20 nm size inorganic silica nanoparticles have been surface modified with a combination of polymeric wetting agents and silicones.The resulting core-shell nanoparticles,prepared as a dispersion in methoxy propyl acetate,provide a much stronger increase in scratch resistance and abrasion resistance of clearcoats and topcoats than unmodified particles,without affecting transparency.Results in various types of polyurethane and baking systems will be higlighted.The improvement depends considerably on the binder type and crosslinking mechanism as well.Best results can be obtained in the range of 1 to 4 % silica nanoparticles on the complete coating formulation.A micro-scospic investigation of the cross-cut section of the film shows a very uniform distribution of the nanoparticles in the film.The new technology can be used to improve properties of e.g.car refinishes and wood coatings.
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