Curing processes in solvent-borne alkyd coatings with different drier combinations

The concern regarding the effect of chems. on the environment has increased considerably in recent years. Nowadays, technol. developments in the coating industry are largely influenced by environmental issues and subsequent legislation. One of these issues is the tendency to replace cobalt as a catalyst with more environmentally friendly alternatives, because studies have indicated possible carcinogenicity. Not much knowledge is available on the effects of catalysts (driers) on the in-depth drying of alkyd coatings. Therefore we have studied the effect of cobalt as a primary drier combined with Ca and Zr as secondary driers on the in-depth curing of high solid solvent-borne alkyds. The profiling of the curing of alkyd coatings is performed with a new high-spatial-resoln. NMR setup. In this study, two effects obsd. in the solvent-borne alkyd coatings are investigated. One is that when Ca and Zr are added as secondary driers the speed of the obsd. crosslinking front increases. Second, in the deeper un-cross-linked region below the front, the signal of the NMR profiles was found to decrease proportional to t. This could be explained by the presence of slowly reacting species that diffuse into the deeper uncured region of the coating, after which they cross-link. The model describing the effect of these reactive species also indicates that the signal decrease is inversely proportional to coating thickness L, which was confirmed by addnl. measurements. [on SciFinder (R)]