JPH0776166A - Thermal record body - Google Patents

Abstract

PURPOSE:To obtain a thermal record body whose thermally recorded information does not become known to a third person by arranging, in sequence on a support body, a thermal recording layer and a peelable masking layer formed by coating process so as to make recorded information unreadable, and arranging a pigment layer on the masking layer. CONSTITUTION:A thermal record body is constituted by arranging a thermal recording layer and a specified masking layer in sequence on the top face of a support body. That is, the masking layer is formed by coating process in a peelable way, so as to make recorded information unreadable. On the top face of the masking layer, a pigment layer is arranged. At this time, as a pigment to be used for the pigment layer, for example, at least one kind is selected from among metal oxide, graphite, mineral, urea formalin resin fine particle, foaming microcapsule, and others. Thus, a thermal record medium whose thermally recorded information does not become known to a third person is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material in which information recorded by a heat-sensitive recording method is not known to a third party.

[0002]

2. Description of the Related Art Utilizing a color reaction between a color former and a color former,
A heat-sensitive recording material in which a recording image is obtained by reacting both color-developing substances with heat energy from a thermal head is well known. Generally, thermal recording materials are relatively inexpensive, and the recording equipment is compact and easy to maintain.
It is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

However, since the thermosensitive recording medium which is generally commercially available is recorded in such a state that the output information can be seen by anyone, it is not suitable for the communication of confidential contents. Therefore, in order to conceal the information output to the thermosensitive recording medium, a method of laminating a base material having a concealing property on the thermosensitive recording layer is disclosed in JP-A-61-248785.
As described in JP-A-2-286391, the preservability of a recorded image may be reduced or fog may be generated on the background portion depending on the type of the adhesive used when the substrates are bonded together. Further, the adhesion between the thermal recording material and the concealing substrate may be incomplete, or curling which is difficult to correct may occur after bonding. Further, the production of these thermal recording bodies requires a step of laminating them using equipment such as a laminator, resulting in high cost.

As a result of earnest studies to solve such a problem, the inventors of the present invention have proposed a heat-sensitive recording material in which a peelable concealing layer is provided on the heat-sensitive recording layer in a coating process (Japanese Patent Application No. 5-957).
41). However, as a result of repeated research, it was found that print marks remain on the surface of the concealing layer depending on recording conditions, and the print marks leak to a third party.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium in which information recorded by the thermosensitive recording system is not known to a third party.

[0006]

SUMMARY OF THE INVENTION The present invention comprises:
A heat-sensitive recording material comprising a heat-sensitive recording layer and a concealing layer which is formed by a coating process and which is peelable and makes the recorded information unreadable. The heat-sensitive recording material is characterized in that a pigment layer is provided on the concealing layer. It is a recording body.

[0007]

The heat-sensitive recording material of the present invention relates to a heat-sensitive recording material which is provided on the heat-sensitive recording layer or the intermediate layer by a coating process and which has a peelable concealing layer. A feature of the present invention is that the print mark is legible by providing a pigment layer on the hiding layer.

As the pigment used in the pigment layer, inorganic fine particles such as metal oxides, metal sulfides, metal carbides, graphite, carbon black, minerals and inorganic salts, urea formalin resin fine particles, organic fine particles of organic pigments, At least one kind is appropriately selected and used from among various non-foaming or foaming microcapsules. Of these, synthetic amorphous silica, calcium silicate, aluminum silicate, calcium carbonate, microcapsules and the like are preferable.

In the pigment layer coating liquid, usually as a binder,
Starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy 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, At least one of melamine resin, amide resin, polyurethane resin and the like is used, and the binder is about 10 to 60% by weight, preferably 10 to 40% by weight, based on the total solid content of the pigment layer.
It is mixed in the range of about. By the way, if the blending ratio of the binder is high, it is easy for printing marks to remain on the pigment layer itself,
The effect of the present invention cannot be obtained. Further, auxiliary agents such as colorants, curing agents, dispersants, defoamers, fluorescent dyes, ultraviolet absorbers and waxes can be appropriately added to the pigment layer coating liquid so long as the effects of the present invention are not impaired. The coating amount of the pigment layer is adjusted within a range of about 0.3 to 80 g / m ² in terms of dry weight.

By incorporating at least one of a metal salt of a higher fatty acid, a wax, and a silicone compound as a peelability improving agent in a layer adjacent to the masking layer, the masking layer can be easily peeled. When the layer adjacent to the concealing layer is a heat-sensitive recording layer, 5 to 50% by weight, preferably 10 to 30% by weight, of the above-mentioned peeling improver relative to the total solid amount of the heat-sensitive recording layer.
It is desirable to adjust within the range. When the layer adjacent to the concealing layer is an intermediate layer, it is desirable to add the peeling improver in an amount of 20% by weight or more, preferably 30% by weight, based on the total solid amount of the intermediate layer.

The higher the opacity of the hiding layer is, the more preferable. Apply the desired amount of coating liquid for forming the hiding layer on a transparent film.
After drying, if the value (opacity) measured according to JIS P 8138 is less than 88%, the recorded image formed on the heat-sensitive recording layer can be easily read from above the hiding layer.
It is preferably 8% or more, and particularly preferably 93% or more.

The hiding layer contains a pigment or dye and an adhesive as main components, and as the pigment, an inorganic or organic white or colored pigment and a dye can be used. For example, calcium carbonate, zinc oxide, aluminum oxide, Titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, talc,
Inorganic pigments such as kaolin, clay, calcined kaolin, bronze powder, carbon black, styrene microballs, nylon powder, polyethylene powder, urea
Examples include formalin resin fillers, phthalocyanines, organic pigments such as metal salts of phthalocyanines, and dyes such as methyl violet. Further, in order to obtain a high hiding effect with a small amount of use, it is desirable to use bronze powder, carbon black, and a pigment or dye having a similar color to the recorded image of the thermosensitive coloring layer, which have excellent hiding properties.

In the hiding layer coating liquid, usually as a binder,
Starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy 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, At least one of melamine resin, amide resin, polyurethane resin and the like is blended in the range of about 20 to 80% by weight based on the total solid content of the hiding layer. Further, a curing agent such as glyoxal, boric acid, dialdehyde starch, or an epoxy compound may be added to further improve the film forming property.

If desired, various auxiliary agents can be added to the coating solution. For example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and fatty acid metal salts. , Antifoaming agents, fluorescent dyes, coloring dyes, metal salts of higher fatty acids, waxes, etc. are appropriately added. The hiding layer coating liquid generally uses water as a dispersion medium and is formed on the heat-sensitive recording layer or the intermediate layer. The coating amount of the masking layer coating liquid is 3 to 80 g / m ^{2 as} a dry weight, preferably 5 to 4
It is adjusted in the range of about 0 g / m ² .

In the present invention, a metal salt of a higher fatty acid, a wax, or the like is used as a peelability improving agent between the heat-sensitive recording layer and the hiding layer.
By providing the intermediate layer containing at least one of the silicone compounds, the masking layer can be peeled off more easily. In the intermediate layer, as a binder together with a peelability improving agent, for example, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose,
Gelatin, casein, gum arabic, polyvinyl alcohol, carboxy 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, polyurethane ionomer and the like are used in combination.

It is also possible to use various pigments in combination, for example, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcination. Examples thereof include inorganic pigments such as kaolin and colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw starch particles, and organic pigments such as polyurethane / polyurea microcapsules.

Further, if necessary, various kinds of surfactants (dispersing agents, wetting agents) such as sodium dioctylsulfosuccinate, antifoaming agents, water-soluble polyvalent salts such as potassium alum, aluminum acetate, etc. in the coating liquid. Auxiliary agents can be added as appropriate. The intermediate layer coating liquid generally uses water as a dispersion medium,
The heat-sensitive recording layer is formed on the heat-sensitive recording layer by the forming method exemplified above. The coating amount of the coating liquid for the intermediate layer is 0.1% by dry weight.
It is adjusted in the range of ¹ to 15 g / m ² , preferably 0.5 to 6 g / m ² .

In the heat-sensitive recording material of the present invention, the recording mechanism used in the heat-sensitive recording layer may be one that develops or changes color by heat, for example, a combination of a colorless or light-colored basic dye and a color former, Examples include a combination of a diazonium salt and a coupler, a combination of a transition metal such as iron and a chelate compound, a combination of an aromatic isocyanate compound and an imino compound, and a combination of a colorless or light-colored basic dye and a colorant. Is preferably used because it is excellent in the recording density, the background portion and the storability of the recorded image. Various known compounds can be used as the colorless or light-colored basic dye, and the following are exemplified. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide,
3- (4-diethylamino-2-methylphenyl) -3
-(4-Dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-dibenzylamino-benzo [a] fluorane, 3- (N-ethyl-N-
p-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3
-Diethylamino-7-dibenzylaminofluorane,
3,6-bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane , 3- (N-ethyl-N-isoamyl) amino-
6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-
7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-
Pentyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (o-chlorophenylamino) fluorane, 3-di (n-butyl) amino-7-
(O-Chlorophenylamino) fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane, 3- (N-ethyl) -P
-Toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3- (N-ethyl-N-flu) Furylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-
Anilinofluorane, 3- (N-methyl-Nn-propylamino) -6-methyl-7-anilinofluorane,
3,3-bis [1- (4-methoxyphenyl) -1-
(4-Dimethylaminophenyl) ethylene-2-yl]
-4,5,6,7-Tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6 , 7
-Tetrachlorophthalide, 3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl]-
4,5,6,7-tetrabromophthalide, 3-p- (p
-Anilinoanilino) anilino-6-methyl-7-chlorofluorane, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'- Xanthene-2′-ylamino] phenyl} propane, 3,6, -bis (dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino) phthalide and the like can be mentioned. Of course, it is not limited to these, and two or more kinds may be used in combination as required.

Further, various known colorants are known as colorants used in combination with the above basic dyes,
For example, the following are exemplified. Inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 4-cumylphenol, hydroquinone monobenzyl ether, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenol,
1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl-2,2-butane, 4,4'-dihydroxydiphenylmethane, 2,2
-Bis (4-hydroxyphenyl) -4-methylpentane, 2,2-bis (4-hydroxyphenyl) heptane, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-
Oxapentane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α -Methyl-α- (4'-hydroxyphenyl) ethyl] benzene, 4,4'-dihydroxydiphenyl sulfide, bis (4-hydroxy-3-)
Methylphenyl) sulfine, benzyl 4-hydroxybenzoate, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, (4
-Hydroxyphenylthio) acetic acid-2- (4-hydroxyphenylthio) ethyl ester, di (p-hydroxyphenylthioethyl) ether, N, N'-di-m-chlorophenylthiourea, N- (phenoxyethyl)- Four
-Phenolic compounds such as hydroxyphenylsulfonamide, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 5- [p- (2- p
-Methoxyphenoxyethoxy) cumyl] salicylic acid,
Aromatic carboxylic acids such as p-chlorobenzoic acid, salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, and antipyrine of zinc thiocyanate. Examples include organic acidic substances such as complexes.

In the heat-sensitive recording material of the present invention, the use ratio of the basic dye contained in the recording layer and the color former is
Although it is not particularly limited, a basic dye 100 is generally used.
10-500 parts by weight, preferably 50-
It is desirable to use about 300 parts by weight of the coloring agent.

In the heat-sensitive recording material of the present invention, a sensitizer can be added to the recording layer according to the purpose. Specific examples of the sensitizer include stearic acid amide and methoxycarbonyl-.
N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebistearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide,
Dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, oxalate-di-p-methylbenzyl,
Oxalic acid-di-p-chlorobenzyl, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy). ) Ethane, 1,2-di (phenoxy) ethane,
1,2-di (4-methylphenoxy) ethane, 1,2-
Di (4-methoxyphenoxy) ethane, 1,2-di (4
-Chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p
-Acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, p- Examples include (4-tolyloxy) biphenyl and 5-bis (4-methoxyphenoxy) -3-oxa-hentane. Among these sensitizers, 1,2-di (3-methylphenoxy) ethane, 1,2-di (phenoxy) ethane, 2-naphthylbenzyl ether, dibenzyl oxalate, and oxalic acid-di-p-methyl. Benzyl, oxalic acid-di-p-chlorobenzyl, 2-naphthylbenzyl ether, p- (4-tolyloxy) biphenyl,
5-bis (4-methoxyphenoxy) -3-oxa-hentane is more preferable because it exhibits a particularly excellent sensitizing effect. The amount of these sensitizers used is not particularly limited, but it is generally desirable to adjust the amount within the range of about 4 parts by weight or less relative to 1 part by weight of the color developing agent.

Further, a preservative improving agent may be used in combination for the purpose of further enhancing preservability of the recorded image as long as the effect is not impaired. Specific examples of such a storability improver include, for example, 1,4-diglycidyloxybenzene,
Epoxy compounds such as 4,4'-diglycidyloxydiphenyl sulfone, diglycidyl terephthalate, and bisphenol A type epoxy resin, 2,2'-methylenebis (4
-Methyl-6-tert-butylphenol), 2,2'-
Methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert-
Butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4,
4'-butylidene bis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,
3-tris (2-methyl-4-hydroxy-5-tert-
Butylphenyl) butane, 4,4'-thiobis (3-methylphenol), 4,4'-dihydroxy-3,
3 ', 5,5'-tetrabromodiphenyl sulfone,
4,4'-dihydroxy-3,3 ', 5,5'-tetramethyldiphenyl sulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-
Hindered phenol compounds such as bis (4-hydroxy-3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 1- [α-methyl-α- (4 '-Hydroxyphenyl) ethyl] -4- [α', α'-bis (4 "-hydroxyphenyl) ethyl] benzene, N, N'-di-2-
Examples thereof include naphthyl-p-phenylenediamine and 2,2'-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate.

In order to prepare a coating liquid for a recording layer containing these substances, water is generally used as a dispersion medium, and a basic dye, a coloring agent, and further a basic dye, a coloring agent, and the like are required by a stirring / milling machine such as a ball mill, attritor, or sand mill. A sensitizer or the like added according to the above is dispersed together or separately to prepare a coating liquid.
In the coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, arabic gum as an adhesive,
Carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, fully saponified and partially saponified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid Copolymer salts, styrene / acrylic acid copolymer salts, styrene / butadiene copolymer emulsions, etc. are used in an amount of 10 to 40% by weight, preferably about 15 to 30% by weight, based on the total solid content.

It is also possible to use various pigments in combination in the coating liquid, for example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, titanium oxide, diatomaceous earth,
Inorganic pigments such as fine particulate anhydrous silica and activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and organic pigments such as raw starch particles can be used.

Further, various auxiliaries can be added to the coating liquid, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt and the like. Dispersant, benzophenone type,
Examples thereof include UV absorbers such as triazole type, defoaming agents, fluorescent dyes, and coloring dyes.

In the present invention, the method for forming the heat-sensitive recording layer, the intermediate layer, the hiding layer, and the pigment layer is not particularly limited, and they can be formed according to a conventionally known and commonly used technique, for example, air knife coating, Varibar blade coating, pure blade coating,
It can be formed by a method of coating and drying a coating liquid on a support by short dwell coating, curtain coating or the like. As the support, paper, synthetic paper, plastic film or the like is appropriately selected and used.

In the present invention, if necessary, a resin layer may be provided on the back side of the recording medium, or an undercoat layer may be provided between the support and the thermosensitive recording layer to improve image quality and sensitivity, and It is possible to add various known techniques in the field of heat-sensitive recording material production, such as processing an adhesive label on the back surface to form an adhesive label, or providing a magnetic layer on the back surface of the recording material. Further, it is conceivable that a processing treatment is applied after coating the hiding layer so that the hiding layer can be peeled off without using a special peeling tool or the like. Examples of such a processing treatment include, for example, a perforation processing, a cutting processing or a punching processing by a method that does not penetrate the hiding layer into an end portion or a part of the support of the recording material, or vice versa. Examples of the process include a process of cutting and punching, and a process of adhering a pull tab to the concealing layer.

When the heat-sensitive recording material of the present invention is used as a slip or receipt, characters or symbols are put on the support by watermarking, or a form or forgery is prevented after coating the base paper or any layer. It is also possible to print the characters, symbols, advertisements, explanations, and the like. It is also possible to enhance the hiding effect by performing a dark color printing process on the back surface of the support or on the pigment layer.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, "part" and "%" in an example show "weight part" and "weight%", respectively, unless there is particular notice.

Example 1 Formation of Undercoat Layer Fired clay (trade name: Ansilex, manufactured by EMC) 1
00 parts, styrene-butadiene copolymer latex (solid content: 50%) 15 parts, polyvinyl alcohol 10
% Aqueous solution 30 parts and water 200 parts were mixed and stirred to prepare an undercoat layer coating liquid. The coating liquid obtained was applied to one side of 160 g / m ² of high-quality paper (paper thickness 180 μm), and the coating amount after drying was 10 g.
/ M ² and by coating and drying so as to form an undercoat layer.

Preparation of solution A 10 parts of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 20 parts of 1,2-di (3-methylphenoxy) ethane, 5% aqueous solution of methylcellulose 5 And 40 parts of water were pulverized with a sand mill until the average particle size became 0.5 μm.

Preparation of Solution B A composition consisting of 30 parts of 4-4'-isopropylidenediphenyl, 5 parts of a 5% aqueous solution of methylcellulose and 80 parts of water was pulverized with a sand mill until the average particle diameter became 0.8 μm.

Formation of thermosensitive recording layer 75 parts of solution A, 115 parts of solution B, 10% aqueous solution of polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.) 8
A coating solution obtained by mixing and stirring 0 parts of the above was coated and dried on the above-mentioned undercoat layer so that the coating amount after drying was 6 g / m ² , to obtain a thermosensitive recording layer. Next, a super calender treatment was performed to form a heat-sensitive recording layer.

Formation of Intermediate Layer 80 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.) and a 30% aqueous dispersion of zinc stearate (trade name: Hydrin Z-7, manufactured by Chukyo Yushi Co., Ltd.) ) A coating solution obtained by mixing and stirring 100 parts was coated and dried on the thermosensitive recording layer so that the coating amount after drying was 4 g / m ² to form an intermediate layer.

Formation of Concealing Layer 65 parts of bronze powder, 40% 10% aqueous solution of polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.)
A coating liquid obtained by mixing and stirring 0 parts, 40 parts of styrene / butadiene copolymer latex (solid content: 50%), and 100 parts of water with a coating amount of 9 g on the above intermediate layer after drying.
/ M ² and by coating and drying so as to form a hiding layer.

Formation of Pigment Layer 100 parts of calcium carbonate, 40% 10% aqueous solution of polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray Co., Ltd.)
A coating solution for a pigment layer was obtained by mixing and stirring 0 part, 40 parts of a styrene / butadiene copolymer latex (solid content: 50%) and 100 parts of water. This coating liquid was applied and dried on the concealing layer so that the coating amount after drying was 3 g / m ² to form a pigment layer.

Regarding the thermal recording material obtained as described above, a commercially available thermal facsimile machine (Panafax UF-
6, recorded by Matsushita Electric Transport Co., Ltd.), the recorded image was not visible at all, and even if light was obliquely applied to the surface of the recording material, the print mark was completely unreadable. In addition, a cut was made from the back surface of the base paper at the end of the thermal recording material, and the hiding layer was easily peeled off with a finger, triggered by the cut.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the pigment layer was not provided.

Recording was performed on the obtained thermosensitive recording medium in the same manner as in Example 1. The recorded image was not visible at all, but when the light was obliquely applied to the surface of the recording medium, the contents could be read from the print marks. It was The base paper at the end of the heat-sensitive recording material was cut from the back side, and the hiding layer could be easily peeled off with a finger, triggered by the cut.

[0040]

The heat-sensitive recording material of the present invention conceals the recorded contents, and the information cannot be read from the print marks, and the concealing layer is easily peeled off when the contents are disclosed. It was a heat-sensitive recording material. Furthermore, since each layer constituting the thermosensitive recording medium can be provided by the coating step,
It is possible to provide a high-quality recording material at an extremely low cost.

Claims (1)

[Claims] 1. A heat-sensitive recording medium comprising a heat-sensitive recording layer and a concealing layer which is formed by a coating process and which is peelable and makes the recorded information unreadable. A thermosensitive recording medium having a layer.