Patent ID: 8097093

Claim:
A method for coating a ferrous metal substrate, comprising: (a) contacting the ferrous metal substrate with an aqueous pretreatment composition having a pH of 4 to 5.5 and comprising: (i) a Group IIIB and/or IVB metal compound; (ii) phosphate ions; and (iii) water, wherein the Group IIIB and/or IVB metal compound is present in the pretreatment composition in an amount of 10 to 150 ppm metal and the weight ratio of Group IIIB and/or IVB metal to phosphate ions in the pretreatment composition is at least 2:1; and wherein the phosphate ions are maintained in a bath of the pretreatment composition in an amount: (i) sufficient to essentially prevent the formation of insoluble rust in the bath; and (ii) insufficient to prevent the deposition of a Group IIIB or IVB metal film having a coverage of at least 10mg/m 2 on the ferrous metal substrate; and (iii) resulting in a weight ratio of phosphate ions to ferric ions of 1.2 to 1.7:1; and then (b) contacting the substrate with a coating composition comprising a film-forming resin to form a coated metal substrate that exhibits corrosion resistance properties.