JP3139638B2 - Thermal recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium. More specifically, the oil-in-water type is excellent in recording runnability, preservability of the heat-sensitive recording medium before and after coloring, and is excellent in workability and environmental security in forming a high-grade heat-sensitive recording medium with gloss. The present invention relates to a heat-sensitive recording medium coated with a radiation-curable resin emulsion to form a cured film.

[0002]

2. Description of the Related Art Conventionally, a heat-sensitive recording medium for obtaining a recorded image by reacting a colorless or light-colored basic dye with an organic or inorganic colorant by heat is relatively inexpensive, and the apparatus is compact and maintenance-free. Therefore, in the field of facsimile and printers, it has rapidly spread in recent years, and needs for thermal recording media such as POS labels, overhead projectors (OHP), second original drawings, cards, and the like are also expanding.

[0003] However, these heat-sensitive recording media have problems in storage stability (especially, fading of a color-developed image by a plasticizer, oil, and water), and also have disadvantages such as background fog. As a method to solve this problem, a method of providing a radiation-curable resin layer on the heat-sensitive layer (Japanese Patent Publication No. 58-35478) or a method of providing a radiation-curable resin layer on the heat-sensitive layer via an intermediate layer has been proposed. There has been proposed a method of obtaining a heat-sensitive recording medium having excellent storage stability and recording characteristics without causing a problem (JP-A-59-26291).

[0004]

However, with the recent diversification and high performance of thermal recording systems, hardware such as thermal printers and facsimile machines have made remarkable progress. Even if the radiation-curable resin is overcoated, there are problems such as adhesion of debris to the thermal head and generation of sound during printing (sticking noise), and a good thermal recording medium has not been obtained. In addition, the radiation-curable resin has a Tg point of 2
A method using a material having a temperature of 00 ° C. or higher (Japanese Patent Laid-Open No. 1-125277),
A method of adding a pigment of 15 microns or less to the resin (Japanese Patent Application Laid-Open No. 1-210381) has also been proposed, but in any case, the high-speed recording characteristics are excellent, the glossiness is high, and the heat-sensitive recording material itself and the color image. The purpose of obtaining a thermosensitive recording medium having excellent storage properties has not yet been achieved.

[0005] Radiation-curable resins are used in many fields because of their simple curing equipment and good productivity. However, radiation-curable resins are used in reactive diluents and other materials due to problems in handling and coating. In many cases, an organic solvent must be used, and the composition has problems in workability and safety in terms of skin irritation, odor, and toxicity. As a means for solving the problem, there is an emulsion of a radiation-curable resin (JP-A-50-79533).

However, it is not possible to obtain a heat-sensitive recording medium having excellent recording characteristics even by overcoating a coating solution in which only a radiation-curable resin is emulsified. It is necessary to impart functions of heat resistance and slidability. In such a case, it is necessary to add an inorganic or organic filler. As an example of the method, there is a method in which an inorganic or organic filler is dispersed in the resin before emulsifying the radiation-curable resin, and this is emulsified and dispersed in water to produce an emulsion composition.
However, in such a case, when an inorganic or organic filler is filled, the stability of the oil-in-water emulsion is reduced, and thus the production of the emulsion becomes difficult, and the gloss of the coating film of such an emulsion composition is reduced. Cause problems. In addition, when a thermosensitive recording medium is obtained by using an emulsion composition obtained by using a non-reactive emulsifier, there is a problem that the storage stability of the thermosensitive recording medium itself and a color image is reduced.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, completed the present invention. That is, the present invention provides: A heat-sensitive recording layer containing a colorless or pale-colored basic dye and a colorant capable of causing the basic dye to develop color when heated is provided on a support, and the overcoat layer is further formed on the heat-sensitive recording medium further formed with an overcoat layer. Acrylic prepolymer or monomer (A) as a coating liquid for forming a layer and a hydrophilic resin having at least one ethylenically unsaturated group and at least one ammonium sulfonate group in a molecule as an emulsifying / dispersing agent A heat-sensitive recording material comprising an oil-in-water type radiation-curable resin emulsion composition containing (B) and a filler (C) as essential components. 2. 2. The heat-sensitive recording material according to item 1, wherein the resin component (B) is one or several compounds represented by formula (1) or (2).

[0008]

Embedded image

(Wherein R is a hydrogen atom or a group having 1 to 25 carbon atoms)
May be the same or different, R ′ represents an alkyl group having 1 to 25 carbon atoms, a benzyl group or a styrene group and may be the same or different, A represents an ethylene or propylene group, X represents a hydrogen atom or A methyl group; m and n each represent an integer of 1 or more; )

[0010]

Embedded image

3. 2. The heat-sensitive recording material according to item 1, wherein the filler (C) is an inorganic pigment, and the content thereof is 0.5 to 50% by weight based on the total solid content in the emulsion composition. Is provided.

The heat-sensitive recording material of the present invention has high gloss, high-speed recording characteristics, excellent heat-sensitive recording material and excellent preservability of a color-developed image, and an organic solvent which has an adverse effect on the human body and the environment in obtaining the heat-sensitive recording material. It is characterized in that a radiation-curable resin-containing oil-in-water emulsion composition containing a filler is not used. The colorless or light-colored basic dye and colorant used in the heat-sensitive recording layer in the present invention are not particularly limited, and those known per se can be used, and on a support using a usual binder. Coated. or,
If necessary, a sensitizer and other additives can be mixed.

Examples of the basic dye include fluoran compounds, triarylmethane compounds, spiropyran compounds, diphenylmethane compounds, thiazine compounds, lactam compounds, fluorene compounds and the like. Examples thereof include the following compounds.

Fluoran compound; 2-anilino-3-
Methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6- (N-methyl-N-cyclohexylamino) -fluoran, 2-anilino-3-methyl-6
-(N-ethyl-N-isopentylamino) fluoran, 2-anilino-3-methyl-6-dibutylaminofluoran, 2- (p-chloroanilino) -3-methyl-
6-diethylaminofluoran, 2- (p-fluoroanilino) -3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6- (p-toluidinoethylamino) fluoran, 2- ( p-toluidino)-
3-methyl-6-diethylaminofluoran, 2- (o
-Chloroanilino) -6-dibutylaminofluoran,
2- (o-fluoroanilino-6-diethylaminofluoran, 2- (o-fluoroanilino) -6-dibutylaminofluoran, 2-anilino-3-methyl-6-piperidinofluoran, 2- Anilino-3-methyl-6
Pyrrolidinofluoran, 2-ethoxyethylamino-3
-Chloro-6-diethylaminofluoran, 2-anilino-3-chloro-6-diethylfluoran, 2-chloro-6-diethylaminofluoran, 2-methyl-6-diethylaminofluoran, 2-anilino-3-methyl −
6-dipentylaminofluoran, 2-anilino-3-
Triarylmethane compounds such as methyl-6- (N-ethyl-N-ethoxypropylamino) fluoran; 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (alias: crystal violet lactone) , 3,3-
Bis (p-dimethylaminophenyl) phthalide, 3-
(P-dimethylaminophenyl) -3- (1,2-dimethylaminoindole-3-isophthalide and the like,

Spiropyran compound; 3-methyl-3-
Spiro-dinaphthopyran, 1,3,3-trimethyl-6
-Nitro-8'-methoxyspiro (indoline-2,
2'-benzopyran); diphenylmethane compounds; N-halophenyl-leuco auramine; thiazine compounds; benzoyl leucomethylene blue; lactam compounds; rhodamine-B-anilinolactam; Bis (dimethylamino)
Fluorene spiro (9,3 ')-6'-dimethylaminophthalide, [3,6-bis (dimethylamino) fluorene spiro (9,3')-6'-pyrrolidinophthalide],
[3-dimethylamino-6-diethylaminofluorenespiro (9,3 ')-6'-pyrrolidinophthalide] and the like. These basic dyes can be used alone or in combination.

Examples of the coloring agent include p-octylphenol, p-tert-butylphenol, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis-
(P-hydroxyphenyl) cyclohexane, 4,4'-
Thiobisphenol, 4,4′-sulfonyldiphenol, bis- (3-allyl-4-hydroxyphenyl) sulfone, novolak-type phenol resin, benzyl p-hydroxybenzoate, ethyl p-hydroxybenzoate,
Dimethyl-hydroxyphthalate, ethyl 5-hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 1,
7-di (hydroxyphenylthio) -3,5-dioxaheptane, 4-isopropoxy-4′-hydroxydiphenylsulfone, methyl bis (4-hydroxyphenyl) acetate, butyl bis (4-hydroxyphenyl) acetate,
Benzyl (bis (4-hydroxyphenyl) acetate) and aromatic carboxylic acids include polyvalent metal salts thereof. These colorants can be used alone or in combination.

The binder as a component forming the heat-sensitive recording layer includes methyl cellulose, methoxy cellulose,
Hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, silica-modified polyvinyl alcohol, alkali salts of styrene acrylate copolymer, polyvinyl pyrrolidone,
Water-soluble materials such as polyacrylamide, polyacrylic acid, starch and derivatives thereof, casein, gelatin, alkali salts of styrene / maleic anhydride copolymer, and alkali salts of iso (or diiso) butylene / maleic anhydride copolymer Or a water-insoluble emulsion such as polyvinyl acetate, a vinyl chloride-vinyl acetate copolymer, polystyrene, a styrene-butadiene-acrylic acid copolymer, or the like.

Examples of the filler include calcium carbonate, magnesium carbonate, magnesium oxide, silica, white carbon, talc, clay, alumina, magnesium hydroxide, aluminum oxide, barium sulfate, polystyrene resin, and urea-formalin resin. . Examples of sensitizers include waxes such as animal and vegetable waxes, polyethylene waxes and synthetic waxes, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, acetyl compounds of aromatic amines, aromatic ether compounds, and biphenyl derivatives. Those which are solid at ordinary temperature and have a melting point of about 80 ° C. or more are exemplified. Other additives include lubricants such as zinc stearate, calcium stearate, and aluminum stearate, and various other surfactants, defoamers, and the like can be added as necessary.

As a method for forming a heat-sensitive recording layer using the above materials, first, a basic dye and a colorant are separately added to a binder, water or other additives as necessary, and a protective colloid such as polyvinyl alcohol. After pulverizing and dispersing with a dispersing machine such as a ball mill, an attritor, or a sand mill together with the substance and the surfactant (usually, the basic dye or colorant is 5 to 70% of the system to be dispersed, and the binder is 5 to 5%). ５０50%, water is 30９０90%, pulverization and dispersion are carried out), and each is mixed to prepare a coating solution for the heat-sensitive recording layer (the ratio of the basic dye to the colorant is usually dry weight). In a ratio of 1: 1 to 1:10), a coating liquid on a support such as paper, plastic sheet, or synthetic paper in an amount of 5 to 40 g / m ^2.
The heat-sensitive recording layer can be obtained by applying a bar coater coating, an air knife coating, a gravure coating, a roll coating coating or the like, and then drying.

In the present invention, an intermediate layer may be provided between the heat-sensitive recording layer and the overcoat layer (the protective layer of the present invention).
When an intermediate layer is provided, hydrophilic or water-dispersible resins such as polyvinyl alcohol, starch, styrene / butadiene latex / acrylic resin emulsion, and solvent soluble materials such as polyester resin and copolymer of acrylic resin and vinyl acetate resin Coating a coating liquid containing a mold resin as a main component and, if necessary, fillers such as calcium carbonate, zinc oxide, talc, kaolin, clay, and colloidal silica, and auxiliaries such as various surfactants, by an ordinary method. By doing so, it can be provided.

As a method for forming an intermediate layer using these materials, for example, the hydrophilic resin, the water-dispersible resin or the solvent-soluble resin is mixed with water or other filler if necessary, The heat-sensitive recording obtained as described above after dispersing with a dispersing machine such as a ball mill, an attritor, a sand mill or the like together with the agent (usually, the resin component is dispersed in an amount of 5 to 80% of the system used for dispersion). An intermediate layer is formed on the layer by applying a bar coater coating, an air knife coating, a gravure coating, a roll coating coating, or the like to a coating amount of ² to 40 g / m ² and drying. On the intermediate layer formed in this manner, and directly on the heat-sensitive layer, an oil-in-water type radiation-curable resin emulsion containing a filler is applied to form an overcoat layer. A thermosensitive recording medium is obtained.

The acrylate prepolymer or monomer (A) used in the overcoat layer includes:
The following are mentioned. As the prepolymer, epoxy (meth) acrylate, urethane (meth) acrylate, polyethylene (meth) acrylate, polyether (meth) acrylate, silicon (meth) acrylate, polybutadiene (meth) acrylate, polystyrylethyl (meth) acrylate, Polyamide (meth) acrylate and the like can be mentioned. As monomers, butyl acrylate, 2-ethylhexyl acrylate, n
Monofunctional monomers such as hexyl acrylate, cyclohexyl acrylate, n-decyl acrylate isobornyl acrylate, dicyclopentenyloxyethyl acrylate, phenoxyethyl acrylate,
4-butanediol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, polyethylene glycol 400 diacrylate, tripropylene glycol diacrylate, bisphenol A diethoxy diacrylate, tetraethylene glycol diacrylate , Neopentyl glycol dihydroxypivalate diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate,
Examples include polyfunctional monomers such as pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate. The amount of the radiation-curable resin (A) to be used is usually from 20 to the total solid content in the emulsion composition.
It is 95% by weight, preferably 40-80% by weight.

Specific examples of the hydrophilic resin (B) used in the present invention include a reactive emulsifier Antox-MS60 (X in the formula (1) is a methyl group) manufactured by Nippon Emulsifier Co., Ltd .; Adecaria Soap SE
-10N (formula (2)), a compound represented by a reactive emulsifier Aqualon HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

The hydrophilic resin (B) functions as an emulsifying and dispersing agent, and a sufficiently stable emulsion can be obtained by itself. However, if desired, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene alkyl Non-ionic surfactants such as ethylene derivatives, polyoxyethylene / polyoxypropylene / block copolymers, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene alkylamines; Fatty acid salts, alkyl sulfates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, alkyl phosphates, polyethoxylates Chiren'arukiru sulfuric acid ester salt,
Various commercially available emulsifying and dispersing agents such as naphthalene sulfonate formalin condensate, special polycarboxylic acid type polymer surfactant, anionic surfactant such as polyoxyethylene alkyl phosphate, etc. A kind or several kinds may be selected and used together with the hydrophilic resin (B).

Here, the amount of the emulsifying / dispersing agent used in the emulsion composition of the present invention is usually 4 to 30% by weight, more preferably 8 to 20% by weight, based on the total solids in the emulsion composition. Range. If the amount is less than 4% by weight, a stable emulsion cannot be obtained.
If the content is more than 10% by weight, there arises a problem that film properties such as water resistance and heat resistance are deteriorated.

By coating and curing the emulsion of the radiation-curable resin having excellent heat resistance as described above via an intermediate layer or directly on the heat-sensitive layer, the heat-sensitive layer can be formed with high gloss without coloring. However, since it is not enough to prevent adhesion of debris and sticking to the head in high-speed printing, the filler (C) is used prior to emulsifying and dispersing the radiation-curable resin. It is essential to disperse in a resin in advance.

As the filler (C), aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, aluminum oxide,
Inorganic fillers such as silicon dioxide, titanium dioxide, talc, clay, kaolin, colloidal silica, metal powders and fillers obtained by surface-treating these inorganic fillers, styrene microballs, polyethylene powder, tetrabromobisphenol A, decabromodiphenyl oxide,
Tricresyl phosphate, triethyl phosphate,
Organic fillers such as tetrafluoride resin, aromatic polyester, aspartic acid ester derivative, zinc stearate, amide amide and polyethylene wax. The amount of the filler (C) to be used is generally in the range of 0.2 to 50% by weight, preferably 0.5 to 30% by weight, based on the total solid content in the emulsion composition of the present invention. 0.
If the content is less than 2% by weight, sufficient recording characteristics cannot be obtained.
If the content is more than the weight percentage, problems such as stability of the air emulsion and reduction in gloss of the coating film occur.

In addition to these fillers (C), it is also possible to add a lubricant such as a phosphate compound, a polyethylene wax or the like, and a reactive silicone compound such as a radical-reactive silicone macromer or a terminal hydroxyl group-modified polyester siloxane. As a method of dispersing these in the radiation-curable resin (A), a generally known method of dispersing them with a disperser such as a ball mill, a roll mill, and a sand mill can be used.

As a photoinitiator usually required when using the ultraviolet curing method, acetophenone,
Benzophenone, benzoin ether, chloroacetophenone, diethoxyacetophenone, hydroxyacetophenone, α-aminoacetophenone, benzylmethylketal, thioxanthone, α-acyloxime ester, acylphosphine oxide, glyoxyester, 3-ketocoumarin, 2-ethylanthraquinone, Examples thereof include camphorquinone, benzyl, and Michler's ketone, and these photoinitiators can be used in the present invention.

The method for emulsifying, dispersing, and dispersing the components forming the above emulsion composition in water is carried out by a generally known method. For example, after dissolving or dispersing the hydrophilic resin (B) and possibly other emulsifying and dispersing agents in water, the radiation curable resin (A) containing the filler (C) may be stirred in advance while stirring. An aqueous phase in which the hydrophilic resin (B) and the emulsifying / dispersing agent are dissolved or dispersed is gradually added, and the mixture is emulsified and dispersed using a high-speed stirrer such as a homomixer or a sand mill or a microfluidizer to thereby form oil droplets in water. There is a method for obtaining a radiation-curable resin emulsion composition, but the method is not limited thereto.

Further, in addition to the radiation-curable resin, the emulsifying / dispersing agent, the pigment and the binder as described above, a reactive silicone compound, a lubricant, a polymer, a leveling agent, a defoaming agent may be added to the emulsion composition. Additives such as an agent, an ultraviolet absorber, a fluorescent dye, a fluorescent pigment, a coloring dye, and a coloring pigment can be appropriately used.

The emulsion composition thus obtained is stable over time, and the emulsion diluted with water as required for coating is also stable. As a method for forming a cured film of this emulsion composition, bar coater coating, air knife coating, gravure coating, offset printing, flexographic printing, screen printing and the like, in a manner known per se, paper, synthetic paper or film The coating is dried on top and irradiated with ultraviolet rays or electron beams to cure the coating.
At that time, when curing with an electron beam, 100 to 500
An electron beam accelerator having an energy of eV is preferable.
On the other hand, when curing can be performed by ultraviolet rays, an ultraviolet irradiation device having a xenon lamp, a high-pressure mercury lamp, or a metal halide lamp is used as a light source, and the amount of light and the arrangement of the light source are determined as necessary.
It is preferable to cure by irradiating 1 to 4 times with a transport speed of 20 to 60 m / min by a lamp having a light amount of 0 to 120 W / cm.

[0033]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. still,
In the examples, parts mean parts by weight.

Example 1 Formation of Thermal Recording Layer [A] Solution: 7 parts of 2- (o-fluoroanilino) -6-diethylamino 18% fluoran p-benzylbiphenyl 18% 25% aqueous solution of PVA 20% water 55% [B] Liquid: bis (3-allyl-4-hydroxyphenyl) sulfone 10 parts 25% PVA aqueous solution 8〃 water 82〃 [C] liquid: calcium carbonate 40 parts 25% PVA aqueous solution 8〃 water 52〃 The above compositions were separately prepared Using a sand grinder, the particles were pulverized and dispersed so that the average particle diameter became 1 to 3 μm.

Next, 25 parts of [A] liquid, 50 parts of [B] liquid,
[C] A coating solution for a heat-sensitive recording layer was prepared by mixing 20 parts of a liquid and 5 parts of a water-containing carboxylated SB latex copolymer (solid content = 50%), and the dry coating amount on a high-quality paper was about 8g
/ M ² and dried to obtain a heat-sensitive recording sheet. Formation of Intermediate Layer PVA 25 parts Water 74 Colloidal Silicate 1 The above composition was mixed to prepare a coating solution for the intermediate layer, and then dried and coated on the heat-sensitive recording sheet obtained above. The amount is 2g
/ M ² and dried to obtain a thermosensitive recording sheet having an intermediate layer.

Formation of Overcoat Layer Dipentaerythritol hexaacrylate 35 parts Trimethylolpropane triacrylate 10 {phenoxyhexaethylene glycol acrylate 5} Photoinitiator (Irgacure 184; Ciba-Geigy) 5} Calcium carbonate (average particle size: 0. 5 µm or less 10 Aqualon HS-10 (Daiichi Pharmaceutical Co., Ltd.) 5 Water 30〃 Mix and emulsify and disperse the above compound (500 with homomixer)
0 rpm x 15 minutes) to prepare a coating liquid of an oil-in-water type radiation-curable resin emulsion composition, and dry coating with a bar coater on the heat-sensitive sheet having an intermediate layer obtained in step 3 g. / M ^2, and cured by irradiating twice with a conveyor speed of 40 m / min using an ultraviolet irradiation device (GS ASE-20; manufactured by Nippon Battery) having an 80 W / cm high-pressure mercury lamp. Thus, a thermosensitive recording medium of the present invention was obtained.

Example 2 A heat-sensitive recording material of the present invention was prepared in the same manner as in Example 1 except that Adekaria Soap SE-10N (manufactured by Asahi Denka Co., Ltd.) was used instead of Aqualon HS-10. I got

Example 3 In Example 1, Aquaron HS-10 was replaced with A
A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that ntox-MS60 (manufactured by Nippon Emulsifier Co., Ltd.) was used.

Example 4 The procedure of Example 3 was repeated except that one part of a polyoxyethylene / polyoxypropylene / block polymerization type surfactant (trade name: Pluronic L-64, Asahi Denka Kogyo KK) was used. In the same manner as in Example 3, a thermosensitive recording medium of the present invention was obtained.

Example 5 A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 3, except that the addition amount of calcium carbonate was changed to 20 parts.

Example 6 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 3, except that a wax emulsion (trade name: Slip Aid SL-140, manufactured by San Nopco Co., Ltd.) was used in combination. .

Example 6 Example 1 was the same as Example 1 except that no intermediate layer was provided.
In the same manner as in the above, a thermosensitive recording medium of the invention was obtained.

Comparative Example 1 Comparative Example 1 was carried out in the same manner as in Example 1, except that polyoxyethylene nonylphenyl ether (trade name: Emulgen 935, manufactured by Kao Corporation) was used instead of Aqualon HS-10. Thermosensitive recording medium was obtained.

Comparative Example 2 A comparative thermosensitive recording medium was obtained in the same manner as in Comparative Example 1, except that the addition amount of calcium carbonate was changed to 20 parts.

Comparative Example 3 A comparative thermosensitive recording medium was obtained in the same manner as in Example 1 except that calcium carbonate was not added.

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

Using each of the thus-obtained thermal recording media, a dot line thermal printer (Matsushita test printer) having a resistance value of 325 Ω is used for printing.
The recording runnability and storage stability were evaluated, and the results are shown in Table 1. The following evaluation criteria were used.

Table 1 Evaluation Results Emulsion Sticky Head Water Resistance Waterproof Plasticizer Resistance Printed Gloss Stability Adhesion Preservation Example 1 ○ ○ ○ ○ ○ ○ ○ 75.1 ○ 2 ○ ○ ○ ○ ○ ○ 70.6 ○ 3 ○ ○ ○ ◎ ○ ○ ○ ○ 84.5 〃 4 ◎ ◎ ◎ ○ ○ ○ 85.2 〃 5 ○ ◎ ◎ ○ ○ ○ 77.8 〃 6 ○ ○ ○ ○ ○ ○ 75.9 Comparative Example 1 △ to × ○ ○ ○ ○ × 61.3 〃 2 × ○ ○ ○ ○ × 42.3 〃 3 ○ △ to × × ○ ○ ○ 89.3 〃 4 − × × × × × 9.3

(1) Emulsion stability test The obtained emulsion composition was allowed to stand in a dryer at 50 ° C. for 2 weeks, and the viscosity (RU type viscometer manufactured by Tokimec Co., Ltd.) and the particle size distribution (LPA manufactured by Otsuka Electronics Co., Ltd.) -3100), and the stability was evaluated by observing the water separation state. A: There is no change in both viscosity and particle size. ；: Almost no change in viscosity and particle size. Δ: Some water separation was observed, but redispersibility was good. X: Separation of an oil phase and an aqueous phase is observed. (2) Sticking evaluation criteria A: During high-speed printing, no sound was recorded at all and recording was performed smoothly. ；: At the time of high-speed printing, recording was performed smoothly with almost no sound. Δ: At the time of high-speed printing, recording failure occurred very slightly. X: The thermal recording medium did not run smoothly and recording failure occurred.

(3) Criteria for evaluation of head scum adhesion A: During high-speed printing, there was no dirt on the head. ；: At the time of high-speed printing, there was almost no dirt on the head. Δ: The head was very slightly stained after high-speed printing. X: The head was dirty after high-speed printing. (4) Water resistance test ；: Even when the thermosensitive recording medium colored as described above was immersed in water at 20 ° C. for 24 hours, there was almost no fading of the colored portion. C: The color-developed part faded when the thermosensitive recording medium colored as described above was immersed in water at 20 ° C. for 24 hours.

(5) Plasticizer resistance test ；: A plasticizer (D
Even when OP) was dropped, there was almost no fading of the color-developed portion. ×: A plasticizer (D) was placed on the heat-sensitive recording material colored as described above.
When OP) was dropped, discoloration of the color-developed portion was observed. (6) Preservation test of printed area ；: Even if the heat-sensitive recording medium colored as described above was left in a dryer at 40 ° C. for 72 hours, there was almost no fading of the colored area. X: When the heat-sensitive recording medium colored as described above was allowed to stand in a drier at 40 ° C for 72 hours, the color-developed portion faded.

[0052]

The heat-sensitive recording material of the present invention obtained by applying and curing a radiation-curable resin-containing resin emulsion has high gloss and high-speed printing without using an organic solvent which adversely affects the human body and the environment. In this case, the recording performance is excellent, and the heat-sensitive recording medium and the color image are well preserved.

Claims (3)

(57) [Claims] 1. A heat-sensitive recording medium comprising a support and a heat-sensitive recording layer containing a colorless or pale-colored basic dye and a colorant capable of causing the basic dye to develop color when heated, and further comprising an overcoat layer. And an acrylate prepolymer or monomer (A) as a coating solution for providing the overcoat layer.
Oil-in-water containing hydrophilic resin (B) and filler (C) as an essential component having the emulsifying and dispersing agent to the molecule one or more ethylenically unsaturated groups and one or more sulfonate ammonium salt and A heat-sensitive recording material using a radiation-curable resin emulsion composition. 2. The heat-sensitive recording medium according to claim 1, wherein the hydrophilic resin (B) is one or more of the compounds represented by the formulas (1) and (2). . Embedded image (Wherein, R is a hydrogen atom or an alkyl group having 1 to 25 carbon atoms and may be the same or different, and R ′ represents an alkyl group having 1 to 25 carbon atoms, a benzyl group or a styrene group, and may be the same or different. , A represents an ethylene or propylene group, X represents a hydrogen atom or a methyl group, and m and n each represent an integer of 1 or more.) 3. The method according to claim 1, wherein the filler (C) is an inorganic pigment, and the content thereof is 0.5 to 50% by weight based on the total solids in the emulsion composition. The thermosensitive recording medium as described.