JP2020131588A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material which suppresses curling due to heat application and has excellent transportability in a heat-sensitive printer. SOLUTION: A heat-sensitive recording layer containing at least a non-photosensitive organic silver salt is provided on a light-transmitting support, and an undercoat layer is provided between the light-transmitting support and the heat-sensitive recording layer. A heat-sensitive recording material in which the glass transition temperature of the thermoplastic resin contained in the undercoat layer is 45 ° C. or higher, and the thickness of the undercoat layer is 3.0 μm or higher. [Selection diagram] None

Description

The present invention relates to a thermal recording material capable of forming an image by heating with a thermal head, and more particularly to a thermal recording material suitable for producing a block copy original.

As a high-quality image recording method, a wet-treated image forming method using a silver halide photosensitive material has long been generally used. However, as the image forming method, a dry image forming method that does not require the above-mentioned wet treatment has been desired because of restrictions on waste liquid treatment such as a developing solution and a fixing liquid and installation of a developing processing facility. As a result, image forming systems such as inkjet printers, electrographs, and dye thermal transfer methods are now in practical use. However, it is difficult for these dry image forming methods to obtain high resolving power required for block copy originals, excellent light-shielding property in an image area, and excellent light transmission in a non-image area.

Under such circumstances, heat-sensitive recording materials utilizing the reaction between a non-photosensitive organic silver salt and an organic reducing agent are disclosed in, for example, Patent Document 1 and Patent Document 2. Such a heat-sensitive recording material is suitable for producing a block copy manuscript because a high-resolution and high-contrast image can be obtained by directly recording a heat-sensitive image with a heat-sensitive printer equipped with a thermal head. In addition to the fact that the recording material is non-photosensitive and does not require a dark room, the direct heat-sensitive thermal printer is low-cost, highly reliable, and easy to miniaturize, so the hurdles for introduction are low. Has advantages.

However, these heat-sensitive recording materials have a drawback that the expansion and contraction balance of the front and back layers is lost due to heat application during printing and curl is generated, which may cause a problem in handling.

In Patent Document 3, by providing a curl prevention layer containing an acrylic resin on the surface of the support opposite to the heat-sensitive recording layer, curl due to curling when the heat-sensitive recording material is wound into a roll shape can be obtained. It is described that it can be improved, and Patent Document 4 describes that the curl due to the above heat application can be improved by a backcoat layer containing an inorganic layered compound such as mica and talc. However, these methods do not have a sufficient effect of suppressing curl due to heat application, and further improvement has been required.

Patent Document 5 has a film thickness of a certain level or more, which is composed of two layers, a layer containing a styrene-butadiene resin as a main component and a layer containing gelatin as a main component, between the light transmitting support and the heat sensitive recording layer. It is described that the curl due to heat application can be improved by providing the undercoat layer to prevent heat shrinkage of the support. However, when the undercoat layer having a film thickness of a certain value or more is provided, there is a drawback that curl is likely to occur, and the transportability in the thermal printer is not sufficiently satisfactory.

Special Table No. 08-505579 Special Table No. 09-504752 Japanese Unexamined Patent Publication No. 08-318675 JP-A-2002-144727 Japanese Unexamined Patent Publication No. 2005-40989

An object of the present invention is to provide a heat-sensitive recording material that suppresses curling due to heat application and has excellent transportability in a heat-sensitive printer.

The above-mentioned problems are solved by the following inventions.
A heat-sensitive recording material having a heat-sensitive recording layer containing at least a non-photosensitive organic silver salt on a light-transmitting support and an undercoat layer between the light-transmitting support and the heat-sensitive recording layer. A heat-sensitive record characterized in that the undercoat layer mainly contains a thermoplastic resin, the glass transition temperature of the thermoplastic resin is 45 ° C. or higher, and the film thickness of the undercoat layer is 3.0 μm or higher. material.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a heat-sensitive recording material that suppresses curling due to heat application and has excellent transportability in a heat-sensitive printer.

The heat-sensitive recording material of the present invention has a light-transmitting support. Examples of such a light-transmitting support include resin films such as polyethylene terephthalate, polyethylene naphthalate, cellulose nitrate, and polycarbonate, and inorganic materials such as glass. In the present invention, the light-transmitting support means a support having a total light transmittance of 60% or more, and more preferably 70% or more. Further, the haze value of the light transmitting support is preferably 10% or less. The light-transmitting support may have a known layer such as an easy-adhesion layer, a hard coat layer, and an antistatic layer. The thickness of the light-transmitting support in the present invention is not particularly specified, but it is preferably 50 μm or more and 300 μm or less in consideration of the balance between curl due to heat application and transportability in the thermal printer. ..

The heat-sensitive recording material of the present invention has an undercoat layer on the above-mentioned light-transmitting support, and the undercoat layer mainly contains a thermoplastic resin as a binder component. Here, "mainly" means that the thermoplastic resin having a glass transition temperature of 45 ° C. or higher is contained in an amount of 50% by mass or more, more preferably 60% by mass or more, based on the total solid content of the undercoat layer. ..

The thermoplastic resin contained in the undercoat layer in the present invention needs to have a glass transition temperature of 45 ° C. or higher. Specifically, polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, polysaccharides typified by dextran, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin and the like can be used as the thermoplastic resin. These thermoplastic resins may be used by being dissolved in water or an organic solvent, or may be used in which latex or polymer molecules in which hydrophobic polymer solids are dispersed in the form of fine particles form micelles and are dispersed. .. Further, as the thermoplastic resin, two or more kinds of resins compatible with each other may be used in combination, if necessary.

The undercoat layer of the present invention may contain fine particles made of an organic or inorganic compound in the layer for the purpose of improving heat insulating properties. Examples of the compound constituting the fine particles include acrylic resin, silicone resin, phenol resin, melamine resin and the like as the organic compound, and silica, alumina, mica, talc, kaolin and the like as the inorganic compound. In forming the undercoat layer, it is preferable to use the fine particles dispersed in the above-mentioned thermoplastic resin. The amount of the fine particles added is preferably less than 50% by mass with respect to the thermoplastic resin contained in the undercoat layer.

In the present invention, the undercoat layer is preferably formed by preparing a coating liquid containing the above-mentioned thermoplastic resin having a glass transition temperature of 45 ° C. or higher, applying the coating liquid on a light-transmitting support, and drying. .. Further, for the purpose of improving the coatability, the coating liquid may contain various surfactants. As the surfactant, any nonionic, anionic or cationic surfactant may be used, and the surfactant is not particularly limited.

The film thickness of the undercoat layer of the present invention needs to be a film thickness that can sufficiently reduce the propagation of thermal energy to the support and effectively suppress curl-like deformation, specifically 3.0 μm or more. It is necessary to be 5.0 μm or more. The upper limit of the film thickness of the undercoat layer is not particularly limited, but is preferably 20 μm or less from the viewpoint of productivity and handleability of the obtained heat-sensitive recording material.

The heat-sensitive recording layer in the present invention contains an organic silver salt. Further, the organic silver salt is a non-photosensitive organic silver salt, which is reduced by being heated together with a reducing agent described later to form a silver image. Specifically, as described in Research Disclosures No. 17029 (II) and No. 29963 (XVI) on heat-developed photosensitive materials, benzoic acid, benzoic acid, bechenic acid, stearic acid, palmitic acid, lauric acid and the like Silver salt of organic acid; silver salt of carboxyalkyl thiourea such as 1- (3-carboxypropyl) thiourea, 1- (3-carboxypropyl) -3,3-dimethylthiourea; Complex of aldehydes with high molecular weight reaction products of aromatic carboxylic acids such as salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, 5,5-thiodisalicylic acid and silver; 3- (2-carboxyethyl) Silver salts or complexes of thiones such as -4-hydroxymethyl-4-thiazolin-2-thione, 3-carboxymethyl-4-methyl-4-thiazolin-2-thione; imidazole, pyrazole, urazole, 1, 2, Silver salts or complexes of carboxylic acids selected from 4-triazole, 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole and benzotriazole; silver salts such as saccharin, 5-chlorosalitylaldoxime; Examples include silver salts of mercaptides. Of these, fatty acid silver having 10 or more carbon atoms is preferable, and silver stearate and silver behenate are particularly preferably used.

In the present invention, the content of the organic silver salt contained in the heat-sensitive recording layer can be appropriately adjusted according to the maximum concentration required, and the silver equivalent value is preferably 0.5 to 2.0 g per square meter.

In the present invention, the heat-sensitive recording layer preferably contains a reducing agent together with the above-mentioned organic silver salt. Examples of such reducing agents include pyrogallol, 4-stearoyl pyrogallol, isopropyl gallate, ethyl 3,4-dihydroxybenzoate, 2,5-dihydroxybenzoic acid and the like described in US Pat. No. 3,074,809. Examples thereof include the polyhydroxyindans described in Japanese Patent No. 3,440,049 or JP-A-06-317870. Further, the compounds represented by the following formulas (I) to (III) described in JP-A-2001-328357 are particularly preferable as the reducing agent used in the present invention.

In the formula (I), R ¹ and R ² are substituents in which the substituent constant σ of Hammett shows a positive value, and ester groups, acetyl groups, amide groups, cyano groups and the like are exemplified. In the formula (II), Z represents a group of atoms necessary for forming a ring structure, and the ring structure includes a cyclic 1,3-diketone, a cyclic diester, a cyclic amide, a heterocycle having a carbonyl group, and the like. Can be mentioned. In formula (III), R ³ and R ⁴ represent an alkyl group, an aralkyl group, an aryl group, an acyl group, an ester group, an amide group, a cyano group, a nitro group, a sulfonyl group and the like, and R ³ and R ⁴ are bonded to each other. It may form a ring structure such as a cyclopentanone skeleton or a cyclohexanone skeleton, or may have a hydrogen atom or a substituent. In formulas (I) to (III), the benzene ring having two hydroxy groups may optionally have a substituent.

The following compounds (1) to (8) are specific examples of the compounds represented by the formulas (I) to (III), but the reducing agent used in the present invention is not limited thereto.

The content of the reducing agent can vary widely depending on the type of reducing agent and the type of organic silver salt, but is preferably 0.1 to 3.0 mol per mol of the organic silver salt, and is preferably 0.5. It is more preferably ~ 2.0 mol. Further, for various purposes, two or more kinds of the above reducing agents may be used in combination.

In order to increase the color neutrality of the silver image formed in the high optical density portion, the thermal recording layer is known in the field of thermography or photothermography together with the above-mentioned non-photosensitive organic silver salt and reducing agent, so-called. It is preferable to contain a color adjusting agent. Examples of color adjusting agents are known in the above-mentioned research disclosures on heat-developed photosensitive materials, No. 17029 (V), No. 29963 (XXII), etc., and specifically, imides typified by phthalimide, 3-mercapto. Mercapto compounds typified by -1,2,4-triazole, phthalazine, phthalazone, 4-methylphthalic acid, tetrachlorophthalic acid and phthalic acid derivatives typified by their anhydrides, 1,3-benzoxazine-2, Examples thereof include benzoxazine derivatives typified by 4-dione. Further, for various purposes, two or more kinds of the above color preparations may be used in combination.

The heat-sensitive recording layer in the heat-sensitive recording material of the present invention, together with the above-mentioned organic silver salt, has various accelerators and stabilizers for the purpose of suppressing and promoting the formation of image silver by reduction and improving the storage stability before and after printing. They may contain precursors. Specifically, benzotriazole, 5-methylbenzotriazole, 5-chlorobenzotriazole, 2-mercaptobenzotriazole, 2-mercaptomen's imidazole, 2-mercaptobenzothiazole, which are well known as photographic stabilizers and inhibitors, 2-Mercaptobenzoxazole, 4-hydroxy-6-methyl-1,3,3a,7-tetrazainden, 1-phenyl-5-mercaptotetrazole, 2-amino-5-mercapto-1,3,4-thiazazole , 3-Mercapto-5-phenyl-1,2,4-triazole, 4-benzamide-3-mercapto-5-phenyl-1,2,4-triazole and the like can be selected. Further, for various purposes, two or more kinds of the above-mentioned accelerator and stabilizer may be used in combination.

In the present invention, the heat-sensitive recording layer preferably contains a binder component together with a color-developing component such as the above-mentioned organic silver salt. A thermoplastic resin is preferable as such a binder component. Examples of the thermoplastic resin include polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, polysaccharides typified by dextran, acrylic resin, polyester resin, polyurethane resin, vinyl chloride resin, vinyl acetate resin, polyolefin resin, and polyvinyl acetal. Examples thereof include resins and polyvinyl butyral resins. These binders may be used by dissolving them in water or an organic solvent, or may be used in which latex or polymer molecules in which hydrophobic polymer solids are dispersed in the form of fine particles form micelles and are dispersed. In the present invention, the binder component preferably forms a transparent film after coating and drying. Further, as for these binder components, two or more kinds of resins compatible with each other may be used in combination, if necessary.

The blending amount of the binder component contained in the thermal recording layer is preferably 10 to 50% by mass with respect to the total solid content of the thermal recording layer.

When the above-mentioned binder component is used together with an organic silver salt, it is preferable that it contains as little free halide ion as possible, such as chloride ion and bromide ion. These halide ions react with silver ions during long-term storage to form photosensitive silver halide, which causes a decrease in the light resistance of the recording material. Specifically, it is preferably 100 ppm or less with respect to the amount of the binder component.

In the present invention, the heat-sensitive recording layer is preferably formed by preparing a coating liquid containing the above-mentioned color-developing component and the like, applying the coating liquid on the above-mentioned undercoat layer, and drying. Further, various surfactants may be contained for the purpose of improving coatability. As the surfactant, any nonionic, anionic or cationic surfactant may be used, and the surfactant is not particularly limited.

The heat-sensitive recording material in the present invention preferably has a protective layer on the above-mentioned heat-sensitive recording layer. The protective layer preferably contains a resin component that can withstand heat application during printing by the thermal head. Such resins are preferably those capable of cross-linking natural or synthetic resins to improve heat resistance, and specifically, gelatin, polyvinyl alcohol, acrylic resin, polyester resin, polyurethane resin, vinyl chloride resin, vinyl acetate resin, etc. Examples thereof include polyolefin resins and polyvinyl acetal resins, and aqueous dispersions of these resins and resins are also commercially available and are easily available.

In the present invention, a protective layer containing a polymer crosslinked by radiation such as an electron beam or light as a resin component is particularly preferable in terms of high room temperature curability and high productivity. Generally, such a layer is obtained by applying a photocurable resin containing a polymerizable oligomer, a monomer, or a photopolymerization initiator in the case of photocrosslinking, and radiating ultraviolet rays or electron beams to cure the layer.

Examples of the polymerizable oligomer include epoxy acrylate, urethane acrylate obtained by reacting various polyols with organic isocyanate and hydroxy group-containing acrylate, polyester acrylate and the like. The monomer is used to reduce the viscosity of the coating liquid and to improve the adhesiveness and the properties of the cured film. Specifically, monofunctional alkylene oxide-modified acrylate, N-vinylpyrrolidone, acryloylmorpholine, and N-vinyl. Examples thereof include polyfunctional polyalkylene glycol acrylates such as caprolactone, isobornyl acrylate and N-vinylformamide, pentaerythritol triacrylate, trimethylolpropane triacrylate, and dipentaerythritol hexaacrylate.

Specific examples of the photopolymerization initiator include benzophenone, methyl orthobenzoylbenzoate, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-hydroxycyclohexylphenylketone and the like. Further, a polymerization inhibitor such as p-methoxyphenol may be contained as another additive.

In the present invention, a solvent-based coating solution in which a polymerizable oligomer or the like is dissolved or dispersed in an organic solvent and mixed with a photopolymerization initiator can be used to form a protective layer containing a photocurable resin. .. A protective layer can be obtained by preparing a coating liquid, applying it, drying it, and then radiating ultraviolet rays or electron beams to cure it.

The protective layer film thickness can vary widely depending on the type of resin component used, the required heat sensitivity, and the matchability with the thermal head, but is selected from the range of 0.1 to 10 μm.

In the present invention, the protective layer may contain various matting agents for the purpose of enhancing transportability. In forming the protective layer, it is preferable to use the matting agent dispersed in the protective layer. A high-speed stirrer such as a homodisper is suitable for dispersing the matting agent.

The amount of the matting agent contained in the protective layer is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, based on the amount of the resin component.

The matting agent can be either an organic or inorganic matting agent. Examples of the organic matting agent include silicone, polytetrafluoroethylene, polymethylmethacrylate and polyacrylate, and examples of the inorganic matting agent include silica, alumina, talc and mica. Commercially available products include, for example, Tospearl (registered trademark) 120, 130, 145, 2000B sold by Momentive Performance Materials Japan LLC as a silicone resin-based matting agent, and AGC S as a silica-based matting agent. Examples thereof include Sunsphere (registered trademark) H-31, H-51, NP-30, etc., which are sold by Aitec Co., Ltd. These are single fine particles, but as the form of the matting agent, either a single fine particle or a fine particle aggregate particle in which fine particles are aggregated may be used, and the average particle size is primary in the case of a single fine particle. The particle size refers to the secondary particle size in the case of fine particle aggregate particles.

In the present invention, there is no particular limitation on the coating method of the undercoat layer, the heat-sensitive recording layer and the protective layer described above, and E.I. D. Cohen, E.I. B. Gutoff, "Modern Coating and Drying Technology", WILEY-VCH, Inc. You can choose from a variety of coating methods, such as those described in New York, 1992. Further, applying a plurality of layers at the same time is particularly preferable in terms of improving productivity.

If necessary, the heat-sensitive recording material of the present invention may further include an intermediate layer, a primer layer, an antistatic layer, and the like in addition to the undercoat layer, the heat-sensitive recording layer, and the protective layer.

According to the present invention, using the above-mentioned thermal recording material, the thermal head is brought into contact with the protective layer of the thermal recording material, and the thermal recording material is conveyed under the thermal head and heated according to the image to obtain an image. it can. The heat-sensitive recording material can be heated at a temperature of up to 400 ° C. by changing the number of heat pulses given by the thermal head, and the density of the image portion can be changed by changing the number of heat pulses. ..

Hereinafter, the present invention will be described with reference to examples, but this description does not limit the present invention. In the description, "%" is based on mass. In addition, Tg indicates the glass transition temperature.

<Example 1>
<Preparation and application of undercoat layer coating solution>
A coating solution was prepared with the following composition to obtain an undercoat layer coating solution A.

(Composition of Undercoat Layer Coating Solution A)
-Buvar® B-74 (manufactured by Eastman Chemical Japan Co., Ltd., polyvinyl butyral, Tg 75 ° C) 21 g
-MEK-AC-2140Z (manufactured by Nissan Chemical Industries, Ltd., surface-modified colloidal silica sol (particle size 12 nm), solid content 40%) 22 g
・ 2-Butanone 108g

The undercoat layer coating solution A is applied to a PET base having a thickness of 125 μm (total light transmittance 92%, haze value 4%) with a wire bar so that the film thickness becomes 3.0 μm after drying, and the temperature is adjusted to 100 ° C. And dried to obtain an undercoat layer.

<Preparation of silver behenate dispersion>
20 g of silver behenate crystals and 22 g of polyvinyl butyral (BuvarB-79, manufactured by Eastman Chemical Japan Co., Ltd.) were added to 175 g of 2-butanone, and a silver behenate dispersion was obtained using a bead mill.

<Preparation and application of thermal recording layer coating solution>
To 15 g of 2-butanone, 0.8 g of polyvinyl butyral (BuvarB-79), 10 g of the silver behenate dispersion, 0.5 g of the example compound (1) as a reducing agent, 0.2 g of tetrachlorophthalic anhydride, and phthalazone 0. 2 g was added to prepare a heat-sensitive recording layer coating solution. This heat-sensitive layer coating liquid was applied onto the undercoat layer already obtained as described above so as to have a silver equivalent of 1.2 g / m ^2, and dried at 80 ° C. to obtain a heat-sensitive recording layer.

<Preparation and application of protective layer coating solution>
To 5.0 g of 2-butanone, 5.0 g of Beamset (registered trademark) 3702 (manufactured by Arakawa Chemical Industry Co., Ltd .; a mixture containing an epoxy acrylate polymer, a polyfunctional acrylate compound, and a photopolymerization initiator) as a photocurable resin. To obtain a solution of 10 g (of which 2.9 g of binder mass) was obtained, and then 0.36 g of silica particles (Tospearl 120 manufactured by Momentive Performance Materials Japan LLC) was added as a matting agent to obtain a three-one motor (three-one motor). A protective layer coating solution was obtained by dispersing at 300 rpm for 3 hours at (registered trademark). On the heat-sensitive recording layer already obtained as described above, a protective layer coating solution is applied so that the film thickness becomes 5.0 μm after drying, dried at 80 ° C., and then irradiated with a high-pressure mercury lamp at an irradiation distance. Irradiation was performed under the conditions of 10 cm and a transport speed of 5 m / min to cure the protective layer, and a heat-sensitive recording material was obtained.

<Example 2>
In the application of the undercoat layer of Example 1, a heat-sensitive recording material was obtained in the same manner as in Example 1 except that the undercoat layer coating solution was applied so that the film thickness after drying was 5.0 μm.

<Example 3>
In the application of the undercoat layer of Example 1, a heat-sensitive recording material was obtained in the same manner as in Example 1 except that the undercoat layer coating solution was applied so that the film thickness after drying was 10 μm.

<Example 4>
The undercoat layer coating solution A of Example 1 was changed to the following undercoat layer coating solution B, and the undercoat layer coating solution was applied so that the film thickness after drying was 3.0 μm in the same manner as in Example 1. A heat-sensitive recording material was obtained.

(Composition of Undercoat Layer Coating Solution B)
-Boncoat (registered trademark) AN-1170 (manufactured by DIC Corporation, acrylic latex, solid content 45%, Tg 60 ° C) 45 g
・ Snowtex (registered trademark) XS (manufactured by Nissan Chemical Industries, Ltd., colloidal silica sol (particle size 4 to 6 nm), solid content 20%) 43 g
・ Pure water 56g

<Example 5>
In the application of the undercoat layer of Example 4, a heat-sensitive recording material was obtained in the same manner as in Example 4 except that the undercoat layer coating solution was applied so that the film thickness after drying was 5.0 μm.

<Example 6>
In the application of the undercoat layer of Example 4, a heat-sensitive recording material was obtained in the same manner as in Example 4 except that the undercoat layer coating solution was applied so that the film thickness after drying was 10 μm.

<Comparative example 1>
In the application of the undercoat layer of Example 1, a heat-sensitive recording material was obtained in the same manner as in Example 1 except that the undercoat layer coating solution was applied so that the film thickness after drying was 1.0 μm.

<Comparative example 2>
In the application of the undercoat layer of Example 4, a heat-sensitive recording material was obtained in the same manner as in Example 4 except that the undercoat layer coating solution was applied so that the film thickness after drying was 1.0 μm.

<Comparative example 3>
The undercoat layer coating solution A of Example 1 was changed to the following undercoat layer coating solution C, and the undercoat layer coating solution was applied so that the film thickness after drying was 3.0 μm in the same manner as in Example 1. A heat-sensitive recording material was obtained.

(Composition of Undercoat Layer Coating Solution C)
-Boncoat R-3380-E (manufactured by DIC Corporation, acrylic latex, solid content 45%, Tg 30 ° C) 47 g
・ Snowtex XS 44g
・ Pure water 50g

<Curl deformation evaluation>
The heat-sensitive recording materials of Examples 1 to 6 and Comparative Examples 1 to 3 thus obtained were cut into 360 mm (width) × 450 mm (length), and a thermal digital printer (TDP (registered) manufactured by Mitsubishi Paper Mills Limited) was cut. A solid image was printed (recording energy density 120 mJ / mm ² , electric capacity 350 W) at a printing speed of 1 msec / line by (trademark) -459: 1200 dpi / 120 lpi, line head). The image size is 360 mm (width) x 250 mm (length).

Only the image portion (360 mm × 250 mm) of the heat-sensitive recording material printed as described above was cut out, and the magnitude of curl deformation was evaluated as follows. The PET base was placed on the horizontal plane with the PET base facing down for 30 minutes, the heights from the horizontal plane at the four corners were measured, and the average value was taken as the magnitude of the curl deformation. Table 1 shows the results as ⊚ when the magnitude of the curl deformation is less than 10 mm, ◯ when it is 10 mm or more and less than 20 mm, and × when it is 20 mm or more.

<Evaluation of transportability>
The unprinted thermal recording materials of Examples 1 to 6 and Comparative Examples 1 to 3 are cut into 360 mm (width) × 1000 mm (length), wrapped around a 3-inch paper cylinder with the coated surface on the outside, and wound at 50 ° C. 2 Stored for a week. After that, a solid image was printed (recording energy density 120 mJ / mm ² , electric capacity 350 W) at a printing speed of 1 msec / line by a thermal digital printer (TDP-459: 1200 dpi / 120 lpi manufactured by Mitsubishi Paper Mills Limited). .. The image size is 360 mm (width) x 250 mm (length).

The state of the coating film including the unprinted portion of the heat-sensitive recording material printed as described above was observed, and the transportability was evaluated. Table 1 shows the results as ◯ when no scratches were observed and × when marked scratches were observed.

As is clear from the results in Table 1, it can be seen that according to the present invention, a heat-sensitive recording material that suppresses curl-like deformation due to printing and has excellent transportability in a heat-sensitive printer can be obtained.

Claims (1)

A heat-sensitive recording material having a heat-sensitive recording layer containing at least a non-photosensitive organic silver salt on a light-transmitting support and an undercoat layer between the light-transmitting support and the heat-sensitive recording layer. A heat-sensitive record characterized in that the undercoat layer mainly contains a thermoplastic resin, the glass transition temperature of the thermoplastic resin is 45 ° C. or higher, and the film thickness of the undercoat layer is 3.0 μm or higher. material.