JP7327351B2 - Thermal recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermal recording medium utilizing a color-developing reaction between a leuco dye and a coloring agent.

A heat-sensitive recording material is well known in which a colorless or light-colored leuco dye and a coloring agent capable of acting as an electron acceptor for the leuco dye are reacted with heat to develop a color to obtain a recorded image.

Its application fields include, for example, register paper and ticket paper for POS (Point of Sales) systems. is increasing. Furthermore, in the same application, since it is also used as a receipt, it is necessary to have good preservability against various chemicals such as oils and plasticizers in the recording part, office supplies, hand cream, etc., and good stampability.

In a heat-sensitive recording medium having a heat-sensitive recording layer containing a leuco dye and a coloring agent as main components on a support, the color-developing reaction is reversible, and it is known that the color-developed image fades over time. It is This decoloring reaction is accelerated in a high-temperature, high-humidity environment, and further progresses rapidly due to contact with oils, plasticizers, etc., and the recorded image may be decolored to the extent that it cannot be read. In order to improve the storability of the recorded area, it has been proposed to add an epoxy compound to the thermosensitive recording layer (see Patent Document 1). has not been obtained. In recent years, the development of colorants with high preservability has progressed, and the addition of a ureaurethane compound to the thermosensitive recording layer (see Patent Document 2) has been proposed, and the above problems are being solved. is low. In order to increase the stability of the non-printed portion (heat-resistant background fogging resistance), it is effective to use a high-melting-point coloring agent, but this also has the problem of lowering the recording sensitivity. , it is difficult to cope with recent high-speed printers and battery-powered handy terminal printers.

To address this problem, 4,4'-bis(3-tosylureido)diphenylmethane has been proposed as a coloring agent (see Patent Document 3). 4,4'-bis(3-tosylureido)diphenylmethane improves the plasticizer resistance and oil resistance of the recording area, but when used alone, there is a problem of low recording sensitivity.

In particular, acid-free paper, which is generally used as a support for heat-sensitive recording media, contains a rosin-based sizing agent and fillers such as clay and talc. A band is generally used, but the pH of the paper surface becomes acidic due to the sulfate radicals remaining in the paper, and the color-developing substances constituting the thermal recording paper react with acidic ions on the surface of the paper. There is a problem that background fogging tends to occur during long-term storage. For this reason, neutral paper containing an alkali filler such as calcium carbonate is sometimes used as a support for heat-sensitive recording media for the purpose of preventing background fogging and reducing papermaking costs.

JP-A-4-286685 JP-A-2002-144746 JP-A-5-147357

SUMMARY OF THE INVENTION The main object of the present invention is to provide a heat-sensitive recording medium which has a high recording density, good resistance to plasticizers in the recorded portion, and excellent resistance to background fogging under high-temperature storage.

The inventors of the present invention have made intensive studies to solve the above object, and found that 4,4'-bis(3-tosylureido)diphenylmethane and 3,3'-diallyl- The inventors have found that the above problems can be solved by using 4,4'-dihydroxydiphenylsulfone together, and have completed the present invention. That is, the present invention relates to the following thermal recording material.

Section 1. A heat-sensitive recording material having a heat-sensitive recording layer containing at least a leuco dye and a colorant on a support, wherein the colorant is 4,4'-bis(3-tosylureido)diphenylmethane and 3,3'-diallyl -A thermal recording material containing 4,4'-dihydroxydiphenyl sulfone.
Section 2. A ratio of 0.2 to 4.0 parts by mass of the 4,4'-bis(3-tosylureido)diphenylmethane to 1.0 parts by mass of the 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone Item 1. The thermal recording material according to item 1, which is contained in.
Item 3. The thermosensitive recording layer further contains a sensitizer, and the content of the sensitizer is 0.5 per 1.0 parts by mass of the 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone. 3. The thermal recording material according to item 1 or 2, which is up to 3.0 parts by mass.
Section 4. Item 4. The item 3, wherein the sensitizer contains at least one selected from the group consisting of diphenylsulfone, 1,2-di(3-methylphenoxy)ethane, and di-p-methylbenzyl oxalate. Thermal recording material.
Item 5. Item 5. The thermal recording material according to any one of Items 1 to 4, wherein the support is neutral paper.
Item 6. Item 6. The thermal recording material according to any one of Items 1 to 5, wherein the support has an ash content of 5 to 25% by mass.

The heat-sensitive recording material of the present invention has a high recording density, good resistance to plasticizers in the recorded portion, and excellent resistance to background fogging under high-temperature storage.

As used herein, the expressions "including" include the concepts "including," "consisting only of substance," and "consisting only of."

Moreover, in the present invention, the "average particle size" refers to a volume-based median size measured by a laser diffraction method. More simply, an electron microscope may be used to measure each particle size from a particle image (SEM image), and an average value of 10 values may be shown.

The present invention provides a heat-sensitive recording material having a heat-sensitive recording layer containing at least a leuco dye and a colorant on a support, wherein the colorant comprises 4,4'-bis(3-tosylureido)diphenylmethane and 3, It is characterized by containing 3'-diallyl-4,4'-dihydroxydiphenylsulfone.

The present invention provides a thermosensitive recording material having a thermosensitive recording layer formed on a support by coating and drying a specific thermosensitive recording layer coating solution containing at least a leuco dye and a colorant. However, the layer structure of the heat-sensitive recording material is not limited to the structure of the support and the heat-sensitive recording layer. It includes a construction, a construction having a back layer on the side opposite to the side of the support having the heat-sensitive recording layer, and the like.

[Support]
The support in the present invention is not particularly limited, but examples thereof include neutral or acidic woodfree paper (neutral paper, acid paper), synthetic paper, transparent or translucent plastic film, white plastic film, and the like. . The thickness of the support is not particularly limited, and is usually about 20 to 200 μm. Moreover, the density of the support is not particularly limited, and is preferably about 0.60 to 0.95 g/cm ³ .

In the present invention, since the background fog during long-term storage can be improved and the effects of the present invention can be fully exhibited, acid paper as well as neutral paper can be used as the support, but neutral paper is preferred. is. The type and production method of the neutral paper are not particularly limited, but pulp fibers, generally calcium carbonate as a filler, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) as a sizing agent, and polyamide as a fixing agent. , acrylamide, cationic starch, etc. can be obtained by papermaking. Such neutral paper preferably has a hot water extraction pH (based on JIS P 8133) of about 6.0 to 11, more preferably 6.5 to 10, and even more preferably 7.5 to 10. preferable. By setting the pH of the neutral paper to 6.0 or higher, it is possible to effectively suppress background fogging during storage of blank paper. On the other hand, by setting the pH to 11 or less, aggregation of the pulp slurry itself can be suppressed. Furthermore, aluminum sulfate can be used as necessary to adjust the pH to the extent that the pH does not fall below 6.0, and the papermaking properties can also be improved. Here, the acidic paper in the present invention has a pH of 2 or more and does not exceed pH 6, preferably about pH 2 to 5.7.

The ash content of the support in the invention is not particularly limited, and is preferably about 5 to 25% by mass, more preferably about 5 to 15% by mass. By setting the ash content of the support to 5% by mass or more, it is possible to suppress deterioration in image quality due to a decrease in the smoothness of the support. On the other hand, by setting the ash content of the support to 25% by mass or less, it is possible to suppress a decrease in paper strength (for example, tensile strength).

The type of pulp fiber used in the present invention, the manufacturing method, etc. are not particularly limited. , or waste paper pulp, and the like.

It should be noted that internal additives for papermaking such as dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, pitch control agents, slime control agents, etc. can be added to the pulp slurry as appropriate depending on the use of the paper. . Starch or the like can also be applied in a size press. As a paper machine, a fourdrinier paper machine, a twin wire paper machine, a cylinder paper machine, a Yankee dryer paper machine, or the like can be appropriately used.

[Thermal recording layer]
The heat-sensitive recording layer in the present invention can contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethyl aminophenyl)-6-dimethylaminophthalide, blue dyes such as fluoran, 3-(N-ethyl-Np-tolyl)amino-7-N-methylanilinofluorane, 3-diethylamino-7- green dyes such as anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3,6-bis(diethylamino)fluorane-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane and other red-forming dyes, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-ani Rinofluorane, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di(n-butyl) ) amino-6-methyl-7-anilinofluorane, 3-di(n-pentyl)amino-6-methyl-7-anilinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluorane, 3 -(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluorane, 3-( N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-dimethylamino-6-methyl-7-ani Rinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 2,2-bis{4-[6'-(N-cyclohexyl -N-methylamino)-3'-methylspiro[phthalid-3,9'-xanthen-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluorane, etc. Black chromogenic dye, 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3 , 3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-p-(p- dimethylaminoanilino)anilino-6-methyl-7-chlorofluorane, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluorane, 3,6-bis(dimethylamino)fluorene-9 -Spiro-3'-(6'-dimethylamino)phthalide and other dyes having an absorption wavelength in the near-infrared region. Of course, it is not limited to these, and two or more kinds can be used together as necessary. Among others, 3-di(n-butyl)amino-6-methyl-7-anilinofluorane, 3-di(n-pentyl)amino-6-methyl-7-anilinofluorane, and 3-(N -Ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane is preferably used because of its excellent recording sensitivity and print preservability. The content of the leuco dye is preferably about 5 to 25% by mass, more preferably about 7 to 20% by mass, based on the total solid content of the thermosensitive recording layer. By making it 5% by mass or more, it is possible to enhance the coloring ability and improve the print density. Heat resistance can be improved by making it 25 mass % or less.

In the heat-sensitive recording layer of the present invention, when 4,4'-bis(3-tosylureido)diphenylmethane is used as a colorant in the heat-sensitive recording layer, the recording portion has excellent plasticizer resistance. Further, when 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone is used as a coloring agent, the recording sensitivity is increased and the recording density is increased while maintaining the plasticizer resistance of the recording area. In addition, background fogging can be prevented when the thermal recording material is placed in a high-temperature environment, so a thermal recording material with good image visibility even after storage in a high-temperature environment can be obtained.

The content of 4,4′-bis(3-tosylureido)diphenylmethane in the thermosensitive recording layer is 0.2 to 4 parts per 1.0 parts by weight of 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone. About 0.0 part by mass is preferable, about 0.3 to 3.5 parts by mass is more preferable, about 0.4 to 3.0 parts by mass is even more preferable, and about 0.5 to 3.0 parts by mass is particularly preferable. By setting the amount to 0.2 parts by mass or more, sufficient plasticizer resistance can be obtained in the recording area. On the other hand, if the content is 4.0 parts by mass or less, the recording sensitivity can be further increased, and the background fogging resistance in a high temperature environment can be improved.

The content of 4,4'-bis(3-tosylureido)diphenylmethane in the thermosensitive recording layer is 0.3 to 5 parts per 1.0 part by mass of the leuco dye from the viewpoint of improving the recording density and plasticizer resistance. 0.0 parts by mass is preferable, 0.3 to 4.0 parts by mass is more preferable, 0.4 to 3.0 parts by mass is still more preferable, and 0.4 to 2 parts by mass is particularly preferable. The content of the 4,4'-bis(3-tosylureido)diphenylmethane can be adjusted within the content range for the above 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone. .

The content of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone in the thermosensitive recording layer is 0.00 per 1.0 part by mass of the leuco dye from the viewpoint of improving recording density and plasticizer resistance. It is preferably 3 to 5.0 parts by mass, more preferably 0.3 to 4.0 parts by mass, still more preferably 0.4 to 3.0 parts by mass, and particularly preferably 0.4 to 2 parts by mass.

Coloring agents in the present invention are 4,4'-bis(3-tosylureido)diphenylmethane and 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, but various other agents may be used if necessary within a range that does not interfere. Known materials can be used together. Specific examples include activated clay, attapulgite, colloidal silica, inorganic acidic substances such as aluminum silicate, 4,4′-isopropylidenediphenol, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfide, hydroquinone mono benzyl ether, 4-hydroxy-4'-benzyloxydiphenylsulfone, benzyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, bis(3-allyl-4 -hydroxyphenyl)sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-allyloxy-4'-hydroxydiphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone and other phenolic compounds; Thiourea compounds such as '-di-m-chlorophenylthiourea, N-(p-toluenesulfonyl)carbamoylic acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoylic acid p-benzyloxyphenyl ester, N- (o-toluoyl)-p-toluenesulfonamide and other organic compounds having a —SO ₂ NH- bond in the molecule, p-chlorobenzoic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4- Aromatic carboxylic acids such as [3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc, magnesium and aluminum of these aromatic carboxylic acids 1 , 5-(3-oxapentylene)-bis(3-(3′-(p-toluenesulfonyl)ureido)benzoate, 1-(4-butoxycarbonylphenyl)-3-tosylurea, Np-toluenesulfonyl- N'-3-(p-toluenesulfonyloxy)phenylurea, N-(p-toluenesulfonyl)-N'-phenylurea, N-(p-toluenesulfonyl)-N'-p-tolylurea, 4,4' - sulfonylurea compounds such as bis(3-(tosyl)ureido)diphenyl ether, 4,4'-bis(3-(tosyl)ureido)diphenylsulfone, diphenylsulfone derivatives represented by the following general formula (1), the following general formula 4,4′-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone represented by (2), 4,4′-bis[(2-methyl-5-phenoxycarbonylaminophenyl) Ureido]diphenylsulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureido-diphenylsulfone, and other ureaurethane derivatives.

（式中、ｎ＝１～６）

(where n = 1 to 6)

In the heat-sensitive recording material of the present invention, the heat-sensitive recording layer may contain, in addition to the specific coloring agent and leuco dye, a preservability improver, a sensitizer, other various auxiliary agents, and the like.

The heat-sensitive recording layer in the present invention may contain a storage-improving agent. This makes it possible to improve the storability of the recording section. Examples of storage improvers include 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'- ethylidenebis(4,6-di-tert-butylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl-m-cresol), 1-[α-methyl-α-(4′-hydroxyphenyl)ethyl]-4-[α′,α′-bis(4″-hydroxyphenyl)ethyl]benzene, 1,1,3-tris(2- methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, tris(2,6-dimethyl-4-tertiary Butyl-3-hydroxybenzyl)isocyanurate, 4,4'-thiobis(3-methylphenol), 4,4'-dihydroxy-3,3',5,5'-tetrabromodiphenylsulfone, 4,4'- Dihydroxy-3,3′,5,5′-tetramethyldiphenylsulfone, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5- dichlorophenyl)propane, hindered phenol compounds such as 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenylsulfone, 4 -Benzyloxy-4'-(2-methylglycidyloxy)diphenylsulfone, diglycidyl terephthalate, epoxy compounds such as cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, N,N'-di- 2-naphthyl-p-phenylenediamine, sodium salt or polyvalent metal salt of 2,2′-methylenebis(4,6-di-tert-butylphenyl) phosphate, bis(4-ethyleneiminocarbonylaminophenyl)methane, etc. The content of the preservability improver may be an amount effective for improving the preservability, but it is usually preferably about 1 to 30% by weight, and 5 to 5% by weight of the total solid content of the thermosensitive recording layer. About 20% by mass is more preferable.

In the present invention, by containing 4,4'-bis(3-tosylureido)diphenylmethane and 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone as colorants, excellent background fog resistance is obtained. It is preferable to further contain a sensitizer in the heat-sensitive recording layer. Thereby, the recording sensitivity can be further increased, and the recording density can be improved. Sensitizers include, for example, stearamide, methoxycarbonyl-N-stearic acid benzamylde, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylol stearamide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p- benzylbiphenyl, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibenzyl oxalate, p-tolylbiphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy)ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2 -diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenyl benzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenethyl dido, N-acetoacetyl-p-toluidine, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, diphenylsulfone and the like. Among these, diphenylsulfone, 1,2-di(3-methylphenoxy)ethane, and di-p-methylbenzyl oxalate are preferable because they are excellent in sensitizing effect without impairing background fog resistance. Used. From the viewpoint of effectively increasing the recording sensitivity and suppressing the background fogging resistance, the content of the sensitizer is set to 1.0 part by mass of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone. , about 0.5 to 3.0 parts by mass, more preferably about 0.7 to 2.3 parts by mass.

The heat-sensitive recording layer, for example, uses water as a dispersion medium, and a leuco dye, a specific coloring agent, and optionally a sensitizer, a storage improver, etc. together or separately by stirring and pulverizing in a ball mill, attritor, sand mill, etc. The coating solution for the heat-sensitive recording layer is prepared by mixing and stirring a dispersion liquid finely dispersed so that the average particle size is 2 μm or less, if necessary, a pigment, a binder, an auxiliary agent, etc., by a machine, and the coating amount is dry weight is preferably about 2 to 12 g/m ² , more preferably about 3 to 10 g/m ² . The thermosensitive recording layer can be formed by dividing it into two or more layers as necessary, and the composition and coating amount of each layer may be the same or different.

In the present invention, in order to improve the whiteness of the heat-sensitive recording layer and improve the image uniformity, the heat-sensitive recording layer may contain a fine particle pigment having a high degree of whiteness and an average particle size of 10 μm or less. Specific examples include calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined kaolin, amorphous silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, and surface-treated carbonic acid. Inorganic pigments such as calcium and silica, and organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, polystyrene resin and raw starch particles can be used. The content of the pigment is preferably an amount that does not lower the color density, that is, 50% by mass or less of the total solid content of the thermosensitive recording layer.

Various resins are usually used as a binder in the coating liquid for the thermosensitive recording layer. Examples of such binders include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, carboxy modified polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, styrene-butadiene copolymer, Urea resins, melamine resins, amide resins, polyurethane resins and the like are included. At least one of these is blended in an amount of preferably about 5 to 50% by mass, more preferably about 10 to 40% by mass, based on the total solid content of the thermosensitive recording layer. When the medium of the coating liquid for the thermosensitive recording layer is water, the hydrophobic resin may be used in the form of latex.

Examples of auxiliary agents include dispersing agents such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and fatty acid metal salts, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, and the like. waxes, hydrazide compounds such as adipic acid dihydrazide, glyoxal, boric acid, dialdehyde starch, methylol urea, glyoxylate, epoxy compounds and other waterproofing agents, antifoaming agents, coloring dyes, fluorescent dyes, and the like.

[Undercoat layer]
In the present invention, an undercoat layer may be provided between the support and the heat-sensitive recording layer, if desired. Thereby, the recording sensitivity can be enhanced.

The undercoat layer preferably contains an oil-absorbing pigment having an oil absorption of 70 ml/100 g or more, particularly about 80 to 150 ml/100 g, and/or plastic hollow particles and/or thermally expandable particles. Here, the oil absorption is a value obtained according to the method described in JIS K 5101.

Various oil-absorbing pigments can be used, and specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle size of primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, more preferably about 0.02 to 3 μm. The content of the oil-absorbing pigment can be selected from a wide range, but is generally preferably about 2 to 95% by mass, more preferably about 5 to 90% by mass, of the total solid content of the undercoat layer.

Examples of plastic hollow particles include those conventionally known, such as particles having a hollowness of about 50 to 99%, the film material of which is made of an acrylic resin, a styrene resin, a vinylidene chloride resin, or the like. Here, the hollowness ratio is a value obtained by the following formula (d/D)×100. In the formula, d represents the inner diameter of the organic hollow particles, and D represents the outer diameter of the organic hollow particles. The average particle diameter of the plastic hollow particles is preferably about 0.5 to 10 μm, more preferably about 1 to 6 μm. The content ratio of the plastic hollow particles can be selected from a wide range, but is generally preferably about 2 to 90% by mass, more preferably about 5 to 70% by mass, of the total solid content of the undercoat layer.

When the oil-absorbing inorganic pigment is used in combination with the plastic hollow particles, the content ratio of the oil-absorbing inorganic pigment and the plastic hollow particles is within the above-mentioned range, and the total amount of the oil-absorbing inorganic pigment and the plastic hollow particles is the total amount of the undercoat layer. About 5 to 90 mass % of the total solid content is preferable, and about 10 to 80 mass % is more preferable.

The undercoat layer is generally formed by coating and drying on a support a coating liquid for the undercoat layer prepared by mixing and stirring pigments, binders, auxiliaries and the like using water as a medium. The coating amount of the undercoat layer coating solution is not particularly limited, but is preferably about 3 to 20 g/m ² in terms of dry mass, more preferably about 5 to 12 g/m ² .

The binder can be appropriately selected from those that can be used in the heat-sensitive recording layer. In particular, oxidized starch, starch-vinyl acetate graft copolymer, polyvinyl alcohol, styrene-butadiene latex, and the like are preferred from the viewpoint of improving coating film strength. Although the content of the binder can be selected from a wide range, it is generally preferably about 5 to 30% by mass, more preferably about 10 to 20% by mass, of the total solid content of the undercoat layer.

[Protective layer]
The heat-sensitive recording material of the present invention preferably has a protective layer on the heat-sensitive recording layer for the purpose of improving the storability of the recorded image against chemicals such as plasticizers and oils, or improving the recording suitability.

For the protective layer, for example, a protective layer coating solution prepared by mixing and stirring a binder, a waterproofing agent, a pigment, an auxiliary agent, etc. using water as a dispersion medium is applied in an amount of dry weight of preferably 0.5. It is formed by coating and drying on the heat-sensitive recording layer so as to be about 5 to 15 g/m ² , more preferably about 1.0 to 8 g/m ² .

Specific examples of binders include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. , ionomer-type urethane-based resin latex, and the like.

Examples of pigments contained in the protective layer include pigments such as kaolin, aluminum hydroxide, precipitated calcium carbonate, and fine particle silica. Among them, kaolin and aluminum hydroxide are preferably used because they cause little decrease in barrier properties against chemicals such as plasticizers and oils and also cause little decrease in recording density.

The protective layer may be formed using a binder and one or more of various auxiliary agents without using a pigment, or may be formed using a binder and a pigment in combination. When used in combination, the content of the binder is not particularly limited and can be appropriately selected from a wide range. more preferred. In addition, the content of the pigment is not particularly limited and can be appropriately selected from a wide range. .

Lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax and ester wax, and surfactants such as sodium dioctylsulfosuccinate (dispersant, wetting agent) may be added to the protective layer coating solution as necessary. , antifoaming agents, and water-soluble polyvalent metal salts such as potassium alum and aluminum acetate. Moreover, in order to further improve the water resistance, water resistance agents such as glyoxal, boric acid, glyoxylate, dialdehyde starch, hydrazide compounds, and epoxy compounds can be used together.

In the protective layer, 2-(2'-hydroxy-3'-dodecyl-5'-methylphenyl) microcapsules encapsulating an ultraviolet absorber that is liquid at room temperature such as benzotriazole, out of the total solid amount of the protective layer , The ultraviolet absorber is preferably about 2 to 40% by mass, more preferably about 2 to 35% by mass, more preferably about 3 to 30% by mass, so that the background yellows due to light exposure. and fading of recorded images can be remarkably suppressed.

[Other layers]
In the present invention, if necessary, a back layer containing a pigment and a binder as main components can be provided on the opposite side of the support to the heat-sensitive recording layer. This makes it possible to further improve storage stability, curl aptitude and printer runnability. In addition, various applications in the field of thermosensitive recording material manufacturing, such as applying adhesive treatment to the back surface to process it into an adhesive label, providing a magnetic recording layer, a coating layer for printing, a thermal transfer recording layer, an inkjet recording layer, etc. Known techniques can be applied as needed.

A linerless label that does not require a release paper can be produced by coating a release layer containing silicon on the protective layer and coating the back surface with an adhesive.

[Thermal recording material]
The method of forming the thermosensitive recording layer, and optionally the undercoat layer, protective layer, and back layer is not particularly limited, and examples thereof include bar coating, air knife coating, vari-bar blade coating, pure blade coating, rod blade coating, and short dwell coating. , curtain coating, die coating, etc., if necessary, the undercoat layer coating solution is coated on the support and dried, then the heat-sensitive recording layer coating solution and protective layer coating solution are applied on the undercoat layer. It is formed by a method such as coating and drying.

The undercoat layer is preferably a layer formed by a blade coating method. This makes it possible to form a heat-sensitive recording layer having a uniform thickness without unevenness of the support, to increase the recording sensitivity, and to improve the barrier properties of the protective layer provided as necessary. The blade coating method includes not only the coating method using a blade represented by the bevel type and the bent type, but also the rod blade method, the bill blade method, and the like.

In the present invention, at least one layer formed on the support is preferably a layer formed by a curtain coating method. As a result, a layer having a uniform thickness can be formed, and the recording sensitivity can be enhanced, and the barrier properties against oil, plasticizer, alcohol, etc. can be enhanced. The curtain coating method is a method in which the coating liquid is flowed down and allowed to fall freely, and is coated on the support in a non-contact manner. It is not particularly limited. In the curtain coating method, layers having a more uniform thickness can be formed by simultaneous multi-layer coating. In simultaneous multi-layer coating, each layer may be formed by coating after laminating each coating liquid and then drying to form each layer, or after coating the coating liquid for forming the lower layer, the lower layer coated surface is wetted without drying. A coating liquid for forming the upper layer may be applied on the surface coated with the lower layer while the coating is still in place, and then dried to form each layer. In the present invention, from the viewpoint of improving the barrier property, it is preferable to simultaneously coat the thermosensitive recording layer and the protective layer in multiple layers.

In the present invention, from the viewpoint of enhancing recording sensitivity and improving image uniformity, super calendering, soft calendering, or the like is performed in an optional process after the formation of each layer or after the formation of all layers. It is preferable to perform smoothing processing using a known method.

In the present invention, in order to increase the added value of the product, a multi-color thermosensitive recording material can also be used. In general, a multicolor thermosensitive recording material is an attempt to utilize a difference in heating temperature or a difference in heat energy, and is generally constructed by sequentially laminating a high-temperature color-developing layer and a low-temperature color-developing layer that develop different color tones on a support. These are roughly classified into two types, the decolorizing type and the additive type. A method using a microcapsule and a multicolor thermosensitive recording material using composite particles composed of an organic polymer and a leuco dye are used. There is a way to manufacture

The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these. "Parts" and "%" indicate "parts by mass" and "% by mass", respectively, unless otherwise specified.

Example 1
・Preparation of coating solution for undercoat layer Plastic hollow particle dispersion (trade name: Ropake SN-1055, hollowness ratio: 55%, average particle size: 1.0 µm, manufactured by Dow Chemical Company, solid content concentration: 26.5% by mass) 120 parts, 50% aqueous dispersion of calcined kaolin (trade name: Ansilex, manufactured by BASF) (average particle size: 0.6 μm), styrene-butadiene latex (trade name: L-1571, Asahi Kasei Chemicals Co., Ltd.) (Concentration of solid content: 48 mass %), 50 parts of a 10% aqueous solution of oxidized starch, and 20 parts of water were mixed to obtain a coating solution for an undercoat layer.

Preparation of liquid A (leuco dye dispersion) 100 parts of 3-di(n-butyl)amino-6-methyl-7-anilinofluorane, sulfone-modified polyvinyl alcohol (trade name: Goselan L-3266, Nippon Synthetic Chemical San Nopco Co., Ltd.), 10 parts of a 5% emulsion of a natural oil-based antifoaming agent (trade name: Nopco 1407H, San Nopco Co., Ltd.), and 90 parts of water. Liquid A was obtained by pulverizing until the median diameter became 0.5 μm by a distribution measuring device SALD2200 (manufactured by Shimadzu Corporation).

Preparation of liquid B (color agent dispersion) 100 parts of 4,4'-bis(3-tosylureido)diphenylmethane, 20% aqueous solution of sulfone-modified polyvinyl alcohol (trade name: Goselan L-3266, manufactured by Nippon Synthetic Chemical Co., Ltd.) A composition consisting of 50 parts, 10 parts of a 5% emulsion of a natural oil-based antifoaming agent (trade name: Nopco 1407H, manufactured by San Nopco), and 90 parts of water was subjected to a sand mill with a laser diffraction particle size distribution analyzer SALD2200 (Shimadzu Corporation). (manufactured by Co., Ltd.) until the median diameter became 1.0 μm to obtain liquid B.

Preparation of solution C (colorant dispersion) 100 parts of 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, sulfone-modified polyvinyl alcohol (trade name: Goselan L-3266, manufactured by Nippon Synthetic Chemical Co., Ltd.) A composition consisting of 50 parts of a 20% aqueous solution, 10 parts of a 5% emulsion of a natural oil-based antifoaming agent (trade name: Nopco 1407H, manufactured by San Nopco), and 90 parts of water was subjected to a sand mill with a laser diffraction particle size distribution analyzer SALD2200 ( (manufactured by Shimadzu Corporation) until the median diameter became 1.0 μm to obtain liquid C.

Preparation of solution D (sensitizer dispersion) 100 parts of diphenyl sulfone, 50 parts of 20% aqueous solution of sulfone-modified polyvinyl alcohol (trade name: Goselan L-3266, manufactured by Nippon Synthetic Chemical Co., Ltd.), natural oil-based antifoaming agent ( A composition consisting of 10 parts of a 5% emulsion (product name: Nopco 1407H, manufactured by San Nopco Co., Ltd.) and 90 parts of water is subjected to a sand mill with a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation) to determine a median diameter of 1.0 μm. Liquid D was obtained by pulverizing until

Preparation of coating liquid for thermosensitive recording layer 20 parts of A liquid, 32.5 parts of B liquid, 15 parts of C liquid, 25 parts of D liquid, aluminum hydroxide (trade name: Hygilite H-42, average particle size 1.0 μm , Showa Denko Co., Ltd.) 35 parts, 150 parts of 10% solution of oxidized starch, 30 parts of 10% aqueous solution of completely saponified polyvinyl alcohol (trade name: PVA110, manufactured by Kuraray Co., Ltd.), zinc stearate dispersion (trade name: Hydrin Z-8-36, solid content concentration 36%, manufactured by Chukyo Yushi Co., Ltd.) 22.2 parts, paraffin wax (trade name: Hydrin P7, solid content concentration 30%, manufactured by Chukyo Yushi Co., Ltd.) 6.7 parts, and water 100 A coating solution for a thermosensitive recording layer was obtained by mixing the composition consisting of the following parts.

・Preparation of thermal recording material As a support, a fine paper with a basis weight of 58 g / m ² (neutral paper with a hot water extraction pH of 8.0, ash content of 7% by mass) was coated on one side with a coating solution for the undercoat layer after drying. An undercoat layer was formed by coating and drying by a blade coating method using a blade coater so that the mass was 5.5 g/m ² . After coating and drying by a curtain coating method using a slide hopper type curtain coating device so as to obtain 5 g/m ² , a super calendering treatment was performed to obtain a thermal recording medium.

Example 2
A heat-sensitive recording material was prepared in the same manner as in Example 1, except that in the preparation of the coating solution for the thermosensitive recording layer of Example 1, 32.5 parts of solution B was changed to 37.5 parts, and 15 parts of solution C was changed to 10 parts. Obtained.

Example 3
A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the coating solution for the thermosensitive recording layer of Example 1, 32.5 parts of solution B was changed to 10 parts and 15 parts of solution C was changed to 32.5 parts. Obtained.

Example 4
In the preparation of the coating solution for the thermosensitive recording layer of Example 1, 25 parts of D solution was added to 7.5 parts, and aluminum hydroxide (trade name: Higilite H-42, average particle size: 1.0 µm, manufactured by Showa Denko KK). A thermal recording material was obtained in the same manner as in Example 1, except that 35 parts was changed to 42 parts.

Example 5
In the preparation of the coating solution for the thermosensitive recording layer of Example 1, 25 parts of D solution was added to 42.5 parts, and aluminum hydroxide (trade name: Higilite H-42, average particle size: 1.0 μm, manufactured by Showa Denko KK). A thermal recording material was obtained in the same manner as in Example 1 except that 35 parts was changed to 28 parts.

Example 6
In the preparation of the coating liquid for the thermosensitive recording layer of Example 1, 1,2-di(3-methylphenoxy)ethane (trade name: KS232S, manufactured by Sanko Co., Ltd., solid content concentration 50%) was used instead of 25 parts of D liquid. A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 20 parts of

Example 7
In the preparation of solution D (sensitizer dispersion) of Example 1, the same amount of di-p-methylbenzyl oxalate (trade name: HS-3520R-N2, manufactured by DIC Corporation) was used instead of 100 parts of diphenylsulfone. ) was used to obtain a thermal recording material in the same manner as in Example 1.

Example 8
The heat-sensitive recording material of Example 1 was prepared in the same manner as in Example 1, except that fine paper with a basis weight of 58 g/m ² (acidic paper with a hot water extraction pH of 5.3 and an ash content of 4% by mass) was used as the support. A heat-sensitive recording material was obtained.

Comparative example 1
A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the coating solution for the thermosensitive recording layer of Example 1, 32.5 parts of solution B was changed to 47.5 parts and 15 parts of solution C was changed to 0 part. Obtained.

Comparative example 2
A thermosensitive recording material was prepared in the same manner as in Example 1 except that in the preparation of the coating solution for the thermosensitive recording layer of Example 1, 32.5 parts of solution B was changed to 0 parts and 15 parts of solution C was changed to 47.5 parts. Obtained.

Comparative example 3
In the preparation of solution C (color agent dispersion) of Example 1, instead of 100 parts of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, the same amount of 2-phenylsulfonylamino-N,N A thermal recording material was obtained in the same manner as in Example 1 except that '-diphenylurea was used.

Comparative example 4
In the preparation of solution C (coloration agent dispersion) of Example 1, instead of 100 parts of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, the same amount of 4-hydroxy-4'-isopropoxy A thermal recording material was obtained in the same manner as in Example 1, except that diphenylsulfone was used.

The thermal recording media prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were subjected to the following evaluations, and the results are shown in Tables 1 and 2.

[Recording Density]
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.24 mJ / dot, and the resulting printed portion was measured with a Macbeth densitometer (RD- 914, manufactured by Macbeth) in the visual mode. The larger the numerical value, the higher the print density. Practically, a recording density of 1.10 or more is required.

[Plasticizer resistance]
A wrap film (trade name: Hi-Wrap KMA-W, manufactured by Mitsui Chemicals, Inc.) is wrapped around a polycarbonate pipe (diameter of 40 mm) in a single layer, and a thermosensitive recording medium after recording in the recording density measurement is placed thereon. A wrap film was wrapped thereon in a single layer and allowed to stand at 40° C. for 24 hours. Then, the storage rate of the recorded portion was obtained by the following formula. The storage rate of the recording density after processing is 80% or more, and there is no problem in use.
Preservation rate (%)=(recording density after processing/recording density before processing)×100

[Heat resistance evaluation]
Each thermal recording material was left at 70° C. for 24 hours, and the blank portion was measured with a Macbeth densitometer. A smaller value is more preferable, and a value of 0.20 or less after treatment poses no problem in use.

Claims (6)

A heat-sensitive recording material having a heat-sensitive recording layer containing at least a leuco dye and a colorant on a support, wherein the colorant is 4,4'-bis(3-tosylureido)diphenylmethane and 3,3'-diallyl -A thermal recording material containing 4,4'-dihydroxydiphenyl sulfone. A ratio of 0.2 to 4.0 parts by mass of the 4,4'-bis(3-tosylureido)diphenylmethane to 1.0 parts by mass of the 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone The heat-sensitive recording material according to claim 1, which is contained in. The thermosensitive recording layer further contains a sensitizer, and the content of the sensitizer is 0.5 per 1.0 parts by mass of the 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone. 3. The thermal recording material according to claim 1, wherein the content is up to 3.0 parts by mass. 4. The sensitizer according to claim 3, wherein the sensitizer contains at least one selected from the group consisting of diphenylsulfone, 1,2-di(3-methylphenoxy)ethane, and di-p-methylbenzyl oxalate. thermal recording material. 5. The thermal recording material according to claim 1, wherein said support is neutral paper. The thermal recording material according to any one of claims 1 to 5, wherein the support has an ash content of 5 to 25% by mass.