EP2251195A1

EP2251195A1 - Lithographic printing plate precursor

Info

Publication number: EP2251195A1
Application number: EP10161836A
Authority: EP
Inventors: Toyohisa Oya
Original assignee: Fujifilm Corp
Current assignee: Fujifilm Corp
Priority date: 2009-05-15
Filing date: 2010-05-04
Publication date: 2010-11-17
Anticipated expiration: 2030-05-04
Also published as: JP5444831B2; EP2251195B1; JP2010264698A; ATE533625T1

Abstract

The present invention provides a lithographic printing plate precursor that exhibits an excellent antiscumming performance while exhibiting an excellent printing durability and that can also achieve an excellent on-press developability. The lithographic printing plate precursor is a lithographic printing plate precursor that has an image recording layer on an aluminum support, wherein the image recording layer contains from 0.01 to 10 mass% of a compound represented by the following general formula (I)

(in the formula, R¹ represents a C_2-10 organic Substituent and R² to R⁷ each independently represent a hydrogen atom or a C_1-10 organic Substituent).

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a lithographic printing plate precursor and in particular relates to a lithographic printing plate precursor that contains a specific cyclic amide compound in its image recording layer. More particularly, the present invention relates to a lithographic printing plate precursor that has both a high printing durability and a strong antiscumming performance.

Description of the Related Art

A lithographic printing plate typically comprises an oleophilic image area that is ink receptive during the printing process and a hydrophilic nonimage area that is fountain solution receptive during the printing process. Lithographic printing is a method that utilizes the fact that water and oleophilic ink repel each other: differences in the ink attachment behavior are produced on the surface of the lithographic printing plate by using the oleophilic image areas on the lithographic printing plate as ink receptive areas and using the hydrophilic nonimage areas on the lithographic printing plate as fountain solution receptive areas (areas not receptive to ink). After ink uptake has been brought about only in the image areas, the ink is transferred to the receiving medium, e.g., paper.
A lithographic printing plate precursor (PS plate) comprising an oleophilic photosensitive resin layer (image recording layer) disposed on a hydrophilic support has heretofore been widely used to produce the aforementioned lithographic printing plate. Platemaking is typically carried out by a method in which the lithographic printing plate precursor is exposed to light through an original image, for example, a lith film, after which the image recording layer corresponding to the image areas remains while the unwanted image recording layer corresponding to the nonimage areas is dissolved and removed by an alkaline developing solution or an organic solvent-containing developing solution, thus forming nonimage areas by exposing the surface of the hydrophilic support and providing the lithographic printing plate.
On the other hand, digitization technology, in which the image data is electronically processed, stored, and output by a computer, has become widespread in recent years, and a variety of new image output methods made possible by this digitization technology have entered into use. Accompanying this, computer-to-plate (CTP) technology has been receiving attention; in computer-to-plate technology, the digitized image data is carried by highly convergent radiation, such as laser light, and the lithographic printing plate is directly produced by scanning photoexposure of the lithographic printing plate precursor with this radiation without going through a lith film. As a consequence, the acquisition of lithographic printing plate precursors adapted to this technology has become an important technical issue.
In addition, the conventional platemaking process for lithographic printing plate precursors has required a step in which, after photoexposure, the unwanted image recording layer is dissolved and removed by, for example, a developing solution; however, a concern with these separately conducted wet processes has also been to render them unnecessary or to simplify them. In particular, attention to the environment has in recent years caused the disposal of the waste solutions discharged in association with wet processes to become a major issue for the industrial sector as a whole, and as a consequence there has been an even stronger desire to address the aforementioned concern.
In this context, the method known as on-press development has been introduced as a simple and convenient platemaking method. In on-press development, an image recording layer is used that enables the removal of unwanted areas of the image recording layer to be carried out during the normal printing process: after photoexposure, the lithographic printing plate is obtained by removal of the unwanted areas of the image recording layer on the press.
The following are examples of specific methods of on-press development: use of a lithographic printing plate precursor that has an image recording layer that can be dissolved or dispersed in the fountain solution, in the ink solvent, or in an emulsion of the fountain solution and ink; mechanical removal of the image recording layer by contact with the blanket or rollers on the press; and mechanical removal of the image recording layer by carrying out contact with rollers or the blanket after the cohesive strength within the image recording layer or the adhesive force between the image recording layer and support has been weakened by penetration by, for example, the fountain solution or the ink solvent.
Unless stated otherwise, in the present invention, the "development processing step" refers to a step in which the hydrophilic surface of the support is exposed by the removal of those areas of the image recording layer on the lithographic printing plate precursor that have not undergone photoexposure, wherein this removal is effected by contact with a fluid (typically an alkaline developing solution, a surfactant-containing developing solution, or an aqueous solution that contains a hydrophilic polymer) using an apparatus (typically an automatic developing apparatus) outside of the press, while "on-press development" denotes a step and a method in which the hydrophilic surface of the support is exposed by the removal of those areas of the image recording layer on the lithographic printing plate precursor that have not undergone photoexposure, wherein this removal is effected by contact with a fluid (typically the printing ink and/or fountain solution) using the press.
After photoexposure the image recording layer is photosensitive because it has not been fixed by the developing process, which creates the potential for fogging in the interval up to printing. Thus, in order to simplify the previously described platemaking technology or convert it to a dry technology or a processless technology, the use is preferred of a light source and an image recording layer that make handling in a bright room or under yellow illumination possible.
Solid-state lasers that emit infrared radiation at wavelengths from 760 to 1200 nm, e.g., semiconductor lasers and YAG lasers, are such a laser light source and are very useful because small, high output solid-state lasers can be acquired inexpensively. UV lasers can also be used.
Various additives intended to provide these lithographic printing plate precursors with an antiscumming character have been introduced (refer, for example, to Japanese Patent Application Publication No. 2005-41206 ). However, it is difficult to balance printing durability with scumming prevention. In particular, as described in Japanese Patent Application Publication No. 2008-247000 , achieving a balance between printing durability and antiscumming performance is problematic when printing durability with respect to UV ink is brought about by the use of a specific binder.

DISCLOSURE OF THE INVENTION

Problem to be solved by the Invention

An object of the present invention is to provide a lithographic printing plate precursor that exhibits an excellent antiscumming performance while exhibiting an excellent printing durability and that can also achieve an excellent on-press developability.

Means to Solve the Problem

As a result of investigations into various image recording layer compositions, the present inventor discovered the unexpected result that a lithographic printing plate precursor having an image recording layer that contained a specific cyclic amide compound could realize both a satisfactory printing durability and an excellent antiscumming performance, even when subjected to long-term storage under severe conditions, and could also realize an excellent on-press developability. The present invention was achieved based on this discovery. It was particularly discovered that this result accrued when a specific polymer was used in the image recording layer in order to provide a high printing durability with respect to UV ink.
Accordingly, the present invention is a lithographic printing plate precursor having an image recording layer on an aluminum support, wherein the image recording layer contains from 0.01 to 10 mass% of a compound represented by the following general formula (I)
(In the formula, R¹ represents a C_2-10 organic substituent and R² to R⁷ each independently represent a hydrogen atom or a C_1-10 organic substituent).
The lithographic printing plate precursor of the present invention can be a negative-working lithographic printing plate precursor, and the image recording layer can additionally contain a polymerization initiator and a polymerizable compound. In addition, a photothermal conversion substance can be incorporated.
In another embodiment, the lithographic printing plate precursor of the present invention can be a positive-working lithographic printing plate precursor in which the imagewise photoexposed region of the image recording layer becomes a nonimage area after development and the image recording layer contains a polymer compound that is insoluble in water and soluble in an aqueous alkaline solution. The polymer compound that is insoluble in water and soluble in aqueous alkalline solution is preferably a novolac resin. In addition, the image recording layer can additionally contain a photothermal conversion substance.
In an embodiment of the image recording layer in the present invention, the image recording layer contains a polymer compound that has at least one structure selected from sulfonamide groups, maleimide groups, and urea structures.
The lithographic printing plate precursor of the present invention can have an intermediate layer, and the present invention is therefore also directed to a lithographic printing plate precursor that has an intermediate layer and the aforementioned image recording layer on an aluminum support in this order.

Effect of the Invention

The lithographic printing plate precursor of the present invention can provide a lithographic printing plate that combines an excellent printing durability with an excellent antiscumming performance. In addition, the lithographic printing plate precursor of the present invention can provide a lithographic printing plate that, even when subjected to long-term storage under severe conditions, achieves after platemaking an excellent antiscumming performance while maintaining an excellent printing durability. Moreover, the lithographic printing plate precursor of the present invention can realize an excellent on-press developability wherein the on-press developability does not deteriorate even when the lithographic printing plate precursor has been subjected to long-term storage. The lithographic printing plate precursor exhibits a very high timewise stability.

Mode for Carrying Out the Invention

The lithographic printing plate precursor of the present invention can be used for either a radical polymerization-based negative-working lithographic printing plate precursor or for a positive-working lithographic printing plate precursor in which after development the photoexposed regions are nonimage areas. The lithographic printing plate precursor of the present invention can also be used as either a lithographic printing plate precursor that is passed through a development processing step or as an on-press developing lithographic printing plate precursor with which printing is performed via direct development on the press.
The lithographic printing plate precursor of the present invention is preferably used for a radical polymerization-based negative-working lithographic printing plate precursor and particularly preferably is used for a radical polymerization-based negative-working on-press developing lithographic printing plate.

< The compound with general formula (I) >

The image recording layer of the lithographic printing plate precursor of the present invention contains from 0.01 to 10 mass% of a compound with the following general formula (I). A preferred content is 0.05 to 7 mass%, a more preferred content is 0.08 to 5 mass%, and a particularly preferred content is 0.10 to 3 mass%.
(In the formula, R¹ represents a C_2-10 organic substituent and R² to R⁷ each independently represent a hydrogen atom or a C_1-10 organic substituent).
R¹ in general formula (I) represents a C_2-10 substituent and any C_2-10 substituent can be selected as long as it can be substituted on the nitrogen atom, but R¹ is preferably C_2-10 alkyl, C_2-10 alkenyl, C_2-10 alkynyl, or C_6-10 aryl.
The alkyl represented by R¹ is C_2-10, preferably C_2-8, and more preferably C_2-4 straight chain, branched, or cyclic alkyl. The alkyl represented by R¹ may be unsubstituted or may bear a substituent group.
Specific examples of the unsubstituted alkyl encompassed by R¹ are ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, isopropyl, isobutyl, s-butyl, t-butyl, isopentyl, neopentyl, 1-methylbutyl, isohexyl, 2-ethylhexyl, 2-methylhexyl, cyclohexyl, cyclopentyl, and so forth.
When R¹ carries a substituent group (that is, when R¹ is substituted alkyl), the alkyl moiety of the substituted alkyl can be exemplified by the divalent organic residues provided by removing any one of the hydrogen atoms on the C_2-10 alkyl groups described above, and the preferred ranges for the number of carbons are also the same as for the alkyl described above.
The substituent groups that can be introduced into the alkyl group encompassed by R¹ can also be exemplified by the hereafter cited monovalent substituents comprising nonmetal atoms. Preferred examples are halogen atoms (-F, -Br, -Cl, -I), the hydroxyl group, alkoxy, aryloxy, the mercapto group, alkylthio, arylthio, the amino group, N-alkylamino, N,N-dialkylamino, N-arylamino, N.N-diarylamino, acyloxy, carbamoyloxy, N-alkylcarbamoyloxy, N-arylcarbamoyloxy, N,N-dialkylearbamoyloxy, N,N-diarylcarbamoyloxy, alkylsulfoxy, arylsulfoxy, acylthio, acylamino, N-alkylacylamino, N-arylacylamino, the ureido group, N-alkylureido, N,N-dialkylureido, N-arylureido, N,N-diarylureido, N'-alkyl-N-alkylureido, N'-alkyl-N-arylureido,
alkoxycarbonylamino, aryloxycarbonylamino, the formyl group, acyl, the carboxyl group, alkoxycarbonyl, aryloxycarbonyl, the carbamoyl group, N-alkylcarbamoyl, N,N-dialkylcarbamoyl, N-arylcarbamoyl, N,N-diarylcarbamoyl, alkylsufinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl, the sulfo group (-SO₃H) and its conjugate base (referred to as the sulfonato group), alkoxysulfonyl, aryloxysulfonyl, sulfinamoyl, N-alkylsulfinamoyl, N,N-dialkylsulfinamoyl, N-arylsulfinamoyl, N,N-diarylsulfinamoyl, sulfamoyl, N-alkylsulfamoyl, N,N-dialkylsulfamoyl, N-arylsulfamoyl,
the cyano group, the nitro group, aryl groups (for example, phenyl, naphthyl, tolyl, mesityl, cumenyl, chlorophenyl, hydroxyphenyl, methoxyphenyl, acetoxyphenyl, benzoyloxyphenyl, methylaminophenyl, dimethylaminophenyl, acetylaminophenyl, carboxyphenyl, methoxycarbonylphenyl, phenoxycarbonylphenyl, cyanophenyl, sulfophenyl, sulfonatophenyl, phosphonophenyl, phosphonatophenyl, and so forth), alkenyl, alkynyl, heterocyclic groups, silyl, hydroxyalkoxy, alkoxyalkoxy, and so forth.
Preferred specific examples of this substituted alkyl are methoxymethyl, methoxycarbonylmethyl, isopropoxymethyl, butoxymethyl, s-butoxybutyl, methoxyethoxyethyl, allyloxymethyl, phenoxymethyl, acetyloxymethyl, methylthiomethyl, tolylthiomethyl, pyridylmethyl, trimethylsilylmethyl, methoxyethyl, ethylaminoethyl, diethylaminopropyl, morpholinopropyl, acetyloxymethyl, benzoyloxymethyl, N-cyclohexylcarbamoyloxyethyl, N-phenylcarbamoyloxyethyl, acetylaminoethyl, N-methylbenzoylaminopropyl., 2-oxoethyl, 2-oxopropyl, carboxypropyl, methoxycarbonylethyl, allyloxycarbonylbutyl, chlorophenoxycarbonylmethyl,
carbamoylmethyl, N-methylcarbamoylethyl, N,N-dipropylcarbamoylmethyl, N- (methoxyphenyl)carbamoylethyl, sulfobutyl, sulfonatobutyl, sulfamoylbutyl, N-ethylsulfamoylmethyl, N,N-dipropylsulfamoylpropyl, N-tolylsulfamoylpropyl, phosphonobutyl, diethylphosphonobutyl, methylphosphonobutyl, methylphosphonatobutyl, phosphonooxypropyl, phosphonatooxybutyl, benzyl, phenethyl, α-methylbenzyl, p-methylbenzyl, and so forth.
The alkenyl encompassed by R¹ can be a C_2-10, preferably C_2-8, and particularly preferably C_2-4 straight chain, branched, or cyclic alkenyl group. The alkenyl encompassed by R¹ may be unsubstituted or may also bear a substituent group.
Specific examples of the unsubstituted alkenyl encompassed by R¹ are vinyl, 1-propenyl, 1-butenyl, cinnamyl, 1-pentenyl, 1-hexenyl, 1-octenyl, 1-methyl-1-propenyl, 2-methyl-1-propenyl, 2-methyl-1-butenyl, allyl, 2-butenyl, 2-methylallyl, 2-methyl-3-butenyl, 3-methyl-2-butenyl, and so forth.
When the alkenyl encompassed by R¹ carries a substituent group (that is, when R¹ is substituted alkenyl), the alkenyl moiety of the substituted alkenyl can be exemplified by the divalent organic residues provided by removing any one of the hydrogen atoms on the C_2-10 alkenyl groups described above, and the preferred ranges for the number of carbons are also the same as for the alkenyl described above.
The substituent groups that can be introduced into the alkenyl group encompassed by R¹ can be exemplified by the substituents described above for the substituted alkyl group.
The alkynyl encompassed by R¹ can be a C_2-10, preferably C_2-8, and particularly preferably C_2-4 straight chain, branched, or cyclic alkynyl group. The alkynyl encompassed by R¹ may be unsubstituted or may also bear a substituent group.
Specific examples of the unsubstituted alkynyl encompassed by R¹ are 2-propynyl, 2-butynyl, 3-butynyl, and so forth.
When the alkynyl encompassed by R¹ carries a substituent group (that is, when R¹ is substituted alkynyl), the alkynyl moiety of the substituted alkynyl can be exemplified by the divalent organic residues provided by removing any one of the hydrogen atoms on the C_2-10 alkynyl groups described above, and the preferred ranges for the number of carbons are also the same as for the alkynyl described above.
The substituent groups that can be introduced into the alkynyl group encompassed by R¹ can be exemplified by the substituents described above for the substituted alkyl group.
The aryl encompassed by R¹ can be a C_6-10, preferably C_6-9, and particularly preferably C_6-8 substituted or unsubstituted aryl group. Examples of this aryl are phenyl, methylphenyl, methoxyphenyl, dimethylphenyl, chlorophenyl, and so forth.
When the aryl encompassed by R¹ carries a substituent group (that is, when R¹ is substituted aryl), the aryl moiety of the substituted aryl can be exemplified by the divalent organic residues provided by removing any one of the hydrogen atoms on the C_6-10 aryl groups described above, and the preferred ranges for the number of carbons are also the same as for the aryl described above.
The substituent groups that can be introduced into the aryl group encompassed by R¹ can be exemplified by the substituents described above for the substituted alkyl group. In addition, a condensed ring may be formed by additionally condensing the benzene ring with another benzene ring or with a heterocycle. Specific examples are naphthyl, indolinyl, indazolyl, benzoimidazolyl, quinolinyl, benzothiophenyl, benzofuranyl, benzothiazolyl, benzooxazolyl and so forth.
R¹ is preferably an alkyl group and more specifically is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, and so forth, wherein ethyl, propyl, and butyl are particularly preferred.
R² to R⁷ each independently represent a hydrogen atom or a C_1-10 organic substituent. When a substituent is represented by R² to R⁷, any substituent may be selected as long as it is a group that can be substituted on the carbon atom.
The organic substituents encompassed by R² to R⁷ can be exemplified by C_1-10 alkyl, C_2-10 alkenyl, C_2-10 alkynyl, C_6-10 aryl, C_1-10 heterocyclic groups, alkoxy, aryloxy, alkylthio, arylthio, N-alkylamino, N,N-dialkylamino, N-arylamino, N,N-diarylamino, acyloxy, carbamoyloxy, N-alkylcarbamoyloxy, N-arylearbamoyloxy, N,N-dialkylcarbamoyloxy, N,N-diarylcarbamoyloxy, alkylsulfoxy, arylsulfoxy, acylthio, acylamino, N-alkylacylamino, N-arylacylamino, the ureido group, N-alkylureido, N,N-dialkylureido, N-arylureido, N,N-diarylureido, N'-alkyl-N-alkylureido, N'-alkyl-N-arylureido,
alkoxycarbonylamino, aryloxycarbonylamino, N-alkyl-N-alkoxycarbonylamino, the formyl group, acyl, the carboxyl group, alkoxycarbonyl, aryloxycarbonyl, the carbamoyl group, N-alkylcarbamoyl, N,N-dialkylcarbamoyl, N-arylcarbamoyl, N,N-diarylcarbamoyl, alkylsufinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl, alkoxysulfonyl, aryloxysulfonyl, sulfinamoyl, N-alkylsulfinamoyl, N,N-dialkylsulfinamoyl, N-arylsulfinamoyl, N,N-diarylsulfinamoyl, sulfamoyl, N-alkylsulfamoyl, N.N-dialkylsulfamoyl, N-arylsulfamoyl, N,N-diarylsulfamoyl, N-alkyl-N-arylsulfamoyl, and so forth.
R² to R⁷ may be bonded to each other to form a ring.
The hydrogen atom and C_1-8 alkyl are preferred for R² to R⁷; the hydrogen atom and C_1-6 alkyl are more preferred; and the hydrogen atom and C_1-4 alkyl (for example, methyl, ethyl, propyl, and butyl) are particularly preferred.
In particularly preferred combinations of R¹ and R² to R⁷ in general formula (I), R¹ is ethyl, propyl, or butyl, and all of R² to R⁷ are the hydrogen atom.
In the most preferred combination, R¹ is ethyl and all of R² to R⁷ are the hydrogen atom. Preferred examples of the compound with general formula (I) are shown below, but the present invention is not limited to these.

(n) denotes a straight-chain group that is free of branching.
With regard to the content of this compound with general formula (I) in the image recording layer, the content in a defined area is determined by extracting the defined area of the produced lithographic printing plate precursor with a suitable solvent, e.g., methanol, and carrying out measurement by gas chromatography using this extract as the sample. The content (%) is then determined by dividing this by the weight of the image recording layer in the defined area. The content of the compound with general formula (I) in the image recording layer can be adjusted by adjusting the quantity of this compound in the bath for applying the image recording layer and by adjusting the drying time for this coating bath.
The other constituent components of the image recording layer of the present invention are described in detail below.

< The image recording layer in a radical polymerizable negative-working lithographic printing plate precursor >

The photopolymerizable photosensitive composition (referred to hereafter as a "photopolymerizable composition") used for the image recording layer of a radical polymerization-based negative-working lithographic printing plate precursor contains as its essential components a polymerization initiator and a polymerizable compound and specifically a compound that contains an addition polymerizable ethylenically unsaturated bond (this compound is referred to below simply as an "ethylenically unsaturated bond-containing compound"), and optionally contains various compounds such as a polymer compound functioning as a binder, a colorant, a plasticizer, a thermal polymerization inhibitor, and so forth.

The ethylenically unsaturated bond-containin compound

The ethylenically unsaturated bond-containing compound in the photopolymerizable composition is a compound that has an ethylenically unsaturated bond whereby, when the photopolymerizable composition is exposed to actinic radiation, addition polymerization, crosslinking, and curing occur under the action of the photopolymerization initiator. The ethylenically unsaturated bond-containing compound can be freely selected from compounds that have at least one and preferably at least two terminal ethylenically unsaturated bonds, and in terms of chemical configuration is, for example, a monomer, a prepolymer (i.e., dimer, trimer, or oligomer), a mixture of the preceding, a copolymer of the preceding, and so forth. The monomer can be exemplified by ester-type radical polymerizable compounds from an unsaturated carboxylic acid (for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid) and an aliphatic polyhydric alcohol compound and by amide-type radical polymerizable compounds from an unsaturated carboxylic acid and an aliphatic polyvalent amine compound. Urethane-type radical polymerizable compounds are also suitable.

The polymerization initiator

The polymerization initiator incorporated in the photopolymerizable composition can be selected as appropriate, based on the wavelength of the light source used, from various polymerization initiators and from systems of two or more polymerization initiators (photoinitiator systems); for example, the initiator systems shown in [0021] to [0023] of Japanese Patent Application Publication No. 2001-22079 are preferred. The use of onium salts is also preferred, and preferred specific examples are described in paragraph numbers [0030] to [0033] of Japanese Patent Application Publication No. 2001-133969 .

Other components

With regard to the polymer compound incorporated in the photopolymerizable composition, a polymer compound is used that not only functions as a film-forming agent for the photopolymerizable composition, but that is also soluble or swellable in aqueous base due to the requirement that the photosensitive layer dissolve in alkaline developing solution. The substances given in [0036] to [0063] of Japanese Patent Application Publication No. 2001-133969 are useful as such a polymer compound. A polymer compound having an ethylenically unsaturated bond in side chain position is particularly preferred.
In addition to the preceding, the addition of the additives (for example, a surfactant in order to improve the coatability) given in [0079] to [0088] of Japanese Patent Application Publication No. 2001-133969 to the photopolymerizable composition is also preferred.

Other layers

In order to prevent the polymerization inhibiting action of oxygen, an oxygen-blocking protective layer is preferably also disposed on the photosensitive layer. Polyvinyl alcohol and its copolymers are examples of the polymer that can be present in this oxygen-blocking protective layer. An adhesive layer or intermediate layer, as shown in [0124] to [0165] of Japanese Patent Application Publication No. 2001-228608 , is preferably also disposed as an underlayer for a photopolymer-type photosensitive layer.

< The infrared laser-responsive radical polymerizable image recording layer >

The infrared laser-responsive polymerizable negative-working image recording layer comprises (A) a photothermal conversion substance, (B) a polymerization initiator, (C) an ethylenically unsaturated bond-containing compound, and, as necessary, (D) a polymer compound functioning as a binder.
An infrared absorber that is a photothermal conversion substance converts absorbed infrared radiation to heat, and the heat thereby produced causes the decomposition of the polymerization initiator, for example, an onium salt, with the production of radicals. The ethylenically unsaturated bond-containing compound is selected from compounds that have a terminal ethylenically unsaturated bond, and as a result the produced radicals induce a chain polymerization reaction to cause curing.
The (A) infrared absorber that is a photothermal conversion substance can be exemplified by the below-described photothermal conversion substances for incorporation in the aforementioned thermal positive-type heat-sensitive layer, while the cyanine dyes described in paragraph numbers [0017] to [0019] of Japanese Patent Application Publication No. 2001-133969 can in particular be given as specific examples of cyanine dyes.
The substances particularly described in [0036] to [0060] of Japanese Patent Application Publication No. 2001-133969 can be used for the (B) polymerization initiator, (C) ethylenically unsaturated bond-containing compound, and optional (D) polymer compound functioning as a binder. With regard to other additives, the addition of the additives (for example, a surfactant in order to improve the coatability) shown in [0061] to [0068] of Japanese Patent Application Publication No. 2001-133969 is also preferred.

< The radical polymerizable image recording layer adapted for on-press development >

The above-described infrared laser-responsive radical polymerizable image recording layer encompasses image recording layers configured to undergo development on the press by the fountain solution or ink. A specific (C) polymerizable compound and (D) polymer compound functioning as a binder and as necessary a hydrophobization precursor must be used in a polymerizable image recording layer with this configuration.

The polymerizable compound

From the standpoint of striking an excellent balance between the hydrophilicity, which is involved with the on-press developability, and the polymerizability, which is involved with the printing durability, an ethylene oxide-modified acrylate isocyanurate is particularly preferred, e.g., tris(acryloyloxyethyl) isocyanurate, bis(acryloyloxyethyl)hydroxyethyl isocyanurate, and so forth.
The radical polymerizable compound is used at preferably 5 to 80 mass% and more preferably 25 to 75 mass%, in each case with respect to the total solids fraction of the image recording layer.

The polymer compound functioning as a binder

The polymer compound functioning as a binder preferably has a hydrophilic group. This hydrophilic group contributes to providing the image recording layer with on-press developability. In particular, the combination of printing durability with developability is made possible by the presence of both a crosslinking group and a hydrophilic group.
For example, an alkylene oxide structure having from 1 to 100 C₂ or C₃ alkylene oxide units is preferred for the hydrophilic group. An alkylene oxide structure having from 2 to 12 units is particularly preferred, and an alkylene oxide structure having from 2 to 8 units is most preferred. The copolymerization of a hydrophilic group-containing monomer may be used to introduce the hydrophilic group into the binder polymer.
Preferred polymer compounds among the preceding are, for example, polymer compounds, as described in Japanese Patent Application Publication No. 2008-195018 , that, in order to improve the film strength in the image areas, have a crosslinking functional group in main chain or side chain position and preferably in side chain position. Curing is promoted by the formation of crosslinks between polymer molecules due to the presence of the crosslinking groups.
Ethylenically unsaturated groups, e.g., the (meth)acrylic group, vinyl group, allyl group, and so forth, and the epoxy group are preferred for the crosslinking functional group, and these groups can be introduced into the polymer by copolymerization or by reaction with the polymer. For example, a reaction between glycidyl methacrylate and a polyurethane or acrylic polymer that has the carboxyl group in side chain position can be utilized, as can the reaction between an epoxy group-containing polymer and an ethylenically unsaturated group-containing carboxylic acid, e.g., methacrylic acid.
The content of the crosslinking group in the binder polymer is preferably 0.1 to 10.0 mmol, more preferably 1.0 to 7.0 mmol, and most preferably 2.0 to 5.5 mmol, in each case per 1 g of the binder polymer.
The binder polymer is particularly preferably a polymer that exhibits film formability, and acrylic resins, polyvinyl acetal resins, and polyurethane resins are preferred.
The binder polymer has a mass-average molar mass (Mw) preferably of at least 2,000, more preferably of at least 5,000, and more preferably of 10,000 to 300,000.
The binder polymer content is 5 to 90 mass%, preferably 5 to 80 mass%, and more preferably 10 to 70 mass%, in each case with reference to the total solids fraction of the image recording layer. An excellent strength for the image region and an excellent image formability are obtained in this range.
The (C) polymerizable compound and (D) binder polymer are preferably used in amounts that provide a mass ratio of 0.4/1 to 1.8/1. 0.7/1 to 1.5/1 is more preferred. With reference to the effects of the present invention, a substantial improvement in the on-press developability or gum developability is realized in this range while the printing durability is maintained intact.

The hydrophobization precursor

A hydrophobization precursor can be used in the image recording layer in order to improve the on-press developability. A hydrophobization precursor denotes a fine particle that upon the application of heat can convert the image recording layer to hydrophobicity. The fine particle is preferably at least one particle selected from hydrophobic thermoplastic polymer fine particles, thermally reactive polymer fine particles, microcapsules that enclose a hydrophobic compound, and microgels (crosslinked polymer fine particles). Preferred among the preceding are polymerizable group-containing polymer fine particles and microgels.
Preferred hydrophobic thermoplastic polymer fine particles can be exemplified by the hydrophobic thermoplastic fine particles described in Research Disclosure No. 33303 of January, 1992, and in the Specifications of Japanese Patent Application Publication Nos. H9-123387 , 9-131850 , 9-171249 , and 9-171250 , and European Patent No. 931,647 .
The polymer constituting such a polymer fine particle can be specifically exemplified by homopolymers, copolymers, and mixtures thereof, from monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinylcarbazole, and acrylates and methacrylates that have a polyalkylene structure. More preferred thereamong are polystyrene and polymethyl methacrylate.
The average particle size of the hydrophobic thermoplastic polymer fine particle is preferably 0.01 to 2.0 µm.
The thermally reactive polymer fine particle can be exemplified by the fine particles of thermally reactive group-functional polymers; these form a hydrophobicized region by crosslinking through a thermal reaction and alteration of the functional group at this time.
The thermally reactive group in a thermally reactive group-functional polymer may be a functional group that carries out any reaction that results in chemical bond formation, but preferred examples are ethylenically unsaturated groups that undergo a radical polymerization reaction (for example, the acryloyl group, methacryloyl group, vinyl group, allyl group, and so forth); cationic polymerizable groups (for example, the vinyl group, vinyloxy group, and so forth); within the realm of functional groups that undergo an addition reaction, the isocyanate group and its blocked derivatives, epoxy group, vinyloxy group, and functional groups bearing the active hydrogen that is the reaction partner for the preceding (these functional groups are exemplified by the amino group, hydroxyl group, carboxyl group, and so forth); within the realm of functional groups that undergo a condensation reaction, the carboxyl group and its amino group and hydroxyl group reaction partners; and within the realm of functional groups that undergo a ring-opening addition reaction, acid anhydrides and, for example, the amino group or hydroxy group reaction partner.
The microcapsules can be exemplified by microcapsules that enclose all or a portion of the constituent components of the image recording layer, as described in Japanese Patent Application Publication Nos. 2001-277740 and 2001-277742 . Constituent components of the image recording layer may also be present outside of the microcapsule. In a preferred embodiment of a microcapsule-containing image recording layer, hydrophobic constituent components are enclosed in the microcapsule and hydrophilic constituent components are present outside the microcapsule.
Another embodiment contains crosslinked resin particles, that is, a microgel. This microgel can contain a portion of the constituent components of the image recording layer in its interior and/or at its surface, and an embodiment in which a reactive microgel is prepared by having the (C) radical polymerizable compound at its surface is particularly preferred from the standpoint of the image formation sensitivity and printing durability.
Known methods can be used for microcapsulation or microgelation of the constituent components of the image recording layer.
The average particle size of the aforementioned microcapsule or microgel is preferably 0.01 to 3.0 µm, more preferably 0.05 to 2.0 µm, and particularly preferably 0.10 to 1.0 µm. An excellent resolution and an excellent timewise stability are obtained in this range.
The content of the hydrophobization precursor is preferably in the range from 5 to 90 mass% as the solids fraction concentration in the image recording layer.
Other components that may be added are, for example, sensitizers; a development accelerator other than that of the present invention, for use in combination therewith; surfactants; colorants; print-out agents; polymerization inhibitors; higher fatty acid derivatives; plasticizers; finely divided inorganic particles; and inorganic layer compounds. In specific terms, the compounds and quantities of addition described in paragraph numbers [0114] to [0159] of Japanese Patent Application Publication No. 2008-284817 are preferred.

< The positive-working image recording layer >

A positive-working image recording layer is an image recording layer in which the imagewise photoexposed regions are developed, and comprises an alkali-soluble polymer compound and a photothermal conversion substance.

The alkali-soluble polymer compound

The alkali-soluble polymer compound encompasses homopolymers that contain an acidic group in the polymer, copolymers thereof, and mixtures of the preceding, wherein the presence of the phenolic hydroxyl group (-Ar-OH) is particularly preferred and novolac resins are an example. Specific preferred examples are novolac resins such as phenol/formaldehyde resins, m-cresol/formaldehyde resins, p-cresol/formaldehyde resins, m-/p-mixed cresol/formaldehyde resins, phenol/cresol (m-, p-, or m-/p- mixtures) mixture/formaldehyde resins, and so forth, and pyrogallol/acetone resins. More particularly, the use is preferred of the polymers given in [0023] to [0042] of Japanese Patent Application Publication No. 2001-305722 .
The image recording layer in the present invention preferably contains at least 50 mass% novolac resin.

The photothermal conversion substance

The photothermal conversion substance has the ability to convert the photoexposure energy into heat and thereby efficiently bring about the extinction of interactions in the photoexposed regions of the heat-sensitive layer. Pigments and dyes that have a light absorption region in the infrared region at wavelengths of 700 to 1200 nm are preferred from the standpoint of the recording sensitivity. In specific terms the following dyes can be used: azo dyes, metal complex salt azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinone imine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts, metal thiolate complexes (for example, nickel thiolate complexes), and so forth. Cyanine dyes are preferred among the preceding, and examples here are the cyanine dyes given by general formula (I) in Japanese Patent Application Publication No. 2001-305722 . The thermal positive-type composition preferably incorporates the same compounds (e.g., sensitivity regulators, print-out agents, dyes, and so forth) and surfactants for improving coatability as the substances previously described for the conventional positive type considered above, and the compounds described in [0053] to [0059] of Japanese Patent Application Publication No. 2001-305722 are particularly preferred.
The heat-sensitive layer of a thermal positive type may be a single layer, or may be elaborated as a two-layer structure as described in Japanese Patent Application Publication No. H11-218914 .
An undercoat layer is preferably disposed between the support and the heat-sensitive layer of the thermal positive type. The components present in this undercoat layer can be exemplified by the various organic compounds given in [0068] of Japanese Patent Application Publication No. 2001-305722 .
This thermal positive-working heat-sensitive lithographic printing plate precursor having a heat-sensitive composition comprising the alkali-soluble polymer compound and photothermal conversion substance disposed on a support, is imagewise photoexposed using an infrared laser and is then developed with an alkaline developing solution. Preferred examples of this developing solution are the developing solutions described in Japanese Examined Patent Publication No. S57-7427 , Japanese Patent No. 3086354 , Japanese Patent Application Publication No. H11-216962 , and Japanese Patent Application Publication Nos. 2001-51406 , 2001-174981 , and 2002-72501 .

< The polymer compound having a specific structural group >

In particular, by using a polymer compound that contains at least one structure selected from sulfonamide groups, maleimide groups, and urea structures, the inventive image recording layer containing a compound with general formula (I) can exhibit an excellent combination of antiscumming performance and printing durability in particular when a UV ink is used.
That is, this specific structural group, i.e., a sulfonamide group, maleimide group, or a urea structure, is believed generally to provide a high printing durability by exhibiting a high cohesiveness and a high film formability. The developability, on the other hand, is poor due to the high cohesiveness. The addition of the previously described compound with general formula (I) to such a binder results in the presence of this compound with its hydrogen bonding capability between the macromolecules and the developability is improved and the antiscumming performance is elevated. In addition, the compound with general formula (I) causes almost no decline in the printing durability, and in particular causes very little reduction in the printing durability with UV inks.
Resins having a group, for example, as given in the following (1) to (3), in main chain position and/or side chain position in the polymer are suitable examples of polymer compounds having the specific structural group that can be used in the image recording layer in the present invention.

(1) Sulfonamide groups (-SO₂NH-R)
(2) Maleimide groups
(3) Urea structures (-NR-C(=O)-NR-)

R in (1) to (3) above represents a hydrogen atom or a possibly substituted hydrocarbyl group.
Among polymers selected from (1) to (3), the (1) sulfonamide group is the most preferred from the standpoint of thoroughly securing the film strength.
A polymer comprising as its main structural component the minimum structural unit derived from a sulfonamide group-containing compound is an example of a (1) sulfonamide group-containing alkali-soluble resin.
Such a compound can be exemplified by compounds that contain in the molecule at least one polymerizable unsaturated group and at least one sulfonamide group in which at least one hydrogen atom is bonded to the nitrogen atom. Preferred thereamong are low molecular weight compounds that contain in the molecule the (meth)acryloyl group, allyl group, or vinyloxy group as well as a unsubstituted or monosubstituted aminosulfonyl group or substituted sulfonylimino group; these compounds can be exemplified by the compounds represented by the following general formulas (i) to (v).
In the preceding general formulas (i) to (v), X¹ and X² each independently represent -O- or -NR⁷. R¹ and R⁴ each independently represent the hydrogen atom or -CH₃. R², R⁵, R⁹, R¹², and R¹⁶ each independently represent possibly substituted C_1-12 alkylene, cycloalkylene, arylene, or aralkylene. R³, R⁷, and R¹³ each independently represent the hydrogen atom or possibly substituted C_1-12 alkyl, cycloalkyl, aryl, or aralkyl. R⁶ and R¹⁷ each independently represent possibly substituted C_1-12 alkyl, cycloalkyl, aryl, or aralkyl. R⁸, R¹⁰, and R¹⁴ each independently represent the hydrogen atom or -CH₃. R¹¹ and R¹⁵ each independently represent a single bond or possibly substituted C_1-12 alkylene, cycloalkylene, arylene, or aralkylene. Y¹ and Y² each independently represent a single bond or CO.
Among compounds represented by general formulas (i) to (v), m-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl)methacrylamide, N-(p-aminosulfonylphenyl)acrylamide, and so forth, are particularly preferred for use for alkali-soluble resins usable by the present invention.
A polymer comprising as its main structural component the minimum structural unit derived from a maleimide group-containing compound is an example of a (2) maleimide group-containing polymer. Such a compound can be exemplified by compounds that contain in the molecule at least one maleimide group with the structural formula given below.
R₁ in general formula (1) represents a freely selected substituent. R₁ is preferably hydrogen; unsubstituted or freely substituted (C₆-C₁₂) aryl; unsubstituted or freely substituted (C₁-C₁₂) alkyl; unsubstituted or freely substituted (C₃-C₁₀) cycloalkyl; an unsubstituted or freely substituted arylsulfonamide group; or an unsubstituted or freely substituted sulfonamide group. At least one substituent selected from halogen, alkyl, -NO₂, and -OH is preferred for the optional substituent(s) on each of the aforementioned groups. R₁ is particularly preferably hydrogen, phenyl, cyclohexyl, or hydroxyphenyl.
R₂ and R₃ in general formula (1) similarly represent freely selected substituents, and R₂ and R₃ are preferably independently selected from the group consisting of hydrogen, halogen, (C₁-C₄) alkyl, and phenyl. R₂ and R₃ are particularly preferably both hydrogen.
The (3) urea structure-containing polymer can be exemplified by polymers in which a structure as given below is a repeat unit.
R¹ and R² in the formulas each represent the hydrogen atom, a halogen atom, alkyl, aryl, or the carboxyl group or salt thereof; R³ represents the hydrogen atom, a halogen atom, alkyl, or aryl; X represents a divalent linking group; and Y represents a possibly substituted divalent aromatic group.
Specific examples are polymers that have a repeat unit derived from, inter alia, the following monomers: (meth)acrylate derivatives such as 1-(N'-(4-hydroxyphenyl)ureido)methyl acrylate, 1-(N'-(3-hydroxyphenyl)ureido)methyl acrylate, 1-(N'-(2-hydroxyphenyl)ureido)methyl acrylate, 2-(N'-(4-hydroxyphenyl)ureido)ethyl acrylate, 4-(N'-(4-hydroxyphenyl)ureido)butyl acrylate, 1-(N'-(4-hydroxyphenyl)ureido)methyl methacrylate, 1-(N'-(3-hydroxyphenyl)ureido)methyl methacrylate, 1-(N'-(2-hydroxyphenyl)ureido)methyl methacrylate, 2-(N'-(4-hydroxyphenyl)ureido)ethyl methacrylate, 4-(N'-(4-hydroxyphenyl)ureido)butyl methacrylate, 4-(N'-(3-hydroxyphenyl)ureido)butyl methacrylate, 4-(N'-(2-hydroxyphenyl)ureido)butyl methacrylate, 4-(N'-(3-hydroxy-4-methylphenyl)ureido)butyl methacrylate, 4-(N'-(2-hydroxy-5-methylphenyl)ureido)butyl methacrylate, 4-(N'-(5-hydroxynaphthyl)ureido)butyl methacrylate, 2-(N'-(4-sulfamoylphenyl)ureido)ethyl acrylate, 2-(N'-(4-sulfamoylphenyl)ureido)ethyl methacrylate, and 2-(N'-(2-hydroxy-5-sulfamoylphenyl)ureido)ethyl methacrylate.
The minimum structural unit having a group selected from the aforementioned (1) to (3) need not be of only one particular type, and copolymers of two or more species of minimum structural units having the same group and copolymers of two or more species of minimum structural units having different groups can also be used.
The repeat unit having a specific structural group as described above preferably constitutes at least 10 mol% and more preferably at least 20 mol% of the aforementioned polymer compound. An adequate increase in the printing durability with respect to UV inks tends to be unavailable at less than 10 mol%.
The monomer that provides a repeat unit having a specific structural group as described above can be copolymerized with, for example, monomer as described in (m1) to (m12) below.

(m1) Acrylate esters and methacrylate esters that contain an aliphatic hydroxyl group, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and so forth.
(m2) Alkyl acrylates, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, benzyl acrylate, 2-chloroethyl acrylate, glycidyl acrylate, and so forth.
(m3) Alkyl methacrylates, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-chloroethyl methacrylate, glycidyl methacrylate, and so forth.
(m4) Acrylamides or methacrylamides, such as acrylamide, methacrylamide, N-methylolacrylamide, N-ethylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-hydroxyethylacrylamide, N-phenylacrylamide, N-nitrophenylacrylamide, N-ethyl-N-phenylacrylamide, and so forth.
(m5) Vinyl ethers, such as ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether, phenyl vinyl ether, and so forth.
(m6) Vinyl esters, such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, vinyl benzoate, and so forth.
(m7) Styrenes, such as styrene, α-methylstyrene, methylstyrene, chloromethylstyrene, and so forth.
(m8) Vinyl ketones, such as methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, phenyl vinyl ketone, and so forth.
(m9) Olefins, such as ethylene, propylene, isobutylene, butadiene, isoprene, and so forth.
(m 10) N-vinylpyrrolidone, acrylonitrile, methacrylonitrile, and so forth.
(m11) Unsaturated imides, such as N-acryloylacrylamide, N-acetylmethacrylamide, N-propionylmethacrylamide, N-(p-chlorobenzoyl)methacrylamide, and so forth.
(m12) Unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, and so forth.

In those cases where development is performed on the press by the fountain solution or ink, i.e., when on-press development is performed, the polymer binder having a specific structural group preferably has copolymerized therein a hydrophilic group in the form of an acrylate or methacrylate that has an alkylene oxide structure that has from 1 to 100 C₂ or C₃ alkylene oxide units. This alkylene oxide structure is particularly preferably an alkylene oxide structure that has 2 to 12 units and most preferably is an alkylene oxide structure that has 2 to 8 units. Copolymerization of a hydrophilic group-containing monomer may be employed in order to introduce the hydrophilic group into the polymer binder.
The following structures are specific examples of polymer binders that have a specific structural group.
The repeat units of homopolymers and copolymers of sulfonamide group-containing polymerizable monomers, e.g., m-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl)methaerylamide, N-(p-aminosulfonylphenyl)acrylamide, and so forth, are particularly preferred for the repeat units of the aforementioned polymer.
The weight-average molecular weight of this polymer binder is preferably at least 2,000 and the number-average molecular weight is preferably at least 500. More preferably, the weight-average molecular weight is 5,000 to 300,000, the number-average molecular weight is 800 to 250,000, and the dispersity (weight-average molecular weight/number-average molecular weight) is 1.1 to 10.
The amount of binder polymer addition in the image recording layer is suitably 10 to 80 mass% of the total solids fraction in the image recording layer and preferably is 20 to 70 mass% and particularly preferably is 25 to 60 mass%.

< Formation of the image recording layer >

The image recording layer is formed in the present invention, for example, as described in paragraph numbers [0142] to [0143] of Japanese Patent Application Publication No. 2008-195018 , by preparing a coating bath by dissolving or dispersing the compound with general formula (1) of the present invention and as necessary the individual compounds described above in a known solvent; applying the coating bath by a known method, e.g., application with a bar coater, on a support on which an intermediate layer may optionally have been disposed by coating; and drying.
Viewed from the perspective of the handling characteristics, fitness for application, and dryability, the bath for applying the image recording layer in the present invention preferably contains an organic solvent having a boiling point at 1 atmosphere of 50°C to 130°C. Preferred examples are acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, 1-propanol, 2-propanol, butanol, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, 1-methoxy-2-propanol, 1-methoxy-2-propan-2-yl acetate, 2-methoxyethanol, 2-ethoxyethanol, and so forth. Preferred thereamong are methyl ethyl ketone, methanol, ethanol, and 1-methoxy-2-propanol. A single one of these solvents may be used or a mixture of a plurality of these solvents may be used.
The coating rate (solids fraction) yielded by coating and drying the image recording layer on the support will vary with the service, but generally 0.3 to 3.0 g/m² is preferred. An excellent sensitivity and excellent film properties for the image recording layer are obtained in this range.

< The intermediate layer >

The lithographic printing plate precursor of the present invention may have an intermediate layer between the support and the image recording layer. The intermediate layer preferably contains a polymer compound and this polymer compound also preferably contains a repeat unit that has at least 1 functional group capable of adsorbing to the aluminum support.
The polymer compound for the intermediate layer is preferably a compound that contains, in addition to an aluminum support-adsorptive functional group, at least one selection from hydrophilic groups, crosslinking groups, and hydrophobic groups. The polymer compound used for the intermediate layer is more preferably a polymer compound provided by the copolymerization of a monomer having an aluminum support-adsorptive group and a monomer having a hydrophilic group. In the case of a radical polymerizable negative type, the polymer compound used for the intermediate layer is particularly preferably a polymer compound provided by the copolymerization of a monomer having an aluminum support-adsorptive group, a monomer having a hydrophilic group, and a monomer having a crosslinking group.
Compounds also suitably used for the intermediate layer include silane coupling agents that have an ethylenic double bond reaction group capable of undergoing addition polymerization, as described in Japanese Patent Application Publication No. H10-282679 , and phosphorus compounds that have an ethylenic double bond reaction group, as described in Japanese Patent Application Publication No. H2-304441 .
The adsorptivity of a compound to the surface of an aluminum support can be determined, for example, by the following method.
A coating solution is prepared in which the sample compound is dissolved in a good solvent, and this coating solution is coated and dried on the support so as to provide a post-drying coating rate of 30 mg/m². The sample compound-coated support is then thoroughly washed with a good solvent, after which the amount adsorbed to the support is determined by measuring the remaining amount of the sample compound that was not removed by the washing. This measurement of the residual amount may be made by a direct quantitation of the amount of the remaining compound, or the determination may be made by quantitating the amount of sample compound dissolved in the wash fluid. Quantitation of the compound can be performed by, for example, fluorescent x-ray measurement, measurement of the absorbance by reflectance spectroscopy, and liquid chromatography. In the present invention, a compound that is aluminum support adsorptive is a compound for which at least 1 mg/m² of the compound remains present even after the described washing process.
A group adsorptive to the surface of an aluminum support is a functional group that can bring about interaction (for example, ionic bonding, hydrogen bonding, coordination bonding, bonding by intermolecular forces) with a substance present in the surface of the aluminum support (for example, aluminum, aluminum oxide, silicate, and so forth). Acidic groups and cationic groups are preferred for the adsorptive group.
The acidic group can be exemplified by the phenolic hydroxyl group, the carboxyl group (-CO₂H), the sulfonic acid group (-SO₃H), the sulfate ester group (-OSO₃H), the phosphonic acid group (-PO₃H₂), the phosphate ester group (-OPO₃H₂), -CONHSO₂-, -SO₂NHSO₂-, -C(=O)-CH₂-C(=O)-, and so forth. The acidic group has an acid dissociation constant (pKa) of preferably not more than 10, more preferably not more than 8, and particularly preferably not more than 6.
The carboxyl group, phosphonic acid group, phosphate ester group, and - C(=O)-CH₂-C(=O)- are more preferred for the acidic group, while the phosphonic acid group and phosphate ester group are particularly preferred. A single one of these groups may be used, or two or more may be used in combination, and a counterion may be present.
The cationic group is preferably an onium group or an N-oxide group. The onium group can be exemplified by ammonium, phosphonium, arsonium, stibonium, oxonium, sulfonium, selenonium, stannonium, and iodonium. Preferred thereamong are ammonium, phosphonium, and sulfonium. Ammonium and phosphonium are more preferred, and ammonium is most preferred. The cationic group is particularly preferably the ammonium group or an N-oxide group. A single one of these groups may be used, or two or more may be used in combination, and a counterion may be present.
The polymer compound used for the intermediate layer preferably also has a hydrophilic group. Preferred hydrophilic groups are the hydroxyl group, the carboxyl group, hydroxyalkyl groups (e.g., hydroxyethyl, hydroxypropyl, and so forth), polyoxyalkylene groups (polyoxyethyl, polyoxypropyl, alkylpolyoxyethyl, alkylpolyoxypropyl), the amino group, the ammonium group, the amide group, the sulfonamide group, the sulfonic acid group, the phosphoric acid group, the phosphonic acid group, and their salts.
The following are more preferred: the hydroxyl group, the carboxyl group, hydroxyalkyl groups (e.g., hydroxyethyl, hydroxypropyl, and so forth), polyoxyalkylene groups (polyoxyethyl, polyoxypropyl, alkylpolyoxyethyl, alkylpolyoxypropyl), the amide group, the sulfonamide group, the sulfonic acid group, the phosphoric acid group, the phosphonic acid group, and their salts.
The following are particularly preferred: polyoxyalkylene groups (polyoxyethyl, polyoxypropyl, alkylpolyoxyethyl, alkylpolyoxypropyl) and the sulfonic acid group and its salts.
The following are preferred examples of polyoxyalkylene group-containing monomers: 2-(2-hydroxyethoxy)ethyl methacrylate, 2-(2-hydroxyethoxy)ethyl acrylate, 2-(2-(2-hydroxyethoxy)ethoxy)ethyl methacrylate, 2-(2-(2-hydroxyethoxy)ethoxy)ethyl acrylate, 2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethyl methacrylate, 2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethyl acrylate, 2-(2-methoxyethoxy)ethyl methacrylate, 2-(2-methoxyethoxy)ethyl acrylate, 2-(2-(2-methoxyethoxy)ethoxy)ethyl methacrylate, 2-(2-(2-methoxyethoxy)ethoxy)ethyl acrylate, 2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl methacrylate, 2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl acrylate, 2-(2-hydroxypropoxy)propyl methacrylate, 2-(2-hydroxypropoxy)propyl acrylate, 2-(2-(2-hydroxypropoxy)propoxy)propyl methacrylate, 2-(2-(2-hydroxypropoxy)propoxy)propyl acrylate, 2-(2-(2-(2-hydroxypropoxy)propoxy)propoxy)propyl methacrylate, 2-(2-(2-(2-hydroxypropoxy)propoxy)propoxy)propyl acrylate, 2-(2-methoxypropoxy)propyl methacrylate, 2-(2-methoxypropoxy)propyl acrylate, 2-(2-(2-methoxypropoxy)propoxy)propyl methacrylate, 2-(2-(2-methoxypropoxy)propoxy)propyl acrylate, 2-(2-(2-(2-methoxypropoxy)propoxy)propoxy)propyl methacrylate, 2-(2-(2-(2-methoxypropoxy)propoxy)propoxy)propyl acrylate, and so forth.
Preferred examples of sulfonic acid group-containing monomers are methacryloyloxybenzenesulfonic acid, acryloyloxybenzenesulfonic acid, allylsulfonic acid, vinylsulfonic acid, 4-vinylbenzenesulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, (3-acryloyloxypropyl)butylsulfonic acid, and salts of the preceding. Vinylsulfonic acid, 4-vinylbenzensulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their salts are more preferred.
2-acrylamido-2-methylpropanesulfonic acid and its salts are particularly preferred for the hydrophilic group-containing monomer.
The polymer compound used for an intermediate layer that is employed in the radical polymerizable negative-working lithographic printing plate precursor of the present invention preferably also contains a crosslinking group. This crosslinking group provides an improved adherence with the image area. Crosslinkability can be imparted to the polymer compound used for the intermediate layer by introducing a crosslinking functional group, e.g., an ethylenically unsaturated bond and so forth, in side chain position on the polymer or by forming a salt structure between a polar substituent in the polymer resin and a compound that contains a counter-charged substituent and an ethylenically unsaturated bond.
Polymer compounds having an ethylenically unsaturated bond in side chain position on the molecule can be exemplified by polymer compounds that are polymers of an ester or amide of acrylic acid or methacrylic acid wherein the residue in the ester or amide (R in -COOR or -CONHR) contains an ethylenically unsaturated bond.
This ethylenically unsaturated bond-containing residue (the above-referenced R) can be exemplified by -(CH₂)_nCR¹=CR²R₃, - (CH₂O)_nCH₂CR¹=CR²R³, -(CH₂CH₂O)_nCH₂CR¹=CR²R³, -(CH₂)_nNH-CO-O-CH₂CR¹=CR²R³, -(CH₂)_NO-CO-CR¹=CR²R³, and -(CH₂CH₂O)₂-X (in the formulas, R¹ to R³ each represent the hydrogen atom, a halogen atom, C_1-20 alkyl, aryl, alkoxy, or aryloxy, wherein R¹ may be bonded with R² or R³ to form a ring; n is an integer from 1 to 10; and X represents a dicyclopentadienyl residue).
The residue in the ester can be specifically exemplified by -CH₂CH=CH₂ (described in Japanese Examined Patent Publication No. H7-21633 ), - CH₂CH₂O-CH₂CH=CH₂, -CH₂C(CH₉)=CH₂, -CH₂CH=CH-C₆H₅, - CH₂CH₂OCOCH=CH-C₆H₅, -CH₂CH₂NHCOO-CH₂CH=CH₂, and -CH₂CH₂O-X (X in the formula represents a dicyclopentadienyl residue).
The residue in the amide can be specifically exemplified by -CH₂CH=CH₂, -CH₂CH₂O-Y (Y in the formula represents a cyclohexene residue), and - CH₂CH₂OCO-CH=CH₂.
The crosslinking group-containing monomer for the polymer resin used for the intermediate layer is preferably an ester or amide of acrylic acid or methacrylic acid that contains a crosslinking group as described above.
The content of the crosslinking group in the polymer compound used for the intermediate layer (content of radical polymerizable unsaturated double bonds by iodine titrimetry) is, per 1 g of the polymer resin, preferably 0.1 to 10.0 mmol, more preferably 1.0 to 7.0 mmol, and most preferably 2.0 to 5.5 mmol. An excellent storage stability and the combination of an excellent sensitivity with an excellent scumming behavior are obtained in this range.
The polymer compound used for the intermediate layer has a weight-average molecular weight preferably of at least 5,000 and more preferably of 10,000 to 300,000 and has a number-average molecular weight preferably of at least 1,000 and more preferably of 2,000 to 250,000. The dispersity (weight-average molecular weight/number-average molecular weight) is preferably 1.1 to 10.
The polymer compound used for the intermediate layer may be a random polymer, block polymer, graft polymer, and so forth, but is preferably a random polymer
A single compound for the intermediate layer may be used or a mixture of two or more may be used.
The content of the compound for the intermediate layer in the bath for applying the intermediate layer is preferably 0.01 to 50 mass%, more preferably 0.1 to 40 mass%, and particularly preferably 0.5 to 30 mass%.
Examples of the polymer compound used for the intermediate layer are shown below, but the present invention is not limited to these.
Various known methods can be used to apply the intermediate layer coating solution on the support. Examples here are bar coater application, rotational application, spray application, curtain coating, dip coating, air knife coating, blade coating, roll coating, and so forth.
The coating rate (solids fraction) for the intermediate layer is preferably 0.1 to 100 mg/m² and more preferably is 1 to 30 mg/m².

< The support >

Known supports are used for the support employed in the lithographic printing plate precursor of the present invention. Preferred thereamong is aluminum sheet that has been surface roughened and anodically oxidized by known methods.
As necessary, a treatment for widening the micropores in the anodic oxidation film and a pore sealing treatment, as described in Japanese Patent Application Publication No. 2001-253181 and Japanese Patent Application Publication No. 2001-322365 , a surface hydrophilicizing treatment with, for example, an alkali metal silicate, as described in US Patent Nos. 2714066 , 3181461 , 3280734 , and 3902734 , or with a polyvinylphosphonic acid, as described in US Patent Nos. 3276868 , 4153461 , and 4689272 , and so forth, can be selected as appropriate for the aforementioned aluminum sheet.
The support preferably has a center-line average roughness of 0.10 to 1.2 µm.
As necessary, a backcoat layer comprising an organic polymer compound as described in Japanese Patent Application Publication No. H5-45885 or a silicon alkoxy compound as described in Japanese Patent Application Publication No. H5-45885 can be disposed on the back surface of the support used in the present invention.

< The protective layer >

A protective layer (an overcoat layer) is preferably disposed on the image recording layer in the lithographic printing plate precursor of the present invention. In addition to its function of blocking oxygen and thereby preventing reactions that inhibit image formation, the protective layer functions to prevent damage to the image recording layer and to prevent ablation during photoexposure with a high intensity laser.
A protective layer with such properties is described, for example, in US Patent No. 3458311 and Japanese Examined Patent Publication No. S55-49729 . A suitable selection from water-soluble polymers and water-insoluble polymers can also be used as the low oxygen permeability polymer employed for the protective layer. Specific examples are polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, water-soluble cellulose derivatives, poly(meth)acrylonitrile, and so forth.
In addition, in order to raise the oxygen blocking performance, an inorganic layer compound, e.g., natural mica, synthetic mica, and so forth, as described in Japanese Patent Application Publication No. 2005-119273 , is preferably incorporated in the protective layer.
Known additives can also be incorporated in the protective layer, for example, a plasticizer to impart flexibility, a surfactant to improve the coatability, finely divided inorganic particles to modulate the slipperiness of the surface, and so forth. The protective layer can also incorporate a sensitizer as described in the discussion of the image recording layer. Particularly when an inorganic layer compound is incorporated, the use is preferred, from the standpoint of dispersing the inorganic layer compound, of modified polyvinyl alcohol and particularly sulfonic acid-modified polyvinyl alcohol.
The protective layer is applied by known methods, and the protective layer coating rate, expressed as the quantity of application after drying, is preferably in the range of 0.01 to 10 g/m², more preferably in the range of 0.02 to 3 g/m², and most preferably in the range of 0.02 to 1 g/m².

< Platemaking and image formation >

A laser is preferred as the light source used for imagewise photoexposure of the lithographic printing plate precursor. The laser used with the present invention is not particularly limited, but suitable examples are solid-state lasers and semiconductor lasers that emit infrared radiation at wavelengths of 760 to 1200 nm, and ultraviolet sources (e.g., high-pressure mercury lamps and so forth), argon lasers, ultraviolet lasers, and semiconductor lasers that emit light at 250 to 420 nm.
An output of at least 100 mW is preferred in the case of infrared lasers, and the photoexposure time per pixel is preferably no more than 20 microseconds and the amount of irradiated energy is preferably from 10 to 300 mJ/cm². In the case of semiconductor lasers that emit light at 250 to 420 nm, an output of at least 0.1 mW is preferred. With any of these lasers, the use of a multibeam laser device is also preferred in order to shorten the photoexposure time.
Development is performed with a developing solution after imagewise photoexposure with the preceding. Developing solutions preferred for use are aqueous solutions that as necessary contain base, organic solvent, surfactant, hard water softener, reducing agent, organic carboxylic acid, inorganic salt, defoamer, and the various optional additives known in the pertinent industry. The developing solutions described in Japanese Examined Patent Publication No. S58-54341 and Japanese Patent Application Publication Nos. H8-248643 , 2002-91015 , and H8-171214 are particularly preferred examples.
When on-press development is performed, the photoexposed lithographic printing plate precursor is mounted on the plate cylinder of the press. When the press is equipped with a laser photoexposure unit, imagewise photoexposure may be performed after the lithographic printing plate precursor has been mounted on the plate cylinder of the press.
When, after the lithographic printing plate precursor has been imagewise photoexposed with, for example, an infrared laser, and without going through a development processing step (e.g., a wet development processing step), printing is performed by feeding printing ink and fountain solution, the image recording layer cured by photoexposure in the photoexposed regions of the image recording layer forms a printing ink receptive area that exhibits an oleophilic surface. On the other hand, in the nonphotoexposed regions, the uncured image recording layer is removed by dissolution or dispersion by the supplied fountain solution and/or printing ink, causing exposure of the hydrophilic surface in these areas. As a result, the fountain solution adheres to the exposed hydrophilic surfaces while the printing ink is taken up by the image recording layer in the photoexposed regions and printing is initiated.
The fountain solution or printing ink may be fed to the plate surface first, but the printing ink is preferably fed first from the standpoint of preventing contamination of the fountain solution by the constituent components of the image recording layer that are removed. The fountain solution and printing ink used here can be selected from the fountain solutions and printing inks employed for ordinary lithographic printing.
Proceeding in this manner, the lithographic printing plate precursor may be subjected to on-press development on an offset press and then directly used for long-run printing.
Platemaking with the lithographic printing plate precursor of the present invention may also proceed through a development processing step, e.g., a wet development processing step, in which case development is carried out between the previously described photoexposure step and the printing step. The method employed for the development process is not particularly limited and can be appropriately determined based on the nature of the image forming layer.

EXAMPLES

The present invention is described in detail by the examples provided below, but the present invention is not limited to these examples.

[Examples 1 to 16 and Comparative Examples 1 to 4]

1. Preparation of the lithographic printing plate precursor

(1) Preparation of support (1)

The rolling oil was removed from the surface of 0.3 mm-thick aluminum sheet (JIS A 1050) by a degreasing treatment for 30 seconds at 50°C using 10 mass% aqueous sodium aluminate solution. After this, the aluminum surface was grained using three implanted nylon brushes with a bristle diameter of 0.3 mm and an aqueous suspension (specific gravity = 1.1 g/cm³) of pumice having a median diameter of 25 µm; this was followed by a thorough rinse with water. This sheet was etched by dipping for 9 seconds in a 45°C 25 mass% aqueous sodium hydroxide solution followed by a water rinse and then dipping for 20 seconds in 20 mass% nitric acid at 60°C followed by a water rinse. The resulting amount of etching of the grained surface was approximately 3 g/m².
A continuous electrochemical roughening treatment was then carried out using 60-Hz AC voltage. The electrolytic solution used for this treatment was a 1 mass% aqueous nitric acid solution (containing 0.5 mass% aluminum ion) and the bath temperature was 50°C. The AC power source waveform provided trapezoidal square wave alternating current with a TP (time required for the current value to go from zero to the peak) of 0.8 msec and a duty ratio of 1 : 1, and the electrochemical roughening was carried out using a carbon electrode as the counterelectrode. Ferrite was used as an auxiliary anode. The current density was 30 A/dm² at the current peak value, and 5% of the current flowing from the power source was branched to the auxiliary anode.
The quantity of electricity in this nitric acid electrolysis was 175 C/dm² for the time in which the aluminum sheet was functioning as an anode. This treatment was followed by a water rinse by spraying.
An electrochemical roughening treatment was then carried out by the same method as for the nitric acid electrolysis, but using the following conditions: electrolytic solution = 0.5 mass% aqueous hydrochloric acid solution (containing 0.5 mass% aluminum ion), bath temperature = 50°C, quantity of electricity = 50 C/dm² for the time in which the aluminum sheet was functioning as an anode. This was followed by a water rinse by spraying.
A 2.5 g/m² direct-current anodic oxidation film was then disposed on this sheet using a current density of 15 A/dm² and using 15 mass% sulfuric acid (containing 0.5 mass% aluminum ion) as the electrolytic solution; this was followed by a water rinse and drying.
In order to secure the hydrophilicity in the nonimage areas, a silicate treatment was subsequently performed for 12 seconds at 70°C using a 2.5 mass% aqueous #3 sodium silicate solution. The Si add-on was 10 mg/m². This was followed by a water rinse to obtain support (1). The center-line average roughness (Ra) of this substrate was measured at 0.51 µm using a needle with a diameter of 2 µm.

(2) Formation of the intermediate layer

An intermediate layer was then disposed on this support by the application of the following intermediate layer coating bath so as to provide a dry coating rate of 28 mg/m².

< Intermediate layer coating bath >

Compound (1), see below, for use for 0.18 g the intermediate layer (undercoat layer)
Hydroxyethyliminodiacetic acid 0.10 g
Methanol 55.24 g
Water 6.15 g

Undercoat layer compound (1)

(3) Formation of the image recording layer

An image recording layer coating bath with the composition given below was bar coated on the intermediate layer that had been formed as described above, followed by drying in an oven at 100°C to form an image recording layer that had a dry coating rate of 1.0 g/m². In the composition given below, the amount (content) of general formula (I) shown in Table 1 is based on the mass of the image recording layer in the finished lithographic printing plate precursor.
The amount (content) of the compound wth general formula (I) or the comparative compound in the image recording layer was adjusted by adjusting the time of the aforementioned drying.
The image recording layer coating bath was obtained by mixing and stirring the below-described photosensitive solution (1) and microgel solution (1) immediately before application.

< Photosensitive solution (1) >

Compound with general formula (1) (type and amount given or comparative compound in Table 1 below)
Polymer compound (1) (structure given below) 0.108 g
Polymer compound having the specific
structural group (refer to Table 1) 0.054 g (selected from the previously described specific examples (1) to (20) of the polymer compound having the specific
structural group)
Infrared absorber (1) (structure given below) 0.030 g
Radical polymerization initiator (1) 0.162 g

(structure given below)

Polymerizable compound
Tris(acryloyloxyethyl) isocyanurate
(NK Ester A-9300, from Shin-Nakamura
Chemical Co., Ltd.) 0.192 g
Low molecular weight hydrophilic compound
Tris(2-hydroxyethyl) isocyanurate 0.062 g
Low molecular weight hydrophilic compound (1) 0.050 g
(structure given below)
Sensitizer, phosphonium compound (1) 0.055 g
(structure given below)
Sensitizer
Benzyldimethyloctylammonium · PF₆ salt 0.018 g
Trimethylglycine 0.01 g
Fluorosurfactant (1) (structure given below) 0.008 g
Methyl ethyl ketone 1.091 g
1-methoxy-2-propanol 8.609 g

< Microgel solution (1) >

Microgel (1) 2.640 g
Distilled water 2.425 g

The structures of the aforementioned polymer compound (1), infrared absorber (1), radical polymerization initiator (1), phosphonium compound (1), low molecular weight hydrophilic compound (1), fluorosurfactant (1), comparative compound C-1, and comparative compound C-2 are provided below.
Polymer compound (1)

The above-referenced microgel (1) was synthesized as follows.

< Synthesis of microgel (1) >

An oil phase component was prepared by dissolving the following in 17 g ethyl acetate: 10 g trimethylolpropane/xylene diisocyanate adduct (Mitsui Takeda Chemical Co., Ltd., Takenate D-110N), 3.15 g pentaerythritol triacrylate (component (C), Nippon Kayaku Co., Ltd., SR444), and 0.1 g Paionin A-41C (Takemoto Oil & Fat Co., Ltd.). 40 g of a 4 mass% aqueous solution of PVA-205 was prepared for the aqueous phase component. The oil phase component and aqueous phase component were mixed and were emulsified for 10 minutes at 12,000 rpm using a homogenizer. The resulting emulsion was added to 25 g distilled water and stirring was performed for 30 minutes at room temperature and then for 3 hours at 50°C. The thusly obtained microgel solution was diluted with distilled water to bring the solids concentration to 15 mass%, and this was used as the above-referenced microgel (1). Measurement of the average particle size of the microgel by a light scattering procedure gave an average particle size of 0.2 µm.

(Quantitation of the compound with general formula (1) and the comparative compounds)

100 cm² of the produced lithographic printing plate precursor was extracted with methanol and quantitative determination of the above-referenced compound in the image recording layer was performed by gas chromatography. This content in the image recording layer is given in mass%.

(Conditions for the gas chromatographic measurement)

A 10 cm × 10 cm sample of the lithographic printing plate material was immersed in special-grade methanol and stirring was performed for 3 hours at room temperature to extract the components of the photosensitive layer. 1 µL of the resulting sample solution was injected onto the GC and quantitative determination was carried out by the absolute calibration curve method.

GC conditions

Instrument:	Agilent 6890 (Agilent Technologies)
Column:	DB-17MS 30 m × 0.25 mm ID, 0.25 µm film thickness (J & W Scientific)
Oven
Temperature:	50°C (held for 5 minutes) → Temperature ramp up at 10°C/minute → 280°C (Held for 2 minutes)
Injection port

Temperature:	280°C
Split:	10
Carrier gas:	He = 1 mL/min
Detector:	FID
Detector
Temperature:	300°C

(4) Formation of protective layer (1)

The protective layer coating bath (1) described below was also bar coated on the image recording layer formed as described above, followed by oven drying for 60 seconds at 120°C to form a protective layer (1) having a dry coating rate of 0. 15 g/m².

< Protective layer coating bath (1) >

Inorganic layer compound dispersion (1) 1.5 g
6 mass% aqueous solution of polyvinyl alcohol
(CKS50 from Nippon Synthetic Chemical Industry
Co., Ltd., sulfonic acid modified, degree of
saponification at least 99 mol%, degree of
polymerization = 300) 0.55 g
6 mass% aqueous solution of polyvinyl alcohol
(PVA-405 from Kuraray Co., Ltd., degree of
saponification = 81.5 mol%, degree of
polymerization = 500) 0.03 g
1 mass% aqueous solution of surfactant
from Nihon Emulsion Co., Ltd. (Emalex 710) 8.60 g
Ion-exchanged water 6.0 g
(Preparation of the inorganic layer compound dispersion (1))
6.4 g of the synthetic mica Somashif ME-100 (Co-op Chemical Co., Ltd.) was added to 193.6 g ion-exchanged water, and dispersion was carried out using a homogenizer until the average particle size reached 3 µm (laser scattering method). The aspect ratio of the resulting dispersed particles was at least 100.

2. Evaluation of the lithographic printing plate precursors

The resulting lithographic printing plate precursors were photoexposed using a Luxel Platesetter T-6000III (Fujifilm Corporation), which was equipped with an infrared semiconductor laser; the conditions were an external drum rotation rate of 1000 rpm, a laser output of 70%, and a resolution of 2400 dpi. Photoexposure was carried out in such a manner that the photoexposed image contained a solid image and the 50% halftone chart of a 20 µm-dot FM screen.
The resulting photoexposed precursor was installed, without a development process, on the plate cylinder of a Lithrone 26 press from the Komori Corporation. Using a fountain solution of Ecolity-2 (Fujifilm Corporation)/tap water = 2/98 (volume ratio) and Values-G(N) black ink (DIC Corporation), on-press development was performed by supplying fountain solution and ink using the standard automatic printing start-up procedure on the Lithrone 26, followed by printing 100 impressions on Mitsubishi special-grade art paper (76.5 kg) at a printing speed of 10,000 impressions per hour.

(A) On-press developability

The on-press developability was evaluated as the number of sheets of printing paper required until on-press development of the nonphotoexposed regions of the image recording layer on the press was completed and ink was not transferred to the nonimage areas. In this case, a smaller number of sheets is indicative of a better on-press developability.

(B) On-press developability after elapsed time

The obtained lithographic printing plate precursor was held for 3 days in a humidistat/thermostat set at 45°C and relative humidity 75%. The on-press developability was subsequently determined using photoexposure and printing as described above.
The timewise stability is taken as being better as the number of sheets is nearer to the number of sheets for on-press development in the absence of the forced holding period as determined in (A) above.

(C) Ordinary printing durability

Printing was continued after carrying out the above-described evaluation of on-press developability. As the number of printed impressions grew, the ink density on the printed material declined due to gradual wear of the image recording layer. The printing durability was evaluated by designating the number of sheets at the printing end point to be the number of sheets when the value measured with a Gretag densitometer for the halftone area percentage of the FM screen 50% halftone had declined 5% from the value measured on the 100th printed impression.

(D) Antiscumming performance after elapsed time

The obtained lithographic printing plate precursor was allowed to stand for 3 days in a humidistat/thermostat set to 45°C and relative humidity 75%, followed by photoexposure as described above, printing using the conditions in (C), and evaluation of the antiscumming performance in the nonimage areas on a three level scale.

+ :: The Antiscumming performance presents no problems from a practical standpoint
Δ :: The antiscumming performance is problematic depending on the requirements
× :: The antiscumming performance is poor and is problematic from a practical standpoint

(E) Printing durability with UV ink

The resulting photoexposed precursor was installed, without a development process, on the cylinder of a DIA IF-2 press from Mitsubishi Heavy Industries, Ltd. Using a 2 volume% aqueous solution of IF 102 fountain solution (FUJIFILM Corporation) and Best Cure UV-BF-WRO standard black ink (T&K TOKA Company), the fountain solution and ink were supplied followed by printing at a printing speed of 10,000 impressions per hour.
The printing end point was taken to be the number of sheets when the image density of the printed material had declined 5% from that at the start of printing.

(F) Antiscumming performance with UV ink after elapsed time

The obtained lithographic printing plate precursor was allowed to stand for 3 days in a humidistat/thermostat set to 45°C and relative humidity 75%, followed by photoexposure as described above, printing using the conditions in (E), and evaluation of the antiscumming performance in the nonimage areas on a three level scale.

Table 1.

Example	Compound with general formula (I) or comparative compound	Content (mass%)	Polymer compound having the specially structured group	On-press developability (sheets)	On-press developability after elapsed time (sheets)	Printing durability, × 1,000 sheets	Anti-scumming behavior after elapsed time	Printing durability with UV ink, × 1,000 sheets	Anti-scumming behavior with UV ink after elapsed time
Example 1	I-1	1.1	(1)	10	12	115	+	10	+
Example 2	I-1	0.01	(1)	13	16	100	+	10	+
Examples 3	I-1	0.05	(1)	12	15	100	+	10	+
Example 4	I-1	0.08	(1)	12	14	100	+	10	+
Example 5	I-1	0.10	(1)	11	14	110	+	10	+
Example 6	I-1	3.0	(1)	10	12	110	+	10	+
Example 7	I-1	5.0	(1)	10	12	100	+	9.5	+
Example 8	I-1	7.0	(1)	11	12	90	+	9	+
Example 9	I-2	1.0	(1)	10	15	110	+	10	+
Example 10	I-3	1.0	(1)	10	18	100	+	10	+
Example 11	1-4	1.2	(1)	10	18	95	+	10	+
Example 12	1-5	1.0	(1)	10	12	90	+	10	+
Example 13	I-6	3.0	(1)	11	15	95	+	9	+
Example 14	I-1	1.1	None	10	12	110	+	7	+
Example 15	I-1	1.1	(7)	11	14	120	+	10	+
Example 16	I-1	1.1	(20)	11	14	115	+	10	+
Comp. Example 1	I-1	0.008	(1)	15	20	100	Δ	10	Δ
Comp. Example 2	I-1	11	(1)	10	15	80	+	4	Δ
Comp. Example 3	C-1	1.1	(1)	15	30	65	+	7	Δ
Comp. Example 4	C-2	1.0	(1)	18	40	60	Δ	6	Δ

The preceding results demonstrate that the lithographic printing plate precursor of the present invention exhibits an excellent on-press developability after elapsed time, printing durability, and antiscumming performance.
In Example 14, 0.162 g was used for the quantity of addition of polymer compound (1) due to the absence of the polymer compound having the specific structural group.
The molecular weights of the polymer compounds having the specific structural group that were used were (1): Mw = 55000, (7) Mw = 53000, and (20) Mw = 55000.

[Examples 17 to 23 and Comparative Examples 5 to 8]

< Thermal negative-working lithographic printing plate precursor >

Lithographic printing plate precursors (Examples 17 to 23 and Comparative Examples 5 to 8) were produced entirely as described in Example 1 of Japanese Patent Application Publication No. 2001-264991 , with the exception that the compound with general formula (I) or a comparative compound (type and quantity given in Table 2) was also added to the image-forming layer in Example 1 of Japanese Patent Application Publication No. 2001-264991 . The residual color in the nonimage areas, the adherence, and the printing durability were evaluated. The amount (content) of general formula (I) shown in the table is based on the mass of the image recording layer in the finished lithographic printing plate precursor.
The antiscumming performance after elapsed time was also evaluated as described in the following.

< Antiscumming performance after elapsed time >

The lithographic printing plate precursor was held for 4 days in a thermostat/humidistat set to 45°C and relative humidity 75%, after which photoexposure and printing were carried out as described above and the antiscumming performance in the nonimage areas was evaluated on a three level scale. With regard to whether residual color was present in the nonphotoexposed regions, the lithographic printing plate precursor was mounted after development in a Heidelberg SOR-M press; 50 sheets were printed; and the presence/absence of ink scumming in the nonphotoexposed regions was visually observed and evaluated as follows.

Antiscumming performance after elapsed time

+ : Unproblematic from a practical standpoint
× : Problematic from a practical standpoint

The results are given in Table 2.

The lithographic printing plate precursor having an image recording layer containing a compound with general formula (I) according to the present invention is demonstrated to have a particularly high printing durability, which also exhibits an excellent balance with the antiscumming performance.

Table 2.

Example	Compound with general formula(I) or comparative compound	Content (mass%)	Residual color in the nonimage areas	Adherence (observation of missing parts of an image)	Printing durability (1,000 sheets)	Anti-scumming performance after elapsed time
Example 17	I-1	1.1	+	+	230	+
Example 18	I-1	0.08	+	+	200	+
Example 19	I-1	0.10	+	+	210	+
Example 20	I-1	3.0	+	+	220	+
Example 21	I-1	5.0	+	+	200	+
Example 22	I-2	1.2	+	+	220	+
Example 23	I-3	1.5	+	+	240	+
Comp. Example 5	I-1	0.008	Δ	+	200	+
Comp. Example 6	I-1	11	+	Δ	170	+
Comp. Example 7	C-1	1.2	Δ	+	180	×
Comp. Example 8	C-2	1.2	+	Δ	150	×

Residual color in the nonimage areas

+ :: Unproblematic from a practical standpoint
Δ :: Problematic depending on the requirements

Adherence

[Examples 24 to 30 and Comparative Examples 9 to 21]

< Thermal negative-working simple-developing lithographic printing plate precursor>

Lithographic printing plate precursors (Examples 24 to 30 and Comparative Examples 9 to 12) were produced entirely as described in Example 1 of Japanese Patent Application Publication No. 2007-316598 , with the exception that the compound with general formula (I) or a comparative compound (type and quantity given in Table 3) was also added to the image-forming layer in Example 1 of Japanese Patent Application Publication No. 2007-316598 . The developability (presence/absence of residual film in nonimage areas) and the printing durability were evaluated using the methods described in the examples of Japanese Patent Application Publication No. 2007-316598 . The amount (content) of general formula (I) shown in the table is based on the mass of the image recording layer in the finished lithographic printing plate precursor.
With regard to the antiscumming performance after elapsed time, holding was carried out for 4 days in a thermostat/humidistat set to 45°C and relative humidity 75%, after which printing was carried out using the conditions described in [0338] of Japanese Patent Application Publication No. 2007-316598 and the attachment of ink to the nonimage areas of the printed material was evaluated and scored as follows.

Antiscummin performance after elapsed time

The results are given in Table 3. The lithographic printing plate precursor having an image recording layer according to the present invention is shown to have a high printing durability, which also exhibits an excellent balance with the developability, and is also shown to exhibit an excellent antiscumming performance with elapsed time.

Table 3.

Example	Compound with general formula (I) or comparative compound	Content (mass%)	Developability	Printing durability (1,000 sheets)	Anti-scumming behavior after elapsed time
Example 24	I-1	1.1	+	65	+
Example 25	I-1	0.08	+	55	+
Example 26	I-1	0.10	+	60	+
Example 27	I-1	3.0	+	60	+
Example 28	I-1	5.0	+	55	+
Example 29	I-2	1.2	+	55	+
Example 30	I-3	1.5	+	53	+
Comp. Example 9	I-1	0.008	+	53	Δ
Comp. Example 10	I-1	11	+	43	+
Comp. Example 11	C-1	1.2	Δ	45	Δ
Comp. Example 12	C-2	1.2	+	44	Δ

Developability + : No residual film; Δ : Slight residual film

[Examples 31 to 39 and Comparative Examples 13 to 15]

< Thermal positive-working lithographic printing plate precursor>

A melt was prepared using an aluminum alloy that contained 0.06 mass% Si, 0.30 mass% Fe, 0.014 mass% Cu, 0.001 mass% Mn, 0.001 mass% Mg, 0.001 mass% Zn, 0.03 mass% Ti, and balance to Al and unavoidable impurities and was subjected to melt processing and filtration, followed by production by DC casting of an ingot with a thickness of 500 mm and a width of 1200 mm. After machining off an average 10 mm thickness of the surface using a planer, the ingot was held with isothermal heating at 550°C for about 5 hours, after which the temperature was dropped to 400°C and rolling into a 2.7 mm-thick rolled plate was performed using a hot rolling machine. A heat treatment at 500°C was additionally carried out using a continuous annealing machine, followed by finishing into a 0.24 mm-thick aluminum sheet by cold rolling. This aluminum sheet was converted to a width of 1030 mm and then subjected on a continuous basis to the surface treatment shown below.

(a) Mechanical surface roughening treatment
A mechanical surface roughening was carried out using rotating roller-shaped nylon brushes; this was carried out while feeding a suspension of polishing agent (silica sand) with a specific gravity of 1.12 and water as a polishing slurry to the surface of the aluminum sheet. The average particle size in the polishing agent was 8 µm and the maximum particle size was 50 µm. The nylon brushes were nylon 6 · 10; the bristle length was 50 mm; and the bristle diameter was 0.3 mm. The bristles in a nylon brush were densely implanted in holes in a 300 mmφ stainless steel cylinder. Three rotating brushes were used. The gap between the two support rollers (200 mmφ) underneath a brush was 300 mm. The brush rollers were pressed down until the load on the drive motor rotating the brush reached +7 kW with respect to the load prior to the application of the brush roller to the aluminum sheet. The direction of brush rotation was the same as the transport direction of the aluminum sheet. The brushes were rotated at 200 rpm.
(b) Alkali etching treatment
The aluminum sheet yielded by the aforementioned mechanical surface roughening treatment was etched by spraying at 70°C with 2.6 mass% sodium hydroxide and 6.5 mass% aluminum ion. 6 g/m² of the aluminum sheet was dissolved. This was followed by a water rinse by spraying.
(c) Desmutting
Desmutting was carried out by spraying with a 1 mass% aqueous nitric acid solution (contained 0.5 mass% aluminum ion) at 30°C; this was followed by a water rinse by spraying. The aqueous nitric acid solution used for desmutting was the waste effluent from the electrochemical surface roughening that used alternating current in an aqueous nitric acid solution.
(d) Electrochemical surface roughening treatment
A continuous electrochemical surface roughening treatment was carried out using 60 Hz alternating voltage. The electrolyte solution was a 10 g/L aqueous nitric acid solution (contained 5 g/L aluminum ion and 0.007 mass% ammonium ion), and the temperature was 80°C. The current density was 30 A/dm² at the current peak value, and the amount of electricity was 130 C/dm² as the sum of the amount of the electricity when the aluminum sheet was operating as an anode. 5% of the current flowing from the power source was branched to an auxiliary anode. This was followed by a water rinse by spraying.
(e) Alkali etch
Etching was carried out at 32°C by spraying the aluminum sheet with 26 mass% sodium hydroxide and 6.5 mass% aluminum ion. 0.20 g/m² of the aluminum sheet was dissolved. This removed the smut component, which consisted mainly of aluminum hydroxide produced during the electrochemical surface roughening with alternating current that was carried out in the preceding stage, and also dissolved the edge region of the produced pits and thereby smoothed these edge regions. This was followed by a water rinse by spraying.
(f) Desmutting
Desmutting was carried out by spraying with a 60°C aqueous solution having a sulfuric acid concentration of 25 mass% (contained 0.5 mass% aluminum ion); this was followed by a water rinse by spraying.
(g) Anodic oxidation treatment
An anodic oxidation treatment was carried out using an anodic oxidation apparatus that employed a two-stage current feed electrolysis procedure (first and second electrolysis sections, length = 6 m each; first and second current feed sections, length = 3 m each; first and second current feed electrodes, length = 2.4 m each). Sulfuric acid was used for the electrolyte bath provided to the first and second electrolysis sections. The electrolyte bath had a sulfuric acid concentration in each case of 170 g/L (contained 0.5 mass% aluminum ion), and the temperature was 43°C. This was followed by a water rinse by spraying. The finished oxidation film quantity was 2.7 g/m².
(h) Treatment with alkali metal silicate
The aluminum support yielded by the anodic oxidation treatment was treated with alkali metal silicate (silicate treatment) by immersion for 10 seconds in a treatment tank that contained a 1 mass% aqueous solution of #3 sodium silicate at 30°C. This was followed by a water rinse by spraying.
(i) Undercoat layer formation
After the alkali metal silicate treatment, the aluminum support provided by the preceding sequence was coated with a coating bath having the composition given below and was dried for 15 seconds at 80°C.

< Undercoat bath composition >

Polymer compound given below 0.3 g
Methanol 100 g
Water 1 g

(j) Formation of the image recording layer (upper layer and lower layer)

The undercoat layer-bearing lithographic printing plate support was then coated with the lower layer coating bath with the composition given below so as to provide a post-drying coating rate of 0.85 g/m², followed by drying for 50 seconds at 140°C using a Perfect Oven PH200 from TABAI with the Wind Control set to 7. After this, the upper layer coating bath with the composition given below was applied so as to give a coating rate of 0.15 g/m², followed by drying at 120°C to yield a heat-sensitive lithographic printing plate. The quantity of the compound with general formula (I) or the comparative compound was adjusted by adjusting the drying time.

< The lower layer coating bath >

Compound with general formula (type and quantity (I) or comparative compound given in Table 4)
Polymer binder having the specific
structure, copolymer of N-(p-aminosulfonylphenyl)methacrylamide/acrylonitrile/methyl methacrylate
(monomer ratio = 36/34/30, weight-average
molecular weight = 50,000) 1.896 g
m,p-cresol novolac (m/p ratio = 6/4,
weight-average molecular weight = 4,500,
contained 0.8 mass% unreacted cresol) 0.237 g
Cyanine dye A with the following
structural formula 0.109 g
4,4'-bishydroxyphenylsulfone 0.063 g
Tetrahydrophthalic anhydride 0.190 g
p-toluenesulfonic acid 0.008 g
2-methoxy-4-(N-phenylamino)benzene
diazonium hexafluorophosphate 0.03 g
Ethyl Violet with the counterion modified
to 6-hydroxy-β-naphthalenesulfone 0.05 g
Fluorosurfactant (MEGAFACE F-176 from
DIC Corporation) 0.035 g
Methyl ethyl ketone 26.6 g
1-methoxy-2-propanol 13.6 g
γ-butyrolactone 13.8 g

< The upper layer coating bath >

m,p-cresol novolac (m/p ratio = 6/4,
weight-average molecular weight = 4,500,
contained 0.8 mass% unreacted cresol) 0.237 g
Cyanine dye A with the structural formula
given above 0.047 g
Dodecyl stearate 0.060 g
3-methoxy-4-diazodiphenylamine
hexafluorophosphate 0.030 g
Fluorosurfactant (MEGAFACE F-176,
DIC Corporation) 0.110 g
Fluorosurfactant (DEFENSA MCF-312,
30 mass% solids, DIC Corporation) 0.120 g
Methyl ethyl ketone 15.1 g
1-methoxy-2-propanol 7.7 g

Using GEOS-G(N) (DIC Corpotation) as the ordinary ink and Best Cure UV-BF-WRO standard black ink (T&K TOKA Company) as the UV ink, the scumming behavior and printing durability were evaluated as described in the following.

(Scumming behavior (residual color in nonimage areas))

With regard to whether residual color was present in the nonphotoexposed regions, the lithographic printing plate precursor was mounted after development in a Heidelberg SOR-M press; 50 sheets were printed; and the presence/absence of ink Scumming in the-nonphotoexposed regions was visually observed and evaluated as follows.

+ : No ink scumming
Δ : Problematic depending on the requirements

(Evaluation of the printing durability)

A high-quality paper was printed using a Heidelberg SOR-M press. The solid black image areas on the resulting printed material were inspected and the number of sheets was counted at which image areas that originally took up ink began to be patchy. A larger number of impressions is indicative of a better printing durability.

Table 4.

Example	Compound with general formula (I) or comparative compound	Content* (%)	Specific structural polymer binder	Ordinary ink		UV ink
Example	Compound with general formula (I) or comparative compound	Content* (%)	Specific structural polymer binder	Scumming behavior (residual color in nonimage areas)	Printing durability (x 1,000 sheets)	Scumming behavior (residual color in nonimage areas)	Printing durability (x 1,000 sheets)
Example 31	I-1	1.1	Given above	+	120	+	55
Example 32	I-1	0.08	Given above	+	110	+	50
Example 33	I-1	0.10	Given above	+	120	+	55
Example 34	I-1	3.0	Given above	+	120	+	55
Example 35	I-1	5.0	Given above	+	120	+	50
Example 36	I-2	1.2	Given above	+	120	+	55
Example 37	I-3	1.5	Given above	+	120	+	55
Example 38	I-1	1.1	(A)**	+	120	+	55
Example 39	I-1	1.1	(B)***	+	120	+	55
Comp. Example 13	I-1	0.008	Given above	Δ	100	Δ	50
Comp. Example 14	I-1	10.5	Given above	+	90	Δ	40
Comp. Example 15	C-1	1.0	Given above	Δ	100	Δ	45

* The content of the compound with general formula (I) or the comparative compound is the content with respect to the mass of the lower layer of the image recording layer.
** Polymer binder in which the N-(p-aminosulfonylphenyl)methacrylamide has been changed to 2-(N'-(4-sulfamoylphenyl)ureido)ethyl methacrylate.
*** Polymer binder in which the N-(p-aminosulfonylphenyl)methacrylamide has been changed to N-(4-sulfamoylphenyl)maleimide.

As may be understood from the results provided above, the lithographic printing plate precursor of the present invention can provide a lithographic printing plate that combines an excellent printing durability with an excellent antiscumming performance, and in particular the lithographic printing plate precursor of the present invention makes possible the heretofore difficult-to-achieve combination of printing durability with scumming prevention during printing with UV inks. Even when subjected to long-term storage under severe conditions, the lithographic printing plate precursor of the present invention can provide after platemaking a lithographic printing plate that achieves an excellent antiscumming performance. Moreover, the lithographic printing plate precursor of the present invention can realize an excellent on-press developability, and its on-press developability does not deteriorate even after storage.

Claims

A lithographic printing plate precursor having an image recording layer on an aluminum support, wherein the image recording layer contains from 0.01 to 10 mass% of a compound represented by the following general formula (I)
(in the formula, R¹ represents a C_2-10 organic substituent and R² to R⁷ each independently represent a hydrogen atom or a C_1-10 organic substituent).
The lithographic printing plate precursor of negative-working type according to claim 1, wherein the image recording layer additionally contains a polymerization initiator and a polymerizable compound.
The lithographic printing plate precursor of negative-working type according to claim 2, wherein the image recording layer additionally contains a photothermal conversion substance.
The lithographic printing plate precursor of positive-working type according to claim 1, wherein the image recording layer contains a polymer compound that is insoluble in water and soluble in an aqueous alkaline solution and the imagewise photoexposed region thereof becomes a nonimage area after development.
The lithographic printing plate precursor of positive-working type according to claim 4, wherein the polymer compound that is insoluble in water and soluble in an aqueous alkaline solution is a novolac resin.
The lithographic printing plate precursor of positive-working type according to claim 4 or 5, wherein the image recording layer additionally contains a photothermal conversion substance.
The lithographic printing plate precursor of negative-working type or positive-working type according to any of claims 1 to 6, wherein the image recording layer contains a polymer compound that has at least one structure selected from sulfonamide groups, maleimide groups, and urea structures.
The lithographic printing plate precursor of negative-working type or positive-working type according to any of claims 1 to 7, that has an intermediate layer and the image recording layer on an aluminum support in this order.