Heat-sensitive recording material

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] The present invention relates to a thermal recording medium that utilizes a color development reaction between a colorless or light-colored electron-donating leuco dye (hereinafter also referred to as "leuco dye") and an electron-accepting color developer (hereinafter also referred to as "color developer"), and is excellent in high-speed printing performance, and further excellent in oil resistance, plasticizer resistance, print running performance, etc.

Background Art

[0002] Generally, a thermal recording medium is obtained by coating a support such as paper, synthetic paper, film, plastic, etc. with a coating liquid containing a colorless or light-colored leuco dye and a color developer, and color develops by an instantaneous chemical reaction due to heating by a thermal head, hot stamp, thermal pen, laser light, etc., and a recorded image is obtained. 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, thermal recording media have also been expanding to various applications such as for various tickets, receipts, labels, bank ATMs, gas and electricity meter readings, and money tickets such as horse racing tickets. Therefore, various performances such as water resistance, plasticizer resistance of the image part, heat resistance of the blank part, oil resistance, and storage stability of the image part and the blank part under harsh conditions have been required. In response to such requirements, a thermal recording medium (Patent Document 1) in which water resistance, plasticizer resistance of the image part, heat resistance of the blank part, etc. are improved by using a combination of specific two types of color developers, and a urea compound (Patent Documents 2 and 3) as a color developer for improving required performances such as color density, whiteness, and storage stability of the printed part of the thermal recording medium have been disclosed. Also, as a method for improving the sensitivity and print quality of a thermal recording medium, it has been proposed to provide an undercoat layer containing hollow particles between the support and the thermal recording layer (Patent Documents 4, 5, etc.).

Prior Art Documents

Patent Documents

[0003] Patent Document 1 JP-A-2015-80852 Patent Document 2 International Publication WO2019 / 044462 Patent Document 3 JP-A-2020-066148 Patent Document 4 JP-A-2020-152027 Patent Document 5 Japanese Patent No. 6782511 Disclosure of the Invention Problems to be Solved by the Invention

[0004] Therefore, an object of the present invention is to provide a thermal recording medium that is excellent in high-speed printing performance among various performances required for a thermal recording medium, and is further excellent in oil resistance, plasticizer resistance, printing running performance, and the like. Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have found that the above problems can be solved by including a specific urea compound as a color developer in a thermal recording layer provided on a support, providing an undercoat layer between the support and the thermal recording layer, and including a specific amount of plastic hollow particles in the undercoat layer, and have completed the present invention. That is, the present invention provides a thermal recording medium in which an undercoat layer is provided on a support, and a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting color developer is provided on the undercoat layer, wherein the thermal recording layer contains a urea compound represented by the following formula (3) as an electron-accepting color developer, the undercoat layer contains a binder and a pigment, the pigment contains 50 to 95% by weight of a solid content, the pigment contains plastic hollow particles, and the plastic hollow particles in the pigment contain 50% by weight or more of a solid content. (3) A third urea compound represented by the following general formula (Chemical Formula 4), [Chemical Formula] (In the formula, R 2represents a hydrogen atom or an alkyl group, and 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. ) [Advantages of the Invention]

[0006] According to the present invention, it is possible to provide a thermal recording medium having coloring performance and excellent high-speed printing property, and further, it is possible to provide a thermal recording medium having excellent oil resistance, plasticizer resistance, print running property, etc. [Embodiments for Carrying Out the Invention]

[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 contains a specific urea compound as an electron-accepting developer, and the undercoat layer contains a specific amount of plastic hollow particles. Hereinafter, various materials used in the thermal recording layer of the thermal recording medium of the present invention will be exemplified, but binders, crosslinking agents, pigments, etc. can also be used in the undercoat layer and each coating layer provided as necessary as long as they do not inhibit the desired effects on the above problems.

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

Chemical formula

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

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

Chemical formula

[0011] In the general formula (Formula 5), n represents 0 or 1, preferably 1. In the general formula (Formula 5), R 3 represents an alkyl group, an aralkyl group or an aryl group which may be substituted or unsubstituted. This alkyl group is, for example, a linear, branched or alicyclic alkyl group, and the number of carbon atoms is preferably 1 to 12. The number of carbon atoms of this aralkyl group is preferably 7 to 12, and the number of carbon atoms of this aryl group is preferably 6 to 12. 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. Also, a plurality of R 3 may be the same or different. The position of R 3 -SO2-O- in the benzene ring of the general formula (Formula 5) may be the same or different, and is preferably the 3-position, 4-position or 5-position.

[0012] Examples of this 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, a lauryl group, and the like.

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

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

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

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

[0017] Also, as the first urea compound of the present invention, for example, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-ethyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-5-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-propyl-phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(1-naphthalenesulfonyloxy)phenyl]urea, N,N'-di-[3-(2-naphthalenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-ethylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-propylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-isopropylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-t-butylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m,p-dimethoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-ethoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-propoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-butoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-cumylbenzylsulfonyloxy)phenyl]urea, N,N'-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, N,N'-di-[3-(benzylsulfonyloxy)phenyl]urea, and the like, but not limited thereto.,

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

[0019] In the general formula (Formula 3), R 2 , R 4 ~R 8 are defined in the same manner as above. In the general formula (Formula 3), R 4 ~R 8 are preferably a hydrogen atom, an alkyl group, or an alkoxy group. In particular, R 4 , R 5 , R 7 , R 8 are preferably a hydrogen atom, and R 6 is preferably a hydrogen atom or an alkyl group. R 6 is particularly preferably an alkyl group. This alkyl group (including those contained in an alkylcarbonyloxy group, an alkylcarbonylamino group, an alkylsulfonylamino group, a monoalkylamino group, and a dialkylamino group), and an aryl group (including those contained in an aryloxy group, an arylcarbonyloxy group, an arylcarbonylamino group, an arylsulfonylamino group, and an arylamino group) are defined in the same manner as the alkyl group and the aryl group in the above general formula (Formula 2). This 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 (Formula 3) m The position of the -SO2-substituted phenyl group is preferably the 3-position, 4-position or 5-position (the same applies to the following general formula (Formula 7) and general formula (Formula 8)). In the general formula (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 (Formula 7) or the following general formula (Formula 8) is preferred.

Chemical formula

Chemical formula

[0021] The third urea compound used in the present invention is represented by the following formula (Formula 4).

Chemical formula

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

Chemical formula

[0023] The content of the urea compound in the heat-sensitive recording layer of the present invention (solid content, total amount when a plurality of urea compounds are included) 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 heat-sensitive recording layer of the present invention is 1.0 to 50.0% by weight, preferably 5.0 to 40.0% by weight. Further, 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 former other than the first to second urea compounds. Examples of such color formers 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, 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-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)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, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)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), the compounds described in WO02 / 081229 or JP-A-2002-301873, and N,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-toluenesulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, aromatic carboxylic acids, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc. Further, an antipyrine complex of zinc thiocyanate, a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acids, etc. are mentioned. These 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-A-2003-154760 is available, for example, under the trade name JKY-224 manufactured by API Corporation. Also, the compounds described in WO02 / 081229, etc. are available under the trade names NKK-395, D-100 manufactured by Nippon Soda Co., Ltd. In addition, it can also contain metal chelate type coloring components such as higher fatty acid metal double salts and polyvalent hydroxyaromatic compounds described in JP-A-10-258577.,

[0025] When the heat-sensitive recording layer of the present invention contains a developer other than the first to second urea compounds, the total content (solid content) of the first to second urea compounds used with respect to all the developers (including the first to second urea compounds) contained in the heat-sensitive recording layer is preferably 50% by weight or more, more preferably 80% by weight or more, still more preferably 90% by weight or more.

[0026] As the leuco dyes used in the present invention, all those known in the conventional pressure-sensitive or heat-sensitive recording paper fields can be used, and there are no particular restrictions, but triphenylmethane compounds, fluoran compounds, fluorene compounds, divinyl compounds, etc. are preferred. Specific examples of typical colorless to pale dyes (dye precursors) are shown below. These dye precursors may be used alone or in admixture of two or more.

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

[0028] <Fluoran-based leuco dye> 3-Diethylamino-6-methylfluoran, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-6-methyl-7-(o-chloroanilino)fluorane, 3-diethylamino-6-methyl-7-(p-chloroanilino)fluorane, 3-diethylamino-6-methyl-7-(o-fluoroanilino)fluorane, 3-diethylamino-6-methyl-7-(m-methylanilino)fluorane, 3-diethylamino-6-methyl-7-n-octylanilinofluorane, 3-diethylamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-chloro-7-p-methylanilinofluorane, 3-diethylamino-6-ethoxyethyl-7-anilinofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-7-(o-chloroanilino)fluorane, 3-diethylamino-7-(p-chloroanilino)fluorane, 3-diethylamino-7-(o-fluoroanilino)fluorane, 3-diethylamino-benz[a]fluorane, 3-diethylamino-benz[c]fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluorane, 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluorane, 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluorane, 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluorane, 3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluorane3-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, 3-(N-ethyl-N-xylylamino)-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-phenylaminophenyl)aminoanilinofluoran, 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluorane,

[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-based 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] <Others> 3-(4-Diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,6-bis(diethylamino)fluorane-γ-(3'-nitro)anilinolactam, 3,6-bis(diethylamino)fluorane-γ-(4'-nitro)anilinolactam, 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrile ethane, 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]-dimethyl methylmalonate

[0032] As the sensitizer used in the present invention, conventionally known sensitizers can be used. Examples of such sensitizers include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montan 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-naphthyl carbonate, 1,4-diethoxynaphthalene, phenyl 1-hydroxy-2-naphthoate, 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, and the like. These sensitizers may be used alone or in combination of two or more.

[0033] Examples of the pigment used 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, etc., and they can also be used in combination according to 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, polyacrylate ester, polyvinyl butyral, polystyrene and their copolymers, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin, etc. These polymer substances can be used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., or can be used in a state of being emulsified or dispersed in a paste form in water or other media, and can also be used in combination according to the required quality.

[0035] Examples of the lubricant used in the present invention include metal fatty acid salts such as zinc stearate and calcium stearate, waxes, silicone resins, etc.

[0036] In the present invention, within a range that does not inhibit the desired effects against the above problems, as stabilizers for improving the oil resistance and the like of the image portion, 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 also be added. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, defoaming agents, antioxidants, fluorescent dyes, etc. can be used.

[0037] The types and amounts of the leuco dye, developer, sensitizer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. Usually, 0.5 to 10 parts by weight of the developer, 0.1 to 10 parts by weight of the sensitizer, 0.5 to 20 parts by weight of the pigment, 0.01 to 10 parts by weight of the stabilizer, and about 0.01 to 10 parts by weight of other components are used with respect to 1 part by weight of the leuco dye. It is appropriate that the binder is about 5 to 25% by weight in the solid content of the heat-sensitive recording layer.

[0038] In the present invention, the leuco dye, developer, and materials added as necessary are atomized to a particle diameter of several microns or less by a pulverizer such as a ball mill, attritor, sand grinder, or an appropriate emulsifying device, and a binder and various additive materials are added according to the purpose to obtain a coating solution. As the solvent used for this coating solution, water or alcohol can be used, and its solid content is about 20 to 40% by weight.

[0039] An undercoat layer is provided between the support and the heat-sensitive recording layer in the heat-sensitive recording body of the present invention. This undercoat layer mainly consists of a binder and a pigment. As the binder used for the undercoat layer, the binders that can be used for the above-described heat-sensitive recording layer can be appropriately used. These binders may be used alone or in combination of two or more.

[0040] The primer layer contains plastic hollow particles as a pigment. The plastic hollow particles used in the present invention have a thermoplastic resin as a shell and contain air or other gases inside, and are minute hollow particles that are already in a foamed state. Examples of the thermoplastic resin include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylate, polyacrylonitrile, polybutadiene, or copolymers thereof. In particular, styrene resins such as polystyrene, acrylic resins such as polyacrylate 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, MH8108A manufactured by Nippon Zeon Co., Ltd., Rohpeik HP-91 manufactured by Rohm & Haas Japan Co., Ltd., Microsphere manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., etc. The volume hollow ratio of the plastic hollow particles used in the present invention is preferably about 40 to 95%. By setting the volume hollow ratio to 40% or more, the heat insulation property can be improved and the coloring performance can be further enhanced. On the other hand, by setting it to 95% or less, the strength of the shell of the hollow particles can be increased to effectively maintain the hollow state, and it becomes easy to obtain a primer layer with good surface strength. Here, the volume hollow ratio is a value obtained by (d3 / D3)×100. In the formula, d represents the inner diameter of the organic hollow particles, and D represents the outer diameter of the organic hollow particles.

[0041] The primer layer may contain pigments other than plastic hollow particles. For example, inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, talc, etc., and organic pigments such as plastic hollow particles can be used. These pigments may be used alone or in combination of two or more. As a pigment other than plastic hollow 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 undercoat layer (solid content). 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 pigment (solid content) in the undercoat layer. In the coating liquid of the undercoat layer, various auxiliaries such as a dispersant, a plasticizer, a pH adjuster, an antifoaming agent, a water retention agent, a preservative, a coloring dye, and an ultraviolet absorber may be appropriately blended as needed.

[0042] The heat-sensitive recording medium of the present invention may further have a protective layer on the heat-sensitive recording layer. This protective layer mainly consists of a binder and a pigment, and a crosslinking agent may be further added thereto. As this binder, the binders that can be used for the above-mentioned heat-sensitive recording layer can be appropriately used, but carboxy-modified polyvinyl alcohol and non-core-shell type acrylic resins having a glass transition point (Tg) higher than 50 °C are preferable. These binders may be used alone or in combination of two or more. Examples of this crosslinking agent include epichlorohydrin-based resins such as polyamine epichlorohydrin resin and polyamide epichlorohydrin resin, polyamide urea-based resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea-based resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, or polyamine / polyamide-based resins such as polyalkylene polyamine polyamide polyurea resin, glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, ammonium chloride, etc. It is preferable to contain an epichlorohydrin-based resin and a polyamine / polyamide-based resin as crosslinking agents in the protective layer because the water resistance becomes particularly good. The amount of the binder in the protective layer or the total amount of the binder and the pigment is usually 80.0 to 100.0% by weight, preferably 90.0 to 100.0% by weight in terms of solid content, and it is preferable that the binder is about 30.0 to 300.0 parts by weight with respect to 100 parts by weight of the pigment. If necessary, various auxiliaries such as lubricants, stabilizers, ultraviolet absorbers, dispersants, defoamers, antioxidants, fluorescent dyes, etc., which can be used for the above-mentioned heat-sensitive recording layer, may be appropriately blended in the coating liquid for the protective layer.

[0043] In the present invention, the means for coating the heat-sensitive recording layer and the coating layers other than the heat-sensitive recording layer, that is, the protective layer, the undercoat layer, etc. are not particularly limited, and can be applied according to well-known and commonly used 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 vent blade coater, a bevel blade coater, a roll coater, a curtain coater, etc. is appropriately selected and used. The coating amount of the heat-sensitive recording layer and the coating layers other than the heat-sensitive recording layer is determined according to the required performance and recording suitability, and is not particularly limited. However, the general coating amount of the heat-sensitive recording layer is 2 to 12 g / m in terms of solid content 2 and the coating amount of the protective layer is preferably 0.5 to 5.0 g / m in terms of solid content. 2 is preferable. In addition, various known techniques in the field of heat-sensitive recording media can be appropriately added as needed, such as performing a smoothing treatment such as supercalendering after coating each coating layer.

Examples

[0044] Hereinafter, the present invention will be illustrated by examples, but it is not intended to limit the present invention. In each of the examples and comparative examples, unless otherwise specified, "parts" means "parts by weight" and "%" means "% by weight".

[0045] For the production of the heat-sensitive recording medium, each dispersion liquid and coating liquid were prepared as follows. [Preparation of each coating liquid] A formulation consisting of the following formulation was stirred and dispersed to prepare coating liquids 1 to 4 for the undercoat layer. <Coating Liquid 1 for Undercoat Layer> Fired kaolin (manufactured by BASF, trade name: Anxilex 90) 40.0 parts Plastic hollow particles (manufactured by Nippon Zeon Co., Ltd., trade name: Nipol MH8108A, hollowness 50%, solid content 27%) 222.2 parts Styrene-butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd., trade name: ST5526, solid content 48%) 10.0 parts <Coating Liquid 2 for Undercoat Layer> Fired kaolin (Anxilex 90) 30.0 parts Plastic hollow particles (Nipol MH8108A) 259.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating Liquid 3 for Undercoat Layer> Fired kaolin (Anxilex 90) 20.0 parts Plastic hollow particles (Nipol MH8108A) 296.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating Liquid 4 for Undercoat Layer> Fired kaolin (Anxilex 90) 10.0 parts Plastic hollow particles (Nipol MH8108A) 333.3 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts

[0046] <Coating Liquid 5 for Undercoat Layer> Plastic hollow particles (Nipol MH8108A) 370.0 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating Liquid 6 for Undercoat Layer> Fired kaolin (Anxilex 90) 60.0 parts Plastic hollow particles (Nipol MH8108A) 148.1 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts <Coating Liquid 7 for Undercoat Layer> Fired kaolin (Anshilex 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 liquid 8 for undercoat layer> Fired kaolin (Anshilex 90) 100.0 parts Styrene-butadiene copolymer latex (ST5526) 10.0 parts Water 50.0 parts

[0047] The developer dispersion liquids (A1 to 5 liquids), leuco dye dispersion liquid (B liquid), and sensitizer dispersion liquid (C liquid) with the following compositions were each wet-milled separately with 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 Fully saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., trade name: PVA117, solid content 10%) 5.0 parts Water 1.5 parts

[0049] Developer dispersion liquid (A2 liquid) Urea compound represented by the following chemical formula (Chemical formula 9) (Hereinafter referred to as "urea compound 2".) 6.0 parts

Chemical formula

[0050] Color developer dispersion (A4 solution) Urea urethane compound represented by chemical formula (Chemical formula 13) (manufactured by Fine Ace Co., Ltd.) UU) 6.0 parts

Chemical formula

[0051] Color developer dispersion (A5 solution) 4-Hydroxy-4'-isopropoxydiphenyl sulfone (manufactured by Mitsubishi Chemical Corporation, trade name: NYDS) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0052] Leuco dye dispersion (B solution) 3-Dibutylamino-6-methyl-7-anilinofluoran (manufactured by Yamamoto Chemical Co., Ltd.) Product name: ODB-2) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0053] Sensitizer dispersion (C solution) 1,2-Bis-(3-methylphenoxy)ethane (manufactured by Sanko Co., Ltd.) Product name: KS232) 6.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

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

[0055] Next, a coating liquid for the protective layer was prepared by mixing a formulation having the following ratios. [Protective layer coating liquid] Aluminum hydroxide dispersion (manufactured by Martinswerke GmbH, Product name: Martifin OL, solid content 50%): 9.0 parts Carboxy-modified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: KL318, degree of polymerization: approximately 1800, saponification degree: 85 - 90 mol%, solid content 10%): 30.0 parts Polyamide epichlorohydrin resin (manufactured by Seiko PMC Co., Ltd., product name: WS4030, solid content 25%): 4.0 parts Modified polyamine resin (manufactured by Tago Chemical Co., Ltd., product name: Sumirez Resin SPI -102A, solid content 45%): 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] On one side of a support (high-quality paper with a basis weight of 47 g / m 2 ), Coating Liquid 1 for the undercoat layer was applied by the knife-over-roll method so that the coating amount in terms of solid content was 10.0 g / m 2 . After drying, an undercoat layer-coated paper was obtained. On the undercoat layer of this undercoat layer-coated paper, the coating liquid for the heat-sensitive recording layer was applied by the rod coating method so that the coating amount in terms of solid content was 6.0 g / m 2 . After drying, it was processed with a supercalender so that the smoothness became 100 - 500 seconds to produce a heat-sensitive recording medium. [Example 2] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 3 for the undercoat layer was used. The blending amount of liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and 18 parts of liquid A4 was further added to the coating liquid for the heat-sensitive recording layer. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this.

[0057] [Example 3] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 3 for the undercoat layer was used. Instead of using liquid A1 in the coating liquid for the heat-sensitive recording layer, liquid A2 was used. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this. [Reference Example 4] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 3 for the undercoat layer was used. Instead of using liquid A1 in the coating liquid for the heat-sensitive recording layer, liquid A3 was used. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this. [Reference Example 5] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 4 for the undercoat layer was used. The blending amount of liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and 18 parts of liquid A2 was further added to the coating liquid for the heat-sensitive recording layer. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this. [Reference Example 6] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 2 for the undercoat layer was used. The blending amount of liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and 18 parts of liquid A3 was further added to the coating liquid for the heat-sensitive recording layer. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this. [Reference Example 7] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 3 for the undercoat layer was used. The blending amount of liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and 18 parts of liquid A3 was further added to the coating liquid for the heat-sensitive recording layer. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this.

[0058] [Reference Example 8] Instead of using the coating liquid 1 for the undercoat layer, coating liquid 5 for the undercoat layer was used. The blending amount of liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and 18 parts of liquid A3 was further added to the coating liquid for the heat-sensitive recording layer. A heat-sensitive recording medium was produced in the same manner as in Example 1 except for this. [Reference Example 9] On the heat-sensitive recording layer of the heat-sensitive recording layer-coated paper, the protective layer coating liquid was applied at a coating amount of 2.0 g / m in terms of solid content2 After coating by the rod blade method so as to obtain the following, drying was carried out, and a heat-sensitive recording medium was produced in the same manner as in Reference Example 8 except that the smoothness was adjusted to 100 to 500 seconds using a supercalender. [Reference Example 10] A heat-sensitive recording medium was produced 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 blending amount of Liquid A1 in the coating liquid for the heat-sensitive recording layer was changed to 18 parts, and further 9 parts of Liquid A3 and 9 parts of Liquid A4 were added to the coating liquid for the heat-sensitive recording layer. [Reference Example 11] A heat-sensitive recording medium was produced 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, Liquid A1 in the coating liquid for the heat-sensitive recording layer was not blended, and 18 parts of Liquid A2 and 18 parts of Liquid A3 were added.

[0059] [Comparative Example 1] A heat-sensitive recording medium was produced in the same manner as in Example 1, except that Coating Liquid 1 for the undercoat layer was changed to Coating Liquid 6 for the undercoat layer. [Comparative Example 2] A heat-sensitive recording medium was produced in the same manner as in Example 3, except that no undercoat layer was provided. [Comparative Example 3] A heat-sensitive recording medium was produced in the same manner as in Example 3, except that Coating Liquid 3 for the undercoat layer was changed to Coating Liquid 8 for the undercoat layer. [Comparative Example 4] A heat-sensitive recording medium was produced in the same manner as in Reference Example 4, except that Coating Liquid 3 for the undercoat layer was changed to Coating Liquid 6 for the undercoat layer.

[0060] [Comparative Example 5] A heat-sensitive recording medium was produced in the same manner as in Reference Example 5, except that Coating Liquid 4 for the undercoat layer was changed to Coating Liquid 6 for the undercoat layer. [Comparative Example 6] A heat-sensitive recording medium was produced in the same manner as in Reference Example 5, except that no undercoat layer was provided. [Comparative Example 7] A heat-sensitive recording medium was produced in the same manner as in Reference Example 5, except that Coating Liquid 4 for the undercoat layer was changed to Coating Liquid 8 for the undercoat layer. [Comparative Example 8] A thermal recording medium was produced in the same manner as in Reference Example 6, except that an undercoat layer was not provided. [Comparative Example 9] A thermal recording medium was produced 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 thermal recording medium was produced in the same manner as in Reference Example 11, except that an undercoat layer was not provided.

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

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

[0063] <High-speed printing suitability> Regarding the produced thermal recording medium, using a Zebra label printer 140XiIII, a barcode (CODE39) was printed in the vertical direction (the barcode is orthogonal to the moving direction of the printer head) and the horizontal direction (the barcode is parallel to the moving direction of the printer head) at a printing level of +10 and a printing speed of 30.4 cm / sec (12 inches / sec). Next, a barcode verification machine (Honeywell, QCPC600, light source 640 nm) was used to perform a reading test on the printed barcode, and the barcode readability was evaluated. The evaluation results were recorded in symbol grades according to the ANSI standard. Symbol grade: The barcode is divided into 10 equal parts perpendicular to the bars, and a reading test is performed once at each location. The average value is represented by a five-level evaluation of (excellent) A, B, C, D, F (poor). <Heat resistance of the blank paper part> For the prepared thermal recording medium, after being treated under environmental conditions of 80 °C for 24 hours, it was left standing under environmental conditions of 23 °C × 50% RH for 3 hours. The density of the non-printed part (blank paper part) was measured with a Macbeth densitometer (RD-914, using an amber filter). The background color development value was calculated from the difference in values before and after the treatment, and the heat resistance of the non-printed part (blank paper part) was evaluated according to the following criteria. Background color development value = (density of the non-printed part after treatment) - (density of the non-printed part before treatment) Excellent: The background color development value is less than 0.3 Acceptable: The background color development value is 0.3 or more and less than 0.5 Unacceptable: The background color development value is 0.5 or more

[0064] <Plasticizer resistance> For the prepared thermal recording medium, using TH-PMD manufactured by Okura Electric Co., Ltd. (thermal recording paper printing tester equipped with a thermal head manufactured by Kyocera Corporation), a checkered pattern was printed at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. The printed thermal recording medium was pasted onto a paper tube after being wrapped once with PVC wrap (Hi-Lap KMA manufactured by Mitsui Chemicals), and then further wrapped three times with PVC wrap and left standing under environmental conditions of 40 °C for 24 hours. The printing density of the printed part was measured with a Macbeth densitometer (RD-914, using an amber filter). The residual rate was calculated from the values before and after the treatment to evaluate the plasticizer resistance. Residual rate (%) = (printing density of the printed part after treatment / printing density of the printed part before treatment) × 100 Excellent: The residual rate is 90% or more Acceptable: The residual rate is 70% or more and less than 90% Unacceptable: The residual rate is less than 70% <Printing running property (head dust resistance)> For the produced thermal recording medium, a 10-cm long grid printing was performed using a Sato label printer (Respri R-8), and the dust (head dust) attached to the thermal head after printing was visually evaluated according to the following criteria. Excellent: Almost no head dust adhesion was observed. Acceptable: Slight head dust adhesion was observed, but there was no dropout or smear of the formed image, and it was at a level with no practical problems. Unacceptable: Considerable head dust adhesion was observed, and dropout and smear of the formed image were seen.

[0065] The results are shown in the following table.

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

4. 4. The thermosensitive recording medium according to claim 1, wherein the volumetric hollowness of the hollow plastic particles is 40 to 95%.

5. The undercoat layer is (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. 6. The thermal recording material according to claim 1, wherein when the undercoat layer contains a pigment other than the plastic hollow particles, the pigment contains calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, or talc.

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

Images