Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Reexamination Certificate
2000-10-25
2002-06-25
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
C205S238000, C205S315000
Reexamination Certificate
active
06409906
ABSTRACT:
BACKGROUND AND FIELD OF THE INVENTION
This invention relates to a new electroplating solution and method for plating tarnish-resistant, bluish-white antimony and antimony alloys. The antimony and antimony alloys have the appearance of decorative “hexavalent chrome” electro-deposited coatings.
DESCRIPTION OF THE PRIOR ART
Electrically deposited coatings are widely used to protect substrate articles in wear-inducing or corrosive environments, as decorative coatings, as tarnish- or corrision-resistant coatings and for many other purposes. The substrate is conductive or has been rendered conductive by electroless plating or the like and is formed to the required shape and dimensions. An electrically deposited coating may be placed on the article prior to depositing an exterior coating or as an exterior coating. The electrically deposited coating is chosen to provide the required combination of strength, toughness, ductility, appearance and other properties and to protect the surface of the article against hostile environments, wear and the like. The coating must possess the desired properties and adhere well to the article.
One of the most widely used coatings is the nickel-chrome, where chrome refers to chrome coatings electroplated from a plating solution containing hexavalent chromium ions onto bright nickel. The hexavalent chrome coatings have a bluish-white, tarnish-resistant appearance which is much desired for many applications. Most of the proposals to date have failed to provide electroplated coatings equivalent to electroplated hexavalent chrome coatings.
The use of electroplated hexavalent chrome coatings has become a problem in recent years because of the serious environmental problems related to solutions containing hexavalent chrome ions. Hexavalent chrome ion-containing solutions are considered to be a toxic pollutant and extensive regulations have been developed to monitor their use and disposition. As a result, a continuing search has been directed to the development of substitute electroplating solutions which can be used to produce electroplated coatings equivalent to hexavalent chrome coatings in appearance and properties, but which do not utilize materials regarded as a toxic pollutant.
Further, hexavalent chrome plating solutions are not suitable for use in barrel plating. Barrel plating requires that a number of relatively small, electrically conductive parts be placed in a barrel so that the parts are cathodic and tumble into and out of electrical contact with other parts contained in the barrel with at least one anodic surface. Since current interruption is detrimental to electroplating chrome from hexavalent chrome ion-containing plating solutions, hexavalent chrome plating has not been considered suitable for use in barrel plating.
Numerous plating techniques, solutions, and alloys have been considered in attempts to replace the widely used bluish-white hexavalent chrome coatings. The first choice was trivalent chromium electroplating solution, but the deposit obtained from this solution is dark because of the iron presence in the deposit. The alloys created for this purpose did not provide the bluish non-tarnishing white color, either. The most known alloys in this order are: “tin-nickel”; “tin-cobalt”, U.S. Pat. No. 3,966,564”; and “nickel-tungsten-boron”, U.S. Pat. No. 5,389,226.
Since the hexavalent chrome coatings are considered to be extremely desirable because of their decorative appearance, their wear and abrasion properties, their tarnish-resistance and their other desirable properties, a continuing search has been directed to the development of electroplating techniques and materials which can produce electroplated coatings equivalent to hexavalent chrome coatings without the environmental problems associated with current hexavalent chrome ion-containing electroplating solutions.
SUMMARY OF THE INVENTION
It is now been found that coatings which have an appearance and tarnish-resistance virtually indistinguishable from hexavalent chrome coatings can be produced from an acidic aqueous electroplating solution for electroplating a metallic coating onto an electrically conductive substrate, the coating comprising at least about 65 weight percent antimony, the solution containing from about 0.5 to about 120 g/l (grams per liter) of antimony, at least one acid in an amount sufficient to maintain the pH of the solution below about 6.0, a complexer and a wetter.
The solution may also contain at least one other metal in an amount equal to from about 0.001 to about 2.0 molar (M) and may be used to produce alloys containing at least about 65 weight percent antimony and at least about 0.1 weight percent of the at least one other metal.
The alloys may contain antimony and more than one other metal.
The invention further comprises electrically conductive articles at least partially coated with a bluish-white, tarnish-resistant electroplated coating having the appearance of a hexavalent chrome coating and comprising one of antimony and antimony alloys with other metals.
DESCRIPTION OF PREFERRED EMBODIMENTS
This invention relates to the use of antimony as a single electrodeposited metal, or in an alloy with Ni (0.1—35% Ni metal) and other metals as a chrome substitute, to aqueous electrolytic baths from which the metallic deposits are obtained, to the process to form the deposits and to the deposits. The chrome electrodeposited from an aqueous solution where the chrome ion is hexavalent has a superior white bluish color and is called in the electroplating industry “hexavalent chrome”. As the restrictions from EPA, and the clean air act on the hexavalent chrome become more and more severe, countless alternatives were developed in attempts to match the desirable hexavalent chrome properties which are appearance, excellent adhesion, abrasion and tarnish- and corrosion-resistances.
The first choice was the “trivalent chrome”, which is chrome metal deposited from an aqueous solution where the chrome ion is in the trivalent form. The “trivalent chrome” meets all the “hexavalent chrome” requirements except the color, which is dark because of the presence of iron in the deposit.
Many alloys were created to fulfill the hexavalent chrome specifications, like tin-nickel binary alloy in acidic bath. The tin-nickel alloy was used in the fifties in very acidic solution pH=0.5 and high fluoride content, the color of the deposit was red. The chemical composition of the bath was modified many times, the most recent modification was not red but still showed some pink variations.
Other alloys like tin-cobalt binary or ternary alloys pH=1-3, U.S. Pat. No. 3,966,564, and the nickel-tungsten, boron alloy pH=6-9, U.S. Pat. No. 5,389,226, are major techniques actually used as chrome substitutes. The color of these alloys is yellowish-white and their properties are more nickel-like than chrome-like.
All these alloys added the barrel application option to the classical chrome plating technology, but failed to match the bluish silvery color obtained from a hexavalent chrome bath. This can be explained by the fact that the metals used in these alloys are yellowish-white in their elemental form.
Antimony is a silver, bluish, tarnish-resistant metal in its elemental form. Before this invention, antimony was not used as a primary or a secondary metal in chrome substitute alloys.
As elemental metal, antimony is a white, blue, silvery, non-tarnishing metal, but it is brittle. Antimony acidic solutions are used by immersion to coat steel with a black film prior to phosphate paint base coating. Few attempts have been made to electroplate antimony and none of them is considered to produce a coating comparable to hexavalent chrome coatings.
According to the present invention, it has been found that bluish-white antimony electroplated deposits having the appearance of a hexavalent chrome coating and comprising at least about 65% antimony can be produced from an acidic, aqueous electroplating solution containing from about 0.5 to about 120 g/l of antimony and at least one acid
Danigan Frank C.
Leader William T.
Scott F. Lindsay
Valentine Donald R.
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