JP2530901B2 - Thermal recording - Google Patents

Description

The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having extremely high recording sensitivity and excellent print pixel reproducibility.

"Prior Art" Conventionally, a thermosensitive recording that utilizes a color reaction between a color-forming agent and a color-forming agent that develops color by contacting the color-forming agent, by contacting both color-forming substances with heat to obtain a color-developed image. The body is well known.

Since such a thermal recording medium is relatively inexpensive, the recording device is compact and the maintenance thereof 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.

With the diversification of applications, the thermal recording material has excellent reproducibility of printing pixels in any area from low density to high density and can obtain high quality recorded images comparable to silver halide photography. Demand is growing. Further, with the increase in speed of recording equipment, there is an increasing demand for a thermal recording material having excellent dynamic recording sensitivity.

Therefore, various methods of forming an undercoat layer between the support and the recording layer have been proposed. For example, JP-A-61-35281 discloses an undercoat in which a general pigment of 2 μm or less is used in combination with a petroleum wax. A method has been proposed in which a layer is formed, the smoothness of the undercoat layer is increased, and the adhesion between the recording layer and the head is improved to improve the sensitivity. In addition, JP-A-61-274989
In the publication, a method is proposed in which an oil-absorbing pigment having an oil absorption of 100 cc / 100 g or more is mixed with the same coloring agent as in the recording layer to enhance the dynamic sensitivity.

"Problems to be solved by the invention" However, even if the undercoat layer is formed by these methods, a recording material having a satisfactory sensitivity cannot always be obtained, and the reproducibility of printed pixels is insufficient, and there is room for improvement. Is left.

Therefore, the inventors of the present invention have earnestly studied the composition of the undercoat layer, and as a result, in the undercoat layer formed by the method as described above, a fine substance such as wax or a coloring agent fills the voids of the pigment to make the undercoat layer dense. As a result, it was confirmed that the heat insulating effect of the undercoat layer was impaired, and as a result the expected high sensitivity could not be obtained.

Therefore, by forming an undercoat layer capable of maximally utilizing the porosity of the oil-absorbing pigment used as the main component to exert an excellent heat insulating effect, and further to provide uniform compression elasticity, further As a result of further earnest research on a method for achieving high image quality and high sensitivity, the present invention has been completed.

"Means for Solving the Problems" The present invention relates to a heat-sensitive recording material having an undercoat layer between a support and a recording layer, wherein the main component of the undercoat layer is IJS K 5101.
Is an oil absorbing pigment having an oil absorption of 100 cc / 100 g or more based on the method, 50% by weight or more of the total adhesive is a latex having a Tg point of 0 ° C. or less, and the coating amount of the undercoat layer after drying is 12
A heat-sensitive recording material characterized by having a density of 0.75 g / cm ³ or less at g / m ² or more.

"Function" In the thermosensitive recording medium of the present invention, the oil-absorbing pigment constituting the undercoat layer has an oil absorption of 100c based on the JIS K 5101 method.
C / 100g or more is selectively used. In particular,
For example, calcined clay, aluminum silicate, calcium silicate, magnesium silicate, sodium aluminosilicate, magnesium aluminosilicate, amorphous silica or the like having the above specific oil absorption amount, or a general pigment treated physically or chemically Examples thereof include inorganic and organic pigments having a specific oil absorption amount. Among them, calcined clay and amorphous silica are most preferably used because they have excellent heat insulating properties and compression elasticity.

By the way, even if a general clay, calcium carbonate, magnesium carbonate, titanium oxide, aluminum hydroxide or the like is used as a main component, sufficient heat insulation and compression elasticity cannot be obtained, and the recording layer and the thermal head are not Adhesion is also poor and satisfactory dynamic sensitivity cannot be obtained.

In the present invention, as an adhesive of the oil absorbing pigment as described above,
Although a latex having a Tg point of 0 ° C. or lower is used, its blending ratio must be 50% by weight or more of the total adhesive. With such a composition, the excellent rubber elasticity and strong adhesive force of the latex effectively act, and the pigment is bound to the support with a small amount of adhesive without significantly impairing the void property of the porous oil-absorbing pigment, In addition, the flexibility of the latex also acts to improve the adhesion between the recording layer and the thermal head, so that a high-sensitivity heat-sensitive recording material can be obtained.

Specific examples of the latex having a Tg point of 0 ° C. or lower include, for example, natural rubber, polybutadiene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methylmethacrylate-butadiene copolymer, 2-vinylpyridine. -Styrene-butadiene copolymer, acrylate-based polymer, acrylate-styrene-based copolymer, vinyl chloride-based polymer, vinylidene chloride-based polymer and the like can be mentioned, but of course, they are not limited thereto.

Also, the adhesive used in combination with these latexes is not particularly limited, and examples thereof include starches such as oxidized starch, oxygen-modified starch, cationic starch, esterified starch, etherified starch, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, methoxy cellulose. , Cellulose derivatives such as hydroxyethyl cellulose, completely (or incompletely) saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyvinyl alcohol such as acetoacetylated polyvinyl alcohol, sodium polyacrylate, polyacrylamide, polyvinylpyrrolidone, acrylic acid amide / acrylic Acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / anhydrous Maleic acid copolymer alkali salt, sodium alginate, gelatin, water-soluble polymers such as casein and the like.

The amount of the adhesive used, including the above-mentioned specific latex, is preferably adjusted in the range of 2 to 40% by weight, preferably 5 to 20% by weight, based on the total solid content of the undercoat layer coating liquid.

In the undercoat layer coating liquid, various auxiliary agents such as a dispersant, a defoaming agent, a coloring dye, and a fluorescent dye can be appropriately added, if necessary, but it is related to the special coating liquid formulation of the present invention. Then, the acrylic thickener is 0.0
Addition of about 5 to 5% by weight remarkably improves the dynamic sensitivity and image quality improvement of the resulting thermosensitive recording medium, and such a formulation is one of the preferred embodiments of the present invention.

As the acrylic thickener, there is a material containing a non-crosslinked alkali-soluble emulsion crosslinked alkali swellable emulsion as a main component of the acrylic polymer, and these are dissolved or swollen by the addition of an alkali such as ammonia or caustic soda. A substance that causes a thickening phenomenon by a physical action such as a hydrogen bond between a polymer and water or the inclusion of water molecules in the polymer.

In particular, since these acrylic thickeners are emulsion type, they have a relatively high solid content concentration, and as a result, it is possible to prepare a high-concentration coating liquid, and addition of a small amount produces a sufficient thickening effect. To demonstrate, carboxymethyl cellulose,
Compared with common thickeners such as methyl cellulose and sodium alginate, the degree of impairing the porosity of the pigment is extremely low.

The undercoating coating solution thus prepared is coated on a support, but when the coating amount after drying is less than 12 g / m ² , the desired effect of the present invention cannot be obtained, and the undercoating layer formed is further formed. If the density exceeds 0.75 g / cm ³ , the desired effect cannot be obtained. Therefore, it is necessary to form an undercoat layer of 12 g / m ² or more, but the coating amount is excessively increased, for example, 25 g / m ^2.
If an undercoat layer having a thickness of more than m ² is formed, the handling property of the obtained recording material is deteriorated, which causes a problem that a large amount of paper dust is generated during cutting. Therefore, it is desirable to adjust the coating amount of the undercoat layer within the range of 12 to 25 g / m ² .

Further, when the density of the undercoat layer exceeds 0.75 g / cm ³ , the void property of the oil-absorbing pigment, which is the main component of the undercoat layer, is not fully utilized, and as a result, the effect of improving the dynamic sensitivity is insufficient. Therefore, it is necessary to form the undercoat layer so that the density is 0.75 g / cm ³ or less.

For this reason, it is desirable to avoid blade coating and the like for the coating method of the undercoat layer, which will accelerate the densification of the coating layer extremely, and coating methods such as air knife coating, bar coating, gravure coating, and curtain coating are preferable. It is preferably applied, but of course has a density of 0.
Blade coating in which the tube pressure of the blade is adjusted to 75 g / cm ³ or less is an effective coating method of the present invention. It is also desirable to avoid treating the surface of the undercoat layer with a super calender or the like before forming the recording layer in the heat-sensitive recording material of the present invention.

The density of the undercoat layer in the present invention is calculated as a value obtained by dividing the dry coating amount of the undercoat layer by the thickness of the undercoat layer (the thickness including the support minus the thickness of the support). It

The heat-sensitive recording material of the present invention is produced by providing a heat-sensitive recording layer on the specific undercoating layer thus formed. The color-forming agent and the color-forming agent constituting the recording layer are colorless or light-colored basic A combination of dyes and acidic substances is preferably used.

Various types of basic dyes that are colorless or light-colored 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 -Dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3-
(2-Methylindol-3-ylphthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindole-3-) Yl) -6-dimethylaminophthalide, 3,3
-Bis (9-ethylcarbazol-3-yl) -6-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -6-dimethylaminophthalide, 3
Triallylmethane dyes such as -p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N -Halophenyl-
Diphenylmethane dyes such as leuco olamine and N-2,4,5-trichlorophenyl leuco auramine, thiazine dyes such as benzoyl leuco methylene blue and p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl -Spiro dyes such as spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine -B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino)
Lactam dyes such as 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-methylaminofluoran, 3-diethylamino-
7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3
-Diethylamino-7-N-chloroethyl-N-methylaminofluoralane, 3-diethylamino-7-diethylaminofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-phenylaminofluorane, 3
-(N-ethyl-p-toluidino) -6-methyl-7-
(P-Toluidino) fluorane, 3-diethylamino-
6-methyl-7-phenylaminofluorane, 3-dibutylamino-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-dibutylamino-7- (o-chlorophenylamino) ) Fluoran, 3-pyrrolidino-6-methyl-7-
p-Butylphenylaminofluorane, 3- (N-methyl-Nn-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-)
Fluoran dyes such as hexyl) amino-6-methyl-7-phenylaminofluorane and 3- (N-ethyl-N-β-ethylhexyl) amino-6-methyl-7-phenylaminofluorane. Of course, the dyes are not limited to these dyes, and two or more dyes may be used in combination.

Various compounds are known as the acidic substance used in combination with the basic dye, and the following are exemplified.

4-tert-butylphenol, α-naphthol, β-naphthol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidene diphenol,
4-phenylphenol, hydroquinone, 4,4'-dihydroxy-diphenylmethane, 4,4'-isopropylidenediphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-cyclohexyl Dendiphenol, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-
Methylphenol), 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, hydroquinone monobenzyl Ether, 4
-Hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone,
2,2'-methylenebis (4-chlorophenol), 1,
3-di [2- (4-hydroxyphenyl) -2-propyl] benzene, bis (3-allyl-4-hydroxyphenyl) sulfone, dimethyl 4-hydroxyphthalate, 4
-Methyl hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate. Tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, p-methoxy 4-hydroxybenzoate. Phenolic compounds such as benzyl, novolac type phenol resin, phenol polymer, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-se
c-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-ter
t-butylsalicylic acid, 3-benzylsalicylic acid, 3-
(Α-Methylbenzyl) salicylic acid, 3-chloro-5-
(Α-Methylbenzyl) salicylic acid, 3-phenyl-5
Aromatic carboxylic acids such as-(α, α-dimethylbenzyl) salicylic acid and 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, magnesium, aluminum, calcium, titanium , Organic acid substances such as salts with polyvalent metals such as manganese, tin and nickel. Of course, these colorants may be used in combination of two or more, if necessary.

The use ratio of the basic dye and the colorant is appropriately selected according to the type of the basic dye or colorant used, and is not particularly limited, but generally with respect to 100 parts by weight of the basic dye. 100 to 700 parts by weight, preferably about 150 to 400 parts by weight of the color former is used.

The heat-sensitive coating liquid containing these is generally prepared by dispersing water and a coloring agent together or separately with a stirring / milling machine such as a ball mill, an attritor, or a sand grinder using water as a dispersion medium. To be done.

In addition, fatty acid amides such as stearic acid amide, methylene bisamide stearic acid, amide amide, palmitic acid amide, coconut fatty acid amide, and 2,2'-methylene bis (4
-Methyl-6-tert-butylphenol), 4,4'-butylidenebutylidenebis (6-tert-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5) -Tert-butylphenyl) butane and other hindered phenols, p-benzylbiphenyl, 1,2-
Ethers such as bis (phenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane, 1,2-bis (3-methylphenoxy) ethane, 2-naphthobenzyl ether, dibenzyl terephthalate, 1- Hydroxy-
2 Esters such as naphthoic acid phenyl ester, 2-
An ultraviolet absorber such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, and various known heat-fusible substances can also be added as sensitizers.

In addition, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica, and activated clay can be added to improve the adhesion of scum to the recording head.

In the present invention, the method for forming the heat-sensitive recording layer is not particularly limited, and the heat-sensitive recording layer can be formed according to a conventionally known and commonly used technique, such as an air knife coater, a blade coater, a bar coater, a gravure coater, and a curtain coater. Appropriate coating equipment of Further, the coating amount of the coating liquid is not particularly limited, and is generally ² to 12 g / m ² in dry weight, preferably 3
Adjusted in the range of ~ 10g / m ² .

An overcoat layer may be provided on the recording layer for the purpose of protecting the recording layer, and a protective layer may be provided on the back surface of the support, and further, an adhesive treatment may be applied to the recording layer. Various known techniques in can be added.

"Examples" Examples will be shown below to specifically describe the present invention, but the present invention is not limited to these. Unless otherwise specified, parts and% in the examples are parts by weight and% by weight, respectively.

Example 1 [Preparation of coating liquid for undercoat layer] Amorphous silica having an oil absorption of 160 cc / 100 g (trade name: Mizuka Seal p-527, manufactured by Mizusawa Chemical Co., Ltd.) 100 parts Styrene-butadiene copolymer latex (Tg point:-
35 ° C) (solid content conversion) 15 parts Hydroxypropylated starch (solid content conversion) 5 parts Dispersant (solid content conversion) 0.5 parts This composition was mixed uniformly and a coating solution for the undercoat layer having a solid content concentration of 30% was prepared. Obtained.

[Formation of undercoat layer]

45 g / m ² of high quality paper is coated and dried with a bar coater so that the coating amount after drying is 15 g / m ² to obtain an undercoat coated paper with a coating layer density of 0.65 g / cm ^3. It was

[Preparation of coating liquid for recording layer]

Preparation of solution A 3- (N-cyclohexyl-N-methylamino) -6
-Methyl-7-phenylaminofluorane 10 parts Dibenzyl terephthalate 20 parts Methylcellulose 5% aqueous solution 15 parts Water 80 parts This composition was ground with a sand mill until the average particle size became 2 µm.

Preparation of Solution B 4,4-isopropylidenediphenol 30 parts Methylcellulose 5% aqueous solution 30 parts Water 70 parts This composition was ground with a sand mill until the average particle size became 2 μm.

Solution A 125 parts, solution B 130 parts, amorphous silica (oil absorption 180cc /
100 g) 30 parts, 150 parts of 20% aqueous solution of oxidized starch and 55 parts of water were stirred and mixed to prepare a coating liquid for recording layer.

[Formation of recording layer]

The resulting recording layer coating liquid was applied to the undercoat coated paper with a Meyer bar so that the coating amount after drying was 5 g / m ^2.
It was dried to obtain a thermosensitive recording paper.

Example 2 The coating amount of the undercoat layer coating liquid was 13 g / m ² and the coating amount density was 0.65.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the undercoat coated paper having g / cm ³ was used.

Example 3 The coating amount of the undercoat layer coating liquid was 20 g / m ² and the coating layer density was 0.64.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the undercoat coated paper having g / cm ³ was used.

Example 4 The coating amount of the undercoat layer coating liquid was 24 g / m ² , and the coating layer density was 0.64.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the undercoat coated paper having g / cm ³ was used.

Example 5 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the oil absorbing pigment of the undercoat layer coating solution was changed to a calcined clay (trade name: Ansilex, manufactured by Engelhard) having an oil absorption of 110 cc / 100 g. . The coating layer density of the undercoat layer was 0.70 g / cm ³ .

Example 6 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the oil absorbing pigment of the undercoat layer coating solution was changed to amorphous silica (trade name: Fineseal CMF, manufactured by Tokuyama Soda Co., Ltd.) having an oil absorption of 130 cc / 100 g. Obtained. The coating layer density of the undercoat layer was 0.68 g / cm ³ .

Example 7 In the preparation of the undercoat layer coating liquid, the coating liquid was prepared by further adding 0.6 parts of an acrylic thickener (non-crosslinked type, trade name: Somalex 50: manufactured by Somar) and 0.02 part of ammonia. In the same manner as in Example 1, a thermal recording paper was obtained. The coating layer density of the undercoat layer was 0.62 g / cm ³ .

Example 8 Example 7 except that the acrylic thickener was changed to a cross-linking type thickener (trade name: Viscarex HV30, manufactured by Kyowa Sangyo Co., Ltd.)
In the same manner as described above, a thermosensitive recording paper was obtained. The coating layer density of the undercoat layer was 0.62 g / cm ³ .

Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the oil absorbing pigment of the undercoat layer coating liquid was changed to normal calcium carbonate having an oil absorption of 35 cc / 100 g. The coating layer density of the undercoat layer is 1.03
It was g / cm ³ .

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 5 except that the undercoat layer coating liquid was applied with a blade coater to form an undercoat layer having a coating layer density of 0.93 g / cm ³ .

Comparative Example 3 The coating amount of the undercoat layer coating liquid was 10 g / m ² , and the coating layer density was 0.67.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the undercoat coated paper having g / cm ³ was used.

Comparative Example 4 Thermal recording was carried out in the same manner as in Example 1 except that the amount of the styrene-butadiene copolymer latex was changed to 5 parts and the amount of the hydroxypropylated starch was changed to 15 parts in the preparation of the undercoat layer coating liquid. Got the paper. The coating layer density of the undercoat layer was 0.76 g / cm ³ .

Using the thermal printer (SONY VP-103, video printer), the 12 types of thermal recording paper obtained in this way were recorded with a printing pulse time of 5 msec and 8 msec, and the color density of each was recorded with a Macbeth densitometer (RD-100R type). , Using an amber filter), and the results are shown in the table. Further, as the evaluation of the print pixel (dot) reproducibility of the obtained recorded image, the ratio of the area of the printed dot to the area of one dot of the thermal head (dot reproducibility) was evaluated according to the following criteria, and the result was obtained. Is also shown in the table.

◎: Dot reproduction rate 86% ○: Dot reproduction rate 71 to 85% △: Dot reproduction rate 61 to 70% ×: Dot reproduction rate 60% As is clear from the results in the "Effects" table, the thermal recording papers obtained in the examples of the present invention have excellent reproducibility of print pixels in any area from low density to high density, and have a high dynamic sensitivity. Was also excellent.

Claims (3)

(57) [Claims] 1. A thermosensitive recording medium having an undercoat layer between a support and a recording layer, wherein the main component of the undercoat layer is JIS K 5101.
Is an oil absorbing pigment having an oil absorption of 100 cc / 100 g or more based on the method, 50% by weight or more of the total adhesive is a latex having a Tg point of 0 ° C. or less, and the coating amount of the undercoat layer after drying is 12
A thermal recording material characterized by having a density of 0.75 g / cm ³ or less at a density of g / m ² or more. 2. The heat-sensitive recording material according to claim 1, wherein the oil absorbing pigment is calcined clay or amorphous silica. 3. An undercoat layer is based on 100 parts by weight of an oil absorbing pigment.
The thermosensitive recording medium according to any one of claims 1 to 2, which contains 0.05 to 5 parts by weight of an acrylic thickener.