The Principle of Corona Treatment
The set-up of a corona system for foil treatment generally consists of one or several high-voltage electrodes arranged at a distance of between 1 to max. 3 mm from a grounded roller. If a high voltage is applied to the electrodes, a corona discharge occurs in the gap between the electrodes and the roller, and a plasma is formed. The electrodes and/or the roller are covered with a non-conductive barrier (e.g. ceramic, quartz or silicone), which has also given rise to the term barrier discharge. If a plastic film is guided over the grounded roller through the discharge gap, the surface of the film becomes oxidized. The oxygen in the air serves as the raw material for this oxidation. As a result of the oxidation reactions, polar groups containing oxygen are implemented in the surface of the plastic, resulting in improved wettability of the surfaces and in most cases also improved bonding on the plastic surface.