THE RHEOLOGICAL PROPERTIES OF AN AQUEOUS ACRYLIC DISPERSION SUITABLE FOR AUTOMOTIVE WATERBORNE BASECOATS

Superior film appearance as well as performance is required of automot ive top-coatings applied using the method of two-coat one-bake (2ClB) in the case of metallic finishes. The basecoats, however, dominate the final film appearance, that is, the metallic effect and the film surf ace smoothness. Waterborne metallic basecoats are rather difficult to maintain a high level of workability and appearance under various spra ying conditions involving a wider range of temperature and humidity. B oth the aluminum flake orientation and the surface smoothness of basec oats, which involve opposite requirements especially in a waterborne s ystem, should be superior before clearcoats are over-coated. In this p aper, we will present a means of incorporating them. The studied model basecoats are composed of three materials, a specific water-dispersib le acrylic resin, an internally crosslinked latex and a melamineformal dehyde resin. The viscosity versus non-volatile content relationship a nd the viscoelastic behavior of the model paints are discussed, in rel ation to the actual spraying workability and the final appearance. (C) 1998 Elsevier Science S.A. All rights reserved.