Offset Quality Control - Application of Wetting Liquids (5)

XI. Management of water tanks

Water tank temperature settings: winter temperature is set to 10 °C, summer temperature is set to 8 °C, the temperature is too low will lead to pull the ink, the temperature is too easy to produce paste version. And often check whether the cooling system is working properly.

Water tank cleaning cycle: It is recommended to replace the water once a week and clean the water tank.

Water tank filter cleaning and replacement: It is recommended to clean it once a week and replace it every month.

Cooling device air filter cleaning: It is recommended to clean it once a week, otherwise it will affect the cooling effect.

Twelve, the choice of alcohol and fountain solution

There are many factories that use edible alcohol or industrial alcohol in the fountain solution. Their components are: Ethanol. When printing, the ink and ink balance is slower and the amount of addition is larger.

It is recommended to use isopropyl alcohol. The printing ink balance is fast, 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, purchase it from a large chemical plant as much as possible, otherwise it will result in insufficient isopropyl alcohol content and affect the wetting effect.

At present, there are many brands of fountain solution additives on the market, and prices vary. Since many factories reduce their printing costs, they often consider only their unit prices, regardless of their wettability, resulting in large amounts of water and poor quality of printed products. The dampening fluid with good wettability has a relatively high unit price, but it has a small amount of addition and a small total amount. The total cost is not necessarily higher than the low price fountain solution additives. If used correctly, it can reduce costs. Therefore, when using fountain solution additives, it is recommended to purchase as much as possible brand fountain solution, such as: Heidelberg superdot fs-12 and so on, the brand fountain solution additive quality is stable, the amount of addition is small, the amount of isopropyl alcohol added is small, when printing The amount of water is small, the ink is not easily emulsified, and the printing quality is stable.

XIII. Consequences of excessive water hardness

The higher the Ca2+, Mg2+ ion content, the higher the water hardness. In the fountain solution, the high Ca2+, Mg2+ ion concentration will cause the ink to emulsify, and in the high-speed printing process, due to temperature causes the dampening solution Mg(HCO3)2 and Ca(HCO3)2 decompose to produce CaCO3 and MgCO3 that are insoluble in water. Calcium adheres to the water roller, which can easily stop the water and cause stencil failure. Adhesion to the ink roller will cause the ink roller to crystallize and affect the ink transfer, resulting in ink roller de-inking.

XIV. Consequences of incorrect use of alcohol and fountain solution

The poor performance of the fountain solution additive or the excessive addition amount will cause the ink to be over-emulsified, resulting in ink roller deinking, ink return water tank, ink accumulation in the upper water roller, poor color balance, ink quit, dull printing and other defects.

The poor quality or excessive use of alcohol may dissolve the ink, resulting in extreme emulsification of the ink and the above malfunction.

If the fountain solution additive does not match the ink used, it will also cause the above malfunction to occur.

Fifteen, offset printing water consumption and water control

Offset fountain solution consumption is mainly the following aspects:

1. Ink emulsification consumes water. The slight emulsification of the ink contributes to a rapid ink-water balance, and the greater the amount of ink, the greater the amount of water needed to compete.

2. Paper absorbs water consumption. Because the various fiber properties and smoothness, evenness, sizing, moisture content, stretch rate and other indicators are not the same, the paper's water absorption during printing is different. In general, non-coated paper absorbs more water than coated paper.

3. Evaporate into space to consume water.

4. Squeeze throws water.

Offset determines the conditions of water consumption

1. The area and distribution of the layout text. The plate area on the printing plate has a large area and a large amount of water.

2. The thicker the printing ink layer, the greater the amount of water used, the thinner the ink layer, and the smaller the amount of water used;

3. The paper fiber structure is loose, the surface is rough, and the paper's water absorption performance is strong; the coated paper, card paper and other structures are dense, the surface is smooth, and the water absorption is small.

4. The ink has good water resistance, low emulsification value and less water consumption.

5. The higher the speed of the offset printing press, the greater the amount of water consumed, the higher the ambient temperature, the lower the humidity, and the smoother air circulation, and the greater the amount of water consumed.

6. The better the quality of the plate, the better the sand treatment, and the smaller the amount of water.

7. Offset printing pressure is high and fountain solution consumption rate is high.

8. The higher the hardness of the blanket, the greater the consumption of fountain solution.

Based on the above reasons, when printing, different amounts of water should be used according to different prints. When replacing printing plates, reduce the amount of water to the plate stencil first, and gradually increase the amount of water to India in the process of registering and coloring. The version is not paste, in order to achieve the use of the smallest amount of water for printing, to avoid large water and ink, thus controlling the printing quality.

(author/Wang Huaming)
<China Packaging>