Effect of curing conditions on the morphology of wax modified coil coatings

Raman spectroscopy and optical light microscopy were applied to analyze the morphology within the bulk and on the surface of wax modified topcoats. To vary the processing conditions resin formulations were coated on primed steel sheets and cured at peak metal temperatures of 230, 240 and 250 °C. By Raman spectroscopy dispersed, spherical wax domains within the bulk and on the surface were detected. These features revealed residues of the polyester based resin and the TiO2 pigment. While the size of the identified lubricant features showed only a slight shift to smaller diameters with increasing peak metal temperature, a significant effect of the curing conditions on the overall number of wax domains and the relative area covered by wax was ascertained. A direct linear correlation between peak metal temperature and relative area covered by wax within the bulk and on the surface of the topcoats was established.