The functional principle
Inside the sliding discharge source, a cold plasma on the basis of a dielectric barrier discharge (DBE) is initially ignited by means of alternating voltage. As shown in adjacent Figure in the middle, this is driven out of the center of the nozzle by the process gas flow and strikes the substrate surface. Here, sliding discharges in the form of long plasma filaments develop towards the earth electrode on the underside of the plasma source. These plasma filaments affect the substrate surface along its contour. This process enables a uniform and comprehensive treatment of surfaces, including possible indentations or cavities. Depending on the source execution and the distance from the source to the substrate (1 – 40 mm), effective treatment widths of between 10 and 120 mm are available.
A very good alternative to wet chemistry
The plasma source concept was developed within the framework of a publicly funded project as an alternative for wet-chemical primers in the preliminary stages of painting and laminating processes on PVC extrusion semi-finished products. As the ambient air in the treatment area is virtually completely displaced, the jet geometry furthermore ensures very homogeneous and reproducible treatment effects – largely independent of the prevailing ambient conditions – and enables, depending on the discharge distance, the utilized process gas and the specific plasma parameters, a very precise adaptation of the surface energy of the substrate to the medium which is to be applied, e. g. paint or adhesive system. Very efficient results have been achieved on PVC as well as on all other common polymer materials.
In close collaboration with industrial partners, the plasma source concept developed at the Fraunhofer IST is to be transposed into a practicable commercial solution in the future in order to provide a decisive contribution towards sustainable and environmentally friendly production processes.
The described results were achieved within the project “Neuartiges Plasmakonzept zur Oberflächenfunktionalisierung von Polymer-Extrusionshalbzeugen bei Atmosphärendruck unter Vermeidung von gesundheitsgefährdenden Stoffen – KF 2004825DF4” (Innovative plasma concept for the surface functionalization of polymer-extrusion semi-finished products at atmospheric pressure under the avoidance of hazardous substances - KF 2004825DF4), which was funded by the German Federal Ministry for Economic Affairs and Energy (BMWi).