Cataphoretic and autophoretic automotive primers - A comparative study

This study has involved the morphological and chemical characterisation of a recently generated epoxy cataphoretic primer and a series 800 autophoretic primer, along with an assessment of their anti-corrosive behaviour and of several other fundamental properties. Morphological characterisation was carried out by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy with energy dispersive spectrometer (SEM/EDS). Chemical characterisation was carried out by Fourier transform infrared absorption spectroscopy and photoacoustic detection (PAS/FTIR). The study of corrosion behaviour included artificial ageing in cabinets (humidity, salt spray and SO2 atmospheres), immersion in automobile liquids, natural atmospheric exposure, and electrochemical impedance spectroscopy. Characterisation of the coatings also included measurements of thickness, adhesion, colour, gloss, hardness and falling weight tests. Both primer coatings offered excellent anti-corrosive behaviour in the different conditions studied in the absence of scribes. The autophoretic coating also showed high pencil hardness (>7H). However, in the presence of coating damage the cataphoretic coating offered greater resistance to the advance of corrosion from the scribes, probably because it incorporated a phosphating-passivating pre-treatment. (C) 2002 Elsevier Science B.V. All rights reserved.