Time and cost effective methods for testing chemical resistance of aluminium metallic pigmented powder coatings

Polyester based powder coatings containing different types of aluminium metallic flake pigments have been investigated with respect to their chemical stability in acid environments. The metallic flakes are made chemically stable by covering them in silica. The degree of silica coverage and the silica morphology are far more important for the chemical stability of the pigments than the silica thickness. The acid resistance of the final powder coating is found to depend on the pigment embedment depth, on the chemical composition and morphology of the powder coating, and on the silica coating of the pigment. The latter being the single most important factor in our study.New chemical resistance tests have been developed. One for the testing of the metallic pigments alone before embedding the pigment in a coating, and another for the cured coating containing these pigments. Additionally TEM cross-sections have been used for investigating the quality of the silica coating on pigments, and optical absorption for comparison of pigment embedment depth. This approach to powder coating development emphasizing the measurement of the quality of each component separately has proven to be robust, reliable, and time and cost effective.By testing of separate components the need for time-consuming quality cheques of cured coatings is reduced while maintaining the ability to predict final paint properties. Further, the uncertainty related to testing many process parameters simultaneously is considerably reduced.