JPH04329180A - Thermosensitive recording medium - Google Patents

Abstract

PURPOSE:To provide a thermosensitive recording medium which has superb durability and suitability for printing, high glossiness and outstanding abrasion resistance and long shelf life, and in addition, which can be used for a prepayment card. CONSTITUTION:The thermosensitive recording medium consists of a thermosensitive recording layer containing a colorless or pale basic dye and a color developer which develops a color through its contact with the dye, and an overcoat layer, formed on a support. The support is made of a base, impregnated with applied ionized radiation-curable resin, which is made waterproof by irradiation with ionized radiation. In addition, the overcoat layer is based mainly on ionized radiation durable resin and cured by irradiation with ionized radiation.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a heat-sensitive recording medium, and more specifically, the present invention relates to a heat-sensitive recording medium that has excellent durability and printability, has strong gloss, has a high printing density, and is also resistant to scratches and has excellent storage stability. More specifically, it relates to a heat-sensitive recording material useful for use in prepaid cards.

0002

[Prior Art] Conventionally, heat-sensitive recording utilizes a color-forming reaction between a color-forming agent and a color-forming agent that develops color when it comes into contact with the color-forming agent, and a color-forming image is obtained by bringing both color-forming substances into contact with heat. The body is well known. Such heat-sensitive 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 calculators, but also in a wide range of fields such as heat-sensitive labels. There is.

However, there are problems with fingerprint resistance and solvent resistance, and for example, when human sebum or solvent comes into contact with the recording layer,
The recording density may decrease or unnecessary coloring called background fog may occur. As a method to eliminate these drawbacks, there is a method of 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. 128347/1983), a method of coating an aqueous emulsion of a resin with film-forming ability and chemical resistance, and a method of coating a water-based emulsion of a resin such as polyvinyl alcohol. Method of applying a water-soluble polymer compound
No. 354) etc. have been proposed.

[0004] However, along with the improvements came new drawbacks.
Furthermore, satisfactory results have not always been obtained. For example, when applying a water-based resin coating on a heat-sensitive recording layer, it is necessary to limit the drying temperature to avoid coloring of the recording layer due to high-temperature drying, which inevitably results in insufficient curing of the resin layer and A phenomenon in which the recording head and the resin layer stick together occurs. Therefore, a method has also 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.

On the other hand, in recent years, there have been attempts to use thermosensitive recording materials as prepaid cards. In that case, the heat-sensitive recording material should be: - strong enough to be used as a card, or strong enough to withstand repeated use with few dents in the support when pressed against nails, protrusions, etc., - visualization, and color. As print quality and sophistication increase, there are demands for excellent printability, (1) high print density, and excellent storage stability such as fingerprint resistance, solvent resistance, and water resistance.

[0006]

SUMMARY OF THE INVENTION The present invention provides a heat-sensitive recording material having excellent strength, printability, and storage stability.

[0007]

[Means for Solving the Problems] In view of the current situation, as a result of intensive research, the present inventors coated and impregnated base paper with ionizing radiation curing resin, irradiated with ionizing radiation of 0.1 to 15 Mrad, and developed a thermosensitive The inventors have discovered that the above-mentioned problems can be solved extremely efficiently by constructing a heat-sensitive recording medium by sequentially providing a recording layer and an overcoat layer containing an ionizing radiation-curable resin, and have completed the present invention. Ta.

The present invention provides a heat-sensitive recording layer comprising, on a support, a heat-sensitive recording layer containing a colorless or light-colored basic dye and a coloring agent capable of forming a color when it comes into contact with the dye, and further provided with an overcoat layer. In the recording medium, the support is paper that has been coated and impregnated with an ionizing radiation-curable resin on a base paper and has been given water resistance by irradiation with ionizing radiation, and the overcoat layer is mainly composed of an ionizing radiation-curable resin and This is a heat-sensitive recording material characterized by having a layer hardened by.

[0009]

[Operation] The base paper used for the support is not particularly limited, and various base papers such as ordinary high-quality paper, medium-quality paper, low-grade paper, and paper containing synthetic pulp can be used. Further, various coated papers such as art paper, coated paper, cast coated paper, etc. in which a pigment coating layer is provided on one or both sides of the base paper can also be used. Paper thickness is 50 to 1000 μm, preferably 18
It is in the range of 0 to 500 μm. Incidentally, if the thickness is less than 50 μm, a product with sufficient strength as a prepaid card cannot be obtained, and if it exceeds 1000 μm, the production cost will increase and there will be problems in correlation with a printing printer.

[0010] The present invention is characterized in that the base paper is coated with and impregnated with an ionizing radiation-curable resin and cured to impart water resistance. Examples of usable ionizing radiation-curable resins include the following prepolymers and monomers. (a) Poly(meth) of aliphatic, alicyclic, araliphatic di- to hexavalent polyhydric alcohol and polyalkylene glycol
Acrylate; (b) Poly(meth)acrylate of polyhydric alcohol in the form of aliphatic, alicyclic, araliphatic, aromatic di- to hexavalent polyhydric alcohol with alkylene oxide added; (c
) poly(meth)acryloyloxyalkyl phosphate; (d) polyester poly(meth)acrylate; (e
) Epoxy poly(meth)acrylate; (f) Polyurethane poly(meth)acrylate; (g) Polyamide poly(meth)acrylate; (h) Polysiloxane poly(meth)acrylate; (i) In the side chain and/or terminal ( Vinyl or diene low polymer having meth)acryloyloxy group; (j) the above (a) to (i)
A prepolymer such as the oligoester (meth)acrylate modified product described above;

In addition, monomers include (a) carboxyl group-containing monomers represented by ethylenically unsaturated mono- or polycarboxylic acids, and carboxylic acid group-containing monomers such as alkali metal salts, ammonium salts, and amine salts thereof; Monomer; (b) An amide group-containing monomer represented by ethylenically unsaturated (meth)acrylamide or alkyl-substituted (meth)acrylamide, vinyl lactams such as N-vinylpyrrolidone; (c) Aliphatic or Sulfonic acid group-containing monomers represented by aromatic vinyl sulfonic acids and their alkali metal salts, ammonium salts, amine salts, etc.; (d) Sulfonic acid group-containing monomers represented by ethylenically unsaturated ethers, etc. hydroxyl group-containing monomer; (e) dimethylaminoethyl (meth)acrylate-
Amino group-containing monomer such as 2-vinylpyridine; (f)
Quaternary ammonium base-containing monomer; (g) alkyl ester of ethylenically unsaturated carboxylic acid; (h) nitrile group-containing monomer such as (meth)acrylonitrile; (i) styrene; (j) vinyl acetate, acetic acid Esters of ethylenically unsaturated alcohols such as (meth)allyl; (k) Mono(meth)acrylates of alkylene oxide addition polymers of compounds containing active hydrogen; (l)
Bifunctional monomer containing an ester group represented by a diester of a polybasic acid and an unsaturated alcohol; (m) 2 consisting of a diester of an alkylene oxide addition polymer of a compound containing active hydrogen and (meth)acrylic acid; Functional monomer; (n) Bisacrylamide such as N,N-methylenebisacrylamide; (o) Difunctional monomer such as divinylbenzene, divinylethylene glycol, divinyl sulfone, divinyl ether, divinyl ketone; (p) Polymer. Ester group-containing polyfunctional monomer represented by polyester of carboxylic acid and unsaturated alcohol; (q
) A polyfunctional monomer consisting of a polyester of an alkylene oxide addition polymer of a compound containing active hydrogen and (meth)acrylic acid; (r) A polyfunctional unsaturated monomer such as trivinylbenzene, etc. . In addition, two or more types of ionizing radiation curing resins as described above may be used in combination.

The above-mentioned resin components are thoroughly mixed using a suitable mixer such as a mixer, and then coated and impregnated onto one or both sides of the base paper using various known methods. The coating amount is appropriately selected depending on the thickness of the base paper, barrier properties, etc., and is adjusted within the range of about 0.1 to 20 g/m2, more preferably about 1 to 10 g/m2 per side. still,
Excessive impregnation of the resin component is not preferable because the impregnated portion of the base paper becomes transparent. Moreover, the viscosity of the ionizing radiation-curable resin to be used may be appropriately adjusted depending on the barrier properties of the target support before coating and impregnation, and the viscosity is not limited. It can also be diluted with an organic solvent such as toluene, xylene, acetic acid, methyl, methyl ethyl ketone, etc., if necessary. Further, the coated/impregnated area can be colored by adding a suitable coloring pigment, fluorescent pigment, coloring dye, fluorescent dye, etc.

[0013] Application methods include gravure coating, offset gravure coating, bar coating, air knife coating, rod blade coating,
Pure blade coating etc. can be used.

The resin component coated and impregnated onto the base paper is cured by irradiation with ionizing radiation. Examples of the ionizing radiation include electron beams, ultraviolet rays, α rays, β rays, γ rays, and X rays. Since alpha rays, beta rays, gamma rays, and X-rays are associated with the problem of danger to the human body, electron beams and ultraviolet rays are preferably used because they are easy to handle and are widely used industrially.

When using an electron beam, the amount of electron beam irradiated is 0.1 to 15 Mrad, more preferably 0.5 to 1 Mrad.
A range of approximately 0 Mrad is desirable. Incidentally, 0.1 Mrad
If it is less than 1, the resin component cannot be sufficiently cured.
Excessive electron beam irradiation exceeding 5 Mrad may cause a decrease in paper strength of the support. 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.

When ultraviolet rays are used, the coating composition contains, for example, thioxanthone, benzoin, benzoin alkyl ether xanthone, dimethylxanthone, benzophenone, anthracene, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, benzyl diphenyl sulfide, anthraquinone, It is necessary to blend a sensitizer such as 1-chloroanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, N,N'-tetraethyl-4,4'-diaminobenzophenone, 1,1-dichloroacetophenone, etc. It is added in an amount of about 0.2 to 10% by weight, preferably about 0.5 to 5% by weight, based on the resin component. In addition, as a light source for ultraviolet irradiation, an ultraviolet lamp, a xenon lamp, a tengusten lamp, etc. are used, and the light source is 5000 to 8000 μW/cm.
UV rays having a certain intensity are preferably irradiated.

The above-mentioned electron beam irradiation method has higher productivity than the ultraviolet irradiation method, and reduces odor and odor due to the addition of sensitizers.
It is preferably used because there is no problem of coloring and it is easy to form a uniform crosslinked structure.

[0018] In the present invention, a heat-sensitive recording layer is provided on the water-resistant base paper thus formed, but there are no particular limitations on the combination of the coloring agent and the coloring agent contained in this 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. Among these, it is preferable to apply a combination of a basic dye and an acidic substance because a recording medium with extremely excellent recording properties can be obtained.

Various types of colorless to light-colored basic dyes are known, including 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, 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-dimethylamino Phthalide, 3,3-bis(2
-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(
Triallylmethane dyes such as 1-methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydryl benzyl ether, N
-halophenyl-leucoauramine, N-2,4,5-
Diphenylmethane dyes such as trichlorophenyl 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-dinaphthopyran , 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo)spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino ) lactam, rhodamine (
Lactam dyes such as o-chloroanilino)lactam, 3
-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 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
-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)fluorane, 3-diethylamino-6- Methyl-7-phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran, 3-(N-ethyl-N-iso-amylamino)-6-methyl-7
-F-nylaminofluorane, 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)fluorane, 3-dibutylamino-7-(o -chlorophenylamino)fluoran, 3-pyrrolidino-6-methyl-7-
Fluoran dyes such as p-butylphenylaminofluorane, etc.

Various types of inorganic or organic acidic substances are also known that develop color upon contact with basic colorless dyes. For example, activated clay, acid clay, attapulgite, bentonite, colloidal silica, aluminum silicate, and other inorganic Acidic substances, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-
Octylcatechol, 2,2'-dihydroxydiphenol, 2,2'-methylenebis(4-methyl-6-te
rt-butylphenol), 4,4'-isopropylidene bis(2-tert-butylphenol), 4,4'
-sec-butylidenediphenol, 4-phenylphenol, 4,4'-isopropylidenediphenol (bisphenol A), 2,2'-methylenebis(4-chlorophenol), hydroquinone, 4,4'-cyclohexylidenediphenol , benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolac type phenolic resin,
Phenolic compounds such as phenol polymers, 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, 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
Aromatic carboxylic acids such as -butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids, etc. Zinc, magnesium, aluminum, calcium, titanium,
Examples include organic acidic substances such as salts with polyvalent metals such as manganese, tin, and nickel.

[0021] In the heat-sensitive recording material of the present invention, the ratio of the coloring agent and the coloring agent used in the recording layer is appropriately selected depending on the type of coloring agent or coloring agent used. When using a basic dye and an acidic substance, the amount is generally 1 to 50 parts by weight, preferably 1 part by weight, per 1 part by weight of the basic dye.
~10 parts by weight of acidic material is used. In preparing coating solutions containing these substances, water is generally used as the dispersion medium;
The coloring agent and the coloring agent are dispersed together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand mill.
Prepared as a coating liquid.

[0022] The coating liquid contains adhesives such as starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride. Acid copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, styrene-butadiene copolymer emulsion, etc. account for 10 to 40% by weight of total solids.
, preferably about 15 to 30% by weight.

Furthermore, various auxiliary agents can be added to the coating solution, such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginate, fatty acid metal salt, etc. Examples include dispersants, benzophenone-based and triazole-based ultraviolet absorbers, other antifoaming agents, fluorescent dyes, and colored dyes.

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

The coating method for the recording layer coating liquid is not particularly limited, and it can be formed according to conventionally known techniques, such as bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating. It is formed by a method of applying and drying a coating liquid, etc. The amount of coating liquid to be applied is also not particularly limited, but it is usually 2 to 12 g/m2 in terms of dry weight, preferably 3 g/m2.
The range is approximately 10 g/m2.

[0026] In the heat-sensitive recording material of the present invention, an overcoat layer containing an ionizing radiation-curable resin as a main component is provided on the recording layer thus formed. The prepolymers, monomers, etc. exemplified for making paper waterproof can also be used. In addition, in the resin component, calcium carbonate,
Inorganic pigments such as barium carbonate, zinc carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, and colloidal silica, and these inorganic pigments as organic Organic materials such as acid surface-treated pigments, styrene microballs, nylon powder, polyethylene powder, urea-formalin resin powder, cellulose acetate powder, polymethyl methacrylate powder, fluororesin powder, epoxy resin powder, benzoguanamine resin powder, raw starch granules, etc. Additives such as pigments, non-electron beam curable resins, antifoaming agents, leveling agents, lubricants, surfactants, plasticizers, and ultraviolet absorbers can be added as appropriate.

Furthermore, by adjusting the types and blending ratios of various additives, it is possible to form heat-sensitive recording materials having a wide range of surface properties from matte to highly glossy. Also,
Examples of non-electron beam curable resins include acrylic resins, silicone resins, alkyd resins, fluororesins, butyral resins, and the like. The resin components as described above are thoroughly mixed using a suitable mixing agitator such as a mixer, and then applied by various known methods, but the viscosity can be adjusted by heating the resin component if necessary.

The resin layer thus formed on the recording layer is cured by irradiation with ionizing radiation, but when using an electron beam, the amount of electron beam irradiated is 0.1 to 15 Mrad,
More preferably, the range is about 0.5 to 10 Mrad. Incidentally, if it is less than 0.1 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 heat-sensitive recording medium, and furthermore, the paper strength of the support may deteriorate. It may cause a decline. Note that the electron beam irradiation method and the case where ultraviolet rays are used are as described above.

Furthermore, in the heat-sensitive recording material of the present invention, when an intermediate layer is provided between the heat-sensitive recording layer and the overcoat layer, storage properties such as oil resistance and water resistance are improved, gloss is improved, and the overcoat layer This is particularly preferable since unnecessary coloring of the heat-sensitive recording layer can be prevented when the heat-sensitive recording layer is provided.

Water-soluble resin and/or water-soluble resin used in this intermediate layer
Examples of water-dispersible resins include the following substances. Fully saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol into which an acetoacetyl group has been introduced by reacting polyvinyl alcohol with diketene, polyvinyl alcohol and fumaric acid, phthalic anhydride, trimellitic anhydride, itaconic anhydride, etc. reaction products with carboxylic acids or esterified products of these reactants, and co-existence of vinyl acetate with 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 product of a polymer, sulfonic acid-modified polyvinyl alcohol obtained as a saponified product of a copolymer of vinyl acetate and an olefin sulfonic acid or its salt such as ethylene sulfonic acid or allyl sulfonic acid, and vinyl acetate. and ethylene, propylene,
Olefin-modified polyvinyl alcohol obtained by saponifying copolymers with olefins such as isobutylene, α-octene, α-dotecene, α-octadodecene, and copolymers of vinyl acetate with nitriles such as acrylonitrile and methacrylonitrile. Nitrile-modified polyvinyl alcohol obtained as a saponified product of vinyl acetate and acrylamide,
Amide-modified polyvinyl alcohol obtained by saponifying a copolymer with an amide such as methacrylamide, polyvinyl alcohol such as pyrrolidone-modified polyvinyl alcohol obtained by saponifying a copolymer of vinyl acetate and N-vinylpyrrolidone, methylcellulose, ethylcellulose,
Cellulose derivatives such as hydroxyethyl cellulose and carboxymethyl cellulose, casein, gum arabic,
Starches such as oxidized starch, etherified 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 and/or water-dispersible resins, various modified polyvinyl alcohols, cellulose derivatives, and casein are preferred, and acetoacetylated polyvinyl alcohol and carboxy-modified polyvinyl alcohol are particularly preferred. Pigments can be added to the intermediate layer to increase smoothness. Specific examples of pigments include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, colloidal silica, and styrene microballs. , nylon powder, polyethylene powder,
Examples include urea-formalin resin fillers and organic pigments such as raw starch granules. The amount used is generally 5 to 500 parts by weight, preferably 80 to 350 parts by weight, based on 100 parts by weight of the resin component.

[0032] Further, in the coating liquid forming the intermediate layer, curing agents such as glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, etc. are added 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 may be added. Various auxiliary agents such as surfactants such as alcohol sulfate ester sodium salts, alginates, fatty acid metal salts, ultraviolet absorbers such as benzophenone type and triazole type, antifoaming agents, fluorescent dyes, and coloring dyes may be added as appropriate. You can also do it.

[0033] 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 mixer, attritor, ball mill, roll mill, or other mixing/stirring machine as necessary, various known methods are used. It is applied onto the heat-sensitive recording layer using a coating device. After coating, it can also be cured and dried by irradiation 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.

The coating amount of the coating liquid forming the intermediate layer is not particularly limited, but if it is less than 0.1 g/m2, the desired effect of the present invention cannot be sufficiently obtained;
If it exceeds 0 g/m2, the recording sensitivity of the heat-sensitive recording medium may be significantly reduced, so it is generally 0.1 to 0.1 in terms of dry weight.
It is adjusted within a range of about 20 g/m2, preferably from 0.5 to 10 g/m2.

Since a recording medium with high recording density and gloss can be obtained by further increasing the smoothness of the surface of the intermediate layer, smoothing treatment is performed using, for example, a super calender to reduce the Bekk smoothness of the surface of the intermediate layer for 50 seconds. It is desirable to adjust the time to 300 seconds or more, more preferably 300 seconds or more. The heat-sensitive recording material of the present invention having the overcoat layer thus obtained can be further smoothed using a super calender or the like to improve recording density and recording density unevenness.

[0036]

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

Example 1 [Formation of support] Oligoester acrylate (manufactured by Toagosei Kagaku Kogyo Co., Ltd.,
Aronix M-8030) 50 parts, monofunctional acrylate (manufactured by Toagosei Chemical Industry Co., Ltd., Aronix M-101)
Electron beam curable resin adjusted to 50 parts was coated and impregnated onto one side of high-quality paper with a paper thickness of 180 μm using a gravure coater so that the dry coating amount was 2 g/m2. The resin component was cured and a support was obtained.

[Preparation of Solution A] A composition consisting of 10 parts of 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 5 parts of a 5% methylcellulose aqueous solution, and 30 parts of water was milled in a sand mill until the average particle diameter was 3 μm. Shattered.

[Preparation of Solution B] 20 parts of benzyl 4-hydroxybenzoate, 5 parts of 5% methylcellulose aqueous solution, 55 parts of water
The composition consisting of 100% was ground in a sand mill until the average particle size was 3 μm.

[Formation of recording layer] 45 parts of liquid A, 80 parts of liquid B, 50 parts of 20% oxidized starch aqueous solution, and 10 parts of water were mixed and stirred on the opposite side of the support from the resin-coated side. The prepared coating liquid was coated with a bar coater so that the coated amount after drying was 5 g/m 2 and dried to obtain a heat-sensitive recording material.

[Formation of intermediate layer] An 8% aqueous solution 1 of acetoacetylated polyvinyl alcohol (trade name: Z-200, manufactured by Nippon Gosei Kagaku Co., Ltd.) was placed on the recording layer of the obtained thermosensitive recording material.
000 parts, calcium carbonate (product name: Softon 1800
, manufactured by Bihoku Funka Co., Ltd.) and 100 parts of water was applied using a bar coater so that the coating amount after drying was 4 g/m2, dried, and then smoothed using a super calender. A heat-sensitive recording material having an intermediate layer having a Bekk smoothness of 500 seconds was obtained.

[Formation of overcoat layer] A prepolymer mixture of polyester polyacrylate and polyurethane polyacrylate (trade name: 78E204) is formed on the intermediate layer.
, manufactured by Mobil Oil Co., Ltd.) using a bar coater to a dry coating amount of 3 g/m2, and then coated with an electron curtain type electron beam irradiation device (CB: 150 type, manufactured by ESI Co., Ltd.) at a dry coating weight of 3 g/m2.
．． The resin component was cured by treatment with an irradiation dose of 5 Mrad to obtain a thermosensitive recording material having an overcoat layer.

Example 2 In forming the recording layer, the resin-coated surface of the support was coated with
A thermosensitive recording material was obtained in the same manner as in Example 1 except that a recording layer was provided.

Example 3 In forming the resin layer, electron beam curing resin was applied to paper with a thickness of 180 μm.
Dry coating amount on both sides of m high-quality paper is 2g/m2 per side.
Examples except that after coating with a gravure coater so that A thermosensitive recording material was obtained in the same manner as in 1.

Example 4 A heat-sensitive recording layer was obtained in the same manner as in Example 1 except that no intermediate layer was provided on the recording layer.

Comparative Example 1 A heat-sensitive recording layer was obtained in the same manner as in Example 1, except that high-quality paper with a paper thickness of 180 μm was used as the support and the recording layer was directly provided.

Comparative Example 2 A heat-sensitive recording layer was obtained in the same manner as in Comparative Example 1 except that no overcoat layer was provided.

The following quality tests were conducted on the six types of heat-sensitive recording materials thus obtained, and the results are shown in Table 1.

(1) Initial printing color density The thermosensitive recording material was tested using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.: Condition 120).
℃, 2 kg/cm2, 10 seconds), and the maximum color density of the recorded image was measured using a Macbeth densitometer (
Measured using Macbeth Co., Ltd., Model RD-100R).

(2) Plasticizer resistance test A vinyl chloride wrap film (manufactured by Mitsui Toatsu Chemical Co., Ltd.) was wrapped three times around a polypropylene pipe (40 mm diameter pipe), and printed colors were printed on it using a thermal gradient tester. The heated heat-sensitive recording material was sandwiched so that the color-forming side of the print was facing outward, and then a vinyl chloride wrap film was wrapped five times over it, and the print density after 72 hours was measured using a Macbeth densitometer. (The larger the number, the better the plasticity resistance.)

(3) Oil resistance test 0.0% salad oil was applied to the recording layer surface of the colored heat-sensitive recording material.
5 cc of the solution was dropped and spread uniformly over the surface, and the print density after being left for 24 hours was measured using a Macbeth densitometer. (The larger the number, the better the oil resistance.)

(4) Water-resistant printing After the colored heat-sensitive recording material was left in water for 15 hours, the print density was measured using a Macbeth densitometer. (The higher the number, the better the water resistance.)

(5) Glossiness The glossiness of the surface of the thermosensitive recording material was measured using a variable angle photometer (MURAKAM).
I COLOR RAB. made by gloss meter
GM-3D) at an incident angle of 60 degrees. (The higher the number, the higher the gloss.)

(6) Heat-sensitive recording using No. 400 sandpaper instead of white cotton cloth using a friction tester for rubbing dye hardness (manufactured by Toyo Seiki Co., Ltd., condition contact load 200 g, number of reciprocations 10 times) The surface of the recording layer was rubbed and the degree of color development was visually judged. ○: Almost no color develops △: Slightly develops color ×: Color develops

(7) Pencil Hardness A line was drawn on the surface of the recording layer of the thermosensitive recording material using a pencil with a lead strength of H at the same pressure, and the degree of indentation of the support was visually judged. ◎: Slightly dented ○: Dented △: Significantly dented

(8) Cut the paper-based thermosensitive recording material into pieces 5.5 cm wide and 30 cm long, fix one end of the test piece so that it is horizontal, and find out how many cm below the horizontal line the tip of the other side is. was measured. (The smaller the number, the stronger the paper stiffness.)

0
(9) UV Printing Suitability After transferring UV ink to the surface opposite to the recording surface using an RI printer (manufactured by Mei Seisakusho), the UV ink was cured using an ultraviolet irradiator, and the printing results were visually evaluated. Visual judgment criteria ◎: Good ○: Fairly good ×: Poor

[0058]

[Table 1]

[0059]

Effects of the Invention As is clear from the results in Table 1, the present invention provides a prepaid card that has excellent durability and printability, has strong gloss, has a high printing density, and is also resistant to scratches and has excellent storage stability. It was a heat-sensitive recording medium for use.

Claims (5)

[Claims] 1. A heat-sensitive recording material comprising a support, a heat-sensitive recording layer containing a colorless or light-colored basic dye and a coloring agent capable of changing color when it comes into contact with the dye, and an overcoat layer. In the above, the support is a base paper coated and impregnated with an ionizing radiation-curable resin to give water resistance by irradiation with ionizing radiation, and the overcoat layer is mainly composed of an ionizing radiation-curable resin and is cured by irradiation with ionizing radiation. A heat-sensitive recording material characterized by having a layer of 2. The heat-sensitive recording material according to claim 1, wherein the base paper has a paper thickness of 50 to 1000 μm. 3. The heat-sensitive recording material according to claim 1, wherein the base paper has a paper thickness of 100 to 500 μm. 4. The heat-sensitive recording material according to claim 1, further comprising an intermediate layer containing a water-soluble resin and/or a water-dispersible resin between the heat-sensitive recording layer and the overcoat layer. 5. The heat-sensitive recording material according to claim 1, which is a heat-sensitive recording material for a prepaid card.