CTP plate and positive PS plate both use an aluminum plate base as a support. However, ordinary aluminum plates do not have hydrophilic and lipophilic properties due to their smooth surface and poor adsorption properties, and their low hardness does not meet the requirements of abrasion resistance for printing. Only after the surface roughening and anodizing can they be a good base for the printing plate.
In printing plates, the surface roughness is often referred to as the grain. The requirements of the CTP plate on the aluminum plate is quite different from those of the PS plate. In the production of the PS plate,after graining and anodizing, they don’t need the sealing treatment. But CTP plate is different.
The photosensitive material of the CTP plate is different from that of PS plate. Take thermal CTP plate for example. In addition to the heat-sensitive light material, other related materials are added such as the promoting and hindering solvent that has a dissolution-inhibiting effect on the thermosensitive imaging composition before exposure, and has the effect of improving development and imaging after exposure. Therefore, the thermal CTP plate must have a special hydrophilic layer.
The photopolymerization layer of the photosensitive plate is composed of photoinitiator system (photoinitiator, co-initiator, sensitizing dye), film-forming resin, photopolymerization monomer or prepolymer, additives, etc.
In order to improve the adhesion and developability of the photopolymerization layer of the CTP plate, an intermediate layer is also required between the plate base and the photosensitive layer. Due to the above circumstances, only the finer grain layer of the aluminum plate is conducive to the high quality of CTP plate.
For PS plate making, the surface roughness Ra value of the aluminum plate is 0.3μm. The Ra value of the aluminum base surface of the CTP plate is preferably about 0.2μm. The aluminum plate surface of the CTP plate is not allowed to have slag inclusion, black and white strips and large grain size.