JP2010003996A - Method of manufacturing electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode foil for an aluminum electrolytic capacitor capable of raising the capacitance of an electrode foil in a breakdown voltage region of ≥170 V and reducing the dielectric loss (tan δ) and the leakage current. <P>SOLUTION: The method of manufacturing the electrode foil for the aluminum electrolytic capacitor includes a first step of immersion in pure water of ≥90°C, a second step of anodic oxidation in an aqueous solution including boric acid or a salt thereof, a third step of immersion in an aqueous solution including an organic acid having ≤6 carbon atoms, and a fourth step of immersion again in pure water of ≥90°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode foil for medium- and high-voltage aluminum electrolytic capacitors.

  In recent years, along with the downsizing and high reliability of electrical equipment and information communication equipment, and the efficiency of energy use for global environmental conservation, miniaturization, reliability improvement, energy efficiency improvement and cost of aluminum electrolytic capacitors have been achieved. There is a growing need for downs, and electrode foils for aluminum electrolytic capacitors are also required to have higher capacitance per unit area than before, as well as to reduce energy consumption and increase efficiency during production.

  Electrode foils for high-voltage anodes in aluminum electrolytic capacitors are subjected to electrochemical or chemical etching treatment to increase the effective surface area, and then hydration treatment is performed, followed by anodic oxidation treatment to form a dielectric film. It is manufactured in the process.

  Hydration before anodizing is intended to form a hydrated film on the surface of the aluminum foil and easily convert it to an oxide film during the anodizing process. It is carried out by immersing in water, and the amount of electricity used during anodizing treatment is saved, and the capacitance is also increased.

In addition, as one of the depolarization treatment that is a means for repairing the defective portion generated in the oxide film during the anodic oxidation treatment, there is an immersion treatment in an aqueous solution such as phosphoric acid or hydroxycarboxylic acid. The treatment is performed in the middle of the anodizing treatment process to expose the defective part in the oxide film on the surface, and after washing with water, again after anodizing to a predetermined voltage and repairing the defective part, washing with water and drying, The electrode foil was for an aluminum electrolytic capacitor.
JP-A-53-135452 Isada Nagata, “Electrolyte Cathode Aluminum Electrolytic Capacitor”, February 24, 1997, Second Edition, First Print, P314

  However, phosphoric acid, hydroxycarboxylic acid, etc. are greatly adsorbed on hydrates, and this influence partially inhibits the exposure of the defective part, leaving hydrates that are not converted to oxides in the film, resulting in dielectrics. The loss (tan δ) could not be reduced sufficiently. In addition, if the concentration of aqueous solution of phosphoric acid or hydroxycarboxylic acid is increased to prevent hydrates from remaining, the amount of hydrates that cannot be converted into oxides will not decrease so much, but the oxide film and aluminum necessary for the dielectric In order to dissolve the base material itself, the capacitance increased by the hydration treatment has been reduced.

  In order to achieve the above object, an aqueous solution containing an organic acid having 6 or less carbon atoms after a first step of immersing in pure water of 90 ° C. or higher and a second step of anodizing in an aqueous solution containing boric acid or a salt thereof. A method for producing an electrode foil for an aluminum electrolytic capacitor, wherein a third step of immersing in an aluminum electrolytic capacitor is performed.

  By using an organic acid having 6 or less carbon atoms, especially oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid in the above method, the effect of the depolarization treatment is the same as that of aqueous solution immersion such as phosphoric acid. Furthermore, since these organic acids are less adsorbed by hydrates, they act on the interface between the hydrate and the oxide film, so that almost no oxide film necessary for the dielectric is dissolved, and dielectric loss occurs. Hydrate that is not converted to an oxide that causes an increase in (tan δ) can be removed.

  Further, the concentration of the aqueous organic acid solution at this time is preferably 0.1 g / L to 30 g / L. If the concentration is lower than this, the effect of depolarization treatment cannot be obtained. It will have adverse effects such as over-dissolution of substances and contamination of organic acids in the next process liquid. Similarly, the temperature of the organic acid aqueous solution is preferably 40 ° C. to 80 ° C. If the temperature is lower than this, a sufficient depolarization effect cannot be obtained, and if it is higher than this, dissolution of the film occurs. The capacitance will decrease.

  Furthermore, if immersion in pure water at 90 ° C. or higher is performed again after the organic acid aqueous solution immersion treatment, the organic acid remaining in the oxide film is discharged, so that the film is effectively repaired in the subsequent re-anodizing treatment step. This makes it possible to produce a better oxide film.

  By performing the treatment of the present invention, it is possible to produce an electrode foil for an aluminum electrolytic capacitor having a large capacity and reduced leakage current and dielectric loss (tan δ).

Examples of the present invention will be described below. As Example 1, 5 cm ² of an aluminum foil etched to a surface expansion magnification of about 20 times is immersed in 95 ° C. pure water for 10 minutes as a first step. Thereafter, as a second step, an aqueous solution containing 10% boric acid is maintained at 80 ° C., the aluminum foil is immersed therein, and the pressure is increased at a current of 50 mA / cm ² , and after reaching 600 V, it is maintained for 20 minutes. Thereafter, the aluminum foil is washed with water and immersed in an aqueous solution of oxalic acid 1 g / L and 60 ° C. for 3 minutes as a third step. Thereafter, the aluminum foil was washed with water, and anodized again with an aqueous solution containing 10% boric acid at a current of 50 mA / cm ² to 600 V to obtain an electrode foil. Thereafter, 400 V was applied to the aluminum foil using the re-anodizing solution, and the leakage current after 1 minute was measured. Then, according to the test method of the electrode foil for EIAJ RC-2364A aluminum electrolytic capacitors, the dielectric loss (tan δ) was measured at a capacitance of 120 Hz.

  As Example 2, after performing from the 1st process to the 3rd process immersed in the oxalic acid aqueous solution similarly to Example 1, it was immersed in the pure water of temperature 95 degreeC again for 5 minutes as a 4th process. The others were measured in the same manner as in Example 1.

  As Example 3, malonic acid was used in place of oxalic acid, and the others were carried out in the same manner as in Example 1 and measured.

  As Example 4, malonic acid was used in place of oxalic acid, and the other measurement was performed in the same manner as in Example 2.

  In Example 5, succinic acid was used in place of oxalic acid, and the other measurement was performed in the same manner as in Example 1.

  As Example 6, succinic acid was used in place of oxalic acid, and the others were measured in the same manner as in Example 2 and measured.

  As Example 7, glutaric acid was used in place of oxalic acid, and the others were carried out in the same manner as in Example 1 and measured.

  As Example 8, glutaric acid was used in place of oxalic acid, and the other measurement was performed in the same manner as in Example 2.

  In Example 9, adipic acid was used in place of oxalic acid, and the other measurement was performed in the same manner as in Example 1.

  As Example 10, adipic acid was used in place of oxalic acid, and the other measurement was performed in the same manner as in Example 2.

  As Comparative Example 1, a production method without performing the third step, and as Comparative Example 2, the third step was immersed in an aqueous solution of 1 g / L of phosphoric acid at 60 ° C. for 3 minutes, and then re-anodized as in Example 1. Went. Thereafter, leakage current, capacitance, and dielectric loss (tan δ) were measured in the same manner as in Example 1.

  As is apparent from Table 1, the electrode foil for an aluminum electrolytic capacitor obtained by the manufacturing method of the present invention has an increase in capacitance of about 7% to 15% and a leakage current of 19% compared to the conventional manufacturing method. The dielectric loss (tan δ) was reduced by about 25% to 30%. As described above, according to the present invention, it is possible to provide an energy efficient electrode foil for an aluminum electrolytic capacitor that can reduce a leakage current and a dielectric loss (tan δ) and that can reduce the size of the capacitor. .

Claims (5)

  In the step of forming an oxide film by anodic oxidation on the etched aluminum foil, after the first step of immersing in pure water of 90 ° C. or higher and the second step of anodizing in an aqueous solution containing boric acid or a salt thereof, A method for producing an electrode foil for an aluminum electrolytic capacitor, comprising performing a third step of immersing in an aqueous solution containing an organic acid having 6 or less carbon atoms.   In the step of forming an oxide film by anodic oxidation on the etched aluminum foil, after the first step of immersing in pure water of 90 ° C. or higher and the second step of anodizing in an aqueous solution containing boric acid or a salt thereof, A third step of immersing in an aqueous solution containing an organic acid having 6 or less carbon atoms, and further immersing in pure water at 90 ° C. or higher again as a fourth step.   3. The aluminum according to claim 1, wherein at least one of oxalic acid, malonic acid, succinic acid, glutaric acid and adipic acid is used alone or in combination as an organic acid having 6 or less carbon atoms. Manufacturing method of electrode foil for electrolytic capacitors.   The manufacturing method of the electrode foil for aluminum electrolytic capacitors of Claim 1, 2, or 3 whose density | concentration of the aqueous solution containing an organic acid is 0.1g / L-30g / L.   The manufacturing method of the electrode foil for aluminum electrolytic capacitors of Claim 1, 2, 3 or 4 whose temperature of the aqueous solution containing an organic acid is 40 to 80 degreeC.