Plasma pretreatment of polymer films as a key issue for high barrier food packagings

Abstract The food packaging industry demands cheap polymer films possessing a high barrier against permeation of gases, moisture and flavor. Candidates for the most successful materials fulfilling these requirements are newly developed laminates of biaxial oriented polypropylene (BOPP) films containing a thin inorganic barrier layer and possessing an oxygen permeability lower than 3 cm3/(m2 dbar) and a moisture permeability lower than 0.05 g/(m2 day). The thin barrier layers are produced by vacuum web coating of BOPP films. In order to achieve high barrier laminates, one key issue along the whole production chain — from film extrusion to lamination — is given by the surface properties of the non-coated films. Non-coated BOPP film surfaces were modified by different kinds of plasma pretreatment and characterized before the vacuum coating process. The functionality — as adhesion and permeation — of coated barrier films and final high barrier laminates was studied as a function of pretreatment parameters. The BOPP homopolymer or copolymer films were either pretreated subsequent to the film production by a standard corona atmosphere plasma or in situ before the vacuum web coating by an oxygen low-pressure plasma. The topography of non-treated and pretreated films was analyzed by atomic force microscopy (AFM) and the chemical surface properties by contact angle measurements as well as X-ray photoelectron spectroscopy (XPS). These BOPP films were vacuum web coated with aluminum (Al), aluminum oxide (AlOx) or silicon oxide (SiOx) and laminated with a two-component adhesive system. Typical pretreatment parameters of BOPP films necessary for high barrier laminates after coating and lamination could be identified.