JP2010058467A - Thermosensitive recording body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording body with excellent coloring sensitivity, image quality, imprinting property, rubbing property, waterproof blocking property, and printability in general printing. <P>SOLUTION: The thermosensitive recording body is provided with a thermosensitive recording layer containing at least colorless or light-colored basic leuco dye and an electron acceptive developer as a coating layer on a support body, and further a protective layer on the thermosensitive recording layer. The thermosensitive recording layer contains a diphenylsulfone compound of specific structure as the electron acceptive developer, and its protective layer contains rice starch particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material that obtains a recorded image by utilizing a coloring reaction between a basic leuco dye and an electron-accepting developer.

  The heat-sensitive recording material is composed of a colorless or light-colored basic leuco dye (hereinafter referred to as “dye”) and an electron-accepting developer (hereinafter referred to as “developer”) such as a phenolic compound. After grinding and dispersing, the coating liquid obtained by mixing the two and adding a binder, filler, sensitivity improver, lubricant and other auxiliaries is used as a support for paper, synthetic paper, film, plastic, etc. A recorded image can be obtained by developing a color by an instantaneous chemical reaction by heating with a thermal head, a hot stamp, a thermal pen, a laser beam or the like. This thermal recording medium is widely used in facsimiles, computer terminal printers, automatic ticket vending machines, measuring recorders, etc., and for various tickets, receipts, labels, bank ATMs, gas It is also used for bills such as for electric meter reading and car betting tickets.

However, since the dye and the developer contained in the heat-sensitive recording layer are easily dissolved in various solvents, when the plasticizer contained in the ink (aqueous, oily) or adhesive comes into contact with the heat-sensitive recording material, Problems related to storage stability such as color development and color density decrease occur. Further, since a delivery slip sheet, an invoice, a receipt, and the like need to be stamped, an appropriate stamping property is required in addition to these storability.
Therefore, a heat-sensitive recording material (Patent Documents 1 and 2) provided with a protective layer containing an inorganic pigment and porous starch particles on the heat-sensitive recording layer, and a heat-sensitive material provided with a protective layer containing starch particles on the heat-sensitive recording layer. Recording materials (Patent Document 3) are used.

JP 2000-289333 A JP 2000-177243 A JP 03-190786

However, a heat-sensitive recording material (such as Patent Document 1) containing a highly oil-absorbing silica in a protective layer or a heat-sensitive recording material (such as Patent Document 2) containing porous starch particles can absorb and fix ink. Therefore, good stampability can be obtained, but since the binder is absorbed into silica and porous particles, it is difficult to obtain surface strength and coating layer strength, and general printability (hereinafter referred to as printability). ) Causes blanket contamination.
In addition, the heat-sensitive recording material (Patent Document 3) containing starch particles (particularly wheat starch) in the protective layer is improved in sealability and printability, but the color sensitivity and long-term storage after storage due to the influence of starch particles. New problems such as a decrease in color development sensitivity (reprintability), a decrease in water blocking resistance, and a scratching property arise.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material that has excellent color development sensitivity, and is excellent in imprintability, scratch resistance, printability, water blocking resistance, and reprintability.

The inventors of the present invention have examined the performance of the thermal recording material for the developer used in the thermal recording layer and the starch particles used in the protective layer. As a result, the specific developer contained in the thermal recording layer and the protective layer contain it. The present inventors have found that the above-mentioned problems can be achieved by the combination with rice starch particles, and have completed the present invention.
That is, the present invention provides a thermosensitive recording layer comprising a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and further a protective layer provided on the thermosensitive recording layer. And the heat-sensitive recording layer as an electron-accepting developer is represented by the following general formula (Formula 1):
(Wherein R ¹ represents a hydrogen atom or a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, and R ² and R ³ each independently represents an alkyl group or an alkenyl group. M and n each represents an integer of 0 to 2.), and the protective layer is a heat-sensitive recording material containing rice starch particles.

  According to the present invention, the diphenylsulfone compound represented by the general formula (Formula 1) is contained in the heat-sensitive recording layer provided on the heat-sensitive recording material, and the rice starch particles are contained in the protective layer provided on the heat-sensitive recording layer. Thus, it is possible to obtain a heat-sensitive recording material having sufficient color development sensitivity, good stamping properties, scratching properties, printability (blanket stains, ink fixing properties), and water blocking resistance.

Embodiments of the present invention will be described below.
The heat-sensitive recording material of the present invention has a heat-sensitive recording layer and a protective layer on a support, and this protective layer is provided in contact with the heat-sensitive recording layer. In addition to the heat-sensitive recording layer and the protective layer, the heat-sensitive recording material of the present invention may be provided with any coating layer normally provided on the heat-sensitive recording material. In particular, the heat-sensitive recording material of the present invention is preferably formed by laminating an under layer, a heat-sensitive recording layer, and a protective layer in this order as a coating layer on a support.

The protective layer of the present invention contains rice starch particles.
Starch has a particle shape when taken out from a plant, and its particle size and shape vary depending on the plant from which the starch is derived (see FIGS. 1 to 4).
The rice starch particles used in the present invention have an average particle diameter of 2 to 7 μm and a polygonal shape. Rice starch particles are corn-derived starch particles (corn starch), wheat-derived starch (wheat starch, shape: convex lens type), potato-derived starch (potato starch), sweet potato-derived starch (sweet potato starch, shape: bell-shaped) ) And starch derived from tapioca (tapioca starch, shape: hemispherical) and the like, the average particle size is small, and the shape is also unique (see FIGS. 1 to 4).

In general, starch gelatinizes when heated with water. When the starch is suspended in water and heated, the starch particles absorb water and gradually expand. When the heating is continued, the starch particles eventually disintegrate and change into a gel. This phenomenon is called gelatinization. Starch gelatinization occurs when water molecules enter the gaps between the starch molecules that have a crystalline structure, loosening the structure and spreading each branch into the water. During the gelatinization process, the starch particle suspension gradually becomes transparent from the cloudy state and rapidly increases in viscosity. When the particles absorb water to the maximum, the viscosity becomes maximum, and the viscosity decreases due to the collapse of the particles.
The gelatinization temperature of the rice starch particles is 63 to 65 ° C. Rice starch particles coexist with water and maintain the particle shape below this temperature. However, when heated above this temperature, the rice starch particles are no longer in particle shape and dissolve in water to form a gel.
In thermosensitive recording paper, starch may be used as a binder in order to increase the film strength of the coating layer. In this case, starch is gelatinized and used. When starch is used in this way, it is not possible to obtain the color developability and sealability of the coating layer, which is the object of the present invention.
Therefore, when preparing a coating containing rice starch particles, it is necessary to adjust the gelatinization temperature of the rice starch particles to below the gelatinization temperature, preferably 60 ° C. or less, more preferably 50 ° C. or less, more preferably 40 ° C. or less. .
In the present invention, the starch may be used in the form of particles as they are taken out from the plant (rice), and in some cases, treatments such as oxidation, etherification and esterification may be performed. The rice starch used in the present invention is different in shape and properties from porous starch particles (such as Patent Document 2) made porous by enzyme treatment.

The properties of the rice starch particles used in the present invention are shown below:
Average particle size: 2-7μm (by laser diffraction method)
Bulk density: 0.3 to 0.7 g / cm ³ (according to JIS Z8901)
Water absorption: 50-100% by weight (according to JIS K7209)
Refractive index: 1.62-1.65 (measured with Abbe refractometer after dissolving in hot water and forming into a film)
Amylopectin content after drying: 80% or more (by hot water extraction method)

  In addition, since the surface of the rice starch particles in the water-based paint swells with water, the function as a binder is expressed, so when the layer containing the rice starch particles is formed by coating and drying, the rice starch Particles adhere at points. For this reason, excellent surface strength or coating layer strength is expressed, and good printability (blanket stain) is expressed. In addition, the starch particles used in the present invention have a void amount present in the particles as compared with inorganic pigments and porous starches such as silica and calcium carbonate, which have been conventionally used for improving the sealability. Since the binder does not easily penetrate into the starch particles, a good surface strength or coating layer strength can be obtained.

Since the protective layer of the present invention contains rice starch particles and becomes softer than inorganic pigments such as silica and calcium carbonate, it is considered that good scratching properties are exhibited. In particular, the shape of the rice starch particles is a polygonal shape, so that the contact area becomes small, and it is considered that good scratching properties are developed.
A coating layer other than the protective layer may contain the rice starch particles.
The protective layer of the present invention can contain a binder, an ultraviolet absorber, a dispersant, an antifoaming agent, an antioxidant, a fluorescent dye, and the like as appropriate in addition to the rice starch particles.

The heat-sensitive recording layer of the present invention contains a dye and a developer, and contains a diphenylsulfone compound represented by the following general formula (Formula 1) as the developer.
Here, R ¹ represents a hydrogen atom or a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, preferably a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms. To express. Examples of the saturated hydrocarbon group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group, an isoamyl group, and the like. As the unsaturated hydrocarbon group, for example, Examples include ethylene, 1-n-propenyl, 2-n-propenyl, isopropenyl, 1-n-butene, 2-n-butene, 3-n-butene and the like.

  R2 and R3 each independently represents an alkyl group or an alkenyl group. Each of the alkyl group and the alkenyl group preferably has 1 to 4 carbon atoms, and more preferably 3 carbon atoms. As an alkenyl group, a vinyl group, an allyl group, and a butenyl group are mentioned, for example, An allyl group is preferable. m and n each represents an integer of 0 to 2, preferably 0 or 1.

  Specific examples of the diphenylsulfone compound represented by the general formula (Formula 1) include 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, bis (3-allyl- 4-hydroxyphenyl) sulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 4-hydroxy-4′-2-propylexidiphenylsulfone, 4-hydroxy-4′-1-propenyldiphenylsulfone, 4-hydroxy- Examples include 4′-ethoxydiphenyl sulfone, 4-hydroxy-4′-n-butoxy diphenyl sulfone, and 4,4′-dihydroxydiphenyl sulfone. Particularly, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, bis (3-allyl-4) from the viewpoint of color development sensitivity and combination with a protective layer containing rice starch. -Hydroxyphenyl) sulfone and 4-hydroxy-4'-allyloxydiphenylsulfone are preferred.

  The heat-sensitive recording layer of the present invention may contain a developer other than the diphenylsulfone compound. As such a developer, any known developer in the field of conventional pressure-sensitive or thermal recording paper can be used, and is not particularly limited. For example, activated clay, attapulgite, colloidal silica, silica Inorganic acidic substances such as aluminum, 4,4′-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4 '-Dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4 -Hydroxyphenylthioethoxy) methane, 1,5-di (4 Hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4 -Bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3) -Methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert-octylphenol), diphenylsulfone bridged compounds described in International Publication WO97 / 16420, and the like Phenolic compounds, phenolic described in International Publication No. WO02 / 081229 or JP2002-301873 Compound, phenol novolac type condensation composition described in International Publication WO 02/098774 or WO 03/029017, urea urethane compound described in International Publication WO 00/14058 or JP 2000-143611, N, N′-di- Thiourea compounds such as m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, zinc bis [4- (n-octyloxycarbonylamino) salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ) Ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, and their aromatic carboxylic acids Acid zinc, magnesium, aluminum, calcium And salts with polyvalent metal salts such as zinc, titanium, manganese, tin and nickel, antipyrine complexes of zinc thiocyanate, and composite zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  As the dye used in the heat-sensitive recording material of the present invention, any of those known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and is not particularly limited. Compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored basic colorless dyes are shown below. These basic colorless dyes may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)
<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino -6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino- 7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-n-dipentylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl- N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7- Nirinofuruoran, 3-cyclohexylamino-6-chloro-fluoran
<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 4-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam, 3,6 -Bis (diethylamino) fluorane-γ- (4'-nitro) anilinolactam, 1,1-bis- [2 ', 2', 2 '', 2 ''-tetrakis- (p-dimethylamino) Nophenyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane, bis- [2, 2,2 ', 2'-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  Furthermore, the heat-sensitive recording layer of the present invention may contain a sensitizer, a binder, a cross-linking agent, a stabilizer, a pigment, a lubricant, and the like as required. Binders, cross-linking agents, pigments, and the like can be used for each coating layer provided as needed, such as an undercoat layer, as long as the desired effects on the above-described problems are not impaired.

  In addition, a conventionally known sensitizer can be used as long as it does not inhibit the desired effect. Examples of such a sensitizer include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montanic acid wax, and polyethylene. Wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, Shu Dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1 , 4-Diethoxynaphthalene, 1-hydroxy-2-naphthoic acid Nyl ester, o-xylene-bis- (phenyl ether), 4- (m-methylphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2- Examples include, but are not limited to, di (3-methylphenoxy) ethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, and phenyl p-toluenesulfonate. It is not something. These sensitizers may be used alone or in combination of two or more.

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

  In the heat-sensitive recording material of the present invention, it is desirable from the viewpoint of water resistance and printing runnability that the binder particularly contains carboxyl-modified polyvinyl alcohol, epichlorohydrin resin and polyamine / amide resin.

  The carboxyl-modified polyvinyl alcohol is a reaction product of polyvinyl alcohol and a polycarboxylic acid such as fumaric acid, phthalic anhydride, melittic anhydride, itaconic anhydride, or an esterified product of these reactants, and further vinyl acetate and maleic acid. And saponified products of copolymers with ethylenically unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, crotonic acid, acrylic acid and methacrylic acid. Specifically, for example, the production method exemplified in Example 1 or 4 of JP-A-53-91995 can be mentioned. Moreover, it is preferable that the saponification degree of carboxyl modified polyvinyl alcohol is 72-100 mol%, and a polymerization degree is 500-2400, More preferably, it is 1000-2000.

  Specific examples of the epichlorohydrin-based resin include polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, and the like, which can be used alone or in combination. Moreover, as an amine which exists in the principal chain of an epichlorohydrin-type resin, the thing from a primary to a quaternary can be used, and there is no restriction | limiting in particular. Further, the degree of cationization and the molecular weight preferably have a cationization degree of 5 meq / g · Solid (measured value at pH 7) and a molecular weight of 500,000 or more because of good water resistance. Specific examples include Sumire Resin 650 (30), Sumire Resin 675A, Sumire Resin 6615 (above, manufactured by Sumitomo Chemical Co., Ltd.), WS4002, WS4020, WS4024, WS4046, WS4010, CP8970 (above, produced by Starlight PMC). Etc.

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

  The content of the epichlorohydrin resin and the modified polyamine / amide resin used in the present invention is preferably 1 to 100 parts by weight, more preferably 5 to 100 parts by weight with respect to 100 parts by weight of the carboxyl-modified polyvinyl alcohol. 50 parts by weight. If the content is too small, the crosslinking reaction becomes insufficient and good water resistance cannot be obtained. If the content is too large, there arises a problem in operability due to an increase in viscosity of the coating liquid or gelation.

  Further, when the protective layer contains carboxyl-modified polyvinyl alcohol, epichlorohydrin resin and polyamine / amide resin, epichlorohydrin resin and / or carboxyl-modified polyvinyl alcohol is added to the heat-sensitive recording layer in contact with the protective layer. It is desirable to contain. By including the component contained in the protective layer, the adhesiveness between the heat-sensitive recording layer and the protective layer is improved, and the immersion water resistance is improved. The epichlorohydrin resin is preferably added in an amount of 0.2 to 5.0 parts by weight (dry weight) in the heat-sensitive recording layer. When the amount of the epichlorohydrin resin added increases, the stability of the paint decreases.

Examples of the pigment used in the present invention include kaolin, (calcined) kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, and silica. It is not limited to these.
Examples of the crosslinking agent used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, chloride chloride Examples include ferric iron, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.
Examples of the lubricant used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

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

The type and amount of the dye, developer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. About 0.5 to 10 parts of developer and 0.5 to 10 parts of pigment are used for 1 part, and the binder is suitably about 5 to 25% in the solid content of the heat-sensitive recording layer.
The ratio of the diphenylsulfone compound represented by the general formula (Formula 1) to the total amount of the developer is 50% by weight or more, preferably 70 to 100% by weight.

The content of the rice starch particles in the protective layer of the present invention is preferably more than 50% by weight, more preferably more than 50% by weight and not more than 80% by weight, based on the total solid content of the protective layer.
Moreover, it is preferable to contain the said binder for water resistance provision to a protective layer, and the content of a binder is about 20 to 100 weight% by solid content with respect to rice starch particle | grains.

By applying the coating liquid having the above composition to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired thermal recording material can be obtained. Moreover, you may use the composite sheet which combined these as a support body.
Dye, developer, and materials to be added as needed are finely pulverized to a particle size of several microns or less with a pulverizer such as a ball mill, attritor or sand glider or an appropriate emulsifier, and depending on the binder and purpose. Various additive materials are added to form a coating solution. Water or alcohol can be used as the solvent used in the paint, and its solid content is about 20 to 40%. Further, the means for applying is not particularly limited, and can be applied according to well-known conventional techniques. For example, various coaters such as an air knife coater, rod blade coater, vent blade coater, bevel blade coater, roll coater, curtain coater, etc. The provided off-machine coating machine or on-machine coating machine is appropriately selected and used. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of ² to 12 g / m ^{2 by} dry weight. Further, the coating amount of the protective layer provided on the thermosensitive recording layer is not particularly limited, and is usually in the range of 1 to 5 g / m ² .

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

  The following examples illustrate the invention but are not intended to limit the invention. In the following description, parts and% indicate parts by weight and% by weight, respectively. The average particle diameter was measured by a laser diffraction / scattering method (manufactured by Malvern, apparatus name: Mastersizer S).

Each layer coating solution was prepared by stirring and dispersing various solutions, dispersions, or coating solutions of the following composition.
[Under layer coating solution]
Baked kaolin (Engelhard, Ansilex, average particle size 3μm) 30% dispersion
100.0 parts Styrene-butadiene copolymer latex (solid content 48%) 40.0 parts Completely saponified polyvinyl alcohol (PVA117) 10% aqueous solution 30.0 parts Water 160.0 parts

The developer dispersion liquid (A liquid), leuco dye dispersion liquid (B liquid), and sensitizer dispersion liquid (C liquid) having the following composition are each wetted separately with a sand grinder until the average particle diameter becomes 0.5 μm. Grinding was performed.
Liquid A (developer dispersion)
4-hydroxy-4'-npropoxydiphenylsulfone 6.0 parts polyvinyl alcohol 10% aqueous solution 18.8 parts water 11.2 parts B liquid (dye dispersion)
3-dibutylamino-6-methyl-7-anilinofluorane (manufactured by Yamada Chemical Co., ODB-2)
2.0 parts polyvinyl alcohol 10% aqueous solution 4.6 parts water 2.6 parts C liquid (sensitizer dispersion)
Dibenzyl oxalate 6.0 parts Polyvinyl alcohol 10% aqueous solution 18.8 parts Water 11.2 parts

Subsequently, the dispersion liquid was mixed at the following ratio to prepare a coating liquid for the heat-sensitive recording layer. The liquid temperature of the coating liquid during the mixing operation was 30 ° C. at the highest.
[Thermosensitive recording layer coating solution]
Liquid A (developer dispersion) 36.0 parts Liquid B (dye dispersion) 13.8 parts Liquid C (sensitizer dispersion) 36.0 parts Carboxyl-modified polyvinyl alcohol (PVA-KL318, manufactured by Kuraray Co., Ltd.) 10% solution
3.0 parts

Next, the dispersion was mixed at the following ratio to obtain a coating solution for the protective layer. The liquid temperature of the coating liquid during the mixing operation was 30 ° C. at the highest.
[Protective layer coating solution]
30% dispersion of rice starch particles (BKK-401, manufactured by Bangkok Starch)
18.0 parts Carboxyl-modified polyvinyl alcohol (PVA-KL318) 10% aqueous solution
30.0 parts Zinc stearate (hydrin Z-7-30, 40% dispersion) 2.0 parts Polyamide epichlorohydrin resin (WS4030, 40% solution) 2.0 parts Modified polyamide resin (Smileze resin SPI106N, 20% solution)
0.5 part

[Example 1]
The under layer coating solution was applied to one side of a support (60 g / m ² base paper) and then dried to obtain an under coated paper having a coating amount of 10.0 g / m ² .
Next, the thermal recording layer coating solution was applied onto the undercoat layer of the undercoat layer coated paper so that the coating amount was 5.0 g / m ² and then dried to obtain a thermal recording layer coated paper.
Next, the protective layer coating solution was applied onto the heat-sensitive recording layer of the heat-sensitive recording layer-coated paper so that the coating amount was 3.0 g / m ² and then dried to obtain a heat-sensitive recording paper.
[Example 2]
Except for using bis (3-allyl-4-hydroxyphenyl) sulfone (manufactured by Nippon Kayaku Co., Ltd., TGSH) instead of 4-hydroxy-4′-n propoxydiphenyl sulfone in the thermal recording layer coating liquid of Example 1. A thermosensitive recording material was produced in the same manner as in Example 1.
[Example 3]
Example 4 was used except that 4,4′-dihydroxydiphenylsulfone (manufactured by Nikka Chemical Co., Ltd., BPS44) was used instead of 4-hydroxy-4′-npropoxydiphenylsulfone in the heat-sensitive recording layer coating liquid of Example 1. A heat-sensitive recording material was produced in the same manner.

[Example 4]
The thermal recording material was the same as in Example 1 except that 4-hydroxy-4'-isopropoxydiphenylsulfone was used instead of 4-hydroxy-4'-npropoxydiphenylsulfone in the thermal recording layer coating liquid of Example 1. Was made.
[Example 5]
Implemented except that 4-hydroxy-4'-allyloxydiphenyl sulfone (manufactured by Nikka Chemical Co., Ltd., BPSMAE) was used instead of 4-hydroxy-4'-npropoxydiphenyl sulfone in the thermal recording layer coating solution of Example 1. A thermosensitive recording material was produced in the same manner as in Example 1.
[Example 6]
A 30% dispersion of rice starch particles (BKK-401) in the protective layer coating liquid of Example 1 was used as a rice starch particle micropearl (R) manufactured by Shimada Chemical Industries, Ltd. (average particle size 4.9 μm, permeation of starch particles). A type micrograph is shown in Fig. 1.) A heat-sensitive recording material was produced in the same manner as in Example 1 except that the dispersion was changed to a 30% dispersion.
[Example 7]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the amount of rice starch particles in the protective layer coating solution of Example 1 was 6 parts.
[Example 8]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the amount of rice starch particles in the protective layer coating solution of Example 1 was 36 parts.

[Comparative Example 1]
Example 1 except that 4,4′-isopropylidenediphenol (Mitsubishi Chemical Co., Ltd., bisphenol A) was used instead of 4-hydroxy-4′-npropoxydiphenylsulfone in the thermal recording layer coating solution of Example 1. A thermosensitive recording material was produced in the same manner as described above.
[Comparative Example 2]
A 30% dispersion of rice starch particles (BKK-401) in the protective layer coating solution of Example 1 is shown in FIG. ) A heat-sensitive recording material was produced in the same manner as in Example 1 except that the 30% dispersion was used.
[Comparative Example 3]
A 30% dispersion of rice starch particles (BKK-401) in the protective layer coating solution of Example 1 is shown in FIG. 3 as a transmission micrograph of wheat starch (manufactured by Nagata Sangyo Co., Ltd., average particle size 15 μm, starch particles). ) A heat-sensitive recording material was produced in the same manner as in Example 1 except that the 30% dispersion was used.
[Comparative Example 4]
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the dispersion of rice starch particles was removed from the protective layer coating solution of Example 1.

The following evaluation was performed about the heat-sensitive recording material obtained above.
<Color development sensitivity>
About the produced thermal recording medium, it printed by the applied energy 0.27mJ / dot using the thermal recording paper printing test machine (The Okura Electric TH-PMD, the Kyocera thermal head was mounted | worn). The recording density of the recording part was measured with a Macbeth densitometer (RD-914).
<Reprintability>
The produced thermal recording material was left in an environment of 50 ° C. and 90% RH for 7 days, and then left in an environment of 23 ° C. and 50% RH for 3 hours. This heat-sensitive recording material was printed with an applied energy of 0.27 mJ / dot using a heat-sensitive recording paper printing tester (equipped with TH-PMD manufactured by Okura Electric Co., Ltd. and a thermal head manufactured by Kyocera Corporation). The recording density of the recording part was measured with a Macbeth densitometer (RD-914).

<Sealability>
The produced thermal recording medium was printed on a white paper portion with a killer whale (registered trademark) mark, wiped with tissue paper after 5 seconds, and visually evaluated.
○: Slightly faint but characters remain clearly △: Fainted but characters can be read ×: Fainted characters cannot be read <Abrasion>
The coated surface was visually evaluated for rubbing color development with steel wool to which a load of 1000 g / cm ² was applied.
○: Almost no color △: Light color x: Dark color

<Printability>
Using a Fogra type printing aptitude tester (Mitsui Denki Seiki Co., Ltd., NST-430), the test was conducted under the following conditions and evaluated visually.
Wet water unit pressure 20kgf / cm ²
Print pressure 50kgf / cm ²
Dampening water (10% isopropyl alcohol) 15 μl
Printing speed 100 to 180 m / min Ink used UV form FLASH DRY FD form TF C71 light green NCM (tack index: 8.5, manufactured by Toyo Ink Manufacturing Co., Ltd.)
○: Almost no ink missing Δ: Slight ink missing X: Many ink missing observed <Water resistance blocking resistance>
10 μl of tap water is dropped onto the coated surface of the blank paper sample, the blank paper sample is overlaid thereon so that the coated surface is in contact with it, and the coating layer is peeled off after being left at room temperature for 24 hours under a load of 10 g / cm ² . Peeling was evaluated.
○: There is no peeling of the coating layer. Δ: The coating layer is slightly peeled. X: Most of the coating layer is peeled off.

The evaluation results are shown in Table 1.
When the diphenylsulfone compound represented by the general formula (Chemical Formula 1) is contained in the heat-sensitive recording layer provided on the heat-sensitive recording material and the rice starch particles are contained in the protective layer, sufficient color development sensitivity can be obtained, and sealability, scratching can be obtained. It can be seen that a heat-sensitive recording material having good printability, printability, water blocking resistance and reprintability can be obtained.

2 is a transmission micrograph of rice starch particles. 2 is a transmission micrograph of corn starch particles. 2 is a transmission micrograph of wheat starch particles. It is a transmission-type photomicrograph of a potato starch particle.

Claims (3)

A heat-sensitive recording material comprising a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and further comprising a protective layer on the heat-sensitive recording layer, The heat-sensitive recording layer has the following general formula (Formula 1) as an electron-accepting developer:
(Wherein R ¹ represents a hydrogen atom or a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, and R ² and R ³ each independently represents an alkyl group or an alkenyl group. And m and n each represents an integer of 0 to 2.), and a protective recording layer containing rice starch particles. The heat-sensitive recording material according to claim 1, wherein the rice starch particles have an average particle diameter of 2 to 7 μm. The heat-sensitive recording material according to claim 1 or 2, wherein the content of rice starch particles in the protective layer is more than 50% by weight based on the total solid content of the protective layer.