JPS63214475A - Thermal recording body - Google Patents

Abstract

PURPOSE:To enhance strength and the preservability of a recording image, by providing a specific intermediate layer and a specific overcoat layer composed of an acrylate-containing curable resin on a recording layer. CONSTITUTION:An intermediate layer based on a water-soluble or water- dispersible resin is provided on a recording layer and an overcoat layer composed of an electron beam curable resin is provided on the intermediate layer and monofunctional or polyfunctional (meth)acrylate having a polar group is contained in the electron beam curable resin. As the water-soluble or water- dispersible resin used in the intermediate layer, acetoacetylated polyvinyl alcohol and carboxy modified polvinyl alcohol are especially pref. By this method, the surface strength of the overcoat layer is improved extremely efficiently and a thermal recording body excellent in the preservability of a recording image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium that has excellent surface strength and excellent storage stability and recording properties of recorded images.

``Prior art'' Conventionally, heat-sensitive technology utilizes a coloring reaction between a coloring agent and a coloring agent that develops color when it comes into contact with the coloring agent, and brings both colored substances into contact with each other using heat to obtain a colored image. Recording bodies are well known. Such recording media are relatively inexpensive, the recording equipment is compact, and maintenance is relatively easy, so they are used not only as recording media for facsimiles and various computers, but also in a wide range of fields such as thermal labels. . However, it has problems in fingerprint resistance and solvent resistance, and has the disadvantage that, for example, when the recording layer comes into contact with human sebum or a solvent, the recording density decreases and unnecessary color development called background fog occurs.

As a method to overcome these drawbacks, a method is proposed in which an aqueous emulsion of a resin having film-forming ability and chemical resistance is coated on the heat-sensitive recording layer (Japanese Patent Laid-Open No. 54-12834).
7) A method of applying a water-soluble polymer compound such as polyvinyl alcohol (Utility Model Application Publication No. 56-125354) has been proposed. However, with the improvements come new drawbacks.
Furthermore, the current situation is that satisfactory results are not necessarily obtained.

For example, when applying an overcoat such as a water-based resin on a heat-sensitive recording layer, it is necessary to limit the drying temperature to avoid color development of the recording layer due to high-temperature drying, which inevitably results in insufficient curing of the resin layer. This causes a phenomenon in which the recording head and the resin layer stick together during recording. For this reason, a method has been proposed in which a resin component that can be cured by electron beams is applied onto the heat-sensitive recording layer and the resin component is cured by electron beams, but this method is still not sufficient in terms of the storage stability of recorded images. A resin layer that is cured by a line may cause the heat-sensitive recording layer to develop color immediately after coating, or may cause adverse effects such as fading of the recorded image.

"Problems to be Solved by the Invention" As a result of intensive research into solving these drawbacks, the present inventors have developed an intermediate layer of water-based resin on the heat-sensitive recording layer, which can then be cured with an electron beam. It was discovered that by overcoating, the storage stability of the recorded image was improved without unnecessary coloring of the recording layer, and a heat-sensitive recording material with excellent recording properties could be obtained. The application was filed as

However, it has become clear that there is still room for improvement in the adhesion between the aqueous resin intermediate layer and the electron beam cured resin overcoat layer. That is, it has been found that when an adhesive tape or the like is applied to the overcoat layer and then peeled off, the overcoat layer peels off. Therefore, as a result of further intensive research into improving this phenomenon, the present inventors found that when a monofunctional or polyfunctional (meth)acrylate having a polar group is contained in the electron beam curable resin forming the overcoat layer, The inventors have completed the present invention by discovering that the surface strength of the coating layer can be improved very efficiently and a heat-sensitive recording material can be obtained which has excellent recorded image storage stability and recording properties.

"Means for Solving the Problems" The present invention provides a heat-sensitive recording layer containing a coloring agent and a coloring agent that develops color upon contact with the coloring agent, and a water-soluble resin or a water-dispersible resin as a main component. In a heat-sensitive recording material, an intermediate layer is provided, and an overcoat layer of an electron beam curable resin is provided on the intermediate layer, and a monofunctional or polyfunctional (meth)acrylate having a polar group in the electron beam curable resin This is a heat-sensitive recording material characterized by containing.

"Function" In the present invention, there are no particular limitations on the combination of the coloring agent and the coloring agent contained in the heat-sensitive recording layer.
Any combination can be used as long as the two come into contact with each other due to heat and cause a coloring reaction.For example, combinations of colorless or light-colored basic dyes and inorganic or organic acidic substances, ferric stearate, etc. can be used. Examples include combinations of higher fatty acid metal salts and phenols such as gallic acid.

However, since the specific overcoat layer of the present invention provided on the recording layer has extremely excellent recording properties especially when applied to a combination of a basic dye and an acidic substance, it is particularly preferable to use a colorless or light-colored base dye. Various types of dyes are known, and the following are exemplified.

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-
Triallylmethane such as bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylvirol-3-yl)-6-dimethylaminophthalide, etc. dyes, 4.4
'-Bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2,
4,5-) Diphenylmethane dyes such as IJ70 lophenyl leuco auramine, thiazine dyes such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue, 3-methyl-spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3-phenyl-
Spiro dyes such as spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine ( Lactam dyes such as p-nitroanilino)lactam and rhodamine(0-chloroanilino)lactam, 3-dimethylamino-7-medoxyfluorane, 3-diethylamino-6-medoxyfluorane, 3-
Diethylamino-7-medoxyfluorane, 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-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-)luidino)-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-ethyl-N-1so-amylamino)-6
-Methyl-7-tunylaminofluorane, 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-xylidinofluoran Oran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-dibutylamino-7-(o-chlorophenylamino)fluoran, 3-pyrrolidino-6-
Fluoran dyes such as methyl-7-p-butylphenylaminofluorane, etc.

In addition, various types of inorganic or organic acidic compounds that change color when they come into contact with basic colorless dyes are known, including inorganic acidic substances such as activated clay, acid clay, attapulgite, bentonite, colloidal silica, and aluminum silicate; 4
-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2゜2'-dihydroxydiphenol, 2.2
'-Methylenebis(4-methyl-5-tart-isobutylphenol), 4,4'-isopropylidenebis(
2terL-butylphenol), 4.4'-5ec
-butylidene diphenol, 4-phenylphenol,
4.4'-isopropylidene diphenol (bisphenol A), 2.2'-methylenebis(4-chlorophenol), hydroquinone, 4°4'-cyclohexylidene diphenol, benzyl 4-hydroxybenzoate, 4
-Phenolic compounds such as dimethyl hydroxyphthalate, hydroquinone monobenzyl ether, novolac type phenolic resin, phenol polymer, benzoic acid, p-t
ert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec~butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,
5-dimethyl-4-hydroxybenzoic acid, salicylic acid,
3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butyl Aromatic carboxylic acids such as salicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, Examples include organic acidic substances such as salts with polyvalent metals such as magnesium, aluminum, calcium, titanium, manganese, tin, and nickel.

In the heat-sensitive recording material of the present invention, the ratio of the color former and color former in the recording layer is appropriately selected depending on the type of color former and color former used, and is not particularly limited. For example, when using a basic colorless dye and an acidic substance,
In general, 1 to 50 parts by weight, preferably 1 to 10 parts by weight, of acidic substances are used per part by weight of basic colorless dye.

To prepare a coating solution containing these substances, the coloring agent and the coloring agent are generally dispersed together or separately using water as a dispersion medium using a stirring/pulverizing machine such as a ball mill, attritor, or sand grinder, and then applied. Prepared as a liquid.

This coating liquid contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, and adhesives.
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, etc. accounts for 10 to 40% by weight of the total solids, preferably 15% by weight.
It is used in an amount of about 30% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid.
For example, dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginates, fatty acid metal salts, ultraviolet absorbers such as benzophenone and triazole, and other antifoaming agents. , fluorescent dyes, colored dyes, and the like.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, halaffin wax, and ester wax, kaolin,
Inorganic pigments such as clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, stearamide, methylene bisamide stearate, oleic acid amide, palmitic acid amide,
Sensitizers such as matcha oleic acid amide and coconut fatty acid amide can also be added.

In the heat-sensitive recording material of the present invention, the method of forming the recording layer is not particularly limited, and can be formed according to conventionally well-known and commonly used techniques, such as bar coating, air knife coating, rod blade coating, pure coating, etc. It is formed by a method of applying and drying a coating liquid using frede coating, silato dwell coating, etc. There are no particular limitations on the amount of coating liquid applied, but it is usually 2 to 1 on dry weight.
2 g/rrf, preferably in the range of about 3 to 10 g/-.

In the heat-sensitive recording material of the present invention, an intermediate layer is first provided on the heat-sensitive recording layer thus obtained. Examples of water-soluble resins or water-dispersible resins used in the intermediate layer include the following substances. Ru.

Completely saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol into which an acetoacetyl group has been introduced by reacting polyvinyl alcohol with diketene, etc., polyvinyl alcohol and fumaric acid, phthalic anhydride, trimellitic anhydride, itaconic anhydride, etc. reaction products with polyhydric carboxylic acids or esterified products of these reactions, as well as vinyl acetate and ethylenically unsaturated carboxylic acids such as maleic acid, fumaric acid, itaconic acid, crotonic acid, acrylic acid, and methacrylic acid. carboxy-modified polyvinyl alcohol obtained as a saponified copolymer of sulfonic acid-modified polyvinyl alcohol obtained as a saponified copolymer of vinyl acetate and an olefin sulfonic acid or its salt such as ethylene sulfonic acid or allyl sulfonic acid. , vinyl acetate and ethylene, propylene, isobutylene, α-octene, α-tothycene, α
- Olefin-modified polyvinyl alcohol obtained by saponifying a copolymer with olefins such as octadodecene,
Nitrile-modified polyvinyl alcohol obtained as a saponified copolymer of vinyl acetate and a nitrile such as acrylonitrile or methacrylate; Amide obtained by saponifying a copolymer of vinyl acetate and an amide such as acrylamide or methacrylamide. Modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol obtained by saponifying a copolymer of vinyl acetate and N-vinylpyrrolidone, cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, casein, gum arabic, oxidized starch, ether Starches such as modified starch, dialdehyde starch, and esterified starch, styrene-butadiene copolymer emulsion,
Vinyl acetate-vinyl chloride-ethylene copolymer emulsion, methacrylate-butadiene copolymer emulsion, etc.

Among these water-soluble resins or water-dispersible resins, m-modified polyvinyl alcohol, cellulose derivatives, and casein are preferred, and acetoacetylated polyvinyl alcohol and carboxy-modified polyvinyl alcohol are particularly preferred.

The amount of water-soluble or water-dispersible resin used is not particularly limited, but it is used in an amount of about 10 to 50% by weight, preferably about 15 to 40% by weight, based on the total solid content in the coating liquid.

Further, a pigment can be added to the intermediate layer in order to increase the smoothness. Specific examples of pigments include calcium carbonate,
Inorganic pigments such as zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, fired clay, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea - Examples include formalin resin filler, organic pigments such as raw starch granules, etc.

The amount used is generally 5 to 500 parts by weight, preferably 80 to 350 parts by weight, per 100 parts by weight of the resin component.
It is preferable that the amount is about 1 part by weight.

Furthermore, curing agents such as glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, etc. are added to the coating solution forming the intermediate layer as necessary. If necessary, lubricants such as zinc stearate, calcium stearate, stearamide, polyethylene wax, carnauba wax, paraffin wax, and ester wax, sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, and lauryl alcohol sulfuric acid may be added. Various auxiliary agents such as surfactants such as ester/sodium salts, alginates, fatty acid metal salts, ultraviolet absorbers such as benzophenone type and triazole type, antifoaming agents, fluorescent dyes, and coloring dyes can also be added as appropriate. .

The coating liquid for forming the intermediate layer is generally prepared as an aqueous coating liquid, and after being thoroughly mixed and dispersed using a mixing/stirring machine such as a mixer, attritor, ball mill, or roll mill as necessary, it is processed using various known coating devices. is coated onto the heat-sensitive recording layer. After coating, it can also be dried by irradiating it with ultraviolet rays or electron beams.

When using a curing agent together, the curing agent can be applied not only in the coating liquid that forms the intermediate layer, but also separately from the coating liquid that forms the intermediate layer. There is no need to worry about life expectancy and there is an advantage of being able to select a strong hardening agent.

Further, if necessary, it is possible to further improve the storage stability by providing a similar coating layer on the back side of the support made of paper, plastic film, synthetic paper, etc. Furthermore, in order to prevent the occurrence of curling, the support may be coated with a non-electron beam cured resin or an electron beam cured resin, conductive treatment may be applied to improve the running properties of the recording medium, or an undercoat layer may be provided 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.

The coating amount of the coating liquid forming the intermediate layer is not particularly limited, but if it is less than 0.1 g/nf, the desired effect of the present invention cannot be sufficiently obtained, and if it is less than 20 g/nf.
If it exceeds d, the recording sensitivity of the heat-sensitive recording medium may be significantly reduced, so it is generally 0.1 to 20 g/dry weight.
rd, preferably adjusted within a range of about 0.5 to 10 g/M.

In the heat-sensitive recording material of the present invention, an overcoat layer of an electron beam curable resin containing a monofunctional or polyfunctional (meth)acrylate having a polar group is provided on the intermediate layer thus formed. , as polar groups, for example, hydroxyl group, carboxyl group, amino group, alkylamino group,
Examples include quaternary ammonium groups, sulfone groups, phosphoric acid groups, etc., with hydroxyl groups, carboxyl groups, amino groups, and alkylamino groups being particularly preferred, among which monofunctional or polyfunctional (meth)acrylates having hydroxyl groups are most preferably used. .

Examples of monofunctional or polyfunctional (meth)acrylates having a hydroxyl group include 2-hydroxyethyl acrylate,
2-hydroxypropyl acrylate, pentaerythritol triacrylate, 2-hydroxy-3-phenoxypropylacrylate, bis(acryloxethyl)hydroxyethyl isocyanurate, N-methylolacrylamide, bifunctional acrylates represented by the following general formula, etc. can be mentioned.

-X-A O■ X: -0-+ CI! ! ±10-n=2
~6-0-+C! 1) 40 +-, In = 1~3
-0-1-C,1)60-)-fin = 1 to 3 As the monofunctional or polyfunctional (meth)acrylate having a carboxyl group, for example, 2-hydroxyethyl acrylate and maleic acid, fumaric acid, itaconic acid, Examples include ester compounds with polybasic acids such as succinic acid, glutaric acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, and trimellitic acid.

Examples of monofunctional or polyfunctional (meth)acrylates having an amino group or an alkylamino group include N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, and N.

Examples include N-diethylaminoethyl methacrylate.

Monofunctional or polyfunctional (meta) with quaternary ammonium group
Examples of acrylate include methyl sulfate-N, N, N
-trimethyl-N-methacryloxyethylammonium and the like.

Examples of the monofunctional or polyfunctional (meth)acrylate having a sulfonic group include sodium methacryloxyethyl sulfonate.

Examples of the monofunctional or polyfunctional (meth)acrylate having a phosphoric acid group include methacryloxyethyl phosphonate, dimethacryloxyethyl phosphonate, and the like.

The content of monofunctional or polyfunctional (meth)acrylate containing a polar group in the electron beam curable resin is desirably adjusted in the range of about 1 to 100% by weight, preferably 10 to 9% by weight.
It is adjusted within a range of about 0% by weight.

The other electron beam curable resins are not particularly limited, and for example, the following prepolymers and monomers that are cured by electron beams may be appropriately selected and used.

(a) Polyester poly (meth)acrylate;
(b) Epoxy poly (meth)acrylate; (C
) Polyurethane poly(meth)acrylate: (d
) Polyamide poly (meth)acrylate; (13
) Polysiloxane poly(meth)acrylate: (
fl Vinyl or diene low polymer having (meth)acryloyl group in side chain and/or terminal;
Prepolymers such as oligoester (meth)acrylate modified products described in al to (f); and the like.

(al) An amide group-containing monomer represented by ethylenically unsaturated (meth)acrylamide or alkyl-substituted (meth)acrylamide, vinyl lactams such as N-vinylpyrrolidone; (b) Alkyl of ethylenically unsaturated carboxylic acid Ester; (C) Monomer containing a nitrile group such as (meth)acrylonitrile; (d) Styrene; (81 Ester of ethylenically unsaturated alcohol such as vinyl acetate and (meth)allyl acetate; (fl Contains active hydrogen) Mono(meth)acrylates of alkylene oxide addition polymers of compounds; (g
l An ester group-containing bifunctional monomer represented by a diester of a polybasic acid and an unsaturated alcohol; (hl A bifunctional monomer consisting of an alkylene oxide addition polymer of a compound containing active hydrogen and a diester of (meth)acrylic acid) Functional monomer; (i) Bisacrylamide such as N,N-methylenebisacrylamide; (J) Bifunctional monomer such as divinylbenzene, divinylethylene glycol, divinyl sulfone, divinyl ether, divinyl ketone; (kl polycarbonate) Ester group-containing polyfunctional monomers represented by polyesters of acids and unsaturated alcohols: (1) Polyfunctional monomers consisting of polyesters of alkylene oxide addition polymers of active hydrogen-containing compounds and (meth)acrylic acid. (-polyfunctional unsaturated monomers such as trivinylbenzene.

etc. monomers.

The amount of the resin to be cured by electron beams is not necessarily limited, but if it is less than 0.1 g/d, the desired effect of the present invention cannot be expected, and if it is less than 0.1 g/d, the desired effect of the present invention cannot be expected. If the coating amount exceeds 0.1~20g10f, there is a risk that the recording sensitivity of the resulting recording medium will decrease significantly.
, more preferably within a range of about 0.3 to 10 g/rrr.

In addition to (meth)acrylates having polar groups as described above, the resin component that is cured by electron beams may contain, if necessary, electron beam-curable resins other than those mentioned above, non-electron beam-curable resins, inorganic pigments, and coloring. Additives such as pigments, fluorescent pigments, fluorescent dyes, other organic dyes, antifoaming agents, leveling agents, lubricants, surfactants, plasticizers, and ultraviolet absorbers can be added as appropriate. By adjusting the type and blending ratio, it is possible to form a heat-sensitive recording material having a wide range of surface properties from high gloss to matte.

The resin components as described above are thoroughly mixed using a suitable mixer such as a mixer, and then coated on the intermediate layer by various known methods. If necessary, the resin components are heated to adjust the viscosity. You can also do

The resin layer formed on the intermediate layer is cured by electron beam irradiation, and the amount of electron beam irradiated is 0.1 to 15 Mr.
ad, more preferably in the range of about 0.5 to 10 Mrad; If it is less than I Mrad, the resin component cannot be sufficiently cured, and if it exceeds 15 Mrad, excessive electron beam irradiation may cause color development or discoloration of the thermosensitive recording material.

As the electron beam irradiation method, for example, a scanning method, a curtain beam method, a broad beam method, etc. can be adopted, and an appropriate acceleration voltage for irradiation is about 100 to 300 KV.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Further, unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight, respectively.

Example 1 ■ Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-phenylaminofluorane 10 parts Methylcellulose 5% aqueous solution 5 parts Water
30 parts of this composition was ground with a sand grinder until the average particle size was 3 μm.

■ B? Prepared at night Benzyl 4-hydroxybenzoate 20 parts Methylcellulose 5% aqueous solution 5 parts Water
55 parts of this composition was ground with a sand grinder until the average particle size was 3 μm.

(2) Formation of Recording Layer 45 parts of liquid A, 80 parts of liquid B, 50 parts of a 20% oxidized starch aqueous solution, and 10 parts of water were mixed and stirred to prepare a coating liquid.

The obtained coating liquid was coated and dried on a 50 g/rf base paper so that the coated amount after drying was 6 g/m to obtain a heat-sensitive recording material.

■ Formation of intermediate layer On the recording layer of the obtained heat-sensitive recording material, a coating liquid having the following composition was applied and dried so that the coating amount after drying was 4t/rd, and then smoothed with a super calender. A thermosensitive recording material having an intermediate layer was prepared.

Polyvinyl alcohol (product name: PVA-1)
7. 1000 parts of an 8% aqueous solution of calcium carbonate (product name: Softon 1800, manufactured by Bihoku Funka Co., Ltd.) (manufactured by Kuraray Co., Ltd.)
100 parts water
100 parts ■ Formation of overcoat layer On the intermediate layer, 80 parts of polyester acrylate prepolymer (product name: M-8030, manufactured by Toagosei Co., Ltd.) and 20 parts of pentaerythritol triacrylate are applied in a dry coating amount of 5.
g/n (3) using an electron curtain type electron beam irradiation device (CB: 150 type, manufactured by ESI).
The resin component was cured by treatment with an irradiation dose of Mrad to obtain a heat-sensitive recording material having an overcoat layer of electron beam-cured resin.

Example 2 An overcoat layer of an electron beam curable resin was prepared in the same manner as in Example 1, except that 2-hydroxy-3-phenoxyprobyl acrylate was used instead of pentaerythritol triacrylate as the resin forming the overcoat layer. A thermosensitive recording material having the following properties was obtained.

Example 3 A thermosensitive recording material having an overcoat layer of an electron beam curable resin was obtained in the same manner as in Example 1 except that acryloxyethyl phthalate was used instead of pentaerythritol triacrylate as the resin forming the overcoat layer. Ta.

Example 4 A thermosensitive product having an overcoat layer of an electron beam curable resin was prepared in the same manner as in Example 1 except that N,N-dimethylaminoethyl acrylate was used instead of pentaerythritol triacrylate as the resin forming the overcoat layer. Obtained a record.

Comparative Example 1 In Example 1, polyester acrylate prepolymer (trade name:
A thermosensitive recording material having an overcoat layer of electron beam curing resin was obtained in the same manner except that 100 parts of M-8030 (manufactured by Toagosei Co., Ltd.) were used and pentaerythritol triacrylate was not used.

Comparative Example 2 A thermosensitive recording material was obtained in the same manner as in Example 1 except that no overcoat layer was provided on the intermediate layer.

The six types of heat-sensitive recording materials thus obtained were tested in a thermal gradient tester (
Manufactured by Toyo Seiki Co., Ltd. under 9 conditions: 120°C, 2kir/cd.

The initial printed color density was measured using a Macbeth densitometer (manufactured by Macbeth Co., Ltd., model RD-100R), and the results are shown in Table 1.

Furthermore, the color density and surface strength of the overcoat layer were evaluated after the plasticizer resistance and oil resistance evaluation tests shown below, and the results are shown in Table 1.

In addition, the glossiness of the surface of the heat-sensitive recording material before printing color was measured and is also listed in Table 1.

[Plasticizer resistance evaluation test]

Wrap vinyl chloride wrap film (manufactured by Mitsui Toatsu ■) three times around a polypropylene vibe (quadruple mllφ tube).
A heat-sensitive recording material that has been colored with a thermal gradient tester is placed on top of it so that the colored side of the print is facing out, and then a vinyl chloride wrap film is wrapped five times over it, and the print density is measured after 72 hours. did.

(The larger the value, the better the plasticizer resistance.) [Oil resistance evaluation test] 0°05c of salad oil was applied to the recording layer surface of the colored heat-sensitive recording material.
c was dropped and spread uniformly over the surface, and after being left for 24 hours, the print density was measured.

(The larger the value, the better the oil resistance.) [Measurement of gloss] Measurement was performed using a variable angle photometer at an incident angle of 60 degrees.

(The larger the number, the higher the gloss.) [Surface strength evaluation test] After adhering cellophane tape (manufactured by NITTO) to the surface of the overcoat layer, it was peeled off and the peeling state of the surface layer was visually judged.

01 No abnormality in the surface layer.

×: There is peeling of the surface layer.

Table 1 "Effects" As is clear from the results in Table 1, the heat-sensitive recording material of the present invention has a high recording density, excellent surface strength and surface gloss, and has extremely good print storage stability. Met.

Claims (4)

[Claims] (1) An intermediate layer mainly composed of a water-soluble resin or a water-dispersible resin is provided on a heat-sensitive recording layer containing a color former and a color former that develops a color when in contact with the color former, and further the intermediate layer A thermosensitive recording material having an overcoat layer of an electron beam curable resin thereon, characterized in that the electron beam curable resin contains a monofunctional or polyfunctional (meth)acrylate having a polar group. record body. (2) The thermosensitive recording material according to claim (1), wherein the polar group is a hydroxyl group. (3) Claim No. 1 in which the polar group is a carboxyl group
) The heat-sensitive recording medium described in item 2. (4) The thermosensitive recording material according to claim (1), wherein the polar group is an amino group or an alkylamino group.