JP2021160099A - Heat-sensitive recording material - Google Patents

Abstract

To provide a heat-sensitive recording material that has a low haze value and has reduced fluctuations in load.SOLUTION: A heat-sensitive recording material has, on a light-transmitting support, a heat-sensitive recording layer containing a non-photosensitive organic silver salt, an organic reductant, and a binder resin; and also has, on the heat-sensitive recording layer, a protective layer containing a UV-curable resin, talc with an average particle size of 1 μm or less, and colloidal silicas with an average particle size 0.1 or less times that of the talc.SELECTED DRAWING: None

Description

The present invention relates to a heat-sensitive recording material capable of forming an image by heating with a thermal head, and particularly to a heat-sensitive recording material suitable for producing a block copy manuscript.

As a high-quality image recording method, a wet-processed image forming method using silver halide has been generally used. However, a dry image forming method that does not use these treatment solutions has been desired for reasons such as waste liquid treatment of a developing solution and a fixing solution, and restrictions on the installation of developing processing equipment. As a result, image forming systems such as inkjet printers, electrographs, and dye thermal transfer methods are now in practical use. However, with these dry image forming methods, it is difficult to obtain the high resolution required for the block copy manuscript and the excellent light transmission in the non-image area.

Under such circumstances, for example, Patent Document 1 discloses a heat-sensitive recording material having a heat-sensitive recording layer containing a non-photosensitive organic silver salt and an organic reducing agent. Such a heat-sensitive recording material is suitable for producing block copy originals because high contrast equivalent to that of the wet silver salt method can be obtained by directly performing heat-sensitive recording with a printer equipped with a thermal head. In addition to the fact that the recording material is non-photosensitive and does not require a dark room, the direct heat-sensitive printer is low cost, the equipment is highly reliable, and it is easy to miniaturize, so the hurdles for equipment introduction are low. Has advantages.

However, in the direct heat-sensitive method, the frictional resistance on the surface of the heat-sensitive recording material in contact with the thermal head changes due to heating, so that the transfer load of the heat-sensitive recording material changes, so-called load fluctuation, partially occurs depending on the recorded image. It adversely affects the transport accuracy of thermal recording materials. In particular, the image required in the block copy manuscript is a so-called binary image without halftones, and the image part (highest density part) and the non-image part (lowest density part) are clearly separated. The shading of the part is expressed by the area ratio of halftone dots. Therefore, the frictional resistance on the surface of the recording material changes due to a sudden temperature change at the boundary between the image portion and the non-image portion, and the load fluctuation may occur frequently. As a result, the image reproducibility of the thermal recording material is significantly reduced. For example, when a halftone dot image is on an extension line of a straight line image perpendicular to the printing direction, the halftone dots existing on the extension line expand and contract, and macroscopically, a white line (color line of a non-image portion) is formed. Alternatively, an image defect that looks like a black line (a line of heat-sensitive color) appears.

On the other hand, in these heat-sensitive recording materials, it is generally practiced to provide a protective layer on the upper layer of the heat-sensitive recording layer for the purpose of protecting the heat-sensitive recording layer or suppressing the generation of head residue adhering to the thermal head. .. Polyvinyl alcohol and acrylic resin are used as the material used for the protective layer, but the ultraviolet curable resin as disclosed in Patent Document 1 or Patent Document 2 described above is preferably used in terms of strength, and is a heat-sensitive recording material. It is known that it is also excellent in transportability.

In order to improve the transportability of the heat-sensitive recording material, Patent Document 3 describes that silicone rubber particles are contained in the protective layer. Further, Patent Document 4 discloses that various organic or inorganic fillers are added to a protective layer containing an ultraviolet curable resin, and Patent Document 5 discloses that talc and colloidal silica are used in combination as a filler of a protective layer. There is.

However, in the heat-sensitive recording material obtained by the above method, although the decrease in image reproducibility due to load fluctuation is improved, the haze value may be increased. If the haze value of the block copy manuscript is high, the image quality of the printing plate made by using the block copy manuscript deteriorates, which may cause a problem.

Special Table No. 08-505579 Special Table No. 09-504752 Japanese Unexamined Patent Publication No. 2005-88457 Japanese Unexamined Patent Publication No. 2007-83589 Japanese Unexamined Patent Publication No. 2000-158819

An object of the present invention is to provide a heat-sensitive recording material having a low haze value and suppressing the occurrence of load fluctuations.

The above-mentioned problems have been achieved by the following inventions.
A heat-sensitive recording layer containing a non-photosensitive organic silver salt, an organic reducing agent, and a binder resin on a light-transmitting support, an ultraviolet curable resin on the heat-sensitive recording layer, talc having an average particle size of 1 μm or less, and A heat-sensitive recording material having a protective layer containing colloidal silica having an average particle size of 0.1 times or less that of the talc.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a heat-sensitive recording material having a low haze value and suppressing the occurrence of load fluctuations.

It is a binary image used to evaluate the load fluctuation.

Hereinafter, the present invention will be described in detail.

The heat-sensitive recording material of the present invention has a light-transmitting support. Examples of such a light-transmitting support 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 transmittance means that the total light transmittance is 60% or more, and more preferably 70% or more. Further, the light-transmitting support may have an easy-adhesion layer, a hard coat layer, or the like.

In the present invention, the heat-sensitive recording layer contains a non-photosensitive organic silver salt.

The organic silver salt contained in the heat-sensitive recording layer of the present invention is a non-photosensitive, colorless or white organic silver salt, which is reduced by being heated together with an organic reducing agent described later to form a silver image. Is. Specifically, benzoic acid, benzoic acid, bechenic acid, stearic acid, palmitic acid, lauric acid and the like as described in Research Disclosures No. 17029 (II) and No. 29963 (XVI) concerning heat-developed photosensitive materials, etc. Silver salts of organic acids; silver salts of carboxyalkyl thioureas such as 1- (3-carboxypropyl) thiourea, 1- (3-carboxypropyl) -3,3-dimethylthiourea; Complex of aldehydes with aromatic carboxylic acids such as salicylic acid, benzoic acid, 3,5-dihydroxybenzoic acid, 5,5-thiodisalicylic acid and silver; 3- (2-carboxyethyl) Silver salts or complexes of thiones such as -4-hydroxymethyl-4-thiazolin-2-thione, 3-carboxymethyl-4-methyl-4-thiazolin-2-thione; imidazole, pyrazole, urazole, 1, 2, Silver salts or complexes of carboxylic acids selected from 4-triazole, 1H-tetrazole, 3-amino-5-benzylthio-1,2,4-triazole and benzotriazole; silver salts such as saccharin, 5-chlorosalitylaldoxime; Examples include silver salts of mercaptides. Of these, silver organic acid having 10 or more carbon atoms is preferable, and silver stearate and silver behenate are particularly preferably used.

In the present invention, the content of the organic silver salt contained in the heat-sensitive recording layer is determined by the maximum concentration required, but the silver equivalent value is preferably 0.5 to 2.0 g per square meter. This silver conversion value can be measured, for example, by fluorescent X-ray measurement.

In the present invention, the heat-sensitive recording layer contains an organic reducing agent together with the above-mentioned non-photosensitive organic silver salt. Examples of such an organic reducing agent include pyrogallol, 4-stearoyl pyrogallol, isopropyl gallate, ethyl 3,4-dihydroxybenzoate, 2,5-dihydroxybenzoic acid and the like described in US Pat. No. 3,074,809. Can be mentioned. In addition, the polyhydroxyindanes described in US Pat. No. 3,440,049 or JP-A-06-317870 can be mentioned.

The content of the organic reducing agent can vary widely depending on the type of the organic reducing agent and the type of the organic silver salt, but is preferably 0.1 to 3.0 mol per mol of the organic silver salt, and is 0. .5 to 2.0 mol is more preferred. Further, for various purposes, two or more kinds of the above organic reducing agents may be used in combination.

In order to increase the color neutrality of the silver image formed in the high optical density portion, the thermal recording layer is known in the field of thermography or photothermography together with the above-mentioned non-photosensitive silver salt and organic reducing agent, so-called. It is preferable to contain a color adjusting agent. Examples of color preparations are known in the above-mentioned research disclosures on heat-developed photosensitive materials, No. 17029 (V), No. 29963 (XXII), etc., and specifically, imides typified by phthalimide, 3-mercapto. Mercapto compounds typified by -1,2,4-triazole, phthalates, phthalazone, 4-methylphthalic acid, phthalic acid derivatives typified by tetrachlorophthalic anhydride, 1,3-benzoxazine-2,4-dione Examples thereof include benzoxazine derivatives represented by. Further, for various purposes, two or more kinds of the above color preparations may be used in combination.

In the heat-sensitive recording material of the present invention, the heat-sensitive recording layer contains various accelerators and stabilizers and precursors thereof for the purpose of suppressing or promoting the formation of image silver by reduction and improving the storage stability before and after heat recording. You may. Specifically, benzotriazole, 5-methylbenzotriazole, 5-chlorobenzotriazole, 2-mercaptobenzotriazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, which are well known as photographic stabilizers and inhibitors, 2-Mercaptobenzoxazole, 4-hydroxy-6-methyl-1,3,3a,7-tetrazyneden, 1-phenyl-5-mercaptotetrazole, 2-amino-5-mercapto-1,3,4-thiazazole , 3-Mercapto-5-phenyl-1,2,4-triazole, 4-benzamide-3-mercapto-5-phenyl-1,2,4-triazole and the like can be selected. Further, for various purposes, two or more kinds of the above-mentioned accelerator and stabilizer may be used in combination.

In the present invention, the binder resin contained in the heat-sensitive recording layer is preferably a thermoplastic resin. Examples of the thermoplastic resin include polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose and hydroxypropyl cellulose, polysaccharides typified by dextran, acrylic resin, polyester resin, polyurethane resin, vinyl chloride resin, vinyl acetate resin, polyolefin resin, and polyvinyl acetal. Examples thereof include resins and polyvinyl butyral resins. These binders may be used by dissolving them in an organic solvent or water, or may be used in which latex or polymer molecules in which hydrophobic polymer solids are dispersed in the form of fine particles form micelles and are dispersed. In the present invention, the binder resin preferably forms a transparent film after coating and drying. Further, as for these binder resins, two or more kinds of resins that are compatible with each other may be used in combination, if necessary. The mass ratio of the organic silver salt to the binder resin is preferably in the range of 0.2 to 3, and the film thickness of the heat-sensitive recording layer is preferably in the range of 5.0 to 20 μm.

The binder resin described above preferably contains as little free halide ions as possible, such as chloride ions and bromide ions. These halide ions react with silver ions during long-term storage to form photosensitive silver halide, which causes a decrease in the light resistance of the recording material. Specifically, it is preferably 100 ppm or less with respect to the resin solid content.

In the present invention, the heat-sensitive recording layer is formed by preparing a coating liquid containing the above-mentioned organic silver salt, organic reducing agent, binder resin, color tone agent, etc., applying the coating liquid on a light-transmitting support, and drying. It is preferable to do so. Further, various surfactants may be contained for the purpose of improving coatability. As the surfactant, any nonionic, anionic, cationic or the like may be used, and the surfactant is not particularly limited.

The heat-sensitive recording material of the present invention has a protective layer on the above-mentioned heat-sensitive recording layer.

In the present invention, the protective layer contains an ultraviolet curable resin. The ultraviolet curable resin is generally obtained by applying a coating liquid containing a polymerizable oligomer, a polyfunctional acrylate compound, a photopolymerization initiator and the like, and irradiating with ultraviolet rays to cure the resin.

Examples of the polymerizable oligomer include epoxy acrylates, urethane acrylates obtained by reacting various polyols with organic isocyanates and hydroxy group-containing acrylates, polyester acrylates and the like. Examples of the polyfunctional acrylate compound include polyalkylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, dipentaerythritol hexaacrylate, U-6LPA, U-10PA, and U-15HA manufactured by Shin-Nakamura Chemical Industry Co., Ltd. Examples thereof include a commercially available polyfunctional urethane acrylate. In addition to the above-mentioned components, a monomer can be contained. The monomer is used to reduce the viscosity of the coating liquid and to improve the adhesiveness and the properties of the cured film. Specific examples thereof include monofunctional alkylene oxide-modified acrylate, N-vinylpyrrolidone, acryloylmorpholine, N-vinylcaprolactone, isobornyl acrylate, and N-vinylformamide.

Specific examples of the photopolymerization initiator include benzophenone, methyl orthobenzoylbenzoate, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone and the like. Further, a polymerization inhibitor such as p-methoxyphenol may be contained as another additive.

In the present invention, the protective layer contains talc having an average particle size of 1 μm or less. This average particle size refers to the average particle size measured using a laser diffraction method. The talc can be obtained and used as a commercially available product. For example, Nano Ace (registered trademark) D600, D600F, D800, D800F, D1000, D1000F and the like manufactured by Nippon Talc Co., Ltd. can be obtained and used. In forming the protective layer, it is preferable to use talc dispersed in the above-mentioned polymerizable oligomer or polyfunctional acrylate compound. A three-one motor (registered trademark) or a high-speed stirrer such as a homodisper is suitable for dispersing talc.

In the present invention, the protective layer contains colloidal silica having an average particle size of 0.1 times or less the average particle size of talc. This average particle size refers to the average particle size measured using the dynamic light scattering method. Commercially available products include, for example, MEK-ST-40, MEK-ST-L, MEK-ST-ZL, EAC-ST, MEK-AC-2140Z, MEK-AC-4130Y, MEK-AC manufactured by Nissan Chemical Industries, Ltd. -5140Z and the like can be obtained and used. In forming the protective layer, colloidal silica is preferably used by being dispersed in the above-mentioned polymerizable oligomer or polyfunctional acrylate compound. A three-one motor or a high-speed stirrer such as a homodisper is suitable for dispersing colloidal silica.

The total content of talc and colloidal silica contained in the protective layer is preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass with respect to 100 parts by mass of the ultraviolet curable resin. The ratio of the contents of talc and colloidal silica in the protective layer is preferably in the range of 1/9 to 9/1 in terms of mass ratio.

In the present invention, the protective layer is formed by further impregnating the coating liquid containing the above-mentioned polymerizable oligomer, polyfunctional acrylate compound, and photopolymerization initiator with the above-mentioned talc and colloidal silica, and applying and drying the coating liquid. After that, it is preferable to irradiate with ultraviolet rays to cure.

The film thickness of the protective layer can vary widely depending on the type of UV curable resin used, the required heat sensitivity, the matchability with the thermal head, etc., but it is preferably selected from the range of 0.1 to 10 μm, more preferably. Is 0.5 to 5 μm.

In the present invention, there is no particular limitation on the coating method of the heat-sensitive recording layer and the protective layer described above, and E.I. D. Cohen, E.I. B. Gutoff, "Modern Coating and Drying Technology", WILEY-VCH, Inc. You can choose from a variety of coating methods as described in New York, 1992. Further, it is possible to apply a plurality of layers at the same time.

If necessary, the heat-sensitive recording material of the present invention further provides an intermediate layer between the heat-sensitive recording layer and the protective layer, and an underlayer between the light-transmitting support and the heat-sensitive recording layer, in addition to the above-mentioned heat-sensitive recording layer and protective layer. An antistatic layer or the like may be provided on the light transmissive support on the back surface side of the coat layer and the thermal recording layer.

Hereinafter, the present invention will be described with reference to examples, but this description does not limit the present invention.

<Example 1>
<Preparation of silver behenate dispersion>
20 g of silver behenate crystals and 20 g of polyvinyl butyral (Buvar® B-79 manufactured by Eastman Chemical Japan Co., Ltd.) were added to 180 g of 2-butanone and dispersed using a bead mill to obtain a silver behenate dispersion. ..

<Preparation and application of thermal recording layer coating liquid>
To 10 g of 2-butanone, 0.5 g of polyvinyl butyral (Buvar B-79), 10 g of the silver behenate dispersion, 0.3 g of ethyl 3,4-dihydroxybenzoate, 0.1 g of tetrachlorophthalic anhydride, 0 phthalazone. .2 g was added and mixed to prepare a heat-sensitive recording layer coating solution. This heat-sensitive recording layer coating liquid is applied to a PET base (total light transmittance 90%) having a thickness of 100 μm so as to have a silver equivalent of 1.5 g / m ^2, and dried at 80 ° C. to obtain a heat-sensitive recording layer. rice field. The coating thickness of the obtained heat-sensitive recording layer after drying was 18 μm.

<Preparation and application of protective layer coating liquid>
To 5.0 g of 2-butanone, 5.0 g of Beamset (registered trademark) 3702 (manufactured by Arakawa Chemical Industry Co., Ltd .; a mixture containing an epoxy acrylate oligomer, a polyfunctional acrylate compound, and a photopolymerization initiator) was added as an ultraviolet curable resin. After obtaining a solution of 10 g (of which the binder mass is 2.9 g), 0.7 g of Nanoace D600 (manufactured by Nippon Tarku Co., Ltd .; average particle size 0.6 μm) as talc and MEK-ST-40 (of which, as colloidal silica) are used. Nissan Chemical Co., Ltd .; average particle size 12 nm) was added in a solid content of 0.65 g, and the mixture was dispersed at 300 rpm for 3 hours with a three-one motor to obtain a protective layer coating solution. On the heat-sensitive recording layer obtained as described above, the protective layer coating liquid is applied with a wire bar so that the coating thickness after drying is 2 μm, dried at 80 ° C., and then a high-pressure mercury lamp. Was irradiated under the conditions of an irradiation distance of 10 cm and a transport speed of 5 m / min to cure the protective layer, and the heat-sensitive recording material of Example 1 was obtained.

<Examples 2 and 3, Comparative Example 3, Comparative Example 4>
In the preparation of the heat-sensitive recording material of Example 1, the protective layer coating liquid 1 was changed to talc and colloidal silica shown in Table 1, and the protective layer was applied in the same manner as in Example 1. , Example 3, Comparative Example 3 and Comparative Example 4 thermal recording materials were obtained.

<Comparative example 1>
In the preparation of the heat-sensitive recording material of Example 1, the heat-sensitive recording material of Comparative Example 1 was obtained in the same manner except that colloidal silica was not added to the protective layer coating liquid.

<Comparative example 2>
In the preparation of the heat-sensitive recording material of Example 1, the heat-sensitive recording material of Comparative Example 2 was obtained in the same manner except that talc was not added to the protective layer coating liquid.

<Haze evaluation>
The heat-sensitive recording materials of Examples 1 to 3 and Comparative Examples 1 to 4 obtained as described above were evaluated using a haze meter HZ-V3 (manufactured by Suga Test Instruments Co., Ltd.), and the results are shown in Table 1. It was shown to. The lower the haze value, the less cloudy it is, which is preferable. Those having a haze value of less than 40% were evaluated as ◯, and those having a haze value of 40% or more were evaluated as x. The results are shown in Table 1.

<Load fluctuation evaluation>
The load variation shown in FIG. 1 was carried out by the thermal printer TDP-750 manufactured by Mitsubishi Paper Mills Limited using the thermal recording materials of Examples 1 to 3 and Comparative Examples 1 to 4 under the condition of a printing speed of 2 msec / line. A binary image was printed to evaluate. The image size of FIG. 1 is 210 mm (width) × 220 mm (length), and within that, a halftone dot image area (a) of 70 mm (width) × 220 mm (length) (image area ratio: 50%, net). Point shape: square, number of lines 100 lpi) and 10 horizontal lines with a thickness of 10 mm and a length of 70 mm facing the width direction at 10 mm intervals in the length direction (the left and right lines are on the extension of each line). Has a linear image area (b) in which) is located. The arrow (c) in FIG. 1 indicates the printing direction. In the heat-sensitive recording material printed in this way, when load fluctuation occurs, the halftone dot image existing on the extension line of the linear image facing the width direction expands and contracts in the printing direction, and is macroscopically white line-shaped. Alternatively, an image defect that looks like a black line appears.

In the heat-sensitive recording material printed as described above, the effect of suppressing load fluctuation was evaluated in two stages, and the results are shown in Table 1. Specifically, the ratio of enlargement or reduction in the printing direction of the halftone dot image existing on the extension line of the linear image was less than 1%, and no image defect appearing as white line or black line was observed. ○, the halftone dot image existing on the extension line of the linear image has an enlargement or reduction ratio of 1% or more in the printing direction, and an image defect that looks like a white line or a black line is observed. It was marked with x. The results are shown in Table 1.

As is clear from the results in Table 1, it can be seen that the present invention provides a heat-sensitive recording material having a low haze value, suppressing the occurrence of load fluctuations, and having excellent image reproducibility.

(A) Halftone dot image area (b) Linear image area (c) Printing direction

Claims (1)

A heat-sensitive recording layer containing a non-photosensitive organic silver salt, an organic reducing agent, and a binder resin on a light-transmitting support, an ultraviolet curable resin on the heat-sensitive recording layer, talc having an average particle size of 1 μm or less, and A heat-sensitive recording material having a protective layer containing colloidal silica having an average particle size of 0.1 times or less that of the talc.

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