Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-07-12
2002-07-16
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S663000, C428S680000, C428S935000, C205S181000, C205S196000, C205S238000, C205S246000
Reexamination Certificate
active
06420053
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to an article which includes a bi-colored electroplated metallic coating, and process for its manufacture.
A previous patent application (PCT/IL97/00158, claiming priority from Israel Patent Application No. 118281, filed May 15, 1996), of the present Applicant Company, described and claimed articles and a process for making the articles, the latter including a colored electroplated metallic coating comprising both nickel and zinc, on an underplate of copper, brass, bright nickel or matt nickel, supported on a metallic or plastic substrate, the variation of color of the electroplated coating being due to factors other than variation in the identity of ions in the electrolyte, namely, electroplating parameters. Examination of the colored coatings obtained in this process showed that, while they possessed subjectively a particular color, they were analytically mixtures of different colors.
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 not 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 socalled 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 usually 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). W. Schwartz, in Plating & Surface Finishing, June 1982, pages 26-29, describes inter alia formulations for electroplating systems, in order to obtain platings of black chromium, nickel or nickel/molybdenum, or (gray) arsenic.
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”,
Martine & Penilla LLP
Nickel Rainbow Ltd.
Zimmerman John J.
LandOfFree
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