JP2024062746A - Lithographic printing plate precursor, method for preparing a lithographic printing plate, and lithographic printing method - Google Patents

Abstract

[Problem] To provide a lithographic printing plate precursor excellent in suppressing crystal precipitation, and to provide a method for producing a lithographic printing plate using the lithographic printing plate precursor, and a lithographic printing method. [Solution] A lithographic printing plate precursor having a support and an image recording layer on the support, the image recording layer containing a non-onium polymerization initiator, a borate compound, an infrared absorber, and compound A which is an onium salt consisting of a cation whose ShapeIndex is two times or less than the cation portion of the infrared absorber. [Selected Figure] None

Description

This disclosure relates to a lithographic printing plate precursor, a method for producing a lithographic printing plate, and a lithographic printing method.

Generally, a lithographic printing plate is composed of an oleophilic image area that accepts ink during the printing process and a hydrophilic non-image area that accepts dampening water. Lithographic printing utilizes the mutual repulsion properties of water and oil-based ink, making the oleophilic image area of the lithographic printing plate the ink-receptive area and the hydrophilic non-image area the dampening water-receptive area (ink non-receptive area) to create a difference in ink adhesion on the surface of the lithographic printing plate, and after ink is applied only to the image area, the ink is transferred to a printing material such as paper to print.
In order to prepare such a lithographic printing plate, a lithographic printing plate precursor (PS plate) having an oleophilic photosensitive resin layer (image recording layer) provided on a hydrophilic support has been widely used. Usually, the lithographic printing plate precursor is exposed through an original such as a lithographic film, and then the image area of the image recording layer is left, and the other unnecessary image recording layer is dissolved and removed with an alkaline developer or an organic solvent, and the hydrophilic support surface is exposed to form a non-image area, thereby obtaining a lithographic printing plate.

Furthermore, due to growing concern about the global environment, environmental issues related to waste liquids accompanying wet processing such as development processing have come into focus.
In response to the above environmental issues, efforts are being made to simplify development or plate making, or to eliminate any processing. One of the simple manufacturing methods is a method called "on-press development." In other words, after exposing a lithographic printing plate precursor to light, it is mounted on a printing press as is, without undergoing conventional development, and unnecessary parts of the image recording layer are removed at an early stage of the normal printing process.
In the present disclosure, a lithographic printing plate precursor that can be used for such on-press development is referred to as an "on-press development type lithographic printing plate precursor."

An example of a conventional lithographic printing plate precursor is described in Japanese Patent Laid-Open No. 2003-233996.
Patent Document 1 describes a lithographic printing plate precursor having a support, a photopolymerizable layer containing a polymerizable compound, a first infrared absorber having a specific structure, and a photopolymerization initiator, and a protective layer containing a second infrared absorber that contains a thermally decomposable group that is changed into a group that is a stronger electron donor upon exposure to heat and/or infrared radiation and that can form a printed image upon exposure to heat and/or infrared radiation.

International Publication No. 2021/259637

An object of one embodiment of the present disclosure is to provide a lithographic printing plate precursor that is excellent in inhibiting crystal precipitation.
Another problem to be solved by another embodiment of the present disclosure is to provide a method for producing a lithographic printing plate using the above-mentioned lithographic printing plate precursor, or a lithographic printing method.

Means for solving the above problems include the following aspects.
<1> A support and an image recording layer on the support,
The lithographic printing plate precursor, wherein the image recording layer comprises a non-onium polymerization initiator, a borate compound, an infrared absorber, and compound A which is an onium salt having a cation whose ShapeIndex is two or less times that of the cation moiety of the infrared absorber.
<2> The lithographic printing plate precursor according to <1>, wherein the cation in the compound A is a cation represented by the following formula (A):

In formula (A), Z represents P or N, and R ^A1 to R ^A4 each independently represent a hydrogen atom, an alkyl group or an aryl group.

<3> The lithographic printing plate precursor according to <1>, wherein the cation in compound A is a cation represented by the following formula (2):

In formula (2), R ²¹ each independently represents an alkyl group, and R ²² represents a hydrogen atom or an alkyl group.

<4> The lithographic printing plate precursor according to <1>, wherein the cation in compound A is a cation represented by the following formula (1):

In formula (1), Z represents P or N, R represents an alkyl group, and each Ar independently represents an aryl group.

<5> The lithographic printing plate precursor according to any one of <1> to <4>, wherein the cation in the compound A has a polymerizable group.

<6> The lithographic printing plate precursor according to any one of <1> to <4>, wherein the clogP of the cation in compound A is 0 or more and 10 or less.

<7> The lithographic printing plate precursor according to any one of <1> to <4>, wherein the anion in the compound A is a conjugate base of an organic acid.
<8> The lithographic printing plate precursor according ^to _any one of <1> to <4>, wherein the anion in Compound A is ^at least one anion selected from the group ^consisting of R ¹ SO ₃ ^- , R ¹ SO ₂ ^- , R ¹ R ² PO 2 ^- , R ^{1 PO 3 2 - , R 1} _CO ² _- ^, R 1 O ^- , R ¹ S - , (R ¹ SO ₂ ) ₂ N ^- , and R ¹ R ² R ³ R ⁴ B ^- .
Each of R ¹ to R ⁴ independently represents a hydrogen atom, an alkyl group, or an aryl group.
<9> The lithographic printing plate precursor according to any one of <1> to <4>, wherein the molar content of the cation in the compound A is 0.2 to 4 times the molar content of the anion in the borate compound.

<10> The lithographic printing plate precursor according to any one of <1> to <4>, wherein the non-onium polymerization initiator contains a compound represented by the following formula (II):

In formula (II), each X independently represents a halogen atom, and ^R3 represents an aryl group.

<11> The lithographic printing plate precursor according to any one of <1> to <4>, further comprising a protective layer on the image recording layer.
<12> The lithographic printing plate precursor according to <11>, wherein the protective layer contains a second infrared absorber that contains a thermally decomposable group that is converted into a group that is a stronger electron donor upon exposure to heat and/or infrared radiation and is capable of forming a printed image upon exposure to heat and/or infrared radiation.

<13> The lithographic printing plate precursor according to <12>, wherein the second infrared absorber is a compound represented by formula (VI).

In formula (VI), Ar ¹ and Ar ² each independently represent an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted benzene ring; W ¹ and W ² each independently represent a sulfur atom, an oxygen atom, or NR ^* ; R ^* represents an optionally substituted alkyl group, NH, or a -CM ¹⁰ M ¹¹ group; M ¹⁰ and M ¹¹ each independently represent an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl group or heteroaryl group; M ¹ and M ² each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, or a group of atoms necessary for M ¹ and M ² to form together an optionally substituted cyclic structure; M ³ and M ⁴ each independently represent an optionally substituted aliphatic hydrocarbon group; M ⁵ to M ⁸ each independently represent a hydrogen atom, a halogen atom, or an optionally substituted aliphatic hydrocarbon group; M ⁹ is a group that is converted by a chemical reaction induced by exposure to infrared light or heat into a group that is a stronger electron donor than ^M9 , and that increases the integrated optical absorbance of the compound of formula (VI) between 350 nm and 700 nm, and optionally has one or more counter ions to obtain an electrically neutral compound.

<14> A step of imagewise exposing the lithographic printing plate precursor according to any one of <1> to <4>;
and removing the image recording layer in the non-image area by supplying at least one selected from the group consisting of printing ink and dampening water on the printing press.

<15> A step of imagewise exposing the lithographic printing plate precursor according to any one of <1> to <4>;
a step of removing the image recording layer in the non-image area by supplying at least one selected from the group consisting of printing ink and dampening water on a printing press to prepare a lithographic printing plate;
and printing with the obtained lithographic printing plate.

According to one embodiment of the present disclosure, a lithographic printing plate precursor having excellent suppression of crystal precipitation can be provided.
According to another embodiment of the present disclosure, it is possible to provide a method for producing a lithographic printing plate using the above-mentioned lithographic printing plate precursor, or a lithographic printing method.

1 is a graph showing an example of an alternating current waveform used in electrochemical graining treatment in a method for producing an aluminum support having an anodized film. FIG. 2 is a side view showing an example of a radial cell in an electrochemical graining treatment using an alternating current in a method for producing an aluminum support having an anodized film. FIG. 2 is a side view showing the concept of a brush graining step used in a mechanical roughening treatment in a method for producing an aluminum support having an anodized film. FIG. 1 is a schematic diagram of an anodizing treatment apparatus used in an anodizing treatment in a method for producing an aluminum support having an anodized coating.

The contents of the present disclosure will be described in detail below. The following description of the components may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment.
In this specification, the use of "to" indicating a range of values means that the values before and after it are included as the lower limit and upper limit.
In addition, in the description of groups (atomic groups) in this specification, descriptions that do not indicate whether they are substituted or unsubstituted include those that have no substituents as well as those that have a substituent. For example, an "alkyl group" includes not only an alkyl group that has no substituents (unsubstituted alkyl groups) but also an alkyl group that has a substituent (substituted alkyl groups).
In this specification, "(meth)acrylic" is a term used as a concept including both acrylic and methacrylic, and "(meth)acryloyl" is a term used as a concept including both acryloyl and methacryloyl.
In addition, the term "process" in this specification includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.
In the present disclosure, "mass %" and "weight %" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
Unless otherwise specified, the measurements of each physical property are carried out at 25°C.
Unless otherwise specified, each component in a composition or each structural unit in a polymer in the present disclosure may be contained alone or in combination of two or more types.
Furthermore, in the present disclosure, the amount of each component in a composition or each structural unit in a polymer means, when a plurality of substances or structural units corresponding to each component or each structural unit in a polymer are present in the composition, the total amount of the corresponding plurality of substances present in the composition or the corresponding plurality of structural units present in the polymer, unless otherwise specified.
Furthermore, in the present disclosure, combinations of two or more preferred aspects are more preferred aspects.
In addition, unless otherwise specified, the weight average molecular weight (Mw) and number average molecular weight (Mn) in the present disclosure are molecular weights detected by a gel permeation chromatography (GPC) analyzer using columns of TSKgel GMHxL, TSKgel G4000HxL, or TSKgel G2000HxL (all product names manufactured by Tosoh Corporation) in a differential refractometer using THF (tetrahydrofuran) as a solvent, and converted using polystyrene as a standard substance.
In the present disclosure, the term "lithographic printing plate precursor" includes not only lithographic printing plate precursors but also throwaway plate precursors. Furthermore, the term "lithographic printing plate" includes not only lithographic printing plates prepared by subjecting a lithographic printing plate precursor to operations such as exposure and development as necessary, but also throwaway plates. In the case of a throwaway plate precursor, the operations of exposure and development are not necessarily required. Note that a throwaway plate is a lithographic printing plate precursor that is attached to an unused plate cylinder when, for example, a portion of the page is printed in one color or two colors in color newspaper printing.
In the present disclosure, "excellent printing durability" refers to a large number of printable sheets of a lithographic printing plate.
The present disclosure will be described in detail below.

(Lithographic printing plate precursor)
The lithographic printing plate precursor according to the present disclosure has a support and an image recording layer on the support, and the image recording layer contains a non-onium polymerization initiator, a borate compound, an infrared absorber, and compound A which is an onium salt consisting of a cation having a ShapeIndex that is no more than twice that of the cation moiety of the infrared absorber.
Furthermore, the lithographic printing plate precursor according to the present disclosure is suitably used as an on-press development type lithographic printing plate precursor.

As a result of investigations, the present inventors have found that in a lithographic printing plate precursor in which an image-forming layer contains a borate compound and an infrared absorber, precipitation of crystals resulting from the borate compound and the infrared absorber may be observed.
The lithographic printing plate precursor according to the present disclosure has an image recording layer that contains a non-onium polymerization initiator, a borate compound, an infrared absorber, and compound A, which is an onium salt consisting of a cation whose Shape Index is two times or less than that of the cation portion of the infrared absorber. It is presumed that compound A can weaken the interaction between the borate compound and the infrared absorber used in combination in the image forming layer, and as a result, can suppress crystal precipitation caused by the borate compound and the infrared absorber. Therefore, the lithographic printing plate precursor according to the present disclosure has excellent suppression of crystal precipitation.

The details of each component of the lithographic printing plate precursor according to this disclosure are described below.

<Image Recording Layer>
The image recording layer contains a non-onium polymerization initiator, a borate compound, an infrared absorbing agent, and compound A which is an onium salt having a cation whose Shape Index is two or less times that of the cation portion of the infrared absorbing agent.
The image recording layer is preferably a negative type image recording layer, and more preferably a water-soluble or water-dispersible negative type image recording layer.
In the planographic printing plate precursor according to the present disclosure, from the viewpoint of on-press developability, the unexposed areas of the image recording layer are preferably removable with at least one of fountain solution and printing ink.

The components contained in the image recording layer are described in detail below.

[Compound A]
The image recording layer contains compound A. Compound A is an onium salt made of a cation having a ShapeIndex of not more than twice that of the cation portion of the infrared absorbing agent.
In the present disclosure, the infrared absorbing agent may be a salt of a cation and an anion, or a compound having a betaine structure, and both are referred to as the "cation moiety."
In addition, compound A is an onium salt consisting of an onium cation and an anion, the Shape Index of which is two times or less than that of the cation part of the infrared absorber. In other words, the infrared absorber and compound A in the present disclosure satisfy a relationship in which, when the Shape Index of the cation part of the infrared absorber is "S _I " and the Shape Index of the cation of compound A is "S _A ", the ratio (S _A /S _I ) is less than 2.

Furthermore, compound A is preferably a compound that does not have polymerization initiation ability.
The Shape Index in this disclosure is a molecular shape index, and is calculated by the following method.
The ShapeIndex is calculated using DataWarrior, an open source program provided by openmolecules.org, version 5.5.0.
Specifically, for a two-dimensional molecular graph structure consisting of atoms other than hydrogen atoms in a molecule, two atoms having the longest topological distance are determined.
The length of the shortest chain connecting these two atoms is longer than any other pair of atoms.
The ShapeIndex is calculated by dividing the number of atoms in the shortest chain connecting the two atoms by the total number of atoms in the molecule.
Therefore, for a completely linear compound, the ShapeIndex is 1.0, and the value decreases as the number of rings or branches in the molecule increases.

The value of the ratio (S _A /S _I ) may be less than 2.0, but is preferably 1.8 or less, and from the viewpoint of printing durability, is more preferably 1.5 or less, and further preferably 1.0 or less.

The Shape Index of the cation of compound A is, for example, 0.90 or less. From the viewpoint of suppressing crystal precipitation, the Shape Index is preferably less than 0.75, more preferably 0.70 or less, even more preferably 0.60 or less, and particularly preferably equal to or less than the Shape Index of the cation moiety of the infrared absorber.
The lower limit of the Shape Index of the cation of compound A is, for example, 0.20 or more, and from the viewpoint of being close to the Shape Index of the borate compound, it is preferably 0.3 or more.
That is, from the viewpoint of satisfying the above ratio (S _A /S _I ) value and being close to the Shape Index of the borate compound, the Shape Index of the cation of compound A is preferably 0.20 to 0.90, more preferably 0.20 to 0.70, and even more preferably 0.30 to 0.70.

From the viewpoint of printing durability and on-press developability, the clogP of the cation in compound A is preferably from -10 to 20, more preferably from -5 to 15, even more preferably from 0 to 10, and particularly preferably from 2 to 8.

In the present disclosure, clogP is calculated by the following method.
DataWarrior (an open source program provided by openmolecules.org) version 5.5.0 is used to calculate clogP, the calculated logarithm of the partition coefficient between n-octanol and water, log(Coctanol/Cwater).

The compound A is not particularly limited as long as it is an onium salt consisting of a cation whose ShapeIndex is twice or less than that of the cation portion of the infrared absorber. From the viewpoint of inhibiting crystal precipitation, however, it is preferably an ammonium salt compound, a phosphonium salt compound, a sulfonium salt compound, or a sulfoxonium salt compound, more preferably an ammonium salt compound, a phosphonium salt compound, or a sulfonium salt compound, further preferably an ammonium salt compound or a phosphonium salt compound, and particularly preferably a phosphonium salt compound.
From the viewpoint of inhibiting crystal precipitation, the phosphonium salt compound is preferably a quaternary phosphonium salt compound, and more preferably a monoalkyltriarylphosphonium salt compound.
From the viewpoint of suppressing crystal precipitation, the ammonium salt compound is preferably a quaternary ammonium salt compound, and more preferably a monoalkyltriarylammonium salt compound.
From the viewpoint of suppressing crystal precipitation, the sulfonium salt compound is preferably a tertiary sulfonium salt compound, and more preferably a monoalkyldiarylsulfonium salt compound.
From the viewpoint of suppressing crystal precipitation, the sulfoxonium salt compound is preferably a trialkylsulfoxonium salt compound.
In addition, the central element of the cation of compound A and the central element of the cation moiety of the infrared absorber are preferably different elements.

The anion contained in compound A may be a monovalent anion or a divalent or higher polyvalent anion, but is preferably a monovalent anion from the viewpoint of suppressing crystal precipitation.
The anion contained in compound A is not particularly limited, but from the viewpoint of suppressing crystal precipitation, it is preferably at least one anion selected from the group consisting of a halide ion, a tetrafluoroborate anion, a hexafluorophosphate anion, a benzenesulfonate anion, a 1-naphthalenesulfonate anion, a 2-naphthalenesulfonate anion, a benzoate anion, a phenylphosphate anion, a phenol anion, a thiophenol anion, a tetraphenylborate anion, and a tosylate anion, more preferably at least one anion selected from the group consisting of a bromide ion, an iodide ion, a tetrafluoroborate anion, and a tosylate anion, further preferably a bromide ion or a tetrafluoroborate ion, and particularly preferably a bromide ion.
From the viewpoints of suppressing crystal precipitation and compound stability over time, the anion contained in compound A is preferably at least one anion selected from the group consisting of bromide ion, iodide ion, tetrafluoroborate anion, benzenesulfonate anion, 1-naphthalenesulfonate anion, 2-naphthalenesulfonate anion, benzoate anion, phenylphosphate anion, and tosylate anion, more preferably at least one anion selected from the group consisting of benzenesulfonate anion, 1-naphthalenesulfonate anion, 2-naphthalenesulfonate anion, and tosylate anion, and particularly preferably at least one anion selected from the group consisting of 1-naphthalenesulfonate anion and tosylate anion.

In addition, the anion contained in compound A is preferably a conjugate base of an organic acid, more preferably a conjugate base of an organic carboxylic acid or an organic sulfonic acid, further preferably a conjugate base of an organic sulfonic acid, and particularly preferably a conjugate base of an aromatic sulfonic acid, from the viewpoints of suppressing crystal precipitation and compound stability over time.
Furthermore, from the viewpoint of suppressing crystal precipitation and compound stability over time, the anion contained in compound A is preferably at least one anion selected from the group consisting of R ¹ SO ₃ ^- , R ¹ SO ₂ ^- , R ¹ R ² PO ₂ ^- , R ¹ PO ₃ ^2- , R ¹ CO ₂ ^- , R ¹ O ^- , R ¹ S ^- , (R ¹ SO ₂ ) ₂ N ^- , and R ¹ R ² R ³ R ⁴ B ^-, more preferably at least one anion selected from the group consisting of R ¹ SO ₃ ^- , R ¹ SO ₂ ^- , R ¹ R ² PO ₂ ^- , R ¹ PO ₃ ^2- , and R ¹ CO ₂ ^-, and particularly preferably R ¹ SO ₃ ^- .
Each of R ¹ to R ⁴ independently represents a hydrogen atom, an alkyl group, or an aryl group.

In addition, from the viewpoint of suppressing crystal precipitation, the anion possessed by compound A is preferably an anion whose conjugate acid has a pKa of 4 or less, and more preferably an anion whose conjugate acid has a pKa of 0 or less.

From the viewpoint of suppressing crystal precipitation, the cation in the above compound A is preferably a cation represented by the following formula (A):

In formula (A), Z represents P or N, and R ^A1 to R ^A4 each independently represent a hydrogen atom, an alkyl group or an aryl group.

In the formula (A), Z is preferably P from the viewpoint of suppressing crystal precipitation.
From the viewpoint of suppressing crystal precipitation, the alkyl group in R ^A1 to R ^A4 in formula (A) is preferably an alkyl group having 1 to 16 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, and particularly preferably an alkyl group having 1 to 8 carbon atoms. In addition, the alkyl group may be a linear alkyl group, a branched alkyl group, or an alkyl group having a ring structure.
The alkyl group may have a substituent. Examples of the substituent include a halogen atom, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a vinyl ether group, an acyl group, an acyloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, a vinyloxycarbonyl group, a (meth)acryloxy group, and a (meth)acrylamide group. The substituent may be further substituted with the above-mentioned substituent.
From the viewpoint of suppressing crystal precipitation, the aryl groups in R ^A1 to R ^A4 in formula (A) are each preferably a phenyl group or a 2,4,6-trimethylphenyl group, and more preferably a phenyl group.
The aryl group may have a substituent. Examples of the substituent include a halogen atom, an alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, an acyl group, an acyloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, a vinyloxycarbonyl group, a (meth)acryloxy group, and a (meth)acrylamide group. The substituent may be further substituted with the above-mentioned substituent.

In addition, from the viewpoint of suppressing crystal precipitation, it is more preferable that the cation in compound A is a cation represented by the following formula (1).

In formula (1), Z represents P or N, R represents an alkyl group, and each Ar independently represents an aryl group.

In the formula (1), Z is preferably P from the viewpoint of suppressing crystal precipitation.
From the viewpoint of suppressing crystal precipitation, R in formula (1) is preferably an alkyl group having 1 to 16 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, and particularly preferably an alkyl group having 1 to 8 carbon atoms. In addition, the alkyl group may be a linear alkyl group, a branched alkyl group, or an alkyl group having a ring structure.
The alkyl group may have a substituent. Examples of the substituent include a halogen atom, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a vinyl ether group, an acyl group, an acyloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, a vinyloxycarbonyl group, a (meth)acryloxy group, and a (meth)acrylamide group. The substituent may be further substituted with the above-mentioned substituent.
In the formula (1), each Ar is preferably a phenyl group or a 2,4,6-trimethylphenyl group, and more preferably a phenyl group, from the viewpoint of suppressing crystal precipitation.
The aryl group may have a substituent, such as a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an acyl group, or an acyloxy group.

Furthermore, from the viewpoints of suppressing crystal precipitation and solubility in a coating solvent, it is more preferable that the cation in the compound A is a cation represented by the following formula (2).

In formula (2), R ²¹ each independently represents an alkyl group, and R ²² represents a hydrogen atom or an alkyl group.

In the formula (2), from the viewpoints of suppressing crystal precipitation and solubility in a coating solvent, R ²¹ is preferably an alkyl group having 1 to 16 carbon atoms, more preferably a branched alkyl group having 3 to 12 carbon atoms, even more preferably a branched alkyl group having 3 to 8 carbon atoms, and particularly preferably a t-butyl group.
In addition, the three R ²¹ in formula (2) are preferably the same group from the viewpoints of suppressing crystal precipitation and solubility in a coating solvent.
In the formula (2), from the viewpoint of suppressing crystal precipitation and solubility in a coating solvent, R ²² is preferably a hydrogen atom or an alkyl group having 1 to 16 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, still more preferably a hydrogen atom, a methyl group, or an ethyl group, and particularly preferably a hydrogen atom.
The alkyl groups in ^R21 and ^R22 may have a substituent. Examples of the substituent include a halogen atom, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a vinyl ether group, an acyl group, an acyloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, a vinyloxycarbonyl group, a (meth)acryloxy group, and a (meth)acrylamide group. The substituent may be further substituted with the above-mentioned substituent.

The cation in the compound A preferably has a polymerizable group from the viewpoints of suppressing crystal precipitation, curability, and solubility in a coating solvent.
The polymerizable group is preferably an ethylenically unsaturated group, and preferred examples thereof include a (meth)acryloxy group, a (meth)acrylamide group, an allyl group, a styryl group, a vinyl ether group, and a vinyl ester group.
Among these, from the viewpoints of suppression of crystal precipitation, curability, and solubility in a coating solvent, it is preferable that the group be at least one type of group selected from the group consisting of a (meth)acryloxy group and a (meth)acrylamide group, and it is more preferable that the group be a (meth)acryloxy group.
In addition, preferred examples of the cation having a polymerizable group include cations obtained by subjecting a compound in which a hydrogen atom is directly bonded to a phosphorus atom or a nitrogen atom to a Michael-type addition reaction with a polymerizable compound (preferably a (meth)acrylic compound, more preferably a (meth)acrylate compound) described below.
Furthermore, the polymerizable compound is preferably a polyfunctional (meth)acrylic compound, and more preferably a polyfunctional (meth)acrylate compound.

Specific examples of the cation that forms compound A include, but are not limited to, the following cations:
In addition, specific examples of compound A preferably include onium salts of any one of the following D1 to D24 and D29 to D31 and one anion selected from the group consisting of a halide ion, a tetrafluoroborate anion, a hexafluorophosphate anion, a benzenesulfonate anion, a 1-naphthalenesulfonate anion, a 2-naphthalenesulfonate anion, a benzoate anion, a phenylphosphate anion, a phenol anion, a thiophenol anion, a tetraphenylborate anion, and a tosylate anion.

The compound A may be added alone or in combination of two or more kinds.
From the viewpoint of suppressing crystal precipitation, the content of compound A is preferably 0.01% by mass to 30% by mass, more preferably 0.05% by mass to 25% by mass, and even more preferably 0.1% by mass to 20% by mass, based on the total mass of the image recording layer.
From the viewpoint of suppressing crystal precipitation, the content of compound A per unit area of the image recording layer is preferably 0.001 g/m ² to 3 g/m ² , more preferably 0.005 g/m ² to 1 g/m ² , even more preferably 0.01 g/m ² to 0.1 g/m ² , and particularly preferably 0.01 g/m ² to 0.05 g/m ² .

In the image recording layer, from the viewpoints of suppressing crystal precipitation and printing durability, the molar content of the cation in compound A is preferably 0.1 to 5 times the molar content of the anion in the borate compound, more preferably 0.2 to 4 times the molar content of the anion in the borate compound, and particularly preferably 0.5 to 3 times the molar content of the anion in the borate compound.

[Non-onium-based polymerization initiator]
The image-recording layer contains a non-onium polymerization initiator.
The non-onium polymerization initiator means a polymerization initiator other than an onium polymerization initiator. Specifically, the non-onium polymerization initiator means a compound other than an onium salt compound that generates a polymerization initiation species such as a radical by accepting one electron through intermolecular electron transfer when an electron of an infrared absorber is excited by exposure to infrared light.

As the non-onium polymerization initiator, known non-onium polymerization initiators used in the image recording layer of a lithographic printing plate precursor can be suitably used.
The non-onium polymerization initiator preferably contains an electron-donating polymerization initiator from the viewpoints of sensitivity, printing durability, on-press developability, and ink receptivity.

From the viewpoints of developability and printing durability, it is preferable that the non-onium polymerization initiator contains a compound represented by the following formula (II) as an electron donating polymerization initiator.

In formula (II), each X independently represents a halogen atom, and ^R3 represents an aryl group.

Specific examples of X in formula (II) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a chlorine atom or a bromine atom is preferred as X because of its excellent sensitivity, and a bromine atom is particularly preferred.
In formula (II), specific examples of ^R3 include a phenyl group and a naphthyl group. Substituents of the aryl group represented by ^R3 include a halogen atom, a hydroxy group, an amide group, an amino group, a cyano group, an alkyl group, and an alkoxy group. Among these, a hydroxy group is preferred as the substituent. A phenyl group substituted with a hydroxy group is preferred as ^R3 .

Specific examples of the electron-accepting polymerization initiator represented by the above formula (II) include those described in WO 2020/262692.

The lowest unoccupied molecular orbital (LUMO) of the electron-accepting polymerization initiator as the non-onium polymerization initiator is preferably −3.00 eV or less, and more preferably −3.02 eV or less, from the viewpoint of improving sensitivity.
The lower limit is preferably −3.80 eV or more, and more preferably −3.60 eV or more.

In the present disclosure, the MO (molecular orbital) energy calculations of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are performed by the following method.
First, free counter ions in the target compound are excluded from the calculation. For example, counter anions are excluded from the calculation in the case of cationic infrared absorbers, and counter cations are excluded from the calculation in the case of anionic borate compounds. "Free" here means that the target compound and its counter ion are not linked by a covalent bond.
The quantum chemical calculation software Gaussian 16 is used, and structural optimization is performed by DFT (B3LYP/6-31G(d)).
The MO energy calculation is performed using the quantum chemistry calculation software Gaussian 16 with the optimal structure obtained by the above structure optimization, and DFT (B3LYP/6-31+G(d,p)/PCM (solvent=methanol)). Note that, for compounds containing iodine, calculations are performed under DFT (B3LYP/DGDZVP/PCM (solvent=methanol)) conditions.
The term "optimal structure" used here means the structure with the most stable total energy obtained by DFT calculation. The most stable structure can be found by repeating structural optimization as necessary.
The MO energy Ebare (unit: heartree) obtained in the above MO energy calculation is converted to Escaled (unit: eV) used as the HOMO and LUMO values in this disclosure by the following formula.
[HOMO calculation formula] Escaled = 0.823168 x 27.2114 x Ebare - 1.07634
[LUMO calculation formula] Escaled = 0.820139 x 27.2114 x Ebare - 1.086039
Note that 27.2114 is simply a coefficient for converting Hartree to eV, and 0.823168 and −1.07634 used in calculating the HOMO, and 0.820139 and −1.086039 used in calculating the LUMO are adjustment coefficients determined so that the calculated HOMO and LUMO of the compound to be calculated match the actually measured values.

The non-onium polymerization initiators may be used alone or in combination of two or more kinds.
The content of the non-onium polymerization initiator is preferably from 0.1% by mass to 50% by mass, more preferably from 0.5% by mass to 30% by mass, and particularly preferably from 0.8% by mass to 20% by mass, based on the total mass of the image recording layer.

[Borate Compounds]
The image recording layer contains a borate compound.
As the borate compound, a tetraarylborate compound or a monoalkyltriarylborate compound is preferable, and from the viewpoint of the stability of the compound, a tetraarylborate compound is more preferable, and a tetraphenylborate compound is particularly preferable.
The counter cation of the borate compound is not particularly limited, but is preferably an alkali metal ion or a tetraalkylammonium ion, and more preferably a sodium ion, a potassium ion, or a tetrabutylammonium ion.
The counter cation of the borate compound may be the cation moiety of the infrared absorbing agent.

A specific example of a preferred borate compound is sodium tetraphenylborate.

From the viewpoints of chemical resistance and printing durability, the highest occupied molecular orbital (HOMO) of the borate compound is preferably −6.00 eV or more, more preferably −5.95 eV or more, even more preferably −5.93 eV or more, and particularly preferably greater than −5.90 eV.
The upper limit is preferably −5.00 eV or less, and more preferably −5.40 eV or less.

Specific examples of preferred borate compounds include the electron-donating polymerization initiators described in WO 2020/262692.

Moreover, it is more preferable that the HOMO value of the HOMO-borate compound of the infrared absorbing agent in the image recording layer is 0.70 eV or less.

The borate compounds may be added either alone or in combination of two or more.
The content of the borate compound is preferably from 0.01 to 30% by mass, more preferably from 0.05 to 25% by mass, and even more preferably from 0.1 to 20% by mass, based on the total mass of the image recording layer.

[Infrared absorbing agent]
The image recording layer contains an infrared absorbing agent.
The infrared absorbing agent is not particularly limited as long as it has a cationic moiety in the molecule, and examples thereof include pigments and dyes.

The ShapeIndex of the cationic portion of the infrared absorber is, for example, preferably 0.2 to 0.8, and more preferably 0.3 to 0.6.

Dyes that can be used as infrared absorbents include commercially available dyes and known dyes that have a cationic moiety in the molecule, such as those described in literature such as "Dye Handbook" (edited by the Society of Organic Synthesis Chemistry, published in 1970). Specific examples include azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts, and metal thiolate complex dyes.

Among infrared absorbing agents, cyanine dyes that have a cationic portion and an anionic portion in the molecule are particularly preferred.

Specific examples of the cyanine dye include the compounds described in paragraphs 0017 to 0019 of JP-A-2001-133969, paragraphs 0016 to 0021 of JP-A-2002-023360, and paragraphs 0012 to 0037 of JP-A-2002-040638, preferably the compounds described in paragraphs 0034 to 0041 of JP-A-2002-278057 and paragraphs 0080 to 0086 of JP-A-2008-195018, particularly preferably the compounds described in paragraphs 0035 to 0043 of JP-A-2007-90850, and the compounds described in paragraphs 0105 to 0113 of JP-A-2012-206495.
In addition, the compounds described in paragraphs 0008 to 0009 of JP-A No. 5-5005 and paragraphs 0022 to 0025 of JP-A No. 2001-222101 can also be preferably used.
As the pigment, the compounds described in paragraphs 0072 to 0076 of JP-A-2008-195018 are preferred.

In addition, as long as the infrared absorbing agent has a cationic portion in the molecule, for example, an infrared absorbing agent that decomposes upon exposure to infrared rays (decomposable infrared absorbing agent) can also be used.
It is presumed that by using a decomposable infrared absorber as the infrared absorber, the infrared absorber or its decomposition products promote polymerization, and further, the decomposition products of the infrared absorber interact with the polymerizable compound, resulting in excellent printing durability.
The decomposable infrared absorbent is preferably an infrared absorbent that has the function of absorbing infrared rays, decomposing, and developing color when exposed to infrared rays.
Hereinafter, the colored compound formed by the decomposable infrared absorber absorbing infrared light and decomposing when exposed to infrared light is also referred to as a "colored body of the decomposable infrared absorber."
The decomposable infrared absorbent preferably has a function of absorbing infrared rays upon exposure to infrared rays and converting the absorbed infrared rays into heat.
The decomposable infrared absorbent may be one that absorbs and decomposes at least a part of light in the infrared wavelength region (wavelength 750 nm to 1 mm), but is preferably an infrared absorbent having a maximum absorption wavelength in the wavelength region of 750 nm to 1,400 nm, and more preferably an infrared absorbent having a maximum absorption wavelength in the wavelength region of 760 nm to 900 nm.
More specifically, the decomposable infrared absorbent is preferably a compound that decomposes upon exposure to infrared light to produce a compound having a maximum absorption wavelength in the wavelength range of 500 nm to 600 nm.

The decomposable infrared absorber is preferably an infrared absorber that decomposes due to heat, electron transfer, or both caused by infrared exposure, and more preferably an infrared absorber that decomposes due to electron transfer caused by infrared exposure. Here, "decomposes due to electron transfer" means that electrons excited from the HOMO (highest occupied molecular orbital) of the decomposable infrared absorber to the LUMO (lowest unoccupied molecular orbital) by infrared exposure transfer intramolecularly to an electron accepting group (a group with a potential close to that of the LUMO) within the molecule, resulting in decomposition.

In addition, as the infrared absorbent and the infrared absorbent that decomposes upon exposure to infrared light, those described in WO 2020/262692 can be suitably used.
Furthermore, as the infrared absorbent that decomposes upon exposure to infrared rays, those described in JP-A-2008-544322 or WO 2016/027886 can be suitably used.
In addition, as the cyanine dye which is a decomposable infrared absorber, the infrared absorbing compounds described in WO 2019/219560 can be suitably used.

Moreover, the highest occupied molecular orbital (HOMO) value of the infrared absorber used in the present disclosure is preferably −5.00 eV or less, and more preferably −5.30 eV or less, from the viewpoints of printing durability and halftone dot reproducibility.
From the viewpoints of printing durability and dot reproducibility, the lower limit is preferably −5.90 eV or more, more preferably −5.75 eV or more, and even more preferably −5.60 eV or more.

The infrared absorbing agent may be used alone or in combination of two or more kinds. Also, a pigment and a dye may be used in combination as the infrared absorbing agent.
The total content of the infrared absorbing agent in the image recording layer is preferably from 0.1% by mass to 10.0% by mass, and more preferably from 0.5% by mass to 5.0% by mass, based on the total mass of the image recording layer.

A preferred embodiment of the present disclosure includes a compound in which an infrared absorbing agent (preferably a cyanine dye) and a borate compound form a salt. Specific examples of the compound in which an infrared absorbing agent and a borate compound form a salt include salts of a cation portion of an infrared absorbing agent (preferably a cyanine dye) and a borate anion (e.g., a tetraphenylborate anion).
When a compound containing a cationic portion of an infrared absorbing agent and a borate anion is used (that is, when a compound forming the above-mentioned salt is used), the image recording layer contains both the infrared absorbing agent and the borate compound.
Furthermore, the compound in which an infrared absorbing agent and a borate compound form a salt may be used in combination with another infrared absorbing agent or another borate compound.

[Relationship between infrared absorber, borate compound, and non-onium polymerization initiator]
In the image recording layer of the present disclosure, it is preferable that the HOMO of the borate compound is −6.0 eV or more, and the LUMO of the non-onium polymerization initiator is −3.0 eV or less.
More preferred embodiments of the HOMO of the borate compound and the LUMO of the non-onium polymerization initiator are as described above.
In the image recording layer of the present disclosure, it is presumed that energy is transferred between the borate compound, the infrared absorbing agent, and the non-onium polymerization initiator.
Therefore, if the HOMO of the borate compound is −6.0 eV or more and the LUMO of the non-onium polymerization initiator is −3.0 eV or less, it is considered that the efficiency of radical generation is improved, and therefore the chemical resistance and printing durability are more likely to be excellent.

From the viewpoints of printing durability and chemical resistance, the HOMO value of the infrared absorber-borate compound is preferably 1.0 eV or less, more preferably 0.70 eV or less, and particularly preferably 0.60 eV or less. From the same viewpoint, the HOMO value of the infrared absorber-borate compound is preferably -0.200 eV or more, more preferably -0.100 eV or more. A negative value means that the HOMO of the borate compound is higher than the HOMO of the infrared absorber.
From the viewpoints of printing durability and chemical resistance, the LUMO value of the LUMO-infrared absorber of the non-onium polymerization initiator is preferably 1.00 eV or less, and more preferably 0.700 eV or less. From the same viewpoint, the LUMO value of the LUMO-infrared absorber of the non-onium polymerization initiator is preferably -0.200 eV or more, and more preferably -0.100 eV or more.
From the same viewpoint, the value of LUMO of the non-onium polymerization initiator minus LUMO of the infrared absorber is preferably 1.00 eV to -0.200 eV, and more preferably 0.700 eV to -0.100 eV. Note that a negative value means that the LUMO of the infrared absorber is higher than the LUMO of the non-onium polymerization initiator.

[Acid color former]
From the viewpoint of visibility, the image recording layer may contain an acid color former.
The term "acid color former" used in the present disclosure means a compound that has the property of developing color and changing the color of the image recording layer when heated in a state in which it accepts an electron-accepting compound (e.g., a proton of an acid, etc.). As the acid color former, in particular, a colorless compound having a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, etc., which quickly opens or cleaves the partial skeleton when it comes into contact with an electron-accepting compound is preferred.

From the viewpoint of UV printing durability, the hydrogen abstraction enthalpy of all hydrogen atoms present in the molecule of the acid color former is preferably −6.5 kcal/mol or more, more preferably −4.0 kcal/mol or more, even more preferably −2.0 kcal/mol or more, and particularly preferably −2.0 kcal/mol to 50 kcal/mol.
The larger the hydrogen abstraction enthalpy, the more the abstraction of hydrogen atoms from the acid color former by polymerization initiating species such as radicals is suppressed, and the longer the polymerization reaction takes place, resulting in excellent curability and printing durability, particularly UV printing durability.

The hydrogen abstraction enthalpy of all hydrogen atoms present in the molecule of the acid color former in the present disclosure is calculated by the following method.
The calculation program used is Gaussian 16, the calculation level is density functional theory (B3LYP/6-31+G**), and the solvent effect is the SCRF method (solvent: methanol). The enthalpy of the reactant and the product are calculated for the reaction with the growing radical by hydrogen abstraction, and the reaction enthalpy is calculated by taking the difference between the two.

More specifically, the method is carried out as follows. In the following chemical reaction formula, the growing radical, LeucoDye-H, the hydrogenated growing radical, and LeucoDye-radical are each modeled using GaussView6, a pre-post software for Gaussian. The calculation conditions are specified as follows: #p opt b3lyp/6-31+g(d,p) scrf=(solvent=methanol, and the charge is set to 0 and multiplicity to 2 for radicals and 0 and multiplicity to 1 for non-radicals. The #p specification is for detailed log output and may be omitted.
The formation enthalpy of the reactant (the sum of the energies of the growing radical and LeucoDye-H) and the formation enthalpy of the product (the sum of the energies of the hydrogen-added growing radical and LeucoDye-radical) are calculated from the energy (unit: heartree) of the optimized structure by performing calculations, and the value obtained by subtracting the formation enthalpy of the reactant from the formation enthalpy of the product is regarded as the hydrogen abstraction enthalpy. The unit is converted as 1 heartree = 627.51 kcal/mol.

For example, the hydrogen abstraction enthalpy for each hydrogen atom in the following compound is:

From the viewpoint of UV printing durability, it is preferable that the acid color former does not have a structure in which a hydrogen atom is directly bonded to a nitrogen atom.
A structure in which a hydrogen atom is directly bonded to a nitrogen atom (N-H structure) is a structure in which a hydrogen abstraction reaction by a radical or the like is likely to occur. A compound that does not have this structure suppresses the abstraction of a hydrogen atom from the acid color former and causes a polymerization reaction to occur for a long time, resulting in excellent curability and excellent printing durability, particularly excellent UV printing durability.

Among these, from the viewpoint of color development, the acid color former used in the present disclosure is preferably at least one compound selected from the group consisting of spiropyran compounds, spirooxazine compounds, spirolactone compounds, and spirolactam compounds.
The hue of the color developed by the acid color former (i.e., the hue of the color formed from the acid color former) is preferably green, blue, or black from the viewpoint of visibility.

Moreover, from the viewpoints of color development and visibility, the acid color former preferably contains a leuco dye, and more preferably is a leuco dye.
The leuco dye is not particularly limited as long as it has a leuco structure, but it preferably has a spiro structure, and more preferably has a spirolactone ring structure.
In addition, the leuco dye is preferably a leuco dye having a phthalide structure or a fluoran structure from the viewpoints of color development and visibility of exposed areas.
Furthermore, from the viewpoints of color development and visibility of exposed areas, the leuco dye having a phthalide structure or a fluoran structure is preferably a compound represented by any one of the following formulas (Le-1) to (Le-3), and more preferably a compound represented by the following formula (Le-2).

In formulae (Le-1) to (Le-3), ERG each independently represents an electron donating group, X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, X ₅ to X ₁₀ each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, Y ₁ and Y ₂ each independently represent C or N, and when Y ₁ is N, X ₁ is not present, and when Y ₂ is N, X ₄ is not present, Ra ₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb ₁ to Rb ₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

From the viewpoints of color development and visibility of exposed areas, the electron-donating group in ERG of formulae (Le-1) to (Le-3) is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, an alkoxy group, or an aryloxy group, still more preferably a monoalkylmonoarylamino group, a diarylamino group, a diheteroarylamino group, or a monoarylmonoheteroarylamino group, and particularly preferably a monoalkylmonoarylamino group.
In addition, from the viewpoints of color development and visibility of exposed areas, the electron-donating group in the above ERG is preferably a di-substituted amino group having an aryl group having a substituent at at least one ortho position or a heteroaryl group having a substituent at at least one ortho position, more preferably a di-substituted amino group having a phenyl group having a substituent at at least one ortho position and an electron-donating group at the para position, still more preferably an amino group having a phenyl group having a substituent at at least one ortho position and an electron-donating group at the para position, and an aryl group or a heteroaryl group, and particularly preferably an amino group having a phenyl group having a substituent at at least one ortho position and an electron-donating group at the para position, and an aryl group having an electron-donating group or a heteroaryl group having an electron-donating group.
In the present disclosure, the ortho position in an aryl group or heteroaryl group other than a phenyl group refers to the bonding position adjacent to the bonding position 1 (e.g., the 2nd position, etc.) when the bonding position of the aryl group or heteroaryl group to another structure is defined as the 1st position.
[0046] Furthermore, from the viewpoints of color development and visibility of exposed areas, the electron-donating group contained in the aryl group or heteroaryl group is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, and particularly preferably an alkoxy group.

In formulae (Le-1) to (Le-3), X ₁ to X ₄ each independently represent, from the viewpoints of color development and visibility of exposed areas, preferably a hydrogen atom or a chlorine atom, and more preferably a hydrogen atom.
In formula (Le-2) or formula (Le-3), X ₅ to X ₁₀ are each independently, from the viewpoint of color development and visibility of the exposed area, preferably a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, a heteroaryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a heteroaryloxycarbonyl group or a cyano group, more preferably a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group or an aryloxy group, further preferably a hydrogen atom, a halogen atom, an alkyl group or an aryl group, and particularly preferably a hydrogen atom.
In terms of color development and visibility of the exposed area, it is preferable that at least one of _Y1 and _Y2 in formulae (Le-1) to (Le-3) is C, and it is more preferable that both of _Y1 and _Y2 are C.
In terms of color development and visibility of the exposed area, Ra ₁ in formulae (Le-1) to (Le-3) is preferably an alkyl group or an alkoxy group, more preferably an alkoxy group, and particularly preferably a methoxy group.
In formulae (Le-1) to (Le-3), Rb ₁ to Rb ₄ each independently represent, from the viewpoints of color development and visibility of the exposed area, preferably a hydrogen atom or an alkyl group, more preferably an alkyl group, and particularly preferably a methyl group.

In addition, from the viewpoints of color development and visibility of exposed areas, the leuco dye having the above-mentioned phthalide structure or fluoran structure is more preferably a compound represented by any one of the following formulas (Le-4) to (Le-6), and even more preferably a compound represented by the following formula (Le-5).

In formulae (Le-4) to (Le-6), ERG each independently represents an electron donating group, X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group, Y ₁ and Y ₂ each independently represent C or N, and when Y ₁ is N, X ₁ is not present, and when Y ₂ is N, X ₄ is not present, Ra ₁ represents a hydrogen atom, an alkyl group, or an alkoxy group, and Rb ₁ to Rb ₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

ERG, X ₁ to X ₄ , Y ₁ , Y ₂ , Ra ₁ , and Rb ₁ to Rb ₄ in formulas (Le-4) to (Le-6) have the same meanings as ERG, X ₁ to X ₄ , Y ₁ , Y ₂ , Ra ₁ , and Rb ₁ to Rb ₄ in formulas (Le-1) to (Le-3), respectively, and preferred embodiments are also the same.

Furthermore, from the viewpoints of color development and visibility of exposed areas, the leuco dye having the above-mentioned phthalide structure or fluoran structure is more preferably a compound represented by any one of the following formulas (Le-7) to (Le-9), and particularly preferably a compound represented by the following formula (Le-8).

In formulae (Le-7) to (Le-9), X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group; Y ₁ and Y ₂ each independently represent C or N; when Y ₁ is N, X ₁ does not exist; when Y ₂ is N, X ₄ does not exist; Ra ₁ to Ra ₄ each independently represent a hydrogen atom, an alkyl group, or an alkoxy group; Rb
_Rb1 to _Rb4 each independently represent a hydrogen atom, an alkyl group, an aryl group or a heteroaryl group, and _Rc1 and _Rc2 each independently represent an aryl group or a heteroaryl group.

X ₁ to X ₄ , Y ₁ and Y ₂ in formulae (Le-7) to (Le-9) have the same meanings as X ₁ to X ₄ , Y ₁ and Y ₂ in formulae (Le-1) to (Le-3), and preferred embodiments are also the same.
In formula (Le-7) or formula (Le-9), Ra ₁ to Ra ₄ are each independently preferably an alkyl group or an alkoxy group, more preferably an alkoxy group, and particularly preferably a methoxy group, from the viewpoints of color development and visibility of the exposed area.
In formulae (Le-7) to (Le-9), Rb ₁ to Rb ₄ are each independently, from the viewpoints of color development and visibility of the exposed area, preferably a hydrogen atom, an alkyl group, or an aryl group substituted with an alkoxy group, more preferably an alkyl group, and particularly preferably a methyl group.
In formula (Le-8), Rc ₁ and Rc ₂ each independently represent, from the viewpoints of color development and visibility of exposed areas, preferably a phenyl group or an alkylphenyl group, and more preferably a phenyl group.
In addition, in terms of color development and visibility of exposed areas, Rc ₁ and Rc ₂ in formula (Le-8) are each independently preferably an aryl group having a substituent at at least one ortho position, or a heteroaryl group having a substituent at at least one ortho position, more preferably an aryl group having a substituent at at least one ortho position, even more preferably a phenyl group having a substituent at at least one ortho position, and particularly preferably a phenyl group having a substituent at at least one ortho position and an electron-donating group at the para position. Examples of the substituents in Rc ₁ and Rc ₂ include the substituents described below.
In formula (Le-8), from the viewpoints of color development and visibility of exposed areas, it is preferable that X ₁ to X ₄ are hydrogen atoms, and Y ₁ and Y ₂ are C.
Furthermore, in formula (Le-8), from the viewpoints of color development and visibility of exposed areas, it is preferred that _Rb1 and _Rb2 each independently represent an aryl group substituted with an alkyl group or an alkoxy group.
Furthermore, in formula (Le-8), from the viewpoints of color development and visibility of the exposed area, _Rb1 and _Rb2 are each preferably independently an aryl group or a heteroaryl group, more preferably an aryl group, still more preferably an aryl group having an electron-donating group, and particularly preferably a phenyl group having an electron-donating group at the para position.
From the viewpoints of color development and visibility of the exposed area, the electron-donating group in _Rb1 , Rb2 _{, Rc1} , and _Rc2 is preferably an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, more preferably an alkoxy group, an aryloxy group, a heteroaryloxy group, or an alkyl group, and particularly preferably an alkoxy group.

In addition, from the viewpoints of color development and visibility of exposed areas, the acid color former preferably contains a compound represented by the following formula (3a) or formula (3b), and more preferably contains a compound represented by the following formula (3a).

In formula (3a), Ar ₁ and Ar ₂ each independently represent an aryl group or a heteroaryl group, and R ₁₀ and R ₁₁ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.
In formula (3b), ERG each independently represents an electron-donating group, n represents an integer of 1 to 5, X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group, Y ₁ and Y ₂ each independently represent C or N, and when Y ₁ is N, X ₁ is not present, and when Y ₂ is N, X ₄ is not present, and R ₁₂ and R ₁₃ each independently represent a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group.

R ₁₀ and R ₁₁ in formula (3a) have the same meanings as Rb ₁ and Rb ₂ in formulas (Le-7) to (Le-9), respectively, and preferred embodiments are also the same.
Ar ₁ and Ar ₂ in formula (3a) have the same meanings as Rc ₁ and Rc ₂ in formulas (Le-7) to (Le-9), respectively, and preferred embodiments are also the same.

ERG, X ₁ to X ₄ , Y ₁ and Y ₂ in formula (3b) have the same meanings as ERG, X ₁ to X ₄ , Y ₁ and Y ₂ in formulas (Le-1) to (Le-3), respectively, and preferred embodiments are also the same.
R ₁₂ and R ₁₃ in formula (3b) have the same meanings as Rb ₂ and Rb ₄ in formula (Le-1), respectively, and the preferred embodiments are also the same.
In formula (3b), n is preferably an integer of 1 to 3, and more preferably 1 or 2.

The alkyl group in formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) may be linear, branched or have a ring structure.
The number of carbon atoms in the alkyl group in formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) is preferably 1 to 20, more preferably 1 to 8, even more preferably 1 to 4, and particularly preferably 1 or 2.
The number of carbon atoms in the aryl group in formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) is preferably 6 to 20, more preferably 6 to 10, and particularly preferably 6 to 8.
Specific examples of the aryl group in the formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, and the like, which may have a substituent.
Specific examples of the heteroaryl group in formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) include a furyl group, a pyridyl group, a pyrimidyl group, a pyrazoyl group, a thiophenyl group, and the like, each of which may have a substituent.

In addition, each group such as a monovalent organic group, an alkyl group, an aryl group, a heteroaryl group, a dialkylanilino group, an alkylamino group, and an alkoxy group in formula (Le-1) to formula (Le-9), formula (3a) or formula (3b) may have a substituent. Examples of the substituent include an alkyl group, an aryl group, a heteroaryl group, a halogen atom, an amino group, an alkylamino group, an arylamino group, a heteroarylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a monoalkylmonoheteroarylamino group, a diarylamino group, a diheteroarylamino group, a monoarylmonoheteroarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, a heteroaryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a heteroaryloxycarbonyl group, and a cyano group. In addition, these substituents may be further substituted with these substituents.

The following compounds are suitable examples of the acid color former. Me represents a methyl group, Et represents an ethyl group, Oct represents an octyl group, and Ph represents a phenyl group.

It is also possible to use commercially available products as colorants, such as ETAC, RED500, RED520, CVL, S-205, BLACK305, BLACK400, BLACK100, BLACK500, H-7001, GREEN300, NIRBLACK78, BLUE220, H-3035, BLUE203, ATP, H-1046, H-2114 (all manufactured by Fukui Yamada Chemical Co., Ltd.), ORANGE-DCF, Vermilion Examples of the dye include n-DCF, PINK-DCF, RED-DCF, BLMB, CVL, GREEN-DCF, and TH-107 (manufactured by Hodogaya Chemical Co., Ltd.), ODB, ODB-2, ODB-4, ODB-250, ODB-BlackXV, Blue-63, Blue-502, GN-169, GN-2, Green-118, Red-40, and Red-8 (manufactured by Yamamoto Chemical Industry Co., Ltd.), and crystal violet lactone (manufactured by Tokyo Chemical Industry Co., Ltd.). Among these commercially available products, ETAC, S-205, BLACK305, BLACK400, BLACK100, BLACK500, H-7001, GREEN300, NIRBLACK78, H-3035, ATP, H-1046, H-2114, GREEN-DCF, Blue-63, GN-169, and crystal violet lactone are preferred because the films they form have good visible light absorptance.

The molar absorption coefficient ε of the color-developing substance produced from the acid color-developing agent is set to 35,000 from the viewpoint of visibility.
It is preferable that the molecular weight is 35,000 or more and 200,000 or less, more preferable that the molecular weight is 50,000 or more and 150,000 or less.

The molar absorption coefficient ε of the color former generated from the acid color former in the present disclosure is measured by the following method.
0.04 mmol of the acid color developer to be measured is precisely weighed into a 100 mL measuring flask.
About 90 mL of acetic acid is added, and after visually confirming that the measurement sample has been completely dissolved, the solution is diluted with acetic acid to 100 mL to prepare dye solution A.
About 80 mL of acetic acid is added to another 100 mL measuring flask, and then 5 mL of ion-exchanged water and 5 mL of the above dye solution A are added using 5 mL volumetric pipettes, and the mixture is gently shaken to mix.
After visually confirming that there is no precipitation of the acid color former, the solution is diluted to 100 mL with acetic acid to prepare dye solution B. Dye solution B has an acid color former concentration of 0.02 mmol/L.
The dye solution B is filled into a measurement cell (quartz glass, light path width 10 mm), and measurement is carried out using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-1800).
The blank was a solution of water:acetic acid = 5:95.
The maximum absorption wavelength in the visible light region (380 nm to 750 nm) is read from the obtained spectrum, and the molar absorption coefficient ε is calculated from the absorbance at that wavelength.

From the viewpoint of visibility, the ring-opening rate of the acid color former calculated by the following formula is preferably 15% or more and 100% or less, more preferably 40% or more and 99% or less, even more preferably 60% or more and 99% or less, particularly preferably 75% or more and 99% or less, and most preferably 85% or more and 99% or less.
Ring opening rate = molar absorption coefficient when 1 molar equivalent of acid is added to acid color former / molar absorption coefficient ε of color former generated from acid color former × 100

From the viewpoint of visibility, the maximum absorption wavelength λmax in the visible light region (380 nm to 750 nm) of the color-developing material produced from the acid color-developing agent is preferably 500 nm to 650 nm, more preferably 520 nm to 600 nm, even more preferably 530 nm to 580 nm, and particularly preferably 540 nm to 570 nm.

The ring opening rate and λmax in the present disclosure are measured by the following methods.
--Preparation of dye solution C--
0.1 mmol of acid color developer is accurately weighed into a 50 mL measuring flask.
About 40 mL of acetonitrile is added, and after visually confirming that the measurement sample has been completely dissolved, the solution is diluted with acetonitrile to 50 mL to prepare dye solution C.
- Preparation of acid solution D -
To a 100 mL measuring flask, 0.2 mmol of CSA (10-camphorsulfonic acid) is added, and about 80 mL of acetonitrile is added. After confirming that the CSA has completely dissolved, the mixture is made up to 100 mL with acetonitrile to prepare acid solution D.
--Preparation of measurement solution E--
Add 5 mL of ion-exchanged water to a 100 mL measuring flask using a volumetric pipette, then add 80 mL of acetonitrile. Add 1 mL of dye solution C and 1 mL of acid solution D, and make up to 100 mL to prepare measurement solution E.
The concentration of the acid color former containing the resulting color former in measurement E was 0.02 mmol/L.
The dye solution E is filled into a measurement cell (quartz glass, light path width 10 mm), and measurement is carried out using an ultraviolet-visible spectrophotometer (Shimadzu Corporation, UV-1800).
The blank was prepared using a solution of water:acetonitrile=5:95.
From the obtained spectrum, the maximum absorption wavelength λmax in the visible light region (380 nm to 750 nm) is read, and the molar absorption coefficient ε is calculated from the absorbance at that wavelength.
The ring opening rate is calculated according to the above-mentioned formula.

From the viewpoint of visibility, it is preferable that the molar absorption coefficient ε of the color-formed material produced from the acid color-former is 35,000 or more, the ring-opening rate of the acid color-former is 40 mol% to 99 mol%, and the maximum absorption wavelength λmax of the color-formed material produced from the acid color-former in the wavelength range of 380 nm to 750 nm is 500 nm to 650 nm.

These acid color formers may be used alone or in combination of two or more kinds.
The content of the acid color former is preferably from 0.5% by mass to 10% by mass, and more preferably from 1% by mass to 5% by mass, based on the total mass of the image recording layer.

[Polymerizable Compound]
The image recording layer preferably contains a polymerizable compound.
In the present disclosure, a polymerizable compound refers to a compound having a polymerizable group.
The polymerizable group is not particularly limited and may be any known polymerizable group, but is preferably an ethylenically unsaturated group. The polymerizable group may be either a radically polymerizable group or a cationic polymerizable group, but is preferably a radically polymerizable group.
Examples of the radically polymerizable group include a (meth)acryloyl group, an allyl group, a vinylphenyl group, and a vinyl group, and from the viewpoint of reactivity, a (meth)acryloyl group is preferred.
The molecular weight of the polymerizable compound (when the polymerizable compound has a molecular weight distribution, the weight average molecular weight) is preferably 50 or more and less than 2,500.

The polymerizable compound used in the present disclosure may be, for example, a radically polymerizable compound or a cationic polymerizable compound, but is preferably an addition-polymerizable compound having at least one ethylenically unsaturated bond (ethylenically unsaturated compound).
The ethylenically unsaturated compound is preferably a compound having at least one terminal ethylenically unsaturated bond, more preferably a compound having two or more terminal ethylenically unsaturated bonds. The polymerizable compound has a chemical form such as a monomer, a prepolymer, i.e., a dimer, a trimer or an oligomer, or a mixture thereof.
Among them, from the viewpoint of printing durability, the polymerizable compound preferably contains a trifunctional or more polymerizable compound, more preferably contains a heptafunctional or more polymerizable compound, and even more preferably contains a ten-functional or more polymerizable compound. Also, from the viewpoint of printing durability of the resulting lithographic printing plate, the polymerizable compound preferably contains a trifunctional or more (preferably heptafunctional or more, more preferably ten-functional or more) ethylenically unsaturated compound, and even more preferably contains a trifunctional or more (preferably heptafunctional or more, more preferably ten-functional or more) (meth)acrylate compound.

Moreover, from the viewpoints of on-machine developability and stain suppression, the polymerizable compound preferably contains a polymerizable compound having two or fewer functionalities, more preferably contains a bifunctional polymerizable compound, and particularly preferably contains a bifunctional (meth)acrylate compound.
From the viewpoints of printing durability, on-press developability, and stain suppression, the content of the difunctional or lower polymerizable compound (preferably a difunctional polymerizable compound) is preferably 5% by mass to 100% by mass, more preferably 10% by mass to 100% by mass, and particularly preferably 15% by mass to 100% by mass, relative to the total mass of the polymerizable compounds in the image recording layer.

-Oligomer-
The polymerizable compound contained in the image recording layer preferably contains a polymerizable compound which is an oligomer (hereinafter, also simply referred to as "oligomer").
In the present disclosure, an oligomer refers to a polymerizable compound having a molecular weight (weight average molecular weight when the molecular weight has a molecular weight distribution) of 600 or more and 40,000 or less and containing at least one polymerizable group.
From the viewpoint of excellent chemical resistance and printing durability, the molecular weight of the oligomer is preferably 1,000 or more and 25,000 or less.

From the viewpoint of improving printing durability, the number of polymerizable groups in one oligomer molecule is preferably 2 or more, more preferably 3 or more, even more preferably 6 or more, and particularly preferably 10 or more.
The upper limit of the number of polymerizable groups in the oligomer is not particularly limited, but the number of polymerizable groups is preferably 20 or less.

From the viewpoints of printing durability and on-press developability, the oligomer preferably has 7 or more polymerizable groups and a molecular weight of 1,000 or more and 40,000 or less, and more preferably has 7 or more polymerizable groups and a molecular weight of 1,000 or more and 25,000 or less.
The image recording layer may contain a polymer component that may be generated during the process of producing the oligomer.

From the viewpoints of printing durability, visibility, and on-press developability, the oligomer preferably contains at least one selected from the group consisting of a compound having a urethane bond, a compound having an ester bond, and a compound having an epoxy residue, and more preferably contains a compound having a urethane bond.
In the present disclosure, the epoxy residue refers to a structure formed by an epoxy group, and means, for example, a structure similar to the structure obtained by the reaction of an acid group (such as a carboxylic acid group) with an epoxy group.

As a compound having a urethane bond, those described in WO 2020/262692 can be preferably used.

Furthermore, as the compound having a urethane bond, a compound in which a polymerizable group is introduced by a polymer reaction into a polyurethane obtained by reacting a polyisocyanate compound with a polyol compound may be used.
For example, a compound having a urethane bond may be obtained by reacting a polyurethane oligomer obtained by reacting a polyol compound having an acid group with a polyisocyanate compound, with a compound having an epoxy group and a polymerizable group.

The number of polymerizable groups in a compound having an ester bond, which is an example of an oligomer, is preferably 3 or more, and more preferably 6 or more.

As a compound having an epoxy residue, which is an example of an oligomer, a compound containing a hydroxy group within the compound is preferred.
The compound having an epoxy residue preferably has 2 to 6 polymerizable groups, and more preferably has 2 to 3 polymerizable groups.
The compound having an epoxy residue can be obtained, for example, by reacting a compound having an epoxy group with acrylic acid.

As the oligomer, commercially available products may be used, such as UA510H, UA-306H, UA-
Examples of the polymerizable monomer include, but are not limited to, EBECRYL 306I, UA-306T (all manufactured by Kyoeisha Chemical Co., Ltd.), UV-1700B, UV-6300B, UV7620EA (all manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), U-15HA (manufactured by Shin-Nakamura Chemical Co., Ltd.), EBECRYL450, EBECRYL657, EBECRYL885, EBECRYL800, EBECRYL3416, EBECRYL860 (all manufactured by Daicel Allnex Corporation).

From the viewpoint of improving chemical resistance, printing durability, and suppression of on-press development residue, the content of the oligomer is preferably 30% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass, based on the total mass of the polymerizable compounds in the image recording layer.

-Low molecular weight polymerizable compound-
The polymerizable compound may further contain a polymerizable compound other than the above-mentioned oligomer.
From the viewpoint of chemical resistance, the polymerizable compound other than the oligomer is preferably a low molecular weight polymerizable compound. The low molecular weight polymerizable compound may be in a chemical form such as a monomer, a dimer, a trimer, or a mixture thereof.
From the viewpoint of chemical resistance, the low molecular weight polymerizable compound is preferably at least one polymerizable compound selected from the group consisting of polymerizable compounds having three or more ethylenically unsaturated groups and polymerizable compounds having an isocyanuric ring structure.

In the present disclosure, the low molecular weight polymerizable compound refers to a polymerizable compound having a molecular weight of 50 or more and less than 800 (weight average molecular weight when the compound has a molecular weight distribution).
From the viewpoint of excellent chemical resistance, printing durability, and on-press development residue suppression, the molecular weight of the low molecular weight polymerizable compound is preferably 100 or more and less than 800, more preferably 300 or more and less than 800, and even more preferably 400 or more and less than 800.

When the polymerizable compound contains a low molecular weight polymerizable compound as a polymerizable compound other than the oligomer (when two or more types of low molecular weight polymerizable compounds are contained, the total amount of the low molecular weight polymerizable compounds), from the viewpoints of chemical resistance, printing durability, and suppression of on-press development residue, the ratio of the oligomer to the low molecular weight polymerizable compound (oligomer/low molecular weight polymerizable compound) is preferably 10/1 to 1/10 by mass, more preferably 10/1 to 3/7, and even more preferably 10/1 to 7/3.

In addition, the polymerizable compounds described in paragraphs 0082 to 0086 of WO 2019/013268 can also be suitably used as low molecular weight polymerizable compounds.

Details of the method of use, such as the structure of the polymerizable compound, whether it is used alone or in combination, and the amount added, can be set arbitrarily.
In particular, from the viewpoint of printing durability, it is preferable that the image recording layer contains two or more kinds of polymerizable compounds.
The content of the polymerizable compounds (when two or more types of polymerizable compounds are contained, the total content of the polymerizable compounds) is preferably 5% by mass to 75% by mass, more preferably 10% by mass to 70% by mass, and even more preferably 15% by mass to 60% by mass, based on the total mass of the image recording layer.

〔particle〕
From the viewpoint of printing durability, the image recording layer preferably contains particles.
The particles may be organic particles or inorganic particles, but from the viewpoint of printing durability, it is preferable that the particles contain organic particles, and it is more preferable that the particles contain polymer particles.
As the inorganic particles, known inorganic particles can be used, and metal oxide particles such as silica particles and titania particles can be suitably used.

The polymer particles are preferably selected from the group consisting of thermoplastic resin particles, thermoreactive resin particles, polymer particles having a polymerizable group, microcapsules containing a hydrophobic compound, and microgels (crosslinked polymer particles). Among them, polymer particles or microgels having a polymerizable group are preferred. In a particularly preferred embodiment, the polymer particles contain at least one ethylenically unsaturated group. The presence of such polymer particles provides the effect of increasing the printing durability of the exposed area and the on-press developability of the unexposed area.
From the viewpoints of printing durability and on-press developability, the polymer particles are preferably thermoplastic resin particles.

As the thermoplastic resin particles, preferred are thermoplastic polymer particles described in Research Disclosure No. 33303 of January 1992, JP-A Nos. 9-123387, 9-131850, 9-171249, and 9-171250, and European Patent No. 931647, etc.
Specific examples of the polymer constituting the thermoplastic resin particles include homopolymers or copolymers of monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinylcarbazole, acrylates or methacrylates having a polyalkylene structure, or mixtures thereof. Preferred examples include copolymers containing polystyrene, styrene and acrylonitrile, or polymethyl methacrylate. The average particle size of the thermoplastic resin particles is preferably 0.01 μm to 3.0 μm.

Thermo-reactive resin particles include polymer particles having a thermo-reactive group. Thermo-reactive polymer particles form hydrophobic regions due to crosslinking caused by the thermal reaction and the resulting changes in functional groups.

The heat-reactive group in the polymer particle having a heat-reactive group may be any functional group that undergoes any reaction as long as a chemical bond is formed, but is preferably a polymerizable group, and examples of such groups include ethylenically unsaturated groups that undergo radical polymerization reactions (e.g., acryloyl groups, methacryloyl groups, vinyl groups, allyl groups, etc.), cationic polymerizable groups (e.g., vinyl groups, vinyloxy groups, epoxy groups, oxetanyl groups, etc.), isocyanato groups or their blocks that undergo addition reactions, epoxy groups, vinyloxy groups, and functional groups having active hydrogen atoms that are their reaction partners (e.g., amino groups, hydroxy groups, carboxy groups, etc.), carboxy groups and their reaction partners, hydroxy groups or amino groups that undergo condensation reactions, and acid anhydrides and their reaction partners, amino groups or hydroxy groups, that undergo ring-opening addition reactions.

As for the microcapsules, as described in, for example, JP-A Nos. 2001-277740 and 2001-277742, at least some of the components of the image recording layer are encapsulated in the microcapsules. The components of the image recording layer can also be contained outside the microcapsules. A preferred embodiment of the image recording layer containing microcapsules is one in which hydrophobic components are encapsulated in the microcapsules and hydrophilic components are contained outside the microcapsules.

The microgel (crosslinked polymer particle) can contain some of the components of the image recording layer on at least one of its surface or interior. In particular, reactive microgels having radically polymerizable groups on their surface are preferred from the viewpoints of the sensitivity of the resulting lithographic printing plate precursor and the printing durability of the resulting lithographic printing plate.

A known method can be used to microencapsulate or microgel the components of the image recording layer.

From the viewpoint of the printing durability, stain resistance and storage stability of the resulting lithographic printing plate, the polymer particles are preferably those obtained by reacting a polyisocyanate compound, which is an adduct of a polyhydric phenol compound having two or more hydroxy groups in the molecule with isophorone diisocyanate, with a compound having active hydrogen.
The polyhydric phenol compound is preferably a compound having a plurality of benzene rings each having a phenolic hydroxy group.
The compound having active hydrogen is preferably a polyol compound or a polyamine compound, more preferably a polyol compound, and even more preferably at least one compound selected from the group consisting of propylene glycol, glycerin, and trimethylolpropane.
Preferred examples of resin particles obtained by reacting a polyisocyanate compound, which is an adduct of a polyhydric phenol compound having two or more hydroxy groups in the molecule and isophorone diisocyanate, with a compound having active hydrogen include the polymer particles described in paragraphs 0032 to 0095 of JP2012-206495A.

Furthermore, from the viewpoint of the printing durability and solvent resistance of the resulting lithographic printing plate, it is preferable that the polymer particles include polymer particles containing a polymer having both i: a constituent unit having a pendant cyano group directly bonded to a hydrophobic main chain, and ii: a constituent unit having a pendant group that includes a hydrophilic poly(alkylene oxide) segment.
A preferred example of the hydrophobic main chain is an acrylic resin chain.
Preferred examples of the pendant cyano group include -[CH ₂ CH(C≡N)]- or -[CH ₂ C(CH ₃ )(C≡N)]-.
Furthermore, the structural unit having a pendant cyano group can be easily derived from an ethylenically unsaturated monomer, such as acrylonitrile or methacrylonitrile, or a combination thereof.
The alkylene oxide in the hydrophilic polyalkylene oxide segment is preferably ethylene oxide or propylene oxide, and more preferably ethylene oxide.
The number of repeating alkylene oxide structures in the hydrophilic polyalkylene oxide segment is preferably 10-100, more preferably 25-75, and even more preferably 40-50.
Preferred examples of resin particles containing both i: a constituent unit having a pendant cyano group directly bonded to the hydrophobic main chain, and ii: a constituent unit having a pendant group containing a hydrophilic polyalkylene oxide segment include those described in paragraphs 0039 to 0068 of JP2008-503365A.

In addition, from the viewpoints of printing durability and on-press developability, the polymer particles preferably have a hydrophilic group.
The hydrophilic group is not particularly limited as long as it has a structure having hydrophilicity, and examples of the hydrophilic group include acid groups such as a carboxy group, a hydroxy group, an amino group, a cyano group, and a polyalkylene oxide structure.
Among these, from the viewpoints of on-press developability and printing durability, a polyalkylene oxide structure is preferred, and a polyethylene oxide structure, a polypropylene oxide structure, or a polyethylene/propylene oxide structure is more preferred.
From the viewpoint of on-press developability and suppression of development residue during on-press development, the polyalkylene oxide structure preferably has a polypropylene oxide structure, and more preferably has a polyethylene oxide structure or a polypropylene oxide structure.
From the viewpoints of printing durability, ink receptivity, and on-press developability, the hydrophilic group preferably contains a structural unit having a cyano group or a group represented by the following formula Z, and
) or a group represented by the following formula Z, and particularly preferably a group represented by the following formula Z:
*-Q-W-Y Formula Z
In formula Z, Q represents a divalent linking group, W represents a divalent group having a hydrophilic structure or a divalent group having a hydrophobic structure, Y represents a monovalent group having a hydrophilic structure or a monovalent group having a hydrophobic structure, either W or Y has a hydrophilic structure, and * represents a bonding site with another structure.

In formula (AN), R ^AN represents a hydrogen atom or a methyl group.

From the viewpoint of printing durability, the polymer contained in the polymer particles preferably contains a structural unit formed from a compound having a cyano group.
The cyano group is preferably introduced into the resin as a structural unit containing a cyano group by using a compound (monomer) having a cyano group. Examples of the compound having a cyano group include acrylonitrile compounds, and (meth)acrylonitrile is preferred.
The structural unit having a cyano group is preferably a structural unit formed from an acrylonitrile compound, and more preferably a structural unit formed from (meth)acrylonitrile, that is, a structural unit represented by the above formula (AN).
When the above polymer contains a polymer having a structural unit having a cyano group, the content of the structural unit having a cyano group, preferably the structural unit represented by the above formula (AN), in the polymer having a structural unit having a cyano group is, from the viewpoint of printing durability, preferably 5% by mass to 90% by mass, more preferably 20% by mass to 80% by mass, and particularly preferably 30% by mass to 60% by mass, relative to the total mass of the polymer having a structural unit having a cyano group.

In addition, from the viewpoints of printing durability, ink receptivity, and on-press developability, it is preferable that the polymer particles contain polymer particles having a group represented by the above formula Z.

Q in the above formula Z is preferably a divalent linking group having 1 to 20 carbon atoms, and more preferably a divalent linking group having 1 to 10 carbon atoms.
Furthermore, Q in the above formula Z is preferably an alkylene group, an arylene group, an ester bond, an amide bond, or a group consisting of a combination of two or more of these, and more preferably a phenylene group, an ester bond, or an amide bond.

The divalent group having a hydrophilic structure for W in the above formula Z is preferably a polyalkyleneoxy group or a group in which --CH ₂ CH ₂ NR ^W -- is bonded to one end of a polyalkyleneoxy group, where R ^W represents a hydrogen atom or an alkyl group.
The divalent group having a hydrophobic structure in W of the above formula Z is preferably -R ^WA -, -O-R ^WA -O-, -R ^W N-R ^WA -NR ^W -, -OC(═O)-R ^WA -O-, or -OC(═O)-R ^WA -O-. Each R ^WA independently represents a linear, branched or cyclic alkylene group having 6 to 120 carbon atoms, a haloalkylene group having 6 to 120 carbon atoms, an arylene group having 6 to 120 carbon atoms, an alkylylene group having 7 to 120 carbon atoms (a divalent group obtained by removing one hydrogen atom from an alkylaryl group), or an aralkylene group having 7 to 120 carbon atoms.

The monovalent group having a hydrophilic structure for Y in the above formula Z is preferably -OH, -C(=O)OH, a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group, or a group in which -CH ₂ CH ₂ NR ^W - is bonded to the other terminal of a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group.
The monovalent group having a hydrophobic structure for Y in the above formula Z is preferably a linear, branched or cyclic alkyl group having 6 to 120 carbon atoms, a haloalkyl group having 6 to 120 carbon atoms, an aryl group having 6 to 120 carbon atoms, an alkaryl group (alkylaryl group) having 7 to 120 carbon atoms, an aralkyl group having 7 to 120 carbon atoms, -OR ^WB , -C(=O)OR ^WB , or -OC(=O)R ^WB , where R ^WB represents an alkyl group having 6 to 20 carbon atoms.

From the viewpoints of printing durability, ink receptivity, and on-press developability, it is more preferable that the polymer particles having a group represented by the above formula Z have W as a divalent group having a hydrophilic structure, Q as a phenylene group, an ester bond, or an amide bond, W as a polyalkyleneoxy group, and Y as a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group.

From the viewpoints of printing durability and on-press developability, the polymer particles preferably contain polymer particles having a polymerizable group, and more preferably contain polymer particles having a polymerizable group on the particle surface.
Furthermore, from the viewpoint of printing durability, the polymer particles preferably contain polymer particles having a hydrophilic group and a polymerizable group. The polymerizable group may be a cationic polymerizable group or a radically polymerizable group, but from the viewpoint of reactivity, it is preferable that the polymerizable group is a radically polymerizable group.
The polymerizable group is not particularly limited as long as it is a polymerizable group, but from the viewpoint of reactivity, an ethylenically unsaturated group is preferred, a vinylphenyl group (styryl group), a (meth)acryloxy group, or a (meth)acrylamide group is more preferred, and a (meth)acryloxy group is particularly preferred.
Furthermore, the polymer in the polymer particles having a polymerizable group preferably has a structural unit having a polymerizable group.
Furthermore, polymerizable groups may be introduced onto the surfaces of the polymer particles by a polymer reaction.

In addition, from the viewpoints of printing durability and on-press developability, the image recording layer preferably contains, as the polymer particles, addition polymerization type resin particles having a dispersible group, and it is more preferable that the dispersible group contains a group represented by the formula Z.

In addition, from the viewpoints of printing durability, ink receptivity, on-press developability, and suppression of development residue during on-press development, the polymer particles preferably contain a resin having a urea bond.
Suitable examples of the resin having a urea bond include those described in WO 2020/262692.

From the viewpoints of printing durability and on-press developability, the image recording layer preferably contains thermoplastic resin particles.
The thermoplastic resin contained in the thermoplastic resin particles is not particularly limited, and examples thereof include polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polybutyl (meth)acrylate, polyacrylonitrile, polyvinyl acetate, copolymers thereof, etc. The thermoplastic resin may be in a latex state.
The thermoplastic resin according to the present disclosure is preferably a resin that forms all or part of a hydrophobic film that forms an image recording layer by melting or softening the thermoplastic resin due to heat generated in the exposure step described below.

From the viewpoints of ink receptivity and printing durability, the thermoplastic resin preferably contains a resin having a structural unit formed from an aromatic vinyl compound and a structural unit having a cyano group.
Suitable examples of resins having a structural unit formed by an aromatic vinyl compound and a structural unit having a cyano group include those described in WO 2020/262692.

The thermoplastic resin contained in the thermoplastic resin particles preferably has a hydrophilic group from the viewpoints of printing durability and on-press developability.
The hydrophilic group is not particularly limited as long as it has a structure having hydrophilicity, and examples thereof include acid groups such as a carboxy group, a hydroxy group, an amino group, a cyano group, and a polyalkylene oxide structure.
From the viewpoints of printing durability and on-press developability, the hydrophilic group is preferably a group having a polyalkylene oxide structure, a group having a polyester structure, or a sulfonic acid group, more preferably a group having a polyalkylene oxide structure or a sulfonic acid group, and even more preferably a group having a polyalkylene oxide structure.

From the viewpoint of on-press developability, the polyalkylene oxide structure is preferably a polyethylene oxide structure, a polypropylene oxide structure, or a poly(ethylene oxide/propylene oxide) structure.
From the viewpoint of on-press developability, the hydrophilic group preferably has a polypropylene oxide structure as the polyalkylene oxide structure, and more preferably has a polyethylene oxide structure or a polypropylene oxide structure.
The number of alkylene oxide structures in the polyalkylene oxide structure is preferably 2 or more, more preferably 5 or more, further preferably 5 to 200, and particularly preferably 8 to 150, from the viewpoint of on-press developability.

From the viewpoint of on-machine developability, the hydrophilic group is preferably a group represented by the above formula Z.

From the viewpoints of printing durability and ink receptivity, the glass transition temperature (Tg) of the thermoplastic resin is preferably from 60° C. to 150° C., more preferably from 80° C. to 140° C., and even more preferably from 90° C. to 130° C.
When the thermoplastic resin particles contain two or more types of thermoplastic resins, the value obtained by the FOX equation described below is referred to as the glass transition temperature of the thermoplastic resin.

In this disclosure, the glass transition temperature of a resin can be measured using differential scanning calorimetry (DSC).
A specific measurement method is performed in accordance with the method described in JIS K 7121 (1987) or JIS K 6240 (2011). In this specification, the glass transition temperature is the extrapolated glass transition onset temperature (hereinafter, sometimes referred to as Tig).
The method for measuring the glass transition temperature will now be described more specifically.
When determining the glass transition temperature, the temperature is maintained at about 50° C. lower than the expected Tg of the resin until the apparatus stabilizes, and then the temperature is heated at a heating rate of 20° C./min to a temperature about 30° C. higher than the temperature at which the glass transition ends, and a differential thermal analysis (DTA) curve or a DSC curve is prepared.
The extrapolated glass transition onset temperature (Tig), i.e., the glass transition temperature Tg in this specification, is determined as the temperature at the intersection of a straight line extending from the low-temperature side baseline of a DTA curve or DSC curve to the high-temperature side and a tangent drawn at the point where the gradient of the curve of the stepwise change in the glass transition is maximum.

When the thermoplastic resin particles contain two or more types of thermoplastic resins, the Tg of the thermoplastic resin contained in the thermoplastic resin particles is determined as follows.
When the Tg of the first thermoplastic resin is Tg1(K), the mass fraction of the first thermoplastic resin relative to the total mass of the thermoplastic resin components in the thermoplastic resin particles is W1, the second Tg is Tg2(K), and the mass fraction of the second resin relative to the total mass of the thermoplastic resin components in the thermoplastic resin particles is W2, the Tg0(K) of the thermoplastic resin particles can be estimated according to the following FOX formula.
FOX formula: 1/Tg0=(W1/Tg1)+(W2/Tg2)
Furthermore, when the thermoplastic resin particles contain three types of resins or when three types of thermoplastic resin particles containing different types of thermoplastic resins are contained in the pretreatment liquid, the Tg of the thermoplastic resin particles can be estimated according to the following formula, as described above, where Tgn(K) is the Tg of the nth resin and Wn is the mass fraction of the nth resin relative to the total mass of the resin components in the thermoplastic resin particles.
FOX formula: 1/Tg0=(W1/Tg1)+(W2/Tg2)+(W3/Tg3)...+(Wn/Tgn)

As a differential scanning calorimeter (DSC), for example, an EXSTAR6220 from SII NanoTechnology can be used.

From the viewpoint of printing durability, the arithmetic mean particle diameter of the thermoplastic resin particles is preferably 1 nm or more and 200 nm or less, more preferably 3 nm or more and less than 80 nm, and even more preferably 10 nm or more and 49 nm or less.

Unless otherwise specified, the arithmetic mean particle size of thermoplastic resin particles in this disclosure refers to a value measured by dynamic light scattering (DLS). The arithmetic mean particle size of thermoplastic resin particles by DLS is measured using a Brookhaven BI-90 (manufactured by Brookhaven Instrument Company) according to the manual for the above instrument.

The weight average molecular weight of the thermoplastic resin contained in the thermoplastic resin particles is preferably 3,000 to 300,000, and more preferably 5,000 to 100,000.

The method for producing the thermoplastic resin contained in the thermoplastic resin particles is not particularly limited, and the thermoplastic resin can be produced by a known method.
For example, it can be obtained by polymerizing, by a known method, a styrene compound, an acrylonitrile compound, and, as necessary, at least one compound selected from the group consisting of an N-vinyl heterocyclic compound, a compound used to form a structural unit having an ethylenically unsaturated group, a compound used to form a structural unit having an acidic group, a compound used to form a structural unit having a hydrophobic group, and a compound used to form other structural units.

Specific examples of the thermoplastic resin contained in the thermoplastic resin particles include those described in WO 2020/262692.

The average particle size of the above particles is preferably 0.01 μm to 3.0 μm, more preferably 0.03 μm to 2.0 μm, and even more preferably 0.10 μm to 1.0 μm, in which case good resolution and stability over time can be obtained.
The average primary particle size of the particles in the present disclosure is measured by a light scattering method, or by taking an electron micrograph of the particles, measuring the particle sizes of 5,000 particles in total on the photograph, and calculating the average value. Note that for non-spherical particles, the particle size is the particle size value of a spherical particle having the same particle area as the particle area on the photograph.
In addition, the average particle size in this disclosure is taken to be the volume average particle size unless otherwise specified.

The image recording layer may contain one type of particles, particularly polymer particles, or may contain two or more types.
Furthermore, from the viewpoints of on-press developability and printing durability, the content of particles, particularly polymer particles, in the image recording layer is preferably 5% by mass to 90% by mass, more preferably 10% by mass to 90% by mass, even more preferably 20% by mass to 90% by mass, and particularly preferably 50% by mass to 90% by mass, relative to the total mass of the image recording layer.
From the viewpoints of on-press developability and printing durability, the content of the polymer particles in the image recording layer is preferably 20% by mass to 100% by mass, more preferably 35% by mass to 100% by mass, even more preferably 50% by mass to 100% by mass, and particularly preferably 80% by mass to 100% by mass, relative to the total mass of the components having a molecular weight of 3,000 or more in the image recording layer.

[Binder Polymer]
The image recording layer may contain a binder polymer.
The polymer particles do not fall under the category of the binder polymer, that is, the binder polymer is a polymer that is not in a particulate form.
The binder polymer is preferably a (meth)acrylic resin, a polyvinyl acetal resin, or a polyurethane resin.

Among them, the binder polymer may suitably be a known binder polymer used in the image recording layer of a lithographic printing plate precursor. As an example, a binder polymer used in an on-press development type lithographic printing plate precursor (hereinafter also referred to as an on-press development binder polymer) will be described in detail.
The binder polymer for on-press development is preferably a binder polymer having an alkylene oxide chain. The binder polymer having an alkylene oxide chain may have a poly(alkylene oxide) moiety in the main chain or in the side chain. It may also be a graft polymer having a poly(alkylene oxide) in the side chain, or a block copolymer of a block composed of a poly(alkylene oxide)-containing repeating unit and a block composed of a non-(alkylene oxide)-containing repeating unit.
When the main chain has a poly(alkylene oxide) moiety, polyurethane resin is preferred. When the main chain has a poly(alkylene oxide) moiety in a side chain, examples of the polymer of the main chain include (meth)acrylic resin, polyvinyl acetal resin, polyurethane resin, polyurea resin, polyimide resin, polyamide resin, epoxy resin, polystyrene resin, novolac type phenolic resin, polyester resin, synthetic rubber, and natural rubber, and (meth)acrylic resin is particularly preferred.

Another preferred example of the binder polymer is a polymer compound (hereinafter also referred to as a star-shaped polymer compound) having a 6- to 10-functional polyfunctional thiol core, a polymer chain bonded to the core via a sulfide bond, and the polymer chain having a polymerizable group.
From the viewpoint of curability, the star-shaped polymer compound preferably has a polymerizable group such as an ethylenically unsaturated group in the main chain or side chain, more preferably in the side chain.
Examples of star-shaped polymer compounds include those described in JP-A-2012-148555 or WO 2020/262692.

The molecular weight of the binder polymer is preferably a weight average molecular weight (Mw) of 2,000 or more, more preferably 5,000 or more, and even more preferably 10,000 to 300,000, as calculated using polystyrene standards by the GPC method.

If necessary, hydrophilic polymers such as polyacrylic acid and polyvinyl alcohol described in JP 2008-195018 A can be used in combination. Also, a lipophilic polymer and a hydrophilic polymer can be used in combination.

From the viewpoints of printing durability and on-press developability, the image recording layer preferably contains a polymer having structural units formed from an aromatic vinyl compound, and more preferably contains a polymer having structural units formed from an aromatic vinyl compound and an infrared absorbing agent that decomposes upon exposure to infrared light.

Moreover, the binder polymer used in the present disclosure preferably has a glass transition temperature (Tg) of 50° C. or higher, more preferably 70° C. or higher, even more preferably 80° C. or higher, and particularly preferably 90° C. or higher, from the viewpoint of suppressing deterioration of on-press developability over time.
The upper limit of the glass transition temperature of the binder polymer is preferably 200° C., more preferably 120° C. or lower, from the viewpoint of ease of penetration of water into the image recording layer.

As the binder polymer having the above glass transition temperature, polyvinyl acetal is preferred from the viewpoint of further suppressing the deterioration of on-press developability over time.
Polyvinyl acetal is a resin obtained by acetalizing the hydroxyl groups of polyvinyl alcohol with an aldehyde.
In particular, polyvinyl butyral obtained by acetalizing (that is, butyralizing) the hydroxyl groups of polyvinyl alcohol with butylaldehyde is preferred.
From the viewpoint of improving printing durability, the polyvinyl acetal preferably has an ethylenically unsaturated group.
Suitable examples of polyvinyl acetal include those described in WO 2020/262692.

The image recording layer in the present disclosure preferably contains a resin having a fluorine atom, and more preferably contains a fluoroaliphatic group-containing copolymer.
By using a resin having a fluorine atom, in particular a fluoroaliphatic group-containing copolymer, it is possible to suppress surface quality abnormalities due to foaming during the formation of the image recording layer, improve the coating surface condition, and further improve the ink receptivity of the formed image recording layer.
Furthermore, an image recording layer containing a fluoroaliphatic group-containing copolymer provides high gradation, for example, high sensitivity to laser light, and provides a lithographic printing plate with good fogging properties against scattered light, reflected light, etc., and excellent printing durability.

As the fluoroaliphatic group-containing copolymer, those described in WO 2020/262692 can be preferably used.

In the image recording layer used in the present disclosure, the binder polymer may be used alone or in combination of two or more kinds.
The binder polymer can be contained in any amount in the image recording layer, but the content of the binder polymer is preferably 1% by mass to 90% by mass, and more preferably 5% by mass to 80% by mass, based on the total mass of the image recording layer.

[Polymerization inhibitor]
From the viewpoint of stability over time, the image recording layer preferably contains a polymerization inhibitor. By containing the polymerization inhibitor in the image recording layer, unnecessary thermal polymerization of a polymerizable compound, particularly a radically polymerizable compound, can be prevented during production or storage of the image recording layer.
Specific examples of the polymerization inhibitor include hydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, t-butylcatechol, benzoquinone, 4,4'-thiobis(3-methyl-6-t-butylphenol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), and N-nitroso-N-phenylhydroxylamine aluminum salt.

From the viewpoint of stability over time, it is preferable that the polymerization inhibitor contains a compound represented by the following formula (Ph):

In formula (Ph), X 1 ^P represents O, S, or NH, Y 1 ^P represents N or CH, R ^P1 represents a hydrogen atom or an alkyl group, R ^P2 and R ^P3 each independently represent a halogen atom, an alkylthio group, an arylthio group, an alkoxy group, an aryloxy group, an alkyl group, an aryl group, an acylthio group, or an acyl group, and mp and np each independently represent an integer of 0 to 4.

In formula (Ph), X 3 ^P is preferably O or S, and more preferably S, from the viewpoint of stability over time.
In the formula (Ph), Y 1 ^P is preferably N from the viewpoint of stability over time.
In view of stability over time, R ^P1 in formula (Ph) is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.
In formula (Ph), R ^P2 and R ^P3 are preferably each independently a halogen atom, an alkylthio group, an arylthio group, an alkoxy group, an aryloxy group, an alkyl group, or an aryl group.
In formula (Ph), mp and np each independently represent, from the viewpoint of stability over time, preferably an integer of 0 to 2, more preferably 0 or 1, and particularly preferably 0.

In the image recording layer used in the present disclosure, the polymerization inhibitor may be used alone or in combination of two or more kinds.
The content of the polymerization inhibitor is preferably from 0.001% by mass to 5% by mass, and more preferably from 0.01% by mass to 1% by mass, based on the total mass of the image recording layer.

[Chain transfer agent]
The image recording layer used in the present disclosure may contain a chain transfer agent. The chain transfer agent contributes to improving the printing durability of the lithographic printing plate.
The chain transfer agent is preferably a thiol compound, more preferably a thiol compound having 7 or more carbon atoms in terms of boiling point (difficulty of volatilization), and further preferably a compound having a mercapto group on an aromatic ring (aromatic thiol compound).The thiol compound is preferably a monofunctional thiol compound.
Specific examples of the chain transfer agent include those described in WO 2020/262692.

The chain transfer agent may be added alone or in combination of two or more kinds.
The content of the chain transfer agent is preferably from 0.01% by mass to 50% by mass, more preferably from 0.05% by mass to 40% by mass, and even more preferably from 0.1% by mass to 30% by mass, based on the total mass of the image recording layer.

[Oil Sensitizer]
The image recording layer preferably further contains an oil sensitizer in order to improve ink receptivity.
Examples of the oil sensitizer include onium compounds, nitrogen-containing low molecular weight compounds, and ammonium compounds such as ammonium group-containing polymers.
In particular, when the protective layer contains an inorganic layer compound, the compound functions as a surface coating agent for the inorganic layer compound, and can suppress a decrease in ink receptivity during printing caused by the inorganic layer compound.

From the viewpoint of ink receptivity, the oil sensitizer is preferably an onium compound.
Examples of the onium compound include phosphonium compounds, ammonium compounds, and sulfonium compounds. From the above viewpoint, the onium compound is preferably at least one selected from the group consisting of phosphonium compounds and ammonium compounds.
Preferred examples of the ammonium compound include nitrogen-containing low molecular weight compounds and ammonium group-containing polymers.
Specific examples of the sensitizer include those described in WO 2020/262692.

The content of the oil sensitizer is preferably 1% by mass to 40.0% by mass, more preferably 2% by mass to 25.0% by mass, and even more preferably 3% by mass to 20.0% by mass, based on the total mass of the image recording layer.

The image recording layer may contain one type of oil sensitizer alone or two or more types of oil sensitizers in combination.
One of the preferred embodiments of the image recording layer used in the present disclosure is an embodiment containing two or more compounds as oil sensitizers.
Specifically, from the viewpoint of achieving both on-press developability and ink receptivity, the image recording layer used in the present disclosure preferably uses, as the oil sensitizer, a phosphonium compound, a nitrogen-containing low molecular weight compound, and an ammonium group-containing polymer in combination, and more preferably uses a phosphonium compound, a quaternary ammonium salt, and an ammonium group-containing polymer in combination.

[Other ingredients]
The image recording layer may contain other components such as a development accelerator, a surfactant, a higher fatty acid derivative, a plasticizer, an inorganic layer compound, etc. For details, see paragraphs 0114 to 0159 of JP-A-2008-284817.
As the development accelerator, for example, those described in WO 2020/262692 may be used.

[Formation of Image Recording Layer]
The image recording layer in the lithographic printing plate precursor according to the present disclosure can be formed, for example, as described in paragraphs [0142] to [0143] of JP2008-195018A, by dispersing or dissolving the above-mentioned necessary components in a known solvent to prepare a coating liquid, applying the coating liquid onto a support by a known method such as bar coater coating, and drying.
As the solvent, a known solvent can be used. Specific examples of the solvent include water, acetone, methyl ethyl ketone (2-butanone), cyclohexane, ethyl acetate, ethylene dichloride, tetrahydrofuran, toluene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetylacetone, cyclohexanone, diacetone alcohol, ethylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether acetate, 1-methoxy-2-propanol, 3-methoxy-1-propanol, methoxymethoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 3-methoxypropyl acetate, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, methyl lactate, and ethyl lactate. The solvent may be used alone or in combination of two or more. The solid content in the coating solution is preferably 1% by mass to 50% by mass.
The coating amount (solid content) of the image recording layer after coating and drying varies depending on the application, but is preferably 0.3 g/m ² to 3.0 g/m ² from the viewpoint of obtaining good sensitivity and good film properties of the image recording layer.
The thickness of the image recording layer is preferably from 0.1 μm to 3.0 μm, and more preferably from 0.3 μm to 2.0 μm.
In the present disclosure, the layer thickness of each layer in the lithographic printing plate precursor is confirmed by preparing a slice by cutting the lithographic printing plate precursor in a direction perpendicular to its surface and observing the cross section of the slice with a scanning electron microscope (SEM).

<Support>
The lithographic printing plate precursor according to the present disclosure has a support.
The support can be appropriately selected from known supports for lithographic printing plate precursors.
The support is preferably a support having a hydrophilic surface (hereinafter, also referred to as a "hydrophilic support").

The support in the present disclosure is preferably an aluminum plate that has been roughened and anodized by a known method. That is, the support in the present disclosure preferably has an aluminum plate and an anodized aluminum coating disposed on the aluminum plate.

It is also preferred that the support has an aluminum plate and an anodized aluminum film disposed on the aluminum plate, the anodized film being located closer to the image recording layer than the aluminum plate, the anodized film having micropores extending in the depth direction from the surface on the image recording layer side, and the average diameter of the micropores on the surface of the anodized film being greater than 10 nm and not greater than 100 nm.
Furthermore, the micropores communicate with the large diameter pores extending from the surface of the anodized film to a depth of 10 nm to 1,000 nm, and with the bottoms of the large diameter pores.
It is preferable that the large diameter pores have an average diameter of 15 nm to 100 nm on the surface of the anodized film, and the small diameter pores have an average diameter of 13 nm or less at the communicating positions.

It is also preferable that the support has an aluminum plate and an anodized aluminum film disposed on the aluminum plate, the anodized film being located closer to the image recording layer than the aluminum plate, the anodized film having micropores extending in the depth direction from the surface on the image recording layer side, the micropores being composed of small diameter pores extending from the surface of the anodized film to a depth of 10 nm to 1,000 nm, and large diameter pores that communicate with the bottoms of the small diameter pores and extend from the communicating position to a depth of 20 nm to 2,000 nm, the small diameter pores having an average diameter of 35 nm or less on the surface of the anodized film, and the large diameter pores having an average maximum diameter of 40 nm to 300 nm.
The support of the above embodiment can be easily prepared by using an aqueous phosphoric acid solution in the first anodizing step and an aqueous sulfuric acid solution in the second anodizing step in the process described below.

The support preferably has a tensile strength of 160 MPa or more.
The tensile strength is measured using an Autograph AGC-H5KN (manufactured by Shimadzu Corporation) as a tensile strength measuring instrument, a sample: JIS Metallic Material Tensile Test Piece No. 5, and a tensile speed: 2 mm/min.

The tensile strength of the support is preferably 160 MPa or more, more preferably 170 MPa or more, and particularly preferably 190 MPa or more.
Further, the maximum value of the tensile strength of the support is not particularly limited, but is preferably 300 MPa or less, more preferably 250 MPa or less, and further preferably 220 MPa or less.
There are no particular limitations on how the tensile strength of the support can be made 160 MPa or more. For example, as described below, a specific amount of magnesium can be contained in the support, or the rolling reduction in the rolling process of the support can be set to a specific amount or more.

The support is preferably an aluminum support. The aluminum plate used for such an aluminum support is made of a dimensionally stable metal containing aluminum as the main component, i.e., aluminum or an aluminum alloy. It is preferably selected from a pure aluminum plate and an alloy containing aluminum as the main component and trace amounts of other elements.

The foreign elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content of foreign elements in the alloy is 10 mass% or less. Pure aluminum plate is preferable, but since completely pure aluminum is difficult to produce due to smelting technology, an alloy containing a small amount of foreign elements is also acceptable. The composition of the aluminum plate used for the aluminum support is not specified, and conventionally known aluminum plates, such as JIS A 1050, JIS A 1100, JIS A 3103, and JIS A 3005, that have the above tensile strength can be appropriately used.

The support is preferably an aluminum support containing 0.020% by mass or more of magnesium. By making the magnesium content (content) of the aluminum support 0.020% by mass or more, a support having a tensile strength of 160 MPa or more can be suitably obtained.
The magnesium content in the support is preferably 0.020% by mass or more, more preferably 0.040% by mass or more, and even more preferably 0.060% by mass or more.
Furthermore, the magnesium content in the support is not particularly limited, but is usually 0.200% by mass or less, preferably 0.150% by mass or less, and more preferably 0.100% by mass or less.

The magnesium content in the support was measured using a photoluminescence analyzer (PDA-5500, manufactured by Shimadzu Corporation).

Furthermore, it is preferable that the support is an aluminum support, and that the aluminum support is obtained by subjecting an aluminum plate constituting the aluminum support to a heat treatment at 250° C. or higher in a rolling step and then subjecting the aluminum plate to cold rolling at a reduction ratio of 80% or higher, thereby making it possible to suitably obtain a support having a tensile strength of 160 MPa or higher.
The tensile strength of the support (preferably an aluminum support) can be controlled by controlling the reduction in the cold rolling step after the heat treatment. The reduction here is an amount calculated by (h1-h2)/h1, where h1 and h2 are the plate thicknesses of the material before and after rolling, respectively, and represents the degree of rolling, and is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more.
The rolling reduction is preferably less than 99%, and more preferably 98% or less.
The thickness of the support (preferably an aluminum plate) is preferably about 0.1 mm to 0.6 mm.

[Anodized film]
The support preferably has an anodized coating.
The anodized film refers to an anodized film (preferably an anodized aluminum film) having extremely fine pores (also called micropores) formed on the surface of a support (preferably an aluminum plate) by anodizing treatment. The micropores extend from the surface of the anodized film opposite the support along the thickness direction (the support side, depth direction).
The average diameter (average opening diameter) of the micropores on the surface of the anodized film is preferably 7 nm to 150 nm, more preferably 10 nm to 100 nm, even more preferably 10 nm to 60 nm, particularly preferably 15 nm to 60 nm, and most preferably 18 nm to 40 nm, from the viewpoints of tone reproducibility, printing durability, and printing stain resistance.
The depth of the micropores is preferably from 10 nm to 3,000 nm, more preferably from 10 nm to 2,000 nm, and even more preferably from 10 nm to 1,000 nm.

The shape of the micropores is usually a substantially straight tube shape (substantially cylindrical shape) in which the diameter of the micropores remains almost constant in the depth direction (thickness direction), but they may also be a cone shape in which the diameter decreases continuously in the depth direction (thickness direction), or a shape in which the diameter decreases discontinuously in the depth direction (thickness direction).
Examples of micropores whose diameter discontinuously decreases in the depth direction (thickness direction) include micropores composed of a large diameter pore portion extending in the depth direction from the surface of the anodized coating film and a small diameter pore portion that communicates with the bottom of the large diameter pore portion and extends in the depth direction from the communicating position.

Specifically, micropores each composed of a large diameter pore extending 10 nm to 1,000 nm in the depth direction from the surface of the anodized film, and a small diameter pore that communicates with the bottom of the large diameter pore and extends a further 20 to 2,000 nm in the depth direction from the communicating position are preferred.
The large diameter hole portion and the small diameter hole portion will be described in detail below.

-Large diameter hole-
The average diameter (average opening diameter) of the large diameter pores on the surface of the anodized film is preferably 7 nm to 150 nm, more preferably 10 nm to 100 nm, even more preferably 15 nm to 100 nm, particularly preferably 15 nm to 60 nm, and most preferably 18 nm to 40 nm, from the viewpoints of tone reproducibility, printing durability, and printing stain resistance.
The average diameter of the large pores is calculated by observing N=4 images of the anodized film surface using a field emission scanning electron microscope (FE-SEM) at a magnification of 150,000 times, measuring the diameter of micropores (large pores) present in an area of 400 nm × 600 nm in the four obtained images, and determining the arithmetic mean value of the diameters.
If the shape of the large-diameter hole is not circular, the equivalent circle diameter is used. The "equivalent circle diameter" is the diameter of a circle when the shape of the opening is assumed to be a circle with the same projected area as the projected area of the opening.

The bottoms of the large diameter holes are preferably located at a depth of 70 nm to 1,000 nm (hereinafter also referred to as depth A) from the surface of the anodized film. In other words, the large diameter holes are preferably holes extending 70 nm to 1,000 nm in the depth direction (thickness direction) from the surface of the anodized film. In particular, in terms of superior effects of the manufacturing method for a lithographic printing plate precursor, the depth A is more preferably 90 nm to 850 nm, even more preferably 90 nm to 800 nm, and particularly preferably 90 nm to 600 nm.
The depth is calculated as the arithmetic mean value by taking a photograph (150,000 times) of the cross section of the anodized film, measuring the depths of 25 or more large diameter holes, and then calculating the depths.

The shape of the large diameter hole is not particularly limited, and may be, for example, a substantially straight tube shape (substantially cylindrical shape) or a cone shape whose diameter decreases in the depth direction (thickness direction), with a substantially straight tube shape being preferred. The shape of the bottom of the large diameter hole is not particularly limited, and may be a curved (convex) shape or a flat shape.
The inner diameter of the large diameter hole is not particularly limited, but is preferably about the same as or smaller than the diameter of the opening. The inner diameter of the large diameter hole may differ from the diameter of the opening by about 1 nm to 10 nm.

- Small diameter hole -
The small diameter hole is a hole that communicates with the bottom of the large diameter hole and extends further in the depth direction (thickness direction) from the communicating position. One small diameter hole usually communicates with one large diameter hole, but two or more small diameter holes may communicate with the bottom of one large diameter hole.
The average diameter of the small diameter pores at the communicating positions is preferably smaller than 15 nm, more preferably 13 nm or less, still more preferably 11 nm or less, and particularly preferably 10 nm or less. There is no particular lower limit, but a value of 5 nm is preferable.

The average diameter of the small pores is calculated by observing the surface of the anodized film with an FE-SEM at a magnification of 150,000 times (N=4 images), measuring the diameter of the micropores (small pores) present in the range of 400 nm × 600 nm in the four images obtained, and determining the arithmetic mean value of the diameters. If the large pores are deep, the upper part of the anodized film (the area where the large pores are located) may be cut (e.g., cut with argon gas) as necessary, and then the surface of the anodized film may be observed with the FE-SEM to determine the average diameter of the small pores.
If the shape of the small hole is not circular, the equivalent circle diameter is used. The "equivalent circle diameter" is the diameter of a circle when the shape of the opening is assumed to be a circle with the same projected area as the projected area of the opening.

The bottoms of the small diameter holes are preferably located at positions extending 20 nm to 2,000 nm in the depth direction from the positions where the small diameter holes communicate with the large diameter holes (corresponding to the above-mentioned depth A). In other words, the small diameter holes are holes extending in the depth direction (thickness direction) from the positions where the small diameter holes communicate with the large diameter holes, and the depth of the small diameter holes is preferably 20 nm to 2,000 nm, more preferably 100 nm to 1,500 nm, and particularly preferably 200 nm to 1,000 nm.
The depth is calculated as the arithmetic mean value by taking a photograph (150,000 times) of the cross section of the anodized film, measuring the depths of 25 or more small diameter holes, and then calculating the depth.

The shape of the small diameter hole is not particularly limited, and may be, for example, a substantially straight tube shape (substantially cylindrical shape) or a cone shape whose diameter decreases in the depth direction, with a substantially straight tube shape being preferred. The shape of the bottom of the small diameter hole is not particularly limited, and may be a curved (convex) shape or a flat shape.
The inner diameter of the small diameter hole is not particularly limited, but may be approximately the same as the diameter at the communicating position, or may be smaller or larger than the above diameter. Note that the inner diameter of the small diameter hole may usually differ from the diameter of the opening by about 1 nm to 10 nm.

The ratio of the average diameter of the large diameter pores on the surface of the anodized film to the average diameter of the small diameter pores at their communicating positions, i.e., (average diameter of the large diameter pores on the surface of the anodized film)/(average diameter of the small diameter pores at their communicating positions), is preferably 1.1 to 13, and more preferably 2.5 to 6.5.
The ratio of the depth of the large diameter hole portion to the depth of the small diameter hole portion, (depth of the large diameter hole portion)/(depth of the small diameter hole portion), is preferably 0.005-50, and more preferably 0.025-40.

The shape of the micropores is generally straight (cylindrical) in which the diameter of the micropores remains almost constant in the depth direction (thickness direction), but may also be conical in which the diameter increases continuously in the depth direction (thickness direction), or may be a shape in which the diameter increases discontinuously in the depth direction (thickness direction).
An example of a micropore whose diameter increases discontinuously in the depth direction (thickness direction) is a micropore composed of a small diameter pore portion extending in the depth direction from the surface of the anodized coating film and a large diameter pore portion that communicates with the bottom of the small diameter pore portion and extends in the depth direction from the communicating position.

Specifically, micropores consisting of small diameter pores extending 10 nm to 1,000 nm in the depth direction from the surface of the anodized film, and large diameter pores that communicate with the bottom of the small diameter pores and extend a further 20 nm to 2,000 nm in the depth direction from the communicating position are preferred.

- Small diameter hole -
The average diameter (average opening diameter) of the small holes on the surface of the anodized film is not particularly limited, but is preferably 35 nm or less, more preferably 25 nm or less, and particularly preferably 20 nm or less. There is no particular lower limit, but 15 nm is preferred.
The average diameter of the small pores is calculated by observing N=4 images of the anodized film surface using a field emission scanning electron microscope (FE-SEM) at a magnification of 150,000 times, measuring the diameter of micropores (large pores) present in an area of 400 nm × 600 nm in the four obtained images, and determining the arithmetic mean value of the diameters.
If the shape of the small diameter hole is not circular, the equivalent circle diameter is used. The "equivalent circle diameter" is the diameter of a circle when the shape of the opening is assumed to be a circle with the same projected area as the projected area of the opening.

The bottoms of the small diameter holes are preferably located at a depth of 70 nm to 1,000 nm (hereinafter also referred to as depth A') from the surface of the anodized film. In other words, the small diameter holes are preferably holes extending 70 nm to 1,000 nm in the depth direction (thickness direction) from the surface of the anodized film.
The depth is calculated as the arithmetic mean value by taking a photograph (150,000 times) of the cross section of the anodized film, measuring the depths of 25 or more large diameter holes, and then calculating the depths.

The shape of the small diameter hole is not particularly limited, and may be, for example, a substantially straight tube shape (substantially cylindrical shape) or a cone shape whose diameter increases in the depth direction (thickness direction), with a substantially straight tube shape being preferred. The shape of the bottom of the small diameter hole is not particularly limited, and may be a curved (convex) shape or a flat shape.
The inner diameter of the small hole is not particularly limited, but is preferably about the same as or smaller than the diameter of the opening. The inner diameter of the small hole may differ from the diameter of the opening by about 1 nm to 10 nm.

-Large diameter hole-
The large diameter hole portion is a hole portion that communicates with the bottom of the small diameter hole portion and extends further in the depth direction (thickness direction) from the communicating position. Usually, two or more small diameter holes may communicate with the bottom of one large diameter hole portion.
The average diameter of the large diameter pores at the communicating positions is preferably from 20 nm to 400 nm, more preferably from 40 nm to 300 nm, further preferably from 50 nm to 200 nm, and particularly preferably from 50 nm to 100 nm.

The average diameter of the large pores is calculated by observing N=4 images of the anodized film surface with an FE-SEM at a magnification of 150,000 times, measuring the diameters of the micropores (large pores) present in the range of 400 nm × 600 nm in the four images obtained, and determining the arithmetic mean value of the diameters. If the small pores are deep, the upper part of the anodized film (the area where the small pores are located) may be cut (for example, cut with argon gas) as necessary, and then the surface of the anodized film may be observed with the FE-SEM to determine the average diameter of the large pores.
If the shape of the large-diameter hole is not circular, the equivalent circle diameter is used. The "equivalent circle diameter" is the diameter of a circle when the shape of the opening is assumed to be a circle with the same projected area as the projected area of the opening.

The bottoms of the large diameter holes are preferably located at positions extending 20 nm to 2,000 nm in the depth direction from the positions where the small diameter holes communicate with the large diameter holes (corresponding to the depth A' described above). In other words, the large diameter holes are holes extending in the depth direction (thickness direction) from the positions where the small diameter holes communicate with the large diameter holes, and the depth of the large diameter holes is preferably 20 nm to 2,000 nm, more preferably 100 nm to 1,500 nm, and particularly preferably 200 nm to 1,000 nm.
The depth is calculated as the arithmetic mean value by taking a photograph (150,000 times) of the cross section of the anodized film, measuring the depths of 25 or more large diameter holes, and then calculating the depths.

The shape of the large diameter hole is not particularly limited, and may be, for example, a substantially straight tube shape (substantially cylindrical shape) or a cone shape whose diameter decreases in the depth direction, with a substantially straight tube shape being preferred. The shape of the bottom of the large diameter hole is not particularly limited, and may be a curved (convex) shape or a flat shape.
The inner diameter of the large diameter hole is not particularly limited, but may be approximately the same as the diameter at the communicating position, or may be smaller or larger than the above diameter. Note that the inner diameter of the large diameter hole may usually differ from the diameter of the opening by about 1 nm to 10 nm.

The support has an anodized coating,
The anodized film is formed by sequentially depositing the following layers from the surface of the anodized film in the depth direction:
an upper layer having a thickness of 30 nm to 500 nm and having micropores with an average diameter of 20 nm to 100 nm;
It is preferable that the micropores have a thickness of 100 nm to 300 nm and have micropores whose average diameter is 1/2 to 5 times the average diameter of the micropores in the upper micropore layer, and that the lower layer has a thickness of 300 nm to 2,000 nm and has micropores whose average diameter is 15 nm or less.

In an on-press development type lithographic printing plate precursor, from the viewpoint of improving image visibility, it is useful that the brightness of the anodized film surface of the support (the surface on which the image recording layer is formed) is high.
In the printing process of a lithographic printing plate, a plate inspection is usually performed to check whether the intended image has been recorded before the printing plate is mounted on a printing press. In the case of an on-press development type lithographic printing plate precursor, it is required to check the image at the stage where the image is exposed, so a means for generating a so-called print-out image in the image-exposed area is applied.
A method for quantitatively evaluating the visibility (image visibility) of the image part of an image-exposed on-press development type lithographic printing plate precursor can be to measure the lightness of the image-exposed part and the lightness of the unexposed part and obtain the difference between them. Here, the lightness can be the lightness L ^* value in the CIE L ^* a ^* b ^* color system, and the measurement can be performed using a color difference meter (SpectroEye, manufactured by X-Rite Corporation). The larger the difference between the lightness of the image-exposed part and the lightness of the unexposed part obtained by the measurement, the easier the image part is to be seen.
It has been found that in order to increase the difference in brightness between the image-exposed and unexposed areas, it is effective to increase ^the brightness L ^* value of the anodized film surface in the CIE L ^* a ^* b ^* color system.

If necessary, the support having the anodized film may have a backcoat layer containing an organic polymer compound described in JP-A-5-45885 or a silicon alkoxy compound described in JP-A-6-35174 on the side opposite to the side on which the constituent layer containing a hydroxy acid compound having two or more hydroxyl groups is formed.

[Production of Aluminum Support Having Anodized Film]
As an example of the support, a method for producing an aluminum support having an anodized film will be described.
The aluminum support having an anodized film can be manufactured by a known method. The manufacturing method of the aluminum support having an anodized film is not particularly limited. A preferred embodiment of the manufacturing method of the aluminum support having an anodized film includes a step of roughening an aluminum plate (roughening treatment step), a step of anodizing the roughened aluminum plate (anodizing treatment step), and a step of contacting the aluminum plate having an anodized film obtained in the anodizing treatment step with an acid aqueous solution or an alkali aqueous solution to expand the diameter of the micropores in the anodized film (pore widening treatment step).

Each step is explained in detail below.

<<Surface roughening treatment process>>
The surface roughening step is a step of performing a surface roughening treatment, including an electrochemical surface roughening treatment, on the surface of the aluminum plate. The surface roughening step is preferably performed before the anodizing step described below, but may not be performed if the surface of the aluminum plate already has a preferred surface shape.

The surface roughening treatment may be performed by electrochemical surface roughening alone, or may be performed by combining electrochemical surface roughening treatment with at least one of mechanical surface roughening treatment and chemical surface roughening treatment.
When mechanical graining and electrochemical graining are combined, it is preferable to carry out the electrochemical graining after the mechanical graining.

The electrochemical roughening treatment is preferably carried out in an aqueous solution of nitric acid or hydrochloric acid.

Mechanical graining is generally performed for the purpose of making the surface of an aluminum plate have a surface roughness Ra of 0.35 μm to 1.0 μm.
The conditions for the mechanical graining treatment are not particularly limited, but the treatment can be carried out, for example, according to the method described in JP-B-50-40047. The mechanical graining treatment can be carried out by a brush graining treatment using a pumice suspension or by a transfer method.
The chemical graining treatment is not particularly limited, and can be carried out according to a known method.

After the mechanical roughening treatment, it is preferable to carry out the following chemical etching treatment.
The chemical etching treatment carried out after the mechanical graining treatment is carried out to smooth the uneven edges of the surface of the aluminum plate, prevent the ink from catching during printing, improve the stain resistance of the lithographic printing plate, and remove unwanted material such as abrasive particles remaining on the surface.
Known chemical etching processes include acid etching and alkali etching. A method that is particularly excellent in terms of etching efficiency is chemical etching using an alkaline solution (hereinafter, also referred to as "alkaline etching process").

The alkaline agent used in the alkaline solution is not particularly limited, but suitable examples include caustic soda, caustic potash, sodium metasilicate, sodium carbonate, sodium aluminate, and sodium gluconate.
The alkaline solution may contain aluminum ions. The concentration of the alkaline agent in the alkaline solution is preferably 0.01% by mass or more, more preferably 3% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less.
Furthermore, the temperature of the alkaline solution is preferably at least room temperature, more preferably at least 30° C., and is preferably at most 80° C., more preferably at most 75° C.

The etching amount is preferably 0.01 g/ ^m2 or more, more preferably 0.05 g/ ^m2 or more, and is preferably 30 g/ ^m2 or less, more preferably 20 g/ ^m2 or less.
The treatment time is preferably 2 seconds to 5 minutes depending on the amount of etching, and more preferably 2 seconds to 10 seconds from the viewpoint of improving productivity.

When alkaline etching treatment is performed after mechanical roughening treatment, it is preferable to perform a chemical etching treatment (hereinafter also referred to as a "desmutting treatment") using a low-temperature acidic solution in order to remove products produced by the alkaline etching treatment.
The acid used in the acidic solution is not particularly limited, but examples thereof include sulfuric acid, nitric acid, and hydrochloric acid. The concentration of the acidic solution is preferably 1 to 50% by mass. The temperature of the acidic solution is preferably 20° C. to 80° C. When the concentration and temperature of the acidic solution are within these ranges, the resistance to dot-like staining in a lithographic printing plate using an aluminum support is further improved.

A preferred embodiment of the surface roughening treatment step will be exemplified below.
-Aspect SA-
The process shown in (1) to (8) is carried out in this order.
(1) Chemical Etching Treatment Using an Alkaline Aqueous Solution (First Alkaline Etching Treatment)
(2) Chemical Etching Treatment Using Acidic Aqueous Solution (First Desmutting Treatment)
(3) Electrochemical graining treatment using an aqueous solution mainly containing nitric acid (first electrochemical graining treatment)
(4) Chemical etching treatment using an alkaline aqueous solution (second alkaline etching treatment)
(5) Chemical Etching Treatment Using Acidic Aqueous Solution (Second Desmutting Treatment)
(6) Electrochemical graining treatment using an aqueous solution mainly containing hydrochloric acid (second electrochemical graining treatment)
(7) Chemical etching treatment using an alkaline aqueous solution (third alkaline etching treatment)
(8) Chemical Etching Treatment Using Acidic Aqueous Solution (Third Desmutting Treatment)

-Aspect SB-
The process shown in (11) to (15) is carried out in this order.
(11) Chemical etching treatment using an alkaline aqueous solution (fourth alkaline etching treatment)
(12) Chemical Etching Treatment Using Acidic Aqueous Solution (Fourth Desmutting Treatment)
(13) Electrochemical graining treatment using an aqueous solution mainly containing hydrochloric acid (third electrochemical graining treatment)
(14) Chemical etching treatment using an alkaline aqueous solution (fifth alkaline etching treatment)
(15) Chemical Etching Treatment Using Acidic Aqueous Solution (Fifth Desmutting Treatment)

Before the treatment (1) of the above aspect SA or before the treatment (11) of the above aspect SB, a mechanical roughening treatment may be carried out as necessary.

The amount of aluminum plate dissolved in the first alkaline etching treatment and the fourth alkaline etching treatment is preferably 0.5 g/m ² to 30 g/m ² , and more preferably 1.0 g/m ² to 20 g/m ² .

The aqueous solution mainly containing nitric acid for use in the first electrochemical graining treatment in embodiment SA may be an aqueous solution for use in electrochemical graining treatment using direct or alternating current, for example, an aqueous solution obtained by adding aluminum nitrate, sodium nitrate, ammonium nitrate, or the like to an aqueous solution of nitric acid at 1 g/L to 100 g/L.
The aqueous solution mainly containing hydrochloric acid used in the second electrochemical graining treatment in embodiment SA and the third electrochemical graining treatment in embodiment SB includes an aqueous solution used in electrochemical graining treatment using direct or alternating current. For example, an aqueous solution obtained by adding 0 g/L to 30 g/L of sulfuric acid to an aqueous solution of 1 g/L to 100 g/L of hydrochloric acid may be included. Note that this aqueous solution may further include nitrate ions such as aluminum nitrate, sodium nitrate, or ammonium nitrate; or chloride ions such as aluminum chloride, sodium chloride, or ammonium chloride.

The AC power waveform for the electrochemical graining treatment may be a sine wave, a square wave, a trapezoidal wave, a triangular wave, etc. The frequency is preferably 0.1 Hz to 250 Hz.
FIG. 1 is a graph showing an example of an alternating current waveform used in electrochemical surface roughening treatment.
In FIG. 1, ta is the anode reaction time, tc is the cathode reaction time, tp is the time from 0 to the peak of the current, Ia is the current at the peak on the anode cycle side, and Ic is the current at the peak on the cathode cycle side. In the trapezoidal wave, the time tp from 0 to the peak of the current is preferably 1 msec to 10 msec. The conditions of one cycle of the AC used in the electrochemical graining treatment are preferably such that the ratio tc/ta of the anode reaction time ta of the aluminum plate to the cathode reaction time tc is 1 to 20, the ratio Qc/Qa of the quantity of electricity Qc when the aluminum plate is the anode to the quantity of electricity Qa when the aluminum plate is the anode is 0.3 to 20, and the anode reaction time ta is in the range of 5 msec to 1,000 msec. The current density is preferably 10 to 200 A/ ^dm2 for both the anode cycle side Ia and the cathode cycle side Ic of the current at the peak value of the trapezoidal wave. Ic/Ia is preferably 0.3 to 20. The total amount of electricity involved in the anodic reaction of the aluminum plate at the time when the electrochemical graining treatment is completed is preferably 25 C/dm ² to 1,000 C/dm ² .

For electrochemical surface roughening treatment using alternating current, an apparatus shown in FIG. 2 can be used.
FIG. 2 is a side view showing an example of a radial cell for electrochemical surface roughening treatment using an alternating current.
2, 50 denotes a main electrolytic cell, 51 denotes an AC power source, 52 denotes a radial drum roller, 53a and 53b denote main electrodes, 54 denotes an electrolyte supply port, 55 denotes an electrolyte, 56 denotes a slit, 57 denotes an electrolyte passage, 58 denotes an auxiliary anode, 60 denotes an auxiliary anode cell, and W denotes an aluminum plate. When two or more electrolytic cells are used, the electrolysis conditions may be the same or different.
The aluminum sheet W is wound around a radial drum roller 52 immersed in a main electrolytic cell 50, and is electrolyzed by main electrodes 53a and 53b connected to an AC power source 51 during the transport process. An electrolyte 55 is supplied from an electrolyte supply port 54 through a slit 56 to an electrolyte passage 57 between the radial drum roller 52 and the main electrodes 53a and 53b. The aluminum sheet W treated in the main electrolytic cell 50 is then electrolyzed in an auxiliary anode cell 60. In this auxiliary anode cell 60, an auxiliary anode 58 is disposed opposite the aluminum sheet W, and the electrolyte 55 is supplied so as to flow through the space between the auxiliary anode 58 and the aluminum sheet W.

The amount of the aluminum plate dissolved in the second alkaline etching treatment is preferably 1.0 g/m ² to 20 g/m ² , and more preferably 2.0 g/m ² to 10 g/m ² , in terms of ease of production of a predetermined lithographic printing plate precursor.

The amount of the aluminum plate dissolved in the third alkaline etching treatment and the fifth alkaline etching treatment is preferably 0.01 g/m ² to 0.8 g/m ² , and more preferably 0.05 g/m ² to 0.3 g/m ² , in terms of ease of production of a predetermined lithographic printing plate precursor.

In the chemical etching treatments using acidic aqueous solutions (first to fifth desmutting treatments), an acidic aqueous solution containing phosphoric acid, nitric acid, sulfuric acid, chromic acid, hydrochloric acid, or a mixed acid containing two or more of these acids is suitably used.
The concentration of the acid in the acidic aqueous solution is preferably 0.5% by mass to 60% by mass.

<<Anodizing process>>
The anodizing process is a process for forming an aluminum oxide film on the surface of the aluminum plate by anodizing the aluminum plate that has been subjected to the surface roughening process. The anodizing process forms an aluminum anodized film having micropores on the surface of the aluminum plate.
The anodizing treatment can be carried out according to a method conventionally known in this field by appropriately setting the production conditions taking into consideration the desired shape of the micropores, etc.

In the anodizing process, an aqueous solution of sulfuric acid, phosphoric acid, oxalic acid, etc. can be mainly used as the electrolyte. In some cases, an aqueous or non-aqueous solution of chromic acid, sulfamic acid, benzenesulfonic acid, etc., or a combination of two or more of these, can also be used. When a direct or alternating current is passed through the aluminum plate in the electrolyte, an anodized film can be formed on the surface of the aluminum plate. The electrolyte may contain aluminum ions.
The content of aluminum ions is not particularly limited, but is preferably 1 g/L to 10 g/L.

The conditions for the anodizing treatment are appropriately set depending on the electrolytic solution used, but generally, appropriate ranges are an electrolytic solution concentration of 1 mass % to 80 mass % (preferably 5 mass % to 20 mass %), a solution temperature of 5°C to 70°C (preferably 10°C to 60°C), a current density of ^0.5 A/dm2 to ⁶⁰ A/dm2 (preferably 5 A/ ^dm2 to 50 A/ ^dm2 ), a voltage of 1 V to 100 V (preferably 5 V to 50 V), and an electrolysis time of 1 second to 100 seconds (preferably 5 seconds to 60 seconds).

The method of anodizing at high current density in sulfuric acid, described in British Patent Specification No. 1,412,768, is a preferred example of anodizing treatment.

The anodizing treatment can be performed multiple times. One or more of the conditions such as the type, concentration, temperature, current density, voltage, and electrolysis time of the electrolyte used in each anodizing treatment can be changed. When the number of anodizing treatments is two, the first anodizing treatment is sometimes called the first anodizing treatment, and the second anodizing treatment is sometimes called the second anodizing treatment. By performing the first anodizing treatment and the second anodizing treatment, anodized films having different shapes can be formed, making it possible to provide a lithographic printing plate precursor with excellent printing performance.
Furthermore, it is also possible to carry out the pore widening treatment described below following the anodizing treatment, and then carry out the anodizing treatment again. In this case, the first anodizing treatment, the pore widening treatment, and the second anodizing treatment are carried out.
By utilizing the above-mentioned first anodizing treatment, pore widening treatment, and second anodizing treatment, it is possible to form micropores each consisting of a large diameter pore portion extending in the depth direction from the surface of the anodized film and a small diameter pore portion that communicates with the bottom of the large diameter pore portion and extends in the depth direction from the communicating position.

<<Pore widening process>>
The pore widening treatment step is a treatment (pore diameter enlargement treatment) for enlarging the diameter of the micropores present in the anodized film formed by the anodized film treatment step described above. This pore widening treatment enlarges the diameter of the micropores, forming an anodized film having micropores with a larger average diameter.

The pore widening treatment can be carried out by contacting the aluminum plate obtained by the above-mentioned anodizing treatment process with an acid aqueous solution or an alkaline aqueous solution. The contacting method is not particularly limited, and examples include the immersion method and the spray method. Among these, the immersion method is preferred.

When an alkaline aqueous solution is used in the pore widening treatment step, it is preferable to use at least one alkaline aqueous solution selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide. The concentration of the alkaline aqueous solution is preferably 0.1% to 5% by mass. It is appropriate to adjust the pH of the alkaline aqueous solution to 11 to 13, and contact the aluminum sheet with the alkaline aqueous solution for 1 to 300 seconds (preferably 1°C to 50 seconds) under conditions of 10°C to 70°C (preferably 20°C to 50°C). In this case, the alkaline treatment liquid may contain metal salts of polyvalent weak acids such as carbonates, borates, and phosphates.

When an aqueous acid solution is used in the pore widening treatment step, it is preferable to use an aqueous solution of an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, or hydrochloric acid, or a mixture thereof. The concentration of the aqueous acid solution is preferably 1% by mass to 80% by mass, more preferably 5% by mass to 50% by mass. It is appropriate to contact the aluminum sheet with the aqueous acid solution for 1 second to 300 seconds (preferably 1 line to 150 seconds) under conditions where the temperature of the aqueous acid solution is 5° C. to 70° C. (preferably 10° C. to 60° C.).
The alkaline or acidic aqueous solution may contain aluminum ions. The content of aluminum ions is not particularly limited, but is preferably 1 g/L to 10 g/L.

The method for producing an aluminum support having an anodized film may include a hydrophilization treatment step in which a hydrophilization treatment is performed after the pore widening treatment step. For the hydrophilization treatment, a known method described in paragraphs 0109 to 0114 of JP-A-2005-254638 can be used.

The hydrophilization treatment is preferably carried out by immersing the substrate in an aqueous solution of an alkali metal silicate such as sodium silicate or potassium silicate, or by applying a hydrophilic vinyl polymer or hydrophilic compound to form a hydrophilic undercoat layer.

Hydrophilization treatment using an aqueous solution of an alkali metal silicate such as sodium silicate or potassium silicate can be carried out according to the methods and procedures described in U.S. Pat. Nos. 2,714,066 and 3,181,461.

<Undercoat layer>
The lithographic printing plate precursor according to the present disclosure preferably has an undercoat layer (sometimes called an intermediate layer) between the image recording layer and the support. The undercoat layer strengthens the adhesion between the support and the image recording layer in the exposed area and facilitates peeling of the image recording layer from the support in the unexposed area, thereby contributing to improving developability while suppressing a decrease in printing durability. In addition, in the case of infrared laser exposure, the undercoat layer functions as a heat insulating layer, thereby preventing the heat generated by exposure from diffusing to the support and decreasing sensitivity.

Compounds used in the undercoat layer include polymers having adsorptive groups and hydrophilic groups that can be adsorbed to the support surface. In order to improve adhesion to the image recording layer, polymers having adsorptive groups and hydrophilic groups and further having crosslinkable groups are preferred. Compounds used in the undercoat layer may be low molecular weight compounds or polymers. Two or more compounds may be mixed together as necessary.

When the compound used in the undercoat layer is a polymer, it is preferably a copolymer of a monomer having an adsorptive group, a monomer having a hydrophilic group, and a monomer having a crosslinkable group.
As _the adsorptive group capable of being adsorbed to the surface of the support, a phenolic hydroxy group _, a carboxy group, _-PO3H2 , _-OPO3H2 , _{-CONHSO2- , -SO2NHSO2-} , or _-COCH2COCH3 is preferred. As the hydrophilic group, a sulfo group or a salt thereof, or a salt of a carboxy group is preferred. As the crosslinkable group, an acryl group, a _methacryl group, an acrylamide group, a methacrylamide group, an allyl group, or the like is preferred.
The polymer may have a crosslinkable group introduced by salt formation between a polar substituent of the polymer and a compound having an ethylenically unsaturated bond and a substituent having an opposite charge to the polar substituent, or may further be copolymerized with a monomer other than the above-mentioned monomers, preferably a hydrophilic monomer.

Specifically, preferred examples include a silane coupling agent having an addition-polymerizable ethylenic double bond reactive group described in JP-A-10-282679 and a phosphorus compound having an ethylenic double bond reactive group described in JP-A-2-304441. Also preferred are low-molecular or high-molecular compounds having a crosslinkable group (preferably an ethylenically unsaturated group), a functional group that interacts with the support surface, and a hydrophilic group described in JP-A-2005-238816, JP-A-2005-125749, JP-A-2006-239867, and JP-A-2006-215263.
More preferred examples include polymers having an adsorptive group, a hydrophilic group and a crosslinkable group capable of being adsorbed onto the surface of a support, as described in JP-A Nos. 2005-125749 and 2006-188038.

The content of the ethylenically unsaturated group in the polymer used in the undercoat layer is preferably from 0.1 mmol to 10.0 mmol, more preferably from 0.2 mmol to 5.5 mmol, per gram of the polymer.
The weight average molecular weight (Mw) of the polymer used in the undercoat layer is preferably 5,000 or more, and more preferably from 10,000 to 300,000.

In addition to the above-mentioned compounds for the undercoat layer, the undercoat layer may contain a chelating agent, a secondary or tertiary amine, a polymerization inhibitor, a compound having an amino group or a functional group having polymerization inhibition ability and a group that interacts with the support surface (e.g., 1,4-diazabicyclo[2.2.2]octane (DABCO), 2,3,5,6-tetrahydroxy-p-quinone, chloranil, sulfophthalic acid, hydroxyethylethylenediaminetriacetic acid, dihydroxyethylethylenediaminediacetic acid, hydroxyethyliminodiacetic acid, etc.) to prevent staining over time.

The undercoat layer is applied by a known method. The coating amount (solid content) of the undercoat layer is preferably 0.1 mg/m ² to 100 mg/m ² , and more preferably 1 mg/m ² to 30 mg/m ² .

<Protective Layer>
The lithographic printing plate precursor according to the present disclosure preferably has a protective layer (sometimes called an "overcoat layer") on the surface of the image recording layer opposite the support.
The lithographic printing plate precursor according to the present disclosure preferably has a support, an image recording layer, and a protective layer in this order.
The protective layer may have a function of preventing the image-forming inhibiting reaction by blocking oxygen, as well as a function of preventing the occurrence of scratches in the image-recording layer and ablation during exposure to high-intensity laser light.

Protective layers having such properties are described in, for example, U.S. Patent No. 3,458,311 and Japanese Patent Publication No. 55-49729. As the low oxygen permeable polymer used in the protective layer, either a water-soluble polymer or a water-insoluble polymer can be appropriately selected and used, and two or more types can be mixed and used as necessary, but from the viewpoint of on-press developability, it is preferable that the protective layer contains a water-soluble polymer.
In the present disclosure, a water-soluble polymer means a polymer that has a solubility in water at 25° C. of more than 5% by mass.
Examples of the water-soluble polymer used in the protective layer include polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, cellulose derivatives, polyethylene glycol, and poly(meth)acrylonitrile.
The hydrophilic polymer preferably contains at least one selected from the group consisting of modified polyvinyl alcohol and cellulose derivatives.
The modified polyvinyl alcohol is preferably an acid-modified polyvinyl alcohol having a carboxy group or a sulfo group, specifically, the modified polyvinyl alcohols described in JP-A-2005-250216 and JP-A-2006-259137.
Examples of the cellulose derivatives include methyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose.

Among the above water-soluble polymers, it is preferable to contain polyvinyl alcohol, and it is more preferable to contain polyvinyl alcohol having a degree of saponification of 50% or more.
The degree of saponification is preferably 60% or more, more preferably 70% or more, and even more preferably 85% or more. There is no particular upper limit to the degree of saponification, so long as it is 100% or less.
The degree of saponification is measured according to the method described in JIS K 6726:1994.
In addition, one preferred embodiment of the protective layer includes a layer containing polyvinyl alcohol and polyethylene glycol.

When the protective layer in the present disclosure contains a water-soluble polymer, the content of the water-soluble polymer relative to the total mass of the protective layer is preferably 1% by mass to 99% by mass, more preferably 3% by mass to 97% by mass, and even more preferably 5% by mass to 95% by mass.

The protective layer preferably comprises a hydrophobic polymer.
The hydrophobic polymer refers to a polymer which dissolves in an amount of less than 5 g in 100 g of pure water at 125° C. or which does not dissolve at all.
Examples of hydrophobic polymers include polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, poly(alkyl(meth)acrylate)s (e.g., polymethyl(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, etc.), and copolymers of combinations of raw material monomers for these resins.
The hydrophobic polymer preferably contains a polyvinylidene chloride resin.
Furthermore, the hydrophobic polymer preferably contains a styrene-acrylic copolymer (also called a styrene-acrylic resin).
Furthermore, from the viewpoint of on-press developability, the hydrophobic polymer is preferably in the form of hydrophobic polymer particles.

The hydrophobic polymer may be used alone or in combination of two or more types.

When the protective layer contains a hydrophobic polymer, the content of the hydrophobic polymer is preferably 1% by mass to 70% by mass, more preferably 5% by mass to 50% by mass, and even more preferably 10% by mass to 40% by mass, based on the total mass of the protective layer.

In the present disclosure, the area ratio of the hydrophobic polymer on the surface of the protective layer is preferably 30 area % or more, more preferably 40 area % or more, and even more preferably 50 area % or more.
The upper limit of the area ratio of the hydrophobic polymer on the surface of the protective layer is, for example, 90 area %.
The area ratio of the hydrophobic polymer to the surface of the protective layer can be measured as follows.
Using a PHI nano TOFII time-of-flight secondary ion mass spectrometer (TOF-SIMS) manufactured by ULVAC-PHI, a Bi ion beam (primary ions) was irradiated onto the surface of the protective layer at an accelerating voltage of 30 kV, and the peaks of ions (secondary ions) corresponding to the hydrophobic portions (i.e., regions formed by the hydrophobic polymer) emitted from the surface were measured to map the hydrophobic portions, and the area of the hydrophobic portions per ¹⁰⁰ μm2 was measured to determine the occupied area ratio of the hydrophobic portions, which was defined as the "occupied area ratio of the hydrophobic polymer on the protective layer surface."
For example, when the hydrophobic polymer is an acrylic resin, the measurement is performed based on the C ₆ H ₁₃ O ^- peak, and when the hydrophobic polymer is polyvinylidene chloride, the measurement is performed based on the C ₂ H ₂ Cl ⁺ peak.
The above occupied area ratio can be adjusted by the amount of hydrophobic polymer added, etc.

It is preferable that the protective layer contains a second infrared absorbing agent (hereinafter, also referred to as a specific infrared absorbing agent, to be distinguished from the infrared absorbing agent contained in the image recording layer) that contains a thermally decomposable group that changes to a group that is a stronger electron donor upon exposure to heat and/or infrared radiation and that can form a printed image upon exposure to heat and/or infrared radiation.

The specific infrared absorbing agent is preferably a compound represented by the following formula (VI):

In formula (VI), Ar ¹ and Ar ² each independently represent an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted benzene ring; W ¹ and W ² each independently represent a sulfur atom, an oxygen atom, or NR ^* ; R ^* represents an optionally substituted alkyl group, NH, or a -CM ¹⁰ M ¹¹ group; M ¹⁰ and M ¹¹ each independently represent an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl group or heteroaryl group; M ¹ and M ² each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, or a group of atoms necessary for M ¹ and M ² to form together an optionally substituted cyclic structure; M ³ and M ⁴ each independently represent an optionally substituted aliphatic hydrocarbon group; M ⁵ to M ⁸ each independently represent a hydrogen atom, a halogen atom, or an optionally substituted aliphatic hydrocarbon group; M ⁹ is a group that is converted by a chemical reaction induced by exposure to infrared light or heat into a group that is a stronger electron donor than ^M9 , and which increases the integrated optical absorbance of the compound of formula (VI) between 350 nm and 700 nm, optionally with one or more counter ions to obtain an electrically neutral compound.

In formula (VI), M ⁹ is preferably selected from any one of -(N=CR ¹⁷ )a-NR ⁵ -CO-R ⁴ , -(N=CR ¹⁷ )b-NR ⁵ -SO ₂ -R ⁶ , -(N=CR ¹⁷ )c-NR ¹¹ -SO-R ¹² , -SO ₂ -NR ¹⁵ R ¹⁶ , and -S-CH ₂ -CR ⁷ (H)i-d(R ⁸ )d-NR ⁹ -COOR ¹⁸ , where a, b, c, and d are each independently 0 or 1. Furthermore, M ⁹ may contain one or more counter ions in order to obtain an electrically neutral compound.

R ¹⁷ represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or heteroaryl group, or an atomic group necessary to form a cyclic structure together with R ⁵ or R ¹¹ .
^R4 represents -OR ¹⁰ , -NR ¹³ R ¹⁴ , or -CF ₃ , where R ¹⁰ represents an optionally substituted aryl or heteroaryl group, or an optionally branched aliphatic hydrocarbon group.
R ¹³ and R ¹⁴ each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or heteroaryl group, or a group of atoms necessary for R ¹³ and R ¹⁴ to combine together to form a cyclic structure.
R ⁶ represents an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl or heteroaryl group, -OR ¹⁰ , -NR ¹³ R ¹⁴ , or -CF ₃ .
R ⁵ represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an SO ₃ ^- group, -COOR ¹⁸ , an optionally substituted aryl group or heteroaryl group, or a group of atoms necessary to form a cyclic structure together with at least one of R ¹⁰ , R ¹³ , and R ¹⁴ .
R ¹¹ represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl or heteroaryl group.
R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or heteroaryl group, or a group of atoms necessary for R ¹⁵ and R ¹⁶ to combine together to form a cyclic structure.
R ¹² represents an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl or heteroaryl group.
^R7 and ^R9 each independently represent a hydrogen atom or an optionally substituted aliphatic hydrocarbon group.
R ⁸ represents --COO-- or --COOR ⁸ , where R ⁸ represents a hydrogen atom, an alkali metal cation, an ammonium ion, or a mono-, di-, tri-, or tetra-alkylammonium ion.
R ¹⁸ represents an optionally substituted aryl or heteroaryl group, or an alpha-branched aliphatic hydrocarbon group.

In formula (VI), Ar ¹ and Ar ² each preferably independently represent an optionally substituted aryl group. The ring represented by Ar ¹ and Ar ² is preferably a benzene ring or a naphthalene ring.
Preferably, W ¹ and W ² each represent -C(CH ₃ ) ₂ .
Preferably, ^M1 and ^M2 together represent the atoms necessary to form an optionally substituted 5-membered ring or a benzene ring.
It is preferred that ^M3 and ^M4 each independently represent an optionally substituted aliphatic hydrocarbon group.
It is preferable that M ⁵ , M ⁶ , M ⁷ and M ⁸ each represent a hydrogen atom.
M ⁹ preferably represents -NR ⁵ -CO-R ⁴ , -NR ⁵ -SO ₂ -R ⁶ , -NR ¹¹ -SO-R ¹² , or -SO ₂ -NR ¹⁵ R ^16. Here, R ⁴ , R ⁵ , R ⁶ , R ¹¹ , R ¹² , R ¹⁵ , and R ¹⁶ are synonymous with the above-mentioned R ⁴ , R ⁵ , R ⁶ , R ¹¹ , R ¹² , R ¹⁵ , and R ^16. In particular, M ⁹ more preferably represents -NR ⁵ -CO-R ⁴ or -NR ⁵ -SO ₂ -R ^6. In this case, R ⁴ is preferably -OR ¹⁰ , and R ¹⁰ is preferably an optionally branched aliphatic hydrocarbon group. ^R5 is a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl or heteroaryl group, ^R6 is an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl or heteroaryl group, and ^M9 optionally contains one or more counterions to obtain an electrically neutral compound.

The specific infrared absorbing agent, specifically, the compound represented by formula (VI), may be a neutral dye, an anionic dye, or a cationic dye depending on the type and number of the substituents.
The compound represented by formula (VI) preferably contains an anionic group or an _acid group in the structure, such as _-CO2H , ^-C0NHS02Rh , _-SO2NHCORi , _-SO2NHSO2Rj , _-PO3H2 , _{-OPO3H2 , -OSO3H} , -S- _SO3H , _-S03H , or a salt thereof. Here, ^Rh _, ^Ri , and ^Rj each independently represent an aryl group or an alkyl group, and a methyl group is preferred. Examples of the ^salt include alkali metal salts or ammonium salts, ^and mono-, di-, tri-, or tetra-alkylammonium salts are preferred.
The anionic group or acid group is preferably present on the benzene ring of Ar ¹ or Ar ² , or on the aliphatic hydrocarbon group of M ³ or M ^4. The benzene ring of Ar ¹ or Ar ² , or the aliphatic hydrocarbon group of M ³ or M ⁴ , on which the anionic group or acid group is present, may have another substituent. The other substituent may be selected from a halogen atom, a cyano group, a sulfone group, a carbonyl group, or a carboxylate group.
In particular, the compound represented by formula (VI) preferably has a _-CO2H , -CONHSO2Me, _-SO2NHCOMe , _{-SO2NHSO2 , -PO3H2 , -SO3} group, or a salt thereof, present on the aliphatic hydrocarbon group of ^M3 or ^M4 , where Me represents _a methyl group.

In the compound represented by formula (VI), the optional counter ion for obtaining an electrically neutral compound may be, for example, an anion such as a halogen, a sulfonate, a perfluorosulfonate, a tosylate, a tetrafluoroborate, a hexafluorophosphate, an aryl borate, or an aryl sulfonate. In addition, the salt structure of the compound represented by formula (VI) may be an alkali metal salt or an ammonium salt.

Specific examples of the compound represented by formula (VI) are shown below. In the following specific examples, M ⁺ is L ⁺ , Na ⁺ , K ⁺ , _NH4 ⁺ , _R3NH ^+, where each R independently represents a hydrogen atom, an optionally substituted alkyl group, or an optionally substituted aryl group.

When the protective layer contains a specific infrared absorbing agent, the content of the specific infrared absorbing agent is preferably 1% by mass to 40% by mass, more preferably 2% by mass to 20% by mass, and even more preferably 4% by mass to 10% by mass, relative to the total mass of the protective layer.

From the viewpoint of suppressing development defects, the protective layer preferably contains a filler.
Examples of the filler include inorganic particles, organic resin particles, and inorganic layered compounds. Among them, inorganic layered compounds are preferred. By using an inorganic layered compound, it is possible to effectively prevent redeposited matter from the roll surface from directly adhering to the surface of the image recording layer.
The inorganic particles include metal oxide particles such as silica particles.
The organic resin particles include crosslinked resin particles.
The inorganic layered compound is a particle having a thin, tabular shape, and examples thereof include mica groups such as natural mica and synthetic mica, talc represented by the formula: 3MgO.4SiO.H ₂ O, taeniolite, montmorillonite, saponite, hectorite, zirconium phosphate, and the like.
The inorganic layered compound preferably used is a mica compound, for example, _{a mica group such as natural mica or synthetic mica represented by the formula: A(B,C)2-5D4O10 ( OH} ,F,O) ₂ (wherein A is K, Na or Ca, B and C are Fe(II), Fe(III), Mn, Al, Mg or V, and D is Si or Al).

In the mica group, natural micas include muscovite, sodalite, phlogopite, biotite and lepidolite.Synthetic micas include non-swelling micas such as fluorphlogopite _KMg3 ( _AlSi3O10 ) _F2 , potassium _tetrasilicic mica _KMg2.5Si4O10 ) _F2 , and swelling micas such as Na _tetrasilicic mica _NaMg2.5 ( _Si4O10 ) _F2 , _Na or Li taeniolite (Na, _Li ) _Mg2Li ( _Si4O10 ) _F2 , and montmorillonite-based Na or Li hectorite (Na,Li) _{1 / 8Mg2} / _5Li1 / ₈ ( _Si4O10 ) _F2.Synthetic smectite is also useful.

Among the above mica compounds, fluorine-based swellable mica is particularly useful. That is, swellable synthetic mica has a layered structure consisting of unit crystal lattice layers with a thickness of about 10 Å to 15 Å (1 Å = 0.1 nm), and the metal atom substitution in the lattice is significantly larger than other clay minerals. As a result, the lattice layers have a positive charge deficiency, and to compensate for this, cations such as Li ⁺ , Na ⁺ , Ca ²⁺ , and Mg ²⁺ are adsorbed between the layers. These cations interposed between the layers are called exchangeable cations and can be exchanged with various cations. In particular, when the cations between the layers are Li ⁺ and Na ⁺ , the ionic radius is small, so the bond between the layered crystal lattices is weak, and the mica swells greatly with water. When shear is applied in this state, it easily cleaves and forms a stable sol in water. Swellable synthetic mica has a strong tendency in this way, and is particularly preferably used.

From the viewpoint of diffusion control, the shape of the mica compound is such that the thinner the thickness, the better, and the larger the planar size, the better, as long as it does not impede the smoothness of the coating surface or the transmittance of actinic rays. Therefore, the aspect ratio is preferably 20 or more, more preferably 100 or more, and particularly preferably 200 or more. The aspect ratio is the ratio of the major axis to the thickness of the particle, and can be measured, for example, from a projection of the particle in a microscopic photograph. The larger the aspect ratio, the greater the effect that can be obtained.

The particle size of the mica compound is preferably 0.3 μm to 20 μm, more preferably 0.5 μm to 10 μm, and particularly preferably 1 μm to 5 μm in terms of average major axis. The average particle thickness is preferably 0.1 μm or less, more preferably 0.05 μm or less, and particularly preferably 0.01 μm or less. Specifically, for example, in the case of swellable synthetic mica, which is a representative compound, the preferred embodiment is a thickness of about 1 nm to 50 nm and a surface size (major axis) of about 1 μm to 20 μm.

The content of the inorganic layered compound is preferably 1% by mass to 60% by mass, and more preferably 3% by mass to 50% by mass, based on the total mass of the protective layer. Even when multiple types of inorganic layered compounds are used in combination, it is preferable that the total amount of the inorganic layered compounds is within the above content. Within the above range, oxygen barrier properties are improved and good sensitivity is obtained. In addition, a decrease in ink adhesion can be prevented.

The protective layer may contain known additives such as a plasticizer to impart flexibility, a surfactant to improve coatability, and inorganic particles to control the surface slipperiness. The protective layer may also contain an oil sensitizer as described for the image recording layer.

The protective layer is applied by a known method. The coating amount (solid content) of the protective layer is preferably 0.01 g/m ² to 10 g/m ² , more preferably 0.02 g/m ² to 3 g/m ² , and particularly preferably 0.02 g/m ² to 1 g/m ² .
The thickness of the protective layer in the lithographic printing plate precursor according to the present disclosure is preferably 0.1 μm to 5.0 μm, and more preferably 0.3 μm to 4.0 μm.

The lithographic printing plate precursor according to the present disclosure may have layers other than those described above.
The other layers are not particularly limited, and any known layers may be used. For example, a backcoat layer may be provided on the side of the support opposite to the image recording layer, if necessary.

(Method of preparing a lithographic printing plate and lithographic printing method)
[0033] The method for producing a lithographic printing plate according to the present disclosure is not particularly limited, but preferably includes a step of exposing a lithographic printing plate precursor to light in an imagewise manner (exposure step), and a step of supplying at least one selected from the group consisting of printing ink and fountain solution to the exposed lithographic printing plate precursor on a printing press to remove the image recording layer in non-image areas (on-press development step).
The lithographic printing method according to the present disclosure preferably includes a step of exposing a lithographic printing plate precursor to light in an imagewise manner (exposure step), a step of supplying at least one selected from the group consisting of printing ink and fountain solution on a printing press to remove the image recording layer in non-image areas to prepare a lithographic printing plate (on-press development step), and a step of printing with the obtained lithographic printing plate (hereinafter also referred to as a "printing step").

<Exposure process>
The method for producing a lithographic printing plate according to the present disclosure preferably includes an exposure step of exposing a lithographic printing plate precursor imagewise to form an exposed area and an unexposed area. The lithographic printing plate precursor according to the present disclosure is preferably exposed imagewise by laser exposure through a transparent original having a line image, a halftone dot image, or the like, or by laser light scanning based on digital data.
The wavelength of the light source is preferably 750 nm to 1,400 nm. As a light source with a wavelength of 750 nm to 1,400 nm, a solid-state laser or semiconductor laser that emits infrared rays is suitable. With regard to the infrared laser, the output is preferably 100 mW or more, the exposure time per pixel is preferably 20 microseconds or less, and the amount of irradiation energy is preferably 10 mJ/cm ² to 300 mJ/cm ^2. In addition, it is preferable to use a multi-beam laser device in order to shorten the exposure time. The exposure mechanism may be any of an internal drum type, an external drum type, a flatbed type, and the like.
Image exposure can be carried out by a conventional method using a plate setter, etc. In the case of on-press development, the lithographic printing plate precursor may be mounted on a printing press and then image exposure may be carried out on the printing press.

<On-press development process>
The method for producing a lithographic printing plate according to the present disclosure preferably includes an on-press development step of supplying at least one selected from the group consisting of printing ink and fountain solution on a printing press to remove the image recording layer in non-image areas.
The on-press development method will be described below.

[On-press development method]
In the on-press development method, it is preferable that an oil-based ink and an aqueous component are supplied to the image-exposed lithographic printing plate precursor on a printing press, and the image recording layer in the non-image areas is removed to prepare a lithographic printing plate.
That is, after image exposure, the lithographic printing plate precursor is mounted on a printing press as it is without any development treatment, or the lithographic printing plate precursor is mounted on a printing press and then image exposure is performed on the printing press, and then an oil-based ink and an aqueous component are supplied to print. In the early stage of printing, the uncured image recording layer is dissolved or dispersed by either or both of the supplied oil-based ink and aqueous component in the non-image area and removed, exposing a hydrophilic surface in that area. Meanwhile, in the exposed area, the image recording layer cured by exposure forms an oil-based ink receptive area having an oleophilic surface. The first thing supplied to the plate surface may be an oil-based ink or an aqueous component, but it is preferable to supply an oil-based ink first in order to prevent the aqueous component from being contaminated by the component of the image recording layer that has been removed. In this way, the lithographic printing plate precursor is developed on the press and used as it is for printing a large number of sheets. As the oil-based ink and aqueous component, printing ink and fountain solution for normal lithographic printing are preferably used.

<Printing process>
The lithographic printing method according to the present disclosure includes a printing step of supplying printing ink to a lithographic printing plate to print a recording medium.
The printing ink is not particularly limited, and various known inks can be used as desired. Preferred examples of the printing ink include oil-based inks and ultraviolet-curable inks (UV inks).
In the printing process, dampening water may be supplied as necessary.
The printing step may be carried out consecutively to the on-press development step or the developer development step without stopping the printing press.
The recording medium is not particularly limited, and any known recording medium can be used as desired.

In the method for producing a lithographic printing plate and the lithographic printing method according to the present disclosure, the entire surface of the lithographic printing plate precursor may be heated as necessary before exposure, during exposure, or between exposure and development. Such heating promotes the image formation reaction in the image recording layer, and can provide advantages such as improved sensitivity and printing durability and stabilized sensitivity. Heating before development is preferably performed under mild conditions of 150°C or less. This embodiment can prevent problems such as hardening of non-image areas. It is preferable to use very strong conditions for heating after development, preferably in the range of 100°C to 500°C. Within the above range, sufficient image strengthening effect can be obtained and problems such as deterioration of the support and thermal decomposition of the image area can be suppressed.

(Laminate)
The laminate according to the present disclosure is formed by laminating at least the planographic printing plate precursor according to the present disclosure.
Furthermore, the laminate according to the present disclosure comprises a lithographic printing plate precursor according to the present disclosure laminated thereon, and a protective material that is placed at least on top of the laminated on-press development type lithographic printing plate precursor to protect the on-press development type lithographic printing plate precursor, and it is preferable that the moisture content of the protective material is 10% or less.

Since a lithographic printing plate precursor is a thin plate with a metal support, if the plate is bent, scratched or deformed at the corners, sides or inside, problems such as blurred images when exposed to light or uneven ink distribution when printed can easily occur.
Therefore, in order to protect the lithographic printing plate precursor, when constructing a laminate in which multiple precursors are stacked, it is common to place a protective material for every predetermined number of precursors to ensure that the precursors are protected.
Then, with the protective material in place, the master is packaged in a packaging material to form a package, which is then handled (transported, stored, etc.). By disposing the protective material, for example, the master is less likely to deform (bend, etc.) during handling, thereby preventing damage to the master. Furthermore, even if an external force is applied, part of the force is absorbed by the protective material, preventing deformation or damage to the master.

The preferred aspects of the lithographic printing plate precursor in the laminate according to the present disclosure are the same as the preferred aspects of the lithographic printing plate precursor according to the present disclosure described above.

<Protective materials>
The laminate according to the present disclosure has a protective material that is disposed at least on the top of the laminated lithographic printing plate precursors and protects the lithographic printing plate precursors, and it is preferable that the moisture content of the protective material is 10% by mass or less.
From the viewpoint of suppressing development failure, the moisture content of the protective material is preferably 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 3% by mass or less. The lower limit of the moisture content is 0% by mass.
The moisture content (equilibrium moisture content) of the protective material in this disclosure is measured by a measurement method according to JIS P 8202 (1998).

Examples of the material for the protective material include thick paper, cardboard, plastic, etc., and among these, cardboard or plastic is preferred from the viewpoint of suppressing development defects, and plastic is more preferred.
As the plastic, known polymers can be used, such as polyester, polycarbonate, polyolefin, etc., with polyester being preferred.
The size (length x width) of the protective material is not particularly limited and can be appropriately selected depending on the planographic printing plate precursor to be used. For example, the size may be the same as the planographic printing plate precursor or slightly larger than the planographic printing plate precursor.
The thickness of the protective material is not particularly limited, but from the viewpoints of strength, moisture permeability, and suppression of development defects, it is preferably from 10 μm to 10 mm, and more preferably from 100 μm to 5 mm.

It is also preferable to place protective material not only at the top of the laminate but also at the bottom.

<Interleave paper>
The laminate according to the present disclosure may have an interleaf paper between the two laminated lithographic printing plate precursors.
Furthermore, an interleaf paper may be provided between the lithographic printing plate precursor and the protective material.
Furthermore, an interleaf paper may be provided at the bottom of the laminate.

As the material for the interleaving paper used in the present disclosure, in order to suppress material costs, it is preferable to select a low-cost raw material. For example, paper using 100% by mass of wood pulp, paper using a mixture of wood pulp and synthetic pulp, and papers having a low-density or high-density polyethylene layer provided on the surface thereof can be used.
Specifically, an example of an acidic paper is made by beating bleached kraft pulp, diluting it to a concentration of 4% by mass, adding a sizing agent to the stock so that the sizing agent is 0.1% by mass of the base paper, a paper strength agent to 0.2% by mass, and further adding aluminum sulfate until the pH is 5.0. However, neutral paper using a neutral sizing agent such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA) as the sizing agent, using calcium carbonate as a filler instead of aluminum sulfate, and having a pH of 7 to 8 is preferably used.
Among these, the interleaf paper is preferably paper, more preferably paper containing aluminum sulfate or calcium carbonate, and particularly preferably paper containing calcium carbonate.
The material of the interleaf paper is preferably paper containing 50% by mass or more of pulp, more preferably paper containing 70% by mass or more of pulp, and particularly preferably paper containing 80% by mass or more of pulp.

The calcium content of the slip paper is preferably 0.15% by mass to 0.5% by mass, more preferably 0.2% by mass to 0.45% by mass, and particularly preferably 0.25% by mass to 0.4% by mass, based on the total amount of the slip paper.
The calcium content of the slip paper can be obtained by subjecting the slip paper to fluorescent X-ray measurement.
The calcium contained in paper is mainly calcium carbonate, which is widely used as a filler in neutral paper and has the effect of increasing the whiteness of the paper.

The basis weight of the slip sheet (measured by the method specified in JIS P8124 (2011)) is not particularly limited, but from the viewpoints of printing durability and on-press developability, it is preferably 29 g/m ² to 80 g/m ² , more preferably 35 g/m ² to 70 g/m ² , and particularly preferably 51 g/m ² to 65 g/m ² .
From the viewpoints of printing durability and on-press developability, the basis weight of the slip sheet is preferably 51 g/m ² or more.
The thickness of the slip sheet (measured by the measurement method specified in JIS P8118 (2014)) is not particularly limited, but is preferably 20 μm to 100 μm, more preferably 42 μm to 80 μm, even more preferably 45 μm to 65 μm, and particularly preferably 45 μm to 55 μm.

In addition, from the viewpoint of suppressing color spots, the moisture content of the slip sheet (the moisture content of the slip sheet when it is stored at 25°C/50% RH and the moisture content of the slip sheet stabilizes) is preferably 0% to 20% by mass, more preferably 0% to 15% by mass, and particularly preferably 0% to 10% by mass, relative to the total mass of the slip sheet.

As the interleaf paper, the interleaf paper described in JP 2010-76336 A can be suitably used.

There are no particular limitations on the shape of the slip sheet, but it may be the same shape as the surface direction shape of the lithographic printing plate precursor or a shape larger than that.

The laminate according to the present disclosure may also be packaged in its entirety by known methods.

The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited thereto. In the examples, "%" and "parts" mean "mass %" and "mass parts", respectively, unless otherwise specified. In the polymer compounds, unless otherwise specified, the molecular weight is the weight average molecular weight (Mw), and the ratio of the repeating units is the molar percentage. The weight average molecular weight (Mw) is a value measured as a polystyrene equivalent value by gel permeation chromatography (GPC).

(Examples 1 to 97 and Comparative Examples 1 to 5)
<Preparation of Support>
<<Surface Treatment A>>
(A-a) Mechanical Roughening Treatment (Brush Grain Method)
Using the apparatus shown in Fig. 3, a mechanical roughening treatment was performed by a rotating bundled brush while supplying a suspension of pumice (specific gravity 1.1 g/ ^cm3 ) as an abrasive slurry to the surface of an aluminum plate. In Fig. 3, 1 is an aluminum plate, 2 and 4 are roller-shaped brushes (bundled brushes in this example), 3 is an abrasive slurry, and 5, 6, 7 and 8 are supporting rollers.
The mechanical roughening treatment was carried out with a median diameter (μm) of the abrasive of 30 μm, four brushes, and a brush rotation speed (rpm) of 250 rpm. The material of the bundled brush was 6-10 nylon, with a brush bristles diameter of 0.3 mm and bristles length of 50 mm. The brush was densely planted in a stainless steel cylinder with a diameter of φ300 mm. The distance between the two support rollers (φ200 mm) at the bottom of the bundled brush was 300 mm. The bundled brush was pressed down until the load of the drive motor rotating the brush was 10 kW more than the load before pressing the bundled brush against the aluminum plate. The rotation direction of the brush was the same as the movement direction of the aluminum plate.

(A-b) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 26% by mass and an aluminum ion concentration of 6.5% by mass onto the aluminum plate obtained above using a spray tube at a temperature of 70°C. Then, washing with water was performed using a spray. The amount of dissolved aluminum was 10 g/ ^m2 .

(A-c) Desmutting treatment in an acidic aqueous solution Next, desmutting treatment was performed in an aqueous nitric acid solution. The aqueous nitric acid solution used in the desmutting treatment was the waste nitric acid solution used in the next step of electrochemical surface roughening. The liquid temperature was 35°C. The desmutting solution was sprayed onto the sample for 3 seconds.

(A-d) Electrochemical roughening treatment Electrochemical roughening treatment was performed continuously using nitric acid electrolysis 60 Hz AC voltage. The electrolyte used was an electrolyte in which aluminum nitrate was added to an aqueous solution of nitric acid 10.4 g/L at a temperature of 35°C to adjust the aluminum ion concentration to 4.5 g/L. The AC power source waveform was the waveform shown in FIG. 1, and the time tp from zero to the peak current was 0.8 msec, the duty ratio was 1:1, and a trapezoidal rectangular wave AC was used to perform electrochemical roughening treatment with a carbon electrode as the counter electrode. Ferrite was used as the auxiliary anode. The electrolytic cell shown in FIG. 2 was used. The current density was 30 A/dm ² at the peak current value, and 5% of the current flowing from the power source was shunted to the auxiliary anode. The amount of electricity (C/dm ² ) was 185 C/dm ² , which was the total amount of electricity when the aluminum plate was the anode. Then, washing with water was performed by spraying.

(A-e) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 5 mass% and an aluminum ion concentration of 0.5 mass% onto the aluminum plate obtained above using a spray tube at a temperature of 50°C. Thereafter, washing with water was performed using a spray. The amount of dissolved aluminum was 0.5 g/ ^m2 .

(A-f) Desmutting treatment in an acidic aqueous solution Next, a desmutting treatment was carried out in an aqueous sulfuric acid solution. The aqueous sulfuric acid solution used in the desmutting treatment had a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L. The liquid temperature was 30°C. The desmutting solution was sprayed onto the sample for 3 seconds.

(A-g) Electrochemical roughening treatment Electrochemical roughening treatment was performed continuously using an AC voltage of 60 Hz for hydrochloric acid electrolysis. The electrolyte used was an electrolyte in which aluminum chloride was added to an aqueous solution of 6.2 g/L hydrochloric acid at a liquid temperature of 35°C to adjust the aluminum ion concentration to 4.5 g/L. The AC power source waveform was the waveform shown in Figure 1, and the time tp from zero to the peak of the current was 0.8 msec, the duty ratio was 1:1, and a trapezoidal rectangular wave AC was used to perform electrochemical roughening treatment with a carbon electrode as the counter electrode. Ferrite was used as the auxiliary anode. The electrolytic cell used was that shown in Figure 2.
The current density was 25 A/dm ² at the peak value of the current, and the total amount of electricity (C/dm ² ) in hydrochloric acid electrolysis when the aluminum plate served as the anode was 63 C/dm ^2. Thereafter, washing with water was carried out by spraying.

(Ah) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 5% by mass and an aluminum ion concentration of 0.5% by mass onto the aluminum plate obtained above using a spray tube at a temperature of 50°C. Thereafter, washing with water was performed using a spray. The amount of dissolved aluminum was 0.1 g/ ^m2 .

(A-i) Desmutting in an acidic aqueous solution Next, a desmutting treatment was carried out in an aqueous sulfuric acid solution. Specifically, using waste liquid generated in the anodizing treatment process (aluminum ions 5 g/L dissolved in an aqueous solution of sulfuric acid 170 g/L), desmutting was carried out for 4 seconds at a liquid temperature of 35° C. The desmutting liquid was sprayed onto the sample for 3 seconds.

(A-j) First-stage anodizing treatment The first-stage anodizing treatment was carried out using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 4. Anodizing treatment was carried out under the conditions shown in Table 1, and an anodized film having a predetermined film thickness was formed.
In the anodizing treatment device 610, the aluminum sheet 616 is transported as shown by the arrow in Fig. 4. In the power supply tank 612 in which an electrolytic solution 618 is stored, the aluminum sheet 616 is charged (+) by the power supply electrode 620. Then, in the power supply tank 612, the aluminum sheet 616 is transported upward by the roller 622, and its direction is changed downward by the nip roller 624, and then the aluminum sheet 616 is transported toward the electrolytic treatment tank 614 in which an electrolytic solution 626 is stored, and its direction is changed horizontally by the roller 628. Next, the aluminum sheet 616 is charged (-) by the electrolytic electrode 630, so that an anodized film is formed on the surface of the aluminum sheet 616, and the aluminum sheet 616 that leaves the electrolytic treatment tank 614 is transported to a subsequent process. In the anodizing treatment device 610, a roller 622, a nip roller 624, and a roller 628 constitute a direction changing means, and the aluminum sheet 616 is transported in a mountain shape and an inverted U shape by the rollers 622, 624, and 628 in the space between the power supply tank 612 and the electrolytic treatment tank 614. The power supply electrode 620 and the electrolytic electrode 630 are connected to a DC power source 634.

(A-k) Pore widening treatment The aluminum plate subjected to the above anodization treatment was subjected to a pore widening treatment by immersing it in an aqueous solution of caustic soda having a temperature of 35° C., a caustic soda concentration of 5 mass %, and an aluminum ion concentration of 0.5 mass % under the conditions shown in Table 1. Thereafter, the aluminum plate was washed with water by spraying.

(A-l) Second-stage anodizing treatment The second-stage anodizing treatment was carried out using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 4. Anodizing treatment was carried out under the conditions shown in Table 1, and an anodized film having a predetermined film thickness was formed.

(Am) Third-stage anodizing treatment The third-stage anodizing treatment was carried out using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 4. Anodizing treatment was carried out under the conditions shown in Table 1, and an anodized film having a predetermined film thickness was formed.

From the above surface treatment A, the support A described in Tables 1 and 2 was obtained.

Table 2 summarizes the average diameter (nm) of the large pores on the surface of the anodized film having micropores after the second anodizing treatment process obtained above, the average diameter (nm) at the connecting positions of the small pores, the depth (nm) of the large pores and the small pores, the pit density (density of micropores, unit: pits/ ^μm2 ), and the thickness (nm) of the anodized film from the bottom of the small pores to the surface of the aluminum plate.
The average diameter of the micropores (average diameter of the large diameter pores and the small diameter pores) was determined by observing the surfaces of the large diameter pores and the small diameter pores with an FE-SEM at a magnification of 150,000 times (N=4), measuring the diameters of the micropores (large diameter pores and small diameter pores) present in a range of 400 nm × 600 nm in the four images obtained, and averaging them. When the large diameter pores were deep and it was difficult to measure the diameter of the small diameter pores, or when measuring the enlarged diameter pores in the small diameter pores, the upper part of the anodized film was cut and then the various diameters were determined.
The micropore depth (depth of the large diameter pore portion and the small diameter pore portion) was determined by observing the cross section of the support (anodic oxide film) with an FE-SEM (observation of the depth of the large diameter pore portion: 150,000 times, observation of the depth of the small diameter pore portion: 50,000 times), measuring the depth of any 25 micropores in the obtained image, and averaging the measured values.
In Table 1, the amount of film (AD) in the first anodizing treatment column and the amount of film (AD) in the second anodizing treatment column represent the amount of film obtained by each treatment. The electrolyte used is an aqueous solution containing the components in Table 1.

Using support A, an undercoat layer, an image recording layer, and a protective layer were formed as follows to obtain a lithographic printing plate precursor.

<Formation of Undercoat Layer>
An undercoat layer coating solution having the following composition was applied onto the obtained support A so that the dry coating amount was 0.1 g/m ² to form an undercoat layer.

-- Coating solution for undercoat layer --
Undercoat layer compound (U-1 below, 11% aqueous solution): 0.10502 parts Sodium gluconate: 0.0700 parts Surfactant (Emalex (registered trademark) 710, manufactured by Nippon Emulsion Co., Ltd.): 0.00159 parts Preservative (Biohope L, manufactured by K.I. Kasei Co., Ltd.): 0.00149 parts Water: 2.8719 parts

<Formation of Image Recording Layer>
The following image recording layer coating solution was applied onto the undercoat layer 1 with a bar and dried in an oven at 120° C. for 60 seconds to form an image recording layer with a dry coating amount of 1.0 g/m ² .

--Image recording layer coating liquid--
The following components were dissolved in a mixed liquid of 35 volume % MEK (methyl ethyl ketone) and 65 volume % 1-methoxy-2-propanol to a solid content concentration of 7.0 mass % to prepare image recording layer coating liquid 1.
Non-onium polymerization initiator (4-hydroxyphenyl-tribromomethylsulfone): 60 parts Borate compound (sodium tetraphenylborate (TPB)): not added or 20 parts Infrared absorbing agent (types listed in Tables 3 to 6 below): 20 parts Compound A (types listed in Tables 3 to 6 below): the amount (parts) listed in Tables 3 to 6 below
Acid color former (C-1, structure below): not added or 50 parts; Reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate (82% by weight solution in MEK, FST 510, manufactured by AZ Electronics): 250 parts; Epoxy acrylate oligomer (CN104, manufactured by Arkema): 250 parts; Non-ionic aliphatic polyether polyurethane (Ruco Coat EC4811, manufactured by Rudolf GmbH): 125 parts; Polyvinyl butyral (vinyl butyral-co-vinyl acetate-co-vinyl alcohol, S-LEC BL-10, manufactured by Sekisui Chemical Co., Ltd.): 125 parts; Polyether siloxane copolymer (Tegoglide 410, manufactured by Evonik Polyethylene glycol monomethacrylate acid phosphate (JPA528, manufactured by Johoku Chemical Co., Ltd.): 130 parts Copolymer of vinylphosphonic acid and acrylic acid (Albritect CP 30, manufactured by Rhodia, 20% by weight aqueous dispersion): 120 parts Phosphoric acid: 6.5 parts Hydrophilic fumed silica (Aerosil, manufactured by Evonik ResourceEfficiency GmbH): 85 parts

The infrared absorbing agent contained in the image recording layer is as follows.
The following IR-4 is a salt of the cation portion of an infrared absorbing agent and a borate anion (tetraphenylborate anion).

In addition, D1 to D31 in compound A contained in the image recording layer are the same compounds as D1 to D31 in the specific examples of the cations of compound A described above.

Furthermore, the acid generator C-1 contained in the image recording layer is a compound having the following structure:

<Formation of protective layer>
A protective layer was formed on the image recording layer by the following formation method.
In Examples 94 to 97, no protective layer was formed.

~ Formation of protective layer ~
The following protective layer coating solution was applied onto the image recording layer with a bar and dried in an oven at 110° C. for 120 seconds to form a protective layer with a dry coating amount of 0.3 g/m ² to prepare a lithographic printing plate precursor.

--Protective layer coating solution--
The following components were mixed to prepare a protective layer coating solution.
Water: 2000 parts Polyvinyl alcohol (Mowiol 4-88TM, manufactured by Kuraray Co., Ltd.): 160 parts Polyvinylidene chloride (Diofan A050, manufactured by Solvay Co., Ltd.): 296 parts Acticide LA1206TM (manufactured by Thor Co., Ltd.): 1 part Surfactant (Lutensol A8TM, manufactured by BASF Co., Ltd.): 10 parts Specific infrared absorbing agent (structure shown below): 28 parts Potassium nitrate: 37 parts

<Evaluation of Crystal Precipitation>
A rubber roller (diameter 2 cm) was brought into contact with the obtained lithographic printing plate precursor from the protective layer side to apply pressure. The lithographic printing plate precursor after the application of the contact pressure was stored for 3 days in a saturated atmosphere of 2-methoxypropanol using a vapor chamber. After storage for 3 days, the image recording layer of the lithographic printing plate precursor was observed at an optical magnification of 8 times, and the presence of precipitates in the layer was evaluated.
-Evaluation index-
A: No crystal precipitation was observed.
B: Some crystal precipitation was observed.
C: A large amount of crystal precipitation was observed.

<Evaluation of printing durability>
The obtained lithographic printing plate precursor was exposed at an energy density of 90 mJ/cm ² and 2400 dpi using an Avalon N8-20 plate setter (200 Ipi Agfa Balanced Screening (ABS), manufactured by Agfa Graphics) equipped with an 830 nm infrared laser.
The resulting exposed lithographic printing plate precursor was mounted on the plate cylinder of a Ryobi printing press without development. 50,000 prints were made on uncoated offset paper (70 g) using a compressible blanket. For printing, TOYO FD LED UV EU3 cyan ink and a 3% by weight aqueous solution of Prima AF S1 (Agfa) were used as the dampening solution.
The number of prints at which the density of the dotted line exceeded 8% of the initial density of the print was used to evaluate the printing durability. The density of the dotted line was measured using a Gretag Macbeth densitometer.

The evaluation results are summarized in Tables 3 to 6.

As is clear from Tables 3 to 6, the lithographic printing plate precursors according to the Examples are superior in suppressing crystal precipitation and also have superior printing durability compared to the lithographic printing plate precursors according to the Comparative Examples.

1: Aluminum plate, 2 and 4: Roller brush, 3: Polishing slurry liquid, 5, 6, 7 and 8: Support roller, 50: Main electrolytic cell, 51: AC power source, 52: Radial drum roller, 53a, 53b: Main electrode, 54: Electrolyte supply port, 55: Electrolyte, 56: Auxiliary anode, 57: Electrolyte passage, 58: Auxiliary anode, 60: Auxiliary anode cell, 610: Anodizing treatment device, 612: Power supply cell, 614: Electrolytic treatment cell, 616: Aluminum plate, 618, 26: Electrolyte, 620: Power supply electrode, 6 22, 628: roller, 624: nip roller, 630: electrolytic electrode, 632: tank wall, 634: DC power supply, W: aluminum plate, S: liquid supply direction, Ex: electrolyte discharge direction, ta: anode reaction time, tc: cathode reaction time, tp: time from 0 to peak current, Ia: peak current on the anode cycle side, Ic: peak current on the cathode cycle side, AA: current of the anode reaction of the aluminum plate, CA: current of the cathode reaction of the aluminum plate

Claims (15)

A support and an image recording layer on the support,
The lithographic printing plate precursor, wherein the image recording layer comprises a non-onium polymerization initiator, a borate compound, an infrared absorber, and Compound A which is an onium salt having a cation whose ShapeIndex is two or less times that of the cation moiety of the infrared absorber. The lithographic printing plate precursor according to claim 1 , wherein the cation in the compound A is a cation represented by the following formula (A):

In formula (A), Z represents P or N, and R ^A1 to R ^A4 each independently represent a hydrogen atom, an alkyl group or an aryl group. The lithographic printing plate precursor according to claim 1 , wherein the cation in the compound A is a cation represented by the following formula (2):

In formula (2), R ²¹ each independently represents an alkyl group, and R ²² represents a hydrogen atom or an alkyl group. The lithographic printing plate precursor according to claim 1 , wherein the cation in the compound A is a cation represented by the following formula (1):

In formula (1), Z represents P or N, R represents an alkyl group, and each Ar independently represents an aryl group. The lithographic printing plate precursor according to any one of claims 1 to 4, wherein the cation in compound A has a polymerizable group. The compound A has a clogP of 0 or more and 10 or less.
The lithographic printing plate precursor according to claim 4 . The lithographic printing plate precursor according to any one of claims 1 to 4, wherein the anion in compound A is a conjugate base of an organic acid. ^The lithographic ^{printing plate} precursor ^{according to} _any ^{one of} claims ¹ to ^{4 ,} wherein the anion in compound A is at least one anion selected from the group consisting of ^R1SO3- _{, R1SO2-} ^, _R1R2PO2- ^{, R1PO32- ,} _R1CO2-, ^{R1O- , R1S- ,} ( _R1SO2 ) _2N- ^, and ^{R1R2R3R4B- .}
Each of R ¹ to R ⁴ independently represents a hydrogen atom, an alkyl group, or an aryl group. The lithographic printing plate precursor according to any one of claims 1 to 4, wherein the molar content of the cation in compound A is 0.2 to 4 times the molar content of the anion in the borate compound. The lithographic printing plate precursor according to any one of claims 1 to 4, wherein the non-onium polymerization initiator comprises a compound represented by the following formula (II):

In formula (II), each X independently represents a halogen atom, and ^R3 represents an aryl group. The lithographic printing plate precursor according to any one of claims 1 to 4, which has a protective layer on the image recording layer. The lithographic printing plate precursor according to claim 11, wherein the protective layer contains a thermally decomposable group that is converted to a group that is a stronger electron donor upon exposure to heat and/or infrared radiation, and contains a second infrared absorber that is capable of forming a printing image upon exposure to heat and/or infrared radiation. The lithographic printing plate precursor according to claim 12, wherein the second infrared absorber is a compound represented by formula (VI).

In formula (VI), Ar ¹ and Ar ² each independently represent an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted benzene ring; W ¹ and W ² each independently represent a sulfur atom, an oxygen atom, or NR ^* ; R ^* represents an optionally substituted alkyl group, NH, or a -CM ¹⁰ M ¹¹ group; M ¹⁰ and M ¹¹ each independently represent an optionally substituted aliphatic hydrocarbon group, or an optionally substituted aryl group or heteroaryl group; M ¹ and M ² each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, or a group of atoms necessary for M ¹ and M ² to form together an optionally substituted cyclic structure; M ³ and M ⁴ each independently represent an optionally substituted aliphatic hydrocarbon group; M ⁵ to M ⁸ each independently represent a hydrogen atom, a halogen atom, or an optionally substituted aliphatic hydrocarbon group; M ⁹ is a group that is converted by a chemical reaction induced by exposure to infrared light or heat into a group that is a stronger electron donor than ^M9 , and that increases the integrated optical absorbance of the compound of formula (VI) between 350 nm and 700 nm, and optionally has one or more counter ions to obtain an electrically neutral compound. A step of imagewise exposing the lithographic printing plate precursor according to any one of claims 1 to 4;
and removing the image recording layer in the non-image area by supplying at least one selected from the group consisting of printing ink and dampening water on the printing press. A step of imagewise exposing the lithographic printing plate precursor according to any one of claims 1 to 4;
a step of removing the image recording layer in the non-image area by supplying at least one selected from the group consisting of printing ink and dampening water on a printing press to prepare a lithographic printing plate;
and printing with the obtained lithographic printing plate.