When the dosage of dampening solution and alcohol is set correctly, “water dry” phenomenon occurs. What may be the reason?
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In the offset printing process, the so-called "water-drying" means that the blank portion of the printing plate fails to form a sufficient uniform water film, that is, the non-image portion of the printing plate is insufficient in water. Once the printing plate is dry, it will cause the blank part of the printing plate to become dirty, which will affect the quality of the printed matter, that is to say, the ink and water balance will be out of control during the printing process.
The control of ink balance is related to many factors, including the adjustment ratio of ink volume and water volume, the quality of dampening solution itself, the concentration of dampening solution, the amount and temperature of alcohol, the nature of the ink itself, the pressure of the ink roller, the ambient temperature and humidity. Wait.
If the amount of dampening solution and the amount of alcohol used in the printing process are correct, the reason for the plate "drying" may be that the ink supply roller and the water supply system water roller pressure are improperly set, and may also be used with the dampening solution used in the printing process. Quality related.
If the pressure between the inking roller and the printing plate of the ink supply system is set correctly, the phenomenon of "drying" still occurs, which may be caused by improper pressure setting between the water rollers in the water supply system. Insufficient pressure between the water rolls can easily lead to dry plate phenomenon. In addition, if there is oil on the water roller, it will also affect the water supply volume of the water roller, resulting in "water dry" failure of the plate layout.
Even if the amount of dampening solution and alcohol used in the printing process is set correctly, it does not mean that the quality of the dampening solution is stable. The dampening solution should also have buffering properties for pH, plate protection, wetting, anti-corrosion, bactericidal and anti-foam properties. The buffer in the dampening solution mainly functions to stabilize the pH of the dampening solution, because the dampening solution is generally acidic, and the pH of the dampening solution may fluctuate greatly with the addition of the buffer. Inappropriate will affect the hydrophilic properties of the plate. The protective property of the printing plate means that the hydrophilic property of the printing plate is protected. If it is used improperly, the hydrophilic property of the printing plate is also lowered, and the phenomenon of "drying" occurs. The fungicide prevents algae and microorganisms from growing in the water circulation system and avoids blockage of the pipeline. The anti-foaming agent prevents a large amount of foam from appearing in the water tank and is not conducive to wetting the printing plate.
Therefore, when the phenomenon of "drying" occurs during the offset printing process, it is necessary to first check whether the pressure setting between the inking roller and the water roller is correct, and to clean the water roller regularly. In addition, be sure to use high-quality fountain solution. When selecting the dampening solution, it should be combined with the water quality and other conditions of the factory. Strictly control the amount of dampening solution, the amount of isopropanol (alcohol) and the pH of dampening solution. And indicators such as conductivity.
It can be seen from the above analysis that in addition to the printing plate, the ink supply system and the like, the dampening solution is the most important factor for the occurrence of "water dry" failure in the offset printing process, even if the amount of alcohol and the amount of dampening solution in the dampening solution are used. The settings are correct and will cause "drying" due to other factors.