GB2062010A

GB2062010A - Electroplating Bath and Process

Info

Publication number: GB2062010A
Application number: GB8038947A
Authority: GB
Original assignee: Oxy Metal Industries Corp
Current assignee: Oxy Metal Industries Corp
Priority date: 1978-01-16
Filing date: 1979-01-15
Publication date: 1981-05-20
Also published as: CA1134317A; IT7947654A0; DE2900501C2; AU4339579A; GB2012306B; GB2062009B; SE7900338L; IT1114331B; BR7900282A; AU4339679A; AR219787A1; BR7900283A; MX152135A; AU521274B2; GB2062009A; SE435399B; GB2012306A; DE2900501A1; AU523965B2; MX152015A

Abstract

A non-cyanide acid or substantially neutral zinc electroplating bath and zinc plating process employing said bath which contains an effective amount of a brightening and leveling agent, and which comprises a bath soluble quaternary compound formed by the reaction of butyl nicotinate with an alkylating agent comprising a benzyl halide. The versatility and effectiveness of the brightening and leveling agent of this invention enables improved processing of a wide variety of articles to be carried out, only minimal amounts of the additive agent being required to produce brilliant and smooth zinc deposits.

Description

1

GB 2 062 010 A 1

SPECIFICATION

Electroplating Bath and Process

The present invention relates to a zinc electroplating process using such a bath.

5 Zinc plating processes are in wide-spread commercial use for applying a corrosion resistant, and in some instances, a decorative plating upon a variety of substrates, and more particularly upon ferrous articles e.g. iron or steel. A considerable 10 number of additive agents have been used or proposed for use in zinc electrolytes for improving the brightness and leveling characteristics of the deposit. However, because of environmental and other considerations, increased commercial 15 emphasis has recently been placed on so-called non-cyanide zinc plating solutions of the acid and alkaline types. Brightening and leveling agents employed in such non-cyanide plating solutions in accordance with prior art practice, while effective 20 to produce relatively bright zinc platings, have presented problems in some instances due to the relatively high concentrations required in aqueous solutions to achieve the desired brightening and leveling results. Such aqueous zinc plating 25 solutions have tended to be very selective with respect to the work pieces with which they are effective thus requiring the maintenance of a stock of different brightening agents and solutions for use with different work pieces.

30 Non-cyanide type zinc plating solutions in accordance with the present invention incorporate an additive agent which is particularly effective in producing brilliant zinc platings when employed in only relatively small amounts, which 35 enhances the leveling characteristics of the plating bath, and which is also effective with a broad range of different articles.

According to the present invention an aqueous acid or substantially neutral non-cyanide zinc 40 electroplating bath preferably having a pH of from at least 2 to less than 8, e.g. of at least 3 to 7.9 or 3.5 to 6.3 or 3.9 to 5.8 or 4.0 to 5.5, contains an effective amount of a leveling and brightening agent comprising an effective amount of a 45 leveling and brightening agent comprising a bath soluble quaternary salt having the formula:

[0-C-O-(C#2)3-CH3

55

|0-[-O-(CH2)3-CH3 I

R

-nr I

R

where R represents a benzyl group, and X represents a CI, Br, or I atom.

50 According to a preferred form of the invention an aqueous non-cyanide zinc electroplating bath contains an effective amount of a leveling and brightening agent comprising a bath soluble quaternary salt having the formula:

where R represents a benzyl group, and X represents a CI, Br, or I atom, the bath having a pH of 2 to 6.3.

The brightening and leveling additive agent 60 may be effectively employed in amounts as low as about 0.5 mg/l (0.005 g/l) to concentrations as high as approximately 5 g/l or even 10 g/l with concentrations of from about 2 mg/l up to about 100 mg/l being satisfactory in most instances. 65 The additive agent may be incorporated in aqueous solutions incorporating conventional zinc salts in further combination with inert salts to thereby increase the conductivity of the bath in accordance with known prior art techniques. 70 When operating the electroplating bath at a pH above about 6.8, an organic chelating agent may advantageously be employed to prevent zinc metal from precipitating from the bath.

In accordance with the process aspects of the 75 present invention, brilliant, smooth and adherent zinc platings are attained on metal substrates by contacting with the articles or immersing the articles in an electroplating bath incorporating the aforementioned brightening and leveling agent 80 and subjecting it to an electroplating current at temperatures ranging from approximately 60°F to about 140°F and at current densities broadly ranging from about 5 ASF up to about 200 ASF.

This invention also extends to a zinc 85 electroplating bath which comprises an aqueous, non-cyanide, acid or substantially neutral zinc electroplating bath, that is a bath having a pH ranging from about 2.0 up to less than 8, in particular from 3.5 to 6.3 and incorporating an 90 effective amount of benzyl butyl nicotinate in combination with appropriate concentrations of conventional constituents employed in acid or substantially neutral non-cyanide zinc electroplating baths. The zinc ion, in accordance 95 with conventional practice, may be introduced into the aqueous solution as an aqueous soluble zinc salt, such as zinc sulphate, zinc chloride, zinc fluoroborate, or zinc acetate or mixtures thereof to provide a concentration of zinc ranging from 100 about 5 up to about 105 g/l, with concentrations of zinc ranging from 5 g/l to 70 g/l and especially from about 10 to approximately 70 g/l being preferred.

In addition to the aqueous soluble zinc salt, the 105 bath may further contain, in accordance with conventional practice, inert salts for improving the conductivity of the bath and for further enhancing the appearance of the zinc plate deposit. Such inert salts include sodium chloride, potassium 110 chloride, ammonium chloride, ammonium sulphate, magnesium chloride, or magnesium sulphate which may be employed in

Claims

2

GB 2 062 010 A 2

concentrations ranging from about 1 g/l up to approximately 500 g/l. Additionally, any one of a variety of wetting agents in accordance with conventional practice can also be satisfactorily 5 employed with concentrations thereof typically ranging from about 0.1 up to about 30 g/l. Maintenance of the appropriate pH of the electroplating bath is facilitated by incorporating buffering agents of the types conventionally used 10 in commercial practice such as boric acid or its salts, acetic acid or its salts, and like compounds which are typically present in concentrations of from about 0.5 up to about 100 g/l.

In addition to the quaternized heterocylcic 15 brightener and leveling agent, the aqueous zinc plating solution may further advantageously contain secondary or supporting brighteners of types known in the art, of which linear polyethers having a molecular weight ranging from about 20 400 up to about 1,000,000, for example a polyalkylene glycol, a polyethylene glycol, or a polypropylene glycol; aryl polyethers having a molecular weight ranging from about 400 up to approximately 5,000; a polyglycidol, e.g. 25 polyglycidols having a molecular weight ranging from about 300 up to about 800, and olefin and acetylenic glycol ethers having a molecular weight ranging from about 100 to approximately 5,000 and ethoxylated phenols, an ethoxylated 30 naphthol, an ethoxylated acetylenic glycol, an ethoxylated olefin glycol, or mixtures thereof, are particularly satisfactory. Included within the aforementioned group of secondary supporting brighteners which have been found particularly 35 satisfactory are acetylenic glycol 2,3,7,9-tetramethyl 5-decyne-4,7-diol ethoxylated; /3-naphthol ethoxylated; phenol ethoxylated; polyglycidol; polyoxyethylene; polyoxypropylene; as well as mixtures thereof. Such supporting or 40 secondary brightener agents further enhance the brilliance of the zinc plating deposit and can advantageously be employed in amounts ranging from about 0.25 g/l up to about 20 g/l.

In accordance with the process aspect of the 45 present invention, the zinc electroplating bath is operated within a pH range of about 2.0 to less than 8 and the acidity is adjusted by the addition of sulphuric acid to sulphate baths, or su'.phate-chloride baths, and hydrochloric acid to chloride 50 baths. The bath further preferably incorporates conventional buffering agents to control the pH. In those situations in which the plating bath operates at a substantially neutral pH above about 6.8 to less than 8.0 suitable organic chelating 55 agents are advantageously employed such as nitrilo triacetic acid, ethylene diamine tetraacetic acid or citric acid in amounts ranging from about 0.5 up to approximately 250 g/l so as to prevent the zinc metal ions from precipitating from the 60 bath.

However, it is preferred to operate in the pH range below 6.3 and to avoid the need for such chelating agents.

The electroplating bath can be employed at 65 temperatures ranging from about room temperature up to about 140°F while temperatures of from about 60°F to about 140°F and especially about 60°F to about 90°F are preferred. The electroplating operation can be 70 carried out over a broad range of current densities ranging from about 5 ASF to about 200 ASF especially from 5 to 20 ASF.

The improved levelling attained by employing the primary leveling agent can be still further 75 enhanced in most instances by incorporating controlled effective amounts of methane suiphonic acid or salts thereof such as the sodium potassium, magnesium, or zinc salts. The secondary methane suiphonic acid leveling agent 80 may be employed in amounts ranging from about 0.005 g/l up to about 5.0 g/l while concentrations of about 0.05 to about 0.02 g/l are satisfactory in most instances.

The invention may be put into practice in 85 various ways and one specific embodiment will be described to illustrate the invention with reference to the accompanying example.

Example

A J-shaped steel test specimen was 90 electroplated at a current density of 30 ASF for a period of 20 minutes at a pH of 5.5 in a bath having the following composition:

Constituent Concentration zinc chloride 5 g/l

95 ammonium chloride 100 g/l ethoxylated /3-naphthol

(average MW 900) 10 g/l butylnicotinate benzyl chloride quaternary salt 0.015 g/l

100 The specimen upon completion of plating had a smooth bright zinc electrodeposit.

Zinc deposits in accordance with the present invention can be achieved by employing any one of a variety of plating techniques including barrel 105 plating, tank plating, or continuous plating.

The composition and process enables smooth adherent bright zinc electrodeposits to be obtained from acid or substantially neutral non-cyanide baths.

110 Claims

1. An aqueous acid or substantially neutral non-cyanide zinc electroplating bath containing an effective amount of a leveling and brightening agent comprising a bath soluble quaternary salt 115 having the formula:

0

c—o—(ch2)3—CH3

R

where R represents a benzyl group, and X represents a CI, Br, or I atom.

3

GB 2 062 010 A 3

2. An aqueous non-cyanide zinc electroplating bath containing an effective amount of a leveling and brightening agent comprising a bath soluble quaternary salt having the formula:

0

o—(ch2)3—CH3

R

where R represents a benzyl group, and X represents a CI, Br, or I atom, the bath having a pH of 2 to 6.3.

3. An electroplating bath as claimed in Claim 1

10 or Claim 2 in which the agent comprises butyl nicotinate benzyl chloride quaternary salt.

4. An electroplating bath as claimed in any one of Claims 1 to 3 which also includes an effective amount of a polyether compound as a supporting

15 brightening agent.

5. An electroplating bath as claimed in Claim 4 in which the polyether compound is a polyalkylene glycol, a polyethylene glycol, a polypropylene glycol, a polyglycidol, an

20 ethoxylated phenol, an ethoxylated naphthol, an ethoxylated acetylenic glycol, an ethoxylated olefinic glycol or a mixture thereof.

6. A zinc electroplating bath as claimed in any one of Claims 1 to 5, which also includes as a

25 secondary brightener an acetylenic glycol; an ethoxylated 2,3,7,9-tetramethyl 5-decyne-4,7-diol; and ethoxylated /3-naphthol; an ethoxylated phenol; polyglycidol; polyoxyethylene; or polyoxypropylene; or mixtures thereof.

30 7. An electroplating bath as claimed in any one of Claims 1 to 6 which also includes an effective amount of methane suiphonic acid or at least one salt thereof as a supporting leveling agent.

8. A zinc electroplating bath as claimed in any

35 one of Claims 1 to 7 in which the brightening and leveling agent is present in an amount of from 0.5 mg/l to 5.0 g/l.

9. An electroplating bath as claimed in any one of Claims 1 to 8 in which the quaternary salt is

40 present in an amount of 0.5 mg/l to 10.0 g/l, a polyether compound is present in an amount ranging from 0.25 to 20.0 g/l and methane suiphonic acid or a salt thereof is present in an amount ranging from 0.005 to 5.0 g/l.

45 10. An aqueous acid or substantially neutral non-cyanide zinc electroplating bath comprising boric acid zinc chloride or zinc sulphate, and a benzyl halide quaternary compound of butyl nicotinate.

50 11. An aqueous acid or substantially neutral non-cyanide electroplating bath comprising zinc chloride or zinc sulphate or a mixture thereof, and a benzyl chloride or bromide quaternary salt of butyl nicotinate.

55 12. An electroplating bath as claimed in Claim 1 substantially as specifically described herein with reference to the Example.

13. A process for depositing a bright, smooth, adherent zinc plating on a substrate, which

60 comprises electrodepositing zinc from an aqueous non-cyanide zinc electroplating bath as claimed in any one of Claims 1 to 12.

14. A process as claimed in Claims 13 substantially as specifically described herein with

65 reference to the accompanying Example.

15. An article whenever provided with a zinc electrodeposit by a method as claimed in Claim 13 or Claim 14.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.