Plate imaging technology (5)

Thermally cross-linked plates consist of a heat-sensitive coating and a hydrophilic plate base. The heat-sensitive coating is generally composed of a (alkali) water-soluble film-forming resin (eg, phenolic resin), a heat-sensitive cross-linking agent, and an infrared dye; the hydrophilic plate base can use the same aluminum plate base as the conventional PS plate. The role of the infrared dye is to effectively absorb the infrared laser light energy, and convert the absorbed light energy into heat energy, so that the temperature of the heat-sensitive coating can reach the reaction temperature of the heat-sensitive crosslinking agent; the effect of the heat-sensitive crosslinking agent is Due to the temperature, the film-forming resin reacts to form a spatial network structure, thereby losing the water-solubility of the heat-sensitive coating. Due to the spatial cross-linking effect, the heat-sensitive coating of the exposed area still remains on the plate as a lipophilic printing surface after the development process, and the unexposed area is removed so that the underlying hydrophilic plate base is exposed as a hydrophilic non- Printing surface. In order to further improve the effect of thermal cross-linking, some plates are often subjected to pre-heat treatment of the plate after exposure, thereby further deepening the thermal cross-linking effect (also an increase in the sensitivity of the increase in the mechanism). This type of plate is called a heat-crosslinked plate that requires preheating. The graphic area of ​​the thermal cross-linked plate is composed of a space-crosslinked polymer resin. Therefore, such plates usually have a very high mechanical strength and printability, and generally can print hundreds of thousands of copies, and are suitable for long-run printing. market.
Both thermal transfer plates and thermal phase change plates are processless CTPlates that can be printed without the need for chemical post-processing after imaging, and do not generate ablation debris during laser scanning imaging. And vapor and other waste, therefore, this type of plate is suitable for off-line plate-making, but also for direct plate-making, has received widespread attention. The thermal transfer direct plate consists of a ribbon and an image receiving substrate. The imaged substrate itself has good hydrophilicity (e.g., the aluminum plate of a conventional PS plate), and the main role is to accept the hot wax layer transferred by the ribbon and construct a hydrophilic non-printing surface. The ribbon is composed of a heat-resistant macromolecule substrate and a heat-sensitive layer (thermal wax layer). The hot wax layer is composed of a low melting point polymer material and an infrared dye. The ribbon is in close contact with the image substrate when it is imaged. The laser light energy is absorbed by the dye and converted into heat energy. The temperature of the heat sensitive layer causes the polymer of the hot wax layer to melt, thus transferring the “liquid” hot wax layer. On the receiving substrate, a printed graphic surface is formed. In order to increase the mechanical strength of the image area, it is often necessary to cure the hot wax layer transferred on the surface of the image-bearing substrate at a higher temperature. The principle is to cross-link the hot wax layer to form a spatial network structure.
Although this plate does not require post-development processing, the separation of the ribbon and the image-bearing substrate can cause inconvenience in use and control, adding to variable factors. In contrast, the thermo-induced phase change of direct plates has advantages. This plate consists of a heat-sensitive coating and a supporting substrate. The heat-sensitive coating has sufficient hydrophilicity to be a non-printing surface, but it can be converted into a lipophilicity by the action of thermal energy and become a printed graphic surface. The substrate of this plate is only the support of the heat-sensitive coating and does not participate in the final printing. Therefore, there is no requirement for affinity. According to different purposes of use, it can be either a polymer substrate or a metal plate substrate. AGFa has released a new type of reusable media technology called LITeSPeeD that is worth mentioning. LITeSPeeD is actually a polymer coating liquid that can be sprayed on the surface of any substrate such as a printing plate or plate cylinder to form a polymer film. Therefore, this polymer film is also known as Spray-on-Polymer. After the polymer film is sprayed and laser imaged, no post-processing is required for printing. After printing is completed, the polymer film can be easily washed off and the surface of the plate or plate cylinder can be restored to its original state. Since the support substrate can be reused, the sprayed polymer film is very suitable for direct plate making.
● Inkjet Plates There are two basic types of inkjet plates. One is to coat the photosensitive layer of a traditional PS plate with a layer that accepts ink, and the other is to have excellent hydrophilicity and water retention. The performance of the substrate (for example, the aluminum version of the traditional PS plate). The ink jet direct plate is scanned by computer-controlled reciprocating mechanical movement of the nozzle, and the ink is directly ejected onto the image layer or the hydrophilic substrate on the surface of the photosensitive layer of the PS plate to form an ink image. For the first printing plate, a full UV exposure was performed on the plate after the ink jet, so that the photosensitive layer of the PS plate that had not been ejected onto the ink image was exposed, and then the photosensitive layer of the PS plate could be removed through PS plate development. The following hydrophilic plate base is exposed as a non-printing surface, that is, the inkjet image on the surface of the image receiving layer is only used as a "mask" image in the UV exposure to protect the underlying PS plate photosensitive layer from ultraviolet light. This plate can use conventional water-based ink-jet technology. The image layer should generally have a suitable hydrophilicity and be capable of dissolving in alkaline water to meet the requirements for accepting the ink and the PS plate to be removed during development. For the second plate, the ink image formed by the ink jet is the final oleophilic printing area, and therefore requires the use of special ink ink-jet imaging technology.
Solid Inkjet, also called Phase Change Inkjet, is a better choice. This ink-jet technology uses a polymer solid ink that does not contain any solvent and realizes jet image formation depending on the temperature difference. Therefore, the ink ejected onto the hydrophilic substrate has sufficient mechanical strength to become a printed graphic surface. The advantage of inkjet direct media is that it can use the now mature inkjet technology and traditional PS plate, the disadvantage is that the resolution is not high (mainly limited by the inkjet technology, generally below 1500DPI), the speed is relatively low (by the nozzle Restrictions on reciprocating motion, suitable for printing areas where the resolution is not demanding. (End of the article)

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