JP3309176B2 - Method of forming electrode foil for medium and high pressure aluminum electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrode foil for an aluminum electrolytic capacitor for medium and high pressures.

[0002]

2. Description of the Related Art Conventionally, the anode aluminum foil of an aluminum electrolytic capacitor has been subjected to a hydration treatment on a high-purity aluminum foil having been subjected to a surface enlargement treatment and then anodized to produce crystalline aluminum oxide on the surface. This is used as a dielectric film. By the way, in the above, when forming crystalline aluminum oxide by anodic oxidation, vacancy defects inevitably occur. This vacancy defect is
The aluminum hydroxide generated by the hydration treatment is generated by volume shrinkage that occurs when dehydration occurs, and oxygen gas is sealed inside. If these vacancies are present in the dielectric film, the porosity defects are exposed and deteriorate the film when used as an electrolytic capacitor, so heat treatment, chemical treatment, and mechanical treatment are usually performed after anodizing. To expose vacancies in the film and in the thickness direction generated during the formation of crystalline aluminum oxide, and then perform anodic oxidation treatment to repair the exposed vacancies, thereby reducing the vacancies in the dielectric. A film is formed.

[0003]

However, in the depolarization treatment after the heat treatment, it is difficult to sufficiently expose and repair the vacancy defects by one heat treatment and re-anodization treatment. Repeats these processes a plurality of times. However, it is difficult to expose and repair all vacancy defects even if the above process is repeated many times, and the vacancy is restricted by the production equipment and production efficiency. It was not always an effective means for exposing and repairing defects. Therefore, an object of the present invention is to provide a method for forming an electrode foil, which is effective for a medium-to-high-pressure anode, and is particularly durable by efficiently exposing and repairing the above-described vacancy defects by mild depolarization. It was done.

[0004]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a first step of immersing a high-purity aluminum foil subjected to a surface enlargement treatment in pure water to perform a hydration treatment. And a second step of immersion in an aqueous solution containing a linear dicarboxylic acid, a third step of immersion in pure water to perform hydration, and a depolarization step including heat treatment after anodization. Preferably, the hydration temperature in the first step and the third step is 70 degrees Celsius, respectively.
Degrees or more.

[0005]

Thus, in the above, the vacancy defects generated when the crystalline aluminum oxide is formed by the anodic oxidation treatment are caused by the oxygen gas sealed in the vacancy defects in the depolarization treatment step including the heat treatment. The volume expansion due to the heating causes the oxide layer on the surface of the vacancy defect to be broken, thereby exposing the vacancy defect. The volume expansion in the above becomes remarkable as the temperature increases, and the effect of exposing the vacancy defects increases. However, since the temperature cannot be raised to a temperature higher than the melting point of the underlying metallic aluminum, the temperature has its own limit.
However, according to the present invention, the hydration treatment step in the chemical conversion treatment step is divided into two steps, and a treatment of immersion in a linear dicarboxylic acid aqueous solution is inserted between them, so that the hydration film formed by the preceding hydration treatment The linear dicarboxylic acid is adsorbed on the surface of the substrate, and a new hydration film is formed on the front side of the adsorbed layer by the hydration treatment in the later stage. That is, a hydrated film containing linear dicarboxylic acid is formed in the middle part of the hydrated film, and by performing anodizing treatment on the hydrated film, a crystalline oxide containing linear dicarboxylic acid is generated in the middle part. You.

Next, when the crystalline oxide is subjected to a heat treatment, the linear dicarboxylic acid incorporated in the intermediate portion is thermally decomposed to generate mainly carbon dioxide gas. This thermal decomposition is unlikely to occur when the linear dicarboxylic acid is incorporated in the crystal, and tends to occur when the linear dicarboxylic acid is present on the pore surface.
Therefore, by the heat treatment, the expansion of the oxygen gas in the vacancy defect and the generation of carbon dioxide gas by the decomposition reaction of the linear dicarboxylic acid simultaneously with the expansion of the vacancy defect can be realized extremely efficiently.

Particularly, in the present invention, the oxide containing linear dicarboxylic acid was formed in the intermediate layer because the position of vacancy defects was concentrated in this portion, and thermal decomposition and volume expansion in this portion were performed. In addition, immersion treatment in an aqueous solution containing a linear dicarboxylic acid requires thermal decomposition at a relatively low temperature to form carbon dioxide, resulting in significant volume expansion and anodic oxidation. It is selected because it does not interfere with the electrochemical reaction in the process.

Preferred linear dicarboxylic acids that can be used are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, and tartaric acid. Linear saturated dicarboxylic acids can be used, and citraconic acid, aconitic acid,
Linear unsaturated dicarboxylic acids such as malic acid and citric acid can also be used.

[0009] The usable high-purity aluminum foil is preferably 99.99% or more, which is usually used. However, if it can be expanded for medium-to-high pressure electrolytic capacitors, it should be 99.9% or more. Even with aluminum purity, the intended purpose can be sufficiently achieved.

[0010]

Embodiments of the present invention will be described in detail below in relation to comparative examples. (Example 1) A 99.99% or more high-purity aluminum foil subjected to a surface enlargement treatment was immersed in pure water at 95 ° C for 5 minutes, and then immersed in 85 ° C, 5% oxalic acid aqueous solution for 5 minutes. And immersion treatment again in pure water at 95 ° C. for 5 minutes, followed by 20 mA / cm 2 in a 7 wt% aqueous solution of boric acid at 85 ° C.
Perform anodic oxidation of the ^second formation voltage 400V, after rising to 400V, it performed 15 minutes constant voltage holding, 520 ° C. after reducing the leakage current, a heat treatment for 5 minutes in an air atmosphere, again under the same conditions Anodization was performed, and the quantity of electricity and withstand voltage characteristics at this time were measured. Next, the formed foil was boiled in pure water for 2 hours to perform an accelerated deterioration test, and then the withstand voltage characteristics were measured and compared with the values before the accelerated deterioration test.

(Example 2) A high-purity aluminum foil subjected to a surface enlargement treatment was immersed in pure water at 95 ° C for 2 minutes.
After immersion treatment in a 5% aqueous succinic acid solution at 0 ° C. for 5 minutes, immersion treatment in pure water at 95 ° C. for 5 minutes, and then 20 mA / cm in a 7 wt% boric acid aqueous solution at 85 ° C.
Anodizing at a formation voltage of 400 V in Step ² and raising the voltage to 400 V, holding a constant voltage for 15 minutes, reducing the leakage current, performing a heat treatment at 520 ° C. for 5 minutes in an air atmosphere, and again under the same conditions Anodizing was performed, and the quantity of electricity and withstand voltage characteristics at this time were measured. Next, the formed foil was boiled in pure water for 2 hours to perform an accelerated deterioration test, and then the withstand voltage characteristics were measured and compared with the values before the accelerated deterioration test.

(Comparative Example 1) Comparative Example 1 is an example in which the hydration treatment in Example 1 is performed only once, and the “step of immersing in oxalic acid aqueous solution at 85 ° C. and 5% for 5 minutes” is omitted. are doing. That is, after immersing the high-purity aluminum foil subjected to the surface enlargement treatment in pure water at 95 ° C. for 10 minutes,
Anodizing is performed at a formation voltage of 400 mA at 20 mA / cm ² in a 7 wt% aqueous solution of boric acid at 85 ° C., and after raising the voltage to 400 V, a constant voltage is maintained for 15 minutes to reduce the leakage current. A minute heat treatment was performed in an air atmosphere, anodization was performed again under the same conditions, and the quantity of electricity and withstand voltage characteristics at this time were measured. Next, the formed foil was boiled in pure water for 2 hours to perform an accelerated deterioration test, and then the withstand voltage characteristics were measured and compared with the values before the accelerated deterioration test.

Comparative Example 2 Comparative Example 2 exemplifies a case in which the subsequent hydration treatment in Example 1 is omitted. That is, the high-purity aluminum foil subjected to the surface enlargement process
Immersed in pure water at 85 ° C for 5 minutes, and then immersed in 5% oxalic acid aqueous solution at 85 ° C for 7 minutes.
Formation voltage of 20 mA / cm ² in boric acid solution at 400 V
Anodic oxidation, after raising to 400V, holding a constant voltage for 15 minutes, reducing the leakage current, 520 ℃
A heat treatment for 5 minutes was performed in an air atmosphere, anodization was performed again under the same conditions, and the quantity of electricity and withstand voltage characteristics at this time were measured. Next, the formed foil was boiled and boiled in pure water for 2 hours to perform an accelerated deterioration test, and then the withstand voltage characteristics were measured and compared with the values before the accelerated deterioration.

(Comparative Example 3) In Comparative Example 3, the step of “immersing in a 5% aqueous succinic acid solution at 60 ° C. for 5 minutes” in Example 2 was carried out in the same manner as in “2. 5
For example, a case in which the step of “immersion for a minute” is replaced is shown.
In other words, a high-purity aluminum foil that has been
After immersion in pure water at 95 ° C. for 2 minutes, immersion treatment in 85% aqueous 8% boric acid for 5 minutes, immersion in pure water at 95 ° C. for 5 minutes again, 7wt% of
Formation voltage of 20 mA / cm ² in boric acid solution at 400 V
Anodic oxidation, after raising to 400V, holding a constant voltage for 15 minutes, reducing the leakage current, 520 ℃
A heat treatment for 5 minutes was performed in an air atmosphere, anodization was performed again under the same conditions, and the quantity of electricity and withstand voltage characteristics at this time were measured. Next, the formed foil was boiled in pure water for 2 hours to perform an accelerated deterioration test, and then the withstand voltage characteristics were measured and compared with the values before the accelerated deterioration test.

The results are shown in Table 1.

[Table 1]

As is evident from the above results, in each of the examples, the amount of electricity when re-anodizing is performed is as follows:
Compared to any of Comparative Examples 1 to 3, it is extremely large, and it can be understood from this that the effect of exposing vacancy defects by the heat treatment is remarkable. Further, even after the accelerated deterioration test by boiling for 2 hours in pure water, no decrease in withstand voltage characteristics was observed at all. Further, even when immersion treatment is performed with an aqueous solution of oxalic acid, which is a linear dicarboxylic acid, the effect is small in the case of Comparative Example 2 in which the subsequent hydration treatment is not performed. No effect was obtained even in the case of Comparative Example 3 inserted in the middle of the hydration treatment classified into.

The treatment temperature, treatment time and solution concentration in Examples 1 and 2 are the most preferable conditions for the used linear dicarboxylic acid, and these conditions differ depending on the type of the linear dicarboxylic acid. .
When the hydration treatment is performed at 70 ° C. or less in the first step and the third step, it takes a long time to produce a hydrate and lacks workability. Therefore, the temperature of the hydration treatment is preferably at least 70 ° C. in both the first step and the third step. In addition, the current density and the formation voltage in the anodic oxidation treatment and 52 for exposing the vacancy defect.
As the heat treatment conditions at 0 ° C. for 5 minutes, well-known conditions conventionally applied are applied.

[0018]

As described above, according to the present invention, the immersion treatment step with the aqueous solution of linear dicarboxylic acid is inserted between the hydration treatment steps before and after, so that the porosity defect is eliminated in the depolarization step by heat treatment. Exposure is remarkably accelerated, and the exposure of the vacancy defects is repaired by the re-anodizing treatment, so that the remaining vacancy defects can be significantly reduced, and the durability is excellent. It is possible to provide an aluminum electrode foil for medium and high pressures whose amount is significantly improved.

Continuation of the front page (72) Inventor Takashi Kajiyama 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Inside the Nippon Light Metal Co., Ltd. Group Technology Center (56) References JP-A-6-275473 (JP, A) JP-A-5-335186 (JP, A) JP-A-60-65517 (JP, A) JP-A-8-64480 (JP, A) JP-A-62-186514 (JP, A) (58) Int.Cl. ⁷ , DB name) H01G 9/04 301

Claims (2)

(57) [Claims] A first step of immersing a high-purity aluminum foil having been subjected to a surface enlargement treatment in pure water to perform a hydration treatment;
A second step of immersion treatment in an aqueous solution containing a linear dicarboxylic acid, and a third step of immersion in pure water to perform hydration treatment,
A method for forming an electrode foil for a medium-to-high pressure aluminum electrolytic capacitor, comprising a depolarization step including a heat treatment after anodizing treatment. 2. The method according to claim 1, wherein the hydration temperature in the first step and the third step is 70 ° C. or higher, respectively.