In order to be able to successfully coat, print, lacquer or glue plastic and metal products, the surface has to satisfy a number of requirements. It has to be extremely clean, yet sufficiently active to form a strongly adhering bond with the coating material. These two conditions are fulfilled by plasma treatment. The ions and electrons in the plasma bring about an ultra-fine cleaning on coming into contact with the surface. This eliminates thin residues such as fingerprints, for example. In addition, plasma treatment is a universal and highly efficient method of increasing surface tension, thereby enabling good wetting of lacquers.