JP2631488B2 - Electrolytic capacitor electrode foil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a foil for an electrode of an electrolytic capacitor, and particularly to a foil for an anode of an electrolytic capacitor made of an aluminum alloy.

[Prior art and its problems]

In general, aluminum electrolytic capacitors are made of high-purity (more than 99.9%) aluminum, especially high-purity aluminum with a purity of more than 99.99%. After increasing the effective surface area by performing an appropriate chemical conversion treatment such as anodic oxidation treatment, a dielectric film of aluminum oxide is formed on the foil surface to form an anode, and a thickness of 20% or more with a purity of 99% or more. The aluminum foil surface of about 60 microns is roughened by an etching treatment such as AC electrolytic etching, and the roughened surface is used as a cathode. Separate paper is sandwiched between the anode and the two foils of the cathode, and wound into a cylindrical shape.
And it is constituted by impregnating the separate paper with the electrolytic solution. Since the capacitance of such an electrolytic capacitor is directly proportional to the surface area of the electrode surface, the effective surface area of the electrolytic capacitor anode foil is increased by direct current electrolytic etching of the surface in an aqueous solution such as hydrochloric acid or salt. Is planned. The effective surface area of the aluminum foil is increased in order to increase the capacitance. However, if the etching process performed to increase the effective surface area proceeds excessively, a roughening (etching) process is performed. As a result, the mechanical strength is reduced, resulting in a disadvantage that the aluminum foil constituting the electrode is cut. The increase in the effective surface area of the aluminum foil due to the DC electrolytic etching process will be affected by the etching conditions, but it has been known that the increase is significantly affected by the composition of the aluminum material,
Research in this area has been particularly concentrated. As a result, for example, 99.99% containing 0.0001-1.0% silver
It is proposed to use an aluminum alloy having a purity of at least 9% as a foil for an electrode of an electrolytic capacitor (Japanese Patent Publication No. 42-14289), and a total amount of at least 99.9% of aluminum containing 0.0002 to 0.015% of indium and / or cadmium. Proposal to use alloy as foil for electrode of electrolytic capacitor (Japanese Patent Publication No. 44-29577), Proposal to use aluminum alloy with purity of 99.99% or more containing 0.004 to 0.01% of copper as electrode foil for electrolytic capacitor (Special Publication 45-25
No. 978), an aluminum alloy having a purity of 99.99% or more containing 5 to 200 ppm of antimony, barium or zinc, 0.5 ppm or less of lead or bismuth, and 2 ppm or less of calcium or chromium can be used as an electrode foil for an electrolytic capacitor electrode. Proposal (Japanese Patent Laid-Open No. 50-104710), the total amount is 0.00005-
It has been proposed to use an aluminum alloy having a purity of 99.9% or more containing 0.001% of lead and / or bismuth as a foil for an electrode of an electrolytic capacitor (JP-A-53-114059).
It has been proposed to use an aluminum alloy having a purity of 99.9% or more containing 1 to 1 ppm of indium as an electrolytic capacitor electrode foil (Japanese Patent Publication No. 60-47896), and 0.0004 to 0.001.
5% iron, 0.001-0.008% copper, total amount 0.00001-0.001%
Silver, zinc, cadmium, gallium, indium, tin,
It is proposed to use an aluminum alloy having a purity of 99.99% or more containing nickel and / or nickel as a foil for an electrode of an electrolytic capacitor (Japanese Patent Publication No. 62-37105).
m is defined as the surface portion, and at least one of lead, indium and bismuth is present in the surface portion in a total amount of 0.005 to 0.2%, and in the inner layer portion excluding the surface portion, the amounts of lead, indium and bismuth are each less than 0.0001%. It has been proposed to use an aluminum alloy having an average purity of 99.9% or more as a foil for an electrode of an electrolytic capacitor (Japanese Patent Publication No. 62-42370), and these aluminum alloys are said to have obtained a reasonable effect. Have been done. However, while an electrolytic capacitor is manufactured using an aluminum alloy containing a desired amount of indium or the like, a predetermined period of time has elapsed since a foil made of an aluminum alloy containing a predetermined amount of a metal element such as indium was manufactured. After that, when an electrolytic capacitor was constructed using this foil,
It has been found that although this is an aluminum alloy having the same composition, it does not have the same electrostatic characteristics as the electrolytic capacitor formed shortly after the production of the foil.

DISCLOSURE OF THE INVENTION

The present invention, while examining the above phenomenon in detail, came to the knowledge that this was because a slight amount of corrosion occurred on the surface of the aluminum alloy foil constituting the electrolytic capacitor electrode foil. . That is, since the presence of a metal element such as indium contained in the aluminum alloy promotes a corrosion phenomenon on its surface, it was constituted by using an aluminum foil which was taken out and stored for a long time and anodized. It has been found that the electrolytic capacitor has deteriorated in its electrostatic properties and mechanical properties. The present inventor has conducted further research based on such findings, and as a result, has found that an aluminum alloy foil having at least one compound selected from a silicon-based compound and a phosphorus-based compound interposed on a surface portion thereof is obtained. The electrolytic capacitor formed using the present invention has found that even if a long period of time has elapsed from the production of the foil to the production of the electrolytic capacitor, it has been found that the electrostatic characteristics have not significantly decreased, and the present invention has been made. I did it. As a means for interposing a silicon-based compound and a phosphorus-based compound on this surface portion, for example, the foil surface of an aluminum alloy is treated (immersion, spraying, etc.) with a solution containing a silicon-based compound and a phosphorus-based compound, or thereafter, 300 ° C under vacuum or non-oxidizing atmosphere
It suffices to anneal at the above temperature, and perform an etching treatment to increase the effective surface area of the surface after this annealing,
If a predetermined chemical conversion treatment is performed to form a dielectric film (oxide film) after the etching process, a foil for an electrode element of an electrolytic capacitor can be obtained. And, as the silicon-based compound, at least one selected from the group consisting of silicic acid, silicate and silicate ester can be used, and for example, an aqueous solution of inorganic sodium silicate such as water glass is used. As the phosphorus compound, at least one selected from the group consisting of phosphoric acid, inorganic phosphates, inorganic phosphate esters and phosphonic acid compounds can be used. An aqueous solution of an inorganic phosphate (Na, K, Zn, etc.) such as acid soda can be used. It is more desirable to add a surfactant to these compound solutions so that the surfactant is also present at the same time. Further, as the aluminum alloy used for the electrolytic capacitor electrode foil, metal elements dissolved together with aluminum by etching, for example, iron, silicon, indium,
Copper, silver, zinc, cadmium, gallium, tin, lead, nickel, strontium, thallium, antimony, barium, calcium, sodium, chromium, titanium, vanadium, zirconium selected from a group of at least one or more. For example, it is desirable that the total content be about 200 ppm or less. In particular, a desirable aluminum alloy is 99.99%
4 to 20 Fe in the high purity aluminum base metal
ppm, Si 4-20ppm, Cu 15-60ppm, Zn 0.1-10pp
The content of m and In was adjusted to be 0.5 to 5 ppm. That is, when the content of Fe is too small, less than 4 ppm, although there is no significant adverse effect on the characteristics of the capacitance, the strength of the aluminum foil as an electrode of the wound electrolytic capacitor is undesirably reduced. In addition, if the amount exceeds 20 ppm, the pressure resistance of the chemical conversion film (oxide film) tends to decrease. Therefore, it is desirable that the Fe content in the high-purity aluminum alloy be 4 to 20 ppm. is there. Regarding the contained Si, when the content of Si increases, the production of aluminum alloy foil (hot rolling, cold rolling,
Since the history of (annealing) time greatly changes the solid solution / precipitation state in the aluminum foil matrix, and the characteristics such as capacitance and bending strength vary, the content is desirably 20 ppm or less. Conversely, if the amount is too small, the strength tends to decrease.
~ 20 ppm was desirable. Also, if the Cu content is too low, less than 15 ppm,
The pitting start point at the time of DC electrolytic etching is uniformly present, and the effect of increasing the capacitance is small.
If the content exceeds ppm, the etching tends to proceed excessively, so that the dissolution loss increases, and the bending strength, capacitance and pressure resistance of the aluminum foil tend to decrease. A content of 15 to 60 ppm was desired. Also, if the content of Zn is too small as less than 0.1 ppm,
Variations in the capacitance in the width direction of the aluminum alloy foil tend to be observed. Conversely, when the capacitance exceeds 10 ppm, the etching proceeds excessively, and particularly, the etching proceeds locally (for example, in the width direction of the aluminum foil). Abnormal melting easily occurs at both ends of the coil. Therefore, the Zn content is 0.1
~ 10 ppm was desired. Further, if the content of In is too large, the dissolution loss is too large, and the bending strength and the electrostatic characteristics of the aluminum foil tend to be reduced. Therefore, the content of In is preferably 5 ppm or less. It was. In addition, Fe, Si,
For the addition and adjustment method of alloying elements such as Cu, Zn, In, etc.
There is no particular limitation as long as each alloy element is uniformly dissolved and precipitated, and when these alloy elements are present in a high-purity aluminum metal base metal, Fe, S
What is necessary is just to adjust the addition amount of i, Cu, Zn, In, etc., especially the addition amount of Si so that the content may be within the above range.

Examples 1 to 10 A 99.99% high-purity aluminum base metal was dissolved by an ordinary method, and Fe, Si, Cu, Zn, and In were added and adjusted to the contents as shown in the table. The thus cast aluminum alloy is hot-rolled and cold-rolled into an aluminum alloy foil having a thickness of 100 μm. The aluminum alloy foil thus obtained was immersed in an aqueous solution of No. 3 water glass (concentration 0.5%) and / or an aqueous solution of tetrapolyphosphoric acid (concentration 0.2%). After intervening a trace amount of acid soda, this is heated at 550 ° C in an inert gas atmosphere.
Anneal at In order to prevent the coil-shaped aluminum alloy foil surfaces from adhering to each other at the time of annealing, sodium silicate and sodium tetrapolyphosphate were adhered, and ordinary rolling oil was applied to the surface. The aluminum alloy foil after the above annealing step is left in the air immediately and for one month, and then subjected to a direct current electrolytic etching treatment in an aqueous hydrochloric acid solution, washed with water, and then subjected to a chemical conversion treatment by applying a voltage in a boric acid aqueous solution. Then, an oxide film was formed on the surface, and this was used as a capacitor anode foil, and an electrolytic capacitor element was manufactured using this capacitor anode foil and a conventional aluminum alloy electrolytic capacitor cathode foil.

Comparative Examples 1 to 10 An aluminum alloy obtained by adding the alloy components shown in the table to a 99.99% high-purity aluminum base metal was used, and the treatment with a water glass aqueous solution and a sodium tetrapolyphosphate aqueous solution was omitted. An electrolytic capacitor element was manufactured in the same manner as in the example.

【Characteristic】

The characteristics of the electrolytic capacitor element obtained as described above were examined, and the results are shown in the table.

Claims (7)

(57) [Claims] (1) Fe content of 4 to 20 ppm, Si content of 4 to 20 p
pm, Cu content is 15-60ppm, Zn content is 0.1-10ppm, In
The aluminum alloy foil is made of high-purity aluminum of 99.9% or more whose content is adjusted to 0.5 to 5 ppm, and at least one compound selected from a silicon-based compound and a phosphorus-based compound is present on a surface portion. A foil for an electrolytic capacitor electrode, comprising: 2. The foil for an electrolytic capacitor electrode according to claim 1, wherein the surface of the aluminum alloy foil is treated with a solution containing at least one compound selected from a silicon compound and a phosphorus compound. And then annealed. 3. The foil for an electrolytic capacitor electrode according to claim 1, wherein the silicon-based compound is silicic acid, silicate, or silicate ester. 4. The foil for an electrolytic capacitor electrode according to claim 1 or 2, wherein the phosphorus compound is a phosphoric acid, a phosphate, a phosphate ester, or a phosphonate compound. 5. The foil for an electrolytic capacitor electrode according to any one of claims 1 to 4, wherein the aluminum alloy is silver, cadmium, gallium, tin, lead, nickel, strontium, thallium, antimony, A substance containing at least one selected from the group consisting of sodium, barium, calcium, chromium, titanium, vanadium, and zirconium. 6. The electrolytic capacitor electrode foil according to any one of claims 1 to 5, wherein the content of a metal element dissolved together with aluminum by etching is reduced.
What is less than 200ppm. 7. The foil for an electrolytic capacitor electrode according to any one of claims 1 to 6, wherein the aluminum alloy foil is etched.