JPH07235458A - Aluminum foil for forming electrode of electrolytic capacitor and etching method therefor - Google Patents

Abstract

PURPOSE:To provide an aluminum foil for forming the electrode of an electrolytic capacitor, and an etching method therefor, by which the capacitance can be increased. CONSTITUTION:The aluminum foil for forming the electrode of an electrolytic capacitor has the purity of aluminium of 99.9% or above, cubic orientational occupancy of 90% or above at the core part except 1mum thick from the surface, and the concentration of Mg in the range of 200-2000ppm at the surface layer of 1mum thick from the surface at least on one side of the foil. The foil is subjected to primary electrolytic etching in an aqueous solution containing 3-10% of HCl and 10-40% of H2SO4 at a liquid temperature of 70-90 deg.C and a current density of 10-40A/dm<2>. It is then subjected to secondary electrolytic etching or chemical etching in an aqueous solution containing 3-10% of HCl and/or 1% or less of H2C2O4 at a liquid temperature of 75-90 deg.C and a current density of 0-10A/dm<2>.

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 capacitor electrodes and a method for etching the foil.

[0002]

2. Description of the Related Art Al foil, which is generally used as an electrode material for aluminum electrolytic capacitors, usually has an electrochemical area because its effective area is enlarged to increase the capacitance per unit area. Alternatively, a chemical etching process is performed.

However, a sufficient capacitance cannot be obtained by simply etching the foil. Therefore, generally, in the final annealing step after foil rolling, a high-temperature heat treatment of about 450 ° C. or more is performed in order to improve the etching characteristics of the foil by forming a texture having many cubic orientations, but recently It was not possible to obtain sufficient satisfaction for the requirement for high capacitance of the electrolytic capacitor.

The present invention has been made in view of the above technical background, and an object thereof is to provide an aluminum foil for electrolytic capacitor electrodes capable of increasing electrostatic capacitance and a method for etching the foil.

[0005]

In order to achieve the above object, as a result of intensive research, the inventor has found that a surface concentrated layer of Mg is provided on an aluminum foil having a high cubic orientation occupancy to increase the etching pit density. , And found that a high capacitance foil can be obtained.

The present invention has been made on the basis of such findings, one of which is aluminum purity 99.9.
%, The core orientation excluding the thickness of 1 μm from the surface is 90% or more, and the Mg concentration of the surface layer portion having a thickness of 1 μm from the surface is 200 at least on one side of the foil.
The gist is an aluminum foil for electrolytic capacitor electrodes, which is characterized in that the content is ˜2000 ppm.

The other one is the above aluminum foil,
HCl (hydrochloric acid): 3 to 10%, H ₂ SO ₄ (sulfuric acid): 1
After carrying out primary electrolytic etching in an aqueous solution containing 0 to 40% under the conditions of liquid temperature: 70 to 90 ° C. and current density: 10 to 40 A / dm ² , HCl: 3 to 10% or further H ₂ C ₂ O ₄ (oxalic acid): in an aqueous solution containing 1% or less, liquid temperature: 70 to 95 ° C., current density: 0 to 10 A / d
A gist of the method for etching an aluminum foil for an electrolytic capacitor electrode is that secondary electrolytic etching or chemical etching is performed under the condition of m ² .

The aluminum foil of the present invention requires an aluminum purity of 99.9% or higher because it is 99.9.
If the purity is less than%, the growth of etching pits is hindered by the presence of many impurities during etching, and even the formation of the Mg-concentrated layer within the scope of the present invention fails to form uniform deep tunnel-shaped etching pits. This is because an aluminum foil having a high electric capacity cannot be obtained. It is preferable that the aluminum purity is 99.98% or more.

The cubic orientation occupancy of the core excluding the thickness of 1 μm from the surface is defined to be 90% or more because the combination of the cubic orientation occupancy in this range and the surface enriched layer of Mg results in high electrostatic capacity. This is because the capacity becomes possible, and if the cubic azimuth occupancy rate is less than 90%, the electrostatic capacity cannot be increased.

Mg in the surface layer of the aluminum foil is an element necessary for obtaining pits uniformly dispersed during etching. That is, generally in the initial stage of etching the surface irregularities and oils present on the foil surface, deposits such as roll coating,
Alternatively, non-uniform local dissolution pits are generated from those that have been altered, resulting in non-uniformity (dense / dense) in the etching pit density, and in the remarkable case, the surface is melted like craters. This non-uniformity remains even after the etching is completed, which causes a decrease in capacitance. Therefore, in order to prevent such inconveniences, attempts have been made to control the non-uniformity factor of the etching pits existing on these surfaces, but the inventor has conducted extensive research on this point,
It was found that the aluminum foil having the surface concentrated layer of Mg has the effect of eliminating the locality of etching pits.
That is, if the Mg surface concentrated layer is present, shallow grooves along the (100) direction in the rolling direction and in the direction perpendicular to the rolling direction occur in the rolling surface at the initial stage of etching to cause surface melting. Next, an etching pit grows perpendicularly to the rolling surface from a part of the recess of the groove. Such groove-like surface dissolution occurs at the initial stage of etching, so that surface irregularities on the foil surface, oil, deposits such as roll coating, or those that have deteriorated are removed, and evenly dispersed from the initial stage of etching. The etching pits are generated. In order to obtain such an effect, the Mg concentration needs to be 200 ppm or more in the surface layer portion having a thickness of 1 μm from the surface, but if it exceeds 2000 ppm, the concentration is too high and remarkable surface dissolution occurs, and the total foil thickness decreases. Therefore, a high capacitance foil cannot be obtained. Therefore, the surface concentration range of the amount of Mg is 200 to 20 in the surface layer portion having a thickness of 1 μm from the surface.
It is necessary to set it to 00 ppm. Particularly preferably 500-
It is good to set it to 1000 ppm.

The Mg concentrated layer may be present on at least one side of the foil. Of course, it may exist on both sides. Further, the Mg concentration of the core portion excluding the surface layer portion having a thickness of 1 μm from the surface is preferably less than 1 ppm. If it exceeds 1 ppm, the effect of forming the Mg concentrated layer on the surface layer of the foil is diminished, and the etching pits may communicate with each other inside the foil, so that a sufficient surface expansion ratio may not be obtained.

The production of the aluminum foil containing a high concentration of Mg in the surface layer as described above is not particularly limited, but for example, an aluminum ingot is preferably used with a Mg content of 2 p.
While melting and casting as less than pm (more preferably less than 1 ppm), when another aluminum ingot is melted, a Mg amount of 200 to 2000 ppm is added for casting, and both aluminum ingots are rolled to a predetermined thickness. Just clad like this. Alternatively, Mg may be separately applied to the surface of the aluminum foil not containing Mg as a film having a proper thickness by a method such as ion sputtering, and then heat treatment may be performed to diffuse the Mg to the surface layer portion.

The aluminum foil is subjected to an etching treatment to be used as an electrode material for electrolytic capacitors. The etching conditions are not particularly limited, but the etching method according to the present invention is preferably applied.

This etching method comprises two steps of treatment, and the primary etching is carried out by using an electrolyte solution of HCl + H ₂ SO ₄ system, but the inventor of the present invention selects an appropriate H ₂ SO ₄ concentration during the primary etching. It has been found that the surface dissolution amount can be appropriately suppressed and the uniform dispersibility of the etching pit distribution can be enhanced by setting the range to a certain range. That is, HCl
In the liquid composition of + H ₂ SO ₄ system, the H ₂ SO ₄ concentration is 1
If it is less than 0%, a sufficiently high capacitance foil cannot be obtained because the amount of surface dissolution due to the Mg concentrated layer is large, and if the H ₂ SO ₄ concentration exceeds 40%, the etching pit density becomes too high and partial etching occurs. The pits are combined to reduce the capacitance. Therefore, in the primary etching process, H ₂ S
The O ₄ concentration is 10 to 40%. Particularly preferably 20 to
35%. At this time, other primary etching conditions are as follows: HCl concentration in order to secure the etching pit density, diameter, and pit length sufficient to obtain a sufficient surface area after chemical conversion treatment:
3 to 10%, liquid temperature: 70 to 90 ° C, direct current density: 10
To 40 A / dm ² .

Subsequent to the primary etching, secondary etching is performed for the purpose of expanding the etching pit diameter. The treatment liquid is basically an aqueous hydrochloric acid solution having an HCl concentration of 3 to 10%, but H ₂ C ₂ O ₄ having a concentration of 1% or less may be mixed.
Further, the liquid temperature may be 70 to 95 ° C., and chemical etching without energization of current may be used, or direct current density may be 10 A / dm.
Electrolytic etching of ² or less may be used. If any of the processing conditions in the secondary electrolysis processing is deviated, the effect of enlarging the diameter of the etching pit is insufficient.

By such primary etching and secondary etching, it becomes possible to obtain an Al foil having a higher capacitance than the conventional method.

[0017]

The Mg concentrated layer on the surface layer of the foil eliminates the locality of the etching pits on the surface of the foil during etching and promotes uniform formation. Such an action of the Mg concentrated layer is more effectively exhibited when the Mg concentration of the foil core is less than 1 ppm.

Also, the etching pits are appropriately dispersed by the primary etching treatment, and the hole diameter is enlarged by the secondary etching to increase the surface expansion rate.

[0019]

【Example】

(Example 1) Aluminum ingots of various compositions shown in Table 1 were face-cut, then hot-rolled, clad-rolled to have a structure shown in Table 2, and then cold-rolled (including intermediate annealing).
Then, final annealing was performed at 500 ° C. for 10 hours in an inert gas atmosphere. Note that the sample No. 5 in Table 2 was used as a single foil without being clad.

Then, the occupancy ratio of the cubic orientation of the core of each of the obtained aluminum foils was examined. The results are shown in Table 2.

Next, after performing etching under the following conditions, the obtained aluminum foil was subjected to 25% in a 5% boric acid solution.
The electrostatic capacity when forming to 0V was measured. The results are shown in Table 2 as a relative comparison when the capacitance of Sample No. 5 is 100%.

[Etching conditions] Pretreatment: None Primary etching liquid composition: 5% HCl + 30% H ₂ SO
₄ , liquid temperature: 80 ° C., current density: DC 20 A / dm ² , time: 80 seconds Secondary etching liquid composition: 5% HCl + 0.1% H ₂ C
₂ O ₄ , liquid temperature: 80 ° C., current density: direct current 5 A / dm ² ,
Time: 10 minutes

[Table 1]

[Table 2] As can be seen from the results in Table 2 above, it can be confirmed that the inventive product having the Mg surface concentrated layer within the inventive range can increase the capacitance as compared with the comparative product deviating from the inventive range. It was

Example 2 For each sample in Table 2 above,
After performing the etching by setting the conditions of the primary etching and the secondary etching as shown in Table 3, the capacitance of the obtained aluminum foil was measured at 250 V in 5% boric acid solution. The results are shown in a relative comparison when the capacitance of sample No. 5 in Table 2 is 100%.

[0024]

[Table 3] As can be seen from the results in Table 3 above, it can be confirmed that the implementation product satisfying the conditions of the etching method according to the present invention can increase the capacitance as compared with the comparison product deviating from the conditions.

[0025]

The aluminum foil for electrolytic capacitor electrodes according to the present invention has an aluminum purity of 99.9% or more,
Except for the thickness of 1 μm from the surface, the occupancy rate of the cubic orientation of the core is 9
0% or more, and the Mg concentration of the surface layer portion having a thickness of 1 μm from at least one surface of the foil is 200 to 2000.
Since it is characterized by being ppm, it has excellent etching properties, and an extremely large surface area ratio can be obtained by etching treatment. Therefore, an aluminum foil for an electrolytic capacitor electrode having a large capacitance and excellent electric characteristics can be obtained.

According to the etching method of the present invention, HCl: 3 to 10%,
H ₂ SO _4: in an aqueous solution containing 10-40%, a liquid temperature: 7
After performing the primary electrolytic etching under the conditions of 0 to 90 ° C. and current density of 10 to 40 A / dm ² , HCl: 3 to 1
0% or further, in an aqueous solution containing 1% or less of H ₂ C ₂ O ₄ : liquid temperature: 70 to 95 ° C., current density: 0 to 10 A /
Since secondary electrolytic etching or chemical etching is carried out under the condition of dm ² , the etching pits can be dispersed appropriately, the hole diameter can be expanded, and the electrolytic capacitor having a larger surface area ratio and a larger electrostatic capacity. An electrode foil can be provided.

In the above, the Mg concentration in the core is 2
When the content is less than ppm, the effect of the Mg surface concentrated layer is more effectively exhibited, and the aluminum foil having excellent capacitance can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isoyama Eizo 6-224 Kaiyamacho Sakai-shi, Showa Aluminum Co., Ltd. (72) Inventor Shigeru Endo 6-224 Kaiyamacho Sakai-shi Showa Aluminum Co., Ltd. Within

Claims (4)

[Claims] 1. A cubic orientation occupancy rate of the core portion excluding a thickness of 1 μm from the surface is 90 with an aluminum purity of 99.9% or more.
%, And the Mg concentration of the surface layer portion having a thickness of 1 μm from at least one surface of the foil is 200 to 2000 p.
Aluminum foil for electrolytic capacitor electrodes, which is pm. 2. The aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the core has a Mg concentration of less than 2 ppm. 3. A cubic orientation occupancy rate of the core portion excluding a thickness of 1 μm from the surface is 90 when the aluminum purity is 99.9% or more.
%, And the Mg concentration of the surface layer portion having a thickness of 1 μm from at least one surface of the foil is 200 to 2000 p.
pm is the aluminum foil for electrolytic capacitor electrodes
_{Cl: 3~10%, H 2 SO} 4: in an aqueous solution containing 10-40%, a liquid temperature: 70 to 90 ° C., a current density: 10 to 40
After performing the primary electrolytic etching under the condition of A / dm ² , HCl: 3 to 10% or further H ₂ C ₂ O ₄ :
Electrolytic capacitor electrode characterized by performing secondary electrolytic etching or chemical etching in an aqueous solution containing 1% or less under the conditions of liquid temperature: 70 to 95 ° C. and current density: 0 to 10 A / dm ^2. Method for etching aluminum foil. 4. The method for etching an aluminum foil for electrolytic capacitor electrodes according to claim 3, wherein the core has a Mg concentration of less than 2 ppm.