JPS5952078B2 - Desensitizing liquid for lithographic printing plates - Google Patents

Description

[Detailed description of the invention] The present invention is a planographic plate in which the surface layer is a zinc oxide-resin dispersion system.

This invention relates to a desensitizing liquid used for printing plates. An electrophotographic light-sensitive material having a photoconductive layer in which photoconductive zinc oxide is dispersed in an insulating resin such as a silicone resin or an acrylic resin is subjected to image formation by a conventional method, and then subjected to a desensitization treatment on the non-image area and lithographic printing. It is known to be used as a master.

Desensitizing liquids used in such treatments are often
P such as ferrocyanide or its water-soluble phosphate
The main component is H buffering agent. This ferrocyanide contains Fe(CN)3" and Fe(CN)H" in the liquid.
It dissociates into each ion and exists in equilibrium with these ions. The desensitizing liquid in this condition is zinc oxide~
When in contact with the resin-dispersed photoconductive layer, each ion in the desensitizing liquid reacts with the originally oil-sensitive zinc oxide exposed in the non-image area, thereby desensitizing it. However, in conventional desensitizing liquids, the ferrocyanide deteriorates significantly, which not only causes discoloration and quality deterioration of the liquid, but also causes so-called gear stains and background stains on printed matter.

That is, ferrocyanide undergoes oxidation and/or dissociation, especially upon exposure to light, to form Fe(CN)3'' and Fc(CN).
) H'', which creates an equilibrium between each ion, and a small amount of Fe''
It was discovered that ゛ and Fe'''''' coexist. Each ion combines to form a deep blue color, which discolors the solution, and precipitates to further dissociation upon equilibrium maintenance;
As a result, the value of the corresponding active ingredient decreases and precipitation spreads. Other discolorations and precipitation result from the oxidation of ferrocyanide to ferricyanide and/or the formation of brown complex compounds of ferric ferricyanide. Thus, the effectiveness of the conversion solution, ie, its ability to react with the zinc oxide and render the non-image areas hydrophilic, is gradually lost. The present invention uses amino acids or water-soluble salts thereof in place of ferrocyanide to create a desensitized lithographic printing plate with excellent preservability that does not deteriorate over time and provides printed matter free from gear stains and background stains. It provides liquid.

That is, the desensitizing liquid of the present invention is characterized in that its main components are an amino acid or a water-soluble salt thereof and a water-soluble phosphate.

Amino acids or their water-soluble salts are used like conventional ferrocyanides (zinc oxide - substances that act on the resin-based photoconductive layer to desensitize non-image areas, but they do not deteriorate over time like ferrocyanides). It has the feature of not having any

Such amino acids or water-soluble salts thereof include L-glutamic acid, L-aspartic acid, L-alanine, L-glycine, L-glutamine, L-furin, γ-aminolagic acid, L-asparagine, lysine, and leucine. , cysteine, histidine, methionine, ammonium salts, or alkali metal salts thereof. The appropriate amount to be used is about 10 to 50% by weight based on the total solid content. Water-soluble phosphate is used as a pH buffering agent, and the amount used is preferably about 20 to 80% by weight based on the total solid content.

These salts include primary ammonium phosphate, secondary ammonium phosphate, tertiary ammonium phosphate, and secondary ammonium phosphate.
Examples include soda, tertiary soda phosphate, and the like. In addition to the above components, various organic or inorganic acids can be used as pH regulators in the present invention.

These acids include, for example, phosphoric acid, tartaric acid, malic acid,
These include malonic acid, acetic acid, pyrophosphoric acid, and oxalic acid. The amount used is preferably about 10 to 50% by weight based on the total solid content. The desensitizing liquid of the present invention can be used not only for desensitizing the surface of a zinc oxide-resin dispersion photoconductive layer, but also as a dampening solution during lithographic printing. When used as a desensitizing solution, the concentration is preferably about 80 to 100%, and when used as a dampening solution, the concentration is about 30 to 50%.
Examples and comparative examples are shown below.

Example 1 L-Glutamic acid 10g Primary ammonium phosphate 10g Secondary ammonium phosphate 20g Water
500 ml was thoroughly mixed and dissolved, and the pH was adjusted to 5 with taenoic acid to obtain a desensitized liquid.

For comparison, 10 g of potassium ferrocyanide, 1st phosphoric acid
10 g of ammonium, 20 g of ferric ammonium phosphate,
0.5g of ethyl-17enediaminetetraacetic acid and 35g of citric acid
A desensitizing liquid consisting of (Comparative Example 1), a desensitizing liquid consisting of 10 g of potassium ferrocyanide and 10 g of polyvinylsulfonic acid (Comparative Example 2), and 10 g of potassium ferrocyanide.
A desensitizing solution (Comparative Example 3) consisting of 20 g of sodium sulfite and 20 g of sodium sulfite was prepared.

After storing each of the above desensitizing solutions at room temperature and humidity for 1, 3, 5, 8, and 10 months, absorbent cotton was impregnated to treat the photoconductive layer surface of a commercially available zinc oxide-resin dispersion electrophotographic photosensitive material. The lithographic printing plates were then set in a lithographic printing machine and 300 yen each
0 sheets were printed. The results are shown in the table below. I used a desensitizing liquid instead.

Note that the dampening water used during printing is different* However, the desensitizing solution changes from pale yellow to dark green on the 6th day of preparation, and a considerable amount of precipitate appears, making it easy for printed matter to become smudged.

Example 2 A desensitizing solution obtained by using the same amount of L-aspartic acid in place of L-glutamic acid in Example 1 showed similar results.

Example 3 A desensitizing solution obtained by using the same amount of L-alanine in place of L-glutamic acid in Example 1 also showed good results.

Example 4 The desensitizing solution obtained in Example 1 using L-glycine instead of L-glutamic acid also had good storage stability.

Example 5 A desensitizing solution obtained by using the same amount of L-glutamine in place of L-glutamic acid in Example 1 showed similar results.

Example 6 A desensitizing solution obtained by using the same amount of L-aminolagic acid in place of L-glutamic acid in Example 1 was similarly good.

Example 7 A desensitizing solution obtained by using the same amount of L-asparagine in place of L-glutamic acid in Example 1 also showed good results.

Example 8 A desensitizing solution prepared using the same amount of L-proline in place of L-glutamic acid in Example 1 was similarly good.

Claims (1)

[Claims] 1. A desensitizing liquid for lithographic printing plates whose main components are an amino acid or a water-soluble salt thereof and a water-soluble phosphate.