US3734840A

US3734840A - Electrodeposition of nickel

Info

Publication number: US3734840A
Application number: US00747098A
Authority: US
Inventors: F Passal
Original assignee: M&T Chemicals Inc
Current assignee: M&T Chemicals Inc
Priority date: 1968-07-24
Filing date: 1968-07-24
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22
Also published as: CA947228A; FR2013574A1; DE1936248A1; SE359574B; AT288810B; GB1257935A; CH521448A; ES369801A1; BR6910570D0; NL6911223A

Abstract

AND SALTS THEREOF.

-COOH

AND Y IS CN OR

-NH-(CH2)2-CN

WHEREIN X IS SELECTED FROM THE GROUP CONSISTING OF H, -NH2, AND

Y-CH(-X)-CH2-S-(CH2)2-CN

THIS INVENTION RELATES TO NOVEL COMPOSITIONS AND TO AN IMPROVED PROCESS FOR ELECTROPLATING BRIGHT NICKEL WHICH COMPRISES ELECTRODEPOSITING NICKEL FROM AN AQUEOUS NICKEL ELECTROPLATING BATH CONTAINING (A) AS A FIRST PRIMARY BRIGHTENER AN EFFECTIVE AMOUNT OF A WATER-SOLUBLE ACETYLENIC COMPOUND, (B) A SECONDARY BRIGHTENER AN EFFECTIVE A SECOND COOPERATING PRIMARY BRIGHTENER AN EFFECTIVE AMOUNT OF: (I) A HETEROCYCLIC COMPOUND HAVING AT LEAST TWO NITROGEN ATMOS IN AN OTHERWISE CARBOCYCLIC STRUCTURE WHEREIN AT LEAST ONE NITROGEN ATOM BEARS AT LEAST ONE CYANOETHYL GROUP AND WHEREIN SAID COMPOUND CONTAINS AT LEAST ONE SULFUR ATOM, OR (II) A COMPOUND HAVING THE FORMULA

Description

"United States Patent Office 3,734,840 ELECTRODEPOSITION F NICKEL Frank Passal, Detroit, Mich., assignor to M & T Chemicals Inc, New York, N.Y.

N0 Drawing. Filed July 24, 1968, Ser. No. 747,098 Int. Cl. C2311 /08, 5/46 US. Cl. 204-49 21 Claims ABSTRACT OF THE DISCLOSURE This invention relates to novel compositions and to an improved process for electroplating bright nickel which comprises electrodepositing nickel from an aqueous nickel electroplating bath containing (a) as a first primary brightener an effective amount of a water-soluble acetylenic compound, (b) a secondary brightener, and (c) as a second cooperating primary brightener an effective amount of:

(i) A heterocyclic compound having at least two nitrogen atoms in an otherwise carbocyclic structure wherein at least one nitrogen atom bears at least one cyanoethyl group and wherein said compound contains at least one sulfur atom; or

(ii) A compound having the formula wherein X is selected from the group consisting of H, -.NH and HI!ICH2CH2ON;

and Y is CN or and salts thereof.

This invention relates to a process for nickel plating. More specifically this invention relates to a process for bright nickel plating characterized by outstanding coverage in low current density areas. This invention also relates to novel compositions and compounds.

It is an object of this invention to provide processes and compositions for nickel plating including bright nickel alloy plating. A particular object of this invention is to provide processes and compositions which may be used to provide improved bright nickel plated articles. A further object of this invention is to provide an improved process for the electrodeposition of bright and smooth nickel deposits.

The novel process of this invention for electroplating nickel comprises electrodepositing nickel from an aqueous nickel electroplating bath containing (a) as a first primary brightener an effective amount of a water-soluble acetylenic compound, (b) a secondary brightener, and (c) as a second cooperating primary brightener an effective amount of:

3,734,840 Patented May 22, 1973 wherein X is selected from the group consisting of H, NH and HI ICHzOHzON and Y is ON or and salts thereof.

Addition agents useful as brighteners in nickel plating baths may be divided into two classes (designated primary and secondary brighteners) on the basis of their predominate function.

Primary brighteners are materials used in low or relatively low concentrations, typically 0.0020.2 gram per liter, which by themselves may or may not produce visible brightening action. Those primary brighteners which may exhibit some brightening effects when used alone generally also produce deleterious side-effect such as reduced cathode efliciency, poor deposit color, deposit brittleness and exfoliation, very narrow bright plate range, or failure to plate at all on low current density areas.

Secondary brighteners may be materials which are ordinarily used in combination with primary brighteners but in appreciably higher concentrations than those of the primary brighteners, typically 1 gram per liter to grams per liter. These secondary brighteners may be aromatic sulfonates, sulfonamides or sulfimides (wherein the sulfur atom is bonded directly to the aromatic nucleus) which compounds may be used singly or in combination. These materials, themselves, may produce some brightening or grain-refining effects, but the deposits are not usually mirror-bright and the rate of brightening is usually inadequate.

It is a particular feature of the combination of primary brighteners of this invention that it is not necessary to use, in cooperation with secondary brighteners, auxiliary secondary brighteners such as olefinic or acetylenic aliphatic or aromatic sulfonates, which may be necessary for optimum results when using some prior art primary brighteners. Although the use of auxiliary secondary brighteners such as olefinic or acetylenic aliphatic or aromatically substituted aliphatic sulfonates is not essential, such additives may be used if desired to impart certain desirable characteristics as anti-pitting action, etc.

Ideally, when primary and secondary brighteners of properly chosen and compatible nature are combined it is possible to obtain, over a wide current density range, ductile, leveled deposits which exhibit a good rate of brightening. The rate of brightening and leveling may vary in degree depending on the particular additives chosen and their actual and relative concentrations. A high degree of rate of brightening and leveling is generally desirable, particularly where maximum luster is desired with minimum nickel thicknesses. The concentrations of the secondary brighteners may usually vary within fairly wide limits. The concentrations of the primary brighteners must usually be maintained Within fairly narrow limits in order to maintain desirable properties including good ductility, adequate coverage over low current density areas, etc. Any bright nickel system which can be rendered more tolerant to fluctuations in primary brightener concentrations will have obvious advantages, particularly since the low concentration of primary brighteners and the intrinsic chemical nature of some make strict control by chemical analysis difficult. A primary brightener which can be used over a wide range of concentration is of great value in bright nickel plating.

The basis metals which may be electroplated in accordance with the process of this invention may include copper or copper alloys; ferrous metals including steel, iron, etc.; zinc and its alloys including zinc-base die castings; nickel, etc.

The basis metal may also bear a plate of copper and of semi-bright nickel before being subjected to the process of this invention. As used herein, the term bright nickel plate is meant to include bright alloy plates containing nickel as well as other metals (i.e. cobalt, iron, cobalt-iron, etc.). Thus, alloy deposits containing nickel (such as bright nickel-cobalt deposits) may be obtained according to the process of this invention.

The primary brighteners of the present invention may be useful with e.g. Watts-type baths, high chloride-type baths, and sulfamate-type baths, including those typified by the illustrative baths of Tables I, II, and III.

TABLE I Watts-type baths Nickel sulfate g./l 200 to 400 Nickel chloride g./l 30 to 75 Boric acid g./l 30 to 50 Temperature C 30 to 65 pH 3.5 to 5.0 electrometric with agitation (either mechanical, air, or solution circulation by pumping).

TABLE II High chloride baths Nickel chloride g./l 150 to 300 Nickel sulfate g./l 40 to 225 Boric acid g./l 30 to 50 Temperature C 30 to 65 pH 3.5 to 5.0 electrometric with agitation (either mechanical, air, or solution circulation by pumping).

TABLE III sulfamate-type baths Nickel sulfamate g./l 330 to 600 Nickel chloride g./l 15 to 60 Boric acid g./l 35 to 55 Temperature C 30 to 55 pH 3.5 to 5.0 electrometric with agitation (either mechanical, air, or solution circulation by pumping).

Other nickel plating baths may include those containing as a source of nickel, nickel fluoborate with nickel chloride. In the above tables, the nickel chloride is given as the hexahydrate NiCl -6H O, and the nickel sulfate as the heptahydrate NiSO -7H O. Other compounds, e.g. boric acid and nickel sulfamate, are given on an anhydrous basis.

The plating conditions for electrodeposition from the aforementioned baths may, for example, include temperature of 30 C.65 C., pH of 3.5- electrometric, and preferably 3.8-4.5 and cathode current density of 1-10 amps. per square decimeter. Typical preferred current density of the baths of Table I may be 4-6 amps. per square decimeter. Agitation may be preferred while plating.

The first primary brightener employed in practice of this invention is selected from Water-soluble acetylenic compounds.

Water-soluble acetylenic compounds employed in this invention are characterized by a highly nucleophilic triple bond which is free from steric hindrance and thus has a clear and unimpeded path in approaching the cathode.

The preferred water-soluble acetylenic compounds which may be employed in the process of this invention to produce nickel deposits may include tat-substituted acetylenic compounds exhibiting the structural formula in which each of R and R may be substituents selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, hydroxy-substituted and alkoxy-substituted alkyl, alkenyl, and alkynyl groups, and R and R may together be a carbonyl oxygen; R may be a substituent of the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, hydroxy-substituted and alkoxy-substituted alkenyl and alkynyl groups, and substituted-alkyl groups hav ing the formula:

R4 RA;-

l ter in which each of R and R may be substituents selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, and hydroxy-substituted and alkoxy-substituted alkyl, alkenyl, and alkynyl groups, and when R and R together are carbonyl oxygen, R may be an aryl group, including hydroxy and alkoxy and alkyl-substituted aryl; each of R, and R, may be substituents selected from the group consisting of hydroxy, alkoxy, carboxy-substituted alkoxy, formoxy, alkanoxy, halogen and polyoxy groups. Where R is a substituted-alkyl group having the above illustrated formula, the acetylenic compound may be termed an a, a-disubstituted acetylenic compound, since both carbon atoms vicinal to the same acetylenic bond contain either the same or a different functional group.

The compounds listed in Table IV are illustrative of the water-soluble acetylenic compounds which may be used in practice of the process of this invention.

TABLE IV 2-butyne-1,4-diol 1,4-di- ,B-hydroxyethoxy -2-butyne 1- fi-hydroxyethoxy) -2-butyne-4-o1 1,4-diacetoxy-2-butyne 3-butyne-1,2-diol 3-methyl-l-butyne-3-ol 3-methyl-1-pentyn-3-ol 2-propyn-1-ol 2,5-dimethy1-1-octen-3-yn-5-o1 3-methyl-1-nonyn-3-ol 2,4hexadiyne-1,6-diol 1-methoxy-2-propyne 3-methoxy-3-methyl-4,6-heptadiyne 3-ethoxy-3,5,7-trimethyll-octyne l-formoxy-Z-propyne 1-acetoxy-2-propyne 3-methyl-1-nonyn-3-yl-acetate phenyl-propiolamide phenyl-propiol-N-phenylamide phenyl-propiol-N,N'-dimethylamide 3-methyl-1-butyn-3-yl acetate 1-chloro-6-methoxy-2,4-hexadiyne 3-chloro-3-methyl-4-hexyne 1-bromo-2-propyne 1,2-di-(fi-hydroxyethoxy)-3-butyne 3- (fl-hydroxy- -chloroprop oxy -3 -methyl-4-pentyne 3-(,B-y-epoxypropoxy)-3-methyl-4-pentyne Those acetylenic compounds which may be employed in the instant invention include those containing at least one hydroxy moiety, preferably compounds such as 2- butyne-1,4-diol. v

The first primary brightener may be present in the bath in eifective amounts of 0.002 g./l.0.5 g./l., preferably in effective amounts of 0.005 g./l.-0.10 g./l.

The preferred nickel electroplating baths of this invention include secondary brighteners, present in typical amounts of 1 g./l.80 g./l., preferably 1 g./l.-20 g./1., such as the sulfo-oxygen compounds typical of which is saccharin.

The additional cooperating primary brightener employed in the practice of this invention is:

(i) A heterocyclic compound having at least two nitro gen atoms in an otherwise carbocyclic structure wherein at least one nitrogen atom bears at least one cyanoethyl group and wherein said compound contains at least one active sulfur atom; or

(ii) A compound having the formula wherein X is selected from the group consisting of H, -,NH and HAT-CHzCHzCN and Y is CN or and salts thereof. Suitable salts include alkali metal salts (e.g. Na, K, Li, etc.), ammonium, and alkaline metal salts (Ca, Mg, etc.).

Preferred second primary brighteners used in the practice of this invention include those selected from the group consisting of monocyanoethylated Z-thiohydantoin, di' cyanoethylated Z-thiohydantoin, tn'cyanoethylated 2-thiohydantoin, monocyanoethylated cysteine, dicyanoethylated ethylene thiourea, and [3,;3'-thiodipropionitrile.

Thiohydantoin (I) may be cyanoethylated as herein disclosed to produce 4-mono-B-cyanoethyl thiohydantoin (II), 3,4-di-fi-cyanoethyl thiohydantoin (III), and 3,4,4- tri-fi-cyanoethyl thiohydantoin (W).

HN NH HN NH HN N(CH2CH2CN) i i t It will be apparent to those skilled-in-the-art that each of these Compounds II-IV may each exist in tautomeric equilibrium with its tautomer, e.g. for HI:

H H 0 C& (CHgCHzCN) O C& (CHzCHzCN) HN N(CH CH CN) N N(CH2CH2CN) 2 2 x C C i in The reaction of a heterocyclic thiocarbonyl compound with acrylonitrile is effected under relatively mild conditions. Preferably water is used as a reaction medium. The reaction may be accelerated by use as catalyst of a proton acceptor such as a base such as sodium hydroxide or potassium hydroxide.

Reaction is effected by mixing the components in appropriate mole ratios, preferably in the presence of a reaction medium and preferably accompanied by vigorous agitation. The position and number of the cyanoethyl groups may be readily confirmed by inspection of the infrared spectrum of the compounds, by the Sodium Azide-Iodine Test, elemental analysis, etc.

The temperature during the reaction is controlled to fall in the range of 0 to 70 C. Lower temperatures e.g. 0 C.35 C. favor lower degrees of cyanoethylation, while higher temperatures, e.g. 35 C.70 C. favor higher degrees of cyanoethylation. The time of reaction, depending on the specific compounds reacted, may be from a few minutes, e.g. 5 minutes, to several hours. Commonly it may be 30-60 minutes. At the end of the reaction time, the excess of the acrylonitrile may be removed by volatilization techniques (by heating to C. or higher) or by distillation under vacuum at lower temperatures.

Alkali-insoluble products will precipitate on removal of the excess unreacted acrylonitrile. Alkali-soluble products may be recovered by acidification, e.g. with dilute sulfuric acid. In either case, the product can then be removed by filtration or decantation depending on whether it is crystalline or liquid. Further purification of the crystalline product may be by recrystallization from aqueous solutions or organic solvents or mixtures thereof. Purification of liquid products may be eifected by fractional distillation or solvent extraction.

The additional cooperating primary brightener should be present in the bath in an effective amount of 0.0005 gram per liter to 0.05 gram per liter, preferably 0.001 gram per liter to 0.03 gram per liter.

Other additives which may be used include antipitting agents which may be exemplified by sodium lauryl sulfate and sodium di-N-hexylsulfosuccinate.

Plating of nickel by the novel process of this invention permits attainment of a brilliant, ductile, highly leveled deposit of bright nickel over a wide range of current density.

The basis metals which may be electroplated in accordance with the process of this invention include copper or copper alloys; ferrous metals, including steel, iron, etc.; zinc and its alloys including zinc-base die castings; nickel, etc. Preferably the basis metal bears a plate of copper and of semi-bright nickel before being subjected to the process of this invention.

For the purpose of providing those skilled-in-the-art with a better understanding of this invention, the following examples are set forth wherein all parts are parts by weight unless otherwise specified.

The first primary brighteners acetylenic used were: A 2-butyne-1,4-diol B bis-p-hydroxyethyl ether of Z-butyne, 1,4-diol C 3-methyl-l-butyne-3-ol D phenylpropiolamide The second cooperating primary brighteners used were:

A monocyanoethylated 2-thiohydantoin B dicyanoethylated 2-thiohydantoin C tricyanoethylated-Z-thiohydantoin D monocyanoethylated cysteine E dicyanoethylated ethylene thiourea F ,3,/3'-thiodipropionitrile The secondary brightener used was: A" saccharin (Na salt) The secondary auxiliary brighteners used were:

A'" sodium 3-chloro-2-butene sulfonate B' sodium 2-propene-1-sulfonate C' sodium 1-phenylethene-2-sulfonate The anti-pitting agents used were:

A" sodium lauryl sulfate B" sodium di-N-hexyl-sulfo succinate Brilliant, ductile, highly-leveled deposits with compressive internal stress were obtained after prolonged or extended electrolysis (with periodic primary brightener replenishment) in all cases where the word Good is used in the Results column. The word Poor denotes the attaining of permanent hazy or milky deposits in any part of the current density range after prolonged electrolysis even with periodic primary brightener replenishment.

In Examples 1-28, the electrolyte baths used were Watts baths; high chloride baths were used for Examples 29-35; and sulfamate baths were used for Examples 36-42. In Examples 43-47 cobalt-nickel baths were employed.

The additives were present in the amounts indicated. All runs were made using highly polished brass cathodes with the cathode current densities averaging a.s.d. at a temperature of 60 C. for the Watts and sulfamate baths, and 6 a.s.d. at a temperature of 65 C. for the high chloride bath. The plating time was 30 minutes. To evaluate the degree of leveling the brass cathodes were scratched before plating with a single pass of 4/0 grit emery paper.

In Examples 1-28 the following standard Watts bath was used as a standard solution.

G./l. NiSO -7H O 300 Boric acid 45 Example N0. Additives Amount (g./l.) Results 1 A 0.100 Poor.

2 A 0.100 Good.-

3 A 0. 100 Do;

4 A 0. 100 Do;

5 A 0. 100 Do.

6 A 0.100 Do.

8 B 0.050 Poor.

9- B 0.050 Good.

12 C 0.010 Poor.

13 C 0.010 Good;

15 D 0.100 Poor.

16 D 0.100 Good.

Example No. Additives Amount (g./l.) Results 18 A 0. Poor.

19 A 0. 100 Good.

21 0. 100 Poor.

22 A 0. 100 Good.

C 0. 004 A" 3. 2 B 3. 2

F 0. 002 A 3. 2 B 3. 2

25 A 0. 100 Poor.

26 A 0. 100 Good.

F 0. 002 A 3. 2 C 2. 0

28 D 0. 100 Do.

In Examples 29-35 the following standard high chloride bath was used as a standard solution:

G./l. NiSO 7H O 225 NiCl 6H O 225 Boric acid 45 Example No. Additives Amount (g./l.) Results 29 A 0. 100 Poor.

30 A 0.100 Good.

31 D 0. 050 Do.

32 A 0.100 Do.

0. 002 A" 3. 2 Bl! I 2. 0

In Examples 36-42 the following standard sulfamate bath was used as a standard solution:

In Examples 43-47 the following nickel-cobalt bath was used as a standard solution:

NiSO -7H O g./l 300 CoSO '7H O g /l 80 NiCI 6H O g /l 60 H BO g./l 45 pH electrometric 3.8 Temperature C 60 Percent by weight cobalt in deposit 50 Example No. Additives Amount (g./l.) Results 43 A 0.100 Poor.

44 A 0.100 Good.

45 D 0.100 Do.

F 0.002 A 3.2 B" 2. 0

Examples 48 and 49 illustrate the preparation of the novel compounds of this invention.

EXAMPLE 48 Preparation of monocyanoethyl cysteine A solution of 17. 6-grams of cysteine monohydrochloride in one hundred milliliters of water was mixed with a solution of 9.0 grams (C.'P.) of sodium hydroxide pellets in 25 milliliters of water (at a pH of 11) and stirred magnetically. The volume of the resulting mixture was adjusted to 200 milliliters by the addition of water.

To a first 100 milliliter aliquot of the foregoing mixture, 2.7 grams of acrylonitrile at C. was added dropwise. The mixture was stirred for two hours at room temperature.

The resulting precipitate was filtered and dried to yield a product of 8.75 grams of monocyanoethylated cysteine.

EXAMPLE 49 Preparation of dicyanoethyl cysteine To the second 100 milliliter aliquot prepared in Example 48, 5.5 grams of acrylonitrile at 10 C. were added in drop-sized increments over a 25 minute time interval; the temperature was increased to 15 C. and the reaction mixture stirred at room temperature three hours after which said reaction mixture was acidified to a pH of 2 10 with concentrated hydrochloric acid. A colorless precipitate was obtained. The precipitate was filtered and dried. A yield of 6.8 grams of dicyanoethyl cysteine (60%) exhibiting a melting point of 212 C. to 214 C. was observed (Fisher-Johns apparatus).

Although this invention has been illustrated by reference to specific embodiments, modifications thereof which are clearly within the scope of the invention will be apparent to those skilled-in-the-art.

What is claimed is:

1. The process for electroplating bright nickel which comprises electrodepositing nickel from an aqueous acidic nickel electroplating bath containing (a) as a first primary brightener 0.002 gram per liter to 0.5 gram per liter of a water-soluble acetylenic compound, having no terminal unsaturation (b) 1 gram per liter to grams per liter of at least one sulfo-oxygen secondary brightener selected from the group consisting of aromatic sulfonates, sulfonamides, sulfimides and derivatives thereof, and (c) as a second cooperating primary brightener 0.0005 grams per liter to 0.05 grams per liter of:

(i) A 5-membered ring heterocyclic compound having at least two nitrogen atoms in an otherwise carbocyclic structure wherein at least one nitrogen atom bears at least one cyanoethyl group and wherein said compound contains at least one sulfur atom; or

-(ii) A compound having the formula wherein X is selected from the group consisting of H, 'NH and HfiI-CHzCHzCN; and Y is CN or and salts thereof.

2. The process for electroplating bright nickel as claimed in claim 1 wherein said first primary brightener is 2-butyne-1,4-diol.

3. The process for electroplating bright nickel as claimed in claim 1 wherein said first primary brightener is 1,4-di-(p-hydroxyethoxy)-2-butyne.

4. The process for electroplating bright nickel as claimed in claim 1 wherein said first primary brightener is phenyl-propiolamide.

5. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is monocyanoethylated Z-thiohydantoin.

6. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is dycyanoethylated 2-thiohydantoin.

7. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is tricyanoethylated-Z-thiohydantoin.

8. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is monocyanoethylated cysteine.

9. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is dicyanoethylated ethylene thiourea.

10. The process for electroplating bright nickel as claimed in claim 1 wherein said second cooperating primary brightener is B,B'-thiodipropionitrile.

11. The process for electroplating bright nickel which comprises electroplating nickel from an aqueous nickel electroplating bath containing as a first primary brightener 0.002 gram per liter to 0.5 gram per liter of Z-butyne- 1,4-diol, 1.0 gram per liter to 80 grams per liter of a secondary brightener selected from the group consisting of at least one member of the group consisting of aromatic sulfonates, sulfonamides, sulfimides and derivatives thereof, and as a second cooperating primary brightener 0.0005 gram per liter to 0.05 gram per liter tricyanoethylated-Z-thiohydantoin.

12. An aqueous electrolytic bath for electroplating bright nickel containing (a) as a first primary brightener 0.002 gram per liter to 0.5 gram per liter of a water-soluble acetylenic compound, having no terminal unsaturation (b) 1 gram per liter to 80 grams per liter of at least one sulfooxygen secondary brightener selected from the group consisting of aromatic sulfonates, sulfonamides, sulfimides and derivatives thereof, and (c) as a second cooperating primary brightener 0.0005 gram per liter to 0.05 gram per liter of:

(ii) A compound having the formula wherein X is selected from the group consisting of H, -NH and HlL-CHzOHzCN and Y is CN or and salts thereof.

13. The electroplating bath of claim 12 wherein said water-soluble acetylenic compound is 2-butyne-l,4diol.

14. The electroplating bath of claim 12 wherein said water soluble acetylenic compound is 1,4-di-(fl-hydroxyethoxy -2-butyne.

15. The electroplating bath of claim 12 wherein said water-soluble acetylenic compound is phenylpropiolamide.

16. The electroplating bath of claim 12 wherein said second cooperating primary brightener is monocyanoethylated 2-thiohydantoin.

17. The electroplating bath of claim 12 wherein said second cooperating primary brightener is dicyanoethylated Z-thiohydantoin.

18. The electroplating bath of claim 12 wherein said second cooperating primary brightener is tricyanoethylated Z-thiohydantoin.

19. The electroplating bath of claim 12 wherein said second cooperating primary brightener is monocyanoethylated cysteine.

20. The electroplating bath of claim 12 wherein said second cooperating primary brightener is dicyanoethylated ethylene thiourea.

21. The electroplating bath of claim 12 wherein said second cooperating primary brightener is fi,fi'-thiodipropionitrile.

References Cited UNITED STATES PATENTS 2,712,522 7/1955 Kardos et a1. 204-49 2,978,391 4/1961 DuRose 204-49 3,341,433 9/1967 Passal 204-49 3,528,694 9/1970 Stoddard et a1. 204-49 X 3,630,857 12/1971 DuRose et a1. 204-49 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 260-465 .4