JPH0519453A - Subtractive offset printing plate and production thereof - Google Patents

Abstract

PURPOSE:To produce a satisfactory printing plate with a subtractive developer causing little environmental problem in a generally used additive type automatic developing machine adopting a specified system by using a subtractive offset printing plate having a photosensitive layer contg. a combined diazo photosensitive body and a binder having an acetal skeleton in the molecule. CONSTITUTION:This subtractive offset printing plate has a photosensitive layer contg. at least a diazo photosensitive body and a binder having an acetal skeleton in the molecule.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subtract type offset printing plate. More specifically, the present invention relates to a subtract type offset printing plate which can be well developed even with an automatic developing machine for an additive type offset printing plate.

[0002]

2. Description of the Related Art Additive-type offset printing plates have the advantage that original plates can be manufactured at low cost, and are currently used mainly in the field of newspaper printing. Conventionally, the additive type offset printing plate which has been widely used for general printing needs a lacquer layer or the like on the image portion in order to reinforce the image portion. Therefore, the additive type offset printing plate developer contains a component for removing the non-image area and a lacquer component for reinforcing the image area, and the content of the organic compound reaches as much as 50% by weight. Its physical properties are more viscous than water and are close to those of paint. Such a developing solution is supplied to the printing plate surface in a relatively small amount, and the non-image portion is removed by the strong rubbing of the brush to perform the development. On the other hand, the developer of the subtraction type offset printing plate which does not need to reinforce the image area such as lacquer is an alkaline aqueous solution having an organic compound content of 10% by weight or less, and its physical properties are close to those of water. Then, such a developing solution is supplied to the printing plate surface in a relatively large amount, the rubbing of the brush is hardly required, and the non-image portion is removed by being eluted into the developing solution to perform the development.

[0003]

As described above, the additive type offset printing plate developing solution has a higher concentration of the organic compound than the subtractive type offset printing plate developing solution.
For this reason, disposal of used developer has become an environmental problem. As one of the means for solving the above problems, a method of replacing the developing type developing machine with the subtracting type developing machine can be considered. However, at newspaper companies, etc., exposure of additive type offset printing plates
A plate making line that automatically and continuously develops, punches, and folds a plate has already been installed, so that a printing plate can be efficiently produced in a short time. It is not easy to replace such an expensive plate making line with a plate making line for subtract type offset printing plates.

Further, as another means for solving the above problems, a method of supplying a subtract type developing solution to an additive type developing machine to develop a subtract type printing plate can be considered. However, as described above, since the additive type and subtract type developer compositions and the brush pressure of the developing machine are significantly different, the conventional subtract type developing solution is supplied to the additive type developing machine to develop the subtract type printing plate. However, it was not possible to produce a satisfactory printing plate.

The present invention has been made in view of the above circumstances, and the present inventor supplies a subtractive printing plate and a subtractive developing solution having less environmental problems to an additive type developing machine for brush-developing the printing plate, As a result of diligent studies to provide a subtractive offset printing plate capable of producing a satisfactory printing plate by using a subtractive offset printing plate containing a specific diazo photoconductor and a binder having a specific skeleton, The present invention has been accomplished by finding that the objectives of the objectives have been achieved.

An object of the present invention is to provide a novel subtractive offset printing plate containing at least a diazo photoreceptor and a binder having an acetal skeleton in the molecule in a photosensitive layer. Another object of the present invention is to provide a subtractive offset printing plate having a unique performance of being capable of developing by supplying a subtractive developing solution to a developing machine for the additive type offset printing plate.

Another object of the present invention is to provide a novel developing method for an offset printing plate, which is carried out by supplying a subtractive developing solution to a developing machine for an additive type offset printing plate. Still another object of the present invention is to provide a novel offset printing plate which has few environmental problems and is industrially advantageous.

Still another object of the present invention is to provide a novel plate-making method of an offset printing plate which has few environmental problems and is industrially advantageous. Thus, the object of the present invention is to provide a subtractive offset printing plate characterized in that the photosensitive layer of the offset printing plate contains a binder having at least a diazo photoconductor and an acetal skeleton in the molecule, and the offset printing plate. The plate is imagewise exposed and automatically conveyed, in the presence of a developer,
Printing at right angles to the transport direction of the offset printing plate by pressing the developing brush against the offset printing plate, and also while rotating the developing brush about an axis perpendicular to the plane of the offset printing plate. It is easily achieved by reciprocating along an axis parallel to the plate.

The present invention will be described in detail below. The subtractive offset printing plate of the present invention rotates around an axis perpendicular to the plane of the image-exposed offset printing plate precursor, and along an axis parallel to the plane of the original plate at a right angle to the conveying direction of the original plate. Can be supplied together with the subtract type developer to a developing type developing machine having a developing brush that reciprocates.

Specifically, for example, the diameter of the rotating surface of the developing brush is about 10 to 20 cm, while rotating about an axis perpendicular to the plane of the offset printing plate precursor at a speed of about 200 to 400 times per minute. In addition, development of a developing method in which reciprocation is performed at a rate of about 30 to 150 cm per minute at a right angle to the direction of conveyance of the original plate along an axis parallel to the plane of the original plate at about 15 to 50 cycles per minute. Can be suitably supplied to the machine.

In the present invention, the angle or the like that defines the position and direction of rotation or movement of the brush does not necessarily have to be strict, and the brush rotates about an axis substantially perpendicular to the plane of the printing plate precursor. In addition, the reciprocating motion may be performed along an axis that is substantially perpendicular to the transport direction of the original plate and that is substantially parallel to the plane of the original plate. Furthermore, the mode of rotation and movement of the developing brush is such that the developing brush is printed substantially in the presence of a developing solution in a smaller amount than the developing solution used for the development of the ordinary subtract type offset printing plate. Various modifications may be included as long as they are brought into pressure contact with the plate and development is suitably carried out.

The material of the developing brush is preferably nylon, and the brush pressure for press-contacting the image-exposed printing original plate is preferably 0.15 to the offset printing plate original plate.
It is selected from the range of about 0.45 pounds per square inch. Then, generally, a plurality of developing brushes are attached to each of the front, rear, left and right, and under the above-mentioned conditions, normally,
It is rubbed and developed for about 3 to 30 seconds.

If the transport speed is lower than the above range, the workability may be deteriorated. On the contrary, if the transport speed is higher than the above range, the developing speed may not catch up. Further, if the number of rotations of the developing brush is lower than the above range, the development may be non-uniform. Conversely, if it is higher than the above range, the developing solution may be scattered. is there. As a specific example of such a developing machine, U
A developing machine as described in SP3,682,078 can be used.

The developer used in the present invention may be a conventional alkaline subtraction type developer, but the pH is particularly preferably in the range of 9 to 13. For example, Japanese Patent Publication No. 56-42860 and Japanese Patent Publication No. 60-533.
An alkaline aqueous solution containing an organic compound in an amount of 10% by weight or less as described in each of the No. 06 publications and the like can be mentioned.

Examples of the alkaline compound include inorganic compounds such as sodium silicate, potassium silicate, potassium hydroxide, sodium hydroxide and sodium carbonate, mono-, di- or trimethylamine, mono-, di- or triethylamine, mono-, di- or triethanolamine. , N-butylamine and other organic amine compounds, and the concentration thereof is 0.3 to
A range of 3% by weight is preferred. Examples of the organic compound include benzyl acetate, esters such as ethylene glycol monobutyl acetate, ketones such as methyl isobutyl ketone, alcohols such as ethylene glycol monophenyl ether and benzyl alcohol, and the concentration thereof is 10 Weight% or less, preferably 2 to 10% by weight
Selected from the range. In the present invention, a subtract type developer having the following composition can be preferably used.

Benzyl alcohol 1 to 5% by weight Sodium alkylbenzene sulfonate 1 to 5% by weight Monoethanolamine 0.5 to 3% by weight Water 90 to 97% by weight Such a developing solution is used per 1 square meter of the offset printing plate precursor. Usually, it is supplied to the developing machine so that the amount becomes about 50 to 300 ml.

The subtractive offset printing plate of the present invention, which is particularly suitable when the above subtractive developer is used in the above additive developing machine, has at least a diazo photoconductor and an acetal skeleton in the molecule on the support. It has a photosensitive layer containing a binder. The support is not particularly limited and various known ones may be used, but an aluminum plate is preferable, and further, according to a conventional method, roughening,
Those subjected to surface treatment such as anodization are more preferably used.

The diazo photoconductor may be any diazo photoconductor commonly used as a photoconductor for negative-working photosensitive lithographic printing plates, such as JP-B-47-1167 and JP-B-61-42551. Examples include those described in publications and the like. Specifically, for example, the diazo component is 4-diazonium salt diphenylamine, 4-diazonium salt-4'-methoxydiphenylamine, 4-diazonium salt-4'-methyldiphenylamine, 4-diazonium salt-4'-chlorodiphenylamine, 3-diazonium salt-4,4'-dimethyldiphenylamine, 4
-Diazonium salt-2-carboxydiphenylamine,
Aromatic compounds having a diazo group such as 1-diazonium salt-2-phenoxy-5-chlorobenzene, 1-diazonium salt-4-N, N'-dimethylaminobenzene, 1-diazonium salt-4-morpholinobenzene, and formaldehyde It can be obtained by condensing an active carbonyl compound such as acetaldehyde or butyraldehyde with a catalyst such as sulfuric acid. Further, a non-diazo aromatic ring can be introduced into the main chain by mixing and condensing an aromatic compound other than the diazo monomer together to form a composite diazo resin.

As the anion component of the diazo compound, hexafluorophosphoric acid, tetrafluoroboric acid, p-toluenesulfonic acid, benzenesulfonic acid and the like can be used, but hexafluorophosphoric acid is particularly preferable. In the present invention, the diazo compound has a weight average molecular weight of 1,000 to
The range of 4,000 is preferable.

The diazo compound is contained in the photosensitive layer in an amount of 5 to 50.
It is preferable to use it in a range such that the weight% is obtained. The binder used in the present invention has an acetal skeleton in the molecule. Specific examples include binders containing units represented by the following structural formula (I).

[0021]

[Chemical 1]

In the formula, R represents a hydrogen atom or a lower alkyl group, particularly an alkyl group having 1 to 3 carbon atoms. In the present invention, the unit represented by the above structural formula (I) in the binder is preferably 30 mol% or more, more preferably 30 mol% or more.
-80 mol% is contained, and as other constituents,
For example, the vinyl alcohol skeleton may contain 10 mol% or less, and the vinyl acetate skeleton may contain 60 mol% or less.

Such a binder has, for example, a polymerization degree of 20.
Polyvinyl alcohol having a degree of saponification of 0 to 2,000 and a degree of saponification of 50 to 100% is subjected to an acid catalyst such as hydrochloric acid and a carbonyl compound such as formaldehyde, acetaldehyde, butyraldehyde under the conditions of 30 ° C to 80 ° C for 1 hour to 10 hours. Obtained by reacting. The weight average molecular weight of the binder is preferably about 10,000 to 200,000, and such a binder is used in the range of 5 to 95% by weight, preferably 20 to 90% by weight in the photosensitive layer.

In the present invention, in addition to the above-mentioned binder, in order to improve the developing property and the ink receiving property, for example, JP-A-61-144642, JP-B-52-7364 and JP-B-57-43890 are disclosed. , Other known binders such as acrylic copolymers, polyesters, urethanes, epoxy resins, etc., preferably 4
-Hydroxyphenyl methacrylamide 5-20 mol%, acrylonitrile 15-40 mol%, ethyl acrylate 40-70 mol%, methacrylic acid 3-15 mol%
And an acrylic copolymer having a weight average molecular weight of 30,000 to 150,000, or 20 to 50 mol% of 2-hydroxyethyl methacrylate, 15 to 30 mol% of acrylonitrile, 20 to 50 mol% of ethyl methacrylate, and 3 to 15 methacrylic acid. Weight average molecular weight in mol% of 50,000-
200,000 acrylic copolymer in the photosensitive layer 5 to 95
You may use together in weight%, Preferably it is 20-90 weight%.

The photosensitive layer of the present invention may further contain a stabilizer for maintaining the storage stability of the diazo photoreceptor. Typical stabilizers include organic compounds such as polyacrylic acid, tartaric acid, citric acid, oxalic acid, benzenesulfonic acid and naphthalenesulfonic acid, and inorganic compounds such as phosphoric acid, phosphorous acid and zinc chloride (Japanese Patent Publication No. 57- No. 8460). The amount of these stabilizers added is preferably in the range of 1% by weight to 20% by weight in the photosensitive layer.

A color material for coloring the image area can be further added to the photosensitive layer. Representative colorants include acridine dyes, cyanine dyes, styryl dyes, triphenylmethane dyes and other dyes, phthalocyanine and other pigments, azide compounds and spiropyran compounds for the purpose of visualization by exposure (Japanese Patent Publication No. 40- 220
No. 3, etc.). These coloring materials are contained in the photosensitive layer in an amount of 1% by weight to 1%.
It can be appropriately added within the range of 0% by weight.

To form the photosensitive layer on the support, a photosensitive solution in which a photosensitive component is dissolved in a solvent is prepared and applied by a method such as a whirl, roll coater, die coater or curtain coater. The solvent is not particularly limited, but alcohols such as ethanol and butanol, methyl cellosolve, ethyl cellosolve, methyl cellosolve acetate, cellosolve such as ethyl cellosolve acetate, ketones such as cyclohexanone and methyl ethyl ketone, propylene glycol monomethyl ether, methyl lactate, Examples include ethyl lactate.

The support on which the photosensitive layer is coated is mechanically or electrochemically roughened in 0.3 to 3% by weight hydrochloric acid or 0.5 to 5% by weight nitric acid electrolytic solution, and then 10 to 50. weight%
It is desirable to carry out alumite treatment in sulfuric acid or 10 to 50% by weight phosphoric acid electrolytic solution, and then perform sealing treatment with hot water, sodium silicate, sodium nitrite, etc. (Japanese Patent Publication No. 57-2203).
No. 6, JP-B 57-16918, JP-B 57-496
No. 38, etc.). The thickness of the photosensitive layer is 0.5μm or more and 5μ
It is desirable that the coating be performed so as to be m or less. The photosensitive lithographic printing plate thus obtained was exposed to an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, etc. through a transparent negative original image, and then developed by an automatic processor of the above-mentioned developing system to obtain a good printing plate. can get.

[0029]

The present invention will be described in more detail with reference to the following examples and synthetic examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. Synthesis Example 1 PVF (Polyvinyl Formal) Synthesis Polyvinyl alcohol 8 having a polymerization degree of 500 and a saponification degree of 70% 8
0 g was dissolved in 800 ml dioxane, and then 72 g of formalin (35%) and 8 g of hydrochloric acid (35%) were added to give 75
The reaction was performed while stirring with a stirrer at 7 ° C for 7 hours.
The reaction solution was discharged into a 10% caustic soda aqueous solution to precipitate a polymer. After the discharged liquid was neutralized, it was filtered to obtain a polymer, which was further washed with water. The polymer obtained is 50
After drying under reduced pressure for one day under the condition of -60 ° C, the weight of the product was 77 g (yield 92%). ¹³ C NMR
Composition analysis by: 50 mol% vinyl formal, 5 mol% vinyl alcohol, 45 mol% vinyl acetate
It was found to be a copolymer of The weight average molecular weight measured by gel permeation chromatography (GPC) was 81,000.

Synthesis Example 2 PVB (Polyvinyl Butyral) Synthesis Polyvinyl alcohol 8 having a polymerization degree of 500 and a saponification degree of 70% 8
0 g was dissolved in 800 ml dioxane, 70 g of butyraldehyde and 8 g of hydrochloric acid (35%) were added, and the mixture was heated to 70 ° C.
The reaction was carried out while stirring with a stirrer for 7 hours. Thereafter, in the same manner as in Synthesis Example 1, 96 g (yield 90%) of polyvinyl butyral was obtained. ^A composition analysis by ¹³ CNMR revealed that the copolymer was a vinyl butyral 49 mol%, vinyl alcohol 6 mol%, and vinyl acetate 45 mol%. The weight average molecular weight is 10 by GPC measurement.
It was confirmed to be 1,000.

Synthesis Example 3 PHX (acrylic copolymer) synthesis 4-hydroxyphenylmethacrylamide (HYPM)
A), acrylonitrile (AN), ethyl acrylate (EA), and methacrylic acid (MAA) were synthesized according to the synthesis examples described in JP-A-61-144642. The weight average molecular weight of the obtained polymer was confirmed to be 86,000 by GPC measurement. The molar composition of the copolymer is 14% for HYPMA and 25% for AN by NMR.
%, EA 50%, MAA 11%.

Synthesis Example 4 Diazo Photoreceptor (DR) Synthesis p-diazodiphenylamine sulfate 14.5 g (50 m
(Mol) was dissolved in 40 g of concentrated sulfuric acid under ice cooling, and then 1.05 g
Paraformaldehyde (35 mmol) was added slowly so that the reaction temperature did not exceed 10 ° C. After continuing stirring under ice-cooling for 2 hours, the mixture was added dropwise to 500 ml of ethanol, and the generated precipitate was separated by filtration. After washing the precipitate with ethanol, the precipitate was dissolved in 100 ml of water, and an aqueous solution containing 6.8 g of zinc chloride was added. After filtering off the resulting precipitate,
After washing with ethanol and drying at 25 ° C. for 3 hours, 15 g of diazo resin zinc chloride double salt was obtained. 150 g of this double salt
After dissolving in water of 8 ml, an aqueous solution of 8 g of ammonium hexafluorophosphate was added, the resulting precipitate was filtered off, washed with water and then with ethanol, and dried under reduced pressure at 25 ° C. overnight, Diazo resin hexafluorophosphate 1
2.5 g was obtained.

Synthesis Example 5 Composite diazo photoconductor (DHR) synthesis 11 g (37.5 m) of p-diazodiphenylamine sulfate
, P-hydroxybenzoic acid 1.73 g (12.5 mol)
(mmol) was dissolved in 44 g of concentrated sulfuric acid under ice cooling, and then 1.4 g
Paraformaldehyde (45 mmol) was slowly added, and the condensation reaction was performed while cooling to 10 ° C or lower. After continuing stirring for 2 hours under ice cooling, the mixture was added dropwise to 340 ml of ethanol to precipitate a polymer, which was separated by filtration. After washing the precipitate with ethanol, the precipitate was dissolved in 90 ml of water, an aqueous solution in which 6.6 g of zinc chloride was dissolved was added, and the precipitate formed was filtered off.
It was washed with ethanol. This precipitate was dissolved in 200 ml of water, and an aqueous solution in which 6.1 g of ammonium phosphide was dissolved was added to carry out a salt exchange reaction. Precipitation was carried out while acetone was added dropwise, and the precipitate was separated by filtration and washed with water and ethanol. ℃,
After drying under reduced pressure overnight, 9.8 g of a composite diazo photosensitive material having a diazo unit and a hydroxybenzoic acid unit in the proportions of 75 mol% and 25 mol%, respectively, was obtained.

Synthesis Example 6 PHEMA (acrylic copolymer) synthesis 2-hydroxyethyl methacrylate (HEMA), acrylonitrile (AN), methyl methacrylate (MM)
A), a copolymer of methacrylic acid (MAA) is disclosed in JP-A-60
It was synthesized according to the method described in Example 2 of JP-64351A. The weight average molecular weight of the obtained polymer was confirmed to be 160,000 by GPC measurement. The molar composition of the copolymer is HEMA 50%, AN 20%, MMA2
It was 5% and MAA 5%.

Production Example 1 Preparation of Brush Polished Grain Plate An aluminum plate was grained using a nylon brush and 40 mesh pumice suspension. Then, etch in a 5% caustic soda solution at 50 ° C. for 10 seconds,
After washing with water, it was neutralized and washed with 10% nitric acid. Then, anodizing treatment was performed in a 30% sulfuric acid bath at 30 ° C. and 2.5 A / dm ^{2 for} 2 minutes, and then 80% in a 2% aqueous solution of sodium metasilicate.
Sealing treatment was performed at 20 ° C. for 20 seconds to obtain a brush grain plate.

Production Example 2 Preparation of Electropolished Grain Board An aluminum plate was placed in a 2% hydrochloric acid bath at 25 ° C. and 50 A / d.
After electropolishing at a current density of m ² for 1 minute, it was desmutted in a 5% caustic soda aqueous solution at 40 ° C. for 10 seconds and washed with water. Then, anodizing and sealing treatment were performed under the same conditions as in Production Example 1 to obtain an electrolytically polished grain board.

Example 1 A sensitizing solution having the following composition was prepared, and a whirrer coating was applied to the grained plate obtained by the brush polishing method of Production Example 1 so that the photosensitive film thickness was 1 g / m ² . Polyvinyl formal (PVF synthesis example) 20 g Composite diazo photoreceptor (DHR synthesis example) 4 g Phthalocyanine pigment 4 g Phosphoric acid 0.4 g Methyl lactate 600 g

Next, a subtractive type developer having the following composition was added to a developing device for additive ("LITHOPLATER-").
D ", American Western Lithotech
Made) tank. Sodium metasilicate 40g Benzyl alcohol 20g Water 1000g

The lithographic printing plate precursor coated above was irradiated with a UV ray of 350 mj / cm ^{2 with} a negative film, and then developed with "LITHOPLATER-D" under the following conditions. Brush shape 14cm diameter UNFLAG G
ED brushes (2 on the left and right, 2 on the front and back, 4 dies attached) Brush rotation speed 307 rpm Brush reciprocating motion 23 reciprocations / min Photosensitive lithographic printing plate transport speed 3.5 ft / min Brush pressure 0.20 lbs / sq. Inch When the halftone dot reproduction area of the printed plate was examined, it was found to be 150
From 1% to 99% is reproduced on the screen,
Moreover, the dot weight at 50% was as good as 4.5%.

Example 2 A photosensitive solution having the following composition was prepared in a thickness of 1.5 μm in Production Example 2
Then, whitler was applied to the sand prepared by the electropolishing method to prepare a photosensitive lithographic printing plate. Polyvinyl formal (PVF synthesis example) 6 g Acrylic copolymer (PHX synthesis example) 14 g Diazo resin (DR synthesis example) 2 g Victoria Pure Blue BOH (Hodogaya Chemical Co., Ltd.) 0.4 g Polyacrylic acid "AC20L" (Nippon Pure Chemical) 0.2 g Methyl lactate 500 g The obtained photosensitive lithographic printing plate was treated with the same developer as in Example 1,
When processed with a developing device and developing conditions, halftone dots of 1% to 98% were reproduced on 150 screens.

Comparative Example 1 A photosensitive solution having the following composition was applied in a thickness of 1.5 μm in the same manner as in Example 2 on a whirler to prepare a photosensitive lithographic printing plate. Acrylic copolymer (PHX synthesis example) 20 g Diazo resin (DR synthesis example) 2 g Victoria Pure Blue BOH (Hodogaya Chemical Co., Ltd.) 0.4 g Polyacrylic acid "AC20L" (Nippon Pure Chemical Co., Ltd.) 0.2 g Methyl lactate 500 g

The photosensitive lithographic printing plate thus obtained was treated with the same developing solution, developing device and developing conditions as in Example 1.
With 50 screens, small halftone dots of 10% or less disappeared. The line drawing part was also scratched by the brush, and satisfactory results were not obtained.

Example 3 A sensitizing solution having the following composition was prepared and applied to the brush-polished sand obtained in Production Example 1 with a whirler so as to have a thickness of 1 μm.

[0044]         Polyvinyl butyral (PVB synthesis example) 20g         Composite diazo resin (DHR synthesis example) 4g         Victoria Pure Blue BOH 0.4g         Polyacrylic acid "AC20L" (Nippon Pure Chemical Co., Ltd.) 1g         Methyl lactate 500g

Next, a developer having the following composition was prepared, and an automatic developing machine for additive "LITHOPLATER-G" was prepared.
(Manufactured by Western Lithotech). Benzyl alcohol 3.5% Sodium alkylbenzene sulfonate 3.0% Monoethanolamine 2.0% Water 91.5%

The photosensitive lithographic printing plate precursor applied above was irradiated with UV light of 350 mj / cm ^{2 as} a negative film, and then developed with "LITHOPLATER-G" under the following conditions. Brush shape 14cm diameter FLAGGED
Brushes (2 on the left and right, 2 on the front and back, 4 molds attached) Brush rotation speed 300 rpm Brush reciprocating movement 25 reciprocating / min PS plate conveying speed 2.5 ft / min Brush pressure 0.30 lb / in 2 The halftone dot reproduction area of the lithographic printing plate was as good as 0.5% to 99% on 150 screens.
In addition, no scratches due to the brush were seen on the line drawing.

Comparative Example 2 A photosensitive solution having the following composition was prepared, and whirler coating was applied to the brush-polished grain plate of Production Example 1 so as to have a film thickness of 1 μm to obtain a photosensitive lithographic printing plate. Acrylic copolymer (Example of PHEMA synthesis) 20 g Composite diazo resin (Example of DHR synthesis) 4 g Victoria Pure Blue BOH 0.4 g Polyacrylic acid "AC20L" (manufactured by Nippon Pure Chemical Industries, Ltd.) 1 g Methyl lactate 500 g Obtained photosensitive lithographic printing plate When the plate was treated with the same developing solution, developing device and developing conditions as in Example 3, the non-image area was not completely eluted and a slight coloring of the remaining dye was observed. On the other hand, many scratches due to the brush were generated in the image area, and a satisfactory result was not obtained.

[0048]

INDUSTRIAL APPLICABILITY According to the present invention described above, when a subtract type offset printing plate having a photosensitive layer containing a diazo photoconductor and a binder having an acetal skeleton in the molecule is used, an additive type automatic developing machine of a specific system can be used. It is possible to produce a good printing plate with a subtract type developing solution which has few environmental problems.

Claims (4)

[Claims] 1. A subtractive offset printing plate, wherein the photosensitive layer of the offset printing plate contains at least a diazo photoreceptor and a binder having an acetal skeleton in its molecule. 2. The offset printing plate is developed by bringing a developing brush into pressure contact with the offset printing plate in the presence of a developing solution while automatically conveying the image-exposed offset printing plate. The subtract type offset printing plate according to claim 1. 3. The subtractive offset printing according to claim 2, wherein the brush pressure of the developing brush with respect to the subtractive offset printing plate is 0.15 to 0.45 pounds per square inch. Edition. 4. A subtractive offset printing plate containing at least a composite diazo photoconductor and an acrylic copolymer having a hydroxyl group in a photosensitive layer is image-exposed, and the image-exposed printing plate is automatically conveyed. On the printing plate, a developing brush that reciprocates along an axis parallel to the printing plate surface at right angles to the conveying direction of the printing plate while rotating around an axis perpendicular to the printing plate plane in the presence of a developing solution. A method for making a subtract type offset printing plate, which comprises developing by pressing.