JP2005262549A - Heat-sensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material which is excellent in thermal responding property, image preserving property and water-resistance, and excellent in the seal fixing property for a stamp, a seal or the like. <P>SOLUTION: For this heat-sensitive recording material, on a supporting body, a heat-sensitive coloring layer which develops a color by heat, and a protective layer on the top of the heat-sensitive coloring layer are provided. In the heat-sensitive recording material, the protecting layer contains a polyvinyl alcohol based resin, a chitosan, a crosslinking agent, and an inorganic pigment. As the inorganic pigment in the protective layer, a silica of which the average particle size is 1 to 10 μm is used, and the content of the inorganic pigment in the protective layer is made 30 to 60 mass% of the total solid portion in the protective layer. Preferably, a nonionic or cationic water dispersing binder is contained in the protective layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material in which a heat-sensitive recording layer that is colored by heat on a support and a protective layer are sequentially provided, and particularly excellent in heat responsiveness, image storability, and water resistance, and has stamp fixing properties such as stamps and stamps. The present invention relates to a good thermal recording material.

  The heat-sensitive recording material generally comprises a heat-sensitive recording layer mainly comprising an electron-donating usually colorless or light-colored dye precursor and an electron-accepting color developer on a support, a thermal head, By heating with a thermal pen, laser light, etc., the dye precursor and the developer react instantaneously to obtain a recorded image (see, for example, Patent Document 1 or 2). Such a heat-sensitive recording material has advantages such that recording can be obtained with a relatively simple device, maintenance is easy, noise is not generated, measurement recorder, facsimile, printer, computer terminal, It is used in a wide range of fields such as labels and ticket vending machines.

  In recent years, in particular, thermal recording on financial records such as receipts for gas, water, electricity bills, ATM usage statements for financial institutions, various receipts, thermal recording labels or thermal recording tags for POS systems, etc. Materials are being used.

  In this way, there is a possibility of coming into contact with various chemicals as the use and demand of heat-sensitive recording materials expands widely. For example, office supplies such as water-based ink, oil-based ink, highlighter pen, vermilion, adhesive, diazo developer Alternatively, chemical resistance to cosmetics such as hand creams, hair tonics, and emulsions, and plasticizer resistance contained in polyvinyl chloride films and synthetic leather have been demanded.

  Therefore, for the heat-sensitive recording material, for the purpose of improving the storability of the recorded image, there is a method of forming a water-resistant, chemical-resistant protective layer that prevents penetration of water, oil, plasticizer, etc. on the heat-sensitive recording layer. It has been proposed (see, for example, Patent Document 3, 4 or 5).

  On the other hand, the above-mentioned meter-reading paper and various receipts have many opportunities to be stamped and stamped, and in addition to the imprinted image not smearing, the image may smear even if the finger is rubbed after marking. The heat-sensitive recording material is required to prevent ink from adhering to the finger. However, when a protective layer is provided, the heat-sensitive recording layer is protected from water and chemicals from the outside, but non-drying ink acceptability and absorbability such as vermilion, water-based stamp, oil-based stamp, and so-called imprint fixing property are deteriorated. Had the disadvantages.

For the purpose of improving the sealability of the thermal recording material, protective layers having various structures have been proposed (see, for example, Patent Document 6 or 7). However, even if these methods are used, a heat-sensitive recording material that still has a printing fixability and good recording image storage stability such as chemical resistance has not yet been obtained.
Japanese Patent Publication No.43-4160 Japanese Examined Patent Publication No. 45-14039 JP-A-48-51644 Japanese Patent Laid-Open No. 54-3549 Japanese Patent Laid-Open No. 5-572 Japanese Patent Laid-Open No. 7-257029 JP 2000-289333 A

  The present invention relates to a heat-sensitive recording material, and an object thereof is to provide a heat-sensitive recording material having good thermal responsiveness, image storage stability, water resistance, stamp fixing properties such as stamps and stamps.

  As a result of intensive studies to solve the above problems, the present inventors have found that the problem can be solved as follows.

  (1) A heat-sensitive color-developing layer that is colored by heat on a support and a heat-sensitive recording material in which a protective layer is provided on the heat-sensitive color-developing layer, the protective layer containing a polyvinyl alcohol resin, chitosan, a crosslinking agent, and an inorganic pigment And the average particle diameter of this inorganic pigment is 1-10 micrometers, The content rate of the inorganic pigment in this protective layer is 30-60 mass% with respect to the total solid in this protective layer, It is characterized by the above-mentioned. Thermal recording material.

  (2) The heat-sensitive recording material according to (1), wherein the inorganic pigment contained in the protective layer is silica.

  (3) As the polyvinyl alcohol, 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 (1) or (2), which is contained.

  (4) The heat-sensitive recording material according to any one of (1) to (3), wherein the protective layer contains a water-dispersible binder.

  (5) The heat-sensitive recording material according to (4), wherein the water-dispersible binder is a nonionic or cationic water-dispersible binder.

  In the heat-sensitive recording material of the present invention, polyvinyl alcohol, chitosan, a crosslinking agent, and silica having an average particle diameter of 1 to 10 μm are used for the protective layer, and the content of silica in the protective layer is determined based on the total solid content in the protective layer. By adjusting the content to 30 to 60% by mass, the heat-sensitive recording material having both excellent water resistance and solvent resistance and good stamping ability could be obtained. 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. In addition, water resistance and sealability can be improved by adding a nonionic acrylic emulsion.

  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 in the present invention is one in which at least one protective layer comprising polyvinyl alcohol, chitosan, a pigment, and a crosslinking agent is provided on a heat-sensitive recording layer.

  As the polyvinyl alcohol used in the protective layer of the present invention, in addition to 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, ethylene, vinyl ether having a long chain alkyl group, modified polyvinyl alcohol copolymerized with (meth) acrylamide and the like can also be used.

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

  The degree of polymerization of polyvinyl alcohol used in the present invention is not particularly limited, but is usually selected from the range of 100 to 3,000, and the degree of saponification 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, 50% or more of the acetylamino group of chitin is modified to an amino group by deacetylation, more preferably 90% or more. In use, some or all of the amino groups are converted to ammonium groups with acid before use. As the acid, acetic acid, lactic acid, triphosphoric acid, 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 compatibility with polyvinyl alcohol or the like, a low molecular weight chitosan having a viscosity of 1 to 70 centipoise in a 1% mass aqueous solution at 20 ° C. by a BL type viscometer is preferable. Further, the low molecular weight chitosan has a problem that it is colored yellow to brown over time. In that case, stabilized chitosan as disclosed in JP-A-63-72702 may be used.

  Moreover, the solid content mass blending ratio of polyvinyl alcohol and chitosan is 5: 5 to 9.7: 0.3, preferably 7: 3 to 9: 1. If the amount of chitosan is too small, the water resistance is lowered. If the amount is too large, thickening of the coating liquid and coloration with time of the obtained heat-sensitive recording material tends to be a problem.

  As the binder used in the present invention, a water-dispersible binder can be added in addition to polyvinyl alcohol and chitosan. By adding a water-dispersible binder, affinity with oil-based inks can be improved, and printability and sealability can be improved. Water dispersible binders are generally styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, methyl acrylate / butadiene copolymers, acrylonitrile / butadiene / styrene terpolymers, polyvinyl acetate, vinyl acetate / Examples include acrylic acid ester copolymers, ethylene / vinyl acetate copolymers, polyacrylic acid ester copolymers, styrene / acrylic acid ester copolymers, and polyurethanes. Refers to a functional resin. An acrylic ester resin is particularly preferable from the viewpoint of printability. The water-dispersible binder is preferably a nonionic or cationic water-dispersible binder because chitosan is cationic. 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 in the protective layer, and particularly good solvent resistance and oil-based ink affinity can be obtained within this range.

  The crosslinking agent used in the present invention is an aldehyde compound, a urea resin, a melamine resin, a methylol compound such as a phenol resin, a compound containing an epichlorohydrin residue represented by a polyamide epichlorohydrin resin, an epoxy compound such as a polyfunctional epoxy resin, an isocyanate, etc. Compounds, isocyanate compounds such as blocked isocyanate compounds, and oxidizing agents such as persulfates and peroxides. Among these, glyoxal is superior not only in the manifestation of its effect but also in the supply amount and price. Moreover, the preferable addition amount of the crosslinking agent to the protective layer of this invention is the range of this crosslinking agent 0.1-20 mass% with respect to the sum total of solid content mass of polyvinyl alcohol and chitosan. This range is particularly preferable from the viewpoint of stability of water resistance, oil resistance, printing sensitivity, and recording runnability.

  The inorganic pigment used for the protective layer of the heat-sensitive recording material of the present invention is preferably an inorganic pigment having a volume average particle diameter of 1 to 10 μm measured by a light scattering method.

  Inorganic pigments having an average particle diameter of 1 to 10 μm increase the voids between the particles in the protective layer, making it easier to retain the stamped ink. Therefore, by containing such an inorganic pigment in an amount of 30 to 60% by mass, preferably 32% to 50% by mass, based on the total solid content in the protective layer, the image is preserved while maintaining image preservability by the protective layer. It is possible to significantly improve non-drying ink acceptability, absorbability, so-called imprint fixing properties such as water-based stamps and oil-based stamps. Immediately after imprinting with the stamp, rubbing the imprinted part with a finger or the like, The problem that the stamp ink adheres to the finger can be solved.

  The average particle size of the inorganic pigment of the present invention was determined by dispersing a 20% by mass suspension of the pigment at 5000 rpm for 5 minutes using an ace homogenizer AM-11 (manufactured by Nippon Seiki Seisakusho), and then MICROTRAC HRA 9320-x100. It is shown by the volume average particle diameter measured using (LEEDS & NORTHHRUP).

  If the average particle size of the inorganic pigment contained in the protective layer is smaller than 1 μm, sufficient imprint fixing ability cannot be obtained. On the other hand, if it is larger than 10 μm, the thermal responsiveness of the heat-sensitive recording material is lowered, and sufficient color development sensitivity cannot be obtained.

  Examples of the inorganic pigment having an average particle diameter of 1 to 10 μm include Mizukasil P527 (average particle diameter: 3 μm, manufactured by Mizusawa Chemical Co., Ltd.), Cyloid 74 × 6500 (average particle diameter: 6 μm, manufactured by GRACE), Carplex 101M (average particle diameter: Silica such as 8 μm manufactured by Shionogi Pharmaceutical Co., Ltd., and aluminum hydroxide such as Heidilite H42 (average particle size: 1 μm, Showa Denko) and Heidilite H32 (average particle size: 8 μm, manufactured by Showa Denko) can be used. Is not to be done.

  The inorganic pigments contained in the protective layer can be used in combination of two or more as long as the average particle diameter after mixing is 1 to 10 μm.

  In the case where the inorganic pigment contained in the protective layer is silica, it is particularly preferable because the seal fixing property is greatly improved.

  By including 30-60% by mass of an inorganic pigment having an average particle diameter of 1-10 μm with respect to the total solid content in the protective layer, the image fixing property is improved while maintaining the image storage stability of the protective layer. It becomes possible to make it. When the content of the inorganic pigment is less than 30% by mass with respect to the total solid content of the protective layer, sufficient imprint fixing ability cannot be obtained. On the other hand, when the amount is more than 60% by mass, the thermal responsiveness and the image storage stability are greatly lowered.

  For the purpose of improving recording running properties such as head wear prevention and sticking prevention, the protective layer has higher fatty acid metal salts such as zinc stearate and calcium stearate, higher fatty acid amides such as stearamide, paraffin, polyethylene wax, polyethylene oxide, A lubricant such as castor wax is added as necessary.

Ze'inuinurikoryou protective layer in the present invention is preferably in the range of ^{0.5~5g / m 2, 1~3g / m} 2 is particularly preferred. By setting it within this range, the image storage stability and the seal fixing property are excellent, and a good thermal response can be obtained.

  The electron-donating normally colorless or light-colored dye precursor constituting the heat-sensitive recording layer of the heat-sensitive recording material of the present invention is typically represented by pressure-sensitive recording materials or those used in heat-sensitive recording materials. It is not particularly limited.

As an example of a specific dye precursor,
(1) Triarylmethane compounds: 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, etc.

  (2) Diphenylmethane compounds: 4,4′-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucooramine, N-2,4,5-trichlorophenylleucooramine, etc.

  (3) Xanthene compounds: Rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino- 7-phenylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3-dibutyl Amino-7- (2-chloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- Anilinofluorane, 3-dipentylamino-6-methyl- -Anilinofluorane, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N- Ethyl-N-tolyl) amino-6-methyl-7-phenethylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- ( N-methyl-N-propyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N- Methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluorane, - 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-methylspirodinaphthopyrans, 3-ethylspirodinaphthopyrans, 3,3'-dichlorospirodinaphthopyrans, 3-benzylspirodinaphthopyrans, 3-methylnaphtholopyrans (3-methoxy) Benzo) spiropyran, 3-propyl spirobenzopyran and the like. These dye precursors can be used alone or in admixture of two or more as required.

  The electron-accepting compound used in the heat-sensitive recording material of the present invention is typically represented by a pressure-sensitive recording material or an acidic substance used in a heat-sensitive recording material, but is not limited thereto. Examples thereof include phenol derivatives, aromatic carboxylic acid derivatives, N, N′-diallylthiourea derivatives, allylsulfonylurea derivatives, polyvalent metal salts such as zinc salts of organic compounds, benzenesulfonamide derivatives, and the like.

  Examples of such an electron-accepting compound include the following compounds, but are not limited to these, and may be used alone or in combination of two or more as necessary. Can be used.

  4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-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-dihydro Sidiphenylsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, 3,4,4'-trihydroxydiphenylsulfone, 3,4,3 ', 4'-tetrahydroxydiphenylsulfone, 2,3,4 Trihydroxydiphenylsulfone, 3-phenylsulfonyl-4-hydroxydiphenylsulfone, 2,4-bis (phenylsulfonyl) phenol,

  4-phenylphenol, 4-hydroxyacetophenone, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) pentane, 1,1-bis (4-hydroxyphenyl) hexane, , 1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) hexane, 1,1-bis (4-hydroxyphenyl)- 2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,3-di- [2- (4 -Hydroxyphenyl) -2-propyl] benzene, 1,3-di- [2- (3,4-dihydroxyphenyl) -2-propyl] benzene Zen, 1,4-di- [2- (4-hydroxyphenyl) -2-propyl] benzene, 4,4′-hydroxydiphenyl ether, 3,3′-dichloro-4,4′-hydroxydiphenyl sulfide, bis ( 2-hydroxynaphthyl) methane,

  Methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis (4-hydroxyphenyl) butyl acetate, 4,4'-thiobis (2-tert-butyl-5-methylphenol). Dimethyl 4-hydroxyphthalate, benzyl 4-hydroxybenzoate, methyl 4-hydroxybenzoate, benzyl gallate, stearyl gallate, pentaerythritol tetra (4-hydroxybenzoic acid) ester, pentaerythritol tri (4-hydroxybenzoic acid) ) Ester, dehydration condensate of 2,2-bis (hydroxymethyl) -1,3-propanediol polycondensate and 4-hydroxybenzoic acid,

  N, N′-diphenylthiourea, 4,4′-bis [3- (4-methylphenylsulfonyl) ureido] diphenylmethane, N- (4-methylphenylsulfonyl) -N′-phenylurea, N- (benzenesulfonyl) ) -N '-[3- (4-toluenesulfonyloxyphenyl)] urea, N- (4-toluenesulfonyl) -N'-[3- (4-toluenesulfonyloxyphenyl)] urea,

  Salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4- [2 ′-(4-methoxyphenoxy) ethyloxy] salicylic acid, 3- (octyloxycarbonylamino) salicylic acid or metal salts of these salicylic acid derivatives,

  N- (4-hydroxyphenyl) -4-toluenesulfonamide, N- (2-hydroxyphenyl) -4-toluenesulfonamide, N-phenyl-4-hydroxybenzenesulfonamide and the like.

  The heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention can contain a heat-fusible substance in order to improve its 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 particularly preferably used.

  Specifically, stearic acid amide, N-hydroxymethyl stearic acid amide, N-stearyl stearic acid amide, ethylene bis stearic acid amide, N-stearyl urea, benzyl-2-naphthyl ether, m-terphenyl, 4-benzyl Biphenyl, 2,2′-bis (4-methoxyphenoxy) diethyl ether, α, α′-diphenoxyxylene, bis (4-methoxyphenyl) ether, diphenyl adipate, dibenzyl oxalate, di (4-methylbenzyl ester) ), Di (4-chlorobenzyl) ester oxalate, dimethyl terephthalate, dibenzyl terephthalate, benzenesulfonic acid phenyl ester, bis (4-allyloxyphenyl) sulfone, 1,2-di (3-methylphenoxy) ethane, 1 , 2-diphenoxyethane, - acetyl acetophenone, acetoacetic anilides, fatty acid anilides, and the like known heat-fusible substances. These compounds can be used alone or in combination of two or more. Further, in order to obtain sufficient thermal responsiveness, it is preferable that the heat fusible substance occupies 5 to 50% by mass in the total solid content of the thermosensitive recording layer.

  The heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention can be obtained by mixing each aqueous dispersion obtained by finely pulverizing each color forming component and a resin, and coating and drying on a support.

  As the resin used for the heat-sensitive recording layer, various resins used in normal coating can be used.

  Specifically, starches, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic 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 resin such as alkali salt of maleic anhydride copolymer, and styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene Polymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate ester, styrene / acrylate copolymer, Examples include, but are not limited to, water dispersible resins such as polyurethane.

  For the heat-sensitive recording layer, 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 are used as pigments. Inorganic pigments such as zinc sulfate, amorphous silica, amorphous calcium silicate, colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, and nylon powder can be used.

For heat-sensitive recording layers, higher fatty acid metal salts such as zinc stearate and calcium stearate, higher fatty acid amides such as stearic acid amide, lubricants such as paraffin, polyethylene wax, polyethylene oxide, and caster wax, and the purpose of improving light resistance, Surfactants including anionic and nonionic high molecular weights as UV absorbers such as benzophenone and benzotriazole, dispersing and wetting agents, fluorescent dyes, antifoaming agents, etc. are added as necessary. The The coating amount of the heat-sensitive recording layer is usually preferably 0.1 to 2.0 g / m ^{2 in} terms of the coating amount of the dye precursor.

  As the support used in the present invention, paper is mainly used, but in addition to paper, various woven fabrics, non-woven fabrics, synthetic resin films, synthetic resin laminated papers, synthetic papers, metal foils, vapor-deposited sheets, or bonding them together The composite sheet combined in (1) can be arbitrarily used depending on the purpose.

In the heat-sensitive recording material of the present invention, if necessary, one or more undercoat layers made of a single layer or a plurality of layers of pigment, resin, or the like can be provided between the support and the heat-sensitive recording layer. When the heat-sensitive recording material of the present invention is provided with a undercoat layer, Ze'inuinurikoryou the undercoat layer is preferably ^{1~30g / m 2, 3~20g / m} 2 is more preferable.

  In general, calcined kaolin is used as a pigment for the undercoat layer, but diatomaceous earth, talc, kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, and hydroxide are also used. 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 can be used.

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

  The formation method of a protective layer, a heat-sensitive recording layer, or an undercoat layer is not specifically limited, It can form according to a conventionally well-known technique. Specific examples include air knife coating, rod blade coating, bar coating, blade coating, gravure coating, curtain coating, E-bar coating, and other methods. A recording layer, protective layer or undercoat layer can be formed. In addition, each layer may be formed by various printing machines or the like using a system such as a lithographic plate, a relief plate, a flexo, a gravure, a screen, and a hot melt.

  If necessary, after applying the undercoat layer, after applying the heat-sensitive recording layer, or after applying the protective layer, supercalender treatment can be performed to improve the image quality.

  EXAMPLES The present invention will be described below 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 coating solution for undercoat layer)
Baked kaolin [trade name: Ansilex, oil absorption 90 ml / 100 g, manufactured by Engelhard, Inc.] 100 parts, a composition comprising 24 parts of a 50% solid content styrene / butacene latex and 200 parts of water was mixed and stirred. A coating solution for the coating layer was obtained.

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

(Dispersion A)
Disperse 200 g of 3- (N, N-dibutylamino) -6-methyl-7-anilinofluorane in a mixture of 200 g of a 10% aqueous polyvinyl alcohol solution and 600 g of water, and pulverize with a bead mill until the average particle size becomes 1 μm. did.

(Dispersion B)
400 g of 4-hydroxy-4'-isopropoxydiphenylsulfone was dispersed in a mixture of 400 g of a 10% polyvinyl alcohol aqueous solution and 200 g of water, and pulverized with a bead mill until the average particle size became 1 μm.

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

(Dispersion D)
200 g of calcium carbonate was dispersed in 800 g of a 0.5% sodium polyacrylate aqueous solution 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 the mixture was further stirred to prepare a 10% chitosan aqueous solution.

(Example 1)
<Thermal recording layer>
Using the dispersion liquids A to D, the respective materials were mixed in the proportions shown below, and sufficiently stirred to prepare a thermal recording layer coating solution.
Dispersion A 20 parts Dispersion B 15 parts Dispersion C 30 parts Dispersion D 25 parts 10% polyvinyl alcohol aqueous solution 30 parts Water 30 parts

<Dispersion 1>
200 g of Mizukasil P527 (average particle size: 3 μm, silica manufactured by Mizusawa Chemical Industry) was dispersed in 800 g of a 0.2% sodium polyacrylate aqueous solution and stirred for 5 minutes with a homogenizer to obtain dispersion 1.

<Protective layer>
Using the above dispersion liquid, the respective materials were mixed in the proportions shown below, added water was added so that the solid dispersion concentration was 10%, and the mixture was sufficiently stirred to prepare a protective layer coating liquid.

Dispersion 1 40 parts 10% fully saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 4 parts 40% zinc stearate aqueous solution 2 parts water 80 parts

On one side of high-quality neutral paper with a basis weight of 50 g / m ² , the solid coating amount of the undercoat layer coating liquid is 9 g / m ² , and the solid coating amount of the thermal recording layer coating liquid is the dye precursor. The undercoat layer, the heat-sensitive recording layer, and the protective layer are sequentially coated and dried so that the coating amount is 0.5 g / m ² and the solid coating amount of the coating liquid for the protective layer is 1.5 g / m ^2. A heat-sensitive recording material was produced by calendering.

(Example 2)
A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, the mixing ratio of each dispersion was changed as follows to prepare a protective layer coating liquid.

Dispersion 1 30 parts 10% completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 4 parts 40% zinc stearate aqueous solution 2 parts water 80 parts

(Example 3)
A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, the mixing ratio of each dispersion was changed as follows to prepare a protective layer coating liquid.

Dispersion 1 80 parts 10% completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 4 parts 40% zinc stearate aqueous solution 2 parts water 80 parts

Example 4
<Dispersion 2>
200 g of thyroid 74 × 6500 (average particle size: 6 μm GRACE silica) was dispersed in 800 g of 0.2% sodium polyacrylate aqueous solution and stirred for 5 minutes with a homogenizer to obtain dispersion 2.

  A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, Dispersion 2 was used instead of Dispersion 1.

(Example 5)
<Dispersion 3>
200 g of Heidilite H42 (average particle size: 1 μm, aluminum hydroxide manufactured by Showa Denko) was dispersed in 800 g of 0.2% sodium polyacrylate aqueous solution and stirred for 5 minutes with a homogenizer to obtain dispersion 3.

  A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, Dispersion 3 was used instead of Dispersion 1.

(Example 6)
<Dispersion 4>
200 g of Heidilite H32 (average particle size: 8 μm Showa Denko Aluminum Hydroxide) was dispersed in 800 g of 0.2% sodium polyacrylate aqueous solution and stirred with a homogenizer for 5 minutes to obtain dispersion 4.

  A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, dispersion 4 was used instead of dispersion 1.

(Example 7)
In the protective layer formulation of Example 1, 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 (manufactured by Kuraray Co., Ltd., PVA-217, saponification degree 88%). A thermosensitive recording material was obtained in the same manner as in Example 1.

(Example 8)
In the protective layer formulation of Example 1, thermal recording was performed in the same manner as in Example 1 except that 80 parts of a 10% fully 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.). Obtained material.

Example 9
In the protective layer formulation of Example 1, 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 (manufactured by Denki Kagaku Kogyo Co., Ltd., W100). A heat-sensitive recording material was obtained.

(Example 10)
In the protective layer formulation of Example 1, 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.). A heat-sensitive recording material was obtained.

(Example 11)
In the protective layer formulation of Example 1, 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 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Z200). Thus, a heat-sensitive recording material was obtained.

(Example 12)
In the protective layer formulation of Example 1, 80 parts of 10% fully saponified polyvinyl alcohol aqueous solution and 20 parts of 10% aqueous chitosan aqueous solution were replaced with 64 parts of 10% fully saponified polyvinyl alcohol aqueous solution, 16 parts of 10% aqueous chitosan aqueous solution and 30% nonionic acrylic. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of emulsion (Nishin Chemical Industry Co., Ltd., Vinibran 2865) were replaced.

(Example 13)
In the protective layer formulation of Example 7, 80 parts of 10% partially saponified polyvinyl alcohol aqueous solution and 20 parts of 10% aqueous chitosan aqueous solution were replaced with 64 parts of 10% partially saponified polyvinyl alcohol aqueous solution, 16 parts of 10% aqueous chitosan aqueous solution and 30% nonionic acrylic. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the emulsion was replaced with 6.7 parts of Nissin Chemical Industry Co., Ltd. (Vinibran 2865).

(Example 14)
In the protective layer formulation of Example 8, 80 parts of 10% silanol-modified polyvinyl alcohol aqueous solution and 20 parts of 10% chitosan aqueous solution were combined with 64 parts of 10% silanol-modified polyvinyl alcohol aqueous solution, 16 parts of 10% chitosan aqueous solution and 30% nonionic acrylic emulsion ( A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of Nishin Chemical Industry Co., Ltd., Viniblanc 2585) were replaced.

(Example 15)
In the protective layer formulation of Example 9, 80 parts of 10% epoxy-modified polyvinyl alcohol aqueous solution and 20 parts of 10% chitosan aqueous solution were combined with 64 parts of 10% epoxy-modified polyvinyl alcohol aqueous solution, 16 parts of 10% chitosan aqueous solution and 30% nonionic acrylic emulsion ( A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of Nishin Chemical Industry Co., Ltd., Viniblanc 2585) were replaced.

(Example 16)
In the protective layer formulation of Example 10, 80 parts of 10% diacetone-modified polyvinyl alcohol aqueous solution and 20 parts of 10% chitosan aqueous solution were combined with 64 parts of 10% diacetone-modified polyvinyl alcohol aqueous solution, 16 parts of 10% chitosan aqueous solution and 30% nonionic acrylic emulsion ( A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of Nishin Chemical Industry Co., Ltd., Viniblanc 2585) were replaced.

(Example 17)
In the protective layer formulation of Example 11, 80 parts of 10% acetoacetyl-modified polyvinyl alcohol aqueous solution and 20 parts of 10% chitosan aqueous solution were combined with 64 parts of 10% acetoacetyl-modified polyvinyl alcohol aqueous solution, 16 parts of 10% aqueous chitosan aqueous solution and 30% nonionic acrylic. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of emulsion (Nishin Chemical Industry Co., Ltd., Vinibran 2865) were replaced.

(Example 18)
In the protective layer formulation of Example 1, 80 parts of 10% fully saponified polyvinyl alcohol aqueous solution and 20 parts of 10% aqueous chitosan aqueous solution were replaced with 64 parts of 10% fully saponified polyvinyl alcohol aqueous solution, 16 parts of 10% aqueous chitosan aqueous solution and 30% cationic acrylic. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.7 parts of emulsion (Nishin Chemical Industry Co., Ltd., Vinibran 2647) was replaced.

(Comparative Example 1)
In the protective layer formulation of Example 1, in place of Dispersion 1, Snowtex MP4540 aqueous dispersion (average particle size: 0.5 μm, anionic colloidal silica manufactured by Nissan Chemical Industries, Ltd.) was used. A heat-sensitive recording material was obtained.

(Comparative Example 2)
<Dispersion 5>
Mizukasil P78D (average particle size: 15 μm, manufactured by Mizusawa Chemical Industries, Ltd.) was dispersed in 800 g of 0.2% sodium polyacrylate aqueous solution and stirred for 5 minutes with a homogenizer to obtain Dispersion 5.

  A thermosensitive recording material was obtained in the same manner as in Example 1 except that the dispersion 1 was replaced with the dispersion 5 in the protective layer formulation of Example 1.

(Comparative Example 3)
A thermosensitive recording material was produced in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, the protective layer coating liquid was prepared by changing the mixing ratio of each dispersion as follows.

Dispersion 1 20 parts 10% completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 4 parts 40% zinc stearate aqueous solution 2 parts water 80 parts

(Comparative Example 4)
A thermosensitive recording material was produced in the same manner as in Example 1 except that in the preparation of the protective layer coating liquid of Example 1, the protective layer coating liquid was prepared by changing the mixing ratio of each dispersion as follows.

Dispersion 1 120 parts 10% completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., PVA-117)
80 parts 10% chitosan aqueous solution 20 parts 25% glyoxal aqueous solution 4 parts 40% zinc stearate aqueous solution 2 parts water 80 parts

(Comparative Example 5)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 20 parts of 10% chitosan aqueous solution was replaced with 20 parts of 10% fully saponified polyvinyl alcohol aqueous solution in the protective layer formulation of Example 1.

(Comparative Example 6)
The heat-sensitive recording material was the same as in Example 1 except that 20 parts of 10% chitosan aqueous solution was replaced with 10 parts of 20% anionic acrylic emulsion (Mitsui Chemicals, OM1050) and 10 parts of water in the protective layer formulation of Example 1. Got.

(Comparative Example 7)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 4 parts of the 25% aqueous glyoxal solution was replaced with 4 parts of water in the protective layer formulation of Example 1.

(Comparative Example 8)
A thermosensitive recording material was obtained 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% aqueous chitosan aqueous solution in the protective layer formulation of Example 1.

  The above Examples 1-18 and Comparative Examples 1-8 were used for the following test, and those test results are shown in Table 1.

(1) Thermal response The obtained thermosensitive recording material was printed using a facsimile testing machine TH-PMD manufactured by Okura Electric. A thermal head having a dot density of 8 dots / mm and a head resistance of 1681Ω was used, and energized with a head voltage of 21 V and a printing pulse width of 1.0 ms. The print density was measured with a Macbeth RD-918 reflection densitometer.

(2) Sealing Fixability Imprinting was performed using a dye-based ink X stamper manufactured by Sachihata Industry Co., Ltd., and wiped off with a dry cloth after 10 seconds, and the remaining properties of the stamped characters were evaluated. Evaluation was according to the following indicators.
A: Almost all stamped characters remain.
○: Although slightly thinned, the stamped characters can be clearly recognized.
Δ: The stamped characters are thin but can be recognized somehow.
X: The stamped character cannot be recognized.

(3) Water resistance 0.5 ml of water is dropped on a printed image printed with a pulse width of 1.0 msec used in the evaluation of thermal response, and is rubbed with a finger for 10 seconds. Evaluation was according to the following indicators.
(Double-circle): A protective layer hardly changes and a printing part does not change.
○: The protective layer is peeled off slightly, but the printed part is hardly changed.
(Triangle | delta): Although a protective layer peels, a printing part hardly changes.
X: The protective layer is completely peeled off, and the printed part is also peeled off.

(4) Plasticizer resistance The density after a soft PVC sheet was closely attached to a printed image printed with a pulse width of 1.0 msec used in the evaluation of thermal responsiveness and stored for 72 hours under room temperature conditions was Macbeth RD-918 type Measured with a reflection densitometer. Further, the remaining percentage% of the image area [(processed image area optical density / preprocess image area optical density) × 100] was determined from the image area optical density before and after the process. The greater the residual percentage, the better the plasticizer image storage stability.

  As can be seen from Table 1, Examples 1 to 18 have higher seal fixing properties than Comparative Examples 1 and 3. Also, compared with Comparative Example 2 or 4, the thermal response and the image area plasticizer resistance are high. This is because an inorganic pigment having an average particle diameter of 1 to 10 μm is contained in the protective layer in an amount of 30% by mass to 60% by mass with respect to the total solid content of the protective layer.

  Example 1 is higher in imprint fixing property than Example 5 or 6. This is because silica was used as the inorganic pigment.

  Example 1 has higher water resistance than Comparative Examples 5-8. This is because the protective layer contains polyvinyl alcohol, chitosan and a crosslinking agent.

  From comparison of Example 1 and Examples 7 to 11, polyvinyl alcohol has better water resistance of fully saponified polyvinyl alcohol than partially saponified polyvinyl alcohol, and further silanol-modified polyvinyl alcohol, epoxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol. When at least one of acetoacetyl-modified polyvinyl alcohol is used, the water resistance can be further improved.

  By comparing Example 1 and Examples 7 to 11 with Examples 12 to 18, the addition of nonionic and cationic acrylic emulsions improves water resistance and sealability.

Claims (5)

  In a heat-sensitive recording material in which a heat-sensitive color-developing layer that is colored by heat on a support and a protective layer is provided on the heat-sensitive color-developing layer, the protective layer contains polyvinyl alcohol, chitosan, a crosslinking agent, and an inorganic pigment. The average particle diameter of the inorganic pigment contained in the layer is 1 to 10 μm, and the content of the inorganic pigment in the protective layer is 30 to 60% by mass with respect to the total solid content in the protective layer. Characteristic thermal recording material.   2. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment contained in the protective layer is silica.   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 claim 1 or 2.   The heat-sensitive recording material according to any one of claims 1 to 3, wherein the protective layer contains a water-dispersible binder.   The heat-sensitive recording material according to claim 4, wherein the water-dispersible binder is a nonionic or cationic water-dispersible binder.