After knowing the reason for the low printing durability of the thermal CTP plate, we must first understand the basic principle of thermal CTP plate imaging: photodecomposition chemical reaction occurs in the exposed part of the photosensitive layer of the printing plate, and it dissolves in the developer (alkaline) during development. , to expose the hydrophilic layer, the unexposed part does not react, and remains to form graphic information after development. The direct reason for the low printing durability of thermal CTP plates is that some dots of graphics and text are separated from the plate base, and the screen is dropped. Part of the dots of the text are peeled off after physical and chemical corrosion.
Based on the analysis of the above reasons, the possible reasons and solutions for the low printing durability of thermal CTP plates are as follows:
1. During the development transition, the dot loss is large, and the solid combination between the graphic part of the heat-sensitive CTP plate and the plate base is destroyed (after a long time of development, the photosensitive layer can be dissolved in an alkaline developer).
The way to solve the low printing durability in this respect is to use the signal bar to control the quality of CTP printing and develop digitally to ensure the quality of CTP printing.
2. The protective glue used after the heat-sensitive CTP plate is exposed does not match the printing plate (the heat-sensitive CTP plate will not be printed on the machine for a long time, the hydrophilic layer of the printing plate is easy to oxidize, and the printing plate must be coated with protective glue), resulting in Loss of text information outlets.
The solution to this low run rate is to use a matching plate protection solution recommended by the plate supplier.
3. The pH value of the printing dampening solution is too high (normal printing pH is around 5), which is easy to corrode the graphic part and causes physical and chemical changes (the photosensitive layer of the printing plate can be dissolved in alkaline developing solution), which eventually leads to a decrease in the printing durability. However, it must be noted that when the pH value of the fountain solution is low, it will corrode the hydrophilic layer of the printing plate.
Ensure that the pH value of the printing fountain solution is stable at about 5, and prevent the photosensitive layer of the printing plate from undergoing physical and chemical changes and dissolution. This is the most effective way to solve the low printing durability described above for heat-sensitive CTP plates.
4. The alcohol resistance of the photosensitive layer of the heat-sensitive CTP plate is worse than that of the traditional PS, which causes the printing plate to drop off during the printing process. Therefore, we slightly reduce the content of alcohol or isopropanol while ensuring the pH value and conductivity of the fountain solution are stable.
5. During the printing process, the printing pressure is improper (the blanket and the plate roller directly rub against the printing plate), and the friction with the printing plate causes the screen to drop (less likely). Restore printing pressure to the standard value (less likely).
6. The quality of the plate, the photosensitive layer of the graphic information is weak, and it is not wear-resistant during the printing process. Therefore, different batches or different brands of plates should be purchased for printing experiments.
Huida Print-All Technology company is an advanced and professional manufacturer of producing printing plates, mainly selling CTP, CTCP, and PS plates as well as offering ODM/OEMs, especially for the offset. For more information, please click the official website link here: https://www.huidaoffsetplate.com/.