JP7651486B2 - Thermal recording materials - Google Patents

Description

The present invention relates to a thermal recording material that reduces ejections from the surface of the thermal recording material when irradiated with an infrared laser, and produces high-contrast images.

Wet processing image formation methods using silver halide photosensitive materials have long been commonly used as a high-quality image formation method used in the production of plate materials. However, wet processing image formation methods require waste liquid treatment such as developer and fixer solutions, which places a heavy burden on the environment, and so various dry image formation methods that do not require wet processing have been investigated. Currently, image formation systems such as inkjet printers, electrophotography, and dye thermal transfer systems are in practical use. However, with these dry image formation methods, it is difficult to obtain so-called high-contrast plate materials that have excellent light blocking properties in the image areas and excellent light transmission in the non-image areas.

Dry image formation methods that can obtain a high contrast equivalent to that of wet processing image formation methods using silver halide photosensitive materials include a method of forming an image on a thermal recording material having a thermal recording layer on a support using a thermal head or an infrared laser. Among these, thermal recording methods using infrared lasers are advantageous from the viewpoint of high density recording and high image quality recording. As thermal recording materials that can be imaged by infrared lasers, for example, JP-A-6-194781 (Patent Document 1) discloses a thermal recording material that contains a thermally reducible silver source, a reducing agent for silver ions, a dye that absorbs laser light in the wavelength range of about 500 to 1100 nm, and a polymeric binder, and JP-A-10-29377 (Patent Document 2) discloses a thermal recording material having a thermal layer that contains an organic silver salt, a developer for the organic silver salt, a merocyanine infrared absorbing dye having a specific structure, and a water-soluble binder. In addition, JP 2001-10229 A (Patent Document 3) discloses a thermal color image forming material that contains a non-photosensitive organic silver salt, a reducing agent for silver ions, a binder, a color tone adjusting agent, and an absorbent that absorbs radiation in the wavelength range of 750 to 1100 nm.

Thermal recording methods using infrared lasers involve irradiating a thermal recording material with infrared laser light to locally heat the material, causing the thermal recording layer to develop color and create an image. However, because infrared lasers are high energy, the components contained in the thermal recording material and by-products produced during the color development process of the thermal recording layer volatilize or explode as ejection from the surface of the thermal recording material, causing the problem of contaminating the surface of the thermal recording material and the infrared laser irradiation device.

As a method for solving the above problems, it is known to provide another layer on the thermal recording layer. For example, JP-A-2002-311535 (Patent Document 4) discloses a thermally developable material having a thermally developable image forming layer on a support and a barrier layer containing a specific water-insoluble aromatic polyester, and it is described that the barrier layer effectively prevents the diffusion of fatty acids and other chemical substances from the thermally developable material. JP-A-2004-9583 (Patent Document 5) discloses an image forming material in which an image forming layer containing a non-photosensitive organic silver salt and a reducing agent, and a protective layer are laminated in this order on a support, and the farther from the support the layer is, the more crosslinking agent is contained, and it is described that the image forming material can reduce compounds that emerge to the surface when the latent image after imagewise heating or exposure is heat-developed. However, there has been a demand for further improvement in the effect of reducing ejections generated from the surface of the thermal recording material by irradiation with an infrared laser.

On the other hand, JP-A-11-34495 (Patent Document 6) discloses a thermal recording material having a thermal recording layer and an undercoat layer containing a specific gelatin and a layered inorganic compound on a support, and states that a light transmittance adjustment layer can be provided. In addition, JP-A-2003-1937 (Patent Document 7) discloses a thermal recording material having, in that order, a first thermal coloring layer and a light reflecting layer with a total light transmittance of 30% or less on one side of a transparent support, and a second thermal coloring layer on the other side of the transparent support.

Japanese Unexamined Patent Publication No. 6-194781 Japanese Patent Application Publication No. 10-29377 JP 2001-10229 A JP 2002-311535 A JP 2004-9583 A Japanese Patent Application Publication No. 11-34495 JP 2003-1937 A

The object of the present invention is to provide a thermal recording material that reduces the amount of material ejected from the surface of the thermal recording material when irradiated with an infrared laser, and that can produce high-contrast images.

The above-mentioned problems are solved by the following invention.
A heat-sensitive recording material having an image-forming layer on a light-transmitting support, the image-forming layer containing an infrared absorbing dye having a ratio of a molar absorption coefficient ε(830) at 830 nm to a molar absorption coefficient ε(365) at 365 nm, ε(830)/ε(365), of 4.0 or more, a non-photosensitive organic silver salt, and a reducing agent, and having a total light transmittance of 55% or more based on JIS K7361-1:1997.

The present invention provides a thermal recording material that reduces ejections from the surface of the thermal recording material when irradiated with an infrared laser, and can produce high-contrast images.

The details of the present invention are described below.

The 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 70% or more. 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 is preferably 50 to 300 μm from the viewpoint of handleability.

The thermal recording material of the present invention has an image-forming layer on a light-transmitting support. In the present invention, the image-forming layer means a system in which the area irradiated with an infrared laser develops color and a light-shielding image can be formed.

The image forming layer of the thermal recording material of the present invention contains an infrared absorbing dye having a ratio of the molar absorption coefficient ε(830) at 830 nm to the molar absorption coefficient ε(365) at 365 nm, ε(830)/ε(365), of 4.0 or more. The infrared absorbing dye in the present invention is preferably a dye having absorption in the wavelength region of 600 to 1500 nm, more preferably having an absorption maximum in the wavelength region of 650 to 1200 nm, and even more preferably having an absorption maximum in the wavelength region of 750 to 1100 nm. The infrared absorbing dye in the present invention has low absorption in the wavelength region of 350 to 450 nm, where the emission peak in the ultraviolet region of high-pressure mercury lamps and chemical lamps exists, that is, the above-mentioned ε(830)/ε(365) value is 4.0 or more, so that a thermal recording material that can obtain a high-contrast image by irradiation with an infrared laser can be obtained. The upper limit value of ε(830)/ε(365) is not particularly limited. Examples of such infrared absorbing dyes include compounds having a polymethine skeleton, such as squarylium, cyanine, merocyanine, and bis(aminoaryl)polymethine. Specific examples include compounds represented by the following general formulas (1) to (3), but the present invention is not limited to these.

In the general formulas (1) to (3), R ¹ to R ¹⁰ are substituents, and examples of the substituents include a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an acyl group, an ester group, an amide group, a halogen atom, a hydroxyl group, a thiol group, a thioether group, and a sulfonyl group. These may be the same or different substituents, and may be bonded to other substituents to form a ring structure. In the general formulas (1) to (3), X ^- represents an atom or atomic group having a negative charge, and examples of the atom include a halogen ion, an oxo acid such as a perchlorate ion, a tetrafluoroborate, a hexafluorophosphate, and an alkyl and aryl sulfonate. Specific examples of the compound include, but are not limited to, the following exemplary compounds (1) to (7).

As an example of a method for measuring the molar absorption coefficients (ε (830) and ε (365)) mentioned above, a method can be given in which a 2-butanone solution of an infrared absorbing dye is prepared and the absorption spectrum of the solution is measured using a UV-2600 ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation) in a quartz cell with an optical path length of 1 cm.

In the present invention, a high contrast image means that the difference Dmax-Dmin between the maximum ultraviolet light transmission density (Dmax) of the image area and the ultraviolet light transmission density (Dmin) of the non-image area is 3.0 or more, and more preferably 3.5 or more. An example of a method for measuring the ultraviolet light transmission density is a method in which an X-Rite (registered trademark) 361T manufactured by Videojet X-Rite Inc. is used in ultraviolet light mode.

The content of the infrared absorbing dye is not particularly limited, but is preferably 0.01 to 25% by mass, and more preferably 0.02 to 15% by mass, based on the total solid content of the image forming layer.

In the present invention, the image forming layer may contain a single infrared absorbing dye or may contain two or more types of infrared absorbing dye.

The image-forming layer of the thermal 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 later to form a silver image. Specifically, silver salts of organic acids such as gallic acid, oxalic acid, behenic acid, stearic acid, palmitic acid, and lauric acid as described in Research Disclosure Nos. 17029(II) and 29963(XVI) relating to thermally developable photosensitive materials; silver salts of carboxyalkylthioureas such as 1-(3-carboxypropyl)thiourea and 1-(3-carboxypropyl)-3,3-dimethylthiourea; aldehydes such as formaldehyde, acetaldehyde, and butylaldehyde, and aromatic thioureas such as salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, and 5,5-thiodisalicylic acid. Examples include complexes of silver and polymeric reaction products with carboxylic acids; silver salts or complexes of thiones such as 3-(2-carboxyethyl)-4-hydroxymethyl-4-thiazoline-2-thione and 3-carboxymethyl-4-methyl-4-thiazoline-2-thione; silver salts or complexes of nitrogen-containing heterocycles selected from imidazole, pyrazole, urazole, 1,2,4-triazole, 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole, and benzotriazole; silver salts of saccharin, 5-chlorosalicylaldoxime, and the like; and silver salts of mercaptides. Among these, silver salts of fatty acids having 10 or more carbon atoms are preferred, with silver stearate and silver behenate being particularly preferred.

In the present invention, the content of the non-photosensitive organic silver salt contained in the image forming layer can be appropriately adjusted depending on the ultraviolet light transmittance density required for use as a plate making material, and is preferably 0.2 to 3.0 g/ ^m2 , more preferably 0.5 to 2.0 g/ ^m2 in terms of silver.

It is preferable that the image forming layer of the thermal recording material of the present invention is substantially free of photosensitive silver halide. Here, "substantially free" means that the amount of photosensitive silver halide contained in the image forming layer is less than 1% by mass relative to the total solid content of the image forming layer, which suppresses an increase in transmission density in non-image areas during storage and normal use of the thermal recording material of the present invention, and results in a thermal recording material capable of forming high-contrast images.

The image forming layer of the thermal 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, 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 reducing agents listed above, polyhydroxybenzene compounds and polyhydroxybenzoic acid compounds are preferred from the viewpoint of obtaining high contrast images.

The content of the reducing agent in the image-forming layer can vary widely depending on the type of reducing agent and the type of organic silver salt, but is preferably 0.1 to 3.0 mol, and more preferably 0.5 to 2.0 mol, per mol of organic silver salt. For various purposes, two or more of the above-mentioned reducing agents may be used in combination.

The image forming layer of the thermal recording material of the present invention preferably contains a so-called color toning agent known in the field of thermography or photothermography. Examples of color toning agents are known from Research Disclosure No. 17029 (V) and No. 29963 (XXII) regarding the above-mentioned thermally developable photosensitive material, and specifically include imides such as phthalimide, mercapto compounds such as 3-mercapto-1,2,4-triazole, phthalazine, phthalazone, 4-methylphthalic acid, tetrachlorophthalic acid, and phthalic acid derivatives such as their anhydrides, and benzoxazine derivatives such as 1,3-benzoxazine-2,4-dione. For various purposes, two or more of the above color toning agents may be used in combination.

The image-forming layer of the thermal recording material of the present invention may contain various accelerators, stabilizers, and precursors thereof for the purpose of suppressing or promoting the formation of image silver, improving the storage stability of the thermal recording material before and after image formation, and the like. 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, and the like, which are known as photographic additives. In addition, two or more of the accelerators, stabilizers, and precursors thereof may be used in combination for various purposes.

The image-forming layer of the thermal recording material of the present invention preferably contains a binder component for the purpose of holding the infrared absorbing dye, the non-photosensitive organic silver salt, and the reducing agent. Such a binder component is preferably a thermoplastic resin, and examples thereof include cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, acrylic resins, polyester resins, polyurethane resins, vinyl chloride resins, vinyl acetate resins, polyolefin resins, polyvinyl acetal resins such as polyvinyl butyral resins, and polyvinyl alcohol resins. These binder components may be used by dissolving them in water or an organic solvent, or may be used as latexes 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 image-forming layer of the present invention, the above-mentioned binder components are preferably those that form a light-transmitting coating after drying. Furthermore, these binder components may be used in combination of two or more resins that are compatible with each other as necessary.

The image-forming layer of the thermal recording material of the present invention may contain, in addition to the above-mentioned infrared absorbing dye, non-photosensitive organic silver salt, reducing agent, and binder component, known additives such as ultraviolet absorbers, antioxidants, silane coupling agents, pigments, dyes, pH adjusters, surfactants, defoamers, thickeners, softeners, lubricants, antistatic agents, and antiblocking agents, depending on various purposes.

The method for forming the image forming layer of the heat-sensitive recording material of the present invention includes preparing an image forming layer coating liquid containing the above-mentioned infrared absorbing dye, non-photosensitive organic silver salt, reducing agent, binder component, additives that can be contained in the heat-sensitive recording layer, and a known solvent, and coating and drying the image forming layer coating liquid on the above-mentioned light-transmitting support. The coating amount of the image forming layer coating liquid is preferably 3.0 to 50.0 g/ ^m2 , more preferably 5.0 to 40.0 g/ ^m2 , and even more preferably 8.0 to 30.0 g/ ^m2 , in terms of dry mass.

As long as the above-mentioned elements are provided, the composition of the image-forming layer of the thermal recording material of the present invention is not particularly limited. However, since a high-contrast image can be obtained by irradiation with an infrared laser, the image-forming layer preferably has an infrared absorbing layer containing an infrared absorbing dye on a light-transmitting support, and a thermal recording layer containing a non-photosensitive organic silver salt and a reducing agent on the infrared absorbing layer. In addition, since ejection during irradiation with an infrared laser can be effectively reduced, it is preferable that the image-forming layer has a protective layer on the outermost surface. Therefore, a particularly preferred embodiment of the thermal recording material of the present invention has an infrared absorbing layer, a thermal recording layer, and a protective layer on a light-transmitting support, in this order from the side closest to the light-transmitting support.

When the image-forming layer has an infrared-absorbing layer, the infrared-absorbing layer preferably contains a binder for the purpose of retaining the infrared-absorbing dye. Examples of such binders include binders that can be preferably contained in the image-forming layer. The content of the infrared-absorbing dye in the infrared-absorbing layer is not particularly limited, but is preferably 0.05 to 50% by mass, and more preferably 0.1 to 20% by mass, based on the total solid content of the infrared-absorbing layer.

In one preferred embodiment, the infrared absorbing layer contains a reducing agent in addition to the infrared absorbing dye and binder component. An example of such a reducing agent is the reducing agent contained in the image forming layer. The reducing agents contained in the infrared absorbing layer and the thermal recording layer may be the same or different, and two or more types may be contained.

The infrared absorbing layer is preferably formed by preparing an infrared absorbing layer coating liquid containing the above-mentioned infrared absorbing dye, binder component, reducing agent, additives that can be contained in the image forming layer, and further a known solvent, coating the infrared absorbing layer coating liquid on the above-mentioned light-transmitting support, and drying the same. The coating amount of the infrared absorbing layer coating liquid is preferably 0.01 to 8.0 g/ ^m2 , more preferably 0.05 to 5.0 g/ ^m2 , in terms of dry mass.

When the image forming layer has a thermosensitive recording layer, the thermosensitive recording layer preferably contains a binder for the purpose of retaining the non-photosensitive organic silver salt and the reducing agent. Examples of such binders include binders that can be preferably contained in the image forming layer. The binder component of the thermosensitive recording layer preferably does not contain free halide ions such as chloride ions and 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 thermosensitive recording material of the present invention. Specifically, it is preferable that the content of the binder component is 100 ppm or less.

In the present invention, when the image forming layer has an infrared absorbing layer and a thermosensitive recording layer, it is preferable that the infrared absorbing layer and the thermosensitive recording layer are adjacent to each other, which makes it possible to efficiently form an image by irradiation with an infrared laser, and to obtain an image with a particularly high contrast. As a method for forming a thermosensitive recording layer, it is preferable to prepare a thermosensitive recording layer coating liquid containing the organic silver salt, reducing agent, color toner, binder component, and additives that can be contained in the image forming layer, and further a known solvent, and to coat the thermosensitive recording layer coating liquid on the above-mentioned infrared absorbing layer and dry it to form the layer. In addition, the coating amount of the thermosensitive recording layer coating liquid is preferably 2.0 to 30.0 g/ ^m2 , more preferably 5.0 to 20.0 g/ ^m2 , and even more preferably 7.0 to 15.0 g/ ^m2 in terms of dry mass.

When the image forming layer has a protective layer, it is preferable that it contains at least hydrophilic particles and a hydrophobic resin. By adopting such a configuration, ejection of material during irradiation with an infrared laser can be effectively reduced.

In the present invention, hydrophilic particles refer to particles whose surface is easily wetted by water. Specifically, particles of inorganic materials whose surface is easily wetted by water, such as metals such as gold, silver, and copper, metal oxides such as silica, alumina, and zirconia, layered silicates, and composites thereof, particles of organic materials whose surface is easily wetted by water, such as acrylic particles, styrene particles, and melamine particles, and particles of organic/inorganic composite materials whose surface is easily wetted by water, can be used. An example of a method for determining whether a particle is hydrophilic or not is to measure 10 mL of pure water in a glass beaker, add 0.1 g of particles thereto, stir, and leave for 10 minutes, and if the particles remain floating on the water surface and do not separate, the particles are judged to be hydrophilic. The hydrophilic particles may be subjected to a known surface treatment. Two or more types of hydrophilic particles may be used in combination.

Among the above hydrophilic particles, hydrophilic inorganic particles are preferred because they are highly effective in reducing ejections that occur from the surface of a thermal recording material when irradiated with an infrared laser.

The lower limit of the average particle size of the hydrophilic particles is not particularly limited, but it is preferably 1 μm or more since it is possible to effectively reduce the ejection generated from the surface of the thermal recording material by irradiation with an infrared laser. The upper limit of the average particle size of the hydrophilic particles is not particularly limited, but it is preferably 10 μm or less since it is possible to obtain a high-contrast image. The average particle size can be calculated based on the volume obtained by laser diffraction/scattering particle size distribution measurement. Specifically, a method of measurement using a laser diffraction/scattering particle size distribution measurement instrument MT3000II manufactured by Microtrack Bell Co., Ltd. can be exemplified.

The hydrophilic particles that can be contained in the protective layer of the present invention can be commercially available products. For example, silica particles include the Seahoster (registered trademark) KE series sold by Nippon Shokubai Co., Ltd., the Sunsphere (registered trademark) series sold by AGC Si-Tech Co., Ltd., and the Silica (registered trademark) series sold by Fuji Silysia Chemical Co., Ltd.; alumina particles include the fine alumina SA30 series, SA40 series, and SMM series sold by Nippon Light Metal Co., Ltd.; acrylic particles include the Chemisnow (registered trademark) MX series sold by Soken Chemical Industries Co., Ltd., and the Techpolymer (registered trademark) AQS series sold by Sekisui Chemical Co., Ltd.; melamine particles include the Optobeads (registered trademark) series sold by Nissan Chemical Co., Ltd., and the Eposter (registered trademark) series sold by Nippon Shokubai Co., Ltd., and all of these can be preferably used.

The amount of hydrophilic particles that the protective layer can contain is not particularly limited, but is preferably 1.2 to 40% by mass, and more preferably 1.6 to 30% by mass, based on the total solid content of the protective layer.

The hydrophobic resin that the protective layer can contain is not particularly limited, and may contain known hydrophobic resins such as acrylic resin, urethane resin, silicone resin, acrylic urethane resin, polyester resin, cellulose acetate resin, and epoxy resin. In the present invention, the hydrophobic resin means a resin whose solubility in 100 g of water at 25° C. is less than 1 g. Two or more types of hydrophobic resins may be used in combination.

There are no particular limitations on the components contained in the protective layer or the method of forming it, but it is preferable to form it by applying a protective layer coating liquid containing hydrophilic particles, a polyisocyanate compound, and a polyol compound, as this produces a protective layer that can effectively reduce the ejection of material that is generated on the surface of the thermal recording material by irradiation with an infrared laser. The crosslinking of the polyisocyanate compound and the polyol compound produces various urethane resins, which are hydrophobic resins. The polyisocyanate compound is preferably a compound having two or more isocyanate groups in the molecule. Examples of the polyisocyanate compound include aliphatic polyisocyanate compounds such as dimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, decane diisocyanate, and isophorone diisocyanate; aromatic polyisocyanate compounds such as tolylene diisocyanate, 1,3-phenylene diisocyanate, 1,3-dimethylbenzene-2,6-diisocyanate, and naphthalene-1,4-diisocyanate; and adducts in which one or more of these polyisocyanate compounds form a dimer or trimer; and adducts in which these polyisocyanate compounds react with a divalent or trivalent polyol. Among these, hexamethylene diisocyanate and its adduct are preferred as aliphatic polyisocyanate compounds, and tolylene diisocyanate and its adduct are preferred as aromatic polyisocyanate compounds. These polyisocyanate compounds may be used alone or in combination of two or more types depending on various purposes. As such polyisocyanate compounds, products that are generally sold as isocyanate-based crosslinking agents can be used as they are, and specific product names include the Burnock (registered trademark) series manufactured by DIC Corporation and the Coronate (registered trademark) series manufactured by Tosoh Corporation.

The content of the polyvalent isocyanate compound that can be contained in the protective layer coating liquid in the present invention is preferably 59 to 95% by mass based on the total solid content of the protective layer coating liquid, since this provides excellent alcohol resistance to the surface of the thermal recording material, more preferably 59 to 90% by mass, and even more preferably 59 to 80% by mass.

Examples of polyol compounds that can be contained in the protective layer coating solution of the present invention include cellulose derivatives such as cellulose acetate, hydroxyethyl cellulose, and hydroxypropyl cellulose, and copolymers of polyhydric alcohols and various monomers, such as acrylic polyol, polyether polyol, polyester polyol, and polycarbonate polyol. These polymer compounds may be used alone or in combination of two or more types depending on various purposes. Of these, it is more preferable to use acrylic polyols, and examples of commercially available acrylic polyols include the Acrydic (registered trademark) series (manufactured by DIC Corporation) and the #6000 series (manufactured by Taisei Fine Chemical Co., Ltd.). Therefore, the protective layer of the present invention preferably contains an acrylic urethane resin in which an acrylic polyol and a polyvalent isocyanate are reacted.

In the present invention, the method for forming the protective layer is preferably to prepare a protective layer coating liquid containing the above-mentioned hydrophilic particles, hydrophobic resin, additives that can be contained in the image forming layer, and further a known solvent, and to coat the protective layer coating liquid on the above-mentioned thermosensitive recording layer and dry the same. The coating amount of the protective layer coating liquid is preferably 1.5 to 10 g/ ^m2 , more preferably 2 to 8 g/ ^m2 , in terms of dry mass.

In the present invention, the coating method of the infrared absorbing layer coating liquid, the thermal recording layer coating liquid, and the protective layer coating liquid described above is not particularly limited, and can be selected from various coating methods such as those described in E. D. Cohen, E. B. Gutoff, "Modern Coating and Drying Technology", WILEY-VCH, Inc. New York, 1992. Furthermore, it is particularly preferable to simultaneously coat multiple layers by a slide coating method using a slit-type die coater or a tandem coating method in which coating and drying processes are repeated by combining the same or different types of coater devices, in order to improve productivity.

In addition to the above-mentioned infrared absorbing layer, thermal recording layer, and protective layer, the thermal recording material of the present invention may further include, as necessary, an easy-adhesion layer or a heat-insulating layer between the light-transmitting support and the infrared absorbing layer, an intermediate layer between each of the infrared absorbing layer, the thermal recording layer, and the protective layer, an easy-peeling layer on the protective layer, or an antistatic layer on the surface of the light-transmitting support opposite the surface having the infrared absorbing layer, the thermal recording layer, and the protective layer. However, from the viewpoint of obtaining a high-contrast image as described above, it is preferable that the infrared absorbing layer and the thermal recording layer are adjacent to each other.

The thermal recording material of the present invention has a total light transmittance of 55% or more based on JIS K7361-1:1997. By achieving such a total light transmittance, ejections that occur from the surface of the thermal recording material due to irradiation with an infrared laser are reduced. Since ejections are effectively reduced, a total light transmittance of 59% or more is preferable, and 64% or more is particularly preferable. A specific example of a method for measuring the total light transmittance is a method in which a haze meter HZ-V3 (manufactured by Suga Test Instruments Co., Ltd.) is used with a D65 light source.

The upper limit of the total light transmittance of the heat-sensitive recording material of the present invention is not particularly limited, and can vary widely depending on the absorption in the visible light wavelength region of the infrared absorbing dye contained in the image forming layer, but it is preferably 86% or less because this allows for a high-contrast image to be obtained.

There are no particular limitations on the method for controlling the total light transmittance to 55% or more, and examples include a method for adjusting the content of the infrared absorbing dye in the image forming layer, a method for adjusting the film thickness of the image forming layer, and a method for incorporating a dye or pigment (such as carbon black) other than the infrared absorbing dye in the image forming layer.

By using the above-mentioned thermal recording material, an image can be obtained by irradiating an infrared laser imagewise from the image forming layer side of the thermal recording material. Examples of the light source of the infrared laser include a semiconductor laser, a He-Ne laser, an Ar laser, a carbon dioxide gas laser, a YAG laser, and a fiber laser. The thermal recording material of the present invention can change the density of the image part by changing the energy and exposure time of the infrared laser to be irradiated. As a method for irradiating an infrared laser, a thermal CTP setter used for plate making of flexographic printing plates and offset printing plates can be used. Examples of thermal CTP setters include the AURA series (manufactured by Guangzhou Amsky Technology Co Ltd), the Trendsetter (registered trademark) series (manufactured by Eastman Kodak Co.), and the Achieve (registered trademark) series (manufactured by Eastman Kodak Co.).

One example of a method for measuring the ultraviolet light transmission density of an image portion obtained by irradiating the above-mentioned thermal recording material with an infrared laser using a thermal CTP setter or the like is a method using a transmission densitometer. When measuring the ultraviolet light transmission density, it is preferable to measure a filled-in portion of an image portion of a size suitable for the light receiving portion of the transmission densitometer, rather than a portion of the image portion where image and non-image portions are mixed in a small range, such as a halftone dot or thin line, in order to obtain stability in the measured value. An example of a transmission densitometer that can measure ultraviolet light transmission density is the aforementioned X-Rite 361T.

After obtaining an image as described above, the thermal recording material of the present invention can be suitably used as a light-shielding mask material, a so-called undercoat material, used when making printing plates such as flexographic printing plates and screen printing plates, but it can also be used for other purposes, such as as a photomask in photolithography. Note that the present invention is not limited to this description.

The present invention will be explained below using examples, but the present invention is not limited to these descriptions. In the descriptions, "%" is based on mass.

<Example 1>

<Preparation of Thermal Recording Material 1>
<Preparation and Coating of Infrared Absorbing Layer Coating Solution>
To 81.0 g of 2-butanone and 24.0 g of methanol, 9.0 g of polyvinyl butyral (Butvar (registered trademark) B-79, manufactured by Eastman Chemical Japan Co., Ltd.) and 0.45 g of exemplary compound (5) (IRT, manufactured by Showa Denko K.K., ε(830)/ε(365)=6.2) as an infrared absorbing dye were added to prepare an infrared absorbing layer coating liquid. This infrared absorbing layer coating liquid was applied to a polyethylene terephthalate base having a thickness of 100 μm (total light transmittance 92%, haze value 4%) using a wire bar so that the dry mass was 1.0 g/m ² , and the coating was dried at 60° C. for 1 minute to form an infrared absorbing layer.

<Preparation of Silver Behenate Dispersion>
20.0 g of silver behenate crystals and 22.0 g of polyvinyl butyral (Butvar B-79) were added to 175 g of 2-butanone, and a silver behenate dispersion (average particle size: 0.8 μm) was obtained using a bead mill (DYNO-MILL KD20B, manufactured by Willy & Bachofen) filled with zirconia beads having a diameter of 0.65 mm.

<Preparation and Coating of Thermal Recording Layer Coating Solution>
To 45.0 g of 2-butanone, 4.2 g of polyvinyl butyral (Butvar B-79), 91.2 g of the above-mentioned silver behenate dispersion, 5.0 g of ethyl 3,4-dihydroxybenzoate, 0.1 g of tetrachlorophthalic anhydride, and 1.9 g of phthalazone were added to prepare a thermosensitive recording layer coating liquid. This thermosensitive recording layer coating liquid was applied onto the infrared absorbing layer already obtained as described above using a wire bar to a silver equivalent value of 1.1 g/ ^m2 , and then dried at 80°C for 3 minutes to form a thermosensitive recording layer.

<Preparation and Application of Protective Layer Coating Solution>
To 25.7 g of toluene, 15.2 g of ACRYDIC WBU-1218 (DIC Corporation; acrylic polyol solution, solid content 30% by mass) and 0.35 g of SEAHOSTAR KE-P250 (Nihon Shokubai Co., Ltd.; hydrophilic silica particles, average particle size 2.5 μm) were added, and the whole was homogenized by stirring. Then, 12 g of CORONATE 2715 (Tosoh Corporation; polyisocyanate modified solution, solid content 90% by mass) was added while stirring to obtain a protective layer coating liquid. This protective layer coating liquid was applied to the above-mentioned thermosensitive recording layer using a wire bar so that the dry mass was 4.5 g/m ² , and the mixture was dried at 80° C. for 3 minutes and then heated at 40° C. for 5 days to form a protective layer. In this way, a thermosensitive recording material 1 was obtained. The total light transmittance of the thermosensitive recording material 1 was 71.3%.

<Preparation of Thermal Recording Material 2>
A heat-sensitive recording material 2 was obtained in the same manner as in the heat-sensitive recording material 1, except that 0.60 g of the exemplary compound (5) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of the heat-sensitive recording material 2 was 66.4%.

<Preparation of Thermal Recording Material 3>
A heat-sensitive recording material 3 was obtained in the same manner as in the heat-sensitive recording material 1, except that 0.80 g of the exemplary compound (5) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of the heat-sensitive recording material 3 was 61.7%.

<Preparation of Thermal Recording Material 4>
A heat-sensitive recording material 4 was obtained in the same manner as in the heat-sensitive recording material 1, except that 1.0 g of exemplary compound (5) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of heat-sensitive recording material 4 was 56.4%.

<Preparation of Thermal Recording Material 5>
A heat-sensitive recording material 5 was obtained in the same manner as in the heat-sensitive recording material 1, except that 1.2 g of the exemplary compound (5) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of the heat-sensitive recording material 5 was 53.2%.

<Preparation of Thermal Recording Material 6>
A thermal recording material 6 was obtained in the same manner as in the thermal recording material 1, except that 0.45 g of exemplary compound (1) (ε(830)/ε(365)=18.5) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of the thermal recording material 6 was 85.1%.

<Preparation of Thermal Recording Material 7>
A thermal recording material 7 was obtained in the same manner as in the thermal recording material 1, except that 0.20 g of the exemplary compound (1) was added as an infrared absorbing dye to the infrared absorbing layer coating liquid. The total light transmittance of the thermal recording material 7 was 87.0%.

<Preparation of Thermal Recording Material 8>
A thermal recording material 8 was obtained in the same manner as in the thermal recording material 1, except that 0.07 g of IX-2-IR-14 (manufactured by Nippon Shokubai Co., Ltd., ε(830)/ε(365)=2.6) was used as the infrared absorbing dye in the infrared absorbing layer coating solution. The total light transmittance of the thermal recording material 8 was 80.8%.

<Formation of a Filled-in Image>
The thus obtained heat-sensitive recording materials 1 to 8 were exposed to an infrared laser using a thermal CTP setter (AURA600E, manufactured by Guangzhou Amsky Technology Co., Ltd.) to obtain a 4000 dpi filled-in image (20 mm (width) x 200 mm (length)). The drum rotation speed of the thermal CTP setter was fixed at 300 rpm, and the laser output was 350 mW.

<Evaluation of UV light transmission density>
After the images were obtained as described above, the ultraviolet light transmission densities of the image and non-image areas in the thermal recording materials 1 to 8 were measured in the ultraviolet mode of X-Rite 361T (manufactured by Videojet X-Rite Co., Ltd.) to obtain the maximum ultraviolet light transmission density (Dmax) of the image area and the ultraviolet light transmission density (Dmin) of the non-image area. The calculation results of Dmax-Dmin are shown in Table 1.

<Ejecta evaluation>
After the images were obtained as described above, the periphery of the image area in each of the thermal recording materials 1 to 8 was observed visually and under a microscope to check whether or not there was any contamination around the image area due to the ejected area. The results, which were judged according to the following criteria, are shown in Table 1.

<Eruption Standards>
Excellent: No contamination from ejected material is observed. Good: Very small amounts of ejected material are observed around the image area (not visible to the naked eye but visible under a microscope).
Passable: The ejection material is visible around the image area, but there is no practical problem. Failed: A large amount of ejection material has fallen and accumulated around the image area, making it unusable.

<Example 2>

<Preparation of Thermal Recording Material 9>
A thermal recording material 9 was obtained in the same manner as in thermal recording material 1, except that 0.15 g of a carbon black dispersion (manufactured by Taisei Kako Co., Ltd., TSBK-007, pigment concentration 12%) was added as a solid content to the infrared absorbing layer coating liquid. The total light transmittance of thermal recording material 9 was 62.0%.

<Preparation of Thermal Recording Material 10>
A thermal recording material 10 was obtained in the same manner as in the thermal recording material 1, except that 0.28 g of a carbon black dispersion (manufactured by Taisei Kako Co., Ltd., TSBK-007, pigment concentration 12%) was added as a solid content to the infrared absorbing layer coating liquid. The total light transmittance of the thermal recording material 10 was 52.0%.

<Formation of a Filled-in Image>
The thus obtained thermal recording materials 9 and 10 were exposed to an infrared laser using a thermal CTP setter (AURA600E, manufactured by Guangzhou Amsky Technology Co., Ltd.) to obtain a 4000 dpi filled image (20 mm (width) x 200 mm (length)). The drum rotation speed of the thermal CTP setter was fixed at 300 rpm, and the laser output was 350 mW.

<Evaluation of UV light transmission density>
After the images were obtained as described above, the ultraviolet light transmission densities of the image and non-image areas of the thermal recording materials 9 and 10 were measured in the same manner as in the thermal recording materials 1 to 8, and the maximum ultraviolet light transmission density of the image area (Dmax) and the ultraviolet light transmission density of the non-image area (Dmin) were obtained. The calculation results of Dmax - Dmin are shown in Table 2.

<Ejecta evaluation>
After the images were obtained as described above, the periphery of the image area in the thermal recording materials 9 and 10 was observed visually and under a microscope to check whether or not there was any contamination due to the ejected portion around the image area. The results, which were judged based on the same criteria as those for the thermal recording materials 1 to 8, are shown in Table 2.

As is clear from the results in Tables 1 and 2, the present invention reduces the amount of material ejected from the surface of a thermal recording material when irradiated with an infrared laser, and produces a thermal recording material that can produce high-contrast images.

Claims (1)

A thermal recording material having an image forming layer on a light-transmitting support, which contains an infrared absorbing dye, a non-photosensitive organic silver salt, and a reducing agent, and which has a ratio of the molar absorption coefficient ε(830) at 830 nm to the molar absorption coefficient ε(365) at 365 nm, ε(830)/ε(365), of 4.0 or more, and has a total light transmittance of 55% or more based on JIS K7361-1:1997.