Thermosensitive recording body

Abstract

To provide a thermosensitive recording body which is excellent in alcohol resistance, plasticizer resistance and heat resistant ground fogging properties of a recording part.SOLUTION: There is provided a thermosensitive recording body which has an undercoat layer containing at least hollow particles, an adhesive and an inorganic pigment I and a thermosensitive recording layer containing a leuco dye, a developer and an inorganic pigment II in this order on a support, wherein the thermosensitive recording body contains 5-(N-3-methylphenyl-sulfonamide)-N',N' '-bis-(3-methylphenyl)-isophthalic acid diamide as the developer and a pigment having an oil absorption amount of 130 ml / 100 g or less as the inorganic pigment II.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermal recording medium which utilizes a color-developing reaction between a leuco dye and a color developer. [Background technology]

[0002] Thermosensitive recording media that record color images by utilizing the thermal coloring reaction between colorless or light-colored leuco dyes and phenols or organic acids have been widely used. Such thermosensitive recording media have the advantages of being compact, easy to maintain, and quiet, because color images are formed simply by heating. For this reason, thermosensitive recording media are widely used as various information recording materials in issuing machines such as label printers, automatic ticket vending machines, CD / ATMs, order slip output machines for restaurants, data output machines for scientific research equipment, etc.

[0003] It is known that the color-developing reaction is reversible, and therefore the color-developed image will fade over time. This fade reaction is accelerated in high temperature and high humidity environments, and may progress rapidly upon contact with oil, plasticizers, etc., causing the recorded image to fade to the point where it is unreadable. In recent years, alcohol disinfection and sterilization have become commonplace in everyday life, particularly for the prevention of infectious diseases. That is, there is an increasing demand for improved performance of thermal recording media, such as white paper areas not becoming colored and printed areas not fading even when in contact with alcohol.

[0004] For example, Patent Document 1 proposes a thermosensitive recording medium using a diaryl urea derivative as a color developer. However, the thermosensitive recording medium described in Patent Document 1 has insufficient alcohol resistance and plasticizer resistance, and there is room for improvement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 044462 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENTS The main object of the present invention is to provide a heat-sensitive recording medium which has excellent resistance to alcohol and plasticizers in the recorded area, and excellent resistance to heat-induced background fogging. [Means for solving the problem]

[0007] The present inventors have intensively studied the above-mentioned prior art and have come to solve the above-mentioned problems. That is, the present invention relates to the following thermosensitive recording medium.

[0008] Item 1: A thermal recording medium having, on a support, at least an undercoat layer containing hollow particles, an adhesive, and an inorganic pigment I, and a thermal recording layer containing a leuco dye, a color developer, and an inorganic pigment II in this order, characterized in that the color developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, and the inorganic pigment II contains a pigment having an oil absorption of 130 ml / 100 g or less. Item 2: The thermal recording material according to item 1, wherein the inorganic pigment II contains a pigment having an oil absorption of 65 ml / 100 g or less. Item 3: The thermosensitive recording medium according to any one of items 1 and 2, wherein the inorganic pigment II is at least one selected from calcium carbonate, aluminum hydroxide, and clay. Item 4: The thermosensitive recording material according to any one of Items 1 to 3, wherein the inorganic pigment I contains a pigment having an oil absorption of 130 ml / 100 g or less. Item 5: The thermosensitive recording medium according to any one of Items 1 to 4, wherein the inorganic pigment I is at least one selected from calcium carbonate, aluminum hydroxide, and clay. Item 6: The thermosensitive recording medium according to any one of Items 1 to 5, wherein the content of the inorganic pigment I is 50 parts by mass or less based on the total solid content of the undercoat layer. Item 7: The thermosensitive recording medium according to any one of Items 1 to 6, wherein the hollow particles have a maximum particle diameter (D100) of 10 to 30 μm, an average particle diameter (D50) of 4.0 to 15 μm, a ratio D100 / D50 of the maximum particle diameter (D100) to the average particle diameter (D50) of 1.8 to 3.0, and the volume percentage of particles with a particle diameter of 2.0 μm or less is 1% or less. Item 8: The thermosensitive recording medium according to any one of Items 1 to 7, wherein the hollow particles have a hollow ratio of 80 to 98%. Item 9: The thermosensitive recording medium according to any one of Items 1 to 8, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of −10° C. or lower. Item 10: The thermosensitive recording medium according to any one of Items 1 to 9, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of −30° C. or lower. Item 11: The thermosensitive recording layer contains, as a second developer, a compound represented by the following general formula (1): [ka] a urea-urethane compound represented by the following general formula (2): [ka] (In the formula, n represents an integer of 1 to 6.) and diphenylsulfone-bridged compounds represented by the following general formula (3): [ka] (In the formula, R 0 represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the aralkyl group and the aryl group being optionally substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; 0 may be the same or different. A 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, 1 may be the same or different.) an N,N'-diaryl urea compound represented by the following general formula (4): [ka] (In the formula, R 1 ~R 5 and are 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. Item 12: The thermosensitive recording medium according to item 11, wherein the second developer is contained in an amount of 0.2 to 3 parts by mass per part by mass of the leuco dye. Item 13: The thermosensitive recording medium according to any one of items 1 to 12, further comprising an adhesive layer on at least one surface of the support. Effect of the Invention

[0009] The thermal recording medium of the present invention has excellent resistance to alcohol and plasticizers in the recorded area, and is also excellent in heat resistance to background fogging. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In this specification, the expression "comprise" includes the concepts of "comprise", "consist essentially of" and "consist only of".

[0011] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] The latex in the present invention includes a gel or a dried film state formed by drying a dispersion medium.

[0013] The present invention is a thermosensitive recording medium having, on a support, at least an undercoat layer containing hollow particles, an adhesive, and an inorganic pigment I, and a thermosensitive recording layer containing a leuco dye, a color developer, and an inorganic pigment II, in that order, wherein the color developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, and the inorganic pigment II contains a pigment having an oil absorption of 130 ml / 100 g or less.

[0014] [Support] The support in the present invention is not particularly limited in type, shape, size, etc., and can be appropriately selected from, for example, high-quality paper (acid paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin-laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, nonwoven fabric, synthetic resin film, and various transparent supports. The thickness of the support is not particularly limited, and is usually about 20 to 200 μm. The density of the support is not particularly limited, and is 0.60 to 0.85 g / cm. 3 degree is preferred.

[0015] [Undercoat layer] The thermosensitive recording medium of the present invention has an undercoat layer between the support and the thermosensitive recording layer. The undercoat layer contains hollow particles, an adhesive and an inorganic pigment I.

[0016] (hollow particles) The hollow particles are preferably made of an organic resin from the viewpoint of improving cushioning properties. The undercoat layer, which has high heat insulating properties due to the inclusion of hollow particles, can prevent the diffusion of heat applied to the thermal recording layer and can increase the sensitivity as a thermal recording medium.

[0017] Hollow particles made of organic resins can be divided into expanded and non-expanded types depending on the manufacturing method. Of these two types, expanded hollow particles generally have a larger average particle size and a higher hollow ratio than non-expanded hollow particles. Therefore, expanded hollow particles can provide better sensitivity and image quality than non-expanded hollow particles.

[0018] Non-foamed hollow particles can be produced by polymerizing seeds in a solution, polymerizing other resins so as to encase the seeds, and then swelling and dissolving the internal seeds to remove them, thereby forming internal cavities. When swelling and dissolving the internal seeds to remove them, an alkaline aqueous solution or the like is used. Non-foamed hollow particles with a relatively large average particle size can also be obtained by subjecting core-shell particles, in which core particles having alkali swelling properties are covered with a shell layer not having alkali swelling properties, to an alkali swelling treatment.

[0019] Expanded hollow particles can be produced by preparing particles having a volatile liquid sealed inside a resin, and softening the resin by heating, while vaporizing and expanding the liquid inside the particles.

[0020] The foamed hollow particles have a high hollow ratio and high heat insulation due to the liquid inside being heated and expanded during the manufacturing process, so that the sensitivity of the thermosensitive recording medium can be increased and the recording density can be improved. The improvement in sensitivity is particularly important when coloring a halftone region where the thermal energy applied to the thermosensitive recording layer is small. In addition, if the thermosensitive recording layer is formed via an undercoat layer with high heat insulation, the diffusion of heat applied to the thermosensitive recording layer can be prevented, resulting in excellent image uniformity and improved image quality. Therefore, in this embodiment, it is preferable to use foamed hollow particles that are excellent in improving the heat insulation of the undercoat layer.

[0021] Examples of resins that can be used for the expanded type hollow particles include thermoplastic resins such as styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinyl chloride resin, polyvinylidene chloride resin, acrylic resin (e.g., acrylic resin containing acrylonitrile as a constituent component), styrene resin, vinylidene chloride resin, and copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile. The gas contained inside the expanded type hollow particles is generally propane, butane, isobutane, air, etc. Among the various resins mentioned above, the resin used for the hollow particles is preferably acrylonitrile resin and copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile from the viewpoint of strength for maintaining the shape of the expanded particles.

[0022] The maximum particle diameter of the hollow particles in the present invention is preferably 10 to 30 μm, more preferably 10 to 25 μm, and further preferably 10 to 20 μm. The maximum particle diameter is also called D100. When the maximum particle diameter of the hollow particles is 10 μm or more, the cushioning property of the undercoat layer is improved, so that the adhesion of the thermal recording medium to the thermal head during printing is improved, and a thermal recording medium with high image quality can be obtained. This high image quality can bring about an improvement in the recording density in intermediate tones that are developed with lower energy than that which gives the maximum recording density (Dmax). On the other hand, when the maximum particle diameter of the hollow particles is 30 μm or less, the smoothness of the undercoat layer is improved, so that the thermal recording layer provided via the undercoat layer can be made uniform, and a thermal recording medium with less white spots in the image can be obtained.

[0023] The average particle diameter of the hollow particles in the present invention is preferably 4.0 to 15 μm, more preferably 4.5 to 15 μm. Here, the average particle diameter is the diameter when the volume occupied by the larger particle and the smaller particle is equal when the particle diameter is divided into two, that is, the median diameter which is the particle diameter with a frequency of 50% by volume, and is also called D50. When the average particle diameter of the hollow particles is 4.0 μm or more, the cushioning property of the undercoat layer is improved, so that the adhesion of the thermal recording medium to the thermal head during printing is improved, and a thermal recording medium with high image quality can be obtained. This high image quality can bring about an improvement in the recording density in the intermediate tone which is developed with lower energy than that which gives the maximum recording density (Dmax). On the other hand, when the average particle diameter of the hollow particles is 15 μm or less, the smoothness of the undercoat layer is improved, so that the thermal recording layer provided through the undercoat layer can be made uniform, and a thermal recording medium with less white spots in the image can be obtained.

[0024] The maximum particle size (D100) and the average particle size (D50) of the hollow particles can be measured by a laser diffraction particle size distribution analyzer. Alternatively, the particle sizes can be measured from particle images (SEM images) using an electron microscope, and the average size of 10 particles can be shown.

[0025] The ratio D100 / D50 of the maximum particle size (D100) to the average particle size (D50) of the hollow particles is an index showing the degree of particle size distribution. This ratio D100 / D50 is preferably 1.8 to 3.0, more preferably 2.0 to 2.8. When the D100 / D50 of the hollow particles is 1.8 or more, the hollow particles are sufficiently expanded, the maximum particle size is sufficiently large, the hollow ratio is high, and the heat insulation of the undercoat layer can be improved. On the other hand, when the D100 / D50 of the hollow particles is 3.0 or less, the size of the hollow particles is uniform, so that the smoothness of the undercoat layer is improved and white spots in the image can be suppressed.

[0026] In the particle size distribution obtained by a laser diffraction particle size distribution analyzer, the volume percentage of hollow particles with a particle diameter of 2.0 μm or less is preferably 1% or less. The volume percentage of hollow particles with a particle diameter of 2.0 μm or less is preferably 0.5% or less, and more preferably, no hollow particles are contained. Since hollow particles with a particle diameter of 2 μm or less are too small to provide a sufficient hollow area, it is considered that their contribution to heat insulation is extremely small. By making the volume percentage of hollow particles with a particle diameter of 2 μm or less in the undercoat layer 1% or less, the recording density, image quality, etc. can be improved.

[0027] The hollow particles preferably have a hollow ratio of 80 to 98%, more preferably 90 to 98%. When the hollow ratio of the hollow particles is 80% or more, high heat insulation can be imparted to the undercoat layer containing the hollow particles. On the other hand, when the hollow ratio of the hollow particles is 98% or less, the strength of the film surrounding the hollow portion can be improved, so that the hollow particles do not collapse when the undercoat layer is formed.

[0028] The hollow ratio of hollow particles is determined by measuring the true specific gravity by the IPA method and calculating the true specific gravity value as follows. (1) Sample pretreatment Dry the sample at 60℃ overnight to prepare the sample. (2) Reagents Isopropyl alcohol (IPA: first-grade reagent) (3) Measurement method Accurately weigh the volumetric flask (W1). ·Put about 0.5 g of the dried sample into a measuring flask and weigh it accurately (W2). Add approximately 50 mg of IPA and shake thoroughly to completely remove any air outside the capsule. Add IPA up to the mark and measure (W3). As a blank, add only IPA to the measuring flask up to the mark and measure carefully (W4). (4) Calculation of true specific gravity True specific gravity = {(W2-W1)×((W4-W1) / 100)} / {(W4-W1)-(W3-W2)} (5) Calculation of hollow ratio Hollowness ratio (%)={1-1 / (1.1 / true specific gravity)}×100

[0029] The hollow ratio is expressed by the following formula (d 3 / D 3 ) × 100. In this formula, d represents the inner diameter of the hollow particle, and D represents the outer diameter of the hollow particle.

[0030] The hollow particles in the present invention have a relatively large particle diameter, so that the content ratio of the hollow particles in the undercoat layer can be reduced. The content ratio of the hollow particles is preferably 3 to 40 mass % of the total solid content of the undercoat layer, and more preferably 5 to 35 mass %. When the content ratio of the hollow particles is 3 mass % or more, the heat insulating properties of the undercoat layer can be improved. On the other hand, when the content ratio of the hollow particles is 40 mass % or less, problems are unlikely to occur in terms of coating properties, etc., a uniform undercoat layer can be easily formed, and the recording density can be improved. In addition, the coating strength of the undercoat layer can be increased.

[0031] (glue) Examples of adhesives include polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose, water-soluble polymer materials such as sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin, and their derivatives, as well as emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers, or latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Among these, it is preferable to use an adhesive containing latex. The content of the adhesive can be selected from a wide range, but generally, it is preferably about 20 to 70% by mass, and more preferably about 25 to 60% by mass, of the total solid content of the undercoat layer.

[0032] The adhesive preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. By making the glass transition temperature -10°C or lower, image quality can be improved even in a low energy region. Since the image quality can be further improved in a low energy region, the glass transition temperature is more preferably -30°C or lower. On the other hand, a glass transition temperature of -50°C or lower is undesirable because stickiness occurs, so a glass transition temperature of -40°C or higher is preferable.

[0033] (Inorganic Pigments I) The undercoat layer in the present invention contains inorganic pigment I. From the viewpoint of increasing the recording density and improving the alcohol resistance and plasticizer resistance, it is preferable that the inorganic pigment I contains a pigment having an oil absorption of 130 ml / 100 g or less. The oil absorption of inorganic pigment I is more preferably 125 ml / 100 g or less, and even more preferably 110 ml / 100 g or less. On the other hand, from the viewpoint of effectively reducing printing problems such as the generation of head residue and sticking, it is preferably 40 ml / 100 g or more, and more preferably 80 ml / 100 g or more. Here, the oil absorption is a value determined according to the method of JIS K 5101.

[0034] Various inorganic pigments can be used as the inorganic pigment I, and specific examples include inorganic pigments such as calcium carbonate such as light calcium carbonate, aluminum hydroxide, clay such as calcined kaolin and kaolin, and talc. Among these, it is preferable that the inorganic pigment I is at least one selected from the group consisting of calcium carbonate, aluminum hydroxide, and clay. From the viewpoint of improving color development sensitivity, the content ratio of the inorganic pigment I is preferably 60 mass% or less, more preferably 50 mass% or less, of the total solid content of the undercoat layer. On the other hand, from the viewpoint of effectively reducing printing problems such as the generation of head residue and sticking, it is preferably 20 mass% or more, more preferably 25 mass% or more, of the total solid content of the undercoat layer.

[0035] The undercoat layer is formed on the support by applying a coating material for the undercoat layer, which is prepared by mixing hollow particles, an adhesive, an inorganic pigment I, and, if necessary, an auxiliary, to a water medium, and then drying the coating material. The amount of the coating material for the undercoat layer is not particularly limited, but is preferably 2 to 20 g / m2 in terms of dry mass. 2 The preferred thickness is 2 to 12 g / m 2 degree is more preferable.

[0036] [Thermal recording layer] (Leuco dye) The heat-sensitive recording layer of the heat-sensitive recording medium of the present invention may contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes are given below.

[0037] Specific examples of leuco dyes include blue-coloring dyes such as 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-methylphenyl)-3-(4-dimethylaminophenyl)-6-dimethylaminophthalide, and fluoran; green dyes such as 3-(N-ethyl-Np-tolyl)amino-7-N-methylanilinofluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, and rhodamine B-anilinolactam; Color-forming dyes, such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 3-diethylamino-7-chlorofluoran, red color-forming dyes such as 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-diethyl ... -Di(n-butyl)amino-6-methyl-7-anilinofluoran, 3-di(n-pentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-(N-isoamyl-N-ethylamino)-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-2-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3- (Nn-hexyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-ethylamino]-6-methyl-7-anilinofluoran, 3-[N-(3-ethoxypropyl)-N-methylamino]-6-methyl-7-anilinofluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-di(n-butylamino)-7-(2-chloroanilino)fluoran, 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-Trichlorophenylleucoauramine, 3-diethylamino-7-butylaminofluoran, 3-ethyl-tolylamino-6-methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-(β-ethoxyethyl)aminofluoran, 3-diethylamino-6-chloro-7-(γ-chloropropyl)aminofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-isopropyl)aminofluoran, Soamyl-N-ethylamino)-6-methyl-7-anilinofluoran, 3-dibutylamino-7-chloroanilinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-diethylamino -6-chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 2,2-bis{4-[6'-(N-cyclohexyl-N-methylamino)-3'-methylspiro[phthalido-3,9'-xanthen-2'-ylamino]phenyl}propane, 3-diethylamino-7-(3'-trifluoromethylphenyl)aminofluoran, and other black pigments. Color dyes, 3,3-bis[1-(4-methoxyphenyl)-1-(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-p-(p-dimethylaminoanilino)anilino-6-methyl-7-chlorofluoran, 3-p-(p-chloroanilino)anilino-6-methyl-7-chlorofluoran, 3,Examples of the dyes include dyes having an absorption wavelength in the near infrared region, such as 6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. Of course, the dyes are not limited to these, and two or more compounds can be used in combination as necessary.

[0038] The content of the leuco dye is not particularly limited, and is preferably about 3 to 30% by mass, more preferably about 5 to 25% by mass, and even more preferably about 7 to 20% by mass, of the total solid content of the thermosensitive recording layer. By making it 3% by mass or more, the color development ability can be improved and the recording density can be improved. By making it 30% by mass or less, the heat resistance can be improved.

[0039] (Developer) In the present invention, 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide is contained as a developer. By combining this compound with inorganic pigment II, it is possible to exhibit excellent alcohol resistance and plasticizer resistance of the recorded portion, as well as heat resistance to background fogging.

[0040] The content of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide is not particularly limited and may be adjusted according to the leuco dye used. In general, it is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 1.2 parts by mass or more, and particularly preferably 1.5 parts by mass or more, relative to 1 part by mass of the leuco dye. On the other hand, the content of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3.5 parts by mass or less, relative to 1 part by mass of the leuco dye. By making it 0.5 parts by mass or more, it is possible to improve the recording performance and also improve the alcohol resistance and plasticizer resistance of the recording part. On the other hand, by making it 10 parts by mass or less, it is possible to effectively suppress background fogging in a high-temperature environment.

[0041] Other color developers (second color developers) may be contained as long as they do not impair the effects of the present invention. Specific examples of the second color developers include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidenediphenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidene diphenyl, 4,4'-cyclohexylidene diphenol, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 4,4'-bis(p -Tolylsulfonylaminocarbonylamino)diphenylmethane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2'-bis[4-(4-hydroxyphenyl)phenoxy]diethyl ether, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenyl sulfide , 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-n-propoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, hydroquinone monobenzyl ether, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxy-4' -Methyldiphenyl sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate ester, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4,Phenolic compounds such as 4'-dihydroxydiphenyl ether, or benzoic acid, p-chlorobenzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, aromatic carboxylic acids such as 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-{3-(p-tolylsulfonyl)propyloxy]salicylate, and salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as thiocyanates. Examples of the acidic organic compounds include antipyrine complexes of zinc phosphate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids; thiourea compounds such as Np-toluenesulfonyl-N'-3-(p-toluenesulfonyloxy)phenylurea, Np-toluenesulfonyl-N'-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, and N,N'-di-m-chlorophenylthiourea; organic compounds having a -SO2NH- bond in the molecule such as N-(p-toluenesulfonyl)carbamoyl acid p-cumylphenyl ester, N-(p-toluenesulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and N-(o-toluoyl)-p-toluenesulfamide; and inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate.

[0042] In the present invention, the second developer is preferably a urea urethane compound such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenylsulfone represented by the following general formula (1), a diphenylsulfone crosslinked compound represented by the following general formula (2), an N,N'-diarylurea compound represented by the following general formula (3), a compound represented by the following general formula (4), or 4,4'-bis(3-tosylureido)diphenylmethane. This allows the effects of the present invention to be fully exhibited. [ka] [ka] (In the formula, n represents an integer of 1 to 6.) [ka] (In the formula, R 0 represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the aralkyl group and the aryl group being optionally substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; 0 may be the same or different. A 1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, 1 may be the same or different.) [ka] (In the formula, R 1 ~R 5are 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.

[0043] In the general formula (3) of the N,N'-diaryl urea compound contained as the second color developer, R 0 The alkyl group having 1 to 12 carbon atoms may be linear, branched, or alicyclic, and is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a 2-ethylhexyl group, and a lauryl group. The alkyl group here also includes the alkyl portion of an alkoxy group having 1 to 12 carbon atoms.

[0044] The aralkyl group refers to an arylalkyl group. Examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, and a 3-phenylpropyl group.

[0045] The aryl group refers to a monocyclic or polycyclic group consisting of a 5- or 6-membered aromatic hydrocarbon ring. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. The aryl group here also includes the aryl portion of an aralkyl group.

[0046] Halogen atoms include fluorine, chlorine, bromine and iodine.

[0047] In the general formula (3), multiple R 0The substitution positions of -SO3- may be the same or different. The substitution position is preferably the 3rd, 4th or 5th position, more preferably the 3rd position. In addition, when the aralkyl group having 7 to 12 carbon atoms and the aryl group having 6 to 12 carbon atoms of R2 have a substituent, the number of the substituent is not particularly limited and is, for example, 1 to 4.

[0048] A 1 The alkyl group having 1 to 4 carbon atoms may be either linear or branched, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group.

[0049] Multiple A's 1 The substitution positions of may be the same or different. The substitution position is preferably the 3-position, 4-position or 5-position.

[0050] The N,N'-diaryl urea compound represented by the general formula (3) is not particularly limited, and examples thereof include N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(4-ethylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(2-naphthalenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea, At least one selected from the group consisting of N,N'-di-[3-(benzylsulfonyloxy)phenyl]urea, N,N'-di-[3-(ethanesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[4-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[4-(ethanesulfonyloxy)phenyl]urea, and N,N'-di-[2-(p-toluenesulfonyloxy)]phenylurea is preferred. Among these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is preferred.

[0051] R 1 ~R 5 Examples of the halogen atom include a fluorine atom, a chlorine atom and a bromine atom, with a fluorine atom and a chlorine atom being preferred.

[0052] The alkyl group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Usually, it is an alkyl group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and further preferably an alkyl group having 1 to 4 carbon atoms.

[0053] The alkoxy group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Usually, it is an alkoxy group having 1 to 12 carbon atoms, preferably an alkoxy group having 2 to 8 carbon atoms, more preferably an alkoxy group having 2 to 6 carbon atoms, and even more preferably an alkoxy group having 2 to 4 carbon atoms.

[0054] The alkylcarbonyloxy group may be linear, branched or cyclic, and is preferably a linear or branched alkylcarbonyloxy group, more preferably a linear alkylcarbonyloxy group. Also, an alkylcarbonyloxy group having 1 to 10 carbon atoms is preferred.

[0055] The alkylcarbonylamino group may be linear, branched or cyclic, and is preferably a linear or branched alkylcarbonylamino group, more preferably a linear alkylcarbonylamino group. Also, an alkylcarbonylamino group having 1 to 10 carbon atoms is preferred.

[0056] The alkylsulfonylamino group may be linear, branched or cyclic, and is preferably a linear or branched alkylsulfonylamino group, more preferably a linear alkylsulfonylamino group. Also, an alkylsulfonylamino group having 1 to 10 carbon atoms is preferred.

[0057] The aryl group refers to a monocyclic or polycyclic group consisting of a 5- or 6-membered aromatic hydrocarbon ring. Examples of the aryl group include a phenyl group, a naphthyl group, and a biphenyl group.

[0058] The aryloxy group is preferably an aryloxy group having 6 to 12 carbon atoms. The arylcarbonyloxy group is preferably an arylcarbonyloxy group having 6 to 12 carbon atoms. The arylcarbonylamino group is preferably an arylcarbonylamino group having 6 to 12 carbon atoms. The arylsulfonylamino group is preferably an arylsulfonylamino group having 6 to 12 carbon atoms.

[0059] The monoalkylamino group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. In addition, a monoalkylamino group having an alkyl group with 1 to 10 carbon atoms is preferred.

[0060] The dialkylamino group may be linear, branched or cyclic, preferably linear or branched, more preferably linear. Also, a dialkylamino group having an alkyl group with 1 to 10 carbon atoms is preferred.

[0061] The arylamino group may be a monoarylamino group or a diarylamino group, and is preferably a monoarylamino group having 6 to 12 carbon atoms.

[0062] Specific examples of the compound represented by the general formula (4) include R 1 ~R 5 is an alkyl group or a hydrogen atom, and preferably R 1 ~R 5 is a linear alkyl group having 1 to 8 carbon atoms or a hydrogen atom, and more preferably R 1 ~R 5 is a linear alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and more preferably R 1 ~R 5 is a methyl group or a hydrogen atom.

[0063] Other specific examples of the compound represented by formula (4) include R 1 , R 2 , R 4 and R 5 is a hydrogen atom and R 3is 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 alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, or an arylamino group (preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, still more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group).

[0064] The substitution position of the substituent bonded to one of the benzene rings of the diphenylurea structure in the general formula (4) can be the ortho-position, meta-position or para-position relative to the aminocarbonyl group on the benzene ring, preferably the ortho-position or meta-position, more preferably the meta-position.

[0065] The compound represented by the general formula (4) is not particularly limited, but is preferably at least one selected from the group consisting of 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, 2-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate, and 4-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate. Among these, 3-[(phenylcarbamoyl)amino]phenyl-4-methylbenzenesulfonate is preferred.

[0066] The content ratio of the second color developer is not particularly limited, but is preferably 0.2 to 3 parts by mass per 1 part by mass of the leuco dye, and the content of the second color developer is preferably approximately 0.2 to 0.5 parts by mass per 1 part by mass of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as the first color developer.

[0067] (Inorganic Pigments II) The thermosensitive recording layer in the present invention contains an inorganic pigment II having an oil absorption of 130 ml / 100 g or less. The oil absorption of the inorganic pigment II is preferably 125 ml / 100 g or less, more preferably 100 ml / 100 g or less, and most preferably 65 ml / 100 g or less. This can significantly improve the alcohol resistance and plasticizer resistance. On the other hand, from the viewpoint of effectively reducing printing problems such as head residue generation and sticking, it is preferably 30 ml / 100 g or more. The thermosensitive recording layer in the present invention may contain a pigment having an oil absorption of more than 130 ml / 100 g, as long as it does not impair the effects of the present invention. The content of the pigment having an oil absorption of more than 130 ml / 100 g is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and even more preferably 0.1 parts by mass or less, per 1 part by mass of the pigment having an oil absorption of 130 ml / 100 g or less. It is particularly preferable that no pigment has an oil absorption of more than 130 ml / 100 g. Here, the oil absorption is a value determined according to the method of JIS K 5101.

[0068] Various inorganic pigments can be used as the inorganic pigment II, and specific examples include inorganic pigments such as calcium carbonate such as light calcium carbonate, aluminum hydroxide, clay such as calcined kaolin and kaolin, and talc. Among these, it is preferable that the inorganic pigment II is at least one selected from the group consisting of calcium carbonate, aluminum hydroxide, and clay. The type of the inorganic pigment II may be different from or the same as that of the inorganic pigment I. The content ratio of the inorganic pigment II can be selected from a wide range, but is preferably 10 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 35 mass % of the total solid content of the thermal recording layer.

[0069] In the present invention, a storage property improver can be further contained in the heat-sensitive recording layer, mainly to further improve the storage stability of the color image. Examples of such storage property improvers include 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1-bis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisphenol, and 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisphenol. At least one selected from phenol compounds such as 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy)phenylsulfone, epoxy compounds such as 4-(2-methyl-1,2-epoxyethyl)diphenylsulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenylsulfone, and isocyanuric acid compounds such as 1,3,5-tris(2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl)isocyanuric acid can be used. Of course, the present invention is not limited to these compounds, and two or more compounds can be used in combination as necessary.

[0070] When a storage stability improver is used, the amount used should be an amount effective for improving storage stability, and is usually preferably about 1 to 25 mass %, more preferably about 5 to 20 mass %, of the total solid content of the thermosensitive recording layer.

[0071] A sensitizer can also be contained in the heat-sensitive recording layer in the present invention. This can increase the recording sensitivity. Examples of sensitizers include stearic acid amide, methoxycarbonyl-N-stearic acid benzamild, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bisstearic acid amide, behenic acid amide, methylene bisstearic acid amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, diphenyl sulfone, benzyl p-benzyloxybenzoate, 1-hydroxy-2-phenyl naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, di-p-chlorobenzyl ester of oxalic acid, di-p-methylbenzyl ester of oxalic acid, dibenzyl ester of oxalic acid, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy) ether, and the like. p-methylthiophenyl benzyl ether, 1,4-di(phenylthio)butane, p-acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, 1,2-diphenoxymethylbenzene, di(β-biphenylethoxy)benzene, p-di(vinyloxyethoxy)benzene, 1-isopropylphenyl-2-phenylethane, di-o-chlorobenzyl adipate, 1,2-bis(3,4-dimethylphenyl)ethane, 1,3-bis(2-naphthoxy)propane, diphenyl, benzophenone, and the like. Among these, 1,2-di(3-methylphenoxy)ethane is preferred from the viewpoint of obtaining a sensitizing effect without deteriorating long-term storage stability. These can be used in combination within a range that does not cause problems. The content of the sensitizer may be an amount effective for sensitization, and is usually preferably about 2 to 25% by mass, more preferably about 5 to 20% by mass, and even more preferably about 5 to 15% by mass of the total solid content of the thermal recording layer.

[0072] Other components constituting the heat-sensitive recording layer include adhesives, and if necessary, auxiliary agents such as crosslinking agents, waxes, metal soaps, water-resistant agents, dispersants, colored dyes, and fluorescent dyes can be used.

[0073] Examples of adhesives include polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, water-soluble polymer materials such as sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin, and their derivatives, as well as emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers, or latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Among these, polyvinyl alcohol and latex are preferred. The content of the adhesive can be selected from a wide range, but generally, it is preferably about 5 to 30% by mass, and more preferably about 10 to 20% by mass, of the total solid content of the thermal recording layer.

[0074] By incorporating a crosslinking agent in the thermosensitive recording layer, the water resistance of the thermosensitive recording layer can be improved. Examples of crosslinking agents include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylates, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate, boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, and glyoxylates. These may be used alone or in combination of two or more. The amount of the crosslinking agent used is preferably about 1 to 10% by mass, and more preferably about 1 to 5% by mass, of the total solid content of the thermosensitive recording layer.

[0075] The thermal recording layer is formed on the undercoat layer by, for example, dispersing the leuco dye and developer together with a sensitizer or storage improver, if necessary, or separately, in water as a dispersion medium, together with water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, styrene-maleic anhydride copolymer salt, and other surfactants, using various stirring and wet grinding machines such as ball mills, coball mills, attritors, and vertical and horizontal sand mills, to prepare respective dispersions, and then finely milling the dispersions to an average particle size of 2 μm or less, mixing the inorganic pigment II with the dispersions, and mixing adhesives, auxiliaries, and the like, if necessary, to prepare a coating material for the thermal recording layer, and then drying the coating material. The coating amount of the thermal recording layer is not particularly limited, and the coating amount after drying is 1 to 12 g / m. 2 The preferred thickness is 2 to 10 g / m 2 The preferred range is 2.5 to 8 g / m 2 More preferably, the thickness is about 3 to 5.5 g / m 2 The heat-sensitive recording layer can be formed in two or more layers as required, and the composition and coating amount of each layer may be the same or different.

[0076] [Protective layer] The thermal recording medium may also have a protective layer on the thermal recording layer as necessary. The protective layer preferably contains a pigment and an adhesive. Furthermore, the protective layer preferably contains a lubricant such as polyolefin wax or zinc stearate for the purpose of preventing sticking to the thermal head, and may also contain an ultraviolet absorbing agent. Furthermore, by providing a glossy protective layer, the added value of the product can be increased.

[0077] The pigment contained in the protective layer is not particularly limited, and examples thereof include inorganic pigments such as amorphous silica, kaolin, clay, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, and plastic pigments such as urea-formaldehyde resin filler, etc. The content of the pigment is preferably about 20 to 80 mass %, and more preferably about 30 to 75 mass %, of the total solid content of the protective layer.

[0078] The adhesive contained in the protective layer is not particularly limited, and a water-soluble or water-dispersible aqueous adhesive can be used. The adhesive can be appropriately selected from those that can be used in the thermal recording layer. Among these adhesives, various modified polyvinyl alcohols such as acetoacetyl-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and diacetone-modified polyvinyl alcohol are more preferably used. The content of the adhesive is preferably about 10 to 70% by mass, more preferably about 20 to 50% by mass, of the total solid content of the protective layer.

[0079] The protective layer is formed on the thermosensitive recording layer by, for example, applying a coating material for the protective layer prepared by mixing a pigment, an adhesive, and, if necessary, an auxiliary, etc., in water as a dispersion medium, and then drying the coating material. The amount of the coating material for the protective layer is not particularly limited, and is preferably 0.3 to 15 g / m2 in terms of dry mass. 2 The preferred range is 0.3 to 10 g / m 2 The preferred range is 0.5 to 8 g / m 2 More preferably, the thickness is 1 to 8 g / m 2 The preferred range is 1 to 5 g / m 2The protective layer may be formed in two or more layers as required, and the composition and coating amount of each layer may be the same or different.

[0080] [Other layers] In the present invention, it is preferable that the support has an adhesive layer on at least one side. This can increase the added value of the thermal recording medium. For example, the adhesive layer can be made into adhesive paper, remoistened adhesive paper, delayed tack paper, etc. by applying coating processing with an adhesive, remoistened adhesive, delayed tack type adhesive, etc. on one side. In addition, the surface of the support opposite to the thermal recording layer can be given the function of thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, xeography paper, etc., to make a recording paper capable of double-sided recording. Of course, it can also be made into a double-sided thermal recording medium. In addition, a back layer can be provided to suppress the penetration of oil and plasticizer from the back side of the thermal recording medium, to control curling, and to prevent static electricity. It is also possible to make a linerless label that does not require a release paper by coating processing a release layer containing silicone on the protective layer and coating processing a pressure sensitive adhesive on one side.

[0081] [Thermal recording medium] The thermal recording medium can be manufactured by forming each of the above layers on a support. The method for forming each of the above layers on a support may be any of known coating methods such as the air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, curtain method, slot die method, slide die method, and extrusion method. Each coating material may be applied and dried one by one to form each layer, or the same coating material may be applied in two or more layers. Furthermore, simultaneous multi-layer coating may be performed in which two or more layers are applied at the same time. After each layer is formed or after all layers are formed, the surface may be smoothed using known methods such as super calendaring and soft calendaring. EXAMPLES

[0082] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass", respectively. Particle sizes such as average particle size and maximum particle size were measured using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation). Here, the average particle size is the median size (D50).

[0083] The hollow particles used in the examples and comparative examples are as follows. Hollow particle A: Median diameter (D50) 5.0 μm, maximum particle diameter (D100) 13.5 μm, hollow rate 90%, percentage of particles 2 μm or less 0.2 vol%, solid content 15.0% Hollow particle B: Median diameter (D50) 11 μm, maximum particle diameter (D100) 23 μm, hollow rate 93%, percentage of particles 2 μm or less 0 vol%, solid content 15.0% Hollow particle C: Ropek SN-1055 (Dow), median diameter (D50) 1.0 μm, maximum particle diameter (D100) 1.8 μm, hollow ratio 55%, solid content 26.5% The average particle size (D50) and maximum particle size (D100) of each hollow particle were measured using a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) at a refractive index of 1.70-0.01i.

[0084] The latexes used in the examples and comparative examples are as follows. Latex A: Styrene-butadiene latex development product (Tg: -35℃, particle size 300nm, solid content 48%) Latex B: Styrene-butadiene latex development product (Tg: -10℃, particle size 190nm, solid content 48%) Latex C: Styrene-butadiene latex (product name L-1571, manufactured by Asahi Kasei Corporation, Tg = -3°C, particle size 190 nm, solid content 48%)

[0085] Example 1 (1) Preparation of coating solution for undercoat layer A coating solution for an undercoat layer was obtained by mixing and stirring 100 parts of hollow particles A, 38 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF, oil absorption: 105 ml / 100 g), 79.2 parts of latex A, 32 parts of a 25% solution of oxidized starch, 1.1 parts of carboxymethylcellulose (trade name: Cellogen AG Gum, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 100 parts of water.

[0086] (2) Preparation of leuco dye dispersion (liquid A) 40 parts of 3-di-(n-butyl)amino-6-methyl-7-anilinofluoran, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed and ground using a sand mill (sand grinder manufactured by Imex Co., Ltd.) until the average particle size became 0.5 μm, to obtain a leuco dye dispersion liquid (Liquid A).

[0087] (3) Preparation of developer dispersion liquid (liquid B) 40 parts of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed and ground using a sand mill (sand grinder manufactured by Imex Co., Ltd.) until the average particle diameter became 1.0 μm, to obtain a developer dispersion liquid (Liquid B).

[0088] (4) Preparation of sensitizer dispersion (liquid C) 40 parts of 1,2-di(3-methylphenoxy)ethane (product name: KS-232, manufactured by Sankosha), 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed and ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) until the average particle size became 1.0 μm, thereby obtaining a sensitizer dispersion liquid (Liquid C).

[0089] (5) Preparation of coating solution for thermal recording layer A coating liquid for a thermal recording layer was obtained by mixing and stirring 29.5 parts of solution A, 63.6 parts of solution B, 45.5 parts of solution C, 70 parts of a 10% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA117, saponification degree: 99 mol%, average polymerization degree: 1700, manufactured by Kuraray Co., Ltd.), 20.8 parts of a styrene-butadiene copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Corporation, solid content concentration: 48%), 20 parts of calcium carbonate (trade name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd., oil absorption amount: 56 ml / 100 g), 2 parts of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 150 parts of water.

[0090] (6) Preparation of protective layer coating solution A coating liquid for the protective layer was obtained by mixing and stirring a composition consisting of 317 parts of a 12% aqueous solution of diacetone-modified polyvinyl alcohol (trade name: DF-10, manufactured by Japan Vinyl Acetate & Poval Co., Ltd.), 60 parts of kaolin (trade name: HYDRAGLOSS90, manufactured by KaMin LLC), 0.5 parts of polyethylene wax (trade name: Chemipearl W-400, manufactured by Mitsui Chemicals, Inc., solids concentration: 40%), 5 parts of zinc stearate (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solids concentration: 36%), and 300 parts of water.

[0091] (7) Preparation of thermal recording medium Basis weight 60g / m 2 On one side of the high-quality paper, the coating liquid for the undercoat layer, the coating liquid for the thermal recording layer, and the coating liquid for the protective layer were each applied in an amount of 4.5 g / m2 after drying. 2 , 3.8g / m 2 , 2.3g / m 2 After the undercoat layer, the thermosensitive recording layer, and the protective layer were formed in this order, the surface was smoothed with a supercalender to obtain a thermosensitive recording medium.

[0092] Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in preparing the coating liquid for the thermosensitive layer in Example 1, aluminum hydroxide (product name: Hidilite H-42, manufactured by Showa Light Metals Co., Ltd., oil absorption 43 ml / 100 g) was used instead of calcium carbonate.

[0093] Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Example 1, clay (product name: HG90, manufactured by Kamin, oil absorption 46 ml / 100 g) was used instead of calcium carbonate.

[0094] Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Example 1, calcium carbonate (product name: Brilliant-15, manufactured by Shiraishi Kogyo Co., Ltd., oil absorption capacity 56 ml / 100 g) was used instead of calcium carbonate (product name: Callite KT, manufactured by Shiraishi Kogyo Co., Ltd., oil absorption capacity 120 ml / 100 g).

[0095] Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the undercoat layer in Example 1, 79.2 parts of Latex B was used instead of 79.2 parts of Latex A.

[0096] Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the undercoat layer in Example 1, 79.2 parts of Latex C was used instead of 79.2 parts of Latex A.

[0097] Example 7 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the undercoat layer in Example 1, 100 parts of hollow particles B were used instead of 100 parts of hollow particles A.

[0098] Example 8 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the coating liquid for the undercoat layer in Example 1, the amount of calcined kaolin was changed from 38 parts to 66 parts, the amount of latex A was changed from 79.2 parts to 20.8 parts, and the amount of water was changed from 100 parts to 130 parts.

[0099] Example 9 A thermal recording medium was obtained in the same manner as in Example 1, except that in preparing the coating solution for the undercoat layer, the amount of calcined kaolin was changed from 38 parts to 66 parts, the amount of Latex C was changed from 79.2 parts to 20.8 parts, the amount of Hollow Particles C was changed from 100 parts to 56.6 parts, and the amount of water was changed from 100 parts to 180 parts.

[0100] Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in preparing the coating liquid for the thermosensitive layer in Example 1, amorphous silica (product name: Nipsil E743, manufactured by Tosoh Silica Corporation, oil absorption 150-170 ml / 100 g) was used instead of calcium carbonate.

[0101] Comparative Example 2 (8) Preparation of developer dispersion liquid (liquid D) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone (product name: D-8, manufactured by Nippon Soda Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%), and 20 parts of water were mixed and ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) until the average particle diameter became 1.0 μm, to obtain a developer dispersion liquid (Liquid D).

[0102] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating liquid for the thermosensitive layer in Comparative Example 1, the color developer dispersion liquid D was used instead of the color developer dispersion liquid B.

[0103] The above examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

[0104] [Recording Density] Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded with an applied energy of 0.16 mJ / dot (halftone color density), and the resulting printed area was measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.). The higher the value, the higher the print density. The mid-tone color density was evaluated based on the following criteria: Color density of 0.90 or more: Excellent and also suitable for high-speed printing. Color density of 0.80 or more: required for practical use. Color density less than 0.80: Low sensitivity and many defects such as white spots, which are problematic for practical use.

[0105] [Alcohol resistance] A sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), was immersed in a 75% by volume ethanol solution for 30 minutes, and the optical density of the printed area after processing was measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). The evaluation criteria were as follows: Density of blank area after processing: 1.00 or more: Very good. Density of blank areas after processing: 0.80 or more: No problem in practical use. Density of blank areas after processing is less than 0.80: Printing disappears, causing problems in practical use.

[0106] [Plasticizer resistance] A polycarbonate pipe (diameter 40 mm) was wrapped with three layers of cling film (product name: HI-ES Soft, manufactured by Nippon Carbide Industries Co., Ltd.), and each thermal recording medium that had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation) was placed on top of the film. Three layers of cling film were then wrapped around the film and the material was left to stand for 24 hours in an environment of 40°C. After this, the optical density of the recorded area was measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). The evaluation criteria were as follows: Density of blank area after processing: 1.00 or more: Very good. Density of blank areas after processing: 0.80 or more: No problem in practical use. Density of blank areas after processing is less than 0.80: Printing disappears, causing problems in practical use.

[0107] [100℃ heat resistance] Samples of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), were left to stand in a chamber at 100°C for 1 hour, and the optical density of the blank area after processing was measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). The evaluation criteria were as follows: Density of blank areas after processing: 0.10 or less: Very good. Density of blank areas after processing: 0.20 or less: No problem in practical use. Density of blank area after processing exceeds 0.20: background fogging is severe and is problematic in practical use.

[0108] [Table 1]

[0109] As can be seen from Table 1, the thermal recording media of Examples 1 to 9 are excellent in alcohol resistance and plasticizer resistance, and are also excellent in heat resistance to background fogging. On the other hand, Comparative Example 1 had poor alcohol resistance of the print and extremely poor plasticizer resistance. Comparative Example 2, by changing the color developer, had extremely poor alcohol resistance and, although its plasticizer resistance was slightly better than that of Comparative Example 1, was not suitable for practical use. In addition, the density of the blank area in the 100°C heat resistance was extremely poor.

Claims

1. A thermal recording medium having, on a support, at least an undercoat layer containing hollow particles, an adhesive and an inorganic pigment I, and a thermal recording layer containing a leuco dye, a color developer and an inorganic pigment II in this order, characterized in that the color developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, and the inorganic pigment II contains a pigment having an oil absorption of 130 ml / 100 g or less.

2. 2. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment II contains a pigment having an oil absorption of 65 ml / 100 g or less.

3. 3. The thermosensitive recording material according to claim 1, wherein the inorganic pigment II contains at least one selected from the group consisting of calcium carbonate, aluminum hydroxide, and clay.

4. 3. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment I has an oil absorption of 130 ml / 100 g or less.

5. 3. The heat-sensitive recording material according to claim 1, wherein said inorganic pigment I comprises at least one selected from the group consisting of calcium carbonate, aluminum hydroxide and clay.

6. 3. The thermosensitive recording material according to claim 1, wherein the content of said inorganic pigment I is 50 parts by mass or less based on the total solid content of the undercoat layer.

7. 3. The thermosensitive recording medium according to claim 1, wherein the hollow particles have a maximum particle diameter (D100) of 10 to 30 μm, an average particle diameter (D50) of 4.0 to 15 μm, a ratio D100 / D50 of the maximum particle diameter (D100) to the average particle diameter (D50) of 1.8 to 3.0, and a volume percentage of particles with a particle diameter of 2.0 μm or less is 1% or less.

8. 3. The thermosensitive recording medium according to claim 1, wherein the hollow particles have a hollow ratio of 80 to 98%.

9. 3. The thermosensitive recording medium according to claim 1, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -10° C. or lower.

10. 3. The heat-sensitive recording medium according to claim 1, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of -30° C. or lower.

11. The thermosensitive recording layer contains a second developer represented by the following general formula (1): [Formula 1] a urea-urethane compound represented by the following general formula (2): [Case 2] (In the formula, n represents an integer of 1 to 6.) a diphenylsulfone-bridged compound represented by the following general formula (3): [C3] (In the formula, R ０ represents an alkyl group having 1 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the aralkyl group and the aryl group being optionally substituted with an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a halogen atom; ０ may be the same or different. １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, １ may be the same or different.) an N,N'-diaryl urea compound represented by the following general formula (4): [C4] (In the formula, R １ ~R ５and are 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. The thermal recording medium according to claim 1 or 2, comprising at least one selected from a compound represented by the formula (I) and 4,4'-bis(3-tosylureido)diphenylmethane.

12. 12. The thermosensitive recording medium according to claim 11, wherein the second developer is contained in an amount of 0.2 to 3 parts by mass per part by mass of the leuco dye.

13. 3. The thermosensitive recording medium according to claim 1, further comprising an adhesive layer on at least one surface of the support.