JP3544768B2 - Method of forming electrode foil for electrolytic capacitor - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for forming an electrode foil for an electrolytic capacitor, and more particularly to a method for forming an anode foil having high withstand voltage and high toughness.
[0002]
[Prior art]
In an aluminum electrolytic capacitor, a capacitor element in which an anode foil and a cathode foil of aluminum are wound through a separator paper is impregnated with a driving electrolyte (hereinafter referred to as an electrolyte), and the capacitor element is sealed with an aluminum casing together with a sealing body. It is assembled in a case, and the outer case is sealed.
The anode foil used for the capacitor is prepared by boiling a conventionally etched aluminum foil in pure water and then mixing one or more inorganic acids such as phosphoric acid or boric acid, organic acids such as adipic acid, or salts thereof. It was obtained by electrolytic formation in a liquid.
[0003]
[Problems to be solved by the invention]
The anode foil formed in such a processing solution becomes brittle, particularly when formed at a high pressure of 100 V or more, and is liable to crack. Therefore, when wound around a capacitor element, the leakage current due to the crack generation is reduced. This has the disadvantage of causing an increase and an increase in the aging time. As the electrolytic chemical solution, an organic acid-based chemical solution that can easily treat a waste liquid is desirable. For example, a chemical solution containing adipic acid is limited to a chemical conversion of 400 V.
[0004]
[Means for Solving the Problems]
The chemical conversion method according to the present invention comprises a pure water boil step of immersing the etched aluminum foil in high-temperature pure water for a predetermined time , followed by at least polyacrylic acid or a salt thereof, zirconium, phosphoric acid, phosphorous acid, and hypophosphorous acid. Alternatively, the aluminum foil is immersed in an electrolytic solution containing each salt thereof, and a main chemical conversion step of performing anodic oxidation by applying a voltage for a predetermined time, and the aluminum foil is immersed again in the electrolytic solution. And a re-chemical conversion step of performing anodic oxidation by applying a voltage for a predetermined time.
[0005]
Embodiment 1
The aluminum foil of the experimental sample had a purity of 99.99% and a thickness of 100 microns, was collected to have an area of 20 cm ² , boiled in high-temperature pure water for 5 minutes, and then dried.
[0006]
As a chemical conversion solution, a solution was prepared by dissolving polyacrylic acid in pure water to a concentration of 1.0% by weight and dropping an equal amount of aqueous ammonia. Zirconium was dissolved in this solution to a concentration of 0.01% by weight. This solution was kept at 30 ° C., the aluminum foil used in Example 1 was immersed, and the anode was used as an anode for formation at a current of 1 mA, and the VT curve was measured. Next, the foil after chemical conversion was dried, bent at 45 degrees, re-chemically formed in an electrolytic solution, and its VT curve was measured. It is shown also shown both results in FIG. Next, this bent surface was observed by SEM. This photograph is shown in FIG .
[0007]
Embodiment 2
As a chemical conversion solution, a solution was prepared by dissolving polyacrylic acid in pure water to a concentration of 1.0% by weight and dropping an equal amount of aqueous ammonia. Ammonium phosphate was dissolved in this solution to a concentration of 0.01% by weight. The solution was kept at 30 ° C., and the aluminum foil used in Example 1 was immersed. The aluminum foil was used as an anode to form a chemical with a current of 1 mA, and the VT curve was measured. Next, the foil after chemical conversion was dried, bent at 45 degrees, re-chemically formed in an electrolytic solution, and its VT curve was measured. It is shown also shown both results in Figure 3.
[0008]
[Comparative example]
As a chemical conversion solution, a solution was prepared by dissolving adipic acid in pure water at a concentration of 5.0% by weight and dropping an equal amount of aqueous ammonia. This solution was kept at 30 ° C., and the above-mentioned aluminum foil was immersed, and a chemical conversion was performed at a current of 1 mA using the aluminum foil as an anode, and the VT curve was measured. Next, the foil after chemical conversion was dried, bent at 45 degrees, re-chemically formed in an electrolytic solution, and its VT curve was measured. It is shown also shown both results in Figure 4. Next, this bent surface was observed by SEM. Shows this photograph is shown in FIG. 5.
[0009]
As is clear from the above results, Examples 1 and 2 have higher withstand voltage, higher chemical conversion properties, and clearly higher re-chemical conversion properties after bending than the adipine oxidation of Comparative Example. Comparing the bending surfaces by SEM, it is clear that a film having few cracks and excellent toughness is formed. By changing the type of the additive, it is possible to form films having different pressure resistance.
Even if polyacrylic acid is dissolved in a conventional boric acid, phosphoric acid, or adipic acid-based chemical conversion solution, an increase in pressure resistance is confirmed, and a mixed solution thereof may be used as the chemical conversion solution.
[0010]
【The invention's effect】
As described above, the method for forming an anode foil according to the present invention uses a mixed solution of polyacrylic acid or a salt thereof and zirconium, phosphoric acid, phosphorous acid, hypophosphorous acid or a salt thereof in an electrolytic formation solution. Thus, it is possible to form a high withstand voltage film which is rich in toughness and hardly generates cracks. Moreover, the treatment is easy because it is an organic acid-based chemical conversion solution.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a VT curve according to an embodiment of the present invention.
FIG. 2 is an SEM photograph according to an example of the present invention.
FIG. 3 is a diagram illustrating a VT curve according to another embodiment of the present invention.
FIG. 4 is a diagram showing a VT curve according to a conventional comparative example.
FIG. 5 is an SEM photograph according to a conventional comparative example.

Claims (1)

A pure water boil step of immersing the etched aluminum foil in high-temperature pure water for a predetermined time, and then at least polyacrylic acid or a salt thereof , and zirconium, phosphoric acid, phosphorous acid, hypophosphorous acid or a salt thereof . The aluminum foil is immersed in the electrolytic solution containing the aluminum foil, and the aluminum foil is immersed again in the chemical conversion step of applying a voltage for a predetermined time to perform anodic oxidation and the electrolytic formation solution, and applying a voltage for a predetermined time. A method for producing an electrode foil for an electrolytic capacitor, comprising a re-chemical conversion step of performing anodization.

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