EP2235236A2

EP2235236A2 - Galvanic bath, method for galvanic deposition, and use of a bipolar membrane for separating in a galvanic bath

Info

Publication number: EP2235236A2
Application number: EP08861431A
Authority: EP
Inventors: Hartmut Trenkner; Alexander Jimenez
Original assignee: Coventya GmbH
Current assignee: Coventya GmbH
Priority date: 2007-12-14
Filing date: 2008-12-15
Publication date: 2010-10-06
Anticipated expiration: 2028-12-15
Also published as: WO2009077146A2; ES2396801T3; DE102007060200A1; PL2235236T3; EP2235236B1; WO2009077146A3; BRPI0820988A2; BRPI0820988B1

Abstract

The invention relates to an alkali, galvanic bath for applying zinc or zinc alloys to substrates, wherein the anode chamber and the cathode chamber are separated from each other by a bipolar membrane. The galvanic bath is operated with zinc or zinc alloy baths that can comprise further additives. The invention further relates to a method for galvanic deposition of zinc or zinc alloys on substrates, wherein the substrate is placed in the galvanic bath according to the invention. The invention further relates to the use of bipolar membranes for separating the anode chamber and cathode chamber in galvanic baths, and for avoiding anodic disintegration of organic components of the electrolyte in galvanic baths.

Description

Galvanic bath, process for electrodeposition and use of a bipolar membrane for separation in a galvanic bath

The invention relates to an alkaline, galvanic bath for applying zinc or zinc alloys on substrates, in which the anode space and the cathode space are separated by a bipolar membrane. The electroplating bath is operated with zinc or zinc alloy baths, which may contain other additives. Furthermore, the invention relates to a method for the galvanic deposition of zinc or zinc alloys on substrates, in which the substrate is introduced into the galvanic bath according to the invention. Moreover, the invention relates to the use of bipolar membranes for the separation of anode space and cathode space in electroplating baths and to avoid the anodic decomposition of organic components of the electrolyte in electroplating baths. In order to enable the deposition of functional layers from zinc baths, organic brighteners and wetting agents are added to the bath. Furthermore, the bath contains complexing to allow the deposition of other metals of the zinc alloy. The complexing agent serves to regulate the potential and keep the metals in solution so that the desired alloy composition is achieved. However, the use of the abovementioned organic constituents leads to problems during operation of the baths, as described, for example, in WO 00/06807. There, it is particularly disadvantageous that these baths show a change in color from originally blue-violet to brown after a few hours of operation. The brown color comes from decomposition products, the amount of which increases during the operation of the bath. After several weeks or months, this staining intensifies. This causes considerable disruption of the coating of the workpieces, such as, for example, uneven layer thicknesses or bubble formation. A continuous cleaning of the bath is therefore essential. This is time consuming and expensive.

With phase separation and increasing content of organic contaminants, increasing decorative problems of coating occur and result in decreased productivity. In order to reduce the decorative problems, generally increased dosages of the organic bath additives are carried out, as a result of which the content of degradation products continues to increase.

As remedies, the following methods are known so far: • Bath dilution reduces the concentration of impurities in proportion to the degree of dilution. A dilution is easy to carry out, but has the disadvantage that the amount of electrolyte removed from the bath has to be supplied to cost-intensive disposal. A complete new approach of the bath can be considered in this context as a special case of Badverdünnung.

Activated carbon treatment by stirring 0.5-2 g / L activated charcoal into the bath followed by filtration reduces the concentration of impurities by adsorption on the coal. The disadvantage of this method is that it is labor-intensive and only causes a relatively small reduction.

• Alkaline zinc baths contain a factor of 5 to 10 lower organic content

Additives as acid baths. Accordingly, contamination by decomposition products is generally less critical. In the case of alkaline alloy baths, however, to complex the alloying additive (Fe, Co, Ni, Sn, Mn)

Addition of significant amounts of organic complexing agents required. These are oxidatively degraded at the anode and the accumulated decomposition products have a negative effect on the production process.

EP 1 369 505 A2 discloses a method for cleaning a zinc / nickel electrolyte in a galvanic process in which a part of the process bath used in the process is evaporated until a phase separation into a lower phase Phase, at least one middle phase and an upper phase takes place and the lower and the upper phase are separated. This process requires several stages and is disadvantageous in terms of its energy requirements from a cost point of view.

WO 00/06807 and WO 01/96631 describe electroplating baths for applying zinc-nickel coatings. To the unwanted decomposition of

To avoid additions to the anode, it is proposed to separate the anode from the alkaline electrolyte through an ion exchange membrane.

However, these systems have the disadvantage that the use of such membranes causes a volume overhang in the overall system.

Furthermore, the known in the prior art baths, which are operated without separation of the cathode and anode region, have the disadvantage that in the anodic decomposition of the nitrogen-containing complexing agent cyanide is formed and this accumulates in non-negligible concentration.

Based on this, it was an object of the present invention to provide an alkaline galvanic bath, which eliminates the aforementioned disadvantages, is easy to operate and enables a long life of the galvanic bath. At the same time, a galvanic deposition with a constant layer thickness is to be made possible.

This object is achieved by the generic galvanic bath with the characterizing features of the 1 and the method for the galvanic deposition of zinc or zinc alloys on substrates with the features of claim 17 solved. Claims 20 and 21 mention uses according to the invention. The other dependent claims show advantageous developments.

According to the invention, an alkaline galvanic bath for depositing zinc or zinc alloys on substrates is provided which contains a cathode space with associated cathode and zinc ion-containing catholyte and an anode space with associated anode and anolyte, wherein the cathode space anode space are separated by a separator. According to the invention, a bipolar membrane is used as the separator.

The galvanic bath according to the invention has the following economic and ecological advantages:

a) the service life of the bath is increased, b) saving of sodium hydroxide by the self-formation process in the anolyte after water splitting, c) prevention of excess volume in galvanic zinc electrolyte, d) prevention of oxidation reactions of the organic additives at the anode, e) preservation of a 90% efficiency, f) optimum use of the chemical constituents of the electrolyte, since there is no volume surplus, which must be treated or disposed of in addition to the wastewater, but a volume decrease due to the mass loss of metals and hydrogen in the electrolyte during the deposition process. Ganges is recorded, which can be compensated depending on the sodium hydroxide content in the electrolyte with water, caustic soda or sodium hydroxide solution from the anolyte, g) When used, a layer thickness of consistently high quality is obtained on the coated substrate.

The bipolar membrane preferably has at least one cation exchange membrane, at least one anion exchange membrane and an intermediate layer arranged between these membranes and catalyzing the dissociation of water into protons and hydroxide ions.

The anode is preferably made of nickel, nickel-plated stainless steel, steel or stainless steel. This has the advantage over the known from the prior art electroplating baths, in which usually platined titanium anodes are used, that they are much cheaper.

Preferably, the catholyte contains further metal salts. These include, in particular, salts of iron, nickel, manganese, cobalt and tin or mixtures thereof. Likewise, the catholyte complexing agent may in particular contain amines, polyalkyleneimines, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, further chelate ligands such as acetylacetone, urea, urea derivatives and further complexing ligands in which the complexing functional group contains nitrogen, phosphorus and sulfur. Further optional components of the catholyte are additives selected from the group consisting of brighteners, wetting agents and mixtures thereof. These include preferably benzylpyridinium carboxylate, nicotinic acid. re, N-methylpyridiniumcarboxylate and aldehydes.

The following is an exemplary composition as a novel catholyte listed:

80-250 g / l sodium or potassium hydroxide, 4-20 g / l zinc in the form of a soluble zinc salt, 0.02-20 g / l nickel, iron, kobble, tin in the form of a soluble metal salt as alloying metal, 1-200 g / l complexing agent selected from the group consisting of polyalkenylamines, alkanolamines, polyhydroxycarboxylates and mixtures thereof and 0.1-5 g / l of aromatic and / or heteroaromatic brighteners.

Preferably, the anolyte consists of 50 to 200 g / l NaOH and 950 to 800 g / l water.

The bipolar membrane is preferably thermally stable up to 50 ^° C., particularly preferably up to 60 ^° C.

A further variant of the galvanic bath according to the invention provides that this has a further electrolyte space, which is arranged between the cathode space and the anode space. This additional electrolyte space is separated from the anode space by an ion exchange membrane from the cathode space through the bipolar membrane. In this electrolyte space, a second catholyte is included.

It is preferred that the ion exchange membrane is an anion exchange membrane. But it is also possible to use a cation exchange membrane. The second catholyte preferably has a pH in the range of 1 to 7. Particularly preferably, the second catholyte contains sulfuric acid or sulfuric acid and sodium sulfate. It is likewise possible for carboxylic acid and / or salts thereof, such as, for example, sodium formate or sodium acetate, to be present in the second catholyte.

The use of a second catholyte serves to protect the bipolar membrane. Thus, hydrogen carbonate ions (HCO ₃ -) on the catholyte side of the bipolar membrane with the protons (H +) formed from the water splitting form carbonic acid, which decomposes to carbon dioxide (CO ₂ ) and water. The carbon dioxide which forms can thereby force apart the cation and anion membrane of the bipolar membrane at the connection surface, as a result of which the function of water splitting in protons and hydroxide ions is gradually lost. Due to the additional ion exchange membrane, in particular an anion exchange membrane, it is above all hydroxide ions that arrive at the DC flow in the second catholyte, with neutralization, bicarbonate decomposition and pH increase taking place. It can thus be achieved that the bipolar membrane on the cation exchanger side is no longer impaired by the hydrogencarbonate ions.

The invention likewise provides a process for the galvanic deposition of zinc or zinc alloys on substrates, in which the substrate is introduced into a galvanic bath, as described above, and zinc or zinc alloys are electrodeposited on the substrate.

The deposition is preferably carried out at a Temperature of 20 to 40 ⁰ C, more preferably at a temperature of 25 ⁰ C. The current density is in the deposition preferably in a range of 0.1 to 20 A / dm ² , in particular from 0.5 to 3 A / dm ^second ,

The invention likewise provides the use of a bipolar membrane for separating the anode space and the cathode space in a galvanic bath. The bipolar membrane makes it possible to avoid the anodic decomposition of organic components of the electrolyte in a galvanic bath.

The bipolar membrane used according to the invention preferably has at least one cation exchange membrane, at least one anion exchange membrane and an intermediate layer arranged between the membranes and catalyzing the dissociation of water into protons and hydroxide ions.

The bipolar membranes of the present invention can be prepared using conventional ion exchange membranes. Bipolar membranes can be prepared, for example, by copolymerization of styrene and divinylbenzene or butadiene or by copolymerization of acrylonitrile and butadiene, the cations being firmly bonded to the membrane by, for example, sulfochlorination and the anions firmly bonded to the membrane by chloromethylation and reaction with tertiary amines be bound. The thickness of the bipolar membranes is preferably between about 0.1 and 1 mm. Moreover, the bipolar membranes may optionally include a reinforcing material of various types and shapes, depending on the process by which cation exchange membranes are made. The bipolar membranes of the present invention can be made with any conventional cation exchange membrane, including membranes having such an ion exchange group as a sulfonic acid group or a carboxylic acid group. The most preferred cation exchange membranes include a sulfonic acid group which retains a replacement group even under an acidic condition. Moreover, the cation exchange membrane may include a small amount of an anion exchange group as long as it has cation transport numbers of not less than about 0.9.

The anion exchange layer may be prepared by any conventional anion exchange material having such ion exchange groups as positively charged organic ions, amino or quaternary ammonium groups. The polymeric membrane structure would contain the anion exchange group included in the organic network. The polymer may be a polymer of vinylpyridine, divinylbenzene with the monomers copolymerized in various amounts, such as styrene, ethylene, methacrylic acid or propylene. The anion exchange membrane may comprise a reinforcing matrix which may include polyethylene, polypropylene, polyvinyl chloride and polyvinyl acetate. The anion exchange membrane will preferably have a capacity of between about 1 and about 3 milliequivalents per gram (meq / g). The anion exchange membrane may be a polymerizable type, a homogeneous type or a non-homogeneous type.

In accordance with the invention, the ion exchange membranes are preferably bonded together using an adhesive, such as an "ionic adhesive", which consists of positively and negatively charged ions These adhesives include, but are not limited to, epichlorohydrin, polyethylenimine, polyacrylic acid, polyvinylamine, poly (4-vinyl) pyridine, powdered commercial anion and cation exchange resin, and combinations thereof. After application of the ionic adhesive, the cationic conductive material and the anionic conductive material are preferably hot pressed around a plurality of removable members at sufficient temperature and pressure to bond the material to a bipolar membrane. The removable elements can be removed by extraction or dissolution, leaving a passage for fluids. A preferred adhesive is an aqueous solution containing a mixture of polyacrylic acid and polyethyleneimine, more preferably in a polyethyleneimine: polyacrylic acid ratio of about 6: 1.

Alternatively, the adhesive may include a polyvinylamine in which the amino group is substituted with an alkyl group having from 1 to 4 carbon atoms and the polyvinylamine has a molecular weight between about 10 ⁴ and 10 ⁶ . The concentration of the aqueous polyvinylamine solution may be between about 0.5 and 70% by weight, but the preferred concentration is between about 3 and 15% by weight. Solutions of the aqueous polyvinylamine can be obtained, for example, by a conventional method of acidic or alkaline hydrolysis of polyvinylformamide or polyvinylacetamide with sodium hydroxide solution or hydrochloric acid. A preferred method for preparing an aqueous polyvinylamine solution includes hydro lyse of aqueous polyvinylformamide with a re Salzsäu- at a temperature between about 60 ⁰ C and 100 ⁰ C. The polyvinylformamide concentration in water is preferably between about 1 and 50% by weight, more preferably between about 5 and 20% by weight. The resulting polyvinylamine solutions are still liquid and can be easily applied to the membranes.

The adhesive solutions may be applied to one or both of the ion exchange membranes using any conventional technique, including brushing or wafer coating. The solution is preferably applied at a temperature between about 1O ⁰ C and 50 ⁰ C. It is also possible to impregnate the membranes on both sides with the solution. However, the outer membrane surface is preferably washed free of adhesive during the completion of the bipolar membrane. The thickness of the adhesive layer is preferably between about 0.001 and about 0.05 mm.

In the bipolar membrane of the present invention, the cation exchange membrane can be bound to the anion exchange membrane by any method. However, it is preferable that the cation exchange membrane and the anion exchange membrane are closely adhered to each other with a peel strength of not less than 0.2 kg f / 25 mm in a wet state to prevent separation of the two membranes when the bipolar membrane is in the wet state is used, such as in water splitting. A bipolar membrane with a low peel strength will allow bubbles or inclusions to form at the interface between the anion-conducting membrane and the cation-conducting membrane during use. Bubbles and inclusions cause a reduction in current efficiency per membrane surface unit and a gradual increase over longer periods of use of the membrane potential. Such Diaphragms must be replaced periodically.

Particular preference is given to using a membrane having the following parameters listed in Table 1:

Table 1

With reference to the following figure and the examples of the subject invention is to be described in more detail, without wishing to limit this to the specific embodiments shown here.

Fig. 1 shows a schematic representation of the structure of a galvanic bath according to the invention and the chemical reaction taking place therein.

2 shows a schematic representation of the structure of a further galvanic bath according to the invention with the chemical reactions taking place therein.

Fig. 1 shows schematically the galvanic bath according to the invention. 1 means the bath, 2 the anodes and 3 the cathode or the workpiece to be coated. Also shown are the anolyte 4 surrounding the anode and the catholyte 5 surrounding the cathode. Anolyte and catholyte are separated from one another by a bipolar membrane 6. In the case of the bath according to the invention, the anode space is preferably made smaller than the cathode space, since the essential processes take place there. In the galvanic bath, the electrochemical processes shown in Table 2 take place:

Table 2

(1) ZrT ⁺ + 2 e ^" - ► Zn (metal deposition at the cathode)

(2) Ni ^{+ "} + 2Θ-fr-Ni (metal deposition at the cathode)

(3) Na '+ e ^' ^ _ ± Na (corresponding reaction of charge carrier transport at the cathode)

(4) Na ⁺ + OH ^'- ^ NaOH (dissociation NaOH in the anolyte)

(5) 4 H ₂ O - ► 4 H ⁺ + 4 OH ^' (water-gap reaction in the intermediate layer of the membrane)

(6) 4 OH ^" - ► 2H ₂ O + O ₂ f (anode reactant)

(7) OH ^" + H ^* ^ p ^ H ₂ O (reaction with protons from water splitting in the catholyte)

(8) OH ^"+ Na + + * ^■ NaOH (dissociation NaOH in Kathodentaum)

(9) 4 H ⁺ + 4 e ^" -► 2 H ₂ (cathode reaction of protons)

(10) amines + Zn ^{+ * •} j- * Zn-Amιnkomplex- compounds (z T anions) amines + Nι ⁺⁺ -i = ^ "Nι-Amιnkomplex Verbιndungen (z T anions)

FIG. 2 shows the galvanic bath from FIG. 1, wherein it additionally has a further electrolyte space between the cathode space and the anode space, which contains a second catholyte 7, which in the present case contains sodium sulfate and sulfuric acid (in each case IM) , wherein the further electrolyte space is separated by an ion exchange membrane 6 from the cathode compartment. By means of this variant according to the invention, the formation of CO ₂ on the bipolar membrane can be prevented. Formed carbon dioxide can push apart the cation and anion membrane of the bipolar membrane at the interface, which can be avoided by the further ion exchange membrane.

example 1

A galvanic bath was prepared for the deposition of zinc-nickel alloys with the following components:

Zinc 10.4 g / L (as soluble ZnO),

Nickel 1.2 g / L (as nickel sulphate),

• NaOH 120 g / L, • tetraethylene pentamine 25 g / L,

Triethanolamine 10 g / L,

• gloss additive 0.1 g / L,

This bath was operated with a bipolar membrane. The bipolar membrane was placed in the bath between anode and cathode. Subsequently, iron sheets (7 × 10 cm), which are usually used for Hull cell tests, were used as workpieces to be coated and coated at a current density of 1 to 2 A / dm ² . The movement of the iron sheets was carried out mechanically at a speed of 1, 4 m / min.

Subsequently, the baths were analyzed and supplemented regularly. The replenishment of the baths was carried out according to the results of the Hull cell tests. One at

Production baths usual carryover of 12 L bath / 10,000 Ah was also taken into account and the bath components supplemented accordingly.

Example 2

A galvanic bath was provided for the deposition of zinc with the following components:

Zinc 16, g / L (as soluble ZnO),

Iron 0.4 g / L (as iron sulphate),

• NaOH 120 g / L,

Triethanolamine 50 g / L,

• Brightener additive 0.1 g / L,

This bath was operated with a bipolar membrane. The bipolar membrane was placed in the bath between anode and cathode. Subsequently, iron sheets (7x10 cm) commonly used for hull cell tests were to be coated

Workpieces used and coated at a current density of 1 to 2 A / dm ² . The movement of the iron sheets was carried out mechanically at a speed of 1.4 m / min.

Subsequently, the baths were analyzed and supplemented regularly. The replenishment of the baths took place according to the results of the Hull cell tests. A carryover of 12 L bath / 10,000 Ah, which was common in production baths, was also taken into account and the bath components were supplemented accordingly.

Claims

claims

1. An alkaline galvanic bath for the deposition of zinc or zinc alloys on substrates containing at least one cathode compartment, each with associated cathode and zinkionenhaltigem Katholy lyte and at least one anode compartment, each with associated anode and anolyte, the cathode compartments of the anode compartments by a

Separator are separated, characterized in that the separator is a bipolar membrane.

2. Galvanic bath according to claim 1, characterized in that the bipolar membrane has at least one cation exchange membrane, at least one Anionenaustauschermembran and arranged between the membranes, the dissociation of water into protons and hydroxide ions catalyzing intermediate layer.

3. Galvanic bath according to claim 2, characterized in that the cation exchange membrane comprises at least one material selected from partially or completely fluorinated polymers with carboxylic acid or sulfonic acid functional groups, copolymers of ethylene with acrylic acid, copolymers of

Ethylene with methacrylic acid, styrene polymers having carboxylic acid functional groups or sulfonic acid functional groups, divinylbenzene polymers having carboxylic acid functional groups or sulfonic acid functional groups, derivatives and mixtures thereof.

4. Galvanic bath according to claim 2 or 3, characterized in that the Anionenaustau- schermerabran comprises at least one material which is selected from polymers with partially or completely fluorinated primary chains (main chains), saturated hydrocarbon - primary chains, partially unsaturated primary chains, aromatic or partially aromatic primary chains or saturated primary chains containing heteroatoms, with functional groups selected from positively charged functionalities, amines and derivatives thereof.

5. Galvanic bath according to claim 2 to 4, characterized in that the Anionenaustau- shear membrane is a polymer of vinylpyridine or

Divinylbenzene containing copolymerized monomers selected from the group consisting of styrene, ethylene, methacrylic acid and / or propylene.

6. Galvanic bath according to one of the preceding claims, characterized in that the bipolar membrane to 50 ⁰ C, in particular 60 ⁰ C is thermally stable.

7. Galvanic bath according to one of the preceding claims, characterized in that the anode consists of nickel or this contains substantially.

8. Galvanic bath according to one of the preceding claims, characterized in that the catholyte further metal salts, in particular of iron, nickel,

Manganese, cobalt and tin, or mixtures thereof.

9. Galvanic bath according to one of the preceding claims, characterized in that the catholyte complexing agents, in particular amines, polyalkylenimines, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids, other chelating ligands, such as acetylacetone, urea, urea derivatives and others

Complex ligands in which the complexing functional group contains nitrogen, phosphorus and sulfur.

10. Galvanic bath according to one of the preceding claims, characterized in that the catholyte contains additives selected from the group consisting of brighteners, wetting agents and mixtures thereof.

11. Galvanic bath according to one of the preceding claims, characterized in that the catholyte has the following composition: 80-250 g / l sodium or potassium hydroxide,

4-20 g / l zinc in the form of a soluble zinc salt,

0.02-20 g / l nickel, iron, kobble, tin in the form of a soluble metal salt as alloying metal,

1-200 g / l complexing agent selected from the group consisting of polyalkenylamines, alkanolamines, polyhydroxycarboxylates and mixtures thereof and 0.1-5 g / l of aromatic and / or heteroaromatic

Brilliant.

12. Galvanic bath after one of the previous ones

Claims, characterized in that the anolyte

50 to 200 g / l NaOH and 800 to 950 g / l water.

13. Galvanic bath according to one of the preceding claims, characterized in that the galvanic bath has a further electrolyte space which is separated by the bipolar membrane from the anode space and by an ion exchange membrane from the cathode space and a second catholyte.

14. Galvanic bath according to 13, characterized in that the Ionenaustau- shear membrane is an anion exchange membrane.

15. Galvanic bath according to one of claims 13 or 14, characterized in that the second catholyte has a pH in the range of 1 to 7.

16. Galvanic bath according to one of claims 13 to 15, characterized in that the second catholyte sulfuric acid or sulfuric acid and sodium sulfate and / or carboxylic acid and / or salts thereof.

17. A process for the electrodeposition of zinc or zinc alloys on substrates, in which the substrate is introduced into a galvanic bath according to one of the preceding claims and galvanically deposited on the substrate zinc or zinc alloys.

18. The method according to claim 17, characterized in that the deposition takes place at a temperature of 20 to 40 ⁰ C, in particular at 25 ⁰ C.

19. The method according to any one of claims 17 or 18, characterized in that the deposition takes place at a current density of 0.4 to 5 A / dm ² , in particular from 0.5 to 3 A / dm ² .

20. Use of a bipolar membrane for the separation of anode space and cathode space in a galvanic bath.

21. Use of a bipolar membrane to prevent the anodic decomposition of organic components of the electrolyte in a galvanic bath.

22. Use according to any one of claims 20 or 21, characterized in that the bipolar membrane has at least one cation exchange membrane, at least one anion exchange membrane and an interposed between the membranes, the dissociation of water into protons and hydroxide ions catalyzing intermediate layer.