JP2010013714A - Aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the etching performance of an aluminum foil for electrolytic capacitor by eliminating the adverse influence of B inevitably incorporated therein. <P>SOLUTION: The aluminum foil for electrolytic capacitor electrode has a composition containing, by mass ratio, one or more selected from Ti, V, Cr and Zr by 7 to 50 ppm in total and B by 0.1 to 3 ppm, and the balance ≥99.9% Al with inevitable impurities, and its thickness is 80 to <125 μm. Suitably, the contents of Ti, V, Cr, Zr and B in the composition satisfy (inequality)... 0.1≤[B]/(0.226[Ti]+0.212[V]+0.208[Cr]+0.119[Zr])≤0.3, and the concentration of B within a depth of 1 μm from the surface is controlled to ≤2 times the average content of B in the whole of the foil. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aluminum foil used for an electrode of an electrolytic capacitor, and more particularly to an aluminum foil for an electrolytic capacitor electrode suitable for an anode for medium to high pressure.

In an aluminum foil for an electrolytic capacitor, in order to increase the capacitance per unit area when used as an electrode, a surface expansion treatment by electrolytic etching is generally performed. The form of etching pits formed on the surface by this electrolytic etching treatment is a factor that directly affects the surface expansion ratio of the entire foil. In order to increase the area expansion ratio, it is necessary to avoid local concentration of etching pits at the initial stage of electrolytic etching and to disperse as uniformly as possible.
It is known that the addition of trace elements is effective for improving etching properties. For example, an aluminum alloy for electrolytic capacitor electrodes in which Ti, V, B, etc. are added to make pits uniform is used. It has been proposed (see Patent Documents 1 and 2).
JP-A-6-220561 Japanese Patent Laid-Open No. 10-287944

By the way, in the aluminum alloy for electrolytic capacitors, the high purity aluminum refine | purified to 99.9% or more is used as a base metal, However B as an inevitable impurity is contained in trace amount. In particular, bullion using the segregation method as a purification means is often added as a treatment agent in the purification stage. This inherent B segregates on the foil surface layer in the final annealing (for example, 500 ° C. or more), and is concentrated in the outermost aluminum oxide film. On the other hand, in the aluminum foil for medium and low pressure electrolytic capacitors as shown in Patent Documents 1 and 2, the final annealing temperature is low, so the concentration of B is not remarkable.
This B concentration increases the barrier property of the oxide film, so that the pit generation position is limited in the initial stage of the electrolytic etching process. Therefore, avoiding B concentration on the surface as much as possible promotes the formation of suitable tunnel pits and leads to an improvement in capacitance.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide an aluminum foil for electrolytic capacitor electrodes that suppresses B concentration on the surface layer and enables uniform pit formation.

  That is, among the aluminum foils for electrolytic capacitor electrodes of the present invention, the first present invention is a mass ratio of one or more of Ti, V, Cr, and Zr in a total of 7 to 50 ppm, and B is 0.1 It is characterized in that it contains ˜3 ppm, and the balance is 99.9% or more of Al and inevitable impurities.

The aluminum foil for electrolytic capacitor electrodes according to the second aspect of the present invention is characterized in that, in the first aspect of the present invention, the contents of Ti, V, Cr, Zr, and B (ppm) in the above composition satisfy the following formula. .
(Formula) 0.1 ≦ [B] / (0.226 [Ti] +0.212 [V] +0.208 [Cr] +0.119 [Zr]) ≦ 0.3

  In the aluminum foil for electrolytic capacitor electrodes of the third aspect of the present invention, in the first or second aspect of the present invention, the B concentration (concentration) within 1 μm depth from the foil surface is the B average content of the entire foil. It is characterized by being 2 times or less.

  According to the present invention, Ti, V, Cr, and Zr that form a compound with B are dispersed in a matrix and bonded to B to prevent diffusion to the surface during heat treatment. To ensure solubility during pit extension.

The reasons for limiting the composition and the like specified in the present invention will be described below.
One or more of Ti, V, Cr and Zr: 7 to 50 ppm in total
These elements form a compound with B and are dispersed in the matrix to prevent the surface concentration of B. Moreover, these compounds do not harm etching.
However, if the total amount of these components is less than 7 ppm, the effect is insufficient, while if it exceeds 50 ppm, it causes overdissolution. For this reason, the total content of these elements is set within the above range. For the same reason, it is desirable that the lower limit of the total amount is 10 ppm and the upper limit of the total amount is 20 ppm.

B: 0.1-3 ppm
As described above, B is inevitably contained in an amount of 0.1 ppm or more by addition during refining of the metal. However, if the content exceeds 3 ppm, the film barrier property is increased by B concentrated on the foil surface, thereby inhibiting pitting. For this reason, B content shall be the said range. The upper limit of B can be controlled by limiting the amount of added B.

0.1 ≦ [B] / (0.226 [Ti] +0.212 [V] +0.208 [Cr] +0.119 [Zr]) ≦ 0.3 (formula)
It is desirable that each content of one or more of Ti, V, Cr, and Zr and the content of B satisfy the above formula.
Here, when [B] / (0.226 [Ti] +0.212 [V] +0.208 [Cr] +0.119 [Zr]) is less than 0.1, relative to B, Ti Etc., and B which is not combined with Ti or the like is easily concentrated on the foil surface. Further, when the above value exceeds 0.3, based on the equivalents of a compound of ₂ such as Ti-B, B becomes excessive, the increases likely state free B. As a result, the B diffused on the surface unnecessarily increases the barrier property of the film or locally distributes to make the generation of etching pits uneven.

  In addition to the above components, the aluminum foil of the present invention contains inevitable impurities such as Si, Fe, and Cu. For example, 5 to 50 ppm for Si, 5 to 50 ppm for Fe, and 10 to 100 ppm for Cu. Usually can be included.

The concentration (concentration) of B within 1 μm depth from the foil surface is less than twice the average. When the B concentration on the foil surface layer (including the oxide film) exceeds twice, the barrier property of the film increases as described above. Therefore, it is desirable that the B concentration on the foil surface layer is not more than twice the average value.

The foil thickness of the present application is about 80 to less than 125 μm.

  That is, according to the aluminum foil for electrolytic capacitor electrodes of the present invention, the mass ratio contains one or more of Ti, V, Cr, and Zr in a total of 7 to 50 ppm, B is contained in 0.1 to 3 ppm, and the balance Since it has a composition composed of 99.9% or more of Al and inevitable impurities, B is prevented from concentrating on the surface during the final annealing, and the pits are uniformly formed during etching to increase the pit diameter and the pit length. This contributes to increasing the capacitance.

Hereinafter, an embodiment of the present invention will be described.
In the melting of an aluminum alloy having a purity of 99.9% or more, the amount of added B is limited at the time of refining the base metal so that it becomes 3 ppm or less. Further, Ti, V, Zr, and Cr are added according to the amount of B, and the composition is adjusted to satisfy the above formula.
The aluminum material can be obtained by a conventional method, and the production method is not particularly limited as the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used, and a high-purity aluminum material obtained by continuous casting can also be used. The slab can be homogenized if desired.

  For example, a sheet material having a thickness of about several mm is formed by the hot rolling or continuous casting rolling. This sheet material is cold-rolled to obtain an aluminum alloy foil having a thickness of 80 μm to less than 125 μm by final cold rolling. In addition, you may add degreasing | defatting suitably in the middle of cold rolling or after completion | finish of cold rolling, and you may add 200-280 degreeC and intermediate annealing for 2 to 10 hours suitably in the middle of cold rolling.

After the final cold rolling, a final annealing heat treatment is performed. The heating conditions for the final annealing are important for obtaining a cubic crystal ratio of 95% or more, and in a reducing atmosphere using H ₂ or the like, an inert gas atmosphere such as Ar or N _2, or a mixed gas atmosphere thereof. Then, the aluminum alloy foil is obtained by heating at a temperature rising rate of at least 30 to 100 ° C./hour between 300 to 450 ° C. and heating at 500 ° C. or more for 6 hours or more. In the final annealing, Ti and B and B effectively form a compound, and free B is prevented from concentrating on the surface layer of the foil.

  The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. Electrolytic etching is usually performed by electrolysis using a DC power source. In the present invention, the type of the electrolytic solution is not particularly limited. The etching process can be performed by a surface layer portion removing process, an etching pit generating process, and an etching pit hole diameter expanding process. The surface layer portion removing step is performed by dissolving the surface layer portion including the oxide film. After the surface layer portion is removed, an etching pit generation step for generating etching pits on the aluminum foil surface is performed. After the etching pit generation process, an etching pit hole diameter expanding process is performed. This foil is subjected to a chemical conversion treatment to obtain a necessary withstand voltage, and then a capacitor having a high capacitance is obtained by incorporating it as an electrode in an electrolytic capacitor by a conventional method. The electrode is usually prepared for an anode and is suitably applied to a medium to high voltage electrolytic capacitor.

An embodiment of the present invention will be described below.
A 4N purity aluminum ingot was used and adjusted to the components shown in Table 1 (others: inevitable impurities + 99.9% or more Al), and then an aluminum slab was prepared by a semi-continuous casting method. The slab was subjected to soaking at 580 ° C. for 2 hours or more, and then hot rolled. At that time, the finishing temperature was 230 ° C. to 350 ° C., and the processing rate was 90% or more. After hot rolling, cold rolling was performed. At that time, intermediate annealing was performed at 200 ° C. to 300 ° C. for 2 to 24 hours, and further cold working of 10 to 20% was performed to obtain a 110 μm aluminum foil. In addition, the intermediate annealing was performed at a stage where the processing rate in cold rolling was 95% or more.
The obtained aluminum foil was finally annealed at 550 ° C. × 6 hours. Inventive material No. No. 8 was finally annealed at 570 ° C. for 6 hours. The cubic crystal ratio after the final annealing was 95% or more. Thereafter, pit generation etching was performed by applying a direct current of 300 mA / cm ² for 120 sec in 1 M hydrochloric acid + 3 M sulfuric acid at 80 ° C. After performing pit generation etching, the pit diameter was expanded by dipping in the same solution for 20 min. The obtained etching foil was formed at 300 V, and the capacitance was measured. The capacitance is measured according to the invention material no. 8 was taken as 100, and was shown by relative evaluation.

  Further, the amount of free B in the surface layer (1 μm from the foil surface) was measured by SIMS (secondary ion mass spectrometry) and ESCA (X-ray electron spectroscopy) on the test material after the final annealing.

Claims (3)

  In a mass ratio, one or more of Ti, V, Cr, and Zr are contained in a total of 7 to 50 ppm, B is contained in an amount of 0.1 to 3 ppm, and the balance is composed of 99.9% or more of Al and inevitable impurities. An aluminum foil for electrolytic capacitor electrodes. The aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein the contents (ppm) of Ti, V, Cr, Zr, and B in the composition satisfy the following formula.
(Formula) 0.1 ≦ [B] / (0.226 [Ti] +0.212 [V] +0.208 [Cr] +0.119 [Zr]) ≦ 0.3   3. The aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein the concentration (concentration) of B within a depth of 1 μm from the surface of the foil is not more than twice the average B content of the entire foil.