High Density HAD Plasma Supported Aluminum Oxide Deposition for Transparent Barriers with Superior Mechanical and Gas Diffusion Properties

Vacuum deposition of thin film gas diffusion barrier layers has been in high-volume production for over 60 years in the food packaging industry. This has typically involved the high-rate evaporation of thin aluminum layers onto PET, polypropylene or polylactic acid based substrate materials. However, transparent barriers are also required for applications where product viewing, X-ray screening and microwave-ability are of importance. Materials such as SiOx and AlOx are therefore often used but are often difficult to deposit either with the required optical transparency and barrier performance in the case of SiOx or with sufficient mechanical resilience in the case of AlOx. Recent AlOx performance advances have been made through the use of a high-plasma density assisted co-oxidation process together with conventional thermal evaporation of aluminum. This technology has resulted in a near 20% increase in layer density, a doubling in layer hardness and a near twofold improvement in WVTR performance compared with simple reactive AlOx deposition. Further benefit can be found in terms of increased strain to failure mechanical resistance prior to barrier degradation increasing process yield in downstream lamination lines. This paper summarizes these recent advances and provide insight into the technology implementation in the Al replacement barrier market.