Magnetically enhanced RF discharges for effective pre-treatment of plastic webs at high speed

Based on a capacitively coupled 13.56 MHz RF discharge (CCP), a linear plasma source of hollow-cathode design, 400 mm wide (asymmetric CCP) has been developed for the inline pre-treatment of plastic webs at speeds above 3 m s−1. A magnetic field (B≈10 mT) is applied in the discharge region, to enhance the favorable properties of confined asymmetric CCPs (e.g. good utilization of RF power, close contact of substrate surface and plasma and the additional ion bombardment of the substrate surface). The influences of B on sheath potentials and ion energy distribution are shown by plasma simulation. Furthermore, the shift of the nearly pure capacitive discharge to a more resistive one will be demonstrated by measurements. As an application of the new RF plasma source, the influence of pre-treatment on the barrier properties of Al coated polypropylene (PP) at web speeds vweb=3–6 m s−1 will be shown.