JP7391767B2 - On-press development type lithographic printing plate precursor, method for producing lithographic printing plate, and lithographic printing method - Google Patents

Description

The present disclosure relates to an on-press development type lithographic printing plate precursor, a method for producing a lithographic printing plate, and a lithographic printing method.

In general, a lithographic printing plate consists of a lipophilic image area that receives ink during the printing process and a hydrophilic non-image area that receives dampening water. Lithographic printing takes advantage of the property that water and oil-based ink repel each other, and uses the lipophilic image area of the lithographic printing plate as the ink receiving area, and the hydrophilic non-image area as the dampening water receiving area (non-ink receiving area). This is a method of creating differences in ink adhesion on the surface of a lithographic printing plate, applying ink only to the image area, and then printing by transferring the ink to a printing medium such as paper.
In order to produce this lithographic printing plate, a lithographic printing plate precursor (PS plate) in which an oleophilic photosensitive resin layer (image recording layer) is provided on a hydrophilic support has been widely used. Normally, after exposing a lithographic printing plate precursor to light through an original image such as a lithographic film, the portion of the image-recording layer that will become the image portion remains, and the rest of the unnecessary image-recording layer is removed using an alkaline developer or organic A lithographic printing plate is obtained by making a plate by a method of dissolving and removing it with a solvent and exposing the surface of the hydrophilic support to form a non-image area.

In addition, due to growing interest in the global environment, environmental issues related to waste liquids associated with wet processing such as developing processing are being focused on.
In response to the above environmental issues, efforts are being made to simplify development or plate making and eliminate processing. One of the simple manufacturing methods is a method called "on-press development." That is, after exposing the lithographic printing plate precursor, conventional development is not performed, but the plate is mounted on a printing machine as it is, and unnecessary portions of the image recording layer are removed at the initial stage of the normal printing process.
In the present disclosure, a lithographic printing plate precursor that can be used for such on-press development is referred to as an "on-press development type lithographic printing plate precursor."

As a conventional lithographic printing plate precursor, for example, Patent Document 1 discloses a lithographic printing plate having an uppermost layer containing an infrared absorbing compound having a functional group that is cleavable by heat and/or infrared irradiation on a photopolymerizable layer. The original version is listed.
Further, Patent Document 2 describes a lithographic printing plate precursor having an uppermost layer that changes color upon irradiation with infrared rays on an image recording layer.
Patent Document 3 describes a lithographic printing plate precursor having a photopolymerizable layer containing a polyvinyl acetal binder.
Patent Document 4 describes a lithographic printing plate precursor having a negative image recording layer containing an infrared absorber and thermoplastic polymer particles.

International Publication No. 2019/219560 US Patent No. 8240943 Japanese Patent Application Publication No. 2013-174779 Special table 2018-508385 publication

A problem to be solved by an embodiment of the present disclosure is to provide an on-press development type lithographic printing plate precursor that can suppress deterioration of on-press developability over time.
A problem to be solved by other embodiments of the present disclosure is to provide a method for producing a lithographic printing plate or a lithographic printing method using the above-mentioned on-press development type lithographic printing plate precursor.

Means for solving the above problems include the following aspects.
<1> Having an image recording layer and an outermost layer on a support in this order,
The image recording layer contains a polymer having a glass transition temperature of 70° C. or higher,
The on-press development type lithographic printing plate precursor, wherein the outermost layer contains a color-changing compound.
<2> The image recording layer further contains a polymerizable compound having a molecular weight of 5,000 or less,
The on-press development type lithographic printing plate precursor according to <1>, wherein the difference between the solubility parameter of the polymer and the solubility parameter of the polymerizable compound is 0.8 MPa ^1/2 or more.
<3> The on-press development type lithographic printing plate precursor according to <2>, wherein the polymerizable compound has a solubility parameter of 20.0 MPa ^1/2 or less.
<4> The on-press development type lithographic printing plate precursor according to any one of <1> to <3>, wherein the polymerizable compound is a bifunctional or more functional polymerizable compound.
<5> Where the mass of the polymer in the image recording layer is P and the mass of the polymerizable compound is M, <1> to satisfy the relationship 6.0≧P/M≧0.5. <4> The on-press development type lithographic printing plate precursor according to any one of the above.
<6> The on-press development type lithographic printing plate precursor according to any one of <1> to <5>, wherein the polymer is polyvinyl acetal.
<7> The on-press development type lithographic printing plate precursor according to <6>, wherein the hydroxyl group-containing structural unit in the polyvinyl acetal is 20 mol% or more based on the total structural units of the polyvinyl acetal.
<8> The on-press development type lithographic printing plate precursor according to <6> or <7>, wherein the polyvinyl acetal has an ethylenically unsaturated group.
<9> The on-press development type lithographic printing plate precursor according to <8>, wherein the polyvinyl acetal contains a structural unit having an ethylenically unsaturated group.
<10> The on-press development type lithographic printing plate precursor according to <6>, which contains a compound in which an ethylenically unsaturated group is introduced into the acetal ring of the polyvinyl acetal.

<11> The on-press development type lithographic printing plate precursor according to any one of <1> to <10>, wherein the outermost layer further contains a hydrophobic polymer.
<12> The on-press development type lithographic printing plate precursor according to <11>, wherein the area ratio occupied by the hydrophobic polymer on the surface of the outermost layer is 30 area % or more.
<13> The on-press development type lithographic printing plate precursor according to <11> or <12>, wherein the hydrophobic polymer is a particle.
<14> Any one of <1> to <13>, wherein the lightness change ΔL before and after the exposure is 2.0 or more when exposed to infrared rays with a wavelength of 830 nm at an energy density of 110 mJ/cm ² On-press development type lithographic printing plate precursor.

<15> The on-press development type lithographic printing plate precursor according to any one of <1> to <14>, wherein the color-changing compound contains a compound that develops color due to infrared exposure.
<16> The on-press development type lithographic printing plate precursor according to any one of <1> to <15>, wherein the color-changing compound contains a decomposable compound that decomposes due to infrared exposure.
<17> The on-press development type lithographic printing plate precursor according to any one of <11> to <16>, wherein the color-changing compound is a cyanine dye.
<18> The on-press development type lithographic printing plate precursor according to any one of <1> to <17>, wherein the color-changing compound is a compound represented by the following formula 1-1.

In formula 1-1, R ¹ represents a group represented by any of the following formulas 2 to 4, and R ¹¹ to R ¹⁸ each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -SR ^c or -NR ^d R ^e , R ^a to R ^e each independently represent a hydrocarbon group, and A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ are linked to form a monocyclic or A polycyclic ring may be formed, A ₁ and A ₂ each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, However, the sum of n ₁₁ and n ₁₂ is 2 or more, n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, and R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za represents a counter ion that neutralizes the charge.

In formulas 2 to 4, R ²⁰ , R ³⁰ , R ⁴¹ and R ⁴² each independently represent an alkyl group or an aryl group, Zb represents a counter ion that neutralizes the charge, and the wavy line represents the above formula 1- represents the bonding site with the group represented by L in 1.

<19> The on-press development type lithographic printing plate precursor according to <18>, wherein the color-changing compound is a compound represented by the following formula 1-2.

In formula 1-2, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c or -NR ^d R ^e , R ²³ and R ²⁴ each independently represent a hydrogen atom or -R ^a , and R ^a to R ^e each independently represent a hydrocarbon R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²³ and R ²⁴ may be connected to form a monocyclic or polycyclic ring, and L is an oxygen atom, a sulfur atom, or , -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² each independently may have a substituent. It represents an alkyl group, and Za represents a counter ion that neutralizes charge.

<20> The on-press development type lithographic printing plate according to any one of <18> or <19>, wherein the color-changing compound is a compound represented by any of the following formulas 1-3 to 1-7. Original version.

In formulas 1-3 to 1-7, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c , or -NR ^d R ^e , R ²⁵ and R ²⁶ each independently represent a hydrogen atom, a halogen atom, or -R ^{a ,} and R ^a to R ^e each independently represents a hydrocarbon group, R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²⁵ and R ²⁶ may be connected to form a monocyclic or polycyclic ring, and L is represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² each independently represent a substituent. represents an alkyl group which may have , and Za represents a counter ion that neutralizes charge.

<21> W ¹ and W ² in the above formulas 1-2 to 1-7 are each independently an alkyl group having a substituent, and the above substituent is -(OCH ₂ CH ₂ )-, The on-press development type lithographic printing plate precursor according to <19> or <20>, which is a group having at least a sulfo group, a salt of a sulfo group, a carboxy group, or a salt of a carboxy group.

<22> The image recording layer further contains a polymerization initiator,
The on-press development type lithographic printing plate precursor according to any one of <1> to <21>, wherein the polymerization initiator contains an electron-donating polymerization initiator and an electron-accepting polymerization initiator.
<23> The on-press development type lithographic printing plate precursor according to <22>, wherein the polymerization initiator contains a compound formed by the electron-donating polymerization initiator and the electron-accepting polymerization initiator forming a pair salt.

<24> The on-press development type lithographic printing plate precursor according to <22>, wherein the electron-accepting polymerization initiator contains a compound represented by the following formula (II).

In formula (II), X represents a halogen atom, and R ³ represents an aryl group.

<25> The image recording layer contains an infrared absorber,
The on-press development type lithographic printing plate precursor according to any one of <22> to <24>, wherein the infrared absorber has a HOMO value of 0.70 eV or less.
<26> Any one of <22> to <25>, wherein the image recording layer contains an infrared absorber, and the LUMO of the electron-accepting polymerization initiator - the LUMO of the infrared absorber is 0.70 eV or less The on-press development type lithographic printing plate precursor described in .

<27> The support has an aluminum plate and an aluminum anodic oxide film disposed on the aluminum plate,
The anodic oxide film is located closer to the image recording layer than the aluminum plate,
The anodic oxide film has micropores extending in the depth direction from the surface on the image recording layer side,
The on-press development type lithographic printing plate precursor according to any one of <1> to <26>, wherein the average diameter of the micropores on the surface of the anodic oxide film is more than 10 nm and less than 100 nm.
<28> The micropores communicate with the large diameter hole extending from the surface of the anodic oxide film to a depth of 10 nm to 1,000 nm and the bottom of the large diameter hole, and the micropore communicates with the bottom of the large diameter hole from the communicating position to a depth of 20 nm to 2. ,000nm,
The average diameter of the large diameter pores on the surface of the anodic oxide film is 15 nm to 100 nm,
The on-press development type lithographic printing plate precursor according to <27>, wherein the average diameter of the small diameter holes at the communicating positions is 13 nm or less.

<29> Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of <1> to <28>;
A method for producing a lithographic printing plate, comprising the step of supplying at least one selected from the group consisting of printing ink and dampening water on a printing press to remove an image recording layer in a non-image area.
<30> Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of <1> to <28>;
a step of supplying at least one selected from the group consisting of printing ink and dampening water on the printing press to remove the image recording layer in the non-image area to produce a lithographic printing plate;
a step of printing with the obtained lithographic printing plate;
Lithographic printing method.

According to an embodiment of the present disclosure, it is possible to provide an on-press development type lithographic printing plate precursor that can suppress deterioration of on-press developability over time.
Further, according to another embodiment of the present disclosure, it is possible to provide a method for producing a lithographic printing plate or a lithographic printing method using the above-described on-press development type lithographic printing plate precursor.

FIG. 2 is a schematic cross-sectional view of one embodiment of a support. FIG. 3 is a schematic cross-sectional view of another embodiment of the support. FIG. 2 is a schematic diagram of an anodizing apparatus used for anodizing in a method for manufacturing a support having an anodized film.

Below, the content of the present disclosure will be explained in detail. Although the description of the constituent elements described below may be made based on typical embodiments of the present disclosure, the present disclosure is not limited to such embodiments.
In the present disclosure, "~" indicating a numerical range is used to include the numerical values written before and after it as a lower limit value and an upper limit value.
In the numerical ranges described step by step in this disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. . Furthermore, in the numerical ranges described in this disclosure, the upper limit or lower limit of the numerical range may be replaced with the values shown in the Examples.
Furthermore, in the description of groups (atomic groups) in the present disclosure, descriptions that do not indicate substituted or unsubstituted include those having no substituent as well as those having a substituent. For example, the term "alkyl group" includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).
In the present disclosure, "(meth)acrylic" is a term used as a concept that includes both acrylic and methacrylic, and "(meth)acryloyl" is a term used as a concept that includes both acryloyl and methacryloyl. be.
In addition, the term "process" in this disclosure is used not only to refer to an independent process, but also to include it in this term if the intended purpose of the process is achieved, even if the process cannot be clearly distinguished from other processes. It will be done.
Furthermore, in the present disclosure, "mass %" and "weight %" have the same meaning, and "mass parts" and "weight parts" have the same meaning.
Furthermore, in the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.
In addition, unless otherwise specified, the weight average molecular weight (Mw) and number average molecular weight (Mn) in this disclosure are determined using columns of TSKgel GMHxL, TSKgel G4000HxL, and TSKgel G2000HxL (all product names manufactured by Tosoh Corporation). The molecular weight was detected using a gel permeation chromatography (GPC) analyzer using a solvent THF (tetrahydrofuran) and a differential refractometer, and was calculated using polystyrene as a standard substance.
In the present disclosure, the term "lithographic printing plate precursor" includes not only a lithographic printing plate precursor but also a disposable plate precursor. Further, the term "lithographic printing plate" includes not only a lithographic printing plate prepared by subjecting a lithographic printing plate precursor to operations such as exposure and development, if necessary, but also disposable plates. In the case of a disposable original plate, exposure and development operations are not necessarily required. Note that the disposable plate is a lithographic printing plate precursor that is attached to a plate cylinder that is not used when, for example, a part of the page is printed in one color or two colors in color newspaper printing.
In this disclosure, "excellent printing durability" refers to the ability to print a large number of planographic printing plates, and the printing durability when UV ink is used as the ink during printing is hereinafter referred to as "UV Also called "printing durability."

≪On-press development type lithographic printing plate original plate≫
The on-press development type lithographic printing plate precursor (hereinafter also simply referred to as "lithographic printing plate precursor") according to the present disclosure has an image recording layer and an outermost layer on a support in this order, and the image recording layer comprises: It contains a polymer having a glass transition temperature of 70° C. or higher (hereinafter also referred to as a specific polymer), and the outermost layer contains a color-changing compound.
Further, the lithographic printing plate precursor according to the present disclosure is preferably a negative lithographic printing plate precursor.

In on-press development type lithographic printing plate precursors such as those described in Patent Documents 1 to 4, a decrease in on-press developability may be observed over time. In particular, this decrease in on-press developability over time is likely to occur in lithographic printing plate precursors having an outermost layer containing a color-changing compound, although the reason is not clear.
The image recording layer of an on-press development type lithographic printing plate precursor often contains a high molecular weight material such as a binder polymer and a low molecular weight polymerizable compound. Both exist in a phase-separated manner such that aggregates of low-molecular-weight polymerizable compounds are dispersed in a sea area of high-molecular weight substances in the image-recording layer. A part of the high molecular weight material that makes up the sea part may be fused due to the heat applied over time. As a part of the polymer is fused in the image-recording layer, it becomes difficult for the marking water applied during on-press development to penetrate into the image-recording layer, reducing on-press developability. It is thought that

In the lithographic printing plate precursor according to the present disclosure, the image recording layer contains a polymer having a glass transition temperature of 70° C. or higher.
By using such a high molecular weight material having a high glass transition temperature, fusion itself of the high molecular weight material becomes difficult to occur, and therefore, it is presumed that deterioration of on-press developability over time is suppressed.

[Preferred embodiment]
Preferred embodiments of the present disclosure will be described below.
In the present disclosure, the image recording layer further contains a polymerizable compound having a molecular weight of 5,000 or less (hereinafter also referred to as a specific polymerizable compound) from the viewpoint of suppressing the deterioration of on-press developability over time, and contains a specific polymerizable compound. The difference between the solubility parameter (also referred to as SP value) and the solubility parameter (SP value) of the polymerizable compound is preferably 0.8 MPa ^1/2 or more, more preferably 1.0 MPa ^1/2 or more. , 1.2 MPa ^1/2 or more is more preferable.
The upper limit of the above difference is, for example, 13.0 MPa ^1/2 .

As mentioned above, if there is a difference in SP value between the specific polymer and the specific polymerizable compound, even if some of the specific polymer is fused in the image recording layer, the sea area due to the specific polymer is A state of phase separation continues in which aggregates of low-molecular polymerizable compounds are dispersed. Therefore, it is presumed that the marking water applied during on-press development can more easily permeate into the image recording layer, thereby further suppressing the deterioration of on-press developability over time.

Here, the “solubility parameter (unit: (MPa) ^1/2 )” in the present disclosure uses the Hansen solubility parameter.
The Hansen solubility parameter is a solubility parameter introduced by Hildebrand divided into three components: a dispersion term δd, a polarity term δp, and a hydrogen bond term δh, and is expressed in a three-dimensional space. In the present disclosure, the solubility parameter (hereinafter also referred to as SP value) is expressed as δ (unit: (MPa) ^1/2 ), and a value calculated using the following formula is used.
δ (MPa) ^1/2 = (δd ² + δp ² + δh ² ) ^1/2
The dispersion term δd, polarity term δp, and hydrogen bond term δh have been sought by Hansen and his successors, and are detailed in Polymer Handbook (fourth edition), VII-698 to 711. There is. Further, details of the SP value of Hansen's solubility parameter are described in the document "Hansen Solubility Parameters; A Users Handbook (CRC Press, 2007)" written by Charles M. Hansen.
In the present disclosure, for the Hansen solubility parameter in a partial structure of a compound, a value estimated from the chemical structure can also be used by using the computer software "Hansen Solubility Parameters in Practice (HSPiP ver. 4.1.07)".
In addition, in this disclosure, if the compound is a polymer such as an addition polymerization type resin or a polycondensation type resin, the SP value for each monomer unit is expressed as the total amount multiplied by the mole fraction, and the compound is a polymer such as an addition polymerization resin or a polycondensation resin. In the case of a low-molecular compound that does not have this, the SP value of the entire compound is taken as the SP value.
In the present disclosure, the SP value of the polymer may be calculated from the molecular structure of the resin by the Hoy method described in the Polymer Handbook (fourth edition).

The solubility parameter (SP value) of the specific polymerizable compound is preferably 22.0 MPa ^1/2 or less, more preferably 20.0 MPa ^1/2 or less, and 19.5 MPa ^1/2 or less. It is even more preferable that there be.
The lower limit of the SP value of the specific polymerizable compound is, for example, 10.0 MPa ^1/2 .

Moreover, it is preferable that the specific polymerizable compound is a bifunctional or more functional polymerizable compound.
The specific polymerizable compound may be a bifunctional polymerizable compound, or the specific polymerizable compound may be a heptafunctional or higher functional polymerizable compound (more preferably a 10 functional or higher functional polymerizable compound).

The solubility parameter (SP value) of the specific polymer is preferably 17.5 MPa ^1/2 to 20.0 MPa ^1/2 , and preferably 18.0 MPa ^1/2 to 19.5 MPa ^1/2 . is more preferable.

From the viewpoint of suppressing the deterioration of on-press developability over time, when the mass of the specific polymer in the image recording layer is P and the mass of the specific polymerizable compound is M, 6.0≧P/ It is preferable to satisfy the relationship M≧0.5, more preferably to satisfy the relationship 5.0≧P/M≧0.6, and preferably satisfy the relationship 3.0≧P/M≧0.7. More preferred.

Next, details of each component of the lithographic printing plate precursor according to the present disclosure will be described.

<Image recording layer>
The lithographic printing plate precursor according to the present disclosure has an image recording layer on a support.
The image recording layer in the present disclosure includes a polymer having a glass transition temperature of 70° C. or higher (hereinafter also referred to as a specific polymer).
The image recording layer in the present disclosure preferably contains, in addition to the specific polymer and the specific polymerizable compound, for example, a polymerization initiator, an infrared absorber, and other components.
The image recording layer in the present disclosure is preferably a negative image recording layer, more preferably a water-soluble or water-dispersible negative image recording layer.
In the image recording layer of the present disclosure, from the viewpoint of on-press developability, it is preferable that unexposed areas of the image recording layer are removable with at least one of dampening water and printing ink.

The details of each component contained in the image recording layer will be explained below.

[Specific polymer]
The specific polymer is not particularly limited as long as it has a glass transition temperature of 70° C. or higher, but it is preferably a polymer that does not have a granular shape in the image recording layer.
In the present disclosure, "high molecular weight material" means a compound having a weight average molecular weight of more than 5,000.

In this disclosure, the glass transition temperature (also referred to as Tg) of a resin can be measured using differential scanning calorimetry (DSC).
A specific measuring method is performed according to the method described in JIS K 7121 (1987) or JIS K 6240 (2011). As the glass transition temperature in this specification, extrapolated glass transition initiation temperature (hereinafter sometimes referred to as Tig) is used.
The method for measuring the glass transition temperature will be explained in more detail.
When determining the glass transition temperature, hold the device at a temperature approximately 50°C lower than the expected Tg of the resin until it stabilizes, then heat at a heating rate of 20°C/min to approximately 30°C below the temperature at which the glass transition has completed. Heat to high temperature and generate differential thermal analysis (DTA) or DSC curves.
The extrapolated glass transition onset temperature (Tig), that is, the glass transition temperature Tg in this specification, is the line between the straight line extending the baseline on the low temperature side to the high temperature side in the DTA curve or DSC curve, and the step-like change part of the glass transition. It is determined as the temperature at the intersection with the tangent line drawn at the point where the slope of the curve is maximum.

The glass transition temperature of the specific polymer is preferably 75°C or higher, more preferably 80°C or higher, even more preferably 85°C or higher, and even more preferably 90°C or higher, from the viewpoint of further suppressing the deterioration of on-press developability over time. Particularly preferred.
Further, the upper limit of the glass transition temperature of the specific polymer is 200° C., preferably 120° C. or less, from the viewpoint of ease of water penetration into the image recording layer.

As the specific polymer, known binder polymers (for example, (meth)acrylic resin, polyvinyl acetal, polyurethane, etc.) used in the image recording layer of a lithographic printing plate precursor can be suitably used.
Among these, polyvinyl acetal is preferred from the viewpoint of further suppressing deterioration of on-press developability over time.

Polyvinyl acetal is a resin obtained by acetalizing the hydroxyl group of polyvinyl alcohol with aldehyde.
Particularly preferred is polyvinyl butyral in which the hydroxyl group of polyvinyl alcohol is acetalized (ie, butyralized) with butyraldehyde.
Polyvinyl acetal is obtained by acetalizing the hydroxyl group of polyvinyl alcohol with aldehyde and contains the structural unit represented by (a) below.

Here, R represents the residue of the aldehyde used for acetalization.
Examples of R include a hydrogen atom, an alkyl group, and the ethylenically unsaturated group described below.

The content of the structural unit represented by (a) above (also referred to as the degree of acetalization) is preferably 50 mol% to 90 mol%, more preferably 55 mol% to 85 mol%, based on the total structural units of polyvinyl acetal. More preferably 55 mol% to 80 mol%.

It is preferable that the polyvinyl acetal has an ethylenically unsaturated group from the viewpoint of improving printing durability.
Here, the ethylenically unsaturated group that polyvinyl acetal has is not particularly limited, and from the viewpoint of reactivity, on-press developability, and printing durability, vinyl phenyl group (styryl group), vinyl ester group, vinyl ether group, More preferably, it is at least one group selected from the group consisting of allyl group, (meth)acryloxy group, and (meth)acrylamide group, and vinyl group, allyl group, (meth)acryloxy group, etc. are preferable.

From the viewpoint of improving printing durability, it is preferable that the polyvinyl acetal contains a structural unit having an ethylenically unsaturated group.
The structural unit having an ethylenically unsaturated group may be the above-mentioned structural unit having an acetal ring, or may be a structural unit other than the structural unit having an acetal ring.
Among these, from the viewpoint of increasing crosslinking density during exposure, polyvinyl acetal is preferably a compound in which an ethylenically unsaturated group is introduced into the acetal ring. That is, in the structural unit represented by (a) above, it is preferable that R has an ethylenically unsaturated group.

When the structural unit having an ethylenically unsaturated group is a structural unit other than the structural unit having an acetal ring, for example, a structural unit having an acrylate group, specifically, a structural unit represented by (d) below. There may be.

When the structural unit having an ethylenically unsaturated group is a structural unit other than the structural unit having an acetal ring, the content of this structural unit (also referred to as acrylate group amount) is based on all the structural units of the polyvinyl acetal. It is preferably 1 mol% to 15 mol%, more preferably 1 mol% to 10 mol%.

It is preferable that the polyvinyl acetal further contains a structural unit having a hydroxyl group from the viewpoint of on-press developability. That is, the polyvinyl acetal preferably contains a structural unit derived from vinyl alcohol.
Examples of the structural unit having a hydroxyl group include the structural unit represented by (b) below.

From the viewpoint of on-press developability, the content of the structural unit represented by (b) above (also referred to as the amount of hydroxyl groups) is preferably 5 mol% to 50 mol%, and 10 mol% based on all the structural units of the polyvinyl acetal. -40 mol% is more preferable, and 20 mol% - 40 mol% is even more preferable.

The polyvinyl acetal may further contain other structural units.
Other structural units include, for example, a structural unit having an acetyl group, specifically, a structural unit represented by (c) below.

The content of the structural unit represented by (c) above (also referred to as acetyl group amount) is preferably 0.5 mol% to 10 mol%, and 0.5 mol% to 8 mol%, based on the total structural units of the polyvinyl acetal. is more preferable, and even more preferably 1 mol% to 3 mol%.

Here, the degree of acetalization, the amount of acrylate groups, the amount of hydroxyl groups, and the amount of acetyl groups can be determined as follows.
That is, by ¹ H NMR measurement, the mol content is calculated from the proton peak area ratio of the methyl or methylene moiety of the acetal, the methyl moiety of the acrylate group, and the methyl moiety of the hydroxyl group and the acetyl group.

The weight average molecular weight of the polyvinyl acetal is preferably 18,000 to 150,000.

As mentioned above, the SP value of the polyvinyl acetal is preferably 17.5 MPa ^1/2 to 20.0 MPa ^1/2 , more preferably 18.0 MPa ^1/2 to 19.5 MPa ^1/2 . preferable.

Specific examples [P-1 to P-3] of the above polyvinyl acetal are listed below, but the polyvinyl acetal used in the present disclosure is not limited to these.
In the structure below, "l" is 50 mol% to 90 mol%, "m" is 0.5 mol% to 10% by mass, "n" is 5 mol% to 50 mol%, and "o" is 1 mol% to It is 15 mol%.

As the polyvinyl acetal, commercially available products can be used.
Commercial products of polyvinyl acetal include the S-LEC series (specifically, S-LEC BX-L, BX-1, BX-5, BL-7Z, BM-1, BM-5, BH) manufactured by Sekisui Chemical Co., Ltd. -6, BH-3, etc.

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

The specific polymer can be contained in any amount in the image recording layer, but the content of the specific polymer is 1% by mass to 80% by mass based on the total mass of the image recording layer. The content is preferably 1% by mass to 70% by mass, more preferably 3% by mass to 70% by mass.

[Specific polymerizable compound]
The image recording layer in the present disclosure preferably contains a specific polymerizable compound, as described above.
The specific polymerizable compound can be used without particular limitation as long as it has a molecular weight of 5,000 or less.

The polymerizable group contained in the specific polymerizable compound may be a radically polymerizable group or a cationically polymerizable group, but is preferably a radically polymerizable group.
Examples of the radically polymerizable group include a (meth)acryloyl group, an allyl group, a vinyl phenyl group, a vinyl group, and the like, and a (meth)acryloyl group is preferred from the viewpoint of reactivity.

As the specific polymerizable compound, a difunctional or higher functional polymerizable compound is preferred, a difunctional polymerizable compound is preferred, and a heptafunctional or higher functional polymerizable compound is also preferred.

When the specific polymerizable compound is a bifunctional polymerizable compound, its molecular weight (weight average molecular weight if it has a molecular weight distribution) is preferably 50 to 1,000, and preferably 200 to 900. is more preferable, and even more preferably 300 to 600.

When the specific polymerizable compound is a heptafunctional or higher functional polymerizable compound, its molecular weight (weight average molecular weight if it has a molecular weight distribution) preferably exceeds 1,000, and exceeds 1,000. 000 or less is more preferable.

Specific examples of specific polymerizable compounds are listed below, but the specific polymerizable compounds used in the present disclosure are not limited to these.

The polymerizable compounds used in the image recording layer will be described below, and among them, those having a molecular weight of 5,000 or less can be used as specific polymerizable compounds.

[Polymerizable compound]
In the present disclosure, a polymerizable compound refers to a compound having a polymerizable group.
The polymerizable group is not particularly limited and may be any known polymerizable group, but is preferably an ethylenically unsaturated group. Further, the polymerizable group may be a radically polymerizable group or a cationically polymerizable group, but a radically polymerizable group is preferable.
Examples of the radically polymerizable group include a (meth)acryloyl group, an allyl group, a vinyl phenyl group, a vinyl group, and the like, and a (meth)acryloyl group is preferred from the viewpoint of reactivity.
The molecular weight (weight average molecular weight when having a molecular weight distribution) of the polymerizable compound is preferably 50 or more and 10,000 or less. In the case of the specific polymerizable compound, its molecular weight (or weight average molecular weight if it has a molecular weight distribution) is preferably 100 or more and 4,000 or less.

The polymerizable compound used in the present disclosure may be, for example, a radically polymerizable compound or a cationically polymerizable compound, but may be an addition polymerizable compound having at least one ethylenically unsaturated bond (ethylenic unsaturated compounds).
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 a monomer, a prepolymer, ie, a dimer, trimer or oligomer, or a mixture thereof.
Among these, from the viewpoint of UV printing durability, the polymerizable compound preferably includes a trifunctional or higher functional polymerizable compound, more preferably a heptafunctional or higher functional polymerizable compound, and a 10 functional or higher functional polymerizable compound. It is even more preferable to include a compound. Further, from the viewpoint of UV printing durability of the resulting lithographic printing plate, the polymerizable compound preferably contains an ethylenically unsaturated compound having three or more functionalities (preferably seven functionalities or more, more preferably ten functional or more). It is more preferable to include a (meth)acrylate compound having 3 or more functionalities (preferably 7 or more functionalities, more preferably 10 or more functionalities).

[Oligomer]
The image recording layer preferably contains a polymerizable compound that is an oligomer (hereinafter also simply referred to as "oligomer").
In the present disclosure, an oligomer refers to a polymerizable compound having a molecular weight (weight average molecular weight when having a molecular weight distribution) of 600 to 10,000 and containing at least one polymerizable group.
From the viewpoint of excellent chemical resistance and UV printing durability, the molecular weight of the oligomer is preferably 1,000 or more and 5,000 or less.

Further, from the viewpoint of improving UV printing durability, the number of polymerizable groups in one molecule of the oligomer is preferably 2 or more, more preferably 3 or more, still more preferably 6 or more, and 10 or more. It is particularly preferable that
The upper limit of the number of polymerizable groups in the oligomer is not particularly limited, but the number of polymerizable groups is preferably 20 or less.

From the viewpoint of UV printing durability and on-press developability, the oligomer preferably has 7 or more polymerizable groups and a molecular weight of 1,000 or more and 10,000 or less; It is more preferable that the number of groups is 7 or more and 20 or less, and the molecular weight is 1,000 or more and 5,000 or less.
In addition, when an oligomer is included as a polymerizable compound, a polymer component that may be generated during the process of manufacturing the oligomer may also be included.

From the viewpoint of UV printing durability and on-press developability, the oligomer preferably has at least one type selected from the group consisting of a compound having a urethane bond, a compound having an ester bond, and a compound having an epoxy residue. It is preferable to have a compound having a urethane bond.
In the present disclosure, an epoxy residue refers to a structure formed by an epoxy group, and means a structure similar to a structure obtained by, for example, a reaction between an acid group (such as a carboxylic acid group) and an epoxy group.

(Compound with urethane bond)
The compound having a urethane bond, which is an example of an oligomer, is preferably a compound having at least a group represented by the following formula (Ac-1) or the formula (Ac-2). ) is more preferable.

In formula (Ac-1) and formula (Ac-2), L ¹ to L ⁴ each independently represent a divalent hydrocarbon group having 2 to 20 carbon atoms, and the wavy line portion represents a bond with another structure. Represents a position.
L ¹ to L ⁴ are each independently preferably an alkylene group having 2 to 20 carbon atoms, more preferably an alkylene group having 2 to 10 carbon atoms, and an alkylene group having 4 to 8 carbon atoms. It is even more preferable that there be. Moreover, although the said alkylene group may have a branched or ring structure, it is preferable that it is a linear alkylene group.

The wavy line part in formula (Ac-1) or formula (Ac-2) can be independently bonded directly to the wavy line part in the group represented by the following formula (Ae-1) or formula (Ae-2). preferable.

In formula (Ae-1) and formula (Ae-2), R each independently represents an acryloyloxy group or a methacryloyloxy group, and the wavy line portion is the wavy line in formula (Ac-1) and formula (Ac-2). represents the bonding position with the part.

Further, as the compound having a urethane bond, a compound obtained by introducing a polymerizable group into a polyurethane obtained by a reaction between a polyisocyanate compound and a polyol compound through a polymer reaction may be used.
For example, a compound having a urethane bond may be obtained by reacting a polyurethane oligomer obtained by reacting a polyol compound having an acid group with a polyisocyanate compound with a compound having an epoxy group and a polymerizable group.

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

(Compound with epoxy residue)
The compound having an epoxy residue, which is an example of an oligomer, is preferably a compound containing a hydroxy group within the compound.
Further, the number of polymerizable groups in the compound having an epoxy residue is preferably 2 to 6, more preferably 2 to 3.
The above-mentioned compound having an epoxy residue can be obtained, for example, by reacting a compound having an epoxy group with acrylic acid.

Commercially available products are shown below as specific examples of oligomers, but the oligomers used in the present disclosure are not limited thereto.
Commercially available oligomers include UA-510H, UA-306H, UA-306I, UA-306T (all manufactured by Kyoeisha Chemical Co., Ltd.), UV-1700B, UV-6300B, and UV7620EA (all manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.). )), U-15HA (Shin Nakamura Chemical Industry Co., Ltd.), EBECRYL450, EBECRYL657, EBECRYL885, EBECRYL800, EBECRYL3416, EBECRYL860 (all manufactured by Daicel Ornex Co., Ltd.).

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

[Low molecular polymerizable compound]
The polymerizable compound may further contain a polymerizable compound other than the above oligomer.
The polymerizable compound other than the oligomer is preferably a low-molecular polymerizable compound from the viewpoint of chemical resistance. The low-molecular polymerizable compound may be in a chemical form such as a monomer, dimer, trimer, or a mixture thereof.
In addition, from the viewpoint of chemical resistance, the low-molecular polymerizable compound includes at least one polymerizable compound selected from the group consisting of a polymerizable compound having three or more ethylenically unsaturated groups, and a polymerizable compound having an isocyanuric ring structure. It is preferable that the compound is a compound with a chemical nature.

In the present disclosure, a low-molecular polymerizable compound refers to a polymerizable compound having a molecular weight (weight average molecular weight if it has a molecular weight distribution) of 50 or more and less than 600.
The molecular weight of the low-molecular polymerizable compound is preferably 100 or more and less than 600, more preferably 300 or more and less than 600, from the viewpoint of excellent chemical resistance, UV printing durability, and on-press development scum suppression. It is preferably 400 or more and less than 600.

If the polymerizable compound contains a low-molecular polymerizable compound as a polymerizable compound other than oligomers (if it contains two or more types of low-molecular polymerizable compounds, the total amount), chemical resistance, UV printing durability, and on-press From the viewpoint of suppressing development residue, the ratio of the oligomer to the low-molecular polymerizable compound (oligomer/low-molecular polymerizable compound) is preferably from 10/1 to 1/10, and is preferably 10/1 to 1/10 on a mass basis. The ratio is more preferably 1 to 3/7, and even more preferably 10/1 to 7/3.

Specific examples of low-molecular polymerizable compounds include compounds described in paragraphs 0082 to 0086 of International Publication No. 2019/013268.

The structure of the polymerizable compound, whether it is used alone or in combination, the amount of addition, and other usage details can be set arbitrarily.
Among these, the image recording layer preferably contains two or more kinds of polymerizable compounds from the viewpoint of UV printing durability.
The content of the polymerizable compound (if two or more types of polymerizable compounds are included, the total content of the polymerizable compounds) is preferably 5% by mass to 75% by mass with respect to the total mass of the image recording layer. , more preferably 10% by mass to 70% by mass, and even more preferably 15% by mass to 60% by mass.

The specific polymerizable compound (that is, a polymerizable compound having a molecular weight of 5,000 or less) may be used alone or in combination of two or more.

As mentioned above, the content of the specific polymerizable compound is 6.0≧P/M≧0.5 (more preferably 5.0≧P/M≧0.6, still more preferably 3.0≧ P/M≧0.7) may be added to the image recording layer.
The content of the specific polymerizable compound is preferably 10% by mass to 70% by mass, and 20% by mass to 65% by mass, based on the total mass of the image recording layer, from the viewpoint of suppressing deterioration of on-press developability over time. is more preferred, and even more preferably 25% by mass to 60% by mass.

[Polymerization initiator]
The image recording layer in the present disclosure preferably contains a polymerization initiator.
The polymerization initiator preferably includes an electron-accepting polymerization initiator, and more preferably 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 a polymerization initiator.
An electron-accepting polymerization initiator is a compound that generates polymerization initiation species such as radicals by accepting one electron through intermolecular electron transfer when electrons of an infrared absorber are excited by infrared exposure.
Electron-accepting polymerization initiators are compounds that generate polymerization initiating species such as radicals and cations using energy from light, heat, or both, and include known thermal polymerization initiators, compounds having bonds with low bond dissociation energy, A photopolymerization initiator and the like can be appropriately selected and used. As the electron-accepting polymerization initiator, a radical polymerization initiator is preferable, and an onium salt compound is more preferable.
Further, as the electron-accepting polymerization initiator, an infrared-sensitive polymerization initiator is preferable.

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

As an example of the iodonium salt compound, a diaryliodonium salt compound is preferable, a diphenyliodonium salt compound substituted with an electron-donating group, such as an alkyl group or an alkoxyl group is particularly preferable, and an asymmetric diphenyliodonium salt compound is preferable. . Specific examples include diphenyliodonium hexafluorophosphate, 4-methoxyphenyl-4-(2-methylpropyl)phenyliodonium hexafluorophosphate, 4-(2-methylpropyl)phenyl-p-tolyliodonium hexafluorophosphate. Fluorophosphate, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4-diethoxyphenyliodonium tetrafluoroborate, 4-octyloxy Phenyl-2,4,6-trimethoxyphenyliodonium = 1-perfluorobutanesulfonate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium = hexafluorophosphate, bis(4-t-butylphenyl ) Iodonium hexafluorophosphate.

Examples of counter anions of iodonium salt compounds and sulfonium salt compounds include sulfonate anions, carboxylate anions, tetrafluoroborate anions, hexafluorophosphate anions, p-toluenesulfonate anions, tosylate anions, sulfonamide anions, and sulfonimides. Examples include anions.
Among these, sulfonamide anion or sulfonimide anion is preferred, and sulfonimide anion is more preferred.
As the sulfonamide anion, an arylsulfonamide anion is preferred.
Moreover, as the sulfonimide anion, a bisarylsulfonimide anion is preferable.
Specific examples of the sulfonamide anion or the sulfonimide anion include the compounds described in paragraph 0034 of International Publication No. 2019/013268.

Further, from the viewpoint of developability and UV printing durability of the resulting lithographic printing plate, the electron-accepting polymerization initiator is preferably a compound represented by either the following formula (II) or formula (III). In particular, compounds represented by formula (II) are preferred.

In formulas (II) and (III), X represents a halogen atom, and R ³ , R ⁴ and R ⁵ each independently represent a monovalent hydrocarbon group having 1 to 20 carbon atoms.
In formula (II), it is preferable that X represents a halogen atom and R ³ represents an aryl group.

Specific examples of X in formulas (II) and (III) include fluorine atom, chlorine atom, bromine atom, and iodine atom. Among these, a chlorine atom or a bromine atom is preferable because of its excellent sensitivity, and a bromine atom is particularly preferable.
Further, in formulas (II) and (III), R ³ , R ⁴ and R ⁵ are each independently preferably an aryl group, and among them, from the viewpoint of an excellent balance between sensitivity and storage stability, amide Aryl groups substituted with groups are preferred.

Among the above electron-accepting polymerization initiators, the compound represented by formula (IV) is particularly preferred.

In formula (IV), R ⁴ and R ⁵ each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms. p and q each independently represent an integer from 1 to 5. However, p+q=2 to 6.

Specific examples of the electron-accepting polymerization initiator represented by any of the above formulas (II) to (IV) include compounds shown in the following formulas, but the present disclosure is not limited thereto. do not have.

The lowest unoccupied molecular orbital (LUMO) of the electron-accepting polymerization initiator is preferably -3.00 eV or less, more preferably -3.02 eV or less, from the viewpoint of improving sensitivity and preventing plate skipping. preferable.
Further, the lower limit is preferably -3.80 eV or more, more preferably -3.50 eV or more.
In the present disclosure, calculation of the lowest unoccupied orbital (LUMO) and the later-described highest occupied orbital (HOMO) is performed by the following method.
First, if the compound to be calculated has a counter ion that is not the main structure, the counter ion may be ignored.
Structure optimization was performed using DFT (B3L) using quantum chemical calculation software Gaussian09.
YP/6-31G(d)).
MO (molecular orbital) energy calculation is performed using DFT (B3LYP/6-31+G(d,p)/CPCM (solvent=methanol)) using the structure obtained by the above structure optimization.
The MO energy Ebare (unit: hartree) obtained in the above MO energy calculation is converted into Escaled (unit: eV) used as the HOMO and LUMO values in this disclosure using the following formula.
Escaled=0.823168×27.2114×Ebare-1.07634
Note that 27.2114 is simply a coefficient for converting hartree into eV, and 0.823168 and -1.07634 are adjustment coefficients, and the HOMO and LUMO of the compound to be calculated are calculated based on the actual measured values. determined to suit.

The electron-accepting polymerization initiators may be used alone or in combination of two or more.

The content of the electron-accepting polymerization initiator is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 30% by mass, based on the total mass of the image recording layer. , 0.8% by mass to 20% by mass is particularly preferred.

[Electron-donating polymerization initiator (polymerization aid)]
The image recording layer in the present disclosure preferably contains an electron-donating polymerization initiator (also referred to as a polymerization aid) as a polymerization initiator.
Electron-donating polymerization initiators generate radicals by donating one electron to the orbit of the infrared absorber from which one electron has been removed by intermolecular electron transfer when the electrons of the infrared absorber are excited or intramolecularly transferred by infrared exposure. It is a compound that generates polymerization initiating species such as
The electron donating type polymerization initiator is preferably an electron donating type radical polymerization initiator.

The image recording layer preferably contains a borate compound as an electron-donating polymerization initiator from the viewpoint of printing durability.
From the viewpoint of printing durability, the borate compound is preferably a tetraarylborate compound or a monoalkyltriarylborate compound, and more preferably a tetraarylborate compound.
The counter cation possessed by the borate compound is not particularly limited, but is preferably an alkali metal ion or a tetraalkylammonium ion, more preferably a sodium ion, a potassium ion, or a tetrabutylammonium ion.
Further, the counter cation of the borate compound may be a cationic polymethine dye described as an infrared absorber in the present disclosure. For example, the above borate compound may be used as a counter cation of a cyanine dye.

Preferred examples of the borate compound include sodium tetraphenylborate.

Preferred specific examples of the electron-donating polymerization initiator are B-1 to B-9 below, but it goes without saying that the invention is not limited to these. Furthermore, in the chemical formula below, Ph represents a phenyl group, and Bu represents an n-butyl group.

Further, the highest occupied molecular orbital (HOMO) of the electron-donating polymerization initiator is preferably -6.00 eV or more, and -5.95 eV or more, from the viewpoint of improving sensitivity and preventing plate skipping. More preferably, it is −5.93 eV or more.
Further, the upper limit is preferably −5.00 eV or less, more preferably −5.40 eV or less.

The electron-donating polymerization initiator may be used alone or in combination of two or more.

From the viewpoint of sensitivity and printing durability, the content of the electron-donating polymerization initiator is preferably 0.01% by mass to 30% by mass, and 0.05% by mass based on the total mass of the image recording layer. It is more preferably 25% by mass, and even more preferably 0.1% by mass to 20% by mass.

The polymerization initiator may be a compound in which an electron-donating polymerization initiator and an electron-accepting polymerization initiator form a pair salt.
For example, a compound in which an anion in an electron-donating polymerization initiator and a cation in an electron-accepting polymerization initiator form a pair salt is preferable, and a compound in which an onium cation and a borate anion form a pair salt is preferable. More preferably, the compound is a compound formed by an iodonium cation or a sulfonium cation and a borate anion forming a pair salt, and a compound in which a diaryliodonium cation or a triarylsulfonium cation and a tetraarylborate anion form a pair salt is more preferable. Particularly preferred is a compound formed by forming
Preferred embodiments of the anion in the electron-donating polymerization initiator and the cation in the electron-accepting polymerization initiator are as follows: This is the same as the aspect.
When the image-recording layer contains an anion that is an electron-donating polymerization initiator and a cation that is an electron-accepting polymerization initiator (that is, when it contains a compound forming the above-mentioned counter salt), the image-recording layer shall include an electron-accepting polymerization initiator and the above-mentioned electron-donating polymerization initiator.
Furthermore, a compound in which an electron-donating polymerization initiator and an electron-accepting polymerization initiator form a pair salt may be used as an electron-donating polymerization initiator or as an electron-accepting polymerization initiator. good.
Further, a compound formed by forming a pair salt of an electron-donating polymerization initiator and an electron-accepting polymerization initiator may be used in combination with the electron-donating polymerization initiator described above, or may be used in combination with the electron-donating polymerization initiator described above. It may be used in combination with a polymerization initiator.

[Preferred embodiment of infrared absorber and electron-donating polymerization initiator]
In the image recording layer according to the present disclosure, from the viewpoint of improving sensitivity and printing durability, the value of HOMO of the infrared absorber-HOMO of the electron-donating polymerization initiator is preferably 0.70 eV or less, and 0.70 eV More preferably, it is between -0.10 eV and -0.10 eV.
Note that 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 electron-accepting polymerization initiator and infrared absorber]
In the image recording layer according to the present disclosure, from the viewpoint of improving sensitivity and printing durability, the value of LUMO of the electron-accepting polymerization initiator-LUMO of the infrared absorber is preferably 1.00 eV or less, and 0.80 eV. It is more preferably at most 0.70 eV, even more preferably at most 0.70 eV, particularly preferably from 0.70 eV to -0.10 eV, and most preferably from 0.70 eV to 0.30 eV.
Note that a negative value means that the LUMO of the infrared absorber is higher than the LUMO of the electron-accepting polymerization initiator.

[Infrared absorber]
The image recording layer in the present disclosure includes an infrared absorber.
The infrared absorber is not particularly limited, and examples thereof include pigments and dyes.
As the dye used as the infrared absorber, commercially available dyes and known dyes described in literature such as "Dye Handbook" (edited by the Organic Synthetic Chemistry Association, published in 1972) can be used. Specifically, dyes such as azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinone imine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts, and metal thiolate complexes. can be mentioned.

Preferred among these dyes include cyanine dyes, squarylium dyes, pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes. More preferred are cyanine dyes and indolenine cyanine dyes. Among these, cyanine dyes are particularly preferred.

The infrared absorber is preferably a cationic polymethine dye having an oxygen atom, nitrogen atom, or halogen atom at the meso position. Preferred examples of the cationic polymethine dye include cyanine dyes, pyrylium dyes, thiopyrylium dyes, azulenium dyes, etc., and cyanine dyes are preferred from the viewpoints of ease of availability, solvent solubility during introduction reaction, and the like.

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

Moreover, as the above-mentioned infrared absorber, an infrared absorber that decomposes upon exposure to infrared light can also be suitably used.
As infrared absorbers that decompose by infrared exposure, those described in Japanese Patent Publication No. 2008-544322, International Publication No. 2016/027886, International Publication No. 2017/141882, or International Publication No. 2018/043259 are preferably used. Can be used.
Furthermore, as the infrared absorber that decomposes upon exposure to infrared rays, a decomposable compound used in the outermost layer, which will be described later, may be used.

Only one type of infrared absorber may be used, or two or more types may be used in combination.
Further, a pigment and a dye may be used together as an infrared absorber.

The content of the infrared absorber is 0.1% by mass to 10.0% by mass based on the total mass of the image recording layer.
is preferred, and 0.5% by mass to 5.0% by mass is more preferred.

〔particle〕
The image recording layer in the present disclosure preferably contains particles from the viewpoint of developability and UV printing durability. The particles may be inorganic particles or organic particles.
Among these, the particles preferably include organic particles, and more preferably include polymer particles.
That is, the image recording layer in the present disclosure preferably contains 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.

[Polymer particles]
Examples of the polymer particles include particles containing an addition polymerization type resin (i.e., addition polymer particles), particles containing a polyaddition type resin (i.e., polyaddition type polymer particles), and particles containing a polycondensation type resin (i.e., particles containing a polycondensation type resin). , polycondensation type polymer particles), among others, addition polymerization type polymer particles or polyaddition type polymer particles are preferable.
Further, the polymer particles may be particles containing a thermoplastic resin (ie, thermoplastic polymer particles) from the viewpoint of thermal fusion.

Further, the polymer particles may be in the form of microcapsules, microgels (ie, crosslinked polymer particles), or the like.

The polymer particles are selected from the group consisting of thermoplastic polymer particles, heat-reactive polymer particles, polymer particles having a polymerizable group, microcapsules encapsulating a hydrophobic compound, and microgels (crosslinked polymer particles). is preferred. Among these, polymer particles having a polymerizable group are preferred.
In particularly preferred embodiments, the polymer particles contain at least one ethylenically unsaturated group. The presence of such polymer particles has the effect of increasing the printing durability of exposed areas and the on-press developability of unexposed areas.

As thermoplastic polymer particles, Research Disclosure No. 1, January 1992 is used. Thermoplastic polymer particles described in JP-A-9-123387, JP-A-9-123387, JP-A-9-131850, JP-A-9-171249, JP-A-9-171250, and European Patent No. 931,647 are preferred.

Specific examples of resins constituting thermoplastic polymer particles include ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinylcarbazole, and those having a polyalkylene structure. Mention may be made of homopolymers or copolymers of monomers such as acrylates or methacrylates or mixtures thereof.

From the viewpoint of ink receptivity and UV printing durability, the thermoplastic polymer particles preferably contain a resin having a constitutional unit formed from an aromatic vinyl compound and a constitutional unit having a nitrile group.

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, vinylnaphthalene compounds, etc., 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.

From the viewpoint of ink receptivity, the content of the structural unit formed by the aromatic vinyl compound is preferably higher than the content of the structural unit having a nitrile group, which will be described later, based on the total mass of the thermoplastic resin. It is more preferably 15% by mass to 85% by mass, and even more preferably 30% by mass to 70% by mass.

The structural unit having a nitrile group is preferably introduced using a monomer having a nitrile group.
Examples of the monomer having a nitrile group include acrylonitrile compounds, and (meth)acrylonitrile is preferably mentioned.
As the structural unit having a nitrile group, a structural unit formed from (meth)acrylonitrile is preferable.

From the viewpoint of ink receptivity, the content of the structural unit having a nitrile group is preferably lower than that formed by the aromatic vinyl compound, and is 55% to 90% by mass based on the total mass of the resin. It is more preferable that the amount is 60% by mass to 85% by mass.

In addition, when the resin contained in the thermoplastic polymer particles contains a structural unit formed by an aromatic vinyl compound and a structural unit having a nitrile group, the structural unit formed by an aromatic vinyl compound and a structural unit having a nitrile group are The content ratio (constituent units formed by an aromatic vinyl compound: constituent units having a nitrile group) is preferably 5:5 to 9:1, more preferably 6:4 to 8 on a mass basis. :2.

The resin contained in the thermoplastic polymer particles preferably further includes a structural unit formed from an N-vinyl heterocyclic compound from the viewpoint of UV printing durability and chemical resistance.
Examples of N-vinyl heterocyclic compounds include N-vinylpyrrolidone, N-vinylcarbazole, N-vinylpyrrole, N-vinylphenothiazine, N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam, and N- Vinylimidazole is mentioned, and N-vinylpyrrolidone is preferred.

The content of the structural unit formed by the N-vinyl heterocyclic compound is preferably 5% by mass to 50% by mass, and preferably 10% by mass to 40% by mass, based on the total mass of the thermoplastic resin. More preferred.

The resin contained in the thermoplastic polymer particles may contain a structural unit having an acidic group, but from the viewpoint of on-press developability and ink receptivity, it is preferable not to contain a structural unit having an acidic group. .
Specifically, the content of the structural unit having an acidic group in the thermoplastic resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. preferable. The lower limit of the content is not particularly limited, and may be 0% by mass. Further, the acid value of the thermoplastic resin is preferably 160 mgKOH/g or less, more preferably 80 mgKOH/g or less, and even more preferably 40 mgKOH/g or less. The lower limit of the acid value is not particularly limited, and may be 0 mgKOH/g.
In the present disclosure, the acid value is determined by a measurement method based on JIS K0070:1992.

The resin contained in the thermoplastic polymer particles may contain a structural unit containing a hydrophobic group from the viewpoint of ink receptivity.
Examples of the hydrophobic group include an alkyl group, an aryl group, an aralkyl group, and the like.
The structural unit containing a hydrophobic group is preferably a structural unit formed from an alkyl (meth)acrylate compound, an aryl (meth)acrylate compound, or an aralkyl (meth)acrylate compound; More preferred are structural units.

The content of the structural unit having a hydrophobic group in the resin contained in the thermoplastic polymer particles is preferably 5% to 50% by mass, and preferably 10% to 30% by mass, based on the total mass of the resin. It is more preferable that there be.

The thermoplastic resin contained in the thermoplastic polymer particles preferably has a hydrophilic group from the viewpoint of UV printing durability and on-press developability.
The hydrophilic group is not particularly limited as long as it has a hydrophilic structure, but examples thereof include acid groups such as carboxy groups, hydroxy groups, amino groups, nitrile groups, polyalkylene oxide structures, and the like.
The above-mentioned hydrophilic group is preferably a group having a polyalkylene oxide structure, a group having a polyester structure, or a sulfonic acid group from the viewpoint of UV printing durability and on-press developability. or a sulfonic acid group, and even more preferably a group having a polyalkylene oxide structure.

The polyalkylene oxide structure is preferably a polyethylene oxide structure, a polypropylene oxide structure, or a poly(ethylene oxide/propylene oxide) structure from the viewpoint of on-press developability.
Furthermore, from the viewpoint of on-press developability, among the above-mentioned hydrophilic groups, it is preferable to have a polypropylene oxide structure as the polyalkylene oxide structure, and it is more preferable to have a polyethylene oxide structure and a polypropylene oxide structure.
From the viewpoint of on-press developability, the number of alkylene oxide structures in the polyalkylene oxide structure is preferably 2 or more, more preferably 5 or more, even more preferably 5 to 200, and 8 to 150 is particularly preferred.

Further, from the viewpoint of on-press developability, the hydrophilic group is preferably a group represented by the formula Z described below.

Furthermore, among the hydrophilic groups possessed by the thermoplastic resin, a group represented by the following formula PO is preferable.

In the formula PO, L ^P each independently represents an alkylene group, R ^P represents a hydrogen atom or an alkyl group, and n represents an integer from 1 to 100.
In the formula PO, L ^P is each independently preferably an ethylene group, a 1-methylethylene group, or a 2-methylethylene group, and more preferably an ethylene group.
In the formula PO, R ^P is preferably a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R P is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. It is more preferably an alkyl group, and particularly preferably a hydrogen atom or a methyl group.
In the formula PO, n is preferably an integer of 1 to 10, more preferably an integer of 1 to 4.

The content of the structural unit having a hydrophilic group is preferably 5% by mass to 60% by mass, more preferably 10% by mass to 30% by mass, based on the total mass of the resin.

The resin contained in the thermoplastic polymer particles may further contain other structural units.
Other structural units may contain structural units other than the above-mentioned structural units without particular limitation, and include, for example, structural units formed from acrylamide compounds, vinyl ether compounds, and the like.

The content of other structural units in the thermoplastic resin is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 30% by mass, based on the total mass of the thermoplastic resin.

Examples of the heat-reactive polymer particles include polymer particles having a heat-reactive group.
The heat-reactive resin particles form hydrophobized regions by crosslinking due to thermal reaction and functional group change at that time.

The thermally reactive group in the polymer particle having a thermally reactive group may be any functional group that performs any reaction as long as a chemical bond is formed, but it is preferably a polymerizable group, and examples thereof include: Ethylenically unsaturated groups that undergo radical polymerization reactions (e.g., acryloyl group, methacryloyl group, vinyl group, allyl group, etc.), cationically polymerizable groups (e.g., vinyl group, vinyloxy group, epoxy group, oxetanyl group, etc.), addition reaction isocyanato groups or blocks thereof, epoxy groups, vinyloxy groups, functional groups having active hydrogen atoms that are reaction partners of these groups (e.g., amino groups, hydroxy groups, carboxy groups, etc.), carboxy groups that perform condensation reactions, and reaction Preferred examples include a hydroxy group or amino group as a partner, an acid anhydride that performs a ring-opening addition reaction, and an amino group or hydroxy group as a reaction partner.
The resin having a heat-reactive group may be an addition polymerization type resin, a polyaddition type resin, a polycondensation type resin, or a thermoplastic resin.

Preferably, the microcapsules are those that encapsulate at least a portion of the constituent components of the image recording layer (preferably a hydrophobic compound), as described in, for example, JP-A No. 2001-277740 and JP-A No. 2001-277742. . In an image recording layer containing microcapsules as polymer particles, hydrophobic components (i.e., hydrophobic compounds) among the constituent components of the image recording layer are encapsulated in microcapsules, and hydrophilic components (i.e., hydrophilic compounds) are encapsulated in microcapsules. A configuration in which it is contained outside the capsule is a preferred embodiment.
In order to obtain microcapsules containing the constituent components of the image recording layer, known synthesis methods can be applied.

The microgel (crosslinked polymer particles) can contain a part of the constituent components of the image recording layer on at least one of its surface or inside. In particular, a reactive microgel having a polymerizable group on its surface is preferable from the viewpoint of the sensitivity of the lithographic printing plate precursor and the printing durability of the resulting lithographic printing plate.
In order to obtain a microgel containing the constituent components of the image recording layer, known synthesis methods can be applied.

The polymer particles are adducts of isophorone diisocyanate and polyhydric phenol compounds having two or more hydroxyl groups in the molecule, from the viewpoint of printing durability, stain resistance, and storage stability of the resulting lithographic printing plate. Polyaddition type polymer particles obtained by the reaction of a polyvalent isocyanate compound and a compound having active hydrogen are preferred.
As the polyhydric phenol compound, a compound having a plurality of benzene rings having a phenolic hydroxy group is preferable.
The compound having active hydrogen is preferably a polyol compound or a polyamine compound, more preferably a polyol compound, and still more preferably at least one compound selected from the group consisting of propylene glycol, glycerin, and trimethylolpropane.
Furthermore, water may be used as the compound having active hydrogen. When water is used, the amine produced by the reaction between the isocyanate group of the polyvalent isocyanate compound and water forms a urea bond, and particles can be formed.
As for resin particles obtained by the reaction of a polyhydric isocyanate compound which is an adduct of a polyhydric phenol compound having two or more hydroxyl groups in the molecule and isophorone diisocyanate, and a compound having active hydrogen, International Publication No. Preferred examples include microgels obtained by the preparation method described in paragraphs 0230 to 0234 of No. 2018/043259.

Furthermore, from the viewpoint of printing durability and solvent resistance of the resulting lithographic printing plate, the polymer particles have a hydrophobic main chain, and i) have a nitrile group directly bonded to the hydrophobic main chain. Addition polymer particles containing both a structural unit and ii) a structural unit having a pendant group containing a hydrophilic polyalkylene oxide segment are preferred.
Specifically, as such addition polymer particles, particles described in paragraph 0156 of JP-A No. 2019-64269 are preferable.

(Group represented by formula Z)
The polymer particles in the present disclosure preferably have a group represented by the following formula Z as a hydrophilic group.
In particular, the polymer particles in the present disclosure are preferably addition polymer particles having a hydrophilic group containing a group represented by the following formula Z.
Formula Z: *-Q-W-Y
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, and Y represents a monovalent group having a hydrophilic structure or It represents a monovalent group having a hydrophobic structure, either W or Y has a hydrophilic structure, and * represents a bonding site with another structure.
Moreover, it is preferable that any of the hydrophilic structures included in formula Z include a polyalkylene oxide structure.

Q in the above formula Z is preferably a divalent linking group having 1 to 20 carbon atoms, more preferably a divalent linking group having 1 to 10 carbon atoms.
Further, Q in the above formula Z is preferably an alkylene group, an arylene group, an ester bond, an amide bond, or a group combining 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 in W in the above formula Z is preferably a group containing a polyalkylene oxide structure, and -CH ₂ CH A group to which ₂ NR ^W - is bonded is preferable. Note that R ^W represents a hydrogen atom or an alkyl group, and the same applies to R ^W below.
The divalent group having a hydrophobic structure in W in the above formula Z is -R ^WA -, -OR ^WA -O-, -R ^W NR ^WA -NR ^W -, -OC(=O)- R ^WA -O- or -OC(=O)-R ^WA -O- is preferable. Note that R ^WA each independently represents a straight chain, 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, and a C 6 to 120 arylene group. Represents an alkarylene group (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 in Y of the above formula Z is -OH, -C(=O)OH, a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group, or a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group. It is preferably a group in which -CH ₂ CH ₂ N(R ^W )- is bonded to the other end of the polyalkyleneoxy group. Among these, the monovalent group having a hydrophilic structure is preferably a group containing a polyalkylene oxide structure, such as a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group, or a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group. A group in which -CH ₂ CH ₂ N(R ^W )- is bonded to the other end of a polyalkyleneoxy group is preferred.
The monovalent group having a hydrophobic structure in Y of the above formula Z is a straight chain, 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, It can be 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 preferable. R ^WB represents an alkyl group having 6 to 20 carbon atoms.

In the polymer particles having a group represented by the above formula Z, from the viewpoint of printing durability, ink receptivity, and on-press developability, it is more preferable that W is a divalent group having a hydrophilic structure, It is more preferable that Q is a phenylene group, ester bond, or amide bond, W is a polyalkyleneoxy group, and Y is a polyalkyleneoxy group whose terminal is a hydrogen atom or an alkyl group.
Note that the group represented by formula Z may function as a dispersing group that improves the dispersibility of the polymer particles.

The polymer particles in the present disclosure preferably have a polymerizable group (preferably an ethylenically unsaturated group) from the viewpoint of printing durability and on-press developability, and in particular, it is preferable that the polymer particles have a polymerizable group on the surface. More preferred. By using polymer particles having a polymerizable group, plate skipping (preferably UV plate skipping) can be easily suppressed, and printing durability (preferably UV printing durability) can also be improved.

The polymer particles in the present disclosure are preferably resin particles having a hydrophilic group and a polymerizable group from the viewpoint of printing durability.
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 above-mentioned 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 preferable, such as 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.
Moreover, it is preferable that the resin constituting the polymer particles having a polymerizable group has a structural unit having a polymerizable group.
Note that a polymerizable group may be introduced onto the surface of the polymer particle by a polymer reaction.

In addition, the polymer particles preferably contain a polyaddition resin having a urea bond from the viewpoints of printing durability, ink receptivity, on-press developability, and development scum suppression during on-press development, and the following formula: It is more preferable to include a polyaddition resin having a structure obtained by reacting at least an isocyanate compound represented by (Iso) with water, and a polyaddition resin having a structure obtained by at least reacting an isocyanate compound represented by the following formula (Iso) with water. It is particularly preferable to include a polyaddition type resin having a structure obtained by making the polyethylene oxide structure and a polypropylene oxide structure as the polyoxyalkylene structure. Further, the particles containing the polyaddition resin having a urea bond are preferably microgels.

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

An example of the reaction between the isocyanate compound represented by the above formula (Iso) and water includes the reaction shown below. In addition, the following example is an example using n=0, 4,4-isomer.
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, an amino group is generated, and the resulting amino group and the isocyanate group are react, a urea bond is generated, and a dimer is formed. Further, the following reaction is repeated to form a polyaddition resin having a urea bond.

In addition, in the following reaction, by adding a compound (compound having active hydrogen) that is reactive with an isocyanate group such as an alcohol compound or an amine compound, the structure of the alcohol compound or amine compound can be modified by polyaddition having a urea bond. It can also be introduced into the mold resin.
Preferred examples of the above-mentioned compound having active hydrogen include the compounds having active hydrogen described above.

Further, the polyaddition resin having a urea bond preferably has an ethylenically unsaturated group, and more preferably has a group represented by the following formula (PETA).

In the formula (PETA), the wavy line portion represents the bonding position with another structure.

(Synthesis of polymer particles)
The method for synthesizing the polymer particles is not particularly limited, and any method that can synthesize particles using the various resins described above may be used. Examples of methods for synthesizing polymer particles include known polymer particle synthesis methods such as emulsion polymerization, suspension polymerization, dispersion polymerization, soap-free polymerization, and microemulsion polymerization.
In addition, known microcapsule synthesis methods, microgel (crosslinked resin particles) synthesis methods, etc. may be used to synthesize the polymer particles.

(Average particle size of particles)
The average particle diameter of the 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. Good resolution and stability over time can be obtained within this range.
The average particle size of the particles shall be measured by a light scattering method, or by taking an electron micrograph of the particles, measuring the particle size of a total of 5,000 particles on the photograph, and calculating the average value. do. For non-spherical particles, the equivalent circle diameter of the particle in the photograph is used.
Note that the average particle size of particles in the present disclosure is a volume average particle size unless otherwise specified.

Only one type of particles (preferably polymer particles) may be used, or two or more types may be used in combination.

The content of particles (preferably polymer particles) is preferably 5% to 90% by mass, and 10% to 90% by mass, based on the total mass of the image recording layer, from the viewpoint of developability and printing durability. The content is more preferably 20% by mass to 90% by mass, and particularly preferably 50% by mass to 90% by mass.

[Other ingredients]
The image recording layer in the present disclosure may contain components other than those described above.
Other components include known binder polymers other than the specific polymer, coloring agents, chain transfer agents, low-molecular hydrophilic compounds, fat-sensitizing agents, and other additives.

[Coloring agent]
The image recording layer may contain a color former.
The color former is preferably an acid color former. Moreover, it is preferable that a leuco compound is included as a coloring agent.
The "color former" used in the present disclosure means a compound that has the property of changing the color of the image recording layer by developing or decoloring when stimulated by light or acid, and the "acid color former" It refers to a compound that has the property of changing the color of an image recording layer by developing or decoloring it when heated while accepting an electron-accepting compound (for example, protons such as an acid).
Acid color formers are particularly suitable for colorless color formers that have partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and whose partial skeletons quickly ring-open or cleave when they come into contact with electron-accepting compounds. Compounds are preferred.

Examples of acid color formers include compounds described in paragraphs 0184 to 0191 of JP-A No. 2019-18412.

Among these, the coloring agent 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 coloring properties.
The hue of the color former after color development preferably has maximum absorption in the range of 450 nm to 650 nm from the viewpoint of visibility. The color of the coloring agent after coloring is preferably red, purple, blue, or black-green.

Further, as the coloring agent (preferably acid coloring agent), it is preferable to use a leuco dye from the viewpoint of improving the visibility of the exposed area.
Here, the leuco dye is not particularly limited as long as it has a leuco structure, but preferably has a spiro structure, and more preferably has a spirolactone ring structure.
Further, the leuco dye is preferably a leuco dye having a phthalide structure or a fluoran structure from the viewpoint of improving the visibility of the exposed area.

Further, as a coloring agent (preferably an acid coloring agent), from the viewpoint of improving the visibility of the exposed area, the following formulas (Le-1) to (Le-3), which are leuco dyes having the above-mentioned phthalide structure or fluoran structure, are used. ), 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, and X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group. 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 Y ₁ is When Y 2 is N, X ₁ is absent; when Y ₂ is N, X ₄ is absent; Ra ₁ represents a hydrogen atom, an alkyl group, or an alkoxy group; Rb ₁ to Rb ₄ each independently represents a hydrogen atom, an alkyl group, or an aryl group.

From the viewpoint of color development and visibility of exposed areas, the electron-donating groups in ERG of formulas (Le-1) to (Le-3) include amino groups, alkylamino groups, arylamino groups, and dialkylamino groups. group, monoalkylmonoarylamino group, diarylamino group, alkoxy group, aryloxy group, or alkyl group, preferably amino group, alkylamino group, arylamino group, dialkylamino group, monoalkylmonoarylamino group, It is more preferably a diarylamino group, an alkoxy group, or an aryloxy group, and even more preferably an arylamino group, a monoalkylmonoarylamino group, or a diarylamino group. It is particularly preferable that
In formulas (Le-1) to (Le-3), X ₁ to X ₄ are each independently preferably a hydrogen atom or a chlorine atom, from the viewpoint of improving the visibility of the exposed area; It is more preferable that
In formula (Le-2) or formula (Le-3), X ₅ to X ₁₀ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an amino group, Be an alkylamino group, arylamino group, dialkylamino group, monoalkylmonoarylamino group, diarylamino group, hydroxy group, alkoxy group, aryloxy group, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, or cyano group is preferable, a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, or an aryloxy group is more preferable, a hydrogen atom, a halogen atom, an alkyl group, or an aryl group is even more preferable; It is particularly preferable that there be.
It is preferable that at least one of Y ₁ and Y ₂ in formulas (Le-1) to (Le-3) is C, and both Y ₁ and Y ₂ are C, from the viewpoint of improving the visibility of the exposed area. C is more preferable.
Ra ₁ in formula (Le-3) is preferably an alkyl group or an alkoxy group, more preferably an alkoxy group, and particularly preferably a methoxy group from the viewpoint of improving the visibility of the exposed area.
Rb ₁ to Rb ₄ in formula (Le-1) are each independently preferably a hydrogen atom or an alkyl group, more preferably an alkyl group, and a methyl group. It is particularly preferable that

In addition, from the viewpoint of improving the visibility of the exposed area, the leuco dyes having a phthalide structure or fluoran structure have the following formulas (Le-4) to (Le-6). It is more preferable to be a compound represented by any of the following, and even more preferable to be a compound represented by the following formula (Le-5).

In formulas (Le-4) to (Le-6), ERG each independently represents an electron-donating group, and X ₁ to X ₄ each independently represent a hydrogen atom, a halogen atom, or a dialkylanilino group. represents a group, Y ₁ and Y ₂ each independently represent C or N, when Y ₁ is N, X ₁ is absent, and when Y ₂ is N, X ₄ is 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) are respectively represented by formulas (Le-1) to ( It has the same meaning as ERG, X ₁ to X ₄ , Y ₁ , Y ₂ , Ra ₁ and Rb ₁ to Rb ₄ in Le-3), and its preferred embodiments are also the same.

Further, the leuco dye having a phthalide structure or fluoran structure has the following formulas (Le-7) to (Le-9) from the viewpoint of improving the visibility of the exposed area. A compound represented by any of the following is more preferable, and a compound represented by the following formula (Le-8) is particularly preferable.

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, and Y ₁ and Y ₂ each independently, represents C or N, when Y ₁ is N, X ₁ does not exist, when Y ₂ is N, X ₄ does not exist, and Ra ₁ to Ra ₄ each independently represent hydrogen. represents an 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 formulas (Le-7) to (Le-9) are X ₁ to X ₄ , Y 1 and Y ₂ in formulas (Le-1) to (Le- ₃ ) It has the same meaning as Y ₂ and the preferred embodiments are also the same.
Ra ₁ to Ra ₄ in formula (Le-7) or formula (Le-9) are each independently preferably an alkyl group or an alkoxy group from the viewpoint of improving the visibility of the exposed area, and are an alkoxy group. is more preferable, and a methoxy group is particularly preferable.
Rb ₁ to Rb ₄ in formulas (Le-7) to (Le-9) are each independently substituted with a hydrogen atom, an alkyl group, or an alkyl group or an alkoxy group from the viewpoint of improving the visibility of the exposed area. It is preferably an aryl group, more preferably a hydrogen atom or an alkyl group, and particularly preferably a hydrogen atom or a methyl group.
Rc ₁ and Rc ₂ in formula (Le-8) are each independently preferably a phenyl group or an alkylphenyl group, more preferably a phenyl group, from the viewpoint of improving the visibility of the exposed area. .
Further, in formula (Le-8), from the viewpoint of improving the visibility of the exposed area, 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 viewpoint of improving the visibility of the exposed area, Rb ₁ and Rb ₂ are each independently a hydrogen atom, an alkyl group, or an aryl group substituted with an alkyl group or an alkoxy group. It is preferably a hydrogen atom or an alkyl group.

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

In addition, each group such as a monovalent organic group, an alkyl group, an aryl group, a dialkylanilino group, an alkylamino group, and an alkoxy group in formulas (Le-1) to (Le-9) has a substituent. You can leave it there. Examples of substituents include alkyl groups, aryl groups, halogen atoms, amino groups, alkylamino groups, arylamino groups, dialkylamino groups, monoalkylmonoarylamino groups, diarylamino groups, hydroxy groups, alkoxy groups, aryloxy groups, and acyl groups. group, an alkoxycarbonyl group, an aryloxycarbonyl group, a cyano group, and the like. Moreover, these substituents may be further substituted with these substituents.

Specific examples of the leuco dye having a phthalide structure or fluoran structure that are preferably used include the following compounds (S-1 to S-15).

It is also possible to use the product that is used as an acidic colorant, ETAC, RED500, RED520, CVL, S -205, BLACK305, BLACK100, BLACK100, BLACK500, H -7001, GREEN300, NIRBL ACK78, BLUE220, H -3035, BLUE203, ATP, H-1046, H-2114 (manufactured by Fukui Yamada Chemical Co., Ltd.), ORANGE-DCF, Vermilion-DCF, PINK-DCF, RED-DCF, BLMB, CVL, GREEN-DCF , 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, Red-8 (manufactured by Yamamoto Kasei Co., Ltd.), Crystal Violet Lactone (manufactured by Tokyo Kasei Kogyo Co., Ltd.), and the like.
Among these commercial products, ETAC, S-205, BLACK305, BLACK400, BLACK100, BLACK500, H-7001, GREEN300, NIRBLACK78, H-3035, ATP, H-1046, H-2114, GREEN-DCF, Blue-6 3 , GN-169, and crystal violet lactone are preferable because the visible light absorption rate of the formed film is good.

As the leuco dye, the following compounds are also preferably used from the viewpoint of improving the visibility of the exposed area.

The color formers may be used alone or in combination of two or more.

The content of the color former is preferably 0.5% to 10% by weight, more preferably 1% to 5% by weight, based on the total weight of the image recording layer.

The image recording layer may contain components other than those mentioned above.
Components other than those mentioned above include colorants, print-out agents, polymerization inhibitors, higher fatty acid derivatives, plasticizers, inorganic fine particles, and low-molecular hydrophilic substances described in paragraphs 0181 to 0190 of JP-A No. 2009-255434. Examples include compounds.
Further, as components other than those mentioned above, hydrophobization precursors (fine particles that can convert the image recording layer into hydrophobicity when heat is applied) described in paragraphs 0191 to 0217 of JP-A-2012-187907, Also included are low-molecular hydrophilic compounds, fat-sensitizing agents (for example, phosphonium compounds, nitrogen-containing low-molecular compounds, ammonium group-containing polymers), and chain transfer agents.

[Formation of image recording layer]
The image recording layer in the lithographic printing plate precursor according to the present disclosure can be prepared by dispersing or dissolving the above-mentioned necessary components in a known solvent, for example, as described in paragraphs 0142 to 0143 of JP-A No. 2008-195018. It can be formed by preparing a coating liquid, applying the coating liquid onto a support by a known method such as bar coater coating, and drying.

As the solvent used in the coating liquid, known solvents can be used. Specifically, for example, 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-dimethyl Examples include formamide, dimethyl sulfoxide, γ-butyrolactone, methyl lactate, and ethyl lactate.
The solvents may be used alone or in combination of two or more.
The solid content concentration in the coating liquid is preferably 1% by mass to 50% by mass.

The coating amount (solid content) of the image recording layer after coating and drying varies depending on the application, but from the viewpoint of obtaining good sensitivity and good film properties of the image recording layer, it is 0.3 g/m ^{2 to 3.0 g/m 2} to 3.0 g/m 2 . ^m2 is preferred.
Further, the thickness of the image recording layer in the lithographic printing plate precursor according to the present disclosure is preferably 0.1 μm to 3.0 μm, more preferably 0.3 μm to 2.0 μm.

<Outermost layer>
The lithographic printing plate precursor according to the present disclosure has an outermost layer (also referred to as a protective layer or an overcoat layer) containing a color-changing compound on the image recording layer.

[Color-changing compound]
The outermost layer contains a color-changing compound from the viewpoint of increasing the visibility of the exposed area.

In order to improve the visibility of exposed areas, ^the lithographic printing plate precursor according to the present disclosure has a brightness change ΔL before and after exposure of 2.2. It is preferable that it is 0 or more.
The lightness change ΔL is more preferably 3.0 or more, even more preferably 5.0 or more, particularly preferably 8.0 or more, and most preferably 10.0 or more.
The upper limit of the brightness change ΔL is, for example, 20.0.
In addition, particularly when the outermost layer includes a color-changing compound, it is preferable that the lightness change ΔL satisfies the above-mentioned preferable numerical range.

The lightness change ΔL is measured by the following method.
The lithographic printing plate precursor was processed using a Luxel PLATESETTER T-9800 manufactured by Fujifilm Graphic Systems Co., Ltd. equipped with an infrared semiconductor laser with a wavelength of 830 nm at an output of 99.5%, an outer drum rotation speed of 220 rpm, and a resolution of 2,400 dpi (dots per inch). 1 inch = 25.4 mm) (energy density: 110 mJ/cm ² ). Exposure is performed in an environment of 25° C. and 50% RH.
The change in brightness of the lithographic printing plate precursor before and after exposure is measured.
For the measurement, a spectrophotometer eXact manufactured by X-Rite is used. Using the L ^* value (lightness) of the L ^* a ^* b ^* color system, the absolute value of the difference between the L ^* value of the image recording layer after exposure and the L ^* value of the image recording layer before exposure is calculated as the lightness change ΔL. shall be.

In the present disclosure, a "color-changing compound" refers to a compound whose absorption in the visible light region (wavelength: 400 nm or more and less than 750 nm) changes due to infrared exposure. That is, in the present disclosure, "discoloration" refers to a change in absorption in the visible light region (wavelength: 400 nm or more and less than 750 nm) due to infrared exposure.
Specifically, the color-changing compound in the present disclosure includes (1) a compound whose absorption in the visible light region increases due to infrared exposure compared to before the infrared exposure, and (2) a compound whose absorption in the visible light region increases due to infrared exposure. and (3) a compound that ceases to have absorption in the visible light region due to infrared exposure.
Note that infrared rays in the present disclosure are light rays with a wavelength of 750 nm to 1 mm, preferably light rays with a wavelength of 750 nm to 1,400 nm.

The color-changing compound preferably includes a compound that develops color due to infrared exposure.
Further, the color-changing compound preferably includes a decomposable compound that decomposes due to infrared exposure, and in particular, a decomposable compound that decomposes due to heat, electron transfer, or both due to infrared exposure. is preferred.
More specifically, the color-changing compound in the present disclosure decomposes upon infrared exposure (more preferably decomposes due to heat, electron transfer, or both upon infrared exposure), and prior to infrared exposure It is preferable that the compound exhibits increased absorption in the visible light region, or has absorption at a shorter wavelength, so that it has absorption in the visible light region.
Here, "decomposes by electron transfer" means that the electrons excited from the HOMO (highest occupied orbital) of the color-changing compound to the LUMO (lowest unoccupied orbital) by infrared exposure are This means that there is an intramolecular electron transfer to a nearby group), and decomposition occurs accordingly.

Hereinafter, a decomposable compound, which is an example of a color-changing compound, will be explained.
The decomposable compound may be one that absorbs and decomposes at least a portion of light in the infrared wavelength range (750 nm to 1 mm wavelength range, preferably 750 nm to 1,400 nm wavelength range); A compound having maximum absorption in a wavelength range of 400 nm is preferable.
More specifically, the decomposable compound is preferably a compound that decomposes due to infrared exposure and produces a compound having a maximum absorption wavelength in a wavelength range of 500 nm to 600 nm.

The decomposable compound is preferably a cyanine dye having a group that decomposes upon exposure to infrared rays (specifically, R ¹ in the following formulas 1-1 to 1-7), from the viewpoint of increasing the visibility of the exposed area. preferable.
As the decomposable compound, a compound represented by the following formula 1-1 is more preferable from the viewpoint of improving the visibility of the exposed area.

In formula 1-1, R ¹ represents a group represented by any of the following formulas 2 to 4, and R ¹¹ to R ¹⁸ each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -SR ^c or -NR ^d R ^e is represented, R ^a to R ^e each independently represents a hydrocarbon group, and A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ are connected to form a monocyclic or A polycyclic ring may be formed, A ₁ and A ₂ each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, However, the sum of n ₁₁ and n ₁₂ is 2 or more, n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, and R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za represents a counter ion that neutralizes the charge.

In formulas 2 to 4, R ²⁰ , R ³⁰ , R ⁴¹ and R ⁴² each independently represent an alkyl group or an aryl group, Zb represents a counter ion that neutralizes the charge, and the wavy line represents the above formula 1- represents the bonding site with the group represented by L in 1.

When the compound represented by formula 1-1 is exposed to infrared rays, the R ¹ -L bond is cleaved, L becomes =O, =S, or =NR ¹⁰ , and the compound changes color.

In formula 1-1, R ¹ represents a group represented by any one of formulas 2 to 4 above.
The group represented by Formula 2, the group represented by Formula 3, and the group represented by Formula 4 will be explained below.

In formula 2, R ²⁰ represents an alkyl group or an aryl group, and the wavy line portion represents a bonding site with the group represented by L in formula 1-1.
The alkyl group represented by R ²⁰ is preferably an alkyl group having 1 to 30 carbon atoms, more preferably an alkyl group having 1 to 15 carbon atoms, and still more preferably an alkyl group having 1 to 10 carbon atoms.
The alkyl group may be linear, branched, or have a ring structure.
The aryl group represented by R ²⁰ is preferably an aryl group having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, and even more preferably 6 to 12 carbon atoms.
From the viewpoint of color development, R ²⁰ is preferably an alkyl group.

In addition, from the viewpoint of decomposability and color development, the alkyl group represented by R ²⁰ is preferably a secondary alkyl group or a tertiary alkyl group, and a tertiary alkyl group is preferable. preferable.
Furthermore, from the viewpoint of decomposability and color development, the alkyl group represented by R ²⁰ is preferably an alkyl group having 1 to 8 carbon atoms, and preferably a branched alkyl group having 3 to 10 carbon atoms. More preferably, it is a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.
Here, the alkyl group represented by R ²⁰ may be a substituted alkyl group substituted with a halogen atom (eg, chloro group) or the like.

Specific examples of the group represented by the above formula 2 are listed below, but the present disclosure is not limited thereto. In the following structural formula, ● represents a bonding site with the group represented by L in Formula 1-1.

In formula 3, R ³⁰ represents an alkyl group or an aryl group, and the wavy line portion represents a bonding site with the group represented by L in formula 1-1.
The alkyl group and aryl group represented by R ³⁰ are the same as the alkyl group and aryl group represented by R ²⁰ in Formula 2, and preferred embodiments are also the same.

From the viewpoint of decomposability and color development, the alkyl group represented by R ³⁰ is preferably a secondary alkyl group or a tertiary alkyl group, and more preferably a tertiary alkyl group.
In addition, from the viewpoint of decomposability and color development, the alkyl group represented by R ³⁰ is preferably an alkyl group having 1 to 8 carbon atoms, and a branched alkyl group having 3 to 10 carbon atoms. More preferably, it is a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.
Furthermore, from the viewpoint of decomposability and color development, the alkyl group represented by R ³⁰ is preferably a substituted alkyl group, more preferably a fluoro-substituted alkyl group, and more preferably a perfluoroalkyl group. is more preferred, and trifluoromethyl group is particularly preferred.

From the viewpoint of decomposability and color development, the aryl group represented by R ³⁰ is preferably a substituted aryl group, and examples of the substituent include an alkyl group (preferably an alkyl group having 1 to 4 carbon atoms), an alkoxy groups (preferably alkoxy groups having 1 to 4 carbon atoms), and the like.

Specific examples of the group represented by the above formula 3 are listed below, but the present disclosure is not limited thereto. In the following structural formula, ● represents a bonding site with the group represented by L in Formula 1-1.

In formula 4, R ⁴¹ and R ⁴² each independently represent an alkyl group or an aryl group, Zb represents a counter ion that neutralizes the charge, and the wavy line portion represents the group represented by L in formula 1-1. represents the binding site with.
The alkyl group and aryl group represented by R ⁴¹ or R ⁴² are the same as the alkyl group and aryl group represented by R ²⁰ in Formula 2, and preferred embodiments are also the same.
R ⁴¹ is preferably an alkyl group from the viewpoints of decomposability and color development.
R ⁴² is preferably an alkyl group from the viewpoints of decomposability and color development.

From the viewpoint of decomposability and color development, the alkyl group represented by R ⁴¹ is preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. , methyl group is particularly preferred.
From the viewpoints of decomposability and color development, the alkyl group represented by R ⁴² is preferably a secondary alkyl group or a tertiary alkyl group, and more preferably a tertiary alkyl group.
In addition, from the viewpoint of decomposability and color development, the alkyl group represented by R ⁴² is preferably an alkyl group having 1 to 8 carbon atoms, and a branched alkyl group having 3 to 10 carbon atoms. More preferably, it is a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a tert-butyl group.

Zb in Formula 4 may be a counter ion for neutralizing charges, and the compound as a whole may be included in Za in Formula 1-1.
Zb 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 tetrafluoroborate ion.

Specific examples of the group represented by the above formula 4 are listed below, but the present disclosure is not limited thereto. In the following structural formula, ● represents a bonding site with the group represented by L in Formula 1-1.

In formula 1-1, L is preferably an oxygen atom or -NR ¹⁰ -, and particularly preferably an oxygen atom.
Further, R ¹⁰ in -NR ¹⁰ - is preferably an alkyl group. The alkyl group represented by R ¹⁰ is preferably an alkyl group having 1 to 10 carbon atoms. Further, the alkyl group represented by R ¹⁰ may be linear, branched, or have a ring structure.
Among the alkyl groups, a methyl group or a cyclohexyl group is preferred.
When R ¹⁰ in -NR ¹⁰ - is an aryl group, an aryl group having 6 to 30 carbon atoms is preferred, an aryl group having 6 to 20 carbon atoms is more preferred, and an aryl group having 6 to 12 carbon atoms is even more preferred. Moreover, these aryl groups may have a substituent.

In formula 1-1, R ¹¹ to R ¹⁸ are preferably each independently a hydrogen atom, -R ^a , -OR ^b , -SR ^c , or -NR ^d R ^e .
The hydrocarbon group represented by R ^a to R ^e is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably a hydrocarbon group having 1 to 15 carbon atoms, and even more preferably a hydrocarbon group having 1 to 10 carbon atoms. preferable.
The hydrocarbon group may be linear, branched, or have a ring structure.
As the hydrocarbon group, an alkyl group is particularly preferable.

The alkyl group 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.
Specifically, for example, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, hexadecyl group, octadecyl group. group, eicosyl group, isopropyl group, isobutyl group, s-butyl group, tert-butyl group, isopentyl group, neopentyl group, 1-methylbutyl group, isohexyl group, 2-ethylhexyl group, 2-methylhexyl group, cyclohexyl group, cyclopentyl group and 2-norbornyl group.
Among the alkyl groups, methyl, ethyl, propyl or butyl groups are preferred.

The above alkyl group may have a substituent.
Examples of substituents include alkoxy groups, aryloxy groups, amino groups, alkylthio groups, arylthio groups, halogen atoms, carboxy groups, carboxylate groups, sulfo groups, sulfonate groups, alkyloxycarbonyl groups, aryloxycarbonyl groups, and Examples include groups that combine these.

R ¹¹ to R ¹⁴ in formula 1-1 are each independently preferably a hydrogen atom or -R ^a (i.e., a hydrocarbon group), more preferably a hydrogen atom or an alkyl group, and the following A hydrogen atom is more preferable, except in the following cases.
Among these, R ¹¹ and R ¹³ bonded to the carbon atom bonded to the carbon atom to which L is bonded are preferably an alkyl group, and it is more preferable that the two are linked to form a ring. The ring formed above may be a monocyclic ring or a polycyclic ring. Specific examples of the ring formed include monocycles such as a cyclopentene ring, cyclopentadiene ring, cyclohexene ring, and cyclohexadiene ring, and polycycles such as an indene ring and an indole ring.
Further, R ¹² bonded to the carbon atom to which A ₁ ⁺ is bonded is preferably bonded to R ¹⁵ or R ¹⁶ (preferably R ¹⁶ ) to form a ring, and R 12 bonded to the carbon atom to which A ₂ is bonded. ¹⁴ is preferably linked to R ¹⁷ or R ¹⁸ (preferably R ¹⁸ ) to form a ring.

In formula 1-1, n ₁₃ is preferably 1, and R ¹⁶ is preferably -R ^a (ie, a hydrocarbon group).
Furthermore, R ¹⁶ is preferably linked to R ¹² bonded to the carbon atom to which A ₁ ⁺ is bonded to form a ring. The ring formed is preferably an indolium ring, pyrylium ring, thiopyrylium ring, benzoxazoline ring, or benzimidazoline ring, and from the viewpoint of improving the visibility of the exposed area, an indolium ring is more preferable. These rings may further have a substituent.
In formula 1-1, n ₁₄ is preferably 1, and R ¹⁸ is preferably -R ^a (ie, a hydrocarbon group).
Furthermore, R ¹⁸ is preferably linked to R ¹⁴ bonded to the carbon atom to which A ₂ is bonded to form a ring. The ring formed is preferably an indole ring, pyran ring, thiopyran ring, benzoxazole ring, or benzimidazole ring, and from the viewpoint of improving the visibility of the exposed area, an indole ring is more preferable. These rings may further have a substituent.
R ¹⁶ and R ¹⁸ in Formula 1-1 are preferably the same group, and when each forms a ring, it is preferable that they form a ring with the same structure except for A ₁ ⁺ and A ₂ .

R ¹⁵ and R ¹⁷ in formula 1-1 are preferably the same group. Furthermore, R ¹⁵ and R ¹⁷ are preferably -R ^a (ie, a hydrocarbon group), more preferably an alkyl group, and even more preferably a substituted alkyl group.

In the compound represented by Formula 1-1, from the viewpoint of improving water solubility, R ¹⁵ and R ¹⁷ are preferably substituent alkyl groups.
Examples of the substituted alkyl group represented by R ¹⁵ or R ¹⁷ include groups represented by any of the following formulas (a1) to (a4).

In formulas (a1) to (a4), R ^W0 represents an alkylene group having 2 to 6 carbon atoms, W represents a single bond or an oxygen atom, n _W1 represents an integer from 1 to 45, and R ^W1 represents a carbon Represents an alkyl group having 1 to 12 carbon atoms or -C(=O)-R ^W5 , R ^W5 represents an alkyl group having 1 to 12 carbon atoms, and R ^W2 to R ^W4 each independently represent a single bond or a carbon number 1 ~12 alkylene groups, and M represents a hydrogen atom, a sodium atom, a potassium atom, or an onium group.

In formula (a1), specific examples of the alkylene group represented by R ^W0 include ethylene group, n-propylene group, isopropylene group, n-butylene group, isobutylene group, n-pentylene group, isopentylene group, n- Examples include hexyl group, isohexyl group, etc., with ethylene group, n-propylene group, isopropylene group, or n-butylene group being preferred, and n-propylene group being particularly preferred.
n _W1 is preferably from 1 to 10, more preferably from 1 to 5, particularly preferably from 1 to 3.
Specific examples of the alkyl group represented by R ^W1 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group. group, n-hexyl group, n-octyl group, n-dodecyl group, etc., methyl group, ethyl group, n-propyl group, isopropyl group, or n-butyl group, tert-butyl group are preferable, and methyl group , or ethyl group is more preferable, and methyl group is particularly preferable.
The alkyl group represented by R ^W5 is the same as the alkyl group represented by R ^W1 , and its preferred embodiments are also the same as the preferred embodiments of the alkyl group represented by R ^W1 .

Specific examples of the group represented by formula (a1) are shown below, but the present disclosure is not limited thereto. In the following structural formula, Me represents a methyl group, Et represents an ethyl group, and * represents a bonding site.

In formulas (a2) to (a4), specific examples of the alkylene groups represented by R ^W2 to R ^W4 include methylene group, ethylene group, n-propylene group, isopropylene group, n-butylene group, and isobutylene group. , n-pentylene group, isopentylene group, n-hexyl group, isohexyl group, n-octylene group, n-dodecylene group, etc., and ethylene group, n-propylene group, isopropylene group, or n-butylene group Preferably, ethylene group or n-propylene group is particularly preferable.
In formula (a3), two M's may be the same or different.

In formulas (a2) to (a4), the onium group represented by M includes an ammonium group, an iodonium group, a phosphonium group, a sulfonium group, and the like.
CO ₂ M in formula (a2), PO ₃ M ₂ in formula (a2), and SO ₃ M in formula (a4) may all have an anion structure in which M is dissociated. The counter cation of the anionic structure may be A ₁ ⁺ or a cation that can be included in R ¹ -L in Formula 1-1.

Among the groups represented by formulas (a1) to (a4), groups represented by formula (a1), formula (a2), or formula (a4) are preferred.

In formula 1-1, n ₁₁ and n ₁₂ are preferably the same, each is preferably an integer of 1 to 5, more preferably 1 to 3, even more preferably 1 or 2, and particularly preferably 2.

A ₁ and A ₂ in Formula 1-1 each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, preferably a nitrogen atom.
It is preferable that A ₁ and A ₂ in Formula 1-1 are the same atom.

Za in Formula 1-1 represents a counter ion that neutralizes charge.
If R ¹¹ to R ¹⁸ and R ¹ -L are all charge-neutral groups, Za becomes a monovalent counter anion. However, R ¹¹ to R ¹⁸ and R ¹ -L may have an anion structure or a cation structure. For example, when R ¹¹ to R ¹⁸ and R ¹ -L have two or more anion structures, Za can also be a countercation.
Note that if the cyanine dye represented by formula 1-1 has a structure that is charge-neutral throughout the compound except for Za, Za is not necessary.
When Za is a counter anion, examples thereof include sulfonate ion, carboxylate ion, tetrafluoroborate ion, hexafluorophosphate ion, p-toluenesulfonate ion, perchlorate ion, etc., and tetrafluoroborate ion is preferable.
When Za is a counter cation, examples thereof include alkali metal ions, alkaline earth metal ions, ammonium ions, pyridinium ions, sulfonium ions, etc., and sodium ions, potassium ions, ammonium ions, pyridinium ions, or sulfonium ions are preferable, and sodium ions ion, potassium ion, or ammonium ion.

The decomposable compound is more preferably a compound represented by the following formula 1-2 (ie, cyanine dye) from the viewpoint of improving the visibility of the exposed area.

In formula 1-2, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c , or -NR ^d R ^e , R ²³ and R ²⁴ each independently represent a hydrogen atom or -R ^a , and R ^a to R ^e each independently represent a hydrocarbon group. R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²³ and R ²⁴ may be connected to form a monocyclic or polycyclic ring, and L is an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² each independently represent an alkyl group which may have a substituent. , and Za represents a counter ion that neutralizes the charge.

R ¹ in Formula 1-2 has the same meaning as R ¹ in Formula 1-1, and preferred embodiments are also the same.

In formula 1-2, R ¹⁹ to R ²² are preferably each independently a hydrogen atom, a halogen atom, -R ^a , -OR ^b , or -CN.
More specifically, R ¹⁹ and R ²¹ are preferably hydrogen atoms or -R ^a .
Further, R ²⁰ and R ²² are preferably a hydrogen atom, -R ^a , -OR ^b , or -CN.
-R ^a represented by R ¹⁹ to R ²² is preferably an alkyl group or an alkenyl group.
When all of R ¹⁹ to R ²² are -R ^a , it is preferable that R ¹⁹ and R ²⁰ and R ²¹ and R ²² are linked to form a monocyclic ring or a polycyclic ring.
Examples of the ring formed by connecting R ¹⁹ and R ²⁰ or R ²¹ and R ²² include a benzene ring and a naphthalene ring.

In formula 1-2, R ²³ and R ²⁴ are preferably connected to form a monocyclic or polycyclic ring.
The ring formed by connecting R ²³ and R ²⁴ may be monocyclic or polycyclic. Specific examples of the ring formed include monocycles such as a cyclopentene ring, cyclopentadiene ring, cyclohexene ring, and cyclohexadiene ring, and polycycles such as an indene ring.

In formula 1-2, R ^d1 to R ^d4 are preferably unsubstituted alkyl groups. Further, it is preferable that R ^d1 to R ^d4 are all the same group.
Examples of the unsubstituted alkyl group include unsubstituted alkyl groups having 1 to 4 carbon atoms, and among them, a methyl group is preferred.

In formula 1-2, W ¹ and W ² are each independently preferably substituted alkyl groups from the viewpoint of increasing the water solubility of the compound represented by formula 1-2.
Examples of the substituted alkyl group represented by W ¹ and W ² include groups represented by any of formulas (a1) to (a4) in formula 1-1, and preferred embodiments are also the same.
Further, W ¹ and W ² are each independently an alkyl group having a substituent from the viewpoint of on-press developability, and the above-mentioned substituent is -(OCH ₂ CH ₂ )-, a sulfo group, a sulfo group. A group having at least a salt of a carboxy group, a carboxy group, or a salt of a carboxy group is preferable.

Za represents a counter ion that neutralizes the charge within the molecule.
If R ¹⁹ to R ²² , R ²³ to R ²⁴ , R ^d1 to R ^d4 , W ¹ , W ² , and R ¹ -L are all charge-neutral groups, then Za is a monovalent pair. Becomes an anion. However, R ¹⁹ to R ²² , R ²³ to R ²⁴ , R ^d1 to R ^d4 , W ¹ , W ² , and R ¹ -L may have an anion structure or a cation structure, for example, R When ¹⁹ to R ²² , R ²³ to R ²⁴ , R ^d1 to R ^d4 , W ¹ , W ² , and R ¹ -L have two or more anion structures, Za can also serve as a counter cation.
Note that if the compound represented by Formula 1-2 has a charge-neutral structure as a whole except for Za, Za is not necessary.
Examples where Za is a counter anion are the same as Za in Formula 1-1, and preferred embodiments are also the same. Furthermore, examples where Za is a counter cation are the same as Za in Formula 1-1, and preferred embodiments are also the same.

The cyanine dye as the degradable compound is more preferably a compound represented by any one of the following formulas 1-3 to 1-7 from the viewpoint of degradability and color development.
In particular, from the viewpoint of decomposability and color development, compounds represented by any one of formulas 1-3, 1-5, and 1-6 are preferred.

In formulas 1-3 to 1-7, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c , or -NR ^{d Re} ; R ²⁵ and R ²⁶ each independently represent a hydrogen atom, a halogen atom, or -R ^a ; R ^a to R ^e each independently represents a hydrocarbon group, R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²⁵ and R ²⁶ may be connected to form a monocyclic or polycyclic ring, and L is , represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² are each independently, It represents an alkyl group that may have a substituent, and Za represents a counter ion that neutralizes the charge.

R ¹ , R ¹⁹ to R ²² , R ^d1 to R ^d4 , W ¹ , W ² , and L in Formulas 1-3 to 1-7 are R ¹ , R ¹⁹ to R ²² , and R in Formula 1-2. It has the same meaning as ^d1 to R ^d4 , W ¹ , W ² , and L, and its preferred embodiments are also the same.
R ²⁵ and R ²⁶ in Formula 1-7 are each independently preferably a hydrogen atom or an alkyl group, more preferably an alkyl group, and particularly preferably a methyl group.

Specific examples of cyanine dyes as decomposable compounds are listed below, but the present disclosure is not limited thereto.

Further, as the cyanine dye which is a decomposable compound, an infrared absorbing compound described in International Publication No. 2019/219560 can be suitably used.

Further, as the color-changing compound, an acid color former may be used.
As the acid color former, those described as acid color formers in the image recording layer can be used, and preferred embodiments are also the same.

The color-changing compound may be used alone or in combination of two or more components.
As the color-changing compound, the acid color forming agent described above and the acid generator described below may be used in combination.

The content of the color-changing compound in the outermost layer is preferably 0.10% by mass to 50% by mass, more preferably 0.50% by mass to 30% by mass, based on the total mass of the outermost layer, from the viewpoint of color development. , more preferably 1.0% by mass to 20% by mass.

From the viewpoint of color development, the ratio ^{M X /} M ^Y of ^the content M It is preferably 0.2 or more, more preferably 0.3 or more and 3.0 or less.

[Other ingredients]
In addition to the color-changing compound, the outermost layer may contain other components such as a water-soluble polymer, a hydrophobic polymer, a fat-sensitizing agent, an acid generator, an infrared absorber, and an inorganic layered compound.
The other components will be explained below.

[Water-soluble polymer]
The outermost layer preferably contains a water-soluble polymer from the viewpoint of on-press developability.
In the present disclosure, a water-soluble polymer refers to a solution in which 5 g or more of the polymer is dissolved in 100 g of pure water at 125°C, and a solution in which 5 g of the polymer is dissolved in 100 g of pure water at 125°C is cooled to 25°C. refers to polymers that do not precipitate even when
Examples of the water-soluble polymer used in the outermost layer include polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, water-soluble cellulose derivatives, polyethylene glycol, and poly(meth)acrylonitrile.
As the modified polyvinyl alcohol, acid-modified polyvinyl alcohol having a carboxy group or a sulfo group is preferably used. Specifically, modified polyvinyl alcohols described in JP-A-2005-250216 and JP-A-2006-259137 can be mentioned.

Preferred examples of the water-soluble polymer include polyvinyl alcohol. Among these, it is more preferable to use polyvinyl alcohol having a saponification degree of 50% or more as the water-soluble polymer.
The saponification degree is preferably 60% or more, more preferably 70% or more, and even more preferably 85% or more. The upper limit of the degree of saponification is not particularly limited, and may be 100% or less.
The saponification degree is measured according to the method described in JIS K 6726:1994.

Polyvinylpyrrolidone is also preferred as the water-soluble polymer.
As the hydrophilic polymer, it is also preferable to use polyvinyl alcohol and polyvinylpyrrolidone in combination.

One type of water-soluble polymer may be used alone, or two or more types may be used in combination.

When the outermost layer contains a water-soluble polymer, the content of the water-soluble polymer is preferably 1% by mass to 99% by mass, and 3% by mass to 97% by mass, based on the total mass of the outermost layer. is more preferable, and even more preferably 5% by mass to 95% by mass.

[Hydrophobic polymer]
The outermost layer may include a hydrophobic polymer.
A hydrophobic polymer refers to a polymer that dissolves in less than 5 g in 100 g of pure water at 125° C. or does not dissolve in it.
Examples of hydrophobic polymers include polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, poly(meth)acrylic acid alkyl esters (e.g., poly(meth)methyl acrylate, poly(meth)ethyl acrylate, poly(meth)ethyl acrylate, ) butyl acrylate, etc.), and copolymers made by combining raw material monomers of these polymers.
Moreover, it is preferable that the hydrophobic polymer includes polyvinylidene chloride resin.
Furthermore, the hydrophobic polymer preferably includes a styrene-acrylic copolymer.

Furthermore, the hydrophobic polymer is preferably hydrophobic polymer particles from the viewpoint of on-press developability.

One type of hydrophobic polymer may be used alone, or two or more types may be used in combination.

When the outermost layer contains a hydrophobic polymer, the content of the hydrophobic polymer is preferably 1% by mass to 80% by mass, and 5% by mass to 50% by mass, based on the total mass of the outermost layer. is more preferable.

In the present disclosure, the occupied area ratio of the hydrophobic polymer on the surface of the outermost layer is preferably 30 area % or more, more preferably 40 area % or more, and even more preferably 50 area % or more.
The upper limit of the occupied area ratio of the hydrophobic polymer on the surface of the outermost layer is, for example, 90 area %.
The area ratio occupied by the hydrophobic polymer on the surface of the outermost layer can be measured as follows.
Using a PHI nano TOFII time-of-flight secondary ion mass spectrometer (TOF-SIMS) manufactured by ULVAC-PHI, the surface of the outermost layer is irradiated with a Bi ion beam (primary ions) at an acceleration voltage of 30 kV, and the Bi ion beam (primary ions) is emitted from the surface. The hydrophobic region is mapped by measuring the peak of ions (secondary ions) corresponding to the hydrophobic region (that is, the area formed by the hydrophobic polymer), and the area of the hydrophobic region occupied per 1 μm ² is measured. The occupied area ratio of the hydrophobic polymer is determined, and this is defined as the "occupied area ratio on the surface of the outermost layer of the hydrophobic polymer."
For example, when the hydrophobic polymer is an acrylic resin, measurement is performed using the C ₆ H ₁₃ O ^- peak. Furthermore, when the hydrophobic polymer is polyvinylidene chloride, measurement is performed using the C ₂ H ₂ Cl ⁺ peak.
The occupied area ratio can be adjusted by adjusting the amount of hydrophobic polymer added.

[Sensitizing agent]
The outermost layer may contain a fat-sensitizing agent from the viewpoint of ink receptivity.
As the oil sensitizing agent used in the outermost layer, the oil sensitizing agents described in the above image recording layer can be used, and the preferred embodiments are also the same.

The oil sensitizers may be used alone or in combination of two or more.
When the outermost layer contains an oil-sensitizing agent, the content of the oil-sensitizing agent is preferably 0.5% by mass to 30% by mass, and 1% by mass to 20% by mass, based on the total mass of the outermost layer. % is more preferable.

[Acid generator]
The outermost layer preferably contains an acid generator as a color-changing compound.
The term "acid generator" in the present disclosure refers to a compound that generates an acid when exposed to light or heat, and specifically refers to a compound that decomposes and generates an acid when exposed to infrared light.
The generated acid is preferably a strong acid having a pKa of 2 or less, such as sulfonic acid or hydrochloric acid. The acid color former described above can change color due to the acid generated from the acid generator.

Specifically, from the viewpoint of sensitivity and stability, onium salt compounds are preferable as the acid generator.
Specific examples of onium salts suitable as acid generators include compounds described in paragraphs 0121 to 0124 of International Publication No. 2016/047392.
Among these, sulfonates, carboxylates, BPh ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ and the like of triarylsulfonium or diaryliodonium are preferable. Here, Ph represents a phenyl group.

The acid generators may be used alone or in combination of two or more.
When the outermost layer contains an acid generator, the content of the acid generator is preferably 0.5% to 30% by mass, and 1% to 20% by mass, based on the total mass of the outermost layer. It is more preferable that there be.

In the present disclosure, the outermost layer may have the function of suppressing image formation inhibiting reactions by blocking oxygen, as well as the function of preventing scratches on the surface of the image recording layer and preventing ablation during high-intensity laser exposure.

The outermost layer having such characteristics is described, for example, in US Pat. No. 3,458,311 and Japanese Patent Publication No. 55-49729. As the low oxygen permeability polymer used in the outermost layer, either a water-soluble polymer or a water-insoluble polymer can be selected and used as appropriate, and two or more types can be mixed and used as necessary. can. Specific examples include polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, water-soluble cellulose derivatives, poly(meth)acrylonitrile, and the like.
As the modified polyvinyl alcohol, acid-modified polyvinyl alcohol having a carboxy group or a sulfo group is preferably used. Specifically, modified polyvinyl alcohols described in JP-A-2005-250216 and JP-A-2006-259137 can be mentioned.

[Inorganic layered compound]
The outermost layer preferably contains an inorganic layered compound to enhance oxygen barrier properties. Inorganic layered compounds are particles having a thin tabular shape, and include, for example, mica groups such as natural mica and synthetic mica, talc represented by the formula: 3MgO・4SiO・H ₂ O, taeniolite, montmorillonite, saponite, and hectite. Examples include light, zirconium phosphate, and the like.
The preferably used inorganic layered compound is a mica compound. As a mica compound, for example, the formula: A(B,C) _2-5 D ₄ O ₁₀ (OH, F, O) ₂ [wherein A is K, Na, or Ca, and B and C are It is any one of Fe(II), Fe(III), Mn, Al, Mg, and V, and D is Si or Al. Examples include mica groups such as natural mica and synthetic mica represented by ].

In the mica group, natural micas include muscovite, soda mica, phlogopite, biotite, and lepidolite. Examples of synthetic micas include non-swellable micas such as fluorophlogopite KMg ₃ (AlSi ₃ O ₁₀ )F ₂ , potassium tetrasilicon mica KMg _2.5 Si ₄ O ₁₀ )F ₂ , and Na tetrasilylic mica NaMg _{2. 5} (Si ₄ O ₁₀ ) F ₂ , Na or Li taeniolite (Na, Li) Mg ₂ Li (Si ₄ O ₁₀ ) F ₂ , montmorillonite-based Na or Li hectorite (Na, Li) _1/8 Mg _2/ Examples include swellable mica such as ₅ Li _1/8 (Si ₄ O ₁₀ ) F ₂ . Also useful are synthetic smectites.

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 substitution of metal atoms in the lattice is significantly larger than that of other clay minerals. As a result, the lattice layer lacks positive charge, and to compensate for this, cations such as Li ⁺ , Na ⁺ , Ca ²⁺ , Mg ²⁺ are adsorbed between the layers. The cations interposed between these layers are called exchangeable cations and can be exchanged with various cations. In particular, when the cation between the layers is Li ⁺ or Na ⁺ , the ionic radius is small, so the bond between the layered crystal lattices is weak, and the layer swells greatly with water. When shear is applied in this state, it cleaves easily and forms a stable sol in water. Swellable synthetic mica has this tendency and is particularly preferably used.

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

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

The content of the inorganic layered compound is preferably 1% by mass to 60% by mass, more preferably 3% by mass to 50% by mass, based on the total solid content of the outermost layer. Even when multiple types of inorganic layered compounds are used together, it is preferable that the total amount of the inorganic layered compounds is the above content. Within the above range, oxygen barrier properties are improved and good sensitivity can be obtained. Further, it is possible to prevent deterioration in ink receptivity.

In addition to the above-mentioned components, the outermost layer contains known additives such as a plasticizer to impart flexibility, a surfactant to improve coating properties, and inorganic particles to control surface slipperiness. May contain.

The outermost layer is formed by applying and drying by a known method.
The coating amount (solid content) of the outermost 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 0.1 g/m ² to 2.0 g /m ² is particularly preferred.
The thickness of the outermost layer is preferably 0.1 μm to 5.0 μm, more preferably 0.3 μm to 4.0 μm.

The thickness of the outermost layer is preferably 0.1 to 5.0 times, more preferably 0.2 to 3.0 times, the thickness of the image recording layer described below.

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

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

[Preferred embodiment of support]
An example of a preferred embodiment of the 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 aluminum anodic oxide film disposed on the aluminum plate, and the anodic oxide film is located closer to the image recording layer than the aluminum plate. , the anodic oxide film has micropores extending in the depth direction from the surface on the image recording layer side, and the average diameter of the micropores on the surface of the anodic oxide film is more than 10 nm and less than 100 nm.
Note that the value of lightness L ^* in the L ^* a ^* b ^* color system of the surface of the anodic oxide film on the image recording layer side is preferably 70 to 100.

FIG. 1 is a schematic cross-sectional view of one embodiment of an aluminum support 12a.
The aluminum support 12a has a laminated structure in which an aluminum plate 18 and an aluminum anodic oxide film 20a (hereinafter also simply referred to as "anodized film 20a") are laminated in this order. Note that the anodic oxide film 20a in the aluminum support 12a is located closer to the image recording layer than the aluminum plate 18 is. That is, 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 an aluminum plate.

-Anodized film-
Hereinafter, preferred embodiments of the anodic oxide film 20a will be described.
The anodic oxide film 20a is a film produced on the surface of the aluminum plate 18 by anodizing treatment, and this film is substantially perpendicular to the film surface and is made up of extremely fine micropores 22a, each of which is uniformly distributed. has. The micropores 22a extend along the thickness direction (aluminum plate 18 side) from the surface of the anodic oxide film 20a on the image recording layer side (the surface of the anodic oxide film 20a on the side opposite to the aluminum plate 18 side).

The average diameter (average opening diameter) of the micropores 22a in the anodic oxide film 20a on the surface of the anodic oxide film is preferably greater than 10 nm and less than or equal to 100 nm. Among these, from the viewpoint of the balance between printing durability, stain resistance, and image visibility, 15 nm to 60 nm is more preferable, even more preferably 20 nm to 50 nm, and particularly preferably 25 to 40 nm. The diameter inside the pore may be wider or narrower than the surface layer.
If the average diameter exceeds 10 nm, printing durability and image visibility will be even better. Moreover, if the average diameter is 100 nm or less, printing durability is even better.
The average diameter of the micropores 22a is 400 nm x 600 nm in the four images obtained by observing the surface of the anodic oxide film 20a with a field emission scanning electron microscope (FE-SEM) at a magnification of 150,000 times. The diameters of micropores existing in the range of 50 are measured and calculated as the arithmetic mean value.
Note that when the shape of the micropore 22a is not circular, the equivalent circular diameter is used. "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 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.
Note that the above-mentioned depth is a value obtained by taking a photograph (150,000 times) of the cross section of the anodic oxide film 20a, measuring the depths of 25 or more micropores 22a, and averaging the results.

The shape of the micropore 22a is not particularly limited, and in FIG. 2, it has a substantially straight tube shape (substantially cylindrical shape), but it may also have a conical shape whose diameter decreases toward the depth direction (thickness direction). Further, the shape of the bottom of the micropore 22a is not particularly limited, and may be curved (convex) or planar.

The value of lightness L ^* in the L ^* a ^* b ^* color system of the surface of the aluminum support 12a on the image recording layer side (the surface of the anodic oxide film 20a on the image recording layer side) is preferably 70 to 100. . Among these, 75 to 100 is preferable, and 75 to 90 is more preferable, since the balance between printing durability and image visibility is more excellent.
The above-mentioned lightness L ^* is measured using a color difference meter Spectro Eye manufactured by X-Rite Co., Ltd.

In the support (1), the micropores communicate with a large-diameter hole extending from the surface of the anodic oxide film to a depth of 10 nm to 1,000 nm and the bottom of the large-diameter hole, and extend from the communication position to a depth of 10 nm to 1,000 nm. and a small diameter hole extending from 20 nm to 2,000 nm in diameter, the average diameter of the large diameter hole on the surface of the anodic oxide film is 15 nm to 100 nm, and the average diameter of the small diameter hole at the communicating position. is 13 nm or less (hereinafter, the support according to this embodiment is also referred to as "support (2)") is also preferably mentioned.
FIG. 2 is a schematic cross-sectional view of an embodiment of the aluminum support 12a different from that shown in FIG.
In FIG. 2, the aluminum support 12b includes an aluminum plate 18 and an anodized film 20b having micropores 22b composed of large-diameter holes 24 and small-diameter holes 26.
The micropores 22b in the anodic oxide film 20b have a large diameter hole 24 extending from the surface of the anodic oxide film to a depth of 10 nm to 1,000 nm (depth D: see FIG. 2), and a bottom of the large diameter hole 24. The small diameter hole portion 26 communicates with the hole portion 26 and extends further from the communication position to a depth of 20 nm to 2,000 nm.
Note that the details of the large-diameter hole portion 24 and the small-diameter hole portion 26 are as described in paragraphs 0107 to 0114 of JP-A-2019-162855, for example, and this aspect is also applied to the present disclosure.

[Method for manufacturing aluminum support]
As the method for manufacturing the aluminum support according to the present disclosure, for example, a manufacturing method in which the following steps are performed in order is preferable.
・Surface roughening process: Process of roughening the aluminum plate ・Anodizing process: Anodizing the roughened aluminum plate ・Pore widening process: Anode obtained in the anodizing process Step of bringing an aluminum plate having an oxide film into contact with an acid aqueous solution or an alkaline aqueous solution to enlarge the diameter of micropores in the anodic oxide film. The procedure of each step will be explained in detail below.

(Surface roughening treatment process)
The surface roughening treatment step is a step of performing a surface roughening treatment including electrochemical roughening treatment on the surface of the aluminum plate. Although this step is preferably carried out before the anodizing step described below, it may not be carried out if the surface of the aluminum plate already has a preferable surface shape.
The surface roughening treatment for the aluminum plate can be performed by the method described in paragraphs 0086 to 0101 of JP 2019-162855A.

(Anodizing process)
The procedure of the anodizing process is not particularly limited as long as the above-mentioned micropores are obtained, and known methods may be used.
In the anodizing process, an aqueous solution of sulfuric acid, phosphoric acid, oxalic acid, or the like can be used as an electrolytic bath. For example, the concentration of sulfuric acid may be 100 g/L to 300 g/L.
The conditions for the anodizing treatment are appropriately set depending on the electrolytic solution used, but for example, the solution temperature is 5°C to 70°C (preferably 10°C to 60°C), and the current density is 0.5 A/dm ² to 60 A/dm ^{2 .} (preferably 5 A/dm ² - 60 A/dm ² ), voltage 1 V - 100 V (preferably 5 V - 50 V), electrolysis time 1 second - 100 seconds (preferably 5 seconds - 60 seconds), and film amount 0.1 g. /m ² to 5g/m ² (preferably 0.2g/m ² to 3g/m ² ).

(pore wide processing)
The pore widening process is a process (pore size enlarging process) for enlarging the diameters of micropores (pore diameters) present in the anodic oxide film formed by the above-mentioned anodizing process.
The pore widening treatment can be performed by bringing the aluminum plate obtained by the above-described anodizing treatment step into contact with an acid aqueous solution or an alkaline aqueous solution. The contacting method is not particularly limited, and examples include a dipping method and a spraying method.

<Undercoat layer>
The lithographic printing plate precursor according to the present disclosure preferably has an undercoat layer (sometimes referred to as 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 areas, and makes it easier for the image-recording layer to peel off from the support in the unexposed areas. Contributes to improving developability. In addition, in the case of infrared laser exposure, the undercoat layer functions as a heat insulating layer, which prevents the heat generated by exposure from diffusing into the support and reducing sensitivity.

〔polymer〕
Examples of the compound used in the undercoat layer include polymers having adsorbent groups and hydrophilic groups that can be adsorbed onto the surface of the support. In order to improve the adhesion with the image recording layer, a polymer having an adsorbent group and a hydrophilic group, and further having a crosslinkable group is preferable. The compound used in the undercoat layer may be a low molecular weight compound or a polymer. The compounds used in the undercoat layer may be used in combination of two or more, if necessary.

When the compound used in the undercoat layer is a polymer, a copolymer of a monomer having an adsorbent group, a monomer having a hydrophilic group, and a monomer having a crosslinkable group is preferable.
Adsorptive groups that can be adsorbed onto the support surface include phenolic hydroxy group, carboxy group, -PO ₃ H ₂ , -OPO ₃ H ₂ , -CONHSO ₂ -, -SO ₂ NHSO ₂ -, -COCH ₂ COCH ₃ is preferred. As the hydrophilic group, a sulfo group or a salt thereof, or a salt of a carboxy group is preferable. As the crosslinkable group, an acrylic group, a methacryl group, an acrylamide group, a methacrylamide group, an allyl group, etc. are preferable.
The polymer may have a crosslinkable group introduced by salt formation between a polar substituent of the polymer and a substituent having a counter charge to the polar substituent and a compound having an ethylenically unsaturated bond, or the above-mentioned Other monomers, preferably hydrophilic monomers, may be further copolymerized.

Specifically, the silane coupling agent having an ethylenic double bond reactive group capable of addition polymerization described in JP-A No. 10-282679, the ethylenic double bond described in JP-A No. 2-304441, Preferred examples include phosphorus compounds having a heavy bond reactive group. A crosslinkable group (preferably an ethylenically unsaturated bond group) and a support as described in JP-A Nos. 2005-238816, 2005-125749, 2006-239867, and 2006-215263. Low-molecular or high-molecular compounds having functional groups and hydrophilic groups that interact with the surface are also preferably used.
More preferred examples include polymers having an adsorbent group, a hydrophilic group, and a crosslinkable group that can be adsorbed onto the surface of a support described in JP-A-2005-125749 and JP-A-2006-188038.

The content of ethylenically unsaturated bond groups in the polymer used for the undercoat layer is preferably 0.1 mmol to 10.0 mmol, more preferably 0.2 mmol to 5.5 mmol per 1 g of polymer.
The weight average molecular weight (Mw) of the polymer used in the undercoat layer is preferably 5,000 or more, more preferably 10,000 to 300,000.

[Hydrophilic compound]
The undercoat layer preferably contains a hydrophilic compound from the viewpoint of developability.
The hydrophilic compound is not particularly limited, and known hydrophilic compounds used for undercoat layers can be used.
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 hydroxy group.
In addition, as a hydrophilic compound, a compound having an amino group or a functional group having the ability to inhibit polymerization and a group that interacts with the support surface (for example, 1,4-diazabicyclo[2.2.2]octane (DABCO) , 2,3,5,6-tetrahydroxy-p-quinone, chloranil, sulfophthalic acid, ethylenediaminetetraacetic acid (EDTA) or its salt, hydroxyethylethylenediaminetriacetic acid or its salt, dihydroxyethylethylenediaminediacetic acid or its salt, hydroxy (ethyliminodiacetic acid or a salt thereof, etc.) are preferred.

The hydrophilic compound preferably contains a hydroxycarboxylic acid or a salt thereof from the viewpoint of inhibiting scratches and stains.
Further, a hydrophilic compound, preferably a hydroxycarboxylic acid or a salt thereof, is preferably included in the layer on the aluminum support from the viewpoint of preventing scratches and stains. Further, the layer on the aluminum support is preferably a layer on the side where the image recording layer is formed, and is also preferably a layer in contact with the aluminum support.
As a layer on the aluminum support, an undercoat layer or an image recording layer is preferably mentioned as a layer in contact with the aluminum support. Further, a layer other than the layer in contact with the aluminum support, for example, the outermost layer or the 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 inhibiting scratches and stains.
In addition, in the lithographic printing plate precursor according to the present disclosure, an embodiment in which the surface of the aluminum support on the image recording layer side is surface-treated with a composition (for example, an aqueous solution, etc.) containing at least a hydroxycarboxylic acid or a salt thereof is also preferably mentioned. It will be done. In the above embodiment, at least a portion of the treated hydroxycarboxylic acid or its salt is detected while being contained in a layer on the image recording layer side (for example, an image recording layer or an undercoat layer) in contact with the aluminum support. be able to.
By containing a hydroxycarboxylic acid or its salt 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. The contact angle with water on the surface of the image recording layer side measured by the air droplet method can be easily set to 110° or less, and it has excellent scratch and stain inhibiting properties.

Hydroxycarboxylic acid is a general term for organic compounds that have 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 alcoholic acid ( (See Iwanami Science Dictionary, 5th edition, published by Iwanami Shoten Co., Ltd. (1998)).
The hydroxycarboxylic acid or its salt is preferably represented by the following formula (HC).
Formula (HC): R ^HC (OH) _mhc (COOM ^HC ) _nhc
In formula (HC), ^RHC represents an organic group having a valence of mhc+nhc, ^MHC each independently represents a hydrogen atom, an alkali metal, or onium, and mhc and nhc each 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 ^HC includes a 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 value groups derived from aliphatic hydrocarbons, such as alkylene groups, alkanetriyl groups, alkanetetrayl groups, alkanpentyl groups, alkenylene groups, alkenetriyl groups, and alkenetetrayl groups. groups, alkenpentyl groups, alkynylene groups, alkynetriyl groups, alkynetetrayl groups, alkynepentyl groups, mhc+nhc valence groups derived from aromatic hydrocarbons, such as arylene groups, arenetriyl groups, arenes Examples include a tetrayl group and an arenepentyl group. Examples of the substituent include an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an aryl group, and the like. Specific examples of substituents include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, hexadecyl group, Octadecyl group, eicosyl group, isopropyl group, isobutyl group, s-butyl group, t-butyl group, isopentyl group, neopentyl group, 1-methylbutyl group, isohexyl group, 2-ethylhexyl group, 2-methylhexyl group, cyclohexyl group, Cyclopentyl group, 2-norbornyl group, methoxymethyl group, methoxyethoxyethyl group, allyloxymethyl group, phenoxymethyl group, acetyloxymethyl group, benzoyloxymethyl group, benzyl group, phenethyl group, α-methylbenzyl group, 1- Methyl-1-phenylethyl group, p-methylbenzyl group, cinnamyl group, allyl group, 1-propenylmethyl group, 2-butenyl group, 2-methylallyl group, 2-methylpropenylmethyl group, 2-propynyl group, 2- Butynyl group, 3-butynyl group, phenyl group, biphenyl group, naphthyl group, tolyl group, xylyl group, mesityl group, cumenyl group, methoxyphenyl group, ethoxyphenyl group, phenoxyphenyl group, acetoxyphenyl group, benzyloxyphenyl group , methoxycarbonylphenyl group, ethoxycarbonylphenyl group, phenoxycarbonylphenyl group, and the like. Further, the linking group is composed of at least one atom selected from the group consisting of hydrogen atom, carbon atom, oxygen atom, nitrogen atom, sulfur atom, and halogen atom, and the number of atoms is preferably 1 to 50. It is. Specifically, examples include alkylene groups, substituted alkylene groups, arylene groups, substituted arylene groups, etc., and these divalent groups are linked together by any of amide bonds, ether bonds, urethane bonds, urea bonds, and ester bonds. It may have a similar structure.

Examples of the alkali metal represented by ^MHC include lithium, sodium, potassium, etc., with sodium being particularly preferred. Examples of onium include ammonium, phosphonium, and sulfonium, with ammonium being particularly preferred.
Furthermore, from the viewpoint of scratch and stain inhibiting properties, ^MHC is preferably an alkali metal or 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 molecular weight of the hydroxycarboxylic acid or its salt is preferably 600 or less, more preferably 500 or less, particularly preferably 300 or less. Moreover, it is preferable that the said molecular weight is 76 or more.
Specifically, the hydroxycarboxylic acids constituting the hydroxycarboxylic acids or the salts of the hydroxycarboxylic acids 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, cerebronic acid, quinic acid, shikimic acid, monohydroxybenzoic acid derivatives (salicylic acid, creosotic acid (homosalicylic acid, hydroxy(methyl)benzoic acid), vanillic acid, syringic acid, etc.), dihydroxybenzoic acid derivatives (pyrocatechuic acid, resorcylic acid, protocatechuic acid, gentisic acid, orceric acid, etc.), trihydroxy Benzoic acid derivatives (gallic acid, etc.), phenylacetic acid derivatives (mandelic acid, benzylic acid, atrolactic acid, etc.), hydrocinnamic acid derivatives (melilotic acid, fluoretic acid, coumaric acid, umbelic acid, caffeic acid, ferulic acid, sinapic acid, cerebronic acid, carminic acid, etc.).

Among these, as the hydroxycarboxylic acid or the hydroxycarboxylic acid constituting the salt of the hydroxycarboxylic acid, a compound having two or more hydroxy groups is preferable from the viewpoint of inhibiting scratches and stains. Compounds having three or more hydroxy groups are more preferred, compounds having five or more hydroxy groups are even more preferred, and compounds having 5 to 8 hydroxy groups are particularly preferred.
In addition, as those having one carboxy group and two or more hydroxy groups, gluconic acid or shikimic acid is preferable.
Citric acid or malic acid is preferred as having two or more carboxy groups and one hydroxy group.
Tartaric acid is preferred as having two or more carboxy groups and two or more hydroxy groups.
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) is 0.01 mass based on the total mass of the undercoat layer. % to 50% by weight, more preferably 0.1% to 40% by weight, particularly preferably 1.0% to 30% by weight.

In addition to the above-mentioned undercoat layer compounds, the undercoat layer contains a chelating agent,
It may also contain secondary or tertiary amines, polymerization inhibitors, and the like.

The undercoat layer can be formed by dissolving each of the above-mentioned necessary components in a known solvent to prepare a coating solution, applying the coating solution onto a support by a known method, and drying.
The coating amount (solid content) of the undercoat layer is preferably 0.1 mg/m ² to 300 mg/m ² , more preferably 5 mg/m ² to 200 mg/m ² .

The lithographic printing plate precursor according to the present disclosure may have layers other than those described above.
There are no particular restrictions on the other layers, and known layers may be used. For example, a back coat layer may be provided on the opposite side of the support from the image recording layer side, if necessary.

≪Method for preparing lithographic printing plate and lithographic printing method≫
A lithographic printing plate can be produced by imagewise exposing and developing a lithographic printing plate precursor according to the present disclosure.
A method for producing a lithographic printing plate according to the present disclosure includes a step of imagewise exposing a lithographic printing plate precursor according to the present disclosure (hereinafter also referred to as an "exposure step"), and a step of applying printing ink and dampening on a printing machine. It is preferable to include a step of supplying at least one selected from the group consisting of water to remove the image recording layer in the non-image area (hereinafter also referred to as "on-press development step").
The lithographic printing method according to the present disclosure includes a step of imagewise exposing the lithographic printing plate precursor according to the present disclosure (exposure step), and printing by supplying at least one selected from the group consisting of printing ink and dampening water. A process of removing the image recording layer in the non-image area on the press to produce a lithographic printing plate (on-press development process), a process of printing with the obtained lithographic printing plate (hereinafter also referred to as "printing process"), It is preferable to include.

Hereinafter, preferred embodiments 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. Note that the lithographic printing plate precursor according to the present disclosure can also be developed with a developer.
The exposure step and on-press development step in the method for producing a lithographic printing plate will be described below, but the exposure step in the method for producing a lithographic printing plate according to the present disclosure and the exposure step in the lithographic printing method according to the present disclosure are similar. The on-press development step in the lithographic printing plate production method according to the present disclosure and the on-press development step in the lithographic printing method according to the present disclosure are the same steps.

<Exposure process>
The method for producing a lithographic printing plate according to the present disclosure preferably includes an exposure step of imagewise exposing the lithographic printing plate precursor according to the present disclosure to form exposed areas and unexposed areas. The lithographic printing plate precursor according to the present disclosure is preferably imagewise exposed by laser exposure through a transparent original having a line image, halftone image, etc., or by laser light scanning using digital data.
The wavelength of the light source is preferably 750 nm to 1,400 nm. As the light source with a wavelength of 750 nm to 1,400 nm, solid lasers and semiconductor lasers that emit infrared rays are suitable. Regarding 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 . preferable. Furthermore, it is preferable to use a multi-beam laser device in order to shorten the exposure time. The exposure mechanism may be an inner drum type, an outer drum type, a flatbed type, or the like.
Image exposure can be performed by a conventional method using a platesetter or the like. In the case of on-press development, the lithographic printing plate precursor may be mounted on the printing press, and then image exposure may be performed on the printing press.

<On-press development process>
A method for producing a lithographic printing plate according to the present disclosure includes an on-press development step in which an image recording layer in a non-image area is removed by supplying at least one selected from the group consisting of printing ink and fountain solution on a printing press. It is preferable to include.
The on-press development method will be explained below.

[On-press development method]
In the on-press development method, an image-exposed lithographic printing plate precursor is supplied with oil-based ink and an aqueous component on a printing press, and the image recording layer in the non-image area is removed to produce a lithographic printing plate. is preferred.
In other words, after the lithographic printing plate precursor is imagewise exposed, it is loaded into the printing machine as is without any development processing, or alternatively, after the lithographic printing plate precursor is loaded into the printing press, it is imaged and exposed on the printing press, and then When printing is performed by supplying an oil-based ink and a water-based component, in the early stage of printing, the uncured image recording layer is damaged by either or both of the supplied oil-based ink and water-based component in the non-image area. It is removed by dissolving or dispersing, and the hydrophilic surface is exposed in that area. On the other hand, in the exposed area, the image recording layer hardened by exposure forms an oil-based ink receiving area having a lipophilic surface. The ink that is first supplied to the printing plate may be an oil-based ink or a water-based component, but in order to prevent the aqueous component from being contaminated by the components of the image recording layer from which it has been removed, the oil-based ink is supplied first. It is preferable. In this way, the lithographic printing plate precursor is developed on-press on the printing press and used as it is for printing a large number of sheets. As the oil-based ink and the aqueous component, ordinary printing ink and dampening water for lithographic printing are suitably used.

As a 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 of 300 nm to 450 nm, a lithographic printing plate precursor containing a sensitizing dye having an absorption maximum in this wavelength region in the image recording layer is preferably used, and for the light source of 750 nm to 1,400 nm, the above-mentioned ones are preferably used. It will be done. A semiconductor laser is suitable as a light source of 300 nm to 450 nm.

<Printing process>
The planographic printing method according to the present disclosure includes a printing step of supplying printing ink to a planographic printing plate to print a recording medium.
The printing ink is not particularly limited, and various known inks can be used as desired. Moreover, as the printing ink, oil-based ink or ultraviolet curable ink (UV ink) is preferably mentioned.
Further, in the printing process, dampening water may be supplied as necessary.
Moreover, the printing process may be performed continuously with the on-press development process without stopping the printing press.
There are no particular limitations on the recording medium, 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 the lithographic printing method according to the present disclosure, the lithographic printing may be carried out as necessary before exposure, during exposure, or between exposure and development. The entire surface of the original plate may be heated. Such heating accelerates the image-forming reaction in the image recording layer, and can bring about advantages such as improved sensitivity and printing durability, and stabilization of sensitivity. It is preferable that heating before development is performed under mild conditions of 150° C. or less. With the above aspect, problems such as hardening of non-image areas can be prevented. It is preferable to use very strong conditions for heating after development, preferably in the range of 100°C to 500°C. Within the above range, a 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.

EXAMPLES Hereinafter, the present disclosure will be described in detail with reference to Examples, but the present disclosure is not limited thereto. In this example, "%" and "parts" mean "% by mass" and "parts by mass", respectively, unless otherwise specified. In addition, in a polymer compound, unless otherwise specified, the molecular weight is a weight average molecular weight (Mw), and the ratio of constituent repeating units is a mole percentage. Moreover, the weight average molecular weight (Mw) is a value measured as a polystyrene equivalent value by gel permeation chromatography (GPC) method.

[Examples 1 to 10 and Comparative Example 1]
<Preparation of support>
(a) 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. After that, it was washed with water using a spray. The amount of aluminum dissolved on the surface to be electrochemically roughened later was 5 g/m ² .

(b) Desmutting treatment using an acidic aqueous solution (first desmutting treatment)
Next, a desmut treatment was performed using an acidic aqueous solution. The acidic aqueous solution used for the desmut treatment was an aqueous solution containing 150 g/L of sulfuric acid. The liquid temperature was 30°C. The acidic aqueous solution was sprayed onto the aluminum plate to perform a desmut treatment for 3 seconds. After that, a water washing treatment was performed.

(c) Electrochemical surface roughening treatment Next, electrochemical roughening was performed using an alternating current using an electrolytic solution with a hydrochloric acid concentration of 14 g/L, an aluminum ion concentration of 13 g/L, and a sulfuric acid concentration of 3 g/L. processed. The temperature of the electrolyte was 30°C. The aluminum ion concentration was adjusted by adding aluminum chloride.
The waveform of the alternating current is a sine wave with symmetrical positive and negative waveforms, the frequency is 50 Hz, the anode reaction time and cathode reaction time in one cycle of alternating current are 1:1, and the current density is the peak current value of the alternating current waveform. It was 75A/ ^dm2 . Further, the total amount of electricity received by the aluminum plate in the anode reaction was 450 C/dm ² , and the electrolytic treatment was carried out in 4 times at 112.5 C/dm ² with energization intervals of 4 seconds. A carbon electrode was used as the counter electrode to the aluminum plate. After that, a water washing treatment was performed.

(d) Alkaline etching treatment Etching treatment is performed by spraying an aqueous caustic soda solution with a caustic soda concentration of 5% by mass and an aluminum ion concentration of 0.5% by mass onto the aluminum plate after electrochemical surface roughening treatment at a temperature of 45°C. Ta. The amount of aluminum dissolved on the surface subjected to electrochemical roughening treatment was 0.2 g/m ² . After that, a water washing treatment was performed.

(e) Desmutting treatment using an acidic aqueous solution Next, a desmutting treatment was performed using an acidic aqueous solution. Specifically, an acidic aqueous solution was sprayed onto an aluminum plate to perform a desmut treatment for 3 seconds. The acidic aqueous solution used in the desmutting treatment had a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L. The liquid temperature was 30°C.

(f) First-stage anodizing treatment First-stage anodizing treatment (also referred to as first anodic oxidation treatment) was performed using an anodizing treatment apparatus 610 using direct current electrolysis having the structure shown in FIG. Specifically, a first anodic oxidation treatment was performed under the conditions listed in the "First anodization treatment" column shown in Table 1 below to form an anodic oxide film of a predetermined amount.
The anodizing treatment apparatus 610 shown in FIG. 3 will be described below.
In the anodizing treatment apparatus 610 shown in FIG. 3, the aluminum plate 616 is transported as indicated by the arrow in FIG. An aluminum plate 616 is charged to (+) by a power supply electrode 620 in a power supply tank 612 in which an electrolytic solution 618 is stored. Then, the aluminum plate 616 is conveyed upward by rollers 622 in the power feeding tank 612, turned downward by nip rollers 624, and then conveyed toward the electrolytic treatment tank 614 in which electrolyte solution 626 is stored, and is conveyed by rollers 628. It is turned horizontally. Next, the aluminum plate 616 is charged (-) by the electrolytic electrode 630 to form an anodic oxide film on its surface, and the aluminum plate 616 that has left the electrolytic treatment tank 614 is transported to a subsequent process. In the anodizing device 610, the roller 622, the nip roller 624, and the roller 628 constitute a direction changing means, and the aluminum plate 616 is connected to the rollers 622, 624, and 628 in the area between the power supply tank 612 and the electrolytic treatment tank 614. It is conveyed in a mountain shape and an inverted U shape. The power supply electrode 620 and the electrolytic electrode 630 are connected to a DC power source 634.

(g) Pore widening treatment The above anodized aluminum plate was immersed in a caustic soda aqueous solution having a temperature of 40°C, a caustic soda concentration of 5% by mass, and an aluminum ion concentration of 0.5% by mass under the conditions shown in Table 1 below to perform pore widening treatment. Ta. After that, it was washed with water using a spray.

(h) Second anodizing treatment A second-stage anodizing treatment (also referred to as second anodizing treatment) was performed using an anodizing treatment apparatus 610 using direct current electrolysis having the structure shown in FIG. Specifically, a second anodic oxidation treatment was performed under the conditions listed in the "Second Anodization Treatment" column shown in Table 1 below to form an anodic oxide film of a predetermined amount.

A support was produced as described above.
The brightness L ^* in the L ^* a ^* b ^* color system of the surface of the anodic oxide film in the micropores of the obtained support, the average diameter and depth on the oxide film surface of the large-diameter pores in the micropores, and the depth in the micropores. Average diameter (nm) and depth at the communication position of the small-diameter hole, depth (nm) of the large-diameter hole and small-diameter hole, micropore density, and anodization from the bottom of the small-diameter hole to the aluminum plate surface. The thickness of the film (also referred to as film thickness) is summarized in Table 2.
In Table 1, the amount of coating (AD) in the first anodization treatment column and the amount of coating (AD) in the second anodization treatment column represent the amount of coating obtained in each treatment. Note that the electrolytic solution used is an aqueous solution containing the components shown in Table 1.

<Formation of undercoat layer>
An undercoat layer coating solution having the following composition was applied onto the obtained support so that the dry coating amount was 100 mg/m ² to form an undercoat layer.

[Coating liquid for undercoat layer]
・Compound for undercoat layer (U-1 below): 0.1370 parts ・Sodium gluconate: 0.0700 parts ・Surfactant (Emarex 710, Nippon Emulsion Co., Ltd.): 0.00159 parts ・Preservative (Bio Hope L, K.I. Kasei Co., Ltd.): 0.00149 parts/Wed: 3.29000 parts

<Formation of image recording layer>
An image recording layer coating solution containing each component listed in Table 3 is applied on the undercoat layer (however, the image recording layer coating solution contains each component listed in Table 3 and contains 1-methoxy-2-propanol (MFG). ): Methyl ethyl ketone (MEK): Methanol = 4:4:1 (mass ratio) prepared with a mixed solvent so that the solid content was 6% by mass) was coated with a bar and dried in an oven at 120 ° C. for 40 seconds. An image recording layer with a dry coating weight of 1.3 g/m ² was formed.

Details of each component used in Table 3 are as follows.

[Electron-accepting polymerization initiator]
Int-1: Compound with the following structure, LUMO=-3.21eV
Int-2: onium compound, compound with the following structure, LUMO = -7.32eV

[Infrared absorber]
IR-10: Decomposable infrared absorber, compound with the following structure, HOMO=-5.43eV, LUMO=-3.95eV.
IR-2: Decomposable infrared absorber, compound with the following structure, HOMO=-5.25eV, LUMO=-3.77eV.

[Electron-donating polymerization initiator]
TPB: borate compound, sodium tetraphenylborate, HOMO=-5.90eV)

[Specific polymerizable compound]
M-1: The above M-1 (molecular weight 470.56) in the specific example of the specific polymerizable compound
M-2: The above M-2 (molecular weight 452.55) in the specific example of the specific polymerizable compound
M-3: The above M-3 in the specific example of the specific polymerizable compound (molecular weight 2078.15)

[Specific polymer]
P-1: Polyvinyl acetal with the following structure (l, m, and n are listed in Table 3)
P-2: Polyvinyl acetal with the following structure (l, m, n, and o are listed in Table 3)
P-3: Polyvinyl acetal with the following structure (l, m, and n are listed in Table 3)

[Acid color former]
S-3: Compound with the following structure

[Surfactant]
W-1: Compound with the following structure (weight average molecular weight: 13,000)

<Formation of outermost layer>
On the image recording layer, apply the outermost layer coating solution listed in Table 4 (however, the outermost layer coating solution contained each component listed in Table 4 and was prepared with ion-exchanged water so that the solid content was 20% by mass). (1) was bar coated and oven dried at 120° C. for 60 seconds to form an outermost layer with a dry coating weight of 0.7 g/m ² .
Through the above steps, a lithographic printing plate precursor was obtained.

[Occupied area ratio on the surface of the outermost layer of hydrophobic polymer]
Regarding the obtained lithographic printing plate precursor, the occupied area ratio of the hydrophobic polymer on the surface of the outermost layer was measured by the method described above. The results are shown in Table 4.

Details of each component used in Table 4 are as follows.

[Color-changing compound]
IR-1: Compound with the following structure IR-2: Compound with the above structure IR-3: Compound with the following structure IR-4: Compound with the following structure

[Water-soluble polymer]
Mowiol 8-88: Polyvinyl alcohol, Mowiol 8-88 manufactured by Sigma-Aldrich

[Hydrophobic polymer]
NP-1: Polyvinylidene chloride aqueous dispersion, Diofan (registered trademark) A50 manufactured by Solvin

<Evaluation of lithographic printing plate precursor>
(1) Changes in on-press developability over time The lithographic printing plate precursor prepared as described above was processed using a Kodak Magnus 800 Quantum equipped with an infrared semiconductor laser at an output of 27 W, an outer drum rotation speed of 450 rpm, and a resolution of 2,400 dpi. (dot per inch, 1 inch is 2.54 cm) (irradiation energy equivalent to 110 mJ/cm ² ). The exposure image included a solid image and a 50% AM screen (Amplitude Modulation Screen) halftone chart.
The exposed original plate thus obtained was attached to the cylinder of a chrysanthemum size printing machine SX-74 manufactured by Heidelberg Co., Ltd. without being subjected to any development processing. This printing machine was connected to a dampening water circulation tank with a capacity of 100 L that contained a nonwoven fabric filter and a temperature control device. 80L of 2.0% dampening water S-Z1 (manufactured by FUJIFILM Co., Ltd.) was charged into the circulation device, and used as printing ink such as T&K UV OFS K-HS Sumi GE-M (manufactured by T&K TOKA Co., Ltd.). ) and supplied dampening water and ink using the standard automatic printing start method, and then printed on Tokubishi Art Paper (ream weight: 76.5 kg, manufactured by Mitsubishi Paper Mills Co., Ltd.) at a printing speed of 10,000 sheets per hour. 200 sheets were printed.
In the above-mentioned on-press development, the number of printing sheets required until the ink was not transferred to the non-image area (hereinafter also referred to as the number of on-press development sheets) was determined. It can be said that the smaller the number of sheets to be developed on press, the better the on-press developability.

The above-mentioned measurement of the number of sheets developed on press was carried out for the following three types of lithographic printing plate precursors. The results are shown in Table 5.
1. Lithographic printing plate precursor immediately after production (indicated as "immediately" in the table)
2. A lithographic printing plate precursor immediately after production, wrapped in craft paper and stored in a constant temperature bath at 35°C for 14 days (in the table, it is written as "after 14 days at 35°C")
3. A lithographic printing plate precursor immediately after production, wrapped in craft paper and stored in a constant temperature bath at 45°C for 14 days (in the table, it is written as "after 14 days at 45°C")

(2) Evaluation of printing durability (UV printing durability) The lithographic printing plate precursor prepared as described above was tested on a Kodak Magnus 800 Quantum equipped with an infrared semiconductor laser, output 27W, outer drum rotation speed 450rpm, resolution Exposure was carried out under conditions of 2,400 dpi (irradiation energy equivalent to 110 mJ/cm ² ). The exposed images included a solid image and an AM screen 10% halftone chart.
The exposed original plate thus obtained was attached to the cylinder of a chrysanthemum size printing machine SX-74 manufactured by Heidelberg Co., Ltd. without being subjected to any development processing. This printing machine was connected to a dampening water circulation tank with a capacity of 100 L that contained a nonwoven fabric filter and a temperature control device. 80L of 2.0% dampening water S-Z1 (manufactured by FUJIFILM Co., Ltd.) was charged into the circulation device, and used as printing ink such as T&K UV OFS K-HS Sumi GE-M (manufactured by T&K TOKA Co., Ltd.). ), and after supplying dampening water and ink using the standard automatic printing start method, printing was performed on Tokubishi Art (ream weight: 76.5 kg, manufactured by Mitsubishi Paper Mills Co., Ltd.) paper at a printing speed of 10,000 sheets per hour. 500 sheets were printed.
Continued printing. As the number of prints was increased, the image area gradually wore out and the ink density on the prints decreased. The number of printed copies is the number of printed copies when the value of the halftone dot area ratio of the AM screen 10% halftone dots on printed matter measured with a Gretag densitometer (manufactured by Gretag Macbeth) is 3% lower than the measured value of the 500th printed page. The printing durability was evaluated.
The greater the number of printed sheets, the better the printing durability.

(3) Evaluation of visibility The obtained lithographic printing plate precursor was exposed to light using a Creo Trendsetter 3244VX equipped with a water-cooled 40W infrared semiconductor laser under conditions of an output of 11.5W, an outer drum rotation speed of 220 rpm, and a resolution of 2,400 dpi. . Exposure was performed at 25° C. and 50% RH.
The lithographic printing plate precursor immediately after exposure (indicated as "immediately" in the table) and the lithographic printing plate precursor after the exposed lithographic printing plate precursor has been stored for one day at 25°C and 50% RH (in the table, the lithographic printing plate precursor is (denoted as "after 1 d"), and the color development was measured for each of the following. The measurement was performed using a spectrophotometer CM2600d manufactured by Konica Minolta, Inc. and operation software CM-S100W using the SCE (specular reflection elimination) method. For visibility (visibility), the difference ΔL between the L ^* value of the exposed area and the L ^* value of the unexposed area was determined using the L ^* value (lightness) of the L ^* a ^* b ^* color system. It can be said that the larger the value of ΔL, the better the visibility. The results are listed in Table 5.

As is clear from Table 5, the lithographic printing plate precursors according to Examples have suppressed deterioration in on-press developability over time and have excellent printing durability compared to lithographic printing plate precursors according to Comparative Examples. I understand.
Furthermore, it can be seen that the lithographic printing plate precursors according to Examples also have excellent visibility after exposure.

18: aluminum plate, 12a, 12b: aluminum support, 20a, 20b: anodized film, 22a, 22b: micropore, 24: large diameter hole, 26: small diameter hole, 610: anodizing treatment device, 616: Aluminum plate, 618: Electrolyte, 612: Power supply tank, 614: Electrolytic treatment tank, 616: Aluminum plate, 620: Power supply electrode, 622: Roller, 624: Nip roller, 626: Electrolyte, 628: Roller, 630: Electrolytic electrode , 634: DC power supply

Claims (29)

having an image recording layer and an outermost layer on a support in this order,
The image recording layer has a glass transition temperature of 70° C. or higher and contains a polymer that is polyvinyl acetal ,
An on-press development type lithographic printing plate precursor, wherein the outermost layer contains a color-changing compound. The image recording layer further contains a polymerizable compound having a molecular weight of 5,000 or less,
The on-press development type lithographic printing plate precursor according to claim 1, wherein the difference between the solubility parameter of the polymer and the solubility parameter of the polymerizable compound is 0.8 MPa ^1/2 or more. The on-press development type lithographic printing plate precursor according to claim 2, wherein the solubility parameter of the polymerizable compound is 20.0 MPa ^1/2 or less. The on-press development type lithographic printing plate precursor according to claim 2 or 3, wherein the polymerizable compound is a bifunctional or more functional polymerizable compound. Claims 2 to 4 satisfy the relationship of 6.0≧P/M≧0.5, where P is the mass of the high molecular weight substance and M is the mass of the polymerizable compound in the image recording layer. The on-press development type lithographic printing plate precursor according to any one of the above. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 5 , wherein the structural unit having a hydroxyl group in the polyvinyl acetal is 20 mol% or more based on the total structural units of the polyvinyl acetal. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 6, wherein the polyvinyl acetal has an ethylenically unsaturated group. The on-press development type lithographic printing plate precursor according to claim 7 , wherein the polyvinyl acetal contains a structural unit having an ethylenically unsaturated group. The on-press development type lithographic printing plate precursor according to claim 7 , wherein the polyvinyl acetal is a compound having an ethylenically unsaturated group introduced into the acetal ring. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 9 , wherein the outermost layer further contains a hydrophobic polymer. The on-press development type lithographic printing plate precursor according to claim 10 , wherein the area ratio occupied by the hydrophobic polymer on the surface of the outermost layer is 30% by area or more. The on-press development type lithographic printing plate precursor according to claim 10 or 11 , wherein the hydrophobic polymer is a particle. 13. The lightness change ΔL before and after the exposure is 2.0 or more when exposed to infrared rays with a wavelength of 830 nm at an energy density of 110 mJ/cm ² . On-press development type lithographic printing plate precursor. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 13 , wherein the color-changing compound contains a compound that develops color upon exposure to infrared rays. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 14 , wherein the color-changing compound contains a decomposable compound that decomposes due to infrared exposure. The on-press development type lithographic printing plate precursor according to any one of claims 11 to 15 , wherein the color-changing compound is a cyanine dye. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 16 , wherein the color-changing compound is a compound represented by the following formula 1-1.

In formula 1-1, R ¹ represents a group represented by any of the following formulas 2 to 4, and R ¹¹ to R ¹⁸ each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -SR ^c or -NR ^d R ^e , R ^a to R ^e each independently represent a hydrocarbon group, and A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ are linked to form a monocyclic or A polycyclic ring may be formed, A ₁ and A ₂ each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, However, the sum of n ₁₁ and n ₁₂ is 2 or more, n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, and R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za represents a counter ion that neutralizes the charge.

In formulas 2 to 4, R ²⁰ , R ³⁰ , R ⁴¹ and R ⁴² each independently represent an alkyl group or an aryl group, Zb represents a counter ion that neutralizes the charge, and the wavy line represents the formula 1- represents the bonding site with the group represented by L in 1. The on-press development type lithographic printing plate precursor according to claim 17 , wherein the color-changing compound is a compound represented by the following formula 1-2.

In formula 1-2, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c or -NR ^d R ^e , R ²³ and R ²⁴ each independently represent a hydrogen atom or -R ^a , and R ^a to R ^e each independently represent a hydrocarbon R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²³ and R ²⁴ may be connected to form a monocyclic or polycyclic ring, and L is an oxygen atom, a sulfur atom, or , -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² each independently may have a substituent. It represents an alkyl group, and Za represents a counter ion that neutralizes charge. The on-press development type lithographic printing plate precursor according to claim 17 or 18, wherein the color-changing compound is a compound represented by any one of the following formulas 1-3 to 1-7.

In formulas 1-3 to 1-7, R ¹ represents a group represented by any of the above formulas 2 to 4, and R ¹⁹ to R ²² each independently represent a hydrogen atom, a halogen atom, -R ^a , -OR ^b , -CN, -SR ^c , or -NR ^d R ^e , R ²⁵ and R ²⁶ each independently represent a hydrogen atom, a halogen atom, or -R ^{a ,} and R ^a to R ^e each independently represents a hydrocarbon group, R ¹⁹ and R ²⁰ , R ²¹ and R ²² , or R ²⁵ and R ²⁶ may be connected to form a monocyclic or polycyclic ring, and L is represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and R ^d1 to R ^d4 , W ¹ and W ² each independently represent a substituent. represents an alkyl group which may have , and Za represents a counter ion that neutralizes charge. W ¹ and W ² in the formulas 1-2 to 1-7 are each independently an alkyl group having a substituent, and the substituent is -(OCH ₂ CH ₂ )-, a sulfo group, The on-press development type lithographic printing plate precursor according to claim 18 or 19, which is a salt of a sulfo group, a carboxy group, or a group having at least a salt of a carboxy group. The image recording layer further contains a polymerization initiator,
The on-press development type lithographic printing plate precursor according to any one of claims 1 to 20 , wherein the polymerization initiator contains an electron-donating polymerization initiator and an electron-accepting polymerization initiator. 22. The on-press development type lithographic printing plate precursor according to claim 21 , wherein the polymerization initiator contains a compound formed by the electron-donating polymerization initiator and the electron-accepting polymerization initiator forming a pair salt. The on-press development type lithographic printing plate precursor according to claim 21 , wherein the electron-accepting polymerization initiator contains a compound represented by the following formula (II).

In formula (II), X represents a halogen atom, and R ³ represents an aryl group. the image recording layer contains an infrared absorber,
The on-press development type lithographic printing plate according to any one of claims 21 to 23 , wherein the value of HOMO of the infrared absorber-HOMO of the electron-donating polymerization initiator is 0.70 eV or less. Original version. The image recording layer contains an infrared absorber, and the value of LUMO of the electron-accepting polymerization initiator minus LUMO of the infrared absorber is 0.70 eV or less . The on-press development type lithographic printing plate precursor described in . The support has an aluminum plate and an aluminum anodic oxide film disposed on the aluminum plate,
The anodic oxide film is located closer to the image recording layer than the aluminum plate,
The anodic oxide film has micropores extending in the depth direction from the surface on the image recording layer side,
The on-press development type lithographic printing plate precursor according to any one of claims 1 to 25 , wherein the average diameter of the micropores on the surface of the anodic oxide film is more than 10 nm and less than 100 nm. The micropores communicate with a large-diameter hole extending from the surface of the anodic oxide film to a depth of 10 nm to 1,000 nm and the bottom of the large-diameter hole, and extend from a communication position to a depth of 20 nm to 2,000 nm. It consists of a small diameter hole that extends to the
The average diameter of the large diameter pores on the surface of the anodic oxide film is 15 nm to 100 nm,
The on-press development type lithographic printing plate precursor according to claim 26 , wherein the average diameter of the small diameter hole portion at the communicating position is 13 nm or less. Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of claims 1 to 27 ;
A method for producing a lithographic printing plate, comprising the step of supplying at least one selected from the group consisting of printing ink and dampening water on a printing press to remove an image recording layer in a non-image area. Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of claims 1 to 27 ;
a step of supplying at least one selected from the group consisting of printing ink and dampening water on the printing press to remove the image recording layer in the non-image area to produce a lithographic printing plate;
a step of printing with the obtained lithographic printing plate;
Lithographic printing method.