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

摘要

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 cm{sup}3/(m{sup}2 dbar) and a moisture permeability lower than 0.05 g/(m{sup}2 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 (AEM) 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 (Al{sub}x) or silicon oxide (SiO{sub}x) 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.