Method for depositing zinc-nickel alloys on substrates, aqueous zinc-nickel deposition bath, brightener and use thereof

Abstract

The present invention relates to a method for depositing a zinc-nickel alloy on a substrate, in particular a method for electrolytically depositing a zinc-nickel alloy on a substrate, wherein a zinc-nickel deposition bath is utilized as a catholyte comprising at least one brightener, the at least one brightener having a source that is substantially free of halogen anions, preferably free of halogen anions. The present invention further relates to the respective aqueous zinc-nickel deposition bath, the respective brightener, and the use of each of said brighteners for replenishment 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 an aqueous zinc-nickel deposition bath is utilized as a catholyte comprising at least one brightening agent, the at least one brightening agent having a source that is substantially free of halogen anions, preferably free of halogen anions. The present invention further relates to the respective aqueous zinc-nickel deposition bath, the respective brightening agent, and the use of each of said brightening agents for replenishment in the aqueous zinc-nickel deposition bath. [Background technology]

[0002] Deposition of metal alloys (sometimes also called coatings or protective coatings) onto other metals or metal-coated plastics (usually called substrates) is a well-established technique to enhance the corrosion resistance of such substrates. Deposition is usually performed electrolytically, using the substrate as the anode and cathode in the respective electrolyte (usually known as a deposition or plating bath). A well-known example is the galvanization of a metal substrate with a zinc-nickel alloy.

[0003] There are several advantages to separating the electrolyte by a separator, e.g., a semipermeable membrane, into a catholyte, which is the electrolyte for each cathode compartment, and an anolyte, which is the electrolyte for each anode compartment. In many cases, the anolyte is different from the catholyte. By applying an electrical potential, current flows through the anolyte, through the separator, and into the catholyte, electrolytically depositing a metal alloy onto a substrate.

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

[0005] WO2021 / 123129 A1 discloses a method for depositing a zinc-nickel alloy on a substrate, in which a deposition bath is utilized that comprises at least one complexing agent for nickel ions, the nickel ions having a source that is substantially free of complexing agents, preferably free of complexing agents.

[0006] Indeed, such a method is very efficient and provides excellent corrosion resistance.

[0007] Usually, zinc-nickel deposition baths are often used continuously for long periods, e.g., months, even years. It is generally known that in order to obtain high throughputs, in addition to zinc and nickel ions, organic compounds such as complexing agents and brighteners must be continuously replenished. A certain amount of them, especially the zinc ions, nickel ions and brighteners, are easily incorporated into the zinc alloy layer. Another amount is usually lost by drag-out. Another part is decomposed, e.g., anodically, and remains in decomposed form. Usually, the decomposition is often negligible, since drag-out not only reduces the concentration of the desired compounds, but also the concentrations of undesired decomposition products. The desired compounds are therefore easily replenished.

[0008] In practice, however, such prior art processes also produce large amounts of wastewater, usually contaminated with nickel ions, zinc ions, complexing agents, brighteners (none of which are desirable to dispose of) and at least some of their decomposition products (which are desirable to remove from the process). Environmental demands, sustainability and wastewater demands are increasingly important topics, so there is a constant demand to provide processes that are greener, more sustainable and especially treat resource water more carefully.

[0009] Thus, WO2021 / 123129 A1 proposes a method implemented in a loop to avoid or at least significantly reduce wastewater and wastewater pollution by providing a loop for zinc-nickel precipitation. However, such a loop, if the wastewater is constantly recycled in the loop, significantly affects the concentration levels of the compounds involved, e.g. complexing agents, nickel ions and zinc ions, respectively. Such new developments usually require further insight and very often require long-term observations to identify surprising and unpredictable effects. Since no significant drag-out occurs in such methods, degradation products and undesirable compounds start to accumulate. In fact, this must be prevented. Little research has been carried out so far to identify under what circumstances they can be harmful and how to remove or avoid them. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US2011 / 031127 A1 [Patent Document 2] WO2021 / 123129 A1 Summary of the Invention [Problem to be solved by the invention]

[0011] It was therefore an object of the present invention to provide further improved processes for depositing zinc-nickel alloys on substrates, in particular processes carried out in a loop with a high level of recycling, i.e. in particular wastewater recycling. In particular, it was an object of the present invention to provide processes which are more sustainable by further extending the operating time without compromising the deposit quality, the corrosion resistance of the galvanized substrate, maintaining a stable deposition environment over longer operating times, further extending the life of the deposition baths and avoiding adverse effects on the plating equipment. [Means for solving the problem]

[0012] The object of the present invention is to provide a method for depositing a zinc-nickel alloy on a substrate, comprising the steps of: (a) providing a substrate; (a-1) optionally pre-washing a substrate with water in a pre-wash compartment to obtain a pre-washed substrate and pre-wash water; (b) providing an aqueous zinc-nickel deposition bath as a catholyte in a deposition compartment; - the deposition compartment comprises at least one anode having an anolyte, - the anolyte is separated from the catholyte by at least one membrane, the catholyte being (i) nickel ions, (ii) at least one brightener, and (iii) zinc ions, and (c) contacting the substrate or the pre-cleaned substrate with the catholyte in the deposition compartment such that a zinc-nickel alloy is electrolytically deposited on the substrate, thereby obtaining a zinc-nickel coated substrate; After step (c), the at least one brightener has a lower concentration than before step (c); Including, After step (c), (d) adding a brightener source directly or indirectly to the catholyte, said source being substantially free of halogen anions, preferably free of halogen anions; The problem is solved by a method comprising the steps of:

[0013] Observations over the years have shown that the improved sustainability-inclusive precipitation process for zinc-nickel alloys, preferably by loop or most preferably by closed loop, is relatively sensitive even to small amounts of halogen ions, most preferably chloride ions. As disclosed in WO2021 / 123129 A1, it was thought that relatively small amounts of chloride ions could be co-removed in the precipitation step, for example with sulfate ions, but these independent experiments have shown that even small amounts of halogen anions are undesirable, even if the nickel ion source and the zinc ion source are used without chloride ions. These independent observations have revealed that the main cause of undesirable halogen contamination, especially chloride ion contamination, is the brightener. Brighteners arise directly in the form of counter anions or indirectly in the form of insufficient purification after synthesis. As brighteners are constantly consumed during the precipitation process, typical counter ions such as halogen anions, especially chloride ions, start to accumulate. Such accumulation occurs at relatively low concentration levels, but it has surprisingly been found that even such low concentrations have undesirable effects on equipment parts over time. In particular, it has been observed that the anodic formation of hypochlorite ions sometimes leads to undesirable corrosion of equipment parts including stainless steel and / or said at least one membrane, and relatively high chloride ion concentrations can also have an undesirable effect on the stability of at least one membrane separating the anolyte and catholyte.

[0014] The method of the present invention achieves the above-defined objectives and allows for a loop (also called "operation in a loop"), most preferably even a closed loop, which is most preferred in the context of the present invention, and allows for even longer (i.e. extended) operation times. Independent experiments have shown that by carrying out the method of the present invention and by maintaining the brightener source substantially free of halogen anions, most preferably at least free of chloride ions, said corrosion and / or gassing is significantly reduced or even completely prevented. Furthermore, the method of the present invention allows for the precipitation of, for example, sulfate ions, independently of the halogen ion concentration.

[0015] Moreover, the excellent corrosion resistance of the zinc-nickel plated substrate is not compromised by the method of the present invention. Moreover, due to the at least one membrane, the method of the present invention prevents the formation of harmful cyanide and oxalate anions, which dramatically reduces the wastewater treatment effort and is an important prerequisite for loop, preferably closed loop, operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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".

[0017] Furthermore, in the context of the present invention, the zinc-nickel alloy deposited on the substrate is preferably a zinc-nickel alloy layer, also preferably referred to as a zinc-nickel plating layer. Thus, the method of the present invention is preferably a zinc plating method, which means that in step (c), preferably an electric current is applied.

[0018] Also, in the context of the present invention, the "brightener source" includes the brightener itself, its possible counterions, as well as the educt compounds and residues of synthesis products (eg, leaving groups).

[0019] Step (a): Preparation of substrate In step (a), a substrate is provided.

[0020] Preferred is the method of the present invention, wherein the substrate is a metal substrate, preferably comprising iron, more preferably the substrate is an iron substrate, most preferably a steel substrate.

[0021] The substrate is Barrel use, Preferably, barrel applications include fasteners, most preferably at least screws, nuts, bolts, and washers; and / or Rack applications, Preferably rack applications including fittings, flat plates, L-shaped or U-shaped profiles, and / or pipes, most preferably locker parts, window fittings, door fittings, and furniture fittings, and / or pressure pipes (preferably brake pipes and / or fuel pipes); Preferably, the method of the present invention comprises a substrate for:

[0022] Preferably, the substrate does not comprise or is not cast iron, however, in rare cases, the method of the present invention is preferred where the substrate comprises or is cast iron.

[0023] Step (a-1): Pre-cleaning In step (a-1), the substrate is optionally pre-washed with water in a pre-wash compartment to obtain a pre-washed substrate and pre-wash water. Such pre-washing is preferred. This step is preferably carried out after step (a) and before step (c).

[0024] Pre-washing the substrate in the pre-wash compartment removes potential contamination and / or impurities on the substrate before transferring the substrate to the deposition compartment. Preferably, the pre-washing in the pre-wash compartment is carried out with a pre-wash liquid. Preferably, the pre-wash liquid is aqueous and preferably comprises a hydroxide, preferably a metal hydroxide, even more preferably an alkali metal hydroxide, most preferably sodium hydroxide. The pre-wash liquid is preferably alkaline. Most preferably, the pre-wash liquid is substantially free of organic solvents, preferably free of organic solvents. Most preferably, the only solvent is water.

[0025] Preferred are processes of the present invention, wherein the pre-wash water is at least partially recycled and reused, most preferably reused within the process of the present invention.

[0026] Step (b): Providing an aqueous zinc-nickel deposition bath In step (b), an aqueous zinc-nickel deposition bath is provided as catholyte in the deposition compartment. The aqueous zinc-nickel deposition bath used in the process of the invention is therefore the catholyte. In the following, therefore, the features relating to the aqueous zinc-nickel deposition bath preferably apply equally to the catholyte.

[0027] The method of the present invention is preferred, wherein the aqueous zinc-nickel deposition bath comprises more than 50% by volume of water, more preferably 75% by volume or more, even more preferably 85% by volume or more, and most preferably 92% by volume 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 free of organic solvents.

[0028] The process of the 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, even more preferably 12 to 12.9, most preferably 12.3 to 12.8. In general, the preferred pH range is 12 to 14, preferably 12.3 to 13.5.

[0029] The aqueous zinc-nickel deposition bath comprises (i) nickel ions. Preferred is the process of the invention, in which the aqueous zinc-nickel deposition bath has a total concentration of nickel ions of less than 3 g / L, preferably less than or equal to 2.5 g / L, more preferably less than or equal to 2 g / L (and in any case greater than or equal to 0 g / L, excluding 0 g / L), relative to the total volume of the aqueous zinc-nickel deposition bath.

[0030] In general, it is preferred that the nickel ions have a total concentration 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, and most preferably 0.6 g / L to 2.3 g / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0031] More preferably, the nickel ions have a total concentration 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, and most preferably 0.9 g / L to 1.4 g / L. This is most preferred for barrel applications. However, for rack applications, preferably the 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, and most preferably 0.5 g / L to 0.8 g / L, based on the total volume of the aqueous zinc-nickel deposition bath.

[0032] The aqueous zinc-nickel deposition bath comprises (iii) zinc ions. Preferred is the process of the invention, wherein in the aqueous zinc-nickel deposition bath, the zinc ions have a total concentration of less than 11 g / L, preferably 10 g / L or less, and most preferably 9 g / L or less, based on the total volume of the aqueous zinc-nickel deposition bath.

[0033] Preferably, the zinc ions have a total concentration 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, even more preferably 5.7 g / L to 7.5 g / L, and most preferably 5.9 g / L to 7.3 g / L.

[0034] It is generally preferred that the zinc ions have a total concentration in the range of 6 g / L to 9 g / L.

[0035] The method of the present invention is preferred in which a zinc ion source is added directly or indirectly, preferably indirectly via a mixing unit, to the aqueous zinc-nickel deposition bath. The mixing unit preferably comprises a separate volume of the aqueous zinc-nickel deposition bath (preferably utilized). More preferably, the zinc ions are obtained by dissolving metallic zinc in sodium hydroxide to obtain a zinc hydroxo complex, which allows an efficient stabilization of the zinc ions in the aqueous zinc-nickel deposition bath. This is preferably applied as long as the method of the present invention is carried out. It is therefore most preferably carried out to replenish the zinc ions. Preferably, the nickel ions are also replenished by indirectly adding a nickel ion source via a mixing unit, so that a well-mixed composition is prepared before being transferred to the catholyte and the aqueous zinc-nickel deposition bath, respectively.

[0036] The mixing unit is preferably a separate pre-treatment compartment, most preferably fluidly connected to the precipitation compartment, and most preferably provides thorough mixing to provide homogenization and pre-solubilization, respectively.

[0037] Most preferably, the nickel ions are replenished by a nickel ion source comprising an inorganic nickel salt, more preferably nickel sulfate, most preferably nickel sulfate hexahydrate, and even more preferably without the use of an additional (preferably organic) complexing agent for the nickel ions (see also text below).

[0038] The method of the present invention is preferred in which the nickel ion source does not contain nitrate ions. This most preferably means that neither the nickel salt nor the source contains nitrate ions. By excluding nitrate ions, the concentration of nitrate ions in the catholyte is low or completely prevented. In many cases, nitrates interfere with the overall electrolytic deposition, which is highly undesirable. Furthermore, the nickel ion source does not contain halogen anions, especially chloride ions.

[0039] The method of the present invention is preferred, in which the nickel ion source does not contain organic amines, preferably does not contain any amines. This means most preferably that neither the nickel salt nor the source contains organic amines. Amines are typical complexing agents for nickel ions (see text below for complexing agents for nickel ions). It is therefore preferred that the nickel ion source is substantially free of complexing agents for nickel ions, preferably free of complexing agents for nickel ions. It is therefore preferred that the complexing agents for nickel ions are monitored and controlled independently of the nickel ion source. This is most preferred in loop and closed loop, respectively.

[0040] Most preferred is the process of the invention, wherein the nickel ions of the nickel ion source added to the catholyte replenishing the nickel ions are not complexed prior to contact with an alkaline environment, preferably an environment having a 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 12 to 14, preferably 12.5 to 13.5. Preferably, the nickel ions of the nickel ion source added to the catholyte form a complex only upon contact with an alkaline environment, preferably an environment having a pH as defined above, most preferably the catholyte.

[0041] Preferred is the process of the present invention, wherein the source of nickel ions is an aqueous solution comprising water and a nickel salt dissolved therein, preferably a nickel salt as defined above.

[0042] Advantageously, in the method of the present invention, the total concentration of nickel ions and zinc ions as defined above is usually lower than the concentrations generally known and used in the art of zinc-nickel deposition. Nickel and zinc ions are preferably recycled in the method of the present invention (i.e. indirectly by recycled water such as washing water), so that nickel and zinc ions are not wasted in significant amounts, respectively, and as a result, the overall total concentration in the aqueous zinc-nickel deposition bath is reduced. Therefore, the method of the present invention is preferred, in which at least a portion of the nickel ions and zinc ions circulate in a loop, which loop includes a washing step. More preferred is the method of the present invention, in which at least a portion of the nickel ions, zinc ions, at least one brightener and complexing agent circulate in a loop, which loop includes a washing step.

[0043] At least one brightener In the method of the present invention, the aqueous zinc-nickel deposition bath contains at least one brightener, which is preferably necessary to provide sufficient brightness and luster and to further improve the electrolytic deposition in step (c), and therefore mainly contributes to improving the optical appearance.

[0044] The method of the present invention is generally preferred, in which the at least one brightener has a total concentration in the aqueous zinc-nickel deposition bath 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, and even more 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 applied to both barrel and rack applications.

[0045] Optionally, the process of the invention is preferred, wherein in the aqueous zinc-nickel deposition bath the at least one brightener has a total concentration in the range of 20 mg / L to 650 mg / L, preferably 50 mg / L to 600 mg / L, more preferably 100 mg / L to 550 mg / L, most preferably 150 mg / L to 500 mg / L, relative to the total volume of the aqueous zinc-nickel deposition bath.

[0046] However, in some cases, the process of the invention is preferred, wherein in the aqueous zinc-nickel deposition bath the at least one brightener has a total concentration in the range of 700 mg / L to 1200 mg / L, preferably 750 mg / L to 1100 mg / L, more preferably 800 mg / L to 1000 mg / L, most preferably 850 mg / L to 950 mg / L, relative to the total volume of the aqueous zinc-nickel deposition bath.

[0047] Preferred is the process of the present invention, wherein each of the at least one brightener contains from 4 to 25 carbon atoms, preferably from 5 to 20 carbon atoms, more preferably from 6 to 18 carbon atoms, even more preferably from 7 to 15 carbon atoms, and most preferably from 8 to 13 carbon atoms. In some cases, highly preferred are from 10 to 14 carbon atoms.

[0048] Preferred is the method of the present invention, wherein the brightener source comprises a cationic brightener having a counter anion, a nonionic brightener, and / or an inner salt brightener. Preferably, the inner salt brightener is a betaine brightener.

[0049] At least one brightener - N-heteroaromatic compounds, preferably N-heteroaromatic compounds containing at least one pyridine moiety or at least one pyridinium moiety, an aldehyde, preferably an aldehyde containing at least one aromatic ring, - a ketone, preferably a ketone containing at least one aromatic ring, and - sulfonic acids further comprising a mercapto group, a disulfide moiety, and / or a thioether moiety; Further preferred is the method of the present invention, wherein the compound (preferably one or more compounds) is selected from the group consisting of:

[0050] The method of the present invention is preferred, wherein the N-heteroaromatic compound (preferably as defined above or as preferred throughout the text) further comprises a benzyl group. Most preferably, the at least one brightener comprises at least one such compound (preferably as defined as preferred throughout the text).

[0051] Preferred is the process according to the invention, wherein the N-heteroaromatic compound (preferably as described above as preferred) further comprises (i.e. in addition to the N-heteroatom or, preferably, in addition to the benzyl group as defined above) an amide group, a carboxylate group, a sulfonate group and / or an ester thereof. The amide group is preferably a carboxamide group.

[0052] 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 sulfobetaines, unsubstituted pyridinium sulfobetaines, substituted pyridinium carboxylates, unsubstituted pyridinium carboxylates, substituted pyridinium carboxamides, and unsubstituted pyridinium carboxamides.

[0053] Preferred substituted and unsubstituted pyridinium sulfobetaines include substituted and unsubstituted pyridinium alkyl sulfobetaines. A preferred unsubstituted pyridinium alkyl sulfobetaine is pyridinium propyl sulfobetaine (PPS).

[0054] The method of the present invention is highly preferred, in which the N-heteroaromatic compound containing at least one pyridinium moiety is selected from the group consisting of N-benzyl nicotinate and its esters, N-benzyl nicotinamide, N-benzyl pyridinium, N-benzyl pyridinium sulfonate and its esters, N-alkyl nicotinate and its esters, and N-alkyl nicotinamide. The carboxylate, amide, and sulfonate groups are preferably located at the ortho, meta, or para positions of the pyridinium ring, and most preferably at the meta position. The benzyl group is attached to the ring nitrogen to form a quaternary ring nitrogen atom with a positive charge. In some cases, the method of the present invention is most preferred, in which at least one brightener comprises N-alkyl nicotinate and its esters, and / or N-alkyl nicotinamide. Highly preferred N-alkyl nicotinates include 1-methyl nicotinate (i.e., N-methyl nicotinate), preferably including its salts, esters, and amides.

[0055] In some cases, the method of the present invention is preferred, wherein the N-heteroaromatic compound containing a pyridine moiety is selected from the group consisting of benzylpyridine, nicotinic acid and its esters, benzylnicotinate and its esters, and benzylnicotinamide.In these cases, the benzyl group is not bonded to the ring nitrogen atom.Therefore, the ring nitrogen preferably does not form a positive charge.

[0056] Preferred is the method of the present invention, wherein the at least one polishing agent comprises at least N-benzyl nicotinate, an ester thereof, N-benzyl nicotinamide, N-alkyl nicotinate, an ester thereof, and / or N-alkyl nicotinamide.

[0057] At least one brightener, most preferably a brightener source, is a compound of formula (Ia) and / or an ester thereof, preferably a compound of formula (Ib) and / or an ester thereof

[0058] [ka]

[0059] (In the formula, R 1 represents C1-C4 alkyl, unsubstituted phenylalkylene, or substituted phenylalkylene; R 2 OH, OZ, OR 3 , NH2, or NR 3 R 4 represents Z represents an alkali metal, ammonium or alkylammonium cation, preferably a sodium, potassium, ammonium or tetraalkylammonium cation; R 3 each independently represents an alkyl group, preferably a C1-C4 alkyl group; R 4 each independently represents hydrogen or alkyl, preferably hydrogen or C1-C4 alkyl; X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate, and sulfonate. Highly preferred is a method according to the invention comprising (preferably consisting of):

[0060] In the context of the present invention, R 2 In the formula, "Z" in "OZ" preferably represents a moiety that compensates for the negative charge of the carboxylate group. Preferred OZ includes ONa and / or OK, "Na" represents sodium, and "K" represents potassium.

[0061] Preferably, "NR 3 R 4 " In R 3 and R 4 are the same or different, preferably the same, ie, both are alkyl, preferably both are C1-C4 alkyl.

[0062] In some cases, R 1preferably denotes substituted phenylalkylene. This preferably means that the phenyl moiety comprises one or more substituents. Preferably, the one or more substituents are independently selected from the group consisting of carboxy, hydroxy, sulfonate, amino, C1-C4 alkyl, C1-C4 alkoxy, halogen, carbamoyl, cyano, ester, and salts thereof.

[0063] In the compound of formula (Ia), -C(O)R 2 The moiety is in the ortho, meta, or para position, preferably in the meta position. Compounds of formula (Ib) are compounds of formula (Ia) in which -C(O)R 2 The part is in the meta position.

[0064] R 1 In the preferred method of the invention, the C1-C4 alkyl (preferably also the one or more substituents in the substituted phenyl alkylene as defined above) individually comprises methyl, ethyl, n-propyl, iso-propyl, n-butyl, or iso-propyl, preferably methyl, ethyl, or iso-butyl, most preferably methyl. These preferred alkyl moieties are each R 3 and R 4 This also applies to the preferred C1-C4 alkyl moieties of

[0065] R 1 Preferred is the process of the present invention, wherein the phenyl alkylene comprises benzyl.

[0066] R 2 Preferred is a process according to the invention, wherein M represents ONa, OK (i.e. M represents a sodium or potassium cation) or NH2, preferably ONa (i.e. M represents a sodium cation) or NH2.

[0067] The process of the invention is preferred, wherein X comprises sulfate and / or methylsulfate.

[0068] In X, the sulfonate ion is preferably a sulfonate ion (SO 2-), methanesulfonate, methanedisulfonate, and / or methanetrisulfonate. Most preferred is the process of the invention, wherein X comprises sulfate, methylsulfate, and / or methanesulfonate, and R 1 It is most preferred when contains benzyl.

[0069] At least one brightener, most preferably a brightener source, is selected from the group consisting of compounds (A) to (D).

[0070] [ka]

[0071] Even more preferred is a method of the present invention comprising a compound selected from the group consisting of: Each X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate, and sulfonate, preferably sulfate and methylsulfate.

[0072] With regard to X, most preferably, all of the foregoing apply individually as well to compounds of formulae (A), (B), (C) and (D).

[0073] 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.

[0074] Preferred is the process of the present invention, wherein the ketone comprising at least one aromatic ring comprises benzalacetone and / or naphthyl methyl ketone.

[0075] Preferred is the process of the present invention, wherein the aqueous zinc-nickel deposition bath is substantially free, preferably free, of propane sultone, preferably substantially free, preferably free, of any sultone.

[0076] Nickel ion complexing agent The method of the invention is preferred, in which the aqueous zinc-nickel deposition bath further comprises one or more, preferably one, complexing agent for the nickel ions. The complexing agent is necessary to keep the nickel ions in solution despite the alkaline pH environment. It is preferred to use only one complexing agent, as the total concentration of the complexing agent 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 in principle possible.

[0077] The method of the present invention is preferred, wherein the one or more complexing agents for nickel ions comprise a chelating complexing agent, preferably the chelating complexing agent is the only complexing agent for nickel ions in the aqueous zinc-nickel deposition bath. The use of a chelating complexing agent ensures a more efficient stabilization of the nickel ions in the aqueous zinc-nickel deposition bath. Most preferably, the one or more complexing agents for nickel ions are provided only once when initially setting up the aqueous zinc-nickel deposition bath, and thereafter, substantially no additional complexing agents (either of the same type or of a different type) are preferably added while the method of the present invention is carried out.

[0078] Preferred is a process of the present invention, wherein the one or more complexing agents for nickel ions comprise an amine, preferably a diamine, more preferably an oligoamine, even more preferably a pentamine, and most preferably the aqueous zinc-nickel deposition bath comprises tetraethylenepentamine (even most preferably tetraethylenepentamine alone as the complexing agent for nickel ions).

[0079] Preferred is the process of the present invention wherein the aforementioned amines, including the preferred amines, are the sole complexing agents for nickel ions in the aqueous zinc-nickel deposition bath.

[0080] Preferred diamines include ethylenediamine.

[0081] Preferred oligoamines include diethylenetriamine, triethylenetetramine, and / or tetraethylenepentamine. In some cases, the process of the invention is preferred in which the aqueous zinc-nickel deposition bath comprises one or more of the aforementioned amines rather than tetraethylenepentamine. However, in other cases, the process of the invention is preferred in which the aqueous zinc-nickel deposition bath comprises one or more of the aforementioned amines in addition to tetraethylenepentamine.

[0082] Generally, the process of the invention is preferred, where in the aqueous zinc-nickel deposition bath the one or more complexing agents for nickel ions comprises an amine having one or more, preferably two, primary amine groups and one or more, secondary amine groups.

[0083] Preferred is the process of the invention, wherein the amine having one or more than one, preferably two primary amine groups and one or more than one secondary amine group is the only complexing agent for the nickel ions in the aqueous zinc-nickel deposition bath.

[0084] Furthermore, the process of the present invention is preferred, wherein the aqueous zinc-nickel deposition bath comprises only an initial concentration of the one or more complexing agents for nickel ions for at least one nickel ion turnover, more preferably for at least two nickel ion turnovers, even more preferably for at least three nickel ion turnovers, most preferably for a large number of nickel ion turnovers, and even most preferably over the entire life of the aqueous zinc-nickel deposition bath used as catholyte.

[0085] The process of the invention is preferred, wherein in the aqueous zinc-nickel deposition bath the zinc ions do not form complexes with one or more complexing agents for nickel ions, preferably with amines, more preferably with diamines, and even more preferably with organic complexing agents. Most preferably, the zinc ions in the aqueous zinc-nickel deposition bath are so strong and stable as hydroxo complexes that no complexation of the zinc ions with one or more complexing agents for nickel ions is observed under alkaline conditions.

[0086] Anolyte The deposition compartment also contains an anolyte: in the context of the present invention, the anolyte is typically an electrolyte in direct contact with at least one anode, and 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 while the substrate is located in the deposition compartment.

[0087] Preferred is the process of the invention, wherein the anolyte is an aqueous solution, preferably comprising water and sulfuric acid, most preferably comprising water and 5% to 40% by volume of sulfuric acid, based on the total volume of the anolyte.

[0088] At least one anode Preferred is the process of the present invention, wherein in the deposition compartment, 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 / tantalum oxide on a titanium anode.

[0089] At least one membrane In the deposition compartment, there is the at least one anode and the at least one membrane, the at least one membrane separating the anolyte from the catholyte. Most preferably, the at least one membrane is a semi-permeable membrane, meaning that the at least one membrane is selectively permeable. The process of the invention is preferred, wherein the at least one membrane is a cation-permeable membrane.

[0090] The at least one membrane most preferably only allows the diffusion of protons between the anolyte and catholyte, thereby ensuring efficient distribution of charge between the anolyte and catholyte.

[0091] More preferred is the method of the invention, wherein at least one membrane comprises a fluorinated polymer, preferably polytetrafluoroethylene (PTFE) and / or (preferably or) perfluorosulfonic acid (PFSA).

[0092] In general, the at least one membrane is not particularly limited in the context of the present invention, as long as it preferably provides sufficient separation between the anolyte and the catholyte. Thus, the method of the present invention is preferred, in which the anolyte is separated from the catholyte by at least one separator (most preferably, this separator is a membrane). In other cases, ceramics are preferred as separators. Thus, throughout this specification, the features related to the at least one membrane preferably also apply mutatis mutandis to the at least one separator.

[0093] The method of the invention is preferred, wherein the at least one anode has a distance to the at least one membrane 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, which has the advantage that the volume of the anolyte can be kept low, resulting in a smaller amount of wastewater from the anolyte.

[0094] The main advantage of the method of the invention is that no decomposition products are formed at the anode, due to the at least one membrane separating the anolyte from the catholyte. 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, as they are restricted to the catholyte. The permeation of ions between the catholyte and the anolyte is only possible through the at least one membrane. This is a fundamental requirement for carrying out the method of the invention in a loop, most preferably in a closed loop, most preferably always recycling the initial concentration of said one or more complexing agents for nickel ions. Most preferably, the at least one membrane allows substantially only the permeation of hydrogen ions (formed in the anolyte) into the catholyte.

[0095] Therefore, the method of the present invention is preferred in which the one or more complexing agents for nickel ions are not in contact with at least one anode, and most preferably not in contact with any of the at least one anode. As a result, if the nickel ion source is carefully controlled and no further complexing agent is added in an uncontrolled manner, the concentration of the one or more complexing agents is preferably constant in the catholyte. Rather, it is preferably sufficient to provide only an initial concentration of the one or more complexing agents for nickel ions when setting up the aqueous zinc-nickel deposition bath, preferably the catholyte, and no additional complexing agent needs to be added during the implementation of the method of the present invention.

[0096] 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 not in contact with any of the at least one anode.

[0097] Most preferably, the organic compounds contained in the aqueous zinc-nickel deposition bath (ie, the catholyte) do not come into contact with the at least one anode, and most preferably do not come into contact with any of the at least one anode.

[0098] Furthermore, preferably, due to said separation, cyanide and oxalate anions are not formed at the anode.

[0099] Step (c): Contacting the substrate with an aqueous zinc-nickel deposition bath (i.e., catholyte). In step (c) of the method of the present invention, the substrate or the pre-cleaned substrate (if pre-cleaning is performed) is contacted with the catholyte in the deposition compartment such that a zinc-nickel alloy is electrolytically deposited on the substrate, thereby obtaining a zinc-nickel coated substrate.

[0100] During step (c), the at least one brightener present in the catholyte is usually partially consumed. Thus, after step (c), or after one step (c), which means that the method of the present invention is repeated, the at least one brightener has a lower concentration than before step (c) or each previous step (c). In other words, after step (c), preferably after each step (c), the at least one brightener has a lower total concentration than the total concentration before step (c). This is to some extent acceptable and normal. It also means that the at least one brightener is replenished, but not after each step (c). In other words, the at least one brightener preferably has a total concentration within a concentration range, which has a lower limit and preferably does not fall below the lower limit during the method of the present invention.

[0101] The process of the present invention is preferred, wherein in step (c), the temperature of the catholyte 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, and even more preferably 22°C to 30°C.

[0102] In step (c), a current is applied, preferably 0.3 A / dm 2 ~10A / dm 2 , more preferably 0.4A / dm 2 ~8A / dm 2 , and even more preferably 0.5A / dm 2 ~7A / dm 2Preferably, the method of the present invention applies a current with a current density in the range of

[0103] In step (c), 0.3 A / dm 2 ~2A / dm 2 , more preferably 0.4A / dm 2 ~1.5A / dm 2 , and even more preferably 0.5A / dm 2 ~1A / dm 2 More preferred is the method of the present invention, where the current is applied at a current density in the range of 0.1 to 0.5 μm. This is most preferably applied in barrel applications.

[0104] In step (c), 0.5 A / dm 2 ~8A / dm 2 , more preferably 1.1 A / dm 2 ~7A / dm 2 , more preferably 1.5 A / dm 2 ~6A / dm 2 More preferred is the method of the present invention, where the current is applied at a current density in the range of 0.1 to 1.0 V. This is most preferably applied in rack applications.

[0105] Preferred is a process according to the invention, wherein step (c) is carried out for a period in the range of from 15 minutes to 180 minutes.

[0106] Step (d): Adding a brightener source to the catholyte In step (d) of the method of the present invention, a brightener source is added directly or indirectly to the catholyte. 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. Especially in loops, most preferably closed loops, it is important that no contaminants are introduced or accumulated in such loops over time (even in the case of nearly closed loops).

[0107] In the context of the present invention, the term "loop" means a circulation without drag-out or at least without significant drag-out, preferably in combination with wastewater recycle, while the method of the present invention is carried out. Preferably, it means that the compounds and water present in the aqueous zinc-nickel deposition bath are circulated and reused without drag-out or at least without significant drag-out, most preferably with the proviso that wash water is at least partially (preferably most of it) included in the circulation. Most preferably, the circulation includes the discharge of excess water, most preferably by evaporation, which makes it possible to drain off only the water, without loss of associated compounds. Such excess water is usually formed chemically while the method of the present invention is carried out.

[0108] Preferred is a method of the invention, wherein the method is carried out repeatedly, preferably such that a loop is formed.

[0109] Step (d) is preferably a replenishment step of at least one brightener. Thus, "adding" in step (d) is preferably replenishment (and thus is preferably interchangeable with "adding").

[0110] The brightener source is added directly or indirectly. In the context of the present invention, the term "directly" means that the brightener source is added (directly) to the catholyte. It also means that the brightener source is added to the deposition compartment. The term "indirectly" means that the brightener source is pre-treated separately, preferably pre-dissolved, for example in a separate volume, and / or added to a separate compartment outside the deposition compartment, and introduced into the catholyte in a subsequent step, most preferably in a mixing unit.

[0111] After step (d), the at least one brightener is in a higher total concentration in the catholyte than before step (d).

[0112] The process of the invention is preferred, in which the brightener source replenishes at least one brightener present in the catholyte, and most preferably replenishes only at least one brightener present in the catholyte. Most preferably, it is the only brightener (or the only brighteners). Thus, preferably, the at least one brightener remains the same in its chemical nature while the process of the invention is being carried out.

[0113] The brightener source is substantially free of halogen anions, preferably free of halogen anions. This preferably means that the brightener source is substantially free of fluoride, chloride, bromide and iodide ions, preferably free of fluoride, chloride, bromide and iodide ions. Most preferably, the brightener source is at least substantially free of chloride ions, preferably free of chloride ions. Thus, the accumulation of harmful halogen anions, preferably chloride, from at least this type of source is effectively prevented.

[0114] Step (e): Cleaning of zinc-nickel coated substrate After step (c) or (d), the zinc-nickel coated substrate is preferably washed with water in a washing compartment so as to obtain a washed zinc-nickel coated substrate and washing water. Preferably, the washing water comprises at least a portion of said at least one brightener and / or (preferably and) said one or more complexing agents for nickel ions, most preferably comprises at least a portion of said at least one brightener and / or (preferably and) at least a portion of said one or more complexing agents for nickel ions (both as defined above).

[0115] therefore, (e) washing the zinc-nickel coated substrate with water in a washing compartment to obtain a washed zinc-nickel coated substrate and washing water, the washing water comprising at least a portion of said at least one brightener and / or one or more complexing agents for nickel ions (preferably complexing agents as defined throughout the text, preferably those defined as preferred), Preferably, the method of the present invention further comprises:

[0116] Preferred is a method according to the invention, wherein the washing compartment comprises from 2 to 5 fluidly connected washing sub-compartments forming a washing cascade.

[0117] Such a washing cascade is particularly efficient in cleaning because the concentrations of zinc and nickel ions, as well as complexing and brightening agents washed / washed away from the zinc-nickel coated substrate are effectively reduced in stages, so that the most downstream washing sub-zone has a significantly lower total concentration compared to the most upstream washing sub-zone of the washing cascade which contains the majority of it.

[0118] As already mentioned repeatedly, it is highly preferred that the wash water is not discarded but recycled and at least partially reused. For this purpose, it is preferred that the wash water is further treated. Preferred is a process according to the invention, in which the wash water obtained from one or more washing sub-zones is further treated (preferably as defined throughout the specification) at least from the most upstream washing sub-zone.

[0119] Typically, the wash water contains zinc ions, nickel ions, at least a portion of said at least one brightener, and / or (preferably) at least a portion of said one or more complexing agents for the nickel ions. Usually, their individual concentrations are significantly lower than those in the catholyte. However, in the loop, each of these compounds and ions is preferably recycled and reused. Each treatment is preferably carried out in a respective treatment compartment.

[0120] First treatment section at least a portion of the catholyte, at least a portion of the wash water, and / or at least a portion of the pre-wash water are treated in a first treatment compartment such that water is separated therefrom, resulting in a separated water and a concentrated aqueous solution; At least a portion of the concentrated aqueous solution is returned directly or indirectly to the catholyte; The method of the present invention is preferred.

[0121] More preferably, at least a portion of the catholyte and at least a portion of the wash water are treated in the first processing compartment, most preferably at least a portion of the catholyte and (all or substantially all) the wash water are treated. If portions from different sources are treated in the first processing compartment, they are preferably combined together and treated as a combined portion.

[0122] The process of the invention is preferred, wherein the majority of the catholyte, wash water and / or pre-wash water, preferably individually at least 80% by volume, more preferably at least 85% by volume, even more preferably at least 90% by volume, even more preferably at least 95% by volume, most preferably at least 99% by volume, even most preferably at least 99.9% by volume, is treated in the first processing compartment. In the most preferred case, all of the catholyte, wash water and pre-wash water are treated in the first processing compartment. Most preferably, this applies to the majority of the catholyte and wash water.

[0123] As a result of this treatment, a separated water and a concentrated aqueous solution are formed. This means that this step preferably obtains a separation into two fractions. This does not mean that the water is completely separated from all other compounds. It preferably means that at least a part of the water is separated. The term "separated therefrom" means in a chemical sense that the H2O is separated from all other components, i.e. that a certain amount of H2O is extracted therefrom.

[0124] The separated water obtained is highly preferred, since during the process of the invention water is usually introduced into the catholyte, for example using a nickel ion source to replenish the nickel ions. During the process water is chemically formed in the catholyte (protons are formed at the anode and migrate into the alkaline catholyte). However, in the first treatment section excess water is separated and then removed from the process of the invention, so that an essentially constant amount of catholyte is maintained over time. If such excess water cannot be used in the process of the invention (for example for washing), it is preferably discarded. This is preferably possible, since this water is preferably substantially free of nickel ions, more preferably free of nickel ions. The same applies preferably to zinc ions, complexing agents and brighteners. This water can therefore usually be discarded without further wastewater treatment. This is a highly preferred advantage of the process of the invention. The separated water is preferably extremely pure. Alternatively, this water is preferably used in other industrial processes.

[0125] Therefore, the method of the invention is preferred, in which at least a part of the separated water obtained in the first treatment section is discarded, this part containing 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, most preferably from 0.01 mg / L to 0.1 mg / L, relative to the total amount of the discarded part. This is usually considered to be very pure with respect to nickel ions. Moreover, this is generally characteristic of the separated water.

[0126] The method of the invention is preferred, whereby this portion contains zinc ions in a concentration ranging from 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, most preferably 0.01 mg / L to 0.1 mg / L, relative to the total volume of the waste portion, which is also usually considered to be very pure with respect to zinc ions and is also a typical characteristic of separated water.

[0127] Preferably, the waste water only requires pH adjustment.

[0128] The process in the first process compartment is therefore the separation of water from the components normally present in an aqueous zinc-nickel deposition bath, in other words the water is separated from the nickel ions, the zinc ions, at least one brightener and one or more complexing agents for the nickel ions.

[0129] Preferably, at least a part of the separated water can be reused in the process of the present invention. Thus, the process of the present invention is preferred, in which at least a part of the separated water is utilized as water in step (a-1) and / or step (e). This is because at least a part of the separated water is used in the pre-wash section and / or the wash section. at least a part of the separated water obtained in the first treatment section is returned to the washing section, more preferably to at least one of the washing sub-sections of the washing cascade; The method of the present invention is more preferred, as it dramatically reduces the amount of freshwater used for washing.

[0130] As already mentioned above, water removal is preferably necessary to keep the volume of the catholyte constant. Therefore, the method of the present invention is preferred, in which the catholyte has an essentially constant volume during the implementation of the method of the present invention, most preferably with a condition that the essentially constant volume is maintained without significant drag-out. This is highly preferred in a loop, most preferred in a closed loop. Therefore, preferably at least a part of the catholyte is treated in the first treatment compartment.

[0131] In contrast to the separated water, the concentrated aqueous solution contains each of the various compounds and ions of the catholyte.

[0132] 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 all individually defined as for the catholyte.

[0133] For carrying out a separation, a method according to the invention is preferred, wherein the first processing compartment comprises a separation unit.

[0134] Further preferred is the process according to the invention, wherein the first processing section comprises an evaporator, preferably a vacuum evaporator. These are the preferred means for the separation unit.

[0135] Preferred is the process of the invention, wherein in the vacuum evaporator a vacuum is applied 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.

[0136] Preferred is the process of the invention, wherein in the first treatment section, preferably in a separation unit, more preferably in an evaporator, most preferably in a 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.

[0137] By using an evaporator, preferably a vacuum evaporator, efficient evaporation of the water can be achieved, especially by reducing the atmospheric pressure, which allows efficient separation of the water from the nickel ions, the one or more complexing agents, and the at least one brightener.

[0138] By operating the vacuum evaporator at a temperature between 18° C. and 50° C., undesirable heating or even thermal degradation of the organic compounds, especially the one or more complexing agents and the at least one brightener, is prevented.

[0139] The method of the invention is preferred, in which the vacuum evaporator is operated and controlled based on density measurements of the concentrated aqueous solution, preferably the density of the concentrated aqueous solution is in the range of 1.08 kg / L to 1.30 kg / L, more preferably 1.10 kg / L to 1.26 kg / L, even more preferably 1.15 kg / L to 1.24 kg / L, most preferably 1.20 kg / L to 1.23 kg / L, based on the total volume of the concentrated aqueous solution. The density-based control is very suitable for automatically operating the first processing section, preferably the evaporator, most preferably the vacuum evaporator. The density ranges mentioned above are most preferred. However, higher maximum densities may be tolerated, as long as the concentrated aqueous solution does not form a phase separation. In this case maximum densities such as 1.28 kg / L, 1.30 kg / L, and even 1.32 kg / L may be included. Phase separation usually also depends on the concentrations of e.g. sulfate, carbonate, hydroxide ions (such as sodium and / or potassium), which may vary over time.

[0140] As defined above, the concentrated aqueous solution is aqueous. Therefore, the method of the present invention is preferred, in which 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.

[0141] Therefore, it is further preferred that the process of the present invention wherein the concentrated aqueous solution is fully aqueous, meaning that water is the only solvent.

[0142] By not exceeding the above mentioned preferred maximum density of 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 method of the present invention.

[0143] Preferably, the concentrated aqueous solution is returned to the catholyte directly or indirectly, preferably indirectly via a mixing unit. At least a portion of the concentrated aqueous solution is returned to the catholyte, preferably a major portion thereof, most preferably the concentrated aqueous solution is returned completely. Preferably, the concentrated aqueous solution is returned continuously or stepwise.

[0144] Second treatment section As mentioned above, the preferred nickel ion source comprises sulfate ions. Because nickel ions are consumed in the electrolytically deposited zinc-nickel alloy, whereas sulfate ions are not, sulfate ions typically accumulate over time. Furthermore, catholytes typically tend to form and accumulate carbonate anions. Both anions are typically well soluble in the catholyte. Although some concentrations are acceptable, excessive accumulation of such anions should be avoided.

[0145] therefore, (f) treating at least a portion of the catholyte in a second treatment compartment, preferably by precipitation and / or ion exchange, most preferably by precipitation, such that dissolved anions are separated from the catholyte. Preferably, the method of the present invention further comprises:

[0146] The process of the invention is preferred, in which the dissolved anions comprise at least sulfate, alkylsulfonate (preferably methanesulfonate) and / or alkylsulfate (preferably methylsulfate). The term "dissolved anions" refers to anions that are dissolved in the catholyte prior to step (f), i.e. that are dissolved without the treatment of step (f). This means that step (f) makes it possible to remove at least a portion of the anions that would otherwise remain dissolved and accumulate in the catholyte.

[0147] By applying step (f), the concentration of dissolved anions, most preferably sulfate and / or (preferably and) carbonate ions, in the catholyte is significantly reduced and excessive accumulation is avoided. As a result, the method of the present invention allows for very long operation. Preferably, step (f) is applied when the dissolved anions, individually or in total, reach undesirable concentrations. Preferably, step (f) comprises precipitation to remove one or more of such dissolved anions from the catholyte, most preferably by reducing the temperature of at least a portion of the catholyte in the second treatment zone, thereby reducing the solubility of the respective salts. Most preferably, the treatment in step (f) results in the formation of a solid precipitate, preferably a sodium-containing solid precipitate, most preferably comprising sodium sulfate in addition to at least sodium sulfate or sodium carbonate.

[0148] Preferred is the process of the invention, 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, and most preferably in the range of -1°C to 4°C.

[0149] Therefore, the method of the invention is most preferred, in which the dissolved anions comprise at least sulfate ions, which are preferably separated from the catholyte by precipitated sodium sulfate, which preferably also makes it possible to remove sodium ions, which are usually present in large amounts in the catholyte.

[0150] Halogen anions in aqueous zinc-nickel deposition baths / catholytes As mentioned above, in step (d) a brightener source is added directly or indirectly to the catholyte, said source being substantially free of halogen anions, preferably free of halogen anions. It is highly preferred to maintain a relatively low concentration of halogen anions in the entire catholyte over the entire life of the catholyte. Most preferably, halogen anions are absent.

[0151] The method of the invention is preferred, wherein the catholyte (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 0 g / L to 8 g / L, more preferably 0 g / L to 6 g / L, even more preferably 0 g / L to 5 g / L, most preferably 0 g / L to 4 g / L, and even most preferably 0 g / L to 3 g / L, relative to the total volume of the catholyte. This applies preferably for at least one nickel ion turnover, more preferably for at least two nickel ion turnovers, even more preferably for at least three nickel ion turnovers, most preferably for a large number of nickel ion turnovers, and even most preferably for the entire life of the aqueous zinc-nickel deposition bath used as catholyte.

[0152] Preferred is the process of the invention, provided that in addition to the total concentration of halogen anions mentioned above, the catholyte (i.e. preferably also the aqueous zinc-nickel deposition bath) 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.

[0153] In some cases, the method of the present invention is preferred in which the low concentration limit for 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 inconsequential residual amounts of halogen anions are not a problem.

[0154] It has already been mentioned above that the catholyte may contain further compounds and ions, respectively. The catholyte (i.e. preferably also the aqueous zinc-nickel deposition bath) may (i.e. in addition to (i), (ii), (iii) and preferably one or more complexing agents): (iv) at least one alkali metal cation; (v) sulfate ion, (vi) carbonate ion, and (vii) a halogen anion, Further comprising: However, with respect to the total volume of the cathode fluid, - (i), (iii), and (iv)-(vii) together have a total concentration in the range of 20 g / L to 270 g / L; - The total concentration of halogen anions does not exceed 10 g / L; The method of the present invention is preferred.

[0155] The remarks made above regarding the halogen anions preferably apply here as well.

[0156] This total concentration is deliberately defined as a range, reflecting the state immediately after step (f) is performed, with a lower limit of, for example, 20 g / L, and an upper limit of, for example, 270 g / L, immediately before step (f). In other words, a method of the invention is preferred in which said total concentration is permanently maintained within this range while the method of the invention is performed. This preferably includes repeating the method of the invention.

[0157] As already indicated above, the major contributors to said total concentration are sulfate ions, carbonate ions and at least one alkali metal cation (preferably sodium and / or potassium ions, but mainly sodium ions). When said total concentration reaches said 270 g / L, step (f) is most preferably carried out. However, step (f) can also be carried out at lower total concentrations. However, when said total concentration significantly exceeds 270 g / L, the quality of the precipitation is in some cases already significantly impaired.

[0158] However, a total concentration of 20 g / L or slightly more is usually highly desirable throughout the process of the invention, and this is most preferably achieved after step (f) has been carried out.

[0159] Therefore, the method of the present invention is preferred, in which (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, and most preferably 45 g / L to 220 g / L. In these preferred ranges, the lower limit preferably applies to the state immediately after step (f) is performed, and the upper limit preferably applies to the state immediately before step (f).

[0160] In some cases, the method of the present invention is preferred, where (i), (iii) and (iv)-(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 is most preferably applied just before step (f) is carried out. These are typical and preferred total concentrations which trigger step (f).

[0161] In some cases, the method of the present invention is preferred, wherein (i), (iii) and (iv)-(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, and most preferably 40 g / L to 60 g / L, which is most preferably applied immediately after step (f) has been carried out.

[0162] The process of the present invention is preferred, in which (v) and (vi) together have a total concentration of at least 20 g / L, preferably at least 25 g / L, most preferably at least 30 g / L. Such a total concentration of (v) and (vi) together is usually well tolerated and highly preferred, especially if the upper limit of 60 g / L is not exceeded. It is therefore highly preferred to maintain such a total concentration of (v) and (vi) together throughout the process of the present invention.

[0163] In some cases, the process of the invention is preferred, where (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 a concentration is maintained throughout the process of the invention. Most preferably, the lower limit is applied immediately after step (f) is performed, and the upper limit is preferably applied immediately before step (f).

[0164] In summary, the method of the present invention allows for economical and sustainable continuous operation over long periods of time, i.e., months, weeks, or even years. No nickel-contaminated wastewater is produced over such periods, and no valuable metal ions, complexing agents, or brighteners are lost due to drag-out. Essentially, only the amount of nickel ions, zinc ions, and brighteners consumed needs to be replenished. Furthermore, halogen anions are kept low, so that no adverse effects, such as corrosion, are observed in and on the equipment.

[0165] The present invention also provides a specific aqueous zinc-nickel deposition bath for depositing a zinc-nickel alloy, the bath comprising: (i) nickel ions, (ii) at least one brightening agent; (iii) zinc ions, Including, (iv) at least one alkali metal cation; (v) sulfate ion, (vi) carbonate ion, and (vii) a halogen anion, Further comprising: However, based on the total volume of the aqueous zinc-nickel deposition bath, - (i), (iii), and (iv)-(vii) together have a total concentration in the range of 20 g / L to 270 g / L; - The total concentration of halogen anions does not exceed 10 g / L; For aqueous zinc-nickel deposition baths.

[0166] What has been said above with respect to the process of the invention, in particular with respect to the aqueous zinc-nickel deposition bath and the catholyte respectively utilized in the process of the invention, preferably applies analogously to the aqueous zinc-nickel deposition bath of the invention (preferably, where technically applicable), and most preferably also to what has been said above with respect to the at least one brightener.

[0167] Most preferably, the aqueous zinc-nickel deposition bath of the present invention is not a freshly prepared aqueous zinc-nickel deposition bath, but rather an "in-use" bath, i.e. an utilized aqueous zinc-nickel deposition bath, in other words one that has already been in contact with an electric current, preferably one as defined in step (c) of the method of the present invention.

[0168] The present invention also relates to a process for the deposition of zinc-nickel alloys, comprising the steps of:

[0169] [ka]

[0170] (In the formula, R 1 represents C1-C4 alkyl, unsubstituted phenylalkylene, or substituted phenylalkylene; R 2 OH, OZ, OR 3 , NH2, or NR 3 R 4 represents Z represents an alkali metal, ammonium or alkylammonium cation, preferably a sodium, potassium, ammonium or tetraalkylammonium cation; R 3 each independently represents an alkyl group, preferably a C1-C4 alkyl group; R 4 each independently represents hydrogen or alkyl, preferably hydrogen or C1-C4 alkyl; X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate, and sulfonate. The present invention relates to a specific polishing agent and / or its ester.

[0171] What has been said above with respect to the process of the invention, and in particular with respect to the at least one brightener employed in the aqueous zinc-nickel deposition bath and the catholyte employed in the process of the invention, preferably applies equally to the brighteners of formula (Ia) of the invention (preferably, where technically applicable).This also applies most preferably to the compounds of formula (Ib), (A), (B), (C), (D) and their esters as defined in relation to the process of the invention, and is likewise preferred for the brighteners of the invention.

[0172] R 1 Preferred are brighteners of the present invention, wherein C1-C4 alkyl comprises methyl, ethyl, n-propyl, iso-propyl, n-butyl, or iso-propyl, preferably methyl, ethyl, or iso-butyl.

[0173] R 1 Preferred are brighteners of the present invention wherein the phenyl alkylene comprises benzyl.

[0174] R 2 Preferred are brighteners of the present invention wherein Z represents ONa, OK (i.e., Z represents a sodium or potassium cation), or NH2.

[0175] Preferred are brighteners of the present invention in which X comprises sulfate and / or methylsulfate ions.

[0176] The present invention also relates to a compound of formula (Ia) as a brightener for replenishing the brightener in an aqueous zinc-nickel deposition bath.

[0177] [ka]

[0178] (In the formula, R 1 represents C1-C4 alkyl, unsubstituted phenylalkylene, or substituted phenylalkylene; R 2 OH, OZ, OR 3 , NH2, or NR 3 R 4 represents Z represents an alkali metal, ammonium or alkylammonium cation, preferably a sodium, potassium, ammonium or tetraalkylammonium cation; R 3 each independently represents an alkyl group, preferably a C1-C4 alkyl group; R 4 each independently represents hydrogen or alkyl, preferably hydrogen or C1-C4 alkyl; X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate, and sulfonate. and / or esters thereof.

[0179] What has been said above with respect to the method of the invention, and in particular with respect to the at least one brightener employed in the aqueous zinc-nickel deposition bath and the catholyte employed in the method of the invention, preferably applies equally to the use of the invention (preferably, where technically applicable).This also applies most preferably to the compounds of formulae (Ib), (A), (B), (C), (D) and their esters as defined with respect to the method of the invention, which are likewise preferred for the use of the invention.

[0180] The use of the present invention is highly preferred, in which the brightener source comprises or consists of the compounds of formula (Ia) and their esters as defined throughout this specification, most preferably the compounds of formula (Ia) and their esters as defined throughout this specification as preferred, with the proviso that said source is substantially free of halogen anions, preferably free of halogen anions.What has been said above regarding the brightener source in the context of the method of the present invention preferably also applies to the use of the present invention.

[0181] The use according to the invention, where said compounds of formula (Ia) and their esters and the brighteners (i.e. those which are replenished) in the aqueous zinc-nickel deposition baths are identical, is preferred.

[0182] Highly preferred is the use of the present invention, in which the compound of formula (Ia) and / or said ester thereof is used in a loop, preferably in a zinc-nickel deposition bath, which is utilized in the method for depositing zinc-nickel alloys according to the invention.

[0183] The invention will now be described in more detail by the following non-limiting examples. EXAMPLES

[0184] (I) Synthesis of gloss agents Compound of formula (A) In a 100 mL glass reactor equipped 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 increased to 62° C. After the addition was complete, the resulting reaction mixture was kept at 50° C. for an additional 21 hours.

[0185] As a result, 90.4 g of a colorless solution was obtained (44% by weight, quantitative yield). NMR analysis showed the following: 1 H-NMR (D2O; 400 MHz): δ3.74 (s; 3H); 4.51 (s; 3H); 8.21 (t; 3 J = 8 Hz); 8.92 (d;3 J = 4 Hz; 1H); 9.00 (d; 3 J = 4 Hz; 1H); 9.30 (s; 1H).

[0186] Compound of formula (C) In a 50 mL glass reaction vessel equipped with a reflux condenser, 5 g (40.1 mmol) of nicotinamide was suspended in 15 mL of acetonitrile at 25° C. Then, 8.12 g (40.1 mmol) of benzyl mesylate was added to the suspension and the reaction mixture was stirred for an additional 16 h at 50° C. After completion of the reaction, excess solvent was removed under vacuum.

[0187] As a result, 12.92 g (quantitative yield) of a yellow-orange oil was obtained. NMR analysis showed the following results. 1 H-NMR (d6-DMSO, 400 MHz): δ2.38 (s; 3H); 5.97 (s; 2H); 7.45 - 7.46 (m; 3H); 7.61 (dd; 3 J = 4 Hz; 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 = 4 Hz; 1H); 9.66 (s; 1H). 13 C-NMR (d6-DMSO; 100 MHz): δ39.78; 63.61; 128.36; 129.04; 129.26; 134.19; 143.87; 144.82; 146.45; 148.55; 151.74; 162.74.

[0188] After synthesis, no further purification was necessary due to the absence of harmful halogen ions.

[0189] (II) Refining of polishing agents Alternatively, a commercially available brightener of compound (D) (purchased from BASF, Raschig) with the only difference being that X represents a chloride ion was purified on an ion exchange column to replace the chloride ion with a sulfate ion.

[0190] (III) Test Deposition on Substrate Test aqueous zinc-nickel deposition baths A, B, and C were set up as catholytes in the deposition compartment (about 25 L) for depositing zinc-nickel alloy on a charge of small metal parts (screws M8x55). Test bath A was designed as a comparative example, while B and C were baths according to the invention, i.e. the brightener was modified so that the respective brightener source did not contain a significant amount of halogen ions.

[0191] A, B, and C initially contained about 1.3 g / L of nickel(II) ions, about 8.5 g / L of zinc(II) ions, and a diamine having at least one secondary amine group as a chelating complexing agent for the nickel ions. The pH was about 12.5, strongly alkaline, and was adjusted with sodium hydroxide (initially about 120-140 g / L NaOH). The zinc(II) ions were present as hydroxo complexes.

[0192] The following compounds were used as brighteners: A: Compound (D) (X represents a chloride ion). B: Compound (D) (X represents a sulfate ion (see (II) above)) C: Compound (C) (X represents a mesylate ion (see (I) above))

[0193] The initial concentration of each brightener was approximately 200 mg / L based on the total volume of the respective aqueous zinc-nickel deposition bath.

[0194] Test plating was then carried out until the bath utilization reached 100Ah / L. Test plating was carried out at a temperature of about 25°C to 30°C for about 60 minutes, with a current of about 0.5A / dm per thread charge. 2During this time, the bath parameters outlined in the table below were monitored. Dummy plating was performed using steel plates (20 cm x 30 cm). Typically, the detection limit for chloride in this test was approximately 50 mg / L or less. Nickel ions and brightener were replenished every 10 Ah (brightener was the same). The nickel ion source (nickel sulfate) did not contain any complexing agent or halide ions. Zinc was replenished from metallic zinc dissolved under alkaline pH conditions. No additional complexing agent for zinc ions was used because of the formation of zinc hydroxide complexes under alkaline conditions. The catholyte and anolyte were separated from each other by a cation exchange membrane. Insoluble iridium / tantalum oxide on titanium was used as the anode. The distance between the anode and the respective membrane was less than 5 mm. The anolyte, which contained water and sulfuric acid, was separated from the catholyte by said membrane so that neither the complexing agent nor the brightener came into contact with the anode.

[0195] Due to the separation of the anolyte and catholyte, the catholyte does not contain decomposition products such as cyanide and oxalate ions, which ensures that neither the complexing agent nor the at least one brightener is decomposed in the deposition compartment.

[0196] [Table 1]

[0197] [Table 2]

[0198] [Table 3]

[0199] While using the 100 Ah / L bath, no treatment was necessary in the second treatment compartment, i.e. the critical concentrations of sulfate and carbonate ions had not yet been reached.

[0200] The above test depositions clearly show that the brighteners used in B and C prevent the buildup of halogen ions due to the absence of halogen ions other than chloride ions. Thus, the buildup of chloride ions in particular is significantly prevented. Moreover, the entire deposition method according to the invention can be carried out at relatively low halogen ion concentrations.

[0201] In the test plating, the nickel content in the zinc-nickel alloy was 13-14%.

[0202] In general, the method of the present invention can be implemented not only in rack applications (data not shown) but also in barrel applications (specifically shown above). For rack applications, nickel concentrations of less than 1 g / L are generally preferred, and less than 0.8 g / L are most preferred. Furthermore, the substrate obtained after step (c) can be washed in step (e), and the wash water is further treated to obtain a separated water and a concentrated aqueous solution (data not shown).

Claims

1. 1. A method for depositing a zinc-nickel alloy on a substrate, comprising the steps of: (a) providing a substrate; (a-1) optionally pre-washing a substrate with water in a pre-wash compartment to obtain a pre-washed substrate and pre-wash water; (b) providing an aqueous zinc-nickel deposition bath as a catholyte in a deposition compartment; - the deposition compartment comprises at least one anode having an anolyte; - the anolyte is separated from the catholyte by at least one membrane, the catholyte comprising: (i) nickel ions, (ii) at least one brightener, and (iii) zinc ions, and (c) contacting a substrate or a pre-cleaned substrate with the catholyte in the deposition compartment such that a zinc-nickel alloy is electrolytically deposited on the substrate, thereby obtaining a zinc-nickel coated substrate; after step (c), the at least one brightener has a lower concentration than before step (c); Including, After step (c), (d) adding a brightener source directly or indirectly to said catholyte, said source being substantially free of halogen anions, preferably free of halogen anions. A method comprising:

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

3. 3. The method of claim 1 or 2, wherein the at least one polishing agent comprises at least N-benzyl nicotinate, esters thereof, N-benzyl nicotinamide, N-alkyl nicotinate, esters thereof, and / or N-alkyl nicotinamide.

4. (e) washing the zinc-nickel coated substrate with water in a washing compartment to obtain a washed zinc-nickel coated substrate and washing water, the washing water comprising at least a portion of the at least one brightener and / or one or more complexing agents for nickel ions.

4. The method of claim 1, further comprising:

5. at least a portion of the catholyte, at least a portion of the wash water, and / or at least a portion of the pre-wash water are treated in a first treatment compartment such that water is separated therefrom, resulting in a separated water and a concentrated aqueous solution; directly or indirectly, at least a portion of the concentrated aqueous solution is returned to the catholyte; 5. The method according to any one of claims 1 to 4.

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

7. 7. The method according to any one of claims 1 to 6, wherein the at least one anode has a distance to the at least one membrane 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. 7. The method according to claim 5 or 6, wherein the first processing compartment comprises an evaporator, preferably a vacuum evaporator.

9. (f) treating at least a portion of said catholyte in a second treatment compartment such that dissolved anions are separated from the catholyte, preferably by precipitation and / or ion exchange, most preferably by precipitation.

9. The method of claim 1, further comprising:

10. The catholyte is (iv) at least one alkali metal cation; (v) sulfate ion, (vi) carbonate ion, and (vii) a halogen anion, Further comprising: However, with respect to the total volume of the cathode fluid, - (i), (iii), and (iv) to (vii) together have a total concentration in the range of 20 g / L to 270 g / L; - The total concentration of halogen anions does not exceed 10 g / L; 10. The method according to any one of claims 1 to 9.

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

12. 12. The method according to any one of claims 1 to 11, wherein the catholyte comprises a total concentration of halogen anions 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, and even most preferably in the range of 0 g / L to 3 g / L relative to the total volume of the catholyte.

13. 1. An aqueous zinc-nickel deposition bath for depositing a zinc-nickel alloy, said bath comprising: (i) nickel ions, (ii) at least one brightening agent; (iii) zinc ions, Including, (iv) at least one alkali metal cation; (v) sulfate ion, (vi) carbonate ion, and (vii) a halogen anion, Further including However, 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; - the total concentration of said halogen anions does not exceed 10 g / L; Aqueous zinc-nickel deposition bath.

14. Formula (Ia) 【Chemistry 1】 (In the formula, R 1 represents C1-C4 alkyl, unsubstituted phenylalkylene, or substituted phenylalkylene; R 2 OH, OZ, OR 3 , N.H. 2 , or NR 3 R 4 represents Z represents an alkali metal, ammonium or alkylammonium cation, preferably a sodium, potassium, ammonium or tetraalkylammonium cation; R 3 represents independently alkyl, preferably C1-C4 alkyl; R 4 represents independently hydrogen or alkyl, preferably hydrogen or C1-C4 alkyl; X represents an anion selected from the group consisting of sulfate ion, methyl sulfate ion, formate ion, acetate ion, mesylate ion, tosylate ion, triflate ion, carbonate ion, and sulfonate ion. and / or its esters.

15. Compounds of formula (Ia) as brighteners for replenishing brighteners in aqueous zinc-nickel deposition baths 【Chemistry 2】 (In the formula, R 1 represents C1-C4 alkyl, unsubstituted phenylalkylene, or substituted phenylalkylene; R 2 But OH, OZ, OR 3 , N.H. 2 , or NR 3 R 4 represents Z represents an alkali metal, ammonium or alkylammonium cation, preferably a sodium, potassium, ammonium or tetraalkylammonium cation, R 3 represents independently alkyl, preferably C1-C4 alkyl; R 4 represents independently hydrogen or alkyl, preferably hydrogen or C1-C4 alkyl; X represents an anion selected from the group consisting of sulfate, methylsulfate, formate, acetate, mesylate, tosylate, triflate, carbonate, and sulfonate. and / or esters thereof.

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