JP7378566B2 - On-press development type lithographic printing plate precursor, method for producing a 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 a difference 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), which is formed by providing an oleophilic photosensitive resin layer (image recording layer) 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 that will become the image area of the image recording layer remains, and the remaining unnecessary image recording layer is removed using an alkaline developer or an 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 to light, it is mounted on a printing machine as is without performing conventional development, 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."
Examples of conventional lithographic printing plate precursors or printing methods using lithographic printing plate precursors include those described in Patent Documents 1 to 3.

Patent Document 1 describes a negative planographic printing plate precursor having a support and an image recording layer containing a radical polymerization initiator and a compound having a repeating unit represented by the following general formula (1).

In general formula (1), A represents a single bond or a divalent linking group. Ar represents a benzene nucleus or a naphthalene nucleus. R ¹ represents a hydroxyl group, an alkyl group or an aryl group. i represents an integer from 0 to 3. When i represents an integer of 2 or more, a plurality of R ¹ 's may be the same or different. R ² represents a hydrogen atom, an alkyl group or an aryl group. L represents *-O-**, *-OCO-** or *-OCONH-**. * represents a site that binds to Ar. ** represents a site that binds to Y. Y represents a (m+1)-valent linking group. X represents a (meth)acryloyloxy group.
l represents an integer of 0 or 1. m represents an integer of 1 or 2. However, when l is 0, m is 1. n represents an integer of 1 or 2.

US Pat. No. 5,001,003 includes a substrate having an imageable layer thereon, the imageable layer comprising a free radically polymerizable component, the free radically polymerizable group being initiated to polymerize upon exposure to the imaging radiation. an initiator composition capable of generating sufficient free radicals to produce an initiator composition comprising a diaryliodonium borate; an infrared absorbing cyanine dye having a methine chain linking a heterocyclic group; wherein the methine chain has a chain length of at least 7 carbon atoms, and a primary polymeric binder, and the imageable element further comprises an overcoat disposed on the imageable layer; The overcoat describes an imageable element comprised primarily of poly(vinyl alcohol) having a degree of hydrolysis of 85% or less.

U.S. Pat. No. 5,001,000 describes a substrate and a negative-tone imageable layer disposed on the substrate comprising a free radically polymerizable component and an initiator composition capable of generating free radicals upon exposure to imaging radiation. a negative-tone imageable layer comprising a substance, a radiation absorber, and a polymeric binder; and an outermost water-soluble overcoat layer disposed directly on the negative-tone imageable layer, the outermost water-soluble overcoat layer comprising: and (2) one or more of the above in an amount of at least 1.3% and up to 60% by weight based on the total outermost water-soluble overcoat layer weight. and an outermost water-soluble overcoat layer comprising organic wax particles dispersed in a film-forming water-soluble polymer binder, wherein the organic wax particles form the dried outermost water-soluble overcoat layer. A negative-working lithographic printing plate precursor is described having an average maximum dimension of at least 0.05 μm and at most 0.7 μm, as measured from a scanning electron micrograph of .

Patent Document 1: Japanese Unexamined Patent Publication No. 2017-132227 Patent Document 2: Japanese Patent Publication No. 2010-529490 Patent Document 3: Japanese Patent Application Publication No. 2015-519610

In printing using a lithographic printing plate, for example, the plate surface is cleaned using a plate cleaner or the like during printing. Therefore, there is a need for an on-press development type lithographic printing plate precursor that can yield a lithographic printing plate with excellent chemical resistance to chemicals such as plate cleaners.
The present inventors have discovered that the on-press development type lithographic printing plate precursor (hereinafter also simply referred to as "lithographic printing plate precursor") according to the present disclosure is superior to the lithographic printing plate precursors described in Patent Documents 1 to 3. It has been found that it is possible to further improve the chemical resistance of the resulting lithographic printing plate.

The problems to be solved by the embodiments of the present invention are an on-press development type lithographic printing plate precursor capable of obtaining a lithographic printing plate having excellent chemical resistance, and production of a lithographic printing plate using the above-mentioned on-press development type lithographic printing plate precursor. An object of the present invention is to provide 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 a support, an image recording layer, and an overcoat layer in this order,
The image recording layer includes a binder polymer and an electron-donating polymerization initiator,
The binder polymer has a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound,
An on-press development type lithographic printing plate precursor, wherein the thickness of the overcoat layer is thicker than the thickness of the image recording layer.
<2> The image recording layer further contains a polymerizable compound, and the content of the binder polymer with respect to the total mass of the polymerizable compound in the image recording layer is more than 0% by mass and 400% by mass or less, < The on-press development type lithographic printing plate precursor described in 1>.
<3> The on-press development type lithographic printing plate precursor according to <1> or <2> above, wherein the overcoat layer contains a water-soluble polymer.
<4> The on-press development type lithographic printing plate precursor according to <3> above, wherein the water-soluble polymer contains polyvinyl alcohol having a saponification degree of 50% or more.
<5> The on-press development type lithographic printing plate precursor according to any one of <1> to <4> above, wherein the electron-donating polymerization initiator is a borate compound.
<6> The on-press development type lithographic printing plate precursor according to any one of <1> to <5> above, wherein the electron-donating polymerization initiator is a tetraarylborate compound.
<7> The on-press development type lithographic printing plate precursor according to any one of <1> to <6> above, wherein the electron-donating polymerization initiator is a tetraphenylborate compound.
<8> The on-press development type lithographic printing plate precursor according to any one of <1> to <7> above, wherein the highest occupied orbital of the electron-donating polymerization initiator is −6.0 eV or more.
<9> The on-press development type lithographic printing plate precursor according to any one of <1> to <8> above, wherein the image recording layer further contains an electron-accepting polymerization initiator.
<10> The on-press development type lithographic printing plate precursor according to <9> above, wherein the electron-accepting polymerization initiator is an onium compound.
<11> The on-press development type lithographic printing plate precursor according to <9> or <10> above, wherein the lowest unoccupied orbital of the electron-accepting polymerization initiator is −3.0 eV or less.
<12> The on-press development type lithographic plate according to any one of <9> to <11> above, wherein the electron-accepting polymerization initiator and the electron-donating polymerization initiator form a salt. Original printing plate.
<13> The on-press development type lithographic printing according to any one of <9> to <12> above, wherein the electron-accepting polymerization initiator and the electron-donating polymerization initiator contain an iodonium borate compound. Original version.
<14> The on-press development type lithographic printing plate precursor according to any one of <1> to <13> above, wherein the binder polymer further has a structural unit formed of N-vinylpyrrolidone.
<15> The on-press development type lithographic printing plate precursor according to any one of <1> to <14> above, wherein the image recording layer further contains an infrared absorber.
<16> The on-press development type lithographic printing plate precursor according to <15> above, wherein the infrared absorber is an infrared absorber that decomposes upon exposure to infrared rays.
<17> The on-press development type lithographic printing plate precursor according to <15> or <16> above, wherein the infrared absorber is an infrared absorber that decomposes due to heat caused by infrared exposure, electron transfer, or both.
<18> The on-press development type lithographic printing plate precursor according to any one of <15> to <17> above, wherein the infrared absorber is a cyanine dye.
<19> The on-press development type lithographic printing plate precursor according to any one of <15> to <18> above, wherein the infrared absorber is a compound represented by the following formula 1.

In Formula 1, R ¹ represents a group whose R ¹ -L bond is cleaved by infrared exposure, and R ₁₁ to R ₁₈ each independently represent a hydrogen atom, a halogen atom, -Ra, -ORb, -SRc, or -NRdRe. and Ra to Re each independently represent a hydrocarbon group, A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ may be linked to form a monocyclic or polycyclic ring, and A ₁ and A ₂ each independently represents an oxygen atom, sulfur atom, or nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, provided that the sum of n ₁₁ and n ₁₂ is 2 or more, and n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za neutralizes the charge. represents the counterion.

<20> The on-press development type lithographic printing plate precursor according to <19> above, wherein R ¹ in Formula 1 is a group represented by Formula 2 below.

In Formula 2, R ^Z represents an alkyl group, and the wavy line portion represents a bonding site with the group represented by L in Formula 1 above.

<21> Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of <1> to <20>above;
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.
<22> Imagewise exposing the on-press development type planographic printing plate precursor according to any one of <1> to <20>above;
a step of supplying at least one selected from the group consisting of printing ink and dampening water and removing the image recording layer in the non-image area on the printing press to produce a lithographic printing plate;
A lithographic printing method comprising the step of printing with the obtained lithographic printing plate.

According to an embodiment of the present invention, an on-press development type lithographic printing plate precursor capable of obtaining a lithographic printing plate having excellent chemical resistance, a method for producing a lithographic printing plate using the above-mentioned on-press development type lithographic printing plate precursor, and A lithographic printing method using the above-mentioned on-press development type lithographic printing plate precursor can be provided.

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 this specification, "~" indicating a numerical range is used to include the numerical values written before and after it as the lower limit and upper limit.
Furthermore, in the description of groups (atomic groups) in this specification, 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 this specification, "(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. It is.
Furthermore, the term "process" in this specification refers not only to an independent process, but also to the term "process" when the intended purpose of the process is achieved, even if the process cannot be clearly distinguished from other processes. included. Furthermore, in the present disclosure, "mass %" and "weight %" have the same meaning, and "mass parts" and "weight parts" have the same meaning.
Unless specifically limited, in the present disclosure, each component in the composition or each structural unit in the polymer may be contained alone or in combination of two or more. .
Furthermore, in the present disclosure, the amount of each component in the composition or each structural unit in the polymer is determined when a plurality of substances or structural units corresponding to each component or each structural unit in the polymer are present in the composition. Unless otherwise specified, it means the total amount of the relevant substances present in the composition or the respective constituent units of the relevant plurality present in the polymer.
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 THF (tetrahydrofuran) as a solvent 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.
Furthermore, in the present disclosure, "*" in a chemical structural formula represents a bonding position with another structure.
The present disclosure will be described in detail below.

(On-press development type lithographic printing plate original plate)
The on-press development type lithographic printing plate precursor according to the present disclosure has a support, an image recording layer, and an overcoat layer in this order, and the image recording layer comprises a binder polymer and an electron-donating polymer. contains an initiator, the binder polymer has a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound, and the thickness of the overcoat layer is equal to that of the image recording layer. Thicker than thick.

As a result of extensive studies, the inventors of the present invention have found that by employing the above configuration, it is possible to provide a lithographic printing plate precursor from which a lithographic printing plate with excellent chemical resistance can be obtained.
Although the detailed mechanism by which the above effect is obtained is unknown, it is presumed as follows.
The lithographic printing plate precursor according to the present disclosure includes an electron-donating polymerization initiator and has an overcoat layer that is thicker than the image recording layer. It is thought that this improves the polymerization efficiency of the radically polymerizable compound in the exposed area and improves the strength of the film in the image area obtained after development, thereby improving chemical resistance.
Furthermore, the lithographic printing plate precursor according to the present disclosure includes a binder polymer (hereinafter also referred to as "specific binder polymer") having a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound. include. Chemical resistance is further improved due to the synergistic effect of including all of this specific binder polymer, the above-mentioned overcoat layer, and the above-mentioned electron-donating polymerization initiator, but the mechanism is not clear.

The lithographic printing plate precursor described in Patent Document 1 or 2 does not contain a specific binder polymer, and there is room for further improvement in chemical resistance.
In the lithographic printing plate precursor described in Patent Document 3, there is no description or suggestion of having an overcoat layer thicker than the image recording layer, and the chemical resistance is poor.

Further, it is considered that according to the lithographic printing plate precursor according to the present disclosure, a lithographic printing plate with excellent printing durability can be easily obtained. This is presumed to be due to the above-mentioned improvement in polymerization efficiency, the above-mentioned synergistic effect, etc.
In lithographic printing plates, the ability to print a large number of plates is said to have "excellent printing durability." Further, according to the lithographic printing plate precursor according to the present disclosure, it is considered that a lithographic printing plate with excellent ink receptivity (hereinafter also simply referred to as "ink receptivity") can be easily obtained. This is presumed to be due to the inclusion of the above-mentioned specific binder polymer, the above-mentioned synergistic effect, etc.
Further, according to the lithographic printing plate precursor according to the present disclosure, it is considered that a lithographic printing plate precursor with excellent on-press developability can be easily obtained. This is presumed to be due to the inclusion of a specific binder polymer, which makes it easier for non-image areas to stick to the ink roller during on-press development and be removed (ink tack development), and the synergistic effects mentioned above. .

The lithographic printing plate precursor according to the present disclosure has excellent printing durability, chemical resistance, and ink receptivity by including all the requirements of a specific binder polymer, the above-mentioned overcoat layer, and the above-mentioned electron-donating polymerization initiator. It is considered that the film tends to have excellent effects of being excellent in both the on-press developability and the on-press developability. If even one of the above requirements is lacking, at least one of these effects is considered to be reduced.
In general, in on-press development type lithographic printing plates, chemical resistance is obtained by reducing the solubility of the image area by chemicals such as plate cleaners, or by improving resistance to ink, which is a chemical. It is possible to achieve both the printing durability obtained and the ink receptivity obtained by improving the affinity for ink, or the on-press developability obtained by improving the affinity of the unexposed area with ink. However, the lithographic printing plate precursor according to the present disclosure is considered to be extremely useful in that it is possible to achieve both of these requirements.
The details of each component of the lithographic printing plate precursor according to the present disclosure will be described below.

<Support>
The lithographic printing plate precursor according to the present disclosure has a support.
As the support, a support having a hydrophilic surface (also referred to as "hydrophilic support") is preferable. The hydrophilic surface preferably has a contact angle with water of less than 10°, more preferably less than 5°.
The water contact angle in the present disclosure is measured as the contact angle of a water droplet on a surface at 25° C. (after 0.2 seconds) using DM-501 manufactured by Kyowa Interface Science Co., Ltd.
The support for the lithographic printing plate precursor according to the present disclosure can be appropriately selected from known supports for lithographic printing plate precursors. As the support, an aluminum plate whose surface has been roughened and anodized by a known method is preferable.
The aluminum plate may be further subjected to micropore enlarging and sealing treatments of the anodic oxide film as described in JP-A No. 2001-253181 and JP-A No. 2001-322365, US Pat. No. 2,714, Surface hydrophilization treatment with an alkali metal silicate as described in the specifications of No. 066, No. 3,181,461, No. 3,280,734, and No. 3,902,734, U.S. Appropriately select surface hydrophilic treatment using polyvinylphosphonic acid or the like as described in the specifications of Patent No. 3,276,868, Patent No. 4,153,461, and Patent No. 4,689,272. You can go.
The support preferably has a center line average roughness of 0.10 μm to 1.2 μm.

If necessary, the support may be coated with an organic polymer compound described in JP-A-5-45885 or a silicon alkoxy compound described in JP-A-6-35174 on the side opposite to the image recording layer. It may have a back coat layer containing.

<Image recording layer>
The lithographic printing plate precursor according to the present disclosure has an image recording layer formed on a support.
The image recording layer used in the present disclosure preferably further contains a polymerizable compound from the viewpoints of printing durability and photosensitivity.
The image recording layer used in the present disclosure preferably further contains an electron-accepting polymerization initiator from the viewpoints of printing durability and photosensitivity.
The image recording layer used in the present disclosure preferably further contains an infrared absorber from the viewpoint of exposure sensitivity.
The image recording layer used in the present disclosure may further contain an acid color former to confirm exposed areas before development.
In the lithographic printing plate precursor according to the present disclosure, from the viewpoint of on-press developability, it is preferable that the unexposed areas of the image recording layer are removable with at least one selected from the group consisting of fountain solution and printing ink. .
The details of each component contained in the image recording layer will be explained below.

[Specific binder polymer]
The image recording layer used in this disclosure includes a specific binder polymer.
In the present disclosure, the specific binder polymer is a binder resin that is not in the form of particles, and the polymer particles described below are not included in the specific binder polymer in the present disclosure.
The specific binder polymer has a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound.

-Structural unit formed by aromatic vinyl compound-
The specific binder polymer has a structural unit formed by an aromatic vinyl compound.
The aromatic vinyl compound may be any compound having a structure in which a vinyl group is bonded to an aromatic ring, and examples thereof include styrene compounds and vinylnaphthalene compounds, with styrene compounds being preferred and styrene being more preferred.
Examples of styrene compounds include styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene, α-methylstyrene, and p-methoxy-β-methylstyrene, Styrene is preferred.
Examples of vinylnaphthalene compounds include 1-vinylnaphthalene, methyl-1-vinylnaphthalene, β-methyl-1-vinylnaphthalene, 4-methyl-1-vinylnaphthalene, 4-methoxy-1-vinylnaphthalene, etc. -Vinylnaphthalene is preferred.

Moreover, as the structural unit formed by the aromatic vinyl compound, a structural unit represented by the following formula A1 is preferably mentioned.

In formula A1, R ^A1 and R ^A2 each independently represent a hydrogen atom or an alkyl group, Ar represents an aromatic ring group, R ^A3 represents a substituent, and n represents an integer equal to or less than the maximum number of substituents of Ar. .
In formula A1, R ^A1 and R ^A2 are each independently preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and both are hydrogen atoms. is even more preferable.
In formula A1, Ar is preferably a benzene ring or a naphthalene ring, more preferably a benzene ring.
In formula A1, R ^A3 is preferably an alkyl group or an alkoxy group, more preferably an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and is a methyl group or a methoxy group. is even more preferable.
In formula A1, when a plurality of R ^A3s exist, the plurality of R ^A3s may be the same or different.
In formula A1, n is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

The content of the structural unit formed by the aromatic vinyl compound in the specific binder polymer is preferably 15% by mass to 85% by mass, and preferably 30% by mass to 70% by mass, based on the total mass of the specific binder polymer. It is more preferable that there be.

-Structural unit formed by an acrylonitrile compound-
The specific binder polymer has a structural unit formed by an acrylonitrile compound.
Examples of the acrylonitrile compound include (meth)acrylonitrile, and preferably acrylonitrile.

Further, as the structural unit formed by the acrylonitrile compound, a structural unit represented by the following formula B1 is preferably mentioned.

In formula B1, R ^B1 represents a hydrogen atom or an alkyl group.
In formula B1, R ^B1 is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom.

The content of the structural unit formed by the acrylonitrile compound in the specific binder polymer is preferably 15% by mass to 85% by mass, and preferably 30% by mass to 70% by mass, based on the total mass of the specific binder polymer. is more preferable.

-Structural unit formed by N-vinyl heterocyclic compound-
From the viewpoint of printing durability and chemical resistance, it is preferable that the specific binder polymer further has a structural unit formed from an N-vinyl heterocyclic compound.
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.

Furthermore, as the structural unit formed by the N-vinyl heterocyclic compound, a structural unit represented by the following formula C1 is preferably mentioned.

In formula C1, Ar ^N represents a heterocyclic structure containing a nitrogen atom, and the nitrogen atom in Ar ^N is bonded to the carbon atom indicated by *.
In formula C1, the heterocyclic structure represented by Ar ^N is preferably a pyrrolidone ring, a carbazole ring, a pyrrole ring, a phenothiazine ring, a succinimide ring, a phthalimide ring, a caprolactam ring, and an imidazole ring, and is preferably a pyrrolidone ring. is more preferable.
Furthermore, the heterocyclic structure represented by Ar ^{2 N} may have a known substituent.

The content of the structural unit formed by the N-vinyl heterocyclic compound in the specific binder polymer is preferably 5% by mass to 50% by mass, and 10% by mass to 40% by mass, based on the total mass of the specific binder polymer. % is more preferable.

-Constituent unit having ethylenically unsaturated group-
The specific binder polymer may further have a structural unit having an ethylenically unsaturated group.
Ethylenically unsaturated groups include, but are not limited to, vinyl groups, allyl groups, vinylphenyl groups, (meth)acrylamide groups, and (meth)acryloyloxy groups. ) Preferably it is an acryloyloxy group.
A structural unit having an ethylenically unsaturated group can be introduced into a specific binder polymer by polymer reaction or copolymerization. Specifically, for example, a method in which a compound having an epoxy group and an ethylenically unsaturated group (for example, glycidyl methacrylate, etc.) is reacted with a polymer into which a structural unit having a carboxy group such as methacrylic acid is introduced, It can be introduced by a method such as reacting a compound having an isocyanate group and an ethylenically unsaturated group (such as 2-isocyanatoethyl methacrylate) with a polymer into which a structural unit having a group having an active hydrogen has been introduced. .
In addition, the structural unit having an ethylenically unsaturated group can be obtained by reacting a compound having a carboxyl group and an ethylenically unsaturated group with a polymer into which a structural unit having an epoxy group such as glycidyl (meth)acrylate is introduced. It may be incorporated into a particular binder polymer by any method.
Furthermore, a structural unit having an ethylenically unsaturated group may be introduced into the specific binder polymer by using, for example, a monomer containing a partial structure represented by the following formula d1 or the following formula d2. Specifically, for example, after polymerization using at least the above monomer, an ethylenically unsaturated group is formed by an elimination reaction using a basic compound on a partial structure represented by the following formula d1 or the following formula d2. By doing so, a structural unit having an ethylenically unsaturated group is introduced into the specific binder polymer.

In formula d1 and formula d2, R ^d represents a hydrogen atom or an alkyl group, A ^d represents a halogen atom, X ^d represents -O- or -NR ^N -, and R ^N represents a hydrogen atom or an alkyl group. , * represents a binding site with another structure.
In formulas d1 and d2, R ^d is preferably a hydrogen atom or a methyl group.
In formulas d1 and d2, A ^d is preferably a chlorine atom, a bromine atom, or an iodine atom.
In formulas d1 and d2, X ^d is preferably -O-. When X ^d represents -NR ^N -, R ^N is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom.

Examples of the structural unit having an ethylenically unsaturated group include a structural unit represented by the following formula D1.

In formula D1, L ^D1 represents a single bond or a divalent linking group, L ^D2 represents an m+1 valent linking group, X ^D1 and X ^D2 each independently represent -O- or -NR ^N -, R ^N represents a hydrogen atom or an alkyl group, R ^D1 and R ^D2 each independently represent a hydrogen atom or a methyl group, and m represents an integer of 1 or more.

In formula D1, L ^D1 is preferably a single bond. When L ^D1 represents a divalent linking group, it is preferably an alkylene group, an arylene group, or a divalent group in which two or more of these are bonded, and more preferably an alkylene group having 2 to 10 carbon atoms or a phenylene group.
In formula D1, L ^D2 is preferably a group represented by any one of the following formulas D2 to D6.
In formula D1, both X ^D1 and X ^D2 are preferably -O-. Further, when at least one of X ^D1 and X ^D2 represents -NR ^N -, R ^N is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom.
In formula D1, R ^D1 is preferably a methyl group.
In formula D1, at least one of m R ^D2 is preferably a methyl group.
In formula D1, m is preferably an integer of 1 to 4, more preferably 1 or 2, and even more preferably 1.

In formulas D2 to D6, L ^D3 to L ^D7 represent divalent linking groups, L ^D5 and L ^D6 may be different, * represents a bonding site with X ^D1 in formula D1, and the wavy line portion represents a binding site with X ^D2 in formula D1.

In formula D3, L ^D3 is preferably an alkylene group, an arylene group, or a group in which two or more of these are bonded, and is preferably an alkylene group having 1 to 10 carbon atoms, a phenylene group, or a group in which two or more of these are bonded. More preferred.
In formula D4, L ^D4 is preferably an alkylene group, an arylene group, or a group in which two or more of these are bonded, and is preferably an alkylene group having 1 to 10 carbon atoms, a phenylene group, or a group in which two or more of these are bonded. More preferred.
In formula D5, L ^D5 is preferably an alkylene group, an arylene group, or a group in which two or more of these are bonded, and is preferably an alkylene group having 1 to 10 carbon atoms, a phenylene group, or a group in which two or more of these are bonded. More preferred.
In formula D6, L ^D6 is preferably an alkylene group, an arylene group, or a group in which two or more of these are bonded, and is preferably an alkylene group having 1 to 10 carbon atoms, a phenylene group, or a group in which two or more of these are bonded. More preferred.
In formula D7, L ^D7 is preferably an alkylene group, an arylene group, or a group in which two or more of these are bonded, and is preferably an alkylene group having 1 to 10 carbon atoms, a phenylene group, or a group in which two or more of these are bonded. More preferred.

Specific examples of the structural unit having an ethylenically unsaturated group are shown below, but the structural unit having an ethylenically unsaturated group contained in the binder polymer according to the present disclosure is not limited thereto. In the following specific examples, R each independently represents a hydrogen atom or a methyl group.

The content of the structural unit having an ethylenically unsaturated group in the specific binder polymer is preferably 5% by mass to 60% by mass, and 10% by mass to 30% by mass, based on the total mass of the specific binder polymer. It is more preferable.

-Structural unit with acidic group-
Although the specific binder polymer may contain a structural unit having an acidic group, it is preferable from the viewpoint of on-press developability and ink receptivity that it does not contain a structural unit having an acidic group.
Specifically, the content of the structural unit having an acidic group in the specific binder polymer 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 specific binder polymer 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.

-Structural unit having a hydrophobic group-
The specific binder polymer 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 alkyl group in the alkyl (meth)acrylate compound preferably has 1 to 10 carbon atoms. The alkyl group may be linear or branched, and may have a cyclic structure. Examples of alkyl (meth)acrylate compounds include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, etc. can be mentioned.
The aryl group in the aryl (meth)acrylate compound preferably has 6 to 20 carbon atoms, more preferably a phenyl group. Further, the above aryl group may have a known substituent. As the aryl (meth)acrylate compound, phenyl (meth)acrylate is preferably mentioned.
The alkyl group in the aralkyl (meth)acrylate compound preferably has 1 to 10 carbon atoms. The alkyl group may be linear or branched, and may have a cyclic structure. Further, the number of carbon atoms in the aryl group in the aralkyl (meth)acrylate compound is preferably 6 to 20, and more preferably a phenyl group. As the aralkyl (meth)acrylate compound, benzyl (meth)acrylate is preferably mentioned.

The content of the structural unit having a hydrophobic group in the specific binder polymer is preferably 5% by mass to 50% by mass, and preferably 10% by mass to 30% by mass, based on the total mass of the specific binder polymer. More preferred.

-Structural unit with hydrophilic group-
The specific binder polymer may contain a structural unit having a hydrophilic group from the viewpoint of improving printing durability, chemical resistance, and on-press developability.
The above hydrophilic groups include -OH, -CN, -CONR ¹ R ² , -NR ² COR ¹ (R ¹ and R ² each independently represent a hydrogen atom, an alkyl group, an alkenyl group, or an aryl group). .R ¹ and R ² may be combined to form a ring.) -NR ³ R ⁴ , -N ⁺ R ³ R ⁴ R ⁵ X ^- (R ³ to R ⁵ each independently indicate the number of carbon atoms 1 to 8 alkyl group, X ^- represents a counter anion), a group represented by the following formula PO, and the like.
Among these hydrophilic groups, groups represented by --CONR ¹ R ² or the formula PO are preferred, and groups represented by the formula PO are more preferred.

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 in the specific binder polymer is preferably 5% by mass to 60% by mass, and preferably 10% by mass to 30% by mass, based on the total mass of the specific binder polymer. More preferred.

-Other constituent units-
The specific binder polymer may further contain other structural units. Other structural units may include 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.
Examples of acrylamide compounds include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-butyl(meth)acrylamide, N,N'-dimethyl Examples include (meth)acrylamide, N,N'-diethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-hydroxypropyl (meth)acrylamide, and N-hydroxybutyl (meth)acrylamide.
Examples of vinyl ether compounds include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, tert-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexylmethyl vinyl ether, 4-methylcyclohexyl Methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether, tetrahydrofur Furyl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloroethoxyethyl vinyl ether, Examples include phenylethyl vinyl ether, phenoxypolyethylene glycol vinyl ether, and the like.

The content of other structural units in the specific binder polymer 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 specific binder polymer.

-Production method of specific binder polymer-
The method for producing the specific binder polymer is not particularly limited, and can be produced by a known method.
For example, a styrene compound, an acrylonitrile compound, and optionally the above N-vinyl heterocyclic compound, a compound used to form the above ethylenically unsaturated group-containing structural unit, and a compound used to form the above acidic group-containing structural unit. at least one compound selected from the group consisting of a compound used to form a structural unit having a hydrophobic group, a compound used to form a structural unit having a hydrophobic group, and a compound used to form another structural unit described above, by a known method. It is obtained by polymerization.

-Molecular weight-
The weight average molecular weight of the specific binder polymer is preferably 3,000 to 300,000, more preferably 5,000 to 100,000.

-Concrete example-
Specific examples of specific binder polymers are shown in the table below, but the specific binder polymers used in the present disclosure are not limited thereto.

Furthermore, in the above specific examples, the content ratio of each structural unit can be changed as appropriate according to the preferable range of the content of each structural unit described above.
Moreover, the weight average molecular weight of each compound shown in the above specific example can be changed as appropriate according to the preferable range of the weight average molecular weight of the above-mentioned specific binder polymer.

-Content-
The image recording layer may contain one type of specific binder polymer alone, or may contain two or more types in combination.
The content of the specific binder polymer relative to the total mass of the image recording layer is preferably 5% by mass or more and 95% by mass or less, more preferably 7% by mass or more and 80% by mass or less, and 10% by mass or more and 60% by mass or less. More preferred.

[Electron-donating polymerization initiator]
The image recording layer used in the present disclosure preferably contains an electron-donating polymerization initiator. It is believed that the electron-donating polymerization initiator contributes to improving the chemical resistance and printing durability of the lithographic printing plate. Examples of the electron-donating polymerization initiator include the following five types.
(i) Alkyl or arylate complex: It is believed that the carbon-hetero bond is oxidatively cleaved to generate active radicals. Specific examples include borate compounds and the like.
(ii) Aminoacetic acid compound: It is thought that the C—X bond on the carbon adjacent to nitrogen is cleaved by oxidation to generate active radicals. As X, a hydrogen atom, a carboxy group, a trimethylsilyl group, or a benzyl group is preferable. Specifically, N-phenylglycines (which may have a substituent on the phenyl group), N-phenyliminodiacetic acid (which may have a substituent on the phenyl group), etc. It will be done.
(iii) Sulfur-containing compound: The above-mentioned aminoacetic acid compound in which the nitrogen atom is replaced with a sulfur atom can generate active radicals through a similar action. Specific examples include phenylthioacetic acid (the phenyl group may have a substituent) and the like.
(iv) Tin-containing compound: The above-mentioned aminoacetic acid compound in which the nitrogen atom is replaced with a tin atom can generate active radicals through a similar action.
(v) Sulfinate salts: can generate active radicals upon oxidation. Specific examples include sodium arylsulfinate.

Among these electron-donating polymerization initiators, the image recording layer preferably contains a borate compound. As the borate compound, a tetraarylborate compound or a monoalkyltriarylborate compound is preferable, a tetraarylborate compound is more preferable from the viewpoint of stability of the compound, and a tetraphenylborate compound is particularly preferable.
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.

Preferred examples of the borate compound include sodium tetraphenylborate.

Further, the highest occupied molecular orbital (HOMO) of the electron-donating polymerization initiator used in the present disclosure is preferably −6.00 eV or more, and −5.95 eV or more, from the viewpoint of chemical resistance and printing durability. 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.

In the present disclosure, the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) are calculated by the following method.
First, the counter anion in the compound to be calculated is 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.

B-1 to B-8 and other compounds are shown below as preferred specific examples of the electron-donating polymerization initiator, but it goes without saying that the invention is not limited to these. Furthermore, in the chemical formula below, Bu represents an n-butyl group, and Z represents a counter cation.
Examples of the counter cation represented by Z include Na ⁺ , K ⁺ , N ⁺ (Bu) ₄ , and the like. The above Bu represents an n-butyl group.
Further, as the counter cation represented by Z, onium ion in the electron-accepting polymerization initiator described below is also preferably mentioned.

The electron-donating polymerization initiators may be used alone or in combination of two or more.
The content of the electron-donating polymerization initiator is preferably 0.01% to 30% by mass, more preferably 0.05% to 25% by mass, and 0.1% by mass based on the total mass of the image recording layer. More preferably 20% by mass.

[Polymerizable compound]
The image recording layer in the present disclosure preferably contains a polymerizable compound.
In the present disclosure, even if a compound has polymerizability, a compound that falls under the above-mentioned specific binder polymer, the below-mentioned polymer particles, and a binder polymer other than the below-mentioned specific binder does not fall under the category of a polymerizable compound. do.
The molecular weight of the polymerizable compound (in the case of having a molecular weight distribution, the weight average molecular weight) is preferably 50 or more and less than 2,500, more preferably 50 or more and less than 2,000.
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.

Examples of monomers include unsaturated carboxylic acids (for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.), their esters, and amides. Esters of acids and polyhydric alcohol compounds and amides of unsaturated carboxylic acids and polyhydric amine compounds are used. Additionally, addition reaction products of unsaturated carboxylic acid esters or amides having nucleophilic substituents such as hydroxy groups, amino groups, and mercapto groups with monofunctional or polyfunctional isocyanates or epoxies, and monofunctional or polyfunctional A dehydration condensation reaction product with a functional carboxylic acid is also preferably used. Further, addition reaction products of unsaturated carboxylic acid esters or amides having electrophilic substituents such as isocyanate groups and epoxy groups with monofunctional or polyfunctional alcohols, amines, and thiols, and further halogen atoms, Substitution reaction products of unsaturated carboxylic acid esters or amides having a leaving substituent such as a tosyloxy group with monofunctional or polyfunctional alcohols, amines, and thiols are also suitable. Furthermore, as another example, it is also possible to use a group of compounds in which the above-mentioned unsaturated carboxylic acid is replaced with unsaturated phosphonic acid, styrene, vinyl ether, or the like. These are JP 2006-508380, JP 2002-287344, JP 2008-256850, JP 2001-342222, JP 9-179296, and JP 9-179297. , JP 9-179298, JP 2004-294935, JP 2006-243493, JP 2002-275129, JP 2003-64130, JP 2003-280187, It is described in JP-A No. 10-333321 and the like.

Specific examples of monomers of esters of polyhydric alcohol compounds and unsaturated carboxylic acids include, as acrylic esters, ethylene glycol diacrylate, 1,3-butanediol diacrylate, tetramethylene glycol diacrylate, propylene glycol diacrylate, Examples include trimethylolpropane triacrylate, hexanediol diacrylate, tetraethylene glycol diacrylate, pentaerythritol tetraacrylate, sorbitol triacrylate, isocyanuric acid ethylene oxide (EO) modified triacrylate, and polyester acrylate oligomer. As methacrylic acid esters, tetramethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, pentaerythritol trimethacrylate, bis[p-(3-methacryloxy-2-hydroxypropoxy)phenyl] Examples include dimethylmethane, bis[p-(methacryloxyethoxy)phenyl]dimethylmethane, and the like. Specific examples of amide monomers of polyvalent amine compounds and unsaturated carboxylic acids include methylenebisacrylamide, methylenebismethacrylamide, 1,6-hexamethylenebisacrylamide, 1,6-hexamethylenebismethacrylamide, Examples include diethylene triamine trisacrylamide, xylylene bis acrylamide, xylylene bis methacrylamide, and the like.

Also suitable are urethane-based addition-polymerizable compounds produced using the addition reaction of isocyanate and hydroxyl groups. A vinyl urethane compound containing two or more polymerizable vinyl groups in one molecule, which is obtained by adding a vinyl monomer containing a hydroxy group represented by the following formula (M) to a polyisocyanate compound having two or more isocyanate groups. etc.
_CH2 =C( ^RM4 ) _COOCH2CH ( ^RM5 )OH(M)
In formula (M), R ^M4 and R ^M5 each independently represent a hydrogen atom or a methyl group.

In addition, urethane acrylates described in JP-A-51-37193, JP-A-2-32293, JP-A-2-16765, JP-A-2003-344997, and JP-A-2006-65210, Ethylene described in Japanese Patent Publication No. 58-49860, Japanese Patent Publication No. 56-17654, Japanese Patent Publication No. 62-39417, Japanese Patent Publication No. 62-39418, Japanese Patent Publication No. 2000-250211, Japanese Patent Publication No. 2007-94138 Urethane compounds having an oxide skeleton, urethane compounds having a hydrophilic group described in US Pat. also suitable.

The structure of the polymerizable compound, whether it is used alone or in combination, the amount of addition, and other details can be set arbitrarily.
The content of the polymerizable compound is preferably 5% to 75% by weight, more preferably 10% to 70% by weight, and 15% to 60% by weight based on the total weight of the image recording layer. It is more preferable that it is mass %.
Further, the content of the specific binder polymer relative to the total mass of the polymerizable compounds in the image recording layer is preferably more than 0% by mass and 400% by mass or less, and preferably 25% by mass to 300% by mass. More preferably, it is 50% by mass to 200% by mass.
In the image recording layer, the specific binder polymer and the polymerizable compound preferably have a sea-island structure. For example, a structure can be adopted in which the polymerizable compound is dispersed in the form of islands (a discontinuous layer) in a sea of a specific binder polymer (a continuous phase). It is considered that by setting the content of the specific binder polymer to the total mass of the polymerizable compound within the above range, it is easier to form a sea-island structure.

[Electron-accepting polymerization initiator]
The image recording layer preferably contains an electron-accepting polymerization initiator.
The electron-accepting polymerization initiator used in the present disclosure is a compound that generates polymerization initiating species such as radicals and cations using energy from light, heat, or both, and is a known thermal polymerization initiator or a compound with low bond dissociation energy. A compound having a bond, 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 compound is more preferable.
Further, as the electron-accepting polymerization initiator, an infrared-sensitive polymerization initiator is preferable.
The electron-accepting polymerization initiators may be used alone or in combination of two or more.
Examples of the radical polymerization initiator include (a) organic halides, (b) carbonyl compounds, (c) azo compounds, (d) organic peroxides, (e) metallocene compounds, (f) azide compounds, and (g) ) hexaarylbiimidazole compounds, (i) disulfone compounds, (j) oxime ester compounds, and (k) onium compounds.

As the organic halide (a), for example, compounds described in paragraphs 0022 to 0023 of JP-A No. 2008-195018 are preferable.
As the carbonyl compound (b), for example, compounds described in paragraph 0024 of JP-A No. 2008-195018 are preferred.
(c) As the azo compound, for example, the azo compounds described in JP-A-8-108621 can be used.
(d) As the organic peroxide, for example, compounds described in paragraph 0025 of JP-A No. 2008-195018 are preferred.
As the metallocene compound (e), for example, compounds described in paragraph 0026 of JP-A No. 2008-195018 are preferred.
Examples of the azide compound (f) include compounds such as 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone.
As the hexaarylbiimidazole compound (g), for example, compounds described in paragraph 0027 of JP-A No. 2008-195018 are preferred.
Examples of the disulfone compound (i) include compounds described in JP-A-61-166544 and JP-A-2002-328465.
As the oxime ester compound (j), for example, compounds described in paragraphs 0028 to 0030 of JP-A No. 2008-195018 are preferred.

Among the above electron-accepting polymerization initiators, preferred are oxime ester compounds and onium 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 even more 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.

As an example of the sulfonium salt compound, a triarylsulfonium salt compound is preferable, and a triarylsulfonium salt compound in which at least a part of an electron-withdrawing group, for example, a group on an aromatic ring is substituted with a halogen atom, is particularly preferable. More preferred are triarylsulfonium salt compounds in which the total number of halogen atoms substituted on the ring is 4 or more. Specific examples include triphenylsulfonium hexafluorophosphate, triphenylsulfonium benzoylformate, bis(4-chlorophenyl)phenylsulfonium benzoylformate, bis(4-chlorophenyl)-4-methylphenylsulfonium tetrafluoro. Borate, tris(4-chlorophenyl)sulfonium 3,5-bis(methoxycarbonyl)benzenesulfonate, tris(4-chlorophenyl)sulfonium hexafluorophosphate, tris(2,4-dichlorophenyl)sulfonium hexafluorophos Fart is an example.

Further, as the counter anion of the iodonium salt compound and the sulfonium salt compound, a sulfonamide anion or a sulfonimide anion is preferable, and a sulfonimide anion is more preferable.
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 sulfonimide anion are shown below, but the present disclosure is not limited thereto. In the following specific examples, Ph represents a phenyl group, Me represents a methyl group, and Et represents an ethyl group.

Moreover, one of the preferred embodiments of the present disclosure is an embodiment in which the electron-accepting polymerization initiator and the electron-donating polymerization initiator form a salt.
Specifically, for example, the above-mentioned onium compound may be a salt of an onium ion and an anion (for example, a tetraphenylborate anion) in the above-mentioned electron-donating polymerization initiator. More preferably, an iodonium borate compound is used, in which an iodonium cation (for example, di-p-tolyliodonium cation) in the iodonium salt compound described below and a borate anion in the electron-donating polymerization initiator described above form a salt. It will be done.
In the present disclosure, when the image recording layer contains onium ions and anions in the above-mentioned electron donating polymerization initiator, the image recording layer contains an electron accepting polymerization initiator and an electron donating polymerization initiator.

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 chemical resistance and printing durability.
Further, the lower limit is preferably −3.80 eV or more, more preferably −3.60 eV 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. It is preferably 0.8% by weight to 20% by weight, particularly preferably.

[Infrared absorber]
The image recording layer preferably contains an infrared absorber.
Infrared absorbers 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.
Among these dyes, particularly preferred are cyanine dyes, squarylium dyes, pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes. Further examples include cyanine dyes and indolenine cyanine dyes. Among these, cyanine dyes are particularly preferred.

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, it is preferable that the above-mentioned infrared absorber is an infrared absorber that decomposes upon exposure to infrared rays (hereinafter also referred to as "degradable infrared absorber").
By using an infrared absorbing dye that is decomposed by infrared exposure as the infrared absorbing agent, the infrared absorbing agent or its decomposition product promotes polymerization, and by using a specific binder polymer, a highly polar film can be obtained. Furthermore, it is estimated that the interaction between the decomposed product of the infrared absorber and the binder polymer results in excellent printing durability (UV printing durability) even when UV ink is used. .
The decomposable infrared absorbent is preferably an infrared absorbent that has the function of absorbing infrared rays, decomposing them, and developing color upon exposure to infrared rays. Here, "color development" means that there is almost no absorption in the visible light region (wavelength range of 400 nm or more and less than 750 nm) before infrared exposure, but absorption occurs in the visible light region by infrared exposure. This also includes absorption in a lower wavelength region extending to a longer wavelength in the visible light region.
Hereinafter, a colored compound formed when the decomposable infrared absorber absorbs infrared rays and decomposes upon exposure to infrared rays will also be referred to as a "coloring body of the degradable infrared absorber."
Moreover, it is preferable that the decomposable infrared absorber has a function of absorbing infrared rays and converting the absorbed infrared rays into heat upon exposure to infrared rays.
The above-mentioned decomposable infrared absorber may be one that absorbs and decomposes at least a portion of light in the infrared wavelength range (750 nm to 1 mm); Preferably it is an absorbent.

The decomposable infrared absorbent is preferably an infrared absorbent that decomposes due to heat, electron transfer, or both caused by infrared exposure, and more preferably an infrared absorbent that decomposes due to electron transfer caused by infrared exposure. preferable. Here, "decomposed by electron transfer" means that the electrons excited from the HOMO (highest occupied molecular orbital) of the degradable infrared absorbent to the LUMO (lowest unoccupied molecular orbital) by infrared exposure are transferred to the electron accepting group (LUMO) in the molecule. This means that there is an intramolecular electron transfer to a group with a potential close to that of the molecule, and decomposition occurs as a result.

The decomposable infrared absorber is preferably a cyanine dye that decomposes upon exposure to infrared rays, from the viewpoint of color development and UV printing durability of the resulting lithographic printing plate.
The infrared absorber is preferably a compound represented by the following formula 1 from the viewpoint of color development and UV printing durability of the resulting lithographic printing plate.

In Formula 1, R ¹ represents a group whose R ¹ -L bond is cleaved by infrared exposure, and R ₁₁ to R ₁₈ each independently represent a hydrogen atom, a halogen atom, -Ra, -ORb, -SRc, or -NRdRe. and Ra to Re each independently represent a hydrocarbon group, A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ may be linked to form a monocyclic or polycyclic ring, and A ₁ and A ₂ each independently represents an oxygen atom, sulfur atom, or nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, provided that the sum of n ₁₁ and n ₁₂ is 2 or more, and n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za neutralizes the charge. represents the counterion.

When the cyanine dye represented by formula 1 is exposed to infrared rays, the R ¹ -L bond is cleaved, and L becomes =O, =S or =NR ¹⁰ , and the color former of the degradable infrared absorber is formed. is formed. R ¹ separates to form a radical or an ionic body. These contribute to the polymerization of the polymerizable compound contained in the image recording layer.

In Formula 1, R ₁₁ to R ₁₈ are each independently preferably a hydrogen atom, -Ra, -ORb, -SRc, or -NRdRe.
The hydrocarbon group in Ra to Re is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably a hydrocarbon group having 1 to 15 carbon atoms, and still more preferably a hydrocarbon group having 1 to 10 carbon atoms. The hydrocarbon group may be linear, branched, or have a ring structure.

R ₁₁ to R ₁₄ in Formula 1 are each independently preferably a hydrogen atom or a hydrocarbon group, more preferably a hydrogen atom or an alkyl group, and even more preferably a hydrogen atom.
Moreover, 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 is preferably a 5-membered ring or a 6-membered ring, more preferably a 5-membered ring.
R ₁₂ bonded to the carbon atom to which A ₁ ⁺ is bonded and R ₁₄ bonded to the carbon atom to which A ₂ is bonded are preferably linked to R ₁₅ and R ₁₇ , respectively, to form a ring.

R ₁₅ in Formula 1 is preferably a hydrocarbon group. Further, it is preferable that R ₁₅ and R ₁₂ bonded to the carbon atom to which A ₁ ⁺ are bonded together 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 color development, an indolium ring is more preferable.
R ₁₇ in Formula 1 is preferably a hydrocarbon group. Further, it is preferable that R ₁₇ and R ₁₄ bonded to the carbon atom to which A ₂ is bonded are linked to form a ring. The ring formed is preferably an indole ring, a pyran ring, a thiopyran ring, a benzoxazole ring, or a benzimidazole ring, and from the viewpoint of color development, an indole ring is more preferred.
It is preferable that R ₁₅ and R ₁₇ in Formula 1 are the same group, and when each forms a ring, it is preferable that they form the same ring.

It is preferable that R ₁₆ and R ₁₈ in Formula 1 are the same group.
Furthermore, from the viewpoint of improving the water solubility of the compound represented by Formula 1, R ₁₆ and R ₁₈ are each independently preferably an alkyl group having a (poly)oxyalkylene group or an alkyl group having an anion structure; An alkyl group having a carboxylate group, a carboxylate group or a sulfonate group is more preferable, and an alkyl group having a sulfonate group at the end is even more preferable. The alkyl group mentioned above is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms.
The counter cation of the above anion structure may be a cation included in R ¹ -L in Formula 1 or A ₁ ⁺ , or may be an alkali metal cation or an alkaline earth metal cation.
The counter cation of the sulfonate group may be a cation included in R ¹ -L in Formula 1 or A ₁ ⁺ , or may be an alkali metal cation or an alkaline earth metal cation.
In addition, from the viewpoint of increasing the maximum absorption wavelength of the compound represented by Formula 1, and also from the viewpoint of color development and printing durability in lithographic printing plates, R ₁₆ and R ₁₈ each independently represent an alkyl group or an aromatic ring. Preferably, the alkyl group has The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group or an ethyl group. The alkyl group having an aromatic ring is preferably an alkyl group having an aromatic ring at the end, and more preferably a 2-phenylethyl group, a 2-naphthalenylethyl group or a 2-(9-anthracenyl)ethyl group.

In Formula 1, n ₁₁ and n ₁₂ are preferably the same integer of 0 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 each independently represent an oxygen atom, a sulfur atom, or a nitrogen atom, and preferably a nitrogen atom.
It is preferable that A ₁ and A ₂ in Formula 1 are the same atom.

Za in Formula 1 represents a counter ion that neutralizes charge. Examples of anion species include sulfonate ion, carboxylate ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, p-toluenesulfonate ion, perchlorate ion, etc. Or hexafluoroantimonate ion is preferred. Examples of cationic species include alkali metal ions, alkaline earth metal ions, ammonium ions, pyridinium ions, sulfonium ions, and sodium ions, potassium ions, ammonium ions, pyridinium ions, and sulfonium ions, with sodium ions, More preferred are potassium ions or ammonium ions.
R ₁₁ to R ₁₈ and R ¹ -L may have an anion structure or a cation structure, and if all of R ₁₁ to R ₁₈ and R ¹ -L are charge-neutral groups, Za is a monovalent counter anion, but for example, when R ₁₁ to R ₁₈ and R ¹ -L have two or more anion structures, Za can also be a counter cation.
Further, if the cyanine dye represented by Formula 1 has a charge-neutral structure throughout the compound, Za is not present.

In Formula 1, the group represented by R ¹ whose R ¹ -L bond is cleaved by infrared exposure will be described in detail later.

As the degradable infrared absorber, a cyanine dye represented by the following formula 1-A is more preferable from the viewpoint of color development and UV printing durability of the resulting lithographic printing plate.

In formula 1-A, R ¹ represents a group whose R ¹ -L bond is cleaved by infrared exposure, R ² and R ³ each independently represent a hydrogen atom or an alkyl group, and R ² and R ³ are connected to each other. Ar ¹ and Ar ² each independently represent a group forming a benzene ring or a naphthalene ring, and Y ¹ and Y ² each independently represent an oxygen atom, a sulfur atom, -NR ⁰ - or a dialkylmethylene group, R ⁰ represents a hydrogen atom, an alkyl group or an aryl group, and R ⁴ and R ⁵ each independently represent an alkyl group, a -CO ₂ M group or a -PO ₃ M ₂ group; , M represents a hydrogen atom, Na atom, K atom or onium group, R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, L represents an oxygen atom, a sulfur atom or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group or an aryl group, and Za represents a counter ion that neutralizes the charge.

In formula 1-A, the alkyl group in R ² to R ⁹ and R ⁰ is preferably an alkyl group having 1 to 30 carbon atoms, more preferably an alkyl group having 1 to 15 carbon atoms, and an alkyl group having 1 to 10 carbon atoms. is even more preferable. 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 are combinations of these.

The aryl group in R ⁰ is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 20 carbon atoms, and still more preferably an aryl group having 6 to 12 carbon atoms.
The above aryl group may have a substituent. Examples of substituents include alkyl groups, alkoxy groups, aryloxy groups, amino groups, alkylthio groups, arylthio groups, halogen atoms, carboxy groups, carboxylate groups, sulfo groups, sulfonate groups, alkyloxycarbonyl groups, and aryloxycarbonyl groups. , and groups combining these.
Specifically, for example, phenyl group, naphthyl group, p-tolyl group, p-chlorophenyl group, p-fluorophenyl group, p-methoxyphenyl group, p-dimethylaminophenyl group, p-methylthiophenyl group, p- Examples include phenylthiophenyl group.
Among the aryl groups, phenyl, p-methoxyphenyl, p-dimethylaminophenyl or naphthyl groups are preferred.

It is preferable that R ² and R ³ are connected to form a ring.
When R ² and R ³ are linked to form a ring, a 5-membered ring or a 6-membered ring is preferred, and a 5-membered ring is particularly preferred.

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

The alkyl group represented by R ⁴ or R ⁵ may be substituted alkyl. Examples of the substituted alkyl group represented by R ⁴ or R ⁵ 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 group, and M represents a hydrogen atom, a Na atom, a K 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 and isohexyl group, with ethylene group, n-propylene group, isopropylene group, and n-butylene group being preferred, with n-propylene group being particularly preferred.
n _W1 is preferably 1 to 10, more preferably 1 to 5, particularly preferably 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, n-butyl group, tert-butyl group are preferable, and methyl group, Ethyl group is more preferred, and methyl group is particularly preferred.
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, n-butylene group are preferable. Particularly preferred are ethylene group and n-propylene group.
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.

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

In formula 1-A, each of R ⁴ and R ⁵ is preferably an unsubstituted alkyl group. Preferably, R ⁴ and R ⁵ are the same group.

R ⁶ to R ⁹ each independently represent a hydrogen atom or an alkyl group, preferably a hydrogen atom.
Ar ¹ and Ar ² each independently represent a group forming a benzene ring or a naphthalene ring. The benzene ring and naphthalene ring may have a substituent. Examples of substituents include alkyl groups, 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 acyloxy group, a phosphonic acid group, and a combination thereof. As the substituent, an alkyl group is preferable.
In addition, from the viewpoint of increasing the maximum absorption wavelength of the compound represented by formula 1-A and improving color development and printing durability of the lithographic printing plate, Ar ¹ and Ar ² each independently represent a naphthalene ring. or a group forming a benzene ring having an alkyl group or an alkoxy group as a substituent is preferable, a group forming a benzene ring having a naphthalene ring or an alkoxy group as a substituent is more preferable, and a naphthalene ring or a group forming a benzene ring having an alkoxy group as a substituent is more preferable. A group forming a benzene ring having a group as a substituent is particularly preferred.

In formula 1-A, Ar ¹ or Ar ² is preferably a group that forms a group represented by the following formula (b1).

In formula (b1), R ¹⁹ represents an alkyl group having 1 to 12 carbon atoms. n3 represents an integer from 1 to 4. * represents a binding site.

Za represents a counter ion for neutralizing charges. However, if the compound represented by formula 1-A has a corresponding ionic substituent in its structure and charge neutralization is not required, Za is not necessary. When Za represents an anion species, examples include sulfonate ion, carboxylate ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, p-toluenesulfonate ion, perchlorate ion, etc. Phosphate ions or hexafluoroantimonate ions are preferred. When Za represents a cation species, 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, and sulfonium ions are preferred, and sodium ion, potassium ion or ammonium ion.
R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , Y ¹ and Y ² may have an anion structure or a cation structure, and R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , If all of Y ¹ and Y ² are charge-neutral groups, Za is a monovalent counter anion, but for example, R ¹ to R ⁹ , R ⁰ , Ar ¹ , Ar ² , Y ¹ and When Y ² has two or more anion structures, Za can also be a counter cation.

In the above formulas 1 and 1-A, the group represented by R ¹ whose R ¹ -L bond is cleaved by infrared exposure will be described below.
When L is an oxygen atom in Formula 1 or Formula 1-A, R ¹ is preferably a group represented by any of the following formulas (1-1) to (1-7) from the viewpoint of color development. , a group represented by any one of the following formulas (1-1) to (1-3) is more preferable.

In formulas (1-1) to (1-7), ● represents a bonding site with the oxygen atom represented by L in formula 1 or formula 1-A, and R ²⁰ each independently represents a hydrogen atom, represents an alkyl group, an alkenyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ or -SR ²⁷ , each R ²¹ independently represents a hydrogen atom, an alkyl group or an aryl group, and R ²² represents an aryl group, - OR ²⁴ , -NR ²⁵ R ²⁶ , -SR ²⁷ , -C(=O)R ²⁸ , -OC(=O)R ²⁸ or a halogen atom, R ²³ is an aryl group, an alkenyl group, an alkoxy group or an onium group , R ²⁴ to R ²⁷ each independently represent a hydrogen atom, an alkyl group or an aryl group, R ²⁸ represents an alkyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ or -SR ²⁷ , and Z ¹ represents a counter ion for neutralizing charges.

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

From the viewpoint of color development, R ²⁰ in formula (1-1) is preferably an alkyl group, an alkenyl group, an aryl group, -OR ²⁴ , -NR ²⁵ R ²⁶ or -SR ²⁷ , and an alkyl group, -OR ²⁴ , - NR ²⁵ R ²⁶ or -SR ²⁷ is more preferred, an alkyl group or -OR ²⁴ is even more preferred, and -OR ²⁴ is particularly preferred.
Further, when R ²⁰ in formula (1-1) is an alkyl group, the alkyl group may be an alkyl group having an arylthio group, an alkyloxycarbonyl group, or an arylsulfonyl group at the α-position. An alkyl group having an arylthio group or an alkyloxycarbonyl group is preferred.
When R ²⁰ in formula (1-1) is -OR ²⁴ , R ²⁴ is preferably an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms, even more preferably an isopropyl group or a tert-butyl group, and t -butyl group is particularly preferred.
When R ²⁰ in formula (1-1) is an alkenyl group, the alkenyl group may be an aryl group or an alkenyl group having a hydroxyaryl group.

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

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

From the viewpoint of color development, R ²⁰ in formula (1-4) is preferably an alkyl group or an aryl group, and among the two R ^20s , one is preferably an alkyl group and the other is more preferably an aryl group. The above two R ^20s may be connected to form a ring.
From the viewpoint of color development, R ²⁰ in formula (1-5) is preferably an alkyl group or an aryl group, more preferably an aryl group, and even more preferably a p-methylphenyl group.
From the viewpoint of color development, each R ²⁰ in formula (1-6) is preferably an alkyl group or an aryl group, more preferably a methyl group or a phenyl group.
From the viewpoint of color development, Z ¹ in formula (1-7) may be a counter ion for neutralizing charges, and may be included in Za above as a whole of the compound.
Z ¹ is preferably a sulfonate ion, a carboxylate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, a hexafluoroantimonate ion, a p-toluenesulfonate ion, or a perchlorate ion; Fluorophosphate ion or hexafluoroantimonate ion is more preferred.

When L in Formula 1 or Formula 1-A is an oxygen atom, R ¹ is more preferably a group represented by the following formula (5) from the viewpoint of color development.

In formula (5), R ¹⁵ and R ¹⁶ each independently represent a hydrogen atom, an alkyl group, or an aryl group, E represents an onium group, and * is represented by L in Formula 1 or Formula 1-A. Represents a bonding site with an oxygen atom.

The alkyl group represented by R ¹⁵ or R ¹⁶ is the same as the alkyl group in R ² to R ⁹ and R ⁰ , and the preferred embodiments are also the same as the preferred embodiments of the alkyl group in R ² to R ⁹ and R ⁰ . .
The aryl group represented by R ¹⁵ or R ¹⁶ is the same as the aryl group in R ⁰ , and its preferred embodiments are also the same as the preferred embodiments of the aryl group in R ⁰ .
The onium group represented by E is the same as the onium group in ^R23 , and its preferred embodiments are also the same as the preferred embodiments of the onium group in ^R23 .

In formula (5), the onium group represented by E is preferably a pyridinium group represented by formula (6) below.

In formula (6), R ¹⁷ represents a halogen atom, an alkyl group, an aryl group, a hydroxy group, or an alkoxy group, and when a plurality of R ^17s exist, the plurality of R ^{17s may be the same or different, or the plurality of R 17s} may be the same or different. ¹⁷ may be connected to form a ring. n2 represents an integer from 0 to 4. R ¹⁸ represents an alkyl group or an aryl group. Z _b represents a counter ion for neutralizing charges.

The alkyl group or aryl group represented by R ¹⁷ or R ¹⁸ is the same as the alkyl group in R ² to R ⁹ and R ⁰ or the aryl group in R ⁰ , and preferred embodiments are also the same as the alkyl group or aryl group in R ² to R ⁹ and R ⁰ . The preferred embodiments of the alkyl group or the aryl group in R ⁰ are the same.
The alkoxy group represented by R ¹⁷ is preferably an alkoxy group having 1 to 10 carbon atoms, such as methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, tert-butoxy group, etc. Can be mentioned.
n2 is preferably 0.
The counter ion for neutralizing the charge represented by Z _b is the same as Z ¹ in formula (1-7), and the preferred embodiment is also the same as the preferred embodiment of Z ¹ in formula (1-7). .

Specific examples of the group represented by R ¹ in Formula 1 or Formula 1-A when L is an oxygen atom are listed below, but the present disclosure is not limited thereto. In the following structural formula, TsO ^{2 -} represents a tosylate anion, and ● represents a bonding site with the oxygen atom represented by L in Formula 1 or Formula 1-A.

When L is an oxygen atom and R ¹ is an aryl group or a straight-chain alkyl group, cleavage of the R ¹ --O bond will not occur due to infrared exposure.

When L is a sulfur atom in Formula 1 or Formula 1-A, R ¹ is preferably a group represented by the following formula (2-1).

In formula (2-1), ● represents a bonding site with the sulfur atom represented by L in formula 1 or formula 1-A, and R ²¹ each independently represents a hydrogen atom, an alkyl group, or an aryl group. and R ²² represents an aryl group, an alkenyl group, an alkoxy group or an onium group.

When L is -NR ¹⁰ - in Formula 1 or Formula 1-A, R ¹ bonded to N is preferably a group represented by the following formula (3-1).

In formula (3-1), ● represents a bonding site with the nitrogen atom contained in L in formula 1 or formula 1-A, and X ¹ and X ² each independently represent an oxygen atom or a sulfur atom. , Y represents a group represented by the above formula (2-1).

In the above formula (2-1), regarding the alkyl group, aryl group, alkenyl group, alkoxy group, and onium group represented by R ²¹ and R ²² , in the above formulas (1-1) to (1-7), The descriptions regarding the alkyl group, aryl group, alkenyl group, alkoxy group, and onium group described above can be cited.

In formula 1 or formula 1-A, it is preferable that L represents a sulfur atom or -NR ¹⁰ - and R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group from the viewpoint of improving printing durability.

R ₁ in the above formulas 1 and 1-A is preferably a group represented by the following formula 2.
Furthermore, the group represented by the above formula 2 is preferably a group in which the R ^Z --O bond in formula 2 is cleaved upon exposure to infrared rays.

In formula 2, R ^Z represents an alkyl group, and the wavy line portion represents a bonding site with the group represented by L in formula 1 or formula 1-A.
The alkyl group represented by R ^Z is the same as the preferred embodiments of the alkyl group in R ² to R ⁹ and R ⁰ described above.
From the viewpoint of color development and UV printing durability of the resulting lithographic printing plate, the alkyl group is preferably a secondary alkyl group or a tertiary alkyl group, and is a tertiary alkyl group. is preferred.
In addition, from the viewpoint of color development and UV printing durability of the resulting lithographic printing plate, the alkyl group is preferably an alkyl group having 1 to 8 carbon atoms, and a branched alkyl group having 3 to 10 carbon atoms. It is more preferably an alkyl group, even more preferably a branched alkyl group having 3 to 6 carbon atoms, particularly preferably an isopropyl group or a tert-butyl group, and most preferably a t-butyl group.

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 L in Formula 1 or Formula 1-A.

Specific examples of infrared absorbers that decompose upon exposure to infrared rays are listed below, but the present disclosure is not limited thereto.

Furthermore, as the infrared absorber that decomposes upon infrared exposure, those described in Japanese Patent Application Publication No. 2008-544322 or International Publication No. 2016/027886 can be suitably used.

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 in the image recording layer is preferably 0.1% by mass to 10.0% by mass, more preferably 0.5% by mass to 5.0% by mass, based on the total mass of the image recording layer. preferable.

[Relationship between electron-donating polymerization initiator, electron-accepting polymerization initiator, and infrared absorber]
The image recording layer in the present disclosure includes the electron-donating polymerization initiator, the electron-accepting polymerization initiator, and the infrared absorber, and the electron-donating polymerization initiator has a HOMO of −6.0 eV or more. It is preferable that the electron-accepting polymerization initiator has a LUMO of −3.0 eV or less.
More preferable embodiments of the HOMO of the electron-donating polymerization initiator and the LUMO of the electron-accepting polymerization initiator are as described above.
In the image recording layer of the present disclosure, the electron-donating polymerization initiator, the infrared absorber, and the electron-accepting polymerization initiator transfer energy as shown in the chemical formula below, for example. Guessed.
Therefore, if the HOMO of the electron-donating polymerization initiator is -6.0 eV or more, and the LUMO of the electron-accepting polymerization initiator is -3.0 eV or less, the efficiency of radical generation is improved. It is thought that it tends to have better chemical resistance and printing durability.

From the viewpoint of printing durability and chemical resistance, the difference between the HOMO of the electron-donating polymerization initiator and the HOMO of the infrared absorber is preferably 1.00 eV to -0.200 eV, and 0.700 eV. More preferably, it is between -0.100eV and -0.100eV. Note that a negative value means that the HOMO of the electron-donating polymerization initiator is higher than the HOMO of the infrared absorber.
Further, from the viewpoint of printing durability and chemical resistance, the difference between the LUMO of the infrared absorber and the LUMO of the electron-accepting polymerization initiator is preferably 1.00 eV to -0.200 eV, and 0. More preferably, it is between .700eV and -0.100eV. Note that a negative value means that the LUMO of the infrared absorber is higher than the LUMO of the electron-accepting polymerization initiator.

[Polymer particles]
The image recording layer preferably contains polymer particles.
The polymer particles may be selected from the group consisting of thermoplastic polymer particles, thermoreactive polymer particles, polymer particles having a polymerizable group, microcapsules encapsulating a hydrophobic compound, and microgels (crosslinked polymer particles). preferable. Among these, polymer particles or microgels having polymerizable groups are preferred. In particularly preferred embodiments, the polymer particles contain at least one ethylenically unsaturated polymerizable 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.
Moreover, it is preferable that the polymer particles are thermoplastic polymer particles.

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 polymers constituting the 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. Preferred examples include polystyrene, a copolymer containing styrene and acrylonitrile, or polymethyl methacrylate. The average particle size of the thermoplastic polymer particles is preferably 0.01 μm to 3.0 μm.

Examples of the heat-reactive polymer particles include polymer particles having a heat-reactive group. The heat-reactive polymer 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 An isocyanate group or a block thereof, an epoxy group, a vinyloxy group, a functional group having an active hydrogen atom that is a reaction partner of these groups (e.g., an amino group, a hydroxy group, a carboxy group, etc.), a carboxy group that performs a condensation reaction, Preferred examples include a hydroxy group or amino group as a reaction partner, an acid anhydride that performs a ring-opening addition reaction, and an amino group or hydroxy group as a reaction partner.

Examples of microcapsules include those in which at least a portion of the constituent components of the image recording layer are encapsulated in microcapsules, as described in JP-A-2001-277740 and JP-A-2001-277742. The constituent components of the image recording layer can also be contained outside the microcapsules. A preferred embodiment of the image recording layer containing microcapsules is a structure in which hydrophobic constituents are encapsulated in the microcapsules and hydrophilic constituents are contained outside the microcapsules.

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, reactive microgels having radically polymerizable groups on their surfaces are preferred from the viewpoint of image forming sensitivity and printing durability.

Known methods can be applied to microencapsulate or microgel the constituent components of the image recording layer.

In addition, from the viewpoints of printing durability, stain resistance, and storage stability, as the polymer particles, a polyvalent isocyanate compound that is an adduct of a polyphenol compound having two or more hydroxy groups in the molecule and isophorone diisocyanate is used. , and those obtained by the reaction of 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 containing the active hydrogen-containing compound is preferably a polyol compound or a polyamine compound, more preferably a polyol compound, and further includes at least one compound selected from the group consisting of propylene glycol, glycerin, and trimethylolpropane. preferable.
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, JP-A-2012 Preferred examples include the polymer particles described in paragraphs 0032 to 0095 of Publication No. 206495.

Furthermore, from the viewpoint of printing durability and solvent resistance, the polymer particles have a hydrophobic main chain, i) a structural unit having a pendant cyano group directly bonded to the hydrophobic main chain, and ii) a structural unit having a pendant group containing a hydrophilic polyalkylene oxide segment.
The hydrophobic main chain is preferably an acrylic resin chain.
Preferred examples of the pendant cyano group include -[CH ₂ CH(C≡N)-] or -[CH ₂ C(CH ₃ )(C≡N)-].
Further, the structural unit having the pendant cyano group can be easily derived from an ethylenically unsaturated monomer, such as acrylonitrile or methacrylonitrile, or a combination thereof.
Furthermore, the alkylene oxide in the hydrophilic polyalkylene oxide segment is preferably ethylene oxide or propylene oxide, and more preferably ethylene oxide.
The number of repeats of the alkylene oxide structure in the hydrophilic polyalkylene oxide segment is preferably 10 to 100, more preferably 25 to 75, and even more preferably 40 to 50.
Both a structural unit having a hydrophobic main chain, i) having a pendant cyano group directly bonded to the hydrophobic main chain, and ii) a structural unit having a pendant group containing a hydrophilic polyalkylene oxide segment. Preferred examples of the resin particles containing the above include those described in paragraphs 0039 to 0068 of Japanese Patent Publication No. 2008-503365.

The average particle diameter of the polymer 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 primary particle size of each of the particles in the present disclosure can be measured by a light scattering method, or by taking an electron microscope photo of the particles, measuring the particle size of 5,000 particles in total on the photo, and determining the average primary particle size of each particle. The value shall be calculated. For non-spherical particles, the particle size is defined as the particle size value of a spherical particle having the same particle area as the particle area on the photograph.
Further, the average particle size in the present disclosure is a volume average particle size unless otherwise specified.
The content of polymer particles is preferably 5% by mass to 90% by mass based on the total mass of the image recording layer.

[Acid color former]
The image recording layer used in the present disclosure preferably contains an acid color former.
The "acid color former" used in the present disclosure means a compound that has the property of developing color when heated in a state in which it accepts an electron-accepting compound (for example, a proton 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 such acid color formers include 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide (referred to as "crystal violet lactone"), 3,3-bis(4-dimethylaminophthalide), dimethylaminophenyl) phthalide, 3-(4-dimethylaminophenyl)-3-(4-diethylamino-2-methylphenyl)-6-dimethylaminophthalide, 3-(4-dimethylaminophenyl)-3-(1 ,2-dimethylindol-3-yl)phthalide, 3-(4-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 3,3-bis(1,2-dimethylindole-3) -yl)-5-dimethylaminophthalide, 3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl) )-6-dimethylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-(4-dimethylaminophenyl)-3-(1-methylpyrrole- 3-yl)-6-dimethylaminophthalide,

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

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

3,6-dimethoxyfluoran, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluoran, 3 -diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-N-cyclohexyl-Nn-butylamino-7-methylfluorane, 3-diethylamino-7- Dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-di-n-hexylaminofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-( 2'-fluorophenylamino)fluoran, 3-diethylamino-7-(2'-chlorophenylamino)fluoran, 3-diethylamino-7-(3'-chlorophenylamino)fluoran, 3-diethylamino-7-(2',3 '-dichlorophenylamino)fluoran, 3-diethylamino-7-(3'-trifluoromethylphenylamino)fluoran, 3-di-n-butylamino-7-(2'-fluorophenylamino)fluoran, 3-di- n-butylamino-7-(2'-chlorophenylamino)fluoran, 3-N-isopentyl-N-ethylamino-7-(2'-chlorophenylamino)fluoran,

3-Nn-hexyl-N-ethylamino-7-(2'-chlorophenylamino)fluoran, 3-diethylamino-6-chloro-7-anilinofluorane, 3-di-n-butylamino-6- Chloro-7-anilinofluorane, 3-diethylamino-6-methoxy-7-anilinofluorane, 3-di-n-butylamino-6-ethoxy-7-anilinofluorane, 3-pyrrolidino-6- Methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-morpholino-6-methyl-7-anilinofluorane, 3-dimethylamino-6-methyl-7- Anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di-n-butylamino-6-methyl-7-anilinofluorane, 3-di-n-pentylamino-6 -Methyl-7-anilinofluorane, 3-N-ethyl-N-methylamino-6-methyl-7-anilinofluorane, 3-Nn-propyl-N-methylamino-6-methyl-7 -anilinofluorane, 3-Nn-propyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-Nn-butyl-N-methylamino-6-methyl-7-ani Linofluorane, 3-N-n-butyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-N-isobutyl-N-methylamino-6-methyl-7-anilinofluorane, 3-N-isobutyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-N-isopentyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-Nn- Hexyl-N-methylamino-6-methyl-7-anilinofluorane, 3-N-cyclohexyl-N-ethylamino-6-methyl-7-anilinofluorane, 3-N-cyclohexyl-Nn- Propylamino-6-methyl-7-anilinofluorane, 3-N-cyclohexyl-Nn-butylamino-6-methyl-7-anilinofluorane, 3-N-cyclohexyl-Nn-hexylamino -6-methyl-7-anilinofluorane, 3-N-cyclohexyl-Nn-octylamino-6-methyl-7-anilinofluorane,

3-N-(2'-methoxyethyl)-N-methylamino-6-methyl-7-anilinofluorane, 3-N-(2'-methoxyethyl)-N-ethylamino-6-methyl-7 -anilinofluorane, 3-N-(2'-methoxyethyl)-N-isobutylamino-6-methyl-7-anilinofluorane, 3-N-(2'-ethoxyethyl)-N-methylamino -6-Methyl-7-anilinofluorane, 3-N-(2'-ethoxyethyl)-N-ethylamino-6-methyl-7-anilinofluorane, 3-N-(3'-methoxypropyl )-N-methylamino-6-methyl-7-anilinofluorane, 3-N-(3'-methoxypropyl)-N-ethylamino-6-methyl-7-anilinofluorane, 3-N- (3'-ethoxypropyl)-N-methylamino-6-methyl-7-anilinofluorane, 3-N-(3'-ethoxypropyl)-N-ethylamino-6-methyl-7-anilinofluoran Oran, 3-N-(2'-tetrahydrofurfuryl)-N-ethylamino-6-methyl-7-anilinofluorane, 3-N-(4'-methylphenyl)-N-ethylamino-6- Methyl-7-anilinofluorane, 3-diethylamino-6-ethyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(3'-methylphenylamino)fluoran, 3-diethylamino-6- Methyl-7-(2',6'-dimethylphenylamino)fluoran, 3-di-n-butylamino-6-methyl-7-(2',6'-dimethylphenylamino)fluoran, 3-di-n -Butylamino-7-(2',6'-dimethylphenylamino)fluoran, 2,2-bis[4'-(3-N-cyclohexyl-N-methylamino-6-methylfluoran)-7-yl Aminophenyl]propane, 3-[4'-(4-phenylaminophenyl)aminophenyl]amino-6-methyl-7-chlorofluorane, 3-[4'-(dimethylaminophenyl)]amino-5,7 -Fluoranes such as dimethylfluorane,

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

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

Among these, the acid color forming agent used in the present disclosure is preferably at least one compound selected from the group consisting of spiropyran compounds, spirooxazine compounds, spirolactone compounds, and spirolactam compounds from the viewpoint of color forming properties. preferable.
The hue of the dye after coloring is preferably green, blue, or black from the viewpoint of visibility.

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.

These acid coloring agents may be used alone or in combination of two or more components.
The content of the acid 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.

[Binder polymer other than specific binder polymer]
The image recording layer may contain a binder polymer other than the specific binder polymer (hereinafter also referred to as "other binder polymer").
The above-mentioned specific binder polymer and the polymer corresponding to the above-mentioned polymer particles do not correspond to the above-mentioned other binder polymers. That is, the other binder polymer is a non-particle-shaped polymer that does not have at least one selected from the group consisting of a structural unit formed by a styrene compound and a structural unit formed by an acrylonitrile compound.
As other binder polymers, (meth)acrylic resin, polyvinyl acetal resin, or polyurethane resin is preferable.

Among these, known binder polymers used in image recording layers of lithographic printing plate precursors can be suitably used as the other binder polymers. As an example, a binder polymer used in an on-press development type lithographic printing plate precursor (hereinafter also referred to as a binder polymer for on-press development) will be described in detail.
As the binder polymer for on-press development, a binder polymer having an alkylene oxide chain is preferable. The binder polymer having an alkylene oxide chain may have a poly(alkylene oxide) moiety in the main chain or in the side chain. Further, a graft polymer having poly(alkylene oxide) in a side chain or a block copolymer of a block composed of poly(alkylene oxide)-containing repeating units and a block composed of (alkylene oxide)-free repeating units may be used.
When the main chain has a poly(alkylene oxide) moiety, polyurethane resin is preferred. Main chain polymers with poly(alkylene oxide) moieties in their side chains include (meth)acrylic resins, polyvinyl acetal resins, polyurethane resins, polyurea resins, polyimide resins, polyamide resins, epoxy resins, polystyrene resins, and novolak types. Examples include phenol resin, polyester resin, synthetic rubber, and natural rubber, with (meth)acrylic resin being particularly preferred.

In addition, another preferable example of the binder polymer is a polyfunctional thiol having 6 or more functionalities and 10 or less functionalities as a core, and a polymer chain bonded to this core by a sulfide bond, and the polymer chain has a polymerizable group. (hereinafter also referred to as star-shaped polymer compounds). As the star-shaped polymer compound, for example, a compound described in JP-A No. 2012-148555 can be preferably used.

The star-shaped polymer compound has a polymerizable group such as an ethylenically unsaturated bond in the main chain or a side chain, preferably a side chain, to improve the film strength in the image area as described in JP-A No. 2008-195018. Examples include those that have a chain. The polymerizable group forms crosslinks between polymer molecules, promoting curing.
The polymerizable group is preferably an ethylenically unsaturated group such as a (meth)acrylic group, a vinyl group, an allyl group, a vinylphenyl group (styryl group), an epoxy group, etc. A group (styryl group) is more preferable from the viewpoint of polymerization reactivity, and a (meth)acrylic group is particularly preferable. These groups can be introduced into the polymer by polymer reaction or copolymerization. For example, a reaction between a polymer having a carboxyl group in its side chain and glycidyl methacrylate, or a reaction between a polymer having an epoxy group and a carboxylic acid containing an ethylenically unsaturated group such as methacrylic acid can be used. These groups may be used in combination.

The weight average molecular weight (Mw) of the other binder polymer is preferably 2,000 or more, more preferably 5,000 or more, and 10,000 to 300, as a polystyrene equivalent value determined by GPC method. More preferably, it is 000.

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

In the image recording layer used in the present disclosure, one type of other binder polymer may be used alone, or two or more types may be used in combination.
Other binder polymers can be contained in any amount in the image recording layer, but the content of the binder polymer is preferably 1% by mass to 90% by mass based on the total mass of the image recording layer. It is preferably 5% by mass to 80% by mass.
Further, when the image recording layer in the present disclosure includes another binder polymer, the content of the other binder polymer with respect to the total mass of the above-mentioned specific binder polymer and other binder polymer is more than 0% by mass and not more than 99% by mass. It is preferably 20% by mass to 95% by mass, and even more preferably 40% to 90% by mass.

[Chain transfer agent]
The image recording layer used in this disclosure may contain a chain transfer agent. Chain transfer agents contribute to improving the printing durability of lithographic printing plates.
As a chain transfer agent, a thiol compound is preferable, a thiol compound having 7 or more carbon atoms is more preferable from the viewpoint of boiling point (difficulty in volatilization), and a compound having a mercapto group on an aromatic ring (aromatic thiol compound) is even more preferable. . The thiol compound is preferably a monofunctional thiol compound.

Specific examples of the chain transfer agent include the following compounds.

Only one type of chain transfer agent may be added, or two or more types may be used in combination.
The content of the chain transfer agent is preferably 0.01% to 50% by weight, more preferably 0.05% to 40% by weight, and 0.1% to 30% by weight based on the total weight of the image recording layer. % is more preferable.

[Sensitizing agent]
The image recording layer may contain a fat-sensitizing agent such as a phosphonium compound, a nitrogen-containing low-molecular compound, or an ammonium group-containing polymer in order to improve ink adhesion. In particular, when the overcoat layer contains an inorganic layered compound, these compounds function as a surface coating agent for the inorganic layered compound, and can suppress a decrease in ink receptivity during printing due to the inorganic layered compound.
As the sensitizing agent, it is preferable to use a phosphonium compound, a nitrogen-containing low-molecular compound, and an ammonium group-containing polymer in combination, and it is preferable to use a phosphonium compound, a quaternary ammonium salt, and an ammonium group-containing polymer in combination. is more preferable.

-Phosphonium compounds-
Examples of the phosphonium compound include those described in JP-A No. 2006-297907 and JP-A No. 2007-50660. Specific examples include tetrabutylphosphonium iodide, butyltriphenylphosphonium bromide, tetraphenylphosphonium bromide, 1,4-bis(triphenylphosphonio)butane di(hexafluorophosphate), and 1,7-bis(triphenylphosphonium bromide). Examples include phenylphosphonio)heptane sulfate, 1,9-bis(triphenylphosphonio)nonanenaphthalene-2,7-disulfonate, and the like.

-Nitrogen-containing low molecular weight compounds-
Examples of nitrogen-containing low molecular weight compounds include amine salts and quaternary ammonium salts. Also included are imidazolinium salts, benzimidazolinium salts, pyridinium salts, and quinolinium salts. Among these, quaternary ammonium salts and pyridinium salts are preferred. Specific examples include tetramethylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, dodecyltrimethylammonium p-toluenesulfonate, benzyltriethylammonium hexafluorophosphate, and benzyldimethyloctylammonium hexafluorophosphate. Phate, benzyldimethyldodecylammonium hexafluorophosphate, compounds described in paragraphs 0021 to 0037 of JP-A No. 2008-284858, compounds described in paragraphs 0030 to 0057 of JP-A No. 2009-90645, and the like.

-Ammonium group-containing polymer-
The ammonium group-containing polymer only needs to have an ammonium group in its structure, and a polymer containing 5 mol% to 80 mol% of (meth)acrylate having an ammonium group in a side chain as a copolymerization component is preferable. Specific examples include polymers described in paragraphs 0089 to 0105 of JP-A No. 2009-208458.

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

Specific examples of ammonium group-containing polymers are shown below.
(1) 2-(trimethylammonio)ethyl methacrylate = p-toluenesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 10/90, Mw 45,000)
(2) 2-(trimethylammonio)ethyl methacrylate = hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 20/80, Mw 60,000)
(3) 2-(ethyldimethylammonio)ethyl methacrylate = p-toluenesulfonate/hexyl methacrylate copolymer (mole ratio 30/70, Mw 45,000)
(4) 2-(trimethylammonio)ethyl methacrylate = hexafluorophosphate/2-ethylhexyl methacrylate copolymer (molar ratio 20/80, Mw 60,000)
(5) 2-(trimethylammonio)ethyl methacrylate = methyl sulfate/hexyl methacrylate copolymer (molar ratio 40/60, Mw 70,000)
(6) 2-(Butyldimethylammonio)ethyl methacrylate = hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (mole ratio 25/75, Mw 65,000)
(7) 2-(Butyldimethylammonio)ethyl acrylate = hexafluorophosphate/3,6-dioxaheptyl methacrylate copolymer (mole ratio 20/80, Mw 65,000)
(8) 2-(Butyldimethylammonio)ethyl methacrylate = 13-ethyl-5,8,11-trioxa-1-heptadecanesulfonate/3,6-dioxaheptyl methacrylate copolymer (molar ratio 20/80 , Mw75,000)

The content of the oil-sensitizing agent is preferably 1% by mass to 40.0% by mass, more preferably 2% by mass to 25.0% by mass, and 3% by mass to 20% by mass, based on the total mass of the image recording layer. % is more preferable.

[Development accelerator]
The image recording layer used in this disclosure may include a development accelerator.
As the development accelerator, a hydrophilic high molecular compound or a hydrophilic low molecular compound is preferable.
In the present disclosure, a hydrophilic high molecular compound refers to a compound with a molecular weight (weight average molecular weight if it has a molecular weight distribution) of 3,000 or more, and a hydrophilic low molecular compound refers to a compound with a molecular weight (weight average molecular weight if it has a molecular weight distribution) of 3,000 or more. refers to a compound with a molecular weight) of less than 3,000.

-Hydrophilic polymer compound-
Examples of the hydrophilic polymer compound include cellulose compounds, polyvinyl alcohol, and the like, with cellulose compounds being preferred.
Examples of the cellulose compound include cellulose or a compound in which at least a portion of cellulose is modified (modified cellulose compound), and modified cellulose compounds are preferred.
Preferred examples of the modified cellulose compound include compounds in which at least a portion of the hydroxyl groups of cellulose are substituted with at least one type selected from the group consisting of an alkyl group and a hydroxyalkyl group.
As the modified cellulose compound, an alkylcellulose compound or a hydroxyalkylcellulose compound is preferable, and a hydroxyalkylcellulose compound is more preferable.
As the alkyl cellulose compound, methyl cellulose is preferably mentioned.
As the hydroxyalkyl cellulose compound, hydroxypropyl cellulose is preferably mentioned.

The molecular weight of the hydrophilic polymer compound (weight average molecular weight if it has a molecular weight distribution) is preferably from 3,000 to 300,000, more preferably from 10,000 to 150,000.

-Hydrophilic low molecular compound-
Examples of hydrophilic low-molecular compounds include glycol compounds, polyol compounds, organic amine compounds, organic sulfonic acid compounds, organic sulfamine compounds, organic sulfuric acid compounds, organic phosphonic acid compounds, organic carboxylic acid compounds, betaine compounds, etc. , organic sulfonic acid compounds or betaine compounds are preferred.

Examples of the glycol compound include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol, and ether or ester derivatives of these compounds.
Examples of the polyol compound include glycerin, pentaerythritol, tris(2-hydroxyethyl)isocyanurate, and the like.
Examples of the organic amine compound include triethanolamine, diethanolamine, monoethanolamine, and salts thereof.
Examples of the organic sulfonic acid compound include alkylsulfonic acid, toluenesulfonic acid, benzenesulfonic acid, etc., and salts thereof, and preferably an alkylsulfonic acid having an alkyl group having 8 to 20 carbon atoms.
Examples of organic sulfamine compounds include alkylsulfamic acids and salts thereof.
Examples of the organic sulfuric acid compound include alkyl sulfuric acid, alkyl ether sulfuric acid, and salts thereof.
Examples of the organic phosphonic acid compound include phenylphosphonic acid and salts thereof.
Examples of the organic carboxylic acid compound include tartaric acid, oxalic acid, citric acid, malic acid, lactic acid, gluconic acid, and salts thereof.
Examples of betaine compounds include phosphobetaine compounds, sulfobetaine compounds, carboxybetaine compounds, and trimethylglycine is preferred.

The molecular weight of the hydrophilic low molecular weight compound (weight average molecular weight if it has a molecular weight distribution) is preferably 50 or more and less than 3,000, more preferably 100 to 1,000.

-Content-
The content of the development accelerator relative to the total mass of the image recording layer is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 15% by mass or less, and 1% by mass or more and 10% by mass or less. It is more preferably less than % by mass.

[Other ingredients]
The image recording layer may contain other components such as surfactants, polymerization inhibitors, higher fatty acid derivatives, plasticizers, inorganic particles, and inorganic layered compounds. Specifically, the description in paragraphs 0114 to 0159 of JP-A-2008-284817 can be referred to.

[Formation of image recording layer]
The image recording layer in the lithographic printing plate precursor according to the present disclosure is coated by dispersing or dissolving each of 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 liquid, applying the coating liquid onto a support by a known method such as bar coater coating, and drying. The coating amount (solid content) of the image recording layer after coating and drying varies depending on the application, but is preferably 0.3 g/m ² to 3.0 g/m ² . Within this range, good sensitivity and good film characteristics of the image recording layer can be obtained.
As the solvent, 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.
In the present disclosure, the film thickness of each layer in a lithographic printing plate precursor can be determined by preparing a section cut in a direction perpendicular to the surface of the lithographic printing plate precursor, and observing the cross section of the section using a scanning microscope (SEM). Confirmed by.

<Overcoat layer>
The lithographic printing plate precursor according to the present disclosure has an overcoat layer (sometimes referred to as a "protective layer") on the surface of the image recording layer on the side opposite to the support side.
The thickness of the overcoat layer is greater than the thickness of the image recording layer.
The overcoat layer has the function of suppressing image formation inhibiting reactions by blocking oxygen, as well as the function of preventing scratches in the image recording layer and preventing ablation during high-intensity laser exposure.

Overcoat layers having such characteristics are 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 overcoat 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. However, from the viewpoint of on-press developability, it is preferable to include a water-soluble polymer.
In the present disclosure, a water-soluble polymer refers to a solution in which 1 g or more is dissolved in 100 g of pure water at 70°C, and a solution in which 1 g of polymer is dissolved in 100 g of pure water at 70°C is cooled to 25°C. refers to polymers that do not precipitate even when
Examples of the water-soluble polymer used in the overcoat 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.

Among the above-mentioned water-soluble polymers, it is preferable to include polyvinyl alcohol, and it is more preferable to include polyvinyl alcohol having a saponification degree of 50% or more.
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.
Moreover, as one embodiment of the overcoat layer, an embodiment containing polyvinyl alcohol and polyethylene glycol is also preferably mentioned.

When the overcoat layer in the present disclosure includes a water-soluble polymer, the content of the water-soluble polymer with respect to the total mass of the overcoat layer is preferably 1% by mass to 99% by mass, and preferably 3% by mass to 97% by mass. It is more preferable that the amount is 5% by mass to 95% by mass.

The overcoat layer may contain 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 overcoat 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.

The overcoat layer may contain known additives such as a plasticizer for imparting flexibility, a surfactant for improving coating properties, and inorganic particles for controlling surface slipperiness. Further, the overcoat layer may contain the oil-sensitizing agent described in the image recording layer.

The overcoat layer is applied by a known method. The coating amount (solid content) of the overcoat layer is preferably 0.01g/m ² to 10g/m ² , more preferably 0.02g/m ² to 3g/m ² , and 0.02g/m ² to 1g/m 2 . m ² is particularly preferred.
The thickness of the overcoat layer in the lithographic printing plate precursor according to the present disclosure is preferably 0.1 μm to 5.0 μm, more preferably 0.3 μm to 4.0 μm.
The thickness of the overcoat layer in the lithographic printing plate precursor according to the present disclosure is preferably 1.1 to 5.0 times, and 1.5 to 3.0 times, the thickness of the image recording layer. More preferably, it is twice as large.

<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. Furthermore, in the case of infrared laser exposure, the undercoat layer functions as a heat insulating layer, thereby preventing heat generated by exposure from diffusing into the support and reducing sensitivity.

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 has 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.

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

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

(Method for preparing a 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.
The method for producing a lithographic printing plate according to the present disclosure includes a step of imagewise exposing the on-press development type lithographic printing plate precursor according to the present disclosure (hereinafter also referred to as "exposure step"), and printing on a printing press. It is preferable to include a step of removing the image recording layer in the non-image area by supplying at least one selected from the group consisting of ink and dampening water (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 on-press development type lithographic printing plate precursor according to the present disclosure (exposure step), and at least one selected from the group consisting of printing ink and fountain solution. The process includes the steps of supplying a lithographic printing plate by removing the image recording layer in the non-image area on a printing machine (on-press development process), and printing with the obtained lithographic printing plate (printing process). It is preferable.
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 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 with a wavelength 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 in the case of a light source with a wavelength of 750 nm to 1,400 nm, the above-mentioned ones are preferably used. used. A semiconductor laser is suitable as a light source with a wavelength 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 17, Comparative Examples 1 to 4)
<Preparation of support>
In order to remove rolling oil from the surface of a 0.3 mm thick aluminum plate (material JIS A 1050), it was degreased for 30 seconds at 50°C using a 10% by mass aqueous sodium aluminate solution, and then the hair diameter was reduced to 0. The surface of the aluminum plate was grained using three 3 mm bunched nylon brushes and a pumice-water suspension (specific gravity 1.1 g/cm ³ ) with a median diameter of 25 μm and thoroughly washed with water. Etching was performed by immersing the aluminum plate in a 25% by mass aqueous sodium hydroxide solution at 45°C for 9 seconds, washing with water, and then immersing it in a 20% by mass nitric acid aqueous solution at 60°C for 20 seconds and washing with water. The amount of etching on the grained surface was approximately 3 g/m ² .

Next, electrochemical surface roughening treatment was performed continuously using an alternating current voltage of 60 Hz. The electrolytic solution was a 1% by mass aqueous solution of nitric acid (containing 0.5% by mass of aluminum ions), and the liquid temperature was 50°C. The AC power supply waveform has a time TP of 0.8 ms for the current value to reach the peak from zero, a duty ratio of 1:1, a trapezoidal rectangular wave AC, and electrochemical surface roughening treatment with a carbon electrode as the counter electrode. I did it. Ferrite was used for the auxiliary anode. The current density was 30 A/dm ² at the peak current value, and 5% of the current flowing from the power source was shunted to the auxiliary anode. The amount of electricity in nitric acid electrolysis was 175 C/dm ² when the aluminum plate was the anode. After that, it was washed with water using a spray.

Next, nitric acid electrolysis was performed using a 0.5% by mass aqueous solution of hydrochloric acid (containing 0.5% by mass of aluminum ions) and an electrolytic solution at a temperature of 50°C, with an electrical charge of 50C/ ^dm2 when the aluminum plate was the anode. Electrochemical surface roughening treatment was performed in the same manner as above, followed by washing with water by spraying.
Next, a DC anodic oxide film of 2.5 g/m ² was formed on the aluminum plate at a current density of 15 A/dm ² using a 15 mass % sulfuric acid aqueous solution (containing 0.5 mass % aluminum ions) as an electrolyte, and then washed with water. , and dried to prepare a support. The average pore diameter in the surface layer of the anodic oxide film (surface average pore diameter) was 10 nm.
The pore diameter in the surface layer of the anodic oxide film was measured using an ultra-high resolution SEM (Scanning Electron Microscope, S-900 manufactured by Hitachi, Ltd.) at a relatively low accelerating voltage of 12 V to impart conductivity. The surface was observed at a magnification of 150,000 times without any vapor deposition treatment, 50 pores were randomly selected, and the average value was determined. The standard deviation was less than ±10% of the average value.

<Formation of lithographic printing plate precursor>
On the above support, an undercoat liquid (1) having the following composition was applied to a dry coating amount of 20 mg/m ² and dried in an oven at 100° C. for 30 seconds to produce a support having an undercoat layer.
On the undercoat layer, the following image recording layer coating liquid (1) was coated with a bar and dried in an oven at 100°C for 60 seconds to form an image recording layer with a dry coating weight of 0.60 g/m ² (film thickness = approximately 0.60 μm). was formed to obtain a lithographic printing plate precursor.
Furthermore, after that, an overcoat layer coating liquid (1) having the following composition was coated on the image recording layer and dried in an oven at 100°C for 60 seconds to obtain a dry coating amount of 1.0 g/m ² (film thickness = approximately 1.0 μm). ) was formed to form an overcoat layer (including a hydrophobic portion) to obtain a lithographic printing plate precursor.

[Undercoat liquid (1)]
・The following undercoat compound 1: 0.18 parts ・Methanol: 55.24 parts ・Distilled water: 6.15 parts

-Synthesis of undercoat compound 1-
<<Purification of monomer M-1>>
420 parts of Light Ester P-1M (2-methacryloyloxyethyl acid phosphate, manufactured by Kyoeisha Chemical Co., Ltd.), 1,050 parts of diethylene glycol dibutyl ether, and 1,050 parts of distilled water were added to a separating funnel, stirred vigorously, and then allowed to stand. I placed it. After discarding the upper layer, 1,050 parts of diethylene glycol dibutyl ether was added, stirred vigorously, and then allowed to stand still. The upper layer was discarded to obtain 1,300 parts of an aqueous solution of monomer M-1 (10.5% by mass in terms of solid content).

<<Synthesis of undercoat compound 1>>
53.73 parts of distilled water and 3.66 parts of monomer M-2 shown below were added to a three-necked flask, and the temperature was raised to 55° C. under a nitrogen atmosphere. Next, dropping solution 1 shown below was added dropwise over 2 hours, and after stirring for 30 minutes, 0.386 parts of VA-046B (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the temperature was raised to 80 ° C. Stirred for 1.5 hours. After returning the reaction solution to room temperature (25°C), a 30% by mass aqueous sodium hydroxide solution was added to adjust the pH to 8.0, and then 4-hydroxy-2,2,6,6-tetramethylpiperidine-1 -0.005 part of -oxyl (4-OH-TEMPO) was added. Through the above operations, 180 parts of an aqueous solution of undercoat compound 1 was obtained. The weight average molecular weight (Mw) as a polyethylene glycol equivalent value determined by gel permeation chromatography (GPC) was 170,000.

<<Dropped liquid 1>>
- Monomer M-1 aqueous solution: 87.59 parts - Monomer M-2: 14.63 parts - VA-046B (2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfide) Phate dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.): 0.386 parts, distilled water: 20.95 parts

<Image recording layer coating liquid (1)>
- Infrared absorber listed in Table 1 (compound with the following structure): 0.030 part - Di-p-tolyliodonium PF ₆ salt (manufactured by Aldrich): 0.030 parts if "present" is written in Table 1. 032 parts, 0 parts if "None" is written ・NK Ester A-9300 (manufactured by Shin Nakamura Chemical Industries, Ltd.): 0.100 parts ・A-DPH (manufactured by Shin Nakamura Chemical Industries, Ltd.): 0 .100 parts・Specific binder polymer listed in Table 1: 0.825 parts・BYK306 (Byk Chemie): 0.008 parts・1-methoxy-2-propanol: 8.609 parts・Methyl ethyl ketone: 1.091 parts・Electron-donating polymerization initiator listed in Table 1: amount listed in Table 1

<Overcoat layer coating liquid>
・Poval PVA105 (manufactured by Kuraray Co., Ltd., saponification degree of 80% or more): 0.6 parts by mass ・PEG4000 (manufactured by Tokyo Chemical Industry Co., Ltd.): 0.39 parts by mass ・Surfactant (Rapizol A-80, Japan) (manufactured by Yuyu Co., Ltd.): 0.01 parts by mass Water: Amount that makes the total 10 parts by mass

<Evaluation>
[Printing durability]
The lithographic printing plate precursors obtained in each of the Examples and Comparative Examples were processed using a Fujifilm Luxel PLATESETTER T-6000III equipped with an infrared semiconductor laser at an outer drum rotation speed of 1,000 rpm (revolutions per minute) and a laser output of 70. % and a resolution of 2,400 dpi (dots per inch, 1 inch = 2.54 cm). The exposed images included a solid image and a 50% halftone chart of a 20 μm dot FM screen.
The exposed lithographic printing original plate thus obtained was attached to the plate cylinder of a printing machine LITHRONE 26 manufactured by Komori Corporation, without being subjected to any development treatment. After decelerating the water supply roller by 5% relative to the plate cylinder, dampening water of Ecoality-2 (manufactured by Fujifilm Corporation)/tap water = 2/98 (volume ratio) and Space Color Fusion G black ink ( After supplying dampening water and ink and developing on-press using LITHRONE26's standard automatic printing start method, Tokubishi Art (manufactured by DIC Graphics Corporation) was used at a printing speed of 10,000 sheets per hour. 50,000 sheets of paper (manufactured by Mitsubishi Paper Mills, Ltd., ream weight: 76.5 kg) were printed.
As the number of printed sheets increased, the image recording layer gradually wore out and the ink receptivity decreased, resulting in a decrease in ink density on the printing paper. The number of printed copies is the number of printed copies when the value measured by x-lite (manufactured by x-lite) of the halftone dot area ratio of FM screen 3% halftone dots on printed matter is 5% lower than the measured value of the 100th printed page. The printing durability was evaluated as follows.

〔chemical resistance〕
The lithographic printing plate precursors of each Example or Comparative Example were exposed and printed in the same manner as in the above evaluation of printing durability. Chemical resistance was evaluated in the same manner as in the above evaluation of printing durability, except that a step of wiping the plate surface with a cleaner (Multi Cleaner, manufactured by Fuji Film Co., Ltd.) was added every time 5,000 sheets were printed.
Specifically, the ratio of the number of printed sheets when the step of wiping the printing plate was added to the number of printed sheets in the evaluation of printing durability was used as an index value, and the evaluation was performed according to the following evaluation criteria.
It can be said that the larger the above index value is, the smaller the change in printing durability is, even when a step of wiping the plate surface with a cleaner is added, and the better the chemical resistance is.

-Evaluation criteria-
5: The index value is 95% or more and 100% or less 4: The index value is 80% or more and less than 95% 3: The index value is 60% or more and less than 80% 2: The index value is 40% or more and less than 60% 1: The index value is less than 40%

[On-press developability]
The lithographic printing plate precursor obtained in each Example or Comparative Example was processed using a Luxel PLATESETTER T-6000III manufactured by Fujifilm Corporation equipped with an infrared semiconductor laser at an outer drum rotation speed of 1,000 rpm, a laser output of 70%, a resolution of 2, Exposure was performed at 400 dpi. The exposed image included a solid image, a 50% halftone dot chart of a 20 μm dot FM screen, and a non-image area.
The exposed original plate thus obtained was attached to the plate cylinder of a printing machine LITHRONE 26 manufactured by Komori Corporation, without being subjected to any development treatment. Using dampening water of Ecoity-2 (manufactured by Fujifilm Corporation)/tap water = 2/98 (volume ratio) and Space Color Fusion G yellow ink (manufactured by DIC Graphics Corporation), Komori Co., Ltd. After supplying dampening water and ink and performing on-press development using the standard automatic printing start method of LITHRONE 26, a printing press manufactured by Tokubishi Art Co., Ltd. (manufactured by Mitsubishi Paper Mills Co., Ltd.), Amount: 76.5 kg) 500 sheets of paper were printed.
The number of sheets of printing paper required until the on-press development of the unexposed areas of the image recording layer on the printing press was completed and the ink was not transferred to the non-image areas was measured as the on-press developability. It can be said that the smaller the number of sheets, the better the on-press developability.

[Ink receptivity (initial ink receptivity during printing)]
A lithographic printing plate exposed under the same exposure conditions as in the above evaluation of on-press developability (the exposed image included a solid image and a 50% halftone dot chart of a 20 μm dot FM screen) was manufactured by Co., Ltd. It was attached to the plate cylinder of a printing press LITHRONE 26 manufactured by Komori Corporation. Using dampening water of Ecoity-2 (manufactured by Fujifilm Corporation)/tap water = 2/98 (volume ratio) and Values-G (N) black ink (manufactured by DIC Corporation), LITHRONE26's standard automatic Start printing by supplying dampening water and ink using the printing start method, and print on Tokubishi Art (manufactured by Mitsubishi Paper Mills Co., Ltd., ream weight: 76.5 kg) paper at a printing speed of 10,000 sheets per hour. I made 100 copies.
The ink density in the solid image area is measured using a Macbeth densitometer (manufactured by X-rite, EXACT), and the number of sheets of printing paper required to reach a value of 1.0 or more is calculated as the ink receptivity (initial ink adhesion during printing). The meat quality was evaluated according to the following evaluation criteria as an index value. It can be said that the smaller the number of plates, the better the ink receptivity of the lithographic printing plate.

-Evaluation criteria-
1: The index value is 100 or more sheets 2: The index value is 50 sheets or more and less than 100 sheets 3: The index value is 30 sheets or more and less than 50 sheets 4: The index value is 20 sheets or more and less than 30 sheets 5 :The index value is less than 20 sheets.

In Table 1, the description in the "Type" column of the electron-donating polymerization initiator indicates which of the following compounds 1 to 10 was used.
In Table 1, the description in the "Type" column of the infrared absorber indicates which compound from the following infrared absorbers 1 to 5 was used. Note that the units of HOMO and LUMO below are eV.
In Table 1, the description in the "Type" column of the specific binder polymer column indicates which compound from Polymer 1 to Polymer 2 below was used.
Furthermore, in Table 1, Comparative Example 2 is an example in which the dry coating amount of the overcoat layer was changed to 0.1 g/m ² (film thickness = approximately 0.1 μm).
Details of the compounds listed in Table 1 are as follows. Furthermore, in the chemical structural formula below, Me represents a methyl group and Bu represents a butyl group.

[Synthesis of specific binder polymer]
-Synthesis of binder polymer 1-
300 g of methyl ethyl ketone was placed in a three-neck flask and heated to 80° C. under a nitrogen stream. A mixed solution consisting of 50.0 g of Compound 1 below, 50.0 g of Compound 2 below, 0.7 g of AIBN (azobisisobutyronitrile), and 100 g of methyl ethyl ketone was added dropwise to this reaction vessel over 30 minutes. After the dropwise addition was completed, the reaction was continued for an additional 7.5 hours. Thereafter, 0.3 g of AIBN was added, and the reaction was continued for an additional 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature. The composition ratio of the structural unit formed by Compound 1 and the structural unit formed by Compound 2 was 50:50 (mass ratio), and the weight average molecular weight of Binder Polymer 1 was 75,000. Further, the solid content was 20% by mass.

-Synthesis of binder polymer 5-
300 g of methyl ethyl ketone was placed in a three-neck flask and heated to 80° C. under a nitrogen stream. A mixed solution consisting of 50.0 g of Compound 1, 30.0 g of Compound 2, 20.0 g of Compound 3, 0.7 g of AIBN, and 100 g of methyl ethyl ketone was added dropwise to this reaction vessel over 30 minutes. After the dropwise addition was completed, the reaction was continued for an additional 7.5 hours. Thereafter, 0.3 g of AIBN was added, and the reaction was continued for an additional 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature. The composition ratio of the structural unit formed by compound 1, the structural unit formed by compound 2, and the structural unit formed by compound 3 is 50:30:20 (mass ratio), and the weight average of binder polymer 5 The molecular weight was 75,000. Further, the solid content was 20% by mass.

[Specific binder polymer for comparison (polymer 2)]
Polymer 2: Polymethyl methacrylate (20% by mass 1-methoxy-2-propanol (MFG) solution), weight average molecular weight = 75,000

From the results listed in Table 1, the lithographic printing plate precursor according to the example can provide a lithographic printing plate with excellent chemical resistance, printing durability, and ink receptivity, and also has excellent on-press developability. It can be seen that it is excellent in

The disclosure of Japanese Patent Application No. 2018-142865 filed on July 30, 2018 and the disclosure of Japanese Patent Application No. 2018-205750 filed on October 31, 2018 are Incorporated herein by reference.
All documents, patent applications, and technical standards mentioned herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. , herein incorporated by reference.

Claims (22)

It has a support, an image recording layer, and an overcoat layer in this order,
The image recording layer contains a binder polymer that is not in the form of particles and an electron-donating polymerization initiator,
The binder polymer has a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound,
The overcoat layer contains polyvinyl alcohol and polyethylene glycol,
An on-press development type lithographic printing plate precursor, wherein the thickness of the overcoat layer is thicker than the thickness of the image recording layer. 2. The image recording layer further contains a polymerizable compound, and the content of the binder polymer based on the total mass of the polymerizable compound in the image recording layer is more than 0% by mass and 400% by mass or less. On-press development type lithographic printing plate precursor. The on-press development type lithographic printing plate precursor according to claim 1 or 2 , wherein the polyvinyl alcohol contains polyvinyl alcohol having a saponification degree of 50% or more. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 3 , wherein the electron-donating polymerization initiator is a borate compound. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 4 , wherein the electron-donating polymerization initiator is a tetraarylborate compound. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 5 , wherein the electron-donating polymerization initiator is a tetraphenylborate compound. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 6 , wherein the highest occupied orbital of the electron-donating polymerization initiator is −6.0 eV or more. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 7 , wherein the image recording layer further contains an electron-accepting polymerization initiator. The on-press development type lithographic printing plate precursor according to claim 8 , wherein the electron-accepting polymerization initiator is an onium compound. The on-press development type lithographic printing plate precursor according to claim 8 or 9 , wherein the lowest unoccupied orbital of the electron-accepting polymerization initiator is −3.0 eV or less. The on-press development type lithographic printing plate precursor according to any one of claims 8 to 10 , wherein the electron-accepting polymerization initiator and the electron-donating polymerization initiator form a salt. The on-press development type lithographic printing plate precursor according to any one of claims 8 to 11 , wherein the electron-accepting polymerization initiator and the electron-donating polymerization initiator contain an iodonium borate compound. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 12 , wherein the binder polymer further has a structural unit formed of N-vinylpyrrolidone. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 13 , wherein the image recording layer further contains an infrared absorber. The on-press development type lithographic printing plate precursor according to claim 14 , wherein the infrared absorber is an infrared absorber that decomposes upon exposure to infrared light. The on-press development type lithographic printing plate precursor according to claim 14 or 15, wherein the infrared absorbent is an infrared absorbent that decomposes due to heat caused by infrared exposure, electron transfer, or both. The on-press development type lithographic printing plate precursor according to any one of claims 14 to 16 , wherein the infrared absorber is a cyanine dye. It has a support, an image recording layer, and an overcoat layer in this order,
The image recording layer contains an infrared absorber, a binder polymer that is not in particle shape, and an electron-donating polymerization initiator,
The binder polymer has a structural unit formed from an aromatic vinyl compound and a structural unit formed from an acrylonitrile compound,
The thickness of the overcoat layer is thicker than the thickness of the image recording layer,
The infrared absorber is a compound represented by the following formula 1.
On-press development type lithographic printing plate precursor.


In formula 1, R ¹ represents a group whose R ¹ -L bond is cleaved by infrared exposure, and R ₁₁ to R ₁₈ each independently represent a hydrogen atom, a halogen atom, -Ra, -ORb, -SRc, or -NRdRe. and Ra to Re each independently represent a hydrocarbon group, A ₁ , A ₂ and a plurality of R ₁₁ to R ₁₈ may be linked to form a monocyclic or polycyclic ring, and A ₁ and A ₂ each independently represents an oxygen atom, sulfur atom, or nitrogen atom, n ₁₁ and n ₁₂ each independently represent an integer from 0 to 5, provided that the sum of n ₁₁ and n ₁₂ is 2 or more, and n ₁₃ and n ₁₄ each independently represent 0 or 1, L represents an oxygen atom, a sulfur atom, or -NR ¹⁰ -, R ¹⁰ represents a hydrogen atom, an alkyl group, or an aryl group, and Za neutralizes the charge. represents the counterion. The on-press development type lithographic printing plate precursor according to claim 18 , wherein R ¹ in the formula 1 is a group represented by the following formula 2.

In Formula 2, R ^Z represents an alkyl group, and the wavy line portion represents a bonding site with the group represented by L in Formula 1 above. The on-press development type lithographic printing plate precursor according to any one of claims 1 to 19, wherein the binder polymer further has a structural unit represented by the following formula C1.

In formula C1, Ar ^N represents a heterocyclic structure containing a nitrogen atom, and Ar ^N The nitrogen atom inside bonds with the carbon atom indicated by *. Imagewise exposing the on-press development type lithographic printing plate precursor according to any one of claims 1 to 20 ;
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 20 ;
a step of supplying at least one selected from the group consisting of printing ink and dampening water and removing the image recording layer in the non-image area on the printing press to produce a lithographic printing plate;
A lithographic printing method comprising the step of printing with the obtained lithographic printing plate.