Thermal recording medium

Abstract

To provide a thermal recording medium having good print running properties (especially resistance to head residue adhesion) even during long-run printing. [Solution] The thermal recording medium comprises a support, a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer provided on the thermal recording layer, the thermal recording layer containing at least one urea compound represented by the following general formula (Chemical Formula 1), and the protective layer containing a phosphate ester compound. [Case 1] TIFF0007600479000014.tif37164 (wherein X represents -O- or -NH-, R 1 is a hydrogen atom or -SO2-R 3 R 3 represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R 2 represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

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 good print running properties during long-run printing. [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 such applications, stable printing on thermal recording media is required. However, frequent printing can cause recording paper to stick to the print head or head residue to accumulate on the print head, preventing proper printing. To solve these problems, a technique is known in which a phosphate ester compound is blended into the outermost layer, such as a protective layer (Patent Document 1, etc.). Further, a thermal recording medium that uses a specific urea compound as a developer and has good high-speed printability and the like is known (Patent Document 2, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2012-56184 [Patent Document 2] International Publication WO2022 / 196512 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] However, even with such conventional technology, there are cases where print runnability (resistance to head residue adhesion and sticking resistance) is insufficient during long-run printing, which refers to continuous printing over a long distance, for example, 100 m or more, especially 1000 m or more. SUMMARY OF THE PRESENT EMBODIMENTS The present invention has an object to provide a thermal recording medium having good print running properties (particularly, resistance to head residue adhesion) during long-run printing. [Means for solving the problem]

[0005] As a result of extensive research, the inventors have found that the above problems can be solved by incorporating a specific urea compound as a developer in the thermosensitive recording layer and incorporating a phosphate ester compound in the protective layer provided on the thermosensitive recording layer, thereby completing the present invention. That is, the present invention provides a thermosensitive recording medium comprising a support, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer on the thermosensitive recording layer, the thermosensitive recording layer containing at least one urea compound represented by the following general formula (Chemical Formula 1), and the protective layer 2.5 to 11.5 parts by weight (solid content) A thermosensitive recording medium containing a phosphoric acid ester compound. [ka] (In the formula, X represents -O- or -NH-; R 1 is a hydrogen atom or -SO2-R 3 R 3 represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R 2 represents a hydrogen atom or an alkyl group, and m represents 0 or 1. Effect of the Invention

[0006] The thermal recording medium of the present invention has good print running properties (resistance to head residue adhesion and sticking) and sufficient color development sensitivity. In particular, the resistance to head residue adhesion is good even when a long-run printing (e.g., 100 m or more) is performed with a high-energy thermal printer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The thermosensitive recording medium of the present invention has a thermosensitive recording layer on a support and a protective layer on the thermosensitive recording layer, the thermosensitive recording layer containing a specific urea compound as an electron-accepting developer, and the protective layer containing a phosphate ester compound.

[0008] Examples of various materials that can be used in the thermal recording layer of the thermal recording material of the present invention are given below, but binders, crosslinking agents, pigments, etc. can also be used in each coating layer that is provided as needed, as long as they do not impede the desired effects for the above-mentioned problems. The thermosensitive recording layer of the thermosensitive recording medium of the present invention contains at least one urea compound represented by the following general formula (Chemical Formula 1) as a developer. [ka] (In the formula, X represents -O- or -NH-; R 1 is a hydrogen atom or -SO2-R 3 R 3 represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R 2 represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

[0009] The urea compound is preferably the following (1) or (2): (1) A first urea compound represented by the following general formula (Chemical Formula 2): [ka] (In the formula, R 1 , R 2 and R 3is defined as above.) (2) A second urea compound represented by the following formula (Chemical Formula 3): [ka] (In the formula, R 2 is defined as above, and R 4 ~R 8 The definition of will be explained later.)

[0010] The first urea compound used in the present invention is preferably represented by the following formula (Chemical Formula 4). [ka]

[0011] In the general formula (Chemical formula 2) and the general formula (Chemical formula 4), R 3 represents an optionally substituted alkyl group, aralkyl group, or aryl group, and is preferably a substituted or unsubstituted aryl group. When these are substituted, the substituent is preferably an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom. 3 may be the same or different. R in the benzene ring of general formula (chemical formula 2) 1 The positions of -O- may be the same or different, and are preferably the 3-, 4- or 5-positions. R in the benzene ring of general formula (chemical formula 2) and general formula (chemical formula 4) 3 The positions of -SO2-O- may be the same or different, and are preferably the 3-, 4- or 5-positions.

[0012] The alkyl group is, for example, a linear, branched or alicyclic alkyl group, and the number of carbon atoms is preferably 1 to 12. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, and a lauryl group.

[0013] The number of carbon atoms in the aralkyl group is preferably 7 to 12. 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] The number of carbon atoms in this aryl group is preferably 6 to 12. Examples of this aryl group include unsubstituted aryl groups or aryl groups substituted with an alkyl group, an alkoxy group, an aralkyl group, an aryl group, or a halogen atom, such as a phenyl group, a p-tolyl group, an m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, a 3,4-dimethylphenyl group, a mesitylene group, a p-ethylphenyl group, a p-propylphenyl group, a p-butylphenyl group, a p-methoxyphenyl group, a 3,4-dimethoxyphenyl group, a p-ethoxyphenyl group, a p-chlorophenyl group, a 1-naphthyl group, a 2-naphthyl group, or a t-butylated naphthyl group.

[0015] In the above general formulas (1, 2, 4), R 3 is preferably a group represented by the following formula: [ka] In the above formula, R 4 ~R 8may be the same or different and each represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The second urea compound used in the present invention is preferably N-[2-(3-phenylureido)phenyl]benzenesulfonamide, which is represented by the following formula and is available, for example, from Nippon Soda Co., Ltd. under the trade name NKK1304. [ka]

[0020] 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. When the thermosensitive recording layer of the present invention contains the first and second urea compounds, the content of the second urea compound in the thermosensitive recording layer is preferably 0.1 to 30.0 parts by weight, more preferably 0.5 to 25.0 parts by weight, even more preferably 1.0 to 20.0 parts by weight, and particularly preferably 2.0 to 15.0 parts by weight, relative to 1.0 part by weight of the first urea compound.

[0021] The heat-sensitive recording layer of the present invention may use a color developer other than the first or second urea compound. 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 acetate, 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)phenylacetate, 1,2-bis(4-hydroxyphenyl)phenylacetate, 1,3-bis(4-hydroxyphenyl)phenylacetate, 1,4-bis(4-hydroxyphenyl)phenylacetate, 1,5 ... (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.

[0022] When the thermosensitive recording layer of the present invention contains a developer other than the first or second urea compound, the total content (solid content) of the first and / or second urea compound used relative to the total developer contained in the thermosensitive recording layer (including the first and / or second urea compound) is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0023] 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.

[0024] <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)

[0025] <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,

[0026] <Fluorene-based leuco dye> 3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-Tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0027] <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

[0028] <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

[0029] 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.

[0030] 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.

[0031] Binders that can be used in the present invention include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols, silane-modified acrylic resins, and high Tg acrylic resins (preferably non-core-shell type acrylic resins, the glass transition point (Tg) of which is higher than 50° C. and lower than 95° C.). This Tg can be measured by differential scanning calorimetry (DSC ) is measured. ) Examples of the polymeric substances include (meth)acrylic acid and other acrylic resins made of monomer components (excluding olefins) copolymerizable with (meth)acrylic acid, cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, ethyl cellulose, and acetyl cellulose, starches such as oxidized starch, etherified starch, and esterified starch, styrene-maleic anhydride copolymers, styrene-butadiene copolymers, casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid esters, polyvinyl butyral, polystyrose and copolymers thereof, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. These polymeric substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, and hydrocarbons, and can also be used in a state of being emulsified or dispersed in a paste form in water or other media, and can be used in combination depending on the required quality.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] In the thermosensitive recording medium of the present invention, the protective layer contains a phosphoric acid ester compound. Examples of the phosphate compound used in the present invention include monocaproyl phosphate, monooctyl phosphate, monocapryl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, monophosphate of tetraethylene glycol mononeopentyl ether, monophosphate of triethylene glycol monotridecyl ether, monophosphate of tetraethylene glycol monolauryl ether, monophosphate of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, dicetyl phosphate, distearyl phosphate, diphosphate of tetraethylene glycol mononeopentyl ether, diphosphate of triethylene glycol monotridecyl ether, diphosphate of tetraethylene glycol monolauryl ether, diphosphate of diethylene glycol monostearyl ether, and the like. For example, they are available as "Sepal 328", "Sepal 365", "Sepal 380", "Sepal 440", "Sepal 441", "Sepal 517", "Sepal 521", and "Sepal M835" (all trade names) manufactured by Chukyo Yushi. Among these, Sepal M835 is preferred in the present application. It is a liquid substance at room temperature and does not have a specific melting point, so it is considered to be less likely to adhere to the thermal head during long-term printing compared to zinc stearate, which is usually used as a lubricant. The amount of the phosphoric acid ester compound used in the present invention is preferably 2.5 to 15.0 parts by weight (hereinafter, parts by weight are calculated as solids) and more preferably 2.5 to 11.5 parts by weight, based on 100 parts by weight of the total solids of the coating layer of the outermost layer. If the amount of the phosphoric acid ester compound is less than 2.5 parts by weight, good stick resistance cannot be obtained, and if it exceeds 11.5 parts by weight, print storage stability (plasticizer resistance) may decrease.

[0037] The protective layer of the present invention may contain optional components such as binders and pigments as described for the heat-sensitive recording layer, if necessary. The amount of binder or the total amount of binder and pigment in the protective layer is usually 80.0 to 100.0% by weight, preferably 90.0 to 100.0% by weight, in terms of solid content, and the amount of binder is preferably about 30.0 to 300.0 parts by weight per 100 parts by weight of pigment.

[0038] In addition, a crosslinking agent can be used in combination in the protective layer of the present invention. Examples of the crosslinking agent include epichlorohydrin resins such as polyamine epichlorohydrin resins and polyamide epichlorohydrin resins, polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, and polyalkylene polyamine polyamide polyurea resins, 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. In the present invention, it is preferable that the protective layer contains an epichlorohydrin resin and a polyamine / polyamide resin as crosslinking agents, since this makes the water resistance particularly good.

[0039] The thermosensitive recording medium of the present invention may have a backcoat layer on the opposite side of the support to the thermosensitive recording layer, which may contain a water-soluble polymer, a water-dispersible resin, a pigment, etc. Examples of the water-soluble polymer include polyvinyl alcohols other than ethylene-vinyl alcohol copolymers, such as fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol; proteins, such as casein, soy protein, and synthetic protein; starches, such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch; cellulose derivatives, such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose; polyvinylpyrrolidone; and sodium alginate. Examples of the water-dispersible resin include natural rubber, diene rubber, non-diene rubber, and thermoplastic elastomer. As this pigment, any pigment that can be used in a heat-sensitive recording layer can be used appropriately, but aluminum hydroxide, silica, kaolin, and calcined kaolin are preferred, and aluminum hydroxide is more preferred. This backcoat layer may further contain, as necessary, lubricants, crosslinking agents, ultraviolet absorbers, dispersants, antifoaming agents, fluorescent dyes, and the like that can be used in the thermosensitive recording layer, within the limits that do not impair the desired effects for the above-mentioned problems.

[0040] The backcoat layer preferably contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer. The ethylene-vinyl alcohol copolymer is a polymer having ethylene units and vinyl alcohol units. The ethylene-vinyl alcohol copolymer is usually obtained by polymerizing ethylene and a vinyl ester, and saponifying the resulting ethylene-vinyl ester copolymer, and the ethylene content is preferably 3 to 20 mol %. In order to impart barrier properties, the saponification degree is preferably 80 to 100 mol %. If the saponification degree is less than 80 mol %, sufficient barrier properties and moisture resistance cannot be obtained.

[0041] The ethylene-acrylic copolymer used in the present invention is a copolymer obtained by emulsion polymerization of ethylene and an acrylic monomer. As the acrylic monomer, acrylic acid and methacrylic acid are preferred, and acrylic acid is more preferred. The ethylene-acrylic copolymer is preferably at least one of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-butyl methacrylate copolymer. The copolymer may contain a small amount of a monomer composed of another compound copolymerizable with ethylene and acrylic monomers. Among these, ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer are more preferable, and ethylene-acrylic acid copolymer is further preferable. As a specific example of an ethylene-acrylic copolymer, for example, an aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt is available as ZAIXXEN (registered trademark) AC (copolymerization ratio of acrylic acid: 20%, manufactured by Sumitomo Seika Chemicals Co., Ltd.).

[0042] The content (solid content) of the ethylene-vinyl alcohol copolymer in the backcoat layer is preferably 10 to 80% by weight, more preferably 10 to 50% by weight. The content (solid content) of the ethylene-acrylic copolymer in the backcoat layer is preferably 10 to 80% by weight, more preferably 50 to 80% by weight. However, the total content (solid content) of the ethylene-vinyl alcohol copolymer and the ethylene-acrylic copolymer in the backcoat layer is preferably 50 to 100% by weight, more preferably 50 to 90% by weight, and even more preferably 70 to 90% by weight. The content ratio (solid content) of the ethylene-acrylic copolymer relative to the ethylene-vinyl alcohol copolymer is preferably 2.5 to 40 parts, more preferably 10 to 40 parts, per 10 parts by mass of the ethylene-vinyl alcohol copolymer. The content (solid content) of the pigment in the backcoat layer is preferably 50 to 10% by weight, and more preferably 30 to 10% by weight. The coating amount of the backcoat layer is determined according to the required performance and recording suitability, and is not particularly limited. A typical coating amount is 0.1 to 5 g / m2 in terms of solid content. 2 Of this, 2.5 to 4.5 g / m 2 It is preferable that the thickness is about 100 nm because the thermal recording medium has excellent water vapor barrier properties and good quality.

[0043] The thermosensitive recording medium of the present invention may further have an undercoat layer between the support and the thermosensitive recording layer. The undercoat layer consists primarily of a binder and a pigment. The binder used in the undercoat layer may be an emulsion of a water-soluble polymer or a hydrophobic polymer that is generally used.Specific examples include cellulose derivatives such as polyvinyl alcohol, polyvinyl acetal, hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose, starch and its derivatives, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein, and emulsions of hydrophobic polymers such as polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, and styrene / butadiene / acrylic copolymer.These binders may be used alone or in combination of two or more.

[0044] The pigment used in the undercoat layer may be any known pigment that has been commonly used in the past, such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcined kaolin, clay, talc, or other inorganic pigments. These pigments may be used alone or in combination. The amount of the pigment in the undercoat layer is usually 50 to 95 parts by weight, and preferably 70 to 90 parts by weight, based on 100 parts by weight of the total solid content. The coating solution for the undercoat layer may contain various auxiliary agents, such as dispersants, plasticizers, pH adjusters, defoamers, water retention agents, preservatives, coloring dyes, and ultraviolet protection agents, as required.

[0045] 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

[0046] 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.

[0047] [Preparation of each coating liquid] The following mixture was stirred and dispersed to prepare a coating liquid for the undercoat layer. <Coating fluid for undercoat layer> Calcined kaolin (Imeris, Alphatex HP) 50 parts Plastic hollow particles (Zeon, MH8109) 50 parts Styrene-butadiene copolymer latex (ZEON Co., Ltd., ST5526, Solid content 48%) 10 parts 50 parts water

[0048] The developer dispersions (Liquids A1 to A2), leuco dye dispersion (Liquid B), and sensitizer dispersion (Liquid C) having the following compositions were each prepared by wet grinding in a sand grinder until the average particle size reached 0.5 μm. Developer dispersion liquid (A1 liquid) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (Manufactured by Nippon Soda Co., Ltd., NKK1304, hereinafter referred to as "Urea Compound 1") 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., PVA117, Solid content 10%) 5.0 parts 1.5 parts water Developer dispersion liquid (A2 liquid) N,N'-Di-[3-(p-toluenesulfonyloxy)phenyl]urea (hereinafter referred to as "urea compound 2") 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Leuco dye dispersion (liquid B) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Industry Co., Ltd., ODB-2) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Sensitizer dispersion (liquid C) 1,2-bis-(3-methylphenoxy)ethane (Sankosha, KS232) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0049] 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 1> Developer dispersion liquid (A1 liquid) 18.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 36.0 parts Silica dispersion (Mizukasil P-537, manufactured by Mizusawa Chemical Industries, Ltd., solid content 25%) 17.5 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 30.0 parts <Coating solution for thermal recording layer 2> Developer dispersion liquid (A2 liquid) 18.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 36.0 parts Silica dispersion (Mizukasil P-537) 17.5 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 30.0 parts

[0050] Next, the following components were mixed in the following proportions to prepare a coating liquid for the protective layer. <Coating solution for protective layer> Aluminum hydroxide dispersion (Martinsberg, product name: Martifin OL, solids 50%) 9.0 parts Carboxy-modified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., product name: KL318, Degree of polymerization: about 1700, degree of saponification: 95-99 mol%, solid content: 10%) 30.0 copies Polyamide epichlorohydrin resin (Seiko PMC Corporation, product name: WS4030, Solid content 25%) 4.0 parts Modified polyamine resin (manufactured by Sumitomo Chemical Co., Ltd., product name: Sumirez Resin SPI-102A, Solid content 45%) 2.2 parts Phosphate ester compound (Chukyo Yushi Co., Ltd., Sepal M835, solid content 20%) 3.5 parts Water 22.8 parts

[0051] Next, the following ingredients were mixed together to prepare a coating solution for the backcoat layer. <Coating fluid for backcoat layer> Kaolin (Imeris, product name: Contour 1500) 20 parts Ethylene-vinyl alcohol copolymer (Kuraray Co., Ltd., product name: Exeval RS4104) 10 copies Ethylene-acrylic copolymer (manufactured by Sumitomo Seika Chemicals, product name: ZAIKXEN AC, Melting point: 80-95℃) 40 parts

[0052] [Example 1] Support (basis weight 60g / m 2 The coating solution for the undercoat layer is applied to one side of the paper (high-quality paper) at a coating weight of 6.0 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. On the undercoat layer of this undercoat layer coated paper, the coating solution 1 for the thermal recording layer was applied in a coating amount of 3.0 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 treated with a super calendar so as to obtain a smoothness of 500 to 1000 seconds to prepare a thermosensitive recording layer-coated paper. Next, a protective layer coating solution was applied to the thermal recording layer of the thermal recording layer coated paper in a coating amount of 3.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so as to obtain the above-mentioned composition, the coating was dried to prepare a thermal recording medium.

[0053] [Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the amount of the phosphoric ester compound in the protective layer coating liquid was changed from 3.5 parts to 1.75 parts. [Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the amount of the phosphoric ester compound in the protective layer coating liquid was changed from 3.5 parts to 7.0 parts. [Example 4] A thermal recording medium was prepared in the same manner as in Example 1, except that 3.5 parts of the phosphate ester compound in the coating liquid for the protective layer was replaced with 3.5 parts of a stearyl phosphate potassium salt emulsion (product name: U-Pol 1800, manufactured by Matsumoto Oil Co., Ltd., solids concentration 35%). [Example 5] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Solution 1 for Thermosensitive Recording Layer was replaced with Coating Solution 2 for Thermosensitive Recording Layer. [Example 6] After applying the protective layer coating liquid, apply the backcoat layer coating liquid to the opposite side of the protective layer at a coating weight of 3.5 g / m2 (solid content). 2 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that coating was performed by the rod blade method so as to obtain a thermosensitive recording medium, followed by drying. [Example 7] A thermal recording medium was prepared in the same manner as in Example 1, except that 30.0 parts of the carboxy-modified polyvinyl alcohol aqueous solution (KL318) in the protective layer coating liquid was replaced with 30.0 parts of a carboxy-modified polyvinyl alcohol aqueous solution (manufactured by Kuraray, product name: KL118, degree of polymerization: approximately 1700, degree of saponification: 85-90 mol%, solids content 10%).

[0054] [Comparative Example 1] A thermal recording medium was prepared in the same manner as in Example 2, except that the developer (urea compound 1) in the thermal recording layer coating solution 1 was replaced with 4-hydroxy-4'-benzyloxydiphenylsulfone (manufactured by Nicca Chemical Co., Ltd., product name: BPS-MA3). [Comparative Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that 3.5 parts of the phosphoric acid ester compound in the protective layer coating liquid was replaced with 3.5 parts of zinc stearate (product name: Hydrin Z-7-30, solid content 30%). [Comparative Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that 3.5 parts of the phosphoric ester compound in the protective layer coating liquid was replaced with 1.75 parts of zinc stearate (manufactured by Chukyo Yushi Co., Ltd., Hydrin Z-7-30). [Comparative Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that 3.5 parts of the phosphoric ester compound in the protective layer coating liquid was replaced with 7.0 parts of zinc stearate (Hydrin Z-7-30).

[0055] 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 an applied energy of 0.35 mJ / dot and a printing speed of 50 mm / sec using a TH-PMD (thermal recording paper printing 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.

[0056] <Stick resistance> Using an Okura Electric TH-PMD, printing was performed on the thermal recording medium with an applied energy of 0.34 mJ / dot, a printing speed of 50 mm / sec, and an environment of -10°C. The stick condition and noise during recording were evaluated according to the following criteria. ○: No whiteout and almost no noise △: There is some whiteout, but almost no noise. ×: Frequent whiteout and loud noise

[0057] <Resistance to head residue adhesion> Using a SONY UP-X898MD (medical thermal printer), a solid pattern was printed over a distance of 20 m to 1000 m in S mode, and then the deposits on the thermal head were visually evaluated according to the following criteria. ○: No adhesion occurs △: A small amount of deposits were deposited. ×: Accumulation of deposits observed

[0058] The results are shown in Table 1. [Table 1]

[0059] As shown in Table 1, the thermal recording medium of the present invention has an excellent effect of preventing head residue adhesion during long-run printing without adversely affecting color development sensitivity, and has excellent resistance to head residue adhesion.

Claims

1. A thermal recording medium comprising a support, a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer provided on the thermal recording layer, the thermal recording layer containing at least one urea compound represented by the following general formula (Chemical Formula 1), and the protective layer containing 2.5 to 11.5 parts by weight (solid content) of a phosphoric acid ester compound. [Formula 1] (In the formula, X represents —O— or —NH—; R １ is a hydrogen atom or -SO ２ -R ３ represents R ３ represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R ２ represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

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

3. A thermal recording medium as described in claim 1, wherein the protective layer further contains a carboxy-modified polyvinyl alcohol having a saponification degree of 95 mol or more as a binder.

4. A thermal recording medium as described in claim 1, further comprising a backcoat layer on the opposite side of the support to the thermal recording layer.

5. The thermal recording medium according to claim 4, wherein the backcoat layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

6. A thermal recording medium described in any one of claims 1 to 5, wherein the urea compound is the following (1) or (2). (1) A first urea compound represented by the following general formula (Chemical Formula 2): [chemical 2] (wherein R 1 , R 2 , and R 3 are defined as above.) (2) A second urea compound represented by the following general formula (Chemical Formula 3): [C3] (In the formula, R 2 is defined as above, and R 4 to 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.)

7. A thermal recording medium as described in claim 6, wherein the first urea compound is represented by the following general formula (Chemical Formula 6). [C6] (In the formula, R ９ may be the same or different and each represents an alkyl group or an alkoxy group, and o represents an integer of 0 to 3.

8. The thermal recording medium according to claim 7, wherein the second urea compound is N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

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