JP2012196854A - Thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording material which has excellent recorded image quality in a halftone region and thermal responsiveness, and also has excellent surface strength.SOLUTION: In the thermal recording material having an intermediate layer and a thermal recording layer, in which colors are developed by heat, in this order on a support, the intermediate layer contains a hollow resin having a bellows shape and an inorganic pigment with the primary average particle diameter of 7 to 200 nm.

Description

  The present invention relates to a heat-sensitive recording material having an intermediate layer and a heat-sensitive recording layer that develops color by heat on a support in this order, and is excellent in recording image quality and thermal responsiveness in a halftone region and excellent in coating layer strength. It is about.

  A heat-sensitive recording material generally comprises an electron-donating normally colorless or light-colored dye precursor and a heat-sensitive recording layer mainly composed of an electron-accepting compound on a support, and includes a thermal head, a thermal pen, and a laser. By heating with light or the like, the electron-donating dye precursor and the electron-accepting compound react instantaneously to obtain a recorded image. Such a heat-sensitive recording material has advantages such as that recording can be obtained with a relatively simple device, easy maintenance, no noise generation, etc., measurement recorder, facsimile, printer, computer terminal, It is used in a wide range of fields such as label printing machines, boarding tickets, and ticket issuing machines. In recent years, in particular, receipts for gas, water, electricity charges, etc., ATM usage statements for financial institutions, various receipts, etc., such as financial recording paper, thermal recording labels or thermal recording tags for POS systems, etc. Recording materials are being used.

  As usage diversifies in this way, not only character information but also opportunities to print grayscale images are increasing, and dot reproducibility is good in any region from low print density to high print density. There is a demand for a heat-sensitive recording material excellent in recording image quality that does not cause chipping or density unevenness. In addition, there is a demand for a heat-sensitive recording material having excellent thermal responsiveness as the speed of recording equipment increases.

  As a means for improving the recording image quality of the heat-sensitive recording material, a method has been developed that increases the smoothness of the surface of the heat-sensitive recording layer and improves the adhesion with the thermal head. For example, Patent Document 1 proposes a method in which the surface of the heat-sensitive recording layer is surface-treated at a Beck smoothness of 200 to 1000 seconds. There has also been proposed a method of improving the recording image quality by providing an intermediate layer having heat insulation between the support and the heat-sensitive recording layer to enhance the thermal response of the heat-sensitive recording material. For example, Patent Document 2 includes a method of containing an oil-absorbing pigment in the intermediate layer, Patent Document 3 includes a method of including micro hollow sphere particles in the intermediate layer, Patent Document 4 includes micro hollow, and the porosity is 50 to 95%. A method of providing 3 to 200 μm of the intermediate layer is proposed. Furthermore, by increasing the smoothness of the surface of the intermediate layer, the thickness of the coating film of the heat-sensitive recording layer is made uniform, and a method of reducing the print density unevenness resulting from the film thickness unevenness of the heat-sensitive recording layer has also been developed. . For example, in Patent Document 5, a method of blade coating a coating solution for an intermediate layer having a specific viscosity, Patent Document 6 includes a method in which the intermediate layer contains a minute hollow and the intermediate layer has a Beck smoothness of 2000 seconds or more, Patent Document 7 is a method in which hollow resin particles are contained in the intermediate layer and the intermediate layer is subjected to thermal calendering. In Patent Document 8, two or more intermediate layers are provided, and the standard deviation of the thickness of the thermosensitive recording layer is made constant or less. Has been proposed.

  These conventional improvement methods are approaches by smoothing the surface, improving thermal responsiveness, and uniforming the coating layer thickness, and certain effects can be seen in improving the recording image quality in the high print density range. About satisfactory printing in the middle printing density range, satisfactory results have not yet been obtained.

  Further, when hollow particles are contained in the intermediate layer, it is difficult to uniformly disperse the hollow particles in the layer, so that the smoothness of the intermediate layer is lowered and it becomes difficult to obtain a uniform recording image quality. It is difficult to obtain a sufficient coating layer strength, and the interfacial adhesion between the intermediate layer containing hollow particles and the heat-sensitive recording layer is low, so that the coating strength of the entire heat-sensitive recording material tends to be low. Therefore, in order to improve the recording image quality by increasing the dispersibility of the hollow particles, and to improve the adhesion between the hollow particles and between the intermediate layer and the heat-sensitive recording material to obtain a sufficient coating layer strength, for example, in Patent Document 9 A method in which hollow particles having at least a part of the surface coated with a coating agent are contained in the intermediate layer, and a method in which organic hollow particles having a nanoscale pigment adsorbed on the surface are contained in the intermediate layer are proposed in Patent Document 10. Further, in Patent Documents 11 and 12, by providing a second intermediate layer containing an oil-absorbing pigment between the intermediate layer containing hollow particles and the heat-sensitive recording layer, the smoothness of the intermediate layer is improved, and the intermediate layer and the heat-sensitive layer are heated. A method for improving the interfacial adhesion with the recording layer has been proposed.

  However, even with these proposals, a heat-sensitive recording material capable of achieving both high halftone recording image quality and high thermal response and high coating layer strength has not been obtained.

Japanese Patent Publication No.52-20142 JP 59-1555097 JP 59-5093 A JP 63-299773 A Japanese Patent Laid-Open No. 04-290789 Japanese Unexamined Patent Publication No. 01-30785 Japanese Patent Laid-Open No. 06-262857 International Publication No. 2007/023687 Pamphlet JP 2008-80530 A International Publication No. 2008/006474 Pamphlet JP-A-01-285383 Japanese Patent Laid-Open No. 04-241987

  An object of the present invention is to provide a heat-sensitive recording material which is particularly excellent in halftone recording image quality and thermal response and excellent in coating layer strength.

As a result of intensive studies, the present inventor has found that the above-described problems can be solved by the following invention.
1) In a heat-sensitive recording material having an intermediate layer and a heat-sensitive recording layer that develops color by heat in this order on the support, the intermediate layer contains a hollow resin having a bowl shape and an inorganic pigment having a primary average particle size of 7 to 200 nm. A heat-sensitive recording material.
2) The heat-sensitive recording material as described in 1 above, wherein the intermediate layer contains an inorganic pigment adhering to the hollow resin.
3) The heat-sensitive recording material as described in 1 or 2 above, wherein the inorganic pigment is silica.

  According to the present invention, it is possible to provide a heat-sensitive recording material that is particularly excellent in halftone recording image quality and thermal response and excellent in coating layer strength.

Sectional view of a heat-sensitive recording material provided with an intermediate layer containing a hollow resin having a bowl shape Sectional view of heat-sensitive recording material provided with an intermediate layer containing hollow resin particles that do not have a bowl shape

  Hereinafter, the content of the present invention will be described more specifically. The heat-sensitive recording material of the present invention has at least one each of an intermediate layer and a heat-sensitive recording layer that develops color by heat on a support.

  An example of a cross-sectional view of a heat-sensitive recording material provided with an intermediate layer containing a hollow resin having a bowl shape according to the present invention is shown in FIG. This sectional view is an image taken with a scanning electron microscope after the heat-sensitive recording material of the present invention is cut by ion milling. As shown in FIG. 1, the wrinkle shape referred to here has a cellular structure such that the hollow resin has a floor surface on the support side and a top surface on the thermosensitive recording layer side in the intermediate layer, and the side surface of the cell is It has a plurality of bellows-like ridges. Due to the side bellows structure and the wide internal gap, the hollow resin easily expands and contracts in the vertical direction with respect to the support under pressure, gives the cushioning layer a uniform cushioning effect, and efficiently heats the head and heat. It is possible to make the coloring surface of the recording material closely contact. Furthermore, the intermediate layer also has a high heat insulating effect due to its hollow structure. In the intermediate layer, a plurality of the cells may overlap in the vertical direction, in which case 1 to 5 cells are preferable, and 1 to 3 cells are more preferable. As described above, with the intermediate layer of the present invention, the thermal head and the color-developing surface of the thermal recording material are uniformly and well adhered under pressure so that there is no lack of printing even in halftones during thermal printing. A heat-sensitive recording material having a uniform color density and excellent thermal response can be obtained.

  The method for forming the intermediate layer containing the hollow resin having a ridge shape according to the present invention is not particularly limited. For example, by applying and drying a coating liquid containing thermally expandable resin particles, a method of performing heating and pressure molding treatment can get. The thermally expandable resin particles used at this time may be in a state before expansion or have been expanded.

  Thermally expandable resin particles refer to resin particles whose particle diameter increases upon heating. For example, there are hollow resin particles containing a volatile liquid, and the resin is softened by heating, and at the same time, the volatile liquid is vaporized (volume increase), and the particles expand. More specifically, styrene monomers such as styrene and α-methylstyrene, acrylic monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, isobornyl (meth) acrylate, acrylonitrile, vinylidene chloride monomer, Hollow resin particles in which a polymer and a copolymer such as vinyl acetate monomer are used as an outer shell resin, and low-boiling hydrocarbons such as propane, butane, isobutane, pentane, isopentane, hexane, and heptane are encapsulated as a volatile liquid. In the present invention, from the viewpoint of thermal expansion performance and formation of a bowl shape, a hollow resin in which methyl methacrylate-acrylonitrile copolymer or vinylidene chloride-acrylonitrile copolymer is used as an outer shell resin and isobutane or isopentane is used as a volatile liquid. Particles are particularly preferably used. Further, the outer shell resin may be crosslinked with a polyfunctional monomer. In this case, the expansion start temperature of the thermally expandable resin particles is preferably in the range of 80 to 130 ° C.

  The average particle diameter of the thermally expandable resin particles when not expanded is preferably 1 to 25 μm, more preferably 3 to 10 μm. The volume expands 10 to 50 times by heating, and the hollow ratio is 80% or more. Are preferably used. By setting the average particle diameter to 1 μm or more, a sufficient volume and surface area can be obtained after expansion, and a cocoon shape can be easily formed. In addition, sufficient voids are generated in the particles after heating, and a heat insulating effect is easily obtained. Moreover, it becomes easy to obtain the flatness of the intermediate layer after heat molding by setting the average particle diameter to 25 μm or less. In addition, the average particle diameter in this invention is a volume average particle diameter calculated from the particle size distribution obtained by the laser diffraction / scattering method. In addition, by setting the hollow ratio after heating to 80% or more, sufficient voids are generated in the particles after expansion, and the heat insulating effect is easily obtained. In addition, the shell can be easily made into a thin film, so that the ridge shape can be easily formed. The hollow ratio here is a value obtained by dividing the volume of the hollow portion of the hollow resin by the volume of the hollow particles.

  In the present invention, the intermediate layer further contains an inorganic pigment having a primary average particle diameter of 7 to 200 nm, and preferably the inorganic pigment is present in a state of adhering to the hollow resin in a bowl shape, thereby further improving the recording image quality. It is possible to obtain good coating layer strength, which is another feature of the invention. The presence of micropigments having an appropriate hardness on the wall surfaces of the resin particles facilitates formation of wrinkles in the hollow resin during the molding process and facilitates formation of wrinkle shapes. Further, since the wrinkles are deepened, it is possible to further improve the high elasticity of the particles and further improve the recording image quality. On the other hand, the reason why the coating layer strength is improved is not clear, but an inorganic pigment having a high specific surface area functions as an anchor between the hollow resins, and the hollow resin that is adjacent or overlapped in the vertical direction is subjected to thermoforming by the inorganic pigment. It is presumed to be tightly bound through. It is also presumed that the adhesion between the intermediate layer and the heat-sensitive recording layer is improved by the adhesion of the hydrophilic inorganic pigment to the surface of the hydrophobic hollow resin. The primary average particle diameter referred to in the present invention is obtained by observing inorganic pigment particles with an electron microscope, and determining the average particle diameter using the diameter of a circle equal to the projected area of each primary particle as the particle diameter of the particles. .

  Specific examples of the inorganic pigment having a primary average particle diameter of 7 to 200 nm according to the present invention include kaolin, magnesium carbonate, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, aluminum hydroxide, magnesium hydroxide, and silica. . In particular, silica is preferably used from the viewpoint of coating layer strength. Silica in the present invention refers to amorphous synthetic silica, and any of precipitated silica, colloidal silica, silica gel, dry silica and the like may be used as long as it satisfies the requirements of the present invention. The inorganic pigment used in the present invention may be a commercial product having a desired size, or may be used after being pulverized by wet pulverization or the like so as to satisfy the requirements of the present invention. Moreover, the primary average particle diameter of the inorganic pigment used in the present invention is more preferably 15 to 100 nm. By setting the primary average particle size to 7 nm or more, the aggregation of the inorganic pigment is suppressed and the inorganic pigment can be uniformly distributed between the hollow resins. When the thickness is 200 nm or less, an appropriate number of inorganic pigments effective for the present invention can be distributed around the hollow resin.

  The inorganic pigment may be used by mixing it with a coating solution together with the heat-expandable resin particles, or may be used by adhering to the surface of the heat-expandable resin particles in advance. In particular, when an inorganic pigment is used by adhering to the surface of the thermally expandable resin particles in advance, it is more preferable because the inorganic pigment can be uniformly distributed between the hollow resins after the formation of the ridge shape. The method of attaching the inorganic pigment to the surface of the heat-expandable resin particles in advance is not particularly limited. For example, the inorganic pigment can be obtained by using a desired inorganic pigment as a dispersion stabilizer during polymerization of the heat-expandable resin particles. Also, the heat-expandable resin particles and the desired inorganic pigment are mixed and stirred or rocked with a powder mixer such as a ribbon mixer or a vertical screw mixer, or the heat-expandable resin particles and the desired pigment are mixed. The inorganic pigment dispersion may be mixed and stirred with a homomixer, an agitator or the like. In this case, it is also possible to warm the dispersion to a temperature at which the thermally expandable resin particles do not foam. When the inorganic pigment is mixed with the coating liquid and used, the inorganic pigment adheres to the surface of the softened resin during the heat treatment after coating and drying, and the hollow resin having a bowl shape according to the present invention and An intermediate layer containing an inorganic pigment having an average particle diameter of 7 to 200 nm, preferably present by adhering the inorganic pigment to the bowl-shaped hollow resin is formed.

  The amount of the inorganic pigment to be used is appropriately adjusted so as to be present more efficiently on the surface of the hollow resin from its particle size and specific gravity. An amount up to such an extent that the surface of the unexpanded hollow resin can be coated with an inorganic pigment is suitable, and it is preferably about 0.2 to 20% by mass, more preferably 0.5 to 10% by mass with respect to the hollow resin. It is. If it is less than 0.2% by mass, sufficient coating layer strength cannot be obtained, and if it exceeds 20% by mass, the formation of the ridge shape may be inhibited.

  In the present invention, the shape of the hollow resin can be confirmed by observing the cross section of the heat-sensitive recording material at a magnification of 1000 to 3000 times with a scanning electron microscope or an optical microscope. In the present invention, the ridge shape is the average value of the ridge depth of the side surface relative to the average value from the floor surface to the top surface of the hollow resin, that is, the folds alternately positioned in the direction parallel to the support surface. It is preferable that the average value of the length of 1/2 of the distance between vertices is 1/15 or more. Each length is calculated as an average value obtained by measuring five arbitrary positions in the heat-sensitive recording material sectional view. The cross-section treatment method is arbitrarily selected, and examples thereof include microtome treatment and ion milling treatment. In particular, an ion milling process in which the cross-section is not easily broken during processing is preferable. Further, the adhesion of the inorganic pigment can also be confirmed by observing the element distribution of the cross section of the heat-sensitive recording material that has been subjected to the cross-section processing by the same method, by energy dispersive X-ray analysis.

In the present invention, the coating amount of the intermediate layer containing the thermally expandable resin particles and the inorganic pigment having a primary average particle diameter of 7 to 200 nm is appropriately set within a range that does not impair the desired effect of the present invention. preferably ^{30g / m 2, 3~15g / m} 2 is particularly preferred. The content of the thermally expandable resin particles in the intermediate layer is preferably 20% by mass or more, more preferably 60% by mass or more, based on the total solid content of the intermediate layer.

    The heat-expanding resin particle heat molding treatment method is arbitrarily selected. For example, a chilled nip calender after heating by a scuff dryer, IR dryer, cylinder dryer, Yankee dryer, thermal calender, metal belt calender, hot press, etc. , And press molding with a soft nip calender, super calender, or the like. When the unexpanded thermally expandable resin particles are used, in order to sufficiently expand the particles, the surface on which the thermally expandable resin particles are generally coated is 80 to 250 ° C. at a temperature about 10 to 100 ° C. higher than the expansion start temperature. It is preferable to perform the heat treatment for 0.5 seconds or more at a temperature that falls within the range of In the case of using thermally expanded particles that have been expanded, heat treatment is performed for 0.5 seconds or more at a temperature such that the surface on which the thermally expandable resin particles are coated is equal to or higher than the glass transition temperature of the resin shell. Is preferred.

The support of the present invention may be any of transparent, translucent, and opaque. Paper, various nonwoven fabrics, woven fabric, synthetic resin film, synthetic resin laminated paper, synthetic paper, metal foil, ceramic paper, glass A plate or the like, or a composite sheet combining these can be arbitrarily used depending on the purpose. In particular, when a paper support is used, paper having a density of 0.9 to 1.3 g / cm ³ and a basis weight of 30 to 100 g / m ² is preferably used.

  As the binder, various water-soluble polymer compounds or water-dispersible resins used in ordinary coating can be used for the intermediate layer. Specific examples thereof include starches, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylic acid ester copolymer, acrylamide / Acrylic acid ester / methacrylic acid terpolymer, alkali salt of polyacrylic acid, alkali salt of polymaleic acid, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, Water-soluble resin such as alkali salt of isobutylene / maleic anhydride copolymer, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butane En copolymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate, styrene / acrylate copolymer Examples include, but are not limited to, water-dispersible resins such as coalescence and polyurethane. A binder can be used individually or in mixture of 2 or more types. It is preferable that the usage-amount of a binder shall be 10-400 mass% with respect to a thermally expansible resin particle.

  Further, in the intermediate layer coating solution, other additives such as pigment dispersants, fluorescent dyes, colored dyes and pigments, ultraviolet absorbers, conductive substances, lubricants, water resistance are within the range not impairing the effects of the present invention. Agents, antifoaming agents, antiseptics, etc.

  The method for applying the intermediate layer is not particularly limited, and can be applied according to a conventionally known technique. Specific examples include air knife coating, rod blade coating, bar coating, blade coating, gravure coating, curtain coating, E-bar coating, and the like. In the present invention, air knife coating and curtain coating are particularly preferred from the viewpoint of the stability of the thermally expandable resin particles.

  The heat-sensitive recording layer that develops color by heat in the present invention can be obtained by coating a heat-sensitive recording component that develops color by heat on the intermediate layer. The heat-sensitive recording component is not particularly limited, and any combination that produces a color reaction with the energy applied by the heat-sensitive head can be used. For example, a combination of a colorless or light-colored electron-donating dye precursor and an electron-accepting compound, a combination of an aromatic isocyanate compound and an imino compound, a combination of a colorless or light-colored electron-donating dye precursor and an isocyanate compound, a metal compound And a combination of a coordination compound and a combination of a diazonium salt and a coupler. In terms of color density, ease of color development, ease of color control, etc., usually a combination of a colorless or light-colored electron-donating dye precursor and an electron-accepting compound, a combination of an aromatic isocyanate compound and an imino compound, Usually, a combination of a colorless or light-colored electron-donating dye precursor and an isocyanate compound is preferably used.

  The dye precursors used in the heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention are typically represented by pressure-sensitive recording materials or those used in heat-sensitive recording materials, but are not limited to these. Absent.

A specific example is as follows.
(1) Triarylmethane compounds: 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (P-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (P-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3 -Bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl)- -Dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl)- 6-dimethylaminophthalide, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, etc.

  (2) Diphenylmethane compounds: 4,4-bis (dimethylaminophenyl) benzhydrylbenzyl ether, N-chlorophenylleucooramine, N-2,4,5-trichlorophenylleucooramine, etc.

  (3) Xanthene compounds: Rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino- 6-chloro-7-methylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3-dibutylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-7- (2- Chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dipentylamino-6-methyl-7-anilinofluorane 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilino Luolan, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-phenethylaminofluorane, 3-diethylamino-7-chlorofluorane 3-diethylamino-7-bromofluorane, 3-diethylamino-7-phenoxyfluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, 3- (N-methyl) -N-propyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N -Cyclohexyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfuryl) amino Such as 6-methyl-7-anilinofluoran,

  (4) Thiazine compounds: benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue, etc.

  (5) Spiro compounds: 3-methylspirodinaphthopyrans, 3-ethylspirodinaphthopyrans, 3,3-dichlorospirodinaphthopyrans, 3-benzylspirodinaphthopyrans, 3-methylnaphthyl- (3-methoxybenzo ) Spiropyran, 3-propyl spirobenzopyran and the like can be mentioned, but are not limited thereto, and can be used alone or in admixture of two or more as required.

  Examples of the electron-accepting compound include clay substances, phenol derivatives, aromatic carboxylic acid derivatives, urea derivatives such as N, N′-diallylthiourea derivatives and N-sulfonylureas, and metal salts thereof. Specific examples include clay clay such as acid clay, activated clay, zeolite, bentonite and kaolin, p-phenylphenol, p-hydroxyacetophenone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4. '-N-propoxydiphenylsulfone, 3-phenylsulfonyl-4-hydroxydiphenylsulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenylsulfone, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) pentane, 1,1-bis (4-hydroxyphenyl) hexane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) cyclododecane, 2, 2-bis (4-hydroxyphenyl) Propane, 2,2-bis (4-hydroxyphenyl) hexane, 2,2-bis (4-hydroxyphenyl) octane, 1,1-bis (4-hydroxyphenyl) -2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,3-bis [2- (4-hydroxyphenyl) -2-propyl] benzene, 1,3-bis [2- (3,4-dihydroxyphenyl) -2-propyl] benzene, 1,4-bis [2- (4-hydroxyphenyl) -2-propyl] benzene, 4,4'-dihydroxy Diphenyl ether, bis [4- (4-toluenesulfonyl) aminocarbonylaminophenyl] methane, N- (2-hydroxyphenyl) benzenesulfone Amide, N- (2-hydroxyphenyl) -p-toluenesulfonamide, N- (4-hydroxyphenyl) benzenesulfonamide, N- (4-hydroxyphenyl) -p-toluenesulfonamide, 4,4'-dihydroxy Diphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 3,3'-dichloro-4,4'-dihydroxydiphenylsulfone, 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4 ' -Allyloxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, Np-toluenesulfonyl-N'-3- (p-toluenesulfonyloxy) phenylurea, N- (4-hydroxyphenylsulfonyl) aniline, 3,3'-dichloro-4,4'-dihydro Xidiphenyl sulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, butyl 2,2-bis (4-hydroxyphenyl) acetate, 4,4'-thiobis (2-t-butyl-5-methylphenol) Benzyl p-hydroxybenzoate, chlorobenzyl p-hydroxybenzoate, dimethyl 4-hydroxyphthalate, benzyl gallate, stearyl gallate, salicylanilide, 5-chlorosalicylanilide, novolak phenol resin, modified terpene phenol resin, 3 , 5-di-t-butylsalicylic acid, 3,5-di-t-nonylsalicylic acid, 3,5-didodecylsalicylic acid, 3-methyl-5-t-dodecylsalicylic acid, 5-cyclohexylsalicylic acid, 3,5-bis (Α, α-dimethylbenzyl) salicylic acid, 3-methyl-5- (α- (Tilbenzyl) salicylic acid, 4-n-octyloxycarbonylaminosalicylic acid, and the like, and metal salts such as zinc, nickel, aluminum, calcium, and the like can be mentioned, but are not limited thereto, and as necessary. Two or more types can be used in combination.

  The aromatic isocyanate compound is a colorless or light-colored aromatic isocyanate compound or heterocyclic isocyanate compound that is solid at room temperature. Specifically, 2,6-dichlorophenyl isocyanate, p-chlorophenyl isocyanate, 1 , 3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1,3-dimethylbenzene-4,6-diisocyanate, 1,4-dimethylbenzene-2,5-diisocyanate, 1-ethoxy Benzene-2,4-diisocyanate, 2,5-dimethoxybenzene-1,4-diisocyanate, 2,5-diethoxybenzene-1,4-diisocyanate, 2,5-dibutoxybenzene-1 , 4-diisocyanate, azobenzene-4,4'-diisocyanate, diphenyl ether-4, '-Diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, naphthalene-2,6-diisocyanate, naphthalene-2,7-diisocyanate, 3,3' -Dimethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenyldimethylmethane-4,4'-di Isocyanate, benzophenone-3,3'-diisocyanate, fluorene-2,7-diisocyanate, anthraquinone-2,6-diisocyanate, 9-ethylcarbazole-3,6-diisocyanate, pyrene- 3,8-diisocyanate, naphthalene-1,3,7-triisocyanate, biphenyl-2,4,4'-tri Examples of such substances include isocyanate, 4,4 ′, 4 ″ -triisocyanate-2,5-dimethoxytriphenylamine, p-dimethylaminophenyl isocyanate, tris (4-phenylisocyanate) thiophosphate, and the like. The aromatic isocyanate compounds according to the invention are not limited to these, and can be used alone or in combination of two or more as required.

  These aromatic isocyanate compounds may be used in the form of so-called block isocyanate, which is an addition compound with phenols, lactams, oximes and the like, if necessary, dimer of diisocyanate, For example, it may be used in the form of 1-methylbenzene-2,4-diisocyanate dimer and trimer isocyanurate, or used as a polyisocyanate added with various polyols. Is also possible.

  An imino compound is a colorless or light-colored compound that is solid at room temperature. Specifically, 3-imino-4,5,6,7-tetrachloroisoindoline-1-one, 1,3-diimino-4 , 5,6,7-tetrachloroisoindoline, 1,3-diiminoisoindoline, 1,3-diiminobenz (f) isoindoline, 1,3-diiminonaphtho (2,3-f) isoindoline, 1,3 -Diimino-5-nitroisoindoline, 1,3-diimino-5-phenylisoindoline, 1,3-diimino-5-methoxyisoindoline, 1,3-diimino-5-chloroisoindoline, 5-cyano-1 , 3-Diiminoisoindoline, 5-acetamido-1,3-diiminoisoindoline, 1,3-diimino-5- (1H-1,2,3-triazol-1-yl -Isoindoline, 5- (pt-butylphenoxy) -1,3-diiminoisoindoline, 5- (p-cumylphenoxy) -1,3-diiminoisoindoline, 5-isobutoxy-1,3 -Diiminoisoindoline, 1,3-diimino-4,7-dimethoxyisoindoline, 4,7-diethoxy-1,3-diiminoisoindoline, 4,5,6,7-tetrabromo-1,3-di Iminoisoindoline, 4,5,6,7-tetrafluoro-1,3-diiminoisoindoline, 4,5,7-trichloro-1,3-diimino-6-methylmercaptoisoindoline, 1-iminodiphenic acid imide 1- (cyano-p-nitrophenylmethylene) -3-iminoisoindoline, 1- (cyanobenzothiazolyl- (2 ′)-carbamoylmethylene) 3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2 ') methylene] -3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2')-methylene] -3-imino-4,5,6 , 7-tetrachloroisoindoline, 1-[(cyanobenzimidazolyl-2 ')-methylene] -3-imino-5-methoxyisoindoline, 1-[(1'-phenyl-3'-methyl-5-oxo ) -Pyrazolidene-4 ']-3-iminoisoindoline, 3-imino-1-sulfobenzoimide, 3-imino-1-sulfo-4,5,6,7-tetrachlorobenzoimide, 3-imino -1-sulfo-4,5,7-trichloro-6-methylmercaptobenzoic acid imide, 3-imino-2-methyl-4,5,6,7-tetrachloroisoindoline- Substances such as 1-one can be mentioned, but the imino compound according to the present invention is not limited to these, and can be used alone or in combination of two or more as required.

  The heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention can also contain a heat-fusible compound in order to improve its thermal response. In this case, those having a melting point of 60 to 180 ° C. are preferred, and those having a melting point of 80 to 140 ° C. are particularly preferred.

  Specifically, stearic acid amide, N-hydroxymethyl stearic acid amide, N-stearyl stearic acid amide, ethylene bis stearic acid amide, N-stearyl urea, benzyl-2-naphthyl ether, m-terphenyl, 4-benzyl Biphenyl, 4-acetylbiphenyl, 2,2′-bis (4-methoxyphenoxy) diethyl ether, α, α′-diphenoxyxylene, 1,2-diphenoxyethane, 1,2-bis (3-methylphenoxy) Ethane, bis (4-methoxyphenyl) ether, diphenyl adipate, dibenzyl oxalate, bis (4-methylbenzyl) oxalate, bis (4-chlorobenzyl) oxalate, dimethyl terephthalate, dibenzyl terephthalate, benzenesulfone Acid phenyl ester, bis (4 -Allyloxyphenyl) sulfone, 4-acetylacetophenone, acetoacetate anilides, fatty acid anilides, and the like, and known heat-fusible substances. These compounds can be used alone or in combination of two or more.

  The content of the heat fusible compound is preferably 30 to 200% by mass, more preferably 50 to 150% by mass, with respect to the electron accepting compound. By setting this range, it is possible to obtain a heat-sensitive recording material having good basic characteristics such as thermal responsiveness, saturated density of a color image, and whiteness of the background.

  In addition, for the heat-sensitive recording layer, diatomaceous earth, talc, kaolin, calcined kaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide, Can contain inorganic pigments such as barium sulfate, zinc sulfate, amorphous silica, amorphous calcium silicate, colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, nylon powder, etc. .

  Other additives include higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearamide, and custard wax for the purpose of preventing wear and sticking of heated print heads. In addition, waxes such as dioctyl sulfosuccinate sodium, UV absorbers such as benzophenone and benzotriazole, surfactants, fluorescent dyes and the like can be contained as necessary.

  As the binder for the heat-sensitive recording layer, various water-soluble polymer compounds or water-dispersible resins used in ordinary coating can be used. Specific examples thereof include the binders described as specific examples of the binder used for the intermediate layer. A binder can be used individually or in mixture of 2 or more types.

The coating amount of the heat-sensitive recording layer is usually in the range of 0.1 to 2.0 g / m ^{2 in} terms of the coating amount of the dye precursor, in order to obtain sufficient thermal response, and a more preferable range is 0. 15 to 1.5 g / m ² .

  The heat-sensitive recording material of the present invention is one or more on the heat-sensitive recording layer for the purpose of preventing water coloring, chemical resistance, plasticizer resistance, and coloring (friction fogging) due to rubbing such as scratching. One or more protective layers made of several binders and / or pigments can be provided.

  Examples of the binder used in the protective layer include various water-soluble polymer compounds and water-dispersible resins that are used in ordinary coating. Specific examples thereof include the binders described as specific examples of the binder used for the intermediate layer. A binder can be used individually or in mixture of 2 or more types.

  The protective layer provided on the heat-sensitive recording layer of the heat-sensitive recording material of the present invention may contain a hardening agent such as a compound having an epoxy group or a zirconium salt, or a crosslinking agent, if necessary. Furthermore, a pigment etc. can also be contained in order to improve writability and runnability.

  As pigments used in the protective layer, diatomaceous earth, talc, kaolin, calcined kaolin, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide, barium sulfate, Examples include inorganic pigments such as zinc sulfate, amorphous silica, amorphous calcium silicate, colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, and nylon powder. It is not something. In addition, a pigment can be used individually or in mixture of 2 or more types.

  Other additives include higher fatty acid metal salts such as zinc stearate and calcium stearate to prevent head wear and sticking, and waxes such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearamide, and custard wax. In addition, a dispersant such as sodium dioctyl sulfosuccinate, a surfactant, a fluorescent dye, and the like can also be contained.

The coating amount of the protective layer, 0.2 to 10 g / ^{m 2,} preferably in the range of 1 to 5 g / ^{m 2,} if necessary, also be a multilayer structure of two or more layers.

  The method for forming the heat-sensitive recording layer or the protective layer is not particularly limited, and can be formed according to a conventionally known technique. Specific examples include air knife coating, rod blade coating, bar coating, blade coating, gravure coating, curtain coating, E-bar coating, and other methods. A recording layer can be formed. In the present invention, air knife coating and curtain coating are particularly preferably used in order to protect the wrinkle shape of the intermediate layer.

  In addition, each layer may be formed by various printing machines such as a lithographic plate, a relief plate, a flexo, a gravure, and a screen.

  In the thermosensitive recording material of the present invention, an optional information recording layer such as a protective layer (barrier), an adhesive layer, a magnetic recording layer, an ink jet recording layer, etc. It can also be provided, or a smoothing process such as a calendar process can be performed after coating each layer.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In Examples,% and parts are all based on mass. The coating amount is an absolutely dry coating amount.

Example 1
(1) Preparation of support having intermediate layer <Intermediate layer coating solution>
An intermediate layer coating solution containing thermally expandable resin particles and an inorganic pigment having the following composition was prepared. The thermally expandable resin particles are resin particles having an average particle diameter of 7 μm containing isobutane as a volatile liquid and vinylidene chloride-acrylonitrile as an outer shell resin, and an expansion start temperature is about 100 ° C.
Unexpanded thermally expandable resin particles 20% aqueous dispersion 500 parts Calcium carbonate 20% aqueous dispersion with primary average particle size 200 nm 50 parts Completely saponified polyvinyl alcohol 10% aqueous solution 300 parts

The intermediate layer coating solution prepared above is applied to a paper support having a density of 1.1 g / cm ³ and a basis weight of 60 g / m ² so that the coating amount is 5 g / m ^2, and then a paper surface temperature of 80 The temperature was kept below ℃ and dried. Thereafter, the thermally expandable resin particles were thermally expanded by contacting with a cylinder dryer heated to 160 ° C. for 30 seconds. Subsequently, a super calender treatment was performed at a linear pressure of 500 N / cm to prepare a support having an intermediate layer.

(2) Preparation of coating solution for heat-sensitive recording layer <Electron-donating dye precursor dispersion>
30 parts of 3-dibutylamino-6-methyl-7-anilinofluorane is dispersed in 70 parts of a 2.5% aqueous solution of polyvinyl alcohol, wet-pulverized with a bead mill until the average particle size becomes 0.8 μm, and electron donating properties A dye precursor dispersion was prepared.

<Electron-accepting compound dispersion>
30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone is dispersed in 70 parts of a 2.5% aqueous solution of polyvinyl alcohol and pulverized with a bead mill until the average particle size becomes 0.8 μm to prepare an electron-accepting compound dispersion. did.

<Heat fusible compound dispersion>
30 parts of benzyl-2-naphthyl ether was dispersed in 70 parts of a 2.5% aqueous solution of polyvinyl alcohol and pulverized with a bead mill until the average particle size became 0.8 μm to prepare a thermofusible compound dispersion.

Using the dispersion prepared above, a coating solution for a thermal recording layer having the following composition was prepared.
Electron-donating dye precursor dispersion 100 parts Electron-accepting compound dispersion 100 parts Thermofusible compound dispersion 100 parts Polyvinyl alcohol 10% aqueous solution 200 parts Aluminum hydroxide 30% aqueous dispersion 100 parts Zinc stearate 40% water Dispersion 25 parts Water 60 parts

(3) Preparation of protective layer coating solution A protective layer coating solution having the following composition was prepared.
Kaolin 25% aqueous dispersion with an average particle size of 2 μm 20 parts Zinc stearate 40% aqueous dispersion 1 part Diacetone modified polyvinyl alcohol 10% aqueous solution 100 parts Adipic acid dihydrazide 8% aqueous solution 12.5 parts Water 70 parts

(4) Preparation of thermosensitive recording material On the support having the intermediate layer of (1), the coating solution for the thermosensitive recording layer of (2) is applied so that the coating amount of the dye precursor is 0.5 g / m ^2. And dried to form a heat-sensitive recording layer. Thereafter, the coating liquid for protective layer (3) was applied and dried on the heat-sensitive recording layer so that the coating amount was 2 g / m ^2, and then calendered to produce a heat-sensitive recording material.

Example 2
In Example 1 (1) <Preparation of intermediate layer coating solution> for preparing a support having an intermediate layer, a primary average particle size of 50 nm was used instead of 50 parts of a 20% calcium carbonate aqueous dispersion having a primary average particle size of 200 nm. A heat-sensitive recording material was prepared in the same manner as in Example 1 except that 12.5 parts of a 20% calcium carbonate aqueous dispersion was used.

Example 3
In <Preparation of intermediate layer coating solution> in the preparation of the support having the intermediate layer of Example 1 (1), the primary average particle size of 30 nm was used instead of 50 parts of 20% calcium carbonate aqueous dispersion having a primary average particle size of 200 nm. A thermosensitive recording material was prepared in the same manner as in Example 1 except that 12.5 parts of a 20% aqueous colloidal silica dispersion was used.

Example 4
In Example 1 (1) <Preparation of coating liquid for intermediate layer> in the preparation of a support having an intermediate layer, a primary average particle diameter of 10 nm is used instead of 50 parts of a 20% calcium carbonate aqueous dispersion having a primary average particle diameter of 200 nm. A thermosensitive recording material was prepared in the same manner as in Example 1 except that 12.5 parts of a 20% aqueous colloidal silica dispersion was used.

Example 5
In Example 1 (1) <Preparation of intermediate layer coating solution> for preparing a support having an intermediate layer, a primary average particle size of 7 nm was used instead of 50 parts of a 20% calcium carbonate aqueous dispersion having a primary average particle size of 200 nm. A heat-sensitive recording material was prepared in the same manner as in Example 1 except that 12.5 parts of a 20% aqueous dispersion of dry silica was used.

Example 6
<Heat-expandable resin particle aqueous dispersion with colloidal silica attached>
A dispersion having the following composition was prepared.
Unexpanded thermally expandable resin particle 20% aqueous dispersion 500 parts Colloidal silica 20% aqueous dispersion with primary average particle size 30 nm 12.5 parts 1 hour in a state where the dispersion was heated and maintained at 80 ° C. The mixture was vigorously stirred to prepare an aqueous dispersion of thermally expandable resin particles in which colloidal silica adhered to the surface of the thermally expandable resin particles. At this temperature, the thermally expandable resin particles do not thermally expand.

A thermosensitive recording material was produced in the same manner as in Example 1 except that a coating liquid having the following composition was used as <intermediate layer coating liquid> in the production of the support having the intermediate layer of Example 1 (1).
<Interlayer coating solution>
Thermally expandable resin particles 20% aqueous dispersion with 51% colloidal silica adhered 300 parts fully saponified polyvinyl alcohol 10% aqueous solution 300 parts

Example 7
<Expanded thermally expandable resin particle aqueous dispersion with colloidal silica attached>
The heat-expandable resin particle aqueous dispersion to which the colloidal silica used in Example 6 was attached was heated in a sealed state, and after maintaining the boiling state, the heat-expandable resin particles to which the colloidal silica was attached were vigorously stirred for 5 minutes. Thermal expansion was performed to prepare an expanded thermal expandable resin particle aqueous dispersion in which colloidal silica was adhered.

A thermosensitive recording material was produced in the same manner as in Example 1 except that a coating liquid having the following composition was used as <intermediate layer coating liquid> in the production of the support having the intermediate layer of Example 1 (1).
<Interlayer coating solution>
Expanded thermally expandable resin particle 20% aqueous dispersion with colloidal silica attached
512.5 parts Fully saponified polyvinyl alcohol 10% aqueous solution 300 parts

Comparative Example 1
In the production of the support having the intermediate layer of Example 1 (1), when the coating liquid was dried, the thermally expandable resin particles were expanded at a paper surface temperature of 130 ° C., and the subsequent cylinder dryer and supercalender treatment were not performed. A thermosensitive recording material was prepared in the same manner as in Example 1 except for the above.

Comparative Example 2
In Example 1 (1) <Intermediate layer coating solution> for producing a support having an intermediate layer, a non-expandable material having an average particle diameter of 1 μm and a hollowness of 50% instead of the unexpanded thermally expandable resin particles A heat-sensitive recording material was prepared in the same manner as in Example 1 except that the hollow resin particles were used and the cylinder dryer and the supercalender treatment were not performed.

Comparative Example 3
In Example 1 (1) <Intermediate layer coating solution> for producing a support having an intermediate layer, Example 1 was used except that 50 parts of a 20% aqueous calcium carbonate dispersion having a primary average particle size of 200 nm was not used. A thermosensitive recording material was produced in the same manner.

Comparative Example 4
In Example 1, (1) <Intermediate layer coating solution> for producing a support having an intermediate layer, instead of 50 parts of a light calcium carbonate 20% aqueous dispersion having a primary average particle size of 200 nm, a primary average particle size of 300 nm was used. A heat-sensitive recording material was prepared in the same manner as in Example 1 except that 50 parts of a 20% calcium carbonate aqueous dispersion was used.

Comparative Example 5
In Example 1, (1) <Intermediate layer coating solution> for producing a support having an intermediate layer, a colloidal having a primary average particle size of 5 nm instead of 50 parts of a 20% calcium carbonate aqueous dispersion having a primary average particle size of 200 nm. A thermosensitive recording material was produced in the same manner as in Example 1 except that 12.5 parts of a 20% silica aqueous dispersion was used.

  The following evaluation was performed on the heat-sensitive recording materials prepared in Examples 1 to 7 and Comparative Examples 1 to 5. The results are shown in Table 1.

[Shape shape]
The heat-sensitive recording materials of Examples 1 to 7 and Comparative Examples 1 to 5 were subjected to cross-section processing by ion milling, and observed at a magnification of 1000 times using a Hitachi scanning electron microscope S-2300. Was confirmed. Moreover, when it had a ridge shape, the average value of the depth of the ridge with respect to the average value of the length of the top | upper surface from the cell floor was calculated. For reference, a cross-sectional view of a heat-sensitive recording material provided with an intermediate layer containing non-expandable hollow resin particles in Comparative Example 2 is shown in FIG. In addition, when the element distribution of the cross section of the heat-sensitive recording material subjected to cross-section processing in the same manner as in Examples 1 to 7 was observed by energy dispersive X ship analysis, the inorganic pigment adhered to the hollow resin in all the intermediate layers. Although present, in Examples 6 and 7, a larger amount of inorganic pigment was present in a uniformly dispersed state between the hollow resins.

[Recording quality]
The heat-sensitive recording materials of Examples 1 to 7 and Comparative Examples 1 to 5 were printed using a printing tester TH-PMD manufactured by Okura Engineering Co., Ltd. Using a thermal head with a dot density of 8 dots / mm and a head resistance of 1685Ω, the image quality of characters printed with an applied voltage of 21 volts and applied pulse widths of 0.2 msec, 0.4 msec, and 0.6 msec was visually evaluated. . The evaluation criteria followed the following indicators.
A: Printing defect and printing unevenness hardly exist, and recording density is uniform.
○: Slightly missing or uneven printing is observed, but there is no problem in actual use.
Δ: Print defects and print unevenness exist, and the print density varies.
X: There are many printing defects and uneven printing, and there is a problem in actual use.

[Thermal response]
The heat-sensitive recording materials of Examples 1 to 7 and Comparative Examples 1 to 5 were printed using a printing tester TH-PMD manufactured by Okura Engineering Co., Ltd. Using a thermal head having a dot density of 8 dots / mm and a head resistance of 1685Ω, a solid image was printed with an applied voltage of 21 volts and an applied pulse width of 0.6 msec and 1.0 msec. The printed image was measured with a Gretag Macbeth RD-19 reflection densitometer. The evaluation criteria followed the following indicators. If the print density is 1.0 or more, there is no problem in actual use.
◎: Print density is 1.2 or more ○: Print density is 1.0 or more and less than 1.2 △: Print density is 0.5 or more and less than 1.0 ×: Print density is less than 0.5

[Coating layer strength]
The heat sensitive recording materials of Examples 1 to 7 and Comparative Examples 1 to 5 were printed with an ink having a tack value value of 20 manufactured by DIC Corporation using an RI-1 type printability tester manufactured by Ishikawajima Industrial Machinery Co., Ltd. .4 ml was used and the coating layer strength was evaluated under the condition of a rotation speed of 50 rpm. The evaluation criteria followed the following indicators.
A: Almost no coating layer blur is observed.
○: Slight coating layer is observed, but there is no practical problem.
Δ: Coating layer blur is observed.
X: Large coating layer blurring occurs.

  As is clear from Table 1, in the heat-sensitive recording materials of Examples 1 to 7 in which the intermediate layer contains a hollow resin having a bowl shape and an inorganic pigment having a primary average particle size of 7 to 200 nm, the interlayer has a bowl shape. Compared to the heat-sensitive recording materials of Comparative Examples 1 and 2 that do not contain a hollow resin, the recording image quality and thermal response are excellent. Also, the recording image quality and coating layer strength are superior to those of the heat-sensitive recording materials of Comparative Examples 3 to 5 which do not contain an inorganic pigment having a primary average particle diameter of 7 to 200 nm, which contains a hollow-shaped hollow resin.

Claims (3)

  A heat-sensitive recording material having an intermediate layer and a heat-sensitive recording layer that develops color by heat in this order on a support, wherein the intermediate layer contains a hollow resin having a bowl shape and an inorganic pigment having a primary average particle diameter of 7 to 200 nm. Thermal recording material.   2. The heat-sensitive recording material according to claim 1, wherein the intermediate layer contains an inorganic pigment adhering to the hollow resin.   The heat-sensitive recording material according to claim 1 or 2, wherein the inorganic pigment is silica.