JP2671082B2 - Aluminum foil for electrolytic capacitors - Google Patents

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 electrolytic capacitors, and more particularly to an aluminum foil suitable for low voltage electrolytic capacitors having a low formation voltage.

[0002]

2. Description of the Related Art Conventionally, in aluminum foil for electrolytic capacitors, various studies have been conducted on the relationship between the impurity element in the foil and the characteristics of the electrolytic foil such as capacitance, and the Ti content as an impurity is very small, for example, 5 ppm. If the following, iron, silicon, which was considered to adversely affect the characteristics of the electrolytic foil,
It is well known that even if a small amount of an impurity element such as copper is present in the foil, the electrolytic foil characteristics are not deteriorated. Also, Ti is 5
It is also known that the adverse effect of impurity elements on the electrolytic foil properties can be prevented by adding and coexisting a predetermined amount of B in the foil even if it is present in excess of ppm (Japanese Patent Laid-Open No. 53-1).
No. 07657). Further, by adding B after suppressing the allowable limit of Ti content to an extremely small amount, the effect of further increasing the electrolytic capacity was obtained (Japanese Patent Publication No. 62-8492), Fe,
Aluminum anode foils with limited permissible ranges of Si, Mg, Mn, Cu, Zn and Ni have also been developed (JP-A-62-1).
81416).

[0003]

SUMMARY OF THE INVENTION The present invention is based on the conventional aluminum foil for electrolytic capacitors described above, and has been conventionally studied in order to further study the relationship between impurities in aluminum and electrolytic foil characteristics. B and Fe, S
It was developed as a result of investigating the interaction of these elements by paying attention to V and Ga which are inevitably contained in aluminum ingots in addition to the elements such as i, Cu and Zn. An object of the present invention is to provide an aluminum foil for electrolytic capacitors, which has stable and excellent characteristics in a low voltage region.

[0004]

The aluminum foil for electrolytic capacitors according to the present invention for achieving the above object comprises:
Cu5-60ppm, Si60ppm or less, Fe60p
including pm or less and B3 to 20 ppm, at% B /
The ratio of (at% Ti + at% V) is 5 or more and less than 25, and the purity of Al is 99.96% or more, which is a feature of the invention. Further, (Cu + 1 / 3Zn + 3G)
It is a preferred embodiment that the amount of a) is 50 to 150 ppm.

The aluminum foil for electrolytic capacitors is used after being electrochemically etched, and the etching method differs depending on the operating voltage range, and when used at a low voltage, fine and dense pits are obtained. Since it is necessary to select etching conditions, AC etching is commonly used. In AC etching, an etch pit is formed during the anode half cycle, and a film is formed on the inner wall of the pit during the next cathode half cycle. Further, in the next half cycle of the anode, new defect pits are formed starting from the defective portion of the film, and such a process is repeated to successively form the etch pits.

It is important that the etch pits are formed by being appropriately dispersed, and if the etch pits are too narrowly dispersed, the pits will not coalesce and the effective surface area cannot be increased. However, the number of pits per volume decreases, which is not preferable. The degree of dispersion of etch pits is determined by the amount of defects in the film formed during the half cycle of the cathode in AC etching. Therefore, if the amount of defects in the film can be controlled within a predetermined limit range, the effect of increasing the surface area can be surely obtained. When the amount of defects is too large, the distribution interval of the etch pits becomes narrow, and when the amount of defects is too small, the intervals between the pits become wide, and the effect of expanding the surface area becomes insufficient in both cases.

The amount of defects in the film is influenced by the etching conditions, but is also influenced by the composition and structure of the material.
The present invention comprehensively determines the impurity limit in the aluminum material for keeping the amount of defects in the film in the AC etching within a predetermined range by also considering the interaction of these impurities.

Cu has a function of stabilizing the film. 5
If it is less than ppm, the coating tends to be unstable, and if it exceeds 60 ppm, the self-corrosion action of the aluminum foil becomes strong and the aluminum foil is easily dissolved in the etching solution. If the contents of Si and Fe are too large, the reaction with the etching solution becomes violent and the aluminum foil may be dissolved, so the respective limits are 60 ppm. Ti and V have the effect of increasing the number of defects in the film, and B is an element that weakens the effect. B forms a compound of TiB ₂ and VB ₂ with Ti and V, so that these elements are B / (Ti +
When V) = 2, all the compounds are formed. As a result of experimental examination,
The ratio of B / (Ti + V) in atomic% (at%) is 5 to 25,
When it is preferably set to 8 to 16, the amount of defects in the film formed during the half cycle of the cathode in the AC etching becomes optimum. If the amount of B is too large, streaky defects occur on the surface of the aluminum foil after etching. Therefore, the upper limit of B amount is wt
%, 20 ppm, and at%, the ratio of B / (Ti + V) is 25.

Zn and Ga are elements which, when combined with Cu, are effective in forming etch pits starting from film defects during anodic half cycle in AC etching. Cu + 1 / 3Zn in wt%
An optimum amount of pits is formed in the range of +3 Ga in the total of 50 to 150 ppm. If it is less than 50 ppm, the formation of etch pits is not sufficient, and if it exceeds 150 ppm, the self-corrosion of the foil material becomes so strong that it may be dissolved in the etching solution. If the purity of Al is low, the reaction with the etching solution is likely to occur, so that the purity of Al should be 9 in consideration of the relation with the amount of impurities.
9.96% or more, preferably 99.97% or more.

[0010]

In the present invention, the amount of defects generated in the film formed during the cathode half cycle in AC etching due to the interaction of Ti, V, and B is controlled within a predetermined limit range, and Zn, Ga, and By the mutual effect based on the combination of Cu, an appropriate amount of etch pits are formed during the anodic half cycle, the surface area of the aluminum foil surface is effectively increased, and the electrolytic foil characteristics are improved.

[0011]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 Aluminum having the composition shown in Table 1 was cast by continuous casting, then homogenized, hot-rolled and cold-rolled by a conventional method to obtain a 100 μm foil material, which was heated at 300 ° C. for 2 hours in an argon atmosphere. Was finally annealed. The obtained aluminum foil material was treated with 5 mol / l HCl and 0.05 mol / l H ₂ SO ₄
At 40 ° C. in an aqueous solution consisting, 100 c with an alternating current from 25H _Z
/ Cm ² of electrolytic etching was carried out, followed by chemical conversion to 20 V in a 1 mol / l ammonium adipate aqueous solution, and the capacitance was measured in the same solution. As a result, as shown in Table 2, high values were obtained in all cases.

Comparative Example 1 Aluminum having the composition shown in Table 3 was treated in the same manner as in Example 1 to obtain a 100 μ annealed foil. In Table 3, items that are out of the conditions of the present invention are underlined. The capacitance of the obtained foil material was measured by the same method as in Example 1. Table 4 shows the results
Shown in

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

[Table 4]

As can be seen from Table 4, the ratio of atomic% of B to Ti, V is smaller than the range of the present invention. 1 and N
o. 2 foil, and No. 2 where the ratio is too large. 3 is inferior in electrostatic capacity. No. B content exceeding 20 ppm. In No. 4, since the defect formation of the film is weakened, the effect of increasing the surface area cannot be obtained and the capacitance is low. Furthermore, No. 3, No. No. 4 had streak-like defects on the surface after etching. Cu + 1 / 3Zn + 3
No. in which the amount of Ga is smaller than the predetermined range. No. 5 exceeding a predetermined range No. 6 has a low capacitance because the pits are not formed properly in the etching process. The amount of Cu is out of the predetermined range. 7, No. No. 8 also did not have a proper amount of pits formed and was inferior in characteristics.

[0018]

As described above, according to the present invention, there is provided an aluminum foil for electrolytic capacitors, which has stable and excellent electrostatic characteristics particularly in a region where a working voltage is low.

Claims (1)

(57) [Claims] 1. Cu5-60ppm, Si60ppm or less, Fe60ppm or less and B3-20ppm are included, the ratio of at% B / (at% Ti + at% V) is 5 or more and less than 25, and the amount of (Cu + 1 / 3Zn + 3Ga) is 50-1.
An aluminum foil for an electrolytic capacitor having an A1 purity of 50 ppm and 99.96% or more.