furthermore, with the use of a highly active reducing agent for rapid processing, the color tone (especially yellowish) changes depending on the amount and ratio of use, or fine silver halide grains are used, In order to prevent the image from becoming excessively reddish, especially in the high density part where the density is 2.0 or more, in combination with a leuco dye that develops yellow and cyan colors, the developed silver particle size is reduced. It is preferable to adjust the amount used.

  The color density is preferably adjusted appropriately in relation to the color tone of the developed silver itself. In the present invention, color is developed so as to have a reflection optical density of 0.01 to 0.05 or a transmission optical density of 0.005 to 0.50, and the color tone is adjusted so that an image in the above preferred color tone range is obtained. Is preferred. In the present invention, the sum of the maximum densities at the maximum absorption wavelength of the dye image formed with the leuco dye is preferably 0.01 to 0.50, more preferably 0.02 to 0.30, and particularly preferably 0. It is preferable to develop the color so as to have 0.03 to 0.10.

(Yellow coloring leuco dye)
The photothermographic material is preferably adjusted in color tone using a leuco dye as described above. In the present invention, a color image forming agent whose absorbance at 360 to 450 nm is increased by oxidation is particularly preferably used as a yellow color-forming leuco dye. These color image forming agents are particularly preferably color image forming agents represented by the following general formula (YA).

In the formula, R ₁₁ represents a substituted or unsubstituted alkyl group, R ₁₂ represents a hydrogen atom, a substituted or unsubstituted alkyl group or an acylamino group, and R ₁₁ and R ₁₂ are 2-hydroxyphenylmethyl groups. There is nothing. R ₁₃ represents a hydrogen atom or a substituted or unsubstituted alkyl group, and R ₁₄ represents a group that can be substituted on the benzene ring.

R ₁₁ represents a substituted or unsubstituted alkyl group. When R ₁₂ is a substituent other than a hydrogen atom, R ₁₁ represents an alkyl group. The alkyl group is preferably an alkyl group having 1 to 30 carbon atoms and may have a substituent. Specifically, groups such as methyl, ethyl, butyl, octyl, i-propyl, t-butyl, t-octyl, t-pentyl, sec-butyl, cyclohexyl, 1-methyl-cyclohexyl are preferable, and i-propyl group It is preferably a sterically larger group (i-propyl, i-nonyl, t-butyl, t-amyl, t-octyl, cyclohexyl, 1-methyl-cyclohexyl, adamantyl, etc.), among them secondary or A tertiary alkyl group is preferred, and tertiary alkyl groups such as t-butyl, t-octyl, and t-pentyl groups are particularly preferred. Examples of the substituent that R ₁₁ may have include a halogen atom, an aryl group, an alkoxy group, an amino group, an acyl group, an acylamino group, an alkylthio group, an arylthio group, a sulfonamido group, an acyloxy group, an oxycarbonyl group, and a carbamoyl group. , Sulfamoyl group, sulfonyl group, phosphoryl group and the like.

R ₁₂ represents a hydrogen atom, a substituted or unsubstituted alkyl group or an acylamino group, and the alkyl group is preferably an alkyl group having 1 to 30 carbon atoms, and the acylamino group is preferably an acylamino group having 1 to 30 carbon atoms. Among these, the description of the alkyl group is the same as R ₁₁ described above.

The acylamino group represented by R ₁₂ may be unsubstituted or substituted, and specific examples include an acetylamino group, an alkoxyacetylamino group, and an aryloxyacetylamino group. R ₁₂ is preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 24 carbon atoms, and specific examples include methyl, i-propyl, and t-butyl groups. R ₁₁ and R ₁₂ are not 2-hydroxyphenylmethyl groups.

R ₁₃ represents a hydrogen atom or a substituted or unsubstituted alkyl group, and the alkyl group is preferably an alkyl group having 1 to 30 carbon atoms, and the description of the alkyl group is the same as R ₁₁ described above. R ₁₃ is preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 24 carbon atoms, and specific examples include a methyl, i-propyl, and t-butyl group. Further, it is preferable either R _12, R ₁₃ is a hydrogen atom.

R ₁₄ represents a group substitutable on the benzene ring, and is, for example, the same group as described for the substituent R ₄ in the general formula (RD-1). R ₁₄ is preferably a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms or an oxycarbonyl group having 2 to 30 carbon atoms, and more preferably an alkyl group having 1 to 24 carbon atoms. Examples of the substituent of the alkyl group include an aryl group, an amino group, an alkoxy group, an oxycarbonyl group, an acylamino group, an acyloxy group, an imide group, and a ureido group, and more preferable examples include an aryl group, an amino group, an oxycarbonyl group, and an alkoxy group. preferable. These alkyl group substituents may be further substituted with these substituents.

  Next, the bisphenol compound represented by the following general formula (YB) that is particularly preferably used among the compounds represented by the general formula (YA) will be described.

In the formula, Z represents —S— or —C (R ₂₁ ) (R ₂₁ ′) —, and R ₂₁ and R ₂₁ ′ each represents a hydrogen atom or a substituent. Examples of the substituent represented by R ₂₁ and R ₂₁ ′ include the same groups as the substituents exemplified in the description of R _{1 in} the general formula (RD-1). R ₂₁ and R ₂₁ ′ are preferably a hydrogen atom or an alkyl group.

R ₂₂ , R ₂₃ , R ₂₂ ′ and R ₂₃ ′ each represent a substituent, and examples of the substituent include the same groups as those described for R ₂ and R ₃ in formula (RD-1). . R ₂₂ , R ₂₃ , R ₂₂ ′ and R ₂₃ ′ are preferably an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group, with an alkyl group being more preferred. Examples of the substituent on the alkyl group include the same groups as those described in the description of the substituent in formula (RD-1). R ₂₂ , R ₂₃ , R ₂₂ ′ and R ₂₃ ′ are more preferably tertiary alkyl groups such as t-butyl, t-pentyl, t-octyl and 1-methyl-cyclohexyl groups.

R ₂₄ and R ₂₄ ′ each represent a hydrogen atom or a substituent, and examples of the substituent include the same groups as the substituents described in the description of R ₄ in formula (RD-1).

  Examples of the compounds represented by the general formulas (YA) and (YB) include compounds described in paragraphs “0032” to “0038” of JP-A No. 2002-169249, (II-1) to (II-40), Europe Examples thereof include compounds (ITS-1) to (ITS-12) described in paragraph “0026” of Japanese Patent No. 1,211,093.

  Although the specific example of the bisphenol compound represented by general formula (YA) and (YB) below is shown, it is not limited to these.

  The amount of the compound of general formula (YA) (including hindered phenol compounds and compounds of general formula (YB)) is usually 0.00001 to 0.01 mol, preferably 0.0005, per mol of silver. It is -0.01 mol, More preferably, it is 0.001-0.008 mol.

  The addition ratio of the yellow coloring leuco dye to the total amount of the reducing agents represented by the general formulas (RD1) and (RD2) is preferably 0.001 to 0.2 in terms of molar ratio. It is more preferable that it is 005-0.1.

(Cyan coloring leuco dye)
In the photothermographic material of the present invention, it is preferable to adjust the color tone by using a cyan coloring leuco dye in addition to the yellow coloring leuco dye.

  The cyan color-forming leuco dye may be a colorless or slightly colored compound that is oxidized to a colored form when heated at a temperature of about 80 to 200 ° C. for about 0.5 to 30 seconds. Any leuco dye that can be oxidized by the body to form a pigment can be used. Compounds that are pH sensitive and can be oxidized to a colored state are useful.

  In the present invention, a color image forming agent that increases the absorbance at 600 to 700 nm when oxidized is preferably used. As these compounds, for example, JP-A-59-206831 (particularly compounds having λmax in the range of 600 to 700 nm), compounds of general formula (I) to general formula (IV) in JP-A-5-204087 ( Specifically, the compounds of (1) to (18) described in paragraphs “0032” to “0037”) and compounds of general formulas 4 to 7 in JP-A No. 11-231460 (specifically, paragraph “0105”). No. 1 to No. 79 compounds).

  Cyan chromogenic leuco dyes preferably used are compounds represented by general formula (CLA) and general formula (CLB). The color image forming agent represented by the general formula (CLB) described later is particularly preferable in that it has high color development efficiency, can be adjusted in color tone even when added in a small amount, and is excellent in image storage stability.

  Hereinafter, the compounds of the general formula (CLA) and the general formula (CLB) will be sequentially described.

In the formula, R ₃₁ and R ₃₂ are hydrogen atom, halogen atom, substituted or unsubstituted alkyl group, alkenyl group, alkoxy group, —NHCO—R ₃₀ group (R ₃₀ is an alkyl group, aryl group or heterocyclic group). Or R ₃₁ and R ₃₂ are linked together to form an aliphatic hydrocarbon ring, an aromatic hydrocarbon ring or a heterocyclic ring. A ₃ represents a —NHCO— group, a —CONH— group or a —NHCONH— group, and R ₃₃ represents a substituted or unsubstituted alkyl group, aryl group or heterocyclic group.

Further, -A ₃ -R ₃₃ may be a hydrogen atom. For example, the —A ₃ —R ₃₃ moiety represents a hydrogen atom, or A ₃ represents a —NHCO— group, —CONH— group or —NHCONH— group, and R ₃₃ represents a substituted or unsubstituted alkyl group, aryl Represents a group or a heterocyclic group.

W ₃ represents a hydrogen atom or —CONH—R ₃₅ group, —CO—R ₃₅ group or —CO—O—R ₃₅ group (R ₃₅ is a substituted or unsubstituted alkyl group, aryl group or heterocyclic group), R ₃₄ represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an alkoxy group, a carbamoyl group, or a nitrile group.

R ₃₆ represents a —CONH—R ₃₇ group, a —CO—R ₃₇ group or a —CO—O—R ₃₇ group (R ₃₇ represents a substituted or unsubstituted alkyl group, aryl group or heterocyclic group).

X ₃ represents a substituted or unsubstituted aryl group or heterocyclic group.

In the general formula (CLA), examples of the halogen atom represented by R ₃₁ and R ₃₂ include fluorine, bromine, chlorine atom and the like, and the alkyl group includes an alkyl group having up to 20 carbon atoms (methyl, Ethyl, butyl, dodecyl and the like, and examples of the alkenyl group include alkenyl groups having up to 20 carbon atoms (vinyl, allyl, butenyl, hexenyl, hexadienyl, ethenyl-2-propenyl, 3-butenyl, 1-methyl-3- Propenyl, 3-pentenyl, 1-methyl-3-butenyl and the like, and examples of the alkoxy group include alkoxy groups having up to 20 carbon atoms (methoxy, ethoxy and the like).

Examples of the alkyl group represented by R ₃₀ in the —NHCO—R ₃₀ group include alkyl groups having up to 20 carbon atoms (methyl, ethyl, butyl, dodecyl, etc.), and aryl groups include phenyl and naphthyl. Examples of the heterocyclic group include thienyl, furyl, imidazolyl, pyrazolyl, and pyrrolyl groups. The alkyl group represented by R ₃₃ is preferably an alkyl group having up to 20 carbon atoms, and examples thereof include a methyl, ethyl, butyl, dodecyl group, etc., and the aryl group is preferably an aryl group having 6 to 20 carbon atoms. Examples thereof include phenyl and naphthyl groups, and examples of the heterocyclic group include thienyl, furyl, imidazolyl, pyrazolyl and pyrrolyl groups.

In the —CONH—R ₃₅ group, —CO—R ₃₅ group or —CO—O—R ₃₅ group represented by W ₃ , the alkyl group represented by R ₃₅ is preferably an alkyl group having up to 20 carbon atoms. For example, methyl, ethyl, butyl, dodecyl group and the like are mentioned, and the aryl group is preferably an aryl group having 6 to 20 carbon atoms, such as phenyl, naphthyl group and the like. For example, thienyl, furyl, imidazolyl, pyrazolyl, pyrrolyl group and the like.

Examples of the halogen atom represented by R ₃₄ include fluorine, chlorine, bromine and iodine atoms, and examples of the alkyl group include chain or cyclic alkyl groups such as methyl, butyl, dodecyl and cyclohexyl groups. An alkenyl group having up to 20 carbon atoms (vinyl, allyl, butenyl, hexenyl, hexadienyl, ethenyl-2-propenyl, 3-butenyl, 1-methyl-3-propenyl, 3-pentenyl, 1-methyl- 3-butenyl and the like, and examples of the alkoxy group include methoxy, butoxy, and tetradecyloxy groups. Examples of the carbamoyl group include diethylcarbamoyl and phenylcarbamoyl groups. Nitrile groups are also preferred. Among these, a hydrogen atom and an alkyl group are more preferable. R ₃₃ and R ₃₄ may be connected to each other to form a ring structure.

  The above substituents can further have a single substituent or a plurality of substituents. Typical substituents include halogen atoms (fluorine, chlorine, bromine, etc.), alkyl groups (methyl, ethyl, propyl, butyl, dodecyl, etc.), hydroxyl groups, cyano groups, nitro groups, alkoxy groups (methoxy, ethoxy, etc.) ), Alkylsulfonamide groups (such as methylsulfonamide groups, octylsulfonamides), arylsulfonamide groups (such as phenylsulfonamides, naphthylsulfonamides), alkylsulfamoyl groups (such as butylsulfamoyl), arylsulfamoyls (Phenylsulfamoyl etc.), alkyloxycarbonyl group (methoxycarbonyl etc.), aryloxycarbonyl group (phenyloxycarbonyl etc.), aminosulfonamide group, acylamino group, carbamoyl group, sulfonyl group, sulfinyl group, sulfoxy group, E group, an aryloxy group, an alkoxy group, an alkylcarbonyl group, arylcarbonyl group, and an amino carbonyl group.

R ₃₀ or R ₃₅ is preferably a phenyl group, more preferably a phenyl group having a plurality of halogen atoms and cyano groups as substituents.

-CONH-R ₃₇ group represented by R _36, in -CO-R ₃₇ group or -CO-O-R ₃₇ group, the alkyl group represented by R ₃₇ is preferably an alkyl group having up to 20 carbon atoms A methyl group, an ethyl group, a butyl group, a dodecyl group, and the like. The aryl group is preferably an aryl group having 6 to 20 carbon atoms, such as phenyl and naphthyl. The heterocyclic group includes thienyl, furyl, Examples include imidazolyl group, pyrazolyl group, pyrrolyl group and the like.

As the substituent that the group represented by R ₃₇ can have, the same substituents as those described in the description of R _{31 to} R _{34 in} formula (CLA) can be used.

Examples of the aryl group represented by X ₃ include aryl groups having 6 to 20 carbon atoms such as phenyl and naphthyl groups, and examples of the heterocyclic group include thienyl, furyl, imidazolyl group, pyrazolyl group, pyrrolyl group and the like. Is mentioned.

Examples of the substituent that the group represented by X ₃ can have include the same substituents as those described in the description of R _{31 to} R _{34 in} formula (CLA). The group represented by X ₃ is preferably an aryl group or a heterocyclic group having an alkylamino group (such as methylamino or diethylamino) at the para position.

  These groups may include photographically useful groups.

  Specific examples of the cyan coloring leuco dye represented by the general formula (CLA) are shown below, but the present invention is not limited thereto.

  Next, the compound represented by general formula (CLB) is demonstrated.

In the formula, R ₄₁ , R ₄₂ , Ra and Rb each represent a hydrogen atom, an aliphatic group, an aromatic group, an alkoxy group, an aryloxy group, an acylamino group, a sulfonamide group, a carbamoyl group or a halogen atom. R ₄₃ represents a hydrogen atom, an aliphatic group, an aromatic group, an acyl group, an alkoxycarbonyl group, an aryloxycarboquinyl group, a carbamoyl group, a sulfamoyl group, or a sulfonyl group. X ₄ and X ₅ each represents a group that can be substituted on the benzene ring. m1 and m2 each represent an integer of 0-5. When m1 and m2 are 2 or more, the plurality of X ₄ and X ₅ may be the same or different.

Specific examples of the aliphatic group represented by R ₄₁ , R ₄₂ , Ra and Rb include hydrocarbon groups such as an alkyl group, an alkenyl group and an alkynyl group. These hydrocarbon groups preferably have 1 to 25 carbon atoms, and more preferably 1 to 20 carbon atoms. The alkyl group having 1 to 25 carbon atoms is methyl, ethyl, propyl, i-propyl, t-butyl, pentyl, hexyl, todecyl, etc., the cycloalkyl group is cyclohexyl, cyclopentyl, etc., the alkenyl group is ethenyl-2-propenyl , 3-butenyl, 1-methyl-3-propenyl, 3-pentenyl, 1-methyl-3-butenyl, etc. Examples of the alkynyl group include ethynyl, 1propynyl, propargyl and the like.

Specific examples of the aromatic group represented by R ₄₁ , R ₄₂ , Ra and Rb include aryl groups (phenyl, naphthyl, etc.), heterocyclic groups (pyridyl, thiazolyl, oxazolyl, imidazolyl, furyl, pyrrolyl, pyrazinyl, pyrimidinyl , Pyridazinyl, selenazolyl, sriphoranyl, piperidinyl, pyrazolyl, tetrazolyl and the like.

  Specific examples of the alkoxy group include methoxy, ethoxy, i-propoxy, t-butoxy and the like. Specific examples of the aryloxy group include phenoxy and naphthyloxy. Examples of the acylamino group include acetylamino and benzoylamino. Specific examples of the sulfonamide group include a methanesulfonamide group, a butanesulfonamide group, an octanesulfonamide group, and a benzenesulfonamide group. Examples of the carbamoyl group include an aminocarbonyl group, a methylaminocarbonyl group, a dimethylaminocarbonyl group, a propylaminocarbonyl group, a pentylaminocarbonyl group, a cyclohexylaminocarbonyl group, a phenylaminocarbonyl group, and a 2-pyridylaminocarbonyl group. Examples of the halogen atom include chlorine, bromine and iodine.

R ₄₁ and R ₄₂ are preferably an aliphatic group, an alkoxy group or an aryloxy group, more preferably an alkyl group or an alkoxy group, still more preferably a secondary or tertiary alkyl group or an alkoxy group.
Ra and Rb are preferably a hydrogen atom or an aliphatic group, more preferably a hydrogen atom.

Examples of the aliphatic group, aromatic group, alkoxy group and aryloxy group represented by R ₄₃ include those of the aliphatic group, aromatic group, alkoxy group and aryloxy group represented by R ₄₁ and R ₄₂ . The example given as a specific example is given.

Specific examples of the acyl group represented by R ₄₃ include acetyl, propionyl, butanoyl, hexanoyl, cyclohexanoyl, benzoyl, pyridinoyl and the like.

Specific examples of the alkoxycarbonyl group represented by R ₄₃ include methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl and the like. Specific examples of the aryloxycarboquinyl group include phenoxycarbonyl. Examples of the carbamoyl group include aminocarbonyl, methylaminocarbonyl, dimethylaminocarbonyl, propylaminocarbonyl, pentylaminocarbonyl, cyclohexylaminocarbonyl, phenylaminocarbonyl, 2-pyridylaminocarbonyl and the like.

  Examples of the sulfamoyl group include methylsulfamoyl, dimethylsulfamoyl, phenylsulfamoyl and the like, and examples of the sulfonyl group include methylsulfonyl, butylsulfonyl and octylsulfonyl.

R ₄₃ is preferably a hydrogen atom, an alkyl group, or an acyl group, more preferably a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an acyl group.

Specific examples of the group that can be substituted on the benzene ring represented by X ₄ and X ₅ include alkyl groups having 1 to 25 carbon atoms (methyl, ethyl, propyl, i-propyl, t-butyl, pentyl, hexyl, etc. ), Cycloalkyl groups (cyclohexyl, cyclopentyl, etc.), alkenyl groups (vinyl, allyl, butenyl, hexenyl, hexadienyl, ethenyl-2-propenyl, 3-butenyl, 1-methyl-3-propenyl, 3-pentenyl, 1-methyl -3-butenyl etc.), alkynyl groups (ethynyl, propargyl etc.), glycidyl groups, acrylate groups, methacrylate groups, aryl groups (phenyl, naphthyl etc.), heterocyclic groups (pyridyl, thiazolyl, oxazolyl, imidazolyl, furyl, pyrrolyl, Pyrazinyl, pyrimidinyl, pyridazinyl, selenazolyl, suri Horanyl, piperidinyl, pyrazolyl, tetrazolyl, etc.), halogen atom (chlorine, bromine, iodine, fluorine, etc.), alkoxy group (methoxy, ethoxy, propoxy, pentyloxy, cyclopentyloxy, hexyloxy, cyclohexyloxy, etc.), aryloxy group ( Phenoxy, etc.), alkoxycarbonyl groups (methyloxycarbonyl, ethyloxycarbonyl, butyloxycarbonyl, etc.), aryloxycarbonyl groups (phenyloxycarbonyl, etc.), sulfonamide groups (methanesulfonamide, ethanesulfonamide, butanesulfonamide, hexane) Sulfonamide, cyclohexanesulfonamide, benzenesulfonamide, etc.), sulfamoyl group (aminosulfonyl, methylaminosulfonyl, dimethylaminosulfonyl, Tilaminosulfonyl, hexylaminosulfonyl, cyclohexylaminosulfonyl, phenylaminosulfonyl, 2-pyridylaminosulfonyl, etc.), urethane groups (methylureido, ethylureido, pentylureido, cyclohexylureido, phenylureido, 2-pyridylureido, etc.), acyl groups (Acetyl, propionyl, butanoyl, hexanoyl, cyclohexanoyl, benzoyl, pyridinoyl, etc.), carbamoyl group (aminocarbonyl, methylaminocarbonyl, dimethylaminocarbonyl, propylaminocarbonyl, pentylaminocarbonyl, cyclohexylaminocarbonyl, phenylaminocarbonyl, 2 -Pyridylaminocarbonyl, etc.), amide groups (acetamide, propionamide, butanamide, Xanthamide, benzamide, etc.), sulfonyl group (methylsulfonyl, ethylsulfonyl, butylsulfonyl, cyclohexylsulfonyl, phenylsulfonyl, 2-pyridylsulfonyl, etc.), sulfonamide group (methylsulfonamide, octylsulfonamide, phenylsulfonamide, naphthylsulfonamide) Etc.), amino groups (amino, ethylamino, dimethylamino, butylamino, cyclopentylamino, anilino, 2-pyridylamino, etc.), cyano groups, nitro groups, sulfo groups, carboxyl groups, hydroxyl groups, oxamoyl groups, etc. it can. Further, these groups may be further substituted with these groups.

X ₄ and X ₅ are preferably an alkoxy group, an aryloxy group, a carbamoyl group, an amide group, a sulfonamide group, and an amino group, and more preferably an alkoxy group and an amino group.

  The compound represented by the general formula (CLB) can be easily synthesized by a conventionally known method, for example, the method described in Japanese Patent Publication No. 7-45477.

  Specific examples of the cyan coloring leuco dye represented by the general formula (CLB) are shown below, but the present invention is not limited thereto.

  The addition amount of these cyan color-forming leuco dyes is usually 0.00001 to 0.05 mol, preferably 0.0005 to 0.02 mol, more preferably 0.001 to 0.01 mol, per mol of Ag. is there.

  The addition ratio of the reducing agent represented by the general formula (RD1) and the general formula (RD2) of the cyan color-forming leuco dye is preferably 0.001 to 0.2 in terms of molar ratio. It is more preferable that it is 005-0.1.

  In the photothermographic material of the present invention, the sum of the highest densities at the maximum absorption wavelength of a dye image formed with a cyan leuco dye is preferably 0.01 to 0.50, more preferably 0.02 to 0.30. It is particularly preferable to develop the color so as to have 0.03 to 0.10.

  In the present invention, in addition to the above-described cyan color-forming leuco dye, a magenta color-forming leuco dye or a yellow color-forming leuco dye can be used in combination to enable a finer color tone adjustment.

  The yellow coloring leuco dye and the cyan coloring leuco dye represented by the general formulas (YA) and (YB) are added in the same manner as the addition method of the reducing agent represented by the general formula (RD1). It may be contained in the coating solution by any method such as a solution form, an emulsified dispersion form, a solid fine particle dispersion form, etc. and may be contained in the photographic material.

  The reducing agents of the general formulas (RD1) and (RD2), the yellow coloring leuco dyes of the general formulas (YA) and (YB) and the cyan coloring leuco dyes of the general formulas (CLA) and (CLB) are organic silver Although it is preferable to make it contain in the photosensitive layer (image forming layer) containing salt, one side may be contained in the photosensitive layer and the other may be contained in the non-photosensitive layer adjacent to the photosensitive layer, It may be contained in the photosensitive layer. When the photosensitive layer is composed of a plurality of layers, they may be contained in separate layers.

(binder)
The photosensitive layer and the non-photosensitive layer of the photothermographic material of the present invention can contain a binder for various purposes.

  The binder contained in the photosensitive layer is capable of supporting organic silver salts, silver halide grains, reducing agents, and other components. Suitable binders are transparent or translucent, generally colorless, and are natural polymers. And synthetic polymers and copolymers, and other media for forming a film, for example, those described in paragraph “0069” of JP-A No. 2001-330918. Among these, preferred binders for the photosensitive layer are polyvinyl acetals, and particularly preferred is polyvinyl butyral. These will be described in detail later.

  For the non-photosensitive layers such as the overcoat layer and the undercoat layer, particularly the protective layer and the back coat layer, cellulose esters having a higher softening temperature, particularly polymers such as triacetyl cellulose and cellulose acetate butyrate are preferable. In addition, as needed, said binder can be used in combination of 2 or more type.

The _{binder, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, -O-P = O (OM) 2, -N (R) 2, -N + (R) ₃ (M represents a hydrogen atom or an alkali metal base, R represents a hydrocarbon group), an epoxy group, —SH, —CN, and the like introduced by copolymerization or addition reaction. It is preferable to use, and —SO ₃ M and —OSO ₃ M are particularly preferable. The amount of such a polar group is 1 × 10 ⁻¹ to 1 × 10 ⁻⁸ mol / g, preferably 1 × 10 ⁻² to 1 × 10 ⁻⁶ mol / g.

Such a binder is used in an effective range to function as a binder. This effective range can be easily determined by one skilled in the art. For example, as an index for holding at least the organic silver salt in the photosensitive layer, the ratio of the binder to the organic silver salt is preferably 15: 1 to 1: 2 (mass ratio), and particularly 8: 1 to 1: 1. The range of is preferable. That is, it is preferable that the binder amount of the photosensitive layer is a 1.5~6g / m ^2, more preferably from 1.7~5g / 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.

  It is preferable that the glass transition temperature (Tg) of the binder used by this invention is 70-105 degreeC. Tg can be obtained by measuring with a differential scanning calorimeter, and the intersection of the baseline and the endothermic peak slope is defined as Tg. Tg in the present invention is determined by the method described in “Polymer Handbook” III-139-179 (1966, Wiley and Sun, Inc.) by Brand Wrap et al.

  Tg when the binder is a copolymer resin is obtained by the following formula.

Tg (copolymer) (° C.) = V ₁ Tg ₁ + v ₂ Tg ₂ +... + V _n Tg _{n
Wherein, v 1, v 2 ··· v} n represents the mass fraction of the monomer in the _{copolymer, Tg 1, Tg 2 ··· Tg} n from each monomer in the copolymer Tg (° C.) of the obtained single polymer is represented. The accuracy of Tg calculated according to the above equation is ± 5 ° C.

  Use of a binder having a Tg of 70 to 105 ° C. is preferable because a sufficient maximum density can be obtained in image formation.

  The binder of the present invention has a Tg of 70 to 105 ° C., a number average molecular weight of 1,000 to 1,000,000, preferably 10,000 to 500,000, and a degree of polymerization of about 50 to 1,000. It is. Examples of the polymer or copolymer containing an ethylenically unsaturated monomer as a constituent unit include those described in paragraph No. “0069” of JP-A No. 2001-330918.

  Of these, particularly preferred examples include methacrylic acid alkyl esters, methacrylic acid aryl esters, and styrenes. Among such polymer compounds, a polymer compound having an acetal group is preferably used. Even a polymer compound having an acetal group is more preferably a polyvinyl acetal having an acetoacetal structure, for example, U.S. Pat. Nos. 2,358,836, 3,003,879, 2,828,204, UK The polyvinyl acetal shown by patent 771,155 etc. can be mentioned. As the polymer compound having an acetal group, a compound represented by the general formula (V) described in paragraph “0150” of JP-A No. 2002-287299 is particularly preferable.

As the polyurethane resin that can be used in the present invention, known resins such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. Moreover, it is preferable to have a total of 2 or more hydroxyl groups, at least one at each polyurethane molecule end. Since hydroxyl groups are cross-linked with polyisocyanate which is a curing agent to form a three-dimensional network structure, it is more preferable that the hydroxyl groups are contained in the molecule. In particular, it is preferable that the hydroxyl group is at the molecular end because the reactivity with the curing agent is high. The polyurethane preferably has 3 or more hydroxyl groups at the molecular terminals, and particularly preferably 4 or more. In the present invention, when polyurethane is used, Tg is preferably 70 to 105 ° C., elongation at break is 100 to 2000%, and stress at break is preferably 0.5 to 100 N / mm ² .

  These polymer compounds (polymers) may be used alone or in a blend of two or more.

  In the photosensitive layer according to the present invention, the above polymer is preferably used as a main binder. The main binder mentioned here means “a state in which the polymer occupies 50% by mass or more of the total binder of the photosensitive layer”. Therefore, other polymers may be blended and used within a range of less than 50% by weight of the total binder. These polymers are not particularly limited as long as the polymer of the present invention is soluble. More preferably, a polyvinyl acetate, a polyacryl resin, a urethane resin, etc. are mentioned.

  An organic gelling agent may be contained in the photosensitive layer. Incidentally, the organic gelling agent referred to here has a function of giving a yield value to the system by adding it to an organic liquid, such as polyhydric alcohols, and eliminating or reducing the fluidity of the system. The compound which has.

  It is also a preferred embodiment that the photosensitive layer coating solution contains an aqueous dispersed polymer latex. In this case, a polymer latex in which 50% by mass or more of the total binder in the coating solution for the photosensitive layer is dispersed in water is preferable. Further, when a polymer latex is used in the preparation of the photosensitive layer, 50% by mass or more of the total binder in the photosensitive layer is preferably a polymer latex-derived polymer, and more preferably 70% by mass or more.

  Here, the polymer latex is a water-insoluble hydrophobic polymer dispersed as fine particles in a water-soluble dispersion medium. As the dispersion state, the polymer is emulsified in a dispersion medium, the emulsion is polymerized, the micelle is dispersed, or the polymer molecule has a partially hydrophilic structure, and the molecular chain itself is molecularly dispersed. Any of these may be used. The average particle diameter of the dispersed particles is preferably 1 to 50,000 nm, more preferably in the range of about 5 to 1,000 nm. The particle size distribution of the dispersed particles is not particularly limited, and may have a wide particle size distribution or a monodispersed particle size distribution.

  The polymer latex that can be used in the photothermographic material of the present invention may be a so-called core / shell type latex other than a normal polymer latex having a uniform structure. In this case, it may be preferable to change the Tg of the core and the shell. The minimum film forming temperature (MFT) of the polymer latex is preferably -30 to 90 ° C, more preferably about 0 to 70 ° C. In addition, a film-forming auxiliary may be added to control the minimum film-forming temperature.

  The film-forming aid, also called a plasticizer, is an organic compound (usually an organic solvent) that lowers the minimum film-forming temperature of polymer latex. For example, “Synthetic Latex Chemistry (Souichi Muroi, published by Polymer Publishing Co., Ltd.) , 1970).

  Examples of the polymer species used for the polymer latex include acrylic resins, vinyl acetate resins, polyester resins, polyurethane resins, rubber resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, and copolymers thereof. The polymer may be a linear polymer, a branched polymer, or a crosslinked polymer. The polymer may be a so-called homopolymer in which a single monomer is polymerized or a copolymer in which two or more monomers are polymerized. In the case of a copolymer, it may be a random copolymer or a block copolymer. The molecular weight of the polymer is a number average molecular weight and is usually about 5,000 to 1,000,000, preferably about 10,000 to 100,000. When the molecular weight is too small, the mechanical strength of the photosensitive layer is insufficient, and when the molecular weight is too large, the film forming property is poor and both are not preferable.

  The polymer latex preferably has an equilibrium water content of 0.01 to 2% by mass or less, more preferably 0.01 to 1% by mass at 25 ° C. and 60% RH (relative humidity). For the definition and measurement method of the equilibrium moisture content, for example, “Polymer Engineering Course 14, Polymer Material Testing Method (Edited by Polymer Society, Jinshokan)” can be referred to.

  Specific examples of the polymer latex include latexes described in “0173” of JP-A No. 2002-287299. These polymers may be used alone or as a blend of two or more as necessary. As a polymer seed | species of a polymer latex, what contains about 0.1-10 mass% of carboxylic acid components, such as an acrylate or a methacrylate component, is preferable.

  Furthermore, if necessary, a hydrophilic polymer such as gelatin, polyvinyl alcohol, methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose or the like may be added within a range of 50% by mass or less of the total binder. The addition amount of these hydrophilic polymers is preferably 30% by mass or less based on the total binder of the photosensitive layer.

  Regarding the order of addition of the organic silver salt and the aqueous dispersed polymer latex in the preparation of the coating solution for the photosensitive layer, either may be added first or at the same time, but preferably the polymer latex. There will be later. Furthermore, it is preferable that an organic silver salt and further a reducing agent are mixed before adding the polymer latex. In addition, after mixing the organic silver salt and the polymer latex, if the temperature to be aged is too low, the coated surface shape is impaired, and if it is too high, there is a problem that fog increases, so the coating solution after mixing is 30 to 65 ° C. It is preferable that the above time is elapsed. Furthermore, it is preferable to be aged at 35 to 60 ° C, and a time at 35 to 55 ° C is particularly preferable. In order to maintain the temperature in this way, it is sufficient to keep the temperature of the coating solution preparation tank or the like.

  For coating of the coating solution for the photosensitive layer, it is preferable to use a coating solution that has passed 30 minutes to 24 hours after mixing the organic silver salt and the aqueous polymer latex, and more preferably, 60 minutes after mixing. It is to make -12 hours pass, and it is using the coating liquid which passed 2-10 hours especially preferably.

  Here, “after mixing” means after the organic silver salt and the aqueous polymer latex are added and the additive material is uniformly dispersed.

(Crosslinking agent)
The photosensitive layer can contain a cross-linking agent that can link the binders together by cross-linking. By using a crosslinking agent for the binder, it is known that filming is improved and development unevenness is reduced, but there is also an effect of suppressing fogging during storage and suppressing generation of printout silver after development. is there.

  Examples of the crosslinking agent to be used include various crosslinking agents conventionally used for photographic light-sensitive materials, for example, aldehyde-based, epoxy-based, ethyleneimine-based, vinylsulfone-based, sulfone described in JP-A-50-96216. Acid ester-based, acryloyl-based, carbodiimide-based, and silane compound-based crosslinking agents are used, and the following isocyanate-based, silane compound-based, epoxy-based compounds, and acid anhydrides are preferable.

  Isocyanate-based crosslinking agents are isocyanates having at least two isocyanate groups and adducts thereof (adducts). More specifically, aliphatic diisocyanates, aliphatic diisocyanates having a cyclic group, benzene Diisocyanates, naphthalene diisocyanates, biphenyl isocyanates, diphenylmethane diisocyanates, triphenylmethane diisocyanates, triisocyanates, tetraisocyanates, adducts of these isocyanates, and these isocyanates and di- or trivalent polyalcohols And adducts. As specific examples, isocyanate compounds described on pages 10 to 12 of JP-A-56-5535 can be used.

  In addition, the adduct of isocyanate and polyalcohol has particularly high ability to improve interlayer adhesion and prevent layer peeling, image shift and bubble generation. Such isocyanate may be placed in any part of the photothermographic material. For example, the photosensitive layer of the support such as a photosensitive layer, a surface protective layer, an intermediate layer, an antihalation layer, an undercoat layer in the support (especially when the support is paper, it can be included in the size composition) It can be added to any layer on the side and can be added to one or more of these layers.

  In addition, compounds having a thioisocyanate structure corresponding to the above-mentioned isocyanates are also useful as thioisocyanate crosslinking agents that can be used in the present invention.

  The amount of the crosslinking agent used is usually in the range of 0.001 to 2 mol, preferably 0.005 to 0.5 mol, with respect to 1 mol of silver.

  The isocyanate compound and thioisocyanate compound that can be contained are preferably compounds that function as the above-mentioned crosslinking agent, but good results may be obtained even if the compound has only one functional group.

  Examples of the silane compound include compounds represented by general formulas (1) to (3) disclosed in JP-A No. 2001-264930.

  The epoxy compound that can be used as a crosslinking agent is not particularly limited as long as it has one or more epoxy groups and the number of epoxy groups, molecular weight, and the like. The epoxy group is preferably contained in the molecule as a glycidyl group via an ether bond or an imino bond. The epoxy compound may be any of a monomer, an oligomer, a polymer, etc., and the number of epoxy groups present in the molecule is usually about 1 to 10, preferably 2 to 4. When the epoxy compound is a polymer, it may be either a homopolymer or a copolymer, and a particularly preferred range of the number average molecular weight is about 2,000 to 20,000.

  The acid anhydride used in the present invention is a compound having at least one acid anhydride group represented by the following structural formula. The number of acid anhydride groups, molecular weight, and the like are not particularly limited as long as they have one or more acid anhydride groups.

-CO-O-CO-
Said epoxy compound and acid anhydride may use only 1 type, or may use 2 or more types together. There is no particular restriction on the addition ^{amount, 1 × 10 -6 ~1 × 10} - is preferably 2 mol / m ² range, more preferably in the range of 1 × 10 ^-5 ~1 × 10 ^-3 mol / m ² It is. This epoxy compound or acid anhydride can be added to any layer on the photosensitive layer side of the support, such as the photosensitive layer, surface protective layer, intermediate layer, antihalation layer, subbing layer, etc. It can be added to one layer or two or more layers.

(Silver saving agent)
The photosensitive layer or the non-photosensitive layer may contain a silver saving agent. The silver saving agent as used herein refers to a compound that can reduce the amount of silver necessary to obtain a certain silver image density.

  Although various mechanisms for the function of reducing the required silver amount are conceivable, a compound having a function of improving the covering power of developed silver is preferred. The covering power of developed silver refers to the optical density per unit amount of silver. This silver saving agent can be present in the photosensitive layer, the non-photosensitive layer, or any of them. Preferred examples of the silver saving agent include hydrazine derivative compounds, vinyl compounds, phenol derivatives, naphthol derivatives, quaternary onium compounds, and silane compounds.

  Specific examples of the hydrazine derivative include compounds H-1 to H-29 described in columns 11 to 20 of US Pat. No. 5,545,505, and compounds described to columns 9 to 11 of US Pat. No. 5,464,738. 1 to 12, and compounds H-1-1 to H-1-28, H-2-1 to H-2-9, and H-3 described in paragraphs “0042” to “0052” of JP-A-2001-27790 -1 to H-3-12, H-4-1 to H-4-21, H-5-1 to H-5-5, and the like.

  Specific examples of the vinyl compound include compounds CN-01 to CN-13 described in columns 13 to 14 of US Pat. No. 5,545,515, and compounds HET- described to column 10 of US Pat. No. 5,635,339. 01-HET-02, compounds MA-01-MA-07 described in columns 9-10 of US Pat. No. 5,654,130, compounds IS- described in columns 9-10 of US Pat. No. 5,705,324 01 to IS-04, and compounds 1-1 to 218-2 described in paragraphs “0043” to “0088” of JP-A No. 2001-125224.

  Specific examples of the phenol derivative and the naphthol derivative include compounds A-1 to A-89 described in paragraphs “0075” to “0078” of JP-A No. 2000-267222, and paragraphs “0025” to JP-A No. 2003-66558. Examples thereof include compounds A-1 to A-25 described in “0045”.

  Specific examples of the quaternary onium compound include triphenyltetrazoliums.

  Specific examples of the silane compound include alkoxysilane compounds having two or more primary or secondary amino groups as shown in compounds A1 to A33 described in paragraphs “0027” to “0029” of JP-A No. 2003-5324, or The salt is mentioned.

The addition amount of the silver saving agent is in the range of 1 × 10 ⁻⁵ to 1 mol, preferably 1 × 10 ^{−4 to} 5 × 10 ⁻¹ mol, per 1 mol of the organic silver salt.

  Particularly preferred silver saving agents are compounds represented by the following general formulas (SE1) and (SE2).

General formula (SE1)
Q ₁ -NHNH-Q ₂
In the formula, Q ₁ represents an aromatic group or a heterocyclic group bonded to —NHNH—Q ₂ at a carbon atom, and Q ₂ represents a carbamoyl group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a sulfonyl group, or a sulfamoyl group. Represents.

The aromatic group or heterocyclic group represented by Q ₁ is preferably a 5- to 7-membered unsaturated ring. Preferred examples include benzene, pyridine, pyrazine, pyrimidine, pyridazine, 1,2,4-triazine, 1,3,5-triazine, pyrrole, imidazole, pyrazole, 1,2,3-triazole, 1,2,4. -Triazole, tetrazole, 1,3,4-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-oxadiazole, 1,2,4-oxadiazole, 1 , 2,5-oxadiazole, thiazole, oxazole, isothiazole, isoxazole, thiophene ring residues and the like are preferable, and condensed rings in which these rings are condensed with each other are also preferable.

  These rings may have a substituent, and when they have two or more substituents, these substituents may be the same or different. Examples of substituents include halogen atoms, alkyl groups, aryl groups, carbonamido groups, alkylsulfonamido groups, arylsulfonamido groups, alkoxy groups, aryloxy groups, alkylthio groups, arylthio groups, carbamoyl groups, sulfamoyl groups, cyano Groups, alkylsulfonyl groups, arylsulfonyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups and acyl groups. These substituents may further have a substituent. Examples of preferable substituents include a halogen atom, an alkyl group, an aryl group, a carbonamido group, an alkylsulfonamido group, an arylsulfonamido group, an alkoxy group, and an aryl group. Examples thereof include an oxy group, an alkylthio group, an arylthio group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, a cyano group, a sulfamoyl group, an alkylsulfonyl group, an arylsulfonyl group, and an acyloxy group.

The carbamoyl group represented by Q ₂ is preferably a carbamoyl group having 1 to 50 carbon atoms, more preferably 6 to 40 carbon atoms, such as unsubstituted carbamoyl, methylcarbamoyl, N-ethylcarbamoyl, N-propylcarbamoyl, N-sec-butylcarbamoyl, N-octylcarbamoyl, N-cyclohexylcarbamoyl, Nt-butylcarbamoyl, N-dodecylcarbamoyl, N- (3-dodecyloxypropyl) carbamoyl, N-octadecylcarbamoyl, N- {3- (2,4-t-pentylphenoxy) propyl} carbamoyl, N- (2-hexyldecyl) carbamoyl, N-phenylcarbamoyl, N- (4-dodecyloxyphenyl) carbamoyl, N- (2-chloro-5-dodecyl) Oxycarbonylphenyl) Rubamoiru, N- naphthylcarbamoyl, N-3- pyridylcarbamoyl, N- benzylcarbamoyl, and the like. The acyl group represented by Q ₂ is preferably an acyl group having 1 to 50 carbon atoms, more preferably 6 to 40 carbon atoms. For example, formyl, acetyl, 2-methylpropanoyl, cyclohexylcarbonyl, octanoyl, 2- Examples include hexyldecanoyl, dodecanoyl, chloroacetyl, trifluoroacetyl, benzoyl, 4-dodecyloxybenzoyl, 2-hydroxymethylbenzoyl and the like. The alkoxycarbonyl group represented by Q ₂ is preferably an alkoxycarbonyl group having 2 to 50 carbon atoms, more preferably 6 to 40 carbon atoms, such as methoxycarbonyl, ethoxycarbonyl, i-butyloxycarbonyl, cyclohexyloxycarbonyl. , Dodecyloxycarbonyl, benzyloxycarbonyl and the like. The aryloxycarbonyl group represented by Q ₂ is preferably an aryloxycarbonyl group having 7 to 50 carbon atoms, more preferably 7 to 40 carbon atoms, such as phenoxycarbonyl, 4-octyloxyphenoxycarbonyl, 2-hydroxymethyl. Phenoxycarbonyl, 4-dodecyloxyphenoxycarbonyl, etc. are mentioned. The sulfonyl group represented by Q ₂ is preferably a sulfonyl group having 1 to 50 carbon atoms, more preferably 6 to 40 carbon atoms, such as methylsulfonyl, butylsulfonyl, octylsulfonyl, 2-hexadecylsulfonyl, and 3-dodecyl. Examples include oxypropylsulfonyl, 2-octyloxy-5-tert-octylphenylsulfonyl, and 4-dodecyloxyphenylsulfonyl.

  The sulfamoyl group represented by Q2 is preferably a sulfamoyl group having 0 to 50 carbon atoms, more preferably 6 to 40 carbon atoms, such as an unsubstituted sulfamoyl group, an N-ethylsulfamoyl group, or N- (2-ethylhexyl). Sulfamoyl, N-decylsulfamoyl, N-hexadecylsulfamoyl, N- {3- (2-ethylhexyloxy) propyl} sulfamoyl, N- (2-chloro-5-dodecyloxycarbonylphenyl) sulfamoyl, N- (2-tetradecyloxyphenyl) sulfamoyl and the like.

The group represented by Q ₂ may further have the group exemplified as the substituent of the 5- to 7-membered unsaturated ring represented by Q ₁ at a substitutable position. When it has more than one substituent, these substituents may be the same or different.

As the compound represented by the spotted formula (SE-1), preferably, Q ₁ is preferably a 5- to 6-membered unsaturated ring, and a benzene ring, a pyrimidine ring, a 1,2,3-triazole ring, 1,2,2, 4-triazole ring, tetrazole ring, 1,3,4-thiadiazole ring, 1,2,4-thiadiazole ring, 1,3,4-oxadiazole ring, 1,2,4-oxadiazole ring, thiazole ring More preferred are an oxazole ring, an isothiazole ring, an isoxazole ring, and a ring in which these rings are condensed with a benzene ring or an unsaturated heterocyclic ring. Q ₂ is preferably a carbamoyl group, particularly preferably a carbamoyl group having a hydrogen atom on the nitrogen atom.

  Next, general formula (SE2) will be described.

In the formula, R ¹ represents an alkyl group, an acyl group, an acylamino group, a sulfonamide group, an alkoxycarbonyl group, or a carbamoyl group. R ² represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an acyloxy group, or a carbonate ester group. R ³ and R ⁴ each represents a group that can be substituted on the benzene ring mentioned in the example of the substituent of the general formula (SE1). R ³ and R ⁴ may be connected to each other to form a condensed ring.

R ¹ is preferably an alkyl group having 1 to 20 carbon atoms (methyl, ethyl, i-propyl, butyl, t-octyl, cyclohexyl, etc.), acylamino group (acetylamino, benzoylamino, methylureido, 4-cyanophenylureido) Etc.), carbamoyl groups (butylcarbamoyl, N, N-diethylcarbamoyl, phenylcarbamoyl, 2-chlorophenylcarbamoyl, 2,4-dichlorophenylcarbamoyl, etc.), among which acylamino groups (including ureido groups and urethane groups) are more preferred.

R ² is preferably a halogen atom (more preferably chlorine, bromine), an alkoxy group (methoxy, butoxy, hexyloxy, decyloxy, cyclohexyloxy, benzyloxy, etc.), or an aryloxy group (phenoxy, naphthoxy, etc.).

R ³ is preferably a hydrogen atom, a halogen atom, or an alkyl group having 1 to 20 carbon atoms, and most preferably a halogen atom.

R ⁴ is preferably a hydrogen atom, an alkyl group or an acylamino group, more preferably an alkyl group or an acylamino group. Examples of these preferable substituents are the same as those for R ¹ . When R ⁴ is an acylamino group, R ⁴ is preferably linked to R ³ to form a carbostyryl ring.

In general formula (SE2), when R ³ and R ⁴ are connected to each other to form a condensed ring, the condensed ring is particularly preferably a naphthalene ring. This naphthalene ring may be bonded with the same substituents as those exemplified in the general formula (SE1). When the compound of the general formula (SE2) is a naphthol compound, R ¹ is preferably a carbamoyl group. Of these, a benzoyl group is particularly preferable. R ² is preferably an alkoxy group or an aryloxy group, and particularly preferably an alkoxy group.

  Hereinafter, although the preferable specific example of the silver saving agent of this invention is given, this invention is not limited to these.

(Thermal solvent)
The photothermographic material preferably contains a thermal solvent. Here, the thermal solvent is defined as a material capable of lowering the heat development temperature by 1 ° C. or more as compared with the photothermographic material containing no thermal solvent with respect to the photothermographic material containing the thermal solvent. More preferred is a material that can lower the heat development temperature by 2 ° C. or more, and particularly preferred is a material that can lower the temperature by 3 ° C. or more. For example, with respect to the photothermographic material A containing a thermosolvent, when the photothermographic material A from the photothermographic material A is designated B, the photothermographic material B is exposed to a heat development temperature of 120 ° C. and a heat development time of 20 ° C. When the photothermographic material A has the same exposure amount and heat development time to obtain the density obtained by processing in seconds, the heat development temperature is 119 ° C. or less.

  The thermal solvent has a polar group as a substituent and is preferably represented by the general formula (TS), but is not limited thereto.

General formula (TS) (Y) _n Z
In the formula, Y represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group. Z is a hydroxyl group, carboxyl group, amino group, amide group, sulfonamide group, phosphoric acid amide group, cyano group, imide group, ureido group, sulfoxide group, sulfone group, phosphine group, phosphine oxide group and nitrogen-containing heterocyclic group. Represents a selected group. n represents an integer of 1 to 3, and is the same as the valence of Z. When n is 2 or more, the plurality of Y may be the same or different.

  Y may further have a substituent, and examples of the substituent include a group represented by Z.

  In general formula (TS), Y is a linear, branched or cyclic alkyl group (preferably having 1 to 40 carbon atoms, more preferably 1 to 30 carbon atoms, particularly preferably 1 to 25 carbon atoms such as methyl, ethyl, propyl, i-propyl, sec-butyl, t-butyl, t-octyl, amyl, t-amyl, dodecyl, tridecyl, octadecyl, icosyl, docosyl, cyclopentyl, cyclohexyl, etc., alkenyl group (preferably having 2 to 40 carbon atoms, more Preferably they are 2-30, Most preferably, it is 2-25, for example, vinyl, allyl, 2-butenyl, 3-pentenyl etc.), an aryl group (preferably C6-C40, more preferably 6-30, especially preferable) Is 6-25, for example, phenyl, p-methylphenyl, naphthyl, etc.), a heterocyclic group (preferably having 2-20 carbon atoms) More preferably 2 to 16, particularly preferably 2 to 12, for example represents pyridyl, pyrazinyl, imidazolyl, pyrrolidyl, etc.). These substituents may be further substituted with other substituents. These substituents may be bonded to each other to form a ring.

  Y may further have a substituent, and examples of the substituent include those described in paragraph “0015” of JP-A No. 2004-21068. The reason why development activity is achieved by using a hot solvent is that the hot solvent melts near the development temperature so that it is compatible with substances involved in development, and the reaction at a lower temperature than when no hot solvent is added. This is thought to be possible. Since heat development is a reduction reaction involving a carboxylic acid having a relatively high polarity or a silver ion transporter, it is preferable to form a reaction field having an appropriate polarity with a thermal solvent having a polar group. .

  The melting point of the thermal solvent preferably used in the present invention is 50 to 200 ° C, more preferably 60 to 150 ° C. In particular, in a photothermographic material that emphasizes stability against an external environment such as image storability, which is an object of the present invention, a thermal solvent having a melting point of 100 to 150 ° C. is preferable.

  Specific examples of the thermal solvent include compounds described in paragraph “0017” of JP-A No. 2004-21068, compounds described in paragraph “0027” of U.S. Published Patent No. US2002 / 0025498, MF-1 to MF-3, MF6, MF-7, MF-9 to MF-12, MF-15 to MF-22 can be mentioned.

Preferably the added amount of thermal solvent is 0.01~5.0g / m ^2, more preferably 0.05~2.5g / m ^2, more preferably 0.1 to 1.5 g / m ² It is. The thermal solvent is preferably contained in the photosensitive layer.

  Although the said thermal solvent may be used independently, you may use it in combination of 2 or more type. The thermal solvent may be contained in the coating solution by any method such as a solution form, an emulsified dispersion form, or a solid fine particle dispersion form, and may be contained in the photothermographic material.

  The well-known emulsification dispersion method includes dissolving oil using an oil such as dibutyl phthalate, tricresyl phosphate, glyceryl triacetate or diethyl phthalate, or an auxiliary solvent such as ethyl acetate or cyclohexanone, and mechanically preparing the emulsion dispersion. The method of doing is mentioned. As the solid fine particle dispersion method, the powder of the hot solvent is dispersed in an appropriate solvent such as water by a ball mill, a colloid mill, a vibration ball mill, a sand mill, a jet mill, a roller mill, or an ultrasonic wave to produce a solid dispersion. A method is mentioned. In this case, a protective colloid (for example, polyvinyl alcohol) and a surfactant (for example, an anionic surfactant such as sodium tri-i-propylnaphthalene sulfonate) may be used. In the mills, beads such as zirconia are usually used as a dispersion medium, and Zr and the like eluted from these beads may be mixed in the dispersion. Although it depends on the dispersion conditions, it is usually in the range of 1 m to 1000 ppm. If the Zr content in the light-sensitive material is 0.5 mg or less per 1 g of silver, there is no practical problem. The aqueous dispersion preferably contains a preservative (for example, benzoisothiazolinone sodium salt).

(Anti-fogging agent and image stabilizer)
Any constituent layer of the photothermographic material contains an antifoggant for preventing fogging during storage before thermal development and an image stabilizer for preventing image deterioration after thermal development. It is preferable to keep it.

  Hereinafter, an antifoggant and an image stabilizer that can be used in the present invention will be described.

As reducing agents according to the present invention, reducing agents having protons such as bisphenols and sulfonamidophenols are mainly used, so that these hydrogens are stabilized, the reducing agents are deactivated, and silver ions are reduced. It is preferable that a compound capable of preventing and preventing the reaction is contained. Further, it is preferable to contain a compound capable of oxidatively bleaching silver atoms or metallic silver (silver clusters) generated during storage of raw films and images. Specific examples of compounds having these functions include biimidazolyl compounds and iodonium compounds. The amount of the biimidazolyl compound and iodonium compound added is in the range of 0.001 to 0.1 mol / m ² , preferably 0.005 to 0.05 mol / m ² .

  When the reducing agent used has an aromatic hydroxyl group (—OH), particularly in the case of bisphenols, a nonreducing compound having a group capable of forming a hydrogen bond with these groups should be used in combination. Is preferred. Specific examples of particularly preferable hydrogen bonding compounds include compounds (II-1) to (II-40) described in paragraphs “0061” to “0064” of JP-A-2002-90937.

  On the other hand, many compounds that can release halogen atoms as active species are known as antifoggants and image stabilizers. Specific examples of the compound that generates these active halogen atoms include compounds represented by general formula (9) described in paragraphs “0264” to “0271” of JP-A No. 2002-287299.

  The addition amount of these compounds is preferably within a range in which the increase in printout silver due to the formation of silver halide due to the reaction between the halogen released from the compound and silver ions does not become a problem. Specific examples of compounds that generate these active halogen atoms include, in addition to the above-mentioned patents, compounds (III-1) to (III-) described in paragraphs “0086” to “0087” of JP-A No. 2002-169249. 23), compounds 1-1a to 1-1o and 1-2a to 1-2o described in paragraphs “0031” to “0034” of JP-A-2003-50441, and compounds described in paragraphs “0050” to “0056” 2a to 2z, 2aa to 2ll, 2-1a to 2-1f, compounds 4-1 to 4-32 described in paragraphs “0055” to “0058” of JP-A No. 2003-91054, paragraphs “0069” to “0072” Compound 5-1 to 5-10 described in FIG.

  Antifoggants preferably used in the present invention include, for example, compound examples a to j described in paragraph “0012” of JP-A-8-314059, and thiosulfonates described in paragraph “0028” of JP-A-7-209797. Esters A to K, compound examples (1) to (44) described from page 14 of JP-A No. 55-140833, and compounds (I-1) to (I) described in paragraph “0063” of JP-A No. 2001-13627 I-6), (C-1) to (C-3) described in paragraph “0066”, and compounds (III-1) to (III-108) described in paragraph “0027” of JP-A-2002-90937 As compounds of vinyl sulfones and / or β-halo sulfones, compounds VS-1 to VS-7, compounds HS-1 to HS-5 described in paragraph “0013” of JP-A-6-208192, sulfonylbenzoto Compounds KS-1 to KS-8 described in JP-A No. 2000-330235 as azole compounds, PR-01 to PR-08 described in JP-T-2000-515995 as substituted propene nitrile compounds, JP-A 2002-2002 Examples thereof include compounds (1) -1 to (1) -132 described in paragraphs “0042” to “0051” of No. 207273.

  The antifoggant is generally used in an amount of at least 0.001 mol per 1 mol of silver. Usually, the range is 0.01 to 5 mol, preferably 0.02 to 0.6 mol of the compound per 1 mol of silver.

  In addition to the above compounds, the photothermographic material may contain various compounds conventionally known as antifoggants, but can generate reactive species similar to the above compounds. Even if it is a compound, the compound from which an antifogging mechanism differs may be sufficient. For example, U.S. Pat. Nos. 3,589,903, 4,546,075, 4,452,885, JP-A-59-57234, U.S. Pat. Nos. 3,874,946, 4,756,999. And compounds described in JP-A-9-288328 and JP-A-9-90550. Further, other antifoggants include compounds disclosed in US Pat. No. 5,028,523 and European Patents 600,587, 605,981, and 631,176.

(Toning agent)
The photothermographic material of the present invention forms a photographic image by heat development, and a toning agent (toner) for adjusting the color tone of silver as necessary is dispersed in an (organic) binder matrix. It is preferable to contain.

  Examples of suitable toning agents used are disclosed in RD 17029, U.S. Pat. Nos. 4,123,282, 3,994,732, 3,846,136 and 4,021,249. For example, there are the following.

  Imides (succinimide, phthalimide, naphthalimide, N-hydroxy-1,8-naphthalimide, etc.); mercaptans (3-mercapto-1,2,4-triazole, etc.); phthalazinone derivatives or metal salts of these derivatives (phthalazinone, 4- (1-naphthyl) phthalazinone, 6-chlorophthalazinone, 5,7-dimethyloxyphthalazinone, and 2,3-dihydro-1,4-phthalazinedione); phthalazine and phthalic acids (phthalic acid, Combinations of 4-methylphthalic acid, 4-nitrophthalic acid and tetrachlorophthalic acid); phthalazine and maleic anhydride, and phthalic acid, 2,3-naphthalenedicarboxylic acid or o-phenylene acid derivatives and anhydrides thereof (phthalic acid) 4-methylphthalic acid, 4-nitrophthalic acid and tetrachlorophthalate Combination of at least one compound selected from acid anhydride, etc.). Particularly preferred toning agents are combinations of phthalazinone or phthalazine with phthalic acids and phthalic anhydrides.

(Fluorine surfactant)
In the present invention, a fluorine-based surfactant represented by the following general formula (SF) is used in order to improve film transportability and environmental suitability (accumulation in a living body) in a laser imager (thermal development processing apparatus). Preferably used.

General formula (SF)
(Rf− (L ₁ ) _n1 −) _p − (Y) _m1 − (A) _q
In the formula, Rf represents a substituent containing a fluorine atom, L ₁ represents a divalent linking group having no fluorine atom, Y represents a (p + q) -valent linking group having no fluorine atom, A Represents an anionic group or a salt thereof, n1 and m1 each represents an integer of 0 or 1, p represents an integer of 1 to 3, and q represents an integer of 1 to 3. However, when q is 1, n1 and m1 are not 0 at the same time.

  Examples of the substituent containing a fluorine atom represented by Rf include fluorinated alkyl groups having 1 to 25 carbon atoms (trifluoromethyl, trifluoroethyl, perfluoroethyl, perfluorobutyl, perfluorooctyl, perfluorododecyl. And perfluorooctadecyl) or alkenyl fluoride groups (perfluoropropenyl, perfluorobutenyl, perfluorononenyl, perfluorododecenyl, etc.). Rf preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms. Rf preferably has 2 to 12 fluorine atoms, more preferably 3 to 12.

Examples of the divalent linking group having no fluorine atom represented by L ₁ include an alkylene group (methylene, ethylene, butylene, etc.), an alkyleneoxy group (methyleneoxy, ethyleneoxy, butyleneoxy, etc.), an oxyalkylene group ( Oxymethylene, oxyethylene, oxybutylene, etc.), oxyalkyleneoxy groups (oxymethyleneoxy, oxyethyleneoxy, oxyethyleneoxyethyleneoxy, etc.), phenylene groups, oxyphenylene groups, phenyleneoxy groups, oxyphenyleneoxy groups, or these And a combination of these groups.

  Examples of the anionic group represented by A or a salt thereof include a carboxylic acid group or a salt thereof (sodium, potassium and lithium salts), a sulfonic acid group or a salt thereof (sodium, potassium and lithium salts), a sulfuric acid half ester group or a salt thereof ( Sodium, potassium and lithium salts), phosphoric acid groups or salts thereof (such as sodium and potassium salts) and the like.

  Examples of the (p + q) -valent linking group having no fluorine atom represented by Y include, for example, an atomic group composed mainly of a nitrogen atom or a carbon atom as a trivalent or tetravalent linking group. n1 represents 0 or an integer of 1, and is preferably 1.

  The fluorine-based surfactant represented by the general formula (SF) is an alkyl compound having 1 to 25 carbon atoms into which a fluorine atom is introduced (trifluoromethyl, pentafluoroethyl, perfluorobutyl, perfluorooctyl, perfluorooctadecyl, etc. Compounds) and alkenyl compounds (compounds having a perfluorohexenyl group, perfluorononenyl, etc.), 3- to 6-valent alkanol compounds in which no fluorine atom is introduced, and aromatic compounds having 3 to 4 hydroxyl groups. Or it can obtain by introduce | transducing an anionic group (A) into a compound (partially Rf-ized alkanol compound) obtained by addition reaction and condensation reaction with a heterocyclic compound by sulfate esterification etc.

  Examples of the trivalent to hexavalent alkanol compound include glycerin, pentaerythritol, 2-methyl-2-hydroxymethyl 1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentene, and 1,2,6-hexane. Examples include triol, 1,1,1-tris (hydroxymethyl) propane, 2,2-bis (butanol) -3, aliphatic triol, tetramethylolmethane, D-sorbitol, xylitol, D-mannitol and the like. Examples of the aromatic compound and heterocyclic compound having 3 to 4 hydroxyl groups include 1,3,5-trihydroxybenzene and 2,4,6-trihydroxypyridine.

  Specific examples of the above-mentioned fluorine-based surfactant include compounds (FS-1) to (FS-66) described in paragraphs “0029” to “0040” of JP-A No. 2003-149766, and JP-A No. 2004-021084. Compound 1-1 to 1-4 described in paragraph “0014” of the compound, compounds 2-1 to 2-10 described in paragraph “0019”, a compound described in paragraph “0025” of JP-A-2004-077772 and paragraph And compounds described in “0030”.

  Examples of preferred compounds of the fluorine-based surfactant represented by the general formula (SF) are shown below.

  Further, as fluorine-based surfactants other than those described above, compounds described in paragraph “0035” of JP-A No. 2004-117505, JP-A No. 2000-214554, JP-A No. 2003-156819, JP-A No. 2003-177494, You may use the compound described in 2003-114504, 2003-270754, 2003-270760.

  As a method of adding the fluorine-based surfactant represented by the general formula (SF) to the coating solution, it can be added according to a known addition method. That is, it can be dissolved and added in alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone and acetone, polar solvents such as dimethyl sulfoxide and dimethylformamide. Further, fine particles of 1 μm or less can be dispersed in water or an organic solvent by sand mill dispersion, jet mill dispersion, ultrasonic dispersion or homogenizer dispersion, and added. Many techniques for fine particle dispersion are disclosed, but they can be dispersed according to these techniques. The fluorine-based surfactant represented by the general formula (SF) is preferably added to the outermost protective layer.

The addition amount of the fluorine-based surfactant represented by the general formula (SF) is preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ mol per m ² , and preferably 1 × 10 ⁻⁵ to 1 × 10 ⁻² mol. Particularly preferred. If the range is less than the former range, charging characteristics may not be obtained. If the range exceeds the former range, the humidity dependency is large and the storage stability under high humidity may be deteriorated.

(Surface roughness)
The ten-point average roughness (Rz), maximum roughness (Rt), and centerline average roughness (Ra) in the present invention are defined by the following JIS surface roughness (B0601).

  The ten-point average roughness (Rz) is the peak from the highest to the fifth measured in the direction of the vertical magnification from the straight line that is parallel to the average line and does not cross the cross-sectional curve in the part extracted from the cross-sectional curve by the reference length. The difference between the average value of the altitude and the average value of the altitude at the bottom of the valley from the deepest to the fifth is expressed in micrometers (μm).

  The maximum roughness (Rt) means that when a roughness curve is extracted by a reference length L and a portion extracted by two straight lines parallel to the center line is sandwiched, the interval between the two straight lines is the direction of the vertical magnification of the roughness curve. And the value expressed in μm.

  The centerline average roughness (Ra) is a portion of the measurement length L in the direction of the centerline from the roughness curve, the centerline of the extracted portion is the X axis, the direction of the vertical magnification is the Y axis, When the length curve is represented by y = f (x), it means the value obtained by the following formula expressed in μm.

  As a method for measuring Rz, Rt, and Ra, the humidity was adjusted for 24 hours under a condition where the measurement samples were not overlapped in a 25 ° C./65% RH (relative humidity) environment, and then measured in the environment. Examples of the non-overlapping condition shown here include any of a method of winding with the film edge portion raised, a method of stacking paper with the film sandwiched between the films, and a method of making a frame with cardboard and fixing the four corners. It is. As a measuring apparatus which can be used, for example, WYKO: RSTPLUS non-contact three-dimensional micro surface shape measuring system can be exemplified.

  In order to set Rz, Rt, and Ra on the front and back surfaces of the photosensitive material within the ranges described below, the following technical means can be used for appropriate adjustment.

  1) Kind, average particle diameter, amount added, and surface treatment method of matting agent (inorganic or organic powder) contained in the layer having the photosensitive layer and the layer opposite to the side having the photosensitive layer.

  2) Matting agent dispersion conditions (type of disperser used, dispersion time, type of beads used for dispersion, average particle size, type and amount of dispersant used during dispersion, type of binder polar group, polar group Content).

  3) Drying conditions at the time of application (application speed, distance from the application surface of the hot air blowing nozzle, amount of dry air), and amount of residual solvent.

  4) Type of filter used for filtration of coating solution, filtration time.

  5) Conditions when calendering is performed after coating (calendar temperature 40 to 80 ° C., pressure 490 to 2,940 N / cm, line speed 20 to 100 m, nip number 2 to 6).

  In the present invention, the value of Rz (E) / Rz (B) is preferably 0.1 to 0.7, more preferably 0.2 to 0.6, and 0.3 to 0. Particularly preferred is .55. Here, (E) represents the outermost surface on the photosensitive layer side, and (B) represents the outermost surface on the back coat layer side opposite to the photosensitive layer. By setting the surface roughness within this range, the transportability of the film is particularly good, and the occurrence of density unevenness during thermal development can be remarkably suppressed.

  In the present invention, the value of Ra (E) / Ra (B) is preferably 0.6 to 1.5, more preferably 0.6 to 1.3, and 0.7 to 1.1 is particularly preferred. By setting it within this range, among the effects of the present invention, the fog rise with time is particularly small, the film transportability is good, and the occurrence of density unevenness during thermal development can be further suppressed.

  The photothermographic material of the present invention preferably has a constituent layer containing a plurality of types of matting agents on both sides on the support from the viewpoint of improving the image quality of the image. The average particle size of the matting agent having the maximum average particle size contained in the layer containing the matting agent on the side having the photosensitive layer is Le (μm), and the side opposite to the side having the photosensitive layer across the support That is, when the average particle size of the matting agent having the maximum average particle size contained in the layer containing the matting agent on the side having the backcoat layer is Lb (μm), Lb / Le is 2.0 to 10 It is preferable that it is 3.0, and 4.5 is more preferable.

  By setting Lb / Le within this range, among the effects of the present invention, density unevenness particularly during thermal development can be improved. In the image forming method of the present invention, the value of Rz (E) / Ra (E) is preferably 12 to 60, more preferably 14 to 50. By setting the value of Rz (E) / Ra (E) within this range, among the effects of the present invention, density unevenness during heat development and storage characteristics over time can be improved.

  In the image forming method of the present invention, the value of Rz (B) / Ra (B) is preferably 25 to 65, more preferably 30 to 60. By setting the value of Rz (B) / Ra (B) within this range, among the effects of the present invention, density unevenness especially during thermal development and storage characteristics over time can be improved. About the above-mentioned surface roughness, it carried out with the following method.

(Evaluation of surface roughness)
About the sample before heat development processing, it measured by the method shown below using the non-contact three-dimensional surface-analysis apparatus (The product made by WYKO: RST / PLUS).

1) Objective lens: × 10.0 Intermediate lens: × 1.0
2) Measurement range: 463.4 μm × 623.9 μm
3) Pixel size: 368 × 238
4) Filter: Cylindrical correction and tilt correction 5) Smoothing: Medium smoothing 6) Scanning speed: Low
Ra, Rz, and Rt were defined according to JIS surface roughness (B0601). For each sample of 10 cm × 10 cm, the sample was divided into 100 in a grid pattern at 1 cm intervals, the center of each square region was measured, and the average value was obtained from 100 measurements.

  In the present invention, the case where the layer containing the matting agent is the outermost layer is one of the preferred embodiments. That is, when a non-photosensitive layer is provided on the photosensitive layer side of the photothermographic material or on the opposite side of the photosensitive layer with the support interposed therebetween, the matting agent is used for controlling the surface roughness of the outermost layer. It is preferable to use organic or inorganic powder as

As the powder used, a powder having a Mohs hardness of 5 or more is preferable. As the powder, a known inorganic powder or organic powder can be appropriately selected and used. Examples of the inorganic powder include titanium oxide, boron nitride, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial diamond , Stone meteorite, garnet, mica, silica, silicon nitride, silicon carbide and the like. Examples of the organic powder include powders such as polymethyl methacrylate, polystyrene, and Teflon (registered trademark). Among these, inorganic powders such as SiO ₂ , titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, Cr ₂ O ₃ , mica, etc. are preferable. SiO ₂ and α-Al ₂ O ₃ are preferable, and SiO ₂ is particularly preferable.

In the present invention, the powder is preferably surface-treated, for example. The surface treatment layer is formed by dry pulverizing the inorganic powder material, adding water and a dispersing agent, and performing coarse particle classification by wet pulverization and centrifugal separation. Thereafter, the fine slurry is transferred to a surface treatment tank, where the surface of the metal hydroxide is coated. First, a predetermined amount of an aqueous salt solution such as Al, Si, Ti, Zr, Sb, Sn, Zn or the like is added, and the surface of the inorganic powder particles is coated with a hydrous oxide formed by adding an acid or an alkali that neutralizes the aqueous solution. Water-soluble salts produced as a by-product are removed by decantation, filtration, and washing. Finally, the slurry pH is adjusted, filtered, and washed with pure water. The washed cake is dried with a spray dryer or a band dryer. Finally, the dried product is pulverized by a jet mill into a product. Further, not only aqueous systems but also vapors such as AlCl ₃ and SiCl ₄ can be passed through the non-magnetic inorganic powder, and then steam can be introduced to perform Al and Si surface treatment. For other surface treatment methods, “Characterization of Powder Surfaces”, Academic Press can be referred to.

  In the present invention, it is preferable that the surface treatment is performed with an Si compound or an Al compound. When such a surface-treated powder is used, the dispersion state when the matting agent is dispersed can be improved. The content of Si or Al is preferably 0.1 to 10% by mass of Si and 0.1 to 10% by mass of Al, more preferably 0.1 to 10% by mass with respect to the powder. It is particularly preferable that 5% by mass, Al is 0.1-5% by mass, Si is 0.1-2% by mass, and Al is 0.1-2% by mass. Further, the mass ratio of Si and Al is preferably Si <Al. The surface treatment can be performed by the method described in JP-A-2-83219.

  The average particle diameter of the powder in the present invention is the average diameter in the case of spherical powder, the average major axis length in the case of acicular powder, and the maximum diagonal line of the plate-like surface in the case of plate-like powder. Means the average value of the lengths, and can be easily obtained from measurement by an electron microscope. The organic or inorganic powder preferably has an average particle size of 0.5 to 10 μm, more preferably 1.0 to 8.0 μm.

  The average particle diameter of the organic or inorganic powder contained in the outermost layer on the photosensitive layer side is usually 0.5 to 8.0 μm, preferably 1.0 to 6.0 μm, more preferably 2.0 to 5.0 μm. It is. The addition amount is usually 1.0 to 20% by mass, preferably 2.0 to 15% by mass, more preferably based on the binder amount used for the outermost layer (including the crosslinking agent in the binder amount). It is 3.0-10 mass%.

  The average particle size of the organic or inorganic powder contained in the outermost layer on the side opposite to the photosensitive layer across the support is usually 2.0 to 15.0 μm, preferably 3.0 to 12.0 μm. Preferably it is 4.0-10.0 micrometers. The addition amount is usually 0.2 to 10% by mass, preferably 0.4 to 7% by mass, more preferably based on the binder amount used for the outermost layer (including the crosslinking agent in the binder amount). It is 0.6-5 mass%.

  The variation coefficient 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 method for adding the organic or inorganic powder may be a method in which the organic or inorganic powder is dispersed in the coating solution in advance, or a method in which the organic or inorganic powder is sprayed after the coating solution is applied and before the drying is completed. . When adding several types of powder, you may use both methods together.

(Dye, pigment)
In photothermographic materials, in order to control the amount or wavelength distribution of light transmitted through the photosensitive layer, a filter layer is formed on the same side as or opposite to the photosensitive layer, or a dye or pigment is added to the photosensitive layer. It is preferable to contain.

  As the dye used, known compounds that absorb light in various wavelength regions can be used depending on the color sensitivity of the photographic material. For example, when the photothermographic material is an image recording material using infrared light, a squarylium dye having a thiopyrylium nucleus as disclosed in JP-A-2001-083655 (referred to as a thiopyrylium squarylium dye in the present invention) and It is preferable to use a squarylium dye having a pyrylium nucleus (referred to as a pyrylium squarylium dye in the present invention), a thiopyrylium croconium dye similar to a squarylium dye, or a pyrylium croconium dye.

  The compound having a squarylium nucleus is a compound having 1-cyclobuten-2-hydroxy-4-one in the molecular structure, and the compound having a croconium nucleus is 1-cyclopentene-2-hydroxy in the molecular structure. It is a compound having -4,5-dione. Here, the hydroxyl group may be dissociated. Hereinafter, in the present specification, these pigments are collectively referred to as squarylium dyes for convenience. As dyes, U.S. Pat. No. 5,380,635, JP-A-8-201959, JP-A-2002-040593, 2003-186135, 2003-195450, US Pat. No. 6,689,547, US The compounds described in JP 2004/0259044 A can also be preferably used.

(Support)
Examples of the support material used in the photothermographic material of the present invention include various polymer materials, glass, wool cloth, cotton cloth, paper, metal (aluminum, etc.), etc. A material that can be processed into a flexible sheet or roll is preferred. Therefore, as a support used in the present invention, a plastic film such as a cellulose acetate film, polyester, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide, polyimide, cellulose triacetate (TAC) or polycarbonate (PC) film is used. A biaxially stretched PET film is preferred.

  The thickness of the support is about 50 to 300 μm, preferably 70 to 180 μm.

  In order to improve the charging property, a conductive compound such as a metal oxide and / or a conductive polymer can be included in the constituent layer. These may be contained in any layer, but are preferably contained in the backing layer or the surface protective layer on the photosensitive layer side, the undercoat layer, and the like. The conductive compounds described in columns 14 to 20 of US Pat. No. 5,244,773 are preferably used. Especially, it is preferable to contain a conductive metal oxide in the surface protective layer on the backing layer side. As a result, it was found that the transportability during the heat development process can be improved.

Here, the conductive metal oxide is crystalline metal oxide particles, and those containing oxygen defects and those containing a small amount of hetero atoms forming a donor with respect to the metal oxide used are generally used. In particular, it is particularly preferable because of its high conductivity, and the latter is particularly preferable because it does not give fog to the silver halide emulsion. Examples of metal oxides are ZnO, TiO ₂ , SnO ₂ , Al ₂ O ₃ , In ₂ O ₃ , SiO ₂ , MgO, BaO, MoO ₃ , V ₂ O _5, etc., or a composite oxide thereof, especially ZnO, TiO ₂ and SnO ₂ are preferred. Examples of containing different atoms include, for example, addition of Al, In, etc. to ZnO, addition of Sb, Nb, P, halogen elements, etc. to SnO ₂ , and Nb, Ta to TiO ₂ . Etc. are effective. The amount of these different atoms added is preferably in the range of 0.01 to 30 mol%, particularly preferably 0.1 to 10 mol%. Furthermore, a silicon compound may be added during the production of fine particles in order to improve fine particle dispersibility and transparency.

The metal oxide fine particles used have conductivity, and their volume resistivity is 10 ⁷ Ω · cm or less, particularly 10 ⁵ Ω · cm or less. These oxides are described in JP-A Nos. 56-143431, 56-120519, 58-62647 and the like. Furthermore, as described in Japanese Examined Patent Publication No. 59-6235, a conductive material in which the above metal oxide is attached to other crystalline metal oxide particles or fibrous materials (such as titanium oxide) may be used. . The particle size that can be used is preferably 1 μm or less, but if it is 0.5 μm or less, the stability after dispersion is good and it is easy to use. In order to make the light scattering property as small as possible, it is very preferable to use conductive particles of 0.3 μm or less because a transparent photosensitive material can be formed. Further, when the conductive metal oxide is needle-like or fibrous, the length is preferably 30 μm or less and the diameter is preferably 1 μm or less, particularly preferably the length is 10 μm or less and the diameter is 0.3 μm or less. The thickness / diameter ratio is 3 or more. As the SnO _2, are commercially available from Ishihara Sangyo Kaisha, it can be used SNS10M, SN-100P, SN- 100D, the FSS10M like.

(Component layer)
The photothermographic material of the present invention has at least one photosensitive layer which is an image forming 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. For example, a protective layer is preferably provided on the photosensitive layer for the purpose of protecting the photosensitive layer, and the opposite surface of the support is "sticking" between the photosensitive materials or in the photosensitive material roll. In order to prevent this, a back coat layer is provided.

  As a binder used in these protective layers and backcoat layers, a polymer having a glass transition point (Tg) higher than that of the photosensitive layer and hardly causing scratches or deformation, such as cellulose acetate, cellulose acetate butyrate, and cellulose acetate propio. Polymers such as nates are selected from the binders described above.

  For gradation adjustment or the like, two or more photosensitive layers may be provided on one side of the support or one or more layers on both sides of the support.

(Application of component layers)
The coating of the constituent layers is preferably formed by preparing a coating solution in which the material of each constituent layer described above is dissolved or dispersed in a solvent, applying a plurality of these coating solutions simultaneously, and then performing a heat treatment. Here, “multiple simultaneous multi-layer coating” means that a coating solution for each constituent layer (for example, a photosensitive layer and a protective layer) is prepared, and each layer is repeatedly applied and dried when it is applied to a support. Rather, it means that the respective constituent layers are formed in such a state that simultaneous multilayer coating and drying can be performed. That is, the upper layer is provided before the remaining amount of all the solvents in the lower layer reaches 70% by mass or less (more preferably 90% by mass or less).

  There are no particular restrictions on the method of applying multiple layers of each constituent layer simultaneously, for example, bar coater method, curtain coating method, dipping method, air knife method, hopper coating method, reverse roll coating method, gravure coating method, extrusion coating method. A known method such as the above can be used. Of the various methods described above, the slide coating method and the extrusion coating method are more preferable.

  These coating methods have been described on the side having the photosensitive layer, but the same applies to the case of coating with undercoating when the back layer is provided. Regarding the simultaneous multilayer coating method in the photothermographic material, there is a detailed description in JP-A No. 2000-15173.

The amount of coated silver is preferably selected in accordance with the purpose of the photothermographic material, but is preferably 0.3 to 1.5 g / m ² for the purpose of medical images, 0.5 to 1 0.5 g / m ² is more preferable. Among the amount of coated silver, the amount derived from silver halide preferably accounts for 2 to 18% by mass, more preferably 5 to 15% by mass, based on the total silver amount.

In the present invention, the coating density of silver halide grains having a diameter of 0.01 μm or more (equivalent particle diameter equivalent to a sphere) is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ particles / m ² , and preferably 1 × 10 ¹⁵ to 1 ×. More preferably, 10 ¹⁷ pieces / m ² or less.

Further, the coating density of the non-photosensitive long-chain aliphatic carboxylate is 1 × 10 ⁻¹⁷ to 1 × 10 ⁻¹⁴ per silver halide grain having a diameter of 0.01 μm or more (equivalent particle diameter in terms of sphere). g is preferable, and 1 × 10 ⁻¹⁶ to 1 × 10 ⁻¹⁵ g is more preferable.

  In the case of coating under the conditions within the above range, preferable results are obtained from the viewpoint of the optical maximum density of the silver image per fixed coating silver amount, that is, the silver coating amount (covering power) and the color tone of the silver image. Is obtained.

The photothermographic material of the present invention preferably contains a solvent in the range of 5 to 1,000 mg / m ² during development. It is more preferable to adjust so that it may be 10-150 mg / m < ² >. As a result, a photothermographic material having high sensitivity, low fog and high maximum density is obtained. Examples of the solvent include, but are not limited to, those described in paragraph “0030” of JP-A No. 2001-264930. 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 gas chromatography under conditions suitable for detecting the contained solvent.

(Packaging body)
When storing the photothermographic material, package it with a packaging material with low oxygen permeability and / or moisture permeability in order to prevent density changes and fogging over time, or to improve curling and curling. It is preferable to do. The oxygen transmission rate is preferably 50 ml / atm · m ² · day or less (1 atm is 1.01325 × 10 ⁵ Pa) at 25 ° C., more preferably 10 ml / atm · m ² · day or less, and still more preferably Is 1.0 ml / atm · m ² · day or less. The moisture permeability is preferably 0.01 g / m ² · 40 ° C · 90% RH · day or less (according to JIS Z0208 cup method), more preferably 0.005 g / m ² · 40 ° C. · 90% RH · Day or less, more preferably 0.001 g / m ² · 40 ° C · 90% RH · day or less.

  Specific examples of the packaging material for the photothermographic material include, for example, JP-A-8-254793, JP-A-2000-206653, JP-A-2000-235241, JP-A-2002-062625, JP-A-2003-015261, and 2003-2003. No. 0579790, No. 2003-084397, No. 2003-098648, No. 2003-098635, No. 2003-107635, No. 2003-131337, No. 2003-146330, No. 2003-226439, No. 2003-228152, etc. Is a packaging material. Further, the porosity in the package is 0.01 to 10%, preferably 0.02 to 5%. Nitrogen sealing is performed so that the nitrogen partial pressure in the package is 80% or more, preferably 90% or more. It is good to do. The relative humidity (RH) in the package is 10 to 60%, preferably 40 to 55%.

(Image formation)
For the exposure used for the exposure of the photothermographic material of the present invention, or the exposure in the image forming method of the present invention, various conditions are adopted with respect to the light source, exposure time, etc. suitable for obtaining the desired appropriate image. be able to.

The photothermographic material of the present invention preferably exhibits its characteristics when exposed to light with high illuminance with a light amount of 1 mW / mm ² or more for a short time. The illuminance here refers to the illuminance when the photosensitive material after heat development has an optical density of 3.0. When exposure is performed at such high illuminance, the amount of light (= illuminance × exposure time) required to obtain the required optical density is small, and a high sensitivity system can be designed. More preferably, the light quantity is 2-50 W / mm < ² >, More preferably, it is 10-50 W / mm < ² >.

  The exposure is preferably performed by laser scanning exposure, but various methods can be adopted as the exposure method. For example, as a first preferred method, there is a method using a laser scanning exposure machine in which the angle formed by the scanning surface of the photosensitive material and the scanning laser beam is not substantially perpendicular. Here, “substantially not perpendicular” means that the angle closest to the vertical during laser beam scanning is preferably 55 to 88 degrees, more preferably 60 to 86 degrees, and still more preferably 65 to 84 degrees. , Most preferably 70-82 degrees.

  The beam spot diameter on the exposed surface of the photosensitive material when the laser beam is scanned onto the photosensitive 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 “shift angle” from the vertical of the laser beam incident angle. 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.

  As a second method, it is also preferable to perform exposure using a laser scanning exposure machine that emits scanning laser light that is a vertical multi. Compared with a longitudinal single mode scanning laser beam, image quality degradation such as occurrence of interference fringe-like unevenness is reduced. In order to make a vertical multiplex, methods such as using return light by combining and applying high-frequency superposition are preferable. Note that 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.

  Furthermore, as a third aspect, it is also preferable to form an image by scanning exposure using two or more laser beams. As such an image recording method using a plurality of laser beams, it is used in an image writing unit of a laser printer or a digital copying machine that writes an image line by line in one scan because of a demand for higher resolution and higher speed. For example, Japanese Patent Laid-Open No. 60-166916 is known. This is a method in which laser light emitted from a light source unit is deflected and scanned by a polygon mirror and imaged on a photoconductor via an fθ lens or the like. This is the same laser scanning optical apparatus in principle as a laser imager or the like. It is.

  The image formation of laser light on the photoconductor in the image writing means of a laser printer or digital copying machine is for one line from the image formation position of one laser light for the purpose of writing an image by a plurality of lines in one scan. The next laser beam is imaged by shifting. Specifically, the two light beams are close to each other on the image plane in the sub-scanning direction at an order of several tens of μm, and the print density is 400 dpi (dpi is the number of dots per inch = 2.54 cm). The sub-scanning direction pitch of the two beams is 63.5 μm, and 42.3 μm at 600 dpi. Unlike the method of shifting the resolution in the sub-scanning direction as described above, in the present invention, it is preferable to form an image by condensing two or more lasers at the same place on the exposure surface while changing the incident angle. At this time, the exposure energy on the exposure surface when writing with one normal laser beam (wavelength λ [nm]) is E, and N laser beams used for exposure have the same wavelength (wavelength λ [nm]). ), In the case of the same exposure energy (En), the range of 0.9 × E ≦ En × N ≦ 1.1 × E is preferable. By doing so, energy is secured on the exposure surface, but the reflection of each laser beam to the image forming layer is reduced because the exposure energy of the laser is low, and thus the occurrence of interference fringes is suppressed.

In the above description, the wavelengths of the plurality of laser beams are the same as λ, but those having different wavelengths may be used. In this case, it is preferable that (λ−30) <λ ₁ , λ ₂ ,... Λ _n ≦ (λ + 30) with respect to λ [nm].

In the image recording methods of the first, second, and third aspects described above, as lasers used for scanning exposure, generally well-known solid lasers such as ruby lasers, YAG lasers, glass lasers; Gas lasers such as Ne laser, Ar ion laser, Kr ion laser, CO ₂ laser, CO laser, He—Cd laser, N ₂ laser, excimer laser; InGaP laser, AlGaAs laser, GaAsP laser, InGaAs laser, InAsP laser, CdSnP ₂ lasers, semiconductor lasers such as GaSb lasers; chemical lasers, dye lasers, etc. can be selected and used in a timely manner, but in the present invention, laser diodes (LD) and light emitting diodes (LEDs) are used as light sources. An exposure apparatus is preferably used. In particular, LD is more preferable in terms of high output and high resolution.

Any of these light sources may be used as long as they can generate light having an electromagnetic spectrum in a target wavelength range. For example, in the case of an LD, a dye laser, a gas laser, a solid laser, a semiconductor laser, or the like can be used. Preferred examples of the laser include a fourth harmonic of a YAG laser (Nd: YVO4 266 nm), a rare gas halide excimer laser such as an XeCl laser (308 nm), a KrF laser (248 nm), a KrCl laser (222 nm), and the like. Further, the exposure is performed with high illuminance and generally with a short exposure time of 10 ⁻⁷ seconds or less.

  In a laser used in a laser imager or a laser image setter, the beam spot diameter on the exposed surface of the material when scanned with a photothermographic material is generally 5 to 75 μm as the minor axis diameter and 5 to 5 as the major axis diameter. The laser beam scanning speed can be set to an optimum value for each photosensitive material depending on the sensitivity and laser power at the laser oscillation wavelength inherent to the photothermographic material.

(Laser imager)
The laser imager (heat development processing device) referred to in the present invention has a constitution that is a film supply device represented by a film tray, a laser image recording device, and heat that supplies uniform and stable heat to the entire surface of the photothermographic material. It is composed of a conveying unit from the developing unit and the film supply unit through laser recording to discharging the photothermographic material image-formed by thermal development out of the apparatus.

  The laser imager preferably used has a ratio of the cooling part length to the heat development part length of 1.5 or less, more preferably from 0.1 to 1.2, and particularly preferably from 0.2 to 1.0. Further, it is preferable that the non-photosensitive surface has a faster cooling rate than the photosensitive surface.

  In the present invention, the ratio of the specific photosensitive surface cooling rate to the photosensitive surface cooling rate is preferably 1.1 or more. More preferably, it is 1.1-5.0, Most preferably, it is 1.5-3.0. A means for increasing the cooling rate of the non-photosensitive surface is not particularly limited. However, it is preferable that the non-photosensitive surface is directly brought into contact with a metal plate, a metal roller, a nonwoven fabric, or a flocked roller. More preferably, in order to positively discharge the heat accumulated in these members to the outside, it is also desirable to use a heat sink or a heat pipe in combination.

  Here, the heat developing section length is a transport path length heated to a temperature at which the photographic material is developed in the heat developing apparatus. The cooling unit length is a path length from the heat developing unit to the time when the photosensitive material is discharged from the area where the photographic material is shielded by the laser imager to the room light where the laser imager is installed. By using a laser imager with a short cooling part length in which the ratio of the cooling part length to the heat developing part length is 1.5 or less, it is possible to provide a small-sized laser imager with a high processing speed.

  The cooling time from the exit from the heat developing section to the ejection is arbitrary, but it is preferably 0 to 25 seconds. More preferably, it is 0 to 15 seconds, and particularly preferably 5 to 15 seconds. The path length through which the photographic material passes after exiting the heat developing portion and before discharging is arbitrary, but is preferably 1 to 60 cm. More preferably, it is 5-50 cm, More preferably, it is 5-40 cm.

  The photothermographic material of the present invention may be developed by any method. Usually, the photothermographic material exposed imagewise is heated and developed. The preferred development temperature is 80 to 250 ° C, more preferably 100 to 140 ° C, and still more preferably 110 to 130 ° C. The development time is preferably 1 to 30 seconds, more preferably 3 to 15 seconds, and still more preferably 3 to 10 seconds. If the heating temperature is less than 80 ° C., sufficient image density cannot be obtained in a short time. If the heating temperature exceeds 200 ° C., the binder melts, and not only the image itself such as transfer to a roller but also transportability and developing machine etc. Adversely affect. By heating, a silver image is generated by an oxidation-reduction reaction between an organic silver salt (which functions as an oxidizing agent) and a reducing agent. This reaction process proceeds without any supply of treatment liquid such as water from the outside.

  As a thermal development method, either a drum type heater or a plate type heater may be used, but a plate heater method is preferable. A thermal development method using a plate heater method is preferably a method described in JP-A-11-133572. A laser imager that obtains a visible image by bringing a photothermographic material on which a latent image has been formed into contact with a heating means in a thermal development unit. The heating means is composed of a plate heater, and a plurality of pressing rollers are disposed to face each other along one surface of the plate heater, and the photothermographic photosensitive member is interposed between the pressing roller and the plate heater. The laser imager is characterized in that a material is passed through and heat development is performed.

  The linear velocity of the photosensitive material in the exposure section, the heat development section, and the cooling section is arbitrary, but a higher speed is preferable for rapid processing and improvement in throughput. A preferable linear velocity is 25 to 200 mm / second, more preferably 28 to 150 mm / second, and further preferably 30 to 60 mm / second or less. By setting the conveyance speed within this range, density unevenness during heat development can be improved, and the processing time can be shortened.

  A specific example of the laser imager of this aspect is shown in FIG. In order to perform the exposure process and the thermal development process at the same time, that is, to start development on a part of the sheet that has already been exposed while exposing a part of the sheet sensitive material, an exposure unit and a development unit that perform the exposure process The distance between the two is preferably 0 to 50 cm, and this makes the series of processing time for exposure and development extremely short. The preferable range of this distance is 3 to 40 cm, more preferably 5 to 30 cm. Here, the exposure part refers to a position where light from an exposure light source is irradiated to the photothermographic material, and the development part refers to a position where the photothermographic material is heated for the first time for heat development. In FIG. 1, reference numeral 6 denotes an exposure unit, and a portion where the photosensitive material conveyed from 4 in FIG.

  The heating device, apparatus or means may be a heating means typical as a heat generator using, for example, a hot plate, iron, hot roller, carbon or white titanium. More preferably, the photothermographic material in which the protective layer is provided on the photosensitive layer is subjected to heat treatment by bringing the surface having the protective layer into contact with the heating means for uniform heating, It is preferable from the viewpoints of thermal efficiency, workability, and the like, and it is preferable that the surface having the protective layer is conveyed while being in contact with the heat roller, and is developed by heat treatment. In the present invention, an image obtained by heat development at a heating temperature of 123 ° C. and a development time of 12 seconds is shown on orthogonal coordinates where the unit lengths of the diffusion density (Y axis) and the common logarithmic exposure (X axis) are equal. In the characteristic curve, the average gradation of 0.25 to 2.5 in terms of optical density with diffused light is preferably 2.0 to 4.0. By using such gradations, it is possible to obtain an image with high diagnostic recognizability even if the amount of silver is small.

The image forming method of the present invention is suitable for a compact laser imager having an installation area of 0.4 m ² or less.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the embodiment of this invention is not limited to these. Unless otherwise specified, “part” in the examples represents “part by mass” and “%” represents “% by mass”.
Example 1
<Manufacture of undercoated support>
Corona discharge treatment of 8 W · min / m ² was applied to both sides of a biaxially stretched and heat-fixed 175 μm thick PET film colored with the following blue dye at an optical density of 0.150 (measured with Konica Densitometer PDA-65). The applied photographic support was subbing. That is, on one surface of this photographic support, the undercoating liquid a-1 was applied at 22 ° C. and 100 m / min so that the dry film thickness was 0.2 μm, and dried at 140 ° C. for photosensitivity. An undercoat layer on the side of the conductive layer (image forming layer) was formed (referred to as undercoat lower layer A-1). Also, on the opposite surface, as the backing layer undercoat layer, the following undercoat coating solution b-1 was applied at 22 ° C. and 100 m / min so that the dry film thickness was 0.12 μm, and dried at 140 ° C. An undercoat conductive layer having an antistatic function (referred to as undercoat lower layer B-1) was coated on the backing layer side. A corona discharge of 8 W · min / m ² is applied to the upper surfaces of the undercoat layer A-1 and the undercoat layer B-1, and the following undercoat coating solution a-2 is dried on the undercoat layer A-1. It is coated at 33 ° C. and 100 m / min so as to have a film thickness of 0.03 μm, and dried at 140 ° C. to form an undercoat upper layer A-2. b-2 was applied at a dry film thickness of 0.2 μm at 33 ° C. and 100 m / min, dried at 140 ° C. to form an undercoating upper layer B-2, and the support was further heat treated at 123 ° C. for 2 minutes. The sample was wound up under conditions of 25 ° C. and 50% RH to prepare a subtracted sample.

<Preparation of aqueous polyester A-1 solution>
35.4 parts dimethyl terephthalate, 33.63 parts dimethyl isophthalate, 17.92 parts dimethyl sodium 5-sulfoisophthalate, 62 parts ethylene glycol, 0.065 parts calcium acetate monohydrate, manganese acetate tetrahydrate 0.022 parts were transesterified while distilling methanol at 170-220 ° C. under a nitrogen stream, 0.04 parts of trimethyl phosphate, 0.04 parts of antimony trioxide as a polycondensation catalyst, 6.8 parts of 4-cyclohexanedicarboxylic acid was added, and a theoretical amount of water was distilled off at a reaction temperature of 220 to 235 ° C. for esterification.

  Thereafter, the inside of the reaction system was further depressurized and heated for about 1 hour, and finally subjected to polycondensation at 280 ° C. and 133 Pa or less for about 1 hour to synthesize aqueous polyester A-1. The obtained aqueous polyester A-1 had an intrinsic viscosity of 0.33, an average particle size of 40 nm, and a weight average molecular weight of 80,000 to 100,000.

  Next, 850 ml of pure water was put into a 2 L three-necked flask equipped with a stirring blade, a reflux condenser, and a thermometer, and 150 g of aqueous polyester A-1 was gradually added while rotating the stirring blade. After stirring for 30 minutes at room temperature, the mixture was heated to an internal temperature of 98 ° C. over 1.5 hours and dissolved at this temperature for 3 hours. After completion of the heating, the mixture was cooled to room temperature over 1 hour and allowed to stand overnight to prepare a 15% aqueous polyester A-1 solution.

<Preparation of modified aqueous polyester B-1-2 solution>
1900 ml of the 15% aqueous polyester A-1 solution is placed in a 3 L four-necked flask equipped with a stirring blade, a reflux condenser, a thermometer, and a dropping funnel, and the internal temperature is increased to 80 ° C. while rotating the stirring blade. Heat. Into this, 6.52 ml of a 24% aqueous solution of ammonium peroxide was added, and a monomer mixture (28.5 g of glycidyl methacrylate, 21.4 g of ethyl acrylate, 21.4 g of methyl methacrylate) was dropped over 30 minutes, The reaction is continued for another 3 hours. Then, it cooled and filtered to 30 degrees C or less, and prepared the modified aqueous polyester B-1 solution (vinyl component modification ratio 20%) whose solid content concentration is 18%.

  The solid content concentration was 18% in the same manner except that the vinyl modification ratio was 36% and the modified components were styrene: glycidyl methacrylate: acetoacetoxyethyl methacrylate: butyl acrylate = 39.5: 40: 20: 0.5. A modified aqueous polyester B-2 solution (vinyl component modification ratio 20%) was prepared.

<Preparation of acrylic polymer latex C-1 to C-3>
Acrylic polymer latexes C-1 to C-3 having the monomer composition shown below were synthesized by emulsion polymerization. The solid content concentration was all 30%.

C-1: Styrene / glycidyl methacrylate / butyl acrylate = 20/40/40 (mass ratio) Tg: 20 ° C.
C-2: Styrene / butyl acrylate / t-butyl acrylate / hydroxyethyl methacrylate = 27/10/35/28 (mass ratio) Tg: 55 ° C.
C-3: Styrene / glycidyl methacrylate / acetoacetoxyethyl methacrylate = 40/40/20 (mass ratio) Tg: 50 ° C.
(Photosensitive layer side undercoat underlayer coating solution a-1)
Acrylic polymer latex C-3 (solid content 30%) 70.0 g
5.0 g aqueous dispersion of ethoxylated alcohol and ethylene homopolymer (solid content 10%)
Surfactant (A) 0.1g
Distilled water was added to make 1000 ml, and a coating solution was obtained.
(Photosensitive layer side undercoat upper layer coating solution a-2)
Modified aqueous polyester B-2 (18%) 30.0 g
Surfactant (A) 0.1g
True spherical silica matting agent (Nippon Shokubai Co., Ltd .: Seahoster KE-P50) 0.04g
Distilled water was added to make 1000 ml, and a coating solution was obtained.
(Coating liquid b-1 for backing layer side undercoat layer)
Acrylic polymer latex C-1 (solid content 30%) 30.0 g
Acrylic polymer latex C-2 (solid content 30%) 7.6 g
After heating concentrated so that the solid concentration of SnO ₂ zone Le synthesized by the method described is 10% in Example 1 of SnO ₂ sol (JP-B-35-6616, was adjusted to pH = 10 with aqueous ammonia 180g
Surfactant (A) 0.5g
PVA-613 (polyvinyl alcohol manufactured by Kuraray Co., Ltd.) 5% aqueous solution 0.4 g
Distilled water was added to make 1000 ml, and a coating solution was obtained.
(Backing layer side undercoat upper layer coating solution b-2)
Modified aqueous polyester B-1 (18%) 145.0 g
Spherical silica matting agent (Seahoster KE-P50: supra) 0.2g
Surfactant (A) 0.1g
Distilled water was added to make 1000 ml, and a coating solution was obtained.

  A backcoat layer and a backcoat layer protective layer having the following composition were coated on the undercoat layer B-2 on which the undercoat layer was applied.

<Preparation of backcoat layer coating solution>
While stirring 830 g of methyl ethyl ketone (MEK), 84.2 g of cellulose acetate propionate (manufactured by Eastman Chemical: CAP482-20) and 4.5 g of polyester resin (manufactured by Boston: Vitel PE2200B) were added and dissolved. Next, 0.30 g of an ultraviolet absorber (the type is listed in Table 1) was added, and 4.5 g of a fluorine-based surfactant (Asahi Glass Co., Ltd .: Surflon KH40) dissolved in 43.2 g of methanol and a fluorine-based surfactant. 2.3 g of an agent (Dainippon Ink Co., Ltd .: MegaFag F120K) was added and stirred well until dissolved. Next, 2.5 g of oleyl oleate was added and stirred to prepare a backcoat layer coating solution.

<Preparation of backcoat layer protective layer (surface protective layer) coating solution>
The backcoat layer protective layer was also prepared in the same manner as the backcoat layer coating solution at the following composition ratio. Silica was dispersed in MEK at a concentration of 1% with a dissolver type homogenizer, and finally added.
(Back coat layer protective layer coating solution)
Cellulose acetate propionate (CAP482-20: supra) 10% MEK solution 15g
Monodispersed silica with a monodispersity of 15% (average particle size 10 μm, surface-treated with 1% aluminum of silica) 0.03 g
Fluorine nonionic activator (FN-1) 0.075g
Fluorine-based surfactant (SF-17) 0.01g
Fluorine polymer (FM-1) 0.05g
Stearic acid 0.1g
0.1 g butyl stearate
α-Alumina (Mohs hardness 9) 0.1g
<Preparation of backcoat layer coating solution>
While stirring MEK830 g, 84.2 g of cellulose acetate propionate (CAP482-20: supra) and 4.5 g of polyester resin (Vitel PE2200B: supra) were added and dissolved. To this solution, add 4.5 g of a fluorine-based surfactant (Surflon KH40: supra) dissolved in 43.2 g of methanol and 2.3 g of a fluorosurfactant (Megaphag F120K: supra) until dissolved. Stir well. Next, 2.5 g of oleyl oleate was added. Finally, 75 g of silica (average particle size: 10 μm) dispersed in MEK with a dissolver type homogenizer at a concentration of 1% was added and stirred to prepare a backcoat layer coating solution.

<Preparation of backcoat layer protective layer (surface protective layer) coating solution>
The following composition ratio was prepared in the same manner as the back coat layer coating solution. A dissolver type homogenizer was used for dispersion of silica.

Cellulose acetate propionate (CAP482-20: supra) 10% MEK solution 15g
Monodispersed silica with a monodispersity of 15% (average particle size 10 μm, surface-treated with 1% aluminum of silica) 0.03 g
C ₈ F ₁₇ (CH ₂ CH ₂ O) ₁₂ C ₈ F ₁₇ 0.05 g
Fluorine-based surfactant (SF-17) 0.01g
Fluorine polymer (FM-1) 0.05g
Stearic acid 0.1g
0.1 g butyl stearate
α-Alumina (Mohs hardness 9) 0.1g
FN-1: C ₈ F ₁₇ (CH ₂ CH ₂ O) ₁₂ C ₈ F ₁₇

<Preparation of photosensitive silver halide emulsion A1>
(A1)
Phenylcarbamoylated gelatin 88.3g
10% aqueous methanol solution of compound (AO-1) 10ml
Potassium bromide 0.32g
Finish to 5429 ml with water (B1)
0.67 mol / L silver nitrate aqueous solution 2635 ml
(C1)
Potassium bromide 50.69g
Potassium iodide 2.66g
Finish to 660ml with water (D1)
Potassium bromide 151.6g
Potassium iodide 7.67g
0.93ml potassium hexachloroiridium (IV) (1% aqueous solution)
Potassium hexacyanoferrate (II) 0.004g
Hexachloroosmium (IV) potassium salt 0.004g
Finish to 1982ml with water (E1)
0.4 mol / L potassium bromide aqueous solution The following silver potential control amount (F1)
Potassium hydroxide 0.71g
Finish to 20ml with water (G1)
56% acetic acid aqueous solution 18.0 ml
(H1)
Anhydrous sodium carbonate 1.72 g
Finish to 151 ml with water AO-1: HO (CH ₂ CH ₂ O) _n [CH (CH ₃ ) CH ₂ O] ₁₇ (CH ₂ CH ₂ O) _m H
m + n = 5-7
Using the mixing stirrer shown in Japanese Patent Publication No. 58-58288, while controlling 1/4 of the solution (B1) in the solution (A1) and the total amount of the solution (C1) to 20 ° C. and pAg 8.09, the simultaneous mixing method Was added for 4 minutes and 45 seconds to nucleate. After 1 minute, the entire amount of solution (F1) was added. During this time, pAg was adjusted as appropriate using (E1). After 6 minutes, 3/4 amount of the solution (B1) and the total amount of the solution (D1) were added by a simultaneous mixing method over 14 minutes and 15 seconds while controlling at 20 ° C. and pAg 8.09. After stirring for 5 minutes, the temperature was lowered to 40 ° C., the whole amount of the solution (G1) was added, and the silver halide emulsion was allowed to settle. The supernatant was removed leaving 2 L of the sedimented portion, 10 L of water was added, and after stirring, the silver halide emulsion was precipitated again. The supernatant liquid was removed leaving 1.5 L of the sedimented portion, 10 L of water was further added, and after stirring, the silver halide emulsion was allowed to settle. After leaving the sedimented portion 1.5L and removing the supernatant, the solution (H1) 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 so that the amount was 1,161 g per mole of silver to obtain photosensitive silver halide emulsion A.

  This emulsion was monodispersed cubic silver iodobromide grains having an average grain size of 25 nm, a grain size variation coefficient of 12%, and a [100] face ratio of 92% (silver iodide content: 3.5 mol%).

<Preparation of photosensitive silver halide emulsion B1>
The same procedure as in the preparation of the photosensitive silver halide emulsion A1 was conducted except that the temperature at the time of addition by the simultaneous mixing method was changed to 45 ° C. This emulsion was monodispersed cubic silver iodobromide grains having an average grain size of 55 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92% (silver iodide content: 3.5 mol%).

<Preparation of photosensitive silver halide emulsion C>
The procedure was the same as the preparation of the photosensitive silver halide emulsion A1, except that the potassium bromide used in the preparation of the photosensitive silver halide emulsion A1 was changed to potassium iodide. This emulsion was monodispersed pure silver iodide grains having an average grain size of 25 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92%.

<Preparation of photosensitive silver halide emulsion D>
Preparation of photosensitive silver halide emulsion A1 except that a portion of potassium bromide used in the preparation of photosensitive silver halide emulsion A1 was changed to potassium iodide so that the silver iodide content was 90 mol%. The same was done. This emulsion was monodispersed silver iodobromide grains having an average grain size of 25 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92% (silver iodide content 90 mol%).

<Preparation of photosensitive silver halide emulsion E>
The same procedure as in the preparation of photosensitive silver halide emulsion C was carried out except that the temperature at the time of addition by the simultaneous mixing method was changed to 45 ° C. This emulsion was monodispersed pure silver iodide grains having an average grain size of 55 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92%.

<Preparation of photosensitive silver halide emulsion F>
The procedure was the same as the preparation of the photosensitive silver halide emulsion D except that the temperature at the time of addition by the simultaneous mixing method was changed to 45 ° C. This emulsion was monodispersed silver iodobromide grains having an average grain size of 55 nm, a grain size variation coefficient of 12%, and a [100] face ratio of 92% (silver iodide content: 90 mol%).

<Preparation of photosensitive silver halide emulsion G>
In the preparation of the photosensitive silver halide emulsion C, and after adding the entire amount of the solution F1 after nucleation, except that 0.1% ethanol solution was added 4ml a similar fashion sensitive silver of the following compound (TPPS) Silver emulsion G was prepared. This emulsion was monodispersed pure silver iodide grains having an average grain size of 25 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92%.

<Preparation of photosensitive silver halide grain emulsion H>
In the preparation of the photosensitive silver halide emulsion E, the photosensitive silver halide was prepared in the same manner except that 4 ml of a 0.1% ethanol solution of the following compound (TPPS) was added after adding the whole amount of the solution F1 after nucleation. Emulsion H was prepared. This emulsion was monodispersed pure silver iodide grains having an average grain size of 55 nm, a grain size variation coefficient of 12%, and a [100] plane ratio of 92%.

<Preparation of powdered organic silver salt A>
In 4,720 ml of pure water, 130.8 g of behenic acid, 67.7 g of arachidic acid, 43.6 g of stearic acid, and 2.3 g of palmitic acid were dissolved at 80 ° C. Next, 540.2 ml of a 1.5 mol / L sodium hydroxide aqueous solution was added, and 6.9 ml of concentrated nitric acid was added, followed by cooling to 55 ° C. to obtain a fatty acid sodium solution. While maintaining the temperature of the fatty acid sodium solution at 55 ° C., a photosensitive silver halide grain emulsion (type and amount added are listed in Table 2) and 450 ml of pure water were added and stirred for 5 minutes. Next, 468.4 ml of 1 mol / L silver nitrate solution was added over 2 minutes and stirred for 10 minutes to obtain an organic silver salt dispersion. Thereafter, the obtained organic silver salt dispersion was transferred to a water-washing container, deionized water was added and stirred, and then allowed to stand to float and separate the organic silver salt dispersion, thereby removing the lower water-soluble salts. Thereafter, washing with deionized water and drainage were repeated until the electrical conductivity of the drainage reached 2 μS / cm, and centrifugal dehydration was carried out. Then, the obtained cake-like organic silver salt was converted into an air-flow dryer Flashjet dryer (Seishin). The product was dried until the water content became 0.1% by operating conditions (inlet 65 ° C., outlet 40 ° C.) of nitrogen gas atmosphere and dryer hot air temperature to obtain powdered organic silver salt A. .

<Preparation of preliminary dispersion A>
As a binder for the photosensitive layer, 14.57 g of SO ₃ K group-containing polyvinyl butyral (Tg 75 ° C., containing —SO ₃ K group of 0.2 mmol / g) was dissolved in 1,457 g of MEK, and dissolver DISPERMAT manufactured by VMA-GETZMANN While stirring with a CA-40M type, 500 g of the powdered organic silver salt A was gradually added and mixed thoroughly to prepare a preliminary dispersion A.

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

<Preparation of stabilizer solution>
A stabilizer solution was prepared by dissolving 1.0 g of Stabilizer 1 and 0.31 g of potassium acetate in 4.97 g of methanol.

<Preparation of 2-chlorobenzoic acid solution>
1.488 g of 2-chlorobenzoic acid, 2.779 g of stabilizer 2 and 365 mg of 5-methyl-2-mercaptobenzimidazole are dissolved in 31.3 ml of MEK in the dark to prepare a 2-chlorobenzoic acid solution. did.

<Preparation of additive solution a>
Reducing agent (compound and amount described in Table 1), 0.159 g of yellow chromophoric leuco dye (compound described in Table 1), 0.159 g of cyan chromogenic leuco dye (compound described in Table 1), 1 .54 g of 4-methylphthalic acid and 0.48 g of an ultraviolet absorber (compound described in Table 1) were dissolved in 110.0 g of MEK to obtain an additive solution a.

<Preparation of additive liquid b>
1.56 g antifoggant 2, 0.5 g antifoggant 3, 0.5 g antifoggant 4, 0.5 g antifoggant 5, 3.43 g phthalazine dissolved in 40.9 g MEK and added b.

<Preparation of additive liquid c>
0.2 g of silver saving agent (SE2-2) was dissolved in 39.8 g of MEK to obtain an additive solution c.

<Preparation of additive liquid d>
0.5 g of potassium p-toluenethiosulfonate and 0.5 g of antifoggant 6 were dissolved in 9.0 g of MEK to obtain an additive solution d.

<Preparation of additive liquid e>
1.0 g of VS-1 (antifoggant) was dissolved in 9.0 g of MEK to obtain an additive solution e.

VS-1: (CH ₂ = CHSO ₂ CH ₂ ) ₂ CHOH
<Preparation of photosensitive layer coating solution>
In an inert gas atmosphere (97% nitrogen), 50 g of the photosensitive emulsion dispersion A and 15.11 g of MEK were kept at 21 ° C. with stirring, and the chemical sensitizer S-5 (0.5% methanol solution) 1000 μl was added, and after 2 minutes, 390 μl of antifoggant 1 (10% methanol solution) was added and stirred for 1 hour. Further, 494 μl of calcium bromide (10% methanol solution) was added and stirred for 10 minutes, then gold sensitizer Au-5 corresponding to 1/20 mole of the above organic chemical sensitizer was added, and further stirred for 20 minutes. . Subsequently, 167 μl of a stabilizer solution was added and stirred for 10 minutes, and then 1.32 g of the 2-chlorobenzoic acid solution was added and stirred for 1 hour. Thereafter, the temperature was lowered to 13 ° C. and further stirred for 30 minutes. While maintaining the temperature at 13 ° C., 0.5 g of additive liquid d, 0.5 g of additive liquid e, and 13.31 g of binder used in the preliminary dispersion were added and stirred for 30 minutes, and then tetrachlorophthalic acid (9. (4% MEK solution) 1.084 g was added and stirred for 15 minutes. While continuing stirring, 12.43 g of additive liquid a, 1.6 ml of Desmodur N3300 (aliphatic isocyanate manufactured by Movey) 10% MEK solution, 4.27 g of additive liquid b, 1.0 g of additive liquid c By sequentially adding and stirring, a photosensitive layer coating solution was obtained.

<Preparation of photosensitive layer protective layer lower layer (surface protective layer lower layer)>
To 500 g of acetone, 2,100 g of MEK and 700 g of methanol, 230 g of cellulose acetate butyrate (manufactured by Eastman Chemical: CAB-171-15S) was added, and the mixture was stirred and dissolved with a dissolver. Next, 25 g phthalazine, 3.5 g VS-2 (antifoggant), 1 g FN-2 (fluorine nonionic activator), 1 g SF-17 (exemplary fluorosurfactant), 10 g Stearic acid and 10 g of butyl stearate were added and dissolved with stirring to prepare a photosensitive layer protective layer lower layer coating solution.

<Preparation of photosensitive layer protective layer upper layer (surface protective layer upper layer)>
To 500 g of acetone, 2,100 g of MEK, and 700 g of methanol, 230 g of cellulose acetate butyrate (CAB-171-15S: the above) was added, and the mixture was stirred and dissolved with a dissolver. Next, 25 g of phthalazine, 3.5 g of VS-2 (antifoggant), 1 g of FN-2 (fluorine nonionic activator), 0.5 g of SF-17 (exemplary fluorine surfactant), 1 0.0 g of fluorine-based polymer (FM-1: supra), 10 g of stearic acid and 10 g of butyl stearate were added with stirring and dissolved. Finally, 280 g of 15% monodispersed silica (average particle size 10.0 μm, surface-treated with 1% aluminum of the total amount of silica) dispersed in MEK with a dissolver type homogenizer at a concentration of 5%, A photosensitive layer protective layer upper layer coating solution was prepared by stirring.

VS-2: CH ₂ = CHSO ₂ CH ₂ CH ₂ OCH ₂ CH ₂ SO ₂ CH = CH ₂
FN-2: C ₁₂ F ₂₅ (CH ₂ CH ₂ O) ₁₀ C ₁₂ F ₂₅
<Preparation of photothermographic material sample>
Extrude coater (extrusion) by extruding backcoat layer coating solution and backcoat layer protective layer coating solution prepared as described above onto subbing upper layer B-2 so that the dry film thickness is 3.5 μm, respectively. Application was performed at an application speed of 50 m / min. 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.

  The photosensitive layer coating solution and the photosensitive layer protective layer (surface protective layer) coating solution are extruded and coated at the coating speed of 50 m / min at the coating speed of 50 m / min. Photothermographic material samples 101 to 118 were prepared. Application is a dry film thickness of 15.0 μm of the photosensitive layer, and a dry film thickness of 3.0 μm of the protective layer (surface protective layer) (surface protective layer upper layer 1.5 μm, surface protective layer lower layer 1.5 μm). Then, the film was dried for 10 minutes using a drying air having a drying temperature of 75 ° C. and a dew point temperature of 10 ° C.

  When the surface roughness of the samples 101 to 118 was measured, Rz (E) / Rz (B) = 0.40 and Rz (E) = 1.4 μm. Rz (B) was 3.5 μm. Ra (E) was 0.09 μm, and Ra (B) was 0.12 μm.

  In samples 101 to 118, an absorption peak at a maximum absorption wavelength of 420 nm due to the yellow coloring leuco dye was observed. Further, Samples 101 to 110 and 113 to 118 showed an absorption peak at a maximum absorption wavelength of 640 nm due to the cyan color-forming leuco dye. Further, Samples 111 to 112 showed an absorption peak at a maximum absorption wavelength of 620 nm due to the cyan color-forming leuco dye.

  Sample 113 was prepared by preparing 259.9 g of behenic acid instead of 130.8 g of behenic acid, 67.7 g of arachidic acid, 43.6 g of stearic acid, and 2.3 g of palmitic acid in the preparation of powdered organic silver salt A in sample 105. A sample was prepared in the same manner as Sample 105 except that it was used.

  In Sample 114, 540.2 ml of 1.5 mol / L potassium hydroxide aqueous solution was used instead of 540.2 ml of 1.5 mol / L sodium hydroxide aqueous solution in the preparation of powdered organic silver salt A in Sample 105. A sample was prepared in the same manner as the sample 105 except for the above.

Sample 115 is the same as Sample 105 except that the fluorine-based activator for the backcoat layer protective layer and the photosensitive layer protective layer (upper layer and lower layer) in Sample 105 is changed from SF-17 to C ₈ F ₁₇ SO ₃ Li. A sample was prepared.

Sample 116, as the photosensitive layer binder in the preparation of preliminary dispersion A in the sample 105, SO ₃ K group-containing polyvinyl butyral in place (Tg of 75 ° C., the SO ₃ K 0.2 containing mmol / g) in, SO ₃ A sample was prepared in the same manner as Sample 105 except that K group-containing polyvinyl butyral (Tg 65 ° C., containing SO ₃ K 0.2 mmol / g) was used.

<Evaluation of sample>
Evaluation was carried out simultaneously with exposure with the laser imager (installation area 0.35 m ² ) shown in FIG. 1, and the obtained image was evaluated with a densitometer. Here, “thermal development at the same time as exposure” means a sheet of photosensitive material made of photothermographic material, and development is started on a part of the sheet that has already been exposed while part of the photosensitive material is exposed. Means that. The distance between the exposed part and the developing part was 12 cm. At this time, the conveyance speed from the photosensitive material supply unit to the image exposure unit, the conveyance rate at the image exposure unit, and the conveyance rate at the heat development unit were each 30 mm / second. Further, the position of the bottom surface of the photosensitive material stock tray located at the bottom was 45 cm from the floor surface.

  The photothermographic material produced as described above is set in the film accommodating portion 4 of the laser imager shown in FIG. 1, and is conveyed by the film guide 10 (the conveying roller 2 is set up to the outlet 7 but only a part is shown). The The conveyed photographic material is exposed at the exposure unit 6 from the photosensitive surface side by an exposure machine using an exposure source with a maximum multimode laser of the fourth harmonic of the YAG laser (Nd: YVO4 emission wavelength 266 nm) from the photosensitive surface side. Exposure by laser scanning was given. At this time, an image was formed with the angle of the exposure surface of the photographic material and the exposure laser beam being 75 degrees. In this method, an image with less unevenness and unexpectedly good sharpness or the like was obtained compared to the case where the angle was 90 degrees.

  Thereafter, heat development was performed at 123 ° C. for 10 seconds so that the non-photosensitive surface of the photographic material was in contact with the surface of the developing unit 3 (in the case of continuous processing, the interval time of heat development was 4 seconds). The photothermographic dry imaging material subjected to heat development is cooled by the cooling unit 5 on the non-photosensitive surface side by a cooling member. FIG. 1A is a roller shape, and FIG. Show. The laser imager was operated in a room conditioned at 23 ° C. and 50% RH.

  The exposure was performed in a stepped manner while reducing the exposure energy amount by log E0.05 step by step from the maximum output.

<Packaging materials>
PET 10 μm / PE 12 μm / Aluminum foil 9 μm / Ny 15 μm / polyethylene 50 μm containing 3% carbon, oxygen permeability: 0.02 ml / atm · m ² · 25 ° C · day, moisture permeability: 0.001 g / m ² · 40 ° C 90% RH · day barrier bag (according to JIS Z0208 cup method). Use paper tray.

<Performance evaluation>
The following performance was evaluated for each heat-developed image.

<Image density>
The value of the highest density portion of the image obtained under the above conditions was measured with a densitometer and indicated as the image density.

《Fog》
The value of the unexposed portion of the image obtained under the above conditions was measured with a densitometer and indicated as fog density.

"sensitivity"
The image obtained under the above conditions was subjected to density measurement using a densitometer, and a characteristic curve comprising a horizontal axis—exposure amount and a vertical axis—density was created. In the characteristic curve, the sensitivity was defined by defining the reciprocal of the exposure amount giving a density 1.0 higher than that of the unexposed portion as sensitivity. The sensitivity is expressed as a relative value with the sample 101 as 100.

  Note: Figures in parentheses in the Relative Sensitivity column indicate that the photographic material was heat treated for 10 seconds at a heat development temperature of 123 ° C. before being exposed to white light, and then exposed to white light through an optical wedge (4874K, 30 seconds). In comparison between the sensitivity when thermally developed at 123 ° C. for 10 seconds and the sensitivity when thermally developed at 123 ° C. for 10 seconds after exposure to white light under the same conditions as described above without heat treatment before exposure, the latter The sensitivity relative value of the former when the sensitivity is 100 is shown.

  In this relative comparison, the main cause of the decrease in the relative sensitivity of the sample obtained by heat-treating the photographic material at the heat development temperature before the photographic material is exposed to white light is that the surface of the silver halide grains is caused by the disappearance or reduction of the spectral sensitizing effect It was confirmed by observation / measurement of a change in the spectral sensitivity spectrum, etc. that it was due to a change in the relative relationship between the sensitivity and the internal sensitivity.

《Silver tone in high density area》
A chest X-ray image was printed on each sample, and the heat development processing was performed so that the maximum density was 4.0 or more by appropriately adjusting the processing time. The silver color tone in the high density part after treatment (at a density of 2.5) was visually evaluated using a Schaukasten. A wet processed laser imager film manufactured by Konica was used as a standard sample at this time, and the relative color tone with respect to the standard sample was evaluated visually by 0.5 increments according to the following criteria.

5: The same color tone as the standard sample 4: Almost the same preferred color tone as the standard sample 3: Level slightly different from the standard sample, but practically no problem 2: Color tone clearly different from the standard sample 1: Unpleasant color tone different from the standard sample << Light Irradiation Image Preservability >>
After each sample was exposed and developed in the same manner as described above, the change in the image after standing on a Schaukasten with a luminance of 1,000 lux and allowed to stand for 10 days was visually evaluated in 0.5 increments according to the following criteria. did.

5: Almost no change 4: Slight color change observed 3: Color change and fog increase partially observed 2: Color change and fog increase observed in a considerable part

  From Table 1, it is clear that the sample of the present invention has high sensitivity, low fog, high maximum density, and excellent light irradiation image storage stability and silver tone as compared with the comparative sample. Further, by comparing Samples 116 and 105, it has been found that Sample 105 has better characteristics with respect to fog rise during high-temperature storage.

1 is a schematic configuration diagram of a laser imager (thermal development recording apparatus) for thermally developing a silver salt photothermographic dry imaging material according to the present invention to form an image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Film 2 Conveyance roller 3 Developing part 4 Film accommodating part 5 Cooling part 6 Exposure part 7 Exit 10 Film guide

Claims (3)

In a silver salt photothermographic dry imaging material having a photosensitive layer containing an organic silver salt, photosensitive silver halide grains, a reducing agent and a binder on a support, the photosensitive layer contains an ultraviolet absorber, and A silver salt photothermographic dry imaging material, wherein the photosensitive silver halide grains contain 5 to 100 mol% of silver iodide. In a silver salt photothermographic dry imaging material having a photosensitive layer containing an organic silver salt, photosensitive silver halide grains, a reducing agent and a binder on a support, the photosensitive layer contains an ultraviolet absorber, and The photosensitive silver halide grains contain silver iodide in a proportion of 5 to 100 mol%, and the silver salt photothermographic dry imaging material is exposed with a laser beam having a peak intensity at a wavelength of 200 nm to 350 nm. Silver salt photothermographic dry imaging material. An image forming method comprising exposing the silver salt photothermographic dry imaging material according to claim 1 with a laser beam having a peak intensity at a wavelength of 200 to 350 nm.

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