Printing ink for heat-sensitive recording media

Abstract

Disclosed is a printing ink for heat-sensitive recording media, which is (A) or (B) below: (A) a heat-sensitive color-developing printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the color developer is at least one selected from the group consisting of an N,N'-diaryl urea-based compound represented by general formula (1) (in the formula, R0 represents a C1-12 alkyl group, a C7-12 aralkyl group, or a C6-12 aryl group. The aralkyl group and the aryl group may be substituted with a C1-12 alkyl group, a C1-12 alkoxy group, a C6-12 aryl group, or a halogen atom. A plurality of R0s may be the same or different. A1 represents a hydrogen atom or a C1-4 alkyl group. A plurality of A1s may be the same or different.), a compound represented by general formula (2) (in the formula, R1 to R5 are the same or different, and represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group.), and 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide; and (B) a protective layer printing ink for heat-sensitive recording media, the protective layer printing ink containing an adhesive, a slipperiness imparting agent, and a solvent, wherein the adhesive is a polyvinyl acetal resin, and the slipperiness imparting agent is an alkyl phosphate ester and / or a salt thereof.

Description

Printing ink for thermal recording media

[0001] The present invention relates to a printing ink for a thermosensitive recording medium, a thermosensitive recording medium, and an image recording method.

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

[0003] When used for food applications such as labels, top seals, and bands on transparent containers for salads, prepared foods, etc., 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 a thermosensitive recording medium that has all of warm water resistance, water resistance, ethanol resistance, temperature and humidity resistance, water abrasion resistance, and heat resistance, and that can produce high-density images.The thermosensitive recording medium has a support and a thermosensitive recording layer on the support, and the thermosensitive recording layer contains a specific N,N'-diaryl urea compound and a styrene-acrylic resin.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.

[0005] Furthermore, Patent Document 2 reports a thermosensitive recording layer forming liquid that is free from tailing, has excellent background uniformity without coating unevenness, and is capable of forming a thermosensitive recording layer with small thickness variations, and that contains an electron donating compound, an electron accepting compound having a solubility of 5% by mass or less in 100% ethanol at 20°C, and a solvent.

[0006] Patent Document 3 reports that a thermosensitive coloring film 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, and that the film has both heat resistance and water resistance.

[0007] JP 2022-146283 A JP 2022-151636 A Japanese Patent No. 3382728 A

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a printing ink having thermosensitive coloring properties, a thermosensitive recording medium using the same which has high sensitivity, excellent resistance to background fogging and plasticizer resistance, and an image recording method therefor.

[0009] Another 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.

[0010] 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 printing ink for a thermal recording medium, a thermal recording medium, and an image recording method.

[0011] Item 1: A printing ink for a thermal recording medium, which is the following (A) or (B): (A) A thermal color-developing printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the color developer is a compound represented by the following general formula (1):

[0012] (In the formula, R ０ represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the aralkyl group and the aryl group may be substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; ０ may be the same or different. １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a plurality of A １ may be the same or different, an N,N'-diaryl urea compound represented by the following general formula (2):

[0013] (Where R １ ~R ５are the same or different and represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group. A thermosensitive color-developing printing ink comprising a compound represented by the formula (I) and at least one selected from the group consisting of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide; and (B) a protective layer printing ink for a thermosensitive recording medium containing an adhesive, a slipping agent, and a solvent, the protective layer printing ink for a thermosensitive recording medium comprising a polyvinyl acetal resin as the adhesive and an alkyl phosphate ester and / or a salt thereof as the slipping agent. Item 2: The printing ink according to Item 1, which is (A) a thermosensitive color-developing printing ink. Item 3: The printing ink according to Item 2, wherein the leuco dye is contained in an amount of 15 to 40% by mass, the developer in an amount of 20 to 70% by mass, and the vinylpyrrolidone-vinyl acetate copolymer in an amount of 5 to 35% by mass, based on the total solids content of the thermosensitive color developing printing ink. Item 4: The printing ink according to Item 2 or 3, wherein the vinylpyrrolidone-vinyl acetate copolymer has a molar ratio of vinylpyrrolidone / vinyl acetate of 50 / 50 to 30 / 70. Item 5: The printing ink according to any one of Items 2 to 4, further containing colloidal silica having an average particle size of 45 nm or less, the colloidal silica being contained in an amount of 5 to 30% by mass, based on the total solids content of the thermosensitive color developing printing ink. Item 6: The printing ink according to any one of Items 2 to 5, wherein the solvents are water and alcohol. Item 7: The printing ink according to Item 1, wherein the printing ink is (B) a protective layer printing ink for a thermosensitive recording medium. Item 8: The printing ink according to Item 7, 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 printing ink. Item 9: The printing ink according to Item 7 or 8, wherein the number average molecular weight of the polyvinyl acetal resin is 17,000 to 40,000.Item 10: The printing ink according to any one of Items 7 to 9, 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 11: The printing ink according to any one of Items 7 to 10, further comprising calcined kaolin having an average particle size of 2.0 μm or less, wherein the calcined kaolin accounts for 0.5 to 10 mass% of the total solids content of the protective layer printing ink. Item 12: The printing ink according to any one of Items 7 to 11, wherein the solvent is an alcohol and a cycloalkane. Item 13: The printing ink according to any one of Items 1 to 12, wherein the printing ink is a gravure printing ink. Item 14: A thermal recording medium having, on at least a portion of one or both sides of a support, a thermal recording layer formed using the printing ink according to any one of Items 1 to 6 and 13, and / or a protective layer formed using the printing ink according to any one of Items 1 and 7 to 13. Item 15: The thermosensitive recording medium according to Item 14, 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 16: The thermosensitive recording medium according to Item 14 or 15, wherein a printing layer is provided on at least a portion of the surface of the support opposite to the thermosensitive recording layer. Item 17: The thermosensitive recording medium according to any one of Items 14 to 16, wherein a heat seal layer is provided on at least a portion of one or both surfaces of the support. Item 18: The thermosensitive recording medium according to any one of Items 14 to 17, wherein an undercoat layer is provided between the support and the thermosensitive recording layer. Item 19: The thermosensitive recording medium according to Item 18, wherein the undercoat layer contains a chlorinated polyolefin resin as an adhesive. Item 20: The thermosensitive recording medium according to any one of Items 17 to 19, wherein the thermosensitive recording medium is a top seal cover material. Item 21: An image recording method for recording an image on the thermosensitive recording medium according to any one of Items 14 to 20, using a laser beam or a thermal head.

[0014] A thermosensitive recording medium having a thermosensitive recording layer formed using the thermosensitive color-developing printing ink of the present invention has high sensitivity, excellent background fogging resistance and plasticizer resistance, and also excellent transparency.

[0015] 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.

[0016] In this specification, the expression "comprise" includes the concepts of "comprise," "consist essentially of," and "consist only of."

[0017] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits.

[0018] The latex in the present invention includes a gel or a dried film formed by drying a dispersion medium.

[0019] The printing ink for a thermosensitive recording medium of the present invention is characterized by being either (A) or (B) below: (A) A thermosensitive color-forming printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the color developer is a compound represented by the following general formula (1):

[0020] (In the formula, R ０ represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the aralkyl group and the aryl group may be substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; ０ may be the same or different. １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a plurality of A １ may be the same or different, an N,N'-diaryl urea compound represented by the following general formula (2):

[0021] (In the formula, R １ ~R ５and (B) a protective layer printing ink for a thermal recording medium containing a compound represented by the formula (I) and (C) and at least one selected from the group consisting of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, and (C) a protective layer printing ink for a thermal recording medium containing a polyvinyl acetal resin as the adhesive and an alkyl phosphate ester and / or a salt thereof as the slippage imparting agent.

[0022] The thermosensitive recording medium of the present invention is characterized by having a thermosensitive recording layer formed using the thermosensitive color-developing printing ink of the present invention, and / or a protective layer formed using the protective layer printing ink of the present invention, on at least a portion of one or both sides of the support.

[0023] [Thermosensitive Coloring Printing Ink] (Leuco Dyes) The thermosensitive coloring printing ink of the present invention may contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes are listed below.

[0024] 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, fluoran, 3-(N-ethyl-N-p-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam. green color-forming dyes, red color-forming dyes such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 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-diethylamino-6-methyl-7-anilinofluoran, -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-( N-n-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 black pigments such as 3-(4-chloro-N-methylamino)-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, and 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran. 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 having an absorption wavelength in the near-infrared region, such as 6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Of course, the dyes are not limited to these, and two or more compounds can be used in combination as needed.

[0025] The content of the leuco dye is not particularly limited, and 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-forming printing ink. By making it 15% by mass or more, the color-forming ability can be enhanced and the print density can be improved. By making it 40% by mass or less, the heat resistance can be improved.

[0026] (Color Developer) In the present invention, the color developer contains at least one selected from the group consisting of an N,N'-diaryl urea compound represented by the above general formula (1), a compound represented by the above general formula (2), and 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. This makes it possible to improve print density and exhibit excellent transparency, background fogging resistance, and plasticizer resistance even when alcohol is used as a solvent. Because alcohol can be used as a solvent in this way, the thermosensitive color-forming printing ink of the present invention is suitably used as an ink for gravure printing.

[0027] In the general formula (1) of the N,N'-diaryl urea compound, R ０ The alkyl group having 1 to 12 carbon atoms may be linear, branched, or alicyclic, and is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, and a lauryl group. The alkyl group here also includes the alkyl portion of an alkoxy group having 1 to 12 carbon atoms.

[0028] The aralkyl group refers to an arylalkyl group. Examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, and a 3-phenylpropyl group.

[0029] The aryl group refers to a monocyclic or polycyclic group consisting of a 5- or 6-membered aromatic hydrocarbon ring. Examples of aryl groups having 6 to 12 carbon atoms include phenyl, 1-naphthyl, and 2-naphthyl. The aryl group here also includes the aryl portion of an aralkyl group.

[0030] Halogen atoms include fluorine, chlorine, bromine and iodine.

[0031] In general formula (1), multiple R ０ -SO ３ The substitution positions of - may be the same or different. The substitution position is preferably the 3rd, 4th or 5th position, more preferably the 3rd position. ０ When the aralkyl group having 7 to 12 carbon atoms and the aryl group having 6 to 12 carbon atoms have a substituent, the number of the substituents is not particularly limited, and is, for example, 1 to 4.

[0032] A １ The alkyl group having 1 to 4 carbon atoms may be either linear or branched, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group.

[0033] Multiple A's １ The substitution positions of may be the same or different. The substitution position is preferably the 3-position, 4-position or 5-position.

[0034] The N,N'-diaryl urea compound represented by the general formula (1) is not particularly limited, but examples thereof include N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(4-ethylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(2-naphthalenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea,

[0039] At least one selected from the group consisting of N,N'-di-[3-(benzylsulfonyloxy)phenyl]urea, N,N'-di-[3-(ethanesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methylphenyl]urea, N,N'-di-[4-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[4-(ethanesulfonyloxy)phenyl]urea, and N,N'-di-[2-(p-toluenesulfonyloxy)]phenylurea is preferred. Among these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is preferred.

[0035] R １ ~R ５ Examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom, with a fluorine atom and a chlorine atom being preferred.

[0036] The alkyl group may be linear, branched, or cyclic, and is preferably a linear or branched alkyl group, more preferably a linear alkyl group. Typically, the alkyl group has 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms.

[0037] The alkoxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkoxy group, more preferably a linear alkoxy group. Usually, the alkoxy group has 1 to 12 carbon atoms, preferably an alkoxy group having 2 to 8 carbon atoms, more preferably an alkoxy group having 2 to 6 carbon atoms, and even more preferably an alkoxy group having 2 to 4 carbon atoms.

[0038] The alkylcarbonyloxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, more preferably a linear alkylcarbonyloxy group.Alkylcarbonyloxy groups having 1 to 10 carbon atoms are also preferred.

[0039] The alkylcarbonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonylamino group, more preferably a linear alkylcarbonylamino group. An alkylcarbonylamino group having 1 to 10 carbon atoms is also preferred.

[0040] The alkylsulfonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylsulfonylamino group, more preferably a linear alkylsulfonylamino group. Also, alkylsulfonylamino groups having 1 to 10 carbon atoms are preferred.

[0041] The aryl group refers to a monocyclic or polycyclic group consisting of a 5- or 6-membered aromatic hydrocarbon ring. Examples of the aryl group include a phenyl group, a naphthyl group, and a biphenyl group.

[0042] The aryloxy group is preferably an aryloxy group having 6 to 12 carbon atoms. The arylcarbonyloxy group is preferably an arylcarbonyloxy group having 6 to 12 carbon atoms. The arylcarbonylamino group is preferably an arylcarbonylamino group having 6 to 12 carbon atoms. The arylsulfonylamino group is preferably an arylsulfonylamino group having 6 to 12 carbon atoms.

[0043] The monoalkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched monoalkylamino group, more preferably a linear monoalkylamino group. Furthermore, a monoalkylamino group in which the alkyl group has 1 to 10 carbon atoms is preferred.

[0044] The dialkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched dialkylamino group, more preferably a linear dialkylamino group. Furthermore, a dialkylamino group in which the alkyl group has 1 to 10 carbon atoms is preferred.

[0045] The arylamino group may be a monoarylamino group or a diarylamino group, and is preferably a monoarylamino group having 6 to 12 carbon atoms.

[0046] Specific examples of the compound represented by general formula (2) include R １ ~R ５ is an alkyl group or a hydrogen atom, and preferably R １ ~R ５ is a linear alkyl group having 1 to 8 carbon atoms or a hydrogen atom, and more preferably R １ ~R ５ is a linear alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and more preferably R １ ~R ５ is a methyl group or a hydrogen atom.

[0047] Other specific examples of the compound represented by formula (2) include R １ , R ２ , R ４ and R ５ is a hydrogen atom and R ３ is a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group (preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, even more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group).

[0048] The substitution position of the substituent bonded to one benzene ring of the diphenylurea structure in general formula (2) can be the ortho-, meta-, or para-position relative to the aminocarbonyl group on the benzene ring, preferably the ortho- or meta-position, more preferably the meta-position.

[0049] The compound represented by general formula (2) is not particularly limited, but is preferably at least one selected from the group consisting of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 2-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, and 4-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate. Among these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferred.

[0050] The content of the color developer is not particularly limited, and is preferably about 20 to 70% by mass, more preferably about 25 to 62% by mass, and even more preferably about 28 to 55% by mass, of the total solids content of the thermosensitive color-developing printing ink. By making it 20% by mass or more, recording properties and print storability can be improved. By making it 70% by mass or less, background fogging can be suppressed.

[0051] In addition, the content of the 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, still 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 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.

[0052] Other color developers may be contained as long as they do not impair the effects of the present invention. Specific examples of other color developers 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' -methyldiphenyl 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, 4-hydroxybenzoic acid benzyl 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 aromatic carboxylic acids such as [p-(2-p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, and salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; further, antipyrine complexes of zinc thiocyanate, terephthalic acid, and the like. organic acidic substances such as complex zinc salts of aldehyde acid and other aromatic carboxylic acids; urea compounds such as N-p-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, N-p-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, N-p-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, and 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone; thiourea compounds such as N,N'-di-m-chlorophenylthiourea; compounds having —SO 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; ２ Examples include organic compounds having an NH-bond, activated clay, attapulgite, colloidal silica, aluminum silicate, and other inorganic acidic substances.

[0053] 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 (3), as well as diphenyl sulfone derivatives represented by the following general formula (4). Of course, the compounds are not limited to these, and two or more compounds can be used in combination as needed.

[0054]

[0055] (In the formula, n represents an integer of 1 to 6.)

[0056] (Adhesive) The thermosensitive color-developing printing ink of the present invention contains a vinylpyrrolidone-vinyl acetate copolymer as an adhesive, which enhances color-developing ability, improves print density, and also improves plasticizer resistance.

[0057] The molar ratio of vinylpyrrolidone / vinyl acetate in the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited, but is preferably 50 / 50 to 30 / 70, and more preferably 40 / 60 to 30 / 70. By adjusting the ratio to 50 / 50 to 30 / 70, the print density can be improved.

[0058] The content of the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited, and is preferably about 5 to 35% by mass, more preferably about 9 to 33% by mass, and even more preferably about 12 to 28% by mass, of the total solids content of the thermosensitive color-developing printing ink. By making it 5% by mass or more, adhesion to the substrate can be improved. By making it 35% by mass or less, recording properties can be improved.

[0059] Other adhesives may be added as long as they do not impair the effects of the present invention. Examples of other adhesives that can be used include aqueous adhesives, such as water-soluble adhesives and water-dispersible adhesives. Examples of water-soluble adhesives 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 adhesives include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, etc., or latexes of water-insoluble polymers such as styrene-butadiene copolymer and styrene-butadiene-acrylic copolymer. Furthermore, examples of adhesives that can be used include organic solvent-soluble adhesives. Examples of organic solvent-soluble adhesives include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, polyurethane, saturated polyester, polyester polyurethane, epoxy resin, phenoxy resin, nitrocellulose, melamine resin, chlorinated polyethylene, and chlorinated polypropylene. The adhesives can be used alone or in combination of two or more.

[0060] (Colloidal Silica) In the present invention, the thermosensitive color-developing printing ink can further contain colloidal silica having an average particle size of 45 nm or less. This enhances color development ability and print density without impairing transparency. The average particle size of colloidal silica is preferably 60 nm or less, more preferably 45 nm or less. On the other hand, from the viewpoint of heat resistance, it is preferably 5 nm 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.

[0061] The content of colloidal silica having an average particle size of 45 nm or less is not particularly limited, and is preferably about 5 to 30 mass %, more preferably about 7 to 28 mass %, and even more preferably about 10 to 25 mass %, of the total solids content of the thermosensitive color developing printing ink. By making it 5 mass % or more, the coating strength can be improved. By making it 30 mass % or less, transparency can be maintained.

[0062] (Solvent) The thermosensitive color-developing printing ink of the present invention can contain a solvent. Examples of such solvents include water, alcohol, toluene, cyclohexane, and methylcyclohexane, with a solvent containing water and an 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. Using an alcohol as the solvent makes it possible to use the ink in gravure printing.

[0063] (Storage Improver) In the present invention, the thermosensitive color printing ink may further contain a storage improver, mainly to further improve the storage stability of the color image. Examples of such storage 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 or more compounds selected from the group consisting of 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.

[0064] When a storage stability improver is used, the amount used should be an amount effective for improving storage stability, and usually, the amount is preferably about 1 to 30 mass %, and more preferably about 5 to 20 mass %, of the total solids amount of the thermosensitive color printing ink.

[0065] (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-methylolstearic 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. di(beta-biphenylethoxy)ethane, 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. The content of the sensitizer may be an amount effective for sensitization, and is usually preferably about 2 to 40% by mass, more preferably about 5 to 25% by mass, of the total solids content of the thermosensitive color developing printing ink.

[0066] 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.

[0067] (Crosslinking Agent) A crosslinking agent that hardens the adhesive of the thermosensitive recording layer or other layers can be included in 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.

[0068] (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.

[0069] (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 a range that does not impair the effects of the present invention.

[0070] The heat-sensitive color-developing printing ink of the present invention is generally prepared by dispersing a leuco dye, a color developer, and optionally an adhesive, a sensitizer, and a storage stability improver, together or separately, in water and alcohol as a solvent, using various 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 so that the average particle size is 2 μm or less, and then mixing an adhesive, an auxiliary, etc., as required.

[0071] 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.

[0072] [Protective Layer Printing Ink for Thermal Recording Material] (Adhesive) The protective layer printing ink of the present invention contains a polyvinyl acetal resin as an adhesive, which can improve print storage stability (particularly plasticizer resistance) and thermal head matching (particularly head-cure suitability), as well as transparency.

[0073] 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.

[0074] 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.

[0075] 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 storability (particularly plasticizer resistance) and thermal head matching (particularly head-crack 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).

[0076] The content of such polyvinyl acetal resin is not particularly limited, and is preferably about 75 to 99% by mass, more preferably about 75 to 90% by mass, and even more preferably about 80 to 85% by mass, of the total solids content of the protective layer printing ink. By making it 75% by mass or more, print storage stability (particularly plasticizer resistance) can be improved. By making it 99% by mass or less, thermal head matching (particularly anti-sticking properties) can be improved.

[0077] Other adhesives may be included as long as they do not impair the effects of the present invention. Examples of other adhesives that can be used include aqueous adhesives, such as water-soluble adhesives and water-dispersible adhesives. Examples of water-soluble adhesives 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; polyamide; diisobutylene-maleic anhydride copolymer salt; styrene-maleic anhydride copolymer salt; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible adhesives include emulsions of polyvinyl acetate, polyurethane, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, and the like; and latexes of water-insoluble polymers such as styrene-butadiene copolymer. Examples of other adhesives that can be used include organic solvent-soluble adhesives. Examples of organic solvent-soluble adhesives include vinyl acetate resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, vinylpyrrolidone-vinyl acetate copolymer resins, butyral resins, polyester resins, nitrocellulose resins, styrene resins, etc. The adhesives can be used alone or in combination of two or more.

[0078] (Slippage Imparting Agent) The thermosensitive coloring 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 deposit suitability) and transparency.

[0079] 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.

[0080] 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. The alkyl phosphate ester salts are preferably Na-neutralized or Ca-neutralized.

[0081] 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.

[0082] 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 and reduced printing noise) can be improved. By making it 25% by mass or less, print storage stability (plasticizer resistance) can be improved.

[0083] Other slip imparting agents may be contained as long as they do not impair the effects of the present invention. Examples of other slip imparting 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 slip imparting agents can be used alone or in combination of two or more.

[0084] (Calorinated 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.

[0085] The content of the calcined kaolin having 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.

[0086] (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 an alcohol and a cycloalkane being preferred. Desirably, the alcohol has 5 or fewer carbon atoms. 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. Examples of cycloalkanes include cyclopentane, cyclohexane, cycloheptane, cyclocyclooctane, cyclononane, cyclodecane, methylcyclohexane, methylcyclooctane, dimethylcyclohexane, and ethylcyclohexane. Using an alcohol as the solvent enables the ink to be used in gravure printing.

[0087] Other component materials constituting the protective layer printing ink may further include a crosslinking agent, a pigment, etc., if necessary.

[0088] (Crosslinking Agent) The protective layer printing ink can contain a crosslinking agent that cures the adhesive of the protective layer or other layers. This can improve 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 can improve the water resistance of the protective layer.

[0089] (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 content of the pigment 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.

[0090] The protective layer printing ink of the present invention is generally prepared by mixing an adhesive, a slipping agent, and, if necessary, an auxiliary agent, etc., with an alcohol or cycloalkane as a solvent.

[0091] 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.

[0092] [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 (acidic 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 resins such as polyethylene terephthalate (PET), polyolefin resins such as polypropylene (PP) and polyethylene (PE), etc. 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.

[0093] [Thermal Recording Layer] The thermal recording medium may have a thermal recording layer on the support, if necessary. The thermal recording layer is generally formed on the support by printing using a thermal color-developing printing ink. The thermal recording layer in the present invention is preferably provided on at least a portion of one or both sides of the support, and is a layer formed using the thermal color-developing printing ink of the present invention. When the thermal color-developing printing ink of the present invention is not used, the thermal color-developing ink described in the above section "Thermal Color-developing Printing Ink" can be used without any restrictions on the color developer and adhesive. There are no particular restrictions on the coating amount of the thermal recording layer, and it is 1 to 12 g / m2 in 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 required, and the composition and coating amount of each layer may be the same or different.

[0094] [Protective Layer] A thermosensitive recording medium may also have a protective layer on the support or thermosensitive recording layer, if necessary. The protective layer is generally formed on the support or thermosensitive recording layer by printing using a protective layer printing ink for a thermosensitive recording medium. The protective layer in the present invention is preferably 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 for a thermosensitive recording medium of the present invention. When the protective layer printing ink for a thermosensitive recording medium of the present invention is not used, the protective layer printing ink for a thermosensitive recording medium described in the above section "Protective Layer Printing Ink for a Thermosensitive Recording Medium" can be used without limiting the adhesive and slippage imparting agent. The coating amount of the protective layer is not particularly limited, and is 0.3 to 15 g / m2 in dry mass. ２ The preferred range is 0.3 to 10 g / m ２ More preferably, 0.3 to 8 g / m ２ More preferably, the amount is about 0.5 to 8 g / m ２ The preferred range is 0.5 to 5 g / m ２ The protective layer may be formed in two or more layers as required, and the compositions and coating amounts of the layers may be the same or different.

[0095] [Undercoat Layer] The thermosensitive recording medium of the present invention may have an undercoat layer between the support and the thermosensitive recording layer, if necessary. The undercoat layer preferably contains an adhesive.

[0096] (Adhesive) The adhesive contained in the undercoat layer is not particularly limited, and water-soluble or water-dispersible aqueous adhesives and solvent-based adhesives can be used. Examples of adhesives include water-soluble polymer materials such as polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, 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 derivatives thereof, 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 adhesives are preferably used with supports such as polyester films such as PET film and polyester resin-laminated paper. Among these, adhesives containing latex are preferred. Further, examples of aqueous adhesives or solvent-based adhesives 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, and cellophane. The content of the adhesive can be selected from a wide range, but is generally preferably about 10 to 100% by mass, and more preferably about 15 to 60% by mass, of the total solids content of the undercoat layer.

[0097] The adhesive preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. By setting the glass transition temperature to -10°C or lower, image quality can be improved even in a low energy range. The glass transition temperature is more preferably -30°C or lower, as this 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 preferred.

[0098] 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.

[0099] 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% by mass, and more preferably about 25 to 75% by mass, of the total solids content of the undercoat layer.

[0100] The undercoat layer is formed on the support by, for example, applying a coating liquid for the undercoat layer, which is prepared by mixing an adhesive, 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 case of the thermosensitive recording 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.

[0101] 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.

[0102] [Heat Seal Layer] The thermosensitive recording medium of the present invention may optionally have a heat seal layer on at least a portion of one or both sides of the support. The heat seal layer is preferably provided on the side of the support opposite to the thermosensitive recording layer.

[0103] 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.

[0104] The polyethylene may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), or high-density polyethylene (HDPE).

[0105] The heat seal layer may be unstretched, or may be uniaxially or biaxially stretched.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Examples of the main component constituting 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.

[0111] 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.

[0112] 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.

[0113] 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 ２ or less, more preferably 7.0 g / m ２ More preferably 5.0 g / m or less ２ The following is the result.

[0114] [Printing 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, classification by drying method includes inks for 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.

[0115] [Thermal Recording Medium] The thermal 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. A printing method such as gravure printing is 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 a supercalender or soft calender.

[0116] 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. Examples of image recording methods that can be used include a thermal head printer and laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser, YAG laser, fiber laser, solid-state laser, dye laser, etc.). When laser light is used, the wavelength of the laser light is not particularly limited and can be appropriately selected depending on the purpose.

[0117] 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, prepared foods, etc., 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.

[0118] The present invention will be described in more detail with reference to examples, but 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).

[0119] A. Thermosensitive Recording Material (A) (Example A1) (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 in a vinylpyrrolidone / vinyl acetate molar ratio of 30 / 70, 44.5 parts of water, and 12.5 parts of isopropyl alcohol were mixed, and the mixture was pulverized 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).

[0120] (2) Preparation of color developer dispersion (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 in a molar ratio of vinylpyrrolidone / vinyl acetate 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 color developer dispersion (liquid B).

[0121] (3) Preparation of Thermosensitive Coloring Printing Ink 10 parts of Solution A, 20 parts of Solution B, 3.5 parts of water and 3 parts of isopropyl alcohol were mixed and stirred to obtain a thermosensitive coloring printing ink.

[0122] (4) Preparation of a thermal recording medium Using a five-color gravure printing machine, a thermal color-developing printing ink was applied to one side of a 12 μm thick transparent PET film in an amount of 3.5 g / m after drying. ２ The sheet was then wound up to form a thermosensitive recording layer. Further, an ester adhesive was applied by dry lamination to the surface opposite to the surface on which the thermosensitive color-developing printing ink was printed in an amount of 3 g / m. ２A 30 μm-thick low-density polyethylene film was laminated to obtain a thermosensitive recording medium having a heat-seal layer. The obtained thermosensitive recording medium was wound into small rolls using a slitter, and then cut into a predetermined shape to form a top-sealing lid material, which could be subjected to sealing processing to seal a packaging container for food use.

[0123] (Example A2) A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in the preparation of solutions A and B in Example A1, the amount of the 50% isopropyl alcohol solution of vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts.

[0124] (Example A3) A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in the preparation of Solution A and Solution B in Example A1, the amount of the 50% isopropyl alcohol solution of vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 25 parts, and in the preparation of the thermosensitive color-developing printing ink, the amount of Solution B was changed from 20 parts to 40 parts.

[0125] Example A4 A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in preparing solutions A and B in Example A1, a vinylpyrrolidone-vinyl acetate copolymer having a vinylpyrrolidone / vinyl acetate molar ratio of 50 / 50 was used instead of a vinylpyrrolidone-vinyl acetate copolymer having a vinylpyrrolidone / vinyl acetate molar ratio of 30 / 70.

[0126] (Example A5) A thermal recording medium was obtained in the same manner as in Example A1, except that in preparing solutions A and B in Example A1, a vinylpyrrolidone-vinyl acetate copolymer having a vinylpyrrolidone / vinyl acetate molar ratio of 70 / 30 was used instead of a vinylpyrrolidone-vinyl acetate copolymer having a vinylpyrrolidone / vinyl acetate molar ratio of 30 / 70.

[0127] (Example A6) A thermosensitive recording medium was obtained in the same manner as in Example A1, except that the thermosensitive color-developing printing ink (3) was replaced with the following thermosensitive color-developing printing ink (5).

[0128] (5) 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 having an average 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.

[0129] (Example A7) A thermal recording medium was obtained in the same manner as in Example A1, except that in preparing Solution B in Example A1, 30 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0130] Example A8 A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in preparing Solution B in Example A1, 30 parts of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0131] (Example A9) In the preparation of the thermosensitive recording medium of Example A1, the thermosensitive color-developing printing ink was applied and dried on the thermosensitive recording layer, and the coating amount after drying was 1.0 g / m ２ A thermosensitive recording medium was obtained in the same manner as in Example A1, except that the following (6) ink for protective layer was printed to provide a protective layer.

[0132] (6) Preparation of Ink for Protective Layer 100 parts of acetal resin, 3 parts of zinc stearate, 5 parts of kaolin, 450 parts of isopropyl alcohol and 450 parts of methylcyclohexane were mixed and stirred to obtain an ink for a protective layer.

[0133] (Example A10) A thermal recording medium was obtained in the same manner as in Example A1, except that in the preparation of the thermal recording medium in Example A1, 23 μm thick cellophane was used instead of the 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.

[0134] (Example A11) In the preparation of the thermosensitive recording medium of Example A10, the coating amount after drying was 0.5 g / m ２A thermosensitive recording medium was obtained in the same manner as in Example A10, except that a 25% toluene solution of chlorinated polypropylene resin (product name: S1306 PPHP adhesive varnish, manufactured by Toyo Ink Co., Ltd.) was printed on the undercoat layer so that the thickness of the undercoat layer became equal to or greater than 100 μm, and then the undercoat layer was dried to form a thermosensitive recording layer.

[0135] Comparative Example A1 A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in the preparation of Solution B in Example A1, 30 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0136] (Comparative Example A2) A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in preparing Solution B in Example A1, 30 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0137] Comparative Example A3 A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in the preparation of solutions A and B in Example A1, polyvinylpyrrolidone resin was used instead of vinylpyrrolidone-vinyl acetate copolymer.

[0138] (Comparative Example A4) A thermosensitive recording medium was obtained in the same manner as in Example A1, except that in preparing solutions A and B in Example A1, polyvinyl alcohol having a saponification degree of 80 mol% and a polymerization degree of 250 was used instead of the vinylpyrrolidone-vinyl acetate copolymer.

[0139] The above examples and comparative examples were evaluated by the following methods, and the results are shown in Table 1.

[0140] [Recording Density] <Thermal Printer Printing> Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed on each thermal recording medium with an applied energy of 0.24 mJ / dot, and the resulting printed portion was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured with a spectrodensitometer (X-Rite 504, manufactured by X-Rite Co., Ltd.). (Evaluation) 1.40 or more: Very excellent 1.25 or more but less than 1.40: Excellent 1.10 or more but less than 1.25: No problem in practical use Less than 1.10: Unusable

[0141] <Laser light printing> Using a UV laser marker (trade name: UV laser marker, MD-U1000C, manufactured by Keyence Corporation), each thermal recording medium was irradiated with a laser at a wavelength of 355 nm, an output of 1.2 W, a scan speed of 3,000 mm / sec, and a laser spot diameter of 14 μm, to produce a 10 mm square solid print. The resulting printed area was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured with a spectral densitometer (X-Rite 504, manufactured by X-Rite Corporation). (Evaluation) 1.40 or more: very excellent 1.25 or more but less than 1.40: excellent 1.10 or more but less than 1.25: no problem in practical use Less than 1.10: unusable

[0142] [Background fogging] The background fogging of the non-printed area of ​​each thermal recording medium was measured by placing it on a PPC paper with a whiteness of 85% (JIS P 8148) and using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Co., Ltd.) (Evaluation) Less than 0.10: Excellent 0.10 or more but less than 0.20: No problem for practical use 0.20 or more: Unusable

[0143] [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) A: Less than 20% B: 20% or more and less than 30% C: 30% or more and less than 40% D: 40% or more

[0144] [Plasticizer Resistance] A polycarbonate pipe (40 mm diameter) was wrapped in three layers of cling film (product name: HI-ESU 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 the film, and then wrapped in three layers of cling film. The sample was left to stand for 24 hours in an environment at 40°C. Before and after this treatment, the recording area was placed on PPC paper with a whiteness of 85% (JIS P 8148), and the reflection density was measured with a spectrodensitometer (X-Rite 504, manufactured by X-Rite). The remaining rate of the recording area was calculated using the following formula: remaining rate (%) = (recording density after treatment / recording density before treatment) x 100 (Evaluation) 90% or more: very excellent 70% or more but less than 90%: excellent 50% or more but less than 70%: no problem for practical use Less than 50%: unusable

[0145]

[0146] B. Thermosensitive Recording Material (B) (Example B1) (1) Preparation of Dye Dispersion Liquid (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 in 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 pulverized 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 (Liquid A).

[0147] (2) Preparation of color 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 pulverized using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) to an average particle size of 0.15 μm to obtain a color developer dispersion liquid (liquid B).

[0148] (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 having 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.

[0149] (4) Preparation of protective layer printing ink 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 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 were mixed and stirred to obtain a protective layer printing ink.

[0150] (5) Preparation of a thermal recording medium Using a five-color gravure printing machine, a thermal color developing printing ink was applied to one side of a 12 μm thick transparent PET film in an amount of 3.5 g / m after drying. ２ Further, a coating amount of 1.0 g / m2 was applied on the thermal recording layer so as to be 1.0 g / m2 after drying. ２ The protective layer printing ink was printed on the sheet so that the thickness of the sheet was 1 / 4 of the original thickness, and the sheet was wound up to provide a protective layer. Furthermore, an ester adhesive was applied in an amount of 3 g / m by dry lamination to the surface opposite to the surface on which the thermosensitive color-developing printing ink was printed. ２ A 30 μm-thick low-density polyethylene film was laminated to obtain a thermosensitive recording medium having a heat-seal layer. The obtained thermosensitive recording medium was wound into small rolls using a slitter, and then cut into a predetermined shape to form a top-sealing lid material, which could be subjected to sealing processing to seal a packaging container for food use.

[0151] (Example B2) A thermosensitive recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer ink in Example B1, 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.).

[0152] (Example B3) A thermosensitive recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer ink in Example B1, a polyvinyl acetal resin (trade name: SLECK KS-10, number average molecular weight: 17,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of the polyvinyl acetal resin (trade name: SLECK KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.).

[0153] (Example B4) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer ink in Example B1, 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.).

[0154] (Example B5) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the ink for the protective layer in Example B1, 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.).

[0155] Example B6 A thermosensitive recording medium was obtained in the same manner as in Example B1, except that the following (6) protective layer printing ink was used instead of the (4) protective layer printing ink in Example B1.

[0156] (6) Preparation of protective layer printing ink 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 having an average particle size of 1.2 μm, 450 parts of isopropyl alcohol, and 450 parts of methylcyclohexane were mixed and stirred to obtain a protective layer printing ink.

[0157] (Example B7) A thermal recording medium was obtained in the same manner as in Example B1, except that in the preparation of the thermal recording medium in Example B1, 23 μm thick cellophane was used instead of the 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.

[0158] (Reference Example B1) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer printing ink in Example B1, 90 parts of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) was replaced with 100 parts of acrylic resin (trade name: BR101, number average molecular weight: 160,000, manufactured by Mitsubishi Chemical Corporation).

[0159] (Reference Example B2) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer printing ink in Example B1, 90 parts of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) was replaced with 100 parts of acrylic resin (trade name: BR115, number average molecular weight: 50,000, manufactured by Mitsubishi Chemical Corporation).

[0160] (Reference Example B3) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer printing ink in Example B1, 90 parts of polyvinyl acetal resin (trade 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 (trade name: UC-3080, number average molecular weight: 14,000, manufactured by Toa Gosei Chemical Co., Ltd.).

[0161] (Reference Example B4) A thermal recording medium was obtained in the same manner as in Example B1, except that in preparing the protective layer printing ink in Example B1, 10 parts of zinc stearate (average particle size 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.).

[0162] The above examples and reference examples were evaluated by the following methods, and the results are shown in Table 2.

[0163] [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) A: Less than 20% (Excellent) B: 20% or more but less than 30% (No practical problems) C: 30% or more (Unusable)

[0164] [Heat resistance of background] The background fogging of the non-printed area of ​​each thermal recording medium was measured by placing it on a PPC paper with a whiteness of 85% (JIS P 8148) and using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Co., Ltd.) (Evaluation) Less than 0.15: Excellent 0.15 or more but less than 0.25: No problem in practical use 0.25 or more: Unusable

[0165] [Plasticizer Resistance] A polycarbonate pipe (40 mm diameter) was wrapped with three layers of cling film (product name: HI-ESU 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 the film. Then, three layers of cling film were wrapped around the sample and the sample was left to stand at 40°C for 24 hours. Before and after this treatment, the recorded portion 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). The residual ratio of the recorded portion was calculated using the following formula: residual ratio (%) = (recorded density after treatment / recorded density before treatment) x 100

[0166] [Printing noise] Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), printing noise was evaluated by sensory evaluation when printing was performed on each thermal recording medium at an applied energy of 0.243 mJ / dot. (Evaluation) A: Quiet printing noise B: Slight printing noise (no practical problem) C: Loud printing noise

[0167] [Head residue suitability] Using a label printer (Respli V ex manufactured by Sato Corporation), the heating element of the thermal head after printing 50 cm at a print rate of 100% solid black was observed with a stereo microscope (VH-Z100UR, manufactured by Keyence Corporation) and subjected to a sensory evaluation. (Evaluation) A: No head residue adhesion B: Slight head residue adhesion C: Slight head residue adhesion (no practical problem) D: Much head residue

[0168]

Claims

1. A printing ink for a thermal recording medium, which is the following (A) or (B): (A) A thermal color-developing printing ink containing a leuco dye, a color developer, and a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, the color developer being represented by the following general formula (1): (In the formula, R ０ represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the aralkyl group and the aryl group being optionally substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; ０ may be the same or different. １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, １ may be the same or different.) an N,N'-diaryl urea compound represented by the following general formula (2): (In the formula, R １ ~R ５ are the same or different and represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group. A thermal color-developing printing ink comprising a compound represented by the formula (I) and at least one member selected from the group consisting of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide; and (B) a protective layer printing ink for a thermal recording medium comprising an adhesive, a slipping property imparting agent, and a solvent, the protective layer printing ink for a thermal recording medium comprising a polyvinyl acetal resin as the adhesive and an alkyl phosphate ester and / or a salt thereof as the slipping property imparting agent.

2. The printing ink according to claim 1, which is a thermosensitive color-developing printing ink (A).

3. The printing ink according to claim 2, wherein the total solid content of the thermosensitive color developing printing ink is 15 to 40% by mass of leuco dye, 20 to 70% by mass of color developer, and 5 to 35% by mass of vinylpyrrolidone-vinyl acetate copolymer.

4. The printing ink according to claim 2 or 3, wherein the vinylpyrrolidone / vinyl acetate molar ratio of said vinylpyrrolidone-vinyl acetate copolymer is 50 / 50 to 30 / 70.

5. The printing ink according to claim 2 or 3, further comprising colloidal silica having an average particle size of 45 nm or less, the content of said colloidal silica being 5 to 30 mass % of the total solids content of the thermosensitive color developing printing ink.

6. The printing ink according to claim 2 or 3, which contains water and alcohol as the solvent.

7. The printing ink according to claim 1, which is a printing ink for a protective layer for a thermosensitive recording medium (B).

8. The printing ink according to claim 7, wherein the protective layer printing ink contains 75 to 99 mass% polyvinyl acetal resin and 1 to 25 mass% alkyl phosphate ester and / or its salt of a total solid content of the ink.

9. The printing ink according to claim 7 or 8, wherein the polyvinyl acetal resin has a number average molecular weight of 17,000 to 40,000.

10. A printing ink according to claim 7 or 8, wherein the alkyl phosphate ester salt is neutralized with Na or Ca, and the first acid value of the alkyl phosphate ester is 135 mg KOH / g or less.

11. The printing ink according to claim 7 or 8, 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 solids content of said protective layer printing ink.

12. The printing ink according to claim 7 or 8, which contains an alcohol and a cycloalkane as the solvent.

13. The printing ink according to any one of claims 1 to 3, 7 and 8, which is a gravure printing ink.

14. A thermosensitive recording medium having a thermosensitive recording layer formed on at least a portion of one or both sides of a support using the printing ink according to claim 2 or 3, and / or a protective layer formed using the printing ink according to claim 7 or 8.

15. The thermal recording medium according to claim 14, wherein the support is a semi-transparent or transparent support made of glassine paper or resin-laminated paper, or a transparent film made of cellophane or a synthetic resin film.

16. The thermosensitive recording medium according to claim 14, which has a print layer on at least a part of the surface of the support opposite to the thermosensitive recording layer.

17. The thermosensitive recording medium according to claim 14, which has a heat seal layer on at least a portion of one or both sides of the support.

18. The thermosensitive recording medium according to claim 14, which has an undercoat layer between the support and the thermosensitive recording layer.

19. The heat-sensitive recording medium according to claim 18, wherein the undercoat layer contains a chlorinated polyolefin resin as an adhesive.

20. The thermosensitive recording medium according to claim 17, which is a top seal cover material.

21. A method for recording an image on the thermal recording medium according to claim 14 by using a laser beam or a thermal head.

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