Anticorrosive performance of acrylic-styrene base paints used for steel protection

C.I. ELSNER; A.R. DI SARLI; J.I. AMALVY; A.C. AZNAR

San Pablo, Brasil

Congreso; ABRAFATI 2007; 10° Congreso Internacional de Tintas; 2007

Asociación Brasileira de Fabricantes de Tintas (ABRAFATI)

Polymeric coatings constitute an important part of the corrosion protection industry. In such sense, whereas a great amount of research has been done on “traditional” solvent-based coatings, much less work and “field knowledge” have been gathered with regard to water-based paints. It is known that apart from causing atmospheric pollution, due to organic solvents, they are flammable, explosive, of unpleasant odor and sometimes toxic, they are subject not only to strict fire, health and industrial safety regulations which have to be observed, but also to supply and political factors [1-3]. The use of waterborne coatings started to grow in the 1960’s led by trends in USA. A 1995 report by the House of Commons Environmental Committee stated that even a 30% reduction in volatile organic compounds (VOCs) emissions was insufficient to keep ozone levels at the recommended standards [4]. This fact has accelerated efforts for their reduction or replacement by environmentally friendly products such as the water-based painting systems [5-7]. These have certainly come a long way in their development to become effective in corrosion protection passing through several stages. Among them, some authors reported that, by comparing a waterborne chromate primer with a traditional organic solvent coating, the waterborne paint could favorably replace the conventional one. Moreover, research on formulation and performance of aqueous systems for steel protection is extensive and practical applications are increasingly common. Waterborne coatings for bridges, tanks and structural steel painting systems using two-pack acrylic/epoxy and acrylic emulsion have been also reported [8- 12]. The major purpose of this work is to contribute to a better understanding of the effect of nontoxic anticorrosive pigments on the protective properties of a recently developed waterborne paint [12]. Therefore, the effectiveness of each pigment incorporated to the primer formulation at two (10 or 15%) PVCs was studied using different test methodologies. Zinc tetroxychromate, which provides good performance as anticorrosive pigment in solvent-based paints, was used as reference. However, it should be kept in mind that a pigment showing high protective efficiency in a solvent-based paint, behaves not necessarily equal in a water-based paint. Anyway, due to the lack of experimental data, the other pigments performance was compared with regard to the zinc tetroxychromate. Two phosphate derivatives were used as environmentally friendly pigments, and the fourth one was a tannin-based pigment prepared at CIDEPINT [12]. To characterize the anticorrosive performance of the waterborne paint/steel substrate systems, the test methodologies included exposure to accelerated weathering conditions and/or immersion in a saline aqueous solution. Complementary visual inspections for determining blistering and rusting, as well as measurements of the paint/metal adhesion were carried out. The electrochemical evaluation of each painted steel panel involved determining the value of the water permeability coefficient just after started the immersion period, followed by the periodical monitoring of its corrosion potential and impedance values.