Direct thermal recording material

Abstract

To provide a direct thermal recording material that enables enhancement in the yield of a platemaking material produced by image formation through thermal head heating.SOLUTION: A direct thermal recording material comprises, on a light-transmissive support, in this order from the side closer to the support: a thermosensitive recording layer containing a non-photosensitive organic silver salt and a reducing agent; and a protective layer containing at least carbonyl-modified polyvinyl alcohol and a silicate oligomer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a direct thermal recording material for forming an image by heating with a thermal head, and more particularly to a direct thermal recording material suitable for producing a block copy material. [Background technology]

[0002] As a method for recording high-quality images, a wet-processing image forming method using a silver halide photosensitive material has been generally used for a long time. However, this image forming method requires waste liquid treatment such as a developer and a fixer, and installation of a development processing facility, so a dry-processing image forming method that does not require the wet processing has been desired. As a result, image forming systems such as inkjet printers, electrophotography, and dye thermal transfer systems have been put to practical use at present. However, these dry-processing image forming methods have difficulty in obtaining the high resolution, excellent light shielding properties in image areas, and excellent light transmittance in non-image areas required for a plate material.

[0003] In this context, a direct thermal recording material utilizing the reaction between a non-photosensitive organic silver salt and an organic reducing agent is disclosed, for example, in Patent Document 1. Such a direct thermal recording material is suitable for producing a plate material because it can obtain a high-resolution, high-contrast image by directly recording a thermal image with a thermal printer equipped with a thermal head. In addition, the recording material is non-photosensitive and does not require a darkroom equipped with safelight, and direct thermal type thermal printers have the advantage of being low cost, highly reliable, and easy to miniaturize, making their introduction easy.

[0004] In a direct thermal recording material used in a direct thermal recording method, a protective layer is generally provided on the thermal recording layer to prevent adhesion between the thermal head and the thermal recording layer during printing, i.e., the occurrence of so-called sticking. It is also known that the protective layer contains a crosslinked resin, which is effective in terms of imparting transparency and printability required of a plate material.

[0005] For example, Patent Document 2 discloses a thermal recording material having a protective layer containing a film-forming silicone emulsion, and describes that the protective layer may contain a binder such as fully saponified polyvinyl alcohol or carboxy-modified polyvinyl alcohol, or a hardener such as alkoxysilane. Patent Document 3 discloses a thermal recording material having a protective layer containing long-chain alkyl ether-modified polyvinyl alcohol, and describes that the protective layer contains various crosslinking agents. Patent Document 4 discloses a thermal recording material having a protective layer containing a triazine compound, and describes that the protective layer contains a binder such as carboxy-modified polyvinyl alcohol or acetoacetyl-modified polyvinyl alcohol, or various crosslinking agents.

[0006] However, when such a direct thermal recording material is used to prepare a plate material, the image may be damaged by contact with the thermal head, resulting in a decrease in the yield of the plate material obtained, and an improvement was desired.

[0007] On the other hand, a method for suppressing scratches caused by a thermal head in a direct thermal recording material is known. For example, Patent Document 5 discloses a thermal recording material having a protective layer containing a matting agent, and describes that the matting agent can reduce the occurrence of scratches. However, further improvement is required in terms of the effect of suppressing the decrease in the yield of the plate material. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 08-505579 [Patent Document 2] JP 2000-301839 A [Patent Document 3] JP 2000-118133 A [Patent Document 4] JP 2007-038510 A [Patent Document 5] Special Publication No. 08-503175 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a direct thermal recording material capable of improving the yield of copy material obtained by forming an image by heating with a thermal head. [Means for solving the problem]

[0010] The above problems are solved by the following invention. (1) A direct thermal recording material characterized by having, on a light-transmitting support, at least a thermal recording layer containing a non-photosensitive organic silver salt and a reducing agent, and a protective layer containing at least a carbonyl-modified polyvinyl alcohol and a silicate oligomer, in this order from the side closest to the light-transmitting support. (2) The direct thermal recording material according to (1), wherein the protective layer further contains an aldehyde compound. Effect of the Invention

[0011] According to the present invention, it is possible to provide a direct thermal recording material which is capable of improving the yield of copy material obtained by forming an image by heating with a thermal head. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the details of the embodiment of the present invention will be described.

[0013] The direct thermal recording material of the present invention has a light-transmitting support. Examples of such light-transmitting supports include resin films such as polyethylene terephthalate, polyethylene naphthalate, cellulose nitrate, and polycarbonate, and inorganic materials such as glass. In the present invention, the light-transmitting support means a support having a total light transmittance of 60% or more, and more preferably, the total light transmittance of the support is 70% or more. In addition, the haze value of the light-transmitting support is preferably 10% or less. The light-transmitting support may have known layers such as an easy-adhesion layer, a hard coat layer, and an antistatic layer. The thickness of the light-transmitting support in the present invention is not particularly specified, but from the viewpoint of handling, it is preferably 50 μm or more and 300 μm or less.

[0014] The heat-sensitive recording layer of the direct heat-sensitive recording material of the present invention contains a non-photosensitive organic silver salt. The organic silver salt is reduced by heating together with a reducing agent described below to form a silver image. Specifically, the silver salt may be an organic acid silver salt such as gallic acid, oxalic acid, behenic acid, stearic acid, palmitic acid, or lauric acid as described in Research Disclosure No. 17029(II) or No. 29963(XVI) relating to heat-developable photosensitive materials; a silver salt of a carboxyalkylthiourea such as 1-(3-carboxypropyl)thiourea or 1-(3-carboxypropyl)-3,3-dimethylthiourea; a silver salt of an aldehyde such as formaldehyde, acetaldehyde, or butylaldehyde, or an aromatic amine such as salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, or 5,5-thiodisalicylic acid; Examples of the silver salt include a complex of a polymer reaction product with a carboxylic acid and silver; a silver salt or complex of thiones such as 3-(2-carboxyethyl)-4-hydroxymethyl-4-thiazoline-2-thione and 3-carboxymethyl-4-methyl-4-thiazoline-2-thione; a silver salt or complex of a nitrogen-containing heterocycle selected from imidazole, pyrazole, urazole, 1,2,4-triazole, 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole and benzotriazole; a silver salt of saccharin, 5-chlorosalicylaldoxime, etc.; and a silver salt of a mercaptide. Among these, a silver salt of a fatty acid having 10 or more carbon atoms is preferred, and silver stearate and silver behenate are more preferred.

[0015] In the present invention, the content of the non-photosensitive organic silver salt contained in the thermosensitive recording layer is preferably 5 to 80 mass %, more preferably 10 to 70 mass %, and even more preferably 20 to 65 mass %, based on the total solid content of the thermosensitive recording layer, from the viewpoints of the sensitivity and storage stability of the thermosensitive recording material.

[0016] The heat-sensitive recording layer of the direct heat-sensitive recording material of the present invention contains a reducing agent. Examples of such reducing agents include polyhydroxybenzene compounds such as hydroquinone, catechol, 4-methylcatechol, 4-tert-butylcatechol, chlorohydroquinone, and pyrogallol, polyhydroxybenzoic acid compounds such as gallic acid, methyl gallate, ethyl gallate, propyl gallate, stearyl gallate, 2,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and ethyl 3,4-dihydroxybenzoate, aminophenol compounds such as 2-aminophenol, 3-aminophenol, and 4-aminophenol, 1-phenyl-3-pyrazolidone and its derivatives, hydroxylamines, polyhydroxyindanes described in JP-A-6-317870, and dihydroxybenzoic acid derivatives described in JP-A-2001-328357. Among the above-mentioned reducing agents, polyhydroxybenzene compounds and polyhydroxybenzoic acid compounds are preferred.

[0017] The content of the reducing agent in the thermosensitive recording layer can vary widely depending on the type of reducing agent and the type of organic silver salt, but from the viewpoint of the sensitivity and storage stability of the thermosensitive recording material, it is preferably 0.1 to 3.0 mol per mol of organic silver salt, and more preferably 0.5 to 2.0 mol. For various purposes, two or more of the above-mentioned reducing agents may be used in combination.

[0018] The heat-sensitive recording layer of the direct heat-sensitive recording material of the present invention preferably contains a resin as a binder component that holds the non-photosensitive organic silver salt and the reducing agent. Such resins are not particularly limited, and known resins can be used, such as cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, gelatin, acrylic resins, melamine resins, polyester resins, polyurethane resins, polyvinyl acetal resins such as polyvinyl butyral resins, and polyvinyl alcohol resins. Among them, polyvinyl acetal resins such as polyvinyl butyral resins and polyvinyl alcohol resins are preferred, and polyvinyl acetal resins are more preferred, because they have excellent dispersibility of the non-photosensitive organic silver salt. These resins may be used by dissolving them in water or an organic solvent, or may be used as latex in which hydrophobic polymer solids are dispersed in the form of fine particles, or as polymer molecules dispersed in the form of micelles. In the present invention, the resins described above are preferably those that form a light-transmitting coating after drying. Furthermore, these resins may be used in combination of two or more types of resins that are compatible with each other as necessary.

[0019] In the present invention, the content of the resin contained in the thermosensitive recording layer is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, based on the total solid content of the thermosensitive recording layer, from the viewpoints of the sensitivity and storage stability of the thermosensitive recording material.

[0020] The resin preferably does not substantially contain free halide ions such as chloride ions or bromide ions. Halide ions react with the silver ions of the organic silver salt to form photosensitive silver halide, which causes a decrease in the light resistance of the direct thermal recording material of the present invention. Specifically, the halide ions are preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less relative to the content of the resin.

[0021] The thermosensitive recording layer of the direct thermosensitive recording material of the present invention preferably contains a so-called color toner, which is known in the field of thermography or photothermography. Examples of color toners are known in the above-mentioned Research Disclosure on Photothermographic Materials, items 17029(V) and 29963(XXII), and specifically include imides such as phthalimide, mercapto compounds such as 3-mercapto-1,2,4-triazole, phthalic acid derivatives such as phthalazine, phthalazone, 4-methylphthalic acid, tetrachlorophthalic acid and their anhydrides, and benzoxazine derivatives such as 1,3-benzoxazine-2,4-dione. For various purposes, the above-mentioned color toners may contain two or more kinds.

[0022] In the present invention, the content of the color toning agent contained in the thermosensitive recording layer is preferably 0.10 to 30 mass %, more preferably 0.50 to 20 mass %, and even more preferably 1.0 to 15 mass %, based on the total solid content of the thermosensitive recording layer, from the viewpoints of the sensitivity and storage stability of the thermosensitive recording material.

[0023] The heat-sensitive recording layer of the direct heat-sensitive recording material of the present invention may contain various accelerators, stabilizers and their precursors, together with the organic silver salt, for the purpose of suppressing or promoting the formation of image silver by reduction, improving the storage stability before and after printing, etc. Specifically, they may be selected from benzotriazole, 5-methylbenzotriazole, 5-chlorobenzotriazole, 2-mercaptobenzotriazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene, 1-phenyl-5-mercaptotetrazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 3-mercapto-5-phenyl-1,2,4-triazole, 4-benzamido-3-mercapto-5-phenyl-1,2,4-triazole, etc., which are well known as photographic stabilizers and inhibitors. In addition, two or more of the accelerators and stabilizers may be used in combination for various purposes.

[0024] In addition to the above-mentioned components, the heat-sensitive recording layer may contain known additives such as ultraviolet absorbers, antioxidants, pigments, dyes, pH adjusters, surfactants, defoamers, thickeners, softeners, lubricants, crosslinking agents, antistatic agents, and antiblocking agents.

[0025] As a method for forming the above-mentioned thermosensitive recording layer on a light-transmitting support, it is preferable to prepare a thermosensitive recording layer coating liquid containing the above-mentioned non-photosensitive organic silver salt, a reducing agent, a resin, a color toner, and additives that can be contained in the thermosensitive recording layer, and further a known solvent, and then coat the thermosensitive recording layer coating liquid on the above-mentioned light-transmitting support and dry it to form the layer. The coating amount of the thermosensitive recording layer coating liquid is 2.0 to 30 g / m2 in terms of dry mass in order to obtain a necessary and sufficient UV transmission density as a plate material. 2 is preferable, and 5.0 to 25 g / m 2 More preferably, 8.0 to 20 g / m 2 is more preferred.

[0026] The protective layer in the present invention contains a silicate oligomer. The silicate oligomer in the present invention means an oligomer obtained by hydrolysis and polycondensation of a silicate monomer. Examples of the silicate monomer include tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane. The degree of polymerization of the silicate oligomer is not particularly limited, but the preferred degree of polymerization is 30 or less.

[0027] In the present invention, it is presumed that the silicate oligomer functions as a crosslinking agent for the carbonyl-modified polyvinyl alcohol described below. Therefore, when the direct thermal recording material of the present invention is used to prepare a block copy, image defects are effectively reduced. Tetramethoxysilane is hydrolyzed and polycondensed to form methyl silicate oligomer, and tetraethoxysilane is hydrolyzed and polycondensed to form ethyl silicate oligomer. Either methyl silicate oligomer or ethyl silicate oligomer can be preferably used, or both can be used in combination. In order to effectively reduce image defects when the direct thermal recording material of the present invention is used to prepare a block copy, it is preferable that the protective layer contains at least methyl silicate oligomer.

[0028] Examples of silicate oligomers include methyl silicate oligomer and ethyl silicate oligomer available from Colcoat Co., Ltd. and Mitsubishi Chemical Co., Ltd., and either of these can be preferably used.

[0029] When the direct thermal recording material of the present invention is used to prepare a copy manuscript, image defects are effectively reduced, so that the content of the silicate oligomer in the protective layer is preferably 5 to 90 mass %, more preferably 20 to 70 mass %, and even more preferably 40 to 60 mass %, of the total solid content of the protective layer.

[0030] The protective layer in the present invention contains carbonyl-modified polyvinyl alcohol. When the direct thermal recording material of the present invention is used to prepare a copy manuscript, image defects are effectively reduced, so the content of carbonyl-modified polyvinyl alcohol in the protective layer is preferably 10 to 95% by mass, more preferably 20 to 90% by mass, and even more preferably 30 to 85% by mass of the total solid content of the protective layer. As the carbonyl-modified polyvinyl alcohol, "D Polymer" manufactured by Nippon Acetic Acid & Poval Co., Ltd. can be used. As the "D Polymer", six grades shown in Table 1 below are commercially available, and any of them can be used.

[0031] [Table 1]

[0032] The protective layer may contain a water-soluble resin other than the carbonyl-modified polyvinyl alcohol as long as it does not impair the effects of the present invention. The content of the water-soluble resin in the protective layer is preferably less than 50% by mass of the carbonyl-modified polyvinyl alcohol, and more preferably less than 25% by mass. The water-soluble resin refers to a resin that dissolves in water at a ratio of 5.0% by mass or more. Specific examples of the water-soluble resin include cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, polyvinyl acetal resins such as polyvinyl butyral resins, polyvinyl alcohol resins, gelatin, acrylic resins, melamine resins, polyester resins, polyurethane resins, vinyl acetate resins, and polyolefin resins.

[0033] A crosslinking agent other than the silicate oligomer may be contained within a range that does not impede the effects of the present invention. The crosslinking agent is not particularly limited, but examples thereof include polyisocyanate compounds having two or more isocyanate groups in the molecule, polyepoxy compounds having two or more epoxy groups in the molecule, polyfunctional (meth)acrylate monomers having two or more acryloyl groups and / or methacryloyl groups in the molecule, boric acid, titanium alkoxide, zirconium alkoxide, etc. The content of the crosslinking agent other than the silicate oligomer is preferably 30% by mass or less, more preferably 15% by mass or less, and even more preferably 5% by mass or less, based on the total amount of crosslinking agents including the silicate oligomer.

[0034] The protective layer in the present invention preferably further contains an aldehyde compound as a crosslinking agent other than the silicate oligomer. When the protective layer further contains an aldehyde compound, image defects are particularly effectively reduced when a copy copy is produced using the direct thermal recording material of the present invention. The aldehyde compound is not particularly limited, and known compounds having an aldehyde group such as formaldehyde, acetaldehyde, glyoxal, glutaraldehyde, and glyoxylates (alkali metal salts such as sodium glyoxylate, alkaline earth metal salts such as calcium glyoxylate, etc.) can be used. Among the above, it is particularly preferable to use glyoxylates. The content of the aldehyde compound is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total amount of crosslinking agents including the silicate oligomer.

[0035] The protective layer in the present invention contains an acidic compound having an acid dissociation constant pKa of 4.3 or less. The pKa of the acidic compound in the present invention is a value measured by neutralization titration, and the acidic compound having a pKa of 4.3 or less is not particularly limited, but specifically includes inorganic acids such as sulfuric acid (pKa-3.0), nitric acid (pKa-1.3), and phosphoric acid (pKa2.12), and organic acids such as lactic acid (pKa3.84), maleic acid (pKa1.93), fumaric acid (pKa3.03), citric acid (pKa3.09), p-toluenesulfonic acid (pKa-1.34), and methanesulfonic acid (pKa-2.6). Among these, organic acids are preferred, and lactic acid, fumaric acid, p-toluenesulfonic acid, and methanesulfonic acid are more preferred, and lactic acid and p-toluenesulfonic acid are even more preferred. Two or more of these acidic compounds may be used in combination. Furthermore, in order to ensure a sufficient pot life of the protective layer coating solution during production, the amount of free acid remaining after neutralization (when a salt obtained by neutralizing an acidic compound having a pKa of 4.3 or less is contained in the protective layer, as described below, and the acidic compound is neutralized in the protective layer to produce the salt, the amount of free acid remaining after neutralization) is preferably 0.010 to 5.0 mass %, more preferably 0.030 to 4.0 mass %, and even more preferably 0.050 to 3.0 mass %, relative to the total solids content of the protective layer.

[0036] The protective layer in the present invention contains a salt obtained by neutralizing the above-mentioned acidic compound. In the present invention, the salt obtained by neutralizing the acidic compound is a compound in which the proton of the above-mentioned acidic compound is replaced with another cationic species such as lithium ion, sodium ion, potassium ion, ammonium ion, calcium ion, etc., and in the case of sodium salt, examples thereof include sodium sulfate, sodium nitrate, sodium phosphate, sodium lactate, disodium maleate, monosodium maleate, monosodium fumarate, disodium fumarate, sodium citrate, sodium p-toluenesulfonate, and sodium methanesulfonate. Two or more of these salts may be used in combination. As a method for incorporating the salt of the acidic compound in the protective layer, a basic compound may be incorporated in the protective layer and the above-mentioned acidic compound may be neutralized to generate the salt, or the salt of the acidic compound may be directly added. If the amount of the salt of the acidic compound is too much relative to the acidic compound, pinholes increase, and if the amount of the salt is too little, the prevention of scratches due to contact with a thermal head becomes insufficient. From this viewpoint, the molar ratio of the salt of the acidic compound to the acidic compound is preferably in the range of 0.010 to 10, more preferably in the range of 0.050 to 9.0, and even more preferably in the range of 0.10 to 5.0.

[0037] In the present invention, the protective layer may contain various matting agents for the purpose of improving transportability. When forming the protective layer, it is preferable to use the matting agent by dispersing it in the protective layer. A high-speed stirrer such as a homodisper is suitable for dispersing the matting agent.

[0038] The amount of the matting agent that can be contained in the protective layer is preferably 0.50 to 40 mass %, more preferably 1.0 to 30 mass %, and even more preferably 3.0 to 20 mass %, relative to the content of the resin contained in the protective layer.

[0039] The matting agent may be either organic or inorganic. Examples of organic matting agents include silicone, polytetrafluoroethylene, polymethyl methacrylate, polyacrylate, etc., and examples of inorganic matting agents include silica, alumina, talc, mica, etc. Examples of commercially available products include talc such as Microace (registered trademark) series, Nanoace (registered trademark) series, SG-95, and SG-2000 manufactured by Nippon Talc Co., Ltd., and HC-08L and HC-1L manufactured by Hyogo Clay Co., Ltd., silicone resin matting agents such as Tospearl (registered trademark) 120, 130, 145, and 2000B sold by Momentive Performance Materials Japan LLC, and silica matting agents such as Sunsphere (registered trademark) H-31, H-51, and NP-30 sold by AGC Si-Tech Co., Ltd., and among these, silicone resin matting agents are suitable from the viewpoint of head matching with a thermal head. Although these are single particles, the matting agent may be in the form of either a single particle or a particle aggregate in which particles are aggregated.

[0040] The protective layer in the invention may contain known additives such as ultraviolet absorbers, antioxidants, pigments, dyes, surfactants, dispersants, defoamers, thickeners, softeners, antistatic agents, and antiblocking agents in addition to the above-mentioned components.

[0041] The method for forming the protective layer is preferably to prepare a protective layer coating solution containing a silicate oligomer, a carbonyl-modified polyvinyl alcohol, the above-mentioned water-soluble resin, a crosslinking agent for the water-soluble resin, an acidic compound having a pKa of 4.3 or less, a salt obtained by neutralizing the acidic compound, additives that can be contained in the protective layer, and further a known solvent, and to coat the protective layer coating solution on the above-mentioned thermosensitive recording layer, dry it, and, if necessary, harden it using heat or radiation such as ultraviolet light or electron beams to form the protective layer. The coating amount of the protective layer coating solution is 0.5 to 10 g / m2 in terms of dry mass. 2 is preferable, and 1.0 to 9.0 g / m 2 More preferably, 1.5 to 8.0 g / m 2If the coating amount exceeds the upper limit, the light transmittance decreases and the function as a plate material decreases, whereas if it is below the lower limit, scratches and the like tend to occur during handling.

[0042] In the present invention, the coating method for the thermosensitive recording layer and the protective layer is not particularly limited, and can be selected from various coating methods such as those described in ED Cohen, EB Gutoff, "Modern Coating and Drying Technology", Wiley-VCH, Inc. New York, 1992. Furthermore, it is particularly preferable to coat a plurality of layers simultaneously in terms of improving productivity.

[0043] The direct thermal recording material of the present invention has a thermal recording layer and a protective layer in this order on a light-transmitting support, and may further have an undercoat layer or a heat-insulating layer between the light-transmitting support and the thermal recording layer, or may have an intermediate layer between the thermal recording layer and the protective layer.

[0044] According to the present invention, an image can be obtained by contacting a thermal head with the protective layer of the direct thermal recording material and heating the direct thermal recording material with a heating element while transporting the direct thermal recording material under the thermal head. The direct thermal recording material can be heated to various temperatures up to 400°C by changing the number of heat pulses applied by the thermal head, and the UV transmission density of the image area can be changed by changing the number of heat pulses. EXAMPLES

[0045] The present invention will be described below using examples, but the present invention is not limited to these examples. In the description, "%" is based on mass.

[0046] <Example 1>

[0047] <Preparation of Silver Behenate Dispersion> 20 g of silver behenate crystals and 20 g of Butvar (registered trademark) B-79 (polyvinyl butyral resin manufactured by Eastman Chemical Japan, Ltd.) were added to 180 g of 2-butanone, and dispersed using a beads mill to obtain a silver behenate dispersion.

[0048] <Preparation and Coating of Thermal Recording Layer Coating Solution> 0.5 g of Butvar B-79, 10 g of the silver behenate dispersion, 0.3 g of ethyl 3,4-dihydroxybenzoate, 0.1 g of tetrachlorophthalic anhydride, and 0.2 g of phthalazone were added to 10 g of 2-butanone and mixed to obtain a thermosensitive recording layer coating solution. A 100 μm thick polyethylene terephthalate film (total light transmittance 92%, haze value 4%, 500 mm × 400 mm) was prepared as a light-transmitting support, and the thermosensitive recording layer coating solution was applied to one side of the film so that the dry mass was 13.0 g / m 2 The mixture was then dried at 80° C. for 3 minutes to form a heat-sensitive recording layer.

[0049] <Preparation and Application of Protective Layer Coating Solution> 5.0 g of DF-20 (carbonyl-modified polyvinyl alcohol resin, high viscosity grade, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) was dissolved in 45 g of water and 20 g of 2-propanol, and 5.5 g of Ethyl Silicate 40 (manufactured by Colcoat Co., Ltd.; an oligomer obtained by hydrolyzing and polycondensing ethyl silicate to an average pentamer), 0.071 g of p-toluenesulfonic acid, 0.0100 g of sodium hydroxide, and 0.35 g of Tospearl (registered trademark) 145 (a silicone resin-based matting agent, manufactured by Momentive Performance Materials Japan, LLC, average particle size 4.5 μm) were added thereto, and the mixture was stirred at 300 rpm with a three-one motor for 1 hour to obtain a protective layer coating solution, and the protective layer coating solution was applied onto the above-mentioned thermal recording layer so that the dry mass was 5.0 g / m. 2 The coating was then dried at 90° C. for 3 minutes to form a protective layer, and the coating was then heated at 40° C. for 24 hours to obtain a direct thermal recording material of Example 1.

[0050] <Example 2> A direct thermal recording material of Example 2 was obtained in the same manner as in Example 1, except that 5.5 g of Ethyl Silicate 48 (manufactured by Colcoat Co., Ltd.; an oligomer obtained by hydrolyzing and polycondensing ethyl silicate to an average of 10-mer) was added instead of 5.5 g of Ethyl Silicate 40 to obtain a protective layer coating solution.

[0051] <Example 3> A direct thermal recording material of Example 3 was obtained in the same manner as in Example 1, except that 5.5 g of methyl silicate 51 (manufactured by Colcoat Co., Ltd.; an oligomer obtained by hydrolyzing and polycondensing tetramethoxysilane to an average tetramer) was added instead of 5.5 g of ethyl silicate 40 to obtain a protective layer coating solution.

[0052] <Example 4> A direct thermal recording material of Example 4 was obtained in the same manner as in Example 1, except that 5.5 g of methyl silicate 53A (manufactured by Colcoat Co., Ltd.; an oligomer obtained by hydrolyzing and polycondensing tetramethoxysilane to an average of 7-mer) was added instead of 5.5 g of ethyl silicate 40 to obtain a protective layer coating solution.

[0053] <Example 5> The direct thermal recording material of Example 5 was obtained in the same manner as in Example 1, except that 5.5 g of EMS-485 (manufactured by Colcoat Co., Ltd.; a mixture of methyl silicate oligomer and ethyl silicate oligomer, average decamer) was added instead of 5.5 g of Ethyl Silicate 40 to obtain a protective layer coating solution.

[0054] <Example 6> The direct thermal recording material of Example 6 was obtained in the same manner as in Example 1, except that 5.5 g of MKC (registered trademark) Silicate MS51 (manufactured by Mitsubishi Chemical Corporation; an oligomer obtained by hydrolyzing and polycondensing tetramethoxysilane to an average of 3 to 5 monomers) was added instead of 5.5 g of Ethyl Silicate 40 to obtain a protective layer coating solution.

[0055] <Example 7> The direct thermal recording material of Example 7 was obtained in the same manner as in Example 1, except that 5.0 g of DF-05 (carbonyl-modified polyvinyl alcohol resin, low viscosity grade, manufactured by Nippon Vacuum Acetate & Poval Co., Ltd.) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0056] <Example 8> The direct thermal recording material of Example 8 was obtained in the same manner as in Example 1, except that 5.0 g of DM-20 (carbonyl-modified polyvinyl alcohol resin, high viscosity grade, intermediate saponification grade, manufactured by Nippon Vacuum Acetate & Poval Co., Ltd.) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0057] <Example 9> The direct thermal recording material of Example 9 was obtained in the same manner as in Example 1, except that 0.35 g of Sunsphere (registered trademark) H-51 (silica-based matting agent, average particle size 5.0 μm, manufactured by AGC Si-Tech Co., Ltd.) was added instead of 0.35 g of Tospearl 145 to obtain a protective layer coating solution.

[0058] <Example 10> A direct thermal recording material of Example 10 was obtained in the same manner as in Example 1, except that 2.5 g of DF-20 and 8.0 g of Ethyl Silicate 40 were added to obtain a protective layer coating solution.

[0059] <Example 11> A direct thermal recording material of Example 11 was obtained in the same manner as in Example 1, except that 7.5 g of DF-20 and 3.0 g of Ethyl Silicate 40 were added to obtain a protective layer coating solution.

[0060] <Comparative Example 1> A direct thermal recording material of Comparative Example 1 was obtained in the same manner as in Example 1, except that 5.5 g of tetramethoxysilane was added instead of 5.5 g of ethyl silicate 40 to obtain a protective layer coating solution.

[0061] <Comparative Example 2> A direct thermal recording material of Comparative Example 2 was obtained in the same manner as in Example 1, except that a protective layer coating solution was obtained without adding 5.5 g of Ethyl Silicate 40.

[0062] <Comparative Example 3> A direct thermal recording material of Comparative Example 3 was obtained in the same manner as in Example 1, except that 5.0 g of Kuraray Poval (registered trademark) 25-98R (silanol-modified polyvinyl alcohol resin manufactured by Kuraray Co., Ltd.) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0063] <Comparative Example 4> A direct thermal recording material of Comparative Example 4 was obtained in the same manner as in Example 1, except that 5.0 g of Gohsenex (registered trademark) Z-200 (acetoacetyl-modified polyvinyl alcohol resin manufactured by Mitsubishi Chemical Corporation) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0064] <Comparative Example 5> A direct thermal recording material of Comparative Example 5 was obtained in the same manner as in Example 1, except that 5.0 g of Kuraray Poval 3-86SD (carboxyl-modified polyvinyl alcohol resin manufactured by Kuraray Co., Ltd.) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0065] <Comparative Example 6> A direct thermal recording material of Comparative Example 6 was obtained in the same manner as in Example 1, except that 5.0 g of Kuraray Poval 3-80 (an unmodified polyvinyl alcohol resin manufactured by Kuraray Co., Ltd.) was added instead of 5.0 g of DF-20 to obtain a protective layer coating solution.

[0066] <Comparative Example 7> A direct thermal recording material of Comparative Example 7 was obtained in the same manner as in Example 1, except that a protective layer coating solution was obtained without adding 5.0 g of DF-20.

[0067] The direct thermal recording materials of Examples 1 to 11 and Comparative Examples 1 to 7 thus obtained were cut into rolls with a width of 360 mm, and 20 sheets of each thermal recording material were printed at a printing speed of 1 msec / line using a thermal digital printer (TDP-459: 1200 dpi / 120 lpi, line head, manufactured by Mitsubishi Paper Mills, Ltd.) to obtain a plate material. The image area printed on the plate material was 350 mm (width) x 450 mm (length), and the image area had a 50% halftone dot image (133 lines / inch).

[0068] <Yield evaluation> Of the 20 sheets of copy paper printed as described above, those with five or fewer missing dots were judged to be normal, and the yield of copy paper was calculated as shown in Table 2 below.

[0069] [Table 2]

[0070] As is clear from the results in Table 2, for the direct thermal recording materials of Examples 1 and 2, 17 out of 20 plates were normal, for the direct thermal recording materials of Examples 5 and 11, 18 out of 20 plates were normal, and for the direct thermal recording materials of Examples 3, 4 and Examples 6 to 10, 19 out of 20 plates were normal.

[0071] On the other hand, in the direct thermal recording material of Comparative Example 4, 13 out of 20 plates were normal, in the direct thermal recording materials of Comparative Examples 1, 3, and 5, 12 out of 20 plates were normal, in the direct thermal recording material of Comparative Example 6, 11 out of 20 plates were normal, in the direct thermal recording material of Comparative Example 2, 9 out of 20 plates were normal, and in the direct thermal recording material of Comparative Example 7, 4 out of 20 plates were normal.

[0072] As described above, according to the present invention, a direct thermal recording material can be provided which can improve the yield of the plate material obtained by forming an image by heating with a thermal head.

[0073] <Example 12> A direct thermal recording material of Example 12 was obtained in the same manner as in Example 1, except that 0.25 g of glyoxal was added as the aldehyde compound to obtain a protective layer coating solution.

[0074] <Example 13> A direct thermal recording material of Example 13 was obtained in the same manner as in Example 1, except that 0.25 g of sodium glyoxylate was added as the aldehyde compound to obtain a protective layer coating solution.

[0075] The direct thermal recording materials of Examples 12 and 13 thus obtained were cut into rolls 360 mm wide, and 100 sheets of each thermal recording material were printed at a printing speed of 1 msec / line using a thermal digital printer (TDP-459: 1200 dpi / 120 lpi, line head, manufactured by Mitsubishi Paper Mills, Ltd.) to obtain a plate material. The image area printed on the plate material was 350 mm (width) x 450 mm (length), and the image area had a 50% halftone dot image (133 lines / inch).

[0076] <Yield evaluation> Of the 100 sheets of copy paper printed as described above, those with five or fewer missing dots were judged to be normal, and the yield of copy paper was calculated, as shown in Table 3 below.

[0077] [Table 3]

[0078] As is clear from the results in Table 3, 97 out of 100 plates of the direct thermal recording material of Example 12 were normal, and 99 out of 100 plates of the direct thermal recording material of Example 13 were normal.

[0079] As described above, according to the present invention, a direct thermal recording material can be provided which can improve the yield of the plate material obtained by forming an image by heating with a thermal head.

Claims

1. A direct thermal recording material comprising, on a light-transmitting support, at least a thermal recording layer containing a non-photosensitive organic silver salt and a reducing agent, and a protective layer containing at least a carbonyl-modified polyvinyl alcohol and a silicate oligomer, in this order from the side closer to the light-transmitting support.

2. 2. The direct thermal recording material according to claim 1, wherein the protective layer further comprises an aldehyde compound.

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