Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming multiple superposed electrolytic coatings
Patent
1990-10-24
1992-07-21
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming multiple superposed electrolytic coatings
205170, 205172, 205174, C25D 902
Patent
active
051320037
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improvement of a process for the surface treatment of aluminum or aluminum alloys.
BACKGROUND ART
It is known as to anodize aluminum or its alloy within an electrolytic solution, such as an aqueous solution, of nitric acid, sulphuric acid, or chromic acid, to form a corrosion resistant oxide film. Such alumite treatment is widely utilized in various fields, for example aircraft, automobile, marine vessels, optical instruments, instruments for the chemical industry, and even daily needs such as a pan and a teakettle.
However, an upper surface of the alumite film is generally porous. Therefore, in order to improve the corrosion resistance of the porous layer, it is required to perform one of various sealing treatments, e.g. to dip the product into boiling water.
Further, an alumite film is generally of a silver white color. Therefore, when a colored product such as a building material and daily needs, is desired, it is necessary to provide a coloring treatment in which a dye or a pigment is impregnated into the porous layer of the alumite film. Further, a process for forming a natural color anodic oxidation coating by electrolysis using an electrolyte containing sulphuric acid with sulfosalicylic acid added thereto is also known. However, any of the above described processes can color only a shallow area of the upper layer of the alumite film and thus the colored area is likely to subject to wear and discoloration, so that the alumite film is not necessarily sufficient durable because a deep portion under the shallow area remains porous.
It is an object of the present invention to eliminate the above-described disadvantages of the porior art and to provide a process for the surface treatment of aluminium or aluminium alloys, which is able to color various articles and does not use a toxic material, such as cyanogen, and can produce articles having excellent corrosion and abrasion resistance.
DISCLOSURE OF INVENTION
The above object can be performed by a process the surface treatment of aluminium or aluminium alloy characterized in that the process comprises the steps of:
forming an anodic oxidation coating by conventional methods on the surface of the aluminium or aluminium alloy;
applying an alternating voltage of 10 V.about.30 V within a sulfate solution or nitrate solution of a desired metal to a member on which said anodic oxidation castings was formed by the above step, whereby preferably, the electrolyte is comprised of metal salts of 10.about.25 gr/l, boric acid of 25.about.30 gr/l. and sulforic acid or nitric acid of 0.3.about.0.5 gr/l. Also, preferably, the treatment temperature is within a range of 5.degree. C..about.20.degree. C., and the alternating voltage is 10 V.about.30 V.
Silver is most useful as the metal salt.
Further, the anodic oxidation coating may be an alumite coating formed by conventional methods or it may be an anodic oxidation coating combined with an acrylate resin compound formed by passing an eletric current through a low temperature electrolyte containing a low grade acrylate resin compound capable of being polymerized at an anode with the work piece being the anode, the latter being disclosed in Japanese Patent Applications Sho 61-251914 and Sho 63-249147, both of which were filed by the present applicant.
According to the above described process, the metal within the electrolyte may enter or penetrate into the porous oxidation coating formed on the ground metal of aluminium or its alloy to combine with the aluminium oxide to thereby form a strong and dense composite coating. Accordingly, weatherability, corrosion resistance, heat resistance and wear resistance etc. of the oxidation coating are increased, and the oxidation coating can be variously colored depending upon the kind of metal within the electrolyte and the depth of the coating into which the metal penetrates.
Thus, the process for surface treatment according to the present invention can be successfully utilized in an extremely wide range of fields in order
REFERENCES:
patent: 4310586 (1982-01-01), Sheasby et al.
Chemical Abstracts, vol. 92, No. 10, Mar. 1980, Abstract No. 84887e.
Berenato, III Joseph W.
Niebling John
Ryser David G.
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