JP2004299380A - Thermosensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording material which is excellent in the water resistance of a recording image and surface texture as well as a solvent resistance while having a satisfactory performance for writing and stamping. <P>SOLUTION: The thermosensitive recording material is provided with a thermosensitive coloring layer presenting color with heat on a support and a protective layer on the coloring layer. The protective layer contains a polyvinyl alcohol resin, a chitosan, a bridging agent and a pigment. Colloidal silica is used for the pigment. The preferable compound for the bridging agent is an aldehyde compound or a compound having an epichlorohydrin residues or an isocyanate compound. The combination such as the aldehyde compound/the compound having epichlorohydrin residues, the aldehyde compound/the isocyanate compound or the compound having epichlorohydrin residues/the isocyanate compound is used for the bridging agent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material in which a heat-sensitive recording layer, which develops color by heat, and a protective layer are sequentially provided on a support, and is particularly excellent in water resistance and oil resistance of a recorded image and background, and has good writing and printing properties. It concerns recording materials.

  The thermosensitive recording material is inexpensive, the recording equipment is simple, the printer can be miniaturized, and the maintenance is easy. Therefore, facsimile paper, ATM / CD specifications, gas and water issued by a handy terminal In recent years, it has rapidly spread in fields such as receipts of electricity bills, tickets, tickets, receipts, and labels. As the use and demand of the heat-sensitive recording material have been expanding in various ways, various properties such as image storability, high printing sensitivity, and recording running property have been required. In particular, when used outdoors such as a handy terminal or a terminal such as a food label, image preservability against contact with water, cosmetics, stationery, and chemicals contained in food wraps is the most important. It is an issue.

  For the purpose of improving the image storability, a method of forming a water-resistant and oil-resistant protective layer for preventing penetration of water, oil, plasticizer, etc. on the heat-sensitive recording layer has been proposed. Note that the oil resistance of the present invention refers to resistance to a decrease in recording density and background fog caused by the heat-sensitive recording material coming into contact with oil, a plasticizer contained in wraps, and human sebum.

  For example, a method of forming a film of a film-forming polymer on the surface of a heat-sensitive layer for the purpose of improving rub fogging resistance, storage stability, and matching with a heat-sensitive head (for example, see Patent Document 1), acid resistance (For example, see Patent Document 2), and a method of providing a protective film using a carboxyl group-modified PVA on the surface of a heat-sensitive layer (for example, see Patent Document 3). A method in which a protective film using a combination of a carboxyl group-modified PVA and a polyamide epoxy resin is provided on the surface of a heat-sensitive layer (for example, see Patent Document 4), a coating liquid comprising a colloidal inorganic silicate and a colloidal silica composite particle emulsion is coated on the heat-sensitive layer. (For example, see Patent Document 5) and the like.

  However, in recent years, as recording apparatuses have been further miniaturized and power savings have been advanced, these methods have not been able to satisfy image storability against water, chemicals, and the like while maintaining printing sensitivity and recording traveling performance.

In a heat-sensitive recording layer in which a heat-sensitive coloring layer that is colored by heat on a support and a protective layer is provided on the heat-sensitive coloring layer, a polyvinyl alcohol-based resin, chitosan, or an aldehyde-based compound is used in the heat-sensitive layer or the protection layer. (For example, see Patent Document 6), but when a pigment is used to improve suitability for thermal head, writing and printing, gloss, clearness of printing, There is a problem that water resistance and solvent resistance are impaired. Further, a method of containing chitosan in a protective layer has been proposed for the purpose of improving water resistance, plasticizer resistance, head matching property, and the like (for example, see Patent Documents 7 and 8). It was unsatisfactory in terms of compatibility between the water resistance and oil resistance of the image and the background, and the writing and printing properties.
JP-A-48-051644 JP-A-54-128347 JP-A-56-126193 JP-A-59-162888 JP-A-2-274589 JP-A-61-162383 JP-A-5-572 JP-A-9-175022

  An object of the present invention is to provide a heat-sensitive recording material which overcomes the above-mentioned drawbacks, has excellent water resistance and solvent resistance of a recorded image and background, and has good writing and printing properties.

  The heat-sensitive recording material of the present invention is a heat-sensitive recording material comprising: a heat-sensitive coloring layer which is colored by heat on a support; and a heat-sensitive recording material provided with a protective layer on the heat-sensitive coloring layer. (1) A polyvinyl alcohol resin, chitosan, It contains a crosslinking agent and a pigment, and uses colloidal silica as the pigment.

  (2) The thermosensitive recording material according to (1), wherein an aldehyde compound or a compound having an epichlorohydrin residue is used as the crosslinking agent.

  (3) The method according to (2), wherein (3) a compound having an aldehyde compound and an epichlorohydrin residue, or a compound having an aldehyde compound and an isocyanate compound, or a compound having an epichlorohydrin residue and an isocyanate compound is used as a crosslinking agent. It is a thermosensitive recording material.

  (4) The heat-sensitive recording material according to any one of (1) to (3), wherein cationic colloidal silica is used as the colloidal silica.

  (5) The thermosensitive recording material according to any one of (1) to (4), wherein the ratio of polyvinyl alcohol to the chitosan is from 7: 3 to 9: 1.

  (6) As the polyvinyl alcohol, at least one kind of polyvinyl alcohol selected from unmodified polyvinyl alcohol having a saponification degree of 95% or more, silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol The heat-sensitive recording material according to any one of (1) to (5), which contains an alcohol.

  More preferably, (7) the heat-sensitive recording material according to any one of (1) to (6), wherein the protective layer contains a nonionic or cationic water-dispersible binder.

  The thermosensitive recording material of the present invention has excellent water resistance and solvent resistance by using polyvinyl alcohol, chitosan, a cross-linking agent, and colloidal silica as a pigment in the protective layer, and has excellent writing and printing properties. The material was obtained. In particular, the water resistance was improved by using an aldehyde compound as a crosslinking agent, and the printability and whiteness were improved by using a compound having an epichlorohydrin residue, and the whiteness was improved by using an isocyanate compound. In particular, when at least one of unmodified polyvinyl alcohol having a saponification degree of 95% or more, silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol is used as the polyvinyl alcohol, the water resistance can be further improved. Further, the water resistance and printing property can be improved by adding a nonionic acrylic emulsion, and the printing property and pencil writing property can be improved by increasing the particle size of colloidal silica.

  Hereinafter, the heat-sensitive recording material of the present invention will be described in detail. In the heat-sensitive recording material of the present invention, a heat-sensitive recording layer and a protective layer are sequentially provided on a support.

  The heat-sensitive recording material according to the invention is provided with at least one protective layer made of polyvinyl alcohol, chitosan, a pigment, and a crosslinking agent on the heat-sensitive recording layer.

  As the polyvinyl alcohol used in the protective layer of the present invention, besides ordinary polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, phosphate group-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone Modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, and modified polyvinyl alcohol obtained by copolymerizing ethylene, vinyl ether having a long-chain alkyl group, (meth) acrylamide, and the like can also be used.

  Among these, when it is necessary to further increase the water resistance, unmodified polyvinyl alcohol having a saponification degree of 95% or more, silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol are preferred.

  The degree of polymerization of the polyvinyl alcohol used in the present invention is not particularly limited, but is usually selected from the range of 100 to 3,000. The saponification degree is not particularly limited as long as it is in a water-soluble range, but is usually 70 to 100. It is selected from the range of mol%.

  The chitosan used in the present invention is obtained by deacetylation of chitin. Preferably, chitin is used in which 50% or more of the acetylamino groups are modified into amino groups by deacetylation, and more preferably 90% or more are used. In use, some or all of the amino groups are converted to ammonium groups with an acid before use. As the acid, acetic acid, lactic acid, triphosphate, citric acid, sulfamic acid, hydrochloric acid, sulfuric acid, formic acid, fumaric acid, and maleic acid are usually used. The molecular weight of the chitosan is not particularly limited, but considering the compatibility with polyvinyl alcohol or the like, a low-molecular-weight chitosan having a viscosity of 1 to 70 centipoise of a 1% aqueous solution at 20 ° C. by a BL viscometer is preferable. Further, there is a problem that the low molecular weight chitosan is colored from yellow to brown with the passage of time. In this case, stabilized chitosan as disclosed in JP-A-63-72702 may be used.

  The solid content mass ratio of polyvinyl alcohol to chitosan is preferably from 5: 5 to 9.7: 0.3, more preferably from 7: 3 to 9: 1. If the amount of chitosan is too small, the water resistance is reduced. If the amount is too large, thickening of the coating solution and coloring of the obtained heat-sensitive recording material over time tend to be problematic.

  As the binder used in the present invention, a water-dispersible binder can be added in addition to polyvinyl alcohol and chitosan. By adding the water-dispersible binder, the affinity with the oil-based ink is improved, and the printing suitability and the sealability can be improved. The water-dispersible binder is generally a styrene / butadiene copolymer, an acrylonitrile / butadiene copolymer, a methyl acrylate / butadiene copolymer, an acrylonitrile / butadiene / styrene terpolymer, a polyvinyl acetate, a vinyl acetate / Acrylic ester copolymers, ethylene / vinyl acetate copolymers, polyacrylic ester copolymers, styrene / acrylic ester copolymers, polyurethanes, and the like, and resins emulsified with a dispersant, etc., and self-emulsified Resin. In particular, an acrylate resin is preferable from the viewpoint of printability. Moreover, since chitosan is cationic, the water-dispersible binder is preferably a nonionic and cationic water-dispersible binder. The addition amount of the water-dispersible binder is preferably 5% by mass or more and 60% by mass or less of the total binder content of the protective layer, and particularly good solvent resistance and affinity for oil-based ink can be obtained in this range.

  Crosslinking agents used in the present invention include aldehyde compounds, urea resins, melamine resins, methylol compounds such as phenol resins, compounds containing epichlorohydrin residues represented by polyamide epichlorohydrin resins, epoxy compounds such as polyfunctional epoxy resins, isocyanates Examples include compounds, isocyanate compounds such as blocked isocyanate compounds, and oxidizing agents such as persulfates and peroxides.

  Aldehyde compounds are particularly preferred in terms of water resistance. Aldehyde compounds are represented by formalin, glyoxal and the like, and can be used as long as they generate aldehyde in the coating liquid. In addition, when a compound having an epichlorohydrin residue is used, it is possible to improve the sealability. Further, a compound having an epichlorohydrin residue or an isocyanate compound is preferable in terms of yellowing resistance of chitosan. Here, the isocyanate compound may be used as a blocked isocyanate compound treated with a blocking agent such as a phenol, alcohol, active methylene, mercaptan, amide, imide, and sulfite. When it is desired to achieve both pot life and high water resistance, an isocyanate compound emulsion may be prepared and used according to the method disclosed in JP-A-49-96077. In addition, by using an aldehyde compound and a compound containing an epichlorohydrin residue in combination, it is possible to simultaneously improve the water resistance and the printing property. In addition, by using an aldehyde compound and an isocyanate compound together, both high water resistance and yellowing resistance of chitosan can be achieved. In addition, by using a compound having an epichlorohydrin residue and an isocyanate compound in combination, a protective layer with low yellowing and a good balance between water resistance and printability can be obtained. The preferable amount of the crosslinking agent to be added to the protective layer of the present invention is in the range of 0.1 to 20% by mass based on the total solid content of polyvinyl alcohol and chitosan. This range is particularly preferable from the viewpoints of stability of water resistance, oil resistance, printing sensitivity, and recording running property.

  The colloidal silica used in the present invention preferably has an average particle diameter in the range of 3 to 200 nm because of low sedimentation. The larger the particle size, the better the suitability for thermal head, writing and printing. However, when high transparency is required, the range of 3 to 50 nm is preferable. When colloidal silica is used, the suitability for the thermal head, the writing property, and the printing property can be improved without impairing the gloss and the barrier property. The amount of colloidal silica to be added is usually preferably 5% by mass to 85% by mass of the total solids of the protective layer. More preferably, the content is 10% by mass to 70% by mass.

  Further, among colloidal silicas, cationic colloidal silica has good compatibility with chitosan, and does not easily cause gelling or aggregation of the coating liquid. The cationic colloidal silica is a material in which at least the surface of the silica particles is cationically charged by containing a compound of a polyvalent metal ion such as an aluminum ion or an organic cationic compound on or on the silica surface. Particularly preferred is colloidal silica cationized with basic aluminum.

  In addition to the colloidal silica, a conventionally known pigment may be used in a small proportion. Pigments include diatomaceous earth, talc, kaolin, calcined kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate, Inorganic pigments such as crystalline silica and amorphous calcium silicate, melamine resin fillers, urea-formalin resin fillers, and organic pigments such as polyethylene powder and nylon powder can be used. Among these pigments, aluminum hydroxide is effective for improving abrasion of a thermal recording head, and amorphous silica is effective for improving sticking.

  In addition, the protective layer may contain a higher fatty acid amide such as stearic acid amide, paraffin, polyethylene wax, polyethylene oxide, caster wax, or other wax as required for the purpose of improving recording running properties such as head wear prevention and sticking prevention. Is added.

The coating amount of the solid content of the protective layer in the present invention is preferably 0.3 to 10 g / m ² . When the content is in this range, the image storability, the background storability, and the printing sensitivity are improved.

  The material contained in the heat-sensitive recording layer is not particularly limited, and any combination may be used as long as a color reaction is generated by the energy applied by the heat-sensitive head. For example, there are a combination of a colorless or light-colored electron-donating dye with an electron-accepting color developer, and a combination of an aromatic isocyanate compound and an imino compound.

The colorless or light-colored electron-donating dye precursor used in the present invention is typified by dye precursors used in general pressure-sensitive recording paper, heat-sensitive recording paper, and the like, but is not particularly limited. As a specific example,
(1) Triarylmethane compound: 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (P-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (P-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3 -Bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl)- -Dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl)- 6-dimethylaminophthalide and the like,

  (2) diphenylmethane-based compounds: 4,4'-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucouramine, N-2,4,5-trichlorophenylleucouramine, etc.

  (3) Xanthene compounds: rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino- 7-phenylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3-dibutyl Amino-7- (2-chloroanilino) fluoran, 3-diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7- Anilinofluoran, 3-dipentylamino-6-methyl- -Anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3- (N- Ethyl-N-tolyl) amino-6-methyl-7-phenethylfluoran, 3-diethylamino-7- (4-nitroanilino) fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- ( N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N- Methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluoran, - diethylamino-6-methyl-7- (3-trifluoromethyl) -6-fluoran and the like,

  (4) Thiazine compounds: benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue, etc.

  (5) Spiro compounds: 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3′-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxy Benzo) spiropyran, 3-propylspirobenzopyran and the like can be mentioned. These dye precursors can be used alone or as a mixture of two or more, if necessary.

  The electron-accepting compound is generally represented by an acidic substance. In particular, phenol derivatives, aromatic carboxylic acid derivatives, N, N′-diarylthiourea derivatives, and polyvalent metal salts such as zinc salts of organic compounds are used. .

  Specifically, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, Hydroxydiphenylsulfone, 4-hydroxy-4′-methyldiphenylsulfone, 4-hydroxy-4′-methoxydiphenylsulfone, 4-hydroxy-4′-ethoxydiphenylsulfone, 4-hydroxy-4′-n-butoxydiphenylsulfone, 4-hydroxy-4′-benzyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (3,5-dibromo-4-hydroxyphenyl) sulfone, bis (3,5-dichloro-4-) Hydroxyphenyl) sulfone 3,4-dihydroxydiphenylsulfone, 3,4-dihydroxy-4′-methyldiphenylsulfone, 3,4,4′-trihydroxydiphenylsulfone, 3,4,3 ′, 4′-tetrahydroxydiphenylsulfone, 2, Diphenylsulfone derivatives such as 3,4-trihydroxydiphenylsulfone, 3-phenylsulfonyl-4-hydroxydiphenylsulfone, 2,4-bis (phenylsulfonyl) phenol, 4-t-butylphenol, 2,2′-dihydroxydiphenyl, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-ethylenebis (2-methylphenol), 4,4'-cyclohexylidenebis (2-isopropylphenol), p- Phenylphenol, p-hydroxyacetophenone 1,1-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) Cyclohexane, 2,2-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) -1-phenylethane, 1,3-di- [2- (p-hydroxyphenyl) -2-propyl] benzene 1,3-di- [2- (3,4-dihydroxyphenyl) -2-propyl] benzene, 1,4-di- [2- (p-hydroxyphenyl)- 2-propyl] benzene, 4,4'-hydroxydiphenyl ether, 3,3'-dichloro-4,4'-hydroxydiphenyl sulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis ( Bis (4-hydroxyphenyl) acetic acid esters such as 4-hydroxyphenyl) butyl acetate, 4,4′-thiobis (2-tert-butyl-5-methylphenol), dimethyl 4-hydroxyphthalate, benzoic acid, p Hydroxybenzoate such as ethyl-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, benzyl gallate, stearyl gallate, N, N′-diphenylthiourea , 4,4'-bis (3- (4-methylphenylsulfonyl) ureido Diphenylmethane, N- (4-methylphenylsulfonyl) -N'-phenylurea, salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4- [2 ′-(4-methoxyphenoxy) ethyloxy] salicylic acid, 3- (octyloxycarbonylamino) salicylic acid, metal salts of these salicylic acid derivatives, alkyl esters of gallic acid Phenolic compounds such as novolak-type phenolic resins, naphthoic acid derivatives such as 1-hydroxy-2-naphthoic acid and 2-hydroxy-6-naphthoic acid and metal salts thereof, tartaric acid, oxalic acid, boric acid, citric acid, Organic acids such as atearic acid or Metal salts, N- (p-toluenesulfonyl) -N '-(3-p-toluenesulfonyloxyphenyl) urea, N- (4-hydroxyphenyl) -p-toluenesulfonamide, N- (4 -Hydroxyphenyl) benzenesulfonamide, N- (4-hydroxyphenyl) -1-naphthalenesulfonamide, N- (4-hydroxyphenyl) -2-naphthalenesulfonamide, N- (4-hydroxynaphthyl) -p-toluene Sulfonamide, N- (4-hydroxynaphthyl) benzenesulfonamide, N- (4-hydroxynaphthyl) -1-naphthalenesulfonamide, N- (4-hydroxynaphthyl) -2-naphthalenesulfonamide, N- (3- Hydroxyphenyl) -p-toluenesulfonamide, N- (3-hydroxyphenyl) Nyl) benzenesulfonamide, N- (3-hydroxyphenyl) -1-naphthalenesulfonamide, N- (3-hydroxyphenyl) -2-naphthalenesulfonamide and the like, and known substances such as these can be used alone or Two or more can be mixed and used.

  The aromatic isocyanate compound is a colorless or pale-colored aromatic isocyanate compound which is solid at room temperature, and specifically, 2,6-dichlorophenyl isocyanate, p-chlorophenyl isocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene Diisocyanate, 1,3-dimethylbenzene-4,6-diisocyanate, 1,4-dimethylbenzene-2,5-diisocyanate, 1-ethoxybenzene-2,4-diisocyanate, 2,5-dimethoxybenzene-1,4- Diisocyanate, 2,5-diethoxybenzene-1,4-diisocyanate, 2,5-dibutoxybenzene-1,4-diisocyanate, azobenzene-4,4'-diisocyanate, diphenylether-4,4'-diisocyanate, naphthalene- , 4-Diisocyanate, naphthalene-1,5-diisocyanate, naphthalene-2,6-diisocyanate, naphthalene-2,7-diisocyanate, 3,3′-dimethylbiphenyl-4,4′-diisocyanate, 3,3′-dimethoxy -4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenyldimethylmethane-4,4'-diisocyanate, benzophenone-3,3'-diisocyanate, fluorene-2,7-diisocyanate, anthraquinone-2, 6-diisocyanate, 9-ethylcarbazole-3,6-diisocyanate, pyrene-3,8-diisocyanate, naphthalene-1,3,7-triisocyanate, biphenyl-2,4,4′-triisocyanate, 4,4 ′ , 4 ''-to Isocyanate 2,5-dimethoxy triphenylamine, p- dimethylaminophenyl isocyanate, tris (4-phenylisocyanate) thiophosphate least one such preparative is used.

  If necessary, these aromatic isocyanate compounds may be used in the form of so-called blocked isocyanate, which is an addition compound with phenols, lactams, oximes, etc. It may be used in the form of isocyanurate, which is a dimer or trimer of methylbenzene-2,4-diisocyanate, or may be used as a polyisocyanate added with various polyols or the like.

The imino compound is a colorless or pale-colored compound which is solid at room temperature, and specifically, 3-imino-4,5,6,7-tetrachloroisoindoline-1-one, 1,3-diimino-4 1,5,6,7-tetrachloroisoindoline, 1,3-diiminoisoindoline, 1,3-diiminobenz (f) isoindoline, 1,3-diiminonaphtho (2,3-f) isoindoline, 1,3 -Diimino-5-nitroisoindoline, 1,3-diimino-5-phenylisoindoline, 1,3-diimino-5-methoxyisoindoline, 1,3-diimino-5-chloroisoindoline, 5-cyano-1 , 3-Diiminoisoindoline, 5-acetamido-1,3-diiminoisoindoline, 1,3-diimino-5- (1H-1,2,3-triazol-1-yl -Isoindoline, 5- (pt-butylphenoxy) -1,3-diiminoisoindoline, 5- (p-cumylphenoxy) -1,3-diiminoisoindoline, 5-isobutoxy-1,3 -Diiminoisoindoline, 1,3-diimino-4,7-dimethoxyisoindoline, 4,7-diethoxy-1,3-diiminoisoindoline, 4,5,6,7-tetrabromo-1,3-di Iminoisoindoline, 4,5,6,7-tetrafluoro-1,3-diiminoisoindoline, 4,5,7-trichloro-1,3-diimino-6-methylmercaptoisoindoline, 1-iminodiphenimide , 1- (cyano-p-nitrophenylmethylene) -3-iminoisoindoline, 1- (cyanobenzothiazolyl- (2 ')-carbamoylmethylene)- -Iminoisoindoline, 1-[(cyanobenzimidazolyl-2 ') methylene] -3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2')-methylene] -3-imino-4,5,6, 7-tetrachloroisoindoline, 1-[(cyanobenzimidazolyl-2 ′)-methylene] -3-imino-5-methoxyisoindoline, 1-[(1′-phenyl-3′-methyl-5-oxo) -Pyrazolidene-4 ']-3-iminoisoindoline, 3-imino-1-sulfobenzoic imide, 3-imino-1-sulfo-4,5,6,7-tetrachlorobenzoic imide, 3-imino- 1-sulfo-4,5,7-trichloro-6-methylmercaptobenzoic acid imide, 3-imino-2-methyl-4,5,6,7-tetrachloroisoindoline-1-one And the like.

  In the heat-sensitive recording material of the present invention, a heat-fusible substance can be contained in the heat-sensitive recording layer in order to improve the thermal response. In this case, those having a melting point of 60 ° C to 180 ° C are preferable, and those having a melting point of 80 ° C to 140 ° C are more preferable. Specifically, stearic acid amide, N-hydroxymethylstearic acid amide, N-stearylstearic acid amide, ethylenebisstearic acid amide, N-stearylurea, β-naphthylbenzyl ether, m-terphenyl, 4-benzylbiphenyl 2,2′-bis (4-methoxyphenoxy) diethyl ether, α, α′-diphenoxyxylene, bis (4-methoxyphenyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,2 -Diphenoxyethane, diphenyl adipate, dibenzyl oxalate, di (4-chlorobenzyl) oxalate, di (4-methylbenzyl) oxalate, oxalate diester derivatives, sulfone compounds such as diphenylsulfone, dimethyl terephthalate, Dibenzyl terephthalate, benzenes Known heat-fusible substances such as phonic acid phenyl ester, bis (4-allyloxyphenyl) sulfone, 4-acetylacetophenone, acetoacetic anilides, and fatty acid anilides may be used, and these compounds may be used alone or in combination of two or more. Can also be used. Further, in order to obtain sufficient thermal responsiveness, it is preferable that the heat-fusible substance accounts for 5 to 50% by mass of the total solid content of the heat-sensitive recording layer.

  As the binder used in the heat-sensitive recording layer, various binders used in ordinary coating can be used. Specifically, starches, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylate copolymer, acrylamide / acryl Acid ester / methacrylic acid terpolymer, alkali salt of polyacrylic acid, alkali salt of polymaleic acid, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, isobutylene / Water-soluble binders such as maleic anhydride copolymer alkali salts, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / buta Ene copolymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate, styrene / acrylate copolymer Examples include water-dispersible binders such as coalescing and polyurethane, but are not limited thereto.

  In addition, in the heat-sensitive recording layer, as pigments, diatomaceous earth, talc, kaolin, calcined kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide, Inorganic pigments such as barium sulfate, zinc sulfate, amorphous silica, amorphous calcium silicate, and colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, and nylon powder can be used. .

  In the heat-sensitive recording layer, metal salts of higher fatty acids such as zinc stearate and calcium stearate, lubricants such as paraffin, polyethylene wax, polyethylene oxide and caster wax, ultraviolet absorbers such as benzophenone and benzotriazole, anionic and nonionic A surfactant including a high molecular weight compound, a fluorescent dye, an antifoaming agent and the like are added as necessary.

  The heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention is obtained by mixing each aqueous dispersion obtained by finely pulverizing each color-forming component, a binder and the like, coating the mixture on a support, and drying. The layer structure of the heat-sensitive recording layer may be a single layer or a multilayer.

The coating amount of the heat-sensitive recording layer is usually from 0.1 to 2.0 g / m ^{2 in} terms of the coating amount of the solid content of the dye precursor. Within this range, a sufficient recording density can be obtained, which is economically advantageous.

  The coating liquid for the heat-sensitive recording layer is applied on a support, and paper is mainly used as the support. In addition to paper, various woven fabrics, nonwoven fabrics, synthetic resin films, synthetic resin laminated papers, synthetic papers, metal foils, vapor-deposited sheets, or composite sheets obtained by combining these by lamination or the like can be arbitrarily used.

The heat-sensitive recording material of the present invention may include a single layer or a plurality of intermediate layers between the heat-sensitive recording layer and the protective layer, and a single-layer or a plurality of layers of pigment or resin between the support and the heat-sensitive recording layer, if necessary. One or more undercoat layers can be provided. When the heat-sensitive recording material of the present invention is provided with a undercoat layer, the solid coating amount of the undercoat layer is preferably ^{1~30g / m 2, 3~20g / m} 2 is more preferable.

  As the pigment for the undercoat layer, calcined kaolin is generally used. In addition, diatomaceous earth, talc, kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, and hydroxide Inorganic pigments such as aluminum, magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate, amorphous silica, amorphous calcium silicate, colloidal silica, melamine resin filler, urea-formalin resin filler, polyethylene powder, nylon powder, etc. Organic pigments, and organic spherical particles, organic hollow particles and the like can also be used.

  As the resin of the undercoat layer, various water-soluble resins or water-dispersible resins used in ordinary coating can be used. For example, starches, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylate copolymer, acrylamide / acrylate / Methacrylic acid terpolymer, alkali salt of polyacrylic acid, alkali salt of polymaleic acid, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, isobutylene / maleic anhydride Water-soluble resin such as alkali salt of copolymer, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer Copolymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate copolymer, styrene / acrylate copolymer And water-dispersible resins such as polyurethane.

  The method for forming the heat-sensitive recording layer, the protective layer or the undercoat layer is not particularly limited, and it can be formed according to a conventionally known technique. As a specific example, a coating liquid is applied by a method such as air knife coating, rod blade coating, bar coating, blade coating, gravure coating, curtain coating, and E-bar coating, and then heat-sensitive by drying. A recording layer, a protective layer or an undercoat layer can be formed.

  Further, if necessary, after the undercoat layer is applied, the heat-sensitive recording layer is applied, or after the protective layer is applied, a super calender treatment may be performed to improve the image quality.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. In Examples,% and parts are all based on mass.

(Preparation of dispersion)
Dispersions A, B, C, D, E, and F were prepared by the following method.

(Dispersion A)
200 g of 3- (N, N-dibutylamino) -6-methyl-7-anilinofluoran was dispersed in a mixture of 200 g of a 10% aqueous solution of polyvinyl alcohol and 600 g of water, and pulverized by a bead mill until the average particle diameter became 1 μm. did.

(Dispersion B)
400 g of 2,2-bis (p-hydroxyphenyl) propane was dispersed in a mixture of 400 g of a 10% aqueous solution of polyvinyl alcohol and 200 g of water, and pulverized by a bead mill until the average particle diameter became 1 μm.

(Dispersion C)
400 g of β-naphthyl benzyl ether was dispersed in a mixture of 400 g of a 10% aqueous solution of polyvinyl alcohol and 200 g of water, and pulverized by a bead mill until the average particle diameter became 1 μm.

(Dispersion D)
200 g of calcium carbonate was dispersed in 800 g of a 0.5% aqueous solution of sodium polyacrylate and dispersed for 10 minutes using a homomixer.

(Dispersion E)
200 g of amorphous silica (Mizukasil P527, manufactured by Mizusawa Chemical Co., Ltd.) was dispersed in 800 g of a 0.5% aqueous solution of sodium polyacrylate, and dispersed with a homomixer for 10 minutes.

(10% chitosan aqueous solution)
400 g of water was added to 50 g of chitosan (manufactured by Kuraray Co., Ltd., OTS-2), 50 g of 50% lactic acid was added with stirring, and further stirred to prepare a 10% chitosan aqueous solution.

(50% blocked isocyanate aqueous solution)
6.8 parts of hexamethylene diisocyanate and 8.2 parts of sodium metabisulfite were dissolved in 15 parts of water, added, sealed, and stirred for 20 hours to prepare an aqueous solution of blocked isocyanate.

(Example 1)
<Thermal recording layer>
Using the dispersion liquids of A to D, the respective materials were mixed at the following ratios and sufficiently stirred to prepare a heat-sensitive recording layer coating liquid.
Dispersion A 20 parts Dispersion B 15 parts Dispersion C 15 parts Dispersion D 25 parts 10% aqueous polyvinyl alcohol 30 parts Water 30 parts

The heat-sensitive recording layer coating solution thus prepared is coated on a base paper having a basis weight of 40 g / m ^{2 so} that the solid content of the dye precursor is 0.3 g / m ² , dried, and treated with a super calender. Thus, a material provided with a heat-sensitive recording layer was obtained.

<Protective layer>
The respective materials were mixed at the ratios shown below and sufficiently stirred to prepare a protective layer coating liquid.
10% complete saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 3.2 parts 20% cationic colloidal silica aqueous dispersion (Nissan Chemical Industries, Snowtex AK,
Average particle size 10-20nm 15 parts 40% aqueous solution of zinc stearate 2 parts Water 80 parts

The coating liquid for the protective layer adjusted by the above composition is coated on the heat-sensitive recording layer obtained above so as to have a solid content of 2 g / m ² , dried and supercalendered to obtain a heat-sensitive recording material. Was.

(Example 2)
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that the 25% aqueous glyoxal solution was replaced by the same amount of the 25% aqueous polyacrylamide epichlorohydrin in the formulation of the protective layer in Example 1.

(Example 3)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 3.2 parts of a 25% aqueous glyoxal solution was added to 1.6 parts of a 50% blocked isocyanate aqueous solution and 1.6 parts of water in the formulation of the protective layer of Example 1. Was.

(Example 4)
In the same manner as in Example 1, except that 3.2 parts of the 25% aqueous glyoxal solution was replaced with 1.6 parts of the 25% aqueous glyoxal solution and 1.6 parts of the 25% polyacrylamide epichlorohydrin aqueous solution in the formulation of the protective layer in Example 1. A recording material was obtained.

(Example 5)
Example 1 Except that 3.2 parts of a 25% aqueous glyoxal solution was replaced with 1.6 parts of a 25% aqueous glyoxal solution, 0.8 parts of a 50% aqueous solution of blocked isocyanate and 0.8 parts of water in the formulation of the protective layer of Example 1. A heat-sensitive recording material was obtained in the same manner as described above.

(Example 6)
Except that in the formulation of the protective layer in Example 1, 3.2 parts of a 25% aqueous glyoxal solution was replaced by 1.6 parts of a 25% aqueous solution of polyacrylamide epichlorohydrin, 0.8 parts of a 50% aqueous solution of blocked isocyanate and 0.8 parts of water. A heat-sensitive recording material was obtained in the same manner as in Example 1.

(Example 7)
A thermosensitive recording material was prepared in the same manner as in Example 1, except that 3.2 parts of a 25% aqueous glyoxal solution was replaced with 16 parts of a 5% aqueous boric acid solution and 80 parts of water was replaced with 67.2 parts in the formulation of the protective layer of Example 1. Got.

(Example 8)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the protective layer formulation of Example 1, 80 parts of a 10% aqueous solution of completely saponified polyvinyl alcohol was changed to 60 parts and 20 parts of a 10% aqueous solution of chitosan was changed to 40 parts.

(Example 9)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the protective layer composition of Example 1, 95 parts of a 10% aqueous solution of completely saponified polyvinyl alcohol was changed to 95 parts, and 20 parts of a 10% aqueous solution of chitosan was changed to 5 parts.

(Example 10)
Except that in the formulation of the protective layer of Example 1, the aqueous dispersion of 20% cationic colloidal silica was replaced with a 20% aqueous dispersion of anionic colloidal silica (Snowtex C, manufactured by Nissan Chemical Co., average particle size 10 to 20 nm). A heat-sensitive recording material was obtained in the same manner as in Example 1.

(Example 11)
In the formulation of the protective layer of Example 1, except that 80 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was replaced with 80 parts of a 10% partially saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-217, saponification degree 88%). A heat-sensitive recording material was obtained in the same manner as in Example 1.

(Example 12)
Thermal recording was performed in the same manner as in Example 1 except that 80 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was replaced with 80 parts of a 10% silanol-modified polyvinyl alcohol aqueous solution (R1130, manufactured by Kuraray Co., Ltd.) in the protective layer formulation of Example 1. The material was obtained.

(Example 13)
In the same manner as in Example 1, except that 80 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was replaced with 80 parts of a 10% epoxy-modified polyvinyl alcohol aqueous solution (W100 manufactured by Denki Kagaku Kogyo Co., Ltd.) in the formulation of the protective layer of Example 1. A heat-sensitive recording material was obtained.

(Example 14)
In the same manner as in Example 1 except that 80 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was replaced with 80 parts of a 10% diacetone-modified polyvinyl alcohol aqueous solution (D1700, manufactured by Shin-Etsu Chemical Co., Ltd.) in the formulation of the protective layer of Example 1. A heat-sensitive recording material was obtained.

(Example 15)
Same as Example 1 except that 80 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was replaced with 80 parts of a 10% acetoacetyl-modified polyvinyl alcohol aqueous solution (Z200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) in the formulation of the protective layer of Example 1. Thus, a heat-sensitive recording material was obtained.

(Example 16)
In the formulation of the protective layer of Example 1, 15 parts of an aqueous dispersion of 20% cationic colloidal silica was mixed with 30% aqueous dispersion of cationic colloidal silica (Nissan Chemical Industries, Snowtex AK-YL, average particle size of 70 to 50%). (80 nm) A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 10 parts of water and 5 parts of water were used.

(Example 17)
In the protective layer formulation of Example 1, 80 parts of a 10% aqueous solution of completely saponified polyvinyl alcohol and 20 parts of a 10% aqueous solution of chitosan were converted to 64 parts of a 10% aqueous solution of completely saponified polyvinyl alcohol, 16 parts of an aqueous solution of 10% chitosan and 30% of nonionic acrylic. A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 6.7 parts of the emulsion (Nisshin Chemical Co., manufactured by Vinyblan 2885) was used.

(Example 18)
In the protective layer composition of Example 17, 64 parts of a 10% completely saponified polyvinyl alcohol aqueous solution was added to 64 parts of a 10% epoxy-modified polyvinyl alcohol aqueous solution (W100, manufactured by Denki Kagaku Kogyo Co., Ltd.), and 3.2 parts of a 25% glyoxal aqueous solution was added to 25 parts. A thermosensitive recording material was obtained in the same manner as in Example 17, except that 1.6 parts by weight of an aqueous glyoxal solution, 1.6 parts of a 50% blocked isocyanate aqueous solution and 0.8 parts of water were used.

(Example 19)
In the protective layer composition of Example 18, 15 parts of a 20% aqueous cationic colloidal silica dispersion was added to a 30% aqueous large particle size cationic colloidal silica aqueous dispersion (Snowtex AK-YL, manufactured by Nissan Chemical Industries, Ltd .; (80 nm) A thermosensitive recording material was obtained in the same manner as in Example 18, except that 10 parts and 5 parts of water were used.

(Comparative Example 1)
A thermosensitive recording material was obtained in the same manner as in Example 1, except that 15 parts of the aqueous dispersion of 20% cationic colloidal silica was replaced with 15 parts of the dispersion E in the formulation of the protective layer in Example 1.

(Comparative Example 2)
A thermosensitive recording material was obtained in the same manner as in Example 1, except that 15 parts of an aqueous dispersion of 20% cationic colloidal silica was replaced with 15 parts of water in the formulation of the protective layer in Example 1.

(Comparative Example 3)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the formulation of the protective layer in Example 1, 20 parts of a 10% aqueous solution of chitosan was replaced with 20 parts of a 10% aqueous solution of completely saponified polyvinyl alcohol.

(Comparative Example 4)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 3.2 parts of a 25% aqueous glyoxal solution was replaced with 3.2 parts of water in the formulation of the protective layer in Example 1.

(Comparative Example 5)
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that in the protective layer composition of Example 1, 20 parts of a 10% aqueous chitosan solution was replaced with 10 parts of a 20% anionic acrylic emulsion (OM1050, manufactured by Mitsui Chemicals, Inc.) and 10 parts of water. Got.

(Comparative Example 6)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that no protective layer was provided.

  The liquid properties of the protective layer coating liquids prepared in Examples 1 to 18 and Comparative Examples 1 to 6 were evaluated, and the obtained heat-sensitive recording materials were subjected to the following tests. The test results are shown in Table 1. .

(1) Coating Liquid Property The liquid property of the produced protective layer coating liquid over time was evaluated. The evaluation was based on the following indicators.
A: There was no gelation or agglomeration in the coating liquid, and coating could be performed without any problem.
：: Coating was possible, but the coating liquid was slightly thickened or slightly aggregated.
Δ: Coating was possible, but viscosity increase or aggregation was observed in the coating liquid.
×: The coating liquid was so thickened or agglomerated that coating was impossible.

(2) Printing sensitivity The obtained thermosensitive recording material was printed using a facsimile tester TH-PMD manufactured by Okura Electric. Using a thermal head having a dot density of 8 dots / mm and a head resistance of 1681Ω, current was supplied at a head voltage of 23 V and a print pulse width of 1.0 millisecond. The optical density was measured with a Macbeth RD-918 reflection densitometer. In the five-step evaluation, the larger the numerical value was, the better the printing sensitivity was, and 3 or more was judged to be a practical level.

(3) Plasticizer resistance The heat-sensitive recording material printed under the conditions of (2) was brought into close contact with a commercially available soft vinyl chloride film and a color-developing surface, and was allowed to stand in a high-temperature layer at 40 ° C. and 90% for 2 days. The concentration was measured comparatively. The evaluation was based on the following indicators.
A: Almost no change in the density of the printed portion occurs after the test.
：: After the test, the density of the printed portion slightly decreases.
B: After the test, the density of the printed portion is significantly reduced.
×: Almost no printed portion remains after the test.

(4) Water resistance 5 ml of water is dropped on the thermosensitive recording material printed under the condition of (2) and rubbed with a finger for 10 seconds. The evaluation was based on the following indicators.
A: The protective layer hardly changed, and the printed portion did not change.
：: The protective layer was slightly peeled off, but the printed portion was hardly changed.
Δ: The protective layer was peeled off, but the printed portion was hardly changed.
×: The protective layer was completely peeled off, and the printed portion was also peeled off.

(5) Pencil Writability Characters were written on the obtained heat-sensitive recording material with a pencil, and the pencil writability was evaluated. The evaluation was based on the following indicators.
：: Characters can be written without any problem and the characters are clear.
：: Characters can be written, but lack sharpness.
Δ: The letters are thin.
×: The written character is difficult to confirm.

(6) Imprintability The ink was stamped using a dye ink X stamper manufactured by Shachihata Kogyo Co., Ltd., and after 10 seconds, wiped off with a dry cloth to evaluate the survivability of the imprinted characters. The evaluation was based on the following indicators.
A: Most of the stamped characters remain.
：: Although slightly thin, the stamped characters can be clearly recognized.
Δ: The stamped characters are faint but can be recognized.
X: The stamped character cannot be recognized.

(7) Whiteness The obtained heat-sensitive recording material was left under an atmosphere of 60 degrees for one week, and the whiteness was measured for comparison. The evaluation was based on the following indicators.
A: There is almost no change in whiteness before processing.
：: The degree of whiteness is reduced to such an extent that it cannot be recognized by the naked eye.
Δ: Whiteness is reduced to such an extent that it can be judged with the naked eye.

  As is clear from Table 1, as compared with Example 1 using chitosan, Comparative Examples 3 and 5 are inferior in water resistance. In particular, Comparative Example 5 using an anionic acrylic emulsion has a coating liquid property. Poor water resistance and plasticizer resistance. In addition, in comparison between Example 1 using colloidal silica, Comparative Example 1 and Comparative Example 2, Comparative Example 1 was inferior in coating liquid properties and plasticizer resistance, and Comparative Example 2 was plasticizer resistance. Pencil writing and sealability were poor.

  Furthermore, from the comparison of Examples 1 to 7 and Comparative Example 4, glyoxal was most effective for improving the water resistance, and the whiteness was superior when using polyacrylamide epichlorohydrin and block diisocyanate. Further, the use of polyacrylamide epichlorohydrin improved the sealability.

  Furthermore, from the comparison of Examples 1 to 3 and Examples 4 to 6, it is possible to achieve both water resistance and printability by using glyoxal and polyacrylamide epichlorohydrin as the crosslinking agent, and to use glyoxal and block isocyanate together. Thus, both water resistance and whiteness could be achieved, and whiteness and printability could be improved by using polyacrylamide epichlorohydrin in combination with blocked isocyanate.

  Furthermore, from the comparison between Example 1 and Example 10, by using cationic colloidal silica as the colloidal silica, a coating solution free from gelation and agglomeration can be prepared, and the obtained heat-sensitive recording material also has a plasticizer resistance. Are better.

  Furthermore, from the comparison of Example 1, Example 8, and Example 9, 8: 2 in which the mass blending ratio of polyvinyl alcohol and chitosan is in the range of 7: 3 to 9: 1 indicates that the coating liquid property and the water resistance are high. When the ratio is 6: 4, the water resistance is improved, but the viscosity of the solution is slightly increased. When the ratio is 9.5: 0.5, the water resistance, pencil writing property, and printing property are lower than those in Example 1.

  Furthermore, from the comparison between Example 1 and Examples 11 to 15, polyvinyl alcohol has better water resistance of fully saponified polyvinyl alcohol than partially saponified polyvinyl alcohol, and further has silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, and diacetone-modified. The use of at least one of polyvinyl alcohol and acetoacetyl-modified polyvinyl alcohol can further improve the water resistance.

  Furthermore, from the comparison between Example 1 and Example 17, the addition of the nonionic acrylic emulsion improves the water resistance and the printability.

Furthermore, by comparing Example 1 and Example 16 and Example 18 and Example 19, by increasing the average particle size of the colloidal silica, the sealability and the pencil writing property are improved.

Claims (7)

  In a heat-sensitive recording material in which a heat-sensitive coloring layer colored by heat on a support and a protective layer provided on the heat-sensitive coloring layer, the protection layer contains polyvinyl alcohol, chitosan, a crosslinking agent, and a pigment, and A heat-sensitive recording material using colloidal silica.   2. The heat-sensitive recording material according to claim 1, wherein at least one crosslinking agent selected from the group consisting of an aldehyde compound, a compound having an epichlorohydrin residue and an isocyanate compound is used as the crosslinking agent.   3. The heat-sensitive recording material according to claim 2, wherein a compound having an aldehyde compound and an epichlorohydrin residue, a compound having an aldehyde compound and an isocyanate compound, or a compound having an epichlorohydrin residue and an isocyanate compound are used in combination as the crosslinking agent.   The heat-sensitive recording material according to any one of claims 1 to 3, wherein cationic colloidal silica is used as the colloidal silica.   The thermosensitive recording material according to any one of claims 1 to 4, wherein the mass ratio of the solid content of the polyvinyl alcohol and the chitosan is from 7: 3 to 9: 1.   The polyvinyl alcohol contains at least one polyvinyl alcohol selected from unmodified polyvinyl alcohol having a saponification degree of 95% or more, silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol. The heat-sensitive recording material according to any one of claims 1 to 5, wherein The heat-sensitive recording material according to any one of claims 1 to 6, wherein the protective layer contains a nonionic or cationic water-dispersible binder.