Effect of corona treatment of PE-coated board on water-based flexographic print resistance

The effect of corona treatment of polyethylene-(PE-) coated liquid packaging board on its surface chemistry was quantified using surface energy determination by drop spreading and dyne-liquids, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The increase in total surface energy, due to its polar component, with increasing corona dosage, and its decrease on aging and washing, was strongly correlated to surface oxidation fraction from XPS. A fine structure of nano-mounds formed by oxidised material was revealed by AFM, with size and substrate coverage increasing with corona dosage, but no longer visible after washing. Resistance properties of water-based flexographic prints on these treated PE substrates were tested, with only wet rub resistance exhibiting a significant dependence on corona dosage. This property first increased at lower dosages before decreasing at higher levels, presumably due to worsened water resistance from soluble oxidised material dissolved in the ink film.