Method and aqueous coating compositions for forming anti-stick and

Abstract

A method and aqueous coating composition for forming an anti-stick and insulative coating on cold-rolled, non-oriented, semi-processed steel; cold-rolled, non-oriented, fully-processed steel; cold-rolled motor lamination steel; and punching quality oriented electrical steel. The coating composition has an inorganic portion and an organic portion. The inorganic portion comprises, on a water-free basis and by weight, 3% to 11% Al.sup.+++, 3% to 15% Mg.sup.++ and 78% to 87% H.sub.2 PO.sub.4.sup.- calculated as Al.sub.2 O.sub.3, MgO and H.sub.3 PO.sub.4, respectively, the total weight percentage being 100% on a water-free basis and the concentration being 100 parts by weight on a water-free basis; and either 33 to 250 parts by weight colloidal silica on a water-free basis, together with from 10 to 25 parts by weight chromic anhydride for every 100 parts by weight H.sub.2 PO.sub.4.sup.- calculated as H.sub.3 PO.sub.4, or from 30 to 250 parts by weight aluminum silicate calculated as Al.sub.2 O.sub.3.SiO.sub.2 on a water-free basis. The inorganic portion contains by weight at least 60% water when colloidal silica is used and at least 40% water when aluminum silicate is used. The organic portion comprises a water soluble or dispersible resin containing by weight at least 40% water. The inorganic and organic portions are combined so that the organic content is from about 15 to about 1350 parts by weight per 100 parts Al.sub.2 O.sub.3, MgO and H.sub.3 PO.sub.4 on a water-free basis. The coating composition is applied to the steel and cured at a strip temperature of from about 250.degree. F. (120.degree. C.) to about 750.degree. F. (400.degree. C.) in air.