Acidic zinc or zinc-nickel alloy electroplating baths for depositing zinc or zinc-nickel alloy layers

Abstract

The present invention relates to an acidic zinc or zinc-nickel alloy electroplating bath for depositing a zinc or zinc-nickel alloy layer and a method for zinc or zinc-nickel alloy electroplating using such an electroplating bath. The bath comprises a triazole derivative and a polyethylene glycol derivative.

Description

[0001] This application is a divisional application of an application with a filing date of June 3, 2019, application number 201980039314.3, and invention name “Acidic zinc or zinc-nickel alloy electroplating bath for depositing zinc or zinc-nickel alloy layer”. Technical Field

[0002] The present invention relates to an acidic zinc or zinc-nickel alloy electroplating bath for depositing a zinc or zinc-nickel alloy layer. The present invention further relates to a method for zinc or zinc-nickel alloy electroplating using such an electroplating bath. Background Art

[0003] Zinc and zinc alloy electroplating is a standard method for increasing the corrosion resistance of metal substrates such as cast iron and steel substrates. The most common zinc alloy is zinc-nickel alloy. The electroplating baths used for this purpose are generally divided into acidic and alkaline (cyanide and non-cyanide) electroplating baths.

[0004] Electroplating processes using acid zinc and zinc-nickel alloy electroplating baths show several advantages over alkaline electroplating baths, such as higher current efficiency, higher deposit brightness, electroplating speed, and less hydrogen embrittlement of the electroplated substrate. (Modern Electroplating, M. Schlesinger, M. Paunovic, 4th edition, John Wiley & Sons, 2000, p. 431).

[0005] A disadvantage of zinc and zinc-nickel alloy electroplating methods using acidic electroplating baths relative to alkaline electroplating baths is reduced throwing power. As a result, the thickness of the zinc or zinc-nickel alloy deposits shows a higher local current density dependence. The thickness of the deposit (and likewise the corrosion resistance) is lower in areas of the substrate where the local current density is lower and higher in areas of the substrate where the local current density is higher. The poor throwing power of acidic zinc and zinc-nickel alloy electroplating methods is particularly a problem when electroplating substrates with complex shapes (such as brake calipers) and / or when rack-and-barrel electroplating and drum electroplating (rack-and-barrel electroplating) are used.

[0006] Objectives of the invention

[0007] In view of the prior art, it was therefore an object of the present invention to provide an acidic zinc or zinc-nickel alloy electroplating bath for depositing zinc or zinc-nickel alloy layers which should exhibit an improved electroplating behavior at low local current densities and thus an improved thickness uniformity of the deposit, in particular when electroplating substrates with complex shapes and / or in rack plating and drum plating applications.

[0008] Furthermore, it is an object of the present invention to provide an acid zinc or zinc-nickel alloy electroplating bath which should be able to reduce or ideally avoid burning in high current density areas while improving thickness in low current density areas. Summary of the invention

[0009] These objects, as well as other objects not explicitly stated but directly derivable or discernible by way of introduction from the connections discussed herein, are achieved by an acid zinc or zinc-nickel alloy electroplating bath having all the features of claim 1. Appropriate modifications of the electroplating bath of the present invention are protected in the appended claims 2 to 14. In addition, claim 15 comprises a method for electroplating zinc or zinc-nickel alloys using such an electroplating bath.

[0010] Therefore, the present invention provides an acidic zinc or zinc-nickel alloy electroplating bath for depositing a zinc or zinc-nickel alloy layer, characterized in that the electroplating bath comprises

[0011] (i) at least one zinc ion source

[0012] (ii) at least one triazole derivative having the general formula (I)

[0013]

[0014] in

[0015] R 1 is selected from the group consisting of: hydrogen, thiol, carboxylic acid, amino, methyl, methylsulfonyl, and methyl carboxylate;

[0016] R 2 is hydrogen or phenyl; and

[0017] R 3 is selected from the group consisting of: hydrogen, amino, thiol, and phenyl;

[0018] (iii) at least one first poly(ethylene glycol) derivative having the general formula (II)

[0019] R 4 -[O-CH 2 -CH 2 ] n -OR 5 (II)

[0020] in

[0021] n is in the range of 2 to 200;

[0022] R 4 Selected from the group consisting of: straight or branched chain C 1 -C 18 Alkyl, 4-nonylphenyl and straight or branched C 1 -C18 alkyl;

[0023] R 5 Selected from the group consisting of: -CH 2 -CH 2 -CH 2 -SO 3 Z, -CH 2 -CH 2 -SH and tosyl;

[0024] wherein Z is a monovalent cation, such as a potassium ion, a sodium ion or an ammonium ion; and

[0025] (iv) in the case of a zinc-nickel alloy electroplating bath, at least one source of nickel ions.

[0026] It is thus possible in an unforeseeable manner to provide an acid zinc or zinc-nickel alloy electroplating bath for depositing zinc or zinc-nickel alloy layers which exhibits an improved electroplating behavior at low local current densities and thus an improved thickness uniformity of the deposit, in particular when electroplating substrates with complex shapes and / or in rack plating and drum plating applications. Furthermore, the present invention provides an acid zinc or zinc-nickel alloy electroplating bath which is able to avoid burning in high current density areas while improving thickness in low current density areas.

[0027] Brief description of the form

[0028] The objects, features and advantages of the present invention will also become apparent after reading the following description in conjunction with the tables, in which:

[0029] Table 1 presents experiments (at 1 Ampere) carried out on acid zinc electroplating baths according to examples of the invention and comparative examples outside the invention.

[0030] Table 2 presents experiments (at 1 ampere) conducted on acid zinc-nickel alloy electroplating baths according to examples of the invention and comparative examples outside the invention. DETAILED DESCRIPTION

[0031] The acidic zinc or zinc-nickel alloy electroplating bath of the present invention is preferably a water bath. The water content of such a water bath accounts for more than 80 volume %, preferably more than 90 volume % and more preferably more than 95 volume % of the total solvent used. The pH value of such an acidic zinc or zinc-nickel alloy electroplating bath is in the range of 2 to 6.5, preferably 3 to 6 and more preferably 4 to 6.

[0032] Suitable sources of zinc ions include ZnO, Zn(OH) 2 、ZnCl 2 、ZnSO 4 、ZnCO3 、Zn(SO 3 NH 2 ) 2 , zinc acetate, zinc methane sulfonate and mixtures of the foregoing.

[0033] Suitable sources of nickel ions, which are optionally included only when a zinc-nickel alloy electroplating bath is desired, include NiCl 2 、NiSO 4 、NiSO 4 6H 2 O、NiCO 3 ,Ni(SO 3 NH 2 ) 2 , nickel acetate, nickel methane sulfonate and mixtures thereof.

[0034] The acidic zinc or zinc-nickel alloy electroplating bath of the present invention then further comprises a complexing agent for nickel ions. The complexing agent is preferably selected from aliphatic amines, poly(alkylene imines), non-aromatic polycarboxylic acids, non-aromatic hydroxycarboxylic acids and mixtures thereof.

[0035] The nickel ion source and the complexing agent are preferably added to the electroplating bath as is.

[0036] In one embodiment of the present invention, the nickel ion source is mixed with the nickel ion complexing agent in water before being added to the electroplating bath. Thus, the nickel complexing compound / salt derived from the mixture of the nickel ion complexing agent and nickel ions is added to the electroplating bath as the nickel ion source.

[0037] Suitable aliphatic amines include 1,2-alkyleneimines, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and the like.

[0038] Suitable poly(alkyleneimines) are, for example G-15, G-20 and G-35, all purchased from BASF SE.

[0039] Suitable non-aromatic polycarboxylic acids and non-aromatic hydroxycarboxylic acids preferably include compounds capable of forming chelates with zinc ions and / or nickel ions, such as citric acid, tartaric acid, gluconic acid, α-hydroxybutyric acid, etc., and salts thereof, such as corresponding sodium salts, potassium salts and / or ammonium salts.

[0040] The concentration of the at least one complexing agent for nickel ions is preferably in the range of 0.1 to 150 g / l, more preferably 1 to 50 g / l.

[0041] In the context of the present invention, the expression "electroplating bath" means that an electric current is always applied to such an inventive acidic zinc or zinc-nickel alloy bath. An electroless zinc or zinc-nickel alloy bath will have a different chemical bath composition. Therefore, the present invention is expressly disclaimed from being related to an electroless bath and an electroless bath does not form part of the present invention.

[0042] In one embodiment, the bath is substantially free, and preferably completely free, of alloying metals other than zinc and nickel ions.

[0043] In one embodiment, at least one triazole derivative is selected from the group consisting of: 3-mercapto-1,2,4-triazole; 1,2,4-triazole; 1,2,4-triazole-3-carboxylic acid; 3-amino-1,2,4-triazole; 3-methyl-1H-1,2,4-triazole; 3,5-diamino-1,2,4-triazole; 3-amino-5-mercapto-1,2,4-triazole; 3-(methylsulfonyl)-1H-1,2,4-triazole; 5-phenyl-1H-1,2,4-triazole-3-thiol; 1-phenyl-1H-(1,2,4)-triazole-3-thiol; and 1H-1,2,4-triazole-3-carboxylic acid methyl ester.

[0044] In one embodiment, at least one first poly(ethylene glycol) derivative is selected from the group consisting of: poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (CAS 119438-10-7); poly(ethylene glycol) alkyl (3-sulfopropyl) diether potassium salt (CAS 119481-71-9); poly(ethylene glycol) methyl ether thiol; poly(ethylene glycol) methyl ether tosylate (CAS 58320-73-3) and poly(ethylene glycol) 2-mercaptoethyl ether acetic acid (CAS 165729-81-7).

[0045] In one embodiment, the at least one triazole derivative is 3-mercapto-1,2,4-triazole and the at least one first poly(ethylene glycol) derivative is poly(ethylene glycol) alkyl(3-sulfopropyl) diether potassium salt (CAS 119481-71-9).

[0046] In one embodiment, the concentration of the at least one triazole derivative ranges from 0.5 to 7.5 mg / l, preferably 0.75 to 6.5 mg, and more preferably 1 to 5 mg / l.

[0047] In one embodiment, the concentration of the at least one first poly(ethylene glycol) derivative ranges from 0.5 to 7.5 g / l, preferably 0.75 to 4.5 g / l, and more preferably 1 to 5 g / l.

[0048] In a preferred embodiment, the bath further comprises

[0049] (v) at least one second poly(ethylene glycol) derivative having the general formula (III)

[0050] R 6 -[O-CH 2 -CH 2 ] n -OR 7 (III)

[0051] in

[0052] n is in the range of 2 to 200;

[0053] R 6 Selected from the group consisting of: straight or branched chain C 1 -C 18 Alkyl, -CH 2 -COOH, glycidyl and -CH 2 -CH 2 -NH 2 ;and

[0054] R 7 Selected from the group consisting of: hydrogen, -CH 2 -COOH, glycidyl and -O-CH 3 .

[0055] Such another additive may still improve the wetting behavior of the substrate to be plated without adversely affecting the electroplating itself. If the other additive is a foam reducer (facilitates operating conditions) or a gloss enhancer (improves optical appearance), it may exemplarily help electroplating the substrate.

[0056] The at least one second poly(ethylene glycol) derivative of the general formula (III) is always different in the context of the present invention from the necessary at least one first poly(ethylene glycol) derivative of the general formula (II).

[0057] In the preferred embodiment, the at least one second poly(ethylene glycol) derivative is selected from the group consisting of: octa(ethylene glycol) octyl ether (CAS 26468-86-0), poly(ethylene glycol) bis(carboxymethyl) ether (CAS 39927-08-7), poly(ethylene glycol) diglycidyl ether (CAS 72207-80-8), poly(ethylene glycol) dimethyl ether (CAS 24991-55-7) and poly(ethylene glycol) methyl ether amine (CAS 80506-64-5).

[0058] In said preferred embodiment, the concentration of the at least one second poly(ethylene glycol) derivative is in the range of 0.5 to 7.5 g / l, preferably 0.75 to 4.5 g / l, and more preferably 1 to 5 g / l.

[0059] In a more preferred embodiment, at least one triazole derivative is 3-mercapto-1,2,4-triazole, at least one first poly(ethylene glycol) derivative is poly(ethylene glycol) alkyl(3-sulfopropyl) diether potassium salt (CAS 119481-71-9), and at least one second poly(ethylene glycol) derivative is octa(ethylene glycol) octyl ether (CAS 26468-86-0).

[0060] The acidic electroplating bath according to the present invention optionally further comprises a buffering additive, such as acetic acid, a mixture of acetic acid and corresponding salts, boric acid and the like, in order to maintain a desired pH range during operation of the electroplating bath.

[0061] In a preferred embodiment, the bath is substantially free, preferably completely free, of boric acid.

[0062] The expression "essentially free" in the context of the present invention means a concentration of less than 0.2 g / l, preferably less than 0.1 g / l and more preferably less than 0.05 g / l.

[0063] In one embodiment, the concentration of zinc ions ranges from 5 to 100 g / l, preferably 10 to 50 g / l, and more preferably 15 to 35 g / l.

[0064] In one embodiment (in the case of a zinc-nickel alloy electroplating bath), the concentration of nickel ions ranges from 5 to 100 g / l, preferably 10 to 50 g / l, and more preferably 15 to 35 g / l.

[0065] Furthermore, the object of the invention is also solved by a method for zinc or zinc-nickel alloy electroplating, said method comprising the following steps in this order:

[0066] (i) providing a substrate having a metal surface as a cathode,

[0067] (ii) contacting the substrate with an acidic zinc or zinc-nickel alloy electroplating bath according to the present invention,

[0068] (iii) applying an electric current between the substrate and at least one anode and thereby depositing a zinc or zinc-nickel alloy layer having an improved thickness onto the substrate.

[0069] Suitable anode materials are, for example, zinc, nickel and mixed anodes comprising zinc and nickel.The electroplating bath is preferably maintained at a temperature in the range of 20°C to 50°C.

[0070] The acidic zinc and zinc-nickel alloy electroplating baths according to the invention can be used in all types of industrial zinc and zinc-nickel alloy electroplating processes, such as rack plating, drum plating and high-speed plating of metal strips and wires.

[0071] The current density range applied to the substrate (cathode) and at least one anode depends on the electroplating method. For rack electroplating and drum electroplating, it is preferably applied at 0.3A / dm 2 Up to 5A / dm 2 current density in the range.

[0072] The technical effect of improved throwing power is most preferably used for plating substrates with complex shapes and / or for rack plating and drum plating. Typical substrates with complex shapes include brake calipers, holders, clamps and tubes.

[0073] The phrase "complex shape" with respect to a substrate to be plated by the method of the present invention is defined herein as a shape that produces different local current density values ​​on the surface during electroplating. In contrast, a substrate having, for example, a substantially flat plate-like shape (e.g., a metal strip) is not considered to be a substrate having a complex shape.

[0074] Therefore, the present invention solves the problem of improving thickness in low current density areas by increasing the plating speed in this area, while avoiding burning in high current density areas.

[0075] The following non-limiting examples are provided to illustrate different embodiments of the invention and to facilitate understanding of the invention and are not intended to limit the scope of the invention, which is defined by the claims appended hereto.

[0076] General procedure:

[0077] The electroplating experiments were carried out in a Hull-cell in order to simulate a wide range of local current densities on the substrate ("Hull-cell plate") during electroplating. The substrate material was steel and the dimensions were 100 mm x 75 mm.

[0078] The desired technical effect of improved throwing power was determined by thickness measurements of the deposited zinc and zinc-nickel alloy layers by X-ray fluorescence measurement using a Fischerscope X-ray XDL-B device from Helmut Fischer GmbH. Thickness readings were obtained over a defined distance from the end of the high local current density (HCD) region to the end of the low local current density (LCD) region across the substrate of each respective Hull cell panel (substrate). The thicknesses at corresponding distances of 0.5, 2.5, 5, 7.5, 9.5 and 9.8 cm from the HCD end of each substrate are given in micrometers in Tables 1 and 2. A current of 1 ampere was applied to electroplate the substrates.

[0079] The throwing power of the tested electroplating baths was determined from the thickness values ​​measured across the Hull cell panel.In addition, the optical appearance has been scrutinized for burning in the HCD area, which would have a negative impact on the overall results.

[0080] The inventive effectiveness of the claimed electroplating baths containing the selective combination of additives was determined by comparing their electroplating results on Hull Cell plates with their electroplating results on comparative Hull Cell plates that had been plated with the same standard acid zinc or zinc-nickel alloy electroplating bath except without such selective combination of additives.

[0081] The experiments given in Tables 1 and 2 are numbered in chronological order, wherein the second number in parentheses is the internal experiment number of the applicant.

[0082] All experiments in Tables 1 and 2 have been performed with 3-mercapto-1,2,4-triazole (F1 additive), poly(ethylene glycol) alkyl(3-sulfopropyl) diether potassium salt (CAS 119481-71-9; F2 additive) and octa(ethylene glycol) octyl ether (CAS 26468-86-0, F3 additive).

[0083] The experiments given in Tables 1 and 2 with the symbol "*" after the experimental number in the first column represent comparative examples outside the present invention.

[0084] The numbers in each column below the disclosed distances from the HCD end of 0.5, 2.5, 5, 7.5, 9.5 and 9.8 are the measured thickness of the zinc or zinc-nickel alloy layer on the substrate after electroplating.

[0085] Table 1 shows experiments conducted (at 1 amp) on acid zinc electroplating baths with and without the selective additive combination of the present invention as claimed.

[0086] Table 1: Experiments with acid zinc plating baths

[0087]

[0088] The results given in Table 1 demonstrate that the selective combination of additives F1 and F2 (inventive experiments 8 to 10) shows preferred layer thicknesses in the LCD region at distances of 9.8 and 9.5 from the HCD end of the Hull cell compared to the experiment (Comparative Experiment 1) that does not contain any of the three additives. The same applies when compared to the experiments that only contain F1 (Comparative Experiments 2 to 4) or F2 (Comparative Experiments 5 to 7). Comparative Experiment 11 has too high a concentration of F2, while Comparative Experiment 12 has too high a concentration of F1. Experiments 11 and 12 can thus demonstrate the selectivity of the present invention, which was not even sufficient to find a suitable combination of additives, nor to find their respective specific suitable concentrations. Inventive Experiments 13 and 14 finally show that the combination of F1, F2 and F3 provides even better layer thickness results in the LCD region.

[0089] Table 2 shows experiments conducted (at 1 amp) on acid zinc-nickel alloy electroplating baths with and without the selective additive combination of the present invention as claimed.

[0090] Table 2: Experiments of acid zinc-nickel alloy electroplating bath

[0091]

[0092] The technical effect of the additives F1 and F2, and preferably the selective combination of F1, F2 and F3, has also been successfully demonstrated for zinc-nickel alloy electroplating baths.

[0093] All of the inventive experiments presented in Tables 1 and 2 have demonstrated no significant burning in the HCD region close to the HCD end of the Hull cell (distances of 0.5 and 2.5 cm).

[0094] Although the principles of the present invention have been explained with respect to certain specific embodiments and provided for the purpose of illustration, it should be understood that various modifications thereof will become apparent to those skilled in the art after reading this specification. Therefore, it should be understood that the invention disclosed herein is intended to cover such modifications within the scope of the appended claims. The scope of the present invention is limited only by the scope of the appended claims.

Claims

1. An acidic zinc or zinc-nickel alloy electroplating bath for depositing a zinc or zinc-nickel alloy layer, It is characterized in that The electroplating bath comprises (i) at least a zinc ion source (ii) at least one triazole derivative selected from the group consisting of: 3-mercapto-1,2,4-triazole; 1,2,4-triazole; 1,2,4-triazole-3-carboxylic acid; 3-amino-1,2,4-triazole; 3-methyl-1H-1,2,4-triazole; 3,5-diamino-1,2,4-triazole; 3-amino-5-mercapto-1,2,4-triazole; 3-(methylsulfonyl)-1H-1,2,4-triazole; 5-phenyl-1H-1,2,4-triazole-3-thiol; 1-phenyl-1H-(1,2,4)-triazole-3-thiol; and 1H-1,2,4-triazole-3-carboxylic acid methyl ester; (iii) at least one first poly(ethylene glycol) derivative selected from the group consisting of: poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (CAS 119438-10-7); Poly(ethylene glycol) alkyl (3-sulfopropyl) diether potassium salt (CAS 119481-71-9); poly(ethylene glycol) methyl ether thiol; poly(ethylene glycol) methyl ether tosylate (CAS 58320-73-3) and poly(ethylene glycol) 2-mercaptoethyl ether acetic acid (CAS 165729-81-7); and (iv) in the case of a zinc-nickel alloy electroplating bath, at least a source of nickel ions, wherein the concentration of the at least one triazole derivative is in the range of 0.5 mg / l to 7.5 mg / l; and the concentration of the at least one first poly(ethylene glycol) derivative is in the range of 0.5 g / l to 7.5 g / l.

2. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1, wherein the bath has less than 0.2 g / l of other alloying metals other than zinc and nickel ions.

3. The acidic zinc or zinc-nickel alloy electroplating bath of claim 1 or 2, wherein the at least one triazole derivative is 3-mercapto-1,2,4-triazole and the at least one first poly(ethylene glycol) derivative is poly(ethylene glycol) alkyl(3-sulfopropyl)diether potassium salt (CAS 119481-71-9).

4. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the concentration of the at least one triazole derivative is in the range of 0.75 mg / l to 6.5 mg / l.

5. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the concentration of the at least one triazole derivative is in the range of 1 mg / l to 5 mg / l.

6. The acidic zinc or zinc-nickel alloy electroplating bath of claim 1 or 2, wherein the concentration of the at least one first poly(ethylene glycol) derivative is in the range of 0.75 g / l to 4.5 g / l.

7. The acidic zinc or zinc-nickel alloy electroplating bath of claim 1 or 2, wherein the concentration of the at least one first poly(ethylene glycol) derivative is in the range of 1 g / l to 5 g / l.

8. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the bath is completely free of other alloying metals other than zinc and nickel ions.

9. The acidic zinc or zinc-nickel alloy electroplating bath of claim 1 or 2, wherein the bath further comprises (v) at least one second poly(ethylene glycol) derivative having the general formula (III) R 6 -[O-CH 2 -CH 2 ] n -O-R 7 (III) in n is in the range of 2 to 200; R 6 Selected from the group consisting of: straight chain or branched C 1 -C 18 Alkyl, -CH 2 -COOH, glycidyl and -CH 2 -CH 2 -NH 2 ;and R 7 Selected from the group consisting of: hydrogen, -CH 2 -COOH and glycidyl.

10. The acidic zinc or zinc-nickel alloy electroplating bath of claim 9, wherein the at least one second poly(ethylene glycol) derivative is selected from the group consisting of octa(ethylene glycol) octyl ether (CAS 26468-86-0), poly(ethylene glycol) bis(carboxymethyl) ether (CAS 39927-08-7), poly(ethylene glycol) diglycidyl ether (CAS 72207-80-8), poly(ethylene glycol) dimethyl ether (CAS 24991-55-7), and poly(ethylene glycol) methyl ether amine (CAS 80506-64-5).

11. The acidic zinc or zinc-nickel alloy electroplating bath of claim 9, wherein the concentration of the at least one second poly(ethylene glycol) derivative is in the range of 0.5 g / l to 7.5 g / l.

12. The acidic zinc or zinc-nickel alloy electroplating bath of claim 9, wherein the at least one triazole derivative is 3-mercapto-1,2,4-triazole, the at least one first poly(ethylene glycol) derivative is poly(ethylene glycol) alkyl(3-sulfopropyl) diether potassium salt (CAS 119481-71-9), and the at least one second poly(ethylene glycol) derivative is octa(ethylene glycol) octyl ether (CAS 26468-86-0).

13. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the bath has less than 0.2 g / l boric acid.

14. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the concentration of zinc ions is in the range of 5 g / l to 100 g / l.

15. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein in the case of a zinc-nickel alloy electroplating bath, the concentration of nickel ions is in the range of 5 g / l to 100 g / l.

16. The acidic zinc or zinc-nickel alloy electroplating bath of claim 9, wherein the concentration of the at least one second poly(ethylene glycol) derivative is in the range of 0.75 g / l to 4.5 g / l.

17. The acidic zinc or zinc-nickel alloy electroplating bath of claim 9, wherein the concentration of the at least one second poly(ethylene glycol) derivative is in the range of 1 g / l to 5 g / l.

18. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the bath is completely free of boric acid.

19. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the concentration of zinc ions is in the range of 10 g / l to 50 g / l.

20. The acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein the concentration of zinc ions is in the range of 15 g / l to 35 g / l.

21. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein in the case of a zinc-nickel alloy electroplating bath, the concentration of nickel ions is in the range of 10 g / l to 50 g / l.

22. An acidic zinc or zinc-nickel alloy electroplating bath according to claim 1 or 2, wherein in the case of a zinc-nickel alloy electroplating bath, the concentration of nickel ions is in the range of 15 g / l to 35 g / l.

23. A method for electroplating zinc or zinc-nickel alloy, comprising the following steps in order: (i) providing a substrate having a metal surface as a cathode, (ii) contacting the substrate with an acidic zinc or zinc-nickel alloy electroplating bath according to any one of claims 1 to 22, (iii) applying an electric current between the substrate and at least one anode and thereby depositing a zinc or zinc-nickel alloy layer having an improved thickness onto the substrate.

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