Talking about printing PS plate material

The plate used in the CTF process is mainly the PS plate, which is a pre-coated sensitized plate. It is developed for the rapid development of lithographic printing. PS version body has the characteristics of high resolution, full network reproduction, rich layers, ink balance and easy to grasp, high resistance to force and so on. It is more popular in the printing industry.

1, PS version of the structure and role

The PS plate is a photosensitive offset plate having a multilayer structure. It uses an aluminum plate as a support and the aluminum plate undergoes a variety of processes. The purpose of these processes is to give it photosensitivity and printability.

(1) Roughface granules: Roughface granules are necessary for good quality plates. They can improve the adhesion to the printing plate and shorten the time for vacuuming, thereby reducing halo.

(2) Photosensitive layer: Compared with different plate-making processes and production processes of various plate manufacturers, the photosensitive layer will have various characteristics. Generally, the photosensitive layer will be sensitized based on the wavelength of the photosensitive light source.

(3) Hydrophilic layer: It can prevent the photosensitive coating from remaining in the micropores of the anodic oxide layer, improve the hydrophilic property of the plate, and prevent the plate from being dirty in the printing process.

(4) Anodized layer: The hardness of the surface of the aluminum plate base after anodization is increased, chemical stability is increased, and wear resistance is enhanced. (5) Abrasive structure: The electrolytic coarsening process is used to form a fine sand-mesh structure on the surface of the aluminum plate base, which can make the plate have an ideal dot reproduction condition and good hydrophilicity; for example, the grit structure of Huaguang PS plate. Fine and complex, so that the contact surface of the printing plate with the fountain solution reaches its maximum. (6) Aluminium plate support: Use aluminum plate suitable for PS plate process requirements, dimensional stability, high strength and high purity.

2, PS version of the classification

Due to differences in equipment performance and print grades, there are different requirements for the performance of the PS version. Such as fine prints will require the resolution of the photosensitive layer of the plate, good dot reducibility, a large area of ​​flat screen to be uniform and other requirements, newspaper printing hope printing plate high printing rate, printing time is short, but in general The PS version is mainly divided into two types: photopolymerization and optical dispersion.

The photopolymerization type negative original plate is used, and the diazo photosensitive film in the graphic part is photohardened and remains on the plate. The non-graphical part of the diazo photosensitive film does not see light, so that it does not harden and can be developed. Dissolve and remove; the photo-decomposition type is printed on the positive plate; the non-graphical part of the diazo compound is photo-decomposed and dissolved by the developer solution. The printing plate left on the plate is used as a key element for pre-splicing and printing. The printing production process plays a very important role. Looking at the domestic prepress process, there are two processes: CTF (ComputertoFilm computer directly out of film) and CTP (ComputertoPlate computer-to-plate). They all receive 1-Bit-Tiff screening data, and then go through their own process flow. The final output of the printing plate is just the intermediate link between the CTF and the film. Among them, the CTF process mainly uses the PS version (PresensitizedOffsetPlats), while the CTP mainly uses the CTP version. The plates they use have their own characteristics. In order to make the reader understand the characteristics of the printing plate better, this article will introduce the classification of the printing plate according to the prepress technology.

(1) Upward diffusion type direct plate

This plate is mainly composed of a plate base, a silver salt emulsion layer and a physical development core layer. After laser scanning imaging, diffusion development is performed. The silver ions in the unexposed areas diffuse upward and are reduced to metallic silver by the physical development nuclei of the surface layer and become oleophilic surfaces. The surface layer of the exposed area is still an emulsion layer and has good hydrophilicity. The plate base of this plate can be either a metallic material (such as aluminum metal) or a flexible polymer base (such as a polyester film base), in most cases a flexible polymer base.

(2) Downward diffused silver salt plate

This plate is composed of an aluminum plate base, a physical development core layer, and a silver salt emulsion layer having a good hydrophilic surface. Diffusion imaging is performed after laser scanning imaging. The silver ions in the exposed area diffuse downward and are reduced to metallic silver by the underlying physical development nucleus and become the last lipophilic surface; then the emulsion layer is removed and the surface of the hydrophilic plate base in the exposed area is exposed as a hydrophilic layer. This plate has a very high sensitivity and color sensing range, and is also very resistant to printing forces, suitable for high-end commercial printing.

(3) Silver Salt and PS Plate Composite Direct Plate

This plate mainly uses the high sensitivity and wide color sensing range of the silver salt emulsion layer to complete the laser direct scanning imaging of the plate, and uses the printability of the PS plate to complete the printing process. It is a kind of silver salt photosensitive material and PS version technology builds a combination of direct media. The printability and printability are the same as those of the conventional PS plate. However, the structure of the plate is more complicated and requires multiple exposures, post-processing such as development and fixing, and the process is troublesome.

With the improvement of technology and continuous improvement of production requirements, the silver salt version gradually shows its inadequacies. First of all, due to the use of silver as a diazo compound that is still not visible.

Generally, the lipophilic part of the PS plate should have a high publishing plane of about 3μm. This layer of material is generally a diazo photosensitive resin. It has good lipophilic and hydrophobic properties, can play a very good role in hydrophobicity and oleophilicity, and spreads out the ink. Characteristics, but it also has good wear resistance and acid resistance; PS version of the hydrophilic part is aluminum oxide film, which is high publication base plane about 0.2μm ~ 1μm, hydrophilicity, abrasion resistance, chemical stability The sex is better, so the imprint rate of the printing plate is also higher.

Although the PS version is still the main support line for printing plates in China, but with the development of technology and people's continuous improvement of environmental requirements, PS version has gradually revealed its drawbacks. PS version in the production of high power consumption, high water consumption and high pollution has always been the pain of domestic PS version, while the PS version due to the characteristics of the plate making process, so that his plate making cycle is higher than the CTP version, so for the short version of the actual effect For high-activity jobs, the PS version has its drawbacks. However, it is not said that the emergence of CTP technology will defeat the CTF. As far as the current domestic development pattern is concerned, CTF and CTP technologies will coexist for a long period of time.

Compared with the PS version, the CTP version has more types and varieties of CTP plates. Currently, the three CTP technologies that sell the most in the CTP market are silver salt, thermal and violet lasers. The printing plates produced using these technologies are Silver salt, thermal and photopolymer plates, and CTcP and spray mask plates. The following describes the characteristics of the three mainstream media.

1, silver salt version

The initial application of CTP technology mainly applies light-sensitive technology, that is, through laser scanning to expose the photosensitive material on the plate to achieve the purpose of direct computer plate making. At the time, although the photosensitive plate had a different system, the photosensitive mechanism was not the same, but the core photosensitive materials were silver halides. Therefore, this generation of CTP can be collectively referred to as the silver salt version. Silver salt version of the biggest advantage is the speed of light. So far, the silver salt version is still the fastest photosensitive material, whether it is a thermal plate or violet laser polymer plate, not as fast as silver salt version.

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

Photosensitive materials have always been expensive. Secondly, the printability of silver salt printing is not very good. There are also certain problems in the resistance to ink, and there are also certain requirements for ink. Thirdly, the excessively high photospeed of the silver salt version is required under the premise of the operation of the darkroom, and the preservation of the plate material must be strictly protected from light. Any error in any of the links will cause the plate to be scrapped. The special environment It was very difficult for the plate-making work. Finally, there is the issue of environmental protection. The silver salt version of the development process will bring toxic waste fluids and cause environmental pollution. At present, there are still some companies that use silver salts, but their application has become narrower.

2, thermal version

The heat-sensitive coating consists of a temperature-sensitive polymer or ablation layer and is sensitive to infrared lasers between 800nm ​​and 850nm. When the temperature does not reach the critical value, the plate will not react, and when the temperature exceeds the critical value. At that time, the size and shape of the outlets will not be affected. Therefore, it is possible to produce clean, sharp-edged outlets, and no expansion or contraction of outlets will occur. It is industrially used to produce fine screens. The thermal plate-making machine mainly uses the outer drum structure. The general plate-making speed is about 12 to 24 sheets/4 hours/hour. The thermal plater has relatively good compatibility and can accommodate multiple plates. In addition, it is also possible to bake heat-sensitive plates to improve the print durability, suitable for long-run 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 roughly divided into two major categories. Here are two types of thermal plate:

(1) Hot melt type

The basic composition of this plate is a smooth aluminum plate that does not require roughening, an ink-receptive layer of hot-melt material, and a PVA layer (or silicone). The principle of imaging is to use a semiconductor diode to expose the printing plate. The hot melt material in the heated area is combined with the aluminum plate to form an ink-receptive layer. No light is peeled off or blown off. Then the printing can be performed on the machine.

In the entire processing of the plate, it does not involve the chemical treatment process, so it is more environmentally friendly, and because he has very low sensitivity to natural light, it can work under the light room, processing only need the conventional plate making equipment, the operation is more convenient.

(2) Heat Crosslinking

The thermal cross-linked type is a kind of thermal plate that has a relatively mature technology and has realized large-scale commercial production. The basic composition of the plate is a roughened aluminum base plate and a single-layer PS photosensitive layer. The principle of plate material imaging is mainly through the infrared heat rather than the effect of the spectrum. After a certain temperature is reached, some of the polymers in the photosensitive layer undergo thermal crosslinking reaction to form a latent image; and then the heating, so that the graphic part of the polymer compound is further The cross-linking reaction takes place, the purpose of which is to make the graphic part in the alkaline developer silver salt photosensitive thermosensitive photosensitive 2.6μJ/c2m140μJ/c2m130000~150000μJ/cm2

Resolution 250lpi200lpi300lpi

Operation Safety and Security 300lpi Rinse Squarer Sunlight Resist Print 250,000 Inch 400,000 Inch (Bake 1 Million In India)

Convenience

Applications Commercial, commercial, and 150,000 printers Table 1 The performance of the three plates was not dissolved. The graphic area of ​​the thermal cross-linked plate is composed of a space-crosslinked polymer resin. Therefore, such plates usually have a very high mechanical strength and printability, and generally can print hundreds of thousands of copies, and are suitable for long-run printing. market.

Since there is almost no relationship between the exposure time and the exposure energy of the heat-crosslinked plate, there is no phenomenon of underexposure and overexposure, so that the nature of the graphic part is very stable, and even after a long period of time after exposure, the printing plate remains can use. In addition, thermal cross-linked plates have a low sensitivity to natural light and can also be operated under bright rooms, requiring only conventional plate-making equipment for processing.

3, photosensitive version

Photopolymer plates are usually composed of an aluminum substrate, a photosensitive layer, and a surface layer. The photopolymerizable layer is mainly composed of a polymerizable monomer, an initiator, a spectral sensitizer, and a film-forming resin. The initiator generally adopts a multi-initiator system with a high quantum efficiency. The function of the spectral sensitizer is to effectively extend the photosensitivity range of the initiator to the light emission wavelength region of the laser. The role of the surface layer is mainly to separate the oxygen molecules in the atmosphere to prevent it from entering the photosensitive