Preparation of metallic surfaces with microfibrous topography and their effect on adhesion of hot-melt and thermoset adhesives

Abstract

Various chemical and electrochemical methods have been developed which produce acicular oxide or metal growths on the metal surface, and the adhesion of various polymers to such microfibrous surfaces has been studied. Polyethylene, which normally adheres poorly when applied to metals as a hot-melt coating unless conditions permit its oxidation, gives good adhesion to microfibrous surfaces in the presence of antioxidants. Similar surfaces give good adhesion with ethylene vinyl acetate. Comparative examination of the fracture surfaces enables the phenomenon to be related to theories of adhesion. The effect of microfibrous surfaces on steel, copper and zinc on the adhesion of epoxy resins has been studied using fracture mechanics tests giving values for G c fracture energy. In some cases these strong engineering adhesives give problems with the strength of bond between the metal and microfibrous surface layer. However, in many cases changing from a smooth to a microfibrous surface alters the mechanical response of the adhesive from a brittle to a more ductile one, thus increasing the value of joint toughness. With a rubber-toughened epoxy, the microfibrous surface enables much more of the potential toughness of the resin to be realized.