JP6079555B2 - Thermal recording material - Google Patents

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. Thermosensitive recording media are also used for recording tags and the like.

  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.

  In such applications, tickets, tickets, admission tickets, parking tickets, etc. are used in rainy weather, and in POS label applications such as frozen and refrigerated foods, condensation may occur and water may adhere. It is required that the body has excellent water resistance and does not tear or peel off even when wet.

  Therefore, in order to improve water resistance, it is common to use a combination of a modified polyvinyl alcohol having a reactive group and a curing agent as a binder for the protective layer of the heat-sensitive recording material, for example, acetoacetyl-modified polyvinyl alcohol and water-soluble. The use of a conductive polyamide resin (see Patent Document 1), the use of diacetone-modified polyvinyl alcohol and a polyamidoamine / epichlorohydrin resin (see Patent Document 2) has been proposed. Such a combination of the modified polyvinyl alcohol and the curing agent needs to advance the reaction in order to obtain water resistance. However, since it cannot be stored at high temperatures, it has the disadvantage that it takes time to obtain sufficient water resistance in the muro treatment close to room temperature. Also, when it is stacked in jumbo rolls or large format, there is a difference in retained moisture. May cause unevenness in water resistance.

  In order to solve the above drawbacks, it has been proposed to use water-based emulsions (see Patent Document 3 and Patent Document 4), but water-based emulsions generally have low heat resistance. There is a disadvantage that head wrinkles occur. In addition, there is a drawback in that the chemical resistance, particularly the protection against plasticizers is low. In order to solve these drawbacks, a copolymer resin containing (i) methacrylonitrile and (ii) a vinyl monomer copolymerizable with methacrylonitrile as a water-based emulsion and having a solubility parameter of 12.0 or more. And the vinyl monomer contains 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 amount of the copolymer resin. Combining an emulsion with a polyolefin copolymer resin emulsion (Patent Document 5), adding a polyvinyl alcohol having a crosslinkable modifying group as a stabilizer during or after the aqueous emulsion polymerization (Reference 6) Etc. have been proposed. However, at present, satisfactory results are not always obtained for the heat resistance, chemical resistance and water resistance of the thermal head.

JP 2002-301868 A JP 2002-127601 A JP 09-220857 A JP 09-31001 A JP 2004-74531 A JP 2012-56218 A

  The main object of the present invention is to provide a heat-sensitive recording material that is excellent in water resistance and chemical resistance and does not require a muro treatment.

  As a result of various studies on the above problems, the present inventors have found that the above problems can be solved by including a specific polyvinyl alcohol and a copolymer resin as an adhesive in the protective layer, thereby completing the present invention. It came to. That is, the present invention relates to the following thermal recording material.

Item 1: A thermosensitive recording body comprising a thermosensitive recording layer containing an electron donating compound and an electron accepting compound on a support, and a protective layer containing an adhesive on the thermosensitive recording layer, wherein the protective layer is an adhesive. As polyvinyl alcohol having a saponification degree of 85 to 90 mol% and a polymerization degree of 2000 to 5000 in a total solid amount of 2 to 20% by mass in the total amount of the adhesive, and the protective layer is an adhesive. And (meth) acrylonitrile and a vinyl monomer copolymerizable with (meth) acrylonitrile, and a copolymer resin having a solubility parameter of 12.0 (cal / cm ³ ) ^1/2 or more, The resin contains at least one carboxy group-containing vinyl monomer as a vinyl monomer in a proportion of 1 to 10% by mass in the total solid content of the copolymer resin. .

  Item 2: The thermal recording material according to Item 1, wherein the polyvinyl alcohol is contained in a proportion of 5 to 20% by mass in the total solid content of the adhesive.

  Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the degree of polymerization of the polyvinyl alcohol is 2700 to 5000.

  The heat-sensitive recording material of the present invention is excellent in water resistance and chemical resistance, and does not require any muro treatment to exhibit water resistance.

  The protective layer in the present invention contains (meth) acrylonitrile and a vinyl monomer copolymerizable with (meth) acrylonitrile as an adhesive, and a copolymer resin having a solubility parameter of 12.0 or more. Moreover, this copolymer resin contains at least 1 sort (s) of carboxy group containing vinyl monomer as said vinyl monomer in the ratio of 1-10 mass% in the total solid amount of copolymer resin.

  The proportion of (meth) acrylonitrile in the copolymer resin is not particularly limited as long as the effects of the present invention are achieved, but is preferably about 20 to 80% by mass, and more preferably about 30 to 70% by mass. When the ratio of (meth) acrylonitrile is 20% by mass or more, sufficient water resistance is obtained, and the sticking resistance is not hindered. On the other hand, when it is 80% by mass or less, there is no fear that the production (polymerization) stability of the emulsion is inferior, and the Tg of the copolymer resin does not become higher than necessary. In addition, there is no possibility that the film forming property of the emulsion and the binding property to the filler will be hindered.

  Examples of the carboxy group-containing vinyl monomer include ethylenically unsaturated monobasic carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and ethylenically unsaturated dibasic carboxylic acids such as itaconic acid, maleic acid, and fumaric acid. Examples include acids and monoalkyl esters. These are used singly or in combination of two or more.

  Examples of (meth) acrylonitrile and vinyl monomers copolymerizable therewith include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic other than carboxy group-containing vinyl monomers. Acid butyl, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, ( (Meth) acrylic acid 2-aminoethyl, (meth) acrylic acid 2- (N-methylamino) ethyl, (meth) acrylic acid 2- (N, N-dimethylamino) ethyl, (meth) acrylic acid glycidyl ( (Meth) acrylic acid esters, vinyl acetates such as vinyl acetate and vinyl propionate, styrene, α-methylstyrene Aromatic vinyl monomers such as divinylbenzene, N-substituted unsaturated carboxylic acid amides such as (meth) acrylamide and N-methylol (meth) acrylamide, complex vinyl compounds such as vinylpyrrolidone, vinylidene chloride, fluorine And vinylidene halide compounds such as vinylidene halide, α-olefins such as ethylene and propylene, and dienes such as butadiene. These are used alone or in combination of two or more.

  In the present invention, when such a copolymer resin is used as an adhesive, it may be used in an emulsion state. Examples of the method for producing the copolymer resin emulsion include the method described in JP-A-2004-74531. This resin emulsion is excellent in water resistance after drying the resin itself, it is not necessary to add a curing agent, and there is no problem in the pot life of a coating liquid such as a combination of a modified polyvinyl alcohol and a curing agent. is there.

  If the carboxy group-containing vinyl monomer in the copolymer resin is less than 1% by mass, the polymerization stability may be insufficient, or even if the resin is neutralized with a base after polymerization, the resin particles are not sufficiently softened and the film formability may be insufficient. . On the other hand, if it exceeds 10% by mass, the water resistance is not sufficient, and the resin particles may be dissolved during the neutralization adjustment to cause gelation.

  The solubility parameter of the copolymer resin in the present invention is 12.0 or more. The solubility parameter is described in, for example, Iwanami Dictionary of Physical Chemistry, 4th edition. When the solubility parameter is 12.0 or more, the heat resistance against heat received from the thermal head during use (adhesiveness to the thermal head) is improved, and the internal cohesive force of the resin can be increased. If the solubility parameter is less than 12.0, the thermal sensitivity of the thermal recording layer increases due to insufficient internal cohesion of the resin, so that the thermal recording layer is easily softened and the running stability of the thermal head is lacking. Moreover, it is inferior to chemical resistance, such as a plasticizer. On the other hand, the upper limit of the solubility parameter is not particularly set, but in consideration of the characteristics of the copolymer resin used in the present invention and industrial production efficiency, a range of 14.0 or less is preferable. When the solubility parameter is 14.0 or less, the hydrophilicity of the copolymer resin increases, there is no fear that the water resistance is greatly reduced, and the production of the copolymer resin emulsion is facilitated.

The solubility parameter in the present invention is a value calculated from the total molecular structure of each copolymer component, the total evaporation energy of the atomic group, and the molar volume ratio of the copolymer component. The solubility parameter calculation method is described in Journal of Technology Coatings VOL. 55, No696, P.I. According to description of 100-101, it can calculate based on the following formula 1.
δ = [(ΣΔe _i ) (X) / (ΣΔv _i ) (X)] ^0.5 (Formula 1)
(Δ: solubility parameter, X: molar fraction of monomer used for copolymerization, Δe _i : evaporation energy of each monomer, Δv _i : molar volume)
A copolymer resin having a specific solubility parameter can be prepared by selecting a monomer to be a copolymer component and setting a blending ratio.

  Although the content rate of the copolymer resin in this invention is not specifically limited, About 10-50 mass% is preferable in the total solid of a protective layer from a viewpoint of improving the balance of chemical resistance and water resistance, and 20-40 mass. % Is more preferable, about 25 to 35% by mass is more preferable, and about 28 to 33% by mass is particularly preferable.

  The protective layer in the present invention contains polyvinyl alcohol having a saponification degree of 85 to 90 mol% and a polymerization degree of 2000 to 5000 as an adhesive. When the degree of polymerization is less than 2000, chemical properties, particularly resistance to plasticizers and the like, are poor. On the other hand, when it exceeds 5000, there is a problem that it is difficult to balance the viscosity and the concentration when preparing the coating liquid. The polymerization degree is preferably 2500 to 5000, and more preferably 2700 to 5000. Further, if the degree of saponification is less than 85 mol%, there is a disadvantage that the water resistance is inferior in combination with the copolymer resin. On the other hand, when it exceeds 90 mol%, the compatibility with the copolymer resin is poor, the film-forming property after drying is inferior, and the resistance to the plasticizer or the like cannot be obtained.

  The content rate of this polyvinyl alcohol is 2-20 mass% in the total total solid of the adhesive agent in a protective layer. If it is less than 2% by mass, the effect of barrier properties on chemicals, particularly plasticizers and alcohol, which are characteristic of polyvinyl alcohol, cannot be obtained, and if it exceeds 20% by mass, the water resistance deteriorates. Preferably they are 5 parts-20 mass%, More preferably, they are 8-15 mass%.

  Polyvinyl alcohol includes modified polyvinyl alcohol modified with carboxy group, acetoacetyl group, epoxy group, silanol group, amino group, olefin group, amide group, nitrile group, etc. , Glyoxal, dimethylol urea, polyglycol glycidyl ether, ketene dimer, dialdehyde starch, polyamidoamine epichlorohydrin resin, carbodiimide compound, aziridine compound, hydrazide compound, oxadrine compound, isocyanate compound, etc. Is necessary, and a muro process is required. Without water treatment, the desired water resistance cannot be obtained. In addition, a coating liquid containing a curing agent generally has a short pot life and may affect the environment, and it is not preferable to use a modified polyvinyl alcohol and a curing agent in the protective layer.

  The protective layer may contain a pigment. 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 preferred because they have a small decrease in barrier properties against chemicals such as plasticizers and oils and a small decrease in recording density.

The protective layer has a coating amount of 1 after drying, for example, a coating solution for a protective layer prepared by mixing the specific copolymer resin emulsion in the present invention and an aqueous solution of polyvinyl alcohol, if necessary, with water as a medium. It is formed by applying and drying on a heat-sensitive recording layer to be described later so as to be ˜6 g / m ² .

  Various assistants can be contained in the coating liquid for the protective layer. Examples of the auxiliary agent include lubricants such as zinc stearate, calcium stearate, carnauba wax, paraffin wax, ester wax, surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium polyacrylate, and the like. Examples include ultraviolet absorbers, fluorescent dyes, colored dyes, mold release agents, and antioxidants.

  The heat-sensitive recording layer in the present invention contains an electron donating compound and an electron accepting compound. Examples of the thermal recording system containing these include a combination of a leuco dye and a colorant, a combination of a diazonium salt and a coupler, a combination of a transition element such as iron, cobalt, and copper and a chelate compound, and an aromatic isocyanate compound. Combinations with imino compounds and the like can be mentioned. A combination of a leuco dye and a colorant is preferably used because of excellent color density. The thermal recording layer comprising a combination of a leuco dye and a colorant will be described in detail below, but the present invention is not limited to these combinations.

  Various known leuco dyes and colorants 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 content of the leuco dye is not limited because it varies depending on the colorant to be used, but is preferably about 3 to 50% by mass, particularly preferably about 5 to 40% by mass, based on the total solid content of the heat-sensitive 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 and the like.

  Although the content of the colorant is not limited because it varies depending on the leuco dye used, it is preferably about 10 to 70% by mass, and particularly preferably about 12 to 50% by mass, based on the total solid content of the heat-sensitive recording layer.

  The heat-sensitive recording layer may contain a storability improving agent. Thereby, the storage stability of a recording part can be improved. 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.

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

  The heat-sensitive recording layer may contain a sensitizer. Thereby, the recording sensitivity can be increased. Specific examples of the sensitizer include, for example, stearamide, methylenebisstearate, 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-methoxyphenoxy) ) 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-acetophene Disilazide, N- acetoacetyl -p- toluidine, di (beta-biphenyl ethoxy) benzene, oxalic acid di -p- chlorobenzyl ester, oxalic acid di -p- methylbenzyl ester, and the like oxalic acid dibenzyl ester.

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

The heat-sensitive recording layer uses water as a dispersion medium, leuco dye, colorant, if necessary, sensitizer, preservability improver, etc., or separately with an agitator / pulverizer such as a ball mill, attritor, sand mill, etc. Using a dispersion liquid finely dispersed to have a diameter of 2 μm or less, a coating solution for a thermal recording layer prepared by mixing with an adhesive or the like has a coating amount of ² to ²⁰ g / m ² after drying. Thus, it forms by apply | coating and drying to one side of a support body.

  Adhesives that can be contained in the thermal recording layer coating solution include starches, hydroxyethyl alcohol, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-anhydrous Maleic acid copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, styrene-butadiene copolymer emulsion, urea resin, melamine resin, amide resin, polyurethane resin and the like. Although the content rate of an adhesive agent is not specifically limited, About 5-50 mass% is preferable with respect to the total solid amount of a thermosensitive recording layer.

  Various auxiliary agents can be added to the heat-sensitive recording layer coating liquid as necessary. For example, kaolin, light (heavy) calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, amorphous Pigment such as silica, urea / formalin resin filler, dispersant such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salt, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax And waxes such as ester wax, hydrazine compounds, glyoxal, boric acid, dialdehyde starch, methylol urea, glyoxylate, epoxy compounds and other curing agents, antifoaming agents, coloring dyes and fluorescent dyes.

  Although it does not specifically limit as a support body in this invention, For example, neutral or acidic high quality paper, a synthetic paper, a transparent or translucent plastic film, a white plastic film etc. are mentioned. In addition, although 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 heat-sensitive recording layer. As a result, the recording sensitivity and the recording runnability can be further improved. The undercoat layer supports an undercoat layer coating solution containing an oil-absorbing pigment and / or organic hollow particles and / or thermally expandable particles having an oil absorption of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g, and an adhesive. It is formed by applying and drying on the body. 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 the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, particularly preferably about 0.02 to 3 μm. The content of the oil-absorbing pigment can be selected from a wide range, but generally it is preferably about 2 to 95% by mass, particularly preferably about 5 to 90% by mass, based on the total solid content of the undercoat layer.

  If necessary, a protective layer, a printing layer, a magnetic recording layer, or an ink jet recording layer can be provided on the side of the support opposite to the thermosensitive recording layer (the back side of the thermosensitive recording body). Furthermore, smoothing processing such as supercalendering can be performed in an arbitrary process after the formation of each layer and after the formation of all the layers. Furthermore, various known techniques in the heat-sensitive recording body manufacturing field, such as providing a pressure-sensitive adhesive layer on the back side of the heat-sensitive recording body, 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 “%” in the examples 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 concentration 26.5%), 31 parts styrene-butadiene latex (trade name: L-1571, solid content concentration 48% by Asahi Kasei Chemicals) and carboxymethyl cellulose (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. The mixture was pulverized 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 to obtain a leuco dye dispersion (liquid A).

-Colorant dispersion (liquid B) preparation A composition consisting of 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 (liquid B) was obtained by pulverizing until the median diameter was 1.5 μm using an apparatus SALD2200 (manufactured by Shimadzu Corporation).

-Colorant dispersion (liquid C) preparation A composition comprising 10 parts of a diphenylsulfone cross-linking compound (trade name: D-90, manufactured by Nippon Soda Co., Ltd.), 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was added to a sand mill. Were pulverized until the median diameter was 1.0 μm using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation) to obtain a colorant dispersion (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 (liquid D) was obtained by pulverizing until the median diameter by Shimadzu Corporation was 1.0 μm.

-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 solution for protective layer Copolymer resin (copolymerization component: (meth) acrylonitrile / (meth) acrylic acid alkyl / (meth) acrylic acid 2-hydroxyethyl / (meth) acrylic acid / (meth) acrylamide, ( Ratio of (meth) acrylic acid: 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, Inc.) 128 parts, polyvinyl alcohol A (trade name: JP-45, manufactured by Nihon Acetate / Poval Co., Ltd., saponification degree 86.5-89.5 mol%, polymerization degree 4500) 60 parts of 5% aqueous solution, 58 parts of kaolin (trade name: HYDRAGLOSS 90, manufactured by KaMin LLC), aluminum hydroxide (trade name: Heidilite H) 42M, Showa Denko Co., Ltd.) 4 parts, zinc stearate aqueous dispersion (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%) 8.3 parts, and water 75 parts. The composition was mixed and stirred to obtain a protective layer coating solution.

- a heat-sensitive recording material prepared basis weight of 60 g / m ² on one surface of woodfree paper, undercoat layer coating liquid, heat-sensitive recording layer coating solution, and respectively the protective layer coating liquid application amount after drying 6.0g An undercoat layer, a heat-sensitive recording layer, and a protective layer were sequentially formed by coating and drying so as to be / m ² , 4.5 g / m ² , and 2.0 g / m ² . Thereafter, the surface was smoothed with a super calender and allowed to stand in an environment of 25 ° C. and 50% RH for 24 hours to obtain a heat-sensitive recording material. In addition, no muro treatment was performed.

Example 2
In the preparation of the coating liquid for protective layer of Example 1, the amount of the copolymer resin emulsion was changed to 120 parts instead of 128 parts, and the amount of 5% aqueous solution of polyvinyl alcohol A was changed to 100 parts instead of 60 parts. Obtained a heat-sensitive recording material in the same manner as in Example 1.

Example 3
In the preparation of the coating liquid for protective layer of Example 1, the amount of the copolymer resin emulsion was changed to 128 parts instead of 128 parts, and the amount of 5% aqueous solution of polyvinyl alcohol A was changed to 40 parts instead of 60 parts. Obtained a heat-sensitive recording material in the same manner as in Example 1.

Example 4
In the preparation of the coating solution for the protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol B (trade name: JP-27, manufactured by Nihon Acetate / Poval Co., Ltd., saponification degree 87.0-89.0) A thermosensitive recording material was obtained in the same manner as in Example 2 except that a 5% aqueous solution having a mol% and a polymerization degree of 2700) was used.

Example 5
In the preparation of the coating liquid for protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol C (trade name: JP-33, manufactured by Nihon Acetate / Poval Inc., saponification degree 86.5-89.5) A thermosensitive recording material was obtained in the same manner as in Example 2 except that a 5% aqueous solution having a mol% of 3300) was used.

Example 6
In the preparation of the coating liquid for protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol D (trade name: PVA-235, manufactured by Kuraray Co., Ltd., saponification degree: 87.0-89.0 mol%, polymerization degree: A heat-sensitive recording material was obtained in the same manner as in Example 2, except that 3500) 5% aqueous solution was used.

Example 7
In the preparation of the protective layer coating liquid of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol E (trade name: PVA-220, manufactured by Kuraray Co., Ltd., saponification degree: 87.0-89.0 mol%, polymerization degree) 2200) was used in the same manner as in Example 2 except that a 5% aqueous solution was used.

Example 8
In the preparation of the coating solution for the protective layer of Example 1, the amount of the copolymer resin emulsion was changed to 112 parts instead of 128 parts, and the amount of 5% aqueous solution of polyvinyl alcohol A was changed to 140 parts instead of 60 parts. Obtained a heat-sensitive recording material in the same manner as in Example 1.

Comparative Example 1
In the preparation of the protective layer coating liquid of Example 1, the amount of copolymer resin emulsion was changed to 140 parts instead of 128 parts, and polyvinyl alcohol A was not used. Got the body.

Comparative Example 2
In the preparation of the protective layer coating liquid of Example 1, the amount of the copolymer resin emulsion was changed to 100 parts instead of 128 parts, and the amount of 5% aqueous solution of polyvinyl alcohol A was changed to 200 parts instead of 60 parts. Obtained a heat-sensitive recording material in the same manner as in Example 1.

Comparative Example 3
In the preparation of the protective layer coating liquid of Example 1, the amount of the copolymer resin emulsion was changed to 138 parts instead of 128 parts, and the amount of 5% aqueous solution of polyvinyl alcohol A was changed to 10 parts instead of 60 parts. Obtained a heat-sensitive recording material in the same manner as in Example 1.

Comparative Example 4
In the preparation of the coating liquid for protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol F (trade name: JC-40, manufactured by Nippon Acetate / Poval Co., Ltd., saponification degree of 99.0 mol% or more, A thermal recording material was obtained in the same manner as in Example 2 except that a 5% aqueous solution having a polymerization degree of 4000) was used.

Comparative Example 5
In the preparation of the protective layer coating liquid of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol G (trade name: PVA-124, manufactured by Kuraray Co., Ltd., saponification degree: 98.0-99.0 mol%, polymerization degree) 2400) was used in the same manner as in Example 2 except that a 5% aqueous solution was used.

Comparative Example 6
In the preparation of the coating liquid for protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol H (trade name: JM-33, manufactured by Nihon Acetate / Poval Co., Ltd., saponification degree: 93.5 to 95.5) A thermosensitive recording material was obtained in the same manner as in Example 2 except that a 5% aqueous solution having a mol% of 3300) was used.

Comparative Example 7
In the preparation of the coating liquid for protective layer of Example 2, instead of 100 parts of 5% aqueous solution of polyvinyl alcohol A, polyvinyl alcohol I (trade name: PVA-210, manufactured by Kuraray Co., Ltd., saponification degree: 87.0 to 89. A thermosensitive recording material was obtained in the same manner as in Example 2 except that 50 parts of a 10% aqueous solution having a 0 mol% and a polymerization degree of 1000) was used.

Comparative Example 8
In the preparation of the coating solution for protective layer of Example 2, instead of polyvinyl alcohol A, polyvinyl alcohol J (trade name: PVA-424H, manufactured by Kuraray Co., Ltd., saponification degree 78.5-80.5 mol%, polymerization degree) 2400) was used in the same manner as in Example 2 except that a 5% aqueous solution was used.

Comparative Example 9
In the preparation of the coating liquid for the protective layer of Example 2, instead of polyvinyl alcohol A, acetoacetyl group-modified polyvinyl alcohol K (trade name: Z-410, manufactured by Nippon Synthetic Chemical Co., Ltd., saponification degree: 98.0 mol%, A heat-sensitive recording material was obtained in the same manner as in Example 2 except that a 5% aqueous solution having a polymerization degree of 2300) was used.

Comparative Example 10
A thermosensitive recording material was obtained in the same manner as in Comparative Example 9, except that in the preparation of the protective layer coating solution of Comparative Example 9, 1 part of a 5% aqueous solution of glyoxal was further added.

Comparative Example 11
In the preparation of the coating solution for the protective layer of Example 1, 10 of acetoacetyl-modified polyvinyl alcohol L (trade name: Z-200, manufactured by Nippon Synthetic Chemical Co., Ltd., saponification degree 98.0 mol%, polymerization degree 1100) 350 parts of an aqueous solution, kaolin (trade name: HYDRAGLOSS 90, manufactured by KaMin LLC), 4 parts of aluminum hydroxide (trade name: Heidilite H-42M, manufactured by Showa Denko KK), an aqueous dispersion of zinc stearate (commodity) Name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%) 8.3 parts, 5 parts aqueous solution of glyoxal 7 parts, and 240 parts water mixed and stirred for protective layer A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the coating liquid was prepared.

Comparative Example 12
In the preparation of the coating solution for the protective layer of Example 1, instead of 128 parts of the copolymer resin emulsion (trade name: OT1043Z-1, supra), a styrene-butadiene latex (trade name: L-1571, solid) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 67 parts of 48% partial concentration, solubility parameter: 8.4, manufactured by Asahi Kasei Co., Ltd. were used.

Comparative Example 13
In the preparation of the coating solution for the protective layer of Example 1, a copolymer resin emulsion (product name) having a solubility parameter of 10.56 was used instead of 128 parts of the copolymer resin emulsion (product name: OT1043Z-1, supra). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 62 parts of AM2250, solid content concentration 52%, Showa Polymer Co., Ltd. were used.

  The thermosensitive recording material thus obtained was evaluated as follows. The results were as shown in Table 1. Note that the heat-sensitive recording material obtained in Comparative Example 12 had a problem of causing slight sticking during recording.

(Recording density)
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording body was recorded at an applied energy of 0.24 mJ / dot, and the optical density of the obtained printed portion was measured by a reflection densitometer ( (Trade name: Macbeth densitometer RD-918, manufactured by Gretag Macbeth). The larger the numerical value, the higher the density of printing, and the recording density is preferably 1.20 or more practically.

(Plasticizer resistance)
A wrap film (trade name: High Wrap KMA-W, manufactured by Mitsui Chemicals, Inc.) is wrapped around a polycarbonate pipe (40 mm diameter) in triplicate, and a heat-sensitive recording material after recording in the evaluation of recording density is placed on the wrap film. A wrap film was wrapped in three layers on the top, and the film was left to stand for 24 hours at 40 ° C., and then the optical density of the printed portion was measured as the recording density in the same manner as described above. Further, the storage ratio of the recording unit was calculated based on the following formula. If the recording density after processing is 0.8 or more and the storage rate is 60% or more, preferably 85% or more, there is no practical problem.
Storage rate (%) = (recording density after processing) / (recording density before processing) × 100

(Alcohol resistance)
1 ml of ethyl alcohol was immersed in gauze, the recording surface of the heat-sensitive recording material was rubbed, and fog (ground color) of the heat-sensitive recording layer was measured as an optical density in the same manner as described above. If it is less than 0.10, there is almost no fog and it is excellent in alcohol resistance. The range of 0.10 to 0.20 is slightly fogged, but there is no practical problem. If it exceeds 0.20, the color is changed and it is difficult to read the barcode or the like.

(Water resistance 1)
20 μl of water is dropped with a microsyringe on the protective layer coated surface of the heat-sensitive recording material, the coated surfaces are overlapped with each other, a weight of 100 g / cm ² is placed on the back side, and left in a room temperature room for 24 hours. The working surfaces were peeled off, and the blocking situation was subjected to sensory evaluation based on the following criteria.
(Double-circle): It peels without a problem without resistance.
○: There is a little resistance, but there is no peeling of the protective layer.
(Triangle | delta): Although there is peeling in a protective layer, there is no peeling from a thermosensitive recording layer.
X: It peels off from a thermosensitive recording layer and is unreadable.

(Water resistance 2)
Apply 20 μl of water to the protective layer coating surface of the thermal recording medium with a microsyringe, overlap the coating surfaces together, press the thumb and forefinger strongly for 10 seconds from the back side, and then peel off the coating surfaces to check the blocking situation. Sensory evaluation was performed based on the same criteria as the evaluation of water resistance 1.

Claims (3)

In a thermosensitive recording medium comprising a thermosensitive recording layer containing an electron donating compound and an electron accepting compound on a support, and a protective layer containing an adhesive on the thermosensitive recording layer, the protective layer is saponified as an adhesive. Polyvinyl alcohol having a degree of 85 to 90 mol% and a degree of polymerization of 2000 to 5000 is contained in a proportion of 2 to 20% by mass in the total solid amount of the adhesive, and the protective layer is used as an adhesive (meta ) Containing a vinyl monomer copolymerizable with acrylonitrile and (meth) acrylonitrile and having a solubility parameter of 12.0 (cal / cm ³ ) ^1/2 or more, and the copolymer resin is vinyl A thermosensitive recording material comprising at least one carboxy group-containing vinyl monomer as a monomer in a proportion of 1 to 10% by mass in the total solid content of the copolymer resin.   The heat-sensitive recording material according to claim 1, wherein the polyvinyl alcohol is contained in a proportion of 5 to 20% by mass in the total solid content of the adhesive.   The heat-sensitive recording material according to claim 1 or 2, wherein the degree of polymerization of the polyvinyl alcohol is 2700 to 5000.