JPH0781220A - Thermal recording body - Google Patents

Abstract

PURPOSE:To obtain a thermal recording body having no possibility of occurrence of a phenomenon of wearing a serial thermal head, superior recording running properties, good recording image shelf stability and recording density, and superior writability and printability. CONSTITUTION:In a thermal recording body formed by providing a thermal recording layer containing a color former and a color developer and an overcoat layer on a substrate in order, a graft copolymer of a polyvinyl alcohol on an (acrylamide-acrylic acid derivative-acrylonitrile) copolymer and an aluminum hydroxide is incorporated in the overcoat layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and in particular, it has excellent recording runnability without causing a wear phenomenon of a serial thermal head, and has good recording image storability and recording density. The present invention relates to a heat-sensitive recording material having excellent suitability and printability.

[0002]

2. Description of the Related Art Heretofore, a heat-sensitive recording material capable of forming a color by the heat energy of a heat-sensitive head has been well known. Since such a thermal recording material is relatively inexpensive, and the recording device is compact and its maintenance is relatively easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields such as thermal labels. There is. However, there are drawbacks in that fingerprint resistance and solvent resistance are poor, and, for example, when human skin oils or solvents come into contact with the recording layer, the recording density is reduced, and unnecessary color development called background fog occurs.

As a method for solving such a drawback, a method of coating an aqueous emulsion of a resin having film forming ability and chemical resistance on the heat-sensitive recording layer (Japanese Patent Laid-Open Publication No. 5 (1999) -58242).
No. 4-128347), and a method of applying a water-soluble polymer compound such as polyvinyl alcohol (Act.
No. 54) has been proposed. However, under the present circumstances, new defects are accompanied by the improvement, and satisfactory results are not always obtained.

For example, when an aqueous resin coating is applied on the heat-sensitive recording layer, it is necessary to limit the drying temperature in order to avoid color development of the recording layer due to high temperature drying, which inevitably results in insufficient curing of the resin layer. During recording, a phenomenon occurs such that the recording head and the resin layer adhere to each other. Therefore, the recording runnability is improved by adding a pigment, a lubricant, a curing agent and the like. In addition, when the overcoat layer is formed only of the water-based resin, the writing characteristics and the like are deteriorated, so
Usually, the improvement is attempted by adding a pigment.

However, it has become clear that, depending on the type and amount of the pigment used, it causes a phenomenon in which a serial thermal head used in a word processor, a printer or the like is worn out, and sometimes the thermal head is damaged. . Therefore, the applicant of the present invention invented a heat-sensitive recording material in which aluminum hydroxide is selectively used as a pigment to be mixed in the overcoat layer, and modified polyvinyl alcohol containing a silicon atom is used as an aqueous resin. Application was filed as No. 3-169587.

[0006] By such selection, the quality characteristics of the obtained thermosensitive recording medium are sufficiently improved, but there is still room for improvement in the manufacturing process. That is, a modified polyvinyl alcohol such as a modified polyvinyl alcohol containing a silicon atom has a tendency of a remarkable increase in viscosity of the aqueous solution due to the modification, so that stable coating of the overcoat layer coating liquid is difficult and the operability tends to decrease. confirmed.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and is excellent in recording runnability without causing a wear phenomenon of a serial thermal head.
It is intended to provide a thermosensitive recording medium which is excellent in storability and recording density of recorded images and is also excellent in writing aptitude and printing aptitude.

[0008]

Means for Solving the Problems The present inventors have found that in a thermal recording medium in which a thermosensitive recording layer containing a color former and a color former and an overcoat layer are sequentially provided on a support, The inventors have found that the above object can be achieved by adding a graft copolymer of polyvinyl alcohol and a (acrylamide-vinylpyrrolidone-acrylonitrile) copolymer and aluminum hydroxide to the present invention, and completed the present invention.

[0009]

[Function] The ratio of the polyvinyl alcohol portion and the acrylamide / vinylpyrrolidone / acrylonitrile) copolymer portion of the specific graft copolymer is not particularly limited, but the polyvinyl alcohol portion is relative to the acrylamide / vinylpyrrolidone / acrylonitrile copolymer portion. A range of 5 to 100% by weight is preferable. Also, as the ratio of acrylamide, vinylpyrrolidone, and acrylonitrile,
The amount of acrylamide is preferably 60 to 90% by weight, vinylpyrrolidone is 3 to 25% by weight, and acrylonitrile is 1 to 20% by weight based on the acrylamide / vinylpyrrolidone / acrylonitrile copolymer part. Further, lower alkyl (meth) acrylate, (meth) acrylic acid and the like can be copolymerized in the acrylamide / vinylpyrrolidone / acrylonitrile copolymer within a range that does not impair the effects of the present invention.

The heat-sensitive recording material of the present invention is characterized by containing a graft polymer of polyvinyl alcohol and a (acrylamide-vinylpyrrolidone-acrylonitrile) copolymer in the recording layer. The polymer compound is generally used as an adhesive,
It can also be used as a dispersion aid. The amount of the specific graft copolymer to be used is preferably adjusted in the range of 2 to 30% by weight, preferably 5 to 20% by weight, based on the total solid amount of the recording layer.

In the present invention, the material contained in the heat-sensitive recording layer is not particularly limited, and any combination can be used as long as it causes a color reaction by heat energy from the heat-sensitive head. A combination of a light-colored basic dye and an inorganic or organic acidic substance, a combination of a higher fatty acid metal salt such as ferric stearate and a phenol such as gallic acid, a diazonium compound, a coupler compound and a base when melted by heat. Examples include combinations of compounds exhibiting a sexual atmosphere. However, the specific overcoat layer of the present invention provided on the heat-sensitive recording layer is particularly preferable when applied to a combination of a basic dye and an acidic substance, because a heat-sensitive recording material having extremely excellent recording characteristics can be obtained.

As the colorless or light-colored basic dye, various types are known, and the following are exemplified. 3,3-bis (p-dimethylaminophenyl) -6
-Dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindole-3)
-Yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindole-3-)
Yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -6-dimethylaminophthalide,
3,3-bis (2-phenylindol-3-yl)-
6-Dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6
-Triarylmethane dyes such as dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leukoauramine, N-2,4,5-trichlorophenylleucoaamine, etc. Diphenylmethane dyes, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and other thiazine dyes, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-
Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-
Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3- Diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
Diethylamino-6,7-dimethylfluorane, 3-
(N-ethyl-p-toluidino) -7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino- 7-dibenzylaminofluorane, 3-diethylamino-7-N
-Methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-toluidino) −
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-p-toluidino) -6-methyl-7- (p-
Toluidino) fluorane, 3-dimethylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3
-Di-n-butylamino-6-methyl-7-phenylaminofluorane, 3-di-n-pentylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7- (2-carbomethoxy -Phenylamino) fluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-phenylaminofluorane, 3
-Pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-
Xylidinofluorane, 3-diethylamino-7- (o
-Chlorophenylamino) fluorane, 3-di-n-butylamino-7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3- (N-methyl-) N-n-
Amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-amyl) amino-
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-N-isoamyl) amino-6-methyl-7-
Phenylaminofluorane, 3- (N-methyl-Nn)
-Hexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-hexyl) amino-6-methyl-7-phenylaminofluorane, 3
-(N-ethyl-N-β-ethylhexyl) amino-6
-Methyl-7-phenylaminofluorane, 3- (N-
Ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-cyclopentyl) amino-6-methyl-7-phenylaminofluorane, 2,2-bis {4- [6'-
(N-Cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthene] -2 '
Fluorane dyes such as -ylamino] phenyl} propane. Of course, it is not limited to these dyes,
A combination of two or more dyes is also possible.

Various kinds of compounds are known as colorants used in combination with the above basic dyes, and examples thereof include the following. 4-tert-butylphenol, α-naphthol, β-naphthol, 4-acetylphenol,
4-tert-octylphenol, 4,4'-sec-butylidene diphenol, 4-phenylphenol, 4,
4'-dihydroxy-diphenylmethane, 4,4'-isopropylidenediphenol, hydroquinone, 4,
4'-cyclohexylidene diphenol, 4,4'-
(1,3-dimethylbutylidene) bisphenol, 2,
2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenyl Sulfone, 2,4'-dihydroxydiphenyl sulfone,
4-hydroxy-4'-methyldiphenyl sulfone, 4
-Hydroxy-4'-methoxydiphenyl sulfone, 4
-Hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-3 ', 4'-trimethylene diphenyl sulfone, 4-hydroxy-3', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-
4'-methyldiphenyl sulfone, bis (3-allyl-
4-hydroxyphenyl) sulfone, 1,3-di [2-
(4-hydroxyphenyl) -2-propyl] benzene, hydroquinone monobenzyl ether, bis (4-hydroxyphenyl) acetic acid butyl ester, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4,4'-trihydroxy Benzophenone,
2,2 ', 4,4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, 4-
Propyl hydroxybenzoate, sec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, 4
-Phenyl hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-p- Chlorobenzyl, 4
-Hydroxybenzoic acid-p-methoxybenzyl, novolac type phenolic resin, phenolic compounds such as phenolic polymers, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-
4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid,
3-tert-butylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3-chloro-5- (α-methylbenzyl) salicylic acid, 3-phenyl −5- (α,
α-Dimethylbenzyl) salicylic acid, 3,5-di-α-
Aromatic carboxylic acids such as methylbenzyl salicylic acid, and organic acidic substances such as phenolic compounds, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel etc. Of course, the above-mentioned coloring agents can also be used as needed.
One or more species can be used in combination.

The use ratio of the basic dye and the color developing agent should be appropriately selected according to the types of the basic dye and the color developing agent to be used and is not particularly limited, but in general, the basic dye 1 is used.
About 1 to 7 parts by weight, preferably about 1 to 4 parts by weight, of the coloring agent is used with respect to parts by weight. Preparation of a coating liquid containing these, generally using water as a dispersion medium, a ball mill, attritor, with a stirrer / grinder such as a sand mill, a basic dye,
It is prepared by dispersing a coloring agent together or separately and pulverizing it to an average particle size of 1 μm or less, preferably 0.5 μm or less.

In such a coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride are usually used as binders. Copolymer salt, ethylene / acrylic acid copolymer salt,
Styrene / acrylic acid copolymer salt, natural rubber emulsion, styrene / butadiene copolymer emulsion, acrylonitrile / butadiene copolymer emulsion, methylmethacrylate / butadiene copolymer emulsion, folychloroprene emulsion, vinyl acetate emulsion, ethylene / acetic acid At least one kind of vinyl emulsion or the like is blended in an amount of about 10 to 40% by weight, preferably about 15 to 30% by weight, based on the total solid content of the recording layer.

Various auxiliaries can be further added to the coating liquid, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium, fatty acid metal salt dispersant, stearic acid. Waxes such as zinc, calcium stearate, polyethylene wax, carnauba wax, pachifin wax, ester wax, defoaming agent,
Fluorescent dyes, coloring dyes, etc. are appropriately added.

Further, kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica, in order to improve adhesion of dust to the recording head,
Inorganic pigments such as activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and organic pigments such as raw starch particles can also be added.

Further, in the heat-sensitive recording material of the present invention, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, and coconut fatty acid amide are used as long as the desired effects of the present invention are not impaired. , 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-3-methylphenol), 1,1,3-tris (2-methyl) -4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-
Hindered phenols such as tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, p
-Benzylbiphenyl, p- (4-tolyloxy) biphenyl, 1,5-bis (4-methoxyphenoxy) -3
-Oxa-pentane, 1,2-bis (phenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane,
1,2-bis (3-methylphenoxy) ethane, 1-
Ethers such as (2-methylphenoxy) -2- (4-methoxyphenoxy) ethane, 2-naphtholbenzyl ether, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid phenyl ester, oxalic acid dibenzyl ester, oxalic acid Esters such as di (4-methylbenzyl) ester and oxalic acid di (4-chlorobenzyl) ester, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2-hydroxy-4-benzyloxybenzophenone It is also possible to use an ultraviolet absorber such as the above and various known heat-fusible substances together as a sensitizer. The amount of the sensitizer used is not particularly limited, but it is generally desirable to adjust the amount within a range of about 4 parts by weight or less relative to 1 part by weight of the color developing agent.

The thermal recording material of the present invention comprises paper as a support,
Plastic film, synthetic paper, etc. are used. The coating method of the recording layer is not particularly limited and can be formed according to a conventionally well-known and conventional technique, for example, bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating, etc. Is formed by a method of coating and drying. When a plastic film is used as the support, the coating efficiency can be increased by subjecting the surface to treatments such as corona discharge and electron beam irradiation. Further, the coating amount of the coating liquid is not particularly limited, but is usually 2 to 1 by dry weight.
2 g / m ^2, preferably in the range of about 3 to 10 g / m ^2.

In the method of the present invention, a specific overcoat layer is provided on the heat-sensitive recording layer thus obtained, and polyvinyl alcohol and (acrylamide-vinylpyrrolidone-acrylonitrile) copolymer are used as water-soluble resin. It has a very important feature in using a graft copolymer and selectively using aluminum hydroxide as a pigment to be used in combination.

The above polyvinyl alcohol used as a water-soluble resin and (acrylamido vinylpyrrolidone
Graft copolymer with acrylonitrile) copolymer,
The viscosity of the aqueous solution is lower than that of ordinary modified polyvinyl alcohol, and even if it is used in a large amount as a coating liquid for the overcoat layer, the operability is not deteriorated due to thickening, and the thermal recording material obtained is It is possible to manufacture a thermal recording material of high quality extremely stably without impairing the quality characteristics.

As the aluminum hydroxide selectively used as a pigment, for example, fine grained aluminum hydroxide (chemical formula Al ₂ O ₃ .3H ₂ O or Al (OH)) produced by the Bayer method using bauxite as a raw material is used. ₃ )
Etc. are used. The average particle diameter of such aluminum hydroxide is 5 μm or less, preferably about 3 μm or less. Further, the compounding ratio of the specific polyvinyl alcohol and aluminum hydroxide is not particularly limited, but 0.05 to 1.5 parts by weight of aluminum hydroxide relative to 1 part by weight of the specific polyvinyl alcohol. Parts, preferably 0.1 to 1.1 parts by weight.

In the heat-sensitive recording material of the present invention, various water-soluble resins may be used in combination in the overcoat layer as long as the effects of the present invention are not impaired. Examples of such water-soluble resins include cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, casein, arabic gum, oxidized starch, etherified starch, dialdehyde starch, esterified starch and the like, complete saponification or Partially saponified polyvinyl alcohol, polyvinyl alcohol modified with various functional groups, specifically acetoacetyl modified polyvinyl alcohol, carboxyl modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, olefin modified polyvinyl alcohol, nitrile modified polyvinyl alcohol, amide modified Examples thereof include polyvinyl alcohol, pyrrolidone modified polyvinyl alcohol and modified polyvinyl alcohol containing a silicon atom.

Further, in order to further improve the water resistance and the plasticizer resistance of the overcoat layer, a curing agent may be added to the coating liquid for forming the overcoat layer. Examples of the curing agent include glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, alum, ammonium chloride and the like.

Further, in the coating solution, if necessary, a lubricant such as zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium dioctyl sulfosuccinate, dodecylbenzene sulfone. Sodium acid, surfactant such as sodium lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt, etc., UV absorbers such as benzophenone type, triazole type, antifoaming agent, fluorescent dye, coloring dye, etc. It can also be added as appropriate.

The coating liquid for the overcoat layer is generally prepared as an aqueous coating liquid, and if necessary, sufficiently mixed and dispersed by a mixing / stirring machine such as a mixer, attritor, ball mill, roll mill, etc. The thermal recording layer is coated and dried by a coating device. After application, it can be dried by irradiation with ultraviolet rays or electron beams. The coating amount of the coating liquid is not particularly limited, but is 0.1 g / m 2.
^If it is less than ² , the desired effect of the present invention cannot be sufficiently obtained, and if it exceeds 10 g / m ² , the recording sensitivity of the thermosensitive recording medium may be remarkably reduced, so that it is generally 0.1% by dry weight. to 10 g / m ^2, preferably about 0.5~5g
It is adjusted in the range of about / m ² .

If desired, a super calendering treatment may be applied after coating the heat-sensitive recording layer or after coating the overcoat layer to further improve the image quality and image density. In addition, an undercoat layer consisting of an adhesive and a white pigment is provided, on which a thermosensitive recording layer and an overcoat layer are provided to improve recording density, sensitivity and storability, and to eliminate the influence of oil and plasticizer from the back side. In addition, a back barrier layer composed of an adhesive and a white pigment may be provided on the back surface of the recording material to further improve the storage stability. As the adhesive or white pigment used for the undercoat layer or the back barrier layer, those used for the above-mentioned heat-sensitive recording layer can be appropriately used. Further, various known techniques in the field of producing a heat-sensitive recording material can be added, if necessary, such as a pressure-sensitive adhesive treatment on the back surface of the recording material to process it into an adhesive label.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Unless otherwise specified, "parts" and "%" in the examples represent parts by weight and% by weight, respectively.

Example 1 Preparation of liquid A 10 parts of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of methylcellulose % Aqueous solution 5 parts and water 50 parts were pulverized with a horizontal sand mill until the average particle size became 0.5 μm. Preparation of Solution B A composition consisting of 20 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 30 parts of water was pulverized by a horizontal sand mill until the average particle diameter became 1.0 μm. Formation of recording layer Liquid A 85 parts, liquid B 55 parts, silicon oxide pigment (oil absorption 180
cc / 100 g), a coating solution prepared by mixing and stirring 15 parts of 20% polyvinyl alcohol aqueous solution and 95 parts of water onto a base paper of 50 g / m ² and a coating amount of 5 g / m after drying.
^A thermosensitive recording medium was obtained by applying and drying so as to be ² .

Formation of Overcoat Layer On the obtained thermosensitive recording medium, a coating liquid having the following composition was coated and dried so that the coating amount after drying was 2 g / m ^2, and then smoothed with a super calender. A thermal recording material having an overcoat layer was obtained by processing. 333 parts of a 15% aqueous solution of a graft copolymer of polyvinyl alcohol and (acrylamide / vinylpyrrolidone / acrylonitrile) copolymer, aluminum hydroxide (trade name: HAL-4
2, average particle diameter 1 μm, manufactured by Showa Denko KK) 50 parts,
100 parts of a 30% aqueous dispersion of zinc stearate, di (2-
Ethylhexyl) sodium sulfosuccinate (trade name:
Lapizole B-80, manufactured by NOF CORPORATION, 2 parts, antifoaming agent (solid content 15%) 5 parts, and water 340 parts coating liquid for overcoat layer.

Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that a coating solution having the following composition was applied and dried as the overcoat layer. 333 parts of a 15% aqueous solution of a graft copolymer of polyvinyl alcohol and (acrylamide / vinylpyrrolidone / acrylonitrile) copolymer, aluminum hydroxide (trade name: HAL-42, average particle size 1 μm, Showa Denko KK) 25 Part, aluminum hydroxide (trade name: H
AL-43, average particle size 0.6 μm, manufactured by Showa Denko KK) 25 parts, zinc stearate 30% aqueous dispersion 100
Parts, 2 parts of sodium di (2-ethylhexyl) sulfosuccinate (trade name: Rapisol B-80, manufactured by NOF CORPORATION), 5 parts of antifoaming agent (solid content 15%), and water 34
A composition consisting of 0 parts.

Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was applied and dried as the overcoat layer. 500 parts of a 15% aqueous solution of a graft copolymer of polyvinyl alcohol and (acrylamide / vinylpyrrolidone / acrylonitrile) copolymer, aluminum hydroxide (trade name: HAL-42, average particle diameter 1 μm, Showa Denko KK) 35 Parts, 30 parts of 30% aqueous dispersion of zinc stearate, 2 parts of sodium di (2-ethylhexyl) sulfosuccinate (trade name: Rapisol B-80, manufactured by NOF CORPORATION), antifoaming agent (solid content 15%) ) 5 parts, and 188 parts water.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was applied and dried as the overcoat layer. 667 parts of a 15% aqueous solution of a graft copolymer of polyvinyl alcohol and (acrylamide / vinylpyrrolidone / acrylonitrile) copolymer, 100 parts of a 30% aqueous dispersion of zinc stearate, sodium di (2-ethylhexyl) sulfosuccinate (commodity) Name: Lapizole B-8
0, made by Nippon Oil & Fats Co., Ltd., 2 parts, antifoaming agent (solid content 15)
%) 5 parts, and water 55 parts.

Comparative Example 2 As a composition of the overcoat layer, instead of aluminum hydroxide (trade name: HAL-42, average particle size 1 μm, manufactured by Showa Denko KK), kaolin (trade name: UW-9).
No. 0, average particle diameter 0.5 μm, manufactured by EMC) was used to obtain a thermosensitive recording medium in the same manner as in Example 1.

Comparative Example 3 As the composition of the overcoat layer, instead of the graft copolymer of polyvinyl alcohol and (acrylamide / vinylpyrrolidone / acrylonitrile) copolymer, a modified polyvinyl alcohol aqueous solution containing silicon atoms (trade name: R A thermosensitive recording medium was obtained in the same manner as in Example 1 except that Polymer R-1130, manufactured by Kuraray Co., Ltd.) was used.

The six types of heat-sensitive recording materials thus obtained were subjected to a comparative test by the method described below, and the results are shown in Table 1. Recording density Color tester for thermal recording material (TM-PMD manufactured by Okura Electric Co., Ltd.)
Type, applied voltage: 16V, pulse cycle: 0.51m
s) was used and recorded under the condition of pulse width 0.30 ms,
The recorded density is Macbeth densitometer (Macbeth RD-
914 type).

Thermal Sensitive Serial Head Wear Evaluation Personal Word Processor (Toshiba, Rupo JW
95 HP) was used to print 20 million characters, and the presence or absence of print failure (occurrence of white spots due to head damage) was judged according to the following evaluation criteria. At the same time, observe the surface of the head,
The degree of abrasion was judged according to the following evaluation criteria.

Writability Evaluation The quality of writability with a pencil (HB) was evaluated according to the following evaluation criteria. (Writability) ◎: Can be written smoothly ○: If writing with a little effort, there is no problem in practical use ×: Hard to write, lacking in practicality

Viscosity of Overcoat Layer Coating Liquid The viscosity of the overcoat layer coating liquid was measured with a B-type viscometer (manufactured by Tokyo Keiki Seisakusho) and used as an index of coating suitability of the coating liquid.

[0040]

[Table 1]

[0041]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention has very little abrasion of the thermosensitive serial head, has good recording density, and has excellent writing properties. It was

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support, on which a thermosensitive recording layer containing at least a color former and a color former, and an overcoat layer are sequentially provided. In the overcoat layer, polyvinyl alcohol and (acrylamide-vinyl) are used. (Pyrrolidone / acrylonitrile) copolymer containing a graft copolymer and aluminum hydroxide. 2. The aluminum hydroxide is contained in an amount of 0.05 to 1.5 parts by weight based on 1 part by weight of a graft copolymer of polyvinyl alcohol and a (acrylamide-vinylpyrrolidone-acrylonitrile) copolymer. The heat-sensitive recording material described.