Gas barrier properties of plasma-deposited coatings – Substrate effects

Abstract

Plasma deposition of ultra-thin, glass-like SiOX high gas barrier coatings on conventional packaging materials such as poly(ethylene terephthalate) (PET), oriented polypropylene (OPP) and low density polyethylene (LDPE) films has been investigated. In particular, the influence of the polymer film substrate on the gas barrier properties has been examined. It is obvious that the surface roughness in combination with the gas permeability of the polymer film substrate is the most important parameter to determine the level of oxygen transmission rate (OTR). The roughness of the films increases in the following order: PET<OPP<LDPE and so does the corresponding OTR after deposition of the SiOX coating. The LDPE substrate was found to be more sensitive to variations in the plasma conditions, especially the discharge power and deposition time, than were the PET and OPP. The influence of various plasma parameters, such as discharge power, HMDSO:O2 ratio, pressure, deposition time, pre-treatments, etc. has also been investigated. Careful optimization of the plasma parameters is required since improper parameter settings will lead to poor barrier performance of the SiOX coatings.