JP3593970B2 - Method for producing electrode foil for electrolytic capacitor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an electrode foil for an aluminum electrolytic capacitor.
[0002]
[Prior art]
The electrode foil for an electrolytic capacitor is subjected to an electrode surface enlargement process by electrochemical etching for the purpose of increasing the capacity. In order to realize efficient surface area expansion processing, it is essential to arrange etching hole positions at optimal intervals. Conventionally, however, for this purpose, the distribution of impurities contained in aluminum ingot was adjusted. Then, a method of controlling the etching hole start position is adopted. However, in this method, since the distribution of impurities is not regular, there is a limit in the control accuracy of the etching start hole position.
[0003]
On the other hand, in Japanese Patent Application Laid-Open No. H11-74162, a regular arrangement of pits serving as etching start points is previously formed on an aluminum surface prior to an etching process in connection with a surface enlargement processing technique by a DC etching method. Is a method of obtaining an ideal arrangement of etching holes by setting the etching start point as an etching start point.
[0004]
[Problems to be solved by the invention]
By the way, in the above-described method of forming an array of depressions on the aluminum surface before the start of etching and performing etching using this as an etching start point, after the start of etching, formation of a tunnel-shaped etching hole proceeds only at a controlled position. However, in other portions, it is necessary that the etching does not progress.
[0005]
If the etching proceeds at a position other than the start point, the arrangement of the etching holes is disturbed, and the etching holes are united with each other, resulting in a reduction in the finally obtained surface widening efficiency. In addition, the merging of the etching holes causes a decrease in the mechanical strength of the electrode foil and causes a reduction in the processing speed in the etching step or the subsequent steps.
However, it has not been possible to find a condition under which etching proceeds selectively only at the start point position with respect to the aluminum foil having a depression array serving as an etching start point on the surface.
[0006]
[Means for Solving the Problems]
Then, in order to solve the above-mentioned problem, the present invention is to form a depression on the surface of an aluminum foil corresponding to a desired etching pit position, and then to place the aluminum foil in a chloride solution at a temperature of 60 ° C. or less. The present invention is characterized in that etching pits are arranged in a desired pattern on an electrode foil by performing DC enching at a temperature.
That is, according to the present invention, the aluminum foil having the concave array formed on the surface is subjected to direct current etching using an etching condition of a lower temperature than the normal etching temperature, so that the aluminum foil is selectively formed only at the concave forming position. In this way, the production of an electrode foil having a high surface expansion efficiency is realized by causing the etching to proceed to achieve highly accurate control of the position of the etching hole.
[0007]
Normally, in the process of enlarging the electrode foil by the direct current method, etching is performed at a high temperature of 70 ° C. or higher in order to generate a large number of tunnel-shaped etching holes. In this case, the selective etching is difficult to progress because of the lateral expansion of the tunnel-shaped etching holes generated from the positions of the depressions formed on the surface and the generation of holes at portions where no depressions are formed.
[0008]
On the other hand, it has been found that etching at a low temperature suppresses etching at a portion other than the position where the hole is enlarged and the depression is formed, and it is possible to selectively form a tunnel-shaped etching hole. That is, the present invention is based on such a specific etching behavior newly found for an aluminum foil having a concave arrangement on the surface.
[0009]
In the above description, as a method of forming a regular array of depressions acting as an etching start point, a method of pressing various molds having a regular projection arrangement on an aluminum foil under a constant pressure can be used. As an electrolytic solution for etching, an electrolytic solution containing chloride ions (CL ⁻ ) typified by hydrochloric acid and sodium chloride is used as in the usual method. The electrochemical etching is performed by performing a constant current electrolysis in the electrolytic solution containing chloride ions.
[0010]
In addition, the electrolyte temperature in the present invention is lower than 60 ° C., which is lower than the temperature used in a normal DC method, and in particular, at 25 ° C. to 35 ° C., selective etching is performed only from the depression position. Can be advanced.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a part of an aluminum foil in which an array of depressions 2 serving as etching start points is physically formed on the surface of an aluminum foil 1 prior to etching in the present invention. In order to form such a regular arrangement of the depressions 2 on the aluminum foil 1, a mold having a regular projection arrangement as shown in JP-A-11-74162 is pressed against the aluminum foil to form the depressions 2. Is used. The arrangement of the depressions 2 is usually a hexagonal arrangement or a tetragonal arrangement, which is effective for realizing a high surface expansion efficiency.
[0012]
FIG. 2 shows a state in which a DC electrolytic etching process is performed in an electrolytic solution containing chloride ions after the formation of the recess arrangement, in which 3 is a DC power supply, 4 is an electrolytic cell, 5 is a chloride solution, and 6 is a chloride solution. Denotes a cathode and 7 denotes an etching hole.
In this etching process, the state of the formation of the etching hole remarkably depends on the temperature of the electrolytic solution. That is, at a temperature of 70 ° C. or higher, which is the temperature of the electrolytic solution at which normal electrolytic etching is performed, although the generation of holes from the depression position occurs preferentially, the expansion of holes and the generation of holes from other parts also occur at the same time, The controllability of the hole formation position is reduced. On the other hand, when the temperature of the electrolytic solution is set to 60 ° C. or lower, although the formation and progress of the etching hole are observed at the pit formation position, the enlargement of the hole and the etching at other portions are not observed. Etching from the depression forming position can be performed with good selectivity.
[0013]
From the above results, according to the present invention, extremely good etching hole arrangement precision can be achieved from the combination of the formation of the concave array on the aluminum foil and the DC etching at 60 ° C. or less, and the realization of high surface expansion efficiency can be achieved. It is clear that it is possible.
[0014]
FIG. 3 is a diagram schematically showing an aluminum electrode foil produced by the method of the present invention. FIGS. 4 and 5 show the surface of the aluminum foil actually manufactured by this method and the etching holes are ideally arranged, and the tunnel holes obtained by the replica method, as shown in FIGS. It can be confirmed that the etching holes are regularly formed in accordance with the hexagonally arranged depressions formed in advance on the aluminum foil surface.
[0015]
1. Example 1
The aluminum foil having a purity of 99.99% and a (100) plane orientation rate of 93% was pressed with a pressure of 1 ton / cm ² using a nickel mold having a regular projection arrangement on the surface, thereby pressing the surface of the aluminum foil. A regular array of depressions was formed. The interval between the depression arrays was 10 μm. Thereafter, electrolytic etching was performed for 90 seconds in an electrolytic solution having a current density of 50 mA / cm ² and 30 ° C. in 5 molar hydrochloric acid to obtain an electrode foil having an etching hole formed in the same arrangement as the depression.
[0016]
2. Example 2
An aluminum foil having a regular recess arrangement with a hole interval of 2 μm was etched in the same manner as in Example 1. As a result, the arrangement of the etching holes which coincided with the previously formed etching positions was obtained.
[0017]
【The invention's effect】
As described above, according to the present invention, it is possible to control the position of the etching hole with higher precision than in the conventional method, and as a result, it is possible to produce an electrode foil having high surface expansion efficiency and excellent mechanical strength. In addition, there is an advantage that a high capacity electrolytic capacitor can be provided.
[Brief description of the drawings]
FIG. 1 is a view showing an aluminum foil having a regular array of depressions serving as an etching starting point formed on the surface; FIG. 2 is a view showing a state in which an aluminum foil having a concave arrangement is subjected to a DC etching treatment; FIG. FIG. 4 is a diagram showing a hole formation in a foil. FIG. 4 is a diagram showing a surface scanning electron micrograph of an aluminum foil produced according to the present invention. FIG. 5 is a diagram showing a replica method for an aluminum foil produced according to the present invention. Diagram showing the state of the obtained tunnel hole by a surface scanning electron micrograph.
DESCRIPTION OF SYMBOLS 1 Aluminum foil 2 Depression 3 DC power supply 4 Electrolyzer 5 Chloride solution 6 Cathode 7 Etching hole

Claims (2)

After physically forming a depression corresponding to a desired etching pit position on the surface of the aluminum foil, the aluminum foil is subjected to direct current etching at a temperature of 60 ° C. or less in a chloride solution, so that the electrode foil has a desired shape. A method for producing an electrode foil for an electrolytic capacitor, wherein etching pits are arranged in a pattern as described above. The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the temperature of the DC etching is 25 ° C. to 35 ° C. 6.

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