JP5161611B2 - Direct heat-sensitive lithographic printing plate - Google Patents

Description

  The present invention enables thermal printing with a thermal head that can obtain an image with high resolution and can be handled in a bright room and can be used for printing as it is without requiring a processing solution for plate making. Relates to a direct heat-sensitive lithographic printing plate.

  A CTP (computer-to-plate) printing plate that makes a lithographic printing plate based on a digital signal from computer information is generally exposed to a photosensitive material directly using a laser and developed using a developer. Has been done. However, the treatment of the waste liquid generated by the development process becomes an environmental load. Recently, there is a strong demand for the market with an emphasis on protecting the global environment, and there is a strong demand for improvements in printing plate making systems.

  Therefore, many methods for making a lithographic printing plate without using a processing solution in development processing and the like have been proposed. These are called processless printing plates by not performing development processing using liquid, and as this type of printing plate, the type that removes the image part or non-image part by ablation using laser light, There have been proposed a type in which an image portion is formed by an ink jet method, a type in which an image portion is formed by using heat-meltable or thermoplastic fine particles, and the like. However, in the type using ablation, contamination inside the exposure apparatus due to the ablated surface scattered matter is a problem. In the ink jet type, an image forming substance, that is, a hydrophobic substance is discharged as a liquid on the surface of a printing plate having an ink receiving layer on the outermost surface, and after ink landing on the ink receiving layer, it is solidified or cured by light or heat. Accordingly, there is a problem of plate making instability due to nozzle clogging that is likely to be solidified or cured at the discharge nozzle outlet.

  In the type that uses heat-meltable fine particles, especially when the image is formed by heat and the non-image part is peeled off on the printing machine, the non-image part is peeled off on the printing machine. The accumulation of objects becomes a problem.

  In addition, a type that can be printed as it is without removing the non-image portion has been proposed. For example, there is a heat-sensitive lithographic printing plate described in Patent Document 1. Such a heat-sensitive lithographic printing plate has a layer containing a hydrophilic resin and heat-fusible fine particles on the support as the outermost layer, and there is no waste liquid resulting from development, and it is cheaper than a laser drawing apparatus. Since a head can be used, it is effective as a simple printing plate system. However, the heat-sensitive lithographic printing plate heats a hydrophilic heat-sensitive layer imagewise, and uses the heated portion as an image portion having ink acceptability, while the unheated portion is used as a hydrophilic non-image portion. For this reason, a substance that becomes ink-accepting remains in the non-image area as it is. For this reason, there is a problem that printing stains are likely to occur depending on printing conditions.

In particular, when the above thermal lithographic printing plate is used in a direct thermal method in which thermal printing is performed using a thermal head, the non-printing portion (non-image portion) also comes into contact with the thermal head, so that fogging occurs even though it is weak. Depending on the conditions, there may be inconveniences in printability, such as plate surface contamination at the start of printing (at the time of printing) and stain properties of the halftone dot shadow portion inferior to other types of lithographic printing plates. Several printing plates (Patent Documents 2, 3, and 4) having a hydrophilic layer under the image-forming layer having heat-fusible fine particles have also been proposed, but at the time of printing by a thermal printing method using a thermal head. It did not pay attention to the improvement of dirtiness, and a sufficient effect was not obtained. In particular, Patent Document 4 uses a water-dispersible filler having an average particle size of 0.2 to 10 μm, which affects the surface roughness of the outermost layer. In thermal printing with a thermal head, it is desirable that the outermost layer be as smooth as possible in order to make the heat conduction from the heating element uniform. If the surface roughness exceeds 0.2 μm, printing unevenness occurs, In some cases, good print reproduction could not be obtained.
JP 2001-180144 A JP 2004-195724 A JP 2006-187911 A JP 2000-122269 A

  In view of the above problems, the problem of the present invention is that the direct heat-sensitive lithographic printing plate that is thermally printed with a thermal head that is excellent in workability in a bright room without generation of waste liquid has no print unevenness, and printability, In particular, it is an object of the present invention to provide a direct heat-sensitive lithographic printing plate in which the stain at the time of printing and the stain property of the halftone dot shadow portion are improved and the ink placement at the time of printing the image portion is not hindered.

It has been found that the above object of the present invention can be achieved by the direct thermal lithographic printing plate described below.
1. An intermediate layer containing gelatin and hydrophilic inorganic fine particles having an average particle diameter of 0.1 μm or less is provided on the support as a top layer having a heat sensitive layer containing gelatin and heat-meltable fine particles. A direct heat-sensitive lithographic printing plate characterized by comprising:
2. 2. The direct heat-sensitive lithographic printing plate as described in 1 above, wherein the outermost layer contains substantially no hydrophilic inorganic fine particles.

  According to the present invention, it corresponds to the direct drawing of the thermal head, there is no generation of waste liquid, it is extremely excellent in workability in a bright room, there is no printing unevenness, especially for stains at the start of printing and dot stains. On the other hand, it is possible to provide a direct heat-sensitive lithographic printing plate that is superior to the ink and does not hinder ink loading when the image portion is printed.

  The direct heat-sensitive lithographic printing plate used in the present invention corresponds to a thermal printing (direct drawing) method using a thermal head, and uses a gelatin as a binder on a support, and a layer containing fine particles of heat melting such as latex. As the outermost layer, it has an intermediate layer containing gelatin and hydrophilic inorganic fine particles with an average particle size of 0.1 μm or less directly under the heat-sensitive layer, and is mounted on a printing press after image drawing and printing is performed A lithographic printing plate of the type in which none of the layers is substantially peeled off and dissolved and removed and development is not performed at all.

  The heat-sensitive layer of such a direct heat-sensitive lithographic printing plate maintains hydrophilicity when no heat is applied (non-image part), but when heat is applied, the heat-melting fine particles contained in the part are mutually, Also, the binder is melted, and the heated part is converted into hydrophobicity as a whole. Therefore, in the direct heat-sensitive lithographic printing plate of the present invention, the heat-applied portion is converted to hydrophobic, so that ink can be received during printing. However, even in the non-image area where heat is not applied, hydrophobic heat-melting fine particles are present, and the hydrophilicity of the entire layer is reduced. For this reason, by providing the hydrophilic intermediate layer directly under the outermost layer, the water absorption amount of the moisturizing liquid as the whole plate can be improved, and the printing smearing property is improved. However, if the amount of water absorption is large, the ink loading may be hindered and printing may be adversely affected, and if the water absorption absorbs the intermediate layer becomes weak, the printing durability will be affected. Therefore, as a result of paying attention to these balances, the present inventors have found that gelatin having excellent compatibility between water absorption / retention ability and mechanical strength and hydrophilic inorganic fine particles having an average particle diameter of 0.1 μm or less are contained. By providing a heat-sensitive layer containing gelatin as a binder, it is excellent against smudges at the time of printing and halftone dot shadows, and does not interfere with ink loading at the time of image printing. And found that printing can be performed in a well-balanced manner. Further, hydrophilic inorganic fine particles having an average particle size of 0.1 μm or less are contained in the intermediate layer, so that the smoothness of the outermost layer is not adversely affected. Therefore, even in thermal printing with a thermal head, the outermost fine particles are uniformly formed on the outermost layer. Because of contact, there is no uneven printing.

  The direct heat-sensitive lithographic printing plate of the present invention will be described in detail. The direct heat-sensitive lithographic printing plate of the present invention has a heat-sensitive layer containing gelatin and heat-meltable fine particles as an outermost layer, and an intermediate containing gelatin and hydrophilic inorganic fine particles having an average particle diameter of 0.1 μm or less immediately below the heat-sensitive layer. Has a layer. Of course, in addition to these two layers, a layer for improving the adhesion to the support described later may be applied as an undercoat layer. Moreover, 0.5-10 micrometers is preferable and, as for the thickness of the outermost layer, More preferably, it is 1-5 micrometers. The outermost layer is preferably as smooth as possible so that thermal printing with a thermal head is good, and the centerline surface roughness Ra is preferably 1 μm or less, more preferably 0.5 μm or less.

  In addition, the direct heat-sensitive lithographic printing plate of the present invention is a type of lithographic plate that is mounted on a printing machine after image drawing and does not undergo any development treatment, in which neither layer is substantially peeled off or dissolved even during printing. It is a print version. Therefore, since no development process is performed on the plate making or printing machine, the property for peeling / dissolving / removing is unnecessary, and the heat-sensitive layer and the intermediate layer to be used are cross-linked in order to improve the resistance to mechanical stress during printing as much as possible. It is preferable that the film is hardened.

  The intermediate layer of the direct heat-sensitive lithographic printing plate of the present invention is preferably composed mainly of gelatin for the purpose of improving printability. Here, the constituent main body means that gelatin is 50% by mass or more based on the total dry solid content of the intermediate layer. Moreover, the dye for visibility at the time of coating and various activators for improving coating property can be added suitably. The thickness of the intermediate layer is adjusted according to the type of gelatin and the hardening agent to be described later, but considering the balance between stain resistance and ink loading, it is 1/2 to 2 times the thickness of the outermost layer. It is preferable to do.

  Examples of the hydrophilic inorganic fine particles contained in the intermediate layer of the present invention include colloidal silica, titanium dioxide, and alumina. These sizes are preferably directly below the centerline surface roughness Ra of the heat-sensitive lithographic printing plate so as not to affect the surface roughness of the outermost layer. For example, the output resolution is 600 dpi or more, and 1200 dpi or more. Then, since the reproducibility is greatly influenced by the surface smoothness, it is preferably less than half the center line surface roughness Ra of the outermost layer of the direct heat-sensitive lithographic printing plate. Considering that uniform dispersion functions effectively, the average particle size is 0.1 μm or less, more preferably 0.02 μm or less. The content is preferably 1 to 20% by mass of the hydrophilic inorganic fine particles with respect to gelatin.

  On the other hand, for the purpose of preventing printing soiling in the outermost layer of the direct heat-sensitive lithographic printing plate of the present invention, hydrophilic inorganic fine particles such as colloidal silica, titanium dioxide, and alumina may be included depending on the surface roughness. Apart from the effect on the surface, these hydrophilic inorganic fine particles are present on the outermost surface, so depending on various printing conditions such as printing ink and fountain solution used for printing, printing speed and printing pressure, ink loading on the image area In some cases, it is difficult to obtain a stable printed matter. Therefore, it is preferable that the outermost layer does not substantially contain hydrophilic inorganic fine particles, and it is preferable that 1% by mass or more of hydrophilic inorganic fine particles are not contained in the heat-sensitive layer.

  Next, the gelatin contained in the heat-sensitive layer and the intermediate layer of the present invention will be described. As the gelatin used for the outermost layer and the intermediate layer of the direct heat-sensitive lithographic printing plate of the present invention, any gelatin made from animal collagen can be used, but collagen obtained from pig skin, cow skin, and cow bone can be used. Gelatin as a raw material is preferred. The type of gelatin is not particularly limited, but in addition to lime-processed gelatin and acid-processed gelatin, JP-B-38-4854, JP-B-39-5514, JP-B-40-12237, JP-B-42- No. 26345, US Pat. No. 2,525,753, US Pat. No. 2,594,293, US Pat. No. 2,614,928, US Pat. No. 2,763,639 US Pat. No. 3,118,766, US Pat. No. 3,132,945, US Pat. No. 3,186,846, US Pat. No. 3,312,553, Examples include gelatin derivatives described in British Patent No. 1,033,189 and the like, and these can be used alone or in combination of two or more.

  Further, examples of the hardening agent preferably contained in the heat-sensitive layer and the intermediate layer of the direct heat-sensitive lithographic printing plate of the present invention include inorganic compounds such as chromium alum, aldehydes such as formalin, glyoxal, malealdehyde, and glutaraldehyde. N-methylol compounds such as urea and ethylene urea, mucochloric acid, aldehyde-related compounds such as 2,3-dihydroxy-1,4-dioxane, 2,4-dichloro-6-hydroxy-s-triazine salts, Compounds having active halogen such as 2,4-dihydroxy-6-chloro-s-triazine salt, divinyl sulfone, divinyl ketone, N, N, N-triacryloylhexahydrotriazine, ethyleneimino which is an active three-membered ring Compounds having two or more groups or epoxy groups in the molecule, dia as a polymer hardener May be used alone or two or more of various compounds such as dehydrogenase starch. Further, a hydrophilic resin other than gelatin may be further contained in the heat-sensitive layer and the intermediate layer of the direct heat-sensitive lithographic printing plate of the present invention in a range not exceeding 50% by mass.

  The heat-meltable fine particles according to the present invention will be described. The heat-meltable fine particles according to the present invention are those that are changed from a fine particle form and integrated by melting or fusing together by heating. Specifically, it is a finely divided heat fusible compound that is solid at room temperature, such as thermoplastic resins and waxes, and any solid or water-dispersed compound can be used. Examples include polymer latex that can be dispersed in an aqueous solvent. Examples of these dispersed states include those in which fine particles of a water-insoluble hydrophobic polymer are dispersed and those in which polymer molecules are dispersed in a molecular state or forming micelles. These average particle diameters are preferably 1 to 50000 nm, more preferably 5 to 1000 nm. The particle size distribution of the polymer latex is not particularly limited, and may be a wide particle size distribution or a monodispersed particle size distribution.

  More specifically, for example, thermoplastic resins include polypropylene, polybutadiene, polyisoprene, polystyrene, diene (co) polymers such as ethylene-butadiene copolymer, styrene-butadiene copolymer, and methyl methacrylate-butadiene. Copolymers, synthetic rubbers such as acrylonitrile-butadiene copolymer, polymethyl methacrylate, methyl methacrylate-methacrylic acid copolymer, methyl acrylate- (N-methylolacrylamide) copolymer, (meth) acryl such as polyacrylonitrile Acid ester, (meth) acrylic acid copolymer, polyvinyl acetate, vinyl acetate-vinyl propionate copolymer, vinyl ester (co) polymer such as vinyl acetate-ethylene copolymer, polyvinyl chloride, polyvinylidene chloride , Polystyrene etc. Copolymers thereof, and the like.

  In addition, heat fusible compounds that are solid at room temperature include paraffins and waxes such as carnauba wax, microcrystalline wax, paraffin wax, polyethylene wax, lauric acid, stearic acid, oleic acid, palmitic acid, behenic acid, etc. And fatty acids such as montanic acid and esters and amides thereof. Or aromatic ether, ester, fatty acid amide, etc. are mentioned. Specifically, stearic acid amide, ethylene bis stearic acid amide, methylol behenic acid amide, oleic acid amide, palmitic acid amide and other fatty acid amides, p-benzylbiphenyl, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid Phenyl, dibenzyl oxalate, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, di-o-chlorobenzyl adipate, 1,2-bis (3-methylphenoxy) ethane, 1,2- Bis (3,4-dimethylphenyl) ethane or the like can be used.

These heat-meltable fine particles can be used as a mixture of two or more, if necessary, or may be a plurality of layers. In particular, a resin that self-crosslinks when heated is particularly preferable. The amount contained in the outermost layer of the direct heat-sensitive lithographic printing plate according to the present invention is optimized depending on the balance with the hydrophilic resin used and the desired sensitivity, but is in the range of 0.01 to 10 g / m ² . And preferably 0.1 to 5 g / m ² . More preferably, it is 0.5-2 g / m < ² >.

  The heat-sensitive layer of the direct heat-sensitive lithographic printing plate of the present invention may have a mass ratio in the range of 1: 1 to 10: 1 as the balance between the heat-meltable fine particles and gelatin described above. In detail, it is preferable to optimize the balance between ink transportability and water retention in a printing test depending on the material used.

  In order to coat the outermost layer, an anionic, cationic or nonionic surfactant may be used as an auxiliary agent, and a matting agent, thickener, or antistatic agent may be used. . Furthermore, a heat-sensitive color former, a colorant and the like that do not have photothermal conversion ability for image visibility can also be used.

  As the support of the direct heat-sensitive lithographic printing plate of the present invention, a support having water resistance is preferable as a characteristic to be used as a printing plate. For example, a plastic film, resin-coated paper, water-resistant paper, and the like can be used. Specifically, plastic films such as polyolefins such as polyethylene and polypropylene, polyethersulfone, polyester, poly (meth) acrylate, polycarbonate, polyamide, and polyvinyl chloride, and resin-coated paper with these plastics laminated or coated on the surface, melamine Paper that has been water-resistant by a wet paper strength agent such as formaldehyde resin, urea formaldehyde resin, or epoxidized polyamide resin can be used.

  In addition to the above, it is also possible to use a composite support in which a plastic film and a metal plate (for example, iron, stainless steel, aluminum, etc.) or a material such as paper coated with polyethylene (also referred to as a composite substrate) is appropriately bonded. . These composite base materials may be bonded before forming the outermost layer or intermediate layer of the present invention, may be bonded after forming the outermost layer or intermediate layer, and are bonded immediately before being attached to the printing press. May be combined.

  The thickness of the support is preferably about 100 to 300 μm from the viewpoint of the recording suitability of the thermosensitive plate making apparatus and the lithographic printing press suitability.

  The surface of the above-mentioned support having water resistance is provided with an easy adhesion treatment such as a plasma treatment, a corona discharge treatment, a deep ultraviolet irradiation treatment or an undercoat layer in order to enhance the adhesion with the intermediate layer of the present invention. Processing may be performed.

  As the undercoat layer according to the present invention, a layer containing gelatin or latex is more preferably formed as a single layer or two layers on a support. The thickness of the undercoat layer is usually about 0.1 to 10 μm in dry film thickness. When the two-layer structure is used, the layer close to the water-resistant support (lower layer) is preferably a latex-containing layer from the viewpoint of adhesion to the water-resistant support, Further, the layer closer to the intermediate layer (upper layer) is preferably a layer containing gelatin from the viewpoint of adhesion to the intermediate layer.

  The latex used for the undercoat layer is specifically an acetal resin such as polyvinyl butyral, a polyester resin having a hydroxyl group at the molecular chain end, a (meth) acrylic acid- (meth) acrylic acid ester copolymer, vinylidene chloride. -Vinyl chloride copolymer etc. are mentioned.

  After applying the undercoat layer, an intermediate layer is applied, but in the coating method in which the coating coater is in direct contact with the support, such as wire bar coating and gravure coating, the undercoat layer is preferably cured, It is necessary to add a hardener that hardens gelatin. In the present invention, any hardener that satisfies the effects of the present invention can be used, but typical hardeners include vinyl, vinylsulfone, epoxy, peptide, melamine, and formalin. Aldehyde-based, triazine-based, etc. Among them, vinyl-based and epoxy-based are preferable.

  The undercoat layer is preferably provided with a conductive layer such as a conductive polymer-containing layer or a metal oxide-containing layer described in JP-A-7-20596. Such a conductive layer may be coated on either side as long as it is on the support, but it is preferably coated on the opposite side of the layer having an image forming function with respect to the support. When this conductive layer is provided, the chargeability is improved, the adhesion of dust and the like is reduced, and white spots failure during printing is greatly reduced.

For image formation of the direct heat-sensitive lithographic printing plate of the present invention, for example, a line printer using a thick film or thin film line head, a serial printer using a thin film serial head, or the like can be used. The recording energy density is preferably 10 to 100 mJ / mm ² , and the head image recording density is preferably 600 dpi or more in order to obtain a high-quality output image that can withstand commercial printing.

  Hereinafter, the present invention will be described in detail with reference to examples. In the description, “parts” and “%” are based on mass unless otherwise indicated.

  Double-sided polyethylene coated paper (RC paper) with a thickness of 150 μm is corona discharge processed, and then an intermediate layer coating solution and an outermost layer (image forming layer) coating solution having the following formulation are applied and dried to directly heat-sensitive lithographic printing plate Was made. The dry coating amounts were 1 μm and 2 μm, respectively. The centerline surface roughness Ra of the produced direct heat-sensitive lithographic printing plate was 0.2 μm as measured using a SURFCOM stylus meter manufactured by Tokyo Seimitsu Co., Ltd.

[Outermost layer coating solution]
・ Hydrophilic resin: gelatin (12% aqueous solution) 80 parts (IK3000 manufactured by Nippi)
・ Fusible fine particles; carboxy-modified styrene-butadiene copolymer (solid content 45%)
30 parts (Racstar 7132-C, manufactured by Dainippon Ink & Chemicals, Inc.)
Heat-meltable fine particles: 1,2-bis (3-methylphenoxy) ethane 30 parts (KS-232 manufactured by Sanko) dispersion (30% dispersion)
-Developer: 4-hydroxy-4'-isopropoxydiphenylsulfone 30 parts (D-8 manufactured by Nippon Soda Co., Ltd.) dispersion (30% aqueous dispersion)
Color developing agent: 9 parts of 3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2 manufactured by Yamamoto Kasei Co., Ltd.) dispersion (30% aqueous dispersion)
・ Hardener: 1.2 parts divinyl sulfone

[Intermediate layer coating solution 1]
Gelatin (12% aqueous solution) 80 parts (IK3000 manufactured by Nippi)
・ Divinylsulfone (hardener) 1.2 parts ・ Colloidal silica 5 parts (Snowtex C manufactured by Nissan Chemical Industries, Ltd .; SiO ₂ concentration 20%, particle size 0.01 to 0.02 μm)

  The direct thermosensitive lithographic printing plate produced by the above method was applied at a printing speed of 2 msec / line with a direct thermal printer (equipped with a 1200 dpi thermal print head manufactured by Toshiba Hokuto Electronics Co., Ltd. (head average resistance value 7 kΩ)). A dot image of 120 lpi was recorded under printing conditions of energy 0.02 W / dot.

  Next, the printing machine is 5,000 prints using Hamada Printing Machine's offset printing machine HAMADA H234, the ink is T & K TOKA's Super TEKPLUS Black L, and the dampening liquid is SLM-OD30 made by Mitsubishi Paper Industries. It was.

  When the quality of the printed material was evaluated, the stain at the start of printing (the number of printed materials discharged from the printing machine immediately after the start of printing was a good paper) was good at the 10th sheet, immediately after the start of printing. From the 5th sheet, the number of sheets reaching the appropriate density at the start of printing, which counted the number of sheets printed from the printing machine with the appropriate image density (as an index of ink acceptability (ink transferability) in the image area), was good. Met. In addition, the reproducibility of the shadow part having an image area ratio of 80% or more in the halftone dot part was observed in the state where the printing was started and the printed matter had an appropriate density. Further, the highlight area of the image area ratio 5% of the halftone dot portion of the 5000th printed material was also good.

Instead of the colloidal silica used in the intermediate layer coating liquid 1, another colloidal silica (Nissan Chemical Industries Snowtex ZL; SiO ₂ concentration 40%, particle size 0.07 to 0.1 μm) is 2.5. A heat-sensitive lithographic printing plate was produced in the same manner as in Example 1 except that a part was added. The direct thermal lithographic printing plate produced had a centerline surface roughness Ra of 0.2 μm. Further, printing evaluation was performed in the same manner. The smear at the start of printing, the number of sheets reaching the appropriate density at the start of printing, and the reproducibility of the shadow part with an image area ratio of 80% or more at the halftone part were the same as in Example 1, but the halftone part of the 5000th printed material The image area ratio 5% highlight part had a slightly lower ink density than the 1000th printed material.

Instead of the colloidal silica used in the intermediate layer coating solution 1, a commercially available colloidal alumina (Alumina sol-520 manufactured by Nissan Chemical Industries, Ltd .; Al ₂ O ₃ concentration 20%, particle size 0.01 to 0.02 μm) was used. A heat-sensitive lithographic printing plate was produced in the same manner as in Example 1 except that a part was added. The direct thermal lithographic printing plate produced had a centerline surface roughness Ra of 0.2 μm. Furthermore, when printing evaluation was carried out in the same manner, a good printed matter similar to that in Example 1 was obtained.

In the outermost layer coating solution, commercially available colloidal silica (Snowtex C manufactured by Nissan Chemical Industries, Ltd .; SiO ₂ concentration 20%, particle diameter 0.01 to 0.02 μm) is 5 with respect to the total amount of the outermost layer coating solution. A heat-sensitive lithographic printing plate was produced in the same manner as in Example 1 except that a part was added. The direct thermal lithographic printing plate produced had a centerline surface roughness Ra of 0.2 μm. Further, printing evaluation was performed in the same manner. Although the stain at the start of printing was even better at the third sheet, the number of sheets reaching the appropriate density at the start of printing was the 20th sheet. In addition, the reproducibility of the shadow portion having an image area ratio of 80% or more in the halftone dot portion was observed in a state where the printing was started and the printed matter had an appropriate density. However, the ink density of the highlight area with a 5% image area ratio at the halftone dot portion of the 5000th printed material was slightly lower than that of the 1000th printed material.

Comparative Example 1
A heat-sensitive lithographic printing plate was produced in the same manner as in Example 1 except that the intermediate layer coating solution 1 was changed to the following intermediate layer coating solution 2, and printing evaluation was performed in the same manner. Although the number of sheets reaching the appropriate density at the start of printing was good starting from the fifth sheet, the stain at the start of printing deteriorated to the 30th sheet. As a result, although the highlight area with an image area ratio of 5% was good, the reproducibility of the shadow area with an image area ratio of 80% or more was observed, but partial clogging occurred.

[Intermediate layer coating solution 2]
Gelatin (12% aqueous solution) 80 parts (IK3000 manufactured by Nippi)
・ Divinylsulfone (hardener) 1.2 parts

Comparative Example 2
A heat-sensitive lithographic printing plate was produced directly in the same manner as in Example 1 except that the intermediate layer coating solution 1 was changed to the following intermediate layer coating solution 3, and printing evaluation was performed in the same manner. When printed with a direct thermal printer, the halftone dot image reproduced on the direct heat-sensitive lithographic printing plate showed no uncolored part compared to the plate-making product obtained in Example 1, but the image was partially There was a thin part and the feeling of roughness was strong. Further, although the stain at the start of printing was up to the fifth sheet, the number of sheets reaching the appropriate density at the start of printing deteriorated from the tenth sheet, and the printed image was better than Example 1 because the feeling of shading of the halftone image was reflected. Was not obtained. Further, the image area ratio 5% highlight portion of the halftone dot portion of the 5000th printed material had a lower ink density than the 1000th printed material.

[Intermediate layer coating solution 3]
Instead of the colloidal silica of the intermediate layer coating solution 1, 5 parts of commercially available silica (MP-2040 manufactured by Nissan Chemical Industries, Ltd .; SiO ₂ concentration 40%, average particle size 0.2 μm) was added.

Comparative Example 3
A heat-sensitive lithographic printing plate was produced directly in the same manner as in Example 1 except that the intermediate layer coating solution was changed to the following intermediate layer coating solution 4, and printing evaluation was performed in the same manner. When printing with a direct thermal printer, the halftone dot image reproduced on the direct heat-sensitive lithographic printing plate had a blurring print unevenness that was not partially colored, and a good plate-making product could not be obtained. . The printed matter was reproduced in the same manner, and a good printed matter was not obtained from the start of printing.

[Intermediate layer coating solution 4]
Instead of the colloidal silica of the intermediate layer coating solution 1, 5 parts of commercially available silica (Silicia 435 manufactured by Fuji Silysia Chemical Ltd .; average particle size 2.5 μm) was added.

Comparative Example 4
A heat-sensitive lithographic printing plate was directly produced in the same manner as in Example 1 except that the following outermost layer coating solution 2 was used, and printing evaluation was carried out in the same manner. The appropriate density reached at the start of printing was as good as the 5th sheet, but the stain at the start of printing deteriorated to the 50th sheet. As a result, although the highlight area with an image area ratio of 5% was good, the reproducibility of the shadow area with an image area ratio of 80% or more was observed, but partial clogging occurred.

[Outermost layer coating solution 2]
Hydrophilic resin: 100 parts of silanol group-modified polyvinyl alcohol (10% aqueous solution) (Kuraray R polymer R1130 manufactured by Kuraray Co., Ltd.)
・ Fusible fine particles; carboxy-modified styrene-butadiene copolymer (solid content 45%)
30 parts (Rack Star 7132-C, manufactured by Dainippon Ink & Chemicals, Inc.)
Heat-meltable fine particles: 1,2-bis (3-methylphenoxy) ethane 30 parts (KS-232 manufactured by Sanko) dispersion (30% dispersion)
-Developer: 4-hydroxy-4'-isopropoxydiphenylsulfone 30 parts (D-8 manufactured by Nippon Soda Co., Ltd.) dispersion (30% aqueous dispersion)
Color developing agent: 9 parts of 3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2 manufactured by Yamamoto Kasei Co., Ltd.) dispersion (30% aqueous dispersion)
・ Crosslinking agent: Glyoxal 0.8 parts

Comparative Example 6
A heat-sensitive lithographic printing plate was produced in the same manner as in Example 1 except that the intermediate layer coating solution 1 was changed to the following intermediate layer coating solution 5 and printing evaluation was performed in the same manner. Although the number of sheets reaching the appropriate density at the start of printing was good starting from the fifth sheet, the stain at the start of printing deteriorated to the 30th sheet. Although the reproducibility of the shadow part having an image area ratio of 80% or more was observed, clogging occurred partially.

[Intermediate layer coating solution 5]
-100 parts of polyvinyl alcohol (10% aqueous solution) (PVA117 manufactured by Kuraray Co., Ltd.)
Glyoxal (cross-linking agent) 0.8 part Colloidal silica 5 parts (Nissan Chemical Industries Snowtex C; SiO ₂ concentration 20%, particle size 0.01-0.02 μm)

  As is apparent from the above results, according to the direct heat-sensitive lithographic printing plate of the present invention, when using the direct heat-sensitive method using a thermal head, there is no occurrence of uneven printing in thermal printing, and printing starts (printing). The printing plate surface stain (at the time of printing) and the dot shadow are improved, and there is no hindrance to ink loading when printing the image area. It becomes. In addition, the work can be performed even in a bright room, and the developer is not used, so the environment is very good.

Claims (2)

  An intermediate layer containing gelatin and hydrophilic inorganic fine particles having an average particle diameter of 0.1 μm or less is provided on the support as a top layer having a heat sensitive layer containing gelatin and heat-meltable fine particles. A direct heat-sensitive lithographic printing plate characterized by comprising:   2. The direct heat-sensitive lithographic printing plate according to claim 1, wherein the outermost layer contains substantially no hydrophilic inorganic fine particles.