JP7770296B2 - Method for manufacturing a thermal recording material - Google Patents

Description

The present invention relates to a method for producing a thermal recording material that can achieve high print density, minimal red cast on the background, and excellent manufacturing stability.

A thermal recording material generally comprises a support and a thermal recording layer containing an electron-donating dye precursor (hereinafter referred to as the dye precursor) and an electron-accepting developer (hereinafter referred to as the developer). When the thermal recording layer is heated with a thermal head, thermal pen, laser light, or the like, the dye precursor and developer react instantaneously to produce a recorded image. Such thermal recording materials offer advantages such as the ability to produce recorded images with relatively simple equipment, ease of maintenance, and the absence of noise. They are used in a wide range of applications, including measurement recorders, facsimiles, printers, computer terminals, label printers, and ticket vending machines. In particular, thermal recording materials have recently been used in financial recording paper, such as receipts for gas, water, and electricity bills, ATM statements from financial institutions, and various receipts, as well as thermal recording labels and tags for POS systems.

These applications demand thermal recording materials that produce high print densities. To meet this requirement, the dye precursors are micronized by wet grinding using a grinder such as a sand grinder, ball mill, attritor, or bead mill. Using micronized dye precursors makes them more easily melted when heated, and the molten dye precursor mixes with the developer at the molecular level, accelerating the color-developing reaction.

In addition, thermal recording materials that develop not only black but also red colors are sometimes used. Red thermal recording materials tend to have a more noticeable red cast on the background than black thermal recording materials, so there is a demand for thermal recording materials that have less red cast on the background.

3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran are known as dye precursors that produce a red color. For example, JP 2006-281473 A (Patent Document 1) describes a multicolor thermal recording material containing 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, which has good color separation between low-temperature printed areas and high-temperature printed areas, excellent lightfastness of image areas of each color tone, and suppressed deterioration of color-developing function even during long-term lightfastness tests. However, in recent years, the environments in which thermal recording materials are used have become more severe, and thermal recording materials containing 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide or 3-diethylamino-7-chlorofluoran in the thermal recording layer have not been fully satisfactory in terms of reducing red casts on the background.

It is known that background fogging can be improved by using a nonionic surfactant as a dispersant when wet-milling a dye precursor; this is described, for example, in JP-A-6-206374 (Patent Document 2) and JP-A-2002-283727 (Patent Document 3). However, when this technology is used to disperse 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide or 3-diethylamino-7-chlorofluoran, problems with production stability arise, such as gelation of the dispersion containing the dye precursor, and sedimentation and coagulation of the dispersoid. It is also known that background fogging can be improved by using a styrene-maleic acid copolymer as a dispersant when wet-milling a dye precursor; this is described, for example, in JP-A-8-39931 (Patent Document 4). However, when using this technology, there was a problem of worsening red cast on the background of thermal recording materials that use 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide or 3-diethylamino-7-chlorofluoran.

Japanese Patent Application Laid-Open No. 2006-281473 Japanese Patent Application Publication No. 6-206374 Japanese Patent Application Laid-Open No. 2002-283727 Japanese Patent Application Publication No. 8-39931

The object of the present invention is to provide a method for producing a thermal recording material that can produce a thermal recording material with high print density, minimal red cast on the background, and excellent manufacturing stability.

A method for producing a thermal recording material having a thermal recording layer containing a dye precursor and a color developer on a support, wherein the thermal recording layer contains at least one dye precursor selected from 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, and a maleic acid copolymer with an esterification degree of 15% or more and a nonionic surfactant with an HLB value of 10 or more as a dispersant for the dye precursor, and the method comprises wet-pulverizing the dye precursor under conditions where the content of the nonionic surfactant relative to the dye precursor is 0.15 to 4% by mass.

The present invention provides a method for producing a thermal recording material that can achieve high print density, minimal red cast on the background, and excellent manufacturing stability.

The present invention will be explained in more detail below.

In the present invention, at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran contained as a dye precursor in the thermal recording layer is wet-pulverized using a maleic acid copolymer with an esterification degree of 15% or more and a nonionic surfactant with an HLB value of 10 or more as dispersants, with the content of the nonionic surfactant relative to the dye precursor being 0.15% by mass or more and 4% by mass or less. If the HLB value of the nonionic surfactant is less than 10, gelation is likely to occur when obtaining the dye precursor dispersion, reducing production stability. Furthermore, if the content of the nonionic surfactant is less than 0.15% by mass, a reddish cast will occur on the background, and if the content of the surfactant exceeds 4% by mass, sufficient print density will not be obtained.

In the present invention, nonionic surfactants have hydrophilic groups composed of hydroxyl groups or ether bonds that do not ionize in water. Examples include polyoxyethylene octylphenyl ether, polyoxyethylene-2-ethylhexyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene tridecyl ether, polyoxyethylene castor oil ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyalkylene alkyl ether, polyoxyethylene oleate, polyoxyethylene nonylphenyl ether, sorbitan laurate, sorbitan stearate, sorbitan oleate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan oleate, polyoxyethylene sorbitan trioleate, polyoxyethylene polystyrene phenyl ether, polyethylene glycol, polyoxyethylene polyoxypropylene ether, polyoxyethylene polyoxypropylene alkyl ether, and polyoxyethylene fatty acid esters. These surfactants may be used alone or in combination of two or more. Such nonionic surfactants can be commercially available; for example, Emulgen® MS-110 (polyoxyethylene polyoxypropylene alkyl ether) and Rheodol® TW-L120 (polyoxyethylene sorbitan monolaurate) from Kao Corporation are suitable. Furthermore, in the present invention, a nonionic surfactant content of 0.2% to 4% by mass relative to the total amount of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran contained in the thermosensitive recording layer is preferably in the range of 0.2% to 4% by mass, since this reduces background red cast, provides a thermosensitive recording material with high print density, and excellent manufacturing stability. Furthermore, a nonionic surfactant with an HLB value of 10 or more and 18 or less is preferably in the range of 10 to 18, since this reduces background red cast, provides a thermosensitive recording material with high print density, and excellent manufacturing stability.

The maleic acid copolymer used in the wet grinding of the dye precursor in this invention is a copolymer containing maleic acid as a monomer unit, in which 15% or more of the maleic acid monomer units are esterified (i.e., the degree of esterification is 15% or more). If the degree of esterification is less than 15%, sufficient production stability cannot be achieved even when an appropriate amount of the above-mentioned nonionic surfactant is used in combination. Maleic acid copolymers can be obtained by radical copolymerization of maleic anhydride with various known monomers, followed by esterification and hydrolysis of the maleic anhydride units of the copolymer. Examples include copolymers of α-olefins and maleic acid, copolymers of alkyl vinyl ethers and maleic acid, and copolymers of styrene derivatives and maleic acid. In particular, the maleic acid copolymer used in the present invention preferably has an esterification degree of 15% or more and a mass average molecular weight of 5,000 to 60,000, which allows for excellent production stability when dispersing 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide or 3-diethylamino-7-chlorofluoran, preventing high viscosity and poor pulverization.

One or more of these maleic acid copolymers can be used as needed. Commercially available maleic acid copolymers can also be used; for example, Arakawa Chemical Industries, Ltd.'s Polymaron (registered trademark) 1318 (degree of esterification 70%, average molecular weight 50,000-60,000) and KS-1333 (degree of esterification 70%, average molecular weight 10,000-20,000) are suitable.

In the present invention, 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran can be used in combination. The ratio of the two can be selected at will, taking into consideration the color tone of the image area and the light resistance of the image area. However, a ratio of 3-diethylamino-7-chlorofluoran of 50% or more is preferred, as this results in a vivid vermilion color tone in the image area.

In the present invention, at least one compound selected from 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran is preferably wet-milled using water as the dispersion medium. Examples of dispersion media other than water include water-compatible organic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, and ethylene glycol. From the perspective of dispersion stability, it is preferable that the proportion of water in the entire dispersion medium be 90% by mass or more. In the present invention, "use as a dispersant" means that the above-mentioned dispersion medium contains these compounds during wet milling.

In the present invention, 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran are ground using a variety of wet grinders, such as a sand grinder, ball mill, attritor, or bead mill, until the volume average particle size of the dispersoid containing at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran is preferably 0.1 to 1.5 μm, and then used to prepare the thermosensitive layer coating liquid for the thermosensitive recording layer. When the thermosensitive recording layer contains at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, it is preferable to wet-grind the 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran separately, from the perspective of dispersion stability. Furthermore, if the volume average particle diameter of the dye precursor described above is greater than 1.5 μm, print density may deteriorate. This is because, when a dye precursor with a large volume average particle diameter is used, the dye precursor is less likely to melt when heated, and the molten dye precursor is less likely to mix with the developer at the molecular level, suppressing the color-developing reaction.

The above-mentioned 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran can be commercially available products. An example of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide is Red-40, available from Yamamoto Chemical Industries, Ltd., and an example of 3-diethylamino-7-chlorofluoran is Red-8, also available from Yamamoto Chemical Industries, Ltd. Furthermore, the volume average particle size in this invention refers to the volume average particle size calculated from the particle size distribution obtained by laser diffraction/scattering. Specifically, this can be measured using the MICROTRAC® series manufactured by Microtrac-Bell, Inc., the LA series manufactured by Horiba, Ltd., the SALD® series manufactured by Shimadzu Corporation, or the LS series manufactured by Beckman Coulter, Inc.

In the present invention, when wet-grinding 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, other dispersants that can be used in combination with nonionic surfactants with an HLB value of 10 or more and maleic acid copolymers with an esterification degree of 15% or more include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, phosphate-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and epoxy-modified polyvinyl alcohol. Examples of surfactants include polyvinyl alcohols such as vinyl alcohol, starch or derivatives thereof, cellulose derivatives, proteins such as gelatin and casein, acid-neutralized chitosan, sodium alginate, polyvinylpyrrolidone, ethylene/acrylic acid copolymer salts, styrene/acrylic acid copolymer salts, water-soluble polymer compounds such as polyacrylates, anionic low-molecular surfactants such as dodecylbenzenesulfonates, dialkyl sulfosuccinates, alkylnaphthalenesulfonates, alkyldiphenyletherdisulfonates, and fatty acid metal salts, and nonionic surfactants having an HLB value of less than 10, but are not limited to these, and one or more surfactants can be used as needed. In the present invention, the total solids content of the maleic acid copolymer with an esterification degree of 15% or more, the nonionic surfactant with an HLB value of 10 or more, and the other dispersants that can be used in combination is preferably in the range of 3 to 30% by mass relative to the total amount of dispersoids in the dispersion containing at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran.

In the present invention, when wet-milling at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, the particle size of the media used can be selected appropriately depending on the desired particle size of the dispersoid to be obtained. However, to achieve a sharp particle size distribution and promote atomization, beads with a diameter in the range of 0.2 to 2.0 mm are preferred, and examples of materials include glass, zirconia, and alumina. The bead filling rate in the milling chamber is preferably 30 to 95% by volume. Furthermore, when milling 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, it is desirable to keep the temperature of the dispersion below 50°C. Processing at temperatures higher than 50°C may cause gelation.

In the present invention, when wet-milling at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, it is possible to wet-mill them together with an inorganic dispersoid in order to reduce reddish background color. Examples of inorganic dispersoids include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, amorphous calcium silicate, calcium sulfate, calcium silicate, magnesium carbonate, magnesium silicate, magnesium phosphate, magnesium oxide, magnesium hydroxide, aluminum hydroxide, aluminum silicate, alumina, colloidal alumina, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, colloidal silica, barium sulfate, zinc sulfide, zinc carbonate, satin white, lithopone, zeolite, hydrotalcite, and hydrated halloysite. The proportion of inorganic dispersoids in the total dispersoids is preferably less than 20% by weight. This allows for the production of a thermal recording material with excellent stability. Furthermore, the dispersion liquid after grinding at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran may be heated to a temperature that does not impair the effects of the present invention, and a coating layer made of an organic polymer may be formed on the surface of the ground particles.

Thermal recording materials of the present invention preferably contain 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran in a total content of 1 to 30% by mass relative to the total solids content of the thermal recording layer, since this results in thermal recording materials with high print density and excellent manufacturing stability.

The heat-sensitive recording layer of the heat-sensitive recording material of the present invention can contain at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran as dye precursors, as well as an appropriate combination of dye precursors generally used in pressure-sensitive recording materials and heat-sensitive recording materials. Specific examples include, but are not limited to, those listed below.

Black dye precursors include 3-di-n-butylamino-6-methyl-7-anilinofluoran, 3-di-n-pentylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-di-n-butylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 3-diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran, 3-(N-cyclopentyl-N-ethyl)amino-6-methyl-7- Anilinofluoran, 3-(N-isoamyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-4-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-4-toluidino)-6-methyl-7-(4-toluidino)fluoran, 3-(N-methyl-N-tetrahydrofurfuryl)amino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-(4-n-butylphenylamino)fluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran,

Red dye precursors include 3,3-bis(1-n-butyl-2-methylindol-3-yl)tetrachlorophthalide, 3,3-bis(1-n-butylindol-3-yl)phthalide, 3,3-bis(1-n-pentyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-n-hexyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-n-octyl-2-methylindol-3-yl)phthalide, 3, 3-bis(1-methyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide, 3,3-bis(1-propyl-2-methylindol-3-yl)phthalide, 3,3-bis(2-methylindol-3-yl)phthalide, rhodamine B-anilinolactam, rhodamine B-(o-chloroanilino)lactam, rhodamine B-(p-nitroanilino)lactam, 3-diethylamino 3-diethylamino-5-methyl-7-dibenzylaminofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6-methoxyfluoran, 3-diethylamino-6-methylfluoran, 3-diethylamino-6-methyl-7-chloro-8-benzylfluoran, 3-diethylamino-6,7-dimethylfluoran, 3-diethylamino-6,8-dimethylfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-(N-acetyl-N-methyl)aminofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-n-propoxyfluoran, 3-diethylamino-7-p-methylphenylfluoran, 3-diethylamino-7,8-benzofluoran, 3-diethylaminobenzo[a]fluoran, 3-diethylaminobenzo[c]fluoran, 3-dimethylamino-7-methoxyfluoran, 3-dimethylamino ethylamino-6-methyl-7-chlorofluoran, 3-dimethylamino-7-methylfluoran, 3-dimethylamino-7-chlorofluoran, 3-(N-ethyl-p-toluidino)-7-methylfluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-chlorofluoran, 3-(N-ethyl-N-isoamyl)amino-7,8-benzofluoran, 3-(N-ethyl-N-isoamyl)amino-7-methylfluoran, 3-(N-ethyl-N-n-octyl)amino-6-methyl-7-chlorofluoran, 3-(N-ethyl-N-n-octyl)amino-7,8-benzofluoran, 3-(N-ethyl-N-n-octyl)amino-7-methylfluoran, 3-(N-ethyl-N-n-octyl)amino-7-chlorofluoran, 3-(N-ethyl-N-4-methylphenyl)amino-7,8-benzofluoran, 3-(N-ethoxyethyl-N-ethyl)amino No-7,8-benzofluoran, 3-(N-ethoxyethyl-N-ethyl)amino-7-chlorofluoran, 3-di-n-butylamino-6-methyl-7-chlorofluoran, 3-di-n-butylamino-7,8-benzofluoran, 3-di-n-butylamino-7-chlorofluoran, 3-di-n-butylamino-7-methylfluoran, 3-diallylamino-7,8-benzofluoran, 3-diallylamino-7-chlorofluoran, 3 -Di-n-butylamino-6-methyl-7-bromofluoran, 3-cyclohexylamino-6-chlorofluoran, 3-pyrrolidylamino-7-methylfluoran, 3-ethylamino-7-methylfluoran, 3-(N-ethyl-N-isoamyl)amino-benzo[a]fluoran, 3-di-n-butylamino-6-methyl-7-bromofluoran, 3,6-bis(diethylaminofluoran)-γ-(4'-nitro)anilinolactam,

Green dye precursors include 3-(N-ethyl-N-n-hexyl)amino-7-anilinofluoran, 3-(N-ethyl-N-p-tolyl)amino-7-(N-phenyl-N-methyl)aminofluoran, 3-(N-ethyl-N-n-propyl)amino-7-dibenzylaminofluoran, 3-(N-ethyl-N-n-propyl)amino-6-chloro-7-dibenzylaminofluoran, 3-(N-ethyl-N-4-methylphenyl)amino-7-(N-methyl-N-phenyl)aminofluoran, and 3-(N-ethyl-4-methylphenyl)amino-7 -dibenzylaminofluoran, 3-(N-ethyl-4-methylphenyl)amino-6-methyl-7-dibenzylaminofluoran, 3-(N-ethyl-4-methylphenyl)amino-6-methyl-7-(N-methyl-N-benzyl)aminofluoran, 3-(N-methyl-N-hexyl)amino-7-anilinofluoran, 3-(N-propyl-N-n-hexyl)amino-7-anilinofluoran, 3-(N-ethoxy-N-n-hexyl)amino-7-anilinofluoran, 3-(N-pentyl-N-allyl)amino-6-methyl-7-anilino fluoran, 3-(N-n-pentyl-N-allyl)amino-7-anilinofluoran, 3-di-n-butylamino-6-chloro-7-(2-chloroanilino)fluoran, 3-di-n-butylamino-6-methyl-7-(2-chloroanilino)fluoran, 3-di-n-butylamino-6-methyl-7-(2-fluoroanilino)fluoran, 3-di-n-butylamino-7-(2-chloroanilino)fluoran, 3-di-n-butylamino-7-(2-chlorobenzylanilino)fluoran, 3,3-bis(4-diethylamino-2-ethoxyphene) Nyl)-4-azaphthalide, 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 3-diethylamino-6-methyl-7-benzylaminofluoran, 3-diethylamino-6-methyl-7-dibenzylaminofluoran, 3-diethylamino-6-methyl-7-n-octylaminofluoran, 3-diethylamino-6-methyl-7-(N-cyclohexyl-N-benzyl)aminofluoran, 3-diethylamino-6-methyl-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl fluoran, 3-diethylamino-6-methyl-7-(3-trifluoromethylanilino)fluoran, 3-diethylamino-6-methyl-7-(2-ethoxyanilino)fluoran, 3-diethylamino-6-methyl-7-(4-ethoxyanilino)fluoran, 3-diethylamino-6-chloro-7-(2-chloroanilino)fluoran, 3-diethylamino-6-chloro-7-dibenzylaminofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-ethoxyanilinofluoran Diethyl-7-anilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-methylanilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-n-octylaminofluoran, 3-diethylamino-7-p-chloroanilinofluoran, 3-diethylamino-7-p-methylphenylanilinofluoran, 3-diethylamino-7-(N-cyclohexyl-N-benzyl)aminofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-diethylamino amino-7-(3-trifluoromethylanilino)fluoran, 3-diethylamino-7-(2-trifluoromethylanilino)fluoran, 3-diethylamino-7-(2-ethoxyanilino)fluoran, 3-diethylamino-7-(4-ethoxyanilino)fluoran, 3-diethylamino-7-(2-chlorobenzylanilino)fluoran, 3-dimethylamino-6-chloro-7-dibenzylaminofluoran, 3-dimethylamino-6-methyl-7-n-octylaminofluoran, 3-dimethylamino-7-dibenzylaminofluoran, 3-di Methylamino-7-n-octylaminofluoran, 3-di-n-butylamino-7-(2-fluoroanilino)fluoran, 3-anilino-7-dibenzylaminofluoran, 3-anilino-6-methyl-7-dibenzylaminofluoran, 3-pyrrolidino-7-dibenzylaminofluoran, 3-pyrrolidino-7-(4-cyclohexylanilino)fluoran, 3-dibenzylamino-6-methyl-7-dibenzylaminofluoran, 3,7-bis(dibenzylamino)fluoran, 3-dibenzylamino-7-(2-chloroanilino)fluoran,

Blue dye precursors include 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylaminophenyl)phthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-methyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-aminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-methylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-ethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-ethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-ethylaminophenyl)-4-azaphthalide, Indol-3-yl)-3-(2-ethoxy-4-dimethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-propylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-butylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-pentylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-pentylaminophenyl)-4-azaphthalide 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-hexylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-dihydroxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-dichloroaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-dibromoaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diallylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diallylaminophenyl)-4-azaphthalide yl)-3-(2-ethoxy-4-dihydroxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-dimethoxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethoxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-dicyclohexylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-propoxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-propoxyaminophenyl)-4-azaphthalide -yl)-3-(2-ethoxy-4-di-n-butoxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-n-hexyloxyaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-methylcyclohexylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-methoxycyclohexylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-di-methoxycyclohexylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-pyrrolidylaminophenyl)-4-azaphthalide, 3-( 1-ethyl-2-methylindol-3-yl)-3-(3-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2,3-diethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-chloro-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(3-chloro-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol- 3-(2-methyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(3-bromo-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-n-propyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(3-methyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-n-propyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-allyl-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-hydroxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-cyano-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-cyclohexylethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-methylethoxy-4 -diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-cyclohexylethyl-4-diethylaminophenyl)-4-azaphthalide, 3-(2-ethylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-chloroindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-bromoindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-ethylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide 3-(1-ethyl-2-propylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methoxyindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-ethoxyindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-ethoxyindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-phenylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-aza phthalide, 3-(1-ethyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4,7-diazaphthalide, 3-(1-ethyl-4,5,6,7-tetrachloro-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-4-nitro-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-4-methoxy-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-4-methylamino-2-methylindol-3-yl)- 3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethyl-4-methyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-chloro-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-bromo-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-methyl-2-methylindol-3-yl)-3-(2-ethoxy-4- diethylaminophenyl)-4-azaphthalide, 3-(1-methyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3-(1-n-propyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-n-butyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-n-butyl-2-indol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3-(1-n-pentyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)- aminophenyl)-4-azaphthalide, 3-(1-n-hexyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-n-hexyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3-(1-n-octyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-n-octyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3-(1-n-octyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, diethylaminophenyl)-4,7-diazaphthalide, 3-(1-n-nonyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-methoxy-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-ethoxy-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-phenyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(1-n-pentyl-2-methylindol-3-yl)-3-(2-ethoxy-4- Examples of such compounds include 3-(1-n-heptyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3-(1-n-nonyl-2-methylindol-3-yl)-3-(2-ethoxy-4-diethylaminophenyl)-7-azaphthalide, 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-dimethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylamino-2-n-hexyloxyphenyl)-4-azaphthalide. These compounds can be used alone or in combination of two or more.

Some functional dye precursors have absorption in the near-infrared region. When this dye precursor is used alone or in combination with other dye precursors as a dye precursor for high-temperature color development, the high-temperature color development image has absorption in the near-infrared region, making it possible to create an image that can be automatically read using near-infrared light. When this dye precursor is used in the present invention, it becomes possible to use images that absorb only in the visible region and images that absorb in the near-infrared region in combination, resulting in a highly secure recording material.

Examples of such dye precursors that have absorption in the near-infrared region include 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, 3,3-bis[1,1-bis(4-pyrrolidino phenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3-[1,1-bis(p-diethylaminophenyl)ethylene-2-yl]-6-dimethylaminophthalide, 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 3-[p-(p-dimethylaminoanilino)anilino]-6-methylfluoran, 3-[p-(p-dimethylaminoanilino)anilino]-6-methylfluoran 3-(p-n-butylaminoanilino)-6-methyl-7-chlorofluoran, 3-[p-(p-anilinoanilino)anilino]-6-methyl-7-chlorofluoran, 3-[p-(p-chloroanilino)anilino]-6-methyl-7-chlorofluoran, 3-[p-(p-chloroanilino)anilino]-6-methyl-7-chlorofluoran, 3-[p-(p-chloroanilino)anilino]-6-methyl-7-chlorofluoran, 3-(N-p-tolyl-N-ethylamino)-6,8,8-trimethyl-9-ethyl-8,9-di Examples of dye precursors include hydro-(3,2,e)pyridofluoran, 3-di(n-butyl)amino-6,8,8-trimethyl-8,9-dihydro-(3,2,e)pyridofluoran, 3'-phenyl-7-N-diethylamino-2,2'-spirodi(2H-1-benzopyran), bis(p-dimethylaminostyryl)-p-trisulfonylmethane, and 3,7-bis(dimethylamino)-10-benzoylphenothiazine. These dye precursors can be used alone or in combination with two or more types, as needed. These dye precursors can also be wet dispersed with 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran.

The total content of dye precursors contained in the thermal recording material of the present invention is preferably 1 to 30% by mass based on the total solids content of the thermal recording layer. This allows for sufficient thermal responsiveness.

A variety of known color developers can be used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention. For example, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-octyloxydiphenyl sulfone, 4-hydroxy-4'-dodecyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 2,2'-diallyl-4,4'-sulfonyldiphenyl sulfone, phenol, 3,4-dihydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenyl sulfone, 2,4-bis(phenylsulfonyl)phenol, p-phenylphenol, p-hydroxyacetophenone, 1,1-bis(p-hydroxyphenyl)propane, 1,1-bis(p-hydroxyphenyl)pentane, 1,1-bis(p-hydroxyphenyl)hexane, 1,1-bis(p-hydroxyphenyl)cyclohexane, 2,2-bis(p-hydroxyphenyl)propane Pan, 2,2-bis(p-hydroxyphenyl)hexane, 1,1-bis(p-hydroxyphenyl)-2-ethylhexane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, 1,1-bis(p-hydroxyphenyl)-1-phenylethane, 1,3-bis[2-(p-hydroxyphenyl)-2-propyl]benzene, 1,3-bis[2-(3,4-dihydroxyphenyl)-2-propyl]benzene, 1,4-bis[2-(p-hydroxyphenyl)-2-propyl]benzene, 4,4'-dihydro hydroxydiphenyl ether, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfide, 2,2-bis(4-hydroxyphenyl)methyl acetate, 2,2-bis(4-hydroxyphenyl)butyl acetate, 4,4'-thiobis(2-tert-butyl-5-methylphenol), dimethyl 4-hydroxyphthalate, benzyl 4-hydroxybenzoate, methyl 4-hydroxybenzoate, benzyl gallate, stearyl gallate, salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3,5-di-tert-butyl salicylic acid, 3,5-bis(α-methylbenzyl)salicylic acid, 4-[2'-(4-methoxyphenoxy)ethyloxy]salicylic acid, 3-(octyloxycarbonylamino)salicylic acid or metal salts of these salicylic acid derivatives, N-(4-hydroxyphenyl)-p-toluenesulfonamide, N-(4-hydroxyphenyl)benzenesulfonamide, N-(4-hydroxyphenyl)-1-naphthalenesulfonamide, N-(4-hydroxyphenyl)-2-naphthalenesulfonamide, N-(4-hydroxyphenyl)-p-toluene ... N-(4-hydroxynaphthyl)-p-toluenesulfonamide, N-(4-hydroxynaphthyl)benzenesulfonamide, N-(4-hydroxynaphthyl)-1-naphthalenesulfonamide, N-(4-hydroxynaphthyl)-2-naphthalenesulfonamide, N-(3-hydroxyphenyl)-p-toluenesulfonamide, N-(3-hydroxyphenyl)benzenesulfonamide, N-(3-hydroxyphenyl)-1-naphthalenesulfonamide, N-(3-hydroxyphenyl)-2-naphthalenesulfonamide, 4,4' -bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, 3-(3-tosylureido)phenyl p-toluenesulfonate, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, N-(2-{[(4-methylphenyl)carbamoyl]amino}phenyl)benzenesulfonamide, 4-methyl-N-{2-[(phenylcarbamoyl)amino]phenyl}benzenesulfonamide, 4-methyl-N-(2-{[(4-methylphenyl)carbamoyl]amino}phenyl}benzenesulfonamide Examples of suitable bis(ureido)benzoates include, but are not limited to, N-phenylsulfonyl-N'-phenylurea derivatives, N-butylbutyl-4-[3-(p-toluenesulfonyl)ureido]benzoate, 3,3'-(4,4'methylenediphenyl)bis(ureido p-trisulfone), bis{3-[3'-(p-toluenesulfonyl)ureido]benzoate}, 1,5-(3-oxopentylene)bis{3'-[3'-(p-toluenesulfonyl)ureido]benzoate}, and derivatives of N-phenylsulfonyl-N'-phenylurea. These can be used alone or in combination of two or more.

The content ratio of dye precursors and color developers is determined appropriately depending on the types and combinations of these, but it is preferable that the total amount of color developers relative to the total amount of dye precursors be 100 to 500% by mass, and more preferably 150 to 350% by mass.

In the present invention, the thermal recording layer can contain a low-melting, heat-soluble component (hereinafter referred to as a sensitizer) that accelerates the color-developing reaction in order to further improve its thermal responsiveness. In this case, the sensitizer is preferably a compound with a melting point of 60 to 180°C. Specific examples of sensitizers include fatty acid monoamides such as palmitic acid monoamide and stearic acid monoamide, diphenyl sulfone, N-hydroxymethylstearic acid amide, N-stearylstearic acid amide, ethylene bisstearic acid amide, methylene bisstearic acid amide, methylolstearic acid amide, N-stearyl urea, benzyl-2-naphthyl ether, p-toluenesulfonamide, m-terphenyl, 4-benzylbiphenyl, 2,2'-bis(4-methoxyphenoxy)diethyl ether, and α,α'-diphenoxy. Examples of sensitizers include, but are not limited to, o-xylene, bis(4-methoxyphenyl)ether, diphenyl adipate, dibenzyl oxalate, bis(4-methylbenzyl)oxalate, bis(4-chlorobenzyl)oxalate, dimethyl terephthalate, dibenzyl terephthalate, phenyl benzenesulfonate, bis(4-allyloxyphenyl)sulfone, 1,2-bis(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 4-acetylacetophenone, acetoacetic anilides, and fatty acid anilides. These sensitizers can be used alone or in combination of two or more. To achieve sufficient thermal response, the total amount of sensitizers preferably accounts for 5 to 50% by weight of the total solids content of the thermal recording layer.

The heat-sensitive recording layer may further contain a storage stability improver such as a hindered phenol compound, a hindered amine compound, a phosphate ester derivative, or a benzotriazole derivative, as needed.

Specific examples of hindered phenol compounds that may be used as needed in the heat-sensitive recording layer of the present invention include 1,1,2,2-tetrakis(5-cyclohexyl-4-hydroxy-2-methylphenyl)ethane, 1,1,2,2-tetrakis(3-phenyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-tert-butyl-4-hydroxyphenyl)ethane, 1,1,3-tris(3-cyclohexyl-4-hydroxyphenyl)butane, 1,1,3-tris(5-cyclohexyl-4-hydroxy-o-tolyl)butane, 1,1,3-tris(3-cyclohexyl-4-hydroxy-5-methylphenyl)butane, 1,1,3-tris(3-phenyl-4-hydroxyphenyl)butane, and 1,1,3-tris(3-tert-butyl-4-hydroxyphenyl)ethane. (5-phenyl-4-hydroxy-2-methylphenyl)butane, 1,1,3-tris(3-tert-butyl-4-hydroxyphenyl)butane, 1,1,3-tris(5-tert-butyl-4-hydroxy-2-methylphenyl)butane, 1,1,3,3-tetrakis(5-cyclohexyl-4-hydroxy-2-methylphenyl)propane, 1,1,3,3-tetrakis(3-cyclohexyl-4-hydroxyphenyl)propane, 1,1,5,5-tetrakis(5-cyclohexyl-4-hydroxy-2-methylphenyl)pentane, 1,1,3,3-tetrakis(3-cyclohexyl-4-hydroxyphenyl)pentane, 1,1,3,3-tetrakis(3-phenyl-4-hydroxyphenyl)propane, 1,1,3,3 -tetrakis(5-phenyl-4-hydroxy-2-methylphenyl)propane, 1,1,3,3-tetrakis(3-tert-butyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(5-tert-butyl-4-hydroxy-2-methylphenyl)propane, 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(3-methyl-6-tert-butylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(2-methylphenol), 4,4'-thiobis(2, Examples of suitable esters include, but are not limited to, 4,4'-thiobis(2,6-di-tert-butylphenol), 2,2'-thiobis(4-tert-octylphenol), 2,2'-thiobis(3-tert-octylphenol), 4,4'-butylidenebis(6-tert-butyl-m-cresol), 1-[α-methyl-α-(4'-hydroxyphenyl)ethyl]4-[α',α'-bis(4'-hydroxyphenyl)ethyl]benzene, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, and 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane. These compounds can be used singly or in combination as needed.

Specific examples of hindered amine compounds that may be used as needed in the thermosensitive recording layer of the present invention include, but are not limited to, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, succinic acid bis(2,2,6,6-tetramethyl-4-piperidyl)ester, butane-1,2,3,4-tetracarboxylic acid tetrakis[1,2,2,6,6-pentamethyl(4-piperidyl)]ester, and butane-1,2,3,4-tetracarboxylic acid tetrakis[2,2,6,6-tetramethyl(4-piperidyl)]ester. These compounds may be used alone or in combination as needed.

Specific examples of phosphate ester derivatives that may be used as needed in the thermal recording layer of the present invention include triphenyl phosphate, diphenyl phosphate, bis(4-tert-butylphenyl)phosphate, bis(4,6-di-tert-butylphenyl)phosphate, bis(4-chlorophenyl)phosphate, bis(benzyloxyphenyl)phosphate, 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, dimethyloxyphosphate, diethyloxyphosphate, bis(3,5-di-tert-butyl-4-hydroxyphenyl)phosphate, 3,5-di-tert-butyldiphenyl phosphate, Examples include, but are not limited to, diethyl(3,5-di-tert-butyl-4-hydroxyphenyl)phosphate, sodium salt of 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, calcium salt of 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, zinc salt of 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, ammonium salt and potassium salt of 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, and these compounds can be used alone or in combination as needed.

Specific examples of benzotriazole derivatives that may be used as needed in the heat-sensitive recording layer of the present invention include 2-(2-hydroxyphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, t-aminophenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-tert-butylbenzotriazole, 2-(2-hydroxy-3-dodecyl-5-methylphenyl)benzotriazole, 2-[2-hydroxy-4-(2-ethylhexyl)oxyphenyl]benzotriazole, methyl-3-(3-tert-butyl-5-benzotriazolyl-4-hydroxyphenyl)propionate-polyethylene glycol (molecular weight about 300) condensate, 5-tert-butyl-3-(5-chloro-benzotriazolyl)-4-hydroxybenzene-octyl propionate, 2-(2-hydroxy-3-se c-butyl-5-tert-butylphenyl)-5-tert-butylbenzotriazole, 2-(2-hydroxy-4-methoxy-5-sulfophenyl)benzotriazole sodium salt, 2-(2-hydroxy-4-butoxy-5-sulfophenyl)benzotriazole sodium salt, 2,2'-methylenebis(4-methyl-6-benzotriazolylphenol), 2,2'-methylenebis[4-methyl-6-(5-methylbenzotriazolyl)phenol], 2,2'-methylenebis[4-methyl-6-(5-chlorobenzotriazolyl)phenol], 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazol Examples of suitable compounds include, but are not limited to, 2,2'-methylenebis(4-tert-butyl-6-benzotriazolylphenol), 2,2'-propylidenebis(4-methyl-6-benzotriazolylphenol), 2,2'-isopropylidenebis(4-methyl-6-benzotriazolylphenol), 2,2'-isopropylidenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol], and 2,2'-octylidenebis[4-methyl-6-(5-methylbenzotriazolyl)phenol], and these compounds can be used alone or in combination as needed.

The total amount of the hindered phenol compound, hindered amine compound, phosphate ester derivative, or benzotriazole derivative optionally added to the heat-sensitive recording layer of the present invention is preferably 5 to 500% by mass relative to the dye precursor.

In the present invention, the thermosensitive recording layer can contain various pigments depending on the purpose, such as improving sticking resistance and whiteness. Examples include, but are not limited to, white inorganic pigments such as diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, amorphous calcium silicate, calcium sulfate, calcium silicate, magnesium carbonate, magnesium silicate, magnesium phosphate, magnesium oxide, magnesium hydroxide, aluminum hydroxide, aluminum silicate, alumina, colloidal alumina, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, colloidal silica, barium sulfate, zinc sulfide, zinc carbonate, satin white, lithopone, zeolite, hydrotalcite, and hydrated halloysite, as well as organic pigments and hollow particles. One or more pigments can be used as needed. It is preferable to use 5 to 50% by weight of the pigment based on the total solids content of the thermosensitive recording layer.

In the present invention, the thermosensitive recording layer may contain, as a binder, various water-soluble or water-dispersible polymer compounds used in conventional coating processes. Specific examples include starch or derivatives thereof, cellulose derivatives such as hydroxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose, proteins such as gelatin and casein, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide/acrylic acid ester copolymers, acrylamide/acrylic acid ester/methacrylic acid terpolymers, polyacrylates, polymaleates, styrene/maleic acid copolymer salts, ethylene/maleic acid copolymer salts, and isobutylene/maleic acid copolymer salts, as well as water-soluble polymer compounds such as styrene/butadiene copolymers, acrylonitrile/butadiene copolymers, methyl acrylate/butadiene copolymers, acrylonitrile/butadiene/styrene terpolymers, polyvinyl acetate, vinyl acetate/acrylic acid ester copolymers, ethylene/vinyl acetate copolymers, polyacrylates, styrene/acrylic acid ester copolymers, and polyurethanes, but are not limited to these. One or more types may be used as needed. It is preferable to use a binder in the range of 5 to 30% by mass of the total solid content of the thermal recording layer.

Thermal recording layers may also contain higher fatty acid metal salts such as zinc stearate and calcium stearate, and waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, and castor wax to improve sticking resistance. Furthermore, thermal recording layers may contain various hardeners, crosslinking agents, dispersants, surfactants, fluorescent dyes, coloring dyes, antifoaming agents, preservatives, thickeners, antistatic agents, etc. to provide water resistance.

In the present invention, various components other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran contained in the thermosensitive recording layer of the thermosensitive recording material, such as dye precursors other than the aforementioned 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, color developers, sensitizers, shelf-life improvers, pigments, lubricants, and waxes, are preferably prepared into a dispersion and then used to prepare the thermosensitive recording layer coating liquid. This dispersion can be obtained by dry-milling various components other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran and dispersing them in a dispersion medium, or by mixing the various components in a dispersion medium and wet-milling them. In the present invention, the color developer, sensitizer, etc., either alone or together with a dispersant, are preferably ground into fine particles, preferably to a volume average particle size of 0.1 to 5.0 μm, using water as a dispersion medium, in a variety of wet grinders such as a sand grinder, ball mill, attritor, or bead mill, before being used in the preparation of the thermosensitive recording layer coating liquid. Furthermore, dye precursors other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran are preferably ground into fine particles, separately from the color developer, using water as a dispersion medium, in a variety of wet grinders such as a sand grinder, ball mill, attritor, or bead mill, before being used in the preparation of the thermosensitive recording layer coating liquid.

In the present invention, dispersants used to disperse the various components contained in the thermal recording layer other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, phosphoric acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and epoxy-modified polyvinyl alcohol; starch or derivatives thereof; hydroxyethyl cellulose; methyl cellulose; hydroxypropyl cellulose; ethyl cellulose; Examples of dispersants include, but are not limited to, cellulose derivatives such as carboxymethyl cellulose, proteins such as gelatin and casein, acid-neutralized chitosan, sodium alginate, polyvinylpyrrolidone, water-soluble polymers such as diisobutylene/maleic acid copolymer salt, styrene/isobutylene/maleic acid copolymer salt, styrene/maleic acid copolymer salt, ethylene/acrylic acid copolymer salt, styrene/acrylic acid copolymer salt, and polyacrylate salts, anionic low-molecular-weight surfactants such as dodecylbenzenesulfonate, dialkyl sulfosuccinate, alkylnaphthalenesulfonate, alkyldiphenyletherdisulfonate, and fatty acid metal salts, and nonionic surfactants such as acetylene glycol. One or more dispersants may be used as needed. The total amount of dispersants is preferably 0.5 to 30% by mass based on the total amount of dispersoids contained in the dispersion.

When grinding the various components other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran contained in the thermal recording layer, they may be ground together with inorganic pigments such as magnesium silicate, calcium silicate, magnesium carbonate, calcium carbonate, calcium sulfate, magnesium phosphate, magnesium oxide, aluminum oxide, titanium oxide, magnesium hydroxide, aluminum hydroxide, kaolin, talc, and hydrotalcite. Furthermore, the dispersion obtained after grinding the various components other than at least one of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran may be heated in the range of 40 to 80°C, and a coating layer formed from an organic polymer may be formed on the surfaces of the ground particles.

In the present invention, the solid coating amount of the thermosensitive recording layer is preferably 2 to 15 g/ ^m2 . If it is less than 2 g/ ^m2 , the print density in the low thermal energy region may be low, and if it is more than 15 g/ ^m2 , the improvement in various performances of the thermosensitive recording layer may reach saturation, and the production efficiency during coating of the thermosensitive recording layer may decrease.

In the present invention, an undercoat layer may be provided between the support and the thermosensitive recording layer to improve the smoothness and heat insulation of the support, or to prevent various components contained in the support from adversely affecting the thermosensitive recording layer. The undercoat layer contains a binder and various inorganic or organic pigments, and may also contain hollow particles. Other auxiliary agents that may be contained in the undercoat layer include known agents such as lubricants, antifoaming agents, surfactants, preservatives, fluorescent brighteners, dispersants, thickeners, colorants, antistatic agents, and crosslinking agents.

In the present invention, when an undercoat layer is used, the undercoat layer is formed by coating a coating liquid for the undercoat layer, which is prepared by mixing and stirring a pigment, a binder, and an auxiliary agent in a medium such as water, on a support so that the solid coating amount is preferably 1 to 30 g/m ² , more preferably 4 to 20 g/m ² , and then drying the coating liquid.

Pigments that can be contained in the undercoat layer of the present invention include, for example, inorganic pigments such as talc, kaolin, calcined kaolin, clay, calcined clay, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, magnesium silicate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate, amorphous silica, calcium silicate, diatomaceous earth, and colloidal silica; melamine resin, urea-formaldehyde resin, polyethylene, polystyrene, ethylene-vinyl acetate, styrene microballs, nylon powder, polyethylene powder, urea-formaldehyde resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, and raw starch particles. These can be used alone or in combination of two or more types, but are not limited to these. One or more types can also be used as needed.

The undercoat layer may also contain various water-soluble or water-dispersible polymer compounds used in conventional coatings as binders. Specific examples of such binders include water-soluble polymer compounds such as starch or its derivatives, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide/acrylic acid ester copolymers, acrylamide/acrylic acid ester/methacrylic acid terpolymers, polyacrylates, polymaleates, styrene/maleic acid copolymer salts, ethylene/maleic acid copolymer salts, and isobutylene/maleic acid copolymer salts, as well as water-dispersible polymer compounds such as styrene/butadiene copolymers, acrylonitrile/butadiene copolymers, methyl acrylate/butadiene copolymers, acrylonitrile/butadiene/styrene terpolymers, polyvinyl acetate, vinyl acetate/acrylic acid ester copolymers, ethylene/vinyl acetate copolymers, polyacrylates, styrene/acrylic acid ester copolymers, and polyurethanes, but are not limited to these. One or more binders may be used. The amount of binder used is preferably 10 to 30% by mass of the total solids content of the undercoat layer.

In the present invention, when the various components that can be contained in the undercoat layer are mixed and stirred using water as a medium, a dispersant can be used to improve dispersibility. Examples of dispersants that can be used include polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and modified polyvinyl alcohol; starch or derivatives thereof; cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose, and carboxymethyl cellulose; proteins such as gelatin and casein; acid-neutralized chitosan; sodium alginate; polyvinylpyrrolidone; water-soluble polymer compounds such as diisobutylene/maleic acid copolymer salt, styrene/isobutylene/maleic acid copolymer salt, styrene/maleic acid copolymer salt, ethylene/acrylic acid copolymer salt, styrene/acrylic acid copolymer salt, and polyacrylate salt; anionic low-molecular surfactants such as dodecylbenzenesulfonate, dialkyl sulfosuccinate, alkylnaphthalenesulfonate, alkyldiphenyletherdisulfonate, and fatty acid metal salt; nonionic surfactants such as acetylene glycol; and sodium hexametaphosphate. The dispersants are not limited to these, and one or more types may be used as needed. The total amount of dispersant is preferably 0.1 to 30% by mass of the total amount of dispersoids contained in the dispersion.

In the present invention, the support of the thermal recording material may be transparent, translucent, or opaque, and may be any of paper, various nonwoven fabrics, woven fabrics, synthetic resin films, synthetic resin-laminated paper, synthetic paper, metal foil, ceramic paper, glass plates, or composite sheets combining these, depending on the purpose.

In the present invention, when a paper support is used as the support, examples of the pulp contained in the paper support include various pulps such as softwood bleached kraft pulp (NBKP), hardwood bleached sulfite pulp (LBKP), softwood bleached sulfite pulp (NBSP), hardwood bleached sulfite pulp (LBSP), TMP, CTMP, BCTMP, GP, RGP, CGP, and cotton pulp, various recycled paper pulps such as DIP, and non-wood fibers such as kenaf, but are not limited to these. One or more types can be used as needed.

When a paper support is used as the support in the present invention, the filler contained in the paper support can be appropriately selected from known fillers. Examples of such fillers include inorganic fillers such as calcium carbonate, talc, kaolin, calcined kaolin, amorphous silica, illite, clay, calcined clay, and titanium dioxide, as well as organic fillers such as plastic pigments, but are not limited to these. One or more types can be used as needed.

In the present invention, when a paper support is used as the support, the ash content of the paper support is preferably 0.1 to 25% by mass. If it is less than 0.1% by mass, it is difficult to obtain good formation and smoothness. If it exceeds 25% by mass, smoothness saturates, while the sizing ability and surface strength of the base paper decrease, making the paper more susceptible to breakage when coating the undercoat layer or thermosensitive recording layer. In addition, the basis weight of the paper support is preferably about 20 to 300 g/ ^m2 .

In the present invention, when a paper substrate is used as the support, the paper substrate may contain, as an internal sizing agent (internal sizing agent), for example, a reinforced rosin sizing agent, emulsion sizing agent, or synthetic sizing agent in the case of acidic papermaking, or an alkyl ketene dimer, alkenyl succinic anhydride, higher fatty acid, or neutral rosin sizing agent in the case of neutral papermaking. However, the internal sizing agent is not limited to these, and one or more types may be used as needed. Furthermore, external sizing agents (external sizing agents) include, but are not limited to, styrene-maleic acid copolymers, styrene-acrylic acid copolymers, styrene polymers, isocyanate polymers, rosin, saponified alkyd resins such as tall oil and phthalic acid, polymers such as saponified petroleum resins and rosin, α-olefin-maleic acid copolymers, acrylic ester-acrylic acid copolymers, and alkyl ketene dimers. However, the external sizing agent is not limited to these, and one or more types may be used as needed. Furthermore, in addition to the sizing agents, pulp, and various fillers described above, various internal papermaking aids, such as nonionic, cationic, anionic, or amphoteric retention aids, drainage aids, and paper strength enhancers, can be added to the paper support as needed. Specific examples of retention aids, drainage aids, and paper strength enhancers include polyvalent metal compounds such as aluminum (specifically, aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, etc.), amorphous silica, various starches, urea resins, polyamide/polyamine resins, polyethyleneimine, polyacrylamide, polyamine, polyvinyl alcohol, and polyethylene oxide.

In the present invention, a protective layer can be provided on the thermosensitive recording layer for purposes such as improving sticking resistance, preventing scratches, improving water resistance, improving printability, improving stamping ability, improving inkjet suitability, and improving the plasticizer resistance and chemical resistance of the thermosensitive color image. The protective layer can contain various adhesives, inorganic pigments, various curing agents, various crosslinking agents, ultraviolet absorbers, etc., and can be a single layer or two or more layers laminated. In addition, printing with UV ink or the like can be performed on the surface of the thermosensitive recording layer or protective layer.

In the present invention, the solid coating amount of the protective layer is preferably 0.5 to 5 g/m ^2. If it is less than 0.5 g/m ² , the various properties of the protective layer will not be exhibited, and if it is more than 5 g/m ² , there will be a large loss of thermal energy reaching the thermosensitive recording layer from the thermal head, which may result in a decrease in color development.

In the present invention, the surface of the support opposite to the surface having the thermosensitive recording layer may have a backcoat layer for purposes such as preventing curling and static electricity, and may also be subjected to adhesive processing. Furthermore, the surface of the support having the thermosensitive recording layer or the surface opposite may have a layer containing a material capable of recording information electrically, magnetically, or optically, or an inkjet recording layer. Furthermore, in order to perform printing with laser light, a photothermal conversion material may be incorporated into any layer in the thermosensitive recording material and into the support.

The method for forming each layer in the present invention is not particularly limited and can be formed using well-known techniques. For example, coating devices such as air knife coaters, various blade coaters, various bar coaters, and various curtain coaters, as well as various printing methods such as planographic, relief, intaglio, flexographic, gravure, and screen printing, can be used. Furthermore, to improve surface smoothness, various well-known techniques for manufacturing thermal recording materials can be used, such as the use of equipment such as machine calenders, super calenders, gloss calenders, and brushing.

The present invention will be explained below using examples, but the present invention is not limited to these examples in any way. In the examples, unless otherwise noted, all percentages and parts are by weight. Furthermore, coating amounts are solid coating amounts.

Example 1
(1) Preparation of Dye Precursor Dispersion A The following ingredients were mixed and wet-pulverized in a DYNO (registered trademark)-MILL MULTI-LAB (manufactured by Willy & Bachofen GmbH) under conditions of a bead filling rate in the pulverizing chamber of 80 volume % (glass beads with a diameter of 0.6 mm were used) and a dispersion temperature of 20°C, until the volume average particle size of the dispersoid reached 0.8 μm, thereby obtaining a dye precursor dispersion A.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (Gohsenex (registered trademark) L-3266, manufactured by Mitsubishi Chemical Corporation, dissolved in water)
5 parts of a 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (butyl esterified, degree of esterification 70%) (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene polyoxypropylene alkyl ether 2 parts (Kao Corporation nonionic surfactant, Emulgen MS-110, HLB value 12.7)
0.5 parts of acetylene-based dialcohol composition (manufactured by Nissin Chemical Industry Co., Ltd., Surfynol (registered trademark) 104E)
Water 170 parts

(2) Preparation of Color Developer Dispersion The following ingredients were mixed and wet-pulverized in a DYNO-MILL MULTI-LAB (manufactured by Willy & Bachofen GmbH) under conditions of a bead filling rate in the pulverizing chamber of 80 volume % (glass beads with a diameter of 0.6 mm were used) and a dispersion temperature of 20°C until the volume average particle size of the dispersoid reached 0.8 μm, thereby obtaining a color developer dispersion.
2,2'-diallyl-4,4'-sulfonyldiphenol 200 parts 2-(2'-hydroxy-5'-methylphenyl)benzotriazole 200 parts 1,1,3-tris(5-cyclohexyl-4-hydroxy-o-tolyl)butane
40 parts 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol 440 parts (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
Acetylenic dialcohol composition: 2 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 738 parts

(3) Preparation of Pigment Dispersion Liquid The following ingredients were mixed and stirred to obtain a pigment dispersion liquid.
Precipitated calcium carbonate 150 parts (Tama Pearl (registered trademark) TP-123, manufactured by Okutama Kogyo Co., Ltd.)
15 parts of 10% aqueous ammonium polyacrylate solution (manufactured by GOO Chemical Industry Co., Ltd., Microsol KE-511 diluted with water)
Water 340 parts

(4) Preparation of a Thermosensitive Recording Layer Coating Solution The following ingredients were mixed and thoroughly stirred to obtain a thermosensitive recording layer coating solution.
Dye precursor dispersion A 377.5 parts Developer dispersion 1620 parts Pigment dispersion 505 parts 10% fully saponified polyvinyl alcohol aqueous solution 1300 parts (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., VC-13 dissolved in water)
175 parts of 40% aqueous zinc stearate dispersion (Hydrin L-536, manufactured by Chukyo Yushi Co., Ltd.)
Water 775 parts

(5) Formation of Thermosensitive Recording Layer The thermosensitive recording layer coating solution prepared in (4) above was applied to a sheet of fine paper (ash content: 0.3%) with a basis weight of 200 g/ ^m2 and a hue a* value of 1.6 according to JIS P8150 using an air knife coater to give a solid coating amount of 5 g/ ^m2 , dried to a moisture content of 6.5%, and then calendered using a supercalender to prepare a thermosensitive recording material. The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds (measured using an HL Beck smoothness tester manufactured by Kumagai Riki Kogyo Co., Ltd.).

Example 2
A thermosensitive recording material of Example 2 was prepared in the same manner as in Example 1, except that in the preparation of (1) Dye precursor dispersion A of Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene sorbitan monolaurate 2 parts (Kao Corporation nonionic surfactant, Rheodol TW-L120, HLB value 16.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 170 parts

Example 3
A thermosensitive recording material of Example 3 was prepared in the same manner as in Example 1, except that in the preparation of (1) Dye precursor dispersion A of Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene polyoxypropylene alkyl ether 0.3 parts (Kao Corporation nonionic surfactant, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 171.7 parts

Example 4
A thermosensitive recording material of Example 4 was prepared in the same manner as in Example 1, except that in the preparation of (1) Dye precursor dispersion A of Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene polyoxypropylene alkyl ether 3 parts (Kao Corporation nonionic surfactant, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 169 parts

Example 5
(6) Synthesis of Styrene-Maleic Acid Copolymer A Salt: 45 parts of styrene, 43 parts of maleic anhydride, 300 parts of toluene, and 1 part of Nyper (registered trademark) BW (manufactured by Nippon Oil & Fats Co., Ltd.) were placed in a four-neck flask equipped with a stirrer, thermometer, and reflux condenser, and the mixture was heated in an oil bath under reflux and reacted for 6 hours. 16 parts of butanol and 0.5 parts of hydroquinone were then added to the reaction solution, and the mixture was heated in an oil bath under reflux and reacted for 12 hours. Next, after cooling, the esterified solution was poured into 1500 ml of n-hexane to precipitate a resin, which was then filtered and dried. 350 parts of water and 20 parts of a 25% aqueous ammonia solution were added to the dried resin, and the mixture was hydrolyzed at 60°C for 5 hours, and water was added to adjust the solids concentration to 10%. The resulting styrene-maleic acid copolymer A salt had a degree of esterification of 30% and a weight-average molecular weight of 50,000.

A thermosensitive recording material of Example 5 was prepared in the same manner as in Example 1, except that in the preparation of (1) Dye precursor dispersion A of Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
10% styrene-maleic acid copolymer A salt aqueous solution (butyl esterified, degree of esterification 30%) 5 parts Polyoxyethylene polyoxypropylene alkyl ether 2 parts (nonionic surfactant manufactured by Kao Corporation, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 170 parts

Example 6
(7) Preparation of Dye Precursor Dispersion B The following components were mixed and wet-pulverized in a DYNO-MILL MULTI-LAB (manufactured by Willy & Bachofen GmbH) under conditions of a bead filling rate in the pulverizing chamber of 80 volume % (glass beads with a diameter of 0.6 mm were used) and a dispersion temperature of 20°C, until the volume average particle size of the dispersoid reached 0.8 μm, thereby obtaining a dye precursor dispersion B.
100 parts of 3-diethylamino-7-chlorofluoran (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-8)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of a 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (butyl esterified, degree of esterification 70%) (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene polyoxypropylene alkyl ether 2 parts (Kao Corporation nonionic surfactant, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 170 parts

The thermosensitive recording material of Example 6 was prepared in the same manner as in Example 1 (4) Preparation of the thermosensitive recording layer coating liquid, except that dye precursor dispersion A was replaced with dye precursor dispersion B. The Beck smoothness of the thermosensitive recording layer surface after calendaring was 250 seconds.

Example 7
A thermosensitive recording material of Example 7 was prepared in the same manner as in Example 1, except that in (4) Preparation of the thermosensitive recording layer coating liquid of Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
(4) Preparation of a Thermosensitive Recording Layer Coating Solution The following ingredients were mixed and thoroughly stirred to obtain a thermosensitive recording layer coating solution.
Dye precursor dispersion A 19 parts Dye precursor dispersion B 358.5 parts Developer dispersion 1620 parts Pigment dispersion 505 parts 10% fully saponified polyvinyl alcohol aqueous solution 1300 parts (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., VC-13 dissolved in water)
175 parts of 40% aqueous zinc stearate dispersion (Hydrin L-536, manufactured by Chukyo Yushi Co., Ltd.)
Water 775 parts

Comparative Example 1
An attempt was made to prepare a heat-sensitive recording material of Comparative Example 1 in the same manner as in Example 1, except that in the preparation of (1) dye precursor dispersion A in Example 1, the formulation was changed as follows, but the dye precursor dispersion gelled and a heat-sensitive recording material could not be obtained.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene fatty acid monoester: 2 parts (nonionic surfactant, manufactured by Sanyo Chemical Industries, Ltd., IONET (registered trademark) MO-200, HLB value: 8.4)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 170 parts

Comparative Example 2
A thermosensitive recording material of Comparative Example 2 was prepared in the same manner as in Example 1, except that in the preparation of (1) dye precursor dispersion A in Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 172 parts

Comparative Example 3
A thermosensitive recording material of Comparative Example 3 was prepared in the same manner as in Example 1, except that in the preparation of (1) dye precursor dispersion A in Example 1, the formulation was changed as follows: The Beck smoothness of the thermosensitive recording layer surface after calendering was 250 seconds.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
5 parts of 10% aqueous solution of ammonium salt of styrene-maleic acid copolymer (manufactured by Arakawa Chemical Industries, Ltd., Polymaron 1318 diluted with water)
Polyoxyethylene polyoxypropylene alkyl ether 5 parts (nonionic surfactant manufactured by Kao Corporation, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 167 parts

Comparative Example 4
(8) Synthesis of Styrene-Maleic Acid Copolymer B Salt: 45 parts of styrene, 43 parts of maleic anhydride, 300 parts of toluene, and 1 part of Nyper-BW (manufactured by Nippon Oil & Fats Co., Ltd.) were placed in a four-neck flask equipped with a stirrer, thermometer, and reflux condenser, and the mixture was heated in an oil bath under reflux and reacted for 6 hours. The reaction solution was poured into 1500 ml of n-hexane to precipitate a resin, which was then filtered and dried. 350 parts of water and 20 parts of a 25% aqueous ammonia solution were added to the dried styrene-maleic anhydride copolymer, and the mixture was hydrolyzed at 60°C for 5 hours, and water was added to adjust the solids concentration to 10%. The degree of esterification of the resulting styrene-maleic acid copolymer B salt was 0%, and the weight-average molecular weight was 50,000.

An attempt was made to prepare a heat-sensitive recording material of Comparative Example 4 in the same manner as in Example 1, except that in the preparation of (1) dye precursor dispersion A in Example 1, the formulation was changed as follows, but the dye precursor dispersion gelled and a heat-sensitive recording material could not be obtained.
100 parts of 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide (manufactured by Yamamoto Chemical Industry Co., Ltd., Red-40)
100 parts of 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, Gohsenex L-3266 dissolved in water)
10% styrene-maleic acid copolymer B salt aqueous solution (esterification degree 0%) 5 parts Polyoxyethylene polyoxypropylene alkyl ether 2 parts (nonionic surfactant manufactured by Kao Corporation, Emulgen MS-110, HLB value 12.7)
Acetylenic dialcohol composition 0.5 parts (Nissin Chemical Industry Co., Ltd., Surfynol 104E)
Water 170 parts

The thermal recording materials prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to the following evaluations. The results are shown in Table 1. Note that in Table 1, a "-" indicates that the thermal recording material could not be prepared due to gelation of the dye precursor dispersion, and therefore evaluation of that item was not possible.

[Manufacturing stability]
The state of the dye precursor dispersion during preparation was observed and evaluated according to the following criteria.
Good: The dye precursor dispersion did not gel during or after pulverization.
x: The dye precursor dispersion gelled during or after pulverization.

[Red cast on the skin]
For each of the prepared heat-sensitive recording materials, the hue a* value of the background was measured in an environment of 23° C. and 50% RH according to JIS P8150:2004, and evaluated according to the following criteria.
◎: a* value of the skin part is less than 1.0 ○: a* value of the skin part is 1.0 or more but less than 4.0 ×: a* value of the skin part is 4.0 or more

[Print density]
For each of the prepared thermal recording materials, a solid red image was printed at an applied energy of 0.29 mJ/dot using a facsimile tester TH-PMD manufactured by Ohkura Electric Co., Ltd., under an environment of 23°C and 50% RH. The optical density of the image area was measured under an environment of 23°C and 50% RH using a densitometer (RD19 manufactured by GretagMacbeth) (magenta mode), and evaluated according to the following criteria.
◎: The color density of the printed part is more than 1.2. ○: The color density of the printed part is more than 0.9 and is 1.2 or less. ×: The color density of the printed part is 0.9 or less.

As is clear from Table 1, the method for producing a thermal recording material of the present invention allows for the production of a thermal recording material with high print density, minimal red cast on the background, and excellent manufacturing stability.

Claims (1)

A method for producing a thermal recording material having a thermal recording layer containing a dye precursor and a color developer on a support, wherein the thermal recording layer contains at least one dye precursor selected from 3,3-bis(1-n-butyl-2-methyl-3-indolyl)phthalide and 3-diethylamino-7-chlorofluoran, and a maleic acid copolymer with an esterification degree of 15% or more and a nonionic surfactant with an HLB value of 10 or more as a dispersant for the dye precursor, and the method comprises wet-pulverizing the dye precursor under conditions where the content of the nonionic surfactant relative to the dye precursor is 0.15 to 4% by mass.