JPS6132395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to metal plating. For more details,
The present invention relates to metallic luster finishes on gold alloys and methods of plating to produce such luster finishes.

Gold plating has recently been carried out by several techniques including electrolytic plating, immersion plating, and autocatalytic plating (reduction of gold from a gold solution). Due to the skyrocketing price of gold, the desired properties of gold plating including environmental aging, temperature and humidity cycling, handling, brazeability, TC and ultrasonic weldability, decorative appearance and abrasion resistance Considerable effort has been focused at Metsuki Sangyo on developing methods to create a glossy metallic finish. Alternative metallic gloss finishes used to date include, to name a few:
There are tin films, nickel-boron films, tin-nickel films, and tin-lead films. None of the above finishes were found to be substantially similar in quality to gold. Gold/nickel electrolytic plating has also been employed, but this method is disadvantageous in that chemical control is difficult and electrical connections to the workpiece are required. Electroless gold alloy finishes have been attempted to increase the amount of gold without compromising performance. For example, Japanese Patent Publication No. 33-7514 describes a gold/nickel alloy having wear resistance 1.5 times that of gold. However, the nickel-to-gold ratio is relatively low, at most 15-20%, and therefore meaningful cost savings objectives are difficult to achieve.

One object of the present invention is to provide a metallic luster finish with substantially reduced gold content that exhibits the key performance characteristics of a pure gold metallic luster finish.

Another object of the present invention is to provide a method of forming a metallic luster finish as described above without requiring external application of electricity to the workpiece.

Another object of the invention is to provide a method of forming a metallic luster finish as described above which is relatively simple and easy to control.

These and other objectives will become apparent from the description below. The object is achieved in one embodiment by the method described below. That is, the method includes the following steps: (a) obtaining a workpiece having a metallic luster finish containing at least about 85% by weight of nickel (hereinafter referred to as a nickel-based finish);
(a) a plating source component comprising a monovalent gold compound, and (b) a buffering component such as ammonium hydrogen fluoride, sodium citrate and sodium bicarbonate/ammonium hydroxide, and water-soluble salts, especially carboxylic acids. The processed product is treated in a plating bath containing, for example, sodium and potassium salts. This gold-based finish is an alloy containing gold and nickel with a molecular ratio of nickel to gold ranging from 1:1 to 6:1.

The nickel-based finish produced on the substrate or workpiece may be formed by conventional plating techniques for nickel and nickel alloys. The nickel-based finish can be pure nickel (99.99% pure) or nickel alloyed or combined with elements such as cobalt, boron, and phosphorus. Preferably, the nickel is present in an amount of at least about 85% by weight.
Phosphorus has been found to inhibit gold plating and reduce the temperature stability of the gold-based finish. However, for some applications, the presence of phosphorus is acceptable but preferably does not exceed 6% by weight of the nickel-based finish. Typical nickel-based finishes include nickel (99.99%) and nickel/cobalt/phosphorus (85% each).
10/5% by weight), nickel/phosphorus (95/5% by weight each), and nickel/boron (99/1% by weight each). Typically, the nickel-based finish is relatively uniform in thickness, ranging from 100 to 150 microinches (250 to 375 microcentimeters) in thickness.

A typical bath for obtaining a nickel/phosphorous metallic finish contains nickel chloride, sodium citrate, ammonium hydrogen fluoride, and sodium hypophosphate. Substituting dimethylamine borane for sodium hypophosphate results in a nickel/boron finish. Adding nickel-cobalt will introduce cobalt into the nickel-based finish. The work piece to which the nickel-based finish is applied to the surface is nickel, copper, nickel/
It can be steel or any other base material onto which nickel can be plated.

After applying a nickel-based finish to the processed piece,
The workpiece is prepared for a gilding bath. Typical preparation involves degreasing the surface by washing with a suitable solvent such as methylene chloride, rinsing with an acid solution, then rinsing with copious amounts of water, and rinsing with a potassium cyanide solution containing hydrogen peroxide. Processed at
A rinsing step in deionized water is then included. The thus prepared work piece is ready to be treated in a plating bath. The plating bath is prepared in advance. The plating component of the bath is one or more water-soluble monovalent gold compounds, examples of which include potassium gold cyanide, gold chloride, and gold citrate. A buffer component is also a component of the bath.
Suitable buffers include mixtures of sodium bicarbonate and ammonium hydroxide, ammonium hydrogen fluoride and ammonium citrate and carboxylic acid salts. The buffering component is added to the plating component solution, but care must be taken to avoid inhalation of hydrogen cyanide which may form with some of the mixture. The exact role played by the buffering component is not fully understood. Theoretically, in addition to acting as a buffer, the component would also combine with the nickel in the nickel-based layer to form a soluble complex in the gold plating bath.

The workpiece to be plated is immersed in the bath, which is maintained at a constant temperature, preferably about 90° to 95°C. Stirring is done vigorously the first time, and then during the plating step, stirring is done slowly. After completing the plating process, the plated work piece is rinsed. This method produced a gold-based metallic luster finish with a thickness of over 100 microinches (250 microcentimeters). The gold-based metallic luster finish is an alloy containing nickel and gold with a nickel to gold molecular ratio of 1:1 to 1:6.

The gold-based finish exhibits the physical properties of pure gold plating, except for resistance to salt spray and nitric acid, according to standard test methods. The finish is pale yellow with a nickel-gold luster and is highly touch and abrasion resistant.

The plating components of the plating bath must be present in sufficient amounts to achieve the desired thickness of plating. Generally, the plating component is used in the plating bath 1.
There is at least 3 grams per liter. The buffering component is at least about 75% per liter of bath.
grams and usually present in amounts of 100 grams or more. Plating can be carried out in a suitable container. A preferred vessel has an internal tank lined with an inert material surrounded by a jacket that circulates fluid to heat the plating bath. For the surface to be plated, the gilding compound is about 1 x 10 ^-5 to 10 x 10 ^-5 and preferably 2 x 10 ^-5 to 8 x 10 per square inch (6.45 cm ² ) of the surface to be plated. ^-5 mol/liter is desirable. The buffering component may be present in the range of about ^{3.times.10.sup.-4} to 4.times.10.sup.- ³ moles/liter per square inch (6.45 ^cm.sup.2 ) of the surface being plated.

In order to further explain the invention, examples are described below.

EXAMPLE A bath was prepared consisting of the following: Ingredient concentration (g/) Plating component Potassium gold cyanide 3 Buffer component Sodium bicarbonate 100 Ammonium hydroxide 15 Water Amount required to make 1 liter of total Plating components: Potassium gold cyanide was prepared by dissolving it in deionized water. The buffer component was prepared by adding sodium bicarbonate and ammonium hydroxide to the buffer component solution. Next 1
Sufficient amount of deionized water was added to make a bath solution. Workpieces with 150 microinches (375 microcentimeters) thick pure nickel surfaces were subjected to a cleaning and activation step prior to plating. The nickel-based finish was washed with methylene chloride to reduce the nickel content. The reduced workpiece was then rinsed with a 50% HCl solution at 120°C (49°C) for 1 to 5 seconds after the onset of gas evolution, and then rinsed with cold water for several minutes. The nickel-coated piece is then coated with 10 g/KCN.
and 50 ml/H ₂ O ₂ and the solution was stirred for 10 minutes. The work piece was removed from the solution, rinsed with deionized water, and placed in a plating bath.

The plating bath was preheated to 90°-95°C. After placing the cleaned nickel-coated workpiece into the bath, the solution was stirred for 1 minute and then occasionally stirred for several minutes. The work pieces were removed and rinsed with tap water for several minutes, then with deionized water. A 60 microinch (150 microcentimeter) thick gold plating finish was obtained with a 6:1 nickel to gold molecular ratio.

EXAMPLES AND EXAMPLES The same procedures as in the examples were carried out, except that the baths with the formulations listed below were used. In each example, a nickel and gold alloy metallic gloss finish was obtained.

Example component concentration (g/) Plating component KAu (CN) ₂ 6 Buffer component Ammonium hydrogen fluoride 100 Example component concentration (g/) Plating component KAu (CN) ₂ 3 Buffer component Ammonium citrate Required amount per 100 parts of water Gold plating finishes are nickel and alloys of gold and other elements such as may be present in nickel-based finishes, such as cobalt, boron and phosphorus. The nickel-based finish is essentially pure nickel (99.99
%) gold and nickel alloys give high temperature stable (at least 450°C) gold alloys. The presence of phosphorus in a nickel-based finish results in a gold-based finish that deteriorates at temperatures above 300°C.

The mechanism by which the gold-based finish occurs is not completely understood. The deep penetration of gold appears to deviate from the normal dipping mechanism. Rather, the nickel-based finish appears to be removed to a considerable depth and transferred into the gold plating bath, where the nickel-based finish alloys with the gold and redeposit onto the workpiece. Preferably, the gold-based finish is uniform, strongly adheres to the substrate, and is at least 15 microinches (37.5 microcentimeters) thick. Thicknesses of 60 to 100 microinches (150 to 254 microcentimeters) or greater have been achieved.

Claims (1)

[Claims] 1. A metal plating method that does not require the application of electricity, consisting of the following steps: a. Obtaining a workpiece having a nickel-based finish having at least 85% by weight of nickel; and b. Plating the workpiece. treatment with a bath containing a source component and a buffering component; where the plating source component is
the nickel-based finish contains one or more gold-containing compounds capable of alloying with the nickel; the buffering component forms a nickel complex that is soluble in the bath; On one side,
at a time and temperature sufficient to provide a layer consisting of an alloy of nickel and gold, the molecular ratio of nickel to gold being between 1:1 and 6:1; and the source of nickel in the layer being a nickel-based finish. It is a nickel from. 2. The method of claim 1, wherein the nickel is at least 99% pure by weight. 3. The method according to claim 1, wherein the bath is an aqueous bath. 4. The method according to claim 1, wherein the gold-containing compound is a monovalent gold compound. 5. The method according to claim 1, wherein at least one of the gold-containing compounds is potassium gold cyanide. 6 Approximately 1× gold-containing compound per 6.45 square centimeters (1 square inch) of nickel-based finish surface
The buffering compound is present in the range of 10 ^-5 to 10 x 10 ^-5 moles per 6.45 square centimeters (inch ^square ) of the nickel-based finish.
The method according to claim 1, wherein the amount is present in the range x10 ^-3 mol/. 7 The buffering component is a mixture of sodium bicarbonate and ammonium hydroxide, ammonium hydrogen fluoride,
and ammonium citrate. 8. The nickel-based finish contains nickel and at least one member of the group consisting of cobalt, boron and phosphorus, and at least one member of the group consisting of boron and phosphorus (with the phosphorus not exceeding about 6% by weight), claim 1. The method described in section.