pH and viscosity control of water-based printing inks
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Most Flexo printers understand that in the process of printing with water-based inks, it is necessary to pay attention to the viscosity of the ink and keep it constant. In the laboratory, the operator uses the Zahn cup and the code table to observe. Checking the viscosity is the most common job. If the viscosity of the ink is higher than the expected value, some water will usually be added, but the problem will occur at this time.
If water is used alone to control the viscosity of the ink, the acidity of the ink will decrease as the viscosity becomes smaller each time water is added. The pH of the water is 7, while the pH of the Flexo's aqueous inks is generally controlled by the supplier, usually between 8.5 and 9.5. When the pH value drops, the effect between the ink components will start to change. The lower pH will have a significant loss of color strength. What's more, the ink begins to separate or split to produce muddy phenomenon, high pH. It also leads to a loss of structure and composition.
Today, pH is considered to be the most critical factor in controlling Flexo's mid-range printing. Is pH more important than viscosity? The answer is correct. However, when establishing and maintaining an optimum ink, the pH and viscosity are inseparable and the two are mutually controlled.
Use the correct viscosity adjustment fluid
How to control the pH and viscosity? First, you must use the pHmeter to detect the pH value, understand the acid value of all ink components and additives, and record the changes at any time. Urban water use may vary by as much as one unit at different times in a month. In addition to water to adjust the viscosity, another premixed conditioning solution can also be used. This conditioning solution contains some amount of amines and other ingredients. Usually, the ink provided by the ink supplier can increase the pH of the ink by one. ~1.5, then you can no longer use water to adjust the ink.
Both pH and viscosity are the key to the success of printing. In the environment of printing, pumping, roller, measuring system, printing plate, binding and finishing, materials and drying, the ink is only at the best viscosity. And the pH to get the best color. Many embossers have found that color interactions occur during overprinting, plate liners, or color overprinting, so the most useful way is to increase viscosity and lower pH, which helps the drying process and avoids post-printing. The color is wetted by the previously printed color, as an example: This method obviously requires more than one conditioning fluid to be added to each of the ink dispensers to adjust the desired viscosity. Furthermore, these adjustment fluids must be above the pH of each ink by 1.0 to 1.5.
The meaning of system automation
In the use of ink, the use of automated viscosity and pH control system can effectively detect the stability of ink on the line, thereby reducing ink film and ink loss, while reducing volatile organic compounds (VOCs) (amines, The amount of alcohol or other solvent used can save valuable time for other important tasks for the printing industry.
Today's newer generation of automatic control systems have excellent accuracy and reliability, can be easily operated and repaired, and can be purchased at a lower price than any other unit or single unit control system, some even provide SPC/ISO report.
Last but not least, whether using an automated system or manual operation, the most important thing is to use the conditioning fluid instead of using water.