COMPOSITION FOR SURFACE TREATMENT OF MG-CONTAINING GALVANIZED STEEL SHEET AND MG-CONTAINING GALVANIZED STEEL SHEET SURFACE-TREATED USING SAME

    公开(公告)号:EP3845611A1

    公开(公告)日:2021-07-07

    申请号:EP19853492.7

    申请日:2019-08-16

    申请人: POSCO

    摘要: The present invention relates to a composition for surface treatment of an Mg-containing galvanized steel sheet comprising a trivalent chromium compound, a carboxylated vinylidene copolymer, and a cross-linking agent. The composition for surface treatment according to the present invention forms a chromium (III) film and is also crosslinked in coating and drying of the surface of a galvanized steel sheet, thereby forming a three-dimensional compact molecular structure. Thus, a galvanized steel sheet coated with the composition has a coating film with high ductility, and can reduce moisture and/or oxygen permeability such that, not only does a worked section have excellent corrosion resistance, but also the occurrence of darkening and/or black dots can be prevented even when exposed to high-temperature and high-humidity environment for a long period of time.