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 flowability, and on the other hand, to point out the most suitable tests to characterize the flow properties of industrial powder paints used in automotive industries. The flow properties of 5 powder coatings, containing 0, 0.12, 0.30, 0.53 and 0.96 w/w%, respectively, of a flow 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 fluidization/de-aeration test. The flowability 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 flowability due to a higher cohesivity of additive particles.