JP7368228B2 - Manufacturing method of electrode foil for electrolytic capacitors - Google Patents

Description

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

Regarding the manufacturing method of electrode foil for electrolytic capacitors, the following non-patent document 1 describes an existing chemical forming machine using the conventionally used roll power feeding method (a method in which power is supplied by bringing a metal power feeding roll into direct contact with an aluminum foil). It is disclosed that it is possible to switch to the submerged power supply method (a method of indirectly supplying power to the aluminum foil through an electrolytic solution) relatively easily by simply modifying a part of the . Further, in order to prevent contamination of the electrolytic solution, it is preferable to use the same electrolytic solution in the submerged power supply tank in the chemical formation process, and it is described that an aqueous solution of ammonium adipate is used.

Nakajima et al., “Development and practical application of submerged power supply chemical technology for aluminum foil for electrolytic capacitors,” Electrochemistry and Industrial Physical Chemistry (edited by the Electrochemical Society), 64, No. 7, (1996) p. 801-804

However, in the submerged power supply using an aqueous solution of ammonium adipate in Non-Patent Document 1, there were problems such as increased damage to the chemical conversion film and increased distortion of the electrode foil, resulting in poor appearance.
The present invention solves the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing an electrode foil for an electrolytic capacitor that can reduce damage to a chemical conversion film and distortion of an electrode foil.

The manufacturing method of the present invention capable of solving the above-mentioned problems is a manufacturing method of an electrode foil for an electrolytic capacitor in which power is supplied to an etched electrode foil via an electrolytic solution in a submerged power supply tank, in which the electrolytic solution is made of citric acid. It is characterized by containing ammonium salt and phosphoric acid.
In addition, in this specification, "ammonium salt of citric acid" means triammonium citrate, ammonium dihydrogen citrate, and diammonium hydrogen citrate.
The electrolytic solution used in the production method of the present invention is prepared by adding ammonia water to the above-mentioned "ammonium salt of citric acid" to prepare an aqueous solution (the pH of this solution is, for example, 5.6-5. 9), then adding phosphoric acid (the pH after adding phosphoric acid is about 5.6 to 5.8), or adding ammonia water to an aqueous solution containing citric acid. to generate an ammonium salt of citric acid and adjust the pH (for example, pH 5.6 to 5.9), and then add phosphoric acid to the resulting aqueous solution (the pH after adding phosphoric acid is the same as above). It's okay.

The present invention also provides a method for manufacturing an electrode foil for an electrolytic capacitor having the above characteristics, wherein the concentration of ammonium salt of citric acid in the electrolytic solution is 0.13 to 0.25 mol/l, and It is characterized by a concentration of 0.001 to 0.1 mol/l.

Furthermore, the present invention provides a method for manufacturing an electrode foil for an electrolytic capacitor having the above-mentioned characteristics, in which submerged power supply using the electrolytic solution is performed at a current density of 50 to 200 mA/cm ² for 3 to 20 minutes. It is characterized by:

In the present invention, it is possible to manufacture an electrode foil for an electrolytic capacitor that reduces damage to the chemical conversion film and reduces distortion of the electrode foil, compared to the conventional technology that uses an aqueous ammonium adipate solution as the electrolyte used in the submerged power supply process. Can be done.

It is an appearance photograph of the electrode foil for electrolytic capacitors of an example. 2 is a photograph of the appearance of an electrode foil for an electrolytic capacitor of Comparative Example 1. It is an external photograph of the electrode foil for electrolytic capacitors of Comparative Example 2. It is an appearance photograph of the electrode foil for electrolytic capacitors of Comparative Example 3.

In the method for manufacturing an electrode foil for an electrolytic capacitor of the present invention, an electrolytic solution containing an ammonium salt of citric acid and phosphoric acid is prepared as an electrolytic solution for a submerged power supply tank, and the aluminum foil after the first chemical conversion step is subjected to the electrolysis. Power is supplied through the liquid at a predetermined temperature (preferably 20 to 40°C). The concentration of ammonium salt of citric acid in the electrolytic solution used in the present invention is 0.13 to 0.25 mol/l, for example, when diammonium hydrogen citrate is used as the ammonium salt of citric acid. , the concentration in 1 liter of electrolyte is preferably 35 to 45 g/l (0.155 to 0.199 mol/l), more preferably 38 to 42 g/l, and the concentration of phosphoric acid is 0.001 to 0.1 The amount is preferably mol/l, more preferably 0.003 to 0.02 mol/l.

In addition, the following chemical conversion process is performed on the etched aluminum foil before the submerged power supply process is performed. For example, in the case of etched aluminum foil used for high-voltage electrode foil, it is boiled in pure water for about 1 to 20 minutes, then boric acid-based (boric acid or Chemical formation is performed in a chemical liquid (containing the salt) up to a predetermined voltage by roll power supply (first chemical formation step). At this time, the concentration of boric acid in the chemical conversion liquid is preferably 5 to 10% by weight, and the applied current density, voltage, and voltage application time can be selected as appropriate.
The manufacturing method of the present invention will be described below based on Examples, but the present invention is not limited thereto.

(Example)
Etched aluminum foil (thickness: 120 μm) used for high-voltage electrode foil was prepared, and after hot water boiling in pure water for 10 minutes, it was neutralized with aqueous ammonia as the first chemical conversion step. In a 10% by weight boric acid solution, the voltage was increased under constant current conditions (current density: 20 mA/cm ² ) by roll power supply (electrode foil contact power supply), and after reaching 500V, the voltage was increased to 3 It was maintained for a minute.
Then, a diammonium hydrogen citrate aqueous solution whose pH was adjusted (pH 5.6 to 5.9) with an ammonia aqueous solution (concentration of diammonium hydrogen citrate in electrolyte solution: 40 g/l, 4% by weight, aqueous ammonia concentration 0.1 In-liquid power supply was carried out (for 5 minutes) in an electrolytic solution at 30°C containing 0.005 mol/l of phosphoric acid (mol/l), and 5 to 10% by weight neutralized with aqueous ammonia was used. After increasing the voltage to a predetermined voltage (for example, 540 V) in the boric acid solution, a second chemical conversion step was performed in which the predetermined voltage was maintained for a certain period of time (for example, 40 minutes). The current density of the submerged power supply at this time was 75 mA/cm ² . Thereafter, heat treatment, chemical immersion, and reconversion steps were performed using known methods.

(Comparative example 1)
In-liquid power supply was carried out in the same manner as in the above example except that an ammonium adipate aqueous solution (concentration: 40 g/l) was used as the electrolyte.

(Comparative example 2)
In-liquid power supply was carried out in the same manner as in the above example, except that an ammonium adipate aqueous solution (concentration: 40 g/l) to which 0.005 mol/l of phosphoric acid was added was used as the electrolytic solution.

(Comparative example 3)
Submerged power supply was performed in the same manner as in the above example except that an electrolytic solution to which no phosphoric acid was added was used.

[Evaluation method]
For the above Examples and Comparative Examples 1 to 3, the initial voltage of the electrode foil measured during submerged power supply was measured, and each initial voltage was compared. The voltage drop rates of Comparative Examples 2 and 3 and Examples are percentages based on Comparative Example 1. In addition, for Examples and Comparative Examples 1 to 3, the strain of the electrode foils was measured. The external appearance of the electrode foil of Example is shown in FIG. 1, Comparative Example 1 is shown in FIG. 2, Comparative Example 2 is shown in FIG. 3, and Comparative Example 3 is shown in FIG. Strain was determined by measuring how far the most warped part of the electrode foil was from the horizontal plane. The results are shown in Table 1 below.

From the results in Table 1 above, it can be seen that the electrode foil for electrolytic capacitors (Example) obtained using the manufacturing method of the present invention contains an aqueous solution containing ammonium adipate alone (Comparative Example 1), ammonium adipate and phosphoric acid. It was confirmed that the initial voltage was lower than the electrode foils obtained using the aqueous solution containing phosphoric acid (Comparative Example 2) and the aqueous solution without phosphoric acid (Comparative Example 3), and there was less damage to the chemical conversion coating.

Further, from Table 1 and FIGS. 1 to 4, the electrode foils for electrolytic capacitors of Examples have reduced distortion compared to the electrode foils for electrolytic capacitors of Comparative Examples 1 to 3.

In the examples, diammonium hydrogen citrate was used as a solution in which the pH of citric acid was adjusted with ammonia, but the same effect can be obtained by using triammonium citrate or ammonium dihydrogen citrate.

Further, in the embodiment, the first chemical formation step was entirely powered by roll power, but the final stage of the first chemical formation step may be powered by submerged power supply.

The manufacturing method of the present invention is useful for manufacturing electrode foils with excellent properties with high productivity in manufacturing electrode foils for electrolytic capacitors.

Claims (4)

In a method for manufacturing an electrode foil for an electrolytic capacitor in which electricity is supplied submerged to the etched electrode foil via an electrolyte in a submerged power supply tank,
The electrolyte solution contains ammonium salt of citric acid and phosphoric acid,
A method for producing an electrode foil for an electrolytic capacitor, characterized in that the concentration of ammonium salt of citric acid in the electrolytic solution is 0.13 to 0.25 mol/l . The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the concentration of phosphoric acid in the electrolytic solution is 0.001 to 0.1 mol/l. 3. The electrolytic capacitor according to claim 1, wherein the ammonium salt of citric acid is selected from the group consisting of triammonium citrate, ammonium dihydrogen citrate, and diammonium hydrogen citrate. Method for manufacturing electrode foil for use. The electrode for an electrolytic capacitor according to any one of claims 1 to 3, wherein the submerged power supply using the electrolytic solution is performed at a current density of 50 to 200 mA/cm ² for 3 to 20 minutes. Method of manufacturing foil.