JP2012158108A - Thermal recording material - Google Patents

Abstract

The present invention provides a heat-sensitive recording material that is excellent in recording image quality such as dot reproducibility and thermal responsiveness of a halftone image and uniformity in color density, and excellent in sticking resistance and chemical resistance.
In a heat-sensitive recording material in which an intermediate layer, a heat-sensitive recording layer that develops color by heat, and a protective layer are sequentially laminated on a support, the intermediate layer contains a hollow resin, and acrylonitrile is an essential component in the protective layer. Water-dispersible resin having a core-shell structure consisting of a core and a shell containing methacrylamide as essential components, and at least one water-soluble resin selected from diacetone group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol and carboxyl group-modified polyvinyl alcohol Contains resin.
[Selection] Figure 1

Description

  The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material excellent in recording image quality such as dot reproducibility and thermal response of halftone images, and uniformity of color density, and excellent in sticking resistance and chemical resistance. is there.

  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 that recording can be obtained with a relatively simple apparatus, maintenance is easy, noise is not generated, etc., and a measurement recorder, facsimile, POS / label printer, ATM / CDs, lottery tickets / tickets / admission tickets / numbered ticketing machines, etc. are widely used mainly in the distribution industry.

  On the other hand, in applications that require the output of graphic information including halftones such as video images in addition to text and bar code information, for example, medical diagnostic images, process inspection images at the manufacturing site, etc. There is a demand for a heat-sensitive recording material excellent in recording image quality such as excellent dot reproducibility and thermal responsiveness with no printing defect even in the above region, and uniform color development with little shading unevenness. As a means for improving the dot reproducibility and thermal response of a halftone image, many methods for improving the recording image quality by providing an intermediate layer having heat insulation between the support and the thermal recording layer have been proposed. For example, Patent Literature 1 and Patent Literature 2 contain thermally expandable hollow resin particles in an intermediate layer, and the adhesiveness between the thermal head and the thermal recording surface is enhanced by the cushioning property. However, the improvement in adhesion between the thermal head and the thermal recording surface tends to cause a reduction in sticking resistance. That is, the heated thermal head and the heat-sensitive recording surface are in close contact with each other and sticking easily occurs, leading to various sticking phenomena such as an increase in printing sound and a horizontal blank in the printing screen.

  As a countermeasure against sticking regarding a heat-sensitive recording material having a hollow resin in the intermediate layer, a method of providing a protective layer on the heat-sensitive recording layer is generally performed. As the binder component of the protective layer, for example, Patent Document 3 proposes the use of a water-soluble resin such as diacetone-modified polyvinyl alcohol, Patent Document 4 includes acetoacetyl group-modified polyvinyl alcohol, and Patent Document 5 discloses carboxyl group-modified polyvinyl alcohol. ing. However, these methods do not provide sufficient countermeasures against the severe sticking phenomenon that occurs between the thermal head and the thermal recording surface that are in close contact with each other, and at the same time, the coating layer unevenness of the protective layer is liable to occur, resulting in uneven density. It is difficult to obtain a uniform color developability with little.

  In Patent Document 6, a water-dispersible resin having a core-shell structure composed of a core having acrylonitrile as an essential component and a shell having methacrylamide as an essential component is used as a binder component of a protective layer in a heat-sensitive recording material without an intermediate layer. It has been. However, when this method is used for a heat-sensitive recording material having a hollow resin in the intermediate layer, the protective layer film formed by the water-dispersed resin is harder than the flexible intermediate layer film having cushioning properties. There is a problem that cracks are likely to occur in the protective layer film due to the difference in hardness of the layer film, and the barrier property, which is one of the performances required for the protective layer, is lowered, and as a result, the chemical resistance tends to be impaired. That is, for a heat-sensitive recording material having an intermediate layer rich in cushioning properties, it is highly desired to improve the protective layer accordingly.

  Further, Patent Document 7 has a core-shell structure comprising an intermediate layer containing an inorganic or organic pigment on a support, and a core containing acrylonitrile as an essential component and a shell containing methacrylamide as an essential component as a binder for the protective layer. Although a heat-sensitive recording material containing a water-dispersible resin and polyvinyl alcohol is described, even if such a protective layer is applied to a heat-sensitive recording material having an intermediate layer containing a hollow resin, sufficient sticking resistance Was not obtained, and improvement was demanded.

JP 59-5093 A JP 63-299773 A JP 2007-230233 A JP 2004-358762 A JP 2007-130999 A JP 2000-158815 A International Publication No. 98/006589 Pamphlet

  An object of the present invention is to provide a heat-sensitive recording material that is particularly excellent in dot reproducibility and thermal response of a halftone image, and uniformity in color density, and excellent in sticking resistance and chemical resistance.

  As a result of intensive studies, the present inventors have invented a heat-sensitive recording material that can solve the problem. That is, in a heat-sensitive recording material in which an intermediate layer, a heat-sensitive recording layer that develops color by heat, and a protective layer are sequentially laminated on a support, the core contains a hollow resin and the protective layer contains acrylonitrile as an essential component. And a water-dispersible resin having a core-shell structure comprising a shell containing methacrylamide as an essential component, and at least one water-soluble resin selected from diacetone group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and carboxyl group-modified polyvinyl alcohol This was achieved by inclusion.

  According to the present invention, it is possible to provide a heat-sensitive recording material that is particularly excellent in dot reproducibility and thermal response of a halftone image and uniformity in color density, and excellent in sticking resistance and chemical resistance.

Cross-sectional view of a heat-sensitive recording material in which an intermediate layer containing a hollow resin having a bowl shape and a heat-sensitive recording layer are sequentially provided

  Hereinafter, the content of the present invention will be described more specifically.

  In the present invention, the intermediate layer contains a hollow resin. As such an intermediate layer, for example, JP-A-59-5093, JP-A-63-299773, JP-A-4-290789, JP-A-01-30785, JP-A-06-262857. Examples include various intermediate layers described in International Publication No. 07/023687 pamphlet and the like. In the present invention, the intermediate layer particularly preferably contains a hollow resin having a bowl shape. For example, the intermediate layer containing the hollow resin having a bowl shape is formed by, for example, forming a coating layer containing the thermally expandable resin particles before thermal expansion on the support, and then performing heating and pressure molding treatment. Obtained by the method. The saddle shape mentioned here has a columnar structure in which the hollow resin has a floor surface on the support side and a top surface on the heat-sensitive recording layer side in the intermediate layer, and the floor surface and the top surface are positioned substantially parallel to each other. In addition, the side surface of the column has a plurality of accordion-shaped ridges. The side bellows structure and the wide hollow structure inside make it easy to expand and contract in the vertical direction with respect to the support, give a uniform cushioning property to the thermal recording layer, and efficiently develop the coloring surface of the head and thermal recording material. Can be brought into close contact with each other.

  The shape of the hollow resin contained in the intermediate layer can be confirmed by observing the cross section of the thermosensitive 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. FIG. 1 is a reflected electron image of the heat-sensitive recording material of the present invention before being coated with a protective layer, taken with a scanning electron microscope at a magnification of 1200 times after cross-section processing by ion milling. As shown in this cross-sectional view, it is shown that the hollow resin has a bowl shape in the intermediate layer.

  As thermally expandable resin particles preferably used for forming an intermediate layer containing a hollow resin having a bowl shape, a polymerizable monomer such as acrylate ester, (meth) acrylonitrile, vinylidene chloride, vinyl chloride, styrene is used. And a hollow portion containing a foaming agent selected from water, air, a low-boiling organic solvent, a compound that decomposes by heating to generate a gas, and the like. In the present invention, it is preferable to select a combination of polymerizable monomers, a composition ratio, and a foaming agent so as to facilitate formation of a ridge shape.

  The average particle diameter of the thermally expandable resin particles before thermal expansion is preferably 3 to 25 μm, more preferably 5 to 20 μm. The volume expands 30 to 70 times by heating, and the hollowness is 80% or more. Are preferably used. By setting the average particle diameter to 3 μm or more, a sufficient volume and surface area can be obtained after heating, and a cocoon shape can be easily formed, sufficient voids are formed in the particles after heating, and a heat insulating effect can be easily obtained. By making the average particle size 25 μm or less, the smoothness of the intermediate layer after heat molding can be easily obtained. The average particle size in the present invention is a volume average particle size calculated from the particle size distribution obtained by the laser diffraction / scattering method. Specifically, the Nikkiso Co., Ltd. Microtrack Series, ( It can be measured by LA series manufactured by Horiba, Ltd., SALD series manufactured by Shimadzu Corporation, and LS series manufactured by Beckman Coulter, Inc. Further, by setting the hollow ratio after heating to 80% or more, sufficient voids are generated in the particles after heating, and the formation of the ridge shape is facilitated. The hollow ratio referred to here is a value obtained by dividing the volume of the hollow portion of the thermally expandable resin particles by the total volume of the shell portion and the hollow portion of the thermally expandable resin particles.

  The expansion start temperature of the thermally expandable resin particles is preferably in the range of 80 to 130 ° C. When the expansion start temperature is 80 ° C. or higher, the heat resistance of the shell is good, and it becomes easy to maintain the cocoon shape even when the heat-sensitive recording material of the present invention is stored for a long period of time. By setting the expansion start temperature to 130 ° C. or lower, it becomes easy to form a bowl shape in various heating and pressure forming processes.

  Commercially available products of thermally expandable resin particles include Sekisui Chemical Co., Ltd., Advancel, Netherlands AkzoNovel, Expandacel, Matsumoto Yushi Seiyaku Co., Ltd., Matsumoto Microsphere, Kureha Co., Ltd. A microsphere etc. are mentioned, It can use in this invention, However It is not limited to these.

In this invention, it is preferable that the coating amount of the intermediate | middle layer containing a hollow resin shall be 2-30 g / m < ² >. As a result, the support is sufficiently covered after the heat molding treatment, and the smoothness of the intermediate layer is easily obtained. The content of the hollow resin 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 molding treatment method after forming the coating solution containing the thermally expandable resin particles before thermal expansion on the support is arbitrarily selected. For example, a scuff dryer, IR dryer, cylinder dryer, etc. After the heat treatment by, pressure molding is performed with a super calendar, a heat calendar, or the like, or heating and molding processes are simultaneously performed with a Yankee dryer, a heat calendar, a heat press, or the like. In order to sufficiently expand the particles, it is preferable to perform heat treatment at a temperature about 10 to 100 ° C. higher than the expansion start temperature for 1 second or longer. In addition, when the pressure molding process is performed after the heat treatment, it is easy to form the ridge shape by performing the pressure molding process while maintaining the paper surface temperature above the glass transition temperature of the hollow resin shell. It is preferable that the shape of the heel is maintained even after release. In the case where the heating and molding processes are performed simultaneously, it is preferable that the number of nips is 2 nips or more for a thermal calendar, for example, in order to sufficiently expand and mold the particles.

  The intermediate layer of the present invention can contain various inorganic pigments, organic pigments, and organic-inorganic composite pigments as necessary, as long as the effects of the invention are not impaired. The pigments include 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, zinc sulfate, non- Examples thereof include pigments used for crystalline silica, calcium silicate, colloidal silica, melamine resin, urea-formaldehyde resin, polyethylene, polystyrene, and usually coated paper, and these can be used alone or in combination of two or more. Organic spherical particles, organic hollow particles, and the like can also be used. The content of these inorganic and organic pigments is preferably in the range of 0 to 30% by mass with respect to the heat-expandable resin particles without impairing the effects of the present invention.

  In the intermediate layer, various water-soluble polymer compounds or water-dispersible resins used in normal coating can be used as a binder. Specific examples thereof include starches, hydroxymethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, gelatin, casein, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, diacetone. Modified polyvinyl alcohol, silanol group modified polyvinyl alcohol, sulfonic acid group modified polyvinyl alcohol, phosphate group modified polyvinyl alcohol, butyral group modified polyvinyl alcohol, sodium alginate, polyvinyl pyrrolidone, polyacrylamide, acrylamide / acrylic acid ester copolymer, acrylamide / Acrylic ester / methacrylic acid terpolymer, polyacrylic acid alkali Water soluble resin such as alkali salt of polymaleic acid, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, alkali salt of isobutylene / maleic anhydride copolymer, and styrene / Butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / acetic acid Although water-dispersible resin, such as a vinyl copolymer, a polyacrylic ester, a styrene / acrylic ester copolymer, a polyurethane, is mentioned, it is not limited to these. A binder can be used individually or in mixture of 2 or more types. The amount of the binder used is preferably 5 to 300% by mass, more preferably 10 to 200% by mass with respect to the thermally expandable resin particles.

  In addition, in the coating liquid of the intermediate layer, other additives such as pigment dispersants, fluorescent dyes, coloring dyes, ultraviolet absorbers, conductive substances, lubricants, water resistance, as long as the effects of the present invention are not impaired. An agent, an antifoaming agent, an anti-corrosion agent and the like can be contained.

  In the present invention, a resin and a pigment are mainly used on the heat-sensitive recording layer for the purpose of improving the sticking resistance, preventing scratches, improving the water resistance, and improving the plasticizer resistance and chemical barrier resistance of the thermosensitive color image. A protective layer as a component is coated, and the protective layer includes a water-dispersible resin having a core-shell structure composed of a core containing acrylonitrile as an essential component and a shell containing methacrylamide as an essential component, and diacetone group-modified polyvinyl. It contains at least one water-soluble resin selected from alcohol, acetoacetyl group-modified polyvinyl alcohol, and carboxyl group-modified polyvinyl alcohol.

  In the present invention, a water-dispersible resin having a core-shell structure comprising a core containing acrylonitrile as an essential component and a shell containing methacrylamide as an essential component (hereinafter referred to as a core-shell type acrylic emulsion) is generally seeded with an acrylonitrile emulsion. It is prepared by a seed emulsion polymerization method in which methacrylamide is added as an essential component as a monomer that forms a polymer having different properties, and polymerization is performed. Examples of monomers that can be used in combination with methacrylamide to form a shell include acrylonitrile, styrene, ethyl acrylic acid, butyl acrylic acid, diethylene glycol acrylic acid, acrylic acid esters such as 2-ethylhexyl acrylic acid, allyl methacrylic acid, Examples include methacrylic acid esters such as methyl methacrylic acid, ethyl methacrylic acid, and butyl methacrylic acid, and methacrylic acid. In addition, such a core-shell type acrylic emulsion may be a commercially available product. For example, a commercially available product with a product name such as BM-1000 or OM-1050 may be obtained from Mitsui Chemicals. Is also possible.

  The core-shell type acrylic emulsion has a plurality of excellent functions such as a film strength due to excellent film properties at the core portion and a sticking resistance due to excellent heat resistance at the shell portion. However, when the intermediate layer contains a hollow resin and the protective layer contains only the core-shell type acrylic emulsion as a resin component, sticking resistance is obtained, but due to the difference in hardness between the flexible intermediate layer film and the hard protective layer film, The protective layer film is distorted and easily cracked. As a result, the chemical barrier property, which is one of the performances of the original core-shell type acrylic emulsion, tends to be reduced.

  Therefore, in the present invention, at least one water-soluble resin selected from diacetone group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and carboxyl group-modified polyvinyl alcohol is used in combination with the water-dispersible resin of the core-shell type acrylic emulsion. By using a hybrid resin system of this water-dispersed resin / water-soluble resin, it is possible to prevent the occurrence of cracks in the protective layer film and to achieve excellent sticking resistance, which could not be achieved by each use alone. .

  That is, the modified polyvinyl alcohol is excellent in reactivity with various curing agents and crosslinking agents, and is excellent in water resistance and heat resistance after the reaction. However, even if the modified polyvinyl alcohol is used alone as the resin component of the protective layer, the following two points are insufficient. First, when it has an intermediate layer containing a hollow resin, it has insufficient heat resistance against severe sticking caused by high adhesion between the thermal recording surface and the thermal head, and the second point is a protective layer Since the leveling property of the coating liquid for coating is poor, density unevenness occurs in color development. On the other hand, the present invention can satisfy these performances by using the modified polyvinyl alcohol together with the core-shell type acrylic emulsion.

  The diacetone group-modified polyvinyl alcohol used in the present invention is a partially or completely saponified product of a copolymer of a monomer having a diacetone group and vinyl acetate, for example, a monomer having a diacetone group and vinyl acetate. It can be obtained by saponifying the copolymer.

  The acetoacetyl-modified polyvinyl alcohol used in the present invention is a partially or completely saponified product in which an acetoacetyl group is introduced into the side chain of polyvinyl alcohol. For example, a liquid, gaseous state, or the like in a polyvinyl alcohol solution, dispersion or powder. It can be obtained by addition reaction of diketene.

  The carboxyl group-modified polyvinyl alcohol used in the present invention is a partially or completely saponified product of a copolymer of a monomer having a carboxyl group and vinyl acetate. For example, coexistence of chain transfer agents such as aldehydes and ketones It is obtained by adding sodium acetate to a carbonyl group-containing polyvinyl alcohol obtained by polymerizing and saponifying vinyl acetate under the atmosphere of a specific oxygen concentration and heat treatment, or maleic acid, fumaric acid It is obtained by saponifying a copolymer of ethylenically unsaturated dicarboxylic acid such as itaconic acid, crotonic acid, acrylic acid, methacrylic acid and vinyl acetate. In addition, fumaric acid, phthalic anhydride, anhydrous Reaction product of polyvalent carboxylic acid such as melittic acid and itaconic anhydride and polyvinyl alcohol, or esterification of these reaction products It is obtained as.

  Other modified groups can be appropriately introduced into the modified polyvinyl alcohol as long as the present invention is not impaired. For example, a monomer containing another modified group to be introduced is copolymerized with vinyl acetate. It is obtained by. Examples of monomers copolymerizable with vinyl acetate include α-olefins such as ethylene and propylene, olefin sulfonic acids such as (meth) allyl sulfonic acid, ethylene sulfonic acid and sulfonic acid malate, and (meth) allyl sulfonic acid soda. Olefin sulfonic acid alkali salts such as ethylene sulfonic acid soda, sulfonic acid soda (meth) acrylate, sulfonic acid soda (monoalkyl malate), disulfonic acid soda alkyl malate, N-methylol acrylamide, acrylamide alkyl sulfonic acid alkali salt, etc. Amide group-containing monomers, and N-vinylpyrrolidone derivatives.

  The polymerization degree, saponification degree, and modification rate of the modified polyvinyl alcohol are not particularly limited. However, the degree of polymerization is preferably 300 to 4000, from the viewpoint of solubility, coating property, water resistance of the film, layer strength, and the like. Has a saponification degree of 80% or more, more preferably 90% or more, and a modification rate of about 0.1 to 20 mol%, more preferably 0.5 to 10 mol%.

  In this invention, 5-90 mass% is preferable with respect to the total solid of a protective layer, and, as for the total content in the protective layer of an above-described core-shell type acrylic emulsion and modified polyvinyl alcohol, 15-75 mass% is more preferable. . Moreover, the content ratio of both is as a mass ratio, the range of core shell type acrylic emulsion: modified polyvinyl alcohol = 1: 9-7: 3 is preferable, and the range of 1: 5-2: 1 is more preferable.

  In the present invention, in order to promote the water resistance of the core-shell type acrylic emulsion and the modified polyvinyl alcohol, one or more of various curing agents and crosslinking agents can be used in appropriate combination. The layer containing a curing agent or a crosslinking agent may be either a protective layer or a thermosensitive recording layer in contact with the protective layer. Specific examples thereof include those listed below, but the present invention is not limited thereto.

  Adipic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, dodecanedioic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, sebacic acid dihydrazide dihydrazide dihydride dihydrazide dihydride dihydrazide Polycarboxylic acid hydrazide compounds such as acrylic hydrazide, compounds containing epichlorohydrin residues such as polyamide polyamine epichlorohydrin resin, polyamine epichlorohydrin resin, formaldehyde, acetaldehyde, 2,2-dimethoxyacetaldehyde, 2 , 2-diethoxyacetaldehyde, 2-methoxy-2-ethoxyacetaldehyde, 2,2-dipropoxyacetaldehyde, 2,2-dibut Monoaldehyde compounds such as siacetaldehyde, 2,2-dipentoxyacetaldehyde, 2,2-dihexoxyacetaldehyde, benzyloxyacetaldehyde, polyvalent aldehyde compounds such as glyoxal, glutaraldehyde, dialdehyde, urea-based resin, polyamide-based Resins, polyamine resins, polyamide urea resins, melamine resins, methylol compounds such as phenol resins, epoxy compounds such as polyfunctional epoxy resins, isocyanate compounds, blocked isocyanate compounds, persulfates such as ammonium persulfate and sodium persulfate, chloride Oxidizing agents such as ferric iron, ammonium chloride and peroxides, oxazoline compounds, aziridine compounds, polyvalent metal salts such as Al, Ti, Zr, Mg, etc., calcium glyoxylate, sodium glyoxylate Glyoxylate and the like, boric acid, borax and the like.

  The total amount of the curing agent and the crosslinking agent used in the present invention is appropriately determined depending on the type and the combination thereof with respect to the total amount of the core-shell type acrylic emulsion and the modified polyvinyl alcohol, but is preferably 0 with respect to the total amount. It is used by containing 5 to 40% by mass, more preferably 3 to 30% by mass.

  In the present invention, the protective layer can be used in combination with a binder other than the above-described core-shell acrylic emulsion and modified polyvinyl alcohol for the purpose of adjusting the viscosity as a protective layer coating solution. Specific examples thereof include the binders described as specific examples of the binder used for the intermediate layer. Such binders can be used alone or in admixture of two or more. In that case, 20% by mass or less, more preferably 10% by mass or less, based on the total amount of the above-described core-shell type acrylic emulsion and modified polyvinyl alcohol. It is preferable to do.

  In the present invention, the protective layer contains a pigment in order to improve writing property and printer running property. Specific examples include 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, zinc sulfate, non- Examples include inorganic pigments such as crystalline silica, amorphous calcium silicate, colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, silicone powder, and nylon powder. is not. In addition, a pigment can be used individually or in mixture of 2 or more types.

  Other additives used in the protective layer include higher fatty acid metal salts such as zinc stearate and calcium stearate for the purpose of preventing head wear and sticking, paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearamide, and custard wax. In addition, a dispersant such as sodium dioctyl sulfosuccinate, a wetting agent, an antifoaming agent, a fluorescent dye, an ultraviolet absorber, and the like can also be contained.

In the present invention, the protective layer can be a single layer or a laminate of two or more layers. The coating amount of the protective layer is preferably in a range of 1 to 5 g / ^{m 2.} If the amount is less than 1 g / m ² , various performances of the protective layer may not be exhibited. If the amount is more than 5 g / m ² , the loss of thermal energy reaching the thermal recording layer from the thermal head increases, and the thermal coloring characteristics are deteriorated. You may be invited.

  The heat-sensitive recording layer that develops color by heat in the present invention can be obtained by coating on an 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.

  As the electron-donating dye precursor in the present invention, compounds generally used for pressure-sensitive recording materials and heat-sensitive recording materials can be used, and one or more dye precursors are used in appropriate combination. Specific examples include the following, but the present invention is not limited thereto.

  Examples of black dye precursors include 3-di-n-butylamino-6-methyl-7-anilinofluorane, 3-di-n-pentylamino-6-methyl-7-anilinofluorane, 3 -Diethylamino-6-methyl-7-anilinofluorane, 3-di-n-butylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6 -Methyl-7-xylidinofluorane, 3-diethylamino-7- (2-carbomethoxyphenylamino) fluorane, 3- (N-cyclohexyl-N-methyl) amino-6-methyl-7-anilinofluorane, 3- (N-cyclopentyl-N-ethyl) amino-6-methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethyl) amino- -Methyl-7-anilinofluorane, 3- (N-ethyl-4-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-4-toluidino) -6-methyl-7 -(4-Toluidino) fluorane, 3- (N-methyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3 -Pyrrolidino-6-methyl-7- (4-n-butylphenylamino) fluorane, 3-piperidino-6-methyl-7-anilinofluorane,

  Examples of red dye precursors include 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide and 3,3-bis (1-n-butyl-2-methylindole-3). -Yl) tetrachlorophthalide, 3,3-bis (1-n-butylindol-3-yl) phthalide, 3,3-bis (1-n-pentyl-2-methylindol-3-yl) phthalide, 3,3-bis (1-n-hexyl-2-methylindol-3-yl) phthalide, 3,3-bis (1-n-octyl-2-methylindol-3-yl) phthalide, 3,3- Bis (1-methyl-2-methylindol-3-yl) phthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,3-bis (1-propyl-2-) Methylindol-3-yl) phthali 3,3-bis (2-methylindol-3-yl) phthalide, rhodamine B-anilinolactam, rhodamine B- (o-chloroanilino) lactam, rhodamine B- (p-nitroanilino) lactam, 3-diethylamino-5 -Methyl-7-dibenzylaminofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-6-methylfluorane, 3-diethylamino-6 -Methyl-7-chloro-8-benzylfluorane, 3-diethylamino-6,7-dimethylfluorane, 3-diethylamino-6,8-dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino -7-methoxyfluorane, 3-diethylamino-7- (N Acetyl-N-methyl) aminofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-n-propoxyfluorane, 3-diethylamino-7-p-methylphenylfluorane, 3-diethylamino-7 , 8-benzofluorane, 3-diethylaminobenzo [a] fluorane, 3-diethylaminobenzo [c] fluorane, 3-dimethylamino-7-methoxyfluorane, 3-dimethylamino-6-methyl-7-chlorofluorane 3-dimethylamino-7-methylfluorane, 3-dimethylamino-7-chlorofluorane, 3- (N-ethyl-p-toluidino) -7-methylfluorane, 3- (N-ethyl-N- Isoamyl) amino-6-methyl-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) Amino-7,8-benzofluorane, 3- (N-ethyl-N-isoamyl) amino-7-methylfluorane, 3- (N-ethyl-Nn-octyl) amino-6-methyl-7- Chlorofluorane, 3- (N-ethyl-Nn-octyl) amino-7,8-benzofluorane, 3- (N-ethyl-Nn-octyl) amino-7-methylfluorane, 3- (N-ethyl-Nn-octyl) amino-7-chlorofluorane, 3- (N-ethyl-N-4-methylphenyl) amino-7,8-benzofluorane, 3- (N-ethoxyethyl) -N-ethyl) amino-7,8-benzofluorane, 3- (N-ethoxyethyl-N-ethyl) amino-7-chlorofluorane, 3-n-dibutylamino-6-methyl-7-chlorofluor Oran, 3-n-Djibouti Amino-7,8-benzofluorane, 3-n-dibutylamino-7-chlorofluorane, 3-n-dibutylamino-7-methylfluorane, 3-diallylamino-7,8-benzofluorane, 3 -Diallylamino-7-chlorofluorane, 3-di-n-butylamino-6-methyl-7-bromofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-pyrrolidylamino-7-methylfluor Oran, 3-ethylamino-7-methylfluorane, 3- (N-ethyl-N-isoamyl) amino-benzo [a] fluorane, 3-n-dibutylamino-6-methyl-7-bromofluorane, 3 , 6-bis (diethylaminofluorane) -γ- (4′-nitro) anilinolactam,

  Examples of green dye precursors include 3- (N-ethyl-Nn-hexyl) amino-7-anilinofluorane, 3- (N-ethyl-Np-tolyl) amino-7- (N -Phenyl-N-methyl) aminofluorane, 3- (N-ethyl-Nn-propyl) amino-7-dibenzylaminofluorane, 3- (N-ethyl-Nn-propyl) amino-6 -Chloro-7-dibenzylaminofluorane, 3- (N-ethyl-N-4-methylphenyl) amino-7- (N-methyl-N-phenyl) aminofluorane, 3- (N-ethyl-4) -Methylphenyl) amino-7-dibenzylaminofluorane, 3- (N-ethyl-4-methylphenyl) amino-6-methyl-7-dibenzylaminofluorane, 3- (N-ethyl-4-methyl) Phenyl) amino-6 Methyl-7- (N-methyl-N-benzyl) aminofluorane, 3- (N-methyl-Nn-hexyl) amino-7-anilinofluorane, 3- (N-propyl-Nn- Hexyl) amino-7-anilinofluorane, 3- (N-ethoxy-Nn-hexyl) amino-7-anilinofluorane, 3- (Nn-pentyl-N-allyl) amino-6 Methyl-7-anilinofluorane, 3- (Nn-pentyl-N-allyl) amino-7-anilinofluorane, 3-di-n-butylamino-6-chloro-7- (2-chloroanilino ) Fluorane, 3-di-n-butylamino-6-methyl-7- (2-chloroanilino) fluorane, 3-di-n-butylamino-6-methyl-7- (2-fluoroanilino) fluorane, 3 -N-Dibutylamino -7- (2-chloroanilino) fluorane, 3-di-n-butylamino-7- (2-chlorobenzylanilino) fluorane, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl -7-dibenzylaminofluorane, 3-diethylamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7- (N-cyclohexyl-N-benzyl) aminofluorane, 3 -Diethylamino-6-methyl-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl- 7- (2-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (3-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (2-ethoxyanilino) ) Fluorane, 3-diethylamino-6-methyl-7- (4-ethoxyanilino) fluorane, 3-diethylamino-6-chloro-7- (2-chloroanilino) fluorane, 3-diethylamino-6-chloro-7-di Benzylaminofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-ethylethoxy-7-anilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino -7-methylanilinofluorane, 3-diethylamino-7-dibenzylamino Oran, 3-diethylamino-7-n-octylaminofluorane, 3-diethylamino-7-p-chloroanilinofluorane, 3-diethylamino-7-p-methylphenylanilinofluorane, 3-diethylamino-7- (N-cyclohexyl-N-benzyl) aminofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-7- (3-trifluoromethylanilino) fluorane, 3-diethylamino-7- ( 2-trifluoromethylanilino) fluorane, 3-diethylamino-7- (2-ethoxyanilino) fluorane, 3-diethylamino-7- (4-ethoxyanilino) fluorane, 3-diethylamino-7- (2-chloro) Benzylanilino) fluorane, 3-dimethylamino-6- Loro-7-dibenzylaminofluorane, 3-dimethylamino-6-methyl-7-n-octylaminofluorane, 3-dimethylamino-7-dibenzylaminofluorane, 3-dimethylamino-7-n- Octylaminofluorane, 3-di-n-butylamino-7- (2-fluoroanilino) fluorane, 3-anilino-7-dibenzylaminofluorane, 3-anilino-6-methyl-7-dibenzylamino Fluorane, 3-pyrrolidino-7-dibenzylaminofluorane, 3-pyrrolidino-7- (4-cyclohexylanilino) fluorane, 3-dibenzylamino-6-methyl-7-dibenzylaminofluorane, 3, 7-bis (dibenzylamino) fluorane, 3-dibenzylamino-7- (2-chloroanilino) fluorane,

  Examples of blue dye precursors include 3- (1-ethyl-2-methylindol-3-yl) -3- (4-diethylaminophenyl) phthalide and 3- (1-ethyl-2-methylindole-3- Yl) -3- (2-methyl-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-aminophenyl)- 4-Azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-methylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindole) -3-yl) -3- (2-ethoxy-4-ethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-) The Tilaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl- 2-Methylindol-3-yl) -3- (2-ethoxy-4-di-n-propylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3 -(2-Ethoxy-4-di-n-butylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-di-n -Pentylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-di-n-hexylaminophenyl) -4-azaphthal 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-dihydroxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindole-3) -Yl) -3- (2-ethoxy-4-dichloroaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-dibromoamino) Phenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diallylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2) -Methylindol-3-yl) -3- (2-ethoxy-4-dimethoxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-Ethoxy-4-diethoxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-dicyclohexylaminophenyl) -4- Azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-di-n-propoxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2- Methylindol-3-yl) -3- (2-ethoxy-4-di-n-butoxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- ( 2-Ethoxy-4-di-n-hexyloxyaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-di-) Tilcyclohexylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-di-methoxycyclohexylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-pyrrolidylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (3-Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2,3-diethoxy-4-diethylaminophenyl)- 4-Azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (4-diethylaminophenyl) -4-azaphthalide 3- (1-Ethyl-2-methylindol-3-yl) -3- (2-chloro-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (3-Chloro-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-bromo-4-diethylaminophenyl) -4- Azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (3-bromo-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindole-3- Yl) -3- (2-ethyl-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-n-propyl-) 4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (3-methyl-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl) -2-methylindol-3-yl) -3- (2-nitro-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2- Allyl-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-hydroxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1 -Ethyl-2-methylindol-3-yl) -3- (2-cyano-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methyl) Ruindol-3-yl) -3- (2-cyclohexylethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-methylethoxy -4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-cyclohexylethyl-4-diethylaminophenyl) -4-azaphthalide, 3- (2 -Ethylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-chloroindol-3-yl) -3- (2-ethoxy- 4-Diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-bromoindol-3-yl) -3- (2-ethoxy 4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-ethylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl) -2-propylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methoxyindol-3-yl) -3- (2- Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-ethoxyindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1 -Ethyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1- Ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2 -Ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-ethyl-4,5,6,7-tetrachloro-2-methylindol-3-yl) -3- (2-ethoxy- 4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-4-nitro-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-Ethyl-4-methoxy-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethi -4-methylamino-2-methylindole-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-4-methyl-2-methylindole-3) -Yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide 3- (1-chloro-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-bromo-2-methylindol-3-yl) ) -3- (2-Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-methyl-2-methylindol-3-yl) -3- (2- Toxi-4-diethylaminophenyl) -4-azaphthalide, 3- (1-methyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1 -N-propyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-n-butyl-2-methylindol-3-yl) -3- (2-Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-n-butyl-2-indol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7 -Azaphthalide, 3- (1-n-pentyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthali 3- (1-n-hexyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-n-hexyl-2-methyl) Indol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1-n-octyl-2-methylindol-3-yl) -3- (2-ethoxy- 4-diethylaminophenyl) -4-azaphthalide, 3- (1-n-octyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1 -N-octyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-n-nonyl-2- Tilindole-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-methoxy-2-methylindol-3-yl) -3- (2-ethoxy-4) -Diethylaminophenyl) -4-azaphthalide, 3- (1-ethoxy-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-phenyl- 2-Methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-n-pentyl-2-methylindol-3-yl) -3- (2 -Ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1-n-heptyl-2-methylindol-3-yl) -3- (2-ethoxy 4-diethylaminophenyl) -7-azaphthalide, 3- (1-n-nonyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3,3- Bis (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-dimethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3- ( And 1-ethyl-2-methylindol-3-yl) -3- (4-diethylamino-2-n-hexyloxyphenyl) -4-azaphthalide. These can be used alone or in admixture of two or more.

  Some functional dye precursors have absorption in the near infrared region. When this dye precursor is used alone or in combination with other dye precursors for high-temperature color development, the high-temperature color image is absorbed in the near-infrared region and can be automatically read with near-infrared light. Possible images can be obtained. When this dye precursor is used in the present invention, an image having absorption only in the visible region, an image having absorption in the near-infrared region, and the like can be used in combination, and a recording material with high security can be obtained.

  As such a dye having absorption in the near infrared region, 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-tetra Chlorophthalide, 3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3- [1,1-bis (P-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide, 3- [ p- (p-dimethylaminoanilino) Nilino] -6-methylfluorane, 3- [p- (p-dimethylaminoanilino) anilino] -6-methyl-7-chlorofluorane, 3- (pn-butylaminoanilino) -6 Methyl-7-chlorofluorane, 3- [p- (p-anilinoanilino) anilino] -6-methyl-7-chlorofluorane, 3- [p- (p-chloroanilino) anilino] -6-methyl-7- Chlorofluorane, 3- (Np-tolyl-N-ethylamino) -6,8,8-trimethyl-9-ethyl-8,9-dihydro- (3,2, e) pyridfluorane, 3-di ( n-butyl) amino-6,8,8-trimethyl-8,9-dihydro- (3,2, e) pyridfluorane, 3'-phenyl-7-N-diethylamino-2,2'-spirodi (2H-1 -Benzopyran), Scan (p- dimethylaminostyryl)-p-tri sulfonyl methane, 3,7-bis (dimethylamino) -10-benzoyl-phenothiazine, and the like. These electron donating dye precursors may be used alone or in combination of two or more as required.

  As the electron-accepting developer in the present invention, compounds generally used for heat-sensitive recording materials can be used. Specific examples include the following, but the present invention is not limited thereto.

  Clay materials such as acid clay, activated clay, zeolite, bentonite, kaolin, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-propoxydiphenylsulfone, 4-hydroxy-4 '-Isopropoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, 4-hydroxy-4'-octyloxydiphenylsulfone, 4-hydroxy-4'-dodecyloxydiphenylsulfone, 4-hydroxy-4'- Benzyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenylsulfone, 2,4-bis Phenylsulfonyl) phenol, p-phenylphenol, p-hydroxyacetophenone, 1,1-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxy) Phenyl) hexane, 1,1-bis (p-hydroxyphenyl) cyclohexane, 2,2-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p -Hydroxyphenyl) -2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, 2,2-bis (3-methyl-4-hydroxyphenyl) propane, 1,1-bis ( p-hydroxyphenyl) -1-phenylethane, 1,3-bis [2- (p-hydroxyphenyl) 2-propyl] benzene, 1,3-bis [2- (3,4-dihydroxyphenyl) -2-propyl] benzene, 1,4-bis [2- (p-hydroxyphenyl) -2-propyl] benzene, 4,4'-dihydroxydiphenyl ether, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis (4-hydroxyphenyl) acetic acid Butyl, 4,4′-thiobis (2-tert-butyl-5-methylphenol), dimethyl 4-hydroxyphthalate, benzyl 4-hydroxybenzoate, methyl 4-hydroxybenzoate, benzyl gallate, stearyl gallate, N, N′-diphenylthiourea, 4,4′-bis [3- (4-methylphenylsulfonyl) ureido] Diphenylmethane, N- (4-methylphenylsulfonyl) -N′-phenylurea, salicylanilide, 5-chlorosalicylanilide, salicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5-bis (α-methylbenzyl) ) Salicylic acid, 4- [2 '-(4-methoxyphenoxy) ethyloxy] salicylic acid, 3- (octyloxycarbonylamino) salicylic acid or metal salts of these salicylic acid derivatives, N- (4-hydroxyphenyl) -p-toluenesulfonamide N- (4-hydroxyphenyl) benzenesulfonamide, N- (4-hydroxyphenyl) -1-naphthalenesulfonamide, N- (4-hydroxyphenyl) -2-naphthalenesulfonamide, N- (4-hydroxynaphthyl) ) -P-Toluenesulfonami N- (4-hydroxynaphthyl) benzenesulfonamide, N- (4-hydroxynaphthyl) -1-naphthalenesulfonamide, N- (4-hydroxynaphthyl) -2-naphthalenesulfonamide, N- (3-hydroxyphenyl) ) -P-toluenesulfonamide, N- (3-hydroxyphenyl) benzenesulfonamide, N- (3-hydroxyphenyl) -1-naphthalenesulfonamide, N- (3-hydroxyphenyl) -2-naphthalenesulfonamide, N- (4-methylphenylsulfonyl) -N ′-[3- (4-methylphenylsulfonyloxy) phenyl] urea, bis (4-tosylaminocarboxyaminophenyl) methane, n-butyl-4- (3-p -Toluenesulfonyl) ureidobenzoate, n-butyl-3- ( 3-p-toluenesulfonyl) ureidobenzoate, 2,6-bis [(2-hydroxy-4-tert-butylphenyl) methyl] -4-tert-butylphenol, 2,6-bis [(2-hydroxy-5 Methylphenyl) methyl] -4-methylphenol, 2,6-bis [(2-hydroxy-5-methylphenyl) methyl] -4-tert-butylphenol, and the like. These electron-accepting developers can be used alone or in combination of two or more as required.

  The content ratio of the dye precursor and the electron accepting developer is appropriately determined depending on the type and the combination thereof. The total amount of the electron accepting compound is 100 to 500 with respect to the total amount of the dye precursor. It is used by containing 10% by mass, preferably 140 to 350% by mass.

  The aromatic isocyanate compound is a colorless or light-colored aromatic isocyanate compound or a 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-4,4 -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'-diisocyanate Narate, 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'-trii Examples include cyanate, 4,4 ′, 4 ″ -triisocyanate-2,5-dimethoxytriphenylamine, p-dimethylaminophenyl isocyanate, tris (4-phenylisocyanato) thiophosphate, etc. 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, and is a diisocyanate dimer, 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-diimino Isoindoline, 4,5,6,7-tetrafluoro-1,3-diiminoisoindoline, 4,5,7-trichloro-1,3-diimino-6-methylmercaptoisoindoline, 1-iminodiphenimide 1- (cyano-p-nitrophenylmethylene) -3-iminoisoindoline, 1- (cyanobenzothiazolyl- (2 ′)-carbamoylmethylene)- -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-1 Examples include substances such as -one, 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.

  In addition to the main components described above, known binders, hot melt compounds, preservability improvers, surfactants, and the like may be added to the heat-sensitive recording layer according to the present invention. Those having less influence on the background whiteness are particularly preferred.

  As the binder of the heat-sensitive recording layer, a water-soluble polymer compound or a water-dispersible resin used in usual coating can be used. Specific examples thereof include the adhesives described as specific examples of the binder used in the intermediate layer, and can be used alone or in combination of two or more.

  The hot-melt compound is used as a sensitizer for obtaining sufficient color development sensitivity, for example, stearic acid amide, N-hydroxymethyl stearic acid amide, N-stearyl stearic acid amide, ethylenebisstearic acid amide, p-toluene. Sulfonamide, N-stearyl urea, diphenyl sulfone, benzyl-2-naphthyl ether, m-terphenyl, 4-benzylbiphenyl, 1,2-bis (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 2 , 2'-bis (4-methoxyphenoxy) diethyl ether, α, α'-diphenoxyxylene, bis (4-methoxyphenyl) ether, diphenyl adipate, dibenzyl oxalate, bis (4-chlorobenzyl) oxalate , Dimethyl terephthalate, diben terephthalate And known heat-melting compounds such as benzyl paraben, benzene sulfonic acid phenyl ester, 4,4'-diallyloxydiphenyl sulfone, 4-acetylacetophenone, acetoacetic anilides, fatty acid anilides and salicylanilide. These compounds can be used alone or in combination of two or more.

  The storability improver is used to enhance the storability of the color image portion. For example, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylenebis (4-methyl) is used. -6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis (4,6-di-tert-butylphenol), 2,2'-ethylidene Bis (4,6-di-tert-butylphenol), 2,2'-ethylidenebis (4-ethyl-6-tert-butylphenol), 2,2 '-(2,2-propylidene) bis (4,6- Di-tert-butylphenol), 2,2'-methylenebis (4-methoxy-6-tert-butylphenol), 2,2'-methylenebis (6-t rt-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4,4'-thiobis (5- Methyl-6-tert-butylphenol), 4,4'-thiobis (2-chloro-6-tert-butylphenol), 4,4'-thiobis (2-methoxy-6-tert-butylphenol), 4,4'- Thiobis (2-ethyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-m-cresol), 1- [α-methyl-α- (4'-hydroxyphenyl) ethyl]- 4- [α ', α'-bis (4 "-hydroxyphenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5 -Cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4'-thiobis (3-methylphenol), 4,4'-dihydroxy -3,3 ', 5,5'-tetrabromodiphenylsulfone, 4,4'-dihydroxy-3,3', 5,5'-tetramethyldiphenylsulfone, 2,2-bis (4-hydroxy-3, Hindered phenol compounds such as 5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, N, N'-bis (2-naphthyl) -1,4-phenylenediamine, 2,2'-methylenebis (4,6-di-tert-butylphenyl) Acid soda, 4-{{4- {4- {4-[[4- (1-methylethoxy) phenyl] sulfonyl] phenoxy} butoxy} phenyl} sulfonyl} phenol, diphenylsulfone cross-linked compound, phenol novolac epoxy Resins and the like can be added.

  In the present invention, various pigments can be used as long as the desired effects on the above-described problems are not impaired. For example, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, amorphous calcium silicate, colloidal silica, colloidal Well-known pigments such as white inorganic pigments such as alumina, calcium sulfate, barium sulfate, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, alumina, lithopone, zeolite, and hydrohalloysite can be used.

  In order to give water resistance to higher fatty acid metal salts such as zinc stearate and calcium stearate used for improving sticking resistance, and waxes such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide and caster wax. In addition, various hardeners and cross-linking agents may be incorporated with a dispersant such as sodium dioctylsulfosuccinate, a surfactant, a fluorescent dye, a coloring dye, a bluing agent, and the like.

  In addition, in order to improve light resistance, an antioxidant and an ultraviolet absorber can be contained. Examples of antioxidants include, but are not limited to, hindered amine antioxidants, hindered phenol antioxidants, and sulfide antioxidants. Examples of UV absorbers include organic compounds such as benzotriazole UV absorbers, salicylic acid UV absorbers, benzophenone UV absorbers, and inorganic substances such as zinc oxide, titanium oxide, and cerium oxide. There is no limitation.

The coating amount of the thermosensitive recording layer is usually in the range of 0.15 to 1.5 g / m ^{2 in} terms of the coating amount of the dye precursor, in order to obtain sufficient thermal response. The print density at the time of thermal color development may be low, and if it exceeds 15.0 g / m ² , the improvement of various performances of the thermal recording layer will reach saturation, and the production efficiency at the time of coating the thermal recording layer will be reduced. There is.

  The support of the heat-sensitive recording material 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 plate, etc., or a composite sheet combining these can be arbitrarily used depending on the purpose.

  In the present invention, a back coat layer may be provided on the surface opposite to the surface on which the heat-sensitive recording layer is provided for the purpose of preventing curling, preventing charging, etc., and may further be subjected to adhesive processing or the like. Further, a layer containing a material capable of recording information electrically, magnetically, or optically, an ink jet recording layer, or the like may be provided on the surface on which the thermosensitive recording layer is provided or on the opposite surface. In addition, in order to perform printing with laser light, a photothermal conversion material can be contained in an arbitrary layer and support in the heat-sensitive recording material.

  The formation method of each layer in the present invention is not particularly limited, and can be formed by using a well-known technique, for example, an air knife coater, various blade coaters, various bar coaters, various curtain coaters, and various multi-layers simultaneously. Various printing methods such as a coating apparatus such as a coating coater, a planographic plate, a relief plate, an intaglio plate, a flexo, a gravure, and a screen can be used. Furthermore, in order to improve the surface smoothness, various known techniques in the production of heat-sensitive recording materials can be used, such as the use of machines such as a machine calendar, super calendar, gloss calendar, and brushing.

  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 intermediate layer coated support: Expandable resin particle EXPANSELL 053-40DU (manufactured by AkzoNovel, average particle diameter 10-16 μm before thermal expansion, expansion start temperature 96-103 ° C., expansion coefficient about 50 fold) and 100 parts were dispersed in 200 parts of a 10% aqueous solution of polyvinyl alcohol, density 0.8 g / cm ^3, so as to be 10 g / ^{m 2} as a solid coating amount of fine paper having a basis weight of 120 g / ^{m 2} And then dried with the paper surface temperature kept at 80 ° C. or lower. Furthermore, the contact time between the coated surface side and the heat roll is about 1 second at a linear pressure of 500 N / cm, a processing temperature of 150 ° C., and a processing speed of 40 m / min using a three-stage two-nip thermal calendar with a diameter of 500 mm. The intermediate layer coating support was obtained by heat molding treatment.

(2) Preparation of thermal recording layer coating liquid <Dispersion A>
30 parts of 3-di-n-butylamino-6-methyl-7-anilinofluorane is dispersed in 70 parts of a 2.5% polyvinyl alcohol aqueous solution and pulverized with a bead mill until the average particle size becomes 0.8 μm. Dispersion A was prepared.

<Dispersion B>
Dispersion B was prepared by dispersing 30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone in 70 parts of a 2.5% aqueous polyvinyl alcohol solution and pulverizing with a bead mill until the average particle size became 0.7 μm.

<Dispersion C>
Dispersion C was prepared by dispersing 30 parts of benzyl-2-naphthyl ether in 70 parts of a 2.5% aqueous polyvinyl alcohol solution and pulverizing it with a bead mill until the average particle size became 0.8 μm.

Using the above dispersion, they were mixed according to the formulation shown below and stirred sufficiently to prepare a thermal recording layer coating solution.
Dispersion A 100 parts Dispersion B 100 parts Dispersion C 100 parts 10% polyvinyl alcohol aqueous solution 150 parts 30% light calcium carbonate aqueous dispersion 30 parts 40% zinc stearate aqueous dispersion 10 parts Water 30 parts

(3) Preparation of coating liquid for protective layer It mixed by the mixing | blending shown below, and it stirred sufficiently and produced the coating liquid for protective layers.
25 parts of 20% core-shell acrylic emulsion (Mitsui Chemicals, BM-1000)
10% diacetone group-modified polyvinyl alcohol aqueous solution 350 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 35 parts water 365 parts

(4) Preparation of thermosensitive recording material On the intermediate layer coating support obtained in (1), the coating amount of the coating liquid for (2) thermosensitive recording layer is 0.5 g / m in terms of the coating amount of the dye precursor. ⁽² ) After coating so that the coating amount of the coating liquid for the protective layer is 3.0 g / m ² , calendering is performed. To produce a heat-sensitive recording material.

Example 2
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
50 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
10% diacetone group-modified polyvinyl alcohol aqueous solution 300 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 30 parts water 395 parts

Example 3
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
100 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
10% diacetone group-modified polyvinyl alcohol aqueous solution 200 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 20 parts water 455 parts

Example 4
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
150 parts of 20% core-shell acrylic emulsion (Mitsui Chemicals, BM-1000)
10% diacetone group-modified polyvinyl alcohol aqueous solution 100 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 10 parts water 515 parts

Example 5
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
100 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
10% acetoacetyl group-modified polyvinyl alcohol aqueous solution 200 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 20 parts water 455 parts

Example 6
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
100 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
10% carboxyl group-modified polyvinyl alcohol aqueous solution 200 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 25% polyamide epichlorohydrin resin aqueous solution 16 parts water 459 parts

Comparative Example 1
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
100 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
10 parts unmodified polyvinyl alcohol aqueous solution 200 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 20 parts water 455 parts

Comparative Example 2
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
200 parts of 20% core-shell type acrylic emulsion (Mitsui Chemicals, BM-1000)
40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 20 parts water 555 parts

Comparative Example 3
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
10% diacetone group-modified polyvinyl alcohol aqueous solution 400 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 40 parts water 335 parts

Comparative Example 4
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
10% acetoacetyl group-modified polyvinyl alcohol aqueous solution 400 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% adipic acid dihydrazide aqueous solution 40 parts water 335 parts

Comparative Example 5
A thermosensitive recording material was produced in the same manner as in Example 1 except that the formulation was changed as follows in the production of the protective layer coating liquid of Example 1.
10% carboxyl group-modified polyvinyl alcohol aqueous solution 400 parts 40% aluminum hydroxide aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 25% polyamide epichlorohydrin resin aqueous solution 32 parts water 343 parts

  The produced thermal recording material was subjected to the following evaluation. The evaluation results are shown in Table 1.

Evaluation 1 [Confirmation of ridge shape]
Each of the produced heat-sensitive recording materials was subjected to cross-section processing by ion milling, and observed at a magnification of 1500 times with a Hitachi scanning electron microscope S-2300 to confirm the presence or absence of a ridge shape. 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 surface from the resin floor surface was calculated.

Evaluation 2 [PPS smoothness]
The color development surface of each produced thermal recording material was measured with a Parka Print Surf smoothness meter manufactured by TESTING MACHINES INC., USA.

Evaluation 3 [Dot reproducibility of halftone image]
Each produced thermal recording material was 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 on each condition of applied voltage of 21 volts, applied pulse width of 0.2 msec, 0.4 msec, and 0.6 msec visually evaluated. The evaluation criteria followed the following indicators.
A: There is almost no print defect.
○: There is no problem in actual use although printing is slightly missing.
Δ: Printing defect exists and the recording density varies.
X: Many printing defects exist and are unreadable.

Evaluation 4 [Thermal response]
Each produced thermal recording material was 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, a solid image was printed under the conditions of an applied voltage of 21 volts, 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.
◎: 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

Evaluation 5 [Uniformity of color density]
Each produced thermal recording material was 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, a solid image was printed so as to reach the saturation density region under the conditions of an applied voltage of 21 volts and an applied pulse width of 1.6 msec. The density unevenness of the solid image at this time was confirmed visually. The evaluation criteria followed the following indicators.
A: Light and shade unevenness is hardly recognized.
○: Slight unevenness is observed, but there is no practical problem.
Δ: Density unevenness is observed.
X: Remarkable shading unevenness occurs.

Evaluation 6 [Sticking resistance]
The produced thermal recording material was subjected to test printing at room temperature of 20 ° C. and 65% RH with a handy terminal printer (device name: PREA CT-1) manufactured by Canon Electronics Co., Ltd. The printed printing was evaluated. The evaluation criteria followed the following indicators.
(Double-circle): Sticking sound and printing missing are hardly recognized.
○: Generation of sticking sound and printing leakage are slightly observed, but there is no practical problem.
Δ: Generation of sticking noise and printing leakage are observed. ×: Both sticking noise and printing leakage occur violently.

Evaluation 7 [Chemical resistance]
The heat-sensitive recording surface of the produced heat-sensitive recording material was applied with a cotton swab dipped in a 10% ethanol aqueous solution, and the color fogging at that time was evaluated.
A: Colored fog is hardly recognized.
○: Some color fogging is observed, but there is no practical problem.
Δ: Color fogging gradually occurs after application.
X: Colored fog is intensely generated immediately after application.

  As is apparent from the results in Table 1, Examples 1 to 6 are excellent in all evaluation items of dot reproducibility, thermal response, uniformity of color density, sticking resistance, and chemical resistance of halftone images. On the other hand, Comparative Examples 1 to 5 could not satisfy all the dot reproducibility, thermal response, uniformity of color density, sticking resistance and chemical resistance of halftone images at the same time.

Claims (1)

  In a heat-sensitive recording material in which an intermediate layer, a heat-sensitive recording layer that develops color by heat, and a protective layer are sequentially laminated on a support, the intermediate layer contains a hollow resin and the protective layer contains acrylonitrile as an essential component. A water-dispersible resin having a core-shell structure composed of a shell containing acrylamide as an essential component, and at least one water-soluble resin selected from diacetone group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and carboxyl group-modified polyvinyl alcohol A heat-sensitive recording material.