Plasma methods

Atmospheric pressure plasma and low pressure plasma

Artificially generated plasma is used, for example as a physical surface pre-treatment method. In contrast to "hot" plasmas for plasma welding or plasma cutting, these technologies are called "cold" plasmas. Here, a distinction is made between low-pressure plasma (NDP) and atmospheric-pressure plasma (ADP). ADP systems are typically devices that can be integrated into various automation solutions under normal pressure conditions and where the plasma chamber is located in a head that can travel over the area of a component to be processed. ADP systems are ideal for integration into production lines for industrial applications, for example, for the application of adhesive beads or liquid sealants. 

NDPs are chamber systems in which a vacuum is first created and then a process gas is introduced, which is then sparked off to form plasma. In NDP systems, the components are placed or injected into a chamber. In this vacuum chamber, the plasma can reach and rinse almost the entire exposed surface including cavities of a product, whereas ADP systems are used selectively and are limited in their effective depth and width.  

Method of action of plasma technology

When a plasma hits a surface, molecular and intermolecular bonds are broken and chemical reactions are generated, so that after a plasma process the treated surface has a significantly higher surface energy and a higher oxygen group enrichment. The surface thus allows significantly higher wettability (hydrophilic property) and adhesion (adherence). A change in surface roughness can also be observed. Theoretically, the effects are differentiated as fine or ultra-fine cleaning, as activation or as functionalisation of a surface.

These effects favour the adhesive strength of adhesives, pressure media, plastics or other media and thus the long-term resistance of such connections even under higher loads. As an example, imagine a sensor system installed on the outside of a vehicle that is exposed to splash water and, in winter, aggressive salt water.

The cleaning usually has a penetration depth of nanometres to micrometres. Since every surface is never 100 per cent clean, but has certain boundary layers of impurities, adsorbates and reaction layers (additives, oxides), fine cleaning is necessary for further treatment.