# US 4,396,471 A · Gold plating bath and method using maleic anhydride polymer chelate

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- Number: US 4,396,471 A
- Document ID: US4396471A
- Status: Granted
- Kind: A
- Application number: 06/330,706
- Filed: 1981-12-14
- Granted: 1983-08-02
- Earliest claimed: 1981-12-14
- Assignees: American Chemical & Refining Company Incorporated
- Inventors: Augustus Fletcher; William L. Moriarty
- Web page: https://patentgrep.com/patent/US4396471A

## CPC

- C25D 3/48: of gold
- C25D 3/62: containing more than 50% by weight of gold
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR

## Abstract

An all-purpose gold cyanide electroplating bath utilizes a cobalt, nickel, or indium hardener as a chelate with the acid form of a methyl vinyl ether/maleic anhydride interpolymer. The bath is capable of producing high levels of hardness in deposits that are substantially pure gold; it is efficient, very stable, resistent to contamination, and it is well-suited for utility at a wide range of current densities.

## Claims

### Claim 1

A gold plating bath comprising, on a per liter basis, an aqueous solution of: an alkali metal gold cyanide in an amount providing about 1 to 41 grams of gold, calculated as the metal; free alkali metal cyanide in an amount effective to prevent precipitation of the metal values; an effective amount of an electrolyte ingredient; and about 0.05-10.0 grams of cobalt, nickel, indium, or a mixture thereof, in the form of a chelate with a hydrolyzed interpolymer of a methyl or ethyl vinyl ether and maleic anhydride, said bath having a pH value of about 3.0 to 13.0.

### Claim 2 (depends on 1)

The bath of claim 1 wherein said electrolyte comprises a weak organic acid, and zero to an effective amount of a salt such acid.

### Claim 3 (depends on 2)

The bath of claim 2 wherein said organic acid is citric.

### Claim 4 (depends on 2)

The bath of claim 2 wherein said electrolyte comprises a mixture of said weak organic acid with an inorganic acid selected from the group consisting of acids that furnish the phosphate, nitrate and sulfate radicals.

### Claim 5 (depends on 1)

The bath of claim 1 additionally including an alkali metal hydroxide for adjustment of said pH to said value.

### Claim 6 (depends on 5)

The bath of claim 5 wherein said gold and alkali metal cyanides, and said hydroxide, are compounds of potassium.

### Claim 7 (depends on 1)

The bath of claim 1 wherein said pH value is less than about 7.0, and wherein said bath has a specific gravity of about 4.degree. to 30.degree. Baume.

### Claim 8 (depends on 7)

The bath of claim 7 wherein said pH value is about 4.0 to 6.0.

### Claim 9 (depends on 1, 3, 6)

In a method of electroplating hard gold deposits upon a workpiece, the steps comprising: immersing a workpiece having an electrically conductive surface in the gold plating bath of claim 1, 3, 6, or 7; maintaining the temperature of said bath at about 20.degree. to 75.degree. Centrigrade; applying an electrical potential across said workpiece and an anode to provide a current density of about 0.1 to 165 amperes per square decimeter at said workpiece, and to thereby effect electrodeposition of gold in the desired thickness; and removing the electroplated workpiece from said bath.

### Claim 10 (depends on 9)

The method of claim 9 wherein said temperature is about 35.degree. to 50.degree. Centigrade wherein said pH value is about 4.0 to 6.0, and wherein said current density has a maximum value of 75 amperes per square decimeter, said bath and/or said workpiece being agitated during electroplating.

### Claim 11 (depends on 10)

The method of claim 10 wherein the temperature of said bath is above about 40.degree. Centigrade and said current density is at least 5.0 amperes per square decimeter, said method constituting a high speed electroplating process.