Surface Modification
Surface modification phenomenon that occurs when high-voltage discharge breaks polymer chains on a film surface generates polar groups to improve ink adhesion. This action, known as corona treatment scission, cleaves the carbon-carbon bonds of the polyolefin backbone. Exposed free radicals then react with atmospheric oxygen and moisture to form carboxyl, carbonyl, and hydroxyl groups.
Chemical Mechanism
Electric discharge in the presence of air initiates the degradation of the polymer outer layers. During corona treatment scission, the high-energy electrons fragment the polymer molecules into shorter chains, which increases surface energy but can also create low molecular weight oxidized materials. These small fragments remain weakly bound to the surface.
Process Impact
Operators of printing presses must monitor the level of surface treatment because excessive exposure leads to a cohesive failure of the boundary layer. The occurrence of corona treatment scission can create a weak, powdery layer that compromises the bond between the ink and the substrate. This degradation reduces the long-term stability of the treatment and causes the surface energy to decay during storage.
Consequently, converters carefully balance the treatment power to achieve sufficient wetting without destroying the mechanical integrity of the polymer surface, ensuring that subsequent lamination or printing steps remain robust.
