Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1998-01-21
2000-05-09
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148259, 148260, 148274, 148275, 4273884, C23C 2248
Patent
active
060598964
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to novel compositions and processes for surface treatment of metallic materials containing aluminum as their predominant constituent (e.g., alloys such as Al--Mn, Al--Mg, Al--Si, and the like). These compositions and processes confer outstanding corrosion resistance and adhesion to paint on the surface of aluminum-containing metal before painting this metallic material. The surface treatment of aluminum drawn and ironed (hereinafter usually abbreviated as "DI") cans is a field in which the present invention can be applied to particular benefit. Thus, it is possible by means of the present invention to confer on the surface of aluminum DI cans formed by drawing and ironing sheet aluminum alloy, before carrying out painting and printing, better corrosion resistance and adhesion to paint than with prior methods, and the superior low-friction characteristics needed for smooth conveyance of the cans, which hereinafter may be briefly denoted simply as "mobility".
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 contact than immersion, that are useful for treating the surface of aluminiferous metals, defined as aluminum and its alloys that contain at least 50% 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 (i.e., CrO.sub.3) and hydrofluoric acid (HF) as their essential components and may also contain a conversion accelerator. These baths form 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. However, these chromate type surface treatment solutions are environmentally problematic because the bath, unlike the coating formed with it, contains hexavalent chromium; therefore, the use of treatment solutions which do not contain hexavalent chromium is desirable.
The treatment bath taught in Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 52-131937 [131,937/1977] is typical of the non-chromate-type conversion treatment baths. This treatment bath is an acidic (pH=approximately 1.0 to 4.0) waterbome 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.
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 Laid Open [Kokai or Unexamined] Numbers Sh
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Aoki Tomoyuki
Ehara Ryoji
Motozawa Masahiro
Henkel Corporation
Jaeschke Wayne C.
Jaeschke, Jr. Wayne C.
Oltmans Andrew L.
Sheehan John
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