Nickel electroplating bath designed to replace monovalent copper strike solutions

Abstract

A nickel electroplating bath is disclosed which is suitable for plating, a base layer of nickel over zinc or zinc alloy parts. Subsequent plating onto this base layer can be achieved with copper, chromium or bright nickel with good adhesion and appearance. The nickel electroplating solution proposed comprises an additive package comprising (i) sulphonic acid or sulphonic acid salts, (ii) sulfonated alkoxylate and (iii) organic acid selected from the group consisting of tolylacetic acid, salicylic acid, hydroxy-benzoic acid, benzyloxyacetone and mixtures of the foregoing.

Description

FIELD OF THE INVENTION [0001] This invention details a process, which can be used to electroplate a nickel deposit directly onto zinc or zinc alloy die-castings, thereby eliminating the need to use traditional cyanide based plating baths. BACKGROUND OF THE INVENTION [0002] Zinc parts are often produced as zinc based die-castings. It is common for these to be plated with other metals to improve cosmetic appearance and improve corrosion resistance. This coating generally consists of one or more of the following: copper, nickel, chromium, tin and brass. Traditionally these articles are base plated with a thin layer of monovalent copper from a copper cyanide bath. Because of the toxicity of cyanide and it's impact on the environment and hence, expense of treatment and disposal—it is desirable that an alternative plating solution be found. [0003] There are a number of cyanide-free copper electroplating processes detailed in the literature. For example, U.S. Pat. No. 4,521,282 to Tremmel ...

AI Technical Summary

Benefits of technology

[0009] (c) Subsequent plating of one or more of the following: nickel, chromium, tin, copper or br

Problems solved by technology

While these electrolytes provide a satisfactory deposition of copper (particularly on steel substrates)—it has been found that these processes can be deficient in terms of adhesion as each is based on divalent copper complexes which will exhibit immersion plating by displacement at least to some extent.

This compromises the integrity of the adhesion between the copper and the zinc substrate and is therefore an unsuitable base for subsequent plated layers.

These electrolytes have also been found to be deficient from a commercial standpoint due to the wide disparity between anode and cathode efficiency.

Nickel electrolytes can be used to plate a layer directly onto a zinc or zinc alloy substrate, however this is not practised commercially as these solutions exhibit poor coverage in areas of low current density.

Also, nickel baths are generally run at low pH which is an unsuitable medium for plating zinc based die-castings since the acidic nature of the electrolyte destroys the article before it can be plated, leading to blistering and poor adhesion of subsequent plated layers.