JP7464691B2 - Lithographic printing plate precursor, method for preparing a lithographic printing plate, and lithographic printing method - Google Patents

Description

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

Generally, a lithographic printing plate consists 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 then ink is applied only to the image area, after which the ink is transferred to the printing material such as paper to print.

Currently, in the platemaking process for producing a lithographic printing plate from a lithographic printing plate precursor, image exposure is performed using CTP (computer-to-plate) technology. In other words, image exposure is performed by scanning exposure or the like directly onto the lithographic printing plate precursor using a laser or laser diode, without using a lithographic film.

On the other hand, with the growing concern for the global environment, environmental issues related to waste liquids that accompany wet processing such as development processing have come into focus when it comes to platemaking for lithographic printing plate precursors, and as a result, there has been a trend toward simplifying development processing or eliminating it altogether. A method called "on-press development" has been proposed as one simple development process. On-press development is a method in which after image exposure of a lithographic printing plate precursor, the plate is attached directly to the printing press without undergoing the conventional wet development processing, and the non-image areas of the image recording layer are removed at an early stage of the normal printing process.

When printing using a lithographic printing plate, when printing on paper smaller than the size of the printing plate, as with a normal sheet-fed printing press, the edges of the printing plate are outside the paper surface and do not affect the print quality. However, when printing continuously on rolled paper using a rotary press, such as for newspaper printing, the edges of the printing plate are within the surface of the rolled paper, so ink adhering to the edges is transferred to the paper, causing linear stains (edge stains) and significantly reducing the commercial value of the printed matter.

Conventional lithographic printing plate precursors include those described in, for example, Patent Documents 1 to 3.
Patent Document 1 describes an on-press development type lithographic printing plate precursor having an image recording layer on an aluminum support having an anodized film, the lithographic printing plate precursor having a drooped shape at the edge, a layer containing a compound having support adsorbability on the image recording layer, and the content of the compound is substantially the same within the plane of the layer containing the compound having support adsorbability.

Patent Document 2 describes a lithographic printing plate precursor having an image recording layer on a support, the image recording layer including a color-developing composition containing a compound represented by the following formula (1):

In formula (1), R ¹ represents a group in which the R ¹ -O bond is cleaved by exposure to heat or infrared rays. ^{R 2} and R ³ each independently represent a hydrogen atom or an alkyl group, or R ² and R ³ may be linked to each other to form a ring. Ar ¹ and Ar ² each independently represent a group forming a benzene ring or a naphthalene ring. Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ -, or a dialkylmethylene group. R ⁴ and R ⁵ each independently represent an alkyl group or a group represented by the following formulas (2) to (4). R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group. R ⁰ represents a hydrogen atom, an alkyl group, or an aryl group. Za represents a counter ion for neutralizing the charge. However, the compound represented by formula (1) has at least one group represented by formulae (2) to (4) as R ⁴ or R ⁵ or in R ¹ , Ar ¹ or Ar ² .

In formulas (2) to (4), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms. W represents a single bond or an oxygen atom. n1 represents an integer from 1 to 45. R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or -C(=O)-R ^{14. R 14} represents an alkyl group having 1 to 12 carbon atoms. R ¹² and R ¹³ each independently represent a single bond or an alkylene group having 1 to 12 carbon atoms. M represents a hydrogen atom, a Na atom, a K atom or an onium group.

Patent Document 3 describes a lithographic printing plate precursor having a support, an image recording layer containing a polymerizable compound and a photopolymerization initiator, and a top layer on the image recording layer, the top layer having a thickness of between 0.1 g/ ^m2 and 1.75 g/ ^m2 , the top layer containing an infrared absorber having a thermally dissociable group that is converted into a strong electron-donating group by heat and/or infrared irradiation, and the top layer is capable of forming an image by heat and/or infrared irradiation.

Patent Document 1: International Publication No. 2019/151447 Patent Document 2: International Publication No. 2017/141882 Patent Document 3: International Publication No. 2019/219560

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

Means for solving the above problems include the following aspects.
<1> A lithographic printing plate precursor having on a support a layer containing a color-forming compound having a group that is cleaved by exposure to heat or infrared light, and having a sagging shape in which the sagging amount X is 25 μm to 150 μm and the sagging width Y is 70 μm to 300 μm at the ends of at least two opposing sides of the support.
<2> The lithographic printing plate precursor according to <1>, wherein the layer containing a color-forming compound is an image recording layer.
<3> An image recording layer is provided on a support,
The lithographic printing plate precursor according to <1>, further comprising a layer containing the color-forming compound on the image recording layer.
<4> The lithographic printing plate precursor according to any one of <1> to <3>, wherein the color-forming compound having a group that is cleaved by exposure to heat or infrared light is a compound represented by the following formula (1):

In formula (1), M ¹ is a group that is cleaved by exposure to heat or infrared rays, R ² and R ³ each independently represent a hydrogen atom or an alkyl group, R ² and R ³ may be bonded to each other to form a ring, Ar ¹ and Ar ² each independently represent a group that forms a benzene ring or a naphthalene ring, Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ - or a dialkylmethylene group, R ⁴ and R ⁵ each independently represent an aliphatic hydrocarbon group, R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, R ⁰ represents a hydrogen atom, an alkyl group or an aryl group, and Za represents a counter ion that neutralizes the charge.

<5> The lithographic printing plate precursor according to <4>, wherein at least one group selected from the group consisting of R ⁴ , R ⁵ , M ¹ , Ar ¹ and Ar ² in the compound represented by formula (1) has a hydrophilic group.
<6> The lithographic printing plate precursor according to <5>, wherein the hydrophilic group is a group represented by any one of the following formulas (2) to (5):

In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer from 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or an acyl group having 2 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position with other structures.

<7> The lithographic printing plate precursor according to any one of <4> to <6>, wherein M ¹ in the above formula (1) is -NR ^a R ^b , -NR ^c (SO ₂ R ^d ) or -NR ^e (CO ₂ R ^f ).
wherein R ^a and R ^b each independently represent an aryl group, R ^c , R ^e and R ^f each independently represent an alkyl group or an aryl group, R ^d represents an alkyl group, an aryl group, or -NR ^d1 R ^d2 , and R ^d1 and R ^d2 each independently represent a hydrogen atom, an alkyl group or an aryl group.
<8> The lithographic printing plate precursor according to any one of <4> to <6>, wherein M ¹ in formula (1) is —O—R ¹ .
Here, R ¹ represents a group in which the R ¹ -O bond is cleaved by heat or exposure to infrared rays.
<9> The lithographic printing plate precursor according to <8>, wherein R ¹ is a group represented by the following formula (6):

In formula (6), R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom, an alkyl group or an aryl group, E represents an onium group, and the wavy line portion represents the bonding position to the oxygen atom.

<10> A lithographic printing plate precursor described in <9>, wherein E in the above formula (6) is a pyridinium group represented by the following formula (7).

In formula (7), R ¹⁷ represents a halogen atom, an alkyl group, an aryl group, a hydroxyl group or an alkoxy group. When a plurality of R ^17s are present, the plurality of R ^17s may be the same or different, or the plurality of R ^17s may be linked to form a ring. n2 represents an integer of 0 to 4. R ¹⁸ represents an alkyl group, an aryl group or a group represented by any one of the following formulae (2) to (5). Zb represents a counter ion for neutralizing the charge.

In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer from 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or an acyl group having 2 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position with other structures.

<11> The lithographic printing plate precursor according to <2> or <3>, wherein the image recording layer contains a polymerization initiator and a polymerizable compound.
<12> The lithographic printing plate precursor according to <2>, <3> or <11>, wherein the image recording layer contains polymer particles.
<13> The lithographic printing plate precursor according to any one of <1> to <12>, further comprising a support-adsorbable compound having a molecular weight of 1,000 or less in any one of its layers.
<14> The lithographic printing plate precursor according to any one of <1> to <13>, further comprising a hydrophilic layer in an area within 1 cm from an edge of the image recording layer side of the lithographic printing plate precursor.
<15> A method for preparing a lithographic printing plate, comprising: a step of imagewise exposing the lithographic printing plate precursor according to any one of <1> to <14>; and a step of supplying at least one selected from the group consisting of a printing ink and a fountain solution on a printing press to remove the image-recording layer in a non-image area.
<16> A lithographic printing method comprising: a step of imagewise exposing the lithographic printing plate precursor according to any one of <1> to <14>; a step of supplying at least one selected from the group consisting of a printing ink and a fountain solution to remove the image recording layer in a non-image area on a printing press to prepare a lithographic printing plate; and a step of printing with the obtained lithographic printing plate.

According to one embodiment of the present disclosure, a lithographic printing plate precursor excellent in suppressing edge staining can be provided.
According to another embodiment of the present disclosure, there can be provided a method for producing a lithographic printing plate or a lithographic printing method using the above-mentioned lithographic printing plate precursor.

FIG. 2 is a schematic diagram showing an example of a cross-sectional shape of an end portion of a support of a lithographic printing plate precursor cut by a cutting device. FIG. 2 is a conceptual diagram illustrating an example of a cutting section of a slitter device. FIG. 2 is a schematic cross-sectional view of one embodiment of an aluminum support. FIG. 2 is a schematic cross-sectional view of another embodiment of an aluminum support. 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. FIG. 2 is a side view showing an example of a radial cell in electrochemical graining treatment using an alternating current in a method for producing an aluminum support. 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 the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
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 "step" in this specification includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved. In addition, in this disclosure, "mass %" and "weight %" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
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 of which are product names manufactured by Tosoh Corporation) using a differential refractometer with THF (tetrahydrofuran) as a solvent, and converted using polystyrene as a standard substance.
In this specification, 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.
The present disclosure will be described in detail below.

(Lithographic printing plate precursor)
The lithographic printing plate precursor according to the present disclosure has, on a support, a layer containing a color-forming compound having a group that is cleaved by exposure to heat or infrared light, and has a sagging shape with a sagging amount X of 25 μm to 150 μm and a sagging width Y of 70 μm to 300 μm at the ends of at least two opposing sides of the support.
Furthermore, the lithographic printing plate precursor according to the present disclosure is a negative-working lithographic printing plate precursor, and can be suitably used as an on-press development type lithographic printing plate precursor.

It has been found that the conventional lithographic printing plate precursors described in Patent Documents 1 to 3 do not have sufficient edge stain suppression properties.
As a result of extensive investigations, the present inventors have found that by adopting the above-mentioned configuration, it is possible to provide a lithographic printing plate precursor that is excellent in suppressing edge staining.
Although the detailed mechanism by which the above effects are obtained is unclear, it is speculated as follows.
By including a color-developing compound having a group that is cleaved by exposure to heat or infrared rays in any of the layers, the amount of dye required for color development is reduced, resulting in a smaller amount of hydrophobic material, which is relatively more hydrophilic, suppressing residual film and suppressing edge staining. Furthermore, by having a specific droop shape on the edge of the support, it is presumed that ink transfer due to contact between the edge and the blanket is suppressed, resulting in excellent edge stain suppression.

Furthermore, the lithographic printing plate precursor according to the present disclosure contains in any one of its layers a color-forming compound having a group that is cleaved by exposure to heat or infrared light, and thus has excellent color development and color development over time due to the dye generated from the color-forming compound. Furthermore, the excellent color development property also makes it possible to excellently inspect the exposed lithographic printing plate precursor, and the excellent color development over time also makes it possible to excellently inspect the exposed lithographic printing plate precursor after aging.
Furthermore, the lithographic printing plate precursor according to the present disclosure contains, in one of its layers, a color-forming compound having a group that is cleaved by exposure to heat or infrared light, and has a specific droop shape at the edge of the support, and therefore, although the detailed mechanism is unknown, it also has excellent on-press developability and chemical resistance.

The lithographic printing plate precursor according to the present disclosure has a layer containing a color-forming compound having a group that is cleaved by exposure to heat or infrared rays.
The layer containing the color-forming compound having a group cleaved by heat or infrared exposure is not particularly limited as long as it is any layer on the support, but is preferably at least one layer selected from the group consisting of an image recording layer and a protective layer. From the viewpoint of on-machine developability and chemical resistance, it is more preferably at least an image recording layer. Also, from the viewpoint of color development over time, it is more preferably at least a protective layer.
[0043] Furthermore, from the viewpoint of color development over time, the lithographic printing plate precursor according to the present disclosure preferably has an image recording layer on a support and has a layer containing the above-mentioned color-forming compound on the image recording layer, and more preferably has an image recording layer on a support and has a layer containing the above-mentioned color-forming compound as a protective layer on the image recording layer.
Furthermore, from the viewpoints of edge stain suppression and on-press developability, the lithographic printing plate precursor according to the present disclosure preferably contains a support-adsorbable compound having a molecular weight of 1,000 or less in any one of its layers, and more preferably has a protective layer and contains a support-adsorbable compound having a molecular weight of 1,000 or less in at least the protective layer.

<Drop shape>
The lithographic printing plate precursor according to the present disclosure has a sagging shape with a sagging amount X of 25 μm to 150 μm and a sagging width Y of 70 μm to 300 μm at the ends of at least two opposing sides of the support.
At the end of the support, the vertical distance X from an extension line of the surface of the support on the image recording layer side to the curved portion bent in the thickness direction of the support is called the "sagging amount", and the distance Y of the curved portion in a direction parallel to the surface of the support on the image recording layer side is called the "sagging width".
Fig. 1 shows an example of the cross-sectional shape of the edge of the support of a lithographic printing plate precursor cut by a cutting device. As shown in Fig. 1, the vertical distance of the curved surface portion curved in the thickness direction of the support is the sagging amount X, and the distance of the curved surface portion in the direction parallel to the surface of the support on the image recording layer side is the sagging width Y.
Edge staining in a lithographic printing plate precursor occurs when printing ink components that are pushed from non-image areas to the edges are transferred to the blanket, so it is necessary to increase the amount of sagging at the edges to prevent contact between the edges and the blanket.
From the viewpoints of edge stain suppression, on-press developability, and chemical resistance, the sagging amount X is preferably 35 μm to 150 μm, more preferably 50 μm to 150 μm, and even more preferably 50 μm to 100 μm.
From the viewpoints of edge stain suppression, on-press developability, and chemical resistance, the sagging width Y is preferably in the range of 90 μm to 300 μm, and more preferably 150 μm to 250 μm.
The preferable ranges of the sagging amount X and the sagging width Y are not related to the edge shape of the back surface of the support.

The method for forming the sagging shape is not particularly limited, and any known cutting method can be used, but a suitable example is a method in which the sagging shape is created by adjusting the gap, biting amount, and blade angle between the upper and lower cutting blades of a slitter device.
2 is a conceptual diagram showing the cutting section of the slitter device. In the slitter device, a pair of upper and lower cutting blades 210, 220 are arranged on the left and right. These cutting blades 210, 220 are made of disc-shaped round blades, and the upper cutting blades 210a and 210b are supported coaxially on a rotating shaft 211, and the lower cutting blades 220a and 220b are supported coaxially on a rotating shaft 221. The upper cutting blades 210a and 210b and the lower cutting blades 220a and 220b are rotated in opposite directions. An aluminum support 230 is passed between the upper cutting blades 210a, 210b and the lower cutting blades 220a, 220b and cut to a predetermined width. More specifically, by adjusting the gap between the upper cutting blade 210a and the lower cutting blade 220a of the cutting section of the slitter device in Figure 2, and the gap between the upper cutting blade 210b and the lower cutting blade 220b, it is possible to form an end portion having a droopy shape as shown in Figure 1.
The cutting is preferably performed at least in the portion having the hydrophilized edge layer described below.

<Image Recording Layer>
From the viewpoints of on-press developability and chemical resistance, the image recording layer in the lithographic printing plate precursor according to the present disclosure preferably contains a color-forming compound having a group that is cleaved by exposure to heat or infrared rays.
The image recording layer in the present disclosure is a negative image recording layer, and is preferably a water-soluble or water-dispersible negative image recording layer.
The image recording layer in the present disclosure preferably contains a polymerization initiator and a polymerizable compound, and more preferably contains an infrared absorbing agent other than the color-forming compound, a polymerization initiator, and a polymerizable compound.
The image recording layer in the present disclosure is preferably an on-press development type image recording layer.
Each component contained in the image recording layer will be described in detail below.

--Color-forming compound having a group that is cleaved by exposure to heat or infrared rays--
The color-forming compound having a group that is cleaved by exposure to heat or infrared rays may be a compound having a group that is cleaved by directly absorbing heat or infrared rays, or may be a compound having a group that is cleaved by heat or the like generated when an infrared absorbing agent contained separately absorbs infrared rays.
Furthermore, the color-forming compound having a group that is cleaved by exposure to heat or infrared rays is a compound that develops color by cleavage of the above group.
In the present disclosure, color development refers to the coloring or absorption becoming stronger after heating or exposure than before heating or exposure, and having absorption in the visible light region.
Among these, the color-forming compound having a group that is cleaved by heat or infrared exposure is preferably a decomposable infrared absorber from the viewpoints of edge stain suppression, color development, color development over time, on-machine developability, and chemical resistance, and is more preferably a compound represented by the following formula (A):

In formula A, ⁺ Y ^A1 = has the following structure:

is represented by one of
Y ^A2 - has the following structure:

n is 0, 1, 2 or 3; p and q each independently represent 0, 1 or 2; R ^A1 and R ^A2 each independently represent a hydrocarbon group; or two of R ^A1 , R ^A2 , R ^Ad and R ^Aa together comprise the atoms necessary to form a cyclic structure; at least one of R ^Ad represents a group that is converted into a group that is a stronger electron donor than R ^Ad by a chemical reaction induced by exposure to infrared radiation or heat; or at least one of R ^Aa represents a group that is converted into a group that is a stronger electron donor than R ^Aa by a chemical reaction induced by exposure to infrared radiation or heat; and the other R ^Ad and R ^Aa each independently represent a group selected from the group consisting of a hydrogen atom, a halogen atom, ^{-R Ae} , -OR ^Af , -SR ^Ag and -NR ^Au R ^{Av ;} , R ^Ag , R ^Au and R ^Av each independently represent an aliphatic hydrocarbon group, an aryl group or a heteroaryl group, and the above conversion is one that provides an increase in light absorption between wavelengths of 400 nm and 700 nm.
In addition, the hydrocarbon groups in R ^A1 and R ^A2 , and the aliphatic hydrocarbon groups, aryl groups, or heteroaryl groups in R ^Ae , R ^Af , R ^Ag , R ^Au , and R ^Av may have a substituent.

Moreover, the above R ^Ad that is converted by a chemical reaction is preferably any one of the groups shown below.

In the above formula, Aa, Ab, Ac and Ad each independently represent 0 or 1; -L ^A - represents a bonding group; R ^A17 represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or an optionally substituted heteroaryl group; or R ^A17 and R ^A3 , R ^A17 and R ^A5 , or R ^A17 and R ^A11 together comprise atoms necessary to form a ring structure; R ^A4 is -OR ^A10 , -NR ^A13 R ^A14 or -CF ₃ ; R ^A10 represents an optionally substituted aryl group, an optionally substituted ^heteroaryl group or an α-branched aliphatic hydrocarbon group; ^A14 each independently represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or an optionally substituted heteroaryl group, or R ^A13 and R ^A14 together comprise the atoms necessary to form a ring structure, R ^A3 is a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group or an optionally substituted heteroaryl group, or R ^A3 together with at least one of R ^A10 , R ^A13 and R ^A14 comprise the atoms necessary to form a ring structure, R ^A6 represents an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, an optionally substituted heteroaryl group, -OR ^A10 , -NR ^A13 R ^A14 or -CF ₃ , where R ^A10 , R ^A13 and R ^A14 have the same meaning as in R ^A4 , and R ^A5 represents a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, or an optionally substituted heteroaryl group; or R ^A5 comprises the atoms necessary to form a ring structure together with at least one of R ^A10 , R ^A13 , and R ^A14 ; R ^A11 , R ^A15 , and R ^A16 each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, or an optionally substituted heteroaryl group; or R ^A15 and R ^A16 comprise the atoms necessary to form a ring structure together; R ^A12 represents an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, or an optionally substituted heteroaryl group; R ^A7 and R ^A9 each independently represent a hydrogen atom or an optionally substituted aliphatic hydrocarbon group; R ^A8 represents -COO- or -COOR ^A8' ; ^A8' represents a hydrogen atom, an alkali metal cation, an ammonium ion, or a mono-, di-, tri-, or tetraalkylammonium ion; and R ^A18 represents an optionally substituted aryl group, an optionally substituted heteroaryl group, or an α-branched aliphatic hydrocarbon group.

In addition, as a color-developing compound having a group that is cleaved by exposure to heat or infrared light, from the viewpoints of edge stain suppression, color development, color development over time, on-machine developability, and chemical resistance, it is particularly preferable to use a compound represented by the following formula (1).

In formula (1), M ¹ is a group that is cleaved by exposure to heat or infrared rays, R ² and R ³ each independently represent a hydrogen atom or an alkyl group, R ² and R ³ may be bonded to each other to form a ring, Ar ¹ and Ar ² each independently represent a group that forms a benzene ring or a naphthalene ring, Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ - or a dialkylmethylene group, R ⁴ and R ⁵ each independently represent an aliphatic hydrocarbon group, R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, R ⁰ represents a hydrogen atom, an alkyl group or an aryl group, and Za represents a counter ion that neutralizes the charge.

The compound represented by the above formula (1) is preferably a compound that decomposes upon exposure to heat or infrared rays to produce a compound having a maximum absorption wavelength in the range of 500 nm to 600 nm.
The color-developing mechanism of the compound represented by formula (1) is that M ¹ is cleaved by exposure to heat or infrared rays, resulting in color development. For example, when M ¹ is R ¹ -O-, as described below, the inventors presume that the cleaved oxygen atom forms a carbonyl group, as shown below, and a merocyanine dye, which is a color-developing substance, is generated and develops color.
The present inventors also presume that in order to produce a merocyanine dye, it is important that ^R1 , the bond of which is cleaved by exposure to heat or infrared light, is bonded to the cyanine dye structure via an oxygen atom.

Preferred embodiments of ^M1 in formula (1) will be described later.
Furthermore, R ² to R ⁹ , R ⁰ , Ar ¹ and Ar ² may have a substituent such as a hydrophilic group described below. Examples of the substituent include an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a carboxylate group, a sulfo group, a sulfonate group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a phosphonic acid group, a phosphonate group, and a group combining these groups. Furthermore, when the above group is an anionic group, it may form a salt, and the counter cation may be a cation of a cyanine dye structure, or a proton, a metal cation, an onium, or the like.

The alkyl group for R ² to R ⁹ and R ⁰ in formula (1) is preferably an alkyl group having 1 to 30 carbon atoms, more preferably an alkyl group having 1 to 15 carbon atoms, and even more preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group may be linear, branched, or have a ring structure.
Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a hexadecyl group, an octadecyl group, an eicosyl group, an isopropyl group, an isobutyl group, a s-butyl group, a t-butyl group, an isopentyl group, a neopentyl group, a 1-methylbutyl group, an isohexyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a cyclohexyl group, a cyclopentyl group, and a 2-norbornyl group.
Among these alkyl groups, a methyl group, an ethyl group, a propyl group, or a butyl group is particularly preferred.

The aryl group for R ⁰ is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 20 carbon atoms, and even more preferably an aryl group having 6 to 12 carbon atoms.
The aryl group may have a substituent, for example, an alkyl group, an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a carboxylate group, a sulfo group, a sulfonate group, an alkyloxycarbonyl group, an aryloxycarbonyl group, or a combination thereof.
Specific examples include a phenyl group, a naphthyl group, a p-tolyl group, a p-chlorophenyl group, a p-fluorophenyl group, a p-methoxyphenyl group, a p-dimethylaminophenyl group, a p-methylthiophenyl group, and a p-phenylthiophenyl group.
Of these aryl groups, a phenyl group, a p-methoxyphenyl group, a p-dimethylaminophenyl group, and a naphthyl group are preferred.

It is preferable that ^R2 and ^R3 are linked to form a ring.
When ^R2 and ^R3 are linked to form a ring, the ring is preferably a 5- or 6-membered ring, more preferably a 6-membered ring.

Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ - or a dialkylmethylene group, preferably -NR ⁰ - or a dialkylmethylene group, more preferably a dialkylmethylene group.
R ⁰ represents a hydrogen atom, an alkyl group or an aryl group, and is preferably an alkyl group.

It is preferable that ^R4 and ^R5 are the same group. When ^R4 and ^R5 have an anionic group, it is preferable that ^R4 and ^R5 are the same group except that they have an anionic group and have or do not have a counter cation.
Furthermore, ^R4 and ^R5 are each preferably independently a straight-chain alkyl group or an alkyl group having a terminal sulfonate group, and more preferably a methyl group, an ethyl group, or a butyl group having a terminal sulfonate group.
The counter cation of the sulfonate group may be the quaternary ammonium group in formula (1), or an alkali metal cation or an alkaline earth metal cation.
Furthermore, from the viewpoint of improving the water solubility of the compound represented by formula (1), ^R4 and ^R5 are each independently preferably an alkyl group having an anionic structure, more preferably an alkyl group having a carboxylate group or a sulfonate group, and further preferably an alkyl group having a sulfonate group at the terminal.
Furthermore, from the viewpoints of shifting the maximum absorption wavelength of the compound represented by formula (1) to a longer wavelength and of color development and printing durability in a lithographic printing plate, ^R4 and ^R5 are each preferably independently an alkyl group having an aromatic ring, more preferably an alkyl group having an aromatic ring at a terminal, and particularly preferably a 2-phenylethyl group, a 2-naphthalenylethyl group, or a 2-(9-anthracenyl)ethyl group.

R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, and are preferably a hydrogen atom.
Ar ¹ and Ar ² each independently represent a group forming a benzene ring or a naphthalene ring. The benzene ring and the naphthalene ring may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a carboxylate group, a sulfo group, a sulfonate group, an alkyloxycarbonyl group, an aryloxycarbonyl group, and a group formed by combining these groups, and the like, but an alkyl group is preferred.
[0043] In addition, from the viewpoints of shifting the maximum absorption wavelength of the compound represented by formula (1) to a longer wavelength and of color development and printing durability in a lithographic printing plate, ^Ar1 and ^Ar2 are each preferably independently a group forming a naphthalene ring or a benzene ring having an alkyl group or an alkoxy group as a substituent, more preferably a group forming a naphthalene ring or a benzene ring having an alkoxy group as a substituent, and particularly preferably a group forming a naphthalene ring or a benzene ring having a methoxy group as a substituent.

Za represents a counter ion that neutralizes the charge, and when Za represents an anion species, examples thereof include a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a p-toluenesulfonate ion, a perchlorate ion, and the like, with a hexafluorophosphate ion being particularly preferred.When Za represents a cationic species, an alkali metal ion, an alkaline earth metal ion, an ammonium ion, a pyridinium ion, or a sulfonium ion is preferred, a sodium ion, a potassium ion, an ammonium ion, a pyridinium ion, or a sulfonium ion is more preferred, and a sodium ion, a potassium ion, or an ammonium ion is even more preferred.
R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , Y ¹ and Y ² may have an anionic structure or a cationic structure. When all of R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , Y ¹ and Y ² are electrically neutral groups, Za is a monovalent counter anion. However, when, for example, R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , Y ¹ and Y ² have two or more anionic structures, Za can also be a counter cation.

In formula (1), Ar ¹ or Ar ² is preferably a group that forms a group represented by the following formula (8).

In formula (8), R ¹⁹ represents an alkyl group having 1 to 12 carbon atoms or a group represented by any one of formulas (2) to (4) described below, n3 represents an integer of 1 to 4, and * represents a bonding site.

From the viewpoints of edge stain suppression, on-press developability, and chemical resistance, it is preferable that at least one group selected from the group consisting of R ⁴ , R ⁵ , M ¹ , Ar ¹ , and Ar ² in the compound represented by formula (1) above has a hydrophilic group, it is more preferable that at least one group selected from the group consisting of R ⁴ , R ⁵ , and M ¹ has a hydrophilic group, it is even more preferable that at least one group selected from the group consisting of R ⁴ and R ⁵ has a hydrophilic group, and it is particularly preferable that R ⁴ and R ⁵ each independently have a hydrophilic group.

Examples of the hydrophilic group include a polyalkyleneoxy group, an acid group, a salt of an acid group, an alkoxy group, and a hydroxy group.
Among these, from the viewpoints of edge stain suppression property, on-press developability, and chemical resistance, the hydrophilic group is preferably a group represented by any one of the following formulas (2) to (5), more preferably a group represented by either the following formula (2) or formula (5), and particularly preferably a group represented by the following formula (2).

In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer from 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or an acyl group having 2 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position with other structures.

Specific examples of the alkylene group represented by R ¹⁰ include an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, an n-pentylene group, an isopentylene group, an n-hexyl group, and an isohexyl group. Of these, an ethylene group, an n-propylene group, an isopropylene group, or an n-butylene group is preferred, and an n-propylene group is particularly preferred.
n1 is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 1 to 3.
Specific examples of the alkyl group represented by R ¹¹ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an n-octyl group, and an n-dodecyl group. Of these, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, or a tert-butyl group is preferable, a methyl group or an ethyl group is more preferable, and a methyl group is particularly preferable.
Specific examples of the acyl group for R ¹¹ include an acetyl group, a propionyl group, a pivaloyl group, etc. Among these, an acetyl group is preferable.

Specific examples of the group represented by formula (2) are shown below, but the present disclosure is not limited to these. In the following structural formula, Me represents a methyl group, Et represents an ethyl group, and * represents a bonding site.

In formula (3) or formula (4), specific examples of the alkylene group represented by R ¹² or R ¹³ include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, an n-pentylene group, an isopentylene group, an n-hexyl group, an isohexyl group, an n-octylene group, an n-dodecylene group, and the like. An ethylene group, an n-propylene group, an isopropylene group, or an n-butylene group is preferred, and an ethylene group or an n-propylene group is particularly preferred.
When a group represented by formula (3) or formula (4) is present in a group represented by Ar ¹ or Ar ² of a compound represented by formula (1), R ¹² or R ¹³ is preferably a single bond.
When a group represented by formula (3) or formula (4) is present in ^M1 of a compound represented by formula (1) or as a group represented by ^R4 or ^R5 , ^R12 or ^R13 is preferably an alkylene group.
In formula (4), the two M's may be the same or different.

In formula (3) or formula (4), specific examples of the onium group represented by M include an ammonium group, an iodonium group, a phosphonium group, a sulfonium group, etc.

The ammonium group includes a group represented by the following formula (A1):

In formula (A1), R _a to R _d each independently represent a hydrogen atom or an aryl group, an alkyl group, an alkenyl group, or an alkynyl group having 20 or less carbon atoms. The aryl group, the alkyl group, the alkenyl group, or the alkynyl group may have a substituent. Examples of the substituent include an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 12 carbon atoms, an alkynyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, a halogen atom, an alkylamino group having 1 to 12 carbon atoms, a dialkylamino group having 2 to 12 carbon atoms, an alkylamide group or an arylamide group having 2 to 12 carbon atoms, a carbonyl group, a carboxy group, a cyano group, a sulfonyl group, a thioalkyl group having 1 to 12 carbon atoms, a thioaryl group having 6 to 12 carbon atoms, and a hydroxy group. R _a to R _d are preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 carbon atoms.

Specific examples of ammonium groups are shown below, but the present disclosure is not limited to these. In the following structural formulas, Me represents a methyl group, and Et represents an ethyl group.

The iodonium group includes a group represented by the following formula (B1):

In formula (B1), R _e to R _f each independently have the same definition as R _a to R _d in formula (A1) above. Preferred examples of R _e to R _f include aryl groups having 6 to 20 carbon atoms.

Specific examples of iodonium groups are shown below, but the present disclosure is not limited to these.

The phosphonium group includes a group represented by the following formula (C1):

In formula (C1), R _g to R _j each independently have the same definition as R _a to R _d in formula (A1) above. Preferred examples of R _g to R _j include aryl groups having 6 to 20 carbon atoms.

Specific examples of phosphonium groups are shown below, but the present disclosure is not limited to these.

The sulfonium group includes a group represented by the following formula (D1):

In formula (D1), R _k to R _m each independently have the same meaning as R _a to R _d in formula (A1). Preferred examples include aryl groups having 6 to 20 carbon atoms. Preferred examples of R _k to R _m include aryl groups having 6 to 20 carbon atoms.

Specific examples of sulfonium groups are shown below, but the present disclosure is not limited to these.

Of the above onium groups, ammonium groups are preferred.
When the compound represented by formula (1) contains an onium group, M may be the above-mentioned onium group.
The onium group may be present as an intramolecular onium salt.

Specific examples of the group represented by formula (3) are shown below, but the present disclosure is not limited to these. In the following structural formula, Et represents an ethyl group, and * represents a bonding site.

Specific examples of the group represented by formula (4) are shown below, but the present disclosure is not limited to these. In the following structural formula, Et represents an ethyl group, and * represents a bonding site.

Specific examples of the group represented by formula (5) are shown below, but the present disclosure is not limited to these. In the following structural formula, * represents a binding site.

The compound represented by formula (1) may have one or more groups represented by any one of formulas (2) to (5). The upper limit of the number of groups represented by any one of formulas (2) to (5) is preferably 5. The number of groups represented by any one of formulas (2) to (5) is preferably 1 to 5, more preferably 2 to 3.
The group represented by any one of formulas (2) to (5) may be present as the group represented by R ⁴ or R ⁵ in the compound represented by formula (1), or may be present in the group represented by M ¹ , Ar ¹ or Ar ² .
The group represented by any one of formulas (2) to (5) is particularly preferably R ⁴ and R ^5. In addition, the group represented by any one of formulas (2) to (5) is preferably present in the groups represented by Ar ¹ and Ar ² .

In terms of edge stain suppression properties, color development, and color ^development over time ^, M ¹ in the above formula (1) is preferably ^{--NR.sub.aR.sub.b , --NR.sub.c} ( _{SO.sub.2R.sub.d} ) or ^--NR.sub.e ( _{CO.sub.2R.sub.f} ).
wherein R ^a and R ^b each independently represent an aryl group, R ^c , R ^e and R ^f each independently represent an alkyl group or an aryl group, R ^d represents an alkyl group, an aryl group, or -NR ^d1 R ^d2 , and R ^d1 and R ^d2 each independently represent a hydrogen atom, an alkyl group or an aryl group.

The alkyl group in R ^c to R ^f , R ^d1 and R ^d2 is preferably an alkyl group having 1 to 20 carbon atoms.
The aryl group in R ^a to R ^f , R ^d1 and R ^d2 is preferably an aryl group having 6 to 20 carbon atoms.
The alkyl group and aryl group in R ^a to R ^f , R ^d1 and R ^d2 may have a substituent. Examples of the substituent include an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a carboxylate group, a sulfo group, a sulfonate group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a phosphonic acid group, a phosphonate group, and a group combining these groups. When the above group is an anionic group, it may form a salt, and the counter cation may be a cation of a cyanine dye structure, a proton, a metal cation, an onium, or the like.

Moreover, M ¹ in the above formula (1) is preferably —O—R ¹ from the viewpoints of edge stain suppression, color development, and color development over time.
Here, R ¹ represents a group in which the R ¹ -O bond is cleaved by heat or exposure to infrared rays.

From the viewpoint of color development, R ¹ is preferably a group represented by any one of the following formulas 1-1 to 1-7, and more preferably a group represented by any one of the following formulas 1-1 to 1-3.

In formulas 1-1 to 1-7, ● represents a bonding site with an oxygen atom; R ²⁰ each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ , or -SR ²⁷ ; R ²¹ each independently represents a hydrogen atom, an alkyl group, or an aryl group; R ²² represents an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ , -SR ²⁷ , -C(═O)R ²⁸ , -OC(═O)R ²⁸ , or a halogen atom; R ²³ represents an aryl group, an alkenyl group, an alkoxy group, or an onium group; R ²⁴ to R ²⁷ each independently represent a hydrogen atom, an alkyl group, or an aryl group; and R ²⁸ each independently represents an alkyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ , or -SR ²⁷ , and ^Z1 represents a counter ion that neutralizes the charge.

When R ²⁰ , R ²¹ and R ²⁴ to R ²⁸ are alkyl groups, the preferred embodiments are the same as the preferred embodiments of the alkyl groups in R ² to R ⁹ and R ⁰ .
The alkenyl group for R ²⁰ and R ²³ preferably has 1 to 30 carbon atoms, more preferably 1 to 15 carbon atoms, and even more preferably 1 to 10 carbon atoms.
When R ²⁰ to R ²⁸ are aryl groups, the preferred embodiments are the same as the preferred embodiments of the aryl group for R ⁰ .

From the viewpoint of color development properties, R ²⁰ in formula 1-1 is preferably an alkyl group, an alkenyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ , or -SR ²⁷ , more preferably an alkyl group, -OR ²⁴ , -NR ²⁵ R ²⁶ , or -SR ²⁷ , still more preferably an alkyl group or -OR ²⁴ , and particularly preferably -OR ²⁴ .
When R ²⁰ in formula 1-1 is an alkyl group, the alkyl group is preferably an alkyl group having an arylthio group or an alkyloxycarbonyl group at the α-position.
When R ²⁰ in formula 1-1 is —OR ²⁴ , R ²⁴ is preferably an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms, further preferably an isopropyl group or a t-butyl group, and particularly preferably a t-butyl group.

From the viewpoint of color development, R ²¹ in formula 1-2 is preferably a hydrogen atom.
Furthermore, from the viewpoint of color development, R ²² in formula 1-2 is preferably -C(=O)OR ²⁴ , -OC(=O)OR ²⁴ or a halogen atom, and more preferably -C(=O)OR ²⁴ or -OC(=O)OR ^24. When R ²² in formula 1-2 is -C(=O)OR ²⁴ or -OC(=O)OR ²⁴ , R ²⁴ is preferably an alkyl group.

From the viewpoint of color development, it is preferable that R ²¹ in formula 1-3 is each independently a hydrogen atom or an alkyl group, and it is more preferable that at least one R ¹¹ in formula 1-3 is an alkyl group.
The alkyl group for R ²¹ is preferably an alkyl group having 1 to 10 carbon atoms, and more preferably an alkyl group having 3 to 10 carbon atoms.
Furthermore, the alkyl group in R ²¹ is preferably an alkyl group having a branch containing a ring structure, more preferably a secondary or tertiary alkyl group, and further preferably an isopropyl group, a cyclopentyl group, a cyclohexyl group, or a t-butyl group.
From the viewpoint of color development, R ²³ in formula 1-3 is preferably an aryl group, an alkoxy group or an onium group, more preferably a p-dimethylaminophenyl group or a pyridinium group, and even more preferably a pyridinium group.
The onium group in R ²³ includes a pyridinium group, an ammonium group, a sulfonium group, etc. The onium group may have a substituent. The substituent includes an alkyl group, an alkoxy group, an aryloxy group, an amino group, an alkylthio group, an arylthio group, a halogen atom, a carboxy group, a sulfo group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a group combining these, etc., but an alkyl group, an aryl group, and a group combining these are preferred.
Among these, a pyridinium group is preferred, and examples thereof include an N-alkyl-3-pyridinium group, an N-benzyl-3-pyridinium group, an N-(alkoxypolyalkyleneoxyalkyl)-3-pyridinium group, an N-alkoxycarbonylmethyl-3-pyridinium group, an N-alkyl-4-pyridinium group, an N-benzyl-4-pyridinium group, an N-(alkoxypolyalkyleneoxyalkyl)-4-pyridinium group, and an N-alkoxycarbonylmethyl-4-pyridinium group. An N-alkyl-3,5-dimethyl-4-pyridinium group or an N-alkyl-3-pyridinium group is more preferred, an N-alkyl-3-pyridinium group or an N-alkyl-4-pyridinium group is even more preferred, an N-methyl-3-pyridinium group, an N-octyl-3-pyridinium group, an N-methyl-4-pyridinium group or an N-octyl-4-pyridinium group is particularly preferred, and an N-octyl-3-pyridinium group or an N-octyl-4-pyridinium group is most preferred.
Furthermore, when R ²³ is a pyridinium group, examples of the counter anion include a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a p-toluenesulfonate ion, a perchlorate ion, and the like, with the p-toluenesulfonate ion and the hexafluorophosphate ion being preferred.

From the viewpoint of color development, R ²⁰ in formula 1-4 is preferably an alkyl group or an aryl group, and it is more preferable that one of the two R ²⁰ 's is an alkyl group and the other is an aryl group.
From the viewpoint of color development, R ²⁰ in formula 1-5 is preferably an alkyl group or an aryl group, more preferably an aryl group, and further preferably a p-methylphenyl group.
From the viewpoint of color development, each R ²⁰ in formula 1-6 is preferably an alkyl group or an aryl group, and more preferably a methyl group or a phenyl group.
From the viewpoint of color development, Z ¹ in formula 1-7 may be any counter ion that neutralizes the charge, and the compound as a whole may be included in the above Za.
^Z1 is preferably a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a p-toluenesulfonate ion, or a perchlorate ion, and more preferably a p-toluenesulfonate ion or a hexafluorophosphate ion.

From the viewpoint of color development, R ¹ is more preferably a group represented by the following formula (6).

In formula (6), R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom, an alkyl group or an aryl group, E represents an onium group, and the wavy line portion represents the bonding position to the oxygen atom.

The alkyl group represented by R ¹⁵ or R ¹⁶ is the same as the alkyl group represented by R ² to R ⁹ and R ⁰ , and preferred embodiments thereof are also the same as the preferred embodiments of the alkyl group represented by R ² to R ⁹ and R ⁰ .
The aryl group represented by R ¹⁵ or R ¹⁶ is the same as the aryl group in R ⁰ , and preferred embodiments thereof are also the same as the preferred embodiments of the aryl group in R ⁰ .
The onium group represented by E is the same as the onium group represented by R ²³ , and preferred embodiments thereof are also the same as the preferred embodiments of the onium group represented by R ²³ .

From the viewpoint of color development, it is preferable that E in the above formula (6) is a pyridinium group represented by the following formula (7).

In formula (7), R ¹⁷ represents a halogen atom, an alkyl group, an aryl group, a hydroxyl group or an alkoxy group. When a plurality of R ^17s are present, the plurality of R ^17s may be the same or different, or the plurality of R ^17s may be linked to form a ring. n2 represents an integer of 0 to 4. R ¹⁸ represents an alkyl group, an aryl group or a group represented by any one of the following formulae (2) to (5). Zb represents a counter ion for neutralizing the charge.

In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer of 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position to another structure.

The alkyl group or aryl group represented by ^R17 or ^R18 is the same as the alkyl group in ^R2 to ^R9 and ^R0 or the aryl group in ^R0 , and preferred embodiments are also the same as the preferred embodiments of the alkyl group in ^R2 to ^R9 and ^R0 or the aryl group in ^R0 .
The alkoxy group represented by R ¹⁷ is preferably an alkoxy group having 1 to 10 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, and a tert-butoxy group.
n2 is preferably 0.
The counter ion for neutralizing the charge represented by Zb is the same as ^Z1 in formula (1-7), and preferred embodiments thereof are also the same as the preferred embodiments of ^Z1 in formula (1-7).
In addition, the groups represented by formulae (2) to (5) in R ¹⁸ of formula (7) have the same meanings as the groups represented by formulae (2) to (5) described above, and preferred embodiments are also the same.

Preferred examples of R ¹ are given below, but the present disclosure is not limited thereto. In addition, TsO ^{4 -} represents a tosylate anion, and ● represents a bonding site with an oxygen atom.

Specific examples of the color-forming compound are shown below, but the present disclosure is not limited thereto. In the following structural formula, Me represents a methyl group, and TsO ^{4 −} represents a tosylate anion.

The above color-forming compounds may be used alone or in combination of two or more.
In the image recording layer, the color-forming compound can be contained in any amount. From the viewpoints of edge stain suppression, color development, color development over time, on-machine developability, and chemical resistance, the content of the color-forming compound is preferably 0.1% by mass to 95% by mass, more preferably 1% by mass to 75% by mass, and particularly preferably 1% by mass to 50% by mass, relative to the total mass of the image recording layer.
Furthermore, the content of the color-forming compound in the image recording layer is preferably 1 mg/m ² to 100 mg/m ² , more preferably 10 mg/m ² to 80 mg/m 2, and particularly preferably 20 mg/m ² to 60 mg/m ² , from the viewpoints of edge stain suppression, color development, color development over ^time , on-machine developability, and chemical resistance.

The method for producing the color-forming compound is not particularly limited, and the compound can be produced by a known method.
For example, the compound represented by the above formula (1) can be obtained according to the synthesis method shown below as a synthesis scheme.
For example, preferred methods for introducing a group represented by any one of the above formulas 1-1, 1-5, and 1-6 include the synthetic schemes represented by the following formulas S1 to S3, and preferred methods for introducing a group represented by any one of the above formulas 1-2 to 1-4 include the synthetic scheme represented by the following formula S4.
In addition, DMAP represents N,N-dimethylamino-4-pyridine, AcONa represents sodium acetate, _NEt3 represents triethylamine, and catecol represents catechol. Furthermore, R represents a group corresponding to each part in Formula 1-1 to Formula 1-7.

-Support-adsorbing compound with molecular weight of 1,000 or less-
From the viewpoints of edge stain suppression and on-machine developability, it is preferable that the image recording layer contains a compound that is support-adsorbable, has a molecular weight of 1,000 or less, and does not have an ethylenically unsaturated group in the molecule (also referred to as a "support-adsorbable compound having a molecular weight of 1,000 or less" or a "support-adsorbable compound").
Here, the term "support adsorption" refers to the adsorption of the support to the anodized film. The presence or absence of adsorption of the support to the anodized film can be easily determined by the following method.
That is, a solution is prepared by dissolving the test compound in a readily soluble solvent (e.g., water). This solution is applied to an aluminum support having an anodized film so that the coating amount after drying is 30 mg/ ^m2 , and then dried. Next, the aluminum support to which the test compound has been applied is washed and dried five times using the readily soluble solvent, and the remaining amount of the test compound that has not been washed off is measured. The remaining amount may be measured by directly quantifying the amount of the remaining test compound, or by quantifying the amount of the test compound dissolved in the washing solution. The test compound can be quantified, for example, by X-ray fluorescence measurement, reflection spectrophotometric measurement, or the like.
If the remaining amount is 1 mg/ ^m2 or more, the test compound is determined to have the ability to be adsorbed to the support.

The support-adsorbing compound preferably has a group that exhibits adsorptivity to the anodized film of the aluminum support. Examples of groups that exhibit adsorptivity to the anodized film of the aluminum support include functional groups that can form chemical bonds (e.g., ionic bonds, hydrogen bonds, coordinate bonds) with substances (e.g., metals, metal oxides) or functional groups (e.g., hydroxyl groups) present on the surface of the anodized film. Among these functional groups, acid groups are preferred. The acid group preferably has an acid dissociation constant (pKa) of 7 or less. Examples of acid groups include phenolic hydroxyl groups, carboxy groups, -SO ₃ H, -OSO ₃ H, -PO ₃ H ₂ , -OPO ₃ H ₂ , -CONHSO ₂ -, -SO ₂ NHSO ₂ -, -COCH ₂ COCH ₃ , and the like. In particular, -OPO ₃ H ₂ and -PO ₃ H ₂ are preferred. The acid group may form a salt. Examples of salts formed by the acid group include alkali metal salts, alkaline earth metal salts, and ammonium salts.

The molecular weight of the support-adsorbing compound is 1,000 or less. By having a molecular weight of 1,000 or less, the compound is easily transferred to the surface of the anodized film during on-machine development, providing excellent edge stain prevention effects. The molecular weight is preferably 50 to 1,000, more preferably 50 to 800, and even more preferably 50 to 600.

The support-adsorbing compound does not have an ethylenically unsaturated group in the molecule. An ethylenically unsaturated group is a polymerizable group, and includes groups such as (meth)acrylic groups, vinyl groups, allyl groups, and styryl groups. Since the support-adsorbing compound does not have an ethylenically unsaturated group in the molecule, it is possible to prevent the specific low molecular weight compound from curing together with the image recording layer upon exposure to light.

An oxoacid can be used as the support-adsorbing compound. An oxoacid is a compound in which a hydroxyl group (-OH) and an oxo group (=O) are bonded to the same atom, and the hydroxyl group provides an acidic proton.

Examples of support-adsorbing compounds include phosphoric acid, polyphosphoric acid, metaphosphoric acid, ammonium monophosphate, ammonium diphosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium monophosphate, potassium diphosphate, sodium tripolyphosphate, potassium pyrophosphate, sodium hexametaphosphate, phosphinic acid, ethylphosphonic acid, propylphosphonic acid, i-propylphosphonic acid, butylphosphonic acid, hexylphosphonic acid, octylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2-hydroxyethylphosphonic acid, and their sodium or potassium salts; alkylphosphonic acid monoalkyl esters such as methyl methylphosphonate, methyl ethylphosphonate, and methyl 2-hydroxyethylphosphonate, and their sodium or potassium salts; alkylene diphosphonic acids such as methylene diphosphonic acid and ethylene diphosphonic acid, and their sodium or potassium salts; polyvinyl phosphonic acid, p-toluenesulfonic acid, sodium p-toluenesulfonate, sulfophthalic acid, and citric acid.

As the support-adsorbing compound, a compound represented by the following formula (B) is preferred.

In formula (B), nB represents an integer of 2 to 10, and R ^B1 , R ^B2 and R ^B3 each independently represent a hydrogen atom, an alkyl group or an alkylene oxide group.

The alkyl group in formula (B) is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, and even more preferably an alkyl group having 1 to 3 carbon atoms.
The alkylene oxide group in formula (B) is preferably an alkylene oxide group having 1 to 10 alkylene oxide units having 2 or 3 carbon atoms, more preferably an alkylene oxide group having 1 to 5 alkylene oxide units having 2 or 3 carbon atoms, and even more preferably an alkylene oxide group having 1 to 3 alkylene oxide units having 2 or 3 carbon atoms.

As the support-adsorbing compound, from the viewpoints of edge stain suppression and on-press developability, phosphoric acid, polyphosphoric acid, phosphonic acid or phosphinic acid are particularly preferred.

In addition, from the viewpoints of suppressing edge staining and on-press developability, it is preferable that the support-adsorbing compound contains a hydroxy acid compound having two or more hydroxy groups (hereinafter also referred to as a "specific hydroxy acid compound").

The specific hydroxy acid compound includes a hydroxycarboxylic acid having two or more hydroxy groups and a salt thereof, such as a sodium salt, a potassium salt, a lithium salt, a calcium salt, a magnesium salt, an aluminum salt, or an ammonium salt.
The number of hydroxy groups in the hydroxycarboxylic acid having two or more hydroxy groups is preferably 2 to 15, more preferably 3 to 10, and even more preferably 4 to 7.
The number of carboxy groups in the hydroxycarboxylic acid having two or more hydroxy groups is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3.

From the viewpoint of preventing edge staining, it is preferable that the specific hydroxy acid compound has high hydrophilicity. The hydrophilicity of the specific hydroxy acid compound can be expressed by the ClogP value, which is generally known as an index of the hydrophilicity of a compound. The specific hydroxy acid compound preferably has a ClogP value of 0.5 or less, more preferably -1 or less, and even more preferably -3 or less. Moreover, from the viewpoint of image forming properties in the edge region, the ClogP value of the specific hydroxy acid compound is preferably -10 or more, more preferably -7 or more, and even more preferably -5 or more.
Here, the ClogP value of the specific hydroxy acid compound is a numerical value calculated from the molecular structure using the molecular structure editor software "ChemDraw Professional 2016."

The molecular weight of the specific hydroxy acid compound is preferably 1,000 or less. By having a molecular weight of 1,000 or less, the specific hydroxy acid compound can easily migrate to the surface of the anodized film during on-machine development, effectively contributing to preventing edge staining. The molecular weight of the specific hydroxy acid compound is more preferably 80 to 1,000, even more preferably 100 to 500, and particularly preferably 100 to 300.

Examples of the specific hydroxy acid compound include glyceric acid, gluconic acid, tartaric acid, mevalonic acid, pantoic acid, quinic acid, shikimic acid, gallic acid, caffeic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, sodium gluconate, potassium gluconate, sodium tartrate, and sodium gallate.
As the specific hydroxy acid compound, from the viewpoints of edge stain suppression and on-press developability, gluconic acid, tartaric acid, mevalonic acid, quinic acid, sodium gluconate, potassium gluconate, or sodium tartrate is preferred, gluconic acid, sodium gluconate, or potassium gluconate is more preferred, and gluconic acid is particularly preferred.

The support-adsorbing compound may be used alone or in combination of two or more kinds.
The content of the support-adsorbing compound in the image recording layer is preferably 10 mg/m ² to 150 mg/m ² , more preferably 30 mg/m ² to 100 mg/m ² , and particularly preferably 50 mg/m ² to 100 mg/m ² , from the viewpoints of edge stain suppression and on-press developability.
In addition, from the viewpoints of edge stain suppression and on-machine developability, the content of the support-adsorbing compound is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 15% by mass, and even more preferably 2% by mass to 10% by mass, based on the total mass of the image recording layer.

--Polymerizable compound--
The image recording layer preferably contains a polymerizable compound.
The polymerizable compound used in the present disclosure may be, for example, a radical polymerizable compound or a cationic polymerizable compound, but is preferably an addition polymerizable compound (ethylenically unsaturated compound) having at least one ethylenically unsaturated bond.The ethylenically unsaturated compound is preferably a compound having at least one terminal ethylenically unsaturated bond, and more preferably a compound having two or more terminal ethylenically unsaturated bonds.The polymerizable compound has a chemical form such as, for example, a monomer, a prepolymer, i.e., a dimer, a trimer, or an oligomer, or a mixture thereof.

Examples of monomers include unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.), their esters, and amides. Preferably, esters of unsaturated carboxylic acids and polyhydric alcohol compounds, and amides of unsaturated carboxylic acids and polyvalent amine compounds are used. In addition, addition reaction products of unsaturated carboxylic acid esters or amides having nucleophilic substituents such as hydroxyl groups, amino groups, and mercapto groups with monofunctional or polyfunctional isocyanates or epoxy groups, and dehydration condensation reaction products of monofunctional or polyfunctional carboxylic acids are also preferably used. In addition, addition reaction products of unsaturated carboxylic acid esters or amides having electrophilic substituents such as isocyanate groups and epoxy groups with monofunctional or polyfunctional alcohols, amines, and thiols, and substitution reaction products of unsaturated carboxylic acid esters or amides having eliminable substituents such as halogen atoms and tosyloxy groups with monofunctional or polyfunctional alcohols, amines, and thiols are also suitable. As another example, it is also possible to use a group of compounds in which the above unsaturated carboxylic acids are replaced with unsaturated phosphonic acids, styrene, vinyl ethers, etc. These are described in JP-T-2006-508380, JP-A-2002-287344, JP-A-2008-256850, JP-A-2001-342222, JP-A-9-179296, JP-A-9-179297, JP-A-9-179298, JP-A-2004-294935, JP-A-2006-243493, JP-A-2002-275129, JP-A-2003-64130, JP-A-2003-280187, JP-A-10-333321, etc.

Specific examples of monomers of esters of polyhydric alcohol compounds and unsaturated carboxylic acids include acrylic esters such as ethylene glycol diacrylate, 1,3-butanediol diacrylate, tetramethylene glycol diacrylate, propylene glycol diacrylate, trimethylolpropane triacrylate, hexanediol diacrylate, tetraethylene glycol diacrylate, pentaerythritol tetraacrylate, sorbitol triacrylate, isocyanuric acid ethylene oxide (EO) modified triacrylate, polyester acrylate oligomer, etc. Specific examples of methacrylic esters include tetramethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, pentaerythritol trimethacrylate, bis[p-(3-methacryloxy-2-hydroxypropoxy)phenyl]dimethylmethane, bis[p-(methacryloxyethoxy)phenyl]dimethylmethane, etc. Specific examples of amide monomers of polyamine compounds and unsaturated carboxylic acids include methylene bisacrylamide, methylene bismethacrylamide, 1,6-hexamethylene bisacrylamide, 1,6-hexamethylene bismethacrylamide, diethylenetriamine trisacrylamide, xylylene bisacrylamide, and xylylene bismethacrylamide.

Also suitable are urethane-based addition polymerizable compounds produced by an addition reaction between an isocyanate and a hydroxy group. Specific examples thereof include vinyl urethane compounds containing two or more polymerizable vinyl groups in one molecule, which are obtained by adding a vinyl monomer containing a hydroxy group represented by the following formula (M) to a polyisocyanate compound having two or more isocyanate groups in one molecule, as described in JP-B-48-41708.
_CH2 =C( ^RM4 )COOCH2CH ₍ ^RM5 )OH(M)
In formula (M), R ^M4 and R ^M5 each independently represent a hydrogen atom or a methyl group.

In addition, urethane acrylates described in JP-A-51-37193, JP-B-2-32293, JP-B-2-16765, JP-A-2003-344997, and JP-A-2006-65210, JP-B-58-49860, JP-B-56-17654, JP-B-62-39417, and JP-B-62-39418 Also suitable are urethane compounds having an ethylene oxide skeleton described in JP-A-2000-250211 and JP-A-2007-94138, and urethane compounds having a hydrophilic group described in U.S. Pat. No. 7,153,632, JP-T-8-505958, JP-A-2007-293221 and JP-A-2007-293223.

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.
The content of the polymerizable compound is preferably from 5% by mass to 75% by mass, more preferably from 10% by mass to 70% by mass, and particularly preferably from 15% by mass to 60% by mass, based on the total mass of the image recording layer.

- Polymerization initiator -
The image recording layer in the lithographic printing plate precursor according to the present disclosure preferably contains a polymerization initiator, and more preferably contains a polymerization initiator and a polymerizable compound.
The polymerization initiator preferably contains an electron-accepting polymerization initiator, and more preferably contains an electron-accepting polymerization initiator and an electron-donating polymerization initiator.

<<Electron-accepting polymerization initiator>>
The image recording layer preferably contains an electron-accepting polymerization initiator as the polymerization initiator.
The electron-accepting polymerization initiator is a compound that generates a polymerization initiating species such as a radical by accepting one electron through intermolecular electron transfer when electrons of an infrared absorbing agent are excited by exposure to infrared light.
The electron-accepting polymerization initiator used in the present disclosure is a compound that generates a polymerization initiating species such as a radical or a cation by the energy of light, heat, or both, and can be appropriately selected from known thermal polymerization initiators, compounds having a bond with small bond dissociation energy, photopolymerization initiators, and the like.
As the electron-accepting polymerization initiator, a radical polymerization initiator is preferable, and an onium salt compound is more preferable.
The electron-accepting polymerization initiator is preferably an infrared-sensitive polymerization initiator.
Examples of the electron-accepting radical polymerization initiator include (a) organic halides, (b) carbonyl compounds, (c) azo compounds, (d) organic peroxides, (e) metallocene compounds, (f) azide compounds, (g) hexaarylbiimidazole compounds, (i) disulfone compounds, (j) oxime ester compounds, and (k) onium salt compounds.

As the (a) organic halide, for example, the compounds described in paragraphs 0022 to 0023 of JP-A-2008-195018 are preferable.
As the (b) carbonyl compound, for example, the compounds described in paragraph 0024 of JP-A-2008-195018 are preferable.
As the azo compound (c), for example, the azo compounds described in JP-A-8-108621 can be used.
As the (d) organic peroxide, for example, the compounds described in paragraph 0025 of JP-A-2008-195018 are preferable.
As the (e) metallocene compound, for example, the compounds described in paragraph 0026 of JP-A-2008-195018 are preferable.
(f) Examples of the azide compound include 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone.
As the (g) hexaarylbiimidazole compound, for example, the compounds described in paragraph 0027 of JP-A-2008-195018 are preferable.
(i) Examples of the disulfone compound include the compounds described in JP-A-61-166544 and JP-A-2002-328465.
As the (j) oxime ester compound, for example, the compounds described in paragraphs 0028 to 0030 of JP-A-2008-195018 are preferable.

Among the electron-accepting polymerization initiators, preferred from the viewpoint of curability are oxime ester compounds and onium salt compounds. Among them, from the viewpoint of printing durability, preferred are iodonium salt compounds, sulfonium salt compounds and azinium salt compounds, more preferred are iodonium salt compounds and sulfonium salt compounds, and particularly preferred are iodonium salt compounds.
Specific examples of these compounds are shown below, but the present disclosure is not limited thereto.

Preferred examples of iodonium salt compounds include diaryliodonium salt compounds, more preferred are diphenyliodonium salt compounds substituted with electron-donating groups, such as alkyl or alkoxy groups, and more preferred are asymmetric diphenyliodonium salt compounds. Specific examples include diphenyliodonium hexafluorophosphate, 4-methoxyphenyl-4-(2-methylpropyl)phenyliodonium hexafluorophosphate, 4-(2-methylpropyl)phenyl-p-tolyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4-diethoxyphenyliodonium tetrafluoroborate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium 1-perfluorobutanesulfonate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, and bis(4-t-butylphenyl)iodonium hexafluorophosphate.

Examples of sulfonium salt compounds include triarylsulfonium salt compounds, particularly triarylsulfonium salt compounds in which at least a portion of the electron-withdrawing groups, such as groups on the aromatic ring, are substituted with halogen atoms, and more preferably triarylsulfonium salt compounds in which the total number of halogen atoms substituted on the aromatic ring is 4 or more. Specific examples include triphenylsulfonium hexafluorophosphate, triphenylsulfonium benzoylformate, bis(4-chlorophenyl)phenylsulfonium benzoylformate, bis(4-chlorophenyl)-4-methylphenylsulfonium tetrafluoroborate, tris(4-chlorophenyl)sulfonium 3,5-bis(methoxycarbonyl)benzenesulfonate, tris(4-chlorophenyl)sulfonium hexafluorophosphate, and tris(2,4-dichlorophenyl)sulfonium hexafluorophosphate.

Examples of the counter anion of the iodonium salt compound and the sulfonium salt compound include a sulfonate anion, a carboxylate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a p-toluenesulfonate anion, a tosylate anion, a sulfonamide anion, and a sulfonimide anion.
Among the above, sulfonamide anions and sulfonimide anions are preferred, and sulfonimide anions are more preferred.
The sulfonamide anion is preferably an arylsulfonamide anion.
The sulfonimide anion is preferably a bisarylsulfonimide anion.
Specific examples of sulfonamide anions or sulfonimide anions are shown below, but the present disclosure is not limited thereto. In the following specific examples, Ph represents a phenyl group, Me represents a methyl group, and Et represents an ethyl group.

The lowest unoccupied molecular orbital (LUMO) of the electron-accepting 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.

The electron-accepting polymerization initiator may be used alone or in combination of two or more kinds.
The content of the electron-accepting 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.

<<Electron-donating polymerization initiator (polymerization aid)>>
The image recording layer preferably contains, as a polymerization initiator, an electron-donating polymerization initiator (also called a "polymerization auxiliary"), and more preferably contains an electron-accepting polymerization initiator and an electron-donating polymerization initiator.
The electron-donating polymerization initiator in the present disclosure is a compound that, when an electron of an infrared absorber is excited or moves intramolecularly by exposure to infrared light, donates one electron to an orbital of the infrared absorber from which one electron has been lost through intermolecular electron transfer, thereby generating a polymerization initiating species such as a radical.
The electron-donating polymerization initiator is preferably an electron-donating radical polymerization initiator.
From the viewpoint of improving the printing durability of the lithographic printing plate, the image recording layer more preferably contains an electron-donating polymerization initiator as described below, examples of which include the following five types.
(i) Alkyl or aryl ate complexes: It is believed that the carbon-hetero bond is oxidatively cleaved to generate an active radical. Specifically, borate compounds are preferred.
(ii) N-arylalkylamine compounds: It is believed that the C-X bond on the carbon adjacent to the nitrogen is cleaved by oxidation to generate an active radical. X is preferably a hydrogen atom, a carboxyl group, a trimethylsilyl group, or a benzyl group. Specific examples include N-phenylglycines (which may or may not have a substituent on the phenyl group) and N-phenyliminodiacetic acids (which may or may not have a substituent on the phenyl group).
(iii) Sulfur-containing compounds: Compounds in which the nitrogen atom of the above-mentioned amines is replaced with a sulfur atom can generate active radicals by the same action, such as phenylthioacetic acid (which may or may not have a substituent on the phenyl group).
(iv) Tin-containing compounds: Compounds in which the nitrogen atom of the above-mentioned amines is replaced with a tin atom can generate active radicals by the same action.
(v) Sulfinates: capable of generating active radicals by oxidation. Specific examples include sodium arylsulfinates.

Among these, from the viewpoint of printing durability, the image recording layer preferably contains a borate compound.
From the viewpoints of printing durability and color development, the borate compound is preferably a tetraarylborate compound or a monoalkyltriarylborate compound, and more preferably a tetraarylborate compound.
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.

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

Preferred examples of electron donating polymerization initiators are shown below as B-1 to B-9, but needless to say, they are not limited to these. In the following chemical formulas, Ph represents a phenyl group, and Bu represents an n-butyl group.

Moreover, the highest occupied molecular orbital (HOMO) of the electron donating polymerization initiator used in the present disclosure is preferably −6.00 eV or more, more preferably −5.95 eV or more, and even more preferably −5.93 eV or more, from the viewpoint of improving sensitivity.
The upper limit is preferably −5.00 eV or less, and more preferably −5.40 eV or less.

The electron-donating polymerization initiator may be used alone or in combination of two or more kinds.
From the viewpoints of sensitivity and printing durability, the content of the electron-donating polymerization initiator is preferably from 0.01% by mass to 30% by mass, more preferably from 0.05% by mass to 25% by mass, and even more preferably from 0.1% by mass to 20% by mass, relative to the total mass of the image recording layer.

In the present disclosure, when the image recording layer contains an onium ion and an anion in the above-mentioned electron-donating polymerization initiator, the image recording layer is deemed to contain an electron-accepting polymerization initiator and the above-mentioned electron-donating polymerization initiator.

- Relationship between electron donor polymerization initiators and infrared absorbers -
From the viewpoint of improving sensitivity, the image recording layer in the present disclosure contains the electron-donating polymerization initiator and an infrared absorber described later, and the value of HOMO of the infrared absorber - HOMO of the electron-donating polymerization initiator is preferably 0.70 eV or less, and more preferably 0.70 eV to -0.10 eV.
A negative value means that the HOMO of the electron-donating polymerization initiator is higher than the HOMO of the infrared absorber.

-Preferred embodiments of infrared absorber and electron-accepting polymerization initiator-
In addition, from the viewpoint of improving sensitivity, the infrared absorber described later preferably has an organic anion in which the Hansen solubility parameters δd is 16 or more, δp is 16 to 32, and δh is 60% or less of δp.
From the viewpoint of improving sensitivity, the electron-accepting polymerization initiator in the present disclosure preferably has an organic anion in which, in Hansen solubility parameters, δd is 16 or more, δp is 16 to 32, and δh is 60% or less of δp.

Here, the δd, δp, and δh in the Hansen solubility parameter in the present disclosure use the dispersion term δd [unit: MPa ^0.5 ] and the polar term δp [unit: MPa ^0.5 ] in the Hansen solubility parameter. Here, the Hansen solubility parameter is a solubility parameter introduced by Hildebrand, which is divided into three components, the dispersion term δd, the polar term δp, and the hydrogen bond term δh, and is expressed in a three-dimensional space.
Details of Hansen's solubility parameters are described in the literature "Hansen Solubility Parameters; A Users Handbook (CRC Press, 2007)" written by Charles M. Hansen.

In this disclosure, the δd, δp, and δh in the Hansen solubility parameters of the above organic anions are values estimated from their chemical structures using computer software "Hansen Solubility Parameters in Practice (HSPiP ver. 4.1.07)."

Specific examples of organic anions having a Hansen solubility parameter δd of 16 or more, δp of 16 to 32, and δh of 60% or less of δp preferably include the above-mentioned I-1 to I-15, I-17 to I-21, and I-23 to I-25, as well as the following, but needless to say, are not limited to these. Among these, bis(halogen-substituted benzenesulfonyl)imide anions are more preferably exemplified, and the above-mentioned I-5 is particularly preferably exemplified.

-particle-
From the viewpoint of UV printing durability, the image recording layer preferably contains particles.
The particles may be organic particles or inorganic particles, but from the viewpoint of UV 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 polymer particles, thermoreactive polymer 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 polymerizable 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.
The polymer particles are preferably thermoplastic polymer particles.

As the thermoplastic polymer particles, preferred are those 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 polymer 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 polymer particles is preferably 0.01 μm to 3.0 μm.

Examples of thermally reactive polymer particles include polymer particles having thermally reactive groups. Thermally reactive polymer particles form hydrophobic regions due to crosslinking caused by the thermal reaction and the resulting changes in functional groups.

The thermally reactive groups in the polymer particles having thermally reactive groups may be any functional group that undergoes any reaction as long as a chemical bond is formed, but are preferably polymerizable groups. Preferred 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 an example of the microcapsules, as described in JP-A-2001-277740 and JP-A-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.

Known methods can be applied 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 hydroxyl 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 have a hydrophobic main chain and contain 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 that includes a hydrophilic polyalkylene 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 having a hydrophobic main chain and including 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 UV 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 UV 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, more preferably contains a structural unit represented by the following formula (AN) or a group represented by the following formula Z, and particularly preferably contains 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 UV 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 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 an acrylonitrile compound, 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 UV 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.

From the viewpoint of UV printing durability, the polymer particles preferably contain a structural unit formed from an aromatic vinyl compound.
The aromatic vinyl compound may be any compound having a structure in which a vinyl group is bonded to an aromatic ring, and examples thereof include styrene compounds and vinylnaphthalene compounds, with styrene compounds being preferred, and styrene being more preferred.
Examples of the styrene compound include styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene, α-methylstyrene, and p-methoxy-β-methylstyrene, with styrene being preferred.
Examples of the vinylnaphthalene compound include 1-vinylnaphthalene, methyl-1-vinylnaphthalene, β-methyl-1-vinylnaphthalene, 4-methyl-1-vinylnaphthalene, and 4-methoxy-1-vinylnaphthalene, with 1-vinylnaphthalene being preferred.

In addition, preferred examples of structural units formed by aromatic vinyl compounds include structural units represented by the following formula Z1:

In formula Z1, R ^{2 Z1} and R ^{2 Z2} each independently represent a hydrogen atom or an alkyl group, Ar represents an aromatic ring group, R 2 ^Z3 represents a substituent, and nz represents an integer of 0 or more and the maximum number of substituents of Ar or less.
In formula Z1, R ^{2 Z1} and R ^{2 Z2} each independently preferably represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and further preferably both represent a hydrogen atom.
In formula Z1, Ar is preferably a benzene ring or a naphthalene ring, and more preferably a benzene ring.
In formula Z1, R 2 ^Z3 is preferably an alkyl group or an alkoxy group, more preferably an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and further preferably a methyl group or a methoxy group.
In formula Z1, when a plurality of R ^{2 Z3} are present, the plurality of R 2 ^Z3 may be the same or different.
In formula Z1, nz is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

The polymer particles may contain one type of structural unit formed by an aromatic vinyl compound alone, or may contain two or more types.
In the above polymer particles, the content of the structural unit formed by the aromatic vinyl compound is preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass, and particularly preferably 1% by mass to 10% by mass, relative to the total mass of the polymer particles, from the viewpoint of ink receptivity.

From the viewpoint of UV printing durability, the polymer particles preferably have a crosslinked structure, and more preferably contain a structural unit having a crosslinked structure.
Since the polymer particles have a crosslinked structure, the hardness of the polymer particles themselves is improved, and therefore the strength of the image area is improved. It is believed that this further improves printing durability (UV printing durability) even when using an ultraviolet-curable ink, which is more likely to deteriorate the plate than other inks.
The crosslinked structure is not particularly limited, but is preferably a structural unit obtained by polymerizing a polyfunctional ethylenically unsaturated compound, or a structural unit in which one or more reactive groups form a covalent bond inside a particle. The number of functions of the polyfunctional ethylenically unsaturated compound is preferably 2 to 15, more preferably 3 to 10, even more preferably 4 to 10, and particularly preferably 5 to 10, from the viewpoints of UV printing durability and on-press developability.
In other words, the structural unit having the crosslinked structure is preferably a bifunctional to 15-functional branch unit from the viewpoints of UV printing durability and on-press developability.
The n-functional branch unit refers to a branch unit having n molecular chains, in other words, a structural unit having an n-functional branch point (crosslinked structure).
In addition, it is also preferable to form a crosslinked structure using a polyfunctional mercapto compound.

The ethylenically unsaturated group in the polyfunctional ethylenically unsaturated compound is not particularly limited, but examples thereof include a (meth)acryloxy group, a (meth)acrylamide group, an aromatic vinyl group, and a maleimide group.
The polyfunctional ethylenically unsaturated compound is preferably a polyfunctional (meth)acrylate compound, a polyfunctional (meth)acrylamide compound, or a polyfunctional aromatic vinyl compound.

Examples of the polyfunctional (meth)acrylate compound include diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, tricyclodecane dimethylol diacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol triacrylate, dipentaerythritol hexaacrylate, and tris(β-hydroxyethyl)isocyanurate triacrylate.
Examples of the polyfunctional (meth)acrylate compound include N,N'-methylenebisacrylamide, N-[tris(3-acrylamidopropoxymethyl)methyl]acrylamide, and the like.
The polyfunctional aromatic vinyl compound may, for example, be divinylbenzene.

The number of carbon atoms in the branching unit is not particularly limited, but is preferably 8 to 100, and more preferably 8 to 70.

The polymer particles may contain one type of structural unit having a crosslinked structure, or may contain two or more types of structural units having a crosslinked structure.
In the above polymer particles, the content of the structural unit having a crosslinked structure is, from the viewpoints of UV printing durability and on-press developability, preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 15% by mass, and particularly preferably 1% by mass to 10% by mass, relative to the total mass of the above polymer particles.

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 6 to 120 carbon atoms (a divalent group obtained by removing one hydrogen atom from an alkylaryl group), or an aralkylene group having 6 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 N(R ^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 6 to 120 carbon atoms, an aralkyl group having 6 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 are such that W is a divalent group having a hydrophilic structure, Q is a phenylene group, an ester bond, or an amide bond, W is a polyalkyleneoxy group, and Y is a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group.

From the viewpoints of printing durability, ink receptivity, 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 cationically polymerizable group or a radically polymerizable group, but from the viewpoint of reactivity, it is preferably 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, ink adhesion, on-press developability, and suppression of development residue during on-press development, the above polymer particles preferably contain a resin having a urea bond, more preferably contain a resin having a structure obtained by at least reacting an isocyanate compound represented by the following formula (Iso) with water, and particularly preferably contain a resin having a structure obtained by at least reacting an isocyanate compound represented by the following formula (Iso) with water, and having a polyethylene oxide structure and a polypropylene oxide structure as a polyoxyalkylene structure. In addition, the particles containing the above resin having a urea bond are preferably microgels.

In formula (Iso), n represents an integer from 0 to 10.

An example of the reaction between the isocyanate compound represented by the above formula (Iso) and water is shown below. Note that the following example is an example in which n=0, 4,4-isomer is used.
As shown below, when the isocyanate compound represented by the above formula (Iso) is reacted with water, a part of the isocyanate group is hydrolyzed by the water to generate an amino group, and the generated amino group reacts with the isocyanate group to generate a urea bond, forming a dimer. In addition, the following reaction is repeated to form a resin having a urea bond.
In addition, in the reaction described below, by adding a compound (a compound having active hydrogen) reactive with an isocyanate group, such as an alcohol compound or an amine compound, it is also possible to introduce the structure of an alcohol compound, an amine compound, or the like into a resin having a urea bond.
Preferred examples of the compound having active hydrogen include those described above in relation to the microgel.

In addition, it is preferable that the resin having the above-mentioned urea bond has an ethylenically unsaturated group, and it is more preferable that the resin has a group represented by the following formula (PETA).

In formula (PETA), the wavy line represents the bonding position with other structures.

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 microscope photograph 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 developability and UV 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 developability and UV 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, but from the viewpoints of on-press developability and UV printing durability, it is preferable that the image recording layer does not contain a binder polymer.
The binder polymer is a polymer other than the polymer particles, that is, a binder polymer not in particle 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 by a sulfide bond, and the polymer chain having a polymerizable group. As the star-shaped polymer compound, for example, the compounds described in JP-A-2012-148555 can be preferably used.

Examples of star-shaped polymer compounds include those having a polymerizable group such as an ethylenically unsaturated bond in the main chain or side chain, preferably in the side chain, for improving the film strength in the image area as described in JP-A-2008-195018. The polymerizable group forms a crosslink between polymer molecules, accelerating curing.
As the polymerizable group, an ethylenically unsaturated group such as a (meth)acrylic group, a vinyl group, an allyl group, or a styryl group, or an epoxy group, etc. are preferred, and a (meth)acrylic group, a vinyl group, or a styryl group is more preferred from the viewpoint of polymerization reactivity, and a (meth)acrylic group is particularly preferred. These groups can be introduced into a polymer by a polymer reaction or copolymerization. For example, a reaction between a polymer having a carboxy group in a side chain and glycidyl methacrylate, or a reaction between a polymer having an epoxy group and an ethylenically unsaturated group-containing carboxylic acid such as methacrylic acid can be utilized. These groups may be used in combination.

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 in terms of polystyrene 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.

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 from the viewpoint of on-press developability and UV printing durability, it is preferable that the image recording layer does not contain the binder polymer, or the content of the binder polymer is more than 0 mass% and 20 mass% or less, relative to the total mass of the image recording layer, it is more preferable that the image recording layer does not contain the binder polymer, or the content of the binder polymer is more than 0 mass% and 10 mass% or less, relative to the total mass of the image recording layer, it is even more preferable that the image recording layer does not contain the binder polymer, or the content of the binder polymer is more than 0 mass% and 5 mass% or less, relative to the total mass of the image recording layer, it is particularly preferable that the image recording layer does not contain the binder polymer, or the content of the binder polymer is more than 0 mass% and 2 mass% or less, relative to the total mass of the image recording layer, and it is most preferable that the image recording layer does not contain the binder polymer.

-Infrared absorbing agent-
From the viewpoint of sensitivity, the image recording layer may contain an infrared absorbing agent (also simply referred to as "infrared absorbing agent") other than the color-forming compound.
The infrared absorbing agent is not particularly limited, and examples thereof include pigments and dyes.
As the dye to be used as the infrared absorber, commercially available dyes and known dyes described in literature such as "Dye Handbook" (edited by the Organic Synthesis Chemistry Association, published in 1970) can be used. Specific examples of the dye 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 these dyes, particularly preferred are cyanine dyes, squarylium dyes, pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes. Further examples include cyanine dyes and indolenine cyanine dyes. Of these, cyanine dyes are particularly preferred.

The infrared absorbing agent is preferably a cationic polymethine dye having an oxygen or nitrogen atom at the meso position. Preferred examples of the cationic polymethine dye include cyanine dyes, pyrylium dyes, thiopyrylium dyes, and azulenium dyes. From the viewpoints of availability and solubility in the solvent during the introduction reaction, cyanine dyes are 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.

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 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.

-Acid color former-
The image recording layer preferably contains an acid color former, and the acid color former preferably contains a leuco compound.
The term "acid color former" used in the present disclosure means a compound that has the property of developing or decolorizing a color and changing the color of an 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.

Examples of such acid color formers include 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide (also called "crystal violet lactone"), 3,3-bis(4-dimethylaminophenyl)phthalide, 3-(4-dimethylaminophenyl)-3-(4-diethylamino-2-methylphenyl)-6-dimethylaminophthalide, 3-(4-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(4-dimethylaminophenyl)-3-(2-methylphenyl)phthalide, 3-(4-dimethylaminophenyl)-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide,

3,3-bis[1,1-bis(4-dimethylaminophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3,3-bis[1-(4-dimethylaminophenyl)-1-(4-methoxyphenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3,3-bis[1-(4-pyrrolidinophenyl)-1-(4-methoxyphenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-[1,1-di(1-ethyl-2-methylindo phthalides such as 3-[1,1-di(1-ethyl-2-methylindol-3-yl)ethylene-2-yl]-3-(4-diethylaminophenyl)phthalide, 3-[1,1-di(1-ethyl-2-methylindol-3-yl)ethylene-2-yl]-3-(4-N-ethyl-N-phenylaminophenyl)phthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-n-octyl-2-methylindol-3-yl)-phthalide, 3,3-bis(1-n-octyl-2-methylindol-3-yl)-phthalide, and 3-(2-methyl-4-diethylaminophenyl)-3-(1-n-octyl-2-methylindol-3-yl)-phthalide;

4,4-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenylleucoauramine, rhodamine-B-anilinolactam, rhodamine-(4-nitroanilino)lactam, rhodamine-B-(4-chloroanilino)lactam, 3,7-bis(diethylamino)-10-benzoylphenoxazine, benzoyl leuco methylene blue, 4-nitrobenzoyl methylene blue,

3,6-dimethoxyfluoran, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6,7-dimethylfluoran, 3-N-cyclohexyl-N-n-butylamino-7-methylfluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7-di-n-hexylaminofluoran, 3-diethylamino-7-anilinofluoran, 3 -diethylamino-7-(2'-fluorophenylamino)fluoran, 3-diethylamino-7-(2'-chlorophenylamino)fluoran, 3-diethylamino-7-(3'-chlorophenylamino)fluoran, 3-diethylamino-7-(2',3'-dichlorophenylamino)fluoran, 3-diethylamino-7-(3'-trifluoromethylphenylamino)fluoran, 3-di-n-butylamino-7-(2'-fluorophenylamino)fluoran, 3-di-n-butylamino-7-(2'-chlorophenylamino)fluoran, 3-N-isopentyl-N-ethylamino-7-(2'-chlorophenylamino)fluoran,

3-N-n-hexyl-N-ethylamino-7-(2'-chlorophenylamino)fluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-di-n-butylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methoxy-7-anilinofluoran, 3-di-n-butylamino-6-ethoxy-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-morpholino-6- Methyl-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-di-n-butylamino-6-methyl-7-anilinofluoran, 3-di-n-pentylamino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-methylamino-6-methyl-7-anilinofluoran, 3-N-n-propyl-N-methylamino-6-methyl-7-anilinofluoran, 3-N-n-propyl-N-ethylamino amino-6-methyl-7-anilinofluoran, 3-N-n-butyl-N-methylamino-6-methyl-7-anilinofluoran, 3-N-n-butyl-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-isobutyl-N-methylamino-6-methyl-7-anilinofluoran, 3-N-isobutyl-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-isopentyl-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-hexyl-N-methylamino no-6-methyl-7-anilinofluoran, 3-N-cyclohexyl-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-cyclohexyl-N-n-propylamino-6-methyl-7-anilinofluoran, 3-N-cyclohexyl-N-n-butylamino-6-methyl-7-anilinofluoran, 3-N-cyclohexyl-N-n-hexylamino-6-methyl-7-anilinofluoran, 3-N-cyclohexyl-N-n-octylamino-6-methyl-7-anilinofluoran,

3-N-(2'-methoxyethyl)-N-methylamino-6-methyl-7-anilinofluoran, 3-N-(2'-methoxyethyl)-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-(2'-methoxyethyl)-N-isobutylamino-6-methyl-7-anilinofluoran, 3-N-(2'-ethoxyethyl)-N-methylamino-6-methyl-7-anilinofluoran, 3-N-(2'-ethoxyethyl)-N-ethylamino-6-methyl-7 -Anilinofluoran, 3-N-(3'-methoxypropyl)-N-methylamino-6-methyl-7-anilinofluoran, 3-N-(3'-methoxypropyl)-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-(3'-ethoxypropyl)-N-methylamino-6-methyl-7-anilinofluoran, 3-N-(3'-ethoxypropyl)-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-(3'-ethoxypropyl)-N-ethylamino-6-methyl-7-anilinofluoran, 3-N-(2'-tetrahydrofurfuryl)- N-ethylamino-6-methyl-7-anilinofluoran, 3-N-(4'-methylphenyl)-N-ethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-ethyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(3'-methylphenylamino)fluoran, 3-diethylamino-6-methyl-7-(2',6'-dimethylphenylamino)fluoran, 3-di-n-butylamino-6-methyl-7-(2',6'-dimethylphenylamino)fluoran fluorans such as 4'-(4-phenylaminophenyl)fluoran, 3-di-n-butylamino-7-(2',6'-dimethylphenylamino)fluoran, 2,2-bis[4'-(3-N-cyclohexyl-N-methylamino-6-methylfluoran)-7-ylaminophenyl]propane, 3-[4'-(4-phenylaminophenyl)aminophenyl]amino-6-methyl-7-chlorofluoran, and 3-[4'-(dimethylaminophenyl)]amino-5,7-dimethylfluoran;

3-(2-methyl-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-n-propoxycarbonylamino-4-di-n-propylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-methylamino-4-di-n-propylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-methyl-4-di-n-hexylaminophenyl)-3-(1-n-octyl 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-octyl-2-methylindol-3-yl)-4 or 7-azaphthalide, 3-( 2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4 or 7-azaphthalide, 3-(2-hexyloxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4 or 7-azaphthalide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-phenylindol-3-yl)-4 or 7-azaphthalide, 3-(2-butoxy-4-diethylaminophenyl)-3-(1-ethyl-2-phenylindol-3-yl)-4 or 7-azaphthalide phthalides such as 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 3,6-bis(diethyl ...-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho-(3-methoxybenzo)spiropyran, 3-propyl-spiro-dibenzopyran-3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 3,6-bis(diethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide,

Other examples include 2'-anilino-6'-(N-ethyl-N-isopentyl)amino-3'-methylspiro[isobenzofuran-1(3H),9'-(9H)xanthene-3-one, 2'-anilino-6'-(N-ethyl-N-(4-methylphenyl))amino-3'-methylspiro[isobenzofuran-1(3H),9'-(9H)xanthene]-3-one, 3'-N,N-dibenzylamino-6'-N,N-diethylaminospiro[isobenzofuran-1(3H),9'-(9H)xanthene]-3-one, and 2'-(N-methyl-N-phenyl)amino-6'-(N-ethyl-N-(4-methylphenyl))aminospiro[isobenzofuran-1(3H),9'-(9H)xanthene]-3-one.

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.
From the viewpoint of visibility, the hue of the dye after color development is preferably green, blue or black.

In addition, the acid color former is preferably a leuco dye from the viewpoints of color development and visibility of exposed areas.
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.
From the viewpoints of color development and visibility of exposed areas, the leuco dye is preferably a leuco dye having a phthalide structure or a fluoran structure.
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 formulas (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, or an aryl group.

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 dialkylamino group, a monoalkylmonoarylamino group, a diarylamino group, an alkoxy group, an aryloxy group, or an alkyl group, more preferably an amino group, an alkylamino group, an arylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a diarylamino group, an alkoxy group, or an aryloxy group, still more preferably an arylamino group, a monoalkylmonoarylamino group, or a diarylamino group, and particularly preferably an arylamino group or a monoalkylmonoarylamino 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 dialkylamino group, a monoalkylmonoarylamino group, a diarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl 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.

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-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, or an aryl 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 is particularly preferably a compound represented by the following formula (Le-8).

In formulas (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 is not present; when Y ₂ is N, X ₄ is not present; Ra ₁ to Ra ₄ each independently represent a hydrogen atom, an alkyl group, or an alkoxy group; Rb ₁ to Rb ₄ each independently represent a hydrogen atom, an alkyl group, or an aryl group; and Rc ₁ and Rc ₂ each independently represent an aryl 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 formulae (Le-7) to (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 each independently represent, 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 alkyl group or an alkoxy group, more preferably a hydrogen atom or an alkyl group, and particularly preferably a hydrogen atom or 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 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 the exposed area, it is preferable that _Rb1 and _Rb2 each independently represent a hydrogen atom, an alkyl group, or an aryl group substituted with an alkyl group or an alkoxy group, and more preferably a hydrogen atom or an alkyl group.

The alkyl group in the formulae (Le-1) to (Le-9) may be linear, branched, or have a ring structure.
The number of carbon atoms in the alkyl group in formulas (Le-1) to (Le-9) is preferably 1 to 20, more preferably 1 to 8, even more preferably 1 to 4, and particularly preferably 1 or 2.
The aryl group in formulae (Le-1) to (Le-9) preferably has 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and particularly preferably 6 to 8 carbon atoms.

In addition, each of the monovalent organic groups, alkyl groups, aryl groups, dialkylanilino groups, alkylamino groups, alkoxy groups, etc. in formulas (Le-1) to (Le-9) may have a substituent. Examples of the substituent include an alkyl group, an aryl group, a halogen atom, an amino group, an alkylamino group, an arylamino group, a dialkylamino group, a monoalkylmonoarylamino group, a diarylamino group, a hydroxy group, an alkoxy group, an aryloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a cyano group, etc. In addition, these substituents may be further substituted with these substituents.

Examples of suitable leuco dyes having the above-mentioned phthalide structure or fluoran structure include the following compounds:

Suitable leuco dyes include the following compounds:

As an acid coloring agent, commercially available products can be used, 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, BLACK 305, BLACK 400, BLACK 100, BLACK 500, H-7001, GREEN 300, NIRBLACK 78, H-3035, ATP, H-1046, H-2114, GREEN-DCF, Blue-63, GN-169, and crystal violet lactone are preferred because the films formed have good visible light absorptance.

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.

- 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 having 7 or more carbon atoms from the viewpoint 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 chain transfer agents include the following compounds:

The chain transfer agent may be used 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-
In order to improve ink receptivity, the image recording layer may contain an oil sensitizer such as a phosphonium compound, a nitrogen-containing low molecular weight compound, an ammonium group-containing polymer, etc. In particular, when an inorganic layered compound is contained in the protective layer, these compounds function as a surface coating agent for the inorganic layered compound, and can suppress a decrease in ink receptivity during printing caused by the inorganic layered compound.
As the oil sensitizer, it is preferable to use a phosphonium compound, a nitrogen-containing low molecular weight compound, and an ammonium group-containing polymer in combination, and it is more preferable to use a phosphonium compound, a quaternary ammonium salt, and an ammonium group-containing polymer in combination.

Examples of phosphonium compounds include those described in JP-A-2006-297907 and JP-A-2007-50660. Specific examples include tetrabutylphosphonium iodide, butyltriphenylphosphonium bromide, tetraphenylphosphonium bromide, 1,4-bis(triphenylphosphonio)butane=di(hexafluorophosphate), 1,7-bis(triphenylphosphonio)heptane=sulfate, and 1,9-bis(triphenylphosphonio)nonane=naphthalene-2,7-disulfonate.

Examples of the nitrogen-containing low molecular weight compound include amine salts and quaternary ammonium salts. Other examples include imidazolinium salts, benzimidazolinium salts, pyridinium salts, and quinolinium salts. Among these, quaternary ammonium salts and pyridinium salts are preferred. Specific examples include tetramethylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, dodecyltrimethylammonium p-toluenesulfonate, benzyltriethylammonium hexafluorophosphate, benzyldimethyloctylammonium hexafluorophosphate, benzyldimethyldodecylammonium hexafluorophosphate, and the compounds described in paragraphs 0021 to 0037 of JP 2008-284858 A and paragraphs 0030 to 0057 of JP 2009-90645 A.

The ammonium group-containing polymer may have an ammonium group in its structure, and is preferably a polymer that contains 5 mol % to 80 mol % of a (meth)acrylate having an ammonium group in the side chain as a copolymerization component. Specific examples include the polymers described in paragraphs 0089 to 0105 of JP 2009-208458 A.

The ammonium salt-containing polymer preferably has a reduced specific viscosity (unit: ml/g) value determined according to the measurement method described in JP 2009-208458 A in the range of 5 to 120, more preferably in the range of 10 to 110, and particularly preferably in the range of 15 to 100. When the reduced specific viscosity is converted into a weight average molecular weight (Mw), it is preferably 10,000 to 150,0000, more preferably 17,000 to 140,000, and particularly preferably 20,000 to 130,000.

Specific examples of the ammonium group-containing polymer are shown below.
(1) 2-(trimethylammonio)ethyl methacrylate = p-toluenesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 10/90, Mw 45,000)
(2) 2-(trimethylammonio)ethyl methacrylate = hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 20/80, Mw 60,000)
(3) 2-(ethyldimethylammonio)ethyl methacrylate = p-toluenesulfonate/hexyl methacrylate copolymer (molar ratio 30/70, Mw 45,000)
(4) 2-(trimethylammonio)ethyl methacrylate = hexafluorophosphate/2-ethylhexyl methacrylate copolymer (molar ratio 20/80, Mw 60,000)
(5) 2-(trimethylammonio)ethyl methacrylate = methyl sulfate/hexyl methacrylate copolymer (molar ratio 40/60, Mw 70,000)
(6) 2-(butyldimethylammonio)ethyl methacrylate = hexafluorophosphate / 3,6-dioxaheptyl methacrylate copolymer (molar ratio 25/75, Mw 65,000)
(7) 2-(butyldimethylammonio)ethyl acrylate = hexafluorophosphate / 3,6-dioxaheptyl methacrylate copolymer (molar ratio 20/80, Mw 65,000)
(8) 2-(butyldimethylammonio)ethyl methacrylate = 13-ethyl-5,8,11-trioxa-1-heptadecanesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 20/80, Mw 75,000)
(9) 2-(butyldimethylammonio)ethyl methacrylate = hexafluorophosphate/3,6-dioxaheptyl methacrylate/2-hydroxy-3-methacryloyloxypropyl methacrylate copolymer (molar ratio 15/80/5, Mw 65,000)

The content of the oil sensitizer is preferably 0.01% by mass to 30.0% by mass, more preferably 0.1% by mass to 15.0% by mass, and even more preferably 1% by mass to 10% by mass, relative to the total mass of the image recording layer.

-Other ingredients-
The image recording layer may contain other components such as a surfactant, a polymerization inhibitor, a higher fatty acid derivative, a plasticizer, an inorganic layer compound, etc. For details, the description in paragraphs 0114 to 0159 of JP-A-2008-284817 may be referred to.

--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 about 1 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.

<Support>
The support for the lithographic printing plate precursor according to the present disclosure can be appropriately selected from known hydrophilic supports for lithographic printing plate precursors.
The support is preferably an aluminum support.
The aluminum support is preferably an aluminum support having a hydrophilic surface (hereinafter, also referred to as "hydrophilic aluminum support").
The support is preferably a hydrophilic support.
[0043] From the viewpoint of preventing scratches and stains, the aluminum support in the lithographic printing plate precursor according to the present disclosure has a contact angle with water, as determined by a water drop method in the air, on the surface of the aluminum support on the image recording layer side, of preferably 110° or less, more preferably 90° or less, even more preferably 80° or less, even more preferably 50° or less, particularly preferably 30° or less, more particularly preferably 20° or less, and most preferably 10° or less.

In the present disclosure, the contact angle with water on the surface of the aluminum support on the side of the image recording layer is measured by the following method using a water drop method in the air.
The lithographic printing plate precursor is immersed in a solvent capable of removing the image recording layer (e.g., the solvent used in the coating liquid for the image recording layer), and the image recording layer is scraped off with at least one of a sponge and cotton, thereby dissolving the image recording layer in the solvent to expose the surface of the aluminum support.
The contact angle with water on the exposed surface of the aluminum support on the image recording layer side is measured as the contact angle of a water droplet on the surface at 25° C. (after 0.2 seconds) using a fully automatic contact angle meter (e.g., DM-501 manufactured by Kyowa Interface Science Co., Ltd.) as a measuring device.

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

An example of a preferred embodiment of the aluminum support used in the present disclosure (the aluminum support according to this example is also referred to as "support (1)") is shown below.
That is, the support (1) has an aluminum plate and an anodized aluminum film disposed on the aluminum plate, the anodized film is located on the image recording layer side of the aluminum plate, the anodized film has micropores extending in the depth direction from the surface on the image recording layer side, the average diameter of the micropores on the surface of the anodized film is more than 10 nm and not more than 100 nm, and the lightness L ^* value of the surface of the anodized film on the image recording layer side is 70 to 100 in the L ^* a ^* b ^* color system.

FIG. 3 is a schematic cross-sectional view of one embodiment of the aluminum support 12a.
The aluminum support 12a has a laminated structure in which an aluminum plate 18 and an aluminum anodized film 20a (hereinafter also simply referred to as "anodized film 20a") are laminated in this order. The anodized film 20a in the aluminum support 12a is located closer to the image recording layer than the aluminum plate 18. In other words, the lithographic printing plate precursor according to the present disclosure preferably has at least an anodized film, an image recording layer, and a water-soluble resin layer, in this order, on the aluminum plate.

- Anodized film -
A preferred embodiment of the anodic oxide coating 20a will now be described.
The anodized film 20a is a film produced on the surface of the aluminum plate 18 by anodizing, and has extremely fine micropores 22a that are approximately perpendicular to the film surface and are uniformly distributed. The micropores 22a extend from the surface of the anodized film 20a on the image recording layer side (the surface of the anodized film 20a on the side opposite to the aluminum plate 18) along the thickness direction (toward the aluminum plate 18).

The average diameter (average opening diameter) of the micropores 22a in the anodized coating 20a at the surface of the anodized coating is preferably more than 10 nm and not more than 100 nm. From the viewpoint of a balance between printing durability, stain resistance, and image visibility, the average diameter is more preferably 15 nm to 60 nm, even more preferably 20 nm to 50 nm, and particularly preferably 25 nm to 40 nm. The diameter inside the pores may be wider or narrower than that at the surface layer.
If the average diameter exceeds 10 nm, the printing durability and image visibility are further improved. If the average diameter is 100 nm or less, the printing durability is further improved.
The average diameter of the micropores 22a was calculated as the arithmetic mean value by observing N=4 images of the surface of the anodized coating 20a using a field emission scanning electron microscope (FE-SEM) at a magnification of 150,000 times, measuring the diameters of the micropores present in an area of 400 nm × 600 nm at 50 locations in the four images obtained.
When the shape of the micropores 22a is not circular, the equivalent circle diameter is used, which is the diameter of a circle when the shape of the opening is assumed to be a circle having the same projected area as the projected area of the opening.

The depth of the micropores 22a is not particularly limited, but is preferably 10 nm to 3,000 nm, more preferably 50 nm to 2,000 nm, and even more preferably 300 nm to 1,600 nm.
The above depth is determined by taking a photograph (150,000 times) of a cross section of the anodic oxide film 20a, measuring the depths of 25 or more micropores 22a, and averaging the measured depths.

The shape of the micropore 22a is not particularly limited, and in FIG. 1, it is substantially straight (cylindrical), but it may be a cone whose diameter decreases in the depth direction (thickness direction). The shape of the bottom of the micropore 22a is not particularly limited, and it may be curved (convex) or flat.

The lightness L ^* value in the L ^* a ^* b ^* color system of the surface of the aluminum support 12a facing the image recording layer (the surface of the anodized film 20a facing the image recording layer) is preferably 70 to 100. In particular, a value of 75 to 100 is preferred, and a value of 75 to 90 is more preferred, in terms of achieving a better balance between printing durability and image visibility.
The lightness L ^* is measured using a color difference meter Spectro Eye manufactured by X-Rite Corporation.

In another preferred embodiment of the support (1), the micropores are composed of large-diameter pores extending from the surface of the anodized film to a depth of 10 nm to 1,000 nm, and small-diameter pores that communicate with the bottoms of the large-diameter pores and extend from the communication positions to a depth of 20 nm to 2,000 nm, and the large-diameter pores have an average diameter of 15 nm to 150 nm at the surface of the anodized film, and the small-diameter pores have an average diameter of 13 nm or less at the communication positions (hereinafter, the support according to the above embodiment will also be referred to as "support (2)").
FIG. 4 is a schematic cross-sectional view of an alternative embodiment of the aluminum support 12a to that shown in FIG.
In FIG. 4, an aluminum support 12 b includes an aluminum plate 18 and an anodized film 20 b having micropores 22 b composed of large diameter pores 24 and small diameter pores 26 .
The micropores 22b in the anodized coating 20b are composed of large-diameter pores 24 extending from the surface of the anodized coating to a depth of 10 nm to 1,000 nm (depth D: see FIG. 4), and small-diameter pores 26 that communicate with the bottom of the large-diameter pores 24 and extend from the communicating position to a depth of 20 nm to 2,000 nm.
The large diameter hole portion 24 and the small diameter hole portion 26 will be described in detail below.

The average diameter of the large diameter pores 24 on the surface of the anodized film 20b is the same as the average diameter of the micropores 22a in the anodized film 20a on the surface of the anodized film, that is, more than 10 nm but not more than 100 nm, and the preferred range is also the same.
The method for measuring the average diameter of the large diameter pores 24 on the surface of the anodized film 20b is the same as the method for measuring the average diameter of the micropores 22a in the anodized film 20a on the surface of the anodized film.

The bottom of the large diameter hole 24 is located at a depth of 10 nm to 1,000 nm (hereinafter also referred to as depth D) from the surface of the anodized film. In other words, the large diameter hole 24 is a hole that extends from the surface of the anodized film to a position 10 nm to 1,000 nm in the depth direction (thickness direction). The depth is preferably 10 nm to 200 nm.
The above depth is determined by taking a photograph (150,000 times) of a cross section of the anodic oxide film 20b, measuring the depth of 25 or more large diameter holes 24, and averaging the measured depth.

The shape of the large diameter hole portion 24 is not particularly limited, and examples include an approximately straight tube shape (approximately cylindrical shape) and a cone shape whose diameter decreases in the depth direction (thickness direction), with an approximately straight tube shape being preferred.

As shown in FIG. 4, the small diameter hole 26 is a hole that communicates with the bottom of the large diameter hole 24 and extends further in the depth direction (thickness direction) than the communicating position.
The average diameter of the small diameter holes 26 at the communicating positions is preferably 13 nm or less. In particular, it is preferably 11 nm or less, and more preferably 10 nm or less. There is no particular lower limit, but it is often 5 nm or more.

The average diameter of the small diameter pores 26 is obtained by observing the surface of the anodized film 20a with an FE-SEM at a magnification of 150,000 times (N=4 images), measuring the diameters of the micropores (small diameter pores) present in the range of 400 nm × 600 nm in the four images obtained, and taking the arithmetic average value. Note that, if the large diameter pores are deep, the upper part of the anodized film 20b (the region where the large diameter pores are located) may be cut (e.g., cut with argon gas) as necessary, and then the surface of the anodized film 20b may be observed with the FE-SEM to determine the average diameter of the small diameter pores.
In addition, when the shape of the small diameter hole 26 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 having the same projected area as the projected area of the opening.

The bottoms of the small diameter holes 26 are located at positions extending 20 nm to 2,000 nm in the depth direction from the positions where the small diameter holes 26 communicate with the large diameter holes 24. In other words, the small diameter holes 26 are holes that extend in the depth direction (thickness direction) from the positions where the small diameter holes 26 communicate with the large diameter holes 24, and the depth of the small diameter holes 26 is 20 nm to 2,000 nm. The depth is preferably 500 nm to 2,000 nm.
The above depth is determined by taking a photograph (50,000 times) of the cross section of the anodic oxide film 20b, measuring the depths of 25 or more small diameter holes, and averaging the measured depths.

The shape of the small diameter hole portion 26 is not particularly limited, and examples include an approximately straight tube shape (approximately cylindrical shape) and a cone shape whose diameter decreases in the depth direction, with an approximately straight tube shape being preferred.

-Method for producing aluminum support-
As a method for producing the aluminum support used in the present disclosure, for example, a production method in which the following steps are carried out in order is preferable.
Surface roughening process: a process of roughening the surface of an aluminum plate; Anodizing process: a process of anodizing the surface-roughened aluminum plate; Pore widening process: a process of contacting the aluminum plate having the anodized film obtained in the anodizing process with an acid aqueous solution or an alkaline aqueous solution to enlarge the diameter of the micropores in the anodized film. The procedure for each process is described in detail below.

[Surface roughening treatment process]
The surface roughening step is a step of roughening the surface of the aluminum plate, including electrochemical roughening. This step is preferably performed before the anodizing step described below, but may not be necessary if the surface of the aluminum plate already has a desired 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 mechanical surface roughening treatment and/or 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 graining treatment is preferably carried out in an aqueous solution mainly containing nitric acid or hydrochloric acid, using a direct current or an alternating current.
The method for mechanically roughening the surface is not particularly limited, but may be, for example, the method described in Japanese Patent Publication No. 50-40047.
The chemical roughening treatment is not particularly limited, and known methods can be used.

After the mechanical roughening treatment, the following chemical etching treatment is preferably carried out.
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 printing plate, and remove any unwanted material such as abrasive particles remaining on the surface.
Examples of chemical etching treatments include etching with an acid and etching with an alkali, and a method that is particularly excellent in terms of etching efficiency is a chemical etching treatment using an aqueous alkali solution (hereinafter, also referred to as "alkaline etching treatment").

The alkaline agent used in the alkaline aqueous solution is not particularly limited, but examples thereof include caustic soda, caustic potash, sodium metasilicate, sodium carbonate, sodium aluminate, and sodium gluconate.
The alkaline aqueous solution may contain aluminum ions.
The concentration of the alkaline agent in the alkaline aqueous solution is preferably 0.01% by mass or more, more preferably 3% by mass or more, and is preferably 30% by mass or less.

When the alkaline etching treatment is carried out, it is preferable to carry out a chemical etching treatment (hereinafter also referred to as a "desmutting treatment") using a low-temperature acidic aqueous solution in order to remove products produced by the alkaline etching treatment.
The acid used in the acidic aqueous solution is not particularly limited, but examples thereof include sulfuric acid, nitric acid, and hydrochloric acid. The temperature of the acidic aqueous solution is preferably 20° C. to 80° C.

As the roughening treatment process, it is preferable to carry out the treatments shown in form A or form B in the order shown below.

~A type~
(2) Chemical Etching Treatment Using an Alkaline Aqueous Solution (First Alkaline Etching Treatment)
(3) Chemical Etching Treatment Using Acidic Aqueous Solution (First Desmutting Treatment)
(4) Electrochemical roughening treatment using an aqueous solution mainly containing nitric acid (first electrochemical roughening treatment)
(5) Chemical Etching Treatment Using an Alkaline Aqueous Solution (Second Alkaline Etching Treatment)
(6) Chemical Etching Treatment Using Acidic Aqueous Solution (Second Desmutting Treatment)
(7) Electrochemical graining treatment in an aqueous solution mainly containing hydrochloric acid (second electrochemical graining treatment)
(8) Chemical etching treatment using an alkaline aqueous solution (third alkaline etching treatment)
(9) Chemical Etching Treatment Using Acidic Aqueous Solution (Third Desmutting Treatment)

～B type～
(10) Chemical etching treatment using an alkaline aqueous solution (fourth alkaline etching treatment)
(11) Chemical Etching Treatment Using Acidic Aqueous Solution (Fourth Desmutting Treatment)
(12) Electrochemical roughening treatment using an aqueous solution mainly containing hydrochloric acid (third electrochemical roughening treatment)
(13) Chemical etching treatment using an alkaline aqueous solution (fifth alkaline etching treatment)
(14) Chemical Etching Treatment Using Acidic Aqueous Solution (Fifth Desmutting Treatment)

Before the treatment (2) in the above embodiment A or before the treatment (10) in the above embodiment B, a mechanical roughening treatment (1) may be carried out, if 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 used in the first electrochemical graining treatment in embodiment A includes an aqueous solution used 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 a 1 to 100 g/L aqueous solution of nitric acid.
The aqueous solution mainly containing hydrochloric acid used in the second electrochemical graining treatment in embodiment A and the third electrochemical graining treatment in embodiment B includes an aqueous solution used in a normal 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 solution may further include nitrate ions such as aluminum nitrate, sodium nitrate, and ammonium nitrate; or hydrochloride ions such as aluminum chloride, sodium chloride, and 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. 5 is a graph showing an example of an alternating current waveform used in the electrochemical graining treatment.
In Fig. 5, ta is the anode reaction time, tc is the cathode reaction time, tp is the time from 0 to the peak current, Ia is the peak current on the anode cycle side, Ic is the peak current on the cathode cycle side, AA is the anode reaction current of the aluminum plate, and CA is the cathode reaction current of the aluminum plate. In the trapezoidal wave, the time tp from 0 to the peak current is preferably 1 ms to 10 ms. The conditions of one cycle of AC used for electrochemical roughening are preferably in the range of 1 to 20 for the ratio tc/ta of the anode reaction time ta of the aluminum plate to the cathode reaction time tc, 0.3 to 20 for the ratio Qc/Qa of the quantity of electricity when the aluminum plate is the anode to the quantity of electricity when the aluminum plate is the anode, and 5 ms to 1,000 ms for the anode reaction time ta. The current density at the peak value of the trapezoidal wave is preferably 10 A/ ^dm2 to 200 A/ ^dm2 for both the anode cycle side Ia and the cathode cycle side Ic of the current. Ic/Ia is preferably 0.3 to 20. The total amount of electricity involved in the anode reaction of the aluminum plate at the time when the electrochemical roughening is completed is preferably 25 C/ ^dm2 to 1,000 C/ ^dm2 .

For electrochemical roughening using alternating current, an apparatus as shown in FIG. 6 can be used.
FIG. 6 is a side view showing an example of a radial cell for electrochemical surface roughening treatment using an alternating current.
In Fig. 6, 50 is a main electrolytic cell, 51 is an AC power source, 52 is a radial drum roller, 53a and 53b are main electrodes, 54 is an electrolyte supply port, 55 is an electrolyte, 56 is a slit, 57 is an electrolyte passage, 58 is an auxiliary anode, 60 is an auxiliary anode cell, and W is an aluminum plate. In Fig. 6, arrow A1 indicates the electrolyte supply direction, and arrow A2 indicates the electrolyte discharge direction. 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 or more, and more preferably 2.0 g/m ² to 10 g/m ² , in terms of facilitating the production of a desired printing plate precursor.

The amount of the aluminum plate dissolved in the third alkaline etching treatment and the fourth 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 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 acid concentration of the acidic aqueous solution is preferably 0.5% by mass to 60% by mass.

[Anodizing process]
The procedure for the anodizing treatment step is not particularly limited as long as the above-mentioned micropores can be obtained, and known methods can be used.
In the anodizing process, an aqueous solution of sulfuric acid, phosphoric acid, oxalic acid, etc. can be used as an electrolytic bath. For example, the concentration of sulfuric acid is 100 g/L to 300 g/L.
The conditions for the anodizing treatment are appropriately set depending on the electrolyte used, and examples include 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 1 A/ ^dm2 to 60 A/ ^dm2 ), a voltage of 1 V to 100 V (preferably 5 V to 50 V), an electrolysis time of 1 sec to 100 sec (preferably 5 sec to 60 sec), and a coating weight of 0.1 g/ ^m2 to 5 g/ ^m2 (preferably 0.2 g/ ^m2 to 3 g/ ^m2 ).

[Pore widening treatment]
The pore widening treatment is a treatment (pore diameter enlargement treatment) for enlarging the diameter (pore diameter) of the micropores present in the anodized film formed by the above-mentioned anodizing treatment process.
The pore widening treatment can be carried out by contacting the aluminum plate obtained by the above-mentioned anodizing treatment step with an acid aqueous solution or an alkaline aqueous solution. The contacting method is not particularly limited, and examples thereof include a dipping method and a spraying method.

<Protective Layer>
The lithographic printing plate precursor according to the present disclosure preferably has a protective layer (sometimes called an overcoat layer) on the image recording layer.

From the viewpoint of color development and color development over time, the protective layer preferably contains a color-developing compound having a group that is cleaved by exposure to heat or infrared rays.
Preferred embodiments of the color-forming compound having a group that is cleaved by exposure to heat or infrared rays in the protective layer are the same as the preferred embodiments of the color-forming compound having a group that is cleaved by exposure to heat or infrared rays in the image recording layer, except for the embodiments described below.
The content of the color-forming compound in the protective layer is preferably 0.1 mg/ ^m2 to 100 mg/ ^m2 , more preferably 1 mg/ ^m2 to 50 mg/ ^m2 , and particularly preferably 5 mg/m2 to 40 mg/ ^m2 , from the viewpoints of edge stain suppression, color development, color development over time, on- ^machine developability, and chemical resistance.

From the viewpoints of suppressing edge staining and on-press developability, the protective layer preferably contains a support-adsorbing compound having a molecular weight of 1,000 or less.
Preferred embodiments of the support-adsorbing compound having a molecular weight of 1,000 or less in the protective layer are the same as those of the support-adsorbing compound having a molecular weight of 1,000 or less in the image-recording layer, except for the embodiments described below.
The content of the support-adsorbing compound in the protective layer is preferably 0.1 mg/m ² to 100 mg/m 2, more preferably 1 mg/m ² to 50 mg/m ² , and particularly preferably 5 mg/m ² to 40 mg/m ² , from the viewpoints of edge ^stain suppression and on-press developability.

In addition, the protective layer is not particularly limited, but examples of the protective layer include a layer that has the function of suppressing image formation inhibitory reactions by blocking oxygen, as well as the function of preventing scratches in the image recording layer and ablation during exposure to high-intensity laser light.

Protective layers having such characteristics are described, for example, in U.S. Pat. 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. Specific examples include polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, water-soluble cellulose derivatives, poly(meth)acrylonitrile, etc.
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.

The protective layer preferably contains an inorganic layered compound to improve the oxygen barrier property. The inorganic layered compound is a thin, tabular particle, and examples thereof include mica groups such as natural mica and synthetic mica, talc represented by the formula: _{3MgO.4SiO.H2O} , 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 respect, 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, a representative compound, the preferred embodiment has 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 solid content 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 surface slippage. 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 .

<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 without impairing 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 reducing 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. Compounds used in the undercoat layer may be used in a mixture of two or more types, if 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.
Preferred examples of _the adsorptive group capable of _being adsorbed onto the surface of the support include a phenolic hydroxyl group, a _carboxyl group, _-PO3H2 , _-OPO3H2 , -CONHSO2- _{, -SO2NHSO2-} , and _-COCH2COCH3 . Preferred examples of the hydrophilic group include a sulfo group or a salt thereof, and a salt of a carboxyl group. Preferred examples of the crosslinkable group include an acryl group, a _methacryl group, an acrylamide group, a methacrylamide group, and an allyl group.
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.

Specific examples of suitable compounds include silane coupling agents having an addition-polymerizable ethylenic double bond reactive group described in JP-A-10-282679 and phosphorus compounds having an ethylenic double bond reactive group described in JP-A-2-304441. Also preferably used are low-molecular or high-molecular compounds having a crosslinkable group (preferably an ethylenically unsaturated bond 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 bond 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.

[Hydrophilic Compound]
From the viewpoint of developability, the undercoat layer preferably contains a hydrophilic compound.
The hydrophilic compound is not particularly limited, and any known hydrophilic compound used in an undercoat layer can be used.
The hydrophilic compound in the undercoat layer is preferably the above-mentioned support-adsorbing compound.
Preferred examples of the hydrophilic compound include phosphonic acids having an amino group such as carboxymethyl cellulose and dextrin, organic phosphonic acids, organic phosphoric acids, organic phosphinic acids, amino acids, and hydrochlorides of amines having a hydroxyl group.
Preferred examples of the hydrophilic compound include compounds having an amino group or a functional group having polymerization inhibition ability and a group that interacts with the surface of the support (e.g., 1,4-diazabicyclo[2.2.2]octane (DABCO), 2,3,5,6-tetrahydroxy-p-quinone, chloranil, sulfophthalic acid, ethylenediaminetetraacetic acid (EDTA) or a salt thereof, hydroxyethylethylenediaminetriacetic acid or a salt thereof, dihydroxyethylethylenediaminediacetic acid or a salt thereof, hydroxyethyliminodiacetic acid or a salt thereof, etc.).

From the viewpoint of scratch and stain suppression, the hydrophilic compound preferably contains a hydroxycarboxylic acid or a salt thereof.
From the viewpoint of scratch and stain suppression, the hydrophilic compound, preferably a hydroxycarboxylic acid or a salt thereof, is preferably contained in a layer on the aluminum support. The layer on the aluminum support is preferably a layer on the side on which an image recording layer is formed, and is preferably a layer in contact with the aluminum support.
The layer on the aluminum support is preferably a subbing layer or an image recording layer as a layer in contact with the aluminum support. A layer other than the layer in contact with the aluminum support, such as a protective layer or an image recording layer, may contain a hydrophilic compound, preferably a hydroxycarboxylic acid or a salt thereof.
In the lithographic printing plate precursor according to the present disclosure, the image recording layer preferably contains a hydroxycarboxylic acid or a salt thereof from the viewpoint of scratch and stain suppression.
In another preferred embodiment of the lithographic printing plate precursor according to the present disclosure, the surface of the aluminum support on the image recording layer side is surface-treated with a composition (e.g., an aqueous solution) containing at least a hydroxycarboxylic acid or a salt thereof. In the above embodiment, at least a portion of the treated hydroxycarboxylic acid or a salt thereof can be detected in a layer (e.g., an image recording layer or an undercoat layer) on the image recording layer side that is in contact with the aluminum support.
By including a hydroxycarboxylic acid or a salt thereof in a layer on the image recording layer side that is in contact with the aluminum support, such as an undercoat layer, the surface of the aluminum support on the image recording layer side can be made hydrophilic, and the contact angle with water, as measured by a water drop method in the air, on the surface of the aluminum support on the image recording layer side can be easily made to be 110° or less, resulting in excellent scratch and stain suppression.

Hydroxycarboxylic acid is a general term for organic compounds having one or more carboxy groups and one or more hydroxy groups in one molecule, and is also called hydroxy acid, oxy acid, oxycarboxylic acid, or alcohol acid (see Iwanami Dictionary of Physics and Chemistry, 5th Edition, published by Iwanami Shoten Co., Ltd. (1998)).
The above hydroxycarboxylic acid or a salt thereof is preferably represented by the following formula (HC):
R ^HC (OH) _mhc (COOM ^HC ) _nhc formula (HC)
In formula (HC), R ^HC represents an organic group having a valence of mhc+nhc, each M ^HC independently represents a hydrogen atom, an alkali metal or an onium, mhc and nhc independently represent an integer of 1 or more, and when n is 2 or more, M may be the same or different.

In formula (HC), the mhc+nhc valence organic group represented by R includes an mhc+nhc valence hydrocarbon group. The hydrocarbon group may have a substituent and/or a linking group.
Examples of the hydrocarbon group include mhc+nhc valence groups derived from aliphatic hydrocarbons, such as alkylene groups, alkanetriyl groups, alkanetetrayl groups, alkanpentyl groups, alkenylene groups, alkenetriyl groups, alkenetetrayl groups, alkenepentyl groups, alkynylene groups, alkyntriyl groups, alkyntetrayl groups, alkynpentyl groups, etc., and mhc+nhc valence groups derived from aromatic hydrocarbons, such as arylene groups, arenetriyl groups, arenetetrayl groups, arenepentyl groups, etc. Examples of the substituents other than the hydroxyl group and the carboxyl group include alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, aryl groups, etc. Specific examples of the substituent include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a undecyl group, a dodecyl group, a tridecyl group, a hexadecyl group, an octadecyl group, an eicosyl group, an isopropyl group, an isobutyl group, a s-butyl group, a t-butyl group, an isopentyl group, a neopentyl group, a 1-methylbutyl group, an isohexyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a cyclohexyl group, a cyclopentyl group, a 2-norbornyl group, a methoxymethyl group, a methoxyethoxyethyl group, an allyloxymethyl group, a phenoxymethyl group, an acetyloxymethyl group, a benzoyloxymethyl group, and the like. Examples of the linking group include an alkyl group, a phenyl ... Specific examples include an alkylene group, a substituted alkylene group, an arylene group, and a substituted arylene group, and these divalent groups may have a structure in which a plurality of them are linked together via amide bonds, ether bonds, urethane bonds, urea bonds, or ester bonds.

The alkali metal represented by ^MHC includes lithium, sodium, potassium, etc., and sodium is particularly preferred. The onium includes ammonium, phosphonium, sulfonium, etc., and ammonium is particularly preferred.
Moreover, from the viewpoint of scratch and stain suppression, ^MHC is preferably an alkali metal or an onium, and more preferably an alkali metal.
The total number of mhc and nhc is preferably 3 or more, more preferably 3 to 8, and even more preferably 4 to 6.

The hydroxycarboxylic acid or salt thereof preferably has a molecular weight of 600 or less, more preferably 500 or less, and particularly preferably 300 or less. In addition, the molecular weight is preferably 76 or more.
Specific examples of the hydroxycarboxylic acid constituting the above hydroxycarboxylic acid or the salt of the above hydroxycarboxylic acid include gluconic acid, glycolic acid, lactic acid, tartronic acid, hydroxybutyric acid (2-hydroxybutyric acid, 3-hydroxybutyric acid, γ-hydroxybutyric acid, etc.), malic acid, tartaric acid, citramalic acid, citric acid, isocitric acid, leucinic acid, mevalonic acid, pantoic acid, ricinoleic acid, ricinelaidic acid, cerebroside acid, quinic acid, shikimic acid, monohydroxybenzoic acid derivatives (salicylic acid, creosinoic acid, etc.), and the like. Examples of the benzoic acid derivatives include benzoic acid (homosalicylic acid, hydroxy(methyl)benzoic acid), vanillic acid, syringic acid, etc.), dihydroxybenzoic acid derivatives (pyrocatechuic acid, resorcylic acid, protocatechuic acid, gentisic acid, orselliic acid, etc.), trihydroxybenzoic acid derivatives (gallic acid, etc.), phenylacetic acid derivatives (mandelic acid, benzilic acid, atrolactic acid, etc.), hydrocinnamic acid derivatives (mellitic acid, phloretic acid, coumaric acid, umbellic acid, caffeic acid, ferulic acid, sinapic acid, cerebronic acid, carminic acid, etc.).

Among these, as the hydroxycarboxylic acid constituting the above-mentioned hydroxycarboxylic acid or the salt of the above-mentioned hydroxycarboxylic acid, from the viewpoint of scratch and stain suppression, a compound having two or more hydroxy groups is preferred, a compound having three or more hydroxy groups is more preferred, a compound having five or more hydroxy groups is even more preferred, and a compound having 5 to 8 hydroxy groups is particularly preferred.
As an acid having one carboxy group and two or more hydroxy groups, gluconic acid or shikimic acid is preferred.
As an acid having two or more carboxy groups and one hydroxy group, citric acid or malic acid is preferred.
As an acid having two or more carboxy groups and two or more hydroxy groups, tartaric acid is preferred.
Among these, gluconic acid is particularly preferred as the hydroxycarboxylic acid.

The hydrophilic compounds may be used alone or in combination of two or more.
When the undercoat layer contains a hydrophilic compound, preferably a hydroxycarboxylic acid or a salt thereof, the content of the hydrophilic compound, preferably a hydroxycarboxylic acid or a salt thereof, relative to the total mass of the undercoat layer is preferably 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 40% by mass, and particularly preferably 1.0% by mass to 30% by mass.

In addition to the above-mentioned undercoat layer compounds, the undercoat layer may contain a chelating agent, a secondary or tertiary amine, a polymerization inhibitor, etc. to prevent contamination 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 .

<Edge hydrophilic layer>
From the viewpoint of suppressing edge staining, the lithographic printing plate precursor according to the present disclosure preferably has a hydrophilized layer (also referred to as an "edge hydrophilized layer") in an area within 1 cm from the edge of the surface of the lithographic printing plate precursor on the image recording layer side.
The edge hydrophilization layer may be present at the end of at least one side of the surface of the planographic printing plate precursor facing the image recording layer, or may be present at the ends of all four sides of the surface of the planographic printing plate precursor facing the image recording layer in a quadrilateral shape, but is preferably present in an area within 1 cm from each of the ends of two opposing sides of the surface of the planographic printing plate precursor facing the image recording layer.
The width of the edge hydrophilic layer is not particularly limited, but is preferably from 1 mm to 50 mm.
Furthermore, the lithographic printing plate precursor according to the present disclosure is preferably a lithographic printing plate precursor obtained by cutting at the region where the edge hydrophilized layer is formed.
The edge hydrophilic layer may be present as the outermost layer on the image recording layer side or between each of the layers, but from the viewpoint of suppressing edge staining, it is preferable that the edge hydrophilic layer be present as the outermost layer on the image recording layer side.

The edge hydrophilic layer preferably contains a hydrophilic agent.
The hydrophilizing agent preferably contains a phosphoric acid compound and/or a phosphonic acid compound, and more preferably contains a phosphoric acid compound and/or a phosphonic acid compound and a surfactant as the hydrophilizing agent.
Furthermore, in the above two aspects, it is preferable that the composition contains at least a phosphoric acid compound.

-Surfactants-
As the hydrophilizing agent, it is preferable to use a surfactant.
Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, and at least one surfactant selected from the group consisting of anionic surfactants, nonionic surfactants, and amphoteric surfactants is preferred, and anionic surfactants and/or nonionic surfactants are more preferred. According to the above embodiment, a hydrophilic coating liquid with excellent coating properties can be obtained.
In addition, fluorine-based, silicone-based, and other anionic and nonionic surfactants (typically, fluorine-based or silicone-based anionic or nonionic surfactants) are not preferred as the anionic or nonionic surfactant, since the use of these surfactants leads to poor application properties of the hydrophilic coating liquid, which is not preferred.

Examples of anionic surfactants include fatty acid salts, abietic acid salts, hydroxyalkanesulfonates, alkanesulfonates, dialkylsulfosuccinates, linear alkylbenzenesulfonates, branched alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylphenoxypolyoxyethylenepropylsulfonates, polyoxyethylenearylethersulfate salts, polyoxyethylenealkylsulfophenylether salts, sodium N-methyl-N-oleyltaurates, disodium N-alkylsulfosuccinic acid monoamide salts, petroleum sulfonates, sulfated castor oil, sulfated beef tallow oil, Examples of the sulfuric acid ester salts include fatty acid alkyl ester salts, alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, fatty acid monoglyceride sulfate salts, polyoxyethylene alkyl phenyl ether sulfate salts, polyoxyethylene styryl phenyl ether sulfate salts, alkyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, polyoxyethylene alkyl phenyl ether phosphate salts, partially saponified products of styrene-maleic anhydride copolymers, partially saponified products of olefin-maleic anhydride copolymers, naphthalene sulfonate formalin condensates, etc. Among these, dialkyl sulfosuccinates, alkyl sulfate salts, polyoxyethylene aryl ether sulfate salts, and alkyl naphthalene sulfonates are particularly preferably used.
Specifically, at least one anionic surfactant selected from the group consisting of anionic surfactants represented by formula (IA) or formula (IB) can be mentioned.

In the above formula (IA), R ₁ represents a linear or branched alkyl group having 1 to 20 carbon atoms, p represents 0, 1 or 2, Ar ₁ represents an aryl group having 6 to 10 carbon atoms, q represents 1, 2 or 3, and M ₁ ⁺ represents Na ⁺ , K ⁺ , Li ⁺ or NH ₄ ⁺ . When p is 2, multiple R _1s may be the same or different from each other.
In the above formula (IB), R ₂ represents a linear or branched alkyl group having 1 to 20 carbon atoms; m represents 0, 1, or 2; Ar ₂ represents an aryl group having 6 to 10 carbon atoms; Y represents a single bond or an alkylene group having 1 to 10 carbon atoms; R ₃ represents a linear or branched alkylene group having 1 to 5 carbon atoms; n represents an integer of 1 to 100; and M ₂ ⁺ represents Na ⁺ , K ⁺ , Li ⁺ , or NH ₄ ⁺ . When m is 2, the multiple R _2s may be the same or different from each other; when n is 2 or more, the multiple R _3s may be the same or different from each other.

In the above formula (IA) and formula (IB), preferred examples of R ₁ and R ₂ include CH ₃ , C ₂ H ₅ , C ₃ H ₇ , or C ₄ H _9. Preferred examples of R ₃ include -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, or -CH ₂ CH(CH ₃ )-, and a more preferred example is -CH ₂ CH ₂ -. Furthermore, p and m are preferably 0 or 1, and p is particularly preferably 0. It is preferable that Y is a single bond. Furthermore, it is preferable that n is an integer of 1 to 20.

Specific examples of compounds represented by formula (IA) or formula (IB) include the following compounds.

The anionic surfactant is preferably a polymer compound (anionic polymer surfactant). According to the above aspect, the surface condition is excellent. The polymer compound is not particularly limited as long as it contains at least one type of anionic group as a hydrophilic group.
Examples of the anionic group include a sulfonic acid group, a sulfate group, and a carboxy group. Among these, the sulfonic acid group is preferable.
These anionic groups may form salts, which may be salts with inorganic cations or salts with organic cations.
Examples of inorganic cations include lithium cations, sodium cations, potassium cations, calcium cations, magnesium cations, etc. Lithium cations, sodium cations, and potassium cations are preferred, and sodium cations and potassium cations are more preferred.
The organic cation includes ammonium (NH ₄ ⁺ ), quaternary ammonium, quaternary pyridinium, quaternary phosphonium, etc. Ammonium, quaternary ammonium, and quaternary pyridinium are preferred, and quaternary ammonium is more preferred.
Examples of the polymer compound include a polymer of a monomer having an anionic group in the molecule, a copolymer of a polymer of a monomer having an anionic group in the molecule and one or more other monomers, and a polymer having no anionic group and into which a hydrophilic group has been subsequently introduced.
Examples of monomers having an anionic group in the molecule include styrene derivatives having a sulfonic acid group such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, styrene sulfonic acid, sodium styrene sulfonate, and α-methylstyrene sulfonic acid, olefin sulfonic acids such as maleic anhydride, vinyl sulfonic acid, sodium allyl sulfonate, sodium methallyl sulfonate, sodium isoprene sulfonate, and 3-vinyloxypropane sulfonic acid, acrylamide derivatives having a sulfonic acid group such as 2-acrylamido-2-methylpropane sulfonic acid and sodium 2-acrylamido-2-methylpropane sulfonate, (meth)acrylate derivatives such as sodium 2-sulfoethyl methacrylate, dienesulfonic acids such as butadiene sulfonic acid, and naphthalene sulfonic acid. Among the above monomers, from the viewpoint of edge stain prevention performance, styrene derivatives having a sulfonic acid group or acrylamide derivatives having a sulfonic acid group are preferred, and sodium 4-styrene sulfonate or sodium 2-acrylamido-2-methylpropane sulfonate are more preferred.
It should be noted that a copolymer of the monomer having an anionic group and a monomer having a phosphate ester group in the molecule, which will be described later, corresponds to a phosphoric acid compound rather than an anionic surfactant, and a copolymer of the monomer having a phosphonate ester group in the molecule, which will be described later, corresponds to a phosphonic acid compound rather than an anionic surfactant.
Examples of the polymer compound include partially saponified products of styrene-maleic anhydride copolymers, formalin condensates of sulfonated aromatic compounds including polynuclear aromatic compounds (particularly, formalin condensates of sodium naphthalenesulfonate), partially saponified products of ethylene-maleic anhydride copolymers, sodium salts of polyacrylic acid, sodium salts of polystyrenesulfonic acid, and sodium salts of poly(2-acrylamido-2-methylpropanesulfonic acid).
The weight average molecular weight of the polymer compound is preferably from 2,000 to 1,000,000, more preferably from 3,000 to 700,000, and particularly preferably from 5,000 to 500,000.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene aryl ethers, glycerin fatty acid partial esters, sorbitan fatty acid partial esters, pentaerythritol fatty acid partial esters, propylene glycol mono fatty acid esters, sucrose fatty acid partial esters, polyoxyethylene sorbitan fatty acid partial esters, polyoxyethylene sorbitol fatty acid partial esters, polyethylene glycol fatty acid esters, polyglycerin fatty acid partial esters, polyoxyethylene glycerin fatty acid partial esters, fatty acid diethanolamides, N,N-bis-2-hydroxyalkylamines, polyoxyethylene alkylamines, triethanolamine fatty acid esters, trialkylamine oxides, etc. Among these, polyoxyethylene aryl ethers, polyoxyethylene-polyoxypropylene block copolymers, etc. are preferably used.

Preferred examples of other surfactants include nonionic surfactants such as polyoxyethylene alkyl ethers, such as polyoxyethylene naphthyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, and polyoxyethylene stearyl ether; polyoxyethylene alkyl esters, such as polyoxyethylene stearate; sorbitan alkyl esters, such as sorbitan monolaurate, sorbitan monostearate, sorbitan distearate, sorbitan monooleate, sorbitan sesquioleate, and sorbitan trioleate; and monoglyceride alkyl esters, such as glycerol monostearate and glycerol monooleate.
The nonionic surfactant is preferably a polymer compound having a weight average molecular weight of preferably 2,000 to 1,000,000, more preferably 3,000 to 700,000, and particularly preferably 5,000 to 500,000.

Preferred examples of nonionic surfactants include a surfactant represented by the following formula (II-A) and a surfactant represented by the following formula (II-B).

In the above formula (II-A), R ¹ represents a hydrogen atom or an alkyl group having 1 to 100 carbon atoms, and n and m each represent an integer of 0 to 100, provided that both n and m are not 0.
In the above formula (II-B), R ² represents a hydrogen atom or an alkyl group having 1 to 100 carbon atoms, and n and m each represent an integer of 0 to 100, provided that both n and m are not 0.

Examples of compounds represented by formula (II-A) include polyoxyethylene phenyl ether, polyoxyethylene methyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, etc. Examples of compounds represented by formula (II-B) include polyoxyethylene naphthyl ether, polyoxyethylene methyl naphthyl ether, polyoxyethylene octyl naphthyl ether, polyoxyethylene nonyl naphthyl ether, etc.

In the compounds represented by the above formulas (II-A) and (II-B), the number of repeating units (n) of the polyoxyethylene chain is preferably 3 to 50, more preferably 5 to 30. The number of repeating units (m) of the polyoxypropylene chain is preferably 0 to 10, more preferably 0 to 5. The polyoxyethylene portion and the polyoxypropylene portion may be either a random or block copolymer.
The nonionic aromatic ether surfactants represented by the above formulae (II-A) and (II-B) may be used alone or in combination of two or more kinds.
Specific examples of the compounds represented by formula (II-A) and formula (II-B) are shown below. In addition, the oxyethylene repeating units and oxypropylene repeating units in the following exemplary compound "Y-5" may be either randomly bonded or block-linked.

The edge hydrophilization layer preferably contains an amphoteric surfactant.
Examples of amphoteric surfactants include carboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfuric acid esters, and imidazolines.
The amphoteric surfactant is preferably a polymer compound (amphoteric surfactant polymer). Examples of amphoteric surfactant polymers include sulfobetaine polymers, carboxybetaine polymers, and phosphobetaine polymer compounds, such as those described in JP-A-2013-57747 and JP-A-2012-194535.

Among the above surfactants, anionic surfactants that have a high on-press development promoting effect are particularly preferred, but these surfactants can also be used in combination of two or more. For example, it is preferred to use two or more different anionic surfactants in combination, or to use an anionic surfactant and a nonionic surfactant in combination.

It is preferable to use sodium naphthalene sulfonate, sodium alkyl naphthalene sulfonate, or polyoxyethylene aryl ether, and it is even more preferable to use sodium naphthalene sulfonate or sodium t-butyl naphthalene sulfonate.

The content of the above surfactant does not need to be particularly limited, but is preferably 1% to 95% by weight, more preferably 10% to 90% by weight, and even more preferably 50% to 90% by weight, relative to the total weight of the edge hydrophilization layer. When the content of the surfactant is within the above range, on-press developability is promoted.

In addition, conventionally known cationic surfactants can be used in combination. Examples of cationic surfactants include alkylamine salts, quaternary ammonium salts, polyoxyalkylamine salts, and polyethylene polyamine derivatives.

-Phosphate compounds-
As the hydrophilizing agent, it is preferable to use a phosphoric acid compound. Examples of the phosphoric acid compound include phosphoric acid, metaphosphoric acid, ammonium phosphate, ammonium phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, potassium phosphate, potassium phosphate, sodium tripolyphosphate, potassium pyrophosphate, and sodium hexametaphosphate. Among them, sodium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium hexametaphosphate are preferably used.
The content of the phosphoric acid compound is preferably from 1% by mass to 80% by mass, and more preferably from 10% by mass to 50% by mass, based on the total mass of the edge hydrophilization layer.

As the phosphoric acid compound, a phosphoric acid monoester compound or a phosphoric acid diester compound can be used.
As the phosphoric acid compound, a polymeric compound is preferably used, and a polymeric compound having a phosphoric acid monoester group is more preferable. According to the above-mentioned embodiment, a hydrophilic coating liquid having excellent coatability onto a support can be obtained.
Examples of the polymer compound include a polymer composed of one or more monomers having a phosphate ester group in the molecule, a copolymer of one or more monomers having a phosphate ester group and one or more monomers not having a phosphate ester group, and a polymer in which a phosphate ester group has been introduced into a polymer not having a phosphate ester group.
Examples of monomers having a phosphate group include mono(2-methacryloyloxyethyl) acid phosphate, mono(2-methacryloyloxypolyoxyethylene glycol) acid phosphate, mono(2-acryloyloxyethyl) acid phosphate, 3-chloro-2-acid phosphooxypropyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate, acid phosphooxypolyoxypropylene glycol methacrylate, (meth)acryloyloxyethyl acid phosphate, (meth)acryloyloxypropyl acid phosphate, (meth)acryloyloxy-2-hydroxypropyl acid phosphate, (meth)acryloyloxy-3-hydroxypropyl acid phosphate, (meth)acryloyloxy-3-chloro-2-hydroxypropyl acid phosphate, and allyl alcohol acid phosphate. Among the above monomers, mono(2-acryloyloxyethyl) acid phosphate is preferably used from the viewpoint of edge stain prevention performance. Representative products include Light Ester P-1M (manufactured by Kyoei Chemical Co., Ltd.) and Phosmer PE (manufactured by Unichemical Co., Ltd.).

The polymer compound may be either a homopolymer or a copolymer of a monomer having a phosphate group. The copolymer may be, for example, a copolymer of a monomer having a phosphate group and a monomer having the anionic group, or a copolymer of a monomer having a phosphate group and a monomer containing neither a phosphate group nor an anionic group.
A preferred embodiment of the polymer compound is a copolymer or homopolymer in which the ratio of monomer units having a phosphate ester group in the molecule is 1 mol % to 100 mol %, more preferably 5 mol % to 100 mol %, and even more preferably 10 mol % to 100 mol %.
As the monomer containing neither a phosphate group nor an anionic group, a monomer having a hydrophilic group is preferred. Examples of the hydrophilic group include a hydroxy group, an alkylene oxide structure, an amino group, an ammonium group, and an amide group. Among them, a hydroxy group, an alkylene oxide structure, and an amide group are preferred, an alkylene oxide structure having 1 to 20 alkylene oxide units having 2 or 3 carbon atoms is more preferred, and a polyethylene oxide structure having 2 to 10 ethylene oxide units is even more preferred. Examples include 2-hydroxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, poly(oxyethylene) methacrylate, N-isopropylacrylamide, acrylamide, and the like.
In addition, it is preferable to use a copolymer of the monomer having a phosphate ester group in the molecule and the monomer having an anionic group as the phosphoric acid compound. According to the above-mentioned embodiment, a hydrophilic coating liquid having high coatability and high edge stain prevention performance can be obtained.
In the copolymer of the monomer having a phosphate ester group in its molecule and the monomer having an anionic group, the proportion of the monomer unit having a phosphate ester group in its molecule is preferably 2 mol % to 99 mol %, more preferably 2 mol % to 80 mol %, even more preferably 5 mol % to 70 mol %, and particularly preferably 5 mol % to 50 mol %, based on the total monomer units.
The weight average molecular weight of the polymer compound is preferably from 5,000 to 1,000,000, more preferably from 7,000 to 700,000, and particularly preferably from 10,000 to 500,000.

-Phosphonic acid compounds-
As the hydrophilizing agent, it is preferable to use a phosphonic acid compound. Examples of the phosphonic acid compound include ethylphosphonic acid, propylphosphonic acid, i-propylphosphonic acid, butylphosphonic acid, hexylphosphonic acid, octylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2-hydroxyethylphosphonic acid, and their sodium or potassium salts, alkylphosphonic acid monoalkyl esters such as methyl methylphosphonate, methyl ethylphosphonate, and methyl 2-hydroxyethylphosphonate, and their sodium or potassium salts, alkylene diphosphonic acids such as methylene diphosphonic acid and ethylene diphosphonic acid, and their sodium or potassium salts, and polyvinyl phosphonic acid.
Of these, it is preferable to use polyvinyl phosphonic acid.
The content of the phosphonic acid compound is preferably from 1% by mass to 80% by mass, and more preferably from 10% by mass to 50% by mass, based on the total mass of the edge hydrophilization layer.

The phosphonic acid compound is preferably a polymer compound. According to the above embodiment, a hydrophilic coating liquid having excellent coatability onto a support can be obtained.
Examples of polymeric compounds preferred as the phosphonic acid compound include, in addition to polyvinyl phosphonic acid, polymers composed of one or more monomers having a phosphonic acid group or a phosphonic acid monoester group in the molecule, and copolymers of one or more monomers having a phosphonic acid group or a phosphonic acid monoester group and one or more monomers not containing a phosphonic acid group or a phosphonic acid monoester group.
Examples of the monomer having a phosphonic acid group include vinyl phosphonic acid, ethyl phosphonic acid monovinyl ester, acryloylaminomethyl phosphonic acid, and 3-methacryloyloxypropyl phosphonic acid.
The polymer compound may be either a homopolymer or a copolymer of a monomer having a phosphonate ester group. The copolymer may be, for example, a copolymer of a monomer having a phosphonate ester group and a monomer having the anionic group, or a copolymer of a monomer having a phosphate ester group and a monomer containing neither a phosphate ester group nor an anionic group.
As the monomer containing neither a phosphonate group nor an anionic group, a monomer having a hydrophilic group is preferred. Examples of the hydrophilic group include a hydroxy group, an alkylene oxide structure, an amino group, an ammonium group, and an amide group. Among them, a hydroxy group, an alkylene oxide structure, and an amide group are preferred, an alkylene oxide structure having 1 to 20 alkylene oxide units having 2 or 3 carbon atoms is more preferred, and a polyethylene oxide structure having 2 to 10 ethylene oxide units is even more preferred. Examples include 2-hydroxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, poly(oxyethylene) methacrylate, N-isopropylacrylamide, acrylamide, and the like.
A preferred embodiment of the polymer compound is a copolymer or homopolymer in which the ratio of monomer units having a phosphate ester group in the molecule is 1 mol % to 100 mol %, more preferably 3 mol % to 100 mol %, and even more preferably 5 mol % to 100 mol %.
In addition, as the phosphonic acid compound, a copolymer of the monomer having a phosphonic acid ester group in the molecule and the monomer having an anionic group can be used. According to the above-mentioned embodiment, it is preferable because a hydrophilic coating liquid having high coatability and high edge stain prevention performance can be obtained.
In the copolymer of the monomer having a phosphonate ester group in its molecule and the monomer having an anionic group, the ratio of the monomer unit having a phosphonate ester group in its molecule to the total monomer units is preferably 2 mol % to 99 mol %, more preferably 2 mol % to 80 mol %, even more preferably 5 mol % to 70 mol %, and particularly preferably 10 mol % to 50 mol %.
The weight average molecular weight of the polymer compound is preferably from 5,000 to 1,000,000, more preferably from 7,000 to 700,000, and particularly preferably from 10,000 to 500,000.

- Water-soluble resin -
The hydrophilizing agent preferably contains a water-soluble resin.
Examples of the water-soluble resin include water-soluble resins classified as polysaccharides, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide and copolymers thereof, vinyl methyl ether/maleic anhydride copolymers, vinyl acetate/maleic anhydride copolymers, and styrene/maleic anhydride copolymers.
Examples of polysaccharides include starch derivatives (e.g., dextrin, enzymatically hydrolyzed dextrin, hydroxypropylated starch, carboxymethylated starch, phosphated starch, polyoxyalkylene-grafted starch, cyclodextrin), celluloses (e.g., carboxymethyl cellulose, carboxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, methylpropyl cellulose, etc.), carrageenan, alginic acid, guar gum, locust bean gum, xanthan gum, gum arabic, soybean polysaccharides, and the like.
Among these, dextrin, starch derivatives such as polyoxyalkylene-grafted starch, gum arabic, carboxymethylcellulose, soybean polysaccharides, etc. are preferably used.

These water-soluble resins may be used in combination of two or more kinds.
The content of the water-soluble resin is preferably in the range of 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass, based on the total mass of the edge hydrophilization layer. Within this range, a good hydrophilization protective film with excellent coatability can be obtained.

The above hydrophilizing agents may be used alone, but it is preferable to use two or more hydrophilizing agents in combination, it is more preferable to use one to four hydrophilizing agents in combination, it is even more preferable to use one to three hydrophilizing agents in combination, and it is particularly preferable to use two hydrophilizing agents in combination. When using a combination of multiple hydrophilizing agents, it is preferable to use a surfactant in combination with a phosphoric acid compound or a phosphonic acid compound, and it is more preferable to use an anionic surfactant in combination with a phosphoric acid compound or a phosphonic acid compound.
In addition, when using a single hydrophilizing agent, it is preferable to use a copolymer of a monomer having a phosphate ester group or a phosphonate ester group in the molecule and a monomer having an anionic group in the molecule, it is more preferable to use a copolymer of a monomer having a phosphate ester group in the molecule and a monomer having an anionic group in the molecule, and it is even more preferable to use a copolymer of a monomer having a phosphate ester group in the molecule and a monomer having a sulfonic acid group in the molecule.

- Plasticizer -
The edge hydrophilic layer may contain a plasticizer.
Examples of the plasticizer include plasticizers having a freezing point of 15° C. or lower, such as phthalic acid diesters such as dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di(2-ethylhexyl) phthalate, dinonyl phthalate, didecyl phthalate, dilauryl phthalate, and butyl benzyl phthalate; aliphatic dibasic acid esters such as dioctyl adipate, butyl glycol adipate, dioctyl azelate, dibutyl sebacate, di(2-ethylhexyl) sebacate, and dioctyl sebacate; epoxidized triglycerides such as epoxidized soybean oil; phosphate esters such as tricresyl phosphate, trioctyl phosphate, and trischloroethyl phosphate; and benzoic acid esters such as benzyl benzoate.

The plasticizers may be used alone or in combination of two or more kinds.
The content of the plasticizer is preferably more than 0% by mass and not more than 10% by mass, more preferably more than 0% by mass and not more than 5% by mass, based on the total mass of the edge hydrophilization layer.

-Other optional ingredients-
The edge hydrophilizing layer may contain, in addition to the above components, inorganic salts such as nitrates and sulfates, preservatives, antifoaming agents, and the like.
The edge hydrophilic layer also preferably contains particles such as the microgel described above.
Examples of inorganic salts include magnesium nitrate, sodium nitrate, potassium nitrate, ammonium nitrate, sodium sulfate, potassium sulfate, ammonium sulfate, sodium hydrogen sulfate, and nickel sulfate.
Examples of preservatives include phenol or derivatives thereof, formalin, imidazole derivatives, sodium dehydroacetate, 4-isothiazolin-3-one derivatives, benzoisothiazolin-3-one, benztriazole derivatives, amidine guanidine derivatives, quaternary ammonium salts, derivatives of pyridine, quinoline, guanidine, etc., diazine, triazole derivatives, oxazole, oxazine derivatives, nitrobromoalcohols such as 2-bromo-2-nitropropane-1,3-diol, 1,1-dibromo-1-nitro-2-ethanol, and 1,1-dibromo-1-nitro-2-propanol.
As the defoaming agent, general silicone-based self-emulsifying type, emulsifying type, non-ionic surfactant-based compounds having an HLB value of 5 or less, etc. can be used.

(Method of preparing a lithographic printing plate and lithographic printing method)
A lithographic printing plate can be prepared by imagewise exposing the lithographic printing plate precursor according to the present disclosure and then subjecting it to a development treatment.
The method for producing a lithographic printing plate according to the present disclosure preferably includes a step of exposing the lithographic printing plate precursor according to the present disclosure imagewise to light (hereinafter also referred to as an "exposure step"), and a step of removing the image recording layer in non-image areas on a printing press by supplying at least one selected from the group consisting of printing ink and fountain solution (hereinafter also referred to as an "on-press development step").
The lithographic printing method according to the present disclosure preferably includes a step of exposing the lithographic printing plate precursor according to the present disclosure in an imagewise manner (exposure step), a step of supplying at least one selected from the group consisting of printing ink and fountain solution to remove the image recording layer in non-image areas on a printing press to prepare a lithographic printing plate (on-press development step), and a step of printing with the obtained lithographic printing plate (printing step).
Hereinafter, preferred aspects of each step of the method for producing a lithographic printing plate according to the present disclosure and the lithographic printing method according to the present disclosure will be described in order. The lithographic printing plate precursor according to the present disclosure can also be developed using a developer.
The exposure step and on-press development step in the method for preparing a lithographic printing plate will be described below; however, the exposure step in the method for preparing a lithographic printing plate according to the present disclosure is the same as the exposure step in the lithographic printing method according to the present disclosure, and the on-press development step in the method for preparing a lithographic printing plate according to the present disclosure is the same as the on-press development step in the lithographic printing method according to the present disclosure.
It is also assumed that the outermost layer is partially removed during on-press development, and the remaining portion remains on the surface of the image area or penetrates into the inside of the image area with the printing ink.

<Exposure process>
The method for producing a lithographic printing plate according to the present disclosure preferably includes an exposure step of exposing the lithographic printing plate precursor according to the present disclosure imagewise to form an exposed area and an unexposed area. The lithographic printing plate precursor according to the present disclosure is preferably exposed to laser light through a transparent original having a line image, a halftone dot image, or the like, or imagewise exposed by laser light scanning based on digital data, or the like.
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 a 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 to remove the image recording layer in non-image areas on the printing press.
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.

As the laser for imagewise exposing the lithographic printing plate precursor according to the present disclosure, a light source having a wavelength of 300 nm to 450 nm or 750 nm to 1,400 nm is preferably used. In the case of a light source having a wavelength of 300 nm to 450 nm, a lithographic printing plate precursor containing in an image recording layer a sensitizing dye having an absorption maximum in this wavelength region is preferably used, and as a light source having a wavelength of 750 nm to 1,400 nm, the above-mentioned light sources are preferably used. As a light source having a wavelength of 300 nm to 450 nm, a semiconductor laser is suitable.

<Developer Development Step>
The method for producing a lithographic printing plate according to the present disclosure may be a method including a step of exposing the lithographic printing plate precursor according to the present disclosure to light in an imagewise manner, and a step of removing the image recording layer in the non-image area using a developer to produce a lithographic printing plate (also referred to as a "developer developing step").
In addition, the lithographic printing method according to the present disclosure may be a method including the steps of exposing the lithographic printing plate precursor according to the present disclosure to light in an imagewise manner, removing the image recording layer in the non-image areas using a developer to prepare a lithographic printing plate, and printing with the obtained lithographic printing plate.
As the developer, a known developer can be used.
The pH of the developer is not particularly limited, and may be a strong alkaline developer, but preferred examples of the developer have a pH of 2 to 11. Preferred examples of the developer having a pH of 2 to 11 include developers containing at least one of a surfactant and a water-soluble polymer compound.
In the development process using a strong alkaline developer, the protective layer is removed in a pre-washing step, followed by alkaline development, the alkali is removed in a post-washing step, a gum solution treatment is performed, and then drying is performed in a drying step.
In addition, when the above-mentioned developer containing a surfactant or a water-soluble polymer compound is used, development and gum solution treatment can be carried out simultaneously. Therefore, a post-rinsing step is not particularly required, and development and gum solution treatment can be carried out using one solution, followed by a drying step. Furthermore, removal of the protective layer can be carried out simultaneously with development and gum solution treatment, so a pre-rinsing step is not particularly required. After development, it is preferable to remove excess developer using a squeeze roller or the like, and then carry out drying.

<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 from a lithographic printing plate precursor according to the present disclosure, and in 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 stabilization of sensitivity. Heating before development is preferably performed under mild conditions of 150°C or less. In the above embodiment, problems such as hardening of non-image areas can be prevented. For heating after development, it is preferable to use stronger conditions than those described above, and a range of 100°C to 500°C is preferable. In 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.

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 "% by mass" and "parts by mass", respectively, unless otherwise specified.
Incidentally, A-1, A-4, A-7, A-9, A-13, A-16, A-21, A-46, A-55, AN-1, and AN-2 used in the examples are the same compounds as the above-mentioned A-1, A-4, A-7, A-9, A-13, A-16, A-21, A-46, A-55, AN-1, and AN-2, respectively.

(Examples 1 to 34 and Comparative Examples 1 to 5)
<Preparation of Support 1>
An aluminum plate (aluminum alloy plate) having a thickness of 0.3 mm and made of material 1S was subjected to the following treatments (Ja) to (Jm) to manufacture a support 1. Note that a water washing treatment was performed between all of the treatment steps, and after the water washing treatment, the liquid was removed with a nip roller.

(J-a) Mechanical Roughening Treatment (Brush Grain Method)
Using the apparatus shown in Fig. 7, a mechanical roughening treatment was performed by rotating bundled brushes 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. 7, 1 is an aluminum plate, 2 and 4 are roller-shaped brushes (bundled brushes in this embodiment), 3 is an abrasive slurry, and 5, 6, 7 and 8 are supporting rollers.
In the mechanical roughening treatment, the median diameter (μm) of the abrasive was 30 μm, the number of brushes was 4, and the rotation speed (rpm) of the brush was 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.

(J-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 an aluminum plate at a temperature of 70° C. The amount of aluminum dissolved on the surface to be subsequently subjected to electrochemical graining treatment was 10 g/ ^m2 .

(J-c) Desmutting Treatment Using Acidic Aqueous Solution A desmutting treatment was performed by spraying, as an acidic aqueous solution, a waste solution of nitric acid used in the subsequent electrochemical graining treatment at a liquid temperature of 35° C. onto the aluminum plate for 3 seconds.

(J-d) Electrochemical roughening treatment using nitric acid aqueous solution Electrochemical roughening treatment was performed continuously using an AC voltage of 60 Hz. The electrolyte used was an electrolyte with a liquid temperature of 35°C, which was prepared by adding aluminum nitrate to an aqueous solution of nitric acid 10.4 g/L to adjust the aluminum ion concentration to 4.5 g/L. The AC power source waveform was the waveform shown in Figure 5, 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 using a carbon electrode as a counter electrode. Ferrite was used as the auxiliary anode. The electrolytic cell shown in Figure 6 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 diverted 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.

(J-e) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 27% by mass and an aluminum ion concentration of 2.5% by mass onto an aluminum plate at a temperature of 50° C. The amount of dissolved aluminum was 3.5 g/m ² .

(J-f) Desmutting Treatment Using Acidic Aqueous Solution An acidic aqueous solution having a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L and a liquid temperature of 30° C. was sprayed onto the aluminum plate for 3 seconds to perform a desmutting treatment.

(J-g) Electrochemical roughening treatment using hydrochloric acid solution Electrochemical roughening treatment was performed continuously using an AC voltage of 60 Hz. The electrolyte used was an electrolyte with a liquid temperature of 35°C, which was prepared by adding aluminum chloride to an aqueous solution of 6.2 g/L hydrochloric acid to adjust the aluminum ion concentration to 4.5 g/L. The AC power source waveform was the waveform shown in Figure 5, and the time tp from zero to the peak was 0.8 msec, the duty ratio was 1:1, and a trapezoidal rectangular wave AC was used to perform electrochemical roughening treatment using a carbon electrode as a counter electrode. Ferrite was used as the auxiliary anode. The electrolytic cell shown in Figure 6 was used. The current density was 25 A/dm ² at the peak value of the current, and the amount of electricity (C/dm ² ) in hydrochloric acid electrolysis was 63 C/dm ² as the total amount of electricity when the aluminum plate was the anode.

(J-h) 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 an aluminum plate at a temperature of 60° C. The amount of dissolved aluminum was 0.2 g/ ^m2 .

(J-i) Desmutting treatment using an acidic aqueous solution An aqueous solution of waste liquid (sulfuric acid concentration 170 g/L and aluminum ion concentration 5 g/L) generated in an anodizing treatment process at a liquid temperature of 35° C. was sprayed onto the aluminum plate for 4 seconds to perform a desmutting treatment.

(J-j) First-stage anodizing treatment The first-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 8. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50°C and a current density of 30 A/ ^dm2 , forming an anodized film with a film weight of 0.3 g/ ^m2 .
In the anodizing treatment device 610, the aluminum sheet 616 is transported as shown by the arrow in Fig. 8. In the power supply tank 612 in which an electrolytic solution 618 is stored, the aluminum sheet 616 is charged (+) by a power supply electrode 620. Then, in the power supply tank 612, the aluminum sheet 616 is transported upward by a roller 622, and its direction is changed downward by a nip roller 624, and then the aluminum sheet 616 is transported toward an electrolytic treatment tank 614 in which an electrolytic solution 626 is stored, and its direction is changed horizontally by a roller 628. Next, the aluminum sheet 616 is charged (-) by an 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 direction changing means is constituted by a roller 622, a nip roller 624, and a roller 628, and the aluminum sheet 616 is transported in a mountain shape and an inverted U shape in the space between the power supply tank 612 and the electrolytic treatment tank 614 by the rollers 622, the nip rollers 624, and the rollers 628. The power supply electrode 620 and the electrolytic electrode 630 are connected to a DC power source 634.

(Jk) Pore Widening Treatment The anodized aluminum plate was immersed in an aqueous solution of caustic soda having a caustic soda concentration of 5 mass % and an aluminum ion concentration of 0.5 mass % at 40° C. for 3 seconds to perform a pore widening treatment.

(J-l) Second-stage anodizing treatment The second-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 8. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50°C and a current density of 13 A/ ^dm2 , forming an anodized film with a film weight of 2.1 g/ ^m2 .

(J-m) Hydrophilization Treatment In order to ensure hydrophilicity of non-image areas, the aluminum plate was subjected to a silicate treatment by immersing it in a 2.5% by mass aqueous solution of sodium silicate No. 3 at 50°C for 7 seconds. The amount of Si attached was 8.5 mg/ ^m2 . The average diameter of the micropores was 30 nm.
The anodic oxide film surface of Support 1 had a lightness L ^* value of 72.3 in the L ^* a ^* b ^* color system.

<Formation of Undercoat Layer>
Next, a coating solution (1) for undercoat layer having the following composition was applied onto the support 1 so that the dry coating amount became 20 mg/ ^m2 , thereby forming an undercoat layer.
In Examples 16 and 17, phosphoric acid or gluconic acid was added to the undercoat layer coating solution (1) so that the dry coating amount would be the amount shown in Table 1, and the undercoat layer was formed by coating the solution so that the dry coating amount would be 70 mg/ ^m2 .
In addition, in Examples 25 to 30, no undercoat layer was formed.

[Coating solution for undercoat layer (1)]
Undercoat layer compound (1) having the following structure: 0.18 parts Hydroxyethyliminodiacetic acid: 0.10 parts Methanol: 55.24 parts Water: 6.15 parts

<Formation of Image Recording Layer>
An image recording layer was formed by any one of the following image recording layers (1) to (4) shown in Table 1.

<<Formation of image recording layer (1)>>
An image recording layer coating solution (1) having the following composition was applied onto the undercoat layer or support 1 with a bar and dried in an oven at 100° C. for 60 seconds to form an image recording layer (1) with a dry coating amount of 1.0 g/m ² .
The image recording layer coating solution (1) was prepared by mixing and stirring the following photosensitive solution (1) and a microgel solution immediately before coating.

-Photosensitive solution (1)-
Color-forming compound described in Table 1: Amount to be applied in a dry coating amount described in Table 1 Support-adsorbing compound described in Table 1: Amount to be applied in a dry coating amount described in Table 1 Binder polymer (1) [structure below]: 0.240 parts Polymerization initiator (1) [structure below]: 0.245 parts Borate compound (sodium tetraphenylborate): 0.010 parts Polymerizable compound (tris(acryloyloxyethyl)isocyanurate, NK Ester A-9300, manufactured by Shin-Nakamura Chemical Co., Ltd.): 0.192 parts Low molecular weight hydrophilic compound (tris(2-hydroxyethyl)isocyanurate): 0.062 parts Low molecular weight hydrophilic compound (1) [structure below]: 0.050 parts Fluorine-based surfactant (1) [structure below]: 0.008 parts 2-butanone: 1.091 parts 1-methoxy-2-propanol: 8.609 parts

-Microgel liquid-
Microgel (1): 2.640 parts Distilled water: 2.425 parts

The method for preparing the microgel (1) used in the above microgel solution is described below.
- Preparation of polyisocyanate compound (1) -
To a suspension of 17.78 g (80 mmol) of isophorone diisocyanate and 7.35 g (20 mmol) of the following polyhydric phenol compound (1) in ethyl acetate (25.31 g), 43 mg of bismuth tris(2-ethylhexanoate) (Neostan U-600, manufactured by Nitto Kasei Co., Ltd.) was added and stirred. When the heat generation subsided, the reaction temperature was set to 50° C., and the mixture was stirred for 3 hours to obtain an ethyl acetate solution (50% by mass) of the polyhydric isocyanate compound (1).

- Preparation of microgel (1) -
The following oil phase components and water phase components were mixed and emulsified for 10 minutes at 12000 rpm using a homogenizer. The resulting emulsion was stirred at 45°C for 4 hours, and then 5.20 g of a 10% by mass aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene-octylate (U-CAT SA102, manufactured by San-Apro Co., Ltd.) was added, stirred at room temperature for 30 minutes, and allowed to stand at 45°C for 24 hours. The solid content was adjusted to 20% by mass with distilled water to obtain an aqueous dispersion of microgel (1). The number average particle size was measured by a light scattering method using a laser diffraction/scattering particle size distribution analyzer (LA-920, manufactured by Horiba Ltd.), and was found to be 0.28 μm.

[Oily Phase Components]
(Component 1) Ethyl acetate: 12.0 g
(Component 2) An adduct obtained by adding trimethylolpropane (6 moles) and xylene diisocyanate (18 moles) to which methyl-terminated polyoxyethylene (1 mole, number of repeating oxyethylene units: 90) was added (50% by weight in ethyl acetate solution, manufactured by Mitsui Chemicals, Inc.): 3.76 g
(Component 3) Polyisocyanate compound (1) (as a 50% by mass solution in ethyl acetate): 15.0 g
(Component 4) 65% by weight solution of dipentaerythritol pentaacrylate (SR-399, manufactured by Sartomer Corporation) in ethyl acetate: 11.54 g
(Component 5) 10% ethyl acetate solution of sulfonate surfactant (Paionin A-41-C, Takemoto Oil Co., Ltd.): 4.42 g

[Aqueous Phase Components]
Distilled water: 46.87g

<<Formation of image recording layer (2)>>
On the undercoat layer formed as described above, an image recording layer coating solution (2) having the following composition was applied with a bar, and then dried in an oven at 100° C. for 60 seconds to form an image recording layer (2) having a dry coating amount of 1.0 g/ ^m2 .
The image recording layer coating solution (2) was obtained by mixing and stirring the following photosensitive solution (2) and microgel solution (2) immediately before coating.

[Photosensitive solution (2)]
Color-forming compound described in Table 1: Amount to be applied on a dry basis as described in Table 1 Support-adsorbing compound described in Table 1: Amount to be applied on a dry basis as described in Table 1 Binder polymer (2) [structure below, Mw: 55,000, n: 2 (number of ethylene oxide (EO) units)]: 0.240 parts Borate compound (sodium tetraphenylborate): 0.010 parts Polymerization initiator (1) [structure above]: 0.162 parts Polymerizable compound (tris(acryloyloxyethyl)isocyanurate, NK Ester A-9300, manufactured by Shin-Nakamura Chemical Co., Ltd.): 0.192 parts Low molecular weight hydrophilic compound (1) [structure above]: 0.050 parts Oil sensitizer (phosphonium compound (1) [structure below]): 0.055 parts Oil sensitizer (benzyl-dimethyl-octylammonium.PF ₆ salt): 0.018 parts Ammonium group-containing polymer (1) [structure below, Mw: 50,000, reduced specific viscosity: 45 ml / g]: 0.040 parts Fluorine-based surfactant (1) [structure below]: 0.008 parts 2-butanone: 1.091 parts 1-methoxy-2-propanol: 8.609 parts

[Microgel Liquid (2)]
Microgel (2): 2.640 parts Distilled water: 2.425 parts

The synthesis method of the above microgel (2) is as follows.
-Synthesis of microgel (2)-
As the oil phase component, 10 g of trimethylolpropane and xylylene diisocyanate adduct (Mitsui Chemical Polyurethane Co., Ltd., Takenate D-110N), 3.15 g of pentaerythritol triacrylate (Nippon Kayaku Co., Ltd., SR444), and 0.1 g of alkylbenzene sulfonate (Takemoto Oil Co., Ltd., Paionin A-41C) were dissolved in 17 g of ethyl acetate. As the aqueous phase component, 40 g of a 4% by mass aqueous solution of polyvinyl alcohol (Kuraray Co., Ltd., PVA-205) was prepared. The oil phase component and the aqueous phase component were mixed and emulsified for 10 minutes at 12,000 rpm using a homogenizer. The obtained emulsion was added to 25 g of distilled water, stirred at room temperature for 30 minutes, and then stirred at 50 ° C. for 3 hours. The solid content concentration of the microgel liquid obtained in this way was diluted with distilled water to 15% by mass, and this was used as the above microgel (2). The volume average particle size of the microgel was measured by a light scattering method and was found to be 0.2 μm.

<<Formation of image recording layer (3)>>
On the undercoat layer or support 1 formed as described above, an image recording layer coating solution (3) having the following composition was bar-coated to a thickness of 30 μm, and then dried in an oven at 120° C. for 1 minute to form an image recording layer (3).

[Image Recording Layer Coating Solution (3)]
Color-forming compound shown in Table 1: Amount to be applied on the dry coating amount shown in Table 1 Support-adsorbing compound shown in Table 1: Amount to be applied on the dry coating amount shown in Table 1 2 molar equivalent hydroxyethyl methacrylate adduct of 2,2,4-trimethylhexamethylene diisocyanate (82% by mass solution in methyl ethyl ketone, manufactured by AZ Electronics): 0.250 parts Epoxy acrylate oligomer (manufactured by Arkema): 0.250 parts Bis(4-t-butylphenyl)iodonium tetraphenylborate: 0.045 parts Polyvinyl butyral (S-LEC BX35-Z, manufactured by Sekisui Chemical Co., Ltd.): 0.150 parts Tego Glide 410 (polyether-modified polysiloxane copolymer, manufactured by Evonik Tego Chemie): 0.0015 parts Phosphate compound having methacryloxy group (Sipomer PAM 100, manufactured by Rhodia): 0.130 parts; Copolymer of vinylphosphonic acid and acrylic acid (20% by weight aqueous dispersion, Albritect CP 30, manufactured by Rhodia): 0.024 parts; Mixed solvent of methyl ethyl ketone: 1-methoxy-2-propanol = 35:65 (volume ratio): amount to give a solid content of 35% by volume

<<Formation of image recording layer (4)>>
An aqueous coating solution for an image recording layer containing thermoplastic polymer particles, an infrared absorbing agent, and polyacrylic acid was prepared, and the pH was adjusted to 3.6. The solution was then coated on the undercoat layer or on the support 1 and dried at 50° C. for 1 minute to form an image recording layer (4). The coating amounts of each component after drying are shown below.

Color-forming compound shown in Table 1: Amount equivalent to the dry coating amount shown in Table 1. Support-adsorbing compound shown in Table 1: Amount equivalent to the dry coating amount shown in Table 1. Thermoplastic polymer particles: 0.7 g/ ^m2
Polyacrylic acid: 0.09 g/ ^m2

The thermoplastic polymer particles, infrared absorber IR-01, and polyacrylic acid used in the image recording layer coating liquid are as shown below.

Thermoplastic polymer particles: styrene/acrylonitrile copolymer (molar ratio 50/50), Tg: 99° C., volume average particle size: 60 nm
Polyacrylic acid: Mw: 250,000

<Formation of protective layer>
A protective layer was formed by forming the following protective layer (1) or (2) shown in Table 1.

<<Formation of protective layer (1)>>
A protective layer coating solution (1) having the following composition was applied onto the image recording layer with a bar and dried in an oven at 120° C. for 60 seconds to form a protective layer (1) having a dry coating amount of 0.15 g/m ² .

--Protective layer coating solution (1)--
Color-forming compound described in Table 1: Amount to be applied on a dry basis as described in Table 1 Support-adsorbing compound described in Table 1: Amount to be applied on a dry basis as described in Table 1 Inorganic layered compound dispersion (1) [below]: 1.5 parts Polyvinyl alcohol (CKS50, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., sulfonic acid modified, saponification degree 99 mol% or more, polymerization degree 300) 6% by weight aqueous solution: 0.55 parts Polyvinyl alcohol (PVA-405, manufactured by Kuraray Co., Ltd., saponification degree 81.5 mol%, polymerization degree 500) 6% by weight aqueous solution: 0.03 parts Surfactant (polyoxyethylene lauryl ether, EMALEX 710, manufactured by Nippon Emulsion Co., Ltd.) 1% by weight aqueous solution: 0.86 parts Ion-exchanged water: 6.0 parts

The method for preparing the inorganic layered compound dispersion (1) used in the above protective layer coating solution (1) is shown below.

--Preparation of Inorganic Layered Compound Dispersion (1)--
6.4 g of synthetic mica (Somasif ME-100, manufactured by Co-op Chemical Co., Ltd.) was added to 193.6 g of ion-exchanged water, and dispersed using a homogenizer until the average particle size (laser scattering method) became 3 μm. The aspect ratio of the resulting dispersed particles was 100 or more.

<<Formation of protective layer (2)>>
A protective layer coating solution (2) having the following composition was further applied onto the image recording layer with a bar, and then dried in an oven at 120° C. for 60 seconds to form a protective layer (2) having a dry coating amount of 0.15 g/m ² .

--Protective layer coating solution (2)--
Inorganic layered compound dispersion (1) (obtained above): 1.5 parts Hydrophilic polymer (1) (solid content) [structure below, Mw: 30,000]: 0.55 parts Polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd. CKS50, sulfonic acid modified, saponification degree 99 mol% or more, polymerization degree 300) 6 mass% aqueous solution: 0.10 parts Polyvinyl alcohol (manufactured by Kuraray Co., Ltd. PVA-405, saponification degree 81.5 mol%, polymerization degree 500) 6 mass% aqueous solution: 0.03 parts Surfactant (Emalex 710, product name: manufactured by Nippon Emulsion Co., Ltd.) 1 mass% aqueous solution: 0.86 parts Ion-exchanged water: 6.0 parts

<Formation of Edge Hydrophilic Layer>
In Examples 22 and 25, an edge hydrophilization layer was further formed.
The coating device used was 2NL04 manufactured by Heishin Soubi Co., Ltd.
The coating liquid for forming the edge hydrophilic layer was prepared by adding the components other than the below-described pure water to pure water and stirring the mixture to prepare a coating liquid containing the hydrophilic components.
Compound represented by the following formula P-2 (Mw: 100,000): 5.0 parts by mass Microgel (2): 1.0 part by mass Pure water: 194 parts by mass

The conveying speed was adjusted to a liquid feed rate of 5 cc/min with a clearance of 0.3 mm, and the coating liquid was applied to a solid coating amount of 1.7 g/ ^m2 .
The coating was carried out in two areas (2 locations) with a width of 5 mm and centered at a position 3 cm from each end of two opposing sides of the support.
After coating, the coating was dried at 120° C. for 1 minute to form an edge hydrophilized layer as the outermost layer on the image recording layer side.

<Cutting of lithographic printing plate precursor>
The planographic printing plate precursor obtained as described above was cut using a slitter device as shown in FIG. 2 by adjusting the gap between the upper and lower cutting blades, the amount of engagement, and the blade tip angle, to form a droop shape at the edge as described in Table 1.
The cutting positions were set at the center of the region where the edge hydrophilized layer was formed (positions 3 cm from each of the ends of two opposing sides of the support), and the support was cut at two points.
The sagging amount X and the sagging width Y of the sagging shape are shown in Table 1.

<Evaluation of color development and color development over time>
The lithographic printing plate precursor was exposed to light using a Creo Trendsetter 3244VX equipped with a water-cooled 40 W infrared semiconductor laser under the conditions of an output of 11.7 W, an outer drum rotation speed of 250 rpm, and a resolution of 2,400 dpi (dots per inch, 1 inch = 25.4 mm). The exposure was performed in an environment of 25°C and 50% RH.
The color development of the lithographic printing plate precursor was measured immediately after exposure (color development) and after storage in a dark place (25°C) for 2 hours after exposure (color development over time). Measurements were performed using a spectrophotometer CM2600d manufactured by Konica Minolta, Inc. and operation software CM-S100W, using the SCE (specular reflection excluded) method. Color development was evaluated using the L ^* value (lightness) of the L ^* a ^* b ^* color system, and the difference ΔL between the L ^* value of the exposed area and the L ^* value of the unexposed area. The larger the ΔL value, the better the color development.

<Evaluation of Edge Stain Suppression>
The lithographic printing plate precursor was exposed using a Luxcel PLATESETTER T-6000III equipped with an infrared semiconductor laser manufactured by Fujifilm Corporation under the conditions of an outer drum rotation speed of 1,000 rpm, a laser output of 70%, and a resolution of 2,400 dpi. A chart including a solid image, a 50% halftone dot, and a non-image area was used as the exposed image.
The image-exposed lithographic printing plate precursor was mounted on an offset rotary printing press manufactured by Tokyo Kikai Seisakusho Co., Ltd., and printing was carried out on newsprint at a speed of 100,000 sheets/hour using Soybee KKST-S (red) manufactured by Inktec Corporation as the newspaper printing ink and Toyo ALKY manufactured by Toyo Ink Co., Ltd. as the dampening water. The 1,000th print was sampled at a water mark 1.1 times the water mark for eliminating background staining, and the degree of linear staining caused by the edges of the printing plate precursor was evaluated according to the following criteria.
5: Not dirty at all 4: Intermediate level between 5 and 3 3: Slightly dirty but acceptable level 2: Intermediate level between 3 and 1 (acceptable level)
1: Clearly dirty and unacceptable

<On-press developability evaluation>
The lithographic printing plate precursor was exposed using a Luxel PLATESETTER T-6000III equipped with an infrared semiconductor laser manufactured by Fujifilm Corp. under the conditions of an outer drum rotation speed of 1,000 rpm, a laser output of 70%, and a resolution of 2,400 dpi. The exposed image included a solid image and a 50% halftone dot chart of a 20 μm dot FM screen.
The exposed lithographic printing plate precursor was not developed and was attached to the plate cylinder of a printing machine LITHRONE26 manufactured by Komori Corporation. Using a dampening solution of Ecology-2 (manufactured by Fujifilm Corporation)/tap water=2/98 (volume ratio) and Values-G(N) black ink (manufactured by DIC Graphics Corporation), dampening solution and ink were supplied by the standard automatic print start method of LITHRONE26, and 100 sheets were printed on Tokubishi Art Paper (ream weight: 76.5 kg, manufactured by Mitsubishi Paper Mills, Ltd.) at a printing speed of 10,000 sheets per hour.
The number of sheets of printing paper required until the on-press development of the unexposed parts of the image recording layer was completed on the printing press and no ink was transferred to the non-image parts was counted and evaluated as on-press developability. The fewer the number of sheets, the better the on-press developability.

<Chemical resistance (cleaner printing durability) evaluation>
After the evaluation of the on-press developability, printing was continued. As the number of printed sheets increased, the image recording layer gradually wore away, and the ink concentration on the printed matter decreased. In addition, during printing, the plate surface was wiped with a cleaner (HN-C, manufactured by Fujifilm Corporation) every time 10,000 sheets were printed. The number of printed sheets was counted until the dot area ratio of FM screen 50% dots in the printed matter, measured with a Gretag densitometer, decreased by 5% from the measured value on the 100th printed sheet. The relative printing durability was evaluated, with 100,000 printed sheets being taken as 100. The higher the value, the better the printing durability.
Relative printing durability = (number of prints of the target lithographic printing plate precursor) / 100,000 x 100

The evaluation results are summarized in Table 1.

Note that B-1 and B-2 listed in Table 1 are the following compounds.

From the results shown in Table 1, the lithographic printing plate precursors of Examples 1 to 34, which are the lithographic printing plate precursors according to the present disclosure, are superior in edge stain suppression properties compared to the lithographic printing plate precursors of the comparative examples.
Furthermore, from the results shown in Table 1, the lithographic printing plate precursors of Examples 1 to 34, which are the lithographic printing plate precursors according to the present disclosure, are also excellent in color developability, color developability over time, on-press developability, and chemical resistance.

X: amount of sagging, Y: sagging width, 1: aluminum plate, 2, 4: roller brush, 3: polishing slurry liquid, 5, 6, 7, 8: support roller, 18: aluminum plate, 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: anode reaction current on the aluminum plate, CA: cathode reaction current on the aluminum plate, 10: lithographic printing plate precursor, 12a, 12b: aluminum support, 14: undercoat layer, 16: image recording layer, 20a, 20b: anodized film, 22a, 22b: micropores, 24: large diameter hole portion, 26: small diameter hole portion, D: depth of large diameter hole portion 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, 60: auxiliary anode cell, W: aluminum plate, A1: electrolyte supply direction, A2: electrolyte discharge direction, 210: cutting blade, 210a: upper cutting blade, 210b: upper cutting blade, 211: rotating shaft, 220: cutting blade, 220a: lower cutting blade, 220b: lower cutting blade, 221: rotating shaft, 230: support, 610: anodizing treatment device, 612: power supply tank, 614: electrolytic treatment tank, 616: aluminum plate, 618, 26: electrolyte, 620: power supply electrode, 622, 628: roller, 624: nip roller, 630: electrolytic electrode, 632: tank wall, 634: DC power source

The disclosure of Japanese Patent Application No. 2020-034241, filed on February 28, 2020, is incorporated herein by reference in its entirety.
All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference.

Claims (13)

The image recording layer and the protective layer containing a support-adsorbing compound having a molecular weight of 1,000 or less are disposed on a support in this order,
the image recording layer or the protective layer contains a color-forming compound having a group that is cleaved by exposure to heat or infrared light,
the support has a sagging shape in which the sagging amount X is 25 μm to 150 μm and the sagging width Y is 70 μm to 300 μm at the ends of at least two opposing sides of the support. The lithographic printing plate precursor according to claim 1 , wherein the color-forming compound having a group that is cleaved by exposure to heat or infrared light is a compound represented by the following formula (1):


In formula (1), M ¹ is a group that is cleaved by exposure to heat or infrared rays, R ² and R ³ each independently represent a hydrogen atom or an alkyl group, R ² and R ³ may be bonded to each other to form a ring, Ar ¹ and Ar ² each independently represent a group that forms a benzene ring or a naphthalene ring, Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ - or a dialkylmethylene group, R ⁴ and R ⁵ each independently represent an aliphatic hydrocarbon group, R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, R ⁰ represents a hydrogen atom, an alkyl group or an aryl group, and Za represents a counter ion that neutralizes the charge. The lithographic printing plate precursor according to claim 2, wherein M ¹ in formula (1) is -NR ^a R ^b , -NR ^c (SO ₂ R ^d ) or -NR ^e (CO ₂ R ^f ).
wherein R ^a and R ^b each independently represent an aryl group, R ^c , R ^e and R ^f each independently represent an alkyl group or an aryl group, R ^d represents an alkyl group, an aryl group, or -NR ^d1 R ^d2 , and R ^d1 and R ^d2 each independently represent a hydrogen atom, an alkyl group or an aryl group. The lithographic printing plate precursor according to claim 2 or 3, wherein at least one group selected from the group consisting of R ⁴ , R ⁵ , M ¹ , Ar ¹ and Ar ² in the compound represented by formula (1) has a hydrophilic group. The lithographic printing plate precursor according to claim 4 , wherein the hydrophilic group is a group represented by any one of the following formulas (2) to (5):


In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer from 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or an acyl group having 2 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position with other structures. The lithographic printing plate precursor according to any one of claims 2 to 5 , wherein M ¹ in formula (1) is -O-R ¹ .
Here, R ¹ represents a group in which the R ¹ -O bond is cleaved by heat or exposure to infrared rays. The lithographic printing plate precursor according to claim 6 , wherein R ¹ is a group represented by the following formula (6):


In formula (6), R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom, an alkyl group or an aryl group, E represents an onium group, and the wavy line portion represents the bonding position to the oxygen atom. The lithographic printing plate precursor according to claim 7 , wherein E in formula (6) is a pyridinium group represented by the following formula (7):


In formula (7), R ¹⁷ represents a halogen atom, an alkyl group, an aryl group, a hydroxyl group or an alkoxy group. When a plurality of R ^17s are present, the plurality of R ^17s may be the same or different, or the plurality of R ^17s may be linked to form a ring. n2 represents an integer of 0 to 4. R ¹⁸ represents an alkyl group, an aryl group or a group represented by any one of the following formulas (2) to (5). Zb represents a counter ion for neutralizing the charge.


In formulas (2) to (5), R ¹⁰ represents an alkylene group having 2 to 6 carbon atoms, W ¹ represents a single bond or an oxygen atom, n1 represents an integer from 1 to 45, R ¹¹ represents an alkyl group having 1 to 12 carbon atoms or an acyl group having 2 to 12 carbon atoms, R ¹² and R ¹³ each independently represent a single bond, or an alkylene group or alkyleneoxy group having 1 to 12 carbon atoms, M represents a hydrogen atom, a Na atom, a K atom or an onium group, and M may not be present when the charge can be neutralized by the entire compound represented by formula (1), m1 represents 1, 2, 3 or 4, X ¹ represents -O-, -S- or -CH ₂ -, and the wavy line portion represents the bonding position with other structures. The lithographic printing plate precursor according to any one of claims 1 to 3 , wherein the image recording layer comprises a polymerization initiator and a polymerizable compound. The lithographic printing plate precursor according to any one of claims 1 to 3 , wherein the image recording layer contains polymer particles. The lithographic printing plate precursor according to any one of claims 1 to 10 , further comprising a hydrophilic layer in an area within 1 cm from an edge of the surface of the lithographic printing plate precursor on the image recording layer side. A step of imagewise exposing the lithographic printing plate precursor according to any one of claims 1 to 11 ;
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 11 ;
a step of removing the image recording layer in the non-image area on the printing press by supplying at least one selected from the group consisting of printing ink and dampening water to prepare a lithographic printing plate;
and printing with the obtained lithographic printing plate.