Talking about printing PS version and CTP version

Talking about printing PS version and CTP version

PS version

CTF process. The plates used are mainly PS version, that is, precoated photosensitive plate, which is developed to adapt to the rapid development of lithography. PS version has the characteristics of high resolution, full dot reproduction, rich layers, easy to master the balance of ink and water, and high printing resistance. It is relatively popular in the printing industry

1. Structure and function of PS plate

PS plate is a photosensitive offset plate with multi-layer structure. It uses the aluminum plate as the support, and the aluminum plate has been processed by various processes. The purpose of these processes is to give it photosensitive properties and printability

(1) matte particles: matte particles are necessary for good plates. They can improve the tightness with print film, shorten the vacuum time, and reduce the occurrence of halo

(2) photosensitive layer: compared with different plate making processes and the production processes of various plate manufacturers, the photosensitive layer will have different characteristics. Generally, it is photosensitive according to the wavelength of the photosensitive light source

(3) hydrophilic layer: it can prevent the photosensitive coating from remaining in the pores of the anodic oxide layer, improve the hydrophilic property of the plate, and prevent the printing plate from getting dirty during the printing process

(4) anodic oxidation layer: the hardness, chemical stability and wear resistance of the aluminum plate base surface are enhanced after anodic oxidation treatment. (5) Sand mesh structure: the electrolytic coarsening process is adopted to form a fine sand mesh structure on the base surface of the aluminum plate, which can make the printing plate have ideal point reproduction conditions and good hydrophilicity; For example, the sand mesh structure of Huaguang PS version is fine and complex, so that the contact surface between the printing plate and the fountain solution reaches the maximum with the continuous improvement of consumers' requirements for VOC in the car. (6) Aluminum plate support: use an aluminum plate with stable size, high strength and high purity that meets the process requirements of PS plate

2. Classification of PS version

due to the different performance of equipment and the grade of printed matter, there are different requirements for the performance of PS version. For example, fine printing requires high resolution of the photosensitive layer of the plate, good point reduction, and even large area. Newspaper printing requires high printing resistance and short printing time, but in general, PS plates are mainly divided into two types: photopolymerization and photodispersion

photopolymerization type prints with the original negative image. The diazo photosensitive film of the image and text part is hardened by light and remains on the plate. The diazo photosensitive film of the non image and text part cannot see light, so it will not harden and can be dissolved and removed by the developer; Photolysis type prints with the original positive image. The diazo compounds in the non graphic part decompose under light and are dissolved and removed by the developer. The printing plate left on the plate, as a key element connecting prepress and printing, plays a very important role in the printing production process. In terms of domestic prepress process flow, there are mainly two processes: CTF (computertofilm computer direct film production) and CTP (computertoplate computer direct plate production). They both receive 1-bit-tiff addition data, and then output the printing plate after going through their respective process flow, but CTF has an intermediate link between film production and plate printing. Among them, the CTF process mainly uses PS version (presentitizedoffsetplat pre es coated photosensitive version), while CTP mainly uses CTP version, and the plates they use have their own characteristics. In order to make readers better understand the characteristics of printing plates, this paper will classify and introduce printing plates according to prepress process

(1) upward diffusion direct plate

this plate is mainly composed of plate base, silver salt emulsion layer and physical development core layer. After laser scanning and imaging, diffusion development is carried out. The silver ions in the unexposed area diffuse upward and are reduced to metallic silver under the action of the surface physical developing nucleus, becoming the lipophilic surface; The surface layer of the exposure area is still the emulsion layer, which has good hydrophilicity as far as possible when using oil with relatively high viscosity. The plate base of this plate can be either a metal material (such as aluminum), or a flexible polymer sheet base (such as polyester sheet base), and in most cases, a flexible polymer sheet base

(2) downward diffusion silver salt plate

this plate is composed of aluminum plate base with good hydrophilic surface, physical development core layer and silver salt emulsion layer. Diffusion development is performed after laser scanning imaging. The silver ions in the exposed area diffuse downward and are reduced to metallic silver under the action of the underlying physical developing nucleus, becoming the final lipophilic surface; Then the emulsion layer is removed, and the hydrophilic substrate surface in the exposure area is exposed to become a hydrophilic layer. This kind of plate has a very high sensitivity and color range, and the printing resistance is also very high, suitable for 3 Rotating and sliding for high-end commercial printing

(3) silver salt and PS plate composite direct plate

this plate mainly uses the high sensitivity and wide color range of silver salt emulsion layer to complete the laser direct scanning imaging of the plate, and uses the printing adaptability of PS plate to complete the requirements of the printing process. It is a combination of silver salt photosensitive material and PS plate technology to build a direct plate. The printability and print resistance are exactly the same as those of traditional PS plates, but this kind of plate has a more complex structure and requires multiple exposures, development, fixing and other post-processing, so the process is more troublesome

with the improvement of technology and production requirements, silver salt edition gradually shows its shortcomings. First of all, due to the use of silver, it is still a diazo compound that does not see light

generally, the lipophilic part of PS version should be about 3% higher than the publishing base plane μ m. This layer of material is generally diazo photosensitive resin, which has good lipophilic and hydrophobic properties, can play a good hydrophobic and lipophilic and spread out the ink, and it also has good wear resistance and acid resistance; The hydrophilic part of PS version is aluminum oxide film, which has a high publishing base plane of about 0.2 μ m～1 μ m. Hydrophilicity, wear resistance and chemical stability are relatively good, so the printing plate's printing resistance is also relatively high

ctp version

ctp version has more types and varieties of CTP plates than PS version. Now, the three CTP technologies with the largest sales volume in the CTP market are silver salt, heat sensitive and violet laser respectively. The printing plates produced by these technologies are silver salt version, heat sensitive version and photopolymer version, while others include CTCP and spray mask type plates. The following mainly introduces the characteristics of three mainstream plates

1. At the beginning of the application of silver salt version

CTP technology, photosensitive technology is mainly used, that is, the photosensitive material on the plate is exposed by laser scanning to achieve the purpose of computer direct plate making. At that time, although the photosensitive plates had different systems and photosensitive mechanisms, the core photosensitive materials were all silver halides. Therefore, this generation of CTP can be collectively referred to as silver salt version. The biggest advantage of silver salt plate is its fast photosensitivity. So far, silver salt plate is still the plate with the fastest photosensitivity. Whether it is thermal plate or violet laser polymerization plate, it is not as fast as silver salt plate in terms of speed

silver salt plates are mainly divided into three types: upward diffusion plates, downward diffusion plates and silver salt and PS plate composite plates:

photosensitive materials, so they have always been expensive. Secondly, silver salt plate printing suitability is not very good, there are also some problems in printing resistance, and there are certain requirements for ink. Third, the high photosensitive speed of silver salt plate is based on the requirements of darkroom operation, and the plate must be kept away from light strictly. As long as any link goes wrong, the plate will be scrapped, and the special environmental requirements bring great difficulties to the plate making work. Finally, there is the problem of environmental protection. The development treatment of silver salt plate will bring toxic waste liquid and pollute the environment. At present, some enterprises still use silver salt version, but its application scope has become narrower and narrower

2. Thermal version

the coating of thermal version is composed of temperature sensitive polymer or ablation layer, which is mainly sensitive to 800nm ~ 850nm infrared laser. When the temperature does not reach the critical value, the printing plate will not react, and when the temperature exceeds the critical value, the point size and shape will not be affected. Therefore, it can produce clean points with clear edges, and basically does not expand or shrink the points. It is used to make fine extra lines in industry. The thermal plate making machine mainly adopts the external drum structure, and the general plate making speed is about 12 ~ 24 quarto plates/hour. The compatibility of thermal plate punching machine is relatively good, which can accommodate a variety of plates. In addition, the thermal version can also be baked to improve the printing resistance, which is suitable for long plate printing or UV ink printing. Therefore, thermal technology is more suitable for use in the field of commercial printing

thermal computer direct plate making technology can be generally divided into two categories. The following introduces two kinds of thermal plates:

(1) hot melt type

the basic composition of this plate is a smooth aluminum plate without roughening treatment, and the ink loving layer and PVA layer (or silica gel) of hot melt materials. Its imaging principle is mainly to use semiconductor diodes to expose the printing plate, and the hot-melt material at the heated part is combined with the aluminum plate base to form an inkphile layer. No light is stripped or blown off, and then it can be printed on the machine

in the whole treatment process of the plate, there is no chemical treatment process, so it is more environmentally friendly. Moreover, due to its low sensitivity to natural light, it can work in the open room. During the treatment, only conventional plate making equipment is needed, which is more convenient to operate

(2) thermal crosslinking type

thermal crosslinking type is a kind of heat sensitive plate with mature technology and large-scale commercial production. The basic components of the plate are roughened aluminum base plate and single-layer PS photosensitive layer. The principle of plate imaging is mainly through the heat of infrared rather than the action of spectrum. After reaching a certain temperature, some polymers in the photosensitive layer undergo heat crosslinking reaction under various external loads to form a latent image; Reheat to further crosslink the polymer compound in the graphic part. The purpose is to make the graphic part photosensitive in alkaline developer silver salt 2.6 μ J/c２m140 μ J/c２m130000～150000 μ J/cm2

resolution 250lpi200lpi300lpi

operation safety 300lpi washing square square square sunlight printing resistance 250000 printing 400000 printing (1 million printing after baking)

convenience

application commerce, commercial reporting, 150000 printing business table 1 is not dissolved in the performance comparison of three plates. The graphic area of thermally crosslinked plates is composed of spatially crosslinked polymer resin, so this kind of plates usually have very high mechanical strength and printing resistance, and can generally print hundreds of thousands of copies, which is very suitable for the long plate printing market

since there is almost no relationship between the exposure time and the exposure energy of the thermally crosslinked plate, there is no underexposure and overexposure, so the nature of the graphic part is very stable, and the printing plate can still be used even after a long period of exposure. In addition, the thermal crosslinked plate has a low sensitivity to natural light, and can also work in the open room. Only conventional plate making equipment is required for processing

3. Photosensitive plate

photopolymer plate is usually composed of aluminum plate base, photosensitive layer and