Novel CNSL-based Waterborne Zn-rich Primer Systems for Protective Coatings

By Hong Xu, Fernanda Tavares, Anbu Natesh, Jing Li

Low-VOC waterborne (WB) Zn-rich primers and high performance WB epoxy primers have been developed based on novel Cashew Nutshell Liquid (CNSL)-derived curing agents for industrial and protective coating applications. These unique WB phenalkamines were synthesized from a natural, non-food chain and renewable biomaterial and could help formulate WB primer systems that meet stricter volatile organic compound (VOC) regulations as well as high performance requirements.

This article presents the latest performance studies of new phenalkamine-based WB Zn-rich primers and epoxy primers, and discusses the challenges associated with such formulations. New 2K WB Zn-rich primers were formulated with a water-free phenalkamine curing agent. The study results showed the WB Zn-rich primers had good compatibility with various commercially available solid epoxy dispersions and delivered good cure and mechanical properties; importantly, those WB Zn-rich primers provided superb adhesion to both metal substrates and commercial poly-urethane (PU) topcoats without the use of adhesion promoters.

Excellent corrosion protection and good resistance to undercutting at the scribe were observed after 3000-h Q-Fog exposure. Additionally, newly developed WB high performance primers based on zero-VOC WB phenalkamines were evaluated either in combination with WB Zn-rich primers or by being directly applied over metal substrates. It was found that those WB epoxy primers could enhance corrosion protection as mid-coats to WB Zn-rich primers; when being used direct-to-metal, WB epoxy primers also exhibited good mechanical and adhesion properties that benefited the overall anticorrosion performances.