Heat-sensitive recording body

Abstract

Provided is a heat-sensitive recording body which is environmentally friendly and has excellent water resistance and oil resistance as well as excellent color developing performance.　The heat-sensitive recording body has a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, wherein the electron-accepting developer is an isolated lignin, and the heat-sensitive recording layer contains toluenesulfonamide as a sensitizer.

Description

Thermal recording medium

[0001] This invention relates to a thermosensitive recording medium that utilizes the color-developing reaction between a colorless or pale-colored electron-donating leuco dye (hereinafter also referred to as "leuco dye") and an electron-accepting developer (hereinafter also referred to as "developer"), and that uses isolated lignin as the developer.

[0002] Generally, a thermal recording medium is prepared by applying a coating liquid containing a colorless or pale-colored leuco dye and a color developer to a support such as paper, synthetic paper, film, or plastic, and the color develops through an instantaneous chemical reaction when heated with a thermal head, hot stamp, thermal pen, laser light, etc. Thermal recording media are widely used as recording media for facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, receipts from supermarkets and convenience stores, etc.

[0003] Generally, bisphenols, alkylphenols, novolac-type phenolic resins, aromatic carboxylic acid derivatives and their metal salts, hydroxybenzoic acid esters, sulfonylurea compounds, activated clay, etc. are used as developers. Users of thermal recording media have demanded more environmentally friendly developers than these conventional phenolic materials, and thermal recording media using ascorbic acid (Patent Documents 1 and 2, etc.), saccharin (Patent Document 3, etc.), gluconolactone (Patent Document 4, etc.) as developers have been disclosed. Furthermore, technology using isolated lignin as a developer has also been developed (Patent Documents 5 and 6).

[0004] JP 60-101171 A International Publication No. WO2014 / 143174 JP 59-33189 A International Publication No. WO2017 / 069141 Japanese Patent No. 7163173 Japanese Patent No. 7374980 A

[0005] However, further improvement in the color-developing performance of thermosensitive recording media is desired in the technology using isolated lignin as a color developer as in Patent Document 5. That is, an object of the present invention is to provide a thermosensitive recording media that is environmentally friendly, has excellent water resistance and oil resistance, and also has excellent color-developing performance.

[0006] As a result of extensive research to solve the above problems, the inventors have discovered that by using isolated lignin as a color developer and toluenesulfonamide as a sensitizer, it is possible to achieve environmentally friendly printing, excellent water resistance and oil resistance, and improved color development performance (print density and barcode readability), and have completed the present invention.

[0007] When toluenesulfonamide is used as a sensitizer, the color-developing performance is excellent, but the water resistance of the thermosensitive recording medium is reduced due to the low water resistance of toluenesulfonamide itself. Therefore, when isolated lignin is used as a color developer, the water resistance of the thermosensitive recording medium is improved by using it in combination with toluenesulfonamide because isolated lignin has low water solubility. Furthermore, the present inventors have found that toluenesulfonamide is particularly effective in improving the color-developing performance of isolated lignin compared to other sensitizers.

[0008] That is, the present invention provides a thermosensitive recording medium having a support and a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, wherein the electron-accepting developer contains isolated lignin, and the thermosensitive recording layer further contains toluenesulfonamide as a sensitizer.

[0009] According to the present invention, it is possible to obtain a thermosensitive recording medium which is environmentally friendly, has excellent water resistance, oil resistance and color development performance.

[0010] The thermosensitive recording medium of the present invention uses isolated lignin as a color developer. Natural lignin present in the cell walls of plant cells is complexed with polysaccharides such as cellulose, making isolation difficult. Therefore, it is usually isolated by chemical modification. Isolated lignin, also known as industrial lignin, includes lignosulfonates, kraft lignin, soda lignin, soda-anthraquinone lignin, organolignin, explosive lignin, sulfuric acid lignin, etc.

[0011] Among these isolated lignins, kraft lignin is preferably used in the present invention. Kraft lignin is also called thiolignin or sulfate lignin. Kraft lignin is a compound with hydroxyphenylpropane as a base unit and containing functional groups such as phenolic hydroxy groups, alcoholic hydroxy groups, and thiol groups. Kraft lignin is usually obtained by treating wood with a mixed aqueous solution of sodium hydroxide and sodium sulfide, and is insoluble in water.

[0012] Kraft lignin can be used in the form of an alkaline solution of kraft lignin, powdered kraft lignin obtained by spray-drying an alkaline solution of kraft lignin to obtain a powder, or acid-precipitated kraft lignin obtained by precipitating an alkaline solution of kraft lignin with an acid. The alkaline solution of kraft lignin can be obtained by a known method, such as that described in JP-A-2000-336589, but is not limited to these methods.

[0013] In the present invention, isolated lignin is used as the developer, but a developer other than isolated lignin (hereinafter referred to as a "second electron-accepting developer") may be used in combination. This can provide better performance in terms of color development (print density), etc. However, when a developer other than isolated lignin is used in combination, the environmentally friendly advantage of isolated lignin decreases in proportion to the amount of the developer.

[0014] Examples of such color developers include inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate, 4,4'-isopropylidenediphenol, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 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, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, and 3,4-dihydroxyphenyl-4'-methylphenyl sulfone. sulfone, 1-[4-(4-hydroxyphenylsulfonyl)phenoxy]-4-[4-(4-isopropoxyphenylsulfonyl)phenoxy]butane, the phenol condensation composition described in JP-A 2003-154760, the aminobenzenesulfonamide derivative described in JP-A 8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, 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]benzene, 1,3-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, di(4-hydroxy-3-methylphenyl)sulfide, 2,2'-thiobis(3-tert-octylphenol), 2,phenolic compounds such as 2'-thiobis(4-tert-octylphenol), diphenylsulfone-bridged compounds described in WO97 / 16420, compounds described in WO02 / 081229 or JP2002-301873A, N-(2-(3-phenylureido)phenyl)benzenesulfonamide, 3-(3-tosylureido)phenyl-p-toluenesulfonate, urea urethane compounds, 3-{[(phenylamino)carbonyl]amino}benzenesulfonamide, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, Examples of aromatic carboxylic acids include 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, and 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, as well as salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids.

[0015] These color developers can be used alone or in combination of two or more. In addition, metal chelate color-developing components such as higher fatty acid metal double salts and polyhydroxy aromatic compounds described in JP-A-10-258577 can also be contained.

[0016] Among such second electron-accepting color developers, a color developer having a urea structure (-NHCONH-) is preferred as a color developer to be used in combination with isolated lignin because it has good storage stability. Examples of color developers having a urea structure include color developers represented by the following general formulas (I) and (II): 3-(3-tosylureido)phenyl-p-toluenesulfonate (BASF, DP201, the following general formula (I)) [In the formula, R １ and R ２represents a halogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms; n1 and n2 represent integers of 0 to 3; R １ and R ２ If there are multiple １ Comrades or R ２ They may be the same or different.]

[0017] (wherein X represents —O— or —NH—; R １ is a hydrogen atom or —SO ２ -R ３ represents R ３ represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R ２ represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

[0018] The following urea-urethane compound (UU, manufactured by Chemipro Chemical Co., Ltd., formula below) can also be exemplified.

[0019] In the present invention, the content (solids content) of isolated lignin in the thermosensitive recording layer is preferably 0.5 to 50 wt %, more preferably 1 to 40 wt %, even more preferably 2 to 30 wt %, and most preferably 5 to 20 wt %. In the present invention, even if the content (solids content) of isolated lignin is increased, a thermosensitive paper with high sensitivity can be obtained. As a result, a more environmentally friendly thermosensitive recording medium can be obtained. In the present invention, when isolated lignin and a second electron-accepting developer other than the isolated lignin are used in combination as the developer, the weight ratio of the isolated lignin to the second electron-accepting developer (isolated lignin / second electron-accepting developer) is preferably 90 / 10 to 10 / 90, more preferably 80 / 20 to 20 / 80, and even more preferably 60 / 40 to 25 / 75.

[0020] The thermosensitive recording medium of the present invention can utilize conventional structures except for the use of isolated lignin as a developer and toluenesulfonamide as a sensitizer. That is, the thermosensitive recording medium of the present invention essentially has a thermosensitive recording layer on a support, and may optionally have a protective layer on the thermosensitive recording layer, an undercoat layer between the support and the thermosensitive recording layer, or a backcoat layer on the side of the support opposite the thermosensitive recording layer. In addition, a coating layer appropriately configured depending on the intended use may be provided between these layers.

[0021] 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., depending on the desired quality of the thermal recording medium, and is not particularly limited. A composite sheet combining these may also be used as the support.

[0022] The heat-sensitive recording layer of the present invention essentially contains a leuco dye and a sensitizer in addition to the above-mentioned color developer, and may further contain, optionally, a binder, a pigment, a crosslinking agent, an image stabilizer and other components.

[0023] The leuco dye used in the present invention can be any known leuco dye in the field of conventional pressure-sensitive or heat-sensitive recording paper, and is not particularly limited. However, triphenylmethane compounds, fluoran compounds, fluorene compounds, divinyl compounds, etc. are preferred. Specific examples of representative colorless or pale-colored leuco dyes (dye precursors) are shown below. These leuco dyes may be used alone or in combination.

[0024] <Triphenylmethane leuco dyes> 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)

[0025] <Fluoran-based leuco dyes> 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-anilinofluoran; 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-pyrrolidino-6-methyl-7-anilinofluoran; 3-piperidino-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-xylamino)-6-methyl-7-(p-chloroanilino)fluoran; 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran; 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran; 3-(N-ethyl-N-tetrahydrofurfurylamino)-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;

[0026] <Fluorene-based leuco dyes> 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]

[0027] <Divinyl leuco dyes> 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide; 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide; 3,3-bis-[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide; 3,3-bis-[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide

[0028] <Others> 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-(4'-nitro)anilinolactam; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane; 1,1-bis-[2',2',2'',2''-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-diacetylethane; Bis-[2,2,2',2'-tetrakis-(p-dimethylaminophenyl)-ethenyl]-methylmalonic acid dimethyl ester

[0029] In the present invention, toluenesulfonamide is used as a sensitizer, which improves the color development performance (print density) and durability when isolated lignin is used as a developer.

[0030] In addition to toluenesulfonamide, other sensitizers may be used in combination as the sensitizer. Examples of sensitizers that can be used in combination with toluenesulfonamide include diphenyl sulfone, fatty acid amides such as stearic acid amide and palmitic acid amide, benzyloxynaphthalene, 1,2-di-(3-methylphenoxy)ethane, and di(p-methylbenzyl) oxalate. These sensitizers may be used alone or in combination of two or more. Among these sensitizers, it is preferable to use diphenyl sulfone in order to compensate for the color development performance (print density) when isolated lignin is used as a developer.

[0031] Examples of binders that can be used in the present invention include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-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, and terminal alkyl-modified polyvinyl alcohol; cellulose ethers such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and acetyl cellulose, and derivatives thereof; starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (e.g., hydroxyethylated starch), and cationized starch. Examples of suitable resins include starches, polyacrylamides such as polyacrylamides, cationic polyacrylamides, anionic polyacrylamides, and amphoteric polyacrylamides, urethane resins such as polyester polyurethane resins, polyether polyurethane resins, and polyurethane ionomer resins, acrylic resins composed of (meth)acrylic acid and monomer components copolymerizable with (meth)acrylic acid (excluding olefins), styrene-butadiene resins such as styrene-butadiene copolymers, styrene-butadiene-acrylonitrile copolymers, and styrene-butadiene-acrylic copolymers, polyolefin resins such as polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, and ethylene-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, polyacrylic esters, gum arabic, polyvinyl butyral, polystyrene and copolymers thereof, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. These may be used alone or in combination of two or more.

[0032] Examples of pigments 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, aluminum hydroxide, etc. These may be used alone or in combination of two or more.

[0033] Examples of crosslinking agents that can be used in the present invention include glyoxal, methylol melamine, 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 agents.

[0034] Furthermore, in the present invention, as long as the desired effect for solving the above-mentioned problems is not impaired, image stabilizers that exhibit effects such as oil resistance of recorded images can also be used, such as 4,4'-butylidene(6-t-butyl-3-methylphenol), 2,2'-di-t-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-t-butylphenyl)butane, and 4-benzyloxy-4'-(2,3-epoxy-2-methylpropoxy)diphenylsulfone. In addition, benzophenone-based or triazole-based ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc. can also be used.

[0035] In the present invention, the developer is preferably used in an amount of 0.05 to 4.0 parts by weight, more preferably 0.1 to 3.0 parts by weight, per 1 part by weight of the leuco dye. The types and amounts of the sensitizer, binder, pigment, crosslinker, image stabilizer, and other optional components are determined according to the required performance and recording suitability and are not particularly limited. Typically, however, approximately 0.1 to 10 parts by weight of the sensitizer, 0.5 to 50 parts by weight of the pigment, 0.01 to 10 parts by weight of the image stabilizer, and 0.01 to 10 parts by weight of the other components are used. The binder is preferably used in an amount of approximately 5 to 50 parts by weight (solids) per 100 parts by weight of the thermosensitive recording layer (solids). The lubricant content is preferably approximately 5 to 10 parts by weight (solids) per 100 parts by weight of the thermosensitive recording layer (solids).

[0036] The leuco dye, developer, and other optional additives are pulverized to particle sizes of several microns or less using a grinder such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and a binder and various additives depending on the purpose are added to prepare a coating liquid. The solvent used for this coating liquid can be water or alcohol, and the solid content is about 20 to 40% by weight.

[0037] The thermosensitive recording medium of the present invention may have an undercoat layer between the support and the thermosensitive recording layer. This undercoat layer is mainly composed of a binder and a pigment. As the binder used in the undercoat layer, any of the binders usable in the thermosensitive recording layer described above can be used. These binders may be used alone or in combination of two or more.

[0038] The undercoat layer may contain, for example, inorganic pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, kaolin, calcined kaolin, clay, and talc, and organic pigments such as hollow plastic particles. These pigments may be used alone or in combination of two or more. From the viewpoint of image quality, calcium carbonate is preferred as the pigment. The content of the pigment in the undercoat layer is typically 50 to 95 wt %, and preferably 70 to 90 wt %, based on the solid content of the undercoat layer. The coating liquid for the undercoat layer may contain various auxiliary agents, such as dispersants, plasticizers, pH adjusters, antifoaming agents, water retention agents, preservatives, coloring dyes, and ultraviolet protection agents, as needed.

[0039] In the thermosensitive recording medium of the present invention, a protective layer may be provided on the thermosensitive recording layer. The protective layer may contain the binder, pigment, crosslinking agent, and other components that can be used in the thermosensitive recording layer as described above, provided that the desired effects are not impaired. The protective layer preferably contains a binder and a pigment, and may also contain other components such as a surfactant and a viscosity modifier as necessary.

[0040] Among the binders usable in the thermosensitive recording layer, polyvinyl alcohols and acrylic resins are preferred as binders for the protective layer. As polyvinyl alcohols, fully saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol are preferred. As components (excluding olefins) of acrylic resins copolymerizable with (meth)acrylic acid, 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; modified alkyl acrylate resins such as epoxy resins, silicone resins, and alkyl acrylate resins modified with styrene or its derivatives; (meth)acrylonitrile, acrylic esters, and hydroxy groups. Examples of the acrylic resin include alkyl acrylate esters, and are 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, and octyl (meth)acrylate; epoxy resins; silicone resins; modified alkyl acrylate resins such as alkyl acrylate resins modified with styrene or a derivative thereof; (meth)acrylonitrile; acrylic esters; and hydroxyalkyl acrylic esters. (Meth)acrylonitrile and / or methyl methacrylate are particularly preferred. The acrylic resin is preferably a non-core-shell acrylic resin.

[0041] The protective layer may contain a carboxyl group-containing resin as a binder, and may further contain a polyamine / polyamide resin, in order to improve water resistance, etc. Examples of the carboxyl group-containing resin include the above-mentioned carboxy-modified polyvinyl alcohol, acrylic resin, oxidized starch, and carboxymethyl cellulose.

[0042] Examples of the polyamine / polyamide resin include polyamide urea resin, polyalkylene polyamine resin, polyalkylene polyamide resin, polyamine polyurea resin, modified polyamine resin, modified polyamide resin, polyalkylene polyamine urea formalin resin, and polyalkylene polyamine polyamide polyurea resin.

[0043] In the present invention, when the protective layer contains a pigment, the water resistance and print running properties of the thermosensitive recording medium are improved, and therefore, as this pigment, silica, kaolin, calcined kaolin, and aluminum hydroxide are preferred, and kaolin and aluminum hydroxide are more preferred. When the protective layer of the present invention does not contain a pigment, the blending amount of the binder in the protective layer is usually 70 to 100% by weight, preferably 85 to 100% by weight, in terms of solid content.

[0044] On the other hand, when the protective layer contains a pigment, the total amount of the binder and pigment in the protective layer is usually 80 to 100% by weight, preferably 90 to 100% by weight, in terms of solid content, and the amount of the binder is preferably about 30 to 300 parts by weight per 100 parts by weight of the pigment. The amount of components other than the binder, crosslinking agent, and pigment in the protective layer does not exceed 15% by weight, preferably 10% by weight, respectively.

[0045] Each coating layer that is optionally provided other than the heat-sensitive recording layer and the protective layer can contain the above-mentioned binders, pigments, crosslinking agents and other components to the extent that the desired effects are not impaired.

[0046] The coating method for the thermosensitive recording layer, protective layer, and other coating layers is not particularly limited, and any conventionally known method can be used, such as curtain coating, air knife coating, bar blade coating, rod blade coating, bent blade coating, bevel blade coating, roll coating, or spray coating.

[0047] The coating weight of the thermosensitive recording layer, undercoat layer, protective layer, and other coating layers is determined according to the required performance and recording suitability, and is not particularly limited. For example, the general coating weight of the thermosensitive recording layer is 2 to 12 g / m2 in terms of solid content. ２ The typical coating amount of the protective layer is 1 to 5 g / m2 in solid content. ２Furthermore, various known techniques in the field of thermosensitive recording media can be applied as needed, such as smoothing treatment such as supercalendering after coating each layer.

[0048] The present invention will be illustrated by the following examples, but is not intended to limit the scope of the present invention. In each example and comparative example, "parts" means "parts by weight" and "%" means "% by weight" unless otherwise specified. Each dispersion and coating liquid was prepared as follows.

[0049] The following blend was stirred and dispersed to prepare a coating liquid for an undercoat layer: <Coating liquid for undercoat layer> Calcium carbonate (manufactured by Shiraishi Calcium, trade name: Callite KT) 100.0 parts Styrene-butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd., trade name: ST5526, solid content 48%) 10.0 parts Water 50.0 parts

[0050] The developer dispersions (Liquids A1 to A3), leuco dye dispersion (Liquid B), and sensitizer dispersion (Liquid C) having the following formulations were each wet-ground in a sand grinder until the average particle size reached 0.5 μm. Kraft lignin dispersion (Liquid A) was also wet-ground in a sand grinder until the average particle size reached 3.0 μm.

[0051] Kraft lignin dispersion (liquid A1) Kraft lignin (manufactured by Meadwestbaco, Indulin AT) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., trade name: PVA117, solid content 10%) 5.0 parts Water 1.5 parts

[0052] Developer dispersion (liquid A2) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (manufactured by Nippon Soda Co., Ltd., trade name: NKK1304) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0053] Developer dispersion (liquid A3) 4-hydroxy-4'-isopropoxydiphenyl sulfone (manufactured by Nippon Soda Co., Ltd., trade name: D8) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0054] Developer dispersion (liquid A4) N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (manufactured by Sankosha, trade name: S176) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0055] Leuco dye dispersion (liquid B) 3-dibutylamino-6-methyl-7-anilinofluoran (manufactured by Yamamoto Chemical Industry Co., Ltd., trade name: ODB-2) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0056] Sensitizer dispersion (liquid C1) Toluenesulfonamide (manufactured by Solenis, trade name: Pergaspeed 110) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0057] Sensitizer dispersion (liquid C2) Diphenyl sulfone (Volant Corporation, trade name: DPS) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0058] Sensitizer dispersion (C3 solution) 1,2-di(3-methylphenoxy)ethane (manufactured by Sankosha, trade name: KS232) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0059] Sensitizer dispersion (C4 solution) Stearic acid amide (trade name: Finawax S, manufactured by Fine Organics) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 5.0 parts Water 1.5 parts

[0060] Next, the dispersions were mixed in the following proportions and thoroughly stirred to prepare the following coating solutions for the thermosensitive recording layer: <Coating Solution 1 for Thermosensitive Recording Layer> Kraft lignin dispersion (Solution A1) 3.0 parts Leuco dye dispersion (Solution B) 1.0 part Sensitizer dispersion (Solution C1) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0061] <Coating liquid 2 for thermal recording layer> Kraft lignin dispersion (liquid A1) 2.4 parts Developer dispersion (liquid A3) 0.6 parts Leuco dye dispersion (liquid B) 1.0 parts Sensitizer dispersion (liquid C1) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0062] <Coating liquid 3 for thermosensitive recording layer> Kraft lignin dispersion (liquid A1) 2.4 parts Developer dispersion (liquid A4) 0.6 parts Leuco dye dispersion (liquid B) 1.0 parts Sensitizer dispersion (liquid C1) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0063] <Coating liquid 4 for thermosensitive recording layer> Developer dispersion (liquid A2) 3.0 parts Leuco dye dispersion (liquid B) 1.0 part Sensitizer dispersion (liquid C1) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0064] <Coating Solution 5 for Thermosensitive Recording Layer> Kraft lignin dispersion (Liquid A1) 3.0 parts Leuco dye dispersion (Liquid B) 1.0 part Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0065] <Coating Solution 6 for Thermosensitive Recording Layer> Kraft lignin dispersion (Liquid A1) 3.0 parts Leuco dye dispersion (Liquid B) 1.0 part Sensitizer dispersion (Liquid C2) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0066] <Coating Solution 7 for Thermosensitive Recording Layer> Kraft lignin dispersion (Solution A1) 3.0 parts Leuco dye dispersion (Solution B) 1.0 part Sensitizer dispersion (Solution C3) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0067] <Coating Solution 8 for Thermosensitive Recording Layer> Kraft lignin dispersion (Liquid A1) 3.0 parts Leuco dye dispersion (Liquid B) 1.0 part Sensitizer dispersion (Liquid C4) 1.5 parts Silica dispersion (manufactured by Mizusawa Industrial Chemicals, Ltd., trade name: Mizukasil P-537, solid content 25%) 5.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin L536, solid content 40%) 5.0 parts Completely saponified polyvinyl alcohol aqueous solution (PVA117) 20.0 parts

[0068] [Example 1] Support (basis weight 47 g / m ２ The coating solution for the primer layer was applied to one side of the paper (high-quality paper) at a coating weight of 10.0 g / m2 (solid content). ２ The coated paper was then dried to obtain a primer-coated paper. The coating solution 1 for the thermosensitive recording layer was applied to the primer layer of the primer-coated paper in a coating amount of 6.0 g / m2 (solid content). ２ After coating by the rod blade method so that the coating was as follows, the coating was dried and then processed with a super calendar so that the smoothness was 500 to 1000 seconds to prepare a thermosensitive recording medium.

[0069] [Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 1 for the thermosensitive recording layer was replaced with Coating Liquid 2 for the thermosensitive recording layer. [Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 1 for the thermosensitive recording layer was replaced with Coating Liquid 3 for the thermosensitive recording layer.

[0070] [Comparative Example 1] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Solution 1 for thermosensitive recording layer was replaced with Coating Solution 5 for thermosensitive recording layer. [Comparative Example 2] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Solution 1 for thermosensitive recording layer was replaced with Coating Solution 6 for thermosensitive recording layer.

[0071] [Comparative Example 3] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 1 for the thermosensitive recording layer was replaced with Coating Liquid 7 for the thermosensitive recording layer. [Comparative Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 1 for the thermosensitive recording layer was replaced with Coating Liquid 8 for the thermosensitive recording layer. [Comparative Example 5] A thermosensitive recording medium was prepared in the same manner as in Example 1, except that Coating Liquid 1 for the thermosensitive recording layer was replaced with Coating Liquid 4 for the thermosensitive recording layer.

[0072] The prepared thermosensitive recording medium was evaluated as follows. <Color development performance (print density)> A checkerboard pattern was printed on the prepared thermosensitive recording medium using a thermal printer (TH-PMD) manufactured by Okura Electric Co., Ltd., with applied energies of 0.27 mJ / dot and 0.35 mJ / dot and a printing speed of 50 mm / sec. The density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter). Table 1 shows the density of the printed area at each applied energy.

[0073] <Color development performance (barcode reading)> A barcode (CODE 39) was printed vertically (the moving direction of the printer head and the barcode were perpendicular) on the prepared thermal recording medium using a Zebra 140XiIII label printer at a print level of +10 and a print speed of 101.6 mm / sec, and the printed barcode was then visually evaluated. Excellent: The barcode was clearly readable. Good: The barcode had slight defects, but was fully readable. Fair: The barcode had many defects and the printing was faint, but was readable. Poor: The barcode was not readable.

[0074] <Water Resistance> A checkerboard pattern was printed on the prepared thermosensitive recording medium using a thermal printer (TH-PMD) manufactured by Okura Electric Co., Ltd., with an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec. The printed thermosensitive recording medium was immersed in water at 23°C for 24 hours and then air-dried. The density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter), and the residual rate was calculated.

[0075] Residual rate (%) = (print density of printed area after processing / print density of printed area before processing) x 100 Excellent: Residual rate is 80% or more Good: Residual rate is 70% or more but less than 80% Passable: Residual rate is 60% or more but less than 70% Poor: Residual rate is less than 60%

[0076] <Oil Resistance> A checkerboard pattern was printed on the prepared thermosensitive recording medium at an applied energy of 0.41 mJ / dot and a printing speed of 50 mm / sec using a TH-PMD (thermal recording paper printing tester, equipped with a Kyocera thermal head) manufactured by Okura Electric Co., Ltd. Salad oil was applied to the printed thermosensitive recording medium with a cotton swab and allowed to stand for one week under environmental conditions of 23°C and 50% Rh. After that, the print density of the printed area was measured with a Macbeth densitometer (RD-914, using an amber filter), and the residual rate was calculated from the values ​​before and after treatment to evaluate oil resistance.

[0077] Residual rate (%) = (print density of printed area after processing / print density of printed area before processing) x 100 Excellent: Residual rate is 80% or more Good: Residual rate is 70% or more but less than 80% Passable: Residual rate is 60% or more but less than 70% Poor: Residual rate is less than 60%

[0078] The results obtained are shown in Table 1. The items for color developer and sensitizer indicate the contents (solid content, % by weight) of the color developer and sensitizer in the heat-sensitive recording layer.

[0079]

[0080] As is clear from Table 1, each of the Examples containing isolated lignin as a developer and toluenesulfonamide as a sensitizer was environmentally friendly and improved color development performance (print density and barcode readability) during thermal recording, water resistance, and oil resistance. Note that Example 2 had slightly lower water resistance than the other Examples, but this was because the developer (product name D8) had lower water resistance than the developers of the other Examples. Furthermore, the water resistance of Example 2 presented no practical problems.

[0081] On the other hand, in Comparative Examples 1 to 4, which contained isolated lignin as a color developer but did not contain toluenesulfonamide as a sensitizer, the color development performance (print density and barcode readability) during thermal recording was inferior. In Comparative Example 5, which contained another color developer instead of isolated lignin as a color developer and toluenesulfonamide as a sensitizer, the water resistance and oil resistance were inferior. This is thought to be because, although the use of toluenesulfonamide as a sensitizer improves color development performance as in the above examples, the water resistance of toluenesulfonamide itself is low. Furthermore, when isolated lignin is used as a color developer, due to the low water solubility of isolated lignin, using it in combination with toluenesulfonamide improves the water resistance of the thermal recording medium.

Claims

1. A thermosensitive recording medium comprising a support and a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, wherein the electron-accepting developer contains isolated lignin, and the thermosensitive recording layer further contains toluenesulfonamide as a sensitizer.

2. The thermosensitive recording medium according to claim 1, wherein the isolated lignin is kraft lignin.

3. The thermosensitive recording medium according to claim 1 or 2, wherein the content (solid content) of the isolated lignin in the thermosensitive recording layer is 0.5 to 50% by weight.

4. The heat-sensitive recording medium according to claim 1 or 2, wherein the weight ratio of the developer to the electron-donating leuco dye is 0.05 to 4.

0.

5. A thermosensitive recording medium according to claim 1 or 2, wherein the thermosensitive recording layer contains, in addition to isolated lignin as the electron-accepting color developer, a compound represented by the following general formula (I) or a compound represented by the following general formula (II) as a second electron-accepting color developer: [In the formula, R １ and R ２ represents a halogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms; n1 and n2 represent integers of 0 to 3; R １ and R ２ If there are multiple １ Comrades or R ２ They may be the same or different.] (wherein X represents —O— or —NH—; R １ is a hydrogen atom or —SO ２ -R ３ represents R ３ represents a substituted or unsubstituted alkyl group, aralkyl group, or aryl group; R ２ represents a hydrogen atom or an alkyl group, and m represents 0 or 1.

6. A thermosensitive recording medium according to claim 1 or 2, wherein the thermosensitive recording layer further contains a second electron-accepting color developer other than the isolated lignin, and the weight ratio of the isolated lignin to the second electron-accepting color developer (isolated lignin / second electron-accepting color developer) is 10 / 90 to 90 / 10.

Images