Thermochromic printing ink

Abstract

To provide a printing ink with thermochromic properties.SOLUTION: The present invention provides a thermochromic printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, where the color developer is at least one selected from the group consisting of a specific N,N'-diaryl urea-based compound, a compound represented by general formula (2), and 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermosensitive color-developing printing ink, a thermosensitive recording medium, and an image recording method. [Background technology]

[0002] Thermal recording media, which utilize the color-developing reaction between a leuco dye and a developer, are relatively inexpensive, the recording equipment is compact, and the 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] For food applications such as labels, top seals, and bands on transparent containers for salads and prepared foods, a highly transparent medium is often required so that the contents can be clearly seen. In such cases, a transparent thermal film with a transparent PET film base is generally used.

[0004] Patent Document 1 reports a thermosensitive recording medium having a support and a thermosensitive recording layer on the support, which has all of warm water resistance, water resistance, ethanol resistance, temperature and humidity resistance, water abrasion resistance and heat resistance, and is capable of obtaining high-density images. The thermosensitive recording medium includes 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.

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

[0006] [Patent Document 1] JP 2022-146283 A [Patent Document 2] JP 2022-151636 A Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENT EMBODIMENT 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. [Means for solving the problem]

[0008] The present inventors have intensively studied the above-mentioned prior art and have come to solve the above-mentioned problems. That is, the present invention relates to the following thermosensitive color-developing printing ink, thermosensitive recording medium and image recording method.

[0009] Item 1: A heat-sensitive color-developing printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, the color developer being represented by the following general formula (1):

[0010] [ka] (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. A 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):

[0011] [ka] (In the formula, R 1 ~R 5 and 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 thermosensitive color-developing printing ink comprising at least one member selected from the group consisting of a compound represented by the formula (I) and 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. Item 2: The thermosensitive coloring printing ink according to item 1, wherein the total solid content of the thermosensitive coloring printing ink is 15 to 40 mass% of leuco dye, 20 to 70 mass% of color developer, and 5 to 35 mass% of vinylpyrrolidone-vinyl acetate copolymer. Item 3: The thermosensitive color developing printing ink according to item 1 or 2, wherein the vinylpyrrolidone / vinyl acetate molar ratio of the vinylpyrrolidone-vinyl acetate copolymer is 50 / 50 to 30 / 70. Item 4: The thermosensitive color printing ink according to any one of Items 1 to 3, further comprising colloidal silica having an average particle size of 45 nm or less, the content of the colloidal silica being 5 to 30 mass % of the total solid content of the thermosensitive color printing ink. Item 5: The thermosensitive color developing printing ink according to any one of Items 1 to 4, wherein the solvent comprises water and alcohol. Item 6: The thermosensitive coloring printing ink according to any one of Items 1 to 5, wherein the thermosensitive coloring printing ink is an ink for gravure printing. Item 7: 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 thermosensitive color developing printing ink according to any one of items 1 to 6. Item 8: The thermal recording medium according to item 7, 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. Item 9: The thermosensitive recording medium according to item 7 or 8, which has a protective layer on the thermosensitive recording layer. Item 10: The thermosensitive recording medium according to any one of items 7 to 9, further comprising a print layer on at least a part of the surface of the support opposite to the thermosensitive recording layer. Item 11: The thermosensitive recording medium according to any one of items 7 to 10, which has a heat seal layer on at least a portion of one or both sides of the support. Item 12: The thermosensitive recording medium according to any one of Items 7 to 11, further comprising an undercoat layer between the support and the thermosensitive recording layer. Item 13: The thermosensitive recording material according to item 12, wherein the undercoat layer contains a chlorinated polyolefin resin as an adhesive. Item 14: The thermosensitive recording medium according to any one of items 11 to 13, which is a top-sealing lid material. Item 15: An image recording method for recording an image on the thermal recording medium according to any one of items 7 to 14 by using a laser beam or a thermal head. Effect of the Invention

[0012] A thermosensitive recording medium having a thermosensitive recording layer formed by using the thermosensitive color developing printing ink of the present invention has high sensitivity, excellent resistance to background fogging and plasticizer resistance, and also has excellent transparency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In this specification, the expression "comprise" includes the concepts of "comprise", "consist essentially of" and "consist only of".

[0014] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] The latex in the present invention includes a gel or a dried film state formed by drying a dispersion medium.

[0016] The thermosensitive color-developing printing ink of the present invention is a thermosensitive color-developing printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, and the color developer is a compound represented by the following general formula (1):

[0017] [ka] (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. A 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):

[0018] [ka] (In the formula, R 1 ~R 5 and 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-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide.

[0019] The thermosensitive recording medium of the present invention is characterized in that it has a thermosensitive recording layer formed using the thermosensitive color developing printing ink of the present invention on at least a portion of one or both sides of a support.

[0020] [Thermal color printing ink] (Leuco dye) The heat-sensitive color-developing 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.

[0021] Specific examples of leuco dyes include blue-coloring dyes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluoran; green dyes such as 3-(N-ethyl-Np-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam; 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, red color-forming dyes such as 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-diethyl ... -Di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-pentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3- (Nn-hexyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-ethylamino]-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-methylamino]-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di(n-butylamino)-7-(2-chloroanilino)fluoran, 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-Trichlorophenylleucoauramine, 3-diethylamino-7-butylaminofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluoran, 3-diethylamino-6-chloro-7-(γ-chloropropyl)aminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-isopropyl)aminofluoran, Soamyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-dibutylamino-7-chloroanilinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-diethylamino -6-chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalido-3,9'-xanthene]-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran, and other black pigments. 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 the 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 necessary.

[0022] 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, based on the total solid content of the thermosensitive color-developing printing ink. By making it 15% by mass or more, the color-developing ability can be improved and the print density can be improved. By making it 40% by mass or less, the heat resistance can be improved.

[0023] (Developer) In the present invention, the 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 even when alcohol is used as a solvent, and also to exhibit excellent transparency, background fogging resistance, and plasticizer resistance. Since alcohol can be used as a solvent in this way, the thermosensitive color developing printing ink of the present invention is suitably used as an ink for gravure printing.

[0024] 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.

[0025] 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.

[0026] 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 having 6 to 12 carbon atoms include a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. The aryl group here also includes the aryl portion of an aralkyl group.

[0027] Halogen atoms include fluorine, chlorine, bromine and iodine.

[0028] In the general formula (1), multiple R 0 The substitution positions of -SO3- 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.

[0029] 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.

[0030] 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.

[0031] The N,N'-diaryl urea compound represented by the general formula (1) is not particularly limited, and 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, 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-methyl-phenyl]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.

[0032] 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.

[0033] The alkyl group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Usually, it is an alkyl group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and further preferably an alkyl group having 1 to 4 carbon atoms.

[0034] The alkoxy group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Usually, it is an alkoxy group having 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.

[0035] The alkylcarbonyloxy group may be linear, branched or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, more preferably a linear alkylcarbonyloxy group. Also, an alkylcarbonyloxy group having 1 to 10 carbon atoms is preferred.

[0036] The alkylcarbonylamino group may be linear, branched or cyclic, and is preferably a linear or branched alkylcarbonylamino group, more preferably a linear alkylcarbonylamino group. Also, an alkylcarbonylamino group having 1 to 10 carbon atoms is preferred.

[0037] 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, an alkylsulfonylamino group having 1 to 10 carbon atoms is preferred.

[0038] 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.

[0039] 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.

[0040] The monoalkylamino group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. In addition, a monoalkylamino group having an alkyl group with 1 to 10 carbon atoms is preferred.

[0041] The dialkylamino group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Also, a dialkylamino group having an alkyl group with 1 to 10 carbon atoms is preferred.

[0042] The arylamino group may be a monoarylamino group or a diarylamino group, and is preferably a monoarylamino group having 6 to 12 carbon atoms.

[0043] Specific examples of the compound represented by 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.

[0044] 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 3is 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, still more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group).

[0045] The substitution position of the substituent bonded to one of the benzene rings of the diphenylurea structure in the general formula (2) can be the ortho-position, meta-position or para-position relative to the aminocarbonyl group on the benzene ring, preferably the ortho-position or meta-position, more preferably the meta-position.

[0046] The compound represented by the general formula (2) is not particularly limited, but 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 is preferred. Among these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferred.

[0047] 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, based on the total solid 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.

[0048] In addition, the content of the color developer is generally preferably 0.5 parts by mass or more relative to 1 part by mass of the leuco dye, more preferably 0.8 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 1.2 parts by mass or more, and particularly preferably 1.4 parts by mass or more. In addition, the content of the color developer is preferably 10 parts by mass or less relative to 1 part by mass of the leuco dye, 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. By making it 0.5 parts by mass or more, the recording performance can be improved. On the other hand, by making it 10 parts by mass or less, background fogging in a high-temperature environment can be effectively suppressed.

[0049] 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, benzyl 4-hydroxybenzoate ester, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4,Phenolic compounds such as 4'-dihydroxydiphenyl ether, or benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyl aromatic carboxylic acids such as zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, and these phenolic compounds; salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; and organic acids such as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. Substances, urea compounds such as Np-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, Np-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, N,N'-di-m-chlorophenylthio Examples of the organic compounds include thiourea compounds such as urea, organic compounds having a -SO2NH- bond in the molecule such as N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and N-(o-toluoyl)-p-toluenesulfamide, and inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate.

[0050] 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 represented by the following general formula (3), and diphenyl sulfone derivatives represented by the following general formula (4). Of course, the present invention is not limited to these, and two or more compounds can be used in combination as necessary.

[0051] [ka]

[0052] [ka] (In the formula, n represents an integer of 1 to 6.)

[0053] (glue) The heat-sensitive color-developing printing ink of the present invention contains a vinylpyrrolidone-vinyl acetate copolymer as an adhesive, which enhances the color-developing ability, improves the print density, and improves the plasticizer resistance.

[0054] 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.

[0055] 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, based on the total solid content of the thermosensitive color developing printing ink. By making it 5% by mass or more, the adhesion to the substrate can be improved. By making it 35% by mass or less, the recording properties can be improved.

[0056] Other adhesives may be included as long as they do not impair the effects of the present invention. As the other adhesives, for example, water-soluble adhesives and water-dispersible adhesives can be used. 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 salt, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-maleic anhydride copolymer salt, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid copolymer, polyacrylamide, sodium alginate, gelatin, casein, and gum arabic. Examples of water-dispersible adhesives include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers, and the like, or latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. In addition, examples of adhesives that can be used include organic solvent-soluble adhesives. Examples of organic solvent-soluble adhesives include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, polyurethanes, saturated polyesters, polyester polyurethanes, epoxy resins, phenoxy resins, nitrocellulose, melamine resins, chlorinated polyethylenes, and chlorinated polypropylenes. The adhesives can be used alone or in combination of two or more types.

[0057] (Colloidal Silica) In the present invention, the thermal color-developing printing ink can further contain colloidal silica having an average particle size of 45 nm or less. This can enhance color-developing ability and improve 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 size measured by any of the BET method, the Sears method, and the laser diffraction method. More simply, the particle size can be measured from particle images (SEM images) using an electron microscope, and expressed as the average value of 10 particles.

[0058] The content of the 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 solid content of the thermosensitive color developing printing ink. By making it 5 mass % or more, the coating film strength can be improved. By making it 30 mass % or less, the transparency can be maintained.

[0059] (solvent) The thermosensitive color developing printing ink of the present invention may contain a solvent. Examples of such solvents include water, alcohol, toluene, cyclohexane, methylcyclohexane, etc., and a solvent containing water and alcohol is preferred. The alcohol is preferably an alcohol having 5 or less carbon atoms, and examples of such alcohol having 5 or less carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. By using alcohol as a solvent, the ink can be used for gravure printing.

[0060] (Storage improver) In the present invention, the thermosensitive coloring printing ink can further contain a storage stability improver, mainly for the purpose of further improving the storage stability of the colored image. Examples of such storage stability improvers include 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1-bis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisphenol, and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol. At least one selected from phenol compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenylsulfone, epoxy compounds such as 4-(2-methyl-1,2-epoxyethyl)diphenylsulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenylsulfone, 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 present invention is not limited to these compounds, and two or more compounds can be used in combination as necessary.

[0061] When a storage stability improving agent is used, the amount used should be an amount effective for improving storage stability, and usually, the amount used is preferably about 1 to 30 mass %, and more preferably about 5 to 20 mass %, of the total solid content of the thermosensitive color developing printing ink.

[0062] (sensitizer) The heat-sensitive color-developing printing ink of the present invention may contain a sensitizer. This can increase the recording sensitivity. Examples of sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamild, 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, 1-hydroxy-2-phenyl naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, di-p-chlorobenzyl ester of oxalic acid, di-p-methylbenzyl ester of oxalic acid, dibenzyl ester of oxalic acid, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy) ether, and the like. p-methylthiophenyl benzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. 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 solid content of the thermosensitive color developing printing ink.

[0063] Other component materials 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, and the like.

[0064] (Crosslinking agent) A crosslinking agent that hardens the adhesive of the heat-sensitive recording layer or other layers can be contained in the heat-sensitive color-developing printing ink. This can improve the water resistance of the heat-sensitive 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 the crosslinking agent used is preferably in the range of about 1 to 10 parts by mass relative to 100 parts by mass of the total solid content of the heat-sensitive color-developing printing ink. This can improve the water resistance of the heat-sensitive recording layer.

[0065] (wax) Examples of the wax 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.

[0066] (Metal soap) Examples of the metal soap 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, defoamers, and viscosity regulators can be added to the thermosensitive color-developing printing ink within a range that does not impair the effects of the present invention.

[0067] 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 mixing an adhesive, an auxiliary, etc., as required, with the dispersion obtained by dispersing the particles to have an average particle size of 2 μm or less.

[0068] The thermosensitive color-developing printing ink of the present invention can be used to form a thermosensitive recording layer of a thermosensitive recording medium on at least a part of one or both sides of a support. The method for forming the thermosensitive recording layer is not particularly limited, and a printing method such as gravure printing is preferred.

[0069] [Support] The support 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 them, a semi-transparent or transparent support made of glassine paper or resin-laminated paper, or a transparent film made of cellophane or synthetic resin film is preferable. These can increase the transparency of the non-printed part of the thermal recording medium. Examples of the resin in the resin-laminated paper and synthetic resin film include polyester-based resins such as polyethylene terephthalate (PET), polyolefin-based 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 not particularly limited, and is 0.60 to 2.00 g / cm. 3 degree is preferred.

[0070] [Thermal recording layer] The thermosensitive recording layer in the present invention is provided on at least a portion of one or both sides of the support, and is a layer formed using the thermosensitive color developing printing ink of the present invention.

[0071] The thermosensitive recording layer is generally formed on a support by printing using the thermosensitive color-developing printing ink of the present invention. The coating amount of the thermosensitive recording layer is not particularly limited, and is preferably 1 to 12 g / m2 in terms of dry mass. 2 The preferred thickness 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.

[0072] [Protective layer] The thermal recording medium may also have a protective layer on the thermal recording layer on the side opposite to the support, if necessary. The protective layer preferably contains mainly an adhesive. Furthermore, the protective layer preferably contains a lubricant such as polyolefin wax, zinc stearate, alkyl phosphate ester and / or its salt, for the purpose of preventing sticking to the thermal head, and may also contain an ultraviolet absorber and a pigment. Furthermore, by providing a glossy protective layer, the added value of the product can be increased.

[0073] 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, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, and plastic pigments such as urea-formaldehyde resin filler, etc. The content of the pigment is preferably about 1 to 20 mass %, and more preferably about 1 to 10 mass %, of the total solid content of the protective layer.

[0074] The adhesive contained in the protective layer is not particularly limited, and a water-soluble or water-dispersible aqueous adhesive or a solvent-based adhesive can be used. The adhesive can also be appropriately selected from those that can be used in the thermal recording layer. Among these adhesives, various modified polyvinyl alcohols such as acetoacetyl-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and diacetone-modified polyvinyl alcohol, and polyvinyl acetal resins are more preferably used. The content of the adhesive is preferably 80% by mass or more, more preferably about 90 to 100% by mass, of the total solid content of the protective layer.

[0075] The protective layer is formed on the thermosensitive recording layer by applying a coating material for the protective layer, which is prepared by mixing a pigment, an adhesive, and, if necessary, an auxiliary, in water or alcohol as a dispersion medium, and then drying the coating material. It can also be formed by a printing method such as gravure printing, as in the case of the thermosensitive recording layer. The coating amount of the coating material for the protective layer is not particularly limited, and is 0.3 to 15 g / m2 in terms of dry mass. 2 The preferred range is 0.3 to 10 g / m 2 The preferred range is 0.5 to 8 g / m 2 More preferably, the thickness is 1 to 8 g / m 2 The preferred range is 1 to 5 g / m 2 The protective layer may be formed in two or more layers as required, and the composition and coating amount of each layer may be the same or different.

[0076] [Undercoat layer] The thermosensitive recording medium of the present invention may also have an undercoat layer between the support and the thermosensitive recording layer, if necessary. The undercoat layer preferably contains an adhesive.

[0077] (glue) 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 their derivatives, as well as emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers, or latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. These can be preferably used for supports such as polyester films such as PET films and polyester resin laminated paper. Among these, it is preferable to use an adhesive containing latex. In addition, examples of the aqueous adhesive or solvent-based adhesive include chlorinated polyolefin resins. Chlorinated polyolefin resins can be preferably used for supports such as polyolefin films such as PP films, polyolefin synthetic papers, polyolefin resin laminated papers, papers 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, more preferably about 15 to 60% by mass, of the total solid content of the undercoat layer.

[0078] The adhesive preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. By making the glass transition temperature -10°C or lower, image quality can be improved even in a low energy region. Since the image quality can be further improved in a low energy region, the glass transition temperature is more preferably -30°C or lower. On the other hand, a glass transition temperature of -50°C or lower is undesirable because stickiness occurs, so a glass transition temperature of -40°C or higher is preferable.

[0079] The undercoat layer may contain at least one of the following pigments: 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. Here, the oil absorption is a value determined according to the method of JIS K 5101.

[0080] As the oil-absorbing pigment, various types can be used, and specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle size of the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, and particularly preferably about 0.02 to 3 μm. The amount of the oil-absorbing pigment used can be selected from a wide range, but is generally preferably about 20 to 80 mass % of the total solid content of the undercoat layer, and more preferably about 25 to 75 mass %.

[0081] The undercoat layer is formed on the support by, for example, applying a coating liquid for the undercoat layer prepared by mixing an adhesive, hollow particles, pigments, auxiliaries, etc., with water as a medium, and then drying. Alternatively, it can be formed by a printing method such as gravure printing, as in the case of the thermal 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 thickness is 2 to 12 g / m 2 degree is more preferable.

[0082] 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.

[0083] [Heat seal layer] The thermosensitive recording medium of the present invention may also have a heat seal layer on at least a portion of one or both sides of the support, if necessary. The heat seal layer is preferably provided on the side of the support opposite to the thermosensitive recording layer.

[0084] The heat seal layer in the present invention may be a monolayer film made of a single resin, a monolayer 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.

[0085] The polyethylene may be low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), or high density polyethylene (HDPE).

[0086] The heat seal layer may be unstretched, or may be uniaxially or biaxially stretched.

[0087] The thickness of the heat seal layer is not particularly limited, and is preferably about 10 to 70 μm, more preferably about 20 to 60 μm, and even more preferably about 30 to 50 μm.

[0088] 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.

[0089] 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 attached together using an adhesive.

[0090] 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 adhesives.

[0091] Examples of main components that make up the adhesive include (meth)acrylic acid ester copolymers, α-olefin copolymers, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyurethane, styrene-butadiene copolymers, polyvinyl chloride, epoxy resins, melamine resins, silicone resins, natural rubber, casein, and starch.

[0092] In addition, the heat seal layer and the support may be laminated together after applying an adhesive to the heat seal layer, or the support may be laminated together with the heat seal layer after applying an adhesive to the support, or the heat seal layer may be laminated together with the support, or the adhesive may be applied to both the heat seal layer and the support, and then the heat seal layer and the support may be laminated together. There is no particular limitation thereon.

[0093] The method for applying the adhesive may be appropriately selected from conventionally known methods, and is not particularly limited. Examples of the method include a roll coater, a die coater, and a spray coater.

[0094] The amount of adhesive applied is not particularly limited, but the amount applied (coating amount) after drying is preferably 0.5 g / m 2 More preferably, 1.0 g / m 2 More preferably, 1.5 g / m 2 and preferably 10.0 g / m or more. 2 Less than 7.0 g / m 2 Less than 5.0 g / m, more preferably 5.0 g / m2 The following is the result.

[0095] [Print layer] In the present invention, a printing layer can be provided on at least one of 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 to the thermosensitive recording layer. The printing ink used to form the printing layer can be classified according to printing plate, and includes inks for letterpress, lithographic, intaglio, and stencil printing. In addition, according to the type of drying, inks for permeation drying, evaporation drying, oxidation polymerization drying, and photopolymerization drying (ultraviolet curing type) can be used. For forming the printing layer, printing methods such as flexographic printing, offset printing, gravure printing, and screen printing can be used. Digital printing methods such as plateless on-demand printing and direct printing can also be used. The color tone of the printing ink is not particularly limited, but in particular when thermal recording is performed on the printing layer, it is preferable that the optical density of the printing layer is lower than the optical density of the recording part of the thermal recording layer. The printing pattern may be partial printing or full solid printing, and is preferably a background pattern with an optical density of about 0.1 to 0.6, or fixed information that does not overlap with the thermal recording. For example, when the product is used as a top seal cover material on which variable information such as a product name, expiration date, and barcode is thermally recorded, it is preferable to partially print with white ink on the back side of the thermal record, which is the side opposite the thermal recording layer of the support, thereby improving the readability of the barcode.

[0096] [Thermal recording medium] The thermal recording medium can be manufactured by forming each of the above layers on a support. As a method for forming each of the above layers on a support, any of known coating methods such as printing methods such as gravure printing, air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, curtain method, slot die method, slide die method, and extrusion method may be used. A printing method such as gravure printing is preferable, and gravure printing is more preferable. In addition, 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. Furthermore, simultaneous multi-layer coating in which two or more layers are applied simultaneously may be performed. In addition, after each layer is formed or in any process after all layers are formed, a smoothing treatment can be performed using a known method such as a super calendar or a soft calendar.

[0097] The method of recording an image on the thermal recording medium of the present invention is not particularly limited and can be appropriately selected according to the purpose. For example, a thermal head printer, laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser light, YAG laser light, fiber laser light, solid laser light, dye laser light, etc.) can be used as the image recording method. When using laser light, the wavelength of the laser light is not particularly limited and can be appropriately selected according to the purpose.

[0098] The thermal recording medium of the present invention is highly transparent and has excellent resistance to background fogging and plasticizers, and is therefore suitable for use in food applications, such as labels for transparent containers for salads and side dishes, and as a top seal lid material. In a top seal lid material, the thermosensitive coloring printing ink printed on the front and the white ink printed on the back may increase the concealment, but the thermosensitive recording medium of the present invention can increase the transparency of the surface, making it possible to check information on the ingredients and other related information of the contents while observing the contents through the lid material. In addition, by using it as a top seal lid material, there is no need to attach a thermal label, which improves the efficiency of packaging work and reduces the amount of plastic used. EXAMPLES

[0099] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass", respectively. Particle sizes such as average particle size and maximum particle size were measured using a laser diffraction particle size distribution analyzer LB500 (manufactured by Horiba, Ltd.). Here, the average particle size refers to the median size (D50).

[0100] Example 1 (1) Preparation of dye dispersion (liquid A) 30 parts of 3-di(n-butyl)amino-6-methyl-7-anilinofluoran, 13 parts of a 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer with a vinylpyrrolidone / vinyl acetate molar ratio of 30 / 70, 44.5 parts of water, and 12.5 parts of isopropyl alcohol were mixed and ground using a sand mill (Imex Corporation, sand grinder) until the average particle size became 0.15 μm, to obtain a dye dispersion (Liquid A).

[0101] (2) Preparation of developer dispersion liquid (liquid B) 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, 13 parts of a 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer with a vinylpyrrolidone / vinyl acetate molar ratio of 30 / 70, 44.5 parts of water, and 12.5 parts of isopropyl alcohol were mixed and ground using a sand mill (sand grinder manufactured by Imex) to an average particle size of 0.15 μm to obtain a developer dispersion liquid (Liquid B).

[0102] (3) Preparation of thermosensitive color-developing printing ink 10 parts of Liquid A, 20 parts of Liquid B, 3.5 parts of water and 3 parts of isopropyl alcohol were mixed and stirred to obtain a heat-sensitive color-developing printing ink.

[0103] (4) Preparation of 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 with a dry coating weight of 3.5 g / m 2The sheet was then wound up to form a thermosensitive recording layer. An ester adhesive was then applied at a rate of 3 g / m2 by dry lamination to the other side opposite to the side on which the thermosensitive color-developing printing ink was printed. 2 A low-density polyethylene film having a thickness of 30 μm was laminated to obtain a thermal recording medium having a heat seal layer. The obtained thermal recording medium was wound into a small roll using a slitter, and cut into a predetermined shape to obtain a top seal cover material, which was then subjected to a sealing process to seal a food packaging container.

[0104] Example 2 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing solutions A and B in Example 1, the amount of the 50% isopropyl alcohol solution of vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts.

[0105] Example 3 A thermal recording medium was obtained in the same manner as in Example 1, except that in the preparation of solutions A and B in Example 1, 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 thermal color-developing printing ink, the amount of solution B was changed from 20 parts to 40 parts.

[0106] Example 4 A thermal recording medium was obtained in the same manner as in Example 1, except that in the preparation of solutions A and B in Example 1, 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.

[0107] Example 5 A thermal recording medium was obtained in the same manner as in Example 1, except that in the preparation of solutions A and B in Example 1, 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.

[0108] Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the thermosensitive recording medium in Example 1, the thermosensitive color developing printing ink (3) was replaced with the thermosensitive color developing printing ink (5) described below.

[0109] (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 with 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.

[0110] Example 7 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the B solution in Example 1, 30 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate were used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0111] Example 8 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the B solution in Example 1, 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.

[0112] Example 9 In the preparation of the thermal recording medium of Example 1, the thermal coloring printing ink was applied and dried on the thermal 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 1, except that the following (6) protective layer ink was printed so as to provide a protective layer.

[0113] (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.

[0114] Example 10 A thermal recording medium was prepared in the same manner as in Example 1, except that in place of the 12 μm thick transparent PET, 23 μm thick cellophane was used, and a 20 μm thick polyethylene film was attached to the other side printed with the thermal color-developing printing ink by extrusion lamination.

[0115] Example 11 In the preparation of the thermal recording medium of Example 10, the coating amount after drying was 0.5 g / m 2 A thermal recording medium was obtained in the same manner as in Example 10, except that a 25% toluene solution of chlorinated polypropylene resin (product name: S1306 PPHP adhesive varnish, manufactured by Toyo Ink Co., Ltd.) was printed and dried to form an undercoat layer, and then a thermal color-developing printing ink was printed on the undercoat layer to form a thermal recording layer.

[0116] Comparative Example 1 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the B solution in Example 1, 30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0117] Comparative Example 2 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing solution B in Example 1, 30 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide was used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0118] Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of solutions A and B in Example 1, polyvinylpyrrolidone resin was used instead of the vinylpyrrolidone-vinyl acetate copolymer.

[0119] Comparative Example 4 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing solutions A and B of Example 1, polyvinyl alcohol having a saponification degree of 80 mol% and a polymerization degree of 250 was used instead of the vinylpyrrolidone-vinyl acetate copolymer.

[0120] The above examples and comparative examples were evaluated by the following methods, and the results are shown in Table 1.

[0121] [Recording Density] <Thermal printer printing> Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded with an applied energy of 0.24 mJ / dot. The resulting printed area was placed on a PPC paper with a whiteness of 85% (JIS P 8148) and measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). (evaluation) 1.40 or above: Very good 1.25 or more but less than 1.40: Excellent 1.10 or more and less than 1.25: No practical problems Below 1.10: Not available

[0122] <Laser light marking> Using a UV laser marker (product name: UV laser marker, MD-U1000C, manufactured by Keyence Corporation), each thermal recording medium was irradiated with a laser with 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 print a solid area of ​​10 mm square. The resulting printed area was placed on a PPC paper with a whiteness of 85% (JIS P 8148) and measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). (evaluation) 1.40 or above: Very good 1.25 or more but less than 1.40: Excellent 1.10 or more and less than 1.25: No practical problems Below 1.10: Not available

[0123] [Skin fogging] The background fog of the non-printed areas 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-Rite504, manufactured by X-Rite Corporation). (evaluation) Less than 0.10: Excellent 0.10 or more and less than 0.20: No practical problems 0.20 or more: Unusable

[0124] [Transparency evaluation] The transparency of the non-printed areas of each thermal recording medium was measured using a haze meter (NDH-7000, manufactured by Nippon Denshoku Industries Co., Ltd.). (evaluation) ◎: Less than 20% ○: 20% to less than 30% △: 30% to less than 40% ×: 40% or more

[0125] [Plasticizer resistance] A polycarbonate pipe (40 mmΦ) was wrapped with three layers of cling film (product name: HI-ES Soft, manufactured by Nippon Carbide Industries Co., Ltd.), and a sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.), was placed on top of the cling film, which was then wrapped with three layers of cling film and left to stand for 24 hours in an environment of 40°C. Before and after this treatment, the recording portion was placed on a PPC paper with a whiteness of 85% (JIS P 8148), and the reflection density was measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.). The remaining rate of the recording portion was also calculated using the following formula. Residual rate (%) = (recording density after processing / recording density before processing) x 100 (evaluation) Over 90%: Very good 70% to less than 90%: Excellent 50% to less than 70%: No practical problems Less than 50%: Unavailable

[0126] [Table 1]

Claims

1. A heat-sensitive color-developing printing ink containing a leuco dye, a color developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, comprising a compound represented by the following general formula (1): 【Chemistry 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): 【Chemistry 2】 (In the formula, R １ ~R ５ and 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.

2. The thermosensitive coloring printing ink according to claim 1, wherein the leuco dye is contained in an amount of 15 to 40% by mass, the developer is contained in an amount of 20 to 70% by mass, and the vinylpyrrolidone-vinyl acetate copolymer is contained in an amount of 5 to 35% by mass, based on the total solid content of the thermosensitive coloring printing ink.

3. 3. The heat-sensitive color-developing printing ink according to claim 1, wherein the molar ratio of vinylpyrrolidone / vinyl acetate in said vinylpyrrolidone-vinyl acetate copolymer is from 50 / 50 to 30 / 70.

4. 3. The thermosensitive coloring printing ink according to claim 1, 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 solid content of the thermosensitive coloring printing ink.

5. 3. The heat-sensitive color-developing printing ink according to claim 1, wherein the solvent comprises water and an alcohol.

6. 3. The thermosensitive coloring printing ink according to claim 1, which is a gravure printing ink.

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

8. 8. The thermal recording medium according to claim 7, 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.

9. 8. The thermosensitive recording medium according to claim 7, further comprising a protective layer on the thermosensitive recording layer.

10. 8. The thermosensitive recording medium according to claim 7, further comprising a print layer on at least a part of the surface of the support opposite to the thermosensitive recording layer.

11. 8. The thermosensitive recording medium according to claim 7, which has a heat seal layer on at least a portion of one or both sides of the support.

12. 8. The thermosensitive recording medium according to claim 7, further comprising an undercoat layer between the support and the thermosensitive recording layer.

13. 13. The heat-sensitive recording material according to claim 12, wherein the undercoat layer contains a chlorinated polyolefin resin as an adhesive.

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

15. 8. An image recording method for recording an image on the thermal recording medium according to claim 7 by using a laser beam or a thermal head.

Images