JPS6352600B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a negative photosensitive lithographic printing plate (Pre-
It is called a sensitized plate. Hereafter abbreviated as PS version. )
The present invention relates to a plate-making method for obtaining a lithographic printing plate from a lithographic printing plate, and particularly relates to a plate-making method in which, after development with an alkaline developer containing water as a main solvent, desensitization treatment is performed with an aqueous desensitizing solution.

Conventionally, the plate-making method for negative-tone PS plates having a photosensitive layer containing a diazo compound has consisted of developing with an alkaline solution containing water as the main solvent, washing with water, and desensitizing in this order. water was used, and the waste liquid was simply discarded.

In recent years, from the perspective of pollution prevention, methods have been developed to improve such plate-making methods, such as methods that do not directly discharge the washing waste liquid, such as methods that do not include a washing step at all.
Another method is to circulate and use washing water and to treat the circulating washing water after plate making.

On the other hand, emulsifying type and non-emulsifying type, that is, aqueous solutions are known as desensitizing liquids.
Emulsified desensitizing liquids have the drawbacks of complicated manufacturing methods, high manufacturing costs, and high burden on used waste liquid treatment because they contain water-insoluble lipophilic components, water-insoluble organic solvents, etc. Aqueous solutions are preferred.

In a plate-making method for a negative photosensitive lithographic printing plate having a photosensitive layer containing a diazo compound using a method in which the washing waste liquid is not directly discharged, a method using an aqueous desensitizing liquid having the above-mentioned advantages has been disclosed. It is disclosed in Publication No. 54-8002.

However, when the lithographic printing plate obtained by this plate-making method is used for printing, it has the disadvantage that a considerable amount of paper (wasted paper) is wasted until the normal printing state is reached after printing starts, so it is not satisfactory. isn't it.

Therefore, an object of the present invention is to provide a plate-making method that does not directly discharge the washing water between the development step and desensitization step of a negative PS plate having a photosensitive layer containing a diazo compound, and which uses it as a desensitization liquid. The object of the present invention is to improve the drawbacks of the prior art in the plate making method using a non-emulsifying type.

Another object of the present invention is to provide a method for making the above-mentioned negative PS plate that can be processed with a desensitizing solution, which is simple and inexpensive to produce.

Still another object of the present invention is to provide a method for making the above-mentioned negative PS plate, which makes it possible to obtain an excellent lithographic printing plate with less waste paper.

As a result of various studies, the present inventors have found that the object of the present invention can be achieved by the following plate-making method. That is, in the present invention, a negative photosensitive lithographic printing plate having a photosensitive layer containing a diazo compound on a support is imagewise exposed, developed with an alkaline developer to remove non-image areas, and then desensitized. In the plate-making method, the desensitizing liquid used in the desensitizing treatment is an aqueous solution containing dextrin, an acid, an anionic surfactant, and a nonionic surfactant in an amount of 150 to 1% by weight based on the anionic surfactant. This is a distinctive plate-making method.

The desensitizing liquid used in the present invention is an aqueous solution containing (1) dextrin, (2) acid, (3) anionic surfactant, and (4) nonionic surfactant.

Dextrin is a main component that protects the surface of a lithographic printing plate, and various types are known, but those with high solubility in water are preferred.

Those containing 70% or more of the soluble content in water at 20°C are preferred, and those containing 90% or more are particularly preferred. Although dextrins produced by various modification methods are known, enzyme-modified dextrins are particularly advantageous in terms of operability during the preparation of a desensitizing solution, removability of the desensitizing agent during printing, and the like. The amount of dextrin contained in the desensitizing liquid is preferably in the range of 5 to 30% by weight, particularly preferably in the range of 8 to 25% by weight.

The acid contained in the desensitizing liquid is used primarily for the purpose of adjusting the pH of the desensitizing liquid before use to an acidic range, preferably in the range of 1 to 5, more preferably in the range of 2 to 3. It is. For example, inorganic acids such as phosphoric acid, pyrophosphoric acid, polyphosphoric acid, monosodium phosphate, boric acid, hydrochloric acid, sulfuric acid, nitric acid, etc., such as succinic acid, oxalic acid, citric acid, maleic acid, lactic acid, p-toluenesulfonic acid, benzenesulfonic acid, etc. These organic acids can be used alone or in combination of two or more. Among these, phosphoric acid and succinic acid are particularly preferred. The amount of acid used is such that the PH of the desensitizing solution is in the acidic range, but approximately
It is 0.01 to 5% by weight.

It is essential that both an anionic surfactant and a nonionic surfactant exist in the desensitizing liquid used in the present invention. Products that do not contain anionic surfactants are used when a developer is brought in, such as an automatic developing machine that continuously performs the development process and desensitization process, or a continuous development process, circulating water washing process, and desensitization process. When a desensitizing liquid is circulated and used repeatedly in an automatic processor used for printing, insoluble matter is likely to be generated, and this is presumed to be caused by the insoluble matter adhering to the plate surface, which causes stains during printing.
In addition, those containing no nonionic surfactant have poor oil sensitivity in the image area, resulting in a lot of paper loss, and depending on the type of anionic surfactant, a uniform aqueous solution may not be obtained. By containing an anionic surfactant and a nonionic surfactant, no insoluble matter is generated when the developer is mixed in, the oil sensitivity of the image area can be improved, and a uniform aqueous solution can be obtained. can.

Examples of anionic surfactants used in the present invention include fatty acid salts, alkyl sulfates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylsulfosuccinates, alkyl phosphates, polyoxyalkyl sulfates, and polyoxyalkyl sulfates. Examples include alkyl phenol ether sulfate, naphthalene sulfonic acid formalin condensate, etc. For example, di(2-ethylhexyl)
Alkyl sulfosuccinates such as sodium sulfosuccinate, e.g. polyoxyethylene (20 moles of ethylene oxide) polyoxyethylene alkyl ether salts such as sodium oleyl ether sulfate, e.g. polyoxyethylene (19 moles of ethylene oxide) nonylphenol ether Polyoxyethylene alkyl phenol ether sulfates such as sodium sulfate, naphthalene sulfonate formalin condensates, alkylnaphthalene sulfonates, and the like are preferred, and polyethylene oxide alkyl phenol ether sulfates are particularly preferred. The content of the anionic surfactant is preferably 0.001 to 2% by weight, particularly preferably 0.05 to 1% by weight, based on the total weight of the desensitizing liquid.

Nonionic surfactants used in the present invention include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, glycerin fatty acid ester, and oxyethylene oxypropylene block polymer. However, in order to make the desensitizing liquid into an aqueous solution, it is preferable that the HLB value, which expresses the balance between hydrophilicity and lipophilicity, is about 12 or more.
It is particularly preferred that the HLB value is 13-18. Among those having such HLB, polyoxyethylene alkyl phenol ethers such as polyoxyethylene (the number of moles of ethylene oxide is about 10 to 30) nonyl phenol ether are particularly preferred. The amount of nonionic surfactant contained in the desensitizing liquid is preferably 150 to 1% by weight, particularly preferably 100 to 10% by weight of the anionic surfactant.

In addition to the above-mentioned components, the desensitizing liquid used in the present invention can contain various water-soluble polymer compounds for the purpose of improving film-forming properties and the like. As the water-soluble polymer compound, any compound that has been conventionally considered to be usable in a desensitizing solution can be suitably used.
For example, cellulose ethers such as methylcellulose, ethylcellulose, hydroxypropylcellulose, and carboxymethylcellulose, alginates such as sodium alginate, synthetic polymer compounds such as porvinyl alcohol, polyacrylamide, and copolymers of vinyl methyl ether and maleic anhydride. , gum arabic, etc. Particularly preferred among these is carboxymethylcellulose sodium salt (commonly referred to as CMC). These water-soluble polymer compounds can be used alone or in combination of two or more. The amount of these water-soluble polymer compounds is preferably 50% by weight or less, more preferably 30% by weight or less, based on the weight of the dextrin.

The desensitizing liquid may further contain a water-soluble salt. Suitable water-soluble salts include alkali metal salts, ammonium salts, such as ammonium acetate, sodium acetate, potassium acetate, sodium molybdate, potassium molybdate, sodium borate, ammonium borate, lithium nitrate, sodium nitrate, potassium nitrate, diphosphoric acid. Examples include sodium, tribasic sodium phosphate, dibasic potassium phosphate, tribasic potassium phosphate, tribasic ammonium phosphate, and sodium polyphosphate. Among the above, particularly preferred are sodium (potassium) molybdate, potassium sulfate and sodium (ammonium) borate. Such water-soluble salts can be used alone or in combination of two or more, and are preferably 0.01 to 5% by weight based on the total weight of the desensitizing liquid.
It is used in a range of 0.1 to 1% by weight.

The desensitizing liquid may further contain a wetting agent. As such wetting agents, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerin are preferably used.

The amount of wetting agent is approximately 0.01~ based on the total weight of the desensitizing liquid.
It can be used in an amount of 1% by weight, more preferably 0.1 to 0.5% by weight.

The desensitizing liquid may further contain a coloring agent such as a dye.

The pH on the desensitized printing plate is preferably 9 or less, more preferably 7 or less, from the viewpoint of staining during printing.

The coating amount of the desensitizing liquid in the plate making method of the present invention is preferably from 0.1 g/m ² to 1.5 g/m ² in terms of dry coating weight, particularly preferably from 0.2 to 0.8 g/m ² .

Conventionally known supports for the PS plate used in the present invention can be used, such as paper, plastic laminated paper, metal plates such as aluminum, zinc, and copper, polyethylene terephthalate, polypropylene, and cellulose triacetate. Examples include plastic films such as, metal plates having metals such as chromium and nickel on the surface, paper, and plastic. Among these supports, aluminum plates are particularly preferably used because they have excellent dimensional stability and are inexpensive.

The surface of these supports can be processed to make them hydrophilic, to prevent harmful reactions with the photosensitive composition provided as a layer thereon, and to improve adhesion with the photosensitive layer. preferable. For example, in the case of an aluminum plate, after mechanical, chemical or electrochemical polishing, sodium silicate,
It is preferable to perform immersion treatment in an aqueous solution of potassium fluorozirconate, phosphate, etc. or anodization treatment.

The negative type diazo compound contained as a photosensitive component in the photosensitive layer provided on the support is preferably one that is insoluble in water and soluble in an organic solvent. Typical examples include diazonium salts and/or diazo resins which are condensates of p-diazodiphenylamine and formaldehyde, and phenol salts of p-diazodiphenylamine or fluorocaprin described in Japanese Patent Publication No. 7364/1983. Acids, etc., Special Publication 1977
A diazo resin consisting of an organic solvent-soluble salt of a paraformaldehyde cocondensate of 3-methoxydiphenylamine-4-diazonium chloride and 4-nitrodiphenylamine described in Publication No. 48001, p-diazodiphenylamine and Examples include 2-methoxy-4-hydroxy-5-benzoylbenzenesulfonate, which is a condensate with formaldehyde. Among these condensates, hexafluorophosphate, a condensate of p-diazodiphenylamine and formaldehyde, or 2-methoxy-4-
Hydroxy-5-benzoylbenzene sulfonates are preferred, especially the former.

Although these diazo compounds can be used alone,
In order to improve the physical properties of the photosensitive layer, it is preferable to use it in combination with various resins. Examples of such resins include derivatives of polyvinyl alcohol, copolymers having an alcoholic hydroxyl group in the side chain described in JP-A-50-118802, and copolymers having an alcoholic hydroxyl group in the side chain described in JP-A-55-155355. Examples include copolymers having a phenolic hydroxyl group in a side chain.

Among these: copolymers containing at least 50% by weight of structural units represented by the general formula: (In the formula, R ₁ represents a hydrogen atom or a methyl group, R ₂ represents a hydrogen atom, a methyl group, an ethyl group, or a chloromethyl group, and n is an integer of 1 to 10.) and: aromatic hydroxyl group Preferably, a polymer compound having 1 to 80 mol% of a monomer unit having 1 to 80 mol% and 5 to 90 mol% of an acrylic ester and/or methacrylic ester monomer unit and having an acid value of 10 to 200, The latter is particularly preferred.

The photosensitive layer of the PS plate used in the present invention further includes:
Additives such as dyes, plasticizers, components that provide printout performance, etc. can be added.

A photosensitive layer having such a composition is coated onto a support using a solution in a suitable solvent.

The coating amount of the photosensitive layer provided on the support is
0.1-7g/ ^m2 is preferable, more preferably 0.5-7g/m2
It is 3g/ ^m2 .

The thus obtained PS plate is exposed through a transparent original to a light source rich in actinic rays such as a carbon arc lamp, mercury lamp, metal halide lamp, or tungsten lamp, and then developed in a wet processing process.

The developing solution used in the above development process is an alkaline solution containing water as a main solvent, and an alkaline agent containing an organic solvent, an anionic surfactant, an inorganic salt, etc. as required is used.

Alkaline agents include sodium silicate, potassium silicate, potassium hydroxide, sodium hydroxide,
Inorganic alkaline agents such as lithium hydroxide, tribasic sodium phosphate, sodium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, or mono,
Organic alkaline agents such as di- or triethanolamine or propanolamine are advantageously used. The content of the alkaline agent in the developer is preferably 0.05 to 4% by weight, more preferably 0.1 to 2% by weight.

Useful organic solvents include alcohols such as n-propyl alcohol and benzyl alcohol, and glycol ethers such as phenyl cellosolve. The content of the organic solvent in the developer is preferably 0.5 to 15% by weight, and 1 to 5% by weight.
The range is more preferable.

Examples of anionic surfactants include alkyl sulfate salts such as sodium lauryl sulfate, alkylaryl sulfonates such as dodecylbenzenesulfonic acid, and sulfonates of dibasic fatty acid esters such as sodium di(2-ethylhexyl)sulfosuccinate. Examples of acid salts include alkylnaphthalenesulfonates such as sodium n-butylnaphthalenesulfonate, polyoxyethylene alkyl (phenol) ether sulfates, etc. Among these, alkylnaphthalenesulfones such as n-butylnaphthalenesulfonic acid Acid acids are preferably used. The content of the anionic surfactant in the developer is preferably 0.1 to 5% by weight, and 0.5% by weight.
A range of 1.5% by weight is more preferred.

As the inorganic salt, alkali or alkaline earth water-soluble salts such as phosphoric acid, silicic acid, carbonic acid, sulfite, etc. are used, and alkali or alkaline earth sulfites are particularly preferably used. The content of the inorganic salt in the developer is preferably in the range of 0.05 to 5% by weight, more preferably in the range of 0.1 to 1% by weight.

It is also useful to further contain an antifoaming agent, a wetting agent, etc. in the developing solution, if necessary.

Various conventionally known methods can be used to develop the PS plate which has been imagewise exposed with the developer as described above. Specifically, methods include immersing the image-exposed PS plate in a developer, spraying the developer onto the photosensitive layer of the PS plate from multiple nozzles, and using a sponge moistened with the developer to remove the PS plate. Examples include a method of wiping the photosensitive layer, and a method of applying a developer to the surface of the photosensitive layer of the PS plate using a roller. Further, after the developer is applied to the photosensitive layer of the PS plate in this manner, the surface of the photosensitive layer can be lightly rubbed with a brush or the like.

Development conditions can be appropriately determined by those skilled in the art depending on the above-mentioned development method.

In the present invention, after the PS plate is developed as described above, it is desensitized, but after development, it is preferable to first squeeze the plate to reduce the amount of developer on the plate surface. In the present invention, the squeezed printing plate may be desensitized directly, or it may be washed with circulating water and then squeezed again to be desensitized.

It is preferable to sufficiently squeeze the desensitizing solution so as to reduce the amount of the developer in which the photosensitive layer is dissolved to be mixed into the desensitizing solution.

The amount of liquid remaining on the plate surface to be desensitized is preferably 10 ml or less per 1 m ² of the plate surface, and
It is preferable to make it less than ml.

Squeezing methods include, for example, passing a lithographic printing plate between a pair of elastic rollers whose surfaces are coated with an elastic member such as rubber, and using the nip pressure to remove the developing solution or circulating washing water from the plate surface; or A method in which a flexible elastic plastic material is placed along the transport path of a lithographic printing plate and scraped off developer solution or circulating washing water from the plate surface by sliding it in contact with the plate surface. A method such as scraping can be adopted. Among these methods, a method using a pair of rollers is preferably used because of the simplicity of the device.

The desensitizing process involves rubbing the plate surface with a sponge moistened with a desensitizing agent and then drying it, or supplying an excess of desensitizing liquid onto the lithographic printing plate and squeezing it by passing it between a pair of rollers, and then Although there are methods such as drying, the latter method is effective in the present invention, and is particularly effective when the desensitizing solution is used in circulation.

A block diagram of one embodiment of the apparatus used to carry out the present invention is shown in FIG.

In the figure, 1 is a developing treatment tank, 2 is a circulation washing tank, and 3 is a desensitization treatment tank. Reference numerals 4, 5 and 6 are transport pipes for sending the treatment liquids 1, 2 and 3 above to spray pipes described later, respectively, and 7, 8 and 9 are pumps provided in the liquid transport pipes, respectively. 10A, 10B and 10C are processing liquid spray pipes for spraying the processing liquid from tank 1 onto the printing plate surface; 11 and 12 are processing liquid spray pipes for spraying the processing liquid from tank 2 and tank 3 onto the printing plate surface, respectively. This is a treatment liquid spray pipe for spraying.

13 is a guide roller, 14 and 15 are conveyance rollers, 16 is a pedestal, and 17 is a brush roller. And 18, 19, 20, 21 and 22 are all squeeze rollers. 2
3 is the exposed PS plate, 24 is the PS after desensitization treatment
It is a version.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A grained aluminum plate with a thickness of 0.24 mm was anodized in sulfuric acid to form an oxide film of approximately 2 g/m ² , which was thoroughly washed, immersed in a sodium silicate aqueous solution, thoroughly washed with water, and then dried. A photosensitive solution having the following composition was applied.

[Para-hydroxyphenyl methacrylamide,
Copolymer of acrylonitrile, ethyl acrylate, and methacrylic acid (molar ratios are in the above order)
8.5:24:60.5:7) 5.0 parts by weight Hexafluorophosphate of condensate of P-diazodiphenylamine and paraformaldehyde
0.5 parts by weight Victoria Pure Blue BOH (manufactured by Hodogaya Chemical Industry Co., Ltd.) 0.1 parts by weight Methyl cellosolve 100 parts by weight] The coating amount after drying was 1.8 g/m ² . The negative PS plate obtained in this way is 800mm x 1003mm.
A large number of sheets were cut to the size of , and a transparent negative was passed through them and exposed for 50 seconds from a distance of 80 cm using a 2Kw metal halide lamp.

On the other hand, the developing tank of the automatic processor shown in Figure 1 is filled 16 times with a developer having the composition shown below, the processing tank next to the developing tank is filled 16 times with water, and the next processing tank is filled with a desensitizing solution having the composition shown below. Satisfied 4.

Developer: Phenyl cellosolve 40 parts by weight Diethanolamine 10 parts by weight Sodium n-butylnaphthalenesulfonate
12 parts by weight Antifoaming agent (trade name SM-5512 manufactured by Toray Silicone Co., Ltd.) 0.05 parts by weight Water 937 parts by weight Desensitizing liquid Dextrin (trade name PENON JE-66 (manufactured by Nippon Deka Chemical Co., Ltd.)) 9 Parts by weight Carboxymethyl cellulose sodium salt
0.45 parts by weight Phosphoric acid 0.2 parts by weight Sodium naphthalene sulfonate formalin condensate (trade name Demol N (Kao Atlas K, K
)) 0.5 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 15) Nonylphenol ether (trade name NP-15 (Japan Surf Actant K, K
)) 0.1 part by weight p-hydroxyethylbenzoate 0.05 part by weight Water 90 parts by weight Next, a large number of the exposed PS plates obtained as described above were processed in the above-mentioned automatic processor. Note that the PS plate taken out from the desensitization treatment tank was dried with hot air. Furthermore, the treatment liquids in the washing tank and the desensitizing tank were circulated and used. Exposed like this
Although 300 PS plates were processed, no insoluble matter was observed in the desensitizing solution. In addition, when printing was carried out using the 300th plate, normal prints were obtained in about 5 pages after printing, and it was a plate with excellent oil sensitivity in the image area. No outbreak was observed. For comparison, instead of the above desensitizing liquid, the above desensitizing liquid was prepared by removing only the anionic surfactant Demol N (A), and by removing only the nonionic surfactant NP-15 (B) , and the same treatment as above except for using (C) excluding the anionic surfactant and nonionic surfactant, and when using (A) and (C), it was exposed.
After processing 150 PS plates, insoluble matter was formed in the desensitizing solution, causing stains during printing.

Further, when (B) was used, no insoluble matter was generated, but during printing, it took about 8 sheets to obtain a normal print, and the oil sensitivity of the printed area was poor.

Example 2 The same treatment as in Example 1 was carried out, except that a desensitizing liquid having the following composition was used.

Dextrin (same as Example 1) 10 parts by weight Carboxymethyl cellulose sodium salt
0.45 parts by weight Phosphoric acid 0.25 parts by weight Sodium di(2-ethylhexyl)sulfosuccinate 0.14 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 20) Nonylphenol ether
0.1 part by weight p-hydroxyethylbenzoate 0.05 part by weight Water 90 parts by weight The test results showed that no insoluble matter was generated in the desensitizing solution even after processing 400 exposed PS plates.
When printed with the second printing plate, the image area was excellent in oil sensitivity, and even after 100,000 copies were printed, there was no staining and clear prints were obtained. On the other hand, when the same treatment was carried out except that the above desensitizing liquid with the anionic surfactant removed (D) and the nonionic surfactant removed (E) were used, (D) was used. is 130
When the sheets were processed, insoluble matter was generated in the desensitizing solution, causing stains during printing. Furthermore, when (E) was used, the oil sensitivity of the initial image area during printing was poor.

Example 3 The same treatment as in Example 1 was carried out, except that a desensitizing solution having the following composition was used and the amount of developer used was 25.

Dextrin (same as Example 1) 8 parts by weight Carboxymethyl cellulose sodium salt
0.45 parts by weight Phosphoric acid 0.2 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 19) Nonylphenol ether sodium sulfate 0.5 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 20) Nonylphenol ether
0.08 parts by weight Gum arabic 0.3 parts by weight p-hydroxyethylbenzoate 0.05 parts by weight Water 90 parts by weight The test results showed that no insoluble matter was generated in the desensitizing solution even after processing 600 exposed PS plates.
Furthermore, when printing was carried out, the oil sensitivity of the image area was good, and no staining occurred even after printing 100,000 sheets.

Example 4 The tank next to the developing tank of the automatic processing machine used in Example 1 was filled with desensitizing liquid 16 having the following composition, the roller of the next tank was removed, and no processing liquid was used.

The developer tank was filled with the same developer 16 as used in Example 1, and the exposed PS plate similar to that used in Example 1 was processed.

Dextrin (same as Example 1) 7.5 parts by weight Carboxymethyl cellulose sodium salt
0.45 parts by weight Phosphoric acid 0.15 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 19) Sodium nonylphenol ether sulfate 0.5 parts by weight Polyethylene oxide (average number of added moles of ethylene oxide 15) Nonylphenol 0.05 parts by weight p-hydroxybenzoate 0.04 parts by weight Water 90 parts by weight The test results show that no insoluble matter was observed in the desensitizing solution even after processing 150 exposed PS plates.
When printed, the oil sensitivity of the printed area was good, with a rating of 10
Even after printing 10,000 sheets, no stains were observed. In the treatment using the above desensitizing liquid without the nonionic surfactant, the greasensitivity of the printed area was poor, and in the treatment using the desensitizing liquid without the anionic surfactant, the desensitizing liquid was removed after the 80th sheet. Insoluble matter was generated inside the paper, causing stains during printing.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the configuration of a developing processing apparatus according to the present invention. 1... Development treatment tank, 2... Circulating water washing tank, 3... Desensitization treatment tank, 7, 8 and 9... Pump, 10A, 1
0B, 10C, 11 and 12... Processing liquid spray pipe, 18, 19, 20, 21 and 22... Squeeze roller, 23 and 24... Lithographic printing plate.

Claims (1)

[Claims] In a plate-making method in which a negative photosensitive lithographic printing plate having a photosensitive layer containing a diazo compound on a support is imagewise exposed, developed with an alkaline developer to remove non-image areas, and then desensitized, A plate-making method characterized in that the desensitizing liquid used for desensitizing treatment is an aqueous solution containing dextrin, an acid, an anionic surfactant, and a nonionic surfactant in an amount of 150 to 1% by weight based on the anionic surfactant. .