Imaging Mechanism and Application Analysis of Thermal CTP Plates III

2.2 Hot cross-linked preheated positive CTP plate

This type of plate belongs to Agfa's patented technology. Its imaging composition includes an alkali soluble resin, a latent protonic acid, a cross-linking agent, and an infrared absorber (carbon black). The imaging mechanism is: When the infrared laser is irradiated, the unknown effect in the exposed area can still retain better alkali solubility; the unexposed part does not change. During the pre-warming treatment before development, the unexposed areas undergo thermal cross-link curing based on the acid-catalyzed reaction (the presence of protonic acid), which reduces the alkali solubility, while the exposed areas remain alkali-soluble. The alkaline developer removes the exposed portion during development. The process is shown in Figure 4 on the next page.

Figure 4 Hot cross-linked preheated positive CTP plate development process
This process of plate imaging is just the opposite of the conventional thermal cross-linked negative CTP plate, that is, the cross-linked and non-cross-linked parts are just adjusted. This is due to the fact that the infrared absorber used is different from the negative pattern type, in which carbon black and the protonic acid generated by the infrared exposure undergo an unknown effect, so that the exposed area can still maintain the alkali solubility.

3, free processing CTP plate

According to the data, all companies have treated the thermal-free CTP plate as a key research direction, and put forward a large number of design proposals, and the new program is still being proposed. This is because such a plate material can save development processing costs and improve efficiency.

3.1 Polarity Change-free Handling CTP Plate

Figure 5 polarity change-free processing CTP plate development
The imaging mechanism of this type of plate is: the entire layout is usually hydrophilic before exposure, and the polarity of the exposed area changes during infrared scanning. This change process can be either physical or chemical. Make this part from hydrophilic to oleophilic. After the printing plate is exposed, it is no longer necessary to carry out the development process, that is, the printing requirement is satisfied. This process is shown in Figure 5. Of course, there are also some designs where the layout is first designed to be lipophilic and the polarity is enhanced to become hydrophilic during exposure, so that there is a hydrophilic and lipophilic zone on the plate, which does not require development.

There are many design schemes and methods to change the polarity of a printing plate, and they can be divided into physical and chemical methods. The physical mode of polarity change media is usually dispersed in the hydrophilic binder resin with some hydrophobic thermoplastic polymer particles. The thermoplastic particles have a critical agglomeration temperature, and they soften or melt under heat to make the particles agglomerate in the hydrophilic layer. In the formation of hydrophobic aggregates. The chemically modified polar change medium thermosensitive resins are usually homopolymers or copolymers containing pendant polar functional groups that react under thermal action with other functional groups to form a hydrophobic structure.
(to be continued)