JPWO2013154006A1 - Thermal recording material - Google Patents

Abstract

Disclosed is a heat-sensitive recording material comprising a heat-sensitive color developing layer containing a leuco dye, a developer, and a phenol novolac resin formed from a phenol compound containing 4-t-butylphenol and formaldehyde.

Description

  The present invention relates to a heat-sensitive recording material.

  The heat-sensitive recording material generally has a structure in which a heat-sensitive coloring layer containing a colorless or light-colored dye and a developer as main components is formed on a support such as paper, film or synthetic paper. The heat-sensitive color forming layer develops color by a chemical reaction that occurs when the dye and the developer are melted and brought into contact with heating to obtain a color record.

  In recent years, with the shift to POS systems in retail stores, convenience stores, supermarkets, etc., and the use of automation systems in transportation, the use of heat-sensitive recording materials for labels, tickets, coupon tickets, etc. has become widespread. . In these applications, high storage stability of the thermosensitive recording material is desired.

  So far, studies have been made on the color developer of the heat-sensitive recording material (for example, Patent Documents 1 and 2).

Japanese Patent No. 3733081 Japanese Patent No. 39085959

  However, conventional heat-sensitive recording materials tend to cause fading of the image area (colored portion) due to light, or color development on the background portion (portion other than the colored portion), particularly in terms of light resistance. Further improvement is required.

  Therefore, the main object of the present invention is to further improve the light resistance of the thermosensitive recording material.

  The present invention relates to a thermosensitive recording material comprising a thermosensitive coloring layer containing a phenol novolac resin formed from a leuco dye, a developer, and a phenol compound containing 4-t-butylphenol and formaldehyde.

  According to the knowledge of the present inventors, it is possible to improve the light resistance of the heat-sensitive recording material by using the specific phenol novolac resin as a color developing aid in addition to the color developer.

  The developer may contain at least one compound selected from a phenol compound having a phenolic hydroxyl group and different from the phenol novolac resin and a urea compound having a urea group. The combination of the color developer containing these compounds and the color development aid can provide a particularly remarkable effect of improving light resistance as compared with the conventional color developer.

  According to the present invention, the light resistance of the thermosensitive recording material can be further improved. The heat-sensitive recording material according to the present invention also has good heat resistance and water resistance.

It is sectional drawing which shows one Embodiment of a thermosensitive recording material.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a cross-sectional view showing an embodiment of a heat-sensitive recording material. A heat-sensitive recording material 10 shown in FIG. 1 mainly includes a sheet-like support 1 and a heat-sensitive color developing layer 3 provided on one surface side of the support 1. An intermediate layer 5 may be further provided between the thermosensitive coloring layer 3 and the support 1.

  As the support 1, paper, plastic sheet, synthetic paper, or the like is used.

  The thermosensitive coloring layer 3 contains a leuco dye as a coloring compound, a developer, a phenol novolak resin formed from a phenol compound containing 4-t-butylphenol and formaldehyde.

  The phenol novolac resin is contained in the heat-sensitive color developing layer as a color development aid used for improving the color development performance in combination with a color developer. This phenol novolac resin can be synthesized, for example, from 4-t-butylphenol and phenol and formaldehyde in the presence of an acid catalyst. In the above phenol novolak resin synthesized in the presence of an acid catalyst, the proportion of the condensate having 6 or more nuclei (benzene rings) may be 20% by mass or more, or 50% by mass or more. Thereby, the effect by this invention is show | played more notably.

  As the color developer contained in the heat-sensitive color former, various electron-accepting compounds, for example, a phenol compound having a phenolic hydroxyl group and different from the phenol novolak resin, a thiophenol compound having a thiol group bonded to a phenyl group, Urea compounds having a urea group, thiourea compounds having a thiourea group, organic acids and metal salts thereof can be used.

  The phenol compound as the developer is a phenol resin formed from a phenol compound not containing 4-t-butylphenol and formaldehyde (for example, a phenol novolak resin formed from phenol and formaldehyde), bisphenol A, bisphenol S, etc. The bisphenol compound may be used. Examples of the phenol compound include α-naphthol, β-naphthol, p-octylphenol, 4-t-octylphenol, pt-butylphenol, p-phenylphenol, 1,1-bis (p-hydroxyphenyl) propane, 2, 2-bis (p-hydroxyphenyl) propane (also known as bisphenol A or BPA), 2,2-bis (p-hydroxyphenyl) butane, 1,1-bis (p-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (3-phenyl-4-hydroxyphenyl) propane 4,4′- Cyclohexylidene diphenol, 2,2-bis (3,5-dibromo-4-hydroxypheny ) Propane (also known as tetrabromobisphenol A), 4,4′-isopropylidenebis (2-t-butylphenol), 2,2′-methylenebis (4-chlorophenol), 4,4′-isopropylidenebis ( o-methylphenol), 4,4′-secondary butylidene bisphenol, 4,4′-isopropylidene bis (2-chlorophenol), 4,4′-butylidene bis (6-tertiarybutyl-2-methylphenol) 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-isopropoxy-4′-hydroxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 4-benzyloxy-4 ′ -Hydroxydiphenylsulfone, bis (3-allyl-4- Droxyphenyl) sulfone, 4,4′-diphenol sulfoxide, ethyl p-hydroxybenzoate, isopropyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, benzyl protocatechuate, stearyl gallate, lauryl gallate, gallic acid Octyl, 4-hydroxyphthalic acid dibenzyl, 4-hydroxyphthalic acid dimethyl, salicylanilide, 5-chloro-salicylanilide, bis- (4-hydroxydiphenyl) acetic acid butyl ester, bis- (4-hydroxyphenyl) acetic acid benzyl ester, 1,3-bis (4-hydroxycumyl) benzene, 1,4-bis (4-hydroxychloro) benzene, ethyl 5-hydroxyisophthalate, 3,4-dihydroxy-4′-methyldiphenylsulfone, 1) It is selected from a sphenol compound and a bisphenol S derivative represented by the following formula (2). In the formula (1), R represents an alkyl group such as a methyl group or an ethyl group, and is preferably a methyl group.

  Examples of the thiophenol compound as the developer include 4,4′-thiobisphenol, 4,4′-thiobis (6-tertiarybutyl-2-methylphenol), 1,3-bis (4-hydroxyphenylthio). ) -Propane and 1,8-bis (4-hydroxyphenylthio) -2-hydroxypropane.

  The urea compound as the developer is selected from, for example, a urea resin and a sulfonylurea compound represented by the following formula (3).

  The thiourea compound as the developer is selected from, for example, N, N′-diphenylthiourea and N, N′-di (m-chlorophenyl) thiourea.

  Examples of the organic acid metal salt as the developer include zinc 1-acetyloxy-2-naphthoate, 2-acetyloxy-1, zinc naphthoate, zinc 2-acetyloxy-3-naphthoate, α, α- It is selected from bis (4-hydroxydiphenyl) -α-methyltoluene, an antipyrine complex of zinc thiocyanate, and 3,5-di (α-methylbenzyl) salicylic acid zinc salt.

  Another compound that can be used as a developer is, for example, 2,4'-diphenylsulfone.

  These compounds are used alone or in combination of two or more.

  The bisphenol compound of formula (1) includes, for example, a step of reacting phenol and glyoxylic acid in an acidic reaction solution to produce a hydroxycarboxylic acid compound represented by the following formula (1A), Adjusting the aqueous liquid obtained by mixing to alkaline, extracting the impurities from the aqueous liquid with an organic solvent, adjusting the aqueous liquid to acidic, and extracting the hydroxycarboxylic acid compound from the aqueous liquid with an organic solvent; The step of esterifying the hydroxycarboxylic acid compound extracted from the aqueous liquid to produce the bisphenol compound represented by the formula (1) can be obtained by a method comprising in this order.

  The leuco dye used as the color-forming compound in the heat-sensitive color developing layer can be appropriately selected from compounds generally used for pressure-sensitive recording paper or heat-sensitive recording paper. The leuco dye (color-forming compound) is, for example, at least one selected from the group consisting of a fluoran compound, a triarylmethane compound, a spiro compound, a diphenylmethane compound, a thiazine compound, a lactam compound, and a fluoran compound. It is a compound of this.

  Examples of the fluorane compound include 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dipentylamino-6-methyl-7-aniline. Linofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilino Fluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofluorane, 3- [N-ethyl-N- (3-ethoxypropyl) amino] -6-methyl-7 -Anilinofluorane, 3- (N-ethyl-N-hexylamino) -6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl-7 Anilinofluorane, 3- (N-ethyl-N-tetrahydrofurylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino -6-methyl-7- (p-fluoroanilino) fluorane, 3- [N-ethyl-N- (p-tolyl) amino] -6-methyl-7-anilinofluorane, 3-diethylamino-6- Methyl-5- (p-toluidino) fluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (o-fluoro) Anilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-7- (3,4 Dichloroanilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-ethoxyethylaminofluorane, 3-diethylamino-6-chloro-7-anilinofluor Oran, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-octylfluorane, and 3- [N-ethyl-N- (p-tolyl) amino]- 6-methyl-7-phenethylfluorane is mentioned.

  Examples of triarylmethane compounds include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone or CVL), 3,3-bis (p-dimethylaminophenyl). Phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylaminoindol-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-dimethylaminophthale 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9- Rucarbazol-3-yl) -5-dimethylaminophthalide, 3,3- (2-phenylindol-3-yl) -5-dimethylaminophthalide, and 3-p-dimethylaminophenyl-3- (1) -Methylpyrrol-2-yl) -6-dimethylaminophthalide.

  Examples of the spiro compound include 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3′-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-propylspirodinaphthopyran, 3 -Methylnaphtho- (3-methoxybenzo) spiropyran and 1,3,3-trimethyl-6-nitro-8'-methoxyspiro (indoline-2,2'-benzopyran).

  Examples of the diphenylmethane compound include N-halophenyl-leucooramine, 4,4-bis-dimethylaminophenylbenzhydrylbenzyl ether, and N-2,4,5-trichlorophenylleucooramine.

  Examples of thiazine compounds include benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue.

  Examples of the lactam compound include rhodamine B anilinolactam and rhodamine Bp-chloroanilinolactam.

  Examples of the fluorene compound include 3,6-bis (dimethylamino) fluorene spiro (9,3 ′)-6′-dimethylaminophthalide and 3,6-bis (dimethylamino) fluorene spiro (9,3 ′). -6'-pyrrolidinophthalide and 3-dimethylamino-6-diethylaminofluorene spiro (9,3 ')-6'-pyrrolidinophthalide.

  The chromogenic compounds as the leuco dyes mentioned above are used singly or in combination.

  The thermosensitive coloring layer preferably further contains a binder. As the binder, a water-soluble compound, a water-dispersible compound or an emulsion is used. Examples of the water-soluble compound include methyl cellulose, ethyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, acetyl cellulose, polyvinyl alcohol (PVA), carboxyl group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, silyl group-modified polyvinyl alcohol, and polyvinylpyrrolidone. , Polyacrylamide, polyacrylic acid, starch and derivatives thereof, casein, gelatin, water-soluble isoprene rubber, styrene / maleic anhydride copolymer, and iso (or diiso) butylene / maleic anhydride copolymer. Water dispersible compounds or emulsions include, for example, styrene / butadiene latex, carboxylated styrene / butadiene latex, acrylic acid ester copolymers, styrene / acrylic acid copolymers, ethylene / vinyl acetate copolymers, acrylic / It is selected from urethane copolymers, acrylic / polyester copolymers, and acrylic / silicon copolymers.

  The amount of the phenol novolac resin formed from the phenolic compound containing 4-t-butylphenol and formaldehyde may be 1 to 50% by mass or 1 to 30% by mass based on the mass of the thermosensitive coloring layer. The amount of the leuco dye is usually 1 to 50% by mass and may be 5 to 30% by mass. The amount of the developer is usually 1 to 70% by mass and may be 10 to 50% by mass. The amount of the binder in the thermosensitive coloring layer is usually 1 to 90% by mass. The mass ratio of the developer to the leuco dye is usually 0.5 to 20 times and may be 1 to 5 times. When the amount of each component is within these numerical ranges, the effects of the present invention are more remarkably exhibited.

  The heat-sensitive color forming layer may contain a sensitizer, a stabilizer, a filler, a surfactant, and other additives as necessary. The amount of the sensitizer, stabilizer and filler is usually 0 to 80% by mass. The surfactant and other additives are each added to the thermosensitive coloring layer in an arbitrary ratio, for example, usually in the range of 0 to 30% by mass.

  The sensitizer is preferably solid at room temperature and has a melting point. The melting point of the sensitizer is preferably about 70 ° C or higher. Examples of the sensitizer include waxes such as animal and vegetable waxes and synthetic waxes, higher fatty acids, higher fatty acid amides, higher fatty acid anilides, naphthalene derivatives, aromatic ethers, aromatic carboxylic acid derivatives, aromatic sulfonic acid ester derivatives, carbonic acid or Oxalic acid diester derivatives, biphenyl derivatives, terphenyl derivatives, and sulfone derivatives are used.

  Examples of the wax include wood wax, carnauba wax, shellac, paraffin, montan wax, oxidized paraffin, polyethylene wax, and oxidized polyethylene. Examples of higher fatty acids include stearic acid and behenic acid. Examples of the higher fatty acid amide include stearic acid amide, oleic acid amide, N-methyl stearic acid amide, erucic acid amide, methylol behenic acid amide, methylene bis stearic acid amide, and ethylene bis stearic acid amide. Examples of the higher fatty acid anilide include stearic acid anilide and linoleic acid anilide. Specific examples of naphthalene derivatives include 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 1-hydroxynaphthoic acid phenyl ester, and the like. Examples of the aromatic ether include 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-bis (3-methylphenoxy) ethane, 1,2-bis (4-methoxyphenoxy) ethane, 1 , 2-bis (3,4-dimethylphenyl) ethane, 1-phenoxy-2- (4-chlorophenoxy) ethane, 1-phenoxy-2- (4-methoxyphenoxy) ethane, 1,2-diphenoxymethylbenzene Is mentioned. Examples of the aromatic carboxylic acid derivative include p-benzyloxybenzoic acid benzyl ester and terephthalic acid dibenzyl ester. Examples of the aromatic sulfonic acid ester derivative include p-toluenesulfonic acid phenyl ester, phenyl mesitylene sulfonate, and 4-methylphenyl mesitylene sulfonate. Examples of the carbonic acid or oxalic acid diester derivative include diphenyl carbonate, dibenzyl oxalate, di (4-chlorobenzyl) oxalate, and di (4-methylbenzyl) oxalate. Examples of the biphenyl derivative include p-benzylbiphenyl, p-acetylbiphenyl, and p-allyloxybiphenyl. Examples of the terphenyl derivative include m-terphenyl and a terphenyl isomer mixture. Examples of the sulfone derivative include diphenyl sulfone, 4-methyldiphenyl sulfone, and chlorinated diphenyl sulfone. These sensitizers are appropriately used by selecting one or two or more of these sensitizers.

  As the stabilizer, for example, a phenol derivative and an amine derivative imparting an antioxidant or antiaging effect, or a benzotriazole compound and a benzophenone compound as an ultraviolet absorber can be used.

  Examples of phenol derivatives and amine derivatives include 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-methylenebis (4-ethyl-6-tert-butylphenol), 4,4 ′. -Butylidenebis (6-t-butyl-2-methylphenol), 4,4'-thiobis (6-t-butyl-2-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-) 5-t-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, tetramethylbisphenol S, tetrabromobisphenol S, 4,4′-thiobis (2 -Methylphenol), 4,4′-thiobis (2-chlorophenol), bis (2,2,6,6-tetramethyl-4-sebacate) Peridinyl), tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, tetrakis (1,2,2,6,6-tetramethyl-) 4-piperidyl) -1,2,3,4-butanetetracarboxylate.

  Examples of the benzotriazole compounds include 2- (2′-hydroxy-5′-methyl-phenyl) -benzotriazole and 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) -5. -Chlorobenzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl)- Benzotriazole, 2- (2′-hydroxy-4′-octoxyphenyl) -benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) -benzotriazole, 2- ( 2′-hydroxy-3 ′, 5′-di-t-amylphenyl) -benzotriazole, methylene-bis [2- (2′-hydroxy-5′-dodecanyl phen Le) benzotriazole], and the like.

  Examples of the benzophenone compounds include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone. Bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  Examples of the filler include calcium carbonate, silica, white carbon, talc, clay, alumina, titanium oxide, zinc oxide, aluminum hydroxide, aluminum oxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, barium sulfate, polystyrene resin, urea -Formalin resin, hollow plastic pigment, foamable hollow plastic pigment.

  Surfactants include, for example, fatty acid metal soaps, polycarboxylic acid type polymer activators, sulfates of higher alcohols, sulfates of alkyl polyethers, ethylene oxide adducts of higher alcohols, alkylaryls. Sulfonates, alkyl sulfonic acids, aryl sulfonic acids, phosphate esters, aliphatic phosphate esters, aromatic phosphate esters, polyoxyethylene alkyl sulfate esters, polyoxyethylene aryl sulfate esters, polyoxyethylene Alkylaryl sulfates, dialkylsulfosuccinates, alkylbenzenesulfonates, polyoxyalkylene alkyl ether phosphates, polyoxyalkylene aryl ether phosphates, polyoxyalkylenes Alkyl aryl ether phosphate, sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol 9 (eg, polyoxyethylene nonylphenyl ether), acetylene glycol, ethylene oxide adduct of acetylene glycol, propylene oxide addition of acetylene glycol Products, ethylene oxide and propylene oxide adducts of acetylene glycol, and the like.

  Other additives include lubricants (for example, higher fatty acid metal salts such as zinc stearate and calcium stearate), water resistance agents (for example, glyoxal, glutaraldehyde, dialdehyde, ethylenediamine, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide) Resin, polyamidoamine-epichlorohydrin resin, adipic acid dihydrazide, phthalic acid dihydrazide, boric acid, borax, titanium lactate, ammonium zirconium carbonate and potassium zirconium carbonate), thickener (eg xanthan gum, carboxymethylcellulose), Foaming agents and antifoaming agents (for example, silicon oil, mineral oil), fluorescent whitening agents, fluorescent dyes, colored dyes, colored pigments and the like can be used.

The thermosensitive coloring layer is, for example, a leuco dye, a developer, and the phenol novolak resin, separately with a binder and, if necessary, a sensitizer, a stabilizer, a filler, other additives, etc. A step of preparing a dispersion liquid in which each component is dispersed by wet pulverization using the above medium, a step of preparing a coating liquid by mixing the respective dispersion liquids, and applying and applying the coating liquid on the intermediate layer. And a step of drying the applied coating solution. The wet dispersion for obtaining the dispersion liquid can be performed using a disperser such as a ball mill, an attritor or a sand mill. The dry mass of the thermosensitive coloring layer is usually ² to 20 g / m ² and may be 4 to 10 g / m ² .

  The intermediate layer 5 may be a foam or may contain minute hollow particles dispersed in the intermediate layer 5. Further, the intermediate layer 5 may be a foam containing hollow particles.

  Hollow particles (fine hollow fillers) are particles in which voids are formed, and are formed of, for example, plastic, glass, or ceramic. The material forming the hollow particles is preferably a plastic, and among them, a thermoplastic resin is particularly preferable.

  The hollow particles are preferably spherical. The average particle diameter of the hollow particles is usually 0.2 to 10 μm, preferably 0.5 to 3 μm. The larger the hollow ratio of hollow particles (the ratio of internal voids to the apparent volume), the greater the heat insulation effect, which is preferable. However, the hollow ratio may be limited depending on the particle diameter. The hollow ratio of the hollow particles is preferably 30 to 90% by volume, more preferably 50 to 90% by volume.

  The amount of the hollow particles contained in the intermediate layer is usually 10 to 90% by mass, preferably 40 to 80% by mass, based on the mass of the intermediate layer.

  The foam as the intermediate layer is formed, for example, by foaming foamable hollow particles having a shell made of a thermoplastic resin and containing therein a low boiling point solvent as a foaming agent.

  The intermediate layer may contain other components selected from binders, fillers, stabilizers, dispersants, antifoaming agents and other additives. These components can be appropriately selected from those generally used for pressure-sensitive recording paper and heat-sensitive recording paper. For example, the same materials as those for a heat-sensitive coloring layer described later are used.

  Usually, the amount of binder is 10-50% by weight and the amount of filler is 10-50% by weight. Stabilizers, surfactants, and other additives that are added as necessary are added to the intermediate layer in arbitrary proportions, for example, usually in the range of 0 to 30% by mass.

The intermediate layer is prepared by, for example, mixing and dispersing hollow particles, a binder and a filler, and if necessary, a surfactant and other additives in water to prepare a coating solution for the intermediate layer. Is formed on the support and the coating film is dried. The dry mass of the intermediate layer is usually ^{2 to 20} g / m ² , preferably 5 to 10 g / m ² . The coating solution for the intermediate layer can be applied using a bar coater, a doctor blade, a gravure coater or the like.

  The intermediate layer which is a foam is prepared by mixing and dispersing, for example, expandable hollow particles, a binder and a filler, and, if necessary, a surfactant and other additives in water to form a coating solution for the intermediate layer. Prepare. The coating liquid is applied onto a support, the coating film is dried, and further foamed to form. The foaming treatment is performed, for example, by bringing the coating film into close contact with the surface of a drum dryer having a heater and heating to a temperature (100 to 150 ° C.) at which the thermoplastic resin forming the foamed hollow particle shell is softened. Done.

  The heat-sensitive recording material according to the present embodiment may further include a layer other than the intermediate layer and the heat-sensitive color forming layer as necessary. For example, another intermediate layer may be provided between the intermediate layer and the thermosensitive coloring layer, or an overcoat layer may be provided on the thermosensitive coloring layer. Another intermediate layer and overcoat layer contain, for example, binders and fillers as described above, and other additives added as needed. These additional layers can be formed by applying a coating solution containing each component and drying it, as in the case of the intermediate layer and the thermosensitive coloring layer.

The overcoat layer includes, for example, a binder, a filler, and a lubricant, and a surfactant, a water resistant agent and other additives which are added as necessary. The dry mass of the overcoat layer is usually 1 to 10 g / m ² .

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

1. Formation of Intermediate Layer The following materials were mixed to prepare a coating solution for the intermediate layer. This coating solution was applied onto fine paper having a basis weight of 64 g / m ² , and the coating film was dried to form an intermediate layer of 7 g / m ² .
30% hollow fine particle aqueous dispersion (material = styrene / acrylic acid ester copolymer, average particle size = 1 μm, hollow ratio = 54%) 640 parts 60% calcium carbonate aqueous dispersion 50 parts 48% carboxyl group-modified SBR latex 85 225 parts water

2. Formation of thermosensitive coloring layer The solids in the three kinds of mixture containing the following materials were dispersed while being pulverized using a bead mill until the average particle size became 1 μm, and the [A] liquid, [B] liquid and [ C] solution was obtained.
[A] Liquid (leuco dye)
3-dibutylamino-6-methyl-7-anilinofluorane 30 parts polyvinyl alcohol (PVA) 5 parts water 65 parts [B] solution (developer)
Bisphenol A (BPA) 30 parts Polyvinyl alcohol (PVA) 5 parts Water 65 parts [C] solution (development aid)
4-t-butylphenol and phenol resin formed from phenol and formaldehyde (Shonol CKP-963P, Showa Denko KK)
30 parts polyvinyl alcohol (PVA) 5 parts water 65 parts

Next, a coating solution for a thermosensitive coloring layer having the following composition containing the [A] solution, [B] solution and [C] solution was prepared. The coating solution is applied onto the intermediate layer, and the coating film is dried to form a thermosensitive coloring layer of 6 g / m ² , and a thermosensitive recording material composed of fine paper, the intermediate layer, and the thermosensitive coloring layer is obtained. Obtained.
[A] liquid 50 parts [B] liquid 100 parts [C] liquid 100 parts 60% calcium carbonate aqueous dispersion 83 parts 20% silica aqueous dispersion 250 parts 36% zinc stearate aqueous dispersion 61 parts 10% fully saponified PVA aqueous solution 200 parts water 156 parts

  [C] The liquid was not blended, or the coating aid was prepared by changing the color developing aid of the [C] liquid to a bisphenol S derivative, and a thermosensitive coloring layer was formed in the same manner as above to obtain a thermosensitive recording material. . Furthermore, the developer of the [B] solution was changed to bisphenol S (BPS), 4-hydroxy-4′-isopropoxydiphenyl sulfone, or a bisphenol compound (MBHA) represented by the following formula (10), and the same A heat sensitive recording material was prepared.

3. Evaluation (heat resistance)
After the image was formed, each heat-sensitive recording material was subjected to a heat resistance test in which it was left in a thermostat at 90 ° C. for 24 hours. The reflection density (Macbeth reflection density) of the image part and the background part before and after the test was measured using a Macbeth reflection densitometer (SpectroEyeLT, manufactured by Sakata Engineering Co., Ltd.).
(Light resistance)
After the image was formed, each heat-sensitive recording material was subjected to a light resistance test in which light of 5000 lux was irradiated for 100 hours with a fluorescent lamp. The reflection density (Macbeth reflection density) of the image part and the background part before and after the test was measured using a Macbeth reflection densitometer.
(water resistant)
After the image was formed, a water resistance test was performed in which each heat-sensitive recording material was exposed to tap water at 25 ° C. for 24 hours. The reflection density (Macbeth reflection density) of the image part and the background part before and after the test was measured using a Macbeth reflection densitometer.

  The measurement results are shown in Tables 1 and 2. The residual ratio is a ratio of the reflection density after the test to the reflection density before the test.

  From the results shown in the table, a heat-sensitive recording material using 4-t-butylphenol and a phenol resin (963P) formed from phenol and formaldehyde as a color development aid is bisphenol S as a color development aid in a light resistance test. It was confirmed that the density of the image area was maintained better than the case where the derivative was used, and the color development of the background area was effectively suppressed. Moreover, practically sufficient level was maintained also about heat resistance and water resistance.

  DESCRIPTION OF SYMBOLS 1 ... Support body, 3 ... Thermal coloring layer, 5 ... Intermediate | middle layer, 7 ... Overcoat layer, 10 ... Thermal recording material.

Claims (2)

  A thermosensitive recording material comprising a thermosensitive coloring layer containing a leuco dye, a developer, and a phenol novolac resin formed from a phenol compound containing 4-t-butylphenol and formaldehyde.   The heat-sensitive recording material according to claim 1, wherein the developer contains at least one compound selected from a phenol compound having a phenolic hydroxyl group and different from the phenol novolak resin, and a urea compound having a urea group.

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