JPH04232091A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material excellent in the storage stability of a recording image and the printability to a protective layer by improving the thermal recording material wherein the protective layer is formed on a recording layer. CONSTITUTION:A protective layer containing at least polyvinyl alcohol or modified polyvinyl alcohol (1) with a saponification value of 86-95%, modified polyvinyl alcohol (2) with a saponification value of 96% or more and spherical org. pigment (3) with a mean particle size of 0.5-57mum is provided on a thermal recording layer utilizing the color forming reaction of a basic dye and a developer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a heat-sensitive recording medium, and in particular, by providing a special protective layer on the recording layer, not only the storage stability of the recorded image but also the suitability for printing on the protective layer is improved. The present invention relates to a heat-sensitive recording medium.

0002

[Prior Art] A thermosensitive recording material that utilizes a coloring reaction between a colorless or light-colored basic dye and an organic or inorganic coloring agent to obtain a recorded image by bringing both coloring substances into contact with heat is well known. Are known. Such thermosensitive recording materials are relatively inexpensive;
Since recording devices are compact and easy to maintain, they are used not only as recording media for facsimiles and various computers, but also in a wide range of fields.

[0003] As one field of use, with the expansion of POS (point of sales) systems in retail stores and the like, the number of cases in which they are used as labels is increasing. However, when used as a heat-sensitive label in a supermarket or the like, it comes into contact with water, plastic wrap, oil, etc., which causes the recorded image (print) on the heat-sensitive label to fade. Therefore, heat-sensitive recording materials used in such applications are required to have qualities such as water resistance, plasticizer resistance, and oil resistance.

In order to improve the storage stability of recorded images, a method is proposed in which a protective layer is formed by coating an aqueous emulsion of a resin having film-forming ability and chemical resistance on the heat-sensitive recording layer (Japanese Patent Application Laid-Open No. 1983-1992). 128347) and saponification degree of 80 to 95%.
A method of incorporating polyvinyl alcohol into the undercoat layer, recording layer, and protective layer (Japanese Unexamined Patent Publication No. 123586/1986) has been proposed, but it has not yet achieved a satisfactory effect of improving the storage stability of recorded images. .

[0005] Furthermore, since the protective layer may be printed using various printing methods, it is required to have appropriate printability such as appropriate ink receptivity and surface strength. In particular, offset printing uses dampening water during printing, so if it does not have water repellency, water absorption, and water resistance, problems will occur as halftone reproducibility, gradation reproducibility, contrast, etc. will deteriorate. .

[0006]

[Problems to be Solved by the Invention] Therefore, as a result of intensive research into the composition of the protective layer formed on the heat-sensitive recording layer, the present inventors have found that a protective layer containing a specific resin component and pigment is formed on the recording layer. Once formed, the recorded image has excellent storage stability, especially plasticizer resistance, water resistance, and water plasticizer resistance when it comes into contact with plastic wrap when wet, and printability, especially surface strength and offset printing. The present inventors have discovered that it is possible to obtain a heat-sensitive recording material that has excellent ink receptivity and does not cause sticking or debris adhesion to the recording head, leading to the completion of the present invention.

[0007]

[Means for Solving the Problems] The present invention provides a heat-sensitive recording layer utilizing a coloring reaction between a colorless or light-colored basic dye and a coloring agent. Modified polyvinyl alcohol, saponification degree 9
This heat-sensitive recording material is characterized by being provided with a protective layer containing 6% or more of modified polyvinyl alcohol and (1) a spherical organic pigment having an average particle diameter of 0.5 to 5 μm.

[0008]

[Function] In the heat-sensitive recording material of the present invention, the protective layer on the recording layer contains at least (1) polyvinyl alcohol or modified polyvinyl alcohol with a saponification degree of 86 to 95%, and (2) a saponification degree of 96%.
The above-mentioned modified polyvinyl alcohol and (1) contain a spherical organic pigment having an average particle diameter of 0.5 to 5 μm. When at least one selected from alcohol and silicon-modified polyvinyl alcohol is used, the desired effects of the present invention can be obtained extremely efficiently, so this embodiment is one of the preferred embodiments of the present invention. In addition, the degree of polymerization of these polyvinyl alcohols is generally 200
It is adjusted within a range of about 3,500 to 3,500.

■ Saponification degree contained in the protective layer: 86
~95% polyvinyl alcohol or modified polyvinyl alcohol is one component that effectively acts to adjust the contact angle of the surface of the protective layer to water. That is, by using polyvinyl alcohol or modified polyvinyl alcohol having such a degree of saponification, the contact angle of the surface of the protective layer with water is adjusted to about 50 to 70 degrees, resulting in improved compatibility with dampening water during offset printing. and maintains good receptivity to printing ink. Incidentally, when a protective layer is formed only with polyvinyl alcohol with a saponification degree of 96% or more, the contact angle of the surface of the protective layer with water is 20 to 3.
The angle becomes extremely small at 0 degrees, and the ink receptivity during offset printing is significantly reduced.

However, if the protective layer is formed only with polyvinyl alcohol or modified polyvinyl alcohol with a degree of saponification of 86 to 95%, the water resistance and water plasticizer resistance of the protective layer will decrease. Saponification degree 86-95
% polyvinyl alcohol or modified polyvinyl alcohol and (2) modified polyvinyl alcohol with a saponification degree of 96% or more. That is, modified polyvinyl alcohol with a saponification degree of 96% or more has excellent curability, and has a saponification degree of 8%.
This effectively improves the water resistance and water plasticizer resistance of the protective layer, which cannot be satisfied with 6 to 95% polyvinyl alcohol or modified polyvinyl alcohol alone.

[0011] Therefore, in order to obtain a synergistic effect between the two, the ratio of their combined use is important;
% of polyvinyl alcohol or modified polyvinyl alcohol in an amount of 10 to 500 parts by weight, preferably 50 to 400 parts by weight, of modified polyvinyl alcohol having a degree of saponification of 96% or more.

Furthermore, in addition to the above-mentioned polyvinyl alcohol, the protective layer constituting the heat-sensitive recording material of the present invention contains (1) a spherical organic pigment with an average particle diameter of 0.5 to 5 μm as an essential component. It is made to contain. In other words, spherical organic pigments with such an average particle size can effectively improve the surface strength and water absorption of the protective layer compared to other inorganic pigments and organic pigments, and can also improve the surface strength and water absorption of the protective layer. Since it does not adversely affect storage properties such as water resistance, plasticizer resistance, and water plasticizer resistance, it is extremely effective in achieving the desired effects of the present invention in addition to the effects of the combination with the specific polyvinyl alcohol mentioned above. be. Incidentally, if an organic pigment has an average particle diameter outside the above-mentioned specific range, the balance of properties exhibited by each component constituting the protective layer will be disrupted, and the desired effects of the present invention cannot be achieved.

[0013] Organic pigments exhibiting such characteristics include, for example, polystyrene fillers, nylon fillers, polyethylene fillers, urea-formalin resin fillers, and polystyrene fillers are particularly preferably used. The addition ratio of the organic pigment to the protective layer is generally 5 to 300 parts by weight per 100 parts by weight of polyvinyl alcohol constituting the protective layer.
It is desirable to adjust the amount preferably within a range of about 20 to 200 parts by weight.

In the heat-sensitive recording material of the present invention, the coating liquid for forming the protective layer contains, in addition to the above-mentioned three essential components,
For example, it is possible to use some of the usual binders such as starches, celluloses, proteins, various copolymer salts, and various copolymer emulsions, and to further improve water resistance, for example, glyoxal, Curing agents such as formalin, glycine, glycidyl ester, glycidyl ether, dimethylol urea, ketene dimer, dialdehyde starch, melamine resin, polyamide resin, polyamide-epichlorohydrin resin, ketone-aldehyde resin, borax, boric acid, zirconium ammonium carbonate, etc. They can also be used together.

[0015] In order to further improve printability and sticking, it is also possible to use ordinary inorganic pigments and organic pigments in combination, such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc. Various auxiliary agents such as a lubricant, a surfactant (dispersant, lubricant) such as sodium dioctyl sulfosuccinate, and an antifoaming agent can also be added as appropriate.

The heat-sensitive recording medium of the present invention has an extremely important feature in that a protective layer having a specific composition as described above is provided on the recording layer. is not particularly limited. Therefore, it can be appropriately applied to various ordinary heat-sensitive recording materials.

Examples of the colorless or light-colored basic dye constituting the heat-sensitive recording layer include the following dyes. 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-yl)phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3,3-bis(1
,2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3
-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, etc. allylmethane dye,

Diphenylmethane dyes such as 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-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-naphtho-(
6'-methoxybenzo)spiropyran, 3-propyl-
Spiro dyes such as spiro-dibenzopyran, lactam dyes such as rhodamine-B anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam,

3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran,
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-dibutylamino-6-methyl-7-phenylaminofluorane, 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-N-diethylaminofluorane, 3-(N-ethyl-p- toluidino)-6-methyl-7-phenylaminofluorane, 3-
(N-ethyl-p-toluidino)-6-methyl-7-(
p-Toluidino)fluoran, 3-diethylamino-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)fluoran,
3-dibutylamino-7-(o-chlorophenylamino)fluoran, 3-pyrrolidino-6-methyl-7-p-
Butylphenylaminofluorane, 3-diethylamino-
7-(o-fluorophenylamino)fluorane, 3-
Dibutylamino-7-(o-fluorophenylamino)
Fluoran, 3-(N-methyl-Nn-amyl)amino-6-methyl-7-phenylaminofluoran, 3-
(N-ethyl-Nn-amyl)amino-6-methyl-
7-phenylaminofluorane, 3-(N-ethyl-N
-iso -amyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-methyl-Nn-hexyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl -N-n-hexyl)amino-
6-Methyl-7-phenylaminofluorane, 3-(N
-ethyl-N-β-ethylhexyl)amino-6-methyl-7-phenylaminofluoran and other fluoran dyes.

Further, as specific examples of the coloring agent constituting the heat-sensitive recording layer, the following coloring agents are exemplified. Inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol,
β-naphthol, 4-hydroxyacetophenol, 4
-tert-octylcatechol, 2,2'-dihydroxydiphenol, 4,4'-isopropylidene bis(
2-tert-butylphenol), 4,4'-sec
-butylidenediphenol, 4-phenylphenol, 4,4'-isopropylidenediphenol, 2,2-
Bis(4-hydroxyphenyl)-4-methylpentane, 2,2'-methylenebis(4-chlorophenol),
Hydroquinone, 4,4'-cyclohexylidene diphenol, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2
, 2',4,4'-tetrahydroxybenzophenone,

4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-
Hydroxy-4'-isopropyloxydiphenylsulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 3,4-dihydroxydiphenylsulfone, 3,
4-hydroxydiphenylsulfone derivatives such as 4-dihydroxy-4'-methyldiphenylsulfone, 3'4'
trimethylene-4-hydroxydiphenylsulfone, 3
'4'-trimethylene-2, 6-dimethyl-4-hydroxydifnylsulfone, 3'4'-tetramethylene-4
- 4-hydroxydiphenylsulfone derivatives having a ring at the 3'4' position such as hydroxydiphenylsulfone, 3'4'-tetramethylene-2methyl-4-hydroxydiphenylsulfone,

Dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, -sec-butyl 4-hydroxybenzoate, 4
-pentyl hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 4 -Phenolic compounds such as p-chlorobenzyl hydroxybenzoate, p-methoxybenzyl 4-hydroxybenzoate, novolac type phenolic resin, phenol polymer, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, Terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid,

3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-
Aromatic carboxylic acids such as phenyl-5-(α,α-dimethylbenzyl)salicylic acid and 3,5-di-α-methylbenzylsalicylic acid, bis(3-tert-butyl-4-hydroxy-6-methylphenyl) sulfide , bis(2-methyl-4-hydroxy-6-tert-butylphenyl) sulfide and other sulfide derivatives, as well as these phenolic compounds, aromatic carboxylic acids, etc., such as zinc, magnesium, aluminum, calcium, titanium, Salts with polyvalent metals such as manganese, tin, nickel, etc.
Furthermore, organic acidic substances such as ampyrine complex of zinc thiocyanate, etc.

[0025] The ratio of the basic dye to the coloring agent is appropriately selected depending on the type of basic dye and coloring agent used, and is generally 1 to 5 parts by weight of the basic dye.
About 0 parts by weight, preferably about 2 to 10 parts by weight, of the coloring agent is used.

[0026] Generally, various thermofusible substances are added to the recording layer, and specific examples of thermofusible substances include:
For example, the following substances are exemplified. stearic acid amide,
Stearic acid methylene bisamide, oleic acid amide,
Fatty acid amides such as palmitic acid amide and coconut fatty acid amide, 2,2'-methylenebis(4-methyl-6-te
rt-butylphenol), 4,4'-butylidenebis(6-tert-butyl-3-methylphenol), 2
, 2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,4-di-tert-butyl-3
- Hindered phenols such as methylphenol, 2-
(2'-hydroxy-5-methylphenyl)benzotriazole, ultraviolet absorbers such as 2-hydroxy-4-benzyloxybenzophenone, 1,2-di(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 1-
Phenoxy-2-(4-methylphenoxy)ethane, dimethyl terephthalate, dibutyl terephthalate, dibenzyl terephthalate, dibutyl isophthalate, phenyl 1-hydroxynaphthoic acid, dibenzyl oxalate, and the like.

Among these thermofusible substances, 1 and 2
-di(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 1-phenoxy-2-(4-methylphenoxy)ethane, and oxalic acid dibenzyl ester are preferably used. The amount of the thermofusible substance to be used is generally desirably adjusted within a range of about 4 parts by weight or less per 1 part by weight of the coloring agent.

The coating liquid for forming the recording layer usually contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin,
Casein, gum arabic, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer salt, ethylene/acrylic Acid copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, urea resin, melamine resin, amide resin, etc. accounts for 10 to 40%, preferably 15 to 40%, based on the solid content of the coating liquid. It is blended at about 30%.

Furthermore, various auxiliary agents can be added to the coating liquid as necessary, such as dioctyl sulfosuccinic acid sodium salt, dodecylbenzenesulfonic acid sodium salt, lauryl alcohol sulfuric acid ester sodium salt, fatty acid Dispersants such as metal salts, ultraviolet absorbers such as benzophenone, antifoaming agents, fluorescent dyes, coloring dyes, etc. are added as appropriate.

If necessary, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, kaolin, clay, talc, calcium carbonate, calcined kaolin, titanium oxide, diatomaceous earth, and fine particulate It is also possible to add inorganic pigments such as anhydrous silica and activated clay.

A coating liquid for forming a recording layer containing these substances is generally prepared by using water as a dispersion medium and dispersing it with a stirring/pulverizing machine such as a ball mill or a sand mill. The method for forming the recording layer is not particularly limited; for example, the recording layer can be coated on paper, plastic film, synthetic paper, etc. using an appropriate coating device such as an air knife coater, a variver blade coater, a pure blade coater, or a short dwell coater. It is formed by a method such as coating and drying on a suitable support. The coating amount of the coating liquid is also not particularly limited, and is usually 2 to 12 g/m2 in terms of dry weight, preferably 3 to 10 g/m2.
It is adjusted within a range of about m2.

A protective layer having a specific composition as described above is formed on the heat-sensitive recording layer thus formed, and the protective layer is generally formed by applying a protective layer-forming coating liquid onto the recording layer using a suitable coating device. Formed in a way. Furthermore, if the coating amount of the protective layer forming coating liquid exceeds 20 g/m2 in terms of dry weight, the recording sensitivity of the heat-sensitive recording medium may be significantly reduced. .5-1
It is desirable to adjust within a range of about 0 g/m2.

[0033] If necessary, it is also possible to further improve the storage stability by providing a protective layer on the back side of the heat-sensitive recording material. Furthermore, by providing an undercoat layer on the support,
Various known techniques in the field of heat-sensitive recording material manufacturing may be added as necessary, such as applying an adhesive treatment to the back surface of the recording material and processing it into an adhesive label.

[0034]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is of course not limited to these. Note that "parts" and "%" in the examples indicate "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 ■ Preparation of liquid A: 3-dibutylamino-6-methyl-7
-10 parts of phenylaminofluorane, 1,2-di(3-
A composition consisting of 20 parts of methylphenoxy)ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 40 parts of water was added to
The particles were ground using a horizontal sand mill using 300 m grinding media (made of zirconium) until the average particle diameter was 0.9 μm. (2) Preparation of Solution B: A composition consisting of 30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 80 parts of water was ground in a sand mill until the average particle diameter was 2 μm.

■ Formation of recording layer: 75 parts of liquid A, 1 part of liquid B
15 parts, 80 parts of 10% polyvinyl alcohol aqueous solution,
A recording layer forming coating liquid prepared by mixing and stirring 35 parts of calcium carbonate was applied to base paper at a weight of 50 g/m2, and the coating amount after drying was 6.
A heat-sensitive recording material was obtained by coating and drying so as to obtain a heat-sensitive recording material of g/m2.

■ Formation of protective layer: acetoacetyl group-modified polyvinyl alcohol (10% concentration, degree of saponification 97%)
) 150 parts, polyvinyl alcohol (degree of polymerization 1700,
saponification degree 88%, concentration 10%) 50 parts, kaolin 80 parts,
Polystyrene filler (average particle size 1 μm, concentration 35%
) 40 parts, zinc stearate aqueous emulsion (30%
A coating solution for forming a protective layer prepared by mixing and stirring 20 parts (concentration) and 200 parts of water was applied and dried on the recording layer of the heat-sensitive recording material so that the coating amount after drying was 4 g/m2. A thermosensitive recording material having a protective layer was obtained.

Example 2 Carboxyl group-modified polyvinyl alcohol (10% concentration, saponification degree 98%) was used instead of acetoacetyl group-modified polyvinyl alcohol (10% concentration, saponification degree 97%) in the protective layer forming coating solution. A thermosensitive recording material was obtained in the same manner as in Example 1, except that the thermosensitive recording material was used.

Example 3 Silicon-modified polyvinyl alcohol (10% concentration, saponification degree 97%) was used instead of acetoacetyl group-modified polyvinyl alcohol (10% concentration, saponification degree 97%) in the protective layer forming coating solution.
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 8%) was used.

Example 4 Polystyrene filler (average particle size 1
µm, concentration 35%), except that polystyrene filler (average particle size 4 µm, concentration 30%) was used.
A thermosensitive recording material was obtained in the same manner as in Example 1.

Example 5 Polystyrene filler (average particle size 1
A thermosensitive recording material was obtained in the same manner as in Example 1, except that a melamine resin filler (average particle size: 0.8 μm, concentration: 25%) was used instead of the melamine resin filler (average particle size: 0.8 μm, concentration: 25%).

Example 6 Polyvinyl alcohol (degree of polymerization: 170
0, saponification degree 88%, concentration 10%), polyvinyl alcohol (polymerization degree 1000, saponification degree 90%, concentration 1
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 0%) was used.

Comparative Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1, except that the acetoacetyl group-modified polyvinyl alcohol (10% concentration, saponification degree 97%) of the protective layer forming coating liquid was not used. .

Comparative Example 2 Polyvinyl alcohol (degree of polymerization: 170
A thermosensitive recording material was obtained in the same manner as in Example 1, except that 0.0, saponification degree: 88%, concentration: 10%) was not used.

Comparative Example 3 Polystyrene filler (average particle size 1
Example 1 except that µm, concentration 35%) was not used.
A thermosensitive recording material was obtained in the same manner as above.

Comparative Example 4 Polystyrene filler (average particle size 1
A thermosensitive recording material was obtained in the same manner as in Example 1, except that a polystyrene filler (average particle size: 0.3 μm, concentration: 25%) was used instead of the filler (average particle size: 0.3 μm, concentration: 25%).

Comparative Example 5 Polystyrene filler (average particle size 1
um, concentration 35%), except that melamine resin filler (average particle size 7 μm, concentration 30%) was used.
A thermosensitive recording material was obtained in the same manner as in Example 1.

The following evaluation tests were conducted on the 11 types of heat-sensitive recording materials thus obtained, and the results are listed in Table 1. [Color density] Practical thermal facsimile (manufactured by NTT, NT
The color density of the recorded image obtained by printing with a Macbeth densitometer (manufactured by Macbeth Co., Ltd., Model RD-914) was measured.

[Water Resistance] After printing, the heat-sensitive recording material was immersed in water for 15 hours, and relative evaluation was made based on the print density when taken out using the following evaluation criteria. [Plasticizer resistance] Polypropylene pipe (40 mm diameter pipe) with 3 layers of vinyl chloride wrap film (manufactured by Mitsui Toatsu Chemical Co., Ltd.)
After wrapping the heat-sensitive recording material in layers, sandwiching the heat-sensitive recording material with colored print on it so that the colored side of the print is facing outward, wrap a vinyl chloride wrap film three times over it, and leave it at 40°C for 15 hours. The concentration was evaluated using the following evaluation criteria.

[Water and Plasticizer Resistance] After the recorded heat-sensitive recording material was slightly wetted with water, a test was conducted in the same manner as for the plasticizer resistance described above, and evaluation was made using the following evaluation criteria. [Evaluation Criteria] ◎: There is almost no decrease in recording density.

Good: The recording density is slightly decreased, but there is no practical problem. Δ: The recording density is decreased, causing a practical problem. ×: Significant decrease in recording density, impractical.

[Suitability for Offset Printing] Offset printing was performed on the recording medium, and the reproducibility of halftone dots was relatively evaluated using the following evaluation criteria, and at the same time, the ink transferability was evaluated as follows. (Reproducibility of halftone dots) ◎: Reproducibility of 95% or more. ○: 85-95% is reproduced.

Δ: 65-85% is reproduced. ×: Reproducibility of 65% or less. (Ink Transfer Properties) The ink density after solid black printing was measured using a Macbeth densitometer (manufactured by Macbeth Co., Ltd., model RD-914).

[0054]

[Table 1]

[0055]

[Effects of the Invention] As is clear from the results in Table 1, all of the heat-sensitive recording materials of the present invention had excellent storage stability of recorded images and excellent printability.

Claims (2)

[Claims] [Claim 1] A heat-sensitive recording layer utilizing a coloring reaction between a colorless or light-colored basic dye and a coloring agent is coated with at least (1) polyvinyl alcohol or modified polyvinyl alcohol with a saponification degree of 86 to 95%, and (2) a saponification degree of 96%. % or more of modified polyvinyl alcohol, and (1) a protective layer containing a spherical organic pigment having an average particle diameter of 0.5 to 5 μm. 2. The heat-sensitive recording material according to claim 1, wherein the modified polyvinyl alcohol is at least one selected from carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol.