JPH08216544A - Type area protecting treatment method of negative type lithographic printing plate - Google Patents

Abstract

PURPOSE: To prevent the inking properties of an image part from deteriorating and make it hard to be stained, by a method wherein compound having pivaloyl group is included in diazo type negative type lithographic printing plate and further treated with type are protecting agent having the specific domain in the neighborhood of neutrality. CONSTITUTION: After development, a negative type lithographic printing plate containing diazo resin is added with pivaloyl group-containing compound and further treated with type area protecting agent having the pH of 4.5-10. By employing the sensitizing agent having pivaloyl group, the residual film after development becomes much and unreacted diazo resin in the residual film becomes also much. Thus, the diazo resin and the oil component in ink reacts each other so as to adhere to the non-image part of the plate, resulting in developing stain. Therefore, by using the type area protecting agent having the pH of 4.5-10, the diazo resin left on the plate is quickly dissolved, resulting in preventing the reaction between the diazo resin and the oil component in the ink from occurring. Thus, the inking properties of the image part does not deteriorate and protective treatment, which is less apt to be stained, can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting a plate surface of a negative lithographic printing plate.

[0002]

2. Description of the Related Art Negative lithographic printing plates containing a diazo resin and a binder in a photosensitive layer are widely used. But,
This system generally has low ink receptivity in printing, and if a binder having high ink receptivity is used, the developability is deteriorated.

Therefore, as a method for improving the inking property, for example, JP-A-55-527 and JP-A-63-262.
No. 642, there is known a method of incorporating an oil-sensitizing agent in the photosensitive layer. The oil sensitizer having a pivaloyl group described in JP-A-63-262642 mentioned above is
Although it is excellent in ink receptivity, there is a problem in that when it is left on the printing machine for a long time, printing stains occur.

As described above, compatibility between the inking property and the stain has been a major problem in the negative lithographic printing plate.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a plate surface protecting method for a negative type lithographic printing plate which does not deteriorate the inking property of the image area and is resistant to stains.

[0006]

The object of the present invention is achieved by the following method. (1) After development of a negative lithographic printing plate containing a compound containing a pivaloyl group, a diazo resin and a binder, the pH of the negative lithographic printing plate is set to 4.
A method of protecting a negative type lithographic printing plate using a plate surface protective agent of 5 to 10.

That is, in the present invention, a compound containing a pivaloyl group is contained in a negative lithographic printing plate of diazo type (containing a diazo resin), and the compound is further neutralized (pH 4.5).
It was found that the conventional problems can be solved by treating with the plate surface protective agent of (10) to (10). That is, when the oil sensitizer having a pivaloyl group is used, the residual film after development increases. Such a plate has a large amount of unreacted diazo resin in the residual film, and when it is left on the printing machine for a long time (about 1 hour), the diazo resin reacts with the oil component in the ink to cause the non-reaction of the plate. Since it adheres to the image area, it is considered to cause stains.

Conventionally, a negative type lithographic printing plate has been treated with an acidic plate surface protective agent (gum solution) after development for improving the hydrophilicity of non-image areas, but such stains cannot be prevented. It was In the present invention, the pH of the gum solution is 4.5-10.
It has been found that, by setting the range to, it is possible to solve the stain left on the machine due to the compound containing the pivaloyl group.

The reason why this stain does not occur is not clear,
It is presumed that the diazo resin remaining on the plate rapidly decomposes at a neutral pH, so that the reaction with the oil component in the ink is prevented.

The present invention will be described in more detail below. The pivaloyl group-containing compound used in the present invention is a compound or a pivaloyl group obtained by pivaroylating a compound having a group capable of reacting with a pivalic acid derivative such as pivalic acid or pivalic acid chloride (hydroxyl group, amino group, thiol group, etc.). Examples of the polymer containing a monomer unit having: include [A] pivaloyloxystyrene or a polymer containing a pivaloyloxy-α-methylstyrene unit, for example, p-hydroxystyrene. Alternatively, a pivalic acid esterified product of a copolymer of p-hydroxy-α-methylstyrene with a homopolymerizable or copolymerizable monomer (for example, styrene, acrylonitrile, methyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, etc.) may be mentioned. so That. Examples of the polymer [B] containing a vinyl pivalate unit include a vinyl pivalate homopolymer or copolymer, or a pivalate esterification product of a polymer containing a vinyl alcohol unit. [C] Pivalic acid esterified products of phenol resins can be mentioned. [D] Pivalic acid esterification products of condensation products of polyhydric phenols such as pyrogallol and resorcin and ketones such as acetone and methyl ethyl ketone can be mentioned. [E] Bis pivalic acid ester of bisphenol A can be mentioned.

Among the above compounds, the polymer preferably has a molecular weight of 500 to 50,000, more preferably 1
It is 30,000 to 30,000. The amount of the compound containing these pivaloyl groups added is 0.1 to the binder.
It is preferably 50% by weight, particularly preferably 0.5 to 25% by weight. If it is less than 0.1% by weight, the effect of improving the inking property is insufficient, and if it exceeds 50% by weight, the deterioration of the developability becomes remarkable.

The photosensitive diazo resin used in the present invention is
An aromatic diazonium salt and an active carbonyl group-containing compound,
For example, it is a diazo resin represented by a condensate with formaldehyde. Examples of the diazo resin include organic solvent-soluble diazo resin inorganic salts, which are reaction products of a condensate of p-diazodiphenylamines with aldehydes such as formaldehyde and acetaldehyde, and hexafluorophosphate or tetrafluoroborate, Japanese Patent Publication 47-1
No. 167, the condensate and sulfonates such as p-toluenesulfonic acid or a salt thereof, propylnaphthalenesulfonic acid or a salt thereof, butylnaphthalenesulfonic acid or a salt thereof, dodecylbenzenesulfonic acid or a salt thereof. Examples thereof include an organic solvent-soluble diazo resin organic salt which is a reaction product of a salt, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid or a salt thereof.

Particularly, 6 described in JP-A-59-78340
A high molecular weight diazo compound containing 20% by mole or more of a monomer is preferable. Also suitable is a mesitylene sulfonate obtained by condensing 3-methoxy-4-diazo-diphenylamine with 4,4'-bis-methoxy-methyl-diphenyl ether as disclosed in JP-A-58-27141. Is.

The binder used in the present invention has an acid value of 10 to 200, preferably 20 to 100, is substantially insoluble in water (that is, insoluble in neutral or acidic aqueous solutions), and forms a film. Organic polymer compound having properties that can be dissolved or swelled in an alkaline aqueous solution and is photocurable in the presence of the photosensitive diazo resin to be insoluble or non-swellable in the developer Is preferred. If the acid value is less than 10, development is difficult and
If it exceeds 00, the image strength at the time of development becomes extremely weak.

As a particularly preferable binder, a copolymer containing acrylic acid, methacrylic acid, crotonic acid or maleic acid as an essential component, for example, 2-hydroxyethyl as described in JP-A-50-118802. Acrylate or 2-hydroxyethyl methacrylate,
Multi-component copolymers with acrylonitrile or methacrylonitrile, acrylic acid or methacrylic acid and optionally other copolymerizable monomers, JP-A-53-1209
Acrylic acid or methacrylic acid, acrylic acid, or methacrylic acid, which is a hydroxy group at the terminal and is esterified with a group containing a dicarboxylic acid ester residue, as described in JP-A No. Multi-component copolymer with copolymerizable monomer, JP-A-54-986
No. 14, a monomer having an aromatic hydroxyl group at the terminal (for example, N- (4-hydroxyphenyl) methacrylamide), acrylic acid or methacrylic acid, and optionally other copolymers. Examples thereof include multi-component copolymers with possible monomers, and multi-component copolymers composed of alkyl acrylate, acrylonitrile or methacrylonitrile and unsaturated carboxylic acid as described in JP-A-56-4144. In addition to these, acidic polyvinyl alcohol derivatives and acidic cellulose derivatives are also useful. Further, binders described in JP-B-54-19773, JP-A-57-94747, JP-A-60-182437, JP-A-62-58242 and JP-A-62-123453, in which polyvinyl acetal or polyurethane is alkali-solubilized. Is also useful.

The content of the diazo resin and the binder in the photosensitive composition is appropriately 3 to 30% by weight of the diazo resin and 97 to 70% by weight of the binder, based on the total amount of the two. The smaller the content of the diazo resin is, the higher the sensitivity is. However, when the content is lower than 3% by weight, it is insufficient for photo-curing the binder, and the photo-cured film is swollen by the developing solution during development and the film becomes weak. On the other hand, if the content of the diazo resin is more than 30% by weight, the sensitivity becomes low and practically difficult. Therefore, more preferable ranges are 5 to 25% by weight of the diazo resin and 95 to 75% by weight of the binder.

Various additives can be further added to the photosensitive composition used in the present invention. For example, alkyl ethers (for example, ethyl cellulose, methyl cellulose), fluorine-based surfactants or silicone-based surfactants (for example, JP-A-54-135) for improving coating properties.
004, 57-178242, 57-4024.
No. 8, Japanese Patent Application No. 61-283938), a plasticizer for imparting flexibility and abrasion resistance to the coating film (eg, tricresyl phosphate, dihexyl phthalate,
Dioctyl phthalate, trioctyl phosphate, tributyl phosphate, tributyl citrate, polyethylene glycol, polypropylene glycol), and as coloring substances for visualizing the image area after development, acridine dye, cyanine dye, styryl dye, triaryl Pigments such as methane dye and phthalocyanine (for example, those described in JP-B-56-30859), general stabilizers for diazo resins (phosphoric acid, phosphorous acid, pyrophosphoric acid, oxalic acid, tartaric acid, malic acid, Pyridinedicarboxylic acid, boric acid, benzenesulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, polyacrylic acid and its copolymer, polyvinylphosphonic acid and its copolymer, polyvinylsulfonic acid and its copolymer , 5-ni Ronaphthalene-1-phosphonic acid, 4-chlorophenoxymethylphosphonic acid, sodium phenyl-methyl-pyrazolone sulfonate, 2-phosphonobutanetricarboxylic acid-1,2,4,1-phosphonoethanetricarboxylic acid-1,2,2 , 1-hydroxyethane-1,1-disulfonic acid) can be added. The amount of these additives added varies depending on the intended purpose, but is generally 0.5 to 30% by weight based on the total solid content of the photosensitive composition.

The photosensitive composition of the present invention is dissolved in a suitable organic solvent and coated on a support having a hydrophilic surface so that the dry coating weight is 0.5 to 5 g / m ^2, and the photosensitive lithographic printing plate is then coated. A printing plate can be obtained. The concentration of the photosensitive composition at the time of coating is preferably in the range of 1 to 50% by weight, and the coating solvent used is methanol, ethanol, butanol, ethylene chloride, chlorobenzene, tetrahydrofuran, acetone, methyl ethyl ketone, cyclohexanone. , Ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, 1-methoxy-2-propanol, dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, diacetone alcohol, Also suitable are these mixed solvents, or mixed solvents obtained by adding a small amount of water, toluene or the like to such a solvent or a mixed solvent to a solvent that does not dissolve the diazo resin or the binder.

Suitable supports for applying the photosensitive composition of the present invention are dimensionally stable plates. Such dimensionally stable plate-like materials include those conventionally used as a support for a printing plate, and they can be suitably used in the present invention. Examples of the support include paper, paper laminated with plastics (for example, polyethylene, polypropylene, polystyrene, etc.), aluminum (including aluminum alloys), metal plates such as zinc and copper, cellulose diacetate, and triacetate. Cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate,
Films of plastics such as cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, and the like, papers or plastic films laminated or vapor-deposited with the above metals are included. Among these supports, the aluminum plate is particularly preferable because it is dimensionally remarkably stable and inexpensive.

Among the aluminum plates, roughened aluminum is more preferable, and it can be manufactured by various methods. Wire brush graining,
The surface is grained by brush graining in which a slurry of abrasive particles is poured and roughening with a nylon brush, ball graining, chemical graining, electrolytic graining and complex graining combining these graining methods. Then, if necessary, anodization may be performed with a direct current or an alternating current power source in sulfuric acid, phosphoric acid, oxalic acid, boric acid, chromic acid, sulfamic acid or a mixed acid thereof to form a strong passivation film on the aluminum surface. preferable. The aluminum surface is hydrophilized by such a passivation film itself, and if necessary, it is further disclosed in US Pat. No. 2,714,066.
No. and U.S. Pat. No. 3,181,461, silicate treatment (sodium silicate, potassium silicate), U.S. Pat. No. 2,946,638, potassium fluorozirconate treatment, U.S. Pat. No. 3,201,2
47, phosphomolybdate treatment, German patent 1,091,433, polyacrylic acid treatment, German patent 1,134,093 and British patent 1,230, No. 447, polyvinyl phosphonic acid treatment, JP-B-44-6409, phosphonic acid treatment described in US Pat. No. 3,307,95.
Phytic acid treatment described in JP-A-58-1
6893 and JP-A-58-18291, combined treatments comprising a hydrophilic organic polymer compound and a divalent metal, and sulfonic acid groups described in JP-A-59-101651. It is particularly preferable that the undercoating of the water-soluble polymer has a hydrophilic treatment. As another hydrophilic treatment method, silicate electrodeposition described in U.S. Pat. No. 3,658,662 can also be mentioned.

In the present invention, the coating amount of the photosensitive composition coated on the roughened aluminum plate is preferably 0.3 to 5 g / m ² as a solid content, more preferably 0.
5 to 3.5 g / m ² . The solid content concentration of the photosensitive composition which gives such a coating amount is suitably 1 to 50% by weight, preferably 2 to 20% by weight. As a method for coating the photosensitive composition solution on the aluminum plate, a conventionally known method such as roll coating, bar coating, spray coating, curtain coating, and spin coating can be used. The applied photosensitive composition solution is preferably dried at 50 to 120 ° C. As a drying method, drying may be carried out at a high temperature after preliminary drying by lowering the temperature at the beginning, or directly at a high temperature.

A lithographic printing plate having a photosensitive composition layer coated and dried on a roughened aluminum plate is subjected to imagewise exposure and then developed with an alkaline aqueous solution developer to give a negative relief image to the original image. Is obtained. Suitable light sources for exposure include carbon arc lamps, mercury lamps, xenon lamps, metal halide lamps, strobes, and ultraviolet laser beams.

The alkaline aqueous solution-based developer used in the above-mentioned photosensitive lithographic printing plate has a pH of 8 to 13 and 75% by weight of water.
Refers to those included above, a small amount of organic solvent if necessary,
A surfactant, an alkali agent, an antifouling agent, a water softener, etc. can be added. For example, JP-A-51-77401
JP-A-51-80228, JP-A-53-4420
No. 2 and JP-A-55-52054, which are, for example, organic solvents having a solubility in water of 10% by weight or less at room temperature (benzyl alcohol, ethylene glycol monophenyl ether). ), Alkaline agents (triethanolamine, diethanolamine,
Monoethanolamine, sodium phosphate, sodium carbonate), anionic surfactant (aromatic sulfonate, dialkylsulfosuccinate, alkylnaphthalenesulfonate, fatty acid salt, alkyl sulfate ester salt, nonionic surfactant (polyoxyethylene Alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene polyoxypropylene block polymer),
A weak alkaline aqueous solution prepared by mixing and dissolving water and, if necessary, a compound selected from stain-preventing agents (sodium sulfite, sodium salt of sulfopyrazolone) and water softener (tetrasodium ethylenediaminetetraacetic acid salt, trisodium nitrilotriacetate salt). Is.

The plate surface protective agent for the plate surface protection treatment of the present invention will be described below. The plate surface protective agent of the present invention has a pH
It is in the range of 4.5 to 10. Furthermore, the pH is 4.5 to 8.0.
It is preferable that there is a range of e. Within this range, it is preferable in terms of binder deposits and inking properties. pH of 4.5 to 1
In order to make it zero, generally, a mineral acid, an organic acid, an inorganic salt, an alkaline agent, or the like is added to the plate surface protective agent for adjustment. The appropriate addition amount is 0.01 to 3% by weight.

Examples of the mineral acid include nitric acid, sulfuric acid, phosphoric acid and the like. Examples of the organic acid include citric acid, acetic acid, oxalic acid, malonic acid, p-toluenesulfonic acid, tartaric acid, malic acid, lactic acid, levulinic acid, phytic acid, benzoic acid, butyric acid, maleic acid, picolinic acid, and organic phosphonic acid. To be Examples of the inorganic salt include water-soluble alkali metal salts and ammonium salts such as nitric acid, phosphoric acid, sulfuric acid, molybdic acid, acetic acid, polyphosphoric acid and boric acid, for example, sodium nitrate, potassium nitrate, ammonium nitrate, monosodium phosphate, and dibasic phosphate. Sodium, potassium dibasic phosphate, dibasic potassium phosphate, dibasic ammonium phosphate, dibasic ammonium phosphate, sodium sulfate, potassium sulfate, ammonium sulfate, sodium molybdate, potassium molybdate,
Ammonium molybdate, sodium acetate, potassium acetate, ammonium acetate, sodium tripolyphosphate,
Sodium hexametaphosphate, sodium pyrophosphate,
Examples thereof include sodium borate and ammonium borate. Examples of the alkaline agent include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide, or amines such as ammonia, monoethanolamine, diethanolamine and triethanolamine.
Two or more kinds of mineral acids, organic acids, inorganic salts, alkaline agents and the like may be used in combination.

Various water-soluble resins can be used in the plate surface protective agent used in the present invention. For example, as natural polymer compounds, starches such as kansho starch, potato starch, tapioca starch, wheat starch and cornstarch, carrageenan, laminaran, sea soup mannan, wisteria, Irish moss, agar, and sodium alginate can be obtained from algae. Thing, botanical mucilage such as trouro mallow, mannan, quince seed, pectin, tragacanth gum, karaya gum, xanthine gum, guar bingham, locust bingham, gum arabic, carop gum and benzoin gum, homopolysaccharides such as dextran, glucan and levan and succinoglucan. And microbial mucilages such as heteropolysaccharides such as xanthan gum, proteins such as glue, gelatin, casein and collagen.
In addition to propylene glycol alginate which is a semi-natural product (semi-synthetic product), viscose, methyl cellulose, ethyl cellulose, methyl ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl ethyl cellulose and hydroxypropyl methyl cellulose phthalate. Examples thereof include fibrin derivatives and processed starch. Processed starch includes roasted starch such as white dextrin, yellow dextrin and British gum, enzyme-modified dextrin such as enzyme dextrin and Schardinger dextrin, acid-decomposed starch such as solubilized starch, oxidized starch such as dialdehyde starch and modified pregelatinized starch. Pregelatinized starch such as starch and non-modified pregelatinized starch, starch phosphate, fatty starch, starch sulfate, nitrate nitrate, starch xanthate, esterified starch such as carbamate starch, carboxyalkyl starch, hydroxyalkyl starch, sulfoalkyl Starch, cyanoethyl starch, allyl starch, benzyl starch, carbamylethyl starch, dialkylamino starch and other etherified starch, succinic acid and other ester starch, methylol crosslinked starch, hydroxyalkyl crosslinked starch, phosphoric acid crosslinked starch Cross-linked starch such as dicarboxylic acid cross-linked starch, starch polyacrylamide copolymer, starch polyacrylic acid copolymer, starch polyvinyl acetate copolymer, starch polyacrylonitrile copolymer, cationic starch polyacrylic acid ester copolymer, Examples thereof include starch graft copolymers such as cationic starch vinyl polymer copolymers, starch polystyrene maleic acid copolymers and starch polyethylene oxide copolymers. Polyvinyl alcohol, partially acetalized polyvinyl alcohol, allyl-modified polyvinyl alcohol, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl isobutyl ether, and other modified polyvinyl alcohol, sodium polyacrylate, partially saponified polyacrylate ester , Polyacrylic acid ester copolymer partially saponified products, polyacrylic acid derivatives and polymethacrylic acid derivatives such as polymethacrylate and polyacrylic amide, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinylacetate , Carboxyvinyl polymer, styrene-maleic acid copolymer, styrene-crotonic acid copolymer, and the like. These water-soluble resins may be used in combination of two or more, and preferably 5 to 40% by weight, more preferably 10 to 30% by weight in the plate surface protective agent of the present invention.
It can be contained in the range of. Further, in the present invention, the amount of gum arabic used can be significantly reduced. Although gum arabic may not be used at all, it is preferable to use the gum arabic in combination in an amount of about 1 to 20% by weight based on the total amount of the water-soluble resin to be used, in order to fully exert the non-sensitizing ability of the non-image area.

Further, addition of a surfactant to the plate surface protective agent of the present invention improves the surface state of the coating layer and the like.
A solvent having a solubility in water at 0 ° C of 5% by weight or less can be stably solubilized. Examples of such surfactants include anionic surfactants, nonionic surfactants, amphoteric surfactants, and cationic surfactants. For example, as the anionic surfactant, fatty acid salts, alkylbenzene sulfonates, linear alkylbenzene sulfonates, alkyl sulfates, α-olefin sulfonates, alkyl phosphate ester salts, dialkyl sulfosuccinate ester salts, polyoxyethylene alkyl ethers. , Sulfates, polyoxyethylene alkyl ether phosphates, alkylnaphthalene sulfonates, N-
Examples include lauroyl sarcosine salts, sulfonic acids of naphthalene formalin condensates, and diphenyl ether disulfonates.

As the nonionic surfactant, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene polyoxypropylene block polymers, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, Polyethylene glycol fatty acid esters, polyoxyethylene fatty acid amines,
There are fatty acid monoglycerides, sorbitan fatty acid esters, pentaerythritol fatty acid esters, sucrose fatty acid esters, amine oxides and the like.

Examples of the amphoteric surfactant include alkylcarboxybetaine type compounds, alkylaminocarboxylic acid type compounds, and alkylimidazoline type compounds. Examples of the cationic surfactant include tetraalkylammonium salts, trialkylbenzylammonium salts, alkylimidazolinium salts and the like. Other examples include fluorine-based surfactants and silicon-based surfactants.

Among the surfactants, anionic surfactants and / or nonionic surfactants are particularly effective. Two or more kinds of these surfactants can be used in combination. The amount used is not particularly limited, but a preferable range is 0.01 to 10% by weight based on the total weight of the plate surface protective agent.

The plate surface protective agent used in the present invention is 20 ° C.
It is preferable to contain a solvent having a water solubility of 5% by weight or less, and by adding such a solvent, the oil sensitivity of the image area can be improved. Examples of such solvents include benzyl alcohol, ethylene glycol dibutyl ether, ethylene glycol benzyl ether, ethylene glycol monophenyl ether, hexyl glycol, hexyl diglycol, propyl propylene diglycol, methylphenyl carbitol, ethylene glycol dibutyl ether, Diethylene glycol dibutyl ether, n-amyl alcohol, methylamyl alcohol, isophorone, methylcyclohexanone, acetophenone and the like can be mentioned. Among these, particularly preferable is benzyl alcohol, which has a low odor, high safety, and is relatively inexpensive.

In the present invention, the solvent may be used alone or in combination of two or more kinds, and the amount thereof is suitably 0.1 to 10% by weight based on the total weight of the plate surface protective agent of the present invention.
Particularly preferably, it is 0.5 to 5% by weight. As the amount is less than 0.1% by weight, there is a drawback that the oil sensitivity of the image area is deteriorated. Further, as it exceeds 10% by weight, more solvent adheres to the plate surface, resulting in stickiness or deterioration in drying property. Further, in a solvent whose solubility in water at 20 ° C. is higher than 5% by weight,
There is no or insufficient effect of preventing deterioration of the oil sensitivity of the image area.

In addition, lower alcohols such as glycerin, ethylene glycol and triethylene glycol can be used as a wetting agent, if necessary. These wetting agents are preferably contained in the amount of 0.1 to 0.1 based on the total weight of the plate surface protective agent.
5.0% by weight, more preferably 0.5-3.
Use 0% by weight. Further, a preservative and the like can be added to the plate surface protective agent of the present invention. For example, benzoic acid and its derivative, phenol, formalin, sodium dehydroacetate, 3-isothiazolone compound etc.
It can be added in the range of 2.0% by weight. In addition, defoaming agents, chelating agents, coloring agents and the like which are usually used as plate surface protective agents may be added.

The plate surface protective agent of the present invention can be prepared by stirring and dissolving a solvent, a water-soluble resin, a surfactant, a pH adjusting agent, a wetting agent, and a preservative in water or, if necessary, warm water. Since the plate surface protective agent of the present invention is a non-emulsifying type gum solution, it is not necessary to adjust the aqueous phase and oil phase like an emulsifying type gum solution, and further it is not necessary to emulsify with a homogenizer, etc. Can be created.

Next, one use example of the plate surface protective agent of the present invention will be described. First, the PS plate is imagewise exposed and then developed to prepare a lithographic printing plate. As a method for developing the PS plate image-exposed, various conventionally known methods can be used. Specifically, a method of immersing the image-exposed PS plate in a developer,
A method of spraying a developing solution onto the photosensitive layer of the PS plate from a large number of nozzles, a method of wiping the photosensitive layer of the PS plate with a sponge moistened with the developing solution, and a roller coating of the developing solution on the surface of the photosensitive layer of the PS plate. Method etc. are mentioned.

The lithographic printing plate developed by the above method is washed with water, squeezing the water on the plate surface, and then an appropriate amount of the plate surface protective agent of the present invention is poured onto the plate surface, and a sponge is applied so as to coat the entire surface of the plate. Rub. As a result, the non-image area on the plate surface is protected and the planographic printing plate can be stored. Examples of the treatment method using a plate surface protective agent include automatic gum coating machine treatment performed after development / washing, gum coating performed immediately without water washing after development, and washing with a small amount of washing water after development. An example of automatic gum coater treatment performed after treatment with a rinse liquid containing a surfactant can be given.

When starting printing, the gum on the plate surface may be washed off with water (so-called gum removal), and then printing may be carried out according to a usual procedure. In the plate surface protective agent of the present invention, so-called gum may be used. It is also possible to start printing immediately without dropping. At the time of printing, it is possible to obtain a satisfactory and clear printed matter immediately after printing without producing many defective printed matter as in the past, and one non-image area retains strong hydrophilicity. Therefore, it is possible to obtain a good printed matter without printing stains.

[0038]

EXAMPLES Examples will be described below. Unless otherwise specified,% means% by weight. Example 1 An aluminum plate was immersed in an aqueous sodium phosphate solution for degreasing,
After polishing with a brush, electrolytic etching was performed, followed by anodic oxidation in sulfuric acid, and further immersion in an aqueous solution of sodium silicate for hydrophilic treatment.

The following photosensitive composition A was applied to this hydrophilized aluminum plate to obtain a photosensitive lithographic printing plate (A). The coating amount was 1.5 g / m ² . Photosensitive composition A Binder-1 5.0 g Diazo resin-1 0.5 g Pivaloyl group-containing compound-1 (Table 1) 0.1 g Victoria Pure Blue BOH 0.15 g Sodium t-butylnaphthalene sulfonate 0.15 g Sub Phosphoric acid 0.1 g FC-430 (fluorine-based surfactant) 0.05 g Ethylene glycol monomethyl ether 60 g Methanol 20 g Methyl ethyl ketone 40 g Diazo resin-1 used here is JP-A-59-7834.
It is the hexafluorophosphate salt of the condensate of p-diazodiphenylamine and paraformaldehyde described in No. 0 Synthesis Example 1.

Binder-1 is 2-hydroxyethyl methacrylate / acrylonitrile / methyl methacrylate /
Methacrylic acid copolymer (weight ratio 50/20/26/4,
It is a water-insoluble, alkaline water-soluble film-forming polymer having an average molecular weight of 75,000 and an acid value of 26). Pivaloyl group-containing compound-1 is a pivalic acid ester of poly-p-hydroxystyrene (average molecular weight of 5,000) (esterification rate: 83 mol%).

The photosensitive lithographic printing plate was imagewise exposed and further developed under the following conditions. That is, first, the developer DN-5M (manufactured by Fuji Photo Film Co., Ltd.) is used in the first bath of the automatic developing machine Stapron 900D manufactured by Fuji Photo Film Co., Ltd., water is used in the second bath, and the following is used in the third bath. Each of the plate surface protective agents (B) was charged, and the development processing conditions were such that the developing solution temperature was 30 ° C. and the developing time was 30 seconds. Next, the planographic printing plate was developed.

A part of the plate subjected to the above plate-making treatment is put at 90 ° C. at 35 ° C.
% RH for 12 hours. The lithographic printing plate was placed on a Heidelberg printer SOR-M the next day.
Trans G Sumi N manufactured by Dainippon Ink Co., Ltd. was used as the ink, and 1% EU-4 manufactured by Fuji Photo Film Co., Ltd. added to 10% isopropanol was used as the dampening water.

The inking property was evaluated by determining the number of sheets required for printing on a plate that was forcibly aged. Dirt evaluation is 100
After printing 0 sheets, it was left on the machine (with the ink still applied) for 1 hour, and then the prints printed again were observed for stains. When the photosensitive composition A was used and printing was performed at a speed of 6,000 rotations / hour, a printed matter having a sufficient ink density was obtained on the 10th printing sheet.

A printing plate made of the composition obtained by removing the pivaloyl group-containing compound-1 from the photosensitive composition A required 30 or more printing sheets to obtain a printed matter having a sufficient ink density. In addition, the photosensitive composition contains a pivaloyl group-containing compound-1.
In the presence or absence of the above, the pH of the gum solution was further changed as shown in Table 1, and the evaluation was performed. The results are shown in Table 1.

(B) Plate surface protective agent <Gum solution I> Pure water 750 parts by weight Gum arabic 20 parts by weight Enzyme-modified potato starch 200 parts by weight Viscosity (20%) 10 cps (20 ° C.) Enzyme-modified corn starch 40 parts by weight Viscosity ( 20%) 5 cps (20 ° C.) phosphorylated waxy starch 20 parts by weight Viscosity (20%) 40 cps (20 ° C.) Bound phosphorus per unit 1.0 Sodium dilaurylsulfosuccinate 10 parts by weight Ammonium phosphate 3 parts by weight EDTA Tetrasodium salt 3 parts by weight Ethylene glycol 20 parts by weight Benzyl alcohol 25 parts by weight Sodium dehydroacetate 0.5 parts by weight Emulsion type silicone antifoam agent 0.2 parts by weight pH Table 1 After dissolving starch in warm water at 80 ° C, After cooling, other components were added and dissolved by stirring to prepare a plate surface protective agent.

The gum solution of pH 3.5 in Table 1 is the above gum solution I.
Further, 10 parts by weight of phosphoric acid (85%) was added.

[0047]

[Table 1] No. Pivaloyl group-containing gum pH stain Staining number of sheets Compound-1 Example 1 ○ 5.3 ○ ○ 10 Comparative Example 1 × 3.5 ○ × 30 Comparative Example 2 ○ 3.5 × ○ 10 Comparative Example 3 × 5.3 ○ × 50

From the above results, good results can be obtained when the compound-1 containing the pivaloyl group is contained and the pH is within the range of the present invention.

[0049]

According to the present invention, it is possible to provide a method of protecting the plate surface of a negative type lithographic printing plate which is excellent in the inking property of the image area and can improve the processing performance.

Claims (1)

[Claims] 1. After development of a negative lithographic printing plate containing a compound containing a pivaloyl group, a diazo resin and a binder,
A method of protecting a negative type lithographic printing plate using a plate surface protective agent having a pH of 4.5 to 10.