Thermal recording medium

Abstract

To provide a thermosensitive recording body which uses a color developing system containing both a leuco dye type color developing component and a metal chelate type color-developing component in a thermosensitive recording layer and is significantly improved in heat resistance and yellowing resistance.SOLUTION: There is provided a thermosensitive recording body which has a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting color developing agent on a support, wherein the ratio of the total content (solid content) of the metal chelate type color-developing component to the total (leuco dye type color developing component) content (solid content) of the electron-donating leuco dye and the electron-accepting color developing agent is 0.05 to 0.15.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermal recording medium that utilizes a color-forming system containing a leuco dye-type color-forming component and a metal chelate-type color-forming component, and that has improved heat resistance and yellowing resistance. [Background technology]

[0002] A thermal recording medium generally has a thermal recording layer made of a colorless or light-colored electron-donating leuco dye (hereinafter sometimes simply referred to as "leuco dye") and an electron-accepting color developer (hereinafter sometimes simply referred to as "color developer"; the color-forming component containing these leuco dyes and color developers is also simply referred to as "leuco dye-type color-forming components"), binder, filler, sensitivity enhancer, lubricant, and other auxiliary agents, and is an information recording medium that obtains recorded information (color-forming information) by heat from a thermal head, hot stamp, heat pen, laser light, etc. These thermosensitive recording media are used in a wide range of applications, including measurement recorders, computer terminal printers, facsimiles, automatic ticket vending machines, and barcode labels. However, as recording devices become more diverse and sophisticated, the quality requirements for thermosensitive recording media are becoming more stringent. For example, as recording speeds increase, it is becoming necessary to obtain high-density, clear recorded information even with minimal thermal energy. On the other hand, there is a demand for thermosensitive recording media with excellent storage stability, such as light resistance, heat resistance, water resistance, oil resistance, and plasticizer resistance. Furthermore, thermosensitive recording media that utilize the color-developing reaction between a leuco dye and a color developer have the problem that the recorded information fades over time. To address this problem of faded recorded information, thermosensitive recording media containing a metal chelate-type color-developing component consisting of an electron donor and an electron acceptor have been disclosed (Patent Documents 1 to 4, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 59-89193 [Patent Document 2] Patent Publication No. 06-155915 [Patent Document 3] Patent Publication No. 2010-115836 [Patent Document 4] Patent Publication No. 2018-167483 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, thermosensitive recording media using color-forming systems containing both leuco dye-type color-forming components and metal chelate-type color-forming components in the thermosensitive recording layer have been adopted mainly for the purpose of preventing fading of printed images (e.g., Patent Documents 1 to 3, etc.). However, thermosensitive recording media are also desired to have excellent other properties (e.g., heat resistance, yellowing resistance, etc.). In color-forming systems containing a leuco dye-type color-forming component and a metal chelate-type color-forming component in the thermal recording layer of such thermal recording media, a formulation with a relatively high weight ratio of the metal chelate-type color-forming component to the leuco dye-type color-forming component (i.e., total solids weight of the metal chelate-type color-forming component / total solids weight of the leuco dye-type color-forming component) has been used (for example, in the examples of Patent Documents 1 to 4, this ratio was 1.16, 1.36, 0.5, and 0.19, respectively). [Means for solving the problem]

[0005] The present inventors have extensively investigated formulations with a lower ratio and have found that heat resistance and yellowing resistance are significantly improved when this ratio is 0.15 or less, leading to the completion of the present invention. The inventors have also found that in order to maintain other performance properties of the thermosensitive recording medium (e.g., oil resistance, plasticizer resistance, solvent resistance, etc.), this ratio must be at least 0.05. That is, the present invention provides a thermosensitive recording medium having a thermosensitive recording layer containing a colorless or pale-colored electron-donating leuco dye and an electron-accepting developer on a support, The heat-sensitive recording layer contains, as a metal chelate type color-developing component, iron stearate and a compound represented by the following general formula (Chemical Formula 1): [ka] (wherein R is an alkyl group having 18 to 35 carbon atoms, [ka] (In the formula, R 1 represents an alkyl group having 18 to 35 carbon atoms, and -X- represents -CH2-, -CO2-, -CO-, -O-, -CONH-, -CONR 2 -(In the formula, R 2 represents an alkyl group having 18 to 35 carbon atoms, -SO2-, -SO3- or -SO2NH-, and n represents an integer of 2 or 3. and a polyhydroxy aromatic compound represented by In the thermosensitive recording medium, the ratio of the total content (solid content) of the metal chelate type color-forming component to the total content (solid content) of the electron-donating leuco dye and the electron-accepting color developer in the thermosensitive recording layer is 0.05 to 0.15. BEST MODE FOR CARRYING OUT THE INVENTION

[0006] The heat-sensitive recording layer of the present invention contains a colorless or pale-colored electron-donating leuco dye and an electron-accepting developer (both of which are leuco dye-type color-forming components), and further contains a metal chelate-type color-forming component. In the thermosensitive recording medium of the present invention, iron stearate is used as the higher fatty acid metal salt contained as the electron acceptor in the metal chelate color-forming component used in the thermosensitive recording layer. Compared to other higher fatty acid metal salts commonly used as electron acceptors for metal chelate color-forming components, the present invention using iron stearate has advantages such as excellent heat resistance and yellowing resistance in the non-printed areas.

[0007] Among the metal chelate type color-forming components used in the heat-sensitive recording layer of the present invention, the polyhydroxy aromatic compound contained as an electron donor is represented by the following general formula (Chemical Formula 1). [ka] (wherein R is an alkyl group having 18 to 35 carbon atoms, [ka] (In the formula, R1 represents an alkyl group having 18 to 35 carbon atoms, and -X- represents -CH2-, -CO2-, -CO-, -O-, -CONH-, -CONR 2 -(In the formula, R 2 represents an alkyl group having 18 to 35 carbon atoms.) represents -SO2-, -SO3- or -SO2NH-, and n represents an integer of 2 or 3.)

[0008] The polyhydric hydroxy aromatic compound, in other words, the polyhydric phenol derivative, contained as an electron donor in the thermosensitive recording layer of the present invention must avoid reaction with the electron acceptor and must have high solvent resistance and dispersion stability when it is dispersed in an aqueous or solvent-based binder to prepare a coating solution. For this reason, it is desirable to increase the number of carbon atoms in the substituents other than the color-forming group to 18 to 35. It is also desirable that the number of hydroxyl groups is 2 or 3, and that the hydroxyl groups are adjacent to each other. Specific examples include, but are not limited to, the following. These polyhydric phenols can be used alone or in combination of two or more types as needed. In the formula below, R and R 1 and R 2 is defined as above.

[0009] [ka]

[0010] [ka]

[0011] [ka]

[0012] Next, various materials that can be used in the thermosensitive recording layer of the thermosensitive recording body of the present invention will be exemplified. However, binders, crosslinking agents, pigments, etc. can also be used in coating layers other than the thermosensitive recording layer, i.e., protective layers and undercoat layers, if necessary, to the extent that they do not impair the desired effects for the above-mentioned problems.

[0013] The electron-donating leuco dye used in the present invention can be any known one in the field of conventional pressure-sensitive or heat-sensitive recording paper, and is not particularly limited. However, preferred are triphenylmethane compounds, fluoran compounds, fluorene compounds, and divinyl compounds. Specific examples of representative colorless or pale-colored leuco dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination.

[0014] <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)

[0015] <Fluoran-based leuco dyes> 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-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-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-chlorofluoran; 3-Dibutylamino-6-ethoxyethyl-7-anilinofluoran; 3-Dibutylamino-6-chloro-7-anilinofluoran; 3-Dibutylamino-6-methyl-7-p-methylanilinofluoran; 3-Dibutylamino-7-(o-chloroanilino)fluoran; 3-Dibutylamino-7-(o-fluoroanilino)fluoran; 3-Di-n-pentylamino-6-methyl-7-anilinofluoran; 3-Di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran; 3-Di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran; 3-Di-n-pentylamino-6-chloro-7-anilinofluoran; 3-Di-n-pentylamino-7-(p-chloroanilino)fluoran; 3-Pyrrolidino-6-methyl-7-anilinofluoran; 3-Piperidino-6-methyl-7-anilinofluoran; 3-(N-Methyl-N-propylamino)-6-methyl-7-anilinofluoran; 3-(N-Methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran; 3-(N-Ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran; 3-(N-Ethyl-N-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-anilinofluoran2-(4-Oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran; 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-Benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-Hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 3-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 3-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 3-Diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran; 2,4-Dimethyl-6-[(4-dimethylamino)anilino]-fluoran;

[0016] <Fluorene-based leuco dye> 3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-Tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0017] <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

[0018] <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-(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

[0019] The color developer that can be used in the thermal recording medium of the present invention can be any of those known in the field of conventional pressure-sensitive or thermal recording paper, and is not particularly limited. Examples of the color developer that can be used 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, 4- Benzyl hydroxybenzoate, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 1-[4-(4-hydroxyphenyl)

[0033] bis(4-hydroxyphenyl)-1-phenylethane, 1,5-di(4-hydroxyphenyl)-3-oxapentane, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, 1,1-bis(4-hydroxyphenyl)-1-phenylethane ... phenolic compounds such as 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), diphenyl sulfone-bridged compounds described in WO97 / 16420, compounds described in WO02 / 081229 or JP2002-301873A, and N,Examples of color developers include thiourea compounds such as N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, zinc bis[4-(n-octyloxycarbonylamino)salicylate] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, as well as salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. These color developers can be used alone or in combination. 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane is available, for example, from API Corporation under the trade name JKY-214; the phenol condensation composition described in JP 2003-154760 A is available, for example, from API Corporation under the trade name JKY-224; and the diphenyl sulfone-bridged compound described in International Publication WO97 / 16420 is available from Nippon Soda Co., Ltd. under the trade name D-90. Furthermore, compounds described in WO02 / 081229 and the like are available from Nippon Soda Co., Ltd. under the trade names NKK-395 and D-100.

[0020] Sensitizers usable in the thermal recording medium of the present invention include fatty acid amides such as stearic acid amide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di-(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- Examples of sensitizers include p-tolyl carbonate, phenyl-α-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, and phenyl p-toluenesulfonate. These sensitizers may be used alone or in combination. These sensitizers are generally used mainly to improve the color-forming performance of leuco dye-type color-forming components. However, as a result of examining the effects of sensitizers in the color-forming system of the present invention, it was found that, among these sensitizers, 1,2-di(3-methylphenoxy)ethylene is preferred because it has excellent color-forming performance, yellowing resistance, and plasticizer resistance.

[0021] The binder used in the present invention may be a polyvinyl alcohol 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, or other modified polyvinyl alcohol; (meth)acrylic acid; and a monomer component copolymerizable with (meth)acrylic acid (olefin). Examples of polymeric substances include acrylic resins made of cellulose acetate (excluding cellulose acetate), 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 copolymer, styrene-butadiene copolymer, casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrose and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, and coumarone resin. These polymeric substances can be used by dissolving them in a solvent such as water, alcohol, ketones, esters, or hydrocarbons, or by dispersing them in water or other media in an emulsified or paste-like form, and these can also be used in combination depending on the required quality. The content (solid content) of the binder in the thermosensitive recording layer is preferably about 5 to 25% by weight.

[0022] The thermosensitive recording layer of the present invention may further contain a carboxyl group-containing resin as a binder, and may contain an epichlorohydrin-based resin and a polyamine / polyamide-based resin (excluding those contained in epichlorohydrin-based resins) as a crosslinking agent.

[0023] Examples of the carboxyl group-containing resin used in the present invention include resins containing monofunctional acrylic monomers having a carboxyl group, such as methacrylic acid, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofurfuryl methacrylate, oxidized starch, carboxymethyl cellulose, and carboxyl-modified polyvinyl alcohol in which a carboxyl group has been introduced into polyvinyl alcohol. However, it is particularly preferable to use carboxyl-modified polyvinyl alcohol, which has excellent heat resistance and plasticizer resistance. The carboxyl-modified polyvinyl alcohol used in the present invention can be obtained as a reaction product of polyvinyl alcohol with a polycarboxylic acid such as fumaric acid, phthalic anhydride, mellitic anhydride, or itaconic anhydride, or an ester of these reaction products, or as a saponified copolymer of vinyl acetate with an ethylenically unsaturated dicarboxylic acid such as maleic acid, fumaric acid, itaconic acid, crotonic acid, acrylic acid, or methacrylic acid. Specific examples of the production method include those exemplified in Examples 1 or 4 of JP-A-53-91995. The saponification degree of the carboxyl-modified polyvinyl alcohol is preferably 72 to 100 mol%, and the degree of polymerization is preferably 500 to 2400, more preferably 1000 to 2000.

[0024] The following binders can also be used in combination to the extent that they do not impair the desired performance: polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-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, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminal alkyl-modified polyvinyl alcohol; cellulose ethers and derivatives thereof such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, and acetyl cellulose; polyacrylamide; cationic polyacrylamide; Examples include polyacrylamides such as anionic polyacrylamide and amphoteric polyacrylamide, urethane resins such as polyester polyurethane resins, polyether polyurethane resins and polyurethane ionomer resins, styrene-butadiene resins such as styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer and styrene-butadiene-acrylic copolymer, polyolefin resins such as polyvinyl acetate, vinyl chloride-vinyl acetate copolymer and ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polyacrylic esters, gum arabic, polyvinyl butyral, polystyrose and copolymers thereof, silicone resins, petroleum resins, terpene resins, ketone resins and coumarone resins. These may be used alone or in combination of two or more.

[0025] Specific examples of epichlorohydrin resins used in the present invention include polyamide epichlorohydrin resins and polyamine epichlorohydrin resins, which can be used alone or in combination. Furthermore, the amines present in the main chain of the epichlorohydrin resin can be primary to quaternary amines, with no particular limitations. Furthermore, the degree of cationization and molecular weight are preferably 5 meq / g solid or less (measured at pH 7) and 500,000 or more, due to their good water resistance. Commercially available products include Sumirez Resin 650(30), Sumirez Resin 675A, and Sumirez Resin 6615 (all manufactured by Sumitomo Chemical Co., Ltd.), WS4002, WS4020, WS4024, WS4030, WS4046, WS4010, and CP8970 (all manufactured by Seiko PMC Corporation).

[0026] In the present invention, the polyamine / polyamide resin (excluding those included in the epichlorohydrin resin) means a polyamine resin and / or a polyamide resin, which is a compound different from the epichlorohydrin resin. Specific examples include polyamide urea resin, polyalkylene polyamine resin, polyalkylene polyamide resin, polyamine polyurea resin, modified polyamine resin, modified polyamide resin, polyalkylene polyamine urea formalin resin, and polyalkylene polyamine polyamide polyurea resin. Commercially available products include Sumirez Resin 302 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirez Resin 712 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirez Resin 703 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirez Resin 636 (Sumitomo Chemical Co., Ltd.: polyamine polyurea resin), Sumirez Resin SPI-100 (Sumitomo Chemical Co., Ltd.: modified polyamine resin), Sumirez Resin SPI-102A (Sumitomo Chemical Co., Ltd.: modified polyamine resin), and Sumirez Resin SPI-106N (Sumitomo Chemical Co., Ltd.: modified polyamide resin). ), Sumirez Resin SPI-203(50) (Sumitomo Chemical Co., Ltd.), Sumirez Resin SPI-198 (Sumitomo Chemical Co., Ltd.), Printive A-700 (Asahi Kasei Corporation), Printive A-600 (Asahi Kasei Corporation), PA6500, PA6504, PA6634, PA6638, PA6640, PA6644, PA6646, PA6654, PA6702, and PA6704 (all manufactured by Seiko PMC Corporation: polyalkylene polyamine polyamide polyurea resins), are not particularly limited, and these may be used alone or in combination of two or more. From the viewpoint of color development sensitivity, it is preferable to use polyamine resins (polyalkylene polyamine resins, polyamine polyurea resins, modified polyamine resins, polyalkylene polyamine urea formalin resins, and polyalkylene polyamine polyamide polyurea resins).

[0027] In addition to the above components, the heat-sensitive recording layer of the present invention may contain pigments, lubricants, crosslinking agents, etc. Examples of pigments that can be used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. These may be used alone or in combination of two or more. Examples of the lubricant used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, silicone resins, and the like. Furthermore, in the present invention, a crosslinking agent such as a polyimine resin, glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, or ammonium chloride can also be used in combination, if necessary, within a range that does not impair the desired effect for solving the above problems. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, antifoaming agents, fluorescent dyes, etc. may also be used.

[0028] The types and amounts of the metal chelate color-forming component, electron-donating leuco dye, electron-accepting organic color-developing agent, and other components used in the thermal recording medium of the present invention are determined according to the required performance and recording suitability, and are not particularly limited, but typically, 0.1 to 10 parts by weight of the electron donor polyhydroxy aromatic compound is used per 1 part by weight of iron stearate, which is the electron acceptor for the metal chelate color-forming component.When a pigment is used, typically, 0.5 to 50 parts by weight of the pigment is used per 1 part by weight of higher fatty acid metal salt, which is the electron acceptor for the metal chelate color-forming component. The electron-donating leuco dye is used in an amount of 0.1 to 10 parts by weight per 1 part by weight of the higher fatty acid metal salt, and 0.5 to 10 parts by weight of the electron-accepting organic developer and 0 to 10 parts by weight, preferably 0.5 to 10 parts by weight of the sensitizer are used per 1 part by weight of the electron-donating leuco dye. In the thermosensitive recording layer of the present invention, the ratio of the total content (solid content) of the metal chelate type color-forming components to the total content (solid content) of the electron-donating leuco dye and the electron-accepting color-developing agent (leuco dye type color-forming components) is 0.05 to 0.15, preferably 0.07 to 0.13. The types and amounts of other optional components such as binders, pigments, lubricants, crosslinking agents, image stabilizers, and other components are determined according to the required performance and recording suitability and are not particularly limited, but typically, the binder content is about 5 to 50 parts by weight in solids per 100 parts by weight of the thermosensitive recording layer (solids), and the pigment content is about 0 to 50 parts by weight in solids per 100 parts by weight of the thermosensitive recording layer (solids).When a lubricant is used, the content of the lubricant is preferably about 5 to 10 parts by weight in solids per 100 parts by weight of the thermosensitive recording layer (solids).

[0029] When the thermosensitive recording layer of the present invention further contains a carboxyl group-containing resin as a binder and an epichlorohydrin resin and a polyamine / polyamide resin (excluding those contained in epichlorohydrin resins) as a crosslinking agent, the amount of the carboxyl group-containing resin blended is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, per part by weight of the higher fatty acid metal salt, which is the electron acceptor for the metal chelate color-forming component in the thermosensitive recording layer. If the amount is too small, the coating layer strength and water resistance tend to be insufficient, and if the amount is too large, sensitivity tends to decrease. The blending amounts of the epichlorohydrin resin and polyamine / polyamide resin (excluding those contained in the epichlorohydrin resin) are preferably 1 to 100 parts by weight, and more preferably 5 to 50 parts by weight, per 100 parts by weight of the carboxyl group-containing resin. If the blending amount is too small, the crosslinking reaction will be insufficient and good water resistance will not be obtained, whereas if the blending amount is too large, problems with operability will occur due to increased viscosity and gelation of the coating liquid.

[0030] The thermosensitive recording medium of the present invention may further have a protective layer on the thermosensitive recording layer. The protective layer mainly comprises a binder and a pigment, and may further comprise a crosslinking agent. As the binder, pigment and crosslinking agent, any of the above-mentioned materials usable for the heat-sensitive recording layer can be used.

[0031] In the present invention, an undercoat layer may be provided between the support and the heat-sensitive recording layer, and this undercoat layer mainly comprises a binder and a pigment. The binder used in the undercoat layer may be any of the various binders used in the thermosensitive recording layer described above, and these binders may be used alone or in combination of two or more. The pigments used in the undercoat layer may be any of the various pigments used in the heat-sensitive recording layer described above, and these pigments may be used alone or in combination of two or more. The amount of pigment in the undercoat layer is usually 50 to 95 parts by weight, preferably 70 to 90 parts by weight, based on 100 parts by weight of the total solid content of the undercoat layer. The undercoat layer may contain various auxiliary agents such as dispersants, plasticizers, pH adjusters, antifoaming agents, water-retaining agents, preservatives, coloring dyes, and ultraviolet protection agents, as required.

[0032] The thermosensitive recording medium of the present invention may have a backcoat layer on the surface of the support opposite to the thermosensitive recording layer. The backcoat layer may contain a water-dispersible resin and a pigment. The water-dispersible resin is preferably at least one selected from the group consisting of natural rubber, diene rubber, non-diene rubber, and thermoplastic elastomer. As this pigment, any of the pigments listed above as usable for the 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, etc., which are listed as usable in the above-mentioned thermosensitive recording layer, within the range that does not impair the desired effects for solving the above problems.

[0033] The desired thermosensitive recording medium can be obtained by applying a coating liquid having the composition formulated for each coating layer to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, nonwoven fabric, etc. A composite sheet combining these may also be used as the support. The electron-donating leuco dye, electron-accepting developer, electron acceptor, electron donor, and any other materials added as needed are pulverized to particle sizes of several microns or less using a grinder such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and various additives are added depending on the purpose to prepare a coating liquid. The means for applying each of the above coating layers is not particularly limited, and coating can be performed 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, a curtain coater, or a spray coater can be appropriately selected and used. The coating weight of the thermal recording layer is determined according to the required performance and recording suitability, and is not particularly limited, but a typical coating weight is 2 to 12 g / m2 in solid content. 2 That's about it. Furthermore, various well-known techniques in the field of thermosensitive recording media may be appropriately applied, such as smoothing treatment by supercalendering after coating each coating layer. [Example]

[0034] The present invention will be illustrated by the following examples, but is not intended to limit the scope of the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified. Each dispersion and coating liquid was prepared as follows.

[0035] The following mixture was stirred and dispersed to prepare a coating liquid for the undercoat layer. <Coating liquid for undercoat layer> Calcined kaolin (manufactured by BASF, product name: Ansilex 90) 100.0 parts Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., Product name: PVA117, solid content 10%) 40.0 parts Water 20.0 parts

[0036] The following higher fatty acid metal salt dispersions (Liquids A1 and A2), polyhydric hydroxy aromatic compound dispersion (Liquid B), developer dispersions (Liquids C1 to C3), leuco dye dispersion (Liquid D), sensitizer dispersions (Liquids E1 to E4), and hindered phenol compound dispersion (Liquid F) were each wet-ground in a sand grinder until the average particle size reached 0.5 microns.

[0037] Ferric stearate dispersion (A1 liquid) Ferric stearate 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Iron and zinc behenate double salt dispersion (Liquid A2) Iron-zinc behenate double salt (metal molar ratio in higher fatty acid metal double salt: iron:zinc = 2:1) (ADEKA Corporation, product name: DM-1022) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0038] Polyhydroxy aromatic compound dispersion (liquid B) A stearyl gallate compound represented by the following formula (Chemical Formula 6) (manufactured by Sumitomo Dainippon Pharma Co., Ltd.) Product name: TH-S) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water [ka]

[0039] Developer dispersion liquid (C1 liquid) 4-Hydroxy-4'-isopropoxydiphenyl sulfone (Mitsubishi Chemical Corporation, Product name: NYDS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0040] Developer dispersion liquid (C2 liquid) Diphenyl sulfone-bridged compound (manufactured by Nippon Soda Co., Ltd., product name: D-90) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0041] Developer dispersion liquid (C3 liquid) 4-benzyloxy-4'-hydroxydiphenyl sulfone (Nicca Chemical Co., Ltd.) Product name: BPS-MA3) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0042] Leuco dye dispersion (liquid D) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Industry Co., Ltd., Product name: ODB-2) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0043] Sensitizer dispersion (E1 liquid) 1,2-bis-(3-methylphenoxy)ethane (manufactured by Sanko Co., Ltd., Product name: KS232) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Sensitizer dispersion (E2 liquid) Diphenyl sulfone (Volant, trade name: DPS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0044] Sensitizer dispersion (E3 liquid) Di(parachlorobenzyl) oxalate (manufactured by DIC Corporation, trade name: HS3519) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water Sensitizer dispersion (E4 liquid) Stearic acid amide (Fine Organics, trade name: FinawaxS) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0045] Hindered phenol compound dispersion (Liquid F) 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Manufactured by ADEKA Corporation, product name: ADEKA Arcles DH-37) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0046] Next, the dispersions were mixed in the following proportions to prepare coating solutions 1 and 2 for the thermosensitive recording layer. <Coating liquid 1 for thermosensitive recording layer> Ferric stearate dispersion (A1 liquid) 1.2 parts Polyhydroxy aromatic compound dispersion (liquid B) 0.8 parts Developer dispersion liquid (C1 liquid) 13.0 parts Leuco dye dispersion (liquid D) 7.0 parts Hindered phenol compound dispersion (liquid F) 0.6 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, Solid content 25%) 40.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 60.0 parts

[0047] <Coating liquid 2 for thermosensitive recording layer> Ferric stearate dispersion (A1 liquid) 1.2 parts Polyhydroxy aromatic compound dispersion (liquid B) 0.8 parts Developer dispersion liquid (C1 liquid) 13.0 parts Leuco dye dispersion (liquid D) 7.0 parts Sensitizer dispersion (E1 solution) 4.0 parts Hindered phenol compound dispersion (liquid F) 0.6 parts Silica dispersion (Mizukasil P-537) 40.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 60.0 parts

[0048] <Coating solution 3 for thermosensitive recording layer> Iron and zinc behenate double salt dispersion (liquid A2) 1.5 parts Polyhydroxy aromatic compound dispersion (liquid B) 1.0 part Developer dispersion liquid (C1 liquid) 13.0 parts Leuco dye dispersion (liquid D) 7.0 parts Sensitizer dispersion (E solution) 4.0 parts Hindered phenol compound dispersion (liquid F) 0.6 parts Silica dispersion (Mizukasil P-537) 40.0 parts Fully saponified polyvinyl alcohol aqueous solution (PVA117) 60.0 parts

[0049] [Example 1] Support (47g / m 2 The coating solution for the primer layer was applied to one side of the paper (high-quality paper) at a coating weight of 10.0 g / m2 (solid content). 2 After coating by the bent blade method so that the thickness was as follows, the coated paper was dried to obtain a primer layer coated paper. Next, the coating solution 1 for the thermosensitive recording layer was applied to the undercoat layer of the undercoat-coated paper in a coating amount of 5.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so that the surface had a smoothness of 500 to 1000 seconds, the coating was dried and then treated with a supercalender to prepare a thermosensitive recording medium.

[0050] [Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the coating liquid 1 for the thermosensitive recording layer was changed to the coating liquid 2 for the thermosensitive recording layer. [Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the blending amount of A1 liquid in the thermosensitive recording layer coating liquid 2 was 1.5 parts and the blending amount of B liquid was 1.0 part. [Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the blending amount of A1 liquid in the thermosensitive recording layer coating solution 2 was 0.7 parts and the blending amount of B liquid was 0.35 parts. [Example 5] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the solution C1 in the coating solution 2 for the thermosensitive recording layer was changed to the solution C2.

[0051] [Example 6] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the E1 solution in the coating solution 2 for the thermosensitive recording layer was changed to the E2 solution. [Example 7] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the E1 solution in the coating solution 2 for the thermosensitive recording layer was changed to the E3 solution. [Example 8] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the E1 solution in the coating solution 2 for the thermosensitive recording layer was changed to the E4 solution. [Example 9] A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the blending amount of E1 liquid in coating liquid 2 for thermosensitive recording layer was changed to 6.0 parts.

[0052] [Comparative Example 1] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the amount of A1 liquid in the coating liquid 1 for the thermosensitive recording layer was 1.5 parts, the amount of B liquid in the coating liquid 1 for the thermosensitive recording layer was 1.0 parts, and the amount of C1 liquid in the coating liquid 1 for the thermosensitive recording layer was 6.0 parts. Comparative Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the amount of A1 liquid in the coating liquid 1 for the thermosensitive recording layer was 0.8 parts, the amount of B liquid in the coating liquid 1 for the thermosensitive recording layer was 0.4 parts, and the amount of C1 liquid in the coating liquid 1 for the thermosensitive recording layer was 30.0 parts. Comparative Example 3 A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the amount of A1 liquid in the coating liquid 2 for the thermosensitive recording layer was 0.3 parts, the amount of B liquid in the coating liquid 2 for the thermosensitive recording layer was 0.2 parts, and the amount of C1 liquid in the coating liquid 2 for the thermosensitive recording layer was 5.0 parts. Comparative Example 4 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the amount of A1 liquid in the coating liquid 1 for the thermosensitive recording layer was changed to 0.8 parts, the amount of B liquid in the coating liquid 1 for the thermosensitive recording layer was changed to 0.4 parts, the amount of C1 liquid in the coating liquid 1 for the thermosensitive recording layer was changed to 30 parts, and E1 liquid was changed to E2 liquid. Comparative Example 5 A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the A1 solution in the coating solution 2 for the thermosensitive recording layer was changed to the A2 solution. Comparative Example 6 A thermosensitive recording medium was prepared in the same manner as in Example 2, except that the A1 and B solutions in the thermosensitive recording layer coating solution 2 were not mixed, and 13 parts of C2 solution were added.

[0053] The produced thermosensitive recording medium was evaluated as follows. <Coloring performance (print density)> A checkerboard pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper printing tester, equipped with a Kyocera thermal head) at a printing speed of 50 mm / sec with applied energies of 0.21 mJ / dot, 0.31 mJ / dot, and 0.41 mJ / dot. The print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development performance (print density).

[0054] <Heat resistance> The prepared thermosensitive recording medium was treated under environmental conditions at 70°C for 24 hours, and then left to stand under environmental conditions at 23°C and 50% RH for 3 hours. The density of the non-printed areas (blank areas) was measured using a Macbeth densitometer (RD-914, using an amber filter), and the background color value was calculated from the difference between the values ​​before and after processing. The heat resistance of the non-printed areas (blank areas) was evaluated according to the following criteria. Background color value = (density of non-printed area after processing) - (density of non-printed area before processing) Excellent: Background color value is less than 0.2 Acceptable: Background color value is 0.2 or more and less than 0.5 Unacceptable: Background color value is 0.5 or more

[0055] <Yellowing resistance> The prepared thermosensitive recording medium was left standing under environmental conditions of 40°C and 75% RH for one week, and then left standing under environmental conditions of 23°C and 50% RH for three hours. The b value of the non-printed area (blank area) was measured using a CMS-35SPXM manufactured by Murakami Color Research Laboratory, and the heat resistance of the non-printed area (blank area) was evaluated according to the following criteria. Excellent: b value less than 2.0 Acceptable: b value is 2.0 or more and less than 4.0 Unacceptable: b value is 4.0 or more

[0056] <Oil resistance> A checkerboard pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper printing tester equipped with a Kyocera thermal head) at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. Salad oil was applied to the printed thermal recording medium with a cotton swab and left to stand for one week under environmental conditions of 23°C and 50% RH. After that, the print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter). The residual rate was calculated from the values ​​before and after treatment to evaluate the plasticizer resistance. Residual rate (%) = (print density of printed area after processing / print density of printed area before processing) x 100 Excellent: Survival rate is 90% or more Good: Remaining rate is 80% or more Acceptable: Residual rate is 70% or more but less than 80% Unacceptable: Residual rate less than 70%

[0057] <Plasticizer resistance> A checkerboard pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper printing tester equipped with a Kyocera thermal head) at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. The printed thermosensitive recording medium was attached to a paper tube wrapped once with PVC wrap (Hi-Wrap KMA manufactured by Mitsui Chemicals), and then wrapped with three more layers of PVC wrap on top of that. After leaving it to stand for one week under environmental conditions of 23°C and 50% RH, the print density of the printed area was measured using a Macbeth densitometer (RD-914, using an amber filter). The residual rate was calculated from the values ​​before and after treatment to evaluate plasticizer resistance. Residual rate (%) = (print density of printed area after processing / print density of printed area before processing) x 100 Excellent: Survival rate is 90% or more Good: Remaining rate is 80% or more Acceptable: Residual rate is 70% or more but less than 80% Unacceptable: Residual rate less than 70%

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

Claims

1. A thermosensitive recording medium having a thermosensitive recording layer on a support, the thermosensitive recording layer containing a colorless or pale-colored electron-donating leuco dye and an electron-accepting developer, The heat-sensitive recording layer contains, as a metal chelate type color-developing component, iron stearate and a compound represented by the following general formula (Chemical Formula 1): 【Chemical 1】 (wherein R is an alkyl group having 18 to 35 carbon atoms, 【Chemistry 2】 (In the formula, R １ represents an alkyl group having 18 to 35 carbon atoms, and —X— represents —CH ２ -, -CO ２ -, -CO-, -O-, -CONH-, -CONR ２ - (wherein, R ２ represents an alkyl group having 18 to 35 carbon atoms, —SO ２ -, -SO ３ -or-SO ２ NH—, and n is an integer of 2 or 3. and a polyhydroxy aromatic compound represented by A thermosensitive recording medium in which the ratio of the total content (solid content) of the metal chelate type color-forming component to the total content (solid content) of the electron-donating leuco dye and the electron-accepting color-developing agent in the thermosensitive recording layer is 0.05 to 0.

15.

2. 2. The thermosensitive recording medium according to claim 1, wherein the total content (solid content) of the metal chelate color-forming components in the thermosensitive recording layer is 2.0 to 5.0% by weight.

3. 3. The thermosensitive recording material according to claim 1, wherein the thermosensitive recording layer further contains 1,2-di-(3-methylphenoxy)ethane as a sensitizer.

4. 4. The thermosensitive recording material according to claim 3, wherein the content (solid content) of the sensitizer 1,2-di-(3-methylphenoxy)ethane in the thermosensitive recording layer is 4.0 to 10.0% by weight.

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