Optimising the corrosion resistance of waterborne PUDs for bare and phosphatised steel substrates

 
Achieving a good balance of high gloss, good corrosion resistance, adhesion on both steel and aluminum substrates using water-borne polyurethane primers or direct-to-metal coatings can be quite daunting. This challenge is exacerbated when low surface tension substrates like aluminum alloys can no longer have pretreatments for e.g., chromate conversion coatings (CCC) to help the coating adhere. When it comes to corrosion resistance, there is a tradeoff between using heavy metal corrosion inhibitor vs environmentally friendlier heavy metal free anticorrosive, high gloss vs low gloss, better adhesion with higher VOCs vs. poorer adhesion with low VOCs. In this work, we focused on achieving good corrosion resistance, minimally impacting gloss, improved adhesion with organic corrosion inhibitors and offering heavy-metal anti-corrosives as an option. The challenges we faced and overcame included getting good dispersion, reducing scribe corrosion creep and preventing the gloss loss caused by anticorrosion pigments. We set out to optimize the pigment particle size and the dosage of the corrosion inhibitor in the coating.