JP2013019009A - Method for controlling anodizing electrolytic solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling an electrolytic solution for anodizing aluminum or an aluminum alloy.SOLUTION: The method controls an electrolytic solution for anodizing aluminum or an aluminum alloy, which is composed of each component of: an electrolyte containing at least one of the ammonium compounds derived from an organic acid, boric acid or phosphoric acid; water; and a glycol solvent. The method for controlling the electrolytic solution includes: obtaining each component concentration by measuring a refractive index and an electrical conductivity and/or pH of the electrolytic solution; and replenishing components that are reduced in the anodizing treatment to control a concentration of each component constituting the electrolytic solution.

Description

  The present invention relates to a method of managing an electrolytic solution for anodizing aluminum or aluminum alloy. More specifically, the present invention relates to a method for controlling the concentration of components constituting an anodizing electrolyte used for anodizing aluminum or an aluminum alloy.

  As a surface protective film using a metal mainly composed of aluminum as a structural material, an anodized film (anodized) by anodization in an electrolytic solution (generally also referred to as “chemical conversion solution”) has been known for a long time. . Anodized coatings are widely used because they have corrosion resistance and acidic electrolytes are stable and easy to manage. As the electrolytic solution, an acidic electrolytic solution (usually pH 2 or lower) is usually used, and a smooth and uniform alumite film having a porous structure can be formed.

  However, the alumite coating with a porous structure is vulnerable to heat as the surface treatment of structural members, causing cracks due to the difference in thermal expansion coefficient between the aluminum substrate and the alumite coating, generation of particles, corrosion due to exposure of the aluminum substrate, etc. It was a cause of occurrence. In addition, a large amount of moisture is accumulated and adsorbed inside the pores of the porous structure, and this is released in large quantities as outgas components, resulting in malfunction of the device and anodizing and coexistence with various gases and chemicals including halogenated gas. There has been a problem of causing corrosion of the aluminum substrate.

In order to solve such a problem, various methods have been proposed. For example, a method has been proposed in which a metal containing aluminum as a main component is subjected to anodic oxidation with a chemical conversion solution having a neutral or near neutral pH (Patent Document 1).
Recently, in order to obtain a high-quality non-porous aluminum oxide passive film with a high corrosion resistance and a high quality non-porous aluminum oxide passive film with a small amount of released water, a solvent such as ethylene glycol or diethylene glycol is used as a solvent for the electrolyte. It has been proposed to use a glycol solvent having a small relative dielectric constant (Patent Document 2).

  The electrolytic solution used for such anodization is required to be strictly managed in order to obtain a high-quality alumite film. For example, Patent Document 3 measures any two or more of the electrical conductivity (conductivity), specific gravity, sound velocity, and viscosity of an acidic electrolyte that anodizes aluminum or an aluminum alloy, and based on the measured values of these physical properties. An acid concentration in the electrolyte solution and an aluminum concentration dissolved in the electrolyte solution are calculated, and the acid concentration is adjusted within the control range by adding acid or water to the electrolyte solution. A management method is disclosed. However, in the method for detecting an electrolytic solution using any two or more of electrical conductivity, specific gravity, sound velocity, and viscosity, an electrolytic solution that does not contain an organic solvent can be measured. However, water, organic solvent, and electrolyte 3 can be measured. The concentration of each component cannot be measured.

  In Patent Document 4, in a method of forming an oxide film on the surface of a metal material by anodizing a metal material such as aluminum in the chemical liquid, the composition of the chemical liquid is detected by measuring transmitted light intensity. And the method of adjusting the composition of this chemical conversion liquid according to the detected composition is disclosed. However, in the detection of the composition of the electrolyte solution by near infrared spectroscopy using the transmitted light intensity, the analyzer is expensive and requires a place to install the analyzer, so the facility becomes large. There is a problem that it ends up.

  Electrolyte component analysis techniques include electrolyte concentration analysis by neutralization titration method, water concentration analysis by Karl Fischer method, organic solvent concentration analysis by gas chromatography, etc. It was necessary to take it and lacked quickness, and it was not simple.

International Publication No. 2006/134737 Pamphlet Japanese Patent Laid-Open No. 2008-17984 JP 2002-235194 A JP 2008-050674 A

  In such a situation, the problem of the present invention is that in the anodic oxidation of aluminum or aluminum alloy, each component of the anodizing solution in the case of using a glycol-based solvent that is a non-aqueous organic solvent having a low relative dielectric constant as the electrolyte is used. An object of the present invention is to provide a method for easily analyzing the concentration and managing the concentration of each component.

  As a result of intensive studies to solve the above problems, the present inventors have determined the concentration of each of these components as the refractive index of the electrolytic solution in an electrolytic solution composed of a glycol solvent, water, and a specific ammonium compound as an electrolyte. The present inventors have found that it can be easily obtained by measuring the electric conductivity and / or pH, and that the reduced components can be replenished substantially by replenishing water and ammonia.

That is, the present invention relates to the following inventions.
<1> A method of managing an electrolytic solution for anodization composed of each component of an electrolyte containing at least one ammonium compound derived from an organic acid, boric acid or phosphoric acid, water, and a glycol-based solvent, wherein the concentration of each component is Electrolyte management method for managing the concentration of each component constituting the electrolyte by replenishing the component obtained by measuring the refractive index and the electrical conductivity and / or pH of the electrolyte and reducing the component by anodization .
<2> The composition of the electrolytic solution is in the range of glycol solvent: 50 to 99% by weight, water: 1 to 50% by weight, electrolyte: 0.05 to 20% by weight, and the pH of the electrolytic solution is adjusted to the initial value. The management method according to <1>, wherein the management is performed within a range of ± 0.5.
<3> The management method according to <1> or <2>, wherein the pH of the electrolytic solution is in the range of 6.0 to 9.0.
<4> The management method according to any one of <1> to <3>, wherein the electrolyte includes at least one polyvalent aliphatic carboxylic acid, aromatic carboxylic acid, hydroxycarboxylic acid, or amino acid-derived ammonium compound. .
<5> The management method according to <4>, wherein the ammonium compound is ammonium succinate, ammonium adipate, ammonium sebacate, ammonium dodecanoate, ammonium malate, ammonium tartrate, or ammonium salicylate.
<6> The management method according to any one of <1> to <5>, wherein the glycol solvent is at least one of ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol.
<7> The management method according to any one of <1> to <3>, wherein the glycol solvent is ethylene glycol or diethylene glycol, and the electrolyte is ammonium adipate.
<8> The management method according to any one of <1> to <7>, wherein the reduced component is replenished with water and ammonia.
<9> After obtaining the replenishment amount of water from the refractive index and replenishing the reduced water, the replenishment amount of ammonia is obtained from the electrical conductivity and / or pH, and the ammonia is replenished. The management method described.
<10> An anodizing method for aluminum or aluminum alloy using the electrolytic solution managed by the management method according to any one of <1> to <9>.

  According to the present invention, it is possible to easily measure the concentration of each component of an electrolytic solution for anodization composed of a glycol solvent, water, and an ammonium compound, and based on this, the composition of the electrolytic solution is controlled by adding insufficient components. An electrolytic solution management method that can be used is provided.

It is a figure which shows the relationship between DEG density | concentration and refractive index in case ADA density | concentration is constant. It is a figure which shows the relationship between DEG density | concentration in case ADA density | concentration is constant, and pH. It is a figure which shows the relationship between DEG density | concentration and electrical conductivity in case ADA density | concentration is constant. 2 is an SEM photograph of an anodized film formed with an electrolytic solution (new solution) in Example 1. It is a SEM photograph of the anodic oxide film by the electrolyte solution in Example 2 (after re-preparation). It is a SEM photograph of the anodized film by the electrolyte solution in Example 3 (after re-preparation). 3 is a SEM photograph of an anodized film with an electrolyte solution in Comparative Example 1.

  The present invention relates to a method for managing an electrolytic solution for anodization of aluminum or aluminum alloy, specifically, an electrolyte containing at least one or more ammonium compounds derived from organic acid, boric acid or phosphoric acid, water, and glycol system A method for managing an electrolytic solution for anodization composed of each component of a solvent, wherein the concentration of each component is determined by measuring the refractive index and the electrical conductivity and / or pH of the electrolyte, and reduced by anodizing. The concentration of each component constituting the electrolytic solution is controlled by replenishing the prepared component.

  The electrolytic solution for anodic oxidation of the present invention (hereinafter simply referred to as “electrolytic solution”) is composed of an electrolyte containing at least one or more ammonium compounds derived from an organic acid, boric acid or phosphoric acid, water, and glycol components. Is done. Hereinafter, each component will be described.

First, the electrolytic solution of the present invention contains an electrolyte (hereinafter simply referred to as “electrolyte”) component containing at least one ammonium compound derived from an organic acid, boric acid or phosphoric acid.
The electrolytic solution used in the present invention preferably exhibits a buffering action in the range of pH 4 to 10 in order to buffer the concentration fluctuation of various substances during electrolysis and keep the pH in a predetermined range. The ammonium compound derived from organic acid, boric acid or phosphoric acid can be suitably used as an electrolyte because it exhibits a good buffering action and has high solubility in an electrolytic solution and good dissolution stability.

Examples of the ammonium compound derived from an organic acid include polyvalent aliphatic carboxylic acids, aromatic carboxylic acids, hydroxycarboxylic acids, or ammonium compounds derived from amino acids. Among these, ammonium compounds derived from polyvalent aliphatic carboxylic acids are preferably used.
Specific examples of the ammonium compound derived from the polyvalent aliphatic carboxylic acid include ammonium succinate, ammonium adipate, ammonium sebacate, ammonium dodecanoate, ammonium malate, ammonium tartrate, ammonium salicylate and the like. Of these, ammonium tartrate, ammonium citrate, and ammonium adipate are preferred for reasons such as solution stability, safety, and good buffering action. Among them, ammonium adipate having a solution pH of around 7 is particularly preferably used since a high-purity product can be easily obtained and the pH buffering ability is high.

Next, ammonium borate is mentioned as an ammonium compound derived from boric acid. Examples of phosphoric acid-derived ammonium compounds include diammonium hydrogen phosphate and ammonium dihydrogen phosphate.
Among these ammonium compounds, organic acid-derived ammonium compounds that do not have the possibility of remaining boron and phosphorus elements in the metal oxide film are preferably used.
In addition, these ammonium compounds can be used individually or in combination of 2 or more types.

  Next, another component constituting the electrolytic solution of the present invention is a glycol solvent. The glycol solvent has a low relative dielectric constant and suppresses the electrolysis of water molecules in the electrolytic solution during the anodizing treatment, so that a higher voltage can be applied.

  Specific examples of the glycol solvent include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Of these, ethylene glycol and diethylene glycol are preferably used. These can be used alone or in combination of two or more.

The electrolytic solution is composed of the above electrolyte, glycol solvent, and water, and the composition of the electrolytic solution in the present invention is glycol solvent: 50 to 99% by weight, water: 1 to 50% by weight, electrolyte: 0. It is preferable to control in the range of 0.05 to 20% by weight.
The concentration of the glycol solvent determines the relative dielectric constant of the electrolytic solution in combination with the concentration of water. When the concentration of the glycol solvent is less than 50% by weight, the dielectric constant of the electrolytic solution is increased and the electrolysis of water is promoted. As a result, dissolution of the oxide film is promoted. On the other hand, if it exceeds 99% by weight, the supply source of oxygen necessary for forming the oxide film is extremely reduced, and it is difficult to obtain a high-quality oxide film.
In addition, the concentration of the electrolyte determines the electric conductivity. However, when the concentration of the electrolyte is less than 0.05% by weight, the electric resistance value of the electrolytic solution increases. Is not uniform and a good quality oxide film cannot be obtained. On the other hand, if it exceeds 20% by weight, the electric resistance value becomes low, and even if there are slight irregularities on the surface of the aluminum material, the place where current flows tends to concentrate on the convex part, and it is still difficult to obtain a uniform oxide film.

  The concentration of each component in the electrolytic solution is preferably glycol solvent: 75 to 85% by weight, water: 15 to 25% by weight, electrolyte: 0.1 to 10.0% by weight, more preferably glycol. System solvent: 75 to 85% by weight, water: 15 to 25% by weight, electrolyte: 0.1 to 1.0% by weight.

  In the present invention, the pH of the electrolytic solution is preferably controlled within a range of ± 0.5 of the initial value. Here, the initial value refers to the pH of each component composition (electrolytic solution before performing electrolytic oxidation) when the electrolytic solution is first prepared. Here, the pH is measured with a general pH meter.

When the pH deviates from the initial value ± 0.5, each component of the electrolytic solution is adjusted to the initial value by adding water and ammonia described later.
Furthermore, the pH of the electrolytic solution is preferably in the range of 6.0 to 9.0, more preferably 8.0 to 8.6 in order to adjust the electrolytic solution to the optimum composition for forming a high quality film. Controlled by range.

  The electrolytic solution of the present invention is suitably used for anodic oxidation of aluminum or an aluminum alloy. As the aluminum or aluminum alloy, one in which the content of a specific element (iron, copper, manganese, zinc, chromium) is suppressed is used. The total content of these specific elements is preferably 1.0% by weight or less, more preferably 0.5% by weight or less.

  The aluminum alloy may contain one or more kinds of other arbitrary metals that can form an alloy with aluminum. The type of metal is not particularly limited as long as it is other than the above-mentioned specific elements, but preferred metals include at least one metal selected from the group consisting of magnesium, titanium and zirconium. Among these, magnesium has an advantage that the mechanical strength of the aluminum substrate can be improved. The magnesium concentration is not particularly limited as long as it can form an alloy with aluminum, but is usually 0.5% by weight or more, preferably 1.0% by weight or more, in order to provide sufficient strength improvement. . In order to form a uniform solid solution with aluminum, the content is preferably 6.5% by weight or less, more preferably 5.0% by weight or less, and still more preferably 4.5% by weight or less.

  In the present invention, the electrolytic method for anodic oxidation is not particularly limited as long as the intended effect of the present invention is not significantly impaired. As the current waveform, for example, in addition to direct current, a pulse method in which an applied voltage is periodically interrupted, a PR method in which the polarity is inverted, other alternating current, AC / DC superimposition, incomplete rectification, a modulation current such as a triangular wave, or the like can be used. However, preferably a direct current is used.

  In the present invention, the method for controlling the current and voltage of anodization is not particularly limited, and conditions for forming an oxide film on the surface of aluminum or aluminum alloy can be appropriately combined. Usually, it is preferable to anodize at a constant current and a constant voltage. That is, it is preferable that electrolysis is performed at a constant current up to a predetermined electrolysis voltage Vf, and after the desired electrolysis voltage is reached, the voltage is maintained for a certain period of time for anodization.

At this time, in order to efficiently form an oxide film, the current density is usually 0.001 mA / cm ² or more, preferably 0.01 mA / cm ² or more. However, in order to obtain an oxide film with good surface flatness, the current density is usually 100 mA / cm ² or less, preferably 10 mA / cm ² or less.

  The electrolytic voltage Vf is usually 3 V or higher, preferably 10 V or higher, more preferably 20 V or higher. Since the obtained oxide film thickness is related to the electrolysis voltage Vf, it is preferable to apply the above voltage or more in order to give the oxide film a certain thickness. However, it is usually 1000 V or less, preferably 700 V or less, more preferably 500 V or less. Since the obtained oxide film has a high insulating property, it is preferable to carry out at or below the above voltage in order to form a high-quality oxide film without causing dielectric breakdown.

  In order to increase the thickness of the oxide film, it is necessary to increase the electrolytic voltage. In this case, the ultimate voltage depends on the type of the electrolytic solution. For example, in ethylene glycol, the ultimate voltage for obtaining a good quality aluminum oxide film is 200 V, and the film thickness at that time is about 0.35 μm, but in diethylene glycol, the ultimate voltage can be increased to 400 V, 0.5 μm A good quality aluminum oxide film can be formed.

  Alternatively, an alternating current with a constant peak current value may be used instead of direct current until the electrolytic voltage is reached, and a method of switching to direct current when the electrolytic voltage is reached and holding for a certain time may be used.

  In the present invention, glycol solvents such as ethylene glycol and diethylene glycol are used alone or in combination, which is important for forming an aluminum oxide film having a good electrolysis temperature. Usually, a temperature higher than room temperature is preferred. More preferably, it is the range of 30 degreeC-70 degreeC.

Next, the management method of the electrolytic solution of the present invention will be described.
In the method for managing an electrolytic solution of the present invention, the charged composition (referred to as “initial value”) of an electrolytic solution composed of an electrolyte, water, and a glycol solvent deviates from the initial value by performing anodization treatment of aluminum or an aluminum alloy. In this case, the composition of the electrolytic solution is controlled by replenishing the electrolyte component ammonium compound, water, and glycol solvent, and the electrolytic solution is managed by returning it to a predetermined range (preferably initial value).

The feature of the present invention is that the concentration of each component of the electrolyte, water, and glycol solvent in the electrolytic solution is first determined by measuring the refractive index, electric conductivity, and / or pH of the electrolytic solution. Since the refractive index, electric conductivity, and pH of the electrolytic solution can be easily obtained with a relatively small device, the composition of the electrolytic solution is controlled by adding an insufficient component based on the refractive index.
In addition, the components consumed in the anodic oxidation reaction of aluminum or aluminum alloy are mainly a decrease due to evaporation of water and a decrease due to evaporation of ammonium ions dissociated from the ammonium compound by anodization reaction. The glycol solvent is not consumed in the anodization reaction of aluminum or aluminum alloy.
Therefore, in the electrolytic solution management method of the present invention, as the replenishment of the electrolyte component, the component to be replenished can actually be ammonia and water constituting the ammonium compound of the electrolyte component.
That is, the ammonium compound is indirectly replenished by replenishing ammonia instead of replenishing the electrolyte component ammonium compound itself. Ammonia and water can be replenished by any method of ammonia gas and water or ammonia water.
The glycol solvent does not usually need to be replenished, but if it decreases due to transpiration or the like, it can be replenished.

  Hereinafter, the electrolytic solution management method of the present invention will be described specifically by taking an electrolytic solution using diethylene glycol (DEG) as the glycol solvent and ammonium adipate (ADA) as the electrolyte.

First, calibration curves for refractive index, pH, and electrical conductivity are created for DEG and ADA.
Here, the case where the measurement target is DEG, the ADA concentration is constant, and the calibration curve is used when the DEG concentration is changed as shown in FIGS. 1A to 1C is illustrated.

FIG. 1A is a graph showing the relationship between the refractive index in the electrolyte and the DEG concentration when ADA at 20 ° C. is set to a constant concentration. The horizontal axis represents the DEG concentration in the electrolytic solution, and the vertical axis represents the refractive index. In the concentration range shown in FIG. 1A, the refractive index tends to increase linearly as the DEG concentration increases.
FIG. 1B is a graph showing the relationship between the pH of the electrolyte and the DEG concentration when ADA at 25 ° C. is set to a constant concentration. The horizontal axis represents the DEG concentration in the electrolytic solution, and the vertical axis represents the pH. In the concentration range shown in FIG. 1B, the pH tends to increase linearly as the DEG concentration increases.
FIG. 1C is a graph showing the relationship between the electrical conductivity of the electrolyte and the DEG concentration when ADA at 25 ° C. is set to a constant concentration. The horizontal axis shows the DEG concentration in the electrolyte, and the vertical axis shows the electrical conductivity in logarithm. In the concentration range shown in FIG. 1C, the logarithm of electrical conductivity tends to decrease linearly as the DEG concentration increases to the DEG concentration.

Similarly, a calibration curve is created with the measurement object as ADA. In this case, the DEG concentration may be constant and the ADA concentration may be changed.
By using the prepared ADA concentration and DEG concentration calibration curves for the refractive index, pH, and electrical conductivity, the ADA concentration and DEG concentration can be calculated from the measured values of the refractive index, pH, and electrical conductivity of the electrolyte. .
Note that it is not always necessary to measure both pH and electrical conductivity, but it is preferable to measure both in order to further improve measurement accuracy.

In an electrolytic solution composed of DEG, water, and ADA, after preparing a new solution, the initial concentration is first measured by refractive index, pH, and electrical conductivity.
When anodizing is performed using an electrolytic solution, the composition of the electrolytic solution changes. The composition change of the electrolytic solution is a decrease due to evaporation of water and a decrease due to evaporation of ammonia generated by dissociation of ADA.
As shown in Table 1, the pH of the electrolyte solution is greatly lowered by adipic acid ions that relatively increase due to the evaporation of ammonia, and the electrical conductivity becomes small due to the decrease in ammonia ions. However, the refractive index hardly changes even if there is an increase in excess adipate ions and a decrease in ammonia ions from the initial ADA. That is, the refractive index value represents the amount of DEG and water at the initial ADA concentration shown in FIG.

  That is, Table 1 shows the concentration of each component of the electrolytic solution and the refractive index, pH, and electrical conductivity at that concentration. The electrolyte solution with 0% adipic acid concentration in the table assumes a new solution, and the ADA concentration gradually decreases and the adipic acid concentration increases. This indicates that, by use, ammonia dissociated from ADA evaporated and adipic acid was produced. When ADA decreases and adipic acid increases, the pH of the electrolyte solution tends to decrease and the electric conductivity tends to be a small value. However, the refractive index value hardly changes from the initial ADA, and the pH is 0. It shows that it is hardly affected by the decrease in ammonia exceeding .5.

Next, a method for recovering the electrolytic solution whose composition has been changed by use to the initial concentration will be described.
First, the refractive index of the electrolyte after use is measured. From the measured value of the refractive index, the amount of reduced water is calculated from a calibration curve (FIG. 1) corresponding to the initial ADA concentration, and the reduced amount of water is replenished so that the initial refractive index value is obtained.
Next, ammonia water is replenished until the reduced ammonia reaches the initial pH value. Alternatively, ammonia water is replenished until the electric conductivity reaches the initial value.
When replenishing the pH to the initial value, measure the electrical conductivity, and when replenishing the electrical conductivity to the initial value, measure the pH, and check the initial value to manage the electrolyte. .

  In order to maintain the ADA composition of the present invention having fine adjustment, it is more preferable to measure both the electric conductivity and pH. First, the electric conductivity is measured, and then the pH is measured and added. More preferably, the amount of ammonia to be determined is determined.

  In the present invention, in order to maintain the concentration of the electrolytic solution as described above, only the components reduced by the anodic oxidation treatment are replenished, so that the replenished water and ammonia gas or ammonia water are the minimum necessary. That is, according to the present invention, adding all of the glycol-based solvent, water, and ammonium compound, which are components of the conventional electrolytic solution, not only increases the replenishment amount, but also requires disposal when the treatment tank is exceeded. When the ammonium compound itself is added, the problem that the concentration of the acid constituting the ammonium compound in the electrolytic solution that does not decrease by the electrolytic treatment increases can be solved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is changed. The refractive index, electrical conductivity, and pH were measured as follows.

(1) Measurement of refractive index Using a hand-held refractometer “IN-1α” manufactured by Atago Co., Ltd., measuring the Brix with the electrolyte temperature set to 20 ° C. according to JIS-K0062, and converting the Brix value into the refractive index And asked.
The refractive index can be measured directly with a digital refractometer or the like.
(2) Measurement of electrical conductivity Using a portable electrical conductivity / pH meter WM-22EP manufactured by Toa DKK Corporation, the temperature of the electrolyte was measured at 25 ° C. according to JIS-K0130.
(3) Measurement of pH Using a portable electric conductivity / pH meter WM-22EP manufactured by Toa DK Corporation, the temperature of the electrolyte was measured at 25 ° C. according to JIS-Z8802.

"Example 1"
A sample in which an aluminum alloy substrate was used as a pretreatment was heated to 65 ° C. with a solution prepared by mixing 85 wt% phosphoric acid, 98 wt% sulfuric acid, and 67.5 wt% nitric acid in a volume ratio of 70: 25: 5. The sample was immersed in rocking for 3 minutes and then washed with pure water. Next, an electrolyte solution was prepared with 79.5% by weight of DEG, 20% by weight of water, and 0.5% by weight of ADA. When the refractive index of this electrolytic solution was measured using a handheld refractometer “IN-1α” manufactured by Atago Co., Ltd., Brix was 25.4 (20 ° C.) after being diluted twice with water, and the refractive index of this value was It was calculated to be 1.4215, and the DEG concentration was 79.5% by weight from a calibration curve representing the relationship between the DEG concentration in the electrolyte and the refractive index. Moreover, when the electrical conductivity and pH are measured using a portable electrical conductivity / pH meter manufactured by Toa DKK Corporation, the electrical conductivity is 33.6 mS / m (25 ° C.), and the ADA concentration in the electrolyte and the electrical conductivity are measured. From the calibration curve representing the relationship of conductivity, the ADA concentration was 0.5% by weight, and the pH was 8.45 (25 ° C.).
This electrolyte solution was heated to 50 ° C. and anodized to form a 500 nm thick anodized film on the sample surface. When the surface of the formed oxide film was observed with a scanning electron microscope (SEM), it was confirmed that the film was a high-quality film having no irregularities on the surface (see FIG. 2).

"Example 2"
When the refractive index of the electrolytic solution after the anodic oxidation treatment of Example 1 was measured using the refractometer “IN-1α”, Brix was 25.5 (20 ° C.) after being diluted twice with water. The refractive index of the value can be calculated as 1.4222, and the DEG concentration was 80.0% by weight from a calibration curve representing the relationship between the DEG concentration in the electrolyte and the refractive index. Moreover, when the electric conductivity and pH were measured using the portable electric conductivity / pH meter, the electric conductivity was 30.1 mS / m (25 ° C.) and the pH was 8.11 (25 ° C.). . Using this electrolytic solution, an oxide film was formed by the same treatment as in Example 1 and the surface was observed by SEM. As in Example 1, a high-quality film having no irregularities on the surface was observed. (See FIG. 3).

“Comparative Example 1”
When the refractive index of the electrolytic solution that was subjected to anodization treatment twice without replenishing water and ammonia water was measured using the refractometer “IN-1α”, Brix was 26.4 diluted twice with water. The refractive index of this value can be calculated as 1.426, and the DEG concentration was 83.6% by weight from a calibration curve representing the relationship between the DEG concentration in the electrolyte and the refractive index. Further, when the electric conductivity and pH were measured using the portable electric conductivity / pH meter, the electric conductivity was 24.8 mS / m (25 ° C.) and the pH was 7.40 (25 ° C.). It was. Using this electrolytic solution, an oxide film was formed by the same treatment as in Example 1 and the surface was observed by SEM. Unlike in Examples 1 and 2, there were many fine irregularities on the surface. The film was poor in quality (see FIG. 5).

"Example 3"
When the refractive index of the electrolytic solution after carrying out Comparative Example 1 was measured using the refractometer “IN-1α”, Brix was 26.5 (20 ° C.) after being diluted twice with water. The refractive index was calculated to be 1.4265, and the DEG concentration was 84.0% by weight from a calibration curve representing the relationship between the DEG concentration in the electrolyte and the refractive index. Further, when the electric conductivity and pH were measured using the portable electric conductivity / pH meter, the electric conductivity was 22.6 mS / m (25 ° C.) and the pH was 7.05 (25 ° C.). It was. The ADA concentration was calculated to be 0.44% by weight from a calibration curve representing the relationship between the ADA concentration in the electrolyte and the electrical conductivity.
In order to restore the electrolyte to the initial composition, 4.9 g of reduced water was added to 100 g of the initial preparation amount, and in order to recover further reduced ADA, 25 wt% aqueous ammonia was adjusted to the initial pH value. It was added until it reached 8.45. Then, when the concentration was analyzed again in the same manner as described above, Brix was 25.4 (20 ° C.) after 2-fold dilution with water, and the refractive index of this value could be calculated as 1.4215. From the calibration curve showing the relationship between the concentration and the refractive index, the DEG concentration was 79.5% by weight. The electrical conductivity is 33.6 mS / m (25 ° C.), and the ADA concentration is 0.5% by weight from the calibration curve representing the relationship between the ADA concentration in the electrolytic solution and the electrical conductivity. And all agreed. Using this electrolytic solution, an oxide film was formed by the same treatment as in Example 1, and the surface was observed by SEM. As a result, a high-quality film having no irregularities on the surface was observed as in the formation of the anodized film. (See FIG. 4).

  The present inventors have easily obtained the concentration of each component in an electrolyte solution composed of a glycol solvent, water and an electrolyte by measuring the refractive index and the electrical conductivity and / or pH of the electrolyte solution, and the reduced components. A method of managing an electrolytic solution for anodization of aluminum or aluminum alloy, which is substantially replenished with water and ammonia, is provided.

Claims (10)

  A method for managing an electrolytic solution for anodization of aluminum or aluminum alloy, comprising each component of an electrolyte containing at least one ammonium compound derived from an organic acid, boric acid or phosphoric acid, water and a glycol solvent, The component concentration is determined by measuring the refractive index and the electric conductivity and / or pH of the electrolytic solution, and the concentration of each component constituting the electrolytic solution is controlled by replenishing the component reduced by the anodizing treatment. A method for managing an electrolyte solution.   The composition of the electrolyte solution is in the range of glycol solvent: 50 to 99% by weight, water: 1 to 50% by weight, electrolyte: 0.05 to 20% by weight, and the pH of the electrolyte is ± 0 of the initial value. The management method according to claim 1, wherein management is performed within a range of .5.   The management method according to claim 1 or 2, wherein the pH of the electrolytic solution is in a range of 6.0 to 9.0.   The management according to any one of claims 1 to 3, wherein the electrolyte contains one or more polyvalent aliphatic carboxylic acids, aromatic carboxylic acids, hydroxycarboxylic acids or amino acid-derived ammonium compounds. Method.   The ammonium compound is at least one selected from ammonium succinate, ammonium adipate, ammonium sebacate, ammonium dodecanoate, ammonium malate, ammonium tartrate, and ammonium salicylate. The management method described.   6. The glycol according to claim 1, wherein the glycol solvent is at least one selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Management method.   The management method according to any one of claims 1 to 3, wherein the glycol solvent is ethylene glycol or diethylene glycol, and the electrolyte is ammonium adipate.   The management method according to claim 1, wherein the reduced component is replenished with water and ammonia.   9. The replenishment amount of water to the electrolytic solution is obtained from the refractive index, and after replenishing the reduced water, the replenishment amount of ammonia is obtained from the electrical conductivity and / or pH to replenish the ammonia. The management method described in 1.   10. An anodic oxidation method for aluminum or an aluminum alloy, wherein the electrolytic solution managed by the management method according to claim 1 is used.