Imaging mechanism and application analysis of thermal CTP plate

1.2 Substrate Ink type negative chart CTP plate

This type of plate is generally a waterless offset printing plate, and companies such as Agfa, KPG, and Fuji have relevant patented technologies. Taking Agfa's technology as an example, the aluminum-based surface of the plate is a hydrophilic metal oxide. In fact, it is also hydrophilic. The undercoating of the plate is a photo-decomposition type and is used as a binding resin for a photosensitive imaging layer and a bonding substrate and an overcoat layer. The top coat is a cross-linked cured silicone rubber that is oleophobic and does not absorb infrared radiation.

Its imaging mechanism is that when the infrared light illuminates the plate, the undercoating undergoes a photodecomposition reaction, the adhesion between the adhesive resin and the silicone rubber in the exposed area is reduced, and the exposed area of ​​the silicone rubber and the disassembled under the exposed area are removed during development. The coating resin exposes the surface of the substrate and forms an ink-friendly graphic portion. The imaging process is shown in Figure 2.

Fig. 2 Substrate ink-type negative image CTP media imaging process
Such plate-exposure post-development processes typically utilize mechanical stripping or solvent cleaning to remove the silica gel. Therefore, during the development process, the silicone layer may be scratched or rubbed to damage the plate. In addition, KPG also developed a process-free base-inking CTP version, which will be introduced later.

2, positive-type thermal CTP plate
2.1 solubility change type positive CTP plate

The structure of this plate is generally coated with a thermosensitive layer on a hydrophilic plate base, and the thermosensitive layer is insoluble in alkaline developer and ink-philic. The imaging mechanism is that when the infrared laser scans, the exposed area undergoes a physical or chemical change in heat to become alkali-water soluble, and the exposed part is removed with an alkali developer. The development process is shown in Figure 3.

Figure 3 The dissolution change type positive CTP plate development process
KPG and Fuji's patented technology is that the thermosensitive layer consists of a film-forming resin, an infrared absorber, a solvent blocker, and other additives. Prior to exposure, the blocking solvent forms a hydrogen bond with the film-forming resin, resulting in a solubilizing effect that makes it difficult to dissolve in the lye. In the infrared exposure, the infrared absorbing agent generates heat, so that the heat-sensing composition undergoes a destructive interaction, so that its solubility in the alkaline solution is increased, and development imaging is realized. This process is usually considered as a physical change process. Agfa's imaging plates for such plates include alkali-soluble polymers and infrared-sensitive skin layers that are not infiltrated by the developer.
(to be continued)