Pintura- Cataforesis

Progress in Organic Coatings 46 (2003) 8–20

Cataphoretic and autophoretic automotive primers A comparative study
E. Almeida a,∗ , I. Alves a , C. Brites a , L. Fedrizzi b
a

Instituto Nacional de Engenharia e Tecnologia Industrial (INETI), DMTP/LTR, Estrada do Paço do Luminar, 1649-038 Lisbon, Portugal b ICMMPM Department, University of Rome “La Sapienza”, Via Eudossiana 18, 00184 Rome,Italy Received 10 June 2002; accepted 14 August 2002

Abstract 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, naturalatmospheric 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. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Cataphoresis; Autophoresis; Automotive primers

1. Introduction As is well known, the automotive sector has contributed on a largescale to achieving compliance with increasingly restrictive environmental legislation in the field of surface treatments and most especially, anti-corrosive coatings. It can currently be stated that the anti-corrosive protection of almost all automobile bodywork includes a cataphoretic primer [1]. Meanwhile, an increasing number of automotive components are coated with an autophoretic primer [2].Though electrodeposition was introduced in the automotive industry in the 1960s, in the 1970s anodic electrodeposition rapidly gave way to cathodic electrodeposition due to the greater anti-corrosive protection conferred by the latter and to other film characteristics which had hitherto never been attained with other techniques. At the beginning of the 1990s cathodic systems were based on modifiedepoxy resins containing amino groups. These were dispersed in water by neutralising the amino groups with organic acids. The resins were cross-linked by blocked isocyanates,
∗ Corresponding author. Fax: +351-217-16-3796. E-mail address: elisabete.almeida@ineti.pt (E. Almeida).

Mannich reactions or re-esterification. Pigmentation was based on titanium dioxide and extender pigments. Speciallead-containing pigments such as silicates were used as anti-corrosive agents [3]. Lead also catalyses the curing reaction. The solvent content of these electrocoat systems was low, containing less than 2% organic solvents [3]. Although cathodic electrocoating has been mature technology for a number of years, research and development on this subject has not ended. The first lead-free systems came onto themarket only in the 1990s [4,5], coinciding with attempts to meet other challenges such as achieving further reductions in the volatile organic solvent content and lowering the curing temperature. At the beginning of the 21st century, most of the paints currently used in electrophoretic corrosion-protective OEM automobile coatings are epoxy-based materials that are internally cross-linked...