Composite Engineering - Direct Bonding of plastic PET Films by Plasma Irradiation

This article reviews “plasma bonding” of plastic films. Polyethylene terephthalate (PET) films can be bonded directly by oxygen plasma irradiation and heat-press at low temperatures of 100-160 °C. Functional groups of COOH and OH were detected on the irradiated surface. The irradiated films were kept in the atmosphere for six years, yet they can be bonded tightly. The irradiated surface is extremely active just after the irradiation, and it is still considerably active after five years. Dry- and wet-peel tests on the bonded films suggest that there are two elements, hydrogen bonding and chemical bonding. The films are bonded weakly by these two elements at lower press temperatures due to low densities of bonds, while they are bonded strongly by high density of the pure chemical bonds at higher temperatures. The hydrogen bonding is broken by water penetration into the interface, causing smaller peel strength under the wet-peel test. FTIR results on the non-irradiated, irradiated and bonded samples indicate that COOH and OH groups are created at the surface, they are responsible for the both bondings. The OH is consumed during the heat-press bonding, then dehydrated condensation reaction can be proposed for the chemical bonding. Cross-linking layer may be the origin for the long lifetime of the irradiated active surface.