Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1996-10-15
1998-03-17
Silverberg, Sam
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148259, 148260, C23C 2233
Patent
active
057282340
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a novel composition and method for treating the surface of aluminiferous metals in order thereby to provide such surfaces, prior to their being painted, with an excellent corrosion resistance and paint adherence. The invention may be effectively applied, inter alia, to the surface treatment of drawn-and-ironed (hereinafter usually abbreviated "DI") aluminum cans. When applied to the DI aluminum cans fabricated by the drawing-and-ironing of aluminum alloy sheet, the surface treatment composition and method according to the present invention are particularly effective in providing the surface of such cans, prior to the painting or printing thereof, with an excellent corrosion resistance and paint adherence and also with the excellent slideability required for smooth conveyor transport of the can (abbreviated below simply as "slideability").
BACKGROUND ART
Liquid compositions, which hereinafter are often called "baths" for brevity, even though they may be used by spraying or other methods of establishing intact than immersion, that are useful for treating the surface of aluminiferous metals, defined as aluminum and its alloys that contain at least 45% by weight of aluminum, may be broadly classified into chromate-type treatment baths and non-chromate-type treatment baths. The chromate-type surface treatment baths typically are divided into chromic acid chromate conversion treatment baths and phosphoric acid chromate conversion treatment baths. Chromic acid chromate conversion treatment baths were first used in about 1950 and are still in wide use at present for the surface treatment of, for example, heat exchanger fins and the like. Chromic acid chromate conversion treatment baths contain chromic acid (CrO.sub.3) and hydrofluoric acid (HF) as their essential components and may also contain a invention accelerator. These baths from a coating that contains small amounts of hexavalent chromium. The phosphoric acid chromate conversion treatment bath was invented in 1945 (see U.S. Pat. No. 2,438,877). This conversion treatment bath contains chromic acid (CrO.sub.3), phosphoric acid (H.sub.3 PO.sub.4), and hydrofluoric acid (HF) as its essential components. The main component in the coating produced by this bath is hydrated chromium phosphate (CrPO.sub.4.4H.sub.2 O). Since this conversion coating does not contain hexavalent chromium, this bath is still in wide use at present as, for example, a paint undercoat treatment for the lid and body of beverage cans. non-chromate-type conversion treatment baths. This treatment bath is an acidic (pH=approximately 1.0 to 4.0) waterborne coating solution that contains phosphate, fluoride, and zirconium or titanium or their compounds. Treatment of aluminiferous metal surfaces with this non-chromate-type conversion treatment bath produces thereon a conversion film whose main component is zirconium and/or titanium oxide. The absence of hexavalent chromium is one advantage associated with the non-chromate-type conversion treatment baths; however, the conversion coatings produced by them in many instances exhibit a corrosion resistance and paint adherence that is inferior to those of the coatings generated by chromate-type conversion treatment baths. Moreover, both chromate-type and non-chromate-type conversion treatment baths contain fluorine, which conflicts with the contemporary desire, prompted by environmental concerns, for the practical implementation of fluorine-free surface treatment baths.
The use of water-soluble resins in surface treatment baths and methods intended to provide aluminiferous metals with corrosion resistance and paint adherence is described, for example, in Japanese Patent Application examples of the prior art surface treatment baths and methods, the metal surface is treated with a solution containing a derivative of a polyhydric phenol compound. However, the formation of an acceptably stable resin-containing coating on the aluminiferous metal surface sometimes is highly problematic with these prior art methods,
REFERENCES:
patent: 4517028 (1985-05-01), Lindert
patent: 4795506 (1989-01-01), Sokalski
Aoki Tomoyuki
Yoshida Masayuki
Henkel Corporation
Jaeschke Wayne C.
Silverberg Sam
Szoke Ernest G.
Wisdom, Jr. Norvell E.
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