Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming multiple superposed electrolytic coatings
Reexamination Certificate
1999-08-31
2002-05-21
Koehler, Robert R. (Department: 1775)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming multiple superposed electrolytic coatings
C205S164000, C205S183000, C205S184000, C205S187000, C205S215000, C205S216000, C205S246000, C205S255000, C205S271000, C205S291000, C205S317000, C427S409000, C428S626000, C428S637000, C428S675000, C428S679000, C428S658000, C428S680000, C428S926000, C428S935000, C428S927000
Reexamination Certificate
active
06391181
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a technique for producing colored electroplated nickel coatings and to articles producible by this technique.
BACKGROUND OF THE INVENTION
The electrodeposition of nickel on metal substrates such as steel, copper and brass, is widely used in industry in order to meet both decorative and protective requirements for a wide range of goods. The properties provided by an electrodeposited nickel surface, for engineering applications, are generally adhesion, and corrosion- and wear-resistance, hardness and ductility, while for consumer applications the same qualities are relevant, and additionally the appearance of the surface becomes of great importance as part of the decorative value of the products.
The appearance of an electrodeposited nickel coating is usually described in terms of properties such as brightness, reflectivity, tarnish resistance, smoothness, texture and so forth. For esthetic reasons, the color of the coating is also of importance, especially for consumer applications, but the possibilities for imparting intrinsic color to electrodeposited nickel are very limited.
While aluminum may be provided with an oxide film coating which imparts excellent corrosion- and wear-resistance, by an electrolytic process in which aluminum constitutes the anode—“anodizing”—and while such a coating may be successfully colored, such a technique is not applicable to nickel.
In painting technology, it is known to provide surfaces with pigmented polymeric coatings, in order to obtain articles with a colored finish, but of course the surface is not metallic, and thus cannot for example be selected to be a mirror, matt, full-bright or semi-bright finish. Moreover, the manufacturing process then requires an additional coating-pigmenting step, which it would be desirable to avoid, if this were possible.
It is also known to provide colored metallic finishes on (usually bright) electrodeposited nickel with a restricted range of colors. Thus, various hues and shades of gold can be deposited in this manner from gold cyanide electrolyte, and silver can be plated from cyanide electrolyte from a dissolving silver anode. Similarly, a dark gray-blue finish can be imparted to nickel by electrodeposited ruthenium. Such metallic finishes suffer from the following drawbacks:
(a) the color range is limited to golds, silvers and gray-blues;
(b) the high price of the coloring component makes such processes expensive, and in case stripping is required this would also be expensive;
(c) plating from cyanide electrolytes is neither user-friendly nor environment-friendly;
(d) each color requires its own special electrolyte, so that the plating bath must be changed in order to change the color.
In an attempt to meet in particular the limitation of the narrow range of obtainable colors, a number of formulations have been developed for coloring metal surfaces electrolytically or by dipping. By way of example, a solution of lead acetate, sodium thiosulfate and acetic acid can produce a blue color on electrodeposited nickel; a solution of potassium chlorate, and copper and nickel sulfates can produce brown colors on brass and copper; and a solution of copper sulfate containing acetic acid and glycerol, in addition to ammonium, sodium and zinc chlorides, produces the so-called tiffany green on brass or nickel, by repeated immersion and drying of the articles in question. Production of such single colors is unlikely to be economical, and it should also be noted that similarly to the previously-mentioned overplating techniques using gold, silver or ruthenium, these colors each require particular process conditions and often exotic electrolytes or dipping solutions, so that the plating conditions and the bath must be changed in order to change the color, which features of course add to the difficulties of carrying out operations which are commercially viable. An additional problem in such cases is that the obtainable colors and hues are sensitive to slight changes in plating parameters, so that the results may depend more on the operator's skill, than on a particular formulation and plating conditions.
Another approach to solving the problem of the lack of variety of colors available by simply overplating nickel, has been the electrophoretic technique, which involves the deposition of pigment particles in the micronic size range from a pigment suspension in an electroplating bath. Although this technique does provide a variety of colors in the articles thus produced, at the same time the finishes lack the brilliance of nickel-plated articles and are tarnish-like, semi-bright colors. As we have seen in various known techniques, here too, each color requires its special coloring bath, and changing the color means changing the bath. Moreover, stripping of the color is not practical, so that if the finished article is defective in color or appearance, the defect cannot be repaired.
Although not answering consumer demand for a variety of colors, electrodeposition on a metal cathode of a black coating known as “black oxide” or “black nickel”, is also commercially available, and affords a range from light gray to black anthracite. Black nickel is usually plated onto a brass or nickel base, or onto steel provided with an intermediate layer of zinc, copper or nickel. A variety of electroplating conditions and electrolyte formulations for such purposes have been described in the art, but the formulations virtually all contain zinc, nickel and sulfur, in thiosulfate. These formulations, generally termed “oxidizing liquid” are available in the market, in concentrated liquid form. According to U.S. Pat. Nos. 4,861,441 and 5,011,744, black nickel coatings of excellent quality are said to be obtainable in presence of a strongly oxidizing anion, and cations of Zn and a “coloring metal” i.e. Fe, Co, Ni, Cr, Sn or Cu, at a pH of 1-4, a current density of 5-100 A/dm
2
and a current quantity of 20-200 coulombs/dm
2
. Somewhat similar are processes for obtaining a black electrodeposited coating, described in U.S. Pat. Nos. 4,968,391 and 5,023,146, in which the bath contains additionally a sulfur compound such as a thiocyanate or a thiosulfate, and the preferred current density is 1-50 A/dm
2
. Also described in the literature is a process for obtaining black nickel electroplated coatings from a bath containing Ni, Zn and ammonium cations and thiocyanate anions, at a pH of from 3.5 to 6.0, and a cathode current density of 0.15-0.2 A/dm
2
(Dennis, J. K. & Such T. E., Nickel and Chromium Plating, 2nd Edition, Butterworth, 1986, see also U.S. Pat. No. 2,844,530).
A phenomenon related to the problem of providing electrodeposited colored metallic surfaces is that of light interference in submicronic/micronic electroplated films, in which the color depends on film thickness. For example, cuprous oxide changes its color from an initial violet through blue, green, yellow, orange and red, due to the interference phenomenon, as the film thickness increases (see e.g. Solomon, H., Isserlis, G. and Averil, A. F., “Protective and Decorative Coatings for Metals”, Finishing Publications Ltd., USA, 1978). However, this phenomenon is not commercially viable because of the unreliability of the desired color, since the slightest changes in electroplating parameters or physical variation in the metal surface, leads to an even more dramatic change, in color or hue, of the electroplated film.
The entire contents of the above-mentioned patents and literature references are incorporated by reference herein. Briefly summarized, the need for a viable process for obtaining the unique and vivid beauty of mirror-like full-bright nickel coated metal surfaces in a variety of colors has not been satisfied by techniques known in the art.
OBJECTS OF THE INVENTION
A primary object of the invention is to provide a colored electroplated coating on bright or matt nickel as underplate, and a process for the preparation thereof.
Another object of the invention is to provide a colored electroplated coating, and a process
Gorodetski Larisa
Levinson Leonid
Koehler Robert R.
Lilling & Lilling P.C.
Nickel Rainbow Limited
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