US 4,233,088 AGranted

Phosphatization of steel surfaces and metal-coated surfaces

AssigneeInternational Lead Zinc Research Organization, Inc.

InventorMax Kronstein

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Abstract

A process for inhibiting corrosion and providing a foundation for subsequent application of organic coating systems to metal surfaces, such as steel surfaces and zinc-, lead-, copper- and tin-coated surfaces, comprises the development of a protective phosphatizing reaction coating based on a metal other than the metal which is to be protected either by an immersion treatment or by a spray treatment with a phosphatizing bath which contains the metal phosphate or metal acid phosphate matter for such a treatment in a status nascendi. Such a state is obtained by the use of an aqueous medium containing phosphate ions derived from an alkali metal phosphate, an alkali metal acid phosphate, phosphoric acid or combinations of those and introducing into the aqueous medium a metal oxide based on a metal other than that which is to be treated, preferably an oxide of the metal group of molybdenum, vanadium, tungsten, titanium, lead, manganese and copper, whereby the metal oxide in the aqueous medium forms with the phosphate ions of the aqueous medium the desired freshly prepared metal phosphate or metal acid phosphate to develop on the treated metal surface the required protective reaction coating. The phosphatizing bath can be modified further by introducing into the aqueous medium a ligand-forming organic polymer which is capable of entering the reaction coating formation and said polymer can further be influenced also by the addition into the aqueous medium of a small amount of an acetylenic alcohol or a dialdehyde. Also a dispersing agent, such as formamide or an alkyl-substituted formamide, can be employed to increase the reactivity of the metal oxide component.

A process for inhibiting corrosion, providing an adherent foundation, and, in the case of a zinc-coated surface, eliminating the irregular appearance due to a surface condition which is usually described as the formation of a "spangle" pattern, by pretreating metal surfaces for subsequent application of organic coating systems which comprises

treating a metal surface with a phosphatizing bath comprising a reactive aqueous solution or dispersion prepared by introducing a metal oxide of a metal other than the metal of the metal surface to be treated into an aqueous medium containing phosphate ions released from the dissolving or dispersing of an alkali metal phosphate or an alkali metal acid phosphate or phosphoric acid or combinations thereof and introducing a ligand-forming organic polymer into said aqueous medium;
said introduced metal oxide being an oxide of a metal selected from the group consisting of molybdenum, vanadium, tungsten, lead, titanium, manganese and copper;
and said metal oxide being introduced in an amount approximately stoichiometric with said phosphate ions;
whereby there is formed in said aqueous medium a metal phosphate or a metal acid phosphate of the introduced metal oxide by reaction between the introduced metal oxide and the phosphate ions which is capable of interreacting with the metal of the metal surface being treated and resulting in a protective reaction coating comprised of the metal component of the introduced metal oxide as well as of the metal of the treated metal surface together with the phosphate ions of the phsophatizing bath;
said ligand-forming organic polymer being introduced into said aqueous medium in an amount of from about 5% to about 10% by weight of the reaction-formed metal phosphate or metal acid phosphate in said aqueous medium and becoming a part of said protective reaction coating;
following which the treated metal surface is washed with a water rinse, a so-called chromic acid rinse or rinse containing chromic acid as well as phosphoric acid and again followed by a water rinse.

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Abstract

Claims21