Thermal recording medium

Abstract

To provide a heat-sensitive recording material which is excellent in terms of high-speed printing performance among various properties required for heat-sensitive recording materials, which is also excellent in terms of oil resistance, plasticizer resistance, printing runnability and the like.SOLUTION: A heat-sensitive recording material has a primer coating layer on a supporting body, and also has a heat-sensitive recording layer on the primer coating layer, the heat-sensitive recording layer containing a colorless or pale electron-donating leuco dye and an electron-accepting color developer. The heat-sensitive recording layer contains, as the electron-accepting color developer, a urea compound. The primer coating layer contains 50-95 wt.% of a pigment in terms of solid content, while containing 50 wt.% or more of plastic hollow particles relative to the pigment in terms of solid content.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Generally, a thermal recording medium is prepared by coating a coating liquid containing a colorless or light-colored leuco dye and a color developer on a support such as paper, synthetic paper, film, plastic, etc., and a recorded image is obtained by instantaneous chemical reaction caused by heating with a thermal head, hot stamp, heat pen, laser light, etc. Thermal recording media are widely used as recording media for facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, receipts at supermarkets and convenience stores, etc. In recent years, the use of thermal recording media has expanded to include a wide variety of applications, such as for various tickets, receipts, labels, bank ATMs, gas and electricity meter reading, and vouchers for car and horse racing betting. As a result, a variety of performance characteristics are required, such as water resistance, resistance to plasticizers in the image areas, heat resistance and oil resistance in the blank areas, and storage stability of the image areas and blank areas under harsh conditions. In response to such demands, a thermal recording medium has been disclosed that uses a combination of two specific types of color developers to improve water resistance, plasticizer resistance in image areas, and heat resistance in blank areas (Patent Document 1), as well as urea compounds used as color developers to improve required performance such as color density, whiteness, and storage stability of printed areas of thermal recording mediums (Patent Documents 2 and 3). Furthermore, as a method for improving the sensitivity and printing quality of a thermosensitive recording medium, it has been proposed to provide an undercoat layer containing hollow particles between the support and the thermosensitive recording layer (Patent Documents 4 and 5, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication 2015-80852 [Patent Document 2] International Publication WO2019 / 044462 [Patent Document 3] Patent Publication No. 2020-066148 [Patent Document 4] Patent Publication 2020-152027 [Patent Document 5] Patent 6782511 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

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

[0005] As a result of extensive research, the inventors have discovered that the above problems can be solved by incorporating a specific urea compound as a developer in a thermosensitive recording layer provided on a support, providing an undercoat layer between the support and the thermosensitive recording layer, and incorporating a specific amount of hollow plastic particles in this undercoat layer, thereby completing the present invention. That is, the present invention provides a thermosensitive recording medium comprising an undercoat layer on a support and a thermosensitive recording layer on the undercoat layer, the thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, the thermosensitive recording layer containing the following as the electron-accepting developer: (3) The thermosensitive recording medium contains a urea compound represented by the formula: wherein the undercoat layer contains a binder and a pigment, the pigment content being 50 to 95% by weight in terms of solid content, and the pigment contains hollow plastic particles, the hollow plastic particles comprising the pigment making up 50% by weight or more in terms of solid content. (3) A third urea compound represented by the following general formula (Chemical Formula 4): [ka] (In the formula, R 2 represents a hydrogen atom or an alkyl group, R 4 ~R 8 may be the same or different, and each represents a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group. Effect of the Invention

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

[0007] The thermal recording medium of the present invention has a thermal recording layer on a support and an undercoat layer between the support layer and the thermal recording layer, the thermal recording layer containing a specific urea compound as an electron-accepting developer, and the undercoat layer containing a specific amount of plastic hollow particles. Examples of various materials that can be used in the thermal recording layer of the thermal recording material of the present invention are given below, but binders, crosslinking agents, pigments, etc. can also be used in the undercoat layer and each coating layer provided as necessary, to the extent that they do not impede the desired effects for the above-mentioned problems.

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

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

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

[0011] In the general formula (5), n represents 0 or 1, and preferably 1. In the general formula (Chemical formula 5), ​​R 3 represents an alkyl group, an aralkyl group, or an aryl group, which may be substituted or unsubstituted. The alkyl group is, for example, a linear, branched, or alicyclic alkyl group, and preferably has 1 to 12 carbon atoms. The aralkyl group preferably has 7 to 12 carbon atoms, and the aryl group preferably has 6 to 12 carbon atoms. When these are substituted, the substituent is preferably an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom. In addition, when a plurality of R 3 may be the same or different. R in the benzene ring of the general formula (5) 3 The positions of -SO2-O- may be the same or different, and are preferably the 3-, 4- or 5-positions.

[0012] Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, and a lauryl group.

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

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

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

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

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

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

[0019] In the general formula (Chemical formula 3), R 2 , R 4 ~R 8 is defined as above. In the general formula (Chemical formula 3), R 4 ~R 8 is preferably a hydrogen atom, an alkyl group, or an alkoxy group. 4 , R 5 , R 7 , R 8 is preferably a hydrogen atom, and R 6 is preferably a hydrogen atom or an alkyl group. 6 As the alkyl group, an alkyl group is particularly preferable. The alkyl group (including those included in the alkylcarbonyloxy group, the alkylcarbonylamino group, the alkylsulfonylamino group, the monoalkylamino group, and the dialkylamino group) and the aryl group (including those included in the aryloxy group, the arylcarbonyloxy group, the arylcarbonylamino group, the arylsulfonylamino group, and the arylamino group) are defined in the same manner as the alkyl group and the aryl group in the above general formula (Chemical Formula 2). The alkoxy group is, for example, a linear, branched or alicyclic alkoxy group, and preferably has 1 to 12 carbon atoms. -O-(CONH) in the benzene ring of the general formula (Chemical formula 3) m The position of the -SO2-substituted phenyl group is preferably the 3-position, the 4-position or the 5-position (the same applies to the following general formulae (Chemical Formula 7) and (Chemical Formula 8)). In the general formula (Chemical Formula 3), m represents an integer of 0 to 2, preferably 0 to 1.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0039] In the thermosensitive recording medium of the present invention, an undercoat layer is provided between the support and the thermosensitive recording layer. The undercoat layer consists primarily of a binder and a pigment. As the binder used in the undercoat layer, the binders usable in the above-mentioned thermosensitive recording layer can be appropriately used. These binders may be used alone or in combination of two or more kinds.

[0040] The pigment used in the undercoat layer contains plastic hollow particles. The plastic hollow particles used in the present invention are fine hollow particles that have a thermoplastic resin shell and contain air or other gases inside, and are already in a foamed state. Examples of thermoplastic resins include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid esters, polyacrylonitrile, polybutadiene, or copolymers thereof. In particular, styrene-based resins such as polystyrene, acrylic resins such as polyacrylic acid esters and polyacrylonitrile, copolymers thereof, or copolymer resins mainly composed of polyvinylidene chloride and polyacrylonitrile are preferred. Such organic hollow particles are available as SX8782 manufactured by JSR Corporation, MH5055 and MH8108A manufactured by Nippon Zeon Corporation, Ropeake HP-91 manufactured by Rohm & Haas Japan, and Microsphere manufactured by Matsumoto Yushi Co., Ltd. The volumetric hollow ratio of the plastic hollow particles used in the present invention is preferably about 40 to 95%. By making the volumetric hollow ratio 40% or more, it is possible to improve the heat insulating property and further increase the color development performance. On the other hand, by making it 95% or less, it is possible to increase the strength of the shell of the hollow particles, effectively maintain the hollow state, and easily obtain an undercoat layer with good surface strength. Here, the volumetric hollow ratio is a value calculated by (d3 / D3)×100. In this formula, d indicates the inner diameter of the organic hollow particles, and D indicates the outer diameter of the organic hollow particles.

[0041] The undercoat layer may contain a pigment other than the hollow plastic particles, and for example, inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, talc, and organic pigments such as hollow plastic particles can be used. These pigments may be used alone or in combination of two or more. As the pigment other than the hollow plastic particles, it is preferable to use calcined kaolin. The content of the pigment in the undercoat layer is usually 50 to 95% by weight, preferably 70 to 90% by weight, based on the solid content of the undercoat layer. The content of the plastic hollow particles in the undercoat layer is 50% by weight or more, preferably 70 to 100% by weight, more preferably 80 to 100% by weight, based on the solid content of the pigment in the undercoat layer. 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.

[0042] The thermosensitive recording medium of the present invention may further have a protective layer on the thermosensitive recording layer. This protective layer mainly comprises a binder and a pigment, to which a crosslinking agent may further be added. As the binder, any of the binders usable in the above-mentioned heat-sensitive recording layer can be used appropriately, but preferred are carboxy-modified polyvinyl alcohol and non-core-shell type acrylic resins having a glass transition point (Tg) higher than 50° C. These binders may be used alone or in combination of two or more. Examples of the crosslinking agent include epichlorohydrin resins such as polyamine epichlorohydrin resins and polyamide epichlorohydrin resins, polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, and polyalkylene polyamine polyamide polyurea resins, and other polyamine / polyamide resins, glyoxal, methylol melamine, melamine formaldehyde resins, melamine urea resins, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, and ammonium chloride. It is preferable to incorporate an epichlorohydrin resin and a polyamine / polyamide resin as crosslinking agents in the protective layer, since the water resistance is particularly good. 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 lubricants, stabilizers, ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc., which can be used in the above-mentioned heat-sensitive recording layer, as required.

[0043] In the present invention, the means for coating the thermosensitive recording layer and the coating layers other than the thermosensitive recording layer, i.e., the protective layer, undercoat layer, etc., is not particularly limited, and can be applied according to well-known conventional techniques. For example, an off-machine coater or an on-machine coater equipped with various coaters such as an air knife coater, a rod blade coater, a bent blade coater, a bevel blade coater, a roll coater, or a curtain coater can be appropriately selected and used. The coating weight of the thermal recording layer and the coating layers other than the thermal recording layer is determined according to the required performance and recording suitability, and is not particularly limited. The general coating weight of the thermal recording layer is 2 to 12 g / m2 in terms of solid content. 2 The coating weight of the protective layer is about 0.5 to 5.0 g / m2 in solid content. 2 is preferred. Furthermore, various known techniques in the field of thermal recording media can be added as necessary, such as smoothing treatment such as supercalendering after coating of each coating layer. EXAMPLES

[0044] 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.

[0045] For the production of a thermal recording medium, each dispersion and coating liquid was prepared as follows. [Preparation of each coating liquid] The following compositions were stirred and dispersed to prepare undercoat layer coating solutions 1 to 4. <Coating solution for undercoat layer 1> Calcined kaolin (BASF product name: Ansilex 90) 40.0 parts Plastic hollow particles (manufactured by Nippon Zeon Co., Ltd., product name: Nipol MH8108A, hollow rate 50%, solid content 27%) 222.2 parts Styrene-butadiene copolymer latex (manufactured by Zeon Corporation, Product name: ST5526, solid content 48%) 10.0 parts <Coating solution 2 for undercoat layer> Calcined kaolin (Ansilex 90) 30.0 parts Plastic hollow particles (Nipol MH8108A) 259.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating solution for undercoat layer 3> Calcined kaolin (Ansilex 90) 20.0 parts Plastic hollow particles (Nipol MH8108A) 296.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating solution for undercoat layer 4> Calcined kaolin (Ansilex 90) 10.0 parts Plastic hollow particles (Nipol MH8108A) 333.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts

[0046] <Coating solution for undercoat layer 5> Plastic hollow particles (Nipol MH8108A) 370.0 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating solution 6 for undercoat layer> Calcined kaolin (Ansilex 90) 60.0 parts Plastic hollow particles (Nipol MH8108A) 148.1 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating solution 7 for undercoat layer> Calcined kaolin (Ansilex 90) 50.0 parts Plastic hollow particles (Nipol MH8108A) 185.1 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts Water 50.0 parts <Coating solution 8 for undercoat layer> Calcined kaolin (Ansilex 90) 100.0 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts Water 50.0 parts

[0047] The developer dispersions (Liquids A1 to A5), leuco dye dispersion (Liquid B), and sensitizer dispersion (Liquid C) having the following formulations were each wet-ground using a sand grinder until the average particle size reached 0.5 μm.

[0048] Developer dispersion liquid (A1 liquid) N,N'-Di-[3-(p-toluenesulfonyloxy)phenyl]urea (Hereinafter referred to as "Urea Compound 1") 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117, solids content 10%) 5.0 parts 1.5 parts water

[0049] Developer dispersion liquid (A2 liquid) A urea compound represented by the following chemical formula (9): (hereinafter referred to as "urea compound 2") 6.0 parts [ka] Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Developer dispersion liquid (A3 liquid) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (Hereinafter referred to as "Urea compound 3") 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0050] Developer dispersion liquid (A4 liquid) Urea urethane compound represented by the chemical formula (13) (Fine Ace Co., Ltd.) (Made by UU) 6.0 parts [ka] Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0051] Developer dispersion liquid (A5 liquid) 4-Hydroxy-4'-isopropoxydiphenyl sulfone (Mitsubishi Chemical Corporation, product name: NYDS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0052] Leuco dye dispersion (liquid B) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Industry Co., Ltd.) (product name: ODB-2) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0053] Sensitizer dispersion (liquid C) 1,2-bis-(3-methylphenoxy)ethane (Sankosha, Product name: KS232) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0054] Next, each dispersion was mixed in the following ratio to prepare a coating liquid for the heat-sensitive recording layer. <Coating solution for thermal recording layer> Developer dispersion liquid (A1 liquid) 36.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 25.0 parts

[0055] Next, the following components were mixed in the following proportions to prepare a coating liquid for the protective layer. <Protective layer coating liquid> Aluminum hydroxide dispersion (Martinsberg, Product name: Martyfin OL, solid content 50%) 9.0 parts Carboxy-modified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: KL318, degree of polymerization: about 1800, degree of saponification: 85~90mol%, Solid content 10%) 30.0 parts Polyamide epichlorohydrin resin (manufactured by Seiko PMC Corporation, product name: WS4030, solids content 25%) 4.0 parts Modified polyamine resin (manufactured by Taoka Chemical Co., Ltd., product name: Sumirez Resin SPI) -102A, 45% solids) 2.2 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., product name: Hydrin Z-7-30, Solid content 30%) 2.0 parts

[0056] [Example 1] Support (basis weight 47g / m 2 Coating solution 1 for the undercoat layer is applied to one side of a sheet of high-quality paper (10.0 g / m2) at a coating weight of 10.0 g / m2 (solid content). 2 After coating by the bent blade method so that the above-mentioned coating was performed, the coated paper was dried to obtain a coated paper with an undercoat layer. The coating solution for the thermal recording layer was applied to the undercoat layer of the undercoat layer coated paper at a coating weight of 6.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so as to obtain the above-mentioned coating composition, the coating composition was dried and then processed with a super calendar so as to obtain a smoothness of 100 to 500 seconds to prepare a thermal recording medium. [Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 3 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 18 parts of A4 liquid was added to the coating liquid for the thermosensitive recording layer.

[0057] [Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 3 for the undercoat layer was used instead of Coating Liquid 1 for the undercoat layer, and Liquid A2 was used instead of Liquid A1 in the coating liquid for the thermosensitive recording layer. [Reference example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 3 for the undercoat layer was used instead of Coating Liquid 1 for the undercoat layer, and Liquid A3 was used instead of Liquid A1 in the coating liquid for the thermosensitive recording layer. [Reference example 5] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 4 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 18 parts of A2 liquid was added to the coating liquid for the thermosensitive recording layer. [Reference example 6] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 2 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 18 parts of A3 liquid was added to the coating liquid for the thermosensitive recording layer. [Reference example 7] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 3 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 18 parts of A3 liquid were added to the coating liquid for the thermosensitive recording layer.

[0058] [Reference example 8] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 5 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 18 parts of A3 liquid were added to the coating liquid for the thermosensitive recording layer. [Reference example 9] The protective layer coating solution was applied to the thermal recording layer of the thermal recording layer coated paper at a coating weight of 2.0 g / m2 (solid content).2 A thermosensitive recording medium was prepared in the same manner as in Reference Example 8, except that the coating was performed by the rod blade method so as to obtain a coating having a smoothness of 100 to 500 seconds, followed by drying and processing with a super calendar. [Reference example 10] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 3 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, the amount of A1 liquid in the coating liquid for the thermosensitive recording layer was changed to 18 parts, and 9 parts of A3 liquid and 9 parts of A4 liquid were added to the coating liquid for the thermosensitive recording layer. [Reference example 11] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating liquid 3 for the undercoat layer was used instead of coating liquid 1 for the undercoat layer, and liquid A1 in the coating liquid for the thermosensitive recording layer was not blended, and 18 parts of liquid A2 and 18 parts of liquid A3 were added.

[0059] [Comparative Example 1] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the undercoat layer coating liquid 1 was changed to the undercoat layer coating liquid 6. [Comparative Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 3, except that no undercoat layer was provided. [Comparative Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 3, except that the undercoat layer coating liquid 3 was changed to the undercoat layer coating liquid 8. [Comparative Example 4] A thermosensitive recording medium was prepared in the same manner as in Reference Example 4, except that the undercoat layer coating liquid 3 was changed to the undercoat layer coating liquid 6.

[0060] [Comparative Example 5] A thermosensitive recording medium was prepared in the same manner as in Reference Example 5, except that the undercoat layer coating liquid 4 was changed to the undercoat layer coating liquid 6. [Comparative Example 6] A thermosensitive recording medium was prepared in the same manner as in Reference Example 5, except that no undercoat layer was provided. [Comparative Example 7] A thermosensitive recording medium was prepared in the same manner as in Reference Example 5, except that the undercoat layer coating liquid 4 was changed to the undercoat layer coating liquid 8. [Comparative Example 8] A thermosensitive recording medium was prepared in the same manner as in Reference Example 6, except that no undercoat layer was provided. [Comparative Example 9] A thermosensitive recording medium was prepared in the same manner as in Reference Example 6, except that the undercoat layer coating liquid 2 was changed to the undercoat layer coating liquid 8. [Comparative Example 10] A thermosensitive recording medium was prepared in the same manner as in Reference Example 11, except that no undercoat layer was provided.

[0061] [Comparative Example 11] A thermosensitive recording medium was prepared in the same manner as in Reference Example 11, except that the undercoat layer coating liquid 3 was changed to the undercoat layer coating liquid 8. [Comparative Example 12] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that undercoat layer coating liquid 1 was changed to undercoat layer coating liquid 7, and in the coating liquid for the thermosensitive recording layer, A1 liquid was not blended, and 36.0 parts of A5 liquid was blended. [Comparative Example 13] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that undercoat layer coating liquid 1 was changed to undercoat layer coating liquid 3, and in the coating liquid for the thermosensitive recording layer, A1 liquid was not blended, and 36.0 parts of A5 liquid was blended.

[0062] The prepared thermosensitive recording medium was evaluated as follows. <Color development performance (print density)> A checkered pattern was printed on the prepared thermal recording medium at a printing speed of 50 mm / sec and an applied energy of 0.41 mJ / dot using a TH-PMD (thermal recording paper print tester, equipped with a Kyocera thermal head) manufactured by Okura Electric Co., Ltd. The print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development performance (print density).

[0063] <Suitable for high-speed printing> A barcode (CODE39) was printed on the prepared thermal recording medium in the vertical direction (the barcode was perpendicular to the printer head movement direction) and the horizontal direction (the barcode was parallel to the printer head movement direction) using a Zebra 140XiIII label printer at a print level of +10 and a print speed of 30.4 cm / sec (12 in / sec). Next, the printed barcode was read using a barcode verifier (Honeywell, QCPC600, light source 640 nm) to evaluate the barcode readability. The evaluation results were recorded using the ANSI standard symbol grade. Symbol grade: The barcode is divided into 10 parts vertically and a reading test is carried out once for each part. The average value is expressed as a 5-level rating of A (Excellent), B, C, D, or F (Poor). <Heat resistance of blank areas> The prepared thermal recording medium was treated under environmental conditions of 80° C. for 24 hours, and then left to stand under environmental conditions of 23° C. and 50% RH for 3 hours. The density of the non-printed areas (blank areas) was measured with a Macbeth densitometer (RD-914, using an amber filter), and the background color development value was calculated from the difference in the values ​​before and after processing. The heat resistance of the non-printed areas (blank areas) was evaluated according to the following criteria. Background color value = (density of non-printed area after processing) - (density of non-printed area before processing) Excellent: Background color value is less than 0.3 Acceptable: Background color value is 0.3 or more and less than 0.5 Unacceptable: Background color value is 0.5 or more

[0064] <Plasticizer resistance> A checkered pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper print tester equipped with a Kyocera thermal head) at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. The printed thermosensitive recording medium was attached to a paper tube wrapped once with PVC wrap (Hi-wrap KMA, manufactured by Mitsui Chemicals), and then wrapped with three more layers of PVC wrap. The medium was then left to stand at 40°C for 24 hours. The print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter), and the residual rate was calculated from the values ​​before and after treatment to evaluate the plasticizer resistance. Residual rate (%) = (print density of printed area after processing / print density of printed area before processing) x 100 Excellent: Survival rate is 90% or more Acceptable: Residual rate is 70% or more but less than 90% Not acceptable: Less than 70% remaining <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. Excellent: Almost no head residue was observed. Pass: A small amount of head residue was observed, but the formed image was not blurred or missing, and was not of a level that would cause any practical problems. Poor: A large amount of head residue was observed, and the formed image had gaps and faint spots.

[0065] The results are shown in the table below. [Table 1]

[0066] [Table 2]

Claims

1. A thermosensitive recording medium comprising an undercoat layer provided on a support, and a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer provided on the undercoat layer, wherein the thermosensitive recording layer contains a urea compound represented by the following formula (3) as the electron-accepting developer, the undercoat layer contains a binder and a pigment, the pigment content being 50 to 95% by weight in terms of solid content, and the pigment contains hollow plastic particles, the hollow plastic particles accounting for 50% by weight or more in terms of solid content. (3) A third urea compound represented by the following general formula (Chemical Formula 4): 【Chemistry 4】 (In the formula, R ２ represents a hydrogen atom or an alkyl group; R ４ ~R ８ may be the same or different, and each represents a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group.

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

3. A thermal recording medium as described in claim 1 or 2, wherein the total content (solid content) of the urea compound in the thermal recording layer is 1.0 to 70.0% by weight.

4. A thermal recording medium described in any one of claims 1 to 3, wherein the volumetric hollowness of the plastic hollow particles is 40 to 95%.

5. The undercoat layer, (i) The pigment contains 50 to 95% by weight of solid content, and the pigment contains 80 to 100% by weight of hollow plastic particles in terms of solid content, or (ii) The heat-sensitive recording material according to claim 1, wherein the pigment is contained in an amount of 70 to 90% by weight in terms of solid content, and the pigment contains hollow plastic particles in an amount of 70 to 100% by weight in terms of solid content.

6. A thermal recording medium as described in claim 1 or 5, wherein when the undercoat layer contains a pigment other than plastic hollow particles, the pigment contains calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, or talc.

7. A thermal recording medium according to claim 1, wherein the undercoat layer contains 70 to 100% by weight of hollow plastic particles in the pigment in terms of solid content.

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