JP2007169689A - Aluminum foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To electroless-etch an aluminum foil when roughening the aluminum foil for an electrolytic capacitor through an etching process. <P>SOLUTION: This aluminum foil has a composition comprising 5-40 ppm Si, 5-40 ppm Fe, 20-200 ppm Ni, and the balance 99.9% or more Al with unavoidable impurities; has an orientation factor of cubic crystals of 95% or more; includes Al-Ni-based intermetallic compounds having a diameter of 0.1 to 3 μm in a surface direction in an amount of 100 to 10,000 pieces per square millimeter in a space between the foil surface and a 0.1 μm deep plane from the surface; and includes the Al-Ni-based intermetallic compounds having the diameter of 0.1 to 3 μm in the surface direction in an amount of 10 pieces per square millimeter or less in a space not shallower than a 0.15 μm deep plane. The foil can be adequately etched without needing electrolysis, because an electrochemically nobler substance than Al in the surface layer acts as a discharge site and Al continuously causes a dissolution reaction. The aluminum foil shows an effect of reducing an etching cost and increasing the productivity. <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.

Conventionally, the etching foil for electrolytic capacitors has an aluminum purity of 99.9% or more, Si: 5 to 20 ppm, Fe: 5 to 20 ppm, Cu: 10 to 80 ppm, Pb: 0.1 to 3 ppm, and other trace impurities 1 to Made of 100ppm, manufactured as an aluminum foil that has undergone hot rolling, cold rolling, intermediate annealing, additional rolling, annealing at 500 ° C or more for 3 hours or more, and having a cubic rate of 95% or more. Yes.
The aluminum foil is further subjected to electrolytic etching in a strong acid solution to generate corrosion holes (hereinafter referred to as pits), and then the electrolytic solution or chemical dissolution in the acid solution to change the pit diameter according to the voltage in the formation of the next process. It has expanded to the size.
As a feature of high-purity aluminum foil, since passivation proceeds in an acid solution, chemical solubility is low, and therefore, electrolytic etching is considered indispensable. In order to obtain the required number of pits by electrolytic etching, an amount of electricity of 40 to 60 C / cm ² is required, and a large amount of electricity is consumed to obtain this.
For reducing the amount of electricity described above, it is effective to improve the etching property of the aluminum foil. For example, in Patent Document 1, in an aluminum foil for a low-voltage electrolytic capacitor, 50 to 10,000 / mm ² Al—Ni-based and Al—Fe—Ni-based intermetallic compounds having a particle diameter of 1 to 15 μm are present in the matrix. Thus, it has been proposed to cause the intermetallic compound to act as a starting point of etching pits.
JP 2000-260666 A

However, the surface of the aluminum foil for high-voltage electrolytic capacitor in the conventional pit 0.5~2μm diameter 200,000～300,000 pieces / mm ² have occurred, the intermetallic compound in the patent document 1 The number is insufficient as an etching start point in the aluminum foil for medium and high pressure. In addition, if Al-Ni-based precipitates are present in the matrix, there is no stopping in the growth of etching pits, so excessive etching is likely to occur. Since it cannot generate | occur | produce, there exists a problem that a leakage current increases and the quality of a chemical conversion film falls.

  Conventionally, growth of etching pits is considered to be caused by defects in the surface oxide film, trace elements deposited on the surface layer, and the like as the starting point of electrolysis when direct current electrolysis is performed. For this reason, conventionally, as shown in Patent Document 1, it has been proposed to generate a large number of etching pits by causing the surface of the aluminum foil to be in a state that conforms to a substance serving as a base point of etching pits or defects. . However, high-purity aluminum is passivated by the reaction with acid as described above, and when electrolysis is not performed, the chemical solubility is remarkably lowered and etching pits cannot be generated at present. . For this reason, an electrolytic etching method using a direct current is indispensable, which increases the manufacturing cost.

  The present invention has been made against the background of the above circumstances, and provides an aluminum foil for electrolytic capacitors that can significantly enhance the chemical reactivity of a high-purity aluminum foil and can generate pits without electrolysis.

That is, the aluminum foil for electrolytic capacitors of the present invention is an aluminum foil for electrolytic capacitors used for etching, and contains Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Ni: 20 to 200 ppm by mass ratio. The balance has a composition composed of 99.9% or more of Al and inevitable impurities, the cubic orientation ratio is 95% or more, within the range from the foil surface to the depth direction of 0.1 μm, and in the plane direction, 0. In a depth range of 0.15 μm or more in the depth direction from the foil surface, the Al—Ni-based intermetallic compound having a diameter of 1 to 3 μm is 100 to 10,000 / mm ² , and 0.1 to 3 μm in the plane direction. The diameter of the Al—Ni-based intermetallic compound is 10 pieces / mm ² or less.

Etching foils used for medium- and high-pressure capacitor foils have a large surface area by generating many etching pits that grow vertically from the surface of the aluminum foil. Since the etching pits grow along the cube orientation, a high cubic orientation ratio is required, and generally a cubic orientation occupation ratio of 95% or more is required. Usually, since the length of the etching pit is 20 to 50 μm, it needs to play a role as a discharge site for a time during which the pit can sufficiently grow. In addition, when there is a discharge site inside the foil, pits are bent, or when forming, a normal film cannot be formed on the discharge site, so that problems such as increased leakage current occur. From these facts, the inventors of the present invention, when using it for medium-high pressure foil, that it is important to generate a discharge site having a diameter of 0.1 to 3 μm in the aluminum foil electrode surface layer portion (within 50 nm from the surface layer). I found it.
When a material that is electrochemically more noble than aluminum is placed on the surface of the aluminum foil, it acts as a discharge site for electric charges instead of the origin of etching pits. As a result, the dissolution reaction of aluminum occurs continuously, and etching pits are formed. , Grow without applying current.

  In the present invention, since a metal noble than aluminum or an intermetallic compound acts as a charge discharge site in the local battery reaction, it can be supplemented with a much smaller number than the number of etching pits required. Furthermore, by disposing the discharge site in the extreme surface layer (up to a depth of 0.1 μm), it can be removed as the etching progresses. For this reason, while being able to suppress overmelting at the etching stage, a high-quality film can be obtained in the chemical conversion film in the chemical conversion step.

  The intermetallic compound arranged in the surface layer portion is an Al—Ni-based intermetallic compound. The intermetallic compound is a compound mainly composed of Al and Ni. In addition, an intermetallic compound containing a component such as Fe is also included in the Al—Ni intermetallic compound of the present invention. The Al—Ni intermetallic compound needs to be disposed at a depth of 0.1 μm from the foil surface. When deeper than this, the progress of etching cannot be suppressed. Moreover, the growth of a normal chemical conversion film is hindered by the intermetallic compound remaining in the etching pits, resulting in a film having a large leakage current, so that the quality of the chemical conversion film is significantly lowered. Preferably, it is desirable to arrange it to a depth of 0.05 μm.

  The size of the Al—Ni-based intermetallic compound is 0.1 to 3 μm in terms of a circle. If it is smaller than 0.1 μm, the discharge area becomes small and the dissolution of Al cannot be promoted. On the other hand, when larger than 3 micrometers, it cannot arrange | position to 0.1 micrometer depth from foil surface layer. Preferably it is 0.3-1.5 micrometers.

The number of precipitates of the intermetallic compound is 100 to 10,000 / mm ² in the plane direction within a depth range of 0.1 μm from the surface. If it is less than 100 / mm ^2, the range affected by the local battery phenomenon becomes narrow, and the etching pit density is lowered. As a result, sufficient electrostatic capacity cannot be obtained. On the other hand, when the number is more than 10,000 / mm ² , the etching pits are densely formed and the pit coalescence phenomenon occurs, so that the electrostatic capacity is decreased. Desirably, it is 1,000 to 8,000 pieces / mm ² .

Further, when the Al—Ni-based intermetallic compound is dispersed in the inner layer, the above-described problem occurs. Therefore, at a depth of 0.15 μm or more, the Al—Ni-based intermetallic compound having the above size is 10 in the plane direction. The number of pieces / mm ² or less.

  A similar effect can be obtained even if a metal or intermetallic compound acting as a discharge site is disposed on the foil surface by vapor deposition by ion sputtering or the like, or a physical pressure bonding method.

  Furthermore, the effect | action by each component of this invention and the reason which limited each component are demonstrated. In addition, all the component content in the following is mass ratio.

Si: 5 to 40 ppm, Fe: 5 to 40 ppm
Si and Fe combine with Al to appropriately generate precipitates, suppress coarsening of recrystallized grains, and promote preferential growth of Cube grains. However, if it is less than 5 ppm, the purification cost becomes high, which is unsuitable industrially. On the other hand, in the case where each exceeds 40 ppm, the total amount of precipitates becomes too large to control the preferential growth of Cube grains, so that a high cubic crystal ratio cannot be obtained. For this reason, the content of Si and Fe is set within the above range. A desirable lower limit is 10 ppm for both Si and Fe, and a desirable upper limit is 20 ppm for both Si and Fe.

Ni: 20 to 200 ppm
Ni is an element that generates an intermetallic compound with Al, makes the potential noble, and remarkably enhances the chemical solubility of the surrounding Al. If it is less than 20 ppm, the amount of intermetallic compounds is small and the solubility is low. Furthermore, since recrystallization is promoted too much during rolling, the cubic rate decreases. On the other hand, if it exceeds 200 ppm, the amount of intermetallic compounds is too large and excessive dissolution occurs. Furthermore, in order to suppress recrystallization, a cubic crystal orientation rate falls. Desirably, it is in the range of 40 to 150 ppm.

Aluminum purity: 99.9% or more If the purity is less than 99.9%, an intermetallic compound of unavoidable impurities and aluminum increases, making it 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 99.95% or more.

As described above, the aluminum foil for electrolytic capacitors of the present invention is an aluminum foil for electrolytic capacitors to be used for etching, and has a mass ratio of Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Ni: 20 to 200 ppm is contained, the balance is 99.9% or more of Al and inevitable impurities, the cubic orientation ratio is 95% or more, and within the range from the foil surface to the depth direction of 0.1 μm, In the depth direction of 0.15 μm or more in the depth direction from the foil surface, the Al—Ni intermetallic compound having a diameter of 0.1 to 3 μm in the direction is 100 to 10,000 / mm ² , and 0 in the plane direction. Since the number of Al-Ni intermetallic compounds having a diameter of 1 to 3 μm is 10 / mm ² or less, a substance that is more electrochemically noble than aluminum and disposed on the surface of the aluminum foil serves as a discharge site for electric charges. As a result, the dissolution reaction of aluminum occurs continuously, and good etching can be performed without requiring electrolysis, which has the effect of reducing cost and improving productivity in etching.

  In addition, since the amount of the Al—Ni intermetallic compound is regulated at a depth of 0.15 μm or more, an electrolytic capacitor excellent in chemical conversion film quality can be obtained in the subsequent chemical conversion treatment, and normal chemical film growth can be obtained. 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 99.95% 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 an aluminum foil of about several tens of μm to 100 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 concentrating the Al—Ni-based intermetallic compound in the surface layer part, and it is desirable to heat at 500 ° C. or more for 3 hours or more. For example, an aluminum alloy foil having an oxide film with an average thickness of 20 to 60 mm can be obtained by heating in an inert gas or reducing gas atmosphere under heating conditions of 500 to 600 ° C. × 3 to 36 hours. . In addition, by containing appropriate amounts of Al purity, appropriate amounts of Si, Fe, and Ni, the amount of dispersion of the Al—Ni-based intermetallic compound described above is adjusted to the surface layer (0.1 μm depth from the surface) by adjusting the annealing. And it can adjust appropriately with an inner layer (0.15 micrometer or more).
If the heating temperature of the final annealing is too low or the holding time is too short, the Al—Ni intermetallic compound is not sufficiently concentrated.
Further, as a result of the final annealing, the cubic crystal ratio of the aluminum foil needs to be 95% or more.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by electroless etching using a solution mainly containing hydrochloric acid or a solution not containing hydrochloric acid. However, the present invention may employ electrolytic etching, and in that case, a good roughening rate can be obtained.
In the etching process, the etching solution reacts with Al in the aluminum foil 1 in FIG. 1, and Al 3 ⁺ dissolves into the solution, and e ⁻ is generated in the aluminum foil 1. The Al—Ni-based intermetallic compound 2 in the surface layer portion of the aluminum foil 1 acts as a discharge site, and the above e ⁻ is discharged into the etching solution and reacts with H ^{+ in} the solution to generate H ₂ . As a result, a large number of etching pit base points 3... 3 are generated in the aluminum foil 1.

  As the etching progresses, etching pits 30 grow from the base points 3 ... 3 of the etching pits. On the other hand, the dissolution of the surface layer portion of the aluminum foil 1 advances, so that the Al-Ni intermetallic compound 2 acting as a discharge site is also etched It is removed in the liquid and does not remain in the aluminum foil 1. In addition, the number of Al—Ni-based intermetallic compounds 2 is regulated in the inner layer, and the etching pits are prevented from growing excessively. Due to the above action, pits are formed with high density even without electrolysis without requiring electrolysis, and a high roughening rate can be obtained. 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.

  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 also be used as a material for a low pressure or a cathode of an electrolytic capacitor.

  An ingot of the components shown in Table 1 (remaining Al and unavoidable impurities) was prepared and subjected to soaking treatment at 500 ° C. or more for 30 minutes or more, and then hot rolling at a processing rate of 95 to 99% was performed. At that time, the finishing temperature was 250 to 400 ° C. After hot rolling, cold rolling of 95% or more was performed to prepare a sample having a foil thickness of 110 μm. During cold rolling, intermediate annealing was performed as necessary.

These foils were annealed at 450 to 590 ° C. for 12 hours in an inert atmosphere such as Ar, N ₂ and H ₂ to produce foils having different cubic crystal ratios and Al—Ni precipitate distributions.

For the evaluation of the precipitate, the outermost surface portion was observed with an SEM, and image analysis was performed on particles determined as an Al—Ni-based precipitate by EDS to evaluate the distribution.
Further, regarding the distribution in the depth direction, the surface was removed using a 0.5 M NaOH solution, and the SEM observation image of the surface after the removal was subjected to image analysis to evaluate the distribution. The amount of surface removal was calculated from the weight loss.

The foils having different precipitation distributions were immersed in a sulfuric acid solution of 3 mol / l at 40 ° C. to remove the oxide film. After removing the film, it was washed with water and immersed in a mixed acid solution of 70 ° C., 1 mol / l hydrochloric acid + 3 mol / l sulfuric acid for 60 seconds to generate etching pits. After the pit was generated, it was washed with water and immersed in a 3 mol / l sulfuric acid solution at 75 ° C. for 600 sec to enlarge the pit diameter. After expanding the pit diameter, it was washed with ion-exchanged water and dried.
The obtained etching foil was subjected to chemical conversion at 300 V with a 10 wt% boric acid solution to evaluate the capacitance, and Example 1 was evaluated as 100%.

As shown in Table 1, as in Examples 1 to 7, when the surface layer deposits were 100 to 10,000 / mm ² and the inner layer deposits were 10 / mm ² or less, a high capacitance was obtained. Is obtained.
On the other hand, in Comparative Example 1, since the addition amount of Ni is small and the cubic crystal ratio is low, the capacitance is low. In Comparative Example 2, since the amount of precipitates was small, the capacitance was low due to insufficient dissolution. In Comparative Example 3, since there were too many precipitates, it was excessively dissolved and the capacitance was low.
In Comparative Example 4, since there were too many precipitates at a depth of 0.1 μm or more, excessive dissolution occurred, and the capacitance decreased.

It is the schematic explaining the production | generation process of the etching pit in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum foil 2 Al-Ni type intermetallic compound 3 Etching pit base point 30 Etching pit

Claims (1)

An aluminum foil for electrolytic capacitors to be used for etching, which contains Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Ni: 20 to 200 ppm by mass ratio, and the balance is inevitable with Al of 99.9% or more. Al-Ni intermetallic compound having a composition comprising impurities, having a cubic orientation ratio of 95% or more, and having a diameter of 0.1 to 3 μm in the plane direction within the range from the foil surface to the depth direction of 0.1 μm. the has 100 to 10,000 pieces / mm ^2, and the depth direction 0.15μm or more depths ranging from foil surface, Al-Ni system intermetallic compound of 0.1~3μm radial in plane direction is 10 / Mm < ² > or less, the aluminum foil for electrolytic capacitors characterized by the above-mentioned.

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