Bonding of silicone rubbers on metal: (1) Chemistry of adhesion

The adhesion between high consistency silicone rubbers (HCR) and metal via a primer entails a complex chemistry not completely understood. This series of papers aims at defining the important criteria that govern the bonding of various HCR grades on metal surfaces. In this first study, different primer formulations were tested, thanks to a 90° peel test, showing different effectiveness toward silicone/metal attachment. Their basic components are organotitanate catalysts and a vinyltrialkoxysilane, whereas some other reactants, e.g. 3-mercaptopropyltriethoxysilane, polydimethylsiloxane chains or tetraethoxysilane, are likely introduced to bring supplementary properties to the primer film or to enhance the co-vulcanization with the silicone elastomer. From these bases, a new primer formulation, containing a silicone resin as main component, was developed successfully. However, the question of the primer selectivity for a grade of silicone elastomer still remains an issue.