Heat-sensitive recording material

Abstract

To provide a heat-sensitive recording material which is excellent in terms of high-speed printing performance among various performances required for heat-sensitive recording materials, and which is also excellent in terms of printing runnability, oil resistance, solvent barrier properties and the like.SOLUTION: A heat-sensitive recording material has a heat-sensitive recording layer on a supporting body, the heat-sensitive recording layer containing a colorless or pale electron-donating leuco dye and an electron-accepting color developer, while having a protective layer on the heat-sensitive recording layer. The heat-sensitive recording layer contains, as the electron-accepting color developer, at least one urea compound, and the protective layer contains an acrylic resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermal recording medium that utilizes a color-developing reaction between a colorless or pale-colored electron-donating leuco dye (hereinafter also referred to as "leuco dye") and an electron-accepting developer (hereinafter also referred to as "developer"), and that has excellent high-speed printability, as well as excellent print running properties, oil resistance, solvent barrier properties, etc. [Background technology]

[0002] Generally, a thermal recording medium is prepared by coating a coating liquid containing a colorless or light-colored leuco dye and a color developer on a support such as paper, synthetic paper, film, plastic, etc., and a recorded image is obtained by instantaneous chemical reaction caused by heating with a thermal head, hot stamp, heat pen, laser light, etc. Thermal recording media are widely used as recording media for facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, receipts at supermarkets and convenience stores, etc. In recent years, the use of thermal recording media has expanded to include a wide variety of applications, such as for various tickets, receipts, labels, bank ATMs, gas and electricity meter reading, and vouchers for car and horse racing betting. As a result, a variety of performance characteristics are required, such as water resistance, resistance to plasticizers in the image areas, heat resistance and oil resistance in the blank areas, and storage stability of the image areas and blank areas under harsh conditions. In response to such demands, a thermal recording medium has been disclosed that uses a combination of two specific types of color developers to improve water resistance, plasticizer resistance in image areas, and heat resistance in blank areas (Patent Document 1), as well as urea compounds used as color developers to improve required performance such as color density, whiteness, and storage stability of printed areas of thermal recording mediums (Patent Documents 2 and 3). Further, as a method for improving the storage stability of a thermal recording medium, a method of providing a protective layer on the thermal recording layer is known. It is known that by incorporating a silane-modified acrylic resin into the thermosensitive recording layer or protective layer, it is possible to reduce head wear during printing and improve the image storage stability and water resistance of the thermosensitive recording medium (Patent Documents 4 and 5, etc.). Furthermore, it is known that by incorporating an acrylic resin having a glass transition point (Tg) of more than 50° C. and not more than 95° C. in the protective layer, the thermal recording medium has sufficient water resistance, etc. (Patent Document 6, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication 2015-80852 [Patent Document 2] International Publication WO2019 / 044462 [Patent Document 3] Patent Publication No. 2020-066148 [Patent Document 4] JP 5-574 [Patent Document 5] Patent Publication No. 2000-238432 [Patent Document 6] International Publication WO2010 / 110209 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a thermal recording medium which, among various properties required of a thermal recording medium, is excellent in high-speed printing, and further has excellent print running properties, oil resistance, solvent barrier properties, and the like. [Means for solving the problem]

[0005] As a result of extensive research, the inventors have found that the above problems can be solved by incorporating a specific urea compound as a developer in the thermal recording layer and incorporating an acrylic resin in the protective layer provided on the thermal recording layer, thereby completing the present invention. That is, the present invention relates to a thermosensitive recording medium having a support, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains a urea compound represented by the following (3) as the electron-accepting developer, the protective layer contains an acrylic resin represented by the following (4) or (5), the content of the acrylic resin in the protective layer is 15.0 to 50.0% by weight, and the minimum film-forming temperature (MFT) of the acrylic resin is 0°C to 25°C. (3) A third urea compound represented by the following general formula (Chemical Formula 4): [ka] (In the formula, R 2 represents a hydrogen atom or an alkyl group, R 4 ~R 8 may be the same or different, and each represents 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. (4) A non-core-shell acrylic resin having a glass transition point (Tg) of more than 50°C and not more than 95°C. (5) A silane-modified acrylic resin, which is an aqueous emulsion of core-shell type particles comprising a core made of copolymer A obtained by polymerizing the following (a1), (a2) and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b): (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactants containing sulfates having allyl groups and polyoxyethylene chains Effect of the Invention

[0006] According to the present invention, it is possible to provide a thermal recording medium that has good color development performance and good high-speed printability, and further, it is possible to provide a thermal recording medium that has good print running properties, oil resistance, solvent barrier properties, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The thermosensitive recording medium of the present invention has a thermosensitive recording layer on a support and a protective layer on the thermosensitive recording layer, the thermosensitive recording layer containing a specific urea compound as an electron-accepting developer, and the protective layer containing an acrylic resin. Examples of various materials that can be used in the thermal recording layer of the thermal recording material of the present invention are given below, but binders, crosslinking agents, pigments, etc. can also be used in each coating layer that is provided as needed, as long as they do not impede the desired effects for the above-mentioned problems.

[0008] The urea compound of the present invention is selected from the following (1) and (2). (1) A first urea compound represented by the following general formula (Chemical Formula 5): [ka] (In the formula, R 2 and R 3 is defined as above.) (2) A second urea compound represented by the following general formula (Chemical Formula 3): [ka] (In the formula, R 2 and m are defined as above, and R 4 ~R 8 will be discussed later.) (3) A third urea compound represented by the following formula (Chemical Formula 4): [ka] (In the formula, R 2 is defined as above, and R 4 ~R 8 will be discussed later.)

[0009] Furthermore, the urea compound used in the present invention is selected from the urea compounds represented by the above (1) and (2).

[0010] The first urea compound used in the present invention is represented by the following formula (Formula 5). [ka]

[0011] In the general formula (5), n represents 0 or 1, and preferably 1. In the general formula (Chemical formula 5), ​​R 3 represents an alkyl group, an aralkyl group, or an aryl group, which may be substituted or unsubstituted. The alkyl group is, for example, a linear, branched, or alicyclic alkyl group, and preferably has 1 to 12 carbon atoms. The aralkyl group preferably has 7 to 12 carbon atoms, and the aryl group preferably has 6 to 12 carbon atoms. When these are substituted, the substituent is preferably an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom. In addition, when a plurality of R 3 may be the same or different. R in the benzene ring of the general formula (5) 3 -SO 2 The positions of -O- may be the same or different, and are preferably the 3-, 4- or 5-positions.

[0012] Examples of the alkyl group 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.

[0013] Examples of the aralkyl group include unsubstituted aralkyl groups or aralkyl groups substituted with an alkyl group, an alkoxy group, an aralkyl group, an aryl group or a halogen atom, such as a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, a 3-phenylpropyl group, a p-methylbenzyl group, a m-methylbenzyl group, a m-ethylbenzyl group, a p-ethylbenzyl group, a pi-propylbenzyl group, a pt-butylbenzyl group, a p-methoxybenzyl group, a m-methoxybenzyl group, a o-methoxybenzyl group, a m,p-di-methoxybenzyl group, a p-ethoxy-m-methoxybenzyl group, a p-phenylmethylbenzyl group, a p-cumylbenzyl group, a p-phenylbenzyl group, a o-phenylbenzyl group, a m-phenylbenzyl group, a p-tolylbenzyl group, a m-tolylbenzyl group, a o-tolylbenzyl group and a p-chlorobenzyl group.

[0014] Examples of the aryl group include unsubstituted aryl groups or aryl groups substituted with an alkyl group, an alkoxy group, an aralkyl group, an aryl group, or a halogen atom, such as a phenyl group, a p-tolyl group, a m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, a 3,4-dimethylphenyl group, a mesitylene group, a p-ethylphenyl group, a p-propylphenyl group, a p-butylphenyl group, a p-methoxyphenyl group, a 3,4-dimethoxyphenyl group, a p-ethoxyphenyl group, a p-chlorophenyl group, a 1-naphthyl group, a 2-naphthyl group, or a t-butylated naphthyl group.

[0015] R 2 represents a hydrogen atom or an alkyl group, preferably a hydrogen atom, and the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, or a t-butyl group. R in the benzene ring of general formula (chemical formula 2) 2 may be the same or different, and is preferably the 3rd, 4th or 5th position.

[0016] As the first urea compound of the present invention, a urea compound represented by the following general formula (Formula 6) is more preferable. [ka] In the general formula (chemical formula 6), R 9 represents an alkyl group or an alkoxy group, preferably an alkyl group, and o represents an integer of 0 to 3, preferably 0 to 2, more preferably 0 to 1. The number of carbon atoms in this alkyl group is, for example, 1 to 12, preferably 1 to 8, more preferably 1 to 4. R in the benzene ring of general formula (6) 9 may be the same or different and is preferably the 3rd, 4th or 5th position, preferably the 4th position.

[0017] In addition, examples of the first urea compound of the present invention include N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-ethyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-5-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-propyl-phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(1-naphthalenesulfonyloxy)phenyl]urea, N, N'-di-[3-(2-naphthalenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-ethylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-propylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-isopropylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(pt-butylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m,p-dimethoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-ethoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-propoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-butoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-cumylbenzylsulfonyloxy)phenyl]urea, N,Examples of the urea include, but are not limited to, N'-di-[3-(p-cumylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-phenylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-phenylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-chlorobenzenesulfonyloxy)phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[4-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(ethanesulfonyloxy)phenyl]urea, and N,N'-di-[3-(benzylsulfonyloxy)phenyl]urea.

[0018] The second urea compound used in the present invention is represented by the following formula (Chemical Formula 3). [ka]

[0019] In the general formula (Chemical formula 3), R 2 , R 4 ~R 8 is defined as above. In the general formula (Chemical formula 3), R 4 ~R 8 is preferably a hydrogen atom, an alkyl group, or an alkoxy group. 4 , R 5 , R 7 , R 8 is preferably a hydrogen atom, and R 6 is preferably a hydrogen atom or an alkyl group. 6 As the alkyl group, an alkyl group is particularly preferable. The alkyl group (including those included in the alkylcarbonyloxy group, the alkylcarbonylamino group, the alkylsulfonylamino group, the monoalkylamino group, and the dialkylamino group) and the aryl group (including those included in the aryloxy group, the arylcarbonyloxy group, the arylcarbonylamino group, the arylsulfonylamino group, and the arylamino group) are defined in the same manner as the alkyl group and the aryl group in the above general formula (Chemical Formula 2). The alkoxy group is, for example, a linear, branched or alicyclic alkoxy group, and preferably has 1 to 12 carbon atoms. -O-(CONH) in the benzene ring of the general formula (Chemical formula 3) m -SO 2 The position of the -substituted phenyl group is preferably the 3-position, the 4-position or the 5-position (the same applies to the following general formulae (Chemical Formula 7) and (Chemical Formula 8)). In the general formula (Chemical Formula 3), m represents an integer of 0 to 2, preferably 0 to 1.

[0020] As the second urea compound of the present invention, a urea compound represented by the following general formula (Chemical Formula 7) or the following general formula (Chemical Formula 8) is preferable. [ka] [ka]

[0021] The third urea compound used in the present invention is represented by the following formula (Chemical Formula 4). [ka] In the general formula (Chemical formula 4), R 2 , R 4 ~R 8 is defined as above.

[0022] The third urea compound is preferably N-[2-(3-phenylureido)phenyl]benzenesulfonamide, which is represented by the following formula and is available, for example, from Nippon Soda Co., Ltd. under the trade name NKK1304. [ka]

[0023] The content of the urea compound in the thermosensitive recording layer of the present invention (solid content, total amount when a plurality of urea compounds are contained) is 1.0 to 70.0% by weight, preferably 5.0 to 65.0% by weight, more preferably 10.0 to 60.0 parts by weight. The content of the first urea compound in the thermosensitive recording layer of the present invention is 1.0 to 50.0% by weight, preferably 5.0 to 40.0% by weight, and the content of the second urea compound is 5.0 to 50.0% by weight, preferably 5.0 to 40.0% by weight.

[0024] The heat-sensitive recording layer of the present invention may use a color developer other than the first and second urea compounds. Examples of such color developers include inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate, 4,4'-isopropylidenediphenol, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, and 4-hydroxybenzoic acid. Benzyl, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 1-[4-(4-hydroxyphenyl) phenol condensation compositions described in JP-A-2003-154760, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, bis(p-hydroxyphenyl)butyl acetate, bis(p-hydroxyphenyl)methyl acetate, 1,1-bis( 4-hydroxyphenyl)-1-phenylethane, 1,4-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, 1,3-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, di(4-hydroxy-3-methylphenyl)sulfide, 2,2'-thiobis(3-tert-octylphenol), 2,2'-thiobis(4-tert-octylphenol), compounds described in WO02 / 081229 or JP2002-301873A, and N,Examples of the color developers include thiourea compounds such as N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis[zinc 4-(n-octyloxycarbonylamino)salicylate] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. These color developers can be used alone or in combination of two or more. 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane is available, for example, under the trade name JKY-214 manufactured by API Corporation, and the phenol condensation composition described in JP 2003-154760 A is available, for example, under the trade name JKY-224 manufactured by API Corporation. Compounds described in WO02 / 081229 and the like are available under the trade names NKK-395 and D-100 manufactured by Nippon Soda Co., Ltd. In addition, metal chelate-type color-developing components such as higher fatty acid metal double salts and polyvalent hydroxy aromatic compounds described in JP 10-258577 A can also be contained.

[0025] When the thermosensitive recording layer of the present invention contains a color developer other than the first and second urea compounds, the total content (solid content) of the first and second urea compounds used relative to the total color developers contained in the thermosensitive recording layer (including the first and second urea compounds) is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0026] The leuco dye used in the present invention can be any of those known in the field of conventional pressure-sensitive or heat-sensitive recording paper, and is not particularly limited, but triphenylmethane compounds, fluoran compounds, fluorene compounds, divinyl compounds, etc. are preferred. Specific examples of representative colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

[0027] <Triphenylmethane leuco dye> 3,3-Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)phthalide (also known as malachite green lactone)

[0028] <Fluoran-based leuco dye> 3-Diethylamino-6-methylfluoran, 3-Diethylamino-6-methyl-7-anilinofluoran, 3-Diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran, 3-Diethylamino-6-methyl-7-chlorofluoran, 3-Diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran, 3-Diethylamino-6-methyl-7-(o-chloroanilino)fluoran, 3-Diethylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-Diethylamino-6-methyl-7-(o-fu Fluoroanilino)fluoran, 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran, 3-diethylamino-6-methyl-7-n-octylanilinofluoran, 3-diethylamino-6-methyl-7-n-octylaminofluoran, 3-diethylamino-6-methyl-7-benzylaminofluoran, 3-diethylamino-6-methyl-7-dibenzylaminofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-Diethylamino-7-p-methylanilinofluoran, 3-Diethylamino-6-ethoxyethyl-7-anilinofluoran, 3-Diethylamino-7-methylfluoran, 3-Diethylamino-7-chlorofluoran, 3-Diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-Diethylamino-7-(o-chloroanilino)fluoran, 3-Diethylamino-7-(p-chloroanilino)fluoran, 3-Diethylamino-7-(o-fluoroanilino)fluoran, 3-Diethylamino-benzo[a]fluoran, 3-Diethylamino -benzo[c]fluoran, 3-dibutylamino-6-methyl-fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran, 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran, 3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran,3-dibutylamino-6-methyl-7-chlorofluoran, 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran, 3-dibutylamino-6-chloro-7-anilinofluoran, 3-dibutylamino-6-methyl-7-p-methylanilinofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dibutylamino-7-(o-fluoroanilino)fluoran, 3-di-n-pentylamino-6-methyl-7-anilinofluoran, 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran, 3-Di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran, 3-Di-n-pentylamino-6-chloro-7-anilinofluoran, 3-Di-n-pentylamino-7-(p-chloroanilino)fluoran, 3-Pyrrolidino-6-methyl-7-anilinofluoran, 3-Piperidino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, xylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino) -6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran, 2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran, 2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran, 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran,2-Methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-Chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-Chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-Nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-Amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 2-Phenyl-6-methyl-6-p-(p-fu 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluoran,

[0029] <Fluorene-based leuco dye> 3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-Tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0030] <Divinyl leuco dye> 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide, 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide, 3,3-bis-[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide

[0031] <Other> 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam Fluoran-γ-(4'-nitro)anilinolactam, 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane, 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane, 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane, bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester

[0032] The sensitizer used in the present invention may be a conventionally known sensitizer. Examples of such sensitizers include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-bis-(3-methylphenoxy)ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α- Examples of the sensitizer include naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methylphenoxymethyl)biphenyl, 4,4'-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di(3-methylphenoxy)ethylene, bis[2-(4-methoxy-phenoxy)ethyl]ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, o-toluenesulfonamide, p-toluenesulfonamide, etc. These sensitizers may be used alone or in combination of two or more kinds.

[0033] Pigments usable in the present invention include kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, silica, and the like, and these can also be used in combination depending on the required quality.

[0034] Examples of the binder used in the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, and cellulose derivatives such as ethyl cellulose and acetyl cellulose, casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrene and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin, and the like. These polymeric substances can be used by dissolving them in a solvent such as water, alcohol, ketones, esters, or hydrocarbons, or by dispersing them in water or other media in an emulsified or paste-like form, and these substances can also be used in combination depending on the required quality.

[0035] The lubricant used in the present invention is a fatty acid lubricant such as zinc stearate or calcium stearate. Examples of the suitable binder include acid metal salts, waxes, and silicone resins.

[0036] In the present invention, 4,4'-butylidene (6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, etc. can be added as stabilizers for improving the oil resistance of image areas within a range that does not impair the desired effects for the above-mentioned problems. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, defoamers, antioxidants, fluorescent dyes, etc. can be used.

[0037] The types and amounts of leuco dye, developer, sensitizer, and other various components used in the thermosensitive recording layer of the present invention are determined according to the required performance and recording suitability and are not particularly limited, but usually, 0.5 to 10 parts by weight of developer, 0.1 to 10 parts by weight of sensitizer, 0.5 to 20 parts by weight of pigment, 0.01 to 10 parts by weight of stabilizer, and 0.01 to 10 parts by weight of other components are used per 1 part by weight of leuco dye. The binder is suitably about 5 to 25% by weight of the solid content of the thermosensitive recording layer.

[0038] In the present invention, the leuco dye, developer and materials added as necessary are pulverized to a particle size of several microns or less using a grinding machine such as a ball mill, attritor or sand grinder or an appropriate emulsifying device, and a binder and various additives depending on the purpose are added to prepare a coating liquid. The solvent used for this coating liquid can be water or alcohol, and the solid content is about 20 to 40% by weight.

[0039] In the thermosensitive recording medium of the present invention, a protective layer is further provided on the thermosensitive recording layer, and this protective layer contains an acrylic resin. In the present invention, the acrylic resin is preferably a silane-modified acrylic resin or a high Tg acrylic resin.

[0040] The silane-modified acrylic resin used in the present invention is an aqueous resin emulsion obtained by multistage emulsion polymerization of a plurality of types of polymerizable unsaturated monomers in the presence of a surfactant. This silane-modified acrylic resin is an aqueous emulsion of core-shell type particles comprising a core made of copolymer A obtained by polymerizing the following (a1), (a2), and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b). (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactants containing an allyl group and a sulfate having a polyoxyethylene chain The copolymer A may be obtained by adding a styrene monomer to the above-mentioned (a1), (a2) and (a3) ​​and polymerizing them in the presence of (b), and / or the copolymer B may be obtained by adding a styrene monomer to the above-mentioned (a1) and (a2) and polymerizing them in the presence of (b).

[0041] Regarding <(a1) At least one (meth)acrylic acid ester> In this specification, the term "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid, and is meant to include at least one of acrylic acid and methacrylic acid. The term "(meth)acrylic acid ester" refers to an ester of (meth)acrylic acid, that is, a (meth)acrylate. The term "(meth)acrylate" refers to both an acrylate and a methacrylate, and is meant to include at least one of an acrylate and a methacrylate. In addition, vinyl esters having a structure in which a vinyl group is bonded to oxygen, such as vinyl acetate, are not included in the (meth)acrylates in this specification.

[0042] Specific examples of (meth)acrylates include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, octadecyl (meth)acrylate, behenyl (meth)acrylate, and docosyl (meth)acrylate; and (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. These can be used alone or in combination of two or more.

[0043] In an embodiment of the present invention, the (meth)acrylic acid ester is preferably a (meth)acrylic acid alkyl ester, and specific examples thereof include, but are not limited to, methyl methacrylate (MMA), 2-ethylhexyl acrylate (2EHA), n-butyl acrylate (n-BA), n-butyl methacrylate (n-BMA), and cyclohexyl methacrylate (CHMA).

[0044] Regarding <(a2) Monomer having an alkoxysilyl group and an ethylenic double bond> The monomer having an alkoxysilyl group and an ethylenic double bond refers to a compound capable of imparting an alkoxysilyl group to the aqueous resin emulsion resin obtained by emulsion polymerization reaction, and is not particularly limited as long as it can provide the aqueous resin emulsion according to the present invention. The monomer having an alkoxysilyl group and an ethylenic double bond has both an alkoxysilyl group and an ethylenic double bond, and the alkoxysilyl group and the ethylenic double bond may be bonded via another functional group, such as an ester bond, an amide bond, or an alkylene group. Here, the term "alkoxysilyl group" refers to a silicon-containing functional group that gives a hydroxyl group (Si-OH) bonded to silicon by hydrolysis. Examples of the "alkoxysilyl group" include alkoxysilyl groups such as trimethoxysilyl group, triethoxysilyl group, dimethoxysilyl group, dimethoxymethylsilyl group, diethoxysilyl group, monoethoxysilyl group, and monomethoxysilyl group. In particular, trimethoxysilyl group and triethoxysilyl group are preferred.

[0045] In the present specification, the term "ethylenic double bond" refers to a carbon atom double bond capable of undergoing a polymerization reaction (radical polymerization). Examples of functional groups having such an ethylenic double bond include a vinyl group (CH 2 =CH-), (meth)allyl group (CH 2 =CH-CH 2 - and CH 2 =C(CH 3 )-CH 2 -), (meth)acryloyloxy group (CH 2 =CH-COO- and CH 2 =C(CH 3 )-COO-), (meth)acryloyloxyalkyl group (CH 2 =CH-COO-R- and CH 2 =C(CH 3 Examples include -COO-R- and -COO-CH=CH-COO-. Incidentally, monomers having an alkoxysilyl group and an ethylenic double bond are not included in the above-mentioned (meth)acrylic acid esters.

[0046] An example of the monomer having an alkoxysilyl group and an ethylenic double bond is a compound represented by the following formula (1). R 11 Si(OR 12 )(OR 13 )(OR 14 ) (1) In the formula, R 11 is a functional group having an ethylenic double bond, and R 12 , R 13 and R 14R is an alkyl group having 1 to 5 carbon atoms. 12 , R 13 and R 14 may be the same or different from each other. R 11 Examples of the functional group having an ethylenic double bond include a vinyl group, a (meth)allyl group, a (meth)acryloyloxy group, a 2-(meth)acryloyloxyethyl group, a 2-(meth)acryloyloxypropyl group, a 3-(meth)acryloyloxypropyl group, a 2-(meth)acryloyloxybutyl group, a 3-(meth)acryloyloxybutyl group, and a 4-(meth)acryloyloxybutyl group.

[0047] R 12 , R 13 and R 14 Examples of the alkyl group having 1 to 5 carbon atoms include linear or branched alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, and an n-pentyl group. Examples of the "monomer containing an alkoxysilyl group and having an ethylenic double bond" include vinyltrialkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltri-n-butoxysilane. Specifically, 3-(meth)acryloyloxypropyltrimethoxysilane and 3-(meth)acryloyloxypropyltriethoxysilane are preferred, and 3-methacryloxypropyltrimethoxysilane is particularly preferred. These monomers containing an alkoxysilyl group and an ethylenic double bond can be used alone or in combination.

[0048] Regarding <(a3) Monomer having a carboxyl group and an ethylenic double bond> An example of the monomer having a carboxyl group is (meth)acrylic acid. As described above, (meth)acrylic acid means both acrylic acid and methacrylic acid. It is particularly preferable to use acrylic acid as the (meth)acrylic acid. The "ethylenic double bond" is as defined above.

[0049] Regarding <(b) Polymerizable surfactants containing sulfate salts having an allyl group and a polyoxyethylene chain> Examples of sulfates having an allyl group and a polyoxyethylene group include ammonium sulfates having an allyl group and a polyoxyethylene group, sodium sulfates having an allyl group and a polyoxyethylene group, and potassium sulfates having an allyl group and a polyoxyethylene group.Specific examples include ammonium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates, sodium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates, potassium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates; ammonium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates, sodium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates, potassium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates; and the like.These sulfates may be used alone or in combination.

[0050] As the sulfate having an allyl group and a polyoxyethylene group of the present invention, ammonium sulfate is preferred, i.e., polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt and α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate salt are preferred in the present invention, and in particular, polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt is most desirable in the present invention. Commercially available sulfates having an allyl group and a polyoxyethylene group include, for example, "Aqualon KH-10" (trade name, polyoxyethylene chain length 10) and "Aqualon KH-1025" (trade name, 25% aqueous solution of "Aqualon KH-10"), which are polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salts manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; and "Adeka Reasoap (trademark) SR-1025" which is an α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate salt, manufactured by Asahi Denka Kogyo Co., Ltd.

[0051] The polymerizable unsaturated monomer may contain "other monomers" as long as the desired aqueous resin emulsion is obtained. The "other monomers" refer to monomers other than (meth)acrylic acid esters, monomers having an alkoxysilyl group and an ethylenic double bond, and (meth)acrylic acid. Examples of "other monomers" include, but are not limited to, styrene-based monomers such as styrene and styrene sulfonic acid; unsaturated carboxylic acids and their esters such as itaconic acid, fumaric acid, maleic acid, and the like; and acrylamides such as (meth)acrylamide and diacetone (meth)acrylamide.

[0052] <Multi-stage emulsion polymerization> The silane-modified acrylic resin (aqueous resin emulsion) of the present invention can be obtained by multistage emulsion polymerization of a polymerizable unsaturated monomer in the presence of a surfactant. In one embodiment of the present invention, the polymerizable unsaturated monomer is emulsion-polymerized in a multi-stage process (effectively two stages). The polymerizable unsaturated monomers (a1, a2, a3, and b) used in the polymerization in stages other than the final stage are referred to as polymerizable unsaturated monomer A, and the resulting polymer is referred to as copolymer A. The polymerizable unsaturated monomers (a1, a2, and b) used in the polymerization in the final stage are referred to as polymerizable unsaturated monomer B, and the resulting polymer is referred to as copolymer B. The aqueous resin emulsion finally obtained by the multi-stage emulsion polymerization is obtained by polymerizing a polymerizable unsaturated monomer B with a pre-emulsion obtained by polymerizing a polymerizable unsaturated monomer A.

[0053] The aqueous resin emulsion obtained by the multi-stage emulsion polymerization has a multi-layer structure (core-shell). In the present invention, the polymerizable unsaturated monomer A used in the multistage emulsion polymerization comprises a polymerizable unsaturated monomer A used in a stage other than the final stage and a polymerizable unsaturated monomer B used in the final stage, and the mass ratio of the polymerizable unsaturated monomer B to the polymerizable unsaturated monomer A (polymerizable unsaturated monomer B / polymerizable unsaturated monomer A) is preferably 30 / 70 to 70 / 30, and particularly preferably 40 / 60 to 60 / 40. When the mass ratio of the polymerizable unsaturated monomer B to the polymerizable unsaturated monomer A is within the above range, the aqueous resin composition (aqueous resin emulsion) of the present invention has an excellent balance between coatability and durability (water resistance and solvent resistance).

[0054] In the copolymer A, the proportion of the a2 polymerizable unsaturated monomer relative to the total weight of the a1, a2 and a3 polymerizable unsaturated monomers is preferably 0.05 to 1.0% by weight, more preferably 0.4 to 0.8% by weight, the proportion of the a3 polymerizable unsaturated monomer is preferably 0.5 to 10% by weight, more preferably 2.0 to 6.0% by weight, and the remainder is the a1 polymerizable unsaturated monomer, and the proportion of the a1 polymerizable unsaturated monomer relative to the total weight of the a1, a2 and a3 polymerizable unsaturated monomers is preferably 89 to 99% by weight, more preferably 90 to 98% by weight. In copolymer B, the ratio of the a2 polymerizable unsaturated monomer to the total weight of the a1 and a2 polymerizable unsaturated monomers is preferably 0.01 to 1.0% by weight, more preferably 0.1 to 0.4% by weight, and the remainder is the a1 polymerizable unsaturated monomer, and the ratio of the a1 polymerizable unsaturated monomer to the total weight of the a1 and a2 polymerizable unsaturated monomers is preferably 85 to 99.9% by weight, more preferably 95 to 99.9% by weight. In the synthesis of copolymers A and B (i.e., silane-modified acrylic resins), the ratio of (b) the polymerizable surfactant containing a sulfate having an allyl group and a polyoxyethylene chain to the total weight of the polymerizable unsaturated monomers a1, a2, and a3 is preferably 0.5 to 5% by weight in total in the synthesis process. The silane-modified acrylic resin (aqueous resin emulsion) of the present invention is available, for example, from Henkel Japan Ltd. under the trade name: AQUENCE EPIX BC 21066.

[0055] An example of this multi-stage emulsion polymerization process will now be described. First, (a1) a (meth)acrylic acid ester, (a2) a monomer having an alkoxysilyl group and an ethylenic double bond, and (a3) ​​a monomer having a carboxyl group are uniformly mixed in a reaction vessel to prepare a mixture of polymerizable unsaturated monomers A. Water (or an aqueous medium) is added to a sulfate having an allyl group and a polyoxyethylene group to prepare an aqueous solution, and a mixture of polymerizable unsaturated monomer A is added to this aqueous solution to prepare monomer emulsion A. In a separate container, prepare monomer emulsion B separately from monomer emulsion A. Preparation of monomer emulsion B may be the same as preparation of monomer emulsion A. Specifically, (a1) (meth)acrylic acid ester and (a2) monomer having an alkoxysilyl group and an ethylenic double bond are uniformly mixed to prepare a mixture of polymerizable unsaturated monomers B. A mixture of polymerizable unsaturated monomer B is added to an aqueous solution of sulfate having an allyl group and a polyoxyethylene group to prepare monomer emulsion B.

[0056] Next, water and (b) sulfate having an allyl group and a polyoxyethylene group are charged into a reactor equipped with a stirrer, a thermometer, etc., and a part of the monomer emulsion A and a catalyst are added. While maintaining the temperature inside the reactor at an appropriate temperature, the remaining monomer emulsion A and the catalyst are further dropletized to prepare a pre-emulsion. Monomer emulsion B and a catalyst are added dropwise to this pre-emulsion and polymerized to synthesize the final product, an aqueous resin emulsion, through multi-stage emulsion polymerization. Examples of the catalyst used here include ammonium persulfate, sodium persulfate, potassium persulfate, t-butyl peroxybenzoate, 2,2-azobisisobutyronitrile (AIBN), 2,2-azobis(2-amidinopropane) dihydrochloride, and 2,2-azobis(2,4-dimethylvaleronitrile), and in particular, ammonium persulfate, sodium persulfate, and potassium persulfate are preferred.

[0057] The glass transition point (Tg) of the silane-modified acrylic resin used in the present invention is preferably -10°C to 50°C, more preferably 0°C to 50°C. The glass transition temperature of copolymer A is preferably lower than that of copolymer B. The glass transition temperature of copolymer A is preferably -20 to 20°C, more preferably -10 to 20°C, and particularly preferably -10 to 15°C. The glass transition temperature of copolymer B is preferably 10 to 50°C, more preferably 25 to 50°C, and particularly preferably 30 to 50°C. The minimum film-forming temperature (MFT) of the acrylic resin used in the present invention is preferably 25° C. or lower, and more preferably 0° C. to 25° C. When the minimum film-forming temperature (MFT) is 0° C. to 25° C., the solvent barrier property is particularly good. The glass transition point (Tg) and minimum film formation temperature (MFT) of the acrylic resin are measured by differential scanning calorimetry (DSC).

[0058] The high Tg acrylic resin used in the present invention is a non-core-shell type acrylic resin, and its glass transition point (Tg) is higher than 50° C. and not higher than 95° C. This Tg is measured by differential scanning calorimetry (DSC). This high Tg acrylic resin contains (meth)acrylic acid and a monomer component copolymerizable with (meth)acrylic acid, and it is preferable that the (meth)acrylic acid is 1 to 10 parts by weight per 100 parts by weight of the non-core-shell acrylic resin. (Meth)acrylic acid is alkali-soluble and has the property of turning the non-core-shell acrylic resin into a water-soluble resin by adding a neutralizing agent. By changing the non-core-shell acrylic resin into a water-soluble resin, the binding to the pigment is significantly improved, particularly when the protective layer contains a pigment, and a protective layer having excellent strength can be formed even when a large amount of pigment is contained. Examples of components copolymerizable with (meth)acrylic acid include alkyl acrylate resins such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate, as well as epoxy resins, silicone resins, modified alkyl acrylate resins such as the alkyl acrylate resins modified with styrene or a derivative thereof, (meth)acrylonitrile, acrylic esters, and hydroxyalkyl acrylic esters, but it is particularly preferable to blend (meth)acrylonitrile and / or methyl methacrylate. It is preferable to blend 15 to 70 parts of (meth)acrylonitrile in 100 parts of the non-core-shell type acrylic resin. It is also preferable to include 20 to 80 parts of methyl methacrylate in 100 parts of the non-core-shell type acrylic resin. When (meth)acrylonitrile and methyl methacrylate are contained, it is preferable to mix 15 to 18 parts of (meth)acrylonitrile and 20 to 80 parts of methyl methacrylate in 100 parts of the non-core-shell type acrylic resin.

[0059] Other binders that can be used in the present invention include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols; acrylic resins consisting of (meth)acrylic acid and monomer components (excluding olefins) copolymerizable with (meth)acrylic acid. Examples of such polymeric substances include cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, ethyl cellulose, and acetyl cellulose, starches such as oxidized starch, etherified starch, and esterified starch, styrene-maleic anhydride copolymers, styrene-butadiene copolymers, casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid esters, polyvinyl butyral, polystyrose and copolymers thereof, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins (excluding the above-mentioned silane-modified acrylic resins and high Tg acrylic resins), and the like, depending on the required quality. These polymeric substances can be used by dissolving them in a solvent such as water, alcohol, ketones, esters, and hydrocarbons, or by dispersing them in an emulsified or paste-like form in water or other medium, and can also be used in combination depending on the required quality.

[0060] The protective layer of the present invention contains a binder (including the above-mentioned silane-modified acrylic resin and high Tg acrylic resin), and may contain optional components such as pigments as described for the heat-sensitive recording layer, if necessary. The amount of binder or the total amount of binder and pigment in the protective layer is usually 80.0 to 100.0% by weight, preferably 90.0 to 100.0% by weight, in terms of solid content, and the amount of binder is preferably about 30.0 to 300.0 parts by weight per 100 parts by weight of pigment. The content of the acrylic resin in the protective layer of the present invention is preferably 5.0 to 80.0% by weight, more preferably 5.0 to 60.0% by weight, and further preferably 15.0 to 50.0% by weight. The content of the silane-modified acrylic resin in the protective layer of the present invention is preferably 10.0 to 70.0% by weight, more preferably 30.0 to 60.0% by weight, and the content of the high Tg acrylic resin in the protective layer is preferably 5.0 to 50.0% by weight, more preferably 10.0 to 40.0% by weight. The amount of each of the other components in the protective layer does not exceed 15.0% by weight, preferably 10.0% by weight.

[0061] In addition, a crosslinking agent may be used in combination in the protective layer of the present invention. Examples of the crosslinking agent include epichlorohydrin resins such as polyamine epichlorohydrin resins and polyamide epichlorohydrin resins, polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, and polyalkylene polyamine polyamide polyurea resins, polyamine / polyamide resins such as glyoxal, methylol melamine, melamine formaldehyde resins, melamine urea resins, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, and ammonium chloride. Examples include um. In the present invention, it is preferable that the protective layer contains an epichlorohydrin resin and a polyamine / polyamide resin as crosslinking agents, since this makes the water resistance particularly good.

[0062] The thermosensitive recording medium of the present invention has a thermosensitive recording layer on a support, and an undercoat layer may be provided between the support and the thermosensitive recording layer.

[0063] The undercoat layer consists primarily of a binder and a pigment. The binder used in the undercoat layer may be an emulsion of a water-soluble polymer or a hydrophobic polymer that is generally used.Specific examples include cellulose derivatives such as polyvinyl alcohol, polyvinyl acetal, hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose, starch and its derivatives, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein, and emulsions of hydrophobic polymers such as polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, and styrene / butadiene / acrylic copolymer.These binders may be used alone or in combination of two or more.

[0064] The pigment used in the undercoat layer may be any known pigment that has been commonly used in the past, such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcined kaolin, clay, talc, or other inorganic pigments. These pigments may be used alone or in combination. The amount of the pigment in the undercoat layer is usually 50 to 95 parts by weight, and preferably 70 to 90 parts by weight, based on 100 parts by weight of the total solid content. The coating solution for the undercoat layer may contain various auxiliary agents, such as dispersants, plasticizers, pH adjusters, defoamers, water retention agents, preservatives, coloring dyes, and ultraviolet protection agents, as required.

[0065] In the present invention, the means for coating the thermosensitive recording layer and the coating layers other than the thermosensitive recording layer, i.e., the protective layer, undercoat layer, etc., is not particularly limited, and can be applied according to well-known conventional techniques. For example, an off-machine coater or an on-machine coater equipped with various coaters such as an air knife coater, a rod blade coater, a bent blade coater, a bevel blade coater, a roll coater, or a curtain coater can be appropriately selected and used. The coating weight of the thermal recording layer and the coating layers other than the thermal recording layer is determined according to the required performance and recording suitability, and is not particularly limited. The general coating weight of the thermal recording layer is 2 to 12 g / m2 in terms of solid content. 2 The coating weight of the protective layer is about 0.5 to 5.0 g / m2 in solid content. 2 is preferred. Furthermore, various known techniques in the field of thermal recording media can be added as necessary, such as smoothing treatment such as supercalendering after coating of each coating layer. EXAMPLES

[0066] The present invention will be illustrated in the following examples, but is not intended to limit the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.

[0067] [Silane-modified acrylic resin] In the following preparation examples, aqueous emulsions were prepared from (A) a monomer emulsion (copolymer A) and (B) a monomer emulsion (copolymer B). The polymerizable unsaturated monomers, surfactants, and additives used to prepare (A) and (B) are described below. The Tg of the homopolymer of the polymerizable unsaturated monomer is a literature value, and the Tg of (a) the copolymer of the polymerizable unsaturated monomer and the Tg of (b) the copolymer of the polymerizable unsaturated monomer are values ​​calculated by a theoretical calculation formula.

[0068] <Polymerizable unsaturated monomer> Methyl methacrylate (Methyl methacrylate, hereafter referred to as "MMA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = 105 ° C.) 2-Ethylhexyl acrylate (2-ethylhexyl acrylate, hereafter referred to as "2EHA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = -70°C) n-Butyl acrylate (n-butyl acrylate, hereafter referred to as "n-BA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = -54°C) n-Butyl methacrylate (n-butyl methacrylate, hereafter referred to as "n-BMA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = 20°C) Cyclohexyl methacrylate (cyclohexyl methacrylate, hereafter referred to as "CHMA", manufactured by Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 83°C) 3-Methacryloxypropyltrimethoxysilane (Fujifilm Wako Pure Chemical Industries, Ltd.) Acrylic acid (hereinafter referred to as "AA", Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 106 ° C) Styrene (hereinafter referred to as "St", Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 100 ° C)

[0069] <Surfactant> Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (Aqualon KH10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (hereinafter referred to as "b")

[0070] [Production Example 1] A monomer emulsion was prepared from a plurality of polymerizable unsaturated monomers, a pre-emulsion was then prepared from the monomer emulsion, and an aqueous resin emulsion was synthesized from the pre-emulsion. The specific steps were as follows.

[0071] (A) Preparation of Monomer Emulsion As shown in Table 1, 5 parts by mass of (a1-1) MMA, 23 parts by mass of (a1-3) BA, 10 parts by mass of (a1-4) BMA, 10 parts by mass of (a1-5) CHMA, 0.3 parts by mass of (a2) 3-methacryloxypropyltrimethoxysilane, and 2 parts by mass of (a3) ​​AA were uniformly mixed to prepare a polymerizable unsaturated monomer solution (50.3 parts by mass). The above polymerizable unsaturated monomer solution was added to a uniformly mixed solution of 14 parts by mass of water and 0.1 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, and the mixture was stirred with a stirrer to obtain (A) a monomer emulsion.

[0072] (B) Preparation of Monomer Emulsion (A) As shown in Table 1, 16.6 parts by mass of (a1-1) MMA, 13 parts by mass of (a1-3) BA, 10 parts by mass of (a1-4) BMA, 10 parts by mass of (a1-5) CHMA, and 0.1 parts by mass of (a2) 3-methacryloxypropyltrimethoxysilane were uniformly mixed to prepare a polymerizable unsaturated monomer solution. The above polymerizable unsaturated monomer solution was added to a uniformly mixed solution of 14 parts by mass of water and 0.1 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, and the mixture was stirred with a stirrer to obtain (B) a monomer emulsion.

[0073] (Synthesis of pre-emulsion) A reactor equipped with a stirrer, a condenser, and a thermometer was charged with 78 parts by mass of water and 1.25 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt, and the inside of the system was replaced with nitrogen gas, and the charged liquid was heated to 80°C. Thereafter, (A) a monomer emulsion (containing 50.3 parts by mass of a polymerizable unsaturated monomer, equivalent to 10.1 parts by mass of the polymerizable unsaturated monomer) and 2 parts by mass of a 1% by mass aqueous solution of sodium persulfate (hereinafter also referred to as "SPS") were added to the charge liquid. After a further 10 minutes, while keeping the temperature inside the reactor at 80°C, the remainder of the (A) monomer emulsion (a portion corresponding to 40.2 parts by mass of (a) polymerizable unsaturated monomer) and 4 parts by mass of a 1% aqueous solution of SPS as a polymerization catalyst were each dropped simultaneously over a period of 2 hours to obtain a pre-emulsion (an aqueous resin emulsion based on (a) polymerizable unsaturated monomer).

[0074] (Synthesis of Water-Based Resin Emulsion) The temperature inside the reactor was kept at 80°C, and 30 minutes after the completion of the dropping, the above-mentioned (B) monomer emulsion (containing 49.7 parts by mass of an unsaturated polymerizable monomer) and 4 parts by mass of a 1% aqueous solution of SPS were each dropped simultaneously into the above-mentioned pre-emulsion over a period of 2 hours to obtain an aqueous resin emulsion. The pH of the obtained aqueous resin emulsion was adjusted to 8.0 with aqueous ammonia. The aqueous resin emulsion had a glass transition temperature of -3.8°C for the polymerizable unsaturated monomer (copolymer A), a glass transition temperature of 26.7°C for the polymerizable unsaturated monomer (copolymer B), and a solid content concentration of 45% by mass. The solid content is the mass percentage of the remaining portion relative to the mass before drying after drying in an oven at 105°C for 3 hours. The resulting aqueous resin emulsion is called silane-modified acrylic resin 1.

[0075] [Manufacturing Examples 2-3] The raw material monomers shown in Table 1 were used to synthesize the resins in the same manner as in Production Example 1. The numbers relating to the compositions in the table indicate parts by weight. The resulting aqueous resin emulsions are called silane-modified acrylic resins 2 and 3, respectively.

[0076] [Table 1]

[0077] On the other hand, for producing a thermal recording medium, each dispersion liquid and coating liquid were prepared as follows. [Preparation of each coating liquid] The following composition was mixed and dispersed to prepare a coating liquid for the undercoat layer. <Coating fluid for undercoat layer> Calcined kaolin (BASF product name: Ansilex 90) 100.0 copies Styrene-butadiene copolymer latex (manufactured by Zeon Corporation, Product name: ST5526, solid content 48%) 10.0 parts Water 50.0 parts

[0078] Each dispersion and coating solution was prepared as follows. The following composition was mixed and dispersed to prepare a coating liquid for the undercoat layer. <Coating fluid for undercoat layer> Calcined kaolin (BASF product name: Ansilex 90) 100.0 copies Styrene-butadiene copolymer latex (manufactured by Zeon Corporation, Product name: ST5526, solid content 48%) 10.0 parts Water 50.0 parts

[0079] The developer dispersions (Liquids A1 to A4), leuco dye dispersion (Liquid B), and sensitizer dispersion (Liquid C) having the following compositions were each prepared by wet grinding in a sand grinder until the average particle size became 0.5 μm.

[0080] Developer dispersion liquid (A1 liquid) N,N'-Di-[3-(p-toluenesulfonyloxy)phenyl]urea (Hereinafter referred to as "Urea Compound 1") 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117, solids content 10%) 5.0 parts 1.5 parts water Developer dispersion liquid (A2 liquid) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (hereinafter referred to as "urea compound 2") 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Developer dispersion liquid (A3 liquid) A urea compound represented by the following chemical formula (9): (Hereinafter referred to as "Urea compound 3") 6.0 parts [ka] Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0081] Developer dispersion liquid (A4 liquid) Urea-urethane compound represented by formula (13) (Fine Ace UU) 6.0 parts [ka] Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Developer dispersion liquid (A5 liquid) 4-Hydroxy-4'-isopropoxydiphenyl sulfone (Mitsubishi Chemical Corporation, NYDS) 6.0 units Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0082] Leuco dye dispersion (liquid B) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Industry Co., Ltd., product name: ODB-2) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0083] Sensitizer dispersion (liquid C) 1,2-Di(3-methylphenoxy)ethane (Sankosha, product name: KS232) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0084] Next, each dispersion was mixed in the following ratio to prepare a coating liquid for the heat-sensitive recording layer. <Coating solution for thermal recording layer> Developer dispersion liquid (A1 liquid) 18.0 parts Developer dispersion liquid (A2 liquid) 18.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 9.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 25.0 parts

[0085] Next, protective layer coating solutions 1 to 3 were prepared by mixing the ingredients in the following proportions. <Protective layer coating solution 1> Aluminum hydroxide dispersion (Martinsberg, Product name: Martyfin OL, solid content 50%) 9.0 parts Silane-modified acrylic resin 1 (Tg 18°C, MFT 22°C, Solid content 40%) 10.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., product name: Hydrin Z-7-30, Solid content 30%) 2.0 parts

[0086] <Protective layer coating solution 2> Aluminum hydroxide dispersion (Martifin OL) 9.0 parts Non-core-shell acrylic resin (non-silane modified, styrene acrylic, Tg55℃, MFT18℃, solid content 18%) 22.2 parts Zinc stearate (Hydrin Z-7-30) 2.0 parts <Protective layer coating solution 3> Aluminum hydroxide dispersion (Martifin OL) 9.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 40.0 parts Zinc stearate (Hydrin Z-7-30) 2.0 parts Glyoxal aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., solid content 40%) 3.0 parts <Protective layer coating solution 4> Carboxy-modified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: KL118, solid content 10%<polymerization degree: approx. 1700, saponification degree: 95-99 mol%, sodium acetate: 3% or less) 40.0 parts Polyamide epichlorohydrin resin (manufactured by Seiko PMC Corporation, product name: WS4020, solids 25%) 4.0 parts Modified polyamine resin (manufactured by Taoka Chemical Co., Ltd., product name: Sumirez Resin) SPI-102A, solids content 45%) 2.2 parts Aluminum hydroxide dispersion (Martifin OL) 9.0 parts Zinc stearate (Hydrin Z-7-30) 2.0 parts

[0087] [Reference example 1] Support (basis weight 47g / m 2 The coating solution for the undercoat layer is applied to one side of the paper (high-quality paper) at a coating weight of 10.0 g / m2 (solid content). 2 After coating by the bent blade method so that the above-mentioned coating was performed, the coated paper was dried to obtain a coated paper with an undercoat layer. The coating solution for the thermal recording layer was applied to the undercoat layer of the undercoat layer coated paper at a coating weight of 6.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so as to obtain the above-mentioned composition, the coating was dried to obtain a thermal recording medium. Next, the protective layer coating solution 1 was applied to the thermal recording layer of the thermal recording layer coated paper in a coating amount of 3.0 g / m2 in terms of solid content. 2 After coating by the curtain method so that the coating liquid had a smoothness of 100 to 500 seconds, the coating liquid was dried and then processed with a super calendar to obtain a thermal recording layer. [Reference example 2] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the protective layer coating solution 1, the silane-modified acrylic resin 1 was changed to the silane-modified acrylic resin 2.

[0088] [Reference example 3] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the protective layer coating solution 1, the silane-modified acrylic resin 1 was changed to the silane-modified acrylic resin 3. [Reference example 4] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, Liquid A2 was changed to Liquid A3. [Reference example 5] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the A1 liquid was changed to the A3 liquid. [Reference example 6] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that the protective layer coating solution 1 was changed to the protective layer coating solution 2. [Reference example 7] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the blending amount of A1 liquid was changed to 9 parts and 9 parts of A4 liquid was added. [Example 8] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the A2 liquid was not blended and the amount of the A1 liquid was changed to 36 parts. [Example 9] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the A1 liquid was not blended and the blending amount of the A2 liquid was changed to 36 parts. [Reference example 10] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the A1 liquid and the A2 liquid were not mixed, and 36 parts of the A3 liquid were added.

[0089] [Comparative Example 1] A thermosensitive recording medium was prepared in the same manner as in Reference Example 4, except that the protective layer coating solution 1 was changed to the protective layer coating solution 3. [Comparative Example 2] A thermosensitive recording medium was prepared in the same manner as in Reference Example 4, except that the protective layer coating solution 1 was changed to the protective layer coating solution 4. [Comparative Example 3] A thermosensitive recording medium was prepared in the same manner as in Reference Example 4, except that no protective layer was provided. [Comparative Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 8, except that no protective layer was provided. [Comparative Example 5] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that no protective layer was provided. [Comparative Example 6] A thermosensitive recording medium was prepared in the same manner as in Reference Example 5, except that no protective layer was provided. [Comparative Example 7] A thermosensitive recording medium was prepared in the same manner as in Reference Example 1, except that in the coating liquid for the thermosensitive recording layer, the A1 liquid and the A2 liquid were not mixed, and 36 parts of the A5 liquid were added.

[0090] The prepared thermosensitive recording medium was evaluated as follows. <Color development performance (print density)> A checkered pattern was printed on the prepared thermal recording medium at a printing speed of 50 mm / sec and an applied energy of 0.41 mJ / dot using a TH-PMD (thermal recording paper print tester, equipped with a Kyocera thermal head) manufactured by Okura Electric Co., Ltd. The print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development performance (print density). <Printing performance (resistance to head residue)> A 60 cm long grid pattern was printed on the prepared thermal recording medium using a Sato label printer (Resply R-8), and the residue (head residue) adhering to the thermal head after printing was visually evaluated according to the following criteria. Excellent: Almost no head residue was observed. Pass: A small amount of head residue was observed, but the formed image was not blurred or missing, and was not of a level that would cause any practical problems. Poor: A large amount of head residue was observed, and the formed image had gaps and faint spots.

[0091] <Suitable for high-speed printing> A barcode (CODE39) was printed vertically (the barcode was perpendicular to the printer head movement direction) on the prepared thermal recording medium using a Zebra 140XiIII label printer at a print level of +10 and a print speed of 25.4 cm / sec (10 in / sec). Next, the printed barcode was read using a barcode verifier (Honeywell, QCPC600, light source 640 nm) to evaluate the barcode readability. The evaluation results were recorded using the ANSI standard symbol grade. Symbol grade: The barcode is divided into 10 parts vertically and a reading test is carried out once for each part. The average value is expressed as a 5-level rating of A (Excellent), B, C, D, or F (Poor). <Oil resistance> A checkered pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper print tester equipped with a Kyocera thermal head) at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. Salad oil was applied to the printed thermal recording medium with a cotton swab and left for 24 hours, after which the print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter).

[0092] <Solvent barrier properties> Ethanol (99.5%) was applied to the blank portion of the thermal recording medium with a cotton swab, and the medium was left to stand for 24 hours under environmental conditions of 23°C x 50% RH, after which it was visually evaluated according to the following criteria. Excellent: No color at all Possible: Slight color development Not acceptable: Strong color development <Wet friction> The surface of the protective layer of the prepared thermosensitive recording medium was rubbed back and forth 80 times with tap water on a finger, and peeling of the protective layer and thermosensitive recording layer was visually evaluated according to the following criteria. Excellent: No peeling of the protective layer or thermal recording layer Pass: The protective layer peels off slightly, but the thermal recording layer does not peel off. Not acceptable: The protective layer and thermal recording layer peel off.

[0093] <Water-resistant blocking> For the thermal recording medium thus prepared, 10 ml of tap water was dropped onto the surface of the protective layer, the medium was folded in half so that the surface of the protective layer was on the inside, and the medium was subjected to a pressure of 20 gf / cm 2 After being left to stand for 24 hours under a load of 1000 g, the pieces were peeled off, and the peeling of the protective layer and the thermosensitive recording layer in the area where the water was dropped was visually evaluated according to the following criteria. Excellent: No blocking occurred, and the protective layer and the thermal recording layer did not peel off at all. Pass: Blocking occurs and the protective layer peels off slightly, but the thermal recording layer does not peel off. Unacceptable: Strong blocking occurs, and the protective layer and thermal recording layer peel off. Or the thermal recording medium is destroyed when peeled off. <Immersion friction> The prepared thermosensitive recording medium was immersed in tap water for 10 minutes, the surface of the protective layer was rubbed back and forth with a finger 20 times, and peeling of the protective layer and thermosensitive recording layer was visually evaluated according to the following criteria. Excellent: No peeling of the protective layer or thermal recording layer Pass: The protective layer peels off slightly, but the thermal recording layer does not peel off. Not acceptable: The protective layer and thermal recording layer peel off.

[0094] The results are shown in the table below. [Table 2]

Claims

1. A thermosensitive recording medium having a support, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains a third urea compound represented by the following (3) as the electron-accepting developer, the protective layer contains an acrylic resin represented by the following (4) or (5), the content of the acrylic resin in the protective layer is 15.0 to 50.0% by weight, and the minimum film-forming temperature (MFT) of the acrylic resin is 0°C to 25°C. (3) A third urea compound represented by the following general formula (Chemical Formula 4): 【Chemistry 4】 (In the formula, R ２ represents a hydrogen atom or an alkyl group; R ４ ~R ８ may be the same or different, and each represents 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. (4) A non-core-shell acrylic resin having a glass transition point (Tg) of more than 50° C. and not more than 95° C. (5) A silane-modified acrylic resin which is an aqueous emulsion of core-shell type particles comprising a core made of copolymer A obtained by polymerizing the following (a1), (a2) and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b): (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactant containing a sulfate having an allyl group and a polyoxyethylene chain

2. 2. The thermosensitive recording material according to claim 1, wherein the third urea compound is N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

3. 3. The thermal recording medium according to claim 2, wherein a barcode (CODE 39) is printed vertically (the barcode is perpendicular to the moving direction of the printer head) at a printing speed of 25.4 cm / sec (10 in / sec), the barcode is read by a barcode verifier, and the average value expressed in the ANSI standard symbol grade is B or higher (wherein the symbol grade is the average value when the barcode is divided into 10 parts perpendicular to the bar and a reading test is conducted once for each part, and is expressed on a 5-level scale of A, B, C, D, and F from best to worst).

4. 4. The thermosensitive recording medium according to claim 1, wherein the total content (solid content) of the urea compound in the thermosensitive recording layer is 1.0 to 70.0% by weight.

5. 5. The heat-sensitive recording medium according to claim 1, wherein the protective layer has an acrylic resin content (solid content) of 15.0 to 50.0% by weight.

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