JP3930033B1 - Aluminum foil for electrolytic capacitors - Google Patents

Abstract

A high roughening rate of an aluminum foil for a decapacitor can be obtained by electroless etching.
An aluminum foil for electrolytic capacitors to be used for etching, containing, by mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, and Mn, Ni, Among elements selected from Sn, Ag, Pt, and Au, one or two or more elements are contained as additive elements in a total amount of 20 to 200 ppm, and the balance is composed of 99.9% or more of Al and inevitable impurities. And, when the arrangement state of the additive element is 10 nm deeper than the oxide film-aluminum foil cloth interface, the concentration is 5-50 at the center of the oxide film, and the concentration is 80-150 at the interface. Have a ratio.
[Selection] Figure 1

Description

  The present invention relates to an aluminum foil for electrolytic capacitor electrodes that is suitably used for electrodes of electrolytic capacitors, particularly anodes.

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, Patent Document 1 proposes disposing various elements on the surface of the oxide film or on the interface between the oxide film and the foil substrate. In Patent Document 1, it is pointed out that the element arranged on the surface of the foil acts as a base point of the etching pit, so that it is important to arrange it in the extreme surface layer portion.
JP-A-4-213810

In what is shown in Patent Document 1, it is pointed out that it is important to arrange the element arranged on the surface of the foil because the element arranged on the surface of the foil only acts as a base point of the etching pit. That is, the ionic strength ratio of the oxide film-aluminum interface and the ionic strength ratio inside the substrate excluding the foil surface layer up to 0.1 μm is 1.2-30, and P, V, Ti, Cr, Ni at that time It has been proposed that various elements such as Ta, Zr, C, and Be are 1 to 40 ppm inside the foil excluding the foil surface layer up to 0.1 μm.
When electrolytic etching is performed, there is no problem in the above range as long as the level acts as a base point of etching pits. However, when chemical etching, which is the object of the present invention, is mainly used, the above degree of concentration is not practical because of low reactivity.

In the generation of etching pits mainly composed of chemical dissolution, which is the object of the present invention, it is necessary to rapidly cause a chemical reaction at the oxide film-aluminum interface. For that purpose, the larger the potential difference between the inside of the foil and the interface portion, the more effective, and it is important that a concentration gradient occurs in an extremely narrow region.
Further, since the progress of the etching causes the foil surface to be lost at the same time, it is necessary to continuously cause the reaction even after the etching reaction has occurred, and it is necessary to arrange the reaction element to some extent inside the foil.

  The present invention has been made against the background of the above circumstances, and significantly reduces the chemical reactivity of high-purity aluminum foil, and provides a foil capable of generating pits without using electricity, thereby reducing costs in etching. The purpose is to improve productivity.

  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 40 ppm, Fe: 5 to 40 ppm , Pb: 0.1 to 3 ppm, and among elements selected from Mn, Ni, Sn, Ag, Pt, and Au, one or two or more elements as additive elements are contained in a total amount of 20 to 200 ppm, and the balance Is a composition comprising 99.9% or more of Al and inevitable impurities, and the arrangement state of the additive element is 10 nm deep from the oxide film-aluminum foil cloth interface to the cloth side, the oxide film It is 5 to 50 in the central portion, and has a concentration ratio of 80 to 150 at the interface.

The invention of the aluminum foil for electrolytic capacitors according to claim 2 is characterized in that, in the invention according to claim 1, the Cu content in the inevitable impurities is 10 ppm or less by mass ratio.

A third aspect of the invention of the aluminum foil for electrolytic capacitors according to the first or second aspect of the invention is characterized in that the inevitable impurities have a total amount other than Cu of 100 ppm or less.

  Below, 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.

Pb: 0.1 to 3 ppm
Pb is an element that makes surface dissolution uniform in etching. However, if it is less than 0.1 ppm, the effect cannot be expected, and if it exceeds 3 ppm, the solubility becomes too high and excessive dissolution occurs. Therefore, the content of Pb is defined above. A desirable lower limit is 0.2 ppm, and a desirable upper limit is 1 ppm.

One or more of Mn, Ni, Sn, Ag, Pt, Au: Total amount 20 to 200 ppm
These additive elements cause surface concentration and are present in the vicinity of the foil surface as an aluminum compound, thereby making the potential noble and increasing the surrounding solubility. When these elements are concentrated at the interface between the oxide film and the aluminum foil fabric, the potential difference from the inside increases and a rapid chemical dissolution reaction is exhibited. The greater the potential difference from the inside, the higher the reactivity. Further, by slightly entering the oxide film region, the oxide film is moderately brittle and the uniformity of the etching reaction is improved. However, if the total amount of the additive elements is less than 20 ppm, the above action cannot be obtained. On the other hand, if the content exceeds 200 ppm, pit generation becomes excessive and pit generation efficiency deteriorates due to pit bonding. . For the same reason, it is desirable to set the lower limit to 50 ppm and the upper limit to 180 ppm.

Cu: 10 ppm or less Although Cu is an element that enhances the solubility of aluminum, it does not show a strong surface concentration, so that the etching property of the surface layer cannot be enhanced. On the other hand, as a result of the increased solubility in the interior, excessive dissolution occurs in the pit diameter enlargement process, resulting in a decrease in capacitance. Therefore, it is desirable to suppress it as 10 ppm or less as an impurity. More preferably, it is 5 ppm or less.

Inevitable impurities (total amount is 100ppm or less except Cu)
If the amount of unavoidable impurities is large, pits are generated excessively, pit coalescence occurs, the capacity is reduced, and dissolution proceeds more than necessary. Therefore, the total amount of unavoidable impurities other than Cu is preferably 100 ppm or less. More desirably, it is 20 ppm or less.

Additive element concentration ratio: 10 nm depth is 1,
Oxide film center 5-50, interface 80-150
The above-mentioned additive elements in the oxide film are concentrated in the surface layer portion, pit generation is effectively promoted, and pits grow effectively in the depth direction of the aluminum foil fabric to improve the roughening rate. .
When the concentration of the additive element at the interface is less than 80 in relative ratio, the generation rate is slow and sufficient pits cannot be obtained. On the other hand, when the concentration exceeds 150, excessive reaction occurs and pits are lost. Further, when the concentration of the additive element at the central portion of the oxide film is less than 5 in relative ratio, the resistance of the oxide film is strong and does not react sufficiently, whereas when it exceeds 50, the entire surface is dissolved. For this reason, the said density | concentration ratio is prescribed | regulated.
In addition, what is necessary is just to show the said density | concentration ratio with a total amount, when the said additional element is 2 or more types. The concentration ratio can be represented by, for example, an ionic strength ratio.
The element concentration can be measured using a transmission electron microscope. At that time, the element concentration is obtained as an average value within the analysis spot diameter of the electron microscope. The analysis spot diameter in the transmission electron microscope is usually 2 to 10 nm. However, the analysis spot diameter is not limited as the present invention.

Aluminum purity: 99.9% or more If the purity is less than 99.9%, the uniformity of crystal orientation is lost and normal etching pits cannot be obtained. An aluminum purity of 99.9% or more is necessary to ensure the uniformity of crystal orientation and keep the cubic ratio at 95% or more.

  Note that the aluminum foil immediately before being subjected to the etching treatment needs to have an oxide film with an appropriate thickness formed on the surface. When the thickness of the oxide film is less than 20 mm, the roughening rate is reduced due to excessive surface dissolution. When the thickness exceeds 60 mm, the surface is dissolved locally and the roughening rate is decreased. Is desirable. The oxide film thickness can be measured by, for example, X-ray photoelectron analysis (ESCA).

  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 in terms of mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: It contains 0.1 to 3 ppm, and among elements selected from Mn, Ni, Sn, Ag, Pt, and Au, one or two or more elements are contained as additive elements in a total amount of 20 to 200 ppm, and the balance is 99.99 ppm. When the composition of the additive element is 9% or more and unavoidable impurities and the arrangement state of the additive element is 10 nm deep at the fabric side from the oxide film-aluminum foil fabric interface, 5 to 50, and has a concentration ratio of 80 to 150 at the interface, so that pits are efficiently generated even in electrolytic etching, and a good roughening rate can be obtained. It becomes possible. This makes it possible to reduce costs and improve productivity when manufacturing electrolytic capacitors.

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 additive elements described above in the extreme surface layer portion, and it is desirable to heat at 500 ° C. or higher for 3 hours or longer. For example, oxidation is performed at an average thickness of 20 to 60 mm by heating in a reducing atmosphere using H ₂ or the like or an inert atmosphere such as Ar or N ₂ under a heating condition of 500 to 600 ° C. × 3 to 36 hours. An aluminum alloy foil having a film can be obtained. In a reducing atmosphere, it is possible to use a mixed gas in which an inert gas or a small amount of oxygen is mixed with a reducing gas such as H _2. Similarly, a mixed gas in which oxygen is mixed in an inert atmosphere is used. Can do. The oxygen concentration mixed in the reducing atmosphere or the inert atmosphere can be 10 to 40 ppm, for example.
As a result of the final annealing, the cubic rate of the aluminum foil is desirably 95% or more. Moreover, the said additional element concentrates on a surface layer part by the said annealing. If annealing is performed under vacuum, an oxide film is not properly formed on the surface, and good etching becomes difficult during etching.

  As a result of the above-mentioned final annealing, as shown in FIG. 1, the additive element concentration at a depth of 10 nm from the interface between the oxide film and the aluminum foil fabric to the fabric side is 1, and 5-50 inside the oxide film, the aluminum foil at the interface The concentration distribution of the additive element is obtained at 80 to 150 in the dough. In FIG. 1, the concentration ratio is shown by the ionic strength ratio. In addition to this, the concentration ratio can be indicated by a mass% method.

  In the final annealing, if the heating temperature is too low or the holding time is too short, the concentration of the additive element at the interface does not exceed 80 in relative ratio, and if the oxygen concentration in the atmosphere is too high, It will not be less than 150. Further, if the heating temperature of the final annealing is too low, the concentration of the additive element in the oxide film does not become 5 or more in relative ratio, and if it is too high, it does not become 50 or less.

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 an electrolytic solution mainly composed of hydrochloric acid or an electrolytic solution not containing hydrochloric acid. However, the present invention may employ electrolytic etching, and in that case, a good roughening rate can be obtained.
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 removing the surface layer portion, an etching pit generation step is performed for generating etching pits on the surface of the aluminum foil. After the etching pit generation process, an etching pit hole diameter expanding process is performed.
In the etching process, pits are formed with high density even in electroless process, 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 for a capacitor having a lower formation voltage. It can also be used as a cathode material.

  An ingot of the components shown in Table 1 (remainder: Al) was prepared and subjected to a 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 in an atmosphere of Ar, N ₂ , H ₂ or the like shown in Table 1 to produce a foil having a cubic crystal ratio of 95% or more. Samples with different concentration gradients were obtained by changing the temperature and time during annealing. The oxide film thickness was measured by ESCA (X-ray photoelectron spectroscopy) and is shown in Table 1. The element distribution in the vicinity of the oxide film-aluminum foil interface was observed with a transmission electron microscope (JEM-2010F) at an accelerating voltage of 200 kV using a cross-sectional thin film prepared by ion thinning. Analysis was carried out. During elemental analysis, the analysis spot diameter was 3 nm. The concentration ratio is shown in Table 1 with the ionic strength ratio at a depth of 10 nm from the interface to the fabric side being 1, and the ionic strength ratio at the center of the oxide film and the ionic strength ratio at the interface as relative values.

  These aluminum foils were immersed in a 3 mol / l sulfuric acid solution 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 sulfuric acid solution at 75 ° C. and 3 mol / l for 600 seconds 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% by mass boric acid solution to evaluate the capacitance, and relative evaluation was made with Example 1 as 100%.

As in Examples 1 to 11, in the case of the foil added with the additive element, it is understood that etching pits are generated by chemical dissolution and a high capacitance is obtained.
When the additive element of Comparative Example 1 is not added, etching pits are not generated, and the electrostatic capacity is remarkably reduced. In addition, when the oxide film and the interface were not appropriately concentrated, the values were generally low.

It is a figure which shows the density | concentration distribution of the addition element in the interface vicinity of the oxide film and cloth | dough in aluminum foil.

Claims (3)

  An aluminum foil for electrolytic capacitors to be used for etching, containing, by mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, and Mn, Ni, Sn, Ag, Among elements selected from Pt and Au, one or two or more elements as additive elements are contained in a total amount of 20 to 200 ppm, and the balance has a composition consisting of 99.9% or more of Al and inevitable impurities, and When the arrangement state of the additive element is 10 nm depth from the oxide film-aluminum foil cloth interface to the cloth side, it is 5 to 50 at the center of the oxide film and has a concentration ratio of 80 to 150 at the interface. Aluminum foil for electrolytic capacitors characterized by The aluminum foil for an electrolytic capacitor according to claim 1, wherein the Cu content in the inevitable impurities is 10 ppm or less by mass ratio. The aluminum foil for electrolytic capacitors according to claim 1 or 2, wherein the inevitable impurities have a total amount other than Cu of 100 ppm or less.

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