Printing ink for heat-sensitive recording media

Abstract

Disclosed is a printing ink for a heat-sensitive recording material, which is either the following (A) or (B): (A) a heat-sensitive color-developing printing ink containing a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R0 represents a C1-12 alkyl group, a C7-12 aralkyl group, or a C6-12 aryl group, wherein 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, and multiple R0s may be the same or different, and A1 represents a hydrogen atom or a C1-4 alkyl group, and multiple A1s may be the same or different; a compound represented by the following formula (2): wherein 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 a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent.

Description

Technical Field

[0001] The present invention relates to printing ink for heat-sensitive recording materials, a heat-sensitive recording material, and an image recording method.Background Art

[0002] Heat-sensitive recording materials using color-developing reaction between a leuco dye and a developer are relatively inexpensive, and their recording devices are compact and easy to maintain. Thus, these heat-sensitive recording materials are widely used not only as recording media for faxes, various calculators, and CAD plotters, but also as labeling solutions for food products, including fresh items, boxed lunches, and prepared dishes, medical items, including labels for pharmaceutical management, and process control.

[0003] For labels, top-sealing materials, or bands on clear containers for food products such as salads or prepared meals, high-transparency media are often essential to clearly showcase the content. In these applications, transparent thermal films, including a transparent PET film as a substrate, are commonly used.

[0004] PTL 1 reports a thermosensitive recording medium that has all of the following properties: hot-water resistance, water resistance, ethanol resistance, temperature-humidity resistance, wet-abrasion resistance, and heat resistance, while also producing high-density images. This thermosensitive recording medium contains a support and a thermosensitive recording layer on the support, wherein the thermosensitive recording layer contains a specific N,N'-diaryl urea compound and a styrene-acrylic resin. Additionally, the Examples of PTL 1 disclose the formation of a protective layer containing styrene-acrylic resin, oxidized polyethylene wax, and calcium carbonate with a PET film as the support.

[0005] PTL 2 reports a heat-sensitive-recording-layer-forming liquid capable of forming a heat-sensitive recording layer with excellent surface uniformity without drag and coating unevenness and with minimal thickness variation, and discloses that the heat-sensitive-recording-layer-forming liquid contains an electron-donating compound, an electron-accepting compound with a solubility of 5 mass% or less in 100% ethanol at 20°C, and a solvent.

[0006] PTL 3 reports that a thermal coloring film is obtained by applying a thermal coloring ink onto a support substrate to form a thermal coloring ink layer and then forming a protective layer composed of a resin coating layer containing magnesium oxide on the upper surface of the thermal coloring ink layer, and that the thermal coloring film has both heat resistance and water resistance.Citation ListPatent Literature

[0007] PTL 1: JP2022-146283A PTL 2: JP2022-151636A PTL 3: Japanese Patent No. 3382728 Summary of InventionTechnical Problem

[0008] An object of the present invention is to provide a heat-sensitive color-developing printing ink, a heat-sensitive recording material using the heat-sensitive color-developing printing ink that is highly sensitive and exhibits excellent background fogging resistance and plasticizer resistance, and an image recording method using the heat-sensitive color-developing printing ink.

[0009] In another embodiment, an object of the present invention is to provide a protective-layer printing ink for heat-sensitive recording materials and a heat-sensitive recording material that exhibits excellent printing preservation and thermal head matching using the protective-layer printing ink.Solution to Problem

[0010] In view of the prior art, the present inventors conducted extensive research and succeeded in achieving the objects. Specifically, the present invention relates to the following printing ink for heat-sensitive recording materials, heat-sensitive recording material, and image recording method.Item 1.

[0011] A printing ink for a heat-sensitive recording material, which is either the following (A) or (B): (A) a heat-sensitive color-developing printing ink comprising a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R 0< represents a C 1-12 alkyl group, a C 7-12 aralkyl group, or a C 6-12 aryl group, wherein the aralkyl group and the aryl group may be substituted with a C 1-12 alkyl group, a C 1-12 alkoxy group, a C 6-12 aryl group, or a halogen atom, and multiple R 0< s may be the same or different, and A 1< represents a hydrogen atom or a C 1-4 alkyl group, and multiple A 1< s may be the same or different; a compound represented by the following formula (2): wherein R 1< to 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; and 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide, and (B) a protective-layer printing ink for a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent. Item 2.

[0012] The printing ink according to Item 1, wherein the printing ink is the heat-sensitive color-developing printing ink (A).Item 3.

[0013] The printing ink according to Item 2, wherein the content of the leuco dye is 15 to 40 mass%, the content of the developer is 20 to 70 mass%, and the content of the vinylpyrrolidone-vinyl acetate copolymer is 5 to 35 mass% based on the total solids content of the heat-sensitive color-developing printing ink.Item 4.

[0014] The printing ink according to Item 2 or 3, wherein the molar ratio of vinylpyrrolidone to vinyl acetate in the vinylpyrrolidone-vinyl acetate copolymer is 50 / 50 to 30 / 70.Item 5.

[0015] The printing ink according to any one of Items 2 to 4, further comprising colloidal silica with an average particle diameter of 45 nm or less, wherein the content of the colloidal silica is 5 to 30 mass% based on the total solids content of the heat-sensitive color-developing printing ink.Item 6.

[0016] The printing ink according to any one of Items 2 to 5, comprising water and an alcohol as the solvent.Item 7.

[0017] The printing ink according to Item 1, wherein the printing ink is the protective-layer printing ink for a heat-sensitive recording material (B).Item 8.

[0018] The printing ink according to Item 7, wherein the content of the polyvinyl acetal resin is 75 to 99 mass% and the content of the alkyl phosphate ester and / or a salt thereof is 1 to 25 mass% based on the total solids content of the protective-layer printing ink.Item 9.

[0019] The printing ink according to Item 7 or 8, wherein the polyvinyl acetal resin has a number average molecular weight of 17,000 to 40,000.Item 10.

[0020] The printing ink according to any one of Items 7 to 9, wherein the alkyl phosphate ester salt is in its Na-neutralized or Ca-neutralized form, and the first acid value of the alkyl phosphate ester is 135 mg KOH / g or less.Item 11.

[0021] The printing ink according to any one of Items 7 to 10, further comprising calcined kaolin having an average particle diameter of 2.0 µm or less, wherein the content of the calcined kaolin is 0.5 to 10 mass% based on the total solids content of the protective-layer printing ink.Item 12.

[0022] The printing ink according to any one of Items 7 to 11, comprising an alcohol and a cycloalkane as the solvent.Item 13.

[0023] The printing ink according to any one of Items 1 to 12, wherein the printing ink is a gravure printing ink.Item 14.

[0024] A heat-sensitive recording material comprising a support, and a heat-sensitive recording layer formed of the printing ink of any one of Items 1 to 6 and 13 and / or a protective layer formed of the printing ink of any one of Items 1 and 7 to 13 on at least a portion of one surface or both surfaces of the support. Item 15.

[0025] The heat-sensitive recording material according to Item 14, wherein the support is a translucent or transparent support made of glassine paper or laminated resin paper, or a transparent film made of cellophane or a synthetic resin film.Item 16.

[0026] The heat-sensitive recording material according to Item 14 or 15, comprising a printing layer on at least a portion of the surface of the support opposite to the surface on which the heat-sensitive recording layer is present.Item 17.

[0027] The heat-sensitive recording material according to any one of Items 14 to 16, comprising a heat seal layer on at least a portion of one surface or both surfaces of the support.Item 18.

[0028] The heat-sensitive recording material according to any one of Items 14 to 17, comprising an undercoat layer between the support and the heat-sensitive recording layer.Item 19.

[0029] The heat-sensitive recording material according to Item 18, wherein the undercoat layer contains a chlorinated polyolefin resin as a binder.Item 20.

[0030] The heat-sensitive recording material according to any one of Items 17 to 19, which is for use in a top-sealing lid material.Item 21.

[0031] An image recording method, comprising recording an image on the heat-sensitive recording material of any one of Items 14 to 20 by using laser light or a thermal head.Advantageous Effects of Invention

[0032] The heat-sensitive recording material containing a heat-sensitive recording layer formed using the heat-sensitive color-developing printing ink of the present invention exhibits high sensitivity and excellent background fogging resistance and plasticizer resistance. The heat-sensitive recording material also exhibits excellent transparency.

[0033] The heat-sensitive recording material containing a protective layer formed using the protective-layer printing ink for a heat-sensitive recording material of the present invention exhibits excellent printing preservation and thermal head matching. The heat-sensitive recording material also exhibits excellent transparency.Description of Embodiments

[0034] In the present specification, the expression "comprise" or "contain" includes the concepts of "comprising," "consisting essentially of," and "consisting of."

[0035] In the present specification, a numerical range indicated by "... to ..." means a range including the numerical values given before and after "to" as the lower limit and the upper limit.

[0036] "Latex" as used herein includes one in the form of a gel or dry film formed by drying a dispersion medium.

[0037] The printing ink for a heat-sensitive recording material of the present invention is either the following (A) or (B) : (A) a heat-sensitive color-developing printing ink comprising a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R 0< represents a C 1-12 alkyl group, a C 7-12 aralkyl group, or a C 6-12 aryl group, wherein the aralkyl group and the aryl group may be substituted with a C 1-12 alkyl group, a C 1-12 alkoxy group, a C 6-12 aryl group, or a halogen atom, and multiple R 0< s may be the same or different, and A 1< represents a hydrogen atom or a C 1-4 alkyl group, and multiple A 1< s may be the same or different; a compound represented by the following formula (2): wherein R 1< to 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; and 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide, and (B) a protective-layer printing ink for a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent.

[0038] The heat-sensitive recording material of the present invention also comprises a heat-sensitive recording layer formed of the heat-sensitive color-developing printing ink of the present invention and / or a protective layer formed of the protective-layer printing ink of the present invention on at least a portion of one surface or both surfaces of a support.Heat-sensitive Color-developing Printing InkLeuco Dye

[0039] The heat-sensitive color-developing printing ink of the present invention may contain any of various known colorless or pale-colored leuco dyes. Specific examples of such leuco dyes are described below.

[0040] Specific examples of leuco dyes include dyes capable of developing blue color, such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluoran; dyes capable of developing green color, such as 3-(N-ethyl-N-p-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam; dyes capable of developing red color, such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 3-diethylamino-7-chlorofluoran; dyes capable of developing black color, such as 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, 3-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-alininofluoran, 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-dimethylaminobenzhydrinbenzyl 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-isoamyl-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[phthalide-3,9'-xanthen-2'-ylamino]phenyl}propane, and 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran; dyes having absorption wavelengths in the near-infrared region, such as 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylen-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylen-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, and 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Usable leuco dyes are, of course, not limited to these compounds, and two or more of such compounds can be used in combination as necessary.

[0041] The content of the leuco dye is not particularly limited and is preferably about 15 to 40 mass%, more preferably about 18 to 38 mass%, and even more preferably about 20 to 35 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A leuco dye content of 15 mass% or more can enhance color development ability and thus improve print density, whereas a leuco dye content of 40 mass% or less can enhance heat resistance.Developer

[0042] In the present invention, the developer contained is at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by formula (1), a compound represented by formula (2), and 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. This enables the improvement of print density while also achieving excellent transparency, background fogging resistance, and plasticizer resistance even when an alcohol is used as a solvent. Since alcohols can be used as a solvent, the heat-sensitive color-developing printing ink of the present invention is suitable for use in gravure printing ink.

[0043] In formula (1) for N,N'-diaryl urea compounds, the C 1-12 alkyl group represented by R 0< may be linear, branched, or alicyclic, and is preferably a C 1-6 alkyl group, and more preferably a C 1-3 alkyl group. Examples of C 1-12 alkyl groups 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" as used here also includes the alkyl moiety of a C 1-12 alkoxy group.

[0044] The "aralkyl group" refers to an arylalkyl group. Examples of C 7-12 aralkyl groups include a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, and a 3-phenylpropyl group.

[0045] The "aryl group" refers to a monocyclic or polycyclic group composed of a 5- or 6-membered aromatic hydrocarbon ring. Examples of C 6-12 aryl groups include a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. The "aryl group" as used here also includes the aryl moiety of an aralkyl group.

[0046] Examples of halogen atoms include fluorine, chlorine, bromine, and iodine.

[0047] In formula (1), the substitution positions of the multiple R 0< -SO 3 - groups may be the same or different. The preferred substitution positions are at the 3-position, 4-position, or 5-position, with the 3-position being more preferred. When the C 7-12 aralkyl group and the C 6-12 aryl group represented by R 0< are substituted, the number of substituents is not particularly limited, and may be, for example, 1 to 4.

[0048] The C 1-4 alkyl group represented by A 1< may be either linear or branched, and examples 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.

[0049] The substitution positions of the multiple A 1< groups may be the same or different. The preferred substitution position is the 3-position, 4-position, or 5-position.

[0050] The N,N'-diaryl urea compound represented by formula (1) is preferably, but not particularly limited to, at least one compound selected from the group consisting of 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, 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)]phenyl urea. Of these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is preferred.

[0051] The halogen atom represented by R 1< to R 5< may be a fluorine atom, a chlorine atom, or a bromine atom, with a fluorine atom and a chlorine atom being preferred.

[0052] The alkyl group may be linear, branched, or cyclic, and is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. Typically, the alkyl group is a C 1-12 alkyl group, preferably a C 1-8 alkyl group, more preferably a C 1-6 alkyl group, and even more preferably a C 1-4 alkyl group.

[0053] The alkoxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkoxy group, and more preferably a linear alkoxy group. Typically, the alkoxy group is a C 1-12 alkoxy group, preferably a C 2-8 alkoxy group, more preferably a C 2-6 alkoxy group, and even more preferably a C 2-4 alkoxy group.

[0054] The alkylcarbonyloxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, and more preferably a linear alkylcarbonyloxy group. The alkylcarbonyloxy group is also preferably a C 1-10 alkylcarbonyloxy group.

[0055] The alkylcarbonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonylamino group, and more preferably a linear alkylcarbonylamino group. The alkylcarbonylamino group is also preferably a C 1-10 alkylcarbonylamino group.

[0056] The alkylsulfonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylsulfonylamino group, and more preferably a linear alkylsulfonylamino group. The alkylsulfonylamino group is also preferably a C 1-10 alkylsulfonylamino group.

[0057] The "aryl group" means a monocyclic or polycyclic group formed of one or more 5- or 6-membered aromatic hydrocarbon rings. Examples of aryl groups include a phenyl group, a naphthyl group, and a biphenyl group.

[0058] The aryloxy group is preferably a C 6-12 aryloxy group. The arylcarbonyloxy group is preferably a C 6-12 arylcarbonyloxy group. The arylcarbonylamino group is preferably a C 6-12 arylcarbonylamino group. The arylsulfonylamino group is preferably a C 6-12 arylsulfonylamino group.

[0059] The monoalkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched monoalkylamino group, and more preferably a linear monoalkylamino group. A monoalkylamino group whose alkyl group has 1 to 10 carbon atoms is also preferable.

[0060] The dialkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched dialkylamino group, and more preferably a linear dialkylamino group. A dialkylamino group whose alkyl group has 1 to 10 carbon atoms is also preferable.

[0061] The arylamino group may be a monarylamino group or diarylamino group, and is preferably a C 6-12 monoarylamino group.

[0062] Specific examples of compounds represented by formula (2) include those wherein R 1< to R 5< are each an alkyl group or a hydrogen atom, preferably R 1< to R 5< are each a C 1-8 linear alkyl group or a hydrogen atom, more preferably R 1< to R 5< are each a C 1-4 linear alkyl group or a hydrogen atom, and even more preferably R 1< to R 5< are each a methyl group or a hydrogen atom.

[0063] Other specific examples of compounds represented by formula (2) include those wherein R 1< , R 2< , R 4< , and R 5< are each 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 a C 1-8 alkyl group, even more preferably a hydrogen atom or a C 1-4 alkyl group, and particularly preferably a methyl group).

[0064] The position of the substituent bound to one benzene ring in the diphenylurea structure in formula (2) may be the ortho-position, the meta-position, or the para-position, preferably the ortho-position or the meta-position, and more preferably the meta-position with respect to the aminocarbonyl group on the benzene ring.

[0065] The compound represented by formula (2) is not particularly limited, and is preferably at least one member 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. Of these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferable.

[0066] The content of the developer is not particularly limited and is preferably about 20 to 70 mass%, more preferably about 25 to 62 mass%, and even more preferably about 28 to 55 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the developer of 20 mass% or more can enhance recording characteristics and printing preservation. A content of the developer of 70 mass% or less can decrease background fogging.

[0067] Typically, the content of the developer is 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 even more preferably 1.2 parts by mass or more, and particularly preferably 1.4 parts by mass or more, per part by mass of the leuco dye. The content of the developer is also 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. A content of the developer of 0.5 parts by mass or more can enhance recording performance. A content of the developer of 10 parts by mass or less can effectively decrease background fogging in a high-temperature environment.

[0068] Another developer may be contained as long as the effects of the present invention are not impaired. Specific examples of other developers include phenolic compounds, such as 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenyl, 4,4'-cyclohexylidenediphenol, 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'-dihydroxydiphenylsulfide, 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'-isopropoxy diphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 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, and 4,4'-dihydroxydiphenyl ether; aromatic carboxylic acids, such as 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)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate; salts of these phenolic compounds or aromatic carboxylic acids with, for example, polyvalent metals, such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; antipyrine complex of zinc thiocyanate; organic acidic substances, such as composite zinc salts of terephthalic 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]diphenyl sulfone; thiourea compounds, such as N,N'-di-m-chlorophenylthiourea; organic compounds having a -SO 2 NH-bond in the molecule, such as p-cumylphenyl N-(p-toluenesulfonyl) carbamate, p-benzyloxyphenyl N-(p-toluenesulfonyl)carbamate, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and N-(o-toluoyl)-p-toluenesulfoamide; inorganic acidic substances, such as activated clay, attapulgite, colloidal silica, and aluminum silicate; and the like.

[0069] Furthermore, examples include urea urethane derivatives represented by the following formula (3), such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureido diphenylsulfone; diphenyl sulfone derivatives represented by the following formula (4); and the like. Usable developers are, of course, not limited to these compounds, and two or more of such compounds can be used in combination as necessary. (In the formula, n represents an integer of 1 to 6.)Binder

[0070] The heat-sensitive color-developing printing ink of the present invention contains a vinylpyrrolidone-vinyl acetate copolymer as a binder. This enhances color development ability, improves print density, and increases plasticizer resistance.

[0071] The molar ratio of vinylpyrrolidone to vinyl acetate (vinylpyrrolidone / vinyl acetate) in the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited and is preferably 50 / 50 to 30 / 70, and more preferably 40 / 60 to 30 / 70. A molar ratio of vinylpyrrolidone to vinyl acetate of 50 / 50 to 30 / 70 can improve print density.

[0072] The content of the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited and is preferably about 5 to 35 mass%, more preferably about 9 to 33 mass%, and even more preferably about 12 to 28 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the vinylpyrrolidone-vinyl acetate copolymer of 5 mass% or more can improve adhesion to substrates. A content of the vinylpyrrolidone-vinyl acetate copolymer of 35 mass% or less can enhance recording characteristics.

[0073] The heat-sensitive color-developing printing ink of the present invention may contain other binders as long as they do not impair the effects of the present invention. Such other binders for use may be, for example, an aqueous binder, which is either a water-soluble binder or a water-dispersible binder. Examples of water-soluble binders include polyvinyl alcohol; modified polyvinyl alcohols, such as carboxy-modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, and silicon-modified polyvinyl alcohols; starch and its derivatives; cellulose derivatives, such as methoxy cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and ethyl cellulose; sodium polyacrylate, polyvinylpyrrolidone, polyamide, diisobutylene-maleic anhydride copolymer salts, styrene-acrylic acid copolymer salts, styrene-maleic anhydride copolymer salts, ethylene-maleic anhydride copolymer salts, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid copolymers, polyacrylamide, sodium alginate, gelatin, casein, and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers etc.; and latex of water-insoluble polymers, such as styrene-butadiene copolymers or styrene-butadiene-acrylic copolymers. Furthermore, for example, an organic solvent-soluble binder can be used as a binder. Examples of organic solvent-soluble binders include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, polyurethane, saturated polyester, polyester polyurethane, epoxy resin, phenoxy resin, nitrocellulose, melamine resin, chlorinated polyethylene, and chlorinated polypropylene. These binders can be used alone or in a combination of two or more types.Colloidal Silica

[0074] In the present invention, the heat-sensitive color-developing printing ink may further contain colloidal silica with an average particle diameter of 45 nm or less. This enables enhancement of color development ability without compromising transparency, thereby improving print density. The average particle diameter of colloidal silica is preferably 60 nm or less, and more preferably 45 nm or less. However, from the viewpoint of heat resistance, an average particle diameter of 5 nm or more is preferable. The "average particle diameter" as used here refers to the volume-based median diameter measured by the BET method, Sears method, or laser diffraction. More simply, individual particle diameters can be measured from particle images (SEM images) using an electron microscope, and the average of 10 particles may be used as the average particle diameter.

[0075] The content of the colloidal silica with an average particle diameter 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% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the colloidal silica of 5 mass% or more can improve the strength of the coating film. A content of the colloidal silica of 30 mass% or less enables the maintenance of transparency.Solvent

[0076] The heat-sensitive color-developing printing ink of the present invention may contain a solvent. Examples of such solvents include water, alcohols, toluene, cyclohexane, and methylcyclohexane, with solvents containing water and an alcohol being preferred. For the alcohol, alcohols with 5 or fewer carbon atoms are desirable, and examples of such alcohols with 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. Using an alcohol in the solvent makes the ink usable for gravure printing.Stabilizer

[0077] In the present invention, the heat-sensitive color-developing printing ink may further contain a stabilizer, mainly to further enhance the preservability of colored images. The stabilizer for use may be at least one compound selected from the group consisting of phenol compounds, such as 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; epoxy compounds, such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, 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. Usable stabilizers are, of course, not limited to these compounds, and two or more of such compounds can also be used in combination as necessary.

[0078] When the stabilizer is used, its amount may be an effective amount for improving image preservation. The stabilizer is typically preferably used in an amount of about 1 to 30 mass%, and more preferably about 5 to 20 mass%, based on the total solids content of the heat-sensitive color-developing printing ink.Sensitizer

[0079] The heat-sensitive color-developing printing ink in the present invention may also contain a sensitizer. Use of the sensitizer enhances the recording sensitivity. Examples of usable sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoyl stearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenylsulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzylbiphenyl, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibenzyl oxlate, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl)ether, 1,2-di(3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenylbenzylether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. These sensitizers can be used in combination as long as the combined use does not impair the effects of the present invention. The sensitizer content may be an effective amount for sensitization, and is typically preferably about 2 to 40 mass%, and more preferably about 5 to 25 mass%, based on the total solids content of the heat-sensitive color-developing printing ink.

[0080] For other components constituting the heat-sensitive color-developing printing ink, for example, the following can optionally be used: crosslinking agents, wax, metal soaps, water-resistance-improving agents, pigments, dispersants, colored dyes, and fluorescent dyes.Crosslinking Agent

[0081] The heat-sensitive color-developing printing ink may contain a crosslinking agent for curing the binder in the heat-sensitive recording layer or other layers. 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 a combination of two or more types. A preferred amount of the crosslinking agent is about 1 to 10 parts by mass per 100 parts by mass of the total solids content of the heat-sensitive color-developing printing ink. This enables the improvement of water resistance of the heat-sensitive recording layer.Wax

[0082] Examples of wax include wax such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; higher fatty acid amides, such as stearic acid amide and ethylene bisstearamide; higher fatty acid esters; and derivatives thereof.Metal Soap

[0083] Examples of metal soaps include higher fatty acid polyvalent metal salts, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Additionally, the heat-sensitive color-developing printing ink may optionally contain various aids such as oil repellents, defoaming agents, and viscosity regulators to an extent that does not impair the effects of the present invention.

[0084] The heat-sensitive color-developing printing ink of the present invention is typically prepared using water and an alcohol as solvents, by dispersing a leuco dye and a developer optionally with a binder, a sensitizer, and a stabilizer together or separately by using an agitation and wet grinding machine, such as ball mills, CoBall mills, attritors, or vertical and horizontal sand mills to form a dispersion, and then optionally mixing the thus-prepared dispersion so as to have an average particle diameter of 2 µm or less with a binder and aids.

[0085] The heat-sensitive color-developing printing ink of the present invention can be used to form a heat-sensitive recording layer of a heat-sensitive recording material on at least a portion of one surface or both surfaces of a support. The method for forming a heat-sensitive recording layer is preferably, but not particularly limited to, a printing method such as gravure printing.Protective-layer Printing Ink for Heat-sensitive Recording MaterialBinder

[0086] The protective-layer printing ink of the present invention contains a polyvinyl acetal resin as a binder. This enables improved printing preservation (in particular, plasticizer resistance) and thermal head matching (in particular, head residue suitability), while also enhancing transparency.

[0087] Polyvinyl acetal resins can be produced according to a method such as reacting a polyvinyl alcohol with an aldehyde to acetalize it. Examples of aldehydes include, but are not particularly limited to, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amyl aldehyde, hexyl aldehyde, heptyl aldehyde, 2-ethylhexyl aldehyde, cyclohexyl aldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0088] Examples of polyvinyl acetal resins include polyvinyl butyral resin, in which the acetal group is a butyral group, and polyvinyl acetoacetal resin, in which the acetal group is an acetoacetal group.

[0089] The number average molecular weight of such a 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. A polyvinyl acetal resin with a number average molecular weight of 17,000 can improve printing preservation (in particular, plasticizer resistance) and thermal head matching (in particular, head residue suitability). A polyvinyl acetal resin with a number average molecular weight of 40,000 or less can increase the concentration of the protective layer ink. The "number average molecular weight" in the present invention refers to the number-average molecular weight analyzed by gel permeation chromatography (GPC).

[0090] The content of such a polyvinyl acetal resin is not particularly limited and is preferably about 75 to 99 mass%, more preferably about 75 to 90 mass%, and even more preferably about 80 to 85 mass% based on the total solids content of the protective-layer printing ink. A content of a polyvinyl acetal resin of 75 mass% or more can improve printing preservation (in particular, plasticizer resistance). A content of a polyvinyl acetal resin of 99 mass% or less can improve thermal head matching (in particular, sticking properties).

[0091] The protective-layer printing ink of the present invention may contain other binders as long as they do not impair the effects of the present invention. Such other binders for use may be, for example, an aqueous binder, which is either a water-soluble binder or a water-dispersible binder. Examples of water-soluble binders include polyvinyl alcohol; modified polyvinyl alcohols, such as carboxy-modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, and silicon-modified polyvinyl alcohols; starch and its derivatives; cellulose derivatives, such as methoxy cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and ethyl cellulose; polyvinylpyrrolidone; polyamide; diisobutylene-maleic anhydride copolymer salts; styrene-maleic anhydride copolymer salts; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers etc.; and latex of water-insoluble polymers, such as styrene-butadiene copolymers. Furthermore, for example, an organic solvent-soluble binder can be used as an additional binder. Examples of organic solvent-soluble binders include vinyl acetate resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, vinylpyrrolidone-vinyl acetate copolymer resins, butyral resins, polyester resins, nitrocellulose resins, and styrene resins. These binders can be used alone or in a combination of two or more types.Slipperiness-imparting Agent

[0092] The protective-layer printing ink of the present invention contains an alkyl phosphate ester and / or a salt thereof as a slipperiness-imparting agent. This enables improved thermal head matching (in particular, head residue suitability) as well as enhanced transparency.

[0093] Alkyl phosphate esters are compounds in which at least one hydrogen atom of the three hydroxyl groups of phosphoric acid is replaced with an alkyl group. In particular, a mixture of the monoester (monoalkyl phosphate ester) and diester forms is preferred. The number of carbon atoms in the alkyl group of the ester portion in the alkyl phosphate ester is preferably 12 to 36, more preferably 12 to 30, and even more preferably 12 to 22. The alkyl group may be either linear or branched.

[0094] 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 salt is preferably in its Na-neutralized or Ca-neutralized form.

[0095] The first acid value of the alkyl phosphate ester is not particularly limited and is preferably 135 mg KOH / g or less, more preferably 120 mg KOH / g or less, and even more preferably 100 mg KOH / g or less. The alkyl phosphate ester with a first acid value of 135 mg KOH / g or less enables improved background fogging resistance. The first acid value is measured according to neutralization titration or potentiometry.

[0096] The content of such an alkyl phosphate ester and / or a salt thereof is not particularly limited and is preferably about 1 to 25 mass%, more preferably about 1 to 20 mass%, and even more preferably about 3 to 10 mass% based on the total solids content of the protective-layer printing ink. A content of an alkyl phosphate ester and / or a salt thereof being 1 mass% or more enables improved thermal head matching (slipperiness properties, reduction of printing noise). A content of an alkyl phosphate ester and / or a salt thereof being 25 mass% or less enables enhanced printing preservation (plasticizer resistance).

[0097] The protective-layer printing ink of the present invention may contain other slipperiness-imparting agents as long as they do not impair the effects of the present invention. Examples of other slipperiness-imparting agents include metal salts of higher fatty acids, such as zinc stearate and calcium stearate, and wax, such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, and castor wax. These slipperiness-imparting agents can be used alone or in a combination of two or more types.Calcined Kaolin

[0098] In the present invention, the protective-layer printing ink may further contain calcined kaolin with an average particle diameter of 2.0 µm or less. This can improve thermal head matching (in particular, head residue suitability). The average particle diameter of the calcined kaolin is preferably 1.5 µm or less, and more preferably 1.3 µm or less. From the viewpoint of thermal head cleaning performance, the average particle diameter of the calcined kaolin is preferably 0.1 µm or more. The "average particle diameter" as used here refers to the volume-based median diameter as measured according to the BET method, Sears method, or laser diffraction. More simply, individual particle diameters can be measured from particle images (SEM images) using an electron microscope, and the average of 10 particles may be used as the average particle diameter.

[0099] The content of the calcined kaolin with an average particle diameter 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% based on the total solids content of the protective-layer printing ink. A content of such calcined kaolin being 0.5 mass% or more enables improved thermal head matching (in particular, head residue suitability). A content of such calcined kaolin being 10 mass% or less can reduce the wear of thermal head protection films.Solvent

[0100] The protective-layer printing ink of the present invention may contain a solvent. Examples of such solvents include water, alcohols, cycloalkanes, toluene, and methylcyclohexane, with solvents containing an alcohol and a cycloalkane being preferred. The alcohol is preferably an alcohol with 5 or fewer carbon atoms. Examples of such alcohols with 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. Examples of cycloalkanes include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, methylcyclohexane, methylcyclooctane, dimethylcyclohexane, and ethylcyclohexane. Using an alcohol in the solvent makes the ink usable for gravure printing.

[0101] Other optional component materials of the protective-layer printing ink for use include crosslinking agents and pigments.Crosslinking Agent

[0102] The protective-layer printing ink may contain a crosslinking agent for curing the binder in 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 a combination of two or more types. A preferred amount of the crosslinking agent is about 1 to 10 parts by mass per 100 parts by mass of the total solids content of the protective-layer printing ink. This enables the improvement of water resistance of the protective layer.Pigment

[0103] Examples of the pigments to be contained in the protective layer include, but are not particularly limited to, 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 fillers. The content of the pigment is preferably about 1 to 20 mass%, and more preferably about 1 to 10 mass% based on the total solids content in the protective layer.

[0104] The protective-layer printing ink of the present invention is typically prepared by using an alcohol and a cycloalkane as solvents, and by mixing a binder and a slipperiness-imparting agent, optionally with aids.

[0105] The protective-layer printing ink of the present invention can be used to form a protective layer for the heat-sensitive recording material on at least a portion of one surface or both surfaces of a support. The method for forming a protective layer is preferably, but not particularly limited to, a printing method such as gravure printing.Support

[0106] The support in the present invention is not particularly limited in terms of type, shape, dimensions, etc., and can be appropriately selected and used from among, for example, fine paper (acidic paper and neutral paper), medium-grade paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, cellophane, synthetic resin films, and various other transparent supports. Of these, a translucent or transparent support made of glassine paper or laminated resin paper, or a transparent film made of cellophane or a synthetic resin film is preferable. These ensure enhanced transparency in the non-printing area of the heat-sensitive recording material. Examples of resins used in laminated resin paper or synthetic resin films include polyester resins, such as polyethylene terephthalate (PET), and polyolefin resins, such as polypropylene (PP) and polyethylene (PE). The thickness of the support is not particularly limited and is typically about 5 to 200 µm. The density of the support is also not particularly limited and is preferably about 0.60 to 2.00 g / cm 3< .Heat-sensitive Recording Layer

[0107] The heat-sensitive recording material may optionally contain a heat-sensitive recording layer on the support. The heat-sensitive recording layer is typically formed on a support by performing printing using a heat-sensitive color-developing printing ink. In the present invention, it is preferred that the heat-sensitive recording layer be provided on at least a portion of one surface or both surfaces of the support and be a layer formed by using the heat-sensitive color-developing printing ink of the present invention. When the heat-sensitive color-developing printing ink of the present invention is not used, the heat-sensitive color-developing ink described in the "Heat-sensitive Color-developing Printing Ink" section can be used without limitations on the developer and binder. The coating amount of the heat-sensitive recording layer is not particularly limited and is preferably about 1 to 12 g / m 2< , more preferably about 2 to 10 g / m 2< , even more preferably about 2.5 to 8 g / m 2< , and particularly preferably about 3 to 5.5 g / m 2< , on a dry mass basis. Moreover, the heat-sensitive recording layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.Protective Layer

[0108] The heat-sensitive recording material may optionally contain a protective layer on the support or the heat-sensitive recording layer. The protective layer is typically formed on the support or heat-sensitive recording layer by performing printing using a protective-layer printing ink for heat-sensitive recording materials. In the present invention, it is preferred that the protective layer be provided on at least a portion of one surface or both surfaces of the support and be a layer formed using the protective-layer printing ink for heat-sensitive recording materials of the present invention. When the protective-layer printing ink for heat-sensitive recording materials of the present invention is not used, the protective-layer printing ink for heat-sensitive recording materials described in the "Protective-layer Printing Ink for Heat-sensitive Recording Material" section can be used without limitations on the binder and slipperiness-imparting agent. The coating amount of the protective layer is not particularly limited and is preferably about 0.3 to 15 g / m 2< , more preferably about 0.3 to 10 g / m 2< , even more preferably about 0.3 to 8 g / m 2< , particularly preferably about 0.5 to 8 g / m 2< , and yet more preferably about 0.5 to 5 g / m 2< , on a dry mass basis. Moreover, the protective layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.Undercoat Layer

[0109] The heat-sensitive recording material of the present invention may also optionally contain an undercoat layer between the support and the heat-sensitive recording layer. The undercoat layer preferably contains a binder.Binder

[0110] The binder to be contained in the undercoat layer is not particularly limited and can be an aqueous binder, which is either a water-soluble binder or a water-dispersible binder, or solvent-based binder. Examples of binders include water-soluble polymeric materials, such as polyvinyl alcohols, derivatives thereof, starch, derivatives thereof, 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; emulsions, such as of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers; and latex of water-insoluble polymers, such as styrene-butadiene copolymers, and styrene-butadiene-acrylic copolymers. These can be suitably used on supports, such as polyester films (e.g., PET films), and polyester-based laminated resin paper. Of these, a binder containing latex is preferably used. Additionally, examples of aqueous binders or solvent-based binders include chlorinated polyolefin resins. Chlorinated polyolefin resins can be preferably used on supports, such as polyolefin-based films, such as PP films, paper, such as polyolefin-based synthetic paper, polyolefin-based resin laminated paper, and glassine paper, and cellophane. The content of the binder can be selected from a wide range; typically, the content of the binder is preferably about 10 to 100 mass%, and more preferably about 15 to 60 mass%, based on the total solids content in the undercoat layer.

[0111] It is preferred that the binder contains a binder resin with a glass transition temperature (Tg) of -10° C or lower. A binder resin with a glass transition temperature of -10° C or lower enables improved image quality even in low-energy regions. The glass transition temperature is preferably -30°C or lower because image quality can be further improved in low-energy regions. However, since undesirable stickiness occurs at temperatures -50°C or below, the glass transition temperature is preferably -40°C or higher.

[0112] The undercoat layer may contain at least one pigment selected from the group consisting of oil-absorbing pigments with an oil absorption of 70 ml / 100 g or more, and particularly about 80 to 150 ml / 100 g, organic hollow particles, and thermally expandable particles. The "oil absorption" refers to a value determined according to the method described in JIS K 5101.

[0113] The oil-absorbing pigments for use can be selected from various types. Specific examples include inorganic pigments, such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of the primary particles of the 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; typically, the amount of the oil-absorbing pigment is preferably about 20 to 80 mass%, and more preferably about 25 to 75 mass%, based on the total solids content in the undercoat layer.

[0114] The undercoat layer is formed on a support, for example, by mixing a binder, hollow particles, a pigment, and aids with water as a medium to prepare a coating liquid for undercoat layers, applying the thus-prepared coating liquid for undercoat layers to the support, and then drying the liquid. The undercoat layer can also be formed according to a printing method such as gravure printing, in the same manner for the heat-sensitive recording layer. The coating amount of the coating liquid for undercoat layers is preferably, but not particularly limited to, about 2 to 20 g / m 2< , and more preferably about 2 to 12 g / m 2< , on a dry mass basis.

[0115] Examples of aids to be contained in the coating liquid for undercoat layers include dispersants, such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and metal salts of fatty acids, wax, such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, water-resistance-improving agents, such as hydrazide compounds, boric acid, dialdehyde starch, glyoxylate salts, and epoxy compounds, defoaming agents, coloring dyes, and fluorescent dyes.Heat Seal Layer

[0116] The heat-sensitive recording material of the present invention may also optionally comprise a heat seal layer on at least a portion of one or both surfaces of the support. It is preferred that the heat seal layer be present on the surface of the support opposite to the surface on which the heat-sensitive recording layer is present.

[0117] The heat seal layer in the present invention includes a single-layer film composed of a single resin, and a single-layer or laminated film using multiple resins. Preferable examples of resins that constitute the heat seal layer include polyolefin resins (in particular, polyethylene and polypropylene), polystyrene resins, polyester resins (in particular, polyethylene terephthalate resin), polyamide resins (in particular, nylon), and biodegradable resins.

[0118] The polyethylene may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), or high-density polyethylene (HDPE).

[0119] The heat seal layer may be non-oriented, or uniaxially or biaxially oriented.

[0120] The thickness of the heat seal layer is not particularly limited; the thickness is preferably about 10 to 70 µm, more preferably about 20 to 60 µm, and even more preferably about 30 to 50 µm.

[0121] The heat seal layer may contain additives, such as fillers, anti-blocking agents, antistatic agents, plasticizers, and oxidizing agents. These additives may be used alone or in a combination of two or more.

[0122] The heat seal layer may be formed by extruding a resin onto a support to laminate it or by bonding the support and the heat seal layer using a binder.

[0123] The binder for use in bonding is not particularly limited; the binder may be any of solvent-free binder, organic solvent binder, or water-based binder.

[0124] Examples of main components that constitute the binder include (meth)acrylic acid ester copolymers, α-olefin copolymers, ethylene-vinyl acetate copolymers, polyvinyl alcohols, polyurethane, styrene-butadiene copolymers, polyvinyl chloride, epoxy resins, melamine resins, silicone resins, natural rubber, casein, and starch.

[0125] After a binder is applied onto the heat seal layer, the heat seal layer and the support may be laminated. Alternatively, after a binder is applied onto the support, the support and the heat seal layer may be laminated. Alternatively, after a binder is applied onto both the heat seal layer and the support, the heat seal layer and the support may be laminated. There is no particular limitation in this regard.

[0126] The method for applying a binder can be appropriately selected from known methods without particular limitation. Examples include roll coating, die coating, and spray coating.

[0127] The amount of binder applied is not particularly limited. The amount applied (coating amount) after drying is preferably 0.5 g / m 2< or more, more preferably 1.0 g / m 2< or more, and even more preferably 1.5 g / m 2< or more, and preferably 10.0 g / m 2< or less, more preferably 7.0 g / m 2< or less, and even more preferably 5.0 g / m 2< or less.Printing Layer

[0128] In the present invention, a printing layer can be provided on at least one of the following: on top of the protective layer, between the heat-sensitive recording layer and the protective layer, on top of the heat-sensitive recording layer, between the support and the heat seal layer, and on the surface of the support opposite to the surface on which the heat-sensitive recording layer is present. The printing ink used in forming the printing layer, based on the classification by printing plate type, includes ink for relief printing, planographic printing, intaglio printing, and stencil printing. The printing ink used in forming the printing layer, based on the classification by drying form, includes ink for penetration drying, evaporation drying, oxidative polymerization drying, and photo-polymerization drying (UV-curable). For forming the printing layer, various printing methods can be used, such as flexographic printing, offset printing, gravure printing, and screen printing. Plateless digital printing methods, such as on-demand printing and direct printing can also be used. There is no particular limitation on the color tone of the printing ink; however, especially when heat-sensitive recording is performed on the part corresponding to the printing layer, it is preferred that the optical density of the printing layer be lower than that of the recording area of the heat-sensitive recording layer. The printing pattern may be partial printing or full-surface solid printing. It is preferably a watermark-like background printing with an optical density of about 0.1 to 0.6, or fixed information that does not interfere with heat-sensitive recording. For example, when the heat-sensitive recording material is used as a top-sealing lid material on which variable information such as product names, expiration dates, and barcodes are recorded by heat-sensitive recording, it is preferable to partially make print with white ink on the area corresponding to the back of these heat-sensitive records, which is the surface of the support opposite to the surface on which the heat-sensitive recording layer is present. This leads to improved readability of barcodes and the like.Heat-sensitive Recording Material

[0129] The heat-sensitive recording material can be produced by forming individual layers on a support. The method for forming the layers on a support can be any of printing methods, such as gravure printing, and of known coating methods, such as an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, a curtain method, a slot die method, a slide die method, or an extrusion method. The method is preferably gravure printing or other printing methods, and more preferably gravure printing. Individual paint may be applied and dried to form each layer, or the same paint may be applied in two or more separate layers. Moreover, simultaneous multilayer coating, in which two or more layers are applied simultaneously, may also be performed. After each layer is formed or after all layers are formed, a smoothing process can be performed at any stage using a known method, such as supercalendering or soft calendering.

[0130] The method for recording images on the heat-sensitive recording material of the present invention is not particularly limited and can be appropriately selected according to the intended use. Examples of usable methods for recording images include thermal head printers and laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser light, YAG laser light, fiber laser light, solid-state laser light, and dye laser light). The wavelength of laser light for use is not particularly limited and can be appropriately selected according to the intended use.

[0131] The heat-sensitive recording material of the present invention has high transparency and exhibits excellent background fogging resistance and plasticizer resistance, and is thus suitable for food applications such as labels and top-sealing lid materials of transparent containers for salads and prepared foods. In top-sealing lid materials, although opacity may be increased due to the heat-sensitive color-developing printing ink on the printed surface and the white ink for back printing, the heat-sensitive recording material of the present invention can provide increased transparency of the surface, thereby allowing one to confirm information such as of raw materials of the contents while observing the contents through the lid material. Furthermore, using the heat-sensitive recording material as a top-sealing lid material eliminates the need to attach thermal labels, improving packaging efficiency while reducing plastic consumption.Examples

[0132] The present invention is described in more detail below with reference to Examples. However, the present invention is not limited to these. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "mass%," respectively. Particle diameters, including average particle diameter, are values measured using an LB500 laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd.). The "average particle diameter" refers to the median diameter (D50).A. Heat-sensitive Recording Material (A)Example A 1< (1) Preparation of Dye Dispersion (Liquid A)

[0133] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (liquid A).(2) Preparation of Developer Dispersion (Liquid B)

[0134] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a developer dispersion (liquid B).(3) Preparation of Heat-sensitive Color-developing Printing Ink

[0135] 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, thereby obtaining a heat-sensitive color-developing printing ink.(4) Preparation of Heat-sensitive Recording Material

[0136] A five-color gravure printing machine was used to perform printing with a heat-sensitive color-developing printing ink on one surface of a transparent PET film with a thickness of 12 µm so that the coating amount of the heat-sensitive color-developing printing ink after drying was 3.5 g / m 2< , and the film was wound to form a heat-sensitive recording layer. Furthermore, an ester-based binder was applied in an amount of 3 g / m 2< on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink by a dry lamination method, and a 30 µm thick low-density polyethylene film was bonded to obtain a heat-sensitive recording material with a heat seal layer. The obtained heat-sensitive recording material was wound into small rolls using a slitter and further cut into a predetermined shape to prepare top-sealing lid materials, which were then subjected to a sealing process and used to seal food packaging containers.Example A2

[0137] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts in the preparation of liquid A and liquid B in Example A1.Example A3

[0138] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 25 parts in the preparation of liquid A and liquid B in Example A1, and the amount of liquid B was changed from 20 parts to 40 parts in the preparation of the heat-sensitive color-developing printing ink.Example A4

[0139] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 50 / 50 was used instead of the vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 30 / 70 in the preparation of liquid A and liquid B in Example A1.Example A5

[0140] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 70 / 30 was used instead of the vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 30 / 70 in the preparation of liquid A and liquid B in Example A1.Example A6

[0141] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the following heat-sensitive color-developing printing ink (5) was used instead of the heat-sensitive color-developing printing ink (3) in the preparation of the heat-sensitive recording material in Example A1.(5) Preparation of Heat-sensitive Color-developing Printing Ink

[0142] 10 parts of liquid A, 20 parts of liquid B, 8 parts of a 20% aqueous dispersion of colloidal silica with an average particle diameter of 12 nm, 1.9 parts of water, and 1.9 parts of isopropyl alcohol were mixed and stirred, thereby obtaining a heat-sensitive color-developing printing ink.Example A7

[0143] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate were used instead of 30 parts of the N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Example A8

[0144] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide were used instead of 30 parts of the N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Example A9

[0145] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that after the heat-sensitive color-developing printing ink was applied and dried, printing was further performed with the following protective layer ink (6) on the heat-sensitive recording layer to form a protective layer so that the coating amount after drying was 1.0 g / m 2< in the preparation of the heat-sensitive recording material in Example A1.(6) Preparation of Protective Layer Ink

[0146] 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, thereby obtaining a protective layer ink.Example A10

[0147] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that cellophane with a thickness of 23 µm was used instead of the transparent PET with a thickness of 12 µm, and a polyethylene film with a thickness of 20 µm was laminated according to an extrusion lamination method on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink in the preparation of the heat-sensitive recording material in Example A1.Example A11

[0148] A heat-sensitive recording material was obtained in the same manner as in Example A10, except that printing was performed with a 25% toluene solution of chlorinated polypropylene resin (product name: S1306 PPHP adhesive varnish, manufactured by Toyo Ink Co., Ltd.) to achieve a coating amount of 0.5 g / m 2< after drying, and the solution was dried to form an undercoat layer, followed by performing printing with a heat-sensitive color-developing printing ink on the undercoat layer to form a heat-sensitive recording layer in the preparation of the heat-sensitive recording material in Example A10.Comparative Example A1

[0149] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone were used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Comparative Example A2

[0150] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide were used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Comparative Example A3

[0151] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that polyvinylpyrrolidone resin was used instead of the vinylpyrrolidone-vinyl acetate copolymer in the preparation of liquid A and liquid B in Example A1.Comparative Example A4

[0152] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a polyvinyl alcohol with a degree of saponification of 80 mol% and a degree of polymerization of 250 was used instead of the vinylpyrrolidone-vinyl acetate copolymer in the preparation of liquid A and liquid B in Example A1.

[0153] The Examples and Comparative Examples above were evaluated according to the following methods. Table 1 shows the results.Recording DensityThermal Printer Printing

[0154] A thermal recording tester (product name: TH-PMD, manufactured by Ohkura Electric Co., Ltd.) was used to make recording on each heat-sensitive recording material at an applied energy of 0.24 mJ / dot. The printed area 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).Evaluation

[0155] 1.40 or higher: Excellent 1.25 or higher and less than 1.40: Good 1.10 or higher and less than 1.25: Acceptable for practical use Less than 1.10: Not usable Laser Light Printing

[0156] A UV laser marker (product name: UV Laser Marker, MD-U1000C, manufactured by Keyence Corporation) was used to irradiate each heat-sensitive recording material with laser at a wavelength of 355 nm, output of 1.2 W, scan speed of 3,000 mm / sec, and laser spot diameter of 14 µm to make a solid print of 10 mm square. The obtained printed area 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).Evaluation

[0157] 1.40 or higher: Excellent 1.25 or higher and less than 1.40: Good 1.10 or higher and less than 1.25: Acceptable for practical use Less than 1.10: Not usable Background Fogging

[0158] Each heat-sensitive recording material was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for background fogging in the non-printed area with a spectrodensitometer (X-Rite 504, manufactured by X-Rite)Evaluation

[0159] Less than 0.10: Good 0.10 or higher and less than 0.20: Acceptable for practical use 0.20 or higher: Not usable

[0160] Transparency Evaluation

[0161] The transparency of the non-printed area of each heat-sensitive recording material was measured with a HAZE meter (NDH-7000, manufactured by Nippon Denshoku Industries Co., Ltd.).Evaluation

[0162] A: Less than 20% B: 20% or higher and less than 30% C: 30% or higher and less than 40% D: 40% or higher Plasticizer Resistance

[0163] A polycarbonate pipe (diameter: 40 mm) was wrapped with three layers of plastic wrap (product name: Hi-S Soft, manufactured by Nippon Carbide Industries Co., Inc.). A sample of each heat-sensitive recording material that developed color with a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) was placed on top of the wrapped polycarbonate pipe and further wrapped over with three layers of plastic wrap. The sample was then left to stand at 40°C for 24 hours. Before and after this treatment, the recording area was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for reflective density with a spectrodensitometer (X-Rite 504, manufactured by X-Rite). Additionally, the retention rate of the recording area was calculated using the following formula. Evaluation

[0164] 90% or higher: Excellent 70% or higher and less than 90%: Good 50% or higher and less than 70%: Acceptable for practical use Less than 50%: Not usable Table 1 Recording DensityBackground FoggingTransparencyPlasticizer Resistance %Thermal PrinterLaser LightExample A11.451.580.08A80Example A21.561.650.09B76Example A31.401.520.08A84Example A41.351.380.08A83Example A51.211.240.08A81Example A61.521.590.08A79Example A71.551.640.08A71Example A81.311.550.08A92Example A91.351.600.08A99Example A101.361.420.09B81Example A111.381.420.08B80Comparative Example A11.411.520.54C25Comparative Example A21.371.490.10C31Comparative Example A31.021.080.08A76Comparative Example A41.481.590.08B35 B. Heat-sensitive Recording Material (B)Example B1(1) Preparation of Dye Dispersion (Liquid A)

[0165] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (Liquid A).(2) Preparation of Developer Dispersion (Liquid B)

[0166] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a developer dispersion (Liquid B).(3) Preparation of Heat-sensitive Color-developing Printing Ink

[0167] 10 parts of liquid A, 20 parts of liquid B, 8 parts of a 20% aqueous dispersion of colloidal silica with a particle diameter of 12 nm, 1.9 parts of water, and 1.9 parts of isopropyl alcohol were mixed and stirred, thereby obtaining a heat-sensitive color-developing printing ink.(4) Preparation of Protective-layer Printing Ink

[0168] 90 parts of polyvinyl acetal resin (product 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 (product 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, thereby obtaining a protective-layer printing ink.(5) Preparation of Heat-sensitive Recording Material

[0169] A five-color gravure printing machine was used to perform printing with a heat-sensitive color-developing printing ink on one surface of a transparent PET film with a thickness of 12 µm so that the coating amount after drying was 3.5 g / m 2< , thereby forming a heat-sensitive recording layer. Furthermore, printing was performed with a protective-layer printing ink on the heat-sensitive recording layer so that the coating amount after drying was 1.0 g / m 2< , followed by winding the film, thereby forming a protective layer. Furthermore, an ester-based binder was applied in an amount of 3 g / m 2< on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink by a dry lamination method, and a 30 µm thick low-density polyethylene film was bonded to obtain a heat-sensitive recording material with a heat seal layer. The obtained heat-sensitive recording material was wound into small rolls using a slitter and further cut into a predetermined shape to prepare top-sealing lid materials, which were then subjected to a sealing process and used to seal food packaging containers.Example B2

[0170] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that polyvinyl acetal resin (trade name: S-LEC BM-1, number average molecular weight: 40,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective layer ink in Example B1.Example B3

[0171] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that polyvinyl acetal resin (trade name: S-LEC KS-10, number average molecular weight: 17,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Industries Co., Ltd.) in the preparation of the protective layer ink in Example B1.Example B4

[0172] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that an alkyl phosphate ester compound (trade name: Phosphanol SC6103L, Ca-neutralized salt type, 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.) in the preparation of the protective layer ink in Example B1.Example B5

[0173] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 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.) in the preparation of the protective layer ink in Example B1.Example B6

[0174] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that the following protective-layer printing ink (6) was used instead of the protective-layer printing ink (4) of Example B1.(6) Preparation of Protective-layer Printing Ink

[0175] 90 parts of polyvinyl acetal resin (product 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 (product name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.), 5 parts of a 20% isopropyl alcohol dispersion of calcined kaolin with an average particle diameter of 1.2 µm, 450 parts of isopropyl alcohol, and 450 parts of methylcyclohexane were mixed and stirred, thereby obtaining a protective-layer printing ink.Example B7

[0176] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 23 µm thick cellophane was used instead of the 12 µm thick transparent PET, and a 20 µm thick polyethylene film was bonded by an extrusion lamination method on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink in the preparation of the heat-sensitive recording material in Example B1.Reference Example B1

[0177] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of acrylic resin (trade name: BR101, number average molecular weight: 160,000, manufactured by Mitsubishi Chemical Corporation) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B2

[0178] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of acrylic resin (trade name: BR115, number average molecular weight: 50,000, manufactured by Mitsubishi Chemical Corporation) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B3

[0179] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of styrene-acrylic resin (trade name: UC-3080, number average molecular weight: 14,000, manufactured by Toagosei Co., Ltd.) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B4

[0180] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 10 parts of zinc stearate (average particle diameter: 1.2 µm) were used instead of 10 parts of the alkyl phosphate ester compound (trade name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.

[0181] The Examples and Reference Examples above were evaluated according to the following methods. Table 2 shows the results.Transparency Evaluation

[0182] The transparency of the non-printed area of each heat-sensitive recording material was measured using a HAZE meter (NDH-7000 manufactured by Nippon Denshoku Industries Co., Ltd.).Evaluation

[0183] A: Less than 20%: Good B: 20% or higher and less than 30%: Acceptable for practical use C: 30% or higher: Not usable Heat Resistance of Background

[0184] Each heat-sensitive recording material was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for background fogging of the non-printed area with a spectrodensitometer (X-Rite 504, manufactured by X-Rite).Evaluation

[0185] Less than 0.15: Good 0.15 or more and less than 0.25: Acceptable for practical use 0.25 or more: Not usable Plasticizer Resistance

[0186] A polycarbonate pipe (diameter: 40 mm) was wrapped with three layers of plastic wrap (product name: Hi-S Soft, manufactured by Nippon Carbide Industries Co., Inc.). A sample of each heat-sensitive recording material that developed color with a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) was placed on top of the wrapped polycarbonate pipe and further wrapped over with three layers of plastic wrap. The sample was then left to stand at 40°C for 24 hours. Before and after this treatment, the recording area was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for reflective density with a spectrodensitometer (X-Rite 504, manufactured by X-Rite). Additionally, the retention rate of the recording area was calculated using the following formula. Printing Sound

[0187] A thermal recording tester (product name: TH-PMD, manufactured by Ohkura Electric Co., Ltd.) was used to make recording on each heat-sensitive recording material at an applied energy of 0.243 mJ / dot, during which the printing sound was measured by sensory assessment.Evaluation

[0188] A: Quiet printing sound B: Faint printing noise (acceptable for practical use) C: Loud printing sound Head Residue Suitability

[0189] A label printer (L'esprit V-ex, manufactured by Sato Corporation) was used to perform printing at 100% black solid coverage of 50 cm, and the heating elements of the thermal head were observed using a stereomicroscope (VH-Z100UR, manufactured by Keyence Corporation) and subjected to sensory assessment.Evaluation

[0190] A: No adherence of head residue B: Slight presence of head residue C: Small amount of head residue adhered (acceptable for practical use) D: Significant amount of head residue Table 2 TransparencyBackground FoggingPlasticizer Resistance %Printing SoundHead Residue SuitabilityExample B1A0.0991ABExample B2A0.0990ABExample B3A0.0973ABExample B4A0.1391ABExample B5A0.1892ABExample B6B0.0991AAExample B7A0.0991ABReference Example B1C0.0935ADReference Example B2C0.0940ADReference Example B3A0.0994ADReference Example B4C0.0991CD

Examples

examples

[0132]The present invention is described in more detail below with reference to Examples. However, the present invention is not limited to these. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "mass%," respectively. Particle diameters, including average particle diameter, are values measured using an LB500 laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd.). The "average particle diameter" refers to the median diameter (D50).

A. Heat-sensitive Recording Material (A)

example a 1 <

Example A 1<

(1) Preparation of Dye Dispersion (Liquid A)

[0133]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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (liquid A).

(2) Preparation of Developer Dispersion (Liquid B)

[0134]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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achi...

example a2

[0137]A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts in the preparation of liquid A and liquid B in Example A1.

Technical Field

[0001] The present invention relates to printing ink for heat-sensitive recording materials, a heat-sensitive recording material, and an image recording method.Background Art

[0002] Heat-sensitive recording materials using color-developing reaction between a leuco dye and a developer are relatively inexpensive, and their recording devices are compact and easy to maintain. Thus, these heat-sensitive recording materials are widely used not only as recording media for faxes, various calculators, and CAD plotters, but also as labeling solutions for food products, including fresh items, boxed lunches, and prepared dishes, medical items, including labels for pharmaceutical management, and process control.

[0003] For labels, top-sealing materials, or bands on clear containers for food products such as salads or prepared meals, high-transparency media are often essential to clearly showcase the content. In these applications, transparent thermal films, including a transparent PET film as a substrate, are commonly used.

[0004] PTL 1 reports a thermosensitive recording medium that has all of the following properties: hot-water resistance, water resistance, ethanol resistance, temperature-humidity resistance, wet-abrasion resistance, and heat resistance, while also producing high-density images. This thermosensitive recording medium contains a support and a thermosensitive recording layer on the support, wherein the thermosensitive recording layer contains a specific N,N'-diaryl urea compound and a styrene-acrylic resin. Additionally, the Examples of PTL 1 disclose the formation of a protective layer containing styrene-acrylic resin, oxidized polyethylene wax, and calcium carbonate with a PET film as the support.

[0005] PTL 2 reports a heat-sensitive-recording-layer-forming liquid capable of forming a heat-sensitive recording layer with excellent surface uniformity without drag and coating unevenness and with minimal thickness variation, and discloses that the heat-sensitive-recording-layer-forming liquid contains an electron-donating compound, an electron-accepting compound with a solubility of 5 mass% or less in 100% ethanol at 20°C, and a solvent.

[0006] PTL 3 reports that a thermal coloring film is obtained by applying a thermal coloring ink onto a support substrate to form a thermal coloring ink layer and then forming a protective layer composed of a resin coating layer containing magnesium oxide on the upper surface of the thermal coloring ink layer, and that the thermal coloring film has both heat resistance and water resistance.Citation ListPatent Literature

[0007] PTL 1: JP2022-146283A PTL 2: JP2022-151636A PTL 3: Japanese Patent No. 3382728 Summary of InventionTechnical Problem

[0008] An object of the present invention is to provide a heat-sensitive color-developing printing ink, a heat-sensitive recording material using the heat-sensitive color-developing printing ink that is highly sensitive and exhibits excellent background fogging resistance and plasticizer resistance, and an image recording method using the heat-sensitive color-developing printing ink.

[0009] In another embodiment, an object of the present invention is to provide a protective-layer printing ink for heat-sensitive recording materials and a heat-sensitive recording material that exhibits excellent printing preservation and thermal head matching using the protective-layer printing ink.Solution to Problem

[0010] In view of the prior art, the present inventors conducted extensive research and succeeded in achieving the objects. Specifically, the present invention relates to the following printing ink for heat-sensitive recording materials, heat-sensitive recording material, and image recording method.Item 1.

[0011] A printing ink for a heat-sensitive recording material, which is either the following (A) or (B): (A) a heat-sensitive color-developing printing ink comprising a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R 0< represents a C 1-12 alkyl group, a C 7-12 aralkyl group, or a C 6-12 aryl group, wherein the aralkyl group and the aryl group may be substituted with a C 1-12 alkyl group, a C 1-12 alkoxy group, a C 6-12 aryl group, or a halogen atom, and multiple R 0< s may be the same or different, and A 1< represents a hydrogen atom or a C 1-4 alkyl group, and multiple A 1< s may be the same or different; a compound represented by the following formula (2): wherein R 1< to 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; and 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide, and (B) a protective-layer printing ink for a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent. Item 2.

[0012] The printing ink according to Item 1, wherein the printing ink is the heat-sensitive color-developing printing ink (A).Item 3.

[0013] The printing ink according to Item 2, wherein the content of the leuco dye is 15 to 40 mass%, the content of the developer is 20 to 70 mass%, and the content of the vinylpyrrolidone-vinyl acetate copolymer is 5 to 35 mass% based on the total solids content of the heat-sensitive color-developing printing ink.Item 4.

[0014] The printing ink according to Item 2 or 3, wherein the molar ratio of vinylpyrrolidone to vinyl acetate in the vinylpyrrolidone-vinyl acetate copolymer is 50 / 50 to 30 / 70.Item 5.

[0015] The printing ink according to any one of Items 2 to 4, further comprising colloidal silica with an average particle diameter of 45 nm or less, wherein the content of the colloidal silica is 5 to 30 mass% based on the total solids content of the heat-sensitive color-developing printing ink.Item 6.

[0016] The printing ink according to any one of Items 2 to 5, comprising water and an alcohol as the solvent.Item 7.

[0017] The printing ink according to Item 1, wherein the printing ink is the protective-layer printing ink for a heat-sensitive recording material (B).Item 8.

[0018] The printing ink according to Item 7, wherein the content of the polyvinyl acetal resin is 75 to 99 mass% and the content of the alkyl phosphate ester and / or a salt thereof is 1 to 25 mass% based on the total solids content of the protective-layer printing ink.Item 9.

[0019] The printing ink according to Item 7 or 8, wherein the polyvinyl acetal resin has a number average molecular weight of 17,000 to 40,000.Item 10.

[0020] The printing ink according to any one of Items 7 to 9, wherein the alkyl phosphate ester salt is in its Na-neutralized or Ca-neutralized form, and the first acid value of the alkyl phosphate ester is 135 mg KOH / g or less.Item 11.

[0021] The printing ink according to any one of Items 7 to 10, further comprising calcined kaolin having an average particle diameter of 2.0 µm or less, wherein the content of the calcined kaolin is 0.5 to 10 mass% based on the total solids content of the protective-layer printing ink.Item 12.

[0022] The printing ink according to any one of Items 7 to 11, comprising an alcohol and a cycloalkane as the solvent.Item 13.

[0023] The printing ink according to any one of Items 1 to 12, wherein the printing ink is a gravure printing ink.Item 14.

[0024] A heat-sensitive recording material comprising a support, and a heat-sensitive recording layer formed of the printing ink of any one of Items 1 to 6 and 13 and / or a protective layer formed of the printing ink of any one of Items 1 and 7 to 13 on at least a portion of one surface or both surfaces of the support. Item 15.

[0025] The heat-sensitive recording material according to Item 14, wherein the support is a translucent or transparent support made of glassine paper or laminated resin paper, or a transparent film made of cellophane or a synthetic resin film.Item 16.

[0026] The heat-sensitive recording material according to Item 14 or 15, comprising a printing layer on at least a portion of the surface of the support opposite to the surface on which the heat-sensitive recording layer is present.Item 17.

[0027] The heat-sensitive recording material according to any one of Items 14 to 16, comprising a heat seal layer on at least a portion of one surface or both surfaces of the support.Item 18.

[0028] The heat-sensitive recording material according to any one of Items 14 to 17, comprising an undercoat layer between the support and the heat-sensitive recording layer.Item 19.

[0029] The heat-sensitive recording material according to Item 18, wherein the undercoat layer contains a chlorinated polyolefin resin as a binder.Item 20.

[0030] The heat-sensitive recording material according to any one of Items 17 to 19, which is for use in a top-sealing lid material.Item 21.

[0031] An image recording method, comprising recording an image on the heat-sensitive recording material of any one of Items 14 to 20 by using laser light or a thermal head.Advantageous Effects of Invention

[0032] The heat-sensitive recording material containing a heat-sensitive recording layer formed using the heat-sensitive color-developing printing ink of the present invention exhibits high sensitivity and excellent background fogging resistance and plasticizer resistance. The heat-sensitive recording material also exhibits excellent transparency.

[0033] The heat-sensitive recording material containing a protective layer formed using the protective-layer printing ink for a heat-sensitive recording material of the present invention exhibits excellent printing preservation and thermal head matching. The heat-sensitive recording material also exhibits excellent transparency.Description of Embodiments

[0034] In the present specification, the expression "comprise" or "contain" includes the concepts of "comprising," "consisting essentially of," and "consisting of."

[0035] In the present specification, a numerical range indicated by "... to ..." means a range including the numerical values given before and after "to" as the lower limit and the upper limit.

[0036] "Latex" as used herein includes one in the form of a gel or dry film formed by drying a dispersion medium.

[0037] The printing ink for a heat-sensitive recording material of the present invention is either the following (A) or (B) : (A) a heat-sensitive color-developing printing ink comprising a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R 0< represents a C 1-12 alkyl group, a C 7-12 aralkyl group, or a C 6-12 aryl group, wherein the aralkyl group and the aryl group may be substituted with a C 1-12 alkyl group, a C 1-12 alkoxy group, a C 6-12 aryl group, or a halogen atom, and multiple R 0< s may be the same or different, and A 1< represents a hydrogen atom or a C 1-4 alkyl group, and multiple A 1< s may be the same or different; a compound represented by the following formula (2): wherein R 1< to 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; and 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide, and (B) a protective-layer printing ink for a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent.

[0038] The heat-sensitive recording material of the present invention also comprises a heat-sensitive recording layer formed of the heat-sensitive color-developing printing ink of the present invention and / or a protective layer formed of the protective-layer printing ink of the present invention on at least a portion of one surface or both surfaces of a support.Heat-sensitive Color-developing Printing InkLeuco Dye

[0039] The heat-sensitive color-developing printing ink of the present invention may contain any of various known colorless or pale-colored leuco dyes. Specific examples of such leuco dyes are described below.

[0040] Specific examples of leuco dyes include dyes capable of developing blue color, such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluoran; dyes capable of developing green color, such as 3-(N-ethyl-N-p-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam; dyes capable of developing red color, such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 3-diethylamino-7-chlorofluoran; dyes capable of developing black color, such as 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, 3-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-alininofluoran, 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-dimethylaminobenzhydrinbenzyl 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-isoamyl-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[phthalide-3,9'-xanthen-2'-ylamino]phenyl}propane, and 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran; dyes having absorption wavelengths in the near-infrared region, such as 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylen-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylen-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, and 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Usable leuco dyes are, of course, not limited to these compounds, and two or more of such compounds can be used in combination as necessary.

[0041] The content of the leuco dye is not particularly limited and is preferably about 15 to 40 mass%, more preferably about 18 to 38 mass%, and even more preferably about 20 to 35 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A leuco dye content of 15 mass% or more can enhance color development ability and thus improve print density, whereas a leuco dye content of 40 mass% or less can enhance heat resistance.Developer

[0042] In the present invention, the developer contained is at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by formula (1), a compound represented by formula (2), and 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. This enables the improvement of print density while also achieving excellent transparency, background fogging resistance, and plasticizer resistance even when an alcohol is used as a solvent. Since alcohols can be used as a solvent, the heat-sensitive color-developing printing ink of the present invention is suitable for use in gravure printing ink.

[0043] In formula (1) for N,N'-diaryl urea compounds, the C 1-12 alkyl group represented by R 0< may be linear, branched, or alicyclic, and is preferably a C 1-6 alkyl group, and more preferably a C 1-3 alkyl group. Examples of C 1-12 alkyl groups 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" as used here also includes the alkyl moiety of a C 1-12 alkoxy group.

[0044] The "aralkyl group" refers to an arylalkyl group. Examples of C 7-12 aralkyl groups include a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, and a 3-phenylpropyl group.

[0045] The "aryl group" refers to a monocyclic or polycyclic group composed of a 5- or 6-membered aromatic hydrocarbon ring. Examples of C 6-12 aryl groups include a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. The "aryl group" as used here also includes the aryl moiety of an aralkyl group.

[0046] Examples of halogen atoms include fluorine, chlorine, bromine, and iodine.

[0047] In formula (1), the substitution positions of the multiple R 0< -SO 3 - groups may be the same or different. The preferred substitution positions are at the 3-position, 4-position, or 5-position, with the 3-position being more preferred. When the C 7-12 aralkyl group and the C 6-12 aryl group represented by R 0< are substituted, the number of substituents is not particularly limited, and may be, for example, 1 to 4.

[0048] The C 1-4 alkyl group represented by A 1< may be either linear or branched, and examples 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.

[0049] The substitution positions of the multiple A 1< groups may be the same or different. The preferred substitution position is the 3-position, 4-position, or 5-position.

[0050] The N,N'-diaryl urea compound represented by formula (1) is preferably, but not particularly limited to, at least one compound selected from the group consisting of 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, 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)]phenyl urea. Of these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is preferred.

[0051] The halogen atom represented by R 1< to R 5< may be a fluorine atom, a chlorine atom, or a bromine atom, with a fluorine atom and a chlorine atom being preferred.

[0052] The alkyl group may be linear, branched, or cyclic, and is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. Typically, the alkyl group is a C 1-12 alkyl group, preferably a C 1-8 alkyl group, more preferably a C 1-6 alkyl group, and even more preferably a C 1-4 alkyl group.

[0053] The alkoxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkoxy group, and more preferably a linear alkoxy group. Typically, the alkoxy group is a C 1-12 alkoxy group, preferably a C 2-8 alkoxy group, more preferably a C 2-6 alkoxy group, and even more preferably a C 2-4 alkoxy group.

[0054] The alkylcarbonyloxy group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, and more preferably a linear alkylcarbonyloxy group. The alkylcarbonyloxy group is also preferably a C 1-10 alkylcarbonyloxy group.

[0055] The alkylcarbonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylcarbonylamino group, and more preferably a linear alkylcarbonylamino group. The alkylcarbonylamino group is also preferably a C 1-10 alkylcarbonylamino group.

[0056] The alkylsulfonylamino group may be linear, branched, or cyclic, and is preferably a linear or branched alkylsulfonylamino group, and more preferably a linear alkylsulfonylamino group. The alkylsulfonylamino group is also preferably a C 1-10 alkylsulfonylamino group.

[0057] The "aryl group" means a monocyclic or polycyclic group formed of one or more 5- or 6-membered aromatic hydrocarbon rings. Examples of aryl groups include a phenyl group, a naphthyl group, and a biphenyl group.

[0058] The aryloxy group is preferably a C 6-12 aryloxy group. The arylcarbonyloxy group is preferably a C 6-12 arylcarbonyloxy group. The arylcarbonylamino group is preferably a C 6-12 arylcarbonylamino group. The arylsulfonylamino group is preferably a C 6-12 arylsulfonylamino group.

[0059] The monoalkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched monoalkylamino group, and more preferably a linear monoalkylamino group. A monoalkylamino group whose alkyl group has 1 to 10 carbon atoms is also preferable.

[0060] The dialkylamino group may be linear, branched, or cyclic, and is preferably a linear or branched dialkylamino group, and more preferably a linear dialkylamino group. A dialkylamino group whose alkyl group has 1 to 10 carbon atoms is also preferable.

[0061] The arylamino group may be a monarylamino group or diarylamino group, and is preferably a C 6-12 monoarylamino group.

[0062] Specific examples of compounds represented by formula (2) include those wherein R 1< to R 5< are each an alkyl group or a hydrogen atom, preferably R 1< to R 5< are each a C 1-8 linear alkyl group or a hydrogen atom, more preferably R 1< to R 5< are each a C 1-4 linear alkyl group or a hydrogen atom, and even more preferably R 1< to R 5< are each a methyl group or a hydrogen atom.

[0063] Other specific examples of compounds represented by formula (2) include those wherein R 1< , R 2< , R 4< , and R 5< are each 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 a C 1-8 alkyl group, even more preferably a hydrogen atom or a C 1-4 alkyl group, and particularly preferably a methyl group).

[0064] The position of the substituent bound to one benzene ring in the diphenylurea structure in formula (2) may be the ortho-position, the meta-position, or the para-position, preferably the ortho-position or the meta-position, and more preferably the meta-position with respect to the aminocarbonyl group on the benzene ring.

[0065] The compound represented by formula (2) is not particularly limited, and is preferably at least one member 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. Of these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferable.

[0066] The content of the developer is not particularly limited and is preferably about 20 to 70 mass%, more preferably about 25 to 62 mass%, and even more preferably about 28 to 55 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the developer of 20 mass% or more can enhance recording characteristics and printing preservation. A content of the developer of 70 mass% or less can decrease background fogging.

[0067] Typically, the content of the developer is 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 even more preferably 1.2 parts by mass or more, and particularly preferably 1.4 parts by mass or more, per part by mass of the leuco dye. The content of the developer is also 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. A content of the developer of 0.5 parts by mass or more can enhance recording performance. A content of the developer of 10 parts by mass or less can effectively decrease background fogging in a high-temperature environment.

[0068] Another developer may be contained as long as the effects of the present invention are not impaired. Specific examples of other developers include phenolic compounds, such as 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenyl, 4,4'-cyclohexylidenediphenol, 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'-dihydroxydiphenylsulfide, 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'-isopropoxy diphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 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, and 4,4'-dihydroxydiphenyl ether; aromatic carboxylic acids, such as 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)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate; salts of these phenolic compounds or aromatic carboxylic acids with, for example, polyvalent metals, such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; antipyrine complex of zinc thiocyanate; organic acidic substances, such as composite zinc salts of terephthalic 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]diphenyl sulfone; thiourea compounds, such as N,N'-di-m-chlorophenylthiourea; organic compounds having a -SO 2 NH-bond in the molecule, such as p-cumylphenyl N-(p-toluenesulfonyl) carbamate, p-benzyloxyphenyl N-(p-toluenesulfonyl)carbamate, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and N-(o-toluoyl)-p-toluenesulfoamide; inorganic acidic substances, such as activated clay, attapulgite, colloidal silica, and aluminum silicate; and the like.

[0069] Furthermore, examples include urea urethane derivatives represented by the following formula (3), such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureido diphenylsulfone; diphenyl sulfone derivatives represented by the following formula (4); and the like. Usable developers are, of course, not limited to these compounds, and two or more of such compounds can be used in combination as necessary. (In the formula, n represents an integer of 1 to 6.)Binder

[0070] The heat-sensitive color-developing printing ink of the present invention contains a vinylpyrrolidone-vinyl acetate copolymer as a binder. This enhances color development ability, improves print density, and increases plasticizer resistance.

[0071] The molar ratio of vinylpyrrolidone to vinyl acetate (vinylpyrrolidone / vinyl acetate) in the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited and is preferably 50 / 50 to 30 / 70, and more preferably 40 / 60 to 30 / 70. A molar ratio of vinylpyrrolidone to vinyl acetate of 50 / 50 to 30 / 70 can improve print density.

[0072] The content of the vinylpyrrolidone-vinyl acetate copolymer is not particularly limited and is preferably about 5 to 35 mass%, more preferably about 9 to 33 mass%, and even more preferably about 12 to 28 mass% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the vinylpyrrolidone-vinyl acetate copolymer of 5 mass% or more can improve adhesion to substrates. A content of the vinylpyrrolidone-vinyl acetate copolymer of 35 mass% or less can enhance recording characteristics.

[0073] The heat-sensitive color-developing printing ink of the present invention may contain other binders as long as they do not impair the effects of the present invention. Such other binders for use may be, for example, an aqueous binder, which is either a water-soluble binder or a water-dispersible binder. Examples of water-soluble binders include polyvinyl alcohol; modified polyvinyl alcohols, such as carboxy-modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, and silicon-modified polyvinyl alcohols; starch and its derivatives; cellulose derivatives, such as methoxy cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and ethyl cellulose; sodium polyacrylate, polyvinylpyrrolidone, polyamide, diisobutylene-maleic anhydride copolymer salts, styrene-acrylic acid copolymer salts, styrene-maleic anhydride copolymer salts, ethylene-maleic anhydride copolymer salts, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid copolymers, polyacrylamide, sodium alginate, gelatin, casein, and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers etc.; and latex of water-insoluble polymers, such as styrene-butadiene copolymers or styrene-butadiene-acrylic copolymers. Furthermore, for example, an organic solvent-soluble binder can be used as a binder. Examples of organic solvent-soluble binders include vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, polyurethane, saturated polyester, polyester polyurethane, epoxy resin, phenoxy resin, nitrocellulose, melamine resin, chlorinated polyethylene, and chlorinated polypropylene. These binders can be used alone or in a combination of two or more types.Colloidal Silica

[0074] In the present invention, the heat-sensitive color-developing printing ink may further contain colloidal silica with an average particle diameter of 45 nm or less. This enables enhancement of color development ability without compromising transparency, thereby improving print density. The average particle diameter of colloidal silica is preferably 60 nm or less, and more preferably 45 nm or less. However, from the viewpoint of heat resistance, an average particle diameter of 5 nm or more is preferable. The "average particle diameter" as used here refers to the volume-based median diameter measured by the BET method, Sears method, or laser diffraction. More simply, individual particle diameters can be measured from particle images (SEM images) using an electron microscope, and the average of 10 particles may be used as the average particle diameter.

[0075] The content of the colloidal silica with an average particle diameter 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% based on the total solids content of the heat-sensitive color-developing printing ink. A content of the colloidal silica of 5 mass% or more can improve the strength of the coating film. A content of the colloidal silica of 30 mass% or less enables the maintenance of transparency.Solvent

[0076] The heat-sensitive color-developing printing ink of the present invention may contain a solvent. Examples of such solvents include water, alcohols, toluene, cyclohexane, and methylcyclohexane, with solvents containing water and an alcohol being preferred. For the alcohol, alcohols with 5 or fewer carbon atoms are desirable, and examples of such alcohols with 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. Using an alcohol in the solvent makes the ink usable for gravure printing.Stabilizer

[0077] In the present invention, the heat-sensitive color-developing printing ink may further contain a stabilizer, mainly to further enhance the preservability of colored images. The stabilizer for use may be at least one compound selected from the group consisting of phenol compounds, such as 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; epoxy compounds, such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenyl sulfone, 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. Usable stabilizers are, of course, not limited to these compounds, and two or more of such compounds can also be used in combination as necessary.

[0078] When the stabilizer is used, its amount may be an effective amount for improving image preservation. The stabilizer is typically preferably used in an amount of about 1 to 30 mass%, and more preferably about 5 to 20 mass%, based on the total solids content of the heat-sensitive color-developing printing ink.Sensitizer

[0079] The heat-sensitive color-developing printing ink in the present invention may also contain a sensitizer. Use of the sensitizer enhances the recording sensitivity. Examples of usable sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoyl stearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenylsulfone, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzylbiphenyl, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibenzyl oxlate, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl)ether, 1,2-di(3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenylbenzylether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. These sensitizers can be used in combination as long as the combined use does not impair the effects of the present invention. The sensitizer content may be an effective amount for sensitization, and is typically preferably about 2 to 40 mass%, and more preferably about 5 to 25 mass%, based on the total solids content of the heat-sensitive color-developing printing ink.

[0080] For other components constituting the heat-sensitive color-developing printing ink, for example, the following can optionally be used: crosslinking agents, wax, metal soaps, water-resistance-improving agents, pigments, dispersants, colored dyes, and fluorescent dyes.Crosslinking Agent

[0081] The heat-sensitive color-developing printing ink may contain a crosslinking agent for curing the binder in the heat-sensitive recording layer or other layers. 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 a combination of two or more types. A preferred amount of the crosslinking agent is about 1 to 10 parts by mass per 100 parts by mass of the total solids content of the heat-sensitive color-developing printing ink. This enables the improvement of water resistance of the heat-sensitive recording layer.Wax

[0082] Examples of wax include wax such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax; higher fatty acid amides, such as stearic acid amide and ethylene bisstearamide; higher fatty acid esters; and derivatives thereof.Metal Soap

[0083] Examples of metal soaps include higher fatty acid polyvalent metal salts, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Additionally, the heat-sensitive color-developing printing ink may optionally contain various aids such as oil repellents, defoaming agents, and viscosity regulators to an extent that does not impair the effects of the present invention.

[0084] The heat-sensitive color-developing printing ink of the present invention is typically prepared using water and an alcohol as solvents, by dispersing a leuco dye and a developer optionally with a binder, a sensitizer, and a stabilizer together or separately by using an agitation and wet grinding machine, such as ball mills, CoBall mills, attritors, or vertical and horizontal sand mills to form a dispersion, and then optionally mixing the thus-prepared dispersion so as to have an average particle diameter of 2 µm or less with a binder and aids.

[0085] The heat-sensitive color-developing printing ink of the present invention can be used to form a heat-sensitive recording layer of a heat-sensitive recording material on at least a portion of one surface or both surfaces of a support. The method for forming a heat-sensitive recording layer is preferably, but not particularly limited to, a printing method such as gravure printing.Protective-layer Printing Ink for Heat-sensitive Recording MaterialBinder

[0086] The protective-layer printing ink of the present invention contains a polyvinyl acetal resin as a binder. This enables improved printing preservation (in particular, plasticizer resistance) and thermal head matching (in particular, head residue suitability), while also enhancing transparency.

[0087] Polyvinyl acetal resins can be produced according to a method such as reacting a polyvinyl alcohol with an aldehyde to acetalize it. Examples of aldehydes include, but are not particularly limited to, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amyl aldehyde, hexyl aldehyde, heptyl aldehyde, 2-ethylhexyl aldehyde, cyclohexyl aldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde.

[0088] Examples of polyvinyl acetal resins include polyvinyl butyral resin, in which the acetal group is a butyral group, and polyvinyl acetoacetal resin, in which the acetal group is an acetoacetal group.

[0089] The number average molecular weight of such a 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. A polyvinyl acetal resin with a number average molecular weight of 17,000 can improve printing preservation (in particular, plasticizer resistance) and thermal head matching (in particular, head residue suitability). A polyvinyl acetal resin with a number average molecular weight of 40,000 or less can increase the concentration of the protective layer ink. The "number average molecular weight" in the present invention refers to the number-average molecular weight analyzed by gel permeation chromatography (GPC).

[0090] The content of such a polyvinyl acetal resin is not particularly limited and is preferably about 75 to 99 mass%, more preferably about 75 to 90 mass%, and even more preferably about 80 to 85 mass% based on the total solids content of the protective-layer printing ink. A content of a polyvinyl acetal resin of 75 mass% or more can improve printing preservation (in particular, plasticizer resistance). A content of a polyvinyl acetal resin of 99 mass% or less can improve thermal head matching (in particular, sticking properties).

[0091] The protective-layer printing ink of the present invention may contain other binders as long as they do not impair the effects of the present invention. Such other binders for use may be, for example, an aqueous binder, which is either a water-soluble binder or a water-dispersible binder. Examples of water-soluble binders include polyvinyl alcohol; modified polyvinyl alcohols, such as carboxy-modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, and silicon-modified polyvinyl alcohols; starch and its derivatives; cellulose derivatives, such as methoxy cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and ethyl cellulose; polyvinylpyrrolidone; polyamide; diisobutylene-maleic anhydride copolymer salts; styrene-maleic anhydride copolymer salts; sodium alginate; gelatin; casein; and gum arabic. Examples of water-dispersible binders include emulsions of polyvinyl acetate, polyurethane, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, ethylene-vinyl acetate copolymers etc.; and latex of water-insoluble polymers, such as styrene-butadiene copolymers. Furthermore, for example, an organic solvent-soluble binder can be used as an additional binder. Examples of organic solvent-soluble binders include vinyl acetate resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, vinylpyrrolidone-vinyl acetate copolymer resins, butyral resins, polyester resins, nitrocellulose resins, and styrene resins. These binders can be used alone or in a combination of two or more types.Slipperiness-imparting Agent

[0092] The protective-layer printing ink of the present invention contains an alkyl phosphate ester and / or a salt thereof as a slipperiness-imparting agent. This enables improved thermal head matching (in particular, head residue suitability) as well as enhanced transparency.

[0093] Alkyl phosphate esters are compounds in which at least one hydrogen atom of the three hydroxyl groups of phosphoric acid is replaced with an alkyl group. In particular, a mixture of the monoester (monoalkyl phosphate ester) and diester forms is preferred. The number of carbon atoms in the alkyl group of the ester portion in the alkyl phosphate ester is preferably 12 to 36, more preferably 12 to 30, and even more preferably 12 to 22. The alkyl group may be either linear or branched.

[0094] 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 salt is preferably in its Na-neutralized or Ca-neutralized form.

[0095] The first acid value of the alkyl phosphate ester is not particularly limited and is preferably 135 mg KOH / g or less, more preferably 120 mg KOH / g or less, and even more preferably 100 mg KOH / g or less. The alkyl phosphate ester with a first acid value of 135 mg KOH / g or less enables improved background fogging resistance. The first acid value is measured according to neutralization titration or potentiometry.

[0096] The content of such an alkyl phosphate ester and / or a salt thereof is not particularly limited and is preferably about 1 to 25 mass%, more preferably about 1 to 20 mass%, and even more preferably about 3 to 10 mass% based on the total solids content of the protective-layer printing ink. A content of an alkyl phosphate ester and / or a salt thereof being 1 mass% or more enables improved thermal head matching (slipperiness properties, reduction of printing noise). A content of an alkyl phosphate ester and / or a salt thereof being 25 mass% or less enables enhanced printing preservation (plasticizer resistance).

[0097] The protective-layer printing ink of the present invention may contain other slipperiness-imparting agents as long as they do not impair the effects of the present invention. Examples of other slipperiness-imparting agents include metal salts of higher fatty acids, such as zinc stearate and calcium stearate, and wax, such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, and castor wax. These slipperiness-imparting agents can be used alone or in a combination of two or more types.Calcined Kaolin

[0098] In the present invention, the protective-layer printing ink may further contain calcined kaolin with an average particle diameter of 2.0 µm or less. This can improve thermal head matching (in particular, head residue suitability). The average particle diameter of the calcined kaolin is preferably 1.5 µm or less, and more preferably 1.3 µm or less. From the viewpoint of thermal head cleaning performance, the average particle diameter of the calcined kaolin is preferably 0.1 µm or more. The "average particle diameter" as used here refers to the volume-based median diameter as measured according to the BET method, Sears method, or laser diffraction. More simply, individual particle diameters can be measured from particle images (SEM images) using an electron microscope, and the average of 10 particles may be used as the average particle diameter.

[0099] The content of the calcined kaolin with an average particle diameter 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% based on the total solids content of the protective-layer printing ink. A content of such calcined kaolin being 0.5 mass% or more enables improved thermal head matching (in particular, head residue suitability). A content of such calcined kaolin being 10 mass% or less can reduce the wear of thermal head protection films.Solvent

[0100] The protective-layer printing ink of the present invention may contain a solvent. Examples of such solvents include water, alcohols, cycloalkanes, toluene, and methylcyclohexane, with solvents containing an alcohol and a cycloalkane being preferred. The alcohol is preferably an alcohol with 5 or fewer carbon atoms. Examples of such alcohols with 5 or fewer carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol. Examples of cycloalkanes include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, methylcyclohexane, methylcyclooctane, dimethylcyclohexane, and ethylcyclohexane. Using an alcohol in the solvent makes the ink usable for gravure printing.

[0101] Other optional component materials of the protective-layer printing ink for use include crosslinking agents and pigments.Crosslinking Agent

[0102] The protective-layer printing ink may contain a crosslinking agent for curing the binder in 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 a combination of two or more types. A preferred amount of the crosslinking agent is about 1 to 10 parts by mass per 100 parts by mass of the total solids content of the protective-layer printing ink. This enables the improvement of water resistance of the protective layer.Pigment

[0103] Examples of the pigments to be contained in the protective layer include, but are not particularly limited to, 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 fillers. The content of the pigment is preferably about 1 to 20 mass%, and more preferably about 1 to 10 mass% based on the total solids content in the protective layer.

[0104] The protective-layer printing ink of the present invention is typically prepared by using an alcohol and a cycloalkane as solvents, and by mixing a binder and a slipperiness-imparting agent, optionally with aids.

[0105] The protective-layer printing ink of the present invention can be used to form a protective layer for the heat-sensitive recording material on at least a portion of one surface or both surfaces of a support. The method for forming a protective layer is preferably, but not particularly limited to, a printing method such as gravure printing.Support

[0106] The support in the present invention is not particularly limited in terms of type, shape, dimensions, etc., and can be appropriately selected and used from among, for example, fine paper (acidic paper and neutral paper), medium-grade paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, cellophane, synthetic resin films, and various other transparent supports. Of these, a translucent or transparent support made of glassine paper or laminated resin paper, or a transparent film made of cellophane or a synthetic resin film is preferable. These ensure enhanced transparency in the non-printing area of the heat-sensitive recording material. Examples of resins used in laminated resin paper or synthetic resin films include polyester resins, such as polyethylene terephthalate (PET), and polyolefin resins, such as polypropylene (PP) and polyethylene (PE). The thickness of the support is not particularly limited and is typically about 5 to 200 µm. The density of the support is also not particularly limited and is preferably about 0.60 to 2.00 g / cm 3< .Heat-sensitive Recording Layer

[0107] The heat-sensitive recording material may optionally contain a heat-sensitive recording layer on the support. The heat-sensitive recording layer is typically formed on a support by performing printing using a heat-sensitive color-developing printing ink. In the present invention, it is preferred that the heat-sensitive recording layer be provided on at least a portion of one surface or both surfaces of the support and be a layer formed by using the heat-sensitive color-developing printing ink of the present invention. When the heat-sensitive color-developing printing ink of the present invention is not used, the heat-sensitive color-developing ink described in the "Heat-sensitive Color-developing Printing Ink" section can be used without limitations on the developer and binder. The coating amount of the heat-sensitive recording layer is not particularly limited and is preferably about 1 to 12 g / m 2< , more preferably about 2 to 10 g / m 2< , even more preferably about 2.5 to 8 g / m 2< , and particularly preferably about 3 to 5.5 g / m 2< , on a dry mass basis. Moreover, the heat-sensitive recording layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.Protective Layer

[0108] The heat-sensitive recording material may optionally contain a protective layer on the support or the heat-sensitive recording layer. The protective layer is typically formed on the support or heat-sensitive recording layer by performing printing using a protective-layer printing ink for heat-sensitive recording materials. In the present invention, it is preferred that the protective layer be provided on at least a portion of one surface or both surfaces of the support and be a layer formed using the protective-layer printing ink for heat-sensitive recording materials of the present invention. When the protective-layer printing ink for heat-sensitive recording materials of the present invention is not used, the protective-layer printing ink for heat-sensitive recording materials described in the "Protective-layer Printing Ink for Heat-sensitive Recording Material" section can be used without limitations on the binder and slipperiness-imparting agent. The coating amount of the protective layer is not particularly limited and is preferably about 0.3 to 15 g / m 2< , more preferably about 0.3 to 10 g / m 2< , even more preferably about 0.3 to 8 g / m 2< , particularly preferably about 0.5 to 8 g / m 2< , and yet more preferably about 0.5 to 5 g / m 2< , on a dry mass basis. Moreover, the protective layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.Undercoat Layer

[0109] The heat-sensitive recording material of the present invention may also optionally contain an undercoat layer between the support and the heat-sensitive recording layer. The undercoat layer preferably contains a binder.Binder

[0110] The binder to be contained in the undercoat layer is not particularly limited and can be an aqueous binder, which is either a water-soluble binder or a water-dispersible binder, or solvent-based binder. Examples of binders include water-soluble polymeric materials, such as polyvinyl alcohols, derivatives thereof, starch, derivatives thereof, 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; emulsions, such as of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers; and latex of water-insoluble polymers, such as styrene-butadiene copolymers, and styrene-butadiene-acrylic copolymers. These can be suitably used on supports, such as polyester films (e.g., PET films), and polyester-based laminated resin paper. Of these, a binder containing latex is preferably used. Additionally, examples of aqueous binders or solvent-based binders include chlorinated polyolefin resins. Chlorinated polyolefin resins can be preferably used on supports, such as polyolefin-based films, such as PP films, paper, such as polyolefin-based synthetic paper, polyolefin-based resin laminated paper, and glassine paper, and cellophane. The content of the binder can be selected from a wide range; typically, the content of the binder is preferably about 10 to 100 mass%, and more preferably about 15 to 60 mass%, based on the total solids content in the undercoat layer.

[0111] It is preferred that the binder contains a binder resin with a glass transition temperature (Tg) of -10° C or lower. A binder resin with a glass transition temperature of -10° C or lower enables improved image quality even in low-energy regions. The glass transition temperature is preferably -30°C or lower because image quality can be further improved in low-energy regions. However, since undesirable stickiness occurs at temperatures -50°C or below, the glass transition temperature is preferably -40°C or higher.

[0112] The undercoat layer may contain at least one pigment selected from the group consisting of oil-absorbing pigments with an oil absorption of 70 ml / 100 g or more, and particularly about 80 to 150 ml / 100 g, organic hollow particles, and thermally expandable particles. The "oil absorption" refers to a value determined according to the method described in JIS K 5101.

[0113] The oil-absorbing pigments for use can be selected from various types. Specific examples include inorganic pigments, such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of the primary particles of the 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; typically, the amount of the oil-absorbing pigment is preferably about 20 to 80 mass%, and more preferably about 25 to 75 mass%, based on the total solids content in the undercoat layer.

[0114] The undercoat layer is formed on a support, for example, by mixing a binder, hollow particles, a pigment, and aids with water as a medium to prepare a coating liquid for undercoat layers, applying the thus-prepared coating liquid for undercoat layers to the support, and then drying the liquid. The undercoat layer can also be formed according to a printing method such as gravure printing, in the same manner for the heat-sensitive recording layer. The coating amount of the coating liquid for undercoat layers is preferably, but not particularly limited to, about 2 to 20 g / m 2< , and more preferably about 2 to 12 g / m 2< , on a dry mass basis.

[0115] Examples of aids to be contained in the coating liquid for undercoat layers include dispersants, such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and metal salts of fatty acids, wax, such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, water-resistance-improving agents, such as hydrazide compounds, boric acid, dialdehyde starch, glyoxylate salts, and epoxy compounds, defoaming agents, coloring dyes, and fluorescent dyes.Heat Seal Layer

[0116] The heat-sensitive recording material of the present invention may also optionally comprise a heat seal layer on at least a portion of one or both surfaces of the support. It is preferred that the heat seal layer be present on the surface of the support opposite to the surface on which the heat-sensitive recording layer is present.

[0117] The heat seal layer in the present invention includes a single-layer film composed of a single resin, and a single-layer or laminated film using multiple resins. Preferable examples of resins that constitute the heat seal layer include polyolefin resins (in particular, polyethylene and polypropylene), polystyrene resins, polyester resins (in particular, polyethylene terephthalate resin), polyamide resins (in particular, nylon), and biodegradable resins.

[0118] The polyethylene may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), or high-density polyethylene (HDPE).

[0119] The heat seal layer may be non-oriented, or uniaxially or biaxially oriented.

[0120] The thickness of the heat seal layer is not particularly limited; the thickness is preferably about 10 to 70 µm, more preferably about 20 to 60 µm, and even more preferably about 30 to 50 µm.

[0121] The heat seal layer may contain additives, such as fillers, anti-blocking agents, antistatic agents, plasticizers, and oxidizing agents. These additives may be used alone or in a combination of two or more.

[0122] The heat seal layer may be formed by extruding a resin onto a support to laminate it or by bonding the support and the heat seal layer using a binder.

[0123] The binder for use in bonding is not particularly limited; the binder may be any of solvent-free binder, organic solvent binder, or water-based binder.

[0124] Examples of main components that constitute the binder include (meth)acrylic acid ester copolymers, α-olefin copolymers, ethylene-vinyl acetate copolymers, polyvinyl alcohols, polyurethane, styrene-butadiene copolymers, polyvinyl chloride, epoxy resins, melamine resins, silicone resins, natural rubber, casein, and starch.

[0125] After a binder is applied onto the heat seal layer, the heat seal layer and the support may be laminated. Alternatively, after a binder is applied onto the support, the support and the heat seal layer may be laminated. Alternatively, after a binder is applied onto both the heat seal layer and the support, the heat seal layer and the support may be laminated. There is no particular limitation in this regard.

[0126] The method for applying a binder can be appropriately selected from known methods without particular limitation. Examples include roll coating, die coating, and spray coating.

[0127] The amount of binder applied is not particularly limited. The amount applied (coating amount) after drying is preferably 0.5 g / m 2< or more, more preferably 1.0 g / m 2< or more, and even more preferably 1.5 g / m 2< or more, and preferably 10.0 g / m 2< or less, more preferably 7.0 g / m 2< or less, and even more preferably 5.0 g / m 2< or less.Printing Layer

[0128] In the present invention, a printing layer can be provided on at least one of the following: on top of the protective layer, between the heat-sensitive recording layer and the protective layer, on top of the heat-sensitive recording layer, between the support and the heat seal layer, and on the surface of the support opposite to the surface on which the heat-sensitive recording layer is present. The printing ink used in forming the printing layer, based on the classification by printing plate type, includes ink for relief printing, planographic printing, intaglio printing, and stencil printing. The printing ink used in forming the printing layer, based on the classification by drying form, includes ink for penetration drying, evaporation drying, oxidative polymerization drying, and photo-polymerization drying (UV-curable). For forming the printing layer, various printing methods can be used, such as flexographic printing, offset printing, gravure printing, and screen printing. Plateless digital printing methods, such as on-demand printing and direct printing can also be used. There is no particular limitation on the color tone of the printing ink; however, especially when heat-sensitive recording is performed on the part corresponding to the printing layer, it is preferred that the optical density of the printing layer be lower than that of the recording area of the heat-sensitive recording layer. The printing pattern may be partial printing or full-surface solid printing. It is preferably a watermark-like background printing with an optical density of about 0.1 to 0.6, or fixed information that does not interfere with heat-sensitive recording. For example, when the heat-sensitive recording material is used as a top-sealing lid material on which variable information such as product names, expiration dates, and barcodes are recorded by heat-sensitive recording, it is preferable to partially make print with white ink on the area corresponding to the back of these heat-sensitive records, which is the surface of the support opposite to the surface on which the heat-sensitive recording layer is present. This leads to improved readability of barcodes and the like.Heat-sensitive Recording Material

[0129] The heat-sensitive recording material can be produced by forming individual layers on a support. The method for forming the layers on a support can be any of printing methods, such as gravure printing, and of known coating methods, such as an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, a curtain method, a slot die method, a slide die method, or an extrusion method. The method is preferably gravure printing or other printing methods, and more preferably gravure printing. Individual paint may be applied and dried to form each layer, or the same paint may be applied in two or more separate layers. Moreover, simultaneous multilayer coating, in which two or more layers are applied simultaneously, may also be performed. After each layer is formed or after all layers are formed, a smoothing process can be performed at any stage using a known method, such as supercalendering or soft calendering.

[0130] The method for recording images on the heat-sensitive recording material of the present invention is not particularly limited and can be appropriately selected according to the intended use. Examples of usable methods for recording images include thermal head printers and laser light (e.g., carbon dioxide laser, UV laser, semiconductor laser light, YAG laser light, fiber laser light, solid-state laser light, and dye laser light). The wavelength of laser light for use is not particularly limited and can be appropriately selected according to the intended use.

[0131] The heat-sensitive recording material of the present invention has high transparency and exhibits excellent background fogging resistance and plasticizer resistance, and is thus suitable for food applications such as labels and top-sealing lid materials of transparent containers for salads and prepared foods. In top-sealing lid materials, although opacity may be increased due to the heat-sensitive color-developing printing ink on the printed surface and the white ink for back printing, the heat-sensitive recording material of the present invention can provide increased transparency of the surface, thereby allowing one to confirm information such as of raw materials of the contents while observing the contents through the lid material. Furthermore, using the heat-sensitive recording material as a top-sealing lid material eliminates the need to attach thermal labels, improving packaging efficiency while reducing plastic consumption.Examples

[0132] The present invention is described in more detail below with reference to Examples. However, the present invention is not limited to these. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "mass%," respectively. Particle diameters, including average particle diameter, are values measured using an LB500 laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd.). The "average particle diameter" refers to the median diameter (D50).A. Heat-sensitive Recording Material (A)Example A 1< (1) Preparation of Dye Dispersion (Liquid A)

[0133] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (liquid A).(2) Preparation of Developer Dispersion (Liquid B)

[0134] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a developer dispersion (liquid B).(3) Preparation of Heat-sensitive Color-developing Printing Ink

[0135] 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, thereby obtaining a heat-sensitive color-developing printing ink.(4) Preparation of Heat-sensitive Recording Material

[0136] A five-color gravure printing machine was used to perform printing with a heat-sensitive color-developing printing ink on one surface of a transparent PET film with a thickness of 12 µm so that the coating amount of the heat-sensitive color-developing printing ink after drying was 3.5 g / m 2< , and the film was wound to form a heat-sensitive recording layer. Furthermore, an ester-based binder was applied in an amount of 3 g / m 2< on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink by a dry lamination method, and a 30 µm thick low-density polyethylene film was bonded to obtain a heat-sensitive recording material with a heat seal layer. The obtained heat-sensitive recording material was wound into small rolls using a slitter and further cut into a predetermined shape to prepare top-sealing lid materials, which were then subjected to a sealing process and used to seal food packaging containers.Example A2

[0137] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts in the preparation of liquid A and liquid B in Example A1.Example A3

[0138] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 25 parts in the preparation of liquid A and liquid B in Example A1, and the amount of liquid B was changed from 20 parts to 40 parts in the preparation of the heat-sensitive color-developing printing ink.Example A4

[0139] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 50 / 50 was used instead of the vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 30 / 70 in the preparation of liquid A and liquid B in Example A1.Example A5

[0140] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 70 / 30 was used instead of the vinylpyrrolidone-vinyl acetate copolymer with a molar ratio of vinylpyrrolidone to vinyl acetate of 30 / 70 in the preparation of liquid A and liquid B in Example A1.Example A6

[0141] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the following heat-sensitive color-developing printing ink (5) was used instead of the heat-sensitive color-developing printing ink (3) in the preparation of the heat-sensitive recording material in Example A1.(5) Preparation of Heat-sensitive Color-developing Printing Ink

[0142] 10 parts of liquid A, 20 parts of liquid B, 8 parts of a 20% aqueous dispersion of colloidal silica with an average particle diameter of 12 nm, 1.9 parts of water, and 1.9 parts of isopropyl alcohol were mixed and stirred, thereby obtaining a heat-sensitive color-developing printing ink.Example A7

[0143] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate were used instead of 30 parts of the N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Example A8

[0144] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 5-(N-3-methylphenyl-sulfonamide)-N',N"-bis-(3-methylphenyl)-isophthalic acid diamide were used instead of 30 parts of the N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Example A9

[0145] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that after the heat-sensitive color-developing printing ink was applied and dried, printing was further performed with the following protective layer ink (6) on the heat-sensitive recording layer to form a protective layer so that the coating amount after drying was 1.0 g / m 2< in the preparation of the heat-sensitive recording material in Example A1.(6) Preparation of Protective Layer Ink

[0146] 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, thereby obtaining a protective layer ink.Example A10

[0147] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that cellophane with a thickness of 23 µm was used instead of the transparent PET with a thickness of 12 µm, and a polyethylene film with a thickness of 20 µm was laminated according to an extrusion lamination method on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink in the preparation of the heat-sensitive recording material in Example A1.Example A11

[0148] A heat-sensitive recording material was obtained in the same manner as in Example A10, except that printing was performed with a 25% toluene solution of chlorinated polypropylene resin (product name: S1306 PPHP adhesive varnish, manufactured by Toyo Ink Co., Ltd.) to achieve a coating amount of 0.5 g / m 2< after drying, and the solution was dried to form an undercoat layer, followed by performing printing with a heat-sensitive color-developing printing ink on the undercoat layer to form a heat-sensitive recording layer in the preparation of the heat-sensitive recording material in Example A10.Comparative Example A1

[0149] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone were used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Comparative Example A2

[0150] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that 30 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide were used instead of 30 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea in the preparation of liquid B in Example A1.Comparative Example A3

[0151] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that polyvinylpyrrolidone resin was used instead of the vinylpyrrolidone-vinyl acetate copolymer in the preparation of liquid A and liquid B in Example A1.Comparative Example A4

[0152] A heat-sensitive recording material was obtained in the same manner as in Example A1, except that a polyvinyl alcohol with a degree of saponification of 80 mol% and a degree of polymerization of 250 was used instead of the vinylpyrrolidone-vinyl acetate copolymer in the preparation of liquid A and liquid B in Example A1.

[0153] The Examples and Comparative Examples above were evaluated according to the following methods. Table 1 shows the results.Recording DensityThermal Printer Printing

[0154] A thermal recording tester (product name: TH-PMD, manufactured by Ohkura Electric Co., Ltd.) was used to make recording on each heat-sensitive recording material at an applied energy of 0.24 mJ / dot. The printed area 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).Evaluation

[0155] 1.40 or higher: Excellent 1.25 or higher and less than 1.40: Good 1.10 or higher and less than 1.25: Acceptable for practical use Less than 1.10: Not usable Laser Light Printing

[0156] A UV laser marker (product name: UV Laser Marker, MD-U1000C, manufactured by Keyence Corporation) was used to irradiate each heat-sensitive recording material with laser at a wavelength of 355 nm, output of 1.2 W, scan speed of 3,000 mm / sec, and laser spot diameter of 14 µm to make a solid print of 10 mm square. The obtained printed area 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).Evaluation

[0157] 1.40 or higher: Excellent 1.25 or higher and less than 1.40: Good 1.10 or higher and less than 1.25: Acceptable for practical use Less than 1.10: Not usable Background Fogging

[0158] Each heat-sensitive recording material was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for background fogging in the non-printed area with a spectrodensitometer (X-Rite 504, manufactured by X-Rite)Evaluation

[0159] Less than 0.10: Good 0.10 or higher and less than 0.20: Acceptable for practical use 0.20 or higher: Not usable

[0160] Transparency Evaluation

[0161] The transparency of the non-printed area of each heat-sensitive recording material was measured with a HAZE meter (NDH-7000, manufactured by Nippon Denshoku Industries Co., Ltd.).Evaluation

[0162] A: Less than 20% B: 20% or higher and less than 30% C: 30% or higher and less than 40% D: 40% or higher Plasticizer Resistance

[0163] A polycarbonate pipe (diameter: 40 mm) was wrapped with three layers of plastic wrap (product name: Hi-S Soft, manufactured by Nippon Carbide Industries Co., Inc.). A sample of each heat-sensitive recording material that developed color with a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) was placed on top of the wrapped polycarbonate pipe and further wrapped over with three layers of plastic wrap. The sample was then left to stand at 40°C for 24 hours. Before and after this treatment, the recording area was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for reflective density with a spectrodensitometer (X-Rite 504, manufactured by X-Rite). Additionally, the retention rate of the recording area was calculated using the following formula. Evaluation

[0164] 90% or higher: Excellent 70% or higher and less than 90%: Good 50% or higher and less than 70%: Acceptable for practical use Less than 50%: Not usable Table 1 Recording DensityBackground FoggingTransparencyPlasticizer Resistance %Thermal PrinterLaser LightExample A11.451.580.08A80Example A21.561.650.09B76Example A31.401.520.08A84Example A41.351.380.08A83Example A51.211.240.08A81Example A61.521.590.08A79Example A71.551.640.08A71Example A81.311.550.08A92Example A91.351.600.08A99Example A101.361.420.09B81Example A111.381.420.08B80Comparative Example A11.411.520.54C25Comparative Example A21.371.490.10C31Comparative Example A31.021.080.08A76Comparative Example A41.481.590.08B35 B. Heat-sensitive Recording Material (B)Example B1(1) Preparation of Dye Dispersion (Liquid A)

[0165] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (Liquid A).(2) Preparation of Developer Dispersion (Liquid B)

[0166] 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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a developer dispersion (Liquid B).(3) Preparation of Heat-sensitive Color-developing Printing Ink

[0167] 10 parts of liquid A, 20 parts of liquid B, 8 parts of a 20% aqueous dispersion of colloidal silica with a particle diameter of 12 nm, 1.9 parts of water, and 1.9 parts of isopropyl alcohol were mixed and stirred, thereby obtaining a heat-sensitive color-developing printing ink.(4) Preparation of Protective-layer Printing Ink

[0168] 90 parts of polyvinyl acetal resin (product 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 (product 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, thereby obtaining a protective-layer printing ink.(5) Preparation of Heat-sensitive Recording Material

[0169] A five-color gravure printing machine was used to perform printing with a heat-sensitive color-developing printing ink on one surface of a transparent PET film with a thickness of 12 µm so that the coating amount after drying was 3.5 g / m 2< , thereby forming a heat-sensitive recording layer. Furthermore, printing was performed with a protective-layer printing ink on the heat-sensitive recording layer so that the coating amount after drying was 1.0 g / m 2< , followed by winding the film, thereby forming a protective layer. Furthermore, an ester-based binder was applied in an amount of 3 g / m 2< on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink by a dry lamination method, and a 30 µm thick low-density polyethylene film was bonded to obtain a heat-sensitive recording material with a heat seal layer. The obtained heat-sensitive recording material was wound into small rolls using a slitter and further cut into a predetermined shape to prepare top-sealing lid materials, which were then subjected to a sealing process and used to seal food packaging containers.Example B2

[0170] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that polyvinyl acetal resin (trade name: S-LEC BM-1, number average molecular weight: 40,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective layer ink in Example B1.Example B3

[0171] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that polyvinyl acetal resin (trade name: S-LEC KS-10, number average molecular weight: 17,000, manufactured by Sekisui Chemical Co., Ltd.) was used instead of polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Industries Co., Ltd.) in the preparation of the protective layer ink in Example B1.Example B4

[0172] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that an alkyl phosphate ester compound (trade name: Phosphanol SC6103L, Ca-neutralized salt type, 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.) in the preparation of the protective layer ink in Example B1.Example B5

[0173] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 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.) in the preparation of the protective layer ink in Example B1.Example B6

[0174] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that the following protective-layer printing ink (6) was used instead of the protective-layer printing ink (4) of Example B1.(6) Preparation of Protective-layer Printing Ink

[0175] 90 parts of polyvinyl acetal resin (product 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 (product name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.), 5 parts of a 20% isopropyl alcohol dispersion of calcined kaolin with an average particle diameter of 1.2 µm, 450 parts of isopropyl alcohol, and 450 parts of methylcyclohexane were mixed and stirred, thereby obtaining a protective-layer printing ink.Example B7

[0176] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 23 µm thick cellophane was used instead of the 12 µm thick transparent PET, and a 20 µm thick polyethylene film was bonded by an extrusion lamination method on the surface opposite to the surface on which printing was performed with the heat-sensitive color-developing printing ink in the preparation of the heat-sensitive recording material in Example B1.Reference Example B1

[0177] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of acrylic resin (trade name: BR101, number average molecular weight: 160,000, manufactured by Mitsubishi Chemical Corporation) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B2

[0178] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of acrylic resin (trade name: BR115, number average molecular weight: 50,000, manufactured by Mitsubishi Chemical Corporation) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B3

[0179] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 100 parts of styrene-acrylic resin (trade name: UC-3080, number average molecular weight: 14,000, manufactured by Toagosei Co., Ltd.) were used instead of 90 parts of the polyvinyl acetal resin (trade name: S-LEC KS-1, number average molecular weight: 27,000, manufactured by Sekisui Chemical Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.Reference Example B4

[0180] A heat-sensitive recording material was obtained in the same manner as in Example B1, except that 10 parts of zinc stearate (average particle diameter: 1.2 µm) were used instead of 10 parts of the alkyl phosphate ester compound (trade name: Phosphanol RD720, Na-neutralized salt type, manufactured by Toho Chemical Industry Co., Ltd.) in the preparation of the protective-layer printing ink in Example B1.

[0181] The Examples and Reference Examples above were evaluated according to the following methods. Table 2 shows the results.Transparency Evaluation

[0182] The transparency of the non-printed area of each heat-sensitive recording material was measured using a HAZE meter (NDH-7000 manufactured by Nippon Denshoku Industries Co., Ltd.).Evaluation

[0183] A: Less than 20%: Good B: 20% or higher and less than 30%: Acceptable for practical use C: 30% or higher: Not usable Heat Resistance of Background

[0184] Each heat-sensitive recording material was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for background fogging of the non-printed area with a spectrodensitometer (X-Rite 504, manufactured by X-Rite).Evaluation

[0185] Less than 0.15: Good 0.15 or more and less than 0.25: Acceptable for practical use 0.25 or more: Not usable Plasticizer Resistance

[0186] A polycarbonate pipe (diameter: 40 mm) was wrapped with three layers of plastic wrap (product name: Hi-S Soft, manufactured by Nippon Carbide Industries Co., Inc.). A sample of each heat-sensitive recording material that developed color with a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) was placed on top of the wrapped polycarbonate pipe and further wrapped over with three layers of plastic wrap. The sample was then left to stand at 40°C for 24 hours. Before and after this treatment, the recording area was placed on PPC paper with a whiteness of 85% (JIS P 8148) and measured for reflective density with a spectrodensitometer (X-Rite 504, manufactured by X-Rite). Additionally, the retention rate of the recording area was calculated using the following formula. Printing Sound

[0187] A thermal recording tester (product name: TH-PMD, manufactured by Ohkura Electric Co., Ltd.) was used to make recording on each heat-sensitive recording material at an applied energy of 0.243 mJ / dot, during which the printing sound was measured by sensory assessment.Evaluation

[0188] A: Quiet printing sound B: Faint printing noise (acceptable for practical use) C: Loud printing sound Head Residue Suitability

[0189] A label printer (L'esprit V-ex, manufactured by Sato Corporation) was used to perform printing at 100% black solid coverage of 50 cm, and the heating elements of the thermal head were observed using a stereomicroscope (VH-Z100UR, manufactured by Keyence Corporation) and subjected to sensory assessment.Evaluation

[0190] A: No adherence of head residue B: Slight presence of head residue C: Small amount of head residue adhered (acceptable for practical use) D: Significant amount of head residue Table 2 TransparencyBackground FoggingPlasticizer Resistance %Printing SoundHead Residue SuitabilityExample B1A0.0991ABExample B2A0.0990ABExample B3A0.0973ABExample B4A0.1391ABExample B5A0.1892ABExample B6B0.0991AAExample B7A0.0991ABReference Example B1C0.0935ADReference Example B2C0.0940ADReference Example B3A0.0994ADReference Example B4C0.0991CD

Examples

examples

[0132]The present invention is described in more detail below with reference to Examples. However, the present invention is not limited to these. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "mass%," respectively. Particle diameters, including average particle diameter, are values measured using an LB500 laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd.). The "average particle diameter" refers to the median diameter (D50).

A. Heat-sensitive Recording Material (A)

example a 1 <

Example A 1<

(1) Preparation of Dye Dispersion (Liquid A)

[0133]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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achieved, thereby obtaining a dye dispersion (liquid A).

(2) Preparation of Developer Dispersion (Liquid B)

[0134]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 molar ratio of vinylpyrrolidone to 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 Aimex Co., Ltd.) until an average particle diameter of 0.15 µm was achi...

example a2

[0137]A heat-sensitive recording material was obtained in the same manner as in Example A1, except that the amount of the 50% isopropyl alcohol solution of a vinylpyrrolidone-vinyl acetate copolymer was changed from 13 parts to 6 parts in the preparation of liquid A and liquid B in Example A1.

Claims

1. A printing ink for a heat-sensitive recording material, which is either the following (A) or (B): (A) a heat-sensitive color-developing printing ink comprising a leuco dye, a developer, a vinylpyrrolidone-vinyl acetate copolymer, and a solvent, wherein the heat-sensitive color-developing printing ink contains, as the developer, at least one member selected from the group consisting of a N,N'-diaryl urea compound represented by the following formula (1): wherein R0 represents a C1-12 alkyl group, a C7-12 aralkyl group, or a C6-12 aryl group, wherein 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, and multiple R0s may be the same or different, and A1 represents a hydrogen atom or a C1-4 alkyl group, and multiple A1s may be the same or different; a compound represented by the following formula (2): wherein 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 a heat-sensitive recording material, containing a binder, a slipperiness-imparting agent, and a solvent, wherein the protective-layer printing ink contains a polyvinyl acetal resin as the binder, and an alkyl phosphate ester and / or a salt thereof as the slipperiness-imparting agent.

2. The printing ink according to claim 1, wherein the printing ink is the heat-sensitive color-developing printing ink (A) .

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

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

5. The printing ink according to claim 2 or 3, further comprising colloidal silica with an average particle diameter of 45 nm or less, wherein the content of the colloidal silica is 5 to 30 mass% based on the total solids content of the heat-sensitive color-developing printing ink.

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

7. The printing ink according to claim 1, wherein the printing ink is the protective-layer printing ink for a heat-sensitive recording material (B).

8. The printing ink according to claim 7, wherein the content of the polyvinyl acetal resin is 75 to 99 mass% and the content of the alkyl phosphate ester and / or a salt thereof is 1 to 25 mass% based on the total solids content of the protective-layer printing 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. The printing ink according to claim 7 or 8, wherein the alkyl phosphate ester salt is in its Na-neutralized or Ca-neutralized form, 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 diameter of 2.0 µm or less, wherein the content of the calcined kaolin is 0.5 to 10 mass% based on the total solids content of the protective-layer printing ink.

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

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

14. A heat-sensitive recording material comprising a support, and a heat-sensitive recording layer formed of the printing ink of claim 2 or 3 and / or a protective layer formed of the printing ink of claim 7 or 8 on at least a portion of one surface or both surfaces of the support.

15. The heat-sensitive recording material according to claim 14, wherein the support is a translucent or transparent support made of glassine paper or laminated resin paper, or a transparent film made of cellophane or a synthetic resin film.

16. The heat-sensitive recording material according to claim 14, comprising a printing layer on at least a portion of the surface of the support opposite to the surface on which the heat-sensitive recording layer is present.

17. The heat-sensitive recording material according to claim 14, comprising a heat seal layer on at least a portion of one surface or both surfaces of the support.

18. The heat-sensitive recording material according to claim 14, comprising an undercoat layer between the support and the heat-sensitive recording layer.

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

20. The heat-sensitive recording material according to claim 17, which is for use in a top-sealing lid material.

21. An image recording method, comprising recording an image on the heat-sensitive recording material of claim 14 by using laser light or a thermal head.

Images