JP2009146984A - 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 prevents the deterioration in capacitance by controlling a hydration reaction to suppress reduction in a surface area caused by clogging even when a low-voltage aluminum foil is subjected to hydration treatment with warm water. <P>SOLUTION: The method includes: an etching step of using the aluminum foil as an etching foil; a cleaning step of cleaning the etching foil with a cleaning liquid; and a posttreatment step of executing hydration treatment and heat treatment for the etching foil after cleaning. In the method, the hydration treatment is immersion treatment into an alkali solution containing nitrate ions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  The electrode foil for an aluminum electrolytic capacitor is subjected to chemical or electrochemical etching in order to increase the effective area and increase the capacitance per unit area. Moreover, it is known that when a thermal oxide film or a hydrated oxide film is generated in advance before chemical conversion, the capacitance of the chemical conversion foil increases (for example, see Non-Patent Document 1).

  The purpose of the hydration treatment after etching is to improve the film quality of the anodized film by forming a hydroxide film on the surface of the aluminum foil. Usually, it is performed by immersing an aluminum foil in high-temperature pure water, but a method of treating with a high-temperature pure water to which an amine is added (for example, see Patent Document 1) is also known.

Isaya Nagata, “Electrolyte Cathode Aluminum Electrolytic Capacitor”, Nihon Denki Kogyo Kogyo Co., Ltd., February 24, 1997, Second Edition, First Printing, P266-272 JP-A-2-216810

  In recent years, with the miniaturization of electrolytic capacitors, it is necessary to increase the capacitance per unit area. Therefore, it is important to form a higher quality hydrated film in the hydration treatment after etching. However, the conventional method has not been sufficient to obtain the necessary capacitance.

  That is, when a hydration treatment with warm water is used for a low-pressure aluminum foil, it is difficult to control the hydration reaction, so that the surface area may be reduced due to clogging, resulting in a decrease in capacitance. Therefore, even when a low-pressure aluminum foil is hydrated with warm water, the hydration reaction can be controlled, the surface area reduction due to clogging can be suppressed, and the capacitance reduction does not occur. Was demanded.

  The present invention solves the above-mentioned problem, an etching process using an aluminum foil as an etching foil, a cleaning process for cleaning the etching foil with a cleaning liquid, and a hydration treatment and a heat treatment for the etching foil after cleaning. A method for producing an electrode foil for an electrolytic capacitor, wherein the hydration treatment is an immersion treatment in an alkaline aqueous solution containing nitrate ions. is there.

  The method for producing an electrode foil for an electrolytic capacitor is characterized in that the concentration of nitrate ions in the alkaline aqueous solution is 0.1 to 0.7 mol / L.

  And the pH of the alkaline aqueous solution containing the said nitrate ion is 9-11, and temperature is 40-60 degreeC, It is a manufacturing method of the electrode foil for electrolytic capacitors characterized by the above-mentioned.

  As described above, the present invention provides an electrolytic process including an etching process for obtaining an etching foil, a cleaning process for cleaning the etching foil, and a post-processing process for performing hydration treatment and heat treatment on the etched foil after cleaning. In the production process of capacitor electrode foils, hydration can be controlled by immersing in an alkaline aqueous solution containing nitrate ions, even when low pressure electrode foils are hydrated with warm water. Since the surface area reduction due to clogging can be prevented, an electrode foil having a high electrostatic capacity can be produced.

Examples according to the present invention will be described below. First, in the etching process, in an aqueous solution in which hydrochloric acid (10.0 wt%) and sulfuric acid (1.0 wt%) are mixed, the waveform is sine wave, the frequency is 50 Hz, the current density is 0.5 A / dm ² , and aluminum is used. Electrochemical etching was performed on the original foil (foil width 500 mm).
Next, in the cleaning step, impurities such as chlorine adhering to the etching foil were removed by chemical cleaning with nitric acid, followed by washing with water, and then an etching foil was obtained through the following post-processing steps.

The etching foil was immersed in an alkaline aqueous solution containing nitrate ions shown in Table 1, and then heat treated at 400 ° C. Here, sodium nitrate was used as nitrate ion, and sodium hydroxide aqueous solution was used as alkaline aqueous solution.
Then, after forming by applying a voltage of 20 V in a 8.0 wt% ammonium adipate aqueous solution at a temperature of 85 ° C., the capacitance was measured and the results shown in Table 1 were obtained.
The comparative conditions for the hydration treatment were as follows.
[Examples 1 to 5] Sodium nitrate concentration comparison: 0.05, 0.1, 0.2, 0.7, and 1.0 mol / L, respectively
[Examples 6 to 10] Liquid temperature comparison of hydration liquids: 35, 40, 45, 60, and 65 ° C, respectively
[Examples 11 to 14] pH comparison of hydration liquids: 8, 9, 11, 12 respectively

As Comparative Example 1, a chemical conversion treatment was performed on a product obtained by immersing an etching foil in an aqueous sodium hydroxide solution not containing sodium nitrate and drying it, and the capacitance was measured. Furthermore, as Comparative Examples 2 to 6, the solution temperature of the sodium hydroxide aqueous solution to which sodium nitrate was not added was changed, and the etching foil was immersed and dried, then subjected to chemical conversion treatment, and the capacitance was measured.
In addition, as a conventional example, it was immersed in warm water at 55 ° C. for 1 minute to be hydrated, and the dried one was subjected to chemical conversion treatment, and the capacitance was measured.
Further, as Comparative Examples 7 and 8, the same chemical conversion treatment was applied to those in which the hydration solution was pure water, the sodium nitrate concentration was 0.1 and 0.2 mol / L, and the same pH = 7 as in the conventional example was set. And the capacitance was measured.
The measurement results are shown in Table 1.

[Sodium nitrate concentration comparison]
As can be seen from Table 1, when the electrostatic capacity of Comparative Example 5 is 100, the sodium nitrate concentration of Examples 2 to 4 is 0.1 to 0.7 mol / L. Capacity can be improved. In Example 1 of 0.05 mol / L, a sufficient effect cannot be obtained. Moreover, in Example 5 of 1.0 mol / L, reaction will become excessive and an electrostatic capacitance will reduce.

[Comparison of hydration liquid temperature]
As can be seen from Table 1, when the liquid temperatures of Examples 7 to 9 are 40 to 60 ° C., preferably 45 to 60 ° C., the capacitance can be improved as compared with Comparative Example 5. In Example 6 where the temperature is 35 ° C., a sufficient effect cannot be obtained. Further, in Example 10 at a temperature of 65 ° C., the fine pits are filled, so that the capacitance decreases.
Further, in Comparative Examples 2 to 4 (liquid temperature of 35 to 45 ° C.) without adding sodium nitrate and Comparative Example 6 (liquid temperature of 65 ° C.), it was confirmed that the capacitance was inferior to that of Comparative Example 5 (liquid temperature of 60 ° C.). did it.

[PH comparison of hydration solution]
As can be seen from Table 1, at pH = 9 to 11 in Examples 12 and 13, the capacitance can be improved compared to Example 11 at pH = 8 and Example 14 at pH = 12. At pH = 8, a sufficient effect cannot be obtained, and at pH = 12, the capacitance decreases due to dissolution of the surface.
Furthermore, as Comparative Examples 7 and 8, the same pH as in the conventional example was set to 7, and the sodium nitrate concentrations of 0.1 and 0.2 mol / L were improved in capacitance compared to the conventional example. It was confirmed that there was no.

  In the above example, sodium nitrate was used as the nitrate ion, and the aqueous sodium hydroxide solution was used as the alkaline aqueous solution. As alkaline aqueous solution, potassium hydroxide aqueous solution, ammonia water, sodium aluminate aqueous solution, sodium carbonate aqueous solution, etc. can be used.

  Moreover, this invention is not limited to the said Example, The hydration process (post-process) by immersion to the alkaline aqueous solution containing the nitrate ion of etching foil is made into a well-known pre-processing process, an etching process, and a washing process. You may perform combining suitably.

Claims (3)

Electrode for electrolytic capacitors having an etching process using an aluminum foil as an etching foil, a cleaning process for cleaning the etching foil with a cleaning liquid, and a post-processing process for performing hydration treatment and heat treatment on the etched foil after cleaning. In the foil manufacturing method,
The method for producing an electrode foil for an electrolytic capacitor, wherein the hydration treatment is an immersion treatment in an alkaline aqueous solution containing nitrate ions.   The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the concentration of nitrate ions in the alkaline aqueous solution is 0.1 to 0.7 mol / L.   The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the alkaline aqueous solution containing nitrate ions has a pH of 9 to 11 and a temperature of 40 to 60 ° C.