SURFACE-TREATING AQUEOUS SOLUTION AND TREATMENT METHODS FOR FORMING CORROSION-RESISTANT COATING FILM OVER ZINC OR ZINC ALLOY DEPOSIT

摘要

A chromium-free treating liquid and treatment methods which are for imparting to a zinc or zinc alloy deposit a coating film which is highly corrosion-resistant, has a uniform appearance free from sag stains/puddle stains, has no failure concerning thickness unevenness, and has satisfactory adhesion. The surface-treating aqueous solution, which is for forming a corrosion-resistant coating film over a zinc or zinc alloy deposit, is characterized by comprising (a) an alkali metal silicate (M 2 O€¢nSiO 2 (wherein M represents an alkali metal and n indicates SiO 2 /M 2 O molar ratio)), (b) a water-soluble or water-dispersible silane coupling agent, and (c) a water-soluble or water-dispersible glycidyl ether compound. One of the surface treatment methods for forming a highly corrosion-resistant coating film over a zinc or zinc alloy deposit includes bringing the surface of the zinc or zinc alloy deposit into contact with the surface-treating aqueous solution. The surface-treating aqueous solution is applicable also to the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit and free from hexavalent chromium or from chromium in any form. Namely, another surface treatment method for forming a highly corrosion-resistant coating film over a zinc or zinc alloy deposit comprises bringing the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit into contact with the surface-treating aqueous solution. Furthermore provided is a highly corrosion-resistant coating film formed by bringing the solution into contact with the surface of a zinc or zinc alloy deposit or with the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit.