JPS6280663A - Retouching agent for lithographic printing plate - Google Patents

Abstract

PURPOSE:To reduce an erasing stage and to improve the efficiency of a photoengraving operation by incorporating an aq. phosphoric acid modified starch powder soln. and solvent which dissolves or swells an image part into the titled agent. CONSTITUTION:This retouching agent contains the aq. phosphoric acid modified starch soln. and the solvent which dissolves or swells the image part. The substitution rate (degree of esterification) of the phosphoric acid modified starch is theoretically possible up to 3 degree of esterification at which all of the three hydroxyl groups of the glucose residues of the starch are esterified and the range of the preferable substitution rate is 0.03-1.0 and is more preferably 0.05-0.6. The content of the phosphoric acid modified starch in the retouching agent is more preferably 0.1-3wt%. The solvent which dissolves or swells the image part includes, for example, lactones, etc.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a correcting agent for planographic printing plates, and in particular, the present invention relates to a correcting agent for planographic printing plates. This invention relates to a correction agent used for erasing areas (areas that absorb dampening water and receive oil-based ink).

[Conventional technology]

Japanese Patent Publication No. 51-33442 (This is British Patent No. 1.
Corresponds to No. 408.709. )for. - A photosensitive lithographic printing plate having a photosensitive layer consisting of a quinonediazide compound (
It is also called Pre-3 sensitized plate and abbreviated as 28th edition. It is stated that unnecessary image areas often occur in lithographic printing plates made from ), and it is necessary to correct these.

To give a general example, dirt on the original film or cuts such as when the original film is pasted together may become underexposed areas, which may become image areas (film edge marks), or images of the original film may become underexposed. Some parts may become unnecessary. Furthermore, dirt on the glass of the exposure machine or foreign matter adhering to the printing plate surface may also cause insufficient exposure, resulting in image areas. Therefore, it is necessary to remove these unnecessary image parts.

For example, Japanese Patent Publication No. Sho 46-16047 (which corresponds to British Patent No. 1,272.868) discloses a correction liquid for removing unnecessary image areas of printing plates, which has a carbon number of 3.
Modifiers containing ~6 lactones are disclosed.

That is, as a correcting agent for lithographic printing plates produced by photolithography, (a) 20 to 60% by weight of glycol, polyglycol, glycol ether, or polyglycol ether, (b), other than those listed in (a); organic solvent 10~
50% by weight, (C) 3-25% by weight of water, (d) 0.5-15% by weight of an acid or a substance exhibiting acidity in an aqueous solution, and (e)
Compositions are disclosed which contain 5 to 25% thickening agent and are characterized in that the liquids mentioned under (a), (b) and (C) are completely soluble in one another. Also, JP-A-60-
Japanese Patent No. 17748 discloses a combination of a solvent and phosphonic acid that dissolves or swells the image area.

[Problem that the invention seeks to solve]

Generally, when correcting and removing unnecessary image areas, it often takes a long time to correct them because they are very difficult to see with the naked eye. However, when a known correction agent is used, the correction agent is applied to the non-image areas surrounding the image area to be removed. However, there is a disadvantage in that fringe-like or spot-like stains occur in non-image areas due to the strong acid contained in the correction agent.

Therefore, an object of the present invention is to be able to correct and remove only unnecessary image areas without causing fringe-like or spot-like stains in non-image areas even if it takes a long time to correct film edge marks. It is an object of the present invention to provide a correction agent in which a non-image area to which the agent is attached is not affected by etching or the like.

Yet another object is to provide a lithographic printing plate corrector that can erase only a desired image area without adversely affecting adjacent necessary image areas.

Another object of the present invention is to provide a lithographic printing plate corrector that is capable of quickly erasing image areas.

Yet another object of the present invention is to provide a highly safe lithographic printing plate corrector that does not pose a risk of causing pollution.

[Failure to solve the problem]

In order to achieve the above object, the present inventor has made extensive research and has completed the present invention. The present invention is a lithographic printing plate corrector containing (a) a tJ acid-modified starch aqueous solution and (b) a solvent that dissolves or swells the image area.

As described above, the correcting agent of the present invention is composed of a composition containing a combination of a phosphoric acid-modified starch aqueous solution and a solvent that dissolves or swells the image area, and further contains (C) a surfactant,
(d) water-soluble polymer compound, (e) p It regulator, (
f) a coloring agent and (g) a viscosity modifier, etc. may be included.

Each component contained in the corrector composition of the present invention will be explained in detail below.

The phosphoric acid-modified starch of component (a) used in the present invention is obtained by reacting starch with phosphorus oxychloride, trimetaphosphate (e.g., sodium salt), orthophosphate, polyphosphate, phosphoric acid, organic phosphonic acid, etc. It is phosphoric acid esterified. Depending on the esterification agent, there are monoester type and crosslinked diester type, both of which can be used in the present invention, but monoester type is preferable because it causes less aging phenomenon peculiar to starch. The starches used as raw materials include potato, Japanese lettuce,
Those obtained from wheat, tapioca, corn, glutinous corn, rice, glutinous rice, etc. are used.

The substitution rate (esterification rate) of phosphoric acid-modified starch is theoretically possible up to an esterification rate of 3, in which all three hydroxyl groups of the glucose residues of starch are esterified, but the preferred range of substitution rate is 0. 03 to 1.0, more preferably 0
．． 05 to 0.6.

As mentioned above, the phosphoric acid-modified starch (hereinafter also referred to as "modified starch") used in the present invention is one in which phosphoric acid or a phosphoric acid derivative is ester-bonded to the hydroxyl group of glucose that constitutes the starch. It is a polymer compound containing a unit represented by the general formula.

In the above general formula, R1 to R3 may be the same or different and each represents a hydrogen atom, a phosphoric acid or a phosphoric acid derivative residue.

The synthesis method for the above modified starch is described in "Water-soluble polymers, water-dispersible resins general technical data collection" (Management Development Center Publishing Department)
(published on January 23, 1981, pages 68-69). Modified starch having desired properties can be obtained by variously selecting R1 to R3 in the above general formula.

In addition, in order to improve water solubility, the molecules can be cleaved using an enzyme or the like to reduce the molecular weight.

The content of phosphoric acid modified starch in the modifying agent of the present invention is 0.0
A suitable amount is 5 to 5% by weight, more preferably 0.1 to 3% by weight. These phosphoric acid-modified starches are used as a uniform aqueous solution by dissolving them in water or by heating the water (eg, 70°C to 80°C).

As the solvent that dissolves or swells the image area of component (b),
Examples include lactones, ethers, ketones, alcohols, and hydrocarbon solvents. The lactones include butyrolactone, valerolactone, hexanolactone, etc., and the ethers include glycol ethers. For example, 2-methoxyethanol, 2-ethoxyethanol, 2-isopropoxyethanol, 2
- Glycol monoalkyl ethers such as butyl glycol, glycol monoaryl ethers such as 2-phenylethanol, such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, etc. Diethylene glycol monoalkyl ethers, such as triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol dialkyl ethers, such as ethylene glycol dimethyl ether, e.g. diethylene glycol Dimethyl ether, diethyl.

Diethylene glycol dialkyl ethers such as rangercol diethyl ether are included. Ketones include, for example, methyl ethyl ketone, methyl propyl ketone, diethyl ketone, methyl butyl ketone, methyl isobutyl ketone, ethyl butyl ketone, butylone, methyl amyl ketone, methyl hexyl ketone, valerone, mesityl oxide, diacetone alcohol, cyclohexanone, methyl Includes cyclohexanone, acetophenone, isophorone, acetylacetone, acetonylacetone, etc.

Examples of alcohols include ethanol, butanol, octyl alcohol, and benzyl alcohol.

Examples of hydrocarbon solvents include toluene, xylene, turpentine oil, n-heptane, solvent naphtha, petroleum fraction hydrocarbon solvents having a boiling point of around 120 to 250 DEG C., such as kerosene and mineral spirit.

In addition to these, N,N-dimethylformamide, tetrahydrofuran, dioxane, N-methylpyrrolidone, dimethylsulfoxide and the like may also be mentioned.

The various image dissolving and swelling agents mentioned above can be used alone or in combination of two or more. The above solvent is suitably contained in an amount of 20 to 90% by weight, more preferably 30 to 85% by weight, based on the total weight of the modifier of the present invention.

The modifying agent of the present invention may contain a surfactant (component) if necessary.
C)). Component (C) promotes each component contained in the correcting agent of the present invention to better penetrate into the image area of the lithographic printing plate, and further improves the ability of each component contained in the correcting agent to mix well and become stable. This is effective in making it possible to form a suitable solution. As the surfactant for component (C), anionic and nonionic surfactants are excellent.

Preferred anionic surfactants include alkyl sulfate ester salts, alkylbenzene sulfonate salts, alkylnaphthalene sulfonate salts, dialkyl sulfosuccinate ester salts, alkyl phosphate ester salts, naphthalene sulfonic acid formalin condensate, and polyoxyethylene alkyl sulfate esters. Examples include salts. Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerin fatty acid esters, and oxyethylene. Examples include oxypropylene block copolymers. Among these, surfactants with HLB of 8 or more, which have particularly high wettability, are advantageous.

These surfactants can be used alone or in combination of two or more, and the amount of these surfactants is about 0 based on the total weight of the modifier of the present invention.
．． It is appropriate that the content is 5 to about 20% by weight,
More preferably, it is contained in a range of 3 to 15% by weight.

The modifying agent of the present invention contains water, which is necessary for dissolving the phosphoric acid-modified starch of component (a), and also for dissolving the water-soluble polymer compound of component (d). It is useful for promoting dissolution and further mixing and stabilizing the components with each other. The amount used is approximately 0 based on the total weight of the corrective agent of the present invention.
．． A range of 5 to about 20% by weight, most preferably 1 to 15% by weight is suitable.

The modifier of the present invention further contains a water-soluble polymer compound (component (d)
)), it is possible to give the correcting agent even better performance, i.e., when applying the correcting agent on the lithographic printing plate using a brush, it does not spread easily and does not fade) and has anti-bleeding properties. can. Preferred water-soluble polymer compounds include polyvinylpyrrolidone, methyl cellulose, polyvinyl methyl ether, vinyl methyl ether/flu maleic acid copolymer, polyethylene glycol, polypropylene glycol, vinyl acetate/maleic anhydride copolymer, and the like. The above water-soluble polymer compounds can be used alone or in combination of two or more, and the amount used is 0.5 to 10% by weight strain based on the total weight of the modifier of the present invention.
Preferably, a range of 1 to 5% by weight is appropriate.

The modifier of the present invention exhibits its effect particularly effectively in acidic conditions. However, in the pH range of 1 to 2, there is a risk of destroying the aqueous coating on the surface of the aluminum support, such as the anodic oxide coating, and there is also a theory that fringing stains may occur if the reaction takes place for a long time. Preferably pH
A range of 2 to 6, more preferably 2.5 to 5 is suitable. p required to adjust to the above preferred pH range
)! Preferred examples of the regulator (e) include mineral acids such as phosphoric acid, sulfuric acid, and nitric acid, and organic acids such as citric acid, tannic acid, malic acid, lactic acid, oxalic acid, phytic acid, and organic phosphonic acids. Of these, phosphoric acid and phytic acid are particularly excellent, and are preferably about 0.5 to
It can be contained in an amount of 20% by weight, more preferably in a range of 2 to 8% by weight.

Component (f), the coloring agent used to impart the desired color tone to the modifier of the present invention to provide visual contrast, can be selected from a wide variety of dyes. Particularly preferred dyes include indicator dyes with deep dyeing such as blue, purple, and red, which exhibit excellent effects. However, it goes without saying that it is not necessary to include such a coloring agent.

When a coloring agent is used, the amount used is about 0.001 to about 0.011 parts by weight based on the total weight of the corrective agent of the present invention;
Preferably it is in the range of 0.004 to 0.008% by weight.

It is preferable that the modifier of the present invention further contains a viscosity modifier (component (g)). This gives the corrective agent of the present invention better writability and prevents the corrective agent from dripping from the brush when applying the corrective agent of the present invention to the image area of a lithographic printing plate using a brush, for example. This is effective in preventing any inconvenience from occurring. As such component ((a), the water-soluble polymer compound of component (d) described above also partially functions, but it is preferable to include silicic acid fine powder because it exhibits excellent performance.And The amount used is in the range of 1 to 10% by weight, preferably 3 to 6% by weight, based on the total weight of the modifier.

The correcting agent of the present invention is particularly advantageously used when erasing the image area of a lithographic printing plate obtained by plate making from a PS plate in which a photosensitive layer made of an O-quinonediazide compound is provided on a support. This PS version will be explained in detail below.

The supports used in the above-mentioned PS plate include metal plates such as aluminum (including aluminum alloys), zinc, copper, etc., such as cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate, and acetic acid. 1
Examples include those in which the above metals are laminated or vapor-deposited on plastic films such as cellulose octate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal. Among these supports, aluminum plates are particularly preferred because they are extremely dimensionally stable and inexpensive. Furthermore, a composite sheet in which an aluminum sheet is bonded to a polyethylene terephthalate film as described in Japanese Patent Publication No. 48-18327 is also preferred.

The surface of the support must be hydrophilic. Here, the term "hydrophilic surface" refers to a surface that becomes wet with dampening water and repels ink when the printing plate is mounted on a lithographic printing machine and printed under standard conditions. There are various ways to provide such a hydrophilic surface. In the case of a support having a surface of metal, especially aluminum, surface treatments such as graining treatment, immersion treatment in an aqueous solution of sodium silicate, potassium fluorozirconate, phosphate, etc., or anodization treatment are performed. It is preferable. Also, U.S. Patent No. 2.
An aluminum plate was grained and then immersed in an aqueous sodium silicate solution as described in Japanese Patent Publication No. 714.066, and an aluminum plate was anodized as described in Japanese Patent Publication No. 47-5125. Those which are later immersed in an aqueous solution of an alkali metal silicate are also preferably used. The above-mentioned anodizing treatment is performed using, for example, phosphoric acid,
A current is generated using an aluminum plate as an anode in an electrolytic solution consisting of an aqueous solution or a non-aqueous solution of inorganic acids such as chromic acid, sulfuric acid, and boric acid, or organic acids such as oxalic acid and sulfamino acid, or their salts. It is carried out by flowing.

Also, U.S. Patent No. 3. ．． 658. Silicate electrodeposition as described in '662 is also effective.

Furthermore, Japanese Patent Publication No. 46-27481, Japanese Patent Publication No. 52-5
Also useful are supports that have been subjected to electrolytic duplexing as disclosed in JP-A-8602 and JP-A-52-30503 and subjected to the above-mentioned anodic oxidation treatment. These hydrophilic treatments are performed not only to make the surface of the support hydrophilic, but also to prevent harmful reactions with the photosensitive composition provided thereon, and to improve the adhesion with the photosensitive layer. It is applied for various purposes such as improving the quality of life.

The photosensitive layer provided on the hydrophilic surface of the support consists of an 0-quinonediazide compound, particularly preferably an 0-naphthoquinonediazide compound. Such 0-naphthoquinone diazide compounds are described, for example, in U.S. Pat. No. 3,046,110;
3.046.111, 3.046.115, 3.046.118, 3.046,119
No. 3.046.120, No. 3.046.12
No. 1, - No. 3.046,122, No. 3.046.
No. 123, No. 3.06L No. 430, No. 3.102,
No. 809, No. 3,106,465, No. 3.635
, No. 709 and No. 3.647.443, and can be suitably used. Among these, in particular, 0-naphthoquinonediazide sulfonic acid ester or 0-s7toquinonediazide sulfonic acid ester of an aromatic hydroxy compound, and O-naphthoquinonediazide sulfonic acid amide or 0-naphthoquinonediazide carboxylic acid amide of an aromatic amino compound. Particularly preferred is U.S. Pat. No. 3,635.
7m9, a condensate of pyrogallol and acetone subjected to an ester reaction with 0-naphthoquinonediazide sulfonic acid, U.S. Patent No. 4,028,111
British Patent No. 1.494.043 describes a product obtained by subjecting a polyester having a hydroxyl group at the end to an ester reaction with 0-naphthoquinonediazide sulfonic acid or O-naphthoquinonediazidecarboxylic acid. 0-naphthoquinonediazide sulfonic acid or 0-
A copolymer of p-aminostyrene and other copolymerizable monomers as described in U.S. Pat. Those obtained by subjecting quinonediazide sulfonic acid or 0-naphthoquinonediazidecarboxylic acid to an amide reaction are very good.

Although these 0-quinonediazide compounds can be used alone, it is preferable to mix them with an alkali-soluble resin and provide this mixture as a photosensitive layer. Suitable alkali-soluble resins include novolak-type phenolic resins, specifically phenol formaldehyde resins, O
-cresol formaldehyde resin, m-cresol formaldehyde resin, etc. Additionally, U.S. Patent No. 4
, 123.279, a combination of phenol or cresol substituted with an alkyl group having 3 to 8 carbon atoms, such as t-butylphenol formaldehyde resin, and formaldehyde together with the above-mentioned phenol resin. It is even more preferable to use it in combination with a condensate. The alkali-soluble resin is present in the photosensitive layer in an amount of about 50 to about 85% by weight;
More preferably, it is contained in an amount of 60 to 80% by weight.

Additives such as dyes, plasticizers, and components imparting printout performance can be added to the photosensitive layer made of the 0-quinonediazide compound, if necessary.

The dye is used to give contrast between the image area and the non-image area (support surface) after exposing and developing the PS plate, for example, C, 1, 26, 105.
(Oil Red RR), C, 1°21.260 (Oil Blue Let #308), C, 1,74,350 (Oil Blue), C,! , 52.015 (methylene blue), C, 1,42,555 (crystal violet), and the like are preferred. Such dyes need only be added in sufficient quantities to provide a clear contrast between the color of the hydrophilic surface of the support exposed by exposure and development of the photosensitive printing plate and the remaining portions of the photosensitive layer. Generally about 7% by weight based on the total amount of the photosensitive composition
It is appropriate to contain it in the following range.

Plasticizers are effective for making the photosensitive layer provided on the support have desired flexibility, and include, for example, dimethyl phthalate, diethyl phthalate, dibutyl phthalate,
Heptathalic acid esters such as diisobutyl phthalate, dioctyl phthalate, octyl capryl phthalate, dicyclohexyl phthalate, ditridecyl phthalate, butylbenzyl phthalate, diisodecyl phthalate, diaryl phthalate, dimethyl glycol phthalate, ethyl phthalyl ethyl glycolate, methyl phthalyl Glycol esters such as ethyl glycolate, butylphthalyl butyl glycolate, triethylene glycol cacryl ester, tricresyl phosphate,
Phosphate esters such as triphenyl phosphate, aliphatic dibasic acid esters such as diisobutyl adipate, dioctyl adipate, dimethyl sebacate, dibutyl sebacate, dioctyl azelate, dibutyl maleate, polyglycidyl meccrylate, triethyl citrate, Glycerin triacetyl ester, butyl laurate, etc. are effective.

The plasticizer is contained in an amount of about 5% by weight or less based on the total amount of the photosensitive composition.

The printout material is used so that a visible image can be immediately observed by exposing the photosensitive layer of the PS plate to light. pH indicators such as those described in British Patent No. 1.041,463;
．． Examples include a combination of 0-naphthoquinonediazide-4-sulfonyl chloride and a dye as described in No. 969.118, and a photochromic compound as described in Japanese Patent Publication No. 44-6413. Furthermore, the sensitivity can be increased by adding a cyclic acid anhydride to the photosensitive layer as described in US Pat. No. 4,115,128.

A photosensitive composition comprising such O-quinonediazide is coated onto a support from a solution in a suitable solvent.

Suitable solvents include glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and 2-methoxyethyl acetate, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, and chlorinated hydrocarbons such as ethylene dichloride. .

The coating weight of the photosensitive layer made of an O-quinonediazide compound provided on the support is about 0.5 to about 7 g/m'', more preferably 1.5 to 3 g/m''.

When the thus obtained PS plate is exposed through a transparent original to a light beam rich in actinic rays such as a carbon arc lamp, mercury lamp, metal halide lamp, xenon lamp, or tungsten lamp, that portion becomes alkali-soluble.

Therefore, the exposed portion of the photosensitive layer is eluted by the alkaline aqueous solution, and the hydrophilic surface of the support is exposed.

A preferred alkaline aqueous solution used as a developer is an alkaline aqueous solution containing dissolved silicate. Preferred silicates are those that exhibit alkalinity when dissolved in water, and include, for example, alkali metal silicates such as sodium silicate, potassium silicate, sodium metasilicate, and ammonium silicate. The amount of silicate in the developer solution is generally used from about 1 to about 10% by weight, more preferably from 1 to 8%, most preferably from 2 to 6% by weight, based on the total weight of the developer. Ru. Further, the developer may be alkaline, and preferably has a pit of about 10.5 to about 13.0 at 25°C.
It is 5.

The developer may further contain an organic solvent in an amount of 5% by weight or less based on the total weight. Examples of such organic solvents include benzyl alcohol, 2-butoxyshetanol, triethanolamine, jetanolamine, monoethanolamine, glycerin, ethylene glycol, polyethylene glycol, and polypropylene glycol.

Further, the developer may further contain a surfactant, more preferably an anionic surfactant or an amphoteric surfactant.

As mentioned above, if there is an unnecessary image area on the lithographic printing plate obtained by subjecting the PS plate to image exposure and development, the image area can be erased by applying the correction agent of the present invention on the image area. Ru.

When applying the modifying agent of the present invention to the image area of a lithographic printing plate, it is preferable to apply the modifier after thoroughly rinsing the lithographic printing plate after development with water, rather than immediately after development. As a specific method for applying the correcting agent of the present invention to the image area of a lithographic printing plate, a general method is to impregnate a brush with the correcting agent of the present invention and apply it to the desired image area to be erased. The applied erasing agent is left as is for about 10 seconds to about 1 minute, and then washed with water to wash away the erasing agent, and the image area where the erasing agent was applied is cleanly removed and becomes a non-image area. After that, process in the usual way (
For example, pulling gum. ) and used as a lithographic printing plate.

〔Effect of the invention〕

The correction agent of the present invention has an extremely fast erasing speed in the image area. Therefore, the erasing process is shortened and the efficiency of plate making work is improved.

The correction agent of the present invention has the advantage that a desired image area can be erased without adversely affecting adjacent image areas. Therefore, it is possible to easily erase intricately detailed image areas.

The corrective agent of the present invention is free of deleterious substances such as fluorine compounds. Therefore, there is little risk of harming public health.
Furthermore, the risk of harm to the health of workers who handle it is also reduced.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, "parts" shall mean parts by weight, and "%" shall mean "% by weight."

Example-1 After graining an aluminum alloy plate in a suspension of pumice stone and water with a rotating nylon brush, the amount of dissolved aluminum was 8 g using a 20% aqueous solution of caustic soda.
/m'. After thoroughly washing with running water, pickling with a 25% nitric acid aqueous solution and washing with water. This substrate was subjected to alternating current electrolysis at a current density of 20 A/dm or more in an electrolytic bath containing 0.5 to 2.5% nitric acid as described in JP-A-54-146234.Continued 15
After cleaning the surface by immersing it in a 50° C. aqueous solution of 20% sulfuric acid for 3 minutes, an oxide film of 3 g/rri” was formed in an electrolytic solution containing 20% sulfuric acid as a main component at a bath temperature of 30° C.

After washing with water and drying, 5 parts of an O-naphthoquinonediazide compound synthesized according to the method of Example 1 of U.S. Pat. No. 3,635,709 and 10 parts of an oil-soluble novolac type phenolic resin
A photosensitive solution containing 0.8 parts of dye (Cl74350) and 0.8 parts of dye (Cl74350) dissolved in a mixed solvent consisting of 100 parts of methyl ethyl ketone and 80 parts of cyclohexanone was coated with a rotary coater and dried. Coating amount is 1.5 g/m after drying.
'Met.

The photosensitive lithographic printing plate thus obtained was passed through a positive film and exposed to 70CI11 using a metal halide lamp (2KW).
Exposure was performed for 70 seconds from a distance of 1.
The exposed area was dissolved and removed by immersion in a 5% aqueous solution of sodium silicate No. 74, developed, and then washed with water and dried. In the lithographic printing plate thus obtained, the edges of the positive film remained faintly as an image on the plate surface.

On the other hand, the correction agent of the present invention was prepared as follows. First, 57.0 parts of T-butyrolactone was mixed with hydroxypropylmethylcellulose (methoxy group: 28-30%, hydroxypropoxy group = 7-12%, 2% at 20°C).
The viscosity of the aqueous solution is 40 to 60 cps. ) 1.5 parts and oxyethylene oxypropylene block polymer (
Ethylene oxide is polymerized at both ends of polypropylene glycol with an average molecular weight of 2.000. Molecular weight:
10,000, ethylene oxide content; 8 parts%)5.
0 parts were dispersed. To this dispersion, 1.0 part of phosphoric acid modified starch (viscosity of 0.15.40% substitution rate aqueous solution (25°C) 300 to 400 cps) was added to 9 parts of pure water at 60 to 70°C.
After heating and dissolving, add and disperse, add 22 parts of 2-methoxyethanol, 0.5 part of sodium alkylbenzenesulfonate, and 0 crystal violet.
．． 003R was added, the pH was adjusted to 3.2 with phosphoric acid (85%), and the mixture was sufficiently stirred to form a uniform solution. 4.0 parts of powdered silicon dioxide was added to this and dispersed to obtain a viscous modifier.

Apply the correction agent prepared in this manner to the area on the lithographic printing plate where the edges of the film remain as an image, and leave it for 30 seconds, 5 minutes, 1 part, and 20 minutes, and then apply each step. When the time was up, I washed it off with spray water. The hydrophilic layer was completely exposed in the image area formed by the cut of the film, and even after being left for a long time, there were only traces of etching and no fringe-like stains were found.

The plate that had been corrected in this way was gummed with a 1:1 dilution of Fujifilm's protective gum, product name GU-2, and was installed on an offset printing machine to print 10,000 copies, but the image area was erased. No stains were observed and beautiful prints were obtained. Since the correction agent of the present invention has minimal liquid bleeding, correction work can be carried out with confidence even when erasing small details.
In addition, from a physiological point of view, it was highly safe and had almost no discomfort, and was excellent in usability.

Examples 2 to 5 were prepared in the same manner as in Example 1 to obtain modifiers of the present invention. Using this, erasing was carried out in the same manner as in Example 1, and the results were all good.

Example 2 T-butyrolactone -48 parts by weight cyclohexanone -18 xylene
-12 vinyl methyl ether/anhydride -3 Maleic acid copolymer (trade name Gantrez 5-95 (manufactured by GAF Corporation)) phosphoric acid modified starch (substitution ratio 0.3) -510% aqueous solution oxyethylene oxypropylene -7 Block polymer (same as used in Example 1) Crystal violet -0,003 Powdered silicon dioxide -4 9H was adjusted to 2.5 with phytic acid.

Example 3 γ-Butyrolactone -38 ethylene glycol dimethyl -25 ether petroleum fraction (boiling point 160-180°C, -12 Contains alkylbenzenes having 8-11 carbon atoms) Alkyldiphenyl ether -3 Hydroxypropyl disulfonate Methyl-2 cellulose (same as used in Example 1) Oxyethylene oxypropylene-8 block polymer (oxyethylene 50%, oxypropylene molecular weight 2.250') Phosphoric acid modified starch (substitution ratio 0.2 )-8 10% aqueous acidrhodamine B-0,002 powder silicon dioxide-4 Adjusted to pH 3.3 with phosphoric acid (85%).

Example 4 T-butyrolactone -40 parts by weight ethylene glycol diethyl ether -15-tylcyclohexanone -10 xylene
-10 oxyethylene oxypropylene -8 block polymer (same as used in Example 3) Phosphoric acid modified starch (substitution ratio 0.15) -1010% aqueous hydroxypropylmethyl -2 Cellulose (same as used in Example 1) (same as used) Powdered silicon dioxide -5 Safranin -0,003 phosphoric acid (85
%) was adjusted to p) 13.0.

Example 5 T-butyrolactone - 40.8 parts by weight cyclohexanone - 15 benzyl alcohol
-10xylene -8 Hydroxypropylmethyl -2 Cellulose polyvinylpyrrolidone (K-30) -1 Phosphate modified starch (substitution rate 0.15 > -1010% aqueous oxyethylene oxypropylene -8 block polymer (in Example 3) Same as used) Fluorine surfactant -0,2 (perfluoroalkyl betaine) Dye (CI Ba5ic Red 2.50240)
-0,002 powdered silicon dioxide -4 Adjusted to pH 3,0 with phosphoric acid (85%).

Comparative Example I T-butyrolactone - 50 double units cyclohexanone - 18 xylene
-12 vinyl methyl ether/anhydride -3 Maleic acid copolymer, trade name Gantrez S-95 (GAP Corporation) oxyethylene oxypro -7 Pyrene block polymer (same as used in Example 1) Crystal violet - 0.02 Powdered silicon dioxide -5 Pure water -5 Adjusted to pH 2.5 with phosphoric acid (85%).

Each correction agent was used to erase unnecessary image areas of a lithographic printing plate made in the same manner as in Example 1, and at that time, the erase speed, fringe stains, sharpness of erased areas and boundaries), and this After processing each of the erased plates in the same manner as in Example 1, the printed matter was examined for stains in the erased areas when the plates were set in a printing machine and printed. The results are shown in Table 1.

"Fringe stains", "bleeding", and "print stains" in Table 2
The evaluation was based on the following criteria.

From the results shown in Table 2, when using a correction agent containing phosphoric acid-modified starch, the hydrophilic surface of -C was not etched even after long correction work, and excellent performance was achieved. It can be seen that it holds.

Claims (1)

[Claims] A lithographic printing plate corrector comprising a phosphoric acid-modified starch aqueous solution and a solvent that dissolves or swells an image area.