Heat-sensitive recording medium

Abstract

Provided is a heat-sensitive recording medium which uses kraft lignin as a color developing agent, is environmentally friendly, and has excellent corrosion to a heat-sensitive head during printing. The heat-sensitive recording material is characterized in that a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer is provided on a support body, and the heat-sensitive recording layer contains kraft lignin as the electron-accepting developer, and the kraft lignin contains almost no or at most only 400 ppm of hydrogen sulfide.

Description

Technical Field

[0001] The present invention relates to a thermosensitive recording material that utilizes a color development reaction between a colorless or light-colored electron-donating leucodye (hereinafter also referred to as a "leuco dye") and an electron-accepting developer (hereinafter also referred to as a "developer"), and uses kraft lignin as the developer. Background Art

[0002] Generally speaking, a thermosensitive recording medium is usually formed by applying a coating liquid containing a colorless or light-colored leuco dye and a developer onto a support such as paper, synthetic paper, film, or plastic, and developing the color through an instantaneous chemical reaction caused by heating with a thermal head, thermal stamp, thermal pen, laser, etc., thereby obtaining a recorded image. Thermosensitive recording mediums are widely used as recording media such as fax machines, computer terminal printers, automatic ticket machines, measurement recorders, and receipts for supermarkets and convenience stores.

[0003] As the color developer, bisphenols, alkylphenols, novolac-type phenolic resins, derivatives of aromatic carboxylic acids, metal salts thereof, hydroxybenzoic acid esters, sulfonylurea compounds, activated clay, and the like are generally used.

[0004] In order to provide a thermosensitive recording medium using an environmentally friendly developer, it is known to use isolated lignin as a developer (Patent Document 1, etc.).

[0005] In addition, several countermeasures are known for the corrosion of a thermal head used for printing on a thermosensitive recording medium (Patent Documents 2 to 4, etc.).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-104274

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 62-87362

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 10-264425

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 2000-79715 Summary of the invention

[0012] Problems to be solved by the invention

[0013] In the printing device of thermal recording paper, the thermal head has a glaze layer, a heating element, an electrode, and a protective film on a base plate. It is known that the electrode is usually made of aluminum, which is corroded by ionic substances represented by sodium ions, chloride ions, sulfide ions, etc. If the electrode corrodes, normal printing cannot be performed.

[0014] On the other hand, it is known that if kraft lignin is used as a color developer in order to provide an environmentally friendly thermosensitive recording medium, the thermal head used for printing the thermosensitive recording medium may corrode depending on the usage conditions (see Comparative Example 1, etc., which will be described later). However, conventionally, only countermeasures from the printing device side are known regarding corrosion of the thermal head (Patent Documents 2 to 4, etc.).

[0015] An object of the present invention is to provide a thermosensitive recording medium which uses kraft lignin as a developer, is environmentally friendly, and has excellent thermal head corrosion resistance during printing.

[0016] Means for solving problems

[0017] The present inventors have conducted intensive studies to solve the above problems and have found that the above problems can be solved by using kraft lignin produced by adding an oxidation step in the production process unlike conventional methods and having a reduced hydrogen sulfide content, thereby completing the present invention.

[0018] That is, the present invention is a thermosensitive recording medium, which has a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and the thermosensitive recording layer contains sulfate lignin as an electron-accepting developer, and the sulfate lignin contains almost no or only 400 ppm of hydrogen sulfide at most.

[0019] The present invention is also a method for reducing corrosion of a thermal head when printing on a thermal recording material having a thermal recording layer containing kraft lignin using a thermal head, the method comprising the step of printing on the thermal recording material.

[0020] Effects of the Invention

[0021] According to the present invention, it is possible to provide a thermosensitive recording medium which is excellent in thermal head corrosion resistance during printing even when kraft lignin is used as a developer. DETAILED DESCRIPTION

[0022] Natural lignin present in the cell wall of plant cells is complexed with polysaccharides such as cellulose and is difficult to separate. Therefore, separation is usually carried out by chemical modification. Separated lignin is also called industrial lignin, and separated lignin includes lignin sulfonate, sulfate lignin, soda lignin, soda-anthraquinone lignin, organic lignin, blasted lignin, sulfate lignin, etc.

[0023] In the thermosensitive recording material of the present invention, kraft lignin is used as a color developer.

[0024] Sulfate lignin is also called sulfur lignin or sulfate lignin. Sulfate lignin is a compound with hydroxyphenylpropane as a basic unit and functional groups such as phenolic hydroxyl, alcoholic hydroxyl, and mercapto. Sulfate lignin is usually obtained by allowing a mixed aqueous solution of sodium hydroxide and sodium sulfide to act on wood and is insoluble in water. As the form of use of sulfate lignin, an alkaline solution of sulfate lignin, a powdered sulfate lignin obtained by spray-drying and powdering the alkaline solution of sulfate lignin, and an acid-precipitated sulfate lignin obtained by precipitating the alkaline solution of sulfate lignin with an acid can be used.

[0025] The kraft lignin in the present invention is produced, for example, as described in Japanese Patent Publication No. 2013-527339, and is obtained by a process of black liquor oxidation. When kraft lignin is refined, it is usually refined by the following process: carbonation-neutralized lignin is purified by carbonation-neutralized black liquor, filtered, and then dispersed, extracted with sulfuric acid, filtered and washed. The kraft lignin used in the present invention has a very low content of hydrogen sulfide by adding an oxidation process using oxygen before the carbonation-neutralized process.

[0026] Such kraft lignin contains almost no hydrogen sulfide or only 400 ppm at most, and even if it contains hydrogen sulfide, it is preferably 200 ppm or less, more preferably 100 ppm or less. The lower limit is usually 50 ppm or less, for example, about 10 ppm.

[0027] The content of hydrogen sulfide in kraft lignin can be measured, for example, by using a hydrogen sulfide concentration measuring device to measure the amount of hydrogen sulfide generated when kraft lignin is heated (200° C.) The melting point of kraft lignin is about 170° C., and it can be measured by heating at 200° C.

[0028] The content of lignin in such kraft lignin is preferably 90% by weight or more, more preferably 92 to 100% by weight.

[0029] The density of such kraft lignin at a concentration of 60% is preferably 0.4 to 0.5 g / cm 3 .

[0030] By setting the lignin content within the above range, the content of impurities such as sulfides is reduced, and the influence of corrosion on the thermal head is reduced. In addition, compared with sulfate lignin having a density below the above range, the work efficiency during the dispersion of the chemical is improved, and the amount of sulfate lignin required to form the same dispersion concentration can be reduced.

[0031] As such kraft lignin, there is mentioned Amallin A, a product of West Fraser.

[0032] In the present invention, the above-mentioned kraft lignin is used as a color developer, but a color developer other than kraft lignin may be used in combination, thereby achieving a more excellent effect in terms of color development performance (printing density) and the like.

[0033] Examples of such a color developer include activated clay, attapulgite, colloidal silica, and inorganic acidic substances such as aluminum silicate; 4,4'-isopropylidene diphenol, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxybenzoic acid benzyl ester, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, and 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone. sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane, a phenol condensation composition described in Japanese Patent Application Laid-Open No. 2003-154760, an aminobenzenesulfonamide derivative described in Japanese Patent Application Laid-Open No. 8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-bis(4-hydroxyphenylthio)-3-oxapentane, bis(p-hydroxyphenyl)acetate butyl, bis(p-hydroxyphenyl)acetate methyl, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,4-bis[α-methyl-α-(4'-hydroxyphenyl) phenyl) sulfide, 2,2'-thiobis(3-tert-octylphenol), 2,2'-thiobis(4-tert-octylphenol), phenolic compounds such as the diphenylsulfone crosslinking compound described in WO97 / 16420, compounds described in WO02 / 081229 or Japanese Patent Application Laid-Open No. 2002-301873, N-(2-(3-phenylureido)phenyl)benzenesulfonamide, 3-(3-toluenesulfonylurea)phenyl-p-toluenesulfonate, ureidocarbamate compounds, 3-{[(phenylamino)carbonyl]amino}benzenesulfonamide , and thiourea compounds such as N,N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis[4-(n-octyloxycarbonylamino)salicylic acid zinc] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-toluenesulfonyl)propoxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid aromatic carboxylic acids, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, and antipyrine complexes of zinc thiocyanate, and composite zinc salts of p-formylbenzoic acid (terephthalaldehydic acid) and other aromatic carboxylic acids. These color developers may be used alone or in combination of two or more.Furthermore, a metal chelate type coloring component such as a higher fatty acid metal complex salt or a polyvalent hydroxy aromatic compound described in Japanese Patent Application Laid-Open No. 10-258577 may be contained.

[0034] Among such color developers, as color developers used in combination with kraft lignin, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, or color developers having a urea structure (-NHCONH-) are preferred from the viewpoint of achieving a good balance between color development performance (printing density) and storage stability. Examples of color developers having a urea structure include the following.

[0035] i) N-(2-(3-phenylureido)phenyl)benzenesulfonamide (NKK1304 manufactured by Nippon Soda Co., Ltd., following formula)

[0036]

Chemical formula 1

[0037]

[0038] ii) Urea compound represented by the following general formula (Chemical Formula 2)

[0039]

Chemical formula 2

[0040]

[0041] In the general formula (chemical formula 2), R is an alkyl group or an alkoxy group, preferably an alkyl group, and m represents an integer of 0 to 3, preferably 0 to 2, and more preferably 0 to 1. The number of carbon atoms in the alkyl group is, for example, 1 to 12, preferably 1 to 8, and more preferably 1 to 4.

[0042] The positions of R in the benzene ring of the general formula (Chemical Formula 2) may be the same or different, and are preferably at the 3-position, 4-position or 5-position, and preferably at the 4-position.

[0043] Examples of the urea compound include N,N′-bis-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0044] iii) 3-(3-Toluenesulfonylurea)phenyl-p-toluenesulfonate (made by BASF, DP201, following formula)

[0045]

Chemical formula 3

[0046]

[0047] iv) Urethane urea compound (UU manufactured by CHEMIPRO KASEI Co., Ltd., following formula)

[0048]

Chemical formula 4

[0049]

[0050] v) 3-{[(phenylamino)carbonyl]amino}benzenesulfonamide (SU727 manufactured by Mitsubishi Chemical Co., Ltd., the following formula)

[0051]

Chemical formula 5

[0052]

[0053] In the present invention, the content (solid content) of kraft lignin in the thermosensitive recording layer is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, and even more preferably 2 to 12% by weight.

[0054] In the present invention, when kraft lignin and a color developer other than kraft lignin are used in combination as color developers, the weight ratio of kraft lignin to the color developer other than kraft lignin (kraft lignin / color developer other than kraft lignin) is preferably 90 / 10 to 10 / 90, more preferably 80 / 20 to 20 / 80, and further preferably 60 / 40 to 25 / 75.

[0055] The thermosensitive recording material of the present invention can utilize the conventional configuration except that kraft lignin is used as a color developer.

[0056] That is, the thermosensitive recording medium of the present invention must have a thermosensitive recording layer on a support, may optionally have a protective layer on the thermosensitive recording layer, may have an undercoat layer between the support and the thermosensitive recording layer, and may have a backcoat layer on the side of the support opposite to the thermosensitive recording layer. A coating layer of a suitable configuration according to the purpose of use may also be provided between these other layers.

[0057] The support can be appropriately selected from conventionally known supports such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, nonwoven fabric, etc. according to the quality of the desired thermosensitive recording medium, and is not particularly limited. In addition, a composite sheet formed by combining them can also be used as the support.

[0058] The heat-sensitive recording layer of the present invention necessarily contains a leuco dye in addition to the above-mentioned developer, and may further arbitrarily contain a sensitizer, a binder, a pigment, a cross-linking agent, an image stabilizer, and other components.

[0059] As the leuco dye used in the present invention, all known products in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, although not particularly limited, preferably triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds, etc. The specific examples of representative colorless or light-colored leuco dyes (dye precursors) are shown below. In addition, these leuco dyes can be used alone or in combination of two or more.

[0060] <Triphenylmethane-based leuco dyes>

[0061] 3,3-Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide [also known as crystal violet lactone]; 3,3-Bis(p-dimethylaminophenyl)phthalide [also known as malachite green lactone]

[0062] <Fluoran-based leuco dyes>

[0063] 3-Diethylamino-6-methylfluoran; 3-Diethylamino-6-methyl-7-anilinofluoran; 3-Diethylamino-6-methyl-7-(o-, p-dimethylanilino)fluoran; 3-Diethylamino-6-methyl-7-chlorofluoran; 3-Diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran; 3-Diethylamino-6-methyl-7-(o-chloroanilino)fluoran; 3-Diethylamino-6-methyl-7-(p-chloroanilino)fluoran; 3-Diethylamino-6-methyl-7-(o-fluoroanilino)fluoran; 3-Diethylamino-6-methyl-7-(m-methylanilino)fluoran; 3-Diethylamino-6-methyl-7-n-octylanilinofluoran; 3-Diethylamino-6-methyl-7-n-octylaminofluoran 3-Diethylamino-6-methyl-7-benzylaminofluoran; 3-Diethylamino-6-methyl-7-dibenzylaminofluoran; 3-Diethylamino-6-chloro-7-methylfluoran; 3-Diethylamino-6-chloro-7-anilinofluoran; 3-Diethylamino-6-chloro-7-p-methylanilinofluoran; 3-Diethylamino-6-ethoxyethyl-7-anilinofluoran; 3-Diethylamino-7-methylfluoran; 3-Diethylamino-7-chlorofluoran; 3-Diethylamino-7-(m-trifluoromethylanilino)fluoran; 3-Diethylamino-7-(o-chloroanilino)fluoran; 3-Diethylamino-7-(p-chloroanilino)fluoran; 3-Diethylamino-7-(o-fluoroanilino)fluoran; 3-Diethylamino-benzo[ a〕fluoran; 3-diethylamino-benzo〔c〕fluoran; 3-dibutylamino-6-methyl-fluoran; 3-dibutylamino-6-methyl-7-anilinofluoran; 3-dibutylamino-6-methyl-7-(o-, p-dimethylanilino)fluoran; 3-dibutylamino-6-methyl-7-(o-chloroanilino)fluoran; 3-dibutylamino-6-methyl-7-(p-chloroanilino)fluoran; 3-dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran; 3-dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran; 3-dibutylamino-6-methyl-chlorofluoran; 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran; 3-dibutylamino-6-chloro-7-phenyl Amine fluoran; 3-dibutylamino-6-methyl-7-p-methylanilinofluoran; 3-dibutylamino-7-(o-chloroanilino)fluoran; 3-dibutylamino-7-(o-fluoroanilino)fluoran; 3-di-n-pentylamino-6-methyl-7-anilinofluoran; 3-di-n-pentylamino-6-methyl-7-(p-chloroanilino)fluoran; 3-di-n-pentylamino-7-(m-trifluoromethylanilino)fluoran; 3-di-n-pentylamino-6-chloro-7-anilinofluoran; 3-di-n-pentylamino-7-(p-chloroanilino)fluoran; 3-pyrrolidinyl-6-methyl-7-anilinofluoran; 3-piperidinyl-6-methyl-7-anilinofluoran; 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran;3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-hexylamino)-6-methyl-7-(p-chloroanilino)fluoran; 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isopentylamino)-6-chloro-7-anilinofluoran; 3-(N-ethyl-N-tetramethylamino)-6-methyl-7-anilinofluoran 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran; 3-cyclohexylamino-6-chlorofluoran; 2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran; 2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran; 2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran; 2-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 2-nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 2 -phenyl-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran; 2,4-dimethyl-6-〔(4-dimethylamino)anilino〕-fluoran;

[0064] <Fluorene-based leuco dyes>

[0065] 3,6,6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-Tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0066] <Divinyl leuco dye>

[0067] 3,3-Bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)vinyl]-4,5,6,7-tetrabromophthalide; 3,3-Bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)vinyl]-4,5,6,7-tetrachlorophthalide; 3,3-Bis-[1,1-bis(4-pyrrolidinylphenyl)vinyl-2-yl]-4,5,6,7-tetrabromophthalide; 3,3-Bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinylphenyl)vinyl-2-yl]-4,5,6,7-tetrachlorophthalide

[0068] <Other>

[0069] 3-(4-Diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-Diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide; 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam; 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam Fluoran-γ-(4'-nitro)anilinolactam; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-vinyl]-2,2-dicyanoethane; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-vinyl]-2-β-naphthoylethane; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-vinyl]-2,2-diacetylethane; bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-vinyl]-methylmalonic acid dimethyl ester

[0070] Examples of the sensitizer that can be used in the present invention include diphenyl sulfone, fatty acid amides such as stearic acid amide and palmitic acid amide, benzyloxynaphthalene, 1,2-di-(3-methylphenoxy)ethane, di(p-methylbenzyl) oxalate, etc. These sensitizers can be used alone or in combination of two or more.

[0071] Among these sensitizers, diphenyl sulfone is preferably used in order to improve the color development performance (print density) when kraft lignin is used as a color developer.

[0072] Examples of the binder that can be used in the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, terminal alkyl-modified polyvinyl alcohol and the like; cellulose ethers and derivatives thereof such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose and the like; starches such as starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (e.g., hydroxyethylated starch, etc.), cationized starch and the like; polyacrylamide, cationic poly Acrylamide, anionic polyacrylamide, amphoteric polyacrylamide and other polyacrylamides, polyester polyurethane resins, polyether polyurethane resins, polyurethane ionomer resins and other urethane resins, acrylic resins containing (meth)acrylic acid and monomer components (except olefins) copolymerizable with (meth)acrylic acid, styrene-butadiene copolymers, styrene-butadiene copolymers, styrene-butadiene copolymers and other styrene-butadiene resins, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate copolymers and other polyolefin resins, polyvinyl chloride, polyvinylidene chloride, polyacrylate, gum arabic, polyvinyl butyral, polystyrene and its copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, coumarone resins, etc. These may be used alone or in combination of two or more.

[0073] Examples of the pigment that can be used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide, etc. These can be used alone or in combination of two or more.

[0074] Examples of the crosslinking agent that can be used in the present invention include glyoxal, methylolmelamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, and ammonium chloride.

[0075] In addition, in the present invention, as an image stabilizer that shows an oil resistance effect on recorded images, 4,4'-butylene (6-tert-butyl-3-methylphenol), 2,2'-di-tert-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4-benzyloxy-4'-(2,3-epoxy-2-methylpropyloxy)diphenyl sulfone, etc. may be used within a range that does not hinder the expected effect on the above-mentioned subject.

[0076] Furthermore, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, defoaming agents, antioxidants, fluorescent dyes, and the like may be used.

[0077] In the present invention, the color developer is used in an amount of preferably 0.05 to 4.0 parts by weight, more preferably 0.1 to 3.0 parts by weight, based on 1 part by weight of the leuco dye.

[0078] In addition, the types and amounts of sensitizers, binders, pigments, crosslinking agents, image stabilizers, and other optional components are determined according to the required performance and recording adaptability, and are not particularly limited. Generally, 0.1 to 10 parts by weight of sensitizer, 0.5 to 50 parts by weight of pigment, 0.01 to 10 parts by weight of image stabilizer, and about 0.01 to 10 parts by weight of other components are used. It is appropriate that the binder is about 5 to 50 parts by weight in terms of solid content relative to 100 parts by weight of the thermal recording layer (solid content). It is appropriate that the content of the lubricant is about 5 to 10 parts by weight in terms of solid content relative to 100 parts by weight of the thermal recording layer (solid content).

[0079] The leuco dye, developer and materials added as needed are micronized to a particle size of several microns or less by a pulverizer such as a ball mill, attritors, sand mill or an appropriate emulsifying device, and a binder and various additives according to the purpose are added to prepare a coating liquid. As a solvent used in the coating liquid, water or alcohol can be used, and the solid content is about 20 to 40% by weight.

[0080] The protective layer may contain the binder, pigment, crosslinking agent, and other components that can be used in the above-mentioned thermosensitive recording layer within a range that does not inhibit the desired effect, but preferably contains a binder and a pigment, and may contain other components such as a surfactant and a viscosity modifier as needed.

[0081] As the binder used in the protective layer, polyvinyl alcohols and acrylic resins are preferred among the binders that can be used in the above-mentioned thermosensitive recording layer.

[0082] As the polyvinyl alcohols, completely saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol are preferred.

[0083] Examples of the component (excluding olefin) copolymerizable with the (meth)acrylic acid of the acrylic resin include alkyl acrylate resins such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate, and modified alkyl acrylate resins such as alkyl acrylate resins modified with epoxy resins, silicone resins, styrene or derivatives thereof, and (meth)acrylate. Nitrile, acrylate, hydroxyalkyl acrylate, etc., preferably alkyl acrylate resins such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, and modified alkyl acrylate resins such as alkyl acrylate resins modified by epoxy resin, silicone resin, styrene or its derivatives, (meth)acrylonitrile, acrylate, hydroxyalkyl acrylate. (Meth)acrylonitrile and / or methyl methacrylate are particularly preferred. The acrylic resin is preferably a non-core-shell acrylic resin.

[0084] In order to improve water resistance and the like, the protective layer may contain a carboxyl group-containing resin as a binder, and may also contain a polyamine / polyamide-based resin.

[0085] Examples of the carboxyl group-containing resin include the above-mentioned carboxyl-modified polyvinyl alcohol, acrylic resin, oxidized starch, carboxymethyl cellulose, and the like.

[0086] Examples of the polyamine / polyamide resin include polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, modified polyamine resins, modified polyamide resins, polyalkylene polyamine urea formaldehyde resins, and polyalkylene polyamine polyamide polyurea resins.

[0087] In the present invention, when the protective layer contains a pigment, the pigment is preferably silica, kaolin, calcined kaolin, or aluminum hydroxide, and more preferably kaolin or aluminum hydroxide, from the viewpoint of improving the water resistance and printing transfer properties of the thermosensitive recording medium.

[0088] When the protective layer of the present invention does not contain a pigment, the amount of the binder in the protective layer is usually 70 to 100% by weight, preferably 85 to 100% by weight, based on the solid content.

[0089] On the other hand, when the protective layer contains a pigment, the total amount of the binder and the pigment in the protective layer is usually 80 to 100 wt %, preferably 90 to 100 wt % based on solid content, and the binder is preferably about 30 to 300 parts by weight per 100 parts by weight of the pigment.

[0090] The proportion of ingredients other than binder, crosslinker and pigment in the protective layer does not exceed 15% by weight, preferably does not exceed 10% by weight.

[0091] In each coating layer arbitrarily provided except for the thermosensitive recording layer and the protective layer, the above-mentioned binder, pigment, crosslinking agent, and other components may be used within a range not inhibiting the desired effect.

[0092] The coating method of the thermosensitive recording layer, the protective layer, and other coating layers is not particularly limited, and conventionally known methods such as curtain coating, air knife coating, bar blade coating, rod blade coating, bent blade coating, bevel blade coating, roll coating, and spray coating can be used.

[0093] The coating amount of the thermal recording layer, protective layer, and other coating layers is determined according to the required performance and recording adaptability and is not particularly limited. For example, the usual coating amount of the thermal recording layer is 2 to 12 g / m2 in terms of solid content. 2 The normal coating amount of the protective layer is 1 to 5 g / m 2 about.

[0094] Furthermore, after coating each layer, a smoothing treatment such as super calendering may be performed, and various well-known techniques in the field of thermosensitive recording materials may be appropriately added as necessary.

[0095] [Example]

[0096] The present invention is exemplified below by examples, but is not intended to be limited thereto. It should be noted that, in each example and comparative example, "part" means "part by weight" and "%" means "% by weight" unless otherwise specified.

[0097] Each dispersion liquid and coating liquid was prepared as follows.

[0098] The mixture composed of the following formulation was stirred and dispersed to prepare a coating liquid for an undercoat layer.

[0099] <Coating liquid for primer>

[0100] Calcined kaolin (manufactured by BASF, trade name: ANSILEX 90) 100.0 parts

[0101] Styrene-butadiene copolymer latex (manufactured by ZEON Corporation, trade name: ST5526, solid content 48%) 10.0 parts

[0102] Water 50.0 parts

[0103] The kraft lignin dispersions (liquids A and B) were prepared by wet grinding with a sand mill until the average particle size was 3.0 μm. It should be noted that the kraft lignin used in the A liquid of the kraft lignin dispersion was subjected to a step of oxidizing black liquor in the production process, while the B liquid was not subjected to an oxidation step.

[0104] Kraft lignin dispersion (liquid A)

[0105] Kraft lignin (Amallin A, manufactured by West Fraser), hydrogen sulfide content: 68 ppm, lignin content: 93%, density: 0.45 g / cm 3 , hereinafter referred to as "kraft lignin 1". ) 6.0 parts

[0106] 5.0 parts of a completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., trade name: PVA117, solid content 10%)

[0107] 1.5 parts water

[0108] Kraft lignin dispersion (liquid B)

[0109] Kraft lignin (Meadwestbaco, Indulin AT), hydrogen sulfide content: 1100 ppm, lignin content: 87%, density: 0.35 g / cm 3 , hereinafter referred to as "kraft lignin 2". ) 6.0 parts

[0110] 5.0 parts of a completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., trade name: PVA117, solid content 10%)

[0111] 1.5 parts water

[0112] Next, developer dispersions (A1 to A4 solutions), leuco dye dispersions (B solution), and sensitizer dispersions (C solution) prepared below were separately wet-milled using a sand mill until the average particle size became 0.5 μm.

[0113] Color developer dispersion (A1 solution)

[0114] 4-Hydroxy-4'-isopropoxydiphenyl sulfone (manufactured by Mitsubishi Chemical Co., Ltd., trade name: NYDS) 6.0 parts

[0115] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0116] 1.5 parts water

[0117] Color developer dispersion (A2 solution)

[0118] 6.0 parts of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (hereinafter referred to as "urea compound 1")

[0119] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0120] 1.5 parts water

[0121] Color developer dispersion (A3 solution)

[0122] 4,4'-Dihydroxydiphenyl sulfone (manufactured by Konishi Chemical Industry Co., Ltd., trade name: 44BPS) 6.0 parts

[0123] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0124] 1.5 parts water

[0125] Color developer dispersion (A4 liquid)

[0126] 6.0 parts of N-(2-(3-phenylureido)phenyl)benzenesulfonamide (manufactured by Nippon Soda Co., Ltd., trade name: NKK1304)

[0127] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0128] 1.5 parts water

[0129] Leuco dye dispersion (liquid B)

[0130] 3-Dibutylamino-6-methyl-7-anilinofluoran (manufactured by Yamamoto Chemicals Co., Ltd., trade name: ODB-2) 6.0 parts

[0131] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0132] 1.5 parts water

[0133] Sensitizer dispersion (liquid C)

[0134] Diphenyl sulfone (manufactured by Volant, trade name: DPS) 6.0 parts

[0135] 5.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0136] 1.5 parts water

[0137] Next, the respective dispersions were mixed at the following ratios and stirred sufficiently to prepare thermosensitive recording layer coating solutions 1 and 2.

[0138] <Thermosensitive recording layer coating liquid 1>

[0139] Kraft lignin dispersion (liquid A) 1.5 parts

[0140] 1.05 parts of leuco dye dispersion (liquid B)

[0141] Sensitizer dispersion (liquid C) 1.2 parts

[0142] Silica dispersion (manufactured by Mizusawa Chemical Industry Co., Ltd., trade name: MIZUKASIL P-537, solid content 25%) 5.0 parts

[0143] Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts

[0144] 20.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0145] <Thermosensitive recording layer coating liquid 2>

[0146] Kraft lignin dispersion (liquid A) 0.75 parts

[0147] Color developer dispersion (A1 solution) 0.75 parts

[0148] 1.05 parts of leuco dye dispersion (liquid B)

[0149] Sensitizer dispersion (liquid C) 1.2 parts

[0150] Silica dispersion (MIZUKASIL P-537) 5.0 parts

[0151] Zinc stearate (Hydrin L536) 5.0 parts

[0152] 20.0 parts of fully saponified polyvinyl alcohol aqueous solution (PVA117)

[0153] [Example 1]

[0154] On the support (weight per unit area 47g / m 2 The coating amount is 10.0 g / m 2The primer coating liquid was applied by a curved doctor blade method and then dried to obtain primer-coated paper.

[0155] On the undercoat layer of the undercoat layer coated paper, a coating liquid 1 for a thermal recording layer (sulfate lignin in the thermal recording layer = 10.0%, developer / leuco dye = 1.43) was applied in an amount of 6.0 g / m2 in terms of solid content. 2 After coating by a bar doctor blade method in the manner of , the coating was dried and processed by a super calender so that the smoothness became 500 to 1000 seconds to prepare a thermosensitive recording medium.

[0156] [Example 2]

[0157] A thermosensitive recording material was prepared in the same manner as in Example 1 except that the thermosensitive recording layer coating liquid 1 was replaced with the thermosensitive recording layer coating liquid 2 (sulfate lignin in the thermosensitive recording layer = 5.0%, developer / leuco dye = 1.43).

[0158] [Example 3]

[0159] A thermosensitive recording material was prepared in the same manner as in Example 2 except that the developer dispersion liquid (A1 liquid) was replaced with the developer dispersion liquid (A2 liquid) in the thermosensitive recording layer coating liquid 2 .

[0160] [Example 4]

[0161] A thermosensitive recording material was prepared in the same manner as in Example 2 except that the developer dispersion liquid (A1 liquid) was replaced with the developer dispersion liquid (A3 liquid) in the thermosensitive recording layer coating liquid 2 .

[0162] [Example 5]

[0163] A thermosensitive recording material was prepared in the same manner as in Example 2 except that the developer dispersion liquid (A1 liquid) was replaced with the developer dispersion liquid (A4 liquid) in the thermosensitive recording layer coating liquid 2 .

[0164] [Comparative Example 1]

[0165] A thermosensitive recording material was prepared in the same manner as in Example 1 except that the kraft lignin dispersion liquid (liquid A) was replaced with the kraft lignin dispersion liquid (liquid B) in the thermosensitive recording layer coating liquid 1 .

[0166] [Comparative Example 2]

[0167] A thermosensitive recording material was prepared in the same manner as in Example 2 except that the kraft lignin dispersion liquid (liquid A) was replaced with the kraft lignin dispersion liquid (liquid B) in the thermosensitive recording layer coating liquid 2 .

[0168] [Comparative Example 3]

[0169] A thermosensitive recording material was prepared in the same manner as in Example 3 except that the kraft lignin dispersion liquid (liquid A) was replaced with the kraft lignin dispersion liquid (liquid B) in the thermosensitive recording layer coating liquid 2 .

[0170] [Comparative Example 4]

[0171] A thermosensitive recording material was prepared in the same manner as in Example 4 except that the kraft lignin dispersion liquid (liquid A) was replaced with the kraft lignin dispersion liquid (liquid B) in the thermosensitive recording layer coating liquid 2 .

[0172] [Comparative Example 5]

[0173] A thermosensitive recording material was prepared in the same manner as in Example 5, except that the kraft lignin dispersion liquid (liquid A) was replaced with the kraft lignin dispersion liquid (liquid B) in the thermosensitive recording layer coating liquid 2.

[0174] The produced thermosensitive recording material was evaluated as follows.

[0175] <Color rendering performance (print density)>

[0176] The produced thermosensitive recording medium was printed with an Ichimatsu pattern using a thermal printer (TH-PMD) manufactured by Okura Electric Co., Ltd. at applied energies of 0.27 mJ / dot and 0.35 mJ / dot and a printing speed of 50 mm / sec.

[0177] The density of the printed part was measured using a Macbeth densitometer (RD-914, using an amber filter). The density of the printed part at each applied energy is shown in Table 1 below.

[0178] <Corrosiveness of thermal head>

[0179] The produced thermosensitive recording medium was printed with a thermal printer (TH-PMD) manufactured by Okura Electric Co., Ltd. at 23°C × 50% RH and 40°C × 90% RH at 0.35 mJ / dot and a printing speed of 50 mm / sec. After printing for 50 km, it was confirmed whether white streaks were generated in the image due to heating failure caused by corrosion of the thermal head, and the corrosion of the thermal head was evaluated according to the following criteria.

[0180] 0:Not generated

[0181] ×: Produce

[0182] The evaluation results are shown in the following table. The developer content indicates the developer content (solid content, wt%) in the thermosensitive recording layer.

[0183] [Table 1]

[0184]

[0185] As can be seen from this table, a thermal recording medium using sulfate lignin containing almost no hydrogen sulfide or containing only 400 ppm at most has excellent thermal head corrosion resistance.

Claims

1. A thermosensitive recording medium, wherein: A heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer is provided on a support. The heat-sensitive recording layer contains kraft lignin as an electron-accepting developer. The kraft lignin contains almost no hydrogen sulfide or contains only 400 ppm at most.

2. The thermosensitive recording medium according to claim 1, wherein The content of lignin in the kraft lignin is greater than 90%.

3. The thermosensitive recording medium according to claim 1, wherein The density of the kraft lignin is 0.4 g / cm 3 ~0.5g / cm 3 .

4. The thermosensitive recording medium according to claim 1, wherein The content of kraft lignin in the thermosensitive recording layer is 0.5% by weight to 20% by weight in terms of solid content.

5. The thermosensitive recording material according to any one of claims 1 to 4, wherein The thermosensitive recording layer contains an electron-accepting color developer other than the kraft lignin, and the electron-accepting color developer other than the kraft lignin is 4,4′-dihydroxydiphenyl sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone, or a color developer having a urea structure -NHCONH-.

6. The thermosensitive recording medium according to claim 5, wherein The weight ratio of the developer to the electron-donating leuco dye is 0.05 to 4.

0.

7. A method for reducing corrosion of a thermal head when printing on a thermal recording material having a thermal recording layer containing kraft lignin, the method comprising the step of printing on the thermal recording material according to any one of claims 1 to 4.

8. A method for reducing corrosion of a thermal head when printing on a thermal recording material having a thermal recording layer containing kraft lignin using a thermal head, the method comprising the step of printing on the thermal recording material according to claim 5.

9. A method for reducing corrosion of a thermal head when printing on a thermal recording material having a thermal recording layer containing kraft lignin using a thermal head, the method comprising the step of printing on the thermal recording material according to claim 6.

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