Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-10-10
2004-01-20
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S253000, C148S254000, C148S256000, C148S268000, C148S275000, C427S309000, C427S344000
Reexamination Certificate
active
06679952
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for coating aluminum and aluminum alloy substrates and to a coated article.
BACKGROUND ART
Aluminum and aluminum alloy substrates have the intrinsic luster of the material and are lightweight, and by taking advantage of these properties, they are being used in increasing quantities in a variety of fields. For example, automotive wheels were mostly made of iron in the past but as higher-grade, lightweight cars came to be the order of the day, the demand has been expanding for aluminum wheels made of aluminum alloy substrates.
Generally, aluminum substrates are not sufficiently resistant to corrosion despite the above-mentioned properties so that even a surface mar may readily develop into filiform corrosion and an oxide film also tends to be formed on the surface. Furthermore, aluminum alloy substrates tend to suffer from the floating-up of those other components added for increased strength as surface impurity and if such substrates are directly coated, no sufficient adhesion to the coating film may be obtained. Therefore, these substrates are surface-treated for improved corrosion resistance, adhesion and other performance characteristics.
The technology for surface treatment of an aluminum wheel comprises after degreasing, subjecting it to anodic oxidation, for example by the Alumite process, coloring process, or a chemical coat treatment, for example by the chromate treatment, MBV process, boemite process or the like. Among these processes, the chromate treatment is used with particular advantage, since this treatment can further improve coating film adhesion and corrosion resistance.
However, the chromate treatment gives a khaki-colored chromate coat which overshadows the surface luster of the aluminum or aluminum alloy substrate, although it is capable of imparting good corrosion resistance. Therefore, in uses where the luster of the material is required as is the case with aluminum wheels, the amount of chromium deposition is restricted and consequently no sufficient corrosion resistance can be imparted in some cases.
Japanese Kokai Publication Hei-5-179486 discloses a method of forming a colorless chromate coat for lustrous aluminum wheels, which comprises subjecting the surface of an aluminum wheel to cathode electrolysis with an acidic chromate ion-containing solution to form a transparent chromate coat. Since the chromate coat is transparent in this method, light may penetrate the coat and reach the substrate surface so that the luster of the material is not compromised. However, in view of the recent alertness to the toxicity of chromium, treatment with a chromium-free treating solution is recommended.
At the present, the non-chromate treatment using a chromium-free treating solution is also practiced but the corrosion resistance is insufficient as compared with the chromate treatment, although it is acceptable from the stand point of environmental safety. In order to impart sufficient corrosion resistance, the film thickness must be increased but the luster of the material will be adversely affected in result.
Particularly in coating of aluminum wheels, where a deluxe finish is an important requirement, not only are good corrosion resistance and good adhesion required but the luster of the material must be exploited. However, these requirements cannot be satisfied by the treating technologies referred to above.
While aluminum and aluminum alloy substrates are used for aluminum cans for beverages and foods, the surface treatment technique for them comprises pickling, degreasing and chemical conversion treatment, optionally followed by after treatment.
Japanese Kokoku Publication Hei-3-50838 discloses a surface cleaning agent comprising a ferric ion and sulfuric and/or nitric acid. This is intended to be applied to aluminum cans for beverages to be fabricated by the drawing and ironing (DI) process for the removal of smuts composed of lubricating oil and aluminum powder deposited on the aluminum surface during processing.
Japanese Kokoku Publication Sho-56-33468 discloses a coating agent comprising a zirconium or titanium ion, a phosphate ion and a fluoride ion. This is used for improving the corrosion resistance and coating film adhesion of aluminum cans.
Japanese Kokai Publication Sho-59-219478 discloses a water-borne after-treating agent comprising a reactive functional group-containing organoalkoxysilane compound. This is used for improving the corrosion resistance and coating film adhesion of the aluminum substrate surface subjected to chemical conversion treatment with zinc phosphate.
These technologies provide chromium-free treating agents and are satisfactory in terms of environmental hygiene but the applicable aluminum or aluminum alloy substrate is not for use in applications requiring a luster, such as aluminum cans for beverages and foods and it is questionable whether these are technologies adequate for the pre-treatment for aluminum wheels which are required to retain the luster of the substrate.
In light of the above state of the art, the present invention has for its object to provide a method of coating aluminum and aluminum alloy substrates by which not only a corrosion resistance comparable or even superior to that afforded by chromate treatment can be imparted but also the adhesion to the coating film can be improved, while the luster of aluminum is fully retained, notwithstanding the use of a chromium-free treating solution, as well as a coated article with the surface coated by the above method and having a metallic luster.
SUMMARY OF THE INVENTION
The present invention is directed to a method of coating aluminum and aluminum alloy substrates
which comprises treating an aluminum or aluminum alloy substrate with an acidic solution containing sulfuric acid and 0.2 to 0.4 g/L of a ferric ion and having a pH value of 0.6 to 2.0,
subjecting the same to chemical conversion treatment with an acidic coat-forming agent containing 0.01 to 0.125 g/L of a zirconium or titanium ion, 0.01 to 1.0 g/L of a phosphate ion, and 0.01 to 0.5 g/L of a fluoride ion and having a pH value of 1.5 to 4.0,
followed by coating.
The present invention is further directed to a method of coating aluminum and aluminum alloy substrates
which comprises treating an aluminum or aluminum alloy substrate with an acidic solution containing sulfuric acid and 0.2 to 0.4 g/L of a ferric ion and having a pH value of 0.6 to 2.0,
subjecting the same to chemical conversion treatment with an acidic coat-forming agent containing 0.01 to 0.125 g/L of a zirconium or titanium ion, 0.01 to 1.0 g/L of a phosphate ion, and 0.01 to 0.5 g/L of a fluoride ion and having a pH value of 1.5 to 4.0,
treating the same with an aqueous solution containing 0.1 to 10 g/L of organoalkoxysilane and having a pH value of 10 to 12,
followed by coating.
The present invention is further directed to a coated article
which is coated by the above methods of coating aluminum and aluminum alloy substrates according to the invention.
In the following, the present invention is described in detail.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a method of coating aluminum and aluminum alloy substrates which comprises treating an aluminum or aluminum alloy substrate with an acidic solution, subjecting the same to chemical conversion treatment with an acidic coat-forming agent followed by coating.
Preferred as said aluminum or aluminum alloy substrate (e.g. AC4C or AC4CH) is an aluminum wheel. Since the coating method of the invention not only provides a coating film with good corrosion resistance and adhesion but also insures the surface luster retained, it can be applied with advantage to aluminum wheels which are required to have a lustrous appearance.
In the practice of the invention, the above aluminum or aluminum alloy substrate is degreased where necessary. The above method for degreasing is not particularly restricted but the method used for the routine treatment of aluminum substrates, such as alkali degreasing cleaning, can be employed.
The abo
Maetsuji Keiji
Nobe Kazuo
Oguri Tatsuya
Sato Takayuki
Shimizu Toru
Jordan and Hamburg LLP
Oltmans Andrew L.
Sheehan John
Topy Industries Limited
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