Heat-sensitive recording body and method for producing same

Abstract

[Problem] To provide: a heat-sensitive recording body which is excellent in color developing sensitivity, printing runnability (especially head residue adhesion resistance), and abrasion resistance, and also exhibits excellent printing precision during high-speed printing; and a method for producing the same. [Solution] The heat-sensitive recording body comprises, on a support body in order: an undercoat layer; a heat-sensitive recording layer which contains a colorless or light-colored electron-donating leuco dye, an electron-accepting color developer, and a sensitizer; and a protection layer. The total content (solid content) of the leuco dye, the color developer, and the sensitizer in the heat-sensitive recording layer is 70.0 wt.% or more, and the coating amount of the heat-sensitive recording layer is 2.5 g / m2 or less.

Description

Thermal recording medium and its manufacturing method

[0001] The present invention relates to a thermosensitive recording medium that utilizes a color-forming 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 a method for producing the same.

[0002] Generally, a thermal recording medium is prepared by applying a coating liquid containing a colorless or pale-colored leuco dye and a color developer to a support such as paper, synthetic paper, film, or plastic, and the color develops through an instantaneous chemical reaction when heated with a thermal head, hot stamp, thermal 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 from supermarkets and convenience stores, etc.

[0003] In recent years, the use of thermal recording media has expanded to include a wide variety of applications, such as various tickets, receipts, labels, bank ATMs, gas and electricity meter reading, and cash vouchers for car and horse racing betting. As a result, various performance characteristics are required, such as water resistance, plasticizer resistance in the image area, heat resistance and oil resistance in the blank area, and storage stability of the image area and blank area under harsh conditions.

[0004] In such applications, stable printing on a thermal recording medium is required. However, frequent printing can cause recording paper to stick to the print head or head residue to accumulate on the print head, preventing proper printing. To solve these problems, a technique is known in which a phosphate ester compound is incorporated into the outermost layer, such as a protective layer (see, for example, Patent Document 1). Also known is a thermal recording medium with improved color development sensitivity, which is formed by simultaneously coating and drying a thermal recording layer and a protective layer using a multilayer curtain coating method (see, for example, Patent Document 2).

[0005] JP 2012-56184 A Japanese Patent No. 5626218 A

[0006] However, even with such conventional techniques, it has been difficult to achieve both color development sensitivity and print running properties (resistance to head residue adhesion and sticking resistance). Therefore, an object of the present invention is to provide a thermosensitive recording medium that has good color development sensitivity, print running properties (particularly resistance to head residue adhesion) and abrasion resistance, and also has good print resolution during high-speed printing, and a method for producing the same.

[0007] As a result of extensive research, the present inventors have found that the color development sensitivity improves when the total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer is 70.0% by weight or more. However, a protective layer was provided because a high content of the leuco dye, etc. in the thermosensitive recording layer can cause problems such as head residue and sticking. Furthermore, the provision of the protective layer improves scratch resistance. Furthermore, when the coating weight of the thermosensitive recording layer is 2.5 g / m ２ It was found that by reducing the density to the following level, print resolution during high-speed printing can be improved.

[0008] That is, the present invention provides a thermosensitive recording medium comprising a support, an undercoat layer, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye, an electron-accepting developer, and a sensitizer, and a protective layer, in this order, wherein the total content (solid content) of the leuco dye, the developer, and the sensitizer in the thermosensitive recording layer is 70.0% by weight or more, and the coating amount of the thermosensitive recording layer is 2.5 g / m ２ The following is the result.

[0009] According to the present invention, a thermosensitive recording medium can be obtained which has good color development sensitivity, print running properties (particularly resistance to head residue adhesion) and abrasion resistance, and further has good print definition during high-speed printing.

[0010] The thermosensitive recording medium of the present invention is a thermosensitive recording medium comprising a support, an undercoat layer, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye, an electron-accepting developer and a sensitizer, and a protective layer, in this order, wherein the total content (solid content) of the leuco dye, developer and sensitizer in the thermosensitive recording layer is 70.0% by weight or more, and the coating amount of the thermosensitive recording layer is 2.5 g / m ２ The following is the result.

[0011] Examples of various materials that can be used in the thermal recording layer of the thermal recording medium of the present invention are given below, but binders, crosslinking agents, pigments, etc. can also be used in each coating layer provided as needed, as long as they do not impair the desired effects on the above-mentioned problems.

[0012] <Undercoat Layer> The thermosensitive recording medium of the present invention has an undercoat layer on the support. This undercoat layer is primarily composed of a binder and a pigment. Commonly used emulsions of water-soluble or hydrophobic polymers can be used as the binder for the undercoat layer. Specific examples include water-soluble polymers such as polyvinyl alcohol, polyvinyl acetal, cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose, starch and its derivatives, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymers, acrylic acid amide / acrylic acid ester / methacrylic acid copolymers, styrene / maleic anhydride copolymer alkali salts, isobutylene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein, and emulsions of hydrophobic polymers such as polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid esters, vinyl chloride / vinyl acetate copolymers, polybutyl methacrylate, ethylene / vinyl acetate copolymers, and styrene / butadiene / acrylic copolymers. These binders may be used alone or in combination of two or more.

[0013] The pigment used in the undercoat layer may be any of the conventionally commonly used pigments, including inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcined kaolin, clay, and talc. One or more of these pigments may be used. The amount of pigment in the undercoat layer is typically 50 to 95 parts by weight, and preferably 70 to 90 parts by weight, per 100 parts by weight of the total solids. The coating solution for the undercoat layer may contain various auxiliary agents, such as dispersants, plasticizers, pH adjusters, antifoaming agents, water retention agents, preservatives, coloring dyes, and ultraviolet protection agents, as needed.

[0014] <Thermal Recording Layer> The thermal recording layer contains a colorless or pale-colored electron-donating leuco dye, an electron-accepting developer, and a sensitizer. The leuco dye used in the present invention can be any known leuco dye in the field of conventional pressure-sensitive or thermal recording paper, and is not particularly limited. However, triphenylmethane-based compounds, fluoran-based compounds, fluorene-based compounds, divinyl-based compounds, etc. are preferred. Specific examples of representative colorless or pale-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination.

[0015] <Triphenylmethane leuco dyes> 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)

[0016] <Fluoran-based leuco dyes> 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-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-anilino fluoran, 3-diethylamino-6-chloro-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 Fluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-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-anilino fluoran, 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 aminoanilinofluoran, 2-phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 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,

[0017] <Fluorene-based leuco dyes> 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0018] <Divinyl leuco dyes> 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

[0019] <Others> 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 (amino)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

[0020] Examples of color developers that can be used in the present invention 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, benzyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenyl sulfone, and 2,4'-dihydroxydiphenyl sulfone. Phenyl 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-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]-4 phenyl)phenoxy]butane, 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) 4,4'-bis(3-(phenoxycarbonylamino)methylphenylureido)diphenyl sulfone, compounds described in WO02 / 081229 or JP2002-301873A, and N,Examples of suitable aromatic carboxylic acids include thiourea compounds such as N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, zinc bis[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, as well as salts of these aromatic carboxylic acids with polyvalent metals 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.

[0021] 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, from API Corporation under the trade name JKY-214, and the phenol condensation composition described in JP 2003-154760 A is available, for example, from API Corporation under the trade name JKY-224. Furthermore, compounds described in WO 02 / 081229 and the like are available under the trade names NKK-395 and D-100 from Nippon Soda Co., Ltd. In addition, metal chelate 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.

[0022] The developer may contain a urea compound represented by the following general formula (Chemical Formula 1): This urea compound does not contain bisphenol A or bisphenol S. (wherein X represents —O— or —NH—; R １ is a hydrogen atom or —SO ２ -R ３ represents R ３ represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R ２ represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

[0023] As the color developer, the above-mentioned color developer and this urea compound may be used in combination, or the urea compound may be used alone as the color developer.

[0024] The urea compound is preferably the following (1) or (2): (1) A first urea compound represented by the following general formula (Chemical Formula 2): (In the formula, R １ , R ２ and R ３ is defined as above.) (2) A second urea compound represented by the following formula (Chemical Formula 3): (In the formula, R ２ is defined as above, and R ４ ~R ８ The definition of will be explained later.)

[0025] The first urea compound used in the present invention is preferably represented by the following formula (Chemical Formula 4).

[0026] In the general formula (Chemical Formula 2) and the general formula (Chemical Formula 4), R ３ represents an alkyl group, an aralkyl group, or an aryl group, which may be substituted or unsubstituted, and is preferably a substituted or unsubstituted aryl group. 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. １ The positions of -O- may be the same or different, and are preferably the 3-, 4- or 5-positions. ３ -SO ２ The positions of --O-- may be the same or different, and are preferably the 3-, 4- or 5-positions.

[0027] The alkyl group is, for example, a linear, branched, or alicyclic alkyl group, and preferably has 1 to 12 carbon atoms. 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.

[0028] The number of carbon atoms in this aralkyl group is preferably 7 to 12. Examples of this aralkyl group include unsubstituted 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 p-i-propylbenzyl group, a p-t-butylbenzyl group, a p-methoxybenzyl group, a m-methoxybenzyl group, an 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, an o-phenylbenzyl group, a m-phenylbenzyl group, a p-tolylbenzyl group, a m-tolylbenzyl group, an o-tolylbenzyl group, and a p-chlorobenzyl group.

[0029] The number of carbon atoms in this aryl group is preferably 6 to 12. Examples of this 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, an 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-i-propylphenyl group, a p-t-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.

[0030] In the above general formulas (Chemical Formulas 1, 2, and 4), R ３is preferably a group represented by the following formula: In the above formula, R ４ ~R ８ may be 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.

[0031] 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, a t-butyl group, etc. ２ may be the same or different, and is preferably the 3-, 4- or 5-position.

[0032] As the first urea compound of the present invention, a urea compound represented by the following general formula (Chemical Formula 6) is more preferred. In the general formula (chemical formula 6), R ９ is 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 (Chemical Formula 6) ９ may be the same or different, and is preferably the 3-position, 4-position or 5-position, more preferably the 4-position.

[0033] Further, as the first urea compound of the present invention, for example, 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 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-(p-t-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.

[0034] The second urea compound used in the present invention 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.

[0035] The sensitizer used in the present invention may be a conventionally known sensitizer, such as 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 sensitizers 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.

[0036] The total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer of the present invention is 70.0% by weight or more. A total content (solid content) of 70.0% by weight or more improves color development sensitivity. The total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer is preferably 72.0% by weight or more, more preferably 79.0% by weight. The upper limit of the total content (solid content) is 90% by weight or less.

[0037] The coating amount of the heat-sensitive recording layer of the present invention is 2.5 g / m ２ Preferably, it is 2.4 g / m or less. ２ or less, more preferably 2.1 g / m ２As described above, by setting the total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer to 70.0% by weight or more, the coating amount of the thermosensitive recording layer can be set to 2.5 g / m or less. ２ The lower limit of the coating amount of the thermosensitive recording layer is, for example, 1.2 g / m ２ The coating amount of the thermal recording layer is 1.4 to 2.4 g / m ２ It is more preferable that:

[0038] It is preferable that the thermosensitive recording layer of the present invention does not contain a pigment such as an inorganic pigment. If the thermosensitive recording layer contains a pigment such as an inorganic pigment, the total content (solid content) of the leuco dye, developer, and sensitizer described above will be reduced accordingly, and color development sensitivity may be reduced. Examples of inorganic pigments include kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, and silica. Examples of organic pigments include plastic pigments.

[0039] It is preferable that the thermosensitive recording layer of the present invention does not contain a lubricant. If the thermosensitive recording layer contains a lubricant, the total content (solid content) of the leuco dye, developer, and sensitizer described above will be reduced accordingly, and color development sensitivity may be reduced. Examples of lubricants include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

[0040] Binders that can be used in the heat-sensitive recording layer 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; silane-modified acrylic resins; and high-Tg acrylic resins (preferably non-core-shell type acrylic resins, the glass transition point (Tg) of which is higher than 50° C. and not higher than 95° C.). This Tg can be determined by differential scanning calorimetry (DSC). C). Examples of suitable polymers include (meth)acrylic acid and other acrylic resins composed of monomer components copolymerizable with (meth)acrylic acid (excluding olefins), 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. 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 can also be used in combination depending on the required quality.

[0041] In the present invention, stabilizers for improving the oil resistance of image areas, such as 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, and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, may also be added within the range that does not impair the desired effects for solving the above problems. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like may be used in the thermal recording layer.

[0042] The types and amounts of the leuco dye, developer, sensitizer, and other 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. However, typically, 0.5 to 10 parts by weight of developer, 0.1 to 10 parts by weight of sensitizer, 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 content is preferably approximately 5 to 25% by weight of the solid content of the thermosensitive recording layer. In the present invention, in order to ensure that the total content (solid content) of leuco dye, developer, and sensitizer is 70.0% by weight or more, it is desirable to keep the binder content low. However, if the binder content is less than 5% by weight, the coating properties, particularly curtain film suitability, are reduced, so the lower limit is preferably 5% by weight or more.

[0043] In the present invention, the leuco dye, developer, and other optional additives are pulverized to particle sizes of several microns or less using a grinder such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and then a binder and various additives depending on the purpose are added to prepare a coating liquid. The solvent used in this coating liquid can be water or alcohol, and the solid content is about 20 to 40% by weight.

[0044] <Protective Layer> The thermosensitive recording medium of the present invention has a protective layer on the surface of the thermosensitive recording layer. The thermosensitive recording layer of the present invention has a total content (solids content) of leuco dye, developer, and sensitizer of 70.0% by weight or more. This increases the absolute amount of color former melted during printing, increasing the area of ​​direct contact between the head and the color former and relatively reducing the material that absorbs the melted color former, which tends to deteriorate print runnability and stick resistance. Therefore, in the present invention, a protective layer is essential to obtain a thermosensitive recording medium with good print runnability (especially head residue adhesion resistance) and stick resistance. This protective layer is primarily composed of a binder and a pigment, and a lubricant may be further added. As the binder, any of the binders usable for the thermosensitive recording layer described above can be used as appropriate.

[0045] Examples of pigments include inorganic pigments such as kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, and silica. In particular, when the protective layer contains an inorganic pigment with an aspect ratio of 30 or more, the surface smoothness of the protective layer is improved, thereby improving print running properties (particularly, head residue adhesion resistance). An example of an inorganic pigment with an aspect ratio of 30 or more is kaolin. The aspect ratio is expressed as the value obtained by dividing the maximum diameter of the pigment by its thickness (minimum length).

[0046] Examples of lubricants include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins. When the protective layer contains a lubricant, the surface smoothness of the protective layer is improved, which in turn improves print running properties (particularly, head residue adhesion resistance). As described above, in the present invention, in order to increase the total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer to 70% by weight or more, it is preferable not to contain a lubricant in the thermosensitive recording layer, but to contain a lubricant in the protective layer in order to ensure the smoothness of the thermosensitive recording medium.

[0047] 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 coating liquid for the protective layer may optionally contain various auxiliary agents such as stabilizers, ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc., which can be used in the above-mentioned thermosensitive recording layer.

[0048] The coating amount of the protective layer is 2.5 g / m ２ It is preferably 2.3 g / m or less, and more preferably 2.3 g / m ２ Below 2.0 g / m, most preferably ２ The lower limit of the coating amount of the protective layer can be, for example, 0.4 g / m or less. ２ The coating amount of the protective layer is 0.7 to 2.5 g / m ２ It is more preferable that:

[0049] <Support> Examples of the support include paper, synthetic paper, film, and plastic sheet.

[0050] In the present invention, the means for applying the thermosensitive recording layer and other coating layers, i.e., the protective layer, undercoat layer, etc., is not particularly limited, and coating can be performed according to well-known conventional techniques. For example, an off-machine or on-machine coater equipped with various coaters such as an air knife coater, rod blade coater, vent blade coater, bevel blade coater, roll coater, or curtain coater can be appropriately selected and used. Furthermore, various well-known techniques in the field of thermosensitive recording media can be added as needed, such as smoothing treatment such as supercalendering after the application of each coating layer.

[0051] In particular, when the above-mentioned thermosensitive recording layer and protective layer are formed by applying the coating liquid for the thermosensitive recording layer and the coating liquid for the protective layer by a multi-layer curtain coating method and drying, the coating amount is 2.5 g / m ２ Even at low coating weights below this level, the coverage of the thermosensitive recording layer and protective layer is good, so the surface smoothness of the thermosensitive recording layer and protective layer is increased, further improving print running properties (particularly head residue adhesion resistance). Simultaneous multilayer curtain coating is preferred as the coating method.

[0052] Here, the absence of a pigment in the coating liquid for the thermosensitive recording layer improves color development sensitivity. As mentioned above, if a pigment is added to the coating liquid for the thermosensitive recording layer, the total content of the leuco dye, developer, and sensitizer, which contribute to color development sensitivity, will be reduced accordingly. However, if the content of the leuco dye, etc. in the thermosensitive recording layer is high, print runnability (head residue and sticking) will become an issue, so a protective layer was provided.

[0053] In particular, in the present invention, the coating amount of the heat-sensitive layer and / or the protective layer is 2.5 g / m ２ If the concentration is lower than 70.0 wt %, it is difficult to form a single-layer curtain film, and therefore it is preferable to use a multi-layer curtain coating method. Furthermore, in the present invention, if the total content (solid content) of the leuco dye, developer, and sensitizer in the coating liquid for the thermosensitive recording layer is 70.0 wt % or more, the sensitivity varies greatly depending on the coating amount, so it is preferable to use a multi-layer curtain coating method in order to control the coating amount and maintain constant quality. Furthermore, by using a multi-layer curtain coating method, the coating properties of the coating material are improved, which improves print resolution during high-speed printing and reduces the rate of print defects during high-speed printing.

[0054] The present invention will be illustrated by the following examples, but is not intended to limit the scope of the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.

[0055] [Example 1] A coating liquid for an undercoat layer was prepared by stirring and dispersing the following components: Undercoat layer coating liquid 1 Calcined kaolin (trade name: Ansilex 90, manufactured by Engelhard, <oil absorption 90 cc / 100 g>) 100 parts Styrene-butadiene copolymer latex (solid content 48%) 35.4 parts 10% aqueous solution of polyvinyl alcohol 45 parts Water 157.1 parts Next, the undercoat layer coating liquid was applied to a support (54 g / m ２After blade coating on one side of the base paper, the coated paper was dried to a dry coating weight of 4.0 g / m ２ Thus, a coated paper with a primer layer was obtained.

[0056] The developer dispersions (Liquids A1 to A5), leuco dye dispersion (Liquid B), and sensitizer dispersions (Liquids C1 to C3) having the following formulations were each wet-ground in a sand grinder until the average particle size reached 0.5 microns. A1 liquid (developer dispersion) 4,4'-dihydroxydiphenyl sulfone 5.7 parts Polyvinyl alcohol 10% aqueous solution 5.1 parts Water 9.9 parts A2 liquid (developer dispersion) 4-hydroxy-4'-benzyloxydiphenyl sulfone (Nicca Chemical Co., Ltd., trade name: BPS-MA3) 6.0 parts Polyvinyl alcohol 10% aqueous solution 11.3 parts Water 6.5 parts A3 liquid (developer dispersion) 4,4'-bis (3- (phenoxycarbonylamino) methylphenylureido) diphenyl sulfone (Fine Ace Co., Ltd. UU) 3.5 parts Polyvinyl alcohol 10% aqueous solution 7.4 parts Water 3.3 parts A4 liquid (developer dispersion) N- [2- (3-phenylureido) phenyl] benzenesulfonamide (trade name NKK1304) 6.0 parts Polyvinyl alcohol 10% aqueous solution 7.5 parts Water 9.0 parts A5 solution (developer dispersion) N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (product name S-176) 3.5 parts Polyvinyl alcohol 10% aqueous solution 4.4 parts Water 5.3 parts Solution B (leuco dye dispersion) 3-dibutylamino-6-methyl-7-anilinofluoran (ODB-2) 2.85 parts Polyvinyl alcohol 10% aqueous solution 4.8 parts Water 3.5 parts Solution C1 (sensitizer dispersion) Diphenyl sulfone (manufactured by Sankosha, trade name: DPS) 5.7 parts Polyvinyl alcohol 10% aqueous solution 7.1 parts Water 8.6 parts Solution C2 (sensitizer dispersion) Stearic acid amide (manufactured by Fine Ace, trade name: Finawax) 5.7 parts Polyvinyl alcohol 10% aqueous solution 14.3 parts Water 3.8 parts Solution C3 (sensitizer dispersion) 1,2-bis-(3-methylphenoxy)ethane (manufactured by Sankosha, trade name: KS232) 0.5 parts, 10% aqueous solution of polyvinyl alcohol 0.6 parts, water 0.8 parts,

[0057] Next, the dispersions were mixed in the following proportions to prepare a coating liquid for the thermosensitive recording layer: Coating liquid for thermosensitive recording layer A1 liquid (developer dispersion) 20.7 parts B liquid (leuco dye dispersion) 11.1 parts C1 liquid (sensitizer dispersion) 21.4 parts C2 liquid (sensitizer dispersion) 23.8 parts Polyvinyl alcohol 10% aqueous solution 32 parts

[0058] The following materials were then mixed in the following proportions to prepare a coating liquid for the protective layer: 7.0 parts of flat kaolin (50% dispersion, manufactured by IMERYS under the trade name Contour 1500, aspect ratio: 30), 30 parts of a 10% aqueous solution of polyvinyl alcohol, 4.0 parts of a polyamide epichlorohydrin resin (manufactured by Seiko PMC under the trade name WS4030, solids content 25%), 2.2 parts of a modified polyamine resin (manufactured by Taoka Chemical under the trade name Sumirez Resin SPI-102A, solids content 45%), and 1.7 parts of zinc stearate (manufactured by Hydrin Z-7-30, solids content 30%, particle size 5.5 microns, Chukyo Yushi). Next, a coating film was formed on the undercoat layer of the undercoat-coated paper using a slide curtain coating device, with the coating liquid for the thermosensitive recording layer and the coating liquid for the protective layer being applied from the lower layer side. The coating film was then simultaneously multi-layered and curtain coated at a coating speed of 600 m / min. After drying, the film was subjected to a supercalendering treatment to obtain a dry coating weight of 1.8 g / m. ２ Heat-sensitive recording layer, dry coating weight 0.7 g / m ２ A heat-sensitive recording material having a protective layer of the formula (I) was obtained.

[0059] [Color development sensitivity] Using a TH-PMD manufactured by Okura Electric Co., Ltd., printing was performed on the prepared thermal recording medium with an applied energy of 0.35 mJ / dot or 0.42 mJ / dot. The image density after printing was measured with a Macbeth densitometer (using an amber filter). <Solvent resistance> Ethanol (50.0%) was applied to the blank area of ​​the prepared 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, and then visually evaluated according to the following criteria: ○: No color development at all △: Slight color development, but not a practical problem ×: Strong color development

[0060] <Printing running properties (head residue resistance)> A grid pattern of 10 cm in length was printed on the prepared thermal recording medium using a label printer (Resply R-8) manufactured by Sato Corporation, and the residue (head residue) adhering to the thermal head after printing was visually evaluated according to the following criteria: ◯: Almost no head residue was observed. △: A small amount of head residue was observed, but no gaps or smears were observed in the formed image, and this was of a level that posed no practical problems. ×: A large amount of head residue was observed, and gaps and smears were observed in the formed image.

[0061] <Stick Resistance> The prepared thermal recording medium was subjected to 100 mm solid printing using a thermal handy terminal printer (HT180 manufactured by Canon) in an environment of 0°C, and the printed matter was visually evaluated. ○: No streaky white voids in the printed area △: A few streaky white voids occurred in the printed area ×: Many streaky white voids occurred in the printed area [Print Defect Rate] The prepared thermal recording medium was used to print the Arabic numerals '2' and '3' in solid form using a label thermal printer (product name: 140XiIIIPlus) manufactured by Zebra at a printing speed of 8 inch / s and a printing speed of 2 inch / s, and the print defect rate was calculated using the following formula. Print defect rate = 100 - (colored area at a printing speed of 8 inches / s / colored area at a printing speed of 2 inches / s) (%) The colored area was measured by capturing the print image as digital data, and taking the pixels corresponding to grayscale 0 to 97 as the colored area, and integrating the total number of colored pixels to determine the colored area. The smaller the print defect rate, the finer the printing during high-speed printing, and a print defect rate of 35% or less is considered good.

[0062] [Example 2] Dry coating amount of the thermal recording layer was 2.1 g / m ２ A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the total content (solid content) of the leuco dye, developer and sensitizer in the thermosensitive recording layer was changed to 70.0% by weight. [Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the total content (solid content) of the leuco dye, developer and sensitizer in the thermosensitive recording layer was changed to 70.0% by weight. [Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the total content (solid content) of the leuco dye, developer and sensitizer in the thermosensitive recording layer was changed to 85.0% by weight.

[0063] [Example 5] Dry coating amount of protective layer: 1.0 g / m ２ A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the inorganic pigment in the protective layer was replaced with aluminum hydroxide. [Example 6] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that no lubricant was added to the protective layer. [Example 7] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the inorganic pigment in the protective layer was replaced with aluminum hydroxide. [Example 8] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the developer dispersion in the thermosensitive recording layer was replaced with 23.8 parts of A2 liquid and 14.2 parts of A3 liquid, the sensitizer dispersion was replaced with 1.9 parts of C3 liquid, and the leuco dye blending ratio was changed to 5.0 parts. [Example 9] A thermosensitive recording medium was prepared in the same manner as in Example 8, except that the developer dispersion in the thermosensitive recording layer was replaced with 22.5 parts of A4 liquid and 13.2 parts of A5 liquid.

[0064] [Comparative Example 1] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the total content (solid content) of the leuco dye, developer, and sensitizer was changed to 46.0% by weight by incorporating an inorganic pigment into the thermosensitive recording layer. [Comparative Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that no protective layer was provided.

[0065] The results are shown in Tables 1 and 2.

[0066]

[0067] As shown in Table 1, the thermosensitive recording media of the Examples had excellent color development sensitivity and print running properties. Furthermore, they also had excellent print resolution (print defect rate) during high-speed printing. In the Examples where kaolin with an aspect ratio of 30 or more was used as the inorganic pigment in the protective layer, color development sensitivity was further improved compared to Example 7, where aluminum hydroxide was used as the inorganic pigment. In the case of Example 9, where the developer contained the urea compounds (NKK1304 and S176) represented by the above-mentioned general formula (1), solvent resistance was improved compared to the other Examples.

[0068] On the other hand, in the case of Comparative Example 1, in which the total content (solid content) of the leuco dye, developer, and sensitizer in the thermosensitive recording layer was less than 70.0% by weight, the coating amount of the thermosensitive recording layer was 2.5 g / m ２In addition, the print resolution (print defect rate) during high-speed printing was poor, which is thought to be due to the reduced sensitivity. In the case of Comparative Example 2, in which no protective layer was provided, the color sensitivity was good, but the print running properties were poor.

Claims

1. A thermosensitive recording medium comprising a support, an undercoat layer, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye, an electron-accepting developer and a sensitizer, and a protective layer in this order, wherein the total content (solid content) of the leuco dye, the developer and the sensitizer in the thermosensitive recording layer is 70.0% by weight or more, and the coating amount of the thermosensitive recording layer is 2.5 g / m ２ The following is a thermal recording medium.

2. The coating amount of the protective layer is 2.5 g / m ２ 3. The thermosensitive recording medium according to claim 1, wherein:

3. The thermosensitive recording medium according to claim 1 or 2, wherein the thermosensitive recording layer does not contain an inorganic pigment.

4. The thermosensitive recording medium according to claim 1 or 2, wherein the thermosensitive recording layer does not contain a lubricant.

5. The thermal recording medium according to claim 1 or 2, wherein the developer contains a urea compound represented by the following general formula (1): (In the formula, X represents —O— or —NH—; R １ is a hydrogen atom or -SO ２ -R ３ represents R ３ represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R ２ represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

6. The heat-sensitive recording medium according to claim 1 or 2, wherein the protective layer contains an inorganic pigment having an aspect ratio of 30 or more.

7. The thermosensitive recording medium according to claim 1 or 2, wherein the protective layer contains a lubricant.

8. The thermal recording medium according to claim 1 or 2, wherein the printing defect rate represented by the following formula is 35% or less: 100 - (colored area at a printing speed of 8 inch / s / colored area at a printing speed of 2 inch / s) (%) 9. A method for producing a thermosensitive recording medium according to claim 1 or 2, wherein the thermosensitive recording layer and the protective layer are formed by applying a coating liquid for the thermosensitive recording layer and a coating liquid for the protective layer by a multi-layer curtain coating method, followed by drying.

10. The method for producing a thermosensitive recording medium according to claim 9, wherein the coating liquid for the thermosensitive recording layer does not contain a pigment.

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