US3871974A

US3871974A - Alkaline bright zinc plating

Info

Publication number: US3871974A
Application number: US400240A
Authority: US
Inventors: Joseph R Duchene; Phillip J Dechristopher
Original assignee: Richardson Chemical Co
Current assignee: Richardson Chemical Co
Priority date: 1973-09-24
Filing date: 1973-09-24
Publication date: 1975-03-18
Anticipated expiration: 1992-03-18
Also published as: GB1433716A; FR2244838B1; FR2244838A1; DE2445360A1

Abstract

Non-cyanide, alkaline electroplating baths for bright zinc plating containing quarternized polymeric condensates of alkylene polyamines and epihalohydrins in admixture with alkdehyde type brightners and mercapto substituted heterocyclic compounds capable of producing bright deposits over a broad current density range.

Description

finite States atent Duchene et al.

Mar. 18, 1975 ALKALINE BRIGHT ZINC PLATING Inventors: Joseph R. Duchene, Southfield,

Mich.; Phillip J. DeChristopher, Chicago, Ill.

The Richardson Chemical Company, Des Plaines, lll.

Filed: Sept. 24, 1973 Appl. No.: 400,240

Assignee:

US. Cl 204/55 R Int. Cl. C23b 5/10, C23b 5/46 Field of Search 204/55 R, 55 Y, 43 Z, 44

References Cited UNITED STATES PATENTS 6/1972 Senge et al 204/55 R FOREIGN PATENTS OR APPLICATIONS 307,115 8/l97l U.S.S.R 204/55 R Primary Examiner-G. L. Kaplan Attorney, Agent, or Firm-Alan M. Abrams [57] ABSTRACT 27 Claims, No Drawings ALKALINE BRIGHT ZINC PLATING This invention relates to zinc electroplating and more particularly to alkaline bright zinc electroplating conducted in an aqueous bath free from cyanides.

Zinc electroplating has conventionally been conducted in a plating bath employing alkali metal cyanide salts such as sodium cyanide as a complexing agent to achieve the desired plating operation and to produce bright zinc deposits. However, because of the toxicity of cyanides and more recently because of the environmental considerations adversely affecting the economic employment of these cyanides other plating methods have been sought which avoid and do not require the use of these cyanide salts.

A wide variety of procedures and additives have been suggested for use in zinc plating for the purpose of avoiding cyanides. Most of these employ an alkaline plating bath system utilizing an alkali metal or sodium zincate combined with certain additives to achieve the desired bright zinc deposit. Foremost of these various additives which have been suggested and employed in these highly alkaline bath systems are materials generally classified as polyamines, and especially the relatively simple polyamines such as alkylene diamines, for example ethylenediamine, which reportedly serve as complexing agent replacements for the cyanide salts. These polyamines are usually employed with a variety of other additives conventionally employed in zinc plating, for example grain refiners, brighteners and throwing agents.

While these alkaline systems employing the polyamine type additives do avoid the use of substantial amounts of cyanides, they generally have not been overly successful, however, and the zinc plating deposits typically produced have a number of deficiencies such as a dull or granular finish which render them of little commercial value. Such systems, moreover, typi cally also lack the desired capability of producing a suitable plating deposit over a broad current density range and generally are especially ineffective at the lower current density ranges conventionally used in commercial plating. ln addition, a substantial number of these systems for effective operation still require the presence of some cyanide, although at a reduced concentration, which in effect only minimizes but does not eliminate the problems associated with the use of cyanide salts.

Various other alkaline bath systems have been suggested which also utilize polyamines although generally of more complex nature, and usually in polymeric form and/or interacted with other compounds such as aldehydes and heterocyclic compounds. One of these systems, which has achieved some degree of success, involves the use ofa reaction product or a polymeric condensate of an alkylene polyamine and an epihalohydrin. While this particular polymeric condensate, particularly as a quarternary salt produces smooth, fine grained deposits, such deposits are generally dull or only semi-bright and do not have the degree of brightness or luster desired for most commercial applications.

The deficiency of this system can be corrected and the brightness of the plating deposit substantially improved through the use of conventional zinc brighteners and particularly those ofthe aldehyde type. This improvement, however, usually occurs only when plating at relatively high current densities with the plating deposits produced at low current densities within the range of from 0 to 20 to 40 amperes per square foot remaining dull or semi-bright. This limitation or inability to achieve desirable plating over a broad current density range substantially restricts the usefulness of this system and limits its application to plating objects which are relatively uniform in shape and configuration and precludes its use in plating objects which are irregular or in barrel plating where the plating must be conducted over a broad current density range.

It has now been discovered, however, that this type of plating system can be improved so as to achieve a bright, mirror like deposit over a broad current density range and more significantly even at low current densities by incorporating into such plating bath system certain mercapto substitutednitrogen heterocyclic compounds which render the system of considerable value and utility'in the electroplating of'zinc and capable of operating completely free of cyanides.

Accordingly, an objective of this invention is to provide an alkaline, bright zinc plating bath which does not require or utilize cyanide salts. Another object is to provide such a bath employing a quarternized polymeric condensate of an alkylene polyamine and a hydrin compound in combination with brightening agents which produces a bright, mirror like deposit. A further object is to provide such a bath with the addition ofcertain mercapto substituted heterocyclic compounds capable of producing the bright zinc deposit over a broad current density range. Still another object is to provide a method of zinc electroplating employing such improved bath and capable of effectively operating in a commercially desirable manner completely free of any cyanides. These and objects of this invention will be apparent from the following further detailed description thereof.

The electroplating of zinc in an aqueous alkaline bath in the presence of a polymeric condensate of an alkylene polyamine and a epihalohydrin together with a zinc brightener is effected in accordance with this invention by adding a mercapto substituted nitrogen containing heterocyclic compound to such bath so as to achieve a bright deposit over a broad current density range. This mercapto substituted heterocyclic compound may generally be described as an ortho mercapto substituted pyridine or pyrimidine, that is where the mercapto substituent is positioned on the 2 ring carbon atom. These mercapto substituted pyridines or pyrimidines have the following general formula:

or the tautomers thereof X is selected from the group consisting of N and CR wherein R is selected from the group consisting of hydrogen, hydroxy, mercapto and acyl and wherein R R and R are each independently selected from the group consisting of hydrogen, hydroxy, mercapto, acyl, amino, alkyl, carboxy and carbamoyl.

Examples of mercapto substituted heterocyclic compounds which may be employed either individually or in admixture according to this invention includes pyridines, that is where X of the formula is CR and pyrimidines, that is, where the X is nitrogen. These compounds may be substituted as indicated in the formula and where any of the various R substituents is alkyl or acyl such substituents can contain from one to about five and more preferably from one to three carbon atoms such as methyl, ethyl or propyl, or where acyl such groups as formyl, acetyl or propionyl. Typical examples of these compounds include pyridines such as Z-mercaptopyridine;

2-mercapto-3-acetylpyridine; 2,3-dimercaptopyridine; 2,3-dimercapto-6acetylpyridine; Z-mercapto-3-hydroxypyridine; 2-mercapto-4-hydroxypyridine, 2,4-dimercaptopyridine; 2-mercapto-4,6-dihydroxypyridine; 2-mercapto-4-aminopryidine; 2,6-dimercapto-3-acetylpyridine; 2-mercapto-5-methylpyridine; 2-mercapto5-aminopyridine; 2-mercapto-5-hydroxypyridine; 2-mercapto-6-hydroxypyridine; 2-mercapto-5-carbamoylpyridine; 2,6-dimercapto-3-carboxypyridine; or 2-mercapto-5,6-diethylpyridine; and

pyrimidines such as Z-mercaptopyrimidine; 2,6-dimercaptopyrimidine; Z-mercapto4-aminopyrimidine; 2-mercapto-4,6-dihydroxypyrimidine; 2-mercapto-4-ethylpyrimidine; 2-mercapto-4-hydroxy-6-methylpyrimidine; 2-mercapto-6-acetylpyrimidine; 2-mercapto-4-hydroxy-5,6-diethylpyrimidine; 2,4-dimercaptopyrimidine; or Z-mercapto-6-hydroxypyrimidine.

As indicated, the mercapto pyridines or pyrimidines represented by the above formula may also in many instances exist in tautomeric or isomeric form. For example one of the preferred compounds according to this invention is Z-thiouracil and such compound can exist as Z-mercapto-4-hydroxypyrimidine or 2-thio-4- oxopyrimidine or as an intermediate tautomer as 2-thioxo-4-hydroxypyrimldine and 2,4-dithiouracil can exist as 2,4-dimercaptopyrimidine or 2,4- dithiopyrimidine. All of these tautomeric compounds are accordingly embraced within the compounds which may be used in accordance with this invention as represented by the above formula.

Of the various compounds which may be employed according to the invention the preferred compounds are pyridines or pyrimidines of the formula where the mercapto group is substituted in the 2 ring position and generally also with a hydroxy group in one of the 4 or 6 position. Within this preferred class of compounds the pyrimidines are especially preferred and an example of one of these compounds having particular utility in the bath ofthe invention is 2-thiouracil or Z-mercapto-4,6-dihydroxy pyrimidine.

As indicated the mercapto heterocyclic compounds of the above formula are used in accordance with this invention to improve alkaline plating baths which employ polymeric condensates of alkylene polyamines and epihalohydrin compounds. In general these polymeric condensates are produced by reacting the alkylene polyamine and epihalohydrin compound in a condensation reaction to produce a substantially uncrosslinked, aqueous soluble polymeric condensate. ln accordance with this invention the polymeric condensate is employed as a quarternary salt which involves a further reaction of the polymeric condensate with a suitable quarternizing agent. In general, these polymeric condensates and their quarternary salts may be prepared in accordance with the procedures described i US. Pat. No. 3,642,663.

The epihalohydrin compounds which may be interracted with the alkylene polyamines include epibromohydrin or epichlorohydrin with the epichlorohydrin being particularly preferred in most instances.

The alkylene polyamines which may be reacted with the epihalohydrin have at least one tertiary amino group such as dimethylaminopropylamine (N,N- dimethylpropylenediamine), diethylaminopropylamine (N,N-diethylpropylenediamine), N-aminopropylmorpholine, dimethylaminoethylamine, diethylaminoethylamine, N-aminopropyldiethanolamine, or N- methyliminobispropylamine.

Other alkylene polyamines containing at least one tertiary amino group and at least one secondary amino group may also be employed such as N,N-dimethyl-N- methylpropylenediamine; N,N-dimethyl-N-methyl ethylenediamine; or N,N-diethyl-N-ethylethylenediamine.

Of the various alkylene polyamines which may be condensed with the epihalohydrin either alone or in admixture, the lower alkylene polyamines where the alkylene bridge contains from two to five carbon atoms and where the tertiary amino group is substituted with alkyl groups of from one to about five carbon atoms are preferred particularly when the epihalohydrin is epichlorohydrin with a particularly preferred alkylene polyamine being dimethylaminopropylamine.

In preparing the desired polymeric condensates for use in accordance with this invention, the alkylene polyamine should be condensed with the epihalohydrin compound in a mol ratio of from about 0.5 to 1.75 mols of the amine per 1 mol of the epihalohydrin. Usually a more limited range is preferred, however, and when employing the preferred epichlorohydrin the mol ratio of the polyamine to epichlorohydrin advantageous ranges from about 0.8 to about 1.5 mols of polyamine to 1 mol of epichlorohydrin, that is the mol ratio of the polyamine to the epichlorohydrin ranges from about 0.8:1 to about 1.511, respectively.

As indicated the polymeric condensates employed in accordance with this invention in combination with the mercapto heterocyclic compound and brightener is utilized as a quarternary salt. Suitable quarternizedagents for the polymeric condensates are the lower alkyl halides such as methyl-chloride, -bromide,' or -iodide, ethyl-chloride, -bromideor alpha chloroglycerol, diloweralkyl sulfates such as dimethyl, -diethyl, -dipropyl, or -dibutyl-sulfates; lower alkyl esters of aryl sulfonates such as methyl toluene sulfonate and methyl benzene sulfonate; alkyhalo esters such as ethyl-chloroacetate; alkylene halohydrins such as ethylenechlorohydrin or alkylene oxides such as ethylene oxide and propylene oxide.

The zinc electroplating bath of this invention contains the polymeric condensate in admixture with brightening agents. While these brightening agents as previously discussed improve the luster or brightness of the zinc plating they have a tendency to increase the luster only at the higher current density ranges generally above about 40 or more usually above about 20 amperes per square foot up to about 200 amperes per square foot and do not without the additional presence of the mercapto substituted compounds of this invention produce a bright deposit throughout the entire current density range and particularly at the lower current density ranges conventionally employed in most commercial operations and generally below about 40 or more usually below about 20 down to O amperes per square foot.

These brighteners include those materials conventionally employed in zinc plating and typically contain a carbonyl group of aldehyde functionality which generally may be represented by the formula wherein R and R are independently selected from the group consisting of hydrogen, alkyl, generally containing from one to about carbon atoms, aryl and heterocyclic oxygen and sulfur containing radicals and include, for example, m-hydroxy benzaldehyde, phydroxy benzaldehyde, piperonal, o-hydroxy benzaldehyde, (salicylaldehyde), veratraldehyde, benzaldehyde, B-methoxy propionaldehyde, furfural, glyceraldehyde, anisaldehyde, vanillin, thiophene-2-aldehyde.

Of the various aldehyde materials which may be employed the aryl aldehydes and particularly the benzaldehydes such as anisic aldehyde (pmethoxybenzaldehyde) or vanillin (p-hydroxy-mmethoxybenzaldehyde) or various combinations thereof are preferred. These aldehydes brighteners may be employed in the bath of this invention as addition products with such materials as sodium bis'ulfite to increase their alkaline solubility if desired.

The electroplating bath of this invention may be prepared and operated in accordance with the general procedures conventionally employed for alkaline bright zinc plating. Typically the bath is prepared as an aqueous solution and rendered alkaline by the addition of a suitable alkaline material such an alkali metal hydroxide or carbonate for example sodium or potassium hydroxide. The quantity of alkaline material added should be capable of dissolving the zinc compound employed as the source of the zinc ion in the bath and generally should be in excess of that required to create the desired alkali metal zincate such as sodium zincate as well as to maintain the pH of the solution alkaline and generally above 7 and preferably above l4.

The source of the zinc ion in the bath can be varied and generally any of the zinc compounds conventionally employed in alkaline bright zinc baths may be utilized. Typically such compounds include zinc salts or oxides such as zinc sulfate, zinc acetate or zinc oxide with the zinc sulfate generally being preferred. The amount of zinc in the bath can be varied depending upon the desired results and operating condition but generally is maintained within the range of from about 3 to about grams per liter.

The quantity of the quarternized polymeric condensate utilized in the bath will in general be a function of the particular brightener and mercapto substituted compound employed as well as the particular polymeric condensate utilized. Typically, however, when employing polymeric condensates of such alkylene polyamines as dimethylaminopropylamine and epichlorohydrin, the quantity of the condensate in the bath should range from about 0.25 to about 5 grams per liter with a more limited range of from about 0.3 to about 0.75 grams per liter being preferred especially when used in combination with such mercapto compounds as Z-thiouracil.

The quantity of the mercapto substituted compound employed in the bath in similar fashion is also interrelated to the specific polymeric condensate and aldehyde brightener employed as well as the particular mercapto substituted compound or combination of compounds utilized. Generally, however, the mercapto compound is maintained in the bath within the range of from about 0.01 to about 0.2 grams per liter with a more limited range being preferred of from about 0.025 to about 0.075 grams per liter particularly when employing the preferred mercapto compounds such as 2-thiouracil or 2-mercapto-2,4-dihydroxy pyrimidine.

The brighten'ers used in combination with the quarternized polymeric condensate typically will be present in the bath within the ranges conventionally utilized for alkaline zinc plating baths. Typically this will range from about 0.1 to about 5 grams per liter with a more limited range from about 0.2 to about 0.5 grams per liter being more advantageously employed particularly when employing the preferred benzaldehyde type brighteners.

The electroplating of zinc conducted in accordance with the method of this invention is effected in conventional fashion basically by passing a direct current from a zinc anode through the aqueous alkaline, noncyanide bath of this invention containing essentially the polymeric condensate, brightener and mercapto substi tuted compound to the desired cathode article which is to be electroplated with the zinc. This method may be conducted at temperatures from about 60 to about 100 F. The current densities employed may range from above 0 to about 200 amperes per square foot with a more limited range of from about 0.5 to about amperes per square foot being satisfactory for most plating operations.

The plating bath of this invention may contain further additives of the type conventionally employed in alkaline zinc electroplating baths and include such materials as polyvinyl alcohols, gelatine, polyether alcohols, polyesters, glue and peptone. Of these various materials polyvinyl alcohol or its various derivatives are especially preferred and appear to greatly enhance the mirror like deposits of the platings produced in accordance with this invention. When so employed these polyvinyl alcohols should be utilized in the bath within a range offrom about 0.02 to about 0.2 grams per liter.

The following examples are offered to illustrate the plating bath and electroplating methods of this inventron.

EXAMPLE I Quarternized polymeric condensates of the type employable in the electroplating bath of this invention may be prepared as follows:

A. In a 2-liter, three-necked flask equipped with a stirrer, thermometer, and dropping funnel were placed 452 grams of dimethylaminopropylamine in 820 ml. of water. The solution was cooled to 25 C. with a surrounding water bath, and 368 grams of epichlorohydrin (0.921 mol ratio of epichlorohydrin to dimethylaminopropylamine) was added over a period of 1 hour. The mixture was then stirred for an additional 30 minutes and placed in an autoclave with grams of sodium hydroxide pellets. The autoclave was closed and the mixture stirred and heated to 50 C. Then 300 grams of methyl chloride were charged into the autoclave at 40-50 p.s.i. After the desired amount of methyl chloride was charged, the autoclave was cooled and discharged. The reaction solution is adjusted to a pH of approximately 6-7 with dilute sulfuric acid and the quarternized product thus prepared is recovered.

B. In a 3-liter, three necked flask equipped with a stirrer, thermometer and dropping funnel were placed 306 grams of dimethylaminopropylamine in 3,000 ml. of water. The solution was cooled to 20 C with a surrounding water bath; and 333 grams of epichlorohydrin (1.211 mol ratio of epichlorohydrin to dimethylaminopropylamine) were added over a period of 2 hours. The mixture was then stirred for an additional 30 minutes at a temperature below 25 C followed by stirring at room temperature for V2 hour. The mixture was neutralized to a pH of about 6-7 by using dilute sulfuric acid.

Dimethylsulfate, 378 grams, were added to the mixture while maintaining the pH at 8-9 with N potassium hydroxide in water, and the mixture thereafter heated at reflux for 5 hours and the quarternized polymeric condensate product thereafter recovered in solution.

C. In a 2-liter, three-necked flask equipped with a stirrer, thermometer, and dropping funnel were placed 452 grams of dimethylaminopropylamine in 850 ml. of water. The solution was cooled to 20 to 30 C and 368 grams ofepichlorohydrin (0.9:1 mol ratio of epichlorohydrin to dimethylaminopropylamine) were added over a period of 2 hours. The mixture was then stirred for an additional 30 minutes and placed in a Parr pressure vessel with 100 grams of sodium hydroxide pellets. The bottle was closed and the mixture stirred and heated to 90-95 C. Then 280 grams of methyl chloride was charged to the bottle under a pressure of 40-60 p.s.i. After the desired amount of methyl chloride was metered into the vessel over a period of 3 hours, the vessel was cooled and discharged. The reaction solution was adjusted to a pH of approximately 6-7 with dilute sulfuric acid and about 1,200 grams of the quarternized product were thereafter recovered in solution.

EXAMPLE 11 A series of zinc electroplating tests were conducted in various aqueous alkaline noncyanide, electroplating baths to zinc plate Hull test panels. The plating was carried out in a standard Hull cell (267 ml) with the Hull cell panel in each test run connected as the cathode in the bath. The plating was conducted at an operating current of 1 ampere representing a current density range on the test panel varying from a high range of from about 40 to about 60 amperes per square foot (a.s.f.) to a low range of from about 0.1 to about 0.5 (a.s.f.). The plating time was minutes with the bath operated at a temperature of about 75 F.

1n each of the tests, a bath was prepared and the various components admixed and employed to plate the test samples. The components of the various plating baths are summarized in Table l with the results summarized in Table 11.

TABLE 1 Test Component Concentrations Run in Grams/Liter B C D E F G COMPONENTS A zinc metal as zinc sulfate B sodium hydroxide C polymeric condensate (1) (weight of 50% active solution) D anisic aldehyde adduct with sodium bisulfite E Z-thiouracil F polyvinyl alcohol G p-hydroxy benzaldehyde (l) condensate product of 0.9 mols epichlorohydrin and 1.0 mol dimethyluminopropylaminc quarternized with mcthylchloride.

TABLE ll TEST RUN PLATING RESULTS 1 Grain refined, dull to semi-bright 2 Grain refined, bright but particularly dull at lower current density range 3 Grain refined, bright over entire current density range but lacks luster at lower current density range 4 Grain refined, bright with luster over entire current density ranges 5 Same as test 2 6 Same as test 2 7 Grain refined, slightly brighter but generally the same as test 2 8 Same as test 1 9 Grain refined, semi-bright but particularly dull at lower current density range Grain refined, semi-bright over entire current density range but lacks luster at lower current density range.

Grain refined. slightly brighter at lower current density range but generally the same as test 10 Same as 7 but slightly brighter Same as test 4 The plating tests as summarized in Table II illustrate that the addition of the mercapto substituted compounds in accordance with the procedure of this invention improves the plating ability of the bath containing the polymeric condensate and the aldehyde brightener. Compare for example Test 1 where the deposit produced, while grain refined, has a dull to semi-bright finish. In Test 2 the brightness is improved by the addition of the aldehyde brightener. The brightness at the lower current density range within the range of about 1 to about 8 a.s.f. still remains dull. In test 3 however, upon the addition of the 2-thiouracil, the brightness in the lower current density range is improved so that the deposit has a desirable bright finish over the entire current density range.

EXAMPLE III A series of aqueous alkaline, non-cyanide zinc electroplating baths were prepared to zinc plate Hull test panels. The plating was conducted in a standard Hull cell (267 ml) with the Hull cell panel in each test connected as the cathode of the bath. The plating was conducted at an operating current of l ampere representing a current density range on the test panel varying from a high range of from about 40 to about 60 amperes per square foot (a.s.f.) and a low range of from about 0.2 to about 0.5 (a.s.f.). The plating time was minutes with the bath being maintained at a temperature of about 75 F. The bath in each run had the components and concentrations as shown in Table III.

In each test, a different mercapto substituted compound was employed and the particular compound tested is identified in Table IV. Also for each test, a

"blank bath was used without the mercapto substituted compound to compare the plating deposit produced with and Without the mercapto substituted compound.

In each test run it was observed that the dull plating deposit at the low current density range on the Hull test panel which occurred without the presence of mercapto substituted compound was eliminated when the mercapto substituted compound was added with the result that the deposit in each instance was bright over the entire current density range.

TABLE IV MERCAPTO SU BSTITUTED TEST RUN COMPOUNDS EMPLOYED Z-mercaptopyrimidine 2mercapto-4-amino-(v-hydroxypyrimidin lA-dithioxopyrimidine (dithiouracil) 2-mereapto-3-hytlroxypyridine 5-carboxy-Z-mercaptopyridinc ((i-rnercapto nicotinic acid) We claim:

1. A bright zinc, cyanide free electroplating bath' comprising an aqueous alkaline solution containing a source of zinc ions, from about 0.1 to about 5 grams per liter of a brightener containing a carbonyl group of aldehyde functionality, from about 0.01 to about 0.2 grams per liter of a heterocyclic compound selected from the group consisting of a 2-mercapto substituted pyridine or pyrimidine and from about 0.25 to about 5 grams per liter of a quarternary salt of a polymeric condensate of an alkylene polyamine having at least one tertiary amino group and an epihalohydrin wherein the mol ratio of the polyamine to the epihalohydrin ranges from about 0.521 to 1.75:1, respectively.

2. The electroplating bath of claim 1 wherein the heterocyclic compound has the formula or tautomers thereof wherein X is selected from the group consisting of N and CR where R, is selected from the group consisting of hydrogen, hydroxy, mercapto and acyl; R R and R are each independently selected from the group consisting of hydrogen, hydroxy, mercapto, acyl, amino, alkyl. carboxy and carbamoyl.

3. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-thiouracil.

4. The electroplating bath of claim 2 wherein the heterocyclic compound is Z-mercaptopyrimidine.

5. The electroplating bath of claim 2 wherein the heterocyclic compound is 2,4-dimercaptopyrimidine.

6. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-mercapto-4-amino-6- hydroxypyrimidine.

7. The electroplating bath of claim 2 wherein the heterocyclic compound is 5-carboxy-2-mercaptopyridine.

8. The electroplating bath of claim 2 wherein the heterocyclic compound is 3-hydroxy-2-mercaptopyridine.

9. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-mercapto-4,6- dihydroxypyrimidine.

10. The electroplating bath of claim 1 wherein the brightener is an aldehyde having the formula wherein R, and R are independently selected from the group consisting of hydrogen, alkyl, aryl and heterocyclic oxygen and sulfur containing radicals.

11. The electroplating bath of claim 10 wherein the aldehyde brightener is a benzaldehyde.

12. The electroplating bath of claim 10 wherein the aldehyde is vanillin.

13. The electroplating bath of claim 10 wherein the aldehyde is anisic aldehyde.

14. The electroplating bath of claim 10 wherein the aldehyde is p-hydroxy benzaldehyde.

15. The electroplating bath of claim 1 wherein in the polymeric condensate the alkylene polyamine is dimethylaminopropylamine and the epihalohydrin is enichlorohydrin and the mol ratio of the polyamine to the epichlorohydrin ranges from about 0.811 to about 1.511, respectively and the condensate is substantially uncrosslinked.

16. The electroplating bath of claim 15 wherein the heterocyclic compound is 2'thiouracil, the aldehyde is a mixture of anisic aldehyde and vanillin.

17. The electroplating bath of claim 15 wherein the heterocyclic compound is 2-mercapto-4,6-dihydroxypyrimidine, the brightener is an aldehyde of a mixture of anisic aldehyde and vanillin.

18. The electroplating bath of claim 1 wherein the source of the zinc ions is a water soluble zinc salt.

19. The electroplating bath of claim 18 wherein the zinc salt is zinc sulfate.

20. The electroplating bath ofclaim I wherein in the polymeric condensate the epihalohydrin is epichlorohydrin.

21. The electroplating bath ofclaim I wherein in the polymeric condensate the alkylene polyamine has a tertiary amino group substituted with alkyl groups offrom one to live carbon atoms and the alkylene bridge contains from two to about five carbon atoms.

25. The electroplating bath of claim 1 wherein the pH is above 14.

26. In a process for the electroplating of zinc the improvements comprising effecting the electroplating with the alkaline bath of claim 1 free from any cyanide.

27. The process of claim 26 wherein the plating is conducted at a temperature of from about 60 to about F and at a current density up to about 200 amperes per square foot.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 871 97 -1 Dated March 18 1975 Inventor(s) Joseph R. Duchene and Phillip J. DeChristopher It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 53 add "or -iodide" after "br'omide" Column 5, line 10 "an should be changed to "as" Column 9, line 40 "hydroxypyrimidin" should be changed to "hydroxypyrimidine" Signed and Scaled this A Nest:

RUTH C. MASON C. MARSHALL DANN l-l Hosting ()jficcr (vnmlimzvium'r nflarcnlx and Trademarks

Claims

1. A BRIGHT ZINC, CYANIDE FREE ELECTROPLATING BATJ COMPRISING AN AQUEOUS ALKALINE SOLUTION CONTAINING A SOURCE OF ZINC IONS, FROM ABOUT 0.1 TO ABOUT 5 GRAMS PER LITER OF A BRIGHTENER CONTAINING A CARBONYL GROUP OF ALDEHYDE FUNCTIONALITY, FROM ABOUT 0.01 TO ABOUT 0.2 GRAMS PER LITER OF A HETEROCYCLIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF A 2-MERCAPTO SUBSTITUTED PYRIDINE OOR PYRIMIDINE AND FROM ABOUT 0.25 TO ABOUT 5 GRAMS PER LITER OF A QUARTERNARY SALT OF A POLYMERIC CONDENSATE OF AN ALKYLENE POLYAMINE HAVING AT LEAST ONE TERTIARY AMINO GROUP AND AN EPIHALOHYDRIN WHEREIN THE MOL RATIO OF THE POLYAMINE TO THE EPIHALOHYDRIN RANGES FROM ABOUT 0.5:1 TO 1.75:1 RESPECTIVELY.

2. The electroplating bath of claim 1 wherein the heterocyclic compound has the formula

4. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-mercaptopyrimidine.

6. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-mercapto-4-amino-6-hydroxypyrimidine.

9. The electroplating bath of claim 2 wherein the heterocyclic compound is 2-mercapto-4,6-dihydroxypyrimidine.

10. The electroplating bath of claim 1 wherein the brightener is an aldehyde having the formula

12. The electroplating bath of claim 10 wherein the aldehyde is vanillin.

15. The electroplating bath of claim 1 wherein in the polymeric condensate the alkylene polyamine is dimethylaminopropylamine and the epihalohydrin is enichlorohydrin and the mol ratio of the polyamine to the epichlorohydrin ranges from about 0.8:1 to about 1.5:1, respectively and the condensate is substantially uncrosslinked.

16. The electroplating bath of claim 15 wherein the heterocyclic compound is 2-thiouracil, the aldehyde is a mixture of anisic aldehyde and vanillin.

17. The electroplating bath of claim 15 wherein the heterocyclic compound is 2-mercapto-4,6-dihydroxy-pyrimidine, the brightener is an aldehyde of a mixture of anisic aldehyde and vanillin.

19. The electroplating bath of claim 18 wherein the zinc salt is zinc sulfate.

20. The electroplating bath of claim 1 wherein in the polymeric condensate the epihalohydrin is epichlorohydrin.

21. The electroplating bath of claim 1 wherein in the polymeric condensate the alkylene polyamine has a tertiary amino group substituted with alkyl groups of from one to five carbon atoms and the alkylene bridge contains from two to about five carbon atoms.

22. The electroplating bath of claim 1 wherein in the polymeric condensate the alkylene polyamine is dimethylaminopropylamine.

23. The electroplating bath of claim 1 wherein the polymeric condensate and heterocyclic compound are present in the bath with the ranges of from about 0.3 to about 0.75 and from about 0.025 to about 0.075 grams per liter, respectively.

24. The electroplating bath of claim 1 wherein the bath contains polyvinyl alcohol within the range of from about 0.02 to about 0.2 grams per liter.

25. The electroplating bath of claim 1 wherein the pH is above 14.

27. The process of claim 26 wherein the plating is conducted at a temperature of from about 60* to about 100* F and at a current density up to about 200 amperes per square foot.