Factors affecting the printing durability of the printing plate
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The print durability of a plate is the maximum number of prints a plate can print within the specified print quality. Offset printing is based on the principle that oil and water are difficult to be compatible, and the graphic part and the blank part are printed on the printing plate of the same plane. The printing durability of the printing plate actually depends on the stability of the lipophilic and hydrophilic balance of the graphic part and the blank part. For whatever reason, as long as the stability of any part of it is destroyed, it may lead to the printing plate. The service life is reduced, that is, the printing durability of the printing plate is reduced. The printing plate's resistance to printing is directly related to the economic benefits of offset printing, and it is also an important condition for reducing production costs, increasing production and ensuring printing quality. The low printing durability of the printing plate, in addition to the trouble of the offset printing operation, also directly affects the quality of the printed product.
The printing process involves many complicated physical and chemical phenomena, the influence of various environmental factors and the technical quality of the operators. They will change the balance of lipophilic and hydrophilicity between the graphic part and the blank part of the printing plate to some extent. As a result, the printing durability of the printing plate is reduced. There are many factors that determine the printing durability of the printing plate. It is analyzed in several aspects and discussed with the peers.
1. The quality of the printed version
At present, there are many varieties of printing plates on the market, and the quality is also uneven. In the procurement, you should carefully select different types of plates to meet different printing quality requirements. When selecting, pay attention to the composition of the base, whether the thickness of the photosensitive resin film is consistent, whether the plate sand is too thick or too sharp, etc. Selecting a high-quality plate is a prerequisite for improving the printing durability of the printing plate, and at the same time pay attention to The storage of the printing plate, if the printing plate is improperly stored, caused by a slight exposure caused by strong light, or the storage time is too long and damp, resulting in oxidation of the layout and causing a decrease in smoothness. Even the best plate does not guarantee the high plate quality. Printing resistance.
2. Technical problems of the plate making process
The film density for film printing should generally be above 3.8, the exposure should not be excessive, the developer should be stirred evenly, the water level should be appropriate, the temperature should be appropriate, and the development should be kept too balanced, and the blade speed should be uniform.
The layout should be thoroughly finished. When wiping the retouching paste after the revision, it is washed with a large amount of water and wiped to the non-image portion, which does not cause the local resin film to be thinned. The temperature of the baking plate should not be too high, and should not be excessive. Only in strict accordance with the technical requirements of the plate making process can the printing plate maintain a high printing durability.
3. Problems caused by improper adjustment of the plate
When installing the plate, make sure that there is no foreign matter on the back of the plate. The plate pad should be kept at the proper thickness. Adjust the pressure between the plate and the water roller, blanket and ink roller to avoid too much pressure between each other. During the debugging process, when the printing plate is not inked, the machine should not be idle for too long when the water roller is against the plate. When wiping the stain on the printing plate with the wetting powder, the force on the graphic part should not be too large, so as not to damage the resin film on the printing plate. Do not continue to use the aged water roller sleeve or blanket, and replace it in time. If there is too much ink on both sides and the tail of the blanket, it should be scrubbed clean and the blanket should be carefully scrubbed after each change. The water roller should also be cleaned regularly with a cleaning agent or gasoline. The cleaning roller or the residual gasoline residue should not be left on the water roller sleeve after washing. The hardened ink on the water roller should be carefully scraped clean. It is not advisable to use a pad with too much hardness. The uneven pad should be flattened or replaced to avoid serious plate wear. The blanket should be tightened, especially the newly replaced blanket and pad. There will be slack afterwards and should be tightened in time. At the same time, it should be noted that the ends of the blanket are elastic and uniform, so that one end is too loose and one end is too tight.
4. Problems caused by machine wear
The wear of the printing plate is the main source of the reduction of printing durability. It is a complicated process composed of many factors, and due to the action of oleophilic and hydrophilic, different parts of the printing plate are also subject to different degrees of wear. At present, offset printing also has the effect of pressure. With pressure, friction will inevitably occur. Because of the friction, the graphic part and the blank part of the printing plate are worn away and lose the balance of lipophilic and hydrophilic. The main factor of the reduction of force.
When the roller sleeve of the printing machine is seriously worn, the amount of squeezing is increased, and the impact of the water roller, the ink roller and the blanket cylinder on the printing plate is increased during printing, which directly leads to a decrease in the printing durability of the printing plate. When this happens, replace the accessories or repair them properly. When it is not too serious, it can be cleaned with rubber cleaning reductant, and at the same time, the printing speed should not be too high.
5. Problems with paper, ink and water
If the paper has too much paper powder, containing sand or sand, the pH value is too high or too low, it will affect the blanket and the printing plate. When the paper is out of the powder, the blanket should be scrubbed frequently to prevent the sand from wearing the plate. . When printing, the PH value of the water hopper should be kept at 5-6, and the water bucket should be cleaned frequently to prevent the water hopper from decaying and deteriorating, so that the printing plate is corroded and dirty, which seriously affects the printing durability of the printing plate. Ink should be properly selected according to the quality requirements of different varieties and different printed products, such as varnish, eliminator, dry oil, etc., to avoid the ink viscosity is too high and reduce the printing durability of the printing plate. Since the ink itself has a certain protective effect on the resin film of the printing plate, it should be noted that the amount of ink used in printing should not be too small, otherwise it is easier to wear the printing plate and reduce the printing durability.
Through the above analysis, we can take some measures from the printing process to improve the printing durability of the printing plate: 1 Under the premise of ensuring the printing quality, the minimum pressure between the rollers is maintained, and the friction of the printing plate is reduced. 2 As much as possible to ensure that the surface speed of each roller and ink roller is equal, reducing the plate wear caused by slip. 3 Under the principle that the printing plate can not be dirty, use the least amount of water, and maintain a normal water supply to prevent large water. 4 Correctly grasp the pH value of the water hopper and keep it within the proper range. The change should not be too large. 5 Maintain normal ink supply to prevent flickering. 6 Control the thickness of the ink layer to prevent the print from spreading. 7 Strictly control the emulsification value of the ink, and timely remove the defects such as ink roller deinking caused by emulsification. 8 Reasonable use of drier to prevent early drying of each printing surface. 9 When the machine is stopped, wipe the glue in time to prevent the plate from oxidizing and dirty. 10 avoid all kinds of human damage from the process.