JP3276492B2 - Manufacturing method of aluminum soft foil for cathode of electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum flexible foil for a cathode of an electrolytic capacitor, and more particularly, to a method of expanding an effective area by electrolytic etching to be used. And a method for producing the same.

[0002]

2. Description of the Related Art In order to reduce the size and increase the capacity of an electrolytic capacitor, the aluminum foil for the cathode of the electrolytic capacitor is roughened by electrolytic etching or chemical etching in the same manner as the aluminum foil for the anode, and the effective area (hereinafter referred to as surface area) It is used after expanding. Here, the increase in the surface area is intended to improve the capacitance per unit area, and as a result, to reduce the size and the capacity of the electrolytic capacitor.

In an electrolytic capacitor, since a dielectric film is not formed on a cathode foil, a leakage current and a withstand voltage required for an anode foil are not required. Therefore, the aluminum foil for the cathode is usually designed to be thinner than the aluminum foil for the anode. Therefore, in order to increase the surface area while maintaining the mechanical strength, in the case of the aluminum foil for the cathode, the entire area of the aluminum foil must be uniformly and appropriately dissolved at the time of etching (the entire surface of the foil must be uniform and sufficient). Roughened surface). In the case of a soft aluminum foil for a cathode (a softened aluminum foil obtained by annealing a cold-rolled aluminum foil), in addition to the above-mentioned etching properties, the crystal grain size is further adjusted to an appropriate size. It is required to improve capacitance and strength.

Conventionally, such aluminum soft foils for cathodes of electrolytic capacitors generally have a purity of 99.50 to 99.4%.
An aluminum alloy has been used in which aluminum is pure aluminum or where necessary, an alloy element such as copper is added. However, in this aluminum soft foil for a cathode, upon etching, the solubility is generally non-uniform, and excessive dissolution causes a partial decrease in strength,
On the contrary, there is a problem that a part which is hardly dissolved exists and a sufficient enlargement of the surface area cannot be achieved.

[0005] Therefore, various studies have been made to solve such problems, and as a result, the following methods for manufacturing aluminum foil have been developed and proposed (described).

JP-A-2-51210 discloses that Si: 0.010
~ 0.050wt%, Fe: 0.020 ~ 0.075wt%, Mg: 0.002 ~ 0.010wt
%, Zn: 0.005 to 0.012 wt%, and an ingot of aluminum as an unavoidable impurity containing 0.003 wt% or less of Cu and 0.002 wt% or less of other unavoidable elements, heated at 500 to 550 ° C for 20 hours or more. After homogenizing, hot rough rolling at 440 ° C or higher,
Furthermore, there is described a method for producing an aluminum foil, wherein hot finish rolling is performed under conditions of 400 ° C. or more on the inlet side, 250 ° C. or less on the outlet side, and a time of 2 minutes or less, and then cold rolling without intermediate annealing. I have.

JP-A-3-130340 discloses that Si: 0.010
~ 0.050wt%, Fe: 0.010 ~ 0.035wt%, Mg: 0.002 ~ 0.010wt
%, Zn: 0.005 to 0.012wt%, Cu: 0.001wt% or less, Ti: 0.001w
An aluminum ingot containing t% or less and Ni: 0.002wt% or less is homogenized by heating at 500 to 550 ° C for at least 20 hours, and then at an inlet 400 ° C or higher and an outlet 250 ° C or lower for 2 minutes. A method for producing an aluminum foil is described in which hot rolling is performed under the following conditions and then cold rolling is performed without intermediate annealing.

[0008] JP-A-4-176847 discloses that Al purity is
99.8% or more, Fe: 0.000 to 0.07 wt%, Si: 0.001 to 0.
After heating an aluminum ingot containing 07wt%, Cu: 0.01wt% or less and unavoidable impurities to 550 ° C or more, 250 ° C
The following describes a method for producing an aluminum foil which is cooled and then subjected to rolling at 300 ° C. or lower.

Japanese Patent Application Laid-Open No. 2-240246 describes a method for producing a soft aluminum foil for an electrolytic capacitor by annealing a hard aluminum foil substantially in the absence of an oxygen-containing compound.

[0010]

Problems to be Solved by the Invention JP-A-2-51210, JP-A-3-130340, JP-A-4-76847,
The method described in JP-A-2-240246 (hereinafter referred to as "prior art") generally specifies the composition and manufacturing conditions of an aluminum foil.
It is described that the electrolytic etching property is improved (an aluminum foil with uniform solubility at the time of etching is obtained).

However, as a result of various studies on these prior arts, according to the conventional arts, although the obtained aluminum foil has improved electrolytic etching properties, it is still not sufficient, and the following problems are caused. Uniform solubility at the time of etching (characteristic of uniform moderate dissolution)
Was insufficient, so that the capacitance was not sufficiently improved, and it was confirmed that there was a problem that the capacitance was not sufficient.

That is, in the prior art and in the prior art, the aluminum ingot is homogenized at a temperature of 500 to 550 ° C. for 20 hours or more. Many precipitates are generated, and the uniform solubility at the time of etching is impaired due to the precipitates, resulting in insufficient uniform solubility. In addition, it is general that such long-time heating is performed in about two times, and if it is performed in two times,
There is a relatively long cooling time between the first and second times, during which time the precipitates become very large, which also hinders uniform solubility and results in insufficient uniform solubility.

[0013] In the prior art, since the homogenization treatment of the aluminum ingot and to perform at temperatures above 550 ℃, Al ₆ Fe (electrochemically stable) precipitates during homogenization is Al ₃ Fe (Electrochemically unstable), resulting in a decrease in the uniform solubility during etching and an insufficient uniform solubility.

In the prior art, the aluminum foil is annealed in the absence of oxygen-containing compounds to reduce the thickness of the oxide film on the foil surface and improve the uniform solubility. It is insufficient, and it is not possible to sufficiently improve the uniform solubility. Furthermore, since the thickness of the oxide film is not specified and the composition of the aluminum foil and the soaking conditions are not specified, the uniform solubility is not always improved, and the uniform solubility is not improved. Is very unreliable.

The present invention has been made in view of such circumstances, and an object of the present invention is to solve the problems of the above-mentioned prior arts and to improve the electrolytic etching property (etching) in comparison with these prior arts. It is an object of the present invention to provide a method for producing an aluminum foil for an electrolytic capacitor cathode, which is capable of obtaining an aluminum foil of an electrolytic capacitor cathode which is excellent in uniform solubility at the time of production and as a result, a sufficient improvement in capacitance can be achieved. .

[0016]

In order to achieve the above object, the present invention provides a method for producing an aluminum soft foil for a cathode of an electrolytic capacitor having the following structure. That is, the method for producing an aluminum soft foil for an electrolytic capacitor cathode according to the present invention has an aluminum purity of 99.8% or more,
And Fe: 0.020 to 0.030 wt%, Si: 0.040 wt% or less, Zn:
Aluminum containing 0.009-0.013wt%, Cu: 0.002wt% or less, the balance being unavoidable impurities, 550-500 ℃
For 7 to 15 hours, followed by a homogenization treatment, followed by hot rolling, and then cold rolling to a foil having a thickness of 50 μm or less, and then annealing the foil to obtain a grain size of 50 μm. ~ 100 μ
m and an oxide film thickness of 40 mm or less.

[0017]

According to the method for producing an aluminum foil for electrolytic capacitor cathode according to the present invention, as described above, the composition of aluminum as a starting material is specified and the production process is specified. (Dissolvability) to obtain an aluminum soft foil. In particular, homogenization in the manufacturing process
Heating is performed continuously at 50 to 500 ° C for 7 to 15 hours, followed by hot rolling, then cold rolling and annealing to reduce the crystal grain size to 50 to 100 µm and the oxide film thickness to 40 mm or less. By doing so, the electrolytic etching property of the obtained aluminum soft foil is improved.

That is, aluminum as a starting material is produced by melting and casting, and during the cooling process of this casting, A
l ₆ Fe and Al ₃ Fe are mixed and precipitated. These Al ₆ Fe and Al ₃
When Fe is in a mixed state, it has excellent electrolytic etching properties. However, if the homogenization treatment of this cast aluminum (aluminum ingot) is performed at a temperature of more than 550 ° C., electrochemically stable Al ₆ Fe is changed to an unstable Al ₃ Fe, electrochemically it becomes large unstable Al ₃ Fe content, resulting aluminum foil electrolytic etching properties (uniformity solubility etching)
May decrease, and coarse holes may be generated during electrolytic etching. This tendency becomes stronger as the homogenization temperature rises above 550 ° C.

In the present invention, the homogenization treatment is carried out at 550 to 500 ° C. for 7 hours.
And to perform 15 hours continuously heated, the temperature does not occur in a change in the Al ₃ Fe of Al ₆ Fe, Al ₃ Fe remains unchanged, so that precipitates after casting after homogenization (Al ₆ Fe
And Al ₃ Fe) mixed state is maintained. After this homogenization treatment (heating), hot rolling is performed, then cold rolling is performed, and annealing is performed.
A temperature of about 0 to 380 ° C. is sufficient. As a result, even in the obtained aluminum foil, the above precipitates (Al ₆ Fe and Al ₃ Fe)
It is in a state similar to the mixed state. Therefore, the aluminum foil obtained according to the present invention firstly contains precipitates Al ₆ Fe and Al ₃ Fe
Are excellent in electrolytic etching properties due to being in a mixed state.

Further, since the aluminum foil obtained by the present invention has a crystal grain size of 50 to 100 μm, the surface resistance is stable (without variation), and the oxide film thickness:
Since it is 40 ° or less, the wettability to an etching solution is good, and thereby, the electrolytic etching property is improved, and as a result, the capacitance can be sufficiently improved.

The reasons for limiting the numerical values in the present invention will be described below. First, regarding the composition of the aluminum foil, the reason why the aluminum purity is set to 99.8% or more is that if the content is less than 99.8%, the amount of impurities increases, the capacitance is reduced, and the content becomes insufficient.

Fe forms an intermetallic compound (Al ₃ Fe, Al ₆ Fe, etc.) as a crystal or a precipitate, and is an indispensable element for improving the electrolytic etching property. Fe: 0.020 ~ to generate crystallization or precipitate
Must be 0.030 wt%. If the amount is less than 0.020 wt%, the number of crystallized substances or precipitates is insufficient, so that a uniform and appropriately etched surface cannot be obtained, and the capacitance decreases to be insufficient. Etching pits are likely to occur, and the capacitance is reduced to be insufficient.

Si is an indispensable element for the same reason as Fe described above. However, if Si is more than 0.040 wt%, the crystallized material becomes too large, coarse etching pits are easily generated, and the capacitance is reduced. Therefore, Si: 0.040 wt% or less.

Zn has the effect of improving the electrolytic etching property, and the amount of Zn added is 0.009 to 0.013 wt% because it is 0.00
If the content is less than 9 wt%, the effect is small, and if the content is more than 0.013 wt%, it is difficult to set appropriate etching conditions, a uniform suitable etched surface cannot be obtained, and the capacitance is lowered to be insufficient.

Cu is an element that contributes to the solubility during electrolytic etching. However, if it exceeds 0.002 wt%, Cu precipitates on the aluminum foil surface during electrolytic etching, and as a result, the capacitance decreases and becomes insufficient. Therefore, Cu: 0.002 wt% or less.

The unavoidable impurities include, for example, Mn,
There are Mg, Cr, Ti, Ni, B, V, etc., but in the case of Mn, Mg, Cr, Ti, it may be contained up to about 0.002 wt%.

Next, in the homogenization treatment, the heating temperature was set to 550
The reason why the temperature is set to 500 ° C is that if the temperature exceeds 550 ° C, Al ₆ Fe (electrochemically stable) changes to Al ₃ Fe (electrochemically unstable) during the homogenization treatment. The resulting aluminum foil has a poor electrolytic etching property, cannot provide a uniform and moderately etched surface, and has a reduced capacitance, resulting in insufficient capacitance. This is because the etched surface cannot be obtained, and the capacitance decreases and becomes insufficient.

The reason why the heating time is set to 7 to 15 hours is as follows.
If the time is less than the time, the effect of the homogenization treatment is not sufficient, a uniform moderately etched surface cannot be obtained, the capacitance is reduced and becomes insufficient, and if the time is more than 15 hours, coarse precipitates are generated. This is because the etched surface cannot be obtained, and the capacitance decreases and becomes insufficient.

The reason why the above-mentioned heating is performed continuously is that cooling is performed in the middle and reheating is performed, and if heating is performed in two or more times, precipitates are generated during and after cooling. This is because a large amount is deposited, and a uniform appropriate etching surface cannot be obtained, and the capacitance is reduced to be insufficient.

The reason that the thickness of the obtained aluminum foil is set to 50 μm or less is that, in the case of a conventional foil having poor etching properties, it is necessary to increase the foil thickness and roughen the surface in the depth direction in order to increase the capacitance. However, this foil has a large capacitance even at 50 μm or less, so that the cathode foil becomes thin and the electrolytic capacitor can be made small.

The crystal grain size of the obtained aluminum foil is 50 to
The reason why the thickness is set to 100 μm is that if the thickness is less than 50 μm, the surface resistance varies, so the surface area cannot be increased and the capacitance becomes insufficient.If it exceeds 100 μm, the strength of the aluminum foil decreases and becomes insufficient. Because. Also, the thickness of the oxide film is set to 40 mm or less, if it exceeds 40 mm, the wettability to the etching solution is poor, the etching property is reduced,
This is because the surface area cannot be increased and the capacitance becomes insufficient.

The homogenization treatment and the subsequent hot rolling are performed, but this means that the homogenization treatment and the hot rolling are continuously performed. In other words, the homogenization treatment is performed. This means that hot rolling is not performed after cooling to room temperature or near room temperature. The reason for this is that once it cools down to room temperature,
During the cooling, precipitates such as Al ₃ Fe are deposited, and these precipitates remain without disappearing in the subsequent steps, so that a uniform moderately etched surface cannot be obtained, and the capacitance is lowered and insufficient. Because it becomes. In order to perform such homogenization and hot rolling continuously, hot rolling may be started immediately or relatively quickly after the homogenization (heating).

[0033]

【Example】

(Example 1) An aluminum ingot having a chemical composition (composition) shown in Table 1 was subjected to a homogenization treatment (soaking) under the production conditions shown in Table 2, and subsequently hot-rolled and then cold-rolled to obtain a thickness. : 50 μm foil, and thereafter, this foil was annealed to obtain a temper: O material. Here, the production conditions are all within the range of the production conditions according to the present invention, and the chemical components are within the range of chemical components according to the present invention (Nos. 1 to 4) and outside the range (Nos. 5 to 11). ).

The aluminum foil thus obtained was measured for crystal grain size and oxide film thickness. In addition, these aluminum foils were electrolytically etched and then subjected to a chemical conversion treatment, and then the capacitance was measured. Further, the strength of the aluminum foil after the electrolytic etching was measured.

Here, the crystal grain size was measured by polishing the surface of the aluminum foil, electrolytic etching, micro-observation, and line analysis. The oxide film thickness was measured with an LCR meter using a solution containing 50 g of boric acid and 100 g of borax in 1 liter of pure water, using platinum as a counter electrode.

Electrolytic etching is 10% in 1 liter of pure water.
Electrolyte containing hydrochloric acid + 0.1% sulfuric acid + 2.2% aluminum chloride (40
± 1 ° C), current density: 0.45A / dm ² , AC: 50Hz,
The etching was performed for one minute under electrolytic etching conditions.
The chemical conversion treatment is performed using a chemical conversion solution (70 ± 2.5 ° C.) containing 0.25 ml of phosphoric acid and 1.4 g of ammonium phosphate in 1 liter of pure water under the chemical conversion conditions of 8 minutes for chemical conversion and 3 V for chemical conversion. went. The capacitance was measured using an electrolyte (30 ± 5 ° C.) containing 50 g of boric acid, 50 g of citric acid, and 50 ml of ammonia in 1 liter of pure water at a frequency of 120 Hz using a universal bridge method. went.

In the strength measurement, a test piece having a width of 10 mm and a length of 100 mm was sampled from the aluminum foil after electrolytic etching in parallel with the rolling direction, and fixed between the chuck portions so as to have a length of 50 mm. And a tensile test to determine the breaking strength.

The crystal grain size, oxide film thickness, strength, and
Table 2 shows the measurement results of the capacitance. Regarding the aluminum foil (comparative example) obtained from those outside the range of the chemical components according to the present invention (Nos. 5 to 11), either the capacitance or the strength is low. On the other hand, within the range of the chemical components according to the present invention (No. 1
~ 4), the aluminum foil obtained by the method according to the present invention, the capacitance, both of the strength is high,
Are better.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

Example 2 Chemical components (composition) shown in Table 3
An aluminum ingot having a thickness of 50 μm was homogenized under the manufacturing conditions shown in Table 4, subsequently hot-rolled, and then cold-rolled into a foil having a thickness of 50 μm. O material. Here, all the chemical components are within the chemical component range according to the present invention, and the production conditions are within the production conditions (No. 12 to 15) according to the present invention, and out of the range (No. 16 to 23). There are things.

With respect to the aluminum foil thus obtained, the crystal grain size and the oxide film thickness were measured in the same manner as in Example 1. Also, in the same manner as in Example 1,
After the electrolytic etching and the chemical conversion treatment, the capacitance was measured. Further, the strength of the aluminum foil after electrolytic etching was measured in the same manner as in Example 1.

The crystal grain size, oxide film thickness, strength, and
Table 4 shows the measurement results of the capacitance. Regarding the aluminum foil (comparative example) obtained by the method out of the production condition range (Nos. 16 to 23) according to the present invention, either the capacitance or the strength is low. On the other hand, within the manufacturing condition range according to the present invention (No.
The aluminum foil obtained by the method of 12 to 15) is excellent in both capacitance and strength.

[0046]

According to the method for producing a soft aluminum foil for a cathode of an electrolytic capacitor according to the present invention, the electrolytic capacitor is excellent in electrolytic etching properties (uniform solubility during etching), and as a result, a sufficient improvement in capacitance can be achieved. An aluminum soft foil for a cathode can be obtained.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-90519 (JP, A) JP-A-4-318154 (JP, A) JP-A-5-247609 (JP, A) JP-A-5-905 43972 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22F 1/04-1/057 C22C 21/00-21/18

Claims (1)

(57) [Claims] An aluminum purity of 99.8% or more,
And Fe: 0.020 to 0.030 wt%, Si: 0.040 wt% or less, Zn:
Aluminum containing 0.009-0.013wt%, Cu: 0.002wt% or less, the balance being unavoidable impurities, 550-500 ℃
For 7 to 15 hours, followed by a homogenization treatment, followed by hot rolling, and then cold rolling to a foil having a thickness of 50 μm or less, and then annealing the foil to obtain a grain size of 50 μm. ~ 100 μ
m and a thickness of an oxide film: 40 mm or less.