EP1407894B1

EP1407894B1 - Photosensitive lithographic printing plate precursor

Info

Publication number: EP1407894B1
Application number: EP03022901A
Authority: EP
Inventors: Shunichi c/o Fuji Photo Film. Ltd Kondo
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2002-10-09
Filing date: 2003-10-09
Publication date: 2008-03-05
Anticipated expiration: 2023-10-09
Also published as: EP1407894A3; ATE388023T1; DE60319484T2; DE60319484D1; EP1407894A2; JP2004133125A

Abstract

A photosensitive lithographic printing plate precursor comprises an aluminum support having an intermediate layer and a photopolymerizable photosensitive layer. The intermediate layer comprises a copolymer containing a constituting component having an acid group and a constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution.

Description

FIELD OF THE INVENTION

The present invention relates to a photosensitive lithographic printing plate precursor comprising an aluminum support having provided thereon a photopolymerizable photosensitive layer. More particularly, it relates to a photosensitive lithographic printing plate precursor in which the developing property of the non-image area is improved and the adhesion of photosensitive layer to support is increased and thus both resistance to stain and press life at the printing are fulfilled.

BACKGROUND OF THE INVENTION

In the production of printings using a lithographic printing plate, it is one of the essential conditions to obtain printings free from background stain. In general, the background stain increases with getting a storage period longer after the production of lithographic printing plate precursor, and it becomes severe in the case of storage under high temperature and high humidity conditions. Since in the photopolymerizable photosensitive layer, a radical is generated upon light and a chain reaction polymerization occurs to form an image, it is difficult that the photosensitive lithographic printing plate precursor having such a photopolymerizable photosensitive layer has a good storage stability. Therefore, it has been desired to develop a photosensitive lithographic printing plate precursor, which withstands preservation for a long period of time, particularly preservation under high temperature and high humidity conditions and provides printings free from background stain.
A large number of attempts have been hitherto made for preventing the occurrence of background stain. For instance, there are known a photosensitive lithographic printing plate precursor comprising an anodized aluminum support having an undercoat layer comprising polyvinyl sulfonic acid on the surface of the support and a photosensitive layer containing a diazo compound provided on the undercoat layer (described in West German Patent 1,621,478 ), a photosensitive lithographic printing plate precursor comprising an aluminum support having an undercoat layer comprising polyacrylic acid, etc. on the surface of the support and a photosensitive layer containing a diazo resin provided on the undercoat layer (described in West German Patent 1,091,433 ), a photosensitive lithographic printing plate precursor comprising an aluminum support having an undercoat layer comprising polyacrylamide on the surface of the support and a photosensitive layer provided on the undercoat layer (described in U.S. Patent 3,511,661 ), and a photosensitive lithographic printing plate precursor comprising a photosensitive layer containing a diazo compound and an organic polymer carrier, wherein a polymer organic acid is added to the photosensitive layer in order to improve the preservation stability and to prevent the occurrence of background stain ( JP-A-56-107238 ) (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, sufficient effects cannot be attained in these photosensitive lithographic printing plate precursors and further improvements have been required. Further, a photosensitive adduct containing a combination of a diazo resin having plural side chain diazonium groups with a sulfonated polymer having plural sulfonate groups (for example, sulfonated polyurethane or sulfonated polyester) is described in JP-A-57-5042 . However, the effect for preventing background stain is still insufficient according to the photosensitive adduct. In addition, since the photosensitive adduct is used as the photosensitive layer itself, performances of the photosensitive lithographic printing plate precursor are controlled by the characteristics of the sulfonated polyurethane or sulfonated polyester, etc. used and thus it has a disadvantage in that the range of utility of the lithographic printing plate precursor is extremely restricted.
Moreover, it is known to provide an intermediate layer containing a polymer including a repeating unit of a monomer having sulfonic acid, as a method for restraining the occurrence of background stain due to preservation of a photosensitive lithographic printing plate precursor having a photosensitive layer containing a diazo compound and a polymerizable composition for a long period of time (for example, refer to Patent Document 1).
Although the improvement in preservation stability according to the above technique is highly achieved in a photopolymerization system of low sensitivity, the effect is insufficient in a high-sensitive photopolymerization system, for example, a CTP system, which is exposed with a laser light source.
Such methods of providing the undercoat layer containing a compound having a high solubility in a developing solution or adding such a compound to a photopolymerizable photosensitive layer exhibits a large damage in the exposed area due to the development and causes frequently deterioration of performances, for example, press life, although they are effective for the improvement in background stain.
As a developing solution for a photosensitive lithographic printing plate precursor having a photopolymerizable photosensitive layer on an aluminum support, there is proposed an aqueous solution of a silicate, phosphate, carbonate or hydroxide of alkali metal, etc. or an organic amine compound, etc.
For instance, a developing solution having a high pH of 12 or more and containing an alkali salt of silicic acid and an amphoteric surface active agent is described in JP-A-8-248643 and a developing solution having a pH of 12 or below and containing an alkali salt of silicic acid with the specified ratio of SiO₂/M₂O (wherein M represents an alkali metal) is described in JP-A-11-65129 .
The former developing solution has a problem in that the image area tends to be damaged upon the development with the developing solution having such a high pH in addition to the problem of handling. The latter developing solution has a problem in that the silicate may be gelled and insolubilized upon a slight decrease in pH of the developing solution during the development.
As a developing solution containing no alkali salt of salicic acid, a developing solution comprising an alkali agent, a complexing agent, an anionic surface active agent, an emulsifying agent and an n-alkanoic acid is described in JP-A-61-109052 and a developing solution comprising an alkali agent, a complexing agent, an anionic surface active agent, an amyl alcohol and an N-alkoxyamine is described in West German Patent 1,984,605 . However, these developing solutions damage severely the image area due to the high pH thereof and the organic solvent contained therein and thus, it is difficult to obtain printing performances, for example, press life.
As a developing solution having a relatively low pH (pH of 12 or below) and containing no alkali salt of salicic acid, a developing solution comprising an aqueous potassium hydroxide solution containing an anionic surface active agent is described in JP-A-2000-81711 and a developing solution comprising an aqueous solution of alkali metal carbonate having a pH of from 8.5 to 11.5 is described in JP-A-11-65126 .
Development with such a developing solution having a relatively low pH has a problem in that since the developing solution has essentially a weak power for dissolving a photopolymerizable photosensitive layer, for example, when a printing plate precursor having such a photopolymerizable photosensitive layer, which has been preserved, is processed, the development proceeds only insufficiently, resulting in the disadvantageous occurrence of residual film. In order to solve the problem, it is requested a means, for example, that a polymer binder having a high acid value is used in the photopolymerizable photosensitive layer of printing plate precursor for improving developing property or a monomer having an acid group is used together. However, in case of using the binder having such a high acid value, another problem in printing, for example, a phenomenon in which adhesion of printing ink is disturbed during the printing (so-called blinding) tends to occur.
Furthermore, in order to obtain a lithographic printing plate having improved resistance to stain, for example, background stain and a strong film, a plate-making method is described in JP-A-2003-21908 , wherein a lithographic printing plate precursor having an intermediate layer containing a polymer compound including a constituting component having an acid group and a constituting component having an onium salt is provided and is processed with a developing solution having a pH of from 11.0 to 12.7 and containing an inorganic alkali salt and a nonionic surface active agent having a polyoxyalkylene ether group. This method is practical because it strikes a relatively good balance between the developing property in the unexposed area and the film strength in the exposed area. However, the method has limitations on attempting to further improve the resistance to stain and press life and thus, further development of a more effective intermediate layer has been desired.
EP 1 223 196 describes planographic printing plate precursors where a resin interlayer is placed between a negative image-recording material for heat-mode exposure and a support. This resin interlayer comprises an alkali-soluble polymer substance which dissolves in an alkali developer solution.
EP 1 199 603 relates to a positive photosensitive composition used in manufacturing lithographic printing plates which comprises an alkali-soluble resin, a compound capable of generating an acid upon exposure to radiation and a compound having acid-decomposable groups.
Patent Document 1: JP-A-59-101651

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a photosensitive lithographic printing plate precursor comprising a support having provided thereon a photopolymerizable photosensitive layer, which has a high preservation stability and is prevented from the occurrence of background stain by conducting imagewise exposure, development and printing even after the preservation under high temperature and high humidity conditions for a long period of time after the production thereof.
Another object of the present invention is to provide a photosensitive lithographic printing plate precursor, which exhibits a small damage in the exposed area upon the development, maintains a firm adhesion between the surface of support and the photopolymerizable photosensitive layer and exhibits a high press life.
Other objects of the present invention will become apparent from the following description.
As a result of intensive investigations to achieve the objects described above, it has been found that by incorporating a polymer compound containing a constituting component having an acid group and a constituting component, containing an acetal group, a lactone ring or an oxycarboxy group, capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution, the developing property in the non-image area is increased and the occurrence of background stain is prevented even after the preservation of photosensitive lithographic printing plate precursor. It has also been found that by adopting the above-described intermediate layer, the adhesion between the intermediate layer and the aluminum support in the exposed area is not impaired and the high press life can be achieved.
Specifically, the invention includes the following photosensitive lithographic printing plate precursors.

1. A photosensitive lithographic printing plate precursor comprising an aluminum support having provided thereon an intermediate layer and a photopolymerizable photosensitive layer in this order, wherein the intermediate layer comprises a copolymer containing a constituting component having an acid group and a constituting component, containing an acetal group, a lactone ring or an oxycarboxy group, capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution.
2. A photosensitive lithographic printing plate precursor according to the above acid group is a -COOH, -SO₃H, -OSO₃H, -PO₃H₂, -OPO₃H₂, -CONHSO₂- or a -SO₂NHSO₂- group.
3. A photosensitive lithographic printing plate precursor according to the above 1, wherein the acid group is -COOH.
4. A photosensitive lithographic printing plate precursor according to the above 1, wherein the constituting component having an acid group is represented by formula (1) or (2):

wherein A represents a divalent connecting group; B represents an aromatic group or a substituted aromatic group; D and E each independently represent a divalent connecting group; G represents a trivalent connecting group; X and X' each independently represent an acid group having pKa of not more than 7 or an alkali metal salt or an ammonium salt thereof; R₁ represents a hydrogen atom, an alkyl group or a halogen atom; a, b, d and e each independently represent 0 or 1; and t represents an integer of from 1 to 3. 5. A photosensitive lithographic printing plate precursor according to the above 4, wherein the constituting component having an acid group is represented by formula (1) wherein B represents a phenylene group or a substituted phenylene group in which the substituent is a hydroxy group or an alkyl group having from 1 to 3 carbon atoms; D represents an alkylene group having from 1 to 2 carbon atoms or an alkylene group having from 1 to 2 carbon atoms connected with an oxygen atom; R₁ represents a hydrogen atom or a methyl group; X represents a carboxylic acid group; a is 0; and b is 1.

It is a common procedure to use a polymer compound having a high solubility in a developing solution as the polymer compound in the intermediate layer and a polymer containing a constituting unit having an acid group is employed in an alkali developing solution. In the alkali developing solution, the acid group forms an alkali salt so that the solubility of the polymer is remarkably increased. In order to increase the solubility, it is preferred to elevate an acid value. However, when the acid value is elevated to an excessive degree, problems have arisen in that blinding defect occurs and in that the intermediate layer is dissolved by the root with the alkali penetrated through the photopolymerizable photosensitive layer of the exposed area to cause lack of fine dots and deterioration of press life.
Due to the constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution of the copolymer included in the intermediate layer of the photosensitive lithographic printing plate precursor of the invention, in the unexposed area where the alkali developing solution easily penetrates into the photosensitive layer to contact with the intermediate layer, an acid is generated by the reaction, for example, hydrolysis so that the unexposed area has a property in that the solubility thereof is remarkably increased. On the other hand, the exposed area where the contact with the alkali developing solution is restrained due to the photocured photosensitive layer having less permeability of the alkali developing solution exhibits hydrophobicity. Such a change of the solubility based on the chemical reaction makes it easy to strike a balance between the developing property and the adhesion even when the I/O value of the intermediate layer increases 5%.
According to the above finding, the production of photosensitive lithographic printing plate precursor, which keeps the balance between resistance to stain and press life over a wide range becomes possible.
The I/O value means a ratio of inorganicity/organicity of a compound and is known that it corresponds to many physical properties as described in Yoshio Koda, Yuuki Gainenzu-Kisso to Oyo-, Sankyo Shuppan Publishers (May 10, 1984). A primary scale of the important physical property, for example, solubility to an alkali developing solution in the invention is hydrophilicity and a relation between the hydrophilicity and the I/O value is also described. When the I/O value is large, that is, when the inorganicity is large, the hydrophilicity is high. On the contrary, when the I/O value is small, the oleophilicity is high. A relation between the I/O value and a solubility parameter is described, and there is also described that the correlation therebetween arises under certain conditions.
The I/O value is determined by calculating an inorganicity value and an organicity value from a structural formula of a compound and obtaining a ratio of these values. The organicity value is primarily calculated by a number of carbon atoms. The inorganicity value is calculated by using a value of a functional group calculated by taking influence of a hydroxy group as 100.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described in detail below.

(Intermediate layer)

The photosensitive lithographic printing plate precursor of the invention has a feature in that the intermediate layer thereof comprises a polymer compound including a constituting component having an acid group and a constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution. By providing the intermediate layer comprising such a polymer compound between an aluminum support and a photopolymerizable photosensitive layer as described hereinafter, the resistance to satin of the photosensitive lithographic printing plate precursor during preservation is achieved and the press life is also improved.
The polymer compound (hereinafter also referred to as simply a polymer compound of the invention) includes, for example, a polymer compound obtained by polymerization of a monomer component having an acid group and a monomer component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution. The acid group is preferably an acid group having an acid dissociation constant (pKa) of not more than 7, more preferably -COOH, -SO₃H, -OSO₃H, -PO₃H₂, -OPO₃H₂, -CONHSO₂-, -SO₂NHSO₂-, and particularly preferably -COOH.
Of the polymer compounds according to the invention, a polymer compound wherein the main chain structure thereof comprises a vinyl polymer, for example, an acrylic resin, a methacrylic resin or a polystyrene, a urethane resin, a polyester or a polyamide is preferred. The polymer compound wherein the main chain structure thereof comprises a vinyl polymer, for example, an acrylic resin, a methacrylic resin or a polystyrene is more preferred. A polymer wherein the constituting component having an acid group is a polymerizable compound represented by formula (1) or (2) shown below is particularly preferred.

wherein A represents a divalent connecting group; B represents an aromatic group or a substituted aromatic group; D and E each independently represent a divalent connecting group; G represents a trivalent connecting group; X and X' each independently represent an acid group having pKa of not more than 7 or an alkali metal salt or an ammonium salt thereof; R₁ represents a hydrogen atom, an alkyl group or a halogen atom; a, b, d and e each independently represent 0 or 1; and t represents an integer of from 1 to 3. Of the constituting components having an acid group, those represented by formula (1) or (2) wherein A represents -COO- or -CONH-, B represents a phenylene group or a substituted phenylene group in which the substituent is a hydroxy group, a halogen atom or an alkyl group; D and E each independently represent an alkylene group or a divalent connecting group represented by a molecular formula of C_nH_2nO, C_nH_2nS or C_nH_2n+1N; G represents a trivalent connecting group represented by a molecular formula of C_nH_2n-1, C_nH_2n-1O, C_nH_2n-1S or C_nH_2nN in which n represents an integer of from 1 to 12; X and X' each independently represent a carboxylic acid group, a sulfonic acid group, a phosphonic acid group, a sulfuric acid monoester group or a phosphoric acid monoester group; R₁ represents a hydrogen atom or an alkyl group; a, b, d and e each independently represent 0 or 1, provided that a and b are not 0 at the same time are more preferred. Of the constituting components having an acid group, those represented by formula (1) wherein B represents a phenylene group or a substituted phenylene group in which the substituent is a hydroxy group or an alkyl group having from 1 to 3 carbon atoms; D and E each independently represent an alkylene group having from 1 to 2 carbon atoms or an alkylene group having from 1 to 2 carbon atoms connected with an oxygen atom; R₁ represents a hydrogen atom or a methyl group; X represents a carboxylic acid group; a is 0; and b is 1 are particularly preferred.
Specific examples of the constituting components having an acid group are set forth below, but the invention should not be construed as being limited thereto.
Acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, itaconic acid, maleic acid, maleic anhydride,
The constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution is described below. The constituting component is a constituting component obtained by copolymerization of a monomer having a functional group capable of generating an acid, for example, a carboxylic acid or a sulfonic acid upon a reaction with alkali, for example, a hydrolysis reaction or a ring-opening reaction.
Specific examples of the monomer include those having the structure shown below. The monomer has an acetal group, a lactone ring, an oxycarboxy group or the like. The monomer used should not be construed as being limited to the specific examples.
Moreover, the polymer according to the invention may contain at least one monomer selected from polymerizable monomers set forth in items (1) to (13) described below as a copolymerization component.

(1) acrylamides, methacrylamides, acrylic acid esters, methacrylic acid esters and hydroxystyrenes each having an aromatic hydroxy group, for example, N-(4-hydroxyphenyl)acrylamide, N-(4-hydroxyphenyl)methacrylamide, o-, m- or p-hydroxystyrene, o- or m-bromo-p-hydroxystyrene, o- or m-chloro-p-hydroxystyrene, o-, m- or p-hydroxyphenyl acrylate or o-, m- or p-hydroxyphenyl methacrylate,
(2) unsaturated carboxylic acids, for example, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, half ester of maleic acid, itaconic acid, itaconic anhydride or half ester of itaconic acid,
(3) acrylamids, for example, N-(o-aminosulfonylphenyl)acrylamide, N-(m-aminosulfonylphenyl)acrylamide, N-(p-aminosulfonylphenyl)acrylamide, N-[1-(3-aminosulfonyl)naphthyl]acrylamide or N-(2-aminosulfonylethyl)acrylamide, methacrylamids, for example, N-(o-aminosulfonylphenyl)methacrylamide, N-(m-aminosulfonylphenyl)methacrylamide, N-(p-aminosulfonylphenyl)methacrylamide, N-[1-(3-aminosulfonyl)naphthyl]methacrylamide or N-(2-aminosulfonylethyl)methacrylamide, unsaturated sulfonamides of acrylic acid esters, for example, o-aminosulfonylphenyl acrylate, m-aminosulfonylphenyl acrylate, p-aminosulfonylphenyl acrylate or 1-(3-aminosulfonylphenylnaphthy) acrylate, and unsaturated sulfonamides of methacrylic acid esters, for example, o-aminosulfonylphenyl methacrylate, m-aminosulfonylphenyl methacrylate, p-aminosulfonylphenyl methacrylate or 1-(3-aminosulfonylphenylnaphthyl) methacrylate,
(4) phenylsulfonylacrylamides which may have a substituent, for example, tosylacrylamide and phenylsulfonylmethacrylamides that may have a substituent, for example, tosylmethacrylamide.
A film-forming resin prepared by copolymerization of a monomer described in (5) to (13) below, besides such a monomer containing an alkali-soluble group is preferably used.
(5) acrylic acid esters and methacrylic acid esters each having an aliphatic hydroxy group, for example, 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate,
(6) (substituted) acrylic esters, for example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, cyclohexyl acrylate, octyl acrylate, phenyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, 4-hydroxybutyl acrylate, glycidyl acrylate or N-dimethylaminoethyl acrylate,
(7) (substituted) methacrylic acid esters, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, octyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, 4-hydroxybutyl methacrylate, glycidyl methacrylate or N-dimethylaminoethyl methacrylate,
(8) acrylamides and methacrylamides, for example, acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethylacrylamide, N-hydroxyethylmethacrylamide, N-phenylacrylamide, N-phenylmethacrylamide, N-benzylacrylamide, N-benzylmethacrylamide, N-nitrophenylacrylamide, N-nitrophenylmethacrylamide, N-ethyl-N-phenylacrylamide or N-ethyl-N-phenylmethacrylamide,
(9) vinyl ethers, for example, ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether or phenyl vinyl ether,
(10) styrenes, for example, styrene, α-methylstyrene, methylstyrene or chloromethylstyrene,
(11) vinyl ketones, for example, methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone or phenyl vinyl ketone,
(12) olefins, for example, ethylene, propylene, isobutylene, butadiene or isoprene,
(13) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile or methacrylonitrile.

It is desired that the polymer used in the invention contains not less than 20% by mole, preferably not more than 40% by mole of the constituting component having an acid group and not less than 5% by mole, preferably not less than 20% by mole of the constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution (the constituting component having a lactone ring or an ester structure). When the amount of the constituting component having an acid group included is not less than 20% by mole, the dissolution and removal at the alkali development is more accelerated. When the amount of the constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution included is not less than 5% by mole, the adhesion is more improved by a synergistic effect with the acid group. The constituting components having an acid group may be used individually or in combination of two or more thereof. The constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution may also be used individually or in combination of two or more thereof. Further, two or more polymers according to the invention, which are different in the constituting component, composition ratio or molecular weight, may be used as a mixture. Specific representative examples of the polymer for use in the invention are set forth below, but the invention should not be construed as being limited thereto. The composition ratio in the polymer structure is indicated by mole percent.

	Structure	Number Average Molecular Weight (Mn)
No.1		3,300
No.2		4,000
No.3		3,800
No.4		1,500
No.5		1,800
No.6		2,800
No.7		4,000
No.8		1,700
No.9		2,200
No.10		3,200
No.11		1,000
No.12		1,200

The polymer for use in the intermediate layer of the photosensitive lithographic printing plate precursor according to the invention can be ordinarily prepared using a radical chain polymerization method (refer to F. W. Billmeyer, Textbook of Polymer Science, 3rd Edition, A Wiley-Interscience Publication (1984)). With respect to a molecular weight of the polymer, a number average molecular weight (Mn), which is calculated from an integral intensity ratio of a terminal group to a side-chain functional group measured by NMR, is in a range of from 300 to 5,000, preferably from 500 to 4,800, still more preferably from 800 to 4,500. When the number average molecular weight is less than 300, the adhesion to the support becomes week, resulting in the degradation of press life. The number average molecular weight exceeding 5,000 is also disadvantageous, because the adhesion to the support becomes too strong so that sufficient removal of residue of the photopolymerizable photosensitive layer in the unexposed area cannot be achieved and further, the degradation of deleting property occurs. Although a content of the unreacted monomer included in the polymer may be over a wide range, it is preferably not more than 20% by weight, more preferably not more than 10% by weight.
The polymer having the above-described molecular weight can be obtained by controlling amounts of a polymerization initiator and a chain transfer agent in the copolymerization of corresponding monomers. The term "chain transfer agent" as used herein means a substance capable of transfer an active point of reaction upon a chain transfer reaction in the polymerization reaction. The ease of occurrence of the transfer reaction is represented by a chain transfer constant Cs. The chain transfer constant Cs x 10⁴ (at 60°C) of a chain transfer agent used in the invention is preferably not less than 0.01, more preferably not less than 0.1, and particularly preferably not less than 1. As the polymerization initiator, a peroxide, an azo compound or a redox initiator conventionally used in a radical polymerization is employed as it is. Of these polymerization initiators, the azo compound is particularly preferred.
Specific examples of the chain transfer agent include a halogen compound, for example, carbon tetrachloride or carbon tetrabromide, an alcohol, for example, isopropyl alcohol or isobutyl alcohol, an olefin, for example, 2-methyl-1-butene or 2,4-diphenyl-4-methyl-1-pentene, and a sulfur-containing compound, for example, ethanethiol, butanethiol, dodecanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid, thioglycolic acid, ethyldisulfide, sec-butyldisulfide, 2-hydroxyethyldisulfide, thiosalicylic acid, thiophenol, thiocresol, benzylmercaptan or phenethylmercaptan, but the chain transfer agent should not be construed as being limited thereto. More preferable examples thereof includes ethanethiol, butanethiol, dodecanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid, thioglycolic acid, ethyldisulfide, sec-butyldisulfide, 2-hydroxyethyldisulfide, thiosalicylic acid, thiophenol, thiocresol, benzylmercaptan or phenethylmercaptan, and particularly preferable examples thereof includes ethanethiol, butanethiol, dodecanethiol, mercaptoethanol, mercaptopropanol, methyl mercaptopropionate, ethyl mercaptopropionate, mercaptopropionic acid, thioglycolic acid, ethyldisulfide, sec-butyldisulfide and 2-hydroxyethyldisulfide.
The intermediate layer containing the polymer compound according to the invention is provided by means of various methods on an aluminum support optionally subjected to a hydrophilization treatment as described hereinafter.
The intermediate layer can be provided according to the following methods. Examples of the method include a method of coating a solution containing the polymer compound of the invention dissolved in an organic solvent, for example, methanol, ethanol or methyl ethyl ketone, a mixed solvent thereof or a mixed solvent of the organic solvent with water on the aluminum support and drying to provide the intermediate layer, and a method of immersing the aluminum support in a solution containing the polymer compound of the invention dissolved in an organic solvent, for example, methanol, ethanol or methyl ethyl ketone, a mixed solvent thereof or a mixed solvent of the organic solvent with water, washing with water or cleaning with air and drying to provide the intermediate layer.
In the former method, the solution having the total solid concentration of from 0.005 to 10% by weight is coated by various methods. For example, any of a bar coater coating, a spin coating, a spray coating and a curtain coating may be employed. In the latter method, the total solid concentration of the solution is from 0.005 to 20% by weight, preferably from 0.01 to 10% by weight, an immersion temperature is from 0 to 70°C, preferably from 5 to 60°C, and an immersion time is from 0.1 second to 5 minutes, preferably from 0.5 to 120 seconds.
The solution may be used by controlling a pH preferably in a range of from 0 to 12, more preferably from 0 to 6 using a basic substance, for example, ammonia, triethylamine or potassium hydroxide, an inorganic acid, for example, hydrochloric acid, phosphoric acid, sulfuric acid or nitric acid, a variety of organic acidic substances, for instance, an organic sulfonic acid, for example, nitrobenzenesulfonic acid or naphthalenesulfonic acid, an organic phophonic acid, for example, phenylphophonic acid, an organic carboxylic acid, for example, benzoic acid, fumaric acid or malic acid, or an organic chloride, for example, naphthalenesulfonyl chloride or benzenesulfonyl chloride. Further, in order to improve tone reproducibility of the photosensitive lithographic printing plate precursor, a substance absorbing an ultraviolet ray, visible ray or infrared light may be added to the solution.
A coverage after drying of the compound constituting the intermediate layer according to the invention is suitably from 1 to 100 mg/m², preferably from 2 to 70 mg/m², in total. When the coverage is less than 1 mg/m², the sufficient effects of the intermediate layer cannot be obtained. When the coverage is more than 100 mg/m², the sufficient effects of the intermediate layer also cannot be obtained.

(Photopolymerizable photosensitive layer)

The photosensitive composition of photopolymerization type (hereinafter also referred to as a photopolymerizable composition or a photosensitive composition), which constitutes the photopolymerizable photosensitive layer of the photosensitive lithographic printing plate precursor according to the invention, contains as the essential components, an addition-polymerizable compound having an ethylenically unsaturated bond, a photopolymerization initiator and a polymer binder. Various compounds, for example, a coloring agent, a plasticizer or a thermal polymerization inhibitor are also used together in the photosensitive composition, if desired.
The compound having an ethylenically unsaturated bond is a compound having an ethylenically unsaturated bond capable of conducting addition-polymerization upon the function of a photopolymerization initiator when the photopolymerizable composition is irradiated with an active ray, thereby causing crosslinking or hardening.
The compound having an addition-polymerizable ethylenically unsaturated bond can be appropriately selected from compounds having at least one terminal ethylenically unsaturated bond, preferably compounds having two or more terminal ethylenically unsaturated bonds. Examples of the compound include a compound having the chemical form of a monomer, a prepolymer such as a dimer, a trimer or an oligomer, a mixture thereof and a copolymer thereof.
Examples of the monomer include an ester of an unsaturated carboxylic acid (for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid or maleic acid) with an aliphatic polyhydric alcohol compound and an amide of an unsaturated carboxylic acid with an aliphatic polyvalent amine compound.
Specific examples of monomer of the ester of an unsaturated carboxylic acid with an aliphatic polyhydric alcohol compound include an acrylic acid ester, e.g., ethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol diacrylate, tetramethylene 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, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitol tetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate, tri(acryloyloxyethyl)isocyanurate or polyester acrylate oligomer; a methacrylic acid ester, e.g., 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 dipentaerythritol pentamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate, bis-[p-(3-methacryloxy-2-hydroxypropoxy)phenyl]dimethylmethane or bis-[p-(methacryloxyethoxy)phenyl]dimethylmethane; an itaconic acid ester, e.g., ethylene glycol diitaconate, propylene glycol diitaconate, 1,3-butanediol diitaconate, 1,4-butanediol diitaconate, tetramethylene glycol diitaconate, pentaerythritol diitaconate or sorbitol tetraitaconate; a crotonic acid ester, e.g., ethylene glycol dicrotonate, tetramethylene glycol dicrotonate, pentaerythritol dicrotonate or sorbitol tetracrotonate; an isocrotonic acid ester, e.g., ethylene glycol diisocrotonate, pentaerythritol diisocrotonate or sorbitol tetraisocrotonate; and a maleic acid ester, e.g., ethylene glycol dimaleate, triethylene glycol dimaleate, pentaerythritol dimaleate or sorbitol tetramaleate. Furthermore, mixtures of the above-described ester monomers are exemplified.
Specific examples of monomer of the amide of an unsaturated carboxylic acid with an aliphatic polyvalent amine compound include methylene bisacrylamide, methylene bismethacrylamide, 1,6-hexamethylene bisacrylamide, 1,6-hexamethylene bismethacrylamide, diethylenetriamine trisacrylamide, xylylene bisacrylamide and xylylene bismethacrylamide.
Other examples of such a compound include a vinyl urethane compound having at least two polymerizable vinyl groups in the molecule thereof obtained by subjecting addition of a vinyl monomer having a hydroxy group represented by formula (A) shown below to a polyisocyanate compound having at least two isocyanato groups in the molecule thereof as described in JP-B-48-41708 (the term "JP-B" as used herein means an "examined Japanese patent publication").

CH₂=C(R)COOCH₂CH(R')OH (A)

wherein R and R', which may be the same or different, each represent a hydrogen atom or a methyl group.
Also, examples thereof include urethane acrylates as described in JP-A-51-37193 and JP-B-2-32293 , polyfunctional acrylates or methacrylates, for example, a polyester acrylate or a epoxy acrylate obtained by reacting an epoxy resin with (meth)acrylic acid as described in JP-A-48-64183 , JP-B-49-43191 and JP-B-52-30490 is employed. Further, photocurable monomers and oligomers as described in Nippon Setchaku Kyoukaishi, Vol. 20, No. 7, pages 300 to 308 (1984) are employed.
The compound having an ethylenically unsaturated bond is used in an amount of from 5 to 80% by weight, preferably from 30 to 70% by weight, based on the whole composition of the photopolymerizable photosensitive layer.
The photopolymerization initiator incorporated into the photopolymerizable photosensitive layer of the photosensitive lithographic printing plate precursor according to the invention can be appropriately selected from various kinds of known photopolymerization initiators described in patents and literature depending on a wavelength of light source to be used. A combination system of two or more photopolymerization initiators (photo-initiator system) is also used. Specific examples thereof are set forth below, but the invention should not be construed as being limited thereto.
In case of using visible light having a wavelength of 400 nm or more, an Ar laser, a second harmonic wave of a semiconductor laser or an SHG-YAG laser as the light source, various photo-initiator systems have been proposed. For instance, a certain kind of photo-reducing dyes as described in U.S. Patent 2,850,445 , for example, Rose Bengale, Eosine or erythrosine, and a combination system comprising a dye and an initiator, for example, a composite initiator system comprising a dye and an amine as described in JP-B-44-20189 , a combination of a hexaarylbiimidazole, a radical generator and a dye as described in JP-B-45-37377 , a combination of a hexaarylbiimidazole and a p-dialkylaminobenzylidene kotone as described in JP-B-47-2528 and JP-A-54-155292 , a combination of a cyclic cis-α-dicarbonyl compound and a dye as described in JP-A-48-84183 , a combination of a cyclic triazine and a merocyanine dye as described in JP-A-54-151024 , a combination of a 3-ketocoumarin and an activator as described in JP-A-52-112681 and JP-A-58-15503 , a combination of a biimidazole, a styrene derivative and a thiol as described in JP-A-59-140203 , a combination of an organic peroxide and a dye as described in JP-A-59-1504 , JP-A-59-140203 , JP-A-59-189340 , JP-A-62-174203 , JP-B-62-1641 and U.S. Patent 4,766,055 , a combination of a dye and an active halogen compound as described in JP-A-63-258903 and JP-A-2-63054 , a combination of a dye and a borate compound as described in JP-A-62-143044 , JP-A-62-150242 , JP-A-64-13140 , JP-A-64-13141 , JP-A-64-13142 , JP-A-64-13143 , JP-A-64-13144 , JP-A-64-17048 , JP-A-1-229003 , JP-A-1-298348 and JP-A-1-138204 , a combination of a dye having a rhodanine ring and a radical generator as described in JP-A-2-179643 and JP-A-2-244050 , a combination of a titanocene and a 3-ketocoumarin dye as described in JP-A-63-221110 , a combination of a titanocene, a xanthene dye and an addition-polymerizable ethylenically unsaturated bond-containing compound having an amino group or a urethane group as described in JP-A-4-221958 and JP-A-4-219756 , a combination of a titanocene and a specific merocyanine dye as described in JP-A-6-295061 , or a combination of a titanocene and a dye having a benzopyran ring as described in JP-A-8-334897 are exemplified.
In recent years, with the development of a laser having a wavelength of from 400 to 410 nm (a violet laser) a photo-initiator system having high sensitivity to a wavelength of not more than 450 nm sensitive to such a laser has been developed. Such a photo-initiator system can also be used in the present invention. For example, a combination of a cationic dye and a borate as described in JP-A-11-84647 , a combination of a merocyanine dye and a titanocene as described in JP-A-2000-147763 and a combination of a carbazole dye and a titanocene as described in JP-A-2001-42524 are illustrated. In the invention, the system comprising a titanocene compound is particularly preferred, since it is excellent in sensitivity.
Various kinds of titanocene compounds can be used and, for example, they are appropriately selected from those described in JP-A-59-152396 and JP-A-61-151197 . Specific examples thereof include dicyclopentadienyl-Ti-dichloride, dicyclopentadienyl-Ti-bisphenyl, dicyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, dicyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, dicyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl, dicyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl, dicyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl, dimethylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl, dimethylcyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl and dicyclopentadienyl-Ti-bis-2,6-difluoro-3-(pyr-1-yl)-phen-1-yl.
Dyes preferably used in combination with the titanocene compound include cyanine dyes, merocyanine dyes, xanthene dyes, ketocoumarin dyes and benzopyran dyes. Examples of the cyanine dye preferably include those represented by the formula shown below, but the invention should not be construed as being limited thereto.
wherein Z¹ and Z², which may be the same or different, each represent a non-metallic atomic group necessary for forming a benzimidazole or naphthimidazole ring; R¹¹, R¹², R¹³ and R¹⁴ each represent an alkyl group which may be substituted; X^- represents a counter anion; and n represents 0 or 1.
Specific examples of the cyanine dye are set forth in the table shown below.

R¹¹ R¹² R¹³ R¹⁴ A¹ A² A³ A⁴ X^- n

C₂H₅ C₂H₆ C₂H₅ C₂H₅ Cl Cl Cl Cl I^- 1

C₂H₅ C₂H₅ C₂H₅ C₂H₅ H CF₃ H CF₃ I^- 1

C₂H₅ (CH₂)₂SO₃Na C₂H₅ (CH₂)₂SO₃ ^- Cl Cl Cl Cl - 0
Examples of the merocyanine dye preferably include those represented by the formula shown below, but the invention should not be construed as being limited thereto.

wherein Z³ and Z⁴ each represent a non-metallic atomic group necessary for forming a 5-membered or 6-membered nitrogen-containing heterocyclic ring conventionally used in a cyanine dye; R¹⁵ and R¹⁶ each represent an alkyl group; Q¹ and Q² each represent a non-metallic atomic group necessary for forming a 4-thiazolidinone ring, a 5-thiazolidinone ring, a 4-imidazolidinone ring, a 4-oxazolidinone ring, 5-oxazolidinone ring, a 5-imidazolidinone ring or a 4'-dithiolane ring; L¹, L², L³, L⁴ and L⁵ each represent a methine group; m represents 1 or 2; i and h each represent 0 or 1; 1 represents 1 or 2; j and k each represent 0, 1, 2 or 3; and X^- represents a counter anion.
wherein R¹⁷ and R¹⁸ each independently represent a hydrogen atom, an alkyl group, a substituted alkyl group, an alkenyl group, a substituted alkenyl group, an alkynyl group, a substituted alkynyl group, an alkoxycarbonyl group, an aryl group, a substituted aryl group or an aralkyl group; Z⁶ represents an oxygen atom, a sulfur atom, a selenium atom, a tellurium atom, a nitrogen atom substituted with an alkyl group or an aryl group or a carbon atom substituted with two alkyl groups; Z⁵ represents a non-metallic atomic group necessary for forming a nitrogen-containing 5-membered heterocyclic ring; B¹ represents a substituted phenyl group, an unsubstituted or substituted multinuclear aromatic ring or an unsubstituted or substituted heteroaromatic ring; and B² represents a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an aralkyl group, an alkoxy group, an alkylthio group, an arylthio group, a substituted amino group, an acyl group or an alkoxycarbonyl group, or B¹ and B² may be combined with each other to form a ring.
Specific examples of the merocyanine dye are set forth below.
Examples of the xanthene dye include Rhodamine B, Rhodamine 6G, Ethyl Eosin, alcohol-soluble eosin, Pyronin Y and Pyronin B.
Examples of the ketocoumarin dye preferably include those represented by the formula shown below, but the invention should not be construed as being limited thereto.
wherein R¹⁹, R²⁰ and R²¹ each represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; R²² and R²³ each represent an alkyl group, provided that at least one of R²² and R²³ represents an alkyl group having from 4 to 16 carbon atoms; R²⁴ represents a hydrogen atom, an alkyl group, an alkoxy group, an acyl group, a cyano group, a carboxy group or a group of an ester derivative or amido derivative thereof; R²⁵ represents a heterocyclic residue-CO-R²⁶ having the total number of carbon atoms of from 3 to 17 (wherein R²⁶ represents an alkoxy group or a group shown below) ; or R²⁰ and R²¹ or R²² and R²³ may be combined with each other to form a ring.
Specific examples of the ketocoumarin dye are set forth below.
Examples of the benzopyran dye preferably include those represented by the formula shown below, but the invention should not be construed as being limited thereto.
wherein R²⁷ to R²⁹ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a hydroxy group, an alkoxy group or an amino group, or R²⁷ to R²⁹ may be combined with a carbon atom to form a ring composed of non-metallic atoms together with the carbon atoms; R³¹ represents a hydrogen atom, an alkyl group, an aryl group, a heteroaromatic group, a cyano group, an alkoxy group, a carboxy group or an alkenyl group; R³² represents any one of the groups defined for R³¹ or -Z⁹-R³¹ (wherein Z⁹ represents a carbonyl group, a sulfonyl group, a sulfinyl group or an arylenedicarbonyl group, or R³¹ and R³² may be combined with each other to form a ring composed of non-metallic atoms; Z⁷ represents an oxygen atom, a sulfur atom, NH or a nitrogen atom having a substituent; Z⁸ represents a group represented by the following formula:
wherein G¹ and G², which may be the same or different, each represent a hydrogen atom, a cyano group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyl group, an arylcarbonyl group, an alkylthio group, an arylthio group, an alkylsulfonyl group, an arylsulfonyl group or a fluorosulfonyl group, provided that G¹ and G² do not represent hydrogen atoms at the same time, or G¹ and G² may be combined with each other to form a ring composed of non-metallic atoms together with the carbon atom.
Specific examples of the benzopyran dye are set forth below.
It is known that a photo-initiating function is more improved by adding a hydrogen-donating compound, for example, a thiol compound, e.g., 2-mercaptobenzothiazole, 2-mercaptobenzimidazole or 2-mercaptobenzoxazole, or an amine compound, e.g., N-phenylglycine or an N,N-dialkylamino aromatic alkyl ester to the photopolymerization initiators described above, if desired. The amount of photopolymerization initiator (system) used is from 0.05 to 100 parts by weight, preferably from 0.1 to 70 parts by weight, and more preferably from 0.2 to 50 parts by weight, per 100 parts by weight of the ethylenically unsaturated bond-containing compound.
The polymer binder for use in the photopolymerizable photosensitive layer of the photosensitive lithographic printing plate precursor according to the present invention not only acts as a film-forming agent of the photosensitive layer but also must be soluble in an alkali developing solution. Thus, an organic polymer soluble or swellable in an aqueous alkali solution is ordinarily employed as the polymer binder. The use of a water-soluble organic polymer as the organic polymer makes the lithographic printing plate precursor water-developable. Examples of such an organic polymer include an addition polymer having a carboxylic acid group in the side chain thereof, for example, polymers described in JP-A-59-44615 , JP-B-54-34327 , JP-B-58-12577 , JP-B-54-25957 , JP-A-54-92723 , JP-A-59-53836 and JP-A-59-71048 , that is, a methacrylic acid copolymer, an acrylic acid copolymer, an itaconic acid copolymer, a crotonic acid copolymer, a maleic acid copolymer and a partially esterified maleic acid copolymer.
An acidic cellulose derivative having a carboxylic acid group in its side chain is also used. Further, a polymer obtained by adding a cyclic acid anhydride to an addition polymer having a hydroxy group is useful. Of these polymers, a copolymer of benzyl (meth)acrylate, (meth)acrylic acid and if desired, other addition-polymerizable vinyl monomer and a copolymer of allyl (meth)acrylate, (meth)acrylic acid and if desired, other addition-polymerizable vinyl monomer are particularly preferably used. In addition, polyvinyl pyrrolidone and polyethylene oxide are useful as the water-soluble organic polymer. In order to increase strength of a cured film, an alcohol-soluble polyamide and a polyether of 2,2-bis-(4-hydroxyphenyl)propane with epichlorohydrin are also useful. Polyurethane resins as described in JP-B-7-120040 , JP-B-7-120041 , JP-B-7-120042 , JP-B-8-12424 , JP-A-63-287944 , JP-A-63-287947 , JP-A-1-271741 and JP-A-11-352691 are also useful in the invention.
By introducing a radical reactive group into the side chain of the organic polymer, the strength of a cured film formed therefrom can be increased. For example, a group having an ethylenically unsaturated bond, an amino group or an epoxy group is illustrated as an addition-polymerizable functional group, a mercapto group, a thiol group, a halogen atom, a triazine structure or an onium salt structure is illustrated as a functional group capable of forming a radical upon irradiation with light, and a carboxy group or an imido group is illustrated as a polar group. Of the addition-polymerizable functional groups, the group having an ethylenically unsaturated bond, for example, an acryl group, a methacryl group, an allyl group or a styryl group is particularly preferred. A functional group selected from an amino group, a hydroxy group, a phosphonic acid group, a phosphoric acid group, a carbamoyl group, an isocyanato group, a ureido group, a ureylene group, a sulfonic acid group and an ammonio group is also useful.
In order to maintain the developing property of the composition for the photosensitive layer, it is preferred that the polymer binder for use in the invention has an appropriate molecular weight and acid value. Specifically, the polymer binder having a weight average molecular weight of from 5,000 to 300,000 and an acid value of from 20 to 200 is effectively used. The polymer binder can be mixed in an appropriate amount in the entire composition for the photosensitive layer. When the amount of polymer binder exceeds 90% by weight, it may be difficult to obtain preferred results in view of the strength of image formed. The amount is preferably from 10 to 90% by weight, more preferably from 30 to 80% by weight of the composition for the photosensitive layer. It is preferred that a ratio of the photopolymerizable ethylenically unsaturated bond-containing compound to the organic polymer binder is in a range of from 1/9 to 9/1 by weight. The range is more preferably from 2/8 to 8/2 by weight, and still more preferably from 3/7 to 7/3 by weight.
It is preferred to add a small amount of a thermal polymerization inhibitor in addition to the fundamental components described above to the photosensitive composition for the photosensitive layer in order to prevent undesirable thermal polymerization of the photopolymerizable ethylenically unsaturated bond-forming compound during the production and storage of the photosensitive composition in the invention. Suitable examples of the thermal polymerization inhibitor include hydroquinone, p-methoxyphenol, di-tert-butyl-p-cresol, pyrogallol, tert-butylcatechol, benzoquinone, 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-metyl-6-tert-butylphenol), N-nitrosophenylhydroxylamine primary cerium salt and N-nitrosophenylhydroxylamine aluminum salt. The amount of the thermal polymerization inhibitor added is preferably from about 0. 01 to about 5% by weight based on the total photosensitive composition. Further, a higher fatty acid or a derivative thereof, for example, behenic acid or behenic amide may be added to the photosensitive composition and localized on the surface of the photopolymerizable photosensitive layer during a drying process after coating in order to prevent polymerization inhibition due to oxygen, if desired. The amount of higher fatty acid or derivative thereof added is preferably from about 0. 5 to about 10% by weight based on the total photosensitive composition.
A coloring agent may further be added for the purpose of coloring the photopolymerizable photosensitive layer. Examples of the coloring agent include a pigment, for example, a phthalocyanine pigment, e.g., C. I. Pigment Blue 15:3, 15:4 or 15:6, an azo pigment, carbon black or titanium oxide, and a dye, for example, Ethyl Violet, Crystal Violet, an azo dye, an anthraquinone dye or a cyanine dye. The amount of the coloring agent added is preferably from about 0. 5 to about 20% by weight based on the total photosensitive composition. In addition, an additive, for example, an inorganic filler or a plasticizer, e.g., dioctyl phthalate, dimethyl phthalate or tricresyl phosphate may be added in order to improve physical properties of the cured film. The amount of such an additive added is preferably not more than 10% by weight based on the total photosensitive composition.
The composition for the photopolymerizable photosensitive layer of the photosensitive lithographic printing plate precursor according to the invention is dissolved in an organic solvent and coated on the intermediate layer described hereinbefore. Various kinds of solvents can be used and examples thereof 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 monoethyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether acetate, 3-methoxypropanol, methoxymethoxyethanol, 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, γ-butyrolactone, methyl lactate and ethyl lactate. The organic solvents may be used individually or as a mixture of two or more thereof. The concentration of the solid content in the coating solution is suitably from 1 to 50% by weight.
A surface active agent may be added to the photopolymerizable composition for the photopolymerizable photosensitive layer of the photosensitive lithographic printing plate precursor according to the invention in order to improve surface properties of coating.
A coverage after drying of the photopolymerizable photosensitive layer is preferably in a range of from about 0.1 to about 10 g/m², more preferably from 0.3 to 5 g/m², and still more preferably from 0.5 to 3 g/m².
On the photopolymerizable photosensitive layer described above, an oxygen-isolating protective layer is ordinarily provided in order to prevent from a polymerization inhibiting function of oxygen. A water-soluble vinyl polymer, which is incorporated into the oxygen-isolating protective layer, includes polyvinyl alcohol and a copolymer thereof containing a substantial amount of unsubstituted vinyl alcohol unit sufficient for imparting the desired solubility in water, for example, a partial ester, ether or acetal of polyvinyl alcohol. Polyvinyl alcohol having a hydrolysis rate of from 71 to 100% and a polymerization degree of from 300 to 2,400 is used. Specific examples of the polyvinyl alcohol include PVA-105, PVA-110, PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA-HG, PVA-203, PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224, PVA-217EE, PVA-217E, PVA-220E, PVA-224E, PVA-405, PVA-420, PVA-631 and L-8 manufactured by Kuraray Co., Ltd. Examples of the copolymer include polyvinyl acetate, polyvinyl chloroacetate, polyvinyl propionate, polyvinyl formal and polyvinyl acetal each having the hydrolysis ratio of from 80 to 100% and a copolymer thereof. Other useful polymers include polyvinyl pyrrolidone, gelatin and gum arabic. The water-soluble polymers may be used individually or as a mixture of two or more thereof.
A solvent, which is used for coating the oxygen-isolating protective layer in the photosensitive lithographic printing plate precursor according to the invention, is preferably pure water, however, an alcohol, e.g., methanol or ethanol or a ketone, e.g., acetone or methyl ethyl ketone may be used together with pure water. The concentration of the solid content in the coating solution is suitably from 1 to 20% by weight. To the oxygen-isolating protective layer according to the invention, known additives, for example, a surface active agent for improving coating properties or a water-soluble plasticizer for improving physical properties of the film may be further added. Examples of the water-soluble plasticizer include propionamide, cyclohexanediol, glycerol and sorbitol. A water-soluble (meth)acrylic polymer may also be used. A coverage after drying of the oxygen-isolating protective layer is preferably in a range of from about 0.1 to about 15 g/m², and more preferably from 1.0 to about 5.0 g/m².

(Aluminum support)

Now, the aluminum support of photosensitive lithographic printing plate precursor according to the invention is described below. The aluminum support for use in the invention, which is dimensionally stable, includes an aluminum or aluminum alloy (for example, alloy of aluminum with silicon, copper, manganese, magnesium, chromium, zinc, lead, bismuth or nickel) plate, and a plastic film or paper laminated or deposited with aluminum or aluminum alloy. The thickness of support is ordinarily from about 0.05 to about 1 mm. A composite sheet as described in JP-A-48-18327 is also used.
It is preferred that an aluminum support for use in the invention has a surface roughness of 0.2 to 0.55 µm. In order to obtain such a surface roughness, an aluminum support is subjected to surface treatment as described below. The term "surface roughness of aluminum support" as used herein means a centerline average roughness (arithmetic mean roughness)(Ra) in the direction perpendicular to the rolling direction of aluminum support and it is a value represented by the unit of µm, which is calculated in accordance with the equation shown below wherein a part having a measuring length of L is taken out from the roughness curve measured by means of a contact stylus instrument in the direction of the centerline thereof, the center line of the taken-out part is designated as X-axis, an axis crossing at right angles with the X-axis is designated as Y-axis, and the roughness curve is represented by an equation of Y = f(X). Determination of the measuring length of L and the measurement of average roughness are performed in accordance with JIS B 0601. $Ra = \frac{1}{L} \int_{0}^{L} |f (X)| ⅆ X$

(Graining Treatment)

A method for the graining treatment used includes a mechanical graining method, a chemical graining method and an electrolytic graining method as described in JP-A-56-28893 . Specifically, an electrochemical graining method wherein surface graining is electrochemically conducted in an electrolytic solution of hydrochloric acid or nitric acid, and a mechanical graining method, for example, a wire brush graining method wherein a surface of aluminum plate is scratching with a wire brush, a ball graining method wherein a surface of aluminum plate is grained with abrasive balls and an abrasive or a brush graining method wherein a surface of aluminum plate is grained with a nylon brush and an abrasive may also be employed. The graining methods may be used individually or in combination of two or more thereof. Of these methods, an electrochemical graining method wherein surface graining is electrochemically conducted in an electrolytic solution of hydrochloric acid or nitric acid is preferably used. The current density suitable for use is in a range of from 100 to 400 C/dm². More specifically, it is preferred to perform electrolysis in an electrolytic solution containing from 0.1 to 50% of hydrochloric acid or nitric acid under the conditions of a temperature of from 20 to 100°C, a period of from one second to 30 minutes and a current density of from 100 to 400 C/dm².
The aluminum support subjected to the surface graining treatment is then chemically etched with an acid or an alkali. The method of using an acid as an etching agent takes time for destroying fine structures and thus, it is disadvantageous to industrially apply the method to the invention. Such disadvantage can be overcome by using an alkali as the etching agent. Examples of the alkali agent preferably used in the invention include sodium hydroxide, sodium carbonate, sodium aluminate, sodium metasilicate, sodium phosphate, potassium hydroxide and lithium hydroxide. Preferred ranges of concentration and temperature are form 1 to 50% and 20 to 100°C, respectively. The alkali etching is preferably performed so that a dissolution amount of aluminum is in a range of from 5 to 20 g/m³.
After the etching procedure, the support is subjected to washing with an acid for removing smut remaining on the surface of support. Examples of the acid for use in the acid-washing step include nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid and borofluoric acid. As the method for removing smut after the electrochemical graining treatment, a method of bringing the aluminum support into contact with a 15 to 65% by weight aqueous solution of sulfuric acid having a temperature of from 50 to 90°C as described in JP-A-53-12739 and a method of performing alkali etching as described in JP-B-48-28123 are particularly preferred.

(Anodizing Treatment)

It is preferred that the aluminum support thus-treated is then subjected to anodizing treatment. The anodizing treatment can be conducted in a manner conventionally used in the field of art. Specifically, it is performed by applying a direct current or alternating current to the aluminum support in an aqueous solution or non-aqueous solution containing sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, or a combination of two or more thereof to form an anodic oxide layer on the surface of aluminum support.
The conditions of anodizing treatment cannot be determined generally, since they are widely varied depending on an electrolytic solution to be used. However, ordinarily, a concentration of the electrolytic solution is in a range of from 1 to 80%, a temperature of the electrolytic solution is in a range of from 5 to 70°C, a current density is in a range of from 0.5 to 60 A/dm², a voltage is in a range of from 1 to 100 V, and a period of electrolysis is in a range of from 10 to 100 seconds.
Of the anodizing treatments, a method of anodizing in a sulfuric acid solution with a high current density as described in British Patent 1,412,768 and a method of anodizing using phosphoric acid as an electrolytic bath as described in U.S. Patent 3,511,661 are preferably used.
In the invention, the thickness of anodic oxide layer is preferably from 1 to 10 g/m². When the thickness is less than 1 g/m², the printing plate prepared is liable to be injured, and on the other hand, when the thickness is more than 10 g/m², a large quantity of electric power is necessary and thus economically disadvantageous. The thickness of anodic oxide layer is more preferably from 1.5 to 7 g/m², and still more preferably from 2 to 5 g/m².
In the invention, the aluminum support may further be subjected to sealing treatment of the anodic oxide layer after the graining treatment and anodizing treatment. The sealing treatment is performed by immersing the aluminum support in hot water or a hot aqueous solution containing an inorganic salt or an organic salt, or transporting the aluminum support in a water vapor bath. Moreover, the aluminum support may be subjected to surface treatment, for example, silicate treatment with an alkali metal silicate or immersion in an aqueous solution of potassium fluorozirconate or a phosphate.
On the aluminum support subjected to the surface treatment as described above, the intermediate layer, the photopolymerizable photosensitive layer comprising the photopolymerizable composition and preferably the oxygen-isolating protective layer are coated in this order to prepare the photosensitive lithographic printing plate precursor according to the invention.
Now, a plate-making method of the photosensitive lithographic printing plate precursor of the invention to prepare a lithographic printing plate is described in detail below. The photosensitive lithographic printing plate precursor is exposed imagewise and then developed with a developing solution.

(Developing solution)

A developing solution for use in the plate-making method of the photosensitive lithographic printing plate precursor of the invention is not particularly restricted and, for example, a developing solution containing an inorganic alkali salt and a surface active agent and having a pH of from 11.0 to 12.7 is preferably used.
The inorganic alkali salt is appropriately selected and examples thereof include an inorganic alkali agent, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, sodium silicate, potassium silicate, ammonium silicate, lithium silicate, tertiary sodium phosphate, tertiary potassium phosphate, tertiary ammonium phosphate, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, ammonium hydrogencarbonate, sodium borate, potassium borate and ammonium borate. The inorganic alkali salts may be used individually or in combination of two or more thereof.
In the case of using a silicate in the developing solution, developing property can be easily adjusted by appropriately controlling the mixing ratio of silicon oxide (SiO₂) to alkali oxide (M₂O wherein M represents an alkali metal or an ammonium group), each of which are components of the silicate, and the concentration thereof. Of the aqueous solutions containing the silicate, that having the mixing ratio of silicon oxide (SiO₂) to alkali oxide (M₂O) (a molar ratio of SiO₂/M₂O) of from 0.5 to 3.0 is preferred and that having the mixing ratio of silicon oxide (SiO₂) to alkali oxide (M₂O) of from 1.0 to 2.0 is more preferred. When the molar ratio of SiO₂/M₂O is 0.5 or more, excessive increase in the alkali strength is preferably restrained so that a problem in that an aluminum support is etched can be prevented. The molar ratio of 3.0 or less can preferably improve the development property. The concentration of silicate is preferably from 1 to 10% by weight, more preferably from 3 to 8% by weight, and most preferably from 4 to 7% by weight based on the alkali aqueous solution. When the concentration is less than 1% by weight, the developing property and processing capacity tend to decrease in some cases. On the other hand, when the concentration exceeds 10% by weight, precipitation and crystallization tend to occur and the exhausted solution tends to gelate at the time of neutralization to cause a problem during the treatment of waste solution in some cases.
For the purposes of fine control of the alkali concentration and aid of dissolution of the polymerizable photosensitive layer, an organic alkali agent may be auxiliarily used together with the inorganic alkali agent. Examples of the organic alkali agent include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, n-butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, ethyleneimine, ethylenediamine, pyridine and tetramethylammonium hydroxide. The organic alkali agents may be used individually or in combination of two or more thereof.
The surface active agent is appropriately selected to use. Examples of the surface active agent include a nonionic surface active agent having a polyoxyalkylene ether group, a nonionic surface active agent, for example, a polyoxyethylene alkyl ester, e.g., polyoxyethylene stearate, a sorbitan alkyl ester, e.g., sorbitan monolaurate, sorbitan monostearate, sorbitan distearate, sorbitan monooleate, sorbitan sesquioleate or sorbitan trioleate, or a mono glyceride alkyl ester, e.g., glycerol monostearate or glycerol monooleate; an anionic surface active agent, for example, an alkylbenzenesulfonate, e.g., sodium dodecylbenzenesulfonate, an alkylnaphthalenesulfonate, e.g., sodium butylnaphthalenesulfonate, sodium pentylnaphthalenesulfonate, sodium hexylnaphthalenesulfonate or sodium octylnaphthalenesulfonate, an alkylsulfate, e.g., sodium laurylsulfate, an alkylsulfonate, e.g., sodium dodecylsulfonate, or a sulfosuccinate, e.g., sodium dilaurylsulfosuccinate; and an amphoteric surface active agent, for example, an alkylbetaine, e.g., laurylbetaine or stearylbetaine, or an amino acid. A nonionic surface active agent having a polyoxyalkylene ether group is particularly preferred.
As the nonionic surface active agent having a polyoxyalkylene ether group, a compound having a structure represented by formula (I) shown below is preferably used.

R⁴⁰-O-(R⁴¹-O)_pH (I)
In formula (I), R⁴⁰ represents an alkyl group having from 3 to 15 carbon atoms, which may be substituted, an aromatic hydrocarbon group having from 6 to 15 carbon atoms, which may be substituted or an aromatic heterocyclic group having from 4 to 15 carbon atoms, which may be substituted, wherein the substituent includes an alkyl group having from 1 to 20 carbon atoms, a halogen atom (for example, bromine, chlorine or iodine), an aromatic hydrocarbon group having from 6 to 15 carbon atoms, an aralkyl group having from 7 to 17 carbon atoms, an alkoxy group having from 1 to 20 carbon atoms, an alkoxycarbonyl group having from 2 to 20 carbon atoms and an acyl group having from 2 to 15 carbon atoms; R⁴¹ represents an alkylene group having from 1 to 100 carbon atoms, which may be substituted, wherein the substituent includes an alkyl group having from 1 to 20 carbon atoms and an aromatic hydrocarbon group having from 6 to 15 carbon atoms; and n represents an integer of from 1 to 100.
In formula (I) above, specific examples of the aromatic hydrocarbon group include a phenyl group, a tolyl group, a naphthyl group, an anthryl group, a biphenyl group and a phenanthryl group, and specific examples of the aromatic heterocyclic group include a furyl group, a thienyl group, an oxazolyl group, an imidazolyl group, a pyranyl group, a pyridinyl group, an acrysinyl group, a benzofuranyl group, a benzothienyl group, a benzopyranyl group, a benzoxazolyl group and a benzimidazolyl group.
The part of (R⁴¹-O)_p in formula (I) may comprise two or three kinds of groups as far as R⁴¹ and p are in the above-defined scope. Specifically, it may form a random or block chain comprising, for example, a combination of an ethyleneoxy group and a propyleneoxy group, a combination of an ethyleneoxy group and an isopropyleneoxy group, a combination of an ethyleneoxy group and butyleneoxy group or a combination of an ethyleneoxy group and isobutyleneoxy group. In the invention, the nonionic surface active agents having a polyoxyalkylene ether group may be used individually or as a mixture of two or more thereof. An amount of the nonionic surface active agent having a polyoxyalkylene ether group effectively added is from 1 to 30% by weight, preferably from 2 to 20% by weight in the developing solution. When the amount added is too small, the developing property degrades, and on the other hand, when it is too large, the damage upon development in the exposed area increases, resulting in decrease of press life of a printing plate.
Examples of the nonionic surface active agent having a polyoxyalkylene ether group represented by formula (I) include a polyoxyethylene alkyl ether, e.g., polyoxyethylene lauryl ether, polyoxyethylene cetyl ether or polyoxyethylene stearyl ether, a polyoxyethylene aryl ether, e.g., polyoxyethylene phenyl ether or polyoxyethylene naphthyl ether, and a polyoxyethylene alkylaryl ether, e.g., polyoxyethylene methylphenyl ether, polyoxyethylene octylphenyl ether or polyoxyethylene nonylphenyl ether.
The surface active agents may be used individually or in combination of two or more thereof. A content of the surface active agent in the developing solution is preferably from 0.1 to 20% by weight in terms of solid content.
The pH of developing solution used for the photosensitive lithographic printing plate precursor of the invention is ordinarily from 11.0 to 12.7 and preferably from 11.5 to 12.5. When the pH of developing solution is lower than 11.0, images are hardly formed. On the other hand, when the pH of developing solution exceeds 12.7, the problem in that damage upon development in the exposed area increases tends to occur.
The electric conductivity of developing solution is ordinarily from 3 to 30 mS/cm. When the dielectric constant of developing solution is lower than the above-described range, it may become difficult to dissolve the photopolymerizable photosensitive layer on the aluminum support, thereby accompanying with printing stain. On the other hand, when the dielectric constant of developing solution exceeds the above-described range, the dissolution rate of the photopolymerizable photosensitive layer conspicuously decreases, whereby residual film may occur in the unexposed area. The electric conductivity is preferably in a range of from 5 to 20 mS/cm.

(Exposure and development processing)

The photosensitive lithographic printing plate precursor according to the invention is exposed imagewise with a conventionally known active ray, for example, a carbon arc lamp, a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, a halogen lamp, a helium-cadmium laser, an argon ion laser, an FD-YAG laser, a helium-neon laser or a semiconductor laser (350 to 600 nm), and then subjected to development processing to form images on the aluminum support. After the imagewise exposure but before the development the lithographic printing plate precursor may be subjected to a heating process at a temperature of from 50 to 150°C for a period of from one second to 5 minutes for the purpose of increasing the curing rate of photopolymerizable photosensitive layer.
The photosensitive lithographic printing plate precursor according to the invention ordinarily has an overcoat layer having the oxygen-isolating property as described above on the photopolymerizable photosensitive layer. In order to remove the overcoat layer, there are a method wherein removal of the overcoat layer and removal of the photopolymerizable photosensitive layer of the unexposed area are carried out at the same time using the developing solution and a method wherein the overcoat layer is first removed with water or warm water and then the photopolymerizable photosensitive layer of the unexposed area is removed by the development. To the water or warm water, for example, an antiseptics as described in JP-A-10-10754 or an organic solvent as described in JP-A-8-278636 may be incorporated.
The development of photosensitive lithographic printing plate precursor according to the invention with the developing solution described above is carried out at a temperature of from about 0 to about 60°C, preferably from about 15 to about 40°C in a conventional manner, for example, that the imagewise exposed photosensitive lithographic printing plate precursor is immersed in the developing solution and rubbed with a brush.
When the development processing is performed using an automatic developing machine, the processing ability of the developing solution may be recovered using a replenisher or a fresh developing solution, since the developing solution becomes exhausted with increase in the processing amount.
The photosensitive lithographic printing plate precursor thus-processed is subjected to post-treatment with washing water, a rinsing solution containing a surface active agent or a desensitizing solution containing gum arabic or a starch derivative as described, for example, in JP-A-54-8002 , JP-A-55-115045 and JP-A-59-58431 . These processes may be used in various combinations for the post-treatment of photosensitive lithographic printing plate precursor according to the invention.
A printing plate obtained by the development processing described above can be increased its press life using a post-exposure treatment by a method as described in JP-A-2000-89478 or a heat treatment, for example, burning.
The lithographic printing plate obtained by the processes described above is mounted on an offset printing machine to perform printing, whereby a large number of prints are obtained.
The invention will be described in greater detail with reference to the following examples, but the invention should not be construed as being limited thereto.

EXAMPLE 1

An aluminum plate of IS having a thickness of 0.30 mm was subjected to surface graining using a nylon brush of No. 8 and an aqueous suspension of pumice stone of 800 mesh and washed thoroughly with water. The plate was etched by immersing in a 10% aqueous sodium hydroxide solution at 70°C for 60 seconds, washed with running water, and washed with a 20% aqueous nitric acid solution for neutralization, followed by washing with water. The plate was then subjected to electrolytic surface roughening treatment in a 1% aqueous nitric acid solution using an alternating waveform current of sign wave under the condition of V_A of 12.7 V in an amount of electricity of 300 C/dm² at anode. The surface roughness of the plate measured was 0.45 µm (in Ra) (measurement device: Surfcom^(™) manufactured by Tokyo Seimitu Co., Ltd.; diameter of a contact stylus tip: 2 micrometer). Subsequently, the plate was immersed in a 30% aqueous sulfuric acid solution at 55°C for 2 minutes to conduct desmutting and then subjected to anodic oxidation in a 20% aqueous sulfuric acid solution at 33°C at a current density of 5 A/dm² for 50 seconds while an cathode was arranged on the side of the roughened surface of the plate to form an anodic oxide layer having a thickness of 2.7 g/m².
On the aluminum support thus-obtained, a solution containing Polymer No. 1 (number average molecular weight: 3,300) shown below dissolved in a mixture of water and methanol (5g/95g) was coated and dried at 80°C for 30 seconds to form an intermediate layer. A dry coating weight of the intermediate layer was 10 mg/m².
On the intermediate layer, a high-sensitive photopolymerizable composition P-1 shown below was coated so as to have a dry coating weight of 1.5 g/m², and dried at 100°C for one minute to form a photopolymerizable photosensitive layer.

Compound having ethylenically unsaturated bond (A1)	1.5 parts by weight
Linear organic high molecular polymer (polymer binder) (B1)	2.0 parts by weight
Sensitizer (C1)	0.15 parts by weight
Photopolymerization initiator (D1)	0.2 parts by weight
Dispersion of ε-phthalocyanine (F1)	0.02 parts by weight
Fluorine-containing nonionic surface active agent (Megafac^(™) F177 manufactured by Dai-Nippon Ink & Chemicals, Inc.)	0.03 parts by weight
Methyl ethyl ketone	9.0 parts by weight
Propylene glycol monomethyl ether acetate	7.5 parts by weight
Toluene	11.0 parts by weight

On the photopolymerizable photosensitive layer was coated a 3% by weight aqueous solution of polyvinyl alcohol (saponification degree: 98% by mole, polymerization degree: 500) so as to have a dry coating weight of 2.5 g/m², and dried at 120°C for 3 minutes to form an oxygen-isolating protective layer, whereby a photosensitive lithographic printing plate precursor was prepared.
In order to evaluate the degree of background stain due to preservation of the photosensitive lithographic printing plate precursor, the photosensitive lithographic printing plate precursor was allowed to stand under forced aging conditions (50°C and 80%RH) for 5 days.
The photosensitive lithographic printing plate precursors before and after the forced aging were subjected to scanning exposure of solid image and dot images of from 1 to 99% (every 1%) using an FD-YAG laser (Plate Jet 4 manufactured by CSI Co., Ltd.) in an exposure amount of 100 µJ/cm² at 4,000 dpi under condition of 175 lines/inch, and then subjected to standard processing using an automatic developing machine (LP-850P2 manufactured by Fuji Photo Film Co., Ltd.) provided with Developing Solution 1 shown below and a finishing gum solution (FP-2W manufactured by Fuji Photo Film Co., Ltd.). The condition of pre-heating was such that a temperature of the plate surface reached was 100°C. A temperature of the developing solution was 30°C and a period of immersion in the developing solution was about 15 seconds.
Developing Solution 1 had the composition shown below and the pH thereof was 11.5 at 25°C and the electric conductivity thereof was 5 mS/cm.

Potassium hydroxide	0.15 g
Polyoxyethylene phenyl ether (n=13)	5.0 g
Chelating agent (Chilest ^(™) 400)	0.1 g
Water	94.75 g

EXAMPLES 2 TO 7

Lithographic printing plate precursors were prepared in the same manner as in Example 1 except for changing Polymer No. 1 used in Example 1 to the copolymer for intermediate layer shown in Table 2 below, respectively. The plate-making was conducted using each of the photosensitive lithographic printing plate precursors before and after the forced aging in the same manner as in Example 1.

TABLE 2

Copolymer for Intermediate Layer
	Copolymer for Intermediate Layer
Example 2	No.3 shown hereinbefore
Example 3	No.4 shown hereinbefore
Example 4	No.5 shown hereinbefore
Example 5	No.6 shown hereinbefore
Example 6	No.8 shown hereinbefore
Example 7	No.9 shown hereinbefore

EXAMPLES 8 TO 10

Lithographic printing plate precursors were prepared in the same manner as in Example 1 except for changing the dry coating weight of the intermediate layer to 5m g/m², 15m g/m² and 20m g/m², respectively, and the plate-making was conducted in the same manner as in Example 1.

EXAMPLES 11 TO 15

Lithographic printing plate precursors were prepared in the same manner as in Example 1 except for changing Linear organic high molecular polymer B1 used in Photopolymerizable Composition P-1 of Example 1 to B2 to B6 described below for Photopolymerizable Compositions P-2 to P-6, respectively, and the plate-making was conducted in the same manner as in Example 1.
B2(P-2): Allyl methacrylate/metacrylic acid (70/30 mole%) copolymer (Molecular weight: 50,000)
B3(P-3): Methyl methacrylate/isobutyl methacrylate/metacrylic acid (60/20/20 mole%) copolymer (Molecular weight: 100,000)
B4(P-4): Methyl methacrylate/isopropylacrylamide/metacrylic acid (65/15/20 mole%) copolymer (Molecular weight: 70,000)
B5(P-5):
B6(P-6):

EXAMPLE 16

A lithographic printing plate precursor was prepared in the same manner as in Example 15 except for changing Compound having ethylenically unsaturated bond A1 used in Photopolymerizable Composition P-6 of Example 15 to Compound having ethylenically unsaturated bond A2 described below for Photopolymerizable Composition P-7, and the plate-making was conducted in the same manner as in Example 15.

EXAMPLE 17

A surface of aluminum plate of JIS A1050 having a thickness of 0.24 mm was subjected to graining using a nylon brush and an aqueous suspension of pumice stone of 400 mesh and washed thoroughly with water. The plate was etched by immersing in a 10% aqueous sodium hydroxide solution at 70°C for 60 seconds, washed with running water, and washed with a 20% aqueous nitric acid solution for neutralization, followed by washing with water. The plate was then subjected to electrolytic surface roughening treatment in a 1% aqueous nitric acid solution using an alternating waveform current of sign wave under the condition of V_A of 12.7 V in an amount of electricity of 260 C/dm² at anode. The surface roughness of the plate was measured and found to be 0.55 µm (in Ra). Subsequently, the plate was immersed in a 30% aqueous sulfuric acid solution at 55°C for 2 minutes to conduct desmutting and then subjected to anodic oxidation in a 20% aqueous sulfuric acid solution at a current density of 14 A/dm² so as to form an anodic oxide layer having a thickness of 2.5 g/m², followed by washing with water to prepare Substrate (A).
Substrate (A) was treated with a 0.15% by weight aqueous sodium silicate solution at 22°C for 10 seconds to prepare Substrate (B). Also, Substrate (A) was treated with a 2.5% by weight aqueous sodium silicate solution at 30°C for 10 seconds to prepare Substrate (C). Further, Substrate (A) was treated with a 2.5% by weight aqueous sodium silicate solution at 50°C for 5 seconds to prepare Substrate (D).
On each of Substrates (A) to (D), the intermediate layer, photopolymerizable photosensitive layer and oxygen-isolating protective layer were coated and dried in the same manner as in Example 1 to prepare a photosensitive lithographic printing plate precursor, and the plate-making was conducted in the same manner as in Example 1.

COMPARATIVE EXAMPLE 1

A photosensitive lithographic printing plate precursor was prepared in the same manner as in Example 1 except for eliminating the formation of intermediate layer in Example 1, and the plate-making was conducted in the same manner as in Example 1.
With the lithographic printing plates obtained according to the plate-making methods in Examples 1 to 17 and Comparative Example 1, press life and printing stain were evaluated.
The printing plate was subjected to printing by a printing machine (R 201 Type manufactured by Man Roland Co., Ltd.) using ink (GEOS G Black ^(™) (N) manufactured by Dai-Nippon Ink & Chemicals, Inc.) and the press life was evaluated from the number of sheets in which disappearance of dots of 3% was observed.

The printing stain was evaluated by conducting printing by a printing machine (Dia ^(™) IF2 Type manufactured by Mitsubishi Heavy Industry Co., Ltd.) using ink (GEOS G Red^(™) (S) manufactured by Dai-Nippon Ink & Chemicals, Inc.) and visually observing the printing stain in the non-image area. The results obtained are shown in Table 3 below.

TABLE 3

	Change Ratio of I/O Value before and after Development (%)	Before Forced Aging		After Forced Aging (50°C and 80%RH for 5 days)
	Change Ratio of I/O Value before and after Development (%)	Printing Stain	Press Life (x10⁴)	Printing Stain	Press Life (x10⁴)
Example 1	10	No Stain	15	No Stain	16
Example 2	5	No Stain	16	No Stain	15
Example 3	10	No Stain	17	No Stain	17
Example 4	6	No Stain	15	No Stain	14
Example 5	10	No Stain	14	No Stain	14
Example 6	10	No Stain	15	No Stain	13
Example 7	8	No Stain	17	No Stain	16
Example 8	10	No Stain	16	No Stain	17
Example 9	10	No Stain	14	No Stain	13
Example 10	10	No Stain	14	No Stain	15
Example 11	10	No Stain	15	No Stain	15
Example 12	10	No Stain	16	No Stain	16
Example 13	10	No Stain	18	No Stain	17
Example 14	10	No Stain	20	No Stain	22
Example 15	10	No Stain	18	No Stain	19
Example 16	10	No Stain	13	No Stain	12
Example 17	10	No Stain	16	No Stain	16
Comparative Example 1	-	Slight Background Stain	5	Severe Background Stain	6

As is apparent from the results shown in Table 3, each lithographic printing plate precursor of the examples according to the invention exhibits the sufficient results. On the contrary, the lithographic printing plate precursor prepared without the formation of intermediate layer in Comparative Example 1 exhibits the background stain even before the forced aging.
As described above, by using the photosensitive lithographic printing plate precursor of the invention, the lithographic printing plate free from background stain even after the forced aging and having high press life can be obtained.
As described above, the photosensitive lithographic printing plate precursor of the invention, which comprises an aluminum support having provided thereon an intermediate layer and a photopolymerizable photosensitive layer in this order and the intermediate layer includes a polymer compound containing a constituting component having an acid group and a constituting component capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution, has the improved developing property in the non-image areas and is prevented from the occurrence of background stain even after preservation. Further, the photosensitive lithographic printing plate precursor is advantageous in that the adhesion between the intermediate layer and the aluminum support in the exposed area is not impaired and it can exhibit the high press life.

Claims

A photosensitive lithographic printing plate precursor comprising an aluminum support having provided thereon an intermediate layer and a photopolymerizable photosensitive layer in this order, wherein the intermediate layer comprises a copolymer containing a constituting component having an acid group and a constituting component including an acetal group, a lactone ring or an oxycarboxy group capable of reacting with an alkali developing solution to increase the dissolution rate in the alkali developing solution.
A photosensitive lithographic printing plate precursor according to Claim 1, wherein the acid group is a -COOH, -SO₃H, -OSO₃H, -PO₃H₂, -OPO₃H₂, -CONHSO₂- or a -SO₂NHSO₂- group.
A photosensitive lithographic printing plate precursor according to Claim 2, wherein the acid group is -COOH.
A photosensitive lithographic printing plate precursor according to any preceding Claim, wherein the constituting component having an acid group is represented by formula (1) or formula (2) :

wherein A represents a divalent connecting group; B represents an aromatic group or a substituted aromatic group; D and E each independently represent a divalent connecting group; G represents a trivalent connecting group; X and X' each independently represent an acid group having pKa of not more than 7 or an alkali metal salt or an ammonium salt thereof; R₁ represents a hydrogen atom, an alkyl group or a halogen atom; a, b, d and e each independently represent 0 or 1; and t represents an integer of from 1 to 3.
A photosensitive lithographic printing plate precursor according to Claim 4, wherein the constituting component having an acid group is represented by formula (1) wherein B represents a phenylene group or a substituted phenylene group in which the substituent is a hydroxy group or an alkyl group having from 1 to 3 carbon atoms; D represents an alkylene group having from 1 to 2 carbon atoms or an alkylene group having from 1 to 2 carbon atoms connected with an oxygen atom; R₁ represents a hydrogen atom or a methyl group; X represents a carboxylic acid group; a is 0; and b is 1.