JP2013188955A - Thermal recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording body excellent in recording density, chemical resistance, and sticking resistance.SOLUTION: A thermal recording body includes on a support, a thermal recording layer which contains a leuco dye and a coloring agent, and a protective layer which contains an adhesive. The protective layer in the thermal recording body contains an anionic polyethylene wax which has a melting point of 90°C or above and 110°C or below and an average particle diameter of 0.01 μm or more and 0.1 μm or less by 0.5-20 mass% in the whole solid content of the protective layer.

Description

  The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between an electron-donating compound and an electron-accepting compound and that can obtain a recorded image by a color-forming reaction by thermal energy.

  A heat-sensitive recording material in which a recorded image is obtained by bringing an electron-donating compound and an electron-accepting compound into contact with each other by thermal energy is well known. Such a heat-sensitive recording material is relatively inexpensive, has a compact recording device, and is easy to maintain. Therefore, it is used for recording media such as facsimiles and various computers.

  In recent years, in particular, receipts for gas, water, electricity bills, ATM usage statements for financial institutions, various receipts, etc., financial record sheets (for so-called handy terminals), thermal recording labels for POS systems, and thermal recording labels. Thermal recording materials are also used for recording tags and the like.

  The heat-sensitive recording material for such applications may be used outdoors in the rainy weather or may be used indoors in contact with water, so that the heat-sensitive recording material is excellent in water resistance and may break even when wet. It is required not to peel off.

  In addition, in the thermal recording medium for such use, there are increasing opportunities for various bar codes to be used for thermal recording printing, and there is a demand for a thermal recording medium having barcode printing suitability.

  As the amount of information contained in a barcode increases, there is an increasing demand for high-definition barcode printing. However, high-definition barcodes have the problem that the readability is greatly reduced due to slight changes in the width of the bar or space due to printing failures such as sticking, and missing barcodes due to white spots in printing. Yes. In addition, due to the recent downsizing of recording equipment and power saving, demands for improving thermal response and head matching for thermal heads are increasing.

  That is, there is a need for a heat-sensitive recording material that exhibits the same color density as in the past even at low applied energy due to high speed and low power consumption, and that is free from printing problems such as sticking.

  As a binder for the protective layer of the heat-sensitive recording material, it is common to use a modified polyvinyl alcohol having a reactive group in combination with a water-resistant agent (curing agent) for the purpose of improving water resistance, for example, acetoacetyl-modified polyvinyl. Use of alcohol and water-soluble polyamide resin (see Patent Document 1), use of diacetone-modified polyvinyl alcohol and polyamidoamine / epichlorohydrin resin (see Patent Document 2), and the like. It has also been proposed to use a water-resistant resin (see Patent Document 3).

  The protective layer generally contains an aqueous dispersion of zinc stearate as a countermeasure against sticking due to the heat of the thermal head. However, if it is contained in a large amount in order to suppress sticking, a barrier against plasticizers and oils is contained. There is a drawback that the performance is lowered. In addition to the above, as a countermeasure against sticking, it has been proposed to contain a release agent mainly composed of silicone oil (see Patent Document 4). When such silicone oil is used, it adheres to the thermal head during printing. The problem is that the amount of waste to be increased. In addition, addition of a polyolefin wax having an average particle size of 0.5 to 5 μm has been proposed (see Patent Document 5), but as with zinc stearate, the barrier property against plasticizers and oils is reduced. It is difficult to achieve both chemical resistance and anti-sticking measures.

JP 2002-019196 A JP 2002-127601 A JP 2004-74531 A JP 2003-276334 A JP 2008-324123 A

  The main object of the present invention is to provide a thermal recording material excellent in recording density, chemical resistance and sticking resistance.

  As a result of various studies on the above problems, the present inventors have found that a thermosensitive recording layer containing a leuco dye and a colorant on the support, and further having a protective layer containing an adhesive on the thermosensitive recording layer. In the protective layer, an anionic polyethylene wax having a melting point of 90 ° C. or more and 110 ° C. or less and an average particle size of 0.01 μm or more and less than 0.1 μm is added in an amount of 0.5 to It has been found that the above-mentioned problems can be solved by containing 20% by mass, and the present invention has been completed.

  That is, the present invention relates to the following thermal recording material.

  Item 1: In a heat-sensitive recording material comprising a heat-sensitive recording layer containing a leuco dye and a colorant on a support and a protective layer containing an adhesive, the melting point of the protective layer is 90 ° C. or higher and 110 ° C. or lower. A heat-sensitive recording material comprising 0.5 to 20% by mass of an anionic polyethylene wax having an average particle size of 0.01 μm or more and less than 0.1 μm in the total solid content of the protective layer.

  Item 2: The adhesive is a copolymer resin containing (i) methacrylonitrile, and (ii) a vinyl monomer copolymerizable with methacrylonitrile, and having a solubility parameter of 12.0 or more. Item 2. The monomer includes at least one carboxy group-containing vinyl monomer, and the proportion of the carboxy group-containing vinyl monomer is 1 to 10% by mass in the total solid content of the copolymer resin. Thermal recording material.

  Item 3: The heat-sensitive recording material according to Item 1, wherein the adhesive is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.

  The heat-sensitive recording material of the present invention is excellent in recording density, chemical resistance and sticking resistance.

  The present invention relates to a heat-sensitive recording material comprising a support and a heat-sensitive recording layer containing a leuco dye and a colorant, and a protective layer containing an adhesive, wherein the protective layer has a melting point of 90 ° C. or higher and 110 ° C. or lower. The anionic polyethylene wax having an average particle diameter of 0.01 μm or more and less than 0.1 μm is contained in an amount of 0.5 to 20% by mass in the total solid content of the protective layer.

The polyethylene wax contained in the protective layer in the present invention will be described. Currently, the production and sale of polyethylene wax is roughly classified into the following four methods.
(1) A method of polymerizing at a high temperature and a high pressure with an ethylene radical catalyst, or a method of polymerizing at a low pressure with a Ziegler catalyst.
(2) A method of reducing molecular weight of general molding polyethylene by thermal decomposition.
(3) A method of separating and refining low molecular weight polyethylene produced as a by-product when producing general molding polyethylene.
(4) A method for oxidizing polyethylene for general molding.

  In general, emulsion waxes are obtained by oxidizing a polyethylene wax produced by the methods (1), (2), and (3) among these methods by an oxidation method such as air oxidation to add a carboxyl group or a hydroxyl group. These waxes refer to those produced by the process of (4) above, and these waxes are carboxyl groups and hydroxyl groups in the molecule, so that a small amount of surfactant or a soap-free aqueous solution is stable. Suspensions or aqueous emulsions can be obtained.

  Various physical properties such as melting point, density, and compatibility with other resins of polyethylene wax are very much caused by differences in molecular structure such as length and shortness of the side chain, amount, and difference in molecular weight. In general, polyethylene with many side chains and long polyethylene is of high density type (density 0.96 or more), polyethylene with short side chains and short is low density type (density of 0.93 or less), and density is 0.94 to 0.95. Are classified as medium density type. In the present invention, low density polyethylene having a density of 0.93 or less is preferable.

  The polyethylene wax in the present invention has a melting point of 90 ° C. or higher and 110 ° C. or lower. The lower limit is preferably 95 ° C. or higher. The upper limit is preferably 105 ° C. or lower. As a result, the recording density can be improved, and the barrier properties against plasticizer, oil, and alcohol can be improved. The reason for this is not clear, but the protective layer is a combination of a filler or auxiliary agent such as a pigment mainly using an adhesive as a binder, and the polyethylene is dissolved by heating of the thermal head, for example, in the gap between the pigment and the binder. This is thought to be effective. When the melting point exceeds 110 ° C., it is difficult to enter the gap between the pigment and the binder, the barrier property is lowered, and stickiness is considered to deteriorate due to stickiness. When the temperature is lower than 90 ° C., the melt viscosity is lowered, and the polyethylene film is not formed in the protective layer, so that the barrier property is considered to be lowered.

  The polyethylene wax in the present invention has an average particle size of 0.01 μm or more and less than 0.1 μm. If the average particle diameter is less than 0.01 μm, the particles become unstable and easily aggregate, making industrial production difficult. On the other hand, when the thickness is 0.1 μm or more, it is difficult to disperse the protective layer more uniformly in the protective layer, and the barrier property is considered to be lowered. The lower limit is preferably 0.02 μm or more. The upper limit is preferably 0.08 μm or less, and more preferably 0.06 μm or less.

  When polyethylene wax is used in the form of an emulsion, anionic, nonionic, or cationic ones can be obtained depending on the type of emulsifier. In the present invention, it is used as an anionic emulsion. Nonionic and cationic emulsions generally have anionic heat-sensitive recording layer coatings. When these emulsions are used, aggregates are formed in the heat-sensitive recording layer coating, and color development of the heat-sensitive recording layer is inhibited. It is to do. When an emulsifier is not used, it is difficult to make the average particle size less than 0.1 μm, and thus an emulsion obtained with an anionic dispersant is preferable.

  The content rate of an anionic polyethylene wax is 0.5-20 mass% in the total solid amount of a protective layer. More preferably, it is 2-10 mass%, More preferably, it is 3-6 mass%. By setting it as this range, the effect of this invention can be exhibited without regret.

  The protective layer in the present invention contains at least one aqueous adhesive selected from the group consisting of conventionally known water-soluble adhesives and water-dispersible adhesives as an adhesive. Examples of the adhesive include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, itaconic acid-modified polyvinyl alcohol, starch, oxidized starch, Cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / Maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, poly Water-soluble adhesives such as rilamide, sodium alginate, gelatin, gum arabic, and casein, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate Examples thereof include emulsions such as copolymers, and water-dispersible adhesives such as styrene / butadiene copolymers and styrene / butadiene / acrylic copolymers. Among these, at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol is particularly preferably used for sticking suppression and water resistance.

  The acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol used in the protective layer were obtained by copolymerizing a monomer having an acetoacetyl group, diacetone group, and carboxy group with a vinyl ester, respectively. It is produced by saponifying the resin.

  The degree of saponification is preferably in the range of 85 mol% to 100 mol% of complete saponification, and more preferably about 90 to 100 mol%. About average polymerization degree, about 300-3000 are preferable and about 400-2000 are more preferable. The degree of modification is preferably about 0.5 to 10 mol%, more preferably about 1 to 9 mol%.

  The average degree of polymerization and the degree of saponification may be appropriately selected according to the situation from the concentration, viscosity, coating property or drying property of the coating solution, but the higher the degree, the better the water resistance. If the degree of modification is in the range of about 0.5 to 10 mol%, sufficient water resistance is obtained, and the solubility in water does not decrease, so that the solution concentration can be prevented from being lowered.

  The content ratio of at least one adhesive selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol and carboxy-modified polyvinyl alcohol used in the protective layer is 10 to 90% by mass in the total solid content of the protective layer. Preferably about 15-50 mass% is more preferable.

  In the present invention, the adhesive in the protective layer also contains (i) methacrylonitrile and (ii) a vinyl monomer copolymerizable with methacrylonitrile, and has a solubility parameter of 12.0 or more. It is a polymerization resin, and the vinyl monomer contains at least one carboxyl group-containing vinyl monomer, and the ratio of the carboxyl group-containing vinyl monomer is 1 to 10 in the total solid amount of the copolymer resin. It is preferable that it is mass%. In addition, what is necessary is just to use in the state of an emulsion, when using the said copolymer as an adhesive agent.

  The said copolymer resin emulsion can be manufactured in accordance with the method currently disclosed by Unexamined-Japanese-Patent No. 2004-74531, for example. Since the copolymer resin emulsion has good water resistance after drying of the resin itself, there is no need to add a water-proofing agent, and there is a problem of pot life of the coating liquid caused by combining modified polyvinyl alcohol and a water-proofing agent. There is no feature.

  In the present invention, a pigment can also be contained in the protective layer. Examples of the pigment include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, and calcined kaolin, nylon resin filler, urea / formalin resin filler, Organic pigments such as raw starch particles can be mentioned. Of these, kaolin and aluminum hydroxide are particularly preferably used since they have a small decrease in barrier properties against chemicals such as plasticizers and oils and a small decrease in recording density.

  Furthermore, by containing a water-soluble acidic compound in the protective layer, the stability of the coating liquid for the protective layer can be further enhanced. The water-soluble acidic compound added to the protective layer coating solution is not particularly limited, but boric acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, Water-soluble organic acids having a carboxy group such as adipic acid, pimelic acid, fumaric acid, maleic acid, tartaric acid, citric acid, lactic acid, benzoic acid, phthalic acid, benzenetricarboxylic acid are preferred.

  The addition amount of the water-soluble acidic compound is not particularly limited, but is preferably added so that the pH of the protective layer coating solution is 3.0 to 7.0, and is in the range of 4.0 to 6.0. Is more preferable. By making pH into the range of 3.0-7.0, it can suppress that the viscosity of a coating liquid becomes high with time.

  In addition to the anionic polyethylene wax of the present invention, auxiliary agents that can be added to the protective layer coating solution include, for example, zinc stearate, calcium stearate, carnauba wax, paraffin wax, ester wax and other lubricants, sodium alkylbenzenesulfonate. , Surfactants such as sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium polyacrylate, water-resistant agents such as dialdehyde starch, methylol urea, glyoxylate, epoxy-based compounds, hydrazine-based compounds, and UV absorbers, Auxiliaries such as fluorescent dyes, colored dyes, mold release agents, and antioxidants can be added.

The protective layer in the present invention is, for example, an aqueous solution in which at least one selected from a specific anionic polyethylene wax, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol is dissolved using water as a medium or the above-mentioned The coating amount for the protective layer prepared by mixing a copolymer resin emulsion, if necessary, a pigment, a water-soluble acidic compound, various auxiliaries, etc. is 1 to 6 g / m ² after drying. As described above, it is formed by applying and drying on a heat-sensitive recording layer described later.

  Examples of the thermal recording system having an electron donating compound and an electron accepting compound include a combination of a leuco dye and a colorant, a combination of a diazonium salt and a coupler, a transition element such as iron, cobalt, copper, and a chelate compound. Examples thereof include a combination and a combination of an aromatic isocyanate compound and an imino compound, but a combination of a leuco dye and a colorant is preferably used because of its excellent color density.

  Various known leuco dyes and colorants in the present invention can be used. Specific examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl). ) -6-dimethylaminophthalide, 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6 -Methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) ) Amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p) Toluidino) -6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-chloro-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5 6,7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7- Examples include chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino) phthalide, and the like.

  Of course, it is not limited to these, Moreover, 2 or more types can also be used together. The proportion of the leuco dye used may be appropriately selected depending on the colorant to be used, and is generally about 3 to 50% by mass, particularly about 5 to 40% by mass, based on the total solid content of the thermosensitive recording layer.

  Examples of the colorant include 4,4′-isopropylidenediphenol, 4,4′-cyclohexylidenediphenyl, 1,1-bis (4-hydroxyphenyl) -ethane, 1,1-bis (4-hydroxy). Phenyl) -1-phenylethane, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, 2,2′-bis [4- (4-hydroxyphenyl) phenoxy] diethyl ether, Np-toluenesulfonyl-N′-3- (p -Toluenesulfonyloxy) phenylurea, 4,4′-bis [(4-methyl-3-phen Xoxycarbonylaminophenyl) ureido] diphenylsulfone, 4-hydroxybenzoic acid benzyl ester, N, N′-di-m-chlorophenylthiourea, Np-tolylsulfonyl-N′-phenylurea, 4,4′-bis (P-tolylsulfonylaminocarbonylamino) diphenylmethane, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid zinc, 4- {3- (p-tolylsulfonyl) propyloxy] salicylic acid zinc, 5- [p- ( 2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate, diphenylsulfone cross-linked compound represented by the following general formula (1), and the like.

  The use ratio of the colorant may be appropriately selected according to the leuco dye used, and is generally about 10 to 70% by mass, particularly about 12 to 50% by mass, based on the total solid content of the thermosensitive recording layer.

  The heat-sensitive recording layer may contain a storage stability improver in order to increase the storage stability of the recording part. Specific examples of such preservability improvers include, for example, 2,2′-ethylidenebis (4,6-di-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 1 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 2,2 Hindered phenol compounds such as bis (4-hydroxy-3,5-dimethylphenyl) propane, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone , Diglycidyl terephthalate, cresol novolac epoxy resin, phenol novolac epoxy resin, vinyl Epoxy compounds such as bisphenol A type epoxy resin, N, N'-di-2-naphthyl -p- phenylenediamine, bis (4-ethylene iminocarbonyl aminophenyl) include methane and the like.

  When a preservability improver is used, the proportion used may be an effective amount for improving the preservability, but is usually about 1 to 30% by mass, particularly 5 to 5% of the total solid content of the heat-sensitive recording layer. It is preferable to mix in the range of about 20% by mass.

  The heat-sensitive recording layer may contain a sensitizer in order to increase recording sensitivity. Specific examples of such sensitizers include, for example, stearamide, methylenebis stearamide, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, p -Tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxy) Phenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether 1,4-di (phenylthio) butane, p-acetoluidide, p-aceto Examples include gentizide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester and the like. .

  When a sensitizer is used, the proportion used may be an amount effective for sensitization, but is usually about 2 to 40% by mass, particularly 5 to 25% by mass in the total solid content of the heat-sensitive recording layer. It is preferable to blend in the range of about%.

The heat-sensitive recording layer is, for example, water as a dispersion medium, and a leuco dye, a colorant, if necessary, a sensitizer, a preservability improver, etc. together or separately by means of a stirrer / crusher such as a ball mill, an attritor or a sand mill. Using a dispersion finely dispersed so that the particle diameter is 2 μm or less, a coating solution for a heat-sensitive recording layer prepared by mixing an aqueous adhesive or the like as necessary has a coating amount of 2 to 2 after drying. It is formed by applying and drying on one surface of the support so as to be 20 g / m ² . The aqueous adhesive in the heat-sensitive recording layer preferably contains at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.

  Furthermore, various auxiliary agents can be added to the thermal recording layer coating liquid as necessary. For example, kaolin, light (heavy) calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, Amorphous silica, pigments such as urea / formalin resin filler, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salt, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, Waxes such as paraffin wax and ester wax, hydrazine compounds, glyoxal, boric acid, dialdehyde starch, methylolurea, glyoxylate, epoxy compounds and other water-resistant agents, antifoaming agents, coloring dyes and fluorescent dyes It is.

  The support used in the heat-sensitive recording material of the present invention is not particularly limited, and examples thereof include neutral or acidic high-quality paper, synthetic paper, transparent or translucent plastic film, and white plastic film. In addition, the thickness of a support body is not specifically limited, Usually, it is about 20-200 micrometers.

  In the present invention, if necessary, an undercoat layer can be provided between the support and the thermosensitive recording layer in order to further improve the recording sensitivity and the recording runnability. The undercoat layer generally contains water as a medium, and has an oil absorption amount of 70 ml / 100 g or more, particularly an oil-absorbing pigment and / or organic hollow particles and / or heat-expandable particles of about 80 to 150 ml / 100 g, and an adhesive as a main component. The undercoat layer coating liquid is applied on a support and dried. Here, the oil absorption is a value determined according to the method of JIS K 5101.

  Various types of oil-absorbing pigments can be used. Specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, more preferably about 0.02 to 3 μm. The use ratio of the oil-absorbing pigment can be selected from a wide range, but is generally preferably about 2 to 95% by mass, more preferably about 5 to 90% by mass in the total solid content of the undercoat layer.

  If necessary, a protective layer, a printing layer, a magnetic recording layer, an antistatic layer, or an inkjet recording layer may be provided on the opposite side of the surface of the support on which the thermal recording layer is provided (the back side of the thermal recording body). It is possible to perform a smoothing process using a super calender or the like in an arbitrary process after the formation of each layer or after the formation of all the layers. Moreover, various known techniques in the heat-sensitive recording body production field, such as providing an adhesive layer on the back side of the heat-sensitive recording medium, can be added as necessary.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” indicate “part by mass” and “% by mass”, respectively.

Example 1
-Preparation of undercoat layer coating solution Fine hollow particles (trade name: Ropaque SN-1055) were dispersed in a dispersion obtained by dispersing 60 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF) in 80 parts of water. , 75 parts by Rohm & Haas, solid content 26.5%), 31 parts styrene / butadiene latex (trade name: L-1571, solid content 48% by Asahi Kasei Chemicals) and carboxymethylcellulose (product) Name: Serogen 7A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2.5 parts, similarly, a composition comprising 1 part of carboxymethyl cellulose (trade name: Serogen AG gum, Daiichi Kogyo Seiyaku Co., Ltd.) and 15.5 parts of water are mixed. By stirring, a coating solution for undercoat layer was obtained.

Preparation of leuco dye dispersion (liquid A) A composition comprising 10 parts of 3-di- (n-butyl) amino-6-methyl-7-anilinofluorane, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water. A leuco dye dispersion was obtained by pulverizing with a sand mill using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation) until the median diameter became 0.5 μm. Hereinafter, the obtained leuco dye dispersion is also referred to as A liquid.

Preparation of colorant dispersion (liquid B) A composition comprising 10 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was subjected to laser diffraction particle size distribution measurement with a sand mill. The colorant dispersion was obtained by pulverizing until the median diameter was 1.5 μm using an apparatus SALD2200 (manufactured by Shimadzu Corporation). Hereinafter, the obtained colorant dispersion is also referred to as “Liquid B”.

-Colorant dispersion (liquid C) preparation 10 parts of diphenylsulfone cross-linked compound represented by the general formula (1) (trade name: D-90, a mixture of n of 1 to 7, manufactured by Nippon Soda Co., Ltd.) A composition comprising 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water is pulverized with a sand mill using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation) until the median diameter becomes 1.0 μm, and the colorant is dispersed. A liquid was obtained. Hereinafter, the obtained colorant dispersion is also referred to as “Liquid C”.

-Preparation of sensitizer dispersion (liquid D) A composition comprising 10 parts of di-p-methylbenzyl oxalate, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was mixed with a laser diffraction particle size distribution analyzer SALD2200 using a sand mill. A sensitizer dispersion was obtained by pulverizing until the median diameter by Shimadzu Corporation was 1.0 μm. Hereinafter, the obtained sensitizer dispersion is also referred to as D liquid.

-Preparation of coating solution for heat-sensitive recording layer A solution 33.5 parts, solution B 68 parts, solution C 5 parts, solution D 10.5 parts, fully saponified polyvinyl alcohol (trade name: PVA110, saponification degree: 99 mol%, 30 parts of 10% aqueous solution of average degree of polymerization: 1000, manufactured by Kuraray Co., Ltd., 5 parts of 20% aqueous solution of partially saponified polyvinyl alcohol (trade name: PVA205, degree of saponification: 88 mol%, average degree of polymerization: 500, manufactured by Kuraray Co., Ltd.) , 16.5 parts of butadiene-based copolymer latex (trade name: P-OY72, manufactured by Japan A & L, solid concentration 48%), 42 parts of light calcium carbonate (trade name: Brilliant-15, manufactured by Shiroishi Kogyo Co., Ltd.), A composition comprising 10 parts of paraffin wax emulsion (trade name: Hydrin L-700, manufactured by Chukyo Oil & Fats Co., Ltd., solid content concentration of 30%) and 90.5 parts of water are mixed and stirred for coating for a thermal recording layer. A liquid was obtained.

Preparation of coating liquid (I) for protective layer Acetoacetyl-modified polyvinyl alcohol (trade name: Gohsephimer Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, Japan 210 parts of a 10% aqueous solution of Synthetic Chemical Industry Co., Ltd., also acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimmer Z-100, degree of saponification: 99.4 mol%, average degree of polymerization: 500, degree of modification: 5 mol) %, 80 parts of 20% aqueous solution of Nippon Synthetic Chemical Industry Co., Ltd., 51.5 parts of kaolin (trade name: HYDRAGLOSS 90, KaMin LLC), aluminum hydroxide (trade name: Hydrite H-42M, Showa Denko) ) 4 parts, aqueous dispersion of zinc stearate (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%) 5.6 parts, anionic Ethylene wax emulsion (trade name: Meikax HP-598A, manufactured by Meisei Chemical Co., Ltd., solid concentration 25%, melting point 100 ° C., particle size 0.04 μm) 20 parts, sodium glyoxylate (trade name: SPM-01, Nippon Gosei Co., Ltd.) A composition comprising 5 parts of a 10% aqueous solution (made by Kagaku Kogyo Co., Ltd.) and 53 parts of water was mixed and stirred, and adjusted to pH 5 with a 10% aqueous acetic acid solution to obtain a coating solution for a protective layer. In addition, the average particle diameter of polyethylene wax is a median diameter by a dynamic light scattering particle size distribution analyzer LB-500 (manufactured by Horiba, Ltd.).

-Preparation of thermosensitive recording material The coating amount after drying the undercoat layer coating solution, the thermal recording layer coating solution, and the protective layer coating solution (I) on one surface of a high-quality paper having a basis weight of 60 g / m ² was obtained. After coating and drying so as to be 6.0 g / m ² , 4.5 g / m ² , and 2.0 g / m ² , an undercoat layer, a heat-sensitive recording layer, and a protective layer are sequentially formed. The surface was smoothed to obtain a heat-sensitive recording material.

Example 2
In the preparation of the protective layer coating liquid (I) of Example 1, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: Meikax KSP, manufactured by Meisei Chemical Co., Ltd., solid concentration 24) %, Melting point 95 ° C., particle size 0.03 μm) except that 20 parts were used to obtain a heat-sensitive recording material in the same manner as in Example 1.

Example 3
In the preparation of the protective layer coating liquid (I) of Example 1, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: Nopcoat PEM-17, manufactured by San Nopco, solid concentration: 40) %, Melting point 105 ° C., particle size 0.04 μm), except that 10 parts were used to obtain a heat-sensitive recording material in the same manner as in Example 1.

Example 4
-Preparation of protective layer coating liquid (II) Copolymer resin (copolymerization component: (meth) acrylonitrile / (meth) acrylic acid alkyl / (meth) acrylic acid 2-hydroxyethyl / (meth) acrylic acid / (meth) Acrylamide, (meth) acrylic acid ratio: 5% by mass with respect to the entire copolymer resin, solubility parameter: 12.8, glass transition temperature: 50 ° C., average particle size: 230 nm) (trade name: OT1043Z-1) , Solid content concentration 25%, manufactured by Mitsui Chemicals Co., Ltd. 140 parts, kaolin (trade name: HYDRAGLOSS 90, manufactured by KaMin LLC) 54 parts, aluminum hydroxide (trade name: Hygilite H-42M, Showa Denko Co., Ltd.) 4 parts , 5.6 parts of an aqueous dispersion of zinc stearate (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%) Polyethylene wax emulsion (trade name: Meikatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid concentration 25%, melting point 100 ° C., particle size 0.04 μm) 20 parts and water 220 parts mixed and stirred Thus, a protective layer coating liquid (II) was obtained.

-Preparation of heat-sensitive recording material In the preparation of the heat-sensitive recording material of Example 1, the coating amount after drying the protective layer coating solution (II) was 3.0 g / m instead of the protective layer coating solution (I). ^A heat-sensitive recording material was obtained in the same manner as in Example 1 except that it was applied and dried so as to be ² .

Example 5
In the preparation of the protective layer coating liquid (II) of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: Meikax KSP, manufactured by Meisei Chemical Co., Ltd., solid content concentration: 24) %, Melting point 95 ° C., particle size 0.03 μm) except that 20 parts were used to obtain a heat-sensitive recording material in the same manner as in Example 4.

Example 6
In the preparation of the coating solution for the protective layer of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: Nopcoat PEM-17, manufactured by San Nopco, solid concentration 40%, melting point) A thermosensitive recording material was obtained in the same manner as in Example 4 except that 10 parts (105 ° C., particle size: 0.04 μm) were used.

Comparative Example 1
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 20 parts of the anionic polyethylene wax emulsion was not used in the preparation of the protective layer coating liquid of Example 1.

Comparative Example 2
A thermosensitive recording material was obtained in the same manner as in Example 1, except that 20 parts of the anionic polyethylene wax emulsion was not used in the preparation of the protective layer coating liquid of Example 4.

Comparative Example 3
A thermosensitive recording material was obtained in the same manner as in Example 4 except that in the preparation of the coating solution for the protective layer of Example 4, the amount of the anionic polyethylene wax emulsion was changed to 100 parts instead of 20 parts.

Comparative Example 4
In the preparation of the coating solution for the protective layer of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: SN Coat 287, manufactured by San Nopco, solid concentration 40%, melting point 80 A heat-sensitive recording material was obtained in the same manner as in Example 4 except that 10 parts (° C., particle diameter 0.05 μm) were used.

Comparative Example 5
In the preparation of the coating solution for the protective layer of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic polyethylene wax emulsion (trade name: Meikax HP602A, manufactured by Meisei Chemical Co., Ltd., solid concentration 25%, melting point) A thermosensitive recording material was obtained in the same manner as in Example 4 except that 20 parts (130 ° C., particle size 0.05 μm) were used.

Comparative Example 6
In the preparation of the coating solution for the protective layer of Example 4, a soap-free polyolefin wax dispersion (trade name: Chemipearl W4005, manufactured by Mitsui Chemicals, solid content concentration 40% instead of 20 parts of the anionic polyethylene wax emulsion) A melting point of 110 ° C. and a particle diameter of 0.6 μm was obtained in the same manner as in Example 4 except that 10 parts were used.

Comparative Example 7
In the preparation of the protective layer coating liquid of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, an anionic paraffin wax emulsion (trade name: Hydrin P-7, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 30%, A heat-sensitive recording material was obtained in the same manner as in Example 4 except that 16.7 parts (melting point: 54 ° C., particle size: 1.1 μm) were used.

Comparative Example 8
In the preparation of the coating solution for the protective layer of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, a cationic polyethylene wax emulsion (trade name: Meikax PEC-17, manufactured by Meisei Chemical Co., Ltd., solid content concentration: 22% A melting point of 90 ° C. and a particle diameter of 0.04 μm) was used in the same manner as in Example 4 except that 22.7 parts were used.

Comparative Example 9
In the preparation of the coating liquid for the protective layer of Example 4, instead of 20 parts of the anionic polyethylene wax emulsion, a nonionic polyethylene wax emulsion (trade name: Meikax HP-65, manufactured by Meisei Chemical Co., Ltd., solid content concentration 40%) And a melting point of 100 ° C., a particle diameter of 0.06 μm) were used in the same manner as in Example 4 except that 12.5 parts were used.

  The heat-sensitive recording material thus obtained was allowed to stand for 24 hours under the condition of 40 ° C.-50% RH, and the following items were evaluated. The results are shown in Table 1.

[Recording density]
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.24 mJ / dot, and the resulting printed part was subjected to a Macbeth densitometer (RD). The reflection density was measured in the visual mode (-914, manufactured by Macbeth). The larger the numerical value, the higher the density of printing, and the recording density is preferably 1.20 or more practically.

〔Oil resistance〕
In the recording density measurement, edible oil is applied to the heat-sensitive recording medium after recording, left to stand at 20 ° C. for 24 hours, and then edible oil is wiped off, and the reflection density is measured in the visual mode of the Macbeth densitometer (described above). did. The retention rate of the recording part was calculated | required by the following formula, and oil resistance was evaluated. If the recording density after edible oil coating treatment is 0.6 or more and the storage rate is 50% or more, there is no practical problem.
Storage rate (%) = [measured value (recording density after processing) / recording density before processing] × 100

[Plasticizer resistance]
A wrap film (trade name: High Wrap KMA-W, manufactured by Mitsui Chemicals Co., Ltd.) is wrapped around a polycarbonate pipe (40 mm diameter) in triplicate, and a heat-sensitive recording material after recording in recording density measurement is placed on the wrap film. The wrap film was wrapped in three layers and allowed to stand at 40 ° C. for 24 hours, and then the reflection density of the printed portion was measured in a Macbeth densitometer (described above) visual mode. Further, the storage rate of the recording part was calculated based on the above formula, as in the case of oil resistance. If the recording density after processing is 0.6 or more and the storage rate is 50% or more, there is no practical problem.

[Sticking resistance]
Using a thermal printer (Lesprit, manufactured by SATO), a bar code was printed, and the degree of printing skip was visually observed and evaluated according to the following criteria.
A: Printing skip is not visible at all.
○: Print skipping is slightly visible, but there is no practical problem.
X: Print skipping is clearly recognized, which is a practical problem.

Claims (3)

  On the support, a heat-sensitive recording layer comprising a heat-sensitive recording layer containing a leuco dye and a colorant, and a protective layer containing an adhesive, the melting point in the protective layer is 90 ° C. or higher and 110 ° C. or lower, and the average A heat-sensitive recording material comprising 0.5 to 20% by mass of an anionic polyethylene wax having a particle diameter of 0.01 μm or more and less than 0.1 μm in the total solid content of the protective layer.   The adhesive comprises (i) methacrylonitrile, and (ii) a vinyl resin copolymerizable with methacrylonitrile, and has a solubility parameter of 12.0 or more, and the vinyl monomer is 2. The heat-sensitive composition according to claim 1, comprising at least one carboxy group-containing vinyl monomer, wherein the proportion of the carboxy group-containing vinyl monomer is 1 to 10% by mass in the total solid content of the copolymer resin. Recorded body.   The heat-sensitive recording material according to claim 1, wherein the adhesive is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.