Formula Principle and Wetting of Offset Printing Plate Wetting Liquid

Offset printing plates have undergone the promotion stage of the use of protein plates, gravure plates, and PS plates. With the rapid development of printing technology and the popularity of multicolor high-speed machines, PS plates are popular and are suitable for some large-scale high-end printing products. Good performance, dark tone level, bright tone level reproduction ideal, PS version of the stability is good, not affected by the ambient temperature and humidity, long shelf life, easy to use, printing process is simple, easy to achieve data, standardized control , Has a good rate of India, and dot reproducibility, high resolution, good printability, less water, reducing the paper's flexibility and ink emulsification.

In general, the PS plate production process is: aluminum version of the decontamination process - electrolysis and grinding sand eye - anodizing - sealing hole - coating emulsion - drying - PS version.

1. PS version of the trachoma formation: PS version of the photosensitive resin film is relatively thin, and therefore require the PS version of the trachoma delicate and uniform, the current method of electrolysis more.

2. The purpose of the anodizing of the blank part of the PS plate: to form an oxide film on the aluminum alloy plate of the PS plate, thereby improving the mechanical strength, wear resistance and hydrophilicity of the aluminum alloy plate.

3. The purpose of the PS plate sealing hole is to block the pores of the oxide film and prevent the plate from being contaminated.

4. Surface structure of PS plate

1 positive PS version

Graphic Part - Diazo Compound Blank - Anodized Film

2 negative PS version

Graphic section - Lac layer Blank section - Anodized film

The photo-sensitive film of the positive-type PS plate is decomposed by light, and the photo-sensitive film of the negative PS plate is photo-polymerized. Shaiban process flow: exposure - development - washing - ink and finishing - glue. The PS version is flat from the macro perspective, but it is microscopically inconsistent. The positive version is microscopically speaking: The graphic part is high and the blank part is low. The negative version is microscopically speaking: The graphic part is low, and the blank part is high.

First, PS version of the wetting liquid formula principles and requirements

The formulation of the PS version of the wetting fluid must follow good wetting properties, the emulsification value cannot be less, and the pH of the solution is appropriate. The key is to solve the relationship between the wetting property and the emulsification value. In general, the wetting property is good and the emulsification value is large.

1.PS version wetting fluid must be able to fully wet the layout, in order to achieve the purpose of wetting the PS plate layout, it is necessary to reduce the surface tension, add surfactants, wetting agents, surfactants (carboxymethyl cellulose cmc) . The polar groups in 6501 surfactant, gum arabic and carboxymethyl cellulose (cmc) molecules can be firmly adsorbed on the solid surface, form and complement the colloid layer, and the colloid layer itself has very good water absorption performance. Therefore, the wettability of the printing plate is improved, and the emulsification is also not serious.

2. With cleaning ability.

Can wash the dirty spots on the surface of the PS plate, only add acidic substances such as: phosphoric acid, nitric acid, citric acid, etc. These acidic substances have the cleaning ability. The plate of original offset printing plate gravure plate is zinc alloy, 0.4cm thick. The graphic part of gravure plate is lac, the blank part is the inorganic salt layer, and the inorganic salt layer is added by the acidic substance in the water bucket, added in the clear water. Some electrolytes have an enhanced and stabilizing effect on hydrophilicity and oil resistance, such as phosphoric acid, phosphates, nitrates, and the like.

3 has a very good non-lipid capacity.

Added gum arabic, gum arabic has the role of hydrophilic colloids, the use of the non-lipid capacity of colloids and good water absorption capacity, to consolidate and stabilize the blank part of the four seals, and can reduce the amount of liquid fountain solution. At the same time, gum arabic also has the function of preventing the layout from oxidizing dirt and dirt and restoring the hydrophilicity of the blank part.

4. Can adapt to different climate changes. Add moisture absorbent and moisturizer.

1 Three hydroxyl groups of glycerol molecules can be adsorbed on the surface of the colloidal layer to help absorb the solution.

2 Polyethylene glycol is a good moisturizer. It can absorb moisture when it is shut down, and it is a good wetting agent to reduce the wear of the blank part of the printing plate.

3 The role of ethanol, ethanol (alcohol) (C2H5OH) can not only reduce the surface tension of the solution, but also use its volatility to make the paper absorb minimal moisture.

5. To stabilize the PH value. Adding buffer solvent, the hazard of PH value is too high: the network dot enlarges badly, the blank part is easy to get dirty, and the cleaning ability is poor. The hazard of PH value is too low: acidity is too large, corrosive to the printing plate, the printing plate's resistance to printing force is reduced, drying delays, the ink roller is easy to remove ink. The pH of the wetting fluid is preferably 4 to 5. Stable pH buffers such as: phosphoric acid and sodium dihydrogen phosphate have a buffering effect between them.

H3PO4→H+H2PO-4
NaH2PO4→Na++H2PO4

It generates a homoionic effect between the gates, inhibits hydrogen production, and stabilizes the pH.

In addition, both citric acid and sodium citrate have a cleaning action and a buffering action. [citric acid is a weak acid]

1 Citric acid H3C6H5O7
H3C3H6O7 H2C6H5O7 +H+
H2C6H5O7 HC6H5O7+H+
HC6H5O7
HC6H5O7H+
(The three-step ionization of citrate tribasic acid in solution, "" reversible reaction symbol.)

2 sodium citrate Na3C6H5O7 Na + +HC6H5O7
As most of the citrate HC6H5O73- changes in acidic medium, it is converted into HC6H5O72-ion, which produces a homoionic effect to maintain the proper pH, which is exactly in line with the acidity of the wetting fluid.

6. The loss of inorganic salt layer can be added. It is necessary to add acidic substances. The blank part of the PVA plate is the inorganic salt layer, and the wetting fluid must enrich the loss of the inorganic salt layer. The PS version does not need to be supplemented with inorganic salt layers. The blank part of the PS plate is an anodic oxide film, which is relatively stable to water and air. During the printing process, the electrolysis of the PS plate will not produce large wear.

(to be continued)