Protective layer printing ink for heat-sensitive recording media

Abstract

To provide a protective layer printing ink for heat-sensitive recording media, and a heat-sensitive recording medium obtained using the ink and exhibiting excellent print preservation and thermal head matching properties.SOLUTION: A protective layer printing ink for heat-sensitive recording media comprises a binder, a slipperiness imparting agent, and a solvent, wherein the binder is a polyvinyl acetal resin, and the slipperiness imparting agent is an alkyl phosphate ester and / or a salt thereof. Also provided is a heat-sensitive recording medium that includes a protective layer formed using the protective layer printing ink on at least a part of one or both surfaces of a support.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a printing ink for a protective layer for a thermosensitive recording medium, and to a thermosensitive recording medium. [Background technology]

[0002] Thermal recording media that utilize the color-developing reaction between leuco dyes and color developers are relatively inexpensive, the recording equipment is compact, and maintenance is easy. As a result, they are widely used not only as recording media for facsimiles, various calculators, CAD plotters, etc., but also for food applications such as fresh produce, bento boxes, and prepared dishes, medical applications such as labels for drug management, and labels for process control.

[0003] When used for food applications such as labels, top seals, and bands on transparent containers for salads and prepared foods, a highly transparent medium is often required so that the contents can be clearly seen. In such cases, transparent heat-sensitive film with a transparent PET film base is generally used.

[0004] Patent document 1 reports that a thermosensitive coloring film, which is characterized by having a protective layer of a resin coating layer containing magnesium oxide formed on the top surface of a thermosensitive coloring ink layer formed by applying a thermosensitive coloring ink to the surface of a supporting substrate, has both heat resistance and water resistance.

[0005] Patent Document 2 reports that a thermosensitive recording medium having a support and a thermosensitive recording layer on the support, wherein the thermosensitive recording layer contains a specific color developer compound and a styrene-acrylic resin, has all of warm water resistance, water resistance, ethanol resistance, temperature and humidity resistance, water abrasion resistance, and heat resistance, and in the examples, a PET film is used as the support, and a protective layer containing a styrene-acrylic resin, oxidized polyethylene wax, and calcium carbonate is formed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3382728 [Patent Document 2] Japanese Patent Publication No. 2022-146283 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a protective layer printing ink for a thermal recording medium, and a thermal recording medium using the same which has excellent print storage stability and thermal head matching properties. [Means for solving the problem]

[0008] The present inventors have conducted extensive research in light of the above-mentioned prior art and have come to solve the above-mentioned problems. That is, the present invention relates to the following protective layer printing ink for a thermosensitive recording medium and a thermosensitive recording medium.

[0009] Item 1: A protective layer printing ink for a thermal recording medium containing a binder, a slipping agent, and a solvent, characterized in that the protective layer printing ink for a thermal recording medium contains a polyvinyl acetal resin as the binder and an alkyl phosphate ester and / or a salt thereof as the slipping agent. Item 2: The protective layer printing ink according to Item 1, wherein the protective layer printing ink contains 75 to 99 mass% of polyvinyl acetal resin and 1 to 25 mass% of alkyl phosphate ester and / or salt thereof based on the total solid content of the protective layer printing ink. Item 3: The protective layer printing ink according to Item 1 or 2, wherein the polyvinyl acetal resin has a number average molecular weight of 17,000 to 40,000. Item 4: The protective layer printing ink according to any one of Items 1 to 3, wherein the alkyl phosphate ester salt is neutralized with sodium or calcium, and the first acid value of the alkyl phosphate ester is 135 mgKOH / g or less. Item 5: The protective layer printing ink according to any one of Items 1 to 4, further comprising calcined kaolin having an average particle size of 2.0 μm or less, the content of the calcined kaolin being 0.5 to 10 mass % of the total solid content of the protective layer printing ink. Item 6: The protective layer printing ink according to any one of Items 1 to 5, wherein the solvent contains an alcohol and a cycloalkane. Item 7: The protective layer printing ink according to any one of Items 1 to 6, wherein the protective layer printing ink is a gravure printing ink. Item 8: A thermosensitive recording medium having a protective layer formed on at least a portion of one or both sides of a support using the protective layer printing ink according to any one of Items 1 to 7. Item 9: The thermosensitive recording medium according to Item 8, which has a thermosensitive recording layer between the support and the protective layer. Item 10: The thermosensitive recording medium according to Item 8 or 9, wherein the support is a translucent or transparent support made of glassine paper or resin-laminated paper, or a transparent film made of cellophane or a synthetic resin film. Item 11: The thermosensitive recording medium according to any one of Items 8 to 10, which has a heat seal layer on at least a portion of one or both sides of the support. Item 12: The thermosensitive recording medium according to Item 11, which is a top seal lid material. [Effects of the Invention]

[0010] A thermosensitive recording medium having a protective layer formed using the printing ink for a thermosensitive recording medium protective layer of the present invention has excellent print storage stability and thermal head matching, as well as excellent transparency. DETAILED DESCRIPTION OF THE INVENTION

[0011] In this specification, the expression "comprise" includes the concepts of "comprise," "consist essentially of," and "consist only of."

[0012] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0013] The latex in the present invention includes a gel or a dried film formed by drying a dispersion medium.

[0014] The protective layer printing ink for a thermosensitive recording medium of the present invention is a protective layer printing ink for a thermosensitive recording medium containing a binder, a slipping agent, and a solvent, and is characterized in that it contains a polyvinyl acetal resin as the binder and an alkyl phosphate ester and / or a salt thereof as the slipping agent.

[0015] The thermosensitive recording medium of the present invention is characterized in that it has a protective layer formed on at least a portion of one or both sides of the support using the protective layer printing ink of the present invention.

[0016] [Protective layer printing ink for thermal recording media] (binder) The protective layer printing ink of the present invention contains a polyvinyl acetal resin as a binder, which can improve print storage stability (particularly plasticizer resistance) and thermal head matching (particularly head-cure suitability), as well as transparency.

[0017] Polyvinyl acetal resins are resins that can be produced by, for example, reacting polyvinyl alcohol with an aldehyde to acetalize it. The aldehyde is not particularly limited, and examples thereof include formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0018] Examples of polyvinyl acetal resins include polyvinyl butyral resins in which the acetal group is a butyral group, and polyvinyl acetoacetal resins in which the acetal group is an acetoacetal group.

[0019] The number average molecular weight of such polyvinyl acetal resin is preferably 17,000 to 40,000, more preferably 17,000 to 32,000, and even more preferably 17,000 to 27,000. By setting it to 17,000, print storage stability (particularly plasticizer resistance) and thermal head matching (particularly head deposit suitability) can be improved. By setting it to 40,000 or less, the ink concentration of the protective layer can be increased. The number average molecular weight in the present invention is the number average molecular weight analyzed by GPC (gel permeation chromatography).

[0020] The content of such polyvinyl acetal resin is not particularly limited, and is preferably about 75 to 99 mass % of the total solids content of the protective layer printing ink, more preferably about 75 to 90 mass %, and even more preferably about 80 to 85 mass %. By making it 75 mass % or more, print storage stability (especially plasticizer resistance) can be improved. By making it 99 mass % or less, thermal head matching (especially anti-sticking) can be improved.

[0021] Other binders may be contained as long as they do not impair the effects of the present invention. Examples of other binders that can be used include aqueous binders, such as water-soluble binders and water-dispersible binders. Examples of water-soluble binders include modified polyvinyl alcohols such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol; starch and its derivatives; cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose; polyvinylpyrrolidone; polyamides; diisobutylene-maleic anhydride copolymer salts; styrene-maleic anhydride copolymer salts; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers, as well as latexes of water-insoluble polymers such as styrene-butadiene copolymers. Other binders that can be used include, for example, organic solvent-soluble binders. Examples of organic solvent-soluble binders include vinyl acetate resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, vinylpyrrolidone-vinyl acetate copolymer resins, butyral resins, polyester resins, nitrocellulose resins, and styrene resins. The binders can be used alone or in combination of two or more.

[0022] (Slip-imparting agent) The heat-sensitive color-forming printing ink of the present invention contains an alkyl phosphate ester and / or a salt thereof as a slippage-imparting agent, which can improve thermal head matching (particularly head-cure suitability) and transparency.

[0023] Alkyl phosphates are compounds in which the hydrogen atoms of one or more of the three hydroxyl groups of phosphoric acid are substituted with alkyl groups, and among these, a mixture of a monoester (monoalkyl phosphate) and a diester is preferred. The number of carbon atoms in the alkyl group of the ester moiety in the alkyl phosphate is preferably 12 to 36, more preferably 12 to 30, and even more preferably 12 to 22. The alkyl group may be linear or branched.

[0024] Examples of alkyl phosphate ester salts include inorganic salts, organic amine salts, and basic amino acid salts. Examples of inorganic salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts and calcium salts; ammonium salts; aluminum salts; and zinc salts. Examples of organic amine salts include monoethanolamine salts, diethanolamine salts, and triethanolamine salts. Examples of basic amino acid salts include arginine salts and lysine salts. Alkyl phosphate ester salts are preferably neutralized with sodium or calcium.

[0025] The first acid value of the alkyl phosphate ester is not particularly limited, but is preferably 135 mgKOH / g or less, more preferably 120 mgKOH / g or less, and even more preferably 100 mgKOH / g or less. By adjusting the first acid value to 135 mgKOH / g or less, background fogging resistance can be improved. The first acid value is measured by neutralization titration or potentiometry.

[0026] The content of such alkyl phosphate ester and / or its salt is not particularly limited, and is preferably about 1 to 25% by mass, more preferably about 1 to 20% by mass, and even more preferably about 3 to 10% by mass, of the total solids content of the protective layer printing ink. By making it 1% by mass or more, thermal head matching properties (smoothness, reduced printing noise) can be improved. By making it 25% by mass or less, print storage stability (plasticizer resistance) can be improved.

[0027] Other lubrication agents may be contained as long as they do not impair the effects of the present invention. Examples of other lubrication agents include higher fatty acid metal salts such as zinc stearate and calcium stearate, and waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, and castor wax. The lubrication agents can be used alone or in combination of two or more.

[0028] (calcined kaolin) In the present invention, the protective layer printing ink can further contain calcined kaolin having an average particle size of 2.0 μm or less. This can improve thermal head matching (particularly head debris suitability). The average particle size of the calcined kaolin is preferably 1.5 μm or less, more preferably 1.3 μm or less. On the other hand, from the viewpoint of thermal head cleaning ability, it is preferably 0.1 μm or more. Here, the average particle size refers to the volume-based median diameter measured by any of the BET method, the Sears method, and the laser diffraction method. More simply, particle sizes can be measured from particle images (SEM images) using an electron microscope and expressed as the average value of 10 particles.

[0029] The content of calcined kaolin with an average particle size of 2.0 μm or less is not particularly limited, and is preferably about 0.5 to 10 mass %, more preferably about 0.5 to 7.0 mass %, and even more preferably about 1.0 to 5.0 mass %, of the total solids content of the protective layer printing ink. By making it 0.5 mass % or more, thermal head matching (particularly head debris suitability) can be improved. By making it 10 mass % or less, abrasion of the thermal head protective film can be reduced.

[0030] (solvent) The protective layer printing ink of the present invention can contain a solvent. Examples of such solvents include water, alcohol, cycloalkane, toluene, and methylcyclohexane, with solvents containing alcohol and cycloalkane being preferred. Alcohols with 5 or fewer carbon atoms are desirable, and examples of such alcohols with 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. Examples of cycloalkanes include cyclopentane, cyclohexane, cycloheptane, cyclocyclooctane, cyclononane, cyclodecane, methylcyclohexane, methylcyclooctane, dimethylcyclohexane, and ethylcyclohexane. The use of alcohol as a solvent enables the ink to be used in gravure printing.

[0031] Other component materials constituting the protective layer printing ink may further include a crosslinking agent, a pigment, etc., if necessary.

[0032] (Crosslinking agent) The protective layer printing ink can contain a crosslinking agent that hardens the binder in the protective layer or other layers. This improves the water resistance of the protective layer. Examples of crosslinking agents include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate, boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, and glyoxylates. These may be used alone or in combination of two or more. The amount of crosslinking agent used is preferably in the range of approximately 1 to 10 parts by mass per 100 parts by mass of the total solids content of the protective layer printing ink. This improves the water resistance of the protective layer.

[0033] (pigment) The pigment contained in the protective layer is not particularly limited and examples thereof include inorganic pigments such as amorphous silica, kaolin, clay, light calcium carbonate, heavy calcium carbonate, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, and synthetic layered mica, and plastic pigments such as urea-formalin resin filler. The pigment content is preferably about 1 to 20% by mass, and more preferably about 1 to 10% by mass, of the total solid content of the protective layer.

[0034] The protective layer printing ink of the present invention is generally prepared by mixing an alcohol and a cycloalkane as a solvent with a binder, a slipping agent, and, if necessary, auxiliary agents.

[0035] The protective layer printing ink of the present invention can be used to form a protective layer of a thermosensitive recording medium on at least a part of one or both sides of a support. The method for forming the protective layer is not particularly limited, and a printing method such as gravure printing is preferred.

[0036] [Support] The support used in the present invention is not particularly limited in type, shape, size, etc., and can be appropriately selected from various transparent supports, such as high-quality paper (acid paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, nonwoven fabric, cellophane, synthetic resin film, etc. Among these, translucent or transparent supports made of glassine paper or resin-laminated paper, or transparent films made of cellophane or synthetic resin film, are preferred. These can enhance the transparency of the non-printed areas of the thermal recording medium. Examples of resins in resin-laminated paper and synthetic resin films include polyester-based resins such as polyethylene terephthalate (PET), and polyolefin-based resins such as polypropylene (PP) and polyethylene (PE). The thickness of the support is not particularly limited and is usually about 5 to 200 μm. The density of the support is also not particularly limited and is 0.60 to 2.00 g / cm. 3 The degree is preferable.

[0037] [Thermal recording layer] In the thermosensitive recording medium, a thermosensitive recording layer can be provided between the support and the protective layer, if necessary. The thermosensitive recording layer is generally formed on the support by printing using a thermosensitive color-developing printing ink. The coating amount of the thermosensitive recording layer is not particularly limited, and is preferably 1 to 12 g / m2 in terms of dry mass. 2 The preferred range is 2 to 10 g / m 2 More preferably, 2.5 to 8 g / m 2 More preferably, 3 to 5.5 g / m 2 The heat-sensitive recording layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[0038] [Thermal color printing ink] (leuco dye) The heat-sensitive color-developing printing ink may contain any of various known colorless or light-colored leuco dyes and color developers.

[0039] Specific examples of leuco dyes include blue-coloring dyes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluoran; green dyes such as 3-(N-ethyl-Np-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam; Red color-forming dyes such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-chlorofluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-diethyl ... -Di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-pentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3- (Nn-hexyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-ethylamino]-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-methylamino]-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di(n-butylamino)-7-(2-chloroanilino)fluoran, 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-Trichlorophenylleucoauramine, 3-diethylamino-7-butylaminofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluoran, 3-diethylamino-6-chloro-7-(γ-chloropropyl)aminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-isopropyl)aminofluoran Soamyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-dibutylamino-7-chloroanilinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-diethylamino -6-chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalido-3,9'-xanthene]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran, etc. Color dyes, 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-p-(p-dimethylaminoanilino)anilino-6-methyl-7-chlorofluoran, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluoran, 3,Examples of such dyes include dyes with absorption wavelengths in the near-infrared region, such as 6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. However, the present invention is not limited to these examples, and two or more compounds can be used in combination as needed.

[0040] The content of the leuco dye is not particularly limited, but is preferably about 15 to 40% by mass, more preferably about 18 to 38% by mass, and even more preferably about 20 to 35% by mass, of the total solids content of the thermosensitive color-developing printing ink. By making it 15% by mass or more, the color-developing ability can be improved and the print density can be improved. By making it 40% by mass or less, the heat resistance can be improved.

[0041] (developer) Specific examples of the color developer include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidene diphenyl, 4,4'-cyclohexylidene diphenol, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 4,4'-bis(p- Tolylsulfonylaminocarbonylamino)diphenylmethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2'-bis[4-(4-hydroxyphenyl)phenoxy]diethyl ether, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenyl sulfone 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'- Methyl diphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate ester, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4,Phenolic compounds such as 4'-dihydroxydiphenyl ether, or benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyl]salicylic acid, aromatic carboxylic acids such as zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, and these phenolic compounds; salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; and organic acids such as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. substances, urea compounds such as Np-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, Np-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, N,N'-di-m-chlorophenylthio Examples of suitable organic compounds include thiourea compounds such as urea, organic compounds having an -SO2NH- bond in the molecule such as N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and N-(o-toluoyl)-p-toluenesulfamide, and inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate.

[0042] Further examples include urea urethane derivatives such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenyl sulfone, all of which are represented by the following general formula (1); diphenyl sulfone derivatives represented by the following general formula (2); N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, and 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. Of course, the compounds are not limited to these, and two or more compounds can be used in combination as needed.

[0043] [ka]

[0044] [ka] (In the formula, n represents an integer of 1 to 6.)

[0045] In addition, the content of the color developer is generally preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 1.2 parts by mass or more, and particularly preferably 1.4 parts by mass or more, per part by mass of the leuco dye. Furthermore, the content of the color developer is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3.5 parts by mass or less, per part by mass of the leuco dye. By using an amount of 0.5 parts by mass or more, recording performance can be improved. On the other hand, by using an amount of 10 parts by mass or less, background fogging in high-temperature environments can be effectively suppressed.

[0046] (binder) The thermosensitive color-developing printing ink of the present invention may contain a binder. Examples of the binder include water-soluble and water-dispersible aqueous binders. Examples of water-soluble binders include modified polyvinyl alcohols such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol; starch and its derivatives; cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose; sodium polyacrylate; polyvinylpyrrolidone; polyamide; diisobutylene-maleic anhydride copolymer salts; styrene-acrylic acid copolymer salts; styrene-maleic anhydride copolymer salts; ethylene-maleic anhydride copolymer salts; acrylamide-acrylic acid ester copolymers; acrylamide-acrylic acid ester-methacrylic acid copolymers; polyacrylamide; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers, and the like, as well as latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Organic solvent-soluble binders can also be used. Examples of organic solvent-soluble binders include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, polyurethanes, saturated polyesters, polyester polyurethanes, epoxy resins, phenoxy resins, nitrocellulose, melamine resins, vinylpyrrolidone-vinyl acetate copolymers, chlorinated polyethylene, and chlorinated polypropylene. Binders can be used alone or in combination of two or more. The binder content can be selected from a wide range, but is generally preferably about 5 to 35% by mass, and more preferably about 9 to 33% by mass, of the total solids content of the thermosensitive color-developing printing ink.

[0047] (solvent) The thermosensitive color-developing printing ink can contain a solvent. Examples of such solvents include water, alcohol, toluene, cyclohexane, and methylcyclohexane, with a solvent containing water and alcohol being preferred. The alcohol is preferably an alcohol having 5 or fewer carbon atoms, and examples of such alcohols having 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. The use of alcohol as a solvent allows the ink to be used in gravure printing.

[0048] (Storage improver) In the present invention, the thermosensitive color-forming printing ink may further contain a storage stability improver, mainly to further improve the storage stability of the colored image. Examples of such storage stability improvers include 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1-bis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisphenol, and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol. At least one selected from phenol compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, epoxy compounds such as 4-(2-methyl-1,2-epoxyethyl)diphenyl sulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenyl sulfone, and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid can be used. Of course, the compounds are not limited to these, and two or more compounds can be used in combination as needed.

[0049] When a storage stability improver is used, the amount used should be an amount effective for improving storage stability, and is usually preferably about 1 to 30 mass % of the total solids content of the thermosensitive color printing ink, and more preferably about 5 to 20 mass %.

[0050] (sensitizer) The thermosensitive color-developing printing ink of the present invention may contain a sensitizer, thereby increasing the recording sensitivity. Examples of sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamilide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy) ether, and the like. p-methylthiophenylbenzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. These can be used in combination within a range that does not cause any problems. The content of the sensitizer may be an amount that is effective for sensitization, and is usually preferably about 2 to 40 mass % of the total solid content of the thermosensitive color developing printing ink, and more preferably about 5 to 25 mass %.

[0051] Other components constituting the heat-sensitive color-developing printing ink may further include, if necessary, crosslinking agents, waxes, metal soaps, water-resistant agents, pigments, dispersants, colored dyes, fluorescent dyes, etc.

[0052] (Crosslinking agent) A crosslinking agent that hardens the binder in the thermosensitive recording layer or other layers can be incorporated into the thermosensitive color-forming printing ink. This improves the water resistance of the thermosensitive recording layer. Examples of crosslinking agents include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate, boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, and glyoxylates. These may be used alone or in combination of two or more. The amount of crosslinking agent used is preferably in the range of approximately 1 to 10 parts by mass per 100 parts by mass of the total solids content of the thermosensitive color-forming printing ink. This improves the water resistance of the thermosensitive recording layer.

[0053] (wax) Examples of waxes include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; higher fatty acid amides such as stearic acid amide and ethylene bisstearic acid amide, higher fatty acid esters, and derivatives thereof.

[0054] (metal soap) Examples of metal soaps include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. If necessary, various auxiliary agents such as oil repellents, antifoaming agents, and viscosity adjusters can be added to the thermosensitive color-developing printing ink within the scope of the present invention.

[0055] The heat-sensitive color-developing printing ink of the present invention is generally prepared by dispersing a leuco dye, a color developer, and optionally a binder, a sensitizer, and a storage stability improver, together or separately, in water and alcohol as a solvent, using a variety of stirring / wet grinding machines such as a ball mill, a Co-ball mill, an attritor, or a vertical or horizontal sand mill to prepare a dispersion, and then dispersing the resulting dispersion to an average particle size of 2 μm or less, and mixing, as required, a binder, an auxiliary agent, etc., with the dispersion.

[0056] The thermosensitive color-developing printing ink of the present invention can be used to form a thermosensitive recording layer on at least a portion of one or both sides of a support. The method for forming the thermosensitive recording layer is not particularly limited, but a printing method such as gravure printing is preferred.

[0057] [Protective layer] The protective layer in the present invention is provided on at least a portion of one or both sides of the support, and is a layer formed using the protective layer printing ink of the present invention.

[0058] The protective layer is generally formed on the support or the thermosensitive recording layer by printing using the protective layer printing ink of the present invention. The coating amount of the protective layer is not particularly limited, and is 0.3 to 15 g / m2 in terms of dry mass. 2 The preferred range is 0.3 to 10 g / m 2 The preferred range is 0.3 to 8 g / m 2 More preferably, the amount is 0.5 to 8 g / m 2 The range of 0.5 to 5 g / m is particularly preferable. 2 The protective layer may be formed in two or more layers as needed, and the compositions and coating amounts of the layers may be the same or different.

[0059] [Undercoat layer] The thermosensitive recording medium of the present invention may also have an undercoat layer between the support and the thermosensitive recording layer, if necessary. The undercoat layer preferably contains a binder.

[0060] (binder) Examples of binders include polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, water-soluble polymer materials such as sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin, and their derivatives, as well as emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers, and latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. These are preferably used for supports such as polyester films (e.g., PET film) and polyester resin-laminated paper. Among these, binders containing latex are preferred. Examples of aqueous binders or solvent-based binders include chlorinated polyolefin resins. Chlorinated polyolefin resins can be preferably used for supports such as polyolefin films such as PP film, polyolefin synthetic paper, polyolefin resin-laminated paper, paper such as glassine paper, cellophane, etc. The binder content can be selected from a wide range, but is generally preferably about 10 to 70 mass % of the total solids content of the undercoat layer, and more preferably about 15 to 60 mass %.

[0061] The binder preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. A glass transition temperature of -10°C or lower can improve image quality even in a low energy range. A glass transition temperature of -30°C or lower is more preferable because it can further improve image quality in a low energy range. On the other hand, a glass transition temperature of -50°C or lower is undesirable because stickiness occurs, so a glass transition temperature of -40°C or higher is preferable.

[0062] The undercoat layer may contain at least one of an oil-absorbing pigment having an oil absorption of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g, organic hollow particles, and thermally expandable particles, where the oil absorption is determined according to the method of JIS K 5101.

[0063] Various oil-absorbing pigments can be used, and specific examples include inorganic pigments such as calcined kaolin, amorphous silica, precipitated calcium carbonate, and talc. The average primary particle size of these oil-absorbing pigments is preferably about 0.01 to 5 μm, and particularly about 0.02 to 3 μm. The amount of oil-absorbing pigment used can be selected from a wide range, but is generally preferably about 20 to 80 mass % of the total solids content of the undercoat layer, and more preferably about 25 to 75 mass %.

[0064] The undercoat layer is formed on the support by, for example, applying a coating liquid for the undercoat layer prepared by mixing a binder, hollow particles, pigments, auxiliaries, etc. with water as a medium, and then drying the coating liquid. Alternatively, the undercoat layer can be formed by a printing method such as gravure printing, similar to the protective layer. The amount of the coating liquid for the undercoat layer to be applied is not particularly limited, but is preferably 2 to 20 g / m2 in terms of dry mass. 2 The preferred range is 2 to 12 g / m 2 A degree is more preferable.

[0065] Examples of auxiliaries contained in the coating liquid for the undercoat layer include dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and fatty acid metal salts; waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax; water-resistant agents such as hydrazide compounds, boric acid, dialdehyde starch, glyoxylates, and epoxy compounds; antifoaming agents; coloring dyes; and fluorescent dyes.

[0066] [Heat seal layer] The thermosensitive recording medium of the present invention may also have a heat seal layer on at least a portion of one or both sides of the support, if necessary. The heat seal layer is preferably provided on the side of the support opposite to the thermosensitive recording layer.

[0067] The heat seal layer in the present invention may be a single-layer film made of a single resin, a single-layer or laminated film made of multiple resins, etc. Preferred examples of the resin constituting the heat seal layer include polyolefin resins (particularly polyethylene, polypropylene, etc.), polystyrene resins, polyester resins (particularly polyethylene terephthalate resins), polyamide resins (particularly nylon), biodegradable resins, etc.

[0068] The polyethylene may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), or high-density polyethylene (HDPE).

[0069] The heat seal layer may be unstretched, or may be uniaxially or biaxially stretched.

[0070] The thickness of the heat seal layer is not particularly limited, but is preferably about 10 to 70 μm, more preferably about 20 to 60 μm, and even more preferably about 30 to 50 μm.

[0071] The heat seal layer may contain additives such as a filler, an antiblocking agent, an antistatic agent, a plasticizer, an oxidizing agent, etc. These additives may be used alone or in combination of two or more.

[0072] The heat seal layer may be formed by extrusion laminating a resin onto the support, or the support and the heat seal layer may be bonded together using an adhesive.

[0073] When an adhesive is used for bonding, the adhesive to be used is not particularly limited, and may be any of solvent-free, organic solvent, and water-based types.

[0074] Examples of the main components that make up the adhesive include (meth)acrylic acid ester copolymers, α-olefin copolymers, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyurethane, styrene-butadiene copolymers, polyvinyl chloride, epoxy resins, melamine resins, silicone resins, natural rubber, casein, and starch.

[0075] The heat-sealing layer may be laminated to the support after applying an adhesive to the heat-sealing layer, or the support may be laminated to the heat-sealing layer after applying an adhesive to the support, or the heat-sealing layer may be laminated to the support after applying an adhesive to both the heat-sealing layer and the support, and the heat-sealing layer and the support may be laminated together, and the method is not particularly limited.

[0076] The method for applying the adhesive may be appropriately selected from conventionally known methods, and is not particularly limited, but examples include a roll coater, a die coater, and a spray coater.

[0077] The amount of adhesive to be applied is not particularly limited, but the amount to be applied (coating amount) after drying is preferably 0.5 g / m 2 More preferably, 1.0 g / m 2 More preferably, 1.5 g / m 2 and preferably 10.0 g / m or more. 2 Less than 7.0 g / m 2 or less, more preferably 5.0 g / m 2 The following is the result.

[0078] [Print layer] In the present invention, a printing layer can be provided on at least one of the following: on the protective layer, between the thermosensitive recording layer and the protective layer, on the thermosensitive recording layer, between the support and the heat-seal layer, and on the surface of the support opposite the thermosensitive recording layer. Printing inks used to form the printing layer can be classified by printing plate type, such as inks used for relief printing, lithographic printing, intaglio printing, and stencil printing. Furthermore, by drying method, inks can be classified by penetration drying, evaporation drying, oxidative polymerization drying, and photopolymerization drying (UV-curing) inks. Printing methods such as flexographic printing, offset printing, gravure printing, and screen printing can be used to form the printing layer. Plateless digital printing methods such as on-demand printing and direct printing can also be used. The color tone of the printing ink is not particularly limited, but it is preferable that the optical density of the printing layer be lower than the optical density of the recording portion of the thermosensitive recording layer, especially when thermal recording is performed on the printing layer. The printing pattern can be partial printing or full-surface solid printing. A background pattern with an optical density of approximately 0.1 to 0.6 or fixed information that does not overlap with the thermal recording is preferred. For example, when the product is used as a top seal lid material on which variable information such as a product name, expiration date, or barcode is thermally recorded, it is preferable to partially print with white ink on the back side of the thermal recording layer of the support, which is the side opposite to the thermal recording layer, thereby improving the readability of the barcode.

[0079] [Thermal recording medium] The thermosensitive recording medium can be produced by forming each of the above layers on a support. The method for forming each of the above layers on a support may be any of known coating methods, such as printing methods such as gravure printing, air knife methods, blade methods, gravure methods, roll coater methods, spray methods, dip methods, bar methods, curtain methods, slot die methods, slide die methods, and extrusion methods. Printing methods such as gravure printing are preferred, and gravure printing is more preferred. Each coating material may be applied and dried one layer at a time to form each layer, or the same coating material may be applied in two or more layers. Simultaneous multilayer coating, in which two or more layers are applied simultaneously, may also be performed. After each layer has been formed, or after all layers have been formed, a smoothing treatment may be performed using known methods such as supercalendering or soft calendering.

[0080] The method for recording an image on the thermal recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose. For example, a thermal head printer, laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser light, YAG laser light, fiber laser light, solid laser light, dye laser light, etc.), etc. can be used as the image recording method. When laser light is used, the wavelength of the laser light is not particularly limited and can be appropriately selected depending on the purpose.

[0081] The thermosensitive recording medium of the present invention has high transparency and excellent resistance to background fogging and plasticizers, making it suitable for use in food applications, such as labels for transparent containers containing salads and prepared foods, and as a top-sealing lid material. Top-sealing lid materials can have increased concealment due to the thermosensitive color-developing printing ink printed on the front and the white ink printed on the back. However, the thermosensitive recording medium of the present invention can increase surface transparency, allowing the contents to be observed through the lid material while confirming information about the contents, such as ingredients. Furthermore, using the thermosensitive recording medium as a top-sealing lid material eliminates the need for a thermosensitive label, improving packaging efficiency and reducing the amount of plastic used. [Example]

[0082] The present invention will be explained in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively. Particle sizes such as the average particle size were measured using a laser diffraction particle size distribution analyzer LB500 (manufactured by Horiba, Ltd.). The average particle size here refers to the median diameter (D50).

[0083] Example 1 (1) Preparation of dye dispersion (liquid A) 30 parts of 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 13 parts of a 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer with a vinylpyrrolidone / vinyl acetate ratio of 30 / 70, 44.5 parts of water, and 12.5 parts of isopropyl alcohol were mixed, and the mixture was ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) to an average particle size of 0.15 μm to obtain a dye dispersion (Liquid A).

[0084] (2) Preparation of developer dispersion liquid (liquid B) 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, 13 parts of a 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer with a vinylpyrrolidone / vinyl acetate ratio of 30 / 70, 44.5 parts of water, and 12.5 parts of isopropyl alcohol were mixed and ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) to an average particle size of 0.15 μm to obtain a developer dispersion (Liquid B).

[0085] (3) Preparation of thermosensitive color-developing printing ink 10 parts of solution A, 20 parts of solution B, 8 parts of a 20% aqueous dispersion of colloidal silica with a particle size of 12 nm, 1.9 parts of water, and 1.9 parts of isopropyl alcohol were mixed and stirred to obtain a thermosensitive color-developing printing ink.

[0086] (4) Preparation of protective layer printing ink A protective layer printing ink was obtained by mixing and stirring 90 parts of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.), 10 parts of an alkyl phosphate ester compound (trade name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.), 450 parts of isopropyl alcohol, and 450 parts of methylcyclohexane.

[0087] (5) Preparation of thermal recording medium Using a five-color gravure printing machine, a heat-sensitive color-developing printing ink was applied to one side of a 12 μm thick transparent PET film in a dried amount of 3.5 g / m 2 A thermal recording layer was formed by printing so that the coating amount after drying was 1.0 g / m 2 The protective layer was then printed with a protective layer printing ink and wound up to form a protective layer. Furthermore, an ester adhesive of 3 g / m was applied by dry lamination to the side opposite to the side on which the thermosensitive color developing printing ink was printed. 2 A 30 μm-thick low-density polyethylene film was laminated to obtain a thermal recording medium with a heat-seal layer. The obtained thermal recording medium was wound into small rolls using a slitter, and then cut into a predetermined shape to form a top seal lid material, which could be sealed to seal a food packaging container.

[0088] Example 2 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer ink in Example 1, polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: S-LEC BM-1, number average molecular weight: 40,000, manufactured by Sekisui Chemical Co., Ltd.).

[0089] Example 3 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer ink in Example 1, polyvinyl acetal resin (trade name: SLECK KS-10, number average molecular weight: 17,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: SLECK KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.).

[0090] Example 4 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer ink of Example 1, an alkyl phosphate ester compound (trade name: Phosphanol RD720, Na neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.) was used instead of an alkyl phosphate ester compound (trade name: Phosphanol SC6103L, Ca neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.).

[0091] Example 5 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the ink for the protective layer in Example 1, an alkyl phosphate ester compound (trade name: Phosphanol RL-210, first acid value: 90 to 100 mg KOH / g, manufactured by Toho Chemical Industry Co., Ltd.) was used instead of the alkyl phosphate ester compound (trade name: Phosphanol RD720, Na neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.).

[0092] Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that the following (6) protective layer printing ink was used instead of the (4) protective layer printing ink in Example 1.

[0093] (6) Preparation of protective layer printing ink A protective layer printing ink was obtained by mixing and stirring 90 parts of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.), 10 parts of an alkyl phosphate ester compound (trade name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.), 5 parts of a 20% isopropyl alcohol dispersion of calcined kaolin with an average particle size of 1.2 μm, 450 parts of isopropyl alcohol, and 450 parts of methylcyclohexane.

[0094] Example 7 A thermal recording medium was prepared in the same manner as in Example 1, except that in the preparation of the thermal recording medium of Example 1, 23 μm thick cellophane was used instead of 12 μm thick transparent PET, and a 20 μm thick polyethylene film was attached to the other side printed with the thermal color-developing printing ink by extrusion lamination.

[0095] (Comparative Example 1) A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer printing ink of Example 1, 100 parts of acrylic resin (product name: BR101, number average molecular weight: 160,000, manufactured by Mitsubishi Chemical Corporation) was used instead of 90 parts of polyvinyl acetal resin (product name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.).

[0096] (Comparative Example 2) A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer printing ink of Example 1, 100 parts of acrylic resin (product name: BR115, number average molecular weight: 50,000, manufactured by Mitsubishi Chemical Corporation) was used instead of 90 parts of polyvinyl acetal resin (product name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.).

[0097] (Comparative Example 3) A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer printing ink of Example 1, 90 parts of polyvinyl acetal resin (product name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) was replaced with 100 parts of styrene-acrylic resin (product name: UC-3080, number average molecular weight: 14,000, manufactured by Toa Gosei Chemical Co., Ltd.).

[0098] Comparative Example 4 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the protective layer printing ink of Example 1, 10 parts of zinc stearate (average particle diameter 1.2 μm) was used instead of 10 parts of an alkyl phosphate ester compound (trade name: Phosphanol RD720, Na neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.).

[0099] The above examples and comparative examples were evaluated by the following methods, and the results are shown in Table 1.

[0100] [Transparency evaluation] The transparency of the non-printed area of ​​each thermal recording medium was measured using a haze meter (NDH-7000 manufactured by Nippon Denshoku Co., Ltd.). (evaluation) ○: Less than 20% (excellent) △: 20% or more and less than 30% (no practical problems) ×: 30% or more (unusable)

[0101] [Heat resistance of scalp] The background fogging of the non-printed areas of each thermal recording medium was measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Co.) by placing the medium on a PPC paper with a whiteness of 85% (JIS P 8148). (evaluation) Less than 0.15: Excellent 0.15 or more and less than 0.25: No practical problems 0.25 or more: Unusable

[0102] [Plasticizer resistance] A polycarbonate pipe (40 mm diameter) was wrapped in three layers of cling film (product name: HI-ES Soft, manufactured by Nippon Carbide Industries Co., Ltd.), and a sample of each thermal recording medium, colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), was placed on top of that. This was then wrapped in three layers of cling film and left to stand at 40°C for 24 hours. Before and after this treatment, the recorded area was placed on a PPC paper with a whiteness of 85% (JIS P 8148), and the reflection density was measured using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Corporation). The remaining rate of the recorded area was calculated using the following formula: Residual rate (%) = (recording density after processing / recording density before processing) x 100

[0103] [Printing sound] Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was printed at an applied energy of 0.243 mJ / dot, and the printing sound was subjected to a sensory evaluation. (evaluation) 〇: Quiet printing △: Slight printing noise (no practical problems) ×: Printing noise is loud

[0104] [Head dust aptitude] Using a label printer (Respli V ex, manufactured by Sato Corporation), after printing 50 cm with a print rate of 100% solid black, the heating element of the thermal head was observed with a stereo microscope (VH-Z100UR, manufactured by Keyence Corporation) and subjected to a sensory evaluation. ◎: No head residue 〇: There is a small amount of head residue △: A little head residue attached (no practical problem) ×: A lot of head residue

[0105] [Table 1]

Claims

1. A protective layer printing ink for a thermal recording medium, which contains a binder, a slipping agent, and a solvent, and is characterized in that it contains a polyvinyl acetal resin as the binder and an alkyl phosphate ester and / or a salt thereof as the slipping agent.

2. 2. The protective layer printing ink according to claim 1, wherein the protective layer printing ink contains 75 to 99 mass% of polyvinyl acetal resin and 1 to 25 mass% of alkyl phosphate ester and / or salt thereof based on the total solid content of the protective layer printing ink.

3. 3. The protective layer printing ink according to claim 1, wherein the polyvinyl acetal resin has a number average molecular weight of 17,000 to 40,000.

4. 3. The protective layer printing ink according to claim 1, wherein the alkyl phosphate ester salt is neutralized with sodium or calcium, and the first acid value of the alkyl phosphate ester is 135 mgKOH / g or less.

5. 3. The protective layer printing ink according to claim 1, further comprising calcined kaolin having an average particle size of 2.0 μm or less, the content of said calcined kaolin being 0.5 to 10 mass% of the total solid content of said protective layer printing ink.

6. The protective layer printing ink according to claim 1 or 2, wherein the solvent comprises an alcohol and a cycloalkane.

7. 3. The protective layer printing ink according to claim 1, wherein the protective layer printing ink is a gravure printing ink.

8. 3. A thermosensitive recording medium having a protective layer formed on at least a portion of one or both sides of a support using the protective layer printing ink according to claim 1 or 2.

9. 9. The thermosensitive recording material according to claim 8, further comprising a thermosensitive recording layer between the support and the protective layer.

10. 9. The thermal recording medium according to claim 8, wherein the support is a translucent or transparent support made of glassine paper or resin-laminated paper, or a transparent film made of cellophane or a synthetic resin film.

11. 9. The thermosensitive recording medium according to claim 8, which has a heat seal layer on at least a portion of one or both sides of the support.

12. The thermosensitive recording medium according to claim 11, which is a top seal lid material.

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