Surface energy of corona treated PP, PE and PET films, its alteration as function of storage time and the effect of various corona dosages on their bond strength after lamination

The aim of this study was to analyze how corona dosages above recommended levels affect film surface energy and hydrophobic recovery of such treated film surfaces as well as laminate bond strength of laminates made of these films. The adhesive for lamination was a polyurethane-adhesive with a dry film thickness of ∼5 µm. Polar and dispersive parts of the surface energy were measured frequently according to DIN 55660-2 (Owens-Wendt-Rabel-and-Kaelble method) for up to 140 days after corona treatment. The corona dosage had a value of up to 280 W min/m2. Laminate bond strength was measured according to DIN 55543-5. The effect of corona treatment was highest for low-density polyethylene (PE-LD) films, mean for biaxial-oriented polypropylene (PP-BO) films, and lowest for biaxial-oriented poly(ethylene terephthalate) (PET-BO) films. With increasing storage time, surface energy decreased, as expected. The higher the effect of corona treatment, the faster the polar part of surface energy decreased. At PE-LD, laminate bond strength increased with a higher corona dosage from 0.05 to 8.87 mN/15 mm, whereas at PET-BO and PP-BO laminate bond strength was so high that samples teared before delamination during bond strength testing. By our results is shown that corona dosages above recommended levels resulted in higher laminate bond strength. Only at PP-BO a reduction of laminate bond strength due to ""overtreatment"" was be observed.