JP2002246274A - Electrode foil for aluminum electrolytic capacitor and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the electrode foil for a high capacitance aluminum electrolytic capacitor by suppressing sub-pits spreading into branches in the surface layer of an aluminum foil, and its producing method. SOLUTION: A large number of main pits 1 are provided in the thickness direction from the surface by etching in the opposite sides of an aluminum foil 3 and sub-pits 2 are provided to spread into branches in the way and at the ends other than the surface layer of the main pits 1. Since sub-pits 2 spreading into branches are not formed in the surface layer of the aluminum foil 3, density of the sub-pits 2 effective for the capacitance can be increased and the electrode foil for a high capacitance aluminum electrolytic capacitor having a high mechanical strength can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high reliability of electronic equipment, there has been a strong demand from users for aluminum electrolytic capacitors to be miniaturized. As described above, it is necessary to increase the capacitance per unit area.

A general aluminum electrolytic capacitor is an anode foil having a dielectric oxide film formed by anodic oxidation on the surface of which an effective surface area is enlarged by etching an aluminum foil and a cathode foil having an effective surface area enlarged by etching an aluminum foil. Are wound through a separator to form a capacitor element, and the capacitor element is impregnated with a driving electrolyte, and the capacitor element is sealed in a metal case.

In this type of aluminum electrolytic capacitor,
In order to increase the capacitance or reduce the size, it is essential to increase the effective surface area of the anode foil and increase the capacitance per unit area. Etching technology to increase the effective surface area of the anode foil Is being actively developed.

[0005] The above-mentioned method of etching the anode foil is performed chemically or electrochemically in a hydrochloric acid aqueous solution to which an acid for forming a film such as sulfuric acid, nitric acid, phosphoric acid or oxalic acid is added. The etching method of the anode foil used is
Basically, a method consisting of a pre-etching step to generate main pits and a post-etching step to expand the main pits to a diameter suitable for the working voltage of the aluminum electrolytic capacitor, how many main pits are generated, It is important to efficiently expand the main pit.

As a technique for enlarging the effective surface area of the anode foil, for example, as in the technique described in Japanese Patent Application Laid-Open No. 7-272983, a first technique of electrochemically etching using a direct current in a hydrochloric acid aqueous solution or the like is used. Step etching step, a second etching step using a direct current in an aqueous solution of a neutral salt such as sodium chloride, and etching using a direct current in an aqueous solution containing at least one of hydrochloric acid, sulfuric acid and nitric acid It is described that the effective surface area of the anode foil and the mechanical strength can be improved by the manufacturing method including the third etching step.

[0007]

However, in the above-mentioned conventional technique for enlarging the effective surface area of the anode foil, the main pit formed in the first etching step is provided with sub-pits extending in the middle or at the end of the main pit in a branch shape. In the second-stage etching step for forming the pits, as shown in FIG. 2, a large number of sub-pits 5 extending in a branch shape from the middle of the main pit 4 are formed in the surface layer of the aluminum foil 6 even if the surface is not dissolved. There was a problem in that increasing the capacitance of the foil was hindered. In addition,
FIG. 2 is a schematic view showing a cross section of an etching pit formed on a conventional aluminum foil 6 by etching.

An object of the present invention is to solve the above-mentioned conventional problems. An electrode foil for an aluminum electrolytic capacitor which suppresses subpits extending in the form of a branch on the surface layer of an aluminum foil, has a high mechanical strength, and has a high capacitance is provided. It is intended to provide a manufacturing method.

[0009]

Means for Solving the Problems In order to achieve the above object, the present invention has the following arrangement.

According to the first aspect of the present invention, a plurality of main pits are provided on both surfaces of an aluminum foil in the thickness direction from the surface by an etching process, and the main pits except for the surface layer are formed in the middle and at the ends. In this configuration, the sub-pits extending in a branch shape are provided, and with this configuration, the sub-pits extending in a branch shape are not formed on the surface layer of the aluminum foil. This has the effect that the capacitance can be increased.

According to a second aspect of the present invention, in the first aspect of the present invention, the sub-pits are pits shorter than the main pits. With this configuration, the mechanical strength of the electrode foil for an aluminum electrolytic capacitor is reduced. It has the effect of being able to increase.

According to a third aspect of the present invention, there is provided a first etching step in which an aluminum foil is immersed in an etching solution of an acidic aqueous solution of hydrochloric acid and sulfuric acid or / and nitric acid and a direct current is applied to form main pits; Second etching in which a direct current is applied with a neutral salt etching solution to which an additive has been added in order to effectively generate sub-pits extending in a branch shape in the middle or at the end of the main pit except for the surface layer. And a third etching step for enlarging the diameters of the main pits and sub-pits. According to this method, the surface of the aluminum foil is covered with an oxidizing film, so that the surface of the aluminum foil is Without forming sub-pits extending in branches in the layer,
Since a large number of sub-pits can be generated in the depth direction of the main pit, there is an effect that an electrode foil for an aluminum electrolytic capacitor having high mechanical strength and high capacitance can be stably produced.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the additive comprises oxalic acid, citric acid, phosphoric acid,
At least one selected from boric acid, succinic acid, and malonic acid. The invention according to claim 5, wherein the concentration of the additive is in the range of 0.01 to 1.0%. This method has an effect that the effect obtained by the invention of claim 3 can be more effectively obtained.

[0014]

FIG. 1 is a schematic view showing a cross section of an etching pit of an electrode foil for an aluminum electrolytic capacitor according to an embodiment of the present invention. In the figure, 1 is a main pit extending from the surface of the aluminum foil 3 in the thickness direction.
Reference numeral 2 denotes sub-pits extending in a branch shape in the middle and at the end of the main pit 1 excluding the surface layer. With such a structure of the electrode foil for an aluminum electrolytic capacitor, the capacitance of the electrode foil can be increased and the mechanical strength can be increased.

In the above-mentioned method for manufacturing an electrode foil for an aluminum electrolytic capacitor, first, in a first etching step, the surface of the aluminum foil 3 is uniformly increased in density by increasing the density.
Is important. For this purpose, electrochemical etching is performed using an etching solution of an acidic aqueous solution to which hydrochloric acid and sulfuric acid or / and nitric acid are added.

The acidic aqueous solution has a hydrochloric acid concentration of 2 to 15%.
When the concentration is less than 2%, sufficient pits cannot be obtained, and when the concentration exceeds 15%, dissolution of the surface of the aluminum foil occurs. The preferred range is 4-12%.

The pit formation density can be further increased by adding sulfuric acid and / or nitric acid. This addition amount is preferably in the range of 0.1 to 15%.

The temperature of the etching solution of the acidic solution also has an important influence on the formation of the main pit 1. Temperature is 50 ° C
If it is less than 1, the generation density of the main pit 1 is low.
If the temperature exceeds 00 ° C., the surface of the aluminum foil 3 is melted, so that the temperature of the etching solution is preferably in the range of 50 to 100 ° C.

Next, the second etching step serves to increase the etching pit density by forming sub-pits 2 in the vertical direction on the main pit 1 formed in the first etching step.

The present invention regulates the formation of the sub-pits 2 in the second etching step. That is, a plurality of main pits 1 provided in the thickness direction from the surface by etching on both surfaces of the aluminum foil 3 are provided with sub-pits 2 extending in a branch shape in the middle and at the end of the main pit 1 excluding the surface layer. The configuration is as follows. Thus, an electrode foil for an aluminum electrolytic capacitor having high mechanical strength and high capacitance can be obtained.

The etching solution used in the second etching step is selected from oxalic acid, citric acid, phosphoric acid, boric acid, succinic acid and malonic acid in an aqueous solution of a neutral salt such as sodium chloride, ammonium chloride and potassium chloride. The etching is performed with an etching solution to which at least one or more of the main pits 1 are added, whereby the sub pits 2 extending in a branch shape can be formed in the middle and at the end of the main pit 1 excluding the surface layer.

The concentration of the neutral salt aqueous solution is 0.5 to 10%.
If the concentration is less than 0.5%, the elongation of the sub pit 2 is short, and if it exceeds 10%, a thick oxidized film is formed on the entire surface of the main pit 1 and the sub pit 2
Formation is inhibited. The concentration of the additive is 0.0
When the concentration of the additive is less than 0.01%, sub-pits 2 are formed in the surface layer of the aluminum foil 3, and the concentration of the additive is set to 1%.
If it exceeds 0%, the formation density of the sub-pits 2 will be low.

The temperature of the neutral salt aqueous solution has an important effect on the reaction with the aluminum foil 3. At 70 ° C. or lower, the etching reaction rate is slow, and the etching is difficult to be performed. Dissolution occurs, making it difficult to form sub-pits 2 in the vertical direction, which is the object of the present invention. Therefore, the etchant temperature is 7
0-95 ° C is a suitable range.

Incidentally, if necessary, an intermediate treatment may be performed before the second etching step. This intermediate treatment removes a non-uniform film on the surface of the aluminum foil 3 after the pre-etching step and activates the surface of the aluminum foil 3.

As the liquid used for the intermediate treatment, at least one kind of an acidic aqueous solution selected from hydrochloric acid, hydrofluoric acid and nitric acid is used, and the aluminum foil on which the main pits 1 are formed in the first etching step is used. 3 is immersed.
The acid concentration of this acidic aqueous solution is preferably in the range of 2 to 10%. If the acid concentration is less than 2%, the film is not sufficiently removed, and if it exceeds 10%, the surface of the aluminum foil 3 is dissolved. The temperature of the acidic aqueous solution is 50 to 90.
C. is preferred.

Next, in the third etching step, the main pits 1 and the sub pits 2 formed in the first etching step and the second etching step are
Is to increase the diameter while suppressing the dissolution of the surface.

The etchant used in the third etching step is preferably an etchant obtained by adding at least one of oxalic acid, chromic acid, acetic acid, phosphoric acid, citric acid and boric acid to either sulfuric acid or nitric acid. The concentration of this etching solution is preferably in the range of 0.1 to 5.0%.
If the concentration is less than 0.1%, the surface of the aluminum foil 3 will be dissolved, and if it exceeds 5.0%, an oxide film will be formed too much on the surface of the aluminum foil 3 and it will be difficult for the pit diameter to increase.

According to such a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, when the sub-pit 2 is formed in the second etching step, the aluminum foil 3 is etched by etching with a neutral salt aqueous solution containing an additive. Oxidized films having different thicknesses are formed on the surface of the main pit 1 and the surface of the main pit 1, so that a large number of sub-pits 2 extending in a branch can be generated in the middle and at the end of the main pit 1 excluding the surface layer. In addition, an electrode foil for an aluminum electrolytic capacitor having high mechanical strength and high capacitance can be stably produced.

Hereinafter, the present embodiment will be described in detail using examples.

(Example 1) Purity 99.98%, thickness 10
Using an aluminum foil of 0 μm, an acidic aqueous solution (hydrochloric acid concentration 10%,
The aluminum foil was immersed in an etching solution having a sulfuric acid concentration of 10%), and a direct current having a current density of 20 A / dm ² was applied to the aluminum foil for 25 minutes.
A main pit was formed by applying a voltage of 0 second for etching.

Next, as an intermediate treatment, the substrate was immersed in an aqueous solution of sulfuric acid having a temperature of 40 ° C. and a concentration of 0.5% for 60 seconds.

Next, at a temperature of 7 as a second etching step.
It was immersed in a neutral salt aqueous solution (sodium chloride 3.0%, oxalic acid 0.1%) at 0 ° C., and was subjected to etching by applying a direct current having a current density of 15 A / dm ² for 250 seconds to form sub-pits.

Next, at a temperature of 7 as a third etching step.
It was immersed in a 3% nitric acid aqueous solution at 0 ° C. and a direct current having a current density of 10 A / dm ² was applied for 600 seconds to enlarge the diameters of the main pits and sub pits. The anode foil was washed by washing in an aqueous solution of nitric acid having a concentration of 10% at 50 ° C. for 1 minute to produce an etched anode foil.

(Embodiment 2) In the first embodiment, the second
An etched anode foil was produced in the same manner as in Example 1 except that the neutral salt aqueous solution used in the etching step was replaced with a neutral salt aqueous solution of 3.0% potassium chloride and 0.1% oxalic acid.

(Embodiment 3) In the first embodiment, the second
An anode foil was etched in the same manner as in Example 1 except that the aqueous neutral salt solution used in the etching step was replaced with a neutral aqueous salt solution of 3.0% ammonium chloride and 0.1% oxalic acid.

(Embodiment 4) In the first embodiment, the second
An anode foil was etched in the same manner as in Example 1 except that the neutral salt aqueous solution used in the etching step was replaced with a neutral salt aqueous solution of 3.0% ammonium chloride and 0.2% boric acid.

(Embodiment 5) In the first embodiment, the second
An etched anode foil was prepared in the same manner as in Example 1 except that the aqueous neutral salt solution used in the etching step was replaced with a neutral salt aqueous solution of 3.0% ammonium chloride and 0.1% phosphoric acid.

(Embodiment 6) In the first embodiment, the second
An anode foil was etched in the same manner as in Example 1 except that the aqueous neutral salt solution used in the etching step was replaced with a neutral salt aqueous solution of 3.0% ammonium chloride and 0.3% citric acid.

(Embodiment 7) In the first embodiment, the second
An anode foil was etched in the same manner as in Example 1 except that the neutral salt aqueous solution used in the etching step was replaced with a neutral salt aqueous solution of 3.0% ammonium chloride and 1.0% succinic acid.

(Eighth Embodiment) In the first embodiment, the second
The aqueous solution of the neutral salt used in the etching step was adjusted to 3.0% ammonium chloride, and the added amount of oxalic acid was adjusted to 0.005, 0.01,
Anode foils were etched in the same manner as in Example 1, except that the neutral salt aqueous solutions of 0.05, 0.1, 0.5, 1.0, and 1.5% were used.

(Embodiment 9) In the first embodiment, the first
Example 1 except for using an etching solution in which the acidic aqueous solution in the etching step was adjusted to a hydrochloric acid concentration of 10% and a nitric acid concentration of 10%
In the same manner as described above, an etched anode foil was produced.

(Comparative Example) The same procedure as in Example 1 was carried out except that the neutral salt aqueous solution used in the second etching step was replaced with a neutral salt aqueous solution of 3.0% sodium chloride (no additive). In the same manner as in Example 1, an etched anode foil was produced.

The etched anode foils of Examples 1 to 9 of the present invention and the comparative example were subjected to chemical conversion at a liquid temperature of 90 ° C. in an aqueous 8% boric acid solution at 500 V, and the capacitance of each sample was measured. And bending strength (φ1.0mm,
Under a condition of a load of 50 g and a bending angle of 90 degrees, one reciprocation is defined as one time). The results are shown in (Table 1).

[0044]

[Table 1]

As is clear from Table 1, the anode foils according to Examples 1 to 9 of the present invention have a large number of main pits provided in the thickness direction from the surface by etching on both surfaces of the aluminum foil. By providing subpits extending in a branch shape in the middle and at the end of the main pit except for the surface layer, an anode foil having a higher capacitance and higher mechanical strength than the anode foil of the comparative example can be obtained.

In Examples 1 to 7, sodium chloride, potassium chloride and ammonium chloride were used as the aqueous neutral salt solution, but the present invention is not limited to this.

Further, according to Example 8, the amount of the additive added to the aqueous solution of the neutral salt was adjusted to 0.01 to 1.0%,
An anode foil having a high capacitance and a high mechanical strength can be obtained.

Further, the acidic aqueous solution in the first etching step was changed to an etching solution using hydrochloric acid and nitric acid.
The same characteristics can be obtained.

[0049]

As described above, according to the present invention, a large number of main pits are provided on the both surfaces of the aluminum foil in the thickness direction from the surface by etching, and the main pits except for the surface layer are formed in the middle and at the ends. With the configuration in which the sub-pits extending in a branch shape are provided on the surface layer of the aluminum foil, the sub-pits extending in a branch shape are not formed on the surface layer of the aluminum foil. This has the effect that an electrode foil for an aluminum electrolytic capacitor having a high mechanical strength and a high capacitance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of an etching pit of an electrode foil for an aluminum electrolytic capacitor according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a cross section of an etching pit of a conventional electrode foil for an aluminum electrolytic capacitor.

[Explanation of symbols]

 1 Main pit 2 Sub pit 3 Aluminum foil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuaki Nakanishi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] An aluminum foil is provided with a plurality of main pits on both sides thereof in the thickness direction from the surface by etching, and sub-pits extending in a branch shape in the middle of the main pit except for the surface layer and at the end. Electrode foil for aluminum electrolytic capacitors. 2. The electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the sub pit is a pit shorter than the main pit. 3. A first etching step in which an aluminum foil is immersed in an etching solution of an acidic aqueous solution of hydrochloric acid and sulfuric acid or / and nitric acid and a direct current is applied to form main pits. A second etching step of applying a direct current with an etching solution of a neutral salt to which an additive has been added to effectively generate sub-pits extending in a branch shape in the middle and at the end of the main pit, A method of manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising: a third etching step of enlarging the diameter of a sub-pit. 4. The electrode foil for an aluminum electrolytic capacitor according to claim 3, wherein the additive is at least one selected from chromic acid, oxalic acid, citric acid, phosphoric acid, boric acid, succinic acid, and malonic acid. Production method. 5. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 3, wherein the concentration of the additive is in the range of 0.01 to 1.0%.