Thermal recording medium

Abstract

To provide a heat-sensitive recording body that is excellent in water-resistance plasticity and water resistance of a recording part and also excellent in alcohol resistance of a recording part and a background part.SOLUTION: A heat-sensitive recording body has an undercoat layer containing hollow particles, an adhesive, and an inorganic pigment, provided on a supporting body, and a heat-sensitive recording layer containing a leuco dye, a developer and an adhesive, provided on the undercoat layer. The heat-sensitive recording layer contains, as a preservability improver, 5-(N-3-methylphenyl-sulfonamide)-N',N''-bis-(3-methylphenyl)-isophthalic diamide.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 fades over time. This fade reaction is accelerated in high temperature and high humidity environments, and can 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-based disinfection and sterilization have become commonplace in everyday life, particularly for the prevention of infectious diseases. In other words, there is an increasing demand for improved performance of thermal recording media, such as preventing the background from developing color and preventing the recorded area from faded 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 is insufficient in alcohol resistance, water resistance, and water-resistant 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] A main object of the present invention is to provide a heat-sensitive recording medium which has excellent water resistance to plasticizers and water resistance in the recorded area, and excellent alcohol resistance in both the recorded area and the background area. [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 an undercoat layer containing hollow particles, an adhesive and an inorganic pigment on a support, and a thermal recording layer containing a leuco dye, a color developer and an adhesive on the undercoat layer, wherein the thermal recording layer contains 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as a storage stability improving agent.

[0009] Item 2: The developer is represented by the following general formula (1):

[0010] [ka]

[0011] (wherein R1 and R2 each represent a C1-C4 alkyl group, a C2-C4 alkenyl group, a C1-C4 alkoxyl group, or a halogen atom; m represents an integer of 0 to 2; n represents an integer of 1 to 3; and p and q each represent an integer of 0 to 2).

[0012] Item 3: The thermal recording material according to item 2, wherein the developer represented by the general formula (1) is at least one selected from the group consisting of 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl)sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, and 4-hydroxy-4'-benzyloxydiphenyl sulfone.

[0013] Item 4: The thermosensitive recording medium according to Item 1, wherein the developer is Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea.

[0014] Item 5: The thermosensitive recording medium according to Item 1, wherein the developer is N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

[0015] Item 6: The thermosensitive recording medium according to any one of Items 1 to 5, wherein the content of the storage stability improving agent is 0.1 to 4 parts by mass per 1 part by mass of the color developer.

[0016] Item 7: The thermosensitive recording material according to any one of Items 1 to 6, wherein the hollow particles have an average particle size (D50) of 4.0 to 15 μm, a maximum particle size (D100) of 10 to 30 μm, a ratio (D100 / D50) of the maximum particle size (D100) to the average particle size (D50) of the hollow particles is 1.8 to 3.0, and the volume percentage of the hollow particles having a particle size of 2.0 μm or less is 1% or less.

[0017] 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%.

[0018] Item 9: The thermosensitive recording medium according to any one of items 1 to 8, wherein the undercoat layer contains an adhesive having a glass transition temperature of −10° C. or lower.

[0019] Item 10: The thermosensitive recording medium according to any one of items 1 to 9, which has an adhesive layer on at least one surface of the support. Effect of the Invention

[0020] The thermal recording medium of the present invention has excellent water resistance to plasticizers and water resistance in the recorded area, and has excellent alcohol resistance in both the recorded area and the background area. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In this specification, the expression "comprise" includes the concepts of "comprise", "consist essentially of" and "consist only of".

[0022] 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.

[0023] The latex in the present invention includes a gel or a dried film state formed by drying a dispersion medium.

[0024] In the present invention, the "average particle size" refers to the volume-based median size measured by laser diffraction. More simply, the particle size may be measured from particle images (SEM images) using an electron microscope, and the average value of 10 particles may be used.

[0025] The present invention provides a thermosensitive recording medium having an undercoat layer on a support, the undercoat layer containing hollow particles, an adhesive and an inorganic pigment, and a thermosensitive recording layer on the undercoat layer, the thermosensitive recording layer containing a leuco dye, a color developer and an adhesive, the thermosensitive recording layer containing 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as a storage stability improver.

[0026] [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.

[0027] [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.

[0028] (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.

[0029] 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.

[0030] 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.

[0031] Expanded hollow particles can be produced by preparing particles with a volatile liquid sealed inside the resin, softening the resin by heating, and vaporizing and expanding the liquid inside the particles.

[0032] 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.

[0033] 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), styrene resin, vinylidene chloride resin, and copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile. Gases contained inside the expanded type hollow particles are generally propane, butane, isobutane, air, and the like. Among the various resins mentioned above, the resin used for the hollow particles is preferably acrylonitrile resin or copolymer resin mainly composed of polyvinylidene chloride and acrylonitrile from the viewpoint of strength for maintaining the shape of the expanded particles.

[0034] 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 an energy lower than the energy that 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.

[0035] 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 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 an energy lower than the energy giving 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.

[0036] The maximum particle size (D100) and average particle size (D50) of hollow particles can be measured by a laser diffraction particle size distribution 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.

[0037] 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.

[0038] In the particle size distribution, the volume % of hollow particles having a particle diameter of 2.0 μm or less is preferably 1% or less. The particle size distribution can be determined by a laser diffraction type particle size distribution measuring device. It is also possible to use an electron microscope to measure the particle diameter from particle images (SEM images). The volume % of hollow particles having a particle diameter of 2.0 μm or less is preferably 0.5%, and more preferably, they are not contained. Since hollow particles having a particle diameter of 2 μm or less are too small to have a sufficient hollow area, it is considered that their contribution to heat insulation is extremely small. By making the volume % of hollow particles having a particle diameter of 2 μm or less in the undercoat layer 1% or less, the recording density, image quality, etc. can be improved.

[0039] 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. This improves the recording density for a preferred color developer described below, and at the same time, the effect of the storage stability improver in the present invention can be fully exerted. 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 are not crushed even when the undercoat layer is formed.

[0040] 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

[0041] 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.

[0042] 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 such as streaky coating defects occurring during the formation of the undercoat layer are unlikely to occur, and 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.

[0043] (glue) Examples of the adhesive in the undercoat layer include water-soluble polymer materials such as polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, 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 mass % of the total solid content of the undercoat layer, and more preferably about 25 to 60 mass %.

[0044] The glass transition temperature (Tg) of the adhesive is not particularly limited, but is preferably -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. From the viewpoint of further improving image quality 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.

[0045] (Inorganic pigments) The undercoat layer in the present invention contains an inorganic pigment. From the viewpoint of increasing the recording density and improving the water resistance to plasticizers and the alcohol resistance, the oil absorption of the inorganic pigment is preferably 150 ml / 100 g or less, more preferably 130 ml / 100 g or less, and even more preferably 125 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, the oil absorption is preferably 50 ml / 100 g or more, more preferably 70 ml / 100 g or more, and even more preferably 80 ml / 100 g or more. Here, the oil absorption is a value obtained according to the method of JIS K 5101.

[0046] Various inorganic pigments can be used, and specific examples include calcined kaolin, amorphous silica, light calcium carbonate, talc, kaolin, clay, etc. The average particle size of the primary particles of these inorganic pigments is preferably about 0.01 to 5 μm, more preferably about 0.02 to 3 μm. From the viewpoint of improving water resistance to plasticizers and alcohol resistance, the content of the inorganic pigment 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, the content of the inorganic pigment is preferably 20 mass% or more, more preferably 25 mass% or more, of the total solid content of the undercoat layer.

[0047] The undercoat layer is generally formed on the support by applying a coating material for the undercoat layer, which is prepared by mixing hollow particles, adhesives, inorganic pigments, and, if necessary, auxiliaries, etc., with water as a dispersion medium, and then drying the coating material. The amount of coating material for the undercoat layer is not particularly limited, but is preferably 2 to 20 g / m2 in terms of dry weight. 2 The preferred thickness is 2 to 12 g / m 2 The preferred range is 3 to 8 g / m 2 A degree is even more preferable.

[0048] [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.

[0049] 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.

[0050] 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.

[0051] (Developer) Specific examples of the 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, 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'-dihydr p-hydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl) 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 Nilsulfone, 4-allyloxy-4'-hydroxydiphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, 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-( aromatic carboxylic acids such as zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and zinc 4-[3-(p-tolylsulfonyl)propyloxy]salicylate, and these phenolic compounds and 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, terephthalic acid complexes, and the like. organic acidic substances such as complex zinc salts of aldehyde acid and other aromatic carboxylic acids; 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, and N,N'-di-m-chlorophenylthiourea; organic compounds having a -SONH- bond in the molecule such as Np-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. The color developer is, of course, not limited to these, and two or more compounds can be used in combination as necessary.

[0052] In the present invention, the developer is preferably a diphenylsulfone derivative represented by the following general formula (1), which allows the effects of the present invention to be fully exhibited.

[0053] [ka]

[0054] (In the formula, R1 and R2 each represent a C1 to C4 alkyl group, a C2 to C4 alkenyl group, a C1 to C4 alkoxyl group, or a halogen atom. m represents an integer of 0 to 2, n represents an integer of 1 to 3, and p and q each represent an integer of 0 to 2.)

[0055] Furthermore, it is preferable that the developer represented by the general formula (1) is at least one selected from the group consisting of 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxyphenyl(4'-n-propoxyphenyl)sulfone, 4-allyloxy-4'-hydroxydiphenyl sulfone, and 4-hydroxy-4'-benzyloxydiphenyl sulfone.

[0056] In the present invention, the developer is preferably Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea, which allows the effects of the present invention to be fully exhibited.

[0057] In the present invention, the developer is preferably N-[2-(3-phenylureido)phenyl]benzenesulfonamide, which allows the effects of the present invention to be fully exhibited.

[0058] The content of the developer 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. The content of the developer 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, the recording performance can be improved. On the other hand, by making it 10 parts by mass or less, background fogging in a high-temperature environment can be effectively suppressed.

[0059] The thermosensitive recording layer in the present invention contains 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as a storage stability improving agent. This allows the thermosensitive recording medium of the present invention to have excellent water resistance to plasticizers and water resistance in the recorded area, and excellent alcohol resistance in the recorded area and background area.

[0060] The content of 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as a storage stability improver is not particularly limited and may be adjusted depending on the color developer used. In general, the content is preferably about 0.1 to 4 parts by mass relative to 1 part by mass of the color developer, more preferably about 0.10 to 3 parts by mass, even more preferably about 0.10 to 2 parts by mass, even more preferably about 0.15 to 1 part by mass, and particularly preferably about 0.15 to 1.0 part by mass. By making the content 0.1 part by mass or more, the water resistance to plasticizers and water resistance of the recorded part can be improved, and the alcohol resistance of the recorded part can be improved. On the other hand, by making the content 4 parts by mass or less, the recording density can be improved.

[0061] In the present invention, it is preferable that the storage stability improver not contain urea urethane derivatives such as 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenyl sulfone, and 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenyl sulfone represented by the following general formula (2), and diphenyl sulfone derivatives represented by the following general formula (3).

[0062] [ka]

[0063] [ka]

[0064] (In the formula, n represents an integer of 1 to 6.)

[0065] In addition, if necessary, a storage improver can be further added within a range that does not impair the effects of the present invention, mainly to further improve the storage stability of the colored image. Examples of such storage 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.

[0066] 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.

[0067] 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 sensitization effect without decreasing the water-resistant plasticizer resistance and the alcohol resistance. 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% by mass, more preferably 5 to 20% by mass, and even more preferably 5 to 15% by mass of the total solid content of the heat-sensitive recording layer.

[0068] Other components constituting the heat-sensitive recording layer include adhesives, and if necessary, auxiliary agents such as crosslinking agents, pigments, waxes, metal soaps, water-resistant agents, dispersants, colored dyes, and fluorescent dyes can be used.

[0069] Examples of the adhesive in the thermal recording layer include water-soluble polymer materials such as polyvinyl alcohol and its derivatives, starch and its derivatives, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and ethyl cellulose, 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.

[0070] 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 such as adipic acid dihydrazide, 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, more preferably about 2 to 8% by mass, of the total solid content of the thermosensitive recording layer.

[0071] From the viewpoint of improving the whiteness of the thermosensitive recording layer and the uniformity of the image, a fine particle pigment with high whiteness and an average particle size of 10 μm or less can be contained in the thermosensitive recording layer. For example, 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 can be used. The content of the pigment is preferably an amount that does not reduce the recording density, that is, 50% by mass or less of the total solid content of the thermosensitive recording layer.

[0072] The thermal recording layer is generally formed on the undercoat layer by dispersing a leuco dye, a color developer and a storage stability improver together or separately, and optionally together with a sensitizer or storage stability improver, or separately, in various stirring and wet grinding machines such as ball mills, coball mills, attritors, and vertical and horizontal sand mills together with a water-soluble synthetic polymer compound such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, styrene-maleic anhydride copolymer salt, and optionally with a surfactant, to obtain a dispersion, which is then finely milled to an average particle size of 2 μm or less, and then mixing with an adhesive and, optionally, with an auxiliary, to prepare a coating material for the thermal recording layer, which is then dried and formed on the undercoat layer. 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 More preferably, 2.5 to 8 g / m 2 More preferably, 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.

[0073] [Protective layer] In the thermal recording medium, a protective layer may be provided on the thermal recording layer as required. 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 as an auxiliary agent 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.

[0074] The pigment 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.

[0075] The adhesive 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 usable in the thermal recording layer. Among them, polyvinyl alcohol or modified polyvinyl alcohol is preferred from the viewpoint of improving the binder effect with the pigment and the storage stability of the recording part against solvents such as plasticizers and oils, and 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.

[0076] The protective layer is formed on the thermosensitive recording layer by, for example, applying a coating material for the protective layer, which is prepared by mixing a pigment, an adhesive, and, if necessary, an auxiliary, 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 weight. 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 2 The 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.

[0077] [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 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 a release agent such as silicone on the protective layer and coating processing a pressure sensitive adhesive on the surface opposite to the protective layer.

[0078] [Thermal recording medium] The thermal recording medium can be manufactured by forming each layer on a support. As a method for forming each layer on a support, any of known coating methods such as air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, curtain method, slot die method, slide die method, extrusion method, etc. may be used. 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 in which two or more layers are applied simultaneously may be performed. In addition, after each layer is formed or after all layers are formed, a known method such as a super calendar or soft calendar may be used to perform smoothing treatment at any stage. EXAMPLES

[0079] 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 refers to the median size (D50).

[0080] The hollow particles used in the examples and comparative examples are as follows. Hollow particle A: average particle size (D50) 5.0 μm, maximum particle size (D100) 13.5 μm, D100 / D50 = 2.7, hollow rate 90%, percentage of particles 2 μm or less 0.2 vol%, solid content 15.0%, foamed type. Hollow particle B: average particle size (D50) 11 μm, maximum particle size (D100) 23 μm, D100 / D50 = 2.1, hollow rate 93%, percentage of particles smaller than 2 μm 0 volume%, solid content 15.0%, foamed type. Hollow particle C: Product name "Ropeake SN-1055" (manufactured by Dow Chemical Company), average particle size (D50) 1.0 μm, maximum particle size (D100) 1.8 μm, D100 / D50 = 1.8, hollow rate 55%, percentage of particles 2 μm or less 100% by volume, solid content 26.5%, non-foamed type. The average particle size (D50) and maximum particle size (D100) of each hollow particle were measured using a laser diffraction particle size distribution analyzer SALD2200 (manufactured by Shimadzu Corporation) at a refractive index of 1.70-0.01i.

[0081] 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 (product name L-1571, manufactured by Asahi Kasei Corporation, Tg: -3°C, particle size 190 nm, solid content 48%).

[0082] Example 1 (1) Preparation of paint for undercoat layer A composition consisting of 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% aqueous 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 was mixed and stirred to obtain a coating material for an undercoat layer.

[0083] (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).

[0084] (3-1) Preparation of developer dispersion liquid (B-1 liquid) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone, 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) until the average particle diameter became 1.0 μm to obtain a developer dispersion liquid (Liquid B-1).

[0085] (4-1) Preparation of storage stability improver dispersion (C-1 liquid) 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 size became 1.0 μm, to obtain a storage stability improving agent dispersion (C-1 solution).

[0086] (5) Preparation of sensitizer dispersion (liquid D) 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 D).

[0087] (6) Preparation of coating material for thermosensitive recording layer A composition consisting of 31.8 parts of Liquid A, 63.6 parts of Liquid B-1, 15.9 parts of Liquid C-1, 22.7 parts of Liquid 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 Latex C, 18 parts of aluminum hydroxide (trade name: KH-101, manufactured by KC Corporation), 5 parts of adipic acid dihydrazide (manufactured by Otsuka Chemical Co., Ltd.), and 200 parts of water was mixed and stirred to obtain a coating material for a thermal recording layer.

[0088] (7) Preparation of protective layer paint A composition consisting of 308 parts of a 12% aqueous solution of diacetone-modified polyvinyl alcohol (product name: DF-10, manufactured by Nippon Vinyl Polyvinyl Alcohol Co., Ltd.), 60 parts of kaolin (product name: HYDRAGLOSS90, manufactured by KaMin LLC), 5.6 parts of zinc stearate (product name: Hydrin Z-8, manufactured by Chukyo Yushi Co., Ltd., solids concentration 36%), and 150 parts of water was mixed and stirred to obtain a coating material for the protective layer.

[0089] (8) Preparation of thermal recording medium Basis weight 60g / m 2 On one side of the high-quality paper, the coating material for the undercoat layer, the coating material for the thermal recording layer, and the coating material for the protective layer were each applied in an amount of 4.5 g / m2 after drying. 2 , 4.0g / m 2 , 2.5g / m 2 After the undercoat layer, the thermosensitive recording layer, and the protective layer were successively formed, the surface was smoothed by a supercalender to obtain a thermosensitive recording medium.

[0090] Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the thermosensitive recording layer coating material in Example 1, the amount of C-1 solution was changed from 15.9 parts to 6.8 parts.

[0091] Example 3 A thermal recording material was obtained in the same manner as in Example 1, except that in preparing the coating material for the thermal recording layer in Example 1, the amount of B-1 liquid was changed from 63.6 parts to 39.8 parts, and the amount of C-1 liquid was changed from 15.9 parts to 39.8 parts.

[0092] Example 4 A thermal recording material was obtained in the same manner as in Example 1, except that in preparing the coating material for the thermal recording layer in Example 1, the amount of B-1 liquid was changed from 63.6 parts to 31.8 parts, and the amount of C-1 liquid was changed from 15.9 parts to 47.7 parts.

[0093] Example 5 A thermal recording material was obtained in the same manner as in Example 1, except that in preparing the coating material for the thermal recording layer in Example 1, the amount of B-1 liquid was changed from 63.6 parts to 15.9 parts, and the amount of C-1 liquid was changed from 15.9 parts to 63.6 parts.

[0094] Example 6 (3-2) Preparation of developer dispersion (B-2 liquid) 40 parts of 2,4'-dihydroxydiphenyl sulfone (trade name: 2,4'-BPS, manufactured by Nichika Chemical 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 B-2).

[0095] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion liquid was changed from B-1 liquid to B-2 liquid.

[0096] Example 7 (3-3) Preparation of developer dispersion (B-3 liquid) 40 parts of 4,4'-dihydroxydiphenyl sulfone (product name: 4,4'-BPS, manufactured by Nichika Chemical 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 B-3).

[0097] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion liquid was changed from B-1 liquid to B-3 liquid.

[0098] Example 8 (3-4) Preparation of developer dispersion liquid (B-4 liquid) 40 parts of bis(3-allyl-4-hydroxyphenyl)sulfone (product 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 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-4).

[0099] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion liquid was changed from B-1 liquid to B-4 liquid.

[0100] Example 9 (3-5) Preparation of developer dispersion (B-5 liquid) 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 (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 Corporation) until the average particle diameter became 1.0 μm, to obtain a developer dispersion liquid (liquid B-5).

[0101] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion was changed from B-1 liquid to B-5 liquid.

[0102] Example 10 (3-6) Preparation of developer dispersion (B-6 liquid) 40 parts of 4-hydroxy-4'-benzyloxydiphenyl sulfone (product 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 became 1.0 μm, to obtain a developer dispersion liquid (liquid B-6).

[0103] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion was changed from B-1 liquid to B-6 liquid.

[0104] Example 11 (3-7) Preparation of developer dispersion (B-7 liquid) 40 parts of 4-allyloxy-4'-hydroxydiphenyl sulfone (product name: BPS-MAE, manufactured by Nichika Chemical 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 B-7).

[0105] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion was changed from B-1 liquid to B-7 liquid.

[0106] Example 12 (3-8) Preparation of developer dispersion (B-8 liquid) 40 parts of Np-tolylsulfonyl-N'-3-(p-tolylsulfonyloxy)phenylurea (trade name: PF-201, 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) until the average particle diameter became 1.0 μm, to obtain a developer dispersion (liquid B-8).

[0107] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion was changed from B-1 liquid to B-8 liquid.

[0108] Example 13 (3-9) Preparation of developer dispersion (B-9 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 became 1.0 μm, to obtain a developer dispersion liquid (liquid B-9).

[0109] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the developer dispersion was changed from B-1 liquid to B-9 liquid.

[0110] Example 14 A thermal recording medium was obtained in the same manner as in Example 13, except that in the preparation of the undercoat layer paint of Example 13, the amount of hollow particles A was changed to 46.7 parts instead of 100 parts, the amount of calcined kaolin was changed to 46 parts instead of 38 parts, and the amount of water was changed to 145 parts instead of 100 parts.

[0111] Example 15 A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the undercoat layer paint of Example 13, latex B was used instead of latex A.

[0112] (Example 16) A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the coating material for the undercoat layer in Example 13, latex C was used instead of latex A.

[0113] (Example 17) A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the undercoat layer coating material of Example 13, hollow particles B were used instead of hollow particles A.

[0114] (Example 18) A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the undercoat layer coating material of Example 13, 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.

[0115] Comparative Example 1 A thermal recording material was obtained in the same manner as in Example 1, except that in preparing the coating material for the thermal recording layer in Example 1, the amount of B-1 liquid was changed from 63.6 parts to 79.5 parts, and the amount of C-1 liquid was changed from 15.9 parts to 0 parts.

[0116] Comparative Example 2 (4-2) Preparation of storage stability improver dispersion (C-2 liquid) 40 parts of the diphenyl sulfone derivative represented by the 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 ground using a sand mill (sand grinder, manufactured by Imex Co., Ltd.) until the average particle size became 1.0 μm, thereby obtaining a storage stability improver dispersion (C-2 liquid).

[0117] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for the thermosensitive recording layer in Example 1, the storage stability improving agent dispersion was changed from C-1 liquid to C-2 liquid.

[0118] Comparative Example 3 (4-3) Preparation of storage stability improver dispersion (C-3 solution) 40 parts of 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone (trade name: UU, manufactured by Chemipro Chemical Co., Ltd.) represented by the above general formula (2), 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 storage stability improving agent dispersion (C-3 solution).

[0119] A thermosensitive recording medium was obtained in the same manner as in Example 1, except that in the preparation of the coating material for a thermosensitive recording layer in Example 1, the storage stability improving agent dispersion was changed from C-1 liquid to C-3 liquid.

[0120] Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 11, except that in the preparation of the coating material for the thermosensitive recording layer in Example 11, the storage stability improving agent dispersion was changed from C-1 liquid to C-2 liquid.

[0121] Comparative Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 11, except that in the preparation of the coating material for the thermosensitive recording layer in Example 11, the storage stability improving agent dispersion was changed from C-1 liquid to C-3 liquid.

[0122] Comparative Example 6 In preparing the coating material for the thermosensitive recording layer of Example 12, a thermosensitive recording material was obtained in the same manner as in Example 12, except that the amount of B-8 liquid was changed from 63.6 parts to 79.5 parts, and the amount of C-1 liquid was changed from 15.9 parts to 0 parts.

[0123] Comparative Example 7 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in the preparation of the coating material for the thermosensitive recording layer in Example 12, the storage stability improving agent dispersion was changed from C-1 liquid to C-2 liquid.

[0124] Comparative Example 8 A thermosensitive recording medium was obtained in the same manner as in Example 12, except that in the preparation of the coating material for the thermosensitive recording layer in Example 12, the storage stability improving agent dispersion was changed from C-1 liquid to C-3 liquid.

[0125] Comparative Example 9 In preparing the coating material for the thermosensitive recording layer of Example 13, a thermosensitive recording material was obtained in the same manner as in Example 13, except that the amount of B-9 liquid was changed from 63.6 parts to 79.5 parts, and the amount of C-1 liquid was changed from 15.9 parts to 0 parts.

[0126] Comparative Example 10 A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the coating material for the thermosensitive recording layer in Example 13, the storage stability improving agent dispersion was changed from C-1 liquid to C-2 liquid.

[0127] Comparative Example 11 A thermosensitive recording medium was obtained in the same manner as in Example 13, except that in the preparation of the coating material for the thermosensitive recording layer in Example 13, the storage stability improving agent dispersion was changed from C-1 liquid to C-3 liquid.

[0128] The thus obtained thermosensitive recording medium was subjected to the following evaluations, the results of which are shown in Table 1.

[0129] [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 applied energy of 0.17 mJ / dot (mid-tone color density) and 0.25 mJ / dot (high-tone color density), and the reflection density of the obtained recorded portion was measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.) If the storage stability is the same, the higher the density, the better, and the evaluation was performed using the following criteria as a guide. (Mid-tone color density) 1.00 or higher: Also suitable for high-speed printing, and is extremely excellent. 0.80 or more and less than 1.00: No problem in practical use. Less than 0.80: Low sensitivity and many defects such as white spots, which are problematic in practical use. (High gradation color density) 1.40 and above: Excellent. 1.20 or more and less than 1.40: No problem in practical use. Less than 1.20: The print density is low and is not suitable for practical use.

[0130] [water resistance] A sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.), was immersed in water at 20°C for 24 hours for processing. Before and after this processing, the reflection density of the recorded area was measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.). The remaining rate of the recorded area was calculated using the following formula. The remaining rate was evaluated according to the following criteria. Residual rate (%) = (recording density after processing / recording density before processing) x 100 Survival rate of 80% or more: Very good. Residual rate: 60% or more and less than 80%: No problem in practical use. Residual rate less than 60%: The recording density after processing has decreased significantly and is problematic for practical use.

[0131] [Water and plasticizer resistance] A polycarbonate pipe (40 mmΦ) was wrapped with three layers of cling film (product name: HI-ES 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 Co., Ltd.) and immersed in water for 5 seconds, was placed on top of the cling film, which was then wrapped with three layers of cling film and left to stand for 24 hours in an environment of 40°C. Before and after this treatment, the reflection density of the recorded area was measured with a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.). The remaining rate of the recorded area was calculated using the following formula. The remaining rate was evaluated according to the following criteria. Residual rate (%) = (recording density after processing / recording density before processing) x 100 Survival rate of 80% or more: Very good. Residual rate: 60% or more and less than 80%: No problem in practical use. Residual rate less than 60%: The recording density after processing has decreased significantly and is problematic for practical use.

[0132] [Alcohol resistance] A sample of each thermal recording medium, which had been colored using a label printer (product name: L-2000, manufactured by Ishida Co., Ltd.), was immersed in a 75% by volume aqueous ethanol solution for 10 minutes for processing. Before and after this processing, the reflection densities of the background and recorded areas were measured using a spectrodensitometer (X-Rite504, manufactured by X-Rite Co., Ltd.). The remaining rate of the recorded area was calculated using the following formula. The background density and remaining rate after processing were evaluated according to the following criteria. Residual rate (%) = (recording density after processing / recording density before processing) x 100 Skin density 0.10 or less: Very good. Background density: over 0.10 and 0.20 or less: some fogging has occurred, but no practical problems are encountered. Background density exceeds 0.20: Fog is significant and is problematic for practical use. Survival rate of 80% or more: Very good. Residual rate: 60% or more and less than 80%: No problem in practical use. Residual rate less than 60%: The recording density after processing has decreased significantly and is problematic for practical use.

[0133] [Table 1] [Industrial Applicability]

[0134] The thermal recording medium of the present invention has excellent water resistance, water-resistant plasticizer resistance, and alcohol resistance, and fully meets the demands for improved performance of thermal recording mediums, such as the fact that the background does not develop color even when in contact with alcohol, and the recorded areas do not fade.

Claims

1. A thermosensitive recording medium having an undercoat layer on a support, the undercoat layer containing hollow particles, an adhesive and an inorganic pigment, and a thermosensitive recording layer on the undercoat layer, the thermosensitive recording layer containing a leuco dye, a color developer and an adhesive, the thermosensitive recording layer containing 5-(N-3-methylphenyl-sulfonamido)-N',N''-bis-(3-methylphenyl)-isophthalic acid diamide as a storage stability improver and N-[2-(3-phenylureido)phenyl]benzenesulfonamide as a color developer, a ratio (D100 / D50) of the maximum particle diameter (D100) of the hollow particles to the average particle diameter (D50) of the hollow particles is 1.8 to 3.0; the volume percentage of the hollow particles having a particle diameter of 2.0 μm or less is 1% or less; and the hollow ratio of the hollow particles is 80 to 98%.

2. 2. The thermosensitive recording medium according to claim 1, wherein the content of the storage stability improving agent is 0.1 to 4 parts by mass per 1 part by mass of the color developer.

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

4. 4. The thermal recording medium according to claim 1, wherein one surface of the support has an adhesive layer.

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