Heat-sensitive recording body and method for producing same

Abstract

Provided is a heat-sensitive recording body having excellent cuttability of a heat seal layer. This heat-sensitive recording body has a heat seal layer including a water-dispersible resin binder on one side of a paper substrate, and a heat-sensitive recording layer including a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the other side of the substrate, and has an air resistance of 100,000 seconds or less.

Description

Thermosensitive recording medium and method for producing the same

[0001] The present invention relates to a thermosensitive recording medium provided with a heat-sealing layer and a thermosensitive recording layer on a substrate, and a method for producing the same.

[0002] Generally, a film having a heat-sealing layer is heat-sealed (sheet-sealing treatment) to packaging materials such as formed foods, bags, containers, boxes, cups, lid materials, etc. Further, a label has been developed in which a thermosensitive recording layer is provided on the opposite surface to the heat-sealing layer (thermoplastic resin layer) of this film so that information such as contents can be printed (Patent Document 1).

[0003] JP 2011-8089

[0004] By the way, in the case of the technique described in Patent Document 1, it has been found that the cutting property of the heat-sealing layer during production is inferior. Specifically, the heat-sealing layer protrudes from the cut surface during cutting.

[0005] Therefore, an object of the present invention is to provide a thermosensitive recording medium excellent in the cutting property of the heat-sealing layer and a method for producing the same.

[0006] As a result of intensive studies, the present inventors have found that the cutting property of the heat-sealing layer is improved by containing a water-dispersible resin binder as the heat-sealing layer, and have completed the present invention. Although the reason for this is not clear, it is considered that the heat-sealing layer containing the water-dispersible resin binder can be manufactured by coating, and has a lower tensile strength than the heat-sealing layer manufactured by a general laminating method, making it easier to cut. That is, the present invention has a heat-sealing layer containing a water-dispersible resin binder on one surface of a paper substrate, and a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the other surface of the paper substrate, and has an air permeability resistance of 100,000 seconds or less.

[0007] According to the present invention, a thermosensitive recording medium excellent in the cutting property of the heat-sealing layer can be obtained.

[0008] The specific details of the present invention will be described below. The thermal recording material of the present invention has a heat-seal layer containing a water-dispersible resin binder on one side of the substrate, and a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the other side of the substrate, and has an air permeability resistance of 100,000 seconds or less.

[0009] The heat-seal layer of the present invention contains a water-dispersible resin binder. Examples of water-dispersible resin binders include polyolefins, ethylene-vinyl acetate resins, styrene-acrylic acid ester copolymer resins, acrylic resins, polyester resins, polyvinyl alcohol resins, polyvinyl acetate resins, and polylactic acid resins. Ethylene-methacrylic acid copolymer resins are particularly preferred.

[0010] The heat seal layer of the present invention is preferably a coated layer. As described above, a heat seal layer containing a water-dispersible resin binder can be manufactured by coating, and it is thought that it will have lower tensile strength and be easier to cut than a heat seal layer manufactured by a general lamination method. When coating the heat seal layer of the present invention, an aqueous solution containing the above-mentioned water-dispersible resin binder particles is coated onto one side of a paper substrate and dried, causing the binder particles to dissolve and integrate with each other to form a film-like coated layer.

[0011] The water-dispersible resin binder particles are not limited to particles of water-dispersible (synthetic) resins, but examples include water-dispersible polyolefins and styrene-butadiene copolymers. Among the water-dispersible polyolefins, ethylene-methacrylic acid copolymer resins and ethylene-vinyl acetate copolymer particles are particularly preferred. The water-dispersible resin binder particles do not contain surfactants or organic solvents and are simply resin particles. A specific example of ethylene-methacrylic acid copolymer resin particles is Chemipearl S500, manufactured by Mitsui Chemicals, Inc. A specific example of ethylene-vinyl acetate copolymer is Chemipearl V100, manufactured by Mitsui Chemicals, Inc. A specific example of styrene-butadiene copolymer is Nipol Latex LX407S12, manufactured by Nippon Zeon Corporation.

[0012] Immediately after application, this coating layer appears as aggregated particles of water-dispersible resin binder. However, upon drying, the particles bond together, forming a film-like (layered) coating layer as described above.

[0013] On the other hand, a thermal recording layer is provided on the side of the paper substrate opposite to the side with the heat-seal layer (the other side). The thermal recording layer contains a colorless or light-colored electron-donating leuco dye (hereinafter also referred to as "leuco dye") and an electron-accepting developer (hereinafter also referred to as "developer"), and color is produced by utilizing the color reaction of these.

[0014] With the above configuration, the thermal recording material of the present invention can be used, for example, for sealing bento boxes in convenience stores. Variable information such as ingredient information can be printed on the thermal recording layer, and after wrapping it around the bento box, the heat-seal layer on the back can be heat-sealed to the bento box.

[0015] The air permeability resistance of the thermal recording material of the present invention is 100,000 seconds or less. If the air permeability resistance exceeds 100,000 seconds, it is considered that the heat seal layer has poor permeability, and consequently the heat seal layer is a uniform and high-strength laminate layer, resulting in reduced cutability. In contrast, in the case of a coated layer coated with an aqueous solution containing particles of a water-dispersible resin binder, some particles do not dissolve, leaving minute gaps, which reduces the air permeability resistance to 100,000 seconds or less, and is presumed to reduce the strength compared to a laminate layer, making it easier to cut. The air permeability resistance is measured by a method in accordance with JIS P8117:2009 (Wang-Gan type testing machine method).

[0016] In the thermal recording body of the present invention, the adhesive strength between the thermal recording layer and the heat seal layer is preferably 0.5 N / 15 mm or more, preferably 1.0 N / 15 mm or more, and more preferably 2.0 N / 15 mm or more. If the adhesive strength between the thermal recording layer and the heat seal layer is less than 0.5 N / 15 mm, there is a problem in that the thermal recording layer or the heat seal layer peels off from the substrate. There is no upper limit to the adhesive strength between the thermal recording layer and the heat seal layer, but for example it is 5.0 N / 15 mm. The adhesive strength was measured in accordance with JIS Z1707:2019 7.4 "Heat seal strength test". Two square test pieces with sides of 100 mm were cut out, the coated layers were brought into contact with each other, and heat-sealed at a pressurizing temperature of 130°C, a pressurizing pressure of 2 kgf / cm2, and a pressurizing time of 0.5 seconds. Furthermore, a measurement sample was cut out from the heat-sealed 100 mm square test piece so that the long side was 100 mm and the short side was 15 mm. Subsequently, the peeled long edge portions were clamped in the upper and lower fixtures of a vertical tensile testing machine (Tensilon, manufactured by A&D Company, Ltd.), and the adhesive strength was measured while peeling the sample from the long edge side at a speed of 200 mm / min (T-type).

[0017] In this case, when an undercoat layer is provided between the thermal recording layer and the substrate, the strength of the undercoat layer may decrease and the undercoat layer may peel off depending on the type of pigment contained in the undercoat layer. Therefore, by providing an undercoat layer containing hollow particles as pigment, as described later, between the thermal recording layer and the paper substrate, the adhesive strength between the thermal recording layer and the heat seal layer can be reliably maintained at 1.0 N / 15 mm or higher.

[0018] Next, examples of various materials used in the thermal recording layer of the thermal recording body of the present invention are given, but binders, crosslinking agents, pigments, etc., can also be used in each coating layer provided as needed, to the extent that they do not hinder the desired effect on the above-mentioned problems.

[0019] The paper substrate of the present invention is not particularly limited and can be used as long as it is made from pulp, such as high-quality paper, recycled paper, or coated paper.

[0020] Leuco dyes for the thermal recording layer of the present invention: Any leuco dye known in the field of conventional pressure-sensitive or thermal recording paper can be used in the thermal recording layer of the present invention, and there are no particular limitations, however triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds, etc. are preferred. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used individually or in mixtures of two or more.

[0021] <Triphenylmethane-based leuco dyes> 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)

[0022] <Fluorane-based leuco dyes> 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-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anili Nofluoran, 3-diethylamino-6-chloro-7-p-methylanilinofluoran, 3-diethylamino-6-ethoxyethyl-7-anilinofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(p-chloroanilino)fluoran, 3-diethylamino-7-(o-fluoroanilino)fluoran, 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-7-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-anilinofluorane, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinof Luoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 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-anilino Fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 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) Minophenyl)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-dibutylaminophenyl)aminoanilinofluorane, 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluorane,

[0023] <Fluorene-based leuco dyes> 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0024] <Divinyl Leuco Dyes> 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

[0025] <Others> 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide, 3,3-bis(1-ethyl-2-methylindole-3-yl)phthalide, 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam, 3,6-bis(diethylamino) Mino)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]-methylmalonate dimethyl ester

[0026] Developer for the thermal recording layer: Any developer known in the field of conventional pressure-sensitive or thermal recording paper can be used in the thermal recording layer of the present invention, and is not particularly limited. Examples include 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'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxybenzoate benzyl, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, and 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone. , 3,4-dihydroxyphenyl-4'-methylphenylsulfone, aminobenzenesulfonamide derivatives described in Japanese Patent Publication No. Hei 8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, bis(p-hydroxyphenyl)butyl acetate, bis(p-hydroxyphenyl)methyl acetate, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,4-bis[α-methyl-α-(4'-hydroxy Phenolic compounds such as phenyl)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), diphenyl sulfone crosslinked compounds described in WO97 / 16420, compounds described in WO02 / 081229 or Japanese Patent Publication No. 2002-301873, and N,Examples include thiourea compounds such as 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-tolylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, as well as salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, and also antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids.

[0027] The diphenylsulfone crosslinked compound described in WO97 / 16420 is available from Nippon Soda Co., Ltd. under the trade name D-90. The compounds described in WO02 / 081229, etc., are also available from Nippon Soda Co., Ltd. under the trade names NKK-395 and D-100. In addition, metal chelate-type coloring components such as higher fatty acid metal double salts and polyvalent hydroxyaromatic compounds described in Japanese Patent Publication No. 10-258577 can also be included. Furthermore, phenol developer 4-benzyloxy-4'-hydroxydiphenylsulfone (e.g., BPS-MA3, manufactured by Nikka Chemical Co., Ltd.) and environmentally friendly non-phenol developer urea compounds (e.g., NKK1304, manufactured by Nippon Soda Co., Ltd.) can be used. These developer agents can be used individually or in combination of two or more.

[0028] Sensitizers Conventional known sensitizers can be used as sensitizers for use in the thermal recording layer of the present invention. Such sensitizers include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylenebisamide, montanic acid 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 oxalate), dibenzyl terephthalate, p-benzyloxybenzoate benzyl, di-p-tolyl carbonate, pheny Examples of sensitizers include, but are not limited to, ru-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoate phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methylphenoxymethyl)biphenyl, 4,4'-ethylenedioxy-bis-benzoate dibenzyl ester, dibenzoyloxymethane, 1,2-di(3-methylphenoxy)ethylene, bis[2-(4-methoxyphenoxy)ethyl] ether, p-methyl nitrobenzoate, and p-toluenesulfonate phenyl. These sensitizers may be used individually or in combination of two or more.

[0029] Examples of binders usable in the thermal recording layer of the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-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, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, and cellulose derivatives such as ethylcellulose and acetylcellulose, casein, gum arabic, oxidized starch, etherified starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrene and copolymers thereof, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, coumarone resins, and the like.

[0030] These polymeric substances can be used dissolved in solvents such as water, alcohol, ketones, esters, and hydrocarbons, or dispersed in water or other media in an emulsified or paste-like state, and can be used in combination depending on the required quality.

[0031] Crosslinking Agents Examples of crosslinking agents that can be used in the thermal recording layer of the present invention include glyoxal, methylolmelamine, melamineformaldehyde resin, melamineurea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, and ammonium chloride.

[0032] Pigments that can be used in the thermal recording layer of the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium dioxide, and aluminum hydroxide. Furthermore, when considering the wear resistance of the thermal head, kaolin, calcined kaolin, and aluminum hydroxide are preferred as pigments to be used in the protective layer described later.

[0033] Lubricants that can be used in the thermal recording layer of the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

[0034] Image stabilizers In addition, in the thermal recording layer of the present invention, within the range that does not hinder the desired effects for the above-mentioned problems, image stabilizers that exhibit oil resistance effects on recorded images, such as 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., may be added. Others that can be used include benzophenone-based and triazole-based ultraviolet absorbers, dispersants, defoamers, antioxidants, fluorescent dyes, etc.

[0035] The leuco dye, developer, sensitizer, and any additional materials used in the thermal recording layer of the present invention are pulverized to a particle size of a few microns or less using a pulverizer such as a ball mill, attritor, or sand grinder, or a suitable emulsifier, and then coated with a binder and various additives as needed to form a coating solution. The amount of the above materials is determined according to the required performance and recording suitability and is not particularly limited, but it is preferably about 0.5 to 10 parts by weight of developer and 0.5 to 10 parts by weight of sensitizer per 1 part by weight of leuco dye. The amount of thermal recording layer to be coated is not particularly limited, but it is preferably in the range of 2 to 12 g / m2 in terms of solid content.

[0036] The thermal recording material of the present invention may further have an undercoat layer between the paper substrate and the thermal recording layer. This undercoat layer mainly consists of a binder and a pigment.

[0037] As pigments used in the undercoat layer, inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium dioxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, and talc, and organic pigments such as hollow plastic particles can be used. One or more of these pigments may be used.

[0038] Using organic pigments such as hollow plastic particles as the pigment for the undercoat layer is preferable because it improves the strength of the undercoat layer. In other words, as already mentioned, depending on the type of pigment contained in the undercoat layer (for example, calcined kaolin), the strength of the undercoat layer may decrease and the undercoat layer may peel off. Therefore, by providing an undercoat layer containing hollow particles as a pigment, as described later, between the thermal recording layer and the paper substrate, the strength of the undercoat layer can be improved, and the adhesive strength between the thermal recording layer and the heat seal layer can be improved.

[0039] Hollow particles are microscopic hollow particles that are already in a foamed state, with a thermoplastic resin shell containing air or other gases inside. Examples of thermoplastic resins include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid esters, polyacrylonitrile, polybutadiene, or copolymers thereof. Particularly preferred are styrene-based resins such as polystyrene, acrylic-based resins such as polyacrylic acid esters and polyacrylonitrile, copolymers thereof, or copolymer resins mainly composed of polyvinylidene chloride and polyacrylonitrile. Such organic hollow particles are available as SX8782 from JSR Corporation, MH5055 and MH8108A from Nippon Zeon Corporation, Rohm & Haas Japan Co., Ltd., and Microspheres from Matsumoto Oil & Fat Co., Ltd.

[0040] The volume void ratio of the plastic hollow particles used in the present invention is preferably about 40 to 95%. By setting the volume void ratio to 40% or more, the heat insulation property can be improved and the coloring performance can be further enhanced. On the other hand, by setting it to 95% or less, the strength of the shell of the hollow particles can be increased to effectively maintain the hollow state, and it becomes easy to obtain an undercoat layer with good surface strength. Here, the volume void ratio is a value obtained by (d3 / D3) × 100. In the formula, d represents the inner diameter of the organic hollow particles, and D represents the outer diameter of the organic hollow particles.

[0041] For the purpose of improving the storage stability of the printed image, the heat-sensitive recording layer of the present invention may be provided with a protective layer on the heat-sensitive recording layer within a range that does not inhibit the desired effects on the above problems. The means for coating each layer such as the heat-sealing layer, the undercoat layer, the heat-sensitive recording layer, and the protective layer is not particularly limited, and can be coated according to well-known and commonly used techniques. Examples of the coating method for each layer include the air knife method, the rod blade method, the vent blade method, the bevel blade method, the roll method, the slot type curtain method, the slide type curtain method, the slide hopper type curtain method, the bead type curtain method, the spray method, the die method, etc., and these coating methods are appropriately selected and used. In addition, various known techniques in the field of heat-sensitive recording media can be appropriately added, such as performing a smoothing treatment such as super calendering after coating each layer.

[0042] When the heat-sealing layer is a coating layer, compared with the case of forming the heat-sealing layer by the lamination method, the production speed is improved, and since it can be produced by the same coating machine as the heat-sensitive recording layer that is usually formed by coating, the cost is reduced.

[0043] The manufacturing method of the heat-sensitive recording medium of the present invention includes a first step of coating a heat-sealing layer containing a water-dispersible resin binder on one surface of a paper substrate, and a second step of coating a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the other surface of the paper substrate before or after the first step.

[0044] In particular, in the method for manufacturing a heat-sensitive recording medium of the present invention, when a second step is performed after the first step, the number of times the heat-sensitive recording layer formed in the second step passes through the drying zone can be reduced, so that a heat-sensitive recording medium excellent in whiteness on the heat-sensitive recording layer side can be obtained.

[0045] Hereinafter, the present invention will be illustrated by examples, but it is not intended to limit the present invention. In each of the examples and comparative examples, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.

[0046] [Preparation of each coating liquid] A formulation having the following composition was stirred and dispersed to prepare a coating liquid for the undercoat layer. <Coating liquid 1 for undercoat layer> 100 parts of plastic hollow particles (manufactured by Zeon Corporation, MH8109) 10 parts of styrene-butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd., ST5526, solid content 48%) 50 parts of water

[0047] <Coating liquid 2 for undercoat layer> 100 parts of calcined kaolin (manufactured by BASF, trade name: Anshilex 90) 10 parts of styrene-butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd., ST5526, solid content 48%) 50 parts of water

[0048] The developer dispersion liquids (A1 to 2 liquids), leuco dye dispersion liquid (B liquid), and sensitizer dispersion liquid (C liquid) having the following compositions were each separately wet-milled with a sand grinder until the average particle size reached 0.5 μm.

[0049] Developer dispersion liquid (A1 liquid) 6.0 parts of 4-benzyloxy-4'-hydroxydiphenyl sulfone (manufactured by Nihon Kayaku Co., Ltd., BPS-MA3) 5.0 parts of a fully saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., PVA117, solid content 10%) 1.5 parts of water

[0050] Chromogenic dispersant (Solution A2) Urea compound (Nippon Soda Co., Ltd., NKK1304) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts Chromogenic dispersant (Solution A3) N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0051] Leuco dye dispersion (Solution B) 3-Dibutylamino-6-methyl-7-anilinofluorane (manufactured by Yamamoto Chemical Co., Ltd., ODB-2) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts Sensitizer dispersion (Solution C) 1,2-Bis-(3-methylphenoxy)ethane (manufactured by Sanko Co., Ltd., KS232) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0052] Next, the following dispersions were mixed to prepare a coating solution for the thermal recording layer. <Coating solution for the thermal recording layer> Developer dispersion (Solution A1) 18.0 parts Leuco dye dispersion (Solution B) 18.0 parts Sensitizer dispersion (Solution C) 36.0 parts Silica dispersion (Mizusawa Chemical Co., Ltd., Mizukasil P-537, 25% solids) 17.5 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 30.0 parts

[0053] Next, a protective coating solution was prepared by mixing the following mixtures in the following proportions. <Protective coating solution 1> Aluminum hydroxide dispersion (manufactured by Martinsberg, trade name: Martiffin OL, solids content 50%) 9.0 parts Carboxylated polyvinyl alcohol aqueous solution (manufactured by Kuraray, trade name: KL318, degree of polymerization: approximately 1800, degree of saponification: 85-90 mol%, solids content 10%) 30.0 parts Polyamide epichlorohydrin resin (manufactured by Seikoh PMC, trade name: WS4030, solids content 25%) 4.0 parts Modified polyamine resin (manufactured by Taoka Chemical Co., Ltd., trade name: Sumire's Resin SPI-102A, solids content 45%) 2.2 parts Zinc stearate (manufactured by Chukyo Oil & Fat Co., Ltd., trade name: Hydrin Z-7-30, solids content 30%) 2.0 parts

[0054] <Coating Liquid for Protective Layer 2> Aluminum hydroxide dispersion (Martiffin OL) 9.0 parts Silane-modified acrylic resin (Tg 18°C, MFT 22°C, solids content 40%) 5.0 parts Non-core-shell type acrylic resin (manufactured by Mitsui Chemicals, trade name: ASN1004K, no silane modification, Tg 55°C, MFT 18°C, solids content 18%) 11.1 parts Zinc stearate (Hydrin Z-7-30) 1.0 part Carbodiimide crosslinking agent (Carbodilite SV-02) 2.0 parts

[0055] [Example 1] Paper substrate (basis weight 60 g / m²) ２ On one side of high-quality paper, an ethylene-methacrylic acid copolymer resin (manufactured by Mitsui Chemicals, product name: Chemipearl S500, solids content 42%) is applied as a water-dispersible resin binder, with a coating weight of 6.0 g / m² based on solids. ２ After coating using the rod-blade method, the paper was dried to produce coated paper with a heat-seal layer. On the opposite side of this coated paper with a heat-seal layer, a primer coating liquid was applied at a solid content rate of 6.0 g / m². ２After coating using the bent blade method, the paper was dried to obtain coated paper with a primer layer.

[0056] On the undercoat layer of this undercoated paper, a thermal recording layer coating liquid is applied at a solid content rate of 3.0 g / m². ２ After coating using the rod blade method, the paper was dried and then treated with a supercalender to achieve a smoothness of 500 to 1000 seconds to produce coated paper with a thermal recording layer. Next, protective coating liquid 1 was applied to the thermal recording layer of this coated paper with a solid content of 3.0 g / m². ２ To achieve this, the material was coated using the rod-blade method, then dried to form a protective layer, and a thermal recording body was fabricated.

[0057] [Example 2] A thermal recording body was prepared in the same manner as in Example 1, except that the protective layer coating liquid was not applied. [Example 3] A thermal recording body was prepared in the same manner as in Example 1, except that protective layer coating liquid 2 was used instead of protective layer coating liquid 1. [Example 4] A thermal recording body was prepared in the same manner as in Example 1, except that thermal recording layer coating liquid A2 was used instead of thermal recording layer coating liquid A1.

[0058] [Example 5] A thermal recording body was prepared in the same manner as in Example 1, except that coating liquid 2 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer. [Example 6] A thermal recording body was prepared in the same manner as in Example 1, except that the heat-seal layer coated paper was prepared after the protective layer coated paper. A thermal recording body was prepared in the same manner as in Example 1, except that the undercoat layer, thermal recording layer, and protective layer were formed on one side of the paper substrate, and then the heat-seal layer was formed on the opposite side. [Example 7] A thermal recording body was prepared in the same manner as in Example 1, except that coating liquid A3 for the thermal recording layer was used instead of coating liquid A1 for the thermal recording layer. [Example 8] A thermal recording material was prepared in the same manner as in Example 1, except that a styrene-butadiene copolymer (manufactured by Zeon Corporation, product name: Nipol Latex LX407S12, solid content 46.5%) was used as the water-dispersible resin binder instead of an ethylene-methacrylic acid copolymer resin (manufactured by Mitsui Chemicals, trade name: Chemipearl S500, solid content 42%).

[0059] [Comparative Example 1] When preparing coated paper with a heat-seal layer, polyethylene (MFR 20 g / 10 min, density 0.888 g / cm³, melting point 55°C) was used instead of ethylene-methacrylic acid copolymer resin, and co-extrusion lamination was performed. Specifically, co-extrusion lamination was performed using a T-die at an extrusion temperature of 300°C, and immediately afterward, these molten resins and the paper substrate were pressed and compressed with a cooling roll and a nip roll with a hardness of 95 degrees at a linear pressure of 15 kgf / cm, and then the surface was subjected to surface corona treatment. Otherwise, a thermal recording material was prepared in the same manner as in Example 1.

[0060] [Comparative Example 2] Before applying the heat seal layer, a primer layer, a heat-sensitive layer, and a protective layer were applied to create a protective layer coated paper. Furthermore, a heat seal layer was provided on the protective layer of the protective layer coated paper, except that the same procedure was followed to create the heat seal layer. [Comparative Example 3] When creating the coated paper with a heat seal layer, the heat seal layer was prepared after the protective layer coated paper, and further, a heat seal layer was provided on the protective layer of the protective layer coated paper, except that the same procedure was followed to create the heat seal layer.

[0061] The following evaluations were performed on the fabricated thermal recording material. <Heat seal suitability> Two 100 mm square test pieces were cut from the fabricated thermal recording material, and the protective layer or thermal recording layer was brought into contact with the heat seal layer. The pressure was set at a temperature of 130°C and a pressure of 2 kgf / cm². ２ The test pieces were heat-sealed with a pressurizing time of 0.5 seconds or 1.0 second. The heat-sealable properties were evaluated by visually observing the peeled areas when the heat-sealed test pieces were peeled off by hand, according to the following criteria: ○: Peeling within the paper substrate (paper substrate is destroyed) △: Partial peeling within the paper substrate (paper substrate is partially destroyed) ×: Adheres but peels outside the paper substrate (paper substrate is not destroyed, peeling occurs between coating layers)

[0062] <Waterproof Adhesion> Two 100mm square test pieces were cut from the prepared thermal recording material, and the protective layer or thermal recording layer was brought into contact with the heat seal layer. The pressure was set at a temperature of 130°C and a pressure of 2 kgf / cm². ２The test pieces were heat-sealed with a pressurization time of 0.5 seconds or 1.0 second. The heat-sealed test pieces were immersed in 23°C water for 24 hours and then air-dried. After air-drying, the test pieces were peeled off by hand, and the water-resistant adhesion was visually observed to see if the adhesive state was maintained, and evaluated according to the following criteria: ○: Adhesion state is maintained ×: Adhesion state is not maintained, and it peeled off before being peeled off by hand

[0063] <Cuttable Performance> Using a KOKUYO paper cutter (DN-1), a 100 mm square test piece was cut from the prepared thermal recording material. The cut surface was visually observed, and the cuttable performance was evaluated according to the following criteria: ○: The heat-sealed layer does not protrude from the paper substrate. ×: The heat-sealed layer protrudes from the paper substrate (the heat-sealed layer is difficult to cut).

[0064] <Color Development Performance (Print Density)> A checkerboard pattern was printed on the fabricated thermal recording material using a TH-PMD (thermal recording paper printing tester, equipped with a Kyocera thermal head) manufactured by Okura Electric Co., Ltd., with an applied energy of 0.35 mJ / dot and a printing speed of 50 mm / sec. The print density of the printed area was measured using a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development performance.

[0065] <Oil Resistance> A checkerboard pattern was printed on the prepared thermal recording material using a TH-PMD manufactured by Okura Electric Co., Ltd., with an applied energy of 0.35 mJ / dot and a printing speed of 50 mm / sec. Salad oil was applied to the printed thermal recording material with a cotton swab, and after being left for 24 hours, the print density of the printed area was measured with a Macbeth densitometer. <Air Permeability Resistance> This was measured according to the method in accordance with JIS P8117:2009 (Wang-Gan type testing machine method).

[0066] The evaluation results are shown in Table 1.

[0067]

[0068]

[0069] As shown in Tables 1 and 2, the cutability of the heat-seal layer was excellent in each embodiment. In Embodiment 2, where no protective layer was provided, the oil resistance was inferior to that of the other embodiments, but this does not pose a practical problem.

[0070] On the other hand, in Comparative Example 1, where the heat-seal layer was formed by lamination, the air permeability resistance exceeded 100,000 seconds, and the cutability of the heat-seal layer was poor. Furthermore, the water-resistant adhesion was also poor. The reason for the decrease in water-resistant adhesion is not clear, but the heat-seal layer formed by lamination has a higher smoothness of the coating layer compared to the coating layer of a water-dispersible resin binder. On the other hand, the protective layer or thermal recording layer to be bonded is formed by coating, so there are minute irregularities on the surface. Therefore, the heat-seal layer formed by lamination, which has a high degree of smoothness, is more prone to gaps forming at the adhesive surface when heat-sealed compared to the coating layer of a water-dispersible resin binder, and it is thought that water penetrated through these gaps in the water-resistant adhesion test, resulting in a decrease in adhesion. In Comparative Examples 2 and 3, where the heat-seal layer was formed on the surface of the thermal recording layer, the color development performance decreased because the heat-seal layer was interposed on top of the thermal layer.

Claims

1. A thermal recording body having a heat-seal layer containing a water-dispersible resin binder on one side of the substrate, and a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting color developer on the other side of the paper substrate, wherein the air permeability resistance is 100,000 seconds or less.

2. The heat-seal layer is a coating layer, according to claim 1.

3. The thermal recording body according to claim 1 or 2, wherein the water-dispersible resin binder is an ethylene-methacrylic acid copolymer resin.

4. The thermal recording body according to claim 1 or 2, further comprising an undercoat layer between the paper substrate and the thermal recording layer.

5. The thermal recording body according to claim 4, wherein the undercoat layer contains hollow particles as a pigment.

6. The thermal recording body according to claim 1 or 2, wherein the adhesive strength between the thermal recording layer and the heat seal layer is 0.5 N / 15 mm or more.

7. A method for manufacturing a thermal recording body, comprising: a first step of coating one surface of a paper substrate with a heat-seal layer containing a water-dispersible resin binder; and a second step of coating the other surface of the paper substrate, either before or after the first step, with a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer.

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