JP2000297337A - Aluminum foil for electrolytic capacitor anode, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum foil for electrolytic capacitor anode, hardly causing an etched part at the time of etching. SOLUTION: This aluminum foil for electrolytic capacitor anode contains 5-50 ppm Fe, 6-70 ppm Si, 12-80 ppm Cu, and 0.1-5.0 ppm Pb and (Si content)/(Fe content) and (Cu content)/(Si content) are regulated to 1.1-3.4 and 2.0-4.8, respectively. Aluminum purity is >=99.9%. Such as aluminum foil for electrolytic capacitor anode can be obtained by subjecting the prescribed aluminum ingot to homogenizing treatment, hot rolling, cold rolling, process annealing, finish rolling, and final annealing. Particularly, it is preferable that, as final annealing conditions, holding temperature is regulated to 520-570 deg.C, the total quantity of heat supplied from the beginning of final annealing to its conclusion is regulated to 7.5×103 to 18.0×103 deg.C.h, and the total oxygen concentration in an atmosphere is regulated to <=150 ppm.h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum foil for an anode of an electrolytic capacitor which is easily uniformly dissolved at the time of etching, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, electrode foils for electrolytic capacitors (particularly, anode foils for medium and high pressures) have been produced by etching aluminum foils for electrolytic capacitor anodes. By etching, a large number of tunnel pits are formed on the aluminum foil surface, the surface area of the aluminum foil is enlarged, and an anode foil having a high capacitance can be obtained.

[0003] However, the anode foil obtained by such etching often has a spot-like luster, which sometimes significantly lowers the product value of the anode foil. The point gloss means that when an etching process is performed on an aluminum foil for an anode of an electrolytic capacitor, an unetched portion is locally and scattered, and the reflectance of light in the unetched portion is determined by the reflection of light in the etched portion. It is caused by being larger than the rate. Such dot gloss also occurs in an aluminum foil for an anode of an electrolytic capacitor, which is said to have good etching characteristics.

For example, when the Cu content is 0.004 to 0.0
An aluminum foil for an anode of an electrolytic capacitor having a concentration of 1% (Japanese Patent Publication No. 45-25978), an aluminum foil for an anode of an electrolytic capacitor in which the ratio between the Si content and the Fe content is regulated within a certain range (Japanese Patent Laid-Open No. 1-104743). Gazette), Cu
Aluminum foil for the anode of an electrolytic capacitor having a content of 10 to 60 ppm and an In content and a Sn content of 5 ppm ≦ In + Sn / 1.5 ≦ 10 ppm (JP-A-3-28
No. 3526), an aluminum foil for an anode of an electrolytic capacitor in which the element concentration of Pb, In or Bi in the aluminum foil surface layer 0.1 μm is higher than those in the other parts except the aluminum foil surface layer (Japanese Patent Application Laid-Open JP-A-57-194516) are capable of obtaining an anode foil having good solubility during etching and high capacitance. However, in any of the aluminum foils for the anode of an electrolytic capacitor, an unetched portion is locally and scattered, and a dot gloss is generated. That is, such dot gloss has an adverse effect on capacitance (ie,
It is rare that the capacitance (capacitance decreases), but the appearance is poor, and the consumer (capacitor manufacturer) dislikes it.

Accordingly, the applicant of the present application has filed Japanese Patent Application No. 11-15 / 1997.
No. 424, a proposal was made on aluminum for an electrolytic capacitor electrode, which is unlikely to produce a dot-like luster even when etched. That is, this proposal includes a reaction (anode reaction) of Al → Al ³⁺ + 3e (anode reaction) that occurs at a specific location (for example, a location where γ-Al ₂ O ₃ exists) on the aluminum foil surface during etching, and another specific location. (For example, exposure Pb
), The reaction (cathode reaction) of 2H ⁺ + 2e → H ₂ , which occurs at
That is, etching is uniformly generated on the surface of the aluminum foil so that an unetched portion is hardly generated. When the anodic reaction and the cathodic reaction are extreme, the reaction proceeds only between the two specific places adjacent to each other, and the reaction hardly progresses between the two specific places that are not adjacent to each other and are separated from each other. It is considered that the part that does not become an unetched part.

[0006]

Therefore, the present inventors relate to the above-mentioned proposal of Japanese Patent Application No. 11-15424, which relates to a specific portion that causes an anode reaction,
The invention of Japanese Patent Application No. Hei 10-284,641 discloses an invention in which a specific portion where a cathode reaction is caused is present in a well-balanced manner on the surface of the aluminum foil for the anode of an electrolytic capacitor so that an unetched portion (dot-like luster) hardly occurs even when etched. 11-47
No. 151 was proposed. The present invention relates to a further improved invention of the present invention, wherein the ratio of the Si content to the Fe content in the aluminum foil for the anode of an electrolytic capacitor, and C
By defining the ratio between the u content and the Si content within a certain range, the specific portion causing the anodic reaction and the specific portion causing the cathodic reaction are well-balanced on the aluminum foil surface for the electrolytic capacitor anode. It is intended to be.

[0007]

That is, according to the present invention, there is provided an aluminum alloy having an aluminum purity of 99.9% or more and an Fe content of 5 to 50%.
ppm, Si content: 6 to 70 ppm, Cu content: 1
2-80 ppm, Pb content: 0.1-5.0 ppm, Si content / Fe content is 1.1-3.4, and Cu content / Si content is 2.0-4. The present invention relates to an aluminum foil for an anode of an electrolytic capacitor and a method for producing the same.

The aluminum purity of the aluminum foil for an anode of an electrolytic capacitor according to the present invention is 99.9% or more. When the aluminum purity is less than 99.9%, Fe
Content and Si content are increased, and as a result,
The amount of Si and the amount of precipitated Si also increase, which tends to cause overdissolution during etching, and it is not preferable because the surface area of the aluminum foil cannot be increased. In this specification,
All percentages of the contents of the elements in the aluminum foil are% by weight.

In the aluminum foil for an anode of an electrolytic capacitor according to the present invention, the Fe content is 5 to 50 ppm, particularly preferably 7 to 25 ppm. When the Fe content is less than 5 ppm, the absolute amount of Fe precipitates decreases, the melting start point (etching start point) during etching decreases, and it becomes difficult to increase the surface area of the aluminum foil. When the Fe content is small,
The strength of the aluminum foil itself also decreases. On the other hand, when the Fe content exceeds 50 ppm, the amount of precipitated Fe increases,
This is not preferred because overdissolution is likely to occur during etching and the surface area of the aluminum foil cannot be increased.

[0010] The Si content is 6 to 70 ppm, particularly preferably 7 to 25 ppm. 6p Si content
pm, the absolute amount of Si precipitates decreases,
Dissolution start point during etching (etching start point)
And it becomes difficult to increase the surface area of the aluminum foil. Further, when the Si content is small, the strength of the aluminum foil itself is also weakened. On the other hand, when the Si content is 70 p
If it exceeds pm, the amount of precipitated Si increases, and overdissolution is apt to occur during etching, and the surface area of the aluminum foil cannot be increased.

[0011] The Cu content is 12 to 80 ppm, particularly preferably 20 to 60 ppm. If the Cu content is less than 12 ppm, the anodic reaction on the surface of the aluminum foil is not sufficiently promoted, the etching property becomes poor, and the surface area of the aluminum foil cannot be increased. On the other hand, when the Cu content exceeds 80 ppm, the pitting corrosion potential becomes high, making it difficult to uniformly etch the entire aluminum foil, and may cause an unetched portion.

The Pb content is from 0.1 to 5.0 ppm, particularly preferably from 0.3 to 1.2 ppm. P
When the b content is less than 0.1 ppm, the amount of Pb concentrated on the surface of the aluminum foil also decreases, and the cathode reaction on the surface of the aluminum foil is not sufficiently promoted (accordingly,
The anodic reaction corresponding to the cathodic reaction is not promoted),
This is not preferable because the etching property becomes poor and the surface area of the aluminum foil cannot be increased. Pb content is 5.0
If the content exceeds ppm, the cathodic reaction becomes severe (accordingly, the anodic reaction corresponding to the cathodic reaction becomes severe), and it becomes difficult to uniformly etch the entire aluminum foil, which may cause an unetched portion.

In the aluminum for an anode of an electrolytic capacitor according to the present invention, the ratio of the Si content to the Fe content, that is, the Si content / Fe content is 1.1 to 3.4. If the ratio of the Si content to the Fe content is less than 1.1, the starting point at the time of etching is reduced, and the etching characteristics may be poor. That is, when the Si content is small, a defect occurs in the surface film of the aluminum foil, and the amount of precipitated Si serving as an etching start point decreases,
Etching characteristics may be poor. On the other hand, when the Si content is small, even if the Fe content is large, it is difficult for Fe to precipitate, and therefore, the precipitated Fe that promotes the anode reaction is reduced.
And the etching property is poor, and the surface area of the aluminum foil cannot be increased. On the other hand, when the ratio of the Si content to the Fe content exceeds 3.4, the amount of precipitated Si that becomes a defect in the surface film of the aluminum foil increases, and the amount of precipitated Fe relatively increases.
The anodic reaction becomes excessive, making it difficult to uniformly etch the entire aluminum foil, and may cause an unetched portion.

The ratio of the Cu content to the Si content, ie, C
u content / Si content is 2.0 to 4.8. Si
When the ratio of the Cu content to the content is less than 2.0,
Since the Cu content is relatively small with respect to the Si content, an etching start point is formed, but the anodic reaction does not easily proceed, and it becomes difficult for deep etching pits to be formed, thereby increasing the surface area. There is a possibility that it cannot be achieved enough. On the other hand, if the ratio of the Cu content to the Si content exceeds 4.8, Cu tends to be excessively concentrated on the aluminum foil surface. An excessively concentrated portion becomes a composite oxide film that does not react during etching, and this portion may remain as an unetched portion.

The aluminum foil for an anode of an electrolytic capacitor according to the present invention can be manufactured, for example, as follows. First, if the aluminum purity is 99.9% or more,
Fe content: 5 to 50 ppm, Si content: 6 to 70 p
pm, Cu content: 12 to 80 ppm, Pb content:
0.1 to 5.0 ppm, an Si ingot having an Si content / Fe content of 1.1 to 3.4, and a Cu content / Si content of 2.0 to 4.8. prepare. Then, this aluminum ingot may be subjected to homogenization treatment, hot rolling, cold rolling, intermediate annealing, finish rolling, and final annealing in the manner of producing a normal rolled aluminum foil.

At this time, it is preferable to set the conditions of the final annealing as follows, since it is possible to obtain an aluminum foil for an anode of an electrolytic capacitor which is most unlikely to have a spot-like luster. That is, first, the holding temperature is set to 520 to 570 ° C. If the holding temperature is lower than 520 ° C., Pb
Is difficult to concentrate on the surface of the aluminum foil, the cathode reaction during etching does not sufficiently proceed, and an unetched portion tends to remain. On the other hand, if the holding temperature exceeds 570 ° C., Pb and Cu excessively concentrate on the aluminum foil surface to form a composite oxide film, and this portion tends to remain as an unetched portion.

The total amount of heat supplied from the start to the end of the final annealing is 7.5 × 10 ^{3 to} 18.0 × 10 ³ ° C. · h. It is to be. Here, the total amount of heat supplied has the following meaning. That is, in the final annealing, as shown in FIG. 1, a temperature raising process of raising the temperature of the aluminum foil from room temperature to a predetermined temperature (holding temperature), a holding process of holding the aluminum foil at a predetermined temperature, and a process of holding the aluminum foil at a predetermined temperature. And a cooling process of cooling from the temperature of the above to normal temperature. At this time,
Heat is applied to the aluminum foil in each step. Therefore, the given total amount of heat is the area of the hatched portion surrounded by the trapezoid in FIG. 1, and this is expressed as the total amount of supplied heat in the present invention. That is, the total amount of supplied heat is determined not only by the holding temperature and the holding time but also by the heating rate, the heating time, the cooling rate, and the cooling time. Needless to say, the final annealing may be performed in a pattern that goes through a two-step or three-step heating process and / or a cooling process other than the trapezoid shown in FIG. The total heat supply is 7.5 × 10 ³ ° C. · h. If less than Pb
Is difficult to concentrate on the surface of the aluminum foil, the cathode reaction during etching does not sufficiently proceed, and an unetched portion tends to remain. On the other hand, the total heat supply is 18.0.
× 10 ³ ° C · h. If Pb or Cu exceeds Pb or Cu, it excessively concentrates on the surface of the aluminum foil to form a composite oxide film, and this portion tends to remain as an unetched portion.

The total oxygen concentration in the atmosphere from the start to the end of the final annealing is 150 ppm · h. It is as follows. Here, the total oxygen concentration in the atmosphere means the average oxygen concentration in the annealing atmosphere multiplied by the annealing time. The annealing time is the sum of the temperature raising time, the holding time, and the cooling time. When the total oxygen concentration in the atmosphere is 150 ppm · h. If it exceeds, Pb or Cu concentrated on the surface, or precipitated Fe or Si is likely to be oxidized, adversely affecting the etching property, and the unetched portion tends to remain.

[0019]

EXAMPLES Examples 1 to 12, Reference Examples and Comparative Examples 1 to 9 Fe, Si, and C having a thickness of 500 mm and the contents shown in Table 1.
An aluminum ingot having an aluminum purity of 99.99% containing u and Pb was prepared. The ingot was added at 560 ° C. × 5 h.
After hot-rolling, hot rolling was immediately performed to obtain an aluminum plate having a thickness of 6 mm. This aluminum plate was subjected to cold rolling, intermediate annealing (220 ° C. × 15 h.), Finish rolling, and alkali cleaning. Thereafter, final annealing was performed under an argon gas atmosphere under the following conditions. That is, the average heating rate is 30 ° C./h. And the holding temperature 55
0 ° C., holding time 5 hours, average cooling rate 30 ° C./h.
And Therefore, the total heat supply in the final annealing is 1
2.0 × 10 ³ ° C. · h. Met. The average oxygen concentration in the final annealing atmosphere was 2.98 ppm,
The annealing time was 40.3 hours. Therefore, the total oxygen concentration in the atmosphere is 120 ppm · h. Met. Thus, an aluminum foil for an anode of an electrolytic capacitor having a thickness of 0.1 mm was obtained.

The aluminum foil for the anode of each electrolytic capacitor obtained by the above method was subjected to an etching treatment and a chemical treatment under the following conditions. [Etching treatment]: The aluminum foil for the anode of each electrolytic capacitor was placed in a 0.1% NaOH aqueous solution at 50 ° C. for 60 hours.
It was immersed for 2 seconds for pretreatment. Thereafter, the aluminum foil was immersed in a 1 molar HCl + 3 molar H ₂ SO ₄ aqueous solution at 85 ° C., and electrolytic etching was performed at a current density of DC 0.2 A / cm ² for 4 minutes. Next, the aluminum foil after electrolytic etching was immersed in the above-mentioned 1 molar HCl + 3 molar concentration H ₂ SO ₄ aqueous solution for 10 minutes to complete the etching treatment. The molar concentration in the aqueous solution is m
ol / l. [Chemical conversion treatment]: Each aluminum foil after the above-mentioned etching treatment was treated with a counter electrode of SUS according to the EIAJ method.
304, the chemical conversion treatment was performed at 375 Vf. I went in.

Then, for each foil after the etching treatment, the area ratio of the unetched portion was measured by the following method.
The results are shown in Table 1. The smaller the area ratio of the unetched part,
This means that the surface is uniformly etched, and it is difficult for spot gloss to occur. [Area ratio of unetched portion]: The foil after the etching treatment was photographed with an optical microscope at 37.5 times in 10 visual fields. Each photograph was binarized into an image using an image analyzer, the area ratio of each unetched portion was determined, and the average value was shown in Table 2 as the area ratio of the unetched portion.

The capacitance (μF / cm ² ) of the aluminum foil for the anode of each electrolytic capacitor after the etching and chemical conversion treatments was measured under the following conditions. And
On the basis of the capacitance of the aluminum foil for an electrolytic capacitor anode obtained by the method according to the reference example as a reference (100%), the capacitance of each aluminum foil for an anode of an electrolytic capacitor is expressed in% by relative comparison, This is shown in Table 1. [Capacitance]: One sample foil having a size of 10 mm in width and 50 mm in length was sampled from each of the foils after the above-mentioned etching and chemical conversion treatments. Then, this sample foil is
The electrode was immersed in a 13% aqueous solution of ammonium pentaborate at 13 ° C., and the counter electrode was an etched aluminum foil having a capacitance of 40,000 μF or more, and a capacitance (μF / cm ² ) using an LCR meter in a 120 Hz series equivalent circuit Was measured.

[0023]

[Table 1]

As is evident from the results shown in Table 1, the use of the aluminum foil for the anode of electrolytic capacitors according to Examples 1 to 12 is more effective than the case of the aluminum foil for the anode of electrolytic capacitors according to Comparative Examples 1 to 9. , Fe content, Si content, Cu content, Pb content are within specific ranges,
In addition, since the Si content / Fe content and the Cu content / Si content are within specific ranges, it is possible to obtain an anode foil having high capacitance and few unetched portions.

Examples 13 to 24 The aluminum ingot used in Example 1 was subjected to homogenization, hot rolling, cold rolling, intermediate annealing, finish rolling, and alkali washing under the same conditions as in Example 1. did. Thereafter, the final annealing was performed under an argon gas atmosphere under the conditions shown in Table 2 to obtain an aluminum foil for an anode of an electrolytic capacitor having a thickness of 0.1 mm.

Then, an etching treatment and a chemical conversion treatment are performed under the same conditions as in the first embodiment, and the unetched area ratio and the capacitance (μF / c) are obtained in the same manner as in the first embodiment.
m ² ) was measured, and the results are shown in Table 2. With respect to the capacitance, the capacitance of the aluminum foil for the anode of each electrolytic capacitor is expressed in% by relative comparison with the capacitance of Example 19 as a reference (100%),
This is shown in Table 2.

[0027]

[Table 2]

As is evident from the results shown in Table 2, when the aluminum foil for an anode of an electrolytic capacitor obtained by the method of Examples 13 to 18 was used, the electrolytic solution obtained by the method of Examples 19 to 24 was used. Since the final annealing conditions are set in a preferable range as compared with the case of the aluminum foil for a capacitor anode, it is possible to obtain an anode foil having a high capacitance and a small number of unetched portions.

[0029]

When the aluminum foil for an anode of an electrolytic capacitor according to the present invention is etched to form an anode foil, the definite effect of reducing the area ratio of the unetched portion is unknown. However, the Fe content, the Si content, the Cu content, and the Pb content in the aluminum foil are kept within specific ranges, and the Si content / Fe content, Cu content /
By setting the Si content within a specific range, at the time of etching, a specific portion causing an anodic reaction,
The present inventors presume that a specific location where a cathode reaction occurs can be present in a well-balanced manner on the surface of the aluminum foil for the anode of an electrolytic capacitor, and as a result, an unetched portion hardly occurs.

[0030]

As described above, when the aluminum foil for an anode of an electrolytic capacitor according to the present invention is used, the area ratio of the unetched portion is reduced and the entire surface is uniformly etched. This has the effect of increasing the commercial value of the anode foil.

[Brief description of the drawings]

FIG. 1 is an example of a diagram showing a temperature change in final annealing.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22F 1/00 685 C22F 1/00 685Z 686 686B 691 691Z 691B 1/02 1/02 1/04 1/04 K H01G 9 / 055 H01G 9/04 337

Claims (2)

[Claims] (1) an aluminum purity of 99.9% or more;
Fe content: 5 to 50 ppm, Si content: 6 to 70 p
pm, Cu content: 12 to 80 ppm, Pb content:
0.1-5.0 ppm, and Si content / Fe content is 1.1-3.4, and Cu content / Si content is 2.0-4.8. Aluminum foil for the anode of electrolytic capacitors. 2. The method according to claim 1, wherein the aluminum purity is 99.9% or more.
Fe content: 5 to 50 ppm, Si content: 6 to 70 p
pm, Cu content: 12 to 80 ppm, Pb content:
0.1 to 5.0 ppm, and an aluminum ingot having a Si content / Fe content of 1.1 to 3.4 and a Cu content / Si content of 2.0 to 4.8. A homogenizing treatment, hot rolling, cold rolling, intermediate annealing, finish rolling and final annealing to produce an aluminum foil for an anode of an electrolytic capacitor, wherein the final annealing has a holding temperature of 520.
570 ° C., and the total heat supply from the start to the end of the final annealing is 7.5 × 10 ^{3 to} 18.0 × 1.
0 ³ ℃ · h. And the total oxygen concentration in the atmosphere is 150p
pm · h. A method for producing an aluminum foil for an anode of an electrolytic capacitor, characterized by the following.