JP2000047374A - Plate making method of lithographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate making method of a lithographic printing master plate having excellent workability such that an image of high resolution can be obtd., that a direct drawing method by laser can be used, that an image can be obtd. even in a bright room and that no waste liquid is produced. SOLUTION: This lithographic printing plate is formed of a silver thin film layer comprising granular silver particles having 0.005 to 0.2 μm average particle size on a supporting body, and further forming a hydrophilic polymer layer having 0.01 to 0.5 μm thickness thereon. The supporting body has a hydrophilic surface, or a hydrophilic layer is formed on the supporting body. The silver thin film is removed by exposure to a heat-mode laser to obtain the objective lithographic printing plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of making a lithographic printing plate which can be handled in a bright room and which can perform laser drawing in a heat mode.

[0002]

2. Description of the Related Art A lithographic printing plate comprises an oleophilic image portion which receives oil-based ink and an oil-repellent non-image portion which does not receive ink. Generally, the non-image portion comprises a hydrophilic portion which receives water. Have been. In normal lithographic printing,
Both water and ink are supplied to the plate, and the image area
The non-image area selectively receives water, and printing is performed by transferring the ink on the image area to a printing medium such as paper.

At present, a lithographic printing plate is manufactured by providing a lipophilic ink-receiving layer on a base material such as an aluminum plate, a zinc plate, or paper having a hydrophilized surface. Among these, a PS plate, which is made of a photosensitive material such as a diazo compound or a photopolymer on an aluminum base having a hydrophilic surface, or a silver complex salt on a paper or plastic support using silver halide as a photosensitive material. An image forming apparatus using a diffusion transfer method (DTR method) is generally used.

A method of forming an ink receiving layer (hereinafter referred to as an image layer) by using a diazo compound or a photopolymer is as follows. First, a photosensitive material such as a diazo compound or a photopolymer is formed on a substrate such as a metal plate, paper, a laminate, or an insulating substrate. Apply material. Next, the photosensitive material is irradiated with light to cause a chemical change to change the solubility in a developing solution. Photosensitive materials are classified into two types according to the type of chemical change. The light-irradiated part polymerizes and cures, so that the negative type becomes insoluble in the developer, and conversely, the functional group of the light-irradiated part changes to have solubility in the developer. It is a positive type. In either case, the photosensitive material remaining on the base material after processing with the developer and insoluble in the developer becomes an image layer.

On the other hand, a lithographic printing plate using the DTR method, particularly a lithographic printing plate having a physical development nucleus layer on a silver halide emulsion layer, is disclosed, for example, in US Pat. No. 134,769, No. 4,160,670,
Nos. 4,336,321 and 4,501,811
No. 4,510,228 and 4,621,04
No. 1, etc., the exposed silver halide crystal undergoes chemical development by DTR development to become black silver, forming a hydrophilic non-image portion. The crystals are converted into a silver salt complex by the complexing agent in the developing solution and diffuse to the physical development nucleus layer on the surface, and physical development is caused by the presence of the nucleus to form an image portion mainly composed of ink-receptive physical development silver. Form. A lithographic printing plate in which a physical development nucleus layer and a silver halide emulsion layer are sequentially coated on a grained and anodized aluminum-based support is described in, for example, JP-A-63-260491, JP-A-63-26049. −1161
No. 51, No. 4-282295 and the like. After the above lithographic printing plate is image-exposed and DTR-developed, the silver halide emulsion layer is washed with warm water to form an anodized aluminum base. An image portion mainly composed of physically developed silver is formed.

In the plate making process for making these printing plates, conventionally, an intermediate film or an underprint is prepared from characters, images and photographic originals, and these are collected to prepare an exposure film. Next, a contact exposure method using ultraviolet light or white light was mainly used. Further, a method has also been used in which a complete composition is produced by laminating the composition, and photographing is performed with a plate making camera. However, with the advancement of computers, laser direct writing methods that transmit digital signals from computer information to an exposure apparatus (computer-to-plate) and directly expose a photosensitive material using a laser can be performed. It has become The laser direct writing method has advantages such as low cost, high speed, and high productivity in a wide variety of small lot products because a plate-making film used in the middle can be omitted.

In order to cope with the laser direct writing method, a photosensitive material having high optical sensitivity is preferable. Since diazo compounds and photopolymers involve a photochemical reaction, the optical sensitivity is low, and is several to several hundred mJ / cm ² . Therefore, the laser output device must have a high output, and there are problems such as an increase in size of the device and an increase in cost.

On the other hand, in the case of forming an image by the DTR method using silver halide, the sensitivity is several μJ / cm ² and a simple semiconductor laser or the like allows sufficient exposure. Storage and application to a substrate must be performed in the dark or under a safe light, which has the disadvantage of significantly reducing the efficiency of production and plate making operations. Also, the reaction of a diazo compound or a photopolymer proceeds even under room light or sunlight, and the reactivity changes even at a high temperature. In addition, the presence of oxygen becomes an inhibitor of the reaction. Therefore, before exposure and development, dark room treatment and storage in a low oxygen state were similarly required.

Further, in the above-described image forming method, liquid processing such as using a developing solution is generally performed, and there is a disadvantage that processing of waste liquid is an environmental problem. 1
Since 995, the dumping of wastewater into the ocean has been banned, and the need for non-waste liquefaction and dry treatment has become a requirement of the times.

In order to meet such a demand, a lipophilic metal thin film is provided on a support having a hydrophilic surface, and the lipophilic metal thin film is irradiated with a high-output heat mode laser to remove heat by applying heat. Accordingly, a printing plate of a method of forming an image has been proposed. For example, Japanese Patent Application No. 9-27
JP-A No. 0854, the printing plate having a silver thin film formed thereon by DTR development on a support having a hydrophilic layer is subjected to heat mode laser exposure to perform plate making without development processing. Can be. Japanese Patent Application Laid-Open No. 7-1848 discloses that a metallic silver layer and a hydrophobic layer having a thickness of less than 50 nm are formed on a metal silver layer on a support having a hydrophilic surface or provided with a hydrophilic layer. A heat mode recording material is disclosed, in which a printing original plate provided by applying a silver halide emulsion layer and performing DTR development is subjected to heat mode laser exposure.

In order to produce such a printing original plate, a silver salt diffusion transfer method is effective as a method for forming a silver thin film on a support. In the first method, a physical development nucleus layer provided on a support and a silver halide emulsion layer coated as a silver complex salt donor on the support are passed through a physical developer, and then superposed. There is a method in which silver is deposited on a physical development nucleus by performing combined diffusion transfer development to form a silver thin film. As a method using the method of forming a silver thin film in this way, there is Copirapid (trade name, manufactured by Agfa) or the like.

In a second method, a silver halide emulsion layer coated as a donor of a silver complex salt is coated on a support provided with a physical development nucleus layer and subjected to physical development to wash off the silver halide emulsion layer. And a silver thin film is formed on the physical development nucleus. In order to use this method,
There are Silver Digiplate SDP-αR (trade name, manufactured by Mitsubishi Paper Mills) and Silver Squirrel SDB (trade name, manufactured by E.I. Dupont).

As a third method, a silver halide emulsion layer is coated on a support provided with a hydrophilic layer, and a physical development nucleus layer is coated on the silver halide emulsion layer. There is a method of forming a silver thin film thereon. As a method using this method, a silver digital plate SDP-FH
N (trade name, manufactured by Mitsubishi Paper Mills) and set print (trade name, manufactured by Agfa).

However, the above three methods have problems in that preparation of a silver halide emulsion layer is troublesome and preparation of a silver thin film requires a dark room.

As a fourth method, a support provided with a physical development nucleus layer is prepared by using a silver complex salt dissolved by a silver halide solvent,
There is also a method in which a silver thin film is formed on physical development nuclei by immersion in a liquid containing a reducing agent. This method is
This method is also known as electroless plating. For example, Japanese Patent Publication No. 42-23745 and 43-12882.
And JP-A-5-287542.

However, according to the methods disclosed in these publications, the silver film is ablated by laser exposure, the exposed surface portion is hydrophobized, and stains at the start of printing. For this reason, there have been problems such as low productivity and the need to form a silver film in a shorter time.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithographic printing plate making technique which can be handled in a bright room, is compatible with a direct drawing method using a laser, and has an image having high resolution. And no waste liquid is generated.
An object of the present invention is to provide a method of making a lithographic printing plate having excellent printing performance.

[0018]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following invention.

The method of making a lithographic printing plate according to the present invention comprises the steps of: providing, on a support having a hydrophilic surface or a hydrophilic layer, a granular silver having an average particle size of 0.005 to 0.2 μm; A lithographic printing plate comprising a silver thin film layer composed of particles, and a hydrophilic polymer layer having a thickness of 0.01 to 0.5 μm thereon is subjected to silver exposure using heat mode laser exposure. It is characterized in that the thin film is removed.

In the second aspect of the present invention, the method of making a lithographic printing plate according to the second aspect is characterized in that the hydrophilic layer polymer contains 1 to 30% by weight of a hydrophobic compound.

In the plate making method of a lithographic printing plate according to a third aspect of the present invention, the hydrophobic compound has a mercapto group and at least one hydrophobic substituent.

In a fourth aspect of the present invention, a method of making a lithographic printing plate according to the present invention is characterized in that granular silver particles are formed in the presence of a silver halide solvent.

In the plate making method of a lithographic printing plate according to a fifth aspect of the present invention, the silver halide solvent is an amine compound.

In a sixth aspect of the present invention, a method of making a lithographic printing plate according to the present invention is characterized in that the amine is a compound represented by the following general formula 1.

[0025]

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(Wherein at least one of R 1 to R 5 represents a substituted or unsubstituted amino group, and the other represents a hydrogen atom, a halogen atom, a substituted or unsubstituted saturated or unsaturated alkyl group, cycloalkyl group, An alkoxy group, an aryl group, an alkanoyl group, an aroyl group, and a heterocyclic group, which may be bonded to each other to form a ring.)

In a seventh aspect of the present invention, a method for making a lithographic printing plate according to the present invention is characterized in that the support is made of an aluminum base which has been treated with an acidic treatment solution and then anodized. is there.

According to the present invention, it is possible to make a lithographic printing plate by using a laser in accordance with a desired image, without using a liquid developer or equipment for processing the liquid developer. Further, it is possible to work in a bright room until the plate making process from the lithographic printing original plate and the printing process, and also it is possible to store for a long period of time in a bright room or under oxygen.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an example of a lithographic printing plate precursor according to the present invention when aluminum is used as a support.
The lithographic printing plate precursor (a) according to the present invention has an aluminum base 1
Has a roughened and anodized surface layer 2, a silver thin film 3 is provided thereon, and a hydrophilic polymer layer 4 is provided thereon. In the method of making a lithographic printing plate according to the present invention, first, the lithographic printing plate precursor (a) is irradiated with a laser to obtain a desired image (non-image area exposure). Here, the silver thin film 3 is removed by ablation by laser irradiation, or the adhesion to the aluminum surface is weakened, the silver thin film 3 is removed by means such as vacuuming, and a part of the upper hydrophilic polymer layer remains. The plate making is completed when the anodized surface layer 2 appears in this state. Thereafter, when the apparatus is mounted on a lithographic printing press, the thin hydrophilic polymer layer in the image area is removed at the start of printing, and ink is applied to the remaining silver thin film 3 portion, and in the non-image area, the partially remaining hydrophilic polymer layer is applied. Water is received in each of the anodized surface layers 2 covered with the layers, and lithographic printing is enabled.

In the present invention, 0.01 to
The 0.5 micron thick hydrophilic polymer layer is light transmissive in the infrared spectral region, does not reduce sensitivity when exposed to heat mode laser, and makes the laser irradiated area hydrophobic. It plays a role in preventing the situation.

According to Japanese Patent Application Laid-Open No. 7-1848, a metal silver layer and a hydrophobic layer having a thickness of less than 50 nm are formed on a metal silver layer on a support having a hydrophilic surface or provided with a hydrophilic layer. A method for making a plate by exposing a heat mode recording material including a layer with a heat mode laser is disclosed. It has been suggested that the laser-exposed portion of such a configuration becomes a non-image portion and exhibits a property of receiving water during printing. However, when the contact angle of water irradiated with the YAG laser having an output of 8 W of 1064 nm and measured was over 70 °, it was clearly hydrophobic. When this is printed, it becomes dirty from the start of printing and does not function sufficiently as a printing plate. By providing the thin film of the hydrophilic polymer of the present invention, the contact angle can be reduced, and the film can be made harder to stain.

The hydrophilic polymer used in the present invention may be a natural product such as mannan, pectin, tragacanth gum, karaya gum, xanthin gum, guarant gum, locust bingham, gum arabic and other plant mucilages, dextran, glucan, xanthan gum, and levan gum. And microbial mucilage such as heteropolysaccharides such as succinoglucan, pullulan, curdlan, and xanthan gum.

Also, as a semi-natural product (semi-synthetic product),
Examples include cellulose derivatives, modified gums such as carboxymethyl guar gum, and baked starches such as dextrin.

The synthetic products include polyvinyl alcohol, partially acetalized polyvinyl alcohol, allyl-modified polyvinyl alcohol, modified polyvinyl alcohol such as polyvinyl methyl ether, polyvinyl ethyl ether, and polyvinyl isobutyl ether, polyacrylate, and polyacrylate. And polyacrylic acid derivatives, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, vinylpyrrolidone / vinyl acetate copolymer and the like.

The thickness of the hydrophilic polymer layer to be set is
If it is less than 0.01 micron, the effect on stains is small, and if it is more than 0.5 micron, there is a drawback that ink application of an image portion is delayed.

In the present invention, the hydrophilic polymer layer preferably contains 1 to 30% by weight of a hydrophobic compound. Granular silver particles having a particle size of 0.005 to 0.2 micron are ink-receptive and have a property that an ink can be applied alone. However, by including a hydrophobic compound in the hydrophilic polymer layer, the ink application can be stabilized.

Examples of the hydrophobic compound used in the present invention include known oils such as phthalate esters such as diethyl phthalate and dibutyl phthalate, and phosphate esters such as tricresyl phosphate, and various animal oils and vegetable oils. Can be done. Mercaptotetrazole derivatives having a hydrophobic group such as phenylmercaptotetrazole are also effective.

Among the hydrophobic compounds used in the present invention, those having a mercapto group and one or more hydrophobic substituents are preferred. Examples of such a hydrophobic compound include a mercaptotetrazole derivative such as phenylmercaptotetrazole, a mercaptotriazole derivative represented by the following general formula 2, a mercaptooxadiazole derivative represented by the following general formula 3, and the like. .

[0040]

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[0041]

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In the formula, R6 is an alkyl group, an aryl group or an aralkyl group, and R7 is hydrogen or an acyl group.
Preferably, R6 represents alkyl containing 3 to 16 carbon atoms.

Also, such hydrophobic compounds include:
Compounds that impart ink receptivity are also preferred, for example, JP-B-48-29723, U.S. Pat. No. 3,721,5.
No. 59, etc.

In the present invention, the hydrophilic polymer layer containing the hydrophobic compound is formed by forming a silver thin film and then applying it. The hydrophobic compound may be added to the hydrophilic polymer aqueous solution using a known oil dispersion technique, or may be added to the hydrophilic polymer aqueous solution after being dissolved in an appropriate solvent. Compounds having a mercapto group and one or more hydrophobic substituents are described in JP-A-6-79982 and JP-A-7-2486.
It can also be dissolved using the amine compound described in JP-A No. 30 and added to the hydrophilic polymer.

In the present invention, the average particle size is 0.1.
A silver thin film composed of silver particles of 2 microns or less is used.
The silver thin film composed of such silver particles is easily removed by laser exposure in a heat mode, and has excellent printability. A silver thin film composed of silver particles having an average particle size larger than 0.2 micron or a silver thin film formed by vacuum deposition is difficult to carry ink, and as a result, the image quality of printed matter is deteriorated.

In the present invention, the average particle size is 0.1.
A silver thin film composed of silver particles of 005 to 0.2 microns is used. Such a silver thin film composed of silver particles is easily removed by heat mode laser exposure, and has excellent printability. A silver thin film composed of silver particles having an average particle size of more than 0.2 micron or a silver thin film formed by vacuum evaporation of less than 0.005 micron is difficult to carry ink, and as a result, the image quality of printed matter is deteriorated.

As a typical method for producing a silver thin film composed of granular silver particles, the above-mentioned three types of silver complex salt diffusion transfer method are known. Of the three systems, the first two have configurations that are practically used in plate making cameras and photo mode laser exposure machines. The average grain size of the silver grains formed by these methods is determined by the layer constitution of the plate, the halogen composition of the silver halide emulsion, the average grain size of the emulsion grains, plate components such as a development inhibitor, a developing agent, It depends on the components of the diffusion transfer developer such as a silver solvent and a development inhibitor, and the conditions of the diffusion transfer development. Regarding these factors, for example, US Pat. Nos. 3,728,114, 4,134,769, 4,160,670, 4,336,321,
Nos. 4,501,811 and 4,510,228
No. 4,621,041 and JP-A-63-2
60491, JP-A-3-116151, 4-28
No. 2295, and the like. Controlling the silver particles constituting the silver thin film to 0.2 microns or less can be achieved by optimizing these known techniques.

The third method is disclosed in Japanese Patent Application No. 9-304.
No. 390, 9-304391, 9-304392
Nos. 9-304393 and 9-304394, by optimizing a processing solution comprising a developing agent, a silver halide solvent, a silver salt and the like,
Silver particles constituting the silver thin film can be controlled to 0.005 to 0.2 microns.

The silver thin film used in the present invention is, for example, (i)
A complex salt formed between a silver halide solvent and silver ions, (i
i) a reducing agent, (iii) a physical development nucleus is prepared, (iii) is first applied onto a support, and then a mixture of (i) and (ii) is applied, or (ii) is applied onto the support. ) And (iii) are applied, and (i) is further applied, or a liquid obtained by mixing (i) to (iii) is applied.

As a method for measuring the particle diameter of the silver particles constituting the silver thin film, a photograph is taken with an electron microscope, the size of each silver particle is measured from the photograph, and the average value is calculated. . As a simple method, an average particle may be picked up and its particle size may be measured.

In the method of making a lithographic printing plate according to the present invention,
The efficiency of removing the silver thin film (that is, the sensitivity of the lithographic printing plate in the method of the present invention) depends on the thickness of the silver thin film. Therefore, it is preferable to determine the thickness of the silver thin film based on the laser output used for drawing. If the output is 1 W or more, the thickness can be set thicker. If the output is less than 1 W, it is preferable to set the thickness in the range of 0.05 μm to 5 μm.

In the present invention, the type of silver ions used for preparing a silver film is not particularly limited.
It is selected from silver nitrate and silver halides such as silver chloride, silver bromide, silver iodide, silver chlorobromide, silver chloroiodide, silver iodobromide, silver chlorobromoiodide and the like.

The amount of these silver ions used depends on the thickness of the silver film described above.

In the present invention, hydroquinone, phenylenediamine, phenidone, dimethylphenidone and the like can be used as the type of reducing agent used for preparing a silver film.

As a developing solution for preparing a silver thin film,
Alkaline substances for pH adjustment, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium triphosphate, etc., acidic substances such as sulfuric acid, nitric acid, phosphoric acid, etc., sulfites as preservatives, silver halide Solvents such as thiosulfate, thiocyanate, cyclic imide, 2-mercaptobenzoic acid, amine, etc., thickeners such as hydroxyethylcellulose, carboxymethylcellulose, etc., antifoggants such as potassium bromide, development modifiers such as poly An oxyalkylene compound, an onium compound and the like can be contained. Further, the developing solution includes U.S. Pat.
As described in the specification of US Pat. No. 728, a compound or the like that improves the ink running of the silver thin film on the surface can be used.

In the present invention, when a silver thin film composed of granular silver particles is prepared, it is preferably performed in the presence of a compound serving as a silver halide solvent. The silver thin film thus produced exhibits excellent ink receptivity. Examples of the silver halide solvent used in the present invention include sulfites (eg, anhydrous sodium sulfite, anhydrous potassium sulfite,
Thiosulfate (eg, sodium thiosulfate pentahydrate, ammonium thiosulfate, etc.).

The silver halide solvent is preferably used in an amount of 0.1 to 100 times, more preferably 1 to 50 times, the number of moles of silver ions. These can be used in combination of two or more.

The silver halide solvent used in the present invention is preferably an amine compound. The silver thin film produced in this way exhibits further excellent ink receptivity.
The amine compound used in the present invention is a compound substituted with ammonia, a substituted or unsubstituted saturated or unsaturated alkyl group, cycloalkyl group, alkoxy group, aryl group, alkanoyl group, aroyl group, or heterocyclic group. And these substituents may be bonded to each other to form a ring.

Specific examples are shown below, but the present invention is not limited to these examples.

[0060]

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These amine compounds are used in an amount of 0.1 to 100 times, more preferably 1 to 50 times, the number of moles of silver ions.

Further, as the amines used in the present invention, compounds represented by the following general formula 1 are more preferable.

[0063]

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In the formula, at least one of R 1 to R 5 represents a substituted or unsubstituted amino group, and the other represents a hydrogen atom, a halogen atom, a substituted or unsubstituted saturated or unsaturated alkyl group, cycloalkyl group, or alkoxy group. A group, an aryl group, an acyl group, an aroyl group, and a heterocyclic group, which may be bonded to each other to form a ring.

When the amino group has a substituent, it has a substituted or unsubstituted saturated or unsaturated alkyl group, cycloalkyl group, alkoxy group, aryl group, acyl group, aroyl group, heterocyclic group. And these may be bonded to each other to form a ring.

As the above-mentioned halogen atom, chlorine, bromine,
And iodine.

The above alkyl group may be further substituted with a suitable group (for example, a halogen atom, an alkoxy group, etc.). It preferably has 1 to 10 carbon atoms, such as methyl, ethyl, n-propyl, n-hexyl, trichloromethyl, and vinyl.

The above cycloalkyl group has 3 to 1 carbon atoms.
It is about 0 and may be further substituted with a suitable group (eg, an alkyl group, a halogen atom, an alkoxy group, etc.). For example, it is a cyclohexyl group, a cyclopentyl group or the like.

The above alkoxy group may be linear or branched, and may be further substituted with a suitable group (eg, an alkyl group, a halogen atom, an alkoxy group, etc.). It preferably has 1 to 10 carbon atoms, such as methoxy, ethoxy, n-propoxy, and n-hexyloxy.

The above-mentioned aryl group is preferably an aromatic group such as a phenyl group and a naphthyl group. These aromatic groups are suitable groups (for example, a halogen atom, an alkyl group,
Alkoxy group, nitro group, etc.).

The above-mentioned acyl group may be a straight-chain or branched one having 1 to 6 carbon atoms, for example, formyl group, acetyl group,
And a propionyl group, a pivaloyl group and the like.

The aryl group portion of the aroyl group is preferably an aromatic group such as a phenyl group or a naphthyl group. These aromatic groups are suitable groups (eg, a halogen atom, an alkyl group, an alkoxy group, a nitro group). Etc.).

The above-mentioned heterocyclic group is substituted or unsubstituted, for example, pyridyl, furyl, thienyl and the like.

Specific examples of the compound represented by the general formula 1 are shown below.

[0075]

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These compounds are used in an amount of 0.1 to 100 times, more preferably 1 to 50 times, the number of moles of silver ions.

As the support used in the lithographic printing plate according to the present invention, paper, various films, plastics, paper coated with a resin-like substance, metal, and those obtained by laminating a polyester film or paper on these can be used.

Among them, the aluminum base which has been roughened and anodized has good hydrophilicity and good surface activity. It is particularly preferable because it can be removed by the above method and is strongly adhered to the aluminum surface to impart surface activity with excellent printing durability.

The aluminum plate used for the support according to the present invention includes pure aluminum and various metals, for example,
An aluminum alloy plate containing a small amount of silicon, magnesium, iron, copper, zinc, manganese, chromium, titanium or the like is suitable. A trace amount of impurity metal contained in aluminum or a small amount of metal added arbitrarily has a large effect on the size, shape and distribution of pits obtained by electrolysis, and also on the strength of the aluminum plate give.

The aluminum plate is preferably subjected to a surface treatment so as to be used as a support for an offset printing plate.
In the surface treatment, generally, degreasing, roughening, desmutting, and anodizing are performed, and the treatment is continuously performed using an aluminum coil. After each treatment, if necessary, washing is performed, and the support is dried to obtain a support.

For example, as described in Japanese Patent Application No. 9-51712, in the case of an aluminum support for an offset printing plate, the oxide film formed in the final step of anodic oxidation is the outermost surface. It is presumed that the denatured layer formed by the process immediately before the anodic oxidation is present on the surface of the oxide film. The properties of these modified layers are expected to have a significant effect when forming a silver thin film. However, in existing PS plates and OPC printing plates, the photosensitive layer is usually formed by organic solvent-based coating. Therefore, the influence of these modified layers hardly appears. However, when the adhesion between the silver thin film and the aluminum surface greatly affects the printing durability as in the present invention, the influence of these modified layers appears. The chemical treatment such as desmut treatment immediately before anodization is preferably an acidic treatment solution, and particularly preferably a treatment solution containing nitric acid.

The aluminum processing step is described in Japanese Patent Application No. 9-5 / 1997.
The method is described in detail in EP 1712, in which a roughened and anodized aluminum base is produced using the method described therein.

In the present invention, desmut treatment is an important step in the surface treatment of the aluminum base. The aluminum sheet strip subjected to the electrolytic surface roughening treatment is sufficiently washed with water, but the surface thereof is usually covered with smut, and cannot be removed only by washing with water, but closes the pits. In order to remove the smut, a desmutting process is performed. In the desmut treatment, the smut dissolves and a pit surface appears. The amount of dissolution varies depending on the treatment conditions with the electrolytic solution.
1 to 1 g / m ² is appropriate.

In the desmut treatment, an alkali agent such as sodium hydroxide used for the degreasing treatment, or phosphoric acid, sulfuric acid,
Acids such as nitric acid and perchloric acid, or a mixture thereof can be used, but each has a different smut removing ability, and the removing ability is adjusted according to the type of treatment solution, its concentration, or the treatment temperature. If the desmutting treatment is too strong, the unevenness formed in the roughening step is dissolved to make it flat, and if the desmutting treatment is too weak, the smut remains unpreferably. The remaining smut remains even after the anodic oxidation treatment and causes an abnormal point when forming a silver thin film.

The desmut treatment with the acidic processing solution used in the present invention provides a surface activity capable of producing a preferable physically developed silver. In particular, an acidic processing solution containing nitric acid is preferable because it has a high ability to form physical development nuclei, has good adhesion of developed image silver, and can produce a printing plate having high printing durability. When it is difficult to remove the smut with the acid treatment liquid, a desmut treatment in which the influence of the desmut by the alkali does not remain can be achieved by, for example, a two-step treatment in which the desmut is treated with an alkali and then further treated with an acid treatment liquid.

The roughened and desmutted aluminum strip is then anodized. The anodic oxidation treatment is performed by a known method, for example, as described in Japanese Patent Application No. 9-51712.

In the present invention, when the surface does not become hydrophilic, a hydrophilic layer can be formed and used. Examples of the hydrophilic polymer for forming such a hydrophilic layer include the following examples. These can be used in combination of two or more types in view of printing performance such as background stain resistance and printing durability.

Examples of natural products include those obtained from algae such as starches, seaweed mannan, agar and sodium alginate, and vegetable mucilage such as mannan, pectin, tragacanth gum, karaya gum, xanthin gum, guabing gum, locust bingham, gum arabic, and the like. Dextran,
Glucan, xanthan gum, and homopolysaccharides such as levan, succinoglucan, pullulan, curdlan, and microbial mucilage such as heteropolysaccharides such as xanthan gum, glue, gelatin, proteins such as casein and collagen, chitin and its derivatives and the like. No.

Also, as semi-natural products (semi-synthetic products),
Examples include cellulose derivatives, modified gums such as carboxymethyl guar gum, and modified starches such as baked starches such as dextrin, oxidized starches, and esterified starches.

Synthetic products include polyvinyl alcohol, partially acetalized polyvinyl alcohol, allyl-modified polyvinyl alcohol, modified polyvinyl alcohol such as polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl isobutyl ether, etc., polyacrylates and polyacrylates. Compound, polymethacrylate,
And polyacrylic acid derivatives such as polyacrylamide and polymethacrylic acid derivatives, polyethylene glycol,
Examples include polyethylene oxide, polyvinylpyrrolidone, vinylpyrrolidone / vinyl acetate copolymer, carboxyvinyl polymer, styrene / maleic acid copolymer, and styrene / crotonic acid copolymer.

Among them, gelatin is preferably used when the hydrophilic layer also serves as a silver halide emulsion layer in order to form a silver thin film by a silver complex salt diffusion transfer method.

As the gelatin used for the hydrophilic layer of the lithographic printing plate of the present invention, any gelatin can be used as long as it is made of animal collagen. Collagen obtained from pig skin, cow skin and bovine bone is used as the raw material. Gelatin is preferred. There is no particular limitation on the kind of gelatin, but in addition to lime-treated gelatin and acid-treated gelatin,
No. 4854, No. 39-5514, No. 40-12237
And No. 42-26345, U.S. Pat.
No. 25,753, No. 2,594,293, No. 2,61
No. 4,928, No. 2,763,639, No. 3,11
No. 8,766, No. 3,132,945, No. 3,18
6,846, 3,312,553 and British Patent 1,033,189, etc., and these may be used alone or in combination of two or more. Can be used.

When gelatin is used for the hydrophilic layer, it can be cured with a gelatin hardener. Gelatin hardeners include, for example, inorganic compounds such as chrome alum,
Aldehydes such as formalin, glyoxal, malealdehyde and glutaraldehyde, N-methylal compounds such as urea and ethylene urea, mucochloric acid, 2,3-
Aldehyde analogs such as dihydroxy-1,4-dioxane, 2,4-dichloro-6-hydroxy-S-
Triazine salts, 2,4-dihydroxy-6-chloro-
Compounds having an active halogen such as S-triazine salt, divinyl sulfone, divinyl ketone, N, N, N-
One or two of various compounds such as triacryloylhexahydrotriazine, compounds having two or more active three-membered ethyleneimino groups or epoxy groups in a molecule, and dialdehyde starch as a polymer hardener. More than one species can be used.

The hydrophilic layer of the lithographic printing plate according to the present invention may contain an inorganic substance such as titanium oxide, silicon dioxide, aluminum oxide or the like for the purpose of preventing printing soiling. The proportion to be contained is appropriately determined in a desired range depending on various conditions such as printing ink and fountain solution used for printing, printing speed and printing pressure.

In order to coat the hydrophilic layer of the lithographic printing plate according to the present invention, some of anionic, cationic or nonionic surfactants may be used as an auxiliary, or a matting agent, Thickeners, antistatic agents and the like can also be used.

In the present invention, the silver halide optionally used includes, for example, silver chloride, silver bromide, silver chlorobromide, and silver iodide. Used in Silver halide crystals are rhodium salts, iridium salts, palladium salts, ruthenium salts,
It may contain heavy metal salts such as nickel salts and platinum salts,
The addition amount is from 10 ^-8 to 10 ^-3 mol per mol of silver halide. The crystal form of the silver halide is not particularly limited, and may be cubic to tetradecahedral grains, or core-shell or tabular grains. The silver halide crystal may be a monodisperse or polydisperse crystal, and the average grain size is 0.2 to 0.8 μm.
Range. One preferred example is a monodispersed or polydispersed crystal containing 80 mol% or more of silver chloride, which contains a rhodium salt or an iridium salt.

In the present invention, in order to produce a good silver film, it is preferable to use a physical development nucleus during the production. The physical development nucleus uses a physical development nucleus and, if necessary, a hydrophilic polymer to form a layer by coating in advance. As physical development nuclei, silver, antimony, bismuth, cadmium, cobalt, lead, nickel, palladium, rhodium, gold, platinum and other metal colloid fine particles, and sulfides, polysulfides, selenides of these metals, or those It may be a mixture or a mixed crystal. The physical development nucleus may or may not contain a hydrophilic polymer. Examples of the hydrophilic polymer include gelatin, starch, dialdehyde starch, carboxymethylcellulose, gum arabic, sodium alginate, hydroxyethylcellulose, and polystyrenesulfonic acid. , There is a hydrophilic polymer such as sodium polyacrylate, a copolymer of vinylimidazole and acrylamide, a copolymer of acrylic acid and acrylamide, a polyvinyl alcohol or the like, and the content thereof is 0.5 g.
/ M ² or less. Further, the physical development nucleus layer may contain a developing agent such as hydroquinone, methylhydroquinone, or catechol, or a known hardener such as formalin or dichloro-s-triazine.

In the present invention, a physical development nucleus for performing physical development is contained in a surface layer (physical development nucleus layer) existing above a silver halide emulsion layer as a hydrophilic layer in the case of a monosheet. It may not be provided, or may be provided between the support and the silver halide emulsion layer. For example, the above-mentioned physical development nucleus layer can be provided on an aluminum support which has been previously subjected to anodizing treatment. In the case of two sheets, it may be present above the hydrophilic layer of the sheet used as a lithographic printing material.

The light absorber may be any dye or pigment in general, and examples thereof include carbon black, cyanine, metal-free or metal phthalocyanine, metal dithiolene, and anthraquinone.

When the light absorbing agent is contained in the roughened and anodized aluminum base, a chemical or electrochemical metal coloring method generally called black dyeing can be used. By dyeing an organic or inorganic dye by immersion dyeing, the dye can be introduced into the fine pores of the anodic oxide film, followed by sealing treatment to dye.

Further, on the back surface of the support, a layer containing a matting agent or an antistatic agent may be provided in consideration of transportability in a drawing apparatus or the like.

In the method of making a lithographic printing plate precursor according to the present invention, the laser used for exposing the anodized surface includes a carbon dioxide laser, a nitrogen laser, an Ar laser, a He / Ne laser, a He / Cd laser, and a Kr laser. Gas laser such as laser, liquid (dye) laser, ruby laser, solid laser such as Nd / YAG laser, GaAs / G
aAlAs, semiconductor lasers such as InGaAs lasers, K
An excimer laser such as an rF laser, a XeCl laser, a XeF laser, and Ar ₂ can be used.

[0103]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

Example 1 An A1050 type aluminum plate strip having a width of 300 mm and a thickness of 0.2 mm was moved at a processing speed of 1.3 m / min, immersed in a 4% aqueous sodium hydroxide solution at 50 ° C. for 30 seconds, and washed with water. , The electrolytic cell of the indirect power supply system is filled with 1.5% hydrochloric acid at 20 ° C., and the power supply is set to 20 A / dm ² , 50
Hz, a single-phase alternating current of 60 Hz is applied for 60 seconds to roughen the AC electrolytic surface, rinse with water, then immersed in a 6% nitric acid aqueous solution at 60 ° C. for 30 seconds, desmutted, washed with water, and then 25 ° C., 20%
It was passed through sulfuric acid for 60 seconds, anodized with a direct current of 5 A / dm ² , washed with water, and then dried to obtain an aluminum base for an offset printing plate (aluminum base 1).

On the thus prepared aluminum base, a nucleus coating solution described in Example 2 of JP-A-53-21602 (the copolymer of acrylamide and imidazole of No. 3 as a hydrophilic polymer) was used. 4 mg / m ² ) and dried.

The aqueous solution of inert gelatin was kept at 60 ° C.
By adding a mixed aqueous solution of sodium chloride and potassium bromide (29.5 mol% of potassium bromide) and an aqueous solution of silver nitrate at the same time with vigorous stirring, an average particle size of 0.2
An 8 μm silver chlorobromide emulsion was prepared, and potassium iodide corresponding to 0.5 mol% / 1 mol Ag was added to replace the surface. An emulsion layer containing these silver halide emulsion grains was coated on the above aluminum support and dried to prepare a lithographic printing material. The silver halide emulsion is composed of 70% silver chloride and 2 silver bromide.
This was a monodispersed silver chloroiodobromide emulsion comprising 9.5% and 0.5% silver iodide, wherein 90% by weight of all grains were within ± 30% of the average grain size.

The lithographic printing material thus obtained was unexposed and developed with the following diffusion transfer developer 1 at 23 ° C. for 15 seconds, and the gelatin layer was immediately rinsed off with running water (wash off). A lithographic printing original plate having a silver thin film exposed was prepared.

<Diffusion Transfer Developer 1> Sodium hydroxide 25 g Sodium sulfite 100 g Hydroquinone 25 g 4-Hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone 4 g Sodium ethylenediaminetetraacetate 8 g Sodium thiosulfate 8 g N-methylethanolamine 50g Carboxymethylcellulose 5g Glycerin 40g Add water 1,000ml

When the silver thin film thus produced was photographed with a scanning electron microscope and photographed with a silver thin film, it was found that the silver thin film was composed of granular silver particles. It was in the range of 0.005 to 0.2 microns.

The following overcoat liquid 1 was applied onto the silver thin film thus prepared so that the amount of applied moisture was 15 g / m ² , and dried. (Lithographic printing plate precursor 1) The thickness of the hydrophilic polymer layer was about 0.2 μm.

<Overcoat liquid 1> 10 g of gum arabic 85 g of phosphoric acid 1 g of water 900 ml 1N sodium hydroxide was added to adjust the pH to 7.0 ± 0.1. Add water and 1,000ml

The lithographic printing original plate 1 of the present invention thus prepared was exposed to an 8 W YAG laser having a wavelength of 1064 nm to ablate granular silver particles to obtain a lithographic printing plate 1. When the contact angle of the non-image portion of the lithographic printing plate 1 thus obtained with water was measured, it showed a value of 15 ° or less.

For comparison, a lithographic printing plate precursor a prepared in the same manner except that the overcoat liquid 1 was not applied was also exposed to an 8 W YAG laser having a wavelength of 1064 nm to obtain a lithographic printing plate a. When the contact angle of the non-image portion of lithographic printing plate a with water was measured in the same manner, the value was 65 °.

A lithographic printing plate precursor b was prepared in the same manner except that a hydrophilic polymer layer having a layer thickness of about 0.6 μm was provided by repeatedly applying the overcoat liquid 1. The lithographic printing plate precursor b was also exposed to an 8 W YAG laser having a wavelength of 1064 nm, but the ablation of the granular silver particles was insufficient, and the lithographic printing plate having black streaks formed along the main scanning line of the heat mode laser. b was obtained. When the contact angle of the non-image portion of the lithographic printing plate b with water was measured in the same manner, a value of 15 ° or less was shown.

The lithographic printing plate 1 thus obtained,
a and b were mounted on an offset printing machine (diamond 3H, manufactured by Mitsubishi Heavy Industries, Ltd.), using a plate surface water supply system (AD mode), and using as a dampening solution 2% Nistro Astromark III and 2% isopropyl alcohol. And printing was performed using N type GEOS-G black manufactured by Dai Nippon Ink Co., Ltd. as the ink. The lithographic printing plate a was soiled at the start, and after removing the ink using a plate cleaner, applying a gum solution and restarting, a printed matter free of dirt was obtained. In addition, in the lithographic printing plate b, the ink was difficult to be applied at the start, and after the ink was applied, the ink was applied on the black streaks of the plate, and a thin streak-like stain was generated. On the other hand, for the lithographic printing plate 1, a printed matter free of stains was obtained from the start.
The lithographic printing plate 1 provided with a hydrophilic polymer layer having a thickness of 0.01 to 0.5 μm, which is an embodiment of the present invention, exhibits excellent printing performance at the start and can print 100,000 or more sheets. there were.

Example 2 The aluminum base 1 of Example 1 was added to the following physical developer 1
After immersion at 3 ° C. for 3 minutes and washing with water for 30 seconds, 1.7
A silver thin film having a silver amount of 9 g / m ² was obtained.

Physical developer 2: 1 part of solution B is added to 5 parts of solution A

The following overcoat liquid 2 was applied onto the thus prepared silver thin film so that the amount of applied moisture was 15 g / m ² , and dried. (Lithographic printing plate precursor 2) The thickness of the hydrophilic polymer layer was about 0.2 μm.

<Overcoat Liquid 2> Monoethanolamine 5 g 3-n-octyl-5-mercaptooxadiazole 0.2 g Arabic gum 10 g Sodium dihydrogen phosphate 10 g 85% phosphoric acid 0.5 g Water 900 ml pH = 7. Adjusted to 0 ± 0.1. Add water and 1,000ml

The lithographic printing original plate 2 of the present invention thus produced was exposed to an 8 W YAG laser having a wavelength of 1064 nm to ablate granular silver particles to obtain a lithographic printing plate 2. When the contact angle of the non-image portion of the lithographic printing plate 2 thus obtained with water was measured, it showed a value of 15 ° or less.

The lithographic printing original plate 3 produced in the same manner except that the overcoat liquid 1 of Example 1 was applied instead of the overcoat liquid 2 was also used.
Exposure was performed with a YAG laser of 8 m in m to obtain a lithographic printing plate 3. When the contact angle of the non-image portion of the lithographic printing plate 3 with water was measured in the same manner, a value of 15 ° or less was shown.

The lithographic printing plates 2 and 3 thus obtained were subjected to the same printing test as in Example 1. Although the lithographic printing plates 2 and 3 both obtained printed matter free from the start, the lithographic printing plate 3 required 30 sheets until a sufficient image ink density was obtained.
The planographic printing plate 2 was a good product with 15 sheets. The lithographic printing plate 1 provided with a hydrophilic polymer layer having a thickness of 0.01 to 0.5 μm, which is an embodiment of the present invention, exhibits excellent printing performance at the start and can print 100,000 or more sheets. there were.

Example 3 For comparison with the embodiment described in JP-A-7-1848, a lithographic printing plate was prepared in the same manner as in Example 2 except that overcoat liquid c was applied instead of overcoat liquid 2. A printing original plate c was produced.

The lithographic printing original plate c also has a wavelength of 1064.
The resultant was exposed to light by a YAG laser having a wavelength of 8 W and a planographic printing plate c was obtained. When the contact angle of the non-image portion of the lithographic printing plate c with water was measured in the same manner, the value was 90 °.

<Overcoat liquid c> Monoethanolamine 5 g 3-n-octyl-5-mercaptooxadiazole 0.2 g Sodium dihydrogen phosphate 10 g 85% phosphoric acid 0.5 g Water 900 ml pH = 7.0 ± 0 Adjusted to 1. Add water and 1,000ml

Further, the overcoat liquid 1 of Example 1 was applied onto the lithographic printing original plate c to prepare a lithographic printing original plate d. The lithographic printing original plate d also has a wavelength of 1064 nm.
Exposure was performed with a YAG laser of W, and a planographic printing plate d was obtained, in which ablation of granular silver particles was insufficient and unevenness occurred. When the contact angle of the non-image portion of the lithographic printing plate d with water was measured in the same manner, a value of 15 ° or less was shown.

In the same manner as in Example 1, printing tests were performed on the lithographic printing plates c and d. The lithographic printing plate c becomes dirty at the start, and after removing ink with a plate cleaner,
When the gum solution was applied and restarted, a printed matter free of dirt was obtained. In addition, when the lithographic printing plate d is started, uneven stains appearing as the abrasion unevenness described above occur, and after removing ink using a plate cleaner,
Even when the gum solution was applied, an image without stain was not obtained.

Example 4 135 g / m ² double-sided polyethylene coated paper (RC paper) was provided on one side with a matting layer containing silicon dioxide particles having an average particle size of 5 microns and on the opposite side an average particle size of 7 microns. Silicon dioxide particles, sodium 2,4-dichloro-6-hydroxy-S-triazine as a hardener,
An undercoat layer made of carbon black and gelatin (added to 3.5 g / m ² ), and a silver chloride emulsion (containing 0.8 g / m ² of gelatin) on top of the undercoat layer were converted to silver nitrate in an amount of 1.
Two layers were simultaneously coated in a dark room with a silver halide emulsion layer containing 0 g / m ² and 80 mg / m ² of N-methylolethylene urea as a hardening agent, and dried.

Next, a nucleus comprising palladium sulfide, a copolymer of acrylamide and N-vinylimidazole (an imidazole group content of 2 mol%, an amide group content of 98 mol% and an average degree of polymerization of 1000), hydroquinone, saponin and water The coating solution was coated on the silver halide emulsion layer and dried.

Next, after performing development processing at 30 ° C. for 20 seconds with the following silver complex salt diffusion transfer developer 2 without exposure,
A lithographic printing original plate 4 was prepared by performing a treatment with the following neutralizing solution at 25 ° C. for 20 seconds.

<Silver complex salt diffusion transfer developer 2> Water 700 ml Potassium hydroxide 20 g Anhydrous sodium sulfite 50 g 2-mercaptobenzoic acid 1.5 g 2-methylaminoethanol 15 g Add water 1,000 ml

<Neutralized liquid> Water 600 ml Citric acid 10 g Sodium citrate 35 g Colloidal silica (20% solution) 5 ml Ethylene glycol 5 ml Water was added to 1,000 ml

When the silver thin film thus produced was photographed with a scanning electron microscope and photographed of the silver thin film, it was found that the silver thin film was composed of granular silver particles. The average particle size was measured. It was in the range of 0.005 to 0.2 microns.

The following overcoat liquid 3 was applied onto the silver thin film thus produced so that the amount of moisture applied was 15 g / m ² , and dried. (Lithographic printing plate precursor 4) The thickness of the hydrophilic polymer layer was about 0.2 μm.

<Overcoat Liquid 3> Monoethanolamine 5 g 3-n-octyl-5-mercaptooxadiazole 0.2 g Arabic gum 10 g Pullulan 2 g Sodium dihydrogen phosphate 10 g 85% phosphoric acid 0.5 g Water 900 ml pH = Adjusted to 7.0 ± 0.1. Add water and 1,000ml

The lithographic printing original plate 4 of the present invention thus produced was exposed to an 8W YAG laser having a wavelength of 1064 nm to ablate granular silver particles to obtain a lithographic printing plate 4. The contact angle of the non-image portion of the lithographic printing plate 4 thus obtained with water was measured and found to be 20 °.

For comparison, a lithographic printing original plate e produced in the same manner except that the overcoating liquid 3 was not applied was exposed to a 8W YAG laser having a wavelength of 1064 nm to obtain a lithographic printing plate e. When the contact angle of the non-image portion of the lithographic printing plate e with water was measured in the same manner, a value of 90 ° was shown.

Each of the lithographic printing plates 4 and e obtained as described above was mounted on an offset printing machine (3200MCD, manufactured by RYOBI MAGICS Co., Ltd.), and New Champion Purple N manufactured by Dainippon Ink Co., Ltd. was used as ink. And SLM-OD manufactured by Mitsubishi Paper Mills Co., Ltd.
The solution was diluted to 20 and printed before printing by applying a dampening solution all over the plate surface. In the case of the lithographic printing plate e, dirt is generated from the start, and the plate is stopped and the dirt on the plate surface is removed by Mitsubishi Paper Mills S
After wiping with LM-OHIII and printing again,
Staining occurred on 00 sheets. On the other hand, the lithographic printing plate 4 obtained a good image without stain. It has been found that a lithographic printing plate excellent in ablation suitability and printability can be obtained by providing a hydrophilic polymer layer having a thickness of 0.01 to 0.5 μm, which is an embodiment of the present invention.

[0139]

As described above, the method of making a lithographic printing plate according to the present invention can work even in a bright room and does not use a developing solution, so that the working environment is very good.
In addition, it is possible to cope with a direct drawing method using a laser, to obtain an image having high resolution at low cost, and to provide an excellent effect of having excellent printability.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating an example of a lithographic printing original plate used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aluminum base 2 Surface layer roughened and anodized 3 Silver thin film 4 Hydrophilic polymer layer

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Hideaki Ishiguro F4-2a in Mitsubishi Paper Mills Co., Ltd. 3-4-2 Marunouchi, Chiyoda-ku, Tokyo 2H096 AA07 AA08 BA17 BA20 CA03 CA05 CA20 EA04 GA45 2H114 AA04 AA14 AA22 BA05 DA04 DA06 DA32 DA75 GA09

Claims (7)

[Claims] An average particle size of 0.005 to 0.2 on a support having a hydrophilic surface or provided with a hydrophilic layer.
A lithographic printing plate comprising a silver thin film layer composed of granular silver particles having a thickness of 0.01 μm and a hydrophilic polymer layer having a thickness of 0.01 μm to 0.5 μm thereon is subjected to a heat mode. A method of making a lithographic printing plate, comprising removing a silver thin film using laser exposure. 2. The method according to claim 1, wherein the hydrophilic polymer layer contains 1 to 30% by weight of a hydrophobic compound. 3. The method according to claim 1, wherein the hydrophobic compound has a mercapto group and one or more hydrophobic substituents.
A method for making a lithographic printing plate according to claim 2. 4. The lithographic printing plate making method according to claim 1, wherein the granular silver particles are formed in the presence of a silver halide solvent. 5. The method for making a lithographic printing plate according to claim 4, wherein the silver halide solvent is an amine compound. 6. A method according to claim 5, wherein the amine is a compound represented by the following general formula 1. Embedded image (In the formula, at least one of R 1 to R 5 represents a substituted or unsubstituted amino group, and the other represents a hydrogen atom, a halogen atom,
Represents a substituted or unsubstituted saturated or unsaturated alkyl group, cycloalkyl group, alkoxy group, aryl group, acyl group, aroyl group, or heterocyclic group, which may be bonded to each other to form a ring . ) 7. The method for making a lithographic printing plate according to claim 1, wherein the support is an aluminum base which has been treated with an acidic treatment solution and then anodized.