JPH07112580A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material not having the background color of a support base material and obtaining a sharp image even at the time of high speed printing by using modified polyvinyl alcohol containing a specific amt. of a carboxyl group-containing monomer unit and having a specific saponification value and a specific polymerization degree as a dispersant. CONSTITUTION:In a thermal recording material containing a color forming substance, a coupler allowing the color forming substance to develop a color at the time of heating and a dispersant, modified polyvinyl alcohol with carboxyl group-containing monomer unit content of 3-15mol%, a saponification value of 70-95mol% and a polymerization degree of 50-500 is used as the dispersant. This thermal recording material is excellent in the dispersing capacity of the dispersant of the color forming substance and the coupler and good in the whiteness of its background part. Further, the dispersant used in the thermal recording material has good handling properties because it imparts a low viscosity soln. in high.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heat-sensitive recording material.
More specifically, it relates to a heat-sensitive recording material which is suitable for high-speed printing obtained by using a specific modified polyvinyl alcohol as a dispersant for a color-forming substance and a color-developing agent and has no background color of a support material.

[0002]

2. Description of the Related Art In recent years, a heat-sensitive recording material provided with a heat-sensitive color-forming layer on a paper, a plastic film or a metal vapor-deposited paper to obtain a recorded image by causing a chemical change or a physical change by heat energy to develop a color. , The recording can be obtained by simply heating, it does not require complicated processing such as developing and fixing, there is no noise during recording, and the recording system can be made relatively inexpensive. Widely used as a recording material for telex, facsimile, and various computers. As these recording materials, usually a colorless or slightly pale leuco dye and a thermosensitive coloring layer containing an acidic substance such as an organic acid or a phenolic compound that reacts with the leuco dye to cause the leuco dye to develop color when heated. Recording material is used.

In recent years, especially when used for facsimiles and the like, the printing speed has been increasing year by year. Therefore, there is a demand for a thermal recording material which is clearer and can cope with a higher printing speed. Further, regarding a recorded image, there is a need for a heat-sensitive recording material capable of obtaining a precise and stain-free image not only for characters but also for drawings and photographs. Therefore, there is a demand for a heat-sensitive recording material in which a heat-sensitive dye and a color-developing material are stably dispersed in a particle size of 1 micron or less, have a high density and are thinly present in a heat-sensitive color-developing layer, and are free from background fog of a support material. .

Conventionally, as a dispersant for heat-sensitive dyes and color developers, polyvinyl alcohol of low molecular weight and partially saponified,
Although low molecular weight modified polyvinyl alcohol containing a sulfonic acid group, an alkali metal salt or ester of a copolymer of styrene or α-olefin and maleic anhydride, etc. are used, sufficient performance has not been obtained. Polyvinyl alcohol, which has a low molecular weight and is partially saponified, does not have sufficient dispersibility for dyes and developers.
It cannot be dispersed stably with a particle size of micron or less. The low molecular weight sulfonic acid group-containing modified polyvinyl alcohol is excellent in dispersibility to some extent, but the background color of the support material is considerably observed, so that the performance cannot be said to be sufficient. The maleic anhydride-based copolymer has a fairly background color, and when it is blended with a binder or the like when used as a coating liquid, the compatibility with the binder is poor and problems such as aggregation and thickening of dispersed particles occur. There are many.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dispersant suitable for a heat-sensitive color-developing substance and a developer of a heat-sensitive recording material so that there is no background color of a support base and high-speed printing. The purpose is to provide a heat-sensitive recording material that can obtain a clear image.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a color-developing substance, a color-developing agent and a dispersant which cause the color-developing substance to develop a color upon heating. In the heat-sensitive recording material, the content of the carboxyl group-containing monomer unit is 3 to 15 mol% and the saponification degree is 70 to 9
The present invention has been completed by finding a heat-sensitive recording material characterized by using a modified polyvinyl alcohol having 5 mol% and a polymerization degree of 50 to 500 as a dispersant.

That is, the heat-sensitive recording material of the present invention is used as a dispersant for a color-developing substance and a developer, the content of the carboxyl group-containing monomer unit is 3 to 15 mol%, the degree of saponification is 70 to 95 mol% and the degree of polymerization is. It is characterized by using 50 to 500 modified polyvinyl alcohol.

The polyvinyl alcohol resin used in the present invention is obtained by saponifying polyvinyl acetate obtained by polymerizing or copolymerizing vinyl acetate by a known polymerization method such as bulk, solution, suspension and emulsification. The content of the carboxyl group-containing monomer unit of the modified polyvinyl alcohol used in the present invention thus obtained is 3 to 15 mol%.
And preferably 3 to 10 mol%,
More preferably, it is 3 to 6 mol%. When the content of the carboxyl group-containing monomer unit is less than 3 mol%, the hydrophilicity is low and the dispersion becomes insoluble after the dispersion is completed. When the content of the carboxyl group-containing monomer unit is more than 15 mol%, the whiteness is very poor. The kind of the carboxyl group-containing monomer is not particularly limited, but examples thereof include fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride, and itaconic anhydride. Among these carboxyl group-containing monomers, dibasic acid is preferable, and itaconic acid is more preferable. The saponification degree of the modified polyvinyl alcohol needs to be 70 to 95 mol%, preferably 75 to 95 mol%, and more preferably 75 to 90 mol%. Saponification degree is 70
If the amount is less than mol%, thickening of the foam is severe when the bubbles are bitten. If the degree of saponification is more than 95 mol%, the viscosity of the dispersion becomes too high and the handling becomes difficult, and the solid content concentration of the dispersion is increased. I can't raise it. The degree of polymerization of the modified polyvinyl alcohol of the present invention is required to be 50 to 500, preferably 100 to 300. If the degree of polymerization is less than 50, the dispersion performance will be insufficient, and the efficiency of aggregation and atomization of the dispersion will be reduced. If the degree of polymerization is more than 500, the viscosity will be too high and the handling will be difficult. Cannot increase the solids concentration of. The preferable amount of the dispersant used is 3 to 20 parts by weight based on 100 parts by weight of the total amount of the color-forming substance and the color developer.

The method for producing the modified polyvinyl alcohol of the present invention is not particularly limited, but polyvinyl alcohol is reacted with the above carboxylic acid by a post reaction,
Alternatively, a product obtained by copolymerizing vinyl acetate and an ethylenically unsaturated carboxylic acid and then saponifying is used. Regarding a specific method for producing such a carboxyl group-modified polyvinyl alcohol, Japanese Patent Publication No. 21312/45,
3-91995, 54-28389 and 54
-28390.

The modified polyvinyl alcohol used in the present invention may be copolymerized with another monomer in addition to the above-mentioned carboxylic acid-containing monomer, and the polymer terminal is modified with a chain transfer agent. Can also be used. The ethylenic monomer copolymerizable with vinyl ester is not particularly limited as long as it is copolymerizable with vinyl ester, and examples thereof include α-olefins such as ethylene, propylene, n-butene, isobutene and 1-hexadecene.
Methyl (meth) acrylate, n-butyl (meth) acrylate, 2-vidroxyethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acrylic acid, stearyl (meth) acrylate and the like (meth ) Acrylic acid esters, dimethyl fumarate, dimethyl itaconic acid, dimethyl maleate, monomethyl maleate, esters such as methyl crotonate, methyl vinyl ether,
Vinyl ethers such as butyl vinyl ether, lauryl vinyl ether, stearyl vinyl ether, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid,
Sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid and salts thereof, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-methylol (meth) acrylamide, Nt −
Butoxy (meth) acrylamide, Nt-octyl (meth) acrylamide, N-vinylpyrrolidone and other amide group-containing monomers, dimethylaminoethyl (meth) acrylamide and other quaternary ammonium salt-containing monomers, vinyl Hydroxysilane, (meth) acrylic acid-3-trimethoxysilylpropyl and other silyl group-containing monomers, allyl alcohol, dimethylallyl alcohol, isopropenyl alcohol and other hydroxyl group-containing monomers, allyl acetate, dimethyl allyl acetate, Examples include acetyl group-containing monomers such as isopropenyl acetate.

The color-forming substance used in the present invention is
It is not particularly limited as long as it is used for general pressure sensitive recording paper and heat sensitive recording paper. To give a specific example, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3- (p-dimethylaminophenyl) -3-
(1,2-dimethylindol-3-yl) phthalide,
Triaryl such as 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide and 3,3-bis- (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide Methane compounds, 4,
4'-bisdimethylaminobenzhydrin benzyl ether, diphenylmethane compounds such as N-halophenyl leuco auramine, rhodamine B-anilinolactam,
3-diethylamino-7-benzylaminofluorane,
3-diethylamino-7-butylaminofluorane, 3
-Diethylamino-7- (chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-
7-anilinofluorane, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluorane, 3-diethylamino-6 -Chloro-7- (γ-chloropropyl) aminofluorane, 3
-(N-ethyl-N-isoamyl) -6-methyl-7-
Xanthene-based compounds such as phenylaminofluorane and 3-dibutylamino-6-methyl-7-anilinofluorane, benzoylleucomethylene blue, and p
-Thiazine compounds such as nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-
There are nospiro compounds such as ethyl-spiro-dinaphthopyran, 3-benzylspirodinaphthopyran, and 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, which are used alone or as a mixture of two or more kinds. These color-forming substances are appropriately selected and used depending on the purpose of heat-sensitive recording and desired properties.

As the color developer used in the present invention, a phenol derivative and an aromatic carboxylic acid derivative are preferable, and bisphenols are particularly preferable. Specifically, as phenols, p-octylphenol, p-tert-
Butylphenol, p-phenylphenol, 1,1-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p- Hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethyl-hexane,
2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, dihydroxydiphenyl ether and the like, and aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, p-
Examples thereof include butyl hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and polyvalent metal salts of the above carboxylic acids.

In the present invention, it is preferable to use an aqueous binder in the thermosensitive color developing layer. As a concrete example,
Starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid Terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, polyvinyl acetate, Polyurethane, polyacrylic acid,
Polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, etc. emulsion, styrene / butadiene copolymer, latex such as styrene / butadiene / acrylic copolymer, etc. Can be mentioned. The preferred amount of the aqueous binder added is 1 to 20 parts by weight based on 100 parts by weight of the total amount of the color-forming substance and the color developer.

In the heat-sensitive color-developing layer of the present invention, in addition to the color-developing substance and the developer, if necessary, an auxiliary additive component such as a filler, a surface-active agent, or a heat-sensitive recording material is added to the heat-sensitive recording material. Soluble substances (or lubricants), pressure-color-developing inhibitors and the like can be used in combination. In this case, specific examples of the filler and the heat-fusible substance are the same as those exemplified in connection with the protective layer.

In the present invention, the method for forming the thermosensitive recording layer is not particularly limited, and it is an air knife method, a blade coating method, a gravure method, a roll coating method, a spray method, a dip method, a bar coating method, an extrusion method. Any known coating method such as the above can be used.

In the present invention, the support material of the heat-sensitive recording material is not particularly limited. For example, paper, synthetic fiber paper, synthetic resin film and the like can be used as appropriate. Generally, it is preferable to use paper.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the following, "parts" and "%" mean "parts by weight" and "% by weight", respectively, unless otherwise specified. The value expressed as viscosity in the following description is a value measured with a B-type viscometer manufactured by Tokyo Keiki at 30 ° C. and a rotor rotation speed of 12 rpm.

Example 1 Vinyl acetate and itaconic acid were solution-polymerized in a methanol solvent to obtain polyvinyl acetate in which itaconic acid was copolymerized, and caustic soda was added to a methanol solution of this itaconic acid-modified polyvinyl acetate, followed by a conventional method. After the saponification reaction is carried out with, the degree of polymerization is 185, the degree of saponification is 88 mol%,
Thus, 4 mol% of itaconic acid-modified polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) was obtained. After dissolving this polyvinyl alcohol in distilled water, a leuco dye was added at 20 ° C. to obtain a dispersion stock solution having the following composition. Dispersion liquid preparation Leuco dye (S-205 manufactured by Yamada Chemical Co., Ltd.) 40.9% Carboxyl group-modified PVA 4.1% (modified itaconic acid 4.0 mol%, degree of polymerization 185, degree of saponification 88 mol%) distilled water 54.9 % Antifoaming agent (manufactured by Nisshin Chemical Co., Ltd., Surfynol 440) 0.1% 300 g of the above dispersion liquid was pre-stirred in a beaker for 15 minutes, and then sand grinder (manufactured by Kansai Paint Co., Ltd., batch) Glass beads (soda quartz glass with a diameter of 1.5 to 2.0 mm)
An apparent volume of 300 cc was added, dispersion was carried out at a rotation speed of 2170 rpm for 3 hours while maintaining the liquid temperature at 20 ° C., and the following measurement was carried out in the dispersion process. The test conditions for the above test items are as follows. (1) 1 hour, 2 hours after the start of sand grinder dispersion,
A small amount of the dispersion liquid after 3 hours was collected, and the particle diameter of the dispersed dye was measured by a laser diffraction particle size analyzer (SALD-100 manufactured by Shimadzu Corporation).
0). (2) The viscosity of the dispersion liquid after the dispersion for 3 hours was measured at 30 ° C. (3) The whiteness of the dispersion after 3 hours of dispersion was measured by (Z-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.). The whiteness indicates that 0 is completely white, and the larger the negative value, the more colored. Table 1 shows the above evaluation results.

Examples 2 to 3 The same experiment as in Example 1 was repeated except that the itaconic acid-modified polyvinyl alcohol shown in Table 1 was used in place of the itaconic acid-modified polyvinyl alcohol used in Example 1. The results are shown in Table 1.

Comparative Examples 1 to 8 Experiments were carried out in accordance with Example 1 except that the polyvinyl alcohol shown in Table 1 was used in place of the itaconic acid-modified polyvinyl alcohol used in Example 1. The results are shown in Table 1.

[0021]

[Table 1]

[0022]

As described above, the heat-sensitive recording material of the present invention is excellent in the dispersibility of the dispersant for the color-forming substance and the color developer and has a good whiteness in the background. Furthermore, the dispersant used in the production of the heat-sensitive recording material of the present invention provides a high-concentration and low-viscosity solution, and therefore has good handleability.

Claims (1)

[Claims] 1. A heat-sensitive recording material comprising a color-forming substance, a color-developing agent that develops a color when the color-forming substance is heated, and a dispersant, wherein the content of the carboxyl group-containing monomer unit is 3 to 15.
Mol%, saponification degree 70-95 mol% and degree of polymerization 50-
A heat-sensitive recording material, wherein 500 modified polyvinyl alcohol is used as a dispersant.