JP2006152394A - Aluminum foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain aluminum foil for an electrolytic capacitor suitable to an electrolytic capacitor for medium-high voltage. <P>SOLUTION: The electrolytic capacitor comprises one or more kinds of elements selected from the first group (Pb, Mg, Li and Na) by 0.1 to 20 ppm in total, one or more kinds of elements selected from the second group (Sn, Fe, In, Cr, Zr, Ge and Si) by 10 to 50 ppm in total, and one or more kinds of elements selected from the third group (Ri, Hf, V, Mo, W, Ni, Cu and Zn) by 10 to 100 ppm in total, and the balance Al with inevitable impurities, and also, the total of one or more kinds of elements in the fourth group (Mn, Ga and B) in the inevitable impurities is ≤10 ppm. At the time of etching, pits are formed, so as to be uniformly lined up, thus a capacitor having high electrostatic capacitance per unit area can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aluminum foil for a capacitor used for an electrode of an electrolytic capacitor, and is particularly suitable for an electrolytic capacitor for medium to high voltage.

  In general, the aluminum foil for electrolytic capacitors is made of pure aluminum having a purity of 99.9% or more, which is hot and cold rolled by a conventional method to a thickness of about 100 μm. This aluminum foil is finally annealed to 500 to 600 ° C. for the purpose of removing crystal distortion, etc. before being assembled as a capacitor, surface roughening treatment by electrolytic etching, predetermined amount of chemical conversion treatment (anodic oxidation), etc. Is done.

Etching foils used for medium- and high-voltage electrolytic capacitors are obtained by electrolyzing foils with a uniform crystal orientation in a direct current in an acidic solution and opening countless holes perpendicular to the cross-sectional direction called pits to increase the surface area. It is expanding.
A high cubic rate is essential for medium- and high-pressure etching foils. In order to obtain a high cubic crystal ratio, it is necessary to use high-purity aluminum of 99.9% or more and to contain a specific element in a certain ratio. Moreover, in order to grow a cubic crystal, the annealing process at high temperature is performed.
In addition, various element additions have been proposed to facilitate the generation of the pits. For example, in Patent Document 1, an aluminum foil contains a trace amount of Fe, Ni, Co, Cr, Mn, Zr, Ti, V, Mo, Pb, Bi, In, and Sn to increase the density of etching pits. Attempts to increase have been proposed.
JP-A-8-3673

However, as described above, even if a trace amount of element is added, the improvement of the roughening rate is not sufficient, and further improvement is desired.
By the way, since the oxide film grows on the surface by the heat treatment described above, the aluminum foil can be classified into the outermost oxide film layer, the aluminum-oxide film interface portion, and the three layers inside thereof.
As a result of investigating and studying the influence of various elements, the present inventors have found that the concentration position in annealing differs depending on the element and changes the generation of pits in etching. In addition, for certain elements, we found that even a small amount could inhibit bit generation.
As described above, the present inventors have a specific role in the elements that are characteristically present in each layer, and in order to obtain a high capacitance, it is necessary to ensure a high cubic crystal ratio and a specific element in each layer. The present inventors have found that it is necessary to appropriately contain.

  The present invention has been made against the background of the above circumstances, and by controlling the distribution of elements in each layer by containing an appropriate amount of elements that differ in concentration behavior by heat treatment, a high roughening rate is obtained during etching. It aims at providing the aluminum foil for electrolytic capacitors obtained.

  That is, the aluminum foil for electrolytic capacitors according to the present invention includes one or more elements of the first group (Pb, Mg, Li, Na) in a total amount of 0.1 to 20 ppm, and the second group (Sn, Fe , In, Cr, Zr, Ge, Si), one or more elements in a total amount of 10 to 50 ppm, elements of the third group (Ri, Hf, V, Mo, W, Ni, Cu, Zn) One or more of the above are contained in a total amount of 10 to 100 ppm, the balance is composed of Al and inevitable impurities, and the total amount of the fourth group elements (Mn, Ga, B) in the inevitable impurities is 10 ppm or less It is characterized by that.

Below, the effect | action of the component currently limited by this invention and the reason for limitation are demonstrated. In addition, all the following contents are shown by mass ratio.
First group (Pb, Mg, Li, Na): 0.1 to 20 ppm
These elements are mainly elements that concentrate on or inside the oxide film.
It increases the solubility of the oxide film and partially weakens the film to promote crystallization. Since the oxide film reduces the dispersibility of pits, the dispersibility of pits can be improved by appropriately including one or more of these elements and facilitating removal of the oxide film. Typical examples include Mg and Pb. However, when the content of one or more of the elements of the first group is less than the lower limit in total, the above action cannot be obtained effectively. On the other hand, if the upper limit is exceeded, the oxide film becomes more brittle than necessary, the reaction at the aluminum interface becomes active, and surface loss occurs, so that a high capacity cannot be obtained.

Second group (Sn, Fe, In, Cr, Zr, Ge, Si): 10 to 50 ppm
These elements are elements that concentrate at the interface between the oxide film and the aluminum fabric, and act as the base point of the pits. Since the number of pits is controlled by these elements, it is necessary to contain an appropriate amount of one or more kinds. Representative examples include Fe, Cr, Zr, and Si. However, if the content of these elements is less than the lower limit in total, the action as the pit base point cannot be sufficiently obtained. On the other hand, when the upper limit is exceeded, the activity of the aluminum interface becomes too high, surface dissolution increases, and high capacity cannot be obtained.

Third group (Ri, Hf, V, Mo, W, Ni, Cu, Zn): 10 to 100 ppm
These elements do not show a tendency to concentrate and are present inside the aluminum foil, affecting the pit length. An etching foil with high uniformity of pit length can be obtained by appropriately containing one or more of these elements. Typical examples include Ni, Cu, and Zn. However, when the content of these elements is less than the lower limit in total, the above-described effect cannot be obtained sufficiently. On the other hand, if the upper limit is exceeded, the solubility of the aluminum itself increases, and the pits become larger than necessary, resulting in coalescence of the pits, so that a high capacity cannot be obtained.

Group 4 (Mn, Ga, B): 10 ppm or less These elements need to be reduced as much as possible because they adversely affect pit formation even when contained in minute amounts. However, in consideration of industrial properties, it is 10 ppm or less. For the same reason, it is more desirable to set it at 5 ppm or less.

  As described above, each element has an individual role depending on the position of the element, and the presence of an appropriate amount in each layer and the regulation of the specific element content are required to generate high density and highly uniform pits. It becomes a necessary condition. As the essential component, an element can be selected by any combination in each group (first to third groups). As an example, a combination of Mg, Pb, Fe, Cr, Zr, Si, Ni, Cu, and Zn can be given.

  As described above, according to the aluminum foil for electrolytic capacitors of the present invention, the total amount of one or more elements of the first group (Pb, Mg, Li, Na) is 0.1 to 20 ppm. 10 to 50 ppm in total amount of one or more elements of two groups (Sn, Fe, In, Cr, Zr, Ge, Si), third group (Ri, Hf, V, Mo, W, Ni, Cu or Zn) contains one or more elements of 10 to 100 ppm in total amount, the balance is composed of Al and inevitable impurities, and the fourth group element (Mn, Ga, B) in the inevitable impurities Since the total amount is 10 ppm or less, an aluminum foil having a high cubic ratio and a small number of grains with different orientations can be obtained. During etching, pit dispersibility is improved, pit base points are increased, and pit length uniformity is improved. Action is obtained and the pits are evenly arranged. It is formed. As a result, a capacitor having a high capacitance per unit area can be obtained.

Hereinafter, an embodiment of the present invention will be described.
Preferably, an aluminum material having an aluminum purity of 99.9% or more and prepared to be a component of the present invention is used. 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. In addition, an 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. This sheet material is cold-rolled to obtain an aluminum alloy foil of about several tens of μm to 100 μm. One or more intermediate annealings may be performed during the cold rolling. In the present invention, the conditions for the intermediate annealing are not particularly limited, but for example, treatment in a batch furnace at 200 ° C to 300 ° C for 2 to 24 hours, 250 ° C to 400 ° C, 30 seconds to 5 ° C. The treatment in a continuous furnace for minutes can be shown.
After the final cold rolling, for example, a final annealing process is performed in which heating is performed at 400 to 600 ° C. for 2 to 24 hours. The final annealing treatment is desirably performed in an inert gas, a reducing gas, or a mixed gas atmosphere thereof. A high cubic rate can be obtained by the final annealing treatment.

The aluminum foil obtained through the above steps is then subjected to an etching process.
The etching process is usually performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. The present invention is not particularly limited with respect to specific conditions and the like of this etching treatment, and can be performed according to a conventional method, but DC etching is mainly applied.
In the etching process, pits perpendicular to the foil are uniformly formed, a high roughening rate is obtained, and ineffective dissolution is suppressed. A capacitor having a high capacitance can be obtained by incorporating this foil 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.

Examples of the present invention will be described below in comparison with comparative examples.
Aluminum materials having the compositions shown in Tables 1 and 2 were melted, and aluminum foil was manufactured through hot rolling and cold rolling. In the middle of cold rolling, intermediate annealing at 250 ° C. × 12 hours was performed, and the final cold rolling rate after the intermediate annealing was changed to obtain a final thickness (110 μm thickness) of the same thickness.
These aluminum foils were subjected to final annealing at 550 ° C. × 12 hours in an argon atmosphere. Thereby, an aluminum foil having a cubic crystal ratio of 95% or more could be obtained.

  Further, all high-purity aluminum foils were etched under the following conditions to roughen the aluminum foil.

(DC etching)
A direct current of 200 mA / cm 2 was applied for 120 seconds in a 75 ° C. HCl 1M and H 2 SO 4 3M solution, and then a 50 mA / cm 2 direct current was applied for 600 seconds in an 80 ° C. HCl 2M solution.

(Capacitance measurement)
The etching foil was cut to a size of 1 × 5 cm, formed at 300 ° C. with an 80 ° C. boric acid 80 g / l solution, and the capacity was measured in a 150 g / l adipic acid solution.
The electrostatic capacity measured above was relative evaluated in percentage based on Example 1. These evaluation results are shown in Tables 1 and 2.
As is clear from Tables 1 and 2, all of the examples of the present invention show excellent capacitance.
On the other hand, it became clear that a favorable electrostatic capacity could not be obtained in the comparative example out of the component range of the present invention.

Claims (1)

  One or more elements of the first group (Pb, Mg, Li, Na) in a total amount of 0.1 to 20 ppm, the second group (Sn, Fe, In, Cr, Zr, Ge, Si) 10 to 50 ppm in total amount of one or more elements, and 10 in total amount of one or more elements in the third group (Ri, Hf, V, Mo, W, Ni, Cu, Zn) The aluminum foil for electrolytic capacitors characterized by containing -100 ppm, the remainder is comprised with Al and an unavoidable impurity, and the total amount of the 4th group element (Mn, Ga, B) in an unavoidable impurity is 10 ppm or less.