Heat-sensitive recording body

Abstract

A thermosensitive recording medium having a thermosensitive recording layer comprising a colorless or pale colored electron donating leuco dye and an electron accepting color developing agent on a substrate, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains at least one kind of urea compound represented by the following general formula (Formula 1), and wherein the protective layer contains a phosphate ester compound (wherein X represents -O- or -NH-, R1 represents a hydrogen atom or -SO2-R3, R3 represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R2 represents a hydrogen atom or an alkyl group, m represents 0 or 1).

Description

[Field of the Invention]

[0001] The present invention relates to a thermosensitive recording medium by utilizing a coloring reaction between a colorless or pale colored electron donating leuco dye (referred to as "leuco dye") and an electron accepting color developing agent (referred to as "color developing agent"), which has an excellent thermal printing run-ability during long-run printingd.[Background of the Invention]

[0002] Thermosensitive recording media are ordinarily prepared by applying a coating solution containing a colorless or pale colored leuco dye and a color developing agent onto a substrate such as paper, synthetic paper, film, plastic and the like. Thermosensitive recording medium develops color through an instantaneous chemical reaction when heated by a thermal head, hot stamp, hot pen, laser light or the like to yield a recorded image. Such thermosensitive recording media are used extensively in recording media such as facsimile devices, computer terminal printers, automatic ticket dispensers, recorders for meters, receipts at super markets and convenience stores and the like.

[0003] In recent years, the use of the thermosensitive recording medium is expanding, such as various ticket, receipts, labels, ATM of Bank, meter reading of gas and electricity, cash vouchers, such as car racing or horseracing betting. Therefore, the thermal recording medium is required to have various performances such as water resistance, plasticizer resistance in the image part, heat resistance of blank part, oil resistance, preservation of image and blank parts under harsh conditions, and the like.

[0004] In such applications, it is required to be able to print stably on the thermosensitive recording medium. However, frequent printing can cause the recording paper to stick to the print head or head debris to accumulate on the print head, preventing proper printing. In order to solve such problems, a technique is known in which a phosphate ester compound is added to the outermost layer, such as a protective layer (Patent Document 1, etc.).

[0005] Further, a thermosensitive recording medium which uses a specific urea compound as a color developing agent and has good high-speed thermal printing ability is known (Patent Document 2, etc.).[Prior Art Document][Patent Document]

[0006] Patent Document 1: Japanese Patent Application Laid-Open (kokai) 2012-56184 Patent Document 2: International Publication WO2022 / 196512 [Summary of the Invention][Problems to be solved by the Invention]

[0007] However, even when using such conventional technologies, there are cases where thermal printing run-ability (prevention of head debris adhesion and stick resistance) is insufficient during long-run printing. Long-run printing refers to continuous printing over a long distance, for example, 100 meter or more, and particularly 1000 meter or more.

[0008] Therefore, the object of the present invention is to provide a thermosensitive recording medium that has good thermal printing run-ability (particularly prevention of head debris adhesion) during long-run printing.[Means For Solving the Problem]

[0009] As a result of intensive studies, the present inventors have found that the above problems can be solved by having a thermosensitive recording layer contain a specific urea compound as a color developing agent and by having a protective layer provided on the thermosensitive recording layer contain a phosphate ester compound, and then completed the present invention.

[0010] The present invention provides a thermosensitive recording medium having a thermosensitive recording layer comprising a colorless or pale colored electron donating leuco dye and an electron accepting color developing agent on a substrate, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains at least one kind of urea compound represented by the following general formula (Formula 1), and wherein the protective layer contains a phosphate ester compound (wherein X represents -O- or -NH-, R 1< represents a hydrogen atom or -SO 2 -R 3< , R 3< represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R 2< represents a hydrogen atom or an alkyl group, m represents 0 or 1).[Effect of the Invention]

[0011] A thermosensitive recording medium of the present invention has good thermal printing run-ability (prevention of head debris adhesion and stick resistance) and has sufficient color developing sensitivity. Especially, prevention of head debris adhesion is good even when long-run printing is conducted (for example, 100 meter or more) with a high-energy thermal printer.[Modes For Carrying out the Invention]

[0012] A thermosensitive recording medium of the present invention has a thermosensitive recording layer on a substrate and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains a specific urea compound as an electron accepting color developing agent, and the protective layer contains a phosphate ester compound.

[0013] Hereinafter, various materials used in the thermosensitive recording layer of the thermosensitive recording medium of the present invention will be illustrated, however, binders, cross-linking agents, pigments and the like can also be used for other coating layers within the range that does not impair the desired advantages on the above-mentioned problems.

[0014] In the thermosensitive recording medium of the present invention, the thermosensitive recording layer contains at least one kind of a urea compound represented by the general formula (Formula 1) as the color developing agent. (wherein X represents -O- or -NH-, R 1< represents a hydrogen atom or -SO 2 -R 3< , R 3< represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R 2< represents a hydrogen atom or an alkyl group, m represents 0 or 1).

[0015] The urea compound is preferably the following (1) or (2), (1) a first urea compound represented by the following general formula (Formula 2) (wherein R 1< , R 2< , R 3< , and n are defined as described above), (2) a second urea compound represented by the following general formula (Formula 3) (where R 2< is defined as described above, the definition of R 4< to R 8< are described later).

[0016] The first urea compound used in the present invention is preferably represented by the following formula (Formula 4).

[0017] In the above general formula (Formula 2) and general formula (Formula 4), R 3< represents an alkyl group, an aralkyl group or an aryl group, all of which may be substituted or unsubstituted, and preferably a substituted or unsubstituted aryl group.

[0018] 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. Further, the plurality of R 3< may be the same or different.

[0019] The position of R 1< - O- in the benzene ring in the general formula (Formula 2) may be the same or different, and is preferably the 3-position, 4-position or 5-position.

[0020] The position of R 3< -SO 2 -O- in the benzene ring in the general formula (Formula 2) and general formula (Formula 4) may be the same or different, and is preferably the 3-position, 4-position or 5-position.

[0021] The alkyl group is, for example, a linear, branched or alicyclic alkyl group, preferably having 1 to 12 carbon atoms. The alkyl group includes methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, t-butyl group, cyclopentyl group, hexyl group, cyclohexyl group, 2-ethylhexyl group, a lauryl group and the like.

[0022] The carbon number of the aralkyl group is preferably 7 to 12. The aralkyl group may be an unsubstituted aralkyl group or an aralkyl group substituted by alkyl group, alkoxy group, aralkyl group, aryl group or halogen atom. Examples thereof include benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, p-methylbenzyl group, m-methylbenzyl group, m-ethylbenzyl group, p-ethylbenzyl group, p-iso-propylbenzyl group, p-t-butylbenzyl group, p-methoxybenzyl group, m-methoxybenzyl group, o-methoxybenzyl group, m, p-dimethoxybenzyl group, p-ethoxy-m-methoxybenzyl group, p-phenylmethylbenzyl group, p-cumylbenzyl group, p-phenylbenzyl group, o-phenylbenzyl group, m-phenylbenzyl group, p-tolylbenzyl group, m-tolylbenzyl group, o-tolylbenzyl group and a p-chlorobenzyl group, and the like.

[0023] The carbon number of the aryl group is preferably 6 to 12. The aryl group may be an unsubstituted aryl group or an aryl group substituted by alkyl group, alkoxy group, aralkyl group, aryl group or halogen atom. Examples thereof include phenyl group, p-tolyl group, m-tolyl group, o-tolyl group, 2,5-dimethylphenyl group, 2,4-dimethylphenyl group, 3,5-dimethylphenyl group, 2, 3-dimethylphenyl group, 3,4-dimethylphenyl group, mesitylene group, p-ethylphenyl group, p-iso-propylphenyl group, p-t-butylphenyl group, p-methoxyphenyl group, 3,4-dimethoxyphenyl group, p-ethoxyphenyl group, p-chlorophenyl group, 1-naphthyl group, 2-naphthyl group, t-butylated naphthyl group, and the like.

[0024] In the general formula (Formula 1,2 and 4), R 3< is preferably represented by the following formula:

[0025] In the above formula, R 4< to R 8< may be identical or different from each other, 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.

[0026] R 2< represents a hydrogen atom or an alkyl group, preferably a hydrogen atom. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, which is, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, t-butyl group and the like.

[0027] The position of R 2< in the benzene ring in the general formula (Formula 2) may be the same or different, and is preferably 3-position, 4-position, or 5-position.

[0028] The first urea compound of the present invention is more preferably the first urea compound represented by the following general formula (Formula 6).

[0029] In the general formula (Formula 6), R 9< is alkyl group or alkoxy group, preferably alkyl group. n represents an integer of 0 to 3, preferably 0 to 2, and more preferably 0 to 1. The number of carbon atoms of the alkyl group is, for example, 1 to 12, preferably 1 to 8, and more preferably 1 to 4.

[0030] The position of R 9< in the benzene ring in the general formula (Formula 6) may be the same or different, and is preferably 3-position, 4-position or 5-position, more preferably 4-position.

[0031] Further, the examples of the first urea compound used in the present invention includes, 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-(mesitylene sulfonyloxy) 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, 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. However, the first urea compound of the present invention is not limited to these.

[0032] The second urea compound used in the present invention is preferably N-[2-(3-phenylureido) phenyl] benzenesulfonamide. The compound is represented by the following formula and is available, for example, under the trade name of NKK 1304 manufactured by Nippon Soda Co., Ltd.

[0033] The content (in solid, combined amount when a plurality of urea compounds is contained) of the urea compound in the thermosensitive recording layer of the present invention is from 1.0 to 70.0 weight %, preferably from 5.0 to 65.0 weight %, more preferably 10.0 to 60.0 weight parts.

[0034] The content of the first urea compound in the thermosensitive recording layer of the present invention is from 1.0 to 50.0 weight %, preferably 5.0 to 40.0 weight %. The content of the second urea compound is from 5.0 to 50.0 weight %, preferably 5.0 to 40.0 weight %.

[0035] In the case 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 weight parts, more preferably 0.5 to 25.0 weight parts, further preferably 1.0 to 20.0 weight parts, especially preferably 2.0 to 15.0 weight parts per 1.0 weight parts of the first urea compound.

[0036] The thermosensitive recording layer of the present invention may contain color developing agent(s) other than the first urea compound and the second urea compound. As such color developing agents, for example, activated clay, attapulgite, colloidal silica, inorganic acidic substances such as aluminum silicate and the like, 4,4'-isopropylidene diphenol, 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'-dihydroxy diphenyl sulfone, 2,4'-dihydroxy diphenyl sulfone, 4-hydroxy-4'-isopropoxy diphenyl sulfone, 4-hydroxy-4'-n-propoxy diphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxy phenyl sulfone, 3,4-dihydroxyphenyl-4'-methyl phenyl sulfone, 1-[4-(4-hydroxyphenyl-sulfonyl) phenoxy]-4-[4-(4-isopropoxyphenyl sulfonyl) phenoxy] butane, phenol condensate composition described in Japanese Patent Application Public Disclosure No. 2003-154760, aminobenzene sulfonamide derivatives described in Japanese Patent Application Public Disclosure No. H08-59603, bis(4-hydroxyphenyl thioethoxy) methane, 1,5-di(4-hydroxyphenyl thio)-3-oxapentane, butyl bis(p-hydroxyphenyl) acetate, methyl bis(p-hydroxyphenyl) acetate, 1,1-bis(4-hydroxyphenyl)-1-phenyl ethane, 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 International Publication WO02 / 081229 or Japanese Patent Application Public Disclosure No. 2002-301873, thiourea compounds such as N,N'-di-m-chlorophenyl thiourea and the like, p-chlorobenzoic acid, stearyl gallate, bis[zinc 4-octyloxy carbonylamino salicylate] dihydrate, 4-[2-(p-methoxyphenoxy) ethyloxy] salicylic acid, 4-[3-(p-tolylsulfonyl) propyloxy] salicylic acid, aromatic carboxylic acids such as 5-[p-(2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, and salts of these aromatic carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel and the like, and, furthermore, antipirin complexes of zinc thiocyanate and complex zinc salts of terephthal aldehyde acid with other aromatic carboxylic acids and the like may be cited. These color developing agents may be used individually or as a mixture of at least two of them. 1-[4-(4-hydroxyphenyl-sulfonyl) phenoxy]-4- [4- (4-isopropoxyphenyl sulfonyl) phenoxy] butane is available, for example, under the trade name of JKY-214 produced by API Corporation. The phenol condensate composition described in Japanese Patent Application Public Disclosure No. 2003-154760 is available, for example, under the trade name of JKY-224 produced by API Corporation. The compound described in International Publication WO02 / 081229 is available, for example, under the trade names of NKK-395 and D-100 produced by Nippon Soda Co., Ltd. In addition, high molecular weight aliphatic acid metal complex salts described in Japanese Patent Application Public Disclosure No. H10-258577 and metal chelate type color developing components such as polyvalent hydroxy aromatic compounds and the like may also be present.

[0037] In the case when the thermosensitive recording layer contains color developing agent other than the first or second urea compound, the combined amount(in solid) of the the first and / or second urea compound used is preferably 50 weight % or more, more preferably 80 weight % or more, further preferably 90 weight % or more of the total amount of the color developing agents contained in the thermosensitive recording layer, which contains the first and / or second urea compound.

[0038] All of the leuco dyes well known in the conventional field of pressure sensitive and thermosensitive recording media may be used as the electron donating leuco dye in the present invention. Although the leuco dye is not particularly restricted, triphenylmethane type compounds, fluorane type compounds, fluorene type compounds, divinyl type compounds and the like are preferred as the leuco dye. Specific examples of the typical colorless to pale colored basic colorless leuco dye (leuco dye precursors) are shown below. In addition, these leuco dye precursors may be used individually and also in mixtures of at least two of them.<Triphenylmethane type leuco dyes>

[0039] 3,3-bis(p-Dimethyl aminophenyl)-6-dimethylaminophthalide [alternate name: crystal violet lactone] and 3,3-bis(p-Dimethyl aminophenyl) phthalide [alternate name: malachite green lactone]<Fluorane type leuco dyes>

[0040] 3-Diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluorane, 3-diethylamino-6-methyl- 7-chlorofluoran, 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- octylanilino fluorane, 3-diethylamino-6-methyl-7-n-octylamino fluorane, 3-diethylamino-6- methyl-7-benzylamino fluorane, 3-diethylamino-6-methyl-7-dibenzylamino fluorane, 3-diethylamino-6-chloro-7-methyl fluorane, 3-diethylamino-6-chloro-7-anilino fluorane, 3-diethylamino-6-chloro-7-p-methylanilino fluorane, 3-diethylamino-6-ethoxyethyl-7- anilino fluorane, 3-diethylamino-7-methyl fluorane, 3-diethylamino-7-chloro fluorane, 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-anilino fluorane, 3-dibutylamino-6-methyl-7-(o,p-dimethylanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-butylamino-6-methyl-7-(p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7-(o-fluoroanilino) fluorane, 3-dibutylamino-6-methyl-7-(m- fluoroanilino) fluorane, 3-dibutylamino-6-methyl-chloro fluorane, 3-dibutylamino- 6-ethoxyethyl-7-anilino fluorane, 3-dibutylamino-6-chloro-7-anilino fluorane, 3-dibutylamino-6-methyl-7-p-methylanilino fluorane, 3-dibutylamino-7-(o-chloroanilino) fluorane, 3-dibutylamino-7-(o-fluoroanilino) fluorane, 3-di-n-pentylamino-6-methyl-7- anilino fluorane, 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino) fluorane, 3-di-n- pentylamino-7-(m-trifluoromethylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilino fluorane, 3-di-n-pentylamino-7-(p-chloroanilino) fluorane, 3-pyrolidino-6-methyl-7-anilino fluorane, 3-piperidino-6-methyl-7-anilino fluorane, 3-(N-methyl-N-propylamino)-6-methyl-7-anilino fluorane, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-xylylamino)-6- methyl-7-(p-chloroanilino) fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isoamylamino)-6- chloro-7-anilino fluorane, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilino fluorane, 3-(N-ethyl-N- ethoxypropylamino)-6-methyl-7-anilino fluorane, 3-cyclohexylamino-6-chloro fluorane, 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilino fluorane, 2-(4-oxahexyl)-3- diethylamino-6-methyl-7-anilino fluorane, 2-(4-oxahexyl)-3-dipropylamino-6- methyl-7-anilino fluorane, 2-methyl-6-o-(p-dimethylaminophenyl) aminoanilino fluorane, 2-methoxy-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 2-chloro-3-methyl-6-p-(p-phenylaminophenyl) aminoanilino fluorane, 2-chloro-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 2-nitro-6-p-(p-diethylaminophenyl) aminoanilino fluorane, 2-amino-6-p-(p-diethylaminophenyl) aminoanilino fluorane, 2-diethylamino-6-p-(p- diethylaminophenyl) aminoanilino fluorane, 2-phenyl-6-methyl-6-p-(p- phenylaminophenyl) aminoanilino fluorane, 2-benzyl-6-p-(p-phenylaminophenyl) aminoanilino fluorane, 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilino fluorane, 3-methyl-6-p-(p-dimethylaminophenyl) aminoanilino fluorane, 3-diethylamino-6- p-(p-diethylaminophenyl) aminoanilino fluorane, 3-diethylamino-6-p-(p- dibutylaminophenyl) aminoanilino fluorane and 2,4-dimethyl-6-[(4-dimethylamino) anilino] fluorane.<Fluorene type leuco dye>

[0041] 3,6,6-Tris(dimethylamino) spiro[fluorane-9,3'-phthalide] and 3,6,6'-tris (diethylamino) spiro[fluorane-9,3'-phthalide].<Divinyl type leuco dyes>

[0042] 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-tetra-bromophthalide, 3,3-bis-[1- (4-methoxyphenyl)-1-(4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide<Others>

[0043] 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-cyclohexyl ethylamino-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- y-(3'-nitroanilinolactam, 3,6-bis(diethylamino)fluorane-y-(4'-nitro) anilinolactam, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrilethane, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-B-naphthoylethane, 1,1-bis-[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane and bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester.

[0044] The previously wellknown sensitizers may be used as the sensitizer in the thermosensitive recording medium of the present invention. As such sensitizers, aliphatic acid amides such as stearic acid amide, palmitic acid amide and the like, ethylene bis-amide, montan acid wax, polyethylene wax, 1,2-di-(3-methylphenoxy) ethane, p-benzyl biphenyl, β-benzyloxy naphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxy benzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methyl phenoxymethyl) biphenyl, 4,4'-ethylene dioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxy methane, 1,2-di(3-methylphenoxy) ethylene, bis[2-(4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluene sulfonate, o-toluenesulfonamide, p-toluenesulfonamide, and the like may be listed as examples. These sensitizers may be used individually and as mixtures of at least two of them.

[0045] As a pigment used in the present invention, kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, silica and the like may be used. These pigments may be used in combinations depending on the required quality.

[0046] As the binder usable for the present invention, polyvinyl alcohols such as completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, modified polyvinyl alcohols such as acetoacetylated polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohol, silane-modified acrylic resin, high Tg acrylic resin(preferably a non-core shell type acrylic resin, and its glass transition point (Tg) is higher than 50 degree C and lower than or equal to 95 degree C. The Tg is measured by differential scanning calorimetry (DSC).), other acrylic resin contains (meth)acrylic acid and a monomer that can be copolymerized with (meth)acrylic acid, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, cellulose derivatives such as ethyl cellulose and acetyl cellulose, starches such as oxidized starch, etherified starch, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, casein, gum Arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butylal, polystyrol and their copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, cumaron resins and the like may be listed as examples. The polymeric substances may be used upon dissolving them in a solvent such as water, alcohol, ketones, esters, hydrocarbons and the like or upon emulsifying or dispersing into a paste in water or other media. These polymeric materials may also be used in combinations according to the qualities demanded.

[0047] As the lubricant used in the present invention, fatty acid metal salts such as zinc stearate, calcium stearate, and the like, waxes, silicone resins, and the like may be cited.

[0048] Stabilizing agents that improve oil resistance of recorded images and the like, such as 4,4'-butylidene (6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyl diphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like may also be added in the range that does not adversely affect the desired effects for the problems described above. In addition, a benzophenone type and triazole type UV absorbers, dispersion agent, de-foaming agent, antioxidant, fluorescent dye and the like may also be used.

[0049] The types and amounts of the leuco dye, color developing agent, sensitizer and other various ingredients used in the thermosensitive recording medium of the present invention may be determined according to the required performance and printability. Although the amounts of the color developing agent, the sensitizer, the pigment, the stabilizing agent and the other ingredients are not particularly restricted, from 0.5 parts to 10 parts of the color developing agent, from 0.1 parts to 10 parts of the sensitizer, from 0.5 parts to 20 parts of the pigment, from 0.01 parts to 10 parts of the stabilizing agent and from 0.01 parts to 10 parts of the other ingredients are ordinarily used per 1 part of the leuco dye. The content (in solid) of the binders in the thermosensitive recording layer is suitably around from 5 to 25 weight %.

[0050] The leuco dye, the color developing agent and the other materials added as needed are finely ground into particles with several microns or smaller in size, by using a grinder or a suitable emulsification device such as a ball mill, attritor, sand grinder and the like. The coating solutions are prepared by adding a binder and various additives to these depending on the objective. Water, alcohol and the like can be used as the solvent for the coating solution and the content (in solid) of the coating solution is about from 20 to 40 weight %.

[0051] In the thermosensitive recording medium of the present invention, the protective layer contains a phosphate ester compound.

[0052] The phosphate ester compound used in the present invention include s, such as, monocaproyl phosphate, monooctyl phosphate, monocapryl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, monophosphate ester of tetraethylene glycol mononeopentyl ether, monophosphate ester of triethylene glycol monotridecyl ether, monophosphate ester of tetraethylene glycol monolauryl ether, monophosphate ester of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, dicetyl phosphate, distearyl phosphate, diphosphate ester of tetraethylene glycol mononeopentyl ether, diphosphate ester of triethylene glycol monotridecyl ether, diphosphate ester of tetraethylene glycol monolauryl ether, and diphosphate ester of diethylene glycol monostearyl ether. The phosphate ester compound is available, for example, from Chukyo Yushi CO.,LTD. under the trade name of "Sepal 328", "Sepal 365", "Sepal 380", "Sepal 440", "Sepal 441", "Sepal 517", "Sepal 521", and "Sepal M835".

[0053] Among these, in the present application, Sepal M835 is preferred. Since it is a liquid substance at room temperature and does not have a specific melting point, 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.

[0054] The amount of the phosphate ester compound used in the present invention is preferably 2.5 to 15.0 parts by weight(hereinafter, parts by weight is calculated as solid content.), more preferably 2.5 to 11.5 parts by weight per 100 parts by weight of the total solid of the outermost coating layer. When the amount of the phosphate ester compound is less than 2.5 parts by weight, good stick resistance may not be obtained, whereas when it exceeds 11.5 parts by weight, print storage stability (plasticizer resistance) may decrease.

[0055] The protective layer of the present invention may contain other optional components, such as a binder and a pigment showed about the thermosensitive recording layer as needed.

[0056] The amount of the binder or the combined amount of the binder and the pigment in the protective layer is, in terms of solid content, usually from 80 to 100 weight %, preferably from 90 to 100 weight %. The amount of the binder is preferably about from 30 to 300 parts by weight per 100 parts by weight of the pigment.

[0057] The crosslinking agent may be used in combination in the protective layer of the present invention. Such crosslinking agent includes, for example, epichlorohydrin resins such as poly(amine epichlorohydrin) resins, poly(amide epichlorohydrin) resins and the like; modified modified polyamine / amide resins such as polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, polyalkylene polyamine polyamide polyurea resins, and the like; glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alums (aluminum potassium sulfate), ammonium chloride, and the like.

[0058] It is preferable that the protective layer contains an epichlorohydrin-based resin and a polyamine / polyamide-based resin, which further improves the water resistance.

[0059] The thermosensitive recording medium of the present invention may have a back-coating layer on the opposite side of the thermosensitive recording layer of the substrate. The back-coating layer may contain water-soluble polymer, water-dispersed resin, pigment, etc.

[0060] Examples of the water-soluble polymer include polyvinyl alcohol other than ethylene-vinyl alcohol copolymer, 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, cationic starch, urea phosphate esterified starch, and hydroxyethyl etherified starch; cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose; polyvinylpyrrolidone; and sodium alginate.

[0061] Examples of the water-dispersed resin include natural rubber, diene rubber, non-diene rubber, and thermoplastic elastomer.

[0062] Any pigment that can be used in the thermosensitive recording layer can be used as the pigment, as appropriate, but aluminum hydroxide, silica, kaolin, and calcined kaolin are preferred, and aluminum hydroxide is more preferred.

[0063] This back-coating layer may also contain, as necessary, lubricants, crosslinking agents, UV absorbing agents, dispersants, defoaming agents, fluorescent dyes, etc. that can be used in the thermosensitive recording layer, within the range that does not impair the desired advantages on the above-mentioned problems.

[0064] Preferably, the back-coating layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

[0065] The ethylene-vinyl alcohol copolymer is a polymer having an ethylene unit and a vinyl alcohol unit. The ethylene-vinyl alcohol copolymer is usually obtained by polymerizing ethylene and vinyl ester, and then saponifying the resulting ethylene-vinyl ester copolymer. An ethylene content is preferably 3 to 20 mol %. In order to impart a barrier property, the saponification degree of the ethylene-vinyl alcohol copolymer is preferably 80 to 100 mol %. When the saponification degree is less than 80 mol %, sufficient barrier property and moisture resistance can not be obtained.

[0066] 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.

[0067] The ethylene-acrylic copolymer is preferably one or more 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 consisting of other compound which is copolymerizable with ethylene and acrylic monomer.

[0068] Among these, ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer are more preferable, and ethylene-acrylic acid copolymer is even more preferable.

[0069] As a specific example of the ethylene-acrylic copolymer, for example, an aqueous dispersion of an ethylene-acrylic acid copolymer ammonium salt is available as ZAIKTHENE (registered trademark) AC (copolymerization ratio of acrylic acid: 20%, manufactured by Sumitomo Seika Chemicals Co., Ltd.).

[0070] A content(in solid) of the ethylene-vinyl alcohol copolymer in the back-coating layer is preferably 10 to 80 weight %, more preferably 10 to 50 weight %.

[0071] A content(in solid) of the ethylene-acrylic copolymer in the back-coating layer is preferably 10 to 80 weight %, more preferably 50 to 80 weight %.

[0072] However, a combined amount(in solid) of the ethylene-vinyl alcohol copolymer and the ethylene-acrylic copolymer in the back-coating layer is preferably 50 to 100 weight %, more preferably 50 to 90 weight %, even more preferably 70 to 90 weight %.

[0073] Further, a content ratio (in solid) of the ethylene-acrylic copolymer is preferably 2.5 to 40 weight parts, more preferably 10 to 40 weight parts per 10 weight parts of the ethylene-vinyl alcohol copolymer.

[0074] A content(in solid) of the pigment in the back-coating layer is preferably 50 to 10 weight %, more preferably 30 to 10 weight %.

[0075] The coating amount of the back-coating layer is not limited in particular, but may be determined according to the required performance and the recording suitability. The typical coating amount (in solid) of the back-coating layer is ordinarily in the range of from 0.1 to 5g / m 2< . The coating amount of 2.5 to 4.5g / m is preferable since excellent water vapor barrier property and excellent quality as the thermosensitive recording medium can be obtained.

[0076] The thermosensitive recording medium of the present invention may further have an undercoat layer between the substrate and the thermosensitive recording layer.

[0077] The undercoat layer comprises mainly a binder and a pigment.

[0078] As the binder used for the undercoat layer, commonly used water-soluble polymer or emulsion of hydrophobic polymer may be appropriately used. Specific examples include cellulose derivatives such as polyvinyl alcohol, polyvinyl acetal, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, etc.; water-soluble polymers such as starch and its derivatives, sodium polyacrylic acid, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylate copolymer, alkali salt of styrene / maleic anhydride copolymer, alkaliate of isobutylene / maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, casein, etc.; emulsion of hydrophobic polymer such as polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene / acrylic copolymer, and the like. These may be used individually and as mixtures of at least two of them.

[0079] Any generally used pigment may be used as the pigment in the undercoat layer. As the pigment, for example, inorganic pigment, such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcined kaolin, clay, talc and the like may be used. These pigments may be used alone or in combination of two or more.

[0080] The amount of the pigments in the undercoat layer is ordinarily from 50 to 95 weight parts, preferably from 70 to 90 weight parts per 100 parts by weight of the total solid of the undercoat layer.

[0081] Various aids such as a dispersion agent, plasticizer, pH controlling agent, de-foaming agent, water retention agent, preservative, coloring dye, UV absorber and the like may be added to the cating solution for the undercoat layer, as required.

[0082] In the present invention, the method for coating the thermosensitive recording layer and other coating layers, such as protective layer and undercoat layer, is not limited in particular, but any known conventional techniques may be used. The method for coating may be appropriately selected from off-machine coating machines and on-machine coating machines, which are equipped with coaters such as air knife coater, rod blade coater, bent blade coater, bevel blade coater, roll coater, curtain coater and the like.

[0083] The coating amounts of the thermosensitive recording layer and other coating layers are not limited in particular, but may be determined according to the required performance and the recording suitability. The typical coating amount (in solid) of the thermosensitive recording layer is ordinarily in the range of from 2 to 12g / m 2< and the coating amount of the protective layer is preferably in the range of from 0.5 to 5.0 g / m 2< .

[0084] Furthermore, various technologies known in the thermosensitive recording medium field, such as a flattening treatment such as super calendaring and the like can be applied as needed after coating individual coating layers.[Examples]

[0085] The following Examples illustrate the present invention, but the Examples are not intended to limit the scope of the present invention. In the following description, the terms parts and % indicate parts by weight and weight %, respectively.[Preparation of each coating solution]

[0086] Undercoat layer coating solution was prepared by dispersing and stirring the following formulation:[Undercoat layer coating solution]

[0087] Calcined kaolin (Imeris Minerals Japan.: Alpha-Tex HP)50.0 partsPlastic hollow particle(Zeon Corporation, MH8109)50.0 partsStyrene-butadiene copolymer latex (Zeon Corporation, ST5526, solid content: 48%)10.0 partsWater50.0 parts

[0088] Each of color developing agent dispersion(liquids A1-A2), leuco dye dispersion(liquid B), and sensitizer dispersion (liquid C) having the following blend was wet ground separately by a sand grinder to an average particle size of 0.5 µm.Color developing agent dispersion (liquid A1)

[0089] N-[2-(3-phenylureido)phenyl]benzenesulfonamide(Nippon Soda Co., Ltd. NKK1304, hereinafter referred to as "urea compound 1")6.0 partsFully saponified polyvinyl alcohol aqueous solution (KURARAY CO., LTD.,PVA117, solid content 10 %)5.0 partsWater1.5 parts Color developing agent dispersion (liquid A2)

[0090] N, N'-di- [3- (p-toluenesulfonyloxy) phenyl] urea (hereinafter referred to as "urea compound 2")6.0 partsAqueous solution of completely saponified polyvinyl alcohol (PVA117)5.0 partsWater1.5 parts Leuco dye dispersion (liquid B)3-di buthylamino-6-methyl-7-anilinofluoran

[0091] (Yamamoto Chemicals, Inc., ODB-2)6.0 partsFully saponified polyvinyl alcohol aqueous solution (PVA117)5.0 partsWater1.5 parts Sensitizer dispersion (liquid C)

[0092] 1,2-bis(3-Methylphenoxy) ethane (Sanko Co. Ltd, KS232)6.0 partsFully saponified polyvinyl alcohol aqueous solution (PVA117)5.0 partsWater1.5 parts

[0093] Next, each dispersion was mixed in the following percentage to prepare a thermosensitive recording layer coating solution.<Thermosensitive recording layer coating solution 1>

[0094] Color developing agent dispersion (liquid A1)18.0 partsLeuco dye dispersion (liquid B)18.0 partsSensitizer dispersion (liquid C)36.0 partsSilica dispersion(Mizusawa Industrial Chemicals, Ltd. MIZUKASIL P-537, solid content 25%)17.5 partsFully saponified polyvinyl alcohol aqueous solution (PVA117)30.0 parts <Thermosensitive recording layer coating solution 2>

[0095] Color developing agent dispersion (liquid A2)18.0 partsLeuco dye dispersion (liquid B)18.0 partsSensitizer dispersion (liquid C)36.0 partsSilica dispersion(MIZUKASIL P-537)17.5 partsFully saponified polyvinyl alcohol aqueous solution (PVA117)30.0 parts

[0096] Next, protective layer coating solution was prepared by mixing the following formulations:<Protective layer coating solution>

[0097] Aluminum hydroxide dispersion (Martinsberg: Martifin OL, solid content: 50%)9.0 partsCarboxy-modified polyvinyl alcohol solution (Kuraray Co., Ltd., trade name: KL318, degree of polymerization: about 1700, degree of saponification: 95 to 99 mol%, solid content 10%)30.0 partsPoly(amide epichlorohydrin) resin (Seiko PMC Corporation, trade name:WS4030, solid content 25%)4.0 partsModified polyamine resin (Sumitomo Chemical Co., Ltd. trade name: Sumirez Resin SPI-102A, solid content 45%)2.2 partsPhosphate ester compound (Chukyo Yushi CO.,LTD. trade name :Sepal M835, solid content: 20%)3.5 partsWater22.8 parts

[0098] Back-coating layer coating solution was prepared by mixing the following formulation:[Back-coating layer coating solution]

[0099] kaolin (Imeris Minerals Japan.: trade name contour 1500 )20.0 partsethylene-vinyl alcohol copolymer (KURARAY CO., LTD., trade name exceval RS4104)10.0 partsethylene-acrylic copolymer(Sumitomo Seika Chemicals Co., Ltd. trade name ZAIKTHENE AC, melting point:80-95 degree C)40.0 parts [Example 1]

[0100] The undercoat layer coating solution was applied on one side of a substrate (groundwood free paper with a basis weight of 60 g / m 2< ) by using a bent blade coater with a coating amount (in solid) of 6.0 g / m 2< , and was dried to prepare an undercoated paper.

[0101] The thermosensitive recording layer coating solution 1 was applied on the undercoat layer of the undercoated paper by using a rod blade coater with a coating amount (in solid) of 3.0 g / m 2< and was dried and super calendared so that the smoothness was 500-1000 seconds to prepare a thermosensitive recording layer coated paper.

[0102] Then the protective layer coating solution was applied on the thermosensitive recording layer of the thermosensitive recording layer coated paper by using a rod blade coater with a coating amount (in solid) of 3.0 g / m 2< and was dried to prepare a thermosensitive recording medium.[Example 2]

[0103] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing the amount of the phosphate ester compound from 3.5 parts to 1.75 parts in the protective layer coating solution.[Example 3]

[0104] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing the amount of the phosphate ester compound from 3.5 parts to 7.0 parts in the protective layer coating solution.[Example 4]

[0105] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing 3.5 parts of the phosphate ester compound of to 3.5 parts of a stearyl phosphate ester potassium salt emulsion (trade name: woopol 1800, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., solid content 35%).[Example 5]

[0106] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing the thermosensitive recording layer coating solution 1 to the thermosensitive recording layer coating solution 2.[Example 6]

[0107] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception that after the protective layer coating solution was applied, the back-coating layer coating solution was applied on the opposite side of the protective layer by using a rod blade coater with a coating amount (in solid) of 3.5 g / m 2< and was dried to prepare a thermosensitive recording medium.[Example 7]

[0108] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing 30.0 parts of the carboxy-modified polyvinyl alcohol solution (KL318) to 30.0 parts of a carboxy-modified polyvinyl alcohol solution (Kuraray Co., Ltd., trade name: KL118, degree of polymerization: about 1700, degree of saponification: 85 to 90 mol%, solid content 10%).[Comparative Example 1]

[0109] A thermosensitive recording medium was prepared in the same manner as described in Example 2 with the exception of changing the color developing agent (urea compound 1) to 4-benzyloxy-4'-dihydroxy diphenyl sulfone (Nikka Chemical Co., Ltd., trade name: BPS-MA3) in the thermosensitive recording layer coating solution1[Comparative Example 2]

[0110] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing 3.5 parts of the phosphate ester compound to 3.5 parts of Zinc stearate (Chukyo Yushi Co., Ltd., trade name: HydrinZ-7-30, solid content: 30%) in the protective layer coating solution.[Comparative Example 3]

[0111] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing 3.5 parts of the phosphate ester compound to 1.75 parts of Zinc stearate (Chukyo Yushi Co., Ltd., trade name: HydrinZ-7-30) in the protective layer coating solution.[Comparative Example 4]

[0112] A thermosensitive recording medium was prepared in the same manner as described in Example 1 with the exception of changing 3.5 parts of the phosphate ester compound to 7.0 parts of Zinc stearate (HydrinZ-7-30) in the protective layer coating solution.

[0113] The prepared thermosensitive recording media were evaluated as below.<Color developing property (Recorded density)>

[0114] A checkerboard pattern was printed on the prepared thermosensitive recording medium by using a thermosensitive recording medium print tester (Okura Engineering Co., Ltd. TH-PMD equipped with a thermal head by Kyocera Co.) at applied energy of 0.35 mJ / dot and printing speed of 50mm / sec. The density of the printed portion was measured by using Macbeth Densitometer (RD-914, with Amber filter) to evaluate the color developing property (recorded density).<Stick Resistance >

[0115] Printing was conducted on the prepared thermosensitive recording medium by using TH-PMD of Okura Engineering Co., Ltd. at applied energy of 0.34 mJ / dot and printing speed of 50mm / sec. The condition of stick and the noise during recording was evaluated on the following criteria. Good:No unprinted area is observed and almost no noise Fair:Slight unprinted area is observed but almost no noise Poor:Frequent unprinted area is observed and there is a loud noise <Prevention of head debris)>

[0116] A solid pattern was printed on the prepared thermosensitive recording medium by using UP-X898MD (Medical thermal printer) of Sony Corporation for 20m to 1000m under S mode condition. Deposits stuck to the thermal head after printing was evaluated visually with the following criteria: Good:Almost no deposits to a thermal head Fair:There is a slight buildup of deposits to a thermal head Poor:Accumulation of deposits is observed to a thermal head

[0117] The evaluation results are shown in following Table 1. [Table 1]Thermosensitive recording layerProtective layerBack-coating layerColor developin g propertyStick resistancePrevention of head debrisColor developing agentLubricantFormulated amount (Percentage)20m printing200m printing1000m printing(30cm, L'espritR-8)Example 1urea compound 1phosphate ester compound3.5 parts (5.0%)-1.30GoodGoodGoodGoodGoodExample 2urea compound 1phosphate ester compound1.75 parts (2.5%)-1.30GoodGoodGoodGoodGoodExample 3urea compound 1phosphate ester compound7.0 parts (10.0%)-1.29GoodGoodGoodGoodGoodExample 4urea compound 1stearyl phosphate ester potassium salt3.5 parts (5.0%)-1.31GoodGoodGoodGoodGoodExample 5urea compound 2phosphate ester compound3.5 parts (5.0%)-1.33GoodGoodGoodGoodGoodExample 6urea compound 1phosphate ester compound3.5 parts (5.0%)ethylene-acrylic acid copolymer1.33GoodGoodGoodGoodGoodExample 7urea compound 1phosphate ester compound3.5 parts (5.0%)-1.32GoodGoodGoodFairGoodComp-Example 1BPS-MA3phosphate ester compound1.75 parts (2.5%)-1.29GoodGoodFairPoorGoodComp-Example 2urea compound 1zinc stearate3.5 parts (5.0%)-1.29GoodGoodPoorPoorPoorComp-Example 3urea compound 1zinc stearate1.75 parts (2.5%)-1.30PoorGoodPoorPoorPoorComp-Example 4urea compound 1zinc stearate7.0 parts (10.0%)1.30GoodGoodPoorPoorPoor

[0118] As shown in Table 1, the thermosensitive recording medium of the present invention prevents deposit of head debris head during long-run printing without adversely affecting color developing sensitivity, and prevention of head debris adhesion becomes good.

Claims

1. A thermosensitive recording medium having a thermosensitive recording layer comprising a colorless or pale colored electron donating leuco dye and an electron accepting color developing agent on a substrate, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains at least one kind of urea compound represented by the following general formula (Formula 1), and wherein the protective layer contains a phosphate ester compound (wherein X represents -O- or -NH-, R1 represents a hydrogen atom or -SO2-R3, R3 represents a substituted or unsubstituted alkyl group, an aralkyl group or an aryl group, R2 represents a hydrogen atom or an alkyl group, m represents 0 or 1).

2. The thermosensitive recording medium of claim 1, wherein the content (in solid) of the phosphate ester compound in the thermosensitive recording layer is from 2.5 to 11.5 weight %.

3. The thermosensitive recording medium of claim 1, wherein the content (in solid) of the urea compound in the thermosensitive recording layer is from 1.0 to 70.0 weight %4. The thermosensitive recording medium of claim 1, wherein the protective layer further comprises a carboxy-modified polyvinyl alcohol with a degree of saponification of 95 mol or more as a binder.

5. The thermosensitive recording medium of claim 1, further comprises a back-coating layer on the opposite side of the thermosensitive recording layer of the substrate.

6. The thermosensitive recording medium of claim 5, wherein the back-coating layer contains an ethylene-vinyl alcohol copolymer and an ethylene-acrylic copolymer.

7. The thermosensitive recording medium of any of claims 1 to 6, wherein the urea compound is the following (1) or (2), (1) a first urea compound represented by the following general formula (Formula 2) (wherein R1, R2, R3, and n are defined as described above), (2) a second urea compound represented by the following general formula (Formula 3) (where, R2 is defined as described above, R4 to R8 may be identical or different from each other and represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group),8. The thermosensitive recording medium of claim 7, wherein the first urea compound is represented by the following general formula (Formula 6) (wherein R9 may be identical or different from each other and represent an alkyl group or an alkoxy group, and o represents an integer of 0 to 3).

9. The thermosensitive recording medium of claim 7, wherein the second urea compound is N-[2-(3-phenylureido) phenyl] benzenesulfonamide.

Images