Modification of poly(tetrafluoroethylene) and copper foil surfaces by graft polymerization for adhesion improvement

Abstract

Thermal graft polymerization-induced lamination of surface-modified copper foil to surface-modified poly(tetrafluoroethylene) (PTFE) film was achieved in the presence of an epoxy resin adhesive and glycidyl methacrylate (GMA) monomer, or in the presence of GMA and hexamethylenediamine (HEDA). The copper foil surfaces were pretreated with an organosilane coupling agent (SCA), such as (3-mercaptopropyl)trimethoxysiane, 3-(trimethoxysilyl)propyl methacrylate, or N1-[3-(trimethoxysilyl)propyl]diethylene-triamine. The silanized copper foils were subjected to brief Ar plasma treatment and subsequently to UV-induced graft polymerization with GMA (the Cu-SCA-g-GMA surface). Surface modification of PTFE film included Ar plasma treatment alone, or Ar plasma pretreatment followed by UV-induced graft polymerization with GMA (the GMA-g-PTFE surface). The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. The Cu-SCA-g-GMA/epoxy resin-GMA/PTFE or Cu-SCA-g-GMA/GMA-HEDA/GMA-g-PTFE laminates exhibited T-peel adhesion strengths in excess of 9 N/cm and the joints delaminated by cohesive failure inside the bulk of the PTFE film. The strong adhesion in these Cu foil-PTFE laminates is attributable to the fact that the GMA chains are covalently tethered on both the PTFE and the silanized Cu surfaces, as well the fact that these grafted GMA chains are covalently incorporated into the highly crosslinked network structure of the adhesive at the interphase.