Vor der Plasmabehandlung: Messung der Oberflächenenergie
Jede Materialoberfläche hat eine einzigartige Oberflächenenergie, die bei der Weiterverarbeitung eine entscheidende Rolle spielt. Diese und die damit verbundene Benetzbarkeit einer Oberfläche hat einen großen Einfluss auf die Haftung von Flüssigkeiten auf der Oberfläche, wie z. B. Klebstoffe oder Druckfarben. Techniken wie die Kontaktwinkelmessung lassen konkrete Rückschlüsse auf die Benetzbarkeit von Materialoberflächen zu. Eine Vorbehandlung der meisten Oberflächen vor dem Verkleben mit anderen Materialien ist daher oft unerlässlich, da z. B. die meisten Kunststoffe eine schwer benetzbare Oberfläche haben – der Anteil unpolarer Teile im Kunststoff ist sehr hoch.
What Is Surface Energy?
Surface energy is a key parameter for evaluating solid surfaces. It describes the energetic conditions at the interface and significantly influences the wetting behavior of liquids as well as the resulting adhesion in subsequent processes.
High surface energy generally promotes wetting, while low surface energy can lead to poorer spreading behavior. In industrial surface treatment, it is therefore an important indicator of whether a substrate has been properly prepared for bonding, painting, printing, or coating processes.
Wettability and Adhesion
Wetting describes the behavior of a liquid upon contact with a solid surface. The better a liquid spreads, the higher the wettability generally is. The contact angle is an important measure of this behavior.
Adhesion, on the other hand, describes the quality of bonding between a substrate and a subsequent medium, such as an adhesive, paint, or coating. Wettability and adhesion are closely related but are not identical: good wettability is often an important prerequisite for good adhesion, but it does not replace it.
Plastics, Metals, and Glass
Wetting properties depend heavily on the material.
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Plastics often have comparatively low surface energy. As a result, liquids tend to wet the surface less effectively, which can compromise process reliability during bonding, printing, or coating. -
Metals generally have higher surface energy. However, their wettability can be significantly affected by oxidation, contaminants, or storage conditions. -
Glass is generally highly wettable, but its behavior can be significantly altered by fingerprints, organic residues, or other contaminants.
Why Surface Testing Is Important
Surfaces cannot always be reliably assessed visually. A surface that appears clean to the eye may still be chemically unsuitable for the next process step.
Inspection before or after treatment helps better evaluate surface conditions, make process changes traceable, and improve reproducibility in development, quality assurance, and production.
Connection to Plasma
Plasma treatment is used to specifically modify surfaces and improve their properties for subsequent process steps. These include, among other things, increased wettability and, often, improved adhesion.
If you'd like to learn more about the physical and technological fundamentals of plasma treatment, you'll find a good introduction on the What is Plasma.
How Can a Surface Be Tested?
Various methods are available for evaluating surfaces. The appropriate method depends on the material, the specific application, and the desired measurement accuracy.
