JP2015134425A - Thermosensitive recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensitive recording body having excellent water resistance and yellowing resistance of a blank paper part.SOLUTION: There is provided a thermosensitive recording body which comprises: a thermosensitive recording layer containing a leuco dye and a coloring agent on a support; and a protective layer containing an adhesive on the thermosensitive recording layer, wherein the protective layer contains an acetoacetyl-modified polyvinyl alcohol as an adhesive, the thermosensitive recording layer contains ethylenediaminetetraacetic acid and/or a salt thereof and the thermosensitive recording layer and/or the protective layer contain a crosslinking agent reactive with an acetoacetyl group.

Description

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

  A thermal recording material using a color reaction between a leuco dye and a colorant is relatively inexpensive, has a compact recording device, and is easy to maintain. Therefore, it is widely used in recording media such as facsimiles, various computers, and measuring devices. It is used.

  With the expansion of applications of thermal recording media, there is an increasing demand for thermal recording media having excellent water resistance. In order to increase the water resistance of the heat-sensitive recording material, acetoacetyl-modified polyvinyl alcohol is used as an adhesive for the protective layer, and a hydrazine-based compound is used as a water-resistant agent for acetoacetyl-modified polyvinyl alcohol in the heat-sensitive recording layer (Patent Document 1). And a protective layer containing acetoacetyl-modified polyvinyl alcohol and a hydrazine compound has been proposed (see Patent Document 2). However, any of the thermal recording materials has a problem that the blank paper portion is yellowed with time.

  In order to improve the water resistance and yellowing resistance of the white paper portion, at least acetoacetyl-modified polyvinyl alcohol is used as an adhesive for the heat-sensitive recording layer and / or protective layer, and in at least one of the undercoat layer, the heat-sensitive recording layer, and the protective layer. There has also been proposed a thermal recording medium using a hydrazide compound and having a cold water extract pH (based on JIS P 8133) of the thermal recording medium of 5 to 7 (see Patent Document 3). However, improvement of yellowing is insufficient, and when the support is neutral paper, it is difficult to improve yellowing.

  It has been proposed to contain ethylenediaminetetraacetic acid in the heat-sensitive recording layer for storage stability of the ground color (see Patent Document 4). However, this heat-sensitive recording material suppresses background fogging (decrease in whiteness) caused by the use of an epoxy compound that is an antioxidant. In order to improve the plasticizer resistance of the recording part, a heat-sensitive recording material containing ethylenediaminetetraacetic acid has been proposed as a storage accelerator reaction accelerator to be contained in the heat-sensitive recording layer (see Patent Document 5). .

JP-A-11-314458 JP 2001-121815 A JP 2004-249528 A JP-A-8-282100 Japanese Patent Laid-Open No. 9-175014

  The main object of the present invention is to provide a heat-sensitive recording material excellent in water resistance and yellowing resistance of a white paper portion.

  As a result of intensive studies in view of the above-described conventional technology, the present inventors have solved the above-described problems. That is, the present invention relates to the following thermal recording material.

  Item 1: A thermosensitive recording material comprising a thermosensitive recording layer containing a leuco dye and a colorant on a support, and a protective layer containing an adhesive on the thermosensitive recording layer, wherein the protective layer is acetoacetyl as an adhesive. A heat-sensitive recording material containing modified polyvinyl alcohol, the heat-sensitive recording layer containing ethylenediaminetetraacetic acid and / or a salt thereof, and the heat-sensitive recording layer and / or the protective layer containing a cross-linking agent that reacts with an acetoacetyl group. Recorded body.

  Item 2: The heat-sensitive recording material according to Item 1, wherein the crosslinking agent reacts with an acetoacetyl group and is hydrolyzed in the presence of a divalent metal ion and then oxidized.

  Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the crosslinking agent is a hydrazide compound and / or glyoxal.

  Item 4: The content of ethylenediaminetetraacetic acid and / or a salt thereof contained in the thermosensitive recording layer is 0.1 to 10% by mass in the total solid content of the thermosensitive recording layer, The heat-sensitive recording material according to item.

  Item 5: The heat-sensitive recording material according to any one of Items 1 to 4, wherein the protective layer contains ethylenediaminetetraacetic acid and / or a salt thereof.

  Item 6: The heat-sensitive recording material according to any one of Items 1 to 5, wherein the support is neutral paper.

  Item 7: The heat-sensitive recording material according to any one of Items 1 to 6, wherein the support is neutral paper of hot water extraction pH (based on JIS P 8133) 6 to 11.

  Item 8: The heat-sensitive recording material according to any one of Items 1 to 7, wherein the crosslinking agent is a dicarboxylic acid dihydrazide compound.

  Item 9: The salt of ethylenediaminetetraacetic acid dihydrogenammonium ethylenediaminetetraacetate, disodium ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid dihydrogen dihydrate, trisodium monohydrogenethylenediaminetetraacetate trihydrate Item 8 is at least one selected from the group consisting of a tetrasodium salt of ethylenediaminetetraacetic acid tetrahydrate, dipotassium dihydrogenethylenediaminetetraacetate dipotassium dihydrate, and ethylenediaminetetraacetic acid monopotassium trihydrogen trihydrate. The heat-sensitive recording material according to any one of the above.

  The heat-sensitive recording material of the present invention is excellent in water resistance and yellowing resistance of a white paper portion. Further, the recording density and whiteness are excellent.

  The protective layer in the present invention contains acetoacetyl-modified polyvinyl alcohol as an adhesive. Moreover, in this invention, it is preferable that the protective layer is formed using the coating liquid for protective layers containing acetoacetyl modified polyvinyl alcohol as an adhesive agent. Thereby, an acetoacetyl modified polyvinyl alcohol can be suitably contained in the protective layer. Although the content rate of the acetoacetyl modified polyvinyl alcohol contained in a protective layer is not specifically limited, About 20-100 mass% is preferable in the total solid of a protective layer.

  The degree of saponification of acetoacetyl-modified polyvinyl alcohol is preferably about 85 to 100 mol%. By making the degree of saponification 85% or more, the water resistance can be further enhanced. The saponification degree is more preferably 95 to 99%, and most preferably 98 to 99%. By using in this range, solubility in water can be enhanced. Moreover, the water resistance at the time of using a water-resistant agent together can also be improved.

  The average degree of polymerization of acetoacetyl-modified polyvinyl alcohol is preferably about 400 to 2000. By setting it to 400 or more, sufficient surface strength can be obtained. Moreover, plasticizer resistance and water resistance can be improved. On the other hand, by setting it to 2000 or less, the viscosity of the coating liquid for the protective layer becomes appropriate and stable quality can be obtained.

  The degree of acetoacetylation is preferably about 0.5 to 10 mol%. By setting the degree of acetoacetylation to 0.5 mol% or more, the water resistance can be further enhanced. On the other hand, by making it 10 mol% or less, the solubility in water can be improved, the coating suitability of the coating solution for the protective layer can be improved, and a uniform protective layer can be formed, thereby improving the barrier property. it can.

  The heat-sensitive recording layer in the present invention contains ethylenediaminetetraacetic acid and / or a salt thereof. In the present invention, the heat-sensitive recording layer is preferably formed using a heat-sensitive recording layer coating solution containing ethylenediaminetetraacetic acid and / or a salt thereof. Thereby, ethylenediaminetetraacetic acid and / or a salt thereof can be suitably contained in the heat-sensitive recording layer.

  The content ratio of ethylenediaminetetraacetic acid and / or a salt thereof contained in the heat-sensitive recording layer is not particularly limited, but is preferably about 0.1 to 10% by mass, and about 2 to 8% by mass in the total solid content of the heat-sensitive recording layer. Is more preferable, and 2-6 mass% is still more preferable. By setting it as 0.1 mass% or more, yellowing can be improved effectively. On the other hand, when the content is 10% by mass or less, the whiteness and the recording density can be improved.

  In the present invention, from the viewpoint of enhancing the effect of suppressing yellowing over time, the protective layer preferably contains ethylenediaminetetraacetic acid and / or a salt thereof. Moreover, in this invention, it is preferable that the coating liquid for protective layers contains ethylenediaminetetraacetic acid and / or its salt. Thereby, ethylenediaminetetraacetic acid and / or a salt thereof can be suitably contained in the protective layer.

  The content ratio of ethylenediaminetetraacetic acid and / or a salt thereof contained in the protective layer is preferably 10% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less in the total solid content of the protective layer. By setting the content to 10% by mass or less, whiteness can be improved by suppressing the white paper portion of the thermal recording medium from being colored yellowish green. On the other hand, the lower limit is not particularly limited, but by setting it to 1% by mass or more, yellowing over time can be effectively suppressed.

  When ethylenediaminetetraacetic acid and / or a salt thereof is not contained in the heat-sensitive recording layer but only in the protective layer, the white paper portion of the heat-sensitive recording material is colored yellow-green by setting the content ratio to 10% by mass or less. However, it is difficult to suppress yellowing over time even at 10% by mass. As a content ratio in each layer when contained in both the heat-sensitive recording layer and the protective layer, 2 to 4% by mass is preferable in the total solid amount of the heat-sensitive recording layer, and about 1 to 5% by mass in the total solid amount of the protective layer. Is preferred. By containing a part of the amount contained in the heat-sensitive recording layer in this range in the protective layer, the effect of suppressing yellowing can be remarkably improved, and the effect of improving the recording density can also be obtained.

  In the present invention, it is preferable to use ethylenediaminetetraacetic acid and / or a salt thereof after mixing and grinding with a pigment. Thereby, it is excellent in the effect of yellowing improvement. Specific examples of the pigment include kaolin, calcined kaolin, aluminum hydroxide, aluminum oxide, titanium dioxide, and amorphous silica. Among these, kaolin and calcined kaolin are preferable from the viewpoint of improving the effect of improving yellowing. The ratio of ethylenediaminetetraacetic acid and / or a salt thereof and the pigment to be mixed and pulverized is not particularly limited, but is preferably about 1.5 to 40 parts by mass with respect to 100 parts by mass of the pigment. Further, when ethylenediaminetetraacetic acid and / or a salt thereof is contained in both the heat-sensitive recording layer and the protective layer, from the viewpoint of improving the whiteness, the mixing ratio is about 10 to 40 parts by weight in the heat-sensitive recording layer, and the protective layer. Then, about 1.5-7 mass parts is preferable.

  The reason why yellowing is improved by containing ethylenediaminetetraacetic acid and / or a salt thereof is not known in detail, but the cause of yellowing of the white paper portion over time is a crosslinking agent that reacts with acetoacetyl groups. . In the thermosensitive recording layer, calcium ions and magnesium ions, which are divalent metal ions contained in a pigment such as kaolin, are present. When it was added to a heat-sensitive recording layer containing a crosslinking agent that reacts with an acetoacetyl group such as a hydrazide compound, it was found that yellowing was greatly improved. Therefore, ethylenediaminetetraacetic acid and / or a salt thereof caused yellowing 2 It is thought that it acts on a valent metal ion. Among cross-linking agents, hydrazide compounds are oxidized after hydrolysis in the presence of divalent metal ions after the cross-linking reaction with acetoacetyl-modified polyvinyl alcohol, effectively suppressing the yellowing gradually. it can.

  Specific examples of the salt of ethylenediaminetetraacetic acid include, for example, ethylenediaminetetraacetic acid dihydrogendiammonium dihydrate, ethylenediaminetetraacetic acid disodium, ethylenediaminetetraacetic acid disodium dihydrogensodium dihydrate, ethylenediaminetetraacetic acid monohydrogen trisodium salt Hydrates, ethylenediaminetetraacetic acid tetrasodium tetrahydrate, ethylenediaminetetraacetic acid dihydrogen dipotassium dihydrate, ethylenediaminetetraacetic acid monohydrogen tripotassium dihydrate, and the like.

  Ethylenediaminetetraacetic acid and / or a salt thereof can be used alone or in combination of two or more. Of these, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid dihydrogendiammonium dihydrate, and ethylenediaminetetraacetic acid disodium dihydrogensodium dihydrate are preferred. Ethylenediaminetetraacetic acid has a good balance of whiteness, yellowing and recording density. Well, more preferred.

  The heat-sensitive recording layer and / or protective layer in the present invention contains a cross-linking agent that reacts with acetoacetyl groups. Among these crosslinking agents, it is preferable to contain at least one selected from a hydrazide compound, glyoxal and methylol urea from the viewpoint of improving water resistance. In the present invention, when the adhesive contains acetoacetyl-modified polyvinyl alcohol crosslinked with a crosslinking agent that reacts with an acetoacetyl group, the water resistance of the heat-sensitive recording material can be increased. The heat-sensitive recording layer is preferably formed using a heat-sensitive recording layer coating solution containing such a crosslinking agent. Moreover, it is preferable that a protective layer is formed using the coating liquid for protective layers containing this crosslinking agent.

  In the protective layer coating solution, since the acetoacetyl-modified polyvinyl alcohol and the crosslinking agent react with each other, it is preferable to add the crosslinking agent to the protective layer coating solution immediately before coating on the heat-sensitive recording layer. Further, from the viewpoint of reducing coating defects due to aggregates and improving the pot life of the protective layer coating liquid, it is preferable to include a crosslinking agent in the thermal recording layer coating liquid.

  Specific examples of the hydrazide compound include, for example, benzoic hydrazide, formic hydrazide, acetic hydrazide, propionic hydrazide, n-butyric acid hydrazide, isobutyric acid hydrazide, n-valeric acid hydrazide, isovaleric acid hydrazide, pivalic acid hydrazide, carbohydrazide, Adipic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide polyhydradic acid dihydrazide And acid hydrazide.

  These drazide compounds can be used alone or in combination. Among them, adipic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide dihydrazide diacid, dihydrazide diacid Adipic acid dihydrazide is most preferable in consideration of the effect of imparting water resistance, solubility in water, and safety. Carboxylic acid dihydrazide having less than 4 carbon atoms is improved in reactivity, but there is a possibility that the unrecorded portion of the heat-sensitive recording material is colored red.

  If necessary, other crosslinking agents can be used in combination. Specific examples of other crosslinking agents include, for example, polyvalent amine compounds such as ethylenediamine, polyhydric aldehyde compounds such as glutaraldehyde and dialdehyde, polyamidoamine epichlorohydrin, polyamide epichlorohydrin, polyfunctional epoxy compounds, Examples thereof include polyvalent metal salts (Al, Ti, Zr, Mg, etc.), titanium lactate, boric acid and the like.

  Although the content rate of the crosslinking agent which reacts with an acetoacetyl group is not particularly limited, when it is contained in the protective layer, it is preferably about 0.1 to 10% by mass, and 0.2 to 5% by mass in the total solid content of the protective layer. % Is more preferable. Moreover, when it is made to contain in a thermosensitive recording layer, about 0.1-15 mass% is preferable in the total solid of a thermosensitive recording layer, and about 0.5-10 mass% is more preferable.

The protective layer in the present invention comprises, for example, water as a medium, and an acetoacetyl-modified polyvinyl alcohol aqueous solution, a specific cross-linking agent, and ethylenediaminetetraacetic acid and / or a salt thereof, a pigment, various auxiliary agents, and the like as an adhesive. The coating solution for protective layer prepared by the above is applied on the heat-sensitive recording layer so that the dry weight is preferably about 0.1 to 10 g / m ² , more preferably about 0.5 to 6 g / m ^2. It is formed by drying.

The heat-sensitive recording layer in the present invention is, for example, a leuco dye dispersion and colorant dispersion pulverized to an average particle size of about 0.2 to 2 μm using water as a medium, a specific crosslinking agent, ethylenediaminetetraacetic acid and / or The coating solution for the heat-sensitive recording layer prepared by mixing the salt, and if necessary, an adhesive, a pigment, various auxiliary agents, etc., is preferably about ² to 12 g / m ² , more preferably by dry weight on the support. It is formed by applying and drying on a support so as to be about 3 to 10 g / m ² .

  As the adhesive, in addition to acetoacetyl-modified polyvinyl alcohol, for example, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, starch, oxidized starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein , Gum arabic, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, urea resin, melamine resin, amide Resin, styrene-butadiene resin latex, acrylic resin latex, urethane resin latex and the like can be mentioned.

  Examples of the pigment include inorganic pigments such as aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, kaolin, calcined kaolin, styrene resin filler, acrylic resin filler, nylon resin filler, urea / formalin resin filler, etc. And organic pigments. Of these, acidic pigments such as kaolin, amorphous silica, or calcined kaolin are preferred because they are excellent in the effect of improving yellowing.

  Examples of auxiliary agents include lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sodium polyacrylate, and ultraviolet rays. Absorbers, fluorescent dyes, colored dyes, mold release agents, antioxidants and the like can be mentioned.

  The heat-sensitive recording layer in the present invention contains a leuco dye and a colorant. 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-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl- N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilino Fluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilino Luolan, 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-chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide, etc. It is done.

  Of course, the leuco dye is not limited to the above, and two or more kinds may be used in combination. Further, the content ratio of the leuco dye is not particularly limited and may be adjusted depending on the colorant to be used, and is generally preferably about 5 to 35% by mass in the total solid content of the heat-sensitive recording layer.

  Specific examples of the colorant include, for example, 4,4′-isopropylidenediphenol, 4,4′-cyclohexylidenediphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,4 '-Dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone , Butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] phenolic compounds such as benzene, Np-tri Such as rusulfonyl-N′-phenylurea, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylmethane, Np-tolylsulfonyl-N′-p-butoxyphenylurea, etc. Compounds having a sulfonyl group and a ureido group in the molecule, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salt compounds of aromatic carboxylic acids such as salicylic acid.

  The content ratio of the leuco dye and the colorant is appropriately selected according to the type of leuco dye or colorant used, and is not particularly limited. Generally, the colorant is a leuco dye 100. Preferably it is 100-1000 mass parts with respect to a mass part, More preferably, about 100-500 mass% is used.

  The heat-sensitive recording layer may contain a storability improving agent as necessary. Thereby, the storage stability of a recording part can be improved. 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, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4′- (2-methylglycidyloxy) diphenylsulfone, diglycidyl terephthalate, cresol novolac epoxy resin, Epoxy compounds such as novolac epoxy resin and bisphenol A epoxy resin, N, N′-di-2-naphthyl-p-phenylenediamine, 2,2′-methylenebis (4,6-di-tert-butylphenyl) Examples include sodium or polyvalent metal salts of phosphate, bis (4-ethyleneiminocarbonylaminophenyl) methane, and the like.

  The heat-sensitive recording layer may contain a sensitizer if necessary. Thereby, the recording sensitivity can be increased. 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 Disilazide, N- acetoacetyl -p- toluidine, di (beta-biphenyl ethoxy) benzene, oxalic acid di -p- chlorobenzyl ester, oxalic acid di -p- methylbenzyl ester, and the like oxalic acid dibenzyl ester.

  Although content of a preservability improving agent and a sensitizer is not particularly limited, it is generally desirable to adjust the content to 4 parts by mass or less with respect to 1 part by mass of the colorant.

  In the present invention, it is preferable to have an undercoat layer containing plastic hollow particles between the support and the thermosensitive recording layer. Thereby, the recording sensitivity can be further increased. In addition, the barrier property is improved by the plastic hollow particles staying on the support to form a uniform undercoat layer, preventing the colorant from coming into contact with the alkali filler contained in the plasticizer or neutral paper, A decrease in coloring ability can be suppressed. Examples of the plastic hollow particles include conventionally known particles, for example, particles having a hollow ratio of about 50 to 99% in which the film material is made of an acrylic resin, a styrene resin, a vinylidene chloride resin, or the like. Here, the hollowness is a value obtained by the following formula (d / D) × 100. In the formula, d represents the inner diameter of the organic hollow particles, and D represents the outer diameter of the organic hollow particles. The average particle size of the plastic hollow particles is preferably about 0.5 to 10 μm, more preferably about 1 to 3 μm. By setting the average particle size to 10 μm or less, when the undercoat layer coating solution is applied by a blade coating method, troubles such as streaks and scratches are not caused, and good coating suitability can be obtained.

  The content ratio of the plastic hollow particles can be selected from a wide range, but is generally preferably about 2 to 90% by mass in the total solid content of the undercoat layer. From the viewpoint of improving the color development effect and enhancing the barrier property, the lower limit is more preferably 5% by mass or more, and further preferably 10% by mass or more. On the other hand, from the viewpoint of suppressing wrinkle adhesion to the thermal head, the upper limit is more preferably 80% by mass or less, further preferably 70% by mass or less, particularly preferably 60% by mass or less, and most preferably 50% by mass or less.

  From the viewpoint of improving the effect of suppressing wrinkle adhesion to the thermal head, the undercoat layer preferably contains an oil-absorbing pigment having an oil absorption amount of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g. Moreover, a thermally expansible particle can also be contained. Here, the oil absorption is a value determined according to the method described in JIS K 5101.

  Various oil-absorbing pigments can be used, and 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 content of the oil-absorbing pigment can be selected from a wide range, but is generally preferably about 2 to 95% by mass and more preferably about 5 to 90% by mass in the total solid content of the undercoat layer.

The undercoat layer is generally formed by applying and drying an undercoat layer coating solution prepared by mixing plastic hollow particles, oil-absorbing pigments, adhesives, auxiliaries, etc. on a support with water as a medium. Is done. The coating amount of the undercoat layer coating solution is not particularly limited, but is preferably about 3 to 20 g / m ² , more preferably about 5 to 12 g / m ² in terms of dry weight.

The type, shape, dimensions, etc. of the support used in the present invention are not particularly limited. For example, high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine In addition to paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film, and the like, various transparent supports can be appropriately selected and used. The basis weight of the paper support is about 40 to 200 g / m ² .

  In the present invention, the yellowing of the heat-sensitive recording material over time appears prominently when a neutral paper support is used rather than acidic paper. In this invention, since the effect which suppresses yellowing can fully be exhibited, neutral paper can be used suitably as a support body.

  The type of neutral paper and production method are not particularly limited, but pulp fibers and generally fillers such as calcium carbonate, sizing agents such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), etc., and polyamides as fixing agents, A pulp slurry containing acrylic amide, cationic starch and the like can be obtained by paper making. As such neutral paper, since improvement of yellowing is remarkable, the hot water extraction pH (based on JIS P 8133) is preferably in the range of about 6 to 11, more preferably in the range of 6.5 to 10. A range of 7.5 to 10 is more preferable. By setting the pH to 11 or less, aggregation of the pulp slurry itself can be suppressed. Furthermore, as long as the pH does not become less than 6, the pH can be adjusted by using a sulfuric acid band as necessary, and papermaking properties can be improved.

  Kinds of acid paper and production method are not particularly limited, but pulp fibers and fillers such as kaolin, talc, chlorite, rosin soaps such as reinforced rosin soap and reinforced rosin emulsion, alkenyl succinic acid soap, etc. A so-called synthetic sizing agent, etc., and a pulp slurry containing a sulfuric acid band and the like can be obtained by papermaking. As such an acidic paper, the hot water extraction pH (based on JIS P 8133) is preferably pH 2 or more from the viewpoint of improving the background fog resistance and preventing the deterioration of the support, and from the viewpoint of fixability of the rosin sizing agent. To a range not exceeding 6 is preferable, and a range of about pH 2 to 5.7 is more preferable.

  Kinds of pulp fibers used in the present invention, production method and the like are not particularly limited. For example, various high-yield pulps in addition to chemical pulp and SCP such as softwood pulp and hardwood pulp obtained by KP, SP, AP method, and the like, Or a waste paper pulp etc. are mentioned.

  It should be noted that internal additives for papermaking such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents can be added to the pulp slurry as appropriate depending on the use of the paper. . Moreover, starch etc. can also be apply | coated in a size press. As the paper machine, a long net paper machine, a twin wire type paper machine, a circular net paper machine, a Yankee dryer paper machine and the like can be used as appropriate.

  In the present invention, various known techniques in the field of producing a thermal recording material can be added as necessary. For example, if necessary, a back layer or a pressure-sensitive adhesive layer is provided on the surface opposite to the surface having the thermosensitive recording layer of the support, or an uppermost layer mainly composed of a pigment and an adhesive is provided on the protective layer. can do. A smoothing process using a super calender or the like can be performed after the formation of each layer or in an arbitrary process after the formation of all the layers.

  The method for forming the heat-sensitive recording layer and the protective layer, if necessary, the undercoat layer is not particularly limited. For example, air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, Mayer bar coating, After applying using an appropriate application method such as die coating, it can be dried.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” indicate “part by mass” and “% by mass”, respectively. The average particle diameter is a volume average particle diameter measured by a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation).

Example 1
・ Preparation of coating solution for undercoat layer 60 parts of calcined kaolin (oil absorption: 110 ml / 100 g), 20 parts of styrene-butadiene resin latex (solid content concentration: 50%), hollow particles (trade name: Ropaque SN-1055-R) , Rohm & Haas Co., Ltd.) 26% aqueous dispersion 77 parts, Carboxymethylcellulose (trade name: Cellogen 7A, Daiichi Kogyo Seiyaku Co., Ltd.) 5% aqueous solution 20 parts, Sodium polyacrylate 20% aqueous solution 20 parts, A composition comprising 4.5 parts of a 45% aqueous solution of zirconium carbonate ammonium salt (trade name: Baycoat 20, manufactured by Nippon Light Metal Co., Ltd.) and 120 parts of water was mixed to obtain an undercoat layer coating solution.

Preparation of liquid A (leuco dye dispersion) A composition comprising 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 10 parts, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water. A liquid A was obtained by pulverizing with a sand mill until the average particle size became 1.0 μm.

-Preparation of liquid B (coloring agent dispersion) A composition comprising 10 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water was averaged in an average particle size of 1. By pulverizing to 0 μm, a liquid B was obtained.

-Preparation of liquid C (sensitizer dispersion) A composition comprising 10 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water in a sand mill has an average particle size of 1 C liquid was obtained by grinding to 0.0 μm.

-Preparation of D solution A composition comprising 40 parts of kaolin (trade name: HG-90, manufactured by Huba Co.), 8 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kirest Co., Ltd.) and 48 parts of water is averaged by a sand mill. The liquid D was obtained by pulverizing until the particle diameter became 1.0 μm.

・ E solution preparation A composition comprising 40 parts of kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.), 6 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kirest Co., Ltd.) and 46 parts of water is averaged by a sand mill. The liquid E was obtained by pulverizing until the particle diameter became 1.0 μm.

・ F solution preparation A composition comprising 40 parts of kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.), 4 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kirest Co., Ltd.) and 44 parts of water is averaged by a sand mill. The liquid F was obtained by pulverizing until the particle diameter became 1.0 μm.

-G liquid preparation A composition consisting of 40 parts of kaolin (trade name: HG-90, manufactured by Huba Co.), 12 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Crest Co., Ltd.), and 52 parts of water is averaged in a sand mill. The liquid G was obtained by pulverizing until the particle diameter became 1.0 μm.

・ H liquid preparation A composition consisting of 40 parts of kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.), 16 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Crest Co., Ltd.), and 56 parts of water is averaged with a sand mill. The liquid H was obtained by pulverizing until the particle diameter became 1.0 μm.

-Preparation of liquid I A composition comprising 120 parts of kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.), 2 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Crest Co., Ltd.) and 122 parts of water is averaged by a sand mill. The liquid I was obtained by pulverizing until the particle diameter became 1.0 μm.

-Solution J preparation Kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.) 120 parts, ethylenediaminetetraacetic acid (trade name: Kyrest 3A, manufactured by Kyrest Co., Ltd.) 4 parts, and a composition comprising 124 parts of water averaged with a sand mill The liquid J was obtained by pulverization until the particle diameter became 1.0 μm.

-Preparation of K solution A composition comprising 120 parts of kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.), 8 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kyrest Co., Ltd.) and 128 parts of water is averaged by a sand mill. The liquid K was pulverized until the particle diameter became 1.0 μm.

-Preparation of coating solution for heat-sensitive recording layer 30 parts of liquid A, 90 parts of liquid B, 60 parts of liquid C, 48 parts of liquid D, 70 parts of 10% aqueous solution of polyvinyl alcohol (saponification degree 99%, polymerization degree 2400), solid content A composition comprising 10 parts of a 50% styrene-butadiene resin latex and 7.5 parts of a 35% aqueous dispersion of adipic acid dihydrazide (trade name: ADH-35S, manufactured by NIPPON KOHKO CO., LTD.) Was mixed to produce heat. A recording layer coating solution was obtained.

-Preparation of coating solution for protective layer 250 parts of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Gohsenx (registered trademark) Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), kaolin (trade name: HG-90, Huva) A composition comprising 63 parts, 5 parts of a 30% aqueous solution of zinc stearate, and 150 parts of water was mixed to obtain a coating solution for a protective layer.

・ Preparation of thermosensitive recording medium A coating liquid for an undercoat layer is applied to one side of a high-quality paper (hot water extraction pH 8.8) mainly composed of non-chlorine bleached pulp (ECF) as a neutral paper having a basis weight of 60 g / m ^2. An undercoat layer was formed by applying and drying by pure blade coating so that the application amount after drying was 6 g / m ^2, and then the surface was smoothed by a super calender. The smoothing processing has been primed layer, as a thermal recording layer coating solution and protective layer coating liquid coated amount after drying of ^{4g / m 2, 3g / m} 2 , respectively, applied by Meyer bar coating and After drying, a heat-sensitive recording layer and a protective layer were sequentially formed, and the surface was smoothed with a super calendar to obtain a heat-sensitive recording material.

Example 2
In the preparation of the liquid D of Example 1, ethylenediaminetetraacetic acid diammonium diammonium dihydrate (trade name: Kirest 2N, Kireste) was used instead of 8 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kirest Co., Ltd.). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 8 parts were used.

Example 3
In the preparation of the liquid D of Example 1, ethylenediaminetetraacetic acid disodium dihydrogen dihydrate (trade name: Kirest 3B, Kirest) was used instead of 8 parts of ethylenediaminetetraacetic acid (trade name: Kirest 3A, manufactured by Kirest Co., Ltd.). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 8 parts were used.

Example 4
In the preparation of the thermal recording layer coating liquid of Example 1, 46 parts of E liquid was used instead of 48 parts of D liquid, and kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.) was used in the preparation of the coating liquid for protective layer. A thermosensitive recording material was obtained in the same manner as in Example 1, except that 122 parts of I liquid was used instead of 63 parts, and the amount of water was changed to 30 parts instead of 150 parts.

Example 5
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, 44 parts of F liquid were used instead of 48 parts of D liquid, and kaolin (trade name: HG-90, manufactured by Huba Co., Ltd.) was used in the preparation of the coating liquid for protective layer. A thermal recording material was obtained in the same manner as in Example 1 except that 124 parts of J liquid was used instead of 63 parts, and the amount of water was changed to 30 parts instead of 150 parts.

Example 6
In the preparation of the protective layer coating liquid of Example 1, 128 parts of K liquid was used instead of 63 parts of kaolin (trade name: HG-90, manufactured by Huva), and 20 parts instead of 150 parts of water. A thermosensitive recording material was obtained in the same manner as in Example 1 except that.

Example 7
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, 52 parts of G liquid was used instead of 48 parts of D liquid.

Example 8
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, 56 parts of H liquid was used instead of 48 parts of D liquid.

Example 9
In the preparation of heat-sensitive recording material of Example 1, the chlorine-free bleached pulp (ECF) was used as neutral paper having a basis weight of 60 g / m ² in place of the high-quality paper with a main component of the basis weight of 60 g / m ² A heat-sensitive recording material was obtained in the same manner as in Example 1 except that high-quality paper that was acidic paper (hot water extraction pH 5.3) was used.

Example 10
In the preparation of the thermal recording layer coating liquid of Example 1, a 35% aqueous dispersion of adipic acid dihydrazide was used in the preparation of the protective layer coating liquid (trade name: A thermosensitive recording material was obtained in the same manner as in Example 1 except that 3 parts of ADH-35S (manufactured by Nippon Kako Paint Co., Ltd.) were added.

Example 11
In the production of the thermal recording material of Example 1, instead of the high-quality paper (hot water extraction pH 8.8) mainly composed of non-chlorine bleached pulp (ECF) used as a neutral paper having a basis weight of 60 g / m ^2. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that high-quality paper (hot water extraction pH 6.5) was used.

Example 12
In the production of the thermal recording material of Example 1, instead of the high-quality paper (hot water extraction pH 8.8) mainly composed of non-chlorine bleached pulp (ECF) used as a neutral paper having a basis weight of 60 g / m ^2. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that high-quality paper (hot water extraction pH 10) was used.

Example 13
In the preparation of the heat-sensitive recording layer coating solution of Example 1, a 40% aqueous solution of glyoxal was used instead of 7.5 parts of 35% aqueous dispersion of adipic acid dihydrazide (trade name: ADH-35S, manufactured by Nippon Kako Paint Co., Ltd.). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount was 1.5 parts.

Comparative Example 1
In the preparation of the thermal recording layer coating liquid of Example 1, the same procedure as in Example 1 was conducted except that 20 parts of kaolin (trade name: HG-90, manufactured by Huba Co.) was used instead of 48 parts of D liquid. A heat-sensitive recording material was obtained.

Comparative Example 2
In the preparation of the coating liquid for protective layer of Comparative Example 1, 140 parts of K solution was used instead of 63 parts of kaolin (trade name: HG-90, manufactured by Huba), and 10 parts instead of 150 parts of water. A thermosensitive recording material was obtained in the same manner as in Comparative Example 1 except that.

Comparative Example 3
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, the same procedure as in Example 1 was conducted, except that a 35% aqueous dispersion of adipic acid dihydrazide (trade name: ADH-35S, manufactured by Nippon Kako Paint Co., Ltd.) was not used. A heat-sensitive recording material was obtained.

Comparative Example 4
In the preparation of the protective layer coating liquid of Example 1, instead of 250 parts of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Gohsenx (registered trademark) Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), complete saponification A thermosensitive recording material was obtained in the same manner as in Example 1 except that 250 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: Gohsenol NM-11, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used.

Comparative Example 5
In the production of the thermal recording material of Comparative Example 1, instead of the high-quality paper (hot water extraction pH 8.8) mainly composed of non-chlorine bleached pulp (ECF) used as neutral paper with a basis weight of 60 g / m ^2. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that high-quality paper that was acidic paper (hot water extraction pH 5.3) having a basis weight of 60 g / m ² was used.

  The thermosensitive recording material thus obtained was evaluated as follows. The results were as shown in Table 1.

(Recording density)
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording body is recorded at an applied energy of 0.35 mJ / dot, and the optical density (recording density) of the recording portion is reflected The measurement was performed in a visual mode of a densitometer (trade name: Macbeth densitometer RD-918, manufactured by Gretag Macbeth). The recording density is preferably 1.25 or more.

(Whiteness)
The whiteness on the protective layer side of the unrecorded thermal recording material was measured with a Hunter whiteness meter. Blue was used for the filter. The larger the measured value, the better the background fog resistance.

(Yellowing resistance)
The unrecorded thermal recording material was allowed to stand for 7 days under conditions of 40 ° C. and 90% RH, and then the b ^* value of the background portion on the protective layer side was measured with a color difference meter. It is desirable that the b ^* value is less than 3.

(water resistant)
A drop (approximately 30 μl) of water is dropped on the surface of the 5 cm × 5 cm heat-sensitive recording layer, another heat-sensitive recording layer is stacked on the surface so that the surfaces of the protective layer are in contact with each other, and after naturally dried, the heat-sensitive recording body is manually formed. When the thermal recording material was peeled off, the degree of sticking between the protective layers was evaluated according to the following criteria. The water resistance is better when there is no sticking.
A: The protective layer surfaces are separated naturally.
B: The protective layer surfaces are adhered to each other, but the heat-sensitive recording materials are easily peeled off and the coating layer including the protective layer is not peeled off.
C: The protective layer surfaces adhere to each other, the thermal recording bodies are not peeled off, and the thermal recording bodies are torn.

Claims (9)

  In a heat sensitive recording body comprising a heat sensitive recording layer containing a leuco dye and a colorant on a support, and a protective layer containing an adhesive on the heat sensitive recording layer, the protective layer is an acetoacetyl-modified polyvinyl alcohol as an adhesive A heat-sensitive recording layer, wherein the heat-sensitive recording layer contains ethylenediaminetetraacetic acid and / or a salt thereof, and the heat-sensitive recording layer and / or the protective layer contains a crosslinking agent that reacts with an acetoacetyl group.   The heat-sensitive recording material according to claim 1, wherein the crosslinking agent reacts with an acetoacetyl group and is hydrolyzed in the presence of a divalent metal ion and then oxidized.   The heat-sensitive recording material according to claim 1, wherein the crosslinking agent is a hydrazide compound and / or glyoxal.   The content ratio of ethylenediaminetetraacetic acid and / or a salt thereof contained in the heat-sensitive recording layer is 0.1 to 10% by mass in the total solid content of the heat-sensitive recording layer. The heat-sensitive recording material described.   The heat-sensitive recording material according to claim 1, wherein the protective layer contains ethylenediaminetetraacetic acid and / or a salt thereof.   The heat-sensitive recording material according to claim 1, wherein the support is neutral paper.   The heat-sensitive recording material according to any one of claims 1 to 6, wherein the support is neutral paper having a hot water extraction pH (based on JIS P 8133) of 6 to 11.   The heat-sensitive recording material according to claim 1, wherein the crosslinking agent is a dicarboxylic acid dihydrazide compound.   The ethylenediaminetetraacetic acid salt is ethylenediaminetetraacetic acid dihydrogen diammonium dihydrate, ethylenediaminetetraacetic acid disodium salt, ethylenediaminetetraacetic acid disodium dihydrogen sodium dihydrate, ethylenediaminetetraacetic acid monohydrogen trisodium trihydrate, ethylenediamine Any one of Claims 1-8 which is at least 1 sort (s) chosen from tetrasodium tetraacetate tetrahydrate, ethylenediaminetetraacetic acid dihydrogen dipotassium dihydrate, and ethylenediaminetetraacetic acid monohydrogen trihydrogen potassium dihydrate. The heat-sensitive recording material according to item 1.