Difference between organic zinc-rich primer and inorganic zinc-rich primer


As the electrical conductivity of the organic film former of the organic zinc-rich primer is poor, the zinc powder contents should be increased so as to ensure the electrical conductivity. “SSPCPaint-20” which is issued by Steel Structure Paint Council stipulates that the mass of zinc powders of organic zinc-rich primer should not be less than 77 percents in the total mass of dry film, while the mass of zinc powders of inorganic zinc-rich primer should not be less than 74 percents in the total mass of dry film. This stipulation aims at enhancing the electrical conductivity of the coating. In addition, the caking property of organic resin is better than inorganic resin, which can provide a better assurance for the adhesion of high content zinc powders. The anti-corrosion resistance, electrical conductivity, heat resistance and solvent resistance of organic coating are all poorer than the inorganic coating, but it has good construction performance and high tolerance to the quality of steel surface preparation. Meanwhile, as the epoxy zinc rich primer can be compatible with most of the coatings and also because of the synergistic effect between the complete coating, the service life of complete coating can be extended to 1.5-2.4 times of the single use. This kind of coating is composed with zinc metal powders, organic resin and solvent, which can be divided into organic zinc-rich primer that has high content of zinc powders and excellent corrosion resistance.

zinc powder coating

Although water-soluble inorganic zinc-rich primer has excellent combination property and many advantages, it also has some shortcomings in the practical application, which are as follows: its micro and porous structure will lead to the poor shielding property, the increasing of electro-chemical polarization rate will lead to the early deficiency of coating and the thick coating will lead to crack, besides, it has poorer construction performance than organic zinc-rich primer; although high mole ratio silicate coating has excellent corrosion resistance, it has high viscosity and is easy to gel, besides, it has poor stability. Especially when the waterborne epoxy resin coating material is forming film, epoxy resin latex particles will contact with each other after most of water is evaporated. Meanwhile, the residual moisture and the molecules of curing agent will stay in the interstice of dispersion phase particles. When the moisture begins to evaporate further, the dispersion phase particles will start to congeal, at the same time, the curing agent molecules will diffuse to the boundary and internal of dispersion phase particles, where the curing reaction will be generated. As the diffusion velocity becomes slow, it will be difficult to condense into film between the particles, thus the curing reaction will not carry out completely and will not form uniform and compact film, which will lead to the deterioration of corrosion resistance. In conclusion, compared with solvent zinc rich primer, waterborne zinc rich primer has poorer corrosion resistance and construction performance as well as higher cost.