JP2008019509A - Method of manufacturing aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an increased productivity when manufacturing an aluminum foil for an electrolytic capacitor electrode, by eliminating intermediate annealing. <P>SOLUTION: An aluminum material for an electrolytic capacitor electrode comprises, by mass, 5-40 ppm Si, 5-40 ppm Fe, 0.1-3 ppm Pb, 15-150 ppm Ni and the balance being Al and unavoidable impurities, provided that the amount of Cu contained in the unavoidable impurities is <10 ppm and the total amount of the unavoidable impurities other than Cu is ≤100 ppm. The aluminum material is subjected to cold rolling without undergoing any intermediate annealing and subsequently subjected to a final annealing heat treatment to achieve a high cubic crystal rate. A high cubic crystal rate can be achieved at the final annealing, even without performing any intermediate annealing, so that the productivity can be markedly improved without deteriorating the quality. Moreover, a high cubic crystal rate can be achieved over a broad range of thickness of the aluminum foil, just by the final annealing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an aluminum foil used for an electrode of an electrolytic capacitor.

  In the production of aluminum foil used for electrodes of electrolytic capacitors, conventionally, aluminum purity of 99.9% or more, Si 5-20 ppm, Fe 5-20 ppm, Cu 10-80 ppm, Pb 0.1-3 ppm, and other trace impurities 1-100 ppm. When the aluminum material containing is used and producing an aluminum foil 70-130 micrometers thick using this, as shown in FIG.1 (b), hot rolling, cold rolling, intermediate annealing, and additional rolling are performed. After that, final annealing at 500 ° C. or more for 3 hours or more is performed to ensure a cubic crystal ratio of 95% or more. The aluminum foil is then roughened by electrolytic etching in order to increase the surface area, and then converted into electrolytic capacitor electrodes through chemical conversion treatment. However, the corrosion holes (hereinafter referred to as pits) in the electrolytic etching have a cubic orientation. On the other hand, it grows vertically. For this reason, in order to generate pits uniformly and increase the surface area, a high cube orientation occupation ratio is required as an aluminum foil, and the above-described complicated process is employed (for example, Patent Document 1).

In addition, it has been proposed to control the hot working rate and the cold working rate as a method for obtaining a high cubic crystal ratio without performing an annealing process (hereinafter, intermediate annealing) during cold rolling.
In addition, when the foil thickness is> 150 μm or more, the present inventors have found that a high cubic rate can be obtained by performing final annealing at 500 ° C. or more.

Furthermore, in terms of material, conventionally, high purity aluminum of 99.9% or more is used as a foil that can obtain a high cubic crystal ratio, and Fe, Si, Cu, and Pb are mainly used, and the amount of addition is controlled. Things are known. Fe, Si, and Cu are elements that need to be controlled in order to control the recrystallization behavior of aluminum and to obtain a high cubic rate after final annealing. In particular, Cu is necessary for increasing the recrystallization temperature. If it is 15 ppm or less, recrystallized grains grow during rolling, coarsening of non-cubic grains occurs, and a high cubic rate cannot be obtained. On the other hand, when the concentration is 100 ppm or more, grain growth is inhibited, so that a high cubic rate cannot be obtained. The practical range is 20 to 70 ppm.
Further, as a method of simplifying the intermediate process from the material aspect, a method of adding appropriate amounts of Cu and Ni has been proposed (for example, Patent Document 2).
Japanese Patent Publication No.54-11242 JP-A 63-255911

However, as described above, the method of manufacturing through a complicated process and the method of controlling the processing rate are inferior in manufacturing efficiency and increase the manufacturing cost. In addition, in the case where the foil thickness is thick as described above, intermediate annealing can be omitted by increasing the heating temperature in the final annealing, but since the foil thickness is limited, the thinner aluminum foil There is a problem that it cannot be applied.
Further, the inclusion of Cu has a problem in that it dissolves in the electrolytic solution in the electrolytic capacitor product and reprecipitates when energized, causing a spark failure. Since there is a cause of spark failure, Cu on the surface of the etching foil is removed by immersion in concentrated nitric acid or the like after completion of etching.
The present invention provides a method for producing an aluminum foil for electrolytic capacitors, which can achieve a high cubic crystal ratio over a wide range of foil thicknesses and does not contain a Cu component even without intermediate annealing, and can simplify the etching process. It is to provide.

The present invention focuses on Cu, which is the main element, and has found an element that can replace this element. That is, by adding Ni without adding Cu, a high cubic crystal ratio can be obtained without requiring intermediate annealing and without particularly controlling the processing rate such as hot rolling as in the prior art. I found out.
In general, there are already Cube grains serving as cubic nuclei at the end of hot rolling, and in the middle of cold rolling, partial recrystallization is performed by intermediate annealing, and additional rolling is performed. A high cubic rate is obtained by giving strain to the grains and preferentially growing the Cube grains during the final annealing. However, a foil to which an appropriate amount of a component such as Ni is added does not use such manufacturing conditions, so that the Cube grains are sufficiently grown, so that a high cubic crystal ratio can be obtained only by final annealing of the rolled material.

  That is, among the manufacturing methods of the aluminum foil for electrolytic capacitor electrodes of the present invention, the first invention is a mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, Ni: 15 Aluminum material for electrolytic capacitor electrodes containing ~ 150 ppm, the balance being Al and unavoidable impurities, Cu as the unavoidable impurities being less than 10 ppm, and the total amount of unavoidable impurities other than Cu being 100 ppm or less Is subjected to cold rolling without intermediate annealing, and then a final annealing heat treatment for obtaining a high cubic crystal ratio is performed.

  The method for producing an 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 final annealing heat treatment is performed at 450 to 600 ° C. under heating conditions for 2 to 8 hours. To do.

  The method for producing an aluminum foil for electrolytic capacitor electrodes according to the third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the cubic annealing rate is 95% or more by the final annealing heat treatment.

  Below, the effect | action by each component of this invention and the reason which limited each component are demonstrated. In addition, all the component content in the following is mass ratio.

Si: 5 to 40 ppm, Fe: 5 to 40 ppm
Si and Fe combine with Al to produce moderate precipitates, suppress the coarsening of recrystallized grains, and promote the preferential growth of Cube grains. However, if it is less than 5 ppm, the purification cost becomes high, which is unsuitable industrially. On the other hand, in the case where each exceeds 40 ppm, the total amount of precipitates becomes too large to control the preferential growth of Cube grains, so that a high cubic crystal ratio cannot be obtained.
For this reason, the content of Si and Fe is set within the above range. A desirable lower limit is 10 ppm for both Si and Fe, and a desirable upper limit is 20 ppm for both Si and Fe.

Pb: 0.1 to 3 ppm
Pb is an element that makes surface dissolution uniform in etching. However, if it is less than 0.1 ppm, the effect cannot be expected, and if it exceeds 3 ppm, the solubility becomes too high and excessive dissolution occurs. Therefore, the content of Pb is defined above. A desirable lower limit is 0.2 ppm, and a desirable upper limit is 1 ppm.

Ni: 15 to 150 ppm
Ni is an element that promotes preferential growth of Cube grains, and makes it possible to obtain a high cubic crystal ratio only by final annealing without performing intermediate annealing on an aluminum foil having a wide range of thickness. In order to obtain this effect sufficiently, it is necessary to contain 15 ppm or more. If it is less than 15 ppm, it is difficult to obtain a desired cubic crystal ratio without intermediate annealing because the Cube grain growth is insufficient. On the other hand, when Ni is contained in excess of 150 ppm, the Ni surface concentration after the final annealing becomes too large, and excessive dissolution occurs in etching, so that a cubic crystal ratio of 95% or more is obtained, but the foil is difficult to etch. Therefore, the Ni content is defined as above. The desirable lower limit is 20 ppm, and the desirable upper limit is 100 ppm.

Cu: Less than 10 ppm Cu is an element that suppresses recrystallization of Al. However, in order to suppress the preferential growth of Cube grains, if it is contained in a large amount, it is necessary to make the addition amount of Ni 200 ppm or more. In this case, as described above, excessive dissolution occurs. On the other hand, if the amount of Ni added is less than the range where there is no problem of excessive dissolution, it becomes difficult to obtain a cubic crystal ratio of 95%, and intermediate annealing and additional rolling are appropriately performed to ensure the preferential growth of Cube grains. Therefore, the manufacturing process, which is the gist of this patent, cannot be simplified. For this reason, although it is good not to contain Cu as much as possible, in order not to add other than Cu which is contained in bullion etc. and is inevitable, it shall be less than 10 ppm. Desirably, it is 5 ppm or less.

Other impurities: 100 ppm or less If impurities other than Cu are included exceeding this range, precipitates of impurities and aluminum increase, and it becomes difficult to obtain a high cubic crystal ratio only by adding Ni. Desirably, it is 50 ppm or less.

  In addition, since the cubic crystal ratio of 95% or more is the level currently required, the high cubic crystal ratio in this patent means a cubic crystal ratio of 95% or more.

  As described above, according to the method for producing an aluminum foil for electrolytic capacitor electrodes of the present invention, by mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, Ni: 15 to 150 ppm An aluminum material for electrolytic capacitor electrodes in which the balance is made of Al and unavoidable impurities, Cu as the unavoidable impurities is less than 10 ppm, and the total amount of unavoidable impurities other than Cu is 100 ppm or less Cold rolling without annealing, and then performing a final annealing heat treatment to obtain a high cubic rate, so a high cubic rate can be obtained in the final annealing without intermediate annealing, without losing quality, The productivity can be remarkably improved. Further, a high cubic crystal ratio can be obtained only by final annealing in an aluminum foil having a wide range of foil thicknesses, and a high cubic crystal ratio can be suitably obtained particularly in a wide foil thickness range of 70 to 600 μm.

Hereinafter, an embodiment of the present invention will be described.
The high-purity aluminum material prepared to be a component of the present invention 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, or a high-purity aluminum material obtained by continuous casting can be used. The aluminum material preferably has a purity of 99.95% or more.

As shown in FIG. 1A, the high-purity aluminum material is formed into a sheet material having a thickness of, for example, several millimeters by the hot rolling or continuous casting rolling. This sheet material is cold-rolled to obtain an aluminum alloy foil of about several tens of μm to 100 μm. In addition, you may add degreasing suitably in the middle of cold rolling or after completion | finish of cold rolling. Moreover, intermediate annealing in the middle of cold rolling is not required. However, the present invention does not exclude adding intermediate annealing as desired.
After the final cold rolling, a final annealing heat treatment is performed. Although the heating conditions of the final annealing are not particularly limited as the present invention, for example, conditions of 450 to 600 ° C. and 2 to 8 hours can be exemplified.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching process is performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. The present invention is not particularly limited with respect to specific conditions and the like of this etching treatment, and can be performed according to a conventional method, but DC etching is mainly applied.
In the etching process, a high cubic crystal ratio is obtained by setting the above components, pits are formed at a high density on the foil, and a high roughening ratio is obtained. A capacitor having a high capacitance can be obtained by incorporating this foil as an electrode in an electrolytic capacitor by a conventional method.
The aluminum foil obtained from the aluminum material of the present invention is preferably used as an anode of a medium- and high-voltage electrolytic capacitor, but the present invention is not limited to this and may be used for a capacitor having a lower formation voltage. It can also be used as a material for the cathode of an electrolytic capacitor.

An ingot of the component (remaining Al) shown in Table 1 was prepared and subjected to soaking treatment at 500 ° C. or higher for 30 minutes or longer, and then hot rolled at a processing rate of 95 to 99%. At that time, the finishing temperature was 250 to 400 ° C. After hot rolling, cold rolling of 95% or more was performed to prepare a sample having a foil thickness of 120 μm.
Moreover, in order to investigate the influence of a rolling rate, it rolled at the rate shown in Table 2. At that time, the soaking and hot rolling finish temperatures were the same as in Table 1.

  On the other hand, as a comparative material, a cold rolled material having a foil thickness of 150 μm was subjected to intermediate annealing at 200 to 260 ° C. for 2 to 6 hours, and further subjected to additional rolling to prepare a sample having a foil thickness of 120 μm.

These aluminum foils were subjected to final annealing at 500 to 570 ° C. for 3 to 24 hours in an inert atmosphere such as Ar, N ₂ and H ₂ . The aluminum foil after the final annealing was immersed for 30 seconds in a solution of 35% HCl, 60% HNO ₃ , 48% HF mixed at a volume ratio of 33: 33: 1 for 30 seconds, then washed and dried. Samples were produced in which the crystal grain luster on the cubic and other positions was changed.
This sample was taken into an image analyzer and the cube orientation occupation ratio was evaluated. The results are shown in Tables 1 and 2.

As described above, the aluminum foil of the example in which Cu is less than 10 ppm and Ni is added in the range of 5 to 150 ppm has a cubic crystal ratio of 95% or more without performing intermediate annealing and additional rolling. It was equivalent to the foil after intermediate annealing and final rolling. On the other hand, in the case of containing Cu exceeding 10 ppm, it is possible to obtain a high cubic crystal ratio in both cases where the Ni amount is too small (No. 8) and the Ni amount is appropriate (No. 9) without intermediate annealing. could not. Moreover, the Cu removal process was required after the etching. In addition, even when the amount of Cu was appropriate, when the amount of Ni was excessively small (No. 1) or excessively large (No. 6), the same high cubic ratio could not be obtained. It was confirmed that the example materials of the present invention were not affected by the rolling processing rate, and that a high cubic rate was obtained in a process in which intermediate annealing was not performed.

It is a flowchart which shows the manufacturing process (a) of this invention, and the manufacturing process (b) using the conventional aluminum material.

Claims (3)

  In a mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, Ni: 15 to 150 ppm, the balance is made of Al and unavoidable impurities, and Cu as the unavoidable impurities Is less than 10 ppm, and the total amount of inevitable impurities other than Cu is 100 ppm or less, cold-rolled without intermediate annealing, and then subjected to final annealing to obtain a high cubic rate A method for producing an aluminum foil for an electrolytic capacitor electrode, characterized by performing a heat treatment.   The method for producing an aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein the final annealing heat treatment is performed at 450 to 600 ° C under heating conditions for 2 to 8 hours.   The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1 or 2, wherein a cubic crystal ratio is 95% or more by the final annealing heat treatment.

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