JP2001294960A - Aluminum alloy foil for cathode of electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide aluminum alloy foil applied to the cathode foil of an electrolytic capacitor having high capacitance. SOLUTION: This aluminum alloy foil has a composition containing 100 to 500 ppm Si, 200 to 750 ppm Fe, 20 to 100 ppm Mg, 50 to 120 ppm Zn, <=30 ppm Cu, either or both of Mn and Cr by 40 to 200 ppm in total, other inevitable impurities of <=20 ppm, and the residual Al, and, in particular, Mn and/or Cr is added to the foil by 40 to 200 ppm. The aluminum alloy foil has high tensile strength and, at the time of processing a capacitor, is little in trouble, such as cutting and has good workability. Moreover, the aluminum alloy foil has good etching characteristics, in which the cathode foil of an electrolytic capacitor having high capacitance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy foil having excellent etching characteristics and high tensile strength, suitable for obtaining a cathode foil of an electrolytic capacitor having a high capacitance.

[0002]

2. Description of the Related Art Conventionally, an electrolytic capacitor cathode foil has been manufactured by etching an aluminum alloy foil. Etching is to form fine irregularities on the surface of the aluminum alloy foil, increase the surface area of the foil,
This is performed to increase the capacitance. The etching process is performed in an aqueous solution containing chloride ions. Generally, the higher the chloride ion concentration, the greater the surface area expansion rate of the aluminum alloy foil and the higher the capacitance. However, when the concentration of chloride ions exceeds a certain limit, the dissolution of the aluminum alloy foil surface becomes excessive, and as a result, fine irregularities formed at the beginning of etching are destroyed,
In some cases, the surface area decreases and the capacitance also decreases. In order to suppress such excessive dissolution, etching is performed by adding an acid such as sulfuric acid or oxalic acid to an etching solution.

However, 99.85% of the currently used
In many aluminum alloy foils having an Al purity, even if the above-described etching treatment is performed, excessive melting is likely to occur, and it is difficult to obtain a material having a high capacitance. Generally, the mechanism of the electrochemical dissolution of an aluminum alloy foil in an acidic solution (etching solution) is Al
If an alloy element or an impurity element having an electrode potential higher than the electrode potential exists as a precipitate, Al forms a local battery in which the anode functions as an anode and the precipitate functions as a cathode.
Therefore, a current flows from the cathode to the anode, and Al as the anode becomes a cation and dissolves in the acidic solution.
This becomes more remarkable as the number of precipitates having a cathode, that is, an electrode potential higher than that of Al is increased.

[0004] The present inventors believe that this dissolution mechanism is 99.85.
%, Which occurs during the etching process of the aluminum alloy foil having the purity of% Al, which is considered to cause excessive dissolution. Mg and Zn are added to the aluminum alloy so that excessive dissolution is prevented as much as possible. An aluminum alloy foil for a cathode of an electrolytic capacitor which is excellent in quality has been proposed (Japanese Patent No. 261931).

[0005]

The present invention relates to the improvement of the invention according to the above-mentioned Japanese Patent No. 2651931, and furthermore, by adding a specific amount of a specific element,
It is an object of the present invention to provide an aluminum alloy foil capable of improving etching characteristics and obtaining a cathode foil of an electrolytic capacitor having a higher capacitance.

[0006]

That is, the present invention provides a method for producing Si:
100 to 500 ppm, Fe: 200 to 750 ppm,
Mg: 20 to 100 ppm, Zn: 50 to 120 pp
m, Cu: 30 ppm or less, the amount of one or both of Mn and Cr or the total amount of 40 to 200 ppm, other unavoidable impurity elements: 20 ppm or less, Al: balance, aluminum for electrolytic capacitor cathode characterized by the following: It relates to an alloy foil.

The constituent elements and their contents of the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention are as follows. Note that all ppms in the present invention are based on weight.

[0008] Si is 100 to 500 ppm. S
i is contained in bauxite which is a raw material of aluminum. Aluminum that has not been subjected to the purification step of the three-layer electrolysis method or the segregation method contains such an amount of Si. In order to reduce the content of Si to less than 100 ppm, a special aluminum refining process must be performed, which is not preferable because aluminum becomes expensive. If the Si content exceeds 500 ppm, the Al purity decreases, which is not preferable for use in electrolytic capacitors.

[0009] Fe is 200 to 750 ppm. F
e is also included in the bauxite. Aluminum which has not been subjected to a purification step such as a three-layer electrolysis method contains such an amount of Fe. In order to reduce Fe to less than 200 ppm, a special aluminum purification step must be performed, which is not preferable because aluminum becomes expensive. F
If e exceeds 750 ppm, the presence of a large amount of Fe precipitates cannot be avoided, a local battery is formed between the precipitates and Al, and Al is excessively dissolved in the etching solution, which is not preferable.

[0010] Mg is 20 to 100 ppm. Mg
Is generally not contained in bauxite, and is added to a predetermined amount. It goes without saying that even an element contained in bauxite, such as Fe or Si, may be added to a predetermined amount. Mg forms an intermetallic compound with the above-mentioned Fe and Si, and prevents the formation of a local battery between Fe and Al. When Mg has a lower standard electrode potential than Al and forms an intermetallic compound with Fe having a higher standard electrode potential than Al, the intermetallic compound has a standard electrode potential close to that of Al. Therefore, the difference in the standard electrode potential between Al and Fe, Si, or the like does not become remarkable, and overdissolution of Al in the etching solution can be prevented. Mg is 20pp
If it is less than m, the amount is insufficient to produce an intermetallic compound with Fe or Si, which is not preferable. If Mg exceeds 100 ppm, the purity of Al decreases, which is not preferable for use as an electrolytic capacitor.

[0011] Zn is 50 to 120 ppm. Zn
Is generally not contained in bauxite, and is added to a predetermined amount. Zn is Al
The solid solution improves the strength of the obtained aluminum alloy foil. If Zn is less than 50 ppm, the strength of the aluminum alloy foil is not sufficiently improved, which is not preferable. If Zn exceeds 120 ppm, the standard electrode potential of Al in which Zn forms a solid solution will decrease, the difference in standard electrode potential between Al and Fe or the like will increase, and overdissolution of Al in the etching solution will easily occur, It is not preferable to use for an electrolytic capacitor.

[0012] Cu is 30 ppm or less. Cu may be contained in bauxite, and aluminum that has not been subjected to a purification step such as a three-layer electrolytic method generally contains such a large amount in general. Note that, depending on the type of bauxite, some do not contain Cu, in which case Cu is not contained in the aluminum alloy foil, but as described above, a predetermined amount or less of Cu is added. Is also good. If the content of Cu exceeds 30 ppm, the purity of Al decreases, which is not preferable for use in electrolytic capacitors.

In the present invention, Mn and / or Cr are further added in an amount of 40 to 200 ppm. When Mn and / or Cr is less than 40 ppm, the tensile strength of the obtained aluminum alloy foil decreases. Further, the etching characteristics of the aluminum alloy foil are reduced, the dissolution loss is reduced, and a cathode foil having a high capacitance cannot be obtained. On the other hand, if Mn and / or Cr exceeds 200 ppm, the dissolution loss of the aluminum alloy foil becomes too large, so that a cathode foil having high capacitance cannot be obtained, which is not preferable.

In the present invention, unavoidable impurities may be mixed in addition to the above-mentioned components, and typically, Ti is used. This may be contained in bauxite, and may contain about 20 ppm or less of Ti. If unavoidable elements such as Ti are mixed in more than 20 ppm, the purity of Al decreases, which is not preferable for use in electrolytic capacitors. Among the unavoidable elements, Ti has a standard electrode potential lower than that of Al and hardly forms a solid solution with Al.
Accordingly, an increase in the content results in an increase in the amount of precipitated Ti, and a local battery is formed between Al and Ti, so that Al is excessively dissolved in the etching solution, which is not preferable.

The aluminum alloy foil for an electrolytic capacitor cathode according to the present invention can be rationally obtained, for example, by the following manufacturing method. That is, Si: 100 to 500
ppm, Fe: 200 to 750 ppm, Mg: 20 to 1
00 ppm, Zn: 50 to 120 ppm, Cu: 30 p
pm or less, the amount of either or both of Mn and Cr or the total amount of both is 40 to 200 ppm, the other inevitable impurity elements: 20 ppm or less, and the ingot consisting of Al: the balance is heated at a temperature of 500 ° C. to 550 ° C. for 20 hours. It can be manufactured by homogenizing under the following conditions, performing hot rough rolling and hot finishing rolling, and then performing cold rolling without performing intermediate annealing.

In the present invention, first, before dissolving the aluminum base metal and flowing it into the mold, Mg, Zn, Mn and Cr are added.
To produce an ingot having a specific elemental composition. The reasons for using a specific elemental composition
As described above. Then, the ingot is heated to a temperature of 50
The homogenization treatment is performed under the conditions of 0 to 550 ° C for a time of 20 hours or less. The homogenization process is performed to uniformly disperse each element in the ingot. If the temperature is lower than 500 ° C., it is difficult to form an intermetallic compound of Mg and Fe or Si. In short, each component element may not be uniformly distributed. When the temperature exceeds 550 ° C, Mg and F
Intermetallic compounds with e and Si are less likely to be formed. The fact that the time of the homogenization process is less than 20 hours means that the holding time in the homogenization process may be infinitesimal, and does not mean that the homogenization process is not performed.

After the homogenization treatment, the ingot is subjected to hot rough rolling and hot finish rolling. Hot rough rolling is usually 400
It is applied at a temperature of at least ℃. Accordingly, the entry side temperature of the hot finish rolling is usually set to 400 ° C. or higher. After hot finish rolling, cold rolling is performed immediately, that is, without performing intermediate annealing. An aluminum alloy foil for a cathode having a desired thickness is obtained by cold rolling. Further, final annealing can be performed after cold rolling to obtain an aluminum alloy foil for a cathode of an electrolytic capacitor. Then, an electrolytic capacitor cathode foil can be obtained by subjecting them to an etching treatment.

[0018]

Hereinafter, the present invention will be described based on examples, but the present invention is not limited to the examples. The present invention is an improved invention of the invention according to No. 2651931,
The aluminum alloy foil to which Mn and / or Cr is further added at 40 to 200 ppm has good etching characteristics,
It should be interpreted as being based on the knowledge that a higher capacitance cathode foil is obtained.

EXAMPLES, REFERENCE EXAMPLES AND COMPARATIVE EXAMPLES An aluminum ingot having an elemental composition shown in Table 1 (thickness 5
00 mm). At the temperature of 520 ° C,
The homogenization treatment was performed for one hour. After that, 500 ° C
And hot finish rolling at an inlet side temperature of 500 ° C. to obtain an aluminum plate having a thickness of 5 mm. Subsequently, cold rolling was repeatedly performed without performing intermediate annealing to obtain an aluminum foil having a thickness of 0.05 mm. Then, final annealing was performed at 320 ° C. for 5 hours to obtain an aluminum alloy foil for an electrolytic capacitor.

[0020]

[Table 1]

The aluminum alloy foil for a cathode of an electrolytic capacitor obtained as described above was measured for capacitance and tensile strength by the following measuring methods. The results are shown in Table 2. [Capacitance] Pre-etching treatment conditions: A sample of a predetermined size was cut out from the aluminum alloy foil for each electrolytic capacitor cathode.
0.05% by weight aqueous sodium hydroxide solution (liquid temperature 50 ± 1
C) for 30 seconds. Etching condition: The sample after the pre-etching treatment was treated with 8% by weight hydrochloric acid + 6% by weight aluminum chloride + 0.1
Immersed in an aqueous solution of oxalic acid (solution temperature 40 ° C ± 1 ° C)
The exchange of 50 Hz, 1 at a current density of 0.4 A / cm ²
Electrolytic etching was performed for 20 seconds. Chemical conversion treatment conditions: In an aqueous solution obtained by dissolving 150 g of ammonium adipate in 1000 cm ³ of pure water (liquid temperature 80 ° C. ± 1)
C) at 3 V. Measurement and display of electrostatic capacity:
150 g of ammonium adipate in 1000 cm ³ of pure water
The capacitance (μF / cm ² ) was measured using an LCR meter in an aqueous solution (solution temperature 20 ° C. ± 1 ° C.). The capacitance of the aluminum alloy foil for a cathode of an electrolytic capacitor according to the reference example was defined as a reference (100), and the capacitance in Table 2 was indicated by a ratio thereof. [Tensile strength] A sample having a length of 100 mm and a width of 10 mm was cut out from the aluminum alloy foil for each electrolytic capacitor cathode, and a gauge length of 5 mm was measured with an Instron universal tester.
0 mm, tensile speed 10 mm / min. Was used to measure the tensile strength. Then, the tensile strength of the aluminum alloy foil for a cathode of an electrolytic capacitor according to the reference example was defined as a reference (100), and the tensile strength in Table 2 was indicated by a ratio thereof.

[0022]

[Table 2]

The loss on dissolution in Table 2 is obtained by measuring the weight loss of the sample during the etching treatment. The loss on dissolution of the aluminum alloy foil for the electrolytic capacitor cathode according to the reference example is defined as a reference (100). It is shown as a ratio.

As is clear from the results in Table 2, in the case of the aluminum alloy foil for a cathode of an electrolytic capacitor according to the embodiment,
Both the tensile strength and the capacitance were superior to those according to the reference example. On the other hand, in the case of the aluminum alloy foil for a cathode of an electrolytic capacitor according to the comparative example, both the tensile strength and the capacitance were the same as those according to the reference example, or the capacitance was low.

[0025]

As described above, the aluminum alloy foil for an electrolytic capacitor cathode according to the present invention has excellent etching characteristics, and the electrolytic capacitor cathode foil obtained by etching the aluminum alloy foil has a large capacitance. There is an effect that a large-capacity capacitor can be obtained per unit area. In addition, the aluminum alloy foil for a cathode of an electrolytic capacitor according to the present invention has the effects of having high tensile strength, having few troubles such as cutting during capacitor processing (for example, winding), and improving workability. Furthermore, since the aluminum alloy foil for a cathode of an electrolytic capacitor according to the present invention may have a low Al purity, there is an effect that it can be obtained at low cost using aluminum which has not been subjected to a purification step.

Claims (1)

[Claims] 1. Si: 100 to 500 ppm, Fe: 2
00 to 750 ppm, Mg: 20 to 100 ppm, Z
n: 50 to 120 ppm, Cu: 30 ppm or less, Mn
And the amount of either one or both of Cr is 40 to
200 ppm, other unavoidable impurity elements: 20 ppm
In the following, Al: an aluminum alloy foil for a cathode of an electrolytic capacitor, comprising the remainder.