Every material surface has a specific surface tension. Every liquid (such as ink) also has an inherent tension. Reliable adhesion with long-term stability of printing, gluing or coating requires that the surface tension of the material is greater than that of the liquid. Plastics, for example, have predominantly low surface tensions (often less than 28 mN/m). If these plastics are to be printed, a surface tension of 40 mN/m for solvent inks or a surface tension of 56 mN/m for UV-curing systems is required. If water-based paint systems are used, the surface tension has to be above 72 mN/m.
For many industrial applications it is crucial that adhesives and/or printing inks and surface properties are optimally aligned. Targeted pretreatment with atmospheric-pressure plasma achieves a significant increase in surface tension. This gives materials the optimum capabilities for accepting printing ink (wettability) or adhesion.
To be able to optimally evaluate the process parameters for surface modification with Openair-Plasma®, the surface tension of the starting material has to be determined first. Even in ongoing processes, it has to be remeasured again and again for quality assurance purposes. The most important methods for surface determination are the test ink method (test inks), contact angle measurement (drop volume method), and dynamic measurement with the Surface Analyst™ goniometer or the Mobile Surface Analyser – MSA.