Multi-layer hybrid coatings with high gas barrier properties and optical quality

Abstract

The combustion chemical vapour deposition (CCVD) technology was used to generate thin inorganic silica-coatings on polyethylene terephthalate (PET) films. These SiOx base layers were combined with flexibly configurable hybrid sol-gel layers to create multi-layer systems with improved property profiles, such as high gas barrier against oxygen or water vapour.The inorganic-organic sol-gel hybrid layer is produced by the simultaneous step growth polymerization of three reactants: 3-aminopropyltriethoxysilane, 4,4′-methylene-bis(N,N-diglycidylaniline) and aluminium-tri-sec-butoxide. The controlled sol-gel process allows simultaneous covalent bond formation between the silica, alumina and epoxy resin containing components, which is crucial for the target property of the hybrid material layer.The so synthesized ternary hybrid material layer has a significantly improved gas barrier effect as well as a higher light transmittance compared to the unmodified coating. For the reduction of the Oxygen Transmission Rate (OTR), the exact adjustment of the Al component proved to be the main influencing factor.The combination of CCVD and sol-gel technology is very well suited to create composite systems whose gas barrier properties are sufficient for use in the food and pharmaceutical packaging sector, even for sensitive content. These coatings have very low values for the OTR which range up to 10−1 cm3 / (m2 d bar) as well as adequate transmission rates for water vapour which range up to 100 g / (m2 d). In addition, these composite layers can also ensure light transmission. By applying a coating system based on three single layers, the initial transmittance of the PET film could be exceeded by 1% up to 87%. Thus, composite layers even with a total thickness of about 400 nm, which were completely generated under ambient conditions, can build up a barrier effect on PET films.