Mercaptosilane as additive orpretreatment in acoating system for steel

Abstract

The application of paints is one of the most used protection methods for metals, but the loss of adhesion of the paint film is a commonly observed failure. In order to avoid this deterioration different silanes are studied as adhesion promoters between paints and metals. The aim of this paper was to study the adhesion promotion of mercaptopropyl-trimethoxysilane in a protection system for steel. Two strategies were used in order to incorporate the silane: as an additive in an epoxypolyamide water-borne paint, and as a pretreatment before painting. Adhesion tests were performed during exposure of the painted steel panels in the salt spray chamber. Blistering and rusting degrees were also evaluated during the panel's exposure in the salt spray and humidity chambers. Besides, electrochemical (corrosion potential measurements and ionic and polarization resistances) and service exposure tests were performed. The results show that depending on the environmental conditions, it is better to incorporate the silane in the paint or as a pretreatment. Moreover, the results also depend on the silane concentration and the time of hydrolysis before pretreatment or its incorporation in the paint.