Influence of fountain solution concentration on printing plate printing rate

Recently, we have found that the magenta version is extremely frayed when it comes to printing red and green color products (magenta and cyan are network cables). The number of prints of this product is 65,000 prints, and 7 red prints are shared, and some of the prints are still not very good. The main reason is that the PS version first wears badly from the bite when it is less than 10,000 prints each time. There has never been such a phenomenon. Generally, at least 50,000 seals can be printed on each plate. Analyze the cause of this situation. The pressure between the blanket cylinder and the plate cylinder is normal, and the liner of the blanket is intact. The phenomenon that the blanket has not been printed before (this is no problem with the blanket itself), the plate and the plate pad are both no problem. Checking the four relies on the printing roller did not find any problems, and there was no problem with the pressure between the printing plates. There was no problem with the printing roller itself and the pressure between it and the printing plate. Due to the urgency of the product, it only wastes the PS version to print it.

After repeated analysis, find the reasons. Hearing an assistant, he said, “When I changed the fountain solution today, I accidentally added some wetting powder to the sink of the magenta version. I didn’t care about it at that time. I thought that the dampening powder was more or less. How much relationship." To listen to him this way, the problem is self-evident.

The main component of the printing plate base used in offset printing is metallic aluminum, so it is not stable in acidic media. The dampening solution can produce mild corrosion on the surface of the aluminum plate only when it is a weak acid, resulting in the formation of a hydrophilic inorganic salt layer; if the pH of the dampening solution is too small (strongly acidic), the blank part of the printing plate will suffer from deep corrosion and coarse sand holes. It is not easy to form a strong hydrophilic layer, so that the blank part will affect the ink transfer due to the existence of more dampening fluid, and even the graphic part will be corroded and the bond with the plate base will be destroyed, making the dilute layer of oleophilic The compound layer is peeled off, resulting in the loss of dots and "off-page" phenomenon, thereby reducing the printing plate printing rate.

Nowadays, the plate material used in offset printing generally uses photodecomposition type PS plates. The diazo compound in the blank part of the plate is photolyzed and then removed by a weakly alkaline developing solution. The graphic part is the diazotide covered with the unsawn light by the printing plate film. Photoresist layer. If the pH of the fountain solution is too high, the diazo compound in the graphic part of the plate will be dissolved, resulting in incomplete graphics, which will affect the printing quality. This is one of the reasons for the decline in the print durability of the printing plate.
(Author: Wang Guangsheng)