Thermal recording materials

Abstract

To provide a heat-sensitive recording material which exhibits omission resistance and defect resistance for suppressing the occurrence of omission and defects of a heat-sensitive recording layer and blocking resistance and adhesion worsening resistance for preventing blocking and adhesion worsening of the heat-sensitive recording material.SOLUTION: This heat-sensitive recording material contains a (meth)acrylamide copolymer and has at least a heat-sensitive recording layer, a support, and a re-wettable paste layer in this order. The heat-sensitive recording layer has a composition including mineral oil and hydrophobic silica and a core shell structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-sensitive recording material having a heat-sensitive recording layer on the front surface of a support and a rewettable glue layer on the back surface of the support. [Background technology]

[0002] A thermosensitive recording material having, in order, at least a rewettable adhesive layer containing a rewettable adhesive and a sulfone-modified polyvinyl alcohol, a support, and a thermosensitive recording layer containing a leuco dye and a coloring agent is already known (see, for example, Patent Document 1). The thermosensitive recording material described in Patent Document 1 has excellent adhesive strength when the rewettable adhesive layer is rewetted and excellent adhesion strength of the rewettable adhesive layer to the substrate. However, with regard to the thermosensitive recording material described in Patent Document 1, only an antifoaming agent is described as an example of an auxiliary agent for the coating liquid for the thermosensitive recording layer.

[0003] Regarding the thermal recording material and the defoaming agent, for example, a thermal recording material is known which is characterized by using a leuco dye and a phenolic compound as a developer as the main components, a non-cellulose ether-based water-soluble polymer compound and hydroxyethyl methyl cellulose as the binder in combination, and adding 0.005 to 1.0 parts by weight of a defoaming agent whose main components are a mineral oil-nonionic surfactant per 100 parts by weight of the hydroxyethyl methyl cellulose (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-085030 [Patent Document 2] Japanese Unexamined Patent Publication No. 58-142892 Summary of the Invention [Problem to be solved by the invention]

[0005] A thermosensitive recording layer can be obtained by dispersing a color-forming dye, such as an electron-donating dye, a dye precursor, a basic dye, or a leuco dye, a color developer (also known as an electron-accepting compound or coloring agent), and a binder in a medium such as water to prepare a dispersion, which is then coated on a support such as paper and dried. However, because the color developer has poor dispersibility, a dispersant is used for dispersion. The dispersion is prone to foaming due to the influence of the dispersant and binder. Therefore, an antifoaming agent, as described in Patent Document 2, is used. Dispersions containing antifoaming agents exhibit reduced adhesion to a support, an undercoat layer, etc. when coated and dried on the support, an undercoat layer, etc. As a result, a thermosensitive recording layer obtained by coating and drying a dispersion containing antifoaming agents on a support, an undercoat layer, etc. may be chipped off from the support, the undercoat layer, etc. Furthermore, dispersions containing antifoaming agents deteriorate the compatibility of color-forming dyes, developers, and binders. As a result, a thermosensitive recording layer obtained by coating and drying a dispersion containing antifoaming agents on a support, an undercoat layer, etc. may have defects on the surface of the thermosensitive recording layer.

[0006] The thermosensitive recording material described in Patent Document 1 is suitable for use as, for example, a logistics label. Logistics labels are usually stored in roll paper form or loaded into recording devices. A thermosensitive recording material having a thermosensitive recording layer on the front surface of a support and a rewettable adhesive layer on the back surface of the support comes into contact with the thermosensitive recording layer and the rewettable adhesive layer when in roll paper form. Commonly used adhesives for the rewettable adhesive layer include chloroprene rubbers, polyvinyl alcohols, starches, vinyl acetate copolymers, dextrin, gum arabic, glue, and polyacrylamide. A thermosensitive recording medium having a thermosensitive recording layer on the front surface of a support and a rewettable adhesive layer on the back surface of the support may develop adhesiveness in the rewettable adhesive layer depending on the environment and circumstances, such as a high humidity environment or unexpected moisture absorption. As a result, the thermosensitive recording material may experience blocking. Therefore, it is necessary to reduce such blocking. Furthermore, when the thermosensitive recording material is in the form of roll paper, in a thermosensitive recording layer obtained by coating and drying a dispersion containing an antifoaming agent, the antifoaming agent component migrates into the rewettable adhesive layer. As a result, the adhesiveness of the rewettable adhesive layer may deteriorate.

[0007] In view of the above, an object of the present invention is to provide a thermal recording material that has chipping resistance and defect resistance that suppress the occurrence of chipping and defects in the thermal recording layer, and blocking resistance and adhesion deterioration resistance that prevent blocking and deterioration of the adhesion of the thermal recording material. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into the combination of a binder and a composition having antifoaming properties, and as a result have discovered the following invention. The above-mentioned problems can be solved by the following invention. [1] A thermal recording material having at least a thermal recording layer, a support, and a rewettable adhesive layer in this order, wherein the thermal recording layer contains a composition containing mineral oil and hydrophobic silica and a (meth)acrylamide copolymer having a core-shell structure. [Effects of the Invention]

[0009] The present invention can provide a thermal recording material that has chipping resistance and defect resistance that suppress the occurrence of chipping and defects in the thermal recording layer, as well as blocking resistance and adhesion deterioration resistance that prevent blocking and adhesion deterioration of the thermal recording material. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be specifically described below.

[0011] The thermosensitive recording material has at least a thermosensitive recording layer, a support, and a rewettable adhesive layer in this order. That is, the thermosensitive recording material has a support, a thermosensitive recording layer on the front surface of the support, and a rewettable adhesive layer on the back surface of the support. Here, the terms "front surface" and "back surface" of the support are used for convenience in distinguishing between the surfaces of the support, and do not refer to the front and back surfaces that depend on physical or chemical differences between the support.

[0012] In some embodiments, the thermosensitive recording material has an undercoat layer between the support and the thermosensitive recording layer and / or between the support and the rewettable adhesive layer. This is because it can protect the support from heat and moisture or improve the adhesion of the thermosensitive recording layer. The undercoat layer is a conventionally known layer in the field of thermosensitive recording materials and contains a pigment and a binder.

[0013] The pigment contained in the undercoat layer is one conventionally known in the field of coated paper, and examples of the pigment include diatomaceous earth, talc, clay, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, titanium dioxide, zinc oxide, silicon oxide, amorphous calcium silicate, silica, colloidal silica, colloidal alumina, calcium sulfate, barium sulfate, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, alumina, aluminum hydroxide, magnesium hydroxide, lithopone, zeolite, and hydrated halloysite.

[0014] The binder is a water-soluble or water-dispersible resin conventionally known in the field of coated paper. Examples of binders include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and modified polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, cellulose derivatives such as hydroxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose, proteins such as gelatin and casein, sodium alginate, starches such as starch and its modified products, poly(meth)acrylic acid and its salts, poly(meth)acrylic acid esters, various copolymers of poly(meth)acrylic acid esters such as (meth)acrylic acid amide acrylate copolymers, polyacrylamide, polymaleic acid and its salts, styrene (maleic anhydride) copolymers, and isobutylene (maleic anhydride) copolymers. and salts thereof, water-soluble resins such as various maleic anhydride copolymers, acrylamide acrylate copolymers, acrylamide acrylate ester (meth)acrylic acid copolymers, ethylene maleic anhydride copolymers and salts thereof, styrene maleic anhydride copolymers and salts thereof, isobutylene maleic anhydride copolymers and salts thereof, styrene isobutylene maleic anhydride copolymers and salts thereof, and water-dispersible resins such as polyvinyl acetate, polyurethane, styrene butadiene copolymers, vinyl chloride vinyl acetate copolymers, ethylene vinyl acetate copolymers, styrene butadiene (meth)acrylic acid ester copolymers, and styrene butadiene (meth)acrylic acid ester copolymers.

[0015] Furthermore, the undercoat layer may contain various conventionally known additives as needed, such as dispersants, surfactants, coloring dyes, fluorescent dyes, lubricants, waxes, antifoaming agents, ultraviolet absorbers, curing agents, and crosslinking agents.

[0016] In some embodiments, the thermosensitive recording material has a protective layer on the outer side of the thermosensitive recording layer relative to the support. This is because it can improve the blocking resistance of the thermosensitive recording material or protect the thermosensitive recording layer. The protective layer is a conventionally known layer in the field of thermosensitive recording materials and contains a binder, and optionally a pigment and various additives. Examples of additives include surfactants, coloring dyes, fluorescent dyes, lubricants, antifoaming agents, UV absorbers, curing agents, and crosslinking agents. The binders and pigments are the same as those exemplified for the undercoat layer, and therefore a detailed description is omitted here. In some embodiments, the protective layer contains waxes and / or fatty acid metal salts. This is because it can further improve the blocking resistance of the thermosensitive recording material.

[0017] The undercoat layer and the protective layer can be obtained by coating a coating liquid containing each material using a conventionally known coating device and drying it using a conventionally known drying device.

[0018] The support may be any of those conventionally known in the field of thermal recording materials, such as coated and uncoated paper, synthetic resin-laminated paper, synthetic paper, various nonwoven fabrics, woven fabrics, synthetic resin films, metal foils, ceramic paper, and glass plates, as well as composites or laminates of any of these. In some embodiments, the substrate is paper, such as coated and uncoated papers containing cellulose derived from wood and / or non-wood sources, because this is less environmentally harmful than other substrates.

[0019] The thermosensitive recording layer of the thermosensitive recording material is a color-forming layer containing a color-forming dye, and is a layer conventionally known in the field of thermosensitive recording materials. In some embodiments, the thermosensitive recording layer contains a dye precursor that is a color-forming dye, a color developer, a pigment, and a binder. In some embodiments, the thermosensitive recording layer also contains a sensitizer and various additives as needed.

[0020] Dye precursors are conventionally known in the field of thermal recording materials, and examples thereof include leuco derivatives of triaryls, diphenylmethanes, triphenylmethanes, thiazines, phenothiazines, spiros, spiropyrans, lactams, fluorans, auramines, and indolinophthalides. Each dye precursor has its own unique color tone, and examples of the color tone include black, red, reddish purple, orange, blue, green, and yellow. In some embodiments, the dye precursor is one or more selected from the group consisting of these.

[0021] Examples of dye precursors that give black color include 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-2-tetrahydrofluoran), 3-(N-Hexyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-di-n-butylamino-6-methyl-7-anilinofluoran, 3-di-n-amylamino-6-methyl-7-anilinofluoran, 3-(N-isoamyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-hexyl-N-ethyl)amino-6-methyl

[0033] Examples of the fluoranol include 3-[N-(3-ethoxypropyl)-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-methyl]amino-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di-n-butylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,6-dimethylanilino)fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran, 2,4-dimethyl-6-(4-dimethylaminoanilino)fluoran, and 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran. Examples of dye precursors that develop red colors include 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(p-nitro)anilinolactam, 3,6-bis(diethylamino)fluoran-γ-(o-chloro)anilinolactam, 3-dimethylamino-7-bromofluoran, 3-diethylaminofluoran, 3-diethylamino-6-methylfluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, and 3-diethylamino-7-bromofluoran. fluoran, 3-diethylamino-7,8-benzofluoran, 3-diethylamino-6,8-dimethylfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-tert-butylfluoran, 3-(N-ethyl-N-tolyl)amino-7-methylfluoran, 3-(N-ethyl-N-tolyl)amino-7-ethylfluoran, 3-(N-ethyl-N-isobutyl)amino-6-methyl-7-chlorofluoran, and 3-(N-ethyl-N-isoamyl)amino-7,8-benzofluoran, 3-cyclohexyl Xylamino-6-chlorofluoran, 3-di-n-butylamino-6-methyl-7-bromofluoran, 3-di-n-butylamino-7,8-benzofluoran, 3-tolylamino-7-methylfluoran, 3-tolylamino-7-ethylfluoran, 2-(N-acetylanilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-propionylanilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-benzoylanilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-carbotoxy) 2-(N-anilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-formylanilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-benzylanilino)-3-methyl-6-di-n-butylaminofluoran, 2-(N-allylanilino)-3-methyl-6-di-n-butylaminofluoran, and 2-(N-methylanilino)-3-methyl-6-di-n-butylaminofluoran, 3-diethylamino-7-phenoxyfluoran, 3-(N-ethyl-N-isoamyl)amino-7-phenoxyfluoran, 3,3'-Bis(1-n-butyl-2-methylindol-3-yl)phthalide, 3,3'-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,3'-bis(1-n-octyl-2-methylindol-3-yl)phthalide, 7-(N-ethyl-N-isoamylamino)-3-methyl-1-phenylspiro[(1,4-dihydrochromeno[2,3-c]pyrazole)-4,3' -phthalide], 7-(N-ethyl-N-isoamylamino)-3-methyl-1-p-methylphenylspiro[(1,4-dihydrochromeno[2,3-c]pyrazole)-4,3'-phthalide], and 7-(N-ethyl-Nn-hexylamino)-3-methyl-1-phenylspiro[(1,4-dihydrochromeno[2,3-c]pyrazole)-4,3'-phthalide]. Examples of dye precursors that provide blue color formation include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylaminophenyl)phthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-methyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-n-hexyloxy-4-diethylaminophenyl)-4-azaphthalide, and 3,6-bis(diphenylamino)fluoran. Examples of dye precursors that give green color include 3-(N-ethyl-Nn-hexyl)amino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, 3-(N-ethyl-Np-tolyl)amino-7-(N-phenyl-N-methylamino)fluoran, 3-[p-(p-anilinoanilino)anilino]-6-methyl-7-chlorofluoran, and 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Examples of dye precursors that give yellowish colors include 3,6-dimethoxyfluoran and 1-(4-n-dodecyloxy-3-methoxyphenyl)-2-(2-quinolyl)ethylene.

[0022] The color developer is a material conventionally known in the field of thermal recording materials, which has the property of liquefying or dissolving with an increase in temperature and causing the dye precursor to develop color upon contact with it. Examples of the color developer include organic acid compounds such as phenolic compounds, aromatic carboxylic acid compounds, and polyvalent metal salts of these compounds. The color developer can be present in composite microparticles or microcapsules. Alternatively, the color developer can be present in the form of solid-dispersed microparticles.

[0023] Examples of the color developer include bis(3-allyl-4-hydroxyphenyl)sulfone, 3-(3-tosylureido)phenyl-p-toluenesulfonate, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-octyloxydiphenyl sulfone, and 4-hydroxy-4'-dodecyloxydiphenyl sulfone. 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenyl sulfone, 2,4-bis(phenylsulfonyl)phenol, p-phenylphenol, p-hydroxyacetophenone, 1,1-bis(p-hydroxyphenyl)propane, 1,1-bis(p-hydroxyphenyl)pentane, 1,1-bis(p-hydroxyphenyl)hexane, 1,1-bis(p-hydroxyphenyl)hexane 2,2-bis(p-hydroxyphenyl)cyclohexane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)hexane, 1,1-bis(p-hydroxyphenyl)-2-ethylhexane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, 1,1-bis(p-hydroxyphenyl)-1-phenylethane, 1,3-bis[2-(p-hydroxyphenyl)-2-propyl]benzene, 1,3-bis[2-(3,4-dihydroxyphenyl)-2-propyl]benzene, 1,4-bis[ 2-(p-hydroxyphenyl)-2-propyl]benzene, 4,4′-dihydroxydiphenyl ether, 3,3′-dichloro-4,4′-dihydroxydiphenyl sulfide, methyl 2,2-bis(4-hydroxyphenyl)acetate, butyl 2,2-bis(4-hydroxyphenyl)acetate, 4-[4-(4-{4-[4-(isopropoxy)phenylsulfonyl]phenoxy}butoxy)phenylsulfonyl]phenol, 4,4′-[oxybis(ethyleneoxy-p-phenylenesulfonyl)]diphenol, 4,4'-Thiobis(2-tert-butyl-5-methylphenol), dimethyl 4-hydroxyphthalate, benzyl 4-hydroxybenzoate, methyl 4-hydroxybenzoate, benzyl gallate, stearyl gallate, salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-bis(α-methylbenzyl)salicylic acid, 4-[2'-(4-methoxyphenoxy)ethyloxy]salicylic acid, 3-(octyloxycarbonylamino)salicyl Acids or metal salts of these salicylic acid derivatives, N-(4-hydroxyphenyl)-p-toluenesulfonamide, N-(4-hydroxyphenyl)benzenesulfonamide, N-(4-hydroxyphenyl)-1-naphthalenesulfonamide, N-(4-hydroxyphenyl)-2-naphthalenesulfonamide, N-(4-hydroxynaphthyl)-p-toluenesulfonamide, N-(4-hydroxynaphthyl)benzenesulfonamide, N-(4-hydroxynaphthyl)-1-naphthalenesulfonamide Amide, N-(4-hydroxynaphthyl)-2-naphthalenesulfonamide, N-(3-hydroxyphenyl)-p-toluenesulfonamide, N-(3-hydroxyphenyl)benzenesulfonamide, N-(3-hydroxyphenyl)-1-naphthalenesulfonamide, N-(3-hydroxyphenyl)-2-naphthalenesulfonamide, 4,4′-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, N-[2-(3-phenylureido)phenyl] N-(2-{[(4-methylphenyl)carbamoyl]amino}phenyl)benzenesulfonamide, 4-methyl-N-{2-[(phenylcarbamoyl)amino]phenyl}benzenesulfonamide, 4-methyl-N-(2-{[(4-methylphenyl)carbamoyl]amino}phenyl)benzenesulfonamide, N-butylbutyl-4-[3-(p-toluenesulfonyl)ureido]benzoate, 3,3'-(4,4'-methylenediphenyl)bis(ureido p-trisulfone), bis{3-[3'-(p-toluenesulfonyl)ureido]benzoate}, 1,Examples include 5-(3-oxopentylene)bis{3'-[3'-(p-toluenesulfonyl)ureido]benzoate} and derivatives of N-phenylsulfonyl-N'-phenylurea. In some embodiments, the developer is one or more selected from the group consisting of:

[0024] The pigment and binder contained in the thermosensitive recording layer are the same as those exemplified for the undercoat layer, and therefore a description thereof will be omitted here.

[0025] The sensitizer is a compound that is conventionally known in the field of thermosensitive recording materials, such as a low-melting point heat-soluble component, and improves the color development of the thermosensitive recording material. Examples of the sensitizer include diphenyl sulfone, stearic acid monoamide, N-hydroxymethylstearic acid amide, N-stearylstearic acid amide, ethylenebisstearic acid amide, methylenebisstearic acid amide, methylolstearic acid amide, N-stearyl urea, benzyl-2-naphthyl ether, p-toluenesulfonamide, m-terphenyl, 4-benzylbiphenyl, 2,2'-bis(4-methoxyphenoxy)diethyl ether, α,α'-diphenoxy-o-xylene, Examples of the oxalic acid anhydride include bis(4-methoxyphenyl)ether, diphenyl adipate, dibenzyl oxalate, bis(4-methylbenzyl)oxalate, bis(4-chlorobenzyl)oxalate, dimethyl terephthalate, dibenzyl terephthalate, phenyl benzenesulfonate, bis(4-allyloxyphenyl)sulfone, 1,2-bis(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 4-acetylacetophenone, acetoacetic anilides, and fatty acid anilides. In some embodiments, the sensitizer is one or more selected from the group consisting of:

[0026] The additives that the thermosensitive recording layer may contain as needed are conventionally known ones, such as dispersants, surfactants, coloring dyes, fluorescent dyes, lubricants, antifoaming agents, ultraviolet absorbers, curing agents, crosslinking agents, etc. Furthermore, the additives may include, for example, a copolymer having a core-shell structure as a resin used in combination with the binder.

[0027] The heat-sensitive recording layer contains a composition containing mineral oil and hydrophobic silica, and a (meth)acrylamide copolymer having a core-shell structure.

[0028] The composition containing mineral oil and hydrophobic silica is, for example, a type of oil-based defoaming agent that uses mineral oil as a carrier component (solvent) to enhance the diffusibility of the defoaming component (hydrophobic silica), and is a composition in which hydrophobic silica is blended with mineral oil. Compositions containing mineral oil and hydrophobic silica are commercially available from, for example, Adeka Corporation, San Nopco Corporation, and Wacker Asahi Kasei Silicone Co., Ltd. Mineral oils are well known in the oil field, and examples thereof include mineral oil, petrolatum, paraffin, and liquid paraffin. The mineral oil is liquid mineral oil or solid mineral oil (wax). In some embodiments, the mineral oil is one or more selected from the group consisting of these. Hydrophobic silica is a known substance in the field of paints, and is silica whose surface has been made hydrophobic, and can be obtained by methods such as reacting silanol groups on the silica surface in silica sol with higher alcohols to form esters, hydrolyzing tetraethylsilicic acid to prepare silica hydrogel and then subjecting this to hydrothermal treatment at 100°C in water adjusted to a pH of 11 with sodium hydroxide, reacting silica hydrogel with a methoxysilane coupling agent, reacting with alkylchlorosilane or alkoxychlorosilane, producing hydrophobic organocolloidal silica from a cationic surfactant and anionic colloidal silica by utilizing a dehydration reaction, and treating silica with various silicone oils at high temperatures.

[0029] In some embodiments, the content of the composition containing mineral oil and hydrophobic silica in the thermosensitive recording layer is 0.1% by mass or more and 0.4% by mass or less based on the total solid content forming the thermosensitive recording layer, because this improves the blocking resistance and / or adhesion resistance of the thermosensitive recording material.

[0030] A (meth)acrylamide copolymer having a core-shell structure is obtained by copolymerizing (meth)acrylamide, or (meth)acrylamide and a monomer copolymerizable with (meth)acrylamide, in the presence of a seed emulsion that serves as core particles. A (meth)acrylamide copolymer having a core-shell structure is commercially available from, for example, Mitsui Chemicals, Inc. The seed emulsion that becomes the core particles is a conventionally known polymer, such as a (meth)acrylic acid ester, a styrene butadiene, a styrene (meth)acrylic acid ester, a (meth)acrylic acid ester butadiene, a (meth)acrylonitrile, a (meth)acrylonitrile butadiene, a vinyl chloride, or a vinyl acetate. Examples of monomers copolymerizable with (meth)acrylamide include unsaturated carboxylic acids such as ethylene, propylene, (meth)acrylic acid, itaconic acid, maleic anhydride, fumaric acid, and crotonic acid; aromatic vinyls such as styrene, α-methylstyrene, and divinylbenzene; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-aminoethyl (meth)acrylate, 2-(N-methylamino)ethyl (meth)acrylate, and glycidyl (meth)acrylate; N-substituted unsaturated carboxylic acid amides such as N-methylol (meth)acrylic acid amide; vinyl acetate; vinyl esters; and nitrile group-containing monomers such as (meth)acrylonitrile.

[0031] In some embodiments, the (meth)acrylamide copolymer having a core-shell structure is a (meth)acrylamide copolymer having a core-shell structure such as an acrylonitrile [core] / (meth)acrylamide [shell] copolymer or an acrylonitrile [core] / styrene (meth)acrylamide copolymer [shell], because this improves the chipping resistance, defect resistance, and / or blocking resistance of the thermal recording material.

[0032] In some embodiments, the content of the (meth)acrylamide copolymer having a core-shell structure in the thermosensitive recording layer is 5% by mass or more and 35% by mass or less based on the total solid content forming the thermosensitive recording layer, because this improves the chipping resistance and / or defect resistance of the thermosensitive recording material.

[0033] The thermosensitive recording layer contains a composition containing mineral oil and hydrophobic silica and a (meth)acrylamide copolymer having a core-shell structure, and the coating liquid for forming the thermosensitive recording layer contains a composition containing mineral oil and hydrophobic silica and a (meth)acrylamide copolymer having a core-shell structure, which effectively defoams the coating liquid for forming the thermosensitive recording layer and prevents defects in the thermosensitive recording layer.Furthermore, the combination of the composition containing mineral oil and hydrophobic silica and the (meth)acrylamide copolymer having a core-shell structure does not impair adhesion to the support, thereby preventing chipping of the thermosensitive recording layer. Furthermore, even in the case of a thermal recording material having a rewettable adhesive layer on the back side, the combination of a composition containing mineral oil and hydrophobic silica with a (meth)acrylamide copolymer having a core-shell structure can bring about deterioration of blocking resistance and adhesion resistance.

[0034] In the thermal recording material, the thermal recording layer can be provided on the support or on the undercoat layer by a conventionally known method. For example, the thermal recording layer can be obtained by coating and drying a dispersion for forming the thermal recording layer, which contains a dye precursor, a color developer, a pigment, and a binder, and optionally a sensitizer and various additives, on the support or on the undercoat layer using a conventionally known coating device and drying device. Examples of the coating device include an air knife coater, various blade coaters, various bar coaters, various curtain coaters, and various roll coaters, etc. Coating devices also include those for various printing methods such as lithography, relief printing, intaglio printing, flexography, gravure printing, and screen printing. Examples of the drying device include hot air dryers such as a linear tunnel dryer, an arch dryer, an air loop dryer, and a sine curve air float dryer, an infrared heating dryer, and a dryer that utilizes microwaves.

[0035] The rewettable adhesive layer contains, as its main component, a sizing agent that exhibits adhesive properties upon wetting. The sizing agents used in the rewettable adhesive layer are those conventionally known in the sizing field. Examples of sizing agents include chloroprene rubbers, polyvinyl alcohols, starches, vinyl acetate copolymers such as vinyl acetate acrylate copolymers and vinyl acetate methacrylate copolymers, dextrin, gum arabic, glue, and polyacrylamide. The sizing agent is one or more selected from the group consisting of these. In some embodiments, the adhesive agent is one or more selected from the group consisting of polyvinyl alcohols and starches, because the blocking resistance is improved in relation to the thermosensitive recording layer in contact with the rewettable adhesive layer.

[0036] The rewettable adhesive layer may contain various additives other than the adhesive, such as pigments, antioxidants, ultraviolet absorbers, dyes, antibacterial agents, antifungal agents, fragrances, and flame retardants, as long as the additives do not impair the properties of the adhesive.

[0037] In the thermosensitive recording material, the rewettable adhesive layer can be provided on the support by a conventionally known method. For example, the rewettable adhesive layer can be obtained by applying a coating solution for forming the rewettable adhesive layer, which contains a gluing agent and, if necessary, various auxiliary agents, to the support and drying it using a conventionally known coating device and drying device. The coating device and drying device are the same as those for the thermosensitive recording layer, and therefore, their description will be omitted here.

[0038] The undercoat layer, the thermosensitive recording layer, the protective layer, and / or the rewettable adhesive layer may be subjected to a calendering treatment. The calendering treatment may be achieved using a calendering device conventionally known in the papermaking field. Examples of calendering treatment include a machine calender, a soft-nip calender, a super calender, a multi-stage calender, and a multi-nip calender. [Example]

[0039] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, % by mass and parts by mass represent the amount of dry solids or the amount of substantial components. The coating amount represents the amount of dry solids.

[0040] Example 1 (Support) The support contains pulp, filler, sizing agent and paper strength agent, and has a basis weight of 60 g / m 2 The fine paper used as the support had a Beck smoothness of 60 seconds on both sides and an ash content of 10% by mass.

[0041] (Coating liquid for forming a thermosensitive recording layer) A dispersion of the dye precursor, a dispersion of the developer and sensitizer, and a dispersion of the pigment were prepared using water as a medium and then mixed together. Finally, the following materials were dispersed or dissolved in water to prepare a coating solution. The concentration of the coating solution was 26% by mass. Dye precursor 100 parts by mass Dispersant (sulfonic acid-modified polyvinyl alcohol) 20 parts by mass Developer 200 parts by mass Sensitizer 200 parts by mass Maleic anhydride copolymer 40 parts by mass Acetylene diol nonionic surfactant 2.5 parts by mass Composition containing mineral oil and hydrophobic silica 1.7 parts by mass Aluminum hydroxide 125 parts by mass Amorphous silica 125 parts by mass Dispersant (ammonium polyacrylate) 2.5 parts by mass (Meth)acrylamide copolymer having a core-shell structure: 115 parts by mass Silanol-modified polyvinyl alcohol 115 parts by mass Zinc stearate 80 parts by mass

[0042] The dye precursor used was 3-di-n-butylamino-6-methyl-7-anilinofluoran. The developer used was 4-hydroxy-4'-isopropoxydiphenyl sulfone. The sensitizer used was 1,2-bis(3-methylphenoxy)ethane. The maleic anhydride copolymer used was Arakawa Chemical Industries' Polymaron (registered trademark) 1318, a styrene-maleic anhydride copolymer. The composition containing mineral oil and hydrophobic silica used was San Nopco's Nopco (registered trademark) 8034. The core-shell structured (meth)acrylamide copolymer used was Mitsui Chemicals' Bariastar (registered trademark) BM1000.

[0043] (thermal recording layer) The coating liquid for forming the thermal recording layer was applied to the surface of the support in an amount of 3.5 g / m 2 The coating was then dried so that the coating was uniform and the temperature was adjusted to the desired level, followed by calendering using a supercalender to form a heat-sensitive recording layer.

[0044] (thermal recording material) On the backside of the support on which the thermal recording layer was provided, polyvinyl alcohol (Kuraray Poval (registered trademark) 5-88 of Kuraray Co., Ltd.) was coated in an amount of 17 g / m 2 The resulting layer was coated and dried to form a rewettable adhesive layer, thereby preparing a heat-sensitive recording material.

[0045] <Example 2> Example 2 was obtained by repeating the procedure of Example 1, except that the composition containing mineral oil and hydrophobic silica (San Nopco's Nopco 8034) in Example 1 was changed to a composition containing mineral oil and hydrophobic silica (San Nopco's SN Deformer 154).

[0046] Example 3 Example 3 was obtained by repeating the procedure of Example 1, except that the composition containing mineral oil and hydrophobic silica (San Nopco's Nopco (registered trademark) 8034) in Example 1 was changed to a composition containing mineral oil and hydrophobic silica (Adekanate (registered trademark) B-940) in Example 1.

[0047] Example 4 Example 4 was obtained by repeating the procedure of Example 1, except that the (meth)acrylamide copolymer having a core-shell structure (Mitsui Chemicals, Inc., Barrierstar BM1000) in Example 1 was changed to a (meth)acrylamide copolymer having a core-shell structure (Mitsui Chemicals, Inc., Barrierstar OM1050).

[0048] <Example 5> Example 5 was prepared in the same manner as Example 1, except that the adhesive agent in the rewettable adhesive layer was changed from partially saponified polyvinyl alcohol to gum arabic.

[0049] Example 6 Example 5 was prepared in the same manner as in Example 1, except that the adhesive agent in the rewettable adhesive layer was changed from partially saponified polyvinyl alcohol to starch adhesive.

[0050] <Comparative Example 1> Comparative Example 1 was prepared in the same manner as in Example 1, except that the composition containing mineral oil and hydrophobic silica in Example 1 (San Nopco 8034) was replaced with a metal soap-based composition (San Nopco DF-122).

[0051] <Comparative Example 2> Comparative Example 2 was prepared in the same manner as in Example 1, except that the (meth)acrylamide copolymer having a core-shell structure (Mitsui Chemicals, Inc., Barrierstar BM1000) in Example 1 was changed to an acrylonitrile / acrylamide / acrylic acid terpolymer having no core-shell structure.

[0052] <Comparative Example 3> Comparative Example 3 was prepared in the same manner as in Example 1, except that the composition containing mineral oil and hydrophobic silica (Nopco 8034 manufactured by San Nopco Co., Ltd.) in Example 1 was not blended.

[0053] <Comparative Example 4> Comparative Example 4 was prepared in the same manner as in Example 1, except that the (meth)acrylamide copolymer having a core-shell structure (Mitsui Chemicals, Barrierstar BM1000) was not blended.

[0054] The heat-sensitive recording materials of the Examples and Comparative Examples were evaluated for the following items, and the results are shown in Table 1.

[0055] [Table 1]

[0056] <Flaw resistance> The obtained thermal recording material was cut into A4 size pieces, and 100 sheets of the A4 size thermal recording material were observed for the presence or absence of defects in the thermal recording layer. The defect resistance was evaluated based on the observation results according to the following criteria. In the present invention, a thermal recording material is considered to have defect resistance if it is rated A or B. A: No defects were found on 100 sheets, good. B: Only one in 100 sheets has defects, which is good. C: Defects are found in 2 to 3 sheets out of 100, which is the lower limit for practical production. D: Defects are found on 4 or more sheets per 100 sheets.

[0057] <Chipping resistance> Ten A4-sized thermosensitive recording materials were stacked with the thermosensitive recording layer and rewettable adhesive layer in contact, and an A4-sized metal plate (1 kg) was placed on top of them. The materials were then left to stand for 3 hours in an environment of 23°C and 50% RH. After standing, the stack was unstacked and the thermosensitive recording layer was visually inspected for chipping. The chipping resistance was evaluated based on the observation results using the following criteria. In the present invention, a thermosensitive recording material is considered to have chipping resistance if it is rated A or B. A: No defects found, good condition. B: No chipping is observed, and although there is very slight fuzziness on parts of the surface, it is generally in good condition. C: No chipping is observed, and although there is some fuzz on the surface, it is still at the lower limit of usable condition. D: Defects are observed.

[0058] <Blocking resistance> Ten A4-sized thermal recording materials were stacked with the thermal recording layer and rewettable adhesive layer in contact, and an A4-sized metal plate (1 kg) was placed on top of them. The materials were then left standing at 40°C and 90% RH for 24 hours. The stacked materials were then left standing at 23°C and 50% RH for 3 hours to allow the temperature and moisture of the thermal recording materials to relax. The stack was then unstacked, and the thermal recording layer facing the rewettable adhesive layer was observed. Blocking resistance was evaluated based on the observation results using the following criteria. In the present invention, a thermal recording material is considered to have blocking resistance if it receives a rating of A or B. A: No damage to the heat-sensitive recording layer due to blocking is observed. B: Although it is inferior to A above, damage to the heat-sensitive recording layer due to blocking is not generally observed. C: Slight damage to the heat-sensitive recording layer due to blocking is observed. D: Damage to the heat-sensitive recording layer due to blocking was observed.

[0059] <Resistance to adhesion deterioration> Ten A4-sized thermal recording materials were stacked with the thermal recording layer and rewettable adhesive layer in contact, and an A4-sized metal plate (1 kg) was placed on top of them. The stacked sheets were then left to stand at 40°C and 90% RH for 24 hours. The stacked sheets were then left to stand at 23°C and 50% RH for 3 hours to allow the temperature and moisture content of the thermal recording materials to decrease. The stack was then unstacked, and the A4-sized thermal recording materials were cut into smaller pieces measuring 2.5 cm x 10 cm. The rewettable adhesive layer of the paper strip was soaked in water. The amount of water added to the rewettable adhesive layer was 20 g / m 2 After the rewettable adhesive layer was sufficiently saturated with water, the thermosensitive recording material was placed on the surface of the polystyrene foam so that the rewettable adhesive layer was in contact with the surface. Next, the thermosensitive recording material was pressed against the surface of the polystyrene foam to adhere it to the surface. To press the thermosensitive recording material, a 2 kg hand roller was used, moving back and forth over the entire length of the thermosensitive recording material at a speed of 10 m / min. The thermosensitive recording material was left in its attached state on the polystyrene foam surface for 24 hours under an environment of 23°C and 50% RH. The thermosensitive recording material was then peeled from the polystyrene foam surface and the peel strength was measured according to a method in accordance with ISO 29862:2007, "Self adhesive tapes - Determination of peel adhesion properties." The adhesion resistance was evaluated based on the measurement results using the following criteria. In the present invention, a thermosensitive recording material is considered to have adhesion resistance if it receives a rating of A or B. A: 0.32N / 25mm or more. B: 0.27N / 25mm or more and less than 0.32N / 25mm. C: 0.22N / 25mm or more and less than 0.27N / 25mm. D: Less than 0.22N / 25mm.

[0060] From Table 1, it can be seen that Examples 1 to 6, which satisfy the constitution of the present invention, are heat-sensitive recording materials having chipping resistance, defect resistance, blocking resistance, and adhesion deterioration resistance, while Comparative Examples 1 to 4, which do not satisfy the constitution of the present invention, are heat-sensitive recording materials that cannot obtain any of chipping resistance, defect resistance, blocking resistance, and adhesion deterioration resistance.

Claims

[Claim 1] A thermal recording material having at least a thermal recording layer, a support, and a rewettable adhesive layer in this order, wherein the thermal recording layer contains a composition containing a dye precursor which is a color-forming dye, a color developer, a binder, mineral oil, and hydrophobic silica, and a (meth)acrylamide copolymer having a core-shell structure.

Images