Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
1997-12-29
2001-02-27
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S253000, C428S470000, C252S387000
Reexamination Certificate
active
06193815
ABSTRACT:
TECHNICAL FIELD
This invention relates to a novel liquid surface treatment composition and process for application to aluminiferous metals, which provide the surface of aluminiferous metals, i.e., aluminum and aluminum alloys containing at least 65% by weight of aluminum, with an excellent corrosion resistance and paint adherence. The present invention is applied with particularly good effect in the surface treatment of aluminum alloys in coil and sheet form.
BACKGROUND ART
Liquid compositions, which hereinafter are often called “baths” for brevity, even if used by some other method than immersion, that are in general use for treating the surface of aluminiferous metals can be broadly classified into chromate types and nonchromate types. Chromic acid chromate conversion baths and phosphoric acid chromate conversion baths are typical embodiments of chromate type treatment baths.
Chromic acid chromate conversion baths came into practical use in about 1950 and are still widely used even at present for heat exchanger fin stock and aviation vehicle components. The chromic acid chromate conversion baths contain chromic acid and fluoride as their main components, with the fluoride functioning as a reaction accelerator. These baths coat metal surfaces with conversion coatings containing some quantity of hexavalent chromium.
Phosphoric acid chromate conversion baths originated with the invention disclosed in U.S. Pat. No. 2,438,877. These conversion baths, which contain chromic acid, phosphoric acid, and hydrofluoric acid as their main components, coat metal surfaces with conversion coatings whose main component is hydrated chromium phosphate. Because these conversion coatings do not contain hexavalent chromium, they also are in wide use at present, for such applications as underpaint coatings for beverage can body and lid stock. Nevertheless, since these chromate type surface treatment baths do themselves contain toxic hexavalent chromium even though the coatings produced by them do not, hexavalent chromium-free treatment baths are desired in view of the environmental problems from disposal of the baths, rinse waters, and the like.
Typical of the inventions in the field of the chromium-free nonchromate type surface treatment baths is the process disclosed in Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 52-131937 [131,937/1977]. The treatment bath in that reference consists of an acidic (pH approximately 1.5 to 4.0) aqueous coating solution containing phosphate, fluoride, and zirconium or titanium or both. Treatment of the metal surface with this surface treatment bath forms thereon a protective coating whose main component is zirconium or titanium oxide. (This type of coating is often called a “conversion” coating, because it is believed that it also contains cations from the substrate in the form of oxides and/or phosphates.) An advantage of nonchromate surface treatment baths is that they are free of hexavalent chromium, and this advantage has resulted in their wide use at the present time for treating the surface of drawn-and-ironed (“DI”) aluminum cans and the like. However, the nonchromate baths require longer treatment times for coating formation than chromate surface treatment baths. Shortening surface treatment times has become an important issue in the last few years, because of the increasingly high line speeds being used to boost productivity. Moreover, nonchromate baths yield coatings with a corrosion resistance and paint adherence inferior to those of chromate coatings.
The treatment process disclosed in Japanese Patent Application Laid Open [Kokai or Unexamined] Number Hei 1-246370 [246,370/1989] is an invention whose object is to shorten the aforementioned surface treatment times. In this process, the aluminiferous metal surface is first cleaned with an alkaline degreaser and the cleaned surface is then treated with an acidic (pH 1.5 to 4.0) aqueous solution containing 0.01 to 0.5 g/L of zirconium ions, 0.01 to 0.5 g/L of phosphate ions, 0.001 to 0.05 g/L, measured as its stoichiometric equivalent as fluorine atoms, of “free” fluoride ions, and optionally 0.01 to 1 g/L of vanadium ions. However, when this process is applied to DI aluminum cans, the resulting film does not always have a satisfactory resistance to blackening.
Another nonchromate treatment process is disclosed in Japanese Patent Publication Number Sho 57-39314 [39,314/1982]. Disclosed therein is a treatment process in which the aluminiferous metal surface is treated with an acidic solution containing hydrogen peroxide, one or more selections from zirconium and titanium salts, and one or more selections from phosphoric acid and condensed phosphoric acids. However, this treatment bath is unstable, and, in addition, is also inadequately rapid in terms of surface coating formation. Moreover, this document does not provide a specific description or disclosure of the treatment time, treatment temperature, or treatment process.
It is for these reasons that nonchromate type surface treatment baths are at present almost never used on surface treatment lines for aluminiferous metal coil or sheet where short treatment times are critical.
In summary, then, there has yet to become established in the art a composition or process for treating the surface of aluminiferous metals that can provide short treatment times and is capable of forming a highly corrosion-resistant and strongly paint-adherent coating, but is free of hexavalent chromium.
DISCLOSURE OF THE INVENTION
Problem(s) to Be Solved by the Invention
The present invention is directed to solving the problems described above for the prior art. In specific terms, the present invention provides a composition and process for treating the surface of aluminiferous metals that are able to form rapidly a very corrosion-resistant and highly paint-adherent coating on the surface of aluminiferous metals.
SUMMARY OF THE INVENTION
It has been discovered that a surface treatment composition containing dissolved phosphate ions, dissolved titanium containing substance(s), and dissolved fluoride in particular relative quantities and a particular relative quantity of accelerator selected from a specific group of chemical substances can rapidly form a very corrosion-resistant and highly paint-adherent coating on the surface of aluminiferous metals. The present invention was achieved based on this discovery.
A concentrate or working composition according to the present invention for treating the surface of aluminiferous metals characteristically comprises, preferably consists essentially of, or more preferably consists of, water and the following materials in the relative proportions stated as follows: from 0.010 to 5 parts by weight of phosphate ions; from 0.010 to 2.0 parts by weight, calculated as its stoichiometric equivalent as titanium atoms, of dissolved titanium containing substance(s); from 0.010 to 12 parts by weight, calculated as its stoichiometric equivalent as fluorine atoms, of dissolved molecules and/or anions containing fluorine; and from 0.010 to 2.0 parts by weight of dissolved accelerator. The bases for the specification of these particular weight proportions for each component will be explained in sequence in the discussion of the composition of preferred surface treatment baths, vide infra. Counterions for the necessary constituents explicitly recited above are also necessary if needed for electrical neutrality.
The accelerator increases the speed of coating formation and is selected from the group consisting of oxyacids, such as tungstic acid (i.e., H
2
WO
4
), molybdic acid (i.e., HMoO
3
), permanganic acid (i.e., HMnO
4
), nitric acid (i.e., HNO
3
), nitrous acid (i.e., HNO
2
), hypochlorous acid (i.e., HClO), chlorous acid (i.e., HClO
2
), chloric acid (i.e., HClO
3
), bromic acid (i.e., HBrO
3
), iodic acid (i.e., HIO
3
), perchloric acid (i.e., HClO
4
), perbromio acid (i.e., HBrO
4
), periodic acid (i.e, HIO
4
), orthoperiodic acid (i.e., H
5
IO
6
), and salts of oxyacids; perox
Nakada Kazuya
Wada Hiroyuki
Henkel Corporation
Oltmans Andrew L.
Roylance Abrams Berdo & Goodman L.L.P.
Sheehan John
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