GB2128634A - Electrodeposition of bright nickel-alloy coatings - Google Patents

Abstract

A bath for the electrodeposition of a bright nickel-iron coating contains an antipitting agent which improves the levelling power of the electrolyte and the ductility of the coating, the antipitting agent being a hydroxyethylated oligoamide containing the repeating unit of the general formula <IMAGE> n and p being the same or different and having a value of from 3 to 12 and which repeating units in said general formula are the same or different, the oligoamide containing from 4 to 45 repeating units and terminating in -NH2 and -COOH end groups.

Description

SPECIFICATION Improvements in or relating to the electrodeposition of bright nickel-alloy coatings This invention relates to the electrodeposition of bright nickel-iron alloy coatings which may contain up to 30% by weight iron.

In the electronics industry, manufacture of jewelry furniture and household appliances, medical appliances, sporting goods, parts of bicycles, motorcycles and cars, there is much scope for the use of bright nickel coatings. It has become common practice to replace such coatings with coatings of a bright nickel-iron alloy containing up to 30% by weight of iron. When carrying out nickel-iron alloy plating, it is usual to include in the plating bath three types of additive compound, i.e. brightener, complexing agent and antipitting agent.

The brighteners fall into two categories namely primary brighteners and the secondary brighteners. Examples of primary brighteners which may be employed are the following compounds: saccharin sulphobenzaldehyde, naphthalene trisulphonate, allyl sulphonate, aliphatic and aromatic sulphoacids, sulphonamides, and sulphonimides, as described for example in United States Patent No.

3,974,044, United States Patent No. 3,366,667 indicates that there may be used as secondary brighteners condensation products of ethylene oxide and epichlorhydrin with an acetylenic alcohol or a diol, specifically propargyl alcohol or 1,4butyne diol. According to United States Patent No. 2,647,866, it is possible to use as secondary brighteners quaternary salts containing heterocyclic nitrogen, which salts are, according to United States Patent No. 3,023,151, preferably sulphates. Other secondary brighteners which may be employed include polyamines with a molecular weight of 300 to 24,000 (see United States Patent No. 4,002,543), alkylated amines and sulphonated amines.

While the previously described baths for the electrodeposition of bright nickel-iron alloy coatings are capable of producing high quality alloy coatings, they generally contain antipitting agents of a type conventionally used in bright nickel plating as such. Although such antipitting agents prevent pitting from occurring, their presence is harmful to the characteristics of the coating and in general they are not suitable substances to employ in the aforementioned alloy plating process for nickel iron alloy deposition.

According to one aspect of this invention, there is provided a bath for the electrodeposition of bright nickel-iron alloy coatings which comprises an aqueous solvent containing therein Ni++ ions, Fe++ ions, a brightener, a stabilizer and an antipitting additive which is a hydroxyethylated oligoamide containing repeating unit of the following general formula

wherein n and p are the same or different and have a value of from 3 to 12 and which repeating units in said general formula are the same or different, the oligoamide containing from 4 to 45 repeating units and terminating in -NH2 and -COO H end groups.

This invention also provides a method of producing a bright nickel-iron alloy coating on an electrically conductive substrate, which comprises passing a current through a bath of the aforementioned composition and electrodepositing a nickel-iron alloy on to a cathodic surface provided by said substrate.

The oligoamide employed according to the invention provides antipitting action when employed in what may be an otherwise conventional electrndeposition bath for providing bright nickel-iron alloy coatings comprising a brightener system and a stabilizing (complexing) system for maintaining iron ions in solution, with the particular advantage that'the oligoamide has been founo to improve the leveling power of the electrolyte, and the ductility of the coating, while not affecting the current efficiency of the bath and not leading to any deterioration of other properties such as internal stresses and brightness of the coating.

Whilst the sources of nickel ions and iron ions may be conventional such as described in the afformation in United States Patent No.

4,002,543, it is preferred to employ nickel sulphate and nickel chloride together as source of the nickel ions and ferrous sulphate is the preferred source of iron ions. The complexing agent employed will generally be a hydroxycarboxylic acid such as citric acid or giuconic acid or a water soluble salt thereof. The brightener system will generally include an organic sulphooxygen compound such as saccharin and/or an acetylenic nickel brightener such as a hydroxylated butyene-diol. Boric acid will usually be present in the bath as a conventional further additive.

The oligoamide antipitting agent is preferably present in the bath in a concentration of from 0.1 to 1.5 g/l. As a result of the combination of the oligoamide in such amount with other conventionally used components, soft, ductile, mirror-bright and leveled nickel-iron alloy coatings comprising up to 30% iron and exhibiting high corrosion resistance, absence of pitting and other defects are obtained. The oligoamide additive increases the leveling power of the electrolyte and the ductility of the electrodeposited coating by approximately 7 to 10%.

The following examples illustrate the invention: Example 1 Bright nickel-iron alloy coatings were electrodeposited from an aqueous bath containing: Nickel sulphate 100 gIl Nickel chloride 70 gjl Ferrous sulphate 10 gIl Boric acid 45 g/l Sodium citrate 25 g/l Saccharin 4 g/l Hydroxyethylated butyne-diol 0.2 g/l.

Hydroxyethylated oligoamide, n=p=6 and containing 16 repeating units 0.1 g/l The bath had a temperature of 600C, and a pH of 3.3 and a cathodic current density of 3 to 7 A/dm2. Air was bubbled through the bath during the electrodeposition process.

The electrodeposits obtained were mirrorbright and exhibited low internal stresses and high ductility. The electrodeposits were highly leveled.

Example 2 The procedure of example 1 was repeated using an aqueous electrodeposition bath containing: Nickel sulphate 100 gIl Nickel chloride 70 g/l Ferrous sulphate 10 gIl Boric acid 45 g/l Sodium citrate 2.5 g/l Sodium gluconate 12.5 g/l Saccharin 4.0 gIl Hydroxyethylated butyne-diol 0.2 g/l Hydroxyethylated oligoamide n=p=6 and containing 20 repeated units 0.15 gIl The leveling which was obtained here was greater than that obtained in example 1.

Example 3 An aqueous bath for the electrodeposition of protective-decorative nickel-iron alloy coatings was made up as follows: Nickel sulphate 113.2 g/l Nickel chloride 117.2 gll Ferrous sulphate 4.5 g/l Boric acid 50.0 gIl Sodium citrate 10.0 g/l Sodium gluconate 10.0 g/l Saccharin 4.0 g/l Hydroxyethylated butyne-dioi 0.4 g/l Hydroxyethylated oligoamide n=4, p=6, number of repeating units=30 0.25 g/l The bath was maintained at a temperature of 550C and a pH of 3.5 while maintaining a current density of 1 A/dm2 and cathodic agitation.

The electrodeposited coatings were found to be soft and exhibiting high ductility. While being mirror bright they showed a higher degree of leveling than the coatings obtained in Examples 1 and 2.

Claims (9)

Claims

1. A bath for the electrodeposition of bright nickel-iron alloy coatings which comprises an aqueous solvent containing therein Ni++ ions, Fe++ ions, a brightener, a stabilizer and an antipitting additive which is hydroxyethylated oligoamide containing a repeating unit of the following general formula

wherein n and p are the same or different and have a value of from 3 to 12 and which repeating units in said general formula are the same or different, the oligoamide containing from 4 to 45 repeating units and terminating in -NH2 and -COOH end groups.

2. A bath as claimed in claim 1 which contains from 0.1 to i.5 g/l of the oligoamide.

3. A bath as claimed in claim 1 or 2 which contains nickel sulphate and nickel chloride as a source of Ni++ ions and ferrous sulphate as a source of Fe++ ions.

4. A bath as claimed in any one of the claims 1 to 3 which contains citric acid and/or gluconic acid or a water soluble salt thereof as stabilizer.

5. A bath as claimed in any one of the preceeding claims which contains saccharin and/or hydroxyethylated butyne-diol as a brightener.

6. A bath for the electrodeposition of bright nickel-iron alloy coatings, substantially as described in any one of the foregoing examples.

7. A method of producing a bright nickel-iron alloy coating on an electrically conductive substrate, comprising passing a current through a bath as claimed in any one of the preceding claims and electrodepositing a nickel-iron alloy onto a cathodic surface provided by said substrate coating.

8. A method as claimed in claim 7, which is carried out so as to produce a nickel-iron alloy coating containing up to 30% by weight irons.

9. A method of producing a bright nickel-iron alloy coating on a substrate, substantially as described in any one of the foregoing examples.