JPH0517880B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to a desensitizing treatment liquid for offset printing. In particular, the present invention relates to a desensitizing solution used when printing an offset printing plate by electrophotography. (B) Prior art Generally, in offset printing, a printing plate having an oleophilic image area and a hydrophilic non-image area is used for printing, but since the photosensitive surface of the offset master is originally oleophilic, it is not necessary to undergo lipophilic treatment. If you print without doing this,
Ink also adheres to non-image areas, making it impossible to obtain clean prints. Therefore, before printing, it is necessary to desensitize the non-image area of the master to make it hydrophilic. Therefore, the characteristics that a desensitizing treatment liquid should have are that it exhibits a desensitizing effect on all masters made using different development methods and developers, that there is no performance deterioration during long-term storage, and that it does not desensitize during printing. In addition to the fact that it does not show a decrease in the degreasing ability, it can be desensitized easily and in an extremely short period of time. For this purpose, processing liquids conventionally used in electrophotographic offset masters have been mainly composed of hexacyanoferric salts such as ferrocyanate and ferricyanide salt. In particular, processing solutions containing iron hexacyano salts as a main component have a wide range of latitude depending on the processing conditions.
Good printed matter could be obtained even when circulation was performed or when the processing solution was manually applied to the plate material (hand etching). However, hexacyanoferrous salts may be decomposed by heat or light to generate free cyanide, and desensitizing treatment solutions containing hexacyanoferric salts as a main component have had problems in terms of pollution. For this reason, a cyanide-free type desensitizing solution containing inositohexalic acid ester or its salt as a main ingredient has been proposed, but a solution of sufficiently satisfactory quality has not yet been completed. A disadvantage of using inositohexalic acid ester or its salt as a desensitizing main agent is that the rate of desensitizing film formation is slow. As a specific example, in hand etching, which is performed by soaking a desensitizing liquid in absorbent cotton or sponge and applying it to the surface of the plate by hand, the desensitizing liquid is sufficiently applied to the plate surface, so cyan is removed. The difference in desensitization processing ability with the cyan type is not so noticeable, but when processed using automated desensitization processing equipment (e.g. Mitsubishi Paper Etching Converter OH-11, etc.), there is a difference in ability with the cyan type. There were cases where printed matter was smudged. On the other hand, in consideration of these points, a processing solution with a high film formation rate is disclosed in Japanese Patent Application Laid-Open No. 59-207290.
This is a combination of inositohexalic acid ester or its salt and acidic colloidal silicic acid having a SiOH group and a particle size of 40 mμ or less, and has good rapid film forming properties. However, if this processing liquid is passed through an automated desensitizing device twice or if the processing liquid is applied to the plate surface by hand, the desensitizing process may extend to the image area (toner area). However, the disadvantage is that the ink does not adhere to the image area. (C) Purpose of the Invention The present invention aims to improve the slow desensitizing film formation rate of cyanide-free type processing solutions such as inositohexalic acid esters or their salts, and is easy to manufacture. and the quality is stable,
A further object of the present invention is to provide a desensitizing liquid for lithographic printing that does not cause background smudges on printed matter and has good ink coverage in one pass through an automated desensitizing device. (D) Structure of the Invention As a result of intensive studies by the inventors to solve the above-mentioned problems, the following method was discovered and the present invention was completed. That is, the present invention combines three components, phosphate, ammonium compound, and acidic colloidal silicic acid with a particle size of 40 mμ or less, in a desensitizing treatment solution, and the synergistic effect of these ingredients provides excellent desensitizing ability. It shows good ink adhesion in the printed area and can significantly improve printing durability. Here, to explain the compounds constituting the present invention, phosphates include isosinic acid, phosphatidic acid and its derivatives, sugar phosphoric acid compounds such as glucose-6-phosphoric acid, and organic compounds such as 2-cyanoethyl phosphate. Phosphoric acid and its salts, inorganic phosphates such as dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, calcium dihydrogen phosphate, sodium pyrophosphate, etc. Among inorganic phosphates, dihydrogen phosphate is particularly preferred. . Examples of ammonium compounds include inorganic substances such as ammonium sulfate, ammonium sulfamate, ammonium nitrate, and aqueous ammonia, ammonium salts of organic acids such as ammonium formate, ammonium citrate, ammonium malonate, and ammonium tartrate, ammonium alginate, carboxymethyl cellulose ammonium salt, and alkyltrimethyl ammonium. Examples include ammonium salts of chloride, dimethylaminoethyl methacrylate polymer, and organic quaternary ammonium salts. Colloidal silicic acid is so-called colloidal silica, and it may be prepared from water glass or may be obtained by modifying the surface of these colloids. The amounts of the above-mentioned substances constituting the treatment liquid of the present invention are 1 g to 300 g of phosphate, more preferably 5 g to 100 g, and 0.1 g of ammonium compound in the treatment liquid 1 of the present invention.
g to 200 g, more preferably 1 g to 80 g, and colloidal silicic acid 0.01 g to 20 g, more preferably 0.03 g.
~10g. There are no particular restrictions on the order of dissolution of the treatment liquid of the present invention, but preferably, after completely dissolving the phosphate and ammonium compound in water, the pH is adjusted to 3.0 to 6.0 with an inorganic or organic acid or aqueous ammonia. After that, it is better to add colloidal silicic acid. In addition to the above ingredients, this treatment liquid contains ethylene glycol, glycerin, carboxymethyl cellulose, alginate, gum arabic, etc. as a wetting agent, EDTA, amines, etc. as a rust preventive agent, and salicylic acid, bromonitroalcohol, trichloride, etc. as a rust preventive agent. It can be used by adding an appropriate amount of ethylenetetramine hexaacetate or the like. When printing using this treatment liquid, the treatment liquid can be diluted 6 to 10 times with water and used as a dampening solution. Next, the present invention will be explained with reference to Examples and Comparative Examples. Example 1 Potassium dihydrogen phosphate 3.0g Ammonium sulfamate 1.0g Ammonium citrate 1.0g Acidic colloidal silicic acid (particle size 20mμ) 0.10g Disodium ethylenediaminetetraacetate 0.50g Glycerin 3.0g Distilled water 91.7g Example 2 Pyrophosphoric acid Sodium 3.0g Ammonium tartrate 2.0g Acidic colloidal silicic acid (particle size 20mμ) 0.20g Ammonium alginate 2.5g Inositol 0.5g Distilled water 91.8g Example 3 Sodium 2-aminoethyl phosphate 4.0g Ammonium sulfate 2.0g Acidic colloidal silicic acid (granular 0.20g Sorbitol 3.0g Distilled water 90.8g Comparative example 1 Sodium monohydrogen phosphate 3.0g Sodium citrate 2.0g Acidic colloidal silicic acid (particle size 20mμ) 0.20g Glycerin 3.0g Distilled water 91.8g Comparative example 2 Ammonium nitrate 2.0 g Acidic colloidal silicic acid (particle size 20mμ) 0.20g Ammonium citrate 1.0g Glycerin 3.0g Distilled water 93.8g Comparative example 3 Ammonium dihydrogen phosphate 3.0g Ammonium formate 1.5g Sorbitol 3.0g Distilled water 92.5g Comparative example 4 Phosphoric acid Triammonium 3.0g Ammonium sulfamate 1.0g Acidic colloidal silicic acid (particle size 50mμ) 0.50g Glycerin 3.0g Distilled water 92.8g After forming an image on an electrophotographic light-sensitive material containing a zinc oxide resin dispersion according to a conventional method, A lithographic original plate was prepared by processing with the above-mentioned processing liquid, and printing was performed using a dampening solution diluted 6 times with water, and the results are shown in the table.

[Table] As shown above, in Examples 1 to 3, clear prints without background stains can be obtained, but in Comparative Examples 1 to 4, ink covers the entire master within 10 prints, resulting in clear prints. I couldn't get it.

Claims (1)

[Claims] 1. Phosphate and ammonium compound and particle size 40m
A desensitizing treatment liquid for offset printing, characterized in that it contains acidic colloidal silicic acid having a particle size of less than μ. 2 Phosphate concentration is 1 g/~300 g/, ammonium compound concentration is 0.1 g/~200 g/, and the above colloidal silicic acid concentration is 0.01 g/~20 g/
A desensitizing treatment liquid according to claim 1.