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 i n a roll-to-roll coating process. The oxide layer was either sputtered or e-beam evaporated Al2O3 and the polymer layers were deposited by t he polymer multilayer (PML) method [1,2]. The monomer curing method em ployed to polymerize the PML layers was a parameter affected by varyin g the cross-linking irradiation between ultraviolet light (UV), electr on beam irradiation (eb), and UV followed by eb. O-2 and water vapor p ermeation rates for the three layer structures were up to four orders of magnitude lower than for the PET substrate alone and up to three or ders 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 Al2O 3, while the reverse was true when the Al2O3 was e-beam evaporated. Di stinct 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 orig inal substrate. We hypothesize that this new surface topography is due to electrostatic repulsion of the trapped electrons distorting the li quid monomer layer before the material is fully solidified. (C) 1997 E lsevier Science S.A.