Most Flexo printers understand that when printing with aqueous ink, the viscosity of the ink must be taken into account and kept constant. In the laboratory, operators use the Zahn cup and meter to observe that checking viscosity is the most common job. If the viscosity of the ink is higher than the expected value, some water will be added, but the problem will happen at this time. Now.
If water is used alone to control the viscosity of the ink, each time water is added, the ink's acid value decreases as the viscosity decreases. The pH of water is 7 and Flexo's water-based inks are generally controlled by the supplier, typically between 8.5 and 9.5. When the pH drops, the effect of ink components will begin to change. Lower pH values ​​will have a significant loss of color intensity, and even more, the ink will begin to separate or split and produce muddy phenomena, high pH values. It will also result in the loss of structure and composition.
Today, pH is considered to be the most critical factor in controlling the midrange of Flexo printing. Is pH more important than viscosity? The answer is correct. However, pH and viscosity are inseparable when establishing and maintaining the most suitable ink, and the two are mutually controlled.
Use the correct viscosity adjustment fluid
How to control the pH and viscosity? First, you must use the pH meter to detect the pH, understand the ink composition, the acidity of the additive, and record the changes. Urban water usage may vary by more than one unit at different times of the month. In addition to adjusting the viscosity with water, another pre-mixed adjustment solution can also be used. This adjustment solution contains some amount of amines and other components. Usually, the adjustment solution provided by the printer can increase the pH of the printing ink by 1 ~1.5. At this time, water can no longer be used to adjust ink.
Both the pH and the viscosity are the key to the success of printing. In the establishment of printing, pumps, rollers, measuring systems, printing plates, stapled back operations, materials and drying, the ink is only at the best viscosity. The best color can be obtained with the pH value. Many letterpress printers have found that colors can come into contact with one another during overprinting, platen pad or color overprinting. Therefore, the most useful way is to increase the viscosity and lower the pH, which helps the drying process and avoid post-printing. The color is moistened by the color of the previous printing, for example: This method obviously requires more than one type of adjustment fluid to be added to each ink machine to adjust the required viscosity. Again, these adjustment fluids must be at a pH of 1.0 to 1.5 per ink.
The significance of system automation
In the use of printing ink, the use of automated viscosity and pH control system can effectively detect the stability of the ink on the line, thereby reducing the ink film and ink loss, while reducing the volatile organic compounds (VOCs) (amines, The use of alcohols or other solvents will save the printers valuable time and other important tasks.
Today's newer generation of automatic control systems have excellent accuracy and reliability. They can be easily operated and maintained. Both multi-unit or single-unit control systems can be purchased at a lower price than before, and some even provide SPC/ISO report.
Finally, it must be mentioned that, whether using an automated system or manual operation, the most important thing is to adjust the use of liquid rather than water.
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