The pre-painted photosensitive plate is referred to as the PS Plate, it is a kind of aluminum litho plates. PS plate refers to the printing plate that is pre-coated with a photosensitive layer on the aluminum plate and then sold to the printing house. It is a photosensitive adhesive made of diazo or azide, nitro and other photosensitive agents and resins. It is coated on the plate base and can be stored for later use after drying, so it is called a pre-coated photosensitive plate.
When using PS plate for printing, a series of processes from grinding to baking can be omitted, and it can be directly exposed and developed with the negative film. It has the advantages of simple operation, strong printing durability, stable performance and good quality. It has been widely used abroad, and there are also many production lines for PS plate in China, and the usage is further expanding.
According to the photosensitive principle and process of the photosensitive layer, the pre-coated photosensitive plate aluminum litho plates is divided into a positive PS plate and a negative PS plate.
The positive image type is represented by P, that is, the P type, which is printed with a positive image negative. The positive-type sensitizer is decomposed by using a diazo compound after being exposed to light, and then developed with a dilute alkaline solution to be dissolved, exposing the aluminum plate base, forming the blank part of the printing plate, that is, the non-graphic part, but the part that does not see light. The photosensitive layer has not undergone any change, nor is it dissolved by the dilute alkaline solution, and remains on the plate surface, forming the oleophilic printing part of the printing plate, which can be directly ink-friendly.
In addition, azide compounds are also used to decompose azide groups or change the solubility through hydrogen atom transfer, etc. Add macromolecular compounds such as linear phenolic resins to this photosensitive solution, so that the foundation of graphics and text is firm, without adding lipophilicity. Base paint is used for reinforcement. Therefore, this type of plate is also called inner type.
2, Negative PS plate
The negative image type is represented by N, that is, the N type, which is printed with negative image negatives. Negative-type sensitizers generally use diazo compounds to cross-link or polymerize after exposure to light to become insoluble in the developing solution, while the part that is not exposed to light is soluble in the developing solution. The photosensitive layer exposes the plate base and constitutes a hydrophilic blank part, while the insoluble substances in the visible part are lipophilic and become the basis for graphics and texts. Due to the low abrasion resistance and low printing resistance of this part, in order to improve this weakness, reinforcing base paint is applied on the lithographic, so this type of plate is called appearance.
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