JP2001162963A - Positive type heat sensitive lithographic printing original plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development-free positive type heat sensitive lithographic printing original plate, with which no deterioration of printing performances such as non-staining properties are developed, grounds of an image forming layer developed through its abrasion with laser exposure are checked for scattering, resulting in rarely polluting the optical system of an exposing device. SOLUTION: This positive type heat sensitive lithographic printing original plate is produced by laminating an image forming layer, which is ink-acceptable and abraded with heat, and a water-soluble over-coating layer in the order named on a base plate having a hydrophilic surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive heat-sensitive lithographic printing plate for a computer-to-plate system requiring no development. More specifically, it is possible to record an image by infrared scanning exposure based on a digital signal, and the recorded image can be directly attached to a printing machine and printed without going through a conventional developing process using a liquid. A possible positive type lithographic printing plate.

[0002]

2. Description of the Related Art Numerous studies have been made on printing plates for computer-to-plate systems, which have been remarkably advanced in recent years. Among them, with the aim of further streamlining the process and solving the problem of waste liquid treatment, development-free lithographic printing plate precursors that can be set up on a printing press without exposure and development processing have been studied, and various methods have been studied. Proposed. One of the promising methods is a method using ablation in which exposure is performed with a solid-state high-output infrared laser such as a semiconductor laser or a YAG laser, and the exposed portion is heated with a photothermal conversion agent to cause decomposition and evaporation.

[0003] JP-A-8-48018 and WO9
JP-A-9-37481 discloses a positive-working heat-sensitive lithographic printing plate in which a hydrophilic layer not subject to ablation and an ink receiving layer containing nitrocellulose that can be ablated by absorbing radiation are provided in this order on a hydrophilic metal support. Is disclosed. U.S. Pat. No. 5,605,780 provides a layer in which an infrared absorber is dispersed in a cyanoacrylate polymer on an anodized aluminum support.
A positive printing plate for forming an image by ablation of a laser irradiation unit is disclosed.

In the method using such ablation, there is a problem that decomposed substances scattered from the plate surface due to the ablation contaminate precision parts such as an optical system of a laser exposure apparatus and a working environment outside the apparatus. However, in these devices, it is necessary to provide an ablation waste capturing device, and it is difficult to completely remove contamination even if a capturing device is provided.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to suppress the scattering of scum accompanying the ablation of an image forming layer by laser exposure without deteriorating printing performance such as difficulty in contamination, thereby making it possible to use an optical device of an exposure apparatus. An object of the present invention is to provide a positive heat-sensitive lithographic printing plate which does not need to be developed and does not easily contaminate the system.

[0006]

Means for Solving the Problems The present inventors have found that the above object can be achieved by providing a water-soluble overcoat layer on the image forming layer, and have completed the present invention. That is, the present invention is as follows.

[0007] 1. A positive-working heat-sensitive lithographic printing original plate comprising a substrate having a hydrophilic surface and an ink-receiving, heat-ablated image-forming layer and a water-soluble overcoat layer provided in this order. 2. 2. The positive heat-sensitive lithographic printing plate according to the above 1, wherein the water-soluble overcoat layer and / or the image forming layer contains a photothermal conversion agent. 3. Nitrocellulose, cellulose acetate butyrate, polyvinyl acetate, vinylidene chloride
2. The positive heat-sensitive lithographic printing plate according to the above item 1, containing at least one lipophilic polymer selected from an acrylonitrile copolymer and a cyanoacrylate polymer.

[0008] Here, EP 816070 discloses a water-soluble or water-swellable material comprising a hydrophilic support, an image forming layer in which hydrophobic thermoplastic polymer particles and a photothermal conversion agent are dispersed in a hydrophilic binder, and a hydrophilic polymer. It is described that in a heat-sensitive recording element provided with a protective layer in this order, the protective layer suppresses ablation. However, the heat-sensitive recording element disclosed in this publication has a negative-type image forming method in which heat is generated by laser irradiation to fuse hydrophobic thermoplastic polymer particles into an image area, and a non-irradiated area is dissolved and removed by development to form a non-image area. Ablation here refers to the fact that laser irradiation causes thermal fusion of the polymer particles and at the same time causes damage to the image of the irradiated portion, which results in poor print quality. Therefore, this publication does not relate to a printing plate using a positive type image forming method of removing an irradiated portion by ablation-like destruction by laser irradiation as in the present invention, much less a printing plate using ablation as an image forming method. Does not disclose or suggest the problem of preventing ablation splatter from scattering.

[0009]

Embodiments of the present invention will be described below in detail.

The water-soluble overcoat layer used in the present invention can be easily removed at the time of printing, and contains a resin selected from water-soluble organic or inorganic polymer compounds.
As the water-soluble organic or inorganic polymer compound used here, a film formed by coating and drying has a film-forming ability, specifically, polyvinyl acetate (having a hydrolysis rate of 65% or more). , Polyacrylic acid and its alkali metal salt or amine salt, polyacrylic acid copolymer and its alkali metal salt or amine salt, polymethacrylic acid and its alkali metal salt or amine salt, polymethacrylic acid copolymer and its alkali metal Salt or amine salt,
Polyacrylamide and its copolymer, polyhydroxyethyl acrylate, polyvinylpyrrolidone and its copolymer, polyvinyl methyl ether, polyvinyl methyl ether / maleic anhydride copolymer, poly-2-acrylamide-2-methyl-1-propanesulfone Acid and its alkali metal salt or amine salt, poly-2-acrylamido-2-methyl-1-propanesulfonic acid copolymer and its alkali metal salt or amine salt, gum arabic, cellulose derivative (for example, carboxymethyl cellulose, Carboxyethyl cellulose, methyl cellulose, etc.) and modified products thereof, white dextrin, pullulan, enzymatically decomposed etherified dextrin, and the like. Further, according to the purpose, two or more of these resins can be used in combination.

The overcoat layer of the present invention may contain a photothermal conversion agent which absorbs infrared rays and generates heat in order to increase sensitivity. As the photothermal conversion agent, 70
Any pigment that absorbs light of 0 nm or more may be used, and various pigments and dyes can be used. Examples of pigments include commercially available pigment and color index (CI) handbook, “Latest Pigment Handbook” (edited by Japan Pigment Technical Association, 1977),
"Latest Pigment Application Technology" (CMC Publishing, 1986),
Pigments described in "Printing Ink Technology" (CMC Publishing, 1984) can be used.

Examples of the type of pigment include black pigment, brown pigment, red pigment, purple pigment, blue pigment, green pigment, fluorescent pigment, metal powder pigment, and polymer-bound pigment. Specifically, insoluble azo pigments, azo lake pigments, condensed azo pigments, chelated azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene and perinone pigments, thioindigo pigments, quinacridone pigments, dioxazine pigments, isoindolinone pigments And quinophthalone pigments, dyed lake pigments, azine pigments, nitroso pigments, nitro pigments, natural pigments, fluorescent pigments, inorganic pigments, carbon black, and the like.

These pigments may be used without surface treatment or may be used after surface treatment. The method of surface treatment is a method of surface coating a hydrophilic resin or lipophilic resin,
A method of attaching a surfactant, a method of bonding a reactive substance (for example, silica sol, alumina sol, a silane coupling agent, an epoxy compound, an isocyanate compound, and the like) to the surface of the pigment are considered. The above surface treatment method,
It is described in "Properties and Applications of Metallic Soaps" (Koshobo), "Printing Ink Technology" (CMC Publishing, 1984) and "Latest Pigment Application Technology" (CMC Publishing, 1986). Among these pigments, those that absorb infrared light or near infrared light are particularly preferable because they are suitable for use in lasers that emit infrared light or near infrared light.

As such a pigment absorbing infrared or near infrared rays, carbon black, carbon black coated with a hydrophilic resin and carbon black modified with silica sol are preferably used. Among them, carbon black whose surface is coated with a hydrophilic resin or silica sol is useful as a material which is easily dispersed in a water-soluble resin and does not impair hydrophilicity.

The particle size of the pigment is preferably in the range of 0.01 μm to 1 μm, and more preferably in the range of 0.01 μm to 0.5 μm. As a method for dispersing the pigment, a known dispersion technique used in the production of ink or toner can be used. As the disperser, an ultrasonic disperser,
Sand mills, attritors, pearl mills, super mills, ball mills, impellers, dispersers, KD mills, colloid mills, dynatrons, three-roll mills, pressure kneaders and the like can be mentioned. Details are described in "Latest Pigment Application Technology" (CMC Publishing, 1986).

As the dye, commercially available dyes and known dyes described in literatures (for example, "Dye Handbook" edited by The Society of Synthetic Organic Chemistry, published in 1970) can be used. Specific examples include azo dyes, metal complex salt azo dyes, pyrazolone azo dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinone imine dyes, methine dyes, and cyanine dyes. Among these dyes, those that absorb infrared light or near infrared light are particularly preferable because they are suitable for use in lasers that emit infrared light or near infrared light.

Dyes absorbing infrared or near infrared are described, for example, in JP-A-58-125246 and JP-A-59-125246.
-84356, cyanine dyes described in JP-A-60-78787, JP-A-58-173696,
JP-A-58-181690, JP-A-58-19449
No. 5, methine dyes described in JP-A-58-11
No. 2793, JP-A-58-224793 and JP-A-59-224793.
-48187, JP-A-59-73996, JP-A-Showa-6
Naphthoquinone dyes described in JP-A-52-940, JP-A-60-63744 and the like;
No. 92, etc .; the cyanine dyes described in British Patent 434,875; the dyes described in U.S. Pat. No. 4,756,993;
3,572, cyanine dyes described in JP-A-10-268;
No. 512.

Further, as a dye, US Pat. No. 5,156,
No. 938 is also preferably used, and substituted arylbenzo (thio) pyrylium salts described in U.S. Pat. No. 3,881,924;
No. 42645 (U.S. Pat. No. 4,327,169), a trimethinethiapyrylium salt described in JP-A-58-1810.
No. 51, No. 58-220143, No. 59-41363
Nos. 59-84248, 59-84249, 59-146063, and 59-146061 and pyrylium compounds described in JP-A-59-2161.
No. 46, a cyanine dye disclosed in U.S. Pat. No. 4,283,4.
No. 75, pentamethine thiopyrylium salt and the like, and pyrilium compounds disclosed in Japanese Patent Publication Nos. 5-135514 and 5-19702, Epolig manufactured by Eporin Co.
htIII-178, EpollightIII-130, Ep
Light III-125 and the like are also preferably used. Among these dyes, particularly preferred specific examples are listed below by structural formulas.

[0019]

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[0020]

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The pigment or dye is used in an amount of 1 to 70% by weight, preferably 2 to 50% by weight, based on the total solid content of the overcoat layer, particularly preferably 2 to 30% by weight in the case of a dye, and particularly preferably in the case of a pigment. 20 to 50% by weight. If the amount of the pigment or dye is too small, the sensitivity is lowered. If the amount is too large, the uniformity of the layer is lost and the durability of the layer is deteriorated.

In addition, a nonionic surfactant can be mainly added to the overcoat layer in the case of aqueous solution application for the purpose of ensuring uniformity of application. Specific examples of such a nonionic surfactant include sorbitan tristearate, sorbitan monopalmitate, sorbitan triolate, stearic acid monoglyceride, polyoxyethylene nonylphenyl ether, polyoxyethylene dodecyl ether, and the like. . The proportion of the nonionic surfactant in the total solid content of the overcoat layer is preferably 0.05 to 5% by weight, and more preferably 1 to 3% by weight.

The thickness of the overcoat layer used in the present invention is preferably from 0.05 μm to 4.0 μm, and more preferably from 0.1 μm to 1.0 μm. If it is too thick,
It takes time to remove the overcoat layer during printing,
In addition, a large amount of dissolved water-soluble resin affects the dampening solution, causing adverse effects such as the occurrence of roller strips during printing and the insufficiency of ink on the image area. If it is too thin, the film properties may be impaired.

In the image forming layer of the present invention, a lipophilic polymer which is ablated by heat is used. Suitable lipophilic polymers include, for example, nitrocellulose, cellulose acetate butyrate, polyvinyl acetate, vinylidene chloride acrylonitrile copolymer, cyanoacrylate polymer. Here, the cyanoacrylate polymer is described in U.S. Pat. No. 5,605,780.
Mean cyanoacrylate homopolymers and copolymers. Particularly preferred polymers include nitrocellulose and cyanoacrylate polymers.

The image forming layer of the present invention may contain a photothermal conversion agent which absorbs infrared rays and generates heat in order to increase sensitivity. The photothermal conversion agent contained in the lipophilic image forming layer may be the above-mentioned infrared absorber or pigment, but is preferably a lipophilic dye or pigment. Particularly preferred are carbon black and cyanine dyes exemplified below.

[0026]

Embedded image

The content ratio of the photothermal conversion agent in the image forming layer is as follows:
70% by weight or less of the total amount of the image forming layer, preferably 60% by weight
% By weight or less. If the amount of the photothermal conversion agent is too large, the durability of the layer will be reduced. When a light-to-heat conversion agent is contained in the overcoat layer, the light-to-heat conversion agent in the image forming layer can be made low or non-added depending on the content.

Solvents for coating the image forming layer of the present invention include methanol, ethanol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetone, methyl ethyl ketone, acetylacetone, ethyl acetate, and the like. Amyl acetate, formamide, N-methylformamide, pyrrolidone, N-methylpyrrolidone, gamma-butyrolactone,
Methyl lactate, ethyl lactate, acetonitrile, dichloroethane and the like can be used. These solvents are used alone or in a mixed state.

The thickness of the image forming layer in the present invention after coating and drying is preferably 0.1 to 3 μm. More preferably, it is 0.2 to 2 μm. If it is too thin, the durability of the image forming layer will be poor, and the printing durability during printing will be poor. On the other hand, if the thickness is too large, a great amount of energy is required to remove the image forming layer in an ablation manner, and the laser exposure is prolonged, thereby lowering the productivity of the plate making operation.

As a support having a hydrophilic surface suitably used in the present invention, an aluminum plate can be mentioned. The aluminum plate is a pure aluminum plate or an alloy plate containing aluminum as a main component and containing a trace amount of a different element, and further has a plastic laminated on an aluminum thin film. The foreign elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content of the foreign element in the alloy is at most 10% by weight or less. However, as the aluminum plate applied to the present invention, an aluminum plate of a conventionally known and used material can be appropriately used.

The thickness of the substrate used in the present invention is about 0.05 mm to 0.6 mm, preferably 0.1 mm
To 0.4 mm, particularly preferably 0.15 mm to 0.3 m
m.

It is preferable to roughen the surface of the aluminum plate before using it. When applied to the ink receiving layer made of an organic polymer by roughening, adhesion to the substrate can be easily secured. For roughening, first, a degreasing treatment with, for example, a surfactant, an organic solvent or an alkaline aqueous solution is performed to remove rolling oil on the surface of the aluminum substrate.

The surface roughening treatment of the aluminum plate is carried out by various methods. For example, a method of mechanically roughening the surface, a method of electrochemically dissolving and roughening the surface, and a method of chemically roughening the surface. Is selectively dissolved. Known mechanical methods such as a ball polishing method, a brush polishing method, a blast polishing method, and a buff polishing method can be used as the mechanical method. The chemical method is described in JP-A-54-3118.
No. 7, a method of immersing in a saturated aqueous solution of an aluminum salt of a mineral acid as described in JP-A No. 7 is suitable. As an electrochemical surface roughening method, there is a method in which an alternating current or a direct current is used in an electrolytic solution containing an acid such as hydrochloric acid or nitric acid. Also, an electrolytic surface roughening method using a mixed acid as disclosed in JP-A-54-63902 can be used.

The surface roughening by the above-mentioned method is performed when the center line surface roughness (Ha) of the surface of the aluminum plate is 0.3-1.
It is preferable that the coating be performed within a range of 0 μm. The roughened aluminum plate is subjected to an alkali etching treatment using an aqueous solution of potassium hydroxide or sodium hydroxide as necessary, and further neutralized, and then, if necessary, anodized to enhance abrasion resistance. Processing is performed.
As the electrolyte used for the anodic oxidation treatment of the aluminum plate, various electrolytes that form a porous oxide film can be used, and generally, sulfuric acid, hydrochloric acid, oxalic acid, chromic acid, or a mixed acid thereof is used. The concentration of these electrolytes is appropriately determined depending on the type of the electrolyte. The anodizing treatment conditions vary depending on the electrolyte to be used and cannot be specified unconditionally, but generally the concentration of the electrolyte is 1 to 80% by weight.
Solution, liquid temperature is 5 to 70 ° C, current density is 5 to 60 A / dm ² ,
A voltage of 1 to 100 V and an electrolysis time of 10 seconds to 5 minutes are appropriate. The amount of the formed oxide film is 1.0-5.
0 g / m ^2, it is particularly preferably 1.5 to 4.0 g / m ^2.

As the substrate having a hydrophilic surface used in the present invention, the above-mentioned substrate having a surface treated and having an oxide film may be used as it is. For the purpose of improving the adhesion with the formation layer, a substrate having an oxide film is treated by dipping in an aqueous solution of an alkali silicate such as sodium silicate or polyvinylphosphonic acid, polyacrylic acid, or a polymer having a sulfonic acid group in the side chain. Substrates subjected to an undercoating treatment with an aqueous solution of a copolymer or the like are also suitable.

The substrate having a hydrophilic surface used in the present invention may be, for the purpose of protecting the hydrophilicity of the surface of the hydrophilic support from being destroyed by laser irradiation, on a surface-treated substrate. A hydrophilic protective layer described in JP-A-8-48018 may be provided as necessary.

The heat-sensitive lithographic printing plate precursor of the present invention forms an image by heat. Specifically, direct image-like recording using a thermal recording head or the like, scanning exposure using an infrared laser, high-intensity flash exposure such as a xenon discharge lamp, or infrared lamp exposure is used.
Exposure with a solid-state high-output infrared laser such as a semiconductor laser or a YAG laser that emits infrared rays is preferable. The image-exposed printing master of the present invention can be mounted on a printing press without further processing. When printing is started using the ink and the fountain solution, the overcoat layer is quickly dissolved and removed by contact with the fountain solution, and the ink is deposited on the lipophilic portion of the image forming layer to start printing.

[0038]

The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 (Production of aluminum substrate) An aluminum plate (material 1050) having a thickness of 0.24 mm was
The surface was grained using a pumice water suspension of a mesh, and washed thoroughly with water. The plate was immersed in a 15% by weight aqueous solution of sodium hydroxide for etching, and then washed with water. Further, the resultant was neutralized with 1% by weight of nitric acid, and then subjected to electrolytic surface roughening treatment in a 0.7% by weight of nitric acid aqueous solution using a rectangular wave alternating waveform current at an anode electricity of 160 coulomb / dm ² .
After washing with water, the film was immersed in a 10% by weight aqueous solution of sodium hydroxide for etching, and then washed with water. Next, it was immersed in a 30% by weight sulfuric acid aqueous solution to be desmutted and then washed with water. In addition, 2
Anodizing treatment was performed in a 0% by weight aqueous sulfuric acid solution using a direct current to obtain an oxide film amount of 2.7 g / m ² , followed by washing with water.
Dried.

(Application of Image Forming Layer) The following coating solution A for an image forming layer was applied to the surface-treated aluminum plate and dried at 80 ° C. for 3 minutes to obtain a lithographic printing original plate. The coating amount after drying is 0.36 g / m ²
Met. Coating solution A Poly (methyl-2-cyanoacrylate) (weight average molecular weight 100,000) 1.0 g Dye (IR-24) described in this specification 1.3 g Acetonitrile 44 g

(Application of Overcoat Layer) On the above image forming layer, an overcoat layer coating solution having the following composition was applied and dried at 100 ° C. for 2 minutes to obtain a dry coating weight of about 0.6.
A positive type heat-sensitive lithographic printing plate having a g / m ² overcoat layer was prepared. Overcoat layer coating solution (OC-I) Polyacrylic acid (weight average molecular weight 25,000) 4 g Polyoxyethylene nonylphenyl ether 0.1 g Water 76 g

(Exposure and Print Evaluation) The obtained lithographic printing plate precursor was used as a trend setter (4
A 830 nm semiconductor laser of 0 W was mounted on a mounting plate setter) and exposed with energy of 800 mJ / cm ² . For comparison, the original plate before applying the overcoat layer was similarly exposed. As a result of observing the plate surfaces of both printing plates after exposure, the exposed portion of the printing plate without the overcoat layer almost scattered by ablation, but the printing plate with the overcoat layer showed the trace of the scattering by the ablation. It was clear that scattering by ablation was clearly suppressed by the overcoat layer. The exposed original plate was attached to a Harris Aurelia printing press without any processing, and printing was performed using a fountain solution consisting of a 10% by volume aqueous solution of isopropyl alcohol containing an etchant and ink. As a result, good printed matter without stain was obtained.

Example 2 From the image-forming layer of Example 1, the dye (IR-
The image forming layer except for 24) was provided. Next, an overcoat layer having the following composition (OC-II) was dried at a coating weight of 0.1%.
An original plate for lithographic printing was prepared by coating at 6 g / m ² . Overcoat layer coating solution (OC-II) Polyacrylic acid (weight average molecular weight 25,000) 4 g Dye (IR-11) described in this specification 1 g Polyoxyethylene nonylphenyl ether 0.1 g Water 100 g

The positive type lithographic printing plate thus produced was prepared in the same plate setter as in Example 1 at 900 mJ /
Exposure was in cm ² . Observation of the plate after exposure revealed that scattering due to ablation was suppressed. By printing under the same conditions as in Example 1, a good printed matter without stain was obtained.

Example 3 An undercoating solution consisting of a 0.25% by weight methanol solution of polyacrylic acid (weight average molecular weight: 250,000) was applied on the anodized support used in Example 1 at a coating solution amount of 10 g / m 2. ² and dried at 100 ° C. for 60 seconds.
An aluminum substrate having an undercoat of mg / m ² was prepared. The following image forming layer coating solution B is coated on this substrate,
After drying at 100 ° C. for 60 seconds, a dry coating weight of 1.0 g /
a substrate having an image forming layer m ² was produced. Coating solution B Nitrocellulose (30% isopropanol solution) 10.0 g Hexakis (methoxymethyl) melamine 0.4 g Carbon black 1.2 g Diisopropanolamine salt of p-toluenesulfonic acid (33% isopropanol solution) 4.0 g Methyl ethyl ketone 85 g

An overcoat layer was provided on the thus formed image forming layer in the same manner as in Example 1 to prepare a positive type heat-sensitive lithographic printing original plate. This positive type lithographic printing plate was 400 mJ using a pearl setter manufactured by Prestec.
/ Cm ² . Observation of the plate surface after exposure revealed that scattering of scum by ablation was clearly smaller than that of the comparative plate without the overcoat layer. In printing, a printed matter without stain was obtained, and there was no difference depending on the presence or absence of the overcoat layer.

Examples 4-6 In place of acrylic acid in the overcoat layer of Example 1, sodium polymethacrylate (weight average molecular weight 15,000) was used in Example 4, and polyvinyl alcohol (degree of saponification 88) was used in Example 5. Mol%, degree of polymerization 1000), and in Example 6, polyacrylamide (weight average molecular weight 10,000)
Was used. Otherwise in the same manner as in Example 1, a positive heat-sensitive lithographic printing plate was prepared. Exposure as in Example 1,
Printed. In each plate, scattering of scum due to ablation was suppressed during exposure, and good printed matter without stain was obtained during printing.

Examples 7 to 9 On the substrate having an image forming layer prepared in Example 3, an overcoat layer coating solution (OC-III) having the following composition was applied in the same manner as in Example 3 to obtain a positive heat-sensitive material. A lithographic printing plate was prepared. Here, the dye described in the present specification is (IR-1) in Example 7, (IR-9) in Example 8, and Example 9
Then, (IR-11) was used. Overcoat layer coating solution (OC-III) Polyacrylic acid (weight average molecular weight 25,000) 1 g Dye described in this specification 0.2 g Polyoxyethylene nonylphenyl ether 0.025 g Water 19 g Prepared as described above. When the printing original plate was exposed and printed in the same manner as in Example 3, in each of the plates, scattering of scum due to abrasion was suppressed in the exposure, and good printed matter without stain was obtained in the printing.

[0049]

According to the present invention, the scattering of decomposed substances due to the ablation of the image forming layer by laser exposure is suppressed without deteriorating the printing performance such as difficulty in staining and the like, and the exposure apparatus and the optical system are less contaminated. A positive type heat-sensitive lithographic printing plate precursor requiring no development can be provided.

Claims (3)

[Claims] An original heat-sensitive lithographic printing plate comprising a substrate having a hydrophilic surface and an ink-receiving, heat-ablated image-forming layer and a water-soluble overcoat layer provided in this order. 2. The positive heat-sensitive lithographic printing plate according to claim 1, wherein the water-soluble overcoat layer and / or the image forming layer contains a photothermal conversion agent. 3. The image forming layer according to claim 1, wherein the image forming layer contains at least one lipophilic polymer selected from nitrocellulose, cellulose acetate butyrate, polyvinyl acetate, vinylidene chloride / acrylonitrile copolymer and cyanoacrylate polymer. Positive heat-sensitive lithographic printing plate.