ZHEJIANG ERHUI TECHNOLOGY CO.,LTD , https://www.jahhome.com
Although the size of the printing plate resistance force is related to the quality of the plate material and the quality of the plate making, the printing plate made under the same conditions, as far as possible to take reasonable measures to reduce the damage of the plate, can improve and maintain its resistance to printing force. Here is an example of a offset PS plate, from the following aspects to explore how to improve the printing plate resistance to printing force.
First, reduce the surface friction of the printing plate
During the printing process, the printing plate is rolled and contacted with the water (ink) roller and the blanket under a certain pressure to complete the transmission of the printing graphic and text. During this process, multiple frictions are generated, and the greater the printing pressure, the greater the friction. If the ink pigment particles are coarse or there is dry ink on the ink roller or if the paper is powdered off or the hair loss is serious, then the friction is more severe. In addition, the accuracy of the printing machinery is not high, and poor adjustment or improper use of the printing press can cause additional friction.
All kinds of friction start from printing, it will have a destructive effect on the surface structure of the printing plate, with the increase in the number of printing, the degree of damage to the surface of the printing plate gradually increased.
The abrasion of the blank part of the plate makes the sand grains gradually flattened, thereby weakening the water content of the plate to make the plate dirty. Especially in the bite portion of the layout, since the water (ink) roller and the blanket roller are in contact with each other, there is a noticeable bouncing phenomenon, and the impact force on the plate surface is the greatest. Therefore, it is faster and more serious to be dirty.
The wear and tear of the layout text changes the performance of its oil-resistant and water-resistant properties. For half-tone graphic (points), its low dot area, hydrophilic area is greater than the lipophilic area, is conducive to the expansion of water, it is more likely to lead to the formation of flowers in the low network (smaller network). On the other hand, in the high-lying network area, the lipophilic area is larger than the hydrophilic area, which is conducive to the expansion of the oil. When the mesh and the surrounding sand are worn, they are invaded by polar groups in the ink and form a lipophilic basis. Expanding the oleophilic area of ​​outlets and making them unclear. The phenomenon of flower and paste in general printing plates occurs at the same time.
Therefore, in order to ensure that the pressure of each part of the printing unit is the minimum and the rollers and levels, the following points must be noted:
1. Keep the surface speed between the water (ink) roller and plate cylinder as consistent as possible
2. The axis of the water (ink) roller should be straight and the outside diameter should be the same to keep it running at a constant speed.
3. Control the axial turbulence of the water (ink) roller within the minimum range
4. Use good quality inks and papers. If the quality of the sheet is not good, wash the blanket.
Second, reduce the galvanic corrosion and chemical corrosion of the printing plate
Since the plate of the PS plate is mainly aluminum, aluminum easily reacts with electrolytes and inorganic acids in the fountain solution to produce new inorganic salts and replenish the damaged hydrophilic film. The pH of the fountain solution should be controlled between 5-6. If the pH of the fountain solution is too high, the ink will emulsify severely, and the ink drying time will be delayed and the backside of the printed product will be exacerbated. Moreover, both of them will cause excessive corrosion of the printing plate. In severe cases, the oleophilic layer of the printing plate graphic part will fall off, and the phenomenon of “off the plate†will occur and the printing plate will be scrapped.
The temperature of the fountain solution is to ensure that the high temperature caused by the high-speed friction of the printing plate surface, generally should be controlled between 10-14 degrees. If the temperature of the fountain solution is too high, it will not only accelerate the chemical reaction between the fountain solution and the plate base, but also cause defects such as dirty plates.
2. Water and ink balance
In the printing process, the layout moisture should be controlled within the minimum required and should not be too large. If the layout of the water is large, the amount of ink must also be relatively increased, resulting in the image is not true, the quality of the impression of the print, while speeding up the damage of the printing plate. On the contrary, if the layout is too small, it will cause stencils, dirty plates, etc. It will also accelerate the damage of the plate.
The ink on the plate should be supplied in the required amount, and ensure that there is a certain residual ink layer on the plate after transfer. This not only can reduce the frictional wear on the graphic part, but also can prevent the direct contact of the graphic base with the fountain solution. And it is eroded. On the contrary, the ink layout is too small, not only the ink color of the ink is light, but because the layout graphic is not thin, the corrosion resistance of the resistance fountain solution is also poor, which will accelerate the damage of the printing plate. At the same time, the ink on the ink stick is too little, and the moisture on the plate surface is easily transmitted to the ink, causing the ink roller to deink without ink, resulting in a pattern phenomenon. Of course, supplying too much ink on the layout will make it paste, or cause dirty prints.
3. When the printing is stopped in the middle, it is necessary to give the printing plate to wipe the arabic glue. After the water in the glue evaporates, the dry and solid glue layer not only reduces the surface free energy of the blank part of the printing plate, but also cuts off the contact between the metal surface and the air. Prevents the carbon dioxide in the moist air from reacting with the blank part of the printing plate.
Measures to Improve the Print Resistance of PS Plates in the Printing Process
The printing resistance of a printing plate refers to the highest printing quantity that can be printed by the printing plate under the premise of guaranteeing the quality of the printing product, and also refers to the printing rate. The number of copies of printing plates that are printed depends mainly on the stability of the layout and blank space. Some of these plates are damaged and the plates lose their use value.