Treatment liquid and method for removing lead compound

Abstract

Provided is a treatment liquid for treating an object to be treated having a lead compound-containing deposit bonded to the surface thereof. Said treatment liquid contains a non-oxycarboxylic acid-based chelating agent (A) and an organic acid or a salt thereof (B).

Description

Treatment Liquid and Lead Compound Removal Method

[0001] The present invention relates to a treatment liquid and a lead compound removal method.

[0002] Conventionally, in electrolysis for industrial electrolysis such as electrolytic copper foil production or copper plating, an oxygen evolution electrode is used, in which the surface of an electrode substrate made of a valve metal such as titanium or tantalum, or a valve metal alloy is directly coated with an electrode catalyst layer containing iridium oxide or the like.

[0003] However, when this type of oxygen evolution electrode is used for a certain period or longer, the interface between the electrode substrate and the electrode catalyst layer corrodes, and a passivation layer is formed on the surface of the electrode substrate, which makes it difficult to perform electrolysis. Therefore, it has been necessary to grind the surface of the electrode substrate by a physical method until a new surface is exposed, or newly fabricate an electrolytic electrode from the electrode substrate.

[0004] Furthermore, as an oxygen evolution electrode, when an electrolytic electrode is used in which an intermediate layer containing a metal such as tantalum or niobium with a thickness of 0.5 to 20 µm, a metal oxide, or a metal alloy is formed on the surface of an electrode substrate made of a valve metal such as titanium or tantalum, or a valve metal alloy, and the surface of the intermediate layer is coated with an electrode catalyst layer containing iridium oxide, it is known that interfacial corrosion between the electrode substrate and the catalyst layer is suppressed.

[0005] However, even with the above-mentioned oxygen evolution electrode, when it is used for electrolysis in electrolytic copper foil production or copper plating, lead compounds including lead sulfate or lead oxide adhere to the electrode surface of the electrolytic electrode. During electrolysis, lead contained in the electrolytic solution adheres to the electrode surface as lead oxide, which is a good conductor, but when electrolysis is stopped, lead oxide, which is a conductor, changes to lead sulfate, which is a poor conductor. Furthermore, the lead compounds (lead sulfate or lead oxide) adhering to the electrode surface fall off from the surface of the electrolytic electrode during the start / stop of electrolysis or during electrolysis. As a result, the above-mentioned oxygen evolution electrode, when used as an electrolytic electrode, has uneven current distribution, causes poor copper foil thickness, and has the problem that it cannot be used continuously for a long period of time as an electrolytic electrode.

[0006] In such cases, the oxygen generating electrode had its surface deposits containing lead compounds removed by either physically polishing and scrubbing the surface of the electrolytic electrode used for electrolysis, or by an acid treatment process in which the electrolytic electrode was immersed in a mixed solution of concentrated nitric acid and hydrogen peroxide (Patent Document 1). However, when the oxygen generating electrode was used continuously for three months, it was difficult to remove the electrode deposits containing lead compounds from the electrolytic electrode surface by the aforementioned polishing. Furthermore, although the removal method by the acid treatment process had some effect in removing electrode deposits containing lead compounds, it had problems such as the use of hydrogen peroxide, which is difficult to handle, the use of nitric acid, which has a high environmental impact, and the fact that the removal rate of lead compounds was incomplete, making it essential to use it in combination with physical wiping and peeling work.

[0007] Patent No. 4451471

[0008] The present invention aims to provide a treatment solution and a method for removing lead compounds that can efficiently remove lead compound-containing deposits from a workpiece on which lead compounds have adhered to its surface, and that is safe and environmentally friendly.

[0009] The inventors discovered that a workpiece with lead compound-containing deposits on its surface can be easily dissolved and removed without temperature control or physical peeling processes by immersing it in a treatment solution containing a specific chelating agent and an organic acid or its salt, thus completing the present invention.

[0010] The treatment solution according to the present invention comprises the following components: [1] A treatment solution for treating an object to be treated on which a deposit containing a lead compound is attached to the surface, the treatment solution comprising a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B).

[0011] The treatment solution preferably comprises the following components: [2] The treatment solution according to [1], wherein the mass ratio of the non-oxycarboxylic acid chelating agent (A) to the organic acid or its salt (B) is in the range of 9:1 to 1:9. [3] The treatment solution according to [1] or [2], wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of aminocarboxylic acids, aldonic acids, phosphonic acids, amino acids, and their salts. [4] The treatment solution according to [1] or [2], wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, diaminopropionic acid, hydroxyethylidenediphosphonic acid (HEDP), 1-hydroxyethane-1,1-bis(phosphonic acid), nitrilotris(methylenephosphonic acid), and salts thereof. [5] The treatment solution according to [1] or [2], wherein the organic acid or salt thereof (B) is at least one selected from the group consisting of polycarboxylic acids and salts thereof. [6] The treatment solution according to [1] or [2], wherein the polycarboxylic acid or salt thereof is at least one selected from the group consisting of oxalic acid, tartaric acid, malic acid, malonic acid, succinic acid, adipic acid, fumaric acid, maleic acid, citric acid, aconitic acid, and salts thereof. [7] The treatment solution according to [1] or [2], wherein the lead compound is lead sulfate or lead oxide. [8] The treatment solution according to [1] or [2], wherein the object to be treated is an electrolytic electrode in which a catalyst layer containing a platinum group metal or an oxide thereof is coated on the electrode surface. [9] The treatment solution according to [1] or [2], wherein the workpiece is an electrolytic electrode in which an intermediate layer containing a metal, metal oxide, or metal alloy is coated on the surface of an electrode base made of valve metal or valve metal alloy, and a catalyst layer containing a platinum group metal or its oxide is further coated on the surface of the intermediate layer.

[11] The treatment solution according to [1] or [2], wherein the object to be treated is an electrode separation catalyst separated from an electrolytic electrode having a catalyst layer coated on its electrode surface.

[0012] Furthermore, the lead compound removal method according to the present invention comprises the following configuration:

[12] A lead compound removal method for removing a lead compound from a workpiece on which a deposit containing a lead compound is attached to the surface, comprising: a preparation step of preparing a treatment solution containing a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B); and an immersion step of immersing the workpiece in the treatment solution.

[0013] The lead compound removal method preferably comprises the following components:

[13] The lead compound removal method according to

[12] , wherein the immersion step is performed at 15 to 35°C.

[14] The lead compound removal method according to

[12] or

[13] , further comprising a washing step of washing the object to be treated, wherein the washing step is performed after the immersion step without going through a mechanical removal step by brushing or jet spraying.

[0014] The treatment solution and lead compound removal method of the present invention enable efficient removal of lead compound-containing deposits from a workpiece on which these deposits have adhered to its surface. Furthermore, since physical wiping and stripping are not required, it is possible to avoid uneven or insufficient stripping that can occur when physically rubbing the surface of the workpiece with an abrasive. In addition, the treatment of lead-containing abrasives is also unnecessary. Moreover, since lead compounds do not turn into powder or metal powder is released from the workpiece during the stripping process, concerns about health hazards to workers and dust explosions caused by these factors can be eliminated. Furthermore, because a chelating agent and an organic acid or organic salt are used instead of strong acids such as mineral acids, it is safe and has a low environmental impact.

[0015] Therefore, according to the present invention, it is possible to efficiently remove lead compound-containing deposits from a workpiece on which lead compound-containing deposits have adhered to its surface, and to provide a safe and environmentally friendly treatment solution and lead compound removal method.

[0016] Embodiments of the treatment solution and lead compound removal method are described in detail below. In this specification, numbers connected by "~" represent a numerical range that includes the numbers before and after "~" as the lower and upper limits, respectively. If multiple lower and upper limits are listed individually, any lower and upper limits may be selected and connected by "~".

[0017] The treatment solution of this embodiment contains at least (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or a salt thereof. This provides a treatment solution that is excellent in removing lead compound-containing deposits from the surface of a workpiece (e.g., an electrolytic electrode) on which lead compound-containing deposits have adhered, and is excellent in solubilizing lead. In the following description, unless otherwise specified, the case in which an electrolytic electrode is used as the workpiece will be mainly assumed.

[0018] (A) Non-oxycarboxylic acid chelating agent The chelating agent included in the treatment solution of this embodiment is not particularly limited, and known chelating agents (excluding oxycarboxylic acid-based ones) can be used. By including a non-oxycarboxylic acid chelating agent in the treatment solution, lead compounds (lead sulfate or lead oxide) adhering to the surface of the electrolytic electrode form a water-soluble lead complex, thereby efficiently dissolving and removing the lead compounds from the surface of the electrolytic electrode.

[0019] The non-oxycarboxylic acid chelating agent (hereinafter sometimes simply referred to as "chelating agent") contained in the treatment solution of this embodiment is not particularly limited, but for example, aminocarboxylic acids, aldonic acids, phosphonic acids, amino acids, and their salts can be used. Among those mentioned above, aminocarboxylic acids, phosphonic acids, aldonic acids, and their salts are preferred, and aminocarboxylic acids, phosphonic acids, and their salts are more preferred. These chelating agents may be used individually, or two or more may be used in combination.

[0020] The aminocarboxylic acids and their salts are not particularly limited, but examples include ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, diaminopropionic acid, or their alkali metal salts or lower amine salts having 1 to 4 carbon atoms. Specifically, examples include sodium salts, potassium salts, ammonium salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, laurylamine salts, etc.

[0021] Among those mentioned above, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), and their alkali metal salts are preferred, with sodium salt of ethylenediaminetetraacetic acid, nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA) being more preferred. These chelating agents may be used individually, or two or more may be used in combination.

[0022] Aldonic acids and their salts are not particularly limited, but examples include gluconic acid, glucoheptonic acid, glyceric acid, tetronic acid, pentonic acid, hexonic acid, heptonic acid, etc., or their alkali metal salts or lower amine salts having 1 to 4 carbon atoms. Specifically, examples include sodium salts, potassium salts, ammonium salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, laurylamine salts, etc.

[0023] Phosphonic acids and their salts are not particularly limited, but examples include hydroxyethylidenediphosphonic acid (HEDP), 1-hydroxyethane-1,1-bis(phosphonic acid), nitrilotris(methylenephosphonic acid), aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, etc., or their alkali metal salts or lower amine salts having 1 to 4 carbon atoms. Specifically, examples include sodium salts, potassium salts, ammonium salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, laurylamine salts, etc.

[0024] Among those mentioned above, hydroxyethylidene diphosphonic acid (HEDP), 1-hydroxyethane-1,1-bis(phosphonic acid), nitrilotris(methylenephosphonic acid), and their alkali metal salts are preferred, and hydroxyethylidene diphosphonic acid (HEDP), sodium hydroxyethylidene diphosphonic acid, 1-hydroxyethane-1,1-bis(phosphonic acid), and nitrilotris(methylenephosphonic acid) are more preferred. These chelating agents may be used individually, or two or more may be used in combination.

[0025] The amino acids and their salts are not particularly limited, but examples include alanine, arginine, guanosine, glycine, cysteine, serine, tryptophan, threonine, nicotinic acid, histidine, phenylalanine, proline, methionine, lysine, leucine, etc., or their alkali metal salts or lower amine salts having 1 to 4 carbon atoms. Specifically, examples include sodium salts, potassium salts, ammonium salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, laurylamine salts, etc.

[0026] The chelating agent contained in the treatment solution of this embodiment may be used in the form of an aqueous solution. In this case, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) is used as the solvent, and it is preferably used in the form of an aqueous solution.

[0027] The concentration of the chelating agent contained in the treatment solution of this embodiment can be appropriately selected depending on the purpose, but for example, it can be used without any particular problem as long as it is in the range from 0.1 mass% to the saturation concentration (for example, 52.2 mass% at 20°C, meaning the maximum solubility at each temperature). Preferably, it is in the range of 0.01 mass% to 70 mass% (room temperature 25°C), more preferably in the range of 0.05 mass% to 65 mass% (room temperature 25°C), and even more preferably in the range of 0.1 mass% to 60 mass% (room temperature 25°C). Note that if the concentration of the chelating agent contained in the treatment solution of this embodiment exceeds 70 mass%, the viscosity will become high and there will be no stirring of the liquid at the interface of the deposits, which may result in a reduced reaction. If it is less than 0.01 mass%, the reaction to convert lead sulfate, lead oxide, or organic lead acid in deposits containing lead compounds into water-soluble lead complexes will not occur sufficiently, resulting in insufficient removal efficiency.

[0028] The pH range of the solution containing the chelating agent in this embodiment is preferably in the range of pH 1 to 12, more preferably in the range of pH 2 to 11, and even more preferably in the range of pH 3 to 10. By adjusting the pH within this range, the reaction that converts lead sulfate, lead oxide, or organic lead acid in deposits containing lead compounds into water-soluble lead complexes proceeds predominantly.

[0029] Regarding the chelating agent contained in the treatment solution of this embodiment, the complex formation constant (logK) with respect to lead(II) is preferably in the range of 2 to 21, more preferably in the range of 4 to 20, and even more preferably in the range of 6 to 19. By using a chelating agent with a complex formation constant (logK) within this range in the treatment solution, the reaction of converting lead sulfate, lead oxide, or organic lead acid in deposits containing lead compounds into water-soluble lead complexes proceeds predominantly.

[0030] (B) Organic acid or salt thereof The organic acid or salt thereof contained in the treatment solution of this embodiment is not particularly limited, and known organic acids or salts thereof can be used. The advantage of the above treatment solution containing an organic acid or salt thereof is that lead compounds (lead sulfate or lead oxide) attached to the electrolytic electrode surface form a water-soluble lead complex, thereby efficiently dissolving and removing the lead compounds from the electrolytic electrode surface.

[0031] The organic acid or salt thereof contained in the processing solution of this embodiment is not particularly limited, but for example, a carboxylic acid or a salt thereof can be used. As the carboxylic acid, monocarboxylic acids and polycarboxylic acids can be used without particular limitation, but the use of polycarboxylic acids is preferred.

[0032] Polycarboxylic acids or their salts are not particularly limited, but examples include oxalic acid, tartaric acid, malic acid, malonic acid, succinic acid, adipic acid, fumaric acid, maleic acid, citric acid, aconitic acid, etc., or their alkali metal salts or lower amine salts having 1 to 4 carbon atoms. Specifically, examples include sodium salts, potassium salts, ammonium salts, monoethanolamine salts, diethanolamine salts, triethanolamine salts, laurylamine salts, etc.

[0033] Among those mentioned above, tartaric acid, sodium potassium tartrate, malic acid, succinic acid, citric acid, and diammonium hydrogen citrate are preferred, and sodium potassium tartrate, malic acid, succinic acid, citric acid, and diammonium hydrogen citrate are more preferred. A single polycarboxylic acid or its salt may be used alone, or two or more may be used in combination.

[0034] The organic acid or its salt contained in the processing solution of this embodiment may be used in the form of an aqueous solution. In this case, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) is used as the solvent, and it is preferably used in the form of an aqueous solution.

[0035] The concentration of the organic acid or its salt contained in the processing solution of this embodiment can be appropriately selected depending on the purpose, but for example, it can be used without any particular problem as long as it is in the range from 1% by mass to the saturation concentration (for example, 52.2% by mass at 20°C, meaning the maximum solubility at each temperature). Preferably, it is in the range of 1% by mass to 60% by mass (room temperature 25°C), more preferably in the range of 2% by mass to 55% by mass (room temperature 25°C), and even more preferably in the range of 5% by mass to 50% by mass (room temperature 25°C). Note that if the concentration of the solution containing the organic acid or its salt in this embodiment exceeds 60% by mass, the formation of organic acid lead will proceed predominantly, and there is a risk that a large amount will adhere to the electrode surface, and if it is less than 1% by mass, the reaction to convert lead sulfate or lead oxide in the deposit containing lead compounds into lead complexes will not occur sufficiently, resulting in insufficient removal efficiency.

[0036] The pH range of the solution containing the organic acid or its salt in this embodiment is preferably in the range of pH 1 to 12, more preferably in the range of pH 2 to 11, and even more preferably in the range of pH 3 to 10. By adjusting the pH within this range, the reaction that converts lead sulfate or lead oxide in deposits containing lead compounds into water-soluble lead complexes proceeds predominantly.

[0037] (A) A non-oxycarboxylic acid chelating agent and (B) an organic acid or its salt The treatment solution of this embodiment has the advantage that by using both (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or its salt, i.e., (A) and (B), lead compounds (lead sulfate or lead oxide) attached to the electrolytic electrode surface form a water-soluble lead complex, thereby most efficiently dissolving and removing lead compounds from the electrolytic electrode surface.

[0038] When (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or a salt thereof are used in combination, the mass ratio (A:B) of (A) the non-oxycarboxylic acid chelating agent to (B) the organic acid or a salt thereof contained in the treatment liquid of the present embodiment is preferably in the range of 9:1 to 1:9, more preferably in the range of 7:3 to 3:7, and still more preferably in the range of 6:4 to 4:6. If the ratio is outside this range, there is a possibility that the reaction for converting a lead compound (lead sulfate or lead oxide) in deposits containing the lead compound into a water-soluble lead complex does not proceed sufficiently, which may lead to insufficient removal efficiency.

[0039] The pH range of the treatment liquid of the present embodiment is preferably pH 1 to 12, more preferably pH 2 to 11, and still more preferably pH 3 to 10. By adjusting the pH within this range, the reaction for converting lead sulfate, lead oxide or organic acid lead in deposits containing a lead compound into a water-soluble lead complex proceeds predominantly.

[0040] In the treatment liquid of the present embodiment, a pH adjuster may be used to adjust the pH to a suitable range. As the pH adjuster, one that can adjust the pH to the optimum value during the reaction may be appropriately selected. Examples thereof include inorganic acids such as hydrochloric acid, organic acids such as citric acid, inorganic bases such as hydroxides including sodium hydroxide and potassium hydroxide, and organic bases such as organic amines. One of these compounds may be used alone, or two or more thereof may be used in combination.

[0041] Method for Preparing Treatment Liquid The treatment liquid of the present embodiment may be prepared by separately preparing a solution containing (A) a non-oxycarboxylic acid chelating agent and a solution containing (B) an organic acid or a salt thereof in advance, and then mixing them such that the mass ratio (A:B) of (A) the non-oxycarboxylic acid chelating agent to (B) the organic acid or a salt thereof falls within a predetermined range. Alternatively, the treatment liquid of the present embodiment may be prepared by first weighing (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or a salt thereof to a predetermined mass ratio (A:B), and dissolving the mixture in a solvent such as ion-exchanged water.

[0042] A solution containing (A) a non-oxycarboxylic acid chelating agent, or (B) a solution containing an organic acid or a salt thereof can be prepared by: weighing a predetermined amount of (A) the non-oxycarboxylic acid chelating agent or (B) the organic acid or a salt thereof into a beaker or the like, dissolving it with a solvent such as ion-exchanged water, and stirring and heating the mixture with a glass rod or the like as needed.

[0043] Object to be treated Objects to be treated to which the treatment liquid of the present embodiment can be applied include, for example, electrolytic electrodes having deposits containing a lead compound attached to the surface thereof. Here, the deposit containing a lead compound is a deposit containing a lead compound such as lead sulfate or lead oxide that adheres to the surface of the electrolytic electrode during the process of electrolytic plating or electrolytic production of metal foil.

[0044] Furthermore, objects to be treated to which the treatment liquid of the present embodiment can be applied include not only deteriorated electrolytic electrodes per se, but also, for example, stripped materials physically peeled off in advance by polishing or the like from deteriorated electrolytic electrodes (specifically, catalysts having deposits containing a lead compound attached to the surface thereof, i.e., electrode-separated catalysts).

[0045] The content of the lead compound in the deposit (the deposit on the electrode surface or the deposit on the surface of the electrode-separated catalyst) is not particularly limited, but when 50% or more of the deposit is the lead compound, the treatment liquid of the present embodiment can be suitably applied. The deposit may contain various metal impurities in addition to the lead compound. That is, the treatment liquid of the present embodiment can be suitably applied to electrolytic electrodes (or electrode-separated catalysts) for electrolytic plating or electrolytic production of metal foil whose electrode performance is impaired (i.e., deteriorated) because deposits containing lead compounds such as lead oxide or lead sulfate adhere to the surface thereof.

[0046] The removal amount of the lead compound in the deposit can be measured by the method described in the Examples. Specifically, the peak intensity of lead near Lγ on the electrode surface is measured using an X-ray fluorescence spectrometer, and can be obtained from the peak intensity of lead near Lγ on the electrode surface before being subjected to the treatment liquid (initial intensity) and the peak intensity of lead near Lγ after being immersed in the treatment liquid.

[0047] In this embodiment, the peak intensity of lead on the electrode surface after immersion in the treatment solution is preferably less than 100 cps(Lγ), more preferably less than 75 cps(Lγ), and even more preferably less than 50 cps(Lγ). If the peak intensity of lead on the electrode surface after immersion is less than 100 cps(Lγ), it can be considered that the lead has been sufficiently removed.

[0048] An electrolytic electrode comprises at least an electrode substrate and a catalyst layer covering the surface of the electrode substrate. Furthermore, the electrolytic electrode may further include an intermediate layer between the electrode substrate and the catalyst layer, comprising an electrode substrate, an intermediate layer covering the surface of the electrode substrate, and a catalyst layer covering the surface of the intermediate layer.

[0049] As the electrode substrate, a metallic material can be used, and there are no particular restrictions on the material or shape as long as it has conductivity and appropriate rigidity. For example, valve metals such as titanium, tantalum, niobium, and zirconium, or alloys of valve metals, which have good corrosion resistance, are preferred. Furthermore, if necessary, the electrode substrate may be subjected to appropriate physical and chemical pretreatments such as annealing, surface roughening by blasting, or surface cleaning by pickling.

[0050] The intermediate layer preferably contains a metal, a metal oxide, or a metal alloy. The metal forming the intermediate layer is not particularly limited as long as it has excellent conductivity and corrosion resistance and good adhesion to the electrode substrate and catalyst layer. Typical metals used in the intermediate layer include titanium, tantalum, niobium, zirconium, hafnium, etc., which have excellent corrosion resistance, as well as their oxides or alloys, and these have excellent adhesion to electrode substrates made of valve metal such as titanium. The intermediate layer containing a metal, metal oxide, or metal alloy may contain only one type of metal, or it may be a combination of multiple metals. When using a combination of multiple metals, the ratio can be adjusted as appropriate. Among these, tantalum, titanium, or their oxides or alloys are preferred.

[0051] One method for coating an intermediate layer on an electrode substrate is layer formation by vacuum sputtering. Various devices can be used for vacuum sputtering, such as DC sputtering, high-frequency sputtering, arc ion plating, ion beam plating, and cluster ion beam methods. By appropriately setting conditions such as vacuum level, substrate temperature, target plate composition and purity, and deposition rate (input power), an intermediate layer with desired physical properties can be formed. The thickness of the intermediate layer is usually in the range of 0.1 to 10 μm and can be appropriately selected from practical viewpoints such as corrosion resistance and productivity. Thus, the electrode substrate with the coated surface has excellent properties against thermal oxidation of its surface, that is, it exhibits remarkable characteristics in the growth behavior of the oxide film.

[0052] The catalyst layer can be any known type depending on the application and is not particularly limited, but it is preferable that it contains a platinum group metal or an oxide thereof. In use as a catalyst layer in an electrolytic electrode, as in this embodiment, platinum, iridium, and ruthenium can be preferably used as the platinum group metal. Among these, for example in oxygen evolution reactions where durability is particularly required, a catalyst layer containing a platinum group metal oxide such as iridium oxide is preferred.

[0053] Various methods are known for coating an electrode substrate (or intermediate layer) with a catalyst layer, and an appropriate method can be selected depending on the purpose. For example, a thermal decomposition method can be used. Raw material salts of catalyst layer component metals, such as chlorides, nitrates, alkoxides, and resinates, are dissolved in a solvent such as hydrochloric acid, nitric acid, alcohol, or organic solvent to form a coating solution. This solution is applied to the surface of the electrode substrate (or intermediate layer), dried, and then heated in a firing furnace in an oxidizing atmosphere such as air to form the catalyst layer. The thickness of the catalyst layer is usually in the range of 0.1 to 30 μm. In addition, the catalyst layer may contain only one type of metal, or multiple metals may be used in combination. When multiple metals are used in combination, the ratio of each metal can be adjusted as appropriate.

[0054] Furthermore, it is also possible to form a catalyst layer on the electrode substrate (or intermediate layer) using a thick-film method or CVD method, in which a metal oxide is prepared in advance, a suitable organic binder and organic solvent are added to form a paste, and then printed onto the electrode substrate (or intermediate layer) and fired.

[0055] The electrolytic electrodes to which the processing solution of this embodiment can be applied are those used for metal foil manufacturing electrodes or metal plating electrodes. Specifically, a metal foil manufacturing electrode (for example, a copper foil manufacturing electrode) is an electrode used to continuously manufacture copper foil by plating copper onto a cylindrical cathode and then peeling it off. A metal plating electrode (for example, a copper plating electrode) is an electrode used to form a thin film layer by reducing any metal component (for example, copper) contained in the electrolyte and electrodepositing it onto the object to be plated.

[0056] Lead Compound Removal Method Using the treatment solution of the above embodiment, lead compounds can be removed from a workpiece on which deposits containing lead compounds are attached to the surface. This lead compound removal method (method for treating a workpiece on which deposits containing lead compounds are attached to the surface) includes a preparation step of preparing a treatment solution containing at least (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or a salt thereof, and an immersion step of immersing the workpiece in the prepared treatment solution. Furthermore, the lead compound removal method (method for treating a workpiece on which deposits containing lead compounds are attached to the surface) further includes a washing step of washing the workpiece after the immersion step.

[0057] The preparation step is the step of preparing a treatment solution containing at least (A) a non-oxycarboxylic acid chelating agent and (B) an organic acid or a salt thereof. Details of this treatment solution are as described above. The preparation step may be performed at the same location as the subsequent immersion step, or at different locations. If the preparation step and the immersion step are performed at the same location, the required amount of treatment solution may be prepared in the preparation step each time and provided directly to the immersion step, or the treatment solution may be prepared in bulk in the preparation step, stored in a tank or the like, and provided to the immersion step in the required amount as needed. If the preparation step and the immersion step are performed at different locations, the entities performing each step may be the same, or they may be different.

[0058] The immersion step involves immersing the object to be treated in the treatment solution prepared in the preparation step. By immersing the object to be treated in the treatment solution of this embodiment for a predetermined time, deposits containing lead compounds attached to the surface of the object to be treated can be removed.

[0059] When the object to be processed is an electrolytic electrode used for metal foil manufacturing (for example, copper foil manufacturing), lead compounds adhering to the surface of the electrolytic electrode can impair its performance. In such cases, the lead compounds adhering to the surface of the electrolytic electrode (impaired electrode performance) can be removed by immersing the electrode in the processing solution of this embodiment.

[0060] Specifically, by immersing the electrolytic electrode in the processing solution of this embodiment for several hours, lead sulfate or lead oxide in the electrode surface deposits containing lead compounds can be converted into water-soluble lead complexes, thereby dissolving and removing them.

[0061] Furthermore, when the workpiece is an electrolytic electrode for metal plating (for example, for copper plating), lead compounds such as lead sulfate or lead oxide adhere to the surface of the electrolytic electrode, impairing its performance. In such cases, the lead compounds adhering to the surface of the electrolytic electrode (impairing its performance) can be removed by immersing the electrode in the processing solution of this embodiment.

[0062] Specifically, by immersing the electrolytic electrode in the processing solution of this embodiment for several hours, lead sulfate or lead oxide in the electrode surface deposits containing lead compounds can be converted into water-soluble lead complexes, thereby dissolving and removing them.

[0063] Furthermore, if the object to be treated is a detached material (electrode separation catalyst) that has been physically removed in advance from the surface of the electrolytic electrode by polishing or the like, similarly, the catalyst surface deposits containing lead compounds attached to the electrode separation catalyst (inhibiting its catalytic performance) can be removed by immersing the electrode separation catalyst, which has catalyst deposits containing lead compounds attached to its surface, in the treatment solution of this embodiment.

[0064] Specifically, by immersing the electrode separation catalyst in the processing solution of this embodiment for several hours, lead sulfate or lead oxide in the catalyst surface deposits containing lead compounds can be converted into water-soluble lead complexes and dissolved and removed.

[0065] In this embodiment, when we say that the electrode performance of the electrolytic electrode is impaired, we mean that the weight (thickness) tolerance per unit area of ​​the metal foil or plating produced by electrolysis exceeds the standard value due to the adhesion of electrode surface deposits containing lead compounds to the electrode surface. For example, in the case of continuously manufactured copper foil, 1 m ２ If the weight of the copper foil per unit differs from the standard value by 1% or more, it is determined that the electrode performance of the electrolytic electrode is impaired. By immersing an electrolytic electrode in the processing solution of this embodiment, in which the thickness tolerance of the metal foil or plating produced by electrolysis exceeds the standard value, electrode deposits containing lead compounds can be efficiently removed from the surface of the electrolytic electrode.

[0066] The temperature of the processing liquid during the immersion process is not particularly limited, but for example, it should be in the range of 0 to 100°C, preferably in the range of 10°C to 60°C, more preferably in the range of 20°C to 40°C, even more preferably in the range of 15°C to 35°C where temperature adjustment is less necessary, and most preferably at room temperature (around 25°C) where temperature adjustment is not necessary.

[0067] There are no particular restrictions on the immersion time (the time the electrolytic electrode is immersed in the treatment solution), but it should be sufficient for the lead compound (lead sulfate or lead oxide) adhering to the surface of the object to be treated to be converted into a water-soluble lead complex, etc. The immersion time in the treatment solution is usually 15 minutes to 48 hours, more preferably 30 minutes to 36 hours, and even more preferably 1 hour to 24 hours.

[0068] In the immersion process, a pH adjusting agent may be used to adjust the pH of the treatment solution to a suitable range. The pH adjusting agent should be one that can adjust the pH to the optimal level during the reaction. Examples include inorganic acids such as hydrochloric acid, organic acids such as citric acid, inorganic bases such as hydroxides like sodium hydroxide and potassium hydroxide, and organic bases such as organic amines. These compounds can be used individually or in combination.

[0069] The cleaning step is a process of cleaning the workpiece after it has undergone the immersion step. The cleaning step can be carried out, for example, by washing the surface of the workpiece with water. In the lead compound removal method of this embodiment, as described above, in the preceding immersion step, the lead compounds are converted into water-soluble lead complexes, etc., and the deposits containing lead compounds attached to the surface of the workpiece (electrolytic electrode or electrode separation catalyst) are efficiently removed, so the cleaning step can be carried out under relatively mild conditions. For example, surface cleaning can be performed by flowing water at a typical water supply pressure level of about 0.2 to 0.5 MPa along the surface of the workpiece.

[0070] The cleaning process in this embodiment can be performed after the immersion process without going through other, more powerful pre-cleaning processes. Examples of such pre-cleaning processes include mechanical removal processes such as polishing (brushing) using a brush or paintbrush, or jetting high-pressure water at a pressure of approximately 5 to 100 MPa. In this embodiment, since a pre-cleaning process such as brushing or jetting is not necessarily required, the number of steps can be reduced, and deposits containing lead compounds can be removed from the workpiece easily and at low cost.

[0071] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0072] Details of each component used in the examples and comparative examples are shown in Table 1.

[0073]

[0074] First, solutions containing (A) non-oxycarboxylic acid chelating agents (referred to as mother liquors A2 to A8) and (B) organic acids or organic acid salts (referred to as mother liquors B1 to B5) were prepared to the concentrations shown in Table 1. Specifically, the predetermined amounts of reagents were weighed into beakers, deionized water was added at room temperature, and the mixture was stirred with a glass rod to completely dissolve them, thereby preparing 100 mL each of mother liquors A2 to A8 and mother liquors B1 to B5. Note that mother liquor A1 is commercially available as a 60% by mass solution, so it was used as is without any dilution.

[0075] Using the mother liquors A1-A8 and B1-B5 prepared above, (A) non-oxycarboxylic acid chelating agent and (B) organic acid or organic salt were prepared in the mass ratios shown in Tables 2 and 3, and mixed to make approximately 30 mL of treatment solution. Used electrolytic copper foil electrodes (manufactured by Daiso Engineering Co., Ltd., part number: MD-230, electrode substrate: titanium, catalyst layer: iridium-tantalum oxide, intermediate layer: tantalum, usage period: 1755 hours or more) cut to 10 mm x 30 mm were left standing in the treatment solution prepared above at room temperature for 24 hours. After standing for 24 hours, the electrode surface was washed with water and air-dried, and the lead cps(Lγ) was measured using a handheld X-ray fluorescence analyzer (Olympus VANTA). The wavelength was set to 14.5 keV to 15.0 keV, around the Lγ of lead, considering competition with the characteristic X-rays of iridium contained in the electrode catalyst. Tables 1 and 2 show the results of lead cps(Lγ) before immersion (initial value) and after immersion (after standing). The evaluation criteria for the standing results of used electrolytic copper foil electrodes in the treatment solution were as follows.

[0076] <Evaluation Criteria for Static Results> ○: Values ​​below 100 cps (Lγ) indicate sufficient lead removal. ×: Values ​​of 100 cps (Lγ) or higher indicate insufficient lead removal.

[0077] <Fluorescent X-ray Analysis Conditions> Measurement instrument: Olympus VANTA Target: Rh (Rhodium) Output setting: 20kV, 30mA Measurement time: 20 seconds Measurement atmosphere: Under air Sample preparation: Section of the test electrode cut to a size of 30mm (length) x 10mm (width) x 1mm (thickness)

[0078]

[0079]

[0080] As is clear from Tables 2 and 3, in the treatment solutions using (A) phosphonic acid as a non-oxycarboxylic acid chelating agent and (B) polyvalent carboxylic acid / polyvalent carboxylate salt as an organic acid / organic acid salt (Examples 1-5), in the treatment solutions using (A) aminocarboxylic acid as a non-oxycarboxylic acid chelating agent and (B) polyvalent carboxylate salt as an organic acid / organic acid salt (Examples 6-7), and in the treatment solutions using (A) aminocarboxylic acid salt as a non-oxycarboxylic acid chelating agent and (B) polyvalent carboxylic acid / polyvalent carboxylate salt as an organic acid / organic acid salt (Examples 8-18), the lead level after 24 hours of immersion was less than 100 cps(Lγ), confirming sufficient lead removal. On the other hand, in the treatment solutions using only polyvalent carboxylate salt as (B) organic acid / organic acid salt (Comparative Example 1), in the treatment solution using only polyvalent carboxylic acid as (A) non-oxycarboxylic acid chelating agent (Comparative Example 2), and in the treatment solutions using only polyvalent carboxylate salt as (A) non-oxycarboxylic acid chelating agent (Comparative Examples 3-4), lead removal was insufficient. Furthermore, in treatment solutions (Comparative Examples 5-12) that used (A) non-oxycarboxylic acid chelating agents and (B) organic acids / organic acid salts in combination, but did not use phosphonic acid or polycarboxylic acid / polycarboxylic acid salts as (A) non-oxycarboxylic acid chelating agents, the results showed that lead removal was insufficient regardless of the range in which the mass ratio of (A) non-oxycarboxylic acid chelating agents to (B) organic acids / organic acid salts was set.

[0081] In this embodiment, a non-oxycarboxylic acid chelating agent and an organic acid / organic acid salt are used in combination, and it has been confirmed that setting a specific type of non-oxycarboxylic acid chelating agent and a specific type of organic acid / organic acid salt in a predetermined ratio is effective in removing electrode deposits containing lead compounds from the surface of the electrode.

[0082] Furthermore, the regeneration capability of the treatment solutions described in Examples 9, 15, and 17 above was evaluated for deteriorated electrolytic copper foil electrodes. The regeneration capability was evaluated by measuring the oxygen evolution potential of test specimens of electrolytic copper foil electrodes in three states: (1) new condition, (2) condition with lead deposited on the electrode surface, and (3) condition after lead removal using each treatment solution. The evaluation was based on the changes in the obtained oxygen evolution potential. Lead deposition on the electrode surface was measured by immersing the test specimen electrode in a 300 g / L lead nitrate aqueous solution at 2.5 A / dm ２ This was done by applying electricity for 5 minutes. In addition, lead removal using each treatment solution was carried out by letting it stand for 24 hours.

[0083] <Measurement Conditions for Oxygen Evolution Potential> Measuring Instrument: Hokuto Denko potentiostat galvanostat (model number: HA-151B) Measurement Method: Current interrupter method Electrolyte: 100 g / L sodium sulfate aqueous solution (pH=1) 300 mL Solution Temperature: Room temperature Working Electrode: Electrolytic copper foil electrode (manufactured by Daiso Engineering Co., Ltd., product number: MD-220, 10 mm x 10 mm) Counter Electrode: Platinum plate (25 mm x 25 mm) Reference Electrode: Silver / silver chloride electrode Current Density: 10 mA / cm² ２ 30 mA / cm ２ 50 mA / cm ２ , 100 mA / cm ２

[0084]

[0085] As is clear from Table 4, the oxygen evolution potential, which had risen by more than 30% compared to a new electrode due to lead deposition on the electrode surface, was confirmed to decrease to a level comparable to that of a new electrode after lead removal treatment of the electrode surface using the treatment solutions in Examples 9, 15, and 17. These results indicate that the treatment solution of this embodiment has sufficient ability to regenerate deteriorated electrolytic copper foil electrodes.

[0086] The following describes variations of the invention relating to this disclosure. [Note 1] A treatment solution for treating an object to be treated on which a deposit containing a lead compound is attached to the surface, comprising a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B). [Note 2] The treatment solution according to Note 1, wherein the mass ratio of the non-oxycarboxylic acid chelating agent (A) to the organic acid or a salt thereof (B) is in the range of 9:1 to 1:9. [Note 3] The treatment solution according to Note 1 or 2, wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of aminocarboxylic acids, aldonic acids, phosphonic acids, amino acids, and salts thereof. [Note 4] The treatment solution according to any one of Notes 1 to 3, wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, diaminopropionic acid, hydroxyethylidenediphosphonic acid (HEDP), 1-hydroxyethane-1,1-bis(phosphonic acid), nitrilotris(methylenephosphonic acid), and salts thereof. [Note 5] The treatment solution according to any one of Notes 1 to 4, wherein the organic acid or its salt (B) is at least one selected from the group consisting of polycarboxylic acids and their salts. [Note 6] The treatment solution according to Note 5, wherein the polycarboxylic acid or its salt is at least one selected from the group consisting of oxalic acid, tartaric acid, malic acid, malonic acid, succinic acid, adipic acid, fumaric acid, maleic acid, citric acid, aconitic acid, and their salts. [Note 7] The treatment solution according to any one of Notes 1 to 6, wherein the lead compound is lead sulfate or lead oxide. [Note 8] The treatment solution according to any one of Notes 1 to 7, wherein the object to be treated is an electrolytic electrode whose electrode surface is coated with a catalyst layer containing a platinum group metal or its oxide.[Note 9] The treatment solution according to any one of Notes 1 to 7, wherein the workpiece is an electrolytic electrode in which an intermediate layer containing a metal, metal oxide, or metal alloy is coated on the surface of an electrode substrate made of valve metal or a valve metal alloy, and a catalyst layer containing a platinum group metal or an oxide thereof is further coated on the surface of the intermediate layer. [Note 10] The treatment solution according to Note 9, wherein the metal is one or more selected from titanium, tantalum, niobium, zirconium, and hafnium. [Note 11] The treatment solution according to any one of Notes 1 to 7, wherein the workpiece is an electrode separation catalyst separated from an electrolytic electrode in which a catalyst layer is coated on the electrode surface. [Note 12] A method for removing lead compounds from a workpiece on which deposits containing lead compounds are attached to the surface, comprising: a preparation step of preparing a treatment solution containing a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B); and an immersion step of immersing the workpiece in the treatment solution. [Note 13] The lead compound removal method according to Note 12, wherein the immersion step is performed at 15 to 35°C. [Note 14] The lead compound removal method according to Note 12 or 13, further comprising a washing step of washing the object to be treated, wherein the washing step is performed after the immersion step without going through a mechanical removal step by brushing or jet spraying.

[0087] The treatment solution and lead compound removal method of this embodiment can be used, for example, to remove deposits containing lead compounds from the surfaces of various electrolytic electrodes. Furthermore, the treatment solution and lead compound removal method of this embodiment can also be used, for example, to remove deposits containing lead compounds from detached material (e.g., catalyst) that has been physically removed from the surface of an electrolytic electrode by polishing or other means.

Claims

1. A treatment solution for treating an object to be treated on which a lead compound-containing deposit is attached to the surface, the treatment solution containing a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B).

2. The treatment solution according to claim 1, wherein the mass ratio of the non-oxycarboxylic acid chelating agent (A) to the organic acid or its salt (B) is in the range of 9:1 to 1:

9.

3. The treatment solution according to claim 1 or 2, wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of aminocarboxylic acids, aldonic acids, phosphonic acids, amino acids, and salts thereof.

4. The treatment solution according to claim 1 or 2, wherein the non-oxycarboxylic acid chelating agent (A) is at least one selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), ethylenediaminetetrapropionic acid, nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, diaminopropionic acid, hydroxyethylidenediphosphonic acid (HEDP), 1-hydroxyethane-1,1-bis(phosphonic acid), nitrilotris(methylenephosphonic acid), and salts thereof.

5. The treatment solution according to claim 1 or 2, wherein the organic acid or its salt (B) is at least one selected from the group consisting of polycarboxylic acids and their salts.

6. The treatment solution according to claim 5, wherein the polycarboxylic acid or a salt thereof is at least one selected from the group consisting of oxalic acid, tartaric acid, malic acid, malonic acid, succinic acid, adipic acid, fumaric acid, maleic acid, citric acid, aconitic acid, and salts thereof.

7. The treatment solution according to claim 1 or 2, wherein the lead compound is lead sulfate or lead oxide.

8. The treatment solution according to claim 1 or 2, wherein the object to be treated is an electrolytic electrode in which a catalyst layer containing a platinum group metal or an oxide thereof is coated on the electrode surface.

9. The treatment solution according to claim 1 or 2, wherein the workpiece is an electrolytic electrode in which an intermediate layer containing a metal, metal oxide, or metal alloy is coated on the surface of an electrode substrate made of valve metal or a valve metal alloy, and a catalyst layer containing a platinum group metal or its oxide is further coated on the surface of the intermediate layer.

10. The treatment solution according to claim 9, wherein the metal is one or more selected from titanium, tantalum, niobium, zirconium, and hafnium.

11. The treatment solution according to claim 1 or 2, wherein the object to be treated is an electrode separation catalyst separated from an electrolytic electrode having a catalyst layer coated on its electrode surface.

12. A method for removing lead compounds from a workpiece on which a lead compound-containing deposit is attached to the surface, comprising: a preparation step of preparing a treatment solution containing a non-oxycarboxylic acid chelating agent (A) and an organic acid or a salt thereof (B); and an immersion step of immersing the workpiece in the treatment solution.

13. The method for removing lead compounds according to claim 12, wherein the immersion step is performed at 15 to 35°C.

14. A method for removing lead compounds according to claim 12 or 13, further comprising a cleaning step of cleaning the object to be treated, wherein the cleaning step is performed without going through a mechanical removal step by brushing or jet spraying after the immersion step.

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