Zinc and zinc alloy electroplating additives and electroplating methods

#The present invention relates generally to improvements in the electrodeposition of zinc and zinc alloys from aqueous alkaline plating baths and to new additives for use in such electrodeposition processes.

#Electrodeposition of zinc and zinc alloys, based for example on sodium zincate, has been known for many years. It is not possible to produce a commercially acceptable deposit from a simple sodium zincate electrolyte as the deposit is powdery and dendritic. For this reason, various additives have been proposed to provide improved deposition, such as cyanides (which have obvious environmental problems) and polymers of amines and epichiorohydrin which act as grain refining additives. These polymers are limited to usage in baths having relatively low concentrations of zinc because it is not possible to prevent uncontrolled deposition of zinc at higher metal concentrations. Also, electroplating processes using these additives tend to have poor cathode efficiency, a narrow bright range, a narrow operating window and tend to produce pitted and “burnt” deposits.

#More recently, additives have been proposed which allow higher zinc concentrations to be used, which have significantly reduced burning and pitting and which allow a wider range of operating parameters. Further, the additives enable an excellent deposit distribution (that is, evenness of the deposit across the article being plated, irrespective of its shape in particular areas). This maximises the efficiency of zinc usage. These additives are based generally on polyquaternary amine compounds and are described in U.S. Pat. No. 5,435,898 and U.S. Pat. No. 5,405,523, which also provide further discussion of the prior art.

#N,N′-Bis[3-(dimethylamino)propyl]urea (35 grams), N,N,N′,N′-tetramethyl-1,4-phenylenediamine (15 grams), water (34 grams) and ethanol (47 grams) are introduced into a reaction flask equipped with a reflux condenser, thermometer and stirrer. The reagents are stirred and heated to reflux. 1,4-dichlorobutane (31 grams) is added slowly over 1.5 hours. The mixture is refluxed for 9 hours at 80-85° C. The resulting liquid is allowed to cool to room temperature giving an aqueous solution of the desired product.

#N,N′-Bis[3-(dimethylamino)propyl]urea (36 grams), 3,3′-imino-bis-(N,N-dimethylaminopropylamine) (17.6 grams), and water (103 grams) are introduced into a reaction flask equipped with a reflux condenser, thermometer and stirrer. The reagents are stirred and heated to reflux. 1,4-dichlorobutane (31.8 grams) is added over 0.5 hours and the mixture is refluxed for a further 1.5 hours. Benzyl chloride (11.9 grams) is then added over 0.5 hours and the mixture is refluxed for a further hour. Sodium hydroxide (3.8 grams) is then added as a 50% solution. A further addition of benzyl chloride (5.9 grams) is then added over 0.5 hours and the mixture is refluxed for a further 2 hours. The resulting liquid is allowed to cool to room temperature giving an aqueous solution of the desired product.

#N,N′-Bis[3-(dimethylamino)propyl]urea (36 grams), 3,3′-imino-bis-(N,N-dimethylaminopropylamine) (17.6 grams), and water (96 grams) are introduced into a reaction flask equipped with a reflux condenser, thermometer and stirrer. The reagents are stirred and heated to reflux. 1,4-dichlorobutane (31.8 grams) is then added over 0.5 hours and the mixture is refluxed for a further 1.5 hours. Allyl chloride (7.2 grams) is then added over 0.5 hours and the mixture is refluxed for a further hour. Sodium hydroxide (3.8 grams) is then added as a 50% solution. A farther addition of allyl chloride (3.6 grams) is then added over 0.5 hours and the mixture is refluxed for a further 2 hours. The resulting liquid is allowed to cool to room temperature giving an aqueous solution of the desired product.