Coating processes – With pretreatment of the base – Metal base
Reexamination Certificate
1998-09-16
2001-03-20
Cameron, Erma (Department: 1762)
Coating processes
With pretreatment of the base
Metal base
C427S376400, C427S384000, C427S388400, C427S419800, C427S443200, C106S014150, C106S014210, C106S287110
Reexamination Certificate
active
06203854
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods of and compositions for preventing corrosion of metal substrates. More particularly, the method comprises applying a solution containing an aminosilane and a fluorine-containing inorganic compound to a metal substrate. The method is useful for both preventing corrosion and as a treatment step prior to painting, particularly for metal substrates comprising aluminum or aluminum alloys.
BACKGROUND ART
Most metals are susceptible to corrosion, in particular atmospheric corrosion. Such corrosion will significantly affect the quality of such metals, as well as that of the products produced therefrom. Although this corrosion may sometimes be removed from the metal, such steps are costly and may further diminish the utility of the final product. In addition, when polymer coatings such as paints, adhesives, or rubbers are applied to the metal, corrosion of the base metal material may cause a loss of adhesion between the polymer coating and the base metal. A loss of adhesion between the polymer coating and the base metal can likewise lead to corrosion of the metal. Aluminum alloys are particularly susceptible to corrosion as the alloying elements used to improve the metal's mechanical properties (e.g., magnesium and zinc) will decrease corrosion resistance.
Prior art techniques for improving corrosion resistance of metal, particularly metal sheet, include passivating the surface by means of a heavy chromate treatment. Such treatment methods are undesirable, however, because the chromium is highly toxic, carcinogenic and environmentally undesirable. It is also known to employ a phosphate conversion coating in conjunction with a chromate rinse in order to improve paint adherence and provide corrosion protection. It is believed that the chromate rinse covers the pores in the phosphate coating, thereby improving the corrosion resistance and adhesion performance. Once again, however, it is highly desirable to eliminate the use of chromate altogether. Unfortunately, the phosphate conversion coating is generally not optimally effective without the chromate rinse.
Recently, various techniques for eliminating the use of chromate have been proposed. These include coating the metal with an inorganic silicate followed by treating the silicate coating with an organofunctional silane (U.S. Pat. No. 5,108,793). U.S. Pat. No. 5,292,549 teaches the rinsing of a metal sheet with a solution containing an organofunctional silane and a crosslinking agent in order to provide temporary corrosion protection. The crosslinking agent crosslinks the organofunctional silane to form a denser siloxane film. One significant drawback of the methods of this patent, however, is that the organofunctional silane will not bond well to the metal surface, and thus the coating of U.S. Pat. No. 5,292,549 may be easily rinsed off. Various other techniques for preventing the corrosion of metal sheets have also been proposed. Many of these proposed techniques, however, are ineffective, or require time-consuming, energy-inefficient, multi-step processes.
Thus, there is a need for a simple, low-cost technique for preventing corrosion of metals, particularly aluminum or aluminum alloys, as well as for treating a metal substrate prior to applying polymer coatings such as paints, adhesives, or rubbers.
SUMMARY OF INVENTION
It is an object of this invention to obviate the various problems of the prior art, particularly to obviate the problems associated with chromate use and disposal.
It is another object of this invention to provide improved methods of preventing corrosion of metals.
It is yet another object of this invention to provide improved methods of treating metal surfaces prior to the application of organic polymer coatings, particularly paints, adhesives and rubbers.
In accordance with one aspect of the present invention there is provided a method for treating a metal substrate, comprising the steps of providing a metal substrate and applying a treatment solution to the surface of the metal substrate, wherein the treatment solution comprises a partially hydrolyzed aminosilane and a fluorine-containing inorganic compound. If desired, a polymer coating such as paints, adhesives, or rubbers, may thereafter be applied directly over top of the conversion coating provided by the treatment solution.
In accordance with another aspect of the present invention there is provided a method for coating a metal substrate comprising the steps of providing a metal substrate; cleaning the metal substrate; applying to the surface of the metal substrate a treatment solution comprising a partially hydrolyzed aminosilane and a fluorine-containing inorganic compound to form a conversion coating; and drying the metal substrate.
In accordance with another aspect of the present invention there is provided a method for coating a metal substrate comprising the steps of providing a metal substrate; cleaning the metal substrate; rinsing the metal substrate with water; applying to the surface of the metal substrate a treatment solution comprising an aminosilane and a fluorine-containing inorganic compound to form a conversion coating; optionally rinsing the metal substrate with water, followed by drying the metal substrate
In accordance with yet another aspect of the present invention there is provided a treatment solution comprising a partially hydrolyzed aminosilane and a fluorine-containing inorganic compound.
In accordance with another aspect of the present invention there is provided a method for treating a metal substrate prior to applying a polymer coating, comprising the steps of providing a metal substrate and applying a treatment solution to the surface of the metal substrate, wherein the treatment solution comprises a partially hydrolyzed aminosilane and a fluorine-containing inorganic compound.
It has been found that treatment solutions comprising an aminosilane and a fluorine-containing inorganic compound not only provide good corrosion protection, but also provide good polymer adhesion. Methods according to the present invention do not require the step of deoxidizing the substrate with an acidic solution to remove oxides, resulting in a more efficient process which generates less wastes, and require fewer water rinses, thereby conserving water resources. Further, treatment solutions according to the present invention do not require organic solvents. The treatment solutions can be “refreshed” by supplementation of additional ingredients when titration results indicate the levels of ingredients have fallen below the preferred ranges.
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Paint adhesion and corrosion performance of
Andrus Sceales Starke & Sawall LLP
Brent International PLC
Cameron Erma
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