Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Reexamination Certificate
2000-03-31
2001-10-23
Moore, Margaret G. (Department: 1712)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
C205S101000, C205S271000, C205S698000, C205S595000
Reexamination Certificate
active
06306275
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electroplating, and more particularly to controlling the organic micelle size in a nickel-plating solution.
TECHNICAL BACKGROUND OF THE INVENTION
A nickel coating having a satin finish is desired for various applications on account of its decorative appearance and low glare. Typical applications for satin finish nickel coatings include automotive parts and trim pieces, such as radiator grills and door handles; housings and trim pieces for various photographic and electronic devices, such as cellular telephones, portable video recorders and cameras; furniture components; and the like.
Satin metal coatings have been produced using several different methods. In one method, the surface of a metal substrate is blasted with an abrasive medium such as aluminum oxide to provide a textured surface, which is then electroplated with a bright nickel-plating and chromium electroplating. Another method involves deposition of a satin finish nickel directly without mechanical treatment. This method uses a typical nickel-plating bath, which is admixed with large amounts of insoluble powdery materials in the bath, such as kaolin, talcum, barium sulfate, etc., having a particle size of from about 0.1 to about 0.3 micron. These methods are not generally preferred because they are relatively expensive.
A heretofore preferred process of forming nickel deposits having a uniform satin finish involves the use of an electroplating bath containing a water soluble nickel salt, a primary polishing agent, and an amount of polyethylene oxide polypropylene oxide (PEOPPO) copolymer that is sufficient to form a finely divided dispersion in the bath electrolyte at the operating temperature. In order to achieve an acceptable roughness depth for the deposited coating, it is important that the PEOPPO is dispersed throughout the bath electrolyte in the form of finely divided droplets or micelles. A conventional freshly prepared bath electrolyte will typically exhibit the desired finely divided dispersion of the PEOPPO. However, after a period of time, the finely divided droplets or micelles will coalesce or agglomerate into larger micelles. As the average micelle size increases, the roughness depth of the deposited coatings increases. The stability of the PEOPPO micelles can be improved by adding stabilizing wetting agents such as branch chained alkyl sulfates or sulfonates. This will delay coalescence of the PEOPPO. However, if nothing further is done to counter the growth of the micelles due to coalescence, the roughness depth will increase to an unacceptable level. If this is allowed to occur, the coatings deposited on a substrate article will have an unacceptable roughness depth. Such articles will be rejected and discarded for unacceptable appearance. Further, the bath electrolyte may have to be treated to remove the larger micelles. Treatment of the electrolyte is undesirable because production is suspended while the electrolyte is being treated.
A method to control the uniformity of the satin finish is described in U.S. Pat. No. 3,839,165. The disclosed electroplating method involves continuously removing a portion of the electrolyte from the bath, passing the electrolyte through a heat exchanger in which cooled electrolyte is passed counter-currently and then through a cooling apparatus to cool the electrolyte below the turbidity point of PEOPPO alkylene oxide contained in the electrolyte, passing the cooled electrolyte counter currently through the heat exchanger and re-heating the electrolyte to the bath temperature, and adding the electrolyte back to the bath. During this process, the PEOPPO becomes soluble in the cool electrolyte and the desired finely dispersed micelles are regenerated upon heating the electrolyte back to the operating temperature. Although this method can substantially increase the useful life of the bath electrolyte, the method requires a large amount of energy to cool a portion of the electrolyte below the turbidity point of the alkylene oxide adduct and re-heat the electrolyte back to the bath operating temperature. Accordingly, a process of maintaining the required micelle size that uses less energy, and therefore is less expensive, is desired.
SUMMARY OF THE INVENTION
The invention provides a process for controlling the micelle size distribution of an alkylene oxide adduct dispersion in an electroplating bath. The process comprises the steps of removing a portion of the electrolyte from the electroplating bath, separating the alkylene oxide adduct from the electrolyte that was removed from the electroplating bath, adding additional alkylene oxide adduct to the electroplating bath, and returning the electrolyte to the electroplating bath. The invention provides a simple, economical method of controlling the micelle size of the alkylene oxide adduct dispersed in the plating electrolyte.
In another aspect of the invention, an electroplating process is provided. The electroplating process comprises the steps of providing a plating bath containing an electrolyte, the electrolyte containing a water soluble nickel salt, a primary polishing agent, and an alkylene oxide adduct that is dispersed in the electrolyte; passing an electric current from a substrate that is to be electroplated in the electrolyte, through the electrolyte, and to an electrode; removing a portion of the electrolyte from the electroplating bath; separating the alkylene oxide adduct from the electrolyte that has been removed from the electroplating bath; adding alkylene oxide adduct to the electroplating bath; and returning the electrolyte to the electroplating bath.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The electroplating process of this invention may be conducted in a conventional electroplating bath using an electrolyte containing a water soluble nickel salt, a primary polishing agent, and a PEOPPO.
Examples of suitable water soluble nickel salts that may be used include nickel sulfate hexahydrate and nickel chloride hexahydrate. Combinations of two or more water soluble nickel salts may be used if desired.
A suitable polishing agent is saccharin. Other polishing agents may also provide acceptable results. The polishing agents may be used individually or in combination, and may be employed in a conventional amount, such as from about 0.2 to about 10 grams per liter of the electrolyte.
Suitable alkylene oxide adducts of the formula R
1
[X(R
2
O)
m
(R
3
O)
n
]
p
R
4
. Wherein X is selected from the group consisting of oxygen, sulfur and —NH—, R
1
and R
4
are selected from the group consisting of hydrogen and an organic radical, R
2
and R
3
are selected from the group consisting of ethylene and propylene, m and p are positive integers, and n is zero or a positive integer. The alkylene oxide adducts generally form turbid solutions at a temperature of from about 40° C. to about 75° C. Suitable alkylene oxide adducts, are commercially available and/or may be prepared using known processes. Other suitable alkylene oxide adducts include various polysiloxane polyether copolymers, having a polysiloxane block and one or more polyalkylene oxide blocks, such as a polyethylene oxide and/or polypropylene oxide block. Suitable polysiloxane polyether copolymers are well known and commercially available.
Typical electroplating bath temperatures for the process of this invention are from about 40° C. to about 75° C.
The nickel-electroplating bath of the invention may be used to form a coating having a roughness depth of from about 0.1 to about 6.0 microns. The deposited coatings have a fine to rough satin finish with excellent average thickness and dullness. The satin finish is obtained without any intermediate treatment. Substrates on which the coating may be deposited include iron, brass, copper, nickel, and polymeric materials that have been made conductive, etc. Other metals such as chromium, gold, silver and copper can be plated over the satin nickel deposit while retaining the satin finish.
The electroplating bath may be operated at a current density of from ab
Donovan, III Lawrence P.
Hartrick David P.
Timmer Roger J.
Feely Michael J
Lacks Enterprises, Inc.
Moore Margaret G.
Price Heneveld Cooper DeWitt & Litton
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