JPH10258574A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium having excellent recording sensitivity, recording runnability and printability by reducing skin fog. SOLUTION: The recording medium comprises a primer layer containing pigment and adhesive as main components, and a thermal recording layer containing leuco dye, colorant and adhesive to be sequentially provided. In this case, as the pigment of the primer layer, organic pigment having through holes and oil absorbing amount of 100 ml/100 g or more is used. As the adhesive, hydrophobic resin and polyvinyl alcohol are used together.

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 utilizing a color-forming reaction between a leuco dye and a color former, and more particularly to a heat-sensitive recording material excellent in recording sensitivity and recording running property.

[0002]

2. Description of the Related Art A thermosensitive recording medium is well known in which a colorless or light-colored leuco dye and a coloring agent are used to form a recording image by contacting both coloring substances by heat. Such a thermosensitive recording medium is relatively inexpensive, and its recording equipment is compact and easy to maintain, so that it is used not only as a recording medium for facsimile machines and various computers but also in a wide range of fields.

In particular, in recent years, the speed of recording devices for thermosensitive recording media has been increased, and higher sensitivity of thermosensitive recording media has been required. Leuco dyes, color formers,
Improvement of the material constituting the heat-sensitive recording layer, such as a sensitizer, or improvement of the smoothness of the base paper by blending the base paper or applying pressure calendering (Japanese Patent Publication No. 52-20142, Japanese Patent Application Laid-Open No. 54-115)
255, Japanese Patent Application Laid-Open No. 53-156086), but satisfactory results have not always been obtained. For example, if the recording sensitivity is increased by improving the material of the heat-sensitive recording layer, there is a problem that background fog occurs and the appearance is reduced.

In order to increase the recording sensitivity of a heat-sensitive recording medium, it has been proposed to provide an undercoat layer containing an organic pigment having a low thermal conductivity between the support and the heat-sensitive recording layer, as disclosed in JP-A-59-1.
JP-A-71885, JP-A-60-2397, JP-A-59-171885, and JP-A-5
No. 9-225987. However, these organic pigments have problems in that they have low oil absorbency as compared with inorganic pigments, easily generate thermal head residues during recording, and the undercoat layer is easily peeled off.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material which has little background fog and is excellent in recording sensitivity, recording running property and printability.

[0006]

Means for Solving the Problems In a heat-sensitive recording material comprising a support, an undercoat layer containing a pigment and an adhesive as main components, and a heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive are sequentially provided. As one means for solving the above-mentioned problems, the present invention uses an organic pigment having through holes as a pigment for an undercoat layer, and uses a hydrophobic resin and polyvinyl alcohol in combination as an adhesive.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is characterized in that the pigment particles in the undercoat layer are individually organic pigments having through holes, and the adhesive is a hydrophobic resin and polyvinyl alcohol. The oil absorption of the organic pigment is 1
It is preferably at least 00 ml / 100 g. Oil absorption 100m
If the amount is less than 1/100 g, there is a possibility that the residue adheres to the thermal head and the recording traveling property is reduced, and the recording sensitivity is reduced. The amount of the organic pigment having a through hole is not particularly limited, but may be 50 to 50% with respect to the undercoat layer.
About 90% by weight is preferable. The amount of the adhesive composed of at least a hydrophobic resin and polyvinyl alcohol is 5 to 35% by weight, preferably 8 to 35% by weight, based on the undercoat layer.
It is about 15% by weight.

The organic pigment having a through-hole may have at least one through-hole in the pigment particles. Organic pigments having such through-holes, for example, using a resin particle dissolved in alkaline water such as sodium hydroxide, ammonium hydroxide, potassium hydroxide, triethylamine and the like as a core substance while synthesizing a resin that is not dissolved in alkaline water around it. It is obtained by eluting the core substance with alkaline water.

The resin particles dissolved in alkaline water include, for example, at least one of hydrophobic monomers such as styrene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid. And copolymer particles obtained by emulsion polymerization of at least one of a vinyl monomer of an unsaturated carboxylic acid such as itaconic acid and crotonic acid. The unsaturated carboxylic acid monomer is preferably about 10 to 50% by weight based on all monomers.

As the resin which is not dissolved in alkaline water,
Examples thereof include those obtained by polymerizing at least one of the above-mentioned hydrophobic monomers. Above all, by using a resin containing styrene as a main component as a monomer, an effect that a decrease in the density of a recording portion with time is small can be obtained. Further, as long as the vinyl monomer is not dissolved in alkaline water, at least one of the above-mentioned vinyl monomers of unsaturated carboxylic acids may be copolymerized.

The shape of the particles of the organic pigment having through-holes is not particularly limited. However, when the undercoat layer is formed, the particles do not become too dense and the coating film strength is not reduced, so that the particles are slightly flat spherical. Is preferred. The flatness is preferably about 0 to 30%. The volume average particle diameter is not particularly limited, either, but is 0.1 to 5.0 μm, more preferably 0.1 to 1.2 μm, in consideration of the thickness of the undercoat layer and the strength of the coating film.

Other pigments may be added to the undercoat layer as long as the desired effects of the present invention are not impaired. Other pigments include, for example, inorganic pigments such as calcium carbonate, magnesium carbonate kaolin, calcined kaolin, talc, aluminum hydroxide, aluminum silicate, calcium silicate, magnesium silicate, magnesium aluminosilicate, amorphous silica, titanium oxide, and polystyrene filler. And organic pigments such as acrylic resin fillers, urea-formaldehyde resin fillers, vinylidene chloride hollow particles, and acrylic hollow particles.

The undercoat layer is obtained by mixing and stirring an organic pigment having a through-hole, a latex of a hydrophobic resin, and an aqueous solution of polyvinyl alcohol with water as a dispersion medium, and coating and drying the undercoat layer coating solution on a support. It is formed by this.

Examples of the hydrophobic resin having an adhesive property contained in the undercoat layer include acrylic resins, styrene / butadiene copolymers, polyester polyurethane resins, vinyl acetate / vinyl chloride copolymers, and the like. . Among them, a styrene / butadiene copolymer is preferable because of its excellent adhesion to an organic pigment having a through-hole.

The styrene / butadiene copolymer is one in which the total weight of styrene and butadiene as monomers is 50% by weight or more. In addition, as a monomer, for example, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid may be copolymerized. The ratio of styrene and butadiene is not particularly limited, but is 1: 5 to 5 by weight.
It is about 5: 1.

The degree of polymerization of the polyvinyl alcohol contained in the undercoat layer is from 500 to 3,000, preferably from 10 to 3,000.
It is about 00 to 2000. The saponification degree is 80 or more. Further, the terminal or side chain of polyvinyl alcohol is an organosiloxane, an acetoacetyl group,
It may be substituted with a carboxyl group.

The weight ratio of the styrene / butadiene copolymer and polyvinyl alcohol is 1: 0.5 to 1: 1.
About 5 is preferable. When the proportion of polyvinyl alcohol is increased, the undercoat layer becomes hard and the adhesion to the head may be poor, and the recording properties may be reduced.
About 1: 1.2.

In the undercoat layer coating liquid, if necessary, a water-soluble adhesive such as oxidized starch, casein, methylcellulose, hydroxyethylcellulose, gum arabic, carboxymethylcellulose, a dispersant, an antifoaming agent, a coloring dye, A fluorescent dye, a curing agent, and the like can be appropriately added.

The coating solution for the undercoat layer is applied on a support such as high quality paper (neutral paper, acidic paper), synthetic paper, film, etc., by a coating apparatus used for the production of a general coated body, for example, a blade coater, a roll coater. , A reverse roll coater, a rod blade coater, a chaplex coater, a curtain coater and the like. The amount of the undercoat layer applied is 1 to ²⁰ g / m ² by dry weight, more preferably 2 to 1 g / m ² .
It is about 2 g / m ² .

The thermosensitive recording medium of the present invention can be obtained by providing a thermosensitive recording layer on the undercoat layer thus formed. The heat-sensitive recording layer contains various known leuco dyes and color formers as coloring components.

Examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilide. Linofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-
7-dibenzylaminofluoran, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-
Isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-ani Linofluoran, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 3-di (n-pentyl) amino-6-methyl-
7-anilinofluoran, 3-diethylamino-7-
(O-chloroanilino) fluoran, 3-di (n-butyl) amino-7- (o-chloroanilino) fluoran,
3-diethylamino-7- (o-fluoroanilino) fluoran, 3-di (n-butyl) amino-7- (o-fluoroanilino) fluoran, 3- (N-ethyl-p-
Toluidino) -6-methyl-7-anilinofluoran,
3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3-p- (p-anilinoanilino) anilino-6 -Methyl-7-chlorofluoran, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino Phenyl｝ propane,
3,6, -bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide and the like. Of course, the present invention is not limited to these, and two or more of them can be used as needed.

Examples of the coloring agent include 4-hydroxyacetophenol, 4-tert-octylcatechol,
2′-dihydroxydiphenol, 4,4′-isopropylidenebis (2-tert-butylphenol), 4,
4'-sec-butylidene diphenol, 4-phenylphenol, 4,4'-isopropylidene diphenol (bisphenol A), 4,4 '-(1-phenylethylidene) bisphenol, 2,2-bis (4-hydroxy Phenyl) -4-methylpentane, 2,2′-methylenebis (4-chlorophenol), hydroquinone,
4,4'-cyclohexylidenediphenol, 4,4 '
-Dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, methyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, novolak phenol Resins, phenolic compounds such as phenolic polymers, 4,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4 '-Methyldiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 3,4-dihydroxydiphenylsulfone, 3,
4-hydroxydiphenylsulfone derivatives such as 4-dihydroxy-4'-methyldiphenylsulfone, 4- [2
Aromatics such as-(p-methoxyphenoxy) ethyloxy] zinc salicylate, 4- [3- (p-tolylsulfonyl) propyloxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate Zinc salt of aromatic carboxylic acid, N- (p-tolylsulfonyl) -N- (p-tolyl) urea, 4,4'-bis (N-
compounds having -SO ₂ NH- bond, and the like in the molecule of p- tolylsulfonyl aminocarbonylamino) diphenylmethane.

The ratio of the leuco dye to the colorant is appropriately selected according to the type of the leuco dye and the colorant used, and is not particularly limited. 1 to 10 parts by weight, preferably 2 to
About 5 parts by weight of a coloring agent is used.

The heat-sensitive recording layer is formed, for example, by using water as a dispersion medium,
The average particle diameter of the leuco dye, the color former, and, if necessary, the sensitizer, the preservability improver, and the like together or separately by a stirrer / pulverizer such as a ball mill, an attritor, or a sand mill is about 0.3 to 3 μm. After finely dispersing as described above, a coating solution for a heat-sensitive recording layer prepared by adding the following adhesive is coated on a support and dried.

Examples of the adhesive contained in the coating solution for the heat-sensitive recording layer include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, and the like.
Gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, olefin / acrylic acid copolymer salt,
Diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, styrene / acrylic acid copolymer salt, urea resin, melamine resin, amide resin, styrene / butadiene copolymer latex, polyester Polyurethane latex and the like can be mentioned. Among them, olefin / acrylic acid copolymer salts are preferable because of their excellent adhesion to the undercoat layer.

In the olefin / acrylic acid copolymer salt, examples of the olefin include ethylene, propylene, butylene, and isobutylene. Among them, ethylene is preferred. The ratio of the olefin component in the olefin / acrylic acid copolymer salt is 50 to 90 mo.
About 1% is preferable.

Examples of the salt of the olefin / acrylic acid copolymer salt include a monovalent ammonium salt, a lithium salt, a potassium salt, and a sodium salt.

Examples of sensitizers that may be added to enhance the recording sensitivity as needed include, for example, stearic acid amide, ethylene bistearic acid amide, methylene bisstearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, Benzyl benzyl benzoate, 2-naphthyl benzyl ether, m-terphenyl, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, p-benzylbiphenyl, 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-diphenoxy Ethane, 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane,
p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluidide, p-
Examples include acetophenethidide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, and the like.

Examples of the storability improver added to enhance the storability of a recorded image include 2,2'-methylenebis (4-methyl-6-tert-butylphenol) and
2,2′-ethylenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylidenebis (4,6-
Di-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 4,
4'-thiobis (2-ethyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy- 5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-dihydroxy-3,3 ′, 5,5′-tetra Methyldiphenyl sulfone, 2,2-bis (4-hydroxy-3,5-
Hindered phenol compounds such as dimethylphenyl) propane, 1,4-diglycidyloxybenzene,
Epoxy compounds such as 4′-diglycidyloxydiphenyl sulfone, diglycidyl terephthalate, bisphenol A type epoxy resin, 1- [α-methyl-α- (4′-
Hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene,
N, N'-di-2-naphthyl-p-phenylenediamine, sodium 2,2'-methylenebis (4,6-di-tert-butylphenyl) phosphate and the like. The addition amount of the sensitizer and the storage stability improver is about 1 to 4 parts by weight with respect to 1 part by weight of the leuco dye.

Further, various auxiliaries can be added to the heat-sensitive recording layer coating liquid as needed. As auxiliaries,
For example, pigments such as kaolin, calcium carbonate, calcined kaolin, titanium oxide, amorphous silica, aluminum hydroxide, urea / formalin resin filler, and surfactants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, and sodium lauryl alcohol sulfate. Lubricants such as zinc stearate, calcium stearate, calcium oleate, waxes such as polyethylene wax, carnauba wax, paraffin wax, ester wax, defoaming agents, fluorescent dyes, coloring dye curing agents, and organic particles having through-holes. No.

The method of applying the heat-sensitive recording layer is also not particularly limited, and it can be formed according to a conventionally known and commonly used technique. For example, a method of applying and drying a coating solution for a heat-sensitive recording layer on an undercoat layer by bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating, burr bar coating, curtain coating, die coating, etc. A heat-sensitive recording layer is formed. Although there is no particular limitation on the coating amount of the heat-sensitive recording layer coating composition, usually, 2~12g / m ² in dry weight, preferably 3 to 8 g / m ² approximately.

A protective layer may be provided on the heat-sensitive recording layer or on both sides of the support to enhance the storability and impart a high gloss. After coating each layer, a smoothing treatment such as super calendaring is applied. Can also be applied. further,
A heat-sensitive recording material such as applying a pressure-sensitive adhesive treatment to the back side of the support to process it into an adhesive label, providing a rewetting adhesive layer, or providing a magnetic recording layer, a printing coating layer, and a thermal transfer recording layer Various known techniques in the manufacturing field can be added as necessary.

[0033]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto. Unless otherwise specified, “parts” and “%” in the examples indicate “parts by weight” and “% by weight”, respectively, unless otherwise specified.

Example 1 Preparation of Coating Solution for Undercoat Layer The volume average particle diameter was 0.6 μm and the oil absorption was 150 ml /
250 parts of a 20% dispersion of an organic pigment having 100 g of through-holes (mainly composed of styrene as a monomer), and a styrene-butadiene-based latex having a solid concentration of 48% (styrene: butadiene: butyl acrylate: acrylic acid) 5: 38: 32: 20: 2), 10% of polyvinyl alcohol (polymerization degree 1000, saponification degree 99)
25 parts of the aqueous solution was mixed and stirred to obtain a coating liquid for an undercoat layer.

Solution A Preparation 30 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 5% aqueous solution of methylcellulose 5
Part A and 65 parts of water were pulverized with a sand mill until the average particle diameter became 0.9 μm to obtain a liquid A.

Preparation of Solution B A composition comprising 30 parts of 2,4′-dihydroxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose and 65 parts of water is pulverized with a sand mill until the average particle diameter becomes 1.0 μm. I got

Preparation of Solution C A composition comprising 20 parts of di-p-methylbenzyl oxalate, 5 parts of a 5% aqueous solution of methylcellulose, and 65 parts of water is pulverized by a sand mill until the average particle diameter becomes 1.0 μm, and the solution C is prepared. I got

Preparation of Coating Solution for Thermosensitive Recording Layer 33 parts of A solution, 70 parts of B solution, 70 parts of C solution, 20 parts of 25% aqueous solution of sodium salt of ethylene / acrylic acid copolymer,
Amorphous silica (secondary average particle size 2 μm, oil absorption 180
15 parts, 30 parts of a 30% aqueous dispersion of zinc stearate, polyvinyl alcohol (saponification degree 88,
100 parts of a 10% aqueous solution having a degree of polymerization of 1000) and water 10
The parts were mixed and stirred to obtain a coating solution for a heat-sensitive recording layer.

Preparation of Thermosensitive Recording Material An undercoat layer coating solution and a thermosensitive recording layer coating solution were applied on one surface of a neutral paper of 58 g / m ² at a coating amount of 7 g / m 2 after drying.
^An undercoat layer and a heat-sensitive recording layer were formed by sequentially coating and drying at a concentration of 2.6 g / m ^2, and then subjected to a super calender treatment to obtain a heat-sensitive recording material.

Example 2 In the preparation of the coating liquid for the undercoat layer in Example 1,
8% styrene / butadiene latex (styrene:
Instead of 5 parts of a butadiene: butyl acrylate: acrylic acid monomer weight ratio of 46: 32: 20: 2), a styrene / butadiene-based latex having a solid concentration of 48% (styrene: butadiene: butyl acrylate: acrylic acid) was used. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 5 parts by weight of the monomer was used (65: 22: 10: 2).

Example 3 In the preparation of the coating liquid for the undercoat layer in Example 1, 10 parts of polyvinyl alcohol (degree of polymerization: 1,000, degree of saponification: 99%) was used.
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 25 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 1,700, saponification degree 99%) was used instead of 25 parts of a 25% aqueous solution.

Example 4 In the preparation of the coating solution for the heat-sensitive recording layer of Example 1, instead of 20 parts of a 25% aqueous dispersion of a sodium salt of an ethylene / acrylic acid copolymer, 20 parts of a propylene / acrylic acid copolymer was used. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 25 parts of a 20% aqueous sodium salt dispersion was used.

Example 5 In the preparation of the coating liquid for the undercoat layer in Example 1, an organic pigment having a volume average particle diameter of 0.6 μm and an oil absorption of 150 ml / 100 g having through holes (styrene as a monomer was mainly used). Of a 20% dispersion of the above (a component), the volume average particle diameter is 1.2 μm and the oil absorption is 180 ml / 100.
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 250 parts of a 20% dispersion of an organic pigment having g through-holes (mainly composed of styrene as a monomer) was used.

Example 6 The procedure of Example 1 was repeated, except that 4,4 ′-(1-phenylethylidene) bisphenol was used instead of 2,4′-dihydroxydiphenylsulfone in the preparation of solution B of Example 1. Thus, a thermosensitive recording medium was obtained.

Example 7 In the preparation of the coating liquid for the undercoat layer in Example 1, an organic pigment having a volume average particle diameter of 0.6 μm and an oil absorption of 150 ml / 100 g having through holes (styrene as a monomer was mainly used). Instead of 250 parts of a 20% dispersion), the volume average particle diameter is 0.6 μm, and the oil absorption is 70 ml / 100 g.
Except that 250 parts of a 20% dispersion liquid of an organic pigment having a through hole of the above (mainly composed of styrene as a monomer) was used.
A thermosensitive recording medium was obtained in the same manner as in Example 1.

Example 8 In the preparation of the heat-sensitive recording layer coating liquid of Example 1, polyvinyl alcohol (degree of polymerization: 50) was used instead of 20 parts of a 25% aqueous dispersion of a sodium salt of an ethylene / acrylic acid copolymer.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 25 parts of a 20% aqueous solution (0, a saponification degree of 88%) was used.

Example 9 In the preparation of a coating solution for an undercoat layer in Example 1, a solid concentration of 4
8% styrene / butadiene latex (styrene:
Instead of 5 parts of butadiene: butyl acrylate: acrylic acid monomer weight ratio of 45: 22: 30: 3), an acrylic resin-based latex (methyl methacrylate: butyl acrylate: acrylic acid monomer) having a solid concentration of 48% Example 1 except that 5 parts by weight (48: 48: 4) were used.
In the same manner as in the above, a thermosensitive recording medium was obtained.

Comparative Example 1 Preparation of Undercoat Layer Coating Solution Calcined kaolin (trade name: Ansilex, manufactured by EMC)
Oil absorption 130ml / 100g) 50 parts, solid concentration 48%
5 parts of styrene-butadiene-based latex (styrene: butadiene: butyl acrylate: acrylic acid monomer weight ratio is 46: 32: 20: 2), 10% of polyvinyl alcohol (polymerization degree 1000, saponification degree 99%) 25 parts of an aqueous solution and 200 parts of water were mixed and stirred to obtain a coating liquid for an undercoat layer.

Preparation of Thermosensitive Recording Material Except for using the above undercoat layer coating liquid instead of the undercoat layer coating liquid used in the preparation of the thermosensitive recording body of Example 1,
A thermosensitive recording medium was obtained in the same manner as in Example 1.

Comparative Example 2 In the preparation of the coating solution for the undercoat layer in Example 1, the solid concentration was 4
Instead of 5 parts of 8% styrene-butadiene latex, polyvinyl alcohol (polymerization degree 1000, saponification degree 8
Example 1 except that 25 parts of a 10% aqueous solution (8%) was used.
In the same manner as in the above, a thermosensitive recording medium was obtained.

Comparative Example 3 In the preparation of the coating solution for the undercoat layer in Example 1, 10% of polyvinyl alcohol (degree of polymerization: 1,000, degree of saponification: 99) was used.
Instead of 25 parts of the aqueous solution, a styrene / butadiene-based latex having a solid concentration of 48% (a monomer weight ratio of styrene: butadiene: butyl acrylate: acrylic acid of 45: 2)
2: 30: 3) A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 5 parts were used.

The following evaluation was performed on the thus-obtained thermosensitive recording medium, and the results are shown in Table 1.

[Recording Sensitivity] Thermal Sensitivity Evaluation Machine [Product name: TH-
PMD, manufactured by Okura Electric Co., Ltd.] at an applied voltage of 25 V and an applied energy of 0.24 mJ / dot, and the thermosensitive recording medium was recorded.
-914 type, manufactured by Macbeth Co., Ltd.].

[Head Scrap] Using the above-described thermosensitive evaluation apparatus, 10 sheets of a thermosensitive recording medium were printed in A4 size at an applied voltage of 25 V and an applied energy of 0.50 mj / dot, and the state of the scraps adhering to the thermal head was visually observed. The evaluation was as follows. (Evaluation criteria) A: Almost no residue adheres to the thermal head. ：: A small amount of lees adhered to the thermal head.

[Surface strength] Ink for evaluation of pick strength (T
OKA Printing Ink Super Deluxe
T = 13) was subjected to a printing test with an RI-type printing tester using 0.4 cc, and the degree of peeling of the coating layer surface was visually evaluated as follows. (Evaluation Criteria) A: There is no peeling of the coating film layer, indicating good printability. ：: Peeling of the coating layer was slightly observed. Δ: Peeling of the coating layer is large, which is a practical problem. X: The coating layer was completely peeled off.

[Heat Resistance Underground Fog] The unprinted sample was exposed to an atmosphere of 100 ° C. for 30 minutes, and the color density of the blank portion of the heat-sensitive recording surface was measured in a visual mode using a Macbeth densitometer (RD-914, manufactured by Macbeth). It was measured.

[0057]

[Table 1]

[0058]

As is clear from the results shown in Table 1, all the heat-sensitive recording materials of the present invention were excellent heat-sensitive recording materials having excellent recording sensitivity and recording running property and strong coating film strength. .

Claims (4)

[Claims] 1. A thermosensitive recording medium comprising a support and an undercoat layer containing a pigment and an adhesive as main components and a thermosensitive recording layer containing a leuco dye, a coloring agent and an adhesive, which are successively provided. Wherein the pigment is an organic pigment having through holes, and the adhesive is a hydrophobic resin and polyvinyl alcohol. 2. The oil absorption of an organic pigment having through holes (JIS)
The thermosensitive recording medium according to claim 1, wherein the content of the thermosensitive recording medium is 100 ml / 100 g or more. 3. The thermosensitive recording medium according to claim 1, wherein the hydrophobic resin is a styrene / butadiene copolymer. 4. The thermosensitive recording medium according to claim 1, wherein the adhesive in the thermosensitive recording layer is an olefin / acrylic acid copolymer salt.