Method for depositing zinc-nickel alloy on substrate, aqueous zinc-nickel deposition bath, brightener and use thereof

Abstract

The invention relates to a method for depositing a zinc-nickel alloy on a substrate, in particular to a method for electrolytically depositing a zinc-nickel alloy on a substrate, in which a zinc-nickel deposition bath is used as a catholyte comprising at least one brightener, wherein the at least one brightener has a source substantially free of halogen anions, preferably free of halogen anions. The invention further relates to a corresponding aqueous zinc-nickel deposition bath, to a corresponding brightener and to a corresponding use of the brightener for supplementation in an aqueous zinc-nickel deposition bath.

Description

Technical Field

[0001] The present invention relates to a method for depositing a zinc-nickel alloy on a substrate, in particular to a method for electrolytically depositing a zinc-nickel alloy on a substrate, wherein a zinc-nickel deposition bath is used as a cathode electrolyte comprising at least one brightener, wherein the at least one brightener has a source that is substantially free of halogen anions, preferably free of halogen anions. Furthermore, the present invention relates to a corresponding aqueous zinc-nickel deposition bath, a corresponding brightener and a corresponding use of the brightener for replenishing in an aqueous zinc-nickel deposition bath. Background Art

[0002] The deposition of metal alloys (sometimes also referred to as coatings or protective coatings) on other metals or metal-coated plastics (commonly referred to as substrates) is a well-established technique for improving the corrosion resistance of said substrates. Deposition is usually carried out electrolytically in a corresponding electrolyte (commonly referred to as a deposition or plating bath) using an anode and the substrate as cathode. A well-known example is the electroplating of metal substrates with zinc-nickel alloys.

[0003] There are many advantages to separating the electrolyte into a cathode electrolyte (which is the electrolyte in the corresponding cathode compartment) and an anolyte (which is the electrolyte in the corresponding anode compartment) by means of a separator (e.g., a semipermeable membrane). The anolyte is usually different from the cathode electrolyte. By applying an electric potential, an electric current flows through the anolyte through the separator to the cathode electrolyte to electrolytically deposit a metal alloy on a substrate.

[0004] US 2011 / 031127 A1 discloses an alkaline electroplating bath for electroplating zinc-nickel coatings, which has an anode and a cathode, wherein the anode is separated from the alkaline electrolyte by an ion exchange membrane.

[0005] WO 2021 / 123129 A1 discloses a method for depositing a zinc-nickel alloy on a substrate, wherein a deposition bath comprising at least one nickel ion complexing agent is used, wherein the nickel ions have a source that is substantially free of complexing agent, preferably free of complexing agent.

[0006] In fact, such methods are extremely efficient and provide excellent corrosion protection.

[0007] Typically, zinc-nickel deposition baths are often used continuously for extended periods of time, such as a month or even years. It is generally known that high throughput requires continuous replenishment of zinc and nickel ions and organic compounds, such as complexing agents and brighteners. A certain amount thereof is only incorporated into the zinc alloy layer, in particular zinc ions, nickel ions and brighteners. Another amount is usually lost via drag-out losses. Another part is decomposed, for example, at the anode, and is still present in decomposed form. In general, decomposition is usually negligible, because drag-out losses not only reduce the concentration of desired compounds but also reduce the concentration of undesired decomposition products. Therefore, only the desired compounds are replenished.

[0008] However, in fact, such prior art methods also generate large amounts of wastewater, which is usually mixed with nickel ions, zinc ions, complexing agents, brighteners (all of which do not need to be discarded) and decomposition products of at least some of the foregoing (which need to be removed from the process). As environmental needs, sustainability and wastewater needs are increasingly important topics, there is a continuous need to provide methods that are more environmentally friendly, more sustainable and, in particular, more careful in treating water resources.

[0009] WO 2021 / 123129 A1 therefore proposes a method for avoiding or at least substantially reducing wastewater and wastewater pollution by providing a zinc-nickel deposition loop in a loop. However, if the wastewater is continuously recirculated in the loop, such a loop shows a great influence on the concentration levels of the compounds involved (e.g., complexing agent, nickel and zinc ions, respectively). Generally, further insight into such new developments is needed, which often requires long-term observations to identify unexpected and unpredictable effects. Since no significant loss of effluent occurs in such methods, decomposition products and undesirable compounds begin to accumulate. In fact, this phenomenon must be prevented from occurring. Very often, no research to date has made it possible to identify under what circumstances the substances become harmful and how to remove the substances or avoid the occurrence of the substances.

[0010] Objectives of the invention

[0011] It is therefore an object of the present invention to provide a further improved method for depositing a zinc-nickel alloy on a substrate, in particular a corresponding method carried out in a circuit with a high level of recycled matter, i.e. in particular wastewater recycling. It is an object of the present invention in particular to provide a corresponding method having increased sustainability by further increasing the operating time without compromising the deposition quality, the corrosion resistance of the electroplated substrate and maintaining a stable deposition environment over a longer operating time, including a further increased service life of the corresponding deposition bath and avoiding damage to the corresponding electroplating equipment. Summary of the invention

[0012] The above mentioned object is solved by a method for depositing a zinc-nickel alloy on a substrate, said method comprising the following steps:

[0013] (a) providing the substrate,

[0014] (a-1) optionally, pre-rinsing the substrate with water in a pre-rinsing chamber so as to obtain a pre-rinsed substrate and pre-rinsing water,

[0015] (b) providing an aqueous zinc nickel deposition bath as a cathode electrolyte in a deposition chamber, wherein

[0016] - the deposition chamber comprises at least one anode having an anolyte, and

[0017] - the anolyte is separated from the catholyte by at least one membrane, and

[0018] The cathode electrolyte comprises

[0019] (i) nickel ions,

[0020] (ii) at least one brightener, and

[0021] (iii) zinc ions,

[0022] (c) contacting the substrate or the pre-rinsed substrate with the cathode electrolyte in the deposition chamber so that the zinc-nickel alloy is electrolytically deposited on the substrate and thereby obtaining a zinc-nickel coated substrate, wherein

[0023] the at least one brightener has a lower concentration after step (c) than before step (c),

[0024] It is characterized in that the method comprises the steps of:

[0025] (d) adding directly or indirectly to the cathode electrolyte a brightener source, the source being substantially free of halogen anions, preferably comprising no halogen anions.

[0026] Personal long-term observations have shown that the method for depositing zinc-nickel alloys, including improved sustainability, preferably by means of a loop or most preferably a closed loop, is relatively sensitive to even small amounts of halogen ions, most preferably chloride ions. Although it is believed that relatively small amounts of chloride ions can be removed together with, for example, sulfate ions in the precipitation step disclosed in WO 2021 / 123129 A1, these own experiments have now shown that even with a nickel ion source and a zinc ion source that do not contain chloride ions, even small amounts of halogen anions are undesirable. These personal observations have revealed that a significant contributor to undesirable halogen contaminants, in particular chloride ion contaminants, is brighteners; directly in the form of their opposite anions or indirectly in a form that is not fully purified after synthesis. Because brighteners are constantly consumed during the deposition process, their typical counterions, such as halogen anions, in particular chloride ions, begin to accumulate. Although such accumulation occurs at relatively low concentration levels, it is unexpectedly noted that even such low concentration levels can have undesirable effects on equipment components over time. In particular, it has been observed that, due to the anodic formation of hypochlorite ions, undesirable corrosion can sometimes occur, for example at plant parts comprising stainless steel and / or at the at least one membrane. Relatively high chloride ion concentrations sometimes also show undesirable effects on the stability of at least one membrane separating the anolyte and the catholyte.

[0027] The method of the invention solves the objectives defined above and allows a circuit (also named "operation in a circuit"), most preferably even a closed circuit (which is most preferred in the context of the invention), to be operated for a sustained or even increased (i.e. extended) time. Personal experiments have shown that by carrying out the method of the invention and by making the brightener source substantially free of halogen anions, most preferably at least free of chloride ions, said corrosion and / or gas formation is greatly reduced or even completely avoided. Furthermore, the method of the invention allows, for example, sulfate ions to be precipitated independently of the halogen ion concentration.

[0028] Furthermore, the process according to the invention does not impair the excellent corrosion resistance of the zinc-nickel electroplated substrate. Furthermore, due to the at least one membrane, the process according to the invention prevents the formation of harmful cyanide and oxalate anions. This greatly reduces the effort for wastewater treatment and is an important prerequisite for the operation of a circuit, preferably a closed circuit. DETAILED DESCRIPTION

[0029] In the context of the present invention, the terms "at least one", "one or more than one" and / or "one or more" mean (and are interchangeable with): "one, two, three or more than three".

[0030] Furthermore, in the context of the present invention, the zinc-nickel alloy deposited on the substrate is preferably a zinc-nickel alloy layer. It is preferably also referred to as a zinc-nickel electroplated layer. Therefore, the method of the present invention is preferably an electroplating method. This means that an electric current is preferably applied in step (c).

[0031] Also in the context of the present invention, "brightener source" includes the brightener itself, its possible counterions as well as the remainder of the educt compounds and synthesis products (eg leaving groups).

[0032] Step (a): Providing a substrate:

[0033] In step (a) a substrate is provided.

[0034] The method of the present invention is preferred wherein the substrate is a metal substrate, which preferably comprises iron, more preferably the substrate is an iron substrate, most preferably a steel substrate.

[0035] The method of the present invention is preferred wherein the substrate comprises a substrate for:

[0036] Barrel application,

[0037] It is preferably a fastener, most preferably comprising at least a screw, a nut, a bolt and a washer,

[0038] and / or

[0039] Rack-application

[0040] It preferably comprises fittings, flat, L-shaped or U-shaped sections and / or pipes, most preferably locker components, window fittings, door brackets and furniture fittings and / or pressure pipes, preferably brake pipes and / or fuel pipes.

[0041] Preferably, the substrate does not comprise or is cast iron. However, in some rare cases, the method of the present invention is preferred, wherein the substrate does comprise or is cast iron.

[0042] Step (a-1): Pre-rinsing:

[0043] In step (a-1), the substrate is optionally pre-rinsed with water in a pre-rinsing chamber so that a pre-rinsed substrate and pre-rinsing water are obtained. Such pre-rinsing is preferred. This step is preferably performed after step (a) and before step (c).

[0044] By pre-rinsing the substrate in the pre-rinsing chamber, potential contaminants and / or impurities on the substrate are removed before transferring the substrate to the deposition chamber. Preferably, the pre-rinsing is performed in the pre-rinsing chamber with the aid of a pre-rinsing solution. Preferably, the pre-rinsing solution is an aqueous solution and preferably comprises a hydroxide, preferably a metal hydroxide, even more preferably an alkali metal hydroxide, most preferably sodium hydroxide. The pre-rinsing solution is preferably alkaline. Most preferably, the pre-rinsing solution is substantially free of organic solvents, preferably contains no organic solvents. Most preferably, the only solvent is water.

[0045] The process of the present invention is preferred wherein the pre-rinse water is at least partly recirculated and reused, most preferably reused in the process of the present invention.

[0046] Step (b): Providing an aqueous zinc-nickel deposition bath:

[0047] In step (b), an aqueous zinc-nickel deposition bath is provided in the deposition chamber as a cathode electrolyte. Therefore, the aqueous zinc-nickel deposition bath utilized in the method of the present invention is a cathode electrolyte. Therefore, hereinafter, the features regarding the aqueous zinc-nickel deposition bath preferably also apply to the cathode electrolyte.

[0048] The method of the present invention is preferred, wherein the aqueous zinc-nickel deposition bath comprises more than 50 vol.-% water, more preferably 75 vol.-% or more, even more preferably 85 vol.-% or more, most preferably 92 vol.-% or more, based on the total volume of the aqueous zinc-nickel deposition bath. Preferably, water is the only solvent in the aqueous zinc-nickel deposition bath. Preferably, the aqueous zinc-nickel deposition bath is substantially free of organic solvents, preferably contains no organic solvents.

[0049] The process of the present invention is preferred wherein the aqueous zinc nickel deposition bath is alkaline, preferably having a pH in the range of 10 to 14, more preferably 11 to 13.3, even more preferably 11.5 to 13, yet even more preferably 12 to 12.9, most preferably 12.3 to 12.8. In general, a pH in the range of 12 to 14, preferably 12.3 to 13.5 is preferred.

[0050] The aqueous zinc-nickel deposition bath comprises (i) nickel ions. The method of the present invention is preferred wherein the total concentration of nickel ions in the aqueous zinc-nickel deposition bath is less than 3 g / L, preferably 2.5 g / L or less, more preferably 2 g / L or less (in each case exceeding 0 g / L; i.e. excluding 0 g / L), based on the total volume of the aqueous zinc-nickel deposition bath.

[0051] Typically, it is preferred that the total concentration of nickel ions is in the range of 0.2 g / L to 2.8 g / L, preferably 0.4 g / L to 2.6 g / L, more preferably 0.5 g / L to 2.5 g / L, most preferably 0.6 g / L to 2.3 g / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0052] More preferably, the total concentration of nickel ions is in the range of 0.4 g / L to 1.9 g / L, preferably 0.6 g / L to 1.7 g / L, more preferably 0.7 g / L to 1.6 g / L, even more preferably 0.8 g / L to 1.5 g / L, most preferably 0.9 g / L to 1.4 g / L. This is most preferred for barrel applications. However, for rack applications, the preferred total concentration is in the range of 0.4 g / L to 2 g / L, more preferably 0.5 g / L to 1 g / L, most preferably 0.5 g / L to 0.8 g / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0053] The aqueous zinc-nickel deposition bath comprises (iii) zinc ions. The method of the present invention is preferred wherein the total concentration of zinc ions in the aqueous zinc-nickel deposition bath is less than 11 g / L, preferably 10 g / L or less, most preferably 9 g / L or less, based on the total volume of the aqueous zinc-nickel deposition bath.

[0054] Preferably, the total concentration of zinc ions is in the range of 5 g / L to 9 g / L, more preferably 5.2 g / L to 8.5 g / L, even more preferably 5.4 g / L to 8 g / L, yet even more preferably 5.7 g / L to 7.5 g / L, most preferably 5.9 g / L to 7.3 g / L.

[0055] It is generally preferred that the zinc ions have a total concentration in the range of 6 g / L to 9 g / L.

[0056] The method of the present invention is preferred, wherein a source of zinc ions is added directly or indirectly to the aqueous zinc-nickel deposition bath, preferably indirectly via a mixing unit. The mixing unit preferably comprises a separate volume of a (preferably utilized) aqueous zinc-nickel deposition bath. More preferably, the zinc ions are obtained by dissolving metallic zinc in sodium hydroxide to obtain a zinc hydroxide complex, which allows efficient stabilization of the zinc ions in the aqueous zinc-nickel deposition bath. This is preferably applicable as long as the method of the present invention is carried out. Therefore, it is most preferably carried out for replenishing zinc ions. Preferably, nickel ions are also replenished by indirectly adding a source of nickel ions via a mixing unit, so as to prepare a well-mixed composition, which is then transferred to the cathode electrolyte and the aqueous zinc-nickel deposition bath, respectively.

[0057] The mixing unit is preferably a separate pre-treatment chamber, most preferably fluidly connected to the deposition chamber. It most preferably provides homogenization and pre-dissolution respectively by intensive mixing.

[0058] Most preferably, nickel ions are replenished with the aid of a nickel ion source comprising an inorganic nickel salt, more preferably nickel sulfate, most preferably nickel sulfate hexahydrate, even more preferably without additional (preferably organic) nickel ion complexing agents (see also below).

[0059] The method of the present invention is preferred, wherein the nickel ion source does not contain nitrate ions. This most preferably means that the nickel salt or source does not contain nitrate ions. By excluding nitrate ions, the concentration of nitrate ions in the cathode electrolyte is lower or even completely avoided. In many cases, nitrate interferes with the entire electrolytic deposition and is highly undesirable. In addition, the nickel ion source does not contain halogen anions, specifically no chloride ions.

[0060] The method of the present invention is preferred, wherein the nickel ion source does not contain an organic amine, preferably does not contain any amine. This most preferably means that the nickel salt or source does not contain an organic amine. Amines are typical nickel ion complexing agents (about nickel ion complexing agents, see below). Therefore, preferably, the nickel ion source is substantially free of nickel ion complexing agents, preferably does not contain nickel ion complexing agents. Therefore, it is preferred to monitor and control the nickel ion complexing agent independently of the nickel ion source. This is most preferably in the loop and closed loop, respectively.

[0061] Most preferably is the process of the present invention, wherein the nickel ions of the nickel ion source added to the cathode electrolyte to replenish the nickel ions are not complexed before contact with an alkaline environment, preferably an environment having the following pH: in the range of 10 to 14, more preferably 11 to 13.3, even more preferably 11.5 to 13, even more preferably 12 to 12.9, most preferably 12.3 to 12.8; or in the range of 12 to 14, preferably 12.5 to 13.5. Preferably, the nickel ions of the nickel ion source added to the cathode electrolyte are preferably complexed for the first time when contacting with an alkaline environment, preferably an environment having a pH as defined above, which environment is most preferably the cathode electrolyte.

[0062] The process of the present invention is preferred wherein the source of nickel ions is an aqueous solution comprising water and a nickel salt dissolved therein, preferably a preferred nickel salt as defined above.

[0063] Advantageously, in the process of the invention, the total concentration of nickel and zinc ions as defined above is generally lower than the concentrations generally known and used in the zinc-nickel deposition technology. Since nickel and zinc ions are preferably recycled in the process of the invention (i.e. indirectly by means of recycled water such as rinse water), no significant amount of nickel and zinc ions, respectively, is wasted, thereby resulting in a lower overall total concentration of the aqueous zinc-nickel deposition bath. Therefore, preferred is the process of the invention, wherein at least a portion of the nickel ions and zinc ions circulates in a loop, wherein the loop comprises a rinse step. More preferred is the process of the invention, wherein at least a portion of the nickel ions, zinc ions, at least one brightener and a complexing agent circulates in a loop, wherein the loop comprises a rinse step.

[0064] At least one brightener:

[0065] In the process of the present invention, the aqueous zinc nickel deposition bath comprises at least one brightener. Preferably at least one brightener is required to provide sufficient brightness and gloss and to further improve the electrolytic deposition in step (c). Thus, it primarily contributes to an improved optical appearance.

[0066] It is generally preferred that the process of the present invention wherein the total concentration of at least one brightener in the aqueous zinc-nickel deposition bath is in the range of 5 mg / L to 1200 mg / L, preferably in the range of 10 mg / L to 1000 mg / L, more preferably in the range of 20 mg / L to 800 mg / L, even more preferably in the range of 30 mg / L to 600 mg / L, most preferably in the range of 40 mg / L to 450 mg / L, even most preferably in the range of 45 mg / L to 400 mg / L, based on the total volume of the aqueous zinc-nickel deposition bath. This is most preferably applicable to both barrel as well as rack applications.

[0067] In some cases, the method of the present invention is preferred, wherein the total concentration of at least one brightener in the aqueous zinc-nickel deposition bath is in the range of 20 mg / L to 650 mg / L, preferably in the range of 50 mg / L to 600 mg / L, more preferably in the range of 100 mg / L to 550 mg / L, most preferably in the range of 150 mg / L to 500 mg / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0068] However, in some cases, the method of the present invention is preferred, wherein the total concentration of at least one brightener in the aqueous zinc-nickel deposition bath is in the range of 700 mg / L to 1200 mg / L, preferably in the range of 750 mg / L to 1100 mg / L, more preferably in the range of 800 mg / L to 1000 mg / L, most preferably in the range of 850 mg / L to 950 mg / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0069] Preferred is the process of the present invention, wherein each of the at least one brightener comprises 4 to 25 carbon atoms, preferably 5 to 20 carbon atoms, more preferably 6 to 18 carbon atoms, even more preferably 7 to 15 carbon atoms, most preferably 8 to 13 carbon atoms. In some cases, 10 to 14 carbon atoms are highly preferred.

[0070] Preferably, the method of the present invention, wherein the brightener source comprises a cationic brightener having a counter anion, a nonionic brightener and / or an internal salt brightener. Preferably, the internal salt brightener is a betaine brightener.

[0071] More preferred is the method of the present invention, wherein the at least one brightener is a compound (preferably one or more than one compound) selected from the group consisting of:

[0072] - an N-heteroaromatic compound, which is preferably an N-heteroaromatic compound comprising at least one pyridine moiety or at least one pyridinium moiety;

[0073] - an aldehyde, which is preferably an aldehyde comprising at least one aromatic ring;

[0074] - a ketone, which is preferably a ketone comprising at least one aromatic ring; and

[0075] -sulfonic acid, which additionally comprises a sulfhydryl group, a disulfide moiety and / or a thioether moiety.

[0076] Preferred is the process of the present invention, wherein the N-heteroaromatic compound (preferably as described above, or as described as preferred throughout this text) further comprises a benzyl group. Most preferably, the at least one brightener comprises at least one of said compounds (preferably as defined as preferred throughout this text).

[0077] Preference is given to the process according to the invention, wherein the N-heteroaromatic compound (preferably as described above as preferred) additionally (i.e. in addition to the N-heteroatom or preferably in addition to the benzyl group as defined above) comprises an amide group, a carboxylic acid group, a sulfonic acid group and / or an ester thereof. The amide group is preferably a carboxamide group.

[0078] Preferred is the process of the present invention, wherein the N-heteroaromatic compound comprising at least one pyridinium moiety is selected from the group consisting of substituted pyridinium sulfonobetaines, unsubstituted pyridinium sulfonobetaines, substituted pyridinium carboxylates, unsubstituted pyridinium carboxylates, substituted pyridinium carboxamides and unsubstituted pyridinium carboxamides.

[0079] Preferred substituted and unsubstituted pyridinium sulfobetaines include substituted and unsubstituted pyridinium alkyl sulfobetaines.Preferred unsubstituted pyridinium alkyl sulfobetaines are pyridinium propyl sulfobetaine (PPS).

[0080] Highly preferred is the method of the present invention, wherein the N-heteroaromatic compound comprising at least one pyridinium moiety is selected from the group consisting of: N-benzylnicotinic acid and its esters, N-benzylnicotinamide, N-benzylpyridinium, N-benzylpyridinium sulfonic acid and its esters, N-alkylnicotinic acid and its esters and N-alkylnicotinamide. The carboxylic acid group, amide group and sulfonic acid group are preferably located in the ortho position, meta position or para position of the pyridinium ring, respectively, and most preferably in the meta position. The benzyl group is attached to the ring nitrogen forming a quaternary ring nitrogen atom having a positive charge. In some cases, most preferred is the method of the present invention, wherein at least one brightener comprises N-alkylnicotinic acid and its esters and / or N-alkylnicotinamide. Highly preferred N-alkylnicotinic acid comprises 1-methylnicotinic acid (i.e., N-methylnicotinic acid), preferably including salts, esters and amides thereof.

[0081] In some cases, the method of the present invention is preferred, wherein the N-heteroaromatic compound comprising a pyridine moiety is selected from the group consisting of benzylpyridine, nicotinic acid and its esters, benzylnicotinic acid and its esters, and benzylnicotinamide. In these cases, the benzyl group is not attached to the ring nitrogen atom. Therefore, the ring nitrogen preferably does not form a positive charge.

[0082] Preferred is the process of the present invention, wherein the at least one brightener comprises at least N-benzylnicotinic acid, its esters, N-benzylnicotinamide, N-alkylnicotinic acid, its esters and / or N-alkylnicotinamide.

[0083] Very preferably the process of the present invention, wherein at least one brightener, most preferably a brightener source, comprises (preferably consists of) a compound of formula (Ia) and / or an ester thereof, preferably a compound of formula (Ib) and / or an ester thereof,

[0084]

[0085] in

[0086] R 1 represents a C1 to C4 alkyl group, an unsubstituted phenylalkylene group or a substituted phenylalkylene group,

[0087] R 2 Indicates OH, OZ, OR 3 , NH2 or NR 3 R 4 ,in

[0088] Z represents an alkali metal cation, an ammonium cation or an alkylammonium cation; preferably a sodium cation, a potassium cation, an ammonium cation or a tetraalkylammonium cation;

[0089] R 3 independently represent an alkyl group; preferably a C1 to C4 alkyl group; and

[0090] R 4 independently represent hydrogen or alkyl; preferably hydrogen or C1 to C4 alkyl, and

[0091] X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, methanesulfonate, toluenesulfonate, triflate, carbonate and sulfonate.

[0092] In the context of the present invention, in R 2 In "OZ", "Z" represents a moiety that preferably compensates for the negative charge of the carboxylic acid group. Preferably, OZ comprises ONa and / or OK, wherein "Na" represents sodium and "K" represents potassium.

[0093] Preferably, in the “NR 3 R 4 In the 3 and R 4 are the same or different, preferably the same, that is, both are alkyl groups, preferably both are C1 to C4 alkyl groups.

[0094] In some cases, R 1 Preferably represents a substituted phenylalkylene. This preferably means that the phenyl moiety comprises one or more than one substituent. Preferably, the one or more than one substituent is independently selected from the group consisting of carboxyl, hydroxyl, sulfonate, amino, C1 to C4 alkyl, C1 to C4 alkoxy, halogen, carbamoyl, cyano, ester and salts thereof.

[0095] In the compound of formula (Ia), -C(O)R 2 The compound of formula (Ib) is a compound of formula (Ia), wherein -C(O)R 2 Some are in the interposition.

[0096] Preferably, the method of the present invention is carried out in which R 1 In the above, C1 to C4 alkyl (also preferably, one or more substituents in the substituted phenylalkylene as defined above) individually include methyl, ethyl, n-propyl, isopropyl, n-butyl or isopropyl; preferably methyl, ethyl or isobutyl, most preferably methyl. These preferred alkyl moieties also apply to R 3 and R 4 Preferably the C1 to C4 alkyl moiety.

[0097] Preferably, the method of the present invention is carried out in which R 1 In the phenylalkylene group, the phenylalkylene group includes a benzyl group.

[0098] Preferably, the process of the present invention is carried out in which R 2 It represents ONa, OK (ie, M represents a sodium or potassium cation) or NH2, preferably ONa (ie, M represents a sodium cation) or NH2.

[0099] Preferred is the process of the invention wherein X comprises sulfate and / or methylsulfate.

[0100] In X, the sulfonate group preferably comprises a sulfonate group (SO3 2- ), methanesulfonate, methanedisulfonate and / or methanetrisulfonate. Most preferably, the process of the invention is one in which X comprises sulfate, methylsulfate and / or methanesulfonate, if R 1 Containing a benzyl group is most preferred.

[0101] Even more preferred is the process of the present invention, wherein at least one brightener, most preferably the brightener source comprises a compound selected from the group consisting of compounds (A) to (D)

[0102]

[0103] and esters thereof, wherein

[0104] X individually represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate and sulfonate; preferably selected from the group consisting of sulfate and methylsulfate.

[0105] With regard to X, most preferably all of the foregoing also applies individually to the compounds of the formulae (A), (B), (C) and (D).

[0106] Preferred is the process of the present invention, wherein the aldehyde comprising at least one aromatic ring comprises an alkoxylated benzaldehyde, more preferably vanillin, piperonal and / or anisaldehyde.

[0107] Preferred is the process of the present invention, wherein the ketone comprising at least one aromatic ring comprises benzylidene acetone and / or naphthyl methyl ketone.

[0108] Preferred is the process of the present invention wherein the aqueous zinc nickel deposition bath is substantially free of propane sultone, preferably comprises no propane sultone, more preferably substantially free of any sultones, preferably comprises no sultones.

[0109] Nickel ion complexing agent:

[0110] Preferred is the process of the invention wherein the aqueous zinc nickel deposition bath further comprises one or more than one, preferably one, nickel ion complexing agent. A complexing agent is required to keep the nickel ions in solution despite the alkaline pH environment. The use of only one complexing agent is preferred because its total concentration can be better monitored and controlled. This is most preferred in a loop, preferably a closed loop. However, although only one is preferred, this does not necessarily exclude the use of more than one complexing agent, which is essentially possible.

[0111] The method of the present invention is preferred, wherein the one or more than one nickel ion complexing agent comprises a chelating complexing agent, wherein preferably the chelating complexing agent is the only nickel ion complexing agent in the aqueous zinc-nickel deposition bath. By using a chelating complexing agent, an even more efficient stabilization of the nickel ions in the aqueous zinc-nickel deposition bath is ensured. Most preferably, the one or more than one nickel ion complexing agent is provided only once when the aqueous zinc-nickel deposition bath is initially set up, and when the method of the present invention is carried out, generally preferably no additional complexing agent (neither a complexing agent of the same type nor a different complexing agent) is subsequently added.

[0112] The process of the present invention is preferred wherein the one or more than one nickel ion complexing agent comprises an amine, preferably a diamine, more preferably an oligoamine, even more preferably a pentamine, most preferably the aqueous zinc nickel deposition bath comprises tetraethylenepentamine (even most preferably comprises only tetraethylenepentamine as nickel ion complexing agent).

[0113] The process of the present invention is preferred wherein the aforementioned amines, including the preferred amines, are the sole nickel ion complexing agent in the aqueous zinc nickel deposition bath.

[0114] Preferably the diamine comprises ethylenediamine.

[0115] Preferably the oligomeric amine comprises diethylenetriamine, triethylenetetramine and / or tetraethylenepentamine. In some cases, the process of the present invention is preferred wherein the aqueous zinc-nickel deposition bath comprises one or more of the aforementioned amines other than tetraethylenepentamine. However, in other cases, the process of the present invention is preferred wherein the aqueous zinc-nickel deposition bath comprises one or more of the aforementioned amines in addition to tetraethylenepentamine.

[0116] In general, the process of the present invention is preferred wherein in the aqueous zinc nickel deposition bath, the one or more nickel ion complexing agents comprise an amine having one or more than one, preferably two, primary amine groups and one or more than one secondary amine groups.

[0117] The process of the present invention is preferred wherein an amine having one or more than one, preferably two, primary amine groups and one or more than one secondary amine groups is the sole nickel ion complexing agent in the aqueous zinc nickel deposition bath.

[0118] Furthermore, the method of the present invention is preferred wherein the aqueous zinc-nickel deposition bath contains only an initial concentration of one or more nickel ion complexing agents for at least one nickel ion turnover, more preferably for at least 2 nickel ion turnovers, even more preferably for at least 3 nickel ion turnovers, most preferably for multiple nickel ion turnovers, and even most preferably for the entire useful life of the aqueous zinc-nickel deposition bath used as a cathode electrolyte.

[0119] The process of the present invention is preferred, wherein in the aqueous zinc-nickel deposition bath, the zinc ions do not form complexes with one or more than one nickel ion complexing agents, preferably do not form complexes with amines, more preferably do not form complexes with diamines, even more preferably do not form complexes with organic complexing agents. Most preferably, the zinc ions in the aqueous zinc-nickel deposition bath are strongly stabilized as hydroxide complexes, so that no complex formation of zinc ions with one or more than one nickel ion complexing agents is observed under alkaline conditions.

[0120] Anolyte:

[0121] The deposition chamber also comprises an anolyte. In the context of the present invention, the anolyte is typically an electrolyte in direct contact with at least one anode, wherein the catholyte is an aqueous zinc nickel deposition bath in direct contact at least partially with the cathode (i.e. with the substrate), preferably at least for the time the substrate is in the deposition chamber.

[0122] The process of the present invention is preferred, wherein the anolyte is aqueous, preferably comprising water and sulphuric acid, most preferably comprising water and 5 to 40 vol.-% sulphuric acid, based on the total volume of the anolyte.

[0123] At least one anode:

[0124] The method of the present invention is preferred wherein in the deposition chamber at least one anode is an insoluble anode, preferably an insoluble mixed metal oxide anode, more preferably an insoluble iridium oxide and / or tantalum oxide anode, most preferably an insoluble iridium oxide / tantalum oxide on a titanium anode.

[0125] At least one membrane:

[0126] In the deposition chamber, there is at least one anode and at least one membrane, wherein at least one membrane separates the anolyte from the cathode electrolyte. Most preferably, at least one membrane is a semipermeable membrane. This means that at least one membrane is selectively permeable. The method of the present invention is preferred, wherein at least one membrane is a cation permeable membrane.

[0127] The at least one membrane most preferably only allows diffusion of protons between the anolyte and the catholyte, which ensures efficient distribution of charge between the anolyte and the catholyte.

[0128] The process of the present invention is more preferred, wherein at least one membrane comprises a fluorinated polymer, preferably polytetrafluoroethylene (PTFE) and / or (preferably or) perfluorosulfonic acid (PFSA).

[0129] In general, at least one membrane is not particularly limited in the context of the present invention, preferably as long as sufficient separation is provided between the anolyte and the cathode electrolyte. Therefore, it is preferred that the method of the present invention, wherein the anolyte is separated from the cathode electrolyte by at least one separator, the separator being most preferably a membrane. In other cases, ceramics are preferred as separators. Therefore, throughout this article, the features of at least one membrane preferably also apply to at least one separator after making necessary modifications.

[0130] The method of the present invention is preferred, wherein the distance from at least one anode to at least one membrane is in the range of 0.5 mm to 5.0 mm, preferably 0.75 mm to 4 mm, more preferably 1.0 mm to 3.0 mm. This advantageously allows the volume of the anolyte to be kept low, which in turn results in a low amount of waste water from the anolyte.

[0131] The main advantage of the method of the present invention is that, due to at least one membrane separating the anolyte from the cathode electrolyte, degradation products are not formed anodically. This means that neither the one or more complexing agents nor the at least one brightener are in direct contact with the at least one anode, since the former two are restricted by the cathode electrolyte. The permeation of ions between the cathode electrolyte and the anode electrolyte is only possible through the at least one membrane. This is an essential requirement for carrying out the method of the present invention in a loop, most preferably in a closed loop, which most preferably continuously recirculates the initial concentration of the one or more nickel ion complexing agents. Most preferably, at least one membrane substantially allows only hydrogen ions (formed in the anode electrolyte) to permeate into the cathode electrolyte.

[0132] Thus, it is preferred that the method of the present invention is one in which the one or more nickel ion complexing agents are not in contact with at least one anode, most preferably not in contact with any of the at least one anode. Thus, if the nickel ion source is carefully controlled, the concentration of the one or more complexing agents is preferably constant in the cathode electrolyte, and no further complexing agents are added in an uncontrolled manner. Instead, it is preferred that only an initial concentration of the one or more nickel ion complexing agents is provided when setting up the aqueous zinc-nickel deposition bath, preferably the cathode electrolyte, wherein no additional complexing agent has to be added during the performance of the method of the present invention.

[0133] Preferred is the process of the present invention wherein the at least one brightener is not in contact with the at least one anode, most preferably is not in contact with any of the at least one anode.

[0134] Most preferably, none of the organic compounds contained in the aqueous zinc nickel deposition bath (ie in the cathode electrolyte) is in contact with the at least one anode, most preferably not in contact with any of the at least one anode.

[0135] Furthermore, preferably, no cyanide and oxalate anions are formed anodically as a result of the separation.

[0136] Step (c): contacting the substrate with an aqueous zinc-nickel deposition bath (i.e., catholyte):

[0137] In step (c) of the process of the present invention, the substrate or the pre-rinsed substrate, if pre-rinsed, is contacted with a catholyte in a deposition chamber such that the zinc-nickel alloy is electrolytically deposited onto the substrate and a zinc-nickel coated substrate is thereby obtained.

[0138] During step (c), at least one brightener present in the cathode electrolyte is usually partially consumed. Therefore, after step (c) or after a step (c) (meaning repeating the method of the present invention), at least one brightener has a lower concentration than before step (c) or the corresponding previous step (c). In other words, after step (c), preferably after each step (c), at least one brightener has a total concentration lower than the total concentration before step (c). To a certain extent, this is acceptable and normal. This also means not replenishing at least one brightener after each step (c). In other words, at least one brightener preferably has a total concentration within a concentration range, wherein the concentration range has a lower limit, which is preferably not lower than the bottom limit (undercut) during the method of the present invention.

[0139] Preferred is the process of the present invention, wherein in step (c), the temperature of the cathode electrolyte is in the range of 10°C to 50°C, preferably 15°C to 45°C, more preferably 17°C to 40°C, most preferably 20°C to 35°C, even most preferably 22°C to 30°C.

[0140] Preferably, the process according to the invention is carried out in which a current is applied in step (c), the current preferably having a current density in the range of: 0.3 A / dm 2 Up to 10A / dm 2 , more preferably 0.4A / dm 2 Up to 8A / dm 2 , even more preferably 0.5A / dm 2 Up to 7A / dm 2 .

[0141] More preferred is the process of the present invention, wherein in step (c) an electric current is applied having a current density in the range of: 0.3 A / dm 2 Up to 2A / dm 2 , more preferably 0.4A / dm 2 Up to 1.5A / dm 2 , even more preferably 0.5A / dm 2 Up to 1A / dm 2 This is most preferably suitable for barrel applications.

[0142] More preferred is the process of the present invention, wherein in step (c) an electric current is applied having a current density in the range of: 0.5 A / dm 2 Up to 8A / dm 2 , more preferably 1.1A / dm 2 Up to 7A / dm 2 , even more preferably 1.5A / dm 2 Up to 6A / dm 2 This is most preferably suitable for rack applications.

[0143] Preferred is the process of the present invention, wherein step (c) is performed for a time in the range of 15 minutes to 180 minutes.

[0144] Step (d): Adding a brightener source to the cathode electrolyte:

[0145] In step (d) of the process of the present invention, a brightener source is added directly or indirectly to the cathode electrolyte. The brightener source is characterized in that it is substantially free of halogen anions, preferably free of halogen anions. This is an essential feature in the context of the present invention. In particular, in a loop, most preferably in a closed loop, it is critical that no contamination is incorporated and accumulated in such a loop (even in a nearly closed loop) over time.

[0146] In the context of the present invention, the term "loop" means a circulation preferably in combination with a wastewater recirculation without or at least without significant drag-out losses when carrying out the process of the present invention. It preferably means that the compounds are present in the aqueous zinc-nickel deposition bath as well as in the water circulation and are reused without drag-out losses or at least without significant drag-out losses, most preferably with the proviso that the rinse water is at least partially (preferably a major part thereof) included in the circulation. Most preferably, the circulation includes the discharge of excess water, most preferably by evaporation, which in particular allows only the water to be discharged without losses of the relevant compounds. Such excess water is usually formed chemically during the performance of the process of the present invention.

[0147] Preference is given to the process according to the invention, in which the process is carried out repeatedly, preferably so that a loop is formed.

[0148] Step (d) is preferably a replenishing step for at least one brightener. Thus, in step (d), "adding" is preferably replenishing (and is therefore preferably interchangeable with "adding").

[0149] Adding the brightener source directly or indirectly. In the context of the present invention, the term "directly" means that the brightener source is added (directly) to the cathode electrolyte. This also means that the brightener source is added in the deposition chamber. The term "indirectly" means that the brightener source is, for example, pre-treated separately in a separate volume, preferably pre-dissolved; and / or added to a separate chamber outside the deposition chamber and is introduced into the cathode electrolyte in a subsequent step, most preferably in a mixing unit.

[0150] After step (d), the at least one brightener has a higher total concentration in the cathode electrolyte than before step (d).

[0151] Preferred is the process of the invention wherein the brightener source replenishes at least one brightener present in the cathode electrolyte, most preferably replenishes only at least one brightener present in the cathode electrolyte. Most preferably, this is essentially the only brightening agent (or essentially the only brightening agents). Thus, preferably, the at least one brightening agent remains identical in its chemical nature when carrying out the process of the invention.

[0152] The brightener source is substantially free of halogen anions, preferably contains no halogen anions. This preferably means that the brightener source is substantially free of fluoride ions, chloride ions, bromide ions and iodide ions, preferably contains no fluoride ions, chloride ions, bromide ions and iodide ions. Most preferably, the brightener source is substantially free of at least chloride ions, preferably contains no at least chloride ions. Thus, the accumulation of harmful halogen anions, preferably chlorides, at least from such sources is effectively prevented.

[0153] Step (e): Rinsing the zinc-nickel coated substrate:

[0154] After step (c) or step (d), the zinc-nickel coated substrate is preferably rinsed with water in a rinse chamber, so that a rinsed zinc-nickel coated substrate and rinse water are obtained. Preferably, the rinse water comprises at least a portion of the at least one brightener and / or (preferably and) at least a portion of the one or more nickel ion complexing agents, most preferably at least a portion of the at least one brightener and / or (preferably and) at least a portion of the one or more nickel ion complexing agents, both as defined above.

[0155] Therefore, preferably the method of the present invention further comprises the following steps

[0156] (e) rinsing the zinc-nickel coated substrate with water in a rinsing chamber so as to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water comprises at least a portion of the at least one brightener and / or one or more than one nickel ion complexing agent (preferably a complexing agent as defined throughout this document, preferably defined as a preferred complexing agent).

[0157] The method according to the invention is preferred, wherein the flushing chamber comprises two to five fluidically connected flushing subchambers, thereby forming a flushing cascade.

[0158] Such a flushing cascade is particularly effective in flushing because the concentrations of zinc and nickel ions flushed / washed away from the zinc-nickel coated substrate, as well as the concentrations of complexing agents and brighteners, are effectively stepped down so that most of the downstream flushing subchambers of the flushing cascade contain significantly lower total concentrations thereof than most of the upstream flushing subchambers of the flushing cascade (which contain most of the concentrations).

[0159] As has been mentioned repeatedly above, it is highly preferred not to discard the flushing water, but to recirculate and at least partially reuse it. For this purpose, the flushing water is preferably further treated. The method according to the invention is preferred, wherein the flushing water obtained from one or more flushing subchambers (at least from the majority of upstream flushing subchambers) is further treated (preferably as defined throughout the text).

[0160] Typically, the rinse water contains zinc ions, nickel ions, at least a portion of the at least one brightener and / or (preferably and) at least a portion of the one or more nickel ion complexing agents. Typically, their individual concentrations are significantly lower than the concentration in the cathode electrolyte. However, in the circuit, these compounds and ions are preferably recycled and reused, respectively. The corresponding treatment is preferably carried out in the corresponding treatment chamber.

[0161] First treatment room:

[0162] Preferably the method of the present invention is

[0163] treating at least a portion of the cathode electrolyte, at least a portion of the rinse water and / or at least a portion of the pre-rinse water in a first treatment chamber so that water is separated therefrom, thereby producing separated water and a concentrated aqueous solution,

[0164] Therein, at least a portion of the concentrated aqueous solution is returned directly or indirectly to the cathode electrolyte.

[0165] More preferably, at least a portion of the cathode electrolyte and at least a portion of the rinse water are treated in the first treatment chamber, most preferably at least a portion of the cathode electrolyte and (all or nearly all) the rinse water. If there are portions from different sources to be treated in the first treatment chamber, they are preferably brought together and treated as a combined portion.

[0166] Preferably, the method of the present invention is carried out in which a major part of the cathode electrolyte, flushing water and / or pre-flush water is treated in the first treatment chamber, preferably individually 80 vol.-% or more, more preferably 85 vol.-% or more, even more preferably 90 vol.-% or more, yet even more preferably 95 vol.-% or more, most preferably 99 vol.-% or more, even most preferably 99.9 vol.-% or more. In the most preferred case, all cathode electrolyte, flushing water and pre-flush water are treated in the first treatment chamber. Most preferably, this applies to a major part of the cathode electrolyte and flushing water.

[0167] As a result of this treatment, separated water and a concentrated aqueous solution are formed. This means that in this step preferably a split stream is obtained which is divided into two. It does not mean that the water is completely separated from all other compounds. It preferably means that at least some water is separated. The term "separated therefrom" means that the HO is separated from all other components in a chemical sense, i.e. in the sense that a certain amount of HO is extracted therefrom.

[0168] The separated water obtained is very preferred because during the method of the present invention, water is usually introduced into the cathode electrolyte, for example with the aid of a nickel ion source for replenishing nickel ions. During the method, water is also chemically formed in the cathode electrolyte (protons are formed at the anode, which migrate into the alkaline cathode electrolyte). However, in the first treatment chamber, excess water is separated and subsequently removed according to the method of the present invention, so that a substantially constant volume of the cathode electrolyte can be maintained over time. If such excess water cannot be used in the method of the present invention (for example for flushing), it is preferably disposed of. This is preferably possible because the water is preferably substantially free of nickel ions, more preferably free of nickel ions. The same preferably applies to zinc ions, complexing agents and brighteners. Therefore, the water can usually be disposed of without any further wastewater treatment. This is a very preferred benefit of the method of the present invention; the separated water is preferably very pure. Alternatively, the water is preferably used in other industrial processes.

[0169] Therefore, the method of the present invention is preferred, wherein at least a portion of the separated water obtained in the first treatment chamber is disposed, wherein this portion contains nickel ions in a concentration ranging from 0 mg / L to 1.0 mg / L, preferably from 0 mg / L to 0.5 mg / L, more preferably from 0.01 mg / L to 0.11 mg / L and most preferably from 0.01 mg / L to 0.1 mg / L, based on the total volume of the disposed portion. This is usually regarded as extremely pure for nickel ions. In addition, this is usually a characteristic of the separated water.

[0170] The process of the present invention is preferred wherein this fraction contains zinc ions at a concentration in the range of 0 mg / L to 1.0 mg / L, preferably 0 mg / L to 0.5 mg / L, more preferably 0.01 mg / L to 0.11 mg / L and most preferably 0.01 mg / L to 0.1 mg / L, based on the total volume of the treated fraction. Again, this is generally considered extremely pure for zinc ions and is also a general feature of separated water.

[0171] Preferably, the water to be treated requires only pH adjustment.

[0172] Thus, the treatment in the first treatment chamber is to separate water from the components typically present in an aqueous zinc-nickel deposition bath. In other words, water is separated from nickel ions, zinc ions, at least one brightener, and one or more nickel ion complexing agents.

[0173] Preferably, at least a portion of the separated water can be reused in the method of the present invention. Therefore, preferably the method of the present invention, wherein at least a portion of the separated water is used as water in step (a-1) and / or step (e). This means that at least a portion of the separated water is used in the pre-rinsing chamber and / or the rinsing chamber, respectively. More preferably, the method of the present invention, wherein at least a portion of the separated water obtained in the first treatment chamber is returned to the rinsing chamber, more preferably to at least one of the rinsing subchambers of the rinsing cascade. This greatly ensures the use of fresh water for rinsing.

[0174] As already mentioned above, water removal is preferably required in order to maintain a constant volume of the cathode electrolyte. Therefore, the method of the present invention is preferred, wherein the cathode electrolyte has essentially a constant volume during the performance of the method of the present invention, most preferably essentially a constant volume during the performance of the method of the present invention, provided that an essentially constant volume is maintained without significant carryover losses. This is highly preferred in a loop, most preferably in a closed loop. For the reasons stated, it is preferred to treat at least a portion of the cathode electrolyte in the first treatment chamber.

[0175] The concentrated aqueous solution contains various compounds and ions of the cathode electrolyte, respectively, relative to the separation water.

[0176] The concentrated aqueous solution preferably comprises zinc ions, nickel ions, at least one brightener and / or (preferably and) one or more complexing agents, most preferably the respective owners as defined for the cathode electrolyte.

[0177] For separation, the method of the invention is preferred wherein the first process chamber comprises a partition unit.

[0178] More preferred is the process of the invention, wherein the first process chamber comprises an evaporator, preferably a vacuum evaporator. These are preferred components of the separator unit.

[0179] The process of the invention is preferred wherein a vacuum in the range of 1 mbar to 100 mbar, preferably 5 mbar to 70 mbar, more preferably 10 mbar to 50 mbar, most preferably 15 mbar to 35 mbar is applied in the vacuum evaporator.

[0180] The method of the present invention is preferred, wherein in the first treatment chamber, preferably in the baffle unit, more preferably in the evaporator, most preferably in the vacuum evaporator, water is separated at a temperature in the range of 18°C ​​to 50°C, preferably 23°C to 46°C, more preferably 28°C to 42°C, most preferably 31°C to 40°C.

[0181] By using an evaporator, preferably a vacuum evaporator, efficient evaporation of water can be achieved, in particular by reducing the atmospheric pressure, thereby allowing efficient separation of water from the nickel ions, one or more complexing agents and at least one brightener.

[0182] By operating the vacuum evaporator at a temperature between 18°C ​​and 50°C, undesired heating or even thermal degradation of the organic compounds, in particular the one or more complexing agents and the at least one brightener, is avoided.

[0183] The method of the present invention is preferred, wherein the vacuum evaporator is operated and controlled based on the density measurement result of the concentrated aqueous solution, preferably the density of the concentrated aqueous solution is in the range of 1.08kg / L to 1.30kg / L, more preferably 1.10kg / L to 1.26kg / L, even more preferably 1.15kg / L to 1.24kg / L, most preferably 1.20kg / L to 1.23kg / L based on the total volume of the concentrated aqueous solution. Density-based control is very suitable for automatically operating the first processing chamber, preferably the evaporator, and most preferably the vacuum evaporator. The above density range is the most preferred. However, in some cases, a higher maximum density is acceptable as long as the concentrated aqueous solution does not form a phase separation. This may include, for example, a maximum density of 1.28kg / L, 1.30kg / L, and even 1.32kg / L in some cases. Phase separation also generally depends on, for example, the concentration of sulfate ions, carbonate ions, and hydroxide ions (e.g., sodium and / or potassium), which may change over time.

[0184] As defined above, the concentrated aqueous solution is aqueous. Therefore, the process of the present invention is preferred, wherein the concentrated aqueous solution is homogeneous. This preferably means that the concentrated aqueous solution forms only a single phase; in other words, the concentrated aqueous solution preferably does not form a phase separation. Most preferably, the concentrated aqueous solution does not contain an organic phase separated from the aqueous phase.

[0185] Therefore, even more preferred is the process of the present invention, wherein the concentrated aqueous solution is completely aqueous. This means that water is the only solvent.

[0186] By not exceeding the above-mentioned preferred maximum density, most preferably 1.26 kg / L (or even 1.28 kg / L or 1.30 kg / L or 1.32 kg / L), phase separation is generally avoided in the context of the process of the invention.

[0187] Preferably, the concentrated aqueous solution is returned directly or indirectly, preferably indirectly via a mixing unit, to the cathode electrolyte. At least a portion of the concentrated aqueous solution is returned to the cathode electrolyte, preferably a major portion thereof, most preferably all of the concentrated aqueous solution is returned. Preferably, the concentrated aqueous solution is returned continuously or stepwise.

[0188] Second treatment room:

[0189] As mentioned above, it is preferred that the source of nickel ions comprises sulfate ions. Since nickel ions, but not sulfate ions, are consumed in the electrolytically deposited zinc-nickel alloy, sulfate ions generally accumulate over time. In addition, the cathode electrolyte generally has a tendency to form and accumulate carbonate anions. Both anions are generally well soluble in the cathode electrolyte. Although a certain concentration may be tolerated, excessive accumulation of such anions needs to be avoided.

[0190] Therefore, the method of the present invention is preferred, which further comprises the steps

[0191] (f) treating at least a portion of the cathode electrolyte in a second treatment chamber such that dissolved anions are separated from the cathode electrolyte, preferably by precipitation and / or ion exchange, most preferably by precipitation.

[0192] Preferred is the process of the invention, wherein the dissolved anions comprise at least sulfate ions, alkylsulfonate ions (preferably methanesulfonate ions) and / or alkylsulfate ions (preferably methylsulfate ions). The term "dissolved anions" refers to anions dissolved in the cathode electrolyte before step (f) (i.e. in the absence of the treatment in step (f)). This means that step (f) allows at least partial removal of anions that would otherwise remain dissolved in the cathode electrolyte and thus accumulate.

[0193] By applying step (f), the concentration of dissolved anions, most preferably sulfate ions and / or (preferably and) carbonate ions in the cathode electrolyte is significantly reduced and excessive accumulation is avoided. Therefore, the method of the present invention can be operated for a very long time. Preferably, step (f) is applied when the dissolved anions have reached an undesired concentration individually or in full. Preferably, step (f) comprises precipitation to remove one or more of such dissolved anions from the cathode electrolyte, most preferably by reducing the temperature of at least a portion of the cathode electrolyte in the second treatment chamber and thereby reducing the solubility of the corresponding salt. Most preferably, the treatment in step (f) promotes the formation of a solid precipitate, preferably a sodium-containing solid precipitate, most preferably comprising at least sodium sulfate or sodium sulfate and sodium carbonate.

[0194] The process of the present invention is preferred, wherein the precipitation is carried out at a temperature in the range of -5°C to 11°C, preferably in the range of -4°C to 10°C, more preferably in the range of -3°C to 8°C, even more preferably in the range of -2°C to 6°C, most preferably in the range of -1°C to 4°C.

[0195] Therefore, the method of the present invention is most preferred, wherein the dissolved anions comprise at least sulfate ions, and wherein the sulfate ions are preferably separated from the cathode electrolyte by precipitated sodium sulfate. This preferably also allows the removal of sodium ions, which are usually present in large quantities in the cathode electrolyte.

[0196] Halogen Anions in Aqueous Zn-Ni Deposition Bath / Cathode Electrolyte:

[0197] As mentioned above, in step (d), a brightener source is added directly or indirectly to the cathode electrolyte, the source being substantially free of halogen anions, preferably free of halogen anions. It is highly preferred that a relatively low halogen anion concentration is maintained throughout the cathode electrolyte over the lifetime of the cathode electrolyte. Most preferably, no halogen anions are present.

[0198] Preferred is the process of the present invention, wherein the cathode electrolyte (i.e. preferably, also the aqueous zinc-nickel deposition bath) comprises halogen anions in a total concentration in the range of 0 g / L to 10 g / L, preferably in the range of 0 g / L to 8 g / L, more preferably in the range of 0 g / L to 6 g / L, even more preferably in the range of 0 g / L to 5 g / L, most preferably in the range of 0 g / L to 4 g / L, even most preferably in the range of 0 g / L to 3 g / L, based on the total volume of the cathode electrolyte. This preferably applies to at least one nickel ion turnover, more preferably to at least 2 nickel ion turnovers, even more preferably to at least 3 nickel ion turnovers, most preferably to a plurality of nickel ion turnovers, even most preferably to the entire useful life of the aqueous zinc-nickel deposition bath used as the cathode electrolyte.

[0199] Preferred is the process of the present invention, provided that in addition to the above-mentioned total concentration of halide anions, the cathode electrolyte (i.e. preferably, also the aqueous zinc-nickel deposition bath) also contains chloride ions in a total concentration in the range of 0 g / L to 3 g / L, more preferably 0 g / L to 2.5 g / L, even more preferably 0 g / L to 2 g / L, most preferably 0 g / L to 1 g / L.

[0200] In some cases, the method of the present invention is preferred, wherein the lower limit of the total concentration of halogen anions is not necessarily zero, but is preferably 1 g / L, more preferably 0.5 g / L, and most preferably 0.1 g / L. In many cases, such low but non-interfering residual amounts of halogen anions are not a problem.

[0201] As already mentioned above, the cathode electrolyte may comprise further compounds and ions, respectively. Preference is given to the process of the invention, wherein the cathode electrolyte (i.e. preferably, also the aqueous zinc-nickel deposition bath) further comprises (i.e. in addition to (i), (ii), (iii) and preferably one or more complexing agents)

[0202] (iv) at least one type of alkali metal cation,

[0203] (v) sulfate ions,

[0204] (vi) carbonate ions, and

[0205] (vii) halogen anions,

[0206] Provided that, based on the total volume of the cathode electrolyte,

[0207] - (i), (iii) and (iv) to (vii) together have a total concentration in the range of 20 g / L to 270 g / L, and

[0208] - The total concentration of the halogen anions does not exceed 10 g / L.

[0209] What has been said above about the halogen anions preferably also applies here.

[0210] This total concentration is intentionally defined as a range that reflects the conditions immediately after performing step (f), such as 20 g / L at the lower end, and the conditions immediately before step (f), such as 270 g / L at the upper end. In other words, the process of the invention is preferred wherein the total concentration is permanently maintained within this range when performing the process of the invention. This preferably includes repeating the process of the invention.

[0211] As indicated above, the main contributors to the total concentration are sulfate ions, carbonate ions and at least one type of alkali metal cation (preferably sodium ions and / or potassium ions; however, mainly sodium ions). If the total concentration reaches the 270 g / L, then step (f) is most preferably carried out. However, step (f) can also be carried out even at lower total concentrations. However, if the total concentration significantly exceeds 270 g / L, then the sedimentation quality is already significantly disturbed in some cases.

[0212] On the other hand, throughout the method of the present invention, a total concentration of 20 g / L or slightly higher is generally highly desirable. This is most preferably achieved after performing step (f).

[0213] Therefore, preferred is the process of the present invention, wherein (i), (iii) and (iv) to (vii) together have a total concentration in the range of 25 g / L to 260 g / L, preferably 30 g / L to 250 g / L, more preferably 35 g / L to 240 g / L, even more preferably 40 g / L to 230 g / L, most preferably 45 g / L to 220 g / L. Additionally, within these preferred ranges, the lower limit preferably applies to the conditions directly after performing step (f), wherein the upper limit preferably applies to the conditions directly before step (f).

[0214] In some cases, preferred is a method of the invention wherein (i), (iii) and (iv) to (vii) together have a total concentration in the range of 180 g / L to 270 g / L, preferably 190 g / L to 250 g / L, more preferably 200 g / L to 230 g / L, most preferably 210 g / L to 220 g / L. This most preferably applies directly before carrying out step (f). These are typical and preferred total concentrations for triggering step (f).

[0215] In some cases, preferred is the process of the invention wherein (i), (iii) and (iv) to (vii) together have a total concentration in the range of 20 g / L to 100 g / L, preferably 25 g / L to 85 g / L, more preferably 30 g / L to 73 g / L, even more preferably 35 g / L to 65 g / L, most preferably 40 g / L to 60 g / L. This most preferably applies directly after carrying out step (f).

[0216] Preferred is the process of the invention, wherein (v) and (vi) together have a total concentration of 20 g / L or more, preferably 25 g / L or more, most preferably 30 g / L or more. Such a total concentration of (v) and (vi) together is generally well tolerated and highly preferred, especially when the upper limit of 60 g / L is not exceeded. It is therefore highly preferred that such a total concentration of (v) and (vi) together is maintained throughout the process of the invention.

[0217] In some cases, it is preferred that the method of the present invention wherein (v) alone has a concentration in the range of 15 g / L to 50 g / L, preferably 20 g / L to 45 g / L. Most preferably, such concentration is maintained throughout the method of the present invention. Most preferably, the lower limit applies to the case directly after performing step (f), wherein the upper limit preferably applies to the case directly before step (f).

[0218] In summary, the method of the present invention allows economical, sustainable, continuous operation over an extended period of time, i.e., for months, weeks or even years. During the extended period of time, no waste water contaminated with nickel is produced, and no precious metal ions and complexing agents and brighteners are lost due to loss of carryover liquid. Basically, only the amount of consumed nickel ions, zinc ions and brighteners must be replenished. In addition, the halogen anions are kept at a low level so that no harmful effects, such as corrosion in and on the equipment, are observed.

[0219] The invention also relates to a specific aqueous zinc-nickel deposition bath for depositing a zinc-nickel alloy, the bath comprising

[0220] (i) nickel ions,

[0221] (ii) at least one brightener,

[0222] (iii) zinc ions, and

[0223] Further includes

[0224] (iv) at least one type of alkali metal cation,

[0225] (v) sulfate ions,

[0226] (vi) carbonate ions, and

[0227] (vii) halogen anions,

[0228] Provided that, based on the total volume of the aqueous zinc-nickel deposition bath,

[0229] - (i), (iii) and (iv) to (vii) together have a total concentration in the range of 20 g / L to 270 g / L, and

[0230] - The total concentration of the halogen anions does not exceed 10 g / L.

[0231] The foregoing with respect to the inventive method, in particular with respect to the aqueous zinc-nickel deposition bath and the cathode electrolyte, respectively, utilized in the inventive method, preferably also applies to the aqueous zinc-nickel deposition bath of the invention (preferably if technically applicable). This most preferably applies to the foregoing with respect to the at least one brightener.

[0232] Most preferably, the aqueous zinc-nickel deposition bath of the present invention is not a newly prepared aqueous zinc-nickel deposition bath, but a "in-use" bath, i.e. a used aqueous zinc-nickel deposition bath. In other words, the deposition bath that has been contacted with an electric current is preferably as defined in step (c) of the method of the present invention.

[0233] The present invention also relates to a specific brightener of formula (Ia) and / or its ester, preferably for zinc-nickel alloy deposition

[0234]

[0235] in

[0236] R 1 represents a C1 to C4 alkyl group, an unsubstituted phenylalkylene group or a substituted phenylalkylene group,

[0237] R 2 Indicates OH, OZ, OR 3 , NH2 or NR 3 R 4 ,in

[0238] Z represents an alkali metal cation, an ammonium cation or an alkylammonium cation; preferably a sodium cation, a potassium cation, an ammonium cation or a tetraalkylammonium cation;

[0239] R 3 independently represent an alkyl group; preferably a C1 to C4 alkyl group; and

[0240] R 4 independently represent hydrogen or alkyl; preferably hydrogen or C1 to C4 alkyl, and

[0241] X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, methanesulfonate, toluenesulfonate, triflate, carbonate and sulfonate.

[0242] The foregoing with respect to the process of the present invention, in particular with respect to the at least one brightener utilized in the aqueous zinc-nickel deposition bath and the cathode electrolyte utilized in the process of the present invention, respectively, preferably also applies to the brightener of formula (Ia) of the present invention (preferably if technically applicable). This most preferably also applies to the compounds of formula (Ib), (A), (B), (C), (D) and their esters as defined for the process of the present invention, which are also preferably used for the brightener of the present invention.

[0243] Preferably, the brightener of the present invention comprises 1 In the above, the C1 to C4 alkyl group individually includes a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group or an isopropyl group; preferably a methyl group, an ethyl group or an isobutyl group.

[0244] Preferably, the brightener of the present invention comprises 1 In the phenylalkylene group, the phenylalkylene group includes a benzyl group.

[0245] Preferably, the brightener of the present invention is 2 represents ONa, OK (ie, Z represents a sodium or potassium cation) or NH2.

[0246] Preferred are brighteners according to the invention wherein X comprises sulfate and / or methylsulfate.

[0247] The present invention also relates to the use of a compound of formula (Ia) and / or an ester thereof as a brightener.

[0248]

[0249]

[0250] in

[0251] R 1 represents a C1 to C4 alkyl group, an unsubstituted phenylalkylene group or a substituted phenylalkylene group,

[0252] R 2 Indicates OH, OZ, OR 3 , NH2 or NR 3 R 4 ,in

[0253] Z represents an alkali metal cation, an ammonium cation or an alkylammonium cation; preferably a sodium cation, a potassium cation, an ammonium cation or a tetraalkylammonium cation;

[0254] R 3independently represent an alkyl group; preferably a C1 to C4 alkyl group; and

[0255] R 4 independently represent hydrogen or alkyl; preferably hydrogen or C1 to C4 alkyl, and

[0256] X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate and sulfonate

[0257] It is used to replenish the brightener in aqueous zinc nickel deposition baths.

[0258] The foregoing with respect to the process of the present invention, in particular with respect to the aqueous zinc-nickel deposition bath utilized in the process of the present invention and the at least one brightener utilized in the cathode electrolyte, respectively, preferably also applies to the use of the present invention (preferably if technically applicable). This most preferably also applies to the compounds of formula (Ib), (A), (B), (C), (D) and their esters as defined for the process of the present invention, which are likewise preferably used for the use of the present invention.

[0259] Very preferred is the use according to the invention, wherein the compounds of formula (Ia) and esters thereof as defined herein, most preferably as defined herein as preferred, are contained in the brightener source or the source consists of said compounds, with the proviso that the source is substantially free of halogen anions, preferably free of halogen anions. The aforementioned in the context of the process according to the invention with respect to the brightener source preferably also applies to the use according to the invention.

[0260] Preference is given to the use according to the invention, wherein the compound of formula (Ia) and its ester and the brightener (ie which is to be replenished) in the aqueous zinc-nickel deposition bath are identical.

[0261] Very particular is the use according to the invention, wherein the compound of formula (Ia) and / or said ester thereof is used in a circuit, preferably in a zinc-nickel deposition bath utilized in a process for depositing a zinc-nickel alloy according to the invention.

[0262] The present invention is described in more detail by the following non-limiting examples.

[0263] Examples

[0264] (I) Brightener Synthesis:

[0265] Compound of formula (A):

[0266] In a 100 mL glass reactor with a reflux condenser, 20 g (160 mmol) of nicotinamide was dissolved in 50 ml of water. To this solution, 20.45 g (160 mmol) of dimethyl sulfate was added at 25° C. The temperature was raised to 62° C. After the addition was complete, the reaction mixture obtained was kept at 50° C. for another 21 hours.

[0267] Thus, 90.4 g of a colorless solution were obtained (44 wt.-%; quantitative yield). The NMR analysis was as follows:

[0268] 1 H-NMR (D2O; 400MHz): δ3.74 (s; 3H); 4.51 (s; 3H); 8.21 (t; 3 J=8Hz);8.92(d; 3 J = 4 Hz; 1H); 9.00 (d; 3 J=4Hz; 1H); 9.30 (s; 1H).

[0269] Compound of formula (C):

[0270] In a 50 mL glass reactor with a reflux condenser, 5 g (40.1 mmol) of nicotinamide were suspended in 15 mL of acetonitrile at 25° C. 8.12 g (40.1 mmol) of benzyl methanesulfonate were subsequently added to this suspension and the reaction mixture was stirred for a further 16 hours at 50° C. After the reaction was complete, the excess solvent was removed under vacuum.

[0271] Thus, 12.92 g (quantitative yield) of yellow-orange oil were obtained. NMR analysis was as follows:

[0272] 1 H-NMR (d6-DMSO, 400MHz): δ2.38 (s; 3H); 5.97 (s; 2H); 7.45-7.46 (m; 3H); 7.61 (dd; 3 J=4Hz; 2H); 8.19 (s; 1H); 8.28-8.32 (m; 1H); 8.67 (s; 1H); 9.01 (d; 3 J = 4 Hz; 1H); 9.34 (d; 3 J=4Hz; 1H); 9.66 (s; 1H).

[0273] 13 C-NMR (d6-DMSO; 100MHz): δ39.78; 63.61; 128.36; 129.04; 129.26; 134.19; 143.87; 144.82; 146.45; 148.55; 151.74; 162.74.

[0274] After synthesis, no further purification is required because no harmful halide ions are present.

[0275] (II) Brightener purification:

[0276] In an alternative method, a commercial brightener (available from BASF, Raschig) having the only difference of compound (D) in that X represents chloride ion is purified via an ion exchange column to replace chloride ions with sulfate ions.

[0277] (III) Deposition on test substrates:

[0278] Test aqueous zinc-nickel deposition baths A, B and C were set up as catholytes in a deposition chamber (about 25 L) to deposit zinc-nickel alloys on loads of small metal parts (i.e. screws M8x55). Test bath A was designed as a comparative example, where B and C were baths according to the invention, i.e. the brighteners were modified in such a way that the corresponding brightener sources did not contain significant amounts of halide ions.

[0279] A, B and C initially contained about 1.3 g / L nickel (II) ions, about 8.5 g / L zinc (II) ions and a diamine having at least one additional secondary amine group as a nickel ion chelating complexing agent. The pH was strongly alkaline at about 12.5 and was adjusted with sodium hydroxide (initially about 120 to 140 g / L NaOH). The zinc (II) ions were present as hydroxide complexes.

[0280] As brighteners, the following compounds were used:

[0281] A: Compound (D), wherein X represents a chloride ion;

[0282] B: Compound (D), wherein X represents sulfate (see (II) above)

[0283] C: Compound (C), wherein X represents mesylate (see (I) above)

[0284] The initial concentration of each brightener was about 200 mg / L based on the total volume of the corresponding aqueous zinc nickel deposition bath.

[0285] Subsequently, the electroplating test was carried out until a bath utilization of 100 Ah / L was reached. For each screw load, the 2The electroplating test was carried out at a temperature of about 25°C to 30°C for about 60 minutes. During this time, the bath parameters as outlined in the table below were monitored. Steel plates (20 cm×30 cm) were used for pseudo plating. Typically, in the test of the present invention, the detection limit of chloride ions is about 50 mg / L and lower. Nickel ions and brighteners (same brighteners) are replenished every 10 Ah; the nickel ion source (nickel sulfate) does not contain any complexing agents and halogen ions. Zinc is replenished from metallic zinc dissolved under alkaline pH conditions. Since zinc hydroxide complexes are formed under alkaline conditions, no additional zinc ion complexing agent is used. The cathode electrolyte and the anode electrolyte are separated from each other by a cation exchange membrane. Insoluble iridium oxide / tantalum oxide on titanium is used as an anode. The distance between the anode and the corresponding membrane is less than 5 mm. The anode electrolyte containing water and sulfuric acid is separated from the cathode electrolyte by the membrane so that neither the complexing agent nor the brightener is in contact with the anode.

[0286] Due to the separation between the anolyte and the catholyte, the catholyte does not contain decomposition products, such as cyanide and oxalate ions. This confirms that neither the complexing agent nor the at least one brightener decomposes in the deposition chamber.

[0287] Table 1: Test of Aqueous Zinc Nickel Deposition Bath A (Comparative)

[0288] Ah / L Zn[g / L] Ni[g / L] <![CDATA[Cl - [mg / L]]]> <![CDATA[CO3 2- [g / L]]]> 20 8.8 1.3 <50 <10 40 8.4 1.4 <50 <10 60 7.8 1.6 Approx. 700 10-20 80 7.9 1.4 Approx. 950 10-20 100 9.1 1.4 Approx. 1100 10-20

[0289] Table 2: Test of aqueous zinc-nickel deposition bath B (present invention)

[0290] Ah / L Zn[g / L] Ni[g / L] <![CDATA[Cl - [mg / L]]]> <![CDATA[CO3 2- [g / L]]]> 20 9.1 1.3 <50 <10 40 8.6 1.4 <50 <10 70 8.2 1.5 <50 <10 80 7.5 1.4 <50 <10 100 7.3 1.5 <50 <10

[0291] Table 3: Test of aqueous zinc-nickel deposition bath C (invention)

[0292] Ah / L Zn[g / L] Ni[g / L] <![CDATA[Cl - [mg / L]]]> <![CDATA[CO3 2- [g / L]]]> 20 8.5 1.5 <50 10-20 40 9.0 1.4 <50 10-20 60 8.5 1.2 <50 10-20 80 9.2 1.3 <50 10-20 100 8.7 1.5 <50 10-20

[0293] During the 100 Ah / L bath utilization, no treatment in the second treatment chamber was required, ie the critical concentrations of sulfate ions and carbonate ions had not yet been reached.

[0294] The above test depositions clearly show that, with the use of the brighteners used in B and C, an increase in halogen ions is avoided, since no halogen ions other than chloride ions are present. Thus, any increase in chloride ions in particular is largely avoided. Furthermore, the entire deposition method according to the invention can be carried out based on relatively low halogen ion concentrations.

[0295] During test plating, the nickel content in the zinc-nickel alloy ranged from 13% to 14%.

[0296] In general, the method of the present invention can be carried out for barrel applications (as specifically shown above) and for rack applications (data not shown). Preferably, for rack applications, the nickel concentration is usually less than 1 g / L, most preferably less than 0.8 g / L. In addition, the substrate obtained after step (c) can be rinsed in step (e), wherein the rinse water is further treated to obtain separation water and concentrated aqueous solution (data also not shown).

Claims

1. A method for depositing a zinc-nickel alloy on a substrate, the method comprising the following steps: (a) providing the substrate, (a-1) optionally, pre-rinsing the substrate with water in a pre-rinsing chamber so as to obtain a pre-rinsed substrate and pre-rinsing water, (b) providing an aqueous zinc nickel deposition bath as a cathode electrolyte in a deposition chamber, wherein - the deposition chamber comprises at least one anode having an anolyte, and - the anolyte is separated from the catholyte by at least one membrane, and The cathode electrolyte comprises (i) nickel ions, (ii) at least one brightener, and (iii) zinc ions, (c) contacting the substrate or the pre-rinsed substrate with the cathode electrolyte in the deposition chamber so that the zinc-nickel alloy is electrolytically deposited on the substrate and thereby obtaining a zinc-nickel coated substrate, wherein After step (c) the at least one brightener has a lower concentration than before step (c), characterized in that The method comprises the following steps after step (c): (d) adding directly or indirectly a brightener source to the cathode electrolyte, the source being substantially free of halogen anions, preferably comprising no halogen anions.

2. The method of claim 1, wherein the at least one brightener is a compound selected from the group consisting of: - an N-heteroaromatic compound, which is preferably an N-heteroaromatic compound comprising at least one pyridine moiety or at least one pyridinium moiety; - an aldehyde, which is preferably an aldehyde comprising at least one aromatic ring; - a ketone, which is preferably a ketone comprising at least one aromatic ring; and -sulfonic acid, which additionally comprises a sulfhydryl group, a disulfide moiety and / or a thioether moiety.

3. The method according to claim 1 or 2, wherein the at least one brightening agent comprises at least N-benzylnicotinic acid, its esters, N-benzylnicotinamide, N-alkylnicotinic acid, its esters and / or N-alkylnicotinamide.

4. The method according to any one of claims 1 to 3, further comprising the step of (e) rinsing the zinc-nickel coated substrate with water in a rinsing chamber so as to obtain a rinsed zinc-nickel coated substrate and rinse water, wherein the rinse water comprises at least a portion of the at least one brightener and / or one or more nickel ion complexing agents.

5. The method according to any one of claims 1 to 4, wherein treating at least a portion of the cathode electrolyte, at least a portion of the rinse water and / or at least a portion of the pre-rinse water in a first treatment chamber so that water is separated therefrom, thereby producing separated water and a concentrated aqueous solution, wherein Directly or indirectly, at least a portion of the concentrated aqueous solution is returned to the cathode electrolyte.

6. The method according to claim 5, wherein at least a part of the separated water is used as the water in step (a-1) and / or step (e).

7. The method according to any one of claims 1 to 6, wherein the distance from the at least one anode to the at least one membrane is in the range of 0.5 mm to 5.0 mm, preferably 0.75 mm to 4 mm, more preferably 1.0 mm to 3.0 mm.

8. The method according to any one of claims 5 or 6, wherein the first process chamber comprises an evaporator, preferably a vacuum evaporator.

9. The method according to any one of claims 1 to 8 further comprises the following step (f) of treating at least a portion of the cathode electrolyte in a second treatment chamber so that the dissolved anions are preferably separated from the cathode electrolyte by precipitation and / or ion exchange, most preferably by precipitation.

10. The method of any one of claims 1 to 9, wherein the cathode electrolyte further comprises (iv) at least one type of alkali metal cation, (v) sulfate ions, (vi) carbonate ions, and (vii) halogen anions, Provided that, based on the total volume of the cathode electrolyte, - (i), (iii) and (iv) to (vii) together have a total concentration in the range of 20 g / L to 270 g / L, and - The total concentration of the halogen anions does not exceed 10 g / L.

11. The method of claim 10, wherein (i), (iii) and (iv) to (vii) together have a total concentration in the range of 25 g / L to 260 g / L, preferably 30 g / L to 250 g / L, more preferably 35 g / L to 240 g / L, even more preferably 40 g / L to 230 g / L, most preferably 45 g / L to 220 g / L.

12. A method according to any one of claims 1 to 11, wherein the cathode electrolyte comprises halogen anions, and a total concentration thereof is in the range of 0 g / L to 10 g / L, preferably in the range of 0 g / L to 8 g / L, more preferably in the range of 0 g / L to 6 g / L, even more preferably in the range of 0 g / L to 5 g / L, most preferably in the range of 0 g / L to 4 g / L, even most preferably in the range of 0 g / L to 3 g / L, based on the total volume of the cathode electrolyte.

13. An aqueous zinc-nickel deposition bath for depositing a zinc-nickel alloy, the bath comprising (i) nickel ions, (ii) at least one brightener, (iii) zinc ions, and Further includes (iv) at least one type of alkali metal cation, (v) sulfate ions, (vi) carbonate ions, and (vii) halogen anions, Provided that, based on the total volume of the aqueous zinc-nickel deposition bath, - (i), (iii) and (iv) to (vii) together have a total concentration in the range of 20 g / L to 270 g / L, and - The total concentration of the halogen anions does not exceed 10 g / L.

14. A brightener of formula (Ia) and / or an ester thereof, in R 1 represents a C1 to C4 alkyl group, an unsubstituted phenylalkylene group or a substituted phenylalkylene group, R 2 Indicates OH, OZ, OR 3 , NH2 or NR 3 R 4 ,in Z represents an alkali metal cation, an ammonium cation or an alkylammonium cation; preferably a sodium cation, a potassium cation, an ammonium cation or a tetraalkylammonium cation; R 3 independently represent an alkyl group; preferably a C1 to C4 alkyl group; and R 4 independently represent hydrogen or alkyl; preferably hydrogen or C1 to C4 alkyl, and X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, methanesulfonate, toluenesulfonate, triflate, carbonate and sulfonate.

15. Use of a compound of formula (Ia) and / or an ester thereof as a brightener, in R 1 represents a C1 to C4 alkyl group, an unsubstituted phenylalkylene group or a substituted phenylalkylene group, R 2 Indicates OH, OZ, OR 3 , NH2 or NR 3 R 4 ,in Z represents an alkali metal cation, an ammonium cation or an alkylammonium cation; preferably a sodium cation, a potassium cation, an ammonium cation or a tetraalkylammonium cation; R 3 independently represent an alkyl group; preferably a C1 to C4 alkyl group; and R 4 independently represent hydrogen or alkyl; preferably hydrogen or C1 to C4 alkyl, and X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate and sulfonate It is used to replenish the brightener in aqueous zinc nickel deposition baths.

Images