JP2007169690A - Aluminum foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil for an electrolytic capacitor, which acquires a superior surface-roughened rate after having been etched because pits are uniformly formed thereon at high density. <P>SOLUTION: This aluminum foil has a composition comprising, by mass ratio, 5-100 ppm Si, 5-100 ppm Fe, 10-100 ppm Cu, 0.1-5 ppm Pb, 1-100 ppm Zn, 11-200 ppm W, and the balance 99.9% or more Al with unavoidable impurities; and has an orientation factor of cubic crystals of 95% or more. The total amount of Mn, Mg, Cr, Ti, B, V and Ga in the unavoidable impurities is desirably controlled to 50 ppm or less. The aluminum foil can have uniform pits formed thereon at the high density while inhibiting the dissolution of the surface in an etching step, and imparts high strength and high capacitance to an etched foil. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aluminum foil for electrolytic capacitor electrodes used for electrodes of electrolytic capacitors.

The aluminum foil for electrolytic capacitors increases the electrostatic capacity by generating a large number of corrosion holes (hereinafter referred to as pits) that have grown vertically from the surface and expanding the surface area. Since the etching pits grow along cubic crystals, a high cubic crystal ratio foil is used to generate uniform pits.
Conventionally, the addition and regulation of various elements have been proposed in order to uniformize and increase the density of pits in DC electrolytic etching.
For example, in Patent Document 1, Si: 5-60 ppm, Fe: 5-60 ppm, Cu: 10-70 ppm, Zn: 0.1-40 ppm, Na: 0.001-5 ppm, 0.1 ppm ≦ Ti, V ≦ 5 ppm , 0.1 ppm ≦ Cr, Mn, Zr ≦ 10 ppm, 0.1 ppm ≦ Ga ≦ 30 ppm, Mg ≦ 7 ppm, and (4) ≦ (Ti + V + Cr + Mn + Zr + Na + Ga−Mg) [ppm] ≦ 34 It is proposed that the loss of dissolution is suppressed at the same time that the capacitance is high and the capacitance is high.
Furthermore, Patent Document 2 proposes that the total amount of Ti, V, Cr, Zr, and W be restricted to 10 ppm or less in order to suppress surface dissolution of the aluminum foil.
Furthermore, Patent Document 3 proposes that the content of Zr or V is restricted to 11 to 100 ppm in order to increase the number of pits generated.
Japanese Patent No. 3370246 JP 2001-102271 A JP 2002-97538 A

  However, the conventionally proposed component range cannot bring out the contradictory effect of facilitating pit generation while suppressing surface dissolution. In addition, even if pits are easily generated, there is a problem that the generated pits do not sufficiently contribute to the capacity because of the uniform dispersibility.

  The present invention has been made in the background of the above circumstances, and provides an aluminum foil for electrolytic capacitors that can obtain a uniform and high-density pit form when performing direct current electrolytic etching as an aluminum electrolytic capacitor foil. Is the basic purpose.

  In order to increase the capacity of the capacitor, it is necessary to generate pits that are easy to generate pits and have excellent uniformity while suppressing surface dissolution. In particular, in order to generate pits at a high density, it is necessary to increase the reactivity directly under the oxide film. As a result of intensive research, the amount of pits generated can be significantly increased by adding an appropriate amount of W. Turned out to be possible. Furthermore, by combining Zn, etching pits are made uniform, and an etching foil having high strength and high capacity can be obtained.

  That is, among the aluminum foils for electrolytic capacitors of the present invention, the invention according to claim 1 is an aluminum foil for electrolytic capacitors to be used for etching, and in terms of mass ratio, Si: 5 to 100 ppm, Fe: 5 to 100 ppm Cu: 10 to 100 ppm, Pb: 0.1 to 5 ppm, Zn: 1 to 100 ppm, W: 11 to 200 ppm, with the balance being 99.9% or more of Al and inevitable impurities, cubic The crystal orientation ratio is 95% or more.

  The invention of the aluminum foil for electrolytic capacitors according to claim 2 is the invention according to claim 1, wherein the total amount of Mn, Mg, Cr, Ti, B, V, Ga in the unavoidable impurities is 50 ppm or less. Features.

  Below, the reason which prescribed | regulated the component by this invention is demonstrated.

Si: 5 to 100 ppm
Si is an element that affects the recrystallization of aluminum foil. However, if it is less than 5 ppm, there is no effect, and if it exceeds 100 ppm, the necessary crystal grains cannot be obtained, so the content is set to 5 to 100 ppm. For the same reason, the desirable lower limit is 10 ppm and the upper limit is 20 ppm.

Fe: 5 to 100 ppm
Fe is an element that affects the recrystallization and solubility of aluminum foil. However, if it is less than 5 ppm, crystallization is promoted too much, so that a necessary orientation cannot be obtained. If it exceeds 100 ppm, precipitation of Al—Fe system is increased and solubility is increased, which is not preferable. Therefore, the content of Fe is set to 5 to 100 ppm. For the same reason, the desirable lower limit is 10 ppm, and the desirable upper limit is 40 ppm.

Cu: 10 to 100 ppm
Cu is an element that promotes the growth of pits in etching. However, if it is less than 10 ppm, sufficient pit growth is not performed, and if it exceeds 100 ppm, an excessive dissolution reaction occurs, which is not preferable. Therefore, the Cu content is set to 10 to 100 ppm. For the same reason, the desirable lower limit is 20 ppm, and the desirable upper limit is 70 ppm.

Pb: 0.1-5 ppm
Pb is an element that facilitates initial etching pit generation. However, if it is less than 0.1 ppm, there is no effect, and if it exceeds 5 ppm, surface dissolution is promoted, which is not preferable. Therefore, the Pb content is set to 0.1 to 5 ppm. For the same reason, the desirable lower limit is 0.3 ppm, and the desirable upper limit is 2 ppm.

W: 11-200ppm
W has the effect of making the potential of the aluminum foil surface noble, and adding it makes the foil surface less susceptible to electrochemical corrosion, so that the ineffective dissolution of the surface layer can be suppressed, and the potential difference in the pit-generated portion due to electrolysis Therefore, the pit generation energy is extremely increased and a large amount of etching pits can be generated. When the effect is less than 11 ppm, the potential is not sufficiently improved, and the effect of increasing the etching pit generation efficiency is small. On the other hand, if it exceeds 200 ppm, the potential becomes too noble and the corrosion rate decreases, which is not preferable because the etching rate decreases. Further, since the cubic crystal ratio also decreases, addition beyond this is not preferable. For the same reason, the desirable lower limit is 20 ppm, and the desirable upper limit is 80 ppm.

Zn: 1 to 100 ppm
Zn is an element that uniformly generates etching pits. However, if it is less than 1 ppm, the effect is not obtained, and if it exceeds 100 ppm, the cubic rate decreases, which is not preferable. Therefore, the Zn content is set to 1 to 100 ppm. For the same reason, the desirable lower limit is 10 ppm.

Mn, Mg, Cr, Ti, B, V, Ga: total amount of 50 ppm or less Mn, Mg, Cr, Ti, B, V, and Ga are elements contained as unavoidable impurities. Although these elements increase the solubility of the aluminum foil, it is desirable to regulate the content to 50 ppm or less because it inhibits the uniform generation of pits or causes missing pits. Such a foil can be obtained by using an aluminum block obtained by a three-layer electrolytic method.

Aluminum purity: 99.9% or more If the purity is less than 99.9%, an intermetallic compound between an unavoidable impurity and aluminum increases, and it becomes difficult to obtain a high cubic crystal ratio. Therefore, in order to ensure the uniformity of crystal orientation and keep the cubic rate at 95% or higher, an aluminum purity of 99.9% or higher is required. The purity is desirably 99.98% or more. Further, in order to generate uniform etching pits, a cubic crystal ratio of 95% or more is required, and preferably 97% or more.

  As described above, according to the aluminum foil for electrolytic capacitors of the present invention, it is an aluminum foil for electrolytic capacitors to be used for etching, and by mass ratio, Si: 5 to 100 ppm, Fe: 5 to 100 ppm, Cu: It contains 10 to 100 ppm, Pb: 0.1 to 5 ppm, Zn: 1 to 100 ppm, W: 11 to 200 ppm, with the balance being 99.9% or more of Al and inevitable impurities, and cubic orientation ratio Is 95% or more, pits with excellent uniformity can be generated at a high density while suppressing surface dissolution during etching, and the capacitance per unit area is increased, resulting in high strength and high strength. A high-capacity etching foil can be obtained.

Hereinafter, an embodiment of the present invention will be described.
A high-purity aluminum material prepared to be a component of the present invention with a purity of 99.9% or more is prepared. The aluminum material preferably has a purity of 99.98% or more.
The aluminum material can be obtained by a conventional method, and the production method is not particularly limited in the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used. The slab may be subjected to hot rolling after, for example, soaking at 500 ° C. for 30 minutes or more. The finishing temperature of hot rolling is, for example, 250 to 400 ° C. In addition, a high-purity aluminum material obtained by continuous casting may be used. For example, a sheet material having a thickness of about several mm is formed by the hot rolling or continuous casting rolling.

  The sheet material is cold-rolled to obtain, for example, an aluminum foil having a thickness of 90 μm to 200 μm. In addition, degreasing may be appropriately added during the cold rolling or after the end of the cold rolling, and intermediate annealing may be appropriately added during the cold rolling.

After the final cold rolling, a final annealing heat treatment is performed. The heating conditions for the final annealing are important for making the cubic rate of the aluminum foil 95% or more, and it is desirable to heat at 500 ° C. or more for 1 hour or more. For example, an aluminum alloy having an oxide film with an average thickness of 20 to 60 mm by heating in an inert or reducing atmosphere such as nitrogen, Ar, or H ₂ under heating conditions of 500 to 590 ° C. × 1 to 24 hours A foil can be obtained.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by direct current electrolytic etching using a solution mainly containing hydrochloric acid or a solution not containing hydrochloric acid. However, the etching method is not particularly limited in the present invention.
In etching, pits are formed with high density, and a high roughening rate is obtained. This foil is subjected to a chemical conversion treatment to obtain a required 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 present invention is preferably used as an anode of a medium-high voltage electrolytic capacitor. However, the present invention is not limited to this, and can be used as a material for a low voltage or a cathode of an electrolytic capacitor.

  Prepare aluminum (Al 99.9% or more) material adjusted to the components in the table, perform continuous casting, homogenization treatment (560 ° C. × 4 hours), hot rolling, cold rolling, intermediate annealing (250 ° C. × 6 hours) After final rolling, annealing is performed at 500 to 590 ° C. for 1 to 24 hours in a non-oxidizing atmosphere gas such as nitrogen, argon and hydrogen, and the cubic crystal ratio is 95% or more. A thick foil was prepared as a test material.

The sample was subjected to direct current electrolysis at 3 mA sulfuric acid + 1 M hydrochloric acid solution at 75 ° C. for 2 minutes at 200 mA / cm ² and then immersed in the same solution for 10 minutes. The obtained etching foil was formed in a 100 g / L boric acid solution at 80 ° C. while applying a voltage of 300 V, and the capacitance was measured. The bending strength was determined by measuring the number of times the etching foil was bent at 1φ using an MIT bending tester. The electrostatic capacity is the test material No. The relative value with respect to 1 and the bending strength are the test material No. The results were evaluated as relative values to 6, and the results are shown in the table.

  As a result, in Examples 1-6, it turns out that the electrostatic capacitance is improving by adding W. In particular, since Examples 1 to 5 regulate the amount of inevitable impurities such as Mn, both capacity and strength are improved compared to Example 6 in which the amount of inevitable impurities such as Mn is large. Moreover, in Example 5, it turns out that bending strength improves by compound-adding Zn.

  On the other hand, in Comparative Example 2, since the addition amount of W is small, the capacitance is low, and in Comparative Example 3, the addition amount of W is large, and the cubic crystal ratio is lowered. In Comparative Example 4, since W is not added, the capacity is low. In Comparative Example 5, the cubic crystal ratio is reduced because Zn is excessive.

Claims (2)

  An aluminum foil for electrolytic capacitors to be used for etching, and in terms of mass ratio, Si: 5 to 100 ppm, Fe: 5 to 100 ppm, Cu: 10 to 100 ppm, Pb: 0.1 to 5 ppm, Zn: 1 to 100 ppm, An aluminum foil for electrolytic capacitors, comprising W: 11 to 200 ppm, the balance being 99.9% or more of Al and inevitable impurities, and a cubic crystal orientation ratio of 95% or more.   The aluminum foil for electrolytic capacitors according to claim 1, wherein the total amount of Mn, Mg, Cr, Ti, B, V, and Ga in the unavoidable impurities is 50 ppm or less.