The so-called CTP technology refers to the abbreviation of computer to CTPlate, CTPress, CTProof, CTPaper/Print, and CTcP. The CTP commonly referred to in the current printing industry is from computer to printing plate (CTPlate), which uses a computer to digitize, integrate, and proofread the original image and text on the printing plate, directly imaging them, and then making a printing plate through post-processing processes such as development or no post-processing. CTP technology can be divided into photosensitive CTP technology (visible light, purple laser, UV light) and thermosensitive CTP technology. Below, we will focus on thermosensitive CTP technology.
1、 Classification of thermal sensitive CTP technology
Thermal CTP technology can be divided into the following categories according to the plate material:
(1) Thermal ablation type; (2) Thermal cross-linked plate (preheating type, negative pattern type); (3) Thermal decomposition type plate material (no preheating treatment, positive pattern type); (4) Heat transfer plate material; (5) Thermal induced phase change plate material.
2、 Imaging principle of thermal sensitive CTP technology
Thermosensitive CTP mainly utilizes thermal imaging technology to achieve changes in material properties by relying on changes in the state of the material after the printing plate material absorbs heat.
（1） Thermal ablation type
1. Plate composition
This type of plate is composed of a silicone exclusion layer, a photothermal conversion layer (absorption layer), a hydrophilic layer, and a substrate (as shown in Figure 1).
2. Imaging Principles
The main function of the photothermal conversion layer is to absorb the light energy emitted by infrared lasers and effectively convert the absorbed light energy into thermal energy, causing the temperature of the layout to rise to the level of vaporization temperature. The photothermal conversion layer in the visible area vaporizes under the action of thermal energy, and the corresponding silicone exclusion layer in the corresponding position is removed with the vaporization of the photothermal conversion layer under the action of heat, exposing the hydrophilic oil layer below to become the part of the printing plate that receives the ink; The photothermal conversion layer in the non visible area did not undergo vaporization, and the corresponding silicone exclusion layer did not change, forming the blank part of the printing plate (as shown in Figure 2).
3. Base
The substrate of this type of plate can be either a metal substrate (such as aluminum substrate) or a flexible polymer substrate (such as polyester substrate), which has a wide adaptability. This type of plate material is particularly suitable for in machine direct plate making systems because it can be printed after laser imaging.
Although this type of plate is also a direct plate that does not require post-processing, necessary measures need to be taken to dispose of it during the imaging process due to the generation of ablation vapor and debris, otherwise it will cause pollution to the imaging optics and the environment.
（2） Thermal cross-linked plate (preheating type, negative pattern type)
1. Plate composition
The thermal cross-linked plate is composed of a thermosensitive coating and a hydrophilic substrate. Thermal sensitive coatings are generally composed of (alkaline) water-soluble film-forming resins (phenolic resins), thermal crosslinking agents, and infrared dyes; The hydrophilic version can use the same aluminum version as the traditional PS version (as shown in Figure 3).
2. Imaging Principles
The Work of Infrared Dyes