PML/oxide/PML barrier layer performance differences arising from use of UV or electron beam polymerization of the PML layers

Polymer/oxide/polymer barrier coatings have been fabricated on 50 mu m thick and 100 mu m thick polyethylene terephthalate (PET) substrate in a roll-to-roll coating process. The oxide layer was either sputtered or e-beam evaporated Al2O3 and the polymer layers were deposited by the polymer multilayer (PML) method [1,2]. The monomer curing method employed to polymerize the PML layers was a parameter affected by varying the cross-linking irradiation between ultraviolet light (UV), electron beam irradiation (eb), and UV followed by eb. O-2 and water vapor permeation rates for the three layer structures were up to four orders of magnitude lower than for the PET substrate alone and up to three orders of magnitude lower than for PET with a single oxide layer without PML layers. Significantly better performance was found for sputtered Al2O3 when compared with e-beam evaporated Al2O3, With or without the use of PML layers. Marginally better performance was obtained when PML layers were UV-cured, as compared with eb curing, with sputtered Al2O3, while the reverse was true when the Al2O3 was e-beam evaporated. Distinct differences in surface topography are observed between UV and e-beam-cured samples with W-cured samples having significantly smoother surfaces and as low as 8.5 Angstrom RMS surface roughness. While both e-beam and UV curing appear to remove all traces of substrate surface roughness, the e-beam-cured surfaces appear to have a new, smoother, broader, and longer wavelength, surface roughness relative to the original substrate. We hypothesize that this new surface topography is due to electrostatic repulsion of the trapped electrons distorting the liquid monomer layer before the material is fully solidified. (C) 1997 Elsevier Science S.A.