ABSTRACT
Organofunctional silanes, which were originally discovered for use as adhesion promoters [1] have in recent years proven to be useful in metal pretreatments [2-13] and also as components in corrosion inhibiting primers [14-16]. A conventional coating system consists of a chromate pretreatment film and a chromate-containing primer [17]. A newer coating system consists of a silane-based pretreatment layer and a chromate-free primer, and the future system comprises a silane-containing primer without the need for pretreatment. The two latter systems make use of the adhesion promotion capability of the silanes. In pretreatments, the silanes promote adhesion between the primer and the metal mainly by depositing as a thin hydrophobic layer onto the metal [18]. In the primers the silane is one of the components
of the primer formulation. The main idea of the silane-containing primer is that the complex dispersion consisting of resins, crosslinkers, silane, pigments and additives forms a primer coating with multifunctional properties such as corrosion and chemical resistance, flexibility, durability and compatibility with further paint layers and topcoats. The resin together with the crosslinker builds up the coating. The silane anchors the coating to the metal substrate, i.e., the pretreatment layer is built in the primer layer. During film formation and curing, it is beneficial if the silane interacts with the resin and/or the crosslinker and becomes part of the interpenetrating network.
