JP2007196616A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium which is excellent in water resistance, solvent resistance, color development sensitivity and printing travelability (head scum resistance and stickiness resistance), and which uses no melamine-based resin. <P>SOLUTION: In this thermal recording medium, a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-receiving developer is provided on a substrate, and a protective layer is provided on the thermal recording layer. The thermal recording medium contains the protective layer containing carboxyl-modified polyvinyl alcohol, an epichlorohydrin-based resin, a polyamine/amide-based resin, and a silicic compound. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material excellent in water resistance and solvent resistance and having good color development sensitivity.

In general, a heat-sensitive recording medium is usually a colorless or light-colored electron-donating leuco dye and an electron-accepting developer such as a phenolic compound, which are ground and dispersed in fine particles, and then mixed together. -, A coating liquid obtained by adding a filler, a sensitivity improver, a lubricant and other auxiliary agents to a support such as paper, synthetic paper, film, plastic, thermal head, Color is generated by an instantaneous chemical reaction by heating such as hot stamping, thermal pen, laser light, etc., and a recorded image is obtained. Thermal recording media are widely used in facsimiles, computer terminal printers, automatic ticket vending machines, measuring recorders, etc., and with the diversification of their uses, high levels of image stability and There is a need for stability in the blank section.
However, since the electron-donating leuco dye and the electron-accepting developer contained in the heat-sensitive recording layer are easily dissolved in various solvents, this heat-sensitive recording material can be used in inks such as water-based ink pens and oil-based ink pens, adhesives, and the like. Since there is a problem that the white paper part easily develops color when touched or the color density decreases when chemicals such as plasticizers adhere to the image, a protective layer mainly composed of pigment and resin is provided on the thermal recording layer. Things have been done.
Also, in recent years, the use of thermal recording media has been expanded to various tickets, receipts, labels, bank ATMs, gas and electric meter readings, and car tickets, etc. Severe characteristics that have not been a problem in the past have begun to be required for thermal recording media. For these applications, it is often used outdoors, and the quality performance of the protective layer that can withstand use in harsher environments than before, such as moisture and moisture such as rain, sunlight, and high temperatures in the car in midsummer. Is required.
A water-soluble polymer such as polyvinyl alcohol having excellent adhesion and film-forming properties is used for the protective layer, but water resistance is inferior, so a technique using a crosslinking agent such as glyoxal (Patent Documents 1 and 2), a crosslinking agent Developed a technology that uses polyamide epichlorohydrin and polyethyleneimine in combination (Non-patent Document 1), a technology that contains carboxy-modified polyvinyl alcohol, epichlorohydrin-based resin, and melamine-based resin in the protective layer (Patent Document 3). Has been.

JP-A-8-230324 JP-A-9-164863 JP 2005-335295 A Hiroaki Yokoi “New Polyvinyl Alcohol (PVA) Water-Resistant System” 2005 Paper and Pulp Technology Association Annual Conference Presentation Papers P397-407

However, the performance of the protective layers of these conventional thermosensitive recording materials (Patent Documents 1, 2, Non-Patent Document 1, etc.) is still insufficient. Moreover, although the protective layer (patent document 3) containing a melamine-type resin has favorable water resistance, since there exists a problem that formaldehyde (carcinogenic substance) derived from a melamine-type resin occurs, its use is difficult. It has become to.
Therefore, the present invention provides a heat-sensitive recording material having sufficient water resistance and solvent resistance, excellent print running property (head residue resistance, stick resistance) and sensitivity without using a melamine resin. This is the issue.

  As a result of intensive studies, the present inventors have found that a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support and a thermal recording medium provided with a protective layer thereon are provided. And the protective layer contains a carboxy-modified polyvinyl alcohol, an epichlorohydrin resin, a polyamine / amide resin, and a silicic acid compound. The present invention has been completed.

  According to the present invention, it is possible to obtain a heat-sensitive recording material excellent in water resistance and solvent resistance, and excellent in color development sensitivity and printing runability (head residue resistance, stick resistance) without using a melamine resin. .

The mechanism by which the heat-sensitive recording material having the constitution of the present invention exhibits excellent properties such as water resistance is considered as follows.
In the protective layer of the heat-sensitive recording material of the present invention, the carboxyl group of the carboxy-modified polyvinyl alcohol and the amine or amide portion of the epichlorohydrin resin as the cross-linking agent cause a cross-linking reaction and develop primary water resistance. Next, the hydrophilic part of the modified polyamine resin and the hydrophilic crosslinked part formed by carboxy-modified polyvinyl alcohol and epichlorohydrin resin attract each other, so this crosslinked part is a hydrophobic group of the modified polyamine / amide resin. In other words, the hydrophilic cross-linked site is protected from water by a hydrophobic group, and secondary water resistance is exhibited. For this reason, it is estimated that water resistance stronger than the prior art is obtained. In addition, the hydrophilic part of the polyamine resin is attracted to the hydroxyl group of the carboxy-modified polyvinyl alcohol, and the carboxy-modified polyvinyl alcohol is encased with the hydrophobic group of the polyamine / amide resin outside, and the polyamine / amide resin It is also considered that this cationic site is a kind of cross-linking reaction with the carboxyl group of carboxy-modified polyvinyl alcohol, which is one reason that high water resistance is developed.
In this way, by imparting a higher hydrophobic effect to the reaction site between the carboxy-modified polyvinyl alcohol having excellent solvent resistance used in the protective layer and the cross-linking agent, the binder in the coating layer is free from moisture and moisture. Elution due to moisture can be prevented, water resistance can be improved, and excellent solvent resistance is expressed.
Further, the protective layer of the heat-sensitive recording material of the present invention has a three-dimensional structure by a crosslinking reaction between carboxy-modified polyvinyl alcohol and epichlorohydrin resin, and is a modified polyamine / amide resin that is cationic. Exhibits a dispersion effect on anionic pigments, and is considered to be a porous layer compared to the prior art. For this reason, since the melt of the material with low heat resistance in the coating layer generated under high temperature conditions is adsorbed in the voids in the protective layer, it has excellent print running properties (head residue resistance).
Furthermore, by including a highly oil-absorbing silicic acid compound in the protective layer of the present invention, the resistance to head residue and solvent resistance is improved, and the stick resistance is improved because the contact with the thermal head of the thermal printer can be controlled. .

  The carboxy-modified polyvinyl alcohol used in the protective layer of the present invention is a reaction product of polyvinyl alcohol and a polycarboxylic acid such as fumaric acid, phthalic anhydride, mellitic anhydride, itaconic anhydride, or an ester of these reactants. And a saponified product of a copolymer of vinyl acetate and an ethylenically unsaturated dicarboxylic acid such as maleic acid, fumaric acid, itaconic acid, crotonic acid, acrylic acid or methacrylic acid. Specifically, for example, the production method exemplified in Example 1 or 4 of JP-A-53-91995 can be mentioned. Moreover, it is preferable that the saponification degree of carboxy modified polyvinyl alcohol is 72-100 mol%, and a polymerization degree is 500-2400, More preferably, it is 1000-2000. In the present invention, image quality and sensitivity are improved by using carboxy-modified polyvinyl alcohol. This is because carboxy-modified polyvinyl alcohol has a low Hercules viscosity, that is, it has a high fluidity in a state where rotational force (shear) is applied, and it is easy to immobilize at a low share, so the coating liquid extends smoothly during coating. This is considered to be because the coating layer is solidified immediately after coating, and a uniform coating layer having no unevenness is formed.

It is essential to use an epichlorohydrin resin and a polyamine resin used in the protective layer of the present invention in combination, and sufficient water resistance cannot be obtained when each is used alone. In addition, sufficient water resistance cannot be obtained even with a combination of other general crosslinking agents such as glyoxal and epichlorohydrin resin or modified polyamine resin.
Specific examples of the epichlorohydrin resin used in the protective layer of the present invention include polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, and the like, which can be used alone or in combination. Moreover, as an amine which exists in the principal chain of an epichlorohydrin-type resin, the thing from a primary to a quaternary can be used, and there is no restriction | limiting in particular. Further, the degree of cationization and the molecular weight preferably have a cationization degree of 5 meq / g · Solid (measured value at pH 7) and a molecular weight of 500,000 or more because of good water resistance. Specific examples include Sumire's Resin 650 (30) (manufactured by Sumitomo Chemical), Sumire's Resin 675A (manufactured by Sumitomo Chemical), Sumire's Resin 6615 (manufactured by Sumitomo Chemical), WS4002 (manufactured by Seiko PMC), WS4020. (Made by Starlight PMC), WS4024 (made by Starlight PMC), WS4046 (made by Starlight PMC), WS4010 (made by Starlight PMC), CP8970 (made by Starlight PMC), and the like.

  Polyamine / amide resins include polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, polyalkylene polyamine polyamide polys. Specific examples include urea resin, Sumire Resin 302 (manufactured by Sumitomo Chemical: polyamine polyurea resin), Sumire Resin 712 (manufactured by Sumitomo Chemical: polyamine polyurea resin), Sumire Resin 703 (Sumitomo Chemical). Company: Polyamine polyurea resin), Sumire Resin 636 (Sumitomo Chemical: polyamine polyurea resin), Sumire Resin SPI-100 (Sumitomo Chemical: modified polyamine resin), Sumire Resin SPI-102A Sumitomo Chemical Co., Ltd .: modified polyamine resin), Sumire Resin SPI-106N (Sumitomo Chemical Co., Ltd .: modified polyamide resin), Sumire Resin SPI-203 (50) (Sumitomo Chemical Co., Ltd.), Sumire Resin SPI-198 ( Sumitomo Chemical Co., Ltd.), Principal A-700 (manufactured by Asahi Kasei Co., Ltd.), Principal A-600 (manufactured by Asahi Kasei Co., Ltd.), PA6500, PA6504, PA6634, PA6638, PA6640, PA6664, PA6664, PA6654, PA6702, PA6704 (above, Starlight PMC: Polyalkylene polyamine polyamide polyurea resin), CP8994 (Starlight PMC: polyethyleneimine resin) and the like are not particularly limited, and these may be used alone or in combination of two or more. Is possible.

In the present invention, the silicic acid compound contained in the protective layer is amorphous silica, preferably amorphous silica that has been wet pulverized in the silicic acid compound precipitation step.
In general, there are two methods for producing a silicate compound: a precipitation method in which sodium silicate and sulfuric acid are subjected to an alkali reaction, and a gel method in which sodium silicate and sulfuric acid are subjected to an acidic reaction. The coarse silicic acid compound precipitated by the sum reaction is dried, pulverized and classified, and adjusted to the target particle size.
A preferred silicic acid compound is obtained by subjecting it to a target particle size during the neutralization reaction of sodium silicate, that is, before the precipitated silicic acid compound becomes coarse particles, by performing a wet grinding process in the silicic acid compound precipitation step. It is obtained by wet pulverization. As a result, this particle size distribution can be sharpened. This neutralization reaction and wet pulverization are preferably carried out in several steps. After the neutralization reaction, wet pulverization is performed to adjust the particle size to the target.

From the viewpoint of color development sensitivity, it is preferable to use a silicate compound obtained by neutralizing a sodium silicate aqueous solution containing a large amount of a metal compound with a mineral acid and an acidic metal salt aqueous solution, and the metal compound in the silicate compound The content of is 1.0 to 8.0% by weight in terms of oxide (vs. SiO ₂ % by weight, measured by a fluorescent X-ray analyzer Oxford ED2000 type), more preferably 1.0 to 6.0% by weight. It is preferable. In addition, examples of the metal element constituting the acidic metal salt aqueous solution include alkaline earth metal elements such as magnesium, calcium, strontium, and barium, or acidic metal salt aqueous solution such as titanium, zirconium, nickel, iron, and aluminum. Although a sulfate is mentioned and it does not specifically limit, It is preferable to use aluminum sulfate. Examples of the metal compound contained in the silicic acid compound include oxides of alkaline earth metals such as magnesium oxide, calcium oxide, strontium oxide, and barium oxide, titanium oxide, zirconium oxide, nickel oxide, iron oxide, and aluminum oxide. Although not limited to these, it is preferable to use aluminum oxide from the viewpoint of whiteness and oil absorption.

Examples of preferred silicic acid compound production include those disclosed in Japanese Patent Application Laid-Open No. 2002-274837 or Japanese Patent No. 2908253, in which mineral acid (sulfuric acid) is added in a divided manner to a sodium silicate aqueous solution, Manufactured by wet pulverization so as to obtain a target average particle size in the silicic acid precipitation step.
The average particle diameter of a preferable silicic acid compound is 1.0 to 10 μm, more preferably 1.0 to 5.0 μm, and still more preferably 1.0 to 3.0 μm, as measured by a sedimentation method. When the average particle size is smaller than 1.0 μm, the stick resistance is deteriorated and the problem of adhesion of the head residue occurs. When the average particle size is larger than 10 μm, the head wear resistance is lowered.
Moreover, the oil absorption amount of a preferable silicic acid compound is 100-350 ml / 100g, More preferably, it is 130-350 ml / 100g. If the amount of oil absorption is less than 100 ml / 100 g, the coloring material melted by the heat from the thermal head cannot be sufficiently absorbed and adsorbed, resulting in the problem of residue adhering to the thermal head. Strength decreases.

The blending ratio (dry weight) of the carboxy-modified polyvinyl alcohol resin, epichlorohydrin-based resin, and polyamine-based resin contained in the protective layer of the present invention is carboxy-modified polyvinyl alcohol resin relative to 1 part by weight of the polyamine-based resin. Is preferably 1 to 30 parts by weight, and epichlorohydrin resin is preferably 1 to 15 parts by weight, more preferably 3 to 10 parts by weight of carboxy-modified polyvinyl alcohol resin with respect to 1 part by weight of the modified polyamine / amide resin. Part, epichlorohydrin resin is 1 to 5 parts by weight. If the content of epichlorohydrin resin and modified polyamine / amide resin is too small, the crosslinking reaction becomes insufficient and good water resistance cannot be obtained. This is not preferable because it causes problems. Moreover, it is preferable that the protective layer of this invention contains 20-300 weight part of silicic acid compounds with respect to 100 weight part of carboxy modified polyvinyl alcohol. When the content of the silicic acid compound is small, stick resistance deteriorates, and when the content is large, water resistance and head residue resistance deteriorate.
In the protective layer of the present invention, the blending ratio of the pigment (including the silicate compound) and the total binder (including the carboxy-modified polyvinyl alcohol) is preferably 10 to 500 parts by weight of the binder with respect to 100 parts by weight of the pigment. . When the blending amount is small, the stick resistance is lowered and the problem of head residue adhesion occurs. When the amount is large, the problem of water resistance and head residue adhesion occurs.
The pH of the protective layer coating solution is preferably 6.0 or higher. In particular, epichlorohydrin-based resins are alkali-curable, so that a good cross-linking reaction is performed within this range, and adjusting the pH below this range is not preferable because the cross-linking reaction is inhibited.

Moreover, it is preferable that an epichlorohydrin resin is contained in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention. By including the same epichlorohydrin-based resin as the component contained in the protective layer, the adhesion between the heat-sensitive recording layer and the protective layer is improved, and the immersion water resistance is improved. The epichlorohydrin resin is preferably added in an amount of 0.2 to 5.0 parts by weight (dry weight) to the heat-sensitive recording layer. When the amount of the epichlorohydrin resin added increases, the stability of the paint decreases.
Further, by containing carboxy-modified polyvinyl alcohol, the adhesiveness between the heat-sensitive recording layer and the protective layer is improved, and the immersion water resistance is improved. The carboxy-modified polyvinyl alcohol is preferably contained in an amount of 30% by weight or more based on the total binder of the heat-sensitive recording layer.

  Next, various materials used in the present invention are exemplified, but binders, cross-linking agents, pigments and the like can be used in the protective layer as long as they do not impair the desired effects on the above-mentioned problems. It can also be used for each coating layer provided as needed, including layers.

  The binder used in the present invention includes fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, and olefin modified. Polyvinyl alcohol, nitrile modified polyvinyl alcohol, pyrrolidone modified polyvinyl alcohol, silicone modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer and Cellulose like ethyl cellulose, acetyl cellulose Derivatives, casein, arabic gum, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyral, polystyrose and copolymers thereof, Examples thereof include polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, and coumaro resin. These polymer substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., and are used in the state of being emulsified or pasted in water or other media to achieve the required quality. It can also be used in combination.

Examples of the crosslinking agent used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, chloride chloride Examples include ferric iron, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.
Examples of the pigment used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. As the pigment used in the protective layer, aluminum hydroxide or kaolin is preferable in consideration of the wearability of the thermal head.
Examples of the lubricant used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

Further, in the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol) is used as an image stabilizer exhibiting an oil resistance effect of a recorded image and the like within a range that does not hinder a desired effect on the above problems. ), 2,2′-di-t-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) Butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4-benzyloxy-4 ′-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, etc. Can also be added.
In addition, benzophenone and triazole ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

As the electron-donating leuco dye used in the present invention, those known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and are not particularly limited, but are triphenylmethane compounds, fluoran compounds, and the like. Compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.
<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-diethylamino- 6-methyl-7-chlorofluorane, 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane, 3- Diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane, 3-di Tilamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino- 6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-chloro-7-p-methylanilinofluorane, 3-diethylamino-6-ethoxy Ethyl-7-anilinofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino- 7- (o-chloroanilino) fluorane, 3-diethylamino-7- (p Chloroanilino) fluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-benzo [a] fluorane, 3-diethylamino-benzo [c] fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino-6-methyl-7- ( o-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-dibutylamino-6 -Methyl-7- (m-trifluoromethylanilino) fluorane, 3-dibutylamino- 6-methyl-7-chlorofluorane, 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane, 3-dibutylamino-6-chloro-7-anilinofluorane, 3-dibutylamino-6- Methyl-7-p-methylanilinofluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-di-n-pentylamino -6-methyl-7-anilinofluorane, 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-di-n-pentylamino-7- (m-trifluoro Methylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilinofluorane, 3-di-n-pentylamino-7- (p-chloro) Nilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl -7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-cyclohexylamino) -6-methyl-7 -Anilinofluorane, 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane, 3- (N-ethyl-p-toludino) -6-methyl-7-ani Linofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7-a Linofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofur Oran, 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 2- (4-oxahexyl) -3-dimethyl Amino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-dipropyl Amino-6-methyl-7-anilinofluorane, 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-methoxy-6-p -(P-dimethylaminophenyl) aminoanilinofluorane, 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-chloro-6-p- (p- Dimethylaminophenyl) aminoanilinofluorane, 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-phenyl-6-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-benzyl-6 -P- (p-phenylaminophenyl) aminoanilinofluorane, 2-hydroxy-6-p- (p-phenylamino) Nophenyl) aminoanilinofluorane, 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 3-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 3 -Diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane, 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide], 3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide], <divinyl series Leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide
<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 4-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam, 3,6 -Bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylamino) Enyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane, bis- [2, 2,2 ′, 2′-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  As the electron-accepting developer used in the present invention, those known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and are not particularly limited. For example, activated clay, attapulgite Inorganic acidic substances such as colloidal silica and aluminum silicate, 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methyl Pentane, 4,4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-hydroxy-4′-isopropoxy Diphenyl sulfone, 4-hydroxy-4'-n-propoxy div Nylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4'-methyl Phenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, bis (p -Hydroxyphenyl) butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4'- Hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′- Droxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert-octylphenol), international Phenolic compounds such as diphenylsulfone cross-linking compounds described in WO 97/16420, compounds described in WO 02/081229 or JP-A 2002-301873, N, N′-di-m-chlorophenylthiourea, etc. Thiourea compound, p-chlorobenzoic acid, stearyl gallate, zinc bis [4- (n-octyloxycarbonylamino) salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-Tolylsulfonyl) propyloxy] salicylic acid, 5 -[P- (2-p-methoxyphenoxyethoxy) cumyl] aromatic carboxylic acids of salicylic acid and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel of these aromatic carboxylic acids Examples thereof include salts with salts, antipyrine complexes of zinc thiocyanate, and complex zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. The diphenylsulfone cross-linking compound described in International Publication No. WO97 / 16420 is available as trade name D-90 manufactured by Nippon Soda Co., Ltd. Moreover, the compound as described in international publication WO02 / 081229 etc. is available as Nippon Soda Co., Ltd. brand name NKK-395 and D-100. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  As the sensitizer used in the heat-sensitive recording material of the present invention, a conventionally known sensitizer can be used. Examples of such sensitizers include fatty acid amides such as stearamide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β- Benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis -(Phenyl ether), 4- (m-methyl) Ruphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy- Examples thereof include, but are not limited to, phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, and the like. These sensitizers may be used alone or in combination of two or more.

The types and amounts of the electron-donating leuco dye, electron-accepting developer, and other various components used in the heat-sensitive recording material of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. Usually, about 0.5 to 10 parts of an electron accepting developer and about 0.5 to 10 parts of a sensitizer are used with respect to 1 part of the electron donating leuco dye.
By applying the coating liquid having the above composition to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired thermal recording material can be obtained. Moreover, you may use the composite sheet which combined these as a support body.
The electron-donating leuco dye, electron-accepting developer, and materials to be added as necessary are finely divided to a particle size of several microns or less by a pulverizer such as a ball mill, an attritor, or a sand glider, or an appropriate emulsifier. Depending on the binder and purpose, various additive materials are added to form a coating solution. The means for applying is not particularly limited, and can be applied in accordance with a well-known conventional technique. For example, various coaters such as an air knife coater, a rod blade coater, a vent blade coater, a bevel blade coater, a roll coater, and a curtain coater are provided. An off-machine coating machine or an on-machine coating machine is appropriately selected and used. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of 2 to 12 g / m 2 by dry weight. Moreover, the coating amount of the protective layer provided on the thermosensitive recording layer is not particularly limited, and is usually in the range of 1 to 5 g / m2.

The heat-sensitive recording material of the present invention can further be provided with an undercoat layer such as a polymer material containing a filler under the heat-sensitive recording layer for the purpose of increasing the color development sensitivity. It is also possible to correct the curl by providing a backcoat layer on the opposite side of the support from the thermosensitive recording layer. Further, various known techniques in the heat-sensitive recording material field, such as supercalendering after the application of each layer, can be added as appropriate.

The heat-sensitive recording material of the present invention will be described below with reference to examples. In the following description, “part” and “%” represent “part by weight” and “% by weight”, respectively.
Various solutions, dispersions, or paints were prepared as follows.

[Production of Silicic Acid Compound A]
(1) First step (neutralization rate: 40%); commercially available No. 3 sodium silicate (SiO ₂ : 20.0% by weight, Na ₂ O: 9.5% by weight) in water in a reaction vessel (200 liters) To prepare 200 liters of a 6.7% by weight diluted sodium silicate solution as SiO ₂ . After heating this sodium silicate solution to 85 ° C., an amount of aluminum sulfate corresponding to 20% by weight of the neutralization equivalent (concentration of 8% by weight as Al ₂ O ₃ minutes, hereinafter abbreviated as a band) was dropped at 200 g / min. At a speed, it was added under sufficiently strong agitation so that no coarse gel was generated, and then an amount of sulfuric acid (concentration 98% by weight) corresponding to 30% by weight of the neutralization equivalent was added in the same manner. After completion of the addition, the partially neutralized liquid thus obtained is subjected to aging treatment with stirring, and at the same time circulated by a vertical sand grinder (capacity 2 gallons, 1 mm diameter glass beads filling rate 70% by weight) (with a target particle size of 7 μm). Grinded. This aging and pulverization treatment was performed for 3 hours.
(2) Second step (neutralization rate: 40%); Next, the slurry temperature is raised to 90 ° C., and sulfuric acid having the same concentration as in the first step is 80% by weight of the neutralization equivalent under the same conditions as in the first step. And aged for 32 minutes under stirring.
(3) Third step (neutralization rate: 20%): Subsequently, sulfuric acid having the same concentration was added to the matured slurry at the same rate at an addition rate of 76 g / min. Was wet pulverized so as to be 2 μm.
(4) Performance evaluation: The slurry after completion of the third step was filtered, washed with water, repulped (redispersed) in pure water, and a hydrated silica slurry was recovered. The average particle diameter of the obtained slurry was measured. The slurry was filtered, dissolved in ethanol to a solid content of 10% by weight, filtered again, dried at 105 ° C., and the oil absorption was measured. The obtained silicic acid compound A had an average particle size of 2.3 μm, an oil absorption of 155 ml / 100 g, and an Al ₂ O ₃ content of 2.5%.

[Adjustment of undercoat paint]
Baked kaolin (trade name: Ancilex 90, manufactured by Engelhard)
100 parts Styrene-butadiene copolymer latex (solid content 48%) 40 parts Fully saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA117)
Undercoat paint was prepared by stirring and dispersing 30 parts of 10% aqueous solution and 160 parts of water.

[Adjustment of heat-sensitive coloring layer coating 1]
The leuco dye dispersion (Liquid A) and developer dispersion (Liquid B) having the following composition were separately wet milled with a dyno mill until the average particle diameter was 0.8 μm and 1.1 μm, respectively.
<Liquid A>
40 parts of 3-dibutylamino-6-methyl-7-anilinofluorane fully saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA117)
10% aqueous solution 40 parts water 20 parts
<Liquid B>
4-hydroxy-4'-propoxydiphenylsulfone 15 parts diphenylsulfone (sensitizer) 25 parts carboxy-modified fully saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVAKL-318) 10% aqueous solution 40 parts polyamide epichlorohydrin resin (WS4020) 8 parts water 20 parts
<C liquid>
4-hydroxy-4'-propoxydiphenyl sulfone 15 parts diphenyl sulfone (sensitizer) 25 parts fully saponified polyvinyl alcohol (trade name: PVA117, manufactured by Kuraray Co., Ltd.)
10% aqueous solution 40 parts water 20 parts

  50 parts of A liquid, 120 parts of B liquid, 25 parts of silica (manufactured by Mizusawa Chemical Co., Mizukasil P527), 50 parts of carboxy-modified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-KL318), polyamide epichlorohydrin resin (Product name: WS4020, solid content 25%, degree of cationization: 2.7, molecular weight: 2,200,000, quaternary amine) mixed by Starlight PMC Co., and further added with 280 parts of water and stirred to form a thermosensitive coloring layer. Paint 1 was prepared.

[Adjustment of heat-sensitive layer paint 2]
50 parts of liquid A, 120 parts of liquid C, 25 parts of silica (manufactured by Mizusawa Chemical Co., Ltd., Mizukasil P527), 10 parts of carboxy-modified polyvinyl alcohol 10% (manufactured by Kuraray Co., Ltd., trade name: PVA-KL318) are mixed, and water 280 Part was added and stirred to prepare a thermosensitive coloring layer coating material 2.

[Adjustment of protective coating]
The protective layer paints 1 to 13 were prepared by mixing at the following ratios.
<Protective layer paint 1>
Carboxy-modified polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name: PVA-KL318, polymerization degree: 1800, saponification degree, 99 mol%) 10% solution 100 parts polyamide epichlorohydrin resin (manufactured by Seiko PMC, trade name: WS4020, 25% solid content, degree of cationization: 2.7, molecular weight: 2.2 million, quaternary amine 10 parts modified polyamide resin (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumirez resin SPI-106N, solid content 45%) 3 parts Silica compound A 20% dispersion 50 parts zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin E-366, solid content 40%)
5 copies

<Protective layer paint 2>
Carboxy-modified polyvinyl alcohol PVA-KL318) 10% solution 100 parts polyamide epichlorohydrin resin (WS4020) 10 parts modified polyamide resin (Smiledes resin SPI-106N) 3 parts Silica compound A 20% dispersion 20 parts Zinc stearate (hydrin) E-366) 5 parts

<Protective layer paint 3>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Modified polyamide resin (Smiledes resin SPI-106N) 3 parts Silicate compound A 20% dispersion 100 parts Zinc stearate ( Hydrin E-366) 5 parts

<Protective layer paint 4>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Modified polyamide resin (Smileds resin SPI-106N) 3 parts Silicic acid compound (Mizusawa Chemical Co., Ltd., trade name: Mizukacil) P526, average particle size: 3.0 μm, oil absorption: 200 ml / 100 g) 20% dispersion 50 parts zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 5>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Modified polyamide resin (Smileds resin SPI-106N) 3 parts Silicic acid compound (Mizusawa Chemical Co., Ltd., trade name: Mizukacil) P527, average particle size: 1.6 μm, oil absorption: 130 ml / 100 g) 20% dispersion 50 parts zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 6>
Carboxy modified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA-KL506, polymerization degree: 600, saponification degree 90%) 10% solution 100 parts polyamide epichlorohydrin resin (trade name: WS4020) 10 parts modified polyamide resin ( Sumirez resin SPI-106N) 3 parts Silicic acid compound (Mizucasil P527) 20% dispersion 20 parts

<Protective layer paint 7>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts polyamide epichlorohydrin resin (WS4020) 10 parts modified polyamine resin (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumirez SPI102A, solid content 45%) 3 parts silicic acid compound ( Mizukasil P527) 20% dispersion 50 parts Zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 8>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Modified polyamide resin (Smileds resin SPI-106N) 3 parts Zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 9>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Silicic acid compound (Mizukacil P527) 20% dispersion 120 parts Zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 10>
100% polyamide epichlorohydrin resin (WS4020) 10 parts modified polyamide resin (Smileds) Completely saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA117, polymerization degree: 1700, saponification degree: 99 mol%) 10% solution Resin SPI-106N) 3 parts Silicate compound (Mizukacil P527) 20% dispersion 50 parts Zinc stearate (Hydrin E-366) 5 parts

<Protective layer paint 11>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Polyethyleneimine (trade name: CP8994, solid content 50% by Seiko PMC)
3 parts Silicic acid compound (Mizusawa Chemical Co., Ltd., trade name: Mizukacil P527) 20% dispersion 50 parts Zinc stearate (hydrin E-366) 5 parts

<Protective layer paint 12>
Carboxy-modified polyvinyl alcohol (PVA-KL318) 10% solution 100 parts Polyamide epichlorohydrin resin (WS4020) 10 parts Melamine resin (trade name: Sumirez resin 603M, solid content 60%)
2 parts Silicic acid compound (manufactured by Mizusawa Chemical Co., Ltd., trade name: Mizukasil P527) 20% dispersion 50 parts Zinc stearate (hydrin E-366) 5 parts

[Preparation of thermal recording material 1]
The undercoat paint base paper of 60 g / ^{m 2} coating amount after drying was coated with a blade coater so as to be 8.0 g / ^{m 2.} On this, the heat-sensitive color developing layer coating 1 was applied with a blade coater so that the coating amount after drying was 4.5 g / m ² to obtain a heat-sensitive recording paper.
[Preparation of thermal recording material 2]
The undercoat paint base paper of 60 g / ^{m 2} coating amount after drying was coated with a blade coater so as to be 8.0 g / ^{m 2.} On this, the heat-sensitive color developing layer coating material 2 was applied with a blade coater so that the coating amount after drying was 4.5 g / m ² to obtain a heat-sensitive recording paper.

[Example 1]
The protective layer coating 1 was coated on the heat-sensitive recording medium 1 with a hand-painted bar so that the coating amount after drying was 2.5 g / m2. A calendar process was performed so that the Beck smoothness (after conditioning at 23 ° C. in a 50% environment) was 2000 to 2500 seconds, and a thermosensitive recording material of Example 1 was produced.
[Example 2]
A thermosensitive recording material of Example 2 was produced in the same manner as in Example 1 except that the protective layer paint 2 was used instead of the protective layer paint 1.
[Example 3]
A thermosensitive recording material of Example 3 was produced in the same manner as in Example 1 except that the protective layer paint 3 was used instead of the protective layer paint 1.
[Example 4]
A thermal recording material of Example 4 was produced in the same manner as in Example 1 except that the protective layer paint 4 was used in place of the protective layer paint 1.

[Example 5]
A thermosensitive recording material of Example 5 was produced in the same manner as in Example 1 except that the protective layer paint 5 was used instead of the protective layer paint 1.
[Example 6]
A heat-sensitive recording material of Example 6 was produced in the same manner as in Example 1 except that the protective layer paint 6 was used instead of the protective layer paint 1.
[Example 7]
A heat-sensitive recording material of Example 6 was produced in the same manner as in Example 1 except that the protective layer paint 7 was used instead of the protective layer paint 1.

[Example 8]
The protective layer coating 1 was applied on the above-mentioned heat-sensitive recording medium 2 with a hand-painted bar so that the coating amount after drying was 2.5 g / m ² . A calendar process was performed so that the Beck smoothness (after conditioning at 23 ° C. in a 50% environment) was 2000 to 2500 seconds, and a thermosensitive recording material of Example 1 was produced.

[Comparative Example 1]
A heat-sensitive recording material of Comparative Example 1 was produced in the same manner as in Example 1 except that the protective layer paint 8 was used instead of the protective layer paint 1.
[Comparative Example 2]
A heat-sensitive recording material of Comparative Example 2 was produced in the same manner as in Example 1 except that the protective layer paint 9 was used instead of the protective layer paint 1.
[Comparative Example 3]
A heat-sensitive recording material of Comparative Example 3 was produced in the same manner as in Example 1 except that the protective layer paint 10 was used instead of the protective layer paint 1.
[Comparative Example 4]
A heat-sensitive recording material of Comparative Example 4 was produced in the same manner as in Example 1 except that the protective layer paint 11 was used instead of the protective layer paint 1.
[Comparative Example 5]
A heat-sensitive recording material of Comparative Example 5 was produced in the same manner as in Example 1 except that the protective layer paint 12 was used instead of the protective layer paint 1.

The following evaluation was performed about the heat-sensitive recording material of Examples 1-7 and Comparative Examples 1-5.
[Print density]
Okura thermal printer TH-PMD, pattern NO. Gradation printing was performed at 8 and the print density of the image obtained at # 14 was measured with a Macbeth densitometer RD918. The larger the value, the better the color density.
[Preservation]
The printer, pattern No. A checkerboard printing was performed at 8 and the following storability was evaluated for the colored portion.
[water resistant]
It was immersed in tap water for 24 hours and dried naturally. The color density before and after the test was measured, and the residual ratio (= color density after the test / color density before the test × 100 (%)) was calculated. The higher the residual rate, the better the water resistance.

[Solvent resistance]
Ethanol and ethyl acetate were applied to the surface with a cotton swab and dried naturally.
○: Not colored △: Lightly colored ×: Clearly colored
[Printer aptitude]
Ishida label printer: 2000m checkerboard printing was performed with IP21EX, and the print surface and the thermal head were visually evaluated.
[Head Cass]
○: No residue adhered to the thermal head, and no blurring occurs even after printing 2000 m.
Δ: Print was not faint, but head debris adhered.
×: Print blur due to head residue occurred.
[Stick resistance]
○: No sticking occurred.
X: A stick occurs.

The evaluation results are shown in Table 1.

Claims (3)

A heat-sensitive recording layer having a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and a heat-sensitive recording material provided with a protective layer thereon, the protective layer comprising carboxy-modified polyvinyl A thermosensitive recording material comprising an alcohol, an epichlorohydrin resin, a polyamine / amide resin and a silicate compound. The heat-sensitive recording material according to claim 1, wherein the silicic acid compound is obtained by performing a wet pulverization treatment in a silicic acid compound precipitation step. The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording layer contains an epichlorohydrin resin.