JPH02141754A - Positive/negative type photosensitive planographic printing plate and production of planographic printing plate by using this plate - Google Patents

Abstract

PURPOSE:To obtain the exposed visible image characteristic and sensitivity improved in negative type processing and to improve printing resistance by providing a photosensitive layer contg. an orthoquinone diazide compd., an alkali soluble resin, org. dyes and one kind of a compd. having a specific thiazole ring on a base. CONSTITUTION:The photosensitive layer formed of the photosensitive compsn. which contains the orthoquinone diazide compd., the alkali soluble resin and the org. dyes and contains one kind of the compd. having the thiazole ring expressed by any of the formulas I, II and III is provided on the base. In the formulas I to III, R1 and R2 respectively denote a hydrogen atom, halogen atom, alkyl group, alkoxy group, amino group or nitro group. The exposed visible image characteristic and sensitivity improved in the processing process for obtaining the negative type images are obtd. in this way and the printing resistance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photosensitive lithographic printing plate for both positive and negative types and a method for producing a lithographic printing plate using the same.

[Prior Art] In the process of producing a printing planographic plate, it is widely practiced to use two types of photosensitive planographic printing plates, positive type and negative type, in combination. However, since the materials forming the photoreceptor are different between the positive-working photosensitive lithographic printing plate and the negative-working photosensitive lithographic printing plate, different developers must be used in the development processing of the two. Therefore, when both a positive type and a negative type are used together, there is a significant reduction in work efficiency due to the replacement of the developer in the developing device and the accompanying cleaning of the equipment.

To solve the above-mentioned problems, a technique is known that allows one type of photosensitive lithographic printing plate to be used for both positive and negative types. Examples of such technology include, for example, the
A method of forming a negative image by a specific method from a photosensitive lithographic printing plate using a positive photosensitive composition containing orthoquinone diazide as disclosed in Japanese Patent No. 6-14970 is known. That is, this method normally involves image exposure using a photosensitive lithographic printing plate that can be image-wise exposed and then subjected to development to obtain a positive-tone image, followed by heat treatment, full-surface exposure, and further positive-tone development. A negative image is obtained by subsequent development with a liquid.

However, the above-mentioned photosensitive lithographic printing plates that can be used for both positive and negative types lack clarity in the so-called exposure visible image property, which is the ability to distinguish between exposed and unexposed areas during or after image exposure, and also have negative image quality. However, there is a problem in that the sensitivity is insufficient in the processing process to obtain . Furthermore, despite the recent increase in the number of print runs in this industry, the lithographic printing plates obtained from such photosensitive lithographic printing plates also have the disadvantage of poor printing durability.

[Object of the Invention] An object of the present invention is to provide a photosensitive lithographic printing plate that can be used for both positive and negative types and has improved exposure visibility and sensitivity in the processing process for obtaining negative images. .

Another object of the present invention is to provide a photosensitive lithographic printing plate that can be used for both positive and negative types, making it possible to obtain a lithographic printing plate with improved printing durability.

Another object of the present invention is to provide improved printing durability resulting in improved exposure visibility and sensitivity values in a method for preparing negative-working lithographic printing plates from photosensitive lithographic printing plates that normally exhibit positive action. An object of the present invention is to provide a method for producing a lithographic printing plate having the following properties.

[Structure of the Invention] The above-mentioned object of the present invention is to provide a thiazole ring containing at least an orthoquinone diazide compound, an alkali-soluble resin, and an organic dye and represented by any of the following general formulas (I), (If), and (III). A positive-working/negative-working photosensitive lithographic printing plate characterized by having on a support a photosensitive layer formed from a photosensitive composition containing at least one compound having the following: and the photosensitive lithographic printing plate. This was achieved by providing a method for preparing a lithographic printing plate, characterized in that after imagewise exposure, heat treatment is carried out, and then the entire surface of the photosensitive layer is exposed and then developed with an aqueous alkaline developer. .

General formula (I) General formula (II) General formula (II)
I) (In the formula, R1 and R2 each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an amino group or a nitro group.) The present invention will be described in detail below.

The orthoquinonediazide compound used in the present invention is a compound having at least one orthoquinonediazide group, preferably an orthobenzoquinonediazide group or an orthonaphthoquinonediazide group, and is a compound having various known structures, such as J. L 1oht -
S sensitive systems J (J o
hnWiley & 5ons, Inc., 1
(Published in 1996), pages 339 to 353. In particular various hydroxyl or amino compounds and 1,2-quinonediazide-4-
Esters or amides with sulfonic acid or 1,2-quinonediazide-5-sulfonic acid are preferred;
Particularly preferred are ester compounds of -quinonediazide-4-sulfonic acid. Preferred hydroxyl compounds include:
condensation resin of phenols and carbonyl group-containing compounds,
In particular, resins obtained by condensation in the presence of an acidic catalyst are mentioned. Examples of the phenols include phenol, resorcinol, cresol, pyrogallol, etc., and examples of the carbonyl group-containing compound include aldehydes such as formaldehyde and benzaldehyde, and ketones such as acetone.

Especially phenol/formaldehyde resin, cresol/
formaldehyde resin, and rogallol acetone resin,
Resorcinol benzaldehyde resin is preferred.

Typical specific examples of the orthoquinone diazide compound used in the present invention include benzoquinone-(1,2)-diazide sulfonic acid or naphthoquinone-(1,2)-diazide sulfonic acid and phenol/formaldehyde resin or cresol/formaldehyde resin. ester with,
Sulfonic acid ester of naphthoquinone-(1,2)-diazide sulfonic acid and pyrogallol acetone resin, naphthoquinone-(1,2)-diazide-(2 >-Condensate of 4-sulfonic acid and resorcinol benzaldehyde resin, naphthoquinone-(1,2)-diazide-(2)-4-
Ester compounds of sulfonic acid and resorcinol-pyrogallol-acetone copolycondensates, pyrogallol-acetone copolycondensates, and other orthoquinonediazide compounds include those described in JP-A-50-117503, an ester of a polyester having a hydroxyl group and orthonaphthoquinonediazide sulfonic acid, a homopolymer of p-hydroxystyrene or other monomers copolymerizable therewith, as described in JP-A-50-113305; and an ester of a copolymer of trihydroxybenzophenone and orthoquinonediazide sulfonic acid, or an ester of trihydroxybenzophenone and orthoquinonediazide sulfonic acid.

In the present invention, the content of these orthoquinone diazide compounds is 5 to 60 weight D based on the total solid content of the photosensitive composition.
%, particularly preferably 10 to 50 weight ω%.

The photosensitive lithographic printing plate of the present invention has the general formulas (I) and (II).
) and (III), containing at least one compound having a thiazole ring. In each of the above general formulas (I), (n) and (1), R
1 is preferably an alkyl group having 1 to 3 carbon atoms, an amino group, a nitro group, a halogen atom, or a hydrogen atom, and these are preferably substituted at the 2-position of each thiazole ring. In addition, R2 is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a halogen atom, or a halogen atom having 1 to 3 carbon atoms.
-3 alkoxy groups or nitro groups are preferred.

Examples of compounds having such a thiazole ring include:
Thiazole, 2-methylthiazole, 2゜4-dimethylthiazole, 2-ethylthiazole, 2.4-diethylthiazole, 2-methyl-4-ethylthiazole, 4-
Ethylthiazole, 2-aminothiazole, 2-nitrothiazole, 2-amino-4-nitrothiazole, 2-
Amino-4-methylthiazole, 2-chlorothiazole, 2-bromothiazole, 2-aminobenzothiazole, 2-amino-6-methylbenzothiazole, 2-amino-6-methylbenzothiazole, 2-amino-6-nitro Examples include benzothiazole, 2-amino-6-nitrobenzothiazole, 5-chlorobenzothiazole, 5-promobenzothiazole, 2-methyl-β-naphthothiazole, 2-ethyl-β-naphthothiazole, and the like.

The above compound is contained in the photosensitive composition in an amount ranging from 0.2 to 10% by weight, preferably from 0.5 to 4% by weight based on the total solid content.

An alkali-soluble resin is used in the photosensitive planographic printing plate of the present invention. Such a resin is preferably a compound having an alkali-soluble group such as phenolic water [1, carboxyl group, sulfonic acid group, or phosphoric acid group, and the alkali-soluble resin includes phenols and ketones or aldehydes. Those obtained by condensation in the presence of an acidic catalyst are preferred. Examples of the phenols include phenol, cresol, and p-substituted phenol. Examples of the aldehydes include acetaldehyde and formaldehyde, with formaldehyde being preferred. Acetone is preferred as the ketone.

Preferred alkali-soluble resins include, for example, phenol-formaldehyde resin, cresol-formaldehyde resin, phenol-cresol-formaldehyde co-m condensate resin as described in JP-A-55-57841, and JP-A-55-127553. Copolycondensate resins of p-substituted phenol and phenol or cresol and formaldehyde, condensates of benzaldehyde and polyhydric phenols such as resorcinol-benzaldehyde resins, pyrogallol-benzaldehyde resins, and pyrogallol as described in publications. - Co-ffi of polyhydric phenol and acetone such as resorcinol-acetone resin
$Ii! Examples include base body and xylenol-formaldehyde resin. The content of these alkali-soluble resins is preferably 30 to 9 C1fft%, particularly preferably 50 to 85% by weight, based on the total solid content of the photosensitive composition.

Moreover, the photosensitive composition according to the present invention contains an organic dye. Preferred organic dyes include, for example, Victoria Pure Blue BOH [Hodogaya Chemical] (C142595), Oil Blue 9603 [manufactured by Orient Chemical Industries], and Patent Pure Blue [manufactured by Sumitomo Mikuni Chemical] (CI 4204).
5), Crystal Violet (CI A2555
), brilliant green (C142040), ethyl violet, methyl violet (CI 42)
535), Methyl Green (CI45285), Erythrosin B (Cl 45430), Pesic Tsuksin (CI 42510), Malachite Green (CI 4200G), Oil Red (CI 6)
0505), l-cresol purple, rhodamine B (
C145170), auramine (CI 41000)
), 4-p-diethylaminophenylimino naphthoquinone, cyano-p-diethylaminophenyl acetanilide, etc.; triphenylmethane, diphenylmethane, oxazine, oxatene, iminonaphthoquinone, azomethine, and anthraquinone dyes, Can be mentioned.

The organic dye is preferably 0.01 to 5% by weight, more preferably 0.1 to 3mf based on the total solid content of the photosensitive composition.
It is contained in a proportion of f1%.

In addition to the materials described above, the photosensitive composition used in the photosensitive lithographic printing plate of the present invention can also contain the following additives, if necessary.

In other words, various low molecular weight compounds (e.g. phthalates, triphenyl phosphates, maleate esters, etc.) as plasticizers, surfactants (e.g. fluorine surfactants, ethyl cellulose polyalkylene) as coating properties improvers, etc. nonionic activators represented by ethers, etc.), acid anhydrides, etc. as sensitizers for positive photosensitive compositions. Furthermore, due to exposure to acid or free 1! Compounds which form a group of organic dyes such as those described above and which interact with the dye to change the tone of the dye may also be included as a blindout material for forming a visible image upon exposure to light. Examples of compounds that generate an acid or a free 11i group upon exposure to light include 0-naphthoquinonediazide-4-sulfonic acid halide described in JP-A-50-36209; Esters of lomethyl-2-pyrone, trim-0 methyltriazine, orthonaphthoquinonediazide-4-sulfonic acid diloride described in Special Fail Publication No. 55-6244, and phenols or anilines having electron-withdrawing substituents. Examples include the heromedylvinyloxazole compound and diazonium salts described in JP-A-55-77742. These compounds vary depending on their type, but generally the additive group is present in an amount of 0.01 to 20% by weight, preferably 0.01 to 20% by weight based on the total solid content of the photosensitive composition.
．． 05 to 10% by weight is suitable.

The photosensitive lithographic printing plate of the present invention can be obtained by dissolving the photosensitive composition described above in a suitable solvent and coating the solution on a support. Examples of solvents that can be used include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol isopropyl ether, ethylene glycol moptyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol, propylene glycol 7 Preferable examples include ethers of polyhydric alcohols such as trimethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether, propylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether, but in addition to these, dioxane, tetrahydrofuran, and tetrahydrobilane are preferred. Ethers such as: methyl ethyl ketone, methyl propyl ketone, methyl amyl ketone, methyl amyl ketone, diethyl ketone, diacetone alcohol, cyclopentanone, cyclohexanone, and other ketones; methanol, ethanol, propatool,
Alcohols such as isopropanol, n-butanol, 5ec-butanol, tert-butanol, n-pentanol, isopentanol, n-hexanol, isohexanol; ethyl acetate, propyl acetate, butyl acetate, amyl acetate, hexyl acetate , ethyl propionate, butyl propionate, and other esters can also be used.

Examples of the support used in the photosensitive lithographic printing plate of the present invention include aluminum plates, metal plates such as zinc, copper, and iron, paper on which metals are vapor-deposited, and plastic films, but aluminum plates are most preferred. . Particularly preferred is an aluminum plate that has been subjected to surface treatments such as graining, anodizing, and, if necessary, sealing. The coating ω of the photosensitive composition on the support varies depending on the application, but -0.5 to 3.5 as solid content in the shell.
A range of Q/f is appropriate.

From the photosensitive lithographic printing plate obtained as described above, a positive image can be obtained by developing with a positive developer after image exposure. Further, a negative image can be obtained by performing heat treatment after image exposure, further exposing the entire surface of the photosensitive layer to light, and then developing with an aqueous alkaline developer.

Image exposure of the photosensitive lithographic printing plate in the present invention includes, for example,
The image-formed translucent film is placed in close contact with a photosensitive lithographic printing plate as an original, and exposed to a fluorescent tube, xenon lamp,
This can be carried out by various commonly used methods, such as using a publicly available light source such as a high-pressure mercury lamp charged with a metal halide or a carbon arc lamp.

Further, according to the present invention, the heat treatment following the image exposure is
It is preferable that the heating is carried out at a temperature in the range of 0 to 200°C, preferably 90 to 160°C, for a time of 1 to 30 minutes, preferably 3 to 15 minutes. If the heating temperature is too high, problems such as hardening of the entire surface of the photosensitive layer may occur.

Such heat treatment is generally carried out by leaving the photosensitive lithographic printing plate in heated air for the above-mentioned period of time after image exposure. It is also possible to do so.

The entire surface exposure performed after the heat treatment can be performed using the same apparatus as the image exposure.

In addition, in the method of the present invention, the following developers can be mentioned as the aqueous alkaline developer used for developing the photosensitive lithographic printing plate.

That is, the developer according to the present invention is an alkaline aqueous solution, and the alkaline earth metal used is preferably potassium silicate, lithium silicate, sodium silicate, sodium hydroxide, potassium hydroxide, lithium hydroxide, and tertiary earth metal. Examples include sodium phosphate, sodium diphosphate, tribasic potassium phosphate, potassium diphosphate, sodium carbonate, potassium carbonate, and the like. Among these, a developer containing an alkali silicate such as potassium silicate, lithium silicate, or 1 cum sodium silicate is preferable because it has good development gradation.
] / [M] = 0.5 to 1.5 (here [8!
02 ], [M] 02 f) Shows the T-nyl concentration and the molar concentration of total alkali metals. ) and
A developer containing 0.8 to 8% by weight of 5i02 is preferably used. Among this alkali silicate composition, especially the molar ratio [Si 02 ] / [M] = 0.5 to 0
．． 75 and 0.8 to 4% by weight of 5102 is preferably used because it has a low a degree and is easy to neutralize the developer waste. The ratio is 1 to 8% by weight of SiO2 in a developer! ! It is preferably used because of its high impact and high throughput.

In addition, it is preferable that the alkali silicate contains 20 mol% or more of potassium as the alkali metal in the total alkali metals because it will reduce the generation of insoluble matter in the developer, and more preferably 90 mol% or more of potassium. Most preferably, the potassium content is 100 mol%.

l) H value of the developer preferably used in the present invention is 25°C
is 12 or more, preferably 12.5 to 14.
It is 0.

Furthermore, water-soluble sulfites such as sodium sulfite, potassium sulfite, lithium sulfite, and magnesium sulfite can be added to the developer. The preferred content of sulfite in the developer is 0.05 to 4% by weight, preferably 0.1 to 1% by weight.

Further, in the developer, anionic surfactants and amphoteric surfactants such as those described in JP-A-50-51324 and JP-A-59-7!3255 and JP-A-59-7!
By containing at least one kind of nonionic surfactant as described in JP-A-111246 and JP-A-60-213943, or JP-A-55-95946 and JP-A-56-142528. It is preferable to include a polymer electrolyte as described in the above publication, since it is possible to improve the wettability to the photosensitive composition and further improve the gradation property. There are no particular restrictions on the concentration of the darkening surfactant added, but a concentration of 0.003 to 3% by weight is preferred, and a concentration of 0.006 to 1% by weight is particularly preferred.

Furthermore, the developer used in the present invention can contain an antifoaming agent. Suitable antifoaming agents include organosilane compounds.

Various conventionally known methods can be used to develop the photosensitive lithographic printing plate of the present invention which has been imagewise exposed with the above developer. Specifically, for example, a method of immersing the image-exposed photosensitive lithographic printing plate in a developer, a method of jetting a developer from a number of nozzles onto the photosensitive layer of the photosensitive lithographic printing plate, and a method of ejecting a developer from a number of nozzles; Examples include a method of wiping the photosensitive layer of the photosensitive lithographic printing plate with a sponge moistened with a sponge, and a method of rolling a developer onto the surface of the photosensitive layer of the photosensitive lithographic printing plate. Further, after applying the developer to the photosensitive layer of the photosensitive lithographic printing plate in this manner, the surface of the photosensitive layer may be lightly rubbed with a brush or the like. The developing conditions can be appropriately selected depending on the developing method. - For example, in a developing method by immersion, approximately 1
A method of dipping for 0 to 80 seconds is selected.

[Examples] The present invention will be explained below using Examples, but the present invention is not limited thereto.

Example 1 A photosensitive solution having the following composition was made by UA and coated on a grained aluminum plate with a solid content of 1 using a 0-layer coater.
．． After coating J: sea urchin with a coating amount of 8 Q/f, it was dried to obtain photosensitive lithographic printing plate sample 1.

(Photosensitive liquid composition) Bi-O-gallol acetone resin and naphthoquinone = (1,
2) -Diazide-4-sulfonic acid chloride ester compound (QD-1) 2.3 parts by weight ・Copolymerization of phenol, R1+, p-mixed cresol (each molar ratio is 48:32:20) and formaldehyde Condensation resin 6.7 parts by weight・Novolac resin synthesized from paraoctylphenol and formalin 0.9ffl ff1 part・2-trichloromedyl-5-(β-benzofuryl vinyl)-1
, 0.05 parts by weight of 3,4-oxadiazole, 8 parts by weight of ethylene glycol monomethyl ether, 37 parts by weight of ethylene glycol monoethyl ether, 0°011 parts by weight of thiazole, 0.077 parts by weight of Victoria Pure Blue BOil Photosensitive lithographic printing plate samples 2 to 6 were prepared in the same manner as sample 1 except that thiazole or QD-1 in the photosensitive solution composition was replaced with the compounds shown in Table 1. Each of the above samples 1 to 7 was cut into two sheets, and one of the sheets was exposed to light using a positive type original image, and one of the sheets contained a specific solvent in which 0.1% of sodium benzenesulfonate was added to a 4% solution of sodium metasilicate. The film was developed by immersing it in a liquid developer for 20 seconds at a temperature of 27°C to obtain a clear positive image. Hereinafter, the positive image obtained in this way will be referred to as a positive image.

For exposure, after the positive Wt manuscript formed on lithographic film was brought into close contact with the printing plate, a 2KW metal halide lamp (Idol Fin 2000 made by Iwa 1m) was used as the light source and the light intensity was 8.0.
I accompanied him for 70 seconds at +1W/Ct'. The other sample was treated with a negative original and a step tablet (Eastman Kodak No. 2, density difference 0.1) under the same conditions as above.
21 steps of gray scale) were exposed.

Next, it was left in an air constant temperature bath kept at 140° C. for 5 minutes, and after cooling, light was exposed on the front side under the same conditions as the image exposure without using the original image. Development was carried out under the same conditions using the same developer as that used to form the positive image, and a clear negative image was obtained. The image obtained in this way is called a negative-positive image.

Using the obtained printing plate, printing with oil-based ink was performed under the following printing conditions to evaluate printing durability. Printing durability was expressed as the number of sheets printed at the time when the ink stopped adhering to the image area.

Printing III: Heidel GTO Printing ink: Toyo King New Bright Red (manufactured by Toyo Ink Co., Ltd.) Paper: High quality paper Printing speed: aooo sheets/hour Under these conditions, each printing plate on which the above-mentioned positive-positive image or negative-positive image was formed It was confirmed that both had a printing durability of 100,000 sheets. Further, the exposure visible image quality and sensitivity during the printing plate process are shown in Table 1 along with the results of printing durability.

Comparative Example 1 In the photosensitive liquid composition used to create Sample 1 of Example 1,
Sample 7 was prepared in the same manner except that only thiazole was removed, Sample f18 was prepared in the same manner except that only Victoria Pure Blue BOH was removed, and Sample f18 was prepared in the same manner except that only thiazole and Victoria Pure Blue BOH were removed. Each of the prepared samples 9 was treated and evaluated in the same manner as in Example 1. Although a clear positive-positive image was obtained for sample 9, stable negative-positive image formation was not performed. The results are shown in Table-1.

Comparative Example 2 In the photosensitive liquid composition used to create Sample 1 of Example 1,
Bigalol acetone resin and naphthoquinone (1,2
)-diazide-4-sulfonic acid, an ester of cresol formaldehyde resin and naphthoquinone-(1,2)-diazide-5-sulfonic acid (QD-3) was used, and 2-methylmercapto was used instead of thiazole. Sample 10 prepared in the same manner except for using benzothiazole
, and Sample 11 prepared in the same manner except that jetanolamine was used in place of thiazole, and were treated and evaluated in the same manner as in Example 1.

The results are shown in Table-1.

*IQD-2 nitrihydroxypensifurone and naphthoquinone-(1,
2) Ester compound with diazide-4-sulfonic acid chloride *2QD-3: Cresol formaldehyde resin and naphthoquinone-(
Ester compound with 1,2)-diazido-5-sulfonic acid 3 exposure Visible image property A: ΔD≧0.17 3:0.15≦ΔQ<0.17 C-0,12≦Δ[)<0 .15 [): 0.09≦Δ[)<0.12 E°ΔQ<0.09 where ΔD represents the density difference between the exposed area and the unexposed area.

As is clear from Table 1, Samples 1 to 6 of the present invention containing the compound having a thiazole ring according to the present invention all had stable negative-positive results compared to Samples 7 and 9 that did not contain the compound. It can form images and is excellent in all of sensitivity, exposure visibility and printing durability.

[Effect of the Invention 1] According to the present invention, even in negative processing, it is possible to obtain a lithographic printing plate having improved exposure visibility and sensitivity and improved printing durability. It is possible to provide a photosensitive lithographic printing plate that can also be used as a mold.

Patent applicant Konica Co., Ltd. (and one other person) Representative Patent attorney Miyao Ichinose

Claims (2)

[Claims] (1) Contains at least an orthoquinonediazide compound, an alkali-soluble resin, and an organic dye, and has the following general formula (
It is characterized by having on a support a photosensitive layer formed from a photosensitive composition containing at least one compound having a thiazole ring represented by any one of I), (II) and (III). Photosensitive planographic printing plate for both positive and negative types. General formula (I) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ General formula (II) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ General formula (III) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R_1 and R_2 each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an amino group or a nitro group.) (2) Contains at least an orthoquinone diazide compound, an alkali-soluble resin, and an organic dye, and has the following general formula (
A photosensitive lithographic printing plate having, on a support, a photosensitive layer formed from a photosensitive composition containing at least one compound having a thiazole ring represented by any one of I), (II) and (III). 1. A method for producing a lithographic printing plate, which comprises performing a heat treatment after imagewise exposure, and then developing the photosensitive layer with an aqueous alkaline developer after exposing the entire surface of the photosensitive layer. General formula (I) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ General formula (II) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ General formula (III) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R_1 and R_2 each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an amino group or a nitro group.)