JPH02116591A - Thermal recording body - Google Patents

Abstract

PURPOSE:To enhance a heat-insulation effect and to improve image quality and sensitivity by a method wherein an undercoat layer is mainly composed of an oil-absorbing pigment having an oil absorption more than a specific value, a specific latex is contained one half or more in a total adhesive, and the coating weight and density of the dried undercoat layer are in specific ranges. CONSTITUTION:In a thermal recording body having an undercoat layer between a substrate and a recording layer, the undercoat layer is composed of an oil-absorbing pigment having an oil absorption of 100cc/100g or more based on a JIS K 5101 method, 50wt.% or more of the total amount of an adhesive is a latex having a Tg point of 0 deg.C or less, the coating weight of the dried undercoat layer is 12g/cm<2> or more, and the density thereof is 0.75g/cm<2> or less. As the oil-absorbing pigment, a calcined clay or an amorphous silica is most preferably used because of its superior heat insulating properties and compressive elasticity. The composition of 50wt.% or more of the latex having a Tg point of 0 deg.C or less to the total adhesive realizes the effective action of the superior rubber elasticity and strong adhesion of the latex. In this manner, the pigment is bound on a substrate with a small amount of the adhesive without markedly deteriorating the void volume of the porous oil-absorbing pigment, and a thermal recording body with high image quality and high sensitivity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium having extremely high recording sensitivity and excellent printed pixel reproducibility.

"Prior Art" Conventionally, heat-sensitive recording utilizes a coloring reaction between a coloring agent and a coloring agent that develops color when it comes into contact with the coloring agent, and brings a recoloring substance into contact with heat to obtain a colored image. The body is well known.

Such thermal recording media are relatively inexpensive, the recording device is compact, and maintenance is relatively easy, so they are used not only as recording media for facsimiles and various computers, but also in a wide range of fields.

With the diversification of applications, there is a need for thermal recording materials that have excellent reproducibility of printed pixels in all areas from low density to high density, and that can produce recorded images of high quality comparable to silver halide photography. Demand is increasing. Furthermore, as recording equipment becomes faster, there is an increasing demand for heat-sensitive recording materials with excellent dynamic recording sensitivity.

For this reason, various methods have been proposed for forming an undercoat layer between the support and the recording layer, such as Japanese Patent Application Laid-Open No. 61-3528.
Publication No. 1 describes a method of increasing sensitivity by forming an undercoat layer using a general pigment of 2 μm or less in combination with petroleum wax, increasing the smoothness of the undercoat layer, and improving the adhesion between the recording layer and the head. is proposed. Also, JP-A-61-
Publication No. 274989 states that the oil absorption amount is 100cc/100
A method has been proposed in which the same coloring agent as that of the recording layer is added to an oil-absorbing pigment having a weight of more than 100 g to increase the dynamic sensitivity.

"Problems to be Solved by the Invention" However, even if an undercoat layer is formed using these methods, a recording medium with satisfactory sensitivity cannot necessarily be obtained, and the reproducibility of printed pixels is insufficient, and there is still room for improvement. is left behind.

Therefore, as a result of intensive research into the composition of the undercoat layer, the present inventors found that the undercoat layer formed by the method described above has the following characteristics:
Because micronized substances such as wax and coloring agents fill the voids in the pigment and make the undercoat layer denser, the insulation effect of the undercoat layer is impaired, and as a result, the expected high sensitivity cannot be obtained (i! I came to accept it.

Therefore, by forming an undercoat layer that can make maximum use of the porosity of the oil-absorbing pigment used as the main component and exhibiting an excellent heat insulating effect, it also has uniform compressive elasticity. As a result of further intensive research into methods for achieving higher image quality and higher sensitivity, we have completed the present invention.

"Means for Solving the Problems" The present invention provides a heat-sensitive recording material having an undercoat layer between a support and a recording layer, in which the main component of the undercoat layer conforms to JIS K
Oil absorption amount based on 5101 method is 100cc/100
50% or more of the total adhesive is latex with a Tg point of 0°C or less, and the coating amount of the undercoat layer after drying is 12g/m or more, and the degree of This is a heat-sensitive recording material characterized in that it is 0.75 g/an' or less.

"Function" In the heat-sensitive recording material of the present invention, as the oil-absorbing pigment constituting the undercoat layer, one having an oil absorption amount of 100 cc/100 g or more based on the JIS K 5101 method is selectively used. Specifically, for example, calcined clay, aluminum silicate, calcium silicate, magnesium silicate, sodium aluminosilicate, magnesium aluminosilicate, amorphous silica, etc., which have the above-mentioned specific oil absorption amount, or general pigments can be physically or chemically treated. Examples include inorganic and organic pigments that have been treated to have the above-mentioned specific oil absorption amount, but among them, calcined clay and amorphous silica are most preferably used because they have excellent heat insulation properties and compressive elasticity.

By the way, even if pigments such as clay, calcium carbonate, magnesium carbonate, titanium oxide, and aluminum hydroxide are used as main components, sufficient heat insulation and compressive elasticity cannot be obtained, and the recording layer and thermal head The adhesion is also poor, making it impossible to obtain satisfactory dynamic sensitivity.

In the present invention, as an adhesive for the oil-absorbing pigment as described above, 0
A latex having a Tg point of 0.degree. With such a formulation, the excellent rubber elasticity and strong adhesive force of latex work effectively, and the pigment can be bound to the support with a small amount of adhesive without significantly impairing the porosity of the porous oil-absorbing pigment. Moreover, the flexibility of latex also works to improve the adhesion between the recording layer and the thermal head, so that a thermal recording medium with high image quality and high sensitivity can be obtained.

Specific examples of latexes having a Tg point of 0°C or lower include natural rubber, polybutadiene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, methyl methacrylate-butadiene copolymers,
Examples include 2-vinylpyridine styrene-butadiene copolymer, acrylate polymer, acrylate-styrene copolymer, vinyl chloride polymer, vinylidene chloride polymer, etc., but are not limited to these, of course. do not have.

Furthermore, adhesives used in combination with these latexes are not particularly limited, and include starches such as oxidized starch, oxygen-modified starch, cationic starch, esterified starch, and etherified starch;
Cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, methoxycellulose, hydroxyethylcellulose, polyvinyl alcohols such as fully (or incompletely) saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, sodium polyacrylate, polyacrylamide , polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer Examples include alkali salts, sodium alginate, water-soluble polymers such as gelatin, and casein.

The amount of adhesive used includes the specific latex mentioned above.
2 to 40% by weight, preferably 5% by weight of the total solid content of the undercoat surface coating liquid
It is desirable to adjust the amount within a range of about 20% by weight.

Various auxiliary agents such as dispersants, antifoaming agents, colored dyes, and fluorescent dyes can be added to the undercoating surface coating liquid as necessary, but in relation to the special coating liquid formulation of the present invention. in,
Add an acrylic thickener to 100 parts by weight of the pigment in an amount of 0.
When added in an amount of about 0.5 to 5% by weight, the dynamic sensitivity and high image quality of the resulting heat-sensitive recording material are significantly improved, so such a blend is one of the preferred embodiments of the present invention.

Acrylic thickeners include materials whose main components are acrylic polymers, such as non-crosslinked alkali-soluble emulsions and crosslinked alkali-swellable emulsions, which can be dissolved or swollen by the addition of alkali such as ammonia or caustic soda. It is a substance that causes a thickening phenomenon due to physical effects such as hydrogen bonding between the 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 highly concentrated coating liquids, and even a small amount of addition can provide a sufficient thickening effect. Therefore, compared to ordinary thickeners such as carboxymethylcellulose, methylcellulose, and sodium alginate, the degree of damage to the porosity of pigments is extremely low.

The undercoat coating liquid thus prepared is coated on a support, but if the coating amount after drying is less than 12 g/rrf, the desired effect of the present invention cannot be obtained, and the density of the formed undercoat layer may be lowered. If it exceeds 0.75 g/aa', the desired effect cannot be obtained.

Therefore, it is necessary to form an undercoat layer of 12 g/rrr or more, but if the coating amount is increased excessively, for example, forming an undercoat layer exceeding 25 g/m, the handling suitability of the resulting recording medium will decrease. For example, a problem arises in 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 a range of 12 to 25 g/m.

In addition, if the density of the undercoat layer exceeds 0.75 g/cm3, the porosity of the oil-absorbing pigment, which is the main component of the undercoat layer, will not be utilized to the fullest, resulting in insufficient improvement in dynamic sensitivity. Therefore, it is necessary to form the undercoat layer to have a density of 0.75 g/c1fi3 or less.

For this reason, it is preferable to avoid blade coating, which promotes the densification of the coating layer, and preferable coating methods such as air knife coating, par coating, gravure coating, and curtain coating. .

Furthermore, it is desirable to avoid treating the surface of the undercoat layer with a supercalender 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 the dry coating amount of the undercoat layer divided by the thickness of the undercoat layer (the thickness including the support minus the thickness of the support). Ru.

The heat-sensitive recording material of the present invention is produced by providing a heat-sensitive recording layer on the specific undercoat layer thus formed, and the coloring agent and coloring agent constituting the recording layer are colorless or light-colored basic. Combinations of dyes and acidic substances are preferably used.

Various types of colorless to light-colored basic dyes are known, and examples include the following.

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-methylindole-3-ylphthalide, 3.
3-bis(1,2-dimethylindol-3-yl)-
5-dimethylaminophthalide, 3,3-bis(1゜2-
dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-3
-yl)-6-dimethylaminophthalide, 3.3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3
-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide and other triallylmethane dyes, 4,4'-
Bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2,4,
Diphenylmethane dyes such as 5-trichlorophenylleucoauramine, benzoylleucomethylene blue, p
- Thiazine dyes such as nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphthopyran ( Spiro dyes such as 6'-methoxybenzo)spiropyran and 3-propyl-spiro-dibenzopyran; lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, and rhodamine (0-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-
) Luidino)-7methylfluorane, 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-diethylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-toluidino)
-6-methyl-7-(p-)luidino)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-7phenylaminofluorane, 3-pyrrolidino-6-
Methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7-(O-chlorophenylamino) Fluoran, 3-dibutylamino-7-(0-chlorophenylamino)fluoran, 3-pyrrolidino-6-
Methyl-7-p-7” tylphenylaminofluorane,
3-(N-methyl-Nn-amyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-Nn-amyl)amino-6-methyl-7-phenylaminofluoran oran, 3-(N-ethyl-N-isoamyl)amino-6-methyltophenylaminofluorane,
3-(N-methyl-Nn-hexyl)amino-6-methyltophenylaminofluorane, 3-(N-ethyl-Nn-hexyl)amino-6-methyl-7-phenylaminofluorane, Examples include fluoran dyes such as 3-(N-ethyl-N-β-ethylhexyl)amino-6-methyl-7-phenylaminofluoran. Of course, the dyes are not limited to these dyes, and two or more types of dyes can be used in combination.

Furthermore, various compounds are known as acidic substances to be used in combination with the above-mentioned basic dyes, for example, the following are exemplified.

4-tert-butylphenol, α-naphthol, β
-naphthol, 4-acetylphenol, 4-tert
-octylphenol, L4'-5ec-butylidene diphenol, 4-phenylphenol, hydroquinone, 4,4'-dihydroxy-diphenylmethane,
4.4'-isopropylidenediphenol, 2,2-bis(4-hydroxyphenyl)-4-methylpentane,
4.4'-cyclohexylidene diphenol, 4.4'
-dihydroxydiphenyl sulfide, 4,4'-thiobis(5-tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenyl sulfone, 4-
Hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone,
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)-2propyl)benzene, bis(3-allyl-4-hydroxyphenyl)
Sulfone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 5ec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, 4-hydroxy Phenyl benzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate,
Chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 4-hydroxybenzoic acid 111 p-chlorobenzyl, p-methoxybenzyl 4-hydroxybenzoate, novolac type phenolic resin, phenolic polymer Phenolic compounds such as benzoic acid, p-tert
-Butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-5ec -butyl-4-hydroxybenzoic acid, 3
-Cyclohexyl-4-hydroxybenzoic acid, 3,5-
Dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-
Isopropyl salicylic acid, 3-tert-butylsalicylic acid, 3,5-di-tert-butylsalicylic acid,
3-Benzylsalicylic acid, 3-(α-methylbenzyl)
Salicylic acid, 3-chloro-5-(α-methylbenzyl)
Aromatic carboxylic acids such as salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-diα-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, aluminum, calcium, titanium, manganese,
AM substances such as salts with polyvalent metals such as tin and nickel. Note that, of course, two or more of these coloring agents can be used in combination as necessary.

The ratio of the basic dye and coloring agent to be used is appropriately selected depending on the type of basic dye and coloring agent used, and is not particularly limited, but is generally based on 100 parts by weight of the basic dye. 100-700 parts by weight, preferably 150-4
About 0.00 parts by weight of coloring agent is used.

Thermal coating liquids containing these are generally prepared by using water as a dispersion medium and dispersing the dye and coloring agent together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand grinder. be done.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, valmitic acid amide, coconut fatty acid amide, 2,2'-methylene bis(4
-methyl-5-tertbutylphenol), 4.4'
-butylidene butylidene bis(5-tert-butyl-
3-methylphenol), 1.1.3-tris(2-methyl4-hydroxy-5-tert-butylphenyl)
Hindered phenols such as butane, p-benzylbiphenyl, ■, 2-bis(phenoxy)ethane, 12-bis(4-methylphenoxy)ethane, 1.2-bis(3
-methylphenoxy)ethane, ethers such as 2-naphthol benzyl ether, dibenzyl terephthalate,
Esters such as 1-hydroxy-2-naphthoic acid phenyl ester, ultraviolet absorbers such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-hydroxy-4-benzyloxybenzophenone, and various known Thermofusible substances can also be added as sensitizers.

In addition, kaolin, clay, talc, calcium carbonate, calcined clay,
Inorganic pigments such as titanium oxide, diatomaceous earth, particulate anhydrous silica, and activated clay may also be added.

In the present invention, the method of forming the heat-sensitive recording layer is not particularly limited, and can be formed using conventionally known and commonly used techniques, such as an air knife coater, blade coater, bar coater, gravure coater, curtain coater, etc. Appropriate coating equipment is used.

Furthermore, the amount of coating liquid to be applied is not particularly limited, and is generally 2 to 12 g/i in terms of dry weight, preferably 3 g/i.
It is adjusted in the range of ~Log/m.

In addition, it is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, etc., and it is also possible to provide a protective layer on the back side of the support, or even apply adhesive processing, etc. in the heat-sensitive recording material manufacturing field. Various known techniques can be added.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Further, unless otherwise specified, parts and percentages in the columns indicate parts by weight and percentages by weight, respectively.

Example 1 [Preparation of undercoat surface coating liquid] Oil absorption 160cc/100g amorphous silica (trade name: Mizuriki Seal p-527+ manufactured by Mizusawa Chemical Co., Ltd.)
100 parts styrene-butadiene copolymer latex (T
g point any 35) (solid content equivalent) 15 parts Hydroxypropylated starch (solid content equivalent) 5 parts Dispersant (solid content equivalent) 0.5 parts This composition was mixed uniformly, and the undercoated surface was coated with a solid content concentration of 30%. A coating liquid was obtained.

[Formation of undercoat layer]

The above-mentioned undercoat surface coating liquid was applied to a 45 g/m high-quality paper using a bar coater so that the coating amount after drying was 15 g/rrf, and dried to obtain an undercoat coated paper with a coating layer density of 0.65 g/cm'. Ta.

[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 Methyl cellulose 5% aqueous solution 15 parts Water
80 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

Preparation of Solution B 4. 4-Isopropylidenediphenol 30 parts Methylcellulose 5% aqueous solution 30 parts Water
70 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

125 parts of liquid A, 130 parts of liquid B, amorphous silica (oil absorption 1
80 cc/100 g), 150 parts of a 20% oxidized starch aqueous solution, and 55 parts of water were stirred and mixed to prepare a recording layer coating liquid.

[Formation of recording layer]

The obtained recording layer coating liquid was applied onto the undercoat coated paper using a Mayer bar so that the coated amount after drying was 5 g/m, and dried to obtain a heat-sensitive recording paper.

Example 2 The coating amount of the undercoat surface coating liquid was 13 g/m, and the coating layer density was 0.
．． A thermosensitive recording paper was obtained in the same manner as in Example 1 except that an undercoat coated paper having a coating weight of 65 g/cm1 was used.

Example 3 The coating amount of the coating liquid on the undercoat surface was 20 g/I, and the coating layer density was 0.
．． A thermosensitive recording paper was obtained in the same manner as in Example 1 except that a coated paper with an undercoat of 64 g/am 3 was used.

Example 4 The coating amount of the undercoat surface coating liquid was 24 g/m, and the coating layer density was 0.
．． A thermosensitive recording paper was obtained in the same manner as in Example 1 except that an undercoat coated paper having a coating weight of 64 g/cm 3 was used.

Example 5 The oil absorption amount of the oil-absorbing pigment in the undercoat surface coating liquid was 110cc/100
A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the fired clay (trade name: Ancirefx, manufactured by Engelhard) was used. The coating layer density of the undercoat layer is 0.70g.
/cm3.

Example 6 The oil absorption amount of the oil-absorbing pigment in the undercoat surface coating liquid was 130cc/100
A thermosensitive recording paper was obtained in the same manner as in Example 1, except that amorphous silica (trade name: Fine Seal CMF, manufactured by Tokuyama Soda Co., Ltd.) was used. In addition, the coating layer density of the undercoat layer is 0.6
8 g/cm".

Example 7 In preparing an undercoat surface coating solution, 0.00% of an acrylic thickener (non-crosslinked type, trade name: Somarex 50, manufactured by Somar) was added.
A thermosensitive recording paper was obtained in the same manner as in Example 1, except that 6 parts of ammonia and 0.02 parts of ammonia were further added to prepare a coating solution.

The coating density of the undercoat layer was 0.62 g/cm3.

Example 8 A thermosensitive recording paper was obtained in the same manner as in Example 7 except that the acrylic thickener was replaced with a crosslinked thickener (trade name: Bisryoku Rex HV 30, manufactured by Kyowa Sangyo Co., Ltd.).

The coating layer density of the undercoat layer was 0.62 g/(2)3.

Comparative Example 1 The oil-absorbing pigment of the undercoat surface coating liquid was absorbed 135cc/100
A thermosensitive recording paper was obtained in the same manner as in Example 1, except that g of normal calcium carbonate was used. The coating density of the undercoat layer was 1.03 g/cm1.

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 5, except that the undercoat surface coating liquid was applied with a blade coater to form an undercoat layer with a coating layer density of 2.50 g/L:rn'.

Comparative Example 3 The coating amount of the undercoat surface coating liquid was 10 g/po, and the coating layer density was 0.
．． A thermosensitive recording paper was obtained in the same manner as in Example 1, except that a coated paper with an undercoat of 67 g/cn+' was used.

Comparative Example 4 Heat-sensitive recording was carried out in the same manner as in Example 1, except that in preparing the undercoating surface coating liquid, the amount of styrene-butadiene copolymer latex was changed to 5 parts, and the amount of hydroxypropylated starch was changed to 15 parts. Got paper.

The coating density of the undercoat layer was 0.76 g/cs''. The 12 types of thermal recording paper thus obtained were printed using a thermal printer (SONY VP-103, video printer) for a printing pulse time of 5. m5ec and 8 m5ec were recorded, and each color density was measured using a Macbeth densitometer (RD-10
(using an 0R type amber filter), and the results are listed in the table. In addition, the printed pixels (dots) of the obtained recorded image
As an evaluation of reproducibility, the ratio of the area of printed dots to the area of one dot of the thermal head (dot reproducibility) was evaluated according to the following criteria, and the results are also shown in the table.

◎ Two-dot reproduction rate 86% ○: Dot reproduction rate 71-85% △: Dot reproduction rate 61-70% ×: Dot reproduction rate 60% Table "Effect" As is clear from the results in the table, examples of the present invention The heat-sensitive recording paper obtained in the above had excellent reproducibility of printed pixels in all regions from low density to light density, and also had excellent dynamic sensitivity.

Claims (3)

[Claims] (1) In a thermosensitive recording material having an undercoat layer between the support and the recording layer, the main component of the undercoat layer conforms to JISK5101.
It is an oil-absorbing pigment with an oil absorption amount of 100cc/100g or more based on the law, and 50% by weight or more of the total adhesive has a T temperature of 0°C or less.
The latex has a g point, and the coating amount of the undercoat layer after drying is 12 g/m^2 or more, and the density is 0.75.
A heat-sensitive recording material characterized in that it has a temperature of g/cm^3 or less. (2) The heat-sensitive recording material according to claim (1), wherein the oil-absorbing pigment is calcined clay or amorphous silica. (3) The undercoat layer is 0.0.
Claim containing 05 to 5 parts by weight of an acrylic thickener (
1) The thermosensitive recording material described in (2).