Gas barrier performances of organic-inorganic multilayered films

摘要

Thin inorganic layers such as aluminum oxide (AlOx) and indium cerium oxide (ICO) were deposited by DC magnetron sputtering on polyethylene terephtalate (PET) substrate. A variety of thin acrylate layers polymerized by electron-beam were employed as "under-coating" or "over-coating" for the inorganic layers. The gas barrier performances of the composite films were examined. Although acrylate (Ac) did not show any barrier contribution in PET/Ac structure, applied as the under- or over-coating layer it improved the barrier performance. From the data of gas transmission rates and their activation energies, it is assumed that some under-coating acrylates increase a number of nucleation sites; moreover covers up irregularities and flattens the surface. As for over-coating, interaction between inorganic and organic compounds contributes to the barrier improvement by deterring infiltration through fine structure. Among various combinations of inorganic and organic compounds in this study, the combination of some acrylates possessing six polymerizable acryloyl groups in a molecular unit as under-coating and subsequent ICO deposited layer demonstrates superior barrier performance. Particularly the transmission rate of water vapor has been below the measurable limit. The surface observation using atomic force microscope (AFM) reveals that the surfaces of the acrylates showing better water vapor barrier are smoother. It is conceivable that the smooth surface is most likely attributed to the rapid polymerization of the multi-acryloyl acrylate with no time to be roughened by electrical repulsion.