A new method for the quantitative determination and prediction of sag and levelling in powder coatings

A key area driving developments in the powder coatings industry today is that of improved energy efficiency through reduction of cure temperature. The ability to cure at lower temperatures offers the dual benefit of both reduced energy use on application and broadening the appeal of powder coatings to include temperature sensitive substrates, such as MDF and plastics. One of the main challenges for low temperature curing powders is to have the ability to sufficiently flow and level at the reduced cure temperature in order to obtain a smooth final appearance while keeping good mechanical properties and powder stability. In order to facilitate and support development of such powder coatings, we have recently developed a unique method that allows determination of the sag and levelling behaviour of powder coatings in a quantitative manner. The use of this technique gives valuable insight into the influence of both experimental conditions as well as material properties on the flow and levelling behaviour of powder paints. Furthermore, we have developed a Flow–cure model allowing the quantitative prediction of the sag and levelling behaviour of powder coatings from their rheological and curing properties. Excellent agreement between prediction and experiments was found.