Ink surface tension during the printing process
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Ink surface tension
Did you know that the surface tension of ink plays a crucial role in printing process? The surface tension of ink determines how well it will adhere to the printing pad and transfer onto the desired substrate.
If the surface tension of the ink is higher than that of the product, the ink will contract instead of flow open. To make the product printable so that the ink can adhere better, pre-treatment of the product is necessary.
The surface tension hopefully increased by pretreatment is expressed in mN/m, formerly also in dyn/cm (which is still a widely used term).
For adequate adhesion of conventional printing inks, the surface tension should be between 38 and 40mN/m. UV printing inks require a surface tension of 42 to 46mN/m, while adhesives and water-based inks require surface tensions of 50 to 56 mN/m
Surface testing
Several methods for measuring surface tension are known:
- In the method of water drop angle measurement, a drop of distil[1]led water is applied through a syringe to the surface to be tested. With the help of a slant spinner, the drop is projected onto a screen. Using a needle on the disk, it is possible to determine the angle of the droplet. This method is the most accurate.
- There are also test pens, which use a felt to apply a liquid to the base of the test inks on the surface.
- Test inks, which are applied to the surface using a brush, are another mehode that is done according to a DIN standard (DIN 53364). The test inks are available in values between 28 and 56mN/m. These inks only last for half a year, after this period the value falls, i.e. a higher surface tension is measured than is actually present. This liquid is applied to the product. From the reaction of this liquid, we can derive the surface tension. If the surface tension of the product is greater than that of the test liquid, it will flow open rather than contract into droplets.
Sometimes, when testing the object, a pre-treatment may be required. But one sometimes only needs to clean the product once with alcohol. Grease, condensation, fingerprints,… can cause the measurement of a wrong value. So one should make sure that the product is clean and that one works at room temperature.
