Flash-rust inhibitors

Flash rusting is the phenomenon of formation of small brown rust spots that appear very soon after application of waterbased systems directly to steel. The problem is more prominent when the steel sur­face is active (for example, after blasting) and the pH is <7. To combat this problem, flash-rust inhibitors are added to waterbased coatings. They should have good water solubility. Flat surfaces are relatively easy to protect, while weld areas are considered difficult. Flash-rust inhibition at a weld area can be achieved by a combination of different products. Flash-rust inhibitors are typically based on ammonium and sodium nitrites, benzoates, metaborates and phosphates, occasionally in combination with materials such as morpholine and amino methyl propanol. Some other organic salts are also used, such as amine salts of 2-mercaptobenzothiazolyl succinic acid and calcium or barium salts of linear alkyl naphthalene sulfonic acids. Typically they are used at levels of 0.1 to 1.0 % of the total mass of paint. They also help in pre­venting in-can corrosion upon storage of aqueous paint.

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