A comparative study between Cr(VI)-containing and Cr-free films for coil coating systems

• Published in: Progress in organic coatings 2005-04, Vol.52 (4), p.320-327
• Main Authors: Duarte, R.G., Bastos, A.C., Castela, A.S., Ferreira, M.G.S.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Applied sciences; Chemistry; Coatings. Paints, varnishes and inks; Coil coating; EIS; Electrochemical methods; Exact sciences and technology; Film formation and curing, properties, testing; HDG; Polymer industry, paints, wood; Pre-treatment; Primer; SVET
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/j.porgcoat.2004.05.011

In this work, the protection conferred by Cr(VI)-containing and Cr-free pre-treatments and primers used in hot dip galvanized steel (HDG) coated systems were studied. The EIS results showed a differentiated behaviour for the specimens with Cr(VI) compared to the chromium-free ones. The samples with Cr(VI), both in the pre-treatment and in the primer, presented a better corrosion performance when compared to the Cr-free ones. Moreover, it can be said that the pre-treated and primed samples without Cr(VI) presented lower resistive properties and higher delamination fractions throughout the immersion time. The amount of Cr in the primer also influenced the coating resistance for shorter periods of immersion, but for long periods the passivating effect of Cr seems to be determinant. When topcoat was applied, i.e. for a complete system, the Cr-free specimens performed better than the Cr(VI)-containing ones, perhaps due to a better adhesion of the topcoat to the primer in the former case. This leads to the conclusion that there is a risk in assessing the behaviour of a paint scheme on the basis of the individual behaviour of each layer.