Analysis of Causes of Decreased Print Resistance of Printing Plates

The printing-resistant force of a printing plate refers to the highest printing quantity that a printing plate can print within the guaranteed printing quality range. Offset printing is based on the principle that it is difficult to dissolve oil and water. The graphic and blank sections are printed on the same plane plate. The resistance of a printing plate actually depends on the stability of the lipophilic and hydrophilic balance between the graphic part and the blank part. Regardless of the reason, as long as the stability of any part thereof is destroyed, it may lead to the printing plate. The service life is reduced, that is, the printing plate's resistance to printing is reduced. The strength of the printing plate is directly related to the economic benefits of offset printing production. It is also an important condition for reducing the production cost, increasing the output and ensuring the printing quality. The low printing resistance of the printing plate not only brings trouble to the offset printing operation, but also directly affects the quality of the printed product.

The printing process involves many complex physicochemical phenomena, the influence of various environmental factors and the technical quality of the operators. They will change the balance between the lipophilic and hydrophilic parts of the graphic part and blank part of the printing plate to some extent. As a result, the printing plate's resistance to printing forces is reduced. There are many factors that determine the printing plate's resistance to printing force. We will analyze it in several aspects and discuss it with our peers.

1. The quality problem of the printed version

At present, there are many kinds of printing plates in the market, and the quality is also uneven. When purchasing, different types of plates should be carefully selected to meet different printing quality requirements. When choosing, pay attention to the composition of the substrate, whether the thickness of the photosensitive resin film is the same, whether the plate grain is too thick or too sharp, etc. Selecting a high-quality plate is a prerequisite for improving the printing plate's resistance to printing force, and at the same time, pay attention The storage of the plate, if the plate is stored improperly, is exposed to strong light and causes micro-exposure, or the storage time is too long and damp, resulting in oxidation of the plate and causing the smoothness to decrease. Even the best plate cannot guarantee the high printing plate. Resistance to force.

2. Technical issues of plate making process

The density of the film used in the printing process should be generally 3.8 or more. The exposure should not be excessive. The developer should be stirred evenly. The level of water should be appropriate, the temperature should be maintained properly, and attention should not be paid to over development. The developer must maintain balance and the blade rotation speed should be uniform.

Layout trimming should be thorough. After wiping off the repairing paste after revision, while washing with a large amount of water, the non-graphical portion is wiped, and the partial resin film thinning of the printing plate cannot be caused. The baking temperature should not be too high and cannot be excessive. Only strictly following the technical requirements of the plate making process can the printing plate maintain a high resistance to printing.

3. Problems caused by incorrect adjustment of the plate

When loading the plate, you should make sure that the back of the plate can not be stuck with foreign matter. The plate pad should maintain the proper thickness and adjust the pressure between the plate and the water roller, blanket, and ink roller to avoid too much pressure between them. During the debugging process, when the printing plate is not inked, the machine should not idle for a long time when the water roller relies on the printing plate. When wetting dirt on the plate with the wetting powder, do not apply too much force to the graphic part so as not to damage the resin film on the plate. Aged water roller sleeves or blankets should not be used. Replace them in time. If there are too many ink deposits on both sides of the blanket and on the tail, it should be scrubbed clean, and the blanket should be scrubbed carefully after each change of plate. The water roller should also be cleaned regularly with detergent or gasoline. No detergent or gasoline residue should be left on the water roller cover after washing. The ink stain hardened on the plate roller should be scraped cleanly. Should not use too hard liner, uneven liner should be flattened or replaced, so as to avoid serious wear of the printing plate, the blanket should be given too tight, especially the new blanket and liner, use for some time After loosening, it should be fastened. At the same time, we must also pay attention to the tightness of both ends of the blanket, avoiding one end being too loose and one end being too tight.

4. Problems caused by machine wear

The machine wear of the printing plate is the main source of the reduction of the printing resistance. It is a complicated process composed of many factors. Due to the effects of the oleophilic and hydrophilic effects, different parts of the printing plate are also subjected to wear to varying degrees. At present, the role of pressure is still indispensable for offset printing. With the pressure, friction will inevitably occur. As a result of friction, the graphic and blank parts on the printing plate are worn out and lose the balance of lipophilicity and hydrophilicity. The main factor in reducing the force.

When the roller sleeve of the printing machine wears badly, the amount of turbulence increases, and the impact force of the water roller, the ink roller, and the blanket roller on the printing plate will increase when printing, which directly leads to the reduction of the printing plate resistance to printing force. When this happens, the corresponding parts should be replaced or properly repaired. When it is not too serious, it can be cleaned with a rubber cleaner and reducing agent. At the same time, the speed of printing should not be too high.

5. Paper, ink and fountain solution

If there is too much paper powder, sandy soil or sand, the PH value is too high or too low, it will affect the blanket and printing plate. When the paper is severely chipped and fluffed off, the blanket should be frequently scrubbed to prevent the sand from abrading the plate. . The PH value of the fountain liquid should be maintained at 5-6 during printing, and the bucket must be cleaned frequently to avoid corrosion and deterioration of the fountain bowl, which will cause the printing plate to be corroded and dirty, which will seriously affect the printing plate's resistance to printing forces. Ink should be based on different varieties and different quality requirements of printed products, a reasonable selection of ink adjustment, withdrawal agent, dry oil, etc. for appropriate adjustments to avoid the ink viscosity is too high and reduce the printing plate resistance to printing. Since the ink itself has a certain protective effect on the resin film of the printing plate, the amount of ink used for printing should not be too small, otherwise it is also easier to abrade the printing plate and reduce the resistance to printing force.

Through the above analysis, we can take some measures from the printing process to improve the printing plate's resistance to printing force:

1 Under the premise of guaranteeing the printing quality, keep the minimum pressure between the rollers and reduce the friction of the plate.

2 Make sure that the surface linear velocity of each roller and ink roller is equal as much as possible to reduce the plate wear caused by slippage.

3 Under the principle that the printing plate can not be dirty, use the least amount of water and maintain normal water supply to waterproof large ink.

4 Correctly grasp the PH value of the water fountain solution, and keep it within the appropriate range. The change should not be too great.

5 Maintain normal ink supply to prevent sudden changes.

6 Control the thickness of the ink layer to prevent it from spreading.

7 Strictly control the emulsification value of the ink and promptly remove the disadvantages of ink roller deinking caused by emulsification.

8 Reasonable use of driers to prevent early drying of printed surfaces.

9 Shut off the glue in time to stop the plate from oxidation.

10 to avoid a variety of man-made damage from the process.