JP2013056484A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material which has excellent water resistance and barrier properties.SOLUTION: In the heat-sensitive recording material which includes a heat-sensitive recording layer containing leuco dye and a color developer on the support and a protective layer containing an adhesive, the heat-sensitive recording layer contains polyacrylic acid hydrazide having a hydrazide conversion ratio of 40-90 mol% and having an average molecular weight of 10,000-100,000, and the protective layer contains acetoacetyl-modified polyvinyl alcohol as the adhesive.

Description

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

  A heat-sensitive recording material is known which utilizes a color-forming reaction between a colorless or light-colored leuco dye and an organic or inorganic developer to bring a color-developing image into contact with both color developing substances by heat. Such heat-sensitive recording materials are relatively inexpensive, and the recording equipment is compact and relatively easy to maintain, so that it is not only used as a recording medium for facsimiles and various printers, but also in a wide range of fields such as labels and handy terminals. It is used.

  As the field of use expands, and the recording equipment diversifies and the performance increases, the usage environment of the recording medium is becoming harsh, and not only the image quality and recording sensitivity of the recorded image, but also excellent storage stability and water resistance. What has quality is required.

  Conventionally, in order to increase the water resistance of a heat-sensitive recording material, it has been proposed to use diacetone-modified polyvinyl alcohol as an adhesive for the protective layer and to contain a hydrazine-based compound as a crosslinking agent in the protective layer (Patent Documents 1 and 2). ). It has also been proposed that the protective layer contains acetoacetyl-modified polyvinyl alcohol and a hydrazide compound (Patent Document 3). However, these have a problem that since the protective layer coating liquid contains polyvinyl alcohol and a crosslinking agent at the same time, the protective layer coating liquid tends to thicken and has poor stability (pot life).

  As a means of solving the stability problem of the coating liquid for the protective layer, it has been proposed to use a hydrazide compound in the heat-sensitive recording layer and to use acetoacetyl-modified polyvinyl alcohol or diacetone-modified polyvinyl alcohol as an adhesive for the protective layer. (Patent Documents 4 and 5). Although these have high coating solution stability and good coating suitability, they have problems such as insufficient water resistance and reduced color developability due to hydrazide compounds.

  Examples of crosslinking agents other than hydrazide compounds include polyfunctional semicarbazide compounds (Patent Document 6) and compounds having an epoxy group (Patent Document 7), but they do not have sufficient water resistance.

JP 2008-073892 A JP 2008-213259 A JP 2001-121815 A JP 2004-249528 A JP 11-314457 A JP 2010-058307 A JP 2000-168232 A

  The main object of the present invention is to provide a heat-sensitive recording material excellent in barrier properties and water resistance.

  As a result of various studies on the above problems, the present inventors have found that a thermal recording material comprising a thermal recording layer containing a leuco dye and a developer and a protective layer containing an adhesive on the support. By containing polyacrylic acid hydrazide having a hydrazide conversion rate of 40 to 90 mol% and an average molecular weight of 10,000 to 100,000 in the layer, and containing acetoacetyl-modified polyvinyl alcohol as an adhesive in the protective layer, the above problem Has been found to be solved, and the present invention has been completed. That is, the present invention relates to the following heat-sensitive recording material.

  Item 1: In a heat-sensitive recording material comprising a heat-sensitive recording layer containing a leuco dye and a developer on a support and a protective layer containing an adhesive, the hydrazide conversion rate is 40 to 90 mol% in the heat-sensitive recording layer. And a polyacrylic acid hydrazide having an average molecular weight of 10,000 to 100,000, and a protective layer containing acetoacetyl-modified polyvinyl alcohol as an adhesive.

  Item 2: The heat-sensitive recording material according to Item 1, wherein the content of the polyacrylic hydrazide is 0.2 to 20 parts by mass with respect to 100 parts by mass of acetoacetyl-modified polyvinyl alcohol in the protective layer.

  Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the degree of polymerization of acetoacetyl-modified polyvinyl alcohol in the protective layer is 1000 to 3000.

  Item 4: The thermosensitive recording layer contains polyvinyl alcohol containing a carbonyl group, and the content ratio of the polyvinyl alcohol containing the carbonyl group is 1 to 5% by mass in the total solid content of the thermosensitive recording layer. The heat-sensitive recording material according to any one of the above.

  Item 5: The heat-sensitive recording material according to Item 4, wherein the polyvinyl alcohol containing a carbonyl group is acetoacetyl-modified polyvinyl alcohol.

  Item 6: The heat-sensitive recording according to any one of Items 1 to 5, comprising an undercoat layer containing at least one selected from an organic pigment and an inorganic pigment and an adhesive between the support and the heat-sensitive recording layer. material.

  The heat-sensitive recording material of the present invention is excellent in barrier properties and water resistance. In addition, the recording sensitivity and the print image quality are excellent.

  In the present invention, the thermosensitive recording layer contains polyacrylic acid hydrazide having a hydrazide conversion rate of 40 to 90 mol% and an average molecular weight of 10,000 to 100,000. Thereby, a heat-sensitive recording material having excellent barrier properties and water resistance can be obtained. Polyacrylic acid hydrazide is also called N-aminopolyacrylamide or acrylic acid hydrazide copolymer, and has a high molecular structure, and therefore has a large number of hydrazide groups that can serve as crosslinking points in the molecule. Therefore, the reactivity with acetoacetyl-modified polyvinyl alcohol is particularly high. In the present invention, polyacrylic acid hydrazide is provided between the heat-sensitive recording layer and the protective layer by containing acetoacetyl-modified polyvinyl in the protective layer. When acetoacetyl-modified polyvinyl alcohol forms a film structure, the adhesion strength is increased, and the protective layer component is prevented from penetrating into the heat-sensitive recording layer, thereby greatly improving the interlayer separation, and a uniform layer is formed. It is conceivable that a remarkable effect on the barrier properties and water resistance can be obtained, and the stability of the coating liquid is not impaired.

As a hydrazide conversion rate of polyacrylic acid hydrazide, it is 40-90 mol%, and 50-80 mol% is preferable. The hydrazide conversion rate is defined as the ratio (mol%) of the number of —NHNH ₂ to the number of carboxylic acids in the structural formula. When the hydrazide conversion ratio is less than 40 mol%, it can be a crosslinking point. Sufficient water resistance cannot be obtained because hydrazide is small in the molecule.

  The polyacrylic acid hydrazide is a polymer produced by reacting, for example, polyacrylic acid amide or polyacrylic acid ester such as methyl polyacrylate with hydrazine, and is represented by the following formula (1), for example. . In the formula, m + n = 100 mol%, and the value of n is defined as the hydrazide conversion rate (mol%).

  The average molecular weight of the polyacrylic acid hydrazide is 10,000 to 100,000, preferably 20,000 to 90,000. If the average molecular weight is less than 10,000, sufficient water resistance cannot be obtained, and if it exceeds 100,000, the water solubility of polyacrylic hydrazide is lowered, and a large amount of water as a solvent is required. Therefore, since the density | concentration of a coating liquid falls and time is required for drying, barrier property falls.

  The average molecular weight in the present invention is a number average molecular weight analyzed by GPC (gel verme chromatography). Measuring instrument is LC10A system (manufactured by Shimadzu Corporation), column: TSK-GEL α-2500, TSK-GEL α-4000, TSK-GEL α-6000 (manufactured by Tosoh Corporation), standard: polyethylene oxide (TSK standardPEO kit, Tosoh Corporation) Made by Co., Ltd.).

  The content of polyacrylic hydrazide in the heat-sensitive recording layer is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 20 parts by mass with respect to 100 parts by mass of acetoacetyl-modified polyvinyl alcohol in the protective layer. 0.2-15 mass parts is still more preferable. By setting it as 0.1 mass part or more, barrier property and water resistance can be improved. On the other hand, by setting it to 20 parts by mass or less, it is possible to suppress a decrease in color developability due to the hydrazide compound and improve recording sensitivity and print image quality.

  Further, other crosslinking agents can be used in combination as long as the effects of the present invention are not impaired. Examples of the crosslinking agent include hydrazide compounds other than polyacrylic acid, aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, dimethylol urea compounds, aziridine compounds, blocks Examples include isocyanate compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate, boric acid, boric acid triesters, boron-based polymers, and the like.

  As the adhesive used for the thermal recording coating liquid, any water-soluble binder and water-dispersible binder can be used. Examples of the water-soluble binder include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, and acrylamide. -Water-soluble polymers such as acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein Can be mentioned. Water-dispersible binders include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate. Examples thereof include latex of hydrophobic polymers such as a copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, and acrylic-silicon-urethane composite.

  Especially, it is preferable to contain the polyvinyl alcohol containing a carbonyl group, and it is more preferable to use acetoacetyl modified polyvinyl alcohol. By using polyvinyl alcohol containing a carbonyl group and polyacrylic hydrazide in combination, the water resistance of the thermosensitive recording layer can be improved.

  The content of polyvinyl alcohol containing a carbonyl group in the heat-sensitive recording layer is preferably 1 to 5% by mass in the total solid content of the heat-sensitive recording layer. Water resistance can be improved by setting it as 1 mass% or more. On the other hand, by adjusting the content to 5% by mass or less, the reactivity of polyvinyl alcohol containing a carbonyl group and polyacrylic hydrazide is suppressed, and the application quality is improved without increasing the viscosity of the thermal recording layer coating solution. it can.

  The heat-sensitive recording layer in the present invention can contain various known leuco dyes and developers. In addition, you may contain a sensitizer, a preservability improving agent, a pigment, various adjuvants, etc. as needed. Specific examples of leuco dyes include, for example, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-aniline as a leuco dye that gives a black color. Linofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-arininofluorane, 3 -(N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoromethylani Lino) fluorane, 3- (N-isoamyl-N-ethylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-N-2-tetrahydrofurfurylamino)- -Methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino) -6-methyl-7-anilinofluorane 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N-methylamino] -6 Examples include methyl-7-anilinofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane. Further, if necessary, a leuco dye that develops a color tone different from black, for example, a color tone such as red, magenta, orange, blue, green, etc., may be used.

  The leuco dye is not limited to these, and two or more kinds can be used in combination. The amount of the leuco dye used is not particularly limited, and is preferably about 3 to 30% by mass in the total solid content of the heat-sensitive recording layer.

  In the present invention, when the leuco dye is used as a solid dispersion fine particle state, water is used as a dispersion medium, modified polyvinyl alcohol such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, sulfone-modified polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, In addition to water-soluble polymers such as styrene-maleic anhydride copolymer salts and derivatives thereof, various wet pulverizers such as sand mills, attritors, ball mills, cobo mills, as well as surfactants and antifoaming agents as necessary. To obtain a dispersion liquid dispersed in a dispersion medium, and this dispersion liquid can be used for the preparation of a thermal recording layer coating liquid. Alternatively, after dissolving the leuco dye in a solvent, the solution is emulsified and dispersed in water using the water-soluble polymer as a stabilizer, and then the solvent is evaporated from the emulsion to use the leuco dye as solid fine particles. . In any case, the average particle size of the dispersed particles of the leuco dye used in the solid dispersed fine particle state is preferably 0.2 to 3.0 μm, more preferably 0.3 to 0.3 in order to obtain appropriate recording sensitivity. 1.0 μm.

  As a method of using the leuco dye in the present invention, it can be used as composite particles composed of an organic polymer and a leuco dye, in addition to the solid dispersed fine particle state. The composite particles can be produced by a known method. For example, a method for producing composite particles in which the organic polymer is at least one of polyurea and polyurea-polyurethane will be described below. The composite particles include a leuco dye, and a polymer-forming raw material such as a polyisocyanate compound capable of forming at least one of polyurea and polyurea-polyurethane by polymerization, a water-insoluble organic solvent having a boiling point of 100 ° C. or less. The organic solvent solution is emulsified and dispersed in a hydrophilic protective colloid solution such as polyvinyl alcohol so that the average particle size is about 0.5 to 3 μm, and further, if necessary, a reactive substance such as polyamine is mixed. Thereafter, the emulsion dispersion is heated to volatilize and remove the organic solvent, and then the polymer-forming raw material is polymerized, or the leuco dye is dissolved in the polymer-forming raw material. Then, this solution is emulsified and dispersed to an average particle size of about 0.5 to 3 μm by the above method, and then the polymer-forming raw material is polymerized. Prepared.

  As the developer in the present invention, a known compound can be used. Specific examples of the developer include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidenediphenol, 4-phenylphenol, 4,4′- Dihydroxydiphenylmethane, 4,4′-isopropylidene diphenol, 4,4′-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 4,4′-dihydroxydiphenyl sulfide, 4 , 4′-thiobis (3-methyl-6-tert-butylphenol), 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy -4'-allyloxydiphe Rulsulfone, 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, bis (p-hydroxyphenyl) butyl acetate, phenolic compounds such as methyl bis (p-hydroxyphenyl) acetate, 4-hydroxybenzophenone, 4- Dimethyl hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoate-sec-butyl, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, Phenolic compounds such as chlorophenyl 4-hydroxybenzoate and 4,4′-dihydroxydiphenyl ether, or benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, -Aromatic carboxylic acids such as isopropylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, Organic acidic substances such as salts with polyvalent metals such as magnesium, aluminum and calcium, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, Np-toluenesulfonyl-N ′ -P-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 4,4'- Bis (p-toluenesulfonylaminocarbonylamino) diphenylmethane They include a urea compound.

  In the present invention, the use ratio of the leuco dye and the developer in the heat-sensitive recording layer should be appropriately selected according to the types of the leuco dye and the developer, and is not particularly limited, but generally 1 mass of leuco dye. Preferably, about 1 to 7 parts by mass, more preferably about 1 to 6 parts by mass of the developer is used.

  Furthermore, in order to improve the whiteness and image uniformity, the heat-sensitive recording layer may contain a fine pigment having a high whiteness and an average particle size of 10 μm or less. Specific examples of the pigment include, for example, kaolin, clay, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, talc, calcined clay, calcined kaolin, titanium oxide, zinc oxide, diatomaceous earth, particulate anhydrous silica, activated clay, etc. Organic pigments such as inorganic pigments, styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, raw starch particles and the like can be mentioned. The pigment content is preferably an amount that does not decrease the color density, that is, 50% by mass or less based on the total solid content of the heat-sensitive recording layer.

  Furthermore, the heat-sensitive recording layer can contain a sensitizer for increasing the recording sensitivity. Specific examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoyl stearic acid amide, N-eicosanoic acid amide, ethylene bistearic acid amide, behenic acid amide, and methylenebisstearic acid. Amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-terphenyl, Oxalic acid dibenzyl, oxalic acid-di-p-methylbenzyl, oxalic acid-di-p-chlorobenzyl, p-benzylbiphenyl, tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3 -Mechi Phenoxy) 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- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetoluidide, p-acetophenetide, N- Examples include acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, and the like. The content of these sensitizers is not particularly limited, but it is generally desirable to adjust in a range of about 4 parts by mass or less with respect to 1 part by mass of the developer.

  Further, the heat-sensitive recording layer may contain a storability improving agent for improving the storability of the recorded image. Specific examples of such preservability improvers include, for example, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylenebis (4-methyl-6-tert-butylphenol), 2 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis (4,6-di-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert) -Butylphenol), 2,2'-ethylidenebis (4-methyl-6-tert-butylphenol), 2,2'-ethylidenebis (4-ethyl-6-tert-butylphenol), 2,2 '-(2, 2-propylidene) bis (4,6-di-tert-butylphenol), 2,2′-methylenebis (4-methoxy-6-tert-butyl) Ruphenol), 2,2'-methylenebis (6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert) -Butylphenol), 4,4'-thiobis (5-methyl-6-tert-butylphenol), 4,4'-thiobis (2-chloro-6-tert-butylphenol), 4,4'-thiobis (2-methoxy) -6-tert-butylphenol), 4,4'-thiobis (2-ethyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-m-cresol), 1- [α-methyl -Α- (4'-hydroxyphenyl) ethyl] -4- [α ', α'-bis (4' '-hydroxyphenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4, 4'-thiobis (3-methylphenol), 4,4'-dihydroxy-3,3 ', 5,5'-tetrabromodiphenyl sulfone, 4,4'-dihydroxy-3,3', 5,5'- Tetramethyldiphenylsulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis (4- Hindered phenol compounds such as hydroxy-3,5-dimethylphenyl) propane, N, N′-di-2-naphthyl-p-phenylenediamine, 2,2′-methylenebi (4,6-di -tert- butylphenyl) phosphate sodium, and the like.

  The coating solution for the heat sensitive recording layer may contain auxiliary agents such as the following waxes, metal soaps, colored dyes, colored pigments, fluorescent dyes, oil repellents, antifoaming agents and viscosity modifiers as necessary. it can.

  Examples of waxes include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax, and higher fatty acid amides such as stearic acid amide and ethylenebisstearic acid amide, higher fatty acid esters, and derivatives thereof. Can be mentioned.

  Examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

  The heat-sensitive recording layer is generally dispersed in water as a dispersion medium, and the leuco dye and the developer are dispersed together with or separately from the sensitizer and the storage stabilizer as required by a pulverizer such as a ball mill, an attritor, or a sand mill. Using the resulting dispersion, a coating solution for a thermal recording layer prepared by further mixing an adhesive, a surfactant and, if necessary, an auxiliary agent is formed by coating and drying on a support. Is done.

As a method for forming the thermosensitive recording layer, any of known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, a curtain coater method, a spray method, a dip method, a bar method, and an extrusion method is used. May be. The coating amount of the thermal recording layer coating liquid is not particularly limited, and is preferably about 1 to 12 g / m ² , more preferably ² to 10 g / m ² , and more preferably 2.5 to 5.5 g / m ^{2 in} terms of solid content. m ² is particularly preferred. The thermosensitive recording layer can be divided into two or more layers as required, and the composition and coating amount of each layer can be changed.

  In the present invention, the protective layer contains acetoacetyl-modified polyvinyl alcohol as an adhesive. Thereby, barrier property and water resistance can be improved. Further, for the purpose of preventing sticking to the thermal head, a lubricant such as polyolefin wax and zinc stearate is preferably added to the protective layer, and an ultraviolet absorber can also be included. In addition, the added value of the product can be increased by providing a glossy protective layer.

  1000-3000 are preferable and, as for the polymerization degree of the acetoacetyl modified polyvinyl alcohol in a protective layer, 1500-3000 are more preferable. By setting it to 1000 or more, surface strength and barrier properties can be improved. On the other hand, by setting it to 3000 or less, it is possible to improve the coating suitability and improve the printing image quality without increasing the viscosity of the protective layer coating liquid. In addition, a water-soluble binder and / or a water-dispersible binder mainly composed of a synthetic resin emulsion can be used in combination as long as the effects of the present invention are not impaired.

  Examples of the water-soluble binder include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, and acrylamide. -Water-soluble polymers such as acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein Can be mentioned.

  Water-dispersible binders include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate. Examples thereof include latex of hydrophobic polymers such as a copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, and acrylic-silicon-urethane composite.

  The total content of the adhesive is preferably about 10 to 80% by mass and more preferably about 20 to 75% by mass in the total solid content of the protective layer. By setting it as 10 mass% or more, not only barrier property but surface strength can be raised and generation | occurrence | production of paper dust can be reduced. On the other hand, sticking can be suppressed by setting it as 80 mass% or less.

  When using a water-soluble binder and a water-dispersible binder together, the use ratio is about 5-100 mass parts of water-dispersible binders with respect to 100 mass parts of water-soluble binders.

  The protective layer in the present invention can contain various pigments. Examples of the pigment include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, synthetic mica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined kaolin, nylon resin filler, urea -Organic pigments such as formalin resin filler and raw starch particles. Of these, kaolin and aluminum hydroxide are preferred because they have a small decrease in barrier properties against chemicals such as plasticizers and oils, and a small decrease in recording density.

  The content ratio of the pigment is about 5 to 80% by mass in the total solid content of the protective layer, and particularly preferably about 10 to 70% by mass. By setting the content to 5% by mass or more, the sliding with the thermal head can be improved, and sticking and head wrinkles can be suppressed. On the other hand, by setting it as 80 mass% or more, barrier property can be improved and the function as a protective layer can be improved significantly.

  Moreover, a crosslinking agent can be contained in the protective layer as long as the effects of the present invention are not impaired. Examples of the crosslinking agent include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, and adipic acid dihydrazides. Examples include dihydrazide compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate, boric acid, boric acid triester, boron-based polymers, and the like.

  As the auxiliary agent, for example, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium acrylate glycol polyacrylate compound , Surfactants such as fluorosurfactants, silicon surfactants, phosphate ester surfactants, ether surfactants, or amphoteric surfactants such as betaines, aminocarboxylates, and imidazoline derivatives, Examples include hydrophobic polycarboxylic acid copolymers, ultraviolet absorbers, fluorescent dyes, colored dyes, mold release agents, and antioxidants. The usage-amount of auxiliary agent can be suitably set from a wide range.

  The protective layer is generally coated with a coating solution for the protective layer prepared by mixing water with a medium, acetoacetyl-modified polyvinyl alcohol and, if necessary, other adhesives, pigments and auxiliaries on the heat-sensitive recording layer. It is formed by doing.

As a method for forming the protective layer, any of known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, a curtain coater method, a spray method, a dip method, a bar method, and an extrusion method can be used. May be. The coating amount of the protective layer coating liquid is not particularly limited, and a desired quality can be achieved if the dry weight is about 0.3 to 10 g / m ² , particularly about 0.5 to 8 g / m ² . The protective layer can be divided into two or more layers as required, and the composition and coating amount of each layer can be changed.

In the present invention, an undercoat layer may be provided between the support and the thermosensitive recording layer. The undercoat layer can contain an adhesive and at least one selected from organic pigments and inorganic pigments. Thereby, in particular on a paper support, it is possible to suppress the penetration of the coating solution for the heat-sensitive recording layer and form a uniform coated surface, and the effects of the present invention can be exhibited without regret. The pigment and the adhesive can be appropriately selected from those that can be used for the heat-sensitive recording layer. As a method for forming an undercoat layer on a support, known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, a curtain coater method, a spray method, a dip method, a bar method, and an extrusion method are used. Either may be used. The coating amount of the undercoat layer coating liquid is adjusted so that the dry weight is 1 to 20 g / m ² , preferably 3 to 12 g / m ² .

  Each coating liquid in the present invention can be simultaneously applied by a curtain coater method. Thereby, the production efficiency of the heat-sensitive recording material can be increased, and the energy consumption during production can be further reduced. On the other hand, in sequential coating, the protective layer coating solution penetrates into the porous heat-sensitive recording layer, and if the coating amount of the protective layer is increased to ensure barrier properties, the sensitivity may be reduced. End up. On the other hand, since the interlayer mixing can be suppressed in the simultaneous multilayer coating, the quality such as the barrier property can be improved with a smaller coating amount. Here, the simultaneous multilayer coating is a method in which two or more layers are coated simultaneously, and includes a method in which the upper layer is coated without drying after the lower layer is coated.

  The curtain coater method is a method in which the coating liquid is allowed to flow down and freely drop and applied to the support in a non-contact manner. In the present invention, known methods such as the slide curtain method, the couple curtain method, and the twin curtain method are adopted. There is no particular limitation. Further, as described in JP-A-2006-247611, the coating liquid is ejected downward from the curtain head to form a coating liquid layer on the slope, and the coating liquid is applied from the downward curtain guide portion of the slope. It is also possible to transfer the coating liquid layer onto the web surface by forming a curtain.

  Examples of the support in the present invention include high-quality paper, art paper, synthetic paper, PET film, non-woven fabric medium paper, coated paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, and non-woven fabric. In addition to the synthetic resin film, various transparent supports and the like can be appropriately selected and used.

  In the present invention, a smoothing process using a super calendar can be performed in an arbitrary process after the formation of each layer or after the formation of all the layers. Furthermore, in the present invention, in order to increase the added value of the heat-sensitive recording material, the heat-sensitive recording material can be processed to give a higher function.

  For example, in order to further increase the added value of the product, a multicolor thermosensitive recording material can be used. In general, multicolor thermosensitive recording materials are attempts to utilize the difference in heating temperature or the difference in heat energy, and are generally formed by laminating a high-temperature color-developing layer and a low-temperature color-developing layer that develop colors in different colors on a support. When these are roughly classified, a multicolor thermosensitive recording material is produced by using two types of decoloring type and additive type, a method using a microcapsule, and composite particles comprising an organic polymer and a leuco dye. There is a way.

  In addition, it can be used as pressure-sensitive adhesive paper, re-moistened adhesive paper, and delayed tack paper by applying a coating process such as pressure-sensitive adhesive, re-humidified adhesive, and delayed tack type pressure-sensitive adhesive on the back surface opposite to the thermosensitive recording layer. . Or it can also be set as the thermosensitive recording material which has a layer which can be magnetic-recorded in a back surface by giving magnetic processing. In particular, those subjected to adhesive processing and magnetic processing are useful for applications such as heat-sensitive labels and heat-sensitive magnetic tickets. In addition, by using the back surface, a function as a thermal transfer paper, an ink jet paper, a carbonless paper, an electrostatic recording paper, and a xerographic paper can be added to the recording material to enable double-sided recording. Of course, a double-sided thermal recording material can also be used.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” in the examples represent “part by mass” and “% by mass”, respectively. The average particle diameter was measured using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation).

Example 1
Preparation of coating solution for undercoat layer 40 parts of calcined kaolin with oil absorption of 110 ml / 100 g, plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle size 1.0 μm, manufactured by JSR Corporation ) 230 parts, 30 parts of styrene-butadiene copolymer latex (trade name: L-1571, solid concentration 45%, manufactured by Asahi Kasei) as an adhesive, fully saponified polyvinyl alcohol (trade name: PVA124, polymerization degree 2400, Kuraray) A composition comprising 30 parts of a 15% aqueous solution of sodium dioctylsulfosuccinate (trade name: SN Wet OT-70, manufactured by San Nopco), and 60 parts of water. A coating solution was obtained.

Preparation of mixed dispersion of leuco dye and sensitizer (liquid A) 25 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 1,2-di (3-methylphenoxy) ) A composition comprising 20 parts of ethane, 25 parts of a 20% aqueous solution of sulfone-modified polyvinyl alcohol, and 30 parts of water was pulverized with a sand mill until the average particle size became 0.9 μm, and a leuco dye and a sensitizer were mixed and dispersed. A liquid was obtained. Hereinafter, the obtained mixed dispersion is also referred to as “liquid A”.

・ Preparation of developer dispersion (liquid B) A composition comprising 45 parts of 2,2′-bis (4-hydroxyphenyl) propane, 25 parts of a 20% aqueous solution of sulfone-modified polyvinyl alcohol, and 30 parts of water was added to a sand mill. Were pulverized until the average particle size became 1.5 μm to obtain a developer dispersion. Hereinafter, the obtained developer dispersion is also referred to as B liquid.

Preparation of coating solution for heat-sensitive recording layer 60 parts of A solution, 70 parts of B solution, 10 parts of 60% aqueous dispersion of light calcium carbonate (trade name: Brilliant 15, manufactured by Shiroishi Chemical Co., Ltd.), aluminum hydroxide (trade name) : Heidilite H42, Showa Denko Co., Ltd.) 60% aqueous dispersion 15 parts, heavy calcium carbonate (trade name: Softon 2200, Okutama Kogyo Co., Ltd.) 60% aqueous dispersion 10 parts, fully saponified polyvinyl alcohol (Product) Name: PVA-124, polymerization degree 2400, saponification degree 98.5 mol%, 15 parts aqueous solution 40 parts, acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimmer Z-200, polymerization degree: 1000, 15 parts of 15% aqueous solution of Nippon Synthetic Chemical Industry Co., Ltd., 10 parts of 30% aqueous solution of zinc stearate, glycerin ester emulsion defoamer (trade name: NOP 5 parts aqueous dispersion, 5 parts of 10% aqueous solution of sodium dioctylsulfosuccinate (trade name: SN wet OT-70, manufactured by San Nopco), polyacrylic acid hydrazide (average molecular weight: 1407K, manufactured by San Nopco) A composition comprising 20 parts of a 10% aqueous solution of 20000, hydrazide conversion rate: 80 mol% and 90 parts of water was mixed and stirred to obtain a thermal recording layer coating solution.

-Preparation of coating liquid for protective layer Dispersion obtained by dispersing 50 parts of kaolin (trade name: UW-90, manufactured by BASF) in 100 parts of water, and acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimer) 600 parts of 10% aqueous solution of Z-410, polymerization degree: 2400, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 10 parts of a 30% aqueous dispersion of zinc stearate, and sodium dioctylsulfosuccinate (trade name: SN wet OT-70) And a composition comprising 10 parts of a 10% aqueous solution (manufactured by San Nopco) to obtain a coating solution for a protective layer.

- on one surface of woodfree paper having produced a basis weight of 60 g / m ² of heat-sensitive recording material, an undercoat layer coating solution coated amount after drying and dried such that the 6 g / m ^2, the heat-sensitive recording layer thereon The coating liquid for coating was applied and dried so as to be 4 g / m ^2, and the coating liquid for protective layer was coated and dried so as to be 3 g / m ² , followed by supercalendering, and the thermal recording material was obtained. Obtained.

Example 2
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in preparing the coating solution for the thermosensitive recording layer of Example 1, the hydrazide conversion rate of polyacrylic hydrazide was changed to 50 mol% instead of 80 mol%. .

Example 3
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the average molecular weight of polyacrylic hydrazide was changed to 90000 instead of 20000 in the preparation of the thermosensitive recording layer coating solution of Example 1.

Example 4
A thermosensitive recording material was obtained in the same manner as in Example 1, except that in the preparation of the thermosensitive recording layer coating solution of Example 1, the amount of 10% aqueous solution of polyacrylic hydrazide was changed to 1 part instead of 20 parts. .

Example 5
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the heat-sensitive recording layer coating liquid of Example 1, the amount of 10% aqueous solution of polyacrylic hydrazide was changed to 0.5 parts instead of 20 parts. Obtained.

Example 6
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the thermosensitive recording layer coating liquid of Example 1, the amount of 10% aqueous solution of polyacrylic hydrazide was changed to 60 parts instead of 20 parts. .

Example 7
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, the amount of 15% aqueous solution of fully saponified polyvinyl alcohol was changed to 60 parts instead of 40 parts, and a 15% aqueous solution of acetoacetyl-modified polyvinyl alcohol was not used. A thermosensitive recording material was obtained in the same manner as in Example 1.

Example 8
In the preparation of the coating solution for the protective layer of Example 1, instead of 600 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Goosephimer Z-410, polymerization degree: 2400, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) A heat-sensitive recording material in the same manner as in Example 1 except that 400 parts of a 15% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Goosephimer Z-200, polymerization degree: 1000, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used. Got.

Example 9
The support of Example 1 from woodfree paper having a basis weight of 60 g / m ^2, was changed to synthetic paper having a basis weight of 90 g / m ^2, except for not applying the subbing layer, the heat-sensitive recording layer in Example 1 Obtained.

Comparative Example 1
In the preparation of the coating liquid for protective layer of Example 1, instead of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol (trade name: DF-20, degree of polymerization: 2000, manufactured by Nihon Vineyard-Povar) A thermosensitive recording material was obtained in the same manner as in Example 1 except that a 10% aqueous solution was obtained.

Comparative Example 2
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the thermal recording layer coating liquid of Example 1, a 10% aqueous solution of adipic acid dihydrazide was used instead of the 10% aqueous solution of polyacrylic hydrazide. It was.

Comparative Example 3
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the 10% aqueous solution of polyacrylic hydrazide was not used in the preparation of the thermosensitive recording layer coating liquid of Example 1.

  The heat-sensitive recording material thus obtained was evaluated as follows. The results are shown in Table 1.

(Recording sensitivity and print image quality)
Recording was performed at an applied energy of 0.15 mJ / dot using a thermal recording simulator (TH-PMD, manufactured by Okura Electric Co., Ltd.). The density of the solid recording part was measured in a visual mode of a Macbeth densitometer (trade name: RD914, manufactured by Macbeth). The recording sensitivity is preferably 1.0 or more, and if it is 0.9 or more, there is no practical problem. Further, the print image quality of the solid recording portion was visually observed and evaluated according to the following criteria.
A: There is no omission and the image quality is extremely excellent.
○: Almost no omission is seen, and the image quality is good.
(Triangle | delta): Although omission is seen, image quality is a practical use level.
X: Remarkably many omissions are seen, and the image quality is poor, which is a practical problem.

(Barrier properties)
100% ethanol was applied to the heat-sensitive recording surface, and fogging of the background portion was visually observed and evaluated according to the following criteria.
A: No fogging is seen.
○: Slight fogging is observed but good.
(Triangle | delta): Although fog is seen, it is a practical use level.
X: Fog is seen remarkably and is a problem in practical use.

(water resistant)
One drop of water was dropped on the heat-sensitive recording surface, and immediately after that, it was rubbed 10 times with a finger. The finger was touched and visually observed on the surface, and evaluated according to the following criteria.
A: There is no peeling of the surface, and there is no slime.
○: There is no peeling of the surface, but there is some slime.
(Triangle | delta): There exists slime and the surface peels a little, but it is a practical use level.
X: The slime is severe and the coating layer is completely peeled off, which is a practical problem.

  In a heat-sensitive recording material provided with a heat-sensitive recording layer containing a leuco dye and a developer on a support and a protective layer containing an adhesive, the hydrazide conversion rate in the heat-sensitive recording layer is 40 to 90 mol%, and the average Containing polyacrylic acid hydrazide having a molecular weight of 10,000 to 100,000, and containing acetoacetyl-modified polyvinyl alcohol as an adhesive in the protective layer, it has excellent barrier properties and water resistance, and also has recording sensitivity and print image quality. It can provide excellent thermal recording materials and can be applied not only as recording media for facsimiles and various printers but also in a wide range of fields such as labels and handy terminals.

Claims (6)

  In a heat-sensitive recording material provided with a heat-sensitive recording layer containing a leuco dye and a developer on a support and a protective layer containing an adhesive, the hydrazide conversion rate in the heat-sensitive recording layer is 40 to 90 mol%, and the average A thermosensitive recording material comprising polyacrylic acid hydrazide having a molecular weight of 10,000 to 100,000, and containing acetoacetyl-modified polyvinyl alcohol as an adhesive in the protective layer.   The heat-sensitive recording material according to claim 1, wherein the content of the polyacrylic hydrazide is 0.2 to 20 parts by mass with respect to 100 parts by mass of acetoacetyl-modified polyvinyl alcohol in the protective layer.   The heat-sensitive recording material according to claim 1 or 2, wherein the degree of polymerization of acetoacetyl-modified polyvinyl alcohol in the protective layer is 1000 to 3000.   The polyvinyl alcohol containing a carbonyl group is contained in the thermosensitive recording layer, and the content ratio of the polyvinyl alcohol containing the carbonyl group is 1 to 5% by mass in the total solid content of the thermosensitive recording layer. 2. The heat-sensitive recording material according to item 1.   The heat-sensitive recording material according to claim 4, wherein the polyvinyl alcohol containing a carbonyl group is acetoacetyl-modified polyvinyl alcohol.   The heat-sensitive recording material according to any one of claims 1 to 5, further comprising an undercoat layer containing an adhesive and at least one selected from organic pigments and inorganic pigments between the support and the heat-sensitive recording layer.