JP2011213089A - Heat-sensitive recording medium - Google Patents

Abstract

An object of the present invention is to provide a thermal recording material excellent in recording image quality, water resistance and sticking resistance.
A heat-sensitive recording medium comprising a heat-sensitive recording layer containing a leuco dye, a colorant and a water-based adhesive on a support, and further having a protective layer containing a water-based adhesive on the heat-sensitive recording layer. It contains at least one selected from sodium glyoxylate, di (glyoxylic acid) calcium, and ammonium glyoxylate, and kaolin having an average particle diameter of 0.1 to 1.0 μm, and the content of the kaolin is a protective layer. A heat-sensitive recording material comprising 50 to 70% by mass with respect to the total solid content.
[Selection figure] None

Description

  The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between an electron-donating compound and an electron-accepting compound and that can obtain a recorded image by a color-forming reaction by thermal energy.

  A heat-sensitive recording material in which a recorded image is obtained by bringing an electron-donating compound and an electron-accepting compound into contact with each other by thermal energy is well known. Such a heat-sensitive recording material is relatively inexpensive, has a compact recording device, and is easy to maintain, so it is used for recording media such as facsimiles and various computers.

  In recent years, in particular, receipts for gas, water, electricity bills, ATM usage statements for financial institutions, various receipts, etc., financial record sheets (for so-called handy terminals), thermal recording labels for POS systems, and thermal recording labels. Thermal recording materials are also used for recording tags and the like.

  The heat-sensitive recording material for such applications may be used outdoors in the rainy weather or may be used indoors in contact with water, so that the heat-sensitive recording material is excellent in water resistance and may break even when wet. It is required not to peel off.

  In addition, in the thermal recording medium for such use, there are increasing opportunities for various bar codes to be used for thermal recording printing, and there is a demand for a thermal recording medium having barcode printing suitability.

  As the amount of information contained in a barcode increases, there is an increasing demand for high-definition barcode printing. However, high-definition barcodes have the problem that the readability is greatly reduced due to slight changes in the width of the bar or space due to printing failure such as sticking, or missing barcode due to white spots in printing. Yes. In addition, due to the recent downsizing and power saving of recording devices, there are increasing demands for improving the thermal response and device matching for thermal recording heads.

  That is, there is a need for a heat-sensitive recording material that exhibits the same color density as that of the prior art even at low applied energy due to high speed and power saving, and that is free from printing problems such as sticking.

  For the purpose of improving the water resistance of the heat-sensitive recording material, a method using an acetoacetyl-modified PVA and a water-soluble polyamide resin in the protective layer (see Patent Document 1), the aqueous adhesive in the protective layer is diacetone-modified PVA, Further, a method of containing a polyamidoamine / epichlorohydrin resin in the protective layer and an aqueous adhesive in the heat-sensitive recording layer are diacetone-modified PVA, and further a polyamidoamine / epichlorohydrin resin and a carboxylic acid dihydrazide compound are contained in the heat-sensitive recording layer. A method (see Patent Document 2), a method containing an acetoacetyl-modified resin and a polyamidoamine / epichlorohydrin resin in a protective layer, and a polyvalent carboxylic acid hydrazide compound in a heat-sensitive recording layer (see Patent Document 3), Diacetone acrylamide copolymer modified polyvinyl alcohol as a coating agent , A method of using a water-soluble hydrazine compound and a water-soluble organic amine or ammonia (see Patent Document 4), diacetone-modified polyvinyl alcohol as an adhesive for the protective layer, and a carboxylic acid dihydrazide compound as a crosslinking agent in the heat-sensitive recording layer And a heat-sensitive recording material (see Patent Document 6) containing acetoacetyl-modified PVA, glyoxylate, and glyoxylic acid ester derivative in the protective layer. .

As a technique for suppressing the sticking, it has been reported that a release agent containing silicone oil as a main component is contained in the protective layer (see Patent Document 7). When such silicone oil is used, The problem is that the amount of residue adhering to the head during printing increases.
In addition, it has been reported that sticking is improved by using a vinyl chloride copolymer as a protective layer resin (see Patent Document 8). Even if the sticking in a normal stationary printer is improved, it is insufficient for a low torque printer application represented by a handy terminal printer.
Furthermore, in recent years, it has been desired not to use raw materials containing chlorine or bromine in order to prevent the generation of halogen gas or dioxin during incineration. From this point of view, the use of vinyl chloride copolymer is also desired. Is not preferred.

  Furthermore, it is excellent in recording density and runnability during recording, has very little head wear after continuous printing for a long time, and is an average in the protective layer as a thermal recording material with little whitening of the recorded portion even when printed with high energy. A thermal recording material containing 50 to 300% by weight of kaolin having a particle size of 0.5 μm or less with respect to the aqueous polymer (see Patent Document 9), and protection with improved balance between water resistance and sticking resistance As a heat-sensitive recording material having a layer, a protective layer adhesive is a monomer containing at least (meth) acrylonitrile, (meth) acrylic acid ester and ethylenically unsaturated carboxylic acid, a specific dissolved oxygen in the reaction system aqueous phase There is also a thermal recording material (see Patent Document 10) which is a polymer emulsion obtained by emulsion polymerization under the conditions of the concentration and the specific amount of redox polymerization initiator used. It is draft.

JP 2002-019196 A JP 2002-127601 A JP 2002-301868 A Japanese Patent Laid-Open No. 10-087936 JP 11-314457 A WO2009 / 028646 JP 2003-276334 A Japanese Patent Laid-Open No. 11-254831 JP-A-8-324114 Japanese Patent Laid-Open No. 10-175376

  An object of the present invention is to provide a heat-sensitive recording material excellent in recording image quality, water resistance and sticking resistance.

  As a result of various studies on the above problems, the present inventors have found that a heat-sensitive recording layer containing a leuco dye, a colorant and a water-based adhesive on the support, and a protective layer containing a water-based adhesive on the heat-sensitive recording layer. In the heat-sensitive recording medium, the protective layer contains at least one selected from sodium glyoxylate, di (glyoxylic acid) calcium and ammonium glyoxylic acid, and kaolin having an average particle size of 0.1 to 1.0 μm as a pigment. It has been found that when the content of the kaolin is 50 to 70% by mass with respect to the total solid content of the protective layer, the above problems can be solved, and the present invention has been completed.

  That is, the present invention provides the following thermal recording material.

Item 1: A heat-sensitive recording layer having a heat-sensitive recording layer containing a leuco dye, a colorant and a water-based adhesive on a support, and further having a protective layer containing a water-based adhesive on the heat-sensitive recording layer. And at least one selected from sodium glyoxylate, di (glyoxylic acid) calcium and ammonium glyoxylic acid, and kaolin having an average particle diameter of 0.1 to 1.0 μm as a pigment, and the content of the kaolin is a protective layer A heat-sensitive recording material comprising 50 to 70% by mass with respect to the total solid content.
Item 2: The heat-sensitive recording material according to Item 1, wherein the aqueous adhesive in the protective layer is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.
Item 3: The thermal recording material according to Item 1 or 2, wherein a pH of the coating liquid for the protective layer forming the protective layer is in a range of 3.0 to 7.0.

  The heat-sensitive recording material of the present invention is excellent in recording image quality and water resistance, and also has an effect of excellent sticking resistance.

  The thermal recording material according to the present invention will be described in detail below. In the present invention, in the heat-sensitive recording material having a heat-sensitive recording layer containing a leuco dye, a colorant and a water-based adhesive on the support, and further having a protective layer containing the water-based adhesive on the heat-sensitive recording layer, It contains at least one kind selected from sodium glyoxylate, di (glyoxylate) calcium and ammonium glyoxylate and kaolin having a specific average particle size as a pigment, and the content of the kaolin in the total solid content of the protective layer On the other hand, it is 50 to 70% by mass.

[Glyoxylate]
First, the glyoxylate contained in the protective layer of the present invention will be described.
Examples of the glyoxylate include various salts, including alkali metal and glyoxylic acid metal salts, alkaline earth metal and glyoxylic acid metal salts, amines and glyoxylic acid salts, and preferably A metal salt of at least one glyoxylic acid selected from a metal salt of an alkali metal and glyoxylic acid and a metal salt of an alkaline earth metal and glyoxylic acid. As a metal salt of alkali metal and glyoxylic acid, for example, a metal salt of alkali metal such as sodium or potassium and glyoxylic acid, as a metal salt of alkaline earth metal and glyoxylic acid, as an alkaline earth metal such as magnesium or calcium, and glyoxylic acid Examples of metal salts and metal salts of amines and glyoxylic acid include salts of amines such as ammonia, monomethylamine, dimethylamine, and trimethylamine and glyoxylic acid.

  In particular, in the present invention, it is considered that the hydrophilicity of the carboxylate group introduced into the crosslinked structure is small compared to the carboxylic acid group, which contributes to the improvement of the water resistance of the crosslinked polymer. As the acid salt, a glyoxylate having a lower solubility in water is preferable. Specifically, the solubility in water at 23 ° C. is 0.01 to 100%, particularly 0.1 to 50%, and further 0.5. Those of ˜20% are preferably used. Specifically, examples of glyoxylate having low water solubility include sodium glyoxylate (solubility: about 17%), di (glyoxylate) calcium (solubility: about 0.7%), ammonium glyoxylate ( (Solubility: 14%).

  As a method for producing glyoxylate, a known method can be used. For example, (1) a method based on a neutralization reaction of glyoxylic acid, (2) a salt of glyoxylic acid with an acid dissociation constant larger than glyoxylic acid, And (3) a method by alkaline hydrolysis of glyoxylic acid ester (see, for example, JP-A-2003-300996). In particular, when the alkaline compound used for the neutralization reaction with glyoxylic acid is highly water-soluble, the method of (1) is a salt of an acid whose glyoxylate salt is low in water solubility and has an acid dissociation constant greater than glyoxylic acid. When the water solubility of is high, the method (2) is preferably used.

  The method (1) is usually carried out using water as a medium. Glyoxylic acid and an alkaline compound, for example, an alkali metal hydroxide or an alkaline earth metal hydroxide are reacted in water, and the precipitated glyoxylate salt is reacted with water. It can be produced by filtration and drying.

  The method (2) is also generally carried out in water, and glyoxylate can be obtained in the same manner as the method (1). Examples of the acid salt having a larger dissociation constant than glyoxylic acid used in the method (2) include alkali metal or alkaline earth metal salts of aliphatic carboxylic acids such as sodium acetate, calcium acetate, and calcium propionate. Can be mentioned.

  In particular, when glyoxylic acid is used as a raw material, there is a possibility that glyoxal, which is a by-product when producing the glyoxylate, may be contained in the crosslinking agent, and the content of such glyoxal is 0% by mass. Although it is most desirable, it is preferably 5% by mass or less, particularly 2% by mass or less, and more preferably 1% by mass or less. When the content of glyoxal is high, the stability of the aqueous solution mixed with acetoacetyl-modified polyvinyl alcohol is lowered, and the pot life is shortened. It may be colored with.

  The protective layer contains at least one kind selected from sodium glyoxylate, di (glyoxylic acid) calcium and ammonium glyoxylate as a crosslinking agent, but the content is the amount of aqueous adhesive used in the protective layer in total It is 0.5-20 mass% with respect to it, Preferably it is about 1-10 mass%.

As the water-based adhesive used for the protective layer in the present invention, at least one of conventionally known water-soluble polymers and water-soluble polymer emulsions can be appropriately used.
Specific examples thereof include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, itaconic acid-modified polyvinyl alcohol, starch, oxidized starch, hydroxy Cellulose derivatives such as methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / anhydrous Maleic acid copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylic acid In addition to water-soluble polymers such as luamide, sodium alginate, gelatin, gum arabic, and casein, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene Examples thereof include emulsions such as vinyl acetate copolymers and latexes such as styrene / butadiene copolymers and styrene / butadiene / acrylic copolymers.
Among these, at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol is particularly preferably used for sticking suppression and water resistance.

  The acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol used in the protective layer were obtained by copolymerizing a monomer having an acetoacetyl group, a diacetone group, and a carboxyl group and a vinyl ester, respectively. It is produced by saponifying the resin.

  The degree of saponification is preferably from about 85 mol% to about 100 mol% of complete saponification, more preferably from about 90 to 100 mol%. The average degree of polymerization is preferably about 300 to 3000, and more preferably about 400 to 2000. The degree of modification is preferably about 0.5 to 10 mol%, more preferably about 1 to 9 mol%. The higher the degree of polymerization and the degree of saponification, the better the water resistance, but it is necessary to select from the paint concentration, viscosity, coating property or drying property according to the situation.

  If the degree of modification is in the range of about 0.5 to 10 mol%, sufficient water resistance is obtained, and the solubility in water does not decrease, so that the solution concentration can be prevented from being lowered.

  The amount of at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol and carboxy-modified polyvinyl alcohol used in the protective layer is 10 to 90% by mass, preferably based on the total solid content of the protective layer, About 15-50 mass% is more preferable.

  As the water-based adhesive used for the protective layer, other adhesives can be used in combination as long as the effects of the present invention are not impaired. Examples of such adhesives include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, silicon-modified polyvinyl alcohol, starch, oxidized starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, diisobutylene and maleic anhydride copolymer. Compound salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, urea resin, melamine resin, amide resin, acrylic resin latex, urethane resin latex, etc. Is mentioned.

  In the present invention, as the pigment for the protective layer, kaolin having an average particle size of 0.1 to 1.0 μm is used in the range of 50 to 70% by mass with respect to the total solid content of the protective layer. The average particle size is more preferably 0.2 to 0.8 μm. When the average particle size is less than 0.1 μm, sticking occurs between the thermal head and the thermal recording medium during recording, and the recording runnability is deteriorated. Further, if the content is less than 50% by mass, the sticking resistance is inferior, and if it exceeds 70% by mass, the water resistance is inferior. If the average particle size and content of the kaolin used are within the above ranges, a thermal recording material excellent in recording image quality and excellent in water resistance and sticking resistance can be obtained. The average particle diameter is expressed as a median diameter measured by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation). The pigment dispersion used for the measurement is a region where a pigment slurry having a solid content concentration of 5% by mass prepared by adding 0.05% of a dispersant (sodium polyacrylate) to the pigment can be measured with the measuring device. It was obtained by diluting to a minimum.

  Further, other pigments can be used in combination as long as the effects of the present invention are not impaired. Such pigments include, for example, inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, calcined kaolin, nylon resin filler, urea / formalin resin filler, raw Examples include organic pigments such as starch particles. Among these, aluminum hydroxide is preferably used because it has little deterioration in barrier properties against chemicals such as plasticizers and oils, and also has a small reduction in recording density.

  Furthermore, the stability of the coating liquid for the protective layer is further improved by incorporating a water-soluble acidic compound in the protective layer. The water-soluble acidic compound added to the protective layer coating solution is not particularly limited, but boric acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, Water-soluble organic acids having a carboxyl group such as adipic acid, pimelic acid, fumaric acid, maleic acid, tartaric acid, citric acid, lactic acid, benzoic acid, phthalic acid, benzenetricarboxylic acid and the like are preferable.

  The addition amount of the water-soluble acidic compound is not particularly limited, but is preferably added so that the pH of the protective layer coating solution is 3.0 to 7.0, and is in the range of 4.0 to 6.0. Is more preferable. If pH is the range of 3.0-7.0, it can suppress that the viscosity of a coating liquid becomes high with time.

  Other auxiliary agents that can be added to the coating solution for the protective layer include, for example, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium alkylbenzenesulfonate, sodium dioctylsulfosuccinate, sulfone. Surfactants such as modified polyvinyl alcohol and sodium polyacrylate, water resistant agents such as dialdehyde starch, methylol urea, epoxy compounds, hydrazine compounds, and UV absorbers, fluorescent dyes, colored dyes, mold release agents, oxidation An auxiliary agent such as an inhibitor may be added.

  For the protective layer coating solution, an aqueous solution in which at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol and carboxy-modified polyvinyl alcohol is dissolved, kaolin, sodium glyoxylate, di (glyoxylic acid) calcium and ammonium glyoxylate And, if necessary, other pigments, water-soluble acidic compounds and various auxiliaries are mixed and stirred.

  Next, the thermal recording layer will be described.

  Examples of the thermal recording system having an electron donating compound and an electron accepting compound include a combination of a leuco dye and a colorant, a combination of a diazonium salt and a coupler, and a combination of a transition element such as iron, cobalt and copper and a chelate compound. And a combination of an aromatic isocyanate compound and an imino compound, and the combination of a leuco dye and a colorant is preferably used because of its excellent color density. Hereinafter, the thermosensitive recording layer comprising a combination of a leuco dye and a colorant will be described in detail.

  Various known leuco dyes and colorants can be used. Specific examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl). ) -6-dimethylaminophthalide, 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6 -Methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) ) Amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p) Toluidino) -6-methyl-7-anilinofluorane, 3-di (nbutyl) amino-6-chloro-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3 Piperidino-6-methyl-7-anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6 , 7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7-chloro Fluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino) phthalide and the like can be mentioned.

  Of course, it is not limited to these, Moreover, 2 or more types can also be used together. The amount of the leuco dye used is not limited because it varies depending on the colorant used, but is preferably about 3 to 50% by mass, particularly about 5 to 40% by mass, based on the total solid content of the heat-sensitive recording layer. .

  Examples of the colorant include 4,4′-isopropylidenediphenol, 4,4′-cyclohexylidenediphenyl, 1,1-bis (4-hydroxyphenyl) -ethane, 1,1-bis (4-hydroxy). Phenyl) -1-phenylethane, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 3,3′-diallyl-4,4′- Dihydroxydiphenylsulfone, 2,2′-bis [4- (4-hydroxyphenyl) phenoxy] diethyl ether, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, 4-hydroxybenzoic acid Acid benzyl ester, N, N′-di-m-chlorophenylthiourea, Np-to Rusulfonyl-N′-phenylurea, 4,4′-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4- {3- (p- Examples include zinc tolylsulfonyl) propyloxy] salicylate, zinc 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylate, and a diphenylsulfone bridged compound represented by the following general formula (1).

（式中、ｎは１〜７の整数を表す。）

(In the formula, n represents an integer of 1 to 7.)

  The amount of the colorant used is not limited because it varies depending on the leuco dye used, but it is preferably about 10 to 70% by mass, particularly about 12 to 50% by mass, based on the total solid content of the heat-sensitive recording layer.

  The heat-sensitive recording layer may contain a storability improving agent for increasing the storage stability of the recording portion and a sensitizer for increasing the recording sensitivity. Specific examples of such preservability improvers include, for example, 2,2′-ethylidenebis (4,6-di-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 1 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 2,2 Hindered phenol compounds such as bis (4-hydroxy-3,5-dimethylphenyl) propane, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone , Diglycidyl terephthalate, cresol novolac epoxy resin, phenol novolac epoxy resin, vinyl Epoxy compounds such as bisphenol A type epoxy resin, N, N'-di-2-naphthyl -p- phenylenediamine, bis (4-ethylene iminocarbonyl aminophenyl) include methane and the like.

  When a preservability improver is used, the amount used may be an effective amount for improving the preservability, but it is usually about 1 to 30% by mass with respect to the total solid content of the thermosensitive recording layer. It is preferable to mix | blend in the range of about 5-20 mass%.

  Specific examples of the sensitizer include, for example, stearamide, methylenebisstearate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, p- Tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ) Ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetoluidide, p-acetophene Examples include zido, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, and oxalic acid dibenzyl ester. .

  When a sensitizer is used, the amount used may be an effective amount for sensitization, but is usually about 2 to 40% by mass, particularly 5 to 5% by mass based on the total solid content of the heat-sensitive recording layer. It is preferable to mix in the range of about 25% by mass.

  The heat-sensitive recording layer uses water as a dispersion medium, leuco dye, colorant, if necessary, sensitizer, preservability improver, etc., or separately with an agitator / pulverizer such as a ball mill, attritor, sand mill, etc. After finely dispersing so that the diameter is 2 μm or less, a heat-sensitive recording layer coating solution prepared by adding an aqueous adhesive or the like is applied to one surface of the support and dried. The aqueous adhesive in the heat-sensitive recording layer preferably contains at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.

  Furthermore, various auxiliary agents can be added to the thermal recording layer coating liquid as necessary. For example, kaolin, light (heavy) calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, Amorphous silica, pigments such as urea / formalin resin filler, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salt, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, Examples thereof include waxes such as paraffin wax and ester wax, hydrazine compounds, glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compounds, and other water-resistant agents, antifoaming agents, coloring dyes and fluorescent dyes.

  The support used in the heat-sensitive recording material of the present invention is not particularly limited, and examples thereof include neutral or acidic high-quality paper, synthetic paper, transparent or translucent plastic film, and white plastic film. In addition, although the thickness of a support body is not specifically limited, Usually, it is about 20-200 micrometers.

  In the present invention, if necessary, an undercoat layer can be provided between the support and the thermosensitive recording layer in order to further improve the recording sensitivity and the recording runnability. The undercoat layer has an oil absorption amount of 70 ml / 100 g or more, in particular, about 80 to 150 ml / 100 g of an oil-absorbing pigment and / or organic hollow particles and / or thermally expandable particles, and an undercoat layer coating solution containing an adhesive as a main component. Is formed by coating and drying on a support. Here, the oil absorption is a value determined according to the method of JIS K5101.

  Various types of oil-absorbing pigments can be used. Specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, particularly about 0.02 to 3 μm. The amount of the oil-absorbing pigment used can be selected from a wide range, but generally it is preferably about 2 to 95% by mass, particularly about 5 to 90% by mass, based on the total solid content of the undercoat layer.

  If necessary, a protective layer, a printing layer, a magnetic recording layer, or an ink jet recording layer may be provided on the back side of the support of the heat-sensitive recording medium, or a smoothing process such as supercalendering may be performed after each layer is smeared. Is also possible. Further, various known techniques in the heat-sensitive recording body production field such as providing a pressure-sensitive adhesive layer on the back side of the support of the heat-sensitive recording body can be added as necessary.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” respectively represent “parts by mass” and “% by mass” unless otherwise specified.

Example 1
-Preparation of coating solution for undercoat layer Fine hollow particles (trade name: Ropaque SN-) were obtained by dispersing 60 parts of calcined kaolin (trade name: Ansilex 93, manufactured by Engelhard) in 80 parts of water. 1055, 75 parts by Rohm & Haas, solid content 26.5%), 31 parts styrene-butadiene latex (trade name: L-1571, manufactured by Asahi Kasei Chemicals, solid content 48%), carboxymethylcellulose ( Product name: Serogen 7A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2.5 parts, carboxymethylcellulose (trade name: Serogen AG gum, Daiichi Kogyo Seiyaku Co., Ltd.) 1 part, and 15.5 parts of water were mixed and stirred. The undercoat layer coating solution was obtained.

Preparation of leuco dye dispersion (liquid A) A composition comprising 10 parts of 3-di- (n-butyl) amino-6-methyl-7-anilinofluorane, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water. The mixture was pulverized with a sand mill using a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) until the median diameter became 0.5 μm to obtain a leuco dye dispersion (liquid A).

Preparation of colorant dispersion liquid (liquid B) A composition comprising 10 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water, and a laser diffraction particle size measuring instrument using a sand mill The colorant dispersion (liquid B) was obtained by pulverizing until the median diameter by SALD2200 (manufactured by Shimadzu Corporation) became 1.5 μm.

Colorant dispersion (liquid C) preparation A composition comprising 10 parts of a diphenylsulfone cross-linking compound (trade name: D-90, manufactured by Nippon Soda Co., Ltd.), 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was obtained with a sand mill. A colorant dispersion (liquid C) was obtained by pulverizing until the median diameter was 1.0 μm using a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation).

-Preparation of sensitizer dispersion (liquid D) A composition comprising 10 parts of di-p-methylbenzyl oxalate, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was mixed with a laser diffraction particle size analyzer SALD2200 ( A sensitizer dispersion (liquid D) was obtained by pulverizing until the median diameter by Shimadzu Corporation was 1.0 μm.

Preparation of coating solution for heat-sensitive recording layer Liquid A 33.5 parts, Liquid B 68 parts, Liquid C 5 parts, Liquid D 10.5 parts, fully saponified polyvinyl alcohol (trade name: PVA110, degree of saponification: 99 mol% , Average polymerization degree: 1000, manufactured by Kuraray Co., Ltd. 30 parts, 10% aqueous solution of partially saponified polyvinyl alcohol (trade name: PVA205, saponification degree: 88 mol%, average polymerization degree: 500, manufactured by Kuraray Co., Ltd.) 5 parts, butadiene-based copolymer latex (trade name: P-OY72, manufactured by Japan A & L, solid concentration 48%) 16.5 parts, light calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd.) 42 10 parts of paraffin wax emulsion (trade name: Hydrin L-700, manufactured by Chukyo Oil & Fats Co., Ltd., solid content concentration 30%) and 90.5 parts of water were mixed and stirred to obtain a thermal recording layer coating solution.

Preparation of coating liquid for protective layer Acetoacetyl-modified polyvinyl alcohol (trade name: Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd. 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Z-100, saponification degree: 99.4 mol%, average polymerization degree: 500, modification degree: 5 mol%, Nippon Synthetic Chemical Industry Co., Ltd.) 80 parts of a 20% aqueous solution, Kaolin (trade name: HYDRAGLOSS 90, average particle size: 0.56 μm, manufactured by KaMin LLC), aluminum hydroxide (trade name: Hydylite H-42M, average particle size) : 1.5 μm, Showa Denko Co., Ltd.) 4 parts, zinc stearate aqueous dispersion (trade name: Hydrin Z-8-36, Chukyo Yushi Co., Ltd., solid content concentration 36%) 4.5 parts 2.3 parts of polyethylene wax emulsion (trade name: Chemipearl W400, manufactured by Mitsui Chemicals, solid concentration 40%), 5 parts of 10% aqueous solution of sodium glyoxylate (trade name: SPM-01, manufactured by Nippon Synthetic Chemical Industry) and A composition comprising 53 parts of water was mixed and stirred, and adjusted to pH 5 with a 10% aqueous acetic acid solution to obtain a coating solution for a protective layer. The average particle diameters of kaolin and aluminum hydroxide are median diameters measured by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation).

- a heat-sensitive recording material prepared basis weight of 60 g / m ² on one surface of woodfree paper, undercoat layer coating liquid, heat-sensitive recording layer coating solution, and respectively the protective layer coating liquid application amount after drying 6.0g After coating / drying to form an undercoat layer, a heat-sensitive recording layer, and a protective layer, the surface is smoothed with a super calender after coating / drying so as to be / m ² , 4.5 g / m ² , and 2.0 g / m ² To obtain a heat-sensitive recording material.

Example 2
In the preparation of the protective layer coating liquid of Example 1, di (glucoxylate) calcium (trade name: SPM-02) was used instead of 5 parts of a 10% aqueous solution of sodium glyoxylate (trade name: SPM-01, supra). (Manufactured by Nippon Synthetic Chemical Industry) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 0.5 part was used.

Example 3
Example 1 except that 5 parts of 10% aqueous solution of ammonium glyoxylate was used in place of the 10% aqueous solution of sodium glyoxylate (trade name: SPM-01, supra) in the preparation of the coating solution for the protective layer of Example 1. In the same manner, a heat-sensitive recording material was obtained.

Example 4
In the preparation of the protective layer coating liquid of Example 1, 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Z-200, supra) and acetoacetyl-modified polyvinyl alcohol (trade name: Z-100, supra) In place of 80 parts of a 20% aqueous solution, diacetone-modified polyville alcohol (trade name: DF-10, saponification degree: 98.5 mol%, average polymerization degree: 1000, modification degree: 6 mol%, Japanese vinegar 210 parts of 10% aqueous solution of Bipoval and diacetone-modified polyville alcohol (trade name: DF-05, degree of saponification: 98.5 mol%, average degree of polymerization: 500, degree of modification: 5 mol%, Japan) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 80 parts of a 20% aqueous solution (produced by Binbi-Poval) was used.

Example 5
In the preparation of the protective layer coating liquid of Example 1, 210 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Z-200, supra) and acetoacetyl-modified polyvinyl alcohol (trade name: Z-100, supra) In place of 80 parts of 20% aqueous solution (trade name: T-215, saponification degree: 97 mol%, average polymerization degree: 1100, modification degree: 4 mol%, Nippon Synthetic Chemical Industry) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 370 parts of a 10% aqueous solution manufactured by Kogyo Co., Ltd. was used and water was changed to 0 parts.

Example 6
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 0.5 part of acetic acid was not used in the preparation of the protective layer coating solution of Example 1. The pH of the protective layer coating solution was 7.3.

Comparative Example 1
A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 5 parts of a 10% aqueous solution of sodium glyoxylate (trade name: SPM-01, supra) was not used in the preparation of the coating solution for the protective layer of Example 1. Obtained.

Comparative Example 2
In the preparation of the coating solution for the protective layer of Example 1, instead of 56.5 parts of kaolin (trade name: HYDRAGLOSS 90, supra) and 58.2 parts of water, 38 parts of kaolin (trade name: HYDRAGLOSS 90, supra) were used. A thermosensitive recording material was obtained in the same manner as in Example 1 except that it was used.

Comparative Example 3
In the preparation of the protective layer coating liquid of Example 1, in place of 56.5 parts of kaolin (trade name: HYDRAGLOSS 90, supra) and 58.2 parts of water, 178 parts of kaolin (trade name: HYDRAGLOSS 90, supra) and A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 442.7 parts of water was used.

Comparative Example 4
In the preparation of the protective layer coating liquid of Example 1, in place of 5 parts of a 10% aqueous solution of glyoxal instead of 5 parts of a 10% aqueous solution of sodium glyoxylate (trade name: SPM-01, supra), A heat-sensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 5
In the preparation of the coating liquid for protective layer of Example 1, kaolin (trade name: UW-90, average particle size: 2.3 μm, Engelhart, instead of 56.5 parts of kaolin (trade name: HYDRAGLOSS 90, supra) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 56.5 parts) were used. The average particle diameter of kaolin is a median diameter measured by a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation).

Evaluation of thermal recording material The thermal recording material thus obtained was allowed to stand for 24 hours at 40 ° C. and then evaluated for the following items. The results are shown in Table 1.

[Recording quality]
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.35 mJ / dot, and the image quality of the obtained recorded image was as follows. Visual judgment was made.
A: The recorded image is very clear.
○: The recorded image is clear.
X: The recorded image is slightly unclear.

〔water resistant〕
The protective layer surface of the thermal recording medium is rubbed 3 times with gauze wetted with water, and after 1 minute, the rubbed area is painted with yellow magic ink [registered trademark], and the color development on the surface is visually observed. It was evaluated as follows.
(Evaluation criteria)
A: No color is developed.
○: Although it appears to be slightly colored, there is no practical problem.
X: There is a colored portion, which is a practical problem.

[Sticking resistance]
Using a thermal printer (Lesprit, manufactured by SATO), a barcode was printed, and the degree of printing skip was visually observed and evaluated as follows.
(Evaluation criteria)
A: Printing skip is not visible at all.
○: Print skipping is faint, but there is no practical problem.
X: Print skipping is clearly recognized, which is a practical problem.

[Protective layer coating solution: change in viscosity over time]
About the prepared coating liquid for protective layers, the B-type viscosity mPa * s (60 rpm) immediately after preparation and after leaving for 48 hours was measured.

Claims (3)

  A heat-sensitive recording material comprising a heat-sensitive recording layer containing a leuco dye, a colorant and a water-based adhesive on a support, and a protective layer containing a water-based adhesive on the heat-sensitive recording layer, wherein glyoxylic acid is contained in the protective layer. At least one selected from sodium, di (glyoxylate) calcium, and ammonium glyoxylate, and kaolin having an average particle size of 0.1 to 1.0 μm, and the content of the kaolin is the total solid content of the protective layer 50 to 70% by mass with respect to the heat-sensitive recording material.   The heat-sensitive recording material according to claim 1, wherein the aqueous adhesive in the protective layer is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.   The heat-sensitive recording material according to claim 1 or 2, wherein the protective layer coating liquid for forming the protective layer has a pH of 3.0 to 7.0.