JP5396156B2 - Aluminum alloy foil for electrolytic capacitor cathode and method for producing the same - Google Patents

Description

  The present invention relates to an aluminum alloy foil used for an electrode of an electrolytic capacitor, and more particularly to an aluminum alloy foil suitable for a cathode of an electrolytic capacitor.

An electrolytic capacitor using aluminum alloy foil as an electrode (aluminum electrolytic capacitor) includes an anode and a cathode made of aluminum alloy foil, an electrolytic solution, and capacitor paper (electrolytic paper) as basic components. An oxide film (hereinafter referred to as chemical conversion film) formed on the surface of the aluminum alloy foil constituting the anode functions as a dielectric.
The capacitance (C) of the aluminum electrolytic capacitor can be obtained by the following equation (1) as with the parallel plate capacitor. In Equation (1), ε is the dielectric constant of the dielectric, S is the surface area (cm ² ) of the dielectric, and d is the thickness (cm) of the dielectric. From the equation (1), the capacitance can be increased by increasing the surface area of the dielectric.
C = 8.855 × 10 ⁻⁸ × ε · S / d (μF) (1)

With recent rapid and widespread digitization, there is a strong demand for miniaturization, high reliability, and high performance of aluminum electrolytic capacitors, and further higher capacitance is required.
Usually, in order to increase the specific surface area of the aluminum alloy foil, the surface is electrochemically roughened (etched) in a strong acid solution to increase the capacity. In general, DC electrolytic etching is performed on the high-pressure anode foil, and AC electrolytic etching is performed on the low-pressure anode foil and the cathode foil. In particular, the latter is an etching form in which azimuth-like pits of 1 μm or less are connected in a bunch of grapes, and it is necessary to make the pit diameter finer in order to increase the capacity.

So far, for example, Patent Document 1 includes Fe; 0.02 to 0.15 mass%, Mg; 0.003 to 0.02 mass%, B; 0.001 to 0.015 mass%, and the balance Discloses an aluminum alloy foil for an electrolytic capacitor cathode comprising Al and impurities. In order to improve the solubility of this aluminum alloy foil for an electrolytic capacitor cathode, it is effective to uniformly disperse substances having different potential differences in the aluminum alloy, and it is possible to use an Al-Fe intermetallic compound as the substance. It is based on finding out that it is the best method. Therefore, Patent Document 1 defines the Fe content as 0.02 to 0.15 mass%.
Moreover, in patent document 2, Si: 0.02-0.08 mass%, Fe: 0.02-0.08 mass%, Ti: 0.5-5 mass ppm, V: 0.5-5 mass An aluminum alloy foil for an electrolytic capacitor cathode made of ppm, B: 25 to 100 mass ppm, Cu: 0.003 mass% or less, and other inevitable impurities is disclosed. This aluminum alloy foil for electrolytic capacitor cathode is a cathode having high electrostatic capacity and excellent bending strength by adjusting the content of Si and Fe in the aluminum alloy foil and further increasing the content of B. This is based on the knowledge that a foil can be obtained. The bending strength is necessary to avoid troubles such as cutting in the aluminum alloy foil during capacitor processing.

JP-A-8-255733 JP 2001-335868 A

Although the electrostatic capacity can be improved by the proposals of Patent Document 1 and Patent Document 2, the recent requirements have not been sufficiently satisfied.
An object of the present invention is to provide an aluminum alloy foil for an electrolytic capacitor cathode that has a higher capacitance and is excellent in bending strength.

In AC electrolytic etching, it is important to dissolve aluminum in the anode cycle, that is, balance between pit formation and film formation in the cathode cycle. The present invention specifies the abundance ratio of Ti and B, and adds elements that assist the dissolution by concentrating on the surface of the aluminum alloy foil at a relatively low temperature, such as Ga, and Na, In, Zn, Ni and Mg. Thus, it is intended to obtain an aluminum alloy foil for an electrolytic capacitor cathode that enables uniform etching and has high electrostatic capacity and excellent bending strength.
That is, the aluminum alloy foil for the electrolytic capacitor cathode of the present invention is in mass%,
Si: 0.01 to 0.15%,
Fe: 0.01 to 0.15%,
Cu: 0.005% or less,
Ti: 0.001% or less,
B: 0.0005 to 0.0050%,
Ti / B ≦ 0.5,
Ga: 0.004 to 0.05%,
One or more of Na, In, Zn, Ni and Mg: 0.006 to 0.1% in total,
The balance is made of Al and inevitable impurities.

  The aluminum alloy foil for an electrolytic capacitor cathode according to the present invention as described above is subjected to a homogenization treatment in which an aluminum alloy ingot having the above composition is held at 530 to 630 ° C. for 2 to 24 hours, and then subjected to hot rolling and cold rolling. Can be manufactured by obtaining a foil having a predetermined thickness.

  The aluminum alloy foil for an electrolytic capacitor cathode according to the present invention can provide a high capacitance that has not been achieved conventionally.

The present invention will be described in detail below.
First, the reasons for limiting the composition of the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention (hereinafter simply referred to as an aluminum alloy foil) will be described. In the following description, “%” means “% by mass” unless otherwise specified.
<Si: 0.01 to 0.15%>
Si is an element capable of forming a crystal / precipitate as a starting point of etching as an Al—Fe—Si compound or as a simple substance of Si and imparting bending strength to the aluminum alloy foil.
If Si is less than 0.01%, the absolute content of Si is small, so that formation of crystals / precipitates as the starting point of etching is insufficient, and the effect of improving bending strength cannot be enjoyed. Moreover, the process of reducing Si contained in a melt | dissolution raw material to less than 0.01% invites the cost increase of aluminum alloy foil.
If Si exceeds 0.15%, the amount of crystals / precipitates increases so much that over-dissolution occurs during AC electrolytic etching, resulting in a non-uniform etching pattern, a decrease in capacitance, and resistance to folding. The strength also decreases.
For these reasons, the Si content in the present invention is set to 0.01 to 0.15%. A preferable Si content is 0.01 to 0.10%, and a more preferable Si content is 0.01 to 0.05%.

<Fe: 0.01 to 0.15%>
Fe also forms crystals / precipitates as the starting point of etching as Al-Fe intermetallic compounds and Al-Fe-Si intermetallic compounds, as well as Si, and also provides folding strength to the aluminum alloy foil. It can be an element.
When Fe is less than 0.01%, since the absolute content of Fe is small, formation of crystals / precipitates as starting points of etching is insufficient, and the effect of improving bending strength cannot be enjoyed. Moreover, the process of reducing Fe contained in a melt | dissolution raw material to less than 0.01% invites the cost increase of aluminum alloy foil.
When Fe exceeds 0.15%, the amount of precipitates increases so much that over-dissolution occurs during AC electrolytic etching, resulting in non-uniform etching, and the capacitance decreases.
For these reasons, the Fe content in the present invention is set to 0.01 to 0.15%. A preferable Fe content is 0.01 to 0.10%, and a more preferable Fe content is 0.01 to 0.08%.

<Cu: 0.005% or less>
Cu is required to be reduced as much as possible because it may elute into the electrolyte and short-circuit between the anode and the cathode when charging and discharging are repeated after the aluminum alloy foil is incorporated into the electrolytic capacitor as a product. Therefore, the Cu content in the aluminum alloy foil of the present invention is restricted to 0.005% or less. A preferable Cu content is 0.003% or less, and a more preferable Cu content is 0.0015% or less.

<Ti: 0.001% or less>
Ti makes non-uniform pit growth in the depth direction during AC electrolytic etching and causes a decrease in bending strength, so it must be regulated to 0.001% or less. A preferable Ti content is 0.0008% or less, and a more preferable Ti content is 0.0005% or less.

<B: 0.0005 to 0.0050%>
B has an action of enhancing the etching property of the matrix of the aluminum alloy.
If B is less than 0.0005%, this effect is not sufficiently exhibited.
On the other hand, when B is contained in a large amount exceeding 0.0050%, the above action becomes remarkable, and the growth of pits in the depth direction is inhibited.
For the above reasons, the B content in the present invention is set to 0.0005 to 0.0050%. A preferable B content is 0.0005 to 0.0030%, and a more preferable B content is 0.0010 to 0.0030%.

<Ti / B: 0.5 or less>
As described above, B is an element that improves the etching property. However, if Ti is excessively present, TiB ₂ is formed and B is consumed. Therefore, in order to obtain the effect of improving the etching property by B, Ti (mass%) / B (mass%) is regulated to 0.5 or less. A preferred range of Ti (mass%) / B (mass%) is 0.3 or less, and a more preferred range is 0.15 or less.

<Ga: 0.004 to 0.05%>
Ga has the effect of concentrating on the surface by heat treatment to make the solubility of the surface uniform. If Ga is less than 0.004%, this effect is not sufficiently exhibited. On the other hand, when Ga is contained in a large amount exceeding 0.05%, the above action becomes remarkable, the surface layer of the etching foil is lost, and the capacitance is reduced. For these reasons, the Ga content in the present invention is 0.004 to 0.05%, preferably 0.004 to 0.03%, and more preferably 0.004 to 0.01%.

<One or more of Na, In, Zn, Ni and Mg: 0.006 to 0.1% in total>
Na, In, Zn, Ni, and Mg have the effect of concentrating on the surface by heat treatment and improving the surface solubility uniformly.
If the total of one or more of Na, In, Zn, Ni, and Mg is less than 0.006%, the above-described effect cannot be obtained sufficiently, and fine pits cannot be obtained by AC electrolytic etching.
If the total of one or more of Na, In, Zn, Ni, and Mg exceeds 0.1%, surface solubility becomes too high, surface dissolution becomes excessive, and fine pits may be formed. become unable.
For the above reasons, the total content of one or more of Na, In, Zn, Ni and Mg in the present invention is set to 0.006 to 0.1%. The total content of these elements is preferably 0.007 to 0.08%, and the more preferable total content of these elements is 0.008 to 0.03%.

<Manufacturing method>
The aluminum alloy foil of the present invention is obtained by producing an aluminum ingot (slab) prepared to have the above-described chemical composition, subjecting the slab to homogenization, and then sequentially performing hot rolling and cold rolling. be able to. Hereinafter, the manufacturing method suitable for the aluminum alloy foil of the present invention will be described.
The slab can be obtained by a conventional method such as a semi-continuous casting method. The slab obtained by the semi-continuous casting method usually has a thickness of about 300 to 700 mm.
The slab is homogenized. By the homogenization treatment, the Al—Fe intermetallic compound and the Al—Fe—Si intermetallic compound which are the base points of pit formation are uniformly dispersed.
When the holding temperature of the homogenization treatment is less than 530 ° C., the distribution of the intermetallic compound is not uniform, and local dissolution occurs during AC electrolytic etching. Moreover, when the holding | maintenance temperature of a homogenization process exceeds 630 degreeC, in addition to the danger that a slab will fuse | melt, production cost will become high. Therefore, the holding temperature of the homogenization treatment is set to 530 to 630 ° C. A preferable holding temperature of the homogenization treatment is 560 to 600 ° C.
If the holding time of the homogenization treatment is less than 2 hours, the effect is not sufficiently exhibited. Further, even if the holding time of the homogenization process exceeds 24 hours, it is not possible to obtain a homogenization effect that is commensurate with the energy consumption. Therefore, the holding time for the homogenization treatment is preferably 2 to 24 hours. A more preferable homogenization holding time is 2 to 10 hours.
The homogenization treatment can be performed using a known heating furnace, and the heating method and heating means are not particularly limited.

  Next, the slab subjected to the homogenization treatment is hot-rolled. The slab maintained at the temperature by the homogenization treatment can be directly subjected to hot rolling. By this hot rolling, the slab has a thickness of about 2 to 10 mm. Other conditions in the hot rolling are not particularly limited as the present invention, and may be according to ordinary methods.

After the hot rolling is completed, cold rolling is performed. By cold rolling, the aluminum alloy foil is finished to the final desired thickness. In addition, you may perform intermediate annealing in the middle of cold rolling.
By the above cold rolling, for example, an aluminum alloy foil of about several tens of μm to 100 μm can be obtained, but the thickness of the aluminum alloy foil as a final product is not particularly limited in the present invention.
In addition, heat processing (final annealing) can also be performed after completion | finish of cold rolling.

  The aluminum alloy foil obtained through the above steps is then subjected to alternating current electrolytic etching. In this etching process, fine pits are uniformly formed with high density. A capacitor having a high capacitance can be obtained by incorporating it as an electrode in an electrolytic capacitor by a conventional method.

After adjusting the chemical composition shown in Tables 1 to 3 using 3N purity aluminum ingot, a slab having a thickness of 600 mm was prepared by a semi-continuous casting method.
The slab was subjected to a homogenization treatment for 4 hours at 575 ° C., and then subjected to hot rolling and cold rolling in accordance with a conventional method to obtain an aluminum alloy foil having a thickness of 0.005 mm. The aluminum alloy foil was degreased and then heat treated by holding at 330 ° C. for 4 hours in an argon gas atmosphere to obtain a test material.

<Capacitance measurement>
The obtained test material was subjected to AC electrolytic etching under the following conditions.
AC electrolytic etching conditions Liquid composition: HCl 80 ml / l, AlCl ₃ · 6H ₂ O 60 g / l, HNO ₃ 7 ml / l
Electrolysis conditions: current density 0.1 A / cm ² , frequency 30 Hz, electrolysis time 100 s

After performing the chemical conversion treatment on the test material subjected to AC electrolytic etching, the capacitance was measured. The results are shown in Tables 1 to 3. The method for measuring the capacitance is as follows. In Tables 1 to 3, No. 1 in Table 1 is shown. The electrostatic capacity obtained for 1 is represented by an index of 100.
Chemical conversion treatment conditions (conforming to EIAJ (Electronics Industries Association of Japan) law)
Liquid solution: ammonium adipate solution (150 g / l, 85 ° C.)
Applied voltage: 3V
Capacity measurement conditions (conforms to EIAJ method)
Liquid solution: ammonium adipate solution (150 g / l, 30 ° C.)
Measured with LCR meter with 120Hz series equivalent circuit

  In addition, the test material that has been subjected to the above-described AC electrolytic etching is heated in the atmosphere at 400 ° C. for 5 minutes, and is subjected to JIS P 8115 MIT type automatic bending tester in accordance with the EIAJ method. The thickness (times / cm) was measured. The results are shown in Tables 1 to 3. In Table 1, No. It is represented by an index with the bending strength obtained for 1 as 100.

Claims (2)

% By mass
Si: 0.01 to 0.15%,
Fe: 0.01 to 0.15%,
Cu: 0.005% or less,
Ti: 0.001% or less,
B: 0.0005 to 0.0050%,
Ti / B ≦ 0.5,
Ga: 0.004 to 0.05%,
One or more of Na, In, Zn, Ni and Mg: 0.006 to 0.1% in total,
An aluminum alloy foil for an electrolytic capacitor cathode, wherein the balance consists of Al and inevitable impurities. % By mass
Si: 0.01 to 0.15%,
Fe: 0.01 to 0.15%,
Cu: 0.005% or less,
Ti: 0.001% or less,
B: 0.0005 to 0.0050%,
Ti / B ≦ 0.5,
Ga: 0.004 to 0.05%,
One or more of Na, In, Zn, Ni and Mg: 0.006 to 0.1% in total,
A homogenization treatment is performed in which an aluminum alloy ingot consisting of Al and inevitable impurities is held at 530 to 630 ° C. for 2 to 24 hours,
Thereafter, hot rolling and cold rolling are performed to obtain a foil having a predetermined thickness, and a method for producing an aluminum alloy foil for an electrolytic capacitor cathode.