JPH0456863A - Plate making method for planographic printing plate - Google Patents

Abstract

PURPOSE:To improve sensitivity and tone reproducibility by placing a specific photosensitive planographic printing plate under a reduced pressure to remove the dissolved oxygen in the photosensitive layer, then subjected the printing plate to image exposing and developing after substitution with gaseous nitrogen. CONSTITUTION:The photosensitive planographic printing plate provided with the photopolymerizable photosensitive layer contg. a compd. having at least one piece of ethylenic unsatd. bonds which can be photopolymerized by active rays, a photopolymn. initiator and a linear org. high polymer and a transparent protective layer having the oxygen permeability of 30 to 300cc/m<2>.day.atm (25 deg.C/35% humidity) is placed under the reduced pressure to remove the dissolved oxygen in the photosensitive layer. The printing plate is then subjected to the image exposing and developing after substitution with the gaseous nitrogen. The dissolved oxygen contained in the photosensitive layer is removed by placing the photosensitive planographic printing plate under the reduced pressure in such a manner, by which the effect of prohibiting the polymn. by oxygen is eliminated and, therefore, the sensitivity and the tone reproducibility are improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for making a lithographic printing plate.

[Conventional technology]

A photosensitive composition is prepared by mixing a polymerizable compound having an addition-polymerizable unsaturated bond, a photopolymerization initiator, and, if necessary, a binder having an appropriate film-forming ability and a thermal polymerization inhibitor. Methods for duplicating images using manual techniques are currently known. That is, U.S. Patent No. 2.92
No. 7.022, No. 2, No. 902.356 or No. 3.
As described in No. 870.524, this type of photosensitive composition undergoes photopolymerization, hardens, and becomes insolubilized by irradiation with light.
A desired cured image of the photopolymerizable composition can be formed by irradiating light through the desired negative image and removing only the unexposed areas using a suitable solvent (hereinafter simply referred to as development). It goes without saying that this type of photosensitive composition is extremely useful for making printing plates and the like.

In addition, in recent years, increased sensitivity to ultraviolet rays and methods of forming images using lasers have been studied, and methods such as UV projection exposure for printing plate creation, laser direct plate making, laser facsimile, and holography are already in practical use. , high-sensitivity photosensitive materials that can be used in these applications have been developed.

In these photopolymerizable photosensitive layers, the reaction proceeds by radical polymerization, but the polymerization is inhibited by oxygen. For this purpose, JP-A-50-59101 discloses that an oxygen permeation-preventing coating layer such as polyethylene terephthalate, cellophane, polyvinylidene chloride, polyvinyl chloride, polyvinyl alcohol, polypropylene, or polyethylene is provided on the photopolymerizable photosensitive layer. It is stated that it should be provided.

Further, in JP-A-63-262645, an attempt has been made to convert dissolved oxygen in the photosensitive layer into a singlet state by preliminary exposure in the presence of a dye so as not to inhibit polymerization.

However, this system had insufficient sensitivity and required a large amount of light for preliminary exposure.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for making a lithographic printing plate with high sensitivity and excellent tone reproducibility.

[Means to solve the problem]

In order to achieve the above object, the present inventor has conducted extensive research and as a result 1) on a support, ll) a polymerizable compound having at least one ethylenically unsaturated bond that can be photopolymerized by actinic rays; a photopolymerizable photosensitive layer containing a photopolymerization initiator and a linear organic polymer; 111) an oxygen permeability of 30 to 300 cc/m'day;
-atm (25°C/35% humidity), a photosensitive lithographic printing plate provided with a transparent protective layer is placed under reduced pressure to remove dissolved enzymes in the photosensitive layer, and after replacing with nitrogen gas, images are formed. The present invention was developed based on the fact that a lithographic printing plate with high sensitivity and excellent tone reproducibility can be obtained by exposure and development.

In the present invention, by placing the photosensitive lithographic printing plate under reduced pressure, dissolved oxygen contained in the photosensitive layer is removed and the polymerization inhibiting effect caused by oxygen is eliminated, thereby increasing sensitivity and improving tone reproducibility. becomes possible. In addition, in order to prevent oxygen in the air from flowing into the photosensitive layer again after removing dissolved oxygen by reducing the pressure, it is possible to remove oxygen by reducing the pressure on the photosensitive layer, but under normal pressure the oxygen barrier property A transparent protective layer is provided. This protective layer has an oxygen permeability of 30~
300CC/ml-day-atm (25℃/humidity 35
%)belongs to. If the oxygen permeability is outside this range, oxygen removal under reduced pressure and oxygen blocking under normal pressure cannot be performed appropriately.

The reduced pressure conditions can be arbitrarily set depending on the oxygen permeability of the protective layer, but it is more preferable to leave it standing at 5 mmHg or less for 1 minute or more. It is preferable to return the pressure from the reduced pressure state to normal pressure using nitrogen gas, and then leave it standing in a nitrogen atmosphere for 1 minute or more.

In the present invention, image exposure is preferably carried out within 10 minutes after taking out the photosensitive lithographic printing plate from the vacuum container,
More preferably, it is carried out within 5 minutes.

In the present invention, if necessary, by heating during or after image exposure, sensitivity can be increased without impairing tone reproducibility. The heating temperature is preferably 200°C or less, more preferably 40 to 150°C.

As the support used in the present invention, a dimensionally stable plate-like material is used. Examples of the dimensionally stable plate-like material include paper, paper laminated with plastic (for example, polyethylene, polypropylene, polystyrene, etc.), and materials such as aluminum (including aluminum alloys), zinc, copper, etc. Metal plates, furthermore, for example cellulose diacetate, cellulose triacetate, cellulose propionate,
Examples include plastic films such as cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc., and paper or plastic films laminated or vapor-deposited with metals such as those mentioned above. Among these supports, aluminum plates are particularly preferred because they are extremely dimensionally stable and inexpensive. Furthermore, a composite sheet in which an aluminum sheet is bonded to a polyethylene terephthalate film as described in Japanese Patent Publication No. 48-18327 is also preferred.

In addition, in the case of a support having a metal surface, especially aluminum, surface treatments such as graining treatment, immersion treatment in an aqueous solution of sodium silicate, potassium fluorozirconate, phosphate, etc., or anodization treatment are performed. Preferably.

Furthermore, an aluminum plate that has been grained and then immersed in an aqueous sodium silicate solution can be preferably used. As described in Japanese Patent Publication No. 47-5125, an aluminum plate which is anodized and then immersed in an aqueous solution of an alkali metal silicate is preferably used. The above anodizing treatment can be carried out using an electrolytic solution, for example, of an aqueous or non-aqueous solution of an inorganic acid such as phosphoric acid, chromic acid, sulfuric acid, or boric acid, or an organic acid such as oxalic acid or sulfamic acid, or a salt thereof, or a combination of two or more thereof. This is carried out by passing an electric current through the aluminum plate as an anode.

Also effective is silicate electrodeposition as described in US Pat. No. 3,658,662.

Furthermore, Japanese Patent Publication No. 46-27481, Japanese Patent Publication No. 525860
Also useful is a surface treatment that combines a support subjected to electrolytic duplexing as disclosed in No. 2, JP-A-52-30503, and the above-mentioned anodic oxidation treatment and sodium silicate treatment.

Also suitable are those which have been sequentially subjected to mechanical roughening, chemical etching, electrolytic etching, anodic oxidation, and sodium silicate treatment as disclosed in JP-A No. 56-28893.

Furthermore, after these treatments, water-soluble resins such as polyvinylphosphonic acid, polymers and copolymers having sulfonic acid groups in their side chains, polyacrylic acid, water-soluble metal salts (e.g. zinc borate), or Undercoating with yellow dye, amine salt, etc. is also suitable.

These hydrophilic treatments are performed not only to make the surface of the support hydrophilic, but also to prevent harmful reactions of the photopolymerizable composition provided thereon, and to improve the adhesion of the photosensitive layer. It is done for the ring.

The polymerizable compound having at least one ethylenically unsaturated bond that can be photopolymerized by actinic rays used in the present invention is a compound having at least one terminal ethylenically unsaturated bond, preferably two or more terminal ethylenically unsaturated bonds. To be elected.

For example, it has chemical forms such as monomers, prepolymers, ie, dimers, trimers, and oligomers, or mixtures thereof, and copolymers thereof. Examples of monomers and copolymers thereof include unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid,
Examples include esters of crotonic acid, isocrotonic acid, maleic acid, etc.) and aliphatic polyhydric alcohol compounds, and amides of unsaturated carboxylic acids and aliphatic polyhydric amine compounds.

Specific examples of esters of aliphatic polyhydric alcohol compounds and unsaturated carboxylic acids include ethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol diacrylate, and tetraethylene glycol diacrylate. Methylene glycol diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane tri(acryloyloxypropyl) ether, trimethylolethane triacrylate, hexanediol diacrylate, 1,4-cyclohexanediol diacrylate, tetraethylene glycol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol diacrylate,
Examples include dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitol tetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate, tri(acryloyloxyethyl)isocyanurate, polyester acrylate oligomer, and the like.

Examples of methacrylic acid esters include tetramethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, Hexanediol dimethacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritol hexamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate, bis[p-(3-methacryloxy) -2
-hydroxypropoxy)phenyl]dimethylmethane,
Examples include bis-[p-(acryloxyethoxy)phenylfudimethylmethane.

As the itaconic acid ester, ethylene glycol shitaconate, propylene glycol shitaconate, 1
．． 3-butanediol shiitaconate, 1,4-butanediol shiitaconate, tetramethylene glycol shiitaconate, pentaerythritol shiitaconate,
Examples include sorbitol tetrataconate.

Examples of crotonic acid esters include ethylene glycol dicrotonate, tetramethylene glycol dicrotonate, pentaerythritol dicrotonate, and sorbitol tetramaleate.

Isocrotonic acid esters include ethylene glycol diisocrotonate, pentaerythritol diincrotonate, sorbitol tetraisocrotonate, and the like.

Examples of maleic esters include ethylene glycol simarate, triethylene glycol simarate, pentaerythritol simarate, and sorbitol tetramaleate.

Furthermore, mixtures of the aforementioned ester monomers may also be mentioned.

Specific examples of amides of aliphatic polyvalent amine compounds and unsaturated carboxylic acids include methylene bis-acrylamide, methylene bis-methacrylamide, 1.
Examples include 6-hexamethylenebisacrylamide, 1,6-hexamethylenebismethacrylamide, diethylenetriamine trisacrylamide, xylylenebisacrylamide, xylylenebismethacrylamide, and the like.

As another example, the following general formula (
Examples include vinyl urethane compounds containing two or more polymerizable vinyl groups in one molecule to which a vinyl monomer containing a hydroxyl group shown in A) is added.

[1: H, = C (R) COOCH, mouth H (R') Kano (A) (However, R and R'
indicates H or CH3. ) In addition, urethane acrylates as described in JP-A-51-37193, JP-A-4864183,
Polyfunctional acrylates and methacrylates such as polyester acrylates and epoxy acrylates made by reacting epoxy resin and (meth)acrylic acid as described in Japanese Patent Publication No. 49-43191 and Japanese Patent Publication No. 52-30490. I can give it to you. Furthermore, those introduced as photocurable monomers and olicomers in Japan Adhesive Association Journal Vol. 20, No. 7.300-308 (1984) can also be used. The amount used is 5 to 90% by weight (based on the total ingredients).
Hereinafter, it will be abbreviated as %. ), preferably 10 to 70%.

Examples of the photopolymerization initiator used in the present invention include benzyl, benzoin, benzoin ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone, and trihalomethyltriazine compounds; Certain photoreducible dyes, such as rose bengal, eosin, erythrosin, etc., or systems based on combinations of dyes and initiators, such as complex initiation systems of dyes and amines (
(Special Publication No. 44-20189, etc.), system of hexaarylbiimidazole, radical generator and dye (Special Publication No. 44-20189, etc.);
5-37377, etc.), systems of hexaarylbiimidazole and P-dialkylaminobenzylidene ketone (Japanese Patent Publication No. 47-2528, JP-A-54-155292, etc.), systems of dyes and organic peroxides (Japanese Patent Publication No. 1983-155292, etc.) -1641
No., JP-A-59-1504, JP-A-59-14020
No. 3, JP-A-59-189340, U.S. Patent No. 476
6055, JP-A-61-174203, etc.), systems of dyes and active halogen compounds (JP-A-54-15102, JP-A-58-15503, JP-A-63)
-178105, JP-A-63-258903, JP-A-2-63054, etc.), dye and borate compound systems (JP-A-62-143044, JP-A-62-143044, etc.);
JP-A-62-150242, JP-A-61-13140
No., JP-A-64-13141, JP-A-64-1314
No. 2, JP-A-64-13143, JP-A-64-131
No. 44, JP-A-64 No. 17048, JP-A-64721
No. 50, JP-A-1-229003, JP-A-1-29'
No. 8348, JP-A No. 1-138204, etc.).

Any linear organic polymer can be used as long as it is compatible with the photopolymerizable ethylenically unsaturated compound. good. Preferably, a linear organic polymer is selected which is soluble or swellable in water or weakly alkaline water and is capable of being developed in water or weakly alkaline water. The linear organic polymer is used not only as a film-forming agent of the composition, but also as a water, weak alkaline water, or organic solvent developer depending on the use. For example, water development becomes possible when a water-soluble organic high molecular weight polymer is used. Examples of such linear organic polymers include addition polymers having carboxylic acid in the side chain,
For example, Japanese Patent Publication No. 59-44615, Japanese Patent Publication No. 54-343
No. 27, Special Publication No. 58-12577, Special Publication No. 54-25
No. 957, JP-A-54-92723, JP-A-5953
836, JP-A No. 59-71048, namely methacrylic acid copolymers, acrylic acid copolymers, itaconic acid copolymers, crotonic acid copolymers, maleic acid copolymers, partial Examples include esterified maleic acid copolymers. Similarly, there are acidic cellulose derivatives having carboxylic acid in their side chains. In addition, an addition polymer having a hydroxyl group to which a grooved acid anhydride is added is useful. Especially among these [benzyl (meth)acrylate/
(meth)acrylic acid/other addition-polymerizable vinyl monomers as necessary] copolymers and [allyl (meth)acrylate/(meth)acrylic acid/other addition-polymerizable vinyl monomers as necessary) copolymers is suitable. Other useful water-soluble linear organic polymers include polyvinylpyrrolidone and polyethylene oxide. In addition, to increase the strength of the cured film, alcohol-soluble nylon or 2. Also useful are 2-bis-(4-hydroquinphenyl)-propane and shrimp chlorohydrinopholiether. Any amount of these linear organic high molecular weight polymers can be mixed into the entire composition. However, if it exceeds 90%, it will not give favorable results in terms of image strength, etc. to be formed. Preferably it is 30-85%. In addition, photopolymerizable ethylenically unsaturated compounds and linear organic polymers are
The weight ratio is preferably in the range of 1/9 to 7/3. A more preferable range is 3/7 to 515.

In addition to the above-mentioned basic ingredients, in the present invention, a small amount of a thermal polymerization inhibitor is added to prevent unnecessary thermal polymerization of polymerizable ethylenically unsaturated compounds during the production or storage of the photosensitive composition. It is desirable to add. Suitable thermal polymerization inhibitors include nohydroquinone, p-methoxyphenol, di-t-phthyl-p-cresol, pyrogallol, t-butylcatechol, benzoquinone, 4,4'-thiobis(3-methyl-6-t-butylphenol). ), 2
．． Examples thereof include 2'-methylenebis(4-methyl-5-t-butylphenol) and N-nitrosophenylhydroxyamine cerous salt. The amount of thermal polymerization inhibitor added is
Approximately 0.0% based on the weight of the total composition. G1% to 1% to about 5%. If necessary, higher fatty acid derivatives such as behenic acid or behenic acid amide may be added to prevent polymerization inhibition caused by oxygen, and may be unevenly distributed on the surface of the photosensitive layer during the drying process after coating. . The amount of the higher fatty acid derivative added is preferably about 0.5 to about 10% of the total composition. Furthermore, dyes or pigments may be added for the purpose of coloring the photosensitive layer. The amount of dyes and pigments added is approximately 0.5% to the total composition.
About 5% is preferred. In addition, inorganic fillers and other known additives may be added to improve the physical properties of the cured film.

When applying the photopolymerizable composition of the present invention onto a support, it can be used after being dissolved in various organic solvents.

The solvents used here include acetone, methyl ethyl ketone, cyclohexane, ethyl acetate, ethylene dichloride, tetrahydrofuran, toluene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether,
Propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetylacetone, cyclohexanone, diacetone alcohol ethylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether acetate, 3-methoxypropanol, methoxy Methoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 3-methoxypropyl acetate, N,N-dimethylformamide, dimethyl sulfoxide, T- These include butyrolactone, methyl lactate, and ethyl lactate. These solvents can be used alone or in combination. The appropriate concentration of solids in the coating solution is 2 to 50% by weight.

The coating amount is about 0.1 g/m' to about 10 g/m' after drying.
g/m'' range is appropriate. More preferably 0.5~
5 g/m'.

The oxygen permeability used in the present invention is 30 to 300 cc/
Materials for forming the "transparent protective layer smaller than m"day-atm (25°C/35% humidity) include polyvinyl alcohol, especially polyvinyl alcohol with a degree of saponification of 95 mol% or more, polyvinyl chloride, polyacrylonitrile. Examples include. The coating amount of the protective layer is 0.01 g/m' to 50 g/m', more preferably 0.01 g/m' to 50 g/m' in weight after drying.
．． 1 to 10 g/m' is suitable. A method of applying such a protective layer is described, for example, in U.S. Pat. No. 3.458.31.
It is described in detail in No. 1 and Special Publication No. 5549729.

After imagewise exposure of a photosensitive material using the photopolymerizable composition of the present invention, unexposed areas of the photosensitive layer are removed with a developer to obtain an image. Preferred developing solutions for using these photopolymerizable compositions in preparing lithographic printing plates include those disclosed in Japanese Patent Publication No. 57-74
Examples include developers such as those described in No. 27, including sodium silicate, potassium silicate, sodium hydroxide, potassium hydroxide, lithium hydroxide, tribasic sodium phosphate, dibasic sodium phosphate, and triphosphoric acid. Suitable are aqueous solutions of inorganic alkaline agents such as ammonium, ammonium diphosphate, sodium metasilicate, sodium bicarbonate, aqueous ammonia, etc., and organic alkaline agents such as monoethanolamine or (λjetanolamine). The concentration of the solution is 0.1 to 10% by weight, preferably 0.
It is added in an amount of 5 to 5% by weight.

In addition, the alkaline aqueous solution may contain surfactants, benzyl alcohol, 2-phenoxyethanol, 2
- Small amounts of organic solvents such as butoxetanol may be included. For example, those described in US Pat. No. 3,375,171 and US Pat. No. 3,615,480 can be mentioned.

Furthermore, JP-A-50-26601 and JP-A-58-54341
The developing solutions described in Japanese Patent Publication No. 56-39464 and Japanese Patent Publication No. 56-42860 are also excellent.

The plate-making method for a lithographic printing plate of the present invention provides good results, particularly when performing image exposure using a laser light source.

Light sources include ultra-high pressure, high pressure, medium pressure, and low pressure mercury lamps,
Chemical lamps, carbon arc lamps, cannon lamps, tungsten lamps, metal halide lamps, fluorescent lamps, sunlight, and various laser light sources such as He-Ne laser, A
An r+ laser, a semiconductor laser, a YAG laser, etc. can be used.

〔Effect of the invention〕

The present invention has made it possible to make a lithographic printing plate with high sensitivity and excellent tone reproducibility.

〔Example〕

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

(Preparation of photosensitive material) The surface of an aluminum plate having a thickness of 0.30 mm was grained using a nylon brush and a 400 mesh water suspension of pumice stone, and then thoroughly washed with water. After etching by immersing in IJum (10% hydroxide) at 70° C. for 60 seconds, washing with running water, neutralizing with 20% nitric acid, and then washing with water. This was heated to 160°C in a 1% nitric acid aqueous solution using a sinusoidal alternating current waveform under the condition of VA = 12.7 V.
Electrolytic surface roughening treatment was carried out using a special anode electricity amount of Coulomb/dm2. When the surface roughness was measured, it was found to be 0.6μ (R,
display). Subsequently, it was immersed in a 30% sulfuric acid aqueous solution and desmutted at 55°C for 2 minutes, and then desmutted in a 20% sulfuric acid aqueous solution at a current density of 2 A/dm2 so that the thickness of the anodic oxide film was 2.7 g/m'. Anodized for minutes.

On the thus treated aluminum plate, a photosensitive composition having the following composition was coated so that the dry coating weight was 14 g/m' and dried at 80° C. for 2 minutes to form a photosensitive layer.

Chill 2, tlg Photopolymerization initiator x3 Fluorinated nonionic surfactant 0.03 g Methyl ethyl ketone 20 g
A 3% by weight aqueous solution with a degree of polymerization of 1000) was applied in a dry coating amount of 2.
g/m'' and dried at 100°C for 2 minutes to create a protective layer.The oxygen permeability of this protective layer was 37.
cc/m' ・day -atm (25℃/humidity 35
%) (Gasperm-10 manufactured by JASCO Corporation)
(measured at 0).

(Plate Making/Evaluation) Next, using these light-sensitive materials, the sensitivity and tone reproducibility were compared between cases where they were placed under reduced pressure (heating after image exposure, if necessary) and cases where they were not placed under reduced pressure. For depressurization treatment, the sample placed in a vacuum desiccator was placed in a vacuum pump (Hitachi 4).
After maintaining the pressure at 1.0 mmHg for 30 minutes using VP-C5), the pressure was returned to normal pressure using nitrogen gas, and after being allowed to stand for 5 minutes, it was taken out from the vacuum dessicator and image exposure was performed within 5 minutes.

Image exposure is 1.7 ++nn/s on a flat carrier
54 m/s perpendicular to the plate moving at a speed of ec
This was done by writing halftone dots at 65 lines/inch using an Ar'' laser beam (spot diameter 35μ) moving at a speed of 30% and 70% of
This was done by measuring the area of halftone dots.

When heating was performed, after image exposure, the film was heated in an oven at 60° C. for 5 minutes and then developed.

(When heating was not performed, the image was developed 1 minute after exposure.

) The development is I went.

Potassium K silicate [Total potassium oxide 25℃ in the following developer solution. Soak for 1 minute The results are shown in Table 1.

As a result, both photosensitive materials A and B had high sensitivity and improved tone reproducibility by performing the reduced pressure treatment, and the sensitivity could be further increased by heating after exposure.

Claims (2)

[Claims] (1) i) on a support, ii) a polymerizable compound having at least one ethylenically unsaturated bond that can be photopolymerized by actinic rays, a photopolymerization initiator, and a linear organic polymer; iii) an oxygen permeability of 30 to 300 cc/m^2・da;
A photosensitive lithographic printing plate provided with a transparent protective layer of Y.ATM (25°C/humidity 35%) is placed under reduced pressure to remove dissolved oxygen in the photosensitive layer, and then replaced with nitrogen gas. A method for making a lithographic printing plate characterized by exposure and development. (2) The method according to claim (1), characterized in that development is carried out after heat treatment during or after image exposure.