security films of the type used to make tamper - evident adhesive tape , also methods and apparatus for making the films . a polymer substrate film e . g . of hdpe , is plasma treated while passing over a roller . corona discharge is generated between a discharge electrode and the roller . the roller has a conductive external surface with a relief pattern or cut pattern constituting an array of indicia such as the word “ void ”. the roller surface may be a layer of conductive polymer , laser cut to make the pattern . no plasma forms on the outer surface in pattern regions where the roller surface is recessed , so a subsequently applied coloured polymeric ink layer adheres poorly in those regions . an adhesive layer and protective release layer are applied over the ink layer .