Basic knowledge: CTP classification (2)

2. Photopolymerized CTP Plate

The photopolymerization CTP plate is mainly composed of a three-part aluminum plate, a photosensitive layer and a protective layer. The photosensitive layer is mainly composed of a film-forming resin, a sensitizing dye, a photoinitiator, a monomer or an oligomer, and a stable film. Agents and other additives. The protective layer is a polyvinyl alcohol oxygen barrier layer, which is mainly used to block the oxygen blocking effect of monomers or oligomers. The imaging principle is that after scanning of the plate material by the laser light source, the sensitizing dye in the photosensitive layer of the visible part first absorbs the photon energy into an excited state, and then transfers the energy to the photoinitiator, and the photoinitiator decomposes to form free radicals. The base initiates the polymerization of monomers or oligomers and cures to form a graphic portion. The portion where no light was seen was removed by development to form a blank portion. It should be noted that before the development, the protective layer of the non-visible part should be washed away, and then the high-sensitivity polymer layer should be dissolved with an alkaline developer. After the development is completed, the protective layer is completely removed with a brush. Finally, the plate is washed with a synthetic resin solution. The synthetic resin can not only improve the hydrophilicity of the blank part, but also enhance the lipophilicity of the graphic part, and can be printed after drying.

Photopolymerization CTP Plate Features

(1) The photosensitive layer of the photopolymerizable CTP plate is very thin, and the graphic part and the blank part are basically in the same plane, which belongs to the traditional offset printing type, and has a high sensitivity, and the plate making speed is fast.

(2) The developer used in the photopolymerizable CTP plate is alkaline, and the film-forming resin and monomer or oligomer in the photosensitive layer have a certain degree of acidity, can be dissolved in the alkali solution and removed by development, and alkali The developer has little pollution and is environmentally friendly.

(3) Photopolymerization type CTP plate can use violet laser diode (410nm), argon ion laser (488nm), FDYAG laser (532nm), infrared laser diode (830nm) and other plate photosensitive light sources, and its cost is lower. And the photopolymerized CTP plate can withstand printing force of more than 1 million Indians after baking.

3. Thermal type CTP plate

There are many types of thermal-type CTP plates, but there are mainly two types that are relatively mature at present, namely, hot-melt type and thermal cross-link type.

Thermally melted CTP plate is mainly composed of three parts: aluminum plate, ink-receptive layer and PVA layer (used in conventional offset printing) or silica gel (used in waterless offset printing) without roughening. The imaging principle is to use semiconductor laser diode exposure. The thermosensitive coating (ie, the ink receptive layer) on the plate is ink-receptive and insoluble in alkaline potions. After exposure, the coating absorbs energy, increases solubility, and can be dissolved in alkaline solutions. During development, the exposed portion is dissolved in alkaline solution to form a blank portion of the printing plate. The non-exposed portion is insoluble and forms the graphic portion of the printing plate. After development, it is generally cleaned and glued before printing on the machine.

The thermal cross-linked CTP plate mainly consists of a roughened aluminum plate and a single-layer PS photosensitive layer. Its imaging principle is through infrared exposure. When exposed, the photothermal conversion material converts the light energy of the infrared laser into thermal energy, which causes a thermal cross-linking reaction of some of the polymers in the photosensitive layer to form a latent image; and further heating, the cross-linking reaction of the molecular compound in the graphic part further occurs. So that the graphic part is not dissolved in the alkaline developer. It should be noted that when the preheating is performed, a part of the reaction occurs in the blank portion, so that the image of the blank portion is removed during the development. If the temperature is too high, a hot mist will form on the plate; if the temperature is too low, the graphic part will be lightened or weakened.

Thermal CTP Plate Features

(1) The thermal CTP plate has a low natural light sensitivity and is exposed by infrared laser light, so it can be operated under bright room conditions.

(2) For thermal plates to generate images, the initial thermal threshold must be reached, and thermal energy above the initial threshold will not change the dot shape. It is the only technology that can control the predicted results, the quality is easy to control, the publishing quality is stable, and the exposure is stable. The printing plate can be extended to 6 months after the development, the quality of the plate will not have the slightest impact.

(3) The heat-sensitive CTP plate has good dot reproducibility, high resolution, sharp and clear edges, easy ink balance during printing, good printing applicability, and plate-resistance after printing. More than 1 million impressions.

In addition to the above-mentioned three major CTP plates, the elimination of CTP plates in recent years has become a hot topic of discussion.

4 free processing CTP plate

The processing-free CTP plate was first introduced by Japan's Asahi Chemicals. Broadly speaking, it means that after the plate is exposed and imaged on the plate-making equipment, it can be printed on the machine without any follow-up processing procedures. Of course, it does not require chemical development and rinsing. It is a real sense-free plate. In a narrow sense, it means that the plates do not require chemical development after being exposed and imaged on the plate-making machine. However, there are still some non-chemical processing processes, such as the removal of the ablation waste from the plates, and the application of protective glue. From the aspect of the plate making method, the free-handling plates can be divided into two types: plate-free plates for DI (printing machine direct imaging) printers and plates that are exposed and imaged on a CTP plate-setter.

Free handling of the characteristics of media

(1) Compared with the traditional CTP plates, the process-free plate eliminates the steps of developing, fixing, cleaning, gluing, and drying, shortens the platemaking cycle, reduces the amount of energy consumed during exposure, and reduces the overall plate making cost. Improves production efficiency and simplifies production processes.

(2) Since the plate-free processing does not require chemical development, rinsing, etc., the chemical-free liquid waste, exhaust gas, and waste residue that will destroy the environment will not be generated in the plate-free plate processing process. This will reduce the environmental pollution, and the operator It is helpful.

(3) Changes in the processing conditions of the plate, changes in the laser energy, the concentration of the processing solution, the temperature, and the speed will all affect the accuracy of the reproduction of the dots, and the processing-free plate without the need for rinsing can make it higher. The quality of stability.

(4) Free-handling plates do not require chemical development processing devices, which saves plant space, which is a big advantage for small companies, but the free-handling plates are more expensive than conventional CTP plates.

The main evaluation index of CTP plate

In view of the large number of CTP plates currently on the market, where should we evaluate CTP plates? What kind of plate meets our printing quality requirements?

(1) Reproduction of outlets. The network points are the basis for printing and copying the graphic and text information. The quality of the printing plate outlets will directly affect the quality of printed Internet sites and thus affect the reproduction of the entire printing process. Therefore, it is very important to select a good reproduction medium for the dots.

The network of CTP plates is the same as the traditional PS plate. It is also composed of sand grains. For a CTP plate to achieve 1% to 99% dot reproduction, the grain size of the plate must be small enough, because the finer the sand, the more sand grains will be supported in the high-gloss mesh, and the stronger the dot, the more important the printing will be. The less likely it is to lose the version. However, the grain size of the dot cannot be too fine, and the fine balance of the printing ink in the fine-grained plate material is small, which is not conducive to the control of printing quality.

(2) Line reproduction. The reproducibility of the lines for a plate generally includes two aspects, the reproduction of very thin lines and the dimensions of the yin and yang lines. The reproduction of very thin lines is closely related to the size of the grain of the plate, especially the uniformity of the sand, since only the edge of the lines of the uniformly distributed sand grains is likely to be smooth. The size of the Yin-Yang line is mainly determined by the coating thickness of the plate. We can compare the changes in the lines by printing the adjacent Yin and Yang lines on the plate.

(3) Ink affinity. The ink affinity of the plate refers to a characteristic of the printing plate graphic part which is selectively inked by the transfer roller. The thickness of the ink on the plate will directly affect the thickness of the ink on the blanket and the paper, and the amount of the ink transferred to the plate. It depends on the level of ink affinity of the printing plate. If the ink-printing portion of the printing plate is low in ink receptivity, the range of controlling the amount of ink in the entire printing is smaller, and the more it is unfavorable to the product quality. In addition, the use of poor ink affinity printing plate, the remaining ink will accumulate in the transfer roller, the ink transfer roller ink film is thickened, both ends of the ink accumulation, resulting in ink splash phenomenon, while reducing the hiding power of the ink . Therefore, CTP plates with good ink receptivity are very important.

In order to improve the ink receptivity of the CTP plate, the photosensitive material of the plate graphic portion should have chemical properties that are close to the pigments, resins, and solvents in the ink.

(4) Hydrophilicity. The hydrophilicity of the plate refers to the property of selectively retaining water on the non-graphic portion of the plate. The amount of water in printing can neither be too much nor too little. Too little, the part that has not been imprinted is easy to get rid of; Too much, it is easy to appear that the imprint is dull, receives the paper is not flush, the paper is distorted, the overprint is not allowed and so on. At present, the main substrate of the CTP plate is aluminum, which is hydrophilic, and the surface is plated and then anodized to form a porous surface, which enhances the total surface area and ultimately improves the hydrophilicity.

In addition, the factors that affect the performance of the CTP plate are the resolution of the plate, the resistance to printing force, the degree of sensitivity, the sensitivity, the size and the uniformity of the coating.

All in all, with the continuous progress of CTP plate making technology and the continuous improvement of the CTP plate material performance, the advantages of CTP plate materials continue to highlight, the continuous improvement of digital workflow, and the continuous improvement of the quality requirements of printed materials, we have reason to believe that CTP plate will inevitably There is a broader development prospect.