Thermal recording body

Abstract

To provide a thermal recording body excellent in coloring sensitivity, printing runnability (specifically, head scum deposition resistance), and scratch resistance, and further having good printing precision at high-speed printing, and also to provide a manufacturing method thereof.SOLUTION: A thermal recording body includes, on a substrate: an undercoat layer; a thermal recording layer including a colorless or pale-colored electron-donating leuco dye, an electron-accepting developer and a sensitizer; and a protective layer, in this order. In the thermal recording layer, a total content (solid content) of the leuco dye, the developer and the sensitizer is 70.0 wt.% or more, and a coating weight of the thermal recording layer is 2.5 g / m2 or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermal recording medium utilizing a color-developing reaction between a colorless or pale-colored electron-donating leuco dye (hereinafter also referred to as a "leuco dye") and an electron-accepting developer (hereinafter also referred to as a "developer"), and a method for producing the same. [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.

[0003] 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.

[0004] In such applications, stable printing on thermal recording media 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 blended into the outermost layer, such as a protective layer (Patent Document 1, etc.). Also known is a thermosensitive recording medium in which the color development sensitivity is improved by simultaneously coating and drying a thermosensitive recording layer and a protective layer by a multi-layer curtain coating method (Patent Document 2, etc.). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-56184 A [Patent Document 2] Patent No. 5626218 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0006] However, even when such conventional techniques are used, it is difficult to achieve both color development sensitivity and print runnability (resistance to head residue adhesion and sticking). Therefore, an object of the present invention is to provide a thermal recording medium having good color development sensitivity, print running properties (particularly, resistance to head residue adhesion), and abrasion resistance, and further having good print resolution during high-speed printing, and a method for producing the same. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that color development sensitivity improves when the total content (solid content) of leuco dye, developer and sensitizer in the thermosensitive recording layer is 70.0% by weight or more. However, when the content of leuco dye, etc. in the thermosensitive recording layer is high, head residue and sticking become an issue, so a protective layer is provided. Furthermore, the provision of the protective layer improves scratch resistance. In addition, when the coating amount of the thermosensitive recording layer is 2.5 g / m 2 It was found that by reducing the amount of ink to less than 100 ppm, printing precision 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. Effect of the Invention

[0009] According to the present invention, it is possible to obtain a thermosensitive recording medium 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The thermosensitive recording medium of the present invention is a thermosensitive recording medium comprising 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, on a support, the total content (solid content) of the leuco dye, developer and sensitizer in the thermosensitive recording layer being 70.0% by weight or more, and the coating amount of the thermosensitive recording layer being 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 necessary, as long as they do not impede the desired effects for the above-mentioned problems.

[0012] <Undercoat layer> The thermal recording medium of the present invention has an undercoat layer on the support. 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.

[0013] 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.

[0014] <Thermal recording layer> The heat-sensitive 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 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.

[0015] <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)

[0016] <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,

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

[0018] <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

[0019] <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

[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-isopropoxyphenylsulfone phenyl)phenoxy]butane, the phenol condensation composition described in JP-A-2003-154760, the aminobenzenesulfonamide derivative 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-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), 4,4'-bis(3-(phenoxycarbonylamino)methylphenylureido)diphenylsulfone, compounds described in WO02 / 081229 or JP2002-301873A, and N,Examples of the 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, and 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 kinds. 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 JP2003-154760A is available, for example, under the trade name JKY-224 manufactured by API Corporation. The 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 polyhydric hydroxy aromatic compounds described in JP-A-10-258577 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. [ka] (In the formula, X represents -O- or -NH-; R 1 is a hydrogen atom or -SO2-R 3 R 3represents 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): [ka] (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): [ka] (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). [ka]

[0026] In the general formula (Chemical formula 2) and the general formula (Chemical formula 4), R 3 represents an optionally substituted alkyl group, aralkyl group, or aryl group, 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. 3 may be the same or different. R in the benzene ring of general formula (chemical formula 2) 1 The positions of -O- may be the same or different, and are preferably the 3-, 4- or 5-positions. R in the benzene ring of general formula (chemical formula 2) and general formula (chemical formula 4) 3 The positions of -SO2-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 the number of carbon atoms is preferably 1 to 12. 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 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.

[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-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.

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

[0032] 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.

[0033] 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.

[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. [ka]

[0035] 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 such compounds 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, and p-toluenesulfonamide. 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. When the total content (solid content) is 70.0% by weight or more, the color development sensitivity is improved. 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 weight of the heat-sensitive recording layer of the present invention is 2.5 g / m 2 or less, preferably 2.4 g / m 2 Less than or equal to 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 / m2 or less. 2 Even if the concentration is reduced below this level, the sensitivity can be maintained to a level acceptable for practical use. The lower limit of the coating weight of the thermal recording layer is, for example, 1.2 g / m 2 The coating weight of the thermal recording layer is 1.4 to 2.4 g / m 2 It is even more preferable that:

[0038] It is preferable that the thermosensitive recording layer of the present invention does not contain an inorganic pigment. If the thermosensitive recording layer contains an inorganic pigment, the total content (solid content) of the leuco dye, developer and sensitizer is reduced accordingly, and the color development sensitivity may decrease. 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.

[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 is reduced accordingly, and the color development sensitivity may decrease. Examples of the lubricant include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, silicone resins, and the like.

[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 lower than 95° C.). This Tg can be measured by differential scanning calorimetry (DS C). ), (meth)acrylic acid and other acrylic resins consisting of monomer components (excluding olefins) copolymerizable with (meth)acrylic acid, 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 are used by dissolving them in solvents such as water, alcohol, ketones, esters, and hydrocarbons, and can also be used in a state of being emulsified or dispersed in a paste form in water or other media, and can be used in combination depending on the required quality.

[0041] 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 the image area 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, antifoaming agents, antioxidants, fluorescent dyes, etc. can be used in the thermal recording layer.

[0042] 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, 0.01 to 10 parts by weight of stabilizer, and 0.01 to 10 parts by weight of other components are used per 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. In the present invention, in order to make the total content (solid content) of the leuco dye, developer and sensitizer 70.0% by weight or more, it is desirable to make the binder content small. However, if the binder content is less than 5% by weight, the coating properties, particularly the curtain film suitability, decrease, so the lower limit is preferably 5% by weight or more.

[0043] 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.

[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 (solid content) of leuco dye, developer and sensitizer of 70.0% by weight or more. As a result, the absolute amount of color former melted during printing increases, the area of ​​direct contact between the head and the color former increases, and the material that absorbs the melted color former relatively decreases, which tends to deteriorate the print running property and the stick resistance. Therefore, in the present invention, it is essential to provide a protective layer in order to obtain a thermosensitive recording medium having print running property (especially, resistance to head residue adhesion) and stick resistance. This protective layer mainly comprises a binder and a pigment, and may further contain a lubricant. As the binder, any of the binders usable in the above-mentioned thermosensitive recording layer can be used appropriately.

[0045] Examples of the pigment 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 having an aspect ratio of 30 or more, the surface smoothness of the protective layer is improved, and the print running properties (particularly, head residue adhesion resistance) are improved. An example of an inorganic pigment having an aspect ratio of 30 or more is kaolin. The aspect ratio is expressed as the maximum diameter of the pigment divided by its thickness (minimum length).

[0046] Examples of the lubricant include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, silicone resins, and the like. When the protective layer contains a lubricant, the surface smoothness of the protective layer is improved, and thus the print running properties (particularly, resistance to head residue adhesion) are improved. As described above, in the present invention, in order to increase the total content (solids content) of 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 smoothness as a 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 solution for the protective layer may contain various auxiliary agents such as stabilizers, ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc., which can be used in the above-mentioned heat-sensitive recording layer, as required.

[0048] The coating weight 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 2.0 g / m 2 It can be as follows: The lower limit of the coating amount of the protective layer is, for example, 0.4 g / m 2 The coating weight of the protective layer is 0.7 to 2.5 g / m 2 It is even more preferable that:

[0049] <Support> The support may be paper, synthetic paper, film, a plastic sheet, or the like.

[0050] 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. 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.

[0051] In particular, when the above-mentioned heat-sensitive recording layer and protective layer are formed by applying the heat-sensitive recording layer coating liquid and the protective layer coating liquid by a multi-layer curtain coating method and drying, the coating amount is 2.5 g / m 2Even with the low coating weight 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 high, and the print runnability (especially head residue adhesion resistance) is further improved. The coating method is preferably a simultaneous multi-layer curtain coating method. EXAMPLES

[0052] 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.

[0053] [Example 1] The following composition was mixed and dispersed to prepare a coating liquid for the undercoat layer. Undercoat layer coating liquid 1 Calcined kaolin (Engelhardt product name: Ansilex 90, <Oil absorption amount 90cc / 100g>) 100 parts Styrene-butadiene copolymer latex (48% solids) 35.4 parts Polyvinyl alcohol 10% aqueous solution 45 parts Water 157.1 parts Next, the undercoat layer coating solution was applied to the support (54 g / m 2 After blade coating on one side of the base paper, the paper is dried to a dry coating weight of 4.0 g / m 2 Thus, a coated paper with an undercoat layer was obtained.

[0054] The developer dispersions (Liquids A1 to 5), leuco dye dispersion (Liquid B), and sensitizer dispersions (Liquids C1 to 3) 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 liquid) 4,4'-Dihydroxydiphenyl sulfone 5.7 parts Polyvinyl alcohol 10% aqueous solution 5.1 parts Water 9.9 parts A2 liquid (developer dispersion liquid) 4-Hydroxy-4'-benzyloxydiphenyl sulfone (manufactured by Nicca Chemical Co., Ltd. Product name: BPS-MA3) 6.0 copies Polyvinyl alcohol 10% aqueous solution 11.3 parts 6.5 parts water A3 liquid (developer dispersion liquid) 4,4'-bis(3-(phenoxycarbonylamino)methylphenylureido)diphenyl sulfone (FineAce UU) 3.5 parts Polyvinyl alcohol 10% aqueous solution 7.4 parts 3.3 parts water A4 liquid (developer dispersion liquid) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (Product name NKK1304) 6.0 copies Polyvinyl alcohol 10% aqueous solution 7.5 parts Water 9.0 parts A5 liquid (developer dispersion liquid) 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 B liquid (leuco dye dispersion liquid) 3-Dibutylamino-6-methyl-7-anilinofluoran (ODB-2) 2.85 copies Polyvinyl alcohol 10% aqueous solution 4.8 parts 3.5 parts water C1 liquid (sensitizer dispersion liquid) Diphenyl sulfone (manufactured by Sankosha, product name: DPS) 5.7 parts Polyvinyl alcohol 10% aqueous solution 7.1 parts Water 8.6 parts C2 liquid (sensitizer dispersion liquid) Stearic acid amide (Finawax, product name, manufactured by FineAce Co., Ltd.) 5.7 parts Polyvinyl alcohol 10% aqueous solution 14.3 parts 3.8 parts water C3 liquid (sensitizer dispersion liquid) 1,2-bis-(3-methylphenoxy)ethane (manufactured by Sankosha, product name: KS232) 0.5 part Polyvinyl alcohol 10% aqueous solution 0.6 parts Water 0.8 parts

[0055] Next, the dispersions were mixed in the following ratio to prepare a coating liquid for the heat-sensitive recording layer. Coating liquid for thermal recording layer A1 liquid (developer dispersion liquid) 20.7 parts Solution B (leuco dye dispersion) 11.1 parts C1 solution (sensitizer dispersion) 21.4 parts C2 liquid (sensitizer dispersion liquid) 23.8 parts Polyvinyl alcohol 10% aqueous solution 32 parts

[0056] The following components were then mixed in the ratio shown below to prepare a coating liquid for the protective layer. Coating liquid for protective layer Flat kaolin (50% dispersion, IMERYS product name: Contour1500: aspect ratio: 30) 7.0 copies Polyvinyl alcohol 10% aqueous solution 30 parts Polyamide epichlorohydrin resin (Seiko PMC Corporation, product name: WS4030, Solid content 25%) 4.0 parts Modified polyamine resin (manufactured by Taoka Chemical Co., Ltd., product name: Sumirez Resin SPI-102A, Solid content 45%) 2.2 parts Zinc stearate (product name: Hydrin Z-7-30, solid content 30%, Particle size 5.5 microns, Chukyo Yushi) 1.7 parts Next, a coating film was formed on the undercoat layer of the undercoat layer coated paper from the bottom side using a slide curtain coating device, and the coating liquid for the thermosensitive recording layer and the coating liquid for the protective layer were simultaneously applied in a multi-layer curtain coating at a coating speed of 600 m / min. After drying, the coating was subjected to a supercalendering process to obtain a dry coating weight of 1.8 g / m. 2 Thermal recording layer, dry coating weight 0.7g / m 2 Thus, a heat-sensitive recording material having a protective layer of the above formula was obtained.

[0057] [Color development sensitivity] The thermal recording medium was printed with an applied energy of 0.35 mJ / dot or 0.42 mJ / dot using a TH-PMD manufactured by Okura Electric Co., Ltd. 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 part of the thermal recording medium with a cotton swab and then left at 23°C x After leaving the sample to stand for 24 hours under 50% RH environmental conditions, the sample was visually evaluated according to the following criteria. ○: No coloring at all △: Slight coloring, but not enough to cause any problems in practical use ×: Strong color development

[0058] <Printing performance (resistance to head residue)> A 10 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. ◯: Almost no head residue was observed. Δ: A small amount of head residue was observed, but the formed image was not blurred or smudged, and was of a level that did not cause any practical problems. ×: A large amount of head residue was observed, and the formed image had missing or faint marks.

[0059] <Stick resistance> The prepared thermal recording medium was subjected to 100 mm solid printing in a 0° C. environment using a thermal handy terminal printer (Canon HT180), and the print was visually evaluated. ○: No streaky white areas on the printed area △: Several white streaks appear in the printed area. ×: Numerous streaky white spots appear on the printed area. [Printing loss rate] The Arabic numerals '2' and '3' were printed solid on the prepared thermal recording medium using a Zebra label thermal printer (product name 140XiIIIPlus) at a printing speed of 8 inch / s and 2 inch / s, and the printing loss rate was calculated using the following formula. Print defect rate = 100-(colored area at print speed of 8 inch / s / colored area at print speed of 2 inch / s) (%) The colored area was measured by capturing the printed image as digital data, determining the pixels corresponding to grayscale levels 0 to 97 as the colored portion, and integrating the total number of colored pixels to determine the colored area. The smaller the rate of print defects, the finer the printing during high-speed printing, and a print defect rate of 35% or less is considered good.

[0060] [Example 2] The dry coating weight of the thermal recording layer is 2.1 g / m 2 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the above was replaced with the above. [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.

[0061] [Example 5] The dry coating weight of the protective layer is 1.0 g / m 2 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the above was replaced with the above. [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 thermal recording medium was prepared in the same manner as in Example 1, except that the developer dispersion in the thermal recording layer was changed to 23.8 parts of A2 liquid and 14.2 parts of A3 liquid, the sensitizer dispersion was changed to 1.9 parts of C3 liquid, and the leuco dye blend 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 changed to 22.5 parts of A4 liquid and 13.2 parts of A5 liquid.

[0062] [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.

[0063] The results are shown in Tables 1 and 2. [Table 1]

[0064] [Table 2]

[0065] As shown in Table 1, the thermosensitive recording medium of the present invention had excellent color development sensitivity and print running properties. Furthermore, the print definition (print defect rate) during high-speed printing was excellent. In each of the Examples in which kaolin having an aspect ratio of 30 or more was used as the inorganic pigment in the protective layer, the color development sensitivity was further improved compared to Example 7 in which aluminum hydroxide was used as the inorganic pigment. In the case of Example 9, in which the developer contained the urea compound represented by the above general formula (1) (NKK1304 and S176), the solvent resistance was improved compared to the other Examples.

[0066] 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 is less than 70.0% by weight, the coating amount of the thermosensitive recording layer is 2.5 g / m 2 In addition, the print resolution (print defect rate) during high-speed printing was poor, which is believed to be due to the reduced sensitivity. In the case of Comparative Example 2 in which no protective layer was provided, the color development sensitivity was good, but the print running properties were poor.

Claims

1. A thermal recording medium comprising a support, an undercoat layer, a thermal 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; the total content (solid content) of the leuco dye, the color developer and the sensitizer in the thermal recording layer is 70.0% by weight or more; The coating amount of the thermal 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. 3. The thermosensitive recording material according to claim 1, wherein the thermosensitive recording layer does not contain an inorganic pigment.

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

5. 3. The thermal recording material according to claim 1, wherein the developer contains a urea compound represented by the following general formula (1): 【Chemistry 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. 3. The thermal recording material according to claim 1, wherein the protective layer contains an inorganic pigment having an aspect ratio of 30 or more.

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

8. 3. The thermosensitive recording material according to claim 1, 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 the thermosensitive recording medium according to claim 1 or 2, comprising the steps of: The method for producing a thermosensitive recording medium includes coating the thermosensitive recording layer and the protective layer with 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.

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