JP2007059629A - Method of manufacturing electrode foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode foil for an electrolytic capacitor which has high bending strength even after etching and anodic oxidation are carried out. <P>SOLUTION: Heat treatment of 150 to 390°C is performed for at least 30 minutes for an electrode foil for an electrolytic capacitor which is formed by forming a dielectric film in an etched aluminum foil surface by anodic oxidation. Since crystalline arrangement of the dielectric film is thereby homogenized, strain in crystal is reduced, thus providing flexibility to the dielectric film and increasing bending strength of the electrode foil. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, an electrode foil for an electrolytic capacitor is obtained by expanding an aluminum foil by etching and forming an aluminum oxide film serving as a dielectric by anodic oxidation (chemical conversion). This oxide film has many defects such as voids, and in order to remove these defects, a depolarization treatment such as immersion in acid or alkali and a re-chemical conversion treatment are performed (for example, see Non-patent Document 1).

  In addition, a technique has been proposed in which a chemical foil for electrolytic capacitor is subjected to a heat treatment at a temperature of 400 to 660 ° C. for 30 minutes or more to expose defects remaining in the dielectric film (for example, see Patent Document 1).

These conventional techniques are very useful techniques for reducing the leakage current of the electrode foil for electrolytic capacitors.
JP 2000-21690 A Isaya Nagata, “Electrolyte Cathode Aluminum Electrolytic Capacitor”, Nippon Electric Storage Industrial Co., Ltd., February 24, 1997, 2nd edition, p. 311-314

  Electrode capacitor electrode foils used as anodes are required to have high capacitance and high bending strength. That is, the electrode foil having a low bending strength is easily cut during the manufacturing process of the capacitor element, and thus the manufacturing efficiency is lowered. Moreover, since the electrode foil with low bending strength is likely to generate burrs when slit to a predetermined width, when used as an electrolytic capacitor, there is a high possibility of shorting with the cathode due to burrs.

  However, in the electrode foil for electrolytic capacitors, in order to respond to the increase in capacity of aluminum electrolytic capacitors, the etching strength is inevitably increased because the surface area of the aluminum etched foil is increased by etching to the deep part of the foil. Tend to decrease. In addition, the electrolytic capacitor electrode foil in which the dielectric film is formed by anodic oxidation has a lower bending strength than before anodic oxidation. Furthermore, when the depolarization process described in Patent Document 1 is performed, the bending strength of the foil further decreases.

  Although the above prior art is very useful for improving characteristics such as reduction of leakage current of the electrode foil for aluminum electrolytic capacitors, no consideration is given to improving the bending strength of the foil.

  In view of the above problems, an object of the present invention is to provide a method for producing an electrolytic capacitor electrode foil having high bending strength even after etching and anodizing.

  In order to solve the above problems, in the method for producing an electrolytic capacitor electrode foil of the present invention, a dielectric film is formed on the surface of the etched aluminum foil by anodic oxidation, and then the temperature of the aluminum foil is 150 to A heat treatment at 390 ° C. is performed for 30 minutes or more.

  In the present invention, an electrolytic capacitor electrode foil having a high bending strength can be provided by subjecting the electrode foil for an electrolytic capacitor subjected to etching and anodization to a heat treatment at a temperature of 150 to 390 ° C. for 30 minutes or more. it can.

  In the method for producing an electrode foil for an electrolytic capacitor according to the present invention, a dielectric film is formed on the surface of the etched aluminum foil by anodic oxidation, and then the heat treatment at 150 to 390 ° C. is performed on the aluminum foil for 30 minutes or more. Do. As a result, the bending strength is improved. The reason for this is that when the electrode foil for an aluminum electrolytic capacitor is subjected to a heat treatment at a temperature of 150 to 390 ° C. for 30 minutes or more, the crystal arrangement of the dielectric film becomes uniform, resulting in less distortion between crystals. It is considered that the suppleness is provided and the bending strength of the electrode foil is increased.

  FIG. 1 and FIG. 2 are diagrams for explaining the bending test apparatus and how to count the number of bendings.

  In the present invention, an etched aluminum foil is first immersed in pure water at a temperature of 90 ± 2 ° C. for 5 minutes, and then adjusted to a specific resistance of 450 Ω · cm, pH 6.5, and a liquid temperature of 85 ± 2 ° C. Anodization is performed in an aqueous ammonium solution up to a voltage of 300 V, and then the application of the same voltage is continued for 15 minutes. Next, a depolarization treatment including a heat treatment for 5 minutes in an atmosphere at a temperature of 550 ° C. and a 5-minute immersion treatment in a 3.0 wt% phosphoric acid aqueous solution is performed, and then a repair conversion is performed in the aqueous ammonium phosphate solution. . The depolarization treatment and the repair conversion were performed three times.

  The thus produced electrode foil for electrolytic capacitors was heat-treated in an air atmosphere at the temperature and time shown in Table 1. In addition, what did not heat-process to the electrode foil for electrolytic capacitors was made into the conventional example.

  And after cutting the electrode foil for electrolytic capacitors of an Example and a prior art example into a 1 cm x 10 cm test piece, while attaching a test piece to the bending test apparatus shown in FIG. 1, it bends until a test piece fractures | ruptures. The number of times until the fracture occurred was defined as the bending strength. In FIG. 1, 1 is a test piece, 2 is a plunger, 3 is a clamp for applying a load, 4 is a bending device, 5 is a bending device mounting surface, 6 is a bending portion, and 7 is a distance from the clamp to the bending portion. In this example, it is 7 cm.

  In such a bending test, the number of times of bending is 90 ° as shown by arrow 8 in FIG. As shown, the other side was also folded. As test conditions at that time, the radius of curvature of the bent portion 6 was 3.5 mm, the load was 2.5 N, and the bending repetition rate was 6 times / second. The bending test results obtained in this way are shown in Table 1. In addition, the numerical value of Table 1 is an average value of the number of samples n = 12.

  As can be seen from Table 1, the bending strength can be significantly improved as compared with the conventional example by subjecting the electrode foil for electrolytic capacitors to a heat treatment at a temperature of 150 to 390 ° C. for 30 minutes or more.

  As the heat treatment conditions, it is preferable to carry out a sufficient time at an appropriate temperature. If the temperature is less than 150 ° C., the bending strength cannot be improved even if the treatment is performed for a long time. If the heat treatment time is short under conditions exceeding 390 ° C., the bending strength decreases. Therefore, the temperature is set to 150 to 390 ° C. as the heat treatment condition. In addition, since the difference in heat treatment time is small between 5 hours and 20 hours, it can be set to 30 minutes or more and 5 hours or less in consideration of man-hours.

  In addition, the heat treatment of the present invention can also reduce the leakage current of the electrolytic capacitor electrode foil and improve the water resistance.

  In addition, you may perform the heat processing of this invention not only in an air atmosphere but in inert gas atmospheres, such as nitrogen and argon, and a vacuum atmosphere. Furthermore, in the above embodiment, the present invention is applied to the electrode foil for medium-pressure electrolytic capacitors. However, the present invention may be applied to an electrode foil for high-voltage electrolytic capacitors having an anodic oxidation voltage of 400 V or more. Of course, the present invention may be applied to electrode foils for low-voltage electrolytic capacitors, but from the viewpoint of improving the bending strength, the etching pits are advanced in a tunnel shape, and the anodized film is When the present invention is applied to an electrode foil for an electrolytic capacitor for medium and high voltage formed to be thick, the effect is remarkable.

It is an external view of a bending test apparatus. It is explanatory drawing of how to count the frequency | count of bending.

Explanation of symbols

1 Test piece 2 Plunger 3 Clamp 4 to apply load 4 Bending device 6 Bending part

Claims (1)

A dielectric foil is formed on the surface of the etched aluminum foil by anodic oxidation, and then the aluminum foil is subjected to heat treatment at a temperature of 150 to 390 ° C. for 30 minutes or more. Method.

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