JP3276089B2 - Method for producing anode foil for electrolytic capacitor - 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 manufacturing an anode foil for an electrolytic capacitor having a large capacitance.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electric and electronic equipment, the miniaturization of electrolytic capacitors has also been required at the same time.
In order to reduce the size of the electrolytic capacitor, it is particularly necessary to increase the surface area of the anode foil and increase the capacitance per unit area.

Conventionally, in an electrolytic capacitor using an aluminum foil, electrolytic etching has been performed in order to increase the surface area of the anode foil, and a large number of concave portions (etching pits) progressing in the thickness direction have been provided on the surface. Various studies have been made on the electrolytic etching process.

[0004] The present applicant has also conducted various studies on electrolytic etching, and as a result, has found that the surface condition of the aluminum foil during electrolytic etching has a great effect. That is, it has been found that the less the rolling oil or the like adheres to the surface of the aluminum foil and the cleaner it is, the better the electrolytic etching characteristics become and the more the anode foil has a large capacitance. Based on this finding, the present applicant has filed a patent application for a technology for cleaning the surface of an aluminum foil (see Japanese Patent Publication No. 5-12436).

[0005]

SUMMARY OF THE INVENTION The present invention relates to an improvement of the invention according to the above-mentioned patent application, in which the surface of an aluminum foil is cleaned and the starting point of an etching pit formed on the aluminum foil surface by electrolytic etching. By providing such fine irregularities, the electrostatic capacity of the anode foil for an electrolytic capacitor can be greatly increased by electrolytic etching.

[0006]

That is, according to the present invention, an aluminum foil is coated with an alkali metal compound selected from the group consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate. After performing the primary treatment with the first surface treatment agent containing, secondary with a second surface treatment agent containing dibasic sodium phosphate or tribasic sodium phosphate, an anionic surfactant, and an organic reducing agent The present invention relates to a method for producing an anode foil for an electrolytic capacitor, which comprises performing a treatment and then performing an electrolytic etching.

[0007] The first surface treatment agent used in the present invention contains an alkali metal compound. As the alkali metal compound, sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate are used alone or in combination. In particular, it is preferable to use sodium hydroxide as the alkali metal compound. The first surface treatment agent is generally used in the form of an aqueous solution, and is preferably used in the form of an aqueous solution in which the concentration of the alkali metal compound is adjusted to about 0.1 to 10% by weight. Further, an anionic surfactant, an organic reducing agent, and the like described below may be added to the first surface treatment agent.

[0008] The surface of the aluminum foil is subjected to a primary treatment with the first surface treatment agent, the surface is cleaned, and then the surface of the aluminum foil is secondarily treated with a second surface treatment agent. The second surface treating agent contains dibasic sodium phosphate or tribasic sodium phosphate, an anionic surfactant, and an organic reducing agent. The second surface treatment agent also
It is generally used in the form of an aqueous solution, and it is preferable to use the compound in the form of an aqueous solution in which the total concentration of these compounds is adjusted to about 5 to 50% by weight.

The anionic surfactant contained in the second surface treating agent includes fatty acids, alkylbenzene sulfonates, alkyl sulfonates, α-olefin sulfonates, dialkyl sulfosuccinates, α-sulfonated salts. Fatty acid salt, alkyl naphthalene sulfonate, N-methyl-N-oleyl taurine, alkyl phosphate, alkyl sulfate, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, polyoxyethylene alkyl Various substances such as phenyl ether sulfate, naphthalene sulfonate formaldehyde condensate, and polyoxyethylene alkyl ether sulfate are used.

As the organic reducing agent contained in the second surface treating agent, any organic reducing agent can be employed as long as it has a function of preventing oxidation of the surface of the aluminum foil. Specifically, monoethanolamine, ethylenediamine, hydrazine, formaldehyde, acetaldehyde, L-ascorbic acid and the like are used.

In the second surface treating agent, the mixing ratio of the anionic surfactant or the organic reducing agent with respect to the dibasic sodium phosphate or the tribasic sodium phosphate is not critically determined. For 100 parts of sodium or tribasic sodium phosphate (parts by weight, the same applies hereinafter), about 50 to 500 parts of an anionic surfactant and about 20 to 450 parts of an organic reducing agent are preferred. If the amount of the anionic surfactant is less than 50 parts, the surface of the aluminum foil tends not to be uniformly treated, and if it exceeds 500 parts, the effect tends to reach its limit. If the amount of the organic reducing agent is less than 20 parts, the ability to prevent the oxidation of the aluminum foil surface tends to be weak, depending on the reducing power of the reducing agent. It tends to be saturated.

After the surface of the aluminum foil is secondarily treated with the second surface treating agent, the aluminum foil is etched by a conventionally known method to obtain an anode foil for an electrolytic capacitor.

[0013]

【Example】

Examples 1 to 6 An aluminum foil having a thickness of 0.100 mm and a purity of 99.99% was first
It was treated with a first surface treating agent (aqueous solution) containing sodium hydroxide (A component) at the ratio shown in Table 1. Then, it was treated with a second surface treating agent containing sodium dibasic phosphate (component B), sodium alkylnaphthalene sulfonate (component C) and monoethanolamine (component D) in the proportions shown in Table 1. Then, it was annealed at a high temperature in an inert gas atmosphere, and was subjected to a current density of 8A / 100c in a 5% hydrochloric acid aqueous solution at 75 ° C.
A DC current of m ² was passed to perform electrolytic etching for 500 seconds. Subsequently, a chemical conversion treatment was performed at a voltage of 375 V in a boric acid solution at 85 ° C. to form an anode foil. Then, the capacitance of the anode foil was measured by an AC bridge method (frequency: 120 Hz), and is shown in Table 1.

Example 7 An anode foil was prepared in the same manner as in Example 1 except that sodium carbonate (Component A) was used in place of sodium hydroxide (Component A) at the ratio shown in Table 1. The capacitance was measured.

Example 8 In place of dibasic sodium phosphate (component B), tribasic sodium phosphate (component B) was contained at the ratio shown in Table 1.
The anode foil was prepared and the capacitance was measured in the same manner as in Example 1, except that the types of the other components were not changed and the proportions were as shown in Table 1.

Example 9 An anode foil was prepared and the capacitance was measured in the same manner as in Example 7, except that the proportion of each component was as shown in Table 1.

Comparative Example 1 A single surface treatment was carried out on an aluminum foil having a thickness of 0.100 mm and a purity of 99.99% using a commercially available surface treating agent (Comparative Example 1, a 3% aqueous solution of Almeco 383, manufactured by Henkel Hakusui). Done.
After the surface treatment, the same treatment as in Example 1 was performed to form an anode foil, and the capacitance was measured.

[0014]

[Table 1]

As is clear from the results in Table 1, using the first surface treatment agent and the second surface treatment agent shown in the examples,
It can be seen that the anode foil obtained by subjecting the aluminum foil to electrolytic etching after treating the aluminum foil in two stages has an increased capacitance as compared with the conventional one. In particular, when sodium hydroxide is contained in the first surface treatment agent as a composition component, it can be seen that the capacitance is significantly increased.

[0016]

The operation of the present invention is not clear, but is presumed as follows. That is, when the aluminum foil surface is subjected to the primary treatment with the first surface treatment agent, the rolling oil or the like adhering to the aluminum foil surface can be satisfactorily removed, and then the aluminum foil surface is secondarily treated with the second surface treatment agent. It is presumed that when the treatment is performed, fine irregularities serving as starting points of etching pits are provided on the aluminum foil surface during electrolytic etching. For example, using a surface treatment agent obtained by mixing the components of the first surface treatment agent and the components of the second surface treatment agent,
If the surface of the aluminum foil is treated only once, the rolling oil and the like adhering to the surface of the aluminum foil can be satisfactorily removed, but fine irregularities serving as starting points of etching pits cannot be provided. That is, the present invention, on the surface of the aluminum foil, by performing the primary treatment with the first surface treatment agent, and then the secondary treatment with the second surface treatment agent, to exhibit the above-described unique action It is possible.

[0017]

Therefore, when electrolytic etching is performed on an aluminum foil that has been subjected to the primary treatment and the secondary treatment, etching pits are formed at a high density, so that a high capacitance anode foil can be obtained. This has the effect. That is, the anode foil for an electrolytic capacitor obtained by the method according to the present invention has an effect of increasing the capacitance as compared with the anode foil obtained by the conventional method.

Continuation of front page (58) Fields investigated (Int. Cl. ⁷ , DB name) C23G 1/14 C22F 1/04 C23F 1/20 C25F 3/04 H01G 9/055

Claims (1)

(57) [Claims] 1. A primary treatment of a surface of an aluminum foil with a first surface treating agent containing an alkali metal compound selected from the group consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate. After performing a secondary treatment with a second surface treating agent containing dibasic sodium phosphate or tribasic sodium phosphate, an anionic surfactant, and an organic reducing agent, and then performing electrolytic etching A method for producing an anode foil for an electrolytic capacitor, comprising: