Adhesion improvement of epoxy resin/polyimide joints by amine treatment of polyimide surface

Polyimide (PI) surfaces were modified to improve the adhesion strength of epoxy resin/PI joints by immersing in amine solutions. Adhesion strength of epoxy resin/amine-treated PI joints were measured depending on structure, molecular weight, concentration, treatment time and drying temperatures of amines. There was an optimum drying temperature fox maximum adhesion strength after amine-treatment of PI surface. The optimum drying temperature and the maximum adhesion strength increased with increasing the molecular weight of diamines or polyamines. Poly(amic amide) was formed by the reaction of primary amine of diamines and imide group of PI, and the other primary amine of poly(amic amide) reacted with the imide groups of adjacent PI chains to form cross-linked structure. In this way, adhesion strength of epoxy resin/PI joints was improved by reinforcing the weak PI surface layer. Another additional adhesion mechanism could be the chemical reaction of epoxide in the epoxy resin and unreacted amine of poly(amic amide). Adhesion strength decreased at above the optimum drying temperature since poly(amic amide) was imidized. The adhesion mechanisms and existence of optimum drying temperature were investigated using FT i.r., contact angle goniometer, X-ray photoelectron spectroscopy and rheometric dynamic spectroscopy.