EP2039810A2 - Method and devices for increasing the service life of a process solution for chemical-reductive metal coating - Google Patents

Abstract

Process for increasing the service life of a process solution for chemical-reductive metal deposition involves monitoring the pH of the process solution, feeding a part of the process solution through a weakly acidic cation exchanger, feeding the solution from the cation exchanger back to the process solution, monitoring the functionality of the cation exchanger, and charging the cation exchanger for renewed use. Process for increasing the service life of a process solution for chemical-reductive metal deposition involves monitoring the pH of the process solution, feeding a part of the process solution, optionally after diluting, through a weakly acidic cation exchanger by decreasing the pH of the solution, feeding the solution from the cation exchanger back to the process solution, monitoring the functionality of the cation exchanger in the run-off of the cation exchanger, and charging the cation exchanger for renewed use with ions of a coating metal on approaching the pH in the run-off of the cation exchanger. An independent claim is also included for a device for carrying out the above process.

Description

The invention relates to a method and apparatus for extending the useful life of a process solution used in chemical-reductive metal deposition. The chemical-reductive metal deposition is used to coat workpieces with a metal coating (Cu, Ni, Ag or Au).

For the chemical-reductive metal deposition of non-ferrous metals (non-ferrous metals) on the surface of a base material (eg metal or pretreated plastic), the following, greatly simplified, reaction equation can be set up by way of example for nickel deposition:

3NaH ₂ PO ₂ + 3H ₂ O + NiSO ₄ → 3 NaH ₂ PO ₃ + H ₂ SO ₄ + Ni + 2H ₂ (Equation 1)

In the case of chemical-reductive metal deposition, reducing agents (here NaH ₂ PO ₂ ) and metal ions of the coating metal (here Ni ²⁺ ) are consumed and at the same time the oxidized reducing agent (here NaH ₂ PO ₃ ) and protons are formed as reaction products equivalent to the amount of metal deposited. these lower the pH in the process solution.

Due to numerous side reactions, about 3.3 mol of the reducing agent are required for the deposition of one mole of nickel. In this case, elemental phosphorus, which is formed by side reactions of the reducing agent, alloyed into the resulting metal layer.

According to the state of the art, the redosing of the reducing agent and of the metal ions of the coating metal takes place by adding the appropriate salts and adjusting the pH by adding alkalis to the process solution. Through the process of metal deposition, pH adjustment, replenishment of the consumed components and removal of base material, foreign substances accumulate in the process solution, disrupting the process of metal deposition and adversely affecting the quality of the layers produced. To remove the foreign substances is usually a Teilverwurf the process solution, with their sewage treatment is problematic because of the complex composition.

The usual unit of measure for the service life of the process solution is the metal throughput MTO (= "metal turn-over"). This is referred to as 1 MTO if the metal content of the process solution is reacted once and added again. According to the prior art, the compressive stress in the nickel-phosphorus layer disadvantageously already after 2 to 4.5 MTO in a tensile stress and therefore the useful life of the process solution is usually limited to 5 MTO.

To extend the service life of a process solution for chemical-reductive nickel deposition, it is necessary to separate the registered foreign substances by means of suitable methods. For this purpose, various methods are proposed:

Already 1953 were in US 2,726,968 and US 2,726,969 Regeneration process using a weakly basic phosphine acid activated anion exchange material for the regeneration of process solutions for the chemical reductive nickel deposition. This is intended to separate orthophosphite from the process solution and release hypophosphite into the process solution. The weakly basic anion exchange materials are directly applied with process solution, which is why the pH of the process solution must not exceed the value of pH 5, otherwise the weakly basic anion exchange material from the hypophosphite loading is converted back to the form of the free base, which is not capable of ion exchange , A separation of interfering cations does not occur in this method. The post-dosing of the metal ions is carried out by adding nickel salts, wherein US 2,726,969 By using basic nickel salts such as nickel hydroxide or nickel carbonate at the same time a pH adjustment without the use of other alkalis to be achieved. However, the use of these sparingly soluble compounds has the disadvantage that it contaminates the process solution with solids, which can be incorporated into the deposited metal layers and thus adversely affect their properties. These procedures have evolved in the Practice not enforced, since in particular the use of phosphinic acid for activation of the anion exchanger charged their cost-effectiveness.

DD 36,889 discloses a process for the continuous regeneration of acid solutions for chemical nickel plating in which the solution is passed through a combination of a nickel-loaded weakly acidic cation exchanger and a hypophosphite-loaded, (weak to) moderately basic anion exchanger. The weakly acidic cation exchanger is to be used for adjusting the pH and for subsequent addition of nickel ions, while the weak to medium basic anion exchanger is to be used for the subsequent addition of hypophosphite and the separation of orthophosphite. The weakly acidic cation exchanger and the (weak to medium) basic anion exchanger are connected in series with a matched capacity.

The monitoring of the functionality of the cation exchanger is intended in DD 36,889 via the coloring of the weakly acidic cation exchange resin. As soon as it has changed from green (nickel loading) to a yellowish white (unloaded exchanger), the exchangers should be regenerated. This color change of the weakly acidic cation exchange resin is very poorly usable for the control of the functionality of the ion exchanger, since a process solution for the chemical-reductive nickel deposition itself is intensely colored green.

In the regeneration of the weakly to moderately strong basic anion exchanger, in DD 36,889 the transfer into the hypophosphite loading by applying a hypophosphite solution on the previously loaded with chloride anion exchanger. In a weak to medium basic anion exchanger in the chloride loading, however, an exchange of chloride for hypophosphite is not possible because chloride is bound by the exchanger more solid than hypophosphite and even orthophosphite.

By the in DD 36,889 described circuit - weak acid cation exchanger before weak to medium strong basic anion exchanger - carried by the weakly acidic cation exchangers increase the pH to pH values above pH 5. Since a weak to medium basic anion exchanger is only fully functional in a pH range below pH 4, the in DD 36,889 described precursor of a weakly acidic cation exchanger and the resulting shift in the pH value an uncontrolled release of anions that were bound to the weakly basic anion exchanger.

In the process according to DD 36,889 the use of a strongly acidic cation exchanger is ruled out, as it would lower the pH of the solution too much and this would not lead to optimal deposition conditions. Sulfate or chloride ions present in the solution would be the second part of the DD 36,889 described regeneration system, which regulates the budget of hypophosphite and orthophosphite ions disturb.

Because of the described deficits, the in DD 36,889 do not enforce the regeneration method described in practice.

The object of the invention is to provide methods and devices with which the useful life of a process solution for the chemical-reductive metal coating can be extended.

The object is achieved by a method for extending the service life of a process solution for chemical-reductive metal deposition, in which the metal ions of the coating metal consumed in the metal deposition are metered in and the pH value in the process solution is adjusted. The replenishment of the metal ions and the pH adjustment is carried out with the aid of at least one weakly acidic cation exchanger, which is loaded with ions of the coating metal. For this purpose, the pH value in the process solution is monitored and, when the pH of the process solution falls, part of the process solution, optionally after dilution, is passed through the weakly acidic cation exchanger 14 . The solution prepared by the weakly acidic cation exchanger 14 is returned to the process solution directly.

The functionality of the weakly acidic cation exchanger is monitored by controlling the pH in the effluent of the weakly acidic cation exchanger 14 , the cation exchanger exchanging the pH value in the effluent of the weakly acidic cation exchanger for the pH of the process solution for reuse with ions of the Coating metal is loaded.

It has been found that, with the aid of the weakly acidic cation exchanger, it is also possible to adjust the pH of an acidic process solution in parallel to the replenishment of the metal ions. This is achieved by the fact that the weakly acidic cation exchanger, when it comes into contact with the process solution, binds the H ⁺ ions formed in the metal deposition. This eliminates the need for prior art addition of alkalis and metal salts in the process solution to bind the H ⁺ ions and nachzudosieren the spent metal ions in an advantageous manner.

By the addition of the ions of the coating metal without interfering counterions and the pH adjustment without addition of alkali, the salt entry into the process solution is considerably reduced by the process according to the invention with the weakly acidic cation exchanger. By this simple method, in which a conventional system for chemical-reductive metal deposition only needs to be supplemented with the weakly acidic cation exchanger according to the invention, the useful life of the process solution can be significantly extended.

The solution is enriched with ions of the coating metal by the weakly acidic cation exchanger. The risk of undesirable metal deposition from such enriched solutions is great, especially if a sufficient amount of reducing agent is present.

The direct introduction according to the invention of the solution preparing by the weakly acidic cation exchanger (and enriched with ions of the coating metal) into the process solution minimizes undesired metal deposition.

Depending on the desired phosphorus content (2.5% to more than 15%) in the deposited metal layer, the pH of the process solution is adjusted to a nominal value of pH 3 to pH 6. The phosphorus content of the deposited metal layer increases with the H + ion concentration in the process solution. As soon as the pH of the process solution has dropped below the nominal value by 0.1 to a maximum of 1 pH unit during the metal deposition, the task of the process solution, optionally after dilution, is loaded onto the weakly acidic cation exchanger, which is coated with ions of the coating metal is, started.

The monitoring of the functionality of the weakly acidic cation exchanger is carried out by controlling the pH in the feed (or in the solution to be abandoned) and in the course of the weakly acidic cation exchanger. The capacity of the weakly acidic cation exchanger is exhausted as soon as the pH in the outlet of the exchanger has almost equaled that of the feed (difference <0.2 pH units).

At the end of the period of use, d. H. When the capacity of the ion exchange column is exhausted, the ion exchange material can be exchanged or the flow of the process solution can be diverted to another cation exchanger.

By comparing the pH value in the course of the weakly acidic cation exchanger with the pH of the process solution, the end of the period of use of the weakly acidic cation exchanger can be determined according to the invention, before the pH value and the content of ions of the coating metal in the process solution exceed the tolerance range of the process leaves. The method according to the invention therefore makes it possible to keep the content of ions of the coating metal and the pH of the process solution almost constant.

Due to the almost constant process conditions in the chemical-reductive metal coating according to the invention a particularly uniform deposition of the metal is achieved on the workpiece to be coated.

The term ion exchanger is understood in the context of the present invention in each case a device which z. B. in the form of a column, column or filter chamber is either partially or completely filled with an ion exchange material. There are used organic or inorganic ion exchange materials, which have functional groups that are capable of ion exchange. The ion exchange materials may be solid or liquid. According to the structure of the functional groups of the ion exchange material used, the ion exchanger can be further characterized, e.g. as strongly acidic or weakly acidic cation exchanger or as weakly basic or strongly basic anion exchanger. The substances bound by the ion exchanger can be removed again by regeneration of the functional groups, the regeneration in cocurrent or countercurrent is possible.

A dilute process solution is understood below to mean a process solution which is diluted (for example by mixing with the rinse solution) to a content of 5% to 90% of the concentration of the process solution, preferably 10 to 50%. By rinsing the coated workpiece following the metal coating, ingredients of the process solution are extracted into the rinse solution. As a result, foreign substances, such as the oxidized reducing agent, the counterions of the reducing agent, usually Na ⁺ , and other interfering ions in the rinse solution. The rinse solution thus also represents a dilute process solution from which the foreign substances can be removed. In the text below, the term dilute process solution therefore includes the rinse solution.

The replenishment of the metal ions of the coating metal consumed in the metal deposition is carried out by applying the process solution or a dilute process solution to a weakly acidic cation exchanger which is loaded with the cations of the coating metal. This releases metal ions into the process solution. Advantageously, no disturbing counterions are introduced into the process solution.

Surprisingly, the process solution can be contacted directly with ion exchange materials without resulting in significant metal deposition on the materials. This can be achieved by cooling the process solution to temperatures <60 ° C prior to application to the ion exchanger. Alternatively, metal deposition on the ion exchange materials can be avoided by adding a dilute process solution to the ion exchange materials. The process solution (if appropriate after dilution) is preferably added to the one or more ion exchangers at a flow rate of less than 20 m / h, more preferably less than 10 m / h.

The volume flow of process solution V̇ _P , which is passed through the regenerator to set the desired concentration c _{F, g} , can be calculated according to Equation 2, which is valid for the stationary state. $${\dot{\mathrm{V}}}_{\mathrm{P}}\mathrm{=}\frac{{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{z}}}{{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{z}}\mathrm{-}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{R}}}\mathrm{\cdot }\left(\frac{{\dot{\mathrm{m}}}_{\mathrm{F}}}{{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{z}}\mathrm{-}{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{R}}}\mathrm{\cdot }\frac{{\dot{\mathrm{m}}}_{\mathrm{F}}}{{\mathrm{c}}_{\mathrm{F}\mathrm{.}\mathrm{9}}}\mathrm{-}\dot{{\mathrm{V}}_{\mathrm{EA}}}\left(\mathrm{1}\mathrm{-}{\mathrm{\gamma }}_{\mathrm{R}}\right)\right)$$

Its value is determined by the introduction of foreign substances into the process solution (ṁ _F ), the foreign substance concentrations in the feed (c _{F, z} ) and in the effluent (c _{F, R} ) of the cleaning device and by the degree of return of the withdrawn components (γ _R ). The mass flow of the foreign substance input can be determined by the stoichiometry of the deposited amount of nickel. The degree of recycling depends on what proportion of the rinse solution is transferred to the coating vessel to compensate for the evaporation losses, and may be between 0 and 1.

In a further embodiment of the invention, the above-described replenishment of the ions of the coating metal is combined with a process in which interfering cations that accumulate in the process solution during metal deposition are separated by means of at least one strongly acidic cation exchanger which has been previously loaded with protons ,

Preferably, this separation of the interfering cations is temporarily performed as needed in a special cleaning process. This essentially serves to remove cations which are introduced from the base material into the process solution during metal deposition. For this purpose, the process solution is brought into contact with a strongly acidic cation exchanger, which was previously loaded with protons.

In this cleaning process but also contained in the process solution ions of the metal to be deposited are removed and entered protons in the process solution. The cations of the coating metal must then be subsequently metered in and the protons introduced during the purification of the process solution must be removed again. In order to be able to use the cations of the coating metal again, the eluate obtained in the regeneration of the strongly acidic cation exchanger is used after a pH adjustment for the loading of the weakly acidic cation exchanger with the cations of the coating metal.

Preferably, the ions of the coating metal are replenished by a weakly acidic cation exchanger, which is loaded with the corresponding cations of the coating metal. At the same time, it binds the protons that have been introduced into the process solution through the cleaning process.

Another possible use of the invention is a method for extending the service life of a process solution for the chemical-reductive metal deposition, in which the consumed in the metal deposition reducing agent and the metal ions of the coating metal is post-dosed and the pH in the process solution can be adjusted, with interfering cations and Anions that accumulate in the process solution during metal deposition are removed from the process solution or a dilute process solution using ion exchange processes. For the separation of interfering cations, at least one strongly acidic cation exchanger is used for this, which was previously loaded with protons, while the weakly basic anion exchanger is converted by protons into the protonated form for the removal of the interfering anions. Preferably used the protons released by the strongly acidic cation exchanger as described above, when it binds interfering cations.

In this process, the reducing agent in the form of a water-soluble salt, preferably sodium hypophosphite (NaH 2 PO 2), or a corresponding solution, is preferably added directly into the process solution or into a dilute process solution.

The separation of the interfering anions via the weakly basic anion exchanger and the interfering cations via the strongly acidic cation exchanger preferably takes place from a dilute process solution. Preferably, the interfering cations are separated by the strongly acidic cation exchanger and the interfering anions are separated from the flushing system by the weakly basic anion exchanger. After the cations of the coating metal are removed by the strongly acidic cation exchanger in addition to the cationic impurities from the base material but also the towed into the rinse solution, the strongly acidic cation exchanger must be regenerated more frequently than if it were part of a separate auxiliary circuit of a membrane electrolysis cell. The rinsing solution thus purified is returned to the process solution to compensate for the evaporation losses occurring in the metal deposition.

In a preferred embodiment of the invention, the method described above for the separation of interfering anions or interfering cations from a dilute process solution (or rinse solution) with the above-described pH adjustment and post-dosing of the metal ions using the weakly acidic cation exchanger loaded with metal ions ,

Preferably, the supply of the metal ions of the coating metal in the previously purified solution by means of a weakly acidic cation exchanger, which has been previously loaded with the metal ions of the coating metal. As a result, the pH in the recirculated solution is increased, and it becomes the metal ions of the coating metal separated by the strongly acidic cation exchanger returned to the process solution. The eluate of the strongly acidic cation exchanger can be used after a pH adjustment for the loading of the weakly acidic cation exchanger with the metal ions of the coating metal.

Furthermore, the invention relates to a device for extending the service life of a process solution for the chemical-reductive metal deposition, consisting of at least one weakly acidic cation exchanger for use for the pH adjustment and the post-dosing of ions of the coating metal in a plant for the chemical-reductive metal deposition. The device has elements which serve to connect the inlet and outlet of the weakly acidic cation exchanger 14 with at least one container containing the process solution, dilute process solution, cooled process solution or pretreated process solution. Furthermore, the device includes associated peripherals, such. As pumps, valves, measuring devices for pH, conductivity, temperatures.

The weakly acidic cation exchanger 14 is connected with its feed to at least one container containing process solution, dilute process solution or cooled process solution or pretreated process solution. The effluent of the weakly acidic cation exchanger 14 is directly connected to at least one container containing process solution. In addition, the device contains measuring devices for monitoring the pH of the process solution and the pH in the effluent of the weakly acidic cation exchanger 14.

The solution is enriched with ions of the coating metal by the weakly acidic cation exchanger. The risk of undesirable metal deposition from such enriched solutions is great, especially if a sufficient amount of reducing agent is present. The direct introduction according to the invention of the effluent of the weakly acidic cation exchanger into the process solution minimizes undesirable metal deposition between the cation exchanger and the process bath.

The measuring device for monitoring the pH in the course of the weakly acidic cation exchanger 14 makes it possible to continuously monitor the functionality of the weakly acidic cation exchanger, since the weakly acidic cation exchanger, as long as it is loaded with ions of the coating metal, raises the pH of the ( acidic) solution takes place. As soon as the ion exchanger is discharged, the pH value of the effluent corresponds to that of the discontinued solution.

By comparing the pH in the course of the weakly acidic cation exchanger with the pH of the process solution, the exhaustion of the weakly acidic cation exchanger can thus be determined according to the invention before the pH value and the content of the process solution to ions of the coating metal leaves the tolerance range of the process. The device therefore makes it possible to keep the content of ions of the coating metal and the pH of the process solution almost constant.

Due to the almost constant process conditions in the chemical-reductive metal coating according to the invention a particularly uniform deposition of the metal is achieved on the workpiece to be coated.

The measuring device for monitoring the pH value is also suitable for connection to a computer and thus makes an automatic change to a second cation exchanger and the automatic control of the regeneration process possible.

For its use according to the invention, the weakly acidic cation exchanger is loaded with the cations of the coating metal. Preferably, this is done in two steps: First, the weakly acidic cation exchanger for conditioning, with an alkali, preferably with sodium hydroxide, converted into the salt form. For loading, it is then brought into contact with a water-soluble salt of the coating metal in dissolved form. In the case of chemical-reductive nickel deposition For example, for the loading of metal ions, an aqueous solution of nickel sulfate or nickel chloride is chosen.

The loading of metal ions is preferably carried out in two stages with different concentrations of metal salt solutions, wherein in the second stage - preferably carried out by a circulation - a complete loading with metal ions of the coating metal. This step-by-step procedure ensures complete transfer of the weakly acidic resin into the charge of ions of the coating metal and, at the same time, good material utilization of the ions of the coating metal used.

After the loading process, the ion exchanger is washed with demineralized water to remove the corresponding sodium salts from the ion exchanger, so that they are not entered into the process solution as foreign substances.
In its use according to the invention, the weakly acidic cation exchanger is charged with process solution and releases metal ions into it. At the same time he binds protons. The maximum proton uptake capacity of the weakly acidic cation exchanger is achieved upon complete conversion to the salt form. The capacity is controlled by the pH in its course. In this case, the efficiency of the pH correction decreases when the complete discharge of the weakly acidic cation exchanger has been achieved and the pH value in the effluent of the weakly acidic cation exchanger approaches the pH value of the feed of the weakly acidic cation exchanger.

When fully discharged, the weakly acidic cation exchanger is in the H form. For renewed use according to the invention, the weakly acidic cation exchanger must be converted back into the salt form with an alkali and then loaded with ions of the coating metal. The weakly acidic cation exchanger regenerated in this way can be used again for the pH adjustment as well as for the subsequent addition of metal ions.

The weakly acidic cation exchanger has a high selectivity for protons, so that the protons formed in the chemical-reductive metal deposition are bound by this cation exchanger. In return, the metal ions previously bound to the cation exchanger are released into the process solution.

The divalent cations used for metal deposition are more strongly bound by the weakly acidic cation exchanger than monovalent cations. Advantageously, the exchanger can therefore be easily converted into the salt form with sodium hydroxide solution and then loaded with the divalent cations of the coating metal. The column capacity of the weakly acidic cation exchanger is selected according to the desired service life and the amount of metal to be deposited.

Preferably, the cation exchanger contains a weakly acid cation exchange material having carboxylic acid groups as functional groups.

It was found that the weakly acidic cation exchanger brought into direct contact with the process solution and not only replenished the ions of the coating metal, but also the pH of the process solution can be adjusted. This is achieved by the fact that the weakly acidic cation exchanger, when it comes into contact with the process solution, binds the H ⁺ ions formed in the metal deposition. By using the weakly acidic cation exchanger loaded with the cations of the coating metal, it is advantageously not necessary to add alkalis and metal salts to the process solution according to the prior art in order to bind the H ⁺ ions and to replenish the spent metal ions.

Since it is surprisingly possible to adjust the pH in the process solution with the aid of the weakly acidic cation exchanger which is brought into contact with the process solution, it is also unnecessary to add alkalis to the process solution as required by the prior art.

By the addition of the ions of the coating metal without interfering counterions and the pH adjustment without addition of alkali, the addition of salts into the process solution is considerably reduced by the weakly acidic cation exchanger according to the invention in comparison with the prior art. If a conventional system for chemical-reductive metal deposition is supplemented solely with the weakly acidic cation exchanger according to the invention, the useful life of the process solution can be significantly increased.

Another object of the invention is a device for extending the service life of a process solution for the chemical-reductive metal deposition, consisting of at least one loaded with H + ions strongly acidic cation exchanger for use for the removal of interfering cations in a plant for the chemical-reductive metal deposition. The device has elements for recycling the process solution or cooled or pretreated process solution via the strongly acidic cation exchanger 15. The strongly acidic cation exchanger 15 is connected with its inlet and its outlet directly to at least one container containing process solution, dilute process solution or cooled process solution or pretreated process solution. Furthermore, the device contains associated peripherals, such. As pumps, valves, measuring devices for pH, conductivity, temperatures.

The invention also relates to the combination of the weakly acidic cation exchanger described above with the strongly acidic cation exchanger described above in a device for use in a chemical-reductive metal deposition plant in order to extend the useful life of a process solution for chemical-reductive metal deposition. The device contains at least one strongly acidic cation exchanger for the removal of interfering cations, which is connected in series or in parallel with at least one weakly acidic cation exchanger for use for the pH adjustment and subsequent addition of ions of the coating metal. The apparatus also includes elements which cool the compound of the weakly acidic cation exchanger and the strongly acidic cation exchanger with at least one container, the process solution, dilute process solution Process solution or pretreated process solution contains serve. Furthermore, the device contains associated peripherals, such. As pumps, valves, measuring devices for pH, conductivity, temperatures.

Furthermore, the invention relates to the combination of the strongly acidic H + ions-loaded strong acid cation exchanger 15 described above with the weakly acidic cation exchanger 14 loaded with ions of the coating metal.

In this combination, the strongly acidic cation exchanger is preceded by the weakly acidic cation exchanger.

By loaded with H + ions strongly acidic cation exchanger interfering cations are removed from the process solution, the z. B. originate from the material to be coated. At the same time, however, ions of the coating metal are bound by the strongly acidic cation exchanger and the pH value in the applied solution is lowered. By abandoning the course of the strongly acidic cation exchanger to the weakly acidic cation exchanger, the pH of the solution is raised again and enriched with ions of the coating metal.

Advantageously, it thus makes it possible to combine the strongly acidic H + ion-laden strong acid cation exchanger 15 with the ions of the coating metal loaded weakly acidic cation exchanger 14 to remove interfering cations from the process solution, adjust the pH and enrich the process solution with ions of the coating metal.

In a preferred embodiment of the invention, the abovementioned ion exchangers are column exchangers which are filled with a solid, water-insoluble, ion exchange material. The organic or inorganic ion exchange material contains functional groups capable of ion exchange. These column exchangers can be regenerated in cocurrent or countercurrent.

In an alternative embodiment of the invention, the above-mentioned ion exchange materials are each part of a filter or membrane apparatus. This contains in each case a regenerable, organic or inorganic ion exchanger material, which is preferably introduced into the filter or membrane apparatus in a form capable of ion exchange.

In a further embodiment of the invention, liquid ion exchange materials are used in at least one of the ion exchange materials used. The one or more ion exchangers in this embodiment each consist of a container which contains a liquid immiscible with the process solution, in which an ion exchange material is distributed or dissolved. Preferably, in this embodiment, the ion exchange material consists of a reagent containing the functional groups required for the ion exchange action, e.g. be used in the reactive extraction.

• ● mindestens einem Beschichtungsbehälter,
• ● einem Spülsystem,
• ● und mindestens einer der oben beschriebenen Vorrichtungen zur Verlängerung der Nutzungsdauer einer Prozesslösung für die chemisch-reduktive Metallabscheidung.

Another object of the invention is a system for the chemical-reductive metal deposition consisting of:

• ● at least one coating container,
• ● a flushing system,
• ● and at least one of the above-described devices for extending the useful life of a process solution for the chemical-reductive metal deposition.

Furthermore, the system contains connecting cables between the individual components as well as the associated peripherals, such as pumps, valves, measuring devices for pH, conductivity, temperatures etc.
The coating container contains the process solution in which the workpiece to be coated is immersed.

In its simplest embodiment, the plant according to the invention consists of a coating container, a rinsing system and a device with a weakly acidic cation exchanger for pH adjustment as described above and subsequent metering of the metal to be deposited, which is connected to inlet and outlet with the coating container.

Preferably, the process solution is cooled before being contacted with the sensitive components of the devices, particularly the ion exchange materials and the membranes. By cooling, in particular, the risk of undesired metal deposition on these components is reduced. The process solution prepared by the device must be returned to the process temperature before being returned to the coating vessel.

In a preferred embodiment of the plant described above, the inlet and the outlet of the weakly acidic or strongly acidic cation exchanger are therefore connected to the coating vessel via a heat exchanger. The heat exchanger uses the energy of the cooling process for the warm-up process of purified process solution.

1. a.) schwachsaurem Kationenaustauschermaterial oder schwachsauren Kationenaustauschern für die pH-Wert-Einstellung und Nachdosierung von Ionen des Beschichtungsmetalls und
2. b.) Ionen beladenem starksaurem Kationenaustauschermaterial oder H+-Ionen beladenen starksauren Kationenaustauschern 11, 15 für die Entfernung störender Kationen

zur Verlängerung der Nutzungsdauer einer Prozesslösung für die chemisch-reduktive Metallabscheidung.Another object of the invention is the use of a combination of

1. a.) weakly acidic cation exchange material or weakly acidic cation exchangers for the pH adjustment and post-dosing of ions of the coating metal and
2. b.) ion-charged strong acid cation exchange material or H + -ionic strongly acidic cation exchangers 11, 15 for the removal of interfering cations

for extending the useful life of a process solution for chemical-reductive metal deposition.

The weakly acidic cation exchanger loaded with ions of the coating metal is preferably used as the last step in the work-up. Its process is initiated directly into the process solution.

Compared with the state of the art, the useful life of a process solution for the chemical-reductive metal coating can be considerably extended by the invention. Advantageously, this results in a considerable saving of starting materials. At the same time reduce the disposal costs, which are not inconsiderable according to the prior art.

Furthermore, the invention advantageously achieves virtually constant process conditions in the case of the chemical-reductive metal coating and thus a particularly uniform deposition of the metal on the workpiece to be coated. Due to the low impurity content of the process solution, which is achieved in the system according to the invention, nickel-phosphorus layers can be deposited, which are in the compressive stress range, which in particular causes the quality of the coating of the deposition.

Fig. 1

Anlage mit schwachsaurem Kationenaustauscher zur pH-Wert-Einstellung und Nachdosierung von Ionen des Beschichtungsmetalls

Fig. 2:

Anlage mit Wärmetauscher und schwachsaurem Kationenaustauscher zur pH-Wert-Einstellung und Nachdosierung von Ionen des Beschichtungsmetalls

With reference to the following drawings, embodiments of the invention are shown and described schematically. Showing:

Fig. 1

Plant with weakly acidic cation exchanger for pH adjustment and post-dosing of ions of the coating metal

Fig. 2:

Plant with heat exchanger and weak acid cation exchanger for pH adjustment and post-dosing of ions of the coating metal

Fig. 1 shows a scheme of a plant for chemical-reductive metal coating, in which by means of a coated with ions of the coating metal low-acid cation exchanger 14, the required ions of the coating metal are replenished without interfering anions and at the same time the pH of the process solution is adjusted and thus prolongs the useful life of the process solution can be.

The plant after Fig. 1 consists of a coating container 1, a multi-stage flushing system 3 in cascade connection and a weakly acidic cation exchanger 14 , as well as connecting pipes and associated peripherals, such as pumps, valves, measuring devices for pH, conductivity, temperatures, etc. The latter have not been included for reasons of clarity Fig. 1 located. The coating container 1 contains process solution in which a workpiece 2 to be coated is immersed. The workpiece 2 to be coated has a steel surface.

The multi-stage flushing system 3 consists of three cascaded containers containing an aqueous rinse solution. Between the left and right rinse tanks 3 , as indicated by the broken line in FIG Fig. 1 indicated, but not shown, another rinsing bin queued. The left washing container 3 contains a feed for fresh water. The right rinse tank 3 is connected to the coating tank 1.

The weakly acidic cation exchanger 14 is connected with its inlet and outlet to the coating container 1 , so that a certain volume flow of the process solution can be passed over him.

The weakly acidic cation exchanger consists of an ion exchange column 14 which is filled with the weakly acidic cation exchange polymer Lewatit CNP 80 from Lanxess AG, Leverkusen, Germany. However, it is also possible to use comparable weakly acidic cation exchanger polymers from other manufacturers, e.g. C 104 of Fa. Purolite, Ratingen, Germany.

This weakly acidic cation exchange polymer is loaded with ions of the coating metal prior to use. For this purpose, the ion exchanger is first converted into the salt form with sodium hydroxide solution and then loaded with ions of the coating metal by the application of a metal salt solution. In the case of chemical reductive nickel plating, the weakly acidic cation exchange polymer is loaded with nickel ions, for which purpose a NiSO ₄ solution is passed over the ion exchange column. This loading is carried out in two steps with nickel salt solutions of different concentrations, the first Loading step, a deficiency of nickel ions is applied to the ion exchanger. Due to the selectivity of the cation exchanger an almost complete removal of the nickel ions from the feed solution is achieved, which is discarded after loading and treated by wastewater technology. In the second loading step, a complete loading of the weakly acidic cation exchanger with nickel is achieved by using an excess of nickel ions when loading the ion exchanger and recycling the feed solution.

After the loading process with nickel, the weakly acidic cation exchanger is washed with demineralized water in order to remove interfering ions from the polymer bulk layer. By this rinsing process, the excess of nickel ions is removed again from the polymer bulk layer. The course of the second fraction of the loading process is intermediately stacked together with the first fraction of the rinse water and used in the subsequent loading of the weakly acidic cation exchanger as the first loading fraction.

The process solution is composed in a known manner. In the new batch, the ions of the coating metal in the form of nickel sulfate (6.0 g Ni ²⁺ / l) are added. The reducing agent is added in the form of sodium hypophosphite (17.0 g H ₂ PO ₂ ^- / l). By means of organic acids contained in the process solution, the solution is buffered in the range of pH 4 to pH 5.

For the deposition of nickel-phosphorus alloys on the steel surface of a workpiece 2 to be coated with the in Fig. 1 shown system as follows:

The temperature of the process solution surrounding the workpiece 2 to be coated is adjusted to 85 ° C. Metal ions deposit on the steel surface of the workpiece 2 to be coated. In the deposition elemental phosphorus, which is formed by side reactions of the reducing agent, alloyed into the resulting metal layer, whereby a nickel-phosphorus alloy is formed. Through the redox process of chemical-reductive metal deposition is the Reducing agent sodium hypophosphite oxidized to sodium orthophosphite. This consumption of reducing agent is compensated for by adding sodium hypophosphite to the process solution.

Due to the metal deposition, the pH value and the nickel content in the process solution also decrease. Therefore, the pH in the process solution is monitored. If the pH of the process solution falls below a specified value, e.g. from pH 4.5 to pH 4.2, then a partial stream of the process solution is passed through the weakly acidic cation exchanger 14 at a flow rate <5 m / h. This results in the course of the weakly acidic cation exchanger 14, an increase in the nickel content of 5 g / l to 8 g / l and an increase in the pH of 4.2 to pH> 5.

By controlling the pH in the effluent of the weakly acidic cation exchanger 14, the functionality of the weakly acidic cation exchanger is monitored. With increasing metal release, the weakly acidic cation exchanger is converted into the H + form, which is why the pH falls in the course of the cation exchanger. When the pH in the effluent of the weakly acidic cation exchanger approaches the pH of the process solution (in this case pH 4.5), the cation exchanger is re-used for re-use, as described above, into the nickel charge.

In the case of metal coating, the high treatment temperatures result in evaporation losses in the process solution. These evaporation losses are compensated, in the rinsing solution from the rinsing system 3, by the in Fig. 1 indicated by an arrow line, is fed from the right rinsing bath in the process solution, since in this container, the concentration of Spülwasserinhaltsstoffe is highest.
In the following table test parameters are listed, which were obtained in the described comparative experiment. new approach after 5.5 MTO after 8 MTO Comparative experiment after 5.5 MTO Ni ²⁺ 6.0 g / l 6.0 g / l 5.5 g / l 5.5 g / l Na ⁺ 6.0 g / l 48.7 g / l 68.1 g / l 74.5 g / l H ₂ PO ₂ ^- 17.0 g / l 20.0 g / l 24.0 g / l 17.0 g / l H ₂ PO ₃ ^- 0.0 g / l 150.3 g / l 218.5 g / l 150.3 g / l SO ₄ ^2- 9.8 g / l <10 g / l <10 g / l 63.8 g / l organ. acids 45 g / l 45 g / l 45 g / l 45 g / l PH value 4.5 4.8 5.0 5.0 temperature 85 ° C 90 ° C 90 ° C 90 ° C deposition 12 to 14 μg / h 10 μm / h <5 μm / h <5 μm / h

In the comparative experiment (see right-hand column of the table), the salt content in the process solution rises to high values already after a metal throughput of 5.5 MTO due to the introduced or formed foreign substances (in particular Na +, SO ₄₂ -, H ₂ PO ₃ -). so that at this time, the deposition rate at 90 ° C to values <5 microns / h drops and the properties of the deposited layers no longer meet the requirements.

When using the weakly acidic cation exchanger 14 according to the invention (see the two middle columns of the table), however, the SO ₄₂ content of the process solution does not increase with increasing metal throughput, since the nickel ions are introduced into the process solution without interfering SO ₄₂ . In contrast to the comparative experiment, the Na + content increases considerably slower here, since the adjustment of the pH without addition of NaOH in the process solution .. By using the weakly acidic cation exchanger 14, the process solution by the slower increase in the impurity content up to a Metal throughput of about 8 MTO can be used. The useful life of the process solution is thus almost doubled by the use according to the invention of the weakly acidic cation exchanger 14.

Fig. 2 shows a scheme of a system for chemical-reductive metal coating with a weakly acidic cation exchanger 14, which via a heat exchanger 4 with the coating container 1 is connected. With regard to the coating container 1 and the rinsing system 3, this system is designed according to the system Fig. 1 built up. As further components, this plant contains a storage tank 5 and a stack container 13, which are each connected via the heat exchanger 4 with the coating container 1.

The weakly acidic cation exchanger 14 corresponds in its construction to that Fig. 1 , In contrast to Fig. 1 However, he is not directly connected to the coating container 1 in this system, but with its inlet to the feed tank 5 and with its outlet to the stack container 13th

For metal coating in this system is in principle how to Fig. 1 described, proceed. However, the weakly acidic cation exchanger 14 is loaded here with cooled process solution. For this purpose, a volume flow of the process solution is passed through the heat exchanger 4 and cooled in this from the treatment temperature of 85 ° C to temperatures <50 ° C. This cooled solution is collected in the storage tank 5, and passed from this over the weakly acidic cation exchanger 14. By the weakly acidic cation exchanger 14 takes place in analogy to Fig. 1 , an enrichment of the treated solution with nickel ions and an increase in the pH. The treated solution is collected in the stack container 13 and returned to the coating container 1 via the heat exchanger 4.

By using the heat exchanger 4, the weakly acidic cation exchanger 14 is subjected to a cooled process solution, which significantly reduces the risk of a chemical-reductive metal deposition on the cation exchange polymer.

List of used reference signs:

1

coating tank

2

to be coated workpiece

3

(multi-stage) flushing system

4

heat exchangers

5

Storage tank for process solution to be cleaned

13

Stacking container for purified process solution

14

Low-acid cation exchanger for post-dosing of the coating metal

15

Strongly acidic cation exchanger for cleaning the process solution

16

replenishment containers

H ₂ O

fresh water

NaH ₂ PO ₂

reducing agent

Claims (7)

Method for extending the useful life of a process solution for chemical-reductive metal deposition, in which the reducing agent consumed in the metal deposition, as well as ions of the coating metal are metered in and the pH of the process solution is adjusted, wherein the subsequent metering of the ions of the coating metal and the pH value Adjustment with the aid of at least one weakly acid cation exchanger (14) loaded with ions of the coating metal, characterized in that the pH of the process solution is monitored, that when the pH of the process solution falls, a portion of the process solution, optionally after dilution, by the weak acidic cation exchanger (14) is passed and the solution prepared by the weakly acidic cation exchanger (14) solution of the process solution is fed back directly, that on the control of the pH in the course of the weakly acidic cation exchanger (14) the operability of schwa acidic cation exchanger is monitored, that when approaching the pH in the course of the weakly acidic cation exchanger to the pH of the process solution, the cation exchanger is loaded again for reuse with ions of the coating metal. Device for extending the service life of a process solution for the chemical-reductive metal deposition, consisting of at least one weakly acidic cation exchanger (14) for use for the pH adjustment and subsequent addition of ions of the coating metal in a system for chemical-reductive metal deposition, characterized in that the device comprises elements for recirculating the process solution or cooled or pretreated process solution through the weakly acidic cation exchanger (14) containing the weakly acidic cation exchanger (14) with its feed to at least one container, the process solution, dilute process solution or cooled process solution or pretreated process solution is connected, that the weakly acidic cation exchanger (14) is connected with its flow directly to at least one container containing process solution, that the Device has measuring devices for monitoring the pH of the process solution and the pH in the course of the weakly acidic cation exchanger (14). Apparatus according to claim 2, characterized in that the one or more ion exchangers (14, 15) are column exchangers containing at least one solid, water-insoluble, organic or inorganic ion exchange material and can be regenerated in cocurrent or countercurrent. Apparatus according to claim 2, characterized in that the one or more ion exchangers (14, 15) each part of a filter or membrane apparatus, which contains at least one regenerable, organic or inorganic ion exchange material. Apparatus according to claim 2, characterized in that the one or more ion exchangers (14, 15) each consist of a container which contains a liquid immiscible with the process solution, in which an ion exchange material is distributed. Plant for chemical-reductive metal deposition, consisting of at least one coating container (1), a flushing system (3) and associated peripherals, such. As pumps, valves, measuring devices for pH, conductivity, temperatures, characterized in that it contains at least one device for extending the service life of a process solution for the chemical-reductive metal deposition according to claim 2. Plant according to claim 6, comprising at least one device according to claim 2, characterized in that the inlet and the outlet of the weak acid cation exchanger (14) and / or the strong acid cation exchanger (15) directly or via a heat exchanger (4) with the coating container (1 ) are connected.

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