Characterization of flow properties of powder coatings used in the automotive industry

Abstract

The aim of this work was, on the one hand, to gain a better understanding of the effect of flow additive content on the powder f lowability, and on the other hand, to point out the most suitable tests to characterize the f low properties of industrial powder paints used in automotive industries. The f low properties of 5 powder coatings, containing 0, 0.12, 0.30, 0.53 and 0.96 w/w%, respectively, of a f low additive and an industrial batch, were tested using both conventional and novel characterization techniques. The lubricant used was a silica powder. Test methods employed were a packing test, a circular shear cell (Peschl), a powder rheometer and a f luidization/de-aeration test. The f lowability of powder batches is significantly improved with increasing lubricant content up to an optimal value of about 0.53%. SEM images of different powder samples showed that the optimal point corresponds to a critical additive content where the amount of additive is high enough to form a continuous film around the particles. Beyond this critical content, the particle-lubricant contacts are replaced by lubricant-lubricant contacts. This phenomenon leads to a degradation of f lowability due to a higher cohesivity of additive particles.