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Abstract

A surface-treated sheet for fuel tanks includes a cold-rolled steel sheet with a low carbon content, a zinc or zinc-based alloy plating layer formed on the steel sheet, and a chromate film coated on the zinc or zinc-based alloy plating layer. The chromate film is formed from a chromate solution. The chromate solution includes a subject solution and an aqueous silane solution in an amount ranging from 5 to 50% by weight of the subject solution. The subject solution contains a chrome aqueous solution where the concentration of chrome is in the range of 5-50 g/l and the ratio of trivalent chrome to the chrome content is in the range of 0.4 to 0.8. Phosphoric acid in an amount ranging from 20 to 150% by weight with respect to the chrome content, fluoric acid in an amount ranging from 10 to 100% by weight with respect to the chrome content, colloidal silica having pH of 2-5 in an amount ranging from 50 to 2000% by weight with respect to the chrome content, and sulfuric acid in an amount ranging from 5 to 30% by weight with respect to the chrome content are mixed with the chrome aqueous solution. The aqueous silane solution contains 2-10 wt % of Epoxy-based silane and has a pH of 2-3. A resin coating layer is formed on one side or both sides of the chromate film. The resin coating layer is formed from a resin solution. The resin solution includes a phenoxy resin solution having a molecular weight of 25,000-50,000, colloidal silica of 10-20 phr with respect to the phenoxy resin content, and melamine resin of 2-15 phr with respect to the phenoxy resin content.

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