The composition and characteristics of dampening solution
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The fountain solution plays a very important role in the printing process. In the high-speed printing process, the printed portion can maintain hydrophilic and oil-repellent for a long time, so that the field and the dots can be kept clear. The fountain solution makes the non-printed areas insensitive and remains repelled with ink. The dampening solution can also control the plate temperature during printing, taking away the friction between the parts and the heat generated during the operation of the ink to lower the temperature. In addition, the dampening solution also promotes the emulsification of the ink during the printing process to ensure a certain degree of emulsification, so that the ink has good running property and quickly achieves the ink balance. The ingredients of the dampening solution include tap water, dampening solution concentrate and alcohol substitute.
First, the role of alcohol in dampening solution
● Reduce the surface tension of the dampening solution and enhance the wetting ability of the plate.
● Increase the viscosity of the dampening solution to make it easy to pass the gap between the crucible and the crucible.
● Accelerate ink emulsification but also prevent excessive emulsification of the ink.
● Help the evaporation of water to remove heat and have a cooling effect.
Second, tap water (Tap water)
Tap water accounts for about 85% of the fountain solution. The measure of tap water is expressed by the degree of hardness, which is expressed in HC. HC is a portion indicating the amount of calcium and magnesium in tap water, and the unit is oF (1oF = 10 mg/l calcium carbonate), which is a method for expressing French hardness.
Low HC: indicates that the tap water is soft water and contains a small amount of dissolved salt; high HC: indicates that the tap water is hard water and contains a large amount of dissolved salts.
Tap water hardness range:
0oF<-soft->9oF<-recommended range->27oF<-hard->45oF
We must note that the HC value of tap water will change with the weather. Hard water containing dissolved salts can cause the pores of the rubber roller to clog and affect its normal daily operation. Soft water accelerates the emulsification of the ink, causing rapid oxidation of the plate and accelerated decay of machine parts.
Third, the characteristics of dampening solution
1. pH (pH)
● The most ideal dampening solution pH is between 4.8 and 5.5.
● If the pH of the base is too alkaline (pH > 5.5), the ink-repellent layer of the printed portion will be dissolved, resulting in a decrease in the printing durability of the printing plate, and the ink tends to adhere to the non-printing place. In addition, the contrast between the field and the outlet will be reduced and the gloss will be reduced. In addition, because the hydrophilic groups are greatly increased, the ink is excessively emulsified, resulting in an imbalance of ink.
● If the pH is too acidic (pH < 4.8), the desiccant in the ink will be attacked and the drying speed will be slowed down.
●Because of the buffering effect in the fountain solution concentrate, it is not too accurate to use the pH to measure its dose.
2. Surface tension
The surface tension of the fountain solution is lower than that of tap water, which reduces the flow rate of the fountain solution and maintains the stability of the water and ink. It also allows prints to have good dot gain, gloss, print field and dot contrast.
3. Alcohol (Isopropyl alcohol-IPA)
Alcohol has three major effects, including:
● It has a high viscosity so that it has a good flow from the sink to the plate. Adding 12% algebraic alcohol will increase the viscosity from 1 to 1.7.
● The interface tension between water and ink will be reduced, so that the ink balance can be reached faster and the printing can be continuously operated, reducing the amount of paper loss.
● Reduce the surface tension between water and the printing plate to form a film, so that the amount of dampening solution is further reduced.
4. Temperature control
• The cooling system must be used to reduce alcohol evaporation, algae growth and to maintain water flow and average printing speed.
● Alcohol has good volatility, which allows the temperature of the dampening solution to be controlled.
● The optimum temperature of the dampening solution tank should be 10-12oC. If the temperature is too low, the moisture in the air will condense on the printing machine.
5. Protection function
Because the metal part of the printing press is to be corroded, the dampening solution contains anti-corrosive substances.
6. Conductivity (Conductivity)
The conductivity value is expressed in μs/cm. Since different brands of dampening fluids have different characteristics, it is difficult to set an optimum conductivity value. The conductivity value actually indicates how much fountain solution concentrate is added.
● The numerical value of the conductivity value is proportional to the amount of the additive, but the pH value will remain unchanged to a certain extent. Only the conductivity value will change with the concentration of the fountain solution; therefore, the conductivity value can be given a comparison. Accurate method to measure the shade of the dampening solution.
● The circulation system of the dampening solution must be cleaned regularly and the conductivity should be kept in the range of 700-1700 μS/cm. However, different brands of dampening solutions have different values, such as Vegra's dampening solution should be kept within 1000-1300μS/cm.
Fourth, how to check the fountain solution
1. How to prepare the "ideal" fountain solution
● First we must measure the HC value of tap water.
● Measure the pH value according to the minimum amount of the fountain solution recommended by the supplier.
● Add the appropriate generation of alcohol, you must measure the conductivity value before using the dampening solution, as it can be used as a reference value.
2. How to control the quality of dampening solution
● First check if the alcohol content of the added generation is appropriate. Excessive alcohol will lower the conductivity, but if too little alcohol will increase the conductivity.
● Measure the conductivity value.
● Measure the pH value.
● Check the dosimeter regularly for proper operation.
Fifth. How to eliminate or reduce the amount of alcohol used in dampening solution
Eliminating or reducing the use of alcohol on dampening solutions can save you money. In general, the supplier will give two product choices:
1. Alcohol reducers
This is the easiest way to achieve alcohol reduction, which allows the alcohol content to be reduced from 12% to 5% without any change in printing conditions.
2. Alcohol substitute
This is a method that completely eliminates the use of alcohol, but must be compatible with other printing conditions, such as: the leeches must have the proper hardness, different water pressure and so on.