JP7606473B2 - On-press development type printing original plate, method for making printing plate, and printing method - Google Patents

Description

The present invention relates to an on-press development type printing original plate, a method for making a printing plate, and a printing method.

Generally, a lithographic printing plate consists of an oleophilic image area that accepts ink during the printing process and a hydrophilic non-image area that accepts dampening water. Lithographic printing utilizes the mutual repulsion properties of water and oil-based ink, making the oleophilic image area of the lithographic printing plate the ink-receptive area and the hydrophilic non-image area the dampening water-receptive area (ink-non-receptive area) to create a difference in ink adhesion on the surface of the lithographic printing plate, and then ink is applied only to the image area, after which the ink is transferred to the printing material such as paper to print.

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

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

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

In an attempt to suppress the occurrence of edge stains, Patent Document 1 discloses a lithographic printing plate precursor having an image recording layer on a support, in which a region of the plate surface on the image recording layer side extending from an edge of the plate surface to 5 mm inward contains a water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20° C. of 10 g/L or more per unit area which is 50 mg/ ^m2 or more higher than the content per unit area of the water-soluble compound in regions other than the above region.
Patent Document 2 discloses an on-press development type lithographic printing plate precursor having an image recording layer on an aluminum support having an anodized film, the edge of the lithographic printing plate precursor having a drooped shape, the image recording layer having support adsorption properties, a molecular weight of 1,000 or less, and containing a compound having no unsaturated double bond group in the molecule, and the content of the compound is substantially the same within the plane of the image recording layer.

International Publication No. 2016/052443 International Publication No. 2019/044700

The above-mentioned Patent Document 1 describes polyols, betaines, organic sulfonates, organic sulfates, organic carboxylic acids or salts thereof, and amino acids as water-soluble compounds having a molecular weight of 60 to 300 and a solubility in water at 20° C. of 10 g/L or more.
The lithographic printing plate precursor described in Patent Document 1 is characterized in that the content of the water-soluble compound in the edge regions is intentionally made higher than in regions other than the edge regions by, for example, applying a coating liquid containing the above-mentioned water-soluble compound only to the edge regions of the lithographic printing plate precursor.
However, it has been found that a lithographic printing plate precursor that intentionally contains a large amount of a water-soluble compound in the edge region has a problem in that image forming properties are reduced in the edge region.

The above-mentioned Patent Document 2 describes an oxoacid as a compound that has support adsorption properties, has a molecular weight of 1,000 or less, and does not have an unsaturated double bond group in the molecule.
Incidentally, on-press development type printing plate masters may be stored for a long period (e.g., 12 months) after production and then used for plate making. In such a case, that is, even after the passage of time, it is desirable to be able to suppress the occurrence of the above-mentioned edge staining.
However, in the on-press development type lithographic printing plate precursor described in Patent Document 2, it has been found that it is difficult to suppress the occurrence of edge stains even after aging.

The problem that the present invention aims to solve is to provide an on-press development type printing original plate that is prevented from edge contamination not only after production but also after aging, a method for making a printing plate using an on-press development type printing original plate, and a printing method using an on-press development type printing original plate.
Furthermore, according to the present invention, it is possible to provide an on-press development type lithographic printing plate precursor in which deterioration of image formability in edge regions is suppressed.

Means for solving the above problems are described below .
[1 ]
An on-press development type printing plate precursor having at least one constituent layer on an aluminum support having an anodized film, the on-press development type printing plate precursor having a drooped edge, the at least one constituent layer containing a hydroxy acid compound having two or more hydroxyl groups, a molecular weight of 60 to 300, and a content of a water-soluble compound having a solubility in water at 20°C of 10 g/L or more being substantially uniform within the plane of the constituent layer,
The on-press development type printing plate precursor has an image recording layer,
The on-press development type printing original plate has a protective layer,
The on-press development type printing plate precursor has a layer containing the hydroxy acid compound as a protective layer.
［ 2 ］
The on-press development type printing plate precursor according to [ 1 ], wherein the on-press development type printing plate precursor has an undercoat layer.
［ ３ ］
The on-press development type printing plate precursor according to [ 1 ] or [2] , wherein the protective layer contains a polyvinyl alcohol resin.
［ 4 ］
The on-press development type printing plate precursor according to any one of [1] to [ 3 ], wherein the image recording layer contains an infrared absorbing agent, a polymerization initiator, a polymerizable compound, and a polymer compound.
［ 5 ］
The on-press development type printing plate precursor according to [ 4 ], wherein the polymer compound is a polymer compound containing a structural unit derived from a styrene compound and/or a structural unit derived from an acrylonitrile compound.
［ ６ ］
The on-press development type printing original plate according to [5], wherein in the polymer compound containing a structural unit derived from a styrene compound and a structural unit derived from an acrylonitrile compound, a compositional ratio of the structural unit derived from a styrene compound to the structural unit derived from an acrylonitrile compound is 4:1 to 1:4.
［ ７ ］
The on-press development type printing plate precursor according to any one of [ 4 ] to [ 6 ], wherein the polymer compound is a polymer particle.
［ 8 ］
The on-press development type printing plate precursor according to [ 7 ], wherein the polymer particles are thermoplastic particles.
［ ９ ］
An on-press development type printing plate precursor having at least one constituent layer on an aluminum support having an anodized film, the on-press development type printing plate precursor having a drooped edge, the at least one constituent layer containing a hydroxy acid compound having two or more hydroxyl groups, a molecular weight of 60 to 300, and a content of a water-soluble compound having a solubility in water at 20°C of 10 g/L or more being substantially uniform within the plane of the constituent layer,
The on-press development type printing plate precursor has a non-photosensitive layer, and all of the constituent layers are non-photosensitive,
The on-press development type printing plate precursor has an undercoat layer.
[ 10 ]
The on-press development type printing plate precursor according to [ 9 ], wherein the on-press development type printing plate precursor has a protective layer.
［ １１ ］
The on-press development type printing plate precursor according to [ 10 ], wherein the protective layer contains a polyvinyl alcohol resin.
［ １２ ］
The on-press development type printing plate precursor according to any one of items [ 9 ] to [ 11 ], wherein the constituent layer containing the hydroxy acid compound is a non-photosensitive layer.
[ 13 ]
The on-press development type printing plate precursor according to any one of items [ 9 ] to [ 11 ], wherein the layer containing a hydroxy acid compound is an undercoat layer.
[ 14 ]
The on-press development type printing plate precursor according to [ 10 ] or [ 11 ], wherein the constituent layer containing the hydroxy acid compound is a protective layer.
［ １５ ］
The on-press development type printing plate precursor according to any one of [1] to [ 14 ], wherein the hydroxy acid compound has a ClogP value of 0.5 or less.
［ １６ ］
The on-press development type printing plate precursor according to any one of [1] to [ 15 ], wherein the molecular weight of the hydroxy acid compound is 1,000 or less.
［ １７ ］
The on-press development type printing plate precursor according to any one of [1] to [ 16 ], wherein the content of the hydroxy acid compound is 10 to 200 mg/ ^m2 .
［ １８ ］
The on-press development type printing plate precursor according to any one of [1] to [ 17 ], wherein the arithmetic mean height Sa of the outermost layer surface on the side opposite to the side having the constituent layer containing the hydroxy acid compound is 0.3 to 20 μm.
［ １９ ］
The on-press development type printing plate precursor according to any one of [1] to [ 18 ], wherein the arithmetic mean height Sa of the outermost layer surface on the side having the component layer containing the hydroxy acid compound is 0.3 to 20 μm.
［ ２０ ］
The on-press development type printing plate precursor according to any one of [1] to [19], wherein the average diameter of micropores on the surface of the anodized coating is 10 to 100 nm, and the lightness L* value in the L*a* b * color system of the surface of the anodized coating on the side of the component layer containing the hydroxy acid compound is 60 to 100.
［ ２１ ］
The on-press development type printing plate precursor according to any one of [1] to [20], wherein the micropores in the anodized film are composed of large-diameter pores extending 10 nm to 1,000 nm in the depth direction from the surface of the anodized film, and small-diameter pores that communicate with bottoms of the large-diameter pores and extend 20 nm to 2,000 nm in the depth direction from the communicating positions, the large-diameter pores having an average diameter of 15 nm to 100 nm at the surface of the anodized film, and the small-diameter pores having an average diameter of 13 nm or less at the communicating positions.
［ ２２ ］
The on-press development type printing plate precursor according to any one of [1] to [ 21 ], wherein the sagging shape of the end portion of the on-press development type printing plate precursor is a sagging amount X of 25 to 150 μm and a sagging width Y of 70 to 300 μm.
［ ２３ ］
A method for preparing a printing plate, comprising: a step of imagewise exposing the on-press development type printing plate precursor according to any one of [1] to [ 8 ]; and a step of supplying at least one of printing ink and dampening water on a printing press to remove an unexposed area of an image recording layer in the imagewise exposed on-press development type printing plate precursor.
［ 24 ］
A printing method comprising: a step of supplying at least one of printing ink and dampening water to the on-press development type printing plate precursor according to any one of [ 9 ] to [ 14 ] on a printing press to remove a non-photosensitive layer in the on-press development type printing plate precursor to prepare a throwaway plate; and a step of carrying out printing using the prepared throwaway plate.
The present invention relates to the above items [1] to [ 24 ], but other items (for example, the following items (1) to (30)) are also described below.

(1) An on-press development type printing plate precursor having at least one constituent layer on an aluminum support having an anodized film, wherein an edge of the on-press development type printing plate precursor has a drooping shape, and the at least one constituent layer contains a hydroxy acid compound having two or more hydroxyl groups, and the content of a water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20° C. of 10 g/L or more is substantially uniform within the plane of the constituent layer. (2) The on-press development type printing plate precursor according to (1), wherein the hydroxy acid compound has a ClogP value of 0.5 or less.
(3) The on-press development type printing plate precursor according to (1) or (2), wherein the molecular weight of the hydroxy acid compound is 1,000 or less.
(4) The on-press development type printing plate precursor according to any one of (1) to (3), wherein the content of the hydroxy acid compound is 10 to 200 mg/ ^m2.
(5) The on-press development type printing plate precursor according to any one of (1) to (4), wherein the arithmetic mean height Sa of the outermost layer surface on the side opposite to the side having the constituent layer containing the hydroxy acid compound is 0.3 to 20 μm.
(6) The on-press development type printing plate precursor according to any one of (1) to (5), wherein the arithmetic mean height Sa of the outermost layer surface on the side having the constituent layer containing the hydroxy acid compound is 0.3 to 20 μm.
(7) The on-press development type printing plate precursor according to any one of (1) to (6), wherein the average diameter of micropores on the surface of the anodized coating is 10 to 100 nm, and the lightness L* value in the L*a*b* color system of the surface of the anodized coating on the side of the component layer containing the hydroxy acid compound is 60 to 100.
(8) The on-press development type printing plate precursor according to any one of (1) to (7), wherein the micropores in the anodized film are composed of large-diameter pores extending 10 nm to 1,000 nm in a depth direction from a surface of the anodized film, and small-diameter pores that communicate with bottoms of the large-diameter pores and extend 20 nm to 2,000 nm in a depth direction from the communicating positions, the large-diameter pores having an average diameter of 15 nm to 100 nm at the surface of the anodized film, and the small-diameter pores having an average diameter of 13 nm or less at the communicating positions.
(9) The on-press development type printing plate precursor according to any one of (1) to (8), wherein the sagging shape of the end portion of the on-press development type printing plate precursor is a sagging amount X of 25 to 150 μm and a sagging width Y of 70 to 300 μm.
(10) The on-press development type printing plate precursor according to any one of (1) to (9), which has an image recording layer.
(11) The on-press development type printing plate precursor according to (10), wherein the image recording layer contains an infrared absorbing agent, a polymerization initiator, a polymerizable compound, and a polymer compound.
(12) The on-press development type printing plate precursor according to (11), wherein the polymer compound is a polymer compound containing a structural unit derived from a styrene compound and/or a structural unit derived from an acrylonitrile compound.
(13) The on-press development type printing plate precursor according to (12), wherein in the polymer compound containing a structural unit derived from a styrene compound and a structural unit derived from an acrylonitrile compound, a compositional ratio of the structural unit derived from a styrene compound to the structural unit derived from an acrylonitrile compound is 4:1 to 1:4.
(14) The on-press development type printing plate precursor according to any one of (11) to (13), wherein the polymer compound is a polymer particle.
(15) The on-press development type printing plate precursor according to (14), wherein the polymer particles are thermoplastic particles.
(16) The on-press development type printing plate precursor according to any one of (1) to (15), which has an undercoat layer.
(17) The on-press development type printing plate precursor according to any one of (1) to (16), which has a protective layer.
(18) The on-press development type printing plate precursor according to (17), wherein the protective layer contains a polyvinyl alcohol resin.
(19) The on-press development type printing plate precursor according to any one of (10) to (18), wherein the layer containing the hydroxy acid compound is an image recording layer.
(20) The on-press development type printing plate precursor according to any one of (11) to (18), wherein the layer containing the hydroxy acid compound is an undercoat layer.
(21) The on-press development type printing plate precursor according to any one of (12) to (18), wherein the layer containing the hydroxy acid compound is a protective layer.
(22) The on-press development type printing plate precursor according to any one of (1) to (9), wherein the on-press development type printing plate precursor has a non-photosensitive layer, and all of the constituent layers are non-photosensitive.
(23) The on-press development type printing plate precursor according to any one of (1) to (9) and (22), which has an undercoat layer.
(24) The on-press development type printing plate precursor according to any one of (1) to (9) and (22) to (23), wherein the on-press development type printing plate precursor has a protective layer.
(25) The on-press development type printing plate precursor according to (24), wherein the protective layer contains a polyvinyl alcohol resin.
(26) The on-press development type printing plate precursor according to any one of (22) to (25), wherein the layer containing the hydroxy acid compound is a non-photosensitive layer.
(27) The on-press development type printing plate precursor according to any one of (23) to (25), wherein the layer containing the hydroxy acid compound is an undercoat layer.
(28) The on-press development type printing plate precursor according to (24) or (25), wherein the constituent layer containing the hydroxy acid compound is a protective layer.
(29) A method for preparing a printing plate, comprising: a step of imagewise exposing the on-press development type printing plate precursor according to any one of (10) to (21); and a step of supplying at least one of printing ink and dampening water on a printing press to remove an unexposed area of the image recording layer in the imagewise exposed on-press development type printing plate precursor.
(30) A printing method comprising the steps of: supplying at least one of printing ink and dampening water to the on-press development type printing plate precursor according to any one of (22) to (28) on a printing press to remove a non-photosensitive layer in the on-press development type printing plate precursor to prepare a throwaway plate; and carrying out printing using the prepared throwaway plate.

According to the present invention, it is possible to provide an on-press development type printing original plate in which edge contamination is prevented not only after production but also after aging, a method for making a printing plate using an on-press development type printing original plate, and a printing method using an on-press development type printing original plate.
Furthermore, according to the present invention, it is possible to provide an on-press development type lithographic printing plate precursor in which deterioration of image formability in edge regions is suppressed.

1 is a graph showing an example of an alternating current waveform used in electrochemical graining treatment. FIG. 2 is a side view showing an example of a radial cell in electrochemical surface roughening treatment using an alternating current. FIG. 2 is a schematic diagram showing the cross-sectional shape of an edge portion of a planographic printing plate precursor. FIG. 2 is a conceptual diagram illustrating an example of a cutting section of a slitter device. FIG. 2 is a side view showing the concept of a brush graining process used in mechanical roughening treatment in the production of an aluminum support. FIG. 2 is a schematic diagram of an anodizing treatment device used in anodizing treatment.

The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In the description of groups (atomic groups) in this specification, when there is no indication of substituted or unsubstituted, the term encompasses both unsubstituted and substituted groups. For example, the term "alkyl group" encompasses not only alkyl groups without a substituent (unsubstituted alkyl groups) but also alkyl groups with a substituent (substituted alkyl groups).
In this specification, "(meth)acrylic" is a term used as a concept including both acrylic and methacrylic, and "(meth)acryloyl" is a term used as a concept including both acryloyl and methacryloyl.
In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.
In the present invention, a combination of two or more preferred embodiments is a more preferred embodiment.
In this specification, unless otherwise specified, the mass average molecular weight (Mw) and the number average molecular weight (Mn) are molecular weights detected by a gel permeation chromatography (GPC) analyzer using columns of TSKgel GMHxL, TSKgel G4000HxL, or TSKgel G2000HxL (all of which are product names manufactured by Tosoh Corporation) in a differential refractometer using THF (tetrahydrofuran) as a solvent, and converted using polystyrene as a standard substance.
In this specification, the term "printing plate" includes not only lithographic printing plate precursors but also throwaway plate precursors. Furthermore, the term "printing plate" includes not only lithographic printing plates prepared by subjecting a lithographic printing plate precursor to operations such as exposure and development as necessary, but also throwaway plates. In the case of throwaway plate precursors, the operations of exposure and development are not necessarily required. A throwaway plate is a lithographic printing plate that is attached to an unused plate cylinder when, for example, in color newspaper printing, a portion of the page is printed in one color or two colors. A throwaway plate is also called a water plate, a dummy plate, a blank plate, an empty plate, etc.
The present invention will be described in detail below.

[On-press development type printing original plate]
The on-press development type printing plate precursor according to the present invention is at least composed of an aluminum support having an anodized film and a constituent layer containing a hydroxy acid compound having two or more hydroxyl groups, and within the plane of the constituent layer, the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20° C. of 10 g/L or more is substantially the same, It is an on-press development type printing master plate.

The on-press development type printing plate precursor (hereinafter, sometimes referred to as printing plate precursor) according to the present invention has the above-mentioned configuration, which provides the excellent effect of preventing edge staining not only after production but also after aging. Furthermore, the on-press development type lithographic printing plate precursor has the excellent effect of suppressing deterioration of image forming properties in edge regions.
The on-press development type printing plate precursor according to the present invention will be described in detail below.

[Aluminum support having an anodized film]
An aluminum support having an anodized film which constitutes an on-press development type printing plate precursor will be described.

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

The foreign elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, titanium, etc. The content of the foreign elements in the alloy is 10 mass% or less. Pure aluminum plate is preferable, but since completely pure aluminum is difficult to produce due to smelting technology, an alloy plate containing a small amount of foreign elements may be used. The aluminum plate used for the aluminum support is not specified in composition, and conventionally known aluminum plates, such as JIS A 1050, JIS A 1100, JIS A 3103, JIS A 3005, etc., can be appropriately used.
The thickness of the aluminum plate is preferably about 0.1 to 0.6 mm.

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

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

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

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

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

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

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

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

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

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

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

In an on-press development type lithographic printing plate precursor, from the viewpoint of improving image visibility, it is useful that the brightness of the anodized film surface of the aluminum support (the surface on which the image recording layer is formed) is high.
In the printing process of a lithographic printing plate, a plate inspection is usually performed to check whether the intended image has been recorded before the printing plate is mounted on a printing press. In the case of an on-press development type lithographic printing plate precursor, it is required to check the image at the stage where the image is exposed, so a means for generating a so-called print-out image in the image-exposed area is applied.
A method for quantitatively evaluating the visibility (image visibility) of the image part of an image-exposed on-press development type lithographic printing plate precursor can be to measure the lightness of the image-exposed part and the lightness of the unexposed part and obtain the difference between them. Here, the lightness can be the lightness L* value in the CIE L*a*b* color system, and the measurement can be performed using a color difference meter (SpectroEye, manufactured by X-Rite Corporation). The larger the difference between the lightness of the image-exposed part and the lightness of the unexposed part obtained by the measurement, the easier the image part is to be seen.
It has been found that in order to increase the difference in brightness between the image-exposed and unexposed areas, it is effective to increase the brightness L* value of the anodized film surface in the CIE L*a*b* color system. In other words, the brightness L* value is preferably 60 to 100.

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

(Production of aluminum support having an anodized coating)
The aluminum support having an anodized film can be manufactured by a known method. The manufacturing method of the aluminum support having an anodized film is not particularly limited. A preferred embodiment of the manufacturing method of the aluminum support having an anodized film includes a step of roughening an aluminum plate (roughening treatment step), a step of anodizing the roughened aluminum plate (anodizing treatment step), and a step of contacting the aluminum plate having an anodized film obtained in the anodizing treatment step with an acid aqueous solution or an alkali aqueous solution to expand the diameter of the micropores in the anodized film (pore widening treatment step).

Each process is explained in detail below.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In the anodizing process, aqueous solutions of sulfuric acid, phosphoric acid, oxalic acid, etc. can be mainly used as the electrolyte. In some cases, aqueous or non-aqueous solutions of chromic acid, sulfamic acid, benzenesulfonic acid, etc., or combinations of two or more of these, can also be used. When a direct or alternating current is passed through the aluminum plate in the electrolyte, an anodized film can be formed on the surface of the aluminum plate. The electrolyte may contain aluminum ions. There are no particular restrictions on the content of aluminum ions, but a content of 1 to 10 g/L is preferred.

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

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

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

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

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

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

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

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

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

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

[Constituent layer containing hydroxy acid compound having two or more hydroxyl groups]
A constituent layer (hereinafter also referred to as a "specific constituent layer") that contains a hydroxy acid compound having two or more hydroxyl groups and that constitutes an on-press development type printing plate precursor will be described.
The specific component layer contains a hydroxy acid compound having two or more hydroxyl groups.

(Hydroxy acid compound having two or more hydroxyl groups)
The specific component layer contains a hydroxy acid compound having two or more hydroxyl groups (hereinafter, also referred to as a "specific hydroxy acid compound").

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

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

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

Examples of the specific hydroxy acid compound include glyceric acid, gluconic acid, tartaric acid, mevalonic acid, pantoic acid, quinic acid, shikimic acid, gallic acid, caffeic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, sodium gluconate, potassium gluconate, sodium tartrate, and sodium gallate.
Preferred specific hydroxy acid compounds include gluconic acid, tartaric acid, mevalonic acid, quinic acid, sodium gluconate, potassium gluconate, and sodium tartrate.

The specific hydroxy acid compound may be used alone or in combination of two or more types.

The content of the specific hydroxy acid compound in the specific component layer is preferably from 10 to 300 mg/ ^m2 , more preferably from 30 to 200 mg/ ^m2 , and even more preferably from 50 to 100 mg/ ^m2 , from the viewpoint of image forming properties in the edge regions.
The content of the specific hydroxy acid compound is substantially the same in the plane of the specific component layer. Here, "the content of the specific hydroxy acid compound is substantially the same in the plane of the specific component layer" means that the specific hydroxy acid compound is almost uniformly present in the plane of the specific component layer, and there is no substantial difference in the content of the specific hydroxy acid compound between the center and the end of the on-press development type printing plate precursor. That is, it means that there is no content difference other than the content difference of the specific hydroxy acid compound in the plane of the specific component layer that may normally occur when the specific component layer is applied.
Therefore, the present invention differs from intentionally applying a specific hydroxy acid compound only to the edges of an on-press development type printing plate precursor, thereby creating a state in which the content of the specific hydroxy acid compound at the edges is greater than the content of the specific hydroxy acid compound in areas other than the edges.

In the plane of the specific component layer, the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water of 10 g/L or more at 20°C is substantially the same. Here, "the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water of 10 g/L or more at 20°C is substantially the same in the plane of the specific component layer" means that the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water of 10 g/L or more at 20°C is almost uniformly present in the plane of the specific component layer, and there is no substantial difference in the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water of 10 g/L or more at 20°C at the center and end parts of the on-press development type printing plate master. That is, it means that there is no content difference other than the content difference of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water of 10 g/L or more at 20°C in the plane of the specific component layer that can usually occur when the specific component layer is applied.
Therefore, the present invention differs from intentionally applying a water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20°C of 10 g/L or more only to the edges of an on-press development type printing plate master, thereby creating a state in which the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20°C of 10 g/L or more at the edges is greater than the content of the water-soluble compound having a molecular weight of 60 to 300 and a solubility in water at 20°C of 10 g/L or more in areas other than the edges.

Preferred examples of water-soluble compounds having a molecular weight of 60 to 300 and a solubility in water at 20°C of 10 g/L or more include polyols, betaines, organic sulfonates, organic sulfates, organic carboxylic acids or their salts, and amino acids. Specific examples of these are described in paragraphs 0022 to 0027 of WO2016/053443.

A specific component layer is a component layer that contains a specific hydroxy acid compound, so when a component layer of an on-press development type lithographic printing plate precursor and a disposable plate precursor, such as an image recording layer, undercoat layer, protective layer or non-photosensitive layer, contains a specific hydroxy acid compound, the component layer corresponds to a specific component layer.

[On-press development type lithographic printing plate precursor]
Hereinafter, an on-press development type lithographic printing plate precursor (hereinafter also referred to as "lithographic printing plate precursor"), which is one embodiment of the on-press development type printing plate precursor according to the present invention, will be described.
The lithographic printing plate precursor has an image recording layer on the aluminum support having the above-mentioned anodized film.

[Image Recording Layer]
According to one preferred embodiment of the image recording layer in the lithographic printing plate precursor, the image recording layer contains an infrared absorbing agent, a polymerization initiator, a polymerizable compound, and a polymer compound. The image recording layer preferably further contains a chain transfer agent.
According to another preferred embodiment of the image recording layer, the image recording layer contains an infrared absorbing agent, heat-fusible particles, and a binder polymer.

(Infrared absorber)
The infrared absorbing agent has a function of being excited by infrared rays and transferring electrons and/or energy to a polymerization initiator, etc., and also has a function of converting the absorbed infrared rays into heat. The infrared absorbing agent preferably has a maximum absorption in the wavelength range of 750 to 1,400 nm. Examples of the infrared absorbing agent include dyes and pigments, and dyes are preferably used.

As the dye, commercially available dyes and known dyes described in documents such as "Dye Handbook" (edited by the Organic Synthesis Chemistry Association, published in 1970) can be used. Specific examples of the dye include azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts, and metal thiolate complex dyes.
Of the dyes, cyanine dyes, squarylium dyes and pyrylium salts are preferred, cyanine dyes are more preferred, and indolenine cyanine dyes are particularly preferred.

Examples of cyanine dyes include cyanine dyes represented by the following formula (a).

In formula (a), X ¹ represents a hydrogen atom, a halogen atom, -N(R ⁹ )(R ¹⁰ ), -X ² -L ¹ or a group shown below. Here, R ⁹ and R ¹⁰ may be the same or different, and each independently represents an aromatic hydrocarbon group having 6 to 10 carbon atoms, an alkyl group having 1 to 8 carbon atoms, or a hydrogen atom, or R ⁹ and R ¹⁰ may be bonded to each other to form a ring. The aromatic hydrocarbon group having 6 to 10 carbon atoms or the alkyl group having 1 to 8 carbon atoms may have a substituent. Both R ⁹ and R ¹⁰ are preferably phenyl groups. ^{X 2} represents an oxygen atom or a sulfur atom, and L ¹ represents a hydrocarbon group having 1 to 12 carbon atoms or a hydrocarbon group having 1 to 12 carbon atoms containing a hetero atom. Here, the hetero atom represents N, S, O, a halogen atom, or Se. In the groups shown below, ^Xa- has the same meaning as ^Za- described below, and Ra represents a hydrogen atom or a substituent selected from an alkyl group, an aryl group, a substituted or unsubstituted amino group, and a halogen atom.

In formula (a), R ¹ and R ² each independently represent a hydrocarbon group having 1 to 12 carbon atoms. From the viewpoint of storage stability of the image recording layer coating liquid, R ¹ and R ² are preferably a hydrocarbon group having 2 or more carbon atoms, and it is particularly preferable that R ¹ and R ² are bonded to each other to form a 5-membered or 6-membered ring.

In formula (a), Ar ¹ and Ar ² may be the same or different and each represents an aromatic hydrocarbon group. The aromatic hydrocarbon group may have a substituent. Preferred aromatic hydrocarbon groups include a benzene ring group and a naphthalene ring group. Preferred substituents include a hydrocarbon group having 12 or less carbon atoms, a halogen atom, and an alkoxy group having 12 or less carbon atoms. ^{Y 1} and Y ² may be the same or different and each represents a sulfur atom or a dialkylmethylene group having 12 or less carbon atoms. R ³ and R ⁴ may be the same or different and each represents a hydrocarbon group having 20 or less carbon atoms. The hydrocarbon group having 20 or less carbon atoms may have a substituent. Preferred substituents include an alkoxy group having 12 or less carbon atoms, a carboxy group, and a sulfo group. R ⁵ , R ⁶ , R ⁷ , and R ⁸ may be the same or different and each represents a hydrogen atom or a hydrocarbon group having 12 or less carbon atoms. In terms of the ease of availability of raw materials, a hydrogen atom is preferred. Za ^- represents a counter anion. However, when the cyanine dye represented by formula (a) has an anionic substituent in its structure and charge neutralization is not required, ^Za- is not necessary. From the viewpoint of storage stability of the image recording layer coating solution, ^Za- is preferably a halide ion, a perchlorate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, or a sulfonate ion, and more preferably a perchlorate ion, a hexafluorophosphate ion, or an arylsulfonate ion.

In the cyanine dye represented by formula (a), it is more preferable that X ¹ is a diphenylamino group, and further more preferable that X ¹ is a diphenylamino group, and Y ¹ and Y ² are both dimethylmethylene groups.

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

The infrared absorbing agent may be used alone or in combination of two or more kinds.
The content of the infrared absorbing agent is preferably from 0.05 to 30% by mass, more preferably from 0.1 to 20% by mass, and even more preferably from 0.2 to 10% by mass, based on the total solid content of the image recording layer.

(Polymerization initiator)
The polymerization initiator is a compound that generates polymerization initiating species such as radicals or cations by the energy of light, heat, or both, and can be appropriately selected from known thermal polymerization initiators, compounds having bonds with small bond dissociation energy, photopolymerization initiators, etc.
The polymerization initiator is preferably an infrared-sensitive polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator. Two or more types of radical polymerization initiators may be used in combination.

The radical polymerization initiator may be either an electron-accepting polymerization initiator or an electron-donating polymerization initiator.

<Electron-Accepting Polymerization Initiator>
Examples of the electron-accepting polymerization initiator include organic halides, carbonyl compounds, azo compounds, organic peroxides, metallocene compounds, azide compounds, hexaarylbiimidazole compounds, disulfone compounds, oxime ester compounds, and onium salt compounds.

As the organic halide, for example, the compounds described in paragraphs 0022 to 0023 of JP-A-2008-195018 are preferable.
As the carbonyl compound, for example, the compounds described in paragraph 0024 of JP-A-2008-195018 are preferable.
Examples of the azo compound include the azo compounds described in JP-A-8-108621.
As the organic peroxide, for example, the compounds described in paragraph 0025 of JP-A-2008-195018 are preferable.
As the metallocene compound, for example, the compounds described in paragraph 0026 of JP-A-2008-195018 are preferable.
Examples of the azide compound include compounds such as 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone.
As the hexaarylbiimidazole compound, for example, the compounds described in paragraph 0027 of JP-A-2008-195018 are preferable.
Examples of the disulfone compound include the compounds described in JP-A-61-166544 and JP-A-2002-328465.
As the oxime ester compound, for example, the compounds described in paragraphs 0028 to 0030 of JP-A-2008-195018 are preferred.

Among the electron-accepting polymerization initiators, onium salts such as iodonium salts, sulfonium salts, and azinium salts are more preferred. Iodonium salts and sulfonium salts are particularly preferred. Specific examples of iodonium salts and sulfonium salts are shown below, but the present invention is not limited to these.

Preferred examples of iodonium salts include diphenyliodonium salts, particularly diphenyliodonium salts having an electron-donating group as a substituent, for example, diphenyliodonium salts substituted with an alkyl group or an alkoxy group, and asymmetric diphenyliodonium salts are also preferred. Specific examples include diphenyliodonium hexafluorophosphate, 4-methoxyphenyl-4-(2-methylpropyl)phenyliodonium hexafluorophosphate, 4-(2-methylpropyl)phenyl-p-tolyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, 4-hexyloxyphenyl-2,4-diethoxyphenyliodonium tetrafluoroborate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium 1-perfluorobutanesulfonate, 4-octyloxyphenyl-2,4,6-trimethoxyphenyliodonium hexafluorophosphate, and bis(4-t-butylphenyl)iodonium hexafluorophosphate.

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

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

<Electron-donating polymerization initiator>
The electron-donating polymerization initiator contributes to improving the printing durability of a lithographic printing plate produced from a lithographic printing plate precursor. Examples of the electron-donating polymerization initiator include the following five types. (i) Alkyl or aryl ate complexes: It is believed that the carbon-hetero bond is cleaved by oxidation to generate an active radical. Specific examples include borate compounds. (ii) Aminoacetic acid compounds: It is believed that the C-X bond on the carbon adjacent to the nitrogen is cleaved by oxidation to generate an active radical. X is preferably a hydrogen atom, a carboxy group, a trimethylsilyl group, or a benzyl group. Specific examples include N-phenylglycines (which may have a substituent on the phenyl group), N-phenyliminodiacetic acid (which may have a substituent on the phenyl group), and the like. (iii) Sulfur-containing compounds: Compounds in which the nitrogen atom of the aminoacetic acid compound described above is replaced with a sulfur atom can generate an active radical by the same action. Specific examples include phenylthioacetic acid (which may have a substituent on the phenyl group). (iv) Tin-containing compounds: Compounds in which the nitrogen atom of the aminoacetic acid compound described above is replaced with a tin atom can generate active radicals by the same action. (v) Sulfinates: Can generate active radicals by oxidation. Specific examples include sodium arylsulfinates.

Among the electron donating polymerization initiators, borate compounds are preferred. As the borate compound, tetraarylborate compounds or monoalkyltriarylborate compounds are preferred, and from the viewpoint of compound stability, tetraarylborate compounds are more preferred.
The counter cation of the borate compound is preferably an alkali metal ion or a tetraalkylammonium ion, and more preferably a sodium ion, a potassium ion or a tetrabutylammonium ion.

Specific examples of the borate compound include the compounds shown below, in which X _c ⁺ represents a monovalent cation, preferably an alkali metal ion or a tetraalkylammonium ion, more preferably an alkali metal ion or a tetrabutylammonium ion, and Bu represents an n-butyl group.

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

(Polymerizable compound)
The polymerizable compound may be, for example, a radical polymerizable compound or a cationic polymerizable compound, but is preferably an addition polymerizable compound (ethylenically unsaturated compound) having at least one ethylenically unsaturated bond.As the ethylenically unsaturated compound, a compound having at least one terminal ethylenically unsaturated bond is preferred, and a compound having two or more terminal ethylenically unsaturated bonds is more preferred.The polymerizable compound can have a chemical form such as, for example, a monomer, a prepolymer, i.e., a dimer, a trimer or an oligomer, or a mixture thereof.

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

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

Also suitable are urethane-based addition-polymerizable compounds produced by an addition reaction between an isocyanate and a hydroxy group. Specific examples thereof include vinyl urethane compounds containing two or more polymerizable vinyl groups in one molecule, which are obtained by adding a vinyl monomer containing a hydroxy group represented by the following formula (M) to a polyisocyanate compound having two or more isocyanate groups in one molecule, as described in JP-B-48-41708.
_CH2 =C( ^RM4 ) _COOCH2CH ( ^RM5 )OH(M)
In formula (M), R ^M4 and R ^M5 each independently represent a hydrogen atom or a methyl group.

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

Details of the method of use such as the structure of the polymerizable compound, whether it is used alone or in combination, and the amount added can be arbitrarily set in consideration of the final use of the lithographic printing plate precursor.
The content of the polymerizable compound is preferably from 1 to 50% by mass, more preferably from 3 to 30% by mass, and even more preferably from 5 to 20% by mass, based on the total solid content of the image recording layer.

(Polymer Compound)
The polymer compound may function as a binder polymer in the image recording layer, or may be present in the image recording layer as a particulate polymer compound (polymer particles).

<Binder Polymer>
As the binder polymer, a polymer having film properties is preferable, and preferred examples thereof include a (meth)acrylic resin, a polyvinyl acetal resin, and a polyurethane resin.

The binder polymer used in the image recording layer is preferably a binder polymer having an alkylene oxide chain. The binder polymer having an alkylene oxide chain may have a poly(alkylene oxide) moiety in the main chain or in the side chain. It may also be a graft polymer having a poly(alkylene oxide) moiety in the side chain, or a block copolymer of a block composed of a repeating unit containing a poly(alkylene oxide) moiety and a block composed of a repeating unit not containing an (alkylene oxide) moiety.
When the main chain has a poly(alkylene oxide) moiety, polyurethane resin is preferred. When the side chain has a poly(alkylene oxide) moiety, examples of the main chain polymer include (meth)acrylic resin, polyvinyl acetal resin, polyurethane resin, polyurea resin, polyimide resin, polyamide resin, epoxy resin, polystyrene resin, novolac type phenolic resin, polyester resin, synthetic rubber, and natural rubber, and (meth)acrylic resin is particularly preferred.

The alkylene oxide is preferably an alkylene oxide having 2 to 6 carbon atoms, and ethylene oxide or propylene oxide is particularly preferred.
The number of repeating alkylene oxides in the poly(alkylene oxide) moiety is preferably 2-120, more preferably 2-70, and even more preferably 2-50.
If the number of alkylene oxide repetitions is 120 or less, the deterioration of printing durability due to wear and the deterioration of ink receptivity are suppressed, which is preferable.

The poly(alkylene oxide) moiety is preferably contained as a side chain of the binder polymer in a structure represented by the following formula (AO), and more preferably contained as a side chain of the (meth)acrylic resin in a structure represented by the following formula (AO).

In formula (AO), y represents an integer of 2 to 120, R ₁ represents a hydrogen atom or an alkyl group, and R ₂ represents a hydrogen atom or a monovalent organic group.
The monovalent organic group is preferably an alkyl group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, an isohexyl group, a 1,1-dimethylbutyl group, a 2,2-dimethylbutyl group, a cyclopentyl group, and a cyclohexyl group.
In formula (AO), y is preferably an integer of 2 to 70, more preferably an integer of 2 to 50. _R1 is preferably a hydrogen atom or a methyl group, particularly preferably a hydrogen atom. _R2 is particularly preferably a hydrogen atom or a methyl group.

The binder polymer may have a crosslinking property in order to improve the film strength of the image area. In order to impart crosslinking properties to the polymer, a crosslinkable functional group such as an ethylenically unsaturated bond may be introduced into the main chain or side chain of the polymer. The crosslinkable functional group may be introduced by copolymerization or by polymer reaction.
Examples of the polymer having an ethylenically unsaturated bond in the main chain of the molecule include poly-1,4-butadiene and poly-1,4-isoprene.
Examples of the polymer having an ethylenically unsaturated bond in a side chain of the molecule include polymers of esters or amides of acrylic acid or methacrylic acid, in which the residue of the ester or amide (-COOR or -CONHR R) has an ethylenically unsaturated bond.

Examples of the residue having an ethylenically unsaturated bond (the above R) include - ^{(CH2)nCR1A=CR2A R3A, -(CH2O)nCH2CR1A=CR2A R3A, -(CH2CH2O)nCH2CR1A} _{= CR2A} ^{R3A , -} _{( CH2} ^{) nNH} _{- CO -} ^{O -} _{CH2CR1A = CR2A} ^{R3A , -} ( _CH2 ) _{n -} O- ^CO - ^CR1A ₌ ^{CR2A R3A} and -( _CH2CH2O ) ₂ ^-XA ₍ wherein R ^A1 to R ^A3 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an alkoxy group or an aryloxy group, and R ^A1 and R ^A2 or R ^A3 may be bonded to each other to form a ring. n represents an integer of 1 to 10. X ^A represents a dicyclopentadienyl residue.

Specific examples of ester residues include _-CH2CH = _CH2 , _-CH2CH2O - _CH2CH = _CH2 , _-CH2C ( _{CH3 )} = _CH2 , -CH2CH=CH _{-C6H5 , -CH2CH2OCOCH} =CH _{-C6H5 , -CH2CH2 - NHCOO} - _CH2CH = _CH2 and _-CH2CH2O - _X (wherein X represents a _{dicyclopentadienyl} residue).
Specific examples of amide residues include -CH ₂ CH=CH ₂ , -CH ₂ CH ₂ -Y (wherein Y represents a cyclohexene residue) and -CH ₂ CH ₂ -OCO-CH=CH ₂ .

A crosslinkable binder polymer cures when, for example, a free radical (polymerization initiation radical or a propagating radical in the polymerization process of a polymerizable compound) is added to the crosslinkable functional group, and addition polymerization occurs between the polymers directly or via the polymerization chain of the polymerizable compound, forming crosslinks between the polymer molecules. Alternatively, an atom in the polymer (for example, a hydrogen atom on a carbon atom adjacent to a functional crosslinking group) is abstracted by a free radical to generate a polymer radical, which then bonds to each other to form crosslinks between the polymer molecules and cure.

The content of crosslinkable groups in the binder polymer (the content of radically polymerizable unsaturated double bonds determined by iodometric titration) is preferably 0.1 to 10.0 mmol, more preferably 1.0 to 7.0 mmol, and even more preferably 2.0 to 5.5 mmol per gram of binder polymer, from the viewpoints of good sensitivity and good storage stability.

Specific examples 1 to 11 of binder polymers are shown below, but the present invention is not limited to these. In the example compounds below, the numbers listed next to each repeating unit (numbers listed next to main chain repeating units) indicate the molar percentage of the repeating unit. The numbers listed next to side chain repeating units indicate the number of repeats of the repeating portion. Additionally, Me represents a methyl group, Et represents an ethyl group, and Ph represents a phenyl group.

The molecular weight of the binder polymer is, in terms of polystyrene, a mass average molecular weight (Mw) measured by GPC method of 2,000 or more, preferably 5,000 or more, and more preferably 10,000 to 300,000.

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

The binder polymer may be used alone or in combination of two or more kinds.
The content of the binder polymer is preferably from 1 to 90% by mass, and more preferably from 5 to 80% by mass, based on the total solid content of the image recording layer.

<Polymer Particles>
The image recording layer preferably contains polymer particles. The polymer particles contribute to improving on-press developability. The polymer particles are preferably polymer particles that can convert the image recording layer to hydrophobicity when heat is applied. The polymer particles are preferably at least one selected from hydrophobic thermoplastic polymer particles, heat-reactive polymer particles, polymer particles having a polymerizable group, microcapsules containing a hydrophobic compound, and microgels (crosslinked polymer particles).

Suitable examples of the hydrophobic thermoplastic polymer particles include those described in Research Disclosure No. 33303 published in January 1992, JP-A-9-123387, JP-A-9-131850, JP-A-9-171249, JP-A-9-171250, and European Patent No. 931647.
Specific examples of the polymer constituting the hydrophobic thermoplastic polymer particles include homopolymers or copolymers of monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile, vinylcarbazole, acrylates or methacrylates having a polyalkylene structure, or mixtures thereof. Preferred are polystyrene, copolymers containing styrene and acrylonitrile, and polymethyl methacrylate. The average particle size of the hydrophobic thermoplastic polymer particles is preferably 0.01 to 2.0 μm.

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

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

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

The microgel (crosslinked polymer particle) can contain some of the components of the image recording layer in at least one of its interior and surface. In particular, from the viewpoint of image formation sensitivity and printing durability, it is preferable to make the microgel reactive by having a radical polymerizable group on its surface.

In order to microencapsulate or microgel the components of the image recording layer, known methods can be used.
The average particle size of the microcapsules or microgels is preferably 0.01 to 3.0 μm, more preferably 0.05 to 2.0 μm, and particularly preferably 0.10 to 1.0 μm. Good resolution and stability over time can be obtained within this range.

The polymer particles may be used alone or in combination of two or more kinds.
The content of the polymer particles is preferably from 5 to 90% by mass, more preferably from 5 to 80% by mass, and even more preferably from 10 to 75% by mass, based on the total solid content of the image recording layer.

As the polymer compound contained in the image recording layer, a polymer compound containing a structural unit derived from a styrene compound and/or a structural unit derived from an acrylonitrile compound is also preferred. From the viewpoint of contributing to on-press developability, this polymer compound can be suitably used as a binder polymer or polymer particles.

Examples of styrene compounds include styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene, α-methylstyrene, p-methoxy-β-methylstyrene, etc., with styrene being preferred.

Examples of acrylonitrile compounds include acrylonitrile, methacrylonitrile, etc., with acrylonitrile being preferred.

In a polymeric compound containing a styrene compound and an acrylonitrile compound as structural units, it is preferable that the composition ratio of structural units derived from the styrene compound and structural units derived from the acrylonitrile compound is 4:1 to 1:4.

The image recording layer may contain chain transfer agents, low molecular weight hydrophilic compounds, oil sensitizers, and other ingredients.

(Chain Transfer Agent)
The chain transfer agent contributes to improving the printing durability of a lithographic printing plate prepared from the lithographic printing plate precursor.
The chain transfer agent is preferably a thiol compound, more preferably a thiol having 7 or more carbon atoms from the viewpoint of boiling point (difficulty of volatilization), and further preferably a compound having a mercapto group on an aromatic ring (aromatic thiol compound). The thiol compound is preferably a monofunctional thiol compound.

Specific examples of chain transfer agents include the following compounds:

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

(Low molecular hydrophilic compound)
The low molecular weight hydrophilic compound contributes to improving the on-press developability of the lithographic printing plate precursor without decreasing the printing durability of the lithographic printing plate produced from the lithographic printing plate precursor. Compounds having a molecular weight of less than 1,000 are preferred, compounds having a molecular weight of less than 800 are more preferred, and compounds having a molecular weight of less than 500 are even more preferred.
Examples of low molecular weight hydrophilic compounds include water-soluble organic compounds such as glycols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol, and their ether or ester derivatives, glycerin, Polyols such as pentaerythritol and tris(2-hydroxyethyl)isocyanurate; organic amines such as triethanolamine, diethanolamine, and monoethanolamine and their salts; organic sulfones such as alkylsulfonic acid, toluenesulfonic acid, and benzenesulfonic acid. Acids and their salts, organic sulfamic acids such as alkylsulfamic acid and their salts, organic sulfuric acids such as alkyl sulfates and alkyl ether sulfates and their salts, organic phosphonic acids such as phenylphosphonic acid and their salts, tartaric acid, oxalic acid, citric acid Examples of the organic carboxylic acids include acid, malic acid, lactic acid, gluconic acid, amino acids, and their salts, and betaines.

The low molecular weight hydrophilic compound is preferably at least one selected from polyols, organic sulfates, organic sulfonates and betaines.

Specific examples of organic sulfonates include alkyl sulfonates such as sodium n-butylsulfonate, sodium n-hexylsulfonate, sodium 2-ethylhexylsulfonate, sodium cyclohexylsulfonate, and sodium n-octylsulfonate; alkyl sulfonates containing ethylene oxide chains such as sodium 5,8,11-trioxapentadecane-1-sulfonate, sodium 5,8,11-trioxaheptadecane-1-sulfonate, sodium 13-ethyl-5,8,11-trioxaheptadecane-1-sulfonate, and sodium 5,8,11,14-tetraoxatetracosane-1-sulfonate. Sulfonates: arylsulfonates such as sodium benzenesulfonate, sodium p-toluenesulfonate, sodium p-hydroxybenzenesulfonate, sodium p-styrenesulfonate, sodium dimethyl isophthalate-5-sulfonate, sodium 1-naphthylsulfonate, sodium 4-hydroxynaphthylsulfonate, disodium 1,5-naphthalenedisulfonate, and trisodium 1,3,6-naphthalenetrisulfonate; and the compounds described in paragraphs 0026 to 0031 of JP-A No. 2007-276454 and paragraphs 0020 to 0047 of JP-A No. 2009-154525. The salt may be a potassium salt or a lithium salt.

Examples of organic sulfates include sulfates of alkyl, alkenyl, alkynyl, aryl, or heterocyclic monoethers of polyethylene oxide. The number of ethylene oxide units is preferably 1 to 4, and the salt is preferably a sodium salt, potassium salt, or lithium salt. Specific examples include the compounds described in paragraphs 0034 to 0038 of JP 2007-276454 A.

As betaines, compounds in which the number of carbon atoms in the hydrocarbon substituent on the nitrogen atom is 1 to 5 are preferred, and specific examples include trimethylammonium acetate, dimethylpropylammonium acetate, 3-hydroxy-4-trimethylammoniobutyrate, 4-(1-pyridinio)butyrate, 1-hydroxyethyl-1-imidazolioacetate, trimethylammonium methanesulfonate, dimethylpropylammonium methanesulfonate, 3-trimethylammonio-1-propanesulfonate, and 3-(1-pyridinio)-1-propanesulfonate.

Low molecular weight hydrophilic compounds have a small structure in the hydrophobic portion and have almost no surfactant effect, so the dampening water does not penetrate into the exposed areas (image areas) of the image recording layer and reduce the hydrophobicity or film strength of the image areas, and the ink receptivity and printing durability of the image recording layer can be maintained at a good level.

The low molecular weight hydrophilic compounds may be used alone or in combination of two or more kinds.
The content of the low molecular weight hydrophilic compound is preferably from 0.5 to 20% by mass, more preferably from 1 to 15% by mass, and even more preferably from 2 to 10% by mass, based on the total solid content of the image recording layer.

(Oil Sensitizer)
The oil sensitizer contributes to improving the ink receptivity (hereinafter also simply referred to as "ink receptivity") of the lithographic printing plate produced from the lithographic printing plate precursor. Examples of the oil sensitizer include phosphonium compounds, nitrogen-containing low molecular weight compounds, and ammonium group-containing polymers. In particular, when the lithographic printing plate precursor has a protective layer containing an inorganic layer compound, these compounds function as a surface coating agent for the inorganic layer compound and have the function of suppressing the decrease in ink receptivity caused by the inorganic layer compound during printing.
As the oil sensitizer, it is preferable to use a phosphonium compound, a nitrogen-containing low molecular weight compound, and an ammonium group-containing polymer in combination, and it is more preferable to use a phosphonium compound, a quaternary ammonium salt, and an ammonium group-containing polymer in combination.

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

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

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

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

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

The content of the oil sensitizer is preferably 0.01 to 30 mass %, more preferably 0.1 to 15 mass %, and even more preferably 1 to 10 mass %, of the total solids content of the image recording layer.

(Other ingredients)
The image recording layer may contain, as other components, a surfactant, a print-out agent, a polymerization inhibitor, a higher fatty acid derivative, a plasticizer, inorganic particles, an inorganic layer compound, etc. Specifically, the above-mentioned components described in paragraphs 0114 to 0159 of JP-A-2008-284817 can be used.

The image recording layer may contain a specific hydroxy acid compound. In this case, the image recording layer corresponds to the specific component layer.

(Formation of Image Recording Layer)
The image recording layer can be formed, for example, as described in paragraphs 0142 to 0143 of JP-A-2008-195018, by dispersing or dissolving the necessary components in a known solvent to prepare a coating solution, applying the coating solution 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 from the viewpoint of obtaining good sensitivity and good film properties of the image recording layer, it is preferably about 0.3 to 3.0 g/ ^m2 .

An on-press development type lithographic printing plate precursor can have an undercoat layer (sometimes called an intermediate layer) between the image recording layer and the support, and a protective layer (sometimes called an overcoat layer) on top of the image recording layer.

[Undercoat layer]
The undercoat layer strengthens the adhesion between the support and the image recording layer in the exposed area and facilitates peeling of the image recording layer from the support in the unexposed area, thereby contributing to improving developability without impairing printing durability. In addition, in the case of infrared laser exposure, the undercoat layer functions as a heat insulating layer, thereby preventing the heat generated by exposure from diffusing to the support and decreasing the sensitivity.

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

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

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

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

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

The undercoat layer may contain a specific hydroxy acid compound. In this case, the undercoat layer corresponds to the specific component layer.

The undercoat layer can be formed by coating and drying using a known method. The coating amount (solid content) of the undercoat layer after drying is preferably 0.1 to 100 mg/ ^m2 , more preferably 1 to 30 mg/ ^m2 .

[Protective Layer]
The protective layer has a function of suppressing reactions that inhibit image formation by blocking oxygen, as well as a function of preventing the occurrence of scratches in the image recording layer and ablation during exposure to high-intensity laser light.

Protective layers having such characteristics are described, for example, in U.S. Pat. No. 3,458,311 and Japanese Patent Publication No. 55-49729. As the low oxygen permeable polymer used in the protective layer, either a water-soluble polymer or a water-insoluble polymer can be appropriately selected and used, and two or more types can be mixed and used as necessary. Specific examples include polyvinyl alcohol resins (including polyvinyl alcohol and modified polyvinyl alcohol), polyvinylpyrrolidone, water-soluble cellulose derivatives, poly(meth)acrylonitrile, etc.
The polyvinyl alcohol is preferably polyvinyl alcohol having a degree of saponification of 50% or more. The degree of saponification of polyvinyl alcohol is preferably 60% or more, more preferably 70% or more, and even more preferably 85% or more. There is no particular upper limit to the degree of saponification, and the degree of saponification may be 100% or less.
The degree of saponification can be measured according to the method described in JIS K 6726:1994.
The modified polyvinyl alcohol is preferably an acid-modified polyvinyl alcohol having a carboxy group or a sulfo group, specifically, the modified polyvinyl alcohols described in JP-A-2005-250216 and JP-A-2006-259137.
Among the water-soluble polymers, polyvinyl alcohol resins are preferred.

The protective layer preferably contains an inorganic layered compound to improve the oxygen barrier property. The inorganic layered compound is a particle having a thin plate-like shape, and examples thereof include mica group such as natural mica and synthetic _mica , talc represented by the formula: 3MgO.4SiO.H2O, taeniolite, montmorillonite, saponite, hectorite, zirconium phosphate, and the like.
The inorganic layered compound preferably used is a mica compound. Examples of the mica compound include mica groups such as natural mica and _{synthetic mica} represented by the formula: A(B,C) _2-5D4O10 (OH,F,O) ₂ (wherein A is K, Na, or Ca, B and C are Fe(II), Fe(III), Mn, Al, Mg, or V, and D is Si or Al).

In the mica group, natural micas include muscovite, sodalite, phlogopite, biotite and lepidolite.Synthetic micas include non-swelling micas such as fluorphlogopite _KMg3 ( _AlSi3O10 ) _F2 , potassium _tetrasilicic mica _KMg2.5Si4O10 ) _F2 , and swelling micas such as Na tetrasilicic mica _NaMg2.5 ( _Si4O10 ) _F2 , Na or Li taeniolite (Na, _Li ) _Mg2Li ( _Si4O10 ) _F2 , and montmorillonite-based _Na or _Li hectorite (Na,Li) _{1 /} 8Mg2 _/5Li1 / ₈ ( _{Si4O10 ) F2.Synthetic} smectite is also useful.

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

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

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

The content of the inorganic layered compound is preferably 0 to 60% by mass, and more preferably 3 to 50% by mass, based on the total solid content of the protective layer. Even when multiple types of inorganic layered compounds are used in combination, it is preferable that the total amount of the inorganic layered compounds is within the above content. Within the above range, oxygen barrier properties are improved and good sensitivity is obtained. In addition, a decrease in ink adhesion can be prevented.

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

The protective layer may contain a specific hydroxy acid compound. In this case, the protective layer corresponds to the specific component layer.

The protective layer can be formed by coating and drying using a known method. The coating amount (solid content) of the protective layer after drying is preferably 0.01 to 10 g/ ^m2 , more preferably 0.02 to 3 g/ ^m2 , and particularly preferably 0.02 to 1 g/ ^m2 .

[Disposable original plate]
A disposable printing plate precursor, which is another embodiment of the on-press development type printing plate precursor according to the present invention, will be described below.
A throwaway plate precursor is a plate for producing a throwaway plate through a plate-making process similar to that of a lithographic printing plate precursor (however, image exposure is not required), and does not basically have photosensitivity. As is well known in the printing industry, a throwaway plate is attached to a plate cylinder when it is necessary to print a part of a page in two colors or one color in color newspaper printing (multicolor printing), for example.

The sacrificial plate precursor has a non-photosensitive layer on the aluminum support having the above-mentioned anodized film. Here, "non-photosensitive" means that it has substantially no photosensitivity to light from a light source used in the image exposure process of a normal lithographic printing plate precursor that is used in a printing process together with the sacrificial plate precursor. "Substantially no photosensitivity" means that no polymerization reaction occurs within the range in which the sacrificial plate precursor is normally used.
In the throwaway master, all of the constituent layers are non-photosensitive.

(Non-photosensitive layer)
The non-photosensitive layer is a layer which can be removed on a printing press by at least one of an acidic to alkaline dampening solution and a printing ink.
The non-photosensitive layer may contain a resin. The resin is mainly used for the purpose of improving the film strength of the non-photosensitive layer. The resin contained in the non-photosensitive layer may be a conventionally known resin used as a binder polymer in the image recording layer of a normal lithographic printing plate precursor, and is preferably a resin having film properties. Among them, acrylic resin, polyvinyl acetal resin, polyurethane resin, etc. are preferred.

The resin contained in the non-photosensitive layer preferably has a hydrophilic group, which contributes to imparting on-press developability to the non-photosensitive layer.
Examples of the hydrophilic group include a hydroxy group, a carboxy group, an alkylene oxide structure, an amino group, an ammonium group, an amide group, a sulfo group, a phosphate group, and the like, and among these, an alkylene oxide structure having 1 to 9 alkylene oxide units each having 2 or 3 carbon atoms is preferred. To impart a hydrophilic group to a resin, for example, a monomer having a hydrophilic group can be copolymerized.

A preferred example of the resin contained in the non-photosensitive layer is a polymer compound having a polyoxyalkylene chain in the side chain. By containing a polymer compound having a polyoxyalkylene chain in the side chain in the non-photosensitive layer, the permeability of the dampening water is promoted, and the on-press developability is improved.
Other preferred examples of the polymer compound having a polyoxyalkylene chain in its side chain and the resin contained in the non-photosensitive layer are described in paragraphs 0085 to 0102 of JP-A-2017-65184.

The resin contained in the non-photosensitive layer preferably has a mass average molecular weight (Mw) of 2,000 or more, more preferably 5,000 or more, and even more preferably 10,000 to 300,000.

The content of the resin contained in the non-photosensitive layer is suitably 3 to 90 mass % relative to the total solid content of the non-photosensitive layer, preferably 5 to 80 mass %, and more preferably 10 to 70 mass %.

The non-photosensitive layer may further contain, as necessary, surfactants, colorants, print-out agents, polymerization inhibitors, higher fatty acid derivatives, plasticizers, inorganic fine particles, inorganic layered compounds, co-sensitizers, chain transfer agents, etc. Specifically, the compounds and amounts of addition described in paragraphs 0114 to 0159 of JP-A No. 2008-284817, paragraphs 0023 to 0027 of JP-A No. 2006-091479, and paragraph 0060 of US Patent Publication No. 2008/0311520 can be preferably used.

The non-photosensitive layer may contain a specific hydroxy acid compound. In this case, the non-photosensitive layer corresponds to the specific component layer.

(Formation of Non-Photosensitive Layer)
The non-photosensitive layer can be formed by dispersing or dissolving the necessary components in a known solvent to prepare a coating solution, applying the coating solution by a known method such as bar coater coating, and drying. The coating amount (solid content) of the non-photosensitive layer after drying is preferably 0.05 to 1.0 g/ ^m2 , more preferably 0.1 to 0.7 g/ ^m2 , from the viewpoint of achieving both on-machine developability and scratch resistance.

In the throwaway plate precursor, the non-photosensitive layer may be provided directly on the aluminum support having an anodized film, or may be provided on an undercoat layer provided on the aluminum support having an anodized film. As the undercoat layer, the undercoat layer described for the on-press development type lithographic printing plate precursor can be used.
The sacrificial plate precursor may further have a protective layer on the non-photosensitive layer. As the protective layer, the protective layers described in relation to the on-press development type lithographic printing plate precursor can be used.

The on-press development type printing original plate of the present invention has a droop shape at the end.

FIG. 3 is a schematic diagram showing the cross-sectional shape of an edge portion of a lithographic printing plate precursor, which is one embodiment of a printing plate precursor.
3, the lithographic printing plate precursor 1 has a sag 2 at its edge. The distance X from the upper end of an edge surface 1c of the lithographic printing plate precursor 1 (the boundary point between the sag 2 and the edge surface 1c) to the intersection point between an extension line of the edge surface 1c and an extension line of the image recording layer surface (protective layer surface if a protective layer is formed) 1a is referred to as the "sag amount X," and the distance Y from the point where the image recording layer surface 1a of the lithographic printing plate precursor 1 starts to sag to the intersection point is referred to as the "sag width Y."

In terms of the sagging shape of the edge, the sagging amount X is preferably 25 μm or more, more preferably 35 μm or more, and even more preferably 40 μm or more. The upper limit of the sagging amount X is preferably 150 μm from the viewpoint of preventing deterioration of on-machine developability due to deterioration of the edge surface condition. When on-machine developability deteriorates, ink may adhere to the remaining image recording layer, which may cause edge staining. If the sagging amount X is too small, the ink adhered to the edge may be easily transferred to the blanket, which may cause edge staining. When the sagging amount X is in the range of 25 to 150 μm, if the sagging width Y is small, the occurrence of cracks at the edge increases, and printing ink may accumulate there, which may cause edge staining. From this viewpoint, the sagging width Y is preferably in the range of 70 to 300 μm, and more preferably in the range of 80 to 250 μm. The above sagging amount and sagging width ranges are not related to the edge shape of the support surface 1b of the lithographic printing plate precursor 1.
Usually, at the edge of the lithographic printing plate precursor 1, sagging occurs at the boundary B between the image recording layer and the support, and on the support surface 1b, similar to the image recording layer surface 1a.

The formation of the end portion having the above-mentioned drooped shape can be achieved, for example, by adjusting the cutting conditions of the printing plate precursor.
Specifically, this can be achieved by adjusting the gap between the upper and lower cutting blades, the amount of engagement, the blade angle, etc., of the slitter device used when cutting the printing plate master.
FIG. 4 is a conceptual diagram showing an example of the cutting section of a slitter device. In the slitter device, a pair of upper and lower cutting blades 10 and 20 are arranged vertically. The cutting blades 10 and 20 are circular blades on a disk, and the upper cutting blades 10a and 10b are supported coaxially on a rotating shaft 11, and the lower cutting blades 20a and 20b are supported coaxially on a rotating shaft 21. The upper cutting blades 10a and 10b and the lower cutting blades 20a and 20b are rotated in opposite directions. The printing plate 30 is cut to a predetermined width by passing between the upper cutting blades 10a and 10b and the lower cutting blades 20a and 20b. An end having a droopy shape can be formed by adjusting the gap between the upper cutting blade 10a and the lower cutting blade 20a and the gap between the upper cutting blade 10b and the lower cutting blade 20b in the cutting section of the slitter device.

In the on-press development type printing plate precursor according to the present invention, the arithmetic mean height Sa of the outermost layer surface on the side opposite to the side having the specific component layer is preferably 0.3 to 20 μm. Here, the side opposite to the side having the specific component layer means the side opposite to the side having the specific component layer with respect to the aluminum support.
In the on-press development type printing plate precursor according to the present invention, the arithmetic mean height Sa of the outermost layer surface on the side having the specific component layer is preferably 0.3 to 20 μm. Here, the side having the specific component layer means the side having the specific component layer with respect to the aluminum support.
By providing an outermost layer surface having such characteristics, the on-press development type printing master plate of the present invention, even when stacked in a form in which no interleaf paper is sandwiched between the master plates (also referred to as interleaf-less), is excellent in performance, such as preventing multiple feeding in the process of removing the master plates from the stack, preventing scratches caused by the convex portions provided on the outermost layer surface of the master plate, and preventing development delays caused by the convex portions provided on the outermost layer surface of the master plate.

The outermost surface on the side opposite to the side having the specific component layer is the surface of the backcoat layer if a backcoat layer is present on the opposite side, and is the surface of the support if no layer is present on the opposite side.
For example, when forming the protrusions described below, the printing plate may have the backcoat layer as the outermost layer and have a plurality of protrusions containing a polymer compound on the backcoat layer, or the support may have the support as the outermost layer and have a plurality of protrusions containing a polymer compound on the support.

When the image recording layer or the protective layer is the outermost layer, the outermost surface on the side having the specific component layer is the surface of the image recording layer or the surface of the protective layer.
For example, when forming protrusions as described below, the printing plate precursor may have the image recording layer or protective layer as the outermost layer, and may have a plurality of protrusions containing a polymer compound on the image recording layer or protective layer.

The arithmetic mean height Sa of the outermost layer surface on the side opposite to the side having the specific component layer is more preferably 0.5 to 10 μm, and further preferably 0.5 to 7 μm.
The arithmetic mean height Sa of the outermost layer surface on the side having the specific component layer is more preferably 0.5 to 10 μm, and further preferably 0.5 to 7 μm.

The arithmetic mean height Sa of the outermost layer surface is measured according to the method described in ISO 25178. Specifically, a Micromap MM3200-M100 manufactured by Ryoka Systems Co., Ltd. is used to measure three or more locations selected from the same sample, and the average of these measurements is taken as the arithmetic mean height Sa. The measurement range is a 1 cm x 1 cm area randomly selected from the sample surface.

In order to achieve the requirement that the arithmetic mean height Sa of the outermost layer surface be 0.3 to 20 μm, it is preferable that the outermost layer be formed into a shape having projections and recesses.
Specifically, for example, there are mentioned an embodiment in which the outermost layer contains particles having an average particle size of 0.5 to 20 μm (embodiment 1), and an embodiment in which the outermost layer has a plurality of protrusions containing a polymer compound as a main component (embodiment 2). Here, the main component means the component with the highest content ratio (mass %).

In aspect 1, the particles having an average particle diameter of 0.5 to 20 μm are not particularly limited, but are preferably at least one type of particles selected from organic resin particles and inorganic particles.

Preferred examples of the organic resin particles include particles made of synthetic resins such as poly(meth)acrylic acid esters, polystyrene and derivatives thereof, polyamides, polyimides, polyolefins such as low-density polyethylene, high-density polyethylene, and polypropylene, polyurethanes, polyureas, and polyesters, and particles made of natural polymers such as chitin, chitosan, cellulose, crosslinked starch, and crosslinked cellulose.
Among these, synthetic resin particles have the advantages that the particle size can be easily controlled and that the desired surface properties can be easily controlled by surface modification.

Regarding the method for producing organic resin particles, for a relatively hard resin such as polymethyl methacrylate (PMMA), it is possible to make the resin into fine particles by a crushing method, but a method for synthesizing particles by an emulsion suspension polymerization method is preferably adopted from the viewpoint of ease and accuracy of controlling the particle size.
Methods for producing organic resin particles are described in detail in, for example, "Ultrafine Particles and Materials" edited by the Society of Materials Science of Japan, published by Shokabo in 1993, and "Preparation and Application of Fine Particles and Powders" edited by Haruma Kawaguchi, published by CMC Publishing in 2005.

Organic resin particles are also available as commercially available products, for example, cross-linked acrylic resins MX-40T, MX-80H3wT, MX-150, MX-180TA, MX-300, MX-500, MX-1000, MX-1500H, MR-2HG, MR-7HG, MR-10HG, MR-3GSN, MR-5GSN, MR-7G, MR-10G, MR-5C, MR-7GC manufactured by Soken Chemical & Chemical Industry Co., Ltd., styryl resin-based SX-350H, SX-500H manufactured by Sekisui Chemical Co., Ltd. Examples of the resins include MBX-5, MBX-8, MBX-12, MBX-15, MBX-20, MB20X-5, MB30X-5, MB30X-8, MB30X-20, SBX-6, SBX-8, SBX-12, and SBX-17, polyolefin resins manufactured by Mitsui Chemicals, Inc., and Chemipearl W100, W200, W300, W308, W310, W400, W401, W405, W410, W500, WF640, W700, W800, W900, W950, and WP100.

Examples of inorganic particles include silica, alumina, zirconia, titania, carbon black, graphite, _BaSO4 , ZnS, _MgCO3 , _CaCO3 , ZnO, CaO, _WS2 , _MoS2 , MgO, _SnO2 , α- _Fe2O3 , α-FeOOH, SiC, _{CeO2 ,} BN, SiN, MoC, BC, WC, titanium carbide, corundum, artificial diamond, garnet, silica, tribolith, diatomaceous earth, and dolomite.

The particles are preferably particles having a hydrophilic surface, and include organic resin particles having a hydrophilic surface and inorganic particles having a hydrophilic surface.
The organic resin particles having a hydrophilic surface are preferably organic resin particles coated with at least one inorganic compound selected from the group consisting of silica, alumina, titania and zirconia, and more preferably organic resin particles coated with silica.
The organic resin constituting the organic resin particles having a hydrophilic surface is preferably at least one resin selected from the group consisting of polyacrylic resins, polyurethane resins, polystyrene resins, polyester resins, epoxy resins, phenolic resins, and melamine resins.

Below, organic resin particles having a hydrophilic surface will be described in detail using organic resin particles coated with silica (hereinafter also referred to as "silica-coated organic resin particles") as an example, but the organic resin particles having a hydrophilic surface are not limited to this.

The silica-coated organic resin particles are particles made of an organic resin and are surface-coated with silica. It is preferable that the organic resin particles constituting the core do not soften or become sticky due to moisture in the air or temperature.
Examples of the organic resin constituting the organic resin particles in the silica-coated organic resin particles include polyacrylic resins, polyurethane resins, polystyrene resins, polyester resins, epoxy resins, phenol resins, and melamine resins.

Preferred examples of materials for forming a silica layer that covers the surface of the silica-coated organic resin particles include compounds having an alkoxysilyl group, such as condensates of alkoxysiloxane-based compounds, in particular, siloxane-based materials, specifically, silica particles such as silica sol, colloidal silica, and silica nanoparticles.
The silica-coated organic resin particles may be configured such that silica particles are attached as a solid component to the surface of the organic resin particles, or such that a siloxane-based compound layer is formed on the surface of the organic resin particles by a condensation reaction of an alkoxysiloxane-based compound.

Silica does not necessarily have to cover the entire surface of the organic resin particles, and it is preferable that the surface is covered with at least 0.5% by mass or more based on the total mass of the organic resin particles. That is, the presence of silica on at least a part of the surface of the organic resin particles improves the affinity of the organic particle surface with the coexisting water-soluble polymer, for example, polyvinyl alcohol (PVA), and even when subjected to external stress, the particles are prevented from falling off, and excellent scratch resistance and ease of peeling during lamination without interleaving paper can be maintained. Therefore, the term "silica coating" also includes the state in which silica is present on at least a part of the surface of the organic resin particles.
The surface coating state of silica can be confirmed by morphological observation using a scanning electron microscope (SEM) etc. The amount of silica coating can be confirmed by detecting Si atoms using elemental analysis such as fluorescent X-ray analysis and calculating the amount of silica present therein.

There are no particular limitations on the method for producing silica-coated organic resin particles, and the method may involve making silica particles or a silica precursor compound coexist with a monomer component that is the raw material for the organic resin particles, thereby forming a silica surface coating layer at the same time as forming the organic resin particles, or it may involve forming organic resin particles, and then physically attaching silica particles to the surface, and then fixing the particles.

An example of a method for producing silica-coated organic resin particles is given below. First, silica and raw resin (more specifically, raw resin such as a monomer capable of suspension polymerization, a prepolymer capable of suspension cross-linking, or a resin liquid that constitutes the organic resin) are added to water containing a suspension stabilizer appropriately selected from water-soluble polymers such as polyvinyl alcohol, methyl cellulose, and polyacrylic acid, and inorganic suspension agents such as calcium phosphate and calcium carbonate, and then stirred and mixed to prepare a suspension in which the silica and raw resin are dispersed. At this time, a suspension having a desired particle size can be formed by adjusting the type of suspension stabilizer, its concentration, the stirring rotation speed, etc. Next, the suspension is heated to start a reaction, and the resin raw material is suspension polymerized or suspension cross-linked to generate resin particles. At this time, the coexisting silica is fixed to the resin particles that are hardened by polymerization or cross-linking reaction, especially near the surface of the resin particles due to its physical properties. Thereafter, the suspension is separated into solid and liquid, the suspension stabilizer attached to the particles is removed by washing, and the suspension is dried. Thus, approximately spherical silica-coated organic resin particles of the desired particle size to which silica is fixed are obtained.

In this way, the conditions can be controlled during suspension polymerization or suspension crosslinking to obtain silica-coated organic resin particles of the desired particle size, or silica-coated organic resin particles can be produced without strict control and then subjected to mesh filtration or the like to obtain silica-coated organic particles of the desired size.

Regarding the amounts of raw materials added to the mixture when producing silica-coated organic particles by the above method, for example, when the total amount of raw material resin and silica is 100 parts by mass, first, 0.1 to 20 parts by mass of a suspension stabilizer is added to 200 to 800 parts by mass of water as a dispersion medium, and thoroughly dissolved or dispersed. Then, the mixture of 100 parts by mass of raw material resin and silica is added to the liquid, and the stirring speed is adjusted so that the dispersed particles have a predetermined particle size. After this particle size adjustment, the liquid temperature is raised to 30 to 90°C, and the reaction is allowed to proceed for 1 to 8 hours.

Regarding the method for producing silica-coated organic resin particles, the above-mentioned method is one example, and silica-coated organic resin particles obtained by methods described in detail in, for example, JP-A Nos. 2002-327036, 2002-173410, 2004-307837, and 2006-38246 can also be suitably used in the present invention.

Silica-coated organic resin particles are also available as commercial products. Specific examples of silica/melamine composite particles include Optobeads 2000M, Optobeads 3500M, Optobeads 6500M, Optobeads 10500M, Optobeads 3500S, and Optobeads 6500S, all manufactured by Nissan Chemical Industries, Ltd. Examples of silica/acrylic composite particles include Art Pearl G-200 transparent, Art Pearl G-400 transparent, Art Pearl G-800 transparent, Art Pearl GR-400 transparent, Art Pearl GR-600 transparent, Art Pearl GR-800 transparent, and Art Pearl J-7P, all manufactured by Negami Chemical Industries, Ltd. Examples of the silica/urethane composite particles include Art Pearl C-400 transparent, C-800 transparent, P-800T, U-600T, U-800T, CF-600T, and CF800T, all of which are manufactured by Negami Chemical Industrial Co., Ltd.; and Dynamic Beads CN5070D and Danplacoat THU, all of which are manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

The above describes organic resin particles using silica-coated organic resin particles as an example, but the same can be done with organic resin particles coated with alumina, titania or zirconia by using alumina, titania or zirconia instead of silica.

The shape of the above particles is preferably spherical, but may also be flat or spindle-shaped, which has an elliptical projection.

In aspect 1, the average particle size of the particles is preferably 0.5 to 10 μm, more preferably 0.5 to 5 μm.

The average particle size of the particles means the volume average particle size, and the volume average particle size is measured by a laser diffraction/scattering type particle size distribution analyzer. Specifically, for example, the particle size distribution analyzer "Microtrac MT-3300II" (manufactured by Nikkiso Co., Ltd.) is used for the measurement.
For other particles, the average particle size is measured by the above measurement method unless otherwise specified.

In the embodiment 1, the in-plane density of the particles having an average particle size of 0.5 to 20 μm is preferably 10,000 particles/mm ² or less. The in-plane density is more preferably 100 to 5000 particles/mm ² , and further preferably 100 to 3000 particles/mm ² .

The in-plane density can be confirmed by observing the surface of the printing plate precursor with a scanning electron microscope (SEM). Specifically, the surface of the printing plate precursor is observed at five points with a scanning electron microscope (SEM), the number of particles is counted, and the number of particles is converted into the number of particles per ^mm2 of the observation field area, and the average value is calculated.

The outermost layer on the side opposite to the side having the specific component layer preferably contains a binder in addition to particles having an average particle size of 0.5 to 20 μm.
Examples of the binder include novolak resins such as phenol formaldehyde resin, m-cresol formaldehyde resin, p-cresol formaldehyde resin, m-/p-mixed cresol formaldehyde resin, and phenol/cresol (m-, p-, or m-/p-mixed) mixed formaldehyde resin, resol resin, pyrogallol, acetone resin, epoxy resin, saturated copolymer polyester resin, phenoxy resin, polyvinyl acetal resin, vinylidene chloride copolymer resin, polybutene, polybutadiene, polyamide, and unsaturated copolymer polyester resin. It is preferable that the toner contains at least one selected from the group consisting of ster resin, polyurethane, polyurea, polyimide, polysiloxane, polycarbonate, epoxy resin, chlorinated polyethylene, aldehyde condensation resin of alkylphenol, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylate, carboxyvinyl polymer, acrylic resin copolymer resin, hydroxycellulose, hydroxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, cellulose acetate, methylcellulose, and carboxymethylcellulose. A water-insoluble resin is preferable to prevent the risk of dissolution in dampening water during on-press development.

The binder preferably contains at least one selected from the group consisting of polyurethane, acrylic resin, polystyrene, and polyethylene.
In the above-mentioned embodiment 1, it is preferable that the particles and the binder each independently include at least one selected from the group consisting of polyurethane, acrylic resin, polystyrene, and polyethylene.

The outermost layer on the side opposite to the side having the specific component layer may contain other components in addition to the above particles and binder. Examples of other components include known additives, such as surfactants.

The thickness of the outermost layer on the side opposite to the side having the specific component layer is preferably 0.5 to 10 μm, more preferably 0.5 to 5 μm, and even more preferably 0.5 to 3 μm.

Examples of the polymer compound constituting the multiple protrusions containing the polymer compound in aspect 2 as a main component include novolak resins such as phenol formaldehyde resin, m-cresol formaldehyde resin, p-cresol formaldehyde resin, m-/p-mixed cresol formaldehyde resin, and phenol/cresol (m-, p-, or m-/p-mixed) mixed formaldehyde resin, resol resin, pyrogallol acetone resin, epoxy resin, saturated copolymer polyester resin, phenoxy resin, polyvinyl acetal resin, vinylidene chloride copolymer resin, polybutene, and polybutadiene. At least one polymer compound selected from the group consisting of polyamide, unsaturated copolymer polyester resin, polyurethane, polyurea, polyimide, polysiloxane, polycarbonate, epoxy resin, chlorinated polyethylene, aldehyde condensation resin of alkylphenol, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylate, carboxyvinyl polymer, acrylic resin copolymer resin, hydroxycellulose, hydroxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, cellulose acetate, methylcellulose, and carboxymethylcellulose is preferred.

Among them, water-soluble polymers are more preferable from the viewpoint of excellent developability even if the detached protrusions move to the image recording layer.Specific examples thereof include polyacrylates, carboxyvinyl polymers, acrylic resin copolymer resins, hydroxycellulose, hydroxymethylcellulose, polyvinyl alcohol, modified polyvinyl alcohol, polyvinylpyrrolidone, cellulose acetate, methylcellulose, and carboxymethylcellulose.
The modified polyvinyl alcohol is preferably an acid-modified polyvinyl alcohol having a carboxy group or a sulfo group, specifically, the modified polyvinyl alcohols described in JP-A-2005-250216 and JP-A-2006-259137.

The shape and height of the protrusions are not particularly limited, but it is preferable that the arithmetic mean height Sa is 0.3 to 20 μm.
The method for forming the striped protrusions (striped coating film) is not particularly limited, and the striped protrusions can be easily formed by applying a composition containing at least one selected from the group consisting of particles and polymer compounds by at least one method selected from the group consisting of a bar coating method, an inkjet printing method, a gravure printing method, a screen printing method, a spray coating method, and a slot die coating method.
The method for forming the dot-shaped protrusions (dot coating film) is not particularly limited, but they can be easily formed by applying a composition containing at least one selected from the group consisting of particles and polymer compounds by at least one method selected from the group consisting of a spray application method, an inkjet printing method, and a screen printing method.
The method for forming the dashed line-shaped protrusions (dashed line coating film) is not particularly limited, but they can be easily formed by applying a composition containing at least one selected from the group consisting of particles and polymer compounds by at least one method selected from the group consisting of an inkjet printing method and a screen printing method.

The binder contained in the outermost layer in embodiment 2 may be the same polymer compound as the polymer compound contained in the protrusions, and the same applies to preferred embodiments.
In aspect 2, from the viewpoint of preventing detachment of the protrusions, it is preferable that the binder contained in the outermost layer and the polymer compound contained in the protrusions contain the same type of resin. Here, the resin being the same type means that the resin type, such as polyurethane, acrylic resin, polystyrene, or polyethylene, is the same, and it is not necessary that all of the structural units in the resin are the same.

[Method of making a printing plate]
The method for producing a printing plate according to the present invention will be described using a lithographic printing plate precursor which is a printing plate precursor according to the present invention. The method for producing a printing plate includes a step of exposing the lithographic printing plate precursor to light (exposure step), and a step of removing the unexposed part of the image recording layer of the lithographic printing plate precursor after the image exposure on a printing press with at least one of printing ink and fountain solution (on-press development step).

[Exposure process]
Image exposure is preferably carried out by a method in which digital data is scanned and exposed with an infrared laser or the like.
The wavelength of the exposure light source is preferably 750 to 1,400 nm. As a light source having a wavelength of 750 to 1,400 nm, a solid-state laser or semiconductor laser that emits infrared light is suitable. The exposure mechanism may be any of an internal drum type, an external drum type, a flatbed type, etc.
The exposure step can be carried out by a known method using a plate setter, etc. Alternatively, after the lithographic printing plate precursor is mounted on a printing press equipped with an exposure device, image exposure may be carried out on the printing press.

[On-press development process]
In the on-press development step, when printing is started by supplying printing ink and fountain solution on the printing press without carrying out any development treatment on the lithographic printing plate precursor after image exposure, the unexposed parts of the lithographic printing plate precursor are removed at an early stage during printing, and the surface of the hydrophilic support is exposed, forming non-image parts. As the printing ink and fountain solution, known printing inks and fountain solutions for lithographic printing are used. Either the printing ink or the fountain solution may be supplied first to the surface of the printing plate precursor, but it is preferable to supply the printing ink first in order to prevent the fountain solution from being contaminated by the removed image recording layer components.
In this manner, the lithographic printing plate precursor is developed on-machine on an offset printing press and is used as is for printing a large number of sheets.

The method for producing a printing plate according to the present invention may include other known steps in addition to the steps described above. Examples of other steps include a plate inspection step for checking the position and orientation of the printing plate before each step, and a confirmation step for checking the printed image after the on-press development step.

[Printing method]
The printing method according to the present invention will be described using a throwaway plate as a printing plate precursor according to the present invention. The printing method includes a step of removing the non-photosensitive layer from the throwaway plate precursor on a printing press with at least one of printing ink and dampening water to prepare a throwaway plate, and a step of carrying out printing using the prepared throwaway plate.
The step of preparing the throwaway plate can be carried out in the same manner as the on-press development step described above.

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

[Examples 1 to 49 and Comparative Examples 1 to 6]

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

(J-a) Mechanical Roughening Treatment (Brush Grain Method)
Using an apparatus as shown in Fig. 5, a mechanical roughening treatment was performed by a rotating bundled brush while supplying a suspension of pumice (specific gravity 1.1 g/ ^cm3 ) as an abrasive slurry to the surface of an aluminum plate. In Fig. 5, 31 is an aluminum plate, 32 and 34 are roller-shaped brushes (bundled brushes in this embodiment), 33 is an abrasive slurry, and 35, 36, 37 and 38 are supporting rollers.
In the mechanical roughening treatment, the median diameter (μm) of the abrasive was 30 μm, the number of brushes was 4, and the rotation speed (rpm) of the brush was 250 rpm. The material of the bundled brush was 6-10 nylon, with a brush bristles diameter of 0.3 mm and bristles length of 50 mm. The brush was densely planted in a stainless steel cylinder with a diameter of φ300 mm. The distance between the two support rollers (φ200 mm) at the bottom of the bundled brush was 300 mm. The bundled brush was pressed down until the load of the drive motor rotating the brush was 10 kW more than the load before pressing the bundled brush against the aluminum plate. The rotation direction of the brush was the same as the movement direction of the aluminum plate.

(J-b) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 26% by mass and an aluminum ion concentration of 6.5% by mass onto an aluminum plate at a temperature of 70° C. The amount of aluminum dissolved on the surface to be subsequently subjected to electrochemical graining treatment was 10 g/ ^m2 .

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

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

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

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

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

(J-h) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 5% by mass and an aluminum ion concentration of 0.5% by mass onto an aluminum plate at a temperature of 60° C. The amount of dissolved aluminum was 0.2 g/ ^m2 .

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

(J-j) First-stage anodizing treatment The first-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 6. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50°C and a current density of 30 A/ ^dm2 , forming an anodized film with a film weight of 0.3 g/ ^m2 .

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

(J-l) Second-stage anodizing treatment The second-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 6. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50°C and a current density of 13 A/ ^dm2 , forming an anodized film with a film weight of 2.1 g/ ^m2 .

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

<Preparation of Support 2>
An aluminum plate (aluminum alloy plate) having a thickness of 0.3 mm and made of material 1S was subjected to the following treatments (F-a) to (F-g) to produce a support 2. Note that a water washing treatment was performed between all treatment steps, and after the water washing treatment, the liquid was removed with a nip roller.

(F-a) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda having a caustic soda concentration of 26% by mass and an aluminum ion concentration of 6.5% by mass onto an aluminum plate at a temperature of 70° C. The amount of aluminum dissolved on the surface to be subsequently subjected to electrochemical graining treatment was 5 g/ ^m2 .

(Fb) Desmutting Treatment Using Acidic Aqueous Solution As the acidic aqueous solution, an aqueous solution having a sulfuric acid concentration of 150 g/L and a liquid temperature of 30° C. was sprayed onto the aluminum plate for 3 seconds to perform a desmutting treatment.

(F-c) Electrochemical graining treatment Electrochemical graining treatment was performed using an electrolytic solution with a hydrochloric acid concentration of 14 g/L, an aluminum ion concentration of 13 g/L, and a sulfuric acid concentration of 3 g/L, and an alternating current. The temperature of the electrolytic solution was 30° C. The aluminum ion concentration was adjusted by adding aluminum chloride.
The AC current waveform was a sine wave with symmetrical positive and negative waveforms, the frequency was 50 Hz, the anode reaction time and cathode reaction time in one AC current cycle were 1:1, and the current density was 75 A/ ^dm2 at the peak current value of the AC current waveform. The total amount of electricity that the aluminum plate was responsible for the anode reaction was 450 C/ ^dm2 , and the electrolysis was performed in ^four separate sessions of 112.5 C/dm2 with a current application interval of 4 seconds. A carbon electrode was used as the counter electrode of the aluminum plate.

(F-d) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution of caustic soda with a caustic soda concentration of 5% by mass and an aluminum ion concentration of 0.5% by mass onto an aluminum plate at a temperature of 45° C. The amount of aluminum dissolved on the surface that had been subjected to the electrochemical graining treatment was 0.2 g/ ^m2 .

(Fe) Desmutting Treatment Using Acidic Aqueous Solution An acidic aqueous solution having a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L and a liquid temperature of 35° C. was sprayed onto the aluminum plate for 3 seconds to perform a desmutting treatment.

(F-f) First-stage anodizing treatment The first-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis having the structure shown in Fig. 6. Anodizing treatment was performed using a 150 g/L phosphoric acid aqueous solution as the electrolytic solution under conditions of a solution temperature of 35°C and a current density of 4.5 A/ ^dm2 , forming an anodized film with a film weight of 1 g/ ^m2 .

(F-g) Second-stage anodizing treatment The second-stage anodizing treatment was performed using an anodizing apparatus using direct current electrolysis with the structure shown in FIG. 6. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50° C. and a current density of 13 A/dm ² , forming an anodized film with a film weight of 2.1 g/m ^2. Thereafter, washing with water was performed by spraying. The average diameter of the micropores in the support 2 was 40 nm.
The anodic oxide film surface of Support 2 had a lightness L* value of 83.7 in the L*a*b* color system.

<Preparation of Support 3>
An aluminum plate (aluminum alloy plate) of material 1S having a thickness of 0.19 mm was degreased by immersing in a 40 g/L aqueous sodium hydroxide solution at 60° C. for 8 seconds, and then washed with demineralized water for 2 seconds. The aluminum plate was electrochemically roughened in an aqueous solution containing 12 g/L hydrochloric acid and 38 g/L aluminum sulfate (18-hydrate) using an alternating current for 15 seconds at a temperature of 33° C. and a current density of 130 A/dm ^2. After washing with demineralized water for 2 seconds, the aluminum plate was desmutted by etching with a 155 g/L aqueous sulfuric acid solution at 70° C. for 4 seconds, and then washed with demineralized water at 25° C. for 2 seconds. The aluminum plate was anodized in a 155 g/L aqueous sulfuric acid solution for 13 seconds at a temperature of 45° C. and a current density of 22 A/dm ² , and then washed with demineralized water for 2 seconds. The substrate was then treated with a 4 g/L aqueous solution of polyvinyl phosphonic acid at 40° C. for 10 seconds, washed with desalted water at 20° C. for 2 seconds, and dried to produce Support 3. Support 3 had a surface roughness Ra of 0.21 μm and an anodized film weight of 4 g/ ^m2 . The average diameter of micropores in Support 3 was 7 nm.
The anodic oxide film surface of Support 3 had a lightness L* value of 73.5 in the L*a*b* color system.

<Preparation of Support 4>
A 0.3 mm-thick aluminum plate (aluminum alloy plate) made of 1S material was subjected to the following treatments (A-a) to (A-g) to prepare a support 4. Note that a water-rinsing treatment was performed between all treatment steps, and after the water-rinsing treatment, the liquid was removed with a nip roller.

(A-a) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution having a caustic soda concentration of 26% by mass, an aluminum ion concentration of 6.5% by mass, and a temperature of 70° C. onto an aluminum plate. The amount of etching on the surface of the aluminum plate that was subsequently subjected to electrochemical graining treatment was 5 g/ ^m2 .

(Ab) Desmutting Treatment Using Acidic Aqueous Solution As the acidic aqueous solution, an aqueous solution having a sulfuric acid concentration of 150 g/L and a liquid temperature of 30° C. was sprayed onto the aluminum plate for 3 seconds to carry out a desmutting treatment.

(Ac) Electrochemical graining treatment using hydrochloric acid solution Electrochemical graining treatment was performed using an electrolytic solution with a hydrochloric acid concentration of 14 g/L, an aluminum ion concentration of 13 g/L, and a sulfuric acid concentration of 3 g/L, and an alternating current. The temperature of the electrolytic solution was 30° C. The aluminum ion concentration was adjusted by adding aluminum chloride.
The AC current waveform was a sine wave with symmetrical positive and negative waveforms, the frequency was 50 Hz, the anode reaction time and cathode reaction time in one AC current cycle were 1:1, and the current density was 75 A/ ^dm2 at the peak current value of the AC current waveform. The total amount of electricity that the aluminum plate was responsible for the anode reaction was 450 C/ ^dm2 , and the electrolysis was performed in ^four separate sessions of 112.5 C/dm2 with a current application interval of 4 seconds. A carbon electrode was used as the counter electrode of the aluminum plate.

(A-d) Alkaline Etching Treatment An etching treatment was performed by spraying an aqueous solution having a caustic soda concentration of 5 mass% and an aluminum ion concentration of 0.5 mass% at a temperature of 45° C. onto an aluminum plate. The amount of etching on the surface of the aluminum plate that had been subjected to the electrochemical graining treatment was 0.2 g/ ^m2 .

(A-e) Desmutting treatment using an acidic aqueous solution A waste liquid generated in an anodizing treatment process at a liquid temperature of 30°C (an aqueous solution having a sulfuric acid concentration of 170 g/L and an aluminum ion concentration of 5 g/L) was sprayed onto the aluminum plate for 3 seconds as an acidic aqueous solution, thereby carrying out a desmutting treatment.

(A-f) Anodizing treatment was performed using an anodizing device using direct current electrolysis with the structure shown in Fig. 6. Anodizing treatment was performed using a 170 g/L aqueous sulfuric acid solution as the electrolytic solution under conditions of a solution temperature of 50°C and a current density of 30 A/ ^dm2 , forming an anodized film with a film weight of 2.4 g/ ^m2 .
In an anodizing treatment apparatus 410 shown in Fig. 6, an aluminum sheet 416 is transported as indicated by an arrow in Fig. 6. In a power supply tank 412 in which an electrolytic solution 418 is stored, the aluminum sheet 416 is charged (+) by a power supply electrode 420. Then, in the power supply tank 412, the aluminum sheet 416 is transported upward by a roller 422, and its direction is changed downward by a nip roller 424, and then the aluminum sheet 416 is transported toward an electrolytic treatment tank 414 in which an electrolytic solution 426 is stored, and its direction is changed horizontally by a roller 428. Next, the aluminum sheet 416 is charged (-) by an electrolytic electrode 430, so that an anodized film is formed on the surface of the aluminum sheet 416, and the aluminum sheet 416 that leaves the electrolytic treatment tank 414 is transported to a subsequent process. In the anodizing treatment device 410, a direction changing means is constituted by the roller 422, the nip roller 424 and the roller 428, and the aluminum plate 416 is transported in a mountain shape and an inverted U shape in the space between the power supply tank 412 and the electrolytic treatment tank 414 by the rollers 422, 424 and 428. The power supply electrode 420 and the electrolytic electrode 430 are connected to a DC power source 434.

(A-g) Pore widening treatment The anodized aluminum plate was immersed in an aqueous solution of caustic soda with a caustic soda concentration of 5% by mass and an aluminum ion concentration of 0.5% by mass at 40° C. for 3 seconds to perform a pore widening treatment. Then, the plate was washed with water by spraying. The average diameter of the micropores was 30 nm.
The luminosity L* value of the anodized film surface of Support 4 in the L*a*b* color system was 81.4.

<Formation of Undercoat Layer 1>
An undercoat layer 1 was formed on the support by coating an undercoat layer coating solution (1) having the following composition so that the dry coating amount was 26 mg/ ^m2 .

(Undercoat Layer Coating Solution (1))
Undercoat layer compound (2) (structure shown below) 0.13 parts Hydroxyethyliminodiacetic acid 0.05 parts Tetrasodium ethylenediaminetetraacetate 0.05 parts Polyoxyethylene lauryl ether 0.03 parts Water 61.39 parts

The numbers in the parentheses to the right of each structural unit in the above undercoat layer compound (2) represent the mass ratio, and the numbers in the parentheses to the right of the ethyleneoxy units represent the repeating number.

<Formation of Undercoat Layer 2>
An undercoat layer 2 was formed on the support by coating an undercoat layer coating solution (2) having the following composition so that the dry coating amount was 93 mg/m ² .

(Undercoat Layer Coating Solution (2))
Specific hydroxy acid compound 0.90 parts Polyoxyethylene lauryl ether 0.03 parts Water 61.39 parts

<Formation of Undercoat Layer 3>
An undercoat layer 3 was formed on the support by coating an undercoat layer coating solution (3) having the following composition so as to give a dry coating amount of 11 mg/ ^m2 .

(Undercoat Layer Coating Solution (3))
Undercoat layer compound (3) (structure shown below) 0.13 parts Polyoxyethylene lauryl ether 0.03 parts Water 61.39 parts

<Formation of Image Recording Layer 1>
An image recording layer coating solution (1) having the following composition was applied with a bar and dried in an oven at 100° C. for 60 seconds to form an image recording layer 1 having a thickness of 1.2 μm.
The image recording layer coating solution (1) was obtained by mixing and stirring the following photosensitive solution (1) and microgel solution (1) immediately before coating.

(Photosensitive solution (1))
Binder polymer (6) 23% by mass solution in 1-methoxy-2-propanol (structure below)
0.2891 parts of binder polymer (7) 23% by weight 1-methoxy-2-propanol solution (structure below)
0.4574 parts of infrared absorbing agent (1) (structure shown below) 0.0278 parts of borate compound (1) (sodium tetraphenylborate)
0.015 parts of polymerization initiator (1) (structure shown below) 0.2348 parts of polymerizable compound (1) (tris(acryloyloxyethyl)isocyanurate, NK Ester A-9300 40% 2-butanone solution, manufactured by Shin-Nakamura Chemical Co., Ltd.)
0.2875 parts of low molecular weight hydrophilic compound (1) (tris(2-hydroxyethyl)isocyanurate
0.0287 parts of low molecular weight hydrophilic compound (2) (trimethylglycine)
0.0147 parts of anionic surfactant 1, 30% by weight aqueous solution (structure shown below) 0.25 parts of ultraviolet absorber (1) (TINUVIN 405, manufactured by BASF Ltd.) (structure shown below)
0.04 parts fluorine-based surfactant (1) (structure below) 0.004 parts phosphonium compound (1) (structure below) 0.020 parts 2-butanone 5.346 parts 1-methoxy-2-propanol 3.128 parts methanol 0.964 parts pure water 0.036 parts

(Microgel Liquid (1))
Microgel (1) (solid content concentration 21.8% by mass) 2.243 parts 1-methoxy-2-propanol 0.600 parts

(Preparation of Microgel (1))
The method for preparing the microgel (1) used in the above microgel solution is described below.

<Preparation of polyisocyanate compound (1)>
To a suspension of 17.78 parts (80 molar equivalents) of isophorone diisocyanate and 7.35 parts (20 molar equivalents) of the following polyhydric phenol compound (1) in ethyl acetate (25.31 parts), 0.043 parts of bismuth tris(2-ethylhexanoate) (Neostan U-600, manufactured by Nitto Kasei Co., Ltd.) was added and stirred. When the heat generation subsided, the reaction temperature was set to 50° C., and the mixture was stirred for 3 hours to obtain an ethyl acetate solution (50% by mass) of the polyhydric isocyanate compound (1).

<Preparation of Microgel (1)>
The following oil phase components and water phase components were mixed and emulsified for 10 minutes at 12,000 rpm using a homogenizer. The resulting emulsion was stirred at 45°C for 4 hours, and then 5.20 parts of a 10% by mass aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene-octylate (U-CAT SA102, manufactured by San-Apro Co., Ltd.) was added, stirred at room temperature for 30 minutes, and allowed to stand at 45°C for 24 hours. The solid content was adjusted to 21.8% by mass with distilled water to obtain an aqueous dispersion of microgel (4). The volume average particle size was measured by a light scattering method using a dynamic light scattering particle size distribution measuring device LB-500 (manufactured by Horiba, Ltd.), and was found to be 0.28 μm.

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

(Aqueous Phase Components)
Distilled water 46.87 parts

<Synthesis of binder polymer (6)>
78.0 g of 1-methoxy-2-propanol was weighed into a three-neck flask and heated to 70 ° C. under a nitrogen gas flow. A mixed solution consisting of 52.1 g of Blenmer PME-100 (methoxydiethylene glycol monomethacrylate, manufactured by Nippon Oil & Fats Co., Ltd.), 21.8 g of methyl methacrylate, 14.2 g of methacrylic acid, 2.15 g of hexakis (3-mercaptopropionic acid) dipentaerythritol, 0.38 g of V-601 (2,2'-azobis (isobutyric acid) dimethyl, manufactured by Wako Pure Chemical Industries, Ltd.), and 54 g of 1-methoxy-2-propanol was added dropwise to this reaction vessel over 2 hours and 30 minutes. After completion of the dropwise addition, the temperature was raised to 80 ° C., and the reaction was continued for another 2 hours. A mixed solution consisting of 0.04 g of V-601 and 4 g of 1-methoxy-2-propanol was added, and the temperature was raised to 90° C., and the reaction was continued for 2.5 hours. After the reaction was completed, the reaction solution was cooled to room temperature.
To the above reaction solution, 137.2 g of 1-methoxy-2-propanol, 0.24 g of 4-hydroxytetramethylpiperidine-N-oxide, 26.0 g of glycidyl methacrylate, and 3.0 g of tetraethylammonium bromide were added and thoroughly stirred, and then heated at 90°C.
After 18 hours, the reaction solution was cooled to room temperature (25° C.) and then diluted with 99.4 g of 1-methoxy-2-propanol.
The binder polymer (6) thus obtained had a solid content concentration of 23% by mass and a polystyrene-equivalent weight average molecular weight of 35,000 as measured by GPC.

<Synthesis of binder polymer (7)>
78.00 g of 1-methoxy-2-propanol was weighed into a three-neck flask and heated to 70 ° C. under a nitrogen gas flow. A mixed solution consisting of 52.8 g of Blenmer PME-100 (methoxydiethylene glycol monomethacrylate, manufactured by Nippon Oil & Fats Co., Ltd.), 2.8 g of methyl methacrylate, 25.0 g of methacrylic acid, 6.4 g of hexakis (3-mercaptopropionic acid) dipentaerythritol, 1.1 g of V-601 (2,2'-azobis (isobutyric acid) dimethyl, manufactured by Wako Pure Chemical Industries, Ltd.), and 55 g of 1-methoxy-2-propanol was added dropwise to this reaction vessel over 2 hours and 30 minutes. After completion of the dropwise addition, the temperature was raised to 80 ° C., and the reaction was continued for another 2 hours. After 2 hours, a mixed solution consisting of 0.11 g of V-601 and 1 g of 1-methoxy-2-propanol was added, and the temperature was raised to 90° C., and the reaction was continued for 2.5 hours. After the reaction was completed, the reaction solution was cooled to room temperature.
To the above reaction solution, 177.2 g of 1-methoxy-2-propanol, 0.28 g of 4-hydroxytetramethylpiperidine-N-oxide, 46.0 g of glycidyl methacrylate, and 3.4 g of tetrabutylammonium bromide were added and thoroughly stirred, and then heated at 90°C.
After 18 hours, the reaction solution was cooled to room temperature (25° C.) and then diluted with 0.06 g of 4-methoxyphenol and 114.5 g of 1-methoxy-2-propanol.
The binder polymer (7) thus obtained had a solid content concentration of 23% by mass and a weight average molecular weight of 15,000 in terms of polystyrene measured by GPC.

<Formation of Image Recording Layer 2>
An image recording layer coating solution (2) having the following composition was applied with a bar and then dried in an oven at 70° C. for 60 seconds to form an image recording layer 2 having a thickness of 0.6 μm.

(Image Recording Layer Coating Solution (2))
Polymerizable compound 1 * 1 0.15 parts Polymerizable compound 2 * 2 0.1 parts Graft copolymer 2 * 3 0.825 parts Klucel M * 4 0.020 parts Irgacure 250 * 5 0.032 parts Infrared absorber 1 (structure below) 0.02 parts Sodium tetraphenylborate 0.03 parts Byk 336 * 6 0.015 parts Black-XV * 7 0.04 parts n-propanol 7.470 parts Water 1.868 parts * 1: UA510H (manufactured by Kyoeisha Chemical Co., Ltd., a reaction product of dipentaerythritol pentaacrylate and hexamethylene diisocyanate)
*2: ATM-4E (manufactured by Shin-Nakamura Chemical Co., Ltd., ethoxylated pentaerythritol tetraacrylate)
*3: Graft copolymer 2 is a polymer particle of a graft copolymer of poly(ethylene glycol) methyl ether methacrylate/styrene/acrylonitrile=10:9:81, which is a dispersion containing 24% by mass in a solvent of n-propanol/water having a mass ratio of 80/20. The volume average particle size is 193 nm.
*4: Klucel M refers to hydroxypropyl cellulose available from Hercules.
*5: Irgacure 250 is an iodonium salt available from Ciba speciality Chemicals as a 75% propylene carbonate solution and has the structure iodonium, (4-methylphenyl) [4- (2-methylpropyl) phenyl], -hexafluorophosphate.
*6: Byk 336 is a modified dimethylpolysiloxane copolymer available from Byk Chemie in a 25% xylene/methoxypropyl acetate solution.
*7: Black-XV (the following compound, manufactured by Yamamoto Chemical Industry Co., Ltd.)

<Formation of Image Recording Layer 3>
An aqueous coating solution for the image recording layer containing the thermoplastic polymer particles, the infrared absorbing agent and polyacrylic acid was prepared, the pH of which was adjusted to 3.6, and then the solution was coated on a support and dried at 50° C. for 1 minute to form an image recording layer 3. The coating amounts of each component after drying are shown below.

Thermoplastic polymer particles 0.7 g/ ^m2
Infrared absorber IR-01 1.20× ^10-4 g/ ^m2
Polyacrylic acid 0.09 g / ^m2

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

Thermoplastic polymer particles: styrene/acrylonitrile copolymer (molar ratio 50/50), Tg: 99° C., volume average particle size: 60 nm
Infrared absorbent IR-01: an infrared absorbent having the following structure

Polyacrylic acid Mw: 250,000

<Formation of Image Recording Layer 4>
An image recording layer coating solution (4) having the following composition was applied with a bar and dried in an oven at 100° C. for 60 seconds to form an image recording layer 4 having a thickness of 0.6 μm.

(Image Recording Layer Coating Solution (4))
Infrared absorber 4 (structure below) 0.030 parts Polymerization initiator I (structure below) 0.032 parts Polymerizable compound (1) A-9300 (manufactured by Shin-Nakamura Chemical Co., Ltd.) (structure below)
0.05 parts of polymerizable compound (2) A-DPH (manufactured by Shin-Nakamura Chemical Co., Ltd.) (structure shown below)
0.05 parts of binder polymer 3 (see below) 0.825 parts of surfactant BYK306 (manufactured by Byk Chemie)
0.008 parts 1-methoxy-2-propanol 8.609 parts methyl ethyl ketone 1.091 parts

(Synthesis of Binder Polymer 3)
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 the following compound 1, 30.0 g of the following compound 2, 20.0 g of the following compound 3, 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 another 7.5 hours. Then, 0.3 g of AIBN was added, and the reaction was continued for another 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature to obtain binder polymer 3. The weight average molecular weight of the obtained binder polymer 3 was 75,000.

<Formation of Image Recording Layer 5>
An image recording layer coating solution (5) having the following composition was applied with a bar and dried in an oven at 70° C. for 60 seconds to form an image recording layer 5 having a thickness of 0.6 μm.

(Image Recording Layer Coating Solution (5))
To the above image recording layer coating solution (2), 0.093 parts of Art Pearl J-6PF (average particle size: 4 μm) (highly crosslinked acrylic resin, manufactured by Negami Chemical Industries, Ltd.) was added to prepare an image recording layer coating solution.

<Formation of Non-Photosensitive Layer 6>
A non-photosensitive layer coating solution (6) having the following composition was applied with a bar and dried in an oven at 100° C. for 60 seconds to form a non-photosensitive layer 6 having a thickness of 0.05 μm.

(Non-photosensitive layer coating solution (6))
Nonionic surfactant 1 (structure shown below) 0.02 parts Colorant (OIL YELLOW 105, Orient Chemical Industries Co., Ltd.)
0.015 parts methyl ethyl ketone 5.587 parts 1-methoxy-2-propanol 3.725 parts methanol 3.104 parts

<Formation of Protective Layer 1>
A protective layer coating solution (1) having the following composition was applied with a bar and dried in an oven at 120° C. for 60 seconds to form a protective layer 1 having a thickness of 0.18 μm.

(Protective Layer Coating Solution (1))
Inorganic layered compound dispersion (1) (see below) 2.212 parts Polyvinyl alcohol (Gohselan L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., sulfonic acid modified, saponification degree 85 mol%) 6 mass % aqueous solution
1.440 parts surfactant (Paionin A-32-B (see below), Takemoto Oil Co., Ltd.) 40% by weight aqueous solution)
0.014 parts of surfactant (Surfynol 465 (see below), manufactured by Nissin Chemical Industry Co., Ltd.)
0.006 parts/Pure water 3.955 parts

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

<Formation of Protective Layer 2>
A protective layer coating solution (2) having the following composition was applied with a bar and dried in an oven at 120° C. for 60 seconds to form a protective layer 2 having a thickness of 0.8 μm.

(Protective Layer Coating Solution (2))
Polyvinyl alcohol (Poval PVA105, manufactured by Kuraray Co., Ltd.)
0.6 parts polyethylene glycol (PEG 4000, manufactured by Tokyo Chemical Industry Co., Ltd.)
0.39 parts of surfactant (Rapisol A-80 (see below), manufactured by NOF Corp.)
0.01 part/pure water: 9 parts

<Formation of protective layer 3>
A protective layer coating solution (3) having the following composition was applied with a bar and dried in an oven at 120° C. for 60 seconds to form a protective layer 3 having a thickness of 0.5 μm.

(Protective Layer Coating Solution (3))
Polyvinyl alcohol (Gohselan L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., sulfonic acid modified, saponification degree 85 mol%) 0.500 parts Surfactant (Lapisol A-80 (above) 0.024 parts Anionic surfactant 1 (above) 0.333 parts Pure water 18,000 parts

[Preparation of printing plate]
The above supports, undercoat layers, image recording layers, non-photosensitive layers and protective layers were combined as shown in Table A to prepare lithographic printing plate precursors of Examples 1 to 43 and 45, sacrificial plate precursors of Examples 46 to 48, and lithographic printing plate precursors of Comparative Examples 1 to 6.
The lithographic printing plate precursor of Example 44 was prepared by combining the above-mentioned support, undercoat layer, image recording layer and protective layer as shown in Table A, and further forming the following backcoat layer 1.
The throwaway plate master of Example 49 was prepared by using the same combination of support, undercoat layer, image recording layer and protective layer as in Example 46, and further forming the following backcoat layer 2.

<Formation of Backcoat Layer 1>
A backcoat layer coating solution (1) having the following composition was applied with a bar to the side of the support opposite to the side having the specific component layer (protective layer) and dried at 100° C. for 30 seconds to form a backcoat layer 1 having a thickness of 1.2 μm.

(Backcoat Layer Coating Solution (1))
- Acrylic resin (BR-605, manufactured by Mitsubishi Chemical Corporation)
11.072 parts of organic smectite (Sumecton-SEN (tabular particles), manufactured by Kunimine Kogyo Co., Ltd.) 0.500 parts of acrylic particles (Art Pearl J-6PF, manufactured by Negami Chemical Industries Co., Ltd.)
0.975 parts surfactant (Rheodol TW-S106V (polyoxyethylene (6) sorbitan monostearate), manufactured by Kao Corporation) 0.250 parts 2-butanone 74.123 parts 1-methoxy-2-propanol 8.720 parts methanol 4.360 parts

<Formation of backcoat layer 2>
A backcoat layer coating solution (2) having the following composition was applied with a bar to the side of the support opposite to the side having the specific component layer (protective layer) and dried at 100° C. for 30 seconds to form a backcoat layer 2 having a thickness of 1.2 μm.

(Backcoat Layer Coating Solution (2))
- Acrylic resin (BR-73, manufactured by Mitsubishi Chemical Corporation)
11.072 parts of organic smectite (Sumecton-SEN (tabular particles), manufactured by Kunimine Kogyo Co., Ltd.) 0.500 parts of acrylic particles (Art Pearl J-6PF, manufactured by Negami Chemical Industries Co., Ltd.)
0.975 parts surfactant (Rheodol TW-S106V (polyoxyethylene (6) sorbitan monostearate), manufactured by Kao Corporation) 0.250 parts 2-butanone 74.123 parts 1-methoxy-2-propanol 8.720 parts methanol 4.360 parts

For the lithographic printing plate precursor of Comparative Example 6, after coating the image recording layer, without drying, an aqueous solution of the comparative compound was coated using a coating device 2NL04 manufactured by Heishin Kikai Co., Ltd. That is, the clearance of the coating device was fixed at 0.3 m, and the amount of liquid sent was adjusted to coat the aqueous solution of the comparative compound in a width of 6 mm at a position 3 cm from the edge so as to obtain the content of the comparative compound shown in Table A. The plate was then oven-dried at 100°C for 60 seconds.

In Table A, the layer to which a specific hydroxy acid compound or a comparative compound is added represents a constituent layer (undercoat layer, image recording layer, non-photosensitive layer, protective layer) of a printing plate precursor containing the specific hydroxy acid compound or the comparative compound. The constituent layer can be formed by adding the specific hydroxy acid compound or the comparative compound to a coating solution for the corresponding constituent layer to prepare a coating solution, and coating the coating solution.
In Comparative Example 6, the amount of the comparative compound (citric acid) added is described as 200/0, which indicates that the amount of the comparative compound added in the edge region is 200 mg/ ^m2 and the amount of the comparative compound added in the region other than the edge is 0 mg/ ^m2 .

In the lithographic printing plate precursor of Example 44, the backcoat layer contained resin particles having an average particle diameter of 4 μm, and the arithmetic mean height Sa of the outermost layer (backcoat layer) surface on the side opposite to the side having the specific component layer was 1.8 μm.
In the lithographic printing plate precursor of Example 45, the image recording layer contained resin particles having an average particle diameter of 4 μm, and the arithmetic mean height Sa of the surface of the outermost layer (image recording layer) on the side having the specific component layer (undercoat layer) was 1.5 μm.
In the throwaway plate master of Example 49, the backcoat layer contained resin particles having an average particle diameter of 4 μm, and the arithmetic mean height Sa of the outermost layer (backcoat layer) surface on the side opposite to the side having the specific component layer was 1.8 μm.

<Cutting the printing plate>
The printing plate precursor was cut using a rotary blade as shown in FIG. 4, with the gap between the upper and lower cutting blades, the amount of engagement, and the blade tip angle adjusted, to form a droop shape at the edge.
The lithographic printing plate precursor of Comparative Example 6 was cut at the center of the 6 mm wide area where the aqueous solution of the comparative compound was applied, to obtain a lithographic printing plate precursor having a droop shape at the edge and a 3 mm wide area of the comparative compound.
The sagging amount X and the sagging width Y of the sagging shape are shown in Table A.

[Evaluation of printing plate]
The printing plate precursor was evaluated for edge stain prevention and image forming properties at the edge as follows.

<Prevents edge staining over time>
The lithographic printing plate precursors of Examples 1 to 45 and Comparative Examples 1 to 6 were exposed using a Luxcel PLATESETTER T-6000III equipped with an infrared semiconductor laser manufactured by FUJIFILM Corporation under the conditions of an outer drum rotation speed of 1,000 rpm, a laser output of 70%, and a resolution of 2,400 dpi. A chart including a solid image, a 50% halftone dot, and a non-image area was used as the exposed image.
The image-exposed lithographic printing plate precursors and the throwaway plates of Examples 46 to 49 were mounted on an offset rotary printing press manufactured by Tokyo Kikai Seisakusho Co., Ltd., and printing was performed on newsprint at a speed of 100,000 sheets/hour using Soybee KKST-S (red) manufactured by Inktec Co., Ltd. as newspaper printing ink and Toyo ALKY manufactured by Toyo Ink Co., Ltd. as dampening water. The 1,000th printed sheet was sampled at a water mark 1.1 times the water mark for eliminating background staining, and the degree of linear staining caused by the edge of the printing plate precursor was evaluated according to the following criteria. The results are shown in Table A as edge stain prevention and no aging.
5: Not dirty at all 4: Intermediate level between 5 and 3 3: Slightly dirty but acceptable level 2: Intermediate level between 3 and 1 (acceptable level)
1: Clearly dirty and unacceptable

<Edge stain prevention, after aging>
The printing plate precursors of Examples 1 to 49 and Comparative Examples 1 to 6 were left for 10 days in an environment with a relative humidity of 70% and a temperature of 25° C. (corresponding to leaving them for 12 months in a normal environment (relative humidity of 50% and temperature of 25° C.)). Thereafter, the edge stain prevention property was evaluated in the same manner as above. The results are shown in Table A as edge stain prevention property after aging.

<Image Formability at Edges>
The lithographic printing plate precursors of Examples 1 to 45 and Comparative Examples 1 to 6, which had been image-exposed in the same manner as in the evaluation of edge stain prevention property and without aging, were mounted on an offset rotary printing press manufactured by Tokyo Kikai Seisakusho Co., Ltd., and printed on newsprint at a speed of 100,000 sheets/hour using Soybee KKST-S (red) manufactured by Inktec Corporation as the newspaper printing ink and Eco7 N-1 manufactured by Sakata Inx Corporation as the fountain solution. The 1,000th, 10,000th, 50,000th and 100,000th printed sheets were sampled, and the image formability in the region up to 1 mm inward from the edge of the printing plate precursor was evaluated according to the following criteria.
5: Images are still printed even after 100,000 copies.
4: Images are still printed even after 50,000 copies.
3: The image is still printed even after 10,000 copies.
2: The image is still printed even after 1,000 copies.
1: After printing 1,000 sheets, the image is not printed.

From the results shown in Table A, it can be seen that the printing plate precursor containing the specific hydroxy acid compound according to the present invention exhibits excellent edge stain prevention properties not only after production but also after aging, and the edge stain prevention properties are well maintained over a long period of time. In contrast, the printing plate precursors of Comparative Examples 1-5, which contain comparative compounds other than the specific hydroxy acid compound, have poor edge stain prevention properties after aging. The citric acid used in Comparative Example 4 is a hydroxy acid having one hydroxyl group, and has poor edge stain prevention properties after aging. It can be said that the fact that excellent edge stain prevention properties are maintained even after aging due to the difference in the number of hydroxyl groups in this way is an unexpected and surprising effect.
It is also seen that the lithographic printing plate precursor according to the present invention has good image forming properties at the edges. In contrast, the lithographic printing plate precursor of Comparative Example 6 has poor image forming properties at the edges. This effect of good image forming properties at the edges can also be said to be an unexpected and surprising effect caused by the difference in the number of hydroxyl groups.
In addition, Examples 1 to 12, 14 to 28, 30 to 33, 37 to 40, 44 to 46, and 49 should be read as Reference Examples 1 to 12, 14 to 28, 30 to 33, 37 to 40 , 44 to 46, and 49, respectively.

According to the present invention, it is possible to provide an on-press development type printing original plate in which edge contamination is prevented not only after production but also after aging, a method for making a printing plate using an on-press development type printing original plate, and a printing method using an on-press development type printing original plate.
Furthermore, according to the present invention, it is possible to provide an on-press development type lithographic printing plate precursor in which deterioration of image formability in edge regions is suppressed.

This application is based on a Japanese patent application (Patent Application No. 2020-011914) filed on January 28, 2020, and a Japanese patent application (Patent Application No. 2020-103357) filed on June 15, 2020, the contents of which are incorporated by reference into this application.

REFERENCE SIGNS LIST 1 Lithographic printing plate precursor 1a Image recording layer surface 1b Support surface 1c End surface 2 Droop 10 Cutting blade 10a Upper cutting blade 10b Upper cutting blade 11 Rotating shaft 20 Cutting blade 20a Lower cutting blade 20b Lower cutting blade 21 Rotating shaft 30 Printing plate precursor 31 Aluminum plate 32, 34 Roller-shaped brush 33 Polishing slurry liquid 35, 36, 37, 38 Support roller 50 Main electrolytic cell 51 AC power source 52 Radial drum roller 53a, 53b Main electrode 54 Electrolyte supply port 55 Electrolyte 56 Slit 57 Electrolyte passage 58 Auxiliary anode 60 Auxiliary anode cell 410 Anodizing device 412 Power supply cell 414 Electrolytic cell 416 Aluminum plate 418, 426 Electrolyte 420 Power supply electrode 422, 428 Roller 424 Nip roller 430 Electrolysis electrode 432 Tank wall 434 DC power source B Boundary between image recording layer surface and support W Aluminum plate X Droop amount Y Droop width

Claims (24)

An on-press development type printing plate precursor having at least one constituent layer on an aluminum support having an anodized film, wherein an edge of the on-press development type printing plate precursor has a drooped shape, and the at least one constituent layer contains a hydroxy acid compound having two or more hydroxyl groups, has a molecular weight of 60 to 300, and has a solubility in water at 20°C of 10 g/L or more, and the content of the water-soluble compound is substantially uniform within the plane of the constituent layer,
the on-press development type printing plate precursor has an image recording layer,
The on-press development type printing plate precursor has a protective layer,
The on-press development type printing plate precursor, wherein the constituent layer containing the hydroxy acid compound is a protective layer. 2. The on-press development type printing plate precursor according to claim 1 , which has an undercoat layer. 3. The on-press development type printing plate precursor according to claim 1, wherein the protective layer contains a polyvinyl alcohol resin. 4. The on-press development type printing plate precursor according to claim 1, wherein the image recording layer contains an infrared absorbing agent, a polymerization initiator, a polymerizable compound, and a polymer compound. 5. The on-press development type printing plate precursor according to claim 4 , wherein the polymer compound contains a structural unit derived from a styrene compound and/or a structural unit derived from an acrylonitrile compound. 6. The on-press development type printing original plate according to claim 5, wherein in the polymer compound containing a structural unit derived from a styrene compound and a structural unit derived from an acrylonitrile compound, a compositional ratio of the structural unit derived from a styrene compound to the structural unit derived from an acrylonitrile compound is 4 :1 to 1:4. The on-press development type printing plate precursor according to any one of claims 4 to 6 , wherein the polymer compound is a polymer particle. 8. The on-press development type printing plate precursor according to claim 7 , wherein the polymer particles are thermoplastic particles. An on-press development type printing plate precursor having at least one constituent layer on an aluminum support having an anodized film, wherein an edge of the on-press development type printing plate precursor has a drooped shape, and the at least one constituent layer contains a hydroxy acid compound having two or more hydroxyl groups, has a molecular weight of 60 to 300, and has a solubility in water at 20°C of 10 g/L or more, and the content of the water-soluble compound is substantially uniform within the plane of the constituent layer,
The on-press development type printing plate precursor has a non-photosensitive layer, and all of the constituent layers are non-photosensitive,
The on-press development type printing plate precursor has an undercoat layer. The on-press development type printing plate precursor according to claim 9 , which has a protective layer. The on-press development type printing plate precursor according to claim 10 , wherein the protective layer contains a polyvinyl alcohol resin. The on-press development type printing plate precursor according to any one of claims 9 to 11 , wherein the constituent layer containing the hydroxy acid compound is a non-photosensitive layer. The on-press development type printing plate precursor according to any one of claims 9 to 11 , wherein the layer containing the hydroxy acid compound is an undercoat layer. The on-press development type printing plate precursor according to claim 10 or 11 , wherein the constituent layer containing the hydroxy acid compound is a protective layer. The on-press development type printing plate precursor according to any one of claims 1 to 14 , wherein the hydroxy acid compound has a ClogP value of 0.5 or less. 16. The on-press development type printing plate precursor according to any one of claims 1 to 15 , wherein the molecular weight of the hydroxy acid compound is 1,000 or less. The on-press development type printing plate precursor according to any one of claims 1 to 16 , wherein the content of the hydroxy acid compound is 10 to 200 mg/ ^m2 . 18. The on-press development type printing plate precursor according to claim 1, wherein the arithmetic mean height Sa of the outermost layer surface on the side opposite to the side having the constituent layer containing a hydroxy acid compound is 0.3 to 20 μm. 19. The on-press development type printing plate precursor according to any one of claims 1 to 18 , wherein the arithmetic mean height Sa of the outermost layer surface on the side having the component layer containing a hydroxy acid compound is 0.3 to 20 μm. 20. The on-press development type printing plate precursor according to any one of claims 1 to 19, wherein an average diameter of micropores on a surface of the anodized coating is 10 to 100 nm , and a lightness L* value in the L*a*b* color system of a surface of the anodized coating on a side of a component layer containing a hydroxy acid compound is 60 to 100. 21. The on-press development type printing plate precursor according to claim 1, wherein the micropores in the anodized film are composed of large diameter pores extending 10 nm to 1,000 nm in a depth direction from a surface of the anodized film, and small diameter pores that communicate with bottoms of the large diameter pores and extend 20 nm to 2,000 nm in a depth direction from the communicating positions, the large diameter pores having an average diameter of 15 nm to 100 nm at the surface of the anodized film, and the small diameter pores having an average diameter of 13 nm or less at the communicating positions. The on-press development type printing plate precursor according to any one of claims 1 to 21, wherein the sagging shape of the end portion of the on-press development type printing plate precursor is a sagging amount X of 25 to 150 µm and a sagging width Y of 70 to 300 µm. 9. A method for preparing a printing plate, comprising: a step of imagewise exposing the on-press development type printing plate precursor according to any one of claims 1 to 8 ; and a step of supplying at least one of printing ink and dampening water on a printing press to remove an unexposed area of an image recording layer in the imagewise exposed on-press development type printing plate precursor. A printing method comprising the steps of: supplying at least one of printing ink and dampening water to an on-press development type printing plate precursor according to any one of claims 9 to 14 on a printing press to remove a non-photosensitive layer in the on-press development type printing plate precursor to prepare a throwaway plate; and carrying out printing using the prepared throwaway plate.

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