JPH08269601A - Aluminum foil for electrolytic capacitor anode and its production - Google Patents

Abstract

PURPOSE: To obtain Al foil for an electrolytic capacitor anode which is expanded in effective surface area and improved in electrostatic capacity by specifying the Cu content in high-purity Al and specifying the contents of Cu, oxygen atoms and Al oxide of a front layer. CONSTITUTION: The Al material having purity of Al of >=99.95%, contg. 0.0003 to 0.0024wt.% Cu and consisting of the balance inevitable impurities is rolled 1 to 4 times and the reduction ratio over the entire part after the end of the final rolling stage is confined to <=75%, by which the Al foil is obtd. At this time, a rolling mill lubricant added with 0.03 to 0.25mol/l org. molecule bonded with Cu, such as copper acetate, is used. The Cu concn. at the depth of 2nm from the front surface of the resulting Al foil is specified to 0.0010 to 0.0040%, the oxygen atoms are specified to 25 to 35% and the Al oxide is specified to 20 to 30%. The Al foil contributes to an increase in the start point of etching pits, an improvement in electrolytic etching property and an improvement in electrostatic capacity when the Al foil is used as an electrolytic capacitor anode.

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 electrolytic capacitor anode for enlarging the effective area of the surface of the aluminum foil to improve the capacitance of the capacitor and a method for producing the same.

[0002]

2. Description of the Related Art Usually, an aluminum foil used as an electrode of an electrolytic capacitor is subjected to a treatment for increasing the effective surface area of the aluminum foil by electrolytic etching for the purpose of miniaturizing the capacitor and increasing its capacity. Is given. By this electrolytic etching, small recesses (hereinafter referred to as "etching pits") are formed on the surface of the aluminum foil, and as a result, the effective area of the surface of the aluminum foil used for the electrodes of the capacitor is enlarged. By using the aluminum foil having the expanded effective area as an electrode of the capacitor and improving the capacitance per unit area, the electrolytic capacitor can be downsized and the capacitance can be increased.

The aluminum foil subjected to such electrolytic etching must be one that does not melt or collapse during etching, and the etching pits are perpendicular to the thickness direction of the aluminum foil. It also needs to be grown to form a good etching layer. In addition, it is preferable that the starting points of the etching pits are finely and uniformly dispersed and a large number of them are present.

In order to produce such an aluminum foil,
Various manufacturing methods have been developed. Specifically, a manufacturing method by adjusting the composition of a specific impurity (Japanese Patent Laid-Open No. Hei 5-
No. 5145, JP-A-4-124806), a manufacturing method by limiting soaking conditions (JP-A-2-201249)
No. 4-176847), a manufacturing method by surface treatment (JP-A-5-12436), and a manufacturing method by limiting annealing conditions (JP-A-4-3115).
No. 50) and the like are known.

Further, usually, a deposit such as Cu, In, Sn or Ti is formed at the starting point of the etching pit, and a high quality etching pit is formed by adjusting these impurities contained in the aluminum foil. Methods are also known (Japanese Patent Laid-Open Nos. 3-253534 and 4-21).
3810, JP-A-4-213811).

[0006]

However, the above-described method for forming etching pits is not possible in the above-described method of forming etching pits by increasing the concentration of elements such as Cu and In, which are the starting points of etching pits, on the surface of aluminum foil, or by sputtering or wet plating. In the oxide film formed on the surface of the aluminum foil or the surface thereof, the concentration distribution of the element is adjusted, and since the method for forming these etching pits is a solid-solid reaction, The element cannot be uniformly distributed on the surface of the aluminum foil or on the oxide film. Therefore, there is a certain limit to the improvement of the capacitance in the capacitor using the aluminum foil etched by the above-mentioned etching pit forming method.

The present invention has been made in view of the above problems. By treating the surface of an aluminum foil in a liquid phase, the starting points of etching pits are increased and the electrolytic etching property is improved. An object of the present invention is to provide an aluminum foil for an electrolytic capacitor anode, which can improve the electrostatic capacity, and a method for manufacturing the same.

[0008]

The aluminum foil for electrolytic capacitor anodes according to the present invention has an Al purity of 99.95.
% Or more Cu: 0.0003 to 0.0024% by weight, the balance being an unavoidable impurity, and an aluminum foil having a Cu concentration of 0.0010 to 0.0040% at a depth of 2 nm from the surface. And 25 to 35% oxygen atoms and 20 to 30% aluminum oxide.

In the method for producing an aluminum foil for an electrolytic capacitor anode according to the present invention, the purity of Al is 99.95% or more, Cu: 0.0003 to 0.0024% by weight is contained, and the balance is inevitable impurities. Aluminum material,
Using Cu-bonded organic molecules added 0.03 to 0.25 mol / liter, a rolling lubricating oil is used to roll 1 to 4 times, and the overall working rate after the final rolling step is 75%. It is characterized by the following.

[0010]

The present inventors have made various attempts to develop an aluminum foil for electrolytic capacitor anodes, which can increase the starting point of etching pits and improve the electrolytic etching property to improve the electrostatic capacitance as compared with the conventional case. An experimental study was conducted. As a result, the electrostatic capacity is improved by cold rolling using a lubricating oil to which Cu-bonded organic molecules are added, and further static rolling is performed by performing cold rolling a plurality of times. It was found that the electric capacity can be improved.

This is because the lubricating oil or organic molecules in the lubricating oil are adsorbed on the surface of the aluminum foil newly appeared by cold rolling, and a natural oxide film is formed so as to take in these molecules. Is considered to be the starting point of the etching pits, and a large number of fine etching pits are generated during the electrolytic etching, whereby the effective area of the surface of the aluminum foil can be increased.

The reasons for limiting the composition of the aluminum foil according to the present invention and the cold rolling conditions will be described below.

Purity of Al (aluminum): 99.95
% , It is preferable that the aluminum foil used as the anode of the capacitor has a high purity in order to manufacture a high-quality electrolytic capacitor. However, when the purity of Al is lower than 99.95%, a large number of precipitates and crystallized substances of Fe or Si which are unavoidable impurities are generated, and these precipitates cause coarse pores during electrolytic etching. Will end up. Therefore, as the effective area of the surface of the aluminum foil decreases, the capacitance also decreases. Therefore, the purity of Al is set to 99.95% or more.

Cu (copper): 0.0003 to 0.002
4 wt% Cu is an element that precipitates during etching and is added as a starting point of etching pits. Further, this Cu determines the electrostatic capacity of the aluminum foil by the balance with Cu contained in the lubricating oil for rolling described later.

FIG. 3 shows an aluminum foil rolled at a rolling reduction of 50% using a lubricating oil to which copper acetate (divalent) was added at 0.20 mol / liter in the three rolling processes including the final rolling process. It is a graph which shows the relationship between Cu content and the electrostatic capacitance of this aluminum foil. As shown in FIG. 3, when the Cu content was 1.0 × 10 ⁻³ wt%, the electrostatic capacity was the largest. With the Cu content as a boundary, the capacitance of the aluminum foil decreases when the Cu content is low or high. This is because when the Cu content is low, the number of the starting points of the etching pits in the aluminum foil during etching is not sufficient, while when the Cu content is high, it is effective on the surface of the aluminum foil. It is considered that this is because the surface dissolution occurs without increasing the area.

Further, from the graph shown in FIG. 3, the content of Cu in the aluminum foil is 0.0 because the capacitance of the aluminum foil is 46 μF / cm ² or more.
Preferably 003 to 0.0024% by weight,
Further, it is more preferably 0.00038 to 0.0024% by weight.

Regarding the content of the unavoidable impurities in the balance, if the content is equal to or less than the content of the metal ingot secondarily refined by the segregation method or the three-layer method, the capacitance is not lowered. The permissible amounts of each element in this case are as follows, and the unit is% by weight.

Si: 0.0060, Fe: 0.006
0, Mn: 0.0015, Cr: 0.0010, Zn:
0.0030, Ti: 0.0010, Ni: 0.001
0, Ga: 0.0030, Pb: 0.0005, B:
0.0020, Sn: 0.0010. Next, the conditions for forming an aluminum foil into an aluminum foil by cold rolling, specifically, the lubricating oil for rolling, the number of times the organic molecule-added lubricating oil is used, and the whole after the last rolling step using the lubricating oil. The processing rate of will be described.

The lubricating oil for rolling aluminum has a purity of 99.98% and Cu of 0.001.
Using an aluminum material containing 0% by weight, the concentration is 0, 0.02, 0.05, 0.10, 0.15, 0.2.
Each lubricating oil to which copper acetate (divalent) of 0, 0.25 and 0.30 mol / liter was added was used only in the final rolling step and rolled at a rolling reduction of 60%. Then, the produced aluminum foil was subjected to electrolytic etching to expand the effective area of the surface, and then subjected to chemical conversion treatment with a voltage of 20 V to measure the capacitance of each aluminum foil. The result is shown in Figure 1.
It is indicated by "○" plotted in the graph diagram of. FIG. 1 is a graph showing the relationship between the concentration of copper acetate (divalent) and the capacitance of the aluminum foil produced by rolling when rolling using a lubricating oil to which copper acetate (divalent) is added. Is.

As shown in the graph connecting the "○" s plotted in the graph of FIG. 1, when the lubricating oil added with copper acetate (divalent) was used for rolling, the capacitance was remarkably increased. When the added concentration is changed to 0.20 mol / liter, the electrostatic capacity becomes the largest. This is considered to be because when copper acetate (divalent) has this addition concentration, a large number of starting points of etching pits are distributed on the surface of the aluminum foil. On the other hand, if the concentration of copper acetate (divalent) exceeds 0.20 mol / liter and is added to the lubricating oil, the capacitance will decrease. This is considered to be because, although the starting points of the etching pits on the surface of the aluminum foil are extremely large, the aluminum foil causes surface dissolution without expanding the effective area.

From the graph of FIG. 1, the capacitance is 4
In order to obtain 6 μF / cm ² or more, it is preferable that the addition concentration of copper acetate (divalent) is 0.03 to 0.25 mol / liter. Therefore, in the cold rolling, a lubricating oil containing 0.03 to 0.25 mol / liter of Cu-bonded organic molecules is used. The more preferable concentration of copper acetate (divalent) added is 0.034 to 0.25 mol / liter.

Although copper acetate (divalent) is selected as a lubricant to be added to the rolling lubricating oil in view of its stability and solubility, copper formate (divalent) may also be used. Good. In addition, regarding the copper-containing inorganic substance, there is no substance that dissolves in the lubricating oil by 0.03 mol / liter or more, and even if added to the lubricating oil, the capacitance of the aluminum foil cannot be improved. Therefore, the substances added to the lubricating oil are limited to those consisting of organic molecules.

Number of times the organic molecule-added lubricating oil is used: 1 to 4 times In the graph of FIG. 1, not only when the lubricating oil added with copper acetate (divalent) is used for rolling only in the final rolling step described above, Also shown is the relationship between the concentration of copper acetate (divalent) and the capacitance when the lubricant is used for rolling in the previous two to five previous rolling steps including the final rolling step. In the rolling process from the previous 2 times to the previous 5 times including this final rolling process, only the above-mentioned final rolling process is copper acetate (divalent).
Rolling was performed under the same conditions as in the case of using the lubricating oil added with.

As shown in this FIG. 1, copper acetate (2
When using a lubricating oil with a valency value), the aluminum foil has a higher capacitance than when rolling with a lubricating oil with a copper acetate (divalency value) rolling only in the final rolling step. Obtainable.

Further, when the lubricating oil to which copper acetate (divalent) is added is used for the previous four rolling steps including the final rolling step, the aluminum foil is reduced in capacitance,
In the previous 5 rolling processes including the final rolling process, copper acetate (2
When using a lubricating oil added with a (valence), the aluminum foil will have a significantly reduced capacitance.

Further, as shown in the graph of FIG. 1, when rolling is performed using a lubricating oil to which copper acetate (divalent) is added, as the number of times of use is increased, the addition concentration becomes smaller. The maximum capacitance is reached.

From the above, the number of times the organic molecule-added lubricating oil is used, that is, the number of times of cold rolling using the organic molecule-added lubricating oil is 1 to 4 times in several rolling steps. To do.

Overall processing rate after use of lubricating oil: 75% or less . FIG. 2 shows a lubricating oil which is not added with copper acetate (divalent) after rolling using the lubricating oil with addition of copper acetate (divalent). FIG. 6 is a graph showing the relationship between the overall processing rate of the aluminum material by this rolling and the electrostatic capacity of the aluminum foil in the case of rolling using. As shown in FIG. 2, the overall processing rate when rolling was performed using a lubricating oil to which copper acetate (divalent) was added, and then rolling was performed using a lubricating oil to which copper acetate (divalent) was not added. The capacitance decreases as the value increases. This is because as the processing rate of the aluminum material increases, the surface area of the newly appearing aluminum foil, that is, the area where the organic molecules are not attached, increases, which reduces the distribution amount of Cu on the surface. Conceivable.

Therefore, the overall processing rate after using the lubricating oil, that is, the overall processing rate of the aluminum material after rolling using the lubricating oil to which organic molecules are added is set to 75% or less.

[0030]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that depart from the claims of the present invention. First, for aluminum foil containing Cu with Al purity shown in Table 1 below, copper acetate (divalent) having the concentration shown in Table 1 below
Cold rolling was performed several times using the lubricating oil added with.
Further, in the rolling at this time, also in the case of rolling using a lubricating oil to which copper acetate (divalent) is added, it is indicated by “◯” in the column of “number of rolling steps from the end” in Table 1 below.

The columns 6 to 1 in the column "Number of steps from final rolling" in Table 1 below indicate the final rolling step.
Is a column indicating how many times before the final rolling step the rolling step is. For example, in Example No. 1, the lubricating oil to which copper acetate was added was used only in the final rolling step, and in Example No. 3 in the final rolling step and the rolling step one time before, a total of two rolling steps. Copper acetate (2
It is shown that the rolling was performed using a lubricating oil added with (value). In addition, Table 1 below also shows the overall processing rate of the aluminum material after rolling using the lubricating oil to which copper acetate (divalent) was added last.

[0032]

[Table 1]

After rolling the aluminum foil having the composition shown in Table 1, the electrolytic solution shown in Table 2 below was used for electrolytic etching under the electrolytic conditions shown in Table 3 below.
Then, a chemical conversion treatment was performed by applying a voltage of 20 V using the chemical conversion treatment liquid shown in Table 2 below.

[0034]

[Table 2]

[0035]

[Table 3]

After the aluminum foil was subjected to the chemical conversion treatment as described above, the capacitance was measured using the LCR meter in the electrolyte solution for capacitance measurement shown in Table 2 above. The measurement conditions were 120 Hz and 1V. The measurement results are shown in Table 4 below.

[0037]

[Table 4]

As shown in Table 4 above, Example Nos. 1 to 1
For No. 4, the capacitance is 46.0 μF / cm
^{It was 2} or more, and an aluminum foil having a high capacitance could be obtained.

On the other hand, Comparative Example No. 1 is a case of rolling without using lubricating oil to which copper acetate (divalent) was added, and Comparative Examples No. 2 to 6 were copper acetate (2
The value of Comparative Example Nos. 7 to 10 is copper acetate (2).
Value) was used for rolling using a lubricating oil in which the added amount was more than a predetermined amount, and the electrostatic capacity was 46 μF / in both comparative examples.
It was less than or equal to cm ² , and the size was lower than that of the example.

Regarding Comparative Examples No. 11 to 13,
This is the case where the processing rate after the last rolling using the lubricating oil to which copper acetate (divalent) was added exceeds 75%, and Comparative Example N
For o14, the content of Cu in the aluminum foil was less than the predetermined range, for Comparative Example No. 15, the content of Cu in the aluminum foil was more than the predetermined range, and for Comparative Example No16. When the aluminum purity of the aluminum foil was less than the predetermined range, all the comparative examples had low capacitance.

Regarding the aluminum foils of the above Examples and Comparative Examples, Cu and O at a depth of 2 nm from the surface thereof
And the concentration of Al oxide was analyzed. The results are shown in Table 5 below.

[0042]

[Table 5]

As shown in Table 5 above, Cu of each example,
The concentrations of O and Al oxide were both values within the scope of the claims of the present invention.

[0044]

As described above, according to the present invention,
By cold rolling an aluminum material with a specified composition using a specified lubricating oil, the starting points of the etching pits during electrolytic etching can be finely and uniformly distributed in large numbers, increasing the capacitance. It is possible to produce an aluminum foil for an electrolytic capacitor anode that can be manufactured.

[Brief description of drawings]

FIG. 1 shows a case where rolling is performed using a lubricating oil to which copper acetate (divalent) is added, copper acetate (2
It is a graph showing the relationship between the concentration of (value) and the capacitance of the aluminum foil produced by rolling.

FIG. 2 shows the entire aluminum material obtained by rolling using a lubricating oil to which copper acetate (divalent) is added and then rolling using a lubricating oil to which copper acetate (divalent) is not added. FIG. 6 is a graph showing the relationship between the processing rate and the capacitance of the manufactured aluminum foil.

FIG. 3 is a graph showing the relationship between the content of copper in the aluminum foil and the capacitance of the aluminum foil.

Claims (2)

[Claims] 1. The purity of Al is 99.95% or more and Cu:
An aluminum foil containing 0.0003 to 0.0024% by weight and the balance being unavoidable impurities, having a Cu concentration of 0.0010 to 0.0040% and an oxygen atom of 25 at a depth of 2 nm from the surface. To 35% and oxide of aluminum 20 to 30%, an aluminum foil for an anode of an electrolytic capacitor. 2. The purity of Al is 99.95% or more and Cu:
An aluminum material containing 0.0003 to 0.0024% by weight, the balance being inevitable impurities, and 0.03 to 0.25 mol / liter of Cu-bonded organic molecules were used as a lubricating oil for rolling. Then, the aluminum foil for electrolytic capacitor anodes is rolled 1 to 4 times, and the overall working rate after the final rolling step is 75% or less.