JP2000158841A - Plate surface cleaning agent for lithographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate surface cleaning agent for lithographic printing plate wherein an image silver having improved cleaning and desensitization effects in a non-image part is utilized as an ink receptivity without exerting adverse influence on a silver image. SOLUTION: An image silver containing a polymer having ethylene oxy- groups and carboxy groups on side chains is utilized as an ink receptivity, And an image silver containing a compound which has carboxy groups at least on an terminal of polyalkylene oxy groups having ethylene oxy groups as main body is utilized as an ink receptivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate cleaning agent for a lithographic printing plate utilizing image silver as ink receptivity. In particular, the present invention relates to a plate cleaning agent for a silver salt printing plate using an aluminum plate as a support.

[0002]

2. Description of the Related Art A lithographic printing plate in which a transferred silver image obtained by a silver complex salt diffusion transfer method (DTR method) can be immediately used as ink acceptability is already known. Part 1
One type is a lithographic printing plate having, in this order, at least a silver halide emulsion layer and a physical development nucleus layer on a support (eg, a paper base coated with a polyethylene resin, a polyethylene terephthalate base, etc.), for example, US Pat. No. 3,721,559. No. 3490905, No. 33
No. 85701, No. 3814603, No. 34543
No. 98, No. 3764323, No. 3099209
No., JP-B-44-27242, 48-30562
No., JP-A-53-9603, JP-A-53-21602,
Nos. 54-103104 and 56-9750.

The above lithographic printing plate has a physical development nucleus on the surface of the emulsion layer using gelatin as a binder, and the silver halide crystals in the exposed emulsion layer undergo chemical development by DTR development to become black silver. To form a hydrophilic non-image portion mainly composed of gelatin. On the other hand, unexposed silver halide crystals are converted into a silver salt complex by the silver salt complexing agent in the developing solution and diffused to the physical development nucleus layer on the surface. An image portion mainly composed of physically developed silver is formed. Here, the silver image part is used as ink acceptability.
The gelatin surface in the non-image area is subjected to printing as ink repellency.

[0004] Another type is a lithographic printing plate having a silver halide emulsion layer on a physical development nucleus supported on a roughened and anodized aluminum support (hereinafter referred to as an aluminum lithographic printing plate). Are known, for example,
-216236, and JP-A-6-81194. After exposure and development of the lithographic printing plate, the silver halide emulsion layer is washed off (washed off) to expose an image portion composed of a metallic silver film and a non-image portion composed of an aluminum anodized surface.

Although the two lithographic printing plates differ in construction and plate making method, they are common in making the image silver ink receptive. These lithographic printing plates are composed of an image portion that receives oily ink and a non-image portion that is hydrophilic and receives water. Thus, normal lithographic printing supplies both water (humidifying liquid) and ink to the printing plate, the image portion selectively receives color ink, the non-image portion selectively receives water, and the ink on the image is, for example, received. This is done by transferring it to a substrate such as paper. In these types of printing, if the hydrophilic non-image area deteriorates for some reason, lipophilic ink adheres to the area and causes soiling. Therefore, it is necessary to remove the attached ink and restore the hydrophilicity of the area.

On the other hand, in the field of planographic printing plates, PS plates (presensitized plates) using a photosensitive resin are known and widely used. In the field of the PS plate, a cleaning agent (also called a plate cleaner) is generally used for the above purpose, and many attempts have been made in the past. If you mention some patent publications,
For example, JP-A-52-15702 and JP-A-53-210
No. 2, 6-32081, 6-155959
No. 7-125470.

[0007] The above-mentioned detergent is an organic solvent and a surfactant for removing the ink, a water-soluble polymer for stabilizing the dispersion of the organic solvent (accelerating the emulsification), and an insensitive agent for desensitizing the non-image area. It is mainly composed of an oiling agent and the like. Also,
It is also known to use fine powder. These cleaning agents are generally strong acids and strong alkalis, thereby increasing the desensitizing ability. An alkaline detergent having a pH of 10 or more using a silicate as a desensitizing agent,
An acidic detergent having a pH of 3 or less using phosphoric acid and phosphoric acid is usually used.

[0008] The cleaning operation is usually performed by including a cleaning agent in a sponge or the like and wiping the entire plate surface of the printing plate. Therefore, since the cleaning agent is applied not only to the non-image portion where the stain has occurred but also to the image portion, it is necessary not to affect the image portion.

The photosensitive resin image of the PS plate and the silver image of the present invention have different physical and chemical properties, and the thickness of the silver film is very thin compared to the thickness of the resin layer forming the image. Images are susceptible to physical and chemical influences. Therefore,
It was not possible to simply apply the PS plate cleaner.
For example, a detergent having a pH of 3 or less using phosphoric acid as a desensitizing agent dissolves a silver image and lowers printing durability. Further, the cleaning agent using the fine powder wears the silver image. In addition, the use of a silicate-based cleaning agent causes inconveniences such as making a silver image hydrophilic.

JP-A-6-344680 discloses a plate surface cleaning agent for a lithographic printing plate to which the present invention is directed, and discloses the use of glycol ethers. This cleaning agent was not sufficiently effective in cleaning and desensitizing lithographic printing plates using an aluminum plate as a support.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plate cleaning agent for a lithographic printing plate which utilizes image silver having an excellent washing effect and desensitizing effect without adversely affecting a silver image as ink acceptability. To provide. In particular, it is to provide a cleaning agent suitable for a lithographic printing plate using an aluminum plate as a support.

[0012]

SUMMARY OF THE INVENTION The above objects of the present invention are as follows.
This has been achieved by the following configuration. (1) A plate cleaning agent for a lithographic printing plate utilizing image silver as ink receptivity, comprising a polymer having an ethyleneoxy group and a carboxy group in a side chain. (2) A plate cleaning agent for a lithographic printing plate utilizing image silver as ink receptivity, characterized by containing a compound having a carboxy group at at least one terminal of a polyalkyleneoxy group mainly composed of an ethyleneoxy group.

The present inventors have conducted intensive studies to enhance the desensitizing property without adversely affecting the silver image, and as a result, have found that the above compounds have a high effect.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The polymer having an ethyleneoxy group and a carboxy group in the side chain used in the detergent of the present invention is, for example, a monomer having an ethyleneoxy group in the side chain of a polymerizable double bond and a polymer having an ethyleneoxy group in the side chain of the polymerizable double bond. A copolymer with a monomer having a carboxy group in the chain, and a copolymer in which an ethyleneoxy group is added to one carboxy group of a monomer having two carboxy groups on the side chain of a polymerizable double bond such as maleic acid And the like.
These polymers can be represented by the following general formulas 1 and 2.

[0015]

Embedded image In the formula, X represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, L represents a divalent linking group, A represents an alkyleneoxy group unit mainly composed of an ethyleneoxy group, and q represents an alkyleneoxy group. R represents a hydrogen atom or an organic group; B represents a monomer having a carboxy group and a polymerizable double bond; D represents a copolymerizable ethylenically unsaturated monomer; ~ 99 mol%, m is 1 ~
50 mol% and n represents 0 to 49 mol%.

[0016]

Embedded image In the formula, A, R and q have the same meanings as in the general formula 1, M represents a cation such as a hydrogen atom, an alkali metal or an ammonium ion, E represents a copolymerizable ethylenically unsaturated monomer, and l represents 1 to 90 mol%, m represents 10 to 99 mol%.

The polymer of the general formula 1 will be described in detail. In the formula, X is preferably a hydrogen atom or a methyl group. L is a single or composite divalent linking group consisting of an alkylene group, an alkynylene group, an arylene group, an oxygen atom, a nitrogen atom, and a sulfur atom;
4 or a composite group of these alkylene groups and carbonyl groups. A represents an alkyleneoxy group unit mainly composed of an ethyleneoxy group, and examples thereof include a homopolymer of an ethyleneoxy group and a copolymer of an ethyleneoxy group and a propyleneoxy group or a butyleneoxy group.
At this time, the copolymer may be either a random copolymer or a block copolymer. However, it is essential that the number of repeating units of the ethyleneoxy group is larger than that of the other alkyleneoxy groups. Preferably, it is a copolymer with an ethyleneoxy group alone or a propyleneoxy group in which the ethyleneoxy group accounts for 60% or more. q represents a repeating unit of an alkyleneoxy group, and preferably ranges from 2 to 100, more preferably from 3 to 50.

R represents a hydrogen atom or an alkyl, alkenyl, or aryl group having 1 to 20 carbon atoms, and these groups may be further substituted with a halogen, a hydroxy group, or an alkoxy group. B represents a monomer having a carboxy group and a polymerizable double bond. For example, acrylic acid, methacrylic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid or their acid anhydrides can be mentioned. They may be in the form of a salt with an alkali metal atom or the like. Preferably, it is maleic anhydride. D represents a copolymerizable ethylenically unsaturated monomer. For example,
Acrylic acid, methacrylic acid, alkyl esters of acrylic acid or methacrylic acid, derivatives of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, acrylamide, N-vinylpyrrole, N-vinylcarbazole, N-vinylpyrrolidone, etc. -Vinyl compounds, vinyl ethers, allyl ethers, styrene, α-olefins, etc., and styrene is preferred. More preferably, monomer D is not included,
Even if it is contained, it is at most 20 mol%. 1 represents 1 to 99 mol%, m represents 1 to 50 mol%, and n represents 0 to 49 mol%.
Preferably, 1 is 30 to 90 mol%, m is 10 to 50 mol%, and n is 0 to 20 mol%.

The molecular weight of the polymer of the general formula 1 is in the range of about 1,000 to 100,000, preferably about 2000 to 50,000 in terms of number average molecular weight. These polymers are known and manufactured and sold by various surfactant manufacturers. For example, there is the Maria Rim series of NOF Corporation.

Next, the polymer of the general formula 2 will be described in detail. A, R and q are the same as those described in the general formula 1. M represents a hydrogen atom, an alkali metal atom such as sodium or potassium, or a cation such as ammonium. E represents a copolymerizable ethylenically unsaturated monomer. For example, acrylic acid, methacrylic acid, alkyl esters of acrylic acid or methacrylic acid, acrylonitrile, methacrylonitrile, derivatives of acrylic acid or methacrylic acid such as acrylamide, N-vinylpyrrole, N-vinylcarbazole, N-vinylpyrrolidone, etc. N-vinyl compound, vinyl ether, allyl ether, styrene,
α-olefin and the like. It is preferably an α-olefin, and more preferably an α-olefin having 4 to 20 carbon atoms. l
Represents 1 to 90 mol%, m represents 10 to 99 mol%, and preferably 1 represents 20 to 50 mol%.

The molecular weight of the polymer of the general formula 2 is in the range of about 1,000 to 100,000, preferably about 2,000 to 50,000 in terms of number average molecular weight. These polymers are known and manufactured and sold by various manufacturers as surfactants. For example, Bunsan G-20 manufactured by Kyoeisha Chemical Co., Ltd.
0 series and Floren G-700 series.

The polymer represented by the general formulas 1 and 2 is used in an amount of about 5 to 200 g, preferably 10 to 10 g per liter of the detergent.
It is contained in the range of 0 g.

Next, compounds having a carboxy group at at least one terminal of a polyalkyleneoxy group mainly composed of an ethyleneoxy group will be described in detail. Examples of the polyalkyleneoxy group include a homopolymer of an ethyleneoxy group and a copolymer of an ethyleneoxy group and a propyleneoxy group or a butyleneoxy group. At this time, the copolymer may be either a random copolymer or a block copolymer. However, it is essential that the number of repeating units of the ethyleneoxy group is larger than that of the other alkyleneoxy groups.
Preferably, it is a copolymer with an ethyleneoxy group alone or a propyleneoxy group in which the ethyleneoxy group accounts for 60% or more. The repetition of the alkyleneoxy group is preferably in the range of 2 to 200, more preferably 3 to 100. The carboxy group may be present at only one terminal, but is preferably present at both terminals. The above compound can be represented by the following general formula 3.

[0024]

Embedded image In the formula, A and q have the same meanings as those in the general formula 1. L ₁ represents a divalent linking group such as alkylene, alkynylene, and arylene. Preferably an alkylene group having 1 to 6 carbon atoms,
It is an alkenylene group or an arylene group. R ₁ is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, -L ₂
It represents a -COOM _2. L ₂ has the same meaning as that of L _1. Preferably from -L ₂ -COOM _2. M ₁ and M ₂ each represent a hydrogen atom, an alkali metal atom such as sodium or potassium,
Represents a cation such as ammonium. q is preferably 2
~ 200, more preferably 3 ~ 100.

The compound of the general formula 3 is contained in an amount of 5 to 200 g, preferably 20 to 100 g, per liter of the detergent.

In the cleaning agent of the present invention, in addition to the above compounds,
It is preferable to include an organic solvent having an action of dissolving the ink. As the organic solvent, a hydrocarbon fraction and a petroleum fraction having a boiling point in the range of 120 to 350 ° C. are preferable. For example, cyclohexane, benzyl alcohol, limonene,
Alkylbenzene, K Solvent manufactured by Nippon Oil Co., Ltd.
No. 3 solvent, No. 5 solvent and the like can be mentioned, and among them, limonene is preferable. The hydrocarbon solvent is preferably used in the range of 10 to 60% by weight of the detergent.
In this case, if a small amount of an alcohol-based solvent or a glycol-based ether compound is added, the ink solubility can be further increased.

It is preferable that the detergent further contains a surfactant. As the surfactant, JP-A-6-32
No. 081, anionic and nonionic surfactants. In particular, a nonionic surfactant having a polyethyleneoxy group is preferred. For example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, and polyoxyethylene adducts of acetylenol are included.

In addition, a water-soluble polymer can be contained. For example, gum arabic, starch derivatives such as dextrin, alginic acid, carboxymethyl cellulose,
Examples include polyethylene glycol, polyvinyl alcohol, polystyrene sulfonic acid, and maleic anhydride copolymer.

The cleaning agent may further contain commonly used buffers, preservatives, preservatives, wetting agents and the like, if necessary. Examples thereof include inorganic acids such as phosphoric acid and sulfuric acid, organic acids such as succinic acid and propionic acid, and complexing agents such as iminodiacetic acid and ethylenediaminetetraacetic acid. Further, colloidal silica, alumina sol and the like can be contained.

The pH of the cleaning agent of the present invention is preferably in the range of 3-5. When the pH is lower than 3, the silver image portion is dissolved to reduce the printing durability, and when the pH is higher than 5, the stain on the non-image portion is hardly removed.

The plate surface cleaning solution of the present invention is applied to a lithographic printing plate utilizing a silver image portion as ink receptivity. The planographic printing plates are roughly classified into two types as described above. One type is a lithographic printing plate in which an undercoat layer also serving as an antihalation layer, a silver halide emulsion layer, and a physical development nucleus layer are applied in this order on a paper base or polyethylene terephthalate film base coated with a polyethylene resin. It is.

In the second type, a physical development nucleus is supported on a roughened and anodized aluminum support,
This is a lithographic printing plate on which a halogenated emulsion layer is provided. A lithographic printing plate having an intermediate layer suitably provided between a physical development nucleus and a silver halide emulsion layer may be used. The cleaning agent of the present invention is particularly suitable for the lithographic printing plate using the latter aluminum plate as a support.

The silver halide emulsion used in the lithographic printing plate of the present invention includes silver chloride, silver bromide, silver iodide, silver chlorobromide, silver chloroiodobromide, and silver iodobromide. Although silver chloride is mainly used (meaning silver chloride of 50 mol% or more) is preferable. The emulsion type may be either a negative type or a positive type. These silver halide emulsions can be chemically or spectrally sensitized as necessary.

Gelatin is preferably used as the hydrophilic colloid in the silver halide emulsion layer when preparing silver halide grains. Various gelatins such as acid-treated gelatin and alkali-treated gelatin can be used as the gelatin.
Further, those modified gelatins (for example, phthalated gelatin, amidated gelatin, etc.) can also be used. Further, hydrophilic polymer compounds such as polyvinylpyrrolidone, various starches, albumin, polyvinyl alcohol, gum arabic, and hydroxyethyl cellulose can be contained.

In the former lithographic printing plate having a gelatin layer as a non-image portion, a silver halide emulsion layer containing gelatin and an undercoat layer contain a gelatin crosslinking agent (hardener) to form a strong gelatin film. Need to be formed. On the other hand, in the latter aluminum lithographic printing plate, since the silver halide emulsion layer and the like are removed and the aluminum surface is exposed to form a non-image portion, the hydrophilic colloid used in the silver halide emulsion layer is substantially Desirably does not contain a hardener.

The aluminum support used in the present invention is a roughened and anodized aluminum plate, preferably the one described in US Pat. No. 5,427,889.

The physical development nucleus of the physical development nucleus layer used in the present invention may be one used in a known silver complex salt diffusion transfer method, for example, a colloid such as gold or silver, or a water-soluble salt such as palladium or zinc. Metal sulfide mixed with sulfide can be used. Various hydrophilic colloids can be used as the protective colloid. For details and manufacturing method,
For example, Focal Press, London New York (1972), Andre Lott and Edith
See Weide, "Photographic Silver Halide Diffusion Processes".

The lithographic printing plate used in the present invention is generally treated with an alkali developer after image exposure. As such a developer, any one of an ordinary photographic developer containing a developing agent such as hydroquinone, a developer of a silver diffusion transfer method containing hypo and the like, or a high alkali developer obtained by converting them into an activator can be used.

[0039]

EXAMPLES The present invention will be described below with reference to examples, but is of course not limited thereto.

EXAMPLE 1 Electrolytic surface roughening treatment and anodizing of an aluminum support were carried out according to the method described in US Pat. No. 5,427,889, on a plate having an average diameter of about 5 μm.
0.35 μm pits of about 5,60 per 100 μm ²
And the average diameter of these pits is 0.08
A 0.30 mm thick aluminum plate having a thickness of 0.3 μm was obtained.
This aluminum plate was anodized after the surface roughening treatment, and had an average roughness (Ra) of 0.5 to 0.6 μm.

A physical development nucleus solution composed of a silver sol prepared by the Curey Lea method was applied to the aluminum support, and then dried. The amount of silver contained in the physical development nucleus layer was 3 mg / m ² .

As a silver halide emulsion, alkali-treated gelatin was used as a protective colloid, and potassium hexachloroiridate (IV) having an average particle size of 0.2 μm was prepared by a control double jet method in an amount of 0.006 m / mol of silver.
A mol-doped silver chloroiodobromide emulsion (AgBr 20 mol%, AgI 0.4 mol%) was prepared. Further, this emulsion was subjected to sulfur gold sensitization, and the sensitizing dye represented by Chemical Formula 4 was added in an amount of 3 to 1 g of silver.
mg was used for spectral sensitization.

[0043]

Embedded image

A surfactant was added to the silver halide emulsion thus prepared, and the silver amount was 2 g / m ² (gelatin amount 2.
3 g / m ² ) and dried to obtain a lithographic printing material.

A 633 nm red LD was used for the lithographic printing material.
An image was output by an output device using a laser as a light source, and then processed by a plate-making processor (SLT-85N automatic developing machine manufactured by DuPont) to prepare a lithographic printing plate. The plate-making processor includes a developing step (immersion at 21 ° C. for 15 seconds), a washing step (separating the emulsion layer with a scrub roller while spraying a washing liquid at 33 ° C. for 10 seconds), and a finishing step (21 ° C. 5 seconds shower) and a drying step. The water washing process of the plate making processor is carried out through a tank for storing 30 liters of the washing liquid, a unit for supplying the lithographic printing material from the tank to the lithographic printing material via a pump and peeling and removing the emulsion layer, and a filtration filter arranged outside the system from the tank. It is composed of a unit that circulates washing water.
As the filtration filter, a cylindrical 5 μm filter was used.

The following developing solution, washing solution and finishing solution were used. <Developer> Sodium hydroxide 20 g Hydroquinone 20 g 1-Phenyl-3-pyrazolidinone 2 g Sodium sulfite 80 g Monomethylethanolamine 6 g 2-Mercapto-5-n heptyloxasiasol 0.5 g Sodium thiosulfate 6 g Ethylenediaminetetraacetate sodium salt 5 g Polyethylene glycol (Average molecular weight 400) 10 g Water is added to adjust the total amount to 1 liter. pH is 13.
Adjusted to zero.

<Washing solution> First potassium phosphate 40 g Sodium sulfite 10 g Monomethylethanolamine 6 g 2-Mercapto-5-n heptyl oxathiazole 0.5 g Water is added to adjust the total volume to 1 liter. pH 6.0
Was adjusted.

<Finishing liquid> 15 g of gum arabic 10 g of sodium monophosphate 2-g of 2-mercapto-5-n-heptyl-oxadiazole Water is added to adjust the total volume to 1 liter. The pH was adjusted to 6.0.

The printing plate prepared by the above operation was heated at 50 ° C. for 5 days by forcibly attaching a fingerprint to a non-image portion of the printing plate so that printing stains were easily generated. This printing plate was attached to a printing machine (Heidelberg MO: Alcolor water supply device; manufactured by Heidelberg), and printing was performed using New Champion Boku H ink manufactured by Dainippon Ink Co., Ltd. and a commercially available humidifying solution for PS plates. As a result, fingerprint-like ink stains occurred on the non-image area. Printing was interrupted, and the plate surface was wiped with a sponge containing the following cleaning agent. After that, printing was started again, and non-image areas were evaluated for ink stains. Table 1 shows the evaluation results.
Shown in

The ink stain was evaluated according to the following criteria according to the number of printed sheets where the ink stain occurred. ○: No ink stain is generated even when printing 10,000 sheets or more. Δ: Ink stain occurs on about 5,000 sheets. ×: Ink stain occurs on 1,000 sheets or less.

<Detergent> Water 300 g Sodium hydroxide 6 g Gum arabic 7 g Compound A 35 g Phosphoric acid (85% solution) 18 g Polyoxyethylene oleyl ether 80 g Polyoxyethylene nonyl phenyl ether 100 g Limonene 160 g 2-phenoxyethanol 160 g Water to 1000 g Adjust so that pH adjusted to 3.6. Detergents were prepared by variously changing the above compound A.
Details are shown in Table 1 below.

[0052]

[Table 1]

[0053]

Embedded image

[0054]

Embedded image

[0055]

Embedded image

From the above results, it can be seen that the cleaning agent of the present invention is much better than the comparison.

Example 2 Various cleaning agents were prepared by adjusting the pH of the cleaning agents 1 and 8 in Example 1 with phosphoric acid. Details are shown below. Detergent 1-1: Adjusted to pH 1.5 with the same composition as Detergent 1. Detergent 1-2: adjusted to pH 2.5 with the same composition as detergent 1. Detergent 1-3: adjusted to pH 3.5 with the same composition as Detergent 1. Detergent 1-4: adjusted to pH 4.5 with the same composition as Detergent 1. Detergent 1-5: adjusted to pH 5.5 with the same composition as detergent 1. Detergent 8-1: adjusted to pH 1.5 with the same composition as detergent 8. Detergent 8-2: adjusted to pH 2.5 with the same composition as detergent 8. Detergent 8-3: adjusted to pH 3.5 with the same composition as detergent 8. Detergent 8-4: adjusted to pH 4.5 with the same composition as detergent 8. Detergent 8-5: adjusted to pH 5.5 with the same composition as detergent 8.

Using the above cleaning agent, ink stain was evaluated in the same manner as in Example 1. At the same time, the printing durability was also evaluated.
The printing durability was evaluated according to the following criteria, based on the number of printed sheets when printing became impossible due to poor ink transfer of a silver image or skipped line images. Table 2 shows the results. ：: 100,000 sheets have no problem. Δ: Unable to print on about 50,000 sheets. ×: Printing is not possible with 10,000 sheets or less.

[0059]

[Table 2]

From the above results, it can be seen that the cleaning agent of the present invention enhances the desensitization of non-image areas without adversely affecting the printing durability of silver images.

Example 3 With respect to the cleaning agents 9 and 10 shown in Table 1 of Example 1, a cleaning agent having a changed pH was prepared in the same manner as in Example 2 and tested in the same manner. As a result, the same results as those of Examples 8-1 to 8-5 were obtained.

[0062]

According to the present invention, there is provided a plate cleaning agent for a lithographic printing plate that utilizes image silver as an ink receptivity, which does not adversely affect a silver image and has an excellent non-image area cleaning effect and desensitizing effect. realizable.

Claims (4)

[Claims] A plate cleaning agent for a lithographic printing plate utilizing image silver as ink receptivity, comprising a polymer having an ethyleneoxy group and a carboxy group in a side chain. 2. A lithographic printing plate surface cleaning method using an image silver as ink receptivity, characterized in that it contains a compound having a carboxy group at at least one terminal of a polyalkyleneoxy group mainly composed of an ethyleneoxy group. Agent. 3. The plate surface cleaning agent according to claim 1, wherein the pH is 3 to 5. 4. The plate surface cleaning agent according to claim 1, wherein the lithographic printing plate is a lithographic printing plate having a physical development nucleus layer and a silver halide emulsion layer on an aluminum support.