Palladium-nickel alloy plating solution

Abstract: A novel palladium-nickel alloy plating solution provides a uniform electrodeposited film with excellent gloss at a high electric current density. A palladium-nickel alloy plating solution comprises a water-soluble palladium salt, a water-soluble nickel salt, ammonia, an ammonium salt, and 3-pyridinesulfonic acid, which are solved in water. Further additives may be added in the solution.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating solution for electroplating of a palladium-nickel alloy excellent in gloss on electric parts, decorative articles, or the like. 2. Description of the Related Background Art The plating of palladium-nickel alloy shows excellent gloss and excellent corrosion resistance, and, therefore, is frequently used for formation of electric contacts of connector or printed circuit board as well as for various decorative articles. There is a palladium-nickel alloy plating solution prepared, for example, by mixing a water-soluble palladium salt such as dichlorodiamminepalladium in an amount of Pd of 10-50 g/l, a water-soluble nickel salt such as nickel sulfate in an amount of Ni of 10-70 g/l, and 10-70 g/l of an ammonium salt such as ammonium sulfate for stabilization of ammonia with each other, and then by adding aqueous ammonia to adjust a pH around the neutral. This solution, however, has a range of electric current density too narrow to obtain a plating film having satisfactory glossiness, so that the productivity of plated products may not be increased so high. SUMMARY OF THE INVENTION The present invention provides a novel palladium-nickel alloy plating solution which can provide a uniform electrodeposited film excellent in gloss even at a high electric current density. The object of the present invention can be achieved by a palladium-nickel alloy plating solution comprising a water-soluble palladium salt, a water-soluble nickel salt, ammonia, an ammonium salt, and 3-pyridinesulfonic acid, which are dissolved in water. The water-soluble palladium salt used in the palladium-nickel alloy plating solution according to the present invention may be one selected from the group consisting of palladium salts such as palladium chloride, palladium sulfate, and the like, and of palladium complex salts such as dichlorodiamminepalladium. There is no specific restriction on the selection. The water-soluble nickel salt may be one selected from the group consisting of nickel chloride, nickel sulfate, nickel acetate, and double salts and complex salts thereof. There is no specific restriction on the selection. 3-pyridinesulfonic acid, which is added in the palladium-nickel alloy plating solution according to the present invention, is used in such an amount that the effect of addition can be recognized, normally in an amount of 1-10 g/l. Further, if desired, additives such as a smoothing agent, a gloss agent, a stress reducing agent, a surfactant, and the like conventionally known can be added into the solution. The electroplating using the palladium-nickel alloy plating solution according to the present invention rarely presents a defect such as a pit, which is likely to be present in an electrodeposited film at a high electric current density, can provide uniform alloy plated products excellent in gloss, and can provide beautiful alloy plated products without cloud or haze and without color change at a low electric current density. The palladium-nickel alloy plating solution according to the present invention can provide a uniform palladium-nickel alloy electrodeposited film with excellent gloss and without a defect in the broad range of electric current density, whereby permitting relaxation of electroplating conditions and enhancing the productivity while reducing the production cost of deposited products. DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples Added were 50 g/l of dichlorodiamminepalladium (25 g/l of Pd), 100 g/l of nickel sulfate (hexahydrate) (22 g/l of Ni), 50 g/l of ammonium sulfate, and 100 ml/l of 28 % aqueous ammonia. Further, 5 g/l of 3-pyridinesulfonic acid was added to the mixture thereby to prepare a plating solution (pH 7.74). Using the plating solution, electroplating of palladium-nickel alloy was conducted with a cathode of preliminarily electropolished brass plate of 6 cm × 10 cm in variations of electric current density between 0.3 A/dm 2 and 25 A/dm 2 at 60 °C to obtain respective films of 2 µm, and electrodeposited films thus obtained were evaluated as to Pd contents (weight %), glossiness, and appearance. Surface observation was also carried out using a scanning electron microscope to obtain an average particle size of deposited crystal grains. The results of the tests are shown in Table 1. Another plating solution (pH 7.5) was prepared in the same composition as the above except that no 3-pyridinesulfonic acid was added. Plating of palladium-nickel alloy was conducted using the another plating solution in the same manner as above. Electrodeposited films thus obtained therefrom were evaluated in the same manner as above. The evaluation results are shown in Table 2. Pd-Ni Alloy Plating Solution According to the Present Invention Electric current density (A/dm 2 ) Pd contents (wt %) Glossiness Deposited crystal grain average size (µm) Appearance 0.3 72.13 280 0.9 Specular gloss 1.0 76.77 278 0.8 Specular gloss 2.0 73.22 269 0.7 Specular gloss 5.0 67.80 272 0.6 Specular gloss 10.0 68.55 286 0.4 Specular gloss 15.0 65.70 274 0.35 Specular gloss 20.0 60.68 277 0.30 Specular gloss 25.0 56.31 281 0.25 Specular gloss Comparative Pd-Ni Alloy Plating Solution Electric current density (A/dm 2 ) Pd contents (wt %) Glossiness Deposited crystal grain average size (µm) Appearance 0.3 63.15 38 Unmeasurable Black burnt 1.0 67.66 17 Unmeasurable Black burnt 2.0 71.75 98 1.5 Cloud 5.0 64.68 274 1.2 Specular gloss 10.0 65.23 272 0.9 Specular gloss 15.0 64.03 267 0.7 Specular gloss 20.0 63.80 279 0.5 Specular gloss 25.0 58.63 118 1.2 Cloud As seen in the results, the palladium-nickel alloy electrodeposited films obtained by using the palladium-nickel alloy plating solution according to the present invention with 3-pyridinesulfonic acid have excellent properties in the broad range of electric current density. Many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof, as defined in the claims.

Claims: A palladium-nickel alloy plating solution comprising a water-soluble palladium salt, a water-soluble nickel salt, ammonia, an ammonium salt, and 3-pyridinesulfonic acid, which are dissolved in water. A palladium-nickel alloy plating solution according to Claim 1, wherein said water-soluble palladium salt is a palladium salt selected from the group consisting of palladium chloride and palladium sulfate. A palladium-nickel alloy plating solution according to Claim 1, wherein said water-soluble palladium salt is dichlorodiamminepalladium. A palladium-nickel alloy plating solution according to Claim 1, wherein said water-soluble nickel salt is one selected from the group consisting of nickel chloride, nickel sulfate, nickel acetate, and double salts and complex salts thereof. A palladium-nickel alloy plating solution according to Claim 1, wherein 3-pyridinesulfonic acid is used in an amount of 1-10 g/l. A palladium-nickel alloy plating solution according to Claim 1, wherein an additive selected from the group consisting of a smoothing agent, a gloss agent, a stress reducing agent, and a surfactant is contained.

Inventors: HIRANO TOMIO, TSUKAMOTO MASASSKI, HIRANO, TOMIO, TSUKAMOTO, MASASSKI
Applicants: YAZAKI CORP, YAZAKI CORPORATION
Application year: 1993
Main classification: C25D3
IPC codes: C25D3