Low Temperature Transparent Nanoplatelet Hybrid Gas Barrier Coating Materials via Sol-gel Process

A novel hybrid coating based on a combination of nanoparticles, sol-gel and organic chemistry is reported. It can be applied to a large variety of surfaces even at low processing temperatures, and it cures below 150°C. Furthermore, fabrication of the hybrid films on polymer sheets can be done under ambient conditions. No vacuum techniques are required. Boehmite nanoplatelet composite hybrid organic/inorganic coating materials have been successfully prepared via this approach. The coating process involves the dispersion of boehmite nanoparticles that are suspended without significant agglomeration. 3-glycidoxy propyl trimethoxy silane (GPTMS) was adopted as dispersant for the nanoplatelets and functions also as a network former. This induces flexibility in the hybrid film due to the organic functional groups. Transparent cured coatings from flexible to brittle were obtained from a single coating step with thicknesses in excess of 10 μm depending on the ratio of the inorganic/organic reagents and their concentrations. Barrier coatings with more than 60wt% ceramic nanoplatelets were achieved, yet they still display transparency of more than 95% to visible light with no cracks or other discernable defects. Several substrates have been successfully tested including poly (ethylene terephthalate) (PET). Moreover water permeability for cured coated PET films is reduced to less than 0.01 g/m2/d. Excellent mechanical properties such as flexibility and hardness are demonstrated by nanoindentation and scratch tests.