EP1829703A1

EP1829703A1 - Infrared sensitive planographic printing plate precursor

Info

Publication number: EP1829703A1
Application number: EP07004149A
Authority: EP
Inventors: Ikuo Kawauchi
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2006-03-01
Filing date: 2007-02-28
Publication date: 2007-09-05
Anticipated expiration: 2027-02-28
Also published as: ATE408521T1; EP1829703B1; DE602007000123D1; JP4680098B2; JP2007233096A

Abstract

The present invention provides an infrared sensitive planographic printing plate precursor including: a support; a recording layer disposed on or above a surface of the support and capable of forming an image by infrared irradiation, the recording layer containing a resin that is water-insoluble and alkali-soluble, and an infrared absorbent; and an organic polymer layer disposed on or above the opposite surface of the support to the recording layer, wherein the coefficient of static friction between the recording layer and the organic polymer layer is in the range of from 0.45 to 0.60.

Description

TECHNICAL FIELD

The present invention relates to an infrared sensitive planographic printing plate precursor. More particularly, the present invention relates to an infrared sensitive planographic printing plate precursor with improved prevention of damage to a recording layer when the infrared sensitive planographic printing plate precursors are stacked.

BACKGROUND ART

Laser technology has made remarkable progress in recent years. In particular, high-power and compact solid lasers, semiconductor lasers and the like, having an emission wavelength within the near infrared and infrared regions are now readily available. In a planographic printing field, such lasers are advantageously used as light sources for exposing planographic printing precursors so as to produce printing plates directly according to digital data from a computer or the like.
A recording layer of such a positive planographic printing plate precursor for direct plate-making using infrared laser includes as essential components an alkali-soluble resin and an infrared absorbent which absorbs light and generates heat. In unexposed portions (i.e., an image area), the infrared absorbent acts as a dissolution inhibitor, which interacts with the alkali-soluble resin to substantially lower the solubility of the alkali-soluble resin. On the other hand, in exposed portions (i.e., a non-image area), the interaction of the infrared absorbent and the alkali-soluble resin becomes weak due to the heat generated, and the infrared absorbent dissolves in the alkaline developer to form an image. Such a positive planographic printing plate precursor, however, has problems in that the mechanical strength of the recording layer is insufficient. During manufacture, transportation and handling of the printing plate precursor, if the plate surface contacts with various members strongly, defects is generated on the printing surface, and missing portions appear in the developed image area.
To reduce such problems, planographic printing plate precursors are usually packaged with interleaf sheets (partitioning papers) interposed between adjacent printing plate precursors. The interleaf sheets, however, have problems of 1) increase costs and 2) problems in disposal. Accordingly, "interleaf sheet-less" is desirable. Recently, as Computer-to-plate (CTP) systems become common, more and more exposure devices are provided with printing plate autoloaders. Such autoloaders, however, have the problem that the interleaf sheets need to be removed in advance from the stack through a bothersome manual operation, and that, even in an autoloader equipped with a device for automatically removing interleaf sheets, the printing plate precursors sometimes become scratched when removing the interleaf sheets. To avoid these problems, demand for planographic printing plate precursors stacked without interleaf sheets is increasing.
A known technique towards packaging without interleaf sheets is to provide supports with a back surface designed to reduce mechanical damage to photosensitive layers caused by contact between the photosensitive layers and the back surface of the supports.
For example, a photosensitive planographic printing plate precursor with a coating layer provided at a surface on the opposite side to that of a photosensitive layer on a support is proposed. The coating layer has a glass transition temperature of 60°C or above and is formed by at least one resin selected from a group consisting of saturated copolyester resins, phenoxy resins, polyvinylacetal resins and vinylidene chloride copolymer resins (see Japanese patent application laid-open ( JP-A) No. 2005-62456 ). Also, a photosensitive planographic printing plate precursor with a rough-surfaced organic polymer layer provided at a surface on the opposite side to that of a photosensitive layer on a support is also proposed (see, for example, JP-A No. 2002-254843 ).
As described above, by the method of using a photosensitive planographic printing plate precursor having a back coat layer including an organic polymer has achieved a certain effect of reducing damage to the photosensitive layer. However, depending on the relationship of the surface physical properties between the back coat layer and the photosensitive layer, it is not a method that can be applied in practice from the point of view of storage and transportation, because of problems such as the difficulty in forming a stack of planographic printing plate precursors due to slipping between plate materials when the plate materials are stacked, or displacement between plate materials that may occur, even after being formed into a stack of planographic printing plate precursors, due to vibrations during transportation.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide an infrared sensitive planographic printing plate precursor that, when stacked with no interleaf sheets, is easy to form into a stack of printing plate precursors, encounters no displacement between the plate materials in a stack of planographic printing plate precursors due to vibrations, and effectively inhibits damage to the recording layer.
After intensive studies, the present inventors have found that the following infrared sensitive planographic printing plate precursor (hereinafter, sometimes refers to as " planographic printing plate precursor ") was effective in solving the above object, and completed the present invention.
That is, the infrared sensitive planographic printing plate precursor of the present invention is an infrared sensitive planographic printing plate precursor including: a support; a recording layer disposed on or above a surface of the support and capable of forming an image by infrared irradiation, the recording layer containing a resin that is water-insoluble and alkali-soluble, and an infrared absorbent; and an organic polymer layer disposed on or above the opposite surface of the support to that of the recording layer, wherein the coefficient of static friction between the recording layer and the organic polymer layer is in the range of from 0.45 to 0.60.
When the coefficient of static friction between the recording layer and the organic polymer layer of the planographic printing plate precursor of the present invention is in the above-described range, both the recording layer and the organic polymer layer are considered to be in a preferable condition such that the contact surfaces between the layers has appropriate lubricity and shows no adhesion when the precursors are stacked.
As a result, it is supposed that the planographic printing plate precursors of the present invention are easy to stack, and even when the obtained stack of planographic printing plate precursors is transported, displacement between the plate materials due to vibrations is prevented. It is also supposed that damage to the recording layer is effectively inhibited even when the plate materials are rubbed against each other during storage or transportation in a stacked condition.
According to the present invention, an infrared sensitive planographic printing plate precursor that, when stacked with no interleaf sheet, is easy to form a stack of printing plate precursors, in which no displacement occurs between the plate materials in a stack of planographic printing plate precursors by vibrations, and effectively inhibits damage to the recording layer, is provided.

DETAILED DESCRIPTION OF THE INVENTION

The infrared sensitive planographic printing plate precursor of the present invention is an infrared sensitive planographic printing plate precursor including: a support; a recording layer disposed on or above a surface of the support and capable of forming an image by infrared irradiation, the recording layer containing a resin that is water-insoluble and alkali-soluble and an infrared absorbent; and an organic polymer layer disposed on or above the opposite surface of the support to that of the recording layer, wherein the coefficient of static friction between the recording layer and the organic polymer layer is in the range of from 0.45 to 0.60.
As described above, in the present invention, the coefficient of static friction between the recording layer and the organic polymer layer must be in the range of from 0.45 to 0.60. Furthermore, the coefficient of static friction is preferably in the range of from 0.45 to 0.58. When the coefficient of static friction is less than 0.45, a stack of planographic printing plate precursors formed with no interleaf sheets tends to encounter displacement during transportation, and when the coefficient of static friction exceeds 0.60, scratches tend to be generated when the planographic printing plate precursor are rubbed together.
In the present specification "... to ..." represents a range including the numeral values represented before and after "to" as a minimum value and a maximum value, respectively.
In the present invention, the coefficient of static friction is measured by the method according to the horizontal method as described in "Kami oyobi Itagami no Masatsu Keisu Shiken Houhou (Test Method for Determining Coefficient of Friction of Paper and Board)" of JIS P 8147 defined by Japanese Industrial Standards. More specifically, the method is carried out as follows: two photosensitive planographic printing plate precursors of the same configuration are prepared, or one photosensitive planographic printing plate precursor is cut into two pieces, and one is placed on a horizontal plate with the outermost surface of the recording layer side up, and the other is mounted with the outermost surface of the recording layer side in contact with a weight in such a manner that the outermost surface of the recording layer side of the photosensitive planographic printing plate precursor on the horizontal plate is in contact with the outermost surface of the support back surface of the photosensitive planographic printing plate precursor mounted on the weight. Subsequently the weight is moved parallely by pulling at a rate of 10.0 mm/minute. The coefficient of static friction refers to the peak friction force exhibited at the moment when the weight starts to move.
As a method for achieving a coefficient of static friction within the above-described range, a method of adjusting the smoothness of the recording layer and/or the organic polymer layer, a method of adjusting the surface energy of the recording layer and/or the organic polymer layer, a method of adding a slip agent to the recording layer and/or the organic polymer layer, or the like is used. Among them, the method of adjusting the smoothness of the recording layer and/or the organic polymer layer is preferable from the viewpoint of easy adjustment of the coefficient of static friction.
As a method for adjusting the smoothness of the recording layer and/or the organic polymer layer, specifically, the means listed below can be used. These means may be used alone or in combination of two or more of them.

(1) A matt layer is formed on the recording layer.
(2) A long-chain alkyl group-containing polymer is internally added to the recording layer.
(3) A matting agent is internally added to the recording layer.
(4) The surface of the recording layer is roughened.
(5) A matt layer is formed on the organic polymer layer.
(6) A long-chain alkyl group-containing polymer is internally added to the organic polymer layer.
(7) A matting agent is internally added to the organic polymer layer.
(8) The surface of the organic polymer layer is roughened.
(9) The surface roughness of the support is adjusted.
(10) The polymers constituting the recording layer or the organic polymer layer are appropriately selected.
(11) Conditions in the coating method are adjusted.

The coefficient of static friction of the present invention varies depending on the polymers constituting the organic polymer layer and the recording layer, and the smoothness of the coated surface condition. Therefore, as a means for controlling the coefficient of static friction, from the viewpoint of ease of control, it is particularly preferable to appropriately select the organic polymer(s) constituting the organic polymer layer, and to control the coating conditions.
The matt layer used in the above-described means (1) is not particularly limited as long as it does not affect the image forming ability and developability of the recording layer. Specifically it is preferable to use a matt layer as described in paragraphs (0058) through (0059) in JP-ANo. 11-52559 .
The matt layer used in the above-described means (5) is not particularly limited as long as it does not impair the function of the organic polymer layer, and matting agents and methods for applying the same as described in JP-A No. 2003-63162 can be used.
As the above-described means (2) and (6), specifically, it is preferable to internally add a long-chain alkyl group-containing polymer having a structure shown below.
Favorable examples of the long-chain alkyl group-containing polymer for use in the invention include a copolymer represented by the following Formula (I).
In Formula (I), X and X' each independently represent a single bond or divalent linking group. m represents an integer of from 20 to 99, preferably an integer of from 30 to 90, and more preferably an integer of from 45 to 80. n represents an integer of from 6 to 40, preferably an integer of from 12 to 30, and more preferably an integer of from 14 to 20. The connecting bonds represented by a dotted line mean the presence of a methyl group or a hydrogen atom at the end thereof.
Specific examples of the divalent linking group represented by X and X' in Formula (I) include straight-chain, branched, or cyclic alkylene groups having 1 to 20 carbon atoms, straight-chain, branched, or cyclic alkenylene groups having 2 to 20 carbon atoms, alkynylene groups having 2 to 20 carbon atoms, arylene groups having 6 to 20 carbon atoms (monocyclic or heterocyclic), -OC(=O)-, -OC(=O)Ar-, -OC(=O)O-, -OC(=O)OAr-, -C(=O)NR-, -C(=O)NAr-, -SO₂NR-, -SO₂NAr-, -O-(alkyleneoxy or polyalkyleneoxy), -OAr-(aryleneoxy or polyaryleneoxy), -C(=O)O-, -C(=O)O-Ar-, -C(=O)Ar-, -C(=O)-, -SO₂O-, -SO₂OAr-, -OSO₂-, -OSO₂Ar-, -NRSO₂-, -NArSO₂-, -NRC(=O)-, -NArC(=O)-, -NRC(=O)O-, -NArC(=O)O-, -OC(=O)NR-, -OC(=O)NAr-, -NAr-, -NR-, -N⁺RR'-, -N⁺RAr-, -N⁺ArAr'-, -S-, -SAr-, -ArS-, heterocyclic group (3 to 12 membered monocyclic or condensed rings containing at least one or more heteroatoms such as nitrogen, oxygen or sulfur), -OC(=S)-, -OC(=S)Ar-, -C(=S)O-, -C(=S)OAr-, -C(=S)OAr-, -C(=O)S-, -C(=O)SAr-, -ArC(=O)-, -ArC(=O)NR-, -ArC(=O)NAr-, -ArC(=O)O-, -ArC(=O)S-, -ArC(=S)O-, -ArO-, and -ArNR-. In the groups above, R and R' each independently represent a hydrogen atom, a straight-chain, branched, or cyclic alkyl group, alkenyl group, or alkynyl group. Ar and Ar' each independently represent an aryl group.
The above-described linking groups may form a linking group in combination of two or more of them.
Among the above linking groups, arylene groups (monocyclic or heterocyclic) having 6 to 20 carbon atoms, -C(=O)NR-, -C(=O)NAr-, -O- (alkyleneoxy or polyalkyleneoxy), -OAr- (aryleneoxy or polyaryleneoxy), -C(=O)O=, -C(=O)O-Ar-, -C(=O)-, -C(=O)Ar-, -S-, -SAr-, -ArS-, -ArC(=O)-, -ArC(=O)O-, -ArO-, -ArNR-, and the like are preferable, arylene groups having 6 to 20 carbon atoms (monocyclic or heterocyclic), -C(=O)NR-, -C(=O)NAr-, -O- (alkyleneoxy, polyalkyleneoxy), -OAr- (aryleneoxy, polyaryleneoxy), -C(=O)O-, -C(=O)O-Ar-, -SAr-, -ArS-, -ArC(=O)-, -ArC(=O)O-, -ArO-, -ArNR-, and the like are more preferable.
Furthermore, the above-described linking groups may have a substituent, and examples of the substituent include straight-chain, branched, or cyclic alkyl groups having 1 to 20 carbon atoms, straight-chain, branched, or cyclic alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms, aryl groups having 6 to 20 carbon atoms, acyloxy groups having 1 to 20 carbon atoms, alkoxycarbonyloxy groups having 2 to 20 carbon atoms, aryloxycarbonyloxy groups having 7 to 20 carbon atoms, carbamoyloxy groups having 1 to 20 carbon atoms, carbonamide groups having 1 to 20 carbon atoms, sulfonamide groups having 1 to 20 carbon atoms, carbamoyl groups having 1 to 20 carbon atoms, sulfamoyl groups having 0 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, aryloxy groups having 6 to 20 carbon atoms, aryloxycarbonyl groups having 7 to 20 carbon atoms, alkoxycarbonyl groups having 2 to 20 carbon atoms, N-acylsulfamoyl group having 1 to 20 carbon atoms, N-sulfamoylcarbamoyl groups having 1 to 20 carbon atoms, alkylsulfonyl group having 1 to 20 carbon atoms, arylsulfonyl groups having 6 to 20 carbon atoms, alkoxycarbonylamino groups having 2 to 20 carbon atoms, aryloxycarbonylamino groups having 7 to 20 carbon atoms, amino groups having 0 to 20 carbon atoms, imino groups having 1 to 20 carbon atoms, ammonio groups having 3 to 20 carbon atoms, a carboxy group, a sulfo group, an oxy group, a mercapto group, alkylsulfinyl groups having 1 to 20 carbon atoms, arylsulfinyl groups having 6 to 20 carbon atoms, alkylthio groups having 1 to 20 carbon atoms, arylthio groups having 6 to 20 carbon atoms, ureido groups having 1 to 20 carbon atoms, heterocyclic groups having 2 to 20 carbon atoms, acyl groups having 1 to 20 carbon atoms, sulfamoylamino groups having 0 to 20 carbon atoms, silyl groups having 2 to 20 carbon atoms, a hydroxy group, halogen atoms (for example, fluorine atom, chlorine atom, or bromine atom), a cyano groups, and a nitro groups.
The long-chain alkyl group-containing polymer is more preferably, for example, an acrylic copolymer represented by the following Formula (II).
In Formula (II), X and X' each independently represent a single bond or divalent linking group. X and X' in Formula (II) are the same as X and X' in the above-described Formula (I), and the preferable examples are also the same. m represents an integer of from 20 to 99, preferably an integer of from 30 to 90, and more preferably an integer of from 45 to 80. n represents an integer of from 6 to 40, preferably an integer of from 12 to 30, and more preferably an integer of from 14 to 20. The connecting bonds represented by a dotted line mean the presence of a methyl group or a hydrogen atom at the end thereof.
The long-chain alkyl group-containing polymer is still more preferable, for example, an acrylic copolymer represented by the following Formula (III).
In Formula (III), X and X' each independently represent a single bond or divalent linking group. X and X' in Formula (III) are the same as X and X' in the above-described Formula (I), and the preferable examples are also the same. m represents an integer of from 20 to 99, preferably an integer of from 30 to 90, and further preferably an integer of from 45 to 80. n represents an integer of from 6 to 40, more preferably an integer of from 12 to 30, and further preferably an integer of from 14 to 20. The connecting bonds represented by a dotted line mean the presence of a methyl group or a hydrogen atom at the end thereof.
The long-chain alkyl group-containing polymer is most preferably, for example, an acrylic copolymer represented by the following Formula (IV) or (V).
In Formulae (IV) and (V), m represents an integer of from 20 to 99, preferably an integer of from 30 to 90, and more preferably an integer of from 45 to 80. n represents an integer of from 6 to 40, more preferably an integer of from 12 to 30, and still more preferably an integer of from 14 to 20. The connecting bonds represented by a dotted line mean the presence of a methyl group or a hydrogen atom at the end thereof.

A monomer copolymerized with the long-chain alkyl group-containing monomer and the carboxy group-containing vinyl monomer may be appropriately selected according to the functions of the layer to which the long-chain alkyl group-containing polymer is internally added, and examples thereof include hydrophilic monomers.
As the hydrophilic monomers, the monomers having following acidic groups (1) to (5) are preferable from the viewpoints of solubility in an alkaline developing solution and sensitivity.

(1) phenol group (-Ar-OH);
(2) sulfonamide group (-SO₂NH-R);
(3) active imide group (-SO₂NHCOR, -SO₂NHSO₂R, or -CONHSO₂R);
(4) sulfonic acid group (-SO₃H); or
(5) phosphoric acid group (-OPO₃H₂).

In the groups (1) through (5), Ar represents a divalent aryl linking group that may have a substituent; and R represents a hydrocarbon group that may be substituted.
Examples of monomers having the phenol group (1) include acrylamides, methacrylamides, acrylic acid esters and methacrylic esters each having a phenol group, and hydroxystyrenes.
Examples of the monomers having the sulfonamide group (2) include compounds having one or more sulfonamide groups in the structure above and one or more polymerizable unsaturated groups in the molecule. Among them, low-molecular weight compounds having an acryloyl, allyl, or vinyloxy group and a sulfonamido group in the molecule are preferable. Examples thereof include the compounds represented by the following Formulae (i) to (v).
In 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 group, cycloalkylene group, arylene group, or aralkylene group having 1 to 12 carbon atoms that may have a substituent. R³, R⁷, and R¹³ each independently represent a hydrogen atom, alkyl group, cycloalkyl group, aryl group or aralkyl group having 1 to 12 carbon atoms that may have a substituent. R⁶ and R¹⁷ each independently represent an alkyl group, cycloalkyl group, aryl group, or aralkyl group having 1 to 12 carbon atoms which may have a substituent. R⁸, R¹⁰, and R¹⁴ each independently represent a hydrogen atom or -CH₃. R¹¹ and R¹⁵ each independently represent a single bond or an alkylene group, cycloalkylene group, arylene group or aralkylene group having 1 to 12 carbon atoms that may have a substituent. Y¹ and Y² each independently represent a single bond or -CO-.
In particular, among the compounds represented by Formulae (i) to (v), m-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl) methacrylamide, N-(p-aminosulfonylphenyl) acrylamide, and the like is preferably used for the planographic printing plate precursor of the present invention.
Examples of the monomers having the active imide group (3) include compounds having one or more active imide groups represented by the structural formula above and one or more polymerizable unsaturated groups in the molecule. Among them, preferable are the compounds having one or more active imide groups represented by the following formula and one or more polymerizable unsaturated groups in the molecule.
Specifically, N-(p-toluenesulfonyl) methacrylamide, N-(p-toluenesulfonyl) acrylamide, and the like is preferably used.
Examples of the monomer having the sulfonic acid group (4) include compounds having one or more sulfonic acid groups and one or more polymerizable unsaturated groups in the molecule.
Examples of the monomer having the phosphate group (5) include compounds having one or more phosphate groups and one or more polymerizable unsaturated groups in the molecule thereof.
Among the hydrophilic monomers above, monomers having a phenol group (1), a sulfonamide group (2), or an active imide group (3) are preferably; and monomers having a phenol group (1) or a sulfonamide group (2) are particularly preferable, from the points of solubility in alkaline developing solutions, development latitude, and film strength.

Examples of other monomers copolymerized with the long-chain alkyl group-containing monomer and the carboxy group-containing vinyl monomer include the following compounds (6) to (16):

(6) aliphatic hydroxyl group-containing acrylic and methacrylic esters such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate;
(7) acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, amyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, glycidyl acrylate, N-dimethylaminoethyl acrylate, polyethylene glycol monoacrylate, and polypropylene glycol monoacrylate;
(8) methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, amyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, glycidyl methacrylate, N-dimethylaminoethyl methacrylate, polyethylene glycol monomethacrylate, and polypropylene glycol monomethacrylate;
(9) acrylamides and methacrylamideacrylamides such as acrylamide, methacrylamide, N-methylolacrylamide, N-ethylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-hydroxyethylacrylamide, N-phenylacrylamide, N-nitrophenylacrylamide, and N-ethyl-N-phenylacrylamide;
(10) vinyl ethers such as ethyl vinylether, 2-chloroethyl vinylether, hydroxyethyl vinylether, propyl vinylether, butyl vinylether, and phenyl vinylether;
(11) vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, and vinyl benzoate;
(12) styrenes such as styrene, α-methylstyrene, methylstyrene, and chloromethylstyrene;
(13) vinylketones such as methyl vinylketone, ethyl vinylketone, propyl vinylketone, and phenyl vinylketone;
(14) olefins such as ethylene, propylene, isobutylene, butadiene, and isoprene;
(15) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile, methacrylonitrile, and the like; and
(16) unsaturated imides such as maleimide, N-acryloylacrylamide, N-acetylmethacrylamide, N-propionylmethacrylamide, and N-(p-chlorobenzoyl)methacrylamide.

Any one of known copolymerization methods such as graft copolymerization, block copolymerization, and random copolymerization may be used for copolymerization of the long-chain alkyl group-containing monomer, carboxy group-containing vinyl monomer, hydrophilic monomer, and, and other monomers.
In addition, these monomers may be used respectively in combination of two or more in the copolymerization. When the carboxy group-containing monomers are used in combination of two or more, the total mole ratio of the monomers is preferably in the range of 20 to 99 mol %.
Specific examples of the long-chain alkyl group-containing polymer in the present invention include followings, but are not limited to them.
As the long-chain alkyl group-containing polymer, those having a weight average molecular weight of 5,000 or more, and a number average molecular weight of 1,000 or more are preferably used. Further preferably, in terms of polystyrene, the weight average molecular weight is 10,000 to 5,000,000, and particularly preferably 10,000 to 2,000,000, and further preferably 20,000 to 1,000,000. The long-chain alkyl group-containing polymer may be used alone or in combination of two or more.
The amount of residual monomers in the layer to which the long-chain alkyl group-containing polymer is internally added is preferably 10 mass% or less, and more preferably 5 mass% or less, to avoid the problems of transfer of the planographic printing plate precursor according to the invention onto the recording layer in contact therewith during stacking and to the roller during production.
The long-chain alkyl group-containing polymer may be internally added to the organic polymer layer and/or the recording layer. The organic polymer layer and recording layer are obtained by preparing a coating solution containing the long-chain alkyl group-containing polymer mixed with other components, and coating and drying the solution on a substrate. In this way, the long-chain alkyl group-containing polymer and the organic polymer constituting the organic polymer layer undergo phase separation, and the long-chain alkyl group-containing polymer self aggregates and fine projections out from the surface are formed.
It is thus possible to adjust the smoothness (the surface roughness) of the layers by forming such fine projections on the recording layer and the organic polymer layer.
The addition amount of the long-chain alkyl group-containing polymer with respect to the total solid matter of the recording layer is preferably about 0.1 to 20 mass%, and more preferably 0.5 to 10 mass%. When the content is less than 0.1 mass%, the formation of pits and projections is insufficient, and the effect of improving scratch resistance cannot be sufficiently achieved, and when the content exceeds 20 mass%, the strength of the recording layer tends to decrease, which results in deterioration of printing durability.
Furthermore, the addition amount of the long-chain alkyl group-containing polymer with respect to the total solid matter of the organic polymer layer is preferably about 0.01 to 30 mass%, more preferably 0.1 to 20 mass%, and particularly preferably 0.5 to 10 mass%. Either when the content is less than 0.01 mass%, or exceeds 30 mass%, the formation of pits and projections (fine projections) is insufficient and the effect of improving scratch resistance cannot be sufficiently achieved.
The above-described means of (3) and (7) may be specifically achieved by adding fine particles of a conventionally known matting agent to the layer. The fine particles of the matting agent which can be used may be dispersed in the coating solution when the recording layer and/or the organic polymer layer are formed, and may be added to the recording layer, and more preferably are able to be dissolved or dispersed in a developing solution. By adjusting the type, particle size, and content of the fine particles of a matting agent, the smoothness (surface roughness) of the recording layer and/or the organic polymer layer can be readily controlled.
As the above-described means of (4) and (8), any methods can be used as long as they can roughen the surface condition of the recording layer and/or the organic polymer layer. Specifically, for example, a method of applying a coating solution containing materials for forming the recording layer or the organic polymer layer onto the support, and drying by blowing high pressure air can be used. Thus, the surface condition of the dried recording layer and/or the organic polymer layer can be roughened.
As the above-described means of (9), for adjusting the smoothness after the formation of the recording layer and/or the organic polymer, a method of adjusting the surface roughness of the support may be also employed. As to the surface roughness of the support, the type, thickness, and the like of the materials constituting the recording layer and/or the organic polymer layer must be taken into consideration.

[Recording layer]

The recording layer, which is included in the planographic printing plate precursor of the present invention, is a layer which is capable of forming an image by irradiation of infrared ray, and may have a single layer structure or multilayer structure. When the recording layer is of single layer type, it comprises a resin that is water-insoluble and alkali-soluble and an infrared ray absorbing agent. When the recording layer is of multilayer type, it comprises a resin that is water-insoluble and alkali-soluble, and at least either the layer which lies nearest to the support (hereinafter, sometimes referred to as "lower layer") and the layer which lies farthest from the support (hereinafter, sometimes referred to as "uppermost layer") is composed as a layer containing an infrared ray absorbing agent.

(Resin that is water-insoluble and alkali-soluble)

The resin that is water-insoluble and alkali-soluble which is used in the recording layer of the present invention (hereinafter, sometimes referred to as "alkali-soluble resin") include homopolymers containing an acidic group in the main chain and/or side chain of the polymers, copolymers thereof, or mixtures thereof. Accordingly, the recording layer of the present invention has a property of dissolving in an alkaline developing solution upon contact. The alkali-soluble resin used in the present invention is not particularly limited as long as it is conventionally known, but preferably a polymer compound having in the molecule thereof at least one acidic group selected from (1) phenolic hydroxy groups, (2) sulfonamide groups, (3) active imide groups, and (4) carboxylic acid groups. Examples thereof include followings, but not limited to them.

(1) Examples of the polymer compound having a phenolic hydroxy group include novolak resins such as a phenol formaldehyde resin, m-cresol formaldehyde resin, p-cresol formaldehyde resin, m-/p-mixed cresol formaldehyde resin, phenol /cresol (may be either m-, p-, or mixture of m-/p-), or mixed formaldehyde resin, and a pyrogallol acetone resin.
As preferable examples of the alkali-soluble resin having a phenolic hydroxy group include a resins formed by condensation of a substituted phenol represented by the following Formula (i) and an aldehyde.
In Formula (i), R¹ and R² each represent a hydrogen atom, an alkyl group, or a halogen atom. The alkyl group is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 to 2 carbon atoms. The halogen atom is either a fluorine atom, chlorine atom, bromine atom or iodine atom, preferably a chlorine atom or bromine atom. R³ represents an alkyl group or a cycloalkyl group having 3 to 6 carbon atoms.
Specific examples of the substituted phenols include isopropyl phenol, t-butyl phenol, t-amyl phenol, hexyl phenol, cyclohexyl phenol, 3-methyl-4-chloro-6-t-butyl phenol, isopropyl cresol, t-butyl cresol, and t-amyl cresol. Among them, t-butyl phenol and t-butyl cresol are preferable.
Examples of the aldehydes used for the condensation with the substituted phenol include aliphatic and aromatic aldehydes such as formaldehyde, acetaldehyde, acrolein, or crotonaldehyde. Among them, formaldehyde or acetaldehyde is preferable.
Other examples of the alkali-soluble resin having a phenolic hydroxy group include polymer compounds having a phenolic hydroxy group in the side chain thereof. Examples of the polymer compound having a phenolic hydroxy group in the side chain thereof include polymer compounds obtained by homopolymerization of a polymerizable monomer comprising a low molecular weight compound having one or more each of phenolic hydroxyl group and polymerizable unsaturated bond, or by copolymerization of the monomer and another polymerizable monomer.
Examples of the polymerizable monomer having a phenolic hydroxy group include acrylamide, methacrylamide, acrylic acid ester, methacrylic acid ester, or hydroxy styrene having a phenolic hydroxy group. Specifically, preferable examples include N-(2-hydroxyphenyl) acrylamide, N-(3-hydroxyphenyl) acrylamide, N-(4-hydroxyphenyl) acrylamide, N-(2-hydroxyphenyl) methacrylamide, N-(3-hydroxyphenyl) methacrylamide, N-(4-hydroxyphenyl) methacrylamide, o-hydroxyphenyl acrylate, m-hydroxyphenyl acrylate, p-hydroxyphenyl acrylate, o-hydroxyphenyl methacrylate, m-hydroxyphenyl methacrylate, p-hydroxyphenyl methacrylate, o-hydroxy styrene, m-hydroxy styrene, p-hydroxy styrene, 2-(2-hydroxyphenyl)ethyl acrylate, 2-(3-hydroxyphenyl)ethyl acrylate, 2-(4-hydroxyphenyl)ethyl acrylate, 2-(2-hydroxyphenyl)ethyl methacrylate, 2-(3-hydroxyphenyl)ethyl methacrylate, and 2-(4-hydroxyphenyl)ethyl methacrylate. The resins having a phenolic hydroxy group may be used in combination of two or more.
Furthermore, examples of the alkali-soluble resin having a phenolic hydroxy group used in the present invention include an alkali-soluble resin as described in JP-A No. 11-288089 , in which the phenolic hydroxy group of the above-described alkali-soluble resin having a phenolic hydroxy group is at least partially esterified.
(2) Examples of the alkali-soluble resin having a sulfonamide group include polymer compounds obtained by homopolymerization of a polymerizable monomer having a sulfonamide group, or by copolymerization of the monomer and another polymerizable monomer. Examples of the polymerizable monomer having a sulfonamide group include polymerizable monomers comprising a low molecular weight compound having within the molecule one or more each of sulfonamide group -NH-SO₂-, in which at least one hydrogen atom is bound to a nitrogen atom, and polymerizable unsaturated bond. Among them, low molecular weight compounds having an acryloyl group, allyl group, or vinyloxy group, and a substituted or monosubstituted aminosulfonyl group or substituted sulfonylimino group are preferable.
Specific examples of the alkali-soluble resin having a sulfonamide group include those described in Japanese Patent Application Publication ( JP-B) No. 7-69605 .
(3) The alkali-soluble resin having an active imide group preferably has an active imide group (-CO-NH-SO₂-) within the molecule thereof, and examples of the polymer compound include polymer compounds obtained by homopolymerization of a polymerizable monomer comprising a low molecular weight compound having within one molecule thereof one or more each of active imide group and polymerizable unsaturated bond, or by copolymerization of the monomer and another polymerizable monomer.
As specific examples of the compound include N-(p-toluenesulfonyl) methacrylamide, N-(p-toluenesulfonyl) acrylamide, and the like can be preferably used.
(4) Examples of the alkali-soluble resin having a carboxylic acid group include polymer compounds obtained by homopolymerization of a polymerizable monomer comprising a low molecular weight compound having one or more carboxylic acid groups and one or more polymerizable unsaturated groups in the molecule, or by copolymerization of the monomer and other polymerizable monomer. Specific examples of the polymerizable monomer having a carboxylic acid group include α, β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, or itaconic acid. Also, unsaturated carboxylic acids which are monoesters of the hydroxyl group of an acrylate or methacrylate having a hydroxyl group in the side chain thereof (for example, 2-hydroxyethylethyl acrylate or methacrylate) and a dibasic acid (for example, succinic acid, glutaric acid, or phthalic acid) are preferable examples.

Furthermore, as the alkali-soluble resin of the present invention, polymer compounds in which two or more of the above-described polymerizable monomers having a phenolic hydroxy group, polymerizable monomers having a sulfonamide group, polymerizable monomers having an active imide group, and polymerizable monomers having a carboxylic acid group have been polymerized, or polymer compounds obtained by copolymerizing two or more of the above polymerizable monomers and another polymerizable monomer can be used.
In the present invention, when the alkali-soluble resin is a copolymer of the above-described monomer having an acidic group (phenolic hydroxy group, sulfonamide group, active imide group, or carboxylic acid group) and another polymerizable monomer, the content of the monomer for imparting alkali solubility is preferably 10 mol% or more, and more preferably 20 mol% or more from the viewpoint of alkali solubility.
Examples of the monomer component to be copolymerized with the above-described monomers having an acidic group include the following compounds (m1) to (m11), but are not limited to them.

(m1) Acrylic acid esters and methacrylic acid esters having an aliphatic hydroxy group 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, acrylic acid -2-chloroethyl, or 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, or glycidyl methacrylate.
(m4) Acrylamide or methacrylamide such as acrylamide, methacrylamide, N-methylol acrylamide, N-ethylacrylamide, N-hexyl methacrylamide, N-cyclohexyl acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, N-nitrophenyl acrylamide, or N-ethyl-N-phenyl acrylamide.
(m5) Vinyl ethers such as ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxy ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether, or phenyl vinyl ether.
(m6) Vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butylate, or vinyl benzoate.
(m7) Styrenes such as styrene, α-methyl styrene, methyl styrene, or chloromethyl styrene.
(m8) Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, or phenyl vinyl ketone.
(m9) Olefins such as ethylene, propylene, isobutylene, butadiene, or isoprene.
(m10) N-vinyl pyrrolidone, acrylonitrile, methacrylonitrile, and the like.
(m11) Unsaturated imide such as maleimide, N-acryloyl acrylamide, N-acetyl methacryl amide, N-propionyl methacrylamide, or N-(p-chlorobenzoyl)methacrylamide.

As a method for copolymerizing the alkali-water-soluble polymer compound, conventionally known methods such as a graft copolymerization method, a block copolymerization method, or a random copolymerization method may be used.
In the present invention, when the alkali-soluble resin is a homopolymer or copolymer of the above-described polymerizable monomer having an acidic group, the weight average molecular weight thereof is preferably 2,000 or more, and further preferably 5,000 to 300,000. In the present invention, when the alkali-soluble resin is a resin such as a phenol formaldehyde resin or cresol aldehyde resin, the weight average molecular weight thereof is preferably 500 to 50,000, more preferably 700 to 20,000, and particularly preferably 1,000 to 10,000.
When the recording layer has a multilayer structure, the alkali-soluble resin used for the uppermost layer of the recording layer is preferably a resin having a phenolic hydroxy group in that it exhibits a strong hydrogen bonding property in unexposed portions, and a part of hydrogen bonds is readily released in exposed portions. Novolak resins are further preferable.
In the present invention, two or more types of alkali-soluble resins, which exhibit different rates of dissolution in alkaline aqueous solution, may be used in combination. In such case, the mixed ratio is optional. As the alkali-soluble resin to be mixed with the resin having a phenolic hydroxy group which is preferably used for the uppermost layer of the recording layer of multilayer type, acrylic resins are preferable, and acrylic resins having a sulfoamide group or carboxylic acid group are more preferable in that they have low compatibility with the resin having a phenolic hydroxy group.
When the recording layer has a multilayer structure, the above-described alkali-soluble resin is used for the lower layer of the recording layer, and the lower layer itself must develop high alkali solubility, particularly in non-image regions. Also during printing, it must develop resistance to various printing chemicals and stable printing durability under various printing conditions. Therefore, it is preferable to select a resin which does not impair the properties. From that viewpoint, it is preferable to select a resin which is superior in solubility in an alkali developing solution, dissolution resistance to various printing chemicals, and physical strength. As to the alkali-soluble resin used for the lower layer, it is preferable to select a resin having a low solvent solubility, which will not be dissolved by the coating solvent when the uppermost layer, is applied. By selecting such resins, undesirable compatibility at the interface between the two layers is inhibited.
From these viewpoints, as the alkali-soluble resin contained in the lower layer, among the above-described alkali-soluble resins, acrylic resins are preferable. Among them, acrylic resins having a sulfonamide group are preferable.
From the above-described viewpoint, examples of the alkali-soluble resin used for the lower layer include, in addition to the above-described examples, water-insoluble and alkali-soluble polyamide resins, epoxy resins, polyvinyl acetal resins, styrenic resins, and urethane resins. Among them, urethane resins and polyvinyl acetal resins are preferable.
The water-insoluble and alkali-soluble poly urethane resin (hereinafter, appropriately referred to as "polyurethane resin") is not limited as long as it is insoluble in water and soluble in alkali aqueous solutions, and preferably has a carboxyl group in the polymer main chain thereof. Specific examples thereof include a polyurethane resin having a basic skeleton derived from a reaction product of a diisocyanate compound represented by the following Formula (ii) and at least one of diol compounds having a carboxyl group represented by the following Formula (iii) or (iv).

OCN-R¹-NCO (ii)
In Formula (ii), R¹ represent a divalent linking group. Examples of the divalent linking group include an aliphatic hydrocarbon, an alicyclic hydrocarbon, or an aromatic hydrocarbon, and preferable examples include alkylene groups having 2 to 10 carbon atoms, and arylene groups having 6 to 30 carbon atoms. The arylene group may be two or more ring structures bonded through a divalent organic linking group such as a single bond or methylene group, or may be a condensed polycyclic structure. As necessary, R¹ may have another functional group which does not react with an isocyanate group (for example, an ester group, urethane group, amide group, or ureido group).
R¹ in Formula (ii) may have a substituent, and examples of the substituent which can be introduced include substituents which are inactive to the isocyanate group, such as a halogen atom (-F, -Cl, -Br, or -I), an alkyl group, alkoxyl group, an alkyl ester group, or a cyano group.
As the diisocyanate compound, in addition to those in the range of the compound represented by Formula (ii), for example, high molecular weight diisocyanate compounds in which a polymer compound such as oligomer or polymer comprising the below-mentioned diol compound has isocyanate groups at both the ends thereof can be used.
In Formula (iii), R² represents a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, an alkoxy group, or an aryloxy group. R² may have a substituent, and examples of the substituent, which can be introduced, include a cyano group, a nitro group, a halogen atom (-F, -Cl, -Br, or -I), -CONH₂, -COOR⁶, -OR⁶, -NHCONHR⁶, -NHCOOR⁶, -NHCOR⁶, -OCONHR⁶, and -CONHR⁶ (wherein R⁶ represents an alkyl group having 1 to 10 carbon atoms, or aralkyl group having 7 to 15 carbon atoms).
Preferable examples of R² include a hydrogen atom, an unsubstituted alkyl group having 1 to 8 carbon atoms, and an unsubstituted aryl group having 6 to 15 carbon atoms.
In Formula (iii) or (iv), R³, R⁴, and R⁵ may be same or different from each other, and each represents a single bond or divalent linking group. Examples of the divalent linking group include an aliphatic hydrocarbon or an aromatic hydrocarbon. R³, R⁴, and R⁵ may have a substituent, and examples of the substituent, which can be introduced, include an alkyl group, an aralkyl group, an aryl group, an alkoxy group, and a halogen atom (-F, -Cl, -Br, or -I).
Preferable examples of R³, R⁴, and R⁵ include an unsubstituted alkylene group having 1 to 20 carbon atoms, an unsubstituted arylene group having 6 to 15 carbon atoms, and further preferable examples include an unsubstituted alkylene group having 1 to 8 carbon atoms. As necessary, R³, R⁴, and R⁵ may have another functional group which does not react with the isocyanate group in Formula (ii) (for example, an ester group, an urethane group, an amide group, an ureido group, or an ether group).
Furthermore, two or more of R², R³, R⁴, and R⁵ may be bound to each other to form a ring structure.
In Formula (iv), Ar represents a trivalent aromatic hydrocarbon which may have a substituent, and preferably represents an aromatic group having 6 to 15 carbon atoms.
Specific examples of the diisocyanate compound represented by Formula (ii) include the followings, however the present invention is not limited to them.
Aromatic diisocyanate compounds such as dimers of 2,4-tolylene diisocyanate and 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-xylylene diisocyanate, metaxylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, or 3,3'-dimethylbiphenyl-4,4'-diisocyanate; aliphatic diisocyanate compounds such as hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate, lysine diisocyanate, or dimmer acid diisocyanate; alicyclic diisocyanate compounds such as isophorone diisocyanate, 4,4'-methylene bis(cyclohexylisocyanate), methylcyclohexane-2,4(or 2,6)diisocyanate, or 1,3-(isocyanatemethyl) cyclohexane; and diisocyanate compounds which is a reactant of diol and diisocyanate, such as an adduct of 1 mol of 1,3-butyleneglycol and 2 mol of tolylene diisocyanate.
Among them, those having aromatic ring(s) such as 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, or tolylene diisocyanate are more preferable from the viewpoint of scratch resistance.
Specific examples of the diol compound having a carboxyl group represented by Formula (iii) or (iv) include the followings, however the present invention is not limited to them.
3,5-dihydroxybenzoic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxyethyl)propionic acid, 2,2-bis(3-hydroxypropylpropionic acid, 2,2-bis(hydroxymethyl)acetic acid, bis-(4-hydroxyphenyl)acetic acid, 4,4-bis-(4-hydroxyphenyl)pentane acid, and tartaric acid.
Among them, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxyethyl)propionic acid are preferable from the viewpoint of reactivity with isocyanate.
The polyurethane resin may be formed using two or more each of the diisocyanate compound represented by the above-described Formula (ii), and the diol compound having a carboxyl group represented by Formula (iii) or (iv).
In addition to the diol compound having a carboxyl group represented by Formula (iii) or (iv), another diol compound having no carboxyl group and may have a substituent which does not react with the isocyanate group in Formula (ii) may be used in combination to an extent which does not deteriorate alkali developability.
The polyurethane resin can be synthesized by heating the above-described diisocyanates compound and diol compound in an aprotonic solvent together with a known catalyst having an activity according to the reactivity of each compound.
The molar ratio between the diisocyanate compound and diol compound to be used is preferably 0.8:1 to 1.2:1. In cases where an isocyanate group remains at the terminal end of the polymer, the resin is treated with an alcohol, an amine, or the like to obtain a polyurethane resin with no remaining isocyanate group.
The weight average molecular weight f the polyurethane resin is preferably 1,000 or more, and further preferably in the range of 5,000 to 100,000. The polyurethane resin may be used alone or in combination of two or more types of them.
Next, the water-insoluble and alkali-soluble polyvinyl acetal resin is further described. The polyvinyl acetal resin used in the present invention is not particularly limited as long as it is insoluble in water and soluble in an alkali aqueous solution. Particularly, a polyvinyl acetal resin represented by Formula (v) is preferable.
[n1=5~85mol%. n2=0~60mol%, n3=0~20mol%, n4=3~60mol%]
Among the structural units above, the polyvinylacetal resin represented by Formula (v) contains structural units (i) to (iv), specifically a vinyl acetal component of structural unit (i) and a carboxyl group-containing ester component of structural unit (iv) as essential components and a vinylalcohol component of structural unit (ii) and a unsubstituted ester component of structural unit (iii) as other additional components, and may contain at least one of each structural unit. n1 to n4 each represent the component ratio (mol %) of each structural unit.
In structural unit (i), R¹ represents an alkyl group that may be substituted, a hydrogen atom, a carboxyl group, or a dimethylamino group. The substituent group is, for example, a carboxyl, hydroxyl, chloro, bromo, urethane, ureido, tertiary amino, alkoxy, cyano, nitro, amido, or ester group, or the like.
Specific examples of the groups R¹ in structural unit (i) include a hydrogen atom, methyl, ethyl, propyl, butyl, pentyl and carboxy groups, halogen atoms (-Br, -Cl, etc,.) and a cyano group-substituted methyl group, a 3-hydroxybutyl group, a 3-methoxybutyl group, a phenyl group, and the like; and among them, a hydrogen atom and propyl and phenyl groups are particularly preferable.

n1 is preferably in the range of 5 to 85 mol %, more preferably in the range of 25 to 70 mol %.
n2 is preferably in the range of 0 to 60 mol %, more preferably in the range of 10 to 45 mol %.
In structural unit (iii), R² represents an unsubstituted alkyl group. An alkyl group having 1 to 10 carbon atoms is preferable, and in particular, a methyl or ethyl group is more preferable, from the viewpoint of developing efficiency.
n3 is preferably in the range of 0 to 20 mol % and more preferably in the range of 1 to 10 mol%.

In structural unit (iv), R³ represents a carboxyl group-containing aliphatic, alicyclic, or aromatic hydrocarbon group; and those having 1 to 20 carbon atoms are preferable. The hydrocarbon group in structural unit (iv) above is preferably a hydrocarbon group prepared mainly in reaction of an acid anhydride such as succinic anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, or cis-4-cyclohexene-1,2-dicarboxylic anhydride and the resudual -OH group of polyvinylacetal, and among them, a condensate with phthalic anhydride or succinic anhydride is more preferable. It may be a hydrocarbon group obtained by using another cyclic acid anhydride.
In structural unit (iv), R³ may have a substituent other than a carboxyl group. Examples of the substituent groups include those represented by the following structures.
In the Formulae above, R⁴ represents an alkyl, aralkyl, or aryl group having 1 to 20 carbon atoms that may be substituted, and the substituent group that may be introduced is -OH, -C=N, -Cl, -Br, or -NO₂.
Specific examples of the group R³ in structural unit (iv) include, but are not limited to, the followings:

-C₂H₄COOH

-CH=CH-COOH
n4 is preferably in the range of 3 to 60 mol %, more preferably in the range of 10 to 55 mol %, from the viewpoint of developing efficiency.
The polyvinylacetal resin represented by Formula (v) can be prepared by forming an acetal in reaction of a polyvinylalcohol and an aldehyde and additionally allowing the residual hydroxy group to react with an acid anhydride.
Examples of the aldehydes for use include, but are not limited to, formaldehyde, acetaldehyde, propionaldehyde, butylaldehyde, pentylaldehyde, hexylaldehyde, glyoxylic acid, N,N-dimethylformamide di-n-butylacetal, bromoacetaldehyde, chloroacetaldehyde, 3-hydroxy-n-butylaldehyde, 3-methoxy-n-butylaldehyde, 3-(dimethylamino)-2,2-dimethyl propionaldehyde, cyanoacetaldehyde, and the like.
The acid content of the polyvinylacetal resin is preferably contained in the range of 0.5 to 5.0 meq/g (i.e., KOH (mg): 84 to 280) and more preferably in the range of 1.0 to 3.0 meq/g.
The molecular weight of the polyvinylacetal resin is preferably, approximately 5,000 to 400,000, more preferably approximately 20,000 to 300,000, as the weight-average molecular weight determined by gel permeation chromatography. These polyvinylacetal resins may be used alone or in combination of two or more.
The alkali-soluble resins for use in the lower layer may be used alone or in combination of two or more.
When the recording layer has a single layer structure, the content of the alkali-soluble resin is preferably 30 to 99 mass %, more preferably 40 to 95 mass %, with respect to the total solid matter in the recording layer, from the viewpoints of the sensitivity and durability of recording layer.
When the recording layer has a multilayer structure, the content of the alkali-soluble resin is preferably 40 to 98 mass %, more preferably 60 to 97 mass %, with respect to the total solid matter in the uppermost layer, from the viewpoints of the sensitivity and durability of recording layer.
The content of the alkali-soluble resin in the lower layer is preferably 40 to 95 mass %, more preferably 50 to 90 mass % with respect to the total solid matter in the lower layer.

(Development inhibitor)

The recording layer may contain a development inhibitor for improvement in its inhibition (solubilization-suppressing potential). When the recording layer has a multilayer structure, the development inhibitor is preferably contained in the uppermost layer.
The development inhibitor is not particularly limited, if it has interaction with the alkali-soluble resin, substantially reduces the solubility of the alkali-soluble resin in the developing solution in the unexposed region, and has a weaker interaction and thus become soluble in the developing solution in the exposed region; and quaternary ammonium salts, polyethylene glycol compounds, and others are used favorably. There are some in the photo-thermal converting agents and image-coloring agents described below that function as a development inhibitor, and these compounds may also be used favorably.
The quaternary ammonium salt is not particularly limited, and examples thereof include tetraalkylammonium salts, trialkylarylammonium salts, dialkyl diarylammonium salts, alkyltriarylammonium salts, tetraarylammonium salts, cyclic ammonium salts, and bicyclic ammonium salts.
Typical examples thereof include tetrabutylammonium bromide, tetrapentylammonium bromide, tetrahexylammonium bromide, tetraoctylammonium bromide, tetralaurylammonium bromide, tetraphenylammonium bromide, tetranaphthylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium iodide, tetrastearylammonium bromide, lauryltrimethylammonium bromide, stearyltrimethylammonium bromide, behenyltrimethylammonium bromide, lauryltriethylammonium bromide, phenyltrimethylammonium bromide, 3-trifluoromethylphenyltrimethylammonium bromide, benzyltrimethylammonium bromide, dibenzyldimethylammonium bromide, distearyldimethylammonium bromide, tristearylmethylammonium bromide, benzyltriethylammonium bromide, hydroxyphenyltrimethylammonium bromide, N-methylpyridinium bromide, and the like. In particular, the quaternary ammonium salts described in JP-A Nos. 2003-167332 and 2003-107688 are preferable.
From the viewpoints of development inhibition efficiency and easiness in coating the alkali-soluble resin, the amount of the quaternary ammonium salt added is preferably 0.1 to 50 mass %, more preferably 1 to 30 mass %, with respect to the total solid matter in the recording layer when a single-layered recording layer is used. Alternatively when a multi-layered recording layer is used, it is preferably 0.1 to 50 mass %, more preferably 1 to 30 mass %, with respect to the total solid matter in the top layer.
The polyethylene glycol compound is not particularly limited, and examples thereof include compounds having a structure presented the following Formula (vi).

R⁶¹ - (- O - (R⁶³ - O -)m - R⁶²)_n Formula (vi)
In Formula (vi), R⁶¹ represents a polyvalent alcohol or phenol residue; and R⁶² represents a hydrogen atom or an alkyl, alkenyl, alkynyl, alkyloyl, aryl or aryloyl group having 1 to 25 carbon atoms that may be substituted. R⁶³ represents an alkylene residue that may be substituted; m is an average of 10 or more; and n is an integer of 1 or more and 4 or less.
Examples of the polyethylene glycol compounds represented by Formula (vi) include polyethylene glycols, polypropylene glycols, polyethylene glycol alkylethers, polypropylene glycol alkylethers, polyethylene glycol arylethers, polypropylene glycol arylethers, polyethylene glycol alkylarylethers, polypropylene glycol alkylarylethers, polyethylene glycol glycerol esters, polypropylene glycol glycerol esters, polyethylene sorbitol esters, polypropylene glycol sorbitol esters, polyethylene glycol fatty acid esters, polypropylene glycol fatty acid esters, polyethylene glycol-modified ethylenediamines, polypropylene glycol-modified ethylenediamines, polyethylene glycol-modified diethylenetriamines, and polypropylene glycol-modified diethylenetriamines.
Typical examples thereof include polyethylene glycol 1000, polyethylene glycol 2000, polyethylene glycol 4000, polyethylene glycol 10000, polyethylene glycol 20000, polyethylene glycol 5000, polyethylene glycol 100000, polyethylene glycol 200000, polyethylene glycol 500000, polypropylene glycol 1500, polypropylene glycol 3000, polypropylene glycol 4000, polyethylene glycol methylether, polyethylene glycol ethylether, polyethylene glycol phenylether, polyethylene glycol dimethylether, polyethylene glycol diethylether, polyethylene glycol diphenylether, polyethylene glycol laurylether, polyethylene glycol dilaurylether, polyethylene glycol nonylether, polyethylene glycol cetylether, polyethylene glycol stearylether, polyethylene glycol distearylether, polyethylene glycol behenylether, polyethylene glycol dibehenylether, polypropylene glycol methylether, polypropylene glycol ethylether, polypropylene glycol phenylether, polypropylene glycol dimethylether, polypropylene glycol diethylether, polypropylene glycol diphenylether, polypropylene glycol laurylether, polypropylene glycol dilaurylether, polypropylene glycol nonylether, polyethylene glycol acetyl ester, polyethylene glycol diacetyl ester, polyethylene glycol benzoate ester, polyethylene glycol laurate ester, polyethylene glycol dilaurate ester, polyethylene glycol nonyl acid ester, polyethylene glycol cetyl acid ester, polyethylene glycol stearoyl ester, polyethylene glycol distearoyl ester, polyethylene glycol behenic acid ester, polyethylene glycol dibehenic acid ester, polypropylene glycol acetyl ester, polypropylene glycol diacetyl ester, polypropylene glycol benzoate ester, polypropylene glycol dibenzoate ester, polypropylene glycol laurate ester, polypropylene glycol dilaurate ester, polypropylene glycol nonyl acid ester, polyethylene glycol glycerol ether, polypropylene glycol glycerol ether, polyethylene glycol sorbitol ether, polypropylene glycol sorbitol ether, polyethylene glycol-modified ethylenediamines, polypropylene glycol-modified ethylenediamines, polyethylene glycol-modified diethylenetriamines, polypropylene glycol-modified diethylenetriamines, and polyethylene glycol-modified pentamethylene hexamines.
From the viewpoints of development inhibition efficiency and image-forming property, the amount of the polyethylene glycol compound added is preferably 0.1 to 50 mass %, more preferably, 1 to 30 mass %, with respect to the total solid matter in the recording layer, when a single-layered recording layer is used. When a multi-layered recording layer is used it is preferably 0.1 to 50 mass %, more preferably 1 to 30 mass %, with respect to the total solid matter in the top layer.
Although such a measure to improve the inhibition (solubilization-suppressing potential) often leads to deterioration in sensitivity, addition of the lactone compound described in JP-A No. 2002-361066 to the top layer is effective in avoiding the deterioration in sensitivity.
Combined use of a thermal-decomposable substance, such as onium salt, o-quinonediazide compound, aromatic sulfone compound, or aromatic sulfonic ester compound, that substantially decreases the solubility of the alkali-soluble resin when it is not decomposed, with the compound above as solubilization inhibitor is preferable, for improvement of the inhibition of the developing solution in the image region.
Examples of the onium salts for use in the invention include diazonium salts, ammonium salts, phosphonium salts, iodonium salts, sulfonium salts, selenonium salts, arsenium salts, and the like; examples of particularly favorable onium salts include the 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 ; the ammonium salts described in U.S. Patent Nos. 4,069,055 and 4,069,056 and JP-A No. 3-140140 ; the phosphonium salts described in D. C. Necker et al., Macromolecules, 17, 2468 (1984), C. S. Wen et al., Teh, Proc. Conf. Rad. Curing ASIA, p. 478 Tokyo, Oct (1988), and U.S. Patent Nos. 4,069,055 and 4,069,056 ; the iodonium salts described in J. V. Crivello et al., Macromolecules, 10(6), 1307 (1977), Chem. & Eng. News, Nov. 28, p. 31 (1988), EP Patent No. 104,143 , U.S. Patent Nos. 5,041,358 and 4,491,628 , and JP-A Nos. 2-150848 and 2-296514 ; the 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 Patent Nos. 370,693 , 233,567 , 297,443 , and 297,442 , U.S. Patent Nos. 4,933,377 , 3,902,114 , 4,491,628 , 4,760,013 , 4,734,444 , and 2,833,827 , and Germany Patent Nos. 2,904,626 , 3,604,580 , and 3,604,581 ; the selenonium salts described in J. V. Crivello et al., Macromolecules, 10(6), 1307 (1977), and J. V. Crivello et al., J. Polymer Sci, Polymer Chem. Ed., 17, 1047 (1979); the arsonium salts described in C. S. Wen et al., Teh, Proc. Conf. Rad. Curing ASIA, p. 478 Tokyo, Oct (1988); and the like.
Among the onium salts above, diazonium salts are particularly preferable. Particularly favorable diazonium salts are those described in JP-A No. 5-158230 .
Examples of the counter ions for the onium salt include anions of 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, p-toluenesulfonic acid, and the like.
Among them, anions of hexafluorophosphoric acid and an alkyl aromatic sulfonic acid such as triisopropylnaphthalenesulfonic acid or 2,5-dimethylbenzenesulfonic acid are favorable.
Favorable quinonediazides include o-quinonediazide compounds. The o-quinonediazide compound for use in the invention is a compound containing at least one o-quinonediazide group that increases its alkali-solubility by thermal decomposition; and compounds in various structures may be used. The o-quinonediazide accelerates solubilization of the top layer, while losing its function as a development inhibitor and converting itself into an alkali-soluble substance by thermal decomposition.
Examples of the o-quinonediazide compounds include the compounds described in J. Corsair, "Light Sensitive Systems" (John Wiley & Sons Inc.) p. 339 to 352, and o-quinonediazidesulfonic esters and amides, which are prepared in reaction with an aromatic polyhydroxy compound or an aromatic amino compound, are particularly favorable. The esters of benzoquinone-(1,2)-diazidesulfonyl chloride or naphthoquinone-(1,2)-diazide-5-sulfonyl chloride and a pyrogallol-acetone resin described in JP-B No. 43-28403 and the esters of benzoquinone-(1,2)-diazidesulfonyl chloride or naphthoquinone- (1,2)-diazide-5-sulfonyl chloride and a phenol-formaldehyde resin described in U.S. Patent Nos. 3,046,120 and 3,188,210 are also used favorably.
In addition, esters of naphthoquinone-(1,2)-diazide-4-sulfonyl chloride and a phenol formaldehyde resin or a cresol-formaldehyde resin and esters of naphthoquinone-(1,2)-diazide-4-sulfonyl chloride and a pyrogallol-acetone resin are also used favorably. Other useful o-quinonediazide compounds are disclosed in many patents, for example, in JP-A Nos. 47-5303 , 48-63802 , 48-63803 , 48-96575 , 49-38701 , and 48-13354 ; JP-B Nos. 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 ; British Patent Nos. 1,227,602 , 1,251,345 , 1,267,005 , 1,329,888 , and 1,330,932 ; German Patent No. 854,890 ; and others.
When a single-layered recording layer is used, the amount of the o-quinonediazide compound added is preferably in the range of 1 to 50 mass %, more preferably 5 to 30 mass % with respect to the total solid matter in the recording layer. When a multi-layered recording layer is used, it is preferably in the range of 1 to 50 mass %, more preferably 5 to 30 mass %, and particularly preferably10 to 30 mass %, with respect to the total solid matter in the top layer. These compounds may be used alone or in combination of two or more.
The polymers of the (meth)acrylate monomer having two or more perfluoroalkyl groups and having 3 to 20 carbon atoms in the molecule described in JP-A No. 2000-187318 are preferably used additionally, for the purpose of strengthening the inhibition of recording layer surface and improving the surface resistance to scratching.
When a single-layered recording layer is used, the addition amount is preferably 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, with respect to the total solid matter in the recording layer. When a multi-layered recording layer is used, it is preferably 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, with respect to the total solid matter in the top layer.

(Infrared absorbent)

The recording layer according to the invention contains an infrared absorbent.
Addition of an infrared absorbent having the absorption maximum in the infrared region and a photo-thermal converting potential makes it possible to record an image on the planographic printing plate precursor according to the invention by irradiation of infrared laser.
The infrared absorbent for use in the invention is not particularly limited, if it is a dye absorbing infrared or near-infrared light and generating heat, and any one of known infrared absorbents may be used.
When the recording layer according to the invention has a multilayer structure, at least one of the layer closest to the support (lower layer) and the layer farthest from the support (uppermost layer) is a layer containing the infrared absorbent, and it is preferable to add an infrared absorbent both to the lower and uppermost layers.
Examples of the infrared absorbents for use include commercially available dyes and the dyes described in literatures (e.g., "Dye Handbook" Soc. Synthetic Organic Chemistry Ed., 1970). Typical examples thereof include azo dyes, metal complex salt azo dyes, pyrazolone azo dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinonimine dyes, methine dyes, cyanine dyes, and the like. Among these dyes, those absorbing infrared or near-infrared light are particularly preferable in the invention, because they are more compatible with lasers emitting infrared or near-infrared light.
Favorable examples of the dyes include the cyanine dyes described in JP-A Nos. 58-125246 , 59-84356 , and 60-78787 and U.S. Patent No. 4,973,572 ; the methine dyes described in JP-ANos. 58-173696 , 58-181690 , and 58-194595 ; the naphthoquinone dyes described in JP-ANos. 58-112793 , 58-224793 , 59-48187 , 59-73996 , 60-52940 , and 60-63744 ; the squalilium dyes described in JP-A No. 58-112792 ; the cyanine dyes described in British Patent 434,875 ; and the like.
Other favorable examples of the dyes include the infrared-absorbing sensitizers described in U.S. Patent No. 5,156,938 , and particularly favorable examples thereof include the substituted arylbenzo(thio)pyrylium salts described in U.S. Patent No. 3,881,924 ; the trimethinethiapyrylium salts described in JP-A No. 57-142645 ( U.S. Patent No. 4,327,169 ); the pyrylium compounds described in JP-A Nos. 58-181051 , 58-220143 , 59-41363 , 59-84248 , 59-84249 , 59-146063 , and 59-146061 ; the cyanine dyes described in JP-ANo. 59-216146 ; the pentamethinethiopyrylium salts described in U.S. Patent No. 4,283,475 ; the pyrylium compounds described in JP-B No. 5-13514 and 5-19702 ; and the like; as well as commercial products such as EpolightIII-178, EpolightIII-130, and EpolightIII-125 manufactured by Epolin Inc.
Other particularly favorable examples thereof include the infrared-absorbing dyes represented by Formulae (I) and (II) described in U.S. Patent No. 4,756,993 .
Among these dyes, particularly preferable are cyanine dyes, squalilium dyes, pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes. Cyanine dyes and indolenine cyanine dye are further more preferably, and examples of the particularly preferable dyes include cyanine dyes represented by the following Formula (a).
In Formula (a), X¹ represents a hydrogen or halogen atom, -NPh₂, X²-L¹ or a group shown below. X² represents an oxygen, nitrogen, or sulfur atom; and L¹ represents a hydrocarbon group having 1 to 12 carbon atoms, a hetero atom-containing aromatic ring, a hetero atom-containing hydrocarbon group having 1 to 12 carbon atoms. The hetero atom is N, S, O, a halogen atom, or Se. Xa^- is the same as W^1- described below; and R^a represents a hydrogen atom or a substituent group selected from alkyl, aryl, and substituted or unsubstituted amino groups, and halogen atoms.
In Formula (a), R¹ and R² each independently represent a hydrocarbon group having 1 to 12 carbon atoms. R¹ and R² each preferably represent a hydrocarbon group having two or more carbon atoms, and R¹ and R² particularly preferably bind to each other, forming a 5- or 6-membered ring, from the point of the storage stability of the recording layer coating solution.
Ar¹ and Ar² each independently represent an aromatic hydrocarbon group that may be substituted. Favorable aromatic hydrocarbon groups include benzene and naphthalene rings. Favorable substituent groups include hydrocarbon groups having 12 or fewer carbon atoms, halogen atoms, and alkoxy groups having 12 or fewer carbon atoms. Y¹ and Y² each independently represent a sulfur atom or a dialkylmethylene group having 12 or fewer carbon atoms. R³ and R⁴ each independently represent a hydrocarbon group having 20 or fewer carbon atoms that may have one or more substituents. Favorable substituent groups include alkoxy groups having 12 or fewer carbon atoms, a carboxyl group, and a sulfo group. R⁵, R⁶, R⁷ and R⁸ each independently represent a hydrogen atom or a hydrocarbon group having 12 or fewer carbon atoms. It is preferably a hydrogen atom, from the availability of raw material. W^1- represents a counter anion. However, when the cyanine dye represented by Formula (a) has an anionic substituent group in its structure, there is no need for neutralization of electric charge, and thus, no W^1- is needed. W^1- is preferably a halide, perchlorate, tetrafluoroborate, hexafluorophosphate, or sulfonate ion, particularly preferably, a perchlorate, hexafluorophosphate, or arylsulfonate ion, form the point of the storage stability of the recording-layer coating solution.
When a multi-layered recording layer is used, the infrared absorbent is preferably added to the uppermost layer of recording layer or the layer close to it, form the viewpoint of sensitivity. It is possible to make the layer more sensitive and the unexposed region more alkali-resistant, particularly by adding a dye having solubilization-suppressing potential such as cyanine dye together with an alkali-soluble resin having a phenol group to the layer. These infrared absorbents may be added to the lower layer or the uppermost layer, or alternatively to both uppermost and lower layers. It is possible to raise the sensitivity further, by adding it to the lower layer. When infrared absorbents are added both to the uppermost and lower layers, they may be the same as or different from each other.
Alternatively, the infrared absorbent may be added to a layer formed separately from the recording layer. When an additional layer is used, the layer added with the absorbent is preferably close to the recording layer.
The amount of the infrared absorbent added is preferably 3 to 50 mass %, more preferably, 5 to 40 mass %, with respect to the total solid matter in the recording layer, when a single-layered recording layer is used. When the recording layer is a multi-layered recording layer, the amount of the infrared absorbent added to the uppermost layer is preferably 0.01 to 50 mass %, more preferably 0.1 to 30 mass %, and particularly preferably 1.0 to 30 mass %, with respect to the total solid matter in the uppermost layer. It is possible to obtain a recording layer favorable in sensitivity and durability, by adjusting the addition amount in the range above. Alternatively when added to the lower layer, the infrared absorbent is added in an amount of preferably 0 to 20 mass %, more preferably 0 to 10 mass %, and particularly preferably 0 to 5 mass %, with respect to the total solid matter in the lower layer.
When the infrared absorbent is added to the lower layer, use of an infrared absorbent having solubilization-suppressing potential leads to deterioration in the solubility of the lower layer, but also to possible improvement in the solubility of the lower layer due to the heat generated by the infrared absorbent during infrared laser irradiation, and thus, the compounds added and the addition amounts thereof should be selected, considering the balance thereof. It is difficult to obtain improvement in solubility in the region close to the support separated by 0.2 to 0.3 µm because of diffusion of the heat generated by irradiation, and thus, addition of an infrared absorbent to the lower layer may lead to deterioration in solubility and also in sensitivity. For that reason, an addition amount that decreases the solubilization speed of the lower layer in developing solution (25 to 30°C) to 30 nm/sec is not favorable, even if it is in the range above.

(Other additives)

In forming the recording layer, various additives may be added as needed in addition to the components above in the ranges that do not impair the advantageous effects of the invention.
When a multi-layered recording layer is used, the additives below may be added only to the lower or uppermost layer of recording layer or both to the uppermost and lower layers.

An acid anhydride, phenol or organic acid may be added to the recording layer for improvement in sensitivity.
The acid anhydride is preferably a cyclic acid anhydride, and typical examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 3,6-endoxy-tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, α-phenylmaleic anhydride, succinic anhydride, pyromellitic anhydride and the like, as described in U.S. Patent No. 4,115,128 . Favorable examples of non-cyclic acid anhydrides include acetic anhydride and the like.
Examples of the phenols include bisphenol A, 2,2'-bishydroxydiphenylsulfone, 4,4'-bishydroxydiphenylsulfone, 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, and the like.
Examples of the organic acids include the sulfonates, sulfinates, alkyl sulfates, phosphonic acids, phosphoric esters and carboxylic acids described in JP-A Nos. 60-88942 and 2-96755 ; and typical 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-toluyl acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid, ascorbic acid, and the like.
When a single-layered recording layer is used, the content of the acid anhydride, phenol or organic acid is preferably 0.05 to 20%, more preferably 0.1 to 15 mass %, and particularly preferably 0.1 to 10 mass %, with respect to the total solid in the recording layer. When a multi-layered recording layer is used, the content of the acid anhydride, phenol or and organic acid is preferably 0.05 to 20 mass %, more preferably 0.1 to 15 mass %, and particularly preferably 0.1 to 10 mass %, with respect to the total solid in the lower or uppermost layer of the recording layer.

The nonionic surfactant described in JP-A Nos. 62-251740 and 3-208514 , the amphoteric surfactant described in JP-A Nos. 59-121044 and 4-13149 , the siloxane compound described in EP Patent No. 950517 , or the fluorine-containing copolymer described in JP-A Nos. 62-170950 , 11-288093 , and 2003-057820 may be added to the recording layer, for improvement in coatability and stability during processing under the development condition.
When a single-layered recording layer is used, the content of the surfactant is preferably 0.01 to 15 mass %, more preferably 0.05 to 5 mass %, and particularly preferably 0.1 to 0.5 mass %, with respect to the total solid in the recording layer rate.
When a multi-layered recording layer is used, the content of the surfactant is preferably 0.01 to 15 mass %, more preferably 0.1 to 5.0 mass %, and still more preferably 0.5 to 2.0 mass %, with respect to the total solid in the lower or uppermost layer of recording layer.

<Baking-out agent/colorant>

A baking-out agent or an image-coloring agent such as dye or pigment may be added to the recording layer to obtain a visible image immediately after heating by exposure.
Typical examples of the baking-out agents are combinations of a compound that generates an acid by heating induced by light exposure (photo-induced acid-releasing agent) and an organic dye that can form a salt therewith. Specific examples thereof include combination of the o-naphtoquinonediazide-4-sulfone halide described in JP-A Nos. 50-36209 or 53-8128 and a salt-forming organic dye; and combination of the trihalomethyl compound described in JP-ANos. 53-36223 , 54-74728 , 60-3626 , 61-143748 , 61-151644 or 63-58440 and a salt-forming organic dye. The trihalomethyl compounds include oxazole and triazine compounds, and both of them give a baked-out image superior in storability and definition.
In addition to the salt-forming organic dyes described above, other dyes may be used as the image-coloring agents. Favorable dyes including the salt-forming organic dyes include oil-soluble dyes and basic dyes. Typical 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 (manufactured by Orient Chemical Industries); Victoria Pure Blue, crystal violet lactone, crystal violet (CI42555), methyl violet (CI42535), ethyl violet, rhodamine B (CI145170B), malachite green (CI42000), methylene blue (CI52015), and the like. The dyes described in JP-A No. 62-293247 are particularly preferable.
When a single-layered recording layer is used, the dye is preferably added in an amount of preferably 0.01 to 10 mass %, preferably 0.1 to 3 mass %, with respect to the total solid matter in the recording layer.
When a multi-layered recording layer is used, the dye is added in an amount of 0.01 to 10 mass %, preferably 0.1 to 3 mass %, with respect to the total solid matter in the lower or uppermost layer of recording layer.

A plasticizer may be added to the recording layer for improvement in the flexibility of the coated film.
Examples thereof include butylphthalyl, polyethylene glycol, tributyl citrate, diethyl phthalate, dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, tricresyl phosphate, tributyl phosphate, trioctyl phosphate, tetrahydrofurfuryl oleate, acrylic or methacrylic acid oligomers and polymers, and the like.
When a single-layered recording layer is used, the plasticizer is added at a rate of 0.5 to 10 mass %, preferably 1.0 to 5.0 mass %, with respect to the total solid matter in the recording layer.
When the recording layer has a multilayer structure, it is added at a rate of 0.5 to 10 mass %, preferably 1.0 to 5.0 mass %, with respect to the total solid matter in the lower or uppermost layer of recording layer.

<Wax>

A compound lowering the static friction coefficient of the surface may be added to to the uppermost layer of the single- or multi-layered recording layer according to the invention for improvement in resistance to scratch. Typical examples thereof include the compounds having a long-chain alkylcarboxylic ester described in U.S. Patent No. 6,117,913 and Japanese Patent Application Nos. 2001-261627 , 2002-032904 , and 2002-165584 filed by the applicant, and the like.
When a single-layered recording layer is used, the addition amount thereof is preferably 0.1 to 10 mass %, preferably 0.5 to 5.0 mass %, with respect to the total solid matter in the recording layer.
When the recording layer has a multilayer structure, the rate thereof in the uppermost layer of recording layer is preferably 0.1 to 10 mass % and more preferably 0.5 to 5 mass %.

[Formation of recording layer]

The recording layer of the planographic printing plate precursor according to the invention is formed by dissolving the components constituting the recording layer in a solvent and coating the solution.
Examples of the solvents for use 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 in combination of two or more.
When a multi-layered recording layer is used, the lower and uppermost layers of recording layer are in principle formed in two separate layers.
Examples of the methods of forming the two separate layers include a method of using the difference in solvent solubility of the components contained in the uppermost and lower layers, a method of coating the uppermost layer, then drying it rapidly and thus removing the solvent, and the like.
Details of these methods are described in JP-A No. 2002-251003 .
It is also possible to make the uppermost and lower layers partially compatible with each other to the order that is favorable for obtaining the advantageous effects of the invention and for providing the recoding layer with a new function. In such a case, it is possible to make the layers partially compatible with each other, for example, by controlling the difference in solvent solubility, or by controlling the vaporization speed of the solvent in the uppermost layer coated.
The concentration of the components (total solid including additives) excluding solvents in the recording-layer coating solution to be coated on the substrate is preferably 1 to 50 mass %.
Various coating methods including, for example, bar coater coating, spin coating, spray coating, curtain coating, immersion, air knife coating, blade coating, roll coating, and the like, may be used for coating.
In the case of a multi-layered recording layer, the uppermost layer is favorably coated by a non-contact method, for prevention of damage to the lower layer during application. Alternatively, a bar coater coating method, a commonly used method for solution-based coating although it is a contact-type method, may be used, and, if used, the uppermost layer is preferably coated while the bar coater is driven in the normal rotation, for prevention of the damage to the lower layer.
When a single-layered recording layer is used, the coating amount of the recording layer after drying is preferably in the range of 0.3 to 3.0 g/m² and more preferably in the range of 0.5 to 2.5 g/m².
When a multi-layered recording layer is used, the coating amount of the lower layer components after drying is preferably in the range of 0.5 to 4.0 g/m² and more preferably in the range of 0.6 to 2.5 g/m². It is possible to obtain an image superior in printing durability, by making the content 0.5 g/m² or more and an image favorable in reproducibility and sensitivity by making it 4.0 g/m² or less.
The coating amount of the uppermost layer components after drying is preferably in the range of 0.05 to 1.0 g/m² and more preferably in the range of 0.08 to 0.7 g/m². It is possible to obtain an image favorable in development latitude and scratch resistance by making it 0.05 g/m² or more and an image favorable in sensitivity by making it 1.0 g/m² or less.
The coating amount of the lower and uppermost layers combined after drying is preferably in the range of 0.6 to 4.0 g/m² and more preferably in the range of 0.7 to 2.5 g/m². It is possible to obtain an image favorable in printing durability by making it 0.6 g/m² or more and an image favorable in image reproducibility and sensitivity by making it 4.0 g/m² or less.

[Organic polymer layer]

In the invention, a support characteristically has an organic polymer layer on or above the surface thereof opposite to that of the recording layer.
Hereinafter, components constituting the organic polymer layer will be described.

(Organic polymer)

The organic polymer layer contains an organic polymer as a base polymer forming the layer. The following are examples of the organic polymer which are preferably used as the base polymer, but the organic polymer is not limited to them.
Specifically, novolak resins and pyrogallol acetone resins such as a phenol formaldehyde resin, m-cresol formaldehyde resin, p-cresol formaldehyde resin, m-/p-mixed cresol formaldehyde resin, and phenol /cresol (may be m-, p-, or mixture of m-/p-) mixed formaldehyde resin.
Specific examples include at least one resin selected from the group consisting of a saturated copolymeric polyester resin, a phenoxy resin, a polyvinyl acetal resin, a vinylidene chloride copolymer resin, and a polystyrene resin.
The saturated copolymeric polyester resin is one containing a dicarboxylic acid unit and a diol unit. Examples of the dicarboxylic acid unit of polyester for use in the present invention include aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, tetrabromophthalic acid, or tetrachlorophthalic acid; and saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid, succinic acid, oxalic acid, suberic acid, sebacic acid, malonic acid, or 1,4-cyclohexanedicarboxylic acid.
Examples of the diol unit include aliphatic chain diols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol' 1,3-butylene glycol, 2,3-butylene glycoL¹,4-butylene glycol, neopentyl glycol, hexane diol, 2,2,4-trimethyl-1,3-pentanediol; and ring diol such as 1,4-bis-β-hydroxyethoxy cyclohexane, cyclohexane dimethanol, tricyclodecane dimethanol, bisphenoldioxy ethyl ether, or bisphenoldioxypropyl ether.
These dicarboxylic acid and diol units are used as copolymer units, in which there are at least one type of each of dicarboxylic acid units and diol units, and there are two or more types of one or other of them, copolymerized. The properties of the copolymer are determined by the copolymerization composition and molecular weight thereof.
The organic polymer layer in the present invention can be provided by film thermocompression or by a melt lamination method, however application from a solution is more preferable for efficiently providing a thin layer. Accordingly, when a copolymer polyester resin is used as the organic polymer, the resin is preferably non-crystalline and readily soluble in various industrial organic solvents.
When a copolymer polyester resin used as the organic polymer, the molecular weight is preferably 10,000 or more from the viewpoint of the film strength of the organic polymer layer.
Phenoxy resins are, as is the case with epoxy resins, prepared from bisphenol A and epichlorohydrin, and exhibit superior chemical resistance and adhesive properties to epoxy resin but without the assistance of curing agents or catalysts, thus are preferable as a main component of the back coat.
Polyvinyl acetal resins are resins prepared by acetalizing polyvinyl alcohol with aldehydes such as butyl aldehyde or formaldehyde, and polyvinyl butyral resin and polyvinyl formal resin are preferably used. The physical and chemical properties of these polyvinyl acetal resins vary with the degree of acetalization, and the composition ratio of hydroxy groups and acetyl groups and degree of polymerization. In the organic polymer layer in the present invention, those polyvinyl acetal resins having a glass transition temperature of 60°C or higher are preferable.
As vinylidene chloride copolymer resins, copolymer resins of a vinylidene chloride monomer, vinyl monomers such as vinyl chloride, vinyl acetate, ethylene, or vinyl methyl ether, and acryl monomers such as (meth)acrylic acid ester or (meth)acrylonitrile may be used. Among these, vinylidene chloride copolymers containing acrylonitrile in the range of 20 mol% or less are preferable because they are readily soluble in general-purpose organic solvents.
The content of the organic polymer in the total solid matter of the organic polymer layer is preferably 99.99 to 70 mass%, more preferably 99.9 to 80 mass%, and particularly preferably 99.5 to 90 mass%.
The organic polymer layer may contain another hydrophobic polymer compound as needed, in addition to the organic polymer. Favorable examples of the hydrophobic polymer compounds include polybutene, polybutadiene, polyamide, unsaturated copolymeric polyester resins, polyurethane, polyurea, polyimide, polysiloxane, polycarbonate, epoxy resins, chlorinated polyethylene, alkylphenol aldehyde condensation resins, polyvinyl chloride, polyvinylidene chloride, polystyrene, acrylic resins and the copolymers thereof, hydroxycellulose, polyvinylalcohol, cellulose acetate, carboxymethylcellulose, and the like.
Other favorable hydrophobic polymer compounds include copolymers containing the following monomer (1m) to (12m) as the structural unit and having a molecular weight normally of 10,000 to 200,000:

(1m) aromatic hydroxyl group-containing acrylamides, methacrylamides, acrylic esters, methacrylic esters and hydroxystyrenes, such as N-(4-hydroxyphenyl)acrylamide, N-(4-hydroxyphenyl)methacrylamide, o-, m- and p-hydroxystyrenes, o-, m- and p-hydroxyphenyl acrylates and methacrylates;
(2m) aliphatic hydroxyl group-containing acrylic esters and methacrylic esters such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate;
(3m) unsubstituted and substituted acrylic esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, cyclohexyl acrylate, octyl acrylate, phenyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, 4-hydroxybutyl acrylate, glycidyl acrylate, and N-dimethylaminoethyl acrylate;
(4m) unsubstituted and substituted methacrylic esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, octyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, 4-hydroxybutyl methacrylate, glycidyl methacrylate, and N-dimethylaminoethyl methacrylate;
(5m) acrylamides and methacrylamides such as acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-cyclohexylmethacrylamide, N-hydroxyethylacrylamide, N-hydroxyethylacrylamide, N-phenylacrylamide, N-phenylmethacrylamide, N-benzylacrylamide, N-benzylmethacrylamide, N-nitrophenylacrylamide, N-nitrophenylmethacrylamide, N-ethyl-N-phenylacrylamide and N-ethyl-N-phenylmethacrylamide;
(6m) vinyl ethers such as ethyl vinylether, 2-chloroethyl vinylether, hydroxyethyl vinylether, propyl vinylether, butyl vinylether, octyl vinylether, and phenyl vinylether;
(7m) vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, and vinyl benzoate;
(8m) styrenes such as styrene, methylstyrene, and chloromethylstyrene;
(9m) vinyl ketones such as methyl vinylketone, ethyl vinylketone, propyl vinylketone, and phenyl vinylketone;
(10m) olefins such as ethylene, propylene, isobutylene, butadiene, and isoprene;
(11m) N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile, and methacrylonitrile; and
(12m) acrylamides such as N-(o-aminosulfonylphenyl)acrylamide, N-(m-aminosulfonylphenyl)acrylamide, N-(p-aminosulfonylphenyl)acrylamide, N-(1-(3 -aminosulfonyl)naphthyl)acrylamide, and N-(2-aminosulfonylethyl)acrylamide; methacrylamides such as N-(o-aminosulfonylphenyl)methacrylamide, N-(m-aminosulfonylphenyl)methacrylamide, N-(p-aminosulfonylphenyl)methacrylamide, N-(1-(3-aminosulfonyl)naphthyl)methacrylamide, and N-(2-aminosulfonylethyl)methacrylamide; unsaturated sulfonamides of acrylic ester such as o-aminosulfonylphenyl acrylate, m-aminosulfonylphenyl acrylate, p-aminosulfonylphenyl acrylate, and 1-(3-aminosulfonylphenylnaphthyl)acrylate; and unsaturated sulfonamides of methacrylic ester such as o-aminosulfonylphenyl methacrylate, m-aminosulfonylphenyl methacrylate, p-aminosulfonylphenyl methacrylate, and 1-(3-aminosulfonylphenylnaphthyl) methacrylate.

In addition, monomers described above may be copolymerized with another copolymerizable monomer. Favorable hydrophobic polymer compounds also include, but are not limited to, copolymers obtained by copolymerization of the monomers above and additional modification with, for example, glycidyl acrylate, glycidyl methacrylate, or the like.
These hydrophobic polymer compounds may be added in an amount in the range of 50 mass % or less with respect to the total solid matter in the organic polymer layer, but are added preferably in an amount of 30 mass % or less, however the amount is preferably 30 mass% or less in order to capitalize on the properties of the saturated copolymeric polyester resin, the phenoxy resin, the polyvinyl acetal resin, and the vinylidene chloride copolymerization resin, which are preferably used as the organic polymer.

(Other components)

A plasticizer, a surfactant and other additives may be added as needed to the organic polymer layer in the range that does not impair the advantageous effects of the invention, for improvement in flexibility and coated surface and adjustment of the lubricity.
Favorable examples of the plasticizers include phthalic esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthanolate, diisobutyl phthalate, dioctyl phthalate, octyl capryl phthalate, dicyclohexyl phthalate, ditridecyl phthalate, butylbenzyl phthalate, diisodecyl phthalate, and diallyl phthalate; glycol esters such as dimethylglycol phthalate, ethylphthalyl ethylglycolate, methylphthalyl ethylglycolate, butylphthalyl butylglycolate, and triethylene glycol dicaprylic ester; phosphate esters such as tricrezyl phosphate and triphenyl phosphate; aliphatic dibasic esters such as isobutyl adipate, dioctyl adipate, dimethyl sebacate, dibutyl sebacate, dioctyl azelate, and dibutyl maleate; polyglycidyl methacrylate, triethyl citrate, glycerol triacetyl ester, butyl laurate, and the like.
The amount of the plasticizer added to the organic polymer layer varies according to the kind of the organic polymer used for the organic polymer layer, and is preferably added in an amount in the range that does not decrease the glass transition temperature of the polymer layer to 60°C or lower.
The surfactants include anionic, cationic, nonionic and amphoteric surfactants. Typical examples thereof include nonionic surfactants such as polyoxyethylene alkylethers, polyoxyethylene alkylphenylethers, polyoxyethylene polystyrylphenylethers, polyoxyethylene polyoxypropylene alkylethers, glycerols partially esterified with a fatty acid, sorbitans partially esterified with a fatty acid, pentaerythritols partially esterified with a fatty acid, propylene glycol monofatty acid esters, sucroses partially esterified with a fatty acid, polyoxyethylene sorbitans partially esterified with a fatty acid, polyoxyethylene sorbitols partially esterified with a fatty acid, polyethylene glycol fatty acid esters, polyglycerins partially esterified with a fatty acid, polyoxyethylene-modified castor oils, polyoxyethylene glycerols partially esterified with a fatty acid, fatty acid diethanol amides, N,N-bis-2-hydroxyalkylamines, polyoxyethylene alkylamine, triethanolamine fatty acid esters, and trialkylamine oxides; anionic surfactants such as fatty acid salts, abietate salts, hydroxyalkanesulfonate salts, alkanesulfonate salts, dialkyl sulfosuccinate ester salts, straight-chain alkylbenzenesulfonate salts, branching-chain alkylbenzenesulfonate salts, alkylnaphthalenesulfonate salts, alkylphenoxypolyoxyethylenepropyl sulfonate salts, polyoxyethylenealkylsulfophenylether salts, N-methyl-N-oleyltaurine sodium salt, N-alkyl-sulfoscuccinic monoamide disodium salts, petroleum sulfonate salts, sulfated beef tallow oil, sulfate ester salts of a fatty acid alkyl ester, alkylsulfate ester salts, polyoxyethylene alkylether sulfate ester salts, fatty acid monoglyceride sulfate ester salts, polyoxyethylene alkylphenylether sulfate ester salts, polyoxyethylene styrylphenylether sulfate ester salts, alkylphosphate ester salts, polyoxyethylene alkylether phosphate ester salts, polyoxyethylene alkylphenylether phosphate ester salts, partial hydrolysates of styrene/maleic anhydride copolymers, partial hydrolysates of olefin/maleic anhydride copolymers, and formalin condensates of naphthalenesulfonate salts; cationic surfactants such as alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamine salts, and polyethylene polyamine derivatives; amphoteric surfactants such as carboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfate esters, and imidazolines; and the like. In the surfactants above, the polyoxyethylene in the polyoxyethylene-based surfactants may be replaced with a polyoxyalkylene such as polyoxymethylene, polyoxypropylene, or polyoxybutylene, and those surfactants are also included in the examples.
Still more preferable surfactants are fluorochemical surfactants containing a perfluoroalkyl group in the molecule. Examples of the fluorochemical surfactants include anionic surfactants such as perfluoroalkylcarboxylate salts, perfluoroalkylsulfonate salts, and perfluoroalkylphosphate esters; ampholytic surfactants such as perfluoroalkylbetaines; cationic surfactants such as perfluoroalkyltrimethylammonium salt; and nonionic surfactants such as perfluoroalkylamine oxides, perfluoroalkylethyleneoxide adducts, oligomers containing perfluoroalkyl and hydrophilic groups, oligomers containing perfluoroalkyl and oleophilic groups, oligomers containing perfluoroalkyl, hydrophilic and oleophilic groups, and urethanes containing perfluoroalkyl and oleophilic groups; and the like.
The surfactants may be used alone or in combination of two or more, in an amount of preferably in the range of 0.001 to 10 mass %, more preferably 0.01 to 5 mass % in the organic polymer layer.
The organic polymer layer may contain additionally other additives including dye for coloring, silane-coupling agent for improvement in adhesion to aluminum support, diazonium salt-containing diazo resin, organic phosphonic acid, organic phosphoric acid, cationic polymer, and lubricant such as common wax, higher fatty acid, higher fatty acid amide, dimethylsiloxane-based silicone compound, modified dimethylsiloxane, or polyethylene powder.
The thickness of the organic polymer layer is arbitrary, if it is a thickness resistant to scratching on the recording layer without use of insert paper, and is normally in the range of 0.05 to 50 µm, more preferably 0.5 to 25 µm, and still more preferably 1.0 to 20 µm. When the thickness is in the range above, it is possible to prevent scratching or the like on the recording layer effectively, even when the planographic printing plate precursors are handled as stacked.

(Formation of organic polymer layer)

The organic polymer layer according to the invention is formed by preparing a coating solution by dissolving the components for the organic polymer layer and coating the coating solution on the face of the substrate opposite to the recording layer (rear face).
The organic solvents described in JP-A No. 62-251739 may be used alone or in combination as the solvent. Examples of the solvents 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 may be used alone or as a mixture.

(Properties of organic polymer layer)

The organic polymer layer preferably has a dynamic friction coefficient of the organic polymer layer surface in the range of 0.20 to 0.70, for maximizing the advantageous effects of the invention.
The dynamic friction coefficient is a value determined according to standard ASTM D1894, the disclosure of which is incorporated by reference herein, by bringing the organic polymer layer surface in contact with the surface of the recording layer formed on the face of support opposite to the organic polymer layer.
As described above, the infrared sensitive planographic printing plate precursor of the present invention has a coefficient of static friction between the recording layer and the organic polymer layer in the range of from 0.45 to 0.60, thus is able to create a state that the contact surface between the recording layer and the organic polymer layer has appropriate lubricity with no adhesive property. Therefore, a stack of planographic printing plate precursors can be readily formed with no interleaf sheets, and displacement between the plate materials in the formed stack of planographic printing plate precursors due to vibrations can be prevented. Furthermore, even when the plate materials are stacked with no interleaf sheets, an excellent effect can be achieved of effectively inhibiting damage to the recording layer in the manufacturing, plate-making, and other processes or in transfer during packaging or transportation after shipping as a product.

[Support]

The support for use in the planographic printing plate precursor according to the invention is not particularly limited, if it is a dimensionally stable plate-shaped material having needed strength and durability, and examples thereof include paper, papers laminated with a plastic film (such as of polyethylene, polypropylene, or polystyrene), metal plates (such as of aluminum, zinc, and copper), plastic films (such as of cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinylacetal), papers and plastic films laminated or vapor-deposited with the metal above, and the like.
Among them, the support for use in the invention is preferably a polyester film or an aluminum plate, and particularly preferable an aluminum plate, as it is superior in dimensional stability and relatively cheap. Favorable aluminum plates are pure aluminum plates and alloy plates containing aluminum as the main component and small amounts of foreign elements, or may be plastic films laminated or deposited with aluminum. The foreign elements in the aluminum alloys include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content of the foreign elements in the alloy is 10 mass % at the maximum.
Although the most preferable aluminum in the invention is pure aluminum, the aluminum plate may contain a small amount of foreign elements, as it is difficult to prepare completely pure aluminum due to the problems in refining process.
As described above, the aluminum plates to be used in the invention are not particularly specified, and any one of the aluminum plates known and used in the art may be used arbitrarily. The thickness of the aluminum plate for use in the invention is approximately 0.1 mm to 0.6 mm, preferably 0.15 mm to 0.4 mm, and particularly preferably 0.2 mm to 0.3 mm.
The aluminum plate may be surface-treated as needed, for example, by surface-roughening treatment, anodizing treatment, or the like. Hereinafter, the surface treatments will be described briefly.
If desired, the surface of the aluminum plate is subjected, before surface roughening, to degreasing treatment for removing the rolling oils on the surface thereof with a surfactant, organic solvent, aqueous alkaline solution, or the like. Various methods may be used for surface roughening of aluminum plates, and examples thereof include methods of scratching mechanically, dissolving the surface electrochemically, and dissolving selectively the surface chemically. The mechanical methods include various methods known in the art such as ball milling, brush milling, blast milling, and buff milling. The electrochemical surface roughening may be conducted, for example, in an electrolyte containing hydrochloric acid or nitric acid by applying alternate or direct current. Alternatively, the combined mechanical and electrochemical method described in JP-ANo. 54-63902 may also be sued.
The aluminum plate surface-roughened in this manner may be etched in an alkaline solution and neutralized and then subjected to an anodizing treatment if desired for improvement in the water holding property and abrasion resistance of the surface. Any one of various electrolytes that can form porous oxide layer may be used as the electrolyte for use in the anodizing treatment of the aluminum plates, and such an electrolyte is generally sulfuric acid, phosphoric acid, oxalic acid, chromic acid, or the mixture thereof. The concentration of the electrolyte is decided according to the kind of the electrolyte.
The conditions for the anodic oxidation vary according to the electrolytes used and are not particularly specified, but are generally suitable if the concentration of the electrolytes is 1 to 80 mass %; the liquid temperature, 5 to 70°C; the electric current density, 5 to 60 A/dm²; the voltage, 1 to 100 V; and the electrolysis period, 10 seconds to 5 minutes. The anodized layer formed in an amount of less than 1.0 g/m² often results in insufficient printing durability, makes the non-image portion of planographic printing plate more susceptible to damage, and consequently, encounters the problems of "scratch staining", i.e., adhesion of ink to the damaged region during printing.
After the anodizing treatment, the aluminum surface is hydrophilized as needed.
Examples of the hydrophilizing treatment used in the invention include the treatments with an alkali metal silicate (e.g., aqueous sodium silicate solution) disclosed in U.S. Patent Nos. 2,714,066 , 3,181,461 , 3,280,734 and 3,902,734 .
By this method, the support is immersed or electrolyzed in an aqueous sodium silicate solution. Alternatively, the support may be subjected to the methods of treating it with potassium fluorozirconate disclosed in JP-B No. 36-22063 and of treating it with polyvinylphosphonic acid disclosed in U.S. Patent Nos. 3.276,868 , 4,153.461 , and 4,589,272 .

(Organic undercoat layer)

An organic undercoat layer may be formed as needed between the support and the recording layer of the planographic printing plate precursor according to the invention.
Components for the organic undercoat layer include various organic compounds, and examples thereof include carboxymethylcellulose, dextrin, gum arabic, amino group-containing phosphonic acids such as 2-aminoethylphosphonic acid, phenylphosphonic acids that may be substituted, naphthylphosphonic acid, alkylphosphonic acids, glycerophosphonic acid, and organic phosphonic acids such as methylenediphosphonic acid and ethylenediphosphonic acid, phenylphosphoric acid that may be substituted, organic phosphoric acids such as naphthylphosphoric acid, glycerophosphoric acid and alkylphosphoric acid, phenylphosphinic acids that may be substituted, organic phosphinic acids such as naphthylphosphinic acid, glycerophosphinic acid and alkylphosphinic acid, amino acids such as glycine and β-alanine, and hydrochloride salts of a hydroxy group-containing amine such as triethanolamine hydrochloride salts; and these compounds my be used as a mixture of two or more.
The organic undercoat layer preferably contains an onium group-containing compound. The onium group-containing compounds are described in detail, for example, in JP-A Nos. 2000-10292 , 2000-108538 , and 2000-241962 .
Preferable among them are the compounds selected from the group consisting of polymer compounds having a structural unit represented, for example, by poly(p-vinylbenzoic acid) in the molecule. Typical examples thereof include copolymers of p-vinylbenzoic acid and vinylbenzyltriethylammonium chloride, copolymers of p-vinylbenzoic acid and a vinylbenzyltrimethylammonium salt, and the like.
The organic undercoat layer is formed, for example, by the following methods of: preparing a solution by dissolving the organic compound in water, an organic solvent such as methanol, ethanol or methylethylketone, or a mixed solvent thereof and applying and drying the solution on an aluminum plate; and preparing a solution by dissolving the organic compound in water, an organic solvent such as methanol, ethanol or methylethylketone, or a mixed solvent thereof, immersing an aluminum plate in the solution and thus allowing the compound to be adsorbed, washing the plate, for example, with water, and drying the plate. In the former method, it is possible to apply a solution at an organic compound concentration of 0.005 to 10 mass % by various methods. In the latter method, the solution concentration is 0.01 to 20 mass %, preferably 0.05 to 5 mass %; the immersion temperature is 20 to 90°C, preferably 25 to 50°C; and the immersion period is 0.1 second to 20 minute, preferably 2 second to 1 minute. The solution used may be adjusted with a basic substance such as ammonia, triethylamine or potassium hydroxide, or an acidic substance such as hydrochloric acid or phosphoric acid into the pH range of 1 to 12. In addition, a yellow dye may be added for improvement in the printing reproducibility of the recording layer.
The amount of the organic undercoat layer coated is preferably 2 to 200 mg/m² and more preferably 5 to 100 mg/m². It is possible to obtain sufficient printing durability when the coating amount is in the range above.
The infrared-sensitive planographic printing plate thus prepared is then exposed to an image-shaped light and then developed.

[Platemaking]

An image is formed on the planographic printing plate precursor according to the invention by heat. Specific plate-making methods include direct image recording for example by thermal recording head, scanning exposure to infrared laser, high-illumination flash irradiation for example by xenon discharge lamp, infrared lamp irradiation, and the like; and exposure to a semiconductor laser emitting an infrared light having a wavelength of 700 to 1,200 nm or a high-output infrared solid laser such as YAG laser is favorable.
The planographic printing plate precursor according to the invention after light exposure is developed and post-processed, for example, with a finisher or a protective gum, before giving a printing plate. Any one of known processing machines such as automatic developing machine may be used for these treatments.
Any one of known processing agents may be used, as it is selected, as the processing agent for use in development and posttreatment of the planographic printing plate precursor according to the invention.
The developing solution is favorably a developing solution at a pH in the range of 9.0 to 14.0, preferably 12.0 to 13.5. Any one of known aqueous alkaline solutions may be used as the developing solution. Among the aqueous alkaline solutions above, particularly favorable developing solutions include commonly-used aqueous solutions at a pH of 12 or more containing an alkali silicate or a mixture of bases and an silicon compound, so-called "silicate developing solutions", and the solutions containing no alkali silicate but containing a non-reducing sugar (organic compound having a buffering action) and a base described in JP-ANos. 8-305039 and 11-109637 and others, so-called "non-silicate developing solutions".
The developing solution preferably contains an anionic surfactant and/or an amphoteric surfactant, for acceleration of development and prevention of scum generation.
When the planographic printing plate according to the invention is burnt, it is preferably done according to the method known in the art of using a baking conditioner and a burning processor.
The planographic printing plate after such treatments is then supplied to an offset printing machine, in which it is used for printing on numerous papers.
The planographic printing plate precursor according to the invention in such a configuration is superior in handling efficiency, because the damage of the recording layer is prevented effectively even when they are stacked without interleaf sheets.

EXAMPLES

Hereinafter, the invention will be described in detail with reference to Examples, but it should be understood that the invention is not restricted thereby.

Examples 1 to 7, and Comparative Examples 1 to 3

[Preparation of support]

Molten aluminum was prepared by using an aluminum alloy in a composition (consisting of Al, Si: 0.06 mass %, Fe: 0.30 mass %, Cu: 0.026 mass %, Mn: 0.001 mass %, Mg: 0.001 mass %, Zn: 0.001 mass %, Ti: 0.02 mass %, and unavoidable impurities); and the molten aluminum was filtered and molded into ingots having a thickness of 500 mm and a width of 1,200 mm by DC casting. The surface of the ingot was scraped to an average depth of 10 mm by a surface grinder, and the ingot was heated consistently at 550°C for approximately 5 hours, and hot-rolled into a rolled plate having a thickness of 2.7 mm after it is cooled to a temperature of 400°C. The plate was heat-treated additionally at 500°C in a continuous annealing machine, and cold-rolled into a JIS1050 aluminum plate having a thickness of 0.24 mm. The width and the length of the average crystal grain in the aluminum plate obtained were respectively 50 µm and 300 µm. After the aluminum plate was cut to a width of 1,030 mm, it was subjected to the following surface treatment.

As surface treatment, the following treatments (a) to (k) were continuously conducted. After each of the treatments and water washing, liquid on the plate was removed with nip rollers.

(a) Mechanical surface-roughening treatment

While supplying a suspension (specific gravity: 1.12) of an abrasive agent (pumice) in water, as an abrading slurry, onto a surface of the aluminum plate, the surface was subjected to mechanical surface-roughening treatment with rotating roller-form nylon brushes. The average grain size of the abrasive agent was 30 µm. The maximum grain size was 100 µm. The material of the nylon brushes was 6,10-nylon, the bristle length thereof was 45 mm, and the bristle diameter thereof was 0.3 mm. The nylon brushes were each obtained by making holes in a stainless steel cylinder having a diameter of 300 mm and then planting bristles densely therein. The number of the rotating brushes used was three. The distance between the two supporting rollers (diameter: 200 mm) under each of the brushes was 300 mm. Each of the brush rollers was pushed against the aluminum plate until the load of a driving motor for rotating the brush became 7 kW larger than the load before the brush roller was pushed against the aluminum plate. The rotating direction of the brush was the same as the moving direction of the aluminum plate. The speed of rotation of the brush was 200 rpm.

(b) Alkali etching treatment

A 70°C aqueous solution having a NaOH (caustic soda) concentration of 2.6mass % and an aluminum ion concentration of 6.5 mass % was sprayed onto the aluminum plate obtained as described above to etch the aluminum plate, thereby dissolving 10 g/m² of the aluminum plate. Thereafter, the aluminum plate was washed with sprayed water.

(c) Desmut treatment

The aluminum plate was subjected to desmut treatment with a 30°C aqueous solution having a nitric acid concentration of 1 mass % (and containing 0.5 mass % of aluminum ions), which was sprayed, and then washed with sprayed water. The aqueous nitric acid solution used in the desmut treatment was waste liquid from a process of conducting electrochemical surface-roughening treatment using alternating current in an aqueous nitric acid solution.

(d) Electrochemical surface-roughening treatment

Alternating voltage having a frequency of 60 Hz was used to conduct electrochemical surface-roughening treatment continuously. The electrolyte used at this time was a 10.5 g/L solution of nitric acid in water (containing 5 g/L of aluminum ions and 0.007mass % of ammonium ions), and the temperature thereof was 50°C. The time TP until the current value was raised from zero to a peak was 0.8 msec, and the duty ratio of the current was 1:1. The trapezoidal wave alternating current was used, and a carbon electrode was set as a counter electrode to conduct the electrochemical surface-roughening treatment. Ferrite was used as an auxiliary anode. An electrolytic bath used is a radial cell type bath.
The density of the current was 30 A/dm² when the current was at the peak. The total electricity quantity when the aluminum plate functioned as an anode was 220 C/dm². 5% of the current sent from the power source was caused to flow into the auxiliary anode. Thereafter, the aluminum plate was washed with sprayed water.

(e) Alkali etching treatment

An aqueous solution having a caustic soda concentration of 26 mass % and an aluminum ion concentration of 6.5 mass % was used for spray to etch the aluminum plate at 32°C so as to dissolve 0.50 g/m² of the aluminum plate, thereby removing smut components made mainly of aluminum hydroxide and generated when the alternating current was used to conduct the electrochemical surface-roughening treatment in the previous process, and further dissolving edges of formed pits so as to be made smooth. Thereafter, the aluminum plate was washed with sprayed water.

(f) Desmut treatment

The aluminum plate was subjected to desmut treatment with a 30°C aqueous solution having a sulfuric acid concentration of 15mass % (and containing 4.5 mass % of aluminum ions), which solution was sprayed. The aluminum plate was then washed with sprayed water. The aqueous nitric acid solution used in the desmut treatment was waste liquid from the process of conducting the electrochemical surface-roughening treatment using the alternating current in the aqueous nitric acid solution.

(g) Electrochemical surface-roughening treatment

Alternating voltage having a frequency of 60 Hz was used to conduct electrochemical surface-roughening treatment continuously. The electrolyte used at this time was a 5.0 g/L solution of hydrochloric acid in water (containing 5 g/L of aluminum ions), and the temperature thereof was 35°C. The time TP until the current value was raised from zero to a peak was 0.8 msec, and the duty ratio of the current was 1:1. The trapezoidal wave alternating current was used, and a carbon electrode was set as a counter electrode to conduct the electrochemical surface-roughening treatment. Ferrite was used as an auxiliary anode. The electrolyte bath used was a radial cell type bath.
The density of the current was 25 A/dm² when the current was at the peak. The total electricity quantity when the aluminum plate functioned as an anode was 50 C/dm². Thereafter, the aluminum plate was washed with sprayed water.

(h) Alkali etching treatment

An aqueous solution having a caustic soda concentration of 26 mass % and an aluminum ion concentration of 6.5 mass % was sprayed onto the aluminum plate to etch the plate at 32°C so as to dissolve 0.10 g/m² of the plate, thereby removing smut components made mainly of aluminum hydroxide and generated when the alternating current was used to conduct the electrochemical surface-roughening treatment in the previous process, and further dissolving edges of formed pits so as to be made smooth. Thereafter, the aluminum plate was washed with sprayed water.

(i) Desmut treatment

The aluminum plate was subjected to desmut treatment with a 60°C aqueous solution having a sulfuric acid concentration of 25 mass % (and containing 0.5 mass % of aluminum ions), which solution was sprayed. The aluminum plate was then washed with sprayed water.

(j) Anodizing treatment

An anodizing machine in two stage power feeding electrolysis (the length of each of first and second electrolyzing sections being 6 m, the length of each of first and second power feeding sections being 3 m, and the length of each of first and second power feeding electrodes being 2.4 m) was used to conduct anodizing treatment. Sulfuric acid was used in the electrolytes supplied to the first and second electrolyzing sections. The electrolytes each had a sulfuric acid concentration of 50 g/L (and contained 0.5mass % of aluminum ions), and the temperature thereof was 20°C. Thereafter, the plate was washed with sprayed water. The density of ultimately formed oxide film was 2.7 g/m².

(k) Treatment with alkali metal silicate

The aluminum support obtained by the anodizing treatment was immersed into a treatment tank containing a 30°C aqueous solution of #3 sodium silicate (concentration of sodium silicate: 1mass %) for 10 seconds, so as to subject the support to treatment with the alkali metal silicate (silicate treatment). Thereafter, the support was washed with sprayed water. In this way, a support whose surface had been made hydrophilic with silicate was obtained for an infrared sensitive planographic printing plate precursor.

2.Formation of back coat layer (organic polymer layer)

A back coat solution having the following composition was prepared, and the back coat solution was applied onto the support obtained as described above on a side opposed to a side having a recording layer, with the coating amount was varied by adjusting the wet amount with the depth of the groove of the bar coater. Subsequently, the support was dried in an oven at 150°C for 30 seconds to provide a back coat layer (organic polymer layer). The coating amount of the obtained organic polymer layer after drying is shown in Table 1.

-Back coat solution-
Organic polymer (compounds shown in Table 1)	25 g
Surfactant (fluorochemical surfactant B, structure shown below)	0.05g
Solvent (shown in Table 1 below)	100 g

Table 1

	Organic polymer	Solvent	Coating amount of organic polymer layer (g/m²)	Coefficient of static friction	Displacement between the stack of planographic printing plate precursors	Scratches on recording layer
Example 1	Polystyrene	Methyl ethyl ketone	2	0.48	A	A
Example 2	Polystyrene	Methyl ethyl ketone	15	0.53	A	A
Example 3	Polystyrene	Methyl ethyl ketone	5	0.51	A	A
Example 4	Polyethylene terephthalate	1,1,1,3,3,3-hexafluoro-2 -propanol	5	0.45	A	A
Example 5	Saturated polymer polyester resin (KEMIT K-588)	Methyl ethyl ketone	3	0.58	A	A
Example 6	Vinylidene chloride-acrylonitrile copolymer resin (SALAN F-310)	Methyl ethyl ketone	5	0.53	A	A
Example 7	Polyvinyl butyral resin (DENKA BUTYRAL K-3000)	Methyl ethyl ketone	5	0.55	A	A
Comparative Example 1	-	-	-	-	A	B
Comparative Example 2	Polystyrene + Dodecyl stearate (95 mass%: 5mass%)	Methyl ethyl ketone	3	0.33	B	B
Comparative Example 3	Epoxy resin (EPICOAT 1001)	Methyl ethyl ketone	5	0.62	A	A

In Comparative Example 1, no back coat layer (organic polymer layer) was formed.
In Comparative Example 2, the back coat layer (organic polymer layer) was formed using a back coat solution containing 25 g of a mixture of polystyrene and dodecyl stearate in place of 25 g of an organic polymer. In the mixture, the mixed ratio between polystyrene and dodecyl stearate was as follows: polystyrene : dodecyl stearate = 95 mass% : 5 mass%.

[Formation of organic undercoat layer]

On the opposite side of support to that on which the organic polymer layer was formed, being the surface on which the surface treatment was carried out, an undercoat solution having the following composition was applied using a bar coater, and then the resultant layer was dried at 80°C for 15 seconds to form a undercoat layer. The coated amount after drying was 18 mg/m².

-Organic undercoat solution-

Polymer compound shown below 0.3g

Methanol 100 g

[Formation of recording layer (multilayer)]

The below-described lower layer coating solution 1 was applied using a bar coater onto the aluminum support having an organic undercoat layer such that the coating amount after drying was 0.85 g/m² Subsequently the support was dried at 160°C for 44 seconds, and immediately cooled with cold air at 17 to 20°C until the temperature of the support was lowered to 35°C to form a lower layer. Subsequently, the below-described upper layer coating solution 2 was applied using a bar coater such that the coating amount after drying was 0.22 g/m². The support was dried at 148°C for 25 seconds, and slowly cooled with air at 20 to 26°C to form an upper layer.

In such a manner, photosensitive planographic printing plate precursors of Examples 1 to 7, and Comparative Examples 1 to 3 were prepared.

<Lower layer coating solution 1>
N-(4-aminosulfonylphenyl) methacrylamide/acrylonitrile/methyl methacrylate (36/34/30: weight average molecular weight 60,000, acid value 2.65)	1.73 g
Novolak resin
(2,3-xylenol /m-cresol/p-cresol ratio = 10/20/70, weight average molecular weight 3300)	0.192 g
Cyanine dye A (structure shown below)	0.134 g
4,4'-bishydroxyphenylsulfone	0.126 g
Tetrahydrophthalic anhydride	0.190 g
p-toluenesulfonic acid	0.008 g
3-methoxy-4-diazodiphenylamine hexafluorophosphate	0.032 g
Ethyl Violet in which counter ion had been substituted with 6-hydroxynaphthalenesulfonic acid	0.0781 g
Polymer 1 (structure shown below)	0.035 g
Methyl ethyl ketone	25.41 g
1-methoxy-2-propanol	12.97 g
γ-butyrolactone	13.18 g

<Upper layer coating solution 2>
m,p-cresol novolak (m/p ratio = 6/4, weight average molecular weight 4500, containing 0.8 mass% of unreacted cresol	0.3479 g
Polymer 3 (structure shown below, MEK 30% solution)	0.1403 g
Cyanine dye A (structure shown above)	0.0192 g
Polymer 1 (structure shown above)	0.015 g
Polymer 2(structure shown below)	0.00328 g
Quaternary ammonium salt (structure shown below)	0.0043 g
Surfactant	0.008 g
(polyoxyethylene sorbit fatty acid ester, HLB 8.5, trade name: GO-4, manufactured by Nikko Chemicals Co., Ltd.)
Methyl ethyl ketone	6.79 g
1-methoxy-2-propanol	13.07 g

Examples 8 to 14, and Comparative Examples 4 to 6

[Formation of back coat layer (organic polymer layer)]

A back coat solution having the following composition was prepared, and the back coat solution was applied onto the support obtained as described above on the side opposite to the side having the recording layer, with the coating amount was varied by adjusting the wet amount with the depth of the groove of the bar coater. Subsequently, the support was dried in an oven at 150°C for 30 seconds to provide a back coat layer (organic polymer layer). The coating amount of the obtained organic polymer layer after drying is shown in Table 2.

-Back coat solution-
Organic polymer (compounds listed in Table 2 below)	25 g
Surfactant (fluorochemical surfactant B, structure shown above)	0.05g
Solvent (shown in Table 2)	100 g

Table 2

	Organic polymer	Solvent	Coating amount of organic polymer layer (g/m²)	Coefficient of static friction	Displacement between the stack of planographic printing plate precursors	Scratches on recording layer
Example 8	Polystyrene	Methyl ethyl ketone	2	0.48	A	A
Example 9	Polystyrene	Methyl ethyl ketone	15	0.53	A	A
Example 10	Polystyrene	Methyl ethyl ketone	5	0.51	A	A
Example 11	Polyethylene terephthalate	1,1,1,3,3,3-hexafluoro-2-pr opanol	5	0.45	A	A
Example 12	Saturated polymer polyester resin (KEMIT K-588)	Methyl ethyl ketone	3	0.58	A	A
Example 13	Vinylidene chloride-acrylonitrile copolymer resin (SALAN F-310)	Methyl ethyl ketone	5	0.53	A	A
Example 14	Polyvinyl butyral resin (DENKA BUTYRAL K-3000)	Methyl ethyl ketone	5	0.55	A	A
Comparative Example 4	-	-	-	-	A	B
Comparative Example 5	Polystyrene + Dodecyl stearate (95 mass% : 5mass%)	Methyl ethyl ketone	3	0.33	B	A
Comparative Example 6	Epoxy resin (EPICOAT 1001)	Methyl ethyl ketone	5	0.62	A	B

In Comparative Example 4, no back coat layer (organic polymer layer) was formed.
In Comparative Example 5, the back coat layer (organic polymer layer) was formed using a back coat solution containing 25 g of a mixture of polystyrene and dodecyl stearate in place of 25 g of an organic polymer. In the mixture, the mixed ratio between polystyrene and dodecyl stearate was as follows: polystyrene : dodecyl stearate = 95 mass% : 5 mass%.

[Formation of recording layer (single layer)]

A recording layer coating solution 3 described below was applied onto the surface of the support on the side opposite to the side having the organic polymer layer. Subsequently, the support was dried in an oven at 150°C for 1 minute to form photosensitive planographic printing plate precursors having a positive recording layer with a dry film thickness of 2.0 g/m² in Example 8 through 14, and Comparative Examples 4 through 6.

<Recording layer coating solution 3>
m,p-cresol novolak	0.90 g
(m/p ratio = 6/4, weight average molecular weight 7500, containing 0.5 mass% of unreacted cresol)
Methacrylic acid/ethyl methacrylate/isobutyl methacrylate (Molar ratio: 26/37/37) copolymer	0.10 g
Cyanine dye A (structure shown above)	0.04 g
2,4, 6-tris(hexyloxy) benzenediazonium-2-hydroxy-4-methoxybenzophenone-5-sulfonate	0.01 g
p-toluenesulfonic acid	0.002 g
Tetrahydrophthalic anhydride	0.05 g
Dye of Victoria Pure Blue BOH in which the counter ion had been substituted by 1-naphthalenesulfonic acid anion	0.015 g
Fluorochemical surfactant (trade name: MEGAFAC F-176, manufactured by Dainippon Ink and Chemicals, Incorporated)	0.02 g
Methyl ethyl ketone	15 g
1-methoxy-2-propanol	7 g

The infrared sensitive planographic printing plate precursors of Examples and Comparative Examples obtained above were evaluated as to "1. Measurement of coefficient of static friction", "2. Displacement between the stack of planographic printing plate precursors by vibrations", and "3. Development of damage to the recording layer (scratches) by transportation".

1.Measurement of coefficient of static friction

The coefficient of static friction of the infrared sensitive planographic printing plate precursors obtained above was measured by the above-described method. The results of the measurement are shown in Tables 1 and 2.

2. Displacement between plate materials in the stack of planographic printing plate precursors by vibrations

The infrared sensitive planographic printing plate precursors obtained above were respectively cut into pieces of 1030 mm x 800 mm, and 300 pieces thereof prepared. The pieces of the planographic printing plate precursor were stacked in stacks of 30 pieces, with a 0.5 mm sheet of cardboard placed at the top and bottom and with no interleaf sheets. The stacks were placed on a palette, and moved at a speed of 20 Km per hour and stopped using a forklift, repeated five times. Subsequently, displacement in the bundles of the stacks was observed visually.
Those in which displacement occurred were indicated by "B", and those in which no displacement occurred were indicated by "A". The results are shown in Tables 1 and 2.

3. Evaluation of development of damage to the recording layer (scratches) by transportation

The infrared sensitive planographic printing plate precursors obtained above were respectively cut into pieces of 1030 mm x 800 mm, and 30 pieces thereof prepared. The 30 pieces were stacked with no interleaf sheets, and a sheet of cardboard having a thickness of 0.5 mm was placed top and bottom of the stack. The four corners of the stack were taped together, and then wrapped with aluminum kraft paper. The package was further packed into a cardboard box, the box was sealed with tape, and thus a package condition with no interleaf sheets was achieved. The box was placed on a palette, transported 2000 km by truck, and then opened. The infrared sensitive planographic printing plate precursors after opening was set in an automatic developing machine (trade name: LP-940HII, manufactured by Fuji Photo Film Co., Ltd.) charged with a developing solution (trade name: DT-2, manufactured by Fuji Photo Film Co., Ltd.) at a ratio of 1:8, and developed at a developing temperature of 32°C, and developing time of 12 second. The electric conductivity of the developing solution at that time was 43 mS/cm. The planographic printing plates after development were observed visually for the presence or absence of dropout in the image area caused by transportation, and evaluated. Those in which no dropout occurred in the image area were indicated by "A", and those in which dropout occurred in the image area were indicated by "B". The results are shown in Tables 1 and 2.
As shown in Tables 1 and 2, the infrared radiation photosensitive planographic printing plates (Examples) having a coefficient of static friction between the recording layer and the organic polymer layer in the range of the present invention readily formed a stack of planographic printing plate precursors when stacked with no interleaf sheets, and no displacement due to vibrations was observed between the plate materials in the stacks of planographic printing plate precursors. Furthermore, even when the stacks of planographic printing plate precursors was packaged and the like, no dropout was observed in the image area, which indicates that damage to the recording layer (scratches) was inhibited.

Claims

An infrared sensitive planographic printing plate precursor comprising:
a support;

a recording layer disposed on or above a surface of the support and capable of forming an image by infrared irradiation, the recording layer comprising a resin that is water-insoluble and alkali-soluble and an infrared absorbent; and

an organic polymer layer disposed on or above the opposite surface of the support to that of the recording layer,
wherein the coefficient of static friction between the recording layer and the organic polymer layer is in the range of from 0.45 to 0.60.
The infrared sensitive planographic printing plate precursor of Claim 1, wherein the coefficient of static friction between the recording layer and the organic polymer layer is in a range of from 0.45 to 0.58.
The infrared sensitive planographic printing plate precursor of Claim 1 or 2, wherein the organic polymer layer comprising an organic polymer, and the organic polymer is selected from the group consisting of a novolak resin, a saturated copolymeric polyester resin, a phenoxy resin, a polyvinyl acetal resin, a vinylidene chloride copolymer resin, and a polystyrene resin.
The infrared sensitive planographic printing plate precursor of any one of Claims 1 to 3, wherein the content of the organic polymer in the organic polymer layer is in a range of from 99.99 to 70 mass% with respect to the total solid content of the organic polymer layer.
The infrared sensitive planographic printing plate precursor of any one of Claims 1 to 4, wherein the organic polymer layer further comprises a fluorochemical surfactant.
The infrared sensitive planographic printing plate precursor of Claim 5, wherein the fluorochemical surfactant is a fluorochemical surfactant containing a perfluoroalkyl group in the molecule thereof.
The infrared sensitive planographic printing plate precursor of any one of Claims 1 to 6, wherein the thickness of the organic polymer layer is in a range of from 0.05 to 0.5 µm.
The infrared sensitive planographic printing plate precursor of any one of Claims 1 to 7, wherein the resin that is water-insoluble and alkali-soluble is a resin that is water-insoluble and alkali-soluble having a phenolic hydroxy group.
The infrared sensitive planographic printing plate precursor of Claim 8, wherein the resin that is water-insoluble and alkali-soluble having a phenolic hydroxy group is a novolak resin.