JP2696882B2 - Manufacturing method of electrode foil for aluminum electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor.

Conventional technology Electrode foil for aluminum electrolytic capacitors (hereinafter referred to as electrode foil)
In order to reduce the size and cost of a capacitor, an aluminum foil whose surface area is enlarged by electrochemically or chemically etching an aluminum foil is used. Various etching methods have been studied to increase the surface area, and conventionally, for this purpose, etching has been divided into two stages. That is, in the first-stage etching, an etching pit is generated using an aqueous solution obtained by adding a porous film-forming acid to hydrochloric acid, and then, in the second-stage etching,
Cl ^- has the aim of surface area enlarged by growing etched bits with a neutral salt solution containing.

Problems to be Solved by the Invention In the conventional method, there was a problem in the relationship between the effect of etching to increase the surface area and the reduction in aluminum dissolution. That is, even if the aluminum dissolution weight loss is increased by the progress of etching, not only etching pits do not grow, but also the surface dissolution proceeds and the surface area is not proportionally increased, not only does not contribute to the increase of the capacitance, but also the electrode foil. However, there is a disadvantage that the mechanical strength is also impaired. Therefore, as the electrode foil, the effect of increasing the surface area is insufficient in promoting the miniaturization and cost reduction of the aluminum electrolytic capacitor, which has been a problem.

An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which can increase the surface area while maintaining the mechanical strength of the electrode foil. .

Means for Solving the Problems In order to achieve the above object, a method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to the present invention comprises the steps of:
In an etching method performed in two stages of steps, before the second stage etching and in the middle of the second stage etching,
Intermediate treatment for electrochemically or chemically forming a surface oxide film is performed at least once in an aqueous solution containing 0.01 to 20% of NH ₄ ⁺ or Na ⁺ , and the second-stage etching includes sodium chloride, ammonium chloride, Cl of potassium chloride ^- of neutral salts containing at least one kind of 0.1 to 10
% Is performed in an aqueous solution containing 0.1% by weight.

According to the above-described manufacturing method, etching pits can be grown without losing surface and mechanical strength due to the progress of etching, and the surface area can be increased in proportion to aluminum electrolytic weight loss.

 The operation of each etching step will be described below.

(First Stage Etching) In order to form etching pits with high density and uniformity, it is necessary to have an appropriate hydrochloric acid concentration and an appropriate addition of an acid capable of forming a porous film. If the hydrochloric acid concentration is less than 2%, the etching effect is small, while if it exceeds 15%, the entire surface is dissolved. Therefore, the range of 2 to 15% is preferable, and the range of 3 to 8% is particularly preferable. The amount of the acid that can form the porous film is either sulfuric acid, oxalic acid, or phosphoric acid.
If it is less than 0.01, the formation of the porous film is insufficient, while if it exceeds 5%, the film formation reaction becomes strong, and the growth of the generated etching pits in the length direction is suppressed. Therefore, a range of 0.01 to 5% is preferable, and a particularly preferable range is 0.05 to 1%. Within such a preferred range, a porous film having high density and uniform pores is formed on the aluminum surface, and the pores are eroded by Cl ⁻ to form etching pits. Since the other parts are covered with the film, surface dissolution is suppressed, and as a result, high-density and uniform etching pits are generated. Etch temperature also has an important effect, 50 ° C
Below 100 ° C., the etching effect is small, while above 100 ° C., the entire surface is dissolved. Therefore, the range of 50 to 100 ° C is preferable, and the range of 70 to 90 ° C is particularly preferable.
When the current density is less than 3 A / dm ² , the etching effect is small. On the other hand, when the current density exceeds 70 A / dm ² , the entire surface is dissolved. Therefore, the range of 3 to 70 A / dm ² is preferable, and the range of 10 to 40 A / dm ² is particularly preferable.

(Intermediate Processing) In the present invention, intermediate processing is performed before the second-stage etching after the first-stage etching or in the middle of the second-stage etching. This process inherits the fact that the surface area expansion has been performed in proportion to the aluminum dissolution loss due to the generation of new etching pits in the first stage etching, and also in the second stage etching, the surface area expansion does not saturate together with the aluminum dissolution loss, In order to further increase the proportion, in the second stage etching, the etching is concentrated and the etching pits become excessively large, the adjacent etching pits are destroyed, or the surface is prevented from dissolving. Have

That is, in the present invention, a surface oxide film is electrochemically or chemically formed on the aluminum surface in the middle of the etching so that a new etching pit can be uniformly generated and grown even in the second stage etching, and the oxide film is By etching again while protecting the already formed etching pits, new etching pits are formed to increase the surface area. In the present invention, in order to form a surface oxide film on the aluminum surface, electrochemical or chemical treatment is performed in an aqueous solution containing NH ₄ ⁺ and Na ⁺ , and the concentration is less than 0.01%. In this case, the effect of forming a surface oxide film is small. On the other hand, if it exceeds 20%, the surface oxide film is formed too much, so that etching pits are less likely to occur when etching and concentration tends to occur. Therefore, the concentration is preferably in the range of 0.01 to 20%, particularly preferably 0.1 to 20%.
It is in the range of ~ 10%.

When the liquid temperature is 40 ° C. or lower, the effect of forming a surface oxide film is small, while when the temperature exceeds 90 ° C., the surface oxide film is formed too much, and the effect of generating etching pits is reduced. Therefore, the liquid temperature is preferably in the range of 40 to 90 ° C., particularly preferably 60 to 90 ° C.
It is in the range of ~ 80 ° C. Here, the intermediate treatment according to the present invention can be carried out many times before the second stage etching or in the middle of the second stage etching, and by repeating the treatment, the surface area increasing effect is proportional to the processing circuit. Increase.

(Second-stage etching) The second-stage etching is performed after the first-stage etching.
In order to further generate etching pits while suppressing surface dissolution in combination with the intermediate treatment and simultaneously grow the etching pits generated in the first-stage etching, Cl such as sodium chloride, ammonium chloride, potassium chloride or the like is used.
^- it is necessary to etching in an aqueous solution of neutral salt containing. In any of these neutral salt aqueous solutions, if the concentration is less than 0.1%, the etching effect is small.
If it exceeds 0%, the entire surface is dissolved.

Therefore, the concentration is preferably in the range of 0.1 to 10%, and particularly preferably in the range of 1 to 3%. Within such a preferred range, etching pits can be newly generated with almost no surface melting, and at the same time, etching pits generated by the first-stage etching can be grown. In the second stage etching, the liquid temperature is preferably in the range of 50 to 100 ° C., particularly preferably in the range of 70 to 90 ° C., and the current density is preferably in the range of 3 to 70 A / dm ² , as in the first stage etching. Particularly preferred is a range of 4 to 20 A / dm ² .

According to the etching of the present invention, an electrode foil for an aluminum electrolytic capacitor having a very large surface area enlarging effect, in which uniform etching pits having a high density and an appropriate etching pit diameter are generated in proportion to the aluminum dissolution loss, is produced. Is possible.

Examples Examples of the present invention will be described below together with comparative examples.

As a sample, high-purity annealed aluminum having a purity of 99,99% and a thickness of 100 μm was used.

<Comparative Example> The first-stage etching was performed by applying a direct current having a current density of 20 A / dm ² for 90 seconds with an aqueous solution at a liquid temperature of 80 ° C. to which 7% of hydrochloric acid and 0.1% of sulfuric acid were added. Sodium 5
% Was added and a direct current having a current density of 10 A / dm ² was applied for 320 seconds with an aqueous solution at a liquid temperature of 80 ° C.

<Example> After the first stage etching was performed in the same manner as in the comparative example,
The immersion treatment is performed for 40 seconds in a 0.1% aqueous solution of ammonium formate at 90 ° C., and the second stage etching is performed in the same manner as in the comparative example.

After forming the etching foils of the above two examples in an aqueous boric acid solution at 370 V, the capacitance and bending strength (1.0R, 200
Table 1 shows the results of measurement of g load and bending angle of 90 °.

Effect of the Invention As described above, the method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to the present invention includes an etching method in which etching is performed in two stages, a first stage and a second stage, wherein the etching is performed before the second stage etching and in the second stage. NH ₄ ⁺ or Na in the middle of the step etching
^In an aqueous solution containing 0.01 to 20% ⁺ , an intermediate treatment for electrochemically or chemically forming a surface oxide film is performed at least once or more, and the second-stage etching is performed by using a chloride such as sodium chloride, ammonium chloride, potassium chloride or the like. ^- among the neutral salts containing, which was to perform the direct current etching in an aqueous solution comprising at least one of 0.1% to 10%, the intermediate processing surface NH ₄ ⁺ or Na ⁺ and in an aqueous solution containing 0.01% to 20% Since the oxide film is formed electrochemically or chemically, an excellent effect of forming a surface oxide film is obtained, and as a result, etching pits can be efficiently generated during etching. Things. Further, since the aqueous solution of the second-stage etching contains a neutral salt, it is possible to generate and grow etching pits while suppressing surface dissolution with the neutral salt, thereby increasing the surface area. You can do it.

The intermediate treatment in an aqueous solution containing 0.01 to 20% of NH ₄ ⁺ or Na ⁺ is performed not only in the middle of the second etching but also before the second etching.
Before the second-stage etching, after the first-stage etching is completed, the surface of the aluminum foil is in an active state without a film. In this state, NH ₄ ⁺ or Na ⁺ is added.
By performing an intermediate treatment in an aqueous solution containing 0.01 to 20% to form a surface oxide film, the effect of enlarging the surface area in the subsequent second stage etching is further enhanced, and the capacitance is maintained while maintaining the mechanical strength. It is possible to obtain an electrode foil for an aluminum electrolytic capacitor having a large value.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Naomi Endo 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (72) Inventor Nobuyoshi Kanzaki 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-169131 (JP, A) JP-A-57-131399 (JP, A )

Claims (2)

(57) [Claims] In an etching method in which etching is performed in two stages, a first stage and a second stage, NH ₄ ⁺ or Na ^{+ is} added before the second stage etching and in the middle of the second stage etching.
Is carried out at least once in an aqueous solution containing 0.01 to 20% of the surface oxide film electrochemically or chemically, and the second-stage etching is performed by using Cl ⁻ such as sodium chloride, ammonium chloride or potassium chloride. A method for producing an electrode foil for an aluminum electrolytic capacitor, comprising performing DC etching in an aqueous solution containing 0.1 to 10% of at least one of neutral salts containing 2. The first stage etching includes performing direct current etching in an aqueous solution containing 0.01% to 5% of at least one of a porous film-forming acid composed of 2 to 15% of hydrochloric acid, sulfuric acid, oxalic acid and phosphoric acid. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein