Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-06-26
2004-08-17
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S447000, C427S387000, C427S388100, C148S275000, C106S014410, C205S324000
Reexamination Certificate
active
06777094
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the field of metal surface protection and more particularly, to a surface treatment that increases paintability and corrosion resistance of magnesium and magnesium alloy surfaces.
BACKGROUND OF THE INVENTION
The light weight and strength of magnesium and magnesium alloys makes products fashioned thereform highly desirable for use in manufacturing critical components of, for example, high performance aircraft, land vehicles and electronic devices.
One of the most significant disadvantages of magnesium and magnesium alloys is corrosion. Exposure to the elements causes magnesium and magnesium alloy surfaces to corrode quickly, corrosion that is both unesthetic and reduces strength.
One strategy used to improve corrosion resistance of metal surfaces is painting. As the surface is protected from contact with corrosive agents, corrosion is prevented. However, many types of paint do not bind well to magnesium and magnesium alloy surfaces.
Methods based on chemical oxidation of an outer metal layer using chromate-solutions are known in the art as useful for treating magnesium and magnesium alloy surfaces to increase paint adhesion, see for example U.S. Pat. Nos. 2,035,380 or 3,457,124. However the low corrosion resistance of treated surfaces and environmental unfriendliness of chromate solutions are definite disadvantages of these methods.
In WO 99/02759 is described a method of providing a protective coating to a magnesium surface by polymerizing an electrostatically deposited resin comprising a variety of functional groups.
Several methods of metal surface treatment using silane solutions have been disclosed, see for example U.S. Pat. Nos. 5,292,549, 5,750,197, 5,759,629 and 6,106,901. saline solutions are environmentally friendly and lend excellent corrosion resistance to treated metal surfaces. Silane residues from the solution bind to a treated metal surface preventing oxidation and forming a layer to which commonly-used polymers such as paint adhese, see U.S. Pat. No. 5,750,197. Although applied with success to steel, aluminum, zinc and respective alloys, magnesium and magnesium alloys have not been successfully treated with silane solutions.
U.S. Pat. No. 5,433,976 teaches alkaline solutions for the treatment of metal surfaces the solutions including an inorganic silicate, inorganic aluminate, a cross-linking agent, and a silane. However, U.S. Pat. No. 5,433,976 does not teach the use of this solution for treating magnesium.
Another strategy used to improve corrosion resistance of metal surfaces is anodization, see for example U.S. Pat. Nos. 4,978,432 and 5,264,113. In anodization, a metal surface is electrochemically oxidized to form a protective layer. Although anodization of magnesium and magnesium alloys affords protection against corrosion, adhesion of paint to anodized magnesium surfaces is not sufficient. Further, as discussed in U.S. Pat. No. 5,683,522, often anodization fails to form a protective layer on the entire surface of a complex workpiece.
It would be highly advantageous to have a method for treating magnesium or magnesium alloy surfaces so as to increase corrosion resistance beyond what is known in the art.
SUMMARY OF THE INVENTION
The present invention is of a method, a composition and a method for making the composition for increasing the corrosion resistance of a magnesium or magnesium alloy surface. The composition is a water/organic solution of one or more hydrolyzed silanes. By binding silane moieties to the magnesium surface, an anti-corrosion coating on a magnesium workpiece is produced.
According to the teachings of the present invention there is provided a composition useful for treating of a magnesium or magnesium alloy surface to increase polymer adhesion and corrosion resistance of the surface, the composition being a silane solution having a pH greater than about 4 and including at least one hydrolyzable silane in a water miscible solvent.
The solvent is one or more materials chosen from amongst water, alcohols, acetone, ethers and ethyl acetate.
The silanes are one or more silanes having at least one non hydrolyzable functiona; group chosen from amongst amino, vinyl, ureido, epoxy, mercapto, isocyanato, methacrylato, vinylbenzene and sulfane functional groups. Suitable silanes include, for example, vinyltrimethoxysilane, bis-triethoxysilylpropyl tetrasulfane, aminotrimethoxysilane, and ureidopropyltrimethoxysilane.
According to a feature of the present invention, the total concentration of hydrolyzable silanes in the silane solution is preferably between about 0.1% and about 30%, more preferably between about 0.5% and about 20% and even more preferably between about 1% and about 5%.
There is also provided according to the teachings of the present invention a method of treating a magnesium or magnesium alloy surface by preparing a silane treatment solution as described above and bring the solution in contact with the surface.
According to a feature of the present invention, preparation of the silane solution includes hydrolyzing the silanes in an aqueous solution having a pH of less than about 6, the pH achieved by adding acid, preferably acetic acid, to the hydrolyzing solution.
According to a feature of the present invention, preparation of the silane solution includes adding a base, preferably KOH, NaOH and NH
4
OH, to the solution so that the final pH, subsequent to the addition of solvent, is at the desired value.
According to a feature of the present invention, when the treated surface is not anodized the pH of the silane solution is more than about 6, preferably more than about 8.
According to a feature of the present invention, one solution used to treat and anodized surface is where at least one of the hydrolyzable silanes in the silane solution is bis-triethoxysilylpropyl tetrasulfane and the solution preferably has a pH of between about 5 and about 8, more preferably of between about 6 and about 7. According to a feature of the present invention, when treating an anodized surface with a bis-triethoxysilylpropyl tetrasulfane solution, the total concentration of hydrolyzable silanes in the silane solution is preferably between about 0.1% and about 5%, more preferably between about 0.8% and about 2% and even more preferably between about 1% and about2%.
Alternatively, according to a feature of the present invention, when the treated surface is anodized, the silane solution can include at least two different hydrolyzable silanes, the first being a nonfunctional bisilyl (e.g. 1,2 bis-(triethoxysilyl) ethane, 1,2-bis-(trimethoxysilyl) ethane, 1,6-bis-(trialkoxysilyl) hexanes and 1,2-bis-(triethoxysilyl)ethylene,) and the second a vinylsilane (e.g. vinyltrimethoxysilane). By “nonfunctional bisilyl” is meant that excepting the function that connects the two silicon atoms together, the functional groups of the silane are all hydrolyzable.
According to a feature of the present invention, when treating an anodized surface with a silane solution including two hydrolyzable silanes the pH of the solution is preferably between about 4 and about 7, more preferably between about 4 and about 5.
According to a feature of the present invention, when treating an anodized surface with a silane solution including two hydrolyzable silanes the total concentration of hydrolyzable silanes in the silane solution is preferably between about 0.1% and about 30%, more preferably between about 0.5% and about 20% and even more preferably between about 1% and about 5%.
According to a feature of the present invention, when treating an anodized surface with a silane solution including two hydrolyzable silanes the molar ratio of hydrolyzable nonfunctional bisilyl to hydrolyzable vinylsilane is preferably between about 50:50 and about 10:90 and more preferably between about 20:80 and about 10:90.
According to a further feature of the present invention, prior to the contact of the silane solution with the surface, the surface is pretreated, for example with a hydrogen fluoride solution.
According to a still further
Alonim Holding Agricultural Cooperative Society Ltd.
Buttner David J.
Friedman Mark M.
Keehan Christopher
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