JPS63115786A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance brightness, adhesion properties and water resistance, by providing a thermal color forming layer comprising a diazo compound, a coupler and a styrene-maleic anhydride copolymer on a base, and providing a protective layer comprising a water-soluble high molecular weight material thereon. CONSTITUTION:A diazo compound, a coupler and a styrene-maleic anhydride copolymer or at least one selected from salts and esters of the styrene-maleic acid anhydride copolymer are mixed and are dispersed together with a water-soluble high molecular weight material by a sand mill or the like to prepare a coating liquid. The coating liquid is applied to a base, followed by drying to provide a thermal color forming layer, and a protective layer comprising a water-soluble high molecular weight material as a main constituent is provided on the color forming layer to produce a thermal recording material. The thermal recording material has an enhanced brightness, and has extremely favorable adhesion between the thermal color forming layer and the protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a diazo thermosensitive recording material. For more details,
The present invention relates to a diazo thermosensitive recording material having a protective layer.

(Prior Art) As a recording material used in a heat-sensitive recording method, a leuco color-forming heat-sensitive recording material is usually used.

However, this heat-sensitive recording material has the disadvantage that color may develop in unexpected areas due to harsh handling, heating, or adhesion of solvents after recording, which may stain the recorded image. As a heat-sensitive recording material without such drawbacks,
In recent years, research on diazo color-forming heat-sensitive recording materials has been actively carried out. A method is disclosed in which thermal recording is performed on a recording material using a chemical component (including a substance that becomes basic when heated), and then light irradiation is performed to decompose unreacted diazo compounds and stop color development. Diazo heat-sensitive recording materials are excellent as heat-sensitive recording materials that can be photofixed in this way, but because the diazo compound is originally colored, and even after photodecomposition, it takes on a yellowish tinge. Not only does it tend to have poor whiteness as a heat-sensitive recording material, but also the whiteness of non-printed areas after optical fixation is not satisfactory. In order to solve this problem, when a large amount of whitening agent is added to the heat-sensitive coloring layer,
There are drawbacks such as a decrease in heat sensitivity and color density, an increase in the weight of the heat-sensitive material, and problems with the stability of the coating liquid during production. Therefore, as a method to improve whiteness without causing these drawbacks, a method has recently been developed in which a protective layer is provided on the heat-sensitive coloring layer and a whitening agent, anti-sticking agent, etc. is added to this protective layer. It has been proposed, and it has been found that the method of providing such a protective layer is extremely convenient for application to labels etc. printed on heat-sensitive materials before thermal printing.

(Problem to be solved by the invention) In this case, it goes without saying that the stronger the adhesiveness between the protective layer and the heat-sensitive coloring layer, the better. It must be able to withstand various environments such as the adhesion of water droplets, and from this point of view, there has been a demand for improvement in the adhesiveness of the surface protective layer, including its water resistance.

Accordingly, a first object of the present invention is to provide a heat-sensitive material with improved whiteness and which can be photofixed.

A second object of the present invention is to provide a heat-sensitive recording material with excellent whiteness and having a protective layer suitable for printing before thermal printing.

A third object of the present invention is to provide a heat-sensitive recording material having a protective layer of a water-soluble polymer with improved adhesiveness and excellent water resistance.

Furthermore, a fourth object of the present invention is to provide a method for improving the water resistance of a water-soluble polymer protective layer provided on a heat-sensitive layer.

(Means for Solving the Problems) The above-mentioned aspects of the present invention are such that a protective layer containing a water-soluble polymer as a main component is provided on a heat-sensitive coloring layer containing a diazo compound and a coupler as main components provided on a support. A diazo thermosensitive material having a layer, wherein the thermosensitive coloring layer contains at least one selected from a styrene-maleic anhydride copolymer or a salt thereof, and a styrene-maleic anhydride ester. This was achieved using a diazo thermosensitive recording material with special characteristics.

The diazo compound used in the present invention has the general formula ArN2+
It is a diazonium salt represented by It is a compound that can.

These diazonium salts are disclosed, for example, in JP-A-59-190
It can be arbitrarily selected from known ones such as those described in No. 866.

The coupler used in the present invention forms a dye by coupling with a diazo compound (diazonium salt), and specific examples thereof include resorcinol, phloroglucin, 2.
Sodium 3-hydroxynaphthalene-6-sulfonate, 1-hydroxy-2-naphthoic acid morpholinopropylamide, 1゜5-dihydroxynaphthalene, 2.3-dihydroxynaphthalene, 2.3-dihydroxy-6-sulfanylnaphthalene, 2- Hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoic acid-2°-methylamide, 2-hydroxy-3-
Naphthoic acid ethanolamide, 2-hydroxy-3-naphthoic acid octylamide, 2-hydroxy-3-naphthoic acid-N-dodecyl-oxy-probylamide, 2-hydroxy-3-naphthoic acid tetradodecylamide, acetanilide, acetylamide Acetanilide, benzoylacetanilide, 1-phenyl-3-methyl-5-pyrazolone, 2,4-bis(benzoylacetamino)toluene,
1.3-Bis(pivaloylacetaminomethyl)benzene, 1-(2', 4", 6").

-trichlorophenyl)-3-benzamido-5-pyrazolone, ■-(2°, 4°, 6”-trichlorophenyl)-3-anilino-5-pyrazolone, ■-phenyl-3-phenylacetamido-5-pyrazolone, etc. Furthermore, by using two or more of these compulsions in combination, an image of any tone can be obtained.

It is preferable to add a basic substance to the recording layer of the heat-sensitive recording material of the present invention, if necessary, for the purpose of making the system basic and promoting the coupling reaction.

As these basic substances, used are sparingly water-soluble or water-insoluble basic substances, and substances that generate alkali upon heating.

Basic substances include inorganic and organic ammonium salts,
organic amines, amides, urea and thiourea and their derivatives,
Examples include nitrogen-containing compounds such as thiazoles, virols, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidacillines, triazoles, morpholines, piperidines, amidines, formazines, and pyridines. . These basic substances are
Two or more types can be used in combination.

Furthermore, a hydroxy compound, a carbamate ester compound, an aromatic alkoxy compound, or an organic sulfonamide compound can be added to the heat-sensitive recording material of the present invention as a sensitizer for improving thermal color development. These compounds lower the melting point of the coupling component or basic substance, or improve the thermal permeability of the microcapsule wall,
As a result, the practical concentration is considered to be high.

Specific examples of hydroxy compounds include pt-butylphenol, pt-octylphenol, p-α-cumylphenol, pt-pentylphenol, m-xylenol, 2.5-dimethylphenol, 2.4. 5-
Trimethylphenol, 3-methyl-4-isopropylphenol, p-benzylphenol, 0-cyclo-hexylphenol, p-(diphenylmethyl)phenol, i-(α,α-(diphenylethyl)phenol, O-phenylphenol, Ethyl p-hydroxybenzoate, chloropyr p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-methoxyphenol, p-butoxyphenol,
p-pentyloxyphenol, p-benzyloxyphenol, dimethylvanillin 3-hydroxyphthalate,
1.1-bis(4-hydroxyphenyl)dodecane, 1
．． 1-bis(4-hydroxyphenyl)-2-ethyl-
Hexane, 1,1-bis(4-hydroxyphenyl)-
2-Methyl-pentane, 2,2-bis(4-hydroxyphenyl)-hebutane vanillin, 2-t-butyl-4-
Methoxyphenol, 2゜6-simethoxyphenol,
Phenolic compounds such as 2,2"-dihydroxy-4-methoxybenzophenone, 2,5-dimethyl-2,5
-hexanediol, resorcinol di(2-hydroxyethyl) ether, resorcinol mono(2-hydroxyethyl)ether, salicyl alcohol, 1.4
-di(hydroxyethoxy)benzene, p-xylylene diol, 1-phenyl-1,2-ethanediol, diphenylmethanol, 1,1-diphenylethanol,
2-Methyl-2-phenyl-1,3-propanediol, 2,6-dihydroxymethyl-p-cresol benzyl ether, 2,6-dihydroxymethyl-p-cresol benzyl ether, 3-(o-methoxyphenoxy)- Examples include alcohol compounds such as 1,2-propanediol. Specific examples of carbamate compounds include N-phenylcarbamate ethyl ester,
Examples include benzyl N-phenylcarbamate, phenethyl N-phenylcarbamate, benzyl carbamate, butyl carbamate, isopropyl carbamate, and the like. Specific examples of aromatic alkoxy compounds include 2-methoxybenzoic acid, 3,5-dimethoxyphenylacetic acid, 2-methoxynaphthalene, 1,3.5-trimethoxybenzene, p-
Examples include dimethoxybenzene, p-benzyloxymethoxybenzene, and the like.

Specific examples of organic sulfonamides include p-toluenesulfonamide, O-toluenesulfonamide, benzenesulfonamide, p-toluenesulfonanilide, N-(
p-methoxyphenyl)-p-toluenesulfonamide, N-(o-methoxyphenyl)-p-)luenesulfonamide, N-(p-chlorophenyl)-p-)luenesulfonamide, N-(o-chlorophenyl> -p-toluenesulfonamide, N-(p-tolyl)-p-)luenesulfonamide, N-(0-lyl)-1)-toluenesulfonamide, N-(0-hydroxyphenyl)
-p-toluenesulfonamide, N-benzyl-p-toluenesulfonamide, N-(2-phenethyl)-p-
Toluenesulfonamide, N-(2-hydroxyethyl)-p-1 luenesulfonamide, N-(3-methoxypropyl)-p-)luenesulfonamide, methanesulfonanilide, N-(p-)lyl)sulfonamide , N-(o-tolyl)sulfonamide, N-(p-methoxyphenyl)sulfonamide, N-(O-methoxy)
Sulfonamide, N-(p-chlorophenyl)sulfonamide, N-(0-10 lophenyl)sulfonamide,
N-(2,4-t-silyl)sulfonamide, N-(p
-ethoxyphenyl)sulfonamide, N-benzylmethanesulfonamide, N-(2-phenoxyethyl)methanesulfonamide, 1,3-bis(methanesulfonylamino)benzene, 1,3-bis(p-toluenesulfonylamino) ) propane, etc., but are not limited to these.

These compounds can be used by making microcapsules together with the microcapsule core material described below, or by being added to the coating solution of the heat-sensitive recording material and being present outside the microcapsules, but they can be used by dispersing them in water with the microcapsules. It is preferable to use these compounds in combination. 0.01 to 10 per part by weight of the coupling component! ff is 1 part, preferably 0.1 to 5 parts by weight, but may be selected as appropriate to adjust the coloring density to the desired level.

It is important to use at least one of the diazo compound, coupler, and basic substance used as necessary in the heat-sensitive recording material of the present invention as the core material of the microcapsules in order to improve the storage stability of the recorded image and the stability of the heat-sensitive material. Preferable from the viewpoint of raw storage. When two types are contained in the core material of a microcapsule, they may be the same microcapsule or different microcapsules as long as the combination does not cause a coloring reaction. Other ingredients not contained in the core material of the microcapsules are used in the heat-sensitive layer outside the microcapsules.

The particle size of the microcapsules used in the present invention is adjusted to 20μ or less. Generally, if the particle size exceeds 20 μm, the print quality tends to be poor.

In particular, when heating with a thermal head is performed from the coated layer side, the thickness is preferably 8 μm or less to avoid pressure fog.

The microcapsules used in the present invention may be destroyed by heat or pressure, but it is possible to cause the core of the microcapsule and/or the reactive substance present outside the microcapsule to penetrate through the microcapsule wall by heating. It is preferable that it be possible.

The microcapsules preferably used in the present invention are produced by dissolving or dispersing the reactive substance contained in the core substance in a water-insoluble organic solvent as necessary, emulsifying it, and then forming a microcapsule wall around it by polymerization. It is obtained by The organic solvent preferably has a boiling point of 180°C or higher; specifically, phosphoric acid esters, phthalic acid esters, other carboxylic acid esters, fatty acid amides, alkylated biphenyls, alkylated phenols, chlorinated paraffins, alkylated Naphthalene, diarylethane, etc. are used. Specific examples include tricresyl phosphate, trioctyl phosphate, octyldiphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol dibenzoate, dioctyl sebacate, dibutyl sebacate,
Dioctyl adipate, trioctyl trimellitate,
Acetyl triethyl citrate, octyl maleate, dibutyl maleate, isopropylbiphenyl, isoamyl biphenyl, chlorinated paraffin, diisopropylnaphthalene, 1.1°-ditolylethane, 2,4-di-t
ert-aminophenol, N,N-dibutyl-2-butoxy-5-tert-octylaniline, N,N'
-diphenylformamidine, N, N', N'
-triphenylbenzamidine, N,N'-diphenylbenzamidine, and the like.

Among these, butyl phthalate, tricresyl phosphate,
Ester solvents such as diethyl phthalate and dibutyl maleate are particularly preferred.

Details of the above-mentioned preferred microcapsules are described, for example, in JP-A-59-190886.

Since the heat-sensitive recording material of the present invention uses a diazo compound as a coloring agent, the diazo compound can be decomposed by light irradiation after thermal printing and photofixing can be performed. In this case, in order to improve the durability of the printed image after optical fixation against light and heat, and to prevent discoloration of unprinted areas which tend to have a high yellowish tinge, in the present invention, hindered Preference is given to using phenolic compounds and/or derivatives thereof.

The above-mentioned hindered phenol may be present in the core of the microcapsule or outside.

These compounds may be used alone or in combination of two or more, and may also be used in combination with other known anti-fading agents.

In the present invention, it is preferable to use the camping component at a ratio of 0.1 to 30 m (i1 part) and the basic substance at a ratio of 0.1 to 30 parts by weight per 1 part by weight of the diazo compound. It is preferable to apply 0.05 to 5.0 g/rd.

The diazo compound used in the present invention, the coupling component, the hindered phenol or its derivative used as necessary, the basic substance, and other additives are mixed with water-soluble polymers using a sand mill or the like when not microencapsulated. Preferred water-soluble polymers that are preferably used in solid dispersion include water-soluble polymers used when making microcapsules (for example, JP-A-59-19
(see No. 0886), in this case, the diazo compound, the camping component, and the basic substance used if necessary are each added in an amount of 5 to 40% by weight with respect to the water-soluble polymer solution.

The dispersed particle size is preferably 10 microns or less.

In the heat-sensitive recording material of the present invention, a protective layer containing a water-soluble polymer as a main component is provided on the heat-sensitive color forming layer as described later, and the adhesiveness between this protective layer and the heat-sensitive color forming layer is to be made good. Therefore, in the present invention, in particular, the solid substances added to the heat-sensitive coloring layer, such as couplers, basic substances, sensitizers, etc.
As a protective colloid used when dispersing to a particle size of about The preferred molecular weight of the styrene-maleic anhydride copolymer is 20,000 to 10
The degree of esterification is preferably 20,000 to 70,000, particularly preferably 30,000 to 70,000, and the degree of esterification is preferably 20% to 50%, particularly 35% to 50%.
% is preferred.As the alcohol used for esterification, any known alcohol can be used as appropriate, but alcohols such as ethyl alcohol and isopropyl alcohol are particularly preferred.

In addition, when used as a salt, the neutralizing salt includes Na, N
A mixture of a/NH3, NH3 alone, amines, etc. are preferred.

A heat-melting substance can be used in the heat-sensitive coloring layer in the present invention in order to increase the heat recording density.

The heat-melting substance is a substance that is solid at room temperature and has a melting point of 50 to 150°C and melts when heated by a thermal head, and is a substance that dissolves a diazo compound, a coupling component, or a basic substance. The heat-fusible substance is dispersed in the form of particles of 0.1 to 10 microns and used in an amount of solid content of 0.2 to 7 g/rd. Specific examples of heat-melting substances include fatty acid amides, N-substituted fatty acid amides, ketone compounds, urea compounds, esters, and the like.

The thermosensitive color forming layer in the present invention can be coated using a suitable binder.

As a binder, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, arabic acid, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene- Various emulsions such as vinyl acetate copolymers can be used. The amount used is 0.5 to 20 g/rrr, preferably 0.5 to 5 g/m in terms of solid content.

In the present invention, in addition to the above materials, citric acid is used as an acid stabilizer.
Tartaric acid, oxalic acid, boric acid, phosphoric acid, pyrophosphoric acid, etc. can be added.

Furthermore, it is preferable to include latex having a minimum film forming temperature of 60° C. or higher from the viewpoint of increasing the whiteness of the non-printed area.

In the heat-sensitive coloring layer of the present invention, as mentioned above, at least one of the diazo compound, the coupling component, and the basic substance added as necessary is preferably encapsulated in microcapsules. In addition to these, if necessary, a coating solution containing latex, hindered phenol, and other additives with a minimum film-forming temperature of 60°C or higher is prepared and coated on a support such as paper or synthetic resin film. , coated and dried using coating methods such as bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, etc.
A heat-sensitive recording layer having a solid content of 2.5 to 25 g/rtr is provided. Another method is to prepare a coating solution by adding the main components such as coupling components and basic substances and other additives as core materials of microcapsules, solid dispersing them, or dissolving them as an aqueous solution and then mixing them. , coated on a support and dried to form a precoated eyebrow with a solid content of 2 to 10 g/rrf, and further coated with microcapsules containing a diazo compound as a main component and other additives, if necessary. It is also possible to apply and dry a coating solution containing latex having a minimum film forming temperature of 60° C. or higher to form a layered layer with a solid content of 1 to 30 g/rd. The laminated type heat-sensitive coloring layer may be laminated in the reverse order of the lamination described above, and the coating method may be sequential coating or simultaneous coating of the laminated layers.

This laminated heat-sensitive recording material exhibits particularly excellent performance in long-term storage.

On the recording surface of the heat-sensitive recording material of the present invention, a protective layer containing a water-soluble polymer as a main component is provided on the heat-sensitive coloring layer provided as described above. The water-soluble polymer used for the protective layer can be arbitrarily selected from water-soluble polymers having film-forming ability. The water-soluble polymer may be a water-soluble anionic polymer, nonionic polymer, or amphoteric polymer. As the anionic polymer, both natural and synthetic polymers can be used, for example -coo- Examples include those having a 1-3O3- group. Specific examples of anionic natural polymers include gum arabic and alginic acid, and examples of semi-synthetic products include carboxymethyl cellulose, phthalated gelatin, sulfated starch, sulfated cellulose, and lignin sulfonic acid.

Synthetic products include maleic anhydride (including hydrolyzed) copolymers, acrylic (including methacrylic) polymers and copolymers, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and the like.

Examples of nonionic polymers include polyvinyl alcohol, hydroxyethyl cellulose, and methyl cellulose.

Examples of amphoteric compounds include gelatin.

In particular, among these water-soluble polymers, silanol-modified PVA (for example, JP-A It is preferable to use colloidal silica (see No. 58-193189), colloidal silica, or a combination of these.

The protective layer provided in the present invention has the purpose of adding a fluorescent whitening agent to increase the whiteness of the non-printing area, improving the printing permeability, and preventing sticking to the thermal head during thermal printing. Pigments such as silica, kaolin, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, calcium carbonate, etc., fine powders such as styrene beads, urea-melamine resin, etc., and/or full-strength soaps can also be used. .

It is preferable to use these additives in a range of 0.2 to 7 g/r+.

Hoi! The layer can be applied in the same manner as the heat-sensitive coloring layer. The coating amount is preferably 1 to 5 g/rd.

When the heat-sensitive recording material of the present invention is applied to a label, a desired image is printed thereon by flexographic printing using ink containing a dye dissolved in a solvent. Since the ink used uses a solvent, flexographic printing can be easily performed without dissolving the protective layer, and since it dries quickly, no blocking occurs. Furthermore, when a water-insoluble or slightly water-soluble dye is used, the printed image will not bleed or disappear due to water droplets that often adhere during product distribution.

As the paper used for the support of the present invention, heat-extracted neutral paper with a pH of 3 to 9 (described in JP-A-55-14281) sized with a neutral sizing agent such as an alkyl ketene dimer is used. It is advantageous in terms of storage stability.

In addition, in order to prevent the coating liquid from penetrating the paper and to improve the contact between the recording heat head and the heat-sensitive recording layer, it is advantageous to use the paper described in JP-A-57-116687 and which has a Bekk smoothness of 90 seconds or more. It is.

Also, paper having an optical surface roughness of 8μ or less and a thickness of 40 to 75μ, described in JP-A-58-136492, JP-A-58-136492.
Paper with a density of 0°9 g/cd or less and an optical contact ratio of 15% or more as described in No. 8-69091, JP-A-58-6909
Valve-treated paper beaten to 400 cc or more with Canadian standard freeness (JIS, 8121) as described in No. 7, paper that prevents coating liquid from seeping in, and Yankee machine as described in JP-A-58-65695. The glossy side of paper-made base paper is used as the coated surface to improve the color density and resolution, and the paper described in Japanese Patent Application No. 145872/1987, in which the base paper is subjected to corona discharge treatment to improve coating permeability, etc. can also be used in the present invention with good results. In addition to these,
Normal! Any support used in the field of X3 thermal recording paper can be used as the support in the present invention.

(Effects of the Invention) Since the heat-sensitive recording material of the present invention has a protective layer on the heat-sensitive coloring layer, whitening agents, etc., which were conventionally included in the heat-sensitive coloring layer, can be removed.
It can be added to the protective layer.

This not only improves the stability of the coating solution for the heat-sensitive coloring layer, but also improves the degree of whitening of the heat-sensitive recording material. In particular, in the present invention, since the heat-sensitive recording layer contains a small amount of styrene-maleic anhydride copolymer and its salt or ester, the adhesion between the heat-sensitive recording layer and the protective layer is extremely high. Since the water resistance of the protective layer was significantly improved, a particularly great effect can be obtained when the heat-sensitive recording material of the present invention is applied to labels and the like.

(Examples) Hereinafter, the present invention will be described in more detail according to Examples, but the present invention is not limited thereto.

Example 1 3.45 parts of the following diazo compound and xylylene diisocyanate and trimethylolpropane (3:1) adduct 18
1 part was added to a mixed solvent of 24 parts of tricresyl phosphate and 5 parts of ethyl acetate and dissolved.

This diazo compound solution was mixed with polyvinyl alcohol 5.
2 parts dissolved in 58 parts water, 20 parts
The mixture was emulsified and dispersed at ℃ to obtain an emulsion having an average particle size of 2.5μ. Add 100 parts of water to the resulting emulsion and heat to 60°C while stirring.
After 2 hours, a capsule liquid containing a diazo compound in the core substance was obtained.

(Diazo compound) C4Hq C4H9 Next, 10 parts of 2-hydroxy-3-naphthoic acid anilide, 10 parts of triphenylguanidine, and 40 parts of hydroquinone monobenzyl ether were mixed with isobutyl ester of 5% styrene-maleic anhydride copolymer (molecular weight 30,000, degree of esterification 35%, neutralized salt Na/NH3-7/3) 20
0 parts and dispersed in a ball mill for 24 hours to obtain an average particle size of 2.
A dispersion of the μm coupling component, triphenylguanidine and hydroquinone monobenzyl ether was obtained.

Next, a coating liquid having the following composition was prepared.

Capsule solution 50 parts Dispersion of the above coupling components, etc. 50 parts 40% calcium carbonate Dispersion 5 parts 20% Zn stearate Dispersion 3 parts 45% with MFT of 65°C
SBR latex (contains 83% bound styrene)
10 parts of this coating solution was coated on a surface of high quality I (50 glof) using a coating bar to give a dry coating of ifflilog/%, and dried at 50° C. for 1 minute to obtain a heat-sensitive coloring layer.

A protective layer having the composition shown below was coated on the obtained heat-sensitive coloring layer using a coating bar so as to have a dry weight of 3 g/rrr, and was dried at 50° C. for 1 minute to obtain a heat-sensitive material.

Plate 1 and plate bottom 10% silanol-modified polyvinyl alcohol (Kuraray ■
R-2105) 50 parts water
50 parts 30% Colloidal silica (Snowtex) 20 parts 40% Kaolin dispersion 10 parts 50%
Kayaphor S (fluorescent brightener) 1.0 parts Example 2゜Except that the molecular weight of the isobutyl ester of the styrene-maleic anhydride copolymer used in Example 1 was changed from 30,000 to 70,000. A heat-sensitive recording material was obtained in exactly the same manner as in Example 1.

Example 3 The molecular weight of the isobutyl ester of the styrene-maleic anhydride copolymer used in Example 1 was changed from 30,000 to 70,000, and the degree of esterification was changed from 35% to 50%. A heat-sensitive recording material was obtained in exactly the same manner as in Example 1.

Example 4 In the protective layer composition of Example 1, ordinary polyvinyl alcohol (polymerization degree 1,000.
A heat-sensitive recording material was obtained in exactly the same manner as in Example 1, except that a material with a degree of saponification of 98% was used.

Comparative Example 1゜Compared to Example 1, except that polyvinyl alcohol (ffi degree 500, saponification degree 88%) was used instead of the isobutyl ester of the styrene-maleic anhydride copolymer used in Example 1. A heat-sensitive recording material was obtained.

Comparative Example 2 A coating liquid having the protective layer composition used in Example 4 was applied onto the heat-sensitive coloring layer used in Comparative Example 1 to obtain a heat-sensitive recording material.

The heat-sensitive recording material obtained as described above was immersed in water for 24 hours. After that, it was taken out and rubbed with a finger, and the state of the film peeling was observed.

The results are shown in Table 1.

Table 1 These results show that the isobutyl styrene-acid anhydride added to the heat-sensitive layer greatly contributes to the coating strength of the protective layer, demonstrating the effectiveness of the present invention.

Claims (1)

[Scope of Claims] 1) A heat-sensitive recording material having a protective layer containing a water-soluble polymer as a main component on a heat-sensitive coloring layer containing a diazo compound and a coupler as main components provided on a support, A heat-sensitive recording material, wherein the heat-sensitive coloring layer contains at least one selected from styrene-maleic anhydride copolymer or a salt thereof, and ester of styrene-maleic anhydride copolymer. 2) The heat-sensitive recording material according to claim 1, wherein the diazo compound is encapsulated in microcapsules.