Why does the ink color change? How to fix it?
Time:2025-03-04
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Quantity of stock solution supplied
1. Cause analysis
The supply of water is too much, so that the pH value of water is smaller, causing ink separation (connection material and pigment separation), resulting in uncontrollable water consumption, resulting in ink color change, sometimes produce dirty plate phenomenon, while increasing water, dirty plate phenomenon is more serious; If the supply amount of the moisturizing liquid is less, the pH value of the moisturizing liquid will increase, and the insufficient hydrophilic layer will be added to the blank part of the printing plate, which can not resist the intrusion of ink, resulting in large water consumption of the printing plate, resulting in paste plate and ink color discoloration.
For example: Printing is a large area of gradual gradual dot, found in the printing process gradually paste plate, ink color change, thought it was dirty plate phenomenon, increase the water consumption, the problem has not been solved, so immediately shut down, clean the plate with plate cleaning agent, measure the pH value of the moistening solution, adjust the supply of the moistening solution, so that the pH value of the moistening solution is reduced to about 5.0, the problem is solved.
2. Elimination method
Replace the moistening solution, or adjust the supply of the moistening solution, so that the pH value of the moistening solution is controlled at 5.0 ~ 5.5.
Replace the moistening solution, or adjust the supply of the moistening solution, so that the pH value of the moistening solution is controlled at 5.0 ~ 5.5.
Alcohol addition ratio
1. Cause analysis
The proportion of alcohol added is too large, although it can reduce the surface tension of water, make the water film thin, and the wettability (that is, spreading) of the plate surface is good, but it will cause the reaction of alcohol in water with the liquid colloid of the plate, resulting in coagulation phenomenon, resulting in large water and ink, resulting in ink discoloration; On the contrary, the proportion of alcohol added is not enough, it will cause the surface tension of water is high, the wettability of the layout is poor, and the water quantity must be increased to make the ink not dirty, so the ink color is discolored.
For example: A printing of packaging paper, due to the failure to pay attention to the alcohol has been used up, resulting in a 6% reduction in the proportion of alcohol, dirty plate phenomenon, increase the amount of water, dirty plate phenomenon disappeared, but the ink color gradually discolored, stop the inspection, control window plate display alcohol content reduced to less than 6%, replace the alcohol barrel, so that the alcohol content of 10%, start the printing water to the previous amount, There are no dirty plates, and the ink is normal.
2. The elimination method controls the water in the tank so that the set ratio of alcohol is consistent with the actual value. Alcohol set ratio of 10% ~ 14%; Isopropyl alcohol is set at 8% to 13%.
Hardness of water
1. Cause analysis
The hardness of water is high, the calcium oxide, magnesium oxide and other substances contained in the water will be transferred to the surface of the ink roller together with the chemical composition of the ink and the paper powder and the spray powder, resulting in the ink roller deinking and ink transfer can not be controlled, and the fatty acids contained in these substances will also lead to the increase of the ink alkaline, which is easy to cause the paste phenomenon and cause the ink color discoloration.
For example: the long-term use of high hardness of tap water, easy to make the ink roll produce crystals, causing the ink roll crystallization, and the printing reflects the large amount of water, the water pattern is thicker (mainly when printing the field version, if the alcohol ratio is low, this phenomenon will occur), causing paste version, dirty version, printing dark, and easy to block the water tank water pipe.
2. Elimination methods
The use of softened water to reduce the amount of water, so that the water lines become finer, not easy to paste the plate, the gloss of the printing product is improved, and the crystallites on the surface of the ink roller are relatively reduced.
Moistening fluid replacement time
1. Cause analysis
Due to the long-term circulation of the moistening liquid, there will be too many microorganisms in the moistening liquid, which will cause the deterioration of the moistening liquid, resulting in unstable water supply and ink color discoloration.
For example, when printing a quarter cover, sampling inspection found that the ink color on both sides of the print was discolored. Stop the inspection found that the layout is still very wet, and concluded that the water caused the printing plate layout water volatilization slowly. Check the water roller ink mark pressure is normal, reduce the water consumption, the middle of the dirty plate, the analysis may be the wet plate liquid has not been replaced for a long time, resulting in the wet plate liquid deterioration, resulting in uncontrollable water film. After replacing the water tank, the printing ink is normal.
2. Elimination methods
Replace the water conditioner in the water tank regularly. Install a drain pipe in the water outlet of the water tank, and connect the upper water outlet to the water pipe of the machine, which can quickly clean the water tank. If a filter cloth cover is installed at the return port to keep the water in the water tank clean, the water pipe can be prevented from being blocked for a long time.
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Anna Zhang