JP2002283734A - Thermal recording material - Google Patents

Abstract

[PROBLEMS] To provide a heat-sensitive recording material which causes little increase in minimum density, decrease in print density and deterioration of color tone due to storage and little generation of white powder. A heat-sensitive recording layer containing a substantially non-photosensitive organic silver salt, an organic reducing agent, a color tone agent, and a binder is provided on a transparent support, and 50% by weight or more of the heat-sensitive layer binder is hydrophobic. A heat-sensitive recording material which is a binder and has a distribution coefficient (logP) of at least one of the organic reducing agent and the color tone agent of 1.5 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material capable of forming an image by heating with a thermal head, and more particularly, to a heat-sensitive recording material which hardly causes a decrease in printing density or color tone due to storage and little white powder. Related to recording materials.

[0002]

2. Description of the Related Art As a high quality image recording method, an image forming method of a wet process using silver halide has been generally used for a long time. However, because of wet processing,
An image forming method that does not use these processing solutions has been desired because of waste liquid treatment of processing chemicals and restrictions on installation of facilities such as piping. As a result, application of an image forming system such as an ink jet printer, electrophotography, dye thermal transfer, and direct thermal method is currently being studied as a hard copy material. However, none of these dry image forming methods is quite satisfactory in fields requiring excellent granularity, high space and density resolution, such as medical images.

Under these circumstances, a heat-sensitive recording material comprising a substantially light-insensitive organic acid silver salt and an organic reducing agent, which has been known for a long time in US Pat. Nos. 3,074,809 and 3,080254, etc. Is used for direct thermal image recording by a printer equipped with a thermal head as described in JP-T 8-505579 and JP-T 9-504752, so that the maximum density and smoothness that cannot be obtained by other recording methods A transmission image with gradation can be obtained, which is suitable for application to the field of medical images. Further, the recording material is non-photosensitive, and is excellent in handleability for the user.

In such an application, a recording material is required to have a certain degree of transparency in order to coat a heat-sensitive recording layer and a protective layer on a transparent support and to observe a recorded image as transmitted light on a Schaucusten. You. In Japanese Patent Application Laid-Open No. 8-505579, a highly transparent recording solution is prepared by using a water-soluble binder such as polyvinyl alcohol and a dispersing aid to prepare a substantially transparent reducing agent solution and preparing a heat-sensitive layer coating solution. The material is getting.

However, the use of a water-soluble binder in the heat-sensitive layer can cause an undesired increase in base density and a decrease in image density before image recording, particularly under high humidity, and an increase in image density especially in an intermediate density range after image recording. And the color tone deteriorated, and the recording material was not satisfactory.

In order to solve this problem, a hydrophobic binder is often used as a binder for the heat-sensitive layer. However, when a necessary amount of a reducing agent or a color tone agent having sufficient activity is contained, the crystallization during storage is difficult. As a result, the activity is impaired, the printing density is reduced, the color tone is deteriorated, and further, white powder is generated on the surface. This has been strongly demanded.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material which hardly causes a decrease in print density or color tone due to storage and generates less white powder.

[0008]

The above objects have been achieved by the following means. A heat-sensitive recording layer containing a substantially non-photosensitive organic silver salt, an organic reducing agent, a color tone agent, and a binder on a transparent support, and 50% by weight of the heat-sensitive layer binder
The above is a hydrophobic binder, and at least one of the organic reducing agent and the color tone agent has a partition coefficient (logP) of 1.5.
A heat-sensitive recording material characterized by the above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. 50% by weight or more of the binder in the heat-sensitive recording layer of the present invention is a hydrophobic binder. The hydrophobic binder referred to herein is a polymer that does not substantially dissolve in water, and examples thereof include an acrylic resin, a polyester resin, a polyurethane resin, a vinyl chloride resin, a vinyl acetate resin, a polyolefin resin, and a polyvinyl acetal resin. The resin may be used by dissolving it in an organic solvent, or may be a latex in which a hydrophobic polymer solid is dispersed in fine particles or a resin in which polymer molecules form micelles and are dispersed.
In the present invention, among these, those which form a transparent film after coating and drying are preferable. If necessary, two or more resins compatible with each other may be used in combination. In the case of water-based coating, as an auxiliary for dispersing additives,
Alternatively, in order to adjust the liquid properties such as the viscosity of the coating liquid, a hydrophilic binder may be used together with the hydrophobic binder component within a range not less than 50%. However, for the purposes of the present invention,
The content of the hydrophobic binder component is more preferably 70% or more.

It is preferable that the binder used in the heat-sensitive recording layer contains as little free halide ions as chloride ions and bromide ions. These halide ions react with silver ions during long-term storage to form photosensitive silver halide, which causes a reduction in light resistance of the recording material. Specifically, the content is preferably 100 ppm or less based on the resin solid content.

The organic reducing agent used in the heat-sensitive recording material of the present invention has a distribution coefficient (logP) of 1.5 or more, and more preferably 2.0 or more. This well-known value is the logarithm of the n-octanol / water partition coefficient (P), which is a useful parameter that can characterize the hydrophilicity / hydrophobicity of a wide range of compounds. In general, the partition coefficient is determined by calculation without experiment, and in the present invention, CS ChemDraw Pro Ver. 4.
5, Crippen's fragmentation: J. Chem. Inf. Comput.
Sci., 27, 21 (1987). As the organic reducing agent, phenol, hydroquinone, catechol, compounds having a pyrogallol structure and the like are used,
In particular, catechol derivatives are preferred from the balance between activity and stability. The following general formulas [I] to [I] described in Japanese Patent Application No. 2000-21476.
Compounds represented by the formula [II] are also particularly preferably used.

[0012]

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In the general formula [I], R1 and R2 are substituents having a positive Hammett's substituent constant σ. In the general formula [II], Z represents an atom group necessary for forming a ring structure. In the general formula [III], R3 and R4 are a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group, an aryl group, an acyl group, an ester group, an amide group,
Represents a cyano group, a nitro group, a sulfonyl group, R3 and R4
May combine with each other to form a ring structure. General formulas [I] to [I
In II], the benzene ring having a dihydroxy group may optionally have a substituent.

Specific examples and partition coefficients of the organic reducing agent of the present invention are shown below, but the reducing agent used in the present invention is not limited to these.

[0015]

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[0016]

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[0017]

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The addition amount of these reducing agents can vary widely depending on the type of the reducing agent and the type of the organic silver salt, but is generally about 0.1 to 3 mol, preferably about 0.1 to 3 mol, per mol of the organic silver salt.
0.3 mol to 2 mol.

A different reducing agent may be used as an auxiliary reducing agent for the purpose of improving gradation and increasing the maximum density. Such auxiliary reducing agents are not particularly limited, and are described in Research Disclosure No. 17 relating to photothermographic materials.
The compounds described in Section 029 (III), System B, and Section 29996 (VIII) can be used.

The reducing agent used in the present invention can be prepared by various methods known to those skilled in the art, for example, by dissolving in a suitable organic solvent.
It is added as a solid dispersion using a ball mill or the like, or emulsified and dispersed together with other additives to form an emulsion. The reducing agent does not necessarily need to be added to the layer containing the organic silver salt, but may be added to another layer or may be added separately.

In the heat-sensitive recording material of the present invention, a toning agent is used because the formed reduced silver image shows cool black.
Examples of the toning agent include the above-mentioned Research Disclosure No. 17029 (V) and No. 29963 (X
XII) and the like, and include imides, mercapto compounds, phthalazine, phthalazinone, phthalic acid derivatives, benzoxazine derivatives and the like. In order to achieve the object of the present invention, the distribution coefficient of the toning agent is 1.5 or more.

Specific examples and distribution coefficients of the toning agents are shown below, but the toning agents used in the present invention are not limited to these.

[0023]

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[0024]

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[0025]

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The organic silver salt used in the heat-sensitive recording layer of the present invention is a substantially light-insensitive, colorless or white silver salt, which is reduced by heating with a reducing agent described later to convert silver. What happens. Specifically, Research Disclosure No. 17029 on photothermographic materials
Silver salts of organic acids such as gallic acid, oxalic acid, behenic acid, stearic acid, palmitic acid, lauric acid and the like as described in (II) and 29996 (XVI); 1- (3-carboxypropyl ) Silver salts of carboxyalkylthioureas such as thiourea and 1- (3-carboxypropyl) -3,3-dimethylthiourea; aldehydes such as formaldehyde, acetaldehyde, butyraldehyde and salicylic acid, benzoic acid, 3,5-
Complex of silver with a polymer reaction product of an aromatic carboxylic acid such as dihydroxybenzoic acid and 5,5-thiodisalicylic acid; 3- (2
-Carboxyethyl) -4-hydroxymethyl-4-thiazoline
Silver salts or complexes of thiones such as -2-thione, 3-carboxymethyl-4-methyl-4-thiazoline-2-thione; imidazole, pyrazole, urazole, 1,2,4 triazole and 1H-tetrazole, 3- Amino-5-benzylthio-1,2,4
Silver salts or complexes of nitrogen acids selected from -triazole and benzotriazole; silver salts such as saccharin and 5-chlorosalicylaldoxime; and silver salts of mercaptides. Among these, fatty acid silver having 10 or more carbon atoms is preferable, and silver stearate, silver behenate and the like are particularly preferably used.

These organic silver salts or complexes can be dissolved or dispersed in a suitable solvent such as water, aliphatic hydrocarbons, esters, alcohols, ethers or the like, or in an appropriate solvent. It can be easily obtained by mixing a dissolved or dispersed silver salt such as silver nitrate. It is preferable to remove extraneous salts from the obtained crystals by washing with water or the like. In the present invention, the obtained crystals are dispersed by a high-speed stirrer, a ball mill, a sand mill, a colloid mill, a vibration mill, an ultrasonic disperser, a homogenizer or the like, and are preferably used as a stable dispersion.
At this time, if necessary, a surfactant may be used as a dispersing aid, and a polymer compound may be used as a protective colloid.

The amount of silver in the above-mentioned reducible silver source used in the present invention is determined by the required maximum concentration, but is generally 3 g / m ² or less, preferably 0.5 to 2.0 g, as silver amount.

In the heat-sensitive recording material of the present invention, various accelerators, stabilizers and precursors thereof may be used for the purpose of suppressing or promoting the formation of image silver by reduction, and improving the preservability before and after printing. Good. Specifically, adipic acid, phthalic acid, gluconic acid, maleic acid, 2-hydroxy-1-naphthoic acid, organic acids such as tetrachlorophthalic anhydride and its anhydrides, and photographic stabilizers and inhibitors are often used. Known benzotriazole, 5-methylbenzotriazole, 5-chlorobenzotriazole, 2-mercaptobenzotriazole, 2-mercaptomensimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 4-hydroxy-6-methyl -1,3,3a, 7-tetrazaindene, 1-phenyl-5-mercaptotetrazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 3-mercapto-5-phenyl-1,2, 4-triazole, 4-benzamide-3
-Mercapto-5-phenyl-1,2,4-triazole can be selected.

The coating liquid for forming the heat-sensitive recording layer of the present invention includes:
In addition, pigments, waxes, thickeners, coating aids, and the like may be added as necessary.

In the present invention, a protective layer can be provided for the purpose of preventing scratches on the recording material due to contact with the thermal head and reducing abrasion of the thermal head. The protective layer preferably contains a matting agent in the protective layer binder for the purpose of reducing glare and preventing blocking.

As the matting agent used in the present invention, fine particles of known organic or inorganic compounds which are insoluble in the solvent of the coating solution are used. For example, organic compounds include polymethyl acrylate, polymethyl methacrylate, polystyrene, and polytetrafluoroethylene, and inorganic compounds include silica (silicon dioxide), titanium dioxide, talc (magnesium silicate), and alumina. Among these, it is preferable to use wet silica for the heat-sensitive recording material of the present invention formed on a transparent support. The average particle diameter of the wet-process silica is preferably less than 0.7 times the thickness of the protective layer, and the particle diameter distribution is preferably as narrow as possible. Further, in the present invention, it is preferable to use fumed silica or colloidal silica in combination.

For the protective layer, a binder that can withstand heating during printing by the thermal head is used. Generally, natural or synthetic resins are crosslinked to improve heat resistance.Specifically, gelatin, polyvinyl alcohol, acrylic resin, polyester resin, polyurethane resin, vinyl chloride resin, vinyl acetate resin, polyolefin resin, It is preferable to select from polyvinyl acetal resin and the like,
These resins and aqueous dispersions of these resins are also commercially available and easily available.

The crosslinking agent for the layer obtained by coating and drying these resin dispersions and polymer solutions is selected from aldehydes, methylol compounds, epoxy compounds, amino resins such as melamine and benzoguanamine, and isocyanate compounds, depending on the polymer. It is. In the present invention, the type and amount of the cross-linking agent must be selected so that the cross-linking can proceed rapidly at room temperature without practically causing a problem such as an increase in the minimum concentration.

A protective layer made of a polymer cross-linked by radiation such as an electron beam or light is particularly preferable in terms of room temperature curing and high productivity. Generally, such a layer is obtained by applying a photocurable resin containing a polymerizable oligomer, a monomer, and in the case of photocrosslinking, a photoinitiator and the like, and radiating ultraviolet rays or electron beams to cure the layer.

Examples of the polymerizable oligomer include epoxy acrylate, urethane acrylate and polyester acrylate obtained by reacting various polyols, organic isocyanate and hydroxyl-containing acrylate. The monomer is used for lowering the viscosity of the coating liquid and improving the properties of the adhesive property and the cured film.Specifically, monofunctional alkylene oxide-modified acrylate, N-vinylpyrrolidone, acryloylmorpholine, N-vinylcaprolactone, Examples include polyfunctional polyalkylene glycol acrylates such as isobornyl acrylate and N-vinylformamide, pentaerythritol triacrylate, trimethylolpropane triacrylate, and dipentaerythritol hexaacrylate. In addition, these polymerizable oligomers are dispersed in water by emulsification or the like, and a water-soluble or water-dispersible monomer is added for the purpose of improving the properties of the cured film to prepare an aqueous coating solution, followed by coating and drying. The protective layer can also be obtained by radiating ultraviolet rays or electron beams and curing.

Specific examples of the photoinitiator include benzophenone, methyl orthobenzoyl benzoate and 2-hydroxy-2.
-Methyl-1-phenyl-propan-1-one, 1-hydroxycyclohexylphenyl ketone, and the like. Further, as other additives, a polymerization inhibitor such as p-methoxyphenol may be contained. In the case of aqueous coating liquid,
These photoinitiators and additives are preferably added after emulsification using a surfactant or the like.

In order to improve the matching property with the thermal head, the protective layer of the present invention may contain a slipping agent such as zinc stearate and calcium stearate, if necessary, in addition to the matting agent. Is also good. In this case, it is preferable that these are added as a water dispersion in the case of aqueous coating and dispersed in a suitable monomer or the like by a known method in the case of radiation curable resin coating. Further, a surfactant may be contained for improving coatability. The surfactant is not particularly limited, and any nonionic, anionic or cationic surfactant may be used.

The thickness of the protective layer can vary widely depending on the type of binder used, the required thermal sensitivity, and the matching property with the thermal head, but is generally 0.1 to 10 microns, preferably 0.5 to 5 microns. Selected from a range.

The heat-sensitive recording material of the present invention can be coated on various supports. For example, resin films such as polyethylene terephthalate, polyethylene naphthalate, cellulose nitrate, and polycarbonate, resin-coated paper, baryta paper, synthetic paper, glass, metal, and the like can be given. The support may be transparent or opaque, but is preferably transparent in the present invention. These supports may be processed for easy adhesion. Further, a colored support may be used to improve the visibility as a transmission image.

The coating method of the heat-sensitive recording material of the present invention is not particularly limited, and is described in E. Cohen, E. Gutoff, "Modern Coati
ng and Drying Technology ", VCH Publishers, Inc. Ne
w York, 1992. Further, simultaneous application of a plurality of layers is particularly preferable from the viewpoint of improving productivity.

The heat-sensitive recording material of the present invention may be provided with an intermediate layer, an undercoat layer, an antistatic layer and the like, if necessary, in addition to the heat-sensitive recording layer and the protective layer.

[0043]

EXAMPLES The present invention will be described below in detail with reference to examples, but is of course not limited thereto. Example 1 <Preparation of silver behenate> 34 g of behenic acid was added to 960 g of water at 90 ° C, and 1N-sodium hydroxide aqueous solution 100 was added with vigorous stirring.
ml was dropped over about 30 minutes, and the temperature was lowered to 40 ° C. there
A solution in which 15.3 g of silver nitrate was dissolved in 220 g of water to which 22.5 ml of 1N-phosphoric acid was added was added dropwise over about 60 minutes. The obtained crystals were taken out by suction filtration, washed with water until the conductivity of the washing water became 30 μS / cm or less, and dried to obtain 90% converted silver behenate crystals.

<Preparation of Silver Behenate Dispersion> 20 g of the above silver behenate crystals and polyvinyl butyral (“But” manufactured by Sorcia)
8 g of var "B-79) was added to 92 g of 2-butanone, and a silver behenate dispersion having an average particle size of 1 micron or less was obtained using a bead mill.

<Preparation and application of coating solution for heat-sensitive recording layer> To 100 g of 2-butanone, 15 g of polyvinyl butyral (“Butvar” B-79 manufactured by Sorcia), and an organic reducing agent shown in Table 1 or the following comparative reducing agent were added. Mmol equivalent, tetrachlorophthalic anhydride 0.15 g, 5-methylbenzotriazole 0.14 g,
0.26 g of the comparative toning agent TC-1, 0.35 g of adipic acid, and 35 g of the above-mentioned silver behenate dispersion were added to prepare a coating solution for the heat-sensitive recording layer. This heat-sensitive layer coating solution was used as a silver amount on a 175 micron thick PET base.
The composition was applied to 3 g / m ² and dried to obtain a heat-sensitive layer.

<Comparative compound and its partition coefficient>

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<Preparation and Coating of Coating Solution for Protective Layer> In 60 g of 2-propanol, 30 g of urethane acrylate oligomer (non-yellowing, viscosity 5000 mPa · s), 50 g of 1,6-hexanediol diacrylate, 50 g of 2-hydroxy-2- Methyl-1-phenyl-
3.2 g of propan-1-one, 2 g of wet silica (manufactured by Nippon Silica Industry Co., Ltd., average particle size 1.5 microns), 50 g of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, 30% by weight / isopropanol), stearin 1 g of zinc acid was added and dispersed by a disper at 8000 rpm for 20 minutes to obtain a protective layer coating liquid. This was applied to the already obtained heat-sensitive recording layer so as to have a solid content of about 2.5 g, dried, and then subjected to a high-pressure mercury lamp (80
(W / cm), and cured at an irradiation distance of 10 cm and a speed of 10 m / min.

Thermal recording is performed using a thermal head (TDK Corporation).
(LH4409, manufactured by KK) and the applied voltage and pulse width were changed to change the color density. As for the color tone, a color development part having a transmission density of about 1.0 was visually evaluated on a five-point scale. 5 is most preferable in the cool-black tone image, and the temperature is adjusted to 4 or 3, the image becomes a warm tone image, 1 is red-brown having a low density, and 3 or less is an unacceptable level for practical use. In order to obtain the results after storage under moist heat, unprinted samples were stored at 50 ° C. and 60% RH for 1 week, and then subjected to the same thermal printing.

[0049]

[Table 1]

From Table 1, it is apparent that the heat-sensitive recording material of the present invention does not decrease in the maximum density and does not deteriorate in color tone even when stored under high temperature and high humidity.

Example 2 <Preparation and application of coating solution for heat-sensitive recording layer> 2-butanone (100 g)
With polyvinyl butyral (“Butvar” B-
79) 15 g, 1.3 g of organic reducing agent RC-1, 0.15 g of tetrachlorophthalic anhydride, 0.14 g of 5-methylbenzotriazole, table
The color tone agent described in 2 or the comparative color tone agent was added in an amount of 1.8 mmol, 0.35 g of adipic acid and 35 g of the above-mentioned silver behenate dispersion to prepare a coating solution for the heat-sensitive recording layer. Apply this heat-sensitive layer coating liquid to a thickness of 17
The composition was applied to a 5-micron PET base so as to have a silver amount of 1.3 g / m ² and dried to obtain a heat-sensitive layer.

<Preparation and application of protective layer coating solution>
The same protective layer coating solution as above was applied onto the heat-sensitive recording layer in the same manner, dried, and cured by ultraviolet rays. The obtained sample was subjected to printing in the same manner as in Example 1, and the maximum density, color tone, and the state of generation of white powder on the sample surface after storage for one week at 50 ° C. and 60% RH were observed.

[0053]

[Table 2]

From Table 2, it is clear that the heat-sensitive recording material of the present invention does not have a decrease in density or color tone and no white powder even when stored under high temperature and high humidity.

Example 3 <Preparation of aqueous silver behenate dispersion> 20 g of the silver behenate crystals prepared in Example 1 and 32 g of 5% by weight polyvinyl alcohol (PVA203 manufactured by Kuraray Co., Ltd.) were added to 48 g of water. Using a bead mill, a 20% by weight silver behenate dispersion having an average particle size of 1 micron or less was obtained.

<Preparation of Reducing Agent / Additive Dispersion> 10% by Weight
58 g of polyvinyl alcohol (PVA203), 10 g of 5% by weight sodium dodecylbenzenesulfonate, 0.2 mol equivalent of the organic reducing agent shown in Table 3, tetrachlorophthalic anhydride 7.6
g, 2-mercapto-5-methylbenzimidazole 6 g, Table 3
A colorant equivalent to 70 mmol and water was added to make 250 g by adding water to obtain a reducing agent / additive dispersion liquid using a bead mill.

<Preparation and Coating of Coating Solution for Water-Based Thermosensitive Recording Layer>
The following hydrophilic resin or polymer latex was converted to 64.3 g by adding ion-exchanged water to 20 g in terms of solid content, 29.2 g of the aqueous silver behenate dispersion and 6.5 g of the reducing agent / additive dispersion were added, and the aqueous thermal recording layer was coated. Liquid. This heat-sensitive layer coating liquid was applied to a 175-micron-thick PET base so as to have a silver amount of 1.3 g / m ² and dried to obtain a heat-sensitive layer.

<Hydrophilic resin and polymer latex> P-1: Polyvinyl alcohol (PVA217 / Kuraray) P-2: Hydroxypropylcellulose (HPC-SL / Nippon Soda) P-3: SBR latex (Luckstar 3307B / Dainippon Ink) P-4: Urethane resin dispersion (Hydran HW-95)
0 / Same as above) P-5: Modified urethane resin dispersion (Paterachor H-2090 / Same as above)

<Coating solution for water-based protective layer> Superflex®
175 g of 5100 (a UV-curable urethane acrylate aqueous dispersion manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content: 40%), 10.5 g of pentaerythritol triacrylate, 2-hydroxy-2-methyl
3.5 g of 1-phenyl-propan-1-one (dispersed with a nonionic surfactant having an HLB of 15) was added thereto, and silica fine particles (manufactured by Nippon Silica Industry Co., Ltd., dispersed in water with Disper: The particle size and amount are described in Table 2), Snowtex
C (colloidal silica, particle size 10-20 nm, solid content about 20
%: The amount is described in Table 2.) Zinc stearate fine particle dispersion (average particle size: 0.3 micron, solid content: 20%) 3.5
g and water to make 280 g. This was applied to the already obtained water-based thermosensitive recording layer to a dry amount of about 2.5 g, dried, and irradiated with a high-pressure mercury lamp (80 W / cm) at an irradiation distance of 10 cm.
The composition was cured at a speed of 7 m / min.

The obtained sample was subjected to printing in the same manner as in Examples 1 and 2. Further, the density, color tone and the state of white powder generation on the sample surface after storage for one week at 50 ° C. and 60% RH were checked. Observed.

[0061]

[Table 3]

From Table 2, it can be seen that the heat-sensitive recording material of the present invention, which has been coated with water, has little deterioration in density and color tone without increasing the minimum density or generating white powder even when stored under high temperature and high humidity. It is clear that.

[0063]

According to the present invention, it is possible to provide a recording material that does not increase in minimum density, has little deterioration in density and color tone, and does not generate white powder even when stored under high temperature and high humidity. .

Claims (1)

[Claims] 1. A heat-sensitive recording layer containing a substantially non-photosensitive organic silver salt, an organic reducing agent, a color tone agent and a binder on a transparent support, wherein at least 50% by weight of the heat-sensitive layer binder is hydrophobic. A heat-sensitive recording material, wherein the partitioning coefficient (logP) of at least one of the organic reducing agent and the color tone agent is 1.5 or more.