JP3429605B2 - 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 heat-sensitive recording material utilizing a color-forming reaction between a leuco dye and a coloring agent.
More specifically, the present invention relates to a heat-sensitive recording material excellent in water resistance and sticking resistance (resistance to sticking of the heat-sensitive recording layer surface to a thermal head during recording).

[0002]

2. Description of the Related Art A heat-sensitive recording material is known in which a color image is obtained by contacting both color-forming substances with heat by utilizing a color-forming reaction between a colorless or light-colored leuco dye and an organic or inorganic color-forming agent. Has been. Since such a heat-sensitive recording material is relatively inexpensive and the recording equipment is compact and its maintenance is easy, it is used in a wide range of fields such as a recording medium for facsimiles and various computers.

As one of the fields of use thereof, a heat-sensitive recording material for a handy terminal has attracted attention. Since such a thermal recording material for a handy terminal is used outdoors even in rainy weather, it does not come off even if the thermal recording layer surface gets wet,
Moreover, it is required to have excellent sticking resistance. For the purpose of improving the water resistance of the heat-sensitive recording layer, Japanese Patent Laid-Open No.
JP-A-36-343, JP-A-54-133352 and JP-A-54-133352 describe a method of adding a waterproofing agent to the heat-sensitive recording layer, and JP-B-57-14998 and JP-B-57-57.
No. 18520 and Japanese Patent Application Laid-Open No. 2-8084 describe a method of using a hydrophobic polymer emulsion as an adhesive in a thermosensitive recording layer. However, an adhesive excellent in sufficient water resistance and sticking resistance is further described. Agents are required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat sensitive recording material having excellent water resistance and sticking resistance.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors, by using a polymer emulsion obtained by polymerizing a specific monomer under specific emulsion polymerization conditions as an adhesive, water resistance is improved. It was found that the resistance and the sticking resistance were improved, and the present invention could be completed.

That is, the present invention provides a thermosensitive recording medium comprising a support and a thermosensitive recording layer containing a leuco dye, a coloring agent and an adhesive, wherein the adhesive is at least (meth).
Provided is a thermosensitive recording medium, which is a polymer emulsion obtained by emulsion-polymerizing a monomer containing acrylonitrile, (meth) acrylic acid ester and ethylenically unsaturated carboxylic acid under the following conditions and conditions. It is a thing. The conditions are such that, during emulsion polymerization of the monomer, the oxygen concentration of the reaction system aqueous phase is kept lower than the oxygen concentration of the 0.5% sodium bisulfite aqueous solution. When emulsion-polymerizing the monomer, an oxidizing agent-reducing agent-
A redox polymerization initiator composed of an activator is used, and the amount of the oxidizing agent used is 0.00 based on 100 parts by weight of the monomer.
1 to 0.1 parts by weight.

The present invention also provides the above-mentioned thermosensitive recording medium, wherein the (meth) acrylic acid ester is ethyl acrylate and / or butyl acrylate.

The present invention further provides the above-mentioned thermosensitive recording medium in which the ethylenically unsaturated carboxylic acid is itaconic acid and / or methacrylic acid.

Furthermore, the present invention provides the above-mentioned thermosensitive recording medium, wherein the polymer of the polymer emulsion has a glass transition temperature of 0 to 30 ° C.

The present invention also provides the above-mentioned thermosensitive recording medium in which a water-soluble polyvalent metal salt is contained in the thermosensitive recording layer.

Further, the present invention provides the above-mentioned thermosensitive recording medium, wherein the dry film of the polymer emulsion has a toluene-soluble portion of 5% or less and a toluene-insoluble portion having a toluene swelling degree of 200% or less. .

(Meth) Acrylonitrile In the present invention, it is essential to use (meth) acrylonitrile as a part of the monomer. This (meta)
Acrylonitrile is added for the purpose of improving sticking resistance.

(Meth) Acrylic Acid Ester The (meth) acrylic acid ester used in the present invention includes methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate. , Butyl methacrylate, 2-ethylhexyl methacrylate, and the like, among which ethyl acrylate and butyl acrylate are preferable. This (meth) acrylic acid ester is added for the purpose of improving the sticking resistance.

Ethylenically Unsaturated Carboxylic Acid Examples of the ethylenically unsaturated carboxylic acid used in the present invention include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and maleic acid, and among them, methacrylic acid is preferred. , Itaconic acid. This ethylenically unsaturated carboxylic acid is added for the purpose of increasing the mechanical stability of the polymer emulsion.

Other Monomers In the present invention, other copolymerizable monomers may be added as long as the desired effects are not impaired.
Examples include butadiene, isoprene, styrene,
Examples include α-methylstyrene, methylstyrene, vinyl chloride, acrylamide, N-methylol acrylamide and the like.

The proportions of the above-mentioned (meth) acrylonitrile, (meth) acrylic acid ester and ethylenically unsaturated carboxylic acid monomers to be used are not particularly limited, but for example, (meth) acrylonitrile may be added to 100 parts by weight of (meth) acrylonitrile. ) A range of 50 to 500 parts by weight of acrylic acid ester and 1 to 50 parts by weight of ethylenically unsaturated carboxylic acid is preferable.

Emulsion polymerization is then carried out at the above-mentioned proportions of the respective monomers used. Emulsion polymerization can be carried out in an aqueous system using each of the above-mentioned monomers, an emulsifier and a redox polymerization initiator.

[0018] The emulsifier used in the emulsifier present invention, can be used anionic or nonionic emulsifiers which are conventionally used, the use of emulsifiers having radical polymerizability, stability of the polymer emulsion obtained It is also advantageous for improving the sticking resistance of the thermal recording material and the background color development. Examples of the emulsifier having radical polymerization ability include the following general formula (1)
Examples include those shown in (3).

[0019]

[Chemical 1]

(In the formula, R represents an alkyl group, and n usually has a value of 2 to 20)

The amount of the emulsifier used is 0.5 based on all the monomers.
˜5.0 wt% is preferred. If it is less than 0.5% by weight, the mechanical stability of the produced polymer emulsion is low and the polymerization rate is slow. On the contrary, if it exceeds 5.0% by weight,
The resulting heat-sensitive recording material may have reduced sticking resistance, water resistance and color development.

Redox Polymerization Initiator The redox polymerization initiator used in the present invention is an oxidizing agent.
It is a redox polymerization initiator composed of a reducing agent and an activator.
Hydroperoxides and / or persulfates are used as oxidizing agents, for example as hydroperoxides,
Cumene hydroperoxide, t-butyl hydroperoxide, diisopropylbenzene hydroperoxide, p
-Menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide and the like, and examples of the persulfate include potassium persulfate and ammonium persulfate. . The amount of the oxidizing agent used is 0.001 to 0.1 part by weight, preferably 0.01 to 0.1 part by weight, based on 100 parts by weight of all the monomers.
It is 0.1 part by weight. If the amount used is less than 0.001 part by weight, not only the reaction for a long time is required to complete the polymerization, but also the reaction is not completed. The chemical resistance and sticking resistance of the recording material are deteriorated, which is not preferable.

As the reducing agent, glucose, dextrose, formaldehyde sodium sulfoxylate (Rongalit), sodium thiosulfate and the like are used.

As the activator, ferrous sulfate, copper sulfate,
Hexacyanoiron (III) potassium or the like can be used. The reducing agents and activators are used in appropriate amounts depending on the combination of the respective initiator systems.

Emulsion Polymerization Using the above-mentioned various monomers, emulsifiers and polymerization initiators,
Subsequently, emulsion polymerization is performed. This emulsion polymerization is carried out by keeping the oxygen concentration of the reaction system aqueous phase lower than the oxygen concentration of the 0.5% sodium bisulfite aqueous solution. Due to the low oxygen concentration, the amount of the polymerization initiator can be extremely reduced, and a stable polymer emulsion can be obtained in a relatively short time.

Next, one example in the case of emulsion polymerization will be described in detail. First, a reaction vessel is charged with deionized water deoxidized by a deoxygenation module (hereinafter referred to as deoxygenated deionized water) and a small amount of an emulsifier. Separately, a monomer and a small amount of an emulsifier are added to deoxygenated deionized water to emulsify to prepare a monomer emulsion, which is placed in a dropping device. Bisulfite is added and / or deoxygenated nitrogen gas is introduced into the liquid and bubbled in two of the reaction vessel and the dropping device. The oxygen concentration of the reaction system aqueous phase is zero, for example, by immersing the electrode in an aqueous solution of 0.5% sodium bisulfite.
Using a dissolved oxygen concentration meter (manufactured by Toa Denpa Co., Ltd.) calibrated to ppm, until it shows zero ppm or less,
Continue the above deoxidation operation. Subsequently, the redox polymerization initiator is dissolved in deoxygenated deionized water in the reaction vessel. With the above preparations completed, emulsion polymerization is carried out at a temperature not lower than the decomposition temperature of the redox polymerization initiator, for example not higher than 50 ° C, preferably not higher than 30 ° C.

This condition is a dissolved oxygen concentration that cannot be achieved by merely replacing the reaction system with nitrogen as in the conventional emulsion polymerization method. This can be achieved for example by adding bisulfite and / or thoroughly bubbling nitrogen gas as described above. When the dissolved oxygen concentration exceeds this level, the polymerization does not proceed, the molecular weight cannot be increased, the sticking resistance may decrease, and it is necessary to increase the amount of the polymerization initiator and / or the emulsifier.

In order to further improve the sticking resistance of the polymer emulsion thus obtained, a polyvalent metal salt may be added to the polymer emulsion. By this addition, the carboxylic acid in the polymer can be metal-crosslinked and the sticking resistance is further improved. The polyvalent metal salt may be a divalent or trivalent metal salt, and a water-soluble salt is preferable. For example, magnesium, zinc, calcium, aluminum, nickel, tin,
Examples include acetates such as chromium, chlorides, sulfates, carbonates and the like. Among them, zinc ammonium carbonate is preferable. The polyvalent metal salt is preferably added in an amount of 0.5 to 1.0 equivalent based on the carboxylic acid present.

In the present invention, the glass transition point of the polymer obtained by emulsion polymerization is preferably 0 to 30 ° C. If the glass transition point is lower than 0 ° C, the sticking resistance may be poor, and conversely, if it exceeds 30 ° C, the adhesiveness may be lowered. Further, in the polymer emulsion used in the present invention, it is preferable that the dry film has a toluene-soluble portion of 5% or less and the insoluble portion has a toluene swelling degree of 200% or less. When the toluene-soluble portion of the dry film is more than 5% and the degree of toluene swelling of the insoluble portion is more than 200%, the sticking resistance of the thermal recording material is poor.

Examples of the leuco dye used in the leuco dye present invention, any of various known can be used, and specific examples thereof, for example 3,3-bis (p- dimethylaminophenyl) -6-dimethyl Aminophthalide, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 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-N-diethylaminofluorane, 3- ( N
-Ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino)-
6-methyl-7- (p-toluidino) fluorane, 3-
Diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl -7-anilinofluoran, 3-
(N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane, 3-dimethylamino-6
-Methyl-7-xylidinofluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-di (n-butyl) amino-7- (o-chloroanilino) fluorane, 3-pyrrolidino-6-methyl- 7-p-butylanilinofluorane and the like can be mentioned. Two or more of these leuco dyes can be used in combination, if necessary.

Coloring Agent As the coloring agent which reacts with the leuco dye to develop a color, various known coloring agents can be used, for example, 4,4′-sec-butylidene diphenol, 4-phenylphenol, 4,4 ′.
-Dihydroxy-diphenylmethane, 4,4'-isopropylidene diphenol, 4,4'-cyclohexylidene bisphenol, 4,4 '-[1,3-phenylene bis (1-methylethylidene)] bisphenol, 4,4'
-(1,3-dimethylbutylidene) bisphenol, 4,
4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4 '
-Methyldiphenyl sulfone, 4-hydroxy-4'-
Methoxydiphenyl sulfone, 4-hydroxy-4'-
Isopropoxydiphenyl sulfone, 4-hydroxy-
3 ', 4'-trimethylene diphenyl sulfone, 4-hydroxy-3'-, 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl ) Phenolic compounds such as sulfone, 4-hydroxybenzoic acid-p-methoxybenzyl, novolac type phenol resin and phenol polymer, sulfonylurea derivatives such as 4,4′-bis (p-toluenesulfonylaminocarbonylamine) diphenylmethane, 3,5-dimethyl-
4-hydroxybenzoic acid, 3-isopropylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3-chloro-5- (α-methylbenzyl) salicylic acid , 3-phenyl-5- (α, α-dimethylbenzyl)
Zinc salts of aromatic carboxylic acids such as salicylic acid, 3,5-di-α-methylbenzyl salicylic acid, 4- (2-p-methoxyphenoxyethoxy) salicylic acid and 4- (3-p-tolylsulfonylpropyloxy) salicylic acid Etc. Among these, 4,4'-bis (p-toluenesulfonylaminocarbonylamine) diphenylmethane is preferable because of excellent storage stability of recorded images. Of course, these colorants may be used in combination of two or more, if necessary.

Usage Ratio The usage ratio of the specific adhesive (the above-mentioned polymer emulsion) in the present invention is not particularly limited, but is 3 to 30% by weight as a polymer based on the total solid content of the heat-sensitive recording layer, The range of 5 to 25% by weight is preferable. The proportions of the leuco dye and the coloring agent used are appropriately selected according to the types of the leuco dye and the coloring agent used, but generally 100 to 700 parts by weight of the coloring agent, preferably 1 part by weight of the leuco dye. About 100 to 400 parts is preferable.

In order to prepare a coating liquid for forming a heat-sensitive recording layer containing these substances, water is generally used as a dispersion medium, and for example, a leuco is applied to an agitator / crusher such as a ball mill, an attritor or a sand grinder to which an adhesive is added. It is prepared by dispersing the dye and color former together or separately. At that time, it is also possible to use a dispersant, and as the dispersant to be used, polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and styrene-maleic anhydride are used. In addition to water-soluble polymers such as copolymer salts and their derivatives, surfactants can be mentioned. Further, a defoaming agent or the like can also be used.

In the present invention, the above-mentioned specific adhesive is used in the heat-sensitive recording layer, but various known adhesives can be used in combination as long as the desired effects of the present invention are not impaired. For example, starches, bidroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene.
Acrylic acid copolymer salts, styrene / acrylic acid copolymer salts, styrene / butadiene copolymer emulsions, etc.
It can be used for the whole adhesive to the extent that the object of the present invention is not impaired.

If necessary, a water-proofing agent such as glyoxal, methylolmelamine, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride or ammonium zirconium carbonate may be added to the coating solution. Good.

Further, in the present invention, a sensitizer may be used in combination for increasing the recording sensitivity. Specific examples of the sensitizer include 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane and 1-phenoxy-2.
-(4-methylphenoxy) ethane, parabenzyl biphenyl, naphthylbenzyl ether, benzyl-4-methylthiophenyl ether, 1-hydroxy-2-naphthoic acid phenyl ester, oxalic acid dibenzyl ester, oxalic acid-di-p-methyl Benzyl ester, oxalic acid-di-p-chlorobenzyl ester, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, 1-hydroxynaphthoic acid phenyl ester and various known heat-fusible substances Examples include substances. Although the amount of the sensitizer used is not particularly limited, it is generally desirable to adjust the amount within a range of about 400 parts by weight or less relative to 100 parts by weight of the color developing agent.

It is permissible to add a storability improver in order to further improve the storability of the heat-sensitive recording layer.
Examples of such a preservability improver include 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 1,1,3-tris (2-methyl). -4-Hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,
1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4- (2-methyl-1,2-epoxyethyl) diphenylsulfone, 4- (2-ethyl-1,2-epoxy) Ethyl) diphenyl sulfone, 4
-(2-Methyl-glycidyl) diphenyl sulfone. Of course, it is not limited to these, and two or more kinds of compounds can be used in combination as required.

Various auxiliaries can be added to the coating solution. Examples of the dispersant include sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, and fatty acid metal salt. A benzophenone-based or triazole-based ultraviolet absorber, other defoaming agents, fluorescent dyes, coloring dyes and the like are added as necessary.

Further, zinc stearate, calcium stearate, stearic acid amide, stearic acid methylenebisamide, polyethylene wax, carnauba wax,
Lubricants such as paraffin wax and ester wax, kaolin, clay, talc, calcium carbonate, calcined clay,
Inorganic pigments such as titanium oxide, diatomaceous earth, fine anhydrous silica, activated clay and the like can also be added.

The method for forming the heat-sensitive recording layer is not particularly limited, and the coating solution is applied to the support and dried by, for example, air knife coating, varibar blade coating, pure blade coating, short dwell coating or the like. It is formed by a method or the like. Further, the coating amount of the coating liquid is not particularly limited, but is usually ² to 12 g / m ² in dry weight,
The range is preferably about 3 to 10 g / m ² .

The support that can be used in the present invention is not particularly limited and may be one that has been generally used as a support for a thermal recording medium. Examples include paper, film, synthetic paper and the like.

In the present invention, if necessary, on the heat-sensitive recording layer, or on the back surface of the support, a protective layer mainly composed of an adhesive and a pigment having excellent film-forming properties, and further on the protective layer,
Various publicly known in the field of heat-sensitive recording material production, such as providing a glossy layer containing a resin cured by ionizing radiation or providing an undercoat layer between the support and the heat-sensitive recording layer to enhance recording sensitivity. Technology can be applied.
Of course, it is also possible to improve the image quality and recording density by applying a super calender treatment after forming the undercoat layer, the heat-sensitive recording layer and the protective layer.

[0043]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. In addition, "part" and "%" in the examples mean "part by weight" and "% by weight", respectively, unless otherwise specified.

Production of Polymer Emulsion A 1-liter flask equipped with a stirrer, a thermometer, a condenser, a dropping funnel, a nitrogen gas vent tube, and an electrode for an oxygen concentration meter was charged with methacryloxy polyethylene glycol-2-ethylhexyl sulfosuccinic acid as an emulsifier. 1.5 g of soda, 0.002 g of ferrous sulfate and 200 g of water were charged. The oxygen concentration at this time was 5 to 7 ppm. Separately, in a 1 liter beaker, 150 g of butyl acrylate, 200 g of ethyl acrylate, 150 g of acrylonitrile,
Methacrylic acid 10g, methacryloxy polyethylene glycol-2-ethylhexyl sodium sulfosuccinate 1.5
g and 228 g of water were charged and emulsified with a homomixer.
The oxygen concentration at this time was 8 to 9 ppm. Fill the beaker and flask containing the monomer emulsion with nitrogen gas.
When blown at a rate of 0 to 100 ml / min for 2 hours, 0.5
An oximeter calibrated to zero with an aqueous solution of% sodium bisulfite showed 0 ppm. After the oxygen concentration of both systems became 0 ppm or less, 20 g of a 0.3% aqueous solution of monomer emulsion, t-butyl hydroperoxide and 20 g of a 0.5% aqueous solution of formaldehyde sodium sulfoxylate were added to the flask over 3 hours. It was dripped in. During this time, the system temperature is 30-
Keep at 34 ° C. After the dropping was completed, the temperature was maintained at the same temperature for 1 hour for thermal formation. After neutralizing the system by adding 5 g of 10% caustic soda,
Water was added to a solid concentration of 45% to obtain a polymer emulsion.

Liquid A Preparation As a leuco dye, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane 10 parts, 1,2-di (3
-Methylphenoxy) ethane 20 parts, a composition containing 10 parts of a 10% aqueous solution of methylcellulose, 1 part of a 5% aqueous solution of a naphthalenesulfonic acid formalin condensate, and 64 parts of water having an average particle diameter of 0.8 μm with a sand grinder. It was pulverized until it became a liquid A.

Composition of Liquid B Preparation Coloring Agent: 4,4′-isopropylidenediphenol 30 parts, methylcellulose 10% aqueous solution 5 parts, naphthalenesulfonic acid formalin condensate 5% aqueous solution 1 part, and water 64 parts The product was pulverized with a sand grinder until the average particle diameter became 0.8 μm to obtain a liquid B.

Example 1. Liquid A 100 parts, Liquid B 100 parts,
25 parts of the polymer emulsion (solid concentration 45%) obtained by the above production, polyvinyl alcohol (trade name: P
VA 117, manufactured by Kuraray Co., Ltd.) 20% 10% aqueous solution, fine particle silicon oxide 15 parts, light calcium carbonate 5 parts, zinc stearate 30% dispersion 20 parts, and dioctyl sodium sulfosuccinate 5% aqueous solution 2 parts The coating liquid obtained by mixing and stirring the materials is a basis weight of 64 g / m ^2.
On one surface of the neutral paper, the coated amount was dried so that the coating amount after drying was 5 g / m ² , dried, and subjected to a super calender treatment to obtain a thermosensitive recording medium.

Example 2. In the production of a polymer emulsion, instead of 1.5 g of sodium methacryloxyglycol-2-ethylhexyl sulfosuccinate charged as an emulsifier in a flask and a beaker, 1.5 g of sodium dodecylbenzenesulfonate as an emulsifier in a flask and an emulsifier in a beaker As sodium dodecylbenzene sulfonate (1.5 g) and polyoxyethylene lauryl ether (styrene oxide polymerization degree 50) 15 g
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

Example 3. In the preparation of the polymer emulsion, instead of 20 g of a 0.3% aqueous solution of t-butyl hydrobell oxide, 0.3 of cumene hydroperoxide is used.
10 g of 15% aqueous solution and 0.1% of ammonium persulfate
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 g of the aqueous solution was used.

Example 4. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 5 g of a 10% aqueous solution of calcium acetate was added to the obtained polymer emulsion in the production of the polymer emulsion.

Example 5. In the production of polymer emulsion, 10 g of itaconic acid instead of 10 g of methacrylic acid
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

Example 6. In the preparation of solution B, 4,4'-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4-hydroxy-4'-isopropoxydiphenyl sulfone was used instead of isopropylidenediphenol.

Example 7. In the preparation of solution B, 4,4'-
4,4'-bis (p-toluenesulfonylaminocarbonylamine) instead of isopropylidene diphenol
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that diphenylmethane was used.

Comparative Example 1. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 150 g of butyl acrylate was used instead of 150 g of acrylonitrile in the production of the polymer emulsion.

Comparative Example 2. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 150 g of butyl acrylate and 200 g of ethyl acrylate were used instead of 150 g of butyl acrylate and 200 g of ethyl acrylate in the production of the polymer emulsion.

Comparative Example 3. Instead of 20 g of a 0.3% aqueous solution of t-butyl hydroperoxide and 20 g of a 0.5% aqueous solution of sodium formaldehyde sulfoxylate, 20 g of a 5% aqueous solution of t-butyl hydroperoxide and sodium formaldehyde sulfone were used in the preparation of the polymer emulsion. Xylate 5% aqueous solution 20g
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

Comparative Example 4. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the polymer emulsion was produced without blowing nitrogen gas into the beaker and the flask containing the monomer emulsion in the production of the polymer emulsion.

Comparative Example 5. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 56 parts of a 20% aqueous solution of polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray Co., Ltd.) was used in place of 25 parts of the polymer emulsion. .

The polymer emulsion and the thermal recording material thus obtained were evaluated as follows, and the obtained results are shown in Table 1 and Table 2, respectively.

Evaluation of polymer emulsion [Viscosity of polymer emulsion] Solid concentration 45%, 30 ° C.
The viscosity of the polymer emulsion in 1. was measured with a B-type viscometer.

[PH of polymer emulsion] Solid concentration 4
PH of the polymer emulsion at 5%, 25 ° C
It was measured with a meter (manufactured by Horiba Ltd.).

[Glass Transition Point] The thickness after drying is about 50 μm.
The glass transition point of the polymer film obtained by applying the polymer emulsion on an aluminum foil so that it becomes m, and drying (drying at 60 ° C. for 5 hours) is measured by a differential thermal analyzer (manufactured by Seiko Denshi Kogyo KK). Measured.

[Toluene Resistance] 3 cm × 3 cm polymer film (W) used in the measurement of the above glass transition point
Was immersed in 10 ml of toluene at 25 ° C. for 24 hours, and the amount of polymer film (A) eluted in toluene was measured.
In addition to determining / W, the polymer film amount (B) swollen with toluene was measured to determine B / W.

Evaluation of Thermal Recording Material [Whiteness] The whiteness of the thermal recording layer was measured with a Hunter whiteness meter in order to evaluate the degree of white fog.

[Color density] Applied energy of 0.2 using a heat-sensitive simulator (TH-PMD manufactured by Okura Electric Co., Ltd.)
Recording on a thermosensitive recording medium at mj / dot, the color density of the obtained recorded image was measured by a Macbeth densitometer (Macbeth RD-1).
00R type).

[Head lees] A thermal simulator (TH-PMD manufactured by Okura Electric Co., Ltd.) was used to apply energy of 0.4.
After recording on a thermosensitive recording medium of about 10 m at mj / dot, the residue adhering to the head was observed. ◎ ・ ・ ・ There is no meal. ○ ・ ・ ・ Slightly dusted, but printed and there is no problem. × ・ ・ ・ A lot of dregs and trouble in printing.

[Water resistance] The thermosensitive recording medium is immersed in water for 1 minute and taken out, the recording surfaces are superposed, dried and then peeled off. ○ ・ ・ ・ ・ ・ The recording surface is peeled off without any problem. × ・ ・ ・ The recording material breaks when peeled off.

[Sticking resistance] After recording on a thermosensitive recording medium using a thermal simulator (TH-PMD manufactured by Okura Electric Co., Ltd.) with an applied energy of 0.4 mj / dot,
The degree of sticking occurring in the recorded image was visually judged. ◎ ・ ・ ・ There is almost no sticking. ○: There is some sticking. ×: There is a lot of sticking.

[0069]

[Table 1]

[0070]

[Table 2]

[0071]

According to the present invention, a heat-sensitive recording material having excellent water resistance and sticking resistance is provided.

─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Yoshihiro Shimizu 1-6-12 Higashi-Naruo-cho, Nishinomiya-shi, Hyogo (56) References JP-A-58-153693 (JP, A) JP-A-57-161195 (JP, A) JP 57-77393 (JP, A) JP 6-322345 (JP, A) JP 5-318911 (JP, A) JP 2-72993 (JP, A) JP 5 -222108 (JP, A) JP-A-4-135786 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/28-5/34 C09J 133/02 C09J 133/08 C09J 133/20

Claims (6)

(57) [Claims] 1. A thermosensitive recording medium comprising a support and a thermosensitive recording layer containing a leuco dye, a coloring agent and an adhesive, wherein the adhesive is at least (meth) acrylonitrile or (meth) acrylic acid ester. And a monomer containing an ethylenically unsaturated carboxylic acid, which is a polymer emulsion obtained by emulsion polymerization under the following conditions and conditions. During emulsion polymerization of the monomer, the oxygen concentration in the reaction system aqueous phase is kept lower than the oxygen concentration in the 0.5% sodium bisulfite aqueous solution. When emulsion-polymerizing the monomer, an oxidizing agent-reducing agent-
A redox polymerization initiator composed of an activator is used, and the amount of the oxidizing agent used is 0.00 based on 100 parts by weight of the monomer.
1 to 0.1 parts by weight. 2. The heat-sensitive recording material according to claim 1, wherein the (meth) acrylic acid ester is ethyl acrylate and / or butyl acrylate. 3. The heat-sensitive recording material according to claim 1, wherein the ethylenically unsaturated carboxylic acid is itaconic acid and / or methacrylic acid. 4. The heat-sensitive recording material according to claim 1, wherein the polymer of the polymer emulsion has a glass transition temperature of 0 to 30 ° C. 5. The heat-sensitive recording material according to claim 1, wherein a water-soluble polyvalent metal salt is contained in the heat-sensitive recording layer. 6. The heat-sensitive material according to claim 1, wherein the dry film of the polymer emulsion has a toluene-soluble portion of 5% or less and a toluene-insoluble portion has a toluene swelling degree of 200% or less. Record body.