ZINC-RICH EPOXY PRIMERS BASED ON LAMELLAR ZINC DUST

Zinc-rich primers ore dispersions of zinc dust in organic or inorganic vehicles. When such primers ore applied, a close contort is observed between the zinc particles and also between them and the substrate. Du ring initial stage of the exposure, the film is porous and the mechani sm of action is mainly by cathodic protection. Thus, the process gives zinc corrosion products, which fill the pores and confer high imperme ability and hardness on the film. Problems such as the sedimentation i n the con of zinc particles and their heterogeneous distribution in th e film, led to an investigation of the behaviour of lamellar and spher ical zinc (both alone and in admixtures dispersed in a vehicle based o n an epoxy resin as the film-farming material. The film adhesion, and its behaviour to weathering, in a 100% humidity cabinet and in a salt spray (fag) chamber were assessed. Adhesion measurements enable an est imate to be mode of the critical pigment volume concentration of the s ample and led to the conclusion that the lamellar zinc pigment increas ed the adhesion of The film to the substrate. An analysis of the exper imental results show that the critical pigment Volume concentration de creased as the spherical zinc/lamellar zinc ratio decreased. The bed r esults were obtained at pigment volume concentration levels very close to the corresponding critical pigment concentration. The lower critic al pigment volume concentration values of those samples having lamella r zinc in their composition did not seem to affect the electrical cont act between particles and between them and the substrate. The corrosio n resistance in The tests carried oat was similar to that shown by the coating based on spherical zinc at higher pigment volume concentratio n.