JP2006030342A - Image recording material and lithographic printing original plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image recording material which suppresses fogging discoloration under a white light and suppresses deterioration of sensitivity to a change in color in image exposure, and also to provide a lithographic printing original plate having the image recording material as an image recording layer. <P>SOLUTION: The image recording material contains: (A) a radical initiator; (B) a compound which causes a change in color by the action of a radical; and (C) a compound which generates a radical capturing chemical species upon heating. The lithographic printing original plate has the image recording material as an image recording layer. A method is also provided by which discoloration after imagewise exposure of (B) the compound which causes a change in color by the action of a radical in the image recording layer is suppressed by heating the lithographic printing original plate after imagewise exposure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image recording material and a lithographic printing plate precursor that produce a printout image by image exposure.

  In recent years, in the field of lithographic printing, computer-to-plate technology has been developed in which lithographic printing plate precursors are directly exposed to laser on the basis of digital data such as computers without using a lithographic film. A lithographic printing plate of the type has been developed.

  However, the conventional high-sensitivity laser recording lithographic printing plate is fogged when exposed to the most commonly used Ar (488, 514.5 nm) or FD-YAG (532 nm) laser inner drum plate setter on the market. There was a problem that it was likely to occur. That is, for example, when a negative type plate is used as a light-sensitive material, if a solid image is exposed on one side of the plate, if the opposite side is a non-image area, a thin development defect fogging occurs, and the opposite side In the case of a mesh (when the opposite side is 180 ° with respect to the light source) is a mesh, there is a problem that a halftone dot becomes thick, and improvement has been desired.

  In addition, conventional high-sensitivity printing plates compatible with Ar lasers and FD-YAG lasers can be removed from cardboard packaging under red light, loaded into plate setter cassettes, and sometimes manually placed into plate setters. A plate was inserted, and it was necessary to work under a dark red light. In contrast, ordinary diazo printing plates can be handled easily under yellow light or under UV-cut white light, and the safety light suitability for high-sensitivity laser recording lithographic printing plates is greatly improved from the market in terms of workability. It was a request.

  On the other hand, Patent Document 1 (Japanese Patent Laid-Open No. 2000-35673) discloses a lithographic printing plate comprising at least (A) an aluminum support and (B) a laser-sensitive recording layer in the ultraviolet to visible light region ( A plate making method of a lithographic printing plate is described, wherein exposure is performed with an inner drum type plate setter using a semiconductor laser beam of 360 to 450 nm). Further, it is described that according to this plate making method, it is possible to handle under a yellow light, and fog does not occur even in exposure with an inner drum type plate setter.

On the other hand, in the plate making process of the conventional lithographic printing plate precursor, a step of dissolving and removing unnecessary portions of the image recording layer with a developer or the like is necessary after exposure. In recent years, such additional wet processing is performed. One of the problems is to make the processing unnecessary or simplified.
As one of the simple plate making methods that respond to this, for example, an exposed plate mounted on a printing machine using a lithographic printing plate precursor having an image recording layer that can be dissolved or dispersed in printing ink and / or fountain solution A method called on-press development has been proposed in which printing ink and / or dampening water is supplied to remove unexposed portions of the image recording layer to obtain a lithographic printing plate.

  For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 47-8657) discloses a photosensitive composition containing polyvinylpyrrolidone, a polymer polycarboxylic acid, an olefinically unsaturated monomer, and optionally a photoinitiator and a polymerization inhibitor. It is described that a printing plate can be obtained that can be immediately attached to a printing press and printed without post-exposure processing.

A lithographic printing plate precursor is usually designed so that a printout image appears upon image exposure. This print-out image is used to identify whether or not the original has been exposed in a lithographic printing plate precursor that is developed after image exposure. Plate inspection before printing is performed on the developed image. . However, in the case of an on-press development type or no processing (no development) type lithographic printing plate precursor that does not involve a development processing step before printing, this printout image is also used for plate inspection at the stage of attaching the printing plate to the printing press. It is done. For example, Patent Document 3 discloses an unprocessed lithographic printing plate precursor using a compound that generates an acid, base, or radical by light or heat and a compound that changes color by interacting with the generated acid, base, or radical. Are listed.
JP 2000-35673 A JP-A-47-8657 JP-A-11-277927

Since the conventional printout image is not fixed, if the lithographic printing plate precursor is exposed to white light after image exposure, the part that was not exposed to light during image exposure will also undergo color change (fogging discoloration due to white light). As a result, there has been a problem that the difference in brightness from the color-changed portion due to image exposure is reduced, and the image visibility is deteriorated. Such deterioration of image visibility due to white light color change is not particularly accompanied by a development processing step before printing, and in the case of on-press development type or non-processing (no development) type lithographic printing plate precursor, Since this means that sufficient plate inspection at the stage of attachment to the printing press cannot be performed, an improvement thereof has been desired. The present invention solves this problem.
That is, an object of the present invention is to provide an image recording material that is compatible with suppression of fog discoloration due to white light and color change sensitivity during image exposure, and a lithographic printing plate precursor using the image recording material as an image recording layer. It is in. Another object of the present invention is to provide a method for suppressing color change after imagewise exposure of a lithographic printing plate precursor.

The present invention is as follows.
1. An image recording material comprising (A) a radical initiator, (B) a compound that changes color by the action of a radical, and (C) a compound that generates a chemical species that traps radicals by heating.
2. An image recording layer containing (A) a radical initiator, (B) a compound that changes color by the action of a radical, and (C) a compound that generates a chemical species that captures radicals by heating on a support. A lithographic printing plate precursor having.

  3. 2. The lithographic printing plate precursor as described in 1 above, wherein the image recording layer further contains (D) a radical polymerizable compound.

  4). 4. The lithographic printing plate precursor as described in 3 above, wherein the image recording layer is an image recording layer removable with printing ink and / or fountain solution.

  5. 5. The lithographic printing plate precursor as described in 3 or 4 above, wherein the image recording layer has photosensitivity in the range of 250 nm to 420 nm.

  6). 5. The lithographic printing plate precursor as described in 3 or 4 above, wherein the image recording layer further contains an infrared absorber.

  7). Any of the above 2 to 6, wherein the compound that generates a chemical species that captures radicals by heating (C) has a phenolic hydroxyl group protected by a group that can be decomposed by heat. The lithographic printing plate precursor described in 1.

8). The lithographic printing plate precursor as described in any one of 2 to 6 above is imagewise exposed and then subjected to heat treatment, whereby (B) a compound that causes a color change by the action of radicals contained in the image recording layer Of suppressing color change after imagewise exposure.

  9. The light source for imagewise exposure is laser light. (B) The color change after imagewise exposure of a compound that causes a color change due to the action of radicals (B) contained in the image recording layer. How to suppress.

The operation mechanism of the present invention is presumed as follows.
When a lithographic printing plate precursor having a print-out image using a color change caused by the action of radicals is exposed to white light after image exposure, radicals are also generated in unexposed areas during image exposure, causing color change. If a radical scavenger is added to the image recording layer in order to suppress it, fog discoloration due to white light can be suppressed, but on the other hand, the sensitivity of printout image formation is also reduced. The inventors of the present invention include in the image recording material a compound that generates a chemical species that captures radicals by heating, and uses the image recording material as an image recording layer of a lithographic printing plate precursor to form a printout image. By subsequently generating a radical scavenger by heating, it was possible to achieve both suppression of fog discoloration due to white light and discoloration sensitivity during image exposure.

  According to the present invention, it is possible to provide an image recording material, a lithographic printing plate precursor, and a method for suppressing color change after image-like exposure, which are both capable of suppressing fog discoloration due to white light and discoloration sensitivity during image exposure.

<Compounds that change color by the action of radicals>
A conventionally known leuco dye can be arbitrarily used as the compound that causes a color change by the action of the radical of the present invention (hereinafter also referred to as a radical color changing agent). Specific examples of suitable leuco dyes include bis (4-dimethylaminophenyl) phenylmethane (also known as leucomalachite green), bis (4-diethylamino-o-tolyl) (p-chlorophenyl) methane, tris (4-diethylamino- o-tolyl) methane, tris (p-dimethylaminophenyl) methane (also known as leucocrystal violet), tris (p-dihexylaminophenyl) methane, bis (4-diethylamino-o-tolyl) (3,4-dimethoxyphenyl) Aminotriarylmethanes such as methane, bis (4-diethylamino-o-tolyl) (p-benzylthiophenyl) methane, bis (p-dimethylamino-o-tolyl) (p-α-methoxyacetamido) methane, 3, 6-bis (diethylamino) -9-phenylxan , Aminoxanthenes such as 3-amino-6-dimethylamino-2-methyl-9- (o-chlorophenyl) xanthene, 3,6-bis (diethylamino) -9- (o-ethoxycarbonylphenyl) thioxanthene, Aminothioxanthenes such as 3,6-bis (dimethylamino) thioxanthene, 3,6-bis (diethylamino) -9,10-dihydro-9-phenylacridine, 3,6-bis (pentylamino) -9,10 -Amino-9,10-dihydroacridines such as dihydro-9-methylacridine; aminophenoxazines such as 3,7-bis (diethylamino) phenoxazine; aminophenothiazines such as 3,7-bis (ethylamino) phenothiazine 3,7-bis (diethylamino) -5-hexyl-5,10 Aminodihydrophenazines such as dihydrophenazine, aminodiphenylmethanes such as bis (p-dimethylaminophenyl) anilinomethane, leucodamines such as 4-amino-4′-dimethylaminodiphenylamine, 4-amino-α, β- Aminohydrocinnamic acids such as dicyanohydrocinnamic acid methyl ester, hydrazines such as 1- (2-naphthyl) -2-phenylhydrazine, 1,4-pis (ethylamino) -2,3-dihydroanotraquinone Amino-2,3-dihydroanthraquinones such as phenethyl anilines such as N, N-diethyl-p-phenethyl aniline are used.

  Of these leuco dyes, aminotriarylmethanes are preferred, those in which at least two of the aryl groups have an amino group in the para position relative to the bond to the methane carbon atom, and all three are Those having an amino group at the para position are more preferred. In addition, aminotriarylmethanes having an alkyl group, an alkoxy group, or a halogeno atom at the ortho position of the aryl group are excellent in storage stability and are suitable.

In the present invention, the content of the compound that causes a color change by the action of radicals is 0.1 to 25% by mass, preferably 1 to 20% by mass, more preferably 5 to 15% by mass, based on the total solid content of the image recording layer. % Range.
The ratio of the compound that causes a color change by the action of a radical and the radical initiator described later is [compound that causes a color change by the action of radical] / [radical initiator] = 0.1 to 2 on a molar basis. 0.5, preferably 0.4 to 2.0, more preferably 0.8 to 1.5.

  In the present invention, when a compound that causes a color change by the action of a radical to be used has an amino group or a substituted amino group in the compound structure, such as aminotriarylmethanos, an ammonium salt can be formed. It is preferable to add acidic substances such as mineral acids, organic acids or so-called Lewis acids. Discoloration is facilitated by the addition of acidic substances. Typical acidic substances include, for example, sulfonic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, p-toluenesulfonic acid, and halogens such as trichloroacetic acid, trifluoroacetic acid, and burbuoroheptanoic acid. Examples thereof include substituted carboxylic acids, zinc chloride, zinc bromide and iron chloride. The amount of these acidic substances used is usually in the range of 0.1 to 2.0 mol, preferably 0.5 to 1.5 mol, per mol of amino group.

<Compounds that generate chemical species that trap radicals when heated>
The compound of the present invention that generates a chemical species that captures radicals by heating is a compound that decomposes by the action of heat and reacts with the radical to generate a compound that can stop or suppress radical activity. Hereinafter, this compound is also referred to as a radical scavenger precursor.
Chemical species (radical scavengers) that capture radicals include (1) oxygen, (2) phenols and quinones, (3) amines, (4) N-oxides and nitroso, (5) triaryl So-called radical polymerization inhibitors such as methanes can be mentioned as suitable ones.

  (2) Phenols and quinones include phenol, p-methoxyphenol, 2,6-di-t-butyl-4-methoxyphenol, 2,6-di-t-butyl-4-cresol, hydroquinone, catechol , T-butylcatechol, pyrogallol, resorcinol, 4,4′-thiobis (3-methyl-6-tert-butylphenol), 2,2′-methylenebis (4-methyl-6-tert-butylphenol), phenylhydroquinone, hydroquinone , T-butylhydroquinone, 2,5-di-t-butylhydroquinone, benzoquinone and the like.

  (3) Examples of amines include aniline, methoxyaniline, aminophenol, 2,4,6-tri-t-butylaniline, diphenylamine, triphenylamine, 2,2,6,6-tetramethylpiperidine and derivatives thereof. Is mentioned.

  (4) Examples of N-oxides and nitroso include di-t-butyl nitroxide, 2,2,6,6-tetramethylpiperidine-N-oxide and derivatives thereof, N-nitrosophenylhydroxylamine and metal salts thereof Etc.

(5) The triarylmethanes are not particularly limited, but specific examples include the following structures.

The radical scavenger precursor of the present invention is a compound that decomposes by heating to produce a radical scavenger as described above. A compound having a phenolic hydroxyl group protected with a group decomposable by heat is preferable.
Specific examples of the radical scavenger precursor of the present invention are shown below, but the present invention is not limited thereto.

  A preferable addition amount of the radical scavenger precursor is 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, and most preferably 0.5 to 5% by mass with respect to the total solid content of the image recording layer. %.

  Further, the combined use of the radical scavenger precursor and a strong acid or acid generator is preferable because the thermal decomposition efficiency is improved. Examples of strong acids are preferably acids with a pKa of 3 or less, more preferably sulfonic acids, and most preferably sulfonic acids containing halogen atoms. Moreover, as an example of an acid generator, the compound which generate | occur | produces the said acid below pKa3 is preferable, More preferably, a diazonium salt, a sulfonium salt, an iodonium salt, and a sulfonic acid ester are mentioned.

<Heating method>
A method for heating the lithographic printing plate precursor after image exposure is not particularly limited, and a known heating method can be used. For example, a method of directly heating by contact with a heat source such as a heat roller, a method of heating by blowing hot air, a method of heating by irradiating infrared rays generated from an infrared radiator such as a halogen heater or a ceramic heater, or a magnetron A method of irradiating an electromagnetic wave of a predetermined wavelength and resonating a substance such as moisture contained in the image recording layer to heat the electromagnetic wave, applying a high frequency magnetic field from an electromagnetic coil to a metal lithographic printing plate support and induction heating And the like.

  The heating temperature is preferably 75 to 250 ° C, more preferably 90 to 180 ° C. The heating time is preferably 1 to 600 seconds, more preferably 10 to 180 seconds.

Next, a heating method that can be employed in the present invention will be described in detail with reference to the drawings.
As shown in FIGS. 2, 3, and 4, in the image exposure apparatus 10 that is used when heating is performed after exposure, it is preferable that a heating device 38 is disposed in the casing 14, for example. The heating device 38 locally heats (spots) the lithographic printing plate precursor 12 with hot air. As shown in FIG. 3, the heating fan unit 140 is connected to the heating fan unit 140 through a flexible duct 142. And a tubular hot air nozzle 144. The heating fan unit 140 is fixed to the casing 14, and the hot air nozzle 144 is mounted on the carrier 68 together with the exposure head 26. The flexible duct 142 has a distal end portion inserted through the cable bear together with a bundle of optical fibers.

Here, the hot air nozzle 144 on the carrier 68 is disposed adjacent to the exposure head 26 along the sub-scanning direction. The hot air nozzle 144 is supported so that the base end side thereof extends in parallel with the traveling direction of the laser light L, and the tip of the hot air nozzle 144 is located on the planographic printing plate precursor 12 from the base end side toward the front end surface. A bend portion 45 bent so as to face the exposure area A _IR is formed. A rectangular air outlet is opened at the distal end surface of the bend portion 45.

The heating fan unit 140 includes a heating unit 48 made of a halogen heater, a ceramic heater, or the like that heats the air sucked from the outside of the casing 14, and an air supply unit that sends the heated air into the flexible duct 142 in a pressurized state. 50 is provided. The high-temperature air sent into the flexible duct 142 is supplied to the hot air nozzle 144, and is blown as hot air from the outlet 46 of the hot air nozzle 144 to the planographic printing plate precursor 12 mounted on the outer drum 20. At this time, since the bend portion 45 of the hot air nozzle 144 is directed to the exposure area A _IR on the planographic printing plate precursor 12, the hot air blown from the outlet 46 is exposed to the exposure area A _IR in the planographic printing plate precursor 12. (This is appropriately referred to as “heating area A _HT ”), and the recording layer in the heating area A _HT is heated to a predetermined heating temperature.

Here, the heating region A _HT is the center have substantially coincides with the center of the exposure area A _IR, there is a sufficiently large size than the exposure area A _IR along the sub-scanning direction and the main scanning direction. Thus, the heating region A _HT of the lithographic printing plate precursor 12 on becomes a region that includes an exposure region A _IR, hot air blown out from the blowout opening 46, any of the exposure laser beam L of the lithographic printing plate precursor 12 simultaneously irradiated to the region a _IR, blown to the heating region a _HT including the exposure region a _IR, heating region a while the exposure to the exposure area a _IR is completed exposed from the start the exposure by the laser beam L _HT is heated to a predetermined heating temperature.
However, the exposure time from the start of exposure of an arbitrary exposure area A _IR by the laser beam L to the completion of the exposure is substantially the same as the modulation period of the laser beam L corresponding to the sub-scanning speed, and is usually 0.
. It is a short time of about 05 seconds. In such a short time, in order to heat the lithographic printing plate precursor to a desired heating temperature with hot air, for example, the temperature of the hot air needs to be extremely high, which is not practical. Therefore, 50 to 100 times longer than Satoshi of the heating region A _HT exposure region A _IR along the sub-scanning direction, a hot air heating for an arbitrary exposure region A _IR included in the heating region A _HT modulation period 106 It is preferable to be able to continue over 10 <7> times or more. As a result, the heating time for an arbitrary exposure area A _IR can be sufficiently extended, so that the exposure area A _IR can be stably heated to a predetermined heating temperature without significantly increasing the hot air temperature.

Further, the image exposure apparatus 10 is provided with a heating control unit for controlling the heating device 38, and this heating control unit controls the temperature and air volume of hot air supplied from the heating fan unit 140 to the hot air nozzle 144, respectively. Control. The measurement signal equipped with a temperature sensor such as an infrared radiation thermometer on the carrier 68, the temperature (surface temperature) of the heating region A _HT by the temperature sensor is measured, corresponding to the surface temperature of the heating region A _HT center May be output to the heating control unit. As a result, the heating control unit can feedback control the temperature of the heating area A _HT based on the measurement signal, so that the temperature of the central area of the heating area A _HT is accurately and stably maintained at the heating temperature. become able to.

  As shown in FIG. 1, the image exposure apparatus 10 is provided with a carry-out mechanism 84 for carrying the lithographic printing plate precursor 12 detached from the outer drum 20 to the discharge tray 18 in the casing 14. The unloading mechanism 84 includes a plurality of conveying rollers 86 and a plate-shaped guide member 88 arranged along the unloading path of the planographic printing plate precursor 12.

  In the image exposure apparatus 10, after the exposure (image formation) to the lithographic printing plate precursor 12 mounted on the outer drum 20 is completed, the outer drum 20 is rotated in the reverse direction (in the direction of arrow R <b> 2 in FIG. 1) and the chuck mechanism 22. The rear end portion and the front end portion of the planographic printing plate precursor 12 are sequentially released from the outer drum 20. In conjunction with this, the carry-out mechanism 84 rotates the transport roller 86 to start carrying out the lithographic printing plate precursor 12 sent from the outer drum 20 to the entrance of the discharge path to the discharge tray. The original plate 12 is discharged onto the discharge tray 18.

The heating device 38 of the image exposure apparatus 10 according to the present invention, directly into a lithographic printing plate precursor 12 surface and by blowing hot air is intended to heat the spot heating region A _HT of the lithographic printing plate precursor 12, such The heating device is not limited to those using hot air. For example, an infrared radiator such as a halogen heater or a ceramic heater is mounted on the carrier 68, and the lithographic printing plate precursor 12 is irradiated with infrared rays from the radiator. the heating region a _HT be heated spots, also equipped with a magnetron on the carrier 68, by irradiating an electromagnetic wave of predetermined wavelength generated by a magnetron into the recording layer of the lithographic printing plate precursor 12 Te, the recording layer Even if a substance such as water is resonated to perform spot heating (electromagnetic wave heating), an electromagnetic coil is mounted on the carrier 68, and Wave magnetic field is applied to the metallic support of the lithographic printing plate precursor 12, the support may be spot inductively heating.

<Radical initiator>
The radical initiator used in the present invention is a compound that generates radicals by energy of light, heat, or both. In particular, a compound that generates a radical by absorbing a light of 250 nm to 420 nm by combining a radical initiator alone or a combination of a radical initiator and a sensitizing dye described later, and a compound that generates a radical by combining with an infrared absorber. preferable. As such a photo radical generator, a known radical radical initiator, a compound having a bond with a small bond dissociation energy, or the like can be appropriately selected and used.

  Examples of the compound that generates radicals include organic halogen compounds, carbonyl compounds, organic peroxides, azo compounds, azide compounds, metallocene compounds, hexaarylbiimidazole compounds, organic boron compounds, disulfone compounds, and oxime ester compounds. And onium salt compounds.

  Specific examples of the organic halogen compound include Wakabayashi et al., “Bull Chem. Soc Japan” 42, 2924 (1969), US Pat. No. 3,905,815, Japanese Patent Publication No. 46-4605, JP 48-36281, JP 53-133428, JP 55-3070, JP 60-239736, JP 61-169835, JP 61-169837, JP 62- 58241, JP-A 62-212401, JP-A 63-70243, JP-A 63-298339, P. The compounds described in Hutt, “Journal of Heterocyclic Chemistry” 1 (No. 3), (1970) can be mentioned. Of these, oxazole compounds and S-triazine compounds substituted with a trihalomethyl group are preferred.

  More preferable examples include s-triazine derivatives in which at least one mono, di, or trihalogen-substituted methyl group is bonded to the s-triazine ring, and oxadiazole derivatives in which the oxadiazole ring is bonded. Specifically, for example, 2,4,6-tris (monochloromethyl) -s-triazine, 2,4,6-tris (dichloromethyl) -s-triazine, 2,4,6-tris (trichloromethyl) -S-triazine, 2-methyl-4,6-bis (trichloromethyl) -s-triazine, 2-n-propyl-4,6-bis (trichloromethyl) -s-triazine, 2- (α, α, β-trichloroethyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (3,4-epoxyphenyl) -4,6-bis (trichloromethyl) -s-triazine, 2- [1- (P-methoxyphenyl) -2,4-butadienyl] -4,6-bis (trichloromethyl) -s-triazine, 2-styryl-4,6-bis (trichloromethyl) -s-triazine, 2- ( -Methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (pi-propyloxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (p- Tolyl) -4,6-bis (trichloromethyl) -s-triazine, 2- (4-methoxynaphthyl) -4,6-bis (trichloromethyl) -s-triazine, 2-phenylthio-4,6-bis ( Trichloromethyl) -s-triazine, 2-benzylthio-4,6-bis (trichloromethyl) -s-triazine, 2,4,6-tris (dibromomethyl) -s-triazine, 2,4,6-tris ( Tribromomethyl) -s-triazine, 2-methyl-4,6-bis (tribromomethyl) -s-triazine, 2-methoxy-4,6-bis (tribromomethyl) Etc. -s- triazine and the following compounds.

  Examples of the carbonyl compound include benzophenone, Michler ketone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2-chlorobenzophenone, 4-bromobenzophenone, 2-carboxybenzophenone and other benzophenone derivatives, 2,2-dimethoxy- 2-phenylacetophenone, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, α-hydroxy-2-methylphenylpropanone, 1-hydroxy-1-methylethyl- (p-isopropylphenyl) ketone, 1- Hydroxy-1- (p-dodecylphenyl) ketone, 2-methyl- (4 ′-(methylthio) phenyl) -2-morpholino-1-propanone, 1,1,1-trichloromethyl- (p-butylphenyl) Acetophenone derivatives such as ketones, thioxanthone derivatives such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, p- Examples thereof include benzoic acid ester derivatives such as ethyl dimethylaminobenzoate and ethyl p-diethylaminobenzoate.

  As the azo compound, for example, an azo compound described in JP-A-8-108621 can be used.

  Examples of the organic peroxide include trimethylcyclohexanone peroxide, acetylacetone peroxide, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (tert-butyl). Peroxy) cyclohexane, 2,2-bis (tert-butylperoxy) butane, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-2,5-dihydro Peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, tert-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, 2, -Oxanoyl peroxide, succinic peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate , Dimethoxyisopropyl peroxycarbonate, di (3-methyl-3-methoxybutyl) peroxydicarbonate, tert-butyl peroxyacetate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, tert- Butyl peroxyoctanoate, tert-butyl peroxylaurate, tersyl carbonate, 3,3 ′, 4,4′-tetra- (t-butylperoxycarbonyl) benzophenone, 3,3 ′, 4,4 ′ − Tra- (t-hexylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra- (p-isopropylcumylperoxycarbonyl) benzophenone, carbonyldi (t-butylperoxydihydrogen diphthalate), carbonyl And di (t-hexylperoxydihydrogen diphthalate).

  Examples of the metallocene compound include JP-A-59-152396, JP-A-61-151197, JP-A-63-41484, JP-A-2-249, JP-A-2-4705, Various titanocene compounds described in JP-A-5-83588, such as di-cyclopentadienyl-Ti-bis-phenyl, di-cyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl, Di-cyclopentadienyl-Ti-bis-2,4-di-fluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl, di- -Cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-cyclopentadienyl-Ti-bis-2,3,4,5,6-penta Fluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,4,6-trifluoropheny -1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl, di-methylcyclopentadienyl-Ti-bis-2,3,4 , 5,6-pentafluorophen-1-yl, iron-arene complexes described in JP-A-1-304453 and JP-A-1-152109, and the like.

  Examples of the hexaarylbiimidazole compound include the specifications of JP-B-6-29285, US Pat. Nos. 3,479,185, 4,311,783, and 4,622,286. And, specifically, 2,2′-bis (o-chlorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-bromophenyl) )) 4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o, p-dichlorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2 ′ -Bis (o-chlorophenyl) -4,4 ', 5,5'-tetra (m-methoxyphenyl) biidazole, 2,2'-bis (o, o'-dichlorophenyl) -4,4', 5,5 '-Tetraphenylbiimidazole, 2, 2' Bis (o-nitrophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole, 2,2′-bis (o-methylphenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole 2,2′-bis (o-trifluorophenyl) -4,4 ′, 5,5′-tetraphenylbiimidazole and the like.

  Examples of the organoboron compound include JP-A-62-143044, JP-A-62-1050242, JP-A-9-188585, JP-A-9-188686, JP-A-9-188710, JP-A 2000-. No. 131837, Japanese Patent Application Laid-Open No. 2002-107916, Japanese Patent No. 2764769, Japanese Patent Application Laid-Open No. 2002-116539, and Kunz, Martin “Rad Tech '98. Proceeding April 19-22, 1998, Chicago”, etc. The organic borate described in JP-A-6-157623, JP-A-6-175564, JP-A-6-175561, or organic boron oxosulfonium complex, JP-A-6-175554 No. 6, JP-A-6-17555 Organoboron iodonium complex described in JP-A-9-188, organoboron phosphonium complex described in JP-A-9-188710, JP-A-6-34811, JP-A-7-128785, JP-A-7-140589, Examples thereof include organoboron transition metal coordination complexes such as Kaihei 7-306527 and JP-A-7-292014.

  Examples of the disulfone compound include compounds described in JP-A Nos. 61-166544 and 2003-328465.

  Examples of the oxime ester compound include JCS Perkin II (1979) 1653-1660), JCSPerkin II (1979) 156-162, Journal of Photopolymer Science and Technology (1995) 202-232, and JP-A 2000-66385. Compounds, compounds described in JP-A No. 2000-80068, specifically, compounds represented by the following structural formulas may be mentioned.

  Examples of the onium salt compound include S.I. I. Schlesinger, Photogr. Sci. Eng. , 18, 387 (1974), T.A. S. Diazonium salts described in Bal et al, Polymer, 21, 423 (1980), ammonium salts described in US Pat. No. 4,069,055, JP-A-4-365049, etc., US Pat. No. 4,069 , 055, 4,069,056, phosphonium salts described in European Patent Nos. 104,143, US Pat. Nos. 339,049, 410,201, JP -150848, JP-A-2-296514, iodonium salts, European Patent Nos. 370,693, 390,214, 233,567, 297,443, and 297 442, U.S. Pat. Nos. 4,933,377, 161,811, 410,201, 339,049, 4,760,013 No. 4,734,444, No. 2,833,827, German Patent No. 2,904,626, No. 3,604,580, No. 3,604,581 Or a sulfonium salt described in J. V. Crivello et al, Macromolecules, 10 (6), 1307 (1977), J. MoI. V. Crivello et al, J.A. Polymer Sci. , Polymer Chem. Ed. , 17, 1047 (1979), a selenonium salt described in C.I. S. Wen et al, Teh, Proc. Conf. Rad. Curing ASIA, p478 Tokyo, Oct (1988), and onium salts such as arsonium salts.

In the present invention, these onium salts function not as acid generators but as ionic radical initiators.
The onium salts suitably used in the present invention are onium salts represented by the following general formulas (RI-I) to (RI-III).

In the formula (RI-I), Ar ₁₁ represents an aryl group having 20 or less carbon atoms which may have 1 to 6 substituents, and preferred substituents include an alkyl group having 1 to 12 carbon atoms and a carbon number. 1-12 alkenyl group, C1-C12 alkynyl group, C1-C12 aryl group, C1-C12 alkoxy group, C1-C12 aryloxy group, halogen atom, C1-C1 12 alkylamino groups, C1-C12 dialkylamino groups, C1-C12 alkylamide groups or arylamide groups, carbonyl groups, carboxyl groups, cyano groups, sulfonyl groups, C1-C12 thioalkyl groups And a thioaryl group having 1 to 12 carbon atoms. Z ₁₁ ^- represents a monovalent anion, specifically a halogen ion, perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ion, sulfinate ion, thiosulfonate ion, a sulfate ion Can be mentioned. Among these, perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ion and sulfinate ion are preferable from the viewpoint of stability.

In the formula (RI-II), Ar ₂₁ and Ar ₂₂ each independently represent an aryl group having 20 or less carbon atoms which may have 1 to 6 substituents, and preferred substituents include 1 to 1 carbon atoms. 12 alkyl groups, an alkenyl group having 1 to 12 carbon atoms, an alkynyl group having 1 to 12 carbon atoms, an aryl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 1 to 12 carbon atoms, Halogen atom, C1-C12 alkylamino group, C1-C12 dialkylamino group, C1-C12 alkylamide group or arylamide group, carbonyl group, carboxyl group, cyano group, sulfonyl group, carbon Examples thereof include a thioalkyl group having 1 to 12 carbon atoms and a thioaryl group having 1 to 12 carbon atoms. Z ₂₁ ^- represents a monovalent anion. Specific examples include halogen ions, perchlorate ions, hexafluorophosphate ions, tetrafluoroborate ions, sulfonate ions, sulfinate ions, thiosulfonate ions, and sulfate ions. Among these, perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ion, sulfinate ion, and carboxylate ion are preferable from the viewpoint of stability and reactivity.

In the formula (RI-III), R ₃₁ , R ₃₂ and R ₃₃ are each independently an aryl group, alkyl group, alkenyl group or alkynyl having 20 or less carbon atoms, which may have 1 to 6 substituents. Represents a group. Among them, an aryl group is preferable from the viewpoint of reactivity and stability. Examples of the substituent include an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 12 carbon atoms, an alkynyl group having 1 to 12 carbon atoms, an aryl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, Aryloxy group having 1 to 12 carbon atoms, halogen atom, alkylamino group having 1 to 12 carbon atoms, dialkylamino group having 1 to 12 carbon atoms, alkylamide group or arylamide group having 1 to 12 carbon atoms, carbonyl group, carboxyl Group, a cyano group, a sulfonyl group, a thioalkyl group having 1 to 12 carbon atoms, and a thioaryl group having 1 to 12 carbon atoms. Z ₃₁ ^- represents a monovalent anion. Specific examples include halogen ions, perchlorate ions, hexafluorophosphate ions, tetrafluoroborate ions, sulfonate ions, sulfinate ions, thiosulfonate ions, and sulfate ions. Among these, perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, sulfonate ion, sulfinate ion, and carboxylate ion are preferable from the viewpoints of stability and reactivity. More preferred are the carboxylate ions described in JP-A No. 2001-343742, and particularly preferred are the carboxylate ions described in JP-A No. 2002-148790.

  The radical initiator is not limited to the above, but particularly from the viewpoint of reactivity and stability, triazine-based initiators, organic halogen compounds, oxime ester compounds, diazonium salts, iodonium salts, and sulfonium salts are suitable for short-time exposure. This is more preferable because a large amount of radicals are generated.

  When performing imagewise exposure using a light source that emits light in the range of 250 to 420 nm, the above radical initiator is preferably used in combination with a sensitizing dye. By using it in combination with a sensitizing dye, the photopolymerization rate can be increased.

Specific examples of such sensitizing dyes include benzoin, benzoin methyl ether, benzoin ethyl ether, 9-fluorenone, 2-chloro-9-fluorenone, 2-methyl-9-fluorenone, 9-anthrone, and 2-bromo-9. Anthrone, 2-ethyl-9-anthrone, 9,10-anthraquinone, 2-ethyl-9,10-anthraquinone, 2-t
-Butyl-9,10-anthraquinone, 2,6-dichloro-9,10-anthraquinone, xanthone, 2-methylxanthone, 2-methoxyxanthone, thioxanthone, benzyl, dibenzalacetone, p- (dimethylamino) phenylstyryl Examples thereof include ketones, p- (dimethylamino) phenyl p-methylstyryl ketone, benzophenone, p- (dimethylamino) benzophenone (or Michler's ketone), p- (diethylamino) benzophenone, and benzanthrone.

  Furthermore, preferred sensitizing dyes in the present invention include compounds represented by the general formula (I) described in JP-B 51-48516.

In the formula, R ¹⁴ is an alkyl group (for example, methyl group, ethyl group, propyl group, etc.) or a substituted alkyl group (for example, 2-hydroxyethyl group, 2-methoxyethyl group, carboxymethyl group, 2-carboxyethyl group) Etc.). R ¹⁵ represents an alkyl group (eg, methyl group, ethyl group, etc.) or an aryl group (eg, phenyl group, p-hydroxyphenyl group, naphthyl group, thienyl group, etc.).

Z ² is a group of nonmetallic atoms necessary for forming a heterocyclic nucleus containing nitrogen, which is usually used in cyanine dyes, such as benzothiazoles (benzothiazole, 5-chlorobenzothiazole, 6-chlorobenzothiazole, etc.), naphtho Thiazoles (α-naphthothiazole, β-naphthothiazole, etc.), benzoselenazoles (benzoselenazole, 5-chlorobenzoselenazole, 6-methoxybenzoselenazole, etc.), naphthoselenazoles (α-naphthoselenazole) , Β-naphthselenazole, etc.), benzoxazoles (benzoxazole, 5-methylbenzoxazole, 5-phenylbenzoxazole, etc.) and naphthoxazoles (α-naphthoxazole, β-naphthoxazole, etc.).

Specific examples of the compound represented by the general formula (I) are those having a chemical structure combining these Z ² , R ¹⁴ and R ¹⁵ , and many exist as known substances. Therefore, it can be used by appropriately selecting from these known ones. Furthermore, preferable sensitizers in the present invention include merocyanine dyes described in JP-B-5-47095 and ketocoumarin compounds represented by the following general formula (II).

Here, R ¹⁶ represents an alkyl group such as a methyl group or an ethyl group.

  As the sensitizing dye, merocyanine dyes described in JP-A No. 2000-147763 can also be used. Specifically, the following compounds can be mentioned.

  Each of these radical initiators and sensitizing dyes is preferably 0.1 to 50% by mass, more preferably 0.5 to 30% by mass, particularly preferably 0. 0% by mass, based on the total solid content constituting the image recording layer. It can be added at a rate of 8 to 20% by mass. Within this range, good image discoloration sensitivity can be obtained. These radical initiators may be used alone or in combination of two or more. Moreover, these radical initiators may be added to the same layer as other components, or another layer may be provided and added thereto.

  In the present invention, an infrared absorber is used in combination with the radical initiator instead of the sensitizing dye in the image recording layer of the lithographic printing plate precursor when performing imagewise exposure using a light source that emits infrared rays. Is preferred. In general, the infrared absorber has a function of converting the absorbed infrared rays into heat, and the generated heat can cause the radical initiator to thermally decompose and generate radicals. The infrared absorber used in the present invention is a dye or pigment having an absorption maximum at a wavelength of 760 to 1200 nm.

  As the dye, commercially available dyes and known dyes described in documents such as “Dye Handbook” (edited by the Society for Synthetic Organic Chemistry, published in 1970) can be used. Specifically, dyes such as 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, metal thiolate complexes Is mentioned.

  Preferred dyes include, for example, cyanine dyes described in JP-A-58-125246, JP-A-59-84356, JP-A-60-78787, JP-A-58-173696, The methine dyes described in Japanese Laid-Open Patent Publication Nos. 58-181690 and 58-194595, JP-A 58-112793, JP-A 58-224793, JP-A 59-48187, Naphthoquinone dyes described in Japanese Laid-Open Patent Publication Nos. 59-73996, 60-52940 and 60-63744, and squarylium dyes described in Japanese Laid-Open Patent Publication No. 58-112792. And cyanine dyes described in British Patent 434,875.

  In addition, a near infrared absorption sensitizer described in US Pat. No. 5,156,938 is also preferably used, and a substituted arylbenzo (thio) described in US Pat. No. 3,881,924 is also suitable. ) Pyrylium salt, trimethine thiapyrylium salt described in JP-A-57-142645 (US Pat. No. 4,327,169), JP-A-58-181051, 58-220143, 59- No. 41363, 59-84248, 59-84249, 59-146063, 59-146061, pyranyl compounds described in JP-A-59-216146, cyanine dyes described in JP-A-59-216146, Patented in US Pat. No. 4,283,475, such as pentamethine thiopyrylium salt, and Japanese Patent Publication Nos. 5-13514 and 5-19702 Pyrylium compounds are also preferably used. Another example of a preferable dye is a near-infrared absorbing dye described in US Pat. No. 4,756,993 as formulas (I) and (II).

  Particularly preferred among these dyes are cyanine dyes, squarylium dyes, pyrylium salts, nickel thiolate complexes, and indolenine cyanine dyes. Further, cyanine dyes and indolenine cyanine dyes are preferable, and one particularly preferable example is a cyanine dye represented by the following general formula (III).

In the general formula (III), X ¹ represents a hydrogen atom, a halogen atom, -NPh _2, X ² -L ¹ or a group shown below. Here, X ² represents an oxygen atom, a nitrogen atom or a sulfur atom, and L ¹ represents a hydrocarbon group having 1 to 12 carbon atoms, an aromatic ring having a hetero atom, or 1 to 1 carbon atom containing a hetero atom. 12 hydrocarbon groups are shown. In addition, a hetero atom here shows N, S, O, a halogen atom, and Se. Xa ^- the Za described later ^- is defined as for, R ^a represents a hydrogen atom, an alkyl group, an aryl group, a substituted or unsubstituted amino group, substituted or unsubstituted amino group and a halogen atom.

R ¹ and R ² each independently represents a hydrocarbon group having 1 to 12 carbon atoms. From the storage stability of the recording layer coating solution, R ¹ and R ² are preferably hydrocarbon groups having 2 or more carbon atoms, and R ¹ and R ² are bonded to each other to form a 5-membered ring or It is particularly preferable that a 6-membered ring is formed.

Ar ¹ and Ar ² may be the same or different and each represents an aromatic hydrocarbon group which may have a substituent. Preferred aromatic hydrocarbon groups include a benzene ring and a naphthalene ring. Moreover, as a preferable substituent, a C12 or less hydrocarbon group, a halogen atom, and a C12 or less alkoxy group are mentioned. 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 which may have a substituent. Preferred substituents include alkoxy groups having 12 or less carbon atoms, carboxyl groups, and sulfo groups. 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. From the availability of raw materials, a hydrogen atom is preferred. Za ⁻ represents a counter anion. However, when the cyanine dye represented by formula (III) has an anionic substituent in its structure and does not require charge neutralization, Za ^- is not necessary. Preferred Za ⁻ is a halogen ion, a perchlorate ion, a tetrafluoroborate ion, a hexafluorophosphate ion, and a sulfonate ion, particularly preferably a perchlorate ion, a hexagonal salt, in view of the storage stability of the recording layer coating solution. Fluorophosphate ions and aryl sulfonate ions.

Specific examples of the cyanine dye represented by formula (III) that can be suitably used in the present invention include those described in paragraph numbers [0017] to [0019] of JP-A No. 2001-133969. be able to.
Further, other particularly preferable examples include specific indolenine cyanine dyes described in JP-A-2002-278057.

  Examples of the pigment used in the present invention include commercially available pigments and color index (CI) manual, “Latest Pigment Handbook” (edited by Japan Pigment Technology Association, published in 1977), “Latest Pigment Application Technology” (CMC Publishing, 1986), “Printing Ink Technology”, CMC Publishing, 1984) can be used.

  Examples of the pigment include black pigments, yellow pigments, orange pigments, brown pigments, red pigments, purple pigments, blue pigments, green pigments, fluorescent pigments, metal powder pigments, and other polymer-bonded dyes. Specifically, insoluble azo pigments, azo lake pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene and perinone pigments, thioindigo pigments, quinacridone pigments, dioxazine pigments, isoindolinone pigments , Quinophthalone pigments, dyed lake pigments, azine pigments, nitroso pigments, nitro pigments, natural pigments, fluorescent pigments, inorganic pigments, carbon black, and the like. Among these pigments, carbon black is preferable.

  These pigments may be used without surface treatment, or may be used after surface treatment. The surface treatment method includes a method of surface coating with resin or wax, a method of attaching a surfactant, a method of bonding a reactive substance (eg, silane coupling agent, epoxy compound, polyisocyanate, etc.) to the pigment surface, etc. Can be considered. The above-mentioned surface treatment methods are described in “Characteristics and Application of Metal Soap” (Shobobo), “Printing Ink Technology” (CMC Publishing, 1984) and “Latest Pigment Application Technology” (CMC Publishing, 1986). Yes.

  The particle diameter of the pigment is preferably in the range of 0.01 to 10 μm, more preferably in the range of 0.05 to 1 μm, and particularly preferably in the range of 0.1 to 1 μm. Within this range, good stability of the pigment dispersion in the image recording layer coating solution and good uniformity of the image recording layer can be obtained.

  As a method for dispersing the pigment, a known dispersion technique used for ink production or toner production can be used. Examples of the disperser include an ultrasonic disperser, a sand mill, an attritor, a pearl mill, a super mill, a ball mill, an impeller, a disperser, a KD mill, a colloid mill, a dynatron, a three-roll mill, and a pressure kneader. Details are described in "Latest Pigment Applied Technology" (CMC Publishing, 1986).

  The addition of these infrared absorbers to the image recording layer is preferably made the minimum necessary amount in order to suppress side effects that inhibit the polymerization reaction.

  These infrared absorbers are added in a proportion of 0.001 to 50% by mass, preferably 0.005 to 30% by mass, particularly preferably 0.01 to 10% by mass, based on the total solid content of the image recording layer. Can do. Within this range, good color change sensitivity can be obtained without adversely affecting the uniformity of the image recording layer and the film strength.

<Radically polymerizable compound>
The image recording layer of the present invention preferably contains a radical polymerizable compound as a print image forming component. A radically polymerizable compound (hereinafter, also simply referred to as a polymerizable compound) can be polymerized and cured by radicals generated from the radical initiator to form an image portion that is ink-receptive and excellent in printing durability. This polymerizable compound is an addition polymerizable compound having at least one ethylenically unsaturated double bond, and is selected from compounds having at least one ethylenically unsaturated bond, preferably two or more. Such a compound group is widely known in the industrial field, and can be used without any particular limitation in the present invention. These have chemical forms such as monomers, prepolymers, i.e. dimers, trimers and oligomers, or mixtures thereof and copolymers thereof. Examples of monomers and copolymers thereof include unsaturated carboxylic acids (for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, etc.), and esters and amides thereof. In this case, an ester of an unsaturated carboxylic acid and an aliphatic polyhydric alcohol compound, or an amide of an unsaturated carboxylic acid and an aliphatic polyvalent amine compound is used. In addition, an addition reaction product of an unsaturated carboxylic acid ester or amide having a nucleophilic substituent such as a hydroxyl group, amino group or mercapto group with a monofunctional or polyfunctional isocyanate or epoxy, and a monofunctional or polyfunctional compound. A dehydration condensation reaction product with a functional carboxylic acid is also preferably used. Further, an addition reaction product of an unsaturated carboxylic acid ester or amide having an electrophilic substituent such as an epoxy group or an epoxy group with a monofunctional or polyfunctional alcohol, amine or thiol, a halogen group or Also suitable are substitution reaction products of unsaturated carboxylic acid esters or amides having a leaving substituent such as a tosyloxy group with monofunctional or polyfunctional alcohols, amines or thiols. As another example, it is also possible to use a group of compounds substituted with unsaturated phosphonic acid, styrene, vinyl ether or the like instead of the unsaturated carboxylic acid.

  Specific examples of the monomer of an ester of an aliphatic polyhydric alcohol compound and an unsaturated carboxylic acid include acrylic acid esters such as ethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butanediol diacrylate, and tetramethylene glycol. Diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, trimethylolpropane tri (acryloyloxypropyl) ether, trimethylolethane triacrylate, hexanediol diacrylate, 1,4-cyclohexanediol diacrylate , Tetraethylene glycol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate , Pentaerythritol tetraacrylate, dipentaerythritol diacrylate, dipentaerythritol hexaacrylate, sorbitol triacrylate, sorbitol tetraacrylate, sorbitol pentaacrylate, sorbitol hexaacrylate, tri (acryloyloxyethyl) isocyanurate, polyester acrylate oligomer, isocyanuric acid There are EO-modified triacrylate and the like.

  Methacrylic acid esters include tetramethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, Hexanediol dimethacrylate, pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol dimethacrylate, dipentaerythritol hexamethacrylate, sorbitol trimethacrylate, sorbitol tetramethacrylate, bis [p- (3-methacryloxy- 2-hydroxypro ) Phenyl] dimethyl methane, bis - [p- (methacryloxyethoxy) phenyl] dimethyl methane.

Itaconic acid esters include ethylene glycol diitaconate, propylene glycol diitaconate, 1,3-butanediol diitaconate, 1,4-butanediol diitaconate, tetramethylene glycol diitaconate, pentaerythritol diitaconate And sorbitol tetritaconate. Examples of crotonic acid esters include ethylene glycol dicrotonate, tetramethylene glycol dicrotonate, pentaerythritol dicrotonate, and sorbitol tetradicrotonate. Examples of isocrotonic acid esters include ethylene glycol diisocrotonate, pentaerythritol diisocrotonate, and sorbitol tetraisocrotonate. Examples of maleic acid esters include ethylene glycol dimaleate, triethylene glycol dimaleate, pentaerythritol dimaleate, and sorbitol tetramaleate.

  Examples of other esters include, for example, aliphatic alcohol esters described in JP-B-51-47334 and JP-A-57-196231, JP-A-59-5240, and JP-A-59-5241. Those having an aromatic skeleton described in JP-A-2-226149 and those containing an amino group described in JP-A-1-165613 are also preferably used. Furthermore, the ester monomers described above can also be used as a mixture.

  Specific examples of amide monomers of aliphatic polyvalent amine compounds and unsaturated carboxylic acids include methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide, 1,6-hexamethylene bis. -Methacrylamide, diethylenetriamine trisacrylamide, xylylene bisacrylamide, xylylene bismethacrylamide and the like. Examples of other preferable amide monomers include those having a cyclohexylene structure described in JP-B-54-21726.

  In addition, urethane-based addition polymerizable compounds produced by using an addition reaction of isocyanate and hydroxyl group are also suitable, and specific examples thereof include, for example, one molecule described in JP-B-48-41708. A vinyl urethane containing two or more polymerizable vinyl groups in one molecule obtained by adding a vinyl monomer containing a hydroxyl group represented by the following general formula (a) to a polyisocyanate compound having two or more isocyanate groups. Compounds and the like.

_{CH 2 = C (R 4)} COOCH 2 CH (R 5) OH (a)
(However, R ₄ and R ₅ represent H or CH _3. )

  Further, urethane acrylates such as those described in JP-A-51-37193, JP-B-2-32293, JP-B-2-16765, JP-B-58-49860, JP-B-56-17654 Urethane compounds having an ethylene oxide skeleton described in JP-B-62-39417 and JP-B-62-39418 are also suitable. Further, by using addition polymerizable compounds having an amino structure or a sulfide structure in the molecule described in JP-A-63-277653, JP-A-63-260909, and JP-A-1-105238. Can obtain a photopolymerizable composition having an excellent photosensitive speed.

  Other examples include reacting polyester acrylates, epoxy resins and (meth) acrylic acid as described in JP-A-48-64183, JP-B-49-43191 and JP-B-52-30490. And polyfunctional acrylates and methacrylates such as epoxy acrylates. Further, specific unsaturated compounds described in JP-B-46-43946, JP-B-1-40337, and JP-B-1-40336, vinylphosphonic acid compounds described in JP-A-2-25493, and the like are also included. Can be mentioned. In some cases, a structure containing a perfluoroalkyl group described in JP-A-61-22048 is preferably used. Furthermore, Journal of Japan Adhesion Association vol. 20, no. 7, pages 300 to 308 (1984), which are introduced as photocurable monomers and oligomers, can also be used.

About these polymerizable compounds, the details of usage such as the structure, single use or combination, addition amount, etc. can be arbitrarily set according to the performance design of the final lithographic printing plate precursor. For example, it is selected from the following viewpoints.
From the viewpoint of sensitivity, a structure having a large unsaturated group content per molecule is preferable, and in many cases, a bifunctional or higher functionality is preferable. Further, in order to increase the strength of the image area, that is, the cured film, those having three or more functionalities are preferable. Further, different functional numbers and different polymerizable groups (for example, acrylic acid ester, methacrylic acid ester, styrenic compound, vinyl ether type). A method of adjusting both sensitivity and strength by using a compound) is also effective.
In addition, the selection and use method of the polymerized compound is also an important factor for the compatibility and dispersibility with other components in the image recording layer (for example, binder polymer, initiator, colorant, etc.). The compatibility may be improved by using a low-purity compound or using two or more kinds in combination. In addition, a specific structure may be selected for the purpose of improving the adhesion of the substrate and the protective layer described later.

  The polymerizable compound is preferably used in the range of 5 to 80% by mass, more preferably 25 to 75% by mass with respect to the total solid content constituting the image recording layer. These may be used alone or in combination of two or more. In addition, the use method of the addition polymerizable compound can be arbitrarily selected from the viewpoint of polymerization inhibition with respect to oxygen, resolution, fogging, refractive index change, surface adhesiveness, etc. Depending on the case, a layer configuration and coating method such as undercoating and overcoating can be performed.

<Other image recording layer components>
The image recording layer of the present invention further contains additives such as a binder polymer, a surfactant, a colorant, a printout agent, a thermal polymerization inhibitor, a higher fatty acid derivative, a plasticizer, inorganic fine particles, and a low molecular weight hydrophilic compound. , If necessary. These will be described below.

<Binder polymer>
In the present invention, a binder polymer can be used for improving the film strength and film property of the image recording layer and improving the on-press developability. A conventionally well-known thing can be used as a binder polymer without a restriction | limiting, The linear organic polymer which has film property is preferable. Examples of such binder polymers include acrylic resins, polyvinyl acetal resins, polyurethane resins, polyurea resins, polyimide resins, polyamide resins, epoxy resins, methacrylic resins, polystyrene resins, novolac phenolic resins, polyester resins, and synthetic rubbers. And natural rubber.
The binder polymer preferably has crosslinkability in order to improve the film strength of the image area. In order to impart crosslinkability to the binder 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.
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 polymers having an ethylenically unsaturated bond in the side chain of the molecule are polymers of esters or amides of acrylic acid or methacrylic acid where the ester or amide residue (R of -COOR or -CONHR) is Mention may be made of polymers having an ethylenically unsaturated bond.

Examples of the residue (the R) having an ethylenically unsaturated _{bond, - (CH 2) n CR} 1 = CR 2 R 3, - (CH 2 O) n CH 2 CR 1 = CR 2 R 3, - _{(CH 2 CH 2 O) n} CH 2 CR 1 = CR 2 R 3, - (CH 2) n NH-CO-O-CH 2 CR 1 = CR 2 R 3, - (CH 2) n -O-CO —CR ¹ ═CR ² R ³ and — (CH ₂ CH ₂ O) ₂ —X (wherein R ^{1 to} R ³ are each a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, Represents an alkoxy group or an aryloxy group, and R ¹ and R ² or R ³ may combine with each other to form a ring, n represents an integer of 1 to 10. X represents dicyclopentadienyl. Represents a residue).
Specific examples of the ester _{residue, -CH 2 CH = CH 2,} ( described in JP Kokoku _{7-21633.) - CH 2 CH 2} O-CH 2 CH = CH 2, -CH 2 C _{(CH 3) = CH 2,} -CH 2 CH = CH-C 6 H 5, -CH 2 CH 2 OCOCH = CH-C 6 H 5, -CH 2 CH 2 -NHCOO-CH 2 CH = CH 2 and - CH ₂ CH ₂ O—X (wherein X represents a dicyclopentadienyl residue).
Specific examples of the amide residue include —CH ₂ CH═CH ₂ , —CH ₂ CH ₂ —Y (wherein Y represents a cyclohexene residue), —CH ₂ CH ₂ —OCO—CH═CH _2. Is mentioned.

  In the case of a binder polymer having crosslinkability, for example, free radicals (polymerization initiation radicals or growth radicals in the polymerization process of a polymerizable compound) are added to the crosslinkable functional group, and a polymerization chain of a polymerizable compound is formed directly between polymers. Through addition polymerization, a cross-link is formed between the polymer molecules and cured. Alternatively, atoms in the polymer (eg, hydrogen atoms on carbon atoms adjacent to the functional bridging group) are abstracted by free radicals to form polymer radicals that are bonded to each other so that crosslinking between the polymer molecules occurs. Forms and cures.

  The content of the crosslinkable group in the binder polymer (content of unsaturated double bond capable of radical polymerization by iodine titration) is preferably 0.1 to 10.0 mmol, more preferably 1.0, per 1 g of the binder polymer. -7.0 mmol, most preferably 2.0-5.5 mmol. Within this range, good sensitivity and good storage stability can be obtained.

Further, from the viewpoint of on-press developability of the image recording layer unexposed portion, the binder polymer preferably has high solubility or dispersibility in ink and / or fountain solution.
In order to improve the solubility or dispersibility in ink, the binder polymer is preferably lipophilic, and in order to improve the solubility or dispersibility in dampening water, the binder polymer is hydrophilic. Is preferred. For this reason, in the present invention, it is also effective to use a lipophilic binder polymer and a hydrophilic binder polymer in combination.

  Examples of hydrophilic binder polymers include hydroxy groups, carboxyl groups, carboxylate groups, hydroxyethyl groups, polyoxyethyl groups, hydroxypropyl groups, polyoxypropyl groups, amino groups, aminoethyl groups, aminopropyl groups, and ammonium. Preferred are those having a hydrophilic group such as a group, an amide group, a carboxymethyl group, a sulfonic acid group, and a phosphoric acid group.

Specific examples include gum arabic, casein, gelatin, starch derivatives, carboxymethylcellulose and its sodium salt, cellulose acetate, sodium alginate, vinyl acetate-maleic acid copolymers, styrene-maleic acid copolymers, polyacrylic acids and their salts, Polymethacrylic acids and their salts, homopolymers and copolymers of hydroxyethyl methacrylate, homopolymers and copolymers of hydroxyethyl acrylate, homopolymers and copolymers of hydroxypropyl methacrylate, homopolymers and copolymers of hydroxypropyl acrylate, homopolymers of hydroxybutyl methacrylate Polymers and copolymers, homopolymers and copolymers of hydroxybutyl acrylate Polyethylene glycols, hydroxypropylene polymers, polyvinyl alcohols, hydrolyzed polyvinyl acetate, polyvinyl formal, polyvinyl butyral, polyvinyl pyrrolidone, acrylamide homopolymers and copolymers having a hydrolysis degree of 60 mol% or more, preferably 80 mol% or more , Homopolymers and polymers of methacrylamide, homopolymers and copolymers of N-methylolacrylamide, polyvinylpyrrolidone, alcohol-soluble nylon, polyether of 2,2-bis- (4-hydroxyphenyl) -propane and epichlorohydrin, etc. Is mentioned.

The binder polymer preferably has a mass average molecular weight of 5,000 or more, more preferably 10,000 to 300,000, and a number average molecular weight of 1,000 or more, preferably 2000 to 250,000. More preferred. The polydispersity (mass average molecular weight / number average molecular weight) is preferably 1.1 to 10.
The binder polymer may be any of a random polymer, a block polymer, a graft polymer, and the like, but is preferably a random polymer.

The binder polymer can be synthesized by a conventionally known method. Solvents used in the synthesis include, for example, tetrahydrofuran, ethylene dichloride, cyclohexanone, methyl ethyl ketone, acetone, methanol, ethanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, diethylene glycol dimethyl ether, 1-methoxy. Examples include 2-propanol, 1-methoxy-2-propyl acetate, N, N-dimethylformamide, N, N-dimethylacetamide, toluene, ethyl acetate, methyl lactate, ethyl lactate, dimethyl sulfoxide, and water. These may be used alone or in combination of two or more.
As the radical polymerization initiator used for synthesizing the binder polymer, known compounds such as an azo initiator and a peroxide initiator can be used.

A binder polymer may be used independently or may be used in mixture of 2 or more types.
The content of the binder polymer is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and still more preferably 30 to 70% by mass with respect to the total solid content of the image recording layer. Within this range, good image area strength and image formability can be obtained.
Moreover, it is preferable to use (B) polymeric compound and binder polymer in the quantity used as 1 / 9-7 / 3 by mass ratio.

<Surfactant>
In the present invention, it is preferable to use a surfactant in the image recording layer in order to promote on-press developability at the start of printing and to improve the coated surface state. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and fluorosurfactants. Surfactant may be used independently and may be used in combination of 2 or more type.

  The nonionic surfactant used for this invention is not specifically limited, A conventionally well-known thing can be used. For example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polystyryl phenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, glycerin fatty acid partial esters, sorbitan fatty acid partial esters, pentaerythritol Fatty acid partial esters, propylene glycol mono fatty acid esters, sucrose fatty acid partial esters, polyoxyethylene sorbitan fatty acid partial esters, polyoxyethylene sorbitol fatty acid partial esters, polyethylene glycol fatty acid esters, polyglycerin fatty acid partial esters, Polyoxyethylenated castor oil, polyoxyethylene glycerin fatty acid partial esters, fatty acid diethanolamides, N N- bis-2-hydroxyalkylamines, polyoxyethylene alkylamines, triethanolamine fatty acid ester, trialkylamine oxide, polyethylene glycol, copolymers of polyethylene glycol and polypropylene glycol.

  The anionic surfactant used in the present invention is not particularly limited, and conventionally known anionic surfactants can be used. For example, fatty acid salts, abietic acid salts, hydroxyalkane sulfonates, alkane sulfonates, dialkyl sulfosuccinate esters, linear alkyl benzene sulfonates, branched alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl phenoxy poly Oxyethylene propyl sulfonates, polyoxyethylene alkyl sulfophenyl ether salts, N-methyl-N-oleyl taurine sodium salt, N-alkyl sulfosuccinic acid monoamide disodium salt, petroleum sulfonates, sulfated beef oil, fatty acid alkyl esters Sulfates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, fatty acid monoglyceride sulfates, polyoxyethylene alcohols Ruphenyl ether sulfates, polyoxyethylene styryl phenyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, styrene / maleic anhydride Examples thereof include partial saponification products of polymers, partial saponification products of olefin / maleic anhydride copolymers, and naphthalene sulfonate formalin condensates.

The cationic surfactant used in the present invention is not particularly limited, and conventionally known cationic surfactants can be used. Examples thereof include alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamine salts, and polyethylene polyamine derivatives.
The amphoteric surfactant used in the present invention is not particularly limited, and conventionally known amphoteric surfactants can be used. Examples thereof include carboxybetaines, aminocarboxylic acids, sulfobetaines, aminosulfuric esters, and imidazolines.

  Of the above surfactants, the term “polyoxyethylene” can be read as “polyoxyalkylene” such as polyoxymethylene, polyoxypropylene, polyoxybutylene, etc. These surfactants can also be used.

  More preferable surfactants include fluorine-based surfactants containing a perfluoroalkyl group in the molecule. Examples of such fluorosurfactants include anionic types such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and perfluoroalkyl phosphates; amphoteric types such as perfluoroalkyl betaines; Cation type such as trimethylammonium salt; perfluoroalkylamine oxide, perfluoroalkylethylene oxide adduct, oligomer containing perfluoroalkyl group and hydrophilic group, oligomer containing perfluoroalkyl group and lipophilic group, perfluoroalkyl Nonionic types such as an oligomer containing a group, a hydrophilic group and a lipophilic group, and a urethane containing a perfluoroalkyl group and a lipophilic group. Also preferred are the fluorosurfactants described in JP-A-62-170950, JP-A-62-226143 and JP-A-60-168144.

Surfactant can be used individually or in combination of 2 or more types.
The content of the surfactant is preferably 0.001 to 10% by mass and more preferably 0.01 to 7% by mass with respect to the total solid content of the image recording layer.

<Colorant>
In the present invention, various compounds other than these may be added as necessary. For example, a dye having a large absorption in the visible light region can be used as an image colorant. Specifically, Oil Yellow # 101, Oil Yellow # 103, Oil Pink # 312, Oil Green BG, Oil Blue BOS, Oil Blue # 603, Oil Black BY, Oil Black BS, Oil Black T-505 (orientated chemistry) Kogyo Co., Ltd.), Victoria Pure Blue, Crystal Violet (CI42555), Methyl Violet (CI42535), Ethyl Violet, Rhodamine B (CI145170B), Malachite Green (CI42000), Methylene Blue (CI522015), etc., and JP-A-62-2 And dyes described in Japanese Patent No. 293247. Also, pigments such as phthalocyanine pigments, azo pigments, carbon black, titanium oxide, etc. can be suitably used.

  These colorants are preferably added since it is easy to distinguish an image area from a non-image area after image formation. The amount added is preferably 0.01 to 10% by mass with respect to the total solid content of the image recording material.

<Bakeout agent>
In the image recording layer of the present invention, other print-out agents can be used in addition to the above-described print-out system using a compound that causes a color change by the action of radicals. For example, a compound that changes color by an acid or a base can be added. As such a compound, various dyes such as diphenylmethane, triphenylmethane, thiazine, oxazine, xanthene, anthraquinone, iminoquinone, azo, and azomethine are effectively used.

  Specific examples include brilliant green, ethyl violet, methyl green, crystal violet, basic fuchsin, methyl violet 2B, quinaldine red, rose bengal, methanyl yellow, thymol sulfophthalein, xylenol blue, methyl orange, paramethyl red, Congo Fred, Benzopurpurin 4B, α-Naphthyl Red, Nile Blue 2B, Nile Blue A, Methyl Violet, Malachide Green, Parafuchsin, Victoria Pure Blue BOH [manufactured by Hodogaya Chemical Co., Ltd.], Oil Blue # 603 [Orient Chemical Kogyo Co., Ltd.], Oil Pink # 312 [Orient Chemical Co., Ltd.], Oil Red 5B [Orient Chemical Co., Ltd.], Oil Scarlet # 308 [Orient Gaku Kogyo Co., Ltd.], Oil Red OG [Orient Chemical Co., Ltd.], Oil Red RR [Orient Chemical Co., Ltd.], Oil Green # 502 [Orient Chemical Co., Ltd.], Spiron Red BEH Special [made by Hodogaya Chemical Co., Ltd.], m-cresol purple, cresol red, rhodamine B, rhodamine 6G, sulforhodamine B, auramine, 4-p-diethylaminophenyliminonaphthoquinone, 2-carboxyanilino-4-p- Diethylaminophenyliminonaphthoquinone, 2-carboxystearylamino-4-pN, N-bis (hydroxyethyl) amino-phenyliminonaphthoquinone, 1-phenyl-3-methyl-4-p-diethylaminophenylimino-5-pyrazolone, 1-β-naphthyl-4- - include dyes such as diethylamino phenyl imino-5-pyrazolone.

  In addition to the above, a leuco dye known as a material for thermal paper or pressure-sensitive paper is also suitable. Specific examples include crystal violet lactone, malachite green lactone, benzoylleucomethylene blue, 2- (N-phenyl-N-methylamino) -6- (Np-tolyl-N-ethyl) amino-fluorane, 2-anilino. -3-methyl-6- (N-ethyl-p-toluidino) fluorane, 3,6-dimethoxyfluorane, 3- (N, N-diethylamino) -5-methyl-7- (N, N-dibenzylamino) ) -Fluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane, 3- (N, N-diethylamino) -6-methyl-7-anilinofluorane, 3 -(N, N-diethylamino) -6-methyl-7-xylidinofluorane, 3- (N, N-diethylamino) -6-methyl-7-chloro Fluorane, 3- (N, N-diethylamino) -6-methoxy-7-aminofluorane, 3- (N, N-diethylamino) -7- (4-chloroanilino) fluorane, 3- (N, N-diethylamino) -7-chlorofluorane, 3- (N, N-diethylamino) -7-benzylaminofluorane, 3- (N, N-diethylamino) -7,8-benzofluorane, 3- (N, N-dibutyl) Amino) -6-methyl-7-anilinofluorane, 3- (N, N-dibutylamino) -6-methyl-7-xylidinofluorane, 3-piperidino-6-methyl-7-anilinofluorane 3-pyrrolidino-6-methyl-7-anilinofluorane, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,3-bis (1-n-butyl- -Methylindol-3-yl) phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl- 2-methylindol-3-yl) -4-zaphthalide, 3- (4-diethylaminophenyl) -3- (1-ethyl-2-methylindol-3-yl) phthalide, and the like.

  A suitable amount of these dyes is 0.01 to 15% by mass based on the solid content of the image recording layer.

<Thermal polymerization inhibitor>
In the image recording layer of the present invention, in order to prevent unnecessary thermal polymerization of the (C) radical polymerizable compound during production or storage of the image recording layer, a small amount of heat is added in addition to the radical scavenger precursor. A polymerization inhibitor can be added.
Preferred examples of the thermal polymerization inhibitor include the compounds capable of scavenging radicals described in the section of compounds that generate chemical species capable of scavenging radicals by heating.
The addition amount of the thermal polymerization inhibitor is preferably about 5% by mass or less based on the total solid content of the image recording layer.

<Higher fatty acid derivatives, etc.>
In order to prevent polymerization inhibition by oxygen, a higher fatty acid derivative such as behenic acid or behenic acid amide is added to the image recording layer of the present invention, and the surface of the image recording layer is dried during the coating process. It may be unevenly distributed. The amount of the higher fatty acid derivative added is preferably about 0.1 to about 10% by mass with respect to the total solid content of the image recording layer.

<Plasticizer>
The image recording layer of the present invention may contain a plasticizer in order to improve the on-press developability.
Examples of the plasticizer include phthalates such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, dioctyl phthalate, octyl capryl phthalate, dicyclohexyl phthalate, ditridecyl phthalate, butyl benzyl phthalate, diisodecyl phthalate, diallyl phthalate; Glycol esters such as glycol phthalate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, triethylene glycol dicaprylate; Phosphate esters such as tricresyl phosphate and triphenyl phosphate Diisobutyl adipate, dioctyl adipate, dimethyl sebacate, dibutyl sebacate, dioct Ruazereto, aliphatic dibasic acid esters such as dibutyl maleate; polyglycidyl methacrylate, triethyl citrate, glycerin triacetyl ester, butyl laurate in.
The plasticizer content is preferably about 30% by mass or less based on the total solid content of the image recording layer.

<Inorganic fine particles>
The image recording layer of the present invention may contain inorganic fine particles for the purpose of improving the strength of the cured film in the image area and improving the on-press developability of the non-image area.
As the inorganic fine particles, for example, silica, alumina, magnesium oxide, titanium oxide, magnesium carbonate, calcium alginate or a mixture thereof can be preferably mentioned. Even if they are not photothermally convertible, they can be used for strengthening the film, enhancing interfacial adhesion by surface roughening, and the like.
The inorganic fine particles preferably have an average particle size of 5 nm to 10 μm, and more preferably 0.5 to 3 μm. Within the above range, it is possible to form a non-image portion excellent in hydrophilicity that is stably dispersed in the image recording layer, sufficiently retains the film strength of the image recording layer, and hardly causes stains during printing. .
The inorganic fine particles as described above can be easily obtained as a commercial product such as a colloidal silica dispersion.
The content of the inorganic fine particles is preferably 20% by mass or less, and more preferably 10% by mass or less, based on the total solid content of the image recording layer.

<Low molecular hydrophilic compound>
The image recording layer of the present invention may contain a hydrophilic low molecular weight compound for improving on-press developability. Examples of the hydrophilic low-molecular compound include water-soluble organic compounds such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol and the like, and ether or ester derivatives thereof, glycerin, Polyhydroxys such as pentaerythritol, organic amines such as triethanolamine and diethanolamine monoethanolamine and salts thereof, organic sulfonic acids such as toluenesulfonic acid and benzenesulfonic acid and salts thereof, organic phosphonic acids such as phenylphosphonic acid and the like Examples thereof include organic carboxylic acids such as salts thereof, tartaric acid, oxalic acid, citric acid, malic acid, lactic acid, gluconic acid and amino acids, and salts thereof.

<Formation of image recording layer>
In the present invention, several modes can be used as a method for incorporating the above-mentioned image recording layer constituents into the image recording layer. One is a molecular dispersion type image recording layer in which the constituent components are dissolved and applied in an appropriate solvent as described in, for example, JP-A-2002-287334. In another embodiment, as described in, for example, JP-A-2001-277740 and JP-A-2001-277742, all or part of the constituent components are encapsulated in microcapsules and contained in the image recording layer. It is a capsule type image recording layer. further. In the microcapsule type image recording layer, the constituent component may be contained outside the microcapsule. Here, it is preferable that the microcapsule-type image recording layer includes a hydrophobic constituent component in the microcapsule and a hydrophilic constituent component outside the microcapsule. In order to obtain better on-press developability, the image recording layer is preferably a microcapsule type image recording layer.

  As a method of microencapsulating the above-mentioned image recording layer constituent components, known methods can be applied. For example, as a method for producing microcapsules, a method using coacervation as described in the specifications of U.S. Pat. Nos. 2,800,047 and 2,800,498, U.S. Pat. No. 3,287,154, JP-B-38-19574, and 42. -46 method by interfacial polymerization, US Pat. No. 3,418,250, US Pat. No. 3,660,304, by polymer precipitation method, US Pat. No. 3,796,669, isocyanate polyol wall A method using a material, a method using an isocyanate wall material found in US Pat. No. 3,914,511, a urea-formaldehyde system or a urea found in US Pat. Nos. 4001140, 4087376, and 4089802 Formaldehyde-resorcinol system A method using a forming material, a method using a wall material such as melamine-formaldehyde resin and hydroxycellulose, as shown in US Pat. No. 4,025,445, and a monomer polymerization as shown in Japanese Patent Publication Nos. 36-9163 and 51-9079 In situ method, British Patent No. 930422, US Pat. No. 3,111,407 spray drying method, British Patent No. 952807, US Pat. No. 967074 specification, etc. It is not limited to these.

  A preferable microcapsule wall used in the present invention has a three-dimensional cross-linking and has a property of swelling with a solvent. From such a viewpoint, the wall material of the microcapsule is preferably polyurea, polyurethane, polyester, polycarbonate, polyamide, and a mixture thereof, and particularly preferably polyurea and polyurethane. Moreover, you may introduce | transduce into the microcapsule wall the compound which has crosslinkable functional groups, such as an ethylenically unsaturated bond which can be introduce | transduced into said binder polymer.

  The average particle size of the microcapsules is preferably 0.01 to 3.0 μm. 0.05-2.0 micrometers is further more preferable, and 0.10-1.0 micrometer is especially preferable. Within this range, good resolution and stability over time can be obtained.

The image recording layer of the present invention is applied by preparing a coating solution by dispersing or dissolving the necessary components described above in a solvent. Solvents used here include ethylene dichloride, cyclohexanone, methyl ethyl ketone, methanol, ethanol, propanol, ethylene glycol monomethyl ether, 1-methoxy-2-propanol, 2-methoxyethyl acetate, 1-methoxy-2-propyl acetate, dimethoxy Examples include ethane, methyl lactate, ethyl lactate, N, N-dimethylacetamide, N, N-dimethylformamide, tetramethylurea, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, γ-butyllactone, toluene, water, and the like. However, the present invention is not limited to this. These solvents are used alone or in combination. The solid content concentration of the coating solution is preferably 1 to 50% by mass.
The image recording layer of the present invention can also be formed by preparing a plurality of coating solutions in which the same or different components are dispersed or dissolved in the same or different solvents, and repeatedly applying and drying a plurality of times.

Further, the coating amount (solid content) of the image recording layer on the support obtained after coating and drying varies depending on the use, but generally 0.3 to 3.0 g / m ² is preferable. Within this range, good sensitivity and good film properties of the image recording layer can be obtained.
Various methods can be used as a coating method. Examples thereof include bar coater coating, spin coating, spray coating, curtain coating, dip coating, air knife coating, blade coating, and roll coating.

<Support>
The support used for the lithographic printing plate precursor according to the invention is not particularly limited as long as it is a dimensionally stable plate-like material. For example, paper, paper laminated with plastic (eg, polyethylene, polypropylene, polystyrene, etc.), metal plate (eg, aluminum, zinc, copper, etc.), plastic film (eg, cellulose diacetate, cellulose triacetate, cellulose propionate) Cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, etc.), and paper or plastic films on which the above-mentioned metals are laminated or deposited. Preferable supports include a polyester film and an aluminum plate. Among these, an aluminum plate that has good dimensional stability and is relatively inexpensive is preferable.

The aluminum plate is a pure aluminum plate, an alloy plate containing aluminum as a main component and containing a trace amount of different elements, or a plastic laminated on a thin film of aluminum or an aluminum alloy. Examples of foreign elements contained in the aluminum alloy include silicon, iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel, and titanium. The content of foreign elements in the alloy is preferably 10% by mass or less. In the present invention, a pure aluminum plate is preferable, but completely pure aluminum is difficult to manufacture in terms of refining technology, and therefore may contain a slightly different element. The composition of the aluminum plate is not specified, and a publicly known material can be used as appropriate.

  The thickness of the support is preferably from 0.1 to 0.6 mm, more preferably from 0.15 to 0.4 mm, and even more preferably from 0.2 to 0.3 mm.

  Prior to using the aluminum plate, it is preferable to perform a surface treatment such as roughening treatment or anodizing treatment. By the surface treatment, it is easy to improve hydrophilicity and secure adhesion between the image recording layer and the support. Prior to roughening the aluminum plate, a degreasing treatment with a surfactant, an organic solvent, an alkaline aqueous solution or the like for removing rolling oil on the surface is performed as desired.

The surface roughening treatment of the aluminum plate is performed by various methods. For example, mechanical surface roughening treatment, electrochemical surface roughening treatment (surface roughening treatment for dissolving the surface electrochemically), chemical treatment, etc. Surface roughening treatment (roughening treatment that chemically selectively dissolves the surface).
As a method for the mechanical surface roughening treatment, a known method such as a ball polishing method, a brush polishing method, a blast polishing method, or a buff polishing method can be used.
Examples of the electrochemical surface roughening treatment include a method in which an alternating current or a direct current is used in an electrolytic solution containing an acid such as hydrochloric acid or nitric acid. Another example is a method using a mixed acid as described in JP-A-54-63902.

  The surface-roughened aluminum plate is subjected to an alkali etching treatment using an aqueous solution of potassium hydroxide, sodium hydroxide or the like, if necessary, further neutralized, and if desired, wear resistant. In order to increase the anodic oxidation treatment.

As the electrolyte used for the anodizing treatment of the aluminum plate, various electrolytes that form a porous oxide film can be used. In general, sulfuric acid, hydrochloric acid, oxalic acid, chromic acid or a mixed acid thereof is used. The concentration of these electrolytes is appropriately determined depending on the type of electrolyte.
The conditions for anodizing treatment vary depending on the electrolyte used and cannot be specified in general. In general, however, the electrolyte concentration is 1 to 80% by mass solution, the liquid temperature is 5 to 70 ° C., and the current density is 5 to 60 A / day. dm ² , voltage 1 to 100 V, and electrolysis time 10 seconds to 5 minutes are preferable. The amount of the anodized film formed is preferably from 1.0 to 5.0 g / m ^2, and more preferably 1.5 to 4.0 g / m ^2. Within this range, good printing durability and good scratch resistance of the non-image area of the lithographic printing plate can be obtained.

  As the support used in the present invention, the substrate having the above-mentioned surface treatment and having an anodized film may be used as it is, but for further improvement in adhesion to the upper layer, hydrophilicity, resistance to contamination, heat insulation and the like. If necessary, it contains a micropore enlargement treatment, a micropore sealing treatment, and a hydrophilic compound described in Japanese Patent Application Laid-Open Nos. 2001-253181 and 2001-322365. A surface hydrophilization treatment immersed in an aqueous solution can be selected as appropriate.

  The hydrophilization treatment is described in the specifications of US Pat. Nos. 2,714,066, 3,181,461, 3,280,734, and 3,902,734. There are such alkali metal silicate methods. In this method, the support is immersed in an aqueous solution such as sodium silicate or electrolytically treated. In addition, the treatment with potassium zirconate fluoride described in JP-B 36-22063, U.S. Pat. Nos. 3,276,868, 4,153,461 and 4,689, And a method of treating with polyvinylphosphonic acid as described in the specification of No. 272.

  When using a support with insufficient surface hydrophilicity such as a polyester film as the support of the present invention, it is desirable to apply a hydrophilic layer to make the surface hydrophilic. As the hydrophilic layer, at least one element selected from beryllium, magnesium, aluminum, silicon, titanium, boron, germanium, tin, zirconium, iron, vanadium, antimony, and a transition metal described in JP-A-2001-199175 A hydrophilic layer formed by coating a coating solution containing a colloid of oxide or hydroxide, or organic hydrophilicity obtained by crosslinking or pseudo-crosslinking an organic hydrophilic polymer described in JP-A-2002-79772 A hydrophilic layer having a hydrophilic matrix, a hydrophilic layer having an inorganic hydrophilic matrix obtained by sol-gel conversion comprising hydrolysis, condensation reaction of polyalkoxysilane, titanate, zirconate or aluminate, or a metal oxide A hydrophilic layer made of an inorganic thin film having a surface is preferred. Arbitrariness. Among these, a hydrophilic layer formed by applying a coating solution containing a silicon oxide or a hydroxide colloid is preferable.

  Moreover, when using a polyester film etc. as a support body of this invention, it is preferable to provide an antistatic layer in the hydrophilic layer side of a support body, the opposite side, or both sides. In the case where the antistatic layer is provided between the support and the hydrophilic layer, it also contributes to improving the adhesion with the hydrophilic layer. As the antistatic layer, a polymer layer in which metal oxide fine particles or a matting agent are dispersed as described in JP-A-2002-79772 can be used.

The support preferably has a center line average roughness of 0.10 to 1.2 μm. Within this range, good adhesion with the image recording layer, good printing durability and good stain resistance can be obtained.
The color density of the support is preferably 0.15 to 0.65 as the reflection density value. Within this range, good image formability by preventing halation during image exposure and good plate inspection after development can be obtained.

<Undercoat layer>
In the lithographic printing plate precursor according to the invention, it is preferable to provide an undercoat layer of a compound containing a polymerizable group on a support. When an undercoat layer is used, the image recording layer is provided on the undercoat layer. The undercoat layer enhances the adhesion between the support and the image recording layer in the exposed area, and in the unexposed area, the image recording layer is easily peeled off from the support. Will improve.
As the undercoat layer, specifically, a silane coupling agent having an addition polymerizable ethylenic double bond reactive group described in JP-A-10-282679, JP-A-2-304441. Preferable examples include phosphorus compounds having an ethylenic double bond reactive group described in the publication. A compound having a polymerizable group such as a methacryl group or an allyl group and a support adsorbing group such as a sulfonic acid group, a phosphoric acid group or a phosphoric acid ester is also preferred. Furthermore, a compound obtained by adding a hydrophilicity-imparting group such as an ethyleneoxy group to this compound is also suitable.
The coating amount (solid content) of the undercoat layer is preferably from 0.1-100 mg / m ^2, and more preferably 1 to 30 mg / m ^2.

<Back coat layer>
After the surface treatment is performed on the support or after the undercoat layer is formed, a back coat can be provided on the back surface of the support, if necessary.
Examples of the back coat include hydrolysis and polycondensation of organic polymer compounds described in JP-A-5-45885, organometallic compounds or inorganic metal compounds described in JP-A-6-35174. A coating layer made of a metal oxide obtained in this manner is preferred. Among them, it is inexpensive to use a silicon alkoxy compound such as Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) ₄ , Si (OC ₃ H ₇ ) ₄ , Si (OC ₄ H ₉ ) _4. It is preferable in terms of easy availability.

<Protective layer>
In the planographic printing plate precursor of the present invention used in the planographic printing method of the present invention, since the image formation by exposure is not easily affected by oxygen, a protective layer for the purpose of blocking oxygen is not necessarily required. However, if necessary, a protective layer is provided on the image recording layer in order to prevent scratches and the like in the image recording layer, to prevent ablation at the time of high-illuminance laser exposure, and to block oxygen to further increase the image strength. be able to.
In the present invention, exposure is usually carried out in the atmosphere, but the protective layer is an image of low molecular weight compounds such as oxygen and basic substances present in the atmosphere that inhibit the image forming reaction caused by exposure in the image recording layer. This prevents the recording layer from being mixed, and prevents the image formation reaction from being hindered by exposure in the air. Therefore, the properties desired for the protective layer are low permeability of low-molecular compounds such as oxygen, furthermore, good transparency of light used for exposure, excellent adhesion to the image recording layer, and It is preferable that it can be easily removed in an on-press development process after exposure. Various studies have been made on the protective layer having such characteristics, and are described in detail, for example, in US Pat. No. 3,458,311 and JP-B-55-49729.

Examples of the material used for the protective layer include water-soluble polymer compounds that are relatively excellent in crystallinity. Specific examples include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, acidic celluloses, gelatin, gum arabic, and polyacrylic acid.
Among these, when polyvinyl alcohol (PVA) is used as a main component, the best results are obtained for basic characteristics such as oxygen barrier properties and development removability. The polyvinyl alcohol may be partially substituted with an ester, ether or acetal as long as it contains an unsubstituted vinyl alcohol unit for providing the oxygen barrier property and water solubility necessary for the protective layer, and a part of the other You may have a copolymerization component.
Specific examples of the polyvinyl alcohol include those having a hydrolysis degree of 71 to 100 mol% and a polymerization degree in the range of 300 to 2400. Specifically, for example, PVA-105, PVA-110, PVA-117, PVA-117H, PVA-120, PVA-124, PVA-124H, PVA-CS, PVA-CST, PVA manufactured by Kuraray Co., Ltd. -HC, PVA-203, PVA-204, PVA-205, PVA-210, PVA-217, PVA-220, PVA-224, PVA-217EE, PVA-217E, PVA-220E, PVA-224E, PVA-405 , PVA-420, PVA-613, and L-8.

The components of the protective layer (selection of PVA, use of additives, etc.), coating amount, etc. are appropriately selected in consideration of fogging properties, adhesion, scratch resistance, etc. in addition to oxygen barrier properties and development removability. Generally, the higher the hydrolysis rate of PVA (that is, the higher the content of the unsubstituted vinyl alcohol unit in the protective layer), and the thicker the film thickness, the higher the oxygen barrier property, which is preferable in terms of sensitivity. . Further, in order to prevent unnecessary polymerization reaction during production and storage and unnecessary fogging during image exposure, image line weighting, and the like, it is preferable that the oxygen permeability is not excessively high. Accordingly, the oxygen permeability A at 25 ° C. and 1 atm is preferably 0.2 ≦ A ≦ 20 (cc / m ² · day).

  As another composition of the protective layer, glycerin, dipropylene glycol and the like can be added in an amount corresponding to several mass% with respect to the (co) polymer to provide flexibility. Anionic surfactants such as sodium acid salts; amphoteric surfactants such as alkylaminocarboxylates and alkylaminodicarboxylates; nonionic surfactants such as polyoxyethylene alkylphenyl ethers to the (co) polymer Mass% can be added.

  In addition, adhesion of the protective layer to the image area, scratch resistance, and the like are extremely important in handling the lithographic printing plate precursor. That is, when a protective layer that is hydrophilic because it contains a water-soluble polymer compound is laminated on an image recording layer that is oleophilic, the protective layer is easily peeled off due to insufficient adhesion, and polymerization is inhibited by oxygen at the peeled portion. It may cause defects such as poor film hardening due to.

  On the other hand, various proposals have been made to improve the adhesion between the image recording layer and the protective layer. For example, JP-A-49-70702 and British Patent Application No. 1303578 disclose an acrylic emulsion, a water-insoluble vinylpyrrolidone-vinyl acetate copolymer, etc. in a hydrophilic polymer mainly composed of polyvinyl alcohol. It is described that sufficient adhesiveness can be obtained by mixing 20 to 60% by mass and laminating on an image recording layer. Any of these known techniques can be used in the present invention.

  Furthermore, other functions can be imparted to the protective layer. For example, by adding a colorant (for example, a water-soluble dye) that is excellent in the transparency of light used for exposure and that can efficiently absorb light of other wavelengths, safe light is not caused. Suitability can be improved.

The thickness of the protective layer is suitably from 0.1 to 5 μm, particularly preferably from 0.2 to 2 μm.
The method for applying the protective layer is described in detail, for example, in US Pat. No. 3,458,311 and JP-B-55-49729.

<Lithographic printing method>
In the lithographic printing method using the lithographic printing plate precursor according to the present invention, the lithographic printing plate precursor according to the present invention is exposed through a transparent original having a line image, a halftone dot image, or the like, or by laser scanning exposure with digital data. To be exposed. Examples of the exposure light source include a carbon arc, a high-pressure mercury lamp, a xenon lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, a halogen lamp, an ultraviolet light laser, a visible light laser, and an infrared light laser. A laser is particularly preferable, and examples thereof include a semiconductor laser that emits light in the range of 250 to 420 nm, a solid-state laser that emits infrared light in the range of 760 to 1200 nm, and a semiconductor laser. When a laser is used, scanning exposure is preferably performed in an image-like manner according to digital data. In order to shorten the exposure time, it is preferable to use a multi-beam laser device.
When a laser is used, the exposure time per pixel is preferably within 20 μsec.

  In the present invention, as described above, the lithographic printing plate precursor according to the present invention is imagewise exposed and subjected to a heating process for imparting white light safety, followed by a development process, or any development process. Oil-based ink and aqueous component are supplied and printed without going through the process.

<Development processing>
A conventionally known alkaline aqueous solution can be used as the developer used in the development treatment with the developer. For example, sodium silicate, potassium, tribasic sodium phosphate, potassium, ammonium, dibasic sodium phosphate, potassium, ammonium, sodium carbonate, potassium, ammonium, sodium bicarbonate, potassium Examples include inorganic alkaline agents such as ammonium, sodium borate, potassium, ammonium, sodium hydroxide, ammonium, potassium, and lithium. In addition, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, n-butylamine, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolan, diisopropanolamine, Organic alkali agents such as ethyleneimine, ethylenediamine, and pyridine are also used.

These alkali agents are used alone or in combination of two or more. Among the above-mentioned alkaline aqueous solutions, a developing solution that exhibits the effect of the present invention is an aqueous solution containing alkali metal silicate and having a pH of 12 or more. The aqueous solution of alkali metal silicate depends on the ratio and the concentration of silicon oxide SiO ₂ and alkali metal oxide M ₂ O (generally expressed as a molar ratio of [SiO ₂ ] / [M ₂ O]). are possible adjustment of developability, for example, as disclosed in JP-a-54-62004, the molar ratio of SiO ₂ / Na ₂ O 1.0 to 1.5 (i.e. [SiO _2] / [Na ₂ O] is 1.0 to 1.5, and the content of SiO ₂ is 1 to 4% by mass, an aqueous solution of sodium silicate, as described in JP-B-57-7427 [SiO ₂ ] / [M] is 0.5 to 0.75 (ie, [SiO ₂ ] / [M ₂ O] is 1.0 to 1.5), and the concentration of SiO ₂ is 1 to 4% by weight, and the developer is small on the basis of gram atoms of all alkali metals present therein. An alkali metal silicate comprising at least 20% by weight of potassium is preferably used, and the pH of the developer is preferably in the range of 9 to 13.5, more preferably 10 to 13. The developer temperature is preferably 15 to 40 ° C., more preferably 20 to 35 ° C. The development time is preferably 5 to 60 seconds, and more preferably 7 to 40 seconds.

Further, when the photosensitive lithographic printing plate is developed using an automatic developing machine, an aqueous solution (replenisher) having a higher alkali strength than the developer is added to the developer, so that the developer in the developer tank for a long time. It is known that a large amount of photosensitive lithographic printing plate can be processed without replacing the plate. This replenishment method is also preferably applied in the present invention. For example, the molar ratio of SiO ₂ / Na ₂ O in a developer as disclosed in JP-A-54-62004 is 1.0 to 1.5 (that is, [SiO ₂ ] / [Na ₂ O] 1.0 to 1.5), an aqueous solution of sodium silicate having a SiO ₂ content of 1 to 4% by mass, and continuously or intermittently depending on the throughput of the lithographic printing plate precursor An aqueous sodium silicate solution (replenisher) having a SiO ₂ / Na ₂ O molar ratio of 0.5 to 1.5 (ie, [SiO ₂ ] / [Na ₂ O] is 0.5 to 1.5) is used as a developer. Further, the method disclosed in Japanese Patent Publication No. 57-7427, [SiO ₂ ] / [M] is 0.5 to 0.75 (ie, [SiO ₂ ] / [M ₂ O] is 1.0 to 1.5), and an alkali metal silicate developer having a SiO ₂ concentration of 1 to 4% by mass is used. The [SiO ₂ ] / [M] of the alkali metal silicate used as the replenisher is 0.25 to 0.75 (that is, [SiO ₂ ] / [M ₂ O] is 0.5 to 1.5). And a developing method in which both the developer and the replenisher contain at least 20% by mass of potassium based on the gram atoms of all alkali metals present therein is preferably used. .

  The photosensitive lithographic printing plate thus developed is washed with water, surface active as described in JP-A Nos. 54-8002, 55-1115045 and 59-58431. It is post-treated with a desensitizing solution containing a rinse solution containing an agent and the like, gum arabic and starch derivatives. These treatments can be used in various combinations for the post-treatment of the photosensitive lithographic printing plate of the present invention. The planographic printing plate obtained by such processing is loaded on an offset printing machine and used for printing a large number of sheets. As plate cleaners used for removing stains on printing plates, conventionally known plate cleaners for PS plates are used. For example, CL-1, CL-2, CP, CN-4, CN, CG -1, PC-1, SR, IC (manufactured by Fuji Photo Film Co., Ltd.) and the like.

As the plate-making process of the lithographic printing plate precursor used in the plate-making method of the present invention, it is also effective to subject the image after development to full post-heating or full exposure for the purpose of improving image strength and printing durability. . Very strong conditions are used for heating after development. Usually, it is the range of 200-500 degreeC. If the temperature is low, sufficient image strengthening action cannot be obtained. If the temperature is too high, problems such as deterioration of the support and thermal decomposition of the image area occur.

<On-machine development processing>
Specifically, as a method of printing without passing through the development processing step, after exposing the lithographic printing plate precursor to a printing press without passing through the development processing step, the lithographic printing plate precursor to the printing press For example, a method of exposing on a printing machine and printing as it is after mounting.

In the image recording layer of the lithographic printing plate precursor exposed like an image, the exposed portion becomes insoluble by polymerization and curing. When the exposed lithographic printing plate precursor is supplied with an oil-based ink and a water-based component and printed without being subjected to a development process such as a wet development process step, in the unexposed area, the oil-based ink and / or the water-based component, The uncured image recording layer is removed by dissolution or dispersion, and the hydrophilic support surface is exposed in that portion. On the other hand, in the exposed portion, the polymerized and cured image recording layer remains to form an oil-based ink receiving portion (image portion) having a lipophilic surface.
As a result, the aqueous component adheres to the exposed hydrophilic surface, and the oil-based ink is deposited on the image recording layer in the exposed area, and printing is started. Here, the water-based component or oil-based ink may be first supplied to the plate surface, but the oil-based ink is first used in order to prevent the water-based component from being contaminated by the image recording layer in the unexposed area. It is preferable to supply. As the aqueous component and oil-based ink, a dampening water and printing ink for ordinary lithographic printing are used.
In this way, the lithographic printing plate precursor is subjected to on-press development on an offset printing machine and used as it is for printing a large number of sheets.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

1. Preparation of support body To remove rolling oil on the surface of an aluminum plate (material 1050) having a thickness of 0.3 mm, after performing a degreasing treatment at 50 ° C. for 30 seconds using a 10 mass% sodium aluminate aqueous solution, the bristle diameter The aluminum surface was grained using ^three 0.3 mm bundled nylon brushes and a pumice-water suspension (specific gravity 1.1 g / cm ³ ) having a median diameter of 25 μm and washed well with water. This plate was etched by being immersed in a 25 mass% sodium hydroxide aqueous solution at 45 ° C for 9 seconds, washed with water, further immersed in 20 mass% nitric acid at 60 ° C for 20 seconds, and washed with water. The etching amount of the grained surface at this time was about 3 g / m ² .

Next, an electrochemical roughening treatment was performed continuously using an alternating voltage of 60 Hz. The electrolytic solution at this time was a 1% by mass nitric acid aqueous solution (containing 0.5% by mass of aluminum ions) and a liquid temperature of 50 ° C. The AC power source waveform is electrochemical roughening treatment using a trapezoidal rectangular wave alternating current with a time ratio TP of 0.8 msec until the current value reaches a peak from zero, a duty ratio of 1: 1, and a trapezoidal rectangular wave alternating current. Went. Ferrite was used for the auxiliary anode. The current density was 30 A / dm ² at the peak current value, and 5% of the current flowing from the power source was shunted to the auxiliary anode. The amount of electricity in the nitric acid electrolysis was 175 C / dm ² when the aluminum plate was the anode. Then, water washing by spraying was performed.

Next, a 0.5% by mass hydrochloric acid aqueous solution (containing 0.5% by mass of aluminum ions) and an electrolytic solution having a liquid temperature of 50 ° C. and nitric acid electrolysis under the condition of an electric quantity of 50 C / dm ² when the aluminum plate is an anode. In the same manner as above, an electrochemical surface roughening treatment was performed, followed by washing with water by spraying. The plate was provided with a DC anodized film of 2.5 g / m ² at a current density of 15 A / dm ² using 15% by mass sulfuric acid (containing 0.5% by mass of aluminum ions) as an electrolytic solution, then washed with water and dried.

  Next, the support provided up to the anodic oxide film was subjected to a sealing treatment by exposing it to a saturated steam atmosphere at 100 ° C. for 10 seconds, and then treated with a 2.5 mass% aqueous solution of sodium silicate at 30 ° C. for 10 seconds. .

Furthermore, the following undercoat liquid (1) was applied so that the dry coating mass was 5 mg / m ² to prepare a support used in the following experiments.

Undercoat liquid (1)
・ Undercoat compound (1) below 0.017g
・ Methanol 9.00 g
・ Water 1.00g

  When the center line average roughness (Ra) of the obtained support surface was measured using a needle having a diameter of 2 μm, it was 0.51 μm.

2. Preparation of lithographic printing plate precursor Preparation of lithographic printing plate precursor (1) (photopolymer plate material) An image recording layer coating liquid (1) having the following composition is dried on the above-mentioned undercoated support in a dry coating mass of 1.5 g. / M ^2, and dried at 100 ° C. for 1 minute to form an image recording layer. A protective layer coating solution (1) having the following composition was coated thereon so that the dry coating mass was 2.5 g / m ² and dried at 120 ° C. for 1 minute to obtain a lithographic printing plate precursor (1). It was.

<Image recording layer coating solution (1)>
・ Tetramethylol methane tetraacrylate 20g
・ The following binder polymer (1) (average molecular weight 50,000) 30 g
・ The following radical initiator (1) 1g
・ The following sensitizing dye (1) 0.5 g
1 g of radical scavenger precursor (Exemplified Compound I-17 in the present specification)
・ Royco Crystal Violet 0.5g
・ Fluorine nonionic surfactant Megafac F177
(Dai Nippon Ink Chemical Co., Ltd.) 0.5g
・ Methyl ethyl ketone 200g
・ 200 g of propylene glycol monomethyl ether acetate

<Protective layer coating solution (1)>
Polyvinyl alcohol (saponification degree 95 mol%, polymerization degree 800) 40 g
・ Polyvinylpyrrolidone (molecular weight 50,000) 5g
・ Poly (vinyl pyrrolidone / vinyl acetate (1/1)) molecular weight of 75 g
・ 950g of water

Preparation of lithographic printing plate precursor (2) (on-press developing plate material) An image recording layer coating solution (2) having the following composition was bar-coated on the above-mentioned undercoated support, and then an oven was formed at 70 ° C. for 60 seconds. It is dried to form an image recording layer having a dry coating mass of 1.0 g / m ² , and a protective layer coating solution (1) having the above composition is formed thereon so that the dry coating mass is 0.5 g / m ^2. It was applied and dried at 120 ° C. for 1 minute to obtain a lithographic printing plate precursor (2).

<Image recording layer coating solution (2)>
・ 0.2 g of the above radical initiator (1)
-0.1 g of the above sensitizing dye (1)
・ Radical scavenger precursor I-17 0.5g
・ The following binder polymer (2) (average molecular weight 80,000) 6.0 g
・ Polymerizable compound 12.4g
Pentaerythritol triacrylate (manufactured by Nippon Kayaku Co., Ltd., SR444)
・ Royco Crystal Violet 0.5g
・ Tetraethylammonium chloride 0.1g
・ 0.1 g of the following fluorosurfactant (1)
・ Methyl ethyl ketone 70.0g

Preparation of lithographic printing plate precursor (3) (microcapsule on-machine development plate material) A lithographic printing plate precursor except that the image recording layer coating solution (2) is changed to an image recording layer coating solution (3) having the following composition A lithographic printing plate precursor (3) was obtained in the same manner as in (2).

<Image recording layer coating solution (3)>
・ 0.2 g of the above radical initiator (1)
-0.1 g of the above sensitizing dye (1)
・ Radical scavenger precursor I-17 0.5g
・ Binder polymer (2) (average molecular weight 80,000) 3.0 g
-Polymerizable compound 6.2g
Isocyanuric acid EO-modified triacrylate (M-315 manufactured by Toa Gosei Co., Ltd.)
・ Royco Crystal Violet 0.5g
・ 0.1 g of the above-mentioned fluorosurfactant (1)
・ The following microcapsule (1) (in terms of solid content) 10.0 g
・ Methyl ethyl ketone 35.0g
・ 3-methoxy-2-propanol 35.0 g
・ Water 10.0g

(Synthesis of microcapsule (1))
As an oil phase component, trimethylolpropane and xylene diisocyanate adduct (manufactured by Mitsui Takeda Chemical Co., Ltd., Takenate D-110N) 10 g, pentaerythritol triacrylate (manufactured by Nippon Kayaku Co., Ltd., SR444) 4.15 g, And 0.1 g of Pionein A-41C (manufactured by Takemoto Yushi Co., Ltd.) was dissolved in 17 g of ethyl acetate. As an aqueous phase component, 40 g of a 4% by mass aqueous solution of PVA-205 was prepared. The oil phase component and the aqueous phase component were mixed and emulsified for 10 minutes at 12000 rpm using a homogenizer. The obtained emulsion was added to 25 g of distilled water, stirred at room temperature for 30 minutes, and then stirred at 40 ° C. for 3 hours. The microcapsule liquid (1) thus obtained was diluted with distilled water so that the solid content concentration became 20% by mass. The average particle size was 0.25 μm.

Preparation of lithographic printing plate precursor (4) (Comparative example of lithographic printing plate precursor (2))
A lithographic printing plate precursor (4) was obtained in the same manner as the preparation of the lithographic printing plate precursor (2) except that the radical scavenger precursor I-17 was not added to the image recording layer coating liquid (2).

Preparation of lithographic printing plate precursor (5) (Comparative example of lithographic printing plate precursor (2))
Except for changing 0.5 g of the radical scavenger agent I-17 in the image recording layer coating liquid (2) to 0.36 g of the following radical scavenger agent (1), the same as the preparation of the lithographic printing plate precursor (2) Thus, a lithographic printing plate precursor (5) was obtained.

Preparation of lithographic printing plate precursor (6) (on-press development plate material, start system change) Radical initiator (1) of image recording layer coating liquid (2) is changed to the following radical initiator (2), and sensitizing dye A lithographic printing plate precursor (6) was obtained in the same manner as in the production of the lithographic printing plate precursor (2) except that (1) was changed to the following sensitizing dye (2).

Preparation of lithographic printing plate precursor (7) (on-press development plate material, starting system change) Radical initiator (1) of image recording layer coating liquid (2) was changed to radical initiator (3) below, and sensitizing dye A lithographic printing plate precursor (7) was obtained in the same manner as in the preparation of the lithographic printing plate precursor (2) except that (1) was not added.

Preparation of lithographic printing plate precursor (8) (on-press development plate material, starting system change) Except for changing the image recording layer coating solution (2) to the following image recording layer coating solution (4), the lithographic printing plate precursor (2 ), A lithographic printing plate precursor (8) was obtained.

<Image recording layer coating solution (4)>
・ The following infrared absorber (1) 0.05 g
・ The following radical initiator (4) 0.20 g
-Radical scavenger precursor I-17 0.10 g
・ Binder polymer (2) 0.50g
・ Polymerizable compound, Aronix M-215 (manufactured by Toa Gosei Co., Ltd.) 1.00 g
・ Royco Crystal Violet 0.02g
-0.10 g of the above fluorosurfactant (1)
・ Methyl ethyl ketone 18.0g

Preparation of lithographic printing plate precursor (9) (Development plate material on microcapsule type machine, starting system change) A lithographic printing plate except that the image recording layer coating solution (3) is changed to the following image recording layer coating solution (5) A lithographic printing plate precursor (9) was obtained in the same manner as the preparation of the original plate (3).

<Image recording layer coating solution (5)>
The image recording layer coating solution (5) was obtained by mixing and stirring the following photosensitive solution (1) and microcapsule solution (1) immediately before coating.

Photosensitive solution (1)
・ The following binder polymer (3) 0.162 g
・ The above radical initiator (4) 0.100 g
・ The above infrared absorber (1) 0.020 g
・ Radical scavenger precursor I-17 0.050 g
・ Polymerizable compound Aronix M-215 (manufactured by Toa Gosei Co., Ltd.) 0.385 g
・ 0.044 g of the above fluorosurfactant (1)
・ Methyl ethyl ketone 1.091g
・ Propylene glycol monomethyl ether 8.609g

Microcapsule liquid (1)
-Microcapsule (2) synthesized as follows: 2.640 g
・ Water 2.425g

Synthesis of microcapsule (2) As oil phase components, trimethylolpropane and xylene diisocyanate adduct (Mitsui Takeda Chemical Co., Ltd., Takenate D-110N) 10 g, Leucomalachite Green (Tokyo Kasei Co., Ltd.) 5 g 0.5 g of the following radical initiator (5), 0.5 g of the following infrared absorber (2), and 0.1 g of dodecylbenzenesulfonic acid Na salt (manufactured by Takemoto Yushi Co., Ltd., Pionein A-41C) Dissolved in 17 g of ethyl. As an aqueous phase component, 40 g of a 4% by mass aqueous solution of PVA-205 was prepared. The oil phase component and the aqueous phase component were mixed and emulsified for 10 minutes at 12000 rpm using a homogenizer. To the obtained emulsion, 0.38 g of tetraethylenepentamine and 25 g of distilled water were added, stirred at room temperature for 30 minutes, and then stirred at 65 ° C. for 3 hours. The microcapsule solution thus obtained was diluted with distilled water so that the solid content concentration became 20% by mass. The average particle size was 0.3 μm.

Preparation of lithographic printing plate precursors (10) to (13) (change of on-press development plate material and radical scavenger precursor) The radical scavenger precursor I-17 of the image recording layer coating liquid (2) is shown in Table 1 below. Except for changing as shown, lithographic printing plate precursors (10) to (13) were obtained in the same manner as in the preparation of the lithographic printing plate precursor (2).

Preparation of lithographic printing plate precursor (14) (on-press development plate, no protective layer) Lithographic printing is carried out in the same manner as the preparation of lithographic printing plate precursor (2) except that no protective layer is provided on the image recording layer. An original plate (14) was obtained.

Production of lithographic printing plate precursor (15) (on-press development plate, no protective layer) Lithographic printing is carried out in the same manner as the production of lithographic printing plate precursor (8) except that no protective layer is provided on the image recording layer. A plate original plate (15) was obtained.

Preparation of lithographic printing plate precursors (16) to (20) (change of on-press development plate material and radical discoloring agent) The radical discoloring agent leuco crystal violet of the image recording layer coating liquid (2) was changed as shown in Table 2 below. Except that, lithographic printing plate precursors (16) to (20) were obtained in the same manner as in the production of the lithographic printing plate precursor (2).

3. Image exposure method <Exposure of lithographic printing original plates (1) to (7), (10) to (20)>
The lithographic printing plate precursor is subjected to an oscillation wavelength of 405 nm (lithographic printing plate precursors (1) to (5), (10) to (14)) or 375 nm using an exposure head composed of an optical system using a DMD spatial modulation element. Exposure with a semiconductor laser of (lithographic printing plate precursors (6) to (7)) under the conditions of an output of 2 mW, an outer drum with a peripheral length of 900 mm, a drum rotation speed of 800 rpm, a resolution of 2400 dpi, and a pixel drawing time of 0.9 microseconds did.

<Exposure of planographic printing original plates (8) to (9) and (15)>
The exposure was performed with a Trend setter 3244VX manufactured by Creo equipped with a water-cooled 40 W infrared (830 nm) semiconductor laser under the conditions of an output of 9 W, an outer drum rotating speed of 210 rpm, and a resolution of 2400 dpi.

4). Heat treatment method The lithographic printing plate precursor after image exposure was placed in an oven, heated by blowing hot air, and held at 140 ° C. for 100 seconds.

5. Development processing <Development processing of planographic printing plate precursor (1)>
Image exposure and development of the heat-treated original plate were carried out by diluting DP-4 developer (produced by Fuji Photo Film Co., Ltd.) 18 times with water and dipping at 30 ° C. for 15 seconds. Next, GU-7 (manufactured by Fuji Photo Film Co., Ltd.) gum solution was diluted twice with water to treat the plate surface.

<Development of planographic printing plate precursors (2) to (20)>
As described in the printing method below, the image-exposure and heat-treated original plate was mounted on a printing press without developing, and on-press development was performed.

6). Printing Method The lithographic printing plate precursor (1) is subjected to image exposure, heat treatment and development treatment as described above, and then attached to a printing machine SOR-M manufactured by Heidelberg, and fountain solution [EU-3 (Fuji Photo Film). Etch solution manufactured by Co., Ltd.) / Water / isopropyl alcohol = 1/89/10 (volume ratio)] and TRANS-G (N) black ink (manufactured by Dainippon Ink & Chemicals, Inc.) Printing was performed at a printing speed of.

The lithographic printing plate precursors (2) to (13) are subjected to image exposure and heat treatment as described above, and are each attached to a cylinder of a printing machine SOR-M manufactured by Heidelberg without using a developing solution. Immersion water using IF201 (Fuji Photo Film Co., Ltd. etchant) / water = 4/96 (volume ratio)] and TRANS-G (N) black ink (Dainippon Ink Chemical Co., Ltd.) After the ink was supplied, printing was performed at a printing speed of 6000 sheets per hour.

7. Evaluation of the white light discoloration of the lithographic printing plate precursor The unexposed lithographic printing plate precursor is heat-treated by the above method so that the illuminance on the surface of the lithographic printing plate precursor is 400 lux under a white fluorescent light. It was installed, exposed to light for 2 hours, and the color difference sensitivity by white light was evaluated by measuring the lightness difference ΔL of the lithographic printing plate precursor before and after white light exposure.
The brightness difference ΔL was measured with a color difference meter CR-221 (manufactured by Minolta Co., Ltd.). If ΔL is 0.2 or less, it can be determined that a sufficient discoloration suppressing effect has been obtained.

[Example 1]
When the lithographic printing plate precursor (1) was image-exposed as described above, the exposed area developed color and the brightness contrast (image visibility) between the image area and the non-image area was good. Subsequently, as described above, the heat treatment and the development treatment were performed, and then printing was performed on 10,000 sheets, and a good printed matter having a non-image portion stain and a sufficient image portion ink density was obtained.
In addition, as a result of the white light discoloration evaluation, the brightness difference ΔL before and after the white light exposure was 0.2 or less, and a good discoloration suppressing effect in the non-image area was obtained.

[Example 2]
When the lithographic printing plate precursors (2), (3), and (6) to (20) were used for image exposure as described above, the exposed portion developed color in any of the original plates, and the image portion and the non-image portion The brightness contrast (image visibility) was good. Next, heat treatment was performed by the above-described method, and the sheet was attached to a printing machine without performing development processing, and printing was performed on 100 sheets. At this point, the removal of the unexposed portion of the image recording layer on the printing press was completed on any of the original plates, and a printed matter free from ink stains in the non-image portion was obtained. Thereafter, 10000 sheets were further printed, and a good printed matter having a sufficient ink density in the image area without any stain on the non-image area was obtained from any of the original plates.
In addition, as a result of the white lamp discoloration evaluation, the brightness difference ΔL before and after the white lamp exposure was 0.2 or less in any of the original plates, and a good discoloration suppressing effect in the non-image area was obtained.

[Comparative Example 1]
When the lithographic printing plate precursor (4) was image-exposed as described above, the exposed area was colored, and the brightness contrast (image visibility) between the image area and the non-image area was good. Subsequently, it heat-processed and it attached to the printing machine without carrying out the image development process, and 100 printing was implemented. At this time, the removal of the unexposed portion of the image recording layer on the printing machine was completed, and a printed matter free from ink stains in the non-image portion was obtained. Thereafter, 10,000 sheets were further printed, and a good printed matter having a non-image area stain and a sufficient image area ink density was obtained.
However, as a result of the white lamp discoloration evaluation, the brightness difference ΔL before and after the white lamp exposure was 0.5 or more, and the non-image area was colored.

[Comparative Example 2]
Except for not carrying out the heat treatment, the lithographic printing plate precursor (2) was subjected to image exposure, attached to a printing machine and subjected to printing 100 sheets without being subjected to heat treatment and development treatment in the same manner as in Example 2. At this time, the removal of the unexposed portion of the image recording layer on the printing machine was completed, and a printed matter free from ink stains in the non-image portion was obtained. Thereafter, 10,000 sheets were further printed, and a good printed matter having a non-image area stain and a sufficient image area ink density was obtained.
However, as a result of the white lamp discoloration evaluation, the brightness difference ΔL before and after the white lamp exposure was 0.5 or more, and the non-image area was colored.

[Comparative Example 3]
When the lithographic printing plate precursor (5) was image-exposed as described above, the brightness contrast (image visibility) between the image area and the non-image area was poor. At this time, the brightness difference ΔL between the exposed portion and the non-exposed portion was 0.2 or less. Subsequently, it heat-processed and it attached to the printing machine without carrying out the image development process, and 100 printing was implemented. At this time, the removal of the unexposed portion of the image recording layer on the printing machine was completed, and a printed matter free from ink stains in the non-image portion was obtained. Thereafter, 10,000 sheets were further printed, and a good printed matter having a non-image area stain and a sufficient image area ink density was obtained. Thereafter, further printing was performed for 10,000 sheets. However, although there was no stain on the non-image area, the ink density in the image area decreased from the 5000th sheet onward, and a good printed matter could not be obtained.
Further, as a result of the white light discoloration evaluation, the brightness difference ΔL before and after the white light exposure was 0.2 or less, and a good discoloration suppressing effect in the non-image area was obtained.

  As is apparent from the above results, the lithographic printing plate precursor of the present invention and the heat treatment after image exposure can prevent fogging discoloration due to white light without lowering the color change sensitivity during image exposure. .

It is a side view which shows the structure of an image exposure apparatus. It is a side view which shows the structure of the exposure apparatus of the post-exposure heating method (heating by a surface). It is a perspective view which shows the exposure head (exposure simultaneous local heating) and its feeding mechanism in the image exposure apparatus shown by FIG. FIG. 2 is a perspective view showing an exposure head (post-exposure local heating) and its feed mechanism in the image exposure apparatus shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image exposure apparatus 12 Planographic printing plate precursor 14 Casing 16 Feeding plate 18 Discharge tray 20 Outer drum 22 Chuck mechanism (holding member)
24 guide roller 26 exposure head (exposure means)
28 Feeding mechanism (exposure means)
30 Light source box 32 Light source device 34 Feed mechanism 35 Conveying roller 36 Guide member 38 Heating device 40 Heat resistant film 42 Film guide 44 Pressure roller 45 Bend portion 46 Blowout port 48 Heating portion 50 Air feeding portion 52 Elastic layer 54 Excitation coil 56 Temperature sensor 58 Lens unit 60 Fiber holder (exposure head)
62 Guide rail 64 Motor unit 66 Screw shaft 68 Carrier (carrier member)
69 Female thread member 70 Optical fiber 72 Laser 74 Heat sink 76 Connector array 78 Cable bear 80 Bare guide 82 Link piece 84 Unloading mechanism 86 Conveying roller 88 Guide member 140 Heating fan unit (heating means)
142 Flexible duct (heating means)
144 Hot air nozzle (heating means)
146 Heating member 148 Coil unit 150 Core metal L Laser light R1, R2 Drum rotation direction S Exposure head feed direction A _IR exposure area A _HT heating area

Claims (9)

  An image recording material comprising (A) a radical initiator, (B) a compound that changes color by the action of a radical, and (C) a compound that generates a chemical species that traps radicals by heating.   An image recording layer containing (A) a radical initiator, (B) a compound that changes color by the action of a radical, and (C) a compound that generates a chemical species that captures radicals by heating on a support. A lithographic printing plate precursor having.   The lithographic printing plate precursor as claimed in claim 2, wherein the image recording layer further comprises (D) a radical polymerizable compound.   4. The lithographic printing plate precursor as claimed in claim 3, wherein the image recording layer is an image recording layer removable with printing ink and / or fountain solution.   The lithographic printing plate precursor as claimed in claim 3 or 4, wherein the image recording layer has photosensitivity in a range of 250 nm to 420 nm.   5. The lithographic printing plate precursor as claimed in claim 3, wherein the image recording layer further contains an infrared absorber.   7. The compound according to claim 2, wherein the compound that generates a chemical species that captures radicals by heating (C) is a compound having a phenolic hydroxyl group protected by a group decomposable by heat. The lithographic printing plate precursor described in Crab.   The lithographic printing plate precursor according to any one of claims 2 to 6 is imagewise exposed and then subjected to a heat treatment, whereby a color change is caused by the action of (B) radicals contained in the image recording layer. A method of suppressing color change after imagewise exposure of a compound.   9. The color change after imagewise exposure of a compound which causes a color change by the action of radical (B) contained in the image recording layer according to claim 8, wherein the light source for imagewise exposure is laser light. How to suppress.

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