DE2445359A1 - CYANIDE-FREE, SHINY ZINC COATS CREATING GALVANIZATION BATH - Google Patents

Description

DR. MÜLLER-BORE DlPI.-ING. C-RU ¹ ENING D-P '-.- CHEM. DR. DEUFEL

DIPL.-CHEM. CR. SCHÖN DIPL.-7HYS. H ERTEL 24 A 535 9 PATENT LAWYERS

2 Sep 3 ! 974

D / S / Gl - R 1143

RICHARDSON CHEMICAL COMPAKT, Des Piaines, 111. / USA

Cyanide-free, shiny zinc coatings producing stage

The invention "relates to the electrodeposition of zinc and is particularly concerned with an alkaline electrodeposition of shiny zinc coatings, which in one an aqueous bath that is free of cyanides is carried out.

The galvanic zinc deposit is usually in one Electroplating bath carried out in which alkali metal cyanide salts, such as sodium cyanide, as a complexing · Medium can be used to perform the desired electroplating process and create zinc deposits that are shiny and are smooth-grained. As a result of the toxicity of the cyanides, which can pose significant environmental problems, one is up looking for other electroplating processes in which Implementation can be dispensed with the use of these cyanide salts.

A large number of processes and additives can be used to carry out

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tion of a galvanic zinc deposit with the purpose proposed been to avoid cyanides. When performing most of these procedures, an alkaline electroplating is used bad system used in which an alkali metal, v / ie sodium zincate, is used together with additives to the to produce the desired shiny zinc deposit with a smooth or fine-grained mirror-like surface. the Most of these various additives that have been used in highly alkaline bath systems are materials that can can generally be classified as polyamines, in particular the relatively simple polyamines, such as, for example Alkylenediamines, for example ethylenediamine, may be mentioned, which serve as a substitute for complexing agents for the cyanide salts. These polyamines are commonly used with a variety of other additives used, which are used in the usual way for zinc electroplating, "for example the grain-refining agent, Brighteners and finishing agents.

Alkaline systems in which polyamine additives are used work while avoiding the use of considerable amounts Amounts of cyanides, however, they have not proven successful. The galvanic zinc coatings produced using them suffer from a number of disadvantages, for example a matte or grainy surface, so these coatings are of little value. In addition, such Systems do not produce a smooth, mirror-like galvanic deposition within a wide current density range, where they are generally particularly ineffective in the lower current density ranges, which are usually the case with technical Electroplating are adhered to. It also requires a significant number of these systems to be effective Procedure still the presence of some cyanide, albeit in a reduced concentration, which although the problems

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which are associated with the use of cyanide salts, reduced in size, however, cannot be eliminated.

Various other alkaline bath systems have become known in which polyamines are also used, but which are of a more complex nature. Usually they are in polymeric form and / or after a reaction with other compounds, such as, for example, aldehydes and heterocyclic compounds are used, for example a reaction product or a polymeric condensate of an alkylene polyamine with an epihalohydrin in question. Some of these materials have been used with some success, in general However, they have disadvantages insofar as the deposits obtained do not have the desired gloss or do not have a smooth and fine-grained surface like them is required for most purposes. In addition, some of these systems are generally not capable of fine-grain mirror-like ones Generate deposits within a wide range of current densities, particularly within the range low current density between 0 and 20 and 40 A / 0.09 m. This inability to achieve a desired electrodeposition within Carrying out a wide range of current densities degrades the suitability of these systems and limits their application to Objects to be electroplated, which have a relatively uniform shape, so that the electroplating of objects irregularly shaped or galvanized in drums carried out within a wide range of current densities has to be omitted.

It has now been found that certain quaternized polymers Condensates of alkylene polyamines with 1,3-dihalo-2-propanols can be used in a cyanide-free zinc plating bath, typically also with Gloss formers, producing fine-grained glossy coatings

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will. It was also found that when such polymeric condensates are substituted with certain mercapto heterocyclic compounds are used, the desired glossy as well as mirror-like deposition within one wide current density range is achieved, this range also including the critical range with low current densities.

The object of the invention is to create an alkaline, galvanizing bath producing shiny zinc coatings, in which no cyanide salts are used. The invention provides a bath in which a quaternized polymeric condensate of an alleylenepolyamine and a 1,3-dihalo-2-propanol is used, which has a smooth and capable of producing fine-grained deposits. These polymeric condensates can be used with brighteners, which produce shiny as well as mirror-like deposits. Certain mercapto-substituted heterocyclic compounds can be added to the bath be added, which have a shiny and fine-grained zinc deposit within a wide range of current densities able to separate. The invention provides a method for galvanic zinc deposition when it is carried out a bath improved in this way is used, this process being carried out on an industrial scale can and does not require the use of any cyanides.

The galvanic zinc deposition in an aqueous alkaline bath is carried out according to the invention in such a way that a Quaternized polymeric condensate from an alkylene polyanine and a 1,3-dihalo-2-propanol are added to such a bath is, smooth as well as fine-grained deposits are obtained. In general, these polymeric condensates are in the way that the alkylenepolyamine as well as the dihalopropanol are produced converted into a condensation reaction,

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being an essentially non-crosslinked, soluble in water polymeric condensate is obtained. According to the invention, the polymeric condensate is used as a quaternary salt, which is another Reaction of the polymeric condensate with a suitable quaternizing agent conditional.

The dihalopropanols that reacted with the alkylene polyamines consist, for example, of 1,3-dibromo-2-propanol, 1,3-Diiodo-2-propanol or 1,3-dichloro-2-propanol, whereby the 1,3-dichloro-2-propanol is particularly preferred in most cases.

The alkylene polyamines that reacted with the dihalopropanol v / can have at least one tertiary amino group. Mentioned are for example dimethylaminopropylamine (N, N-dimethylpropylenediamine), Diethy lamin opr opy lamin (N, ΪΓ-Diethy! Propylenediamine), N-aminopropylmorpholine, dimethylaminoethylamine, diethy1-aminoethylamine, N-aminopropyl diethanolamine or N-methyliminobispropylamine.

Other alkylene polyamines which contain at least one tertiary amino group and at least one secondary amino group, can also be used, for example N, N-dimethyl-N'-me thy! propylenediamine, N, N-dimethy1-N'-methylethylenediamine or N, N-diethyl-N'-ethylethylenediamine.

Of the various alkylenepolyamines that are made with the dihalopropanol can be condensed either alone or in mixture, the lower alkylene polyamines, in which the Alkylene bridge contains 2 to 5 carbon atoms, the tertiary Amino group is substituted by alkyl groups having 1 to about 5 carbon atoms, then particularly preferred if the Dihalopropanol consists of 1,3-dichloro-2-propanol, with a particularly preferred alkylene polyamine from dimethylaminopropylamine consists.

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To prepare the polymeric condensates used according to the invention, the alleylene polyamine should be condensed with the dihalopropanol in a molar ratio of about 0.5 "to 1.75 mol of the amine per 1 mol of the dihalopropanol. However, a somewhat more limited range is usually used If the preferred 1,3-dichloro-2-propanol is used, the molar ratio of the polyamine to the -1,3-dichloro-2-propanol will advantageously vary between about 0.8 and about 1.5 moles of the polyamine per 1 mole of dichloropropanol.Usually, the condensation is carried out by customary methods over a period of about 1 to 3 hours, the temperature being kept between 15 and 40 ^° C.

As already mentioned, the polymeric condensate according to the invention is used to effect a grain refinement of the deposit, used as a quaternary salt. These Quaternization can be done by customary methods. Suitable Quaternizing agents for the polymeric condensates are the lower alkyl halides, such as methyl chloride, bromide or iodide, ethyl chloride, bromide or iodide, α-chloroglycerin, di-lower alkyl sulfates, such as, for example, Birnethy1-, Diethyl, dipropyl or dibutyl sulfates, lower alkyl esters of aryl sulfonates, such as methyl toluenesulfonate and methylbenzenesulf onate, alkyl halogen esters, such as ethyl chloroacetate, Alkylenhalogenhydriüe, such as ethylene chlorohydrin, or alkylene oxides, such as ethylene oxide or propylene oxide.

Generate the polymeric condensates used according to the invention a grain-refined or smooth deposit. Such a deposit usually does not have the gloss that is found in the is desired in most cases. Therefore, according to a preferred Embodiment of the invention brighteners together with the

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polymeric condensate used to be both smooth and shiny To produce coatings. These brighteners consist of materials that are commonly used for zinc electroplating be set. They typically contain a carbonyl group with aldehyde functionality and can be represented by the formula

C = O

are reproduced, wherein R ₁ and Rp are independent of one another. represent hydrogen, alkyl radicals having 1 to about 10 carbon atoms, aryl radicals and heterocyclic oxygen and sulfur-containing radicals. Examples include m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, piperonal, o-hydroxybenzaldehyde (salicylaldehyde), vanillin, veratraldehyde, benzaldehyde, ß-methoxypropionaldehyde, furfural, glyceraldehyde and anisaldehyde and thiophene-2-aldehyde *

Of the various aldehyde materials that can be used, the aryl aldehydes, especially the benzaldehydes, such as anisaldehyde (p-methoxybenzaldehyde) or vanillin (p-hydroxy-m-methoxybenzaldehyde), or various combinations of which preferred. These aldehyde brighteners can be used alongside other compounds in the bath according to the invention are, such as sodium bisulfite, to optionally to increase their alkali solubility.

In most cases, the use of these brighteners significantly improves the gloss of the deposit. This often occurs only in the areas of higher current density, which are generally above about 40 or mostly above about 20 A / 0.09 m ² (square foot) up to about 100 to 200 A / 0.09 m ² (square foot ) move. According to the invention, certain Hercapto

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substituted heterocyclic compounds, preferably in combination with the polymeric condensate and the brightener can be used to produce the glossy and fine-grained deposit within a wide range of current densities, in particular within low current density areas, such as those commonly found in most technical practice Electroplating are adhered to, these ranges generally below about 40 or usually between

2
about 20 down to 0 A / 0.09m.

These mercapto-substituted heterocyclic compounds, with the polymeric condensates according to the invention and Brighteners can be used can generally be used as o-mercapto-substituted pyridines or pyrimidines describe, i.e. compounds in which the mercapto substituent sits on the 2-ring carbon atom. These Merkapto-substituted ones Pyridines or pyrimidines can be represented by the following general formula (the Tautomers thereof in embossing):

/ ^N

Il

R ₂ - C5 3X

\ 4

R ₁ - C6 2C

where X is IT or 0-R, where R ^ is hydrogen, II;. ·· ir 3-xy, mercapto or aeyl, and R., R ₂ and R _{7 are} independent of one another Y / assTr toff Hydroxy, Mercapto, Acyl, Amino, A "ü: y"! , Carboxy or cailamoyl mean.

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Examples of mercapto-substituted heterocyclic compounds, either on their own, alone or in a mixture according to Can be used in the present invention are pyridines, in which case X in the formula is C-R, as well as Pyrimidines, i.e. compounds in which X in the formula is nitrogen. These compounds can, as in the formula is indicated, be substituted. Is one of the various R substituents Alkyl or acyl, then these substituents can have up to about 5 and preferably 1 to 3 carbon atoms contain, for example methyl, ethyl or propyl, while in the case of Acy! groups are, for example, formyl-r, Acetyl or propionyl groups can act. Typical examples of these compounds are pyridines such as

2-mercaptopyridine, 2-mercapto-3-acetylpyridine, 2-mercapto-3-hydroxypyridine, 2,3-dimerkaptopyridine, 2, J-dimerkapto-o-acetylpyridine, 2-mercapto-4-hydroxypyridine, 2,4-dimerkaptopyridine, 2-mercapto-4,5-dihydroxypyridine, 2-mercapto-4-aminopyridine, 2, e-Dimerkapto - ^ - acetylpyridine, 2-mercapto-5-methylpyridine, 2-Merkapto ~ 5-aminopyridine, 2-Merkapt0-5-hydroxypyridine, 2-mercapto-6-hydroxypyridine, 2-mercapto-6-carbamoylpyridine, 2,6-dimerkapto-3-carboxypyridine or 2-mercapto-5,6-diethylpyridine,

while from the pyrimidines

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2-mercaptopyrimidine,

2,6-dimercaptopyrimidine,

2-Mer leap to-4-arninopy rimidin,

2-Merkapto-4, β-dihydroxypyrimidine, 2-Merkapto-4 ~ äth.y lpyrimidiri,

2-mercapto-4-hydrozy-6-methylpyriinidine, 2 ~ Merkapto-6-ace ty lpyrimidiri,

2-mercapto-4-hydroxy-5 »6-diethylpyrimidine, 2,4-dimercaptopyrimidine s ov / ie

2-mercapto-6-hydroxypyrimidine

should be mentioned.

As already mentioned, the mercaptopyridines or pyrimidines indicated by the above formula can be used in many Cases exist in tautomeric or isomeric forms. For example one of the compounds preferred according to the invention consists of 2-thiouracil. Such a compound can be called 2-herkapto-4-hydroxypyriniidin or 2-thio-4-oxopyrimidine or as an intermediate tautomer as 2-thioxo-4-hydroxyprimidine, while the 2,4-dithiouracil as 2,4-dimerkaptopyrimidine or 2,4-dithiopyrimidine can occur. All of these tautomeric compounds are therefore included in the compounds which, according to the invention, represented by the formula given above can be used.

Of the various compounds used according to the invention can be, the preferred compounds consist of pyridines or pyrimidines of the formula given, where the mercapto group is substituted in the 2-ring division, where generally a hydroxy group in the 4- or 6-position sits. The pyrimidines are of the preferred class of compounds particularly preferred. Examples of compounds with particular utility in the bath according to the invention are 2-

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Thiouracil and 2-mercapto-4,6-dihydroxyprimidine.

The electroplating bath according to the invention can be according to the general Methods are produced and operated as they are in the usual way for the galvanic application of shiny zinc coatings from an alkaline medium. Typically, the bath is produced as an 'aqueous solution and through the Adding a suitable alkaline material made alkaline, such as by adding an alkali metal hydroxide or carbonate, for example sodium or potassium hydroxide. the The amount of alkaline material added should be sufficient for the zinc compound used as the source of zinc ions in the bath dissolve, which should generally be in excess of the amount required the desired alkali metal zincate, such as llatriuincate, to create. Furthermore, the amount should be sufficient to keep the pH of the solution alkaline, generally above 7 and preferably above 14.

The source of zinc ions in the bath can be made of various materials. They are generally zinc compounds, as they are used in the usual way in alkaline baths with the application of shiny zinc coatings. Typical for such compounds are zinc salts or oxides, for example zinc sulfate, zinc acetate or zinc oxide, the Zinc Sulphate: Generally preferred. The amount of zinc in the bath can vary depending on the results desired as well as the working conditions vary, but generally the amount of zinc is maintained between about 3 and about 15 grams per liter.

The amount of quaternized polymeric condensate present in the Bath being used up is generally a puncture of the j owe-ils used gloss former as well as the Merkapto-substi-

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tuierten compound and the polymeric condensate used in each case. Polymeric condensates of such alkylene polyamines are used, for example from dimethylaminopropylamine and 1,3-dichloro-2-propanol, then the amount of Condensate in the bath will vary between about 0.25 and about 5 grams per liter, with an even more limited range between about 0.3 and about 0.75 g per liter is particularly preferred when one of the preferred mercapto compounds is used.

The amount of the mercapto-substituted compound present in the Bath is used / ended in a similar way is related to the particular polymeric condensate used and the one used Aldehyde brighteners and the mercapto-s-uf-substituted compound or combination used in each case from connections. Generally, however, the mercapto compound in the bath will be within a range of from about 0.01 to about 0.2 grams per liter, with a narrower range between about 0.025 and about 0.075 grams per liter then It is particularly preferred if preferred mercapto compounds, such as 2-th.iouracil or 2-mercapto-4,6-dihydroxypyrimidine, can be used.

The brighteners that are used in combination with the quaternized polymeric condensate are more typical Way in the bath within the ranges that are normally used in alkaline baths for carrying out zinc electroplating be respected. Typically this range will vary from about 0.1 to about 5 grams per liter, where an even narrower range between approximately 0.2 and approximately 0.5 g per liter is preferably used when the preferred benzaldehyde brighteners are used.

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The galvanic deposition of zinc in compliance with the process according to the invention "is carried out in the usual way, namely by passing a direct current from a zinc anode through the aqueous alkaline cyanide-free bath according to the present invention, which essentially substituted the polymeric condensate, a brightener and a mercapto The process can be carried out at temperatures from about 16 to about 38 ° C. (60 to 100 ⁰ P). The current densities maintained can be greater than 0 to about 200 A / 0.09 m ² (square foot), with a narrower range between about 0.5 and about 90 A / 0.09 m having been found to be satisfactory for performing most electroplating methods.

The galvanizing bath according to the invention can contain further additives, as used in the usual way in alkaline zinc electroplating baths, including examples of such Materials polyvinyl alcohols, gelatine, polyether alcohols, Polyester, glue as well as peptone are. Of these various materials, polyvinyl alcohol or its various are used Derivatives are particularly preferred and appear to be the formation of mirror-like deposits produced according to the invention will be to benefit significantly. If these polyvinyl alcohols are used, they should be in the bath in an amount between about 0.02 and about 0.2 grams per liter can be used.

The following examples explain the galvanizing bath according to the invention as well as the electroplating methods according to the invention.

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- 14 Example 1

Quaternized polymeric condensates of the type used in the inventive Electroplating bath can be made as follows:

87.7 g (0.859 mol) of dimethylaminopropylamine and approximately 165 g of deionized water are added to a 11 four-necked round bottom flask equipped with a mechanical stirrer, thermometer, condenser and a pressure-balanced addition funnel. The mixture is cooled to approximately 20 to 25 ^{° C. with cooling.} While maintaining this temperature, 100.0 g (0.775 moles) of 1,3-dichloro-2-propanol are added dropwise over a period of 1 hour with stirring. Then, the mixture is stirred for another half an hour below 30 ⁰ C, thereby forming a prepolymer mixture, which somewhat turbid, but is homogeneous. It is a light yellow liquid with a pH between 5 and 6.

Exactly 383.7 g of the prepolymer mixture are mixed together with approximately 200 ml of deionized water and 38.8 g (0.969 mol) of sodium hydroxide pellets to form a basified pre-alkylation mixture with a pH of approximately 9 and poured out in a couple of pressure vessels stainless steel with a fit of 2 1 given. The vessel is sealed, whereupon about 60 g of a gaseous methyl chloride is poured into the vessel over a period of 4 hours at a pressure of about 3.5 to 4.9 kg / cm, absolute while maintaining the temperature at a value between 87 and 92 ⁰ C. The pressure vessel is then cooled and emptied, a foaming, slightly cloudy amber to orange colored solution being obtained. Using approximately 75 ml of deionized water, this becomes

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Material removed quantitatively from the boiler and filtered, whereby 875.3 g of an aqueous polymer with a pH value of approximately 6 and a pesticide content of 33.3% by weight? » obtain -will. A material balance shows that the prepolymer only 45.2 g (0.895 mol) of the methyl chloride made available recorded. The molar ratios of the reactants in this preparation are therefore as follows: 1.0 mol of dimethylaminopropylamine, 0.90 moles of 1; 3-dichloro-2-propanol, 1.13 moles of sodium hydroxide and 1.04 moles of methyl chloride.

Example 2

A range of aqueous, alkaline, and cyanide-free 'zinc plating baths are made to electroplate Hull test panels. The electroplating is carried out in a standard Hull cell (267 ml), the Hull cell plate being connected as the cathode of the bath in the experiment. The electroplating is carried out at a working current of 1 ampere, which results in a current density on the test plate which is between a high range of about 40 to about 60 A / 0.09 m and a low range of about 0.2 to about 0.5 A / 0.09 m fluctuates. The electroplating time is approximately 10 minutes. The bath is kept at a temperature of approximately 21 ^° C. When carrying out each experiment, the bath contains the components listed in Table I below, which are used in the listed concentrations. The results are summarized in Table II.

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Table I.

component

Zinc metal (as zinc sulfate) NaOH

p-anisaldehyde / bisulfite adduct Vanillin

Polyvinyl alcohol

polymeric condensate (1) heterocyclic compound (2)

5 concentration test in g per 75 liter 2 7.5 1 93.75 3 7, 0.180 7.5 93, 0.012 93.75 - 0.036 0.180 - 10.0 0.012 - 0.036 10.0 0.05

(1) Polymeric condensate prepared according to Example 1 and is diluted with water to give a solution with a pesticide content of about 5.8% by weight.

(2) 2-thiouracil in combination with 2 g / l NaOH for solubilization.

Test attempt no.

Table II

Electroplating results

Electroplating creates a rough, thick and non-sticking black zinc deposit across the entire current density range

The electroplating has a smooth and grain-refined surface and is semi-glossy to mirror-glossy, with the semi-glossy deposits in the _? lower current density range from 0 to 10 A / 0.09 m and the mirror shine occurs at higher ranges

The electroplating is similar to that of Test 2, with the exception that the mirror-like deposit now extends over the entire current density range

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As can be seen from the results summarized in Table II, the addition of the polymer according to the invention has Condensate leads to a grain refinement of the zinc deposition, ■ whereby the further addition of the mercapto-substituted compound the brightening effect of the brightener extends over the entire current density range.

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Claims (32)

2U5359 claims 1. Cyanide-free electroplating bath for applying shiny Zinc deposits, characterized by an aqueous alkaline solution, which is a source of zinc ions as well as a quaternized one polymeric condensate of an alkylene polyamine with at least one tertiary amino group and a 1,3-dihalo-2-propanol contains. 2. Bath according to claim 1, characterized in that the molar ratio of the polyamine to the polymer condensate Dihalopropanol varies between about 0.5: 1 and 1.75: 1. 3. Bath according to claim 1, characterized in that in the polymeric condensate the dihalopropanol from 1,3-dichloro-2-propanol consists. 4. Bath according to claim 1, characterized in that the alkylene polyamine in the polymeric condensate has a tertiary amino group which is substituted with alkyl groups having 1 to 5 carbon atoms, and the alkylene bridge 2 to about Contains 5 carbon atoms. 5. Bath according to claim 1, characterized in that the alkylene polyamine of dimethylarainopropylamine in the polymeric condensate consists. 6. Bath according to claim 1, characterized in that the alkylene polyamine of dimethylaminopropylamine in the polymeric condensate and the dihalopropanol consists of 1,3-dichloro-2-propanol, and the molar ratio of the polyamine to the 1,3-dichloro-2-propanol varies between about 0.8: 1 and about 1.5: 1, the condensate being essentially non-crosslinked. 509818/0730 7. Bath according to claim 1, characterized in that there is a
Contains aldehyde brightener. 8. Bath according to claim 7, characterized in that the gloss former is an aldehyde of the formula: O = where R ₁ and Rp independently of one another are hydrogen,
Alkyl, aryl or heterocyclic oxygen or sulfur-containing radicals. 9. Bath according to claim 8, characterized in that the aldehyde brightener consists of benzaldehyde. 10. Bath according to claim 8, characterized in that the aldehyde consists of vanillin. 11. Bath according to claim 8, characterized in that the aldehyde consists of anisaldehyde. 12. Bath according to claim 8, characterized in that the aldehyde consists of p-hydroxybenzaldehyde. 1-3. Bath according to claim 1, characterized in that it is a heterocyclic compound selected from the group consisting of 2-mercapto-substituted pyridine or pyrimidine contains. 14. Bath according to claim 7, characterized in that it is a heterocyclic compound of the formula: 509818/0730 SH σ σ Il R ₀ CX ² \ or contains tautomers thereof, where X is N or CR. where R. is hydrogen, hydroxy, mercapto or acyl, and R ₁ , Rp and R, independently of one another, are hydrogen, hydroxy, mercapto, acyl, amino, alkyl, carboxy or carbamoyl. 15. Bath according to claim 14, characterized in that the heterocyclic compound consists of 2-thiouracil. 16. Bath according to claim 14, characterized in that the heterocyclic compound consists of 2-mercaptopyrimidine. 17. Bath according to claim 14, characterized in that the heterocyclic compound consists of 2,4-Kimerkaptopyrimidin. 18. Bath according to claim 14, characterized in that the heterocyclic compound of 2-mercapto-4-amino-6-hydroxypyrimidine consists. 19. Bath according to claim 14, characterized in that the heterocyclic compound of 5-carboxy-2-mercaptopyridine consists. 20. Bath according to claim 14, characterized in that the heterocyclic compound consists of 3-hydroxy - 2-mercaptopyridine. 509818/0730 21. Bath according to claim 7, characterized in that the heterocyclic compound of 2-mercapto-4,6-aihydroxy pyrimidine "consists. 22. Bath according to claim 1, characterized in that the polymeric condensate is present in the bath in an amount from about 0.25 "to about 5 grams per liter. 23. Bath according to claim 13, characterized in that the polymeric condensate and the heterocyclic compound in the Bath in amounts of about 0.3 to about 0.75 and about 0.025 to about 0.075 grams per liter, respectively. 24. Bath according to claim 1, characterized in that the source of zinc ions consists of a water-soluble zinc salt, 25. Bath according to claim 24, characterized in that the Zinc salt is composed of zinc sulfate. 26. Bath according to claim 7 »characterized in that the aldehyde in the bath in an amount between about 0.1 and is approximately 5 g per liter. 27. Bath according to claim 14, characterized in that the heterocyclic compound consists of 2-Ihiouracil and the Aldehyde is a mixture of anisaldehyde and vanillin. 28. Bath according to claim 14, characterized in that the heterocyclic compound of 2-mercapto-4,6-dihydroxyprimidine and the aldehyde is a mixture of anisaldehyde and vanillin. 29. Bath according to claim 1, characterized in \ that it contains a polyvinyl alcohol. ■ 5 0 9 818/0730 30. Bath according to claim 1, characterized in that the pH is above 14. 31. Use of the bath according to claim 1 for the galvanic deposition of zinc. 32. Embodiment according to claim 31, characterized in that the electroplating is carried out at a temperature between approximately 16 and approximately 38 ° C (60 and 10O ⁰ JF) and at a current density of 0 to 200 A / 0.09 m (square foot) will, 509818/0730