Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2000-08-16
2002-03-26
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
active
06361592
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of metal treatment. More particularly the invention relates to a method of metal treatment in order to improve corrosion resistance. The method shows particular utility when the metal is to be subsequently painted, or operations such as bonding rubber to metals or bonding metals to metals are to be carried out subsequent to the silane treatment. The method comprises applying a solution containing one or more ureido silanes in admixture with one or more multi-silyl-functional silanes to a metal substrate. The method is particularly suitable for use on cold-rolled steel, zinc, iron, aluminium and aluminium alloy surfaces.
DESCRIPTION OF RELATED ART
Most metals are susceptible to some form of corrosion, in particular atmospheric corrosion including the formation of various types of rust. Such corrosion may significantly affect the quality of such metal substrates, as well as that of the products produced therefrom. Although corrosion may often be removed from the metal substrates, these processes are often, time consuming costly and may further diminish the integrity of the metal. Additionally, where polymer coatings such as paints, adhesives or rubbers are applied to the metal substrates, corrosion of the base metal material may cause a loss of adhesion between the polymer coating and the base metal. Such a loss of adhesion between a coating layer and the base metal may likewise lead to corrosion of the metal.
Metallic coated steel sheet such as galvanized steel for example is used in many industries, including the automotive, construction and appliance industries. In most cases, the galvanized steel is painted or otherwise coated with a polymer layer to achieve a durable and aesthetically-pleasing product. Galvanized steel, particularly hot-dipped galvanized steel, however, often develops “white rust” during storage and shipment. White rust (also called “storage stain”) is typically caused by moisture condensation on the surface of the galvanized steel which reacts with the zinc coating. White rust is aesthetically unappealing and impairs the ability of the galvanized steel to undergo subsequent process steps such as being painted or otherwise coated with a polymer. Thus, prior to such coating, the zinc surface of the galvanized steel must be pretreated in order to remove the white rust which is present, and prevent it from reforming beneath the polymer layer. Various methods are currently employed to not only prevent the formation of white rust during shipment and storage, but also to prevent the formation of the white rust beneath a polymer coating (e.g., paint).
It is well established that prevention of the formation of white rust on hot-dipped galvanized steel during storage and shipping can be achieved by treating the surface of the steel with a thin chromate film. While such chromate coatings do provide resistance to the formation of white rust, chromium is highly toxic 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, however, the phosphate conversion coating is generally not effective without the chromate rinse.
Aluminium alloys are particularly susceptible to corrosion as the alloying elements used to improve the metal's mechanical properties (e.g., copper, magnesium and zinc) will decrease corrosion resistance.
Recently, various techniques for eliminating the use of chromate have been proposed. These include the steps of providing an aqueous alkaline solution comprising an inorganic silicate and a metal salt in an amount to coat a steel sheet, 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 metal sheet with an aqueous solution containing low concentrations of an organofunctional silane and a cross linking agent in order to provide temporary corrosion protection. The cross-linking agent cross-links the organofunctional silane to form a denser siloxane film. The ratio range of silane to cross-linker is 20:1-2:1.
WO 98/30735 discloses a method of preventing corrosion using 2 treatment solutions, applied separately. The first solution employs a multi-silyl-functional silane cross-linker while the second solution employs an organofunctional silane.
U.S. Pat. No. 5,433,976 teaches the rinsing of a metal sheet with an alkaline solution containing a dissolved silicate or aluminate, an organofunctional silane and a cross-linking agent in order to form an insoluble composite layer containing siloxane.
WO 98/19798 relates to a method of preventing corrosion of metal sheet effected by the application of a solution containing one or more hydrolyzed vinyl silanes to the metal sheet. The method is particularly useful as a pretreatment step prior to painting of galvanized steel as the vinyl functionalities promote the adhesion between the metal surface and the paint coating. A disadvantage, however, is that the vinyl silanes do not bond particularly well to the metal surface.
U.S. Pat. Re. 34,675 (re-issue of U.S. Pat. No. 4,689,085) describes coupling agent and primer compositions which comprise a conventional silane coupling agent and bis (trialkoxy) organo compound, and partially hydrolyzed products of such mixtures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of improving corrosion resistance of a metal substrate.
It is another object of the present invention to provide a method of providing a coating for long-term corrosion resistance of a metal substrate sheet which employs a single-step treatment process.
It is a further object of the present invention to provide a treatment solution for providing a coating for corrosion resistance to metal substrate, wherein the treatment composition need not be removed prior to the painting.
It is a further object of the present invention to provide a treatment coating and solution for promoting rubber to metal bonding.
It is a further object of the present invention to provide a treatment solution for promoting metal to metal bonding using adhesives.
The foregoing objects may be accomplished, in accordance with one aspect of the present invention, by providing a method of treating a metal substrate, comprising of the steps of:
(a) providing a metal substrate, the said metal substrate chosen from the group consisting of:
steel;
steel coated with a metal chosen from the group consisting of: zinc, zinc alloy, aluminium and aluminium alloy;
iron;
zinc and zinc alloys;
aluminium; and
aluminium alloy; and
(b) applying a coating on the metal substrate by contacting the metal substrate with a solution containing one or more hydrolyzed or partially hydrolyzed ureido silanes, one or more hydrolyzed or partially hydrolyzed multi-silyl-functional silanes and a solvent and substantially removing the solvent.
One significant advantage of the present invention is that the treatment solution may be applied directly onto the surface of the metal without the need for an underlying layer of silicates, aluminate or other coating. Another significant advantage is the utility of a one step treatment.
The present invention is particularly suitable if, subsequent to treatment of the metal substrate being carried out, the metal substrate is to be painted or coated with a polymer such as an adhesive or rubber. This may take place after one or more silane treatments, and advantageously after curing of said silane treatment(s).
The silane treatment solution may also incorporate one or more organofunctional silanes which have been at least partially hydrolyzed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The applicants have found that corrosion of metal,
Bines Erwin B.
Brown Kevin
Song Jun
Tang Nie
Andrus Sceales Starke & Sawall LLP
Brunsman David
Chemetall PLC
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