Offset quality control - use of fountain solution (two)
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Eleventh, the management of the water tank
The temperature of the water tank is set: the temperature in winter is set to 10 °C, and the temperature in summer is set to 8 °C. If the temperature is too low, the ink will be pulled out. If the temperature is too high, the paste will be produced. And often check if the cooling system is working properly.
Tank cleaning cycle: It is recommended to change the water once a week and clean the tank.
Cleaning and replacement of the water tank filter: It is recommended to clean once a week and replace it every month.
Cooling device air filter cleaning: It is recommended to clean once a week, otherwise it will affect the cooling effect.
Twelfth, the choice of alcohol and dampening solution
Many factories use edible alcohol or industrial alcohol in dampening solution. The composition is: ethanol, which has a slower ink balance during printing and a large amount of addition.
It is recommended to use isopropyl alcohol. The ink balance is fast when printing, and the amount of addition is small, generally: 8%--12%. The better the performance of the fountain solution, the smaller the amount of isopropyl alcohol added.
When purchasing isopropyl alcohol, try to buy from a large chemical plant, otherwise it will lead to insufficient isopropyl alcohol content, affecting the wetting effect.
At present, there are many brands of dampening liquid additives on the market, and the prices are different. Because many factories reduce the printing cost, they only consider the unit price, regardless of their wetting performance, resulting in large water supply and poor quality of printed products. The dampening solution with good wettability has a relatively high unit price, but the added amount is small, the total amount is small, and the total cost is not necessarily higher than the low-priced dampening solution additive. If used correctly, the cost can be reduced. Therefore, it is recommended to use branding fountain solution when using dampening solution additives, such as: Heidelberg superdot fs-12, etc. The brand dampening solution additive has stable quality, small addition amount, small amount of isopropyl alcohol added, and printing time. The amount of water is small, the ink is not easy to emulsify, and the printing quality is stable.
Thirteen, the consequences of excessive water hardness
The higher the content of Ca2+ and Mg2+ ions, the higher the hardness of water. In the dampening solution, the concentration of Ca2+ and Mg2+ ions is too high, which will cause the ink to be emulsified, and in the high-speed printing process, the temperature will cause the dampening solution to be in the dampening solution. Mg(HCO3)2 and Ca(HCO3)2 decompose to form CaCO3 and MgCO3 which are insoluble in water. Calcium adheres to the water roller, which easily blocks the water supply, and a paste failure occurs, which adheres to the ink roller, which will cause the ink roller to crystallize, affecting the ink transfer, and causing the ink roller to be deinked.
Fourteenth, consequences of incorrect use of alcohol and dampening solution
Poor performance of the fountain solution additive or excessive addition will lead to excessive emulsification of the ink, resulting in ink roller deinking, ink return water tank, ink accumulation in the water roller, poor color balance, ink is not dry, prints are dull and other faults.
The quality of the alcohol is not good or the amount is too large, which may dissolve the ink, causing the ink to be extremely emulsified and causing the above failure.
If the fountain solution additive does not match the ink used, it will also cause the above failure.
Fifteenth, offset printing water consumption and water control
Offset fountain solution consumption is mainly in the following aspects:
1. The emulsification of the ink consumes water. The slight emulsification of the ink helps to quickly balance the ink and water, and the larger the amount of ink, the greater the amount of water that needs to be counterbalanced.
2. The paper absorbs the amount of water consumed. Since the fiber characteristics and smoothness, uniformity, sizing degree, water content, and expansion ratio of various papers are different, the water absorption amount of the paper at the time of printing is different. Generally, the uncoated paper absorbs more water than the coated paper.
3. The amount of water consumed by evaporation to the space.
4. Squeeze and throw the amount of water.
Offset determines the conditions of water consumption
1. The area and distribution of the layout part of the layout. The graphic part of the printing plate has a large area and a large amount of water.
2. The thicker the printing ink layer, the larger the water consumption, the thinner the ink layer, and the smaller the water consumption;
3. The paper fiber structure is loose, the surface is rough, and the water absorption property of the paper is strong; the coated paper, card paper and the like are dense in structure, the surface is smooth, and the water absorption is small.
4. The ink has good water resistance, small emulsification value and less water consumption.
5. The higher the speed of the offset printing machine, the more water it consumes. The ambient temperature is high, the humidity is low, the air circulation is comfortable, and the amount of water consumed is large.
6. The better the quality of the plate, the better the sand treatment, and the smaller the water supply.
7. The printing pressure of the offset printing is large, and the consumption rate of the fountain solution is high.
8. The higher the hardness of the blanket, the greater the consumption of dampening solution.
For the above reasons, different printing water should be used according to different printing materials. When replacing the printing plate, the water quantity should be reduced to the printing plate paste, and gradually increase the water volume to the printing process during the color registration process. The version is not smeared, so as to achieve printing with the minimum amount of water, to avoid large water and large ink, thereby controlling the printing quality.