The so-called CTP technology is the English abbreviation from the computer to the printing plate (CTPlate), printing machine (CTPress), proof (CTProof), printed matter (CTPaper / Print) and ordinary PS version (CTcP). In the current printing industry, CTP is often said to be from a computer to a printing plate (CTPlate). It uses a computer to digitally process the original image and text, combine the image and text, and proofread the proof, and then directly image the image on the plate, and then develop Wait for the post-processing process or post-processing-free to make a printing plate. CTP technology can be divided into photosensitive CTP technology (visible light, violet laser, UV light) and thermal CTP technology. The following focuses on thermal CTP technology.
1. Classification of thermal CTP technology
Thermal CTP technology can be divided into the following categories according to the plate material:
(1) Thermal ablation type; (2) Thermally cross-linked plate (preheated type, negative pattern); (3) Thermal decomposition type plate (free of preheating, positive pattern); (4) Thermal transfer Plates; (5) Thermally induced phase change plates.
Second, the imaging principle of thermal CTP technology
Thermal CTP mainly uses thermal imaging technology, and the state of the substance changes after the plate material absorbs heat, so as to realize the change of the material performance.
(1) Thermal ablation type
1. Plate composition
This plate is composed of a silicone oil repellent layer, a light-to-heat conversion layer (light-absorbing layer), an oleophilic layer, and a plate base (see Figure 1).
2. Imaging principles
The main function of the light-to-heat conversion layer is to absorb the light energy emitted by the infrared laser, and effectively convert the absorbed light energy into heat energy, so that the temperature of the plate surface rises to the vaporization temperature level. The light-to-heat conversion layer in the light-seeking area is vaporized under the action of heat energy. The silicone oil-repellent layer at the corresponding position will be removed with the heat-to-heat conversion layer vaporization under the action of heat, leaving the underlying oil-philic layer exposed to become the printing plate receiving ink Part of the text; the light-to-heat conversion layer in the unseen area did not vaporize, and the silicone oil-repellent layer at the corresponding position did not change, forming a blank part of the printing plate (see Figure 2).
3. Edition base
The plate base of this plate can be either a metal plate base (such as aluminum base) or a flexible polymer base (such as polyester base), which has a relatively wide adaptability. This kind of plate material can be printed after laser imaging, so it is especially suitable for on-board plate-making system.
Although this plate is also a direct plate that does not require post-processing, in order to produce ablative vapor and debris during the imaging process, it is necessary to take necessary measures for sewage treatment, otherwise it will cause pollution to the imaging optics and the environment.
(2) Hot cross-linked plates (preheated type, negative type)
1. Plate composition
The thermally cross-linked plate is composed of a heat-sensitive coating and a hydrophilic plate. The heat-sensitive coating is generally composed of (alkaline) water-soluble film-forming resin (phenolic resin), heat-sensitive cross-linking agent and infrared dye; the hydrophilic plate can use the same aluminum plate as the traditional PS plate (Figure 3) .
2. Imaging principles
The role of the infrared dye is to effectively absorb the light energy of the infrared laser, and convert the absorbed light energy into heat energy, so that the temperature of the thermosensitive coating can reach the reaction temperature of the thermosensitive crosslinking agent; the role of the thermosensitive crosslinking agent is Under the action of temperature, it reacts with the film-forming resin to form a space network structure, so that the heat-sensitive coating loses water (alkali) solubility. Due to the effect of spatial cross-linking, the heat-sensitive coating in the visible area undergoes a cross-linking reaction under the action of heat. The film-forming resin changes from small molecules to large molecules, from linear molecules to network molecules. It does not have alkali solubility. After the development process, it remains on the plate surface to become an oleophilic graphic part; the heat-sensitive coating in the unexposed area has no cross-linking reaction, has alkali solubility, and is dissolved during the development process, and the hydrophilic plate becomes exposed The blank part of the water (see Figure 4).
In order to further improve the effect of thermal cross-linking, some plates are often pre-heated after exposure to further deepen the thermal cross-linking effect (also a mechanism for increasing the sensitivity). This type of plate is called a thermally cross-linked plate that requires preheating. The graphic area of the thermally cross-linked plate is composed of spatially cross-linked polymer resins, so this type of plate usually has very high mechanical strength and durability, and can generally print hundreds of thousands of prints, which is very suitable for long-term printing. market.