Introduction to the classification of CTP plates
With the increasing development and application of CTP technology, insiders realize that CTP plates are a core part of this technology. Compared with the traditional plate making process, the processing of CTP plates is a bit more complicated, but its remarkable printability is unmatched by traditional plates, such as the quality of outlets. For this reason, the market for CTP is rising. There are about 30 CTP systems in the UK, and there are about 400 sets worldwide. According to DuPont, it will increase to at least 5,000 units by the year 2000. Therefore, understanding the CTP plate has become more and more important. For the time being, there are mainly five different types of CTP plates, the performance difference between them is very large, and each plate has its own characteristics.
1. Silver salt diffusion transfer type
This type of plate is adapted to a variety of lasers, such as argon ion blue laser, yttrium aluminum garnet laser, ruby laser, etc. due to the use of diffusion transfer imaging technology.
Principle: When the blank part sees light, the light part is dissolved by the developer during development, and the image part which does not see light forms a conjugate on the core layer, and the residual part of the blank part is washed with warm water, and then the oil part is processed by the image part. .
Features: Similar to silver halide film, good sensitivity, fast exposure, moderate contrast, light source is low intensity, low energy consumption laser, CTP plate from different manufacturers is compatible with chemical solution formulation.
Second, the polymer compound type
The polymer compound type CTP plate has a printing suitability similar to that of the conventional PS plate.
Composition: roughened aluminum plate, polymer compound layer, PVA layer. The polymer compound layer includes a sensitizer, a polymerization monomer, a polymerization initiator, a binder, and the like.
Principle: When exposed, the sensitizer absorbs the energy of the laser and, together with the initiator, produces a polymeric group. Before the development, the PVA layer of the unvisited portion is washed off, and the high-sensitivity polymer layer is dissolved by the alkaline developing solution. After the development is completed, the PVA is completely eliminated by the brush. Finally, the plate is washed with a synthetic resin solution, and the synthetic resin not only improves the hydrophilicity of the blank portion, but also enhances the lipophilicity of the image portion, and can be printed after drying. It is worth noting that after the end of the exposure, the polymerization reaction still lasts for several hours. At this time, it is generally stabilized by infrared rays, and the defects of the plate can be removed by the aging effect of infrared rays.
Features: good printability, relatively clean process, after printing, the printing durability is considerable, the printing plate is scratched and brushed.
Third, silver salt emulsion and polymer compound composite type
The composite type (abbreviation) takes into account the advantages of the two previous printing plates.
Composition: roughened aluminum plate, PS photosensitive layer, adhesive layer, silver salt emulsion layer.
Principle: The first exposure, the formation of silver salt latent image, development, rinsing, resulting in a protective layer. Then the second exposure, the polymer layer is seen, the mask is washed away with a brush, the polymer layer is developed with an aqueous solution, and then rinsed with water. After being dried and dried, it can be printed on the machine.
Features: The processing process is complicated, and the chemical sewage is added, but the advantages are also obvious; the energy of the light source is lower than that of the single polymer type, the stability of the latent image is improved, the printing suitability is good, and the printing durability is large after baking. .
Fourth, spray mask type
The fourth CTP plate utilizes spray or spray technology.
Composition: A conventional PS plate with a thin layer of soluble or waxy layer.
Principle: The inkjet head of the CTP system is used to inkjet, expose, and remove the mask, and the subsequent processing is the same as the conventional ps version.
Features: Because it uses the regular PS version, no additional equipment is required, it is the most economical CTP plate.
Five, thermal type
The heat-sensitive CTP plate has a large selection of technologies such as heat-dissolving type, thermal etching type, photo-etching type, thermal cross-linking type, and degradable type. The heat-sensitive printing plate has both direct imaging and through the mask layer. Indirect imaging. The following two types of thermal CTP versions are described below.
1, hot melt type
Composition: light source, aluminum plate without need for roughening, ink layer, PVA layer (for conventional offset printing), silica gel (for waterless offset printing).
Principle: Using a semiconductor laser diode, the image portion is melted to expose the oleophilic layer below, and the residue on the plate is removed to prepare for printing on the machine.
Features: Non-chemical treatment process, from the perspective of environmental protection, it is especially worth promoting the use of the thermal CTP version. Second, you can work in the bright room. As far as the Pearl type is concerned, the print durability is slightly lower (50,000 prints), but it has now increased to 100,000 impressions.
2, heat cross-linking type
Composition: roughened aluminum plate, single layer PS photosensitive layer.
Principle: After a certain temperature is reached by the heat of infrared rays instead of the spectrum, some of the polymers in the photosensitive layer undergo thermal crosslinking reaction to form a latent image; reheating causes the molecular compounds in the graphic part to further crosslink and reflect. It is because the graphic portion is not dissolved in the alkaline developing solution. It is worth mentioning that the blank portion also undergoes partial reaction during preheating, so the image of the blank portion is removed during development. If the temperature is too high, a hot mist will form on the plate; if the temperature is too low, the image will be faded or weakened.
Features: There is almost no relationship between exposure time and exposure energy. In other words, below the energy threshold, external conditions do not affect the quality of the plate; beyond the energy threshold, the size and clarity of the dots are unaffected. Therefore, there is no underexposure and overexposure; the nature of the image is very stable, even after six months of exposure, the plate is still available; in addition, the heat-crosslinking plate has low sensitivity to natural light. Therefore, it can work under the bright room, and only conventional plate making equipment is needed for processing.