JPH01287918A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a high capacitance by a method wherein etched aluminum foil is dipped into high temperature pure water for the prescribed period, then the aluminum foil is dipped into the aqueous-solution containing citric acid or its salt, and the foil is anodicoxodated by applying voltage for the prescribed period. CONSTITUTION:A sheet of aluminum etching foil is prepared, and in, this case, its multiplying factor of etching is set at the prescribed rate against the flat foil which is not etched. The etched aluminum foil is boiled in pure water, then the aluminum foil if dipped into the aqueous solution containing citric acid or its salt, and an anodic oxidizing operation is conducted by applying voltage for the prescribed period. Subsequently, a depolarization treatment is conducted, a heat treatment is performed in a heated atmosphere, and a reanodic-forming process is conducted in the aqueous solution containing adipic acid or its salt. As a result, an electrode foil having high electrostatic capacitance can be obtained.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method of manufacturing an electrode foil for an aluminum electrolytic capacitor. [Prior Art] Generally, this type of electrode foil is made as follows. First, an etched aluminum foil is prepared, the aluminum foil is immersed in an aqueous solution of phosphoric acid or boric acid, and a certain voltage is applied to form an oxide film of a desired thickness. Then, a heat treatment step of leaving the product in a high temperature atmosphere of several 100° C. for several minutes is repeated several times. [Problems to be Solved by the Invention] However, this method has a limit in increasing the capacity, and cannot meet the recent demands for smaller size and higher capacity. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which enables higher capacitance to be obtained.

[Means to solve the problem]

In order to achieve the above object, in the present invention, an etched aluminum foil is first immersed in high-temperature pure water for a predetermined period of time, and then the aluminum foil is immersed in an aqueous solution containing citric acid or its salt. The anodic oxidation is performed by applying a voltage for a predetermined period of time. Subsequently, depolarization treatment, heat treatment in a heated atmosphere, and re-anodization treatment are performed at least once. According to this method, the capacity increases by about 10% compared to the conventional method. In addition, the citric acid concentration in the above aqueous solution is 0.005
~0.1 wt% and the liquid temperature is preferably 70~100°C. Also, ammonia water with a pH of 7~9 and a liquid temperature of 70°C is used for the depolarization treatment. The immersion time is about 1 to 5 minutes. Furthermore, heat treatment is preferably performed at 400 to 500°C for about 1 to 3 minutes, and
In the re-anodizing treatment, the concentration of adipic acid or its salt is 0.01 to 0.5 wt%, and the liquid temperature is 70 to 100.
Preferably it is ℃. [Examples] Specific examples and comparative examples of the present invention will be described below.
The present invention is not limited to this embodiment. <Example 1> (A) An aluminum etched foil with a purity of 99.99% and a thickness of 1100 u was prepared. In this case, the etching magnification is 20 times relative to the unetched flat foil. (B) This aluminum etched foil was heat-treated for 9 minutes in pure water at a liquid temperature of 98° C. or higher. (C) Next, an aqueous solution of citric acid 0.3 g/ε, liquid temperature 85
The aluminum etching foil was immersed in the temperature at a current density of 1
A current of 0 mA/cm'' was applied, the forming voltage was increased to 380 V, and the same voltage was applied for 40 minutes to carry out forming.
, immersed in ammonia water adjusted to pH 7-9 for 3 minutes,
Depolarization treatment was performed. (E) Heat treatment was performed for 2 minutes in a heating atmosphere of 500°C. (F) Immerse again in an aqueous solution in which 0.3 g of adipic acid is dissolved per 12 parts of pure water, at a temperature of 85°C, and at a current density of 10 m.
A current of "A/cm" was applied, the formation voltage was increased to 380V, and the same voltage was applied for 13 minutes to re-formation. (G) The same heat treatment as in (E) above was carried out. (H) The same heat treatment as in (F) above was carried out. The chemical conversion treatment was repeated, and in this case, the chemical conversion voltage was applied for 3 minutes. (I) After washing with water and drying, the capacitance of the chemical conversion foil was measured and found to be 0.803 μF/cm. (J) This chemically formed foil (15 mm x 270 mm) was used as an anode, and an aluminum foil (15 mm x 300 mm) with a purity of 99.2%, thickness of 20 μm, and etching magnification of 50 times was used as a cathode, and the capacitor element was created by winding the foil through a separator. did. When this capacitor element was impregnated with electrolyte and sealed in a case to create an electrolytic capacitor with a rating of 250V and 30μF, its capacity was 31.7
It was μF. Note that between the above step (H) and step (I). An aqueous solution of 25 ml/il of 85 wt% phosphoric acid, adjusted to pH 6.5 with ammonium, and a solution temperature of 30 ml/il.
An electrolytic capacitor to which this step has been added may include a step of immersing it in an aqueous solution at ℃ for 4 minutes, for example.
It is possible to prevent product deterioration due to leakage current in a high temperature storage test at 05°C for 1000 hours. Comparative Example 1> (a) Same as above (A) (b) Same as above (B) (c) Boric acid 80 g/Q and ammonium borate 0.05 g
A chemical formation voltage was applied to an aqueous solution consisting of /β at a liquid temperature of 85° C. under the same conditions as in (C) above. (d) Depolarization treatment was performed under the same conditions as in (D) above. (e) Heat treatment was performed under the same conditions as in (E) above. (f) It was immersed again in an aqueous solution under the same conditions as in (c) above at a liquid temperature of 85°C. The current density (10 mA/cm”), formation voltage (380 V), and application time (13 minutes) were as described above (F
)Same as. (g) Heat treatment was performed under the same conditions as in (E) above. (h) Same as (f) above, but in this case, the voltage application time is 3 minutes. (1) Same as (I) above, but in this case. When the capacitance of the chemically formed foil was measured, it was 0.756μF/Cm
(j) When the same electrolytic capacitor as in (J) above was made, its capacitance was 29.2 μF. Comparison> As mentioned above, according to this example, the capacitance was 29.2 μF. [Effects of the Invention] As explained above, according to the present invention, an etched aluminum foil is boiled in pure water, and then the same aluminum foil is boiled in pure water. immersed in an aqueous solution containing citric acid or its salt,
An electrode foil with high capacitance is manufactured by applying a voltage for a predetermined period of time to perform anodic oxidation, and then re-anodizing in an aqueous solution containing adipic acid or its salt.

Claims (1)

[Claims] (1) A pure water boiling process in which the etched aluminum foil is immersed in high-temperature pure water for a predetermined time, and then the aluminum foil is immersed in an aqueous solution containing citric acid or its salt and a voltage is applied for a predetermined time. A method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which comprises an anodizing step and a re-anodizing step of immersing the electrode foil in an aqueous solution containing adipic acid or its salt and applying a voltage for a predetermined period of time.