JP2013124402A - Aluminum foil for electrolytic capacitor, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum foil for electrolytic capacitors, in which etching pits can be formed with high density and high uniform dispersibility to thereby improve capacitance, and to provide a method for producing the same.SOLUTION: An aluminum alloy slab is prepared which contains 5-30 ppm of Si, 5-30 ppm of Fe, 30-70 ppm of Cu, 0.8-2.0 ppm of Pb, 1-10 ppm of Cr, 15-40 ppm in total of one or more of Mn, Zn, Ga, Sn, and In, 1-10 ppm in total of one or more of Zr, Ti, and V, and 1-10 ppm of REM, with the balance being Al and inevitable impurities. The aluminum alloy slab is subjected to homogenization treatment at 550°C or more for 4 hours or more, followed by hot rolling, and thereafter subjected to cold rolling. After the completion of cold rolling, the cold rolled alloy sheet is subjected to final annealing at 500-580°C for 4 hours or more in an inert gas, a reducing gas, or a mixed gas atmosphere.

Description

  The present invention relates to an electrolytic capacitor aluminum foil used for an electrode of an electrolytic capacitor and a method of manufacturing the same.

Among aluminum foils for electrolytic capacitors, medium- and high-pressure foils are used with direct current electrolysis and numerous pit-shaped holes formed on the surface layer to enlarge (roughen) the surface area. In order to uniformly generate etching pits, a foil having a cube orientation occupation ratio of 95% or more by performing final annealing after cold rolling is used.
In order to improve the density of the etching pits, it is important to add various elements and adjust the content ratio of the additive elements, and various proposals have been made on the additive elements (see, for example, Patent Document 1).

JP 2009-249668 A

However, even if the density of etching pits can be improved, if the distribution is non-uniform, coalescence of etching pits occurs and the surface area decreases. As a result, the electrostatic capacity of the electrolytic capacitor is reduced.
In order to improve the electrostatic capacity, it is necessary not only to increase the density of etching pits but also to make the distribution of etching pits uniform.

  The present invention has been made against the background of the above circumstances, and can be formed by uniformly dispersing etching pits at a high density, and as a result, an aluminum foil for electrolytic capacitors that can improve capacitance, and It aims at providing the manufacturing method.

  Among the aluminum foils for electrolytic capacitors of the present invention, the first present invention is, by mass ratio, Si: 5 to 30 ppm, Fe: 5 to 30 ppm, Cu: 30 to 70 ppm, Pb: 0.8 to 2.0 ppm, Cr: 1 to 10 ppm, one or more of Mn, Zn, Ga, Sn, and In in total 15 to 40 ppm, one or more of Zr, Ti, and V in total of 1 to 10 ppm, REM: It contains 1 to 10 ppm, and the balance has a composition consisting of Al and inevitable impurities.

  The manufacturing method of the aluminum foil for electrolytic capacitors of 2nd this invention is mass ratio, Si: 5-30ppm, Fe: 5-30ppm, Cu: 30-70ppm, Pb: 0.8-2.0ppm, Cr: 1 to 10 ppm, one or more of Mn, Zn, Ga, Sn and In in total 15 to 40 ppm, one or more of Zr, Ti and V in total 1 to 10 ppm, REM: 1 to 2 An aluminum alloy slab containing 10 ppm and the balance being composed of Al and inevitable impurities is homogenized at 550 ° C. or more for 4 hours or more, then hot-rolled, and after the hot rolling, Rolling is performed, and after the cold rolling is completed, final annealing is performed at 500 to 580 ° C. for 4 hours or more in an atmosphere of an inert gas, a reducing gas, or a mixed gas thereof.

  Below, the reasons for limitation such as the composition and production conditions of the aluminum foil for electrolytic capacitors defined in the present invention will be described. In addition, all component content demonstrated below is shown by mass ratio.

Si: 5 to 30 ppm
Fe: 5 to 30 ppm
When Si and Fe are less than 5 ppm, the purity is high and the purification cost increases, which is not desirable industrially. On the other hand, when Si and Fe are more than 30 ppm, the cubic crystal ratio is decreased, and the capacitance is decreased due to excessive dissolution of the foil. For this reason, the content of Si and the content of Fe are set to the above ranges. Any content is desirably a lower limit of 8 ppm and an upper limit of 15 ppm.

Cu: 30 to 70 ppm
Cu is effective in improving the solubility of the aluminum foil and the density of etching pits. If it is less than 30 ppm, both effects are not sufficiently exhibited, which is not preferable. On the other hand, if it exceeds 70 ppm, the cubic crystal ratio due to the final annealing decreases, and the leakage current increases in the electrolytic capacitor, which increases the risk of sparking. For this reason, the Cu content is set within the above range. Desirably, the lower limit is 40 ppm and the upper limit is 60 ppm.

Pb: 0.8 to 2.0 ppm
Pb is effective in improving the solubility of the surface of the aluminum foil and improving dispersibility of etching pits due to embrittlement of the surface oxide film. If it is less than 0.8 ppm, both effects are not sufficiently exhibited, and particularly the dispersibility of the etching pits is reduced, so that the etching pits are coalesced and the electrostatic capacity is reduced. On the other hand, if it exceeds 2.0 ppm, the solubility of the foil surface becomes excessive and the surface collapses, resulting in a decrease in capacitance, which is not preferable. For this reason, the content of Pb is set within the above range. Desirably, the lower limit is 1.2 ppm and the upper limit is 1.6 ppm.

Cr: 1-10ppm
Cr is effective in improving the bulk solubility of the aluminum foil. If it is less than 1 ppm, the effect is not sufficiently exhibited, which is not preferable. On the other hand, if it exceeds 10 ppm, excessive dissolution of the foil locally occurs and the capacitance decreases, which is not preferable. For this reason, the Cr content is set within the above range. Desirably, the lower limit is 2 ppm and the upper limit is 6 ppm.

15 to 40 ppm in total of one or more of Mn, Zn, Ga, Sn, and In
Mn, Zn, Ga, Sn, and In are all elements that have the effect of reducing the potential of the aluminum foil matrix and improving the solubility inside the foil, and contain one or more of these. However, when the total content is less than 15 ppm, the effect is not sufficiently exhibited, which is not preferable. On the other hand, if the total content exceeds 40 ppm, excessive dissolution of the matrix occurs and the capacitance decreases, which is not preferable. For this reason, the total content is set within the above range. Desirably, the lower limit is 20 ppm and the upper limit is 30 ppm.

1 to 10 ppm in total of one or more of Zr, Ti and V
Zr, Ti, and V are all elements that are effective in improving the bulk solubility of the aluminum foil, and contain one or more of these. However, when the total content is less than 1 ppm, the effect is not sufficiently exhibited, which is not preferable. On the other hand, if the total content exceeds 10 ppm, excessive dissolution of the foil occurs and the electrostatic capacity decreases, such being undesirable. For this reason, the total content is set within the above range. Desirably, the lower limit is 2 ppm and the upper limit is 6 ppm.

REM: 1-10ppm
REM is an element that promotes the precipitation of Fe and increases the bulk aluminum purity to increase the cubic rate. Note that REM may be La, Ce, Pr, Nd, or the like alone, or a mixture of two or more thereof, and may be added in the form of misch metal. In the case of a plurality of rare earth elements, the above content means the total amount of the plurality of elements. However, when it is less than 1 ppm, the effect is not sufficiently exhibited, which is not preferable. On the other hand, if it exceeds 10 ppm, the precipitation of Fe becomes excessive and the crystal grains tend to grow abnormally, resulting in a decrease in the cubic crystal ratio. For this reason, the content of REM is determined within the above range. Desirably, the lower limit is 2 ppm and the upper limit is 6 ppm.

Aluminum purity: 99.9% or more In the present invention, the aluminum purity of the aluminum foil is not limited, but aluminum purity of 99.9% or more is desirable. If the aluminum purity is less than 99.9%, the cubic rate decreases, which is not desirable. Inevitable impurities include components specific to bullion. Even if three-layer metal or segregated metal is used, Si, Fe, Cu, Pb, Cr, Mn, Zn, Ga, Sn, In, Zr, Ti, V, and REM are adjusted to 99.9 as the purity of aluminum. If more than% is secured, there is no problem.

Thickness of aluminum foil: 100 μm or more and less than 130 μm In the present invention, the thickness of the aluminum foil is not particularly limited, but a thickness of 100 μm or more and less than 130 μm is desirable. When the foil thickness is less than 100 μm, the cubic crystal ratio is lowered, which is not preferable. On the other hand, when the foil thickness is 130 μm or more, coarse crystals are generated and local characteristics are deteriorated. More desirably, the lower limit is 110 μm and the upper limit is 120 μm.

Thickness of the oxide film on the surface of the aluminum foil: 20 to 100 mm
It is desirable to control the surface oxide film after annealing described later to 20 to 100%. When the thickness is less than 20%, the corrosion resistance of the foil is lowered, the storage stability of the annealed foil is deteriorated, and abnormal causes such as surface oxidation are caused. On the other hand, when the thickness exceeds 100%, uniformity is reduced during etching, which causes a reduction in capacity. For this reason, it is desirable that the surface oxide film thickness after annealing be in the above range. More desirably, the lower limit is 40 mm and the upper limit is 60 mm.

Homogenization treatment: 550 ° C or more, 4 hours or more Homogenization treatment can homogenize the components and structure of the aluminum alloy slab, and after making the aluminum foil, the effect of each element is made uniform during etching, etc. It can be demonstrated. When the processing temperature is less than 550 ° C., the effect is not sufficiently exhibited, which is not preferable. The treatment temperature is desirably 600 ° C. or lower. This is because if it exceeds 600 ° C., there is a risk of melting and the cost increases. Further, the treatment time of less than 4 hours is not preferable because the effect is not sufficiently exhibited. The processing time is desirably 24 hours or less. This is because when the time exceeds 24 hours, the time effect is small and the productivity is lowered.

Hot rolling and cold rolling Hot rolling is performed after the homogenization treatment, and cold rolling is performed after the hot rolling. Any of these rolling can be carried out by a conventional method, and the rolling conditions are not limited to specific conditions.
In addition, intermediate | middle annealing can be performed in the middle of the cold rolling process which manufactures aluminum foil, and the production | generation of the cubic crystal at the time of final annealing can be accelerated | stimulated. However, if the intermediate annealing temperature is less than 200 ° C. or the intermediate annealing time is less than 2 hours, the formation of cubic crystals is insufficient, and the cubic crystal ratio after the final annealing is lowered. On the other hand, when the intermediate annealing temperature exceeds 280 ° C. or the intermediate annealing time exceeds 10 hours, crystal grains other than cubic crystals are generated, and the cubic crystal ratio after the final annealing is lowered. From these points, when performing the intermediate annealing, it is desirable to perform it at 200 to 280 ° C. for 2 to 10 hours.

Final annealing atmosphere As the annealing atmosphere for performing the final annealing, an inert gas, a reducing gas, or a mixed gas atmosphere thereof is used. The reason for this is as follows.
In order to set the annealing rate and the oxide film thickness within appropriate ranges, it is necessary to appropriately select the atmosphere during annealing.
In vacuum annealing, the heat conduction during annealing is significantly deteriorated, so that the rate of temperature rise is reduced. Furthermore, since the oxide film on the foil surface layer becomes thin, it is not preferable. In the case of atmospheric annealing, the oxide film on the foil surface layer becomes thick and the etching property is lowered, which is not preferable. In the case of an inert gas atmosphere such as Ar and N ₂ , an appropriate oxide film can be formed by controlling the dew point and the oxygen partial pressure, but in order to set the annealing rate within a predetermined range, the aluminum foil to be annealed It is necessary to consider the shape, quantity, etc. Industrially, when annealing a coiled aluminum foil in units of Ton, it is desirable to perform with hydrogen gas. This is because the thermal conductivity is high, so that a sufficient annealing rate can be obtained, and since it is a reducing atmosphere, the growth of the oxide film can also be suppressed. However, by selecting appropriate conditions for the reducing gas, the targets of the annealing rate and the oxide film thickness can be achieved, and thus are not excluded. The atmosphere may be a mixture of a reducing gas and an inert gas. In vacuum annealing and atmospheric annealing, the target of annealing speed and oxide film thickness cannot be achieved.

Final annealing: 500 to 580 ° C., 4 hours or longer After the cold rolling, final annealing is performed. The final annealing is for concentrating additive elements on the surface of the aluminum foil and controlling the deposition state on the surface of the foil. When the final annealing temperature is less than 500 ° C., the concentration of the additive element on the surface is insufficient, which is not preferable. On the other hand, when the temperature exceeds 580 ° C., the additive elements are excessively concentrated on the surface. As a result, the starting points of the etching pits become excessive, and the coalescence of the etching pits occurs, resulting in a decrease in capacitance. Also, the case where the final annealing time is less than 4 hours is not preferable because the concentration of the additive element on the surface is insufficient. The final annealing time is desirably 24 hours or less. This is because the treatment over 24 hours is less effective and the productivity is lowered.

  As explained above, according to the present invention, by mass ratio, Si: 5 to 30 ppm, Fe: 5 to 30 ppm, Cu: 30 to 70 ppm, Pb: 0.8 to 2.0 ppm, Cr: 1 to 10 ppm, One type or two or more of Mn, Zn, Ga, Sn, and In are included in a total of 15 to 40 ppm, one or two or more of Zr, Ti, and V are included in a total of 1 to 10 ppm, and REM: 1 to 10 ppm. The aluminum alloy slab having a composition composed of Al and inevitable impurities in the balance is homogenized at 550 ° C. or more for 4 hours or more, then hot-rolled, and after the hot rolling, cold-rolled. After the cold rolling, the final annealing is performed at 500 to 580 ° C. for 4 hours or more in an atmosphere of an inert gas, a reducing gas, or a mixed gas thereof. Can be formed with high density and high uniform dispersibility, it is possible to improve the electrostatic capacity.

Hereinafter, an embodiment of the present invention will be described.
An aluminum alloy prepared to have the composition of the present invention and preferably having an aluminum purity of 99.95% or more can be obtained by a conventional method, and the production method of the present invention is not particularly limited. Absent. For example, a slab obtained by semi-continuous casting or an aluminum material obtained by continuous casting may be used.

  When using an aluminum alloy slab, homogenization is performed at 550 ° C. or more for 4 hours or more, and then hot rolling is performed. For example, an aluminum plate having a thickness of 2 to 10 mm is obtained by this hot rolling or continuous casting rolling.

  Next, the aluminum plate material is cold-rolled to obtain, for example, an aluminum alloy foil having a thickness of 0.10 to 0.13 mm. In addition, you may add degreasing suitably in the middle of cold rolling or after completion | finish of cold rolling, and you may add intermediate annealing of 200-280 degreeC and 2 to 10 hours suitably, for example in the middle of cold rolling.

After cold rolling, final annealing is performed.
The conditions for the final annealing are important for concentrating the above-described additive elements, and in a reducing atmosphere using H ₂ or the like, an inert atmosphere such as Ar or N _2, or a mixed gas atmosphere thereof, 500 to By heating at 580 ° C. for 4 hours or longer, an aluminum alloy foil having an oxide film with an average thickness of, for example, 20 to 100 mm is obtained.
In a reducing atmosphere, it is possible to use a mixed gas obtained by mixing a reducing gas such as H ₂ with an inert gas or a small amount of oxygen. The cubic rate is preferably 95% or more. The said additional element concentrates on a surface layer part by the said annealing. When annealing is performed under vacuum, an oxide film is not properly formed on the surface, and good etching becomes difficult during etching.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching treatment can be performed, for example, by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. In the present invention, the type of the electrolytic solution is not particularly limited.
The etching process can be performed by a surface layer portion removing process, an etching pit generating process, and an etching pit hole diameter expanding process. The surface layer portion removing step is performed by dissolving the surface layer portion including the oxide film. After the surface layer portion is removed, an etching pit generation step for generating etching pits on the aluminum foil surface is performed. After the etching pit generation process, an etching pit hole diameter expanding process is performed. This foil is subjected to a chemical conversion treatment to obtain a necessary 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.
In addition, it is suitable to use the aluminum foil of this invention as an anode of a medium-high voltage electrolytic capacitor.

Examples of the present invention will be described below.
A 4N purity aluminum ingot was used and adjusted to the components shown in Table 1 (others: inevitable impurities + 99.9% or more Al), and then an aluminum slab was produced by a semi-continuous casting method. In addition, as the REM in the component, a misch metal having a composition of (La: 20 wt%, Ce: 50 wt%, Pr: 5 wt%, Nd: 25 wt%) was used.
The aluminum slab was homogenized under the conditions shown in Table 2, and then hot rolled to obtain an aluminum plate having a thickness of 10 mm. Thereafter, cold rolling was performed on the aluminum plate until the thickness became 145 μm. Subsequently, after performing intermediate annealing at 260 ° C. for 4 hours, cold rolling was performed until a foil thickness of 120 μm was obtained to obtain an aluminum foil.
Final annealing was performed on the obtained aluminum foil under the conditions shown in Table 2. After the final annealing, the aluminum foil was etched.

The etching process was performed stepwise as follows.
First, as pretreatment, the aluminum foil was immersed in a solution of 1M hydrochloric acid + 3M sulfuric acid at 80 ° C. for 30 seconds. Subsequently, as the first-stage electrolytic etching, the pretreated aluminum foil was immersed in a solution of 1M hydrochloric acid + 3M sulfuric acid at 80 ° C., and a direct current of 500 mA / cm ² was applied for 120 seconds. Subsequently, as the second-stage electrolytic etching, the aluminum foil after the first-stage electrolytic etching was immersed in a solution of 1 M hydrochloric acid + 3 M sulfuric acid at 80 ° C., and a direct current of 50 mA / cm ² was applied for 600 seconds. The pretreatment corresponds to the surface layer removal step, the first-stage electrolytic etching corresponds to the etching pit generation step, and the second-stage electrolytic etching corresponds to the etching pit hole diameter expanding step.

The aluminum foil after the etching treatment was formed at 270 V in a 100 g / L boric acid solution at 85 ° C., and the capacitance was measured. In addition, electrostatic capacitance is Example No. It was shown by relative evaluation with the electrostatic capacity of 1 specimen as 100.
Moreover, about the obtained test material, the thickness of the oxide film was measured by ESCA (X-ray photoelectron analyzer).
Table 2 shows the measurement results of the capacitance and the thickness of the oxide film.

  As is clear from the measurement results of the capacitance shown in Table 2, in the examples, a high capacitance is obtained. On the other hand, none of the comparative examples deviating from the components or the production conditions of the present invention provided sufficient capacitance.

Claims (2)

  By mass ratio, Si: 5 to 30 ppm, Fe: 5 to 30 ppm, Cu: 30 to 70 ppm, Pb: 0.8 to 2.0 ppm, Cr: 1 to 10 ppm, Mn, Zn, Ga, Sn, In Or it contains 15 to 40 ppm in total, one or two or more of Zr, Ti, and V in total, 1 to 10 ppm in total, and REM: 1 to 10 ppm, with the balance being composed of Al and inevitable impurities. The aluminum foil for electrolytic capacitors characterized by the above-mentioned.   By mass ratio, Si: 5 to 30 ppm, Fe: 5 to 30 ppm, Cu: 30 to 70 ppm, Pb: 0.8 to 2.0 ppm, Cr: 1 to 10 ppm, Mn, Zn, Ga, Sn, In Or it contains 15 to 40 ppm in total, one or two or more of Zr, Ti, and V in total, 1 to 10 ppm in total, and REM: 1 to 10 ppm, with the balance being composed of Al and inevitable impurities. The aluminum alloy slab is homogenized at 550 ° C. or more for 4 hours or more, then hot-rolled, and after the hot rolling, cold-rolled, and after the end of the cold rolling, an inert gas or reduced A method for producing an aluminum foil for an electrolytic capacitor, comprising performing a final annealing at 500 to 580 ° C. for 4 hours or more in an atmosphere of a reactive gas or a mixed gas thereof.