A process for the preparation of a coating layer comprising the steps: (a) applying a coating layer to a substrate from a coating agent of which the resin solids comprise a binder system curable by free-radical polymerization of olefinic double bonds, and containing 0.1 to 4 wt-%, based on resin solids, of a morpholin-2-one derivative sterically hindered by 3,3,5,5-polysubstitution as a light stabilizer; and (b) thermal curing of the applied coating layer.