JPH07180008A - Production of aluminum soft foil for electrolytic capacitor cathode - Google Patents

Abstract

PURPOSE:To produce Al foil for the cathode of an electrolytic capacitor excellent in electrolytic etching properties and capacitance by subjecting an Al ingot having a specified quality to homogenizing treatment under specified temp. conditions, thereafter working it to form into a thin foil shape by hot rolling and cold rolling and executing annealing. CONSTITUTION:An Al ingot having a compsn. contg., by weight, >99.8% Al, 0.020 to 0.030% Fe, <0.040% Si, 0.009 to 0.013% Zn and <0.002% Cu is subjected to continuous heating to 500 to 550 deg.C for 7 to 15 hr, is subjected to homogenizing treatment and is thereafter subjected to hot rolling and cold rolling to work into a foil material having >=50mum thickness. This foil material is annealed at 270 to 380 deg.C to regulate the grain size to 50 to 100mum, and furthermore, a thin Al oxidized film having 540A thickness is formed on the surface of the Al foil. The soft Al foil as the cathode of an electrolytic capacitor excellent in electrolytic etching properties and thus high in capacitance by the increase of the effective surface area can be obtd.

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 soft foil for an electrolytic capacitor cathode, and more specifically, to an aluminum soft foil for an electrolytic capacitor cathode which is used by expanding the effective area by electrolytic etching. Manufacturing method.

[0002]

2. Description of the Related Art For the purpose of reducing the size and increasing the capacity of electrolytic capacitors, the aluminum foil for electrolytic capacitor cathodes is roughened by electrolytic etching or chemical etching in the same manner as in the case of anode aluminum foils. That is used after expanding. Here, the expansion of the surface area is intended to improve the electrostatic capacity per unit area, and as a result, to reduce the size and capacity of the electrolytic capacitor.

By the way, in the electrolytic capacitor, since the dielectric film is not formed on the cathode foil, the leakage current and the withstand voltage required for the anode foil are not required. Therefore, the aluminum foil for cathode is usually designed thinner than the aluminum foil for anode. Therefore, in order to increase the surface area while maintaining the mechanical strength, in the aluminum foil for the cathode, the entire area of the aluminum foil should be uniformly dissolved during the etching (the entire foil surface should be uniform and sufficient). Is required to be roughened). In the case of an aluminum soft foil for cathodes (a cold-rolled aluminum foil that has been annealed to be softened), in addition to the above-mentioned etching properties, the crystal grain size can be adjusted to an appropriate size. It is required to improve capacitance and strength.

Conventionally, such an aluminum soft foil for electrolytic capacitor cathode generally has a purity of 99.50 to 99.4%.
The aluminum was used as it was pure aluminum or an aluminum alloy to which an alloying element such as copper was added if necessary. However, in this aluminum soft foil for a cathode, during etching, the solubility is generally non-uniform, and excessive melting causes partial reduction in strength,
On the contrary, there is a problem that the surface area cannot be sufficiently expanded due to the existence of a portion which is not easily dissolved.

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

In Japanese Patent Laid-Open No. 2-51210, Si: 0.010
~ 0.050wt%, Fe: 0.020 ~ 0.075wt%, Mg: 0.002 ~ 0.010wt
%, Zn: 0.005 to 0.012wt%, Cu: 0.003wt% or less as unavoidable impurities and 0.002wt% or less of other unavoidable elements are heated at 500 to 550 ° C for 20 hours or more. After homogenizing, hot rough rolling at 440 ℃ or more,
Furthermore, a method for producing an aluminum foil is described, which comprises performing hot finish rolling under conditions of 400 ° C or more on the inlet side, 250 ° C or less on the outlet side, and 2 minutes or less in time, and then cold rolling without intermediate annealing. There is.

In Japanese Patent Laid-Open No. 3-130340, 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 heated at 500 to 550 ° C for 20 hours or more to homogenize, and further 400 ° C or more on the inlet side, 250 ° C or less on the outlet side, time 2 minutes A method for producing an aluminum foil is described, which comprises hot rolling under the following conditions and then cold rolling without intermediate annealing.

In Japanese Patent Laid-Open No. 4-176847, Al purity is
99.8% or more, Fe: 0.000 to 0.07 wt%, Si: 0.001 to 0.
After the aluminum ingot containing 07wt%, Cu: 0.01wt% or less and unavoidable impurities is heated to 550 ℃ or more, 250 ℃
The following describes a method for producing an aluminum foil which is cooled and then rolled at 300 ° C. or lower.

Japanese Unexamined Patent Publication (Kokai) No. 240240/1990 describes a method for producing a soft aluminum foil for electrolytic capacitors by annealing a hard aluminum foil in the substantial absence of an oxygen-containing compound.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention JP-A-2-51210, JP-A-3-130340, JP-A-4-176847
The method described in Japanese Patent Application Laid-Open No. 2-240246 ~ (hereinafter referred to as the prior art ~) generally specifies the composition and manufacturing conditions of the aluminum foil, and according to the publication,
It is described that the electrolytic etching property is improved (an aluminum foil having a uniform solubility during etching is obtained).

However, as a result of various studies on these prior arts, according to this prior art, although the obtained aluminum foil is improved in electrolytic etching property, it is not yet sufficient, and it is caused by the following reasons. Uniform solubility at the time of etching (characteristic that evenly and moderately dissolves)
However, it was confirmed that there was a problem that the electrostatic capacity was not sufficient, and therefore the electrostatic capacity was not sufficiently improved.

That is, in the prior art and the prior art, the ingot of aluminum is homogenized under the condition of heating at 500 to 550 ° C. for 20 hours or more. A large amount is deposited, and due to the deposits, the uniform solubility during etching is hindered and the uniform solubility becomes insufficient. Further, such long-time heating is generally performed in two steps, and if performed in two steps,
The cooling time is relatively long between the first time and the second time, and precipitates become very large during this time, which also impedes uniform solubility, resulting in insufficient uniform solubility.

In the prior art, since the ingot of aluminum is homogenized at a temperature of 550 ° C. or higher, Al ₆ Fe (electrochemically stable) of precipitates is Al ₃ Fe during homogenization. (Electrochemically unstable), resulting in a decrease in uniform solubility during etching, resulting in insufficient uniform solubility.

In the prior art, the aluminum foil is annealed in the absence of an oxygen-containing compound to reduce the thickness of the oxide film on the foil surface to improve the uniform solubility. Insufficient to improve uniform solubility. Furthermore, since the thickness of the oxide film is not specified, and the composition of the aluminum foil, the soaking conditions, etc. are not specified, the uniform solubility does not necessarily improve, and the uniform solubility does not improve. However, it is very uncertain.

The present invention has been made in view of such circumstances, and an object thereof is to solve the problems in the above-mentioned prior arts, and to make electrolytic etching (etching) as compared with these prior arts. It is intended to provide a method for producing an aluminum soft foil for an electrolytic capacitor cathode, which is capable of obtaining an aluminum soft foil for an electrolytic capacitor cathode, which is excellent in uniform solubility at the time), and as a result can sufficiently improve electrostatic capacitance. .

[0016]

In order to achieve the above object, the present invention provides a method for producing an aluminum soft foil for an electrolytic capacitor cathode having the following constitution. That is, the production method of the aluminum soft foil for electrolytic capacitor cathode according to the present invention, the aluminum purity is 99.8% or more,
In addition, Fe: 0.020 to 0.030 wt%, Si: 0.040 wt% or less, Zn:
Aluminum containing 0.009 to 0.013 wt% and Cu: 0.002 wt% or less, the balance of which is unavoidable impurities, 550 to 500 ℃
After continuously heating for 7 to 15 hours to homogenize, then hot rolling, then cold rolling to a foil with a thickness of 50 μm or less, and then annealing the foil to obtain a crystal grain size: 50 ~ 100 μ
This is a method for producing a soft aluminum foil for electrolytic capacitor cathodes, which is characterized in that the thickness of the oxide film is 40 Å or less while the thickness is m.

[0017]

As described above, the method for producing the aluminum soft foil for the electrolytic capacitor cathode according to the present invention is characterized in that the electrolytic etching property (uniformity during etching) is determined by specifying the composition of aluminum as the starting material and the manufacturing process. It is intended to obtain an aluminum soft foil excellent in solubility). Especially, the homogenization process in the manufacturing process
Continuous heating at 50-500 ℃ for 7-15 hours, followed by hot rolling, cold rolling and annealing to make grain size: 50-100 μm and oxide film thickness: 40Å 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 casting, but as a precipitate during the cooling process of this casting
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, when homogenizing this cast aluminum (aluminum ingot) at a temperature above 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 pores may occur during electrolytic etching. This tendency becomes stronger as the homogenization treatment temperature exceeds 550 ° C.

In the present invention, the homogenizing 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. Then, this homogenization treatment (heating) is followed by hot rolling, followed by cold rolling and annealing, and the annealing temperature is usually 27
About 0 to 380 ° C is sufficient, and as a result, the above-mentioned precipitates (Al ₆ Fe and Al ₃ Fe) are also obtained in the obtained aluminum foil.
It is in the same state as the mixed state. Therefore, the aluminum foil obtained according to the present invention firstly comprises the precipitates Al ₆ Fe and Al ₃ Fe.
Is excellent in electrolytic etching property due to the 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 (no variation), and the oxide film thickness:
Since it is 40 Å or less, the wettability with respect to the etching solution is good, and these improve the electrolytic etching property, and as a result, the electrostatic capacity 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 aluminum purity is less than 99.8%, the amount of impurities increases and the electrostatic capacity lowers and becomes insufficient.

Fe forms an intermetallic compound (Al ₃ Fe, Al ₆ Fe, etc.) as a crystallized substance or a precipitate and is an essential element for improving the electrolytic etching property, and has a proper number and size. Fe: 0.020〜 for producing crystallized substances or precipitates
It must be 0.030wt%. If it is less than 0.020 wt%, the number of crystallized substances or precipitates is insufficient and a uniform suitable etching surface cannot be obtained, and the electrostatic capacity decreases, which is insufficient, and if it exceeds 0.030 wt%, the crystallized substances become too large and coarse. Etching pits are likely to be generated, and the electrostatic capacity is lowered, which is insufficient.

Si is an indispensable element for the same reason as Fe described above, but if Si: 0.040 wt% or more, the crystallized substance becomes too large and coarse etching pits are likely to occur, resulting in a decrease in capacitance. Therefore, Si: 0.040 wt% or less.

Zn has the effect of improving the electrolytic etching property, and the addition amount of 0.009 to 0.013 wt% is 0.00
This is because if it is less than 9 wt%, the effect is small, and if it exceeds 0.013 wt%, it is difficult to set an appropriate etching condition, a uniform and suitable etching surface cannot be obtained, and the electrostatic capacity is lowered to become insufficient.

Cu is an element that contributes to the solubility during electrolytic etching, but if it exceeds 0.002 wt%, Cu will be deposited on the surface of the aluminum foil during electrolytic etching, and as a result, the capacitance will decrease and become 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, up to about 0.002 wt% may be contained.

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

The heating time of 7 to 15 hours is 7
If the time is less than the time, the effect of the homogenization treatment is not sufficient, a uniform and moderately etched surface cannot be obtained, and the electrostatic capacity is lowered to become insufficient. This is because the etched surface cannot be obtained, and the electrostatic capacity decreases, which is insufficient.

The above heating is carried out continuously when the cooling is performed in the middle and reheating is performed, and when the heating is performed in two or more times, precipitates are formed during the cooling and after the cooling. This is because a large amount is deposited, a uniform and appropriate etching surface cannot be obtained, and the electrostatic capacity is reduced, which is insufficient.

The thickness of the obtained aluminum foil is set to 50 μm or less because it is necessary to increase the thickness of the conventional foil having inferior etching property in order to increase the capacitance and roughen it in the depth direction. 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 value of 100 μm is insufficient when the thickness is less than 50 μm, so the surface area cannot be expanded and the electrostatic capacity becomes insufficient, and when it exceeds 100 μm, the strength of the aluminum foil decreases and becomes insufficient. Because. Also, the oxide film thickness is set to 40 Å or less is that if it exceeds 40 Å, the wettability to the etching solution is poor and the etching property is deteriorated.
This is because the surface area cannot be enlarged and the electrostatic capacity becomes insufficient.

The homogenizing treatment is followed by hot rolling. This means that the homogenizing treatment and the hot rolling are continuously performed. In other words, the homogenizing treatment is carried out. This means that hot rolling is not performed after the material is once cooled to room temperature or near room temperature. The reason for doing this is that once cooled to room temperature,
Precipitates such as Al ₃ Fe precipitate during the cooling, and these precipitates remain without disappearing in the subsequent steps, a uniform and moderately etched surface cannot be obtained, and the capacitance decreases and becomes insufficient. Because it will be. In order to continuously perform such homogenization treatment and hot rolling, hot rolling may be started immediately or relatively promptly after the homogenization treatment (heating).

[0033]

【Example】

(Example 1) Aluminum ingots having the chemical components (compositions) shown in Table 1 were homogenized (soaked) under the production conditions shown in Table 2, followed by hot rolling, and then cold rolling. : 50 μm foil, and then annealed this foil to 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 chemical component range according to the present invention (No. 1 to 4) and out of the range (No. 5 to 11). ).

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

Here, the crystal grain size was measured by the line analysis method after the surface of the aluminum foil was polished and electrolytically etched, followed by microscopic observation. 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 the counter electrode.

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

For 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 so that the distance between the chuck portions was 50 mm. The tensile strength was determined by the method of tensile test.

The above crystal grain size, oxide film thickness, strength, and
Table 2 shows the measurement results of the capacitance. The aluminum foil (comparative example) obtained from the chemical components outside the range of the chemical composition (No. 5 to 11) according to the present invention has low capacitance or strength. On the other hand, within the chemical composition range according to the present invention (No. 1
~ 4), for the aluminum foil obtained by the method according to the present invention, both the capacitance, 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
The aluminum ingot having the following properties was homogenized under the manufacturing conditions shown in Table 4, followed by hot rolling, and then cold rolling into a foil having a thickness of 50 μm, and then annealing this foil to obtain a temper: O material. Here, the chemical components are all within the chemical component range according to the present invention, and the production conditions are within the production conditions according to the present invention (No. 12 to 15) and out of the range (No. 16 to 23). There are some.

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, by the same method as in Example 1,
After electrolytic etching and chemical conversion treatment, the capacitance was measured. Further, the strength of the aluminum foil after electrolytic etching was measured by the same method as in Example 1.

The above 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 outside the manufacturing condition range (No. 16 to 23) according to the present invention, either capacitance or 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]

EFFECTS OF THE INVENTION According to the method for producing an aluminum soft foil for an electrolytic capacitor cathode according to the present invention, the electrolytic capacitor is excellent in electrolytic etching property (uniform solubility during etching), and as a result, sufficient electrostatic capacity can be improved. It becomes possible to obtain an aluminum soft foil for a cathode.

Claims (1)

[Claims] 1. The aluminum purity is 99.8% or more,
In addition, Fe: 0.020 to 0.030 wt%, Si: 0.040 wt% or less, Zn:
Aluminum containing 0.009 to 0.013 wt% and Cu: 0.002 wt% or less, the balance of which is unavoidable impurities, 550 to 500 ℃
After continuously heating for 7 to 15 hours to homogenize, then hot rolling, then cold rolling to a foil with a thickness of 50 μm or less, and then annealing the foil to obtain a crystal grain size: 50 ~ 100 μ
A method for manufacturing a soft aluminum foil for electrolytic capacitor cathodes, characterized in that the thickness of the oxide film is 40 Å or less as well as m.