EP1690685A2

EP1690685A2 - Planographic printing plate precursor

Info

Publication number: EP1690685A2
Application number: EP06002128A
Authority: EP
Inventors: Yusuke c/o Fuji Photo Film Co. Ltd. Hatanaka; Kotaro c/o Fuji Photo Film Co. Ltd. Watanabe
Original assignee: Fujifilm Corp; Fuji Photo Film Co Ltd
Current assignee: Fujifilm Corp
Priority date: 2005-02-09
Filing date: 2006-02-02
Publication date: 2006-08-16
Anticipated expiration: 2026-02-02
Also published as: EP1690685B1; JP4474296B2; JP2006220843A; ATE428559T1; DE602006006233D1; EP1690685A3

Abstract

The planographic printing plate precursor according to the invention is a planographic printing plate precursor, comprising a support and a recording layer formed on the support containing a sulfonium salt (A), an alkali-soluble resin (B), and an infrared absorbent (C), wherein the sulfonium salt (A) has a solubility of 25 mg/ml or more in aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure. The invention provides a high-sensitivity planographic printing plate precursor that allows direct plate making by scanning exposure based on digital signals, for example and also suppresses generation of development scum.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a planographic printing plate precursor, and in particular to a positive planographic printing plate precursor allowing so-called direct plate making by scanning the precursor with an infrared laser beam based on digital signals from computer or the like.

Description of the Related Art

In recent years, progress in laser technology has been remarkable, particularly in higher-output and smaller-size solid state and semiconductor lasers having an emission wavelength in the range from the near-infrared to infrared regions. Accordingly, when plate making is performed directly from digital data from a computer or the like, these lasers are extremely useful as an exposure-light source.
A positive planographic printing plate for use with an infrared laser that uses an infrared laser having an emission in the infrared region as an exposure source is an image-forming material containing, as essential components, a binder resin soluble in an aqueous alkaline solution, and an IR dye or the like that absorbs light and generates heat.
Photosensitive compositions or image-forming materials known in the art, such as those disclosed in WO 97/39894, Japanese Patent Application Laid-Open (JP-A) Nos. 11-44956 and 11-218914, and others, function as a solubilization-inhibiting agent that substantially reduces the solubility of binder resin by interaction of an IR dye or the like in the photosensitive composition with the binder resin in the unexposed region (image region) when compositions are exposed to infrared laser. On the other hand, in the exposed area (non-image region), the IR dye or the like absorbs light and generates heat, lowering the interaction between the IR dye or the like and the binder resin. As a result, during development, the exposed area (non-image region) is dissolved in an alkaline developer to form an image.
However, these types of positive image-forming materials for use with infrared lasers cannot be said to have a sufficiently large difference between the solubilization resistance of the unexposed area (image region) and the solubility of the exposed area (non-image region) under various processing conditions, and therefore have the problems of low stability of development (development latitude) depending on the processing conditions and thus such positive planographic printing plates tend to be overdeveloped when a concentrated developer is used. On the other hand, use of a binder resin less soluble in an alkaline developer for the purpose of avoiding overdevelopment causes a problem that the developing efficiency (sensitivity) decreases in the exposed areas.
For that reason, an onium salt was added for the purpose of expanding the development latitude as in, for example, the image-forming material described in JP-A No. 2002-278050, but there is a tendency for insoluble scum derived from the binder resin (hereinafter, referred to as "development scum") to be generated in the developer of an automatic developing machine during large-volume development, and thus there is a need for improvement in that regard.

SUMMARY OF THE INVENTION

An objective of the invention, which has been made to overcome the problems in the conventional methods, is to provide a high-sensitivity planographic printing plate precursor that allows direct plate making by a scanning exposure based on digital signals from a computer or the like, and suppresses generation of development scum.
After intensive studies, the inventors have found that it is possible to achieve the objective by adding a sulfonium salt superior in solubility in an aqueous alkaline solution to the recording layer, and completed the present invention.
Specifically, the planographic printing plate precursor according to the present invention has a support and a recording layer formed on the support, containing a specific sulfonium salt (A), an alkali-soluble resin (B), and an infrared-light absorbing agent (C), wherein the specific sulfonium salt (A) has a solubility of 25 mg/ml or more in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure. In the present invention, normal room temperature and atmospheric pressure means 25°C and 1 atm.
The mechanism of the invention is not fully clear, but can be inferred as follows:
A sulfonium salt having a solubility such as described above (hereinafter, referred to as "specific sulfonium salt") is very soluble in an aqueous alkaline solution. Thus, it can be inferred that when the specific sulfonium salt is dissolved together with the binder in the developer of automatic developing machine, the specific sulfonium salt functions as a dispersant for the binder resin and, as a result, controls generation of development scum due to aggregation of the binder resin.
In the unexposed areas of the recording layer containing a specific sulfonium salt, an interaction occurs between the specific sulfonium salt and the alkali-soluble resin due to the structure of the onium salt, leading to an increase in the development-inhibiting effect. On the other hand, in the exposed areas, when the interaction is eliminated by the energy of the exposure light, the specific sulfonium salt, which is inherently highly soluble in aqueous alkaline solution, is dissolved in the developer, and as a result, the recording layer is dissolved rapidly.
For these reasons, the difference in the solubility (discrimination) in an aqueous alkaline solution (developer) between the unexposed and exposed areas is expanded, which, in turn, raises sensitivity.
The present invention provides a high-sensitivity planographic printing plate precursor that allows direct plate making by means of scanning exposure based on digital signals from a computer or the like, and suppresses the generation of development scum.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the invention will be described in detail.
A planographic printing plate precursor according to the invention has a support and a recording layer formed on the support having a specific sulfonium salt (A), an alkali-soluble resin (B), and an infrared-light absorbing agent (C), and the specific sulfonium salt (A) is soluble in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at a concentration of 25 mg/ml or more at normal room temperature and atmospheric pressure.

(Recording layer)

The recording layer of the planographic printing plate precursor according to the present invention contains a specific sulfonium salt (A), an alkali-soluble resin (B), and an infrared-light absorbing agent (C) as essential components. These components will be described first in detail.

Specific sulfonium salt (A)]

The specific sulfonium salt according to the present invention should have a solubility of 25 mg/ml or more in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure. For more effective suppression of the generation of development scum, the solubility is preferably 35 mg/ml or more, and more preferably 50 mg/ml or more.
A preferable structure of the specific sulfonium salt according to the present invention is, for example, a compound having three phenyl groups having an alkali-soluble group as the substituent group in the cationic region. Examples of the alkali-soluble groups include -COOH, -OH, -SO₃H, -PO₃H₂ group, and the like, and among them, -COOH and -OH groups are preferable. The phenyl group may have one substituent, or two or more alkali-soluble groups.
Alternatively, the specific sulfonium salt according to the invention may have a structure containing two or more substituents per phenyl group having an alkali-soluble group as the substituent group.
The substitution position of the alkali-soluble group is not particularly limited.
On the other hand, the anionic region of the specific sulfonium salt is, for example, a strongly acidic residue, and is preferably a strongly acidic residue having multiple acidic groups, a strongly acidic residue derived from phosphonic acid, or the like for the purpose of increasing solubility in an aqueous alkaline solution.
Also, when the specific sulfonium salt according to the present invention has a structure containing a phenyl group having an alkali-soluble group as the substituent group, if the solubility thereof is 25 mg/ml or more in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure, the phenyl group may have a substituent other than the alkali-soluble group.
Preferable examples of the substituent groups other than the alkali-soluble group include halogen atoms, a nitro group, alkyl groups having 12 or fewer carbon atoms, alkoxy groups having 12 or fewer carbon atoms, and aryloxy groups having 12 or fewer carbon atoms.
Examples of the strongly acidic residues favorable as the anionic region include halide ions (fluorine, chloride, bromide, and iodine ions), and the residues derived from sulfonic acid compounds, carboxylic acid compounds, inorganic acid compounds, and the like. The compound preferably has a pKa of less than 5. In particular, the strongly acidic residue is preferably a residue containing multiple acid groups.
Among the strongly acidic residues, examples of the inorganic acid compound residues include halide anions, HSO₄ ^- and anions of halogen-containing complex anions such as tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, and hexafluoroantimonate. Among them, a strongly acidic residue derived from an inorganic acid compound containing a fluorine atom is preferable. Specific examples of the inorganic acid compounds containing a fluorine atom include tetrafluoroboric acid, tetrafluoroaluminic acid, tetrafluoroferric acid, tetrafluorogallic acid, hexafluorophosphoric acid, hexafluoroarsenic acid, hexafluoroantimonic acid, hexafluorosilicic acid, hexafluoronickelic acid, hexafluorotitanic acid, hexafluorozirconic acid, and the like; and among them, hexafluorophosphoric acid, tetrafluoroboric acid, hexafluoroantimonic acid, and the like are preferable.
Specific examples of sulfonic acid compounds from which the strongly acidic residue is derived include alkylsulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, octanesulfonic acid, nonanesulfonic acid, decanesulfonic acid, undecanesulfonic acid, dodecanesulfonic acid, tridecanesulfonic acid, tetradecanesulfonic acid, pentadecanesulfonic acid, hexadecanesulfonic acid, heptadecanesulfonic acid, octadecanesulfonic acid, nonadecanesulfonic acid, icosanesulfonic acid, henicosanesulfonic acid, docosanesulfonic acid, tricosanesulfonic acid, and tetracosanesulfonic acid;
haloalkylsulfonic acids such as fluoromethanesulfonic acid, difluoromethanesulfonic acid, trifluoromethanesulfonic acid, chloromethanesulfonic acid, dichloromethanesulfonic acid, trichloromethanesulfonic acid, bromomethanesulfonic acid, dibromomethanesulfonic acid, tribromomethanesulfonic acid, iodomethanesulfonic acid, diiodomethanesulfonic acid, triiodomethanesulfonic acid, fluoroethanesulfonic acid, difluoroethanesulfonic acid, trifluoroethanesulfonic acid, pentafluoroethanesulfonic acid, chloroethanesulfonic acid, dichloroethanesulfonic acid, trichloroethanesulfonic acid, pentachloroethanesulfonic acid, tribromoethanesulfonic acid, pentabromoethanesulfonic acid, triiodoethanesulfonic acid, pentaiodoethanesulfonic acid, fluoropropanesulfonic acid, trifluoropropanesulfonic acid, heptafluoropropanesulfonic acid, chloropropanesulfonic acid, trichloropropanesulfonic acid, heptachloropropanesulfonic acid, bromopropanesulfonic acid, tribromopropanesulfonic acid, heptabromopropanesulfonic acid, triiodopropanesulfonic acid, heptaiodopropanesulfonic acid, trifluorobutanesulfonic acid, nonafluorobutanesulfonic acid, trichlorobutanesulfonic acid, nonachlorobutanesulfonic acid, tribromobutanesulfonic acid, nonabromobutanesulfonic acid, triiodobutanesulfonic acid, nonaiodobutanesulfonic acid,
trifluoropentanesulfonic acid, perfluoropentanesulfonic acid, trichloropentanesulfonic acid, perchloropentanesulfonic acid, tribromopentanesulfonic acid, perbromopentanesulfonic acid, triiodopentanesulfonic acid, periodopentanesulfonic acid, trifluorohexanesulfonic acid, perfluorohexanesulfonic acid, trichlorohexanesulfonic acid, perchlorohexanesulfonic acid, perbromohexanesulfonic acid, periodohexanesulfonic acid, trifluoroheptanesulfonic acid, perfluoroheptanesulfonic acid, trichloroheptanesulfonic acid, perchloroheptanesulfonic acid, perbromoheptanesulfonic acid, periodoheptanesulfonic acid, trifluorooctanesulfonic acid, perfluorooctanesulfonic acid, trichlorooctanesulfonic acid, perchlorooctanesulfonic acid, perbromooctanesulfonic acid, periodooctanesulfonic acid, trifluorononanesulfonic acid, perfluorononanesulfonic acid, trichlorononanesulfonic acid, perchlorononanesulfonic acid, perbromononanesulfonic acid, periodononanesulfonic acid, trifluorodecanesulfonic acid, perfluorodecanesulfonic acid, trichlorodecanesulfonic acid, perchlorodecanesulfonic acid, perbromodecanesulfonic acid, periododecanesulfonic acid, trifluoroundecanesulfonic acid, perfluoroundecanesulfonic acid, trichloroundecanesulfonic acid, perchloroundecanesulfonic acid, perbromoundecanesulfonic acid, periodoundecanesulfonic acid, trifluorododecanesulfonic acid, perfluorododecanesulfonic acid, trichlorododecanesulfonic acid, perchlorododecanesulfonic acid, perbromododecanesulfonic acid, periodododecanesulfonic acid, trifluorotridecanesulfonic acid, perfluorotridecanesulfonic acid, trichlorotridecanesulfonic acid, perchlorotridecanesulfonic acid, perbromotridecanesulfonic acid, periodotridecanesulfonic acid,
trifluorotetradecanesulfonic acid, perfluorotetradecanesulfonic acid, trichlorotetradecanesulfonic acid, perchlorotetradecanesulfonic acid, perbromotetradecanesulfonic acid, periodotetradecanesulfonic acid, trifluoropentadecanesulfonic acid, perfluoropentadecanesulfonic acid, trichloropentadecanesulfonic acid, perchloropentadecanesulfonic acid, perbromopentadecanesulfonic acid, periodopentadecanesulfonic acid, perfluorohexadecanesulfonic acid, perchlorohexadecanesulfonic acid, perbromohexadecanesulfonic acid, periodohexadecanesulfonic acid, perfluoroheptadecanesulfonic acid, perchloroheptadecanesulfonic acid, perbromoheptadecanesulfonic acid, periodoheptadecanesulfonic acid, perfluorooctadecanesulfonic acid, perchlorooctadecanesulfonic acid, perbromooctadecanesulfonic acid, periodooctadecanesulfonic acid, perfluorononadecanesulfonic acid, perchlorononadecanesulfonic acid, perbromononadecanesulfonic acid, periodononadecanesulfonic acid, perfluoroicosanesulfonic acid, perchloroicosanesulfonic acid, perbromoicosanesulfonic acid, periodoicosanesulfonic acid, perfluorohenicosanesulfonic acid, perchlorohenicosanesulfonic acid, perbromohenicosanesulfonic acid, periodohenicosanesulfonic acid, perfluorodocosanesulfonic acid, perchlorodocosanesulfonic acid, perbromodocosanesulfonic acid, periododocosanesulfonic acid, perfluorotricosanesulfonic acid, perchlorotricosanesulfonic acid, perbromotricosanesulfonic acid, periodotricosanesulfonic acid, perfluorotetracosanesulfonic acid, perchlorotetracosanesulfonic acid, perbromotetracosanesulfonic acid, and periodotetracosanesulfonic acid;
cycloalkylsulfonic acid such as cyclopentanesulfonic acid and cyclohexanesulfonic acid;
halogenated cycloalkylsulfonic acids such as 2-fluorocyclopentanesulfonic acid, 2-chlorocyclopentanesulfonic acid, 2-bromocyclopentanesulfonic acid, 2-iodocyclopentanesulfonic acid, 3-fluorocyclopentanesulfonic acid, 8-chlorocyclopentanesulfonic acid, 3-bromocyclopentanesulfonic acid, 3-iodocyclopentanesulfonic acid, 3,4-difluorocyclopentanesulfonic acid, 3,4-dichlorocyclopentanesulfonic acid, 3,4-dibromocyclopentanesulfonic acid, 3,4-diiodocyclopentanesulfonic acid, 4-fluorocyclohexanesulfonic acid, 4-chlorocyclohexanesulfonic acid, 4-bromocyclohexanesulfonic acid, 4-iodocyclohexanesulfonic acid, 2,4-difluorocyclohexanesulfonic acid, 2,4-dichlorocyclohexanesulfonic acid, 2,4-dibromocyclohexanesulfonic acid, 2,4-diiodocyclohexanesulfonic acid, 2,4,6-trifluorocyclohexanesulfonic acid, 2,4,6-trichlorocyclohexanesulfonic acid, 2,4,6-tribromocyclohexanesulfonic acid, 2,4,6-triiodocyclohexanesulfonic acid, tetrafluorocyclohexanesulfonic acid, tetrachlorocyclohexanesulfonic acid, tetrabromocyclohexanesulfonic acid, and tetraiodocyclohexanesulfonic acid;
aromatic sulfonic acids such as benzenesulfonic acid, naphthalenesulfonic acid, anthracenesulfonic acid, phenanthrenesulfonic acid, and pyrenesulfonic acid;
halogenated aromatic sulfonic acid such as 2-fluorobenzenesulfonic acid, 3-fluorobenzenesulfonic acid, 4-fluorobenzenesulfonic acid, 2-chlorobenzenesulfonic acid, 3-chlorobenzenesulfonic acid, 4-chlorobenzenesulfonic acid, 2-bromobenzenesulfonic acid, 3-bromobenzenesulfonic acid, 4-bromobenzenesulfonic acid, 2-iodobenzenesulfonic acid, 4-iodobenzenesulfonic acid, 2,4-difluorobenzenesulfonic acid, 2,6-difluorobenzenesulfonic acid, 2,4-dichlorobenzenesulfonic acid, 2,6-dichlorobenzenesulfonic acid, 2,4-dibromobenzenesulfonic acid, 2,6-dibromobenzenesulfonic acid, 2,4-diiodobenzenesulfonic acid, 2,6-diiodobenzenesulfonic acid, 2,4,6-trifluorobenzenesulfonic acid, 3,4,5-trifluorobenzenesulfonic acid, 2,4,6-trichlorobenzenesulfonic acid, 3,4,5-trichlorobenzenesulfonic acid, 2,4,6-tribromobenzenesulfonic acid, 3,4,5-tribromobenzenesulfonic acid, 2,4,6-triiodobenzenesulfonic acid, 3,4,5-triiodobenzenesulfonic acid, pentafluorobenzenesulfonic acid, pentachlorobenzenesulfonic acid, pentabromobenzenesulfonic acid, pentaiodobenzenesulfonic acid, fluoronaphthalenesulfonic acid, chloronaphthalenesulfonic acid, bromonaphthalenesulfonic acid, iodonaphthalenesulfonic acid, fluoroanthracenesulfonic acid, chloroanthracenesulfonic acid, bromoanthracenesulfonic acid, and iodoanthracenesulfonic acid;
alkyl aromatic sulfonic acids such as p-toluenesulfonic acid, 4-isopropylbenzenesulfonic acid, 3.5-bis(trimethyl)benzenesulfonic acid, 3,5-bis(isopropyl)benzenesulfonic acid, 2,4,6-tris(trimethyl)benzenesulfonic acid, and 2,4,6-tris(isopropyl)benzenesulfonic acid;
halogenated alkyl aromatic sulfonic acids such as 2-trifluoromethylbenzenesulfonic acid, 2-trichloromethylbenzenesulfonic acid, 2-tribromomethylbenzenesulfonic acid, 2-triiodomethylbenzenesulfonic acid, 3-trifluoromethylbenzenesulfonic acid, 3-trichloromethylbenzenesulfonic acid, 3-tribromomethylbenzenesulfonic acid, 3-triiodomethylbenzenesulfonic acid, 4-trifluoromethylbenzenesulfonic acid, 4-trichloromethylbenzenesulfonic acid, 4-tribromomethylbenzenesulfonic acid, 4-triiodomethylbenzenesulfonic acid, 2,6-bis(trifluoromethyl)benzenesulfonic acid, 2,6-bis(trichloromethyl)benzenesulfonic acid, 2,6-bis(tribromomethyl)benzenesulfonic acid, 2,6-bis(triiodomethyl)benzenesulfonic acid, 3,5-bis(trifluoromethyl)benzenesulfonic acid, 3,5-bis(trichloromethyl)benzenesulfonic acid, 3,5-bis(tribromomethyl)benzenesulfonic acid, and 3,5-bis(triiodomethyl)benzenesulfonic acid;
aromatic aliphatic sulfonic acids such as benzylsulfonic acid, phenethylsulfonic acid, phenylpropylsulfonic acid, phenylbutylsulfonic acid, phenylpentylsulfonic acid, phenylhexylsulfonic acid, phenylheptylsulfonic acid, phenyloctylsulfonic acid, and phenylnonylsulfonic acid;
halogenated aromatic aliphatic sulfonic acids such as 4-fluorophenylmethylsulfonic acid, 4-chlorophenylmethylsulfonic acid, 4-bromophenylmethylsulfonic acid, 4-iodophenylmethylsulfonic acid, tetrafluorophenylmethylsulfonic acid, tetrachlorophenylmethylsulfonic acid, tetrabromophenylmethylsulfonic acid, tetraiodophenylmethylsulfonic acid, 4-fluorophenylethylsulfonic acid, 4-chlorophenylethylsulfonic acid, 4-bromophenylethylsulfonic acid, 4-iodophenylethylsulfonic acid, 4-fluorophenylpropylsulfonic acid, 4-chlorophenylpropylsulfonic acid, 4-bromophenylpropylsulfonic acid, 4-iodophenylpropylsulfonic acid, 4-fluorophenylbutylsulfonic acid, 4-chlorophenylbutylsulfonic acid, 4-bromophenylbutylsulfonic acid, and 4-iodophenylbutylsulfonic acid;
alicyclic sulfonic acids such as camphorsulfonic acid and adamantanecarboxylic acid; and the like.
Among them, trifluoromethanesulfonic acid, p-toluenesulfonic acid, and methanesulfonic acid are particularly preferable from the aspects of availability and appropriateness for production.
Specific examples of the carboxylic acid compounds from which the strongly acidic residue is derived include aliphatic unsaturated carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, iso-valeric acid, pivalic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, laurylic acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, icosanoic acid, henicosanoic acid, docosanoic acid, and tricosanoic acid;
halogenated saturated fatty carboxylic acids such as fluoroacetic acid, chloroacetic acid, bromoacetic acid, iodoacetic acid, difluoroacetic acid, dichloroacetic acid, dibromoacetic acid, diiodoacetic acid, trifluoroacetic acid, trichloroacetic acid, tribromoacetic acid, triiodoacetic acid, 2-fluoropropionic acid, 2-chloropropionic acid, 2-bromopropionic acid, 2-iodopropionic acid, trifluoropropionic acid, trichloropropionic acid, pentafluoropropionic acid, pentachloropropionic acid, pentabromopropionic acid, pentaiodopropionic acid, 2,2-bis(trifluoromethyl)propionic acid, 2,2-bis(trichloromethyl)propionic acid, 2,2-bis(tribromomethyl)propionic acid, 2,2-bis(triiodomethyl)propionic acid, trifluorobutyric acid, trichlorobutyric acid, pentafluorobutyric acid, heptachlorobutyric acid, heptafluorobutyric acid, heptabromobutyric acid, heptaiodobutyric acid, heptafluoroisobutyric acid, heptachloroisobutyric acid, heptabromoisobutyric acid, heptaiodoisobutyric acid, trifluorovaleric acid, 5H-perfluorovaleric acid, 5H-perchlorovaleric acid, 5H-perbromovaleric acid, 5H-periodovaleric acid, nonafluorovaleric acid, nonachlorovaleric acid, nonabromovaleric acid, nonaiodovaleric acid, trifluorohexanoic acid, trichlorohexanoic acid, perfluorohexanoic acid, perchlorohexanoic acid, perbromohexanoic acid, periodohexanoic acid, 7-chlorododecafluoroheptanoic acid, 7-chlorododecachloroheptanoic acid, 7-chlorododecabromoheptanoic acid, 7-chlorododecaiodoheptanoic acid, trifluoroheptanoic acid, trichloroheptanoic acid, 7H-perfluoroheptanoic acid, 7H-perchloroheptanoic acid, 7H-perbromoheptanoic acid, 7H-periodoheptanoic acid,
trifluorooctanoic acid, trichlorooctanoic acid, pentadecafluorooctanoic acid, pentadecachlorooctanoic acid, pentadecabromooctanoic acid, pentadecaiodooctanoic acid, trifluorononanoic acid, trichlorononanoic acid, 9H-hexadecafluorononanoic acid, 9H-hexadecachlorononanoic acid, 9H-hexadecabromononanoic acid, 9H-hexadecaiodononanoic acid, perfluorononanoic acid, perchlorononanoic acid, perbromononanoic acid, periodononanoic acid, trifluorodecanoic acid, trichlorodecanoic acid, nonadecafluorodecanoic acid, nonadecachlorodecanoic acid, nonadecabromodecanoic acid, nonadecaiododecanoic acid, trifluoroundecanoic acid, trichloroundecanoic acid, perfluoroundecanoic acid, perchloroundecanoic acid, perbromoundecanoic acid, periodoundecanoic acid, trifluorododecanoic acid, trichlorododecanoic acid, perfluorododecanoic acid, perchlorododecanoic acid, perbromododecanoic acid, periodododecanoic acid, trifluorotridecanoic acid, trichlorotridecanoic acid, perfluorotridecanoic acid, perchlorotridecanoic acid, perbromotridecanoic acid, periodotridecanoic acid, trifluorotetradecanoic acid, trichlorotetradecanoic acid, perfluorotetradecanoic acid, perchlorotetradecanoic acid, perbromotetradecanoic acid, periodotetradecanoic acid, trifluoropentadecanoic acid, trichloropentadecanoic acid, perfluoropentadecanoic acid, perchloropentadecanoic acid, perbromopentadecanoic acid, periodopentadecanoic acid, perfluorohexadecanoic acid, perchlorohexadecanoic acid, perbromohexadecanoic acid, periodohexadecanoic acid, perfluoroheptadecanoic acid, perchloroheptadecanoic acid, perbromoheptadecanoic acid, periodoheptadecanoic acid, perfluorooctadecanoic acid, perchlorooctadecanoic acid, perbromooctadecanoic acid, periodooctadecanoic acid, perfluorononadecanoic acid, perchlorononadecanoic acid, perbromononadecanoic acid, periodononadecanoic acid, perfluoroicosanoic acid, perchloroicosanoic acid, perbromoicosanoic acid, periodoicosanoic acid, perfluorohenicosanoic acid, perchlorohenicosanoic acid, perbromohenicosanoic acid, periodohenicosanoic acid, perfluorodocosanoic acid, perchlorodocosanoic acid, perbromodocosanoic acid, periododocosanoic acid, perfluorotricosanoic acid, perchlorotricosanoic acid, perbromotricosanoic acid, and periodotricosanoic acid;
hydroxy aliphatic carboxylic acids such as glycolic acid, lactic acid, glyceric acid, and 3-hydroxy-2-methylpropionic acid;
halogenated hydroxy aliphatic carboxylic acid such as 3-hydroxy-2-(trifluoromethyl)propionic acid, 3-hydroxy-2-(trichloromethyl)propionic acid, 3-hydroxy-2-(tribromomethyl)propionic acid, 3-hydroxy-2-(triiodomethyl)propionic acid, 2-hydroxy-2-(trifluoromethyl)butyric acid, 2-hydroxy-2-(trichloromethyl)butyric acid, 2-hydroxy-2-(tribromomethyl)butyric acid, and 2-hydroxy-2-(triiodomethyl)butyric acid;
alicyclic carboxylic acids such as cyclohexanecarboxylic acid, camphoric acid, and adamantanoic acid;
halogenated alicyclic carboxylic acids such as 4-fluorocyclohexanecarboxylic acid, 4-chlorocyclohexanecarboxylic acid, 4-bromocyclohexanecarboxylic acid, 4-iodocyclohexanecarboxylic acid, pentafluorocyclohexanecarboxylic acid, pentachlorocyclohexanecarboxylic acid, pentabromocyclohexanecarboxylic acid, pentaiodocyclohexanecarboxylic acid, 4-(trifluoromethyl)cyclohexanecarboxylic acid, 4-(trichloromethyl)cyclohexanecarboxylic acid, 4-(tribromomethyl)cyclohexanecarboxylic acid, and 4-(triiodomethyl)cyclohexanecarboxylic acid;
aromatic carboxylic acid such as benzoic acid, naphthoic acid, anthracenecarboxylic acid, pyrenecarboxylic acid, perylenecarboxylic acid, and pentaphenecarboxylic acid;
halogenated aromatic carboxylic acids such as fluorobenzoic acid, chlorobenzoic acid, bromobenzoic acid, iodobenzoic acid, difluorobenzoic acid, dichlorobenzoic acid, dibromobenzoic acid, diiodobenzoic acid, trifluorobenzoic acid, trichlorobenzoic acid,tribromobenzoic acid, triiodobenzoic acid, tetrafluorobenzoic acid, tetrachlorobenzoic acid, tetrabromobenzoic acid, tetraiodobenzoic acid, pentafluorobenzoic acid, pentachlorobenzoic acid, pentabromobenzoic acid, pentaiodobenzoic acid, fluoronaphthoic acid, chloronaphthoic acid, bromonaphthoic acid, iodonaphthoic acid, perfluoronaphthoic acid, perchloronaphthoic acid, perbromonaphthoic acid, periodonaphthoic acid, fluoroanthracenecarboxylic acid, chloroanthracenecarboxylic acid, bromoanthracenecarboxylic acid, iodoanthracenecarboxylic acid, perfluoroanthracenecarboxylic acid, perchloroanthracenecarboxylic acid, perbromoanthracenecarboxylic acid, and periodoanthracenecarboxylic acid; benzoylformic acid;
alkyl aromatic carboxylic acid such as toluyl acid and 2,4,6-tri(isopropyl)benzoic acid;
haloalkyl aromatic carboxylic acids such as 2-trifluoromethylbenzoic acid, 2-trichloromethylbenzoic acid, 2-tribromomethylbenzoic acid, 2-triiodomethylbenzoic acid, 3-trifluoromethylbenzoic acid, 3-trichloromethylbenzoic acid, 3-tribromomethylbenzoic acid, 3-triiodomethylbenzoic acid, 4-trifluoromethylbenzoic acid, 4-trichloromethylbenzoic acid, 4-tribromomethylbenzoic acid, 4-triiodomethylbenzoic acid, 2-fluoro-4-(trifluoromethyl)benzoic acid, 2-chloro-4-(trichloromethyl)benzoic acid, 2-bromo-4-(tribromomethyl)benzoic acid-2,3,4-trifluoro-6-(trifluoromethyl)benzoic acid, 2,3,4-trichloro-6-(trichloromethyl)benzoic acid, 2,3,4-tribromo-6-(tribromomethyl)benzoic acid, 2,3,4-triiodo-6-(triiodomethyl)benzoic acid, 2-iodo-4-(triiodomethyl)benzoic acid, 2,4-bis(trifluoromethyl)benzoic acid, 2,4-bis(trichloromethyl)benzoic acid, 2,4-bis(tribromomethyl)benzoic acid, 2,4-bis(triiodomethyl)benzoic acid, 2,6-bis(trifluoromethyl)benzoic acid, 2,6-bis(trichloromethyl)benzoic acid, 2,6-bis(tribromomethyl)benzoic acid, 2,6-bis(triiodomethyl)benzoic acid, 3,5-bis(trifluoromethyl)benzoic acid, 3,5-bis(trichloromethyl)benzoic acid, 3,5-bis(tribromomethyl)benzoic acid, 3,5-bis(triiodomethyl)benzoic acid, 2,4,6-tris(trifluoromethyl)benzoic acid, 2,4,6-tris(trichloromethyl)benzoic acid, 2,4,6-tris(tribromomethyl)benzoic acid, 2,4,6-tris(triiodomethyl)benzoic acid, 2-chloro-6-fluoro-3-methylbenzoic acid, trifluoromethylnaphthoic acid, trichloromethylnaphthoic acid, tribromomethylnaphthoic acid, triiodomethylnaphthoic acid,
bis(trifluoromethyl)naphthoic acid, bis(trichloromethyl)naphthoic acid, bis(tribromomethyl)naphthoic acid, bis(triiodomethyl)naphthoic acid, tris(trifluoromethyl)naphthoic acid, tris(trichloromethyl)naphthoic acid, tris(tribromomethyl)naphthoic acid, tris(triiodomethyl)naphthoic acid, trifluoromethylanthracenecarboxylic acid, trichloromethylanthracenecarboxylic acid, tribromomethylanthracenecarboxylic acid, and triiodomethylanthracenecarboxylic acid;
alkoxy aromatic carboxylic acids such as anisic acid, veratric acid, and o-veratric acid;
haloalkoxy aromatic carboxylic acids such as 4-trifluoromethoxybenzoic acid, 4-trichloromethoxybenzoic acid, 4-tribromomethoxybenzoic acid, 4-triiodomethoxybenzoic acid, 4-pentafluoroethoxybenzoic acid, 4-pentachloroethoxybenzoic acid, 4-pentabromoethoxybenzoic acid, 4-pentaiodoethoxybenzoic acid, 3,4-bis(trifluoromethoxy)benzoic acid, 3,4-bis(trichloromethoxy)benzoic acid, 3,4-bis(tribromomethoxy)benzoic acid, 3,4-bis(triiodomethoxy)benzoic acid, 2,5-bis(2,2,2-trifluoroethoxy)benzoic acid, 2,5-bis(2,2,2-trichloroethoxy)benzoic acid, 2,5-bis(2,2,2-tribromoethoxy)benzoic acid, and 2,5-bis(2,2,2-triiodoethoxy)benzoic acid;
hydroxy aromatic carboxylic acids such as salicylic acid, o-pyrocatechuic acid, α-resorcylic acid, gentisic acid, α-resorcylic acid, protocatechuic acid, α-resorcylic acid, and gallic acid;
hydroxy alkoxy aromatic carboxylic acids such as vanillic acid and iso vanillic acid;
nitro aromatic carboxylic acids such as trinitrobenzoic acid;
amino aromatic carboxylic acids such as anthranilic acid;
aromatic aliphatic carboxylic acids such as α-toluyl acid, cinnamic acid, hydratropic acid, 3-phenylpropionic acid, 4-phenylbutyric acid, 5-phenylpentanoic acid, 6-phenylhexanoic acid, 7-phenylheptanoic acid, and 6-(2-naphthyl)hexanoic acid;
hydroxy aromatic aliphatic carboxylic acids such as homogentisic acid;
aromatic hydroxyalkyl carboxylic acids such as mandelic acid, benzyl acid, atrolactic acid, tropic acid, and atroglyceric acid;
oxo carboxylic acids such as 2-formylacetic acid, acetoacetic acid, 3-benzoylpropionic acid, 4-formylbutyric acid, 3-oxovaleric acid, 5-oxovaleric acid, 3,5-dioxovaleric acid, 6-formylhexanecarboxylic acid, 2-oxo-1-cyclohexanecarboxylic acid, 4-(2-ocobutyl)benzoic acid, p-(3-formylpropyl)benzoic acid, 4-formylphenylacetic acid, β-oxocyclohexane propionic acid, and pyruvic acid; and the like.
Among them, benzoylformic acid, acetic acid, and benzoic acid are particularly preferable.
Specific examples of the specific sulfonium salts (S-1) to (S-67) are shown below, but the present invention is not limited thereto.

For each of the specific examples (S-1) to (S-67), the solubility thereof in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at 25°C under 1 atm is also shown.

Specific sulfonium salt No.	R^a	R^b	R^c	Solubility (mg/ml)
S-1	-OH	-OH	-H	30
S-2	-OH	-OH	-Cl	32
S-3	-COOH	-Cl	-Cl	28
S-4	-COOH	-COOH	-Cl	30
S-5	-OH	-COOH	-H	29
S-6	-OH	-COOH	-Cl	28
S-7	-OH	-OH	-OH	50
S-8	-COOH	-COOH	-COOH	41
S-9	-COOH	-CH₃	-CH₃	28

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-10	-OH	-OH	-H	32
S-11	-OH	-OH	-Cl	35
S-12	-COOH	-Cl	-Cl	30
S-13	-COOH	-COOH	-Cl	32
S-14	-OH	-COOH	-H	32
S-15	-OH	-COOH	-Cl	30
S-16	-OH	-OH	-OH	58
S-17	-COOH	-COOH	-COOH	43
S-18	-COOH	-CH₃	-CH₃	30

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-19	-OH	-OH	-H	27
S-20	-OH	-OH	-Cl	28
S-21	-COOH	-Cl	-Cl	25
S-22	-COOH	-COOH	-Cl	27
S-23	-OH	-COOH	-H	26
S-24	-OH	-COOH	-Cl	25
S-25	-OH	-OH	-OH	50
S-26	-COOH	-COOH	-COOH	38
S-27	-COOH	-CH₃	-CH₃	25

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-28	-OH	-OH	-H	28
S-29	-OH	-OH	-Cl	30
S-30	-COOH	-Cl	-Cl	27
S-31	-COOH	-COOH	-Cl	30
S-32	-OH	-COOH	-H	27
S-33	-OH	-COOH	-Cl	26
S-34	-OH	-OH	-OH	47
S-35	-COOH	-COOH	-COOH	36
S-36	-COOH	-CH₃	-CH₃	28

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-37	-OH	-OH	-H	29
S-38	-OH	-OH	-Cl	30
S-39	-COOH	-Cl	-Cl	27
S-40	-COOH	-COOH	-Cl	29
S-41	-OH	-COOH	-H	28
S-42	-OH	-COOH	-Cl	27
S-43	-OH	-OH	-OH	52
S-44	-COOH	-COOH	-COOH	42
S-45	-COOH	-CH₃	-CH₃	27

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-46	-OH	-OH	-H	28
S-47	-OH	-OH	-Cl	30
S-48	-COOH	-Cl	-Cl	26
S-49	-COOH	-COOH	-Cl	28
S-50	-OH	-COOH	-H	26
S-51	-OH	-COOH	-Cl	25
S-52	-OH	-OH	-OH	47
S-53	-COOH	-COOH	-COOH	44
S-54	-COOH	-CH₃	-CH₃	26

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-55	-OH	-OH	-H	32
S-56	-OH	-OH	-Cl	34
S-57	-COOH	-Cl	-Cl	30
S-58	-COOH	-COOH	-Cl	33
S-59	-OH	-COOH	-H	30
S-60	-OH	-COOH	-Cl	28
S-61	-OH	-OH	-OH	49
S-62	-COOH	-COOH	-COOH	45
S-63	-COOH	-CH₃	-CH₃	31

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-64	-OH	-OH	-H	42
S-65	-COOH	-COOH	-COOH	40

Specific sulfonium salt	R^a	R^b	R^c	Solubility (mg/ml)
S-66	-OH	-OH	-H	38
S-67	-COOH	-COOH	-COOH	38

(Preparation of the specific sulfonium salt according to the present invention)

The specific sulfonium salt is generally prepared by a Friedel-Crafts or Grignard reaction of a sulfide compound and an aromatic compound. Such synthetic methods are described, for example, in Journal of the American Chemical Society 112 (16), 1990, pp.6004-6015; The Journal of Organic Chemistry 1998, pp.5571-5573; International Publication (WO) No. 02/081439A1; and European Patent (EP) No. 1113005.
The content of specific sulfonium salt in the recording layer according to the present invention is preferably 1 to 30 wt %, more preferably 3 to 25 wt %, and particularly preferably 5 to 20 wt %, with respect to the total solids in the recording layer, from the viewpoints of sensitivity and generation of development scum.
Further, the specific sulfonium salts may be used alone or in combinations of two or more.
A general onium salt other than the specific sulfonium salts above may be added, in such a combination as a solubilization inhibitor, to the recording layer according to the invention. The general onium salts will be described in the explanation of other components below.
When a specific sulfonium salt and a general onium salt are used in combination, the general onium salt is preferably used in an amount in the range of 0 to 30 wt %, and more preferably 0.5 to 15 wt.

[(B) Alkali-soluble resin]

Examples of the alkali-soluble resin (B) to be used in the invention may include homopolymers containing acidic groups in the main chains and/or the side chains of the resin, their copolymers, or their mixtures.
Among them, polymers having the following acidic groups (1) to (6) in the main chains and/or side chains are preferable in terms of the development resistance, i.e. the suppression of the solubility to an aqueous alkaline solution:

(1) phenol (-Ar-OH),
(2) sulfone amide (-SO₂NH-R),
(3) substituted sulfoneamido based acid group (hereinafter, referred to as active imido group) [-SO₂NHCOR, -SO₂NHSO₂R, -CONHSO₂R]
(4) carboxylic acid group (-CO₂H),
(5) sulfonic acid group (-SO₃H), and
(6) phosphoric acid group (-OPO₃H₂)

Ar in the above-mentioned groups (1) to (6) represents a divalent aryl bonding group optionally comprising a substituent group and R represents a hydrocarbon group optionally comprising a substituent group.
Among the alkali-soluble resin comprising the acidic group selected from the above-mentioned (1) to (6), an alkali-soluble resin comprising (1) phenol, (2) sulfone amide, or (3) active imido group is preferable and an alkali-soluble resin comprising (1) phenol or (2) sulfone amide is more preferable in terms of assurance of the sufficient solubility in an alkaline developer, development latitude, and film strength.
As the alkali-soluble resin comprising the acidic group selected from the above-mentioned (1) to (6), the following can be exemplified.

(1) Examples of the alkali-soluble resin comprising phenol group may include novolak resin such as condensation polymers of phenol and formaldehyde; condensation polymers of m-cresol and formaldehyde, condensation polymers of p-cresol and formaldehyde, condensation polymers of m-/p-mixed cresol and formaldehyde, and condensation polymers of phenol, cresol (m-, p-, or m-/p-mixture) and formaldehyde; and condensation copolymers of pyrogallol and acetone. Further, copolymers obtained by copolymerizing compound comprising phenyl groups in the side chains can be exemplified. Or, copolymers obtained by copolymerizing compounds comprising phenyl groups in the side chains can also be used.
As the compounds comprising phenol group, acrylamide, methacrylamide, acrylic acid ester, methacrylic acid ester, or hydroxystyrene can be exemplified.
(2) Examples of the alkali-soluble resin comprising sulfoneamido group may include polymers obtained by using the minimum component units derived from compounds comprising sulfoneamido group as main constituent components. Examples of such compounds include those having at least one sulfoneamido group comprising at least one hydrogen atom bonded to the nitrogen atom and at least one polymerizable unsaturated group, in the molecules. Among them, low molecular weight compounds comprising acryloyl, allyl, or vinyloxy group as well as substituted or mono-substituted aminosulfonyl group or a substituted sulfonylimino group in molecules are preferable and the following compounds defined by the following (i) to (v) can be exemplified.

Examples thereof include compounds represented by any one of the following general formulae (i) to (v):
In the general formulae (i) to (v), X¹ and X² each independently represent -O-, or -NR⁷-; R¹ and R⁴ each independently represent a hydrogen atom, or -CH₃; R², R⁵, R⁹, R¹² and R¹⁶ each independently represent an alkylene, cycloalkylene, arylene or aralkylene group which may have a substituent and has 1 to 12 carbon atoms; R³, R⁷ and R¹³ each independently represent a hydrogen atom, or an alkyl, cycloalkyl, aryl or aralkyl group which may have a substituent and has 1 to 12 carbon atoms; R⁶ and R¹⁷ each independently represent an alkyl, cycloalkyl, aryl or aralkyl group which may have a substituent and has 1 to 12 carbon atoms; R⁸, R¹⁰ and R¹⁴ each independently represent a hydrogen atom or -CH₃; R¹¹ and R¹⁵ each independently represent a single bond, or an alkylene, cycloalkylene, arylene or aralkylene group which may have a substituent and has 1 to 12 carbon atoms; and Y¹ and Y² each independently represent a single bond or -CO-.
Of the compounds represented by the represented by the general formulae (i) to (v), in particular, the following can preferably be used in the invention: m-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl)methacrylamide and N-(p-aminosulfonylphenyl)acrylamide.
Examples of the monomer having an active imide group in the item (3) include compounds each having in the molecule thereof one or more active imide groups represented by the above-mentioned structural formula and one or more unsaturated groups which can be polymerized with the active imide group(s). Of these compounds, preferable are compounds each having in the molecule thereof one or more active imide groups represented by the following structural formula and one or more unsaturated groups which can be polymerized with the active imide group(s):
Specifically, N-(p-toluenesulfonyl)methacrylamide, N-(p-toluenesulfonyl)acrylamide and others can be preferably used.
Examples of the monomer having a carboxylic acid group in the item (4) include compounds each having in the molecule thereof one or more carboxylic acid groups and one or more unsaturated groups which can be polymerized with the carboxylic acid group(s).
Examples of the monomer having a sulfonic acid group in the item (5) include compounds each having in the molecule thereof one or more sulfonic acid groups and one or more unsaturated groups which can be polymerized with the sulfonic acid group(s).
Examples of the monomer having a phosphoric acid group in the item (6) include compounds each having in the molecule thereof one or more phosphoric acid group and one or more unsaturated groups which can be polymerized with the phophoric acid group(s).
The minimum constituent unit comprising acidic group selected from (1) to (6) composing an alkali-soluble resin of the invention is not necessarily limited to one particular unit, but those obtained by copolymerizing two or more minimum constituent units comprising the same acidic group or two or more minimum constituent units comprising different acidic groups can also be used.
The above-mentioned copolymer contains the compound having the acidic group selected from (1) to (6) to be copolymerized in an amount preferably 10% by mole or more, more preferably 20% by mole or more. If it is less than 10% by mole, the development latitude tends to be improved insufficiently.
In the invention, in the case the compounds are copolymerized to use the obtained copolymer as the alkali-soluble resin, the compounds to be copolymerized may include other compounds without acidic group (1) to (6). Examples of the compounds without acidic group (1) to (6) inclue the following compounds (m1) to (m12), however they should not be limited to these examples.

(m1) Acrylic acid esters and methacrylic acid esters having aliphatic hydroxyl groups such as 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate.
(m2) Alkyl acrylate such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, and glycidyl acrylate.
(m3) Alkyl methacrylate such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, and glycidyl methacrylate.
(m4) Acrylamide or methacrylamide such as acrylamide, methacrylamide, N-methylol acrylamide, N-ethylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-hydroxyethylacrylamide, N-phenylacrylamide, N-nitrophenylacrylamide, and N-ethyl-N-phenylacxrylamide.
(m5) Vinyl ethers such as ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether, and phenyl vinyl ether.
(m6) Vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butylate, and vinyl benzoate.
(m7) Styrenes such as styrene, α-methylstyrene, methylstyrene, and chloromethylstyrene.
(m8) Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, and phenyl vinyl ketone.
(m9) Olefins such as ethylene, propylene, isobutylene, butadiene, and isoprene.
(m10) N-vinylpyrrolidone, acrylonitrile, and methacrylonitrile.
(m11) Unsaturated imides such as maleimide, N-acryloylacrylamide, N-acetylmethacrylamide, N-propionylmethacrylamide, and N-(p-chlorobenzoyl)methacrylamide.
(m12) Unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic anhydride, and itaconic acid.

In the present invention, the alkali-soluble resin is preferably a homopolymer or copolymer of a polymerizable monomer having the phenolic hydroxyl group above or an active imide group, and, in particular, a homopolymer or copolymer of a polimerizable monomer having the sulfonamide group such as m-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl)methacrylamide, N-(p-aminosulfonylphenyl)acrylamide, or the like.
The alkali-soluble resin according to the present invention preferably has a weight-average molecular weight of 2,000 or more and a number-average molecular weight of 500 or more. More preferable is a resin having a weight-average molecular weight of 5,000 to 300,000, a number-average molecular weight of 800 to 250,000, and a molecular weight distribution (weight-average molecular weight / number-average molecular weight) of 1.1 to 10. In particular, when the alkali-soluble resin according to the invention is a phenol formaldehyde resin, a cresol aldehyde resin, or the like, the weight-average molecular weight thereof is preferably 500 to 20,000 and the number-average molecular weight, 200 to 10,000.
These alkali-soluble resins may be used alone or in combinations of two or more.
The content of the alkali-soluble resin in the recording layer according to the present invention is preferably in the range of 30 to 98 wt %, more preferably 40 to 95 wt, and particularly preferably 50 to 90 wt %, with respect to the total solid in the recording layer, from the viewpoints of sensitivity, image-forming property, and film durability.

[(C) Infrared-light absorbing agent]

The infrared-light absorbing agent contained in the recording layer according to the present invention is a substance that absorbs light having a wavelength in the infrared range of 700 nm or more, preferably 750 to 1,200 nm, and capable of photothermal conversion of the light in this range. Specifically, various dyes or pigments that absorb light in the aforementioned wavelength region and generate heat may be used.
As a dye, commercially available dyes and the known dyes described in the publication such as "Dye Handbook" (edited by The Society of Synthetic Organic Chemistry, Japan, published in 1970) can be utilized. Examples include dyes such as azo dyes, metal complex salt azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyane dyes, squarylium pigments, pyrilium salts, metal thiolate complexes, oxomol dyes, diimonium dyes, aminium dyes, and croconium dyes.
Preferable examples of the dye include cyanine dyes described in JP-A Nos. 58-125246, 59-84356, 59-202829, and 60-78787; methine dyes described in JP-ANos. 58-173696, 58-181690, and 58-194595; naphthoquinone dyes described in JP-ANos. 58-112793, 58-224793, 59-48187, 59-73996, 60-52940, and 60-63744; squalirium dyes described in JP-A No. 58-112792; and cyanine dyes described in GB Patent No. 434,875.
Other preferable examples of the dye include near infrared absorbing sensitizers described in U.S. Patent No. 5,156,938; substituted arylbenzo(thio)pyrylium salts described in U.S. Patent No. 3,881,924; trimethinethiapyrylium salts described in JP-ANo. 57-142645 (U.S. Patent No. 4,327,169); pyrylium type compounds described in JP-ANos. 58-181051, 58-220143, 59-41363, 59-84248, 59-84249, 59-146063, and 59-146061; cyanine dyes described in JP-A No. 59-216146; pentamethinethiopyrylium salts described in U.S. Patent No. 4,283,475; and pyrylium compounds described in Japanese Patent Application Publication (JP-B) Nos. 5-13514 and 5-19702.
Additional preferable examples of the dye include near infrared absorbing dyes represented by formulae (I) and (II) as described in U.S. Patent No. 4,756,993.
Among these dyes, particularly preferable are cyanine dyes, phthalocyanine dyes, oxonol dyes, squalirium dyes, pyrylium salts, thiopyrylium dyes, and nickel thiolate complexes. Dyes represented by the following general formulae (a) to (e) are also preferable since such dyes are excellent in terms of photothermal conversion efficiency. The cyanine dyes represented by the following general formula (a) are most preferable for the following reason: when the dyes are used in the photosensitive composition of the invention, the dyes manifest a high degree of polymerizing activity, and the dyes are also excellent in terms of stability and economy.

General formula (a)

In general formula (a), X¹ represents a hydrogen atom, a halogen atom, -NPh₂, X²-L¹ (wherein X² represents an oxygen atom or a sulfur atom, L¹ represents a hydrocarbon group having 1 to 12 carbon atoms, an aromatic cyclic group having a heteroatom, or a hydrocarbon group containing a heteroatom and having 1 to 12 carbon atoms, and the heteroatom referred to herein is N, S, O, a halogen atom, or Se), or a group represented by the following:
wherein Xa^- has the same definition as Za^-, which will be described at a later time, and R^a represents a substituent selected from a hydrogen atom, an alkyl group, an aryl group, a substituted or unsubstituted amino group, or a halogen atom;
R' and R² each independently represents a hydrocarbon group having 1 to 12 carbon atoms, and from the viewpoint of the storage stability of the photosensitive composition of the invention when it is used in a coating solution for forming a recording layer of a planographic printing plate precursor, it is preferable that R¹ and R² each independently represents a hydrocarbon group having 2 or more carbon atoms, and more preferably R¹ and R² are bonded to each other to form a 5-membered or 6-membered ring.
Ar¹ and Ar², which may be the same or different, each represent an aromatic hydrocarbon group which may have a substituent. Preferable examples of the aromatic hydrocarbon group include benzene and naphthalene rings. Preferable examples of the substituent include hydrocarbon groups having 12 or less carbon atoms, halogen atoms, and alkoxy groups having 12 or less carbon atoms.
Y¹ and Y², which may be the same or different, each represents a sulfur atom, or a dialkylmethylene group having 12 or less carbon atoms.
R³ and R⁴, which may be the same or different, each represents a hydrocarbon group which has 20 or less carbon atoms and may have a substituent. Preferable examples of the substituent include alkoxy groups having 12 or less carbon atoms, a carboxyl group, and a sulfo group. R⁵, R⁶, R⁷ and R⁸, which may be the same or different, each represents a hydrogen atom, or a hydrocarbon group having 12 or less carbon atoms, and since the raw materials thereof can easily be obtained, each preferably represents a hydrogen atom.
Za^- represents a counter anion. However, in a case where the cyanine dye represented by general formula (a) has an anionic substituent in the structure thereof and there is accordingly no need to neutralize electric charges in the dye, Za^- is not required. From the viewpoint of the storage stability of the recording layer coating solution, Za^- is preferably an ion of a halogen, perchlorate, tetrafluroborate, hexafluorophosphate, carboxylate or sulfonate. From the viewpoints of compatibility of the dye with the alkali-soluble resin and solubility in the coating solution, Za^- is preferably a halogen ion, or an organic acid ion such as a carboxylic acid ion or sulfonic acid ion, more preferably a sulfonic acid ion, and even more preferably an arylsulfonic acid ion.
Specific examples of the cyanine dye represented by general formula (a), and which can be preferably used in the invention, include dyes in JP-A No. 2001-133969 (paragraphs [0017] to [0019]), JP-ANo. 2002-40638 (paragraphs [0012] to [0038]), and JP-ANo. 2002-23360 (paragraphs [0012] to [0023]), as well as dyes illustrated below.

General formula (b)

In general formula (b), L represents a methine chain having 7 or more conjugated carbon atoms, and the methine chain may have one or more substituent. The substituents may be bonded to each other to form a cyclic structure. Zb⁺ represents a counter cation. Preferable examples of the counter cation include ammonium, iodonium, sulfonium, phosphonium and pyridinium ions, and alkali metal cations (such as Ni⁺, K⁺ and Li⁺).
R⁹ to R¹⁴ and R¹⁵ to R²⁰ each independently represents a substituent selected from hydrogen atom, halogen atom, and cyano, alkyl, aryl, alkenyl, alkynyl, carbonyl, thio, sulfonyl, sulfinyl, oxy and amino groups; or a substituent obtained by combining two or three from among these substituents. Two or three out of R⁹ to R¹⁴ and R¹⁵ to R²⁰ may be bonded to each other to form a cyclic structure.
A dye wherein L in general formula (b) represents a methine chain having 7 conjugated carbon atoms, and each of R⁹ to R¹⁴ and R¹⁵ to R²⁰ represents a hydrogen atom, is preferable since such a dye can be easily obtained and exhibits advantageous effects.
Specific examples of the dye represented by general formula (b), and which can be preferably used in the invention, are illustrated below.

General formula (c)

In general formula (c), Y³ and Y⁴ each independently represent an oxygen, sulfur, selenium or tellurium atom; M represents a methine chain having 5 or more conjugated carbon atoms; R²¹ to R²⁴ and R²⁵ to R²⁸, which may be the same or different, each represents a hydrogen or halogen atom, or a cyano, alkyl, aryl, alkenyl, alkynyl, carbonyl, thio, sulfonyl, sulfinyl, oxy or amino group; and Za^- represents a counter anion, and has the same meaning as Za^- in general formula (a).
Specific examples of the dye which is represented by general formula (c) and which can be preferably used in the invention, are illustrated below.

General formula (d)

In general formula (d), R²⁹ to R³² each independently represents a hydrogen atom, an alkyl group or an aryl group; R³³ and R³⁴ each independently represents an alkyl group, a substituted oxy group, or a halogen atom; n and m each independently represents an integer of 0 to 4; and R²⁹ and R³⁰, or R³¹ and R³² may be bonded to each other to form a ring, or R²⁹ and/or R³⁰ may be bonded to R³³ to form a ring and R³¹ and/or R³² may be bonded to R³⁴ to form a ring. When plural R³³'s and R³⁴'s are present, R³³'s may be bonded to each other to form a ring, or R³⁴'s may be bonded to each other to form a ring.
X² and X³ each independently represents a hydrogen atom, an alkyl group or an aryl group, and at least one of X² and X³ represents a hydrogen atom or an alkyl group.
Q represents a trimethine group or a pentamethine group which may have a substituent, and may be combined with an bivalent organic group to form a cyclic structure. Zc^- represents a counter anion and has the same meanings as Za^- in general formula (a).
Specific examples of the dye represented by general formula (d) and which can be preferably used in the invention, are illustrated below.

General formula (e)

In general formula (e), R³⁵ to R⁵⁰ each independently represents a hydrogen or halogen atom, or a cyano, alkyl, aryl, alkenyl, alkynyl, hydroxyl, carbonyl, thio, sulfonyl, sulfinyl, oxy or amino group, or an onium salt structure, each of which may have a substituent; M represents two hydrogen atoms, a metal atom, a halo metal group, or an oxy metal group. Examples of the metal contained therein include atoms in IA, IIA, IIIB and IVB groups in the periodic table, transition metals in the first, second and third periods therein, and lanthanoid elements. Among these examples, preferable are copper, magnesium, iron, zinc, cobalt, aluminum, titanium, and vanadium.
Specific examples of the dye represented by general formula (e) and which can be preferably used in the invention, are illustrated below.
The pigment used as the infrared absorbent in the invention may be a commercially available pigment or a pigment described in publications such as Color Index (C.I.) Handbook, "Latest Pigment Handbook" (edited by Japan Pigment Technique Association, and published in 1977), "Latest Pigment Applied Technique" (by CMC Publishing Co., Ltd. in 1986), and "Printing Ink Technique" (by CMC Publishing Co., Ltd. in 1984).
Examples of the pigment include black pigments, yellow pigments, orange pigments, brown pigments, red pigments, purple pigments, blue pigments, green pigments, fluorescent pigments, metal powder pigments, and polymer-bonded dyes. Specifically, the following can be used: insoluble azo pigments, azo lake pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene and perynone pigments, thioindigo pigments, quinacridone pigments, dioxazine pigments, isoindolinone pigments, quinophthalone pigments, dyeing lake pigments, azine pigments, nitroso pigments, nitro pigments, natural pigments, fluorescent pigments, inorganic pigments, and carbon black. Among these pigments, carbon black is preferable.
These pigments may be used with or without surface treatment. Examples of surface treatment include a method of coating the surface of the pigments with resin or wax; a method of adhering a surfactant onto the surface; and a method of bonding a reactive material (such as a silane coupling agent, an epoxy compound, or a polyisocyanate) to the pigment surface. The surface treatment methods are described in "Nature and Application of Metal Soap" (Saiwai Shobo), "Printing Ink Technique" (by CMC Publishing Co., Ltd. in 1984). And "Latest Pigment Applied Technique" (by CMC Publishing Co., Ltd. in 1986.
From a viewpoint of stability of a dispersion in a recording layer coating solution, and uniformity of a recording layer, a particle diameter of pigments is preferably in a range of 0.01 µm to 10 µm, further preferably in a range of 0.05 µm to 1 µm, particularly preferably in a range of 0.1 µm to 1 µm.
The method for dispersing the pigment may be a known dispersing technique used to produce ink or toner. Examples of a dispersing machine, which can be used, include an ultrasonic disperser, a sand mill, an attriter, a pearl mill, a super mill, a ball mill, an impeller, a disperser, a KD mill, a colloid mill, a dynatron, a three-roll mill, and a pressing kneader. Details are described in "Latest Pigment Applied Technique" (by CMC Publishing Co., Ltd. in 1986).
From the viewpoints of sensitivity, uniformity of the film to be formed and durability, the pigment or dye can be added to the recording layer in a ratio of 0.01 to 30%, preferably 0.1 to 10%, and more preferably 0.1 to 5% in the case of the dye or 0.2 to 10% in the case of pigment by mass, relative to the total solid contents of the recording layer.

[Other components]

The recording layer according to the present invention may contain various additives as needed.
For example, it is preferable to add a so-called solubilization inhibitor that functions to inhibit solubilization of the alkali-soluble resin (B) when added to the developer, such as an onium salt other than the specific sulfonium salts, an aromatic sulfone compound, an aromatic sulfonic ester compound, a multifunctional amine compound, or the like, for adjustment of the solubility of the recording layer. Among these solubility inhibitors, thermally decomposable substances that inhibit solubilization of the alkali-soluble resin substantially while they are not decomposed, such as onium salts, o-quinonediazide compounds, sulfonic acid alkyl esters and the like are preferably used in combination for further suppressing the solubilization-inhibiting properties of the image region in the developer.
Preferable examples of the onium salt used in the invention include diazonium salts described in S. I. Schlesinger, Photogr. Sci. Eng., 18, 387 (1974), T. S. Bal et al., Polymer, 21, 423 (1980), and JP-ANo. 5-158230; ammonium salts described in U.S. Patent Nos. 4,069,055 and 4,069,056, and JP-A No. 3-140140; phosphonium salts described in D. C. Necker et al., Macromolecules, 17, 2468 (1984), C. S. Wen et al., Teh, Proc. Conf. Rad. Curing ASIA, p478 Tokyo, Oct (1988), and U.S. Patent Nos. 4,069,055 and 4,069,056; iodonium salts described in J. V Crivello et al., Macromolecules, 10 (6), 1307 (1977), Chem. & Eng. News, Nov. 28, p31 (1988), EP No. 104,143, U.S. Patent Nos. 5,041,358 and 4,491,628, and JP-A Nos. 2-150848 and 2-296514; sulfonium salts described in J. V Crivello et al., Polymer J. 17, 73 (1985), J. V Crivello et al., J. Org. Chem., 43, 3055 (1978), W. R. Watt et al., J. Polymer Sci., Polymer Chem. Ed., 22, 1789 (1984), J. V. Crivello et al., Polymer Bull., 14, 279 (1985), J. V. Crivello et al., Macromolecules, 14 (5), 1141 (1981), J. V Crivello et al., J. Polymer Sci., Polymer Chem. Ed., 17, 2877 (1979), EP Nos. 370,693, 233,567, 297,443 and 297,442, U.S. Patent Nos. 4,933,377, 3,902,114, 5,041,358, 4,491,628, 4,760,013, 4,734,444 and 2,833,827, and DE Patent Nos. 2,904,626, 3,604,580 and 3,604,581; selenonium salts described in J. V Crivello et al., Macromolecules, 10 (6), 1307 (1977), J. V Crivello et al., J. Polymer Sci., Polymer Chem. Ed., 17, 1047 (1979); arsonium salts described in C. S. Wen et al., and The Proc. Conf Rad. Curing ASIA, p478, Tokyo, Oct (1988).
Among such onium salts, diazonium salts and quaternary ammonium salts are particularly preferable from the viewpoints of both their capacity of hindering dissolution, and their thermal decomposability. The diazonium salts represented by general formula (I) in the JP-A No. 5-158230 and the diazonium salts represented by general formula (1) in JP-A No. 11-143064 are more preferable, and diazonium salts represented by general formula (1) in the JP-ANo. 11-143064, which have low absorption wavelength peaks within the visible ray range, are most preferable. As the quaternary ammonium salts, those represented by formulae (1) to (10) of [Ka 5] and [Ka 6] of JP-ANo. 2002-229186 are preferable.
Examples of the counter ion of the onium salt include tetrafluoroboric acid, hexafluorophosphoric acid, triisopropylnaphthalenesulfonic acid, 5-nitro-o-toluenesulfonic acid, 5-sulfosalicylic acid, 2,5-dimethylbenzenesulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, 2-nitrobenzenesulfonic acid, 3-chlorobenzenesulfonic acid, 3-bromobenzenesulfonic acid, 2-fluorocaprylnaphthalenesulfonic acid, dodecylbenzenesulfonic acid, 1-naphthol-5-sulfonic acid, 2-methoxy-4-hydroxy-5-benzoyl-benzenesulfonic acid, and p-toluenesulfonic acid. Among these examples, hexafluorophosphoric acid, and alkylaromatic sulfonic acids such as triisopropylnaphthalenesulfonic acid and 2,5-dimethylbezenesulfonic acid are particularly preferable.
The quinonediazide is preferably an o-quinonediazide compound. The o-quinonediazide compound used in the invention is a compound having at least one o-quinonediazide group and having an alkali-solubility increased by being thermally decomposed. The compound may be any one of compounds having various structures.
In other words, the o-quinonediazide compound assists the solubility of the photosensitive material both from the viewpoint of the effects of being thermally decomposed, and thereby losing the function of suppressing the dissolution of the binder, and the effect that the o-quinonediazide itself is changed into an alkali-soluble material.
Preferable examples of the o-quinonediazide compound used in the invention include compounds described in J. Coser, "Light-Sensitive Systems" (John Wiley & Sons. Inc.), pp. 339-352. Particularly preferable are sulfonic acid esters or sulfonamides of o-quinonediazide made to react with various aromatic polyhydroxy compounds or with aromatic amino compounds.
Further preferable examples include an ester made from benzoquinone-(1,2)-diazidesulfonic acid chloride or naphthoquinone-(1,2)-diazide-5-sulfonic acid chloride and pyrogallol-acetone resin, as described in JP-B No. 43-28403; and an ester made from benzoquinone-(1,2)-diazidesulfonic acid chloride or naphthoquinone-(1,2)-diazide-5-sulfonic acid chloride and phenol-formaldehyde resin.
Additional preferable examples include an ester made from naphthoquinone-(1,2)-diazide-4-sulfonic acid chloride and phenol-formaldehyde resin or cresol-formaldehyde resin; and an ester made from naphthoquinone-(1,2)-diazide-4-sulfonic acid chloride and pyrogallol-acetone resin.
Other useful o-quinonediazide compounds are reported in unexamined or examined patent documents, examples of which include JP-A Nos. 47-5303, 48-63802, 48-63803, 48-96575, 49-38701 and 48-13354, JP-B No. 41-11222, 45-9610 and 49-17481, U.S. Patent Nos. 2,797,213, 3,454,400, 3,544,323, 3,573,917, 3,674,495 and 3,785,825, GB Patent Nos. 1,227,602, 1,251,345, 1,267,005, 1,329,888 and 1,330,932, and DE Patent No. 854,890.
The amount of onium salt and/or o-quinonediazide compound added as the decomposable dissolution suppresser(s) is preferably from 1 to 10%, more preferably from 1 to 5%, and even more preferably from 1 to 2% by relative to the total solid contents of the recording layer. The onium salts and the o-quinonediazide compounds may be used either independently or in the form of mixtures of two or more thereof.
The amount of additives other than the o-quinonediazide compound added is preferably from 0.1 to 5%, more preferably from 0.1 to 2%, and even more preferably from 0.1 to 1.5% by mass. The additives and the binder used in the invention are preferably incorporated into the same layer.
A dissolution suppresser having no decomposability may be used in combination. Preferable examples thereof include sulfonic acid esters, phosphoric acid esters, aromatic carboxylic acid esters, aromatic disulfones, carboxylic acid anhydrides, aromatic ketones, aromatic aldehydes, aromatic amines, and aromatic ethers, details of which are described in JP-A No. 10-268512; acidic color-developable dyes which have a lactone skeleton, an N,N-diarylamide skeleton or a diarylmethylimino skeleton and also function as a coloring agent, details of which are described in JP-A No. 11-190903; and nonionic surfactants described, details of which are described in JP-A No. 2000-105454.
In order to enhance sensitivity, the photosensitive composition may also contain a cyclic acid anhydride, a phenolic compound, or an organic acid.
Examples of cyclic acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 3,6-endooxy-Δ4-tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, α-phenylmaleic anhydride, succinic anhydride, and pyromellitic anhydride which are described in U.S. Patent No. 4,115,128.
Examples of phenolic compound include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4'-trihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 4-hydroxybenzophenone, 4,4',4"-trihydroxytriphenylmethane, 4,4',3",4"-tetrahydroxy-3,5,3',5'-tetramethyltriphenylmethane.
Examples of the organic acid include sulfonic acids, sulfonic acids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylic acids, which are described in JP-A No. 60-88942 or 2-96755. Specific examples thereof include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid, and ascorbic acid.
When the cyclic acid anhydride, the phenol or the organic acid is added to a recording layer of a planographic printing plate precursor, the ratio thereof in the recording layer is preferably from 0.05 to 20%, more preferably from 0.1 to 15%, and even more preferably from 0.1 to 10% by mass.
Besides the above-mentioned agents, epoxy compounds, vinyl ethers, and phenol compounds having hydroxymethyl groups as described in Japanese Patent Application Laid-Open No. 8-276558, phenol compounds having alkoxymethyl group and crosslinking compounds having the function of inhibiting dissolution in alkaline solution as described in Japanese Patent Application Laid-Open No. 11-160860 proposed by inventors may be added.
When the recording layer according to the invention is formed, in order to enhance stability in processes which are affected by developing conditions, the following can be added to the coating solution therefor: nonionic surfactants as described in JP-A Nos. 62-251740 and 3-208514; amphoteric surfactants as described in JP-A Nos. 59-121044 and 4-13149; siloxane compounds as described in EP No. 950517; and copolymers made from a fluorine-containing monomer as described in JP-A No. 11-288093.
Specific examples of nonionic surfactants include sorbitan tristearate, sorbitan monopalmitate, sorbitan trioleate, monoglyceride stearate, and polyoxyethylene nonyl phenyl ether. Specific examples of amphoteric surfactants include alkyldi(aminoethyl)glycine, alkylpolyaminoethylglycine hydrochloride, 2-alkyl-N-carboxyethyl-N-hydroxyethylimidazolinium betaine and N-tetradecyl-N,N'-betaine type surfactants (trade name: "Amolgen K", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).
The siloxane compounds are preferably block copolymers made from dimethylsiloxane and polyalkylene oxide. Specific examples thereof include polyalkylene oxide modified silicones (trade names: DBE-224, DBE-621, DBE-712, DBE-732, and DBE-534, manufactured by Chisso Corporation; trade name: Tego Glide 100, manufactured by Tego Co., Ltd.).
The content of the nonionic surfactant and/or the amphoteric surfactant in the photosensitive composition is preferably from 0.05 to 15% by mass, and more preferably from 0.1 to 5% by mass.
To the photosensitive composition of the invention may be added a printing-out agent for obtaining a visible image immediately after the photosensitive composition of the invention has been heated by exposure to light, or a dye or pigment as an image coloring agent.
A typical example of a printing-out agent is a combination of a compound which is heated by exposure to light, thereby emitting an acid (an optically acid-generating agent), and an organic dye which can form salts (salt formable organic dye).
Specific examples thereof include combinations of an o-naphthoquinonediazide-4-sulfonic acid halogenide with a salt-formable organic dye, described in JP-A Nos. 50-36209 and 53-8128; and combinations of a trihalomethyl compound with a salt-formable organic dye, described in each of JP-A Nos. 53-36223, 54-74728, 60-3626, 61-143748, 61-151644 and 63-58440.
The trihalomethyl compound is classified into an oxazol compound or a triazine compound. Both of the compounds provide excellent in stability over the passage of time and produce a vivid printed-out image.
As the image coloring agent, a dye different from the above-mentioned salt-formable organic dye may be used. Preferable examples of such a dye, and of the salt-formable organic dye, include oil-soluble dyes and basic dyes.
Specific examples thereof include Oil yellow #101, Oil Yellow #103, Oil Pink #312, Oil Green BG, Oil Blue BOS, Oil Blue #603, Oil Black BY, Oil Black BS, and Oil Black T-505 (each of which is manufactured by Orient Chemical Industries Ltd.); Victoria Pure Blue, Crystal Violet (CI42555), Methyl Violet (CI42535), Ethyl Violet, Rhodamine B (CI145170B), Malachite Green (CI42000), and Methylene Blue (CI52015).
Dyes described in JP-A No. 62-293247 are particularly preferable. These dyes may be added to the photosensitive composition at a ratio of 0.01 to 10% by mass, and preferably 0.1 to 3% by mass, relative to the total solid contents therein.
Whenever necessary, a plasticizer may be added to the photosensitive composition of the invention to give flexibility to a coating film made from the composition. Examples of the plasticizer include oligomers and polymers of butyl phthalyl, polyethylene glycol, tributyl citrate, diethyl phthalate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tricresyl phosphate, tributyl phosphate, trioctyl phosphate, tetrahydrofurfuryl olete, and acrylic acid and methacrylic acid.

(Layer structure of a recording layer)

The recording layer of a planographic printing plate precursor according to the present invention may be either a single-layered, phase-separated composite, or multi-layered composite layer.
Examples of applicable single-layered recording layers include the configurations of the photosensitive layer described in JP-A No. 7-285275, and WO 97/39894. Examples of applicable phase-separated composite recording layers include the configuration of the photosensitive layers described in JP-A No. 11-44956. In addition, examples of the multi-layered composite recording layers include the configurations of the photosensitive layer described in JP-ANo. 11-218914, US PatentNos. 6352812B1, 6352811B1, 6358669B1, and 6534238B1, and EP Patent No. 864420B1. However, the configuration of the recording layer according to the present invention is not limited thereto.
Further, when used as a recording layer, the multi-layered composite recording layer preferably contains the specific sulfonium salt according to the present invention in the uppermost layer for more effective manifestation of advantageous effects.

(Method of forming a recording layer)

The recording layer according to the present invention can be formed by preparing a recording layer-coating solution by dissolving the components for the recording layer in a solvent, and applying and drying the coating solution on a suitable support. An undercoat layer and other coat layers described below may also be formed as needed in a similar manner.
Examples of the solvents to be used include, but are not limited to, ethylene dichloride, cyclohexanone, methylethylketone, methanol, ethanol, propanol, ethylene glycol monomethylether, 1-methoxy-2-propanol, 2-methoxyethyl acetate, 1-methoxy-2-propyl acetate, dimethoxyethane, methyl lactate, ethyl lactate, N,N-dimethylacetamide, N,N-dimethylformamide, tetramethylurea, N- methylpyrrolidone, dimethylsulfoxide, sulfolane, γ-butylolactone, toluene and the like. These solvents are used alone or as a mixture.
The concentration of the components (total solid portion including additives) in solvent is preferably 1 to 50 wt %.
The amount coated (as solid matter) on the support after coating and drying may vary according to the application, but is generally preferably 0.5 to 5.0 g/m², and more preferably 0.6 to 2.0 g/m², as the coating amount after drying.
When a multi-layered composite recording layer having two recording layers is used, the coating amount of the lower layer is preferably 0.1 to 5.0 g/m² and more preferably 0.2 to 3.0 g/m², and that of the upper layer (top layer) is preferably 0.01 to 5.0 g/m², and more preferably 0.05 to 2.0 g/m².
Various methods may be used for applying the recording layer coating solution. Examples thereof include bar coater coating, spin coating, spray coating, curtain coating, dip coating, air knife coating, blade coating, roll coating, and the like. As the coating amount decreases, the apparent sensitivity increases, but the film properties of the photosensitive layer deteriorates.
A surfactant, for example, the fluorochemical surfactant described in JP-A No. 62-170950 may be added to the coating solution for the recording layer according to the present invention, for improvement of coating efficiency. The preferable addition amount is 0.01 to 1 wt %, and more preferably 0.05 to 0.5 wt %, with respect to the total solids in the recording layer-coating solution.

[Support]

The support used in the planographic printing plate precursor is a plate having dimensional stability. A plate satisfying required physical properties such as strength and flexibility can be used without any restriction. Examples thereof include paper, plastic (such as polyethylene, polypropylene or polystyrene)-laminated papers, metal plates (such as aluminum, zinc and copper plates), plastic films (such as cellulose biacetate, cellulose triacetate, cellulose propionate, cellulose lactate, cellulose acetate lactate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetate films), and papers or plastic films on which, as described above, a metal is laminated or vapor-deposited.
The support is preferably a polyester film or an aluminum plate, and more preferably an aluminum plate, since an aluminum plate is superior in terms of dimensional stability and is also relatively inexpensive.
Preferable examples of the aluminum plate include a pure aluminum plate and alloy plates made of aluminum as a main component with a very small amount of other elements.
A plastic film on which aluminum is laminated or vapor-deposited may also be used.
Examples of other elements contained in the aluminum alloys include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content by percentage of different elements in the alloy is at most 10% by mass. A particularly preferable aluminum plate in the invention is a pure aluminum plate; however, since from the viewpoint of refining a completely pure aluminum cannot be easily produced, a very small amount of other elements may also be contained in the plate.
The aluminum plate used as the support is not specified in terms of the composition thereof. Thus, aluminum plates which are conventionally known can be appropriately used. The thickness of the aluminum plate used in the invention is from about 0.1 to 0.6 mm, preferably from 0.15 to 0.4 mm, and more preferably from 0.2 to 0.3 mm.
If necessary, prior to the surface-roughening treatment, the aluminum plate may optionally be subjected to degreasing treatment, in order to remove rolling oil or the like on the surface, with a surfactant, an organic solvent, an aqueous alkaline solution or the like.
The surface-roughening treatment of the aluminum surface can be performed by various methods such as a mechanical surface-roughening method, a method of dissolving and roughening the surface electrochemically, and a method of dissolving the surface selectively in a chemical manner.
Mechanical surface-roughening methods which can be used may be known methods, such as a ball polishing method, a brush polishing method, a blast polishing method or a buff polishing method. An electrochemical surface-roughening method may be a method of performing surface-roughening in an electrolyte of hydrochloric acid or nitric acid, by use of an alternating current or a direct current. As disclosed in JP-A No. 54-63902, a combination of the two kinds of methods may be used.
An aluminum plate whose surface is roughened as described above is if necessary subjected to alkali-etching treatment and neutralizing treatment. Thereafter, an anodizing treatment is optionally applied in order to improve the water holding capacity and wear resistance of the surface.
The electrolyte used in the anodizing treatment of the aluminum plate is any one selected from various electrolytes which can form a porous oxide film. Among which in general use are electrolytes of sulfuric acid, phosphoric acid, oxalic acid, chromic acid, or a mixed acid thereof. The concentration of the electrolyte may be appropriately decided depending on the kind of electrolyte selected.
Treatment conditions for anodization cannot be specified as a general rule since conditions vary depending on the electrolyte used; however, the following range of conditions are generally suitable: an electrolyte concentration of 1 to 80% by mass, a solution temperature of 5 to 70°C, a current density of 5 to 60 A/dm², a voltage of 1 to 100 V, and an electrolyzing time of 10 seconds to 5 minutes. If the amount of anodic oxide film is less than 1.0 g/m², printing resistance is inadequate or non-image portions of the planographic printing plate tend to become easily damaged and the so-called "blemish stains", resulting from ink adhering to damaged portions at the time of printing, are easily generated.
After the anodizing treatment, the surface of the aluminum is if necessary subjected to treatment for obtaining hydrophilicity. This securance of hydrophilicity treatment may be an alkali metal silicate (for example, an aqueous sodium silicate solution) method, as disclosed in U.S. Patent Nos. 2,714,066, 3,181,461, 3,280,734, and 3,902,734. In this method, the support is subjected to an immersing treatment or an electrolyzing treatment with an aqueous sodium silicate solution.
In addition, the following methods may also be used: a method of treating the support with potassium fluorozirconate, as disclosed in JP-B No. 36-22063, or with polyvinyl phosphonic acid, as disclosed in U.S. Patent Nos. 3,276,868, 4,153,461, and 4,689,272.

(Undercoat layer)

The planographic printing plate precursor according to the present invention is a plate having a recording layer as described above provided on a support, and an undercoat layer may be formed as needed between the support and the recording layer.
When formed, the undercoat layer between the support and the recording layer functions as a heat-insulating layer, inhibiting diffusion of the heat generated by exposure to an infrared laser to the support and allowing more efficient use of an infrared laser, and thus, is advantageous in improving sensitivity. When forming the undercoat layer, the recording layer according to the invention is positioned on the exposure face or in the vicinity thereof, and thus significantly retains its sensitivity to an infrared laser.
Also in the unexposed areas, the recording layer, which is resistant to penetration of the alkaline developer, functions as a protective layer for the undercoat layer, improving development stability, forming an image having superior discrimination, and ensuring image stability over time.
The undercoat layer is a layer containing an alkali-soluble polymer as its principal component and is extremely soluble in the developer. If the undercoat layer is formed close to the support, the exposed area, where the components in the photosensitive layer that becomes more soluble by exposure, is dissolved or dispersed in the developer more readily without generation of undissolved film, for example, when a less active developer is used, which seems to be effective for improving developing efficiency. For that reason, the undercoat layer is thought to be useful.
Various organic compounds may be used as the components for the undercoat layer, and examples thereof include amino group-containing phosphonic acids that may be substituted such as carboxymethylcellulose, dextrin, gum arabic, and 2-aminoethylphosphonic acid; organic phosphonic acid that may be substituted such as phenylphosphonic acid, naphthylphosphonic acid, alkylphosphonic acids, glycerophosphonic acid, methylenediphosphonic acid and ethylenediphosphonic acid; organic phosphoric acids that may be substituted such as phenylphosphoric acid, naphthylphosphoric acid, alkylphosphoric acid and glycerophosphoric acid; organic phosphinic acids such as phenylphosphinic acid, naphthylphosphinic acid, alkylphosphinic acid and glycerophosphinic acid; amino acids such as glycine and β-alanine; hydroxy group-containing amine hydrochloride salts such as triethanolamine hydrochloride salt; and the like. These compounds may be used in combinations of two or more.
In particular, an undercoat layer containing at least one compound selected from the group consisting of organic polymer compounds having the structural unit represented by the following Formula is also preferable.
In the Formula above, R¹¹ represents a hydrogen or halogen atom or an alkyl group; R¹² and R¹³ each independently represent a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, -OR¹⁴, -COOR¹⁵, -CONHR¹⁶, -COR¹⁷ or -CN, or R¹² and R¹³ may bind to each other forming a ring; R¹⁴ to R¹⁷ each independently represent an alkyl or aryl group; X represents a hydrogen or metal atom, or NR¹⁸R¹⁹R²⁰R²¹; R¹⁸ to R²¹ each independently represent a hydrogen atom, an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group, or R¹⁸ and R¹⁹ may bind to each other forming a ring; and m represents an integer of 1 to 3.
An example of a suitable undercoat layer component for the planographic printing plate precursor according to the invention is a polymer compound having an acid group-containing a structural component and an onium group-containing component described in JP-ANo. 2000-241962. Specifically, it is a copolymer of an acid group-containing monomer and an onium group-containing monomer. The acid group is preferably an acid group having an acid dissociation constant (pKa) of 7 or more, more preferably -COOH, -SO₃H, -OSO₃H, -PO₃H₂, -OPO₃H₂, -CONHSO₂-, or -SO₂NHSO₂-, and particularly preferably -COOH. Specific examples of the acid group-containing monomers include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, itaconic acid, maleic acid, maleic anhydride, styrene derivatives having the acid group above, and the like. The onium salt is preferably an onium group having an atom in groups V and VI of the Periodic Table, more preferably an onium salt of a nitrogen, phosphorus or sulfur atom, and particularly preferably an onium salt of a nitrogen atom. Specific examples of the onium salt-containing monomers include methacrylates and methacrylamides having an ammonium group on the side chain, and styrenes having an onium group-containing substituent such as those having a quaternary ammonium group.
In addition, the compounds described in JP-A Nos. 2000-108538, 2002-257484, and 2003-78699, and others may be used as needed.
Such an undercoat layer can be formed, for example, according to the following methods: a method of dissolving the organic compounds in an organic solvent or a mixed solvent of water, methanol, ethanol, methylethylketone, or the like, and applying and drying the solution on an aluminum plate (support); and a method of dissolving the organic compounds in an organic solvent or a mixed solvent of water, methanol, ethanol, methylethylketone, or the like, allowing an aluminum plate (support) to absorb the solution by immersion in the solution, and washing the plate with water or the like and drying it.
In the former method, it is possible to apply the solution of the organic compound at a concentration of 0.005 to 10 wt % by various methods. Alternatively, in the latter method, the concentration of the solution is 0.01 to 20 wt %, preferably 0.05 to 5 wt %; the immersion temperature is 20 to 90°C, preferably 25 to 50°C; and the immersion period is 0.1 second to 20 minutes, preferably 2 seconds to 1 minutes. The solution used may be adjusted to a pH in the range of 1 to 12 by addition of a basic substance such as ammonia, triethylamine, or potassium hydroxide, or an acidic substance such as hydrochloric acid or phosphoric acid. A yellow dye may also be added, for improvement of tone reproducibility in the image-recording material.
The amount of the undercoat layer coated is suitably 2 to 200 mg/m², and preferably 5 to 100 mg/m², from the viewpoint of printing durability.

(Plate-making process for planographic printing plate precursor)

(Exposure)

An image is formed thermally on the planographic printing plate precursor according to the present invention. Specifically, direct image recording with a thermal recording head or the like, scanning exposure with an infrared laser, high-illumination flash exposure with xenon discharge lamp or the like, infrared lamp exposure, or the like is used for this image formation, but exposure to a high-output infrared solid laser emitting a light at a wavelength of 700 to 1,200 nm, such as from an infrared light-emitting semiconductor laser or YAG laser is suitable.
The laser output is preferably 100 mW or more, and it is preferable to use a multi-beam laser device to shorten the exposure period. The exposure period per pixel is preferably 20 µsec or less, and the irradiation energy applied onto the recording material is preferably 10 to 500 mJ/cm².

[Developing treatment]

The developer which may be applied to the developing treatment of the planographic printing plate precursor of the invention is a developer having a pH range from 9.0 to 14.0 and preferably a pH range from 12.0 to 13.5. As the developer (hereinafter this term will represent a developer including a replenisher), a conventionally known aqueous alkali solution may be used.
Examples of the alkali agent include inorganic alkali salts such as sodium silicate, potassium silicate, trisodium phosphate, tripotassium phosphate, triammonium phosphate, disodium hydrogenphosphate, dipotassium hydrogenphosphate, diammonium hydrogenphosphate, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, ammonium hydrogen carbonate, sodium borate, potassium borate, ammonium borate, sodium hydroxide, ammonium hydroxide, potassium hydroxide and lithium hydroxide; and organic alkali agents such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, n-butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, ethyleneimine, ethylenediamine, and pyridine.
These alkali agents may be used alone or in combinations of two or more thereof.
Among the above aqueous alkali solutions, one developer which exerts the effect of the invention is an aqueous solution of a pH 12 or higher so-called "silicate developer" containing alkali silicate as a base, or containing alkali silicate obtained by mixing a base with a silicon compound, and the other more preferable developer is a so-called "non-silicate developer" which does not contain alkali silicate, and contains a non-reducing sugar (organic compound having buffering action) and a base.
In the former, developability of an aqueous solution of alkali metal silicate can be regulated by a ratio (generally expressed by mole ratio of [SiO₂]/[M₂O]) of silicon oxide SiO₂ and alkali metal oxide M₂O. For example, an aqueous solution of sodium silicate in which a mole ratio of SiO₂/Na₂O is 1.0 to 1.5 (that is,[SiO₂]/[Na₂O] is 1.0 to 1.5), and a content of SiO₂ is 1 to 4% by mass as disclosed in JP-A No. 54-62004, and an aqueous solution of alkali metal silicate in which [SiO₂]/[M] is 0.5 to 0.75 (that is, [SiO₂]/[M₂O] is 1.0 to 1.5), a concentration of SiO₂ is 1 to 4% by mass, and the developer contains at least 20% potassium using gram atom of a total alkali metal present therein as a standard, as described in Japanese Patent Application Publication (JP-B) No. 57-7427are preferably used.
A so-called "non-silicate developer" containing no alkali silicate and containing non-reducing sugar and a base is also preferable for application to developing of a planographic printing plate precursor of the invention. When a planographic printing plate precursor is developing-treated using this developer, a surface of a recording layer is not deteriorated, and inking property of a recording layer can be maintained in the good state. Further, planographic printing plate precursors generally have a narrower development latitude and a greater fluctuation in the width of image lines caused by fluctuation in the pH of the developer, and thus, use of a non-silicate developer, which contains a nonreducing sugar that has a buffering action on the fluctuation of pH, is more advantageous than the use of a developer containing a silicate. Further, the nonreducing sugar is less likely to contaminate the conductivity sensor, pH sensor, or the likeused for controlling the solution activity than silicates, and the use of the non-silicate developer is advantageous from that point too. It is also effective in significantly improving discrimination. Presumably, this is because the difference between the exposed and unexposed areas is enhanced by a mild contact (penetration) of the developer, which is important in the present invention.
The aforementioned non-reducing sugar is a sugar having no free aldehyde group or ketone group, and not exhibiting reducing property, and is classified into a trehalose-type oligosaccharide in which reducing groups are bound, a glycoside in which a reducing group of a sugar and a non-sugar are bound, and sugar alcohol obtained by hydrogenating sugars to reduce them. Any of these can be suitable used. In the present invention, the non-reducing sugar disclosed in JP-A 8-305039 Laid-Open, for example, can be suitably used.
Examples of the trehalose type oligosaccharides include saccharose and trehalose. Examples of the glucosides include alkylglucosides, phenolglucosides, and mustard seed oil glucoside. Examples of the sugar alcohols include D, L-arabite, ribitol, xylitol, D, L-sorbitos, D, L-mannitol, D, L-iditol, D, L-talitol, dulcitol, and allodulcitol. Furthermore, maltitol, obtained by hydrogenating a disaccharide, and a reductant obtained by hydrogenating an oligosaccharide (i.e., reduced starch syrup) are preferable. Of these examples, sugar alcohol and saccharose are more preferable. D-sorbitol, saccharose, and reduced starch syrup are even more preferable since they have buffer effect within an appropriate pH range and are inexpensive.
These nonreducing sugars may be used alone or in combinations of two or more. The content of the nonreducing sugar in the non-silicate developer is preferably 0.1 to 30 wt %, and more preferably 1 to 20 wt %, from the viewpoints of availability and promoting higher concentration.
The base combined with the nonreducing sugar(s) may be an alkali agent that has been known so far. Examples thereof include inorganic alkali agents such as sodium hydroxide, potassium hydroxide, lithium hydroxide, trisodium phosphate, tripotassium phosphate, triammonium phosphate, disodium phosphate, dipotassium phosphate, diammonium phosphate, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, ammonium hydrogencarbonate, sodium borate, potassium borate and ammonium borate; and organic alkali agents such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, n-butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, ethyleneimine, ethylenediamine, and pyridine.
The bases may be used alone or in combinations of two or more. Among these bases, sodium hydroxide and potassium hydroxide are preferable. In the present invention, a developer containing an alkali-metal salt of a nonreducing sugar as the principal component may be used as the non-silicate developer, replacing the combined use of a nonreducing sugar and a base.
Alternatively, an alkaline buffer solution containing a weak acid other than the nonreducing sugar and a strong base may be used in the non-silicate developer. The weak acid preferably has a dissociation constant (pKa) of 10.0 to 13.2, and is selected from the weak acids described in "Ionization Constants of Organic Acids in Aqueous Solution" published by Pergmon Press, and others.
Specifically suitable examples thereof include alcohols such as 2,2,3,3-tetrafluoropropanol-1 and trifluoroethanol, trichloroethanol; aldehydes such as pyridine-2-aldehyde and pyridine-4-aldehyde; phenolic hydroxyl group-containing compounds such as salicylic acid, 3-hydroxy-2-naphthoic acid, catechol, gallic acid, sulfosalicylic acid, 3,4-dihydroxysulfonic acid, 3,4-dihydroxybenzoic acid, hydroquinone, pyrogallol, o-, m-, and p-cresols, and resorcinol; oximes such as acetoxime, 2-hydroxybenzaldehyde oxime, dimethyl glyoxime, ethanediamide dioxime, and acetophenone oxime; nucleic acid-derived substances such as adenosine, inosine, guanine, cytosine, hypoxanthine, and xanthine; diethylaminomethylphosphonic acid, benzimidazole, barbituric acid, and the like.
Various surfactants and organic solvents may be added as needed to the developer and replenisher, for improvement or control of developing efficiency, dispersion of development scum, or improvement of the ink compatibility of the image region of a printing plate. The surfactant is preferably an anionic, cationic, nonionic or amphoteric surfactant. In addition, a reducer such as hydroquinone, resorcin, sodium or potassium salt of an inorganic acid such as sulfurous acid or bisulfurous acid as well as an organic carboxylic acid, an antifoaming agent, a water softener, or the like may be added to the developer and replenisher as needed.
The planographic printing plate developed with the developer and replenisher is then post-treated with a rinse solution containing washing water, a surfactant, and the like and with a desensitizing solution containing gum arabic or a starch derivative. These treatments may be used in combination as the post-treatment.
When the PS plate is developed in an automatic developing machine, it is known that it is possible to process a great number of PS plates without exchanging the developer for an extended period of time by adding to the developer an aqueous solution (replenisher) having an alkali strength higher than that of the developer. This replenishing method is also favorable applied to the present invention. Various surfactants and organic solvents may be added, if needed, to the developing and replenishers for the purpose of increasing or decreasing the printing efficiency, dispersing development scum, and improving the ink compatibility on the image portions of the printing plate.
The surfactant is preferably an anionic, cationic, nonionic or amphoteric surfactant. In addition, hydroquinone, resorcin, a reducing agent such as sodium or potassium salt of an inorganic acid such as sodium or potassium sulfite or bisulfite, an organic carboxylic acid, an antifoam agent, and/or a water softener may be added to the developing and replenishers if needed.
The printing plate, after processing using the developing and replenishers, is then post-treated with washing water, a rinsing solution containing surfactants and the like, and/or a desensitizing solution containing gum arabic or a starch derivative. These treatments may be used in various combinations as the post-treatment of the printing plate precursor according to the invention.
In recent years, automatic developing machines for the printing plates have become widely used for the purpose of streamlining and standardizing the plate-making processes in the printing-plate and printing industries. These automatic developing machines generally consist of a developing unit and a post-treatment unit, a unit for conveying printing plates and various stock solution tanks, and units for spraying solutions, wherein the exposed printing plates are developed while they are conveyed horizontally and sprayed via spray nozzles with various solutions pumped out of the stock tanks. Also known is another kind of automatic developing system, wherein the printing plates are conveyed as they are immersed in treatment solution tanks filled with treating solutions one after another by means of the submerged guide rolls or the like. In this type of automatic processing, the plates are processed in the solutions, which are periodically replenished with replenisher according to the number of plates processed and the operating time. In addition, a method of essentially using only unused treating solutions, i.e., a single-round method, may also be used.
In the present invention, if the planographic printing plate obtained after the steps of image exposure, development, water washing and/or rinsing, and/or gumming has unnecessary image portions (e.g., film edge spots on the original image film and the like), elimination of the unnecessary image portions is performed. As the elimination method, although the method described for example in Japanese Patent Application Publication (JP-B) No. 2-13293 wherein an image-elimination solution is applied onto the undesirable image portions and the resulting plate is then washed with water after being left for a certain period; the method described in JP-ANo. 59-174842, wherein the undesirable image portions are eliminated by irradiation of an activated light through an optical fiber and then the resulting plate is developed, may be also used.
The developed planographic printing plate thus obtained may, if desired, be coated with a desensitizing gum before it is sent to the printing process; or the plate is additionally subjected to a baking treatment a planographic printing plate higher in printing durability is desired.
If the planographic printing plate is to be subjected to a baking treatment, the plate is preferably treated before the baking treatments with an affinitizing solution described in JP-B No. 61-2518 JP-B No. 55-28062, JP-A No. 62-31859, or JP-A No. 61-159655.
The methods include application of the affinitizing solution onto planographic printing plates with sponges or cotton moistened therewith, application by immersing the printing plate into a bath filled with the affinitizing solution, and application by an automatic coater. Additionally, adjustment of the coating amount for uniformity by using a squeezee or a squeezee roller after application of the affinitizing solution provides more favorable results.
The suitable coating amount of the affinitizing solution is generally 0.03 to 0.8 g/m² (as dry weight). The planographic printing plate applied with the affinitizing solution is then dried as needed and heated at high temperature in a burning processor (e.g., Burning Processor BP-1300 available from Fuji Photo Film Co.). The temperature and the period of heating vary according to the kind of the components constituting the images, but are preferably in the range of 180 to 300°C for 1 to 20 minutes.
The planographic printing plate that has been subjected to a baking treatment may then be subjected, if needed, to treatments commonly practiced in the art such as water washing and gumming, but if a surface treatment solution containing a water-soluble polymer compound or the like is used, the so-called desensitizing treatment such as gumming or the like may be eliminated. The planographic printing plate obtained after these treatments is then mounted on an offset printing machine or the like, and it is used for printing numerous sheets of paper.

EXAMPLES

Hereinafter, the present invention will be described with reference to Examples, but it should be understood that the scope of the invention is not restricted to these Examples.

[Examples 1 to 3 and Comparative Example 1]

(Preparation of support)

A support was prepared in the steps below using a JIS-A-1050 aluminum plate having a thickness of 0.3 mm.

(a) Mechanical surface roughening treatment

While a suspension containing a polishing agent (silica sand) with a specific gravity of 1.12 and water was supplied as a polishing slurry to the a surface of each aluminum sheet, the and mechanical surface roughening was carried out by rotating roller type nylon brushes. The average particle size of the polishing agent was 8 µm and the maximum particle size was 50 µm. The material of the nylon brushes was 6-10 nylon and hair length and hair diameters were 45 mm and 0.3 mm, respectively. The nylon brushes were produced by implanting the hairs densely in holes formed in stainless cylinders with a diameter of φ300 mm. Three rotating brushes were used. Two supporting rollers (φ200 mm diameter) were placed in lower parts of the brushes with a separation distance of 300 mm. The brush rollers were pushed until the load of the driving motor for rotating the brushes was increased by 7 kW or more from the load before the brush rollers being pushed against the aluminum sheet. The rotation direction of the brushes was the same as the moving direction of the aluminum sheet. The rotation speed of the brushes was 200 rpm.

(b) Alkaline etching treatment

Etching treatment was carried out by spraying an aqueous NaOH solution (NaOH concentration being 26% by weight and also containing an aluminum ion 6.5% by weight) to the aluminum plate at 70°C, to dissolve the aluminum sheet by an amount of 6 g/m². After that, the aluminum sheet was washed with water by spraying.

(c) Desmutting treatment

The aluminum plate was subjected to a desmutting treatment by spraying an aqueous solution containing 1 wt % nitric acid (additionally containing 0.5 wt % aluminum ion) at a temperature of 30°C, and then washed by spraying water. The aqueous nitric acid solutions used for desmutting was the wastewater obtained in the electrochemical surface-roughening step wherein the aluminum plates were electrochemically scratched in an aqueous nitric acid solution using an alternating electrical current.

(d) Electrochemical surface-roughening treatment

The aluminum plates were further scratched electrochemically by continuous use of a 60-Hz alternating current. The electrolyte used was an aqueous solution containing 10.5 g/L nitric acid (containing additionally 5 g/L of aluminum ion) at a temperature of 50°C. The electrochemical surface roughening was performed using a trapezoidal alternating current having a trapezoidal waveform with a transition period (TP) from zero to peak currency of 0.8 msec and a duty ratio of 1:1 with a carbon electrode as the counter electrode. Ferrite was used as the auxiliary anode. The electrolytic bath used was that of a radial cell type.
The electric current density was 30 A/dm² at peak value, and when an aluminum plate is used as the anode, the total amount of electric current applied was 220 C/dm². 5% of the current from the power source was divided and sent to the auxiliary electrode.
Subsequently, the aluminum plates were washed by a spray using well water.

(e) Alkaline etching treatment

The aluminum plate was sprayed with a solution containing 26 wt % caustic soda and 6.5 wt % aluminum ion at 32°C to melt the aluminum plate at 0.20 g/m² to remove the smut mainly containing aluminum hydroxide, which was generated during the previous electrochemical surface-roughening treatment using an alternating electrical current, and to polish the edge portion by dissolving the edge portions of the pits generated. Subsequently, the aluminum plates were washed by a spray using well water.

(f) Desmutting treatment

The aluminum plate was desmutted by spraying an aqueous solution containing 15 wt % nitric acid (containing additionally 4.5 wt % aluminum ion) at a temperature of 30°C, and then washed by a spray using well water. The wastewater obtained in the electrochemical surface-roughening step, wherein the aluminum plates were electrochemically scratched in an aqueous nitric acid solution using an alternating electrical current, was used as the aqueous nitric acid solution for desmutting.

(g) Electrochemical surface roughening treatment

Electrochemical surface roughening treatment was carried out continuously by using 60 Hz AC voltage. The electrolytic solution used in this step was an aqueous solution of hydrochloric acid (the concentration thereof being 7.5 g/L and also containing aluminum ion by 5 g/L) at 35°C. The AC power waveform had a trapezoidal rectangular waveform and a carbon electrode was used as an opposed electrode, to effect the electrochemical surface roughening treatment. Ferrite was used as an auxiliary anode. A radial cell type electrolytic bath was used.
The current density was 25 A/dm² at the peak value of the current and the total electricity quantity was 50 C/dm² when the aluminum sheet was used as an anode.
After that, the resulting aluminum sheet was washed with a water spray.

(h) Alkali etching treatment

Etching treatment was carried out at 32°C for the aluminum sheet by spraying a solution containing 26 wt. % sodium hydroxide and 6.5 wt. % aluminum ion thereon, to dissolve 0.10 g/m² of the aluminum sheet, so as to remove the smut, of which main component is mainly aluminum hydroxide produced during the electrochemical roughening treatment of the surface by using alternating current in the prior step. Further, the edge portions of the pits formed were dissolved to make the edge portions smooth. After that, the aluminum sheet was washed by spraying water spray.

(i) Desmut treatment

Desmut treatment was is carried out by spraying with an aqueous solution of 25% by weight sulfuric acid (containing aluminum ion 0.5% by weight) at 60°C and then washing the resulting aluminum sheet was washed by spraying water spray.

(j) Anodization treatment

As an electrolytic solution, sulfuric acid was used. The electrolytic solution contained sulfuric acid by 170 g/L (and contained aluminum ion 0.5% by weight). The temperature of the electrolytic solution was 43°C. After Then the aluminum sheet was washed with a water by spraying.
The electric current density was about 30 A/dm². Final oxide film thickness was about 2.7 g/m².

Each of the foregoing (a) through (j) steps was sequentially carried out, and the amount of etching in the step (e) was controlled so as to be 3.4 g/m², such that support A was prepared.

Support B was prepared by sequentially carrying out the aforementioned steps (a) to (j) but omitting the steps (g), (h) and (i).

Respective steps were successively performed except that steps (a), (g), (h) and (i) among the aforementioned steps were omitted, a support was prepared.

Respective steps were successively performed except that steps (a), (d), (e) and (f) among the aforementioned steps were omitted, a sum of an electricity amount in a (g) step was adjusted to be 450C/dm² to prepare a support.
Supports A, B, C and D as obtained above were subsequently subjected to the following hydrophilization treatment and undercoating treatment.

(k) Alkali metal silicate salt treatment

An aluminum support obtained by anode oxidation treatment was immersed in a treatment bath containing 1 mass % aqueous solution of No. 3 sodium silicate at a temperature of 30°C for 10 seconds, thereby effecting alkali metal silicate salt treatment (silicate treatment). Thereafter, water washing by spraying using well water was performed. Thereupon, a silicate adhering amount was 3.6 mg/m².

(Undercoating treatment)

An undercoating solution having the following composition was coated on the aluminum support thus obtained after alkali metal silicate salt treatment, and was dried at 80°C for 15 seconds. A covering amount after drying was 15 mg/m².

(Undercoat solution)

a polymer compound (Polymer 1 or Polymer II shown below) 0.3 g
methanol 100 g
water 1 g

(Formation of a recording layer)

Then, a coating solution for undercoat layer A having the composition described below was applied, using a wire bar, onto the support plate having the undercoat layer obtained as described above (the types of the supports are shown in Table 1 below) and dried in a drying oven at 140°C for 50 seconds to obtain a coating amount of 0.85 g/m².
Then, a top-layer coating solution B having the composition described below was applied, using a wire bar, onto the supporting plate having the undercoat layer obtained as described above. After application, the supporting plate was dried at 140°C for 60 seconds to produce the positive planographic printing plate precursor of Examples 1 to 3 and Comparative Example 1 having a total coating amount of 1.07 g/m².

N-(4-Aminosulfonylphenyl)methacrylamide/ 2.13 g acrylonitrile/methyl methacrylate (molar ratio: 36:34:30, weight-average molecular weight: 50,000)
Cyanine dye P (having the following structure) 0.134 g
Bis-p-hydroxyphenyl sulfone 0.126 g
Tetrahydrophthalic anhydride 0.19 g
p-Toluenesulfonic acid 0.008 g
2-Methoxy-4- 0.032 g (N-phenylamino)benzene diazonium-hexafluorophosphate
Ethyl violet 6-naphthalenesulfonic acid 0.078 g
Fluorochemical surfactant 0.023 g
(Tradename: Magafac F-780; manufactured by Dainippon Ink and Chemicals, Inc.)
γ-Butylolactone 13.16 g
Methylethylketone 25.39 g
1-Methoxy-2-propanol 12.95 g

Specific sulfonium salt or comparative sulfonium salt 0.08 g
shown in the Table 1 below
m-Cresol/p-cresol novolak resin 0.341 g
(molar ratio: 60:40, weight, average molecular weight: 5,000)
Cyanine dye P (having the structure above) 0.019 g
Fluorochemical surfactant 0.004 g
(Tradename: Magafac F-780; manufactured by Dainippon Ink and Chemicals, Inc.)
Fluorochemical surfactant 0.001 g
(Tradename: Magafac F-781; manufactured by Dainippon Ink and Chemicals, Inc.)
Methylethylketone 2.63 g
1-Methoxy-2-propanol 5.27 g

Cyanine dye P

[Examples 4 to 6 and Comparative Example 2]

A recording layer coating solution C having the composition described below was applied, using a wire bar, onto the support plate with an undercoat layer (the types of supports are shown in Table 1 below) obtained in a manner similar to Examples 1 to 3. After application of coating solution C, the supporting plate was dried at 140°C for 60 seconds to produce the positive planographic printing plate precursors of Examples 4 to 6 and Comparative Example 2 having a total coating amount of 1.80 g/m².

Specific sulfonium salt or comparative sulfonium salt 0.100 g shown in the Table 1 below
N-(4-Aminosulfonylphenyl)methacrylamide/ 0.75 g acrylonitrile/methyl methacrylate
(molar ratio: 36:34:30, weight-average molecular weight: 50,000)
m-Cresol/p-cresol novolak resin 0.25 g
(molar ratio: 60:40, weight-average molecular weight: 5,000)
p-Toluenesulfonic acid 0.003 g
Tetrahydrophthalic anhydride 0.03 g
Cyanine dye P (having the structure above) 0.017 g
Victoria Pure Blue 0.015 g

Fluorochemical surfactant 0.05 g
(Tradename: Magafac F-177; manufactured by Dainippon Ink and Chemicals, Inc.)
γ-Butylolactone 10 g
Methylethylketone 10 g
1-Methoxy-2-propanol 1 g

(Examples 7 to 9 and Comparative Example 3)

A recording layer coating solution D having the composition described below was applied, using a wire bar, onto the support plate with an undercoat layer (the types of supports are shown in Table 1 below) obtained in a manner similar to Examples 1 to 3. After application of coating solution D, the supporting plate was dried at 150°C for 100 seconds to produce the positive planographic printing plate precursors of Examples 7 to 9 and Comparative Example 3 having a total coating amount of 1.40 g/m².

Specific sulfonium salt or comparative sulfonium salt 0.100 g shown in the following Table 1
N-(4-Aminosulfonylphenyl)methacrylamide/acrylonitrile/methyl methacrylate 2.072 g
(molar ratio: 36:34:30, weight-average molecular weight: 50,000)
Cyanine dye P (having the structure above) 0.052 g
Fluorochemical surfactant 0.017 g
(Tradename: Magafac F-780; manufactured by Dainippon Ink and Chemicals, Inc.)
Ethyl violet 6 naphthalenesulfonic acid 0.078 g
Methylethylketone 25.30 g

[Evaluation of planographic printing plate precursor]

The properties of the positive planographic printing plate precursors of Examples 1 to 9 and Comparative Examples 1 to 3 were evaluated. Precursors that were previously stored at 25°C for 30 days after the recording layer was formed were used in the evaluation tests.

(Evaluation of sensitivity)

A raw image was drawn on each of the positive planographic printing plate precursors obtained in Examples 1 to 9 and Comparative Examples 1 to 3, while the beam intensity wass changed stepwise in a Trendsetter 800 manufactured by Creo Inc. at a drum rotational velocity of 250 rpm, and was developed at a constant liquid temperature of 30°C with a developing period of 12 seconds using a PS Processor LP-940HII manufactured by Fuji Photo Film Co. containing a diluted aqueous solution (1:8) of developer DT-2 manufactured by Fuji Photo Film Co. and a diluted aqueous solution (1:1) of finisher FG-1 manufactured by Fuji Photo Film Co. After development, the plate was then observed with a loupe at a magnification of 50 times, and the exposure beam intensity at which spotty undissolved film was not observed was used as an indicator of sensitivity.
A smaller amount of exposure energy indicates a higher sensitivity. The results are shown in Table 1.

(Evaluation of development scum)

A solid image was drawn on each of the positive planographic printing plate precursors obtained in Examples 1 to 9 and Comparative Examples 1 to 3 in a Trendsetter 800 manufactured by Creo Inc. at a beam intensity of 10W and a drum rotational velocity of 250 rpm, and developed by using a PS7 Processor LP-940HII manufactured by Fuji Photo Film Co. containing a diluted aqueous solution (1:9) of developer DT-2R manufactured by Fuji Photo Film Co., which was previously saturated with carbon dioxide gas to an electrical conductivity of 37 mS/cm, and a diluted aqueous solution (1:1) of finisher FG-1 manufactured by Fuji Photo Film Co. at a liquid temperature of 30°C with a developing period of 12 seconds.
After the development was performed on a total processing area of 100 m², the developer in the automatic developing machine was collected in a transparent bottle, which was left at room temperature for 12 hours, and then the presence of development scum was observed visually. Criteria of the evaluation are: A: almost no development scum, B: some development scum; and C: many development scum. The results are shown in Table 1.

[Solubility of sulfonium salt]

The solubility of the sulfonium salts used in the Examples and Comparative Examples was determined as follows: 50 ml of an aqueous 0.1 mol/L NaOH solution was placed in a transparent glass bottle under the condition of 25°C and 1 atm; then, 50 mg of a sulfonium salt was added thereto and the mixture was stirred for 5 minutes at 25°C while the bottle was sealed; and the solubility was evaluated. If the sulfonium salt was completely dissolved, 50 mg of additional sulfonium salt was added and the mixture was stirred for 5 minutes, and the solubility was evaluated once again. The operation was continued until the sulfonium salt did not dissolve, and the concentration of the sulfonium salt when the dissolved amount reached a maximum value was used as the solubility. The results of these measurements are also shown in Table 1.

[Table 1]

	Supporting plate	Compound for undercoat layer	Sulfonium salt		Sensitivity (W)	Development scum
	Supporting plate	Compound for undercoat layer	No.	Solubility (mg/ml)	Sensitivity (W)	Development scum
Example 1	A	I	S-3	28	8	B
Example 2	B	II	S-35	36	7.5	B
Example 3	C	I	S-16	58	7.5	A
Example 4	D	I	S-20	28	8.5	B
Example 5	A	II	S-67	38	8	B
Example 6	B	I	S-43	52	8	A
Example 7	C	I	S-38	30	8.5	B
Example 8	D	II	S-26	38	8.5	B
Example 9	A	I	S-43	52	8	A
Comparative Example 1	A	I	S-A	5	10	C
Comparative Example 2	A	II	S-B	7	10.5	C
Comparative Example 3	A	I	S-C	20	9	C

The number (No.) of the sulfonium salt shown in Table 1 is the number allocated to the specific sulfonium salt in the Examples above.
The structures of the comparative sulfonium salts (S-A, S-B, and S-C) used in the Comparative Examples are also shown below.
As apparent from Table 1, the planographic printing plate precursors of Examples 1 to 9 having a recording layer containing a specific sulfonium salt according to the present invention has superior sensitivity, and no development scum was generated.
In contrast, the planographic printing plate precursors (of Comparative Examples 1 to 3) having a recording layer containing a comparative sulfonium salt having a solubility outside the preferable range of solubility according to the present invention had either lower sensitivity or generated a greater amount of development scum.

Claims

A planographic printing plate precursor, comprising:
a support; and

a recording layer formed on the support, which recording layer comprises a sulfonium salt (A), an alkali-soluble resin (B), and an infrared absorbent (C),
wherein the sulfonium salt (A) has a solubility of 25 mg/ml or more in an aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure.
The planographic printing plate precursor according to Claim 1, wherein the sulfonium salt (A) has three phenyl groups in its cationic region and at least one of the three phenyl groups has an alkali-soluble group as a substituent group.
The planographic printing plate precursor according to Claim 2, wherein at least two of the three phenyl groups have an alkali-soluble group as a substituent group.
The planographic printing plate precursor according to Claim 3, wherein each of the three phenyl groups has an alkali-soluble group as a substituent group.
The planographic printing plate precursor according to Claim 2, wherein the alkali-soluble group is a group selected from the group consisting of -COOH, -OH, -SO₃H, and -PO₃H₂ groups.
The planographic printing plate precursor according to Claim 5, wherein the alkali-soluble group is a -COOH or -OH group.
The planographic printing plate precursor according to Claim 2, wherein at least one of the three phenyl groups has a substituent other than an alkali-soluble group.
The planographic printing plate precursor according to Claim 7, wherein the substituent group other than the alkali-soluble group is a group selected from the group consisting of halogen atoms, a nitro group, alkyl groups having 12 or fewer carbon atoms, alkoxy groups having 12 or fewer carbon atoms, and aryloxy groups having 12 or fewer carbon atoms.
The planographic printing plate precursor according to Claim 1, wherein the anionic portion of the specific sulfonium salt (A) is a group which is a conjugate base of a strong acid.
The planographic printing plate precursor according to Claim 9, wherein the group which is a conjugate base of a strong acid is a residue derived from a halogen ion, a sulfonic acid compound, a carboxylic acid compound or an inorganic acid compound.
The planographic printing plate precursor according to Claim 10, wherein the residue of the inorganic compound is a group selected from the group consisting of halide anions, HSO₄ ^- and halogen-containing complex anions.
The planographic printing plate precursor according to Claim 11, wherein the residue of the inorganic compound is a group which is a conjugate base of a strong acid derived from an inorganic acid compound containing a fluorine atom.
The planographic printing plate precursor according to Claim 9, wherein the group which is a conjugate base of a strong acid has a pKa of lower than 5.
The planographic printing plate precursor according to Claim 9, wherein the group which is a conjugate base of a strong acid contains multiple acidic groups.
A planographic printing plate precursor, comprising:
a support; and

a recording layer formed on the support, which recording layer comprises a sulfonium salt (A), and an alkali-soluble resin (B),
wherein the sulfonium salt (A) has three phenyl groups in the cationic region, at least one of the three phenyl groups having an alkali-soluble group as a substituent group, and
the sulfonium salt (A) has a solubility of a predetermined value or more in aqueous 0.1 mol/L NaOH solution having a liquid temperature of 25°C at normal room temperature and atmospheric pressure.
The planographic printing plate precursor according to Claim 15, wherein the predetermined value is 25 mg/ml or more.
The planographic printing plate precursor according to Claim 15, wherein the alkali-soluble group is a group selected from the group consisting of -COOH, -OH, -SO₃H, and -PO₃H₂ groups.
The planographic printing plate precursor according to Claim 17, wherein the alkali-soluble group is a -COOH or -OH group.
The planographic printing plate precursor according to Claim 15, wherein at least one of the three phenyl groups has a substituent other than an alkali-soluble group.
The planographic printing plate precursor according to Claim 15, wherein the anionic region of the sulfonium salt (A) is a group which is a conjugate base of a strong acid.