Method for reducing the concentration of iron ions in a trivalent chromium plating bath

Abstract

This invention relates to a method for reducing the iron ion concentration in a trivalent chromium electroplating bath, the method comprising the steps of: (i) providing the trivalent chromium electroplating bath, comprising: (a) trivalent chromium ions, and (b) iron ions; (ii) subjecting at least a portion of the trivalent chromium electroplating bath to air agitation to obtain at least an air-agitated portion of the trivalent chromium electroplating bath; (iii) contacting the air-agitated portion of the trivalent chromium electroplating bath with an ion exchange resin to obtain a resin-treated portion of the trivalent chromium electroplating bath; and (iv) returning the resin-treated portion of the trivalent chromium electroplating bath to the trivalent chromium electroplating bath, provided that the trivalent chromium electroplating bath provided in step (i) has been used or is being used in an application of 18 A / dm³. 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate; - after step (iii), the concentration of iron ions in the resin treatment section of the trivalent chromium plating bath is lower than the concentration in the air agitation section of the trivalent chromium plating bath; and - after step (iv), based on the total volume of the trivalent chromium plating bath, the concentration of iron ions in the trivalent chromium plating bath is lower than 50 mg / L.

Description

Technical Field

[0001] This invention relates to a method for reducing the iron ion concentration in a trivalent chromium electroplating bath. In particular, the trivalent chromium electroplating bath subjected to the method of this invention allows for the electrolytic deposition of a functional chromium layer, also known as a hard chromium layer, on a substrate, especially on an iron-containing substrate, and most particularly on an iron-containing substrate coated with nickel or nickel alloys. Background Technology

[0002] Compared to decorative chromium layers, which are typically significantly thinner than 1 μm (or even less than 500 nm), functional chromium layers generally have a much higher average layer thickness, typically ranging from at least 1 μm to several hundred micrometers, and are characterized by excellent hardness and wear resistance.

[0003] Functional chromium layers obtained from electroplating baths containing hexavalent chromium are known and recognized as the standard in the prior art.

[0004] In recent decades, chromium deposition methods relying on hexavalent chromium have been increasingly replaced by deposition methods relying on trivalent chromium. These trivalent chromium-based methods are healthier and more environmentally friendly.

[0005] WO 2015 / 110627 A1 relates to an electroplating bath for depositing chromium and a method for depositing chromium on a substrate using said electroplating bath.

[0006] US 2,748,069 relates to a chromium plating solution that allows for the very rapid acquisition of a chromium coating with excellent physical and mechanical properties. The chromium plating solution can be used with specific electrolytic methods, such as those known for spot, pin, or pencil plating. In these specific methods, the substrate is typically not immersed in the appropriate plating solution.

[0007] WO 2018 / 185154 A1 discloses a method for electrolytically depositing a chromium or chromium alloy layer on a substrate.

[0008] EP 0 455 403 B1 discloses a process for regenerating a trivalent chromium bath and teaches how to maintain the desired amount of iron cations in the bath at 50 ppm to 100 ppm.

[0009] Typically, deposition methods relying on trivalent chromium are used to electrolytically deposit chromium layers on iron-containing substrates, particularly on nickel or nickel alloy-coated iron-containing substrates, where equipment components made of iron and / or containing copper are often used during the deposition process, for example, to hold the substrate.

[0010] Typically, trivalent chromium plating baths are used multiple times to deposit chromium layers on multiple iron-containing substrates, thereby improving process efficiency and allowing for significant cost reduction.

[0011] However, it is frequently observed that the iron ion concentration in trivalent chromium plating baths continuously increases after repeated use on iron-containing substrates, particularly nickel- or nickel alloy-coated iron-containing substrates and iron-containing equipment components. This increase in iron ion concentration may be due to partial dissolution of the iron-containing substrate and / or the corresponding equipment components in the trivalent chromium plating bath.

[0012] In many cases, an increase in the iron ion concentration in a trivalent chromium plating bath can lead to an undesirable black discoloration of the substrate and may even significantly impair the process of depositing a chromium layer on the substrate, for example by altering the quality of the deposited chromium layer, by reducing the hardness of the deposited chromium layer, and / or by preventing or at least severely inhibiting the chromium deposition process itself.

[0013] Furthermore, after repeated use of this trivalent chromium plating bath, an increase in the concentration of copper and nickel ions in the trivalent chromium plating bath was observed in some cases, which also had a negative impact on the deposition process of chromium on the substrate, such as undesirable discoloration.

[0014] Purpose of the invention

[0015] Therefore, the object of the present invention is to provide a method, particularly for reducing the concentration of contaminating iron ions in a trivalent chromium plating bath used for electrodepositing chromium layers, especially functional chromium layers. Advantageously, the concentration of interfering iron ions decreases with the concentration of copper and / or nickel ions. This method will ensure that the corresponding trivalent chromium plating bath can be used for a long time, preferably throughout its entire lifespan, without compromising the quality of the functional chromium layer (e.g., in terms of hardness and abrasion resistance). Summary of the Invention

[0016] The above objective is achieved by a method for reducing the iron ion concentration in a trivalent chromium electroplating bath, the method comprising the following steps:

[0017] (i) Provide a trivalent chromium plating bath, which comprises:

[0018] (a) Trivalent chromium ions, and

[0019] (b) Iron ions,

[0020] (ii) subjecting at least a portion of the trivalent chromium plating bath to air agitation to obtain at least an air-agitated portion of the trivalent chromium plating bath.

[0021] (iii) The air agitation section of the trivalent chromium electroplating bath is brought into contact with the ion exchange resin to obtain the resin treatment section of the trivalent chromium electroplating bath, and

[0022] (iv) Return the resin treatment portion of the trivalent chromium plating bath to the trivalent chromium plating bath.

[0023] The attached conditions are

[0024] - The trivalent chromium plating bath provided in step (i) has been used or is being used in the application of 18 A / dm 2 Or, in the case of a higher cathode current density, electrodeposit a chromium layer on at least one substrate.

[0025] - After step (iii), the concentration of iron ions in the resin treatment section of the trivalent chromium plating bath is lower than the concentration in the air agitation section of the trivalent chromium plating bath, and

[0026] - After step (iv), based on the total volume of the trivalent chromium plating bath, the iron ion concentration in the trivalent chromium plating bath is less than 50 mg / L.

[0027] By contacting the trivalent chromium plating bath with an ion exchange resin (e.g., in step (iii) of the method of the present invention), the ion exchange resin binds cations, particularly iron ions, which accumulate in the trivalent chromium plating bath over time, thereby reducing the iron ion concentration in the trivalent chromium plating bath.

[0028] However, it has been observed that when the trivalent chromium plating bath is subjected to air agitation (e.g., in step (ii) of the method of the present invention) before contact with the ion exchange resin, the efficiency of reducing the iron ion concentration in the trivalent chromium plating bath can be significantly improved.

[0029] As a result, the method of the present invention combines two advantageous steps to synergistically improve the efficiency of reducing iron ion concentration. This combination ensures a longer lifespan for the trivalent chromium electroplating bath and stable quality of the electrodeposited chromium layer over time, which in turn helps to minimize waste and wastewater.

[0030] By returning the resin-treated portion of the trivalent chromium plating bath to the trivalent chromium plating bath in step (iv), it is preferable to provide a continuous or at least discontinuous (semi-continuous) flow cycle, which ensures the ongoing treatment during the method, thereby ensuring the high quality of the electrodeposited chromium layer over a long period of time, comparable to that of a newly established trivalent chromium plating bath.

[0031] In the preferred embodiment of the method of the present invention, in step (i), the trivalent chromium electroplating bath further comprises (i.e., in addition to iron ions)

[0032] (c) Copper ions, and / or

[0033] (d) Nickel ions,

[0034] The attached conditions are

[0035] - After step (iii), the concentrations of copper ions and / or nickel ions in the resin treatment section of the trivalent chromium plating bath are lower than those in the air agitation section of the trivalent chromium plating bath, wherein preferably the concentrations of copper ions and / or nickel ions in the resin treatment section of the trivalent chromium plating bath are lower than 50 mg / L or less.

[0036] Therefore, in addition to reducing the iron ion concentration in the trivalent chromium plating bath, the concentration of nickel and / or copper ions can also be effectively reduced (and thus maintained at a relatively low concentration) by using the method of the present invention.

[0037] Brief description of the table

[0038] Table 1 shows a schematic correlation between iron ion concentration and the resulting optical appearance of the electrodeposited chromium layer. Further details are given in the "Examples" section below. Detailed Implementation

[0039] In the context of this invention, the terms "at least one" or "one or more" respectively mean (and are interchangeable with) "one, two, three or more" and "one, two, three or more". Furthermore, "trivalent chromium" refers to chromium with an oxidation state of +3. The term "trivalent chromium ion" refers to Cr in its free or complexed form. 3+ Ions. Similarly, "hexavalent chromium" refers to chromium with an oxidation state of +6 and related compounds containing hexavalent chromium ions.

[0040] In the trivalent chromium plating bath provided in step (i) and used or currently used for electrodepositing a chromium layer on at least one substrate, no hexavalent chromium was intentionally added. Therefore, the trivalent chromium plating bath provided in step (i) is substantially free of or contains no hexavalent chromium (except for a very small amount of hexavalent chromium that can be anoly formed).

[0041] The ion exchange resin used in step (iii) has low selectivity for trivalent chromium ions, such that the concentration of trivalent chromium ions in the resin treatment section of the trivalent chromium plating bath is not significantly reduced compared to the air-stirred section of the trivalent chromium plating bath. Conversely, the ion exchange resin used in step (iii) is substantially selective for exchanging iron ions, and preferably also selective for copper and / or nickel and / or zinc ions.

[0042] The method of the present invention includes steps (i), (ii), (iii), and (iv), wherein the preferred order is (i), followed by (ii), followed by (iii), and then (iv). In cases where the method involves a closed-loop cycle, after step (iv), step (i) is performed again, followed by step (ii), followed by step (iii), and then step (iv) is performed again. Preferably, the method of the present invention comprises multiple repetitions of steps (i), (ii), (iii), and (iv).

[0043] Preferably, the trivalent chromium plating bath is an aqueous trivalent chromium plating bath containing trivalent chromium ions and iron ions. In some cases, but less preferably, the trivalent chromium plating bath contains a solvent other than water, preferably an organic solvent. Most preferably, water is the only solvent.

[0044] The present invention relies on the discovery that subjecting at least a portion of a trivalent chromium plating bath to air agitation, and subsequently contacting the air-agitated portion of the trivalent chromium plating bath with an ion exchange resin, removes iron ions from the air-agitated portion of the trivalent chromium plating bath in at least a portion, thereby reducing the iron ion concentration in the trivalent chromium plating bath.

[0045] The trivalent chromium plating bath is preferably used more than once for depositing chromium layers on multiple different substrates, preferably during a continuous process. Preferably, the trivalent chromium plating bath is reused during plating, preferably at least 100 Ah per liter, more preferably at least 150 Ah per liter, more preferably at least 200 Ah per liter, and most preferably at least 300 Ah per liter.

[0046] Since trivalent chromium plating baths are preferably used for depositing chromium layers on multiple substrates, particularly iron-containing substrates, iron ions from the substrate, especially iron-containing substrates, can dissolve from the substrate and accumulate in the trivalent chromium plating bath over time, thereby continuously increasing the iron ion concentration in the trivalent chromium plating bath. By implementing the method of the present invention to reduce the iron ion concentration in the trivalent chromium plating bath, the dissolution of iron ions from the substrate during plating can be balanced, allowing the iron ion concentration in the trivalent chromium plating bath to be kept below a critical limit.

[0047] The method of the present invention allows for maintaining a high-quality chromium layer comparable to that of a newly set trivalent chromium electroplating bath.

[0048] A further important finding is that the efficiency of removing iron ions through ion exchange resins can be significantly improved when air agitation is used.

[0049] Preferably, the air-agitated portion of the trivalent chromium plating bath comes into immediate contact with the ion exchange resin after air agitation. Preferably, the air-agitated portion of the trivalent chromium plating bath is transferred to the ion exchange resin without any interruption or delay after air agitation. This particularly ensures that a large amount of oxygen is present in the air-agitated portion of the trivalent chromium plating bath before it comes into contact with the ion exchange resin, thereby improving the efficiency of iron ion removal. Preferably, in step (ii), the trivalent chromium plating bath is subjected to air agitation for at least 5 minutes.

[0050] According to another important discovery of the present invention, when using a cathode current density of 18 A / dm 2 In high-current electroplating processes, or even larger ones, reducing the iron ion concentration in the trivalent chromium plating bath becomes crucial.

[0051] Although when using a cathode current density of 15 A / dm 2 In electroplating processes with even lower currents, the concentration of iron ions in the trivalent chromium plating bath can usually be controlled to a certain level (and is even desirable in decorative applications), but for the aforementioned cathode current density of 18 A / dm³, this is not possible. 2 This is not the case with high-current electroplating processes, or even higher-current processes. In such high-current electroplating processes, at the relatively high iron ion concentration in the trivalent chromium plating bath, iron can be incorporated into the deposited chromium layer during electroplating, thereby impairing the corrosion resistance of the corresponding sites and causing an undesirable black discoloration of the deposited chromium layer.

[0052] Therefore, maintaining the iron ion concentration in the trivalent chromium plating bath below 50 mg / L is crucial for this high-current plating process (i.e., a cathode current density of 18 A / dm³). 2 (or larger) is crucial.

[0053] Corresponding to the wording used for the method of the present invention, the method of the present invention preferably includes, preferably before step (i) - applying 18A / dm 2 Or a higher cathode current density and use a trivalent chromium plating bath to electrodeposit a chromium layer on at least one substrate.

[0054] This is the preferred equivalent of the first additional condition defined above in the context of this invention, and is preferably used instead of this terminology. Preferably, during electroplating, iron ions accumulate in the trivalent chromium plating bath. Preferably, after an undesirable amount of iron ions is reached, the plating bath undergoes steps (i) to (iv) of the method of the present invention.

[0055] In the preferred method of the present invention, in step (i), based on the total volume of the trivalent chromium electroplating bath, the iron ion concentration in the trivalent chromium electroplating bath is 40 mg / L or lower, preferably 30 mg / L or lower, more preferably 20 mg / L or lower, even more preferably 15 mg / L or lower, and most preferably 11 mg / L or lower.

[0056] In the preferred method of the present invention, after step (iv), the iron ion concentration in the trivalent chromium plating bath is 35 mg / L or lower, preferably 25 mg / L or lower, more preferably 18 mg / L or lower, even more preferably 13 mg / L or lower, and most preferably 10 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

[0057] Preferably, in the method of the present invention, in step (i), the iron ion concentration in the trivalent chromium plating bath is higher than 40 mg / L, and after step (iv), the iron ion concentration in the trivalent chromium plating bath is 40 mg / L or lower, each based on the total volume of the trivalent chromium plating bath. Preferably, in step (i), the iron ion concentration in the trivalent chromium plating bath is higher than 30 mg / L, and after step (iv), the iron ion concentration in the trivalent chromium plating bath is 30 mg / L or lower. More preferably, in step (i), the iron ion concentration in the trivalent chromium plating bath is higher than 20 mg / L, and after step (iv), the iron ion concentration in the trivalent chromium plating bath is 20 mg / L or lower.

[0058] The preferred method of the present invention is wherein, in step (i), the iron ion concentration in the trivalent chromium plating bath is higher than 10 mg / L, and after step (iv), the iron ion concentration in the trivalent chromium plating bath is 10 mg / L or lower, each based on the total volume of the trivalent chromium plating bath.

[0059] In the preferred method of the present invention, in step (iii), based on the total volume of the resin treatment portion of the trivalent chromium electroplating bath, the iron ion concentration in the resin treatment portion of the trivalent chromium electroplating bath is 9 mg / L or lower, preferably 8 mg / L or lower, more preferably 7 mg / L or lower, even more preferably 6 mg / L or lower, even more preferably 5 mg / L or lower, and most preferably 4 mg / L or lower.

[0060] By reducing the iron ion concentration in the trivalent chromium plating bath in step (iii) to below 50 mg / L, particularly to 35 mg / L or lower, 25 mg / L or lower, 18 mg / L or lower, 13 mg / L or lower, 10 mg / L or lower or even below 10 mg / L, the quality of the trivalent chromium plating bath is generally maintained, which allows for the deposition of a high-quality chromium layer on the substrate, comparable to that obtained from a newly set trivalent chromium plating bath.

[0061] In particular, the high ferric ion removal efficiency of the ion exchange resin can be maintained at both high initial ferric ion concentrations, i.e., when the ferric ion concentration in the trivalent chromium electroplating in step (i) is higher than 40 mg / L (including much higher than 40 mg / L), and low initial ferric ion concentrations, i.e., when the ferric ion concentration in the trivalent chromium electroplating in step (i) is 40 mg / L or lower, 30 mg / L or lower, 20 mg / L or lower, preferably 15 mg / L or lower, or even 11 mg / L.

[0062] Preferably, in the method of the present invention, in step (i), the trivalent chromium electroplating bath further comprises

[0063] (c) Copper ions, and / or

[0064] (d) Nickel ions,

[0065] The attached conditions are

[0066] - After step (iii), the concentrations of copper ions and / or nickel ions in the resin treatment section of the trivalent chromium plating bath are lower than those in the air agitation section of the trivalent chromium plating bath.

[0067] Due to the advantageous cation-binding properties of ion exchange resins, ion exchange resins not only remove iron ions from the trivalent chromium plating bath in step (iii), but also remove copper ions and / or nickel ions.

[0068] Therefore, the method of the present invention is preferred, wherein the ion exchange resin has an affinity for iron ions and trivalent chromium ions, wherein the affinity for iron ions is higher than the affinity for trivalent chromium ions. More preferably, the method of the present invention contains an affinity for iron ions, copper ions, nickel ions, and trivalent chromium ions, wherein the affinity for iron ions, copper ions, and nickel ions is higher than the affinity for trivalent chromium ions.

[0069] During electroplating, equipment components are typically used, from which copper ions can dissolve to a certain extent, causing the copper ion concentration in the trivalent chromium plating bath to increase over time, similar to the iron ion concentration in the trivalent chromium plating bath.

[0070] Furthermore, since trivalent chromium plating is typically used to deposit a chromium layer on a nickel or nickel alloy coated substrate during plating, nickel can also dissolve from the nickel or nickel alloy coated substrate, causing the concentration of nickel ions in the trivalent chromium plating bath to increase over time, similar to the concentration of iron ions and / or copper ions in the trivalent chromium plating bath.

[0071] When using this trivalent chromium plating bath during electroplating, the relatively high concentrations of copper and / or nickel ions can negatively impact the electrodeposition of the chromium layer in some cases. Therefore, it is advantageous to reduce the concentration of copper and / or nickel ions in the trivalent chromium plating bath to allow for the deposition of a high-quality chromium layer on the substrate.

[0072] The preferred method of the present invention is subject to the following conditions:

[0073] - After step (iv), based on the total volume of the trivalent chromium plating bath, the concentration of copper ions in the trivalent chromium plating bath is 50 mg / L or less, preferably 40 mg / L or less, more preferably 30 mg / L or less, even more preferably 20 mg / L or less, even more preferably 10 mg / L or less, and most preferably 5 mg / L or less.

[0074] Preferably, in the method of the present invention, the concentration of copper ions in the trivalent chromium electroplating bath in step (i) is higher than 10 mg / L, and the concentration of copper ions in the trivalent chromium electroplating bath after step (iv) is 10 mg / L or lower.

[0075] The preferred method of the present invention is subject to the following conditions:

[0076] - After step (iv), based on the total volume of the trivalent chromium plating bath, the concentration of nickel ions in the trivalent chromium plating bath is 50 mg / L or lower, preferably 40 mg / L or lower, more preferably 30 mg / L or lower, even more preferably 20 mg / L or lower, and most preferably 10 mg / L or lower.

[0077] Preferably, in the method of the present invention, the concentration of nickel ions in the trivalent chromium electroplating bath in step (i) is higher than 20 mg / L, and the concentration of nickel ions in the trivalent chromium electroplating bath after step (iv) is 20 mg / L or lower.

[0078] The preferred method of the present invention is subject to the following conditions:

[0079] - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in the application of 20 A / dm 2 Or larger, preferably 24A / dm 2 Or larger, preferably 28A / dm 2 Or larger, or even better, 32A / dm 2 Or larger, or even better, 36A / dm 2 Or larger, or even more preferably 39A / dm 2 Or larger, with 42A / dm being the optimal choice. 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

[0080] The word "used for" in the term "used for or currently used for electrodepositing chromium layers" is preferably interpreted as "in," making it interpretable as "used for or currently used in electrodepositing chromium layers." In both cases, it indicates that electrodeposition occurred or took place in the context of this invention, and that the defined current density was indeed applied or was applied to the electroplating bath. This generally applies to the methods of this invention.

[0081] Preferably, the trivalent chromium plating bath provided in step (i) has been used or is being used for electrodeposition by applying direct current (DC).

[0082] Preferably, the direct current (DC) is uninterrupted DC, and more preferably, the DC is not pulsed (non-pulsed DC). Furthermore, the DC preferably does not include reverse pulses.

[0083] The preferred method of the present invention is subject to the following conditions:

[0084] - The trivalent chromium plating bath provided in step (i) has been used or is being used in the application of 18 A / dm 2 Up to 75A / dm 2 24A / dm is preferred 2 Up to 71A / dm 2 More preferably 28A / dm 2 Up to 68A / dm 2 Even better, 32A / dm 2 Up to 65A / dm 2 Even better, 36A / dm 2 Up to 61A / dm 2 Even better, 39A / dm 2 Up to 58A / dm 2 The optimal value is 42A / dm. 2 Up to 55A / dm 2 A chromium layer is electrodeposited on at least one substrate under a cathode current density within the specified range. Other combinations are also preferred, such as 28 A / dm². 2 Up to 75A / dm 2 Or 32A / dm 2 Up to 71A / dm 2 .

[0085] In the preferred embodiment of the method of the present invention, the thickness of the chromium layer is 0.5 μm or greater, preferably 0.75 μm or greater, more preferably 0.9 μm or greater, even more preferably 1.0 μm or greater, even more preferably 1.5 μm or greater, and most preferably 2.0 μm or greater.

[0086] In some cases, the method of the present invention is preferred, wherein the thickness of the chromium layer ranges from 1.1 μm to 500 μm, preferably from 2 μm to 450 μm, more preferably from 4 μm to 400 μm, even more preferably from 6 μm to 350 μm, even more preferably from 8 μm to 300 μm, and most preferably from 10 μm to 250 μm.

[0087] In some further cases, the method of the present invention is preferred, wherein the thickness of the chromium layer is 15 μm or greater, preferably 20 μm or greater.

[0088] As described above, when depositing a chromium layer during electrodeposition, it is preferable to obtain a chromium layer with excellent functional properties, which is usually referred to as a hard chromium layer, and preferably not a decorative chromium layer.

[0089] Preferably, it is used when applying 18A / dm 2 A trivalent chromium plating bath, in which a chromium layer is electrodeposited on at least one substrate at a higher cathode current density (preferably with the cathode current density as described above), is used / positioned in the plating section.

[0090] In the preferred embodiment of the method of the present invention, the trivalent chromium plating bath is positioned in the plating section, and steps (ii) and / or (iii) are carried out in a processing section that is separate from the plating section but fluidly connected to it.

[0091] Therefore, the method of the present invention is preferably used in the processing section, preferably separately from the electroplating section. Most preferably, the electroplating section is an electroplating tank.

[0092] In the preferred embodiment of the method of the present invention, the electroplating section and the processing section are fluidly connected to each other via one or more conduits.

[0093] Preferably, the method of the present invention is performed in a manner in which steps (i), (ii), (iii) and (iv) are performed continuously or discontinuously.

[0094] In some cases, the method of the present invention is preferred, wherein steps (i), (ii), (iii), and (iv) are performed sequentially, or even more preferably in a closed loop. This generally preferably means that after providing the trivalent chromium plating bath in step (i), air agitation is performed in step (ii), followed by resin treatment in step (iii), and then returning to the resin treatment portion of the trivalent chromium plating bath as defined in step (iv), wherein after step (iv), step (i) is performed again, followed by steps (ii), (iii), and (iv), etc., respectively.

[0095] This successive execution of steps (i), (ii), (iii), and (iv), preferably in a closed loop, allows for very efficient control of the iron ion concentration, and preferably the addition of copper and / or nickel ion concentrations.

[0096] However, in other cases, it is preferable that this sequence be temporarily interrupted, most preferably after step (iv), and carried out discontinuously or semi-continuously. This is particularly applicable if the iron ion concentration rises slowly and reaches a critical concentration only after a considerable period of time. In such cases, the method of the present invention is preferably carried out temporarily, more preferably repeatedly, until the iron ion concentration in the trivalent chromium plating bath reaches the desired concentration (preferably below 10 mg / L). Thereafter, the method of the present invention is interrupted / suspended until the iron ion concentration reaches the critical concentration again. In this way, resources and energy are better conserved.

[0097] Preferably, in step (i) of the method of the present invention, at least a portion of the trivalent chromium plating bath is provided in the first compartment of the processing section, preferably an overflow compartment. In the first compartment, a portion of the trivalent chromium plating bath is preferably subjected to air agitation, preferably for a period of time as defined herein, such that an air-agitated portion of the trivalent chromium plating bath is obtained (step (ii)). In the second compartment of the processing section, step (iii) of the method of the present invention is preferably performed. Preferably, the second compartment is a column filled with ion exchange resin, and a portion of the trivalent chromium plating bath is contacted with the ion exchange resin at a certain flow rate, preferably a constant flow rate. After performing step (iii), a resin-treated portion of the trivalent chromium plating bath is obtained, which is returned as defined in step (iv) of the method of the present invention. Most preferably, a portion of the trivalent chromium plating bath is pumped from the first compartment to the second compartment and returned to the trivalent chromium plating bath by at least one pump. At this point, the method of the present invention is performed continuously or discontinuously (as described above). In each case, this allows the electrodeposition of a chromium layer to continue on at least one substrate in the plating section, i.e., without interruption of electrodeposition. In other words, the method of the present invention is performed simultaneously, that is, electrodeposition is performed simultaneously. However, in some cases, although the method of the present invention is performed in the processing stage, it is preferable to interrupt the electrodeposition in the electroplating stage while performing the method of the present invention.

[0098] Therefore, the method of the present invention is preferred, wherein in step (iii), an ion exchange resin is provided in an ion exchange column through which the air-stirring portion of the trivalent chromium electroplating bath passes. The ion exchange column defines a limited space for the ion exchange resin, such that replacement, regeneration, and / or modification are performed independently of the first compartment of the electroplating section and / or treatment section.

[0099] In some cases, the method of the present invention is preferred, wherein the method is carried out in an electroplating section. In such cases, it is preferable to interrupt and temporarily stop the electroplating of the chromium layer, respectively. A trivalent chromium plating bath is provided in the electroplating section (step (i)). Air agitation is also performed in the electroplating section (step (ii)). Step (iii) involves adding ion exchange resin in the electroplating section for a defined period of time. Afterward, the resin is removed (or alternatively, the trivalent chromium plating bath is repositioned to another electroplating tank), which means that the resin-treated trivalent chromium plating bath is essentially returned to the trivalent chromium plating bath. However, this batch method is less preferred because removing the ion exchange resin is technically demanding, and the resin is often not completely separated from the resin-treated trivalent chromium plating bath.

[0100] In some cases, the method of the present invention is preferred, wherein the ion exchange resin is provided as a bed through which the air agitation portion of the trivalent chromium plating bath passes. This bed allows for an increase in the contact area between the air agitation portion of the trivalent chromium plating bath and the ion exchange resin.

[0101] The preferred method of the present invention, wherein

[0102] The trivalent chromium plating bath provided in step (i) is used for the electrodeposition simultaneously with steps (ii), (iii), and (iv), or

[0103] The trivalent chromium plating bath provided in step (i) was used for the electrodeposition prior to steps (ii), (iii) and (iv).

[0104] This preference means that in some cases the method of the present invention is preferred, wherein the trivalent chromium plating bath is used in parallel for plating, for example, at the same time as the method of the present invention is performed.

[0105] However, in some other cases, electroplating is preferably already completed, and the corresponding trivalent electroplating bath is no longer used until the method of the present invention is performed. This preferably includes even a repositioned electroplating bath to perform the method of the present invention.

[0106] After performing the method of the present invention, electrodeposition is preferably continued. Preferably, in the method of the present invention, the trivalent chromium electroplating bath obtained after step (iv) is used to apply 18 A / dm². 2 A chromium layer is electrodeposited on at least one substrate (preferably multiple substrates) with a higher cathode current density (preferably, as defined herein). This is then performed in another step (i), preferably in a second or higher sequential step (i) of the method of the invention.

[0107] Typically, after a certain period of time, ion exchange resins become ion-saturated, causing their affinity to decrease. Therefore, after preferably repeating the method of the present invention, it is preferable to clean and regenerate the ion exchange resin. This specifically means that iron ions and preferably nickel and copper ions (a) are stripped from the resin and (b) the resin is repaired, making the ion exchange resin preferably used in further sequences of the method of the present invention.

[0108] The preferred method of the present invention further includes the steps of

[0109] (v) After step (iii), the ion exchange resin is contacted with an acidic and / or alkaline regeneration solution, preferably periodically during the regeneration interval, and then contacted with an alkaline regeneration solution after the regeneration interval.

[0110] In order to strip the bound ions from the ion exchange resin in step (v), the ion exchange resin is contacted with an acidic and / or alkaline regeneration solution.

[0111] Preferably, in step (v), the ion exchange resin is in contact with the acidic regeneration solution more frequently than the alkaline regeneration solution; in rare cases, the ion exchange resin is preferably in contact with the acidic regeneration solution only.

[0112] More preferably, step (v) is performed by contacting the ion exchange resin after step (iii) with both an acidic regeneration solution and an alkaline regeneration solution. Most preferably, step (v) is performed by contacting the ion exchange resin after step (iii) with the acidic regeneration solution a first number of times, followed by contacting it with the alkaline regeneration solution a second number of times, wherein the first number of times is greater than the second number. Alternatively, in a less preferred case, the contact with the alkaline regeneration solution is performed before the contact with the acidic regeneration solution.

[0113] Preferably, in the method of the present invention, the ion exchange resin comprises one or more cation exchange resins. Preferably, one or more cation exchange resins are used in step (iii) of the method of the present invention in a hydrogen-carrying form.

[0114] In the preferred embodiment of the method of the present invention, the ion exchange resin comprises a polystyrene polymer. The cation exchange resin, preferably a resin comprising a polystyrene polymer, typically provides a high affinity for iron ions, and preferably also for copper ions and / or nickel ions.

[0115] The preferred method of the present invention is wherein the ion exchange resin is macroporous.

[0116] Preferably, one or more cation exchange resins comprise two or more different cation exchange resins that have different selectivity for various cations, preferably for iron, nickel and copper ions.

[0117] In some cases, it is preferable to use two or more cation exchange resins to form at least one dual bed.

[0118] In the preferred embodiment of the method of the present invention, the ion exchange resin (preferably as described above) contains acidic functional groups, wherein the acidic functional groups preferably contain one or more groups selected from carboxyl groups, phosphonic acid groups and sulfonic acid groups.

[0119] In some cases, ion exchange resins containing phosphonic acid groups and sulfonic acid groups are highly preferred, with Purolite S-957 being the most preferred. A preferred ion exchange resin is one in which the phosphonic acid groups comprise aminophosphonic acid groups.

[0120] In other cases, ion exchange resins containing carboxyl groups are highly preferred, those containing acetate groups are more preferred, and those containing iminodiacetic acid groups are most preferred. The most preferred ion exchange resins are Lewatit TP-207 and / or Purolite S-930.

[0121] Step (iii) of the method of the present invention can be carried out well by using the preferred ion exchange resin described above.

[0122] The preferred electroplating section includes at least one anode, preferably selected independently from the group consisting of graphite anodes and mixed metal oxide anodes (MMOs), and more preferably from the group consisting of graphite anodes and mixed metal oxide anodes on titanium. Such anodes have shown sufficient resistance in the electroplating bath used. Preferably, at least one anode does not contain any lead or chromium.

[0123] The electrodeposited chromium layer is preferably a chromium alloy layer containing alloying elements. Preferred alloying elements are carbon, nitrogen, and oxygen, with carbon and oxygen being more preferred. Carbon is typically present in the chromium layer because organic compounds are generally present in trivalent chromium plating baths. Preferably, the chromium layer does not contain one, more than one, or all of the elements selected from the group consisting of sulfur, nickel, copper, aluminum, tin, and iron. More preferably, the sole alloying element is carbon, nitrogen, and / or oxygen, more preferably carbon and / or oxygen, and most preferably carbon and oxygen. Preferably, based on the total weight of the chromium layer, the chromium layer contains 90% by weight or more, more preferably 95% by weight or more of chromium.

[0124] The preferred method of the present invention involves a trivalent chromium plating bath in step (i) that is substantially free of or contains no boric acid, and preferably substantially free of or contains no boron-containing compounds. Boron-containing compounds are undesirable because they cause environmental problems. Wastewater treatment containing boron-containing compounds (including boric acid) is both expensive and time-consuming. Furthermore, boric acid typically exhibits poor solubility and therefore tends to form precipitates. Although such precipitates can dissolve upon heating, the corresponding trivalent chromium plating bath cannot be used for plating during this period. There is a significant risk that such precipitates will contribute to a reduction in the quality of the chromium layer.

[0125] Preferably, in the method of the present invention, the trivalent chromium electroplating bath in step (i) is substantially free of or does not contain divalent sulfur-containing organic compounds, and preferably substantially free of or does not contain sulfur-containing compounds having sulfur atoms with an oxidation number lower than +6. In some cases, if sulfur is incorporated into the chromium layer, particularly at 18 A / dm 2 At higher cathode current densities, undesirable discoloration may be observed. However, this does not preclude sulfate ions. Preferably, in some cases, the trivalent chromium plating bath contains sulfate ions, preferably in a total amount ranging from 50 g / L to 250 g / L, based on the total volume of the trivalent chromium plating bath.

[0126] When using a trivalent chromium plating bath to deposit hard functional chromium layers, it is particularly advantageous to eliminate the presence of divalent sulfur-containing organic compounds from the trivalent chromium plating bath.

[0127] The term "does not contain" means that the corresponding compound and / or component was not intentionally added to, for example, a trivalent chromium plating bath. This does not preclude the possibility that such compounds may be introduced as impurities from other chemicals. However, the total amount of such compounds and components is usually below the detection range and therefore not critical in the methods of this invention.

[0128] Preferably, in the method of the present invention, in step (i), the trivalent chromium electroplating bath further comprises one or more compounds selected from the group consisting of:

[0129] - One or more types of halide ions, preferably bromide ions.

[0130] - One or more types of alkali metal cations, preferably sodium and / or potassium.

[0131] - One or more organic complex compounds, preferably aliphatic monocarboxylic organic acids and / or their salts.

[0132] -Sulfate ions, and

[0133] -Ammonium ion.

[0134] Preferably, in step (i), based on the total volume of the trivalent chromium plating bath, the trivalent chromium plating bath contains one or more types of halide ions, preferably bromides, at a concentration of at least 0.06 mol / L, more preferably at least 0.1 mol / L, and even more preferably at least 0.15 mol / L. In particular, the bromide anions effectively suppress the formation of hexavalent chromium at at least one anode.

[0135] Preferably, in step (i), based on the total volume of the trivalent chromium plating bath, the trivalent chromium plating bath contains one or more types of alkali metal cations, preferably sodium and / or potassium, with a total concentration ranging from 0 mol / L to 0.5 mol / L, more preferably from 0 mol / L to 0.3 mol / L, even more preferably from 0 mol / L to 0.1 mol / L, and most preferably from 0 mol / L to 0.08 mol / L. Typically, rubidium, francium, and cesium ions are not used in the trivalent chromium plating bath. Therefore, in most cases, the total amount of alkali metal cations includes lithium, sodium, and potassium metal cations, most preferably sodium and / or potassium.

[0136] Furthermore, the trivalent chromium electroplating bath preferably contains one or more organic complexing compounds, preferably used to complex trivalent chromium ions. Preferably, the one or more organic complexing compounds (and preferred variants thereof) have 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and even more preferably 1 to 3 carbon atoms. The complexing compound primarily forms complexes with the trivalent chromium ions in the trivalent chromium electroplating bath to increase bath stability. Preferably, the molar ratio of trivalent chromium ions to one or more organic complexing compounds ranges from 1:0.5 to 1:10.

[0137] Ammonium ions are preferably provided only by NH4OH and / or NH3.

[0138] In the preferred embodiment of the method of the present invention, the pH range of the trivalent chromium electroplating bath (also preferably provided in step (i) of the method of the present invention) for electrodepositing a chromium layer on at least one substrate is 4.1 to 7.0, preferably 4.6 to 6.8, more preferably 5.1 to 6.5, even more preferably 5.2 to 6.2, even more preferably 5.3 to 6.0, and most preferably 5.4 to 5.9.

[0139] In the preferred embodiment of the method of the present invention, in step (i), the trivalent chromium plating bath contains trivalent chromium ions with a concentration ranging from 10 g / L to 30 g / L, preferably from 14 g / L to 27 g / L, and more preferably from 17 g / L to 24 g / L, based on the total volume of the trivalent chromium plating bath.

[0140] In the preferred method of the present invention, in step (i), the trivalent chromium ions in the trivalent chromium electroplating bath are obtained from a soluble trivalent chromium ion source, typically a water-soluble salt containing said trivalent chromium ions. Preferably, the soluble trivalent chromium ion source contains or is chromium sulfate, more preferably acidic chromium sulfate, and even more preferably chromium sulfate having the general formula Cr2(SO4)3 and a molecular weight of 392 g / mol. In other cases, a soluble trivalent chromium ion source is preferred, wherein the source contains an organic anion as a counterion to the trivalent chromium ions, preferably an organic carboxylic acid anion, and most preferably an aliphatic monocarboxylic acid anion having preferably 10 or fewer carbon atoms (preferably 5 or fewer carbon atoms).

[0141] If the total amount of trivalent chromium ions is significantly below 10 g / L, insufficient chromium deposition will be observed in many cases, and the deposited chromium layer will generally be of poor quality. If the total amount is significantly above 30 g / L, the electroplating bath will become unstable in many cases, including the formation of undesirable precipitates.

[0142] In the preferred method of the present invention, the temperature range of the trivalent chromium electroplating bath used for electrodepositing a chromium layer on at least one substrate is 20°C to 90°C, preferably 30°C to 70°C, more preferably 40°C to 60°C, and most preferably 45°C to 60°C. Optimal electrodeposition can be obtained within the preferred temperature range. If the temperature significantly exceeds 90°C, undesirable evaporation occurs, which can negatively affect the concentration of the bath components. Furthermore, undesirable anode formation of hexavalent chromium is significantly less inhibited. If the temperature is significantly below 20°C, deposition is insufficient in many cases.

[0143] In the preferred embodiment of the method of the present invention, at least one substrate comprises a metal or metal alloy, preferably comprising one or more metals selected from the group consisting of copper, iron, nickel and aluminum, more preferably comprising one or more metals selected from the group consisting of copper, iron and nickel, and most preferably comprising at least iron.

[0144] The method of the present invention is preferred in that at least one substrate contains iron, preferably iron exposed on at least one surface of the substrate. However, substrates containing iron exposed on at least one surface show a tendency for iron ions to dissolve in the trivalent chromium plating bath and begin to accumulate over time.

[0145] The preferred method of the present invention is wherein, in step (i), the iron ion source is at least one substrate and / or means for positioning at least one substrate in the electroplating section.

[0146] The preferred method of the invention involves electrodepositing a chromium layer on the surface of at least one substrate, the surface of which comprises nickel or a nickel alloy (a nickel- or nickel alloy-coated substrate, preferably an iron-containing substrate coated with a nickel or nickel alloy). However, in such cases, the substrate exhibits a tendency for nickel ions to dissolve in the trivalent chromium plating bath and begin to accumulate over time.

[0147] The substrate is preferably coated with a semi-bright nickel coating. A steel substrate coated with a nickel or nickel alloy layer, and preferably a semi-bright coating, is particularly preferred. However, other coatings are preferably present alternatively or separately. In many cases, this coating significantly improves corrosion resistance compared to a metal substrate without it. However, in some cases, at least one substrate is not easily corroded due to a corrosive inert environment (e.g., in an oil bath). In this case, a coating is not necessarily required, and a nickel or nickel alloy layer is preferred.

[0148] In the preferred embodiment of the method of the present invention, step (ii) is performed for a minimum of 5 minutes or longer, more preferably 10 minutes or longer, even more preferably 15 minutes or longer, and most preferably 20 minutes or longer. Experiments have shown that in many cases, time periods significantly shorter than 5 minutes do not significantly improve the efficiency of step (iii) of the method of the present invention. However, using a time period of at least 5 minutes in step (ii) achieves sufficient efficiency in step (iii).

[0149] In the preferred method of the present invention, step (ii) is performed for a maximum of 120 minutes or less, preferably 100 minutes or less, more preferably 70 minutes or less, even more preferably 50 minutes or less, and most preferably 40 minutes or less. This experiment shows that further increasing the time period in step (iii) does not yield additional efficiency.

[0150] The air agitation defined in step (ii) of the method of the present invention is preferably a strong blowing of ambient air, i.e., strong air agitation. It is preferably stronger than the mild air agitation conventionally used to achieve stable bath movement during electroplating.

[0151] The invention is described in more detail by way of the following non-limiting examples.

[0152] Example

[0153] 1. Preparation of trivalent chromium electroplating bath:

[0154] Trivalent chromium electroplating baths (A) (1 L) and (B) (500 L) were prepared, each containing 10 g / L to 30 g / L of trivalent chromium ions (source: alkaline chromium sulfate), 50 g / L to 250 g / L of sulfate ions, at least one organic complex compound (aliphatic monocarboxylic acid), ammonium ions, and bromide ions. The electroplating baths contained neither boric acid nor any boron-containing compounds and no organic compounds with divalent sulfur. The pH range was 5.4 to 5.9.

[0155] The initial concentrations of iron ions in the corresponding test baths prior to steps (ii) and (iii) of the method of the present invention are as follows:

[0156] (A) 100 mg / L

[0157] (B) 20 mg / L,

[0158] Prior to steps (ii) and (iii), each test trivalent chromium plating bath was subjected to an application of 40 A / dm at 50°C. 2 A chromium layer was electrodeposited on a low-carbon steel rod substrate with a cathode current density ranging from 10 mm to 30 mm in diameter, with electrodeposition lasting 15 minutes for test bath (A) and at least 120 minutes for test bath (B). In each case, the thickness of the electrodeposited chromium layer was at least 1 μm, and in many cases at least 5 μm. After electrodeposition, the substrate was visually inspected and graded.

[0159] After electrodeposition, in step (ii), the test bath (A) is subjected to strong air agitation (with ambient air) for the following durations: 1 minute (A-1), 5 minutes (A-5), 15 minutes (A-15), 30 minutes (A-30), 60 minutes (A-60), and 180 minutes (A-180) to obtain the corresponding individual air agitation test trivalent chromium electroplating baths (A-1), (A-5), etc.

[0160] In the comparative test bath (Ac0), no air agitation is applied after step (i), and step (iii) is performed immediately (i.e., after 0 hours). In the further comparative test baths, each bath after step (i) is allowed to stand with agitation for a specific time (3 hours, 6 hours, and 12 hours) before step (iii) is performed. Therefore, step (ii) is not performed in each comparative test bath. Thus, the following corresponding further comparative test baths are obtained: (Ac3), (Ac6), and (Ac12).

[0161] In step (ii), the test bath (B) is subjected to strong air agitation (using ambient air) for 15 minutes to obtain the corresponding air-agitated test bath (B-15). In the control test bath, no air agitation is applied, and step (iii) is performed immediately after step (i) (i.e., after standing for 0 hours); to obtain the control test bath (Bc0).

[0162] In step (iii) of the method of the present invention, test baths (A-1), (A-5), (A-15), (A-30), (A-60), (A-180), (Ac0), (Ac3), (Ac6), (Ac12), (Bc0), and (B-15) are contacted with ion exchange resin (Lewatit TP 207, Lanxess; macroporous, iminodiacetic acid functional group, bead size: 0.4 to 1.25 mm) to obtain test baths with the corresponding resin treatment.

[0163] Test baths (A), namely (A-1), (A-5), etc., were brought into contact with the resin by adding 40 ml of resin to each test bath and gently stirring for 60 minutes. Afterwards, the resin was allowed to settle, the supernatant was decanted, and the iron ion concentration was analyzed.

[0164] Test baths (B), namely (B-15) and (Bc0), were pumped at a flow rate of approximately 175 L / h into a column containing 25 L of resin, allowing them to contact the resin for 9 hours before being returned to the test bath. The iron ion concentration was then measured.

[0165] The results are summarized in Table 1.

[0166] Table 1:

[0167] Iron ions [mg / L] Optical appearance [rating] (A) 100 + (A-1) 57 + (A-5) 43 ++ (A-15) <10 +++ (A-30) <10 +++ (A-60) <10 +++ (A-180) <10 +++ (Ac0) 59 + (Ac3) 69 + (Ac6) 62 + (Ac12) 51 + (B) 20 ++ (Bc0) 14 ++ (B-15) 4 +++

[0168] The ratings are as follows:

[0169] + indicates: Defect, specifically partial and very undesirable black discoloration, skipped plating, or very low deposition rate to the point of no plating at all.

[0170] ++ indicates: Acceptable in a few cases, i.e., frequent black discoloration; skipping deposition in many cases, low deposition rate. +++ indicates: Good, i.e. no skipping deposition, desired deposition rate, no interfering discoloration; comparable to results obtained from an iron-free bath.

[0171] Experimental results clearly show that the method of the present invention can significantly reduce the concentration of iron ions, particularly below 10 mg / L. Example (Ac0) shows that step (ii) substantially improves the efficiency of reducing the iron ion concentration to obtain acceptable electrodeposition results. Examples (A-1) (essentially a comparative example) and (A-5) show that 50 mg / L is the critical limit. Therefore, step (ii) is applied for a sufficient time so that the critical limit is at least weakened. Above 50 mg / L, completely unacceptable electrodeposition results are generally obtained. Slightly below 50 mg / L (Example (A-5)), the electrodeposition results are improved; however, undesirable discoloration is often observed. Examples (A-15) to (A-180) clearly show that excellent electrodeposition results are obtained if the iron ion concentration is below 10 mg / L. 10 mg / L appears to be an acceptable limit if iron ion contaminants are present in the corresponding trivalent chromium plating bath. This is confirmed in test bath (B), particularly (B-15). Although the electrodeposition of (Bc0) is slightly better than that of (B), slight discoloration is observed in (Bc0) in a few cases. This type of discoloration is no longer observed in (B-15).

[0172] In separate tests (data not shown), the removal of nickel and copper ions was investigated. In these separate tests, the concentrations of both nickel and copper ions were significantly reduced (Cu: from 20 mg / L to below 10 mg / L; Nickel: from 43 mg / L to below 20 mg / L, and even below 10 mg / L).

[0173] In further testing experiments, alternative resins were tested, such as (i) S-950, Purolite; macroporous, aminophosphonic acid functional group, bead size: approx. 1.2 mm; (ii) S-957, Purolite; macroporous, phosphonic and sulfonic acid functional groups, bead size: 0.55 to 0.75 mm; and (iii) S-930, Purolite; macroporous, iminodiacetic acid functional group, bead size: approx. 0.6 nm to 0.85 mm. Similar results were obtained with the alternative resins regarding the removal of iron ions as well as nickel and copper ions (data not shown).

[0174] 2. Ion exchange resin cleaning / regeneration:

[0175] Following Example (B-0), the ion exchange resin must be cleaned and regenerated by repeatedly contacting it with a series of acidic (HCl) and alkaline (NaOH) solutions. This is an enhanced cleaning / regeneration process that is typically not required immediately if step (ii) of the method of the present invention is being performed for the first time. For example, following Example (B-15), the ion exchange resin is used again in at least the second step (ii) before being cleaned with an acidic solution (HCl). The cleaned resin is then used again. This process is repeated several times before a series of alkaline (NaOH) and acidic (HCl) solutions are required. Thus, the method of the present invention (i.e., step (ii)) actively influences the cleaning / regeneration of the ion exchange resin.

Claims

1. A method for reducing the iron ion concentration in a trivalent chromium electroplating bath, the method comprising the following steps: (i) Providing the trivalent chromium electroplating bath, comprising: (a) Trivalent chromium ions, and (b) Iron ions, (ii) subjecting at least a portion of the trivalent chromium plating bath to air agitation for at least 5 minutes to obtain at least an air-agitated portion of the trivalent chromium plating bath. (iii) The air-agitation section of the trivalent chromium electroplating bath is brought into contact with the ion exchange resin to obtain the resin treatment section of the trivalent chromium electroplating bath, and (iv) Return the resin treatment portion of the trivalent chromium plating bath to the trivalent chromium plating bath. The attached conditions are - The trivalent chromium electroplating bath provided in step (i) has been used or is being used when applying 18 A / dm 2 Or, in the case of a higher cathode current density, electrodeposit a chromium layer on at least one substrate. - After step (iii), the concentration of iron ions in the resin treatment section of the trivalent chromium plating bath is lower than the concentration in the air agitation section of the trivalent chromium plating bath, and - Following step (iv), based on the total volume of the trivalent chromium plating bath, the iron ion concentration in the trivalent chromium plating bath is less than 50 mg / L. The ion exchange resin in step (iii) contains acidic functional groups, and The trivalent chromium plating bath provided in step (i) is used for electrodeposition simultaneously with steps (ii), (iii), and (iv). or The trivalent chromium plating bath provided in step (i) was used for the electrodeposition prior to steps (ii), (iii), and (iv). The trivalent chromium plating bath is located in the plating section, and steps (ii) and / or (iii) are performed in the processing section, which is separate from but fluidly connected to the plating section.

2. The method according to claim 1, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is 40 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

3. The method according to claim 1, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is 30 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

4. The method according to claim 1, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is 20 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

5. The method according to claim 1, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is 15 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

6. The method according to claim 1, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is 11 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

7. The method according to claim 1 or 2, wherein after step (iv), the iron ion concentration in the trivalent chromium plating bath is 35 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

8. The method according to claim 1 or 2, wherein after step (iv), the iron ion concentration in the trivalent chromium plating bath is 25 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

9. The method according to claim 1 or 2, wherein after step (iv), the iron ion concentration in the trivalent chromium plating bath is 18 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

10. The method according to claim 1 or 2, wherein after step (iv), the iron ion concentration in the trivalent chromium plating bath is 13 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

11. The method according to claim 1 or 2, wherein after step (iv), the iron ion concentration in the trivalent chromium plating bath is 10 mg / L or lower, based on the total volume of the trivalent chromium plating bath.

12. The method according to claim 1 or 2, wherein in step (i), the iron ion concentration in the trivalent chromium plating bath is higher than 10 mg / L, and after step (iv), the iron ion concentration in the trivalent chromium plating bath is 10 mg / L or lower, each based on the total volume of the trivalent chromium plating bath.

13. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 9 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

14. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 8 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

15. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 7 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

16. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 6 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

17. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 5 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

18. The method according to claim 1 or 2, wherein in step (iii), the iron ion concentration in the resin treatment portion of the trivalent chromium plating bath is 4 mg / L or lower, based on the total volume of the resin treatment portion of the trivalent chromium plating bath.

19. The method according to claim 1 or 2, wherein in step (i), the trivalent chromium plating bath further comprises: (c) Copper ions, and / or (d) Nickel ions, The attached conditions are - After step (iii), the concentrations of copper ions and / or nickel ions in the resin treatment section of the trivalent chromium plating bath are respectively lower than the concentrations in the air agitation section of the trivalent chromium plating bath.

20. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used when applying 20 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

21. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used when applying 24 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

22. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in applying 28 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

23. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in applying 32 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

24. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in applying 36 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

25. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in applying 39 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

26. The method according to claim 1 or 2, wherein the condition is: - The trivalent chromium electroplating bath provided in step (i) has been used or is being used in applying 42 A / dm 2 In the case of a higher cathode current density, a chromium layer is electrodeposited on at least one substrate.

27. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 0.5 μm or greater.

28. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 0.75 μm or greater.

29. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 0.9 μm or greater.

30. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 1.0 μm or greater.

31. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 1.5 μm or greater.

32. The method according to claim 1 or 2, wherein the thickness of the chromium layer is 2.0 μm or greater.

33. The method according to claim 1 or 2, wherein steps (i), (ii), (iii) and (iv) are performed continuously or discontinuously.

34. The method according to claim 1 or 2, further comprising the step of (v) After step (iii), the ion exchange resin is contacted with an acidic and / or alkaline regeneration solution.

35. The method according to claim 1 or 2, further comprising the step of The ion exchange resin is periodically contacted with an acidic regeneration solution during the regeneration interval, and then contacted with an alkaline regeneration solution after the regeneration interval.

36. The method according to claim 1 or 2, wherein the acidic functional group comprises one or more groups selected from carboxyl groups, phosphonic acid groups, and sulfonic acid groups.

37. The method according to claim 1 or 2, wherein in step (i), the trivalent chromium plating bath further comprises one or more compounds selected from the group consisting of: - One or more types of halide ions, - One or more types of alkali metal cations - One or more organic complex compounds -Sulfate ions, and -Ammonium ion.

38. The method of claim 37, wherein the halide ion is a bromide ion.

39. The method according to claim 37, wherein the alkali metal cation is sodium and / or potassium.

40. The method of claim 37, wherein the organic complex compound is an aliphatic monocarboxylic organic acid and / or its salt.

41. The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath for electrodepositing the chromium layer on the at least one substrate is 4.1 to 7.

0.

42. The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath used for electrodepositing the chromium layer on the at least one substrate is 4.6 to 6.

8.

43. The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath used for electrodepositing the chromium layer on the at least one substrate is 5.1 to 6.

5.

44. The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath used for electrodepositing the chromium layer on the at least one substrate is 5.2 to 6.

2.

45. The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath for electrodepositing the chromium layer on the at least one substrate is 5.3 to 6.

0.

46. ​​The method according to claim 1 or 2, wherein the pH range of the trivalent chromium plating bath for electrodepositing the chromium layer on the at least one substrate is 5.4 to 5.9.