JP2584472B2 - Thermal recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having a high recording density, excellent gloss, and excellent recording running properties and writing properties.

"Prior art" Conventionally, a thermosensitive recording in which a color-forming image is obtained by contacting both color-forming substances by heat using a color-forming reaction between a color-forming agent and a color-forming agent that forms a color in contact with the color-forming agent. The body is well known. Such a thermosensitive recording medium is relatively inexpensive, and its recording equipment is compact and its maintenance is relatively easy. Therefore, it is used not only as a recording medium for facsimile and various computers but also in a wide field such as a thermosensitive label. I have. However, there are difficulties in fingerprint resistance and solvent resistance. For example, when human sebum or a solvent comes into contact with the recording layer, there is a defect that the recording density is lowered or unnecessary color formation called background fog is caused.

As a method of solving such a defect, a method of applying an aqueous emulsion of a resin having a film forming ability and chemical resistance on a heat-sensitive recording layer (Japanese Patent Laid-Open No. 54-128347).
A method of applying a water-soluble polymer compound such as polyvinyl alcohol (Japanese Utility Model Application Laid-Open No. 56-125354) has been proposed. However, at present, new improvements are accompanied by improvements and satisfactory results have not always been obtained.

For example, when applying an aqueous resin coating on the heat-sensitive recording layer, it is necessary to limit the drying temperature in order to avoid coloring of the recording layer due to high-temperature drying, and inevitably the curing of the resin layer becomes insufficient, and during recording, A phenomenon such as adhesion between the recording head and the resin layer occurs. For this reason, a method has been proposed in which a resin component curable by an electron beam is applied onto the heat-sensitive recording layer, and the resin component is cured by an electron beam. The resin layer that cures in the above step may cause the heat-sensitive recording layer to develop color immediately after coating, or may have a bad effect such as fading of the recorded image.

The present inventors have conducted intensive studies on the solution of such a defect, and as a result, provided an aqueous resin intermediate layer on the heat-sensitive recording layer, and then provided an overcoat layer containing a resin curable by electron beam, the recording, It has been found that a heat-sensitive recording medium having improved print storability without fogging of the layer, having a wide range of surface characteristics and excellent recording characteristics can be obtained, and was previously filed as Japanese Patent Application Laid-Open No. 62-279980.

On the other hand, in recent years, various printers such as video printers that provide photographic high-quality images have been used,
Thermal recording media for printout are also required to have better recording density and gradation. Therefore, the development of thermosensitive recording materials that use plastic film or synthetic paper as a support and has excellent gradation is being promoted. Attempts have been made to provide an overcoat layer such as an aqueous resin on the layer. However, when a recording medium provided with an overcoat layer made of an aqueous resin is recorded by a video printer, particularly under high humidity conditions, the overcoat layer tends to stick to a recording head or a paper feed guide, and it is apparent that a paper jam occurs. It became. Further, the recording density itself is not always in a satisfactory state.

The present inventors have conducted intensive studies on such a problem, and as a result, formed a heat-sensitive recording layer on a plastic film or synthetic paper, provided an aqueous resin intermediate layer on the heat-sensitive recording layer, and then obtained a resin that can be cured with an electron beam. It has been found that by providing an overcoat layer containing the same, it is possible to obtain an excellent recording medium having a high recording density, excellent gradation and preservability, and no sticking to the recording head even under high humidity conditions. Filed as No. 61-246530.

However, even in the recording medium having the excellent characteristics as described above, particularly when recording is performed with a video printer of a type that prints at a high speed, even if an electron beam curable resin is used as a resin for forming the overcoat layer, It has been found that sticking to the recording head occurs.

"Problems to be Solved by the Invention" In view of the present situation, the present inventors have conducted intensive studies on the above-mentioned problems particularly occurring in a thermosensitive recording medium having an overcoat layer of an electron beam-curable resin, and as a result, the present inventors have found that When a specific amount of an organic or inorganic pigment having an average particle size of 15 μm or less is added, a sticking phenomenon to a recording head does not occur even in high-speed recording, and a recording medium having extremely excellent recording running properties and excellent writing properties. Was obtained, and the present invention was completed.

“Means for Solving the Problems” The present invention provides a heat-sensitive recording layer containing a color former and a color former that comes into contact with the color former on a plastic film or synthetic paper. In a thermosensitive recording medium, an intermediate layer having a water-soluble resin or a water-dispersible resin as a main component is provided, and an overcoat layer containing a resin curable by an electron beam is further provided on the intermediate layer. Smoothness is 3000 seconds or more, 0.5 to 1 organic or inorganic pigment having an average particle size of 15 μm or less in the overcoat layer.
It is a thermosensitive recording medium characterized by containing 5% by weight.

"Function" In the present invention, the combination of the color former and the color former contained in the heat-sensitive recording layer is not particularly limited, and any combination may be used as long as the two are brought into contact by heat to cause a color reaction. Examples thereof include a combination of a colorless or light-colored basic dye and an inorganic or organic acidic substance, and a combination of a higher fatty acid metal salt such as ferric stearate and a phenol such as gallic acid. .

However, since the specific overcoat layer of the present invention provided on the recording layer has extremely excellent recording characteristics, particularly when applied to a combination of a basic dye and an acidic substance,
Particularly preferred. Various types of colorless or light-colored basic dyes are known, and examples thereof include the following.

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-bis (9-ethylcarbazol-3-yl) -6
Dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -6-dimethylaminophthalide,
Triallylmethane dyes such as 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydryl benzyl ether, Diphenylmethane dyes such as N-halophenyl-leuco auramine and N-2,4,5-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-
Spiro dyes such as benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, Lactam dyes such as rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-
Methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluoran, 3- (N-ethyl-p-toluidino) -7-methylfluoran, 3-diethylamino-7-N-acetyl-N-methylaminofluoran, 3-diethylamino-
7-N-methylaminofluoran, 3-diethyylamino-7-dibenzylaminofluoran, 3-diethylamino-7-N-methyl-N-benzylaminofluoran, 3-diethylamino-7-N-chloroethyl -N-
Methylaminofluoran, 3-diethylamino-7-N
-Diethylaminofluoran, 3- (N-ethyl-p-
Toluidino) -6-methyl-7-phenylaminofluoran, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluoran, 3-diethylamino-6-methyl-7-phenyl Aminofluoran,
3-diethylamino-7- (2-carbomethoxy-phenylamino) fluoran, 3- (N-ethyl-N-iso
-Amylamino) -6-methyl-7-phenylaminofluoran, 6- (N-cyclohexyl-N-methylamino) -6-methyl-7-phenylaminofluoran, 3
-Pyrrolidino-6-methyl-7-phenylaminofluoran, 3-piperidino-6-methyl-7-phenylaminofluoran, 3-diethylamino-6-methyl-7-
Xylidinofluoran, 3-diethylamino-7- (o
-Chlorophenylamino) fluoran, 3-dibutylamino-7- (o-chlorophenylamino) fluoran,
Fluoran dyes such as 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluoran and the like.

In addition, various inorganic or organic acidic substances which are colored upon contact with a basic colorless dye are also known, for example, inorganic acidic substances such as activated clay, acidic clay, attapulgite, bentonite, colloidal silica, and aluminum silicate.
-Tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol,
2,2'-dihydroxydiphenol, 2,2'-methylenebis (4-methyl-6-tert-isobutylphenol),
4,4'-isopropylidenebis (2-tert-butylphenol), 4,4'-sec-butylidenediphenol, 4-
Phenylphenol, 4,4'-isopropylidene diphenol (bisphenol A), 2,2'-methylenebis (4-chlorophenol), hydroquinone, 4,4'-
Cyclohexylidene diphenol, benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolak phenolic resin, phenolic compounds such as phenolic polymers, benzoic acid, p-tert-butylbenzoic acid, trichlor Benzoic 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-butylsalicylic acid, 3-phenyl-5- (Α, α-dimethylbenzyl) salicylic acid, 3,5-α-methyl Aromatic carboxylic acids such as benzylsalicylic acid, and organic acids such as salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel. Is exemplified.

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

In preparing a coating solution containing these substances, water is generally used as a dispersion medium, and the color former and the color former are dispersed together or separately by a stirring / pulverizer such as a ball mill, an attritor, or a sand grinder, and the coating is performed. It is prepared as a liquid.

In such a coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer as a contact agent Salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, etc., is 10 to 40% by weight of the total solid, preferably 15 to 40% by weight.
About 30% by weight is used.

Further, various auxiliaries can be added to the coating liquid, for example, dispersion of sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, alginic acid, fatty acid metal salt, etc. Agents, benzophenone-based and triazole-based ultraviolet absorbers, other antifoaming agents, fluorescent dyes, coloring dyes and the like.

If necessary, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica, activated clay And sensitizers such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, perfume oleic acid amide, and coconut fatty acid amide.

In the heat-sensitive recording medium of the present invention, a plastic film or synthetic paper is used as a support. A plastic film or synthetic paper is bonded to a coated paper or a high-quality paper with an adhesive, and further, a plastic is laminated on paper. The resulting sheet is also included in the plastic film or synthetic paper of the present invention.

As a plastic film, for example, polyethylene,
Films such as polyester, polyvinyl chloride, polystyrene, nylon and the like are exemplified. As the synthetic paper, for example, synthetic paper produced by a film method or a fiber method is exemplified. The film method includes an internal paper method in which a synthetic resin, a filler and an additive are melt-kneaded and then extruded to form a film, a surface coating method in which a pigment coating layer is provided, a surface treatment method, and the like. Synthetic paper includes synthetic pulp paper and spunbond paper. Among such supports, a plastic film and a film-processed synthetic paper are most preferably used because the remarkable effect of the present invention is remarkable and more excellent recording characteristics are provided.

The method for applying the recording layer is not particularly limited, and the recording layer can be formed according to a conventionally known technique. For example, a coating solution is applied by bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating, or the like. Is formed by a method of applying and drying. When a plastic film is used as the support, the coating efficiency can be increased by subjecting the surface to a treatment such as corona discharge or electron beam irradiation. Although there is no particular limitation on the coating amount of the coating liquid, usually dry weight 2~12g / m ^2, preferably in the range of about 3 to 10 g / m ^2.

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

Fully or partially saponified polyvinyl alcohol,
An acetoacetylated polyvinyl alcohol having an acetoacetyl group introduced by reacting polyvinyl alcohol with diketene, a reaction product of polyvinyl alcohol with a polycarboxylic acid such as fumaric acid, phthalic anhydride, trimellitic anhydride, itaconic anhydride or It is obtained as an esterified product of these reactants, or a saponified product of a copolymer of vinyl acetate and an ethylenically unsaturated carboxylic acid such as maleic acid, fumaric acid, itaconic acid, crotonic acid, acrylic acid, or methacrylic acid. Carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol obtained as a saponified product of a copolymer of vinyl acetate and olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid or a salt thereof, vinyl acetate and ethylene, propylene, isobutylene , Α- octene, α- Dotesen, α
-An olefin-modified polyvinyl alcohol obtained by saponifying a copolymer with an olefin such as octadodecene,
Nitrile-modified polyvinyl alcohol obtained as a saponified product of a copolymer of vinyl acetate and acrylonitrile, a nitrile such as methacrylonitrile, obtained by saponifying a copolymer of vinyl acetate and amides such as acrylamide and methacrylamide. Amide-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol obtained by saponifying a copolymer of vinyl acetate and N-vinylpyrrolidone, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, cellulose derivatives such as carboxymethyl cellulose, casein, gum arabic, oxidized starch,
Starches such as etherified starch, dialdehyde starch, and esterified starch, styrene-butadiene copolymer emulsion, vinyl acetate-vinyl chloride-ethylene copolymer emulsion, methacrylate-butadiene copolymer emulsion, and the like.

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

A pigment can be added to the intermediate layer to increase the smoothness. Specific examples of pigments include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide,
Inorganic pigments such as aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, colloidal silica, etc., organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw starch granules, etc. Is exemplified. In addition,
The amount is generally in the range of 5 to 500 parts by weight, preferably about 80 to 350 parts by weight, based on 100 parts by weight of the resin component.

Further, a curing agent such as glyoxal, methylol melamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, etc. may be added to the coating solution for forming the intermediate layer, if necessary. Lubricant such as zinc stearate, calcium stearate, stearic acid amide, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate as required・ Sodium salt, alginate, surfactant such as fatty acid metal salt, benzophenone,
UV absorbers such as triazoles, defoamers, fluorescent dyes,
Various auxiliaries such as coloring dyes can be added as appropriate.

The coating liquid for forming the intermediate layer is generally adjusted as an aqueous coating liquid, and if necessary, a mixer, an attritor,
After being sufficiently mixed by a mixing / stirring machine such as a ball mill and a roll mill, the mixture is applied on the heat-sensitive recording layer by various known coating apparatuses. After the application, curing and drying may be performed by irradiating ultraviolet rays or electron beams.

When a curing agent is used in combination, the curing agent can be applied not only in the coating liquid for forming the intermediate layer but also separately from the coating liquid for forming the intermediate layer. There is an advantage that there is no need to worry about life and a strong curing agent can be selected.

Further, if necessary, a similar coating layer may be provided on the back side of the thermosensitive recording medium to further improve the storability. Further, various known techniques in the field of heat-sensitive recording materials can be added as necessary, such as providing an undercoat layer on the support, applying a pressure-sensitive adhesive treatment to the back surface of the recording material, and processing the pressure-sensitive adhesive label.

The coating amount of the coating liquid forming the intermediate layer is not particularly limited, can not be obtained sufficiently the desired curing of the present invention is less than 0.1 g / m ^2, also a 20 g / m ² Kosu When because it may significantly reduce the recording sensitivity of the heat sensitive recording material, generally 0.1 to 20 g / m ² in dry weight, preferably 0.5 to 10 g / m ²
It is adjusted within a range.

An overcoat layer containing an electron beam-curable resin and a specific amount of an organic or inorganic pigment is provided on the intermediate layer thus formed, but by increasing the smoothness of the surface of the intermediate layer, a high recording density and gloss can be obtained. To obtain a recording medium having the intermediate layer, the surface Bekk smoothness of the intermediate layer is adjusted to 3000 seconds or more by performing a smoothing treatment using, for example, a super calender.

Examples of the electron beam curable resin forming the overcoat layer include the following prepolymers and monomers.

(A) aliphatic, alicyclic, and aromatic aliphatic poly (meth) acrylates of polyhydric alcohols having 2 to 6 valences and polyalkylene glycols; (b) aliphatic, alicyclic, araliphatic, and aromatic 2 Poly (meth) acrylate of polyhydric alcohol obtained by adding alkyl oxide to polyhydric alcohol having 6 to 6 valences; (c) poly (meth) acryloyloxyalkyl phosphate ester; (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) side chain and / or Vinyl- or diene-based low polymer having a (meth) acryloyloxy group at a terminal; (j) description of the above (a) to (i) And a prepolymer such as a modified product of an oligoester (meth) acrylate.

Examples of the monomer include: (a) a carboxyl group-containing monomer represented by an ethylenically unsaturated mono- or polycarboxylic acid and a carboxylic acid group-containing monomer such as an alkali metal salt, an ammonium salt, and an amine salt thereof. (B) an amide group-containing monomer represented by vinyl lactams such as ethylenically unsaturated (meth) acrylcamide or alkyl-substituted (meth) acrylamide, N-vinylpyrrolidone; (c) aliphatic or aromatic vinyl; Sulfonic acid group-containing monomers represented by sulfonic acids, and sulfonic acid group-containing monomers thereof such as alkali metal salts, ammonium salts and amine salts; (d) hydroxyl group-containing monomers represented by ethylenically unsaturated ethers Monomer; (e) dimethylaminoethyl (meth) acrylate-
(F) quaternary ammonium base-containing monomer; (g) alkyl ester of ethylenically unsaturated carboxylic acid; (h) nitrile group of (meth) acrylonitrile acid (J) esters of ethylenically unsaturated alcohols such as vinyl acetate and (meth) allyl acetate; (k) mono (meth) of an alkylene oxide addition polymer of a compound containing active hydrogen (1) an ester group-containing bifunctional monomer represented by a diester of a polybasic acid and an unsaturated alcohol; (m) an alkylene oxide addition polymer of a compound containing active hydrogen and (meth) acrylic acid (N) bisacrylamide such as N, N-methylenebisacrylamide; (o) divinylben (P) a bifunctional monomer such as divinylethylene glycol, divinyl sulfone, divinyl ether, divinyl ketone, etc .; (p) an ester group-containing polyfunctional monomer represented by a polyester of a polycarboxylic acid and an unsaturated alcohol; A) a polyfunctional monomer comprising a polyester of an alkylene oxide addition polymer of a compound containing active hydrogen and (meth) acrylic acid; and (r) a polyfunctional unsaturated monomer such as trivinylbenzene.

And the like.

Note that an electron beam-curable resin having a glass transition point (Tg) of 150 ° C. or higher after curing is particularly preferable because of its excellent effect of preventing sticking (sticking) to a head in high-speed recording. And polyfunctional monomers such as pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, tris (acryloxyethyl) isocyanurate, polysiloxane polyacrylate, and tetrafunctional or higher oligoester acrylate.

In the thermosensitive recording medium of the present invention, an organic or inorganic pigment having a specific average particle diameter is contained in a specific amount in an overcoat layer containing an electron beam-curable resin as a main component as described above. If the average particle diameter is too large, the effect of improving the anti-sticking property is obtained, but the recording image quality is reduced. Therefore, a pigment having an average particle diameter of 15 μm or less, more preferably 5 μm or less is selectively used. . If the content of the pigment is less than 0.1% by weight, the effect of improving the sticking resistance cannot be sufficiently obtained.
If the ratio exceeds the above range, the recording density and glossiness of the obtained recording medium will decrease, so the content is adjusted to 0.5 to 15% by weight.

Hitherto, a method of improving the sticking resistance and the like by incorporating a pigment in the overcoat layer of a heat-sensitive recording material has been proposed (Japanese Patent Application Laid-Open Nos. 54-128349 and 59-67081). This is also a method of incorporating a large amount of pigment in the overcoat layer, and the method of adding a small amount of pigment such as 25% by weight or less to the overcoat layer containing an electron beam-curable resin as a main component as in the present invention is not at all. unknown. Moreover, by adding a small amount of pigment such as 25% by weight or less, more preferably 15% by weight or less to the overcoat layer containing an electron beam-curable resin as a main component as described above, It is possible to obtain a heat-sensitive recording material having excellent storability, recording characteristics, writing properties, etc. without impairing the surface glossiness, and particularly to obtain this outstanding effect even by adding a very small amount of pigment such as 5% by weight or less. Was completely unexpected.

Thus, in the present invention, as the pigment to be contained in the electron beam-curable resin layer, for example, calcium carbonate, barium carbonate, zinc carbonate, zinc oxide, aluminum oxide,
Inorganic pigments such as titanium dioxide, silicon dioxide, barium hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, colloidal silica, and pigments obtained by surface-treating these inorganic pigments with organic acids, styrene microballs, nylon Powder, polyethylene powder, urea
Formalin resin powder, cellulose acetate powder, polymethyl methacrylate powder, fluororesin powder,
Examples thereof include epoxy resin powder, benzoguanamine resin powder, and organic pigments such as raw starch granules.

These pigments are generally dispersed and mixed in a resin component which is hardened by an electron beam by a suitable mixing stirrer such as a high-speed mixer. However, the pigment particles are converted into primary particles by a device that applies high shearing force such as a kneader or a roll mill. When dispersed, the effect of the present invention is further exhibited. In the resin component, in addition to the above-described prepolymer, monomer, and pigment, if necessary, for example, a non-electron beam curable resin, an antifoaming agent,
Additives such as a leveling agent, a lubricant, a surfactant, a plasticizer, an ultraviolet absorber, a fluorescent dye, a coloring dye, a fluorescent dye, and a coloring pigment can be appropriately added.

By adjusting the type and blending ratio of various additives, it is possible to form a thermosensitive recording medium having a wide range of surface properties from matte to high gloss, but as the non-electron beam curable resin, for example, acrylic resin, silicone resin, Alkyd resin, fluorine resin, butyral resin and the like can be mentioned.

The resin component as described above is sufficiently mixed by a suitable mixing stirrer such as a mixer and then applied on the intermediate layer by various known methods. Adjustments can also be made. Further, connexion to the coating weight is not necessarily limited, can not be the desired effect expected of the present invention is less than 0.1 g / m ^2, lowering the recording sensitivity of the recording material is obtained by a coating amount as exceeding 20 g / m ² Therefore, it is desirable to adjust the amount in the range of about 0.1 to ²⁰ g / m ² , more preferably about 0.3 to 10 g / m ² .

The resin layer formed on the intermediate layer is cured by irradiation with an electron beam, and the amount of the irradiated electron beam is preferably in the range of 0.1 to 15 Mrad, more preferably about 0.5 to 10 Mrad. By the way
If it is less than 0.1 Mrad, the resin component cannot be sufficiently cured, and excessive electron beam irradiation exceeding 15 Mrad may cause coloring or discoloration of the thermosensitive recording medium.

In addition, as a method of irradiating an electron beam, for example, a scanning method, a curtain beam method, a broad beam method, or the like can be adopted, and an acceleration voltage for irradiation is suitably about 100 to 300 KV. In addition, the recording density and the recording density unevenness can be further improved by subjecting the recording body provided with the overcoat layer to a smoothing treatment using a super calender or the like.

"Examples" Examples are shown below to explain the present invention more specifically, but of course the present invention is not limited thereto. Parts and% in the examples are parts by weight and% by weight, respectively, unless otherwise specified.
Is shown.

Example 1 Liquid A preparation 3- (N-cyclohexyl-N-methylamino) -6
Methyl-7-phenylaminofluoran 10 parts Methylcellulose 5% aqueous solution 5 parts Water 30 parts This composition was sand-ground with an average particle size of 3 μm.
m.

Solution B Preparation 4-benzyl benzyl 4-hydroxybenzoate 20 parts Methyl cellulose 5% aqueous solution 5 parts Water 55 parts The average particle diameter of this composition was 3 μm with a sand grinder.
m.

Formation of recording layer 45 parts of solution A, 80 parts of solution B, 50 parts of 20% oxidized starch aqueous solution, water 10
Parts were mixed and stirred to obtain a coating liquid. The obtained coating solution was applied on a synthetic paper of 80 g / m ² (trade name; YUPO, manufactured by Oji Yuka Co., Ltd.) so that the coating amount after drying was 6 g / m ² and dried to obtain a thermosensitive recording medium. .

Formation of Intermediate Layer On the recording layer of the obtained thermosensitive recording medium, a coating liquid having the following composition was applied so that the coating amount after drying was 4 g / m ² , dried, and then smoothed with a super calender. Then, a thermosensitive recording medium having an intermediate layer having a Beck smoothness of 5000 seconds was prepared.

Polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray)
8% aqueous solution of 1000 parts Calcium carbonate (trade name: Softon 1800, manufactured by Bihoku Powder Co., Ltd.) 100 parts Water 100 parts Formation of overcoat layer Prepolymer mixture of polyester polyacrylate and polyurethane polyacrylate on intermediate layer (after curing) With a Tg of 100 ° C or less, trade name: 78E204, manufactured by Mobil Sekiyu KK
00 parts and calcium carbonate having an average particle size of 0.2 μm (trade name: PP
-2, made by Yonesho Lime Industry Co., Ltd.)
/ m ² and treated with an electron curtain type electron beam irradiator (CB: 150 type, manufactured by ESI) at an irradiation dose of 3 Mrad to cure the resin component and obtain a thermosensitive recording material having an overcoat layer. Obtained.

Example 2 An overcoat layer was prepared in the same manner as in Example 1 except that calcium carbonate was replaced by fatty acid surface-treated calcium carbonate having an average particle diameter of 0.15 μm (trade name: Calflex P, manufactured by Yonesho Lime Industry Co., Ltd.). Was obtained.

Example 3 In Example 1, kaolin (trade name: Ultra White 90, trade name: 0.4 μm) was used instead of calcium carbonate.
A thermosensitive recording medium having an overcoat layer was obtained in the same manner except that EBC was used.

Example 4 A heat-sensitive device having an over-auto layer in the same manner as in Example 1 except that titanium dioxide having an average particle size of 0.2 μm (trade name: FA-55-W, manufactured by Furukawa Mining Co., Ltd.) was used instead of calcium carbonate. A recording was obtained.

Example 5 A thermosensitive element having an overcoat layer in the same manner as in Example 1 except that calcium sulfoaluminate (trade name: Satin White, manufactured by Shiraishi Industry Co., Ltd.) having an average particle size of 0.4 μm was used instead of calcium carbonate. A recording was obtained.

Example 6 A heat-sensitive recording material having an overcoat layer was obtained in the same manner as in Example 1, except that talc (trade name: KC clay, manufactured by Chuo Kaolin Co., Ltd.) was used instead of calcium carbonate. .

Example 7 In Example 1, a fluororesin filler having an average particle diameter of 7 μm (trade name: Lubron L-) was used in place of calcium carbonate.
5, manufactured by Daikin Co., Ltd.) to obtain a thermosensitive recording medium having an overcoat layer.

Example 8 A thermosensitive recording material having an overcoat layer in the same manner as in Example 1 except that polystyrene fine powder having an average particle diameter of 0.3 μm (trade name: VONCOAT, manufactured by Dainippon Ink) was used in place of calcium carbonate. I got

Example 9 A thermosensitive recording medium having an overcoat layer in the same manner as in Example 1, except that an epoxy resin fine powder having an average particle diameter of 10 μm (trade name: EP-13, manufactured by Toray Industries Inc.) was used instead of calcium carbonate. I got

Example 10 In Example 1, trimethylolpropane triacrylate (Tg after curing was 25%) was used in place of the prepolymer mixture of polyester polyacrylate and polyurethane polyacrylate as the resin for forming the overcoat layer.
A thermosensitive recording medium having an overcoat layer was obtained in the same manner except that 0 ° C., trade name: M-309, manufactured by Toa Gosei Chemical Co., Ltd.) was used.

Comparative Example 1 A thermosensitive recording medium having an overcoat layer was obtained in the same manner as in Example 1, except that calcium carbonate was not used.

Comparative Example 2 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.

Comparative Example 3 A thermosensitive recording medium having an overcoat layer was obtained in the same manner as in Example 1, except that the amount of calcium carbonate was reduced to 5 parts by 0.05 part.

Comparative Example 4 A thermosensitive recording medium having an overcoat layer was obtained in the same manner as in Example 1 except that the amount of calcium carbonate was increased to 5 parts to 30 parts.

Comparative Example 5 In Example 1, instead of calcium carbonate, polyethylene particles having an average particle diameter of 30 μm (trade name: FLOWSEN U)
F, manufactured by Iron and Steel Chemical Co., Ltd.) to obtain a thermosensitive recording medium having an overcoat layer.

Comparative Example 6 A thermosensitive recording material having an overcoat layer was obtained in the same manner as in Example 1, except that the smoothing treatment on the surface of the intermediate layer was suppressed to a Beck smoothness of 250 seconds.

Using the 16 types of heat-sensitive recording media thus obtained, image recording was performed by a Sony Video Printer UP103, and the running performance (sticking characteristics) of the recording media and the image quality of the recorded image were evaluated. The results were measured using a Macbeth densitometer (manufactured by Macbeth, model RD-100R), and the results are shown in Table 1.

Runnability (sticking characteristics) evaluation standard A: Even when high-speed recording was performed, there was no sticking to the recording head, and the recording was extremely smooth.

…: Even when high-speed recording was performed, there was almost no sticking to the recording head, and the running performance was smooth.

X: The recording medium stuck to the recording head, causing a running failure.

Evaluation criteria for recording image quality ◎: Extremely excellent with no image unevenness.

…: Almost good with almost no image unevenness.

X: Image unevenness is inferior.

Further, the results of evaluation of the glossiness and writability of the surface of the thermosensitive recording medium before image recording shown below are also shown in Table 1.

Gloss: Measured with a variable angle photometer at an incident angle of 60 degrees. (The greater the value, the higher the gloss.) Writability: Writability with a ballpoint pen (Zebra) was evaluated.

◎: Writability is extremely excellent.

…: Writability is good and there is no practical problem.

×: Poor writability, causing practical problems.

"Effects" As is clear from the results in Table 1, the heat-sensitive recording material of the present invention is excellent in recording runnability, writing properties, and image quality, has a high recording density, and has excellent glossiness. Met.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-11680 (JP, A) JP-A-62-279980 (JP, A) JP-A-58-25988 (JP, A) JP-A-63-1988 99984 (JP, A) JP-A-57-188392 (JP, A)

Claims (2)

(57) [Claims] 1. A heat-sensitive recording layer containing a color former and a color former that is colored upon contact with the color former is provided on a plastic film or synthetic paper, and a water-soluble resin or a water-dispersible resin is provided on the heat-sensitive recording layer. In a heat-sensitive recording medium provided with an intermediate layer having a main component, and further provided with an overcoat layer for containing a resin curable by an electron beam on the intermediate layer, the Bekk smoothness of the intermediate layer is 3000 seconds or more. A heat-sensitive recording material, characterized in that the overcoat layer contains 0.5 to 15% by weight of an organic or inorganic pigment having an average particle size of 15 µm or less. 2. The heat-sensitive recording material according to claim 1, wherein the average particle size of the organic or inorganic pigment contained in the overcoat layer is 5 μm or less.