Methods for limiting the degradation of surfactants, methods for cleaning aluminum or aluminum alloys, and methods for producing aluminum materials with cleaned surfaces.

Abstract

The invention relates to a method for limiting the degradation of surfactants, a method for cleaning aluminum or aluminum alloys, and a method for producing aluminum materials with a cleaned surface. The invention aims to propose a technology that can significantly limit the degradation of surfactants without the addition of stabilizers. The problem is solved by a method for limiting the degradation of surfactants in a cleaning fluid of aluminum or aluminum alloys comprising an inorganic acid, iron ions, and 0.1 to 10 g / L of surfactant, where the cleaning fluid has a pH of 2 or less, and this method includes the addition of one or more selected oxo acid salts from the group of mono-oxo acid salts and dioxo acid salts to the cleaning fluid.

Description

Method for inhibiting surfactant decomposition and method for cleaning aluminum or aluminum alloy

[0001] The present invention relates to a method for cleaning aluminum or aluminum alloys that is suitable for degreasing and removing smut from aluminum materials such as aluminum can bodies.

[0002] Aluminum materials such as beverage cans made from aluminum or aluminum alloys have surfaces covered with aluminum oxides, oils, etc. In particular, aluminum cans are usually produced by a drawing process known as drawing and ironing (DI), and aluminum cans produced by this process are covered with aluminum powder (smut) and lubricating oil generated by the shavings during drawing. Therefore, in order to form a strong chemical conversion coating or coating on the aluminum material, it is necessary to first remove aluminum oxides, oils, smut, etc. and clean the aluminum material.

[0003] To clean the surface of aluminum materials, acidic cleaning solutions such as chromic acid, hydrofluoric acid, and even chromium-free and fluorine-free solutions are generally used, which moderately etch and clean the metal surface. Normally, the etching reaction of aluminum in an acidic cleaning solution is initiated by converting aluminum into aluminum ions (Al ３＋ ) and the H in the cleaning solution ＋ is reduced to 1 / 2H ２ Therefore, the acidic cleaning solution contains ferric ions (Fe ３＋ ) is added, this Fe ３＋ is ferrous ion (Fe ２＋ ) is reduced to the cathode reaction ＋ This occurs simultaneously with the reduction of Fe, which accelerates the anodic reaction of aluminum and increases the amount of aluminum dissolved (etched). ３＋ The concentration is controlled and the Fe content is monitored as the reaction proceeds. ２＋ To suppress the increase in concentration, an oxidizing agent is added to ２＋ Fe ３＋ Oxidizing agents have been used to oxidize and reuse the wastewater. Conventionally, peroxides have been used as the oxidizing agents.

[0004] However, when peroxide is added in the presence of iron ions, the surfactant is oxidized and decomposed, resulting in a decrease in surfactant concentration, and the oxidative decomposition products of the surfactant accumulate in the acidic cleaning bath, reducing the cleaning performance of the aluminum surface.Furthermore, an excessive amount of surfactant is required to maintain cleaning performance, which increases the running cost.

[0005] Therefore, various technologies have been developed to prevent surfactant decomposition by oxidizing agents. For example, Patent Document 1 discloses an acidic cleaning solution for aluminum containing 0.05 to 5.0 g / L of one or more compounds selected from mineral acids, oxidizing agents, polyvalent metal ions, surfactants, and C2 to C10 glycols, with the aim of preventing surfactant decomposition by the C2 to C10 glycols. Patent Document 2 discloses a cleaning method for aluminum-based metals using an acidic cleaning aqueous solution containing 0.5 to 25 g / L of at least one inorganic acid, 0.002 to 5 g / L of bromide ions, and 0.05 to 4 g / L of oxidized metal ions, with the cleaning solution having an oxidation-reduction potential of 0.5 to 0.8 V vs. a silver-silver chloride electrode. By controlling the oxidation-reduction potential of the acidic cleaning solution within a predetermined range, the decomposition reaction of the surfactant is suppressed. Furthermore, Patent Document 3 discloses an acidic aqueous solution for cleaning aluminum-based metals, which contains an inorganic acid in an amount that gives a pH of 2 or less, oxidized metal ions, a surfactant, and 0.1 to 5 g / L of a polyhydric alcohol having in one molecule at least two hydroxyl groups directly bonded to adjacent carbon atoms in the main chain, and which aims to prevent decomposition of the surfactant by using the polyhydric alcohol.

[0006] JP-A-4-52289, JP-A-7-113189, JP-A-7-41973

[0007] In order to maintain the cleaning ability of the acidic cleaning bath, it is very important to control the surfactant concentration. However, when a surfactant stabilizer is added to the treatment solution as in the above patent document, if the stabilizer is an organic substance, the chemical oxygen demand (COD) of the cleaning wastewater increases. Ｍｎ ) was a problem.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a technology that can significantly suppress the decomposition of surfactants without adding a stabilizer.

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have discovered that adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to maintain the ferric ion concentration in a cleaning solution within a specific range can suppress the decomposition of surfactants without adding a stabilizer. They have also found that this discovery can be used to solve the above-mentioned problems, leading to the completion of the present invention. That is, the present invention is illustratively specified as follows:

[0010] [1] A method for suppressing surfactant decomposition in a cleaning solution for aluminum or aluminum alloys, the method containing an inorganic acid, iron ions, and 0.1 to 10 g / L of a surfactant, wherein the cleaning solution has a pH of 2 or less, and the method includes a step of adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to the cleaning solution. [2] The method according to [1], wherein the oxoacid salts are added so that the ferric ion concentration in the cleaning solution is within the range of 0.02 to 5 g / L. [3] The method according to [1] or [2], wherein the oxoacid salts include one or more selected from the group consisting of nitrite, hypochlorite, and chlorite. [4] A method for cleaning aluminum or an aluminum alloy, comprising: a preparation step of preparing a cleaning solution by adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to an aqueous solution containing an inorganic acid, iron ions, and 0.1 to 10 g / L of a surfactant so as to maintain a ferric ion concentration in the aqueous solution at 0.02 to 5 g / L; and a cleaning step of cleaning aluminum or an aluminum alloy with the cleaning solution obtained in the above step, wherein the COD of the cleaning solution under the cleaning conditions shown below is Ｍｎ A method for cleaning aluminum or an aluminum alloy, wherein the increase rate (%) of the surface area of ​​144 m is 20% or less using 1 L of the cleaning solution. ２The surface of aluminum or aluminum alloy is cleaned. Cleaning is performed in a cycle of contacting the cleaning solution with the aluminum or aluminum alloy surface for 1.1 seconds and then resting for 1.4 seconds. The cleaning solution that has been in contact with the aluminum or aluminum alloy surface is recovered and reused as a cleaning solution by appropriately replenishing it with acid replenisher. The cleaning solution is appropriately replenished with one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to maintain the above-mentioned ferric ion concentration in the cleaning solution. COD Ｍｎ Increase rate (%) = [(COD of cleaning solution after cleaning Ｍｎ / COD of cleaning solution before cleaning Ｍｎ )−1)]×100(%) [5] The method for cleaning aluminum or an aluminum alloy according to [4], wherein the oxoacid salt comprises at least one selected from the group consisting of nitrite, hypochlorite, and chlorite.

[0011] The present invention provides a method for maintaining cleaning performance using Fe. ３＋ Even if the concentration is maintained, good cleaning performance is maintained because the decomposition of the surfactant is suppressed. In addition, since the decomposition of the surfactant is suppressed, the deterioration of cleaning performance and COD due to the accumulation of surfactant decomposition products are prevented. Ｍｎ In addition, there is no need to add a decomposition inhibitor to suppress the decomposition of the surfactant, so there is little increase in COD Ｍｎ Since the increase in the amount of carbon dioxide is small, a cleaning method for aluminum or aluminum alloys with low environmental impact can be provided, which is therefore useful from both economic and environmental perspectives.

[0012] Hereinafter, embodiments of the present invention will be described in detail. The present invention can be modified as desired without departing from the spirit of the present invention, and is not limited to the following embodiments. In this specification, the term "to" indicating a numerical range includes both the upper and lower limits. For example, "X to Y" means that the range is from X to Y.

[0013] <Cleaning Solution> The cleaning solution contains an inorganic acid, iron ions, and a surfactant. ３＋ The detergent is prepared by adding an oxoacid salt to maintain a predetermined concentration of ions. The pH of the detergent is 2 or less.

[0014] [Inorganic Acid] Examples of inorganic acids include phosphoric acid, sulfuric acid, nitric acid, and hydrofluoric acid, and these may be used alone or in a mixture of two or more. The concentration of the inorganic acid in the cleaning solution is preferably 3 to 10 g / L for phosphoric acid, 5 to 40 g / L for sulfuric acid, 0 to 2 g / L for nitric acid, and 0.1 to 3 g / L for hydrofluoric acid. Examples of inorganic acids include a mixed acid of phosphoric acid, sulfuric acid, and nitric acid, a mixed acid of sulfuric acid and nitric acid, and a mixed acid of sulfuric acid, hydrofluoric acid, and nitric acid. In order to maintain the pH of the cleaning solution within the desired range, the inorganic acid may be added successively in the form of a replenisher.

[0015] [Iron Ions and Ferric Ions] Ferric ions function as an etching accelerator. The ferric ion concentration in the cleaning solution is preferably 0.02 to 5 g / L, more preferably 0.05 to 3 g / L. If the ferric ion concentration is less than 0.02 g / L, the desmutting ability decreases and a sufficient amount of etching cannot be obtained. If the ferric ion concentration exceeds 5 g / L, no difference in cleaning ability is observed, making the cleaning solution uneconomical.

[0016] The ferric ions reduced to ferrous ions by etching are oxidized to ferric ions by adding an oxoacid salt, maintaining the ferric ion concentration. The ferric ion concentration can be confirmed by the oxidation-reduction potential (ORPmV). ORPmV is the ratio of Fe ２＋ / Fe ３＋ The ratio of Fe to ORPmV is determined by setting the total iron concentration to a specific value and keeping the ORPmV constant. ３＋ For example, if the total iron concentration is 500 ppm and the ORP is 540 mV (based on a silver-silver chloride electrode), Fe ３＋ The concentration is about 300 ppm.

[0017] Examples of sources of iron ions include water-soluble iron compounds such as ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, etc. To keep the ferric ion concentration within the desired range, these sources of iron ions may be added successively in the form of a replenisher solution.

[0018] [Surfactant] The surfactant mainly serves to remove oils and lubricants adhering to the aluminum surface. The surfactant may be one or more of nonionic, cationic, anionic, and amphoteric surfactants. Among these, nonionic surfactants are preferred, and alkylene alkyl ether nonionic surfactants are more preferred. The alkyl group of the alkylene alkyl ether may be either linear or branched, and the alkylene group may be ethylene oxide, propylene oxide, or a copolymer of ethylene oxide and propylene oxide. The alkylene alkyl ether nonionic surfactant is specifically, but not limited to, a higher alcohol-based ethylene oxide or a copolymer of ethylene oxide and propylene oxide.

[0019] The concentration of the surfactant in the cleaning solution is preferably 0.1 to 10 g / L, more preferably 0.2 to 5 g / L. If the concentration of the surfactant in the cleaning solution is less than 0.1 g / L, sufficient degreasing properties cannot be obtained. If the concentration of the surfactant is more than 10 g / L, there is no problem with degreasing properties, but the COD of the cleaning wastewater increases. Ｍｎ This is undesirable from the viewpoint of cost and economy.

[0020] [Oxoacid salt] Oxoacid salt is a salt of ferrous ion (Fe ２＋ ) to ferric ions (Fe ３＋ ) to form a dioxoacid. Oxoacid salts include one or more selected from salts of monooxoacids and salts of dioxoacids. Monooxoacids refer to acids having one or more oxygen atoms in the molecule and in which the oxidation number of the element adjacent to the oxygen is +1. Examples include hypochlorous acid, hypobromous acid, and hypoiodous acid. Dioxoacids refer to acids having two or more oxygen atoms in the molecule and in which the oxidation number of the atom adjacent to the oxygen is +3. Examples include chlorous acid, bromous acid, iodous acid, and nitrous acid.

[0021] The salt of a monooxoacid is a salt in which the acidic hydrogen atom in the monooxoacid is substituted with an alkali metal ion, an alkaline earth metal ion, or an ammonium ion (NH ４ ＋) is substituted. A salt of a dioxoacid refers to a salt in which the acidic hydrogen atom in the dioxoacid is substituted with an alkali metal ion, alkaline earth metal ion, or ammonium ion. Examples of alkali metal ions include lithium, sodium, and potassium ions. Examples of alkaline earth metal ions include calcium, magnesium, and barium ions.

[0022] Examples of monooxoacid salts include hypochlorite, hypobromite, and hypoiodite, and examples of dioxoacid salts include chlorite, bromite, iodite, and nitrite. Of these, hypochlorite, chlorite, and nitrite are preferred. Specific examples of hypochlorite include sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite, specific examples of nitrite include sodium nitrite and potassium nitrite, and specific examples of chlorous acid include sodium chlorite and potassium chlorite, but are not limited to these. Sodium hypochlorite is preferred as a monooxoacid salt, and sodium nitrite is preferred as a dioxoacid salt. Note that oxidizing agents other than oxoacid salts can also be used within the scope of the present invention.

[0023] By using an oxoacid salt containing one or more salts selected from monooxoacid salts and dioxoacid salts having a moderate oxidizing power, it is possible to significantly suppress the decomposition of a surfactant even in the coexistence of iron ions and to oxidize ferrous ions to ferric ions. That is, one aspect of the present invention is a method for suppressing the decomposition of a surfactant in a cleaning solution for aluminum or an aluminum alloy, which contains an inorganic acid, iron ions, and 0.1 to 10 g / L of a surfactant, wherein the cleaning solution has a pH of 2 or less and includes the step of adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to the cleaning solution.

[0024] [pH] The pH of the cleaning solution is 2 or less, preferably 0.6 to 2. The pH value in this specification refers to a value measured at the treatment temperature (25°C) using a commercially available pH meter. If the pH exceeds 2, the etching rate of aluminum decreases, and the aluminum surface cannot be sufficiently cleaned. The lower limit of the pH is not particularly limited as long as it does not deviate from the spirit of the present invention, but from the viewpoint of preventing corrosion of the treatment device, a pH of about 1.0 is preferred. The pH of the cleaning solution is mainly controlled by the inorganic acid, but pH adjusters such as other acid components and alkali components may also be used as appropriate.

[0025] [Other Components] The cleaning liquid may contain other components in addition to those described above, such as a surfactant decomposition inhibitor, a chelating agent, an antifoaming agent, an antibacterial agent, etc., in order to improve the liquid stability, workability, etc. One or more of these components may be blended.

[0026] [Surfactant decomposition inhibitor] In view of the effects of the present invention, it is not necessary for the detergent decomposition inhibitor to be contained in the cleaning solution, but this does not exclude its addition to the cleaning solution. Examples of surfactant decomposition inhibitors include, but are not limited to, C2 to C10 glycols described in the above-mentioned patent documents and polyhydric alcohols having at least two hydroxyl groups directly bonded to adjacent carbon atoms in one molecule in the main chain.

[0027] [Chelating Agent] The chelating agent has the role of suppressing a decrease in cleaning efficiency by capturing aluminum ions eluted during cleaning. Examples of the chelating agent include, but are not limited to, organic carboxylic acids such as citric acid, oxalic acid, tartaric acid, and gluconic acid, and organic phosphorus compounds such as etidronic acid, ethylenediaminetetramethylenephosphonic acid, and nitrilotrimethylenephosphonic acid.

[0028] <Aluminum or Aluminum Alloy> Examples of aluminum to be cleaned with the cleaning solution include pure aluminum such as A1000 series, and aluminum alloy plate-shaped or processed materials such as A3000 series and A5000 series.

[0029] <Method for Cleaning Aluminum or Aluminum Alloy> One aspect of the present invention is a method for cleaning aluminum or an aluminum alloy, comprising: a preparation step of preparing a cleaning solution by adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to an aqueous solution containing an inorganic acid, iron ions, and 0.1 to 10 g / L of a surfactant so as to maintain a ferric ion concentration in the aqueous solution at 0.02 to 5 g / L; and a cleaning step of cleaning aluminum or an aluminum alloy with the cleaning solution obtained in the preparation step. The pH of the cleaning solution is 2 or less.

[0030] [Preparation Step] The preparation step is a step of preparing the cleaning solution described above. The cleaning agent may be prepared using raw materials, or a cleaning solution prepared in advance may be procured and used.

[0031] [Cleaning Step] In the cleaning step of cleaning aluminum or an aluminum alloy, the cleaning method is not particularly limited, and examples thereof include a method of bringing the aluminum or aluminum alloy into contact with a cleaning solution. The contact method is not particularly limited, and known methods can be used as appropriate. Examples thereof include a spray method and an immersion method.

[0032] [Treatment Temperature (Cleaning Temperature)] The treatment temperature in the cleaning step is preferably 40 to 85° C., more preferably 50 to 80° C. By setting the temperature within the above range, appropriate etching can be performed.

[0033] [Treatment Time (Cleaning Time)] The treatment time is preferably 20 to 120 seconds, more preferably 25 to 90 seconds. If the treatment time exceeds 120 seconds, excessive etching occurs, which accelerates aging of the treatment bath. If the treatment time is less than 20 seconds, the amount of etching is insufficient, which reduces the desmutting ability.

[0034] [COD Ｍｎ ] COD Ｍｎ COD is also called chemical oxygen demand, and is an index showing the amount of organic matter in water, and specifically, it is the amount of oxygen required when potassium permanganate oxidizes a target substance. Ｍｎ is measured by the method of JIS-K0102.

[0035] [CODＭｎ In this embodiment, in the cleaning process, the COD of the cleaning solution under the cleaning conditions shown below is Ｍｎ The increase rate is 20% or less. Using 1 L of the cleaning solution, the surface area is 144 m ２ The surface of aluminum or aluminum alloy is cleaned. Cleaning is performed in a cycle of contacting the cleaning solution with the aluminum or aluminum alloy surface for 1.1 seconds and then resting for 1.4 seconds. The cleaning solution that has come into contact with the aluminum or aluminum alloy surface is recovered and reused as a cleaning solution by appropriately replenishing the acid replenisher. The cleaning solution is appropriately replenished with one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to maintain the above-mentioned ferric ion concentration in the cleaning solution.

[0036] COD Ｍｎ The increase rate is 144 m ２ When aluminum or aluminum alloy is washed with 1 L of cleaning solution, the COD of the cleaning solution after washing is Ｍｎ The COD of the cleaning solution before cleaning, which does not contain decomposition products of surfactants, Ｍｎ The value is expressed as the rate of increase from COD Ｍｎ Increase rate (%) = [(COD of cleaning solution after cleaning Ｍｎ / COD of cleaning solution before cleaning Ｍｎ )-1] x 100 (%). Ｍｎ The increase rate is the COD caused by the decomposition of surfactants. Ｍｎ The lower the value, the less the deterioration in cleaning performance during operation and the lower the environmental impact.

[0037] In this specification, the cleaning conditions are as described above, but one example is continuous processing. Continuous processing means that in a cleaning line where the can moves at a speed of 3.6 m / min and the moving time is 40 seconds, the cleaning line is sprayed for 1.1 seconds and paused for 1.4 seconds, and the surface area of ​​the object to be treated is 28.8 m per hour for 1 L of cleaning solution. ２ may be a method in which the above is continuously treated for 5 hours.

[0038] The aluminum surface cleaned by the method for cleaning aluminum or an aluminum alloy of the present invention can be washed with water in a conventional manner and then subjected to a chemical conversion treatment using a chromate-based chemical conversion treatment agent such as chromate chromate or chromate phosphate, or a chromium-free chemical conversion treatment agent such as zirconium phosphate or titanium phosphate.

[0039] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0040] (Examples 1 to 10 and Comparative Examples 1 to 7) A 75% aqueous solution of sulfuric acid, a 75% aqueous solution of phosphoric acid, and a 55% aqueous solution of hydrofluoric acid were used as inorganic acids, a 41% aqueous solution of ferric sulfate was used as an iron ion source, and a 53.7% aqueous solution of aluminum ions was used. ２ O ３ An initial cleaning solution was prepared using aluminum hydroxide powder (as a decomposition inhibitor), diethylene glycol as a decomposition inhibitor, and the nonionic surfactant shown below as a surfactant, so as to have the concentration shown in Table 1.

[0041] <Surfactant> Nonion 1:C １６ H ３３ -O-(EO) ２０ Nonion 2:C １２ H ２５ -O-(EO) ５ (PO) １０ Nonion 3:C １４ H ２９ -O-(EO) １４ Nonion 4:C １２ H ２５ -O-(EO) ５ (PO) １５

[0042] <Workpiece> A 6.6 cm diameter, 350 mL capacity (surface area 0.05 m) container obtained by DI (drawing and ironing) processing of an A3004 aluminum alloy plate. ２ ) lubricating oil and smut were used as test materials.

[0043] <Method for measuring free acidity [FA]> Free acidity [FA] was measured by the following method. Exactly 5 mL of the cleaning solution was taken and titrated with 0.1 mol / L aqueous caustic soda solution using phenolphthalein as an indicator. Free acidity [FA] is expressed as the amount (mL) of 0.1 mol / L aqueous caustic soda solution added.

[0044] <Ferric ion (Fe ３＋ ion) concentration measurement method> Fe concentration was measured by titration according to the following procedure. ３＋ The concentration was measured. An appropriate amount (mL) of the cleaning solution was accurately collected and placed in a 300 mL conical beaker, and the total volume was adjusted to approximately 100 mL with water. Hydrochloric acid (1+1) was added to adjust the pH to 1 or less, and then 50 wt% ammonium acetate solution was added little by little to adjust the pH to 2. Approximately 0.1 g of salicylic acid was added as an indicator, and the mixture was heated to 40°C. It was titrated with 0.01 mol / L EDTA solution until the color changed from purple to colorless. Fe was calculated using the following formula: ３＋ The concentration was calculated. ３＋ Concentration (mg / L) = 10 / S × A × 55.85 A: Amount (mL) of 0.01 mol / L EDTA solution used for titration S: Amount (mL) of collected washing solution

[0045] <Method for measuring surfactant concentration> The amount of surfactant present was measured by titration (Cesibol method) according to the following procedure. First, 10 mL of a solution obtained by diluting the cleaning solution exactly 20 times by volume was collected. To this was added 5 mL of a 6N-KOH aqueous solution. Next, 5 mL of 1,2-dichloroethane was added, followed by the addition of two drops of the Victoria Blue indicator shown below. Victoria Blue indicator: A solution prepared by dissolving 0.4 g of Victoria Blue in 1 L of ethanol. Then, titration was carried out with the Cecibol solution shown below, with the development of a bright blue color as the endpoint. Cecibol solution: Cecibol ((FC ６ H ４ ) ４ BNa 2H ２ O) A solution prepared by dissolving 0.1944 g of the surfactant in 1 L of distilled water. In determining the concentration, a calibration curve was prepared in advance using the surfactant to be used.

[0046] <COD ＭｎMeasurement method: Follow the procedure below to measure COD Ｍｎ was measured. ・10 mL of a solution diluted exactly 20 times by volume with the cleaning solution was placed in a 300 mL Erlenmeyer flask. ・Add water to make 100 mL, add 10 mL of sulfuric acid (1+2), and add 5 mL of 20% silver nitrate, shake vigorously, and leave for several minutes. ・Add exactly 10 mL of N / 40 potassium permanganate solution, place the flask in a boiling water bath, and heat for 30 minutes. Ensure that the water level in the boiling water bath is always above the surface of the test water. ・Next, add exactly 10 mL of sodium oxalate solution (N / 40), and back-titrate with N / 40 potassium permanganate solution while maintaining the temperature at 60-80°C. The endpoint is when the solution turns a pale red color. ・Perform a separate blank test under the same conditions. ・Calculate the oxygen consumption (mgO / L) by potassium permanganate using the following formula: COD Ｍｎ = (b-a) x 1000 / 10 x 0.2 x 20 where COD Ｍｎ : Oxygen consumption by potassium permanganate (mg O / L) b: N / 40 potassium permanganate solution required for titration (mL) a: N / 40 potassium permanganate solution required for titration of blank test (mL)

[0047] <COD Ｍｎ Measurement of Increase Rate> Eight cans of test material were treated with the initial cleaning solution shown in Table 1 in 20 L of an acidic cleaning bath heated to the temperature shown in Table 1, intermittently spraying for 1.1 seconds followed by a 1.4 second pause, while 300 mL of the acid replenisher solution shown in Table 2 was replenished every 5 minutes. During this treatment, the oxidizing agent shown in Table 1 was continuously replenished so that the oxidation-reduction potential of the cleaning solution was maintained at the value shown in Table 1. In addition, 1200 mL of the treatment solution was removed every 20 minutes, and the surfactant concentration and free acidity (FA) were measured. When the surfactant decomposed and the concentration decreased, the surfactant replenisher solution shown in Table 3 was replenished each time to achieve the same value as the initial cecibol value. When the FA decreased, adjustment was made with 75% sulfuric acid to maintain the initial FA. The test material was replaced every hour of treatment. Thereafter, the COD values ​​of the initial cleaning solution and the cleaning solution after 5 hours of continuous cleaning were measured. Ｍｎ Measure the COD Ｍｎ The percentage increase in COD was calculated. Ｍｎ Increase rate (%) = (COD of cleaning solution after 5 hours of continuous processing) Ｍｎ / COD of initial liquid Ｍｎ -1) x 100 Note that the surface treatment per 1 L of detergent is for an aluminum surface area of ​​144 m ２ It was.

[0048] <Evaluation of cleaning properties of cleaning agent after cleaning> The cleaning properties of the cleaning solution were evaluated by desmutting ability. The cleaning solution after cleaning was heated to the temperature shown in Table 1, and the container of the uncleaned test material was sprayed for 40 seconds, then rinsed with tap water for 15 seconds and dried. Transparent adhesive tape was attached to the inner surface of the dried container, which was then peeled off and attached to a white backing, and the whiteness of the tape-attached surface was visually compared with the whiteness of the unstained backing surface to which the tape was attached. The best result was when all smut was removed and there was no contamination, and the degree of contamination was evaluated on a 5-point scale as follows, with 5 and 4 points being considered pass. 5: No contamination 4: Trace contamination 3: Slight contamination 2: Moderate contamination 1: Heavy contamination

[0049] <Evaluation of Resistance to Bottom Blackening of Cleaning Agent After Cleaning> The functionality of the cleaning solution was evaluated. The cleaning solution after cleaning was heated to the temperature shown in Table 1, and an uncleaned test container was treated with the solution by spraying for 40 seconds. After rinsing with tap water for 15 seconds, a chemical conversion treatment solution (concentration 1.5 wt %, 40°C) containing "Palcoat N405 Make-up Agent" (manufactured by Nippon Parkerizing Co., Ltd.) was sprayed for 15 seconds for chemical conversion treatment. After rinsing with tap water, the container was rinsed with deionized water and dried at 200°C for 2 minutes. After drying, the container was immersed in boiling tap water at 100°C for 30 minutes. The degree of blackening of the can bottom after immersion in boiling water was evaluated according to the following criteria, with 5 points and 4 points being considered pass. 5: No discoloration at all 4: Slight discoloration 3: Light discoloration 2: Considerable blackening 1: Complete blackening

[0050] The evaluation results are shown in Table 4. In Examples 1 to 9, the COD of the cleaning solution after cleaning was Ｍｎ In Example 10, a dioxoacid salt and hydrogen peroxide were used in combination as oxidizing agents, but the COD of the cleaning solution after cleaning was Ｍｎ On the other hand, in Comparative Examples 1 to 4, the increase rate of COD of the cleaning solution after cleaning was suppressed to about 13%, and the desmutting property and the blackening resistance were excellent. ＭｎIn Comparative Example 5, hydrogen peroxide and a decomposition inhibitor were added to the oxidizing agent, but the addition of the decomposition inhibitor prevented the COD caused by the accumulation of surfactant decomposition products. Ｍｎ The increase rate was 23%, and the COD Ｍｎ In Comparative Example 6, the amount of Fe in the acidic cleaning bath was ３＋ In Comparative Example 7, a dioxo acid salt was used, but Fe ３＋ The concentration was low and the cleaning properties (de-smutting properties) were poor to begin with. Note that although the present invention will be described in detail with reference to specific examples, it will be apparent to those skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope of the present invention.

[0051]

[0052]

[0053]

[0054]

Claims

1. A method for suppressing decomposition of a surfactant in a cleaning solution for aluminum or aluminum alloys, the method comprising: a cleaning solution having a pH of 2 or less; and a step of adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to the cleaning solution.

2. The method according to claim 1, wherein the step of adding ferric ions to the cleaning solution is carried out so that the concentration of ferric ions in the cleaning solution is within the range of 0.02 to 5 g / L.

3. The method according to claim 1, wherein the oxo acid salt comprises at least one selected from the group consisting of nitrite, hypochlorite and chlorite.

4. A method for cleaning aluminum or an aluminum alloy comprising the steps of: preparing a cleaning solution by adding one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to an aqueous solution containing an inorganic acid, iron ions, and 0.1 to 10 g / L of a surfactant so that the ferric ion concentration in the aqueous solution is maintained at 0.02 to 5 g / L; and cleaning the aluminum or aluminum alloy with the cleaning solution obtained in the above step; Ｍｎ The method for cleaning aluminum or an aluminum alloy, wherein the increase rate (%) of the surface area of ​​144 m is 20% or less using 1 L of the cleaning solution. ２ The aluminum or aluminum alloy surface is cleaned. Cleaning is performed in a cycle of contacting the cleaning solution with the aluminum or aluminum alloy surface for 1.1 seconds and then pausing for 1.4 seconds. The cleaning solution that has been in contact with the aluminum or aluminum alloy surface is recovered and reused as a cleaning solution by appropriately replenishing it with acid replenishment solution. The cleaning solution is appropriately replenished with one or more oxoacid salts selected from the group consisting of monooxoacid salts and dioxoacid salts to maintain the above-mentioned ferric ion concentration in the cleaning solution. COD Ｍｎ Increase rate (%) = [(COD of cleaning solution after cleaning Ｍｎ / COD of cleaning solution before cleaning Ｍｎ ) −1] × 100 (%) 5. The method for cleaning aluminum or an aluminum alloy according to claim 4, wherein the oxo acid salt comprises at least one selected from the group consisting of nitrites, hypochlorites and chlorites.