The Development of CTP Technology and the Prospect of PS Edition

The turn of the century marks the period of rapid development and development of CTP technology in the printing industry. Especially between 1995 and 2000, direct plate-making machines suitable for sensitization of various kinds of laser light sources have emerged one after another. The number of CTP systems used in the area has increased dramatically. It is expected that the number of 5,000 units will be reached by the year 2000. It is now realized and exceeded. However, the development speed of CTP in our country is still very slow. The reason may be many, mainly the following two points.
First, after many years of electricity and photofinishing processes, the process has been very mature and can produce very good products. Second, the variety of CTP equipment and plates has made it difficult to tell which device and media are more suitable. In the future development, a lot of investment will make people have a kind of waiting psychology. This kind of analysis and identification process is necessary.

The use of CTP systems does require certain conditions. From the perspective of business operators, the following considerations should be considered: First, does the company have a large amount of plate-making workload? Today's better CTP plate-making equipment has a very fast publishing speed, and how to protect the living source? Adequateness is a big problem; secondly, the number of films and plates used by the company should be relatively large, so the scope of saving films and time is relatively large. If more short-lived versions live, the CTP system will have more advantages. On the contrary, if there are more than 100,000 prints, the advantages of CTP equipment will not show up. Third, the CTP system still needs the support of other hardware, such as the use of digital proofing equipment to replace the traditional proofing equipment, there should be a certain number of single Paper multi-color offset printing press or offset printing offset printing machine and so on. These conditions are not difficult for domestic newspaper and printing companies with advanced equipment. As long as they initially spend a sum of money, the adoption of CTP systems is still easy to implement. However, users are more concerned about the selection and stable supply of CTP plates. With the stable quality and acceptable price of CTP plates, the development of CTP technology has a solid foundation. This article talks about the development of the existing CTP plate.

The adaptability of the photosensitive layer of the CTP plate to the wavelength range of the laser spectrum is often a continuation and development of the old process, resulting in an abrupt change or even a complete replacement of the original technology. This is also true of the CTP plate. Initially, most of the laser light source was in the visible to infrared region, and the photosensitive layer of the PS plate was difficult to shift from the ultraviolet region to the long wavelength region for a time. Therefore, the earliest CTP plate material used was a two-layer composite plate. It is coated on the existing PS plate photosensitive layer with silver salt photosensitive layer, so that the resulting plate is easily scanned by the general laser light source, after silver salt development, and then applied to the underlying resin photosensitive layer exposure After the redevelopment, the plate is obtained. Although this method can achieve the purpose of laser plate-making, but its double-exposure twice to develop, does not show the advantages of laser plate making, on the surface this method seems to remove the film, but it is only the silver salt photosensitive layer Transferred to the original PS plate coating, so this method is the initial transition phase of the CTP plate.

The biggest difference between the sensitization of the CTP system and the sensitization mechanism of the PS plate is that the UV exposure light source is used for the PS plate exposure. In addition to the direct irradiation, there are scattering and refracted light in the printing plate, and the loss of light energy is great. The laser plate making system The laser light source is mostly monochromatic light, and generally a wavelength or a range of wavelengths is selected. This is where the laser plate making equipment is advanced. With the development of science and technology, the improvement of lasers has allowed us to make more choices for CTP systems. The spectral range of current laser sources can range from 350 nm to 1200 nm, which means that from the ultraviolet region to visible light Regional (blue-violet light to red light), up to the infrared spectrum area, all have corresponding laser equipment available, which also makes the choice of laser media more widely. Considering the operating environment, in the phase of photoengraving and electricity separation, long-term darkroom work is performed. People are very willing to take advantage of the development of CTP technology to obtain a new environment of white light or yellow light, such as ultraviolet laser platemakers, violet laser platesetters and far-infrared Laser platemakers have greater development advantages. As a result, photopolymer plates and thermal plates were welcomed as soon as they appeared. In particular, at the Drupa 2000 exhibition, the ultraviolet laser plate-making equipment exhibited attracted a great deal of interest from professionals. From here, we can see that The traditional PS version is expected to achieve the purpose of laser plate making. For example, Puron-Eskofot's Dicon high-speed ultraviolet laser device uses a mercury lamp light source whose emission spectrum is in the ultraviolet and blue-violet light regions. The device can decompose ultraviolet light into multiple light beams and then pass through optical fibers. Passed to the printing plate, this is no different from the conventional PS plate exposure range. The application of this system requires only the addition of a UV CTP plate making machine in the traditional printing plate process flow, and the technical content of the CTP system is completed without much modification of the process method.

CTP plate high-resolution low-power exposure function to produce fine color prints on the plate material requirements, with high sensitivity, high resolution, strong dot reduction, printing performance and other characteristics. To achieve high resolution, it is required that the plate has high contrast performance, and the degree of mutation before and after the exposure is obvious, so that a good printing plate can be easily produced. The laser system can concentrate light energy at a specific wavelength and output light in parallel to provide good conditions for exposure, and it is not difficult for the plate-making machine to have an output resolution greater than 2000 dpi. Currently, CTP plates are used. Whether it is a thermal plate, a silver salt diffusion plate, a silver salt emulsion and a polymer composite plate, or a photopolymer resin plate, it has good resolution performance, and it needs to reach a network cable of 60 lines/cm, 75 lines/cm or even higher. There will not be too many problems. Among them, the thermal imaging technology is more attractive. It absorbs infrared light and converts it into heat, causing the photosensitive layer to change. Before a certain temperature reaches a certain temperature, there will not be any change in the layout, and when the temperature reaches a certain temperature, the photosensitive layer will be sensitized or ablated instantly, and the contrast effect is more prominent. The edge effect of the dot is very small and will not be like an ordinary PS. The plate is deformed due to improper vacuum drawing or intrusion of scattered light during the printing process.

The use of CTP system can effectively increase the speed of plate making. Now many laser direct platemakers can achieve output of 20 to 30 wafers per hour. This requires that the sensitivity of the photosensitive layer be faster, and the light energy used in the exposure. Should be relatively low, it is easy to achieve a high sense of effect, the current sensitivity of CTP, has greatly improved. The current photosensitive materials that have reached or are about to reach the speed can be described in Table 1.

Table 1 Existing photosensitive material sensitivity range

Photosensitive material type Photographic spectrum Wavelength range (nm) Sensitivity range (mJ/cm2)
PS photosensitive layer 300 ~ 450 100 ~ 400
High-sensitivity photosensitive resin CTP plate 350 to 550 0.1 to 10
830 to 1080 50 to 200
Silver halide coating 350 to 850 0.2 to 0.0001
Electrophotographic coating 350～850 >0.001
Thermal resin coating 800 to 1200 10 to 300

The above-mentioned light energy required for exposure of various photosensitive layers is actually continuously improving. For example, the first generation of thermal resin plate, the sensitivity should be about mJ/cm2, and now it can be tens of millijoules. With regard to the ordinary PS plate, whether it is a photolysis type or a photopolymerization type, the light energy required for exposure is relatively high at present. Even if the ultraviolet laser technology is used, low power laser exposure is also required due to the limited energy of the laser tube. For better, it is reasonable to complete a scan in one to two minutes on a split sheet, and no longer shows the superiority of the CTP system.