At present, there are four main types of CTP plates that dominate the market: silver salt type, photopolymerization type, thermal sensitive type (thermal imaging type) and non-treatment type. Below we first look at the characteristics of these plates and their advantages and disadvantages.
The photopolymer CTP plate is mainly composed of aluminum plate base, photosensitive layer and protective layer, in which the photosensitive layer is mainly composed of film resin, infective material, photoinitiator, monomer or oligomer, stabilizer and other additives. The protective layer is the polyvinyl alcohol oxygen isolation layer, which is mainly used to block the polymerization of monomers or oligomers. The imaging principle is that, after the plate is scanned by the laser light source, the sensitizing material in the photosensitive layer of the light part first absorbs the photon energy into the excited state, and then transfers the energy to the photoinitiator. The unseen part is removed by development and forms a blank part. It should be noted that before developing, the protective layer of the unseen part should be washed off first, and then the high-sensitivity polymer layer should be dissolved with alkaline developer solution. After developing, the protective layer should be completely removed with a brush. Finally, the page was scoured with synthetic resin solution. The synthetic resin could not only enter the hydrophilicity of the blank part, but also enhance the hydrophilicity of the picture and text part.
Characteristics of photopolymerized CTP plates
(1) the photoreceptor layer of the photopolymerized CTP plate is very thin, and the picture and text part and blank part are on the same plane, which belongs to the traditional offset printing type, has a high sensitivity, and the plate making speed is fast.
(2) the developer of photopolymerized CTP plate is alkaline, while the film forming resin and monomer or oligomers in the photosensitive layer have certain acidity, which can be dissolved in alkaline solution and removed by development, and the alkaline developer has little pollution, which is conducive to environmental protection.
(3) the photopolymerized CTP plate can use different photosensitive light sources, such as purple laser diode (410nm), argon ion laser (488nm), fdyag laser (532nm), infrared laser diode (830nm), etc. The cost is relatively low, and the photopolymerized CTP plate can withstand more than 1 million prints after being baked.