In Reply to: what to use improve the adhesion of aluminium coated (using vacuum metalizing process) on PC & PMMA without the use of base coat on the plastics posted by Y.H Wan on 12/17/02 at 4:08 AM:
Generally a plasma (or corona of flame) treatment is used. In the plasma treatment, oxygen is grafted on the surface thus increasing the surface energy and decreasing the wetting angle with water. The aluminum then bonds to the oxygen that is grafted on the surface.
However, it is possible to "overtreat" the surface and make the near-surface region brittle thus decreasing the apparent adhesion as the failure is in the near-surface region. Thus there is an acceptable range of wetting angle and the treatment can vary some over the surface but not too much.
For example when properly treating OPP the wetting angle of water decreases from about 106 degrees to about 70 degrees. How fast this occurs depends on the treatment method and plasma properties. Wettability can be measured using ASTM D2578-84 (dyne solution test method). Don Mattox