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Publication numberUS2771380 A
Publication typeGrant
Publication dateNov 20, 1956
Filing dateAug 2, 1954
Priority dateAug 2, 1954
Publication numberUS 2771380 A, US 2771380A, US-A-2771380, US2771380 A, US2771380A
InventorsColeman Joseph J, Dittman Emil M
Original AssigneeBurgess Battery Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of plating copper particles with silver
US 2771380 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

Nov. 20, 1956 J. J. COLEMAN ETAL 2,771,380

' METHOD OF PLATING COPPER PARTICLES WITH SILVER Filed Aug. 2, 1954 WATER- SOLUBLE BODIES COPPER PARTICLES e.g. GLAUBER'S SALT MIXED DRY AQUEOUS IMMERSION SILVER PLATING BATH SILVER PLATED COPPER PARTICLES IN V EN TORS.

METHOD OF PLATING COPPER PARTICLES WITH SILVER Joseph J. Coleman and Emil M. Dittman, Freeport, Ill., assignors to Burgess Battery Company, Freeport, III., a corporation of Delaware Application August 2, 1954, Serial No. 447,409

8 Claims. (Cl. 117-227) This invention relates to a method for plating copper particles with silver, and particularly to an immersion type of method, as distinguished from an electrolytic method, of plating copper particles with silver.

The immersion plating of copper with silver is accomplished by immersing the articles to be plated in an aqueous cyanide silver plating bath, and in the plating of copper particles there is a tendency for the particles to agglomerate or adhere together in the form of small masses or pellets. This has two undesirable effects, the first being that the agglomeration itself is objectionable, and the second being that the copper particles are incompletely coated or plated with silver.

It is an object of the invention to provide a method for the immersion plating of copper particles with silver in which the objectionable agglomeration is avoided and complete and continuous coatings or plates of silver are obtained upon the individual copper particles.

The process of the invention is indicated by the flow sheet shown in the drawing.

The method of the invention is applicable to copper particles of any form including flakes. Such particles are susceptible to agglomeration and the method of the invention is effective in avoiding agglomeration of copper par ticles of any form including flakes during plating thereof with silver. The method has been used with success with particles which range in size from about one millimeter to a few microns in their maximum dimension. silver coated copper particles of this character find usefulness as an ingredient in electrically conductive compositions, as for example, in admixture with a binder or vehicle to form a conductive composition or paint.

In accordance with the invention, the copper particles are immersed in the aqueous silver plating bath in the presence of a medium or agent which maintains the copper particles in separated or dispersed condition. In one procedure, the separating agent is in the form of discrete water-soluble bodies such as crystalline hydrated sodium sulfate (Glaubers salt), potassium sulfate, sodium nitrate or the like. In a preferred procedure, the copper particles are first dry mixed with the discrete bodies and the mixture is immersed in an aqueous cyanide silver plating bath. The water-soluble bodies are larger than the copper particles and the volume of said bodies is substantially greater than that of the copper particles, whereby the copper particles become attached to the surfaces of said bodies in separated or dispersed condition and not in agglomerated condition. A suitable size for the watersoluble bodies is from 0.25 inch to .0014 inch. The water-soluble bodies may be in the form of preformed pellets, or crystals produced by crystallization processes, or granules formed by the fracture of larger bodies.

As an example of the method, 30 parts by weight of flake copper is dry mixed with 400 parts of bodies of hydrated sodium sulfate, Na2SO4-10H2O, in a suitable blender or mixer until the copper particles become attached in the form of a coating of dispersed particles to Small ice the surfaces of the sodium sulfate bodies. The mixture of flake copper and hydrated sodium sulfate bodies is then immersed in 800 parts of a cyanide silver plating solution, constant agitation being maintained during the immersion. The plating bath may be of conventional composition as follows, the proportions being in parts by weight:

Silver cyanide Potassium cyanide 125 Potassium carbonate 25 Water 1825 Agitation is continued until the sodium sulfate becomes dissolved in the plating solution, when it is discontinued and the solution is allowed to stand until the particles have settled to the bottom of the container. During the agitation and solution of the sodium sulfate, a plating of the copper particles with silver takes place by a chemical deposition of silver from the silver cyanide in the plating bath. The silver-coated particles are separated from the plating bath in any suitable manner as by decantation and are then thoroughly washed with water and dried.

It has been found that in the process which has been described the silver is deposited in the form of a complete and continuous coating or plate upon the surfaces of the individual copper particles. The individual particles are visible to the eye, thereby showing their non-agglomeration. The bright silver color of the particles is also visible to the eye, thereby showing the complete coating of the individual particles with silver. Upon analysis the particles are found to contain 12 percent by weight of silver.

To further demonstrate that complete silver coatings are produced upon the individual copper particles by the process of the invention, a conductive composition was prepared containing the particles resulting from the method which is described in the foregoing example. The particles were thoroughly mixed with molten microcrystalline wax, the proportions being 14 parts by weight of microcrystalline wax and and 18 parts of particles. The composition was then cooled to room temperature with solidification-of the microcrystalline wax, and was extruded under pressure into the form of a cylindrical section 4; inch in diameter and 6 inches long. The resistance of the section was measured and found to be less than one ohm.

For comparison purposes, similar copper particles were subjected to a plating method exactly the same as described in the foregoing example except that the hydrated sodium sulfate bodies were dispensed with. The resulting plated copper was in the form of silver-coated masses or pellets which were round or nearly round in shape. The pellets were broken open and the interiors were found to be composed of uncoated copper flakes which upon standing in 'the atmosphere turned dark in color. The silver-coated pellets were subjected to a mild crushing operation to separate the agglomerations into individual particles. When mixed with microerystalline wax in the manner described in the foregoing, the resulting composition exhibits an extremely high resistance such that for practical purposes it is a non-conductor.

The superior conductivity of the composition containing the particles plated in accordance with the present invention is due to the fact that the copper particles are completely coated by silver whereas the other particles are not. Copper is subject to the acquisition in the atmosphere of a surface factor which greatly increases the contact resistance, whereas silver is substantially unaffected in this way.

Invention is claimed as follows:

1. The method of plating copper particles with silver which comprises dry mixing said copper particles with discrete water-soluble bodies whereby said copper particles become attached to the surfaces of said water-soluble bodies, said water-soluble bodies being of a size substantially larger than that of said copper particles and the volume of the water-soluble bodies being greater than that of the copper particles and being sufficient that the copper particles are in dispersed condition on the surfaces of the water-soluble bodies, immersing said mixture in an immersion type aqueous silver plating bath, causing said water-soluble bodies to be dissolved in said plating bath, and separating the resulting silver plated copper particles from said plating bath.

2. The method of plating copper particles with silver which comprises dry mixing said copper particles with discrete water-soluble bodies whereby said copper particles become attached to the surfaces of said watersoluble bodies, said water-soluble bodies being of a size substantially larger than that of said copper particles and the volume of the water-soluble bOdies being greater than that of the copper particles and being suflicient that the copper particles are in dispersed condition on the surfaces of the water-soluble bodies, immersing said mixture in an immersion type aqueous silver plating bath, and causing said water-soluble bodies to be dissolved in said plating bath.

3. The method of plating copper particles with silver which comprises dry mixing said copper particles with discrete water-soluble bodies whereby said copper particles become attached to the surfaces of said water-soluble bodies, immersing said mixture in an immersion type aqueous silver plating bath, and causing said water-soluble bodies to be dissolved in said plating bath.

4. The method of plating copper particles with silver which comprises immersing said copper particles in an immersion type aqueous silver plating bath while attached to the surfaces of undissolved water-soluble bodies of a size greater than that of said copper particles.

5. The method of plating copper particles with silver which comprises dry mixing said copper particles with discrete bodies of crystalline hydrated sodium sulfate whereby said copper particles become attached to the surfaces of said sodium sulfate bodies, said sodium sulfate bodies being of a size substantially larger than that of said copper particles and the volume of sodium sulfate bodies being greater than that of the copper particles and being sufficient that the copper particles are in dispersed condition upon the surfaces of the sodium sulfate bodies, immersing said mixture in an immersion type aqueous silver plating bath, causing said sodium sulfate to be dissolved in said plating bath, and separating the resulting silver plated copper particles from said plating bath.

6. The method of plating copper particles with silver which comprises dry mixing said copper particles with bodies of crystalline hydrated sodium sulfate whereby said copper particles become attached to the surfaces of said sodium sulfate bodies, said sodium sulfate bodies being of a size substantially larger than that of said copper particles and the volume of sodium sulfate bodies being greater than that of the copper particles and being sufficient that the copper particles are in dispersed condition and are not agglomerated upon the surfaces of the sodium sulfate bodies, immersing said mixture in an immersion type aqueous silver plating bath and causing said sodium sulfate to be dissolved in said plating path.

7. The method of plating copper particles with silver which comprises dry mixing said copper particles with bodies of crystalline hydrated sodium sulfate whereby said copper particles become attached to the surfaces of said sodium sulfate bodies, immersing said mixture in an immersion type aqueous silver plating bath, and causing said sodium sulfate to be dissolved in said plating bath.

8. The method as claimed in claim 4 in which the copper particles are in the form of flakes.

References Cited in the file of this patent UNITED STATES PATENTS 1,208,507 Dalby Dec. 12, 1916 2,110,792 Egeberg et al. Mar. 8, 1938 2,113,517 Powell et al. Apr. 5, 1938 2,391,289 Beaver Dec. 18, 1945 2,472,393 Avallone et al. June 7, 1949 2,613,179 Wolfson et al. Oct. 7, 1952 FOREIGN PATENTS 396,250 Great Britain Aug. 3, 1933 OTHER REFERENCES Sanigar: The Electrochemical Society, Preprint 5933, April 27, 1931, pp. 363 to 367.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1208507 *Jul 22, 1916Dec 12, 1916Agnes DalbyPreparation for silvering or gilding metal articles.
US2110792 *Mar 23, 1936Mar 8, 1938Int Silver CoProcess for electrodeposition of silver and products obtained therefrom
US2113517 *Oct 5, 1936Apr 5, 1938Johnson Matthey Co LtdElectrodeposition of silver
US2391289 *Sep 15, 1941Dec 18, 1945Beaver Jr John FBright copper plating
US2472393 *Sep 25, 1944Jun 7, 1949American Steel & Wire CoProcess and bath for copper coating ferrous metal
US2613179 *Jun 19, 1947Oct 7, 1952Int Standard Electric CorpSilver plating
GB396250A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3109014 *Jan 4, 1961Oct 29, 1963Shinetsu Chem Ind CoMethod for preparing monomethyldichlorosilane
US3200167 *Jul 2, 1962Aug 10, 1965Huels Chemische Werke AgProcess for the removal of acetylenic hydrocarbons by selective catalyst hydrogenation
US3202488 *Mar 4, 1964Aug 24, 1965Chomerics IncSilver-plated copper powder
US3476530 *Jun 10, 1966Nov 4, 1969Chomerics IncIron based conductive filler for plastics
US3725308 *Dec 10, 1968Apr 3, 1973M OstolskiElectrically conductive mass
US3962143 *Mar 27, 1974Jun 8, 1976Rca CorporationReactively-bonded thick-film ink
US4419279 *Sep 15, 1980Dec 6, 1983Potters Industries, Inc.Conductive paste, electroconductive body and fabrication of same
US4496475 *Sep 1, 1982Jan 29, 1985Potters Industries, Inc.Conductive paste, electroconductive body and fabrication of same
US4559703 *Apr 24, 1984Dec 24, 1985Centralab, Inc.Process for silver plating rotary contact assemblies
US4652465 *May 7, 1985Mar 24, 1987Nissan Chemical Industries Ltd.Process for the production of a silver coated copper powder and conductive coating composition
US4857233 *May 26, 1988Aug 15, 1989Potters Industries, Inc.Nickel particle plating system
US5175056 *Jun 8, 1990Dec 29, 1992Potters Industries, Inc.Galvanically compatible conductive filler
US5286416 *Sep 22, 1992Feb 15, 1994Potters Industries Inc.Galvanically compatible conductive filler useful for electromagnetic shielding and corrosion protection
US5399432 *Dec 8, 1992Mar 21, 1995Potters Industries, Inc.Galvanically compatible conductive filler and methods of making same
US5750249 *Feb 5, 1993May 12, 1998Potters Industries, Inc.Galvanically compatible conductive filler and methods of making same
DE1295952B *Nov 16, 1962May 22, 1969Chomerics IncVerfahren zum Herstellen von Metallpartikeln fuer das elektrisch Leitendmachen von Kunststoffen
WO1991018740A1 *Jun 7, 1991Dec 12, 1991Potters Industries, Inc.Galvanically compatible conductive filler and methods of making same
Classifications
U.S. Classification427/125, 427/216, 427/217, 252/514, 427/180
International ClassificationB22F1/02, B22F9/24, B22F9/16
Cooperative ClassificationB22F9/24, B22F1/025
European ClassificationB22F9/24, B22F1/02B