Thermal recording medium

Abstract

To provide a heat-sensitive recording material that is excellent in the water resistance and water plasticizer resistance of a recording part as well as the alcohol resistance of the recording part and a base part.SOLUTION: The present disclosure provides a heat-sensitive recording material which comprises, on a supporting body, a primer coating layer that contains an inorganic pigment, hollow particles, and an adhesive, and a heat-sensitive recording layer that contains a leuco dye, color developers, and an adhesive. The color developers include a first color developer and a second color developer. The second color developer is a compound represented by general formula (1) (where, R2 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 may be 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; the plurality of R2's may be the same as or different from each other; A1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and the plurality of A1's may be the same as or different from each other).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermosensitive recording medium. [Background technology]

[0002] Thermosensitive recording media, which record color images by utilizing the thermal color-developing reaction between colorless or light-colored leuco dyes and phenols or organic acids, are widely used. Because color images are formed simply by heating, these thermal recording media offer advantages such as compact recording devices, easy maintenance, and low noise. For these reasons, thermal recording media are widely used as information recording materials in a variety of applications, including label printers and other issuing machines, automatic ticket vending machines, CD / ATMs, order slip output devices in restaurants, and data output devices in scientific research equipment.

[0003] It is known that the color-developing reaction is reversible, resulting in color-developed images that fade over time. This fade reaction is accelerated in high-temperature, high-humidity environments and can progress rapidly upon contact with oil, plasticizers, etc., resulting in the recorded image becoming unreadable. In recent years, alcohol-based disinfection and sterilization have become commonplace in everyday life, particularly for the prevention of infectious diseases. That is, there has been a growing demand for improved performance of thermal recording media, such as preventing color development in blank areas and discoloration of printed areas even when exposed to 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 is insufficient in water resistance, water-resistant plasticizer resistance, and alcohol 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] A main object of the present invention is to provide a thermosensitive recording medium which has excellent water resistance and water-plasticizer resistance in the recorded area, and excellent alcohol resistance in the recorded area and background area. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of 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 thermosensitive recording medium having, on a support, at least an undercoat layer containing an inorganic pigment, hollow particles, and an adhesive, and a thermosensitive recording layer containing a leuco dye, a color developer, and an adhesive, in this order, the color developers containing a first color developer and a second color developer, and the second color developer containing a compound represented by general formula (1): [ka] (wherein R2 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, and the aralkyl group and the aryl group may be 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, and multiple R2s may be the same or different; and A1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and multiple A1s may be the same or different). A thermosensitive recording medium characterized by containing an N,N'-diaryl urea compound represented by the following formula: Item 2: The N,N'-diaryl urea compound represented by the general formula (1) is 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-methyl 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)phenyl]urea )centre Venil ] Item 2. The thermosensitive recording medium according to Item 1, wherein the compound is at least one selected from the group consisting of urea. Item 3: The N,N'-diaryl urea compound represented by the general formula (1) is N,N'-di[3-(p-toluenesulfonyl) Luo Kishi ) Phenyl ] Item 2. The thermosensitive recording medium according to Item 1, which is urea. Item 4: The first color developer is represented by general formula (2) [ka] (In the formula, R 3、 R4 are the same or different and represent an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyloxy group having 2 to 4 carbon atoms, an aralkyloxy group having 7 to 12 carbon atoms, or a halogen atom. m is an integer of 0 to 2, n is an integer of 1 to 3, and p and q are the same or different and represent an integer of 0 to 2. Item 5: The thermosensitive recording material according to Item 4, wherein the diphenyl sulfone derivative represented by the general formula (2) is at least one selected from 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(3-allyl-4-hydroxy)diphenyl sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl) sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, and 4-hydroxy-4'-benzyloxydiphenyl sulfone. Item 6: The thermosensitive recording material according to any one of Items 1 to 3, wherein the first color developer is Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea. Item 7: The thermosensitive recording medium according to any one of Items 1 to 3, wherein the first color developer is N-[2-(3-phenylureido)phenyl]benzenesulfonamide. Item 8: The thermosensitive recording material according to any one of Items 1 to 3, wherein the first color developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. Item 9: The thermosensitive recording medium according to any one of Items 1 to 8, wherein the second color developer is contained in an amount of 0.1 to 3 parts by mass per 1 part by mass of the first color developer. Item 10: The thermosensitive recording medium according to any one of Items 1 to 8, wherein the second color developer is contained in an amount of 0.1 to 1 part by mass per 1 part by mass of the first color developer. Item 11: The thermosensitive recording material according to any one of Items 1 to 10, wherein the hollow particles have a maximum particle size (D100) of 10 to 30 μm, an average particle size (D50) of 4.0 to 15 μm, a ratio D100 / D50 of the maximum particle size (D100) to the average particle size (D50) of 1.8 to 3.0, and a volume percentage of particles having a particle size of 2.0 μm or less is 1% or less. Item 12: The thermosensitive recording medium according to any one of Items 1 to 11, wherein the hollow particles have a hollow ratio of 80 to 98%. Item 13: The thermosensitive recording medium according to any one of Items 1 to 12, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of −10° C. or lower. Item 14: The thermosensitive recording medium according to any one of Items 1 to 13, wherein the adhesive of the undercoat layer contains a binder resin having a glass transition temperature of −30° C. or lower. Item 15: The thermosensitive recording medium according to any one of items 1 to 14, wherein the support has an adhesive layer on at least one surface thereof. [Effects of the Invention]

[0009] The thermosensitive recording medium of the present invention has excellent water resistance and water-resistant plasticizer resistance in the recorded area, and excellent alcohol resistance in the recorded area and background area. DETAILED DESCRIPTION OF THE INVENTION

[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 formed by drying a dispersion medium.

[0013] The present invention provides a thermosensitive recording medium having, on a support, at least an undercoat layer containing an inorganic pigment, hollow particles, and an adhesive, and a thermosensitive recording layer containing a leuco dye, a color developer, and an adhesive, in this order, the thermosensitive recording medium containing a first color developer and a second color developer as the color developer, the second color developer being represented by general formula (1): [ka] (wherein R2 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, and the aralkyl group and the aryl group are 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, and multiple R2s may be the same or different; and A1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and multiple A1s may be the same or different).

[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 also not particularly limited, and is 0.60 to 0.85 g / cm. 3 The degree is preferable.

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

[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 thermosensitive recording layer and increase the sensitivity of the thermosensitive recording medium.

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

[0018] Non-expanded hollow particles can be produced by polymerizing seeds in a solution, polymerizing another resin so that the seeds are wrapped around the seeds, and then swelling and dissolving the seeds to remove them, thereby forming internal cavities. An alkaline aqueous solution or the like is used to swell and dissolve the seeds to remove them. Non-expanded hollow particles with a relatively large average particle size can also be obtained by subjecting core-shell particles, in which alkali-swellable core particles are coated with a shell layer that is not alkali-swellable, to an alkali swelling treatment.

[0019] Expanded hollow particles can be produced by preparing particles in which a volatile liquid is enclosed inside a resin, and then softening the resin by heating, thereby vaporizing and expanding the liquid inside the particles.

[0020] Expanded hollow particles increase the hollow ratio by heating and expanding the liquid inside during the manufacturing process, resulting in high thermal insulation, which can increase the sensitivity of the thermosensitive recording medium and improve recording density. Improved sensitivity is particularly important when coloring a mid-tone region where the thermal energy applied to the thermosensitive recording layer is small. Furthermore, forming a thermosensitive recording layer via a highly insulating undercoat layer can prevent the diffusion of heat applied to the thermosensitive recording layer, resulting in excellent image uniformity and improved image quality. Therefore, in this embodiment, it is preferable to use expanded hollow particles, which are excellent at improving the thermal insulation of the undercoat layer.

[0021] Resins that can be used for the expanded 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 resins mainly composed of polyvinylidene chloride and acrylonitrile. Typical gases contained inside the expanded hollow particles include propane, butane, isobutane, and air. Among the various resins listed above, acrylonitrile resin and copolymer resins mainly composed of polyvinylidene chloride and acrylonitrile are preferred for the resins used for the hollow particles in terms of the strength required to maintain 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 15 to 25 μm. The maximum particle diameter is also referred to as D100. When the maximum particle diameter of the hollow particles is 10 μm or more, the cushioning properties of the undercoat layer are improved, thereby improving the adhesion of the thermosensitive recording medium to the thermal head during printing, resulting in a thermosensitive recording medium with high image quality. This high image quality can result in improved recording density in halftones that are developed with lower energy than that required to achieve 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, allowing the thermosensitive recording layer provided via the undercoat layer to be uniform, resulting in a thermosensitive recording medium with fewer white gaps in the image.

[0023] The average particle diameter of the hollow particles in the present invention is preferably 4.0 to 15 μm, more preferably 7.5 to 15 μm. Here, the average particle diameter is the diameter at which the larger and smaller particles occupy equal volumes when divided into two groups based on particle diameter, i.e., the median particle diameter, also referred to as D50, which is the particle diameter with a 50% volume frequency. When the average particle diameter of the hollow particles is 4.0 μm or greater, the cushioning properties of the undercoat layer are improved, improving adhesion of the thermal recording medium to the thermal head during printing and resulting in a thermal recording medium with high image quality. This high image quality can result in improved recording density in halftones that are developed with lower energy than that required to achieve 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, allowing for uniformity of the thermal recording layer provided through the undercoat layer, resulting in a thermal recording medium with less white gaps in the image.

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

[0025] The ratio D100 / D50 of the maximum particle diameter (D100) to the average particle diameter (D50) of 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 diameter is sufficiently large, the hollow ratio is high, and the heat insulating properties of the primer layer can be improved. On the other hand, when the D100 / D50 of the hollow particles is 3.0 or less, the hollow particles are uniform in size, which improves the smoothness of the primer layer and reduces white spots in the image.

[0026] In the particle size distribution determined by a laser diffraction particle size analyzer, the volume percentage of hollow particles with a particle diameter of 2.0 μm or less is preferably 1% or less. Furthermore, 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 none at all. Hollow particles with a particle diameter of 2 μm or less are too small to provide sufficient hollow regions, and therefore are thought to contribute very little to heat insulation. By keeping the volume percentage of hollow particles with a particle diameter of 2 μm or less in the undercoat layer to 1% or less, it is possible to improve recording density, image quality, etc.

[0027] The hollow particles preferably have a void ratio of 80 to 98%, more preferably 90 to 98%. When the hollow ratio of hollow particles is 80% or more, high heat insulating properties can be imparted to the primer layer containing the hollow particles. On the other hand, when the hollow ratio of hollow particles is 98% or less, the strength of the film surrounding the hollow portion can be improved, thereby making the hollow particles less likely to be crushed during the formation of the primer layer.

[0028] The hollowness of hollow particles can be determined by measuring the true specific gravity using the IPA method and then calculating the hollowness from the true specific gravity value as follows. (1) Sample pretreatment Dry the sample at 60°C overnight to prepare the sample. (2) Reagents Isopropyl alcohol (IPA: first-grade reagent) (3) Measurement method ·Weigh the volumetric flask accurately (W1). ·Place approximately 0.5 g of the dried sample in a measuring flask and weigh it out accurately (W2). Add approximately 50 mg of IPA and shake thoroughly to completely remove any air from the capsule. Add IPA up to the mark and measure (W3). As a blank, add only IPA to the volumetric 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 calculated 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 their content in the undercoat layer can be reduced. The hollow particle content is preferably 3 to 40 mass % of the total solid content of the undercoat layer, and more preferably 5 to 35 mass %. When the hollow particle content is 3 mass % or more, the heat insulating properties of the undercoat layer can be improved. On the other hand, when the hollow particle content is 40 mass % or less, problems are less likely to occur in terms of coatability, etc., a uniform undercoat layer can be easily formed, and 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, carboxymethyl 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, and latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Among these, latex-containing adhesives are preferred. The adhesive content can be selected from a wide range, but is generally preferably about 20 to 70% by weight, and more preferably about 25 to 60% by weight, of the total solids content of the undercoat layer.

[0032] The adhesive preferably contains a binder resin with a glass transition temperature (Tg) of -10°C or lower. A glass transition temperature of -10°C or lower can improve image quality even in low energy regions. A glass transition temperature of -30°C or lower is more preferable because it can further improve image quality in low energy regions. 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) The undercoat layer of the present invention contains an inorganic pigment. From the viewpoints of increasing recording density and improving water resistance to plasticizers and alcohol resistance, the oil absorption of the inorganic pigment is preferably 130 ml / 100 g or less, 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 head residue generation and sticking, the oil absorption is preferably 50 ml / 100 g or more, 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, but calcined kaolin, clay, etc. are preferred. From the viewpoint of improving color development sensitivity, the content of the inorganic pigment is preferably 60% by mass or less, more preferably 50% by 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, the content of the inorganic pigment is preferably 20% by mass or more, more preferably 25% by 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, and, if necessary, an auxiliary agent, 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 range is 2 to 12 g / m 2 A degree is more preferable.

[0036] [Thermal recording layer] (leuco dye) The thermosensitive recording layer of the thermosensitive recording medium of the present invention may contain various known colorless or light-colored leuco dyes. Specific examples of such leuco dyes are listed 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; Red color-forming dyes such as 3,6-bis(diethylamino)fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-chlorofluoran, 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 such dyes include dyes with absorption wavelengths in the near-infrared region, such as 6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide. However, the present invention is not limited to these examples, and two or more compounds can be used in combination as needed.

[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-developing ability can be enhanced 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, the color developer contains a first color developer and a second color developer, and the second color developer contains an N,N'-diaryl urea compound represented by the above general formula (1). The first color developer is the main color developer, and the second color developer also has the effect of improving storage stability. This allows the color developer to exhibit excellent water resistance, water-resistant plasticizer resistance, alcohol resistance, etc.

[0040] Specific examples of the first color developer 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, and 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-methylphenol 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, 4-[3-(p-tolylsulfonyl)propyl]salicylic acid, and aromatic carboxylic acids such as zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, and phenolic compounds thereof, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid and other aromatic carboxylic acids. Organic acidic substances, thiourea compounds such as Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea, Np-tolylsulfonyl-N'-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis(p-toluenesulfonylaminocarbonylamino)diphenylmethane, N,N'-di-m-chlorophenylthiourea, Np-toluenesulfonyl)carbamoic acid p-cumylphenyl ester, N-(p-toluene Examples of suitable first color developers include organic compounds having an -SO2NH- bond in the molecule, such as (sulfonyl)carbamoyl acid p-benzyloxyphenyl ester, N-[2-(3-phenylureido)phenyl]benzenesulfonamide, N-(o-toluoyl)-p-toluenesulfonamide, and 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, as well as inorganic acidic substances, such as activated clay, attapulgite, colloidal silica, and aluminum silicate. The first color developer is, of course, not limited to these, and two or more compounds can be used in combination as needed.

[0041] The thermosensitive recording layer in the present invention preferably contains the diphenyl sulfone derivative represented by the above general formula (2) as the first color developer, which can further improve the color density.

[0042] In general formula (2), the alkyl groups having 1 to 4 carbon atoms represented by R3 and R4 may be either linear or branched, and examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and t-butyl. The alkyl groups herein also include the alkyl moieties of alkoxy groups having 1 to 4 carbon atoms. The alkenyl groups having 2 to 4 carbon atoms may be either linear or branched, and examples thereof include vinyl, n-propenyl, and n-butenyl. The alkenyl groups herein also include the alkenyl moieties of alkenyloxy groups having 2 to 4 carbon atoms. The aralkyl group refers to an arylalkyl group, and examples of aralkyl groups having 7 to 12 carbon atoms include benzyl, 1-phenylethyl, 2-phenylethyl, and 3-phenylpropyl. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. When there are a plurality of R3 and R4, they may be the same or different.

[0043] The substitution positions of R3, R4 and OH are not particularly limited, but the 3rd, 4th or 5th position is preferred. m is preferably 0 or 1, n is preferably 1, and p and q are preferably the same or different and each is 0 or 1.

[0044] The diphenyl sulfone derivative represented by general formula (2) is not particularly limited, and examples thereof include 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(3-allyl-4-hydroxy)diphenyl sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl) sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, and 4-hydroxy-4'-benzyloxydiphenyl sulfone. Hmm? At least one selected from the group consisting of the following is preferred.

[0045] In the present invention, it is also preferable that the first color developer is Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea, which provides an excellent balance between color density and storage stability and allows the effects of the present invention to be fully exerted.

[0046] In the present invention, it is also preferable that the first color developer is N-[2-(3-phenylureido)phenyl]benzenesulfonamide, which provides an excellent balance between color density and storage stability and allows the effects of the present invention to be fully exhibited.

[0047] In the present invention, it is also preferable that the first color developer is 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide. This provides an excellent balance between color density and storage stability, allowing the effects of the present invention to be fully exerted.

[0048] In the general formula (1) of the N,N'-diaryl urea compound contained as the second color developer, the alkyl group of R2 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.

[0049] 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.

[0050] 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.

[0051] Halogen atoms include fluorine, chlorine, bromine and iodine.

[0052] In general formula (1), the substitution positions of multiple R2-SO3- may be the same or different. The substitution position is preferably the 3rd, 4th, or 5th position, more preferably the 3rd position. Furthermore, 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.

[0053] The alkyl group of A1 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.

[0054] The substitution positions of the multiple A1s may be the same or different, and the substitution position is preferably the 3-, 4- or 5-position.

[0055] The N,N'-diaryl urea compound represented by the general formula (1) 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, 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)phenyl]urea )centre Venil ] At least one selected from the group consisting of ureas is preferred, and among these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is preferred.

[0056] The content of the first color developer is preferably about 0.2 to 3 parts by mass per 1 part by mass of the leuco dye. The content of the second color developer is preferably about 0.1 to 3 parts by mass, more preferably about 0.1 to 1 part by mass, per 1 part by mass of the first color developer. By making the content of the second color developer 0.1 parts by mass or more, it is possible to improve storage stability. On the other hand, by making the content of the second color developer 3 parts by mass or less, it is possible to improve color density.

[0057] The content of the N,N'-diaryl urea compound is not particularly limited and may be adjusted depending on the leuco dye used. Generally, it is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.4 parts by mass or more, per part by mass of the leuco dye. On the other hand, the content of the N,N'-diaryl urea compound is preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less, per part by mass of the leuco dye. By adjusting the content to 0.1 parts by mass or more, water resistance, water-resistant plasticizer resistance, and alcohol resistance can be improved. On the other hand, by adjusting the content to 6 parts by mass or less, recording performance can be improved.

[0058] (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, 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, and latexes of water-insoluble polymers such as styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. Among these, polyvinyl alcohol and latex are preferred. The adhesive content can be selected from a wide range, but is generally preferably about 5 to 30% by weight, and more preferably about 10 to 20% by weight, of the total solids content of the thermal recording layer.

[0059] In the present invention, the heat-sensitive recording layer may further contain a storage stability improver, mainly to further improve the storage stability of the color image. Examples of such storage stability 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)phenyl sulfone, epoxy compounds such as 4-(2-methyl-1,2-epoxyethyl)diphenyl sulfone, and 4-(2-ethyl-1,2-epoxyethyl)diphenyl sulfone, 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 compounds are not limited to these, and two or more compounds can be used in combination as needed.

[0060] 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% by mass, more preferably about 5 to 20% by mass, of the total solid content of the thermosensitive recording layer.

[0061] The heat-sensitive recording layer of the present invention may contain a sensitizer, which can enhance the recording sensitivity. Examples of sensitizers include stearic acid amide and methoxycarbonyl-N-benzalkonium stearate. Mido, 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, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, p-benzyl biphenyl, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid dibenzyl ester, p-tolyl biphenyl ether, di(p-methoxyphenoxyethyl) ether, 1,2-di(3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy) Examples include ethane, 1,2-di(4-methoxyphenoxy)ethane, 1,2-di(4-chlorophenoxy)ethane, 1,2-diphenoxyethane, 1-(4-methoxyphenoxy)-2-(3-methylphenoxy)ethane, p-methylthiophenylbenzyl 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, and benzophenone. Among these, 1,2-di(3-methylphenoxy)ethane is preferred from the viewpoint of achieving an excellent balance between color density and storage stability. These can be used in combination within a range that does not cause any problems. The content of the sensitizer may be an amount effective for sensitization, and is usually preferably 2 to 25 mass %, more preferably 5 to 20 mass %, and even more preferably 5 to 15 mass % of the total solid content of the thermosensitive recording layer.

[0062] To improve the whiteness of the thermosensitive recording layer and the uniformity of images, a fine particle pigment with high whiteness and an average particle size of 10 μm or less can be incorporated into the thermosensitive recording layer. Examples of pigments that can be used include inorganic pigments such as calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface-treated calcium carbonate, and silica, as well as organic pigments such as urea-formaldehyde resin, styrene-methacrylic acid copolymer resin, and polystyrene resin. The pigment content is preferably an amount that does not reduce the recording density, i.e., 50% by mass or less of the total solid content of the thermosensitive recording layer.

[0063] 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.

[0064] The inclusion of a crosslinking agent in the thermosensitive recording layer can improve the water resistance of the thermosensitive recording layer. 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 crosslinking agent used is preferably about 1 to 5 mass % of the total solid content of the thermosensitive recording layer.

[0065] The thermosensitive recording layer is formed on the undercoat layer by, for example, dispersing a leuco dye and a developer, each together with a sensitizer or storage stability improver as needed, or separately, in water as a dispersion medium using a variety of stirring and wet grinding machines such as a ball mill, a Co-ball mill, an attritor, or a vertical or horizontal sand mill, together with water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, styrene-maleic anhydride copolymer salt, and other surfactants to prepare respective dispersions, and then micronizing the dispersions to an average particle size of 2 μm or less. This dispersion is then mixed with an adhesive, and, if needed, inorganic pigments, auxiliary agents, etc., to prepare a thermosensitive recording layer coating material, which is then dried. The coating amount of the thermosensitive recording layer is not particularly limited, and the coating amount after drying is 1 to 12 g / m. 2 The preferred range is 2 to 10 g / m 2 More preferably, 2.5 to 8 g / m 2 is more preferably 3 to 5.5 g / m 2 The heat-sensitive recording layer can be formed in two or more layers as needed, and the composition and coating amount of each layer may be the same or different.

[0066] [Protective layer] The thermosensitive recording medium may also have a protective layer on the thermosensitive recording layer, if 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 to prevent sticking to the thermal head, and may also contain an ultraviolet absorber. Furthermore, providing a glossy protective layer can also increase the added value of the product.

[0067] 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, and synthetic layered mica, and plastic pigments such as urea-formaldehyde resin filler.

[0068] 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.

[0069] 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 agent, 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, 1 to 8 g / m 2 The preferred range is 1 to 5 g / m 2 The protective layer may be formed in two or more layers as needed, and the compositions and coating amounts of the layers may be the same or different.

[0070] [Other layers] In the present invention, it is preferable that the support has an adhesive layer on at least one side. This increases the added value of the thermosensitive recording medium. For example, the adhesive layer can be coated on one side with a pressure-sensitive adhesive, rewettable adhesive, delayed-tack type pressure-sensitive adhesive, or the like to produce adhesive paper, rewettable adhesive paper, delayed-tack paper, or the like. Furthermore, the surface of the support opposite the thermosensitive recording layer can be given the functionality of thermal transfer paper, inkjet recording paper, carbonless paper, electrostatic recording paper, xeography paper, or the like, to produce a recording paper capable of double-sided recording. Of course, a double-sided thermosensitive recording medium can also be produced. A backing layer can also be provided to inhibit penetration of oil and plasticizers from the backside of the thermosensitive recording medium, to control curl, and to prevent static electricity. A linerless label that does not require a release paper can be produced by coating a protective layer with a release layer containing silicone and then coating one side with an adhesive.

[0071] [Thermal recording medium] The thermosensitive recording medium can be produced 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 known coating method, 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, or extrusion method. Each coating material may be applied and dried one layer at a time to form each layer, or the same coating material may be applied in two or more layers. Simultaneous multilayer coating, in which two or more layers are applied simultaneously, may also be performed. After each layer has been formed, or after all layers have been formed, the surface may be smoothed using a known method, such as a supercalender or soft calender. [Example]

[0072] The present invention will be explained in more detail with reference to examples, but 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 analyzer SALD2200 (manufactured by Shimadzu Corporation). The average particle size here refers to the median diameter (D50).

[0073] The hollow particles used in the examples and comparative examples are as follows: Hollow particle A: average particle diameter (D50) 5.0 μm, maximum particle diameter (D100) 13.5 μm, hollow rate 90%, proportion of particles 2 μm or less 0.2% by volume, solid concentration 15.0% Hollow particle B: average particle size (D50) 11 μm, maximum particle size (D100) 23 μm, hollow rate 93%, percentage of particles 2 μm or less 0% by volume, solid concentration 15.0% Hollow particle C: Ropeake SN-1055 (Dow) average particle size (D50) 1.0 μm, maximum particle size (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 (Shimadzu Corporation) at a refractive index of 1.70-0.01i.

[0074] The latexes used in the examples and comparative examples are as follows: Latex A: Styrene-butadiene copolymer latex (Tg: -35°C, particle size: 300 nm, solid content: 48%) Latex B: Styrene-butadiene copolymer latex (Tg: -10°C, particle size: 190 nm, solid content: 48%) Latex C: Styrene-butadiene copolymer latex (trade name L-1571, manufactured by Asahi Kasei Corporation, Tg = -3°C, particle size 190 nm, solid content 48%)

[0075] Example 1 (1) Preparation of coating liquid 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), 79.2 parts of latex A, 32 parts of a 25% solution of oxidized starch, 1.1 parts of carboxymethyl cellulose (trade name: Cellogen AG Gum, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and 100 parts of water.

[0076] (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 A).

[0077] (3) Preparation of developer dispersion liquid (liquid B) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone, 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 reached 1.0 μm, to obtain a developer dispersion (Liquid B).

[0078] (4) Preparation of developer dispersion liquid (liquid C) N,N'-di-[3-(p-toluenesulfonyl) Luo Kishi ) Phenyl ] 40 parts of urea, 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 reached 1.0 μm, to obtain a developer dispersion liquid (Liquid C).

[0079] (5) Preparation of sensitizer dispersion (liquid D) 40 parts of 1,2-di(3-methylphenoxy)ethane (trade 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.) to an average particle size of 1.0 μm, to obtain a sensitizer dispersion (Liquid D).

[0080] (6) Preparation of coating solution for thermosensitive recording layer A coating solution for a thermal recording layer was obtained by mixing and stirring 31.8 parts of leuco dye dispersion A, 63.6 parts of developer dispersion B, 15.9 parts of developer dispersion C, 22.7 parts of sensitizer dispersion D, 46.7 parts of a 15% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA110, saponification degree: 99 mol%, average polymerization degree: 1000, manufactured by Kuraray Co., Ltd.), 20.8 parts of styrene-butadiene copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Corporation, solids concentration: 48%), 18 parts of aluminum hydroxide (trade name: Higilite H-42, manufactured by Showa Light Metal Co., Ltd.), 5 parts of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 200 parts of water.

[0081] (7) Preparation of protective layer coating solution A coating liquid for the protective layer was obtained by mixing and stirring a composition consisting of 308 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), 5.6 parts of zinc stearate wax (trade name: HYDRINN Z-8, manufactured by Chukyo Yushi Co., Ltd., solids concentration 36%), and 150 parts of water.

[0082] (8) Preparation of thermal recording medium Basis weight 60g / m 2 On one side of the high-quality paper, a coating liquid for the undercoat layer, a coating liquid for the thermal recording layer, and a protective for layers The coating amount after drying was 4.5 g / m 2 , 3.5g / m 2 , 2.5g / m 2 The coating was then dried to form an undercoat layer, a thermosensitive recording layer, and a protective layer in that order, and the surface was smoothed by a supercalender to obtain a thermosensitive recording medium.

[0083] Example 2 Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, the amount of color developer dispersion C was changed from 15.9 parts to 6.8 parts.

[0084] Example 3 Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in preparing the layer coating liquid, the amount of developer dispersion B was changed from 63.6 parts to 39.8 parts, and the amount of developer dispersion C was changed from 15.9 parts to 39.8 parts.

[0085] Example 4 Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in preparing the layer coating liquid, the amount of developer dispersion B was changed from 63.6 parts to 31.8 parts, and the amount of developer dispersion C was changed from 15.9 parts to 47.7 parts.

[0086] Example 5 (9) Preparation of developer dispersion liquid (liquid E) 40 parts of 2,4'-dihydroxydiphenyl sulfone (trade name: 2,4'-BPS, manufactured by Nicca Chemical Co., Ltd.), 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 reached 1.0 μm, to obtain a developer dispersion liquid (Liquid E).

[0087] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion E was used instead of 63.6 parts of developer dispersion B.

[0088] Example 6 (10) Preparation of developer dispersion liquid (liquid F) 40 parts of 4,4'-dihydroxydiphenyl sulfone (trade name: 4,4'-BPS, manufactured by Nicca Chemical Co., Ltd.), 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 reached 1.0 μm, to obtain a developer dispersion liquid (Liquid F).

[0089] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion F was used instead of 63.6 parts of developer dispersion B.

[0090] Example 7 (11) Preparation of developer dispersion liquid (liquid G) 40 parts of bis(3-allyl-4-hydroxy)diphenyl sulfone (trade name: TG-SH, manufactured by Nippon Kayaku Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed, and the mixture was ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) to an average particle size of 1.0 μm to obtain a color developer dispersion (Liquid G).

[0091] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion G was used instead of 63.6 parts of developer dispersion B.

[0092] Example 8 (12) Preparation of developer dispersion liquid (liquid H) 40 parts of 4-hydroxyphenyl(4'-n-propoxyphenyl) sulfone (trade name: Tomilac KN, manufactured by Mitsubishi Chemical Corporation), 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 reached 1.0 μm, to obtain a developer dispersion (Liquid H).

[0093] Example 1 Heat Sensitive recordA thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion H was used instead of 63.6 parts of developer dispersion B.

[0094] Example 9 (13) Preparation of developer dispersion liquid (liquid J) 40 parts of 4-hydroxy-4'-benzyloxydiphenyl sulfone (trade name: BPS-MBE, manufactured by Nicca Chemical Co., Ltd.), 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 reached 1.0 μm, to obtain a developer dispersion liquid (Liquid J).

[0095] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion J was used instead of 63.6 parts of developer dispersion B.

[0096] Example 10 (14) Preparation of developer dispersion liquid (liquid K) 40 parts of 4-allyloxy-4'-hydroxydiphenyl sulfone (trade name: BPS-MAE, manufactured by Nicca Chemical Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed, and the mixture was ground using a sand mill (sand grinder manufactured by Imex Co., Ltd.) until the median diameter measured with a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) reached 1.0 μm, thereby obtaining a colorant dispersion (Liquid K).

[0097] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion liquid K was used instead of 63.6 parts of developer dispersion liquid B.

[0098] Example 11 (15) Preparation of developer dispersion liquid (L liquid) 40 parts of Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea (trade name: PF201, manufactured by Solenis), 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) to an average particle size of 1.0 μm to obtain a developer dispersion (Liquid L).

[0099] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion L was used instead of 63.6 parts of developer dispersion B.

[0100] Example 12 (16) Preparation of developer dispersion liquid (M liquid) 40 parts of N-[2-(3-phenylureido)phenyl]benzenesulfonamide (trade name: NKK-1304, manufactured by Nippon Soda Co., Ltd.), 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 reached 1.0 μm, to obtain a developer dispersion (liquid M).

[0101] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion liquid M was used instead of 63.6 parts of developer dispersion liquid B.

[0102] Example 13 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in preparing the coating liquid for the undercoat layer of Example 12, the amount of hollow particles A was changed from 100 parts to 46.7 parts, the amount of calcined kaolin (trade name Ansilex 93, manufactured by BASF) was changed from 38 parts to 46 parts, and the amount of water was changed from 100 parts to 145 parts.

[0103] Example 14 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in preparing the coating liquid for the undercoat layer in Example 12, latex B was used instead of latex A.

[0104] Example 15 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in preparing the coating liquid for the undercoat layer in Example 12, Latex C was used instead of Latex A.

[0105] Example 16 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that hollow particles B were used instead of hollow particles A in preparing the coating liquid for the undercoat layer.

[0106] Example 17 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in preparing the coating liquid for the undercoat layer in Example 12, 56.6 parts of hollow particles C were used instead of 100 parts of hollow particles A, and the amount of water was changed to 175 parts instead of 100 parts.

[0107] Example 18 (17) Preparation of developer dispersion liquid (liquid N) 40 parts of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide (trade name: PF425, manufactured by Solenis), 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) to an average particle size of 1.0 μm to obtain a developer dispersion liquid (Liquid N).

[0108] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 63.6 parts of developer dispersion liquid N was used instead of 63.6 parts of developer dispersion liquid B.

[0109] (Comparative Example 1) Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in preparing the layer coating liquid, the amount of developer dispersion B was changed from 63.6 parts to 79.5 parts, and the amount of developer dispersion C was changed from 15.9 parts to 0 parts.

[0110] (Comparative Example 2) (18) Preparation of developer dispersion liquid (liquid O) 40 parts of a diphenyl sulfone derivative represented by the following general formula (3) (trade name: D-90, manufactured by Nippon Soda Co., Ltd.), 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water were mixed, and the mixture was 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 O). [ka] (In the formula, r=1~6)

[0111] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion liquid O was used instead of 15.9 parts of developer dispersion liquid C.

[0112] (Comparative Example 3) (19) Preparation of developer dispersion liquid (liquid P) 40 parts of 4,4-bis(4-methyl-3-phenoxycarbonylaminophenylurea)diphenyl sulfone (trade name: UU, manufactured by Chemipro Chemical Co., Ltd.), 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 reached 1.0 μm, to obtain a developer dispersion liquid (Liquid P).

[0113] Example 1 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion P was used instead of 15.9 parts of developer dispersion C.

[0114] Comparative Example 4 Example 10 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 10, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion C was replaced with 15.9 parts of developer dispersion O.

[0115] (Comparative Example 5) Example 10 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 10, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion P was used instead of 15.9 parts of developer dispersion C.

[0116] (Comparative Example 6) Example 11 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 11, except that in preparing the layer coating liquid, the amount of developer dispersion liquid L was changed from 63.6 parts to 79.5 parts, and the amount of developer dispersion liquid C was changed from 15.9 parts to 0 parts.

[0117] (Comparative Example 7) Example 11 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 11, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion C was replaced with 15.9 parts of developer dispersion O.

[0118] (Comparative Example 8) Example 11 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 11, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion P was used instead of 15.9 parts of developer dispersion C.

[0119] Comparative Example 9 Example 12 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in preparing the layer coating liquid, the amount of developer dispersion liquid M was changed from 63.6 parts to 79.5 parts, and the amount of developer dispersion liquid C was changed from 15.9 parts to 0 parts.

[0120] (Comparative Example 10) Example 12 Heat Sensitive record A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion C was replaced with 15.9 parts of developer dispersion O.

[0121] (Comparative Example 11) Example 12 Heat Sensitive recordA thermosensitive recording medium was obtained in the same manner as in Example 12, except that in the preparation of the layer coating liquid, 15.9 parts of developer dispersion P was used instead of 15.9 parts of developer dispersion C.

[0122] The above examples and comparative examples were evaluated by the following methods, and the results are shown in Table 1.

[0123] [Recording Density] Using a thermal recording evaluation machine (product name: TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed on each thermal recording medium at applied energy of 0.17 mJ / dot (mid-tone color density) and 0.25 mJ / dot (maximum color density), and the resulting printed area was measured with a spectrodensitometer (X-Rite 504, manufactured by X-Rite Co., Ltd.). The higher the value, the higher the print density. The evaluation criteria for half-tone color density are as follows: Color density of 1.00 or more: Excellent for high-speed printing. Color density of 0.80 or more: required for practical use. Color density of 0.80 or less: Low sensitivity and many defects such as white spots, which are problematic for practical use. The maximum color density was evaluated according to the following criteria. Color density 1.40 or more: Very good. Color density of 1.20 or more: required for practical use. Color density 1.20 or less: The print density is low and is not suitable for practical use.

[0124] [water resistance] Each sample of the thermal recording medium was colored using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.) and immersed in water for 24 hours. The optical density of the recorded area after the treatment was measured using a spectrodensitometer (X-Rite 504, manufactured by X-Rite Co., Ltd.). The remaining rate of the recorded area was calculated using the following formula. Residual rate (%) = (recording density after processing / recording density before processing) x 100 The evaluation criteria were as follows: Survival rate of 80% or more: Excellent. Residual rate of 60% or more: No practical problems. Residual rate 60% or less: The recording density after processing is low and is problematic for practical use.

[0125] [Water and plasticizer resistance] A polycarbonate pipe (40 mm diameter) was wrapped in three layers of cling film (product name: HI-ESU Soft, manufactured by Nippon Carbide Industries Co., Ltd.), and a sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Corporation) and immersed in water for 5 seconds, was placed on top of it. Then, cling film was wrapped around it again three times and the sample was left to stand at 40°C for 24 hours. The optical density of the recorded area was then measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite). The remaining rate of the recorded area was calculated using the following formula: Residual rate (%) = (recording density after processing / recording density before processing) x 100 The evaluation criteria were as follows: Survival rate of 80% or more: Excellent. Residual rate of 60% or more: No practical problems. Residual rate 60% or less: The recording density after processing is low and is problematic for practical use.

[0126] [Alcohol resistance] Each sample of thermal recording medium was colored using a label printer (product name: L-2000, manufactured by Ishida Corporation), and then immersed in a 75% by volume aqueous ethanol solution for 10 minutes. The optical density of the blank area and the recorded area was then measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Corporation). The remaining rate of the recorded area was calculated using the following formula: Residual rate (%) = (recording density after processing / recording density before processing) x 100 The evaluation criteria were as follows: White page density 0.10 or less: Excellent. White page density 0.20 or less: Some fogging occurs, but this does not cause any problems in practical use. White page density 0.20 or more: Fog is strong and is problematic for practical use. Survival rate of 80% or more: Excellent. Residual rate of 60% or more: No practical problems. Residual rate 60% or less: The recording density after processing is low and is problematic for practical use. [Table 1]

[0127] As can be seen from Table 1, the thermosensitive recording materials of Examples 1 to 18 were excellent in water resistance, water-resistant plasticizer resistance, and alcohol resistance. On the other hand, D-90 was insufficient as a storage stability improver, and UU caused fogging on the blank pages in terms of alcohol resistance.

Claims

1. A thermosensitive recording medium having, on a support, at least an undercoat layer containing an inorganic pigment, hollow particles, and an adhesive, and a thermosensitive recording layer containing a leuco dye, a color developer, and an adhesive, in this order, wherein the color developers include a first color developer and a second color developer, the first color developer containing N-p-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea and / or 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide, and the second color developer containing a compound represented by general formula (1): 【Chemistry 1】 (In the formula, R ２ 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, and the aralkyl group and the aryl group may be 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; ２ may be the same or different. １ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and a plurality of A １ may be the same or different.

2. The N,N'-diaryl urea compound represented by the general formula (1) is 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 , 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)phenyl]urea.

3. 2. The thermosensitive recording material according to claim 1, wherein the N,N'-diaryl urea compound represented by the general formula (1) is N,N'-di[3-(p-toluenesulfonyloxy)phenyl]urea.

4. The first color developer is represented by the general formula (2) 【Chemistry 2】 (In the formula, R ３、 R ４ are the same or different and represent an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyloxy group having 2 to 4 carbon atoms, an aralkyloxy group having 7 to 12 carbon atoms, or a halogen atom. m is an integer of 0 to 2, n is an integer of 1 to 3, and p and q are the same or different and represent an integer of 0 to 2.

5. 5. The thermosensitive recording material according to claim 4, wherein the diphenyl sulfone derivative represented by the general formula (2) is at least one selected from 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(3-allyl-4-hydroxy)diphenyl sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl) sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, and 4-hydroxy-4'-benzyloxydiphenyl sulfone.

6. 4. The thermosensitive recording medium according to claim 1, wherein said first developer is N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

7. 4. The thermosensitive recording medium according to claim 1, wherein the second developer is contained in an amount of 0.1 to 3 parts by mass per 1 part by mass of the first developer.

8. 4. The thermosensitive recording medium according to claim 1, wherein the second developer is contained in an amount of 0.1 to 1 part by mass per 1 part by mass of the first developer.

9. The thermosensitive recording material according to any one of claims 1 to 3, 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 diameter of 2.0 µm or less is 1% or less.

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

11. 4. 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.

12. 4. 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 −30° C. or lower.

13. 4. The thermosensitive recording medium according to claim 1, wherein the support has an adhesive layer on at least one surface thereof.

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