JP2000228333A - Manufacture of aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase capacitance by subjecting an aluminum foil to a final annealing step after subjecting the aluminum foil obtained by hot rolling and cold rolling to an electrolytic etching step at least once to thereby form a nucleus for forming an etched pit. SOLUTION: When an electrolytic etching step, i.e., an AC etching step in an aqueous solution containing a chloride is performed at least once before a final annealing step after an aluminum slab has been soaked, hot-rolled and cold-rolled into an aluminum foil, a porous etched layer wherein a great number of fine cubic etched cells are arranged in lines is formed. Part of this etched layer is destroyed and aluminum is thus dissolved out. By taking advantage of the fine asperities containing film defects of cells formed by the dissolved aluminum, an etched pit can be formed uniformly at a high density by DC electrolytic etching performed after the final annealing step. Recesses formed by preventing the uniform growth of an oxide film in the final annealing step are utilized as a nucleus for forming the etched pit. The aluminum foil wherein the nucleus for forming the etched pit is uniform at a high density can improve face enlargement ratio and increase capacitance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aluminum foil for an electrode of an electrolytic capacitor.

[0002] In this specification, the term "aluminum" is used to include both aluminum and its alloys.

[0003]

2. Description of the Related Art In recent years, with the miniaturization of electronic equipment, there has been a demand for an improvement in the capacitance of aluminum foil for an electrolytic capacitor electrode incorporated in electronic equipment.

Normally, an aluminum material used for an electrode foil is subjected to an etching process in order to increase the surface area and improve the capacitance. Since the surface area ratio increases as the depth of the etching pit formed by the etching process increases, various processes are performed on the aluminum material as a pre-process of the etching process in order to improve the etching suitability. For example, adjustment of (100) crystal orientation, adjustment of composition by adding trace impurities such as Pb and Bi to aluminum material, degreasing cleaning before final annealing, hydration treatment before final annealing, and crystallinity in final annealing These include an oxide film forming treatment and an oxidation treatment before final annealing (Japanese Patent Publication No. 58-34925, JP-A-3-122260, etc.).

However, simply increasing the depth of the etching pits does not sufficiently improve the area coverage of the electrode foil. To further improve the area coverage, local etching, unetching, and surface dissolution are reduced. Therefore, it is necessary to generate etching pits uniformly and densely on the etching surface. However, the various methods described above are not sufficient in that uniform etching pits are generated. For this reason, the present applicant has disclosed in
No. 5922 proposes to increase the surface area by controlling cylindrical or prismatic projections to be formed at specific intervals on the surface of an aluminum substrate used for an electrode foil.

[0006]

However, Japanese Patent Application Laid-Open No.
The aluminum foil described in No. 45922 can improve the surface area ratio by etching, and various methods of surface roughening are disclosed, but the surface is effectively roughened among various methods. The method or its conditions have not been sufficiently studied.

Therefore, as a result of intensive studies on more effective methods, conditions and forms of surface roughening, they became clear.

The present invention has been made in view of such technical background,
An object of the present invention is to provide a method for manufacturing an aluminum foil for an electrode of an electrolytic capacitor capable of increasing a capacitance by forming a nucleus of an etching pit most effectively in a foil from the viewpoint of improving etching characteristics.

[0009]

In order to achieve the above object, a method for producing an aluminum foil for an electrolytic capacitor electrode according to the present invention comprises the steps of: soaking an aluminum slab; performing hot rolling and cold rolling; After that,
The basic gist is that at least one electrolytic etching is performed and then final annealing is performed.

The electrolytic etching is AC electrolytic etching, AC waveform: sine wave, square wave or triangular wave, frequency: 20 to 1000 Hz, current density: 0.35
４4 A / cm ² , etching electricity: 0.2 to 10 C /
cm ² or DC electrolytic etching, containing 2 to 20 wt% of hydrochloric acid or chloride, or at least one of sulfuric acid, oxalic acid, phosphoric acid and boric acid in a total amount of 40 wt% or less. In the added liquid, it is preferable to perform the process under the conditions of a current density of 0.05 to 0.4 A / cm ² and an electric charge of etching of 0.1 to 5 C / cm ² .

According to the present invention, electrolytic etching is performed before the final annealing, so that fine dents are uniformly and densely formed on the surface of the foil, and the uniform growth of the oxide film is prevented in the subsequent final annealing step. The formed dents are used as nuclei for generating etching pits. In an aluminum foil in which nuclei of etching pits are formed uniformly and at a high density, the capacitance can be increased by ensuring the improvement of the surface area by etching the aluminum foil.

The fine dents for obtaining such an effect have an average circle equivalent diameter of 0.3 to 3 μm and a depth of 0.3 to 5 μm.
μm and a density of 10,000 to 200,000 particles / mm ² are desirable. It should be noted that a depression having an average circle equivalent diameter of 0.3 μm and a depth of 0.3 μm or less is not preferable because it does not become a starting point of a pit generation nucleus.
A pit having a depth of more than 5 μm is not preferable because pits in DC etching after annealing become non-uniform.

[0013] The size and density depressions in the above range are formed by performing at least one electrolytic etching under one of the following two conditions before final annealing.

The first method is AC electrolytic etching.
The reason for employing the AC electrolytic etching is as follows.
That is, when AC etching is performed in an aqueous solution containing chloride, a porous etch layer composed of a series of many fine cubic etch cells is generated. The inner surface of the etch cell is covered with hydroxide generated in the area of the cathode half cycle and anode coating generated in the area of the anode half cycle. These products and films act as protective films against the dissolution of aluminum, but some of them are destroyed and the aluminum is eluted to produce cells having the following defects. Utilizing the fine irregularities with this film defect,
Etching pits can be formed uniformly and at high density in DC electrolytic etching after final annealing. Since an etch layer having such an action is generated, AC electrolytic etching is employed as a means for forming a fine recess.

The reason why the AC waveform is a sine wave, a square wave, or a triangular wave is to use an alternating current of the anode and the cathode for generating the above-described irregularities having the defect. If the frequency is less than 20 Hz, an increase in capacitance cannot be expected due to the small number of dents formed.
If z exceeds z, the dent becomes coarse and is formed non-uniformly, so that an increase in capacitance cannot be expected. Therefore, the frequency needs to be 20-1000 Hz, with a preferred lower limit of 30 Hz and a preferred upper limit of 800 Hz. Current density is less dents are formed to cause the etch pits uniformly is less than 0.35A / cm ^2, exceeds 4A / cm ^2, since the recess is formed nonuniformly becomes coarse, a recess Poor uniform effect. Therefore, the current density needs to be 0.35 to 4 A / cm ^2, and a preferable lower limit is 0.4 A / cm ² . If the amount of etching electricity is less than 0.2 C / cm ² , the effect of uniformly forming a dent is still poor, and the amount of etching electricity is 10 C / c 2.
If it exceeds m ² , dents are formed to be coarse and non-uniform, and in the etching treatment after the final annealing, the growth of pits in the direction perpendicular to the etched surface is hindered, which leads to dissolution over the entire surface and uneven dissolution. Accordingly, the amount of etching electricity is 0.2 to 10 C
/ Cm ^2, and a preferred lower limit is 0.3 C
/ Cm ² , and a preferred upper limit is 3 C / cm ² .

The composition of the AC electrolytic etching bath is not limited, but may be hydrochloric acid, or sulfuric acid, oxalic acid, or hydrochloric acid.
A mixed acid to which phosphoric acid and boric acid are added can be recommended, and a bath temperature of 20 to 80 ° C. can be recommended.

The second method is DC electrolytic etching.
DC electrolytic etching is employed for the following reasons.
That is, even in DC etching, an anode film is formed on the aluminum foil surface. This anode film acts as a protective film against the dissolution of aluminum, but a part of the anode film is broken and aluminum is eluted to form pits.
Therefore, a film defect occurs at the pit generating portion. Utilizing the fine irregularities having this film defect, etching pits can be formed uniformly and at a high density in DC electrolytic etching after final annealing.

The electrolytic bath for DC etching contains a solution containing 2 to 20% by weight of hydrochloric acid or chloride, or a solution containing at least one of sulfuric acid, oxalic acid, phosphoric acid and boric acid in a total amount of 40% by weight or less. . When the concentration is defined as less than 2 wt%, no fine dents are generated and 20 wt%
%, The entire surface is dissolved to inhibit formation of fine and high-density dents. The preferred lower limit of the concentration of hydrochloric acid or chloride is 3 wt%, and the preferred upper limit is 15 wt%.
%. The addition of at least one of sulfuric acid, oxalic acid, phosphoric acid, and boric acid to these liquids promotes the generation of fine dents.
If it exceeds, the entire surface is dissolved. The preferred lower limit of the total amount of these acids is 3 wt%, and the preferred upper limit is 30 wt%. Further, the current density is set at 0.0 to secure the number of occurrences of fine dents and to prevent the entire surface from melting.
5 to 0.4 A / cm ² , preferably 0.1 A
/ Cm ² , and a preferred upper limit is 0.3 A / cm ² . When the amount of etching electricity is less than 0.1 C / cm ² , the number of fine dents is small, and when it exceeds 5 C / cm ² , the length of the dent becomes large.
The range is ² . A preferred lower limit of the amount of etching electricity is 1 C / cm ² , and a preferred upper limit is 5 C / cm ² . When the liquid temperature is lower than 50 ° C., the number of fine dents is small, and when the liquid temperature is higher than 95 ° C., the entire surface is dissolved.
~ 95 ° C is preferred. A particularly preferred lower limit of the liquid temperature is 60
° C, and a particularly preferred upper limit is 85 ° C.

The number of times of such AC or DC electrolytic etching may be one, but may be two or more times in order to further improve the formation state of the nuclei of the etching pits. Further, if necessary, before electrolytic etching, a pretreatment for removing an oxide film on the foil surface and remaining rolling oil may be performed.

The conditions for soaking, hot rolling, cold rolling, and final annealing are not limited, and any conventional method may be used. Further, the chemical composition of the foil is not limited, and high-purity aluminum usually used as a foil material is preferable.
Those having a content of 99 wt% or more are preferred.

[0021]

Next, specific examples of the method for producing an aluminum foil for an electrolytic capacitor electrode of the present invention will be described in detail.

First, an aluminum slab having a purity of 99.99 wt% was sequentially subjected to facing, hot rolling and cold rolling by a conventional method to produce a foil having a thickness of 100 μm. In this experimental example A, AC electrolytic etching was performed before final annealing in Experimental example A, and in direct current electrolytic etching before final annealing in Experimental example B, an aluminum foil for an electrolytic capacitor electrode was produced, and the capacitance was compared.

(Experimental example A) 50 ° C., 10% hydrochloric acid + 0.5
AC electrolytic etching was carried out in an electrolytic bath containing 2% sulfuric acid under the conditions shown in Table 1. This AC electrolytic etching was not performed for Comparative Example 3. Then, these foils were subjected to final annealing at 500 ° C. for 5 hours in an inert gas to obtain aluminum foil for an electrolytic capacitor electrode.

For these aluminum foils, a bath temperature of 7
In a mixed acid bath of 5 ° C., 5% hydrochloric acid + 10% sulfuric acid, DC electrolytic etching was performed under the conditions of a current density of 0.2 A / cm ² and 100 seconds, and chemical etching was further performed with the same solution for 10 minutes. Next, a chemical conversion treatment was performed at 350 V in a boric acid bath, and the capacitance was measured. The capacitance was 1 in Comparative Example 1.
It was relatively evaluated as 00%. Table 1 shows the results.

[0025]

[Table 1]

(Experimental Example B) DC electrolytic etching was performed in an electrolytic bath having the composition and temperature shown in Table 2 under the conditions shown in Table 3. In Comparative Example 35, this DC electrolytic etching was not performed. Then, these foils were subjected to final annealing at 500 ° C. for 5 hours in an inert gas to obtain aluminum foil for an electrolytic capacitor electrode.

[0027]

[Table 2]

For these aluminum foils, a bath temperature of 7
In a mixed acid bath of 5 ° C., 5% hydrochloric acid + 10% sulfuric acid, DC electrolytic etching was performed under the conditions of a current density of 0.2 A / cm ² and 100 seconds, and chemical etching was further performed with the same solution for 10 minutes. Next, a chemical conversion treatment was performed in a boric acid bath at 350 V, and the capacitance was measured. The capacitance was 1 in Comparative Example 35.
It was relatively evaluated as 00%. Table 3 shows the results.

[0029]

[Table 3]

From the results in Tables 1 and 3, it was confirmed that the capacitance could be increased by performing the electrolytic etching under the predetermined conditions before the final annealing.

[0031]

As described above, the method for producing an aluminum foil for an electrolytic capacitor electrode according to the present invention comprises the steps of: soaking an aluminum slab; performing hot rolling and cold rolling to obtain an aluminum foil; Since the foil is subjected to at least one electrolytic etching and then subjected to final annealing, a state in which nuclei of etching pits are uniformly and densely formed on the foil surface is obtained. Thus, the capacitance can be increased.

In particular, the electrolytic etching is AC electrolytic etching, AC waveform: sine wave, square wave or triangular wave, frequency: 20 to 1000 Hz, current density: 0.35
４4 A / cm ² , etching electricity: 0.2 to 10 C /
cm ² , or DC electrolytic etching, containing 2 to 20 wt% of hydrochloric acid or chloride, or at least one of sulfuric acid, oxalic acid, phosphoric acid and boric acid in a total amount of 40 wt% or less. When the current density: 0.05 to 0.4 A / cm ² and the amount of etching electricity: 0.1 to 5 C / cm ^{2 in} the added liquid, the formation of the nuclei of the etching pits is particularly uniform. The density is increased, and the increase in capacitance is assured.

Continued on the front page (72) Inventor Kazuhisa Soumiya 6,224 Kaiyamacho, Sakai City Showa Aluminum Co., Ltd. (72) Inventor Kiminori Sugimoto 6,224 Kaiyamacho Sakai City, Showa Aluminum Corporation (72) Invention Person Tadao Fujihira, 224 Kaiyamacho, Sakai-shi, Showa Aluminum Co., Ltd.

Claims (3)

[Claims] An aluminum slab is soaked in heat, hot-rolled and cold-rolled to form an aluminum foil, and the aluminum foil is subjected to at least one electrolytic etching, followed by final annealing. Of producing aluminum foil for electrolytic capacitor electrodes. 2. The method according to claim 1, wherein the electrolytic etching is AC electrolytic etching, and the AC waveform is a sine wave, a square wave, or a triangular wave.
Frequency: 20-1000 Hz, current density: 0.35-4
A / cm ² , etching electricity: 0.2-10 C / cm
^2. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the method is carried out under the conditions of ² . 3. The electrolytic etching is a direct current electrolytic etching, containing 2 to 20% by weight of hydrochloric acid or chloride, or at least one of sulfuric acid, oxalic acid, phosphoric acid and boric acid in a total of 40% by weight or less. 2. The method according to claim 1, wherein the step (a) is performed in a solution to which is added a current density of 0.05 to 0.4 A / cm ² and an electric charge of etching of 0.1 to 5 C / cm ^2.
3. The method for producing an aluminum foil for an electrolytic capacitor electrode according to item 1.