Assessing the performance of eco-friendly metal pre-treatments

Painted metals for outdoor use undergo a pre-treatment process using heavy metals and lots of energy while producing large amounts of sludge. EU-funded scientists tested green alternatives in a standardised way for meaningful conclusions.

The pre-treatment of metal surfaces in preparation for a coating including paint is one of the most important steps in processing of metals for outdoor use. It both increases corrosion resistance and enhances the adhesion of the subsequent coating. Zinc-phosphating is a commonly used pre-treatment but it is costly and energy-intensive. Of increasing concern, it uses heavy metals and produces a considerable amount of sludge.

Small and medium-sized enterprises (SMEs) working in the field of metal surface painting are under pressure to respond to consumer and legislative demands for an environmentally friendly process. However, taking new processes from lab bench to market has been challenging largely due to lack of standardised and controlled results on performance. A large consortium rose to the challenge with EU funding of the project 'Environmentally acceptable pretreatment system for painting multi metals' (ENABLE) .

Researchers sought to assimilate and present realistic, verifiable and simple-to-understand information to SMEs regarding novel silane- and zirconium-based pre-treatment systems. In order to do this, they had to assess the various specifications for different substrates and increase knowledge regarding the mechanisms of corrosion protection of novel formulations. In addition, they developed accelerated corrosion testing to correlate with field tests and to expedite development.

Scientists demonstrated that the novel pre-treatment systems perform quite well on aluminium and reasonably well on galvanised metals (already coated with a layer of zinc), with mediocre performance on steel. Thus, they require further development and a thorough environmental assessment before they can be of use to a paint shop that treats a wide variety of surface materials in the same processing line.

The ENABLE project made an important contribution to the advancement of environmentally friendly and cost-effective coating technologies for painted metals. Greener alternatives to current practices are not only desired by consumers but will soon be required by legislative restrictions. The consortium provided resources previously lacking, process control experience and accelerated testing required by SMEs to begin evaluating the new pre-treatments in a standardised way to draw relevant conclusions regarding feasibility and market potential.

related link: http://cordis.europa.eu/result/brief/rcn/12401_en.html