The amount of fountain solution and alcohol is set correctly, but it often dries. What could be the reason?
In the lithographic printing process, the so-called "water drying" means that the blank part of the printing plate does not form a sufficient uniform water film, that is, the amount of water in the non-image part on the printing plate is insufficient. Once the water drying phenomenon occurs on the offset printing plate, it will cause the blank part of the printing plate to be dirty, which will affect the quality of the printed product. That is to say, the water-ink balance is out of control during the printing process.
In the offset printing process, the control of water-ink balance is related to many factors, including the adjustment ratio of ink volume and water volume, the quality of the fountain solution itself, the concentration of fountain solution, the amount and temperature of alcohol, the nature of the ink itself, and the pressure of the ink roller , Ambient temperature and humidity, etc.
If the amount of fountain solution and alcohol used in the printing process are correct, the reason for the plate water drying may be caused by the improper setting of the ink roller of the ink supply system and the water roller of the water supply system during the printing process, or it may be It is related to the quality of the fountain solution used in the printing process.
If the printing pressure between the inking roller of the ink supply system and the printing plate is too high, it will accelerate the abrasion of the sand part of the blank part of the printing plate, resulting in a decrease in the hydrophilic performance of the non-image part of the printing plate, making the blank part of the printing plate in the original Under the condition of water supply, it is not possible to obtain a sufficient amount of water, and the phenomenon of water drying on the printing plate surface occurs.
If the pressure setting between the inking roller and the printing plate in the ink supply system is correct, the water drying phenomenon still occurs. The cause may be caused by the improper pressure setting between the water rollers in the water supply system. Especially when using alcohol fountain solution, the surface tension of the alcohol fountain solution is low and the spreadability is good. Even a small amount of fountain solution in the blank part of the printing plate can form a uniform water film, which greatly reduces the Layout water supply. Therefore, the insufficient pressure between the water rollers is more likely to cause the dry plate phenomenon. On the other hand, if oil stains adhere to the water roller, it will also affect the water supply of the water roller, resulting in water drying failure on the printing plate.
Even if the amount of fountain solution and alcohol used in the printing process is set correctly, it does not mean that the quality of the fountain solution used is stable. The fountain solution should also have pH buffering performance, printing plate protection performance, wetting performance, anti-corrosion performance, sterilization performance and anti-foaming performance. The buffer in the fountain solution is mainly used to stabilize the pH value of the fountain solution, because the original solution of the fountain solution is generally acidic. As the amount of buffer added changes, the pH value of the fountain solution will fluctuate greatly. Inappropriate amount will affect the hydrophilic performance of the printing plate. The protective performance of the printing plate refers to the protection of the hydrophilic performance of the printing plate. If used improperly, it will also reduce the hydrophilic performance of the printing plate, resulting in water drying. The fungicide can prevent the growth of algae and microorganisms in the water circulation system, and avoid the blockage of the pipeline; the anti-foam agent can prevent the generation of foam and prevent a large amount of foam in the water tank from conducive to the wetting of the printing plate.
Therefore, when water drying occurs during the offset printing process, you need to first check whether the pressure setting between the inking roller and the water roller is correct, and clean the water roller regularly. In addition, in the printing process, high-quality fountain solution must be selected. When selecting the fountain solution, users should combine the water quality and other conditions of the printing plant to strictly control the amount of fountain solution and isopropyl alcohol ( Alcohol), the amount of fountain solution pH and conductivity and other indicators.
From the above analysis, it can be seen that, in addition to the printing plate, inking and watering system, the fountain solution is the most important factor for water drying failure during the offset printing process, even if the amount of alcohol in the fountain solution and the amount of fountain solution are set. They are all correct, and offset printing can also be caused by other factors.
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