Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating
Reexamination Certificate
2002-10-02
2004-09-28
Koehler, Robert R. (Department: 1775)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating
C205S321000, C205S324000, C205S325000, C205S326000
Reexamination Certificate
active
06797147
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the anodization of light metals such as magnesium and aluminum to provide corrosion-, heat- and abrasion-resistant coatings. The invention is especially useful for forming white anodized coatings on aluminum substrates.
BACKGROUND OF THE INVENTION
Magnesium, aluminum and their alloys have found a variety of industrial applications. However, because of the reactivity of such light metals, and their tendency toward corrosion and environmental degradation, it is necessary to provide the exposed surfaces of these metals with an adequate corrosion-resistant and protective coating. Further, such coatings should resist abrasion so that the coatings remain intact during use, where the metal article may be subjected to repeated contact with other surfaces, particulate matter and the like. Where the appearance of articles fabricated of light metals is considered important, the protective coating applied thereto should additionally be uniform and decorative. Heat resistance is also a very desirable feature of a light metal protective coating.
In order to provide an effective and permanent protective coating on light metals, such metals have been anodized in a variety of electrolyte solutions. While anodization of aluminum, magnesium and their alloys is capable of forming a more effective coating than painting or enameling, the resulting coated metals have still not been entirely satisfactory for their intended uses. The coatings frequently lack the desired degree of hardness, smoothness, durability, adherence, heat resistance, corrosion resistance, and/or imperviousness required to meet the most demanding needs of industry. Additionally, many of the light metal anodization processes developed to date have serious shortcomings which hinder their industrial practicality. Some processes, for example, require the use of high voltages, long anodization times and/or volatile, hazardous substances.
In addition, it will often be desirable to provide an anodized coating on a light metal article that not only protects the metal surface from corrosion but also provides a decorative white finish so that the application of a further coating of white paint or the like can be avoided. Few anodization methods are known in the art to be capable of forming a white-colored decorative finish with high hiding power on aluminum articles, for example.
Thus, there is still considerable need to develop alternative anodization processes for light metals which do not have any of the aforementioned shortcomings and yet still furnish corrosion-, heat- and abrasion-resistant protective coatings of high quality and pleasing appearance.
SUMMARY OF THE INVENTION
Light metal-containing articles may be rapidly anodized to form protective coatings that are resistant to corrosion and abrasion using anodizing solutions containing complex fluorides and/or complex oxyfluorides. The use of the term “solution” herein is not meant to imply that every component present is necessarily fully dissolved and/or dispersed. The anodizing solution is aqueous and comprises one or more components selected from water-soluble and water-dispersible complex fluorides and oxyfluorides of elements selected from the group consisting of Ti, Zr, Hf, Si, Sn, Al, Ge and B.
The method of the invention comprises providing a cathode in contact with the anodizing solution, placing the light metal-containing article as an anode in the anodizing solution, and passing a current through the anodizing solution at a voltage and for a time effective to form the protective coating on the surface of the light metal-containing article. Where the article is comprised of magnesium, the current used should be pulsed. Pulsed direct current or alternating current is preferably used when the article is comprised of aluminum. When using pulsed current, the average voltage is preferably not more than 250 volts, more preferably, not more than 200 volts, or, most preferably, not more than 175 volts, depending on the composition of the anodizing solution selected. The peak voltage, when pulsed current is being used, is preferably not more than 500 volts, more preferably not more than 350 volts, most preferably not more than 250 volts.
DETAILED DESCRIPTION OF THE INVENTION
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, “parts of”, and ratio values are by weight or mass; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise, such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word “mole” means “gram mole”, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical or in fact a stable neutral substance with well defined molecules; and the terms “solution”, “soluble”, “homogeneous”, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained at ambient room temperatures (18 to 25° C.).
There is no specific limitation on the light metal article to be subjected to anodization in accordance with the present invention. Preferably, at least a portion of the article is fabricated from a metal that contains not less than 50% by weight, more preferably not less than 70% by weight, magnesium or aluminum.
In carrying out the anodization of a light metal article, an anodizing solution is employed which is preferably maintained at a temperature between about 5° C. and about 90° C.
The anodization process comprises immersing at least a portion of the light metal article in the anodizing solution, which is preferably contained within a bath, tank or other such container. The light metal article functions as the anode. A second metal article that is cathodic relative to the light metal article is also placed in the anodizing solution. Alternatively, the anodizing solution is placed in a container which is itself cathodic relative to the light metal article (anode). When using pulsed current, an average voltage potential preferably not in excess of 250 volts, more preferably not in excess of 200 volts, most preferably not in excess of 175 volts is then applied across the electrodes until a coating of the desired thickness is formed on the surface of the light metal article in contact with the anodizing solution. When certain anodizing solution compositions are used, good resul
Cameron Mary K.
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Koehler Robert R.
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