Non-cyanide silver plating bath composition

Abstract

Disclosed is an electroplating solution for the deposition of silver; said solution containing silver in the form of a complex of silver with hydantoin or a substituted hydantoin compound; said solution also containing an excess of the hydantoin or substituted hydantoin compound employed, together with an effective quantity of a nonprecipitating electrolyte salt, and also an effective quantity of 2,2′ dipyridyl for the purpose of obtaining a mirror-bright to brilliant deposit.

Description

BACKGROUND OF THE INVENTION [0001] Numerous non-cyanide silver plating processes have been attempted (1). Of these, the only ones to have achieved commercial success have been those employing succinimide, either as a premanufactured silver complex (2, 3), or as a reagent. Succinimide undergoes hydrolysis at pH values above neutrality, which in turn causes the pH of the plating solution, normally in the range of 8 to 9 or so, to become unstable; and also to require frequent replenishment of the succinimide. [0002] Hydantoin (CAS Number 461-72-3) is a cyclic diimide possessing structural features similar to succinimide, and similarly effective as a complexing agent for silver. A series of substituted hydantoins exist, of which the most commonly available commercially is 5,5-dimethylhydantoin (CAS No. 77-71-4). As a class, the hydantoins are soluble in moderate-to-strongly alkaline (pH ≧8) solutions, are capable of forming complexes with silver and other metals, and are more resistant ...

AI Technical Summary

Benefits of technology

[0005] Accordingly, it is an object of this invention to provide a non-cyanide plating solution for the deposition of silver, said solution being capable of yielding mirror-bright to brilliant deposits. It is a further object that the plating solution thus provided be as chemically stable as possible, and free of chemical precipitants.

[0006] One preferred embodiment of the present invention is an electroplating solution for the deposition of silver; said solution comprising silver in the form of a complex of silver with hydantoin or a substituted hydantoin compound; said solution also comprising an excess (i.e., more than a stoichiometric amount based on the silver) of the hydantoin or substituted hydantoin compound, together with an effective quantity of a nonprecipitating electrolyte salt, and also an effective quantity of 2,2′ dipyridyl for the purpose of obtaining a mirror-bright to brilliant deposit. An excess amount of the hydantoin or substituted hydantoin compound ensures the complete (or nearly complete) complexation of the silver.

[0007] Preferably, the electroplating solution further comprises an effective quantity of a pyridine or substituted pyridine compound for the purpose of improving the overall brightness of the deposit obtained. Advantageously, the electroplating solution further comprises an effective quantity of surface-active material for the purpose of further improving the overall brightness and brilliance of the deposit obtained.

[0013] Preferably, the electroplating solution used in the process of the invention further comprises an effective quantity of a pyridine or substituted pyridine compound for the purpose of improving the overall brightness of the deposit obtained. Advantageously, the electroplating solution used in the process of the invention further comprises an effective quantity of surface-active material for the purpose of further improving the overall brightness and brilliance of the deposit obtained. In certain preferred embodiments the surface-active material is selected from the group consisting of Hamposyl C, Hamposyl L, Hamposyl O, Blancol, Blancol N, Rhodacal, and Rhodacal N. In certain preferred embodiments, the pyridine or substituted pyridine compound is selected from the group consisting of nicotinamide, isonicotinamide, 2-aminopyridine, 3-aminopyridine, nicotinic acid and its salts, and isonicotinic acid and its salts. In certain preferred embodiments, the nonprecipitating electrolyte salt is selected from the group consisting of the salts of sulfamic, hydrofluoric, nitric, fluoboric, glycolic, and lactic acids.

Problems solved by technology

Succinimide undergoes hydrolysis at pH values above neutrality, which in turn causes the pH of the plating solution, normally in the range of 8 to 9 or so, to become unstable; and also to require frequent replenishment of the succinimide.