JP2858910B2 - 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.

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) and magnesium (Mg) or even silicon (Si) contained in aluminum as a forming element of precipitated particles. , Al-Fe-based, Al-Mg-based, or even Mg-Si-based by dispersing fine precipitate particles by intermetallic compounds and the like only in the surface layer of the foil, the nucleus serving as the starting point of etching The number of etched pits is increased by increasing the number of precipitated particles in the inside to make the number of etched pits extremely small or desirably absent, thereby preventing the foil from being excessively melted, thereby further increasing the capacitance. It was a success in trying to improve the quality.

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 between the two surface layers.
Fe: 0.001 to 0.3% and Mg: 0.05 to 0.5%, the balance consisting of aluminum and unavoidable impurities, and average particle size
Al-Fe-based and Al-Mg-based intermetallic compound particles of 10 μm or less are dispersed, and 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 the precipitation amount of Si is not more than 20% of their content.

In the surface layer, in addition to the above Fe and Mg, further Si: 0.01 to 0.5
%, Whereby fine precipitated Si particles and Mg ₂ Si particles may be dispersed in the surface layer.

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, Mg, or further Si, the surface dissolution at the time of etching is easy to progress because of the relationship (1), so that the surface layer is used for the purpose of increasing the starting point of the etching pit. It is mainly used to grow the pits deeply and thickly in a tunnel shape, because it is advantageous to rely solely on the inner layer. Therefore, the thickness of the surface layer is ineffective unless it is at least 10 μm or less, preferably 5 μm.
m or less.

The surface layer is Fe: 0.001-0.3% and Mg: 0.05-0.5%
To precipitate Al-Fe-based and Al-Mg-based intermetallic compounds, and to disperse the precipitated particles throughout. These intermetallic compounds are more noble in potential than aluminum and are advantageous for forming an etching starting point. However, when the particle diameter exceeds 10 μm, local surface melting occurs, and the capacitance is reduced.
The average particle diameter is preferably 5 μm or less, more preferably 0.1 μm.
It is desirable that the small particles of 1 to 1.0 μm occupy the majority and that they are uniformly dispersed throughout the surface layer. If the Fe content is less than 0.001% and the Mg content is less than 0.05%, it is difficult to form the above-mentioned intermetallic compound particles, and if the content exceeds Fe: 0.3% and Mg: 0.5%, the particle size becomes 10 μm. It is not preferable because larger particles are formed. In particular, when the content of Mg is excessive, dissolution is likely to occur even under the influence of the oxide. Desirably Fe: 0.003-0.05
%, Mg: 0.1 to 0.3%.

More preferably, 0.01 to 0.5% of Si is allowed in the surface layer. The content of this Si is Al-Fe based, Al
In addition to the Mg-based intermetallic compound, particles of precipitated Si, Mg ₂ Si, etc. are generated and dispersed in the surface layer, which effectively acts to further increase the starting points of etching pits. If the Si content is less than 0.01%, this effect is poor, and if it exceeds 0.5%, particles having a particle diameter of more than 10 μm are formed, and the foil rollability deteriorates. Therefore, the most preferable Si content is about 0.03 to 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 addition, 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 electrolytic capacitor electrolytic foil having the three-layer structure 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,
By controlling the precipitation state of particles such as Al-Fe intermetallic compound within the above-mentioned predetermined range, and further performing aging treatment at a low temperature after the high-temperature treatment, the particles such as Al-Mg-based precipitates and Mg ₂ Si are dispersed. The simplest production is possible by making it strict. 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 7, Comparative Examples 1 to 3) Using high-purity aluminum containing Fe, Mg, and Si in various proportions shown in Table 1 and other trace amounts of inevitable impurities, Various aluminum slabs for the surface layer were manufactured by the continuous casting method and, in some cases, the rapid solidification method 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. Final annealing at 500 ℃ for 5 hours and further at 200 ℃
Various aluminum foil samples were obtained by performing an artificial aging treatment for 30 hours.

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 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%.

──────────────────────────────────────────────────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] (1) It has two surface layers having a thickness of 10 μm or less and one inner layer interposed therebetween, wherein the surface layer contains Fe: 0.001 to 0.3% and Mg: 0.05 to 0.5%. Containing aluminum and inevitable impurities,
In addition, Al-Fe-based and Al-Mg-based intermetallic compound particles having an average particle diameter of 10 μm or less are dispersed, and 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 contains Si: 0.01 to 0.5%,
The average particle diameter of 10μm following claims precipitation Si particles and Mg ₂ Si particles dispersed (1) aluminum foil for electrolytic capacitor electrodes as claimed. 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%.