Thermal recording medium

Abstract

To provide a thermosensitive recording medium which has sufficient water resistance against water or moisture such as rain when being used outdoor, and is excellent in coloring sensitivity, printing quality in high-speed printing, ink adhesion, and solvent resistance.SOLUTION: A thermosensitive recording medium has a thermosensitive recording layer on a support, has sufficient water resistance by containing a specific silane-modified acrylic resin that is aqueous emulsion of core-shell type particles in a protective layer provided on the thermosensitive recording layer, and is excellent in coloring sensitivity, printing quality in high-speed printing, ink adhesion, and solvent resistance.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermosensitive recording medium which is excellent in water resistance, color development sensitivity, print image quality during high-speed printing, ink adhesion and solvent resistance. [Background technology]

[0002] In general, a thermal recording medium is prepared by grinding and dispersing a colorless or pale-colored electron-donating leuco dye (hereinafter referred to as "dye") and an electron-accepting developer (hereinafter referred to as "developer") such as a phenolic compound into fine particles, mixing the two, adding binders, fillers, sensitivity enhancers, lubricants and other auxiliary agents, and coating the resulting coating liquid on a support such as paper, synthetic paper, film or plastic, and the color is developed by an instantaneous chemical reaction upon heating with a thermal head, hot stamp, heat pen, laser light, etc., to obtain a recorded image. Generally, a method of providing a protective layer on the thermal recording layer is known as a method for improving the storage stability of a thermal recording medium. It is known that by incorporating a silane-modified acrylic resin into the thermosensitive recording layer or protective layer, it is possible to reduce head wear during printing and improve the image storage stability and water resistance of the thermosensitive recording medium (Patent Documents 1 and 2, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 5-574 [Patent Document 2] Patent Publication No. 2000-238432 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a thermal recording medium which has sufficient water resistance against moisture such as rain when used outdoors, and which is excellent in color development sensitivity, print image quality during high-speed printing, ink adhesion, and solvent resistance. [Means for solving the problem]

[0005] As a result of extensive research, the inventors have discovered that by incorporating a specific silane-modified acrylic resin, which is an aqueous emulsion of core-shell particles, into the protective layer, the thermal recording medium has sufficient water resistance, and is also excellent in color development sensitivity, print image quality during high-speed printing, ink adhesion, and solvent resistance, thereby completing the present invention. That is, the present invention provides a thermosensitive recording medium having a support, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer on the thermosensitive recording layer, the protective layer containing a silane-modified acrylic resin, The silane-modified acrylic resin is an aqueous emulsion of core-shell type particles having a core made of copolymer A obtained by polymerizing the following (a1), (a2) and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b). (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactants containing sulfates having allyl groups and polyoxyethylene chains Effect of the Invention

[0006] The present invention can provide a thermal recording medium that has sufficient water resistance against moisture such as rain when used outdoors, and is also excellent in color development sensitivity, print image quality during high-speed printing, ink adhesion, and solvent resistance. BEST MODE FOR CARRYING OUT THEINVENTION

[0007] In the thermal recording medium of the present invention, the protective layer provided on the thermal recording layer contains a silane-modified acrylic resin. The silane-modified acrylic resin used in the present invention is an aqueous resin emulsion obtained by multi-stage emulsion polymerization of multiple types of polymerizable unsaturated monomers in the presence of a surfactant. This silane-modified acrylic resin is an aqueous emulsion of core-shell type particles comprising a core made of copolymer A obtained by polymerizing the following (a1), (a2), and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b). (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactants containing an allyl group and a sulfate having a polyoxyethylene chain The copolymer A may be obtained by adding a styrene monomer to the above-mentioned (a1), (a2) and (a3) ​​and polymerizing them in the presence of (b), and / or the copolymer B may be obtained by adding a styrene monomer to the above-mentioned (a1) and (a2) and polymerizing them in the presence of (b).

[0008] Regarding <(a1) At least one (meth)acrylic acid ester> In this specification, the term "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid, and is meant to include at least one of acrylic acid and methacrylic acid. The term "(meth)acrylic acid ester" refers to an ester of (meth)acrylic acid, that is, a (meth)acrylate. The term "(meth)acrylate" refers to both an acrylate and a methacrylate, and is meant to include at least one of an acrylate and a methacrylate. In addition, vinyl esters having a structure in which a vinyl group is bonded to oxygen, such as vinyl acetate, are not included in the (meth)acrylates in this specification.

[0009] Specific examples of (meth)acrylates include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, octadecyl (meth)acrylate, behenyl (meth)acrylate, and docosyl (meth)acrylate; and (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. These can be used alone or in combination of two or more.

[0010] In an embodiment of the present invention, the (meth)acrylic acid ester is preferably a (meth)acrylic acid alkyl ester, and specific examples thereof include, but are not limited to, methyl methacrylate (MMA), 2-ethylhexyl acrylate (2EHA), n-butyl acrylate (n-BA), n-butyl methacrylate (n-BMA), and cyclohexyl methacrylate (CHMA).

[0011] Regarding <(a2) Monomer having an alkoxysilyl group and an ethylenic double bond> The monomer having an alkoxysilyl group and an ethylenic double bond refers to a compound capable of imparting an alkoxysilyl group to the aqueous resin emulsion resin obtained by emulsion polymerization reaction, and is not particularly limited as long as it can provide the aqueous resin emulsion according to the present invention. The monomer having an alkoxysilyl group and an ethylenic double bond has both an alkoxysilyl group and an ethylenic double bond, and the alkoxysilyl group and the ethylenic double bond may be bonded via another functional group, such as an ester bond, an amide bond, or an alkylene group. Here, the term "alkoxysilyl group" refers to a silicon-containing functional group that gives a hydroxyl group (Si-OH) bonded to silicon upon hydrolysis. Examples of the "alkoxysilyl group" include trimethoxysilyl. Cyril alkoxysilyl groups such as a triethoxysilyl group, a dimethoxysilyl group, a dimethoxymethylsilyl group, a diethoxysilyl group, a monoethoxysilyl group, and a monomethoxysilyl group; Lill In particular, a trimethoxysilyl group and a triethoxysilyl group are preferred.

[0012] In this specification, the term "ethylenic double bond" refers to a carbon atom double bond capable of undergoing a polymerization reaction (radical polymerization). Examples of functional groups having such an ethylenic double bond include a vinyl group (CH2=CH-), a (meth)allyl group (CH2=CH-CH2- and CH2=C(CH3)-CH2-), a (meth)acryloyloxy group (CH2=CH-COO- and CH2=C(CH3)-COO-), a (meth)acryloyloxyalkyl group (CH2=CH-COO-R- and CH2=C(CH3)-COO-R-), and -COO-CH=CH-COO-. Incidentally, monomers having an alkoxysilyl group and an ethylenic double bond are not included in the above-mentioned (meth)acrylic acid esters.

[0013] An example of the monomer having an alkoxysilyl group and an ethylenic double bond is a compound represented by the following formula (1). R 1 Si(OR 2 )(OR 3 )(OR 4 ) (1) In the formula, R 1 is a functional group having an ethylenic double bond, and R 2 , R 3 and R 4 R is an alkyl group having 1 to 5 carbon atoms. 2 , R 3 and R 4 may be the same or different from each other. R 1Examples of the functional group having an ethylenic double bond include a vinyl group, a (meth)allyl group, a (meth)acryloyloxy group, a 2-(meth)acryloyloxyethyl group, a 2-(meth)acryloyloxypropyl group, a 3-(meth)acryloyloxypropyl group, a 2-(meth)acryloyloxybutyl group, a 3-(meth)acryloyloxybutyl group, and a 4-(meth)acryloyloxybutyl group.

[0014] R 2、 R 3 and R 4 Examples of the alkyl group having 1 to 5 carbon atoms include linear or branched alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, and an n-pentyl group. Examples of the "monomer containing an alkoxysilyl group and having an ethylenic double bond" include vinyltrialkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltri-n-butoxysilane. Specifically, 3-(meth)acryloyloxypropyltrimethoxysilane and 3-(meth)acryloyloxypropyltriethoxysilane are preferred, and 3-methacryloxypropyltrimethoxysilane is particularly preferred. These monomers containing an alkoxysilyl group and an ethylenic double bond can be used alone or in combination.

[0015] Regarding <(a3) Monomer having a carboxyl group and an ethylenic double bond> An example of the monomer having a carboxyl group is (meth)acrylic acid. As described above, (meth)acrylic acid means both acrylic acid and methacrylic acid. It is particularly preferable to use acrylic acid as the (meth)acrylic acid. The "ethylenic double bond" is as defined above.

[0016] Regarding <(b) Polymerizable surfactants containing sulfate salts having an allyl group and a polyoxyethylene chain> Examples of sulfates having an allyl group and a polyoxyethylene group include ammonium sulfates having an allyl group and a polyoxyethylene group, sodium sulfates having an allyl group and a polyoxyethylene group, and potassium sulfates having an allyl group and a polyoxyethylene group.Specific examples include ammonium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates, sodium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates, potassium polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfates; ammonium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates, sodium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates, potassium α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfates; and the like.These sulfates may be used alone or in combination.

[0017] As the sulfate having an allyl group and a polyoxyethylene group of the present invention, ammonium sulfate is preferred, i.e., polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt and α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate salt are preferred in the present invention, and in particular, polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt is most desirable in the present invention. Commercially available sulfates having an allyl group and a polyoxyethylene group include, for example, "Aqualon KH-10" (trade name, polyoxyethylene chain length 10) and "Aqualon KH-1025" (trade name, 25% aqueous solution of "Aqualon KH-10"), which are polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salts manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; and "Adeka Reasoap (trademark) SR-1025" which is an α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate salt, manufactured by Asahi Denka Kogyo Co., Ltd.

[0018] The polymerizable unsaturated monomer may contain "other monomers" as long as the desired aqueous resin emulsion is obtained. The "other monomers" refer to monomers other than (meth)acrylic acid esters, monomers having an alkoxysilyl group and an ethylenic double bond, and (meth)acrylic acid. Examples of "other monomers" include, but are not limited to, styrene-based monomers such as styrene and styrene sulfonic acid; unsaturated carboxylic acids and their esters such as itaconic acid, fumaric acid, maleic acid, and the like; and acrylamides such as (meth)acrylamide and diacetone (meth)acrylamide.

[0019] <Multi-stage emulsion polymerization> The silane-modified acrylic resin (aqueous resin emulsion) of the present invention can be obtained by multistage emulsion polymerization of a polymerizable unsaturated monomer in the presence of a surfactant. In one embodiment of the present invention, the polymerizable unsaturated monomer is emulsion-polymerized in a multi-stage process (effectively two stages). The polymerizable unsaturated monomers (a1, a2, a3, and b) used in the polymerization in stages other than the final stage are referred to as polymerizable unsaturated monomer A, and the resulting polymer is referred to as copolymer A. The polymerizable unsaturated monomers (a1, a2, and b) used in the polymerization in the final stage are referred to as polymerizable unsaturated monomer B, and the resulting polymer is referred to as copolymer B. The aqueous resin emulsion finally obtained by the multi-stage emulsion polymerization is obtained by polymerizing a polymerizable unsaturated monomer B with a pre-emulsion obtained by polymerizing a polymerizable unsaturated monomer A.

[0020] The aqueous resin emulsion obtained by the multi-stage emulsion polymerization has a multi-layer structure (core-shell). In the present invention, the polymerizable unsaturated monomer A used in the multistage emulsion polymerization comprises a polymerizable unsaturated monomer A used in a stage other than the final stage and a polymerizable unsaturated monomer B used in the final stage, and the mass ratio of the polymerizable unsaturated monomer B to the polymerizable unsaturated monomer A (polymerizable unsaturated monomer B / polymerizable unsaturated monomer A) is preferably 30 / 70 to 70 / 30, and particularly preferably 40 / 60 to 60 / 40. When the mass ratio of the polymerizable unsaturated monomer B to the polymerizable unsaturated monomer A is within the above range, the aqueous resin composition (aqueous resin emulsion) of the present invention has an excellent balance between coatability and durability (water resistance and solvent resistance).

[0021] In the copolymer A, the proportion of the a2 polymerizable unsaturated monomer relative to the total weight of the a1, a2 and a3 polymerizable unsaturated monomers is preferably 0.05 to 1.0% by weight, more preferably 0.4 to 0.8% by weight, the proportion of the a3 polymerizable unsaturated monomer is preferably 0.5 to 10% by weight, more preferably 2.0 to 6.0% by weight, and the remainder is the a1 polymerizable unsaturated monomer, and the proportion of the a1 polymerizable unsaturated monomer relative to the total weight of the a1, a2 and a3 polymerizable unsaturated monomers is preferably 89 to 99% by weight, more preferably 90 to 98% by weight. In copolymer B, the ratio of the a2 polymerizable unsaturated monomer to the total weight of the a1 and a2 polymerizable unsaturated monomers is preferably 0.01 to 1.0% by weight, more preferably 0.1 to 0.4% by weight, and the remainder is the a1 polymerizable unsaturated monomer, and the ratio of the a1 polymerizable unsaturated monomer to the total weight of the a1 and a2 polymerizable unsaturated monomers is preferably 85 to 99.9% by weight, more preferably 95 to 99.9% by weight. In the synthesis of copolymers A and B (i.e., silane-modified acrylic resins), the ratio of (b) the polymerizable surfactant containing a sulfate having an allyl group and a polyoxyethylene chain to the total weight of the polymerizable unsaturated monomers a1, a2, and a3 is preferably 0.5 to 5% by weight in total in the synthesis process. The silane-modified acrylic resin (aqueous resin emulsion) of the present invention is available, for example, from Henkel Japan Ltd. under the trade name: AQUENCE EPIX BC 21066.

[0022] An example of this multi-stage emulsion polymerization process will now be described. First, (a1) a (meth)acrylic acid ester, (a2) a monomer having an alkoxysilyl group and an ethylenic double bond, and (a3) ​​a monomer having a carboxyl group are uniformly mixed in a reaction vessel to prepare a mixture of polymerizable unsaturated monomers A. Water (or an aqueous medium) is added to a sulfate having an allyl group and a polyoxyethylene group to prepare an aqueous solution, and a mixture of polymerizable unsaturated monomer A is added to this aqueous solution to prepare monomer emulsion A. In a separate container, prepare monomer emulsion B separately from monomer emulsion A. Preparation of monomer emulsion B may be the same as preparation of monomer emulsion A. Specifically, (a1) (meth)acrylic acid ester and (a2) monomer having an alkoxysilyl group and an ethylenic double bond are uniformly mixed to prepare a mixture of polymerizable unsaturated monomers B. A mixture of polymerizable unsaturated monomer B is added to an aqueous solution of sulfate having an allyl group and a polyoxyethylene group to prepare monomer emulsion B.

[0023] Next, water and (b) sulfate having an allyl group and a polyoxyethylene group are charged into a reactor equipped with a stirrer, a thermometer, etc., and a part of the monomer emulsion A and a catalyst are added. While maintaining the temperature inside the reactor at an appropriate temperature, the remaining monomer emulsion A and the catalyst are further dropletized to prepare a pre-emulsion. Monomer emulsion B and a catalyst are added dropwise to this pre-emulsion and polymerized to synthesize the final product, an aqueous resin emulsion, through multi-stage emulsion polymerization. Examples of the catalyst used here include ammonium persulfate, sodium persulfate, potassium persulfate, t-butyl peroxybenzoate, 2,2-azobisisobutyronitrile (AIBN), 2,2-azobis(2-amidinopropane) dihydrochloride, and 2,2-azobis(2,4-dimethylvaleronitrile), and in particular, ammonium persulfate, sodium persulfate, and potassium persulfate are preferred.

[0024] The glass transition point (Tg) of the silane-modified acrylic resin used in the present invention is preferably -10°C or more and 50°C or less, more preferably 0°C or more and 50°C or less. The glass transition temperature of copolymer A is preferably lower than that of copolymer B. The glass transition temperature of copolymer A is preferably -20 to 20°C, more preferably -10 to 20°C, and particularly preferably -10 to 15°C. The glass transition temperature of copolymer B is preferably 10 to 50°C, more preferably 25 to 50°C, and particularly preferably 30 to 50°C. The minimum film-forming temperature (MFT) of the silane-modified acrylic resin used in the present invention is preferably 25°C or less. The glass transition point (Tg) and minimum film-forming temperature (MFT) of the silane-modified acrylic resin are measured by differential scanning calorimetry (DSC).

[0025] The protective layer of the present invention contains a binder (including the above-mentioned silane-modified acrylic resin), preferably contains a pigment, and may contain other optional components. The total amount of binder and pigment in the protective layer is usually 80 to 100% by weight, preferably 90 to 100% by weight, in terms of solid content, and the amount of binder is preferably about 30 to 300 parts by weight per 100 parts by weight of pigment. The content of the silane-modified acrylic resin in the protective layer of the present invention is preferably from 10 to 70% by weight, more preferably from 30 to 60% by weight. The amount of each of the other components in the protective layer does not exceed 15% by weight, preferably 10% by weight.

[0026] Next, various materials used in the present invention will be exemplified. The binder, crosslinking agent, pigment, etc. can be used not only in the protective layer but also in each coating layer provided as required, such as the thermal recording layer, to the extent that the desired effects for the above-mentioned problems are not hindered.

[0027] Examples of binders that can be used in the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, and cellulose derivatives such as ethyl cellulose and acetyl cellulose, casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrene and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumaro resin, and the like. These polymeric substances can be used by dissolving them in solvents such as water, alcohols, ketones, esters, and hydrocarbons, or by dispersing them in water or other media in an emulsified or paste-like form, and can also be used in combination depending on the required quality.

[0028] Examples of crosslinking agents that can be used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, carbodiimide resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, ammonium chloride, 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, aluminum hydroxide, etc.

[0029] Pigments that can be used in the present invention include inorganic or organic fillers such as kaolin, calcined kaolin, aluminum hydroxide, silica, calcium carbonate, diatomaceous earth, talc, titanium oxide, etc. In consideration of the abrasion resistance of the thermal head, etc., kaolin, calcined kaolin, and aluminum hydroxide are preferred as pigments used in the protective layer. In addition, the aspect ratio of the pigment is more preferably 30 or more. By adding such a pigment, it is possible to compensate for the shortcomings of acrylic resins with high Tg, such as poor plasticizer resistance and solvent resistance. Furthermore, adding a pigment also has the effect of improving stick resistance. Examples of lubricants that can be used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins. In addition, in the present invention, 4,4'-butylidene (6-t-butyl-3-methylphenol), 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone, etc. can be added as image stabilizers that exhibit oil resistance effects on recorded images within a range that does not impair the desired effects on the above-mentioned problems. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, defoamers, antioxidants, fluorescent dyes, etc. can be used.

[0030] The heat-sensitive recording layer of the present invention contains a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and may further contain a sensitizer, the above-mentioned binder, a crosslinking agent, a lubricant, a pigment, and various other components. The dyes used in the present invention can be any dyes known in the field of conventional pressure-sensitive or heat-sensitive recording paper, and are not particularly limited, but triphenylmethane compounds, fluoran compounds, fluorene compounds, divinyl compounds, etc. are preferred. Specific examples of representative colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more. <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)

[0031] <Fluoran-based leuco dye> 3-Diethylamino-6-methylfluoran; 3-Diethylamino-6-methyl-7-anilinofluoran; 3-Diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran; 3-Diethylamino-6-methyl-7-chlorofluoran; 3-Diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran; 3-Diethylamino-6-methyl-7-(o-chloroanilino)fluoran; 3-Diethylamino-6-methyl-7-(p-chloroanilino)fluoran; 3-Diethylamino-6-methyl-7-(o-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-anilinofluoran;2-(4-Oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran; 2-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-Methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-Chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-Chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-Nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-Amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-Phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran; 2,4-dimethyl-6-[(4-dimethylamino)anilino]-fluoran;

[0032] <Fluorene-based leuco dye> 3,6,6'-Tris(dimethylamino)spiro〔fluorene-9,3'-phthalide〕; 3,6,6'-Tris(diethylamino)spiro〔fluorene-9,3'-phthalide〕 <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

[0033] <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-gamma-(3'-nitro)anilinolactam; 3,6-bis(diethylamino)fluoran-gamma-(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

[0034] The electron-accepting developer used in the present invention may be any of those known in the field of conventional pressure-sensitive or thermal recording paper, and is not particularly limited. Examples of the electron-accepting developer 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-hydroxybenzoate benzyl, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydro 4'-hydroxyphenyl-4'-methylphenyl sulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,4-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl] Benzene, 1,3-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, di(4-hydroxy-3-methylphenyl)sulfide, 2,2'-thiobis(3-tert-octylphenol), 2,2'-thiobis(4-tert-octylphenol), phenolic compounds such as diphenylsulfone-bridged compounds described in International Publication WO97 / 16420, compounds described in International Publication WO02 / 081229 or JP2002-301873A, and N,Examples of the color developers include thiourea compounds such as N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis[zinc 4-(n-octyloxycarbonylamino)salicylate] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. These color developers can be used alone or in combination of two or more. The diphenylsulfone-bridged compound described in International Publication WO97 / 16420 is available under the trade name D-90 manufactured by Nippon Soda Co., Ltd. The compounds described in International Publication WO02 / 081229 and the like are available under the trade names NKK-395 and D-100 manufactured by Nippon Soda Co., Ltd. In addition, metal chelate-type color-developing components such as higher fatty acid metal double salts and polyvalent hydroxy aromatic compounds described in JP-A-10-258577 can also be contained.

[0035] In the present invention, it is preferable to incorporate a sensitizer having a melting point of 90° C. or higher in the heat-sensitive recording layer from the viewpoint of color development sensitivity. If the melting point of the sensitizer is lower than 90° C., sticking and head residue are likely to occur. Examples of sensitizers having a melting point of 90° C. or higher used in the present invention include, but are not limited to, diphenylsulfone, fatty acid amides such as stearic acid amide and palmitic acid amide, benzyloxynaphthalene, 1,2-di-(3-methylphenoxy)ethane, and di(p-methylbenzyl) oxalate. These sensitizers may be used alone or in combination of two or more.

[0036] The types and amounts of the electron-donating leuco dye, electron-accepting developer, sensitizer, and other various 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; however, typically, 0.5 to 10 parts by weight of the electron-accepting developer and approximately 0 to 10 parts by weight of the sensitizer, preferably approximately 0.5 to 10 parts by weight, are used per 1 part by weight of the electron-donating leuco dye.

[0037] The electron-donating leuco dye, the electron-accepting developer, and any other materials added as necessary are pulverized into particles having a particle size of several microns or less using a grinding machine such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and a binder and various other additives depending on the purpose are added to prepare a coating liquid.

[0038] The desired thermal recording medium can be obtained by coating the above coating liquid on 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. In the present invention, in order to increase the color development sensitivity, an undercoat layer of a pigment-containing polymeric substance or the like may be provided under the thermosensitive recording layer. A backcoat layer may be provided on the opposite side of the support to the thermosensitive recording layer to correct curling. The thermosensitive recording medium of the present invention may further include an intermediate layer provided between the thermosensitive recording layer and the protective layer, and a protective layer formed on the intermediate layer.

[0039] The coating method for each layer can be a known coating method such as a blade method, an air knife method, a curtain method, a gravure method, or a roll coater method.

[0040] The coating weight of the protective layer is usually 1 to 5 g / m 2 That's about it. Furthermore, after each layer is applied, various known techniques in the field of thermal recording media, such as smoothing treatment by supercalendering, may be applied as necessary. EXAMPLES

[0041] The present invention will be illustrated by the following examples, but is not intended to limit the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified.

[0042] In the following preparation examples, aqueous emulsions were prepared from (A) a monomer emulsion (copolymer A) and (B) a monomer emulsion (copolymer B). The polymerizable unsaturated monomers, surfactants, and additives used to prepare (A) and (B) are described below. The Tg of the homopolymer of the polymerizable unsaturated monomer is a literature value, and the Tg of (a) the copolymer of the polymerizable unsaturated monomer and the Tg of (b) the copolymer of the polymerizable unsaturated monomer are values ​​calculated by a theoretical calculation formula.

[0043] <Polymerizable unsaturated monomer> Methyl methacrylate (Methyl methacrylate, hereafter referred to as "MMA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = 105 ° C.) 2-Ethylhexyl acrylate (2-ethylhexyl acrylate, hereafter referred to as "2EHA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = -70°C) n-Butyl acrylate (n-butyl acrylate, hereafter referred to as "n-BA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = -54°C) n-Butyl methacrylate (n-butyl methacrylate, hereafter referred to as "n-BMA", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., homopolymer Tg = 20°C) Cyclohexyl methacrylate (cyclohexyl methacrylate, hereafter referred to as "CHMA", manufactured by Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 83°C) 3-Methacryloxypropyltrimethoxysilane (Fujifilm Wako Pure Chemical Industries, Ltd.) Acrylic acid (hereinafter referred to as "AA", Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 106 ° C) Styrene (hereinafter referred to as "St", Fujifilm Wako Pure Chemical Industries, homopolymer Tg = 100 ° C)

[0044] <Surfactant> Polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (Aqualon KH10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (hereinafter referred to as "b")

[0045] [Production Example 1] A monomer emulsion was prepared from a plurality of polymerizable unsaturated monomers, a pre-emulsion was then prepared from the monomer emulsion, and an aqueous resin emulsion was synthesized from the pre-emulsion. The specific steps were as follows.

[0046] (A) Preparation of Monomer Emulsion As shown in Table 1, 5 parts by mass of (a1-1) MMA, 23 parts by mass of (a1-3) BA, 10 parts by mass of (a1-4) BMA, 10 parts by mass of (a1-5) CHMA, 0.3 parts by mass of (a2) 3-methacryloxypropyltrimethoxysilane, and 2 parts by mass of (a3) ​​AA were uniformly mixed to prepare a polymerizable unsaturated monomer solution (50.3 parts by mass). The above polymerizable unsaturated monomer solution was added to a uniformly mixed solution of 14 parts by mass of water and 0.1 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, and the mixture was stirred with a stirrer to obtain (A) a monomer emulsion.

[0047] (B) Preparation of Monomer Emulsion (A) As shown in Table 1, 16.6 parts by mass of (a1-1) MMA, 13 parts by mass of (a1-3) BA, 10 parts by mass of (a1-4) BMA, 10 parts by mass of (a1-5) CHMA, and 0.1 parts by mass of (a2) 3-methacryloxypropyltrimethoxysilane were uniformly mixed to prepare a polymerizable unsaturated monomer solution. The above polymerizable unsaturated monomer solution was added to a uniformly mixed solution of 14 parts by mass of water and 0.1 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt, and the mixture was stirred with a stirrer to obtain (B) a monomer emulsion.

[0048] (Pre-emulsion synthesis) A reactor equipped with a stirrer, a condenser, and a thermometer was charged with 78 parts by mass of water and 1.25 parts by mass of (b) polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ammonium salt, and the inside of the system was replaced with nitrogen gas, and the charged liquid was heated to 80°C. Thereafter, (A) a monomer emulsion (containing 50.3 parts by mass of a polymerizable unsaturated monomer, equivalent to 10.1 parts by mass of the polymerizable unsaturated monomer) and 2 parts by mass of a 1% by mass aqueous solution of sodium persulfate (hereinafter also referred to as "SPS") were added to the charge liquid. After a further 10 minutes, while keeping the temperature inside the reactor at 80°C, the remainder of the (A) monomer emulsion (a portion corresponding to 40.2 parts by mass of (a) polymerizable unsaturated monomer) and 4 parts by mass of a 1% aqueous solution of SPS as a polymerization catalyst were each dropped simultaneously over a period of 2 hours to obtain a pre-emulsion (an aqueous resin emulsion based on (a) polymerizable unsaturated monomer).

[0049] (Synthesis of Water-Based Resin Emulsion) The temperature inside the reactor was kept at 80°C, and 30 minutes after the completion of the dropping, the above-mentioned (B) monomer emulsion (containing 49.7 parts by mass of an unsaturated polymerizable monomer) and 4 parts by mass of a 1% aqueous solution of SPS were each dropped simultaneously into the above-mentioned pre-emulsion over a period of 2 hours to obtain an aqueous resin emulsion. The pH of the obtained aqueous resin emulsion was adjusted to 8.0 with aqueous ammonia. The aqueous resin emulsion had a glass transition temperature of -3.8°C for the polymerizable unsaturated monomer (copolymer A), a glass transition temperature of 26.7°C for the polymerizable unsaturated monomer (copolymer B), and a solid content concentration of 45% by mass. The solid content is the mass percentage of the remaining portion relative to the mass before drying after drying in an oven at 105°C for 3 hours. The resulting aqueous resin emulsion is called silane-modified acrylic resin 1.

[0050] [Manufacturing Examples 2 to 5] The raw material monomers shown in Table 1 were used to synthesize the resins in the same manner as in Production Example 1. The numbers relating to the compositions in the table indicate parts by weight. The resulting aqueous resin emulsions are called silane-modified acrylic resins 2 to 5, respectively.

[0051] [Table 1]

[0052] On the other hand, for producing a thermal recording medium, each dispersion liquid and coating liquid were prepared as follows. [Preparation of each coating liquid] The following mixture was stirred and dispersed to prepare a coating liquid for the undercoat layer. <Coating fluid for undercoat layer> Calcined kaolin (BASF, product name: Ansilex 90) 100.0 parts Styrene-butadiene copolymer latex (manufactured by Zeon Corporation, Product name: ST5526, solid content 48%) 10.0 parts Water 50.0 parts

[0053] The developer dispersion (liquid A), leuco dye dispersion (liquid B), and sensitizer dispersion (liquid C) having the following formulation were each wet-ground in a sand grinder until the average particle size reached 0.5 μm.

[0054] Developer dispersion liquid (liquid A) 4-Hydroxy-4'-isopropoxydiphenyl sulfone (Mitsubishi Chemical Corporation, product name: NYDS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117, solids content 10%) 5.0 parts 1.5 parts water

[0055] Leuco dye dispersion (liquid B) 3-Dibutylamino-6-methyl-7-anilinofluoran (Yamamoto Chemical Industry Co., Ltd., Product name: ODB-2) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0056] Sensitizer dispersion (liquid C) 1,2-bis-(3-methylphenoxy)ethane (Sankosha, Product name: KS232) 6.0 copies Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts 1.5 parts water

[0057] Next, each dispersion was mixed in the following ratio to prepare a coating liquid for the heat-sensitive recording layer. <Coating solution for thermal recording layer> Developer dispersion liquid (liquid A) 36.0 parts Leuco dye dispersion (liquid B) 18.0 parts Sensitizer dispersion (liquid C) 9.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 25.0 parts

[0058] Next, protective layer coating solutions 1 and 2 were prepared by mixing the ingredients in the following proportions. <Protective layer coating solution 1> Aluminum hydroxide dispersion (Martinsberg, Product name: Martyfin OL, solid content 50%) 9.0 parts Silane-modified acrylic resin 1 (Tg 18°C, MFT 22°C, solid content 40%) 10.0 copies Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., product name: Hydrin Z-7-30, Solid content 30%) 2.0 parts

[0059] <Protective layer coating solution 2> Aluminum hydroxide dispersion (Martifin OL) 9.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 40.0 parts Zinc stearate (Hydrin Z-7-30) 2.0 parts Glyoxal aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., solid content 40%) 3.0 parts

[0060] [Example 1] Support (basis weight 47g / m 2 The coating solution for the undercoat layer is applied to one side of the paper (high-quality paper) at a coating weight of 10.0 g / m2 (solid content).2 After coating by the bent blade method so that the above-mentioned coating was performed, the coated paper was dried to obtain a coated paper with an undercoat layer. The coating solution for the thermal recording layer was applied to the undercoat layer of the undercoat layer coated paper at a coating weight of 6.0 g / m2 in terms of solid content. 2 After coating by the rod blade method so as to obtain a thermal recording layer coated paper, the coating was dried. Next, the protective layer coating solution 1 was applied to the thermal recording layer of the thermal recording layer coated paper in a coating amount of 3.0 g / m2 in terms of solid content. 2 After that, the coating was dried and processed with a super calendar so that the smoothness was 100 to 500 seconds to prepare a thermal recording medium.

[0061] [Comparative Example 1] A thermal recording medium was prepared in the same manner as in Example 1, except that in the protective layer coating solution 1, the silane-modified acrylic resin 1 (hereinafter referred to as "acrylic resin A") was changed to acrylic resin B (not modified by silane, non-core-shell type, styrene acrylic, Tg 2°C, MFT 10°C, solids content 40%). [Comparative Example 2] A thermal recording medium was prepared in the same manner as in Example 1, except that in the protective layer coating solution 1, the acrylic resin A was changed to acrylic resin C (not modified by silane, core-shell type, styrene acrylic, Tg 92°C, MFT 50°C, solids content 40%). [Comparative Example 3] A thermal recording medium was prepared in the same manner as in Example 1, except that in the protective layer coating solution 1, 10.0 parts of acrylic resin A was changed to 22.2 parts of acrylic resin D (not modified by silane, non-core-shell type, styrene acrylic, Tg 55°C, MFT 18°C, solids content 18%). [Comparative Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the protective layer coating solution 1 was changed to the protective layer coating solution 2.

[0062] The prepared thermosensitive recording medium was evaluated as follows. <Color development performance (print density)> A checkered pattern was printed on the prepared thermal recording medium using an Okura Electric TH-PMD (thermal recording paper print tester, equipped with a Kyocera thermal head) at a print speed of 50 mm / sec with applied energy of 0.35 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).

[0063] <Suitable for high-speed printing> A barcode (CODE39) was printed vertically (the barcode was perpendicular to the printer head movement direction) on the prepared thermal recording medium using a Zebra 140XiIII label printer at a print level of +10 and a print speed of 25.4 cm / sec (10 in / sec). Next, the printed barcode was read using a barcode verifier (Honeywell, QCPC600, light source 640 nm) to evaluate the barcode readability. The evaluation results were recorded using the ANSI standard symbol grade. Symbol grade: The barcode is divided into 10 parts vertically and a reading test is carried out once for each part. The average value is expressed as a 5-level rating of A (Excellent), B, C, D, or F (Poor).

[0064] <Ink adhesion> The thermal recording surface of the prepared thermal recording medium was printed using offset sheet-fed ink (T&K UV161 ink) on a Roland offset sheet-fed printing press (2 colors), and the UV ink was cured using a UV irradiator (I-Grandage, I-Graphics). Next, an 18 mm wide piece of cellophane tape was applied to the printed surface and a roller (10 cm in diameter, 13 cm in width, weighing 2000 g) was run back and forth over the cellophane tape five times.Then, using a digital force gauge (Nidec-Shimpo, FGX-2), the cellophane tape was pulled with a tensile force of 4.9 N and a tensile angle of 90°, and the adhesion of the ink was visually evaluated according to the following criteria. Excellent: Ink hardly comes off Possible: Ink peels off slightly Poor: Ink is almost completely peeled off

[0065] <Solvent barrier properties> Ethanol (99.5%) was applied to the blank portion of the thermal recording medium with a cotton swab, and the medium was left to stand for 24 hours under environmental conditions of 23°C x 50% RH, after which it was visually evaluated according to the following criteria. Excellent: No color at all Possible: Slight color development Not acceptable: Strong color development

[0066] <Wet friction> The surface of the protective layer of the prepared thermosensitive recording medium was rubbed back and forth 80 times with tap water on a finger, and peeling of the protective layer and thermosensitive recording layer was visually evaluated according to the following criteria. Excellent: No peeling of the protective layer or thermal recording layer Pass: The protective layer peels off slightly, but the thermal recording layer does not peel off. Not acceptable: The protective layer and thermal recording layer peel off.

[0067] <Water-resistant blocking> For the thermal recording medium thus prepared, 10 ml of tap water was dropped onto the surface of the protective layer, the medium was folded in half so that the surface of the protective layer was on the inside, and the medium was subjected to a pressure of 20 gf / cm 2 After being left to stand for 24 hours under a load of 1000 g, the pieces were peeled off, and the peeling of the protective layer and the thermosensitive recording layer in the area where the water was dropped was visually evaluated according to the following criteria. Excellent: No blocking occurred, and the protective layer and the thermal recording layer did not peel off at all. Pass: Blocking occurs and the protective layer peels off slightly, but the thermal recording layer does not peel off. Unacceptable: Strong blocking occurs, and the protective layer and thermal recording layer peel off. Or the thermal recording medium is destroyed when peeled off.

[0068] <Immersion friction> The prepared thermosensitive recording medium was immersed in tap water for 10 minutes, the surface of the protective layer was rubbed back and forth with a finger 20 times, and peeling of the protective layer and thermosensitive recording layer was visually evaluated according to the following criteria. Excellent: No peeling of the protective layer or thermal recording layer Pass: The protective layer peels off slightly, but the thermal recording layer does not peel off. Not acceptable: The protective layer and thermal recording layer peel off.

[0069] The results are shown in the table below. [Table 2]

Claims

1. A thermosensitive recording medium having a support, a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and a protective layer on the thermosensitive recording layer, the protective layer containing a silane-modified acrylic resin, The silane-modified acrylic resin is an aqueous emulsion of core-shell type particles having a core made of copolymer A obtained by polymerizing the following (a1), (a2) and (a3) ​​in the presence of (b), and a shell made of copolymer B obtained by polymerizing the following (a1) and (a2) in the presence of (b). (a1) at least one (meth)acrylic acid ester (a2) Monomer having an alkoxysilyl group and an ethylenic double bond (a3) Monomer having a carboxyl group and an ethylenic double bond (b) Polymerizable surfactant containing a sulfate having an allyl group and a polyoxyethylene chain

2. 2. The thermosensitive recording material according to claim 1, wherein the copolymer A is obtained by adding a styrene monomer to the (a1), (a2) and (a3) ​​and polymerizing them in the presence of (b), and / or the copolymer B is obtained by adding a styrene monomer to the (a1) and (a2) and polymerizing them in the presence of (b).

3. 3. The thermosensitive recording medium according to claim 1, wherein in the copolymer A, the proportion of the a2 component is 0.05 to 1.0% by weight and the proportion of the a3 component is 0.5 to 10% by weight based on the total weight of the a1, a2 and a3 components, and in the copolymer B, the proportion of the a2 component is 0.01 to 1.0% by weight based on the total weight of the a1 and a2 components.

4. 4. The thermosensitive recording medium according to claim 1, wherein the ratio of the component (b) to the total weight of the components a1, a2 and a3 of the copolymers A and B is 0.5 to 5% by weight.

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