Coating liquid for forming thermo-sensitive recording layer, and thermo-sensitive recording medium

Abstract

To provide a thermo-sensitive recording layer formative liquid which enables formation of a thermo-sensitive recording layer that is excellent in plate fogging and texture stability, and is excellent in leveling property and abrasion resistance required for a surface printing coating liquid.SOLUTION: A coating liquid for forming a thermo-sensitive recording layer contains leuco dye fine particles, developer fine particles containing an electron acceptor for developing the color of the leuco dye fine particles, a resin (A), and a solvent, wherein the solvent contains an alcohol solvent and water, when particle size distribution of the particles in the coating liquid is measured by the following measurement method (1), a span value represented by the following expression (1) is 1 to 5. Measurement method (1): [Measurement device] laser diffraction scattering type particle diameter measuring device ("microtrack MT-3300" made by MicrotracBEL Corp.) [Measurement condition] particle refractive index: 1.50, particle shape: sphere and non-absorption. Expression (1): span value=(D90-D10) / D50.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating liquid for forming a thermosensitive recording layer. [Background technology]

[0002] Generally, a thermosensitive recording medium is prepared by coating a support such as paper, synthetic paper, or plastic film with a coating liquid containing a colorless or pale-colored leuco dye and a color developer, and the color develops through an instantaneous chemical reaction when heated by a thermal head, laser light, or the like, to produce a recorded image. Thermosensitive recording media are widely used as recording media for facsimiles, various tickets, measurement recorders, supermarket and convenience store receipts, label stickers, etc. In recent years, in addition to conventional thermosensitive recording media, there has been an increasing demand for hybrid packaging materials that use plastic film as a support substrate and partially provide a thermosensitive recording layer on labels or packaging packages, enabling digital printing in a post-process. Ideally, such packaging materials would be manufactured using a process in which the regular design printing layer and the thermosensitive recording layer are printed simultaneously using the same printing machine. Typically, the design printing layer of the above-mentioned labels and packaging is often printed at high speeds of 150 to 300 m / min in the case of gravure printing. Therefore, when printing a thermosensitive recording layer, the coating liquid for forming the thermosensitive recording layer must have printability, thermosensitive properties, and background stability against friction from the drying oven and guide rolls, which can reach high temperatures. Furthermore, the ink must have physical properties equivalent to those of ordinary surface printing inks, particularly leveling ability and abrasion resistance.

[0003] As a technique for partially providing a thermosensitive recording layer with high background stability through a printing process, for example, a thermosensitive recording layer forming solution has been proposed that contains a leuco dye, an electron-accepting compound as a developer that causes the leuco dye to develop color, and a solvent, the solubility of which in 100% ethanol at 20°C is 5.0% by mass or less (Patent Document 1). However, the thermosensitive recording layer forming solution described in Patent Document 1 has a small span value, which raises concerns about printability and coating resistance, and therefore also raises concerns about plate fogging resistance, background stability, and abrasion resistance. In addition, various methods have been proposed for improving background stability (for example, Patent Documents 2 and 3). However, the coating solutions for thermosensitive recording layers described in Patent Documents 2 and 3 use only water as a solvent, which causes problems with printability.

[0004] On the other hand, instead of the phenolic color developers that have been widely used up to now, for example, N,N'-diphenylurea derivatives that improve the preservability of printed areas, a method for producing the same, and a thermal recording material using the same as a color developer have been proposed (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-151636 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-150764 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-226848 [Patent Document 4] International Publication No. 2019 / 044462 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a coating liquid for forming a thermosensitive recording layer that is excellent in plate fogging resistance and background stability, and is capable of forming a thermosensitive recording layer that is excellent in leveling property and abrasion resistance required for a surface printing coating liquid. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using the coating liquid described below, and have thus achieved the present invention. That is, the present invention relates to the following [1] to

[10] .

[0008] [1] A coating liquid for forming a thermosensitive recording layer, comprising: leuco dye fine particles; color developer fine particles containing an electron acceptor for causing the leuco dye fine particles to develop color; a resin (A); and a solvent, the solvent comprises an alcohol solvent and water; A coating liquid for forming a thermosensitive recording layer, wherein the span value represented by the following formula (1) is 1 to 5 when the particle size distribution of particles in the coating liquid is measured by the following measurement method (1). Measurement method (1): [Measuring equipment] Laser diffraction / scattering particle size analyzer (Microtrac MT-3300, manufactured by Microtrac Bell Co., Ltd.) [Measurement conditions] Particle refractive index: 1.50, particle shape: spherical, non-absorbing Formula (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of the volume-based particle size distribution obtained by the above measurement D50: Cumulative 50% diameter of the volume-based particle size distribution obtained by the above measurement D90: Cumulative 90% diameter of the volume-based particle size distribution obtained by the above measurement

[0009] [2] The coating liquid for forming a thermosensitive recording layer according to [1], wherein D50 is 0.1 to 8 μm when the particle size distribution of particles in the coating liquid is measured by the measurement method (1).

[0010] [3] The coating liquid for forming a thermosensitive recording layer according to [1] or [2], wherein D90, when the particle size distribution of particles in the coating liquid is measured by measurement method (1), is 0.5 to 10 μm.

[0011] [4] The coating liquid for forming a thermosensitive recording layer according to any one of [1] to [3], wherein the color developer particles are non-phenol-based color developer particles.

[0012] [5] The coating liquid for forming a thermosensitive recording layer according to any one of [1] to [4], wherein the content of the alcohol solvent is 0.1 to 20% by mass in 100% by mass of the solvent.

[0013] [6] The coating liquid for forming a thermosensitive recording layer according to any one of [1] to [5], further comprising a surfactant, wherein the surfactant comprises a polyoxyethylene alkylphenyl ether and / or an acetylene glycol surfactant.

[0014] [7] The coating liquid for forming a thermosensitive recording layer according to any one of [1] to [6], further comprising an extender pigment, the extender pigment comprising at least one selected from the group consisting of calcium carbonate, aluminum silicate, barium sulfate, and silica.

[0015] [8] The coating fluid according to any one of [1] to [7], wherein the resin (A) is at least one selected from the group consisting of acrylic resins, urethane resins, polyester resins, and polyolefin resins.

[0016] [9] The coating liquid for forming a thermosensitive recording layer according to any one of [1] to [8], which is for coating onto a film substrate.

[0017]

[10] A thermosensitive recording medium comprising a substrate and a thermosensitive recording layer formed from the coating liquid for forming a thermosensitive recording layer according to any one of [1] to [9]. [Effects of the Invention]

[0018] The present invention makes it possible to provide a coating liquid for forming a thermosensitive recording layer that is excellent in plate fogging resistance and background stability, and that is capable of forming a thermosensitive recording layer that is excellent in leveling property and abrasion resistance required for a surface printing coating liquid. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following describes in detail the embodiments of the present invention. However, the following description of the embodiments or requirements is merely an example of how the present invention can be implemented, and the present invention is not limited to these details as long as it does not deviate from the gist of the present invention.

[0020] <Coating liquid for forming a thermosensitive recording layer> The coating liquid of the present invention is a coating liquid for forming a thermosensitive recording layer, which contains leuco dye microparticles, developer microparticles containing an electron acceptor for causing the leuco dye microparticles to develop color, a resin (A), and a solvent, wherein the solvent contains an alcohol solvent and water, and the particle size distribution of the particles in the coating liquid is measured using the coating liquid as a measurement sample by the following measurement method (1), and the span value represented by the following formula (1) is 1 to 5. Measurement method (1): [Measuring equipment] Laser diffraction / scattering particle size analyzer (Microtrac MT-3300, manufactured by Microtrac Bell Co., Ltd.) [Measurement conditions] Particle refractive index: 1.50, particle shape: spherical, non-absorbing Formula (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of the volume-based particle size distribution obtained by the above measurement D50: Cumulative 50% diameter of the volume-based particle size distribution obtained by the above measurement D90: Cumulative 90% diameter of the volume-based particle size distribution obtained by the above measurement

[0021] When the coating liquid contains an alcohol solvent and water and has a span value represented by formula (1) of 1 to 5, the affinity of the resin (A) with the leuco dye and the developer is improved, and the stability of the leuco dye and the developer is improved, thereby achieving excellent plate fogging properties, leveling properties, heat sensitivity properties, background stability, and abrasion resistance.

[0022] The span value represented by the above formula (1) is 1 to 5, preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2. When the span value represented by the above formula (1) is within the above range, plate fogging, leveling, heat sensitivity, background stability, and abrasion resistance are improved.

[0023] (Embodiments that satisfy the span value expressed by formula (1)) In an embodiment that satisfies the span value represented by the above formula (1), it is preferable to use a bead mill such as a roller mill, ball mill, pebble mill, attritor, sand mill, or gamma mill as the disperser, and the type of beads filled in the disperser is preferably glass beads, zirconia beads, zircon beads, alumina beads, or steel beads. The particle diameter of the beads filled in the disperser, as measured by microscopic observation, is preferably 0.05 to 5 mm, the temperature of the dispersion during dispersion is preferably 10 to 60°C, the dispersion time is preferably 1 to 200 minutes, and the viscosity of the coating fluid of the present invention before dispersion is preferably 100 to 1000 mPa s. In order to satisfy the span value represented by formula (1), it is preferable to disperse uniformly in a short time within the above-mentioned ranges.

[0024] In an embodiment that satisfies the span value represented by the above formula (1), the cumulative 10% diameter (D10) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye microparticles is preferably 0.01 to 1 μm, the cumulative 50% diameter (D50) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye microparticles is preferably 0.1 to 8 μm, and the cumulative 90% diameter (D90) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye microparticles is preferably 0.5 to 10 μm. The above laser diffraction particle size distribution measurement of the leuco dye microparticles was performed on the leuco dye microparticles alone before they were added to a coating liquid.

[0025] In an embodiment that satisfies the span value expressed by the above formula (1), the cumulative 10% diameter (D10) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the color developer microparticles is preferably 0.01 to 1 μm, the cumulative 50% diameter (D50) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the color developer microparticles is preferably 0.1 to 8 μm, and the cumulative 90% diameter (D90) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the color developer microparticles is preferably 0.5 to 10 μm. The above laser diffraction particle size distribution measurement of the color developer microparticles was performed on the leuco dye microparticles alone before they were added to the coating liquid.

[0026] In an embodiment that satisfies the span value represented by the above formula (1), the resin (A) preferably contains a water-soluble resin (a1) and / or an aqueous resin emulsion (a2), and the content of the resin (A) is preferably 4 to 40 mass % and more preferably 10 to 20 mass % relative to the total coating liquid.

[0027] In the above embodiment, the acid value of the water-soluble resin (a1) is preferably 100 mgKOH / g or more, and more preferably 150 to 300 mgKOH / g. The weight-average molecular weight of the water-soluble resin (a1) is preferably 5,000 to 20,000, and more preferably 7,000 to 15,000. The glass transition temperature of the water-soluble resin (a1) is preferably 50 to 200°C, and more preferably 100 to 150°C. Examples of the water-soluble resin (a1) include water-soluble acrylic resins, water-soluble urethane resins, water-soluble rosin resins, and water-soluble maleic acid resins. From the viewpoint of plate fogging properties, water-soluble acrylic resins are preferred.

[0028] In the above embodiment, the aqueous resin emulsion (a2) preferably contains a resin having a glass transition point of 95°C or less, more preferably 90°C or less, and even more preferably 0 to 80°C. The aqueous resin emulsion (a2) preferably has an acid group, and when it has an acid group, the acid value is preferably 30 to 150 mgKOH / g, and more preferably 40 to 100 mgKOH / g. The aqueous resin emulsion (a2) is an aqueous acrylic resin emulsion, an aqueous urethane resin emulsion, an aqueous epoxy resin emulsion, an aqueous polyolefin resin emulsion, an aqueous polyester resin emulsion, or the like. Preferred examples of such emulsions include aqueous polyamide resin emulsions, aqueous polyimide resin emulsions, aqueous polyamideimide resin emulsions, aqueous cellulose-based resin emulsions, and composite aqueous resin emulsions obtained by combining these resins, and the emulsion may contain one or more of these. Among these, from the viewpoints of heat-sensitive properties, background stability, and abrasion resistance, aqueous acrylic resin emulsions, aqueous urethane resin emulsions, aqueous polyester resin emulsions, and aqueous polyolefin resin emulsions are preferred, aqueous acrylic resin emulsions are more preferred, and aqueous styrene-acrylic resin emulsions and aqueous urethane resin emulsions are even more preferred.

[0029] In an embodiment that satisfies the span value represented by the above formula (1), the solvent preferably contains one or more of water, methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, ethylene glycol, propylene glycol, diethylene glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monopropyl ether. The water content is preferably 10 to 95% by mass relative to 100% by mass of the coating liquid, and the alcohol solvent content is preferably 0.1 to 20% by mass relative to 100% by mass of the coating liquid.

[0030] In a preferred embodiment that satisfies the span value represented by the above formula (1), any of nonionic surfactants, anionic surfactants, cationic surfactants, and zwitterionic surfactants can be used as the surfactant. Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, glycerin fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Examples of anionic surfactants include polyoxyethylene alkyl ether carboxylates, linear alkylbenzene sulfonates, lauryl Examples of cationic surfactants include alkylamine salts, alkyltrimethylammonium salts, dialkyldimethylammonium salts, and benzalkonium chloride. The content of the surfactant is preferably 0.1 to 10% by mass relative to 100% by mass of the coating liquid.

[0031] In a preferred embodiment, the extender pigment satisfies the span value expressed by the above formula (1), and examples thereof include inorganic fine powders such as calcium carbonate, silica, zinc oxide, titanium oxide, zirconium oxide, aluminum hydroxide, aluminum silicate, zinc hydroxide, barium sulfate, clay, kaolin, talc, and surface-treated silica. The content of the extender pigment is preferably 0.01 to 2 parts by mass per 1 part by mass of the color developer. The cumulative 50% diameter (D50) of the volume-based particle size distribution of the extender pigment obtained by laser diffraction particle size distribution measurement is preferably 0.1 to 10 μm.

[0032] One particularly preferred embodiment that satisfies the span value represented by the above formula (1) is an embodiment in which a sand mill is used as the disperser, the type of beads filled in the disperser are zirconia beads, the particle size of the beads filled in the disperser measured by microscopic observation is 0.05 to 5 mm, the temperature of the dispersion during dispersion is 10 to 60°C, the dispersion time is 1 to 200 minutes, the resin (A) contains a water-soluble resin (a1) and / or an aqueous resin emulsion (a2), and the content of the resin (A) is 4 to 40 mass % or 10 to 20 mass % relative to the entire coating liquid. Furthermore, one particularly preferred embodiment that satisfies the span value represented by the above formula (1) is a coating composition in which the resin (A) contains a water-soluble resin (a1) and an aqueous resin emulsion (a2), the water-soluble resin (a1) is a water-soluble acrylic resin or a water-soluble urethane resin, the aqueous resin emulsion (a2) is at least one selected from the group consisting of an aqueous acrylic resin emulsion, an aqueous urethane resin emulsion, an aqueous polyester resin emulsion, and an aqueous polyolefin resin emulsion, the solvent contains water and an alcohol-based solvent, and the content of water is 10 to 95% by mass relative to 100% by mass of the coating liquid. % by mass, the content of the alcohol-based solvent is 0.1 to 20% by mass relative to 100% by mass of the coating liquid, the surfactant is a polyoxyethylene alkyl phenyl ether and / or an acetylene glycol-based surfactant and the content of the surfactant is 0.1 to 10% by mass relative to 100% by mass of the coating liquid, the extender pigment is at least one selected from the group consisting of calcium carbonate, aluminum silicate, barium sulfate, and silica, and the cumulative 50% diameter (D50) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the extender pigment is 0.1 to 3 μm.

[0033] (Particle diameter in coating liquid) The cumulative 10% diameter (D10) of the volume-based particle size distribution of particles in the coating solution obtained by the above measurement method (1) is preferably 0.01 to 1 μm, more preferably 0.1 to 0.5 μm. When the D10 is 0.1 μm or more, plate fogging resistance and background stability tend to be improved. Furthermore, when the D10 is 1 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to be improved. The cumulative 50% diameter (D50) of the laser diffraction volume-based particle size distribution of particles in the coating solution obtained by the above measurement method (1) is preferably 0.1 to 8 μm, more preferably 0.5 to 5 μm, even more preferably 0.5 to 3 μm, particularly preferably 0.5 to 2 μm, and most preferably 0.52 to 1 μm. When the D50 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D50 is 8 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The cumulative 90% diameter (D90) of the laser diffraction volume-based particle size distribution of particles in the coating solution obtained by the above measurement method (1) is preferably 0.5 to 10 μm, more preferably 0.9 to 5 μm, and even more preferably 1.5 to 3 μm. When the D90 is 0.9 μm or more, plate fogging resistance and background stability tend to be improved. Furthermore, when the D90 is 10 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to be improved.

[0034] <Leuco dye particles> The coating liquid of the present invention contains leuco dye fine particles. The type of leuco dye is not particularly limited and can be appropriately selected from those used in thermosensitive recording media depending on the purpose. Suitable examples include leuco compounds such as triphenylmethane leuco dyes, fluoran leuco dyes, fluorene leuco dyes, and divinyl leuco dyes.

[0035] Examples of triphenylmethane leuco dyes include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone); 3,3-bis(p-dimethylaminophenyl)phthalide (also known as malachite green lactone); and the like. Fluoran leuco dyes include 3-diethylamino-6-methylfluoran; 3-diethylamino-6-methyl-7-anilinofluoran; 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran; 3-diethylamino-6-methyl-7-chlorofluoran; 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran; 3-diethylamino-6-methyl-7-(o-chloroanilino)fluoran; 3-diethylamino-6-methyl-7-(p-chloroanilino)fluoran. 3-Diethylamino-6-methyl-7-(o-fluoroanilino)fluoran;3-Diethylamino-6-methyl-7-(m-methylanilino)fluoran;3-Diethylamino-6-methyl-7-octylanilinofluoran;3-Diethylamino-6-methyl-7-octylaminofluoran;3-Diethylamino-6-methyl-7-benzylaminofluoran;3-Diethylamino-6-methyl-7-dibenzylaminofluoran;3-Diethylamino-6-chloro-7-methylfluoran;3-Diethylamino-6-chloro -7-Anilinofluoran;3-Diethylamino-6-chloro-7-p-methylanilinofluoran;3-Diethylamino-6-ethoxyethyl-7-anilinofluoran;3-Diethylamino-7-methylfluoran;3-Diethylamino-7-chlorofluoran;3-Diethylamino-7-(m-trifluoromethylanilino)fluoran;3-Diethylamino-7-(o-chloroanilino)fluoran;3-Diethylamino-7-(p-chloroanilino)fluoran;3-Diethylamino-7-(o-fluoroanilino)fluoran Lan;3-Diethylamino-benzo[a]fluoran;3-Diethylamino-benzo[c]fluoran;3-Dibutylamino-6-methyl-fluoran;3-Dibutylamino-6-methyl-7-anilinofluoran;3-Dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran;3-Dibutylamino-6-methyl-7-(o-chloroanilino)fluoran;3-Dibutylamino-6-methyl-7-(p-chloroanilino)fluoran;3-Dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran;3-Dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran;3-Dibutylamino-6-methyl-chlorofluoran;3-Dibutylamino-6-ethoxyethyl-7-anilinofluoran;3-Dibutylamino-6-chloro-7-anilinofluoran;3-Dibutylamino-6-methyl-7-p-methylanilinofluoran;3-Dibutylamino-7-(o-chloroanilino)fluoran;3-Dibutylamino-7-(o-fluoroanilino)fluoran;3-Dipentylamino-6-methyl-7-anilinofluoran 3-Dipentylamino-6-methyl-7-(p-chloroanilino)fluoran;3-Dipentylamino-7-(m-trifluoromethylanilino)fluoran;3-Dipentylamino-6-chloro-7-anilinofluoran;3-Dipentylamino-7-(p-chloroanilino)fluoran;3-Pyrrolidino-6-methyl-7-anilinofluoran;3-Piperidino-6-methyl-7-anilinofluoran;3-(N-Methyl-N-propylamino)-6-methyl-7-anilinofluoran;3-(N-Methyl-N-cyclohexylamino) -6-Methyl-7-anilinofluoran;3-(N-Ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran;3-(N-Ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran;3-(N-Ethyl-p-toluidino)-6-methyl-7-anilinofluoran;3-(N-Ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran;3-(N-Ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran;3-(N-Ethyl-N-tetrahydrofurfurylamino)-6- Methyl-7-anilinofluoran;3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran;3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran;3-cyclohexylamino-6-chlorofluoran;2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran;2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran;2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran2-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran;2-Methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran;2-Chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran;2-Chloro-6-p-(p-dimethylaminophenyl)aminoanilinofluoran;2-Nitro-6-p-(p-diethylaminophenyl)aminoanilinofluoran;2-Amino-6-p-(p-diethylaminophenyl)aminoanilinofluoran;2-Diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran;2-Pheny Examples include 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran; 2,4-dimethyl-6-[(4-dimethylamino)anilino]fluoran, etc.; Examples of fluorene-based leuco dyes include 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]; and the like. Examples of divinyl leuco dyes include 3,3-bis[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide; 3,3-bis[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide; 3,3-bis[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide; and 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide. Other leuco dyes include 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide; 3,6-bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam; 3, Examples include 6-bis(diethylamino)fluoran-γ-(4'-nitro)anilinolactam; 1,1-bis[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane; 1,1-bis[2',2',2",2"-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane; 1,1-bis[2',2',2",2"-tetrakis(p-dimethylaminophenyl)ethenyl]-2,2-diacetylethane; and bis[2,2,2',2'-tetrakis(p-dimethylaminophenyl)ethenyl]-methylmalonic acid dimethyl ester.

[0036] The content of the leuco dye particles is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, relative to 100% by mass of the coating liquid for forming the thermosensitive recording layer. When the content of the leuco dye particles is within the above range, plate fogging, thermosensitive properties, and background stability tend to be improved.

[0037] (Particle size of leuco dye particles) The cumulative 10% diameter (D10) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye microparticles is preferably 0.01 to 1 μm, more preferably 0.1 to 0.5 μm. When the D10 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D10 is 1 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The cumulative 50% diameter (D50) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye microparticles is preferably 0.1 to 8 μm, more preferably 0.5 to 5 μm, even more preferably 0.5 to 3 μm, particularly preferably 0.5 to 2 μm, and most preferably 0.52 to 1 μm. When the D50 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D50 is 8 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The cumulative 90% diameter (D90) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the leuco dye fine particles is preferably 0.5 to 10 μm, and more preferably 0.9 to 5 μm. It is more preferable that the D90 is 0.5 μm or more, and even more preferable that the D90 is 1.5 to 3 μm. When the D90 is 0.5 μm or more, plate fogging resistance and background stability tend to be improved. Furthermore, when the D90 is 10 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to be improved. The laser diffraction particle size distribution measurement of the leuco dye fine particles was carried out on the leuco dye fine particles alone before they were added to the coating liquid.

[0038] <Developer particles> The coating liquid of the present invention contains color developer microparticles. There are no restrictions on the color developer microparticles that can be used, but from the viewpoint of background stability, non-phenolic color developers are preferred. Examples of such non-phenolic color developers include compounds represented by the following general formula (1), compounds represented by the following general formula (2), and compounds represented by the following general formula (3). The content of the color developer microparticles is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass, relative to 100% by mass of the total coating liquid for forming a thermosensitive recording layer. When the content of the color developer microparticles is within the above range, plate fogging resistance, thermosensitive properties, and background stability tend to be improved.

[0039] General formula (1) [ka]

[0040] (In the formula, R 1 may be the same or different and each represent an alkyl group or an alkoxy group, and n represents an integer of 0 to 3.

[0041] General formula (2) [ka]

[0042] (In the formula, R 2 represents a hydrogen atom or an alkyl group, and R 4 ~R 8 may be the same or different and represent a hydrogen atom, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group, and m represents an integer of 0 to 2.

[0043] General formula (3) [ka]

[0044] The blending ratio of the leuco dye microparticle dispersion and the color developer microparticle dispersion in the coating liquid for forming a thermal record of the present invention is preferably 50 to 300 parts by mass, more preferably 100 to 250 parts by mass, of the color developer microparticle dispersion to 100 parts by mass of the leuco dye microparticle dispersion. When the blending ratio is within the above range, the thermal sensitivity and background stability tend to be good.

[0045] (Particle diameter of developer particles) The cumulative 10% diameter (D10) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the developer microparticles is preferably 0.01 to 1 μm, more preferably 0.1 to 0.5 μm. When the D10 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D10 is 1 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The cumulative 50% diameter (D50) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the developer microparticles is preferably 0.1 to 8 μm, more preferably 0.5 to 5 μm, even more preferably 0.5 to 3 μm, particularly preferably 0.5 to 2 μm, and most preferably 0.52 to 1 μm. When the D50 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D50 is 8 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The cumulative 90% diameter (D90) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the developer microparticles is preferably 0.5 to 10 μm, more preferably 0.9 to 5 μm, and even more preferably 1.5 to 3 μm. When the D90 is 0.9 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D90 is 10 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The laser diffraction particle size distribution measurement of the developer particles was carried out on the developer particles alone before they were added to the coating liquid.

[0046] <Resin (A)> Resin (A) is used to retain leuco dye particles and developer particles in the thermosensitive recording layer. Resin (A) is preferably a resin that is soluble or dispersible in water, and preferably contains a water-soluble resin (a1) and / or an aqueous resin emulsion (a2), and preferably contains a water-soluble resin (a1) and an aqueous resin emulsion (a2). Furthermore, resin (A) is preferably at least one resin selected from the group consisting of acrylic resins, urethane resins, polyester resins, and polyolefin resins. The content of resin (A) is preferably 4 to 40% by mass, and more preferably 10 to 20% by mass, relative to 100% by mass of the coating liquid. When the content of resin (A) is within the above range, plate fogging resistance, background stability, and abrasion resistance tend to be good.

[0047] <Water-soluble resin (a1)> The water-soluble resin (a1) functions as a dispersing resin for dispersing the leuco dye particles and the color developer particles. The acid value of the water-soluble resin (a1) is preferably 100 mgKOH / g or more, more preferably 150 to 300 mgKOH / g. When the acid value of the water-soluble resin (a1) is within the above range, the plate fogging resistance, background stability, and rub resistance tend to be improved. The weight-average molecular weight of the water-soluble resin (a1) is preferably 5,000 to 20,000, more preferably 7,000 to 15,000. When the weight-average molecular weight of the water-soluble resin (a1) is within the above range, the plate fogging resistance, background stability, and rub resistance tend to be improved. The glass transition temperature of the water-soluble resin (a1) is preferably 50 to 200°C, more preferably 100 to 150°C. When the glass transition temperature of the water-soluble resin (a1) is within the above range, the plate fogging resistance, background stability, and rub resistance tend to be improved.

[0048] Examples of the water-soluble resin (a1) include water-soluble acrylic resins, water-soluble urethane resins, water-soluble rosin resins, and water-soluble maleic acid resins, and water-soluble acrylic resins are preferred. When a water-soluble acrylic resin is used, plate fogging, background stability, and abrasion resistance tend to be improved.

[0049] <Water-soluble acrylic resin> The water-soluble acrylic resin is a resin obtained by vinyl polymerization of one or more vinyl monomers including a (meth)acrylic acid ester. Examples of the vinyl monomer include alkyl ester compounds of (meth)acrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate; (meth)acrylic acid amide derivatives containing at least one N-substituted methylol group such as N-methylol (meth)acrylamide; dimethylaminoethyl (meth)acrylate; diethylaminoethyl (meth)acrylate; dipropylaminoethyl (meth)acrylate; Examples of the water-soluble acrylic resin include aminoalkyl esters of (meth)acrylic acid such as acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dipropylaminopropyl (meth)acrylate; mono- or diesters of (meth)acrylic acid of glycols such as diethylene glycol and dipropylene glycol; styrene derivatives such as styrene and α-methylstyrene; hydroxyalkyl ester compounds of (meth)acrylic acid such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate; and vinyl compounds having an acid group such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid. These may be used alone or in combination. Among these, styrene derivatives are preferred, that is, the water-soluble acrylic resin is preferably a water-soluble styrene-acrylic resin.

[0050] <Water-soluble urethane resin> The water-soluble urethane resin is a resin having a urethane bond, and is obtained by reacting an organic polyisocyanate compound with a polyol compound to synthesize a urethane prepolymer, and then optionally reacting with a chain extender and a reaction terminator. The polyol compound, chain extender, and reaction terminator have water-soluble groups such as acid groups, which results in a water-soluble urethane resin. Any known organic polyisocyanate compound can be used, including aromatic, aliphatic, and alicyclic difunctional isocyanates, trifunctional isocyanates, etc. Examples of the polyisocyanate (b1) include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, and naphthylene diisocyanate. Aromatic isocyanates such as 1,5-diisocyanate, tetrahydronaphthylene-1,5-diisocyanate, 4,4'-dibenzyl isocyanate, and xylylene diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; and alicyclic diisocyanates such as dicyclohexylmethane diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tolylene diisocyanate.

[0051] In addition, as the trifunctional isocyanate, an adduct or an isocyanurate obtained from an isocyanate compound may be used. Note that an "adduct" is an addition product of an isocyanate compound and trimethylolpropane, and an "isocyanurate" is a trimer of an isocyanate compound. One type of polyisocyanate may be used alone, or two or more types may be used in combination.

[0052] Examples of polyol compounds include polyester diols obtained by polycondensation of low-molecular-weight diol components, such as linear glycols such as 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol, branched glycols such as 1,2-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2-ethyl-2-butyl-1,3-propanediol, and ether-based diols such as diethylene glycol and triethylene glycol, with dibasic acid components such as adipic acid and phthalic acid, or by ring-opening reaction of cyclic ester compounds such as lactones, and oxidized ethylene glycol. Examples of the polyether diol include polyether diols obtained by homopolymerizing or copolymerizing ethylene, propylene oxide, tetrahydrofuran, etc.; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; polyether diol compounds such as alkylene oxide adducts of bisphenol A with ethylene oxide, propylene oxide, etc.; and polycarbonate diols and polybutadiene glycols obtained by reacting a carbonate component such as alkylene carbonate, diallyl carbonate, dialkyl carbonate, etc. or phosgene with the above-mentioned low-molecular-weight diol component.

[0053] <Water-based resin emulsion (a2)> The aqueous resin emulsion (a2) in the present invention refers to a resin that is insoluble or poorly soluble in an aqueous system, but whose dispersion is stabilized by a surfactant or the like. The average particle size of the aqueous resin emulsion (a2) is preferably 10 to 500 nm, and more preferably 30 to 200 nm. From the viewpoints of adhesion to various substrates including polyolefin substrates and abrasion resistance, the aqueous resin emulsion (a2) preferably contains a resin having a glass transition point of 95°C or less, more preferably 90°C or less, and even more preferably 0 to 80°C. When the temperature is within the above range, plate fogging resistance, background stability, and abrasion resistance tend to be improved. The aqueous resin emulsion (a2) preferably contains acid groups, and when it contains acid groups, the acid value is preferably 30 to 150 mgKOH / g, and more preferably 40 to 100 mgKOH / g. When the temperature is within the above range, plate fogging resistance, background stability, and abrasion resistance tend to be improved.

[0054] Preferred examples of the aqueous resin emulsion (a2) include aqueous acrylic resin emulsions, aqueous urethane resin emulsions, aqueous epoxy resin emulsions, aqueous polyolefin resin emulsions, aqueous polyester resin emulsions, aqueous polyamide resin emulsions, aqueous polyimide resin emulsions, aqueous polyamideimide resin emulsions, aqueous cellulose-based resin emulsions, and composite aqueous resin emulsions obtained by combining these resins, and the aqueous resin emulsion (a2) may contain one or more of these. Among these, from the viewpoints of heat-sensitive properties, background stability, and abrasion resistance, aqueous acrylic resin emulsions, aqueous urethane resin emulsions, aqueous polyester resin emulsions, and aqueous polyolefin resin emulsions are preferred, aqueous acrylic resin emulsions are more preferred, and aqueous styrene-acrylic resin emulsions are even more preferred.

[0055] <Water-based acrylic resin emulsion> The monomers used in the synthesis of the aqueous acrylic resin emulsion can be those described above in the section <Water-soluble acrylic resin>.

[0056] <Water-based urethane resin emulsion> The organic polyisocyanate compound and polyol compound used in the synthesis of the aqueous urethane resin emulsion can be those described above in the section "Water-soluble urethane resin."

[0057] When the aqueous resin emulsion (a2) has an acid group, the acid group is preferably neutralized with a basic compound, such as an amine compound or an alkali metal.

[0058] Examples of the amine compound include ammonia; alkylamines such as diethylamine, triethylamine, and ethylenediamine; and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the alkali metal include sodium hydroxide and potassium hydroxide. These may be used alone or in combination of two or more.

[0059] <Solvent> The solvent used in the present invention includes an alcohol solvent and water. The content of the solvent is preferably 30 to 90% by mass, more preferably 40 to 85% by mass, and even more preferably 50 to 80% by mass, relative to 100% by mass of the coating liquid. The water content is preferably 10 to 95% by mass, more preferably 30 to 95% by mass, and even more preferably 50 to 95% by mass, relative to 100% by mass of the solvent. When the water content is within the above range, plate fogging resistance, leveling properties, background stability, and abrasion resistance tend to be improved. The content of the alcohol solvent is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, relative to 100% by mass of the solvent. It is more preferable that the content of the alcohol solvent is 0.1% by mass or more, the leveling property and rub resistance of the coating liquid tend to be improved. Also, the content of the alcohol solvent is 20% by mass or less, the plate fogging property and background stability tend to be improved.

[0060] The alcohol solvent is a solvent having a hydroxyl group, and in the present invention, it is preferable to include an alcohol solvent having a boiling point of 130° C. or less. Examples of alcohol solvents having a hydroxyl group and a boiling point of 130° C. or less include methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, 2-methoxyethanol, 2-methyl-2-butanol, and 3-pentanol. Among these, from the viewpoint of printability such as leveling ability and plate fogging, one or more solvents selected from the group consisting of methanol, ethanol, isopropyl alcohol, and n-propanol are preferred. The content of the alcohol solvent having a boiling point of 130° C. or less is preferably 50 to 100 mass %, more preferably 60 to 100 mass %, and even more preferably 70 to 100 mass %, based on 100 mass % of the alcohol solvent.

[0061] The solvent may also include an alcohol solvent having a boiling point of more than 130° C., and the alcohol solvent is preferably a glycol ether solvent. Specific examples of alcohol solvents having a boiling point of more than 130°C include ethylene glycol, propylene glycol, diethylene glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monopropyl ether. The content of the alcohol solvent having a boiling point of more than 130° C. is preferably 0 to 50 mass %, more preferably 0 to 30 mass %, and even more preferably 0 to 10 mass %, based on 100 mass % of the alcohol solvent.

[0062] <Surfactant> The coating liquid of the present invention preferably further contains a surfactant. As the surfactant, any of nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants can be used, with nonionic surfactants being preferred. The surfactant content is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 4% by mass, relative to 100% by mass of the coating liquid. When the surfactant content is within the above range, plate fogging resistance and background stability tend to improve.

[0063] Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, glycerin fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Examples of anionic surfactants include polyoxyethylene alkyl ether carboxylates, linear alkylbenzene sulfonates, and laurates. Examples of cationic surfactants include alkylamine salts, alkyltrimethylammonium salts, dialkyldimethylammonium salts, and benzalkonium chloride.

[0064] Among these, from the viewpoints of dispersibility of the leuco dye microparticles and the color developer microparticles and printability, it is preferable to contain a polyoxyethylene alkyl phenyl ether and / or an acetylene glycol-based nonionic surfactant, and it is more preferable to contain a polyoxyethylene alkyl phenyl ether and an acetylene glycol-based nonionic surfactant. These surfactants further stabilize the dispersion of the leuco dye microparticles and the color developer microparticles, and contribute to improving printability such as leveling and plate fogging during gravure printing, as well as background stability. The content of the polyoxyethylene alkyl phenyl ether and the acetylene glycol-based nonionic surfactant (either of which may be 0) is preferably 0.1 to 10 mass% relative to 100 mass% of the coating liquid, more preferably 0.5 to 5 mass%, and even more preferably 1 to 4 mass%. When the content of the polyoxyethylene alkyl phenyl ether and the acetylene glycol-based nonionic surfactant is within the above range, plate fogging resistance, leveling ability, and background stability tend to be improved. Furthermore, the mass ratio of the polyoxyethylene alkyl phenyl ether to the acetylene glycol-based nonionic surfactant in the coating liquid is preferably 40:60 to 90:10, more preferably 55:45 to 75:35. When the mass ratio is within the above range, plate fogging resistance, leveling ability, and background stability tend to be improved.

[0065] In the coating solution for forming a thermal record of the present invention, the mass ratio of the color developer particles to the surfactant is preferably 60:40 to 99:1, and more preferably 80:20 to 95:5. When the mass ratio is within the above range, plate fogging resistance, leveling properties, and background stability tend to be improved. In the coating solution for forming a thermal record of the present invention, the mass ratio of the leuco dye fine particles to the surfactant is preferably 50:50 to 95:5, and more preferably 70:30 to 90:10. When the mass ratio is within the above range, plate fogging resistance, leveling properties, and background stability tend to be improved. In the coating liquid for forming a thermal record of the present invention, the mass ratio of the alcohol solvent to the surfactant is preferably 20:80 to 80:20, and more preferably 40:60 to 60:40. When the mass ratio is within the above range, plate fogging resistance, leveling properties, background stability, and abrasion resistance tend to be improved.

[0066] <Extender pigment> The coating fluid of the present invention preferably further contains an extender pigment. Examples of extender pigments include inorganic fine powders such as calcium carbonate, silica, zinc oxide, titanium oxide, zirconium oxide, aluminum hydroxide, aluminum silicate, zinc hydroxide, barium sulfate, clay, kaolin, talc, and surface-treated silica. These may be used alone or in combination. However, from the viewpoints of printability and background stability, it is preferable to contain at least one selected from the group consisting of calcium carbonate, aluminum silicate, barium sulfate, and silica, and it is more preferable to contain calcium carbonate and / or barium sulfate. The content of the extender pigment is preferably 0.01 to 2 parts by mass per part by mass of the developer. When the content of the extender pigment is within the above range, plate fogging resistance and leveling properties tend to be improved.

[0067] The cumulative 10% diameter (D10) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the extender pigment is preferably 0.01 to 1 μm, and more preferably 0.1 to 0.5 μm. When the D10 is 0.1 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D10 is 1 μm or less, leveling properties, heat sensitivity, and abrasion resistance tend to improve. The cumulative 50% diameter of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the extender pigment (D50) is preferably 0.1 to 10 μm, more preferably 0.5 to 7 μm, even more preferably 0.5 to 3 μm, particularly preferably 0.5 to 2 μm, and most preferably 0.52 to 1 μm. When the D50 is 0.1 μm or more, plate fogging and background stability tend to improve. Furthermore, when the D50 is 10 μm or less, leveling properties, heat sensitivity, and abrasion resistance tend to improve. The cumulative 90% diameter (D90) of the volume-based particle size distribution obtained by laser diffraction particle size distribution measurement of the extender pigment is preferably 0.5 to 10 μm, more preferably 0.9 to 5 μm. Preferably, the D90 is 0.9 μm or more, and more preferably 1.5 to 3 μm. When the D90 is 0.9 μm or more, plate fogging resistance and background stability tend to improve. Furthermore, when the D90 is 10 μm or less, leveling properties, heat sensitivity properties, and abrasion resistance tend to improve. The laser diffraction particle size distribution measurement of the extender pigment was carried out on the extender pigment alone before it was added to the coating liquid.

[0068] In the coating liquid for forming a thermosensitive record of the present invention, the mass ratio of the color developer fine particles to the extender pigment is preferably 60:40 to 99:1, and more preferably 80:20 to 95:5. When the mass ratio is within the above range, plate fogging and leveling properties tend to be improved. In the coating solution for forming a thermal record of the present invention, the mass ratio of the leuco dye fine particles to the extender pigment is preferably 50:50 to 95:5, and more preferably 65:35 to 85:15. When the mass ratio is within the above range, plate fogging and leveling properties tend to be improved. In the coating liquid for forming a thermal record of the present invention, the mass ratio of the alcohol solvent to the extender pigment is preferably 20:80 to 75:25, and more preferably 35:65 to 55:45. When the mass ratio is within the above range, plate fogging resistance, leveling properties, background stability, and abrasion resistance tend to be improved.

[0069] <Sensitizer> The coating solution of the present invention can optionally contain a sensitizer. Examples of such sensitizers include fatty acid amides such as stearic acid amide, bisstearic acid amide, and palmitic acid amide; p-toluenesulfonamide; stearic acid, behenic acid, palmitic acid, and other fatty acid metal salts (e.g., calcium, zinc, or aluminum) of fatty acids such as palmitic acid; p-benzylbiphenyl, diphenyl sulfone, benzyl benzyloxybenzoate, 2-benzyloxynaphthalene, 1,2-bis(p-tolyloxy)ethane, 1,2-bis(phenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 1,3-bis(phenoxy)propane, dibenzyl oxalate, p-methylbenzyl oxalate, m-terphenyl, and 1-hydroxy-2-naphthoic acid. The content of the sensitizer is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass, based on 100% by mass of the coating solution for forming the thermosensitive recording layer.

[0070] <Method for producing coating liquid for forming thermosensitive recording layer> The coating liquid for forming the thermosensitive recording layer of the present invention contains leuco dye microparticles, developer microparticles containing an electron acceptor for causing the leuco dye to develop color, resin (A), an alcohol-based solvent, and water. The coating liquid may be produced by putting each component into the same disperser, or a leuco dye microparticle dispersion and a developer microparticle dispersion may be produced in advance and then mixed together. The leuco dye fine particle dispersion can be obtained, for example, by dispersing leuco dye fine particles, resin (A), an alcohol-based solvent, and water using a disperser. The color developer fine particle dispersion liquid can be obtained, for example, by dispersing color developer fine particles, resin (A), an alcohol-based solvent, and water using a disperser.

[0071] <Thermal recording media> A coated product having a thermosensitive recording layer can be obtained by applying the coating liquid of the present invention to a substrate, and the coated product is suitably used as a thermosensitive recording medium. The thermosensitive recording medium has a substrate and a thermosensitive recording layer, and may further have an ink layer and an overcoat layer. A preferred example of the thermosensitive recording medium includes a substrate, an ink layer, a thermosensitive recording layer, and an overcoat layer.

[0072] Suitable examples of the layer structure of a thermosensitive recording medium having a thermosensitive recording layer obtained using the coating liquid of the present invention include the following, but the present invention is not limited thereto. In the following examples, " / " indicates the boundary between layers. Substrate / thermal recording layer ·Base material / ink layer / thermal recording layer ·Base material / thermal recording layer / overcoat layer ·Base material / ink layer / thermal recording layer / overcoat layer

[0073] <Base material> The type and thickness of the substrate are not particularly limited, but a film substrate is preferred, and a plastic film substrate is more preferred. Examples of the substrate include polyolefin substrates, anti-fogging polyolefin substrates, polyester substrates, nylon (polyamide) substrates, and metal oxide depositions of these substrates. Among these, polyolefin substrates are preferred from the viewpoint of blocking resistance, and in the case of polyolefin substrates, it is more preferable to use corona discharge treated polyolefin substrates having functional groups such as hydroxyl groups or carbonyl groups, since this allows for the production of good printed matter. As for plastic substrates, uniaxially or biaxially stretched substrates are preferred.

[0074] <Thermal recording layer> The thermosensitive recording layer is preferably located on a substrate or an ink layer and can be formed using the coating liquid for forming the thermosensitive recording layer of the present invention. From the viewpoints of thermosensitive color development and printing speed, the thickness of the thermosensitive recording layer is preferably 0.2 to 4 μm, more preferably 0.4 to 3 μm.

[0075] <Ink layer> The ink layer is preferably formed by printing and drying an aqueous or oil-based printing ink comprising at least a binder resin and a solvent. The aqueous or oil-based ink may contain, in addition to the binder resin and solvent, a colorant, an aliphatic amide, a hydrocarbon wax, and other additives. The binder resin is not particularly limited and can be selected depending on the type of substrate to be printed and the intended use. As the colorant, organic or inorganic pigments and dyes used in general inks, paints, recording materials, etc., can be used, regardless of whether they are colored or colorless. Examples of organic pigments include azo-based, phthalocyanine-based, anthraquinone-based, perylene-based, perinone-based, quinacridone-based, thioindigo-based, dioxazine-based, isoindolinone-based, quinophthalone-based, azomethine azo-based, dictylopyrrolopyrrole-based, and isoindoline-based pigments. Examples of inorganic pigments include titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, red iron oxide, aluminum, and mica.

[0076] <Overcoat layer> The overcoat layer is preferably formed by applying and drying an overcoat agent containing a binder resin, an extender pigment, a lubricant, a crosslinking agent, etc. Examples of the binder resin include acrylic resin and urethane resin. Examples of the lubricant include polyethylene and zinc stearate. Examples of the crosslinking agent include carbodiimide compounds, zirconium carbonate, and isocyanate compounds.

[0077] <Method of manufacturing a thermal recording medium> The method for producing a thermosensitive recording medium preferably includes a step of forming a thermosensitive recording layer by applying the coating liquid for forming a thermosensitive recording layer of the present invention onto a substrate, and more preferably includes a step of laminating the substrate, ink layer, thermosensitive recording layer, and overcoat layer in this order. Therefore, a more preferred embodiment is as follows: A step of printing a printing ink on a substrate to form an ink layer; a step of applying the coating liquid for forming a thermal recording layer of the present invention onto the ink layer to form a thermal recording layer; It is preferable to have a step of forming an overcoat layer by applying an overcoat agent onto the heat-sensitive recording layer.

[0078] The method for producing a thermosensitive recording medium preferably further includes a step of mixing a leuco dye particle dispersion and a developer particle dispersion to produce a coating liquid for forming a thermosensitive recording layer. The step of producing a coating liquid for forming a thermosensitive recording layer preferably includes, for example, mixing the leuco dye particle dispersion, the developer particle dispersion, and, if necessary, a solvent. Furthermore, the process for producing the coating liquid for forming the thermosensitive recording layer is preferably a process using a leuco dye microparticle dispersion, a color developer microparticle dispersion, water, an alcohol-based solvent, and / or a glycol ether-based organic solvent. By mixing the leuco dye microparticle dispersion and the color developer microparticle dispersion together with an alcohol-based solvent and / or a glycol ether-based organic solvent, a coating liquid for forming the thermosensitive recording layer with better printability can be obtained. The alcohol-based solvent and / or glycol ether-based organic solvent is preferably at least one selected from the group consisting of isopropyl alcohol, n-propanol, and propylene glycol monomethyl ether.

[0079] <Leuco dye fine particle dispersion> The leuco dye microparticle dispersion preferably contains leuco dye microparticles, a resin (A), and a solvent, and may further contain an extender pigment, a surfactant, a sensitizer, etc. The preferred embodiments of the leuco dye microparticles, the resin (A), the solvent, the extender pigment, the surfactant, and the sensitizer in the leuco dye microparticle dispersion can be applied to the preferred embodiments in the coating liquid of the present invention. Furthermore, the preferred values ​​of the span values ​​D10, D50, and D90 expressed by the above formula (1) when the leuco dye microparticle dispersion is used as a measurement sample and measured by the above measurement method (1) can be applied to the preferred values ​​when the coating liquid of the present invention is used as a measurement sample and measured by the above measurement method (1).

[0080] <Color developer particle dispersion> The color developer microparticle dispersion preferably contains color developer microparticles, a resin (A), and a solvent, and may further contain an extender pigment, a surfactant, a sensitizer, etc. Preferred embodiments of the color developer microparticles, the resin (A), the solvent, the extender pigment, the surfactant, and the sensitizer in the color developer microparticle dispersion can be applied to the preferred embodiments in the coating liquid of the present invention. Furthermore, preferred values ​​of the span value, D10, D50, and D90 represented by the above formula (1), when the color developer microparticle dispersion is used as a measurement sample and measured by the above measurement method (1), can be applied to the preferred values ​​when the coating liquid of the present invention is used as a measurement sample and measured by the above measurement method (1).

[0081] The method for producing a thermosensitive recording medium in this embodiment preferably includes printing the surface of a rolled substrate with the ink, the coating liquid for forming a thermosensitive recording layer, and the overcoat varnish, and the respective printing methods are preferably gravure printing or flexographic printing. Both gravure printing and flexographic printing are rolled-up printing methods, which enable high-speed printing and are highly productive.

[0082] Gravure printing usually uses a gravure plate with cells (recesses) on the circumferential surface of a cylindrical cylinder that represent images and / or letters, and the cells are filled with printing ink, which is then printed onto the substrate. This is a printing method in which the substrate is pressed between a gravure plate and an impression cylinder, causing the printing ink filled in the cells to be transferred to the substrate, reproducing images and / or letters on the substrate. In flexographic printing, ink is supplied from a container that stores printing ink directly or via an ink supply pump or the like to an anilox roller, which has an uneven surface. The ink supplied to this anilox roller is transferred to the plate surface by contact with the raised parts of the plate surface, and then further transferred to the plastic substrate by contact between the plate surface and the substrate, finally forming a pattern and / or characters.

[0083] The substrate is preferably in the form of a roll with a specified width so as to be compatible with the winding method. The width of the substrate is appropriately selected based on the plate width of the printing machine to be used and the width of the image (design) portion of the gravure plate. When printing by overlapping multiple colors of printing ink, the printing order of the inks is not particularly limited.

[0084] Each layer is preferably formed by surface printing. When surface printing is performed, it is common to print white ink first, if necessary, and then print colored inks. When multiple colored inks are used, they can be printed in the order of, for example, yellow, magenta, cyan, and black, but this is not particularly limited. In the present invention, it is preferable to form a white ink and / or color ink, a thermosensitive coloring layer, and an overcoat layer to protect the thermosensitive coloring layer by surface printing, but the printing order is not particularly limited except that it is preferable to print the overcoat layer after the thermosensitive recording layer. From the viewpoint of adhesion to the substrate, it is preferable to print the thermosensitive recording layer on an ink layer as an underlayer, and from the viewpoint of visibility, it is preferable to print the thermosensitive recording layer on a white ink or colorless ink.

[0085] In the step of forming the thermosensitive recording layer, the printing speed is not particularly limited, but from the viewpoints of productivity, leveling ability, and background stability, the printing speed is preferably 40 to 300 m / min, more preferably 80 to 250 m / min, and even more preferably 100 to 200 m / min. [Example]

[0086] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the present invention, parts and % represent parts by mass and % by mass unless otherwise noted.

[0087] <Dispersion conditions> Bead Type: Zirconia Bead size: 1.5mm Disperser: Inoue Seisakusho Mighty Mill (MHG-5) Dispersion temperature: 25°C Dispersion time: 15 to 120 minutes

[0088] <Laser diffraction / scattering particle size measurement> Measurement method (1): [Measuring equipment] Laser diffraction / scattering particle size analyzer (Microtrac MT-3300, manufactured by Microtrac Bell Co., Ltd.) [Measurement conditions] Particle refractive index: 1.50, particle shape: spherical, non-absorbing When measuring leuco dye fine particles, color developer fine particles, or extender pigment particles alone, the measurement is performed using the above-mentioned measuring device under conditions that conform to the refractive index and particle shape of each particle.

[0089] (Manufacturing Example A1) [Production of leuco dye particle dispersion A1] Black leuco dye (Fukui Yamada Chemical Industry Co., Ltd., S-205) 29 parts, calcium carbonate (volume average particle diameter (D50) 1 μm) 3 parts, Hiros-VS-1047D (water-soluble resin (a1), 25 parts of a 39.6% solids aqueous solution manufactured by Seiko PMC, 14 parts of JONCRYL PDX-7741 (aqueous resin emulsion (a2), manufactured by BASF), 1 part of a polyoxyethylene polycyclic phenyl ether surfactant (Newcol 780 manufactured by Nippon Nyukazai Co., Ltd.), 1 part of an acetylene glycol surfactant (Acetylenol E00P manufactured by Kawaken Fine Chemicals Co., Ltd.), 25.5 parts of water, and 1.5 parts of IPA (isopropyl alcohol) were mixed and dispersed for 30 minutes under the above-mentioned dispersion conditions to obtain leuco dye microparticle dispersion A1. The particle size distribution of the leuco dye fine particle dispersion A1 was as follows: D10: 0.37 μm, D50: 0.69 μm, D90: 1.70 μm

[0090] (Manufacturing examples A2~A23) [Production of Leuco Dye Microparticle Dispersions A2 to A52] Leuco dye fine particle dispersions A2 to A52 were obtained in the same manner as in Production Example A1, except that the compositions and dispersion times were changed as shown in Tables 1-1 and 1-2.

[0091] [Table 1-1]

[0092] [Table 1-2]

[0093] [Table 1-3]

[0094] [Table 1-4]

[0095] (Manufacturing example B1) [Production of color developer particle dispersion B1] 32 parts of a non-phenolic color developer (N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea), 3 parts of calcium carbonate (volume average particle diameter (D50) 1 μm), 22 parts of Hi-ros VS-1047D (Seiko PMC Corporation, solids content 39.6%, aqueous solvent), 12 parts of JONCRYL PDX-7741 (BASF Corporation), 2 parts of a polyoxyethylene polycyclic phenyl ether surfactant (Nyukol 780, Nippon Nyukazai Co., Ltd.), 1 part of an acetylene glycol surfactant (Acetylenol E00P, Kawaken Fine Chemicals Co., Ltd.), 25 parts of water, and 3 parts of IPA were mixed and dispersed for 30 minutes under the above-mentioned dispersion conditions to obtain color developer microparticle dispersion B1. The particle size distribution of the color developer particle dispersion B1 was as follows: D10: 0.32 μm, D50: 0.56 μm, D90: 1.62 μm

[0096] [Production of color developer particle dispersions B2 to B56] Developer particle dispersions B2 to B56 were obtained in the same manner as in Production Example B1, except that the compositions and dispersion times were changed as shown in Tables 2-1 and 2-2.

[0097] [Table 2-1]

[0098] [Table 2-2]

[0099] [Table 2-3]

[0100] [Table 2-4]

[0101] Details of the abbreviations in Tables 1-1, 1-2, 2-1 and 2-2 are as follows: S-205: Leuco dye manufactured by Fukui Yamada Chemical Industry Co., Ltd. S-176: Developer manufactured by Sanko Co., Ltd. UU: Developer manufactured by Chemipro Chemical Co., Ltd. BP-S / FF-3: Developer manufactured by Nicca Chemical Co., Ltd. Calcium carbonate C1: Heavy calcium carbonate (D10: 0.5 μm, D50: 1.0 μm, D90: 3.4 μm) Calcium carbonate C2: Heavy calcium carbonate (D10: 0.9 μm, D50: 6.7 μm, D90: 7.8 μm) Calcium carbonate C3: Heavy calcium carbonate (D10: 2.2 μm, D50: 8.6 μm, D90: 12 μm) Barium sulfate: Precipitated barium sulfate (D10: 0.4 μm, D50: 1.0 μm, D90: 3.6 μm) Silica: Porous silica (D10: 0.6 μm, D50: 2.7 μm, D90: 5.4 μm) Montmorillonite: inorganic filler (swelling, particle aspect ratio: 500, particle thickness: 1 μm, particle spread: 500 nm) Hiros VS-1047D: Seiko PMC Hiros-X VS-1047D, water-soluble acrylic resin (a1) (styrene acrylic resin), acid value 240 mg KOH / g, Tg 126°C Styrene acrylic resin AC1: Water-soluble acrylic resin (a1), acid value 54 mg KOH / g, Tg 109°C JONCRYL PDX-7741: BASF, water-based acrylic resin emulsion (a2) (styrene acrylic resin), solids content 49.0%, acid value 52 mg KOH / g Neolet's R4000: Covestro Neolet's R-4000, a water-based urethane resin emulsion with a solid content of 35.0% Takelac W-5661: Mitsui Chemicals, Inc. Takelac W-5661, water-based urethane resin emulsion, solids content 35.0% PU1: Water-soluble urethane resin, solid content 27.0%, acid value 35 mg KOH / g SF210: Aqueous urethane resin emulsion (a2) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content 35.0% Z-730: GOO Chemical Industry Co., Ltd. aqueous polyester resin emulsion (a2) solids content 25.0%, acid value 46 mg KOH / g AE-301: Nippon Paper Industries Co., Ltd. aqueous olefin resin emulsion (a2) solids content 30.0% JONCRYL PDX-7357: BASF water-based acrylic resin emulsion (a2), solids content 49.5%, acid value 59 mg KOH / g Hiros-X KE-1148: Seiko PMC Corporation Hiros-X KE-1148, water-based acrylic resin emulsion (a2) (acrylic resin), acid value 31 mg KOH / g, Tg 21°C T5HX: Kaneka Corporation vinyl chloride-vinyl acetate copolymer solids 30% ethyl acetate solution. Newcol 780-60: Nippon Nyukazai Corporation Newcol 780-60 (nonionic surfactant, polyoxyethylene polycyclic phenyl ether). Acetylenol E00P: Kawaken Fine Chemicals Co., Ltd. Acetylenol E00P (nonionic surfactant, acetylene glycol type) Noigen XL400D: Polyoxyalkylene branched decyl ether (nonionic surfactant) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. IPA: Isopropyl alcohol EA: Ethyl acetate

[0102] <Preparation of overcoat varnish> An overcoat varnish was prepared by mixing and stirring 80 parts of acrylic resin 10 (BASF Joncryl PDX-7667, solids content 40.0% aqueous solution), 2 parts of surfactant (Kawaken Fine Chemicals Acetylenol E00P), 2 parts of propylene glycol monomethyl ether, 5 parts of lubricant (polyethylene wax, solids content 25.0% aqueous solution), 12 parts of water, and 18 parts of isopropanol.

[0103] Example 1 100 parts of the leuco dye particle dispersion A1 and 200 parts of the color developer particle dispersion B1 were mixed to obtain a coating liquid for forming a thermosensitive recording layer. The particle size distribution of the coating liquid for forming a thermosensitive recording layer was as follows: D10: 0.34 μm, D50: 0.59 μm, D90: 1.70 μm Next, in a gravure three-color press, in the first unit, white ink (Real NEX63 White BO S3, manufactured by Toyo Ink Co., Ltd.) was diluted with a mixed solvent (MCH / n-propyl acetate / n-propanol = 20 / 65 / 15) to a viscosity of 15 seconds (25°C, Zahn cup No. 3), and a white ink layer was formed using Helio 175L semi-solid printing plate (compressed by plate method, 100%, semi-solid pattern). In the second unit, the above-mentioned coating liquid for forming the thermal recording layer was applied to Helio 175L full solid printing plate (compressed by plate method, 100%, full solid pattern) to form a thermal recording layer. In the third unit, overcoat varnish was applied to Helio 200L full solid printing plate (compressed by plate method, 100%, full solid pattern) to form an overcoat layer, and AF-642S (biaxially oriented polypropylene (OPP) manufactured by Futamura Chemical Co., Ltd.) was applied to form a biaxially oriented polypropylene (OPP) layer. The thermal recording media were obtained by printing continuously on the corona discharge treated surface of a 25μm thick anti-fog grade film at a printing speed of 100m / min under the following printing conditions: temperature 25℃, humidity 60%, oven length 2m, and oven temperature 90℃.

[0104] (Examples 2 to 49, Comparative Examples 1, 2, 4 to 8) A coating liquid for forming a thermosensitive recording layer and a thermosensitive recording medium were obtained in the same manner as in Example 1, except that the leuco dye microparticle dispersion and the developer microparticle dispersion were mixed to obtain the compositions shown in Tables 3-1 and 3-2.

[0105] (Comparative Example 3) A coating solution for forming a thermosensitive recording layer was prepared by dispersing 6.2 parts by mass of a black dye (ODB2, manufactured by Yamamoto Chemical Industry Co., Ltd.) as an electron donor compound, 18.7 parts by mass of a non-phenolic developer (N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea), 40.0 parts by mass of an acrylic resin (A-1125, manufactured by DSM, solids content 19.5% by mass, aqueous solution), 4.6 parts by mass of a styrene-acrylic resin (Joncryl PDX-7741, manufactured by BASF, solids content 41.5% by mass, aqueous solution), 1.9 parts by mass of a surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solids content 10% by mass), 15 parts by mass of water, and 13.6 parts by mass of ethanol for 500 minutes using a sand mill so that the 50% cumulative volume particle size (D50) measured by the above-mentioned measurement method (1) was 0.25 μm. Next, a thermosensitive recording medium was produced in the same manner as in Example 1, except that the above-mentioned coating liquid for forming a thermosensitive record was used.

[0106] <Evaluation> The coating solutions for forming thermosensitive recording layers and the thermosensitive recording media of the Examples and Comparative Examples were evaluated as follows, and the results are shown in Tables 3-1 and 3-2.

[0107] (Plate fogging) The coating solutions for forming a thermosensitive recording layer of the Examples and Comparative Examples were evaluated for plate fogging in gravure printing. The area of ​​the plate fogging was visually determined after 60 minutes of idling on the gravure printing machine under conditions of an ambient temperature of 25°C and a printing speed of 200 m / min. [Judgment criteria] S-plate cover area is 0% or more and less than 10% A: The cover area is 10% or more but less than 20% B Plate cover area is 20% or more but less than 30% C Plate cover area is 30% or more S, A and B are within the ranges that do not pose any problems in practical use.

[0108] (Leveling ability) The coating liquids for forming a thermosensitive recording layer of the Examples and Comparative Examples were visually evaluated for the uniformity of density of the printed surface after gravure printing (presence or absence of print unevenness and / or pinholes). "Print unevenness" refers to a state in which the ink dried film is not formed smoothly during the drying process after printing the coating liquid for forming a thermosensitive recording layer, resulting in the appearance of minute variations in color density on the printed surface. "Pinholes" refers to a state in which the ink dried film is not formed smoothly during the drying process after printing the coating liquid for forming a thermosensitive recording layer, resulting in the appearance of minute dot-like chips on the printed surface. Plate fogging was evaluated in the examples and comparative examples. The area of ​​the plate fogging portion was visually determined and evaluated after 60 minutes of idling of the plate on the gravure printing machine. [Judgment criteria] S No uneven printing or pinholes A: Slight printing unevenness, but no pinholes B: Slight printing irregularities and pinholes C. There are obvious printing irregularities and pinholes. S, A and B are within the ranges that do not pose any problems in practical use.

[0109] (Thermal Sensitivity) The printed portion of the thermosensitive recording medium, consisting of the white ink layer, thermosensitive recording layer, and overcoat layer, was thermocompressed using a heat seal tester, and the resulting print was measured using a reflection densitometer (X-Rite eXact, manufactured by X-Rite Corporation) and evaluated according to the following criteria: The thermocompression conditions were a temperature of 140°C, a load of 2 kg, and a time of 1 second. (Judgment criteria) SS concentration K is 1.70 or more S: Concentration K is less than 1.70 and 1.60 or more A: Concentration K is less than 1.60 and 1.45 or more B. Density K is less than 1.45 and 1.30 or more C. Concentration K is less than 1.30 SS, S, A and B are within the ranges that do not pose any practical problems.

[0110] <Scalp stability> After printing and winding, the printed portion of the thermosensitive recording medium, consisting of a white ink layer, a thermosensitive recording layer, and an overcoat layer, was left in an atmosphere of 50°C / 80% RH for 72 hours, and then measured using a reflection densitometer (X-Rite eXact, manufactured by X-Rite Corporation) and evaluated according to the following criteria. Note that evaluation was not performed on samples whose background density K immediately after printing and winding was 0.35 or higher. (Judgment criteria) S Concentration K is less than 0.15 A: Concentration K is 0.15 or more and less than 0.25 B. Concentration K is 0.25 or more and less than 0.35 C. Concentration K is 0.35 or more S, A and B are within the ranges that do not pose any problems in practical use.

[0111] <Abrasion resistance> After printing and winding, the thermal recording medium was placed on the overcoat layer of the printed area, which consisted of a white ink layer, a thermal recording layer, and an overcoat layer. A sheet of high-quality paper was placed on top of the overcoat layer, and the film was used to evaluate the abrasion resistance. The evaluation conditions were a load of 200g, and 100 round trips of friction. The abrasion resistance was evaluated based on the degree to which either the white ink layer, the thermal recording layer, or the overcoat layer peeled off from the film after the abrasion. Ta. S: Less than 5% of any layer has peeled off from the film A: Any layer has peeled off from the film by 5% or more but less than 15% of the area. B. The area of ​​any layer peeled off from the film is 15% or more but less than 25% C. Any layer has peeled off from the film by 25% or more of its area. S, A and B are within the ranges that do not pose any problems in practical use.

[0112] [Table 3-1]

[0113] [Table 3-2]

[0114] [Table 3-3]

[0115] [Table 3-4]

[0116] From the above results, Comparative Example 1 had poor leveling properties because it did not contain an alcohol-based solvent. Comparative Example 2 had poor plate fogging properties, leveling properties, and background stability because it did not contain water. Comparative Example 3 had poor plate fogging properties, background stability, and abrasion resistance because the span value of the coating liquid represented by formula (1) was less than 1. Comparative Examples 4 and 5 had poor plate fogging properties, leveling properties, and background stability because the span value of the coating liquid represented by formula (1) was more than 5. On the other hand, the examples contained leuco dye microparticles, developer microparticles, resin (A), an alcohol solvent, and water, and the span value of the coating liquid represented by formula (1) was 1 to 5, so the plate fogging properties, background stability, leveling properties, and abrasion resistance were good.

Claims

1. A coating liquid for forming a thermosensitive recording layer, comprising: leuco dye fine particles; color developer fine particles containing an electron acceptor for causing the leuco dye fine particles to develop color; a resin (A); and a solvent, the solvent comprises an alcohol solvent and water; A coating liquid for forming a thermosensitive recording layer, wherein the span value represented by the following formula (1) is 1 to 5 when the particle size distribution of particles in the coating liquid is measured by the following measurement method (1). Measurement method (1): [Measuring device] Laser diffraction / scattering particle size measuring device (Microtrac MT-3300, manufactured by Microtrac Bell Co., Ltd.) [Measurement conditions] Particle refractive index: 1.50, particle shape: spherical, non-absorbing Formula (1): Span value = (D90 - D10) / D50 D10: cumulative 10% diameter of the volume-based particle size distribution obtained by the above measurement D50: cumulative 50% diameter of the volume-based particle size distribution obtained by the above measurement D90: cumulative 90% diameter of the volume-based particle size distribution obtained by the above measurement

2. 2. The coating liquid for forming a thermosensitive recording layer according to claim 1, wherein D50, when the particle size distribution of particles in the coating liquid is measured by the measurement method (1), is 0.1 to 8 μm.

3. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, wherein D90, when the particle size distribution of particles in the coating liquid is measured by the measurement method (1), is 0.5 to 10 μm.

4. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, wherein the color developer fine particles are non-phenol-based color developer fine particles.

5. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, wherein the content of the alcohol solvent is 0.1 to 20% by mass in 100% by mass of the solvent.

6. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, further comprising a surfactant, the surfactant comprising a polyoxyethylene alkylphenyl ether and / or an acetylene glycol surfactant.

7. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, further comprising an extender pigment, the extender pigment comprising at least one selected from the group consisting of calcium carbonate, aluminum silicate, barium sulfate, and silica.

8. The coating liquid according to claim 1 or 2, wherein the resin (A) is at least one selected from the group consisting of acrylic resins, urethane resins, polyester resins, and polyolefin resins.

9. 3. The coating liquid for forming a thermosensitive recording layer according to claim 1, which is for coating on a film substrate.

10. A thermosensitive recording medium comprising a substrate and a thermosensitive recording layer formed from the coating liquid for forming a thermosensitive recording layer according to claim 1 or 2.

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