Diffusing wave spectroscopy for coating film analyses

 
This work presents the use of Diffusing Wave Spectroscopy (DWS) for film analyses. The method is based on dynamic analyses of backscattered light, which gives information about the particle mobility (contained in the product like droplets or fibers). The technique allows to obtain typical drying kinetics of the coating. Two applications will be shown. Firstly, the impact of precoatings on the drying behavior of subsequent coatings will be discussed. Precoatings can significantly increase the drying time of the subsequent layer. The DWS measurements can determine the drying time on the specific substrate. The drying behavior of a polyurethane resin is analyzed on aluminum and on a pretreated aluminum substrate used in aeronautical industry. Secondly, a new approach of correlating characteristic drying times with the Persoz hardness. It was shown that the measured open time (60 min) of 2K-paints with different resin-to-binder ratios correlate linearly with the Persoz hardness (8 days).