Studies on the barrier performance and adhesion strength of novel barrier films for vacuum insulation panels

Novel cost efficient high barrier envelopes are developed for vacuum insulation panels. In order to fulfil the required maximum oxygen permeability (at 23 °C and 50% relative humidity (RH)) of 1 × 10^-14 m³(STP) m^-2 day^-1 Pa^-1 and water vapour transmission rate (at 23 °C and 85% → 0% RH) of 1 × 10^-6 kg m^-2 day^-1, hybrid polymeric (ORMOCER^®) and aluminium barrier layers are combined. Using roll-to-roll processes, these materials are deposited from the liquid or gas phase on top of a poly(ethylene terephthalate) substrate film. The low adhesion strength observed between aluminium and ORMOCER^® layers is significantly increased by the deposition of an additional aluminium oxide layer between the two materials. The lamination of a polyethylene or polypropylene sealing film does not weaken the adhesion strength. The resulting barrier structure has reached an oxygen permeability of lower than 5 × 10^-14 m³(STP) m^-2 day^-1 Pa^-1 (at 37 °C and 30% RH). Electrochemical impedance spectroscopy gives evidence for a possible penetration of the ORMOCER^® lacquer into the aluminium oxide layer (synergistic effect), which explains the improved adhesion and barrier performance due to the aluminium oxide layer.