How to successfully apply alcohol-free printing in production? (one)

When I was conducting research on a large printing company in Shenzhen, I saw that the company was promoting non-alcohol printing and achieved good results. The use of non-alcoholic printing not only reduces printing costs, but is also more environmentally friendly. It can reduce the environmental problems caused by the volatilization of alcohol, and compiles this non-alcoholic printing article so that everyone can better understand and apply it. Alcohol printing.

Alcohol-free printing using alcohol substitutes is more likely to achieve ink-water balance. Printing with a specific thickness of ink film that has not been diluted with alcohol can result in higher-quality prints with fine dots and less emulsification.

Alcohol substitutes

Alcohol replacements differ from IPA (isopropyl alcohol) in several key properties, including their viscosity, surface tension, pH, and conductivity of the fountain solution. Non-alcoholic products cannot be freely applied to different printing presses. This requires close communication with the printing operators and seeks the best fountain solution formulation from suppliers.

In fact, there are many alternatives to alcohol that can be used. They are all composed of one or more chemicals extracted from the chemical groups of glycols and glycol ethers, and some other additives like IPA are also added. And these formulas all try to completely replace the IPA in the fountain solution and provide some unique properties. More importantly, the concentration of alcohol substitutes we use is much lower than the concentration of IPA. Under the same printing conditions, a small amount of alcohol substitutes can achieve 10 to 20 times the effect of containing IPA fountain solution.

Fountain solution viscosity

Adding IPA to the fountain solution greatly increases its viscosity, but many alcohol substitutes have little or no effect on viscosity. Due to the lower viscosity of alcohol substitutes, less fountain solution is measured by extrusion or using a measuring roll on a continuous contact dampening roller. This necessitates an increase in the dampening roller speed, causing many printing operators to mistakenly determine More water must be used when printing with an alcohol substitute fountain solution. In fact, the solution to increase the viscosity to a certain extent is to cool the fountain solution.

Surface Tension

The ability to wet the plate quickly and form a thin film of water is the two key requirements for offset printing on the fountain solution, which is primarily determined by the surface tension of the fountain solution. It is generally believed that the dampening fluid with low surface tension can be used in high-speed printing, but there is also the opposite report in Europe. It is understood that current alcohol alternatives can achieve the low surface tension of IPAs that print operators are accustomed to.

The surface tension of pure water is 72×10-3N/m. In the fountain solution, the alcohol concentration is 10% to 25%, and the surface tension is reduced to (35～45)×10-3N/m. The fountain solution rapidly forms a continuous film covering the entire printing plate. Alcohol-free fountain solutions use surfactants and solvents to reduce surface tension.

Surfactants or surface active additives are all organic chemicals, because of their polar molecular structure, they all tend to concentrate on the interface. Under normal conditions, they are at the interface between fountain solution and air and ink and air. In the case of high-speed printing, these interfaces change rapidly, so the surfactant must disperse quickly to replenish the new interface. A large amount of surfactant in the fountain solution is very important in the printing process, but too much addition will exacerbate ink emulsification.

Printing brightness and gloss

Alcohol is a diluent that actively attacks the ink. It delustens the ink and affects the color. To achieve acceptable color, a thicker ink film is required on the impression cylinder. When used at the proper concentration, alcohol substitutes do not dilute the ink, achieving acceptable colors requires only a small amount of ink and water, so that dots will be more accurate, and the dot gain tendency will decrease.

Conductivity and pH

In printing, it is very important to maintain the consistency and stability of conductivity and pH. The conductivity of the dampening fluid should be measured before printing. Any impurity may cause abnormal conductivity, and the conductivity of the water should be re-examined. During the printing process, both the ink and the paper may contaminate the fountain solution, and the increase in electrical conductivity is normal.

The pH can be measured while measuring conductivity. The pH of the acidic fountain solution should generally be 4.0-5.0. For high-quality printing, it is important to maintain the optimum pH for the fountain solution used. All acidic dampening solutions have a buffering effect to some extent. If the concentration increases, the conductivity will continue to increase at a linear rate, while the pH value will begin to decrease and then tend to be gentle. Therefore, the conductivity can determine the concentration of the fountain solution more than the pH value.

If the pH is too high (greater than 5.5), the plate may be dirty and the water needs to be increased to keep the plate clean. This may result in severe emulsification of the ink. If the pH is too low (less than 3.5), the printing plate may become flowery, the ink will emulsify, the rollers will peel off, and the ink drying time will be prolonged.

Practical application of alcohol substitutes

There are 2 goals for using alcohol-free fountain solution. The first is to use safe materials to produce high quality products; the second is to choose and use non-alcoholic products to achieve better results. Depending on the dampening equipment, water, ink, substrate, and even the job, these choices will also be different.

Pretest alcohol substitutes

If a printing press is replaced with a new fountain solution, it must be tested and tested in advance. The actual test of a printing unit may sometimes be better than a laboratory equipped with various measuring devices. When testing, it should be within the range of measurable tolerances, the best way is to follow the instructions of the equipment. If the tolerances have a certain range, the setting and operating performance of the printing process can be recorded in the file starting from the lower limit.

When using alcohol substitutes, it is important to establish the best ink balance through print trials. Tests have shown that using alcohol-free materials may require adjustments to past production conditions. However, in order to accurately determine this point, the company's production conditions must be quantified.