KR20240157101A - Thermal recorder - Google Patents

Abstract

A heat-sensitive record having a water vapor barrier property against moisture in a heat-sensitive record is provided. The heat-sensitive record is a heat-sensitive record having a heat-sensitive recording layer formed on a support containing a colorless to light-colored electron-donating leuco dye and an electron-accepting developer, and a back coating layer formed on the opposite side to the heat-sensitive recording layer, wherein the back coating layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

Description

Thermal recorder

The present invention relates to a heat-sensitive recording medium having a vapor barrier property on the back surface.

In general, a thermosensitive record is formed by coating a coating solution containing a colorless or light-colored electron-donating leuco dye (hereinafter also referred to as a "leuco dye") and an electron-accepting developer (hereinafter also referred to as a "developer") on a support such as paper, synthetic paper, film, or plastic to form a thermosensitive recording layer, and a recorded image is obtained by coloring through an instantaneous chemical reaction caused by heating by a thermal head, hot stamp, heat pen, laser light, or the like. Thermosensitive records are widely used as recording media such as fax machines, terminal printers for computers, automatic ticket machines, recorders for measuring instruments, and receipts for supermarkets or convenience stores.

In order to obtain good water resistance, a heat-sensitive recording material having a back coating layer containing an adhesive such as polyvinyl alcohol is known (Patent Document 1, etc.). In addition, a paper substrate containing ethylene copolymer polyvinyl alcohol or ethylene-acrylic copolymer is known to have water vapor barrier properties (Patent Documents 2 to 4, etc.).

Japanese Patent Publication No. 2003-175671 Japanese Patent Publication No. 2013-169988 Japanese Patent Publication No. 2014-173201 Japanese Patent Publication No. 2020-190063

Since printers that require high sensitivity, such as those for medical use, print with high energy, the thermal head becomes hot, and if printing continues for a long time while the temperature is high, moisture in the thermal record evaporates, and water droplets are generated from the back side that does not come into contact with the thermal head, causing a problem in the device.

Accordingly, the present invention provides a heat-sensitive recording medium having a water vapor barrier property against moisture in the heat-sensitive recording medium.

The present inventors, as a result of careful examination, have found that the above-mentioned problem can be solved by forming a thermal recording layer on a support of a thermal recording medium, forming a back coating layer on the opposite side to the thermal recording layer, and containing an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer in the back coating layer, thereby completing the present invention.

That is, the present invention is a heat-sensitive recording medium having a heat-sensitive recording layer formed on a support containing a colorless to light-colored electron-donating leuco dye and an electron-accepting developer, and a back coating layer formed on the opposite side to the heat-sensitive recording layer, wherein the back coating layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

According to the present invention, a heat-sensitive recording material having excellent vapor barrier properties on the back side (i.e., the side opposite to the heat-sensitive recording layer of the support) and not generating vapor from the back side even when printed for a long period of time can be obtained.

The thermosensitive recording medium of the present invention has a thermosensitive recording layer containing a leuco dye and a developer on a support, and has a back coating layer on the surface of the support opposite to the thermosensitive recording layer.

The back coating layer of the present invention contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

The ethylene-vinyl alcohol copolymer used in the present invention is a polymer having ethylene units and vinyl alcohol units. The ethylene-vinyl alcohol copolymer is typically obtained by polymerizing ethylene and vinyl ester and saponifying the resulting ethylene-vinyl ester copolymer.

From the perspective of using water-based paints, the ethylene content is appropriate at about 3 to 20 mol%. In addition, in order to provide barrier properties, the saponification degree is appropriate at about 80 to 100 mol%. If the saponification degree is less than 80 mol%, barrier properties and moisture resistance cannot be sufficiently obtained.

The ethylene-acrylic copolymer used in the present invention is a copolymer obtained by emulsion polymerization of ethylene and an acrylic monomer. As the acrylic monomer, acrylic acid and methacrylic acid are preferable, and acrylic acid is more preferable.

As the ethylene-acrylic copolymer, it is preferable that it be at least one of an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-ethyl methacrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-butyl methacrylate copolymer. The copolymer may further include a small amount of a monomer copolymerizable with ethylene and acrylic monomers and other compounds.

Among them, ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer are more preferable, and ethylene-acrylic acid copolymer is even more preferable.

As a specific example of an ethylene-acrylic copolymer, for example, an aqueous dispersion of an ethylene-acrylic acid copolymer ammonium salt, Zaixen (registered trademark) AC (acrylic acid copolymerization ratio 20%, manufactured by Sumitomo Seika Co., Ltd.), is available.

In addition, the back coating layer of the present invention may contain water-soluble polymers, water-dispersible resins, pigments, etc., as long as there is no problem with the water vapor barrier property.

Examples of the water-soluble polymer include polyvinyl alcohols other than ethylene-vinyl alcohol copolymers, such as fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol; proteins such as casein, soy protein and synthetic protein; oxidized starch, cationic starch, urea phosphate ester starch, hydroxyethyl etherified starch, hydroxyethyl etherified starch, cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose and hydroxyethyl cellulose; polyvinyl pyrrolidone, sodium alginate, etc.

Examples of this water-dispersed resin include natural rubber, diene rubber, non-diene rubber, and thermoplastic elastomer.

As this pigment, any pigment usable in a heat-sensitive recording layer can be suitably used, but aluminum hydroxide, silica, kaolin, and calcined kaolin are preferable, and aluminum hydroxide is more preferable.

This back coating layer may additionally, as needed, appropriately contain an activator, a cross-linking agent, an ultraviolet absorber, a dispersant, an antifoaming agent, a fluorescent dye, etc. that can be used in the heat-sensitive recording layer, within a range that does not impede the desired effect for the above task.

The content (solid content) of the ethylene-vinyl alcohol copolymer in the back coating layer is preferably 10 to 80 wt%, more preferably 10 to 50 wt%.

The content (solid content) of the ethylene-acrylic copolymer in the back coating layer is preferably 10 to 80 wt%, more preferably 50 to 80 wt%.

However, the total content (solid content) of the ethylene-vinyl alcohol copolymer and the ethylene-acrylic copolymer in the back coating layer is preferably 50 to 100 wt%, more preferably 50 to 90 wt%, and even more preferably 70 to 90 wt%.

In addition, the content ratio (solid content) of the ethylene-acrylic copolymer to the ethylene-vinyl alcohol copolymer is preferably 2.5 parts to 40 parts, more preferably 10 to 40 parts, per 10 parts by mass of the ethylene-vinyl alcohol copolymer.

In addition, the pigment content (solid content) in the back coating layer is preferably 50 to 10 wt%, more preferably 30 to 10 wt%.

The amount of the back coating layer applied is determined according to the required performance and recording suitability, and is not particularly limited, but a general amount applied is about 0.1 to 5 g/m ² in terms of solid content. Of this, an amount of about 2.5 to 4.5 g/m ² is preferable because it provides excellent vapor barrier properties and also provides excellent quality as a heat-sensitive recording medium.

The heat-sensitive recording layer of the present invention contains a leuco dye and a developer, and may optionally further contain a sensitizer, a binder, a pigment, a cross-linking agent, an image stabilizer, and other components.

As the leuco dye used in the present invention, any known in the art in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and is not particularly limited, but triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds, etc. are preferable. Specific examples of representative colorless to light-colored leuco dyes (dye precursors) are shown below. In addition, these dye precursors can be used alone or in combination of two or more.

<Triphenylmethane Leuco dye>

3,3-Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide [aka crystal violet lactone]; 3,3-Bis(p-dimethylaminophenyl)phthalide [aka malachite green lactone]

<Fluorane Leuco dye>

3-Diethylamino-6-methylfluorane; 3-diethylamino-6-methyl-7-anilinofluorane; 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluorane; 3-diethylamino-6-methyl-7-chlorofluorane; 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluorane; 3-diethylamino-6-methyl-7-(o-chloroanilino)fluorane; 3-diethylamino-6-methyl-7-(p-chloroanilino)fluorane; 3-diethylamino-6-methyl-7-(o-fluoroanilino)fluorane; 3-diethylamino-6-methyl-7-(m-methylanilino)fluorane; 3-diethylamino-6-methyl-7-n-octylanilinofluorane; 3-Diethylamino-6-methyl-7-n-octylanilinofluorane; 3-Diethylamino-6-methyl-7-benzylaminofluorane; 3-Diethylamino-6-methyl-7-dibenzylaminofluorane; 3-diethylamino-6-chloro-7-methylfluorane; 3-diethylamino-6-chloro-7-anilinofluorane; 3-diethylamino-6-chloro-7-p-methylanilinofluorane; 3-diethylamino-6-ethoxyethyl-7-anilinofluorane; 3-diethylamino-7-methylfluorane; 3-diethylamino-7-chlorofluorane; 3-diethylamino-7-(m-trifluoromethylanilino)fluorane; 3-diethylamino-7-(o-chloroanilino)fluorane; 3-Diethylamino-7-(p-chloroanilino)fluorane; 3-diethylamino-7-(o-fluoroanilino)fluorane; 3-diethylamino-benzo[a]fluorane; 3-diethylamino-benzo[c]fluorane; 3-dibutylamino-6-methyl-fluorane; 3-dibutylamino-6-methyl-7-anilinofluorane; 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluorane; 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluorane; 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluorane; 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluorane; 3-Dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluorane; 3-Dibutylamino-6-methyl-chlorofluorane; 3-Dibutylamino-6-ethoxyethyl-7-anilinofluorane; 3-Dibutylamino-6-chloro-7-anilinofluorane; 3-Dibutylamino-6-methyl-7-p-methylanilinofluorane; 3-Dibutylamino-7-(o-chloroanilino)fluorane; 3-Dibutylamino-7-(o-fluoroanilino)fluorane; 3-Di-n-pentylamino-6-methyl-7-anilinofluorane; 3-Di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluorane; 3-Di-n-pentylamino-7-(m-trifluoromethylanilino)fluorane; 3-Di-n-pentylamino-6-chloro-7-anilinofluorane; 3-Di-n-pentylamino-7-(p-chloroanilino)fluorane; 3-pyrrolidino-6-methyl-7-anilinofluorane; 3-piperidino-6-methyl-7-anilirofluorane; 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluorane; 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluorane; 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluorane; 3-(N-Ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran; 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran; 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran; 3-cyclohexylamino-6-chlorofluoran; 2-(4-Oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluorane; 2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluorane; 2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluorane; 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluorane; 2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluorane; 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluorane; 2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluorane; 2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluorane; 2-Amino-6-p-(p-diethylaminophenyl)aminoanilinofluorane; 2-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluorane; 2-Phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluorane; 2-Benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluorane; 2-Hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluorane; 3-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluorane; 3-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluorane; 3-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluorane; 2,4-Dimethyl-6-[(4-dimethylamino)anilino]-fluorane

<Fluorene Leuco dye>

3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-Tris(diethylamino)spiro[fluorene-9,3'-phthalide)

<Divinyl 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

<Other>

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)fluoran-γ-(3'-nitro)anilinolactam; 3,6-bis(diethylamino)fluoran-γ-(4'-nitro)anilinolactam; 1,1-Bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane; 1,1-Bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane; 1,1-Bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane; Bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester

As a developer that can be used in the heat-sensitive recording medium of the present invention, one known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and is not particularly limited, but for example, inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate, 4,4'-isopropylidenediphenol, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxydiphenylsulfide, hydroquinone monobenzyl ether, 4-hydroxybenzoic acid benzyl, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, Bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane, a phenol condensation composition described in Japanese Patent Application Laid-Open No. 2003-154760, an aminobenzenesulfonamide derivative described in Japanese Patent Application Laid-Open No. Hei 8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, bis(p-hydroxyphenyl)butyl acetate, Phenolic compounds such as bis(p-hydroxyphenyl)acetate methyl, 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), N-[2-(3-phenylureide)phenyl]benzenesulfonamide, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, and diphenylsulfone bridged compounds described in WO97/16420, WO02/081229 or Japanese Patent Application Laid-Open No. Examples thereof include the compounds described in No. 2002-301873, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis[4-(n-octyloxycarbonylamino)zinc salicylate] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-trylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, and antipyrine complexes of zinc thiocyanate, complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids, etc. These developers can be used alone or in combination of two or more. 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane is available, for example, from Mitsubishi Chemical Corporation under the trade name TOMILAC214, a phenol condensation composition described in Japanese Patent Application Laid-Open No. 2003-154760 is available, for example, from Mitsubishi Chemical Corporation under the trade name TOMILAC224, and a diphenylsulfone cross-linked compound described in International Publication WO97/16420 is available under the trade name D-90 from Nippon Soda Co., Ltd. In addition, compounds described in WO02/081229 and the like are available under the trade names NKK-395, D-100 from Nippon Soda Co., Ltd.

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

As binders usable in the present invention, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminal alkyl-modified polyvinyl alcohol, cellulose ethers such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and acetyl cellulose and their derivatives, starch, enzymatically modified starch, thermochemically modified starch, oxidized starch, and esterified starch. Starch, etherified starch (e.g., hydroxyethylated starch, etc.), cationic starch, etc.; polyacrylamides, such as polyacrylamide, cationic polyacrylamide, anionic polyacrylamide, and amphoteric polyacrylamide; urethane resins, such as polyester polyurethane resins, polyether polyurethane resins, and polyurethane ionomer resins; acrylic resins composed of (meth)acrylic acid and monomer components copolymerizable with (meth)acrylic acid (excluding olefins); styrene-butadiene resins, such as styrene-butadiene copolymers, styrene-butadiene-acrylonitrile copolymers, and styrene-butadiene-acrylic copolymers; polyolefins, such as polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers. Examples thereof include resins, polyvinyl chloride, polyvinylidene chloride, polyacrylic acid esters, gum arabic, polyvinyl butyral, polystyrene and copolymers thereof, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. These may be used alone or in combination of two or more.

Examples of pigments usable in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. These may be used alone or in combination of two or more.

Examples of crosslinking agents usable in the present invention include glyoxal, methylolmelamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, ammonium chloride, etc.

In addition, in the present invention, as an image stabilizer that exhibits an oil resistance effect of a recorded image, etc., within a range that does not inhibit the desired effect for the above task, 4,4'-butylidene(6-t-butyl-3-methylphenol), 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)diphenylsulfone, etc. can also be used.

In addition, benzophenone or triazole-based ultraviolet absorbers, activators, dispersants, anti-foaming agents, antioxidants, and fluorescent dyes can be used.

The types and amounts of the electron-donating leuco dye, the electron-accepting developer, and other various components used in the thermosensitive recording medium of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. However, typically, for 1 part by weight of the electron-donating leuco dye, about 0.5 to 10 parts by weight of the electron-accepting developer and about 0.5 to 10 parts by weight of the sensitizer are used.

The types and amounts of other optional components such as binders, pigments, cross-linking agents, image stabilizers, and other ingredients are determined according to the required performance and recording suitability and are not particularly limited. However, typically, the binder is suitably used in an amount of 5 to 50 parts by weight of solids per 100 parts by weight of the thermal recording layer (solids content), and the pigment is suitably used in an amount of 0 to 50 parts by weight of solids per 100 parts by weight of the thermal recording layer (solids content). When an activator is used, the content of the activator is suitably used in an amount of 5 to 10 parts by weight of solids per 100 parts by weight of the thermal recording layer (solids content).

In the thermosensitive recording medium of the present invention, a protective layer may be further formed on the thermosensitive recording layer. The protective layer often contains pigment and resin as main components, and binders, pigments, cross-linking agents, etc., which are exemplified as materials that can be used in the thermosensitive recording layer, may be used.

As this binder, any binder usable in the above-described thermal recording layer may be suitably used, and carboxyl-modified polyvinyl alcohol and non-core-shell type acrylic resin are preferable. One or more of these binders may be used.

In addition, as a crosslinking agent, a crosslinking agent usable in the above-described thermal recording layer can be suitably used, and an epichlorohydrin-based resin and a polyamine/polyamide-based resin (excluding those included in the epichlorohydrin-based resin) are preferable.

It is more preferable to contain an epichlorohydrin-based resin and a polyamine/polyamide-based resin together with a carboxyl-modified polyvinyl alcohol in the protective layer, thereby further improving the coloring performance.

This carboxyl-modified polyvinyl alcohol is obtained in the form of a saponified product of, for example, a reaction product of polyvinyl alcohol and a polyhydric carboxylic acid such as fumaric acid, phthalic anhydride, mellitic anhydride, or itaconic anhydride, or an ester product of these reactants, or additionally, a copolymer of vinyl acetate and an ethylenically unsaturated dicarboxylic acid such as maleic acid, fumaric acid, itaconic acid, crotonic acid, acrylic acid, or methacrylic acid. As a specific manufacturing method, there can be mentioned a method exemplified in, for example, Japanese Patent Application Laid-Open No. 53-91995. In addition, the degree of saponification of the carboxyl-modified polyvinyl alcohol is preferably 72 to 100 mol%, and the degree of polymerization is preferably 500 to 2400, more preferably 1000 to 2000.

The glass transition point (Tg) of this non-core shell type acrylic resin is preferably 95°C or lower, and more preferably higher than 50°C. This Tg is measured by differential scanning calorimetry (DSC).

This non-core-shell type acrylic resin contains (meth)acrylic acid and a monomer component copolymerizable with (meth)acrylic acid, and it is preferable that the (meth)acrylic acid is 1 to 10 parts by weight per 100 parts by weight of the non-core-shell type acrylic resin. (Meth)acrylic acid is alkali-soluble and has a property of making the non-core-shell type acrylic resin a water-soluble resin by the addition of a neutralizing agent. By changing the non-core-shell type acrylic resin into a water-soluble resin, especially when the protective layer contains a pigment, the bonding property to the pigment is significantly improved, and a protective layer having excellent strength can be formed even when a large amount of pigment is contained. As components copolymerizable with (meth)acrylic acid, examples thereof include alkyl acrylic acid resins such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate; modified alkyl acrylic acid resins such as alkyl acrylic acid resins modified with epoxy resins, silicone resins, styrene or derivatives thereof; (meth)acrylonitrile, acrylic acid esters, and hydroxyalkyl acrylic acid esters; and it is particularly preferable to blend (meth)acrylonitrile and/or methyl methacrylate. It is preferable that (meth)acrylonitrile is blended in an amount of 15 to 70 parts per 100 parts of the non-core-shell type acrylic resin. In addition, it is preferable that methyl methacrylate is blended in an amount of 20 to 80 parts per 100 parts of the non-core-shell type acrylic resin. When (meth)acrylonitrile and methyl methacrylate are included, it is preferable that (meth)acrylonitrile is blended in an amount of 15 to 18 parts per 100 parts of the non-core-shell type acrylic resin, and methyl methacrylate is blended in an amount of 20 to 80 parts per 100 parts of the non-core-shell type acrylic resin.

This epichlorohydrin resin is a resin characterized by containing an epoxy group in the molecule, and examples thereof include polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, etc., and these can be used alone or in combination. In addition, as the amine present in the main chain of the epichlorohydrin resin, any amine from primary to quaternary can be used, and there is no particular limitation. In addition, since the water resistance is good, the cationization degree and molecular weight are preferably cationization degree of 5 meq/g·Solid or less (measured value at pH 7) and molecular weight of 500,000 or more. Specific examples of ^{epichlorohydrin} resins include Sumirez® Resin 650(30), Sumirez® Resin 675A, Sumirez® Resin 6615 (all manufactured by Sumitomo Chemical Co., Ltd.), WS4002, WS4020, WS4024, WS4030, WS4046, WS4010, CP8970 (all manufactured by Seiko PMC Co., Ltd.).

This polyamine/polyamide-based resin does not have an epoxy group in its molecule, and examples thereof include polyamide urea resin, polyalkylene polyamine resin, polyalkylene polyamide resin, polyamine polyurea resin, modified polyamine resin, modified polyamide resin, polyalkylene polyamine urea formalin resin, polyalkylene polyamine polyamide polyurea resin, and the like, and these can be used alone or in combination. Specific examples of polyamine/polyamide resins include Sumirezu Resin 302 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirezu Resin 712 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirezu Resin 703 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirezu Resin 636 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirezu Resin SPI-100 (Sumitomo Chemical Co., Ltd.: modified polyamine resin), Sumirezu Resin SPI-102A (Sumitomo Chemical Co., Ltd.: modified polyamine resin), Sumirezu Resin SPI-106N (Sumitomo Chemical Co., Ltd.: modified polyamide resin), Sumirezu Resin SPI-203(50) (Sumitomo Chemical Co., Ltd.), Sumirezu Resin SPI-198 (Sumitomo Chemical Co., Ltd.), Examples thereof include Printiv A-700, Printiv A-600 (all manufactured by Asahi Kasei), PA6500, PA6504, PA6634, PA6638, PA6640, PA6644, PA6646, PA6654, PA6702, PA6704 (all manufactured by Seiko PMC: polyalkylene polyamine polyamide polyurea resin), CP8994 (manufactured by Seiko PMC: polyethyleneimine resin), etc. There is no particular limitation, but since the print concentration is good, it is preferable to use a polyamine resin (polyalkylene polyamine resin, polyamine polyurea resin, modified polyamine resin, polyalkylene polyamine urea formalin resin, polyalkylene polyamine polyamide polyurea resin).

When using an epichlorohydrin-based resin and a polyamine/polyamide-based resin together with a carboxyl-modified polyvinyl alcohol in the protective layer, the content is preferably 1 to 100 parts by weight, more preferably 5 to 50 parts by weight, and even more preferably 10 to 40 parts by weight, per 100 parts by weight of the carboxyl-modified polyvinyl alcohol.

As the pigment used in the protective layer, any pigment usable in the above-mentioned heat-sensitive recording layer may be suitably used, and kaolin, calcined kaolin, aluminum hydroxide, and silica are preferable. One or more of these pigments may be used.

The content (solid content) of the binder in the protective layer is preferably 20 wt% or more, more preferably 20 to 80 wt%, and when the protective layer contains a pigment, the content of the pigment and binder is preferably 30 to 300 wt% of the binder as a solid content per 100 wt% of the pigment.

The protective layer coating solution may appropriately contain various auxiliary agents, such as a crosslinking agent, an activator, a stabilizer, an ultraviolet absorber, a dispersant, an anti-foaming agent, an antioxidant, a fluorescent dye, etc., that can be used in the above-mentioned heat-sensitive recording layer, as needed.

Additionally, an undercoat layer can be formed between the support and the thermal recording layer. This undercoat layer is mainly composed of a binder and a pigment.

As a binder used in the lower layer, various binders used in the thermal recording layer described above can be used. One type or two or more types of these binders can be used.

As pigments used in the lower layer, various pigments used in the thermal recording layer described above can be used. One or more of these pigments can be used.

The pigment in the lower layer is usually 50 to 95 parts by weight, preferably 70 to 90 parts by weight, based on 100 parts by weight of the total solid content of the lower layer.

Various auxiliary agents such as dispersants, plasticizers, pH regulators, anti-foaming agents, water retaining agents, preservatives, coloring dyes, and UV blockers can be appropriately mixed into the sublayer as needed.

By coating a coating solution composed of the composition prescribed for each of the above coating layers on any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired heat-sensitive recorder is obtained. In addition, a composite sheet combining these can also be used as a support.

Electron-donating leuco dyes, electron-accepting developer, electron acceptor, electron donor and additional materials as needed are ground into particles of several microns or less using a pulverizer such as a ball mill, attritor or sand grinder or an appropriate emulsifying device, and various additives are added according to the purpose to make a coating solution.

The means for coating each of the above coating layers is not particularly limited, and coating can be performed according to a well-known and commonly used technique. For example, an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a rod blade coater, a bent blade coater, a bevel blade coater, a roll coater, a curtain coater, and a spray coater is appropriately selected and used. The coating amount of the thermal recording layer is determined according to the required performance and recording suitability, and is not particularly limited, but a general coating amount is about 2 to 12 g/m ² in terms of solid content.

In addition, various known technologies in the field of thermal records can be appropriately added, such as performing a smoothing treatment such as super calendaring after coating each coating layer.

[Example]

Hereinafter, the present invention will be illustrated by examples, but the present invention is not intended to be limited thereto. In addition, in each example and comparative example, unless otherwise specifically stated, 'part' represents 'part by weight' and '%' represents 'weight%'.

[Preparation of each coating solution]

A coating solution for the lower layer was prepared by stirring and dispersing a mixture composed of the following proportions.

<Coating solution for lower layer>

Calcined Kaolin (Imellis, Alphatex HP) 50 copies

Plastic Hollow Particles (Zeon Sae, MH8109) 50 pieces

Styrene-butadiene copolymer latex (made by Japan Zeon, ST5526, solid content 48%) 10 parts

　Water 50 copies

Next, coating solutions 1 to 6 for the back coating layer were prepared by mixing the mixtures prepared in the following ratios.

<Coating solution for back coating layer 1>

Kaolin (Imellis Priest, Product Name: Contour 1500) 20 pieces

Ethylene-vinyl alcohol copolymer (manufactured by Kuraray, product name: Exevar RS4104)

Part 10

Ethylene-acrylic copolymer (Sumitomo Seika Co., Ltd., Trade name: Zaixen AC, Melting point: 80 to 95℃) 40 parts

<Coating solution for back coating layer 2>

Kaolin (Imellis, Product Name: Contour 1500) 20 pieces

　Ethylene-Vinyl Alcohol Copolymer (RS4104) 10 parts

　Ethylene-Acrylic Copolymer (Zyxen AC) 20 parts

　Styrene-Butadiene Copolymer Latex (ST5526) 20 pieces

<Coating solution for back coating layer 3>

Kaolin (Contour 1500) 20 pieces

　Ethylene-Acrylic Acid Copolymer (Zyxen AC) 50 pieces

<Coating solution for back coating layer 4>

Kaolin (Contour 1500) 20 pieces

Ethylene-Vinyl Alcohol Copolymer (RS4104) 50 pieces

<Coating solution for white coating layer 5>

Kaolin (Contour 1500) 20 pieces

　Completely saponified polyvinyl alcohol aqueous solution (PVA117) 10 parts

　Ethylene-Acrylic Copolymer (Zyxen AC) 40 parts

<Coating solution for white coating layer 6>

Kaolin (Contour 1500) 20 pieces

　Ethylene-Vinyl Alcohol Copolymer (RS4104) 10 parts

　Styrene-Butadiene Copolymer Latex (ST5526) 40 pieces

The following mixing ratio of the developer dispersion, the leuco dye dispersion, and the sensitizer dispersion were each separately wet-ground using a sand grinder until the average particle size became 0.5 micron.

Dispersion of colorant (A1 solution)

N-[2-(3-phenylureide)phenyl]benzenesulfonamide (Nippon Soda Co., Ltd., NKK1304, hereinafter referred to as 'urea compound') 6.0 parts

Completely saponified polyvinyl alcohol aqueous solution (Kurare, PVA117, solid content 10%) 5.0 parts

　Water Part 1.5

Dispersion of colorant (A2 solution)

　4-Benzyloxy-4'-hydroxydiphenylsulfone (Nikka Chemical Co., Ltd., BPS-MA3) 6.0 parts

　Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts

　Water Part 1.5

Leuco dye dispersion (B solution)

　3-Dibutylamino-6-methyl-7-anilinofluorane (Yamamoto Kasei Co., Ltd., ODB-2) 6.0 parts

　Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts

　Water Part 1.5

Dispersant dispersion (Solution C)

　1,2-Bis-(3-methylphenoxy)ethane (Sankosha, KS232) 6.0 parts

Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts

　Water Part 1.5

Next, each dispersion was mixed in the following ratio to prepare a coating solution for a thermal recording layer.

<Coating solution for thermal recording layer 1>

　Dispersion solution (A1 solution) 18.0 parts

　Royco dye dispersion (B solution) 18.0 parts

　Dispersant Dispersion Solution (C Solution) 36.0 parts

Silica dispersion (Mizusawa Chemical Co., Ltd., Mizukasil P-537, solid content 25%)

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　 17.5

Completely saponified polyvinyl alcohol aqueous solution (PVA117) 30.0 parts

<Coating solution for thermal recording layer 2>

　Dispersion solution (A2 solution) 18.0 parts

　Royco dye dispersion (B solution) 18.0 parts

　Dispersant Dispersion Solution (C Solution) 36.0 parts

Silica Dispersion (Mizukasil P-537) 17.5 parts

Completely saponified polyvinyl alcohol aqueous solution (PVA117) 30.0 parts

Next, a coating solution for a protective layer was prepared by mixing a mixture prepared in the following ratio.

<Coating solution for protective layer>

Aluminum hydroxide dispersion (Martinsberg, product name: Matifin OL, solid content 50%) 9.0 parts

Carboxylic modified polyvinyl alcohol aqueous solution (manufactured by Kuraray, product name: KL318, degree of polymerization: approx. 1700, degree of saponification: 95 to 99 mol%, solid content 10%) 30.0 parts

Polyamide epichlorohydrin resin (manufactured by Seiko PMC, product name: WS4030, solid content 25%) 4.0 parts

Modified polyamine resin (Sumitomo Chemical Co., Ltd., product name: Sumirezu Resin SPI-102A, solid content 45%) 2.2 Part

Zinc stearate (made by Chukyo Oil & Fat Co., product name: Hydrin Z-7-30, solid content 30%) 2.0 parts

　Water 22.8

[Example 1]

A coating solution for the undercoat was applied to one side of a support (high-quality paper having a basis weight of 60 g/m ² ) using the bent blade method so that the coating amount in terms of solid content was 6.0 g/m ² , and then dried to obtain a coated paper for the undercoat.

A coating solution 1 for a thermal recording layer was applied on the lower layer of the lower layer coated paper using a rod blade method so that the coating amount in terms of solid content was 3.0 g/ ^m2 , and then dried and processed using a super calendar so that the smoothness became 500 to 1000 seconds, thereby producing a thermal recording layer coated paper.

Next, a protective layer coating solution was applied onto the thermal recording layer of the thermal recording layer coated paper using a rod blade method so that the solid content was 3.0 g/ ^m2 , and then drying was performed to produce a protective layer coated paper.

Next, on the surface opposite to the protective layer of the protective layer coating paper, the coating solution 1 for the back coating layer was applied using the rod blade method so that the solid content was 3.5 g/ ^m2 , and then drying was performed to produce a thermal recorder.

[Example 2]

A thermal recorder was produced in the same manner as in Example 1, except that the coating amount of the coating solution for the back coating layer was set to 2.0 g/ ^m2 .

[Example 3]

A thermal recorder was produced in the same manner as in Example 1, except that the coating amount of the coating solution for the back coating layer was set to 2.5 g/ ^m2 .

[Example 4]

A thermal recorder was produced in the same manner as in Example 1, except that the coating amount of the coating solution for the back coating layer was set to 4.5 g/ ^m2 .

[Example 5]

A thermal recorder was produced in the same manner as in Example 1, except that the coating solution for the back coating layer was 30 parts of ethylene-vinyl alcohol copolymer and 20 parts of ethylene-acrylic copolymer.

[Example 6]

A thermal recorder was produced in the same manner as in Example 1, except that the coating solution for the back coating layer was 40 parts of ethylene-vinyl alcohol copolymer and 10 parts of ethylene-acrylic copolymer.

[Example 7]

A thermal recording body was produced in the same manner as in Example 1, except that the thermal recording layer coating solution 2 was used instead of the thermal recording layer coating solution 1.

[Example 8]

A thermal recorder was produced in the same manner as in Example 1, except that coating solution 2 for the back coating layer was used instead of coating solution 1 for the back coating layer.

[Comparative Example 1]

A thermal recorder was produced in the same manner as in Example 1, except that coating solution 3 for the back coating layer was used instead of coating solution 1 for the back coating layer.

[Comparative Example 2]

A thermal recorder was produced in the same manner as in Example 1, except that coating solution 4 for the back coating layer was used instead of coating solution 1 for the back coating layer.

[Comparative Example 3]

A thermal recorder was produced in the same manner as in Example 1, except that coating solution 5 for the back coating layer was used instead of coating solution 1 for the back coating layer.

[Comparative Example 4]

A thermal recorder was produced in the same manner as in Example 1, except that coating solution 6 for the back coating layer was used instead of coating solution 1 for the back coating layer.

[Comparative Example 5]

A thermal recorder was produced in the same manner as in Example 1, except that the coating solution for the back coating layer was not applied.

The following evaluation was conducted on the produced thermal record.

<Color development performance (factor concentration)>

For the produced thermal record, a check pattern was printed using a TH-PMD (thermal recording paper printing tester, equipped with a thermal head made by Kyocera) manufactured by Okura Electric Co., Ltd. at an applied energy of 0.35 mJ/dot and a printing speed of 50 mm/sec. The printing density of the printing section was measured using a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development performance.

<Double-sided moisture-proofing performance>

For the manufactured thermal recorder, performance evaluation was conducted under the following two conditions.

(1) Storage at 23℃×50%RH×24 hours → Factor under 23℃×50%RH conditions

(2) Storage at 35℃×80%RH×24 hours → Factor under 23℃×50%RH conditions

That is, using the UP-X898MD (medical thermal printer) from SONY, after printing one volume (20 m) of a plain pattern under the S mode condition, the moisture-proof performance was evaluated by visually observing whether water droplets were attached to the damper section of the printer on the opposite side of the thermal head, using the following criteria.

○: No water droplets attached

△: Water droplets adhere, but disappear quickly

×: Water droplets stick and don't disappear for several minutes

××: Water droplets stick and don't disappear for hours

<Blocking the winding>

The thermal records were processed into small rolls (110 mm × 20 m), left to stand for 24 hours under environmental conditions of 35°C × 80%RH, and then visually evaluated using the following criteria.

○: No blocking at all, no peeling of the protective layer or back coating layer.

×: Blocking occurs and the protective layer and/or back coating layer are peeled off.

The results are shown in Table 1.

[Table 1]

As shown in Table 1, the thermal recording material of the present invention has an excellent water vapor barrier property that prevents adhesion of water droplets on the reverse side without adversely affecting color development sensitivity.

Claims (4)

A heat-sensitive recording material having a heat-sensitive recording layer formed on a support containing a colorless to light-colored electron-donating leuco dye and an electron-accepting developer, and a back coating layer formed on the opposite side of the heat-sensitive recording layer, wherein the back coating layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.
In the first paragraph,
A heat-sensitive recording medium, wherein the content ratio (solid content) of an ethylene-acrylic copolymer to an ethylene-vinyl alcohol copolymer is 2.5 parts to 40 parts by mass per 10 parts by mass of the ethylene-vinyl alcohol copolymer.
In paragraph 1 or 2,
A heat-sensitive recording medium, wherein the total content (solid content) of ethylene-vinyl alcohol copolymer and ethylene-acrylic copolymer in the back coating layer is 50 to 90 wt%.
In any one of claims 1 to 3,
A heat-sensitive recording medium having a coating amount of 2.5 to 4.5 g/ ^m2 of a back coating layer.