JP2001305740A - Processing method for planographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planographic printing plate having satisfactory printing and stain resistances. SOLUTION: The surface of a planographic printing plate using surface- roughened and anodically oxidized aluminum having a psychometric lightness of <=78 as the base and utilizing a silver complex salt diffusion transfer process is processed with a silicate-containing processing solution after forming a silver image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithographic printing plate using an aluminum plate as a support, and more particularly to a method for processing a lithographic printing plate using a silver complex salt diffusion transfer method.

[0002]

2. Description of the Related Art A planographic printing plate using a silver complex salt diffusion transfer method (DTR method) is disclosed in "Focal Press, London New York (1972)," by Andrelot and Edith Weide, "Photographic Silver Halide. Some examples are described in "Diffusion Processes", pp. 101-130.

As described therein, a lithographic printing plate using the DTR method includes a two-sheet type in which a transfer material and an image receiving material are separated, or a monolithic type in which they are provided on a single support. Two types of sheet type are known. For a two-sheet type lithographic printing plate, see JP-A-57-158.
It is described in detail in Japanese Patent Publication No. 844. The mono-sheet type is described in detail in JP-B-48-30562, JP-B-51-15765, JP-A-51-111103, and JP-A-52-150105.

[0004] A lithographic printing plate using paper as a support is difficult to print with high quality including printing durability due to plate elongation during printing and penetration of moisture. A film support is used for the purpose of improving these problems and improving printing performance. For example, a cellulose acetate film, a polyvinyl acetal film, a polystyrene film, a polypropylene film, a polyethylene terephthalate film, or a composite film obtained by coating a polyester, polypropylene, or polystyrene film with a polyethylene film can be used as the support.

[0005] However, lithographic printing plates using a film as a support are improved in terms of plate elongation and moisture penetration, as compared with paper-based printing plates, but they have improved printing durability, water retention and printing. The problem remains in terms of the ability to hang the plate on the machine.

In order to solve the above-mentioned various problems of the lithographic printing plate using a paper or a film as a support, a lithographic printing plate of a silver salt type using a metal, particularly an aluminum plate as a support has been known. JP-A-57-118244, JP-A-57-158844
And JP-A-62-260491, JP-A-3-116151, and JP-A-4-82295.

It is known that a lithographic printing plate using an aluminum plate as a support is treated with a silicate at the time of manufacturing a base or treated with a silicate at the time of development in order to increase stain resistance. Also in the silver salt method, a method using a silicate for development processing in JP-A-7-199471 or JP-A-10-44637
It has been proposed to use a silicate treated base in the issue. However, when these methods are used in a silver salt system, there has been a problem that the adhesion between the silver image and the aluminum base is weakened and the printing durability is deteriorated.

Further, JP-A-6-317908 and JP-A-11-223952
No. reports that alkalis and salts are added to the washing solution to reduce the effect of the composition change of the washing solution due to the introduction of the developing solution into the washing solution. However, in this case, there is a problem that the ink adhesion of the silver image is deteriorated, the silver image does not accept the ink during printing, and as a result, a phenomenon that the printing durability becomes insufficient (ink peeling) occurs. Was.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithographic printing plate having a sufficient printing durability and good stain resistance.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithographic printing plate using a silver complex salt diffusion transfer method on a roughened and anodized aluminum support having a brightness index of 78 or less. This was achieved by processing with a processing solution containing silicate after image formation.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the term "after silver image formation" refers to the state after 0.2 g / m ² or more of silver is deposited on an unexposed portion on a plate surface. 0.2g / m ^{2 for} stencil surface treatment
After the silver is deposited, a second development step of further depositing silver, a washing step of removing the emulsion layer, a gumming step, an etching step on a machine performed before printing, etc. It is possible in the process, and it is particularly preferable to perform the treatment in the second developing step from the viewpoint of handleability and the like. It is also possible to perform treatment with a treatment liquid containing silicate over a plurality of steps.

As the silicate used in the present invention, various alkali metal silicates such as sodium silicate, potassium silicate and lithium silicate are preferable. The molar ratio of SiO2 / M2O of the alkali metal silicate is preferably 0.5 to 4 (M is an alkali metal salt). The amount used varies depending on the processing solution, but it is 0.01 to 10% by weight, preferably 0.05 to 6% by weight in terms of SiO2. Further, the pH is preferably 8 or more, more preferably 9 to 13 in order to prevent gelation of silicic acid.

In the present invention, when the development is divided into two times and the silicate treatment is carried out in the second development, the second developing solution contains, in addition to silicate, a developing agent such as polyhydroxybenzenes, 3 -Pyrazolidinones, preservatives such as sodium sulfite, thickeners such as carboxymethylcellulose, antifoggants such as potassium bromide, 1-phenyl-5-mercaptotetrazole, development modifiers such as polyoxyalkylene compounds, etc. Additives and the like.
In addition to the silicate, an alkaline substance such as potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium tertiary phosphate, or an amine compound can be contained.

The pH of the second developer is usually about 10 to 14, preferably about 12 to 14. However, the pretreatment (for example, anodizing) conditions of the aluminum support of the lithographic printing plate to be used, the photographic element, It depends on the image, the type and amount of various compounds in the developer, the development conditions, and the like.

In the present invention, the treatment with the silicate can be carried out in a washing step for removing the gelatin layer. Washing is performed at a temperature of about 20 to 40 # C. In order to further increase the printing durability, it is preferable to use a sulfite, such as sodium sulfite, sodium bisulfite, potassium sulfite, potassium bisulfite, lithium sulfite, ammonium sulfite, or the like, in order to further increase the printing durability. The amount is 0.001 ~
It is preferably 0.2 mol / L, more preferably 0.01 to 0.1 mol / L. It is also possible to include an enzyme or a compound having a mercapto group or a thione group as described in JP-A-10-133381. It is also possible to divide the washing step into multiple stages and to treat a part of the washing step with a treatment liquid containing silicate.

In silver salt printing plates, gumming is usually performed to protect the plate surface. The gum solution can also contain a silicate. The gum solution is arabic gum, dextrin, sodium alginate, hydroxyethyl starch,
It is preferable to have a protective colloid such as carboxymethylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone, polystyrenesulfonic acid, and polyvinyl alcohol.

In the present invention, the lightness index means the lightness index L * of the CIE1976L * a * b * color space adopted at the 18th CIE London Congress in 1975, and L * = 116 (Y / Yn) 1 Defined in / 3-16. Here, the Y value is the tristimulus value Y in the XYZ color system.
Yn is a Y value of standard light on the perfect diffuse reflection surface, and is defined as Yn = 100. These values are JIS8Z2
It can be measured by the method described in 2. If the value of L * is too black, the visibility of the image and the non-image portion is deteriorated, so that it may not be too low. L * is preferably 78 or less, more preferably 75 to 68.

The color tone of the aluminum support is affected by all steps of aluminum surface treatment such as surface roughening, desmutting, anodizing, and post-treatment. In particular, the effects of roughening and desmutting are great. This is because the surface has a high impurity concentration, so smut different in color from the ground of the base is generated in the roughening process, and the smut is dissolved and removed in the desmutting process, so the amount of smut remaining in both processes is determined. And the color tone of the base changes accordingly. In roughening, chemical polishing or electrolytic polishing is indispensable to segregate smut having a high impurity concentration on the surface.

The aluminum support used in the present invention has an aluminum purity of 93% by weight or more, preferably 99% by weight or more. As the aluminum impurities, elements commonly used as aluminum alloys such as iron, silicon, copper, manganese, magnesium, chromium, zinc, titanium, bismuth, lead, zirconium, and nickel can be used. Particularly preferred aluminum alloys include 1050, 1100, and 3003.

The aluminum support used in the present invention is rolled by a known method. That is, a slab is cast by dissolving and holding an aluminum ingot, and a surface cutting step of cutting an impurity structure portion of the slab surface by a facer at a rate of 3 to 10 mm is performed.
0 ° C., performing a soaking process of holding for 6 to 12 hours, and then hot rolling to a thickness of 5 to 40 mm,
Cold rolling is performed at room temperature to a predetermined thickness. In addition, after annealing and homogenizing the rolled structure etc. afterwards for the uniformity of the structure,
Cold rolling is performed to a specified thickness, and straightening is performed to obtain a plate with good flatness. The thickness of the support usually ranges from about 0.13 to 0.50 mm.

The support used in the present invention is subjected to a degreasing treatment, a roughening treatment, an anodizing treatment and the like which are generally used in this technical field. A support made in this order is used.

The aluminum plate used in the present invention is subjected to a degreasing treatment to remove fatty substances from the surface. Examples of the degreasing treatment include solvent degreasing such as trichlene and thinner, emulsion degreasing mixed with a surfactant, kerosene, triethanolamine, and sodium hydroxide, acid degreasing, and alkali degreasing.

The aluminum plate used in the present invention is subjected to a surface roughening treatment in order to improve the adhesion to the photosensitive layer and to improve the water retention. There are mechanical treatment, chemical treatment, and electrochemical treatment as a method of surface roughening treatment. These treatments are performed alone or in combination, but in particular, in order to control the color tone of the base, chemical treatment, electrochemical treatment, Processing is essential. The shape of the surface is generally represented by a roughness meter, and the size of the surface is center line average roughness;
1.0 μm is appropriate.

As the mechanical surface roughening treatment, a ball grain method, a nylon brush method, a buff polishing method, a blast polishing method, or the like can be used. Chloride,
There is a method of chemically dissolving aluminum with fluoride or the like.

Since the electrochemical graining treatment method can finely control the grain shape and surface roughness depending on the composition of the electrolytic solution and the electrolytic conditions as compared with other methods, it is preferable to use this method. preferable. The electrochemical graining treatment can be performed by direct current, alternating current, or a combination of both. As the AC wave, a single-phase or three-phase commercial AC or a sine wave in the range of 10 to 300 Hz including these, a square wave,
There are typhoons and the like.

The electric power supplied to the aluminum plate is an electrolytic solution.
Depends on the composition, temperature, distance between electrodes, etc.
In general, the voltage is 1 to 60
A / dm ^TwoThe electricity is used in the range of 50-4000C. Also
The distance between the electrode and the aluminum plate is preferably in the range of 1 to 10 cm.
New

As the electrolyte, an aqueous solution of nitric acid or a salt thereof, hydrochloric acid or a salt thereof, or one or a mixture of two or more thereof can be used. If necessary, sulfuric acid,
Phosphoric acid, chromic acid, boric acid, organic acids, or salts thereof, ammonium salts, amines, surfactants, other corrosion inhibitors, corrosion accelerators, and stabilizers can also be used.

As the concentration of the electrolyte, the concentration of the above-mentioned acids is as follows.
It is preferably 0.1 to 10%, and the concentration of aluminum ions in the electrolyte is maintained in the range of 0 to 10 g / L. The temperature of the electrolyte is preferably from 0 to 60 ° C.

In the present invention, desmut refers to a chemical etching step performed between surface roughening and anodic oxidation. Desmutting can be performed using an acid or alkali, but acid treatment is preferred. . As the acid, nitric acid, phosphoric acid, chromic acid, sulfuric acid, hydrochloric acid, hydrofluoric acid and the like can be used alone or as a mixture of several kinds. Sodium hydroxide, sodium carbonate, potassium hydroxide,
Potassium carbonate, potassium tertiary phosphate, sodium aluminate, sodium silicate and the like can be used alone or as a mixture of several kinds. Also, the concentration of the desmut liquid,
The processing time requires a concentration that can completely remove the smut. Since the amount of smut generation depends on the roughening treatment method at the preceding stage, the required degree of desmutting depends on the roughening method. However, since the degree of smut removal can be easily observed with a scanning microscope, the degree of desmut from which smut is completely removed can be easily determined by observing the surface of the aluminum treated with the scanning microscope. Actually, there is also a relation of waste liquid treatment, and the total amount of acid or alkali is about 5 to 40%, and the treatment time is 30 seconds to
Two minutes is preferred. The processing temperature is preferably from 40 to 60 ° C.

In the present invention, the desmutting step can be divided into two or more times. In this case, it is possible to combine acid desmut and alkali desmut, but it is preferable to use alkali desmut first.

After performing such a roughening treatment and a desmutting treatment, an anodic oxidation treatment is performed. Sulfuric acid, phosphoric acid, oxalic acid, chromic acid or an organic acid (eg, sulfamic acid, benzenesulfonic acid, etc.) or a mixture thereof is preferable for the anodizing electrolyte, and an acid having low solubility of the formed oxide film is particularly preferable. .

Since the anodic oxide film is formed only on the anode, a direct current is usually used as the current. The conditions of anodic oxidation are as follows: solution concentration 1-40%, current density 0.1-10A / dm ² , voltage 10-100V
Used in the range. The thickness of the anodic oxide film is changed depending on the current density and time, and is appropriately adjusted depending on the printing durability of the printing plate, but 3 g / m ² or less, preferably 2.8 g / m ^{2 to} 1 g /
m ^2, and more preferably preferably becomes 2.3g / m ² ~1g / m ² required. The temperature affects the hardness of the anodic oxide film, and the hardness increases at a low temperature, but the processing is usually performed at a temperature near normal temperature because of poor flexibility. The amount of anodic oxide film created is JIS
It can be measured based on H86807 “Coating Mass Method”.

After the anodic oxidation treatment, a post-treatment can be performed if necessary. As the post-treatment, methods known to those skilled in the art, for example, post-treatment with inorganic salts such as silicate treatment, fluorozirconic acid treatment, organic polymer treatment such as gum arabic, polyvinyl phosphonic acid, polyvinyl sulfonic acid, hydration There is a sealing treatment and the like.

In the present invention, a physical development nucleus layer may be provided between the aluminum support and the photosensitive silver halide emulsion layer in order to further increase the amount of physically developed silver deposited. The physical development nucleus of the physical development nucleus layer used in the present invention may be one used in a known silver complex salt diffusion transfer method, for example, gold,
Colloids such as silver, and metal sulfides obtained by mixing sulfides with water-soluble salts such as palladium and zinc can be used. Various hydrophilic colloids can be used as the protective colloid. For details and manufacturing methods, see Focal
Press, London New York (1972), by Andrelot and Edith Weide, "Photographic Silver Halide Diffusion Processes"
Can be referred to.

Various hydrophilic colloids can be used as protective colloids in the photosensitive silver halide emulsion layer of the printing plate of the present invention. That is, various gelatins such as acid-treated gelatin, alkali-treated gelatin, gelatin derivatives, and grafted gelatin can be used, and hydrophilic polymer compounds such as polyvinylpyrrolidone, various starches, albumin, polyvinyl alcohol, gum arabic, and hydroxyethyl cellulose. Can be contained. Examples of the hydrophilic colloid used include gelatin, a gelatin derivative, polyvinyl alcohol, and polyvinylpyrrolidone. Preferably, a substantially hardener is used to facilitate release of the hydrophilic colloid layer after physical development. It is desirable to use a hydrophilic colloid layer containing no.

The types of the photosensitive silver halide emulsion used in the present invention include commonly used silver chloride, silver bromide,
It is selected from silver iodide, silver chlorobromide, silver chloroiodobromide, silver iodobromide and the like. The emulsion type may be either a negative type or a positive type. These silver halide emulsions can be chemically or spectrally sensitized as necessary.

In the present invention, the silver halide emulsion layer may contain benzotriazole or a derivative thereof, or a nitrogen-containing heterocyclic compound having a mercapto group or a thione group. The amount is 1-100 mg / m ² , preferably 5
3030 mg / m ² .

Examples of the benzotriazole derivative include 5-methylbenzotriazole, 5-chlorobenzotriazole and the like. Examples of the heterocycle of the nitrogen-containing heterocyclic compound having a mercapto group or a thione group include imidazole, imidazoline, thiazole, thiazoline, oxazole, oxazoline, pyrazolidone, trizole, thiadiazole, oxadiazole, tetrazole, pyridine, pyrimidine, pyridazine, pyrazine, There are triazine and the like, and among them, imidazole, triazole and tetrazole are preferable.

Specific examples of the nitrogen-containing heterocyclic compound having a mercapto group or a thione group are shown below. 2-mercapto-4-fenlimidazole, 2-mercapto-1
-Benzylimidazole, 2 mercapto-1-butyl-
Benzimidazole, 1 ethyl-2-mercapto-benzimidazole, 2 mercapto-benzimidazole,
1,3 diethyl-benzimidazoline-2-thione,
1,3 dibenzyl-imidazolidin-2-thione, 2,
2-dimercapto-1,1′-decamethylene-diimidazoline-2-thione, 2-mercapto-4-phenylthiazole, 2-mercapto-benzothiazole, 2-mercaptonaphthothiazole, 3-ethyl-benzothiazoline-2-thione, 3-dodecyl-benzothiazoline-2
-Thione, 2-mercapto-4,5-diphenyloxazole, 2-mercaptobenzoxazole, 3-pentyl-benzoxazoline-2-thione, 1-phenyl-3-methylpyrazolidone-5-thione, 3-mercapto- 4-allyl-5-pentadecyl-1,2,4-triazole, 3-mercapto-5-nonyl-1,2,4-
Triazole, 3-mercapto-5-nonyl-5-1,
2,4-triazole, 3-mercapto-4-allyl-
5-pentadecyl-1,2,4-triazole, 3-mercapto-4-amino-5-heptadecyl-1,2,4
-Triazole, 2-mercapto-5-phenyl-5-
Pentadecyl-1,3,4-thiadiazole, 2-mercapto-5-n-heptyl-oxathiazole, 2-mercapto-5-phenyl-1,3,4-oxadiazole, 5-mercapto-1-phenyl-tetrazole, 2
-Mercapto-5-nitropyridine, 1-methyl-quinoline-2 (1H) -thione, 3-mercapto-4-methyl-6-phenylpyridazine, 2-mercapto-5,6
-Diphenyl-pyrazin, 2-mercapto-4,6-
Diphenyl 1,3,5 triazine, 2-amino-4-mercapto-6-benzyl-1,3,5-triazine,
1,5-dimercapto-3,7-diphenyl-S-triazolino [1,2-a] -S-triazoline and the like.

In the present invention, a developing agent such as polyhydroxybenzenes, 3-pyrazolidinones, preservatives,
E.g. sodium sulfite, thickeners such as carboxymethylcellulose, antifoggants such as potassium bromide,
1-phenyl-5-mercaptotetrazole, development modifier,
For example, additives such as a polyoxyalkylene compound can be included. In addition to the silicate, an alkaline substance such as potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium tertiary phosphate, or an amine compound can be contained.

[0041]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In addition,% shows weight% unless there is a notice.

Example 1 A 1050 aluminum plate was degreased with a 4% aqueous sodium hydroxide solution at 50 ° C. for 1 minute, washed with water, polished with a 400 mesh pumicestone suspension using a rotating nylon brush, and polished with a rotating nylon brush. AC density 50A / dm ² at 20 ° C
For 60 seconds, followed by desmutting with 20% phosphoric acid at 50 ° C. for 1 minute. Then in a 25% sulfuric acid solution at a temperature of 20 ℃
Anodizing was performed at a current density of 3 A / dm ² and a processing time of 45 seconds. The L * of this base was measured using an ND1001DP colorimeter manufactured by Nippon Denshoku Industries Co., Ltd., and found to be 73.2.

A coating amount of 3 mg / m ² on the prepared aluminum support
A palladium sulfide nucleus is coated as a physical development nucleus so that a silver chloride emulsion containing 0.5% iodine (average particle size 0.3 μm)
m) was gold-sulfur sensitized and dye-sensitized to red, and coated and dried with silver nitrate so as to have a coating amount of 2.0 g / m ² to prepare a photosensitive lithographic printing plate.

The lithographic printing plate obtained in this manner has an image setter SDP-α24 whose light source is a red semiconductor laser.
Image exposure and full screen exposure were performed at 2400 dpi and 175 lpi with 00 (manufactured by Mitsubishi Paper Mills). Next, the developing time was changed as shown in Table 1 at 22 ° C., and immediately after the first developing treatment, sodium silicate was converted to SiO 2 in a developing solution having the same composition as the first developing solution. In the second developer, the amount of which was changed as
The immersion development was performed at 10 ° C. for 10 seconds. Immediately thereafter, the emulsion layer was washed off with water in a rewash mode of a plate making processor (P-α880 manufactured by Mitsubishi Paper Mills). The plate making processor includes a developing process (22 ° C.), a rinsing process (washing off the emulsion layer with a scrub roller while spraying rinsing water at 35 ° C.), a finishing process (21 ° C., shower), and a drying process. It is composed of The washing process is a closed type that circulates 20L of washing water stored in the storage tank with a pump, sprays it onto a lithographic printing plate, then filters it with a filter, collects it in the storage tank, and reuses it. .

The constitutions of the used developing solution, washing solution and finishing solution are as follows. <Developer> 20 g of sodium hydroxide 20 g of hydroquinone 1 g of 1-phenyl-3-pyrazolidinone 2 g of anhydrous sodium sulfite 80 g 6 g of N-methylethanolamine 5 g of sodium ethylenediaminetetraacetate 5 g Make up to 1000 mL with deionized water. pH (25 ° C) = 13.4

<Washing solution> 2-mercapto-5-n-heptyl-oxanediol 0.5 g triethanolamine 13 g sodium bisulfite 10 g potassium dihydrogen phosphate 40 g proteinase 1 g Water is added to adjust the total amount to 1000 cc. . pH 6.0
Was adjusted. Bioprolase as a proteolytic enzyme
AL-15 (bacterial proteinase, manufactured by Nagase & Co., Ltd.) was used.

<Finishing solution> Gum arabic 10 g Phosphoric acid 0.5 g Sodium nitrate 20 g Polyethylene glycol # 400 100 g 2-Mercapto-5-n-heptyloxane diol 0.5 g Make up to 1000 mL with deionized water. The pH was adjusted to 6.5 with sodium hydroxide.

[0048]

[Table 1]

The lithographic printing plate thus prepared was printed by a printing machine Sprint 226 (Komori Corporation).

Table 2 shows the printing results. The printing durability represents the number of halftone dots or fine lines. As an evaluation of the stain, water was supplied during printing to clean the entire surface of the plate, and water was supplied again to check how many times the non-image portion was stained. In this case, it can be said that the better the printing plate, the more the stain can be removed with a small number of sheets.

[0051]

[Table 2]

As can be seen from Table 2, when the silicate treatment is performed before silver deposition, no printing durability is obtained. On the other hand, in the present invention in which the silicate treatment is performed after silver deposition, both the printing durability and stain resistance are excellent. You can see that.

Example 2 A base was prepared in the same manner as in Example 1, except that the desmut time was changed as shown in Table 3 and L * was changed. When the developing treatment was performed under the following conditions, the results shown in Table 3 were obtained.

[0054]

[Table 3]

As can be seen from Table 3, when L * is large, the printing durability cannot be obtained by this method.

Example 3 A plate was prepared in the same manner as in Example 1, and the developing solution was developed at 22 ° C. for 12 seconds using a developing solution containing no silicate. The test was conducted in the same manner as in Example 1 except that sodium bisulfite was added and the solution was washed with a washing solution adjusted to pH 10.0 with sodium hydroxide or sulfuric acid. Table 4 shows the results.

<Washing solution> 2-Mercapto-5-n-heptyl-oxanediol 0.5 g Triethanolamine 13 g Protease 1 g Water is added to adjust the total amount to 1000 cc. pH 6.0
Was adjusted. Bioprolase as a proteolytic enzyme
AL-15 (bacterial proteinase, manufactured by Nagase & Co., Ltd.) was used.

[0058]

[Table 4]

From Table 4, it can be seen that the use of a silicate in the washing solution is effective for the stain resistance. Further, it can be seen that the printing durability is poor unless a sulfite is added.

[0060]

According to the present invention, a lithographic printing plate having a surface roughness of anodized aluminum having a lightness index of 78 or less and using a silver complex salt diffusion transfer method as a support is treated with a silicate-containing plate after forming a silver image. By treating with a liquid, a lithographic printing plate having sufficient printing durability and stain resistance can be obtained.

Claims (2)

[Claims] 1. A processing solution containing a silicate after forming a silver image on a lithographic printing plate using a silver complex salt diffusion transfer method using a roughened and anodized aluminum having a lightness index of 78 or less as a support. A method of processing a lithographic printing plate, characterized in that the method is performed by: 2. The method for processing a lithographic printing plate according to claim 1, wherein the silver image is formed and then processed with a processing solution containing a sulfite and a silicate.