DEFECTS IN POWDER COATINGS ON HOT-DIPPED GALVANIZED STEEL

The occurrence of pinholes in the powder coating of hot-dipped galvani zed steel items is investigated. A polyester powder resin crosslinked with triglycidylisocyanurate was used as a model system. The effects o f a rheological modifier on the curing process and on the cured materi al were investigated. The effect of the substrate was studied by using steel with two different silicon contents. The results show that pinh oles are likely to appear if the surface's silicon content lies in a g iven range, which in turn will produce a rough zinc surface. Phosphate s and silanes were used as conversion coatings, but neither had an eff ect on the occurrence of pinholes. The rheological modifier improves t he flow properties and helps to solve most pinhole problems.