a. Internal Transfer Plates A typical plate among these plates is the Silvalith plate supplied by Agfa. The plate consists of an aluminum plate base, a rinse core layer and a silver salt emulsion layer. During the imaging process, the diffusion of the silver salt after laser exposure forms a metallic silver salt coating on the surface of the unexposed aluminum base. This is the image part. The silver salt emulsification layer is then removed to expose the surface of the aluminum substrate to form a non-image area. Since the unexposed part is the final printed part, this is also a positive solar pattern plate, which should be exposed under red safe light with a wavelength range of 630nm to 680nm (laser range for argon ion lasers and laser diodes). , printing plate can withstand up to 10,000 India India.
b. External Transfer Plates Typical of this type of plate is Silver Digi-Plate from Mitsubishi, consisting of a substrate (paper or PET), a silver salt emulsification layer, and a rinse core layer. During the exposure and imaging process, the silver salt of the non-exposed areas is diffused, and the metallic silver is deposited on the top layer of the developing and rinsing core layer to form a graphic printing area. The non-graphic area is the exposed area (using a hydrophilic, stable gelatin emulsion Floor). This plate is a positive sun-type plate, its resistance to India can reach 10,000 to 20,000 India.
Typical photopolymer plates are Brilia LPA plates supplied by Fujifilm and Diamond LA-2 plates supplied by Mitsubishi. This plate is composed of aluminum plate, radical polymerization layer and outer layer.
The imaging process of the photopolymer type plate material is such that the exposed portion of the photopolymer layer undergoes a cross-linking reaction under the influence of the stimulated polymerization, is insoluble in the developer, and forms a graphic printed portion. Unexposed areas are washed away by the developer to form a non-image area.
Due to the sensitivity enhancement effect, the sensitivity of this plate is equivalent to 1 thousand times the sensitivity of ordinary PS plates. In order to prevent the generation of radicals in the photopolymer layer caused by contact with oxygen in the air, an oxygen-barrier outer protective layer is provided. Plates should be washed with alkaline aqueous developer under a red safety laser. This kind of plate can withstand up to 100,000 impressions.
Thermal reaction plate
a. Heat-Resistant Plates Typical of this plate is Kodak's 830 thermal plate, which consists of an aluminum plate substrate and a heat-sensitive cross-linking reaction layer. The imaging process is that the dye component capable of absorbing infrared light in the heat-sensitive cross-linking reaction layer generates heat after absorbing infrared laser light, and generates an acid by co-existing an acid generator through thermal decomposition. When the plate material is heated at a temperature of 130-140 degrees Celsius for about 30 seconds, a cross-linking reaction occurs at the exposed portion of the laser light. The soluble phenolic resin acts together with the generated acid to make the water-dissolving agent in the developer, thereby accelerating the printing area of ​​the image. Formation. The plate is a negative sun-type plate. The unexposed areas are washed away by the developer to expose the aluminum substrate, forming a non-graphical portion.
The heating process before exposure is not easy to control. The plate was processed with an aqueous developer under bright room conditions. This plate has a reproducible resolution of 4.6 microns, which is equivalent to a 600 line 1% range. When printing is not baked, the printing force is 200,000 impressions. After printing, the printing resistance can reach more than 100.
When the heat-reactive plate was first introduced, it was a sun-character plate of negative chart, which was later changed to a sun-positive pattern plate that was not preheated when the second-generation version came out.
b. Nail type plate
Representative of this type of media is the Pearl Plate supplied by Presstek. There are two types of media: fountain solution and no fountain solution. The waterless printing plate consists of a plate base (aluminum or PET), an ink receptive layer, a metal film layer and a silicone resin layer. The imaging process consists of heating the metal film with an infrared laser, and then removing the topmost oleophobic silicone layer exposing the ink-receptive layer to form a printed part of the image. The unexposed part of the silicone layer is a non-graphical part. The above process is done on the printing press as part of the printing process without the need for stamping operations. Plates are imaged under bright room conditions, with a resistance force of up to 50,000 impressions.
The water-based printing plate material also consists of 4 parts; plate base (aluminum or PET), ink-receptive layer, metal film layer and hydrophilic layer. The imaging process of the image part is the same as that of the anhydrous plate, but the non-graphic part is formed on the hydrophilic layer. During printing, the fountain solution adheres to the hydrophilic layer and the ink adheres to the ink-receptive layer.
Discolored Plates A typical discolored plate is Asahi's no-clean thermal plate, consisting of an aluminum plate and a photosensitive layer. The imaging process is as follows: The surface of the photosensitive layer that is originally hydrophilic is heated by a nearby infrared laser, and the pigment in the photosensitive layer absorbs heat to make it become an ink-receptive surface, and forms a graphic printing site. The unexposed part of the surface is composed of a hydrophilic resin, and after the fine sand treatment, the fountain solution is maintained and becomes a non-graphic part. This plate does not require punching, and it can withstand up to 50,000 impressions.
Composite Plate The representative composite plate is a CTX plate provided by Poly Light Co., Ltd. It is composed of an aluminum plate base, an ordinary PS plate photosensitive layer and a silver salt photosensitive layer. The imaging process is as follows: Firstly, the upper silver salt photosensitive layer is exposed to form an image mask. Then expose the mask part as if it were an ordinary PS version. The sensitivity of the plate is as high as that of the silver salt plate. And with the advantages of ordinary PS version.
The disadvantage of the composite plate is that the plate-making time is as long as that of the ordinary PS plate. The silver salt photosensitive layer needs to be developed and fixed, and then the emulsion layer is removed.
Concluding remarks The first computer-to-plate format was the silver salt diffusion transfer plate, which is still used in narrow-web printing. However, thermal-type plates are used more in wide-format printing. The plate is easy to handle in the light room c conditions, the resolution is relatively high and it is more resistant to printing.
It should be pointed out that computer-to-plate materials must not only meet all the requirements of platemaking, but also be comparable to ordinary PS version technology in terms of price, processing speed, work efficiency, and environmental protection. At present, the computer-to-platemaking technology still has unsatisfactory performance compared with the ordinary PS plate, and it is necessary to continuously improve the equipment and plate materials.
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