High speed in-line treatment of plastic webs for vacuum coating
Beside the layer quality a good adhesion between coating and polymer substrate is a precondition for the manufacture of quality thin film products. Due to the inertness of most polymer surfaces an appropriate treatment of substrates prior deposition is necessary. Typical examples for the necessity of pretreatment are the deposition of barrier layers on BOPP film and the deposition of layer systems on organic hardcoat for window films. The classic methods are the corona treatment as a separate step prior vacuum coating and the plasma (glow discharge) treatment as in-line process. However, we could show that energetic ion bombardment typical for sputter etching processes is superior to simple plasma treatment in many applications. Two technical solutions for the pretreatment of substrates by sputter etching will be presented. The Web Treater uses an asymmetric RF discharge to power a plasma and to maintain an energetic ion bombardment also for electrically insulating substrates without restrictions in film thickness. MF bias treatment is a method suitable especially for plastic film substrates up to 100 micrometers thick. High treatment doses can be achieved due to the large treatment area. Both methods combine the surface activation effects by plasma radicals and radiation with the particle removal and cross linking action caused by energetic ion bombardment. Since electrical substrate charging is avoided by nature additional neutralizer is not necessary.