JPH0958134A - Thermal recording - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a heat-sensitive recording material in which the recording density is not significantly reduced even when immersed in hot water and the background fog is less likely to occur. A heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive on a support, an intermediate layer containing an aqueous resin,
And a thermosensitive recording medium in which an overcoat layer obtained by curing an electron beam-curable compound by irradiating with an electron beam is sequentially provided, and 1,1,1-tris-p-hydroxyphenyl is used as a coloring agent in the thermosensitive recording layer. Ethane or 1- [α-
Methyl-α- (p-hydroxyphenyl) ethyl] -4
A thermosensitive recording medium containing-[α ', α'-bis (p-hydroxyphenyl) ethyl] benzene.

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 utilizing a color-forming reaction between a leuco dye and a color-developing agent, and more particularly to a heat-sensitive recording material excellent in hot water resistance of a recorded image.

[0002]

2. Description of the Related Art Heretofore, a thermosensitive recording medium has been well known in which a coloring image of a leuco dye and a coloring agent is utilized to bring both coloring substances into contact with each other to obtain a recorded image. Since such a thermal recording material is relatively inexpensive, and the recording equipment is compact and its maintenance is relatively easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields such as thermal labels. There is. But,
Such a heat-sensitive recording material is poor in fingerprint resistance, solvent resistance, etc., and, for example, when human skin oils or solvents come into contact with the heat-sensitive recording layer, the recording density is lowered, or undesired color formation called background fog occurs. There is.

In order to improve such a defect, an intermediate layer containing an aqueous resin as a main component is provided on the heat-sensitive recording layer, and then the layer containing an electron beam-curable compound is irradiated with an electron beam. A heat-sensitive recording material provided with an overcoat layer obtained by curing an electron beam-curable compound is disclosed in Japanese Patent Publication No. 1-4.
Although it is described in Japanese Patent No. 2835, there is a problem that the recording density is lowered when it is soaked in hot water, or background fog is generated.
It cannot be used in applications requiring 100 ° C.

Further, in order to enhance the storability of recorded images under high temperature and high humidity conditions, 1- [α-methyl-
α- (p-hydroxyphenyl) ethyl] -4-
A thermosensitive recording medium containing [α ', α'-bis (p-hydroxyphenyl) ethyl] benzene is disclosed in JP-A-2-29.
Although it is described in Japanese Patent No. 381, JP-A-2-202481, and JP-A-2-239977, there is a problem that the recording density is lowered or the background fog occurs when immersed in hot water.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material which is less likely to have a decrease in recording density even when immersed in hot water and has less background fog.

[0006]

The present invention relates to a heat-sensitive recording layer containing a leuco dye, a color former and an adhesive on a support,
An intermediate layer containing an aqueous resin, and a thermosensitive recording medium sequentially provided with an overcoat layer obtained by curing an electron beam-curable compound by irradiating with an electron beam, in the thermosensitive recording layer, 1,1, 1-Tris-p-hydroxyphenylethane or 1- [α-methyl-α- (p-hydroxyphenyl) ethyl] -4- [α ', α'-bis (p
By including -hydroxyphenyl) ethyl] benzene, the above problems were solved and completed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention irradiates a support with a heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive, an intermediate layer containing a water-based resin, and an electron beam-curable compound irradiated with an electron beam. In the thermosensitive recording medium in which the overcoat layers cured by the above are sequentially provided, 1,1,1-tris-p-hydroxyphenylethane or 1- [α-methyl- α- (p-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (p
-Hydroxyphenyl) ethyl] benzene is contained, and the amount used is not particularly limited, but the range is 20 to 60% by weight, preferably 30 to 50% by weight based on the total solid amount of the heat-sensitive recording layer. desirable. Of course, other various known colorants may be used in combination as long as the desired effects of the present invention are not impaired.

Various known leuco dyes can be used, and specific examples thereof include the following. 3,3-bis (p-dimethylaminophenyl) -6
-Dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindole-3)
Yl) phthalide and other triallylmethane dyes, 4,
4'-bis (dimethylaminobenzhydrylbenzyl ether), N-halophenyl-leuco auramine, N-
Diphenylmethane dyes such as 2,4,5-trichlorophenylleuco auramine, benzoyl leuco methylene blue, thiazine dyes such as p-trobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3 -Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-
Spiro dyes such as dinaphthopyran, 3-methyl-naphtho- (6'-methoxybenzo) -spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o- Lactam dyes such as chloroanilino) lactam, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3-
(N-ethyl-N-isoamylamino) -7-chloroanilinofluorane, 3-di (n-butyl) amino-7-
Fluoran dyes such as (o-chloroanilino) fluorane and 3-di (n-butyl) amino-6-methyl-7-anilinofluorane. Among them, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane is particularly preferable because it is excellent in storage stability of recorded images.

The use ratio of the leuco dye and the specific coloring agent is not particularly limited, but generally 1 to 10 parts by weight of the coloring agent, and more preferably 1 part by weight of the leuco dye.
-5 parts by weight.

Further, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3 is used as a preservative improving agent for the recorded image in the thermosensitive recording layer.
-Tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane or at least one selected from 2,2'-methylenebis (4,6-di-tert-butyl) phosphate The storage stability and hot water resistance of the image are further improved. Examples of the salt of 2,2′-methylenebis (4,6-di-tert-butyl) phosphate include potassium, sodium, ammonium, calcium, magnesium and aluminum.

These leuco dyes, color formers and storability improvers have an average particle size of 0.5 with water as a dispersing medium, together or separately by stirring and crushing with an attritor, sand mill or the like. It is finely dispersed until it becomes ~ 3 µm, and then mixed and stirred with an adhesive or the like to prepare a coating liquid for the thermal recording layer.

As the adhesive, a water-dispersible resin such as a styrene / butadiene copolymer emulsion, a vinyl acetate / vinyl chloride / ethylene copolymer emulsion, a methyl methacrylate / butadiene copolymer emulsion, and starches, hydroxyethyl cellulose. , Methyl cellulose, carboxymethyl cellulose, casein, gum arabic, fully saponified (partially saponified) polyvinyl alcohol, silicon modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride Examples thereof include water-soluble resins such as copolymer salts, ethylene / acrylic acid copolymer salts, and styrene / acrylic acid copolymer salts. The amount of the adhesive used is about 25 to 40% by weight of the total solid content of the thermosensitive recording layer. From the viewpoint of water resistance, the adhesive preferably contains a water-dispersible resin in an amount of 60% by weight or more of the total adhesive.

Further, various auxiliary agents can be appropriately added to the coating liquid for the heat-sensitive recording layer, if necessary, and examples thereof include sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate and sodium lauryl alcohol sulfate-sodium salt. Examples thereof include dispersants such as salts, alginates and fatty acid metal salts, ultraviolet absorbers such as benzophenone and triazole, and defoamers, fluorescent dyes, coloring dyes and pigments.

Examples of the pigment include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay, inorganic pigments such as colloidal silica, styrene microballs, and the like. Nylon powder,
Polyethylene powder, urea formalin resin filler,
It is also possible to add organic pigments such as.

The method of applying the heat-sensitive recording layer is not particularly limited, and it can be formed according to a conventionally well-known and conventional technique. For example, bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating. It is formed by a method of coating and drying a coating liquid on a support such as high-quality paper, coated paper, synthetic paper, or film. The coating amount of the coating liquid is also not particularly limited, but it is usually in the range of about ² to ²⁰ g / m ² , preferably about 3 to 15 g / m ² in terms of dry weight.

As the support, a synthetic paper or film which is stable against hot water is preferable, and the coating efficiency can be improved by subjecting the surface of the support to corona discharge, electron beam irradiation or the like.

In the heat-sensitive recording material of the present invention, an intermediate layer coating solution containing an aqueous resin as a main component is applied and dried on the thus obtained heat-sensitive recording layer to form an intermediate layer. Examples of the aqueous resin (water-soluble resin, water-dispersible resin) used include the following. Completely saponified or partially saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, Cellulose derivatives such as carboxymethyl cellulose, casein, gum arabic, oxidized starch, etherified starch, water-soluble resins such as starches such as dialdehyde starch, esterified starch, styrene / butadiene copolymer emulsion, vinyl acetate / vinyl chloride / Water-dispersible resins such as ethylene copolymer emulsion and methacrylate / butadiene copolymer emulsion.

Among these aqueous resins, various modified polyvinyl alcohols, cellulose derivatives and casein are preferable, and acetoacetyl group-modified polyvinyl alcohols and carboxy-modified polyvinyl alcohols are more preferable in terms of heat resistance and barrier properties. The amount of such an aqueous resin used is not particularly limited, but is 10 to 50% by weight, preferably 15 to 50% by weight based on the total solid content in the coating liquid.
About 40% by weight is used.

A pigment may be added to the intermediate layer in order to enhance smoothness. Specific examples of the pigment include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide,
Inorganic pigments such as silicon dioxide, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw starch granules, etc. Is an example.
The amount used is generally 5 to 500 parts by weight, preferably 80 to 35 parts by weight, based on 100 parts by weight of the aqueous resin component.
It is compounded in the range of about 0 parts by weight.

Further, in the coating liquid for the intermediate layer, a curing agent such as glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, etc., for enhancing water resistance. Is better to add. In addition, if necessary, zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax, lubricants such as ester wax, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, sodium salt, Surfactants such as alginates and fatty acid metal salts, various auxiliaries such as benzophenone-based and triazole-based UV absorbers, defoamers, fluorescent dyes, coloring dyes and the like can also be added as appropriate.

The coating liquid for the intermediate layer is generally prepared as an aqueous coating liquid, and if necessary, sufficiently mixed and dispersed by a mixing / stirring machine such as a mixer, an attritor, a ball mill, a roll mill or the like, and then the various known coatings described above. It is coated on the heat-sensitive recording layer by a device. After the application, curing and drying may be performed by irradiating ultraviolet rays or electron beams.

The coating amount of the coating liquid for the intermediate layer is not particularly limited, but if it is less than 0.1 g / m ² , the desired effect of the present invention cannot be sufficiently obtained, and 20 g / m. ²
If it exceeds, the recording sensitivity of the thermosensitive recording medium may be remarkably reduced, so that the dry weight is generally 0.1 to 20 g /
m ² , preferably adjusted in the range of about 0.5 to 10 g / m ² .

If desired, a similar coat layer may be provided on the back side of the thermosensitive recording medium to further improve the shelf life. Further, various well-known techniques in the field of heat-sensitive recording material manufacturing, such as providing an undercoat layer on the support, smoothing the surface with a super calender, or applying an adhesive treatment to the back surface of the recording material to process it into an adhesive label, etc. Can be added if necessary.

On the intermediate layer thus formed, an overcoat layer is provided which is cured by irradiating an electron beam curable compound with an electron beam in order to maintain excellent surface strength in hot water resistance. As the electron beam curable compound that forms the overcoat layer, the following monomers and oligomers or mixtures thereof are used.

(A) Radical-polymerizable monofunctional monomer Acrylic acid, ethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, phenoxyethyl acrylate, triloxy Ethyl acrylate, nonylphenoxyethyl acrylate, tetrahydrofurfuryloxyethyl acrylate, 1,3-dioxolane acrylate, phenoxydiethylene glycol acrylate, benzyl acrylate, butoxyethyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, Carbitol acrylate, isobonyl acrylate Rate and so on.

(B) Radical-polymerizable polyfunctional monomer 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, tripropylene glycol diacrylate, dicyclopentanyl diacrylate, butylene glycol diacrylate, penta Erythritol diacrylate, trimethylolpropane triacrylate, propylene oxide modified trimethylolpropane triacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, caprolactone modified dipentaerythritol hexaacrylate, tetramethylolmethane tetraacrylate, etc. .

(C) Radical Polymerizable Oligomer (Prepolymer) Polyester (poly) acrylate, polyurethane (poly) acrylate, epoxy (poly) acrylate, polyol (poly) acrylate, silicone (poly) acrylate and the like.

Further, 2-chloroethyl vinyl ether,
Cationic polymerizable monomers or oligomers such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, triethylene glycol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether can also be used. When a cationically polymerizable monomer or oligomer is added, a cationic polymerization initiator is required. The cationic polymerization initiator is not particularly limited as long as it is a substance that initiates cationic polymerization with an electron beam, and examples thereof include diazonium salts, iodonium salts, sulfonium salts, metallocene compounds and the like. The addition amount of these cationic polymerization initiators is preferably about 0.1 to 10 parts by weight with respect to 100 parts by weight of the cationically polymerizable monomer or / and oligomer, and if less than 0.1 parts by weight, the polymerization initiation ability is insufficient. If the amount is more than 10 parts by weight, not only the effect is saturated, but also the solubility of the cationic polymerization initiator is deteriorated, which may cause adverse effects such as poor transparency of the coating film.

After curing, a glass transition point (Tg) of the formed resin of 150 ° C. or higher is particularly preferable because it has an excellent effect of preventing sticking (sticking) to the head during high-speed recording. In addition to the electron beam curable compound in the overcoat layer, if necessary, for example, a non-electron beam curable compound, an antifoaming agent, in addition to the electron beam curable compound.
Additives such as a leveling agent, a lubricant, a surfactant, a plasticizer, an ultraviolet absorber, a fluorescent dye, a coloring dye, a pigment, a fluorescent pigment and a coloring pigment can be appropriately added. Examples of the non-electron beam curable compound include acrylic resin, silicone resin, alkyd resin, fluororesin, butyral resin and the like.

The coating solution for forming the overcoat layer is thoroughly mixed with an appropriate mixing stirrer such as a mixer and then coated on the intermediate layer by various known methods. The viscosity can be adjusted by heating the coating liquid. Further, the coating amount is not necessarily limited, but if the coating amount is less than 0.1 g / m ² , the desired effect of the present invention cannot be expected, and if the coating amount exceeds 20 g / m ² , the recording sensitivity of the obtained recording medium decreases. 0.
1 to 20 g / m ² , more preferably 0.3 to 10 g / m
^It is desirable to adjust within the range of about ² . If necessary, the surface of the intermediate layer may be subjected to corona treatment in order to improve the adhesion between the intermediate layer and the overcoat layer.

After coating the coating liquid for forming the overcoat layer on the intermediate layer, the amount of electron beam to be irradiated is preferably in the range of 150 kGy or less. Incidentally, excessive electron beam irradiation exceeding 150 kGy may cause coloring or discoloration of the thermosensitive recording medium. As an electron beam irradiation method, for example, a scanning method, a curtain beam method, a broad beam method, or the like can be adopted, and an accelerating voltage for irradiation is 100 to
About 300 KV is suitable.

Further, the recording density and the unevenness of the recording density can be further improved by subjecting the thermosensitive recording medium provided with the overcoat layer to a smoothing treatment with a super calender or the like.

[0033]

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 the examples, "parts" and "%" represent "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 Preparation of solution A 30 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 5% aqueous solution of methylcellulose 5
Parts and 65 parts of water were pulverized with a sand mill until the average particle size became 2 μm.

Preparation of solution B 1- [α-methyl-α- (p-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (p-hydroxyphenyl) ethyl] benzene (mp. 224 ° C.) 40 Parts, 5 parts of a 5% aqueous solution of methyl cellulose, and 55 parts of water were pulverized with a sand mill until the average particle size became 2 μm.

Solution C Preparation 1,1,3-Tris (2-methyl-4-hydroxy-5)
A composition consisting of 40 parts of cyclohexylphenyl) butane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was ground by a sand mill until the average particle size became 2 μm.

Formation of Thermosensitive Recording Layer Liquid A 50 parts, liquid B 100 parts, liquid C 25 parts, SB latex (trade name: Polylac 750K, manufactured by Mitsui Toatsu Co., Ltd.) 30 parts (as solid content) and water 45. The coating solution for the heat-sensitive recording layer obtained by mixing and stirring the parts is a synthetic paper (trade name: YUPO FP
G, manufactured by Oji Yuka Synthetic Paper Co., Ltd.) was transferred using a gravure roll so that the coating amount after drying was 10 g / m ^2, and then smoothed by a bar provided behind the gravure roll and dried. The thermosensitive recording layer was formed by adjusting the coating amount so that the coating amount was 5 g / m ² .

Formation of Intermediate Layer Acetoacetyl group-modified polyvinyl alcohol (trade name;
Z-200, manufactured by Nippon Gohsei Co., Ltd.) 10% aqueous solution 100
Onto the heat-sensitive recording layer was applied 0 part, kaolin (trade name; UW90, manufactured by Engelhart) 200 parts, 25 parts of a 5% aqueous solution of glyoxal, and 400 parts of water by mixing and stirring. An intermediate layer was formed by coating and drying so that the coating amount after drying was 2 g / m ² .

Formation of Overcoat Layer 100 parts of an electron beam curable compound pentaerythritol triacrylate (trade name; PET-3, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 10 parts of light calcium carbonate were mixed and stirred on the intermediate layer. After applying the coating liquid so as to be 2 g / m ² , an electron curtain type electron beam irradiation device (CB: 1
50 type, manufactured by ESI) at an irradiation dose of 40 kGy to cure the electron beam curable compound to form an overcoat layer, thereby obtaining a thermosensitive recording medium.

Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that in the formation of the thermosensitive recording layer of Example 1, 15 parts of D liquid having the following composition was further added to the coating liquid for the thermosensitive recording layer. Obtained. Preparation of solution D A composition comprising 40 parts of sodium 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, 5 parts of a 5% aqueous solution of methylcellulose and water 55 was added to a sand mill so that the average particle diameter was 2 μm. Crushed until

Example 3 In the preparation of the liquid C of Example 1, 1,1,3-tris (2
As in Example 1, except that 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane was used instead of -methyl-4-hydroxy-5-cyclohexylphenyl) butane. A thermosensitive recording medium was obtained.

Example 4 In the preparation of solution B of Example 1, 1- [α-methyl-α-
(P-Hydroxyphenyl) ethyl] -4- [α ',
Example 1 except that 1,1,1-tris-p-hydroxyphenylethane (mp. 246 ° C.) was used instead of α′-bis (p-hydroxyphenyl) ethyl] benzene.
A thermosensitive recording medium was obtained in the same manner as described above.

Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the liquid C was not used in the formation of the thermosensitive recording layer of Example 1.

Example 6 In the same manner as in Example 1 except that 50 parts of solution B and 75 parts of solution C were used in place of 100 parts of solution B and 20 parts of solution C in the formation of the thermosensitive recording layer of Example 1. A thermosensitive recording medium was obtained.

Example 7 In the preparation of solution A of Example 1, 3-di (n-butyl) amino-6- was used instead of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane. Methyl-7- (o-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that chloroanilino) fluorane was used.

Comparative Example 1 In the preparation of solution B of Example 1, 1- [α-methyl-α-
(P-Hydroxyphenyl) ethyl] -4- [α ',
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4,4′-dihydroxybenzophenone (mp.218 ° C.) was used instead of α′-bis (p-hydroxyphenyl) ethyl] benzene.

Comparative Example 2 In the preparation of solution B of Example 1, 1- [α-methyl-α-
(4'-Hydroxyphenyl) ethyl] -4- [α ',
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4,4′-dihydroxydiphenylsulfone (mp. 248 ° C.) was used instead of α′-bis (p-hydroxyphenyl) ethyl] benzene.

Comparative Example 3 In the preparation of solution B of Example 1, 1- [α-methyl-α-
(4'-Hydroxyphenyl) ethyl] -4- [α ',
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 2,4′-dihydroxydiphenylsulfone (mp.183 ° C.) was used instead of α′-bis (p-hydroxyphenyl) ethyl] benzene.

Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the overcoat layer was not provided on the intermediate layer.

The following quality tests were carried out on each of the heat sensitive recording materials thus obtained, and the results are shown in Table 1. (1) Initial printing color density Each thermal recording medium was evaluated with a thermal recording evaluation machine (TM, manufactured by Okura Electric Co., Ltd.).
-PMD type), applied energy 0.5 mj / d
Recording was performed at OT, and the recording density of the obtained recorded image was measured with a Macbeth densitometer (Macbeth RD-914 type).

(2) Evaluation of Hot Water Resistance The printed thermal recording medium was dipped in hot water of 95 ° C. for 10 seconds and 10 minutes, and the following evaluations were carried out.

Storability of blank paper The density of the blank paper portion after hot water treatment was measured with a Macbeth densitometer (Model RD-914, manufactured by Macbeth Co.).

Print storability The density of the printed part after hot water treatment was measured with a Macbeth densitometer (RD-914 type, manufactured by Macbeth Co.) to calculate the density maintenance rate. Maintenance ratio = (print density after processing) / (initial print color density) x
100

Surface Strength The surface condition after hot water treatment was visually evaluated as follows. ○: There is no problem in the film formation state on the surface. ×: The surface is eluted and the thermal recording layer is exposed.

[0055]

[Table 1]

[0056]

As is clear from the results of Table 1, the thermosensitive recording medium of the present invention showed little reduction in recording density even when immersed in hot water, and had less background fog.

Claims (3)

[Claims] 1. A heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive on a support, an intermediate layer containing an aqueous resin,
And a thermosensitive recording medium in which an overcoat layer obtained by curing an electron beam-curable compound by irradiating with an electron beam is sequentially provided, and 1,1,1-tris-p-hydroxyphenyl is used as a coloring agent in the thermosensitive recording layer. Ethane or 1- [α-
Methyl-α- (p-hydroxyphenyl) ethyl] -4
A thermosensitive recording medium containing-[α ', α'-bis (p-hydroxyphenyl) ethyl] benzene. 2. A heat-sensitive recording layer containing 1, 1 as a storage stability improving agent.
1,3-tris (2-methyl-4-hydroxy-5-te
rt-Butylphenyl) butane, 1,1,3-tris (2
-Methyl-4-hydroxy-5-cyclohexylphenyl) butane or at least one member selected from 2,2'-methylenebis (4,6-di-tert-butyl) phosphate. body. 3. The leuco dye is 3-di (n-butyl) amino-6-methyl-7-anilinofluorane.
Alternatively, the thermosensitive recording medium according to claim 2.