JPS5929198A - Plate surface protecting agent for planographic printing press - Google Patents

Abstract

PURPOSE:To provide a plate surface protecting agent having desensitizing power while keeping the sensitivity of an image part and excellent in coating surface quality, obtained by adding alkali metal or ammonium hexametaphosphate to a water soluble org. high molecular compound soluble in cold water and having film forming property. CONSTITUTION:5-35wt% one kind or more water soluble org. high molecular compound (A) soluble in cold water and having film forming property selected from dextrin, soluble starch, water soluble fibrous ether, a water soluble vinyl polymer, purulan and a purulan derivative, malei resin, Stractan and aluginate and 0.02-2% alkali metal or ammonium hexametaphosphate (B) are contained to obtain a plate surface protecting agent for a planographic printing plate.

Description

[Detailed description of the invention] The present invention relates to a plate surface protective agent for lithographic printing plates.

When making a lithographic printing plate, a plate surface protectant,
A gumming process is performed in which a so-called gumming liquid is applied.

This is done to prevent dirt from adhering to the plate surface and causing printing stains after the plate is made and before it is put on the printing press, and also to prevent it from being scratched if it is stored stacked or comes into contact with foreign objects. It is something. The most important thing is that the printing plate is directly exposed to the air, which prevents the non-image areas from becoming less oleaginous due to oxidation, etc., and is essential because it has the effect of increasing the oleaginability. .

As the gum liquid, an aqueous solution of gum arabic with a concentration of about 15 to 30% by weight has been used for a long time. Gum arabic is extremely excellent as a plate surface protectant in terms of desensitizing effect, film forming properties, solubility, etc. On the other hand, gum arabic has a strong desensitizing effect, so when used as a plate surface protectant, it often reduces the fat sensitivity of the image area, resulting in a large number of defective prints before a print with a satisfactory ink density can be obtained. This will cause In order to prevent this, it is common practice to coat the image area with oil or fat before gumming, but this is not preferred because it complicates the process and reduces workability, as well as contaminating drainage fluid and causing health problems.

Therefore, attempts have been made to use water-soluble organic polymer compounds other than gum arabic as plate surface protectants. For example, JP-A-52-56603, JP-A-54-97102,
West German Patent No. 2504594 and Soviet Patent No. 623,755 describe water-soluble organic polymers as substitutes for gum arabic, such as degistrin, pullulan and pullulan derivatives, carboxyl group-containing polyacrylamide derivatives, and methyl (meth)acrylate grafted polyacrylamide copolymers. Compounds are described. However, both are inferior to gum arabic in their ability to desensitize non-image areas of printing plates. Moreover, they have poor coating suitability, and have the disadvantage that when aqueous solutions of these plate surface protectants are applied to exposed and developed planographic printing plates using a gum coater, it is difficult to apply them uniformly and the coating is uneven. was.

Therefore, an object of the present invention is to provide a printing plate protectant that maintains the desensitization property of the non-image area, does not impair the oil sensitivity of the image area, and has the ability to protect the plate surface with good coated surface quality. be.

As a result of intensive research in order to achieve the above object, the present inventors have developed a water-soluble organic polymer compound other than gum arabic that is substantially soluble in cold water and has film-forming properties as a stain-preventing and surface-improving agent. It has been discovered that by adding an alkali metal salt or ammonium salt of hexametaphosphate, it is possible to obtain a plate surface protectant that does not reduce the oil sensitivity of the image area, has excellent coated surface quality, and has oil desensitizing power. Ta.

That is, the present invention provides: (a) one species selected from the group consisting of dexi-phosphorus, soluble starch, water-soluble cellulose ether, water-soluble vinyl polymer, pullulan and pullulan derivatives, sterapic, structan, and alginate; Water-soluble organic polymer compounds 5 to 3 which are substantially soluble in cold water and have film-forming properties as described above.
5% by weight and (b) 0.02 to 2% by weight of an alkali metal salt or ammonium salt of hexametaphosphate.

Examples of the alkali metal salt or ammonium salt of hexametaphosphate used in the present invention include sodium hexametaphosphate, potassium hexametaphosphate, and ammonium hexametaphosphate.

The amount of the alkali metal salt or ammonium salt of hechirametaphosphate added is 0.02 to 2% by weight, more preferably 0.05 to 0.5% by weight, in the plate surface protective agent.

Dextrins used in the present invention are obtained by hydrolyzing starch, and have different properties depending on the method and degree of hydrolysis, ranging from those that are soluble only in hot water to those that are almost soluble in cold water. The dextrin used in the present invention preferably has a water-soluble content of at least 60% by weight in water at 20°C, more preferably more than 70% by weight.

Adjusting the total water soluble content by mixing low water soluble content with high water soluble content is a suitable method in the practice of this invention. If a solution having a low soluble content is used, the oil sensitivity of the image area may be reduced, and the aqueous solution may have poor aging properties and solidify.

In addition, the soluble starch, water-soluble cellulose ether, water-bathable vinyl polymer, pullulan and pullulan derivatives, sterapic, structan, and alginate used in the present invention can be used in water at 20°C for at least
It has a soluble content of 0% by weight, more preferably 70% by weight.
It is desirable to contain more than % by weight of water soluble content.

In addition to the above, acids, preservatives, wetting agents, and other inorganic salts can be added to the plate surface protectant of the present invention.

Wetting agents prevent the protective agent on the plate from drying out during drying, thereby making it easier to remove during subsequent washes or when the plate is mounted on a printing press and a dampening roller contacts the plate surface. help. Rapid removal of the film of the plate protectant helps ink adhesion in the image area.

Useful wetting agents include low molecular weight polyols such as polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol, glycerin, and the like. Other useful wetting agents include anionic surfactants and nonionic surfactants. Alkylbenzene sulfonates as anionic surfactants include alkylnaphthalene sulfonates, naphthalene sulfonic acid condensates, dialkyl sulfosuccinates, alkyl sulfonates having 8 or more carbon atoms, (R: alkyl group or H), alkylphenol type Phosphate ester, alkyl type phosphate ester, fatty acid salt soap, rosin acid soap, castor oil sulfate ester salt, sulfate ester salt of argyl alcohol having 8 or more carbon atoms, nitrate ester salt of alkyl allyl ether, polyoxyethylene Examples include sulfate ester salts of alkyl ethers. Among these, aliphatic or aromatic sulfonates are excellent in their low foaming properties. Nonionic surfactants include ethoxyaliphatic fluorinated carbon, ethoxylated vegetable oil, ethoxylated aliphatic alcohol, polyoxyethylene aliphatic alcohol, ethoxylated alkylphenol, tetramethyldecynediol,
Examples include sorbitol and sorbitan derivatives. The HLB of these nonionic surfactants ranges from 10 to 1.
8 is the most useful.

Generally, the amount of wetting agent added is 0.05 to 5 in the plate surface protectant.
The amount is preferably 0.1 to 2% by weight.

Addition of acids and other inorganic salts adjusts the pH and enhances the hydrophilic effect of the substrate. Examples of acids include phosphoric acid, citric acid, oxalic acid, tartaric acid, boric acid, aliphatic or aromatic sulfonic acids, and organic phosphonic acids. Other inorganic salts include sodium nitrate, sodium sulfate, calcium nitrate, magnesium nitrate, magnesium sulfate,
Sodium phosphate, ammonium phosphate, ammonium nitrate, ammonium sulfate, sodium acetate, sodium tartrate, mono, di and trisodium phosphate, mono, di and triammonium phosphate, and the like are useful.

The amount of these acids and other inorganic salts to be added is such that the solution containing these acids and other inorganic salts will not corrode the plate. Generally, an acid or other inorganic salt is added to adjust the pH to about 2.5 to about 9.5. Among these, phosphoric acid and phosphate salts are the most useful.

The plate surface protective agent of the present invention can be used for various lithographic printing plates, but in particular, a photosensitive lithographic printing plate (preliminarily imparted with photosensitivity) having an aluminum plate as a support and a photosensitive layer thereon is used. It can be suitably used for a lithographic printing plate obtained by imagewise exposure and development of a printing plate (called a PS plate). Preferred examples of such PS plates include those made of diazo resin (a salt of a condensate of p-diazodiphenylamine and paraformaldehyde) and shellac as described in British Patent No. 1,350,521. GB 1,460,978 and GB 1,505,7 in which a photosensitive layer consisting of a mixture is provided on an aluminum plate.
39, in which a photosensitive layer made of a mixture of a diazo resin and a polymer having hydroxyethyl methacrylate units or hydroxyethyl acrylate units as main repeating units is provided on an aluminum plate. Negative PS version, and JP-A-1985
This includes a positive PS plate in which a photosensitive layer made of a mixture of an o-quinone diazide photosensitive material and a novolak type phenol resin is provided on an aluminum plate, as described in Japanese Patent No. 125,806.

Further, there are PS plates in which a photosensitive layer of a photocrosslinkable photopolymer is provided on an aluminum plate as specifically shown in U.S. Pat. No. 3,860,528, and U.S. Pat.
A PS plate in which a photosensitive layer of a photopolymerizable photopolymer composition as described in the specifications of No. 072,528 and No. 4,072,527 is provided on an aluminum plate, British Patent No. 1, No. 235,281 and No. 1,495,8
Also preferred is a PS plate in which a photosensitive layer made of a mixture of azide and a water-soluble polymer is provided on an aluminum plate as described in each specification of No. 61.

Next, an example of the use of the plate surface protective agent of the present invention when a PS plate is used will be described.

First, the PS plate is imaged exposed and then developed to create a lithographic printing plate. After washing this lithographic printing plate with water and squeezing the water on the plate surface, pour an appropriate amount of the plate surface protectant of the present invention onto the plate surface,
Rub this with a sponge to coat the entire surface of the plate. This protects the non-image areas on the plate surface and allows the lithographic printing plate to be stored. To start printing, the gum on the plate is washed off with water, and then printing is carried out according to the normal procedure.

By using the plate surface protective agent of the present invention, there is no need to use oil-based protective ink, which was conventionally used to maintain the oil-sensitivity of the image area, in the plate-making process, which is extremely advantageous in terms of workability and prevention of drainage contamination. becomes. Furthermore, during printing, it is possible to immediately obtain sufficiently clear printed matter without producing many defects as in the conventional method.

This will be explained below using examples.

Example 1 140 parts by weight of dextrin with a water-soluble content of 95% or more (cream dextrin manufactured by Matsutani Chemical Industry Co., Ltd.) and 60 parts by weight of dextrin with a water-soluble content of about 90% (white dextrin manufactured by Matsutani Chemical Industry Co., Ltd.) were heated at 40°C. It was dissolved in 800 parts by weight of water heated to . After cooling to room temperature, 5 weights of a 33% aqueous solution of sodium isobutylnaphthalene sulfonate, 2 parts by weight of sodium hexametaphosphate, and 2 parts by weight of primary ammonium phosphate were dissolved to prepare a printing plate protectant of the present invention.

On the other hand, naphthoquinone-1,2-diazide-5 of polyhydroxyphenyl obtained by condensation polymerization of acetone and pyrogallol is described in Japanese Patent Publication No. 43-28403.
- A photosensitive liquid was prepared by dissolving 1 part by weight of a sulfonic acid ester and 2 parts by weight of a novolak type cresol formaldehyde resin in 40 parts by weight of methyl cellosolve. Thickness 0.2
A grained aluminum plate of mm was thoroughly washed and dried, and the photosensitive solution was coated on it using a rotary coater and dried to produce a positive-positive type PS plate having a photosensitive layer of about 2.0 g/m2, The film was exposed using a halftone positive film, developed with a 3% by weight aqueous sodium silicate solution, washed with water, and dried.

The above printing plate was divided into three parts, one of which was coated with 14°Be gum arabic (approximately 27% aqueous solution of gum arabic), which is conventionally used as a plate surface protectant, and the excess was wiped off with a cloth (sample A).

The other one was coated with the previously prepared plate surface protectant of the present invention, and the excess was similarly wiped off with a cloth (Sample B).

On the other one, a plate surface protectant obtained by removing sodium hexametaphosphate from the previously prepared plate surface protectant of the present invention was applied, and the excess was wiped off with a cloth (Sample C).

Samples A, B, and C were placed in a constant temperature and humidity chamber at a temperature of 60°C.
After storing it for a day, remove the plate protectant in the usual way.
Printing was carried out on an offset printing machine according to the usual method.

The number of defective sheets until clear prints were obtained was 35 for A, 5 for B, and 5 for C. Regarding the ease of staining during printing, A and B were not stained easily, but C was easily stained.

Sample B using the plate surface protectant according to the present invention was excellent in both the oil-sensitivity of the image area and the oil-insensitivity of the non-image area. Furthermore, when the plate surface protectant was applied, the coated image quality was satisfactory for both A and B, but in C, streaks were noticeable after wiping with a cloth.

Example 2 60 parts by weight of dextrin with a water-soluble content of 95% by weight or more, 160 parts by weight of Amicol 1B (manufactured by Nippon Chemical Co., Ltd.) which is a soluble starch with a water-soluble content of 95% by weight or more, 4 parts by weight of sodium hexametaphosphate, phosphorus. 1 part by weight of acid, 5 parts by weight of a 20% aqueous solution of sodium dioctyl sulfosuccinate, and 77 parts by weight of water.
A plate surface protective agent was prepared by dissolving the mixture in 0 parts by weight. This was used in the same printing plate as in Example 1.

As a result of printing with an offset printing machine, the number of defective sheets until clear prints were obtained was 5, and no staining occurred at all, and the performance as a plate protection agent was satisfactory.

Example 3 30 parts by weight of dextrin with a water-soluble content of 95% by weight or more, 80 parts by weight of Structan, 1-hydroxyethane-1,1
- 2.5 parts by weight of a 50% aqueous solution of diphosphonic acid, 5 parts by weight of sodium isopropylnaphthalene sulfonate, 1 part by weight of primary ammonium phosphate, 1 part by weight of sodium hexametaphosphate
Parts by weight and 0.05 parts by weight of an aqueous emulsion solution (solid content 40% by weight) of silicone oil were dissolved in 800 parts by weight of water to prepare a plate surface protectant.

On the other hand, a negative PS plate made of diazo resin described in Example 7 of Japanese Patent Publication No. 55-34929 was exposed, developed, washed with water, and dried in the same manner as described in Example 7, and then divided into three parts. . One of them was coated with 14°B'e gum arabic using a gum coater (G800-II, manufactured by Fuji Photo Film Co., Ltd.) (sample A). On the other side, the plate surface protectant prepared earlier was applied using a gum coater (Sample B
).

The remaining printing plate was coated with a plate protective agent obtained by removing sodium hexametaphosphate from the previously prepared plate protective coating using a gum coater (Sample C). A, B and C as in Example 1
After storing the three samples in a constant temperature and humidity machine at a temperature of 45° C. and a humidity of 85% for 7 days, they were processed in a conventional manner and printed using an offset printing machine.

The number of defective sheets until a clear print is obtained is 250 sheets for A and 250 sheets for B.
There were 18 sheets of paper and 20 sheets of C, but C was easily stained. On the other hand, B was extremely satisfactory. Furthermore, when the plate surface protectant was applied with a gum coater, the coated surface quality was satisfactory for both A and B, but in C, coating unevenness by the coater was noticeable.

Example 4 30 parts by weight of dextrin with a water-soluble content of 95% or more and soluble starch Amicol 1B (manufactured by Nippon Deka Chemical)
80 parts by weight were dissolved in 800 parts of water at a temperature of 40°C, and then cooled, 1 part by weight of sodium laurylbenzenesulfonate, 2 parts by weight of sodium hexametaphosphate, 2 parts by weight of citric acid, 5 parts by weight of methanol, and p-oxybenzoic acid. A plate surface protectant was prepared by dissolving 0.1 part by weight of ethyl acid. Example 3
When this was used as a plate surface protectant for the printing plates used in Example 3 in the same manner as in Example 3, the number of defective sheets until clear prints were obtained even after being stored for 7 days at a temperature of 45 degrees Celsius and a humidity of 85% was No staining occurred after 20 sheets, and the performance as a plate surface protectant was extremely satisfactory.

Claims (1)

[Claims] (a) One or more selected from the group consisting of degistrin, soluble starch, water-soluble cellulose ether, water-soluble vinyl polymer, pullulan and pullulan derivatives, sterapic, structan, and alginate, substantially soluble in cold water and a film-forming water-soluble organic polymer compound 5 to 35
% by weight and (b) 0.02-2% by weight of an alkali metal salt or ammonium salt of hegysametaphosphate.