Post-cure waterborne inorganic zinc rich paint


Post-cure waterborne inorganic zinc rich paint mainly uses sodium silicate (also known as water glass) as the adhesive. It is coated on the surface of steel after mixing with zinc powder. When the coating becomes dry, the acid curing agent, such as dilute phosphoric acid H3PO4 can be sprayed on the steel surface so as to solidify the coating, in which the phosphoric acid curing agent will react with sodium silicate and generate silicic acid and sodium phosphate, the by-product. The silicic acid will react with zinc powder and generate zinc silicate polymer. While sodium phosphate can dissolve in water and can be washed by water after the coating becomes solidified. In the cure reaction, phosphoric acid can also react with zinc powder and generate insoluble zinc phosphate, which can help to increase the compactness of coating. Zinc powder can also react with CO2 and water and generate insoluble basic carbonate calcium [3Zn(OH)2•2ZnCO3] that will have shielding protection effect on the coating. However, this kind of inorganic zinc rich paint is seldom used now.

Self-cure waterborne inorganic zinc rich paint can react with silicate by using carbon dioxide and moisture in the air, which can generate carbonate as well as generate zinc silicate polymer after the reaction between zinc powder and silicate. This kind of zinc rich paint will keep the sensitivity to water until the hydrosolvent completely volatiles from the paint film. Besides, its solidification will be influenced a lot by the dampness and temperature. It is mainly used in the inner walls of storage tanks that contain refined oil products and chemicals. By accelerating the curing process, it can be cured completely and play the effect of corrosion protection.

After 24 hours of coating, clear water and sea water can be sprayed on the coating. Afterwards, close the cabin or storage tank, repeatedly spraying water 3-4 times in 48 hours. Dry it after removing the water. Check the cure degree by coins, the coating can be considered to cure completely once the zinc metal powder cannot be scraped and the coating surface appears to be shiny natural color of zinc powder. The curing mechanism of solvent borne self-cure inorganic zinc rich painting is also complex. Ethyl orthosilicate, of which the molecular structure is Si(0CH2CH3)4, can be hydrolyzed and generate ethyl silicate solution that contains hydroxide radical. Partially hydrolyzed ethyl silicate will continuously carry on the hydrolysis-condensation reaction and generate network polymer when it is coated after mixing with zinc powders.