Offset Printing: CTP Plates VS PS Plate

 The plate used in the CTF process is mainly PS plate, which is pre-coated photosensitive plate, which is developed to adapt to the rapid development of lithographic printing and offset printing. The PS plate features high resolution, full dot reproduction, rich layers, easy-to-master ink balance, and high printing endurance. It is popular in the printing industry.

PS plate for offset printing is a kind of photosensitive offset printing plate material with multi-layer structure. It uses an aluminum plate as a support, and the aluminum plate is processed by a variety of processes. The common alloy is 1050 and1060 aluminum sheet. It has the following structures:

1. Rough surface particles: Rough surface particles are necessary for good printing plate. They can improve the adhesion to the exposure film, shorten the time of vacuuming, and reduce the occurrence of halo.

2. Sensitive layer: Compared with the different plate-making processes and the production processes of each plate manufacturer, the photosensitive layer will have a variety of different characteristics.

3. Hydrophilic layer: It can prevent the photosensitive coating from remaining in the micropores of the anodized layer, thus improving the hydrophilic properties and preventing the printing plate from being dirty during the printing process.

4. Anodized layer: The hardness, chemical stability and wear resistance of the aluminum plate is increased after anodizing treatment.

5. Grain structure: The electrolytic roughening process is used to form a fine grain structure on the surface of the aluminum base plate, which can make the printing plate have ideal dot reproduction conditions and good hydrophilicity.

6. Aluminum plate: The aluminum plate for making PS plate should be of stable size, high strength, and high purity.

Compared with PS plate, there are more types and varieties of CTP plates. The main types are silver salt, thermal and photopolymer printing plate.

The coating of the thermal CTP plate is composed of a temperature-sensitive polymer or ablation layer, which is mainly sensitive to infrared lasers from 800nm to 850nm. It can produce clean dots with clear edges, and basically no dot expansion or shrinkage.

In addition, the thermal plate can be baked to improve the printing durability, which is suitable for long printing or printing with UV ink. Therefore, thermal technology is more suitable for use in the commercial printing field.

Original Source: https://www.alumhm.com/a/offset-printing-ctp-plates-vs-ps-plate.html