JPH09275040A - Chemical method for electrode foil for medium and high voltage aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce remaining hole defects and improve durability by promoting the exposure of hole defects in depolarization process by heat treatment and repairing by reanodic oxidation treatment by inserting immersion treatment process by of pre- and post-hydration treatment. SOLUTION: Hydration treatment process in chemical treatment process is divided into two, and a treatment for immersing in an aqueous solution of direct chain dicarbonic acid is inserted between the two. By doing this, a hydration film containing direct chain dicarbonic acid is created in the intermediate portion of hydration film, and a crystalline oxide containing direct chain dicarbonic acid is formed by performing anodic oxidation treatment to the hydration film. Next, when heat treatment is performed to the crystalline oxide, the direct chain dicarbonic acid surrounded by the intermediate portion is thermally cracked, carbon dioxide gas is generated due to decomposition reaction direct chain dicarbonic acid at the same time with the expansion of oxygen gas in the hole defect, and exposure of hole defect can be realized very efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical conversion method which is particularly effective for electrode foils for aluminum electrolytic capacitors for medium and high voltages.

[0002]

2. Description of the Related Art Conventionally, the anode aluminum foil of aluminum electrolytic capacitors has been subjected to hydration treatment on a surface-treated high-purity aluminum foil and then anodized to produce crystalline aluminum oxide on the surface. However, this is used as a dielectric film. By the way, in the above, vacancy defects are inevitably generated when forming crystalline aluminum oxide by anodic oxidation. This vacancy defect is
It is generated due to volume contraction that occurs when aluminum hydroxide produced by the hydration treatment is dehydrated, and oxygen gas is confined inside. When this vacancy defect is present in the dielectric film, when used as an electrolytic capacitor, the vacancy defect is exposed and the film deteriorates, so heat treatment, chemical treatment, or mechanical treatment is usually performed after anodizing. To expose vacancy defects in the film and in the thickness direction that occur when crystalline aluminum oxide is formed, and then to perform anodization again to repair the exposed vacancy defects and reduce the number of vacancy defects. It forms a film.

[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-anodizing treatment. Repeats these processes multiple times. However, no matter how many times the above process is repeated, it is difficult to expose / repair all the vacancy defects, and the vacancy is restricted due to the manufacturing equipment and the production efficiency. It was not always an effective means for exposing and repairing defects. Therefore, the present invention aims to provide a method of chemically forming an electrode foil, which is particularly effective for medium- and high-voltage anodes, which has excellent durability by efficiently exposing and repairing the above-mentioned vacancy defects by a mild depolarization treatment. It was done.

[0004]

In order to achieve the above-mentioned object, the present invention is a first step of immersing a surface-treated high-purity aluminum foil in pure water for hydration treatment. And a second step of soaking in an aqueous solution containing a linear dicarboxylic acid, a third step of soaking in pure water for hydration treatment, and a depolarizing treatment step including heat treatment after anodizing treatment. The hydration treatment temperature in the first step and the third step is preferably 70 degrees Celsius, respectively.
It is more than once.

[0005]

However, in the above, the vacancy defects generated when the crystalline aluminum oxide is formed by the anodic oxidation treatment are the oxygen gas trapped in the vacancy defects in the depolarization treatment step including the heat treatment. When heated, the volume expands and the oxide layer on the surface layer of the vacancy defects is destroyed to expose the vacancy defects. The volume expansion in the above becomes more remarkable as the temperature becomes higher, and the effect of exposing the vacancy defects becomes greater, but the temperature cannot be raised to a high temperature beyond the melting point of the metallic aluminum as the base, and 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, and the treatment of immersing in the aqueous solution of the linear dicarboxylic acid is inserted therebetween, so that the hydrated film formed by the hydration treatment in the previous stage is inserted. The linear dicarboxylic acid is adsorbed on the surface of, and a new hydrated film is formed on the front side of this adsorption layer by the hydration treatment in the latter stage. That is, a hydrated film containing a linear dicarboxylic acid is formed in the middle part of the hydrated film, and an anodizing treatment is performed on this hydrated film to produce a crystalline oxide containing a linear dicarboxylic acid in the middle part. It

Then, when the crystalline oxide is subjected to heat treatment, the linear dicarboxylic acid taken in the middle portion is thermally decomposed to mainly generate carbon dioxide gas. This thermal decomposition is unlikely to occur when the linear dicarboxylic acid is incorporated in the crystal, and is likely to occur when it is present on the surface of the pores,
Therefore, by the heat treatment, the expansion of oxygen gas in the vacancy defects and the generation of carbon dioxide gas due to the decomposition reaction of the linear dicarboxylic acid can realize the exposure of the vacancy defects extremely efficiently.

Particularly in the present invention, the oxide containing the linear dicarboxylic acid is formed in the intermediate layer because the positions of the vacancy defects are concentrated in this portion, and the thermal decomposition and the volume expansion are caused in this portion. The effect cannot be fully exerted unless the above occurs, and the immersion treatment in an aqueous solution containing a linear dicarboxylic acid causes thermal decomposition into carbon dioxide at a relatively low temperature, which causes significant volume expansion and anodic oxidation. It is selected because it does not interfere with the electrochemical reaction in the process.

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

The high-purity aluminum foil that can be used is preferably 99.99% or more, which is usually used, but if it can be surface-expanded for medium- and high-voltage electrolytic capacitors, it is 99.9% or more. Even if it is of aluminum purity, it is possible to achieve the intended purpose sufficiently.

[0010]

Embodiments of the present invention will be described in detail below in relation to comparative examples. (Example 1) A surface-treated 99.99% or more high-purity aluminum foil was immersed in pure water at 95 ° C for 5 minutes, and then immersed in a 5% oxalic acid aqueous solution at 85 ° C for 5 minutes. And again immersed 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.
^After the formation voltage of 400V was anodized and increased to 400V, the voltage was kept constant for 15 minutes, the leakage current was reduced, and then heat treatment was performed at 520 ° C for 5 minutes in the atmosphere, and again under the same conditions. Anodization was performed, and the amount of electricity and withstand voltage characteristics at this time were measured. Next, this formed foil was boiled in pure water for 2 hours for 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 surface-expansion treatment was immersed in pure water at 95 ° C for 2 minutes, and then 6
Immersion treatment was carried out for 5 minutes in a 5% aqueous succinic acid solution at 0 ° C. and again for 5 minutes in pure water at 95 ° C., and then 20 mA / cm 2 in a 7 wt% boric acid aqueous solution at 85 ° C.
^2. Anodizing the formation voltage of 400V and raising to 400V, holding the constant voltage for 15 minutes to reduce the leakage current, heat treatment at 520 ° C for 5 minutes in the atmosphere, and again under the same conditions. Was anodized and the amount of electricity and withstand voltage characteristics at this time were measured. Next, this formed foil was boiled in pure water for 2 hours for 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 illustrates a case where the hydration treatment in Example 1 was performed only once and the “step of immersing in oxalic acid aqueous solution at 85 ° C. for 5 minutes for 5 minutes” was omitted. are doing. That is, the high-purity aluminum foil subjected to the surface expansion treatment is immersed in pure water at 95 ° C. for 10 minutes,
Anodization was performed at a formation voltage of 400 V at 20 mA / cm ² in a 7 wt% boric acid aqueous solution at 85 ° C., and after rising to 400 V, a constant voltage was maintained for 15 minutes to reduce the leakage current, and then at 520 ° C., 5 The heat treatment for 1 minute was performed in the air atmosphere, the anodic oxidation was performed again under the same conditions, and the amount of electricity and the withstand voltage characteristic at this time were measured. Next, this formed foil was boiled in pure water for 2 hours for 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 illustrates the case where the latter hydration treatment in Example 1 is omitted. That is, the high-purity aluminum foil that has been subjected to surface expansion treatment is heated to 95 ° C.
After immersing in pure water for 10 minutes, immersing in 5% oxalic acid aqueous solution at 85 ° C for 5 minutes
Formation voltage 400 V of 20 mA / cm ^{2 in} aqueous boric acid solution
Anodic oxidation was performed, and after the voltage was raised to 400 V, a constant voltage was maintained for 15 minutes to reduce the leakage current and then 520 ° C.
A heat treatment for 5 minutes was performed in an air atmosphere, anodization was performed again under the same conditions, and the amount of electricity and withstand voltage characteristics at this time were measured. Next, this formed foil was boiled in pure water for 2 hours to carry out an accelerated deterioration test, and then the withstand voltage characteristic was measured and compared with the value before the accelerated deterioration.

Comparative Example 3 In Comparative Example 3, the step of “immersing in 5% succinic acid aqueous solution at 60 ° C. for 5 minutes” in Example 2 was carried out by adding “85 ° C., 8% aqueous boric acid solution”. 5
The case where it replaces with the process of "dipping treatment for minutes" is illustrated.
That is, the high-purity aluminum foil subjected to surface expansion treatment,
After immersing in pure water at 95 ° C for 2 minutes, immersing in 8% boric acid aqueous solution at 85 ° C for 5 minutes, immersing again in pure water at 95 ° C for 5 minutes, and then immersing at 85 ° C 7 wt% of
Formation voltage 400 V of 20 mA / cm ^{2 in} aqueous boric acid solution
Anodic oxidation was performed, and after the voltage was raised to 400 V, a constant voltage was maintained for 15 minutes to reduce the leakage current and then 520 ° C.
A heat treatment for 5 minutes was performed in an air atmosphere, anodization was performed again under the same conditions, and the amount of electricity and withstand voltage characteristics at this time were measured. Next, this formed foil was boiled in pure water for 2 hours for 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 clear from the above results, in any of the examples, the amount of electricity when reanodized was as follows:
It is extremely large compared to any of Comparative Examples 1 to 3, and it can be understood that the effect of exposing the vacancy defects by the heat treatment is remarkable. Further, even after the accelerated deterioration test by boiling boiling for 2 hours in pure water, no decrease in withstand voltage characteristics was observed. Further, even when the dipping treatment is carried out 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 carried out. Also in the case of Comparative Example 3 which was inserted in the middle of the hydration treatment classified into No. 3, no effect was obtained.

The treatment temperature, treatment time and liquid concentration in the above Examples 1 and 2 are the most preferable conditions for the linear dicarboxylic acid used, and these conditions differ depending on the type of linear dicarboxylic acid. .
Further, when the temperature of the hydration treatment is 70 ° C. or lower in the first step and the third step, it takes a long time to produce a hydrate, and workability is lost. Therefore, the hydration temperature is preferably at least 70 ° C. or higher in both the first step and the third step. In addition, 52 for exposing the current density and the formation voltage in the anodizing treatment and the vacancy defects.
The heat treatment conditions of 0 ° C. and 5 minutes are based on the known conditions that have been conventionally practiced.

[0018]

As described above, according to the present invention, since the dipping treatment step with the linear dicarboxylic acid aqueous solution is inserted between the hydration treatment steps before and after, the vacancy defects in the depolarization step due to the heat treatment are The exposure is remarkably promoted, 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 in which the amount is remarkably improved.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takashi Kajiyama 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Technical Center

Claims (2)

[Claims] 1. A first step of immersing a high-purity aluminum foil subjected to surface expansion treatment in pure water for 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 for hydration treatment,
A method for forming an electrode foil for a medium-high voltage aluminum electrolytic capacitor, comprising a depolarization treatment step including heat treatment after anodizing treatment. 2. The method for forming an electrode foil for a medium-high pressure aluminum electrolytic capacitor according to claim 1, wherein the hydration treatment temperature in each of the first step and the third step is 70 ° C. or higher.