JP2858909B2 - Aluminum foil for electrolytic capacitor electrodes - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum foil for an electrode of an electrolytic capacitor.

In this specification, "%" for an alloy component indicates% by weight unless otherwise specified.

2. Description of the Related Art In recent years, there has been an increasing demand for smaller and lighter electrolytic capacitors, and for that purpose, various studies have been made to further improve the capacitance.

An aluminum foil for an electrolytic capacitor electrode is generally used by increasing its surface area by performing electrical or electrochemical etching to increase the capacitance. It is well known that this has a significant effect.

Therefore, conventionally, in order to obtain as large an area coverage as possible by this etching, high-purity aluminum having a purity of 99.98 to 99.99% has been used as the aluminum foil for the electrode, and inevitably Fe, Si, etc. Regarding existing impurities, consideration is also given to the production so as to make the solid solution as much as possible without precipitating them. That is, the presence of the precipitate causes the overdissolution phenomenon of the foil, and not only lowers the capacitance, but also increases the leakage current after the formation, and the presence of the precipitate has been regarded as rather harmful. .

Problems to be Solved by the Invention However, the aluminum foil for an electrode manufactured according to the conventional basic concept as described above is, from the points of purity of the aluminum material used, restrictions on the manufacturing method, strength retention, etc. There is naturally a limit to increasing the capacitance, and it has not always been possible to obtain sufficient satisfaction with the recent demand for further increasing the capacitance.

The present inventors have focused on the fact that it is effective to increase the starting point of etching as much as possible on the foil surface and generate etching pits with high density in order to further improve the capacitance. Various studies were conducted on the effects of the components.

As a result, the presence of precipitated particles due to the precipitation of alloy components is
While having a detrimental surface that causes the overdissolution phenomenon of the foil, a close observation has revealed that the number and density of etching pits have increased. That is, at the time of etching, the presence of the precipitate can be known as that it functions as an etching nucleus, and the starting point of the etching hit originates from around the precipitate particle or from the particle itself. Was. Thus, it has been found that the cause of the overdissolution phenomenon in the foil due to the presence of the precipitate particles is that the precipitate particles exist inside the foil.

Means for Solving the Problems Based on the above findings, the present invention utilizes iron (Fe) contained in aluminum as a forming element of precipitated particles, and forms fine precipitated particles of Al-Fe intermetallic compound. By dispersing only in the surface layer of the foil to increase the number of nuclei serving as starting points of etching.In the interior, the number of precipitated particles is extremely small or desirably absent. As a result, it was possible to prevent the foil from being excessively melted, thereby achieving a further improvement in the capacitance.

Therefore, the aluminum foil for an electrolytic capacitor electrode according to the present invention has two surface layers having a thickness of 10 μm or less, and one inner layer interposed therebetween, and the surface layer includes:
Fe: Al-Fe-based intermetallic compound particles containing 0.001 to 0.3%, the balance being aluminum and unavoidable impurities and having an average particle diameter of 10 μm or less are dispersed, and the inner layer is made of Fe, Si, Cu
Is made of high-purity aluminum whose content is regulated to 0.01% or less, respectively, and the precipitation amount of Fe and Si is 20% or less of those contents.

In the surface layer, in addition to the above-mentioned Fe, as elements further forming a compound with Al-Fe, Si: 0.5% or less, Mn: 0.5% or less, Cu: 0.5% or less.
% Or less, and Ni: 0.5% or less.

In order to promote the tunnel-like growth of the etching pit, the inner layer has a Miller index (100) plane occupancy of 8%.
Preferably, it is 0% or more.

Hereinafter, the components of the present invention will be described in more detail.

First, the reason why the thickness of the surface layer is regulated to 10 μm or less is that the overall thickness of the aluminum foil for the electrolytic capacitor electrode is generally formed to about 75 to 100 μm. Is about 10% or less of the total thickness to reduce the corrosion loss at the time of etching and prevent a remarkable decrease in foil strength. In other words, since the surface layer contains Fe and other elements, the surface dissolution at the time of etching is likely to proceed due to the fact that the surface layer is mainly used for the purpose of increasing the starting point of the etching pit. This is because it is advantageous that the pits are grown deeply and thickly in a tunnel-like manner solely depending on the inner layer. Therefore, the thickness of the surface layer should be at least 10
There is no effect unless it is less than μm, and preferably it should be 5 μm or less.

The surface layer contains 0.001 to 0.3% of Fe to precipitate the Al-Fe intermetallic compound and to disperse the precipitated particles throughout. An Al-Fe intermetallic compound is more noble in potential than aluminum and is advantageous for forming an etching starting point. However, when the particle size exceeds 10 μm, surface dissolution occurs locally,
Decrease capacitance. Preferably, small particles having an average particle diameter of 5 μm or less, more preferably 0.1 to 1.0 μm, occupy the majority, and are desirably uniformly dispersed throughout the surface layer. In the Fe content, it is
If it is less than 0.001%, it is difficult to generate the Al-Fe intermetallic compound particles, and if it exceeds 0.3%, particles having a particle size larger than 10 μm are not preferable. Desirably Fe: 0.003
The content is preferably about 0.05%.

In the surface layer, an element that further forms a compound with Al-Fe, that is,
One or more of Si, Mn, Cu, and Ni,
Both are allowed to contain up to 0.5%. The inclusion of these elements generates particles of precipitated Si, Al-Mn, Al-Cu, etc., in addition to the Al-Fe intermetallic compound, which are dispersed in the surface layer to further etch pits. Can effectively work to increase the starting point of However, when the content of any of the elements exceeds 0.5%, the particle diameter becomes 10 μm.
Larger particles are formed, or work hardening is increased, resulting in poor foil rollability. Therefore, the allowable content of these elements is at most 0.5%, preferably at most 0.2%.

The inner layer, as described above, allows the etching pits formed by the surface layer to have a high density to progress deeper in a tunnel-like manner, thereby increasing the area coverage and preventing overdissolution. Therefore, it is necessary to increase the Al purity and reduce the content of impurities to reduce the number of precipitated particles, or desirably, to a state in which no precipitated particles are present.
Therefore, Fe as an unavoidable impurity,
The content of each of Si and Cu needs to be 0.01% or less, and particularly, the precipitation amount of Fe and Si is 20% of the content.
The following must be regulated: All of them exceed the above upper limit and contain excessive amounts of Fe, Si, and Cu, and when the amount of precipitation of Fe and Si increases, this leads to an over-dissolution phenomenon, which leads to a decrease in capacitance. In addition, since Cu has a large solid solubility limit, the amount of precipitation does not become a particular problem in the above content range. Other impurities, for example, Mn, Mg, Cr, Pb are each 0.005% or less, Z
As long as n and Ga are not more than 0.01%, their content is acceptable.

In order to increase the surface area of the inner layer by causing the etching pits to progress in a tunnel shape, it is desirable that the crystal structure has a high occupancy of the Miller index (100) plane crystal. That is, the (100) plane crystal occupancy is preferably at least 80% or more, and more preferably 90% or more.

In the production of the three-layer electrolytic capacitor electrode foil according to the present invention, the constituent materials of the surface layer and the inner layer are separately manufactured,
After they are press-bonded by hot rolling, cold rolling and, if necessary, intermediate annealing are performed to perform foil rolling to produce a predetermined thickness. And by performing the final annealing,
The simplest production can be achieved by controlling the precipitation state of the particles such as the Al-Fe intermetallic compound within the above-mentioned predetermined range. In the case of this manufacturing method, it is needless to say that it is necessary to use a material having a higher Fe content than the material of the inner layer as the material of the surface layer. However, the aluminum foil of the present invention is not limited to the above-described manufacturing method. For example, the aluminum foil may be manufactured by a method in which the materials for the surface layer and the inner layer are separately manufactured, and both are bonded in the final step.

In the production of surface layer components, harmful coarse metal particles in the layer are often generated during casting solidification. Therefore, in order to avoid the formation of coarse particles,
When the amount of Fe is relatively large, it is particularly desirable to manufacture the surface layer material slab into a supersaturated solid solution by employing a rapid solidification method at a cooling rate of 10 ° C./sec or more.

According to the aluminum foil of the present invention, the number of tunnel-like pits formed by etching is smaller than that of a conventional aluminum foil for a capacitor electrode manufactured as a single-layer foil made of high-purity aluminum having a general purity of 99.98 to 99.99%. Increase,
The capacitance can be further improved, and the demand for a lighter and smaller electrolytic capacitor can be more suitably met.

Examples (Examples 1 to 12, Comparative Examples 1 to 3) High-purity aluminum containing Fe, Si, Mn, Cu, and Ni in various proportions shown in Table 1 and other trace amounts of unavoidable impurities. Various aluminum slabs for the surface layer were produced by semi-continuous casting and, in some cases, by rapid solidification at a cooling rate of 30 ° C./sec. These slabs were hot-rolled to produce a surface layer sheet having a thickness of 5 mm.

On the other hand, an aluminum slab with a purity of 99.99% and a thickness of 300 mm containing 0.001% of Fe, 0.001% of Si and 0.004% of Cu,
It was homogenized at 0 ° C. for 20 hours to obtain an inner layer material.

Then, a sheet for the surface layer is superimposed on both surfaces of the material for the inner layer, and after being pressed by hot rolling, cold rolling and foil rolling are performed to obtain an aluminum clad foil having a thickness of 0.1 mm. It was finally annealed at 480 ° C. for 5 hours to obtain various aluminum foil samples.

In each of the various samples obtained above, the thickness of the surface layer was about 1.6 μm, and the (100) plane crystal occupancy of the inner layer was
It was in the range of 85-95%, and the precipitation amount of Fe, Si, and Cu inside was 10% or less of the content. The size of the precipitated particles in the surface layer was as shown in Table 1.

Therefore, the various samples were subjected to electrolytic etching and chemical formation under the following conditions.

[Electrolytic etching conditions]

Electrolyte: 4% aqueous hydrochloric acid solution Temperature: 70 ° C Current density: 17 A / dm ² hours: 6 minutes [Chemical formation conditions] Chemical solution: boric acid 20 g / + ammonium borate 20 g / solution temperature: 20 ± 5 ° C. Current density : 1200 mA / dm ² Formation voltage: 350 V Then, the capacitance of each of the samples was examined. The results are shown in Table 1 in comparison with the conventional foil.

The conventional foil is made of high-purity aluminum having the same composition as the aluminum material for the inner layer of the above embodiment,
Hot rolling, foil rolling, final annealing (480 ° C x 5 hours in vacuum)
Was manufactured into a single-layer foil having a thickness of 0.1 mm, and the (100) plane crystal occupation ratio was 95%.

(Examples 13 to 16) Aluminum slabs having the compositions shown in Table 2 were hot-rolled to produce surface layer sheets having a thickness of 5 mm.

On the other hand, a high-purity aluminum slab having a purity of 99.98% and a thickness of 300 mm containing Fe: 0.006%, Si: 0.006%, and Cu: 0.002% was homogenized at 600 ° C. for 20 hours to obtain an inner layer material.

Then, the sheet for the surface layer is superimposed on both sides of the sheet for the inner layer, hot-rolled and pressed, then cold-rolled, foil-rolled,
Intermediate annealing (300 ° C × 10 hours), foil rolling (rolling rate 15%) to form a 0.1 mm thick clad foil,
The final annealing was performed at 40 ° C. for 5 hours to obtain various aluminum foil samples.

In each of the samples obtained in this manner, the thickness of the surface layer was about 1.6 μm, and the (100) plane crystal occupancy of the inner layer was 85 to 85%.
It was in the range of 90%, and the precipitation amount of Fe, Si, and Cu inside was 10% or less of the content. The size of the precipitated particles in the surface layer was as shown in Table 2.

Therefore, the various samples were subjected to electrolytic etching and chemical formation under the same conditions as described above, and their respective capacitances were examined. The results are shown in Table 2 in comparison with the conventional foil.

The conventional foils in Table 2 were made of high-purity aluminum having the same composition as the aluminum material for the inner layer of the above embodiment, and were homogenized, hot-rolled, foil-rolled, and finally annealed (540 ° C. in vacuum).
× 5 hours) to produce a single-layer foil having a thickness of 0.1 mm and a (100) plane crystal occupancy of 92%.

──────────────────────────────────────────────────の Continuing on the front page (72) Makoto Tanio, Inventor: 6,224, Kaiyamacho, Sakai City, Osaka Prefecture (72) Inventor: Takeshi Nishizaki 6,224, Kaiyamacho, Sakai City, Osaka Prefecture: Aluminum Showa Inside (72) Inventor Takashi Tamura 6,224 Kaiyamacho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (72) Inventor's name Kenji 6,224 Kaiyamacho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (56) References JP-A-59-65424 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 21/00-21/18 H01G 9/04

Claims (3)

(57) [Claims] The present invention has two surface layers having a thickness of 10 μm or less and one inner layer interposed therebetween. The surface layer contains 0.001 to 0.3% of Fe, the balance being aluminum and unavoidable impurities. Consisting of and an average particle diameter of 10 μm
The following Al-Fe intermetallic compound particles are dispersed, The inner layer is made of high-purity aluminum in which the contents of Fe, Si, and Cu are each regulated to 0.01% or less, and Fe and
An aluminum foil for an electrolytic capacitor electrode, wherein the amount of Si deposited is 20% or less of the content thereof. 2. The surface layer further comprises one or more of Si: 0.5% or less, Mn: 0.5% or less, Cu: 0.5% or less, Ni: 0.5% or less.
The aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the aluminum foil contains at least one kind. 3. The crystal occupation ratio of the Miller index (100) plane of the inner layer is 8
The aluminum foil for an electrolytic capacitor electrode according to claim 1 or 2, wherein the aluminum foil is at least 0%.