TITLE OF THE INVENTION

LITHOGRAPHIC PRINTING PLATE PRECURSOR TECHNICAL FIELD

[0001]
The present invention relates to a lithographic printing plate precursor capable of undergoing a direct plate making by image exposure with laser.

BACKGROUND ART

[0002]
In general, a lithographic printing plate is composed of an oleophilic image area accepting ink and a hydrophilic non-image area accepting dampening water in the process of printing. Lithographic printing is a printing method utilizing the nature of water and oily ink to repel with each other and comprising rendering the oleophilic image area of the lithographic printing plate to an ink-receptive area and the hydrophilic non-image area thereof to a dampening water-receptive area (ink-unreceptive area), thereby making a difference in adherence of the ink on the surface of the lithographic printing plate, depositing the ink only to the image area, and then transferring the ink to a printing material, for example, paper.

In order to produce the lithographic printing plate, a lithographic printing plate precursor (PS plate) comprising a hydrophilic support having provided thereon an oleophilic photosensitive resin layer (image-recording layer) is used. Specifically, the PS plate is exposed through a mask, for example, a lith film, and then subjected to development processing, for example, with an alkaline developer to remove the unnecessary image-recording layer corresponding to the non-image area by dissolving while leaving the image-recording layer corresponding to the image area, thereby obtaining the lithographic printing plate.

[0003]
Due to the recent progress in the technical field, nowadays the lithographic printing plate can be obtained by a CTP (computer-to-plate) technology. Specifically, a lithographic printing plate precursor is directly subjected to scanning exposure using laser or laser diode without using a lith film and developed to obtain a lithographic printing plate.

[0004]
With the progress described above, the issue on the lithographic printing plate precursor has transferred to improvements, for example, in image-forming property corresponding to the CTP technology, printing property or physical property. Also, with the increasing concern about global environment, as another issue on the lithographic -"' printing plate precursor, an environmental problem on waste liquid discharged accompanying the wet treatment, for example, development processing comes to the front.

[0005]
In response to the environmental problem, simplification of development or plate making or non-processing has been pursued. As one method of simple plate making, a method referred to as an "on-press development" is practiced. Specifically, according to the method after exposure of a lithographic printing plate precursor, the lithographic printing plate precursor is mounted as it is on a printing machine without conducting conventional development and removal of the unnecessary area of image-recording layer is performed at an early stage of printing step.

Also, as a method of simple development, a method referred to as a "gum development" is practiced wherein the removal of the unnecessary area of image-recording layer is performed using not a conventional high alkaline developer but a finisher or gum solution of near-neutral pH.

[0006]
In the simplification of plate making operation as described "^ above, a system using a lithographic printing plate precursor capable of being handled in a bright room or under a yellow lamp and a light source is preferred from the standpoint of workability. Thus, as the light source, a semiconductor laser emitting an infrared ray having a wavelength of 760 to 1,200 or a solid laser, for example, YAG laser, is used. An UV laser is also used.

[0007]
As the lithographic printing plate precursor capable of undergoing on-press development, for instance, a lithographic printing plate precursor having provided on a hydrophilic support, an image-recording layer (heat-sensitive layer) containing microcapsules having a polymerizable compound encapsulated therein is described in Patent Documents 1 and 2. Also, a lithographic printing plate precursor having provided on a support, an image-recording layer (photosensitive layer) containing an infrared absorbing agent, a radical polymerization initiator and a polymerizable compound is described in Patent Document 3.

[0008]
Further, a lithographic printing plate precursor comprising a support having thereon an image-recording layer which contains an active ray absorbing agent, a polymerization initiator and a polymerizable compound and is capable of being removed with printing ink, dampening water or both of them and further a protective layer (overcoat layer) containing an inorganic stratiform compound in this order is described in Patent Document 4. In this way, it is known that a lithographic printing plate precursor having high sensitivity and excellent in on-press development property is obtained by incorporating the inorganic stratiform compound into the protective "" layer.

However, the inorganic stratiform compound penetrates in the image-recording layer at the step of coating or drying and is hardly removed, thereby causing a problem in that ink receptivity decreases^ t ^ at the initiation of printing and on the way of printing.

[0009]
On the other hand, a lithographic printing plate precursor capable of undergoing on-press development having provided on a support, an image-recording layer containing a polymerizable compound and a graft polymer having a polyethylene oxide chain in its side chain or a block polymer having a polyethylene oxide block is described in Patent Document 4. However, the lithographic printing plate precursor is insufficient in compatibility between the sensitivity and the on-press development property.

PRIOR ART DOCUMENT PATENT DOCUMENT

[0010]
Patent Document 1: JP-A-2001-277740
Patent Document 2: JP-A-2001-277742
Patent Document 3: JP-A-2002-287334
Patent Document 4: JP-A-2005-119273
Patent Document 5: U.S. Patent Publication No. 2003/0064318 DISCLOSURE OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE

[0011]
An object of the present invention is to provide a lithographic printing plate precursor of on-press development type which is capable of being image-recorded with laser and exhibits sufficient ink receptivity while maintaining high sensitivity. MEANS FOR SOLVING THE PROBLEMS

[0012]
(1) A lithographic printing plate precursor comprising a support, an image-recording layer and a protective layer in this order, wherein the protective layer contains an inorganic stratiform compound and the image-recording layer contains a polymer compound containing a poly (alkylene oxide) moiety in which a number of repeating units of alkylene oxide is from 10 to 120.

(2) The lithographic printing plate precursor as described in (1) above, wherein the polymer compound does not substantially contain a perfluoroalkyl group.

(3) The lithographic printing plate precursor as described in (1) or (2) above, wherein the image-recording layer contains an infrared absorbing agent, a radial polymerization initiator and a radical polymerizable compound.

(4) The lithographic printing plate precursor as described in any one of (1) to (3) above, wherein the number of repeating units of alkylene oxide is from 20 to 50.

(5) The lithographic printing plate precursor as described in any ^ one of (1) to (4) above, wherein the polymer compound contains a structure represented by formula (1) shown below in its side chain:

[0013]
Formula (1)

[0014]
In formula (1), y represents from 10 to 120, R1 represents a hydrogen atom or an alkyl group, and R2 represents a hydrogen atom or an organic group.

[0015]
(6) The lithographic printing plate precursor as described in any one of (1) to (5) above, wherein the inorganic stratiform compound is mica.

(7) The lithographic printing plate precursor as described in any one of (1) to (6) above, wherein the image-recording layer contains at least any one selected from an ammonium salt and a phosphonium salt.

(8) The lithographic printing plate precursor as described in (7) above, wherein a counter anion of the ammonium salt or phosphonium salt is an organic borate anion.

(9) The lithographic printing plate precursor as described in (7) or (8) above, wherein the ammonium salt is represented by formula (2) shown below:

[0016] Formula (2)

[0017]
In formula (2), R3 to R6 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group, and X" represents a counter anion.

[0018]
(10) The lithographic printing plate precursor as described in (9) above, wherein in formula (2), at least one of R3 to R6 is an aryl group or an aralkyl group.

(11) The lithographic printing plate precursor as described in (7) or (8) above, wherein the ammonium salt is a polymer containing a repeating unit represented by formula (3) shown below:

[0019]

[0020]
In formula (3) , Ru represents a hydrogen atom or a methyl group, Li represents a connecting group, R12 to R14 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group, and X" represents a counter anion.

[0021]
(12) The lithographic printing plate precursor as described in (11) above, wherein in formula (3), L1 represents a connecting group containing at least one group selected from a phenylene group, a carbonyloxy group and a carbonylimino group.

(13) The lithographic printing plate precursor as described in any one of (1) to (12) above, wherein the image-recording layer is an image-recording layer which is capable of forming an image after image exposure by supplying at least any of printing ink and dampening water on a printing machine to remove an unexposed area.

(14) The lithographic printing plate precursor as described in any one of (1) to (13) above, wherein a content of the polymer compound containing a poly(alkylene oxide) moiety in which a number of repeating units of alkylene oxide is from 10 to 120 is from 10 to 90% by weight based on a total solid content of the image-recording layer.

ADVANTAGE OF THE INVENTION

[0022]
According to the present invention, a lithographic printing plate precursor of on-press development type which is capable of being image-recorded with laser and exhibits sufficient ink receptivity while maintaining high sensitivity can be provided. MODE FOR CARRYING OUT THE INVENTION

[0023] [Lithographic printing plate precursor]
The lithographic printing plate precursor according to the invention comprises an image-recording layer on a support and a protective layer on the image-recording layer. The lithographic printing plate precursor may comprise an undercoat layer between the support and the image-recording layer.

Hereinafter, the constituting element, component and the like of the lithographic printing plate precursor according to the invention will be described.

[0024] (Protective layer)
The lithographic printing plate precursor according to the invention has a protective layer (overcoat layer) on the image-recording layer. The protective layer has a function for preventing occurrence of scratch in the image-recording layer and preventing ablation at the time of laser exposure of high illuminance, in addition to the function for restraining an inhibition reaction against the image formation by means of oxygen blocking.

[0025]
With respect to the protective layer having such an oxygen blocking property, there are described, for example, in U.S. Patent 3,458,311 and JP-B-55-49729. As a polymer having low oxygen permeability for use in the protective layer, any water-soluble polymer and water-insoluble polymer can be appropriately selected to use. Specifically, for example, polyvinyl alcohol, a modified polyvinyl alcohol, polyvinyl pyrrolidone, a water-soluble cellulose derivative and poly(meth)acrylonitrile are exemplified. More specifically, polymers described in paragraph Nos. [0172] to [0175] of JP-A-2008-195018 are exemplified.

[0026]
According to the invention, the protective layer contains an inorganic stratiform compound. The inorganic stratiform compound contributes to achieve high sensitivity while reducing the load of on-press development due to protective layer, because it can highly ^ maintain the oxygen blocking property even when the coating thickness of the protective layer is decreased.
In the protective layer according to the invention, it is preferred to contain the inorganic stratiform compound and to use the polymer having low oxygen permeability described above as a binder polymer.

[0027]
The inorganic stratiform compound described above is a particle having a thin tabular shape and includes, for instance, a mica, for example, natural mica represented by formula: A (B, C)2-5 D4 O10 (OH, F, 0)2, (wherein A represents any of K, NaandCa, B and C each represents any of Fe (II), Fe(III), Mn, Al, Mg and V, and D represents Si or Al) or synthetic mica, talc represented by formula: 3MgO-4S10 -H20, teniolite, montmorillonite, saponite, hectolite and zirconium phosphate.

[0028]
In the micas described above, as the natural mica, muscovite, paragonite, phlogopite, biotite and lepidolite are exemplified. Also, as the synthetic mica, non-swellable mica, for example, fluorphlogopite KMg3(AlSi30io) F2 or potassium tetrasilic mica ^ KMg2.5 (Si4010) F2, and swellable mica, for example, Na tetrasilic mica NaMg2.5(Si4O10 )F2, Na or Li teniolite (Na, Li)Mg2Li (Si4010) F2, or montmorillonite-based Na or Li hectolite (Na, Li)i/8Mg2/5Lii/8 (Si4O10)F2 are exemplified. Further, synthetic smectite is also useful.

[0029]
In the invention, of the inorganic stratiform compounds, mica is preferred and fluorine-based swellable mica, which is a synthetic inorganic stratiform compound, is particularly useful. Specifically, the swellable synthetic mica and an swellable clay mineral, for example, montmorillonite, saponite, hectolite or bentonite have a laminate structure comprising a unit crystal lattice layer having thickness of approximately 10 to 15 angstroms, and metallic atom substitution in the lattices thereof is remarkably large in comparison with other clay minerals. As a result, the lattice layer results in lack of positive charge and to compensate it, a cation, for example, Na+, Ca2+ or Mg2+ is adsorbed between the lattice layers. The cation intervening between the layers is called an exchangeable cation and is exchanged with various cations. Particularly, in the case where the cation between the layers is Li+ or Na+, since the ionic radius is small, the bond between the stratiform crystal lattices is weak, thereby greatly swelling with water. When share is applied under such a condition, the stratiform crystal lattices are easily cleaved to form a stable sol in water. The bentnite and swellable synthetic mica strongly show this tendency and are useful in the invention. In particular, the swellable synthetic mica is preferably used.

[0030]
As for the shape of the inorganic stratiform compound for use in the invention, from the standpoint of control of diffusion, the thickness is preferably smaller and as long as the smoothness of the ^ coated surface and the transmission of actinic radiation are not damaged, the plane size is preferably larger. Therefore, an aspect ratio is preferably 20 or more, more preferably 100 or more, and particularly preferably 200 or more. The aspect ratio is a ratio of major axis to thickness of particle and can be determined, for example, from a projection drawing of particle by a microphotography. As the aspect ratio is larger, the effect obtained is higher.

[0031]
As for a particle diameter of the inorganic stratiform compound for use in the invention, an average major axis is from 0.3 to 20 urn, preferably from 0.5 to 10 μm, and particularly preferably from 1 to 5 urn. Also, an average thickness of the particle is 0.1 μm or less, preferably 0.05 μm or less, and particularly preferably 0.01 urn or less. For example, with respect to the swellable synthetic mica that is the representative compound of the inorganic stratiform compound, the thickness is approximately from 1 to 50 nm and the plain size is approximately from 1 to 20 μ m.

[0032]
When such an inorganic stratiform compound particle having a large aspect ratio is incorporated into the protective layer, strength of the coated layer increases and penetration of oxygen or moisture can be effectively inhibited and thus, the protective layer can be prevented from deterioration due to deformation, and even when the lithographic printing plate precursor is preserved for a long period of time under a high humidity condition, deterioration of the image-forming property in the lithographic printing plate precursor due to the change of humidity is prevented and the excellent preservation stability is obtained.

[0033]
The content of the inorganic stratiform compound in the protective layer is preferably from 5/1 to 1/100 in terms of weight ratio to the amount of binder used in the protective layer. When a plurality of inorganic stratiform compounds is used in combination, it is also preferred that the total amount of the inorganic stratiform compounds fulfills the above-described weight ratio.

[0034]
Also, the protective layer can contain known additives, for example, plasticizer for imparting flexibility, a surfactant for improving coating property or an inorganic fine particle for controlling surface slipping property. Further, an ammonium salt or phosphonium salt described below with respect to the image-recording layer can also be incorporated into the protective layer.

[0035]
The protective layer can be coated by a known method. The coating amount of the protective layer is preferably in a range form 0.01 to 10 g/m2, more preferably in a range from 0.02 to 3 g/m2, most preferably in a range from 0.02 to 1 g/m2, in terms of the coating amount after drying.

[0036] (Image-recording layer)
The image-recording layer according to the invention is characterized by containing a polymer compound containing a poly (alkylene oxide) moiety in which a number of repeating units of alkylene oxide is from 10 to 120. Thus, good on-press development property and good ink receptivity can be obtained. Hereinafter, the polymer compound containing a poly (alkylene oxide) moiety is referred to as a specific polymer compound.

The mechanism of improving the ink receptivity by the specific polymer compound is estimated as follows. An alkylene oxide long chain of the specific polymer compound interacts with a surface of the inorganic stratiform compound, for example, mica and the specific polymer compound covers the surface of the inorganic stratiform compound to decrease hydrophilicity of the surface of the inorganic stratiform compound, thereby improving the ink receptivity.

[0037]
Further, the image-recording layer according to the invention preferably contains (B) an infrared absorbing agent, (C) a radical polymerization initiator and (D) a radical polymerizable compound.

Hereinafter, the respective elements which can be contained in the image-recording layer will be described in order.

[0038]
(A) Specific polymer compound containing number of repeating units, of alkylene oxide from 10 to 120
The specific polymer compound containing a number of repeating units of alkylene oxide from 10 to 120 for use in the lithographic printing plate precursor according to the invention may have a poly (alkylene oxide) moiety in the main chain thereof or the side chain thereof, or may be a graft polymer having a poly (alkylene oxide) in its side chain or a block copolymer composed of a block containing a poly(alkylene oxide) and a block constituted by a repeating unit not containing an alkylene oxide.

In the case where the poly (alkylene oxide) moiety is present in the main chain, a polyurethane resin is preferred. In the case where the poly (alkylene oxide) moiety is present in the side chain, a polymer constituting its main chain includes an acrylic resin, a polyvinyl acetal resin, a polyurethane resin, a polyurea resin, a polyimide resin, a polyamide resin, an epoxy resin, a methacrylic resin, a polystyrene resin, a novolac type phenolic resin, a polyester resin, a synthesis rubber and a natural rubber and, in particular, an acrylic resin is preferred.

[0039]
The specific polymer compound does not substantially contain a perfluoroalkyl group. The terminology "does not substantially contain a perfluoroalkyl group" as used herein means that a weight ratio of fluorine atoms present as the perfluoroalkyl group in the specific polymer compound is less than 0.5% by weight, and it is preferred not to contain the perfluoroalkyl group. The weight ratio of fluorine atom is determined by an elemental analysis method.

Also, the term "perfluoroalkyl group" means the all hydrogen atoms of an alkyl group are substituted with fluorine atoms.

[0040]
The alkylene oxide is preferably an alkylene oxide having from 2 to 6 carbon atoms, and particularly preferably an ethylene oxide or a propylene oxide.

A repeating number of alkylene oxide in the poly (alkylene oxide) moiety is from 10 to 120, preferably from 20 to 70, and more preferably from 20 to 50.

When the repeating number of alkylene oxide is less than 10, the improvement in the ink receptivity is not obtained. Also, when the repeating number of alkylene oxide exceeds 120, both printing durability due to abrasion and printing durability due to the ink receptivity are deteriorated.

[0041]
The poly(alkylene oxide) moiety is preferably contained as a side chain of the specific polymer compound, in a structure represented by formula (1) shown below. More preferably, it is contained as a side chain of an acrylic resin in a structure represented by formula (1) shown below.

[0042] Formula (4)

[0043]
In formula (1), y represents from 10 to 120, preferably in a range from 20 to 70, and more preferably from in a range from 20 to ^ 50. Ri represents a hydrogen atom or an alkyl group. R2 represents a hydrogen atom or an organic group. The organic group is preferably an alkyl group having from 1 to 6 carbon atoms and includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an ^ n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an isohexyl group, a 1,1-dimethylbutyl group, a 2, 2-dimethylbutyl group, a cyclopentyl group and a cyclohexyl group.

Above all, R1 is preferably a hydrogen atom or a methyl group and most preferably a hydrogen atom. R2 is most preferably a hydrogen atom or a methyl group.

[0044]
The specific polymer compound may have a crosslinking property in order to improve the film strength of the image area. In order to impart the crosslinking property to the polymer, a crosslinkable functional group, for example, an ethylenically unsaturated bond is introduced into a main chain or side chain of the polymer. The crosslinkable functional group may be introduced by copolymerization.

Examples of the polymer having an ethylenically unsaturated bond in the main chain thereof include poly-1,4-butadiene and poly-1, 4-isoprene.

Examples of the polymer having an ethylenically unsaturated bond in the side chain thereof include a polymer of an ester or amide of acrylic acid or methacrylic acid, which is a polymer wherein the ester or amide residue (R in -COOR or -CONHR) has an ethylenically unsaturated bond.

[0045]
Examples of the residue (R described above) having an
(wherein R1 to R3 each represents a hydrogen atom, a halogen atom or an alkyl group having from 1 to 20 carbon atoms, an aryl group, alkoxy group or aryloxy group, or R1 and R2 or R1 and R3 may be combined with each other to form a ring, n represents an integer from 1 to 10. X represents a dicyclopentadienyl residue).

[0046]
Specific examples of the ester residue include -CH2CH=CH2 (described in JP-B-7-21633) , -CH2CH20-CH2CH=CH2, -CH2C(CH3) =CH2, -CH2CH=CH-C6H5, -CH2CH2OCOCH=CH-C6H5, -CH2CH2-NHCOO-CH2CH=CH2 and -CH2CH20-X (wherein X represents a dicyclopentadienyl residue) .

Specific examples of the amide residue include -CH2CH=CH2,
-CH2CH2-Y (wherein Y represents a cyclohexene residue) and
-CH2CH2-OCO-CH=CH2.

[0047]
The specific polymer compound having crosslinkable property is cured, for example, by addition of a free radical (a polymerization initiating radical or a growing radical of a polymerizable compound in the process of polymerization) to the crosslinkable functional group of the polymer and undergoing addition polymerization between the polymers directly or through a polymerization chain of the polymerizable compound to form crosslinkage between the polymer molecules. Alternately, it is cured by generation of a polymer radical upon extraction of an atom (for example, a hydrogen atom on a carbon atom adjacent to the functional crosslinkable group) in the polymer by a free radial and connecting the polymer radicals with each other to form cross-linkage between the polymer molecules.

[0048]
The content of the crosslinkable group (content of the radical polymerizable unsaturated double bond determined by iodine titration) in the specific polymer compound is preferably from 0.1 to 10.0 mmol, more preferably from 1.0 to 7.0 mmol, most preferably from 2.0 to 5. 5 mmol, based on 1 g of the polymer compound. In the range described above, good sensitivity and good preservation stability can be obtained.

[0049]
The specific polymer compound according to the invention may further contain a copolymerization component as long as the effects of the invention are not impaired, for the purpose of improving various performances, for example, image strength. As the structure of preferred copolymerization component, a structure represented by formula (4) shown below is exemplified.

[0050] Formula (4)

[0051]
In formula (4) , R21 represents a hydrogen atom or a methyl group, and R22 represents a substituent.
Preferred examples for R22 include an ester group, an amido group, a cyano group, a hydroxy group and an aryl group. Among them, an ester group, an amido group or a phenyl group which may have a substituent is preferred. Examples of the substituent for the phenyl group include an alkyl group, an aralkyl group, an alkoxy group and an acetoxymethyl group.

[0052]
The copolymerization component represented by formula (4) includes, for example, an acrylate, a methacrylate, an acrylamide, ^ a methacrylamide, an N-substituted acrylamide, an N-substituted methacrylamide, an N,N-disubstituted acrylamide, an N,N-disubstituted methacrylamide, a styrene, an acrylonitrile and a methacrylonitrile. Preferably, an acrylate, a methacrylate, an acrylamide, a methacrylamide, an N-substituted acrylamide, an N-substituted methacrylamide, an N,N-disubstituted acrylamide, an N,N-disubstituted methacrylamide, a styrene and the like are ^ exemplified.

[0053]
Specifically, an acrylate, for example, an alkyl acrylate (in which the alkyl group preferably has from 1 to 20 carbon atoms) (for example, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, ethylhexyl acrylate, octyl acrylate, 2,2-dimethylhydroxypropyl acrylate, 5-hydroxypentyl acrylate, trimethylolpropane monoacrylate, pentaerythritol monoacrylate, glycidyl acrylate or benzyl acrylate) or an aryl acrylate (for example, phenyl acrylate), a methacrylate, for example, an alkyl methacrylate (in which the alkyl group preferably has from 1 to 20 carbon atoms) (for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, octyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 2,2-dimethyl-3-hydroxypropyl methacrylate, trimethylolpropane monomethacrylate, pentaerythritol monomethacrylate or glycidyl methacrylate), a styrene, for example, styrene or an alkylstyrene (for example, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, butylstyrene, hexylstyrene, chloromethylstyrene, ethoxymethylstyrene or acetoxymethylstyrene), acrylonitrile, methacrylonitrile, and a radical polymerizable compound having a carboxylic acid (for example, acrylic acid, methacrylic acid or a salt of these acid groups) are exemplified. Acrylonitrile is more preferred from the standpoint of printing durability.

[0054]
A ratio of the repeating unit containing a poly (alkylene oxide) ^ moiety to the total repeating units constituting the specific polymer compound is not particularly restricted and is preferably from 0.5 to 80% by mole, and more preferably from 0.5 to 50% by mole.

[0055]
Specific examples (1) to (13) of the specific polymer compound for use in the invention are set forth below, but the invention should not be construed as being limited thereto. A ratio of the repeating units is indicated as a molar ratio.

[0056]

[0057]

[0058]
The weight average molecular weight (Mw) of the polymer compound according to the invention is preferably 2,000 or more, more preferably 5,000 or more, and still more preferably from 10,000 to 300,000.

[0059]
According to the invention, a hydrophilic polymer compound, for example, polyacrylic acid or polyvinyl alcohol described in JP-A-2008-195018 may be used together, if desired. Further, an oleophilic polymer compound and a hydrophilic polymer compound may be used in combination.

[0060]
As for the configuration of the specific polymer compound according to the invention, it may be present as a binder acting as a bond of each ingredient or in the form of fine particle in the image-recording layer. In the case of existing in the form of fine particle, the average particle size thereof is in a range from 10 to 1, 000 nm, preferably in a range from 20 to 300 nm, and particularly preferably in a range from 30 to 120 nm.

[0061]
The content of the specific polymer compound according to the invention is not particularly restricted' and is ordinarily from 10 to 90% by weight, preferably from 10 to 80% by weight, particularly preferably from 15 to 70% by weight, based on the total solid content of the image-recording layer.

[0062]

(B) Infrared absorbing agent

The infrared absorbing agent has a function of converting the infrared ray absorbed to heat and a function of being excited by the infrared ray to perform electron transfer and/or energy transfer to a radical polymerization initiator described hereinafter. The infrared absorbing agent for use in the invention is a dye or pigment having an absorption maximum in a wavelength range from 760 to 1,200 nm.

[0063]
As the infrared absorbing agent, compounds described in Paragraph Nos. [0058] to [0087] of JP-A-2008-195018 are used.

As preferred examples of the infrared absorbing agent, a cyanine dye, a squarylium dye, a pyrylium dye and a nickel thiolate complex are exemplified. As particularly preferred examples of the infrared ^ absorbing agent, a cyanine dye represented by formula (a) shown below is exemplified.

[0064]
Formula (a)

[0065]
In formula (a), X1 represents a hydrogen atom, a halogen atom, -N(R9) (R10), - X2- L1} or a group shown below.

R9 and R10, which may be the same or different, each represents an aromatic hydrocarbon group having from 6 to 10 carbon atoms which may have a substituent, an alkyl group having from 1 to 8 carbon atoms which may have a substituent or a hydrogen atom, or R9 and R10 may be combined with each other to form a ring. Among them, a phenyl group is preferred.

X2 represents an oxygen atom or a sulfur atom, L1 represents a hydrocarbon group having from 1 to 12 carbon atoms, an aromatic ring containing a hetero atom or a hydrocarbon group having from 1 to 12 carbon atoms and containing a hetero atom.

The hetero atom used herein indicates N, S, 0, a halogen atom or Se. In the group shown below, Xa~ has the same meaning as Za~ defined hereinafter, and Ra represents a hydrogen atom or a substituent selected from an alkyl group, an aryl group, a substituted or unsubstituted amino group and a halogen atom.

[0066]

[0067]
R1 and R2 each independently represents a hydrocarbon group having from 1 to 12 carbon atoms. In view of the preservation stability of a coating solution for image-recording layer, it is preferred that R1 and R2 each represents a hydrocarbon group having two or more carbon atoms, and further, it is particularly preferred ^ that R1 and R2 are combined with each other to form a 5-membered or 6-membered ring.

[0068] Ar1 and Ar2, which may be the same or different, each represents an aromatic hydrocarbon group which may have a substituent. Preferred examples of the aromatic hydrocarbon group include a benzene ring and a naphthalene ring. Also, preferred examples of the substituent include a hydrocarbon group having 12 or less carbon atoms, a halogen atom and an alkoxy group having 12 or less carbon atoms. Y1 and Y2, which may be the same or different, each represents a sulfur atom or a dialkylmethylene group having 12 or less carbon atoms. R3 and R4, which may be the same or different, each represents a hydrocarbon group having 20 or less carbon atoms, which may have a substituent. Preferred examples of the substituent include an alkoxy group having 12 or less carbon atoms, a carboxyl group and a sulfo group. R5, R6, R7 and R8, which may be the same or different, each represents a hydrogen atom or a hydrocarbon group having 12 or less carbon atoms. In view of the availability of raw materials, a hydrogen atom is preferred. Za~ represents a counter anion. However, Za" is not necessary when the cyanine dye represented by formula (a) has an anionic substituent in the structure thereof and neutralization of charge is not needed. In view of the preservation stability of a coating solution for image-recording layer, preferred examples of Za" include a halide ion, a perchlorate ion, a tetrafluoroborate ion, a hexafluorophosphate ion and a sulfonate ion, and particularly preferred examples thereof include a perchlorate ion, a hexafluorophosphate ion and an arylsulfonate ion.

[0069]
Specific examples of the cyanine dye represented by formula (a), which can be preferably used in the invention, include those described in Paragraph Nos. [0017] to [0019] of JP-A-2001-133969, ^ Paragraph Nos. [0012] to [0021] of JP-A-2002-23360 and Paragraph Nos. [0012] to [0037] of JP-A-2002-40638.

The infrared absorbing agents may be used only one kind or in combination of two or more kinds thereof.

[0070]
As the pigment, compounds described in Paragraph Nos. [0072] to [007 6] of JP-A-2008-195018 are preferred. The pigment may be used together with the dye described above.

[0071]
The content of the infrared absorbing agent in the image-recording layer according to the invention is preferably from 0.1 to 10.0% by weight, more preferably from 0.5 to 5.0% by weight, based on the total solid content of the image-recording layer.

[0072] (C) Radical polymerization initiator
The radical polymerization initiator for use in the invention is a compound which generates a radical upon light irradiation. The -^ radical generated causes polymerization curing of a radical polymerizable compound.

[0073]
The radical polymerization initiator preferably used in the invention includes an onium salt, for example, an iodonium salt, a sulfonium salt, a diazonium salt or an azinium salt. Specific examples thereof include compounds described in U.S. Patent 4,708, 925, JP-A-7-20629 and JP-A-2008-195018.

Also, a benzylsulfonate described in U.S. Patents 5,135,838 and 5,200,544, an active sulfonic acid ester described in JP-A-2-100054, JP-A-2-100055 and JP-A-9-197671, an imido ester, for ^ example, a sulfonic acid ester of N-hydroxyimido compound described in JP-A-2008-1740, a disulfone compound described in JP-A-61-166544 and JP-A-2002-328465, an oxime ester compound described in J. C. S. Perkin II, 1653-1660 (1979), J. C. S. Perkin II, 156-162 (1979), Journal of Photopolymer Science and Technology, 202-232 (1995), JP-A-2000-66385, JP-A-2000-80068 and JP-A-2008-195018, and a haloalkyl-substituted s-triazine compound described in JP-A-7-271029 are exemplified.

[0074]
Among them, an onium salt is preferred, and an iodonium salt, a sulfonium salt and an azinium salt are most preferred. Specific examples of these compounds are set forth below, but the invention should not be construed as being limited thereto.

[0075]
Examples of the iodonium salt include diphenyliodonium hexafluorophosphate,
4-methoxyphenyl-4-(2-methylpropyl)phenyliodonium hexafluorophosphate, 4- (2-methylpropyl)phenyl-p-tolyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4-diethoxyphenyliodonium tetrafluoroborate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium 1-perfluorobutanesulfonate and 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate.

[0076]
Examples of the sulfonium salt include triphenylsulfonium hexafluorophosphate, triphenylsulfonium benzoylformate, bis(4-chlorophenyl)phenylsulfonium benzoylformate, bis(4-chlorophenyl)-4-methylphenylsulfonium tetrafluoroborate and tris(4-chlorophenyl)sulfonium 3,5-bis(methoxycarbony1)benzenesulfonate.

[0077]
Examples of the azinium salt include 1-cyclohexylmethyloxypyridinium hexafluorophosphate, l-cyclohexyloxy-4-phenylpyridinium hexafluorophosphate, l-ethoxy-4-phenylpyridinium hexafluorophosphate, 1-(2-ethylhexyloxy)-4-phenylpyridinium hexafluorophosphate, 4-chloro-l-cyclohexylmethyloxypyridinium hexafluorophosphate, l-ethoxy-4-cyanopyridinium hexafluorophosphate, 3, 4-dichloro-l-(2-ethylhexyloxy)pyridinium hexafluorophosphate, l-benzyloxy-4-phenylpyridinium hexafluorophosphate, l-phenethyloxy-4-phenylpyridinium hexafluorophosphate,
1-(2-ethylhexyloxy)-4-phenylpyridinium p-toluenesulfonate,
1-(2-ethylhexyloxy)-4-phenylpyridinium perfluorobutanesulfonate,
1-(2-ethylhexyloxy)-4-phenylpyridinium bromide and
1-(2-ethylhexyloxy)-4-phenylpyridinium tetrafluoroborate.

[0078]
The radical polymerization initiator can be added preferably in an amount from 0.1 to 50% by weight, more preferably in an amount from 0.5 to 30% by weight, particularly preferably in an amount from 0.8 to 20% by weight, based on the total solid content constituting the image-recording layer.

[0079] (D) Radical polymerizable compound
The radical polymerizable compound for use in the invention is an addition-polymerizable compound having at least one ethylenically unsaturated double bond, and it is preferably selected from compounds having at least one, preferably two or more, terminal ethylenically unsaturated double bonds. Such compounds are widely known in the field of art and they can be used in the invention without any particular limitation. The compound has a chemical form, for example, a monomer, a prepolymer, specifically, a dimer, a trimer or an oligomer, or a mixture thereof or a (co)polymer thereof.

[0080]
Specific examples of the radical polymerizable compound include compounds described in Paragraph Nos. [0089] to [0098] of JP-A-2008-195018. Among them, esters of aliphatic polyhydric alcohol compound with an unsaturated carboxylic acid (for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid or maleic acid) are preferably exemplified. Other preferable radical polymerizable compound includes polymerizable compounds containing an isocyanuric acid structure described in JP-A-2005-329708.

[0081]
Among them, an isocyanuric acid ethylene oxide-modified ^ acrylate, for example, tris(acryloyloxyethyl) isocyanurate or bis(acryloyloxyethyl)hydroxyethyl isocyanurate is particularly preferred, because it is excellent in balance between hydrophilicity relating to the on-press development property and polymerization ability relating to the printing durability.

[0082]
In the invention, the radical polymerizable compound is preferably used in a range from 5 to 80% by weight, more preferably in a range from 25 to 75% by weight, based on the total solid content of the image-recording layer.

[0083] (E) Ammonium salt or phosphonium salt
While the ink receptivity of the lithographic printing plate precursor according to the invention can be improved by adding the specific polymer compound containing a number of repeating units of alkylene oxide from 10 to 120, the ink receptivity is further improved by using together with at least any one selected from an ammonium --salt and a phosphonium salt. Among them, the ammonium salt is preferably used. In the case of incorporating the inorganic stratiform compound into the protective layer, the compound functions as a surface covering agent for the inorganic stratiform compound to prevent deterioration of the ink receptivity.

[0084]
As preferred phosphonium compound, phosphonium compounds described in JP-A-2006-297907 and JP-A-2007-50660 are exemplified. Specific examples of the phosphonium compound include tetrabutylphosphonium iodide, butyltriphenylphosphonium bromide, tetraphenylphosphonium bromide, 1,4-bis (triphenylphosphonio) butane di(hexafluorophosphate), 1,7-bis(triphenylphosphonio)heptane sulfate and 1,9-bis(triphenylphosphonio)nonane naphthalene-2,7-disulfonate.

[0085]
As the ammonium salt, an ammonium salt represented by formula (2) shown below is preferred. [0086]
Formula (2)

[0087]
In formula (2), R3 to R6 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group. Among them, an aryl group or an aralkyl group is preferred.

[0088]
The alkyl group represented by any one of R3 to R6 includes a straight-chain, branched or cyclic alkyl group having from 1 to 18 carbon atoms. Specifically, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, an n-amyl group, an isoamyl group, a sec-amyl group, a tert-amyl group, a neopentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a cyclohexyl group, a cyclohexylmethyl group, a cyclopentyl group, a cyclopropylmethyl group, a cyclohexylmethyl group, a cyclobutylmethyl group, a straight-chain or branched heptyl group, a cyclopentylethyl group, a straight-chain or branched octyl group, a straight-chain or branched nonyl group, a straight-chain or branched decyl group, a straight-chain or branched dodecyl group and a straight-chain or branched octadecyl group are preferred. Of these groups, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, an n-amyl group, an isoamyl group, a sec-amyl group, a tert-amyl group, a neopentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a cyclohexyl group, a cyclohexylmethyl group and a straight-chain or branched octyl group are more preferred.

[0089]
The aralkyl group represented by any one of R3 to R6 includes, for example, a benzyl group, a phenethyl group, a 3-phenylpropyl group, a naphthylmethyl group, a 2-naphthylethyl group and a 3-naphthylpropyl group. Among them, a benzyl group is preferred.

[O090]
The aryl group has preferably from 6 to 30 carbon atoms, more preferably from 6 to 20 carbon atoms, particularly preferably from 6 to 12 carbon atoms and includes, for example, a phenyl group, a p-methylphenyl group and a naphthyl group.

[0091]
Also, R3 to Re may have a substituent. As the substituent, a trifluoromethyl group, a fluoro group, a chloro group, a bromo group, a methoxy group, a hydroxy group, a nitro group, a vinyl group, a dimethyl amino group, a phenyl group, a methoxycarbonyl group and an ethoxycarbonyl group are preferred. Among them, a fluoro group, a chloro group, a bromo group, a methoxy group, a hydroxy group, a vinyl group, a phenyl group, a methoxycarbonyl group and an ethoxycarbonyl group are more preferred.

These groups may further substituted with the substituent in a similar manner.

[0092]
All of R3 to R6 may be the same or different from each other, or two of the three may be the same, and any appropriate combination may be selected.

[0093]
X" represents a counter anion. The counter anion may be an organic anion or an inorganic anion. As X", F~, Cl", Br", I", a benzenesulfonate anion which may have a substituent, a methylsulfate anion, an ehtylsulfate anion, a propylsulfate anion, a butylsulfate anion which may be branched, an amylsulf ate anion which may be branched,

PF6~, BF4~ and B(C6F5)4~ are exemplified. Among them, Cl~, Br", a benzenesulfonate anion, a toluenesulfonate anion, a methylsulfate anion, an ehtylsulfate anion, a propylsulfate anion, PFf, BF4~ and B(C6F5)4" are preferred.

[0094]
Specific examples of the ammonium salt represented by formula
(2) include tetramethylammonium hexafluorophosphate,
tetrabutylammonium hexafluorophosphate, dodecyltrimethylammonium
p-toluenesulfonate, benzyltriethylammonium hexafluorophosphate,
benzyldimethyloctylammonium hexafluorophosphate,
benzyldimethyldodecylammonium hexafluorophosphate.

[0095]
As the ammonium salt, an imidazolinium salt, a benzimidazolinium salt, a pyridinium salt and a quinolinium salt are -" also exemplified.

[0096]
Further, as the ammonium salt, a polymer containing an ammonium group is also exemplified. As the polymer containing an ammonium ^ group, a polymer containing a repeating unit represented by formula

(3) shown below is preferred.

[0097]
Formula (3)

[0098]
In formula (3), Rn represents a hydrogen atom or a methyl group. R12 to R14 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group. Among them, an aryl group and an aralkyl group are preferred.

[0099]
The alkyl group represented by any one of R12 to R14 includes a straight-chain, branched or cyclic alkyl group having from 1 to 10 carbon atoms. Specifically, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, an n-amyl group, an isoamyl group, a sec-amyl group, a tert-amyl group, a neopentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a cyclohexyl group, a cyclohexylmethyl group, a cyclopentyl group, a cyclopropylmethyl group, a cyclohexylmethyl group, a -^ cyclobutylmethyl group, a straight-chain or branched heptyl group, a cyclopentylethyl group, a straight-chain or branched octyl group, a straight-chain or branched nonyl group and a straight-chain or branched decyl group are preferred. Among them, a methyl group, an ^ ethyl group, an n-propyl group, an isopropyl group, a cyclopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, an n-amyl group, an isoamyl group, a sec-amyl group, a tert-amyl group, a neopentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a cyclohexyl group, a cyclohexylmethyl group and a straight-chain or branched octyl group are more preferred.

All of R12 to Ri4 may be the same or different from each other, or two of the three may be the same.

[0100]
The aryl group has preferably from 6 to 30 carbon atoms, more preferably from 6 to 20 carbon atoms, particularly preferably from 6 to 12 carbon atoms and includes, for example, a phenyl group, a p-methylphenyl group and a naphthyl group.

[0101]
Li represents a connecting group. As the connecting group, a connecting group containing at least one selected from a phenylene group, a carbonyloxy group and a carbonylimino group is exemplified. Among them, a connecting group containing a carbonyloxy group is preferred and as a specific example, -COO(CH2)n- is exemplified, n represents an integer from 1 to 4, and is more preferably 2 or 3.

[0102]
X" represents a counter anion. The counter anion may be an organic anion or an inorganic anion and is preferably an organic sulfonate anion having a substituent selected from an aryl group, an aralkyl group and an alkyl group having 6 or more carbon atoms, a borate anion or PF4". Among them, an organic borate anion or PF4" is preferred.

As the organic borate anion, an organic borate anion having a structure represented by formula (5) shown below is more preferred. When the counter anion is the organic borate anion, since curing of the image area further proceeds with increase in sensitivity and water permeability is inhibited, the ink receptivity can further be improved to achieve good printing durability.

[0103]
Formula (5)

[0104]
In formula (5), R1 to R4 each independently represents a monovalent organic group. The monovalent organic group represented by any one of R1 to R4 includes, for example, an alkyl group, an alkenyl group, an aryl group, an alkynyl group and a cycloalkyl group and among them, an aryl group is preferred. The organic group may have a substituent. As the substituent which may be introduced, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a halogen atom, an alkoxy group, an alkoxycarbonyl group, an amino group, a cyano group, an amido group, a urethane group, a sulfo group, a thioalkoxy group, a carboxyl group and the like are exemplified.

Above all, R1 to R4 each preferably represents an aryl group having an electron withdrawing group as a substituent. As the ^ electron withdrawing group introduced into the aryl group, a halogen atom or a fluoroalkyl group is preferred and among them, a fluorine atom or a trifluoromethyl group is preferred.

[0105]
The polymer containing a repeating unit represented by formula (3) described above may contain other copolymerization component.

The other copolymerization component is not particularly restricted ^. as long as it is copolymerizable and is preferably a (meth) acrylate. R in -COQR of a side chain of (meth) acrylate includes an alkyl group having from 1 to 21 carbon atoms, an aralkyl group, an aryl group, -(C2H40)n-R5 and - (C3H60)n-R5« R5 represents a hydrogen atom, a methyl group or an ethyl group, n represents an integer form 1 to 3.

In the case of containing other copolymerization component, the content of repeating init represented by formula (3) in the polymer compound is preferably in a range from 5 to 80% by mole.

[0106]
As to the ammonium salt-containing polymer described above, its reduced specific viscosity value (unit: cSt/g/ml) determined according to the measuring method described below is preferably in a range from 5 to 120, more preferably in a range from 10 to 110, and particularly preferably in a range from 15 to 100.

[0107]
In a 20 ml measuring flask was weighed 3.33 g of a 30% polymer solution (1 g as a solid content) and the measuring flask was filled up to the gauge line with N-methyl pyrrolidone. The resulting solution was put into an Ubbelohde reduced viscometer (viscometer constant: 0.010 cSt/s), a period for running down of the solution at 30°C was measured and the viscosity was calculated according to a conventional manner using a calculating formula (Kinetic viscosity = Viscometer constant x Period for liquid to pass through a capillary (sec)).

[0108]
Specific examples of the ammonium group-containing polymer are set forth below.

(1) 2-(Trimethylammonio)ethyl methacrylate p-toluenesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio: 10/90)

(2) 2-(Trimethylammonio)ethyl methacrylate hexafluorophosphate /3,6-dioxaheptyl methacrylate copolymer (molar ratio: 20/80)

(3) 2-(Ethyldimethylammonio)ethyl methacrylate p-toluenesulfonate/hexyl methacrylate copolymer (molar ratio: 30/70)

(4) 2-(Trimethylammonio)ethyl methacrylate hexafluorophosphate /2-ethylhexyl methacrylate copolymer (molar ratio: 20/80)

(5) 2-(Trimethylammonio)ethyl methacrylate methylsulfate/hexyl methacrylate copolymer (molar ratio: 40/60)

(6) 2-(Butyldimethylammonio)ethyl methacrylate hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (molar ratio: 20/80)

(7) 2-(Butyldimethylammonio)ethyl acrylate hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (molar ratio: 20/80)

(8) 2- (Butyldimethylarnmonio) ethyl methacrylate 13-ethyl-5,8,11-trioxa-l-heptadecanesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio: 20/80)

(9) 2-(Butyldimethylammonio)ethyl methacrylate hexafluorophosphate/3,6-dioxaheptyl methacrylate/2-hydroxy-3-methacryloyloxypropyl methacrylate copolymer (molar ratio: 15/80/5)

(10) N-2-(Butyldimethylammonio)ethyl.methacrylamide hexafluorophosphate/3,6-dioxaheptyl methacrylate /methacrylamide copolymer (molar ratio: 20/40/40)

(11) 4-(Butyldimethylammoniomethyl)styrene hexafluorophosphate/3, 6-dioxaheptyl methacrylate copolymer (molar ratio: 20/80)

[0109]
The content of the ammonium salt or phosphonium salt described above is preferably from 0.01 to 30.0% by weight, more preferably from 0.1 to 15.0% by weight, still more preferably from 1 to 5% by weight, based on the total solid content of the image-recording layer.

[0110] (F) Hydrophobilizing precursor
According to the invention, a hydrophobilizing precursor can be used in order to improve the on-press development property. The hydrophobilizing precursor for use in the invention means a fine particle capable of converting the image-recording layer to be hydrophobic when heat is applied. The fine particle is preferably at least one particle selected from hydrophobic thermoplastic polymer fine particle, thermo-reactive polymer fine particle, microcapsule having a hydrophobic compound encapsulated andmicrogel (crosslinked polymer fine particle) . Among them, polymer fine particle having a polymerizable group and microgel are preferred.

[0111]
As the hydrophobic thermoplastic polymer fine particle, hydrophobic thermoplastic polymer fine particles described, for example, in Research Disclosure, No. 333003, January (1992), JP-A-9-123387, JP-A-9-131850, JP-A-9-171249, JP-A-9-171250 and European Patent 931,647 are preferably exemplified.
Specific examples of the polymer constituting the polymer fine ^ particle include a homopolymer or copolymer of a monomer, for example, ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinyl carbazole or an acrylate or methacrylate having a polyalkylene structure and a mixture thereof. Among them, polystyrene and polymethyl methacrylate are more preferred.

[0112]
The average particle size of the hydrophobic thermoplastic polymer fine particle for use in the invention is preferably from 0.01 to 2.0 um.

[0113]
The thermo-reactive polymer fine particle for use in the invention includes polymer fine particle having a thermo-reactive group and forms a hydrophobilized region by crosslinkage due to thermal reaction and change in the functional group involved therein.

[0114]
As the thermo-reactive group of the polymer fine particle having a thermo-reactive group for use in the invention, a functional group performing any reaction may be used as long as a chemical bond is formed and an ethylenically unsaturated group (for example, an acryloyl group, a methacryloyl group, a vinyl group or an allyl group) performing a radical polymerization reaction, a cationic polymerizable group (for example, a vinyl group or a vinyloxy group), an isocyanate group performing an addition reaction or a blocked form thereof, an epoxy group, a vinyloxy group and a functional group having an active hydrogen atom (for example, an amino group, a hydroxy group or a carboxyl group) as the reaction partner thereof, a carboxyl group performing a condensation reaction and a hydroxyl group or an amino group as the reaction partner thereof, and an acid anhydride performing a ring opening addition reaction and an amino group or a hydroxyl group as the reaction partner thereof are preferably exemplified.

[0115]
As the microcapsule for use in the invention, microcapsule having all or part of the constituting components of the image-recording layer encapsulated as described, for example, in JP-A-2001-277740 and JP-A-2001-277742 is exemplified. The constituting components of the image-recording layer may be included outside the microcapsules. It is a more preferred embodiment of the image-recording layer containing microcapsules that hydrophobic constituting components are encapsulated in the microcapsules and hydrophilic components are included outside the microcapsules.

[0116]
According to the invention, an embodiment containing a crosslinked resin particle, that is, microgel may be used. The microgel can contain a part of the constituting components of the image-recording layer in the inside and/or on the surface thereof.

Particularly, an embodiment of a reactive microgel containing a radical polymerizable compound on the surface thereof is preferred in view of the image-forming sensitivity and printing durability.

[0117]
As a method for microencapsulation or microgelation of the constituting components of the image-recording layer, known methods can be used.

[0118]
The average particle size of the microcapsule or microgel is preferably from 0.01 to 3.0 urn, more preferably from 0.05 to 2.0 urn, particularly preferably from 0.10 to 1.0 urn. In the range described above, good resolution and good time lapse stability can be achieved.

[0119]
The content of the hydrophobilizing precursor is preferably in a range from 5 to 90% by weight based on the solid content concentration of the image-recording layer.

[0120] (G) Hydrophilic low molecular weight compound

The image-recording layer according to the invention may contain a hydrophilic low molecular weight compound in order to improve the on-press development property without accompanying the decrease in the printing durability.

The hydrophilic low molecular weight compound includes a water-soluble organic compound, for example, a glycol compound, e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol or tripropylene glycol, or an ether or ester derivative thereof, a polyhydroxy compound, e.g., glycerine, pentaerythritol or tris(2-hydroxyethyl) isocyanurate, an organic amine compound, e.g., triethanol amine, diethanol amine or monoethanol amine, or a salt thereof, an organic sulfonic acid compound, e.g., an alkyl sulfonic acid, toluene sulfonic acid or benzene sulfonic acid, or a salt thereof, an organic sulfamic acid compound, e.g., an alkyl sulfamic acid, or a salt thereof, an organic sulfuric acid compound, e.g., an alkyl sulfuric acid or an alkyl ether sulfuric acid, or a salt thereof, an organic phosphonic acid compound, e.g., phenyl phosphonic acid, or a salt thereof, an organic carboxylic acid, e.g., tartaric acid, oxalic acid, citric acid, malic acid, lactic acid, gluconic acid or an amino acid, or a salt thereof and a betaine compound.

[0121]
According to the invention, it is preferred to incorporate at least one compound selected from a polyol compound, an organic sulfate compound, an organic sulfonate compound and a betaine compound into the image-recording layer.

[0122]
Specific examples of the organic sulfonate compound include an alkylsulfonate, for example, sodium n-butylsulfonate, sodium n-hexylsulfonate, sodium 2-ethylhexylsulfonate, sodium cyclohexylsulfonate or sodium n-octylsulfonate; an alkylsulfonate containing an ethylene oxide chain, for example, sodium
5, 8,11-trioxapentadecane-l-sulfonate, sodium
5,8,11-trioxaheptadecane-l-sulfonate, sodium
13-ethyl-5,8,ll-trioxaheptadecane-l-sulfonate or sodium
5, 8,11,14-tetraoxatetracosane-l-sulfonate; and an arylsulfonate, for example, sodium benzenesulfonate, sodium p-toluenesulfonate, sodiump-hydroxybenzenesulfonate, sodium p -styrenesulfonate, sodium isophthalic acid dimethyl-5-sulfonate, sodium 1-naphtylsulfonate, sodium 4-hydroxynaphtylsulfonate, disodium 1,5-naphthalenedisulfonate or trisodium 1, 3, 6-naphthalenetrisulfonate. The salt may also be potassium salt or lithium salt.

[0123]
As the organic sulfate compound, a sulfate of alkyl, alkenyl, alkynyl, aryl or heterocyclic monoether of polyethylene oxide is exemplified. The number of ethylene oxide unit is preferably from 1 to 4. The salt is preferably a sodium salt, a potassium salt or a lithium salt.

[0124]
As the betaine compound, a compound wherein a number of carbon atoms included in a hydrocarbon substituent on the nitrogen atom is from 1 to 5 is preferred. Specific examples thereof include trimethylammonium acetate, dimethylpropylammonium acetate, 3-hydroxy-4-trimethylammoniobutyrate, 4-(l-pyridinio)butyrate, 1-hydroxyethyl-l-imidazolioacetate, trimethylammonium methanesulfonate, dimethylpropylammonium methanesulfonate, 3-trimethylammonio-l-porpanesulfonate and 3-(1-pyridinio)-1-porpanesulfonate.

[0125]
Since the hydrophilic low molecular weight compound has a small structure of hydrophobic portion and almost no surface active function, degradations of the hydrophobicity and film strength in the image area due to penetration of dampening water into the exposed area (image area) of the image-recording layer are prevented and thus, the ink receptive-property and printing durability of the image-recording layer can be preferably maintained.

[0126]
The amount of the hydrophilic low molecular weight compound added to the image-recording layer is preferably from 0.5 to 20% by weight, more preferably from 1 to 10% by weight, still more preferably from 2 to 8% by weight, based on the total solid content of the image-recording layer. In the range described above, good on-press development property and printing durability are obtained.

The hydrophilic low molecular weight compounds may be used individually or as a mixture of two or more thereof.

[0127] (H) Surfactant
In the image-recording layer according to the invention, a surfactant can be used in order to promote the on-press development property and to improve the state of coated surface. The surfactant includes, for example, a nonionic surfactant, an anionic surfactant, a cat ionic surfactant, an amphoteric surfactant and a fluorine-based surfactant. The surfactants may be used individually or in combination of two or more thereof. In the case where a halide ion is contained in the surfactant as an impurity or a counter ion, it is preferred to remove the halide ion or exchange the halide ion with other anion by a method, for example, desalting or ion exchange.

[0128]
The nonionic surfactant for use in the invention is not particular restricted, and those hitherto known can be used. Examples of the nonionic surfactant include a polyoxyethylene alkyl ether, a polyoxyethylene alkyl phenyl ether, a polyoxyethylene polystyryl phenyl ether, a polyoxyethylene polyoxypropylene alkyl ether, a glycerin fatty acid partial ester, a sorbitan fatty acid partial ester, a pentaerythritol fatty acid partial ester, a propylene glycol monofatty acid ester, a sucrose fatty acid partial ester, a polyoxyethylene sorbitan fatty acid partial ester, a polyoxyethylene sorbitol fatty acid partial ester, a polyethylene glycol fatty acid ester, a polyglycerol fatty acid partial ester, a polyoxyethylenated castor oil, a polyoxyethylene glycerol fatty acid partial ester, a fatty acid diethanolamide, an N,N-bis-2-hydroxyalkylamine, a polyoxyethylene alkylamine, a triethanolamine fatty acid ester, a trialkylamine oxide, a polyethylene glycol and a copolymer of polyethylene glycol and polypropylene glycol.

[0129]
The anionic surfactant for use in the invention is not particularly restricted and those hitherto known can be used. Examples of the anionic surfactant include a fatty acid salt, an abietic acid salt, a hydroxyalkanesulfonic acid salt, an alkanesulfonic acid salt, a dialkylsulfosuccinic ester salt, a straight-chain alkylbenzenesulfonic acid salt, a branched alkylbenzenesulfonic acid salt, an alkylnaphthalenesulfonic acid salt, an alkylphenoxypolyoxyethylene propylsulfonic acid salt, a polyoxyethylene alkylsulfophenyl ether salt, N-methyl-N-oleyltaurine sodium salt, an N-alkylsulfosuccinic monoamide disodium salt, a petroleum sulfonic acid salt, sulfated beef tallow oil, a sulfate ester slat of fatty acid alkyl ester, an alkyl sulfate ester salt, a polyoxyethylene alkyl ether sulfate ester salt, a fatty acid monoglyceride sulfate ester salt, a polyoxyethylene alkyl phenyl ether sulfate ester salt, a polyoxyethylene styrylphenyl ether sulfate ester salt, an alkyl phosphate ester salt, a polyoxyethylene alkyl ether phosphate ester salt, a polyoxyethylene alkyl phenyl ether phosphate ester salt, a partial saponification product of styrene/maleic anhydride copolymer, a partial saponification product of olefin/maleic anhydride copolymer and a naphthalene sulfonate formalin condensate.

[0130]
The cationic surfactant for use in the invention is not particularly restricted and those hitherto known can be used. Examples of the cationic surfactant include an alkylamine salt, a quaternary ammonium salt, a polyoxyethylene alkyl amine salt and a polyethylene polyamine derivative. As the counter anion of the cationic surfactant, it is preferred to select an anion other than a halide ion (for example, a sulfate ion, a hydrogen sulfate ion, a hydroxide ion, a phosphate ion, an alkylsulfonate ion or an arylsulfonate ion).

The amphoteric surfactant for use in the invention is not particularly restricted and those hitherto known can be used. Examples of the amphoteric surfactant include a carboxybetaine, an aminocarboxylic acid, a sulfobetaine, an aminosulfuric ester and an imidazoline.

[0131]
In the surfactant described above, the term "polyoxyethylene" can be replaced with "polyoxyalkylene", for example, polyoxymethylene, polyoxypropylene or polyoxybutylene, and such surfactants can also be used in the invention.

[0132]
Further, a preferred surfactant includes a fluorine-based surfactant containing a perfluoroalkyl group in its molecule. Examples of the fluorine-based surfactant include an ionic type, for example, a perfluoroalkyl carboxylate, a perfluoroalkyl sulfonate or a perfluoroalkylphosphoric acid ester; an amphoteric type, for example, a perfluoroalkyl betaine; a cationic type, for example, a perfluoroalkyltrimethylammonium salt; and a nonionic type, for example, a perfluoroalkylamine oxide, a perfluoroalkyl ethylene oxide adduct, an oligomer having a perfluoroalkyl group and a hydrophilic group, an oligomer having a perfluoroalkyl group and an oleophilic group, an oligomer having a perfluoroalkyl group, a hydrophilic group and an oleophilic group or a urethane having a perfluoroalkyl group and an oleophilic group. Further, fluorine-based surfactants described in JP-A-62-170950, JP-A-62-226143 and JP-A-60-168144, for example, a copolymer of an acrylate or methacrylate containing a perf luoroalkyl group and a poly (oxyalkylene) acrylate or methacrylate and a both terminal perfluoroalkyl etherified product of a polyoxypropylene-polyoxyethylene block copolymer are also preferably exemplified.

[0133]
The surfactants can be used individually or in combination of two or more thereof.
The content of the surfactant is preferably from 0.01 to 10% by weight, more preferably from 0.1 to 5% by weight, based on the total solid content of the image-recording layer. When the content is 0.01% by weight or more, the surface active performance is sufficiently exerted and uniformity of the state of coated surface is obtained. Also, when the content is 10% by weight or less, coating repelling does not occur to obtain good performance, in the case of further coating a layer, for example, a protective layer, on the image-recording layer.

[0134] (I) Other components
To the image-recording layer according to the invention, if desired, as other component, for example, a coloring agent, a print-out agent, a polymerization inhibitor, a higher fatty acid derivative, a plasticizer, an inorganic fine particle, an inorganic stratiform compound, a cosensitizer or a chain transfer agent may further be added. Specifically, compounds and amounts added thereof described, for example, in Paragraph Nos. [0114] to [0159] of JP-A-2008-284817, Paragraph Nos. [0023] to [0027] of JP-A-2006-91479 and Paragraph No. [0060] of U.S. Patent Publication No. 2008/0311520 are preferably used.

[0135]
(J) Formation of image-recording layer
The image-recording layer according to the invention is formed by dispersing or dissolving each of the necessary components described above in a known solvent to prepare a coating solution and coating the solution on a support by a known method, for example, bar coater coating and drying as described in Paragraph Nos. [0142] to [0143] of JP-A-2008-195018. The coating amount (solid content) of the image-recording layer formed on the support after coating and drying may be varied according to the intended purpose but is in general preferably from 0.3 to 3.0 g/m2. In the range described above, good sensitivity and good film property of the image-recording layer can be obtained.

[0136]
(Undercoat layer)
In the lithographic printing plate precursor according to the invention, an undercoat layer (also referred to as an intermediate layer) is preferably provided between the image-recording layer and the support. The undercoat layer strengthens adhesion between the support and the image-recording layer in the exposed area and makes removal of the image-recording layer from the support in the unexposed area easy, thereby contributing improvement in the developing property without accompanying degradation of the printing durability.

Further, it is advantageous that in the case of infrared laser exposure, since the undercoat layer acts as a heat insulating layer, decrease in sensitivity due to diffusion of heat generated upon the exposure into the support is prevented.

[0137]
As a compound for use in the undercoat layer, specifically, for example, a silane coupling agent having an addition-polymerizable ethylenic double bond reactive group described in JP-A-10-282679 and a phosphorus compound having an ethylenic double bond reactive group described in JP-A-2-304441 are exemplified. A polymer resin having an adsorbing group capable of adsorbing to a surface of the support, a hydrophilic group and a crosslinkable group as described in JP-A-2005-125749 and JP-A-2006-188038 is more preferably exemplified. The polymer resin is preferably a copolymer of a monomer having an adsorbing group, a monomer having a hydrophilic group and a monomer having a crosslinkable group. More specifically, a polymer resin which is a copolymer of a monomer having an adsorbing group, for example, a phenolic hydroxy group, a carboxyl group, -P03H2, -OPO3H2, -CONHSO2-, -S02NHS02- or -COCH2COCH3, a monomer having a hydrophilic sulf o group and a monomer having a polymerizable crosslinkable group, for example, a methacryl group or an allyl group. The polymer resin may contain a crosslinkable group introduced by a salt formation between a polar substituent of the polymer resin and a compound containing a substituent having a counter charge to the polar substituent of the polymer resin and an ethylenically unsaturated bond and also may be further copolymerized with a monomer other than those described above, preferably a hydrophilic monomer.

[0138]
The content of the unsaturated double bond in the polymer resin for undercoat layer is preferably from 0.1 to 10.0 mmol, most preferably from 2.0 to 5.5 mmol, based on 1 g of the polymer resin.

The weight average molecular weight of the polymer resin for undercoat layer is preferably 5,000 or more, more preferably from 10,000 to 300,000.

[0139]
The undercoat layer according to the invention may contain a chelating agent, a secondary or tertiary amine, a polymerization inhibitor or a compound containing an amino group or a functional group having polymerization inhibition ability and a group capable of interacting with a surface of aluminum support (for example, 1, 4-diazobicyclo[2,2, 2]octane (DABCO),
2,3,5,6-tetrahydroxy-p-quinone, chloranil, sulfophthalic acid,
hydroxyethylethylenediaminetriacetic acid,
dihydroxyethylethylenediaminediacetic acid or
hydroxyethyliminodiacetic acid) in addition to the compounds for the undercoat layer described above in order to prevent the occurrence of stain due to the lapse of time.

[0140]
The undercoat layer is coated according to a known method. The coating amount (solid content) of the undercoat layer is preferably from 0.1 to 100 mg/m2, and more preferably from 1 to 30 mg/m2.

[0141]
(Support)
As the support for use in the lithographic printing plate precursor according to the invention, a known support is used. Among them, an aluminum plate subjected to roughening treatment and anodizing treatment according to a known method is preferred.

Also, other treatments, for example, an enlarging treatment or sealing treatment of micropores of the anodized film described in JP-A-2001-253181 and JP-A-2001-322365 or a surface hydrophilizing treatment, for example, with an alkali metal silicate as described in U.S. Patents 2,714,066, 3,181,461, 3,280,734 and 3,902,734 or polyvinyl phosphonic acid as described in U.S. Patents 3,276,868, 4,153,461 and 4,689,272 may be appropriately selected and applied to the aluminum plate, if desired.

The support preferably has a center line average roughness of 0.10 to 1.2 urn.

[0142]
The support may have a backcoat layer containing an organic polymer compound described in JP-A-5-45885 or an alkoxy compound of silicon described in JP-A-6-351745, provided on the back surface thereof, if desired.

[0143] [Plate making method]
Plate making of the lithographic printing plate precursor according to the invention is preferably performed by an on-press development method. The on-press development method includes a step in which the lithographic printing plate precursor is imagewise exposed and a printing step in which oily ink and an aqueous component are supplied to the exposed lithographic printing plate precursor without undergoing any development processing to perform printing, and it is characterized in that the unexposed area of the lithographic printing plate precursor is removed in the course of the printing step. The imagewise exposure may be performed on a printing machine after the lithographic printing plate precursor is mounted on the printing machine or may be separately performed using a platesetter or the like. In the latter case, the exposed lithographic printing plate' precursor is mounted as it is on a printing machine without undergoing a development processing step. Then, the printing operation is initiated using the printing machine with supplying oily ink and an aqueous component and at an early stage of the printing the on-press development is carried out. Specifically, the image-recording layer in the unexposed area is removed and the hydrophilic surface of support is revealed therewith to form the non-image area. As the oily ink and aqueous component, printing ink and dampening water for conventional lithographic printing can be employed, respectively.

The on-press development method is described in more detail below.

[0144]
As the light source used for the image exposure in the invention, a laser is preferred. The laser for use in the invention is not particularly restricted and includes, for example, a solid laser or semiconductor laser emitting an infrared ray having a wavelength of 760'to 1,200 nm.

With respect to the infrared ray laser, the output is preferably 100 mW or more, the exposure time per pixel is preferably within 20 microseconds, and the irradiation energy is preferably from 10 to 300 mJ/cm2. With respect to the laser exposure, in order to shorten the exposure time, it is preferred to use a multibeam laser device.

[0145]
The exposed lithographic printing plate precursor is mounted on a plate cylinder of a printing machine. In case of using a printing machine equipped with a laser exposure apparatus, the lithographic printing plate precursor is mounted on a plate cylinder of the printing machine and then subjected to the imagewise exposure.

[0146]
When dampening water and printing ink are supplied to the imagewise exposed lithographic printing plate precursor to perform printing, in the exposed area of the image-recording layer, the image-recording layer cured by the exposure forms the printing ink receptive area having the oleophilic surface. On the other hand, in the unexposed area, the uncured image-recording layer is removed by dissolution or dispersion with the dampening water and/or printing ink supplied to reveal the hydrophilic surface in the area. As a result, the dampening water adheres on the revealed hydrophilic surface and the printing ink adheres to the exposed area of the image-recording layer, whereby printing is initiated.

[0147]
While either the dampening water or printing ink may be supplied at first on the surface of lithographic printing plate precursor, it is preferred to supply the printing ink at first in view of preventing the dampening water from contamination with the component of the image-recording layer removed.

Thus, the lithographic printing plate precursor according to the invention is subjected to the on-press development on an offset printing machine and used as it is for printing a large number of sheets.

EXAMPLE

[0148]
The present invention will be described in more detail with reference to the following examples, but the invention should not be construed as being limited thereto.

[0149]
Examples 1 to 12 and Comparative Examples 1 to 4

[0150]
[Preparation of Lithographic printing plate precursors (1) to (12) and (41) to (44)] (1) Preparation of Support (No.l)
An aluminum plate (material: JIS A 1050) having a thickness of 0.3 mm was subjected to a degreasing treatment at 50°C for 30 seconds using a 10% by weight aqueous sodium aluminate solution in order to remove rolling oil on the surface thereof and then grained the surface thereof using three nylon brushes embedded with bundles of nylon bristle having a diameter of 0.3 mm and an aqueous suspension (specific gravity: 1.1 g/cm3) of pumice having a median size of 25 μm, followed by thorough washing with water. The plate was subjected to etching by immersing in a 25% by weight aqueous sodium hydroxide solution of 45°C for 9 seconds, washed with water, then immersed in 20% by weight nitric acid at 60°C for 20 seconds, and washed with water. The etching amount of the grained surface was about 3 g/m2.

[0151]
Then, using an alternating current of 60 Hz, an electrochemical roughening treatment was continuously carried out on the plate. The electrolytic solution used was a 1% by weight aqueous nitric acid solution (containing 0.5% by weight of aluminum ion) and the temperature of electrolytic solution was 50°C. The electrochemical roughening treatment was conducted using an alternating current source, which provides a rectangular alternating current having a trapezoidal waveform such that the time TP necessary for the current value to reach the peak from zero was 0.8 msec and the duty ratio was 1:1, and using a carbon electrode as a counter electrode. A ferrite was used as an auxiliary anode. The current density was 30 A/dm2 in terms of the peak value of the electric current, and 5% of the electric current flowing from the electric source was divided to the auxiliary anode. The quantity of electricity in the nitric acid electrolysis was 175 C/dm2 in terms of the quantity of electricity when the aluminum plate functioned as an anode. The plate was then washed with water by spraying.

[0152]
The plate was further subjected to an electrochemical roughening treatment in the same manner as in the nitric acid electrolysis above using as an electrolytic solution, a 0. 5% by weight aqueous hydrochloric acid solution (containing 0.5% by weight of aluminum ion) having temperature of 50°C and under the condition that ^ the quantity of electricity was 50 C/dm2 in terms of the quantity of electricity when the aluminum plate functioned as an anode. The plate was then washed with water by spraying.

The plate was then subjected to an anodizing treatment using as an electrolytic solution, 15% by weight sulfuric acid (containing 0.5% by weight of aluminum ion) at a current density of 15 A/dm2 to form a direct current anodized film of 2.5 g/m2, washed with water and dried to prepare Support (1).

Thereafter, in order to ensure the hydrophilicity of the non-image area, Support (1) was subjected to silicate treatment using a 2.5% by weight aqueous sodium silicate No. 3 solution at 60°C for 10 seconds. Subsequently, the plate was washed with water to obtain Support (2) . The adhesion amount of Si was 10 mg/m2. The center line average roughness (Ra) of the support was measured using a stylus having a diameter of 2 um and found to be 0.51 urn.

[0153]
(2) Formation of Undercoat layer
Coating solution (1) for undercoat layer shown below was coated on Support (2) so as to have a dry coating amount of 20 mg/m2 to prepare a support having an undercoat layer for using in the experiments described below.

[0154]

Compound (1) for undercoat layer having 0.18 g structure shown below
Hydroxyethyliminodiacetic acid 0.10 g
Methanol 55.24 g
Water 6.15 g

[0155]
Compound (1) for undercoat layer

[0156] (3) Formation of Image-recording layer
Coating solution (1) for image-recording layer having the composition shown below was coated on the undercoat layer formed as described above by a bar and dried in an oven at 100°C for 60 seconds to form an image-recording layer having a dry coating amount of 1.0 g/m2.
Coating solution (1) for image-recording layer was prepared by mixing Photosensitive solution (1) shown below with Microgel solution (1) shown below just before the coating, followed by stirring.

[0157]
Specific polymer compound (shown in Table 1 0.240 g using the number of specific example described hereinbefore)
Infrared absorbing dye (1) having structure 0.030 g shown below
Radical polymerization initiator (1) having 0.162 g structure shown below
Radical polymerizable compound 0.192 g
(Tris(acryloyloxyethyl) isocyanurate (NK ESTER A-9300, produced by Shin-Nakamura Chemical Co., Ltd.))
Hydrophilic low molecular weight compound 0.062 g
(Tris(2-hydroxyethyl) isocyanurate)
Hydrophilic low molecular weight compound (1) 0.050 g having structure shown below
Ammonium salt (compound shown in Table 1) Amount shown in Table 1
Fluorine-based surfactant (1) having 0.008 g -"structure shown below
2-Butanone 1.091 g l-Methoxy-2-propanol 8.609 g

[0158]

Microgel (1) 2.640 g
Distilled water 2.425 g

[0159]
The structures of Polymerization initiator (1) , Infrared absorbing dye (1), Hydrophilic low molecular weight compound (1) and
Fluorine-based surfactant (1) and preparation method of Microgel (1) are shown below.

[0160]

[0161]

An oil phase component was prepared by dissolving 10 g of adduct of trimethylol propane and xylene diisocyanate (TAKENATE D-110N, produced by Mitsui Chemicals Polyurethanes, Inc.)3.15 g of pentaerythritol triacrylate (SR444, produced by Nippon Kayaku Co., Ltd.) and 0.1 g of PIONIN A-41C (produced by Takemoto Oil & Fat Co., Ltd.) in 17 g of ethyl acetate. As an aqueous phase component, 40 g of a 4% by weight aqueous solution of PVA-205 was prepared. The oil phase component and the aqueous phase component were mixed and emulsified using a homogenizer at 12,000 rpm for 10 minutes. The resulting emulsion was added to 25 g of distilled water and stirred at room temperature for 30 minutes and then at 50°C for 3 hours. The microgel liquid thus-obtained was diluted using distilled water so as to have the solid content concentration of 15% by weight to prepare Microgel (1) . The average particle size of the microgel was measured by a light scattering method and found to be 0.2 urn.

[0162] (4) Formation of Protective layer
Coating solution (1) for protective layer having the composition shown below was coated on the image-recording layer described above by a bar and dried in an oven at 120°C for 60 seconds to form a protective layer having a dry coating amount of 0.15 g/m2, thereby preparing Lithographic printing plate precursors (1) to (12) for Examples 1 to 12 and Lithographic printing plate precursors (41) to (43) for Comparative Examples 1 to 3, respectively.

Lithographic printing plate precursor (44) for Comparative Example 4 was prepared in the same manner as the preparation of Lithographic printing plate precursor (1) expect for using Coating solution (2) for protective layer in place of Coating solution (1) for protective layer described above.

[0163]
Dispersion of inorganic stratiform compound 1.5 g (1) shown below
Aqueous 6% by weight solution of polyvinyl 0.55 g alcohol (CKS 50, sulfonic acid-modified, saponification degree: 99% by mole or more, polymerization degree: 300, produced by Nippon Synthetic Chemical Industry Co., Ltd.)

Aqueous 6% by weight solution of polyvinyl 0.03 g alcohol (PVA-405, saponification degree: 81.5 % by mole, polymerization degree: 500, produced by Kuraray Co., Ltd.)

Aqueous 1% by weight solution of surfactant 0.86 g (EMALEX 710, produced by Nihon Emulsion Co., Ltd.)
Ion-exchanged water 6.0 g

[0164]

To 193.6 g of ion-exchanged water was added 6.4 g of synthetic mica (SOMASIF ME-100, produced by CO-OP Chemical Co., Ltd.) and the mixture was dispersed using a homogenizer until an average particle size (according to a laser scattering method) became 3 μm. The aspect ratio of the inorganic particle thus-dispersed was 100 or more.

[0165]

Aqueous 6% by weight solution of polyvinyl 0.55 g alcohol (CKS 50, sulfonic acid-modified, saponification degree: 99% by mole or more, polymerization degree: 300, produced by Nippon Synthetic Chemical Industry Co., Ltd.)

Aqueous 6% by weight solution of polyvinyl 0.03 g alcohol (PVA-405, saponification degree: 81.5 % by mole, polymerization degree: 500, produced by Kuraray Co., Ltd.)

Aqueous 1% by weight solution of surfactant 0.86 g (EMALEX 710, produced by Nihon Emulsion Co., Ltd.)
Ion-exchanged water 6.0 g

[0166]
The structures of the comparative polymer compounds used in the comparative examples are shown below.

[0167]
(Mw: 70,000) Polymer compound (23)

[0168]
[Evaluation of Lithographic printing plate precursor]

[0169]
(1) On-press development property
The lithographic printing plate precursor thus-obtained was exposed by LUXEL PLATESETTER T-6000III equipped with an infrared semiconductor laser produced by FUJIFILM Corp. under the conditions of a rotational number of an external drum of 1,000 rpm, laser output of 70% and resolution of 2,400 dpi. The exposed image contained a solid image and a 50% halftone dot chart of a 20 μm -dot FM screen. The exposed lithographic printing plate precursor was mounted without undergoing development processing on a plate cylinder of a printing machine (LITHRONE 26, produced by Komori Corp.). Using dampening water (ECOLITY-2 (produced by FUJIFILM Corp.)/tap water = 2/98 (volume ratio)) and VALUES-G (N) Black Ink (produced by Dainippon Ink & Chemicals, Inc.), the dampening water and ink were supplied according to the standard automatic printing start method of LITHRONE 26 to conduct printing on 100 sheets of TOKUBISHI ART paper (76.5 kg) at a printing speed of 10,000 sheets per hour.

A number of the printing papers required until the on-press development of the unexposed area of the image-recording layer on the printing machine was completed to reach a state where the ink was not transferred to the printing paper in the non-image area was measured to evaluate the on-press development property. The results obtained are shown in Table 1.

[0170]
(2) Printing durability caused by image abrasion
After performing the evaluation for the on-press development property described above, the printing was continued. As the increase in a number of printing papers, the image-recording layer was gradually abraded to cause decrease in the ink density on a printed material. A number of printed materials wherein a value obtained by measuring a halftone dot area rate of the 50% halftone dot of FM screen on the printed material using a Gretag densitometer decreased by 5% from the value measured on the 100th printed material of the printing was determined to evaluate the printing durability. The results obtained are shown in Table 1.

[0171]
(3) Printing durability caused by ink receptivity of image area (index of ink receptivity)
After performing the evaluation for the on-press development property described above, the printing was continued. As the increase in a number of printing papers, the ink receptivity in the image area was gradually deteriorated to cause decrease in the ink density on a printed material. A number of printed materials wherein a value

obtained by measuring a halftone dot area rate of the 50% halftone dot of FM screen on the printed material using a Gretag densitometer ^ decreased by 5% from the value measured on the 100th printed material of the printing was determined to evaluate the printing durability. The results obtained are shown in Table 1. Incidentally, the discrimination of the decrease in the ink density caused by either the abrasion or the deterioration of the ink receptivity of the image-recording layer area was conducted by SEM observation of the printing plate after the decrease in the ink density.

[0172]
Examples 13 to 22 and Comparative Examples 5 to 7

[0173]
[Preparation of Lithographic printing plate precursors (21) to (29) and (45) to (47)] (1) Formation of Image-recording layer

Coating solution (4) for image-recording layer shown below was coated on the support having the undercoat layer described above by a bar and dried in an oven at 70°C for 60 seconds to form an image-recording layer having a dry coating amount of 0.6 g/m2 to form an image-recording layer.

[0174]
Specific polymer compound shown in Table 2 4.0 g
Infrared absorbing dye (2) having structure 0.2 g shown below
Photoinitiator (IRGACURE 250, produced by Ciba 0.5 g Specialty Chemicals, Inc.)
Radical polymerizable compound (SR-399, 1.50 g
produced by Sartomer Co.)
Mercapto-3-triazole 0.2 g
BYK 336 (produced by Byk-Chemie GmbH) 0.4 g
KLUCEL M (produced by Hercules Chemical Co., 4.8 g Inc.)
ELVACITE 4026 (produced by Ineos Acrylica, 2.5 g Inc.)
n-Propanol 55.0 g
2-Butanone 17.0 g

[0175]
The compounds indicated using their trade names in the composition above are shown below.

IRGACURE 250: (4-Methoxyphenyl)[4-(2-methylpropyl)phenyl]iodonium hexafluorophosphate (75% by weight propylene carbonate solution) SR-399: Dipentaerythritol pentaacrylate BYK 336: Modified dimethylpolysiloxane copolymer (25% by weight xylene/methoxypropyl acetate solution) KLUCEL M: Hydroxypropyl cellulose (2% by weight aqueous solution) ELVACITE 4026: Highly branched polymethyl methacrylate (10% by weight 2-butanone solution)

[0176]
Infrared absorbing dye (2)

[0177] (2) Formation of Protective layer
Coating solution (1) for protective layer described above was coated on the image-recording layer described above by a bar and dried in an oven at 120°C for 60 seconds to form a protective layer having a dry coating amount of 0.15 g/m2, thereby preparing Lithographic printing plate precursors (21) to (29) for Examples 13 to 21 and Lithographic printing plate precursors (45) to (46) for Comparative Examples 5 and 6, respectively.

Lithographic printing plate precursor (47) for Comparative Example 7 was prepared in the same manner as the preparation of Lithographic printing plate precursor (13) expect for using Coating solution (2) for protective layer in place of Coating solution (1) for protective layer.

[0178] [Preparation of Lithographic printing plate precursor (30)]
Lithographic printing plate precursor (30) for Example 22 was prepared in the same manner as the preparation of Lithographic printing plate precursor (21) expect for using Coating solution (5) for image-recording layer in which Aqueous dispersion of fine polymer particle (1) shown below was used in place of the specific polymer compound in Coating solution (4) for image-recording layer. The amount of the aqueous dispersion of fine polymer particle added was 19.0 g in Coating solution (5) for image-recording layer.

[0179]
(Preparation of Aqueous dispersion of fine polymer particle (1))
A stirrer, a thermometer, a dropping funnel, a nitrogen inlet tube and a reflux condenser were attached to a 1,000 ml four-neck flask and while carrying out deoxygenation by introduction of nitrogen gas, 20 g of polyethylene glycol methyl ether methacrylate (PEGMA, average repeating unit number of ethylene glycol: 50), 200 g of distilled water and 200 g of n-propanol were charged therein and heated until the internal temperature reached 70°C. Then, a mixture of 10 g of styrene (St), 80 g of acrylonitrile (AN) and 0.8 g of 2, 2' -azobisisobutyronitrile previously prepared was dropwise added to the flask over a period of one hour. After the completion of the dropwise addition, the reaction was continued as it was for 5 hours. Then, 0.4 g of 2,2' -azobisisobutyronitrile was added and the internal temperature was raised to 80°C. Thereafter, 0.5 g of 2, 2' -azobisisobutyronitrile was added over a period of 6 hours. At the stage after reacting for 20 hours in total, the polymerization proceeded 98% or more to obtain Aqueous dispersion of fine polymer particle (1) of PEGMA/St/AN (18/9/73 in a weight ratio) . The particle size distribution of the fine particle polymer had the maximum value at the particle size of 150 nm.

[0180]
The particle size distribution was determined by taking an electron microphotograph of the fine polymer particle, measuring particle sizes of 5,000 fine particles in total on the photograph, and dividing a range from the largest value of the particle size measured to 0 on a logarithmic scale into 50 parts to obtain occurrence frequency of each particle size by plotting. With respect to the aspherical particle, a particle size of a spherical particle having a particle area equivalent to the particle area of the aspherical particle on the photograph was defined as the particle size.

[0181] [Evaluation of Lithographic printing plate precursor]
Lithographic printing plate precursors (21) to (30) and (45) to (47) were evaluated in the same manner as in examples 1 to 12 and Comparative Examples 1 to 3. The results obtained are shown in Table 2.

[0182]
Examples 23 and 24

[0183] [Preparation of Lithographic printing plate precursor (31)]
Lithographic printing plate precursor (31) for Example 23 was prepared in the same manner as the preparation of Lithographic printing plate precursor (21) expect for using Coating solution (6) for image-recording layer which was prepared by further adding 0.3 g of Compound (cl) shown below to Coating solution (5) for image-recording layer.

[0184]
[Preparation of Lithographic printing plate precursor (32)]
Lithographic printing plate precursor (32) for Example 24 was prepared in the same manner as the preparation of Lithographic printing plate precursor (21) expect for using Coating solution (7) for image-recording layer which was prepared by further adding 0.3 g of Compound (dl) shown below to Coating solution (5) for image-recording layer.

[0185] [Evaluation of Lithographic printing plate precursor]

Lithographic printing plate precursors (31) and (32) were evaluated in the same manner as in examples 1 to 12 and Comparative Examples 1 to 3. The results obtained are shown in Table 3.

[0186]

[0187]

[0188]

[0189]

[0190]
In Tables 1 and 2, Comparative Examples 4 and 7 using the protective layer which does not contain the inorganic stratiform compound exhibit low printing durability resulting from low sensitivity due to the insufficient oxygen blocking property. On ^ the other hand, although Comparative Examples 1, 2 and 5 using the protective layer which contains the inorganic stratiform compound maintain high sensitivity and exhibit good printing durability caused by abrasion, they exhibit low ink receptive property because of using the polymer compound in which the number of repeating units of alkylene oxide is smaller than the range according to the invention. On the contrary, in Comparative Examples 3 and 6 using the polymer compound in which the number of repeating units of alkylene oxide is larger than the range according to the invention, the printing durability caused by abrasion is decreased. Contrary to the above results, the examples according to the invention can achieve good balance between the on-press development property, printing durability caused by abrasion and ink receptivity while maintaining high sensitivity.

[0191]

[0192]

[0193]

[0194]
From Table 3, it can be seen that by adding the onium salt as (cl) or (dl), the ink receptivity on the plate surface is further improved to increase the printing durability in comparison with Lithographic printing plate precursor (30) which do not contain the onium salt.

INDUSTRIAL APPLICABILITY

[0195]
The lithographic printing plate precursor according to the invention is capable of conducting image-recording with laser and on-press development, exhibits sufficient ink receptivity while maintaining high sensitivity, and can be favorably used in various printing fields.

[0196]
Although the invention has been described in detail and by reference to specific embodiments, it is apparent to those skilled in the art that it is possible to add various alterations and modifications insofar as the alterations and modifications do not deviate from the spirit and the scope of the invention.

This application is based on a Japanese patent application filed on March 30, 2009 (Japanese Patent Application No. 2009-83710) and a Japanese patent application filed on September 1, 2009 (Japanese Patent Application No. 2009-202013), and the contents thereof are incorporated herein by reference.

CLAIMS

[Claim 1]
A lithographic printing plate precursor comprising a support, an image-recording layer and a protective layer in this order, wherein the protective layer contains an inorganic stratiform compound and the image-recording layer contains a polymer compound containing a poly (alkylene oxide) moiety in which a number of repeating units of alkylene oxide is from 10 to 120.

[Claim 2]
The lithographic printing plate precursor as claimed in Claim 1, wherein the polymer compound does not substantially contain a perfluoroalkyl group.

[Claim 3]
The lithographic printing plate precursor as claimed in Claim 1 or 2, wherein the image-recording layer contains an infrared absorbing agent, a radial polymerization initiator and a radical polymerizable compound.

[Claim 4]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 3, wherein the number of repeating units of alkylene oxide is from 20 to 50.

[Claim 5]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 4, wherein the polymer compound contains a structure represented by formula (1) shown below in its side chain: Formula (1)

wherein, in the formula (1), y represents from 10 to 120, Rx represents a hydrogen atom or an alkyl group, and R2 represents a hydrogen atom or an organic group.

[Claim 6]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 5, wherein the inorganic stratiform compound is mica.

[Claim 7]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 6, wherein the image-recording layer contains at least any one selected from an ammonium salt and a phosphonium salt.

[Claim 8]
The lithographic printing plate precursor as claimed in Claim 7, wherein a counter anion of the ammonium salt or phosphonium salt is an organic borate anion.

[Claim 9]
The lithographic printing plate precursor as claimed in Claim 7 or 8, wherein the ammonium salt is represented by formula (2) shown below:

Formula (2)

wherein in the formula (2), R3 to R6 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group, and X" represents a counter anion.

[Claim 10]
The lithographic printing plate precursor as claimed in Claim 9, wherein in formula (2), at least one of R3 to R6 is an aryl group or an aralkyl group.

[Claim 11]
The lithographic printing plate precursor as claimed in Claim 7 or 8, wherein the ammonium salt is a polymer containing a repeating unit represented by formula (3) shown below: Formula (3)

wherein in the formula (3), R11 represents a hydrogen atom or a methyl group, L1 represents a connecting group, R12 to R14 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or an aralkyl group, and X' represents a counter anion.

[Claim 12]
The lithographic printing plate precursor as claimed in Claim 11, wherein in formula (3), Li represents a connecting group containing at least one group selected from a phenylene group, a carbonyloxy group and a carbonylimino group.

[Claim 13]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 12, wherein the image-recording layer is an image-recording layer which is capable of forming an image after image exposure by supplying at least any of printing ink and dampening water on a printing machine to remove an unexposed area.

[Claim 14]
The lithographic printing plate precursor as claimed in any one of Claims 1 to 13, wherein a content of the polymer compound containing a poly(alkylene oxide) moiety in which a number of repeating units of alkylene oxide is from 10 to 120 is from 10 to 90% by weight based on a total solid content of the image-recording layer.