JP5971864B2 - Method for producing thermal recording material - Google Patents

Description

  The present invention relates to a heat-sensitive recording material utilizing a color development reaction between a leuco dye and a developer.

  Thermal recording paper using a heat-developing reaction between a leuco dye (electron-donating color-forming compound) and a developer (electron-accepting compound) is widely used, for example, as disclosed in Patent Documents 1 to 3 and the like. It has become. Generally, in thermal recording paper, leuco dye and developer are separately dispersed into fine particles, then mixed together, and a binder, filler, sensitivity improver, lubricant and other auxiliary agents are added. The coating solution obtained in this manner is applied to a support such as paper and film, and color recording is obtained by an instantaneous chemical reaction by heating. In such a heat-sensitive recording paper, various colors can be developed by selecting a variety of colorless dyes.

  In recent years, thermal recording systems have become widespread and their uses have diversified, and importance has been placed on increasing the recording speed and improving the image quality, that is, increasing the density to increase the resolution. For this reason, the thermal energy of the thermal head of the recording device tends to be smaller, and the thermal recording paper used for it has sufficient color sensitivity to obtain a clear color record even with a small amount of heat. Is required.

  In thermal recording (thermal printing) in which thermal coloring material is developed with a thermal head, development of thermal recording materials that can achieve high color density with less printing energy is highly desirable from the viewpoints of energy saving and longer life of thermal head. It is rare. Usually, the heat-sensitive recording material is a colorant such as a leuco dye, a developer such as 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, a sensitizer such as 2-benzyloxynaphthalene, and the like. Accordingly, a material made of a lubricant such as zinc stearate is dispersed in the binder. For example, Patent Document 4 describes a heat-sensitive recording material using 2-benzyloxynaphthalene as a sensitizer. This heat-sensitive recording material relates to a heat-sensitive recording material excellent in thermal responsiveness capable of obtaining a high-density color image with low heat energy.

No.43-4160 Japanese Patent Publication No.45-14039 JP 48-27736 A JP 61-199987

  An object of the present invention is to provide a heat-sensitive recording material that is more excellent in moisture resistance and heat resistance, has high recording sensitivity, and has excellent dot reproducibility.

In order to solve the above problems, the thermosensitive recording material of the present invention is provided on a support with a thermosensitive recording layer containing at least a leuco dye, a sensitizer, a developer, an antioxidant, and an additive,
In the thermosensitive recording layer, with respect to the total solid content of the thermosensitive recording layer,
As the sensitizer, 10-32% by mass of at least one of 1,2-bis (3-methylphenoxy) ethane or 1,2-diphenoxyethane,
As the developer, 10 to 28% by mass of 2,4′-dihydroxydiphenylsulfone,
As the antioxidant, 0.1 to 10% by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, and
As the additive, α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) is used. It shall contain 3-15 mass%.

  Further, the heat-sensitive recording material of the present invention is a mixture dispersion obtained by wet-mixing and pulverizing the sensitizer, the developer, and the antioxidant in the presence of a water-soluble dispersant. It may be contained in the heat-sensitive recording layer.

  In the heat-sensitive recording material of the present invention, the average particle diameter of the mixed dispersion may be in the range of 0.7 to 1.2 μm.

  In the heat-sensitive recording material of the present invention, the additive may be wet pulverized in the presence of a water-soluble dispersant, and the average particle size may be in the range of 0.3 to 0.8 μm.

  According to the present invention, it is possible to obtain a heat-sensitive recording material having excellent moisture resistance and heat resistance, high recording sensitivity, and excellent dot reproducibility.

  There are various combinations of heat-sensitive recording materials to be contained in the heat-sensitive recording layer of the heat-sensitive recording material. Specifically, as a sensitizer, at least one of 1,2-bis (3-methylphenoxy) ethane or 1,2-diphenoxyethane, and as a developer, 2,4′-dihydroxydiphenylsulfone, and In addition, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane as an antioxidant and α- {4-[(hydroxyphenyl) sulfonyl as an additive ] Phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) is used in a specific blending amount As a result, the inventors have found that the balance of moisture resistance, heat resistance, and recording sensitivity is most excellent, and have reached the present invention.

  That is, the heat-sensitive recording material of the present invention is provided with a heat-sensitive recording layer containing at least a leuco dye, a sensitizer, a developer, an antioxidant, and an additive on the support, And 10 to 32% by mass of at least one of 1,2-bis (3-methylphenoxy) ethane or 1,2-diphenoxyethane as the sensitizer with respect to the total solid content of the heat-sensitive recording layer. The developer contains 10 to 28% by mass of 2,4′-dihydroxydiphenylsulfone, and 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexane) as an antioxidant. Hexylphenyl) butane is contained in an amount of 0.1 to 10% by mass, and α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (polymerization degree n = 1 to 7) as an additive. ) (Oxyethylene o 3 to 15% by mass of xylethyleneoxy-p-phenylenesulfonyl-p-phenylene).

  The leuco dye used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention is not particularly limited, and one or more known leuco dyes used in the field of heat-sensitive recording materials can be used. Examples of such leuco dyes include triphenylmethane, fluoran, phenothiazine, auramine, spiropyran, and indolylphthalide leuco dyes. Specific examples include, for example, 2-anilino-3-methyl-6-dibutylaminofluorane, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) ) -4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3- (N-ethyl-Np-toluidino) -6-methyl-7-anilinofluorane, 3- (N -Ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-di (n- Til) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-7- (o-chloroanilino) fluorane, 3-di (n-pentyl) amino-6-methyl-7- Anilinofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m -Trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6-methylfluorane, 3-cyclohexylamino-6-chlorofluorane, 3- (N-ethyl) -N-hexylamino) -6-methyl-7- (p-chloroanilino) fluorane and 3,6-bis (dimethylamino) fluor Ren-9-spiro-3 '- (6'-dimethylamino) phthalide and the like.

  Of these leuco dyes, fluoran leuco dyes are preferred. Specifically, preferably 2-anilino-3-methyl-6-dibutylaminofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n- Butyl) amino-7- (o-chloroanilino) fluorane and 3- (N-ethyl-Np-toluidino) -6-methyl-7-anilinofluorane are preferred, and 2-anilino-3 is particularly preferred. -Methyl-6-dibutylaminofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane are preferred. This is because the balance between heat resistance and recording sensitivity is particularly excellent.

  The content of the leuco dye in the heat-sensitive recording layer is preferably in the range of 6 to 12% by mass, more preferably 7 to 11% by mass, based on the total solid content of the heat-sensitive recording layer. This is because when the content is in the range of 6 to 12% by mass, a heat-sensitive recording material having good color development sensitivity and heat resistance can be obtained. If it is less than 6% by mass, the recording sensitivity tends to decrease. On the other hand, if it exceeds 12% by mass, the dot reproducibility tends to decrease.

  The leuco dye can be pulverized with a stirring / pulverizing machine such as a ball mill or a sand mill using water as a dispersion medium. It is preferable to add a water-soluble dispersant to the dispersion medium. Examples of the water-soluble dispersant include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, sulfone-modified polyvinyl alcohol, and hydroxypropylmethylcellulose. In particular, hydroxypropylmethylcellulose is more preferably used because it is excellent in micronization and can be dispersed with a small addition amount. The leuco dye may be pulverized alone, but it is mixed with a sensitizer, developer, and antioxidant, which will be described later, and mixed and pulverized at the same time, so the average particle size tends to be fine and the recording sensitivity is improved. Can be made.

  The average particle size of the leuco dye is preferably 0.2 to 0.7 μm, more preferably 0.3 to 0.5 μm. When the thickness is in the range of 0.2 to 0.7 μm, the dispersion efficiency is good, and a heat-sensitive recording material with excellent image quality can be obtained. If it is less than 0.2 μm, the whiteness tends to decrease. On the other hand, if it exceeds 0.7 μm, the recording sensitivity tends to decrease.

  In the present invention, at least one of 1,2-bis (3-methylphenoxy) ethane and 1,2-diphenoxyethane is used as a sensitizer. These two sensitizers have a relatively low melting point and a high affinity with leuco dyes, so they have a high sensitization effect. For high-sensitivity thermal recording paper that does not require heat resistance, such as fax machines and various printer papers. It is used. Among these, 1,2-bis (3-methylphenoxy) ethane is a material that is excellent in heat resistance and recording sensitivity and is preferably used. At least one sensitizer selected from 1,2-bis (3-methylphenoxy) ethane and 1,2-diphenoxyethane is contained in an amount of 10 to 32% by mass based on the total solid content of the thermosensitive recording layer, More preferably, it is made to contain 15-20 mass%. When the content is less than 10% by mass, the recording sensitivity is lowered. Moreover, when content exceeds 32 mass%, heat resistance will fall. When only one of 1,2-bis (3-methylphenoxy) ethane and 1,2-diphenoxyethane is used, the content of one of them is 10 with respect to the total solid content of the thermosensitive recording layer. If it is used in combination with 1,2-bis (3-methylphenoxy) ethane and 1,2-diphenoxyethane, the total content is 10 to 32% by mass. Good.

  In the present invention, other sensitizers may be further used as long as the effects of the present invention are not impaired. Examples of other sensitizers include stearic acid amide, stearic acid methylene bisamide, stearic acid ethylene bisamide, 4-benzylbiphenyl, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di- (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, 2-naphthylbenzyl ether, 1- (2 -Naphthyloxy) -2-phenoxyethane, 1,3-di (naphthyloxy) propane, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, dibutyl terephthalate, dibenzyl terephthalate Etc.

  In the present invention, 2,4'-dihydroxydiphenylsulfone is used as the developer. Since 2,4'-dihydroxydiphenyl sulfone is excellent in recording sensitivity, it can be preferably used. The content of 2,4'-dihydroxydiphenyl sulfone is 10 to 28% by mass, preferably 13 to 20% by mass, based on the total solid content of the thermosensitive recording layer. When the content is less than 10% by mass, the recording sensitivity is lowered. Moreover, when it exceeds 28 mass%, dot reproducibility will fall.

  The average particle size of 2,4'-dihydroxydiphenylsulfone is not particularly limited, but is preferably 0.7 to 1.2 µm, more preferably 0.8 to 1.0 µm. When the thickness is in the range of 0.7 to 1.2 μm, the dispersion efficiency is good, and a heat-sensitive recording material with excellent image quality is easily obtained. If it is less than 0.7 μm, the dot reproducibility may be lowered. On the other hand, if it exceeds 1.2 μm, the recording sensitivity tends to decrease.

  Moreover, in this invention, you may further use another color developer in the range which does not inhibit the effect made into the objective of this invention. Examples of other developers include 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 4,4′-isopropylidenediphenol, 4,4′-cyclohexene. Silidene diphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-dihydroxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, 4-hydroxy- Phenolic properties such as 4′-methyldiphenylsulfone, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene Compound, Np-tolylsulfonyl-N′-phenylurea, 4,4′-bis [(4-methyl- 3-phenoxycarbonylaminophenyl) ureido] diphenylmethane, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, Np-tolylsulfonyl-N′-p-butoxyphenyl Compounds having a sulfonyl group and a ureido group in the molecule such as urea, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5- [P- (2-p-methoxyphenoxyethoxy) cumyl] zinc salts of aromatic carboxylic acids such as salicylic acid.

  In the present invention, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is contained in the heat-sensitive recording layer as an antioxidant. 1,1,3-Tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane has an effect as an antioxidant and is used for obtaining the storability of a recorded image. Use in combination with a sensitizer and a developer is further effective in improving plasticizer resistance and heat resistance. The content of the antioxidant in the heat-sensitive recording layer is in the range of 0.1 to 10% by mass with respect to the total solid content of the heat-sensitive recording layer. More preferably, it is 1-5 mass%. If it is less than 0.1% by mass, the plasticizer resistance is lowered. Moreover, when it exceeds 10 mass%, heat resistance will fall.

  In the present invention, α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethylene) is further added as an additive in the heat-sensitive recording layer. Oxy-p-phenylenesulfonyl-p-phenylene). The additive is used to obtain the storability of the recorded image, but when used in combination with the above-described sensitizer and developer, the plasticizer resistance, water resistance, and heat resistance are improved. The preservability with respect to the agent and the like can be improved. The content of the additive in the heat-sensitive recording layer is 3 to 15% by mass, preferably 3 to 8% by mass, based on the total solid content of the heat-sensitive recording layer. When the content in the heat-sensitive recording layer is less than 3% by mass, the plasticizer resistance and water resistance are lowered. Moreover, when it exceeds 15 mass%, heat resistance will fall.

  Α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) as an additive is It is preferable to grind using a water-soluble dispersant such as polyvinyl alcohol. When wet pulverization is performed in the presence of a water-soluble dispersant, the average particle diameter tends to be finer, and it can be more suitably used as a preservability improver for oils, plasticizers and the like.

  The average particle diameter of α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) is 0. .3 to 0.8 μm is preferable, and 0.4 to 0.6 μm is more preferable. When the thickness is in the range of 0.3 to 0.8 μm, the dispersion efficiency is good, and a thermal recording material with excellent image quality is easily obtained. If it is less than 0.3 μm, the recording sensitivity tends to decrease, and if it exceeds 0.8 μm, the dot reproducibility tends to decrease.

  Sensitizer (at least one of 1,2-bis (3-methylphenoxy) ethane or 1,2-diphenoxyethane), developer (2,4′-dihydroxydiphenylsulfone), and antioxidant The agent (1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane) can be individually pulverized so as to have a desired particle diameter. However, in the present invention, it is preferable that the sensitizer, the developer, and the antioxidant are mixed in the presence of a water-soluble dispersant and simultaneously pulverized. This is because the average particle diameter tends to be fine and the recording sensitivity is improved. As a pulverization method, water can be used as a dispersion medium, and pulverization can be performed by a stirring / pulverizing machine such as a ball mill or a sand mill. It is preferable to add a water-soluble dispersant to the dispersion medium. As the water-soluble dispersant, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, sulfone-modified polyvinyl alcohol, hydroxypropyl methylcellulose, and the like can be used. In particular, hydroxypropylmethylcellulose is more preferably used because it is excellent in micronization and can be dispersed with a small addition amount.

  The average particle size of the mixed dispersion is preferably 0.7 to 1.2 μm, more preferably 0.8 to 1.0 μm. When the thickness is in the range of about 0.7 to 1.2 μm, the dispersion efficiency is good, and a heat-sensitive recording material with excellent image quality can be obtained.

  In addition, the heat-sensitive recording layer may contain a known pigment used for a normal heat-sensitive recording material. Specific examples of the pigment include, for example, kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, amorphous silica, titanium oxide, magnesium carbonate, magnesium silicate, aluminum hydroxide, colloidal silica, urea-formalin resin filler, plastic pigment, and the like. Is mentioned. The content of these pigments in the heat-sensitive recording layer is not particularly limited, but is preferably 1 to 35% by mass based on the total solid content of the heat-sensitive recording layer.

  The heat sensitive recording layer preferably contains an adhesive. For example, polyvinyl alcohol of various molecular weights, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, acrylic acid amide-acrylic acid ester copolymer Polymers, water-soluble polymer materials such as acrylic acid amide-acrylic acid ester-methacrylic acid terpolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein, and polyacetic acid Vinyl, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer Body, and styrene - butadiene - latex of a hydrophobic polymer such as an acrylic copolymer. Can be used in combination with one or more kinds.

  The content of the adhesive in the heat-sensitive recording layer is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, based on the total solid content of the heat-sensitive recording layer. If it is in the range of 5 to 40% by mass, there is no problem with the strength of the thermosensitive recording layer, and there is no fear of a decrease in recording sensitivity. In the case where a water-soluble dispersant is used at the time of pulverization of the material to be contained in the heat-sensitive recording layer such as the leuco dye, the sensitizer or the developer, the water-soluble dispersant is used as it is in the heat-sensitive recording layer. It can also be used as an adhesive contained.

  The heat-sensitive recording layer may contain various auxiliaries as necessary in addition to the above-described materials. Examples of such auxiliary agents include lubricants (for example, zinc stearate, calcium stearate, polyethylene wax, polyolefin resin emulsion, etc.), antifoaming agents, wetting agents, preservatives, fluorescent whitening agents, dispersing agents, thickeners, Known materials such as a colorant, an antistatic agent, and a crosslinking agent can be used.

  As the support used in the heat-sensitive recording material of the present invention, paper, coated paper coated with pigment and latex on the surface, synthetic paper having a multilayer structure made of polyolefin resin, plastic film, or these A composite sheet or the like can be selected.

  As a method for providing the heat-sensitive recording layer on the support, the heat-sensitive recording layer coating liquid can be applied to the support and dried. The thermal recording layer coating solution can be obtained by mixing the above-mentioned various materials dissolved or dispersed in water.

  The method for applying the coating solution for the heat-sensitive recording layer to the support is not particularly limited. For example, air knife coating, varibar blade coating, pure blade coating, gravure coating, rod blade coating, short dwell coating, curtain Any conventionally known coating methods such as coating, bar coating, and die coating can be employed.

The coating amount of the heat-sensitive recording layer coating liquid on the support is not particularly limited, but is preferably 1 to 10 g / m ² in terms of solid weight per side of the support, and more preferably 4 to it is preferable to 7 g / ^{m 2.}

An undercoat layer may be provided between the support and the thermosensitive recording layer as necessary. The recording sensitivity and the recording running property can be further improved. The undercoat layer can be a pigment coating layer mainly composed of a pigment and an adhesive. The coating amount of the undercoat layer is not particularly limited, preferably in the 3 to 10 g / ^{m 2,} and more preferably a 5~8g / ^{m 2.}

  The pigment used for the undercoat layer is not particularly limited, and examples thereof include inorganic pigments such as calcined clay, calcined kaolin, amorphous silica, light calcium carbonate, and talc. The content of the pigment in the undercoat layer is not particularly limited, but is preferably 50 to 90% by mass and more preferably 60 to 80% by mass with respect to the total solid content of the undercoat layer.

  As the adhesive used in the undercoat layer, the adhesive used in the heat-sensitive recording layer can be used as appropriate, and starch-vinyl acetate graft copolymers, various polyvinyl alcohols, and styrene / butadiene copolymer latex are particularly preferable. . Examples of the various polyvinyl alcohols include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. Although it does not specifically limit also about content of the adhesive agent in undercoat, 1-20 mass% is preferable with respect to the total solid of undercoat, and 2-10 mass% is more preferable.

  Moreover, various auxiliary agents can be used for the undercoat layer as required. Examples of such auxiliaries include lubricants, antifoaming agents, wetting agents, preservatives, fluorescent brighteners, dispersants, thickeners, colorants, antistatic agents, crosslinking agents, and the like.

  As a method of providing the undercoat layer on the support, it can be provided by applying an undercoat layer coating solution to the support and drying it. The undercoat layer coating solution can be obtained by dissolving or dispersing the various materials described above in water.

  The method for applying the coating solution for the undercoat layer is not particularly limited. For example, air knife coating, varibar blade coating, pure blade coating, gravure coating, rod blade coating, short dwell coating, curtain coating, die coating Any conventionally known coating method such as the above can be employed.

  In the heat-sensitive recording material of the present invention, it is preferable to further provide a protective layer on the heat-sensitive recording layer. As the component constituting the protective layer, known pigments, adhesives, various auxiliary agents and the like can be used.

  Examples of the pigment used in the protective layer include amorphous silica, kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, urea-formalin resin filler, etc. Plastic pigments and the like.

  Examples of the adhesive used for the protective layer include polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl acetal, polyethyleneimine, polyvinylpyrrolidone, acrylic resin, starch and derivatives thereof, cellulose and derivatives thereof, gelatin, and casein. Of these, polyvinyl alcohol or modified polyvinyl alcohol is preferred because it is particularly excellent in the protection of the heat-sensitive recording layer against solvents such as plasticizers and oils. And various modified polyvinyl alcohols are more preferably used. Among these modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohol having a polymerization degree of 500 to 5000, particularly 700 to 4500, and diacetone-modified polyvinyl alcohol having a polymerization degree of 500 to 3000, particularly 700 to 3000 are preferably used.

  In addition, various protective agents such as lubricants, antifoaming agents, wetting agents, preservatives, fluorescent whitening agents, dispersing agents, thickening agents, coloring agents, antistatic agents, crosslinking agents, etc. You may add an auxiliary agent suitably.

The coating amount of the protective layer is preferably 0.5 to 2.0 g / m ^{2 in} terms of solid content, and more preferably 0.8 to 1.5 g / m ² . The method for applying the coating solution for the undercoat layer is not particularly limited. For example, conventional methods such as air knife coating, varibar blade coating, pure blade coating, gravure coating, rod blade coating, short dwell coating, curtain coating, die coating, etc. Any known coating method can be employed.

  Examples are shown below, but the present invention is not particularly limited thereto. Moreover, unless otherwise indicated, the part and% in an example show a mass part and mass%, respectively.

<Example 1>
(Formation of undercoat layer)
Water 2 parts by weight calcined clay (trade name: manufactured by BASF, Ansilex 93) 80 parts by weight polyvinyl alcohol 10% aqueous solution (trade name: manufactured by Kuraray Co., Ltd., PVA-217) 2 parts by weight styrene / butadiene copolymer latex (solid content Density 40%)
(Product name: Nippon A & L, Smartex PA-9281) 16 parts by mass

This composition was mixed and stirred to obtain an undercoat layer coating solution. This undercoat layer coating solution was applied and dried on one surface of the fine paper so that the coating amount after drying was 5 g / m ² to form an undercoat layer.

(Preparation of liquid A)
2-anilino-3-methyl-6-dibutylaminofluorane (trade name: Yamada Chemical Co., Ltd., ODB-2) 25 parts by mass polyvinyl alcohol 10% aqueous solution (trade name: Kuraray Co., Ltd., PVA-217) 40 parts by mass 35 parts by weight of water

  This composition was pulverized with a ball mill until the average particle size became 0.5 μm to obtain Liquid A.

(Preparation of B liquid)
1,2-bis (3-methylphenoxy) ethane (trade name: manufactured by Sanko Co., Ltd., KS-232) 20 parts by mass 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) Butane (trade name: manufactured by Asahi Denka Co., Ltd., DH-43) 1 part by mass 2,4′-dihydroxydiphenyl sulfone (trade name: manufactured by Nikka Chemical Co., Ltd., BPS-24C) 14 parts by mass of polyvinyl alcohol 10% aqueous solution (commodity Name: Kuraray, PVA-217)
20 parts by weight water 45 parts by weight

  This composition was pulverized with a ball mill until the average particle size became 0.9 μm to obtain a liquid B.

(Preparation of liquid C)
α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) (trade name: Nippon Soda) D-90) 25 mass parts polyvinyl alcohol 10% aqueous solution (trade name: Kuraray Co., Ltd., PVA-217) 40 mass parts water 35 mass parts

  This composition was pulverized with a ball mill until the average particle size became 0.6 μm to obtain liquid C.

(Preparation of thermal recording layer coating solution)
A liquid 10 parts by mass B liquid 45 parts by mass C liquid 8 parts by mass Calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., Hakuenka PZ) 8 parts by mass polyvinyl alcohol 10% aqueous solution (trade name: Kuraray Co., Ltd., PVA-217) 5 parts by mass styrene・ Butadiene copolymer latex (solid content: 40%)
(Product name: Nippon A & L, Smartex PA-9281) 6 parts by weight water 18 parts by weight

  The composition was mixed and stirred to obtain a thermal recording layer coating solution.

(Formation of heat-sensitive layer)
A thermal recording layer was formed by applying and drying the thermal recording layer coating solution on the undercoat layer so that the coating amount after drying was 5 g / m ² .

(Preparation of D liquid)
Aluminum hydroxide 30 parts by mass Polyvinyl alcohol 10% aqueous solution (trade name: PVA-217, manufactured by Kuraray Co., Ltd.) 20 parts by mass Water 50 parts by mass

  This composition was pulverized with a ball mill until the average particle size became 0.7 μm to obtain a liquid D.

(Preparation of coating solution for protective layer)
D liquid 45 mass parts polyvinyl alcohol 10% aqueous solution (trade name: Kuraray Co., Ltd., PVA-217) 35 mass parts zinc stearate dispersion 36%
(Trade name: manufactured by Chukyo Yushi Co., Ltd., Himicron F-930) 6 parts by mass crosslinking agent (trade name: KBX-0155, manufactured by Showa Polymer Co., Ltd.) 12 parts by mass water 2 parts by mass

  This composition was mixed and stirred to obtain a protective layer coating solution.

(Formation of protective layer)
A protective layer coating solution is applied and dried on the heat-sensitive recording layer so that the coating amount after drying is 0.8 g / m ² to provide a protective layer, followed by supercalender treatment. A heat-sensitive recording material was obtained.

<Example 2>
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount of liquid B was 55 parts by mass and the amount of liquid C was 3 parts by mass in the preparation of the thermal recording layer coating liquid.

<Example 3>
The coating amount of the undercoat layer coating solution after drying is changed to 8 g / m ² , the coating amount of the thermal recording coating solution after drying is changed to 7 g / m ² , and the protective layer coating solution A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the coating amount after drying was changed to 1.5 g / m ² .

<Example 4>
In the preparation of the liquid B, except that 20 parts by mass of 1,2-bis (3-methylphenoxy) ethane was changed to 20 parts by mass of 1,2-diphenoxyethane (trade name: KS-235, manufactured by Sanko), A heat-sensitive recording material was obtained in the same manner as in Example 1.

<Example 5>
Example 1 except that the blending amount of 1,2-bis (3-methylphenoxy) ethane was 15 parts by mass and the blending amount of 2,4′-dihydroxydiphenylsulfone was 20 parts by mass in the preparation of liquid B. In the same manner, a heat-sensitive recording material was obtained.

<Example 6>
Example 1 except that the blending amount of 1,2-bis (3-methylphenoxy) ethane was 24 parts by mass and the blending amount of 2,4′-dihydroxydiphenylsulfone was 10 parts by mass in the preparation of liquid B. In the same manner, a heat-sensitive recording material was obtained.

<Example 7>
In the preparation of solution B, the amount of 1,2-bis (3-methylphenoxy) ethane was 15 parts by mass, and 1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane A thermosensitive recording material was obtained in the same manner as in Example 1 except that the amount was 5 parts by mass and the amount of 2,4′-dihydroxydiphenylsulfone was 15 parts by mass.

<Comparative Example 1>
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the amount of 1,2-bis (3-methylphenoxy) ethane was changed to 3 parts by mass in the preparation of Liquid B.

<Comparative example 2>
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the amount of 1,2-bis (3-methylphenoxy) ethane was 35 parts by mass in the preparation of Liquid B.

<Comparative Example 3>
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was not blended in the preparation of solution B.

<Comparative example 4>
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the amount of 1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was 20 parts by mass in the preparation of Liquid B. Got.

<Comparative Example 5>
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the amount of 2,4′-dihydroxydiphenyl sulfone was changed to 5 parts by mass in the preparation of the liquid B.

<Comparative Example 6>
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount of 2,4′-dihydroxydiphenylsulfone was 35 parts by mass in the preparation of Liquid B.

<Comparative Example 7>
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the heat-sensitive recording layer coating liquid, the amount of the liquid B was 70 parts by mass and the liquid C was not added.

<Comparative Example 8>
In preparation of liquid B, 20 parts by mass of 1,2-bis (3-methylphenoxy) ethane was mixed with 2- (2′-hydroxy-5′-methylphenyl) benzotriazole (trade name: Cellozol K-840 / Chukyo). A thermal recording material was obtained in the same manner as in Example 1 except that the amount was changed to 20 parts by mass.

(1) Color development test Using a thermal tester (TH-PMD / manufactured by Okura Electric Co., Ltd.), thermal recording was performed on the thermal recording layer of the obtained thermal recording medium under the following conditions.
Applied voltage 24.0V
Printing pulse width 1.0msec
Printing energy 0.50mj / dot

After the thermal recording, the density of the recorded portion was visually determined and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

(2) Moisture resistance test Using a thermal tester (TH-PMD / manufactured by Okura Electric Co., Ltd.), thermal recording was performed on the thermal recording layer of the obtained thermal recording medium under the following conditions.
Applied voltage 24.0V
Printing pulse width 1.0msec
Printing energy 0.50mj / dot

The thermal recording material on which thermal recording was performed was placed under a high humidity condition of 40 ° C. × 90% RH for 24 hours, and the density of the recorded portion after placement was judged visually, and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

(3) Heat resistance test Using a thermal testing machine (TH-PMD / manufactured by Okura Electric Co., Ltd.), thermal recording was performed on the thermal recording layer of the obtained thermal recording medium under the following conditions.
Applied voltage 24.0V
Printing pulse width 1.0msec
Printing energy 0.50mj / dot

The heat-sensitive recording material on which the heat-sensitive recording was performed was kept for 24 hours under a high-temperature drying condition at 60 ° C., and the density of the recorded portion after placement was visually determined and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

(4) Water Resistance Test Using a thermal tester (TH-PMD / manufactured by Okura Electric Co., Ltd.), thermal recording was performed on the thermal recording layer of the obtained thermal recording medium under the following conditions.
Applied voltage 24.0V
Printing pulse width 1.0msec
Printing energy 0.50mj / dot

The heat-sensitive recording material on which heat-sensitive recording was performed was immersed in tap water for 24 hours, and after natural drying, the density of the recorded portion was visually determined and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

(5) Plasticizer resistance test Using a thermal tester (TH-PMD / manufactured by Okura Electric Co., Ltd.), thermal recording was performed on the thermal recording layer of the obtained thermal recording medium under the following conditions.
Applied voltage 24.0V
Printing pulse width 1.0msec
Printing energy 0.40mj / dot

40 ° C. × 90% in a state where a polyvinyl chloride film (trade name: Dialap / Mitsubishi Resin Co., Ltd.) is in contact with the recording portion and the non-recording portion on the heat-sensitive recording layer of the heat-sensitive recording material subjected to heat-sensitive recording. The sample was placed under high humidity conditions of RH for 24 hours, and the density of the recorded part after placement was visually determined and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

(6) Dot reproducibility test Using a thermal evaluation machine (trade name: SA4T, manufactured by Toshiba Tec Corporation), the thermal recording medium was solidly colored at a printing speed of 152.4 mm / sec and a printing density of -10, and the color of the recording area was developed. The properties were visually observed and evaluated in the following three stages.
A: The color developability after the test is very clear and there is no problem in practical use. ○: The color developability after the test is clear and there is no problem in practical use. X: The color developability after the test is not clear and there is a problem in practical use.

  The average particle diameter of each particle used in each Example and Comparative Example was measured by a scattering laser light diffraction method (Leeds + Northrup) using a microtrack.

  As shown in Table 1, the thermal recording materials obtained in Examples 1 to 7 all have high dot reproducibility, and the image stability obtained by recording is particularly excellent in moisture resistance and plasticizer resistance.

  As is apparent from the above, the present invention is excellent in dot reproducibility without adversely affecting various properties, and the image stability obtained by recording is a quality with less fading due to external conditions such as humidity, heat, water, and plasticizer. Stable thermal recording material can be obtained.

Claims (3)

A method for producing a heat-sensitive recording material, wherein a heat-sensitive recording layer containing at least a leuco dye, a sensitizer, a developer, an antioxidant, and an additive is provided on a support ,
In 100% by mass of the mixed dispersion, 15 to 24% by mass of the sensitizer, 10 to 24% by mass of the developer, 1 to 5% by mass of the antioxidant, and a water-soluble dispersant are wet-mixed and pulverized. To make a mixed dispersion
A coating liquid is prepared by mixing the mixed dispersion and the additive, and a thermal recording layer is formed by applying the coating liquid,
As the sensitizer, 1,2-bis (3-methylphenoxy) ethane or 1,2-diphenoxyethane is used,
As the developer, 2,4′-dihydroxydiphenylsulfone is used,
As the antioxidant, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is used,
as well as,
As the additive, α- {4-[(hydroxyphenyl) sulfonyl] phenyl} -ω-hydroxypoly (degree of polymerization n = 1-7) (oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene) is used. A method for producing a heat-sensitive recording material, wherein the method is used . 2. The method for producing a thermal recording material according to claim 1 , wherein an average particle size of the mixed dispersion is in a range of 0.7 to 1.2 μm. It said additive, which has been wet-milled in the presence of a water-soluble dispersant, according to claim 1 or 2, the average particle size is characterized to be in the range of 0.3~0.8μm A method for producing a thermal recording material.