JPH09240164A - Plate surface protecting agent for lithographic plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the power of desensitizing a non-image area, the part of a flaw in particular, by using a malic acid salt. SOLUTION: As to a malic acid salt, an alkali metal salt, e.g. a sodium salt, a potassium salt, a lithium salt and an ammonium salt, can be cited. One or two kinds or more of these salts can be used jointly. The potassium salt is preferable. The concentration of the malic acid salt in a plate surface protecting agent is suitably 4.0-25wt.%. More preferably, it is 5.0-15wt.%. When it is less than 4.0wt.%, the power of preventing a flaw on a non-image area lessens. When it exceeds 25wt.%, the forming performance of ink on an image deteriorates. A main solvent in regard to the plate surface protecting agent is water. The plate surface protecting agent can be prepared by adding an acid salt of a malic acid, e.g. an acid sodium salt of the malic acid and an acid potassium salt of the malic acid, as the malic acid salt to the water.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a plate surface protective agent for a lithographic printing plate.

[0002]

2. Description of the Related Art When making a lithographic printing plate, a gumming step of applying a plate surface protective agent, a so-called gum solution, is carried out in the final step. This prevents printing stains from adhering to the plate surface until it is applied to the printing machine after plate making,
It is also provided to prevent scratches on the printing plate when they are stored in a stack or hit by a foreign substance.
The most important purpose of gumming is to prevent the plate surface from being directly exposed to the air and to reduce the desensitizing property of the non-image area due to the oxidation phenomenon, etc., and further to enhance the desensitizing property. Gumming is an integral part of the plate making process.
As a gum solution, for a long time, a composition obtained by adding a surfactant, a pH adjusting agent, a preservative and the like to an aqueous solution of gum arabic having a concentration of about 15 to 30% by weight has been used. However, gum arabic is a natural product and is produced only in a very limited area in the world, and its harvest is affected by the climate of the area and the supply is unstable. Furthermore, gum arabic has a strong desensitizing action, so that the oil sensitivity of the image area is often lowered, and a large number of defective prints may be produced until a print having a satisfactory ink density is obtained in printing. .

Therefore, many attempts have been made to use various water-soluble organic polymer compounds in place of gum arabic as a plate surface protective agent. For example, in JP-A-54-97102, dextrin, stellabic, tractane,
Alginates, polyacrylic acids, hydroxyethyl cellulose, polyvinylpyrrolidone, polyacrylamide, methyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose and carboxyalkyl cellulose salts are shown, and JP-B-54-4.
No. 1921 discloses pullulan or a pullulan derivative, JP-A-58-197091 discloses polyvinylpyrrolidone, and JP-A-56-133193 discloses polyvinyl alcohol. It was inferior to gum arabic in terms of its chemical power.

Further, in an attempt to improve the desensitizing power, carboxyalkylated starch (Japanese Patent Laid-Open Nos. 62-7595 and 62-9995) and phosphorylated starch (Japanese Laid-Open Patent Publication Nos. 62-11692 and 62-11952). It has been proposed to use a modified starch such as JP-A No. 62-11693) as a plate surface protective agent. However, when a modified starch such as carboxyalkylated starch or phosphorylated starch is used as a plate surface protective agent, if the solution is stored at a low temperature for a long time, the starch will be aged and precipitate in a gel form. It was often found to be completely useless. Further, although these modified starches are excellent in desensitizing power, they are still used under severe conditions, for example, the developing solution is fatigued, the elution ability is decreased, and the developability of the photosensitive lithographic printing plate is deteriorated over time. When a part of the photosensitive layer to be eluted remained in the non-image area of the lithographic printing plate after development due to deterioration, the desensitizing power was inferior to that of gum arabic.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a plate surface protective agent which is excellent in desensitizing power in non-image areas, particularly in areas where scratches occur. Still another object of the present invention is to provide a plate surface protective agent that does not impair the oil sensitivity of the image area.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that the use of malate significantly increases the desensitizing power of non-image areas, especially scratches. The present invention has been made, and the present invention has been accomplished. That is, the present invention is a plate surface protective agent for a lithographic printing plate, which contains a malic acid salt.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the malate of the present invention include alkali metal salts such as sodium salt, potassium salt and lithium salt, and ammonium salt. These salts can be used alone or in combination of two or more. Preferred is a potassium salt. The maltate concentration in the plate surface protective agent of the present invention is suitably 4.0 to 25% by weight. It is more preferably 5.0 to 15% by weight. If it is less than 4.0% by weight, the ability to prevent scratches on the non-image area will be reduced, and if it exceeds 25% by weight, the ink receptivity on the image will be poor. The main solvent in the plate surface protective agent of the present invention is water. The plate surface protective agent of the present invention can be produced by adding malic acid acidic salt, such as malic acid acidic sodium salt or malic acid acidic potassium salt, to water as the malic acid salt. Further, the plate surface protective agent of the present invention,
It can be produced by adding malic acid and at least one selected from alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and a base such as ammonium hydroxide to water. In this case, the malate may be added so that the concentration thereof is within the above range. Alkali metal hydroxides such as sodium hydroxide and hydroxide in a ratio of 0.5 to 1.5, preferably 0.7 to 1.3, based on the number of moles of malic acid. It suffices to add at least one selected from bases such as potassium and lithium hydroxide, and ammonium hydroxide. The malic acid to be used may be a dl body, a d body or an l body.

In the present invention, a water-soluble organic polymer compound may be used in combination with the above-mentioned malate as its component. Examples of such a polymer compound include
Cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, roasted dextrin, enzyme-modified dextrin, oxidized starch, acid-treated starch, pre-gelatinized starch, esterified starch, etherified starch, cross-linked starch and other processed starch, D
-Sorbit, alginate, locust bean gum,
Natural or semi-synthetic polymer compounds such as tractane, stellabic, pullulan and the like can be mentioned. Further, synthetic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyvinyl methyl ether, polyethylene oxide, copolymers of vinyl methyl ether and maleic anhydride, and copolymers of vinyl acetate and maleic anhydride are also used. it can. Furthermore, when gum arabic is used in combination, gum arabic can achieve the object of the present invention in a significantly smaller amount than conventionally used.

A plate surface protective agent is generally used in an acidic region, that is, at pH.
It is advantageous to use it in the range of 2.5 to 6.0. The pH of the aqueous solution of malate is in the range of 2.5 to 6.0,
If necessary, a mineral acid, an organic acid, an inorganic salt or the like is added. The amount added is usually 0.01 to 2% by weight. Examples of the organic acid include citric acid, acetic acid, oxalic acid, malonic acid, p-toluenesulfonic acid, tartaric acid, lactic acid, levulinic acid, and organic phosphonic acid. As the mineral acid, nitric acid, sulfuric acid, phosphoric acid, etc. are useful. . At least one of mineral acid, organic acid or inorganic salt
You may use together or 2 or more types.

The addition of a surfactant to the plate surface protective agent of the present invention improves the surface condition of the coating film. Surfactants that can be used include anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants. Examples of the anionic surfactant include aliphatic alcohol sulfate ester salts, aliphatic alcohol phosphate ester salts, dibasic fatty acid ester sulfonates, fatty acid amide sulfonates, alkylaryl sulfonates, formaldehyde condensed naphthalene sulfonates, and the like. Used. As the cationic surfactant, alkylamine salts, quaternary ammonium salts and the like are used. As the amphoteric surfactant, alkyl carboxybetaines, alkyl imidazolines and the like are used. As the nonionic surfactant, polyethylene glycol alkyl ether, polyethylene glycol alkyl ester, sorbitan alkyl ester, polyoxypropylene polyoxyethylene ether, etc. are used. Two or more 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 of the plate surface protective agent.

In addition to the above components, a lower polyhydric alcohol such as glycerin, ethylene glycol or triethylene glycol can be used as a lubricant, if necessary. The content of these lubricants in the composition is preferably 0.1 to 5.0% by weight, more preferably 0.5 to 3.0% by weight. In addition to the above, a preservative and the like can be added to the plate surface protective agent of the present invention. For example, benzoic acid and its derivatives, phenol, formalin, sodium dehydroacetate and isothiazolone compounds can be added in the range of 0.005 to 2.0% by weight.

The plate surface protective agent of the present invention can be used for various lithographic printing plates. In particular, a photosensitive lithographic printing plate having an aluminum plate as a support and a photosensitive layer thereon (previously It is suitable for the planographic printing plate obtained by imagewise exposing and developing a printing plate having PS. A preferred such PS plate is, for example, a mixture of shellac and a diazo resin (a salt of a condensate of p-diazodiphenylamine and paraformaldehyde) as described in British Patent 1,350,521. With a photosensitive layer consisting of an aluminum plate, British Patent Nos. 1,460,978 and 1,50
No. 5,739, wherein a photosensitive layer comprising a mixture of a diazo resin and a polymer having a hydroxyethyl methacrylate unit or a hydroxyethyl acrylate unit as a main repeating unit is provided on an aluminum plate. A negative PS plate as described above, and a positive PS in which a photosensitive layer made of a mixture of an o-quinonediazide photosensitive material and a novolac type phenolic resin as described in JP-A No. 50-125806 is provided on an aluminum plate. Edition included. Further, a PS having a light-sensitive layer of a photocrosslinkable photopolymer as illustrated in U.S. Pat. No. 3,860,426 on an aluminum plate.
Edition, US Pat. Nos. 4,072,528 and 4,072,5.
P provided with a photosensitive layer of a photopolymerizable photopolymer composition as described in each specification of No. 27 on an aluminum plate.
S version, British Patents 1,235,281 and 1,495,
A PS plate having a photosensitive layer made of a mixture of azide and a water-soluble polymer as described in each specification of No. 861 provided on an aluminum plate is also preferable.

Next, one example of use of the plate surface protective agent of the present invention when a PS plate is used will be described. Image exposure of PS plate,
Then, development is performed to prepare a lithographic printing plate. This lithographic printing plate is washed with water and squeezed with water on the plate surface, then an appropriate amount of the plate surface protective agent of the present invention is poured onto the plate surface, and the plate surface is rubbed with a sponge so as to coat the entire surface. As a result, the non-image area on the plate surface is protected and the planographic printing plate can be stored.
When printing is started, the gum on the printing plate is washed off with water, and then printing is performed according to a normal procedure.
Further, even if an automatic gum coater is used, the application can be performed uniformly. In addition to the plate surface protective agent of the present invention, when the plate surface protective agent is immediately supplied to the entire plate surface without being washed with water after development using an automatic developing machine and then applied, an aqueous solution containing a surfactant after development. Immediately after rinsing with, or after rinsing with water, when applied to the plate surface, after development, after rinsing with circulating water rinsing water, when supplied and applied to the plate surface, and after development, rinsing with circulating water rinsing water, surfactant It is preferably used in any case, such as when it is applied to the plate surface after being treated with the contained aqueous solution. Further, it is also suitable as a plate surface protective agent used for plate placement on a printing machine. Further, it is also preferably used as a plate surface protective agent when the above-mentioned negative and positive PS plates are treated with a common developing solution.

[0014]

By using the plate surface protective agent for a lithographic printing plate of the present invention, excellent desensitizing property can be imparted to the non-image area, particularly to the scratched area, while the image area of the image area is reduced. Does not impair oil sensitivity. Therefore, at the time of printing, without producing many defective prints as in the past,
Immediately after printing, it is possible to obtain a sufficiently detailed printed matter.

The present invention will be described in more detail with reference to the following examples. Unless otherwise specified,% means% by weight.

【Example】

[Examples 1 and 2] Six aluminum plates having a thickness of 0.24 mm were used.
It was dipped in a 7% aqueous solution of sodium triphosphate at 0 ° C. to degrease it, washed with water, and then rubbed with a nylon brush while flowing a solution of pumice suspended in water to grain it. After washing with water, 70 ° C
5% of potassium silicate (SiO ₂ / K ₂ O molar ratio 2.0) kept in
It was immersed in the aqueous solution for 30 to 60 seconds. After thoroughly washing with water, it was dried. 2.0 parts by weight of 2-hydroxyethyl methacrylate copolymer (synthesized by the method of Example 1 of British Patent 1,505,739), 2-methoxy-4-, a condensate of p-diazodiphenylamine and paraformaldehyde.
Hydroxy-5-benzoylbenzenesulfonate 0.1
2 parts by weight, Oil Blue # 603 (manufactured by Orient Chemical Industry Co., Ltd.) 0.03 parts by weight, 2-methoxyethanol 15
Parts by weight, 10 parts by weight of methanol, ethylene chloride 5.
0 parts by weight of a photosensitive solution was applied to the above support to obtain a photosensitive lithographic printing plate having a coating dry weight of 1.8 g / m ² . This printing plate was exposed using a halftone negative film to give sodium sulfite 3.0 parts by weight, benzyl alcohol 30.0 parts by weight, triethanolamine 20.0% by weight, monoethanolamine 5 parts by weight, t-butylnaphthalene. After development with an aqueous developer containing 10 parts by weight of sodium sulfonate and 1000 parts by weight of pure water, the product was washed with water and dried. On the surface of the lithographic printing plate thus prepared, a plate surface protective agent (I) having the following composition,
(II) was applied in a sponge, and the excess was wiped off with a cloth to give a printing sample. The coating amount was 0.1 g / m ² (dry weight).

(I) d, l-malic acid 80 g sodium hydroxide 12 g potassium hydroxide 17 g pure water 1000 g (II) d, l-malic acid 80 g potassium hydroxide 34 g pure water 1000 g

In order to evaluate the ink receptivity of these printing samples and the desensitizing power of the scratches in the non-image areas, the samples were left in advance at 35 ° C. and 85% RH for 3 days. did. The samples were mounted on a printing machine (Hamaduster offset printing machine), and printing was started according to a usual method. As an index of ink receptivity, the number of prints until the ink at that time adheres to the image area and a good printed material is obtained,
The results are shown in Table 1 below. In addition, the non-image area on the plate was scratched before printing, and the reproducibility of scratches on the printed matter after printing was recorded in the scratch stain column in Table 1. The evaluation criteria for scratches and stains are as follows. A: Scratches on the plate are not visible on the printed matter. B: Scratches on the plate are slightly visible on the printed matter. C: Scratches on the plate are reproduced on the printed matter.

[Comparative Examples 1 and 2] A lithographic printing plate treated under exactly the same conditions as in Example 1 up to the developing treatment was used instead of the plate surface protective agent used in Example 1 (III). ) And (IV) were applied and dried. Coating amount is 0.1g / m ²
(Dry weight). These were used as printing samples for comparison. (III) Gum arabic 60 parts by weight Hydroxypropyl transferase-modified dextrin (Penon JE-66, Nitate Kagaku Co., Ltd.) 80 parts by weight Sodium isopropylnaphthalene sulfonate (35% aqueous solution) 5 parts by weight Sodium dehydroacetate 0.3 parts by weight Parts Pure water 1000 parts by weight Phosphoric acid (85%) was used to adjust the pH to 3.5. (IV) Enzyme-modified dextrin (Amicol 7H manufactured by Nitto Kagaku Co., Ltd.) 60 parts by weight Hydroxypropylated enzyme-modified dextrin (Penon JE-66 manufactured by Nitto Kagaku Co., Ltd.) 80 parts by weight Sodium isopropylnaphthalene sulfonate (35%) Aqueous solution) 5 parts by weight Sodium dehydroacetate 0.3 parts by weight Pure water 1000 parts by weight Phosphoric acid (85%) was used to adjust the pH to 3.5. Similar to Examples 1 and 2, the ink receptivity and the desensitizing power of the scratched portion of the non-image area were evaluated. The results are shown in Table 1 below.
Put together.

[0019]

[Table 1] ──────────────────────────────── Plate surface protective agent for the non-image area at the start of printing Ink inking Property (sheet) Scratch stain ──────────────────────────────── Example 1 (I) 9 A Example 2 ( II) 9 A ──────────────────────────────── Comparative Example 1 (III) 40 C Comparative Example 2 (IV) 9 C ─────────────────────────────────

As is clear from the results shown in Table 1, the use of the plate surface protective agent for a lithographic printing plate of the present invention imparts excellent desensitizing property to the non-image area, particularly to the scratched area. As a result, there is no stain on the printed matter, and the ink receptivity is good, and a good printed matter can be obtained immediately after the start of printing.

Claims (1)

[Claims] 1. A plate surface protective agent for a lithographic printing plate comprising malate.